Proceedings - SPIE Digital Library

Jump to Content

Increase text size Decrease text size

SPIE DL Tab

SPIE Proceedings Tab

SPIEDL Journals Tab

SPIE eBooks Tab

My Subscription | My Email Alerts | My Article Collections

BROWSE PROCEEDINGS

Proceedings

BROWSE JOURNALS

Journals

BROWSE SPIE eBOOKS

SPIE eBooks

SUBSCRIPTIONS & PRICING

GENERAL INFORMATION

Search Volume | RSS Feeds

RSS
Previous Volume Next Volume

Volume 7122 Photomask Technology 2008

Hiroichi Kawahira, Larry S. Zurbrick October 2008

Conference Location: Monterey, CA, USA Conference Date: Tuesday 7 October 2008

SECTION LISTING

Add

Add Items to Cart

View

View Items in Cart

SELECTED: Export Citations | Show Only | Show All | Show/HideHide Summaries | Add to MyArticles | Email

back to top

Front Matter

Select this Article OPEN ACCESS		Front Matter: Volume 7122 Proceedings of SPIE Proc. SPIE 7122, 712201 (2008); http://dx.doi.org/10.1117/12.817633 Online Publication Date: Nov 25, 2008 Full Text: \| Download PDF
	+ -	Show Abstract This PDF file contains the front matter associated with SPIE Proceedings Volume 7122, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

back to top

Plenary Paper from Advanced Lithography 2008

Select this Article		Lithography and design in partnership: a new roadmap Andrew B. Kahng Proc. SPIE 7122, 712202 (2008); http://dx.doi.org/10.1117/12.813418 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We discuss the notion of a 'shared technology roadmap' between lithography and design from several perspectives. First, we examine cultural gaps and other intrinsic barriers to a shared roadmap. Second, we discuss how lithography technology can change the design technology roadmap. Third, we discuss how design technology can change the lithography technology roadmap. We conclude with an example of the 'flavor' of technology roadmapping activity that can truly bridge lithography and design.

back to top

Invited Session

Select this Article		Mask industry assessment: 2008 Greg Hughes and Henry Yun Proc. SPIE 7122, 712204 (2008); http://dx.doi.org/10.1117/12.802143 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Microelectronics industry leaders routinely name the cost and cycle time of mask technology and mask supply as top critical issues. A survey was created with support from SEMATECH and administered by David Powell Consulting to gather information about the mask industry as an objective assessment of its overall condition. The survey is designed with the input of semiconductor company mask technologists, merchant mask suppliers, and industry equipment makers. This year's assessment is the seventh in the current series of annual reports. With ongoing industry support, the report can be used as a baseline to gain perspective on the technical and business status of the mask and microelectronics industries. The report will continue to serve as a valuable reference to identify the strengths and opportunities of the mask industry. The results will be used to guide future investments pertaining to critical path issues. This year's survey is basically the same as the 2005 through 2007 surveys. Questions are grouped into categories: General Business Profile Information, Data Processing, Yields and Yield Loss Mechanisms, Delivery Times, Returns, and Services. Within each category is a multitude of questions that create a detailed profile of both the business and technical status of the critical mask industry.

Select this Article		PMJ panel discussion overview on mask complexities, cost, and cycle time in 32-nm system LSI generation: conflict or concurrent? Kunihiro Hosono and Kokoro Kato Proc. SPIE 7122, 712207 (2008); http://dx.doi.org/10.1117/12.803743 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract This is a report on a panel discussion organized in Photomask Japan 2008, where the challenges about "Mask Complexities, Cost, and Cycle Time in 32-nm System LSI Generation" were addressed to have a look over the possible solutions from the standpoints of chipmaker, commercial mask shop, DA tool vendor and equipments makers. The wrap-up is as follows: Mask complexities justify the mask cost, while the acceptable increase rate of 32nm-mask cost significantly differs between mask suppliers or users side. The efficiency progress by new tools or DFM has driven their cycle-time reductions. Mask complexities and cost will be crucial issues prior to cycle time, and there seems to be linear correlation between them. Controlling complexity and cycle time requires developing a mix of advanced technologies, and especially for cost reduction, shot prices in writers and processing rates in inspection tools have been improved remarkably by tool makers. In addition, activities of consortium in Japan (Mask D2I) are expected to enhance the total optimization of mask design, writing and inspection. The cycle-time reduction potentially drives the lowering of mask cost, and, on the other, the pattern complexities and tighter mask specifications get in the way to 32nm generation as well as the nano-economics and market challenges. There are still many difficult problems in mask manufacturing now, and we are sure to go ahead to overcome a 32nm hurdle with the advances of technologies and collaborations by not only technologies but also finance.

back to top

Mask Materials for Optical Extensions

Select this Article		Characterization of binary and attenuated phase shift mask blanks for 32nm mask fabrication Thomas Faure, Emily Gallagher, Michael Hibbs, Louis Kindt, Ken Racette, Richard Wistrom, Amy Zweber, Alfred Wagner, Yasutaka Kikuchi, Toru Komizo, and Satoru Nemoto Proc. SPIE 7122, 712209 (2008); http://dx.doi.org/10.1117/12.801950 \| Cited 4 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract During the development of optical lithography extensions for 32nm, both binary and attenuated phase shift Reticle Enhancement Technologies (RETs) were evaluated. The mask blank has a very strong influence on the minimum feature size and critical dimension (CD) performance that can be achieved on the finished reticle and can have a significant impact on the ultimate wafer lithographic performance. Development of a suitable high resolution binary mask making process was particularly challenging. Standard chrome on glass (COG) binary blanks with 70 nm thick chrome films were unable to support the required minimum feature size, linearity, and through pitch requirements. Two alternative mask blank configurations were evaluated for use in building high resolution binary masks: a binary (BIN) mask blank based on the standard attenuated PSM blank and an Opaque MoSi on Glass (OMOG) mask blank consisting of a newly- developed opaque MoSi [1]. Data comparing the total process bias, minimum feature size, CD uniformity, linearity, through pitch, etch loading effects, flatness, film stress, cleaning durability and radiation durability performance of the different binary and attenuated PSM mask blanks are reported. The results show that the new OMOG binary blank offers significant mask performance benefits relative to the other binary and attenuated PSM mask blanks. The new OMOG blank was the opaque mask blank candidate most capable of meeting 32nm binary mask fabrication requirements..

Select this Article		Impact of the OMOG substrate on 32 nm mask OPC inspectability, defect sensitivity, and mask design rule restrictions Karen Badger, Yutaka Kodera, Emily Gallagher, and Mark Lawliss Proc. SPIE 7122, 71220A (2008); http://dx.doi.org/10.1117/12.801951 \| Cited 3 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Aggressive optical proximity correction (OPC) has enabled the extension of advanced lithographic technologies to the 32nm node. The associated sub-resolution features, feature-feature spacings, and fragmented edges in the design data are difficult to reproduce on masks and even more difficult to inspect. The patterns themselves must be differentiated from defects for inspectability, while the ability to recognize small deviations must be maintained for sensitivity. This must be done without restricting necessary OPC design features. The semi-transparent nature of industry-standard 6% attenuated phase shift substrates introduces a host of problems relative to inspectable dimensions and subsequent defect sensitivities. The result is a reduction in inspectability, defect sensitivity and the inability to inspect smaller critical dimensions and OPCed features. The introduction of a binary-type attenuated phase shift film improves the ability to inspect smaller critical dimensions and smaller OPC features without loss of inspectability and sensitivity extending the capability of existing inspection hardware for 32nm ground rule masks. This paper introduces inspection characterization results for this new film, opaque MoSi on glass (referred to as OMOG in this paper) and draws a correlation between the film's transmission qualities and inspectability of 32nm OPC features. The paper will further show a correlation between OPC feature size and defect sensitivity for 32nm ground rule designs. Aerial Image (AIMS) analysis will be used to identify areas where the enhanced inspection capability can be leveraged to avoid unnecessary restrictions on OPC.

Select this Article		Evaluation of 32nm advanced immersion lithography pellicles N. Zhou, K. Racette, M. Hibbs, T. Mizoguchi, D. Hasselbeck, M. Barrett, R. Nolan, F. Houle, J. Ritter, A. Wagner, and M. Caterer Proc. SPIE 7122, 71220B (2008); http://dx.doi.org/10.1117/12.801663 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Advanced immersion lithography utilizes higher numerical aperture (NA) stepper lenses resulting in higher angles of light illumination through photomasks. Transmission in conventional pellicles (830 nm thickness) is generally maximized at 0 degree illumination and decreases significantly at the higher angles. Most pellicle suppliers have developed thinner pellicle membranes (~280 nm) which allow considerably improved transmission of light at angles up to 20 degrees. In addition, aluminum frames have been shortened, potentially allowing inspection closer to the inside of the frame and reduced mask flatness distortion upon pellicle mount. Suppliers have also developed advanced adhesives which reduce outgassing even beyond the low levels obtained with current 45 nm pellicles. In this paper, advanced immersion pellicles from several suppliers are evaluated and compared with conventional 45 nm pellicles for the following quality parameters: physical durability, foreign material, ease of demounting and glue removal, chemical outgassing, mask flatness distortion and susceptibility to radiation damage. Improvements in mask inspection and pellicle optical transmission at higher incident angles are also evaluated and are discussed.

back to top

Advanced Mask Processing

Select this Article		Road to a zero degree total temperature range post exposure bake process Tobias Wähler and Peter Dress Proc. SPIE 7122, 71220C (2008); http://dx.doi.org/10.1117/12.801369 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract With tighter CD uniformity requirements, a tighter temperature control during a Post Exposure Bake (PEB) process for photomask production becomes more and more important. CD non uniformities can be partially ascribed to deficiencies of the measurement devices used for the process qualification of a PEB hotplate system. In this paper, a new routine is proposed to overcome the deficiencies of the measurement devices used, so that further improvement of the hotplate performance becomes possible. Using a 25 point sensor array, we finally achieved a bake performance of the hotplate system described in terms of "real" total temperature range on the mask surface, of 0.4°C during temperature ramp-up and below 0.1°C at steady state for a final mean temperature of 100°C. This is a first step in the right direction towards a temperature range of zero for the bake process.

Select this Article		Study of second-generation Proximity Gap Suction Development System (PGSD-II) for mask fabrication Hideaki Sakurai, Masatoshi Terayama, Mari Sakai, Masamitsu Itoh, Osamu Ikenaga, Hideo Funakoshi, Norifumi Sato, Kenji Nakamizo, Masato Nomura, Yoshihiko Saito, Junji Nakao, and Naoya Hayashi Proc. SPIE 7122, 71220D (2008); http://dx.doi.org/10.1117/12.801424 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Development process for 3x nm node devices and beyond is becoming a great issue in mask fabrication. The following items, such as uniformity, repeatability, loading effect and defect must be improved. To evolve the development process, TEL, DNP Omron and Toshiba have been jointly developed next generation equipment which is called "Second-generation PGSD (Gen.2)". In this paper, PGSD Gen.2 concept is introduced and its performance is reported.

Select this Article		Process control of chrome dry etching by complete characterization of the RF power delivery Björn Sass, Ralf Schubert, Thomas Jakubski, Sebastian Mauermann, Pavel Nesladek, Andreas Wiswesser, Karl-Heinz Gindra, and Ray Malone Proc. SPIE 7122, 71220E (2008); http://dx.doi.org/10.1117/12.801080 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In order to fulfil the upcoming requirements for photomasks there is a need for improving the process stability (reproducibility) of the unit processes in photomask fabrication. In order to understand and minimize the etch contribution to the CD stability impedance sensors integrated into the capacitively coupled radio frequency (RF) circuit (bias circuit) have shown a big potential. The last step towards a full characterization of the RF properties is the integration of impedance sensors in the inductively coupled RF circuit (source). This kind of sensor measures voltage, current and phase angle for the fundamental (13.56 MHz) and higher harmonics (up to the 5th harmonic). In this paper we are describing the integration of the Z-Scan sensors into the source RF matchbox and its impact on the RF and CD characteristics of the mask etcher. The central point is the correlation of impedance data to CD data. We will also compare the responses for bias and source impedance measurements.

Select this Article		Integrating Cr and MoSi etch for optimal photomask critical dimension uniformity and phase uniformity Richard Wistrom, Toru Komizo, Satoru Nemoto, and A. Gary Reid Proc. SPIE 7122, 71220F (2008); http://dx.doi.org/10.1117/12.801570 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Two key parameters of attenuated phase shift masks are critical dimension uniformity (CDU) and phase uniformity. This study examines the important role that plasma etch plays in determining these parameters. For optimal results, the impact which Cr and MoSi etch have on uniformity must be understood not only individually, but also as a complementary pair. A two-step MoSi etch was developed; the first step was tuned to have a higher etch bias at the edge than at the center, while the second step had a very uniform etch bias. By controlling the fraction of the MoSi consumed by each step, the MoSi etch was adapted to complement the Cr etch and thus optimize overall CDU and phase uniformity.

Select this Article		Electric field-induced progressive CD degradation in reticles Gavin C. Rider Proc. SPIE 7122, 71220G (2008); http://dx.doi.org/10.1117/12.801403 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Reticles have been found to be susceptible to damage by the Electric Field induced Migration of chrome (EFM) at field levels >100x lower than those that cause ESD. The experimental quantification data are reviewed briefly and detailed AFM imagery is presented illustrating the nature of the reticle degradation process. The characteristics of EFM and its very low onset threshold have significant implications for the protection of advanced reticles so a new reticle handling methodology is proposed which is designed to minimize the risk of field induced damage.

Select this Article		Don't kill canaries! Introducing a new test device to assess the electrostatic risk potential to photomasks Thomas Sebald Proc. SPIE 7122, 71220H (2008); http://dx.doi.org/10.1117/12.801407 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Electrostatic protection is an issue for all masks, whether during mask production, shipping, storage, handling or inspection and exposure. Up to now, only manual electrostatic field measurements, or expensive and elaborate analyses with Canary reticles have given hints about the risks of pattern damage by ESD events. A new test device is being introduced, which consists of electrostatic field sensors, integrated INSIDE a closed fused quartz housing which has the outside dimensions of a 6 inch mask. This device can be handled and used like a normal 6 inch reticle. It can be handled and processed while recording the electrostatic charges on the chrome patterns created by friction or field induction just as a reticle would "see" during normal processing.

back to top

Patterning Technologies and Tools

Select this Article		Damage mechanisms and process optimization for photomasks with sub-resolution assist features L. Kindt, E. Gallagher, J. Levin, Y. Kodera, Y. Okawa, and Y. Sasaki Proc. SPIE 7122, 71220I (2008); http://dx.doi.org/10.1117/12.801568 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Sub-Resolution Assist Features (SRAFs) are typically the smallest features on a photomask and amplify many of the challenges in mask manufacturing. During the initial stages of process development, resist feature adhesion is the dominate damage mechanism. Throughout mask fabrication, the influence of inherent material properties and wet processing can eventually delaminate SRAFs. The various mechanisms that cause SRAF damage will be presented systematically. Process optimization steps to address the failure mechanisms will be presented. Data illustrating the improved process window for small features will be included.

Select this Article		New electron optics for mask writer EBM-7000 to challenge hp 32nm generation Takashi Kamikubo, Steven Golladay, Rodney Kendall, Victor Katsap, Kenji Ohtoshi, Munehiro Ogasawara, Shinsuke Nishimura, Rieko Nishimura, Osamu Iizuka, Takahito Nakayama, Shunji Shinkawa, Tetsurou Nishiyama, and Shuichi Tamamushi Proc. SPIE 7122, 71220J (2008); http://dx.doi.org/10.1117/12.801725 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Semiconductor scaling is expected to continue to hp32nm and beyond, accompanied by explosive data volume expansion. Required minimum feature size at hp 32nm will be less than 50nm on the mask, according to ITRS2007⁽¹⁾. EBM 7000 is a newly designed mask writer for the hp32 nm node with an improved electron optical column providing the beam resolution (10 nm measured in situ) and beam current density (200 A/cm²) necessary for cost effective mask production at hp32nm node. In this paper we report on column improvements, the in situ beam blur measurement method and writing results from EBM 7000. Written patterns show dose margin (CD change [nm] / 1 % dose change) of .94 nm /1 % dose for line/space arrays using chemically amplified resist PRL009 and our standard processing. Using a simple model to relate the measured beam intensity distribution to the measured dose margin, we infer an effective total blur of 30 nm, dominated by a contribution of 28 nm from the resist exposure and development process. Further evidence of the dominance of the process contribution is the measured improvement in dose margin to .64 nm/% dose obtained by modifying our standard process. Even larger process improvements will be needed for successful fabrication of hp22nm masks.

Select this Article		E-beam exposure system using multi column cell (MCC) with CP for mask writing Akio Yamada, Hiroshi Yasuda, and Masaki Yamabe Proc. SPIE 7122, 71220K (2008); http://dx.doi.org/10.1117/12.801564 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In the Mask D2I project at ASET, the authors designed a novel electron beam exposure system using the concepts of MCC (multi column cell), CP (character projection), and VSB (variable shaped beam) to improve the throughput of electron beam exposure systems. They presented outlines of a proof-of-concept system of MCC, and have shown the performances of VSB and CP in the system. They evaluated the impacts on beam position in one column cell caused by deflections in another column cell. The impacts were found to be less than 0.1nm in presence of major deflections in the neighboring column cell. Hence it was concluded that there was no noticeable impact on deflections cause by the neighboring column cells in the MCC system.

Select this Article		Results obtained with the CHARPAN Engineering Tool and prospects of the ion Mask Exposure Tool (iMET) Elmar Platzgummer, Hans Loeschner, and Gerhard Gross Proc. SPIE 7122, 71220L (2008); http://dx.doi.org/10.1117/12.801441 \| Cited 6 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Projection Mask-Less Patterning (PMLP) is based on many hundred thousands of ion beams working in parallel. A PMLP proof-of-concept tool has been realized as part of the European project CHARPAN (Charged Particle Nanotech) and has been presented at SPIE Photomask BACUS 2007. Using 10 keV protons, 16nm hp resolution has been demonstrated in non- CAR materials (HSQ) with 25μC/cm² exposure dose. The system is upgraded to a CHARPAN Engineering Tool (CHET) with a laser-interferometer controlled vacuum stage and a CMOS based programmable Aperture Plate System (APS) providing ca. 40,000 beams with < 20nm spot size. The engineering of an ion Mask Exposure Tool (iMET) for the 22nm hp mask node has been started; main iMET features are discussed.

Select this Article		Effects of heated substrates on bimetallic thermal resist for lithography and grayscale photomask applications James M. Dykes, Polly Tsui, Jenny Leung, and Glenn H. Chapman Proc. SPIE 7122, 71220M (2008); http://dx.doi.org/10.1117/12.801560 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Bimetallic thin-films of Bi/In act as negative thermal resists when laser exposure pulse (7mJ/sq. cm for 4 nsec) converts the film into a transparent eutectic metallic oxide alloy. Resist transparency varies with exposed laser power, changing from <0.1% (3.0 OD) unexposed to >60% (0.22 OD) exposed. This generates direct-write gray scale photomasks, and adding a feedback system where the transparency is measured and adjusts the writing process to account for local variations in the film, achieves >64 gray level control. These resists are also wavelength invariant, operating from visible to EUV with a resolution >42nm after development using a diluted RCA-2 solution (HCl:H₂O₂:H₂0 @ 1:1:48) with a gamma of 2-18. Longer duration exposures with lower instantaneous intensities result in lower gammas, while shorter exposures with higher energies give higher gammas. One limitation on these resists is that the exposure energy must be delivered in a single pulse. This limitation puts pulse energy requirements into the mJ per pulse range: greater than desired for EUV exposure systems. Bimetallic thermal resists remain almost unaffected during a sub-threshold exposure that does not reach the activation energy. It has been shown that the resist and substrate can be heated below the threshold energy, to temperatures of at least 90°C, without creating any exposure of the resist. In this research, Bi/In resists are heated through a range of substrate temperatures, measured for their optical exposure requirements and gammas under these conditions, and used to determine if substrate heating can improve the film's sensitivity.

back to top

DPL Implementation I

Select this Article		Revisiting the layout decomposition problem for double patterning lithography Andrew B. Kahng, Chul-Hong Park, Xu Xu, and Hailong Yao Proc. SPIE 7122, 71220N (2008); http://dx.doi.org/10.1117/12.801992 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In double patterning lithography (DPL) layout decomposition for 45nm and below process nodes, two features must be assigned opposite colors (corresponding to different exposures) if their spacing is less than the minimum coloring spacing.^5,11,14 However, there exist pattern configurations for which pattern features separated by less than the minimum coloring spacing cannot be assigned different colors. In such cases, DPL requires that a layout feature be split into two parts. We address this problem using a layout decomposition algorithm that incorporates integer linear programming (ILP), phase conflict detection (PCD), and node-deletion bipartization (NDB) methods. We evaluate our approach on both real-world and artificially generated testcases in 45nm technology. Experimental results show that our proposed layout decomposition method effectively decomposes given layouts to satisfy the key goals of minimized line-ends and maximized overlap margin. There are no design rule violations in the final decomposed layout. While we have previously reported other facets of our research on DPL pattern decomposition,6 the present paper differs from that work in the following key respects: (1) instead of detecting conflict cycles and splitting nodes in conflict cycles to achieve graph bipartization,⁶ we split all nodes of the conflict graph at all feasible dividing points and then formulate a problem of bipartization by ILP, PCD⁸and NDB⁹ methods; and (2) instead of reporting unresolvable conflict cycles, we report the number of deleted conflict edges to more accurately capture the needed design changes in the experimental results.

Select this Article		Evaluation of Double Process Lithography (DPL) with bi-layer photo-resist process for contact layer-patterning Gong Chen and Kevin Wu Proc. SPIE 7122, 71220O (2008); http://dx.doi.org/10.1117/12.800988 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Double Process Lithography (DPL) has been widely accepted as a viable printing technique for critical layers at 45nm nodes and below. In addition, DPL technique also allows us to use available process tool-sets with less capability to develop the next node CMOS devices in early research and development stages with additional photo-masks. One practical issue of applying DPL technique is the process crosstalk, which is the impact of the existing etched patterns after the 1st process to the overall lithography performance during the 2nd printing process. In this paper, we evaluated the DPL process for contact holetype patterning with a 193nm silicon-containing bi-layer photo-resist. We explained the bi-layer photoresist process flow and its low process cross-talk characteristics when applied in our DPL process. We also discussed the challenges of printing small contacts in the DPL process. The preliminary experiment results indicated that silicon-containing photo-resist process is a good candidate for DPL process in the contact hole-type of patterns, and it has good characteristics of low process cross-talk. The flexibility of the drydevelop process in bi-layer resist also offered us another way to form small contacts in the substrate film. At the end, we provided some suggestions in contact pattern decomposition algorithm and related exposure-tool alignment strategies for future implementation of DPL technology.

Select this Article		Mask defect printability in the spacer patterning process Seiro Miyoshi, Shinji Yamaguchi, Takashi Hirano, Hiromitsu Mashita, Hidefumi Mukai, Ayumi Kobiki, Yuuji Kobayashi, Kohji Hashimoto, and Soichi Inoue Proc. SPIE 7122, 71220P (2008); http://dx.doi.org/10.1117/12.801410 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We studied the mask defect printability for both opaque and clear defects in the spacer patterning process. The spacer patterning process consists of the development of photoresist film, the etching of the core film using the photoresist pattern as the etching mask, the deposition of a spacer film on both sides of the core film pattern, and the removal of the core film. The pattern pitch of the spacer film becomes half that of the photoresist. The opaque defect and the clear defect of the mask, respectively, resulted in an "open-short complex" defect and a short defect in the spacer pattern, The defect size of both the opaque and clear defect became smaller as the process proceeded from the development to the core film etching and the spacer pattern fabrication. The decrease of the mask defect printability during the spacer process is likely to be related to the reduction of the line width roughness (LWR) and to the reduction of mask enhanced factor (MEF). The acceptable mask defect size was also studied from the viewpoint of the defect printability to the spacer pattern for both the opaque and clear defect, and found to be 55-60nm, which was relaxed from that in ITRS2007.

back to top

DPL Implementation II

Select this Article		Printability verification for double-patterning technology Gerard Luk-Pat, Petrisor Panaite, Kevin Lucas, Christopher Cork, Vincent Wiaux, Staf Verhaegen, and Mireille Maenhoudt Proc. SPIE 7122, 71220Q (2008); http://dx.doi.org/10.1117/12.801545 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract For keeping pace with Moore's Law of reducing the feature sizes on integrated circuits, the driving forces have been reductions in the exposure-tool wavelength, and increases in the lens numerical aperture (NA). With extreme ultra-violet (EUV) lithography and 3rd-generation immersion delayed for production use, these driving forces are now stalled at a wavelength of 193 nm and an NA of 1.35. Therefore, double-patterning technology (DPT) is needed for printing 22 nm device node features. With DPT, a 22 nm layout is split into two patterns. Each pattern is printed using 32 nm node lithography technology, and the original pattern is recovered by a logical summation (the Boolean OR operation) of these two separately exposed patterns. DPT presents several challenges for printability verification. First, the etch target can be very different from the resist target because significant biasing is used to improve the lithography process window. Second, overlaps between the two patterns produce new problems such as sharp-cornered pinching at pattern junctions, and bridging between patterns. Finally, there are additional process variations: misalignment between the two patterns, and twice as many dose and defocus dimensions. We present results from a full-chip DPT-verification tool that addresses these challenges. We also provide examples of lithography problems that are specific to DPT, and describe possible guidance for the resolution enhancement techniques (RET) and design tools.

Select this Article		Double dipole RET investigation for 32 nm metal layers Carl Babcock, Yi Zou, Derren Dunn, Zachary Baum, Zengqin Zhao, Itty Matthew, and Pat LaCour Proc. SPIE 7122, 71220R (2008); http://dx.doi.org/10.1117/12.801789 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract For 32 nm test chips, aggressive resolution enhancement technology (RET) was required for 1x metal layers to enable printing minimum pitches before availability of the final 32 nm exposure tool. Using a currently installed immersion scanner with 1.2 numerical aperture (NA) for early 32 nm test chips, one of the RET strategies capable of resolving the minimum pitch with acceptable process latitude was dipole illumination. To avoid restricting the use of minimum pitch to a single orientation, we developed a double-expose/single-develop process using horizontal and vertical dipole illumination. To enable this RET, we developed algorithms to decompose general layouts, including random logic, interconnect test patterns, and SRAM designs, into two mask layers: a first exposure (E1) of predominantly vertical features, to be patterned with horizontal dipole illumination; and, a second exposure (E2) of predominantly horizontal features, to be patterned with vertical dipole illumination. We wrote this algorithm into our OPC program, which then applies sub-resolution assist features (SRAFs) separately to the E1 and E2 masks, coordinating the two to avoid problems with overlapping exposures. This was followed by two-mask OPC, using E1 and E2 as mask layers and the original layout (single layer) as the target layer. In this paper, we describe some of the issues with decomposing layout by orientation, issues that arise in SRAF application and OPC, and some approaches we examined to address these issues.

Select this Article		Double-patterning decomposition, design compliance, and verification algorithms at 32nm hp Alexander Tritchkov, Petr Glotov, Sergiy Komirenko, Emile Sahouria, Andres Torres, Ahmed Seoud, and Vincent Wiaux Proc. SPIE 7122, 71220S (2008); http://dx.doi.org/10.1117/12.801381 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Double patterning (DP) technology is one of the main candidates for RET of critical layers at 32nm hp. DP technology is a strong RET technique that must be considered throughout the IC design and post tapeout flows. We present a complete DP technology strategy including a DRC/DFM component, physical synthesis support and mask synthesis. In particular, the methodology contains: - A DRC-like layout DP compliance and design verification functions; - A parameterization scheme that codifies manufacturing knowledge and capability; - Judicious use of physical effect simulation to improve double-patterning quality; - An efficient, high capacity mask synthesis function for post-tapeout processing; - A verification function to determine the correctness and qualify of a DP solution; Double patterning technology requires decomposition of the design to relax the pitch and effectively allows processing with k1 factors smaller than the theoretical Rayleigh limit of 0.25. The traditional DP processes Litho-Etch-Litho- Etch (LELE) [1] requires an additional develop and etch step, which eliminates the resolution degradation which occurs in multiple exposure processed in the same resist layer. The theoretical k₁ for a double-patterning technology applied to a 32nm half-pitch design using a 1.35NA 193nm imaging system is 0.44, whereas the k₁ for a single-patterning of this same design would be 0.22 [2], which is sub-resolution. This paper demonstrates the methods developed at Mentor Graphics for double patterning design compliance and decomposition in an effort to minimize the impact of mask-to-mask registration and process variance. It also demonstrates verification solution implementation in the chip design flow and post-tapeout flow.

back to top

RET and OPC/ORC I

Select this Article		Pixel-based SRAF implementation for 32nm lithography process Byung-Sung Kim, Yoo-Hyun Kim, Sung-Ho Lee, Sung-Il Kim, Sang-Rok Ha, Juhwan Kim, and Alexander Tritchkov Proc. SPIE 7122, 71220T (2008); http://dx.doi.org/10.1117/12.801310 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A Pixel-based sub-resolution assist feature (SRAF) insertion technique has been considered as one of the promising solutions by maximizing the common process window. However, process window improvement of the pixel-based SRAF technique is limited by the simplification of SRAFs for mask manufacturability. Mask simplification and mask rule check (MRC) constraints parameters for pixel-based SRAF technique are the critical factors for mask production without a big loss of its benefit. In this study, correlation of MRC control was analyzed in terms of the robustness to process variation for a contact layer of 32nm device node. An optimum condition of MRC constraints was selected by balancing the process window and mask manufacturability. In addition, a novel and practical methodology for 32nm device node development was proposed to keep the mask complexity low and to take full advantage of process window improvement using pixel-base SRAF insertion.

Select this Article		Model-based assist feature placement: an inverse imaging approach Amyn Poonawala, Benjamin Painter, and Jeffrey Mayhew Proc. SPIE 7122, 71220U (2008); http://dx.doi.org/10.1117/12.801539 \| Cited 4 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The continuing reduction in feature dimensions and tightening of process constraints have led to an increasing demand for model-based approaches, which can efficiently explore the AF solution space, and achieve AF configurations not easily accessible via rules. In this work, we approach the AF placement problem as an inverse imaging problem. We discuss the generation of an inverse mask field and its use in determining the assist feature location. The results are compared with the single iteration intensity-field based AF placement with regard to symmetry, speed, memory, convergence, and accuracy. Several results with different pitches and illumination conditions are presented to demonstrate the robustness and adaptability of the inverse mask AF placement.

Select this Article		Optimizing models based OPC fragmentation using genetic algorithms Domenico A. Dipaola and Ian Stobert Proc. SPIE 7122, 71220V (2008); http://dx.doi.org/10.1117/12.801551 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Models Based Optical Proximity Correction (MBOPC) is used extensively in the semiconductor industry to achieve robust pattern fidelity in modern lithographic processes. Much of the complexity in OPC algorithms is handled by advanced commercial software packages. These packages give users the ability to set many parameters in the OPC code decks which are used to customize the recipes for specific design styles and manufacturing process settings. Some of the most important parameters in traditional OPC recipes are the fragmentation rules, which determine how edges of polygons are fragmented in a traditional edge-based correction algorithm. It is important to find settings which can deliver good results on a wide variety of complex layout styles. One approach to setting these parameters is through a Design of Experiments (DOE) approach where many different settings are tested in a systematic fashion, in an attempt to find appropriate fragmentation rules for a wide variety of layouts. This is a very straight-forward and powerful technique, but it can be very computationally expensive, particularly as the number of independent variables becomes large. In this paper we examine the usefulness of Genetic Algorithm (GA) optimization techniques for setting the fragmentation parameters. Our work is focused on using GAs to tune parameters rather than on core algorithms used in mask data correction. We use challenging metal layout patterns and optimize fragmentation rules to try to minimize residual edge placement errors, while trying to generate fragmentation that does not result in excessive runtime, or mask manufacturing challenges.

Select this Article		Single exposure is still alive: gate patterning at 45nm technology node Klaus Herold, Donald J. Samuels, Derren Dunn, Amr Abdo, and Chandrasekhar Sarma Proc. SPIE 7122, 71220W (2008); http://dx.doi.org/10.1117/12.801526 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A single patterning solution is still desirable to keep the costs low for high volume wafer manufacturing. This paper will outline the process steps necessary to scale the single patterning approach for gate level from 65mn into the 45nm technology node. They consist mainly of the introduction of a new software for optical proximity correction, the introduction of model based process window correction, the switch to model based etch proximity correction, and support of an ultra dense SRAM cell. All technology requirements could be met with this single patterning solution.

Select this Article		Advanced mask technique to improve bit line CD uniformity of 90 nm node flash memory in low-k1 lithography Jong-doo Kim, Jae-young Choi, Jea-hee Kim, and Jae-won Han Proc. SPIE 7122, 71220X (2008); http://dx.doi.org/10.1117/12.801557 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As devices size move toward 90nm technology node or below, defining uniform bit line CD of flash devices is one of the most challenging features to print in KrF lithography. There are two principal difficulties in defining bit line on wafer. One is insufficient process margin besides poor resolution compared with ArF lithography. The other is that asymmetric bit line should be made for OPC(Optical Proximity Correction) modeling. Therefore advanced ArF lithography scanner should be used for define bit line with RETs (Resolution Enhancement Techniques) such as immersion lithography, OPC, PSM(Phase Shift Mask), high NA(Numerical Aperture), OAI(Off-Axis Illumination), SRAF(Sub-resolution Assistant Feature), and mask biasing.. Like this, ArF lithography propose the method of enhancing resolution, however, we must spend an enormous amount of CoC(cost of ownership) to utilize ArF photolithography process than KrF. In this paper, we suggest method to improve of bit line CD uniformity, patterned by KrF lithographic process in 90nm sFlash(stand alone Flash) devices. We applied new scheme of mask manufacturing, which is able to realize 2 different types of mask, binary and phase-shift, into one plate. Finally, we could get the more uniform bit lines and we expect to get more stable properties then before applying this technique.

Select this Article		OPC hotspot identification challenges: ORC vs. PWQ on wafer Andre Poock, Sarah McGowan, Francois Weisbuch, Guido Schnasse, and Rajesh Ghaskadvi Proc. SPIE 7122, 71220Y (2008); http://dx.doi.org/10.1117/12.801574 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The identification of OPC induced litho hotspots within the product design is essential and a must to make sure that a new OPC model is working correctly and does no harm to the design and future product. Several techniques and methods for OPC verification and identification of hotspots are known and long adopted within the field. An optical rule check done by the simulation software after OPC is one way of identifying hotspots within the design of the whole chip. This is typically done by using a DRC-type width or space check on simulation contours (nominal exposure contour or process window contours). However, the pass/fail nature of this check at a single CD value requires good calibration of the simulation model to avoid false positives and ease of disposition at tapeout. Another method is the process window qualification method which uses the defect inspection of a focus exposure matrix wafer for OPC hotspot identification. However, this can not be done prior to ordering a mask. Based on a 45nm line space layer OPC qualification, we will demonstrate how optical rule check and process window qualification is performed, what the individual results will be, and how they can be used for OPC quality evaluation. The general goal of this work is to show the capabilities of optical rule check and process window qualification, compare both methods, and detect limitations.

Select this Article		Challenges for the quality control of assist features for 45nm node technology and beyond Lin Wang, Todd Lukanc, Makoto Takahashi, Hung-Eil Kim, Khoi Phan, Taichi Yamazaki, Yosuke Kojima, Wataru Nozaki, Takashi Haraguchi, and Yoshimitsu Okuda Proc. SPIE 7122, 71220Z (2008); http://dx.doi.org/10.1117/12.800916 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Current flash memory technology is facing more and more challenges for 45nm and 32nm node technology. To get good CD and yield control, optimized RET, OPC modeling and DFM techniques have to be applied [1]. To enhance process window (PW) and better CD control for main features, assist features (SB) have to be used. Simulation and wafer evaluation show that the SB CD performance is very critical. Based on OPC simulation, we can get a very good prediction about the CD size and placement of assist features. However, we can not always get what we want from mask suppliers. For 45nm node technology and beyond, The SB CD size (~ 20nm at 1X) has almost pushed to the current mask process limit. Wafer fabs have a very big concern about the stability of linearity signatures from different suppliers and different products in order to keep high accuracy of OPC models. Actually the CD linearity signature varies from one mask supplier to another and also varies from product to product. To improve the SB CD control, the ideal goal is to make "flat" linearity for all mask suppliers. By working closely with TPI mask supplier, we come up solutions to improve SB CD control to get "flat" linearity. Also technology development is causing more severe SB printability, we proposed a methodology to use AIMS for predicting SB printability. Wafer results proved the feasibility for these methodologies.

back to top

Advanced Cleaning

Select this Article		Impact of MegaSonic process conditions on PRE and sub-resolution assist feature damage Stefan Helbig, Sabine Urban, Elizabeth Klein, and Sherjang Singh Proc. SPIE 7122, 712210 (2008); http://dx.doi.org/10.1117/12.801408 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The use of MegaSonic energy is widely accepted in photomask cleaning. For the advanced technology nodes, beyond 65nm, the problem of damaged sub resolution assist features (SRAF) becomes highly prevalent. Such feature damages are often related to the application of MegaSonic energy. We investigated the influence of common cleaning media and MegaSonic parameters for damaging SRAF patterns. A special option of our cleaning tool was utilized to test a large number of different settings with low resources for test mask and defect inspections. In this paper we will present the results of our investigations and present conditions for MegaSonic cleaning which will enable the wide use of this technology beyond the 45nm technology node.

Select this Article		Tunable droplet momentum and cavitation process for damage-free cleaning of challenging particles Roman Gouk, James Papanu, Fred Li, Jason Jeon, Tong Liu, and Rao Yalamanchili Proc. SPIE 7122, 712211 (2008); http://dx.doi.org/10.1117/12.801549 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Particle removal without damage has been demonstrated for <60nm photomask sub-resolution assist features with droplet momentum cleaning technology that employs NanoDroplet^TM mixed-fluid jet nozzle. Although 99%+ particle removal efficiency can be achieved for standard Si₃N₄ particles with broad size distribution, there are some cleaning challenges with small (<100nm) and large contact area (>500nm) particles. It was found that tunable uniform cavitation can provide the additional physical assist force needed to improve cleaning efficiency of these challenging particles while meeting the damage-fee cleaning requirement. An integrated cleaning process was developed that combines both droplet momentum and damage-free cavitation technology. Cleaning tests were performed with different types of challenging particles. The results showed 5-8% particle removal efficiency improvement as compared to momentum based only cleaning. All masks were processed using the Tetra^TM mask cleaning tool configured with NanoDroplet^TM mixed fluid jet technology and full face megasonics.

Select this Article		Phase shift improvement in ArF/KrF haze-free mask cleaning Cathy Liu, Shirley Zhao, Eric Guo, Shinichi Hasegawa, Keiichi Nemoto, and Tsuneaki Kuwajima Proc. SPIE 7122, 712212 (2008); http://dx.doi.org/10.1117/12.801439 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The continuous evolution of LSI design rules has created an increased demand for the use of KrF and ArF phase-shift photomasks (EPSMs). One of the critical issues in the use of those photomasks, especially ArF half-tone photomasks, has been the generation of optical hazes known as (NH4)2SO4. The other critical issue has been a relatively large phase shift of those ArF and KrF photomasks caused by so-called haze-free mask cleaning.. In the present study we used an SPM integrated clean (as a reference) consisting of heated SPM, diluted SC-1 and heated UPW (widely known for rinsing), and a haze-free integrated mask clean consisting of Ozonated-water with a simultaneous 222nm Excimer UV irradiation, diluted SC-1 and heated UPW. We found that both Ozonated-water with a simultaneous 222nm Excimer UV irradiation and the diluted SC-1 (the components of the haze-free integrated clean) caused a sizable phase shift during the mask clean. We also found that the other component of the haze-free integrated clean, the heated UPW developed a relatively large phase shift in those photomasks. We have confirmed that the more we repeat the use of the 172nm Excimer UV light irradiation treatment before the clean, the less (more improved) phase shift has been realized in the haze-free clean. We found that the haze-free integrated clean also developed the CD shifts of the above photomasks and that those CD shifts could be recovered (reduced) drastically by the use of the 172nm Excimer UV light irradiation before the clean.

back to top

Haze Contamination Control

Select this Article		Crystal growth printability in an advanced foundry FAB: a correlation study between STARlight and ultra broadband BrightField inspection technologies Teng Hwee Ng, Mohammed Fahmy bin Rahmat, Barry Saville, Patrick Pak, WeeTeck Chia, Aaron Chin, Mike VanRiet, Russell Dover, and Raj Badoni Proc. SPIE 7122, 712213 (2008); http://dx.doi.org/10.1117/12.801868 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In advanced IC manufacturing reticle contamination through crystal growth causing printed defects is a major source of yield loss. This crystal growth requires frequent inspection to ensure reticles are free from such contamination (reticle requalification). STARlight is the industry accepted method for mask inspection in wafer fabs for reticle re-qualification (requal) . The principal focus of this paper is a study correlating the detection of contamination (crystal growth) on logic product masks found with STARlight to defects that can be found on a print-check wafer (a photo-resist test wafer). A critical component in this study was the translation of reticle coordinates to wafer coordinates and integrating the results between high-resolution broadband DUV BrightField inspection (BF) and scanning electron microscope (SEM) review. All of the STARlight defect locations were reviewed using the SEM regardless if the defect was found on opaque or on clear surfaces of the mask. As such defects being SEM reviewed were classified as either 'printing', 'early-warning' or 'non-printing'. BF defect inspection results after repeater analysis were compared with STARlight results to determine the correlations. SEM Defect Review was performed on STARlight inspection results and the resulting classified data was correlated to the BF defect inspection results.

Select this Article		Report of latent contamination factors inducing lithographic variation Jin Ho Ryu, Kang Joon Seo, Ji Sun Ryu, and Chang Yeol Kim Proc. SPIE 7122, 712215 (2008); http://dx.doi.org/10.1117/12.801433 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We have investigated the factors having influence on the lithographic fidelity variation in 193nm masks. Significant researches have been studied that haze contamination, resulting from the absorption of chemical residual ions and mask container out-gassing in mask fabrication, is one of the major component to reduce the optimized lithography condition such as Best Focus, Depth of Focus and Exposure latitude of individual feature. And also environment being containing humidity, ambient AMC (airborne molecular contamination) react with high exposure energy to form crystal growth of ionic molecular complex such as ammonium sulfate causing abnormal printability. Moreover, optical issue of organic pellicle membrane is thoroughly considered that perfluoro polymer degradation induced by high photon energy affect the transmittance intensity. Consequently, these photophysical alterations bring about the lithographic variation and cause considerable defects in wafer printing. In this paper, we tried to verify the influence grade inducing the lithographic variation among the latent contamination factors consisting of mask back-side quartz contamination, the growth of exposure energy based haze phenomena, thin organic pellicle membrane degradation and modified character of MoSiN surface. Metrological inspection and photochemical reaction evaluations were conducted with several equipments including AIMS, Scatterometer, XPS, SIMS, FT-IR, UV, ArF acceleration laser to demonstrate the proposal mechanism of correlation between lithographic variation and latent contamination factors. The optical issues and lifetime of ArF PSM were simulated with the evaluation of effects of pellicle degradation and surface modification.

Select this Article		Detection of progressive transmission loss due to haze with Galileo mask DUV transmittance mapping based on non imaging optics Steven Labovitz, Guy Ben-Zvi, Vladimir Dmitriev, Erez Graitzer, and Eitan Zait Proc. SPIE 7122, 712216 (2008); http://dx.doi.org/10.1117/12.801558 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In this paper, we expand on our earlier work^1,2 reporting the use of high sensitivity DUV transmission metrology as a means for detection of progressive transmission loss on mask and pellicle surfaces. We also report a use case for incoming reticle qualification based on DUV transmission uniformity. Traditional inspection systems rely on algorithms to locate discrete defects greater than a threshold size (typically > 100nm), or printing a wafer and then looking for repeating defects using wafer inspection and SEM review. These types of defect inspection do not have the ability to detect transmission degradation at the low levels where it begins to impact yield. There are numerous mechanisms for transmission degradation, including haze in its early, thin film form, electric-field induced field migration, and pellicle degradation. During the early development of haze, it behaves as a surface film which reduces 193nm transmission and requires compensation by scanner dose. The film forms in a non-uniform fashion, resulting from non-uniformity of exposure on the pattern side due to varying dose passing through the attenuating layers. As this non-uniformity evolves, there is a gradual loss of wafer critical dimension uniformity (CDU) due to a degradation of the exposure dose homogeneity. Electric-field induced migration also appears to manifest as a non-uniform transmission loss, typically presenting with a radial signature. In this paper we present evidence that a DUV transmission measurement system, Galile^TM, is capable of detecting low levels of transmission loss, prior to CDU related yield loss or the appearance of printing defects. Galileo is an advanced DUV transmission metrology system which utilizes a wide-band, incoherent light source and non-imaging optics to achieve sensitivities to transmission changes of less than 0.1%. Due to its very high SNR, it has a fast MAM time of less than 1 sec per point, measuring a full field mask in as little as 30 minutes. A flexible user interface enables users to easily define measurement recipes, threshold sensitivities, and time-based tracking of transmission degradation. The system measures through pellicle under better than class 1 clean air conditions.

Select this Article		A new paradigm for haze improvement: retardation of haze occurrence by creating mask substrate insensitive to chemical contamination level Han-Shin Lee, Jaehyuck Choi, Jin-Sik Jung, Jong-Keun Oh, Soo-Jung Kang, Hae-Young Jeong, Sang-Gyun Woo, and HanKu Cho Proc. SPIE 7122, 712217 (2008); http://dx.doi.org/10.1117/12.801422 Online Publication Date: Oct 20, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Haze issues are getting more serious since size of Haze defect printable on the water surface that could matter is decreasing further with reduced pattern size. Many efforts have been made to reduce the contamination level on the photomask surface by applying wet or dry processes. We have successfully reduced surface contamination down to subppb level for organic and inorganic chemicals. No matter how well the mask surface is cleaned, chemical contaminant cannot be perfectly eliminated from the surface. As long as contaminants exist on the surface, they are getting aggregated around certain points with higher energy to create defects on it during laser exposure. Also, the cleaned mask surface could be contaminated again during following processes such as shipping and storage. Here, we propose a new paradigm for Haze retardation where we severely decelerate defect generation and growth rather than eliminate chemical contaminants on the mask surface. We have made mask surface on which chemical contaminants are hardly accumulated to generate Haze defects even during laser exposure. By creating mask surface insensitive to chemical impurity level up to a certain degree, we are able to retard Haze occurrence much better than by reducing surface impurities down to sub-ppb level. This approach has another advantage of allowing a freedom for mask environment during the process of shipping, storage, and exposure. We further investigate how the treated mask surface should have strong resistance against chemical contaminant aggregation towards Haze defect generation around specific points with high energy.

Select this Article		Simulation analysis of backside defects printability in 193nm photolithography Jisun Ryu, Dongwook Lee, Jinho Ryu, Sookyeong Jeong, SangPyo Kim, and Changyeol Kim Proc. SPIE 7122, 712218 (2008); http://dx.doi.org/10.1117/12.801437 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Backside defects a few micrometers in size are serious concern in lithography because they can degrade the image quality on a wafer. It was known that defects attached on the backside affected the printing images on a wafer by locally altering the partial coherence (σ) and the transmitted intensity of the illumination. The ability to detect and to simulate their impact of defects on the backside is one of the key components in ensuring quality of photomask. The purpose of this study is to determine the minimum size of defects on the backside which would be affected printability in 193nm photolithography. It was investigated to the influence of wafer critical dimension (CD) variation according to illumination and NA, that of refraction according to defect size. For this study, a reticle was designed to include line and space patterns, contact patterns and isolated patterns on the front side. And the type of defects attached on the backside was made of chrome to investigate the relation between transmittance of backside defects and its printability. The correlation of measurements made with UV and DUV-based inspection system; simulation performed with a 193nm aerial image measurement system. Besides the allowable size of backside defects was determined using the criterion of a maximum intensity variation of 10%.

back to top

Wafer Plane Inspection

Select this Article		Optimal mask characterization by Surrogate Wafer Print (SWaP) method Kurt R. Kimmel, Ingo Hoellein, Jan Hendrick Peters, Paul Ackmann, Brid Connolly, and Craig West Proc. SPIE 7122, 712219 (2008); http://dx.doi.org/10.1117/12.801685 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Traditionally, definition of mask specifications is done completely by the mask user, while characterization of the mask relative to the specifications is done completely by the mask maker. As the challenges of low-k1 imaging continue to grow in scope of designs and in absolute complexity, the inevitable partnership between wafer lithographers and mask makers has strengthened as well. This is reflected in the jointly owned mask facilities and device manufacturers' continued maintenance of fully captive mask shops which foster the closer mask-litho relationships. However, while some device manufacturers have leveraged this to optimize mask specifications before the mask is built and, therefore, improve mask yield and cost, the opportunity for post-fabrication partnering on mask characterization is more apparent and compelling. The Advanced Mask Technology Center (AMTC) has been investigating the concept of assessing how a mask images, rather than the mask's physical attributes, as a technically superior and lower-cost method to characterize a mask. The idea of printing a mask under its intended imaging conditions, then characterizing the imaged wafer as a surrogate for traditional mask inspections and measurements represents the ultimate method to characterize a mask's performance, which is most meaningful to the user. Surrogate wafer print (SWaP) is already done as part of leading-edge wafer fab mask qualification to validate defect and dimensional performance. In the past, the prospect of executing this concept has generally been summarily discarded as technically untenable and logistically intractable. The AMTC published a paper at BACUS 2007 successfully demonstrating the performance of SWaP for the characterization of defects as an alternative to traditional mask inspection [1]. It showed that this concept is not only feasible, but, in some cases, desirable. This paper expands on last year's work at AMTC to assess the full implementation of SWaP as an enhancement to mask characterization quality including defectivity, dimensional control, pattern fidelity, and in-plane distortion. We present a thorough analysis of both the technical and logistical challenges coupled with an objective view of the advantages and disadvantages from both the technical and financial perspectives. The analysis and model used by the AMTC will serve to provoke other mask shops to prepare their own analyses then consider this new paradigm for mask characterization and qualification.

Select this Article		High resolution inspection with wafer plane die: database defect detection Carl Hess, Mark Wihl, Rui-fang Shi, Yalin Xiong, and Song Pang Proc. SPIE 7122, 71221A (2008); http://dx.doi.org/10.1117/12.801867 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract High Resolution reticle inspection is well-established as a proven, effective, and efficient means of detecting yieldlimiting mask defects as well as defects which are not immediately yield-limiting yet can enable manufacturing process improvements. Historically, RAPID products have enabled detection of both classes of these defects. The newlydeveloped Wafer Plane Inspection (WPI) detector technology meets the needs of some advanced mask manufacturers to identify the lithographically-significant defects while ignoring the other non-lithographically-significant defects. Wafer Plane Inspection accomplishes this goal by performing defect detection based on a modeled image of how the mask features would actually print in the photoresist. This has the effect of reducing sensitivity to non-printing defects while enabling higher sensitivity focused in high MEEF areas where small reticle defects still yield significant printing defects on wafers. This approach has several important features. The ability to ignore non-printing defects and to apply additional effective sensitivity in high MEEF areas enables advanced node development. In addition, the modeling allows the inclusion of important polarization effects that occur in the resist for high NA operation. This allows for the results to better match wafer print results compared to alternate approaches. Finally, the simulation easily allows for the application of arbitrary illumination profiles. With this approach, users of WPI can make use of unique or custom scanner illumination profiles. This allows the more precise modeling of profiles without inspection system hardware modification or loss of company intellectual property. A previous paper [1] introduced WPI in D:D mode. This paper examines the operation and results for WPI in Die:Database mode.

Select this Article		Wafer plane inspection evaluated for photomask production Emily Gallagher, Karen Badger, Mark Lawliss, Yutaka Kodera, Jaione Tirapu Azpiroz, Song Pang, Hongqin Zhang, Eugenia Eugenieva, Chris Clifford, Arosha Goonesekera, and Yibin Tian Proc. SPIE 7122, 71221B (2008); http://dx.doi.org/10.1117/12.801945 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Wafer Plane Inspection (WPI) is a novel approach to inspection, developed to enable high inspectability on fragmented mask features at the optimal defect sensitivity. It builds on well-established high resolution inspection capabilities to complement existing manufacturing methods. The production of defect-free photomasks is practical today only because of informed decisions on the impact of defects identified. The defect size, location and its measured printing impact can dictate that a mask is perfectly good for lithographic purposes. This inspection - verification - repair loop is timeconsuming and is predicated on the fact that detectable photomask defects do not always resolve or matter on wafer. This paper will introduce and evaluate an alternative approach that moves the mask inspection to the wafer plane. WPI uses a high NA inspection of the mask to construct a physical mask model. This mask model is used to create the mask image in the wafer plane. Finally, a threshold model is applied to enhance sensitivity to printing defects. WPI essentially eliminates the non-printing inspection stops and relaxes some of the pattern restrictions currently placed on incoming photomask designs. This paper outlines the WPI technology and explores its application to patterns and substrates representative of 32nm designs. The implications of deploying Wafer Plane Inspection will be discussed.

Select this Article		Wafer plane inspection with soft resist thresholding Carl Hess, Rui-fang Shi, Mark Wihl, Yalin Xiong, and Song Pang Proc. SPIE 7122, 71221C (2008); http://dx.doi.org/10.1117/12.801866 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Wafer Plane Inspection (WPI) is an inspection mode on the KLA-Tencor TeraSca^TM platform that uses the high signalto- noise ratio images from the high numerical aperture microscope, and then models the entire lithographic process to enable defect detection on the wafer plane[1]. This technology meets the needs of some advanced mask manufacturers to identify the lithographically-significant defects while ignoring the other non-lithographically-significant defects. WPI accomplishes this goal by performing defect detection based on a modeled image of how the mask features would actually print in the photoresist. There are several advantages to this approach: (1) the high fidelity of the images provide a sensitivity advantage over competing approaches; (2) the ability to perform defect detection on the wafer plane allows one to only see those defects that have a printing impact on the wafer; (3) the use of modeling on the lithographic portion of the flow enables unprecedented flexibility to support arbitrary illumination profiles, process-window inspection in unit time, and combination modes to find both printing and non-printing defects. WPI is proving to be a valuable addition to the KLA-Tencor detection algorithm suite. The modeling portion of WPI uses a single resist threshold as the final step in the processing. This has been shown to be adequate on several advanced customer layers, but is not ideal for all layers. Actual resist chemistry has complicated processes including acid and base-diffusion and quench that are not consistently well-modeled with a single resist threshold. We have considered the use of an advanced resist model for WPI, but rejected it because the burdensome requirements for the calibration of the model were not practical for reticle inspection. This paper describes an alternative approach that allows for a "soft" resist threshold to be applied that provides a more robust solution for the most challenging processes. This approach is just finishing beta testing with a customer developing advanced node designs.

Select this Article		AIMS and resist simulation Ulrich Strößner, Holger Seitz, Robert Birkner, Rigo Richter, and Thomas Scherübl Proc. SPIE 7122, 71221D (2008); http://dx.doi.org/10.1117/12.801226 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The AIM^TM45-193i is the established tool for mask performance qualification and defect printing analysis in the mask shop under scanner conditions. Vector effects are taken into account by the proprietary Zeiss vector effect emulator. In several studies an excellent correlation to wafer prints has been reported. However, a systematic offset to wafer prints in terms of mask error enhancement factor (MEEF) and exposure latitude has been observed which is attributed to well known resist effects. The AIMS^TM measures the aerial image in resist whereas in a real lithography process further image blur of the latent image is caused by photo acid diffusion during wafer processing and resist development. To explain the gap between the AIM^TM and wafer prints we have investigated aerial images in combination with an easy to use resist model. It does take resist effects into account with sufficient accuracy to explain printing behavior of photo masks but without the need to calibrate lots of parameters of the actually used resist which usually are not known to a mask shop. The resist effects predominantly reduce the image contrast and thus increase the MEEF and the sensitivity to mask defects. This somewhat counterintuitive behavior is labeled "contrast enhancement by contrast reduction". Additionally application of the resist model improves the agreement of e.g. the exposure latitude or MEEF measured by the AIMS^TM compared to wafer prints.

Select this Article		AIMS-45 image validation of contact hole patterns after inverse lithography at NA 1.35 E. Hendrickx, R. Birkner, M. Kempsell, A. Tritchkov, G. Vandenberghe, and T. Scheruebl Proc. SPIE 7122, 71221E (2008); http://dx.doi.org/10.1117/12.801559 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The AIMS^TM-45, when used in scanner mode, can emulate image intensity as seen in resist on the wafer at scanner illumination conditions. We show that this feature makes AIMS^TM-45 well-suited to analyze patterns treated with inverse lithography. We have used an inverse lithography technique by Mentor Graphics, to treat a random contact hole layout (drawn at minimal pitch 115nm) for imaging at NA 1.35. The combination of the dense 115nm pitch and available NA of 1.35 makes Quasar illumination necessary, and the inverse lithography treatment automatically generated optimal (model-based) Assist Features (AF) for all geometries in the design. The mask, after inverse lithography treatment, has CH patterns with numerous AF of different sizes and orientations, and is a challenge for both mask making and mask qualification. We have analyzed the inverse lithography masks with the model-based AF using an AIMS^TM-45 aerial image measurement tool, and compare the results of the AIMS^TM-45 to wafer data obtained after exposure on an ASML XT:1900i. A first benefit of AIM^TM-45 is that the most meaningful quantity (image in resist) is generated without the intermediate steps of doing multiple reticle SEM measurements followed by extensive simulation. A second point of interest is that the AIMS^TM-45 generates image intensities, which allows a direct validation of the intensity-driven inverse litho conversion. Both features prove the value of the AIMS^TM-45 for analyzing inverse litho masks and geometries.

back to top

Inspection

Select this Article		Auto-classification and simulation of mask defects using SEM and CAD images Tung-Yaw Kang, Hsin-Chang Lee, H. Zhang, K. Yamada, Y. Kitayama, K. Kobayashi, and Peter Fiekowsky Proc. SPIE 7122, 71221F (2008); http://dx.doi.org/10.1117/12.801411 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Mask defect disposition gets more difficult and time-consuming with each progressive lithography node. Mask inspection tools commonly use 250 nm wavelength, giving resolution of 180 nm, so critical defect sizes are far less than the optical resolution - too small for defect analysis. Thus the rate of false or nuisance defect detection is increasing rapidly and analysis of detected defects is increasingly difficult. As to judging the wafer printability of defects, AIMS (Aerial Image Measurement System) tools are commonly used but are also time-consuming if defect count is high. For improving the efficiency of mask defect disposition, we propose the combination of a SEM defect review tool and defect disposition and simulation software, which use high-resolution SEM images of defects to do defect review, defect disposition, and wafer printing simulation of defects automatically or manually. The SEM defect review tool, DIS-05 developed by Holon Co. Ltd., is designed for defect review and disposition using reference images derived from e-beam files or CAD database. This tool uses the Automated Defect Analysis Software (ADAS) developed from AVI LLC. to interface the inspection tool and the DIS-05. ADAS detects false defects before SEM imaging and performs aerial image simulation from the SEM and CAD images to estimate the wafer CD error caused by each defect. We report on its speed (>300 defects/hour), classification accuracy and simulation accuracy when used with masks at the 45 nm technology node and beyond. This combination of SEM and ADAS is expected to significantly accelerate process development and production for the 45 and 32 nm nodes. It will also increase the masksper- day throughput of inspection and AIMS tools by shifting most defect review to ADAS software using SEM images. At preliminary tests showed the combination tool can do auto defect disposition and simulation with promising results.

Select this Article		Novel mask inspection flow using Sensitivity Control Layers (SCL) on the TeraScanHR-587 platform Shad Hedges, Chin Le, Mark Eickhoff, Mark Wylie, Tim Simmons, Venu Vellanki, and Jeff McMurran Proc. SPIE 7122, 71221G (2008); http://dx.doi.org/10.1117/12.801480 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Conventional photomask inspection techniques utilize global sensitivity for all inspected area in the die; SRAF and OPC features become the sensitivity-limiters, which can result in reduced visibility to defects of interest (DOI). We describe the implementation of Sensitivity Control Layer (SCL), a novel database inspection methodology for the KLA-Tencor TerascanHR platform. This methodology enables inspection at maximum sensitivity in critical die-areas via "layer definition" during job set-up and sensitivity management of the layers during inspection. Memory device inspection performance was improved through the use of up to six control layers to increase sensitivity in the active area while reducing nuisance detections by as much as 100X. The corresponding inspection time was reduced by 30%, illustrating the potential for substantial throughput advantage using SCL. Post-inspection analysis and improved disposition accuracy of the SCL-enabled inspections will also benefit cycle time and higher throughput. In all test cases, sensitivity parameters were increased in the regions of interest over baseline inspections run with typical production-use methodologies. SCL inspection management and application on OPC structures, SRAFs, and MRC violations (slivers) are discussed in detail.

Select this Article		Evaluating practical vs. theoretical inspection system capability with a new programmed defect test mask designed for 3X and 4X technology nodes Joshua Glasser and Tim Pratt Proc. SPIE 7122, 71221H (2008); http://dx.doi.org/10.1117/12.801546 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Programmed defect test masks serve the useful purpose of evaluating inspection system sensitivity and capability. It is widely recognized that when evaluating inspection system capability, it is important to understand the actual sensitivity of the inspection system in production; yet unfortunately we have observed that many test masks are a more accurate judge of theoretical sensitivity rather than real-world usable capability. Use of ineffective test masks leave the purchaser of inspection equipment open to the risks of over-estimating the capability of their inspection solution and overspecifying defect sensitivity to their customers. This can result in catastrophic yield loss for device makers. In this paper we examine some of the lithography-related technology advances which place an increasing burden on mask inspection complexity, such as MEEF, defect printability estimation, aggressive OPC, double patterning, and OPC jogs. We evaluate the key inspection system component contributors to successful mask inspection, including what can "go wrong" with these components. We designed and fabricated a test mask which both (a) more faithfully represents actual production use cases; and (b) stresses the key components of the inspection system. This mask's patterns represent 32nm, 36nm, and 45nm logic and memory technology including metal and poly like background patterns with programmed defects. This test mask takes into consideration requirements of advanced lithography, such as MEEF, defect printability, assist features, nearly-repetitive patterns, and data preparation. This mask uses patterns representative of 32nm, 36nm, and 45nm logic, flash, and DRAM technology. It is specifically designed to have metal and poly like background patterns with programmed defects. The mask is complex tritone and was designed for annular immersion lithography.

back to top

Defect Repair

Select this Article		Nanomachining photomask repair of complex patterns Tod Robinson, Andrew Dinsdale, Mike Archuletta, Ron Bozak, and Roy White Proc. SPIE 7122, 71221I (2008); http://dx.doi.org/10.1117/12.801297 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Improvements in repair process, software, and AFM tip technology have brought about an overall 2D shape reconstruction capability to nanomachining that has not been previously imagined. Repair results are shown for various processes to highlight their relative strengths and weaknesses. The impact of technical improvements is shown in the advances in repair dimensional precision and overall imaging performance. The greater technical potential of nanomachining is realized in this examination for mask repair scaled to smaller repair geometries while repairing larger defects that may span these critical patterns.

Select this Article		Practical laser mask repair in the contemporary production environment Tod Robinson, Roy White, Mike Archuletta, and Ron Bozak Proc. SPIE 7122, 71221J (2008); http://dx.doi.org/10.1117/12.801301 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract It has been found that the femtosecond DUV laser mask repair tool has significant utility in the repair of unknown foreign material (FM) contamination of sizes ranging from 50 nm to 30 μm with highly variable z-heights both isolated and within critical complex patterns. Another significant ROI is the repair of masks which have already been pelliclized (through pellicle repair or TPR) where the laser repair tool may work in conjunction with existing through-pellicle inspection hardware to detect and remove FM and correct pattern errors. The capability of the tool is also explored for repairs in patterns including the 45 nm technology node.

Select this Article		Advanced process capabilities for electron beam based photomask repair in a production environment Anthony Garetto, Christof Baur, Jens Oster, Markus Waiblinger, and Klaus Edinger Proc. SPIE 7122, 71221K (2008); http://dx.doi.org/10.1117/12.801554 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The cost and time associated with the production of photolithographic masks continues to grow, driven by the ever decreasing feature size, advanced mask technologies and complex resolution enhancing techniques. Thus employment of a high-resolution, comprehensive mask repair tool becomes a key element for a successful production line. The MeRiT® utilizes electron beam induced chemistry to repair both clear and opaque defects on a variety of masks and materials with the highest available resolution and edge placement precision. This paper describes the benefits of the electron beam induced technique as employed by the MeRiT® system for a production environment.

back to top

RET and OPC/ORC II

Select this Article		32nm 1-D regular pitch SRAM bitcell design for interference-assisted lithography Robert T. Greenway, Kwangok Jeong, Andrew B. Kahng, Chul-Hong Park, and John S. Petersen Proc. SPIE 7122, 71221L (2008); http://dx.doi.org/10.1117/12.801883 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As optical lithography advances into the 45nm technology node and beyond, new manufacturing-aware design requirements have emerged. We address layout design for interference-assisted lithography (IAL), a double exposure method that combines maskless interference lithography (IL) and projection lithography (PL); cf. hybrid optical maskless lithography (HOMA) in [2] and [3]. Since IL can generate dense but regular pitch patterns, a key challenge to deployment of IAL is the conversion of existing designs to regular-linewidth, regular-pitch layouts. In this paper, we propose new 1-D regular pitch SRAM bitcell layouts which are amenable to IAL. We evaluate the feasibility of our bitcell designs via lithography simulations and circuit simulations, and confirm that the proposed bitcells can be successfully printed by IAL and that their electrical characteristics are comparable to those of existing bitcells.

Select this Article		Convergence-based OPC method for dense simulations Tamer Desouky Proc. SPIE 7122, 71221M (2008); http://dx.doi.org/10.1117/12.801431 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As the process of migration of Optical process correction (OPC) recipes continues to go from sparse to dense computations, a run time effectiveness issue persists to remain for huge structures that exist in some metal and active layers designs. Even for 45 and 32 nm technology nodes, some polygons might be several microns in width consuming a vast amount of simulation time and order of magnitudes more than sparse simulations to converge. Practically, this problem is pronounced, which is usually the case, when the design comprises these huge structures and other small critical ones that needs many iterations and careful tuning to converge. And thus, a considerable amount of run time will be wasted while applying these sophisticated recipes on big structures that could originally converge within few iterations using a simple recipe. In this context, a convergence-based dense OPC recipe is proposed to deal with designs that have both types of structures. The basic idea is to check convergence prior starting next iteration and skip the rest of the iterations if the whole simulated frame has converged within a predefined tolerance. Also, a reasonable way to define tolerances is explored.

Select this Article		Combination of rule and pattern based lithography unfriendly pattern detection in OPC flow Jae-Hyun Kang, Jae-Young Choi, Yeon-Ah Shim, Hye-Sung Lee, Bo Su, Walter Chan, Ping Zhang, Joanne Wu, and Keun-Young Kim Proc. SPIE 7122, 71221N (2008); http://dx.doi.org/10.1117/12.801312 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Foundry companies encounter again and again the same or similar lithography unfriendly patterns (Hot-spots) in different designs within the same technology node and across different technology nodes, which eluded design rule check (DRC), but detected again and again in OPC verification step. Since Model-based OPC tool applies OPC on whole-chip design basis, individual hot-spot patterns are treated same as the rest of design patterns, regardless of its severity. We have developed a methodology to detect those frequently appeared hot-spots in pre-OPC design, as well as post OPC designs to separate them from the rest of designs, which provide the opportunity to treat them differently in early OPC flow. The methodology utilizes the combination of rule based and pattern based detection algorithms. Some hotspot patterns can be detected using rule-based algorithm, which offer the flexibility of detecting similar patterns within pre-defined ranges. However, not all patterns can be detected (or defined) by rules. Thus, a pattern-based approach is developed using defect pattern library concept. The GDS/OASIS format hot-spot patterns can be saved into a defect pattern library. Fast pattern matching algorithm is used to detect hot-spot patterns in a design using the library as a pattern template database. Even though the pattern matching approach lacks the flexibility to detect patterns' similarity, but it has the capability to detect any patterns as long as a template exists. The pattern-matching algorithm can be either exact match or a fuzzy match. The rule based and pattern based hot-spot pattern detection algorithms complement each other and offer both speed and flexibility in hot spot pattern detection in pre-OPC and post-OPC designs. In this paper, we will demonstrate the methodology in our OPC flow and the benefits of such methodology application in production environment for 90nm designs. After the hot spot pattern detection, examples of special treatment to selected hot spot patterns will be shown.

Select this Article		Automated OPC model collection, cleaning, and calibration flow Martin Drapeau, Brian S. Ward, and Brad Falch Proc. SPIE 7122, 71221O (2008); http://dx.doi.org/10.1117/12.801525 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract OPC model calibration requires thousands of experimental data points. These are then used to calibrate an OPC model. Today, the majority of these steps are performed manually. Metrology for example involves taking the CD-SEM offline for an operator to program it. Considerable time savings is possible by writing the CD-SEM recipe offline. Experimental data preparation is also often performed manually. Manual review of thousands of data points is a tedious task prone to human errors. Here again, automation can greatly alleviate the engineering effort, reduce cycle-time and improve data quality. Data quality improvement alone has been shown to have a significant benefit to model calibration accuracy and predictability. In this paper we present an automated solution for the currently engineering effort intensive components of the OPC model calibration flow. The flow we present is integrated inside the OPC environment. We suggest best practices identified through the implementation of an automated flow, and discuss benefits. Our results demonstrate the capability and quantify the benefits which automation brings in human effort, reduced time to accurate model and improved model quality.

back to top

Simulation and Modeling I

Select this Article		Improvements in accuracy of dense OPC models Chidam Kallingal, James Oberschmidt, Ramya Viswanathan, Amr Abdo, and OSeo Park Proc. SPIE 7122, 71221Q (2008); http://dx.doi.org/10.1117/12.801695 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Performing model-based optical proximity correction (MBOPC) on layouts has become an integral part of patterning advanced integrated circuits. Earlier technologies used sparse OPC, the run times of which explode when the density of layouts increases. With the move to 45 nm technology node, this increase in run time has resulted in a shift to dense simulation OPC, which is pixel-based. The dense approach becomes more efficient at 45nm technology node and beyond. New OPC model forms can be used with the dense simulation OPC engine, providing the greater accuracy required by smaller technology nodes. Parameters in the optical model have to be optimized to achieve the required accuracy. Dense OPC uses a resist model with a different set of parameters than sparse OPC. The default search ranges used in the optimization of these resist parameters do not always result in the best accuracy. However, it is possible to improve the accuracy of the resist models by understanding the restrictions placed on the search ranges of the physical parameters during optimization. This paper will present results showing the correlation between accuracy of the models and some of these optical and resist parameters. The results will show that better optimization can improve the model fitness of features in both the calibration and verification set.

Select this Article		Defining a physically accurate laser bandwidth input for optical proximity correction (OPC) and modeling Ivan Lalovic, Oleg Kritsun, Sarah McGowan, Joseph Bendik, Mark Smith, and Nigel Farrar Proc. SPIE 7122, 71221R (2008); http://dx.doi.org/10.1117/12.801556 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In this study, we discuss modeling finite laser bandwidth for application to optical proximity modeling and correction. We discuss the accuracy of commonly-used approximations to the laser spectrum shape, namely the modified Lorentzian and Gaussian forms compared to using measurement-derived laser fingerprints. In this work, we show that the use of the common analytic functions can induce edge placement errors of several nanometers compared to the measured data and therefore do not offer significant improvement compared to the monochromatic assumption. On the other hand, the highlyaccurate laser spectrum data can be reduced to a manageable number of samples and still result in sub 0.5nm error through pitch and focus compared to measured spectra. We have previously demonstrated that a 23-point approximation to the laser data can be generated from the spectrometry data, which results in less than 0.1nm RMS error even over varied illumination settings. We investigate the further reduction in number of spectral samples down to five points and consider the resulting accuracy and model-robustness tradeoffs. We also extend our analysis as a function of numerical aperture and illumination setting to quantify the model robustness of the physical approximations. Given that adding information about the laser spectrum would primarily impact the model-generation run-times and not the run-times for the OPC implementation, these techniques should be straightforward to integrate with current full-chip OPC flows. Finally, we compare the relative performance of a monochromatic model, a 5-point laser-spectral fingerprint, and two Modified Lorentzian fits in a commercial OPC simulator for a 32nm logic lithography process. The model performance is compared at nominal process settings as well as through dose, focus and mask bias. Our conclusions point to the direction for integration of this approach within the framework of existing EDA tools and flows for OPC model generation and process-variability verification.

Select this Article		Benchmark of rigorous methods for electromagnetic field simulations Sven Burger, Lin Zschiedrich, Frank Schmidt, Peter Evanschitzky, and Andreas Erdmann Proc. SPIE 7122, 71221S (2008); http://dx.doi.org/10.1117/12.801248 \| Cited 3 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We have developed an interface which allows to perform rigorous electromagnetic field (EMF) simulations with the simulator JCMsuite and subsequent aerial imaging and resist simulations with the simulator Dr.LiTHO.With the combined tools we investigate the convergence of near-field and far-field results for different DUV masks. We also benchmark results obtained with the waveguide-method EMF solver included in Dr.LiTHO and with the finite-element-method EMF solver JCMsuite. We demonstrate results on convergence for dense and isolated hole arrays, for masks including diagonal structures, and for a large 3D mask pattern of lateral size 10 microns by 10 microns.

Select this Article		Fast and accurate hybrid subgrid and subcell finite-difference time-domain methods for the simulation of mask electromagnetic effects in sub-45nm lithography Michael S. Yeung Proc. SPIE 7122, 71221T (2008); http://dx.doi.org/10.1117/12.801351 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Subgrid and subcell FDTD (S-FDTD) methods are described. They can be used for the fast and accurate simulation of mask electromagnetic effects in sub-45nm lithography. The accuracies of the S-FDTD methods are verified by comparison with FDTD and with a very accurate pseudospectral reference solution. The S-FDTD methods are an order of magnitude or more faster than FDTD. Furthermore, the S-FDTD methods require much less memory than FDTD for time marching. Hence, much larger mask areas can be simulated with S-FDTD than with FDTD.

Select this Article		An efficient method for transfer cross coefficient approximation in model based optical proximity correction Romuald Sabatier, Caroline Fossati, Salah Bourennane, and Antonio Di Giacomo Proc. SPIE 7122, 71221U (2008); http://dx.doi.org/10.1117/12.801623 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Model Based Optical Proximity Correction (MBOPC) is since a decade a widely used technique that permits to achieve resolutions on silicon layout smaller than the wave-length which is used in commercially-available photolithography tools. This is an important point, because masks dimensions are continuously shrinking. As for the current masks, several billions of segments have to be moved, and also, several iterations are needed to reach convergence. Therefore, fast and accurate algorithms are mandatory to perform OPC on a mask in a reasonably short time for industrial purposes. As imaging with an optical lithography system is similar to microscopy, the theory used in MBOPC is drawn from the works originally conducted for the theory of microscopy. Fourier Optics was first developed by Abbe to describe the image formed by a microscope and is often referred to as Abbe formulation. This is one of the best methods for optimizing illumination and is used in most of the commercially available lithography simulation packages. Hopkins method, developed later in 1951, is the best method for mask optimization. Consequently, Hopkins formulation, widely used for partially coherent illumination, and thus for lithography, is present in most of the commercially available OPC tools. This formulation has the advantage of a four-way transmission function independent of the mask layout. The values of this function, called Transfer Cross Coefficients (TCC), describe the illumination and projection pupils. Commonly-used algorithms, involving TCC of Hopkins formulation to compute aerial images during MBOPC treatment, are based on TCC decomposition into its eigenvectors using matricization and the well-known Singular Value Decomposition (SVD) tool. These techniques that use numerical approximation and empirical determination of the number of eigenvectors taken into account, could not match reality and lead to an information loss. They also remain highly runtime consuming. We propose an original technique, inspired from tensor signal processing tools. Our aim is to improve the simulation results and to obtain a faster algorithm runtime. We consider multiway array called tensor data T CC. Then, in order to compute an aerial image, we develop a lower-rank tensor approximation algorithm based on the signal subspaces. For this purpose, we propose to replace SVD by the Higher Order SVD to compute the eigenvectors associated with the different modes of TCC. Finally, we propose a new criterion to estimate the optimal number of leading eigenvectors required to obtain a good approximation while ensuring a low information loss. Numerical results we present show that our proposed approach is a fast and accurate for computing aerial images.

back to top

Simulation and Modeling II

Select this Article		Scanner-specific separable models for computational lithography Stefan Hunsche, Xu Xie, Qian Zhao, Hua-Yu Liu, Peter Nikolsky, and Anthony Ngai Proc. SPIE 7122, 71221V (2008); http://dx.doi.org/10.1117/12.801706 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The usage of conventional OPC models traditionally was confined to the specific process conditions at which the models were. Separable models for computational lithography (CL), including OPC and post-OPC layout verification, allow extrapolation of the calibrated model and accurate prediction at process conditions different from the exact settings used for model calibration. This capability enables significantly reduced turnaround time in early process development, and it opens the way for new applications such as model based process optimization. It relies on sufficiently accurate modeling of litho process components as separate subsystems, in particular mask, scanner optics, and resist process. Inclusion of actual machine parameters of the exposure tool in the optical model can improve model accuracy and predictability, while 'actual machine parameters' may represent either a specific scanner type or an individual exposure tool. We study the impact of machine parameters that can be incorporated in a modern computational litho model, by analyzing their relative effect on predicted CD measurements and extract a ranking in terms of their expected benefit for model separability. An experimental study demonstrates improved model accuracy and separability by inclusion of either scanner-type specific model data or individual machine-specific metrology data in the CL model building process.

Select this Article		Considering MEEF in inverse lithography technology (ILT) and source mask optimization (SMO) Linyong Pang, Guangming Xiao, Vikram Tolani, Peter Hu, Thomas Cecil, Thuc Dam, Ki-Ho Baik, and Bob Gleason Proc. SPIE 7122, 71221W (2008); http://dx.doi.org/10.1117/12.803801 \| Cited 7 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Mask Error Enhancement Factor (MEEF) plays an increasingly important role in the DFM and RET flow required to continue shrinking designs in the low-k1 lithography regime. The ability to model and minimize MEEF during lithography optimization and RET application is essential to obtain a usable process window (PW). In Inverse Lithography Technology (ILT), MEEF can be included in the cost function as a nonlinear factor, so that the inversion minimizes MEEF, in addition to optimizing PW and edge placement error (EPE). ILT has been shown to optimize masks for a given source. Using ILT for contemporaneous Source and Mask co-Optimization (SMO) can provide further benefit by balancing the complexity of mask and source. Results demonstrating the benefits of "MEEF-aware" ILT and SMO for advanced technology nodes are presented in this paper.

Select this Article		Smoothing based model for images of buried EUV multilayer defects near absorber features Chris H. Clifford and Andrew R. Neureuther Proc. SPIE 7122, 71221X (2008); http://dx.doi.org/10.1117/12.801311 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A modification has been made to the fast simulator RADICAL which allows it to simulate the reflected field from an EUV mask with a buried defect 15,000 times faster than the finite difference time domain method (FDTD). This new version uses an advanced single surface approximation (SSA) instead of ray tracing to model the defective multilayer stack. RADICAL with SSA can simulate a 32nm line space pattern with a buried defect in 4.0s. The accuracy of this method is verified with comparisons to FDTD simulations and good agreement is shown. The ability of this method to simulate large layouts with arbitrary defects is demonstrated. A 1.5μm x 1.5μm layout with an arbitrary buried defect and multilayer surface roughness is simulated in 75s. An alternative algebraic fast model for buried defects near absorber lines is also investigated based on the linear relationship between the surface height of isolated buried defects and the aerial image dip strength. However, the interaction is shown to be too complicated for accurate representation with the model proposed.

Select this Article		Simulation-based EUV source and mask optimization Tim Fühner, Andreas Erdmann, and Peter Evanschitzky Proc. SPIE 7122, 71221Y (2008); http://dx.doi.org/10.1117/12.801436 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Source and mask optimization has become a promising technique to push the limits of 193 nm immersion lithography. As the introduction of EUV lithography is at least delayed to the 22 nm technology node, sophisticated resolution enhancement techniques will already be required at a very early stage. Thus, pinpointing ideal mask layouts, mask materials, and illumination settings are as important aspects for EUV as for optical lithography. In this paper, we propose the application of global optimization techniques to identify appropriate process conditions for EUV lithography, using rigorous mask and imaging simulations.

back to top

DFM

Select this Article		DFM viewpoints of cell-level layout assessments and indications for concurrent layout optimization Chung-Min Fu, Ping-Heng Yeh, Yi-Kan Cheng, and Simon Klaver Proc. SPIE 7122, 71221Z (2008); http://dx.doi.org/10.1117/12.802244 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Design-for-manufacturing (DFM) is becoming an actual design practice among IC manufacturers, designers and EDA companies. Layout assessment by design-rule-check (DRC) using EDA tools is a common practice today to ensure well-manufactured design geometries. Standalone DFM tools, which require iteration loops of DFM analysis and fixing, do not fit well in design flows and are considered cumbersome. A better layout assessment method for DFM issues is required: one that gives actionable feedback, and that can be used with automatic optimization in early design stages. The latter is needed to avoid costly design re-spins that will consume critical time-to-market as well as use a lot of engineering resources, reticles and wafer material costs. For example, a DFM checking tool may report the hotspot types and locations, but this information is not sufficient for designers to decide tradeoffs between different fixing choices and to take care of trade-off between physical and electrical design constraints at the same time. When model-based properties are introduced such as lithographic contour, the tradeoffs between rule-based and model-based properties can only be resolved by the automatic and concurrent optimization. This work demonstrates a methodology of DFM scoring of layout based on preferred rules compliance, lithography GATE printability, as well as the layout fixing. The electrical impact on gates is analyzed and showed reduced variability (compared to nominal behavior) in gate performance. Designers can get visual feedback of the layout quality, as well as improvement suggestions. Takumi TKE software is used to demonstrate automatic and concurrent optimization. The method applies to both cell-level and custom designs.

Select this Article		Concurrent optimization of MDP, mask writing, and mask inspection for mask manufacturing cost reduction Masaki Yamabe, Tadao Inoue, Masahiro Shoji, Hiroshi Yasuda, Hiromichi Hoshi, and Masakazu Tokita Proc. SPIE 7122, 712220 (2008); http://dx.doi.org/10.1117/12.802966 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As the feature size of LSI shrinks the cost of mask manufacturing and turn-around-time (TAT) continues to increase. These increases are reaching to points of great concerns. Association of Super-Advanced Electronics Technologies (ASET) Mask Design, Drawing, and Inspection Technology Research Department (Mask D2I) launched a 4-year program for reducing mask manufacturing cost and TAT by concurrent optimization of MDP, mask writing, and mask inspection that involves exploitation of close relationships and synergism among them. The task will be accomplished by sharing four key avenues: a) common data format, b) clever use of repeating patterns, c) pattern prioritization based on design intent, and d) parallel processing. Under the concurrent optimization scheme, mask pattern priorities that we call as Mask Data Rank (MDR) are extracted from the design side, and repeating patterns are extracted from mask pattern data. These are fed-forward to mask writing and mask inspection sides. In mask writing, MDR is employed to optimize the writing conditions; and in Character Projection (CP) writing, repeating patterns are utilized for that purpose. In mask inspection, MDR is used to optimize defect judgment conditions, and repeating patterns are utilized for efficient review. For mask writing, we are developing a parallel e-beam writing system Multi Column Cell (MCC). Furthermore, we are developing an integrated diagnostic system for e-beam mask writer, and a technology for defect judgment technology based on defect printability in mask inspection. In this paper we describe details of our activity, its status, and some recent results.

Select this Article		Design for manufacturability guideline development: integrated foundry approach Hyesung Lee, Yeon-Ah Shim, Jae-Young Choi, Kwang-Seon Choi, Joanne Wu, Bo Su, Xinwei Zhou, and Kenny Kim Proc. SPIE 7122, 712221 (2008); http://dx.doi.org/10.1117/12.801421 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract It has been widely accepted that to ensure good yield in IC wafer manufacturing, early adaptation of DFM (Design for Manufacturability) guidelines in design phase is required and it is particularly true in Foundry business. Integrated foundry approaches for DFM guideline development were presented in this paper. With emphasis of process variations and process sensitivity impact on design patterns, we describe the procedure of the combination of rule-based and simulation-based lithographical hotspot pattern characterizations. An evaluation of process sensitivity metrics for analyzing potential pattern hotspots is then described. In addition, based on hotspot pattern severity, repeated patterns from different designs are saved into a pattern library as knowledge deposition tool and those patterns can be easily identified later in new designs through pattern search, which is much faster than simulation based hotspot detections. With this approach, a set of DFM compliance rules is derived to designs in the design implementation stage for both 110nm and 90nm technology nodes, striving to gain more yield, device performance, and improve time-to-volume production.

Select this Article		Flexible sensitivity inspection with TK-CMI software for criticality-awareness Frank A. J. M. Driessen, Jamila Gunawerdana, Yakuko Saito, Hideo Tsuchiya, and Yoshitake Tsuji Proc. SPIE 7122, 712222 (2008); http://dx.doi.org/10.1117/12.803593 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In this paper we present the method that NuFlare photomask inspection systems can use to strongly reduce pseudo detections by use of TK-CMI software. The NuFlare inspection system is capable to detect the smallest defects in the 45 and 32-nm nodes and has recently been introduced to production. It links up with a compute cluster with Takumi's Criticality-Marker Information software (TK-CMI). TK-CMI quickly analyzes the ~200GB post-OPC layout or multi-layer pre-OPC layout and assigns various types of criticality regions. The basic set of criticalities is made to address the challenges that typical maskmakers experience. The TKCMI system also supports design-intent-based criticalities. The NuFlare inspection system uses this full-mask criticality information and generates flexible inspection recipes that inspect low-criticality areas with relaxed sensitivity resulting in reduction of pseudo detections in such regions.

Select this Article		Improving contact and via process latitude through selective upsizing C. Yuan, G. Abeln, B. Anthony, G. Chen, S. Robertson, and P. Walker Proc. SPIE 7122, 712223 (2008); http://dx.doi.org/10.1117/12.801187 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract This paper describes a simple technique to improve the process latitude for contact and via printing. The technique applies a selective upsizing algorithm to the mask data during the mask preparation step. For each contact or via, the algorithm looks for available spaces by checking relevant layers near it. When spaces are available, selective edges of a contact or via will be sized to improve the process latitude. This paper describes algorithms used to implement this technique. Multiple designs of various design styles are used to demonstrate the effectiveness of the algorithms. The implications on mask preparation, mask making and wafer processing are also discussed.

Select this Article		Assist feature aware double patterning decomposition Christopher Cork, Levi Barnes, and Gerard Luk-Pat Proc. SPIE 7122, 712224 (2008); http://dx.doi.org/10.1117/12.801562 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Double patterning has gained prominence as the most likely lithographic methodology to help keep Moore's law going towards 32nm 1/2 pitch lithography. While solutions, to date, have focused mainly on gap splitting to avoid minimum spacing violations, the decomposition should, ideally, also attempt to optimize the process window of the decomposed masks. A major contributor to process window sensitivity is the correct placement of sub-resolvable assist features. These features are placed once the polygons of each mask are defined, i.e. post decomposition. If some awareness of this downstream process step is made available to the double patterning decomposition stage, then a more robust decomposition can be achieved.

back to top

EUV Mask Processing and Substrates

Select this Article		Development status of EUVL mask blanks Kazuaki Shiromo Proc. SPIE 7122, 712225 (2008); http://dx.doi.org/10.1117/12.801427 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Extreme ultraviolet lithography (EUVL) is the most promising lithographic technology to fabricate the next generation devices with a 20~30 nm feature size or smaller. The production of the EUVL mask blank is one of the critical issues to realize the EUVL because of various kinds of stringent requirements. For instance, a <+/-5 ppb/K thermal expansion coefficient (CTE) and a <30 nm surface flatness of the polished substrate, a high and uniform reflectivity at the 13~14 nm wavelength of the reflective multilayer film, and a low defect density as small as 30nm of the blank. Most of these requirements are different from the optical lithography mask blank and some are specific to the EUVL blank. We have continuously been developing all of key materials and processes essential to prepare the EUVL mask blank, and we showed a good progress in its performance improvement. Our low thermal expansion material (LTEM) showed the CTE properties requirements defined in SEMI P37, which were 0 +/- 5 ppb/K mean CTE at 22°C and < +/-3 ppb/K CTE spatial variation across 6 inch square substrate. ~30nm flatness was demonstrated on both front and back surfaces of the LTEM polished substrate, which was very close to the most stringent flatness requirement of SEMI P37. Ta-based absorber film and anti-reflective film were also developed. Their film properties almost met SEMI P38 class A, and the absorbers showed good etching and patterning performances with the inductively coupled plasma etching process. In addition, the thinner resist coating process was developed. As a consequence, Asahi Glass has a capability to deliver the ready-to-write EUVL blank which is the most suitable for the EUVL process developments by using the full field exposure tools.

Select this Article		Chemical durability studies of Ru-capped EUV mask blanks Takeya Shimomura and Ted Liang Proc. SPIE 7122, 712226 (2008); http://dx.doi.org/10.1117/12.803065 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Surface cleaning has become one of the most critical processes in photomask manufacturing in the last few years because of the demands for high cleaning efficiency with no film loss and no damage to fragile patterns. The requirement is getting tighter as the feature-size shrinks. In addition, EUV masks pose further unique challenges in the cleaning process, because of the reflective multilayer (ML) mask structure, which is sensitive to surface damage, and a more frequent cleaning requirement due to the lack of pellicle protection during handing and usage. To address the challenge of ML surface damage from EUV mask cleaning processes, this paper presents the chemical durability of Ru-capped ML blanks against two types of chemistries: a mixture of sulfuric acid and hydrogen peroxide (SPM) and ozonated water (DIO3). The authors found that SPM slightly oxidized the Ru capping layer, but with minimal effect to EUV reflectivity. It was observed that DIO3 damaged the Ru capping layer and resulted in a significant EUV reflectivity drop. An alloyed Ru-capping layer showed improved durability against DIO3 damage. The changes to the Ru-surface were characterized with atomic force microscopy (AFM) and X-ray photo electron spectroscopy (XPS).

Select this Article		EUVL practical mask structure with light shield area for 32nm half pitch and beyond Takashi Kamo, Hajime Aoyama, Toshihiko Tanaka, Osamu Suga, Tsukasa Abe, Tadahiko Takikawa, Naoya Hayashi, Tsutomu Shoki, Youichi Usui, and Morio Hosoya Proc. SPIE 7122, 712227 (2008); http://dx.doi.org/10.1117/12.801576 \| Cited 5 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The effect of mask structure with light shield area on the printability in EUV lithography was studied. When very thin absorber on EUVL mask is used for ULSI application, it then becomes necessary to create EUV light shield area on the mask in order to suppress possible leakage of EUV light from neighboring exposure shots. We proposed and fabricated two types of masks with very thin absorber and light shield area structure. For both types of masks we demonstrated high shield performances at light shield areas by employing a Small Field Exposure Tool (SFET).

Select this Article		Control of the sidewall angle of an absorber stack using the Faraday cage system for the change of pattern printability in EUVL Il-Yong Jang, Sung-Min Huh, Seong-Yong Moon, Sang-Gyun Woo, Jin-Kwan Lee, Sang Heup Moon, and HanKu Cho Proc. SPIE 7122, 712228 (2008); http://dx.doi.org/10.1117/12.801413 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A patterned TaN substrate, which is candidate for a mask absorber in extreme ultra-violet lithography (EUVL), was etched to have inclined sidewalls by using a Faraday cage system under the condition of a 2-step process that allowed the high etch selectivity of TaN over the resist. The sidewall angle (SWA) of the patterned substrate, which was in the shape of a parallelogram after etching, could be controlled by changing the slope of a substrate holder that was placed in the Faraday cage. The performance of an EUV mask, which contained the TaN absorber of an oblique pattern over the molybdenum/silicon multi-layer, was simulated for different cases of SWA. The results indicated that the optical properties, such as the critical dimension (CD), an offset in the CD bias between horizontal and vertical patterns (H-V bias), and a shift in the image position on the wafer, could be controlled by changing the SWA of the absorber stack. The simulation result showed that the effect of the SWA on the optical properties became more significant at larger thicknesses of the absorber and smaller sizes of the target CD. Nevertheless, the contrast of the aerial images was not significantly decreased because the shadow effect caused by either sidewall of the patterned substrate cancelled with each other.

back to top

EUV Mask Process Correction

Select this Article		Pattern placement correction due to bending in EUVL masks Seh-Jin Park, Chandhok Manish, Marilyn Kamna, Chuan Hu, Guojing Zhang, Fabian C. Martinez, Nathan Wilcox, Kamgmin Hsia, and Alan R. Stivers Proc. SPIE 7122, 71222C (2008); http://dx.doi.org/10.1117/12.801542 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Extreme Ultraviolet Lithography (EUVL) masks have residual stress induced by several thin films on low thermal expansion material (LTEM) substrates. The stressed thin films finally result in convex out-of-plane displacement (OPD) of several 100s of nm on the pattern side of the mask. Since EUVL masks are chucked on EUVL scanners differently from on e-beam writer, the mask pattern placement errors (PPE) are necessary to be corrected for to reduce overlay errors. In this paper, experimental results of pattern placement error correction using standard chrome on glass (COG) plate will be discussed together with simulations. Excellent agreement with simple bending theory is obtained. Suitability of the model to compensate for other EUVL-related PPEs due to mask non-flatness will be discussed.

back to top

EUV Mask Inspection I

Select this Article		Signal analysis for the actinic full-field EUVL mask blank inspection system Takeshi Yamane, Teruo Iwasaki, Toshihiko Tanaka, Tsuneo Terasawa, Osamu Suga, and Toshihisa Tomie Proc. SPIE 7122, 71222D (2008); http://dx.doi.org/10.1117/12.801420 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We have developed an actinic full-field inspection system to detect multilayer phase defect with dark field imaging. With this system, programmed phase defects on a mask blank were observed. The system can detect phase defects caused by a 1.5 nm high and 60 nm wide protrusion on a multilayer surface. Background intensity and signal to background ratio (SBR) of the observed defect images are analyzed with simulation. The background intensities were calculated with the model that it is generated by light scattered from mask surface roughness. The result indicates that the larger outer NA (numerical aperture) leads to an increase in the background intensity. In this correlation of NA with the background intensity, the calculation and experimental results correspond well. The defect images were simulated using the point spread function (PSF) of flare generated by mirror surface roughness employing Fourier technique. The SBRs of simulated defect images corresponded well with the SBRs of the observed images. These results support the calculation and simulation models are proper.

Select this Article		Benchmarking EUV mask inspection beyond 0.25 NA Kenneth A. Goldberg, Iacopo Mochi, Patrick P. Naulleau, Hakseung Han, and Sungmin Huh Proc. SPIE 7122, 71222E (2008); http://dx.doi.org/10.1117/12.801529 \| Cited 5 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The SEMATECH Berkeley Actinic Inspection Tool (AIT) is an EUV zoneplate microscope dedicated to photomask research. Recent upgrades have given the AIT imaging system selectable numerical aperture values of 0.25, 0.30, and 0.35 (4 equivalent). The highest of which provides resolution beyond the current generation of EUV lithography research tools, giving above 75% contrast for dense-line features with 100-nm half-pitch on the mask, and above 70% for 88-nm half-pitch. To improve the imaging system alignment, we used through-focus images of small contacts to extract aberration magnitudes and compare with modeling. The astigmatism magnitude reached a low value of 0.08 waves RMS. We present the results of performance benchmarking and repeatability tests including contrast, and line width measurements.

back to top

EUV Mask Inspection II

Select this Article		The study of EUVL mask defect inspection technology for 32-nm half-pitch node device and beyond Hiroyuki Shigemura, Tsuyoshi Amano, Yasushi Nishiyama, Osamu Suga, Tsuneo Terasawa, Yukiyasu Arisawa, Hideaki Hashimoto, Norio Kameya, Masaya Takeda, Nobutaka Kikuiri, Ryoichi Hirano, and Masatoshi Hirono Proc. SPIE 7122, 71222F (2008); http://dx.doi.org/10.1117/12.801550 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In this paper, we will report on our experimental and simulation results on the impact of EUVL mask absorber structure and of inspection system optics on mask defect detection sensitivity. We employed a commercial simulator EM-Suite (Panoramic Technology, Inc.) which calculated rigorously using FDTD (Finite-difference time-domain) method. By using various optical constants of absorber stacks, we calculated image contrasts and defect image signals as obtained from the mask defect inspection system. We evaluated the image contrast and the capability of detecting defects on the EUVL masks by using a new inspection tool made by NuFlare Technology, Inc. (NFT) and Advanced Mask Inspection Technology, Inc. (AMiT). This tool is based on NPI-5000 which is the leading-edge photomask defect inspection system using 199nm wavelength inspection optics. The programmed defect masks with LR-TaBN and LRTaSi absorbers were used which had various sized opaque and clear extension defects on hp-160nm, hp-225nm, and hp- 325nm line and space patterns. According to the analysis, reflectivity of EUVL mask absorber structures and the inspection optics have large influence on image contrast and defect sensitivity. It is very important to optimize absorber structure and inspection optics for the development of EUVL mask inspection technology, and for the improvement of performance of EUV lithographic systems.

Select this Article		An investigation of EUV lithography defectivity Kevin D. Cummings, Thomas Laursen, Bill Pierson, Sang-in Han, Robert Watso, Youri van Dommelen, Brian Lee, Yunfei Deng, Bruno La Fontaine, Thomas Wallow, Uzo Okoroanyanwu, Obert Wood, Anna Tchikoulaeva, Christian Holfeld, Jan Hendrick Peters, et al. Proc. SPIE 7122, 71222G (2008); http://dx.doi.org/10.1117/12.801528 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We have used ASML's full field step-and-scan exposure tool for extreme ultraviolet lithography (EUVL), known as an Alpha Demo Tool, to investigate one of the critical issues identified for EUVL, defectivity associated with EUV masks. The main objective for this work was to investigate the infrastructure currently in place to examine defects on a EUV reticle and identify their consequence in exposed resist. Unlike many previous investigations this work looks at naturally occurring defects in a EUV exposed metal layer from a 45 nm node device. The EUV exposure was also integrated into a standard process flow where the other layers were patterned using more conventional 193-nm lithography techniques. This presentation correlates reticle level defectivity to resulting wafer exposures. Defect inspection data from both the 28xx family of KLA-Tencor wafer inspection tool and Terascan reticle inspection tools are presented. Defect populations were characterized with a KLA 5200 Review SEM. Observed defectivity modes were analyzed using both conventional defect inspection methodology as well as advanced techniques in order to gain further insight. We find good correlations between reticle level defects and the resulting wafer exposure defects.

back to top

EUV Mask Repair

Select this Article		Study of EUVL mask defect repair using FIB-GAE method Tsuyoshi Amano, Yasushi Nishiyama, Hiroyuki Shigemura, Tsuneo Terasawa, Osamu Suga, Kensuke Shiina, Fumio Aramaki, Ryoji Hagiwara, and Anto Yasaka Proc. SPIE 7122, 71222H (2008); http://dx.doi.org/10.1117/12.801214 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We evaluated a new FIB-GAE (Focused Ion Beam-Gas Assisted Etching) repairing process for the absorber defects on EUVL mask. XeF₂ gas and H₂O gas were used as etching assist agent and etching stop agent respectively. The H₂O gas was used to oxidize Ta-nitride side-wall and to inactivate the remaining XeF₂ gas after the completion of defect repair. At the Photomask Japan 2008 we had reported that side-etching of Ta-nitride caused CD degradation in EUVL. In the present paper we report on the performance of defect repair by FIB, and of printability using SFET (Small Field Exposure Tool). The samples evaluated, were in form of bridge defects in hp225nm L/S pattern. The cross sectional SEM images certified that the newly developed H₂O gas process prevented side-etching damage to TaBN layer and made the side-wall close to vertical. The printability also showed excellent results. There were no significant CD changes in the defocus characterization of the defect repaired region. In its defect repair process, the FIB method showed no signs of scan damage on Cr buffered EUV mask. The repair accuracy and the application to narrow pitched pattern are also discussed.

Select this Article		Analysis of process margin in EUV mask repair with nano-machining Su-Young Lee, Geun-Bae Kim, Hong-Seok Sim, Sang-Hyeon Lee, Hwa-Sung Kim, Jung-Hwan Lee, Hwan-Seok Seo, Hak-Seung Han, Seong-Sue Kim, Seong-Yong Moon, Sang-Gyun Woo, Ron Bozak, Andrew Dinsdale, Tod Robinson, David Lee, et al. Proc. SPIE 7122, 71222I (2008); http://dx.doi.org/10.1117/12.801415 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Reduced design rules demand higher sensitivity of inspection, and thus small defects which did not affect printability before require repair now. The trend is expected to be similar in extreme ultraviolet lithography (EUVL) which is a promising candidate for sub 32 nm node devices due to high printing resolution. The appropriate repair tool for the small defects is a nanomachining system. An area which remains to be studied is the nano-machining system performance regarding repair of the defects without causing multilayer damage. Currently, nanomachining Z-depth controllability is 3 nm while the Ru-capping layer is 2.5 nm thick in a Buffer-less Ru-capped EUV mask. For this report, new repair processes are studied in conjunction with the machining behavior of the different EUVL mask layers. Repair applications to achieve the Edge Placement(EP) and Z-depth controllability for an optimal printability process window are discussed. Repair feasibility was determined using a EUV micro exposure tool (MET) and Actinic Imaging Tool (AIT) to evaluate repairs the 30 nm and 40 nm nodes. Finally, we will report the process margin of the repair through Slitho-EUVTM simulation by controlling side wall angle, Z-depth, and EP (Edge Placement) on the base of 3-dimensional experimental result.

Select this Article		Ga implantation and interlayer mixing during FIB repair of EUV mask defects Yasushi Nishiyama, Tsuyoshi Amano, Hiroyuki Shigemura, Tsuneo Terasawa, Osamu Suga, Tomokazu Kozakai, Fumio Aramaki, Kensuke Shiina, Anto Yasaka, and Ryoji Hagiwara Proc. SPIE 7122, 71222J (2008); http://dx.doi.org/10.1117/12.801428 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract EUV mask damage caused by Ga focused ion beam irradiation during the mask defect repair was studied. The concentration of Ga atom implanted in the multilayer through the buffer layer and distributions of recoil atoms were calculated by SRIM. The reflectivity of the multilayer was calculated from the Ga distribution below the capping layer surface. To validate the calculation, Ga focused ion beam was irradiated on the buffer layer. The EUV reflectivity was measured after the buffer layer etching process. The measured reflectivity change was considerably larger than the one predicted from the absorption of light by the implanted Ga. The large reflectivity loss was primarily due to the absorption of light by chromium silicide residue which was generated by the intermixing of the buffer and the capping layer. Both lowering of the acceleration voltage and using thicker buffer layer were found to be effective in reducing this intermixing. The reduction of the reflectivity loss by using thicker buffer layer was confirmed by our experiments. An aerial image of patterns with etching residue formed by the intermixing was simulated. When the thickness of the intermixed layer happened to be 8 nm and the size of the resulting residue was larger than 100 nm, then the impact of the estimated absorption by the residue on the linewidth of 32 nm hp line pattern became more than 5 %.

back to top

Masks for Nano-Imprint Lithography

Select this Article		Defect inspection of imprinted 32 nm half pitch patterns Kosta Selinidis, Ecron Thompson, Ian McMackin, Joseph Perez, S. V. Sreenivasan, and Douglas J. Resnick Proc. SPIE 7122, 71222K (2008); http://dx.doi.org/10.1117/12.801948 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Step and Flash Imprint Lithography redefines nanoimprinting. This novel technique involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed leaving a patterned solid on the substrate. Compatibility with existing CMOS processes requires a mask infrastructure in which resolution, inspection and repair are all addressed. The purpose of this paper is to understand the limitations of inspection at half pitches of 32 nm and below. A 32 nm programmed defect mask was fabricated. Patterns included in the mask consisted of an SRAM Metal 1 cell, dense lines, and dense arrays of pillars. Programmed defect sizes started at 4 nm and increased to 48 nm in increments of 4 nm. Defects in both the mask and imprinted wafers were characterized scanning electron microscopy and the measured defect areas were calculated. These defects were then inspected using a KLA-T eS35 electron beam wafer inspection system. Defect sizes as small as 12 nm were detected, and detection limits were found to be a function of defect type.

Select this Article		Evaluation of e-beam repair for nanoimprint templates Marcus Pritschow, Volker Boegli, Joerg Butschke, Mathias Irmscher, Douglas Resnick, Holger Sailer, Kosta Selinidis, and Ecron Thompson Proc. SPIE 7122, 71222L (2008); http://dx.doi.org/10.1117/12.801946 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Two essential process steps of the template fabrication chain are inspection and repair. The widely introduced gas assisted e-beam etching and deposition technique for mask repair offers crucial advantages, especially regarding the resolution capability. We started the evaluation of a new e-beam repair test stand based on the Zeiss MeRiT technology for UV-NIL template repair. For this purpose, templates with programmed defects of different shapes and sizes have been designed and fabricated. The repair experiments were focused on the development of recipes for quartz etching and deposition specifically tailored for NIL repair requirements Both, clear and opaque programmed defects have been repaired and the results have been analyzed. After recipe optimization, templates with repaired programmed defects have been imprinted on a Molecular Imprints Imprio 250 tool. By comparing template and imprint results we investigated the repair capability.

back to top

Mask Business

Select this Article		Diamonds in the rough: key performance indicators for reticles and design sets Paul Ackmann Proc. SPIE 7122, 71222M (2008); http://dx.doi.org/10.1117/12.801543 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The discussion on reticle cost continues to raise questions by many in the semiconductor industry. The diamond industry developed a method to judge and grade diamonds. [1, 11] The diamond-marketing tool of "The 4Cs of Diamonds" and other slogans help explain the multiple, complex variables that determine the value of a particular stone. Understanding the critical factors of Carat, Clarity, Color, and Cut allows all customers to choose a gem that matches their unique desires. I apply the same principles of "The 4Cs of Diamonds" to develop an analogous method for rating and tracking reticle performance. I introduced the first 3Cs of reticle manufacturing during my BACUS presentation panel at SPIE in February 2008. [2] To these first 3Cs (Capital, Complexity, and Content), I now add a fourth, Cycle time. I will look at how our use of reticles changes by node and use "The 4Cs of Reticles" to develop the key performance indicators (KPI) that will help our industry set standards for evaluating reticle technology. Capital includes both cost and utilization. This includes tools, people, facilities, and support systems required for building the most critical reticles. Tools have highest value in the first two years of use, and each new technology node will likely increase the Capital cost of reticles. New technologies, specifications, and materials drive Complexity for reticles, including smaller feature size, increased optical proximity correction (OPC), and more levels at sub-wavelength. The large data files needed to create finer features require the use of the newest tools for writing, inspection, and repair. Content encompasses the customer's specifications and requirements, which the mask shop must meet. The specifications are critical because they drive wafer yield. A clear increase of the number of masking levels has occurred since the 90 nm node. Cycle time starts when the design is finished and lasts until the mask house ships the reticle to the fab. Depending on the level of Complexity, a reticle can take from as few as one, to more than forty, days to build. By using the 4Cs, I can show how the reticle build has changed from the 90 nm technology node. I will begin by delineating proposed KPIs for reticles.

Select this Article		Accelerated data communication of semiconductor design files Gregory H. Fairbank Proc. SPIE 7122, 71222N (2008); http://dx.doi.org/10.1117/12.801750 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The new Flume data communication protocol takes a unique approach to addressing the effects of latency in long-distance data transmission. In addition to managing the data itself through compression, delta processing and error correction, Flume eliminates the impact of latency by transmitting a continuous stream of data without ever pausing to wait for acknowledgements from the data receiver. Transmission times are accelerated by 5X - 100X and these speedups continue at least linearly with added bandwidth. A second, optional mode of operation, transmits separate pieces of the data to be transmitted to different locations which can then exchange data among themselves to recreate the complete data at all sites.

Select this Article		Compute resource management and turn around time control in mask data prep Travis Lewis, Scott Goad, Kenneth Jantzen, Ahmed Nouh, Minyoung Park, Emile Sahouria, and Steffen Schulze Proc. SPIE 7122, 71222O (2008); http://dx.doi.org/10.1117/12.801544 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract With each new process technology node chip designs increase in complexity and size, and mask data prep flows require more compute resources to maintain the desired turn around time (TAT) at a low cost. Securing highly scalable processing for each element of the flow - geometry processing, resolution enhancements and optical process correction, verification and fracture - has been the focal point so far. The utilization for different flow elements depends on the operation, the data hierarchy and the device type. This paper introduces a dynamic utilization driven compute resource control system applied to large scale parallel computation environment. The paper will analyze performance metrics TAT and throughput for a production system and discuss trade-offs of different parallelization approaches in data processing regarding interaction with dynamic resource control. The study focuses on 65nm and 45nm designs.

back to top

SEM CD Metrology

Select this Article		International photomask linewidth comparison by NIST and PTB J. Potzick, R. Dixson, R. Quintanilha, M. Stocker, A. Vladar, E. Buhr, W. Häßler-Grohne, B. Bodermann, C. G. Frase, and H. Bosse Proc. SPIE 7122, 71222P (2008); http://dx.doi.org/10.1117/12.801435 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In preparation of the international Nano1 linewidth comparison on photomasks between 9 national metrology institutes, NIST and PTB have started a bilateral linewidth comparison in 2008, independent of and prior to the Nano1 comparison in order to test the suitability of the mask standards and the general approach to be used for the Nano1 comparison. This contribution describes the rationale of both comparisons, the design of the mask comparison standards to be used and the measurement methods applied for traceable photomask linewidth metrology at NIST and PTB.

Select this Article		Re-calibration of the NIST SRM 2059 master standard using traceable atomic force microscope metrology Ronald Dixson, James Potzick, and Ndubuisi G. Orji Proc. SPIE 7122, 71222Q (2008); http://dx.doi.org/10.1117/12.801923 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The current photomask linewidth Standard Reference Material (SRM) supplied by the National Institute of Standards and Technology (NIST), SRM 2059, is the fifth generation of such standards for mask metrology. An in house optical microscope tool developed at NIST, called the NIST ultra-violet (UV) microscope, was used in transmission mode to calibrate the SRM 2059 photomasks. Due to the limitations of available optical models for determining the edge response in the UV microscope, the tool was used in a comparator mode. One of the masks was selected as a master standard - and the features on this mask were calibrated using traceable critical dimension atomic force microscope (CD-AFM) dimensional metrology. The optical measurements were then used to determine the relative offsets between the widths on the master standard and individual masks for sale to customers. At the time of these measurements, however, the uncertainties in the CD-AFM reference metrology on the master standard were larger than can now be achieved because the NIST single crystal critical dimension reference material (SCCDRM) project had not been completed. Using our CD-AFM at NIST, we have performed new measurements on the SRM 2059 master standard. The new AFM results are in agreement with the prior measurements and have expanded uncertainties approximately one fourth of those of the earlier results for sub-micrometer features. When the optical comparator data for customers masks are reanalyzed using these new AFM results, we expect to reduce the combined reported uncertainties for the linewidths on the actual SRMs by at least 40 % for the nominal 0.25 μm features.

Select this Article		A study of the limited area scanning system in the mask CD-SEM Toshi Iwai, Soichi Shida, Mitsuo Hiroyama, Takayuki Nakamura, Hisaya Sakaguchi, Hiroki Ueno, Masaru Higuchi, and Tatsuya Aihara Proc. SPIE 7122, 71222R (2008); http://dx.doi.org/10.1117/12.801418 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Measurement of resist critical dimensions (CDs) utilizing a scanning electron microscope (SEM) based metrology system causes the resist to change due to irradiation effects of the electrons. A new and novel scanning approach has been developed in an effort to minimize the effects electron irradiation and exposure during the measurement process. This technique is especially pertinent in view of the tightening requirements for process control to achieve single digit CD uniformity on leading edge photo masks being produced today. The measurement of OPC features necessitates utilization of SEM based metrology due to resolution requirements, but the effects of high magnification imaging presents unique challenges. By controlling the scanned region of interest (ROI) it is possible to reduce exposure and irradiation effects. This paper will detail this new approach as it is utilized on the LWM9045 SEM Metrology system. The LWM9000SEM mask CD SEM was introduced earlier.

Select this Article		Exploring new metrology for complex photomask patterns Masaru Higuchi, Tatsuya Aihara, Hideaki Saito, Isao Yonekura, Jotaro Suzuki, Emily Gallagher, and Ian P. Stobert Proc. SPIE 7122, 71222S (2008); http://dx.doi.org/10.1117/12.801994 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Photomask pattern sizes are usually defined by a one-dimensional Critical Dimension (CD). As mask pattern shapes become more complex, a single CD no longer provides sufficient information to characterize the mask feature. For simple square contacts, an area measurement is generally accepted as a better choice for determining contact uniformity. However, the area metric may not adequately characterize complex shapes; it does not lend itself to CD metrology and it ignores pattern placement. This paper investigates new ways of measuring complex mask shapes with aggressive Optical Proximity Correction (OPC). An example of more informative metric is center of gravity. This new metric will be compared to more traditional mask characterization variables like CD mean to target, CD uniformity, and Image Placement (IP). Wafer simulations of the mask shapes will be used to understand which mask pattern metrics are most representative of the image transferred to wafer images. The results will be discussed in terms of their potential to improve mask quality for 32nm technology and beyond.

Select this Article		New method of 2-dimensional metrology using mask contouring Ryoichi Matsuoka, Yoshikazu Yamagata, Akiyuki Sugiyama, and Yasutaka Toyoda Proc. SPIE 7122, 71222T (2008); http://dx.doi.org/10.1117/12.802137 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We have developed a new method of accurately profiling and measuring of a mask shape by utilizing a Mask CD-SEM. The method is intended to realize high accuracy, stability and reproducibility of the Mask CD-SEM adopting an edge detection algorithm as the key technology used in CD-SEM for high accuracy CD measurement. In comparison with a conventional image processing method for contour profiling, this edge detection method is possible to create the profiles with much higher accuracy which is comparable with CD-SEM for semiconductor device CD measurement. This method realizes two-dimensional metrology for refined pattern that had been difficult to measure conventionally by utilizing high precision contour profile. In this report, we will introduce the algorithm in general, the experimental results and the application in practice. As shrinkage of design rule for semiconductor device has further advanced, an aggressive OPC (Optical Proximity Correction) is indispensable in RET (Resolution Enhancement Technology). From the view point of DFM (Design for Manufacturability), a dramatic increase of data processing cost for advanced MDP (Mask Data Preparation) for instance and surge of mask making cost have become a big concern to the device manufacturers. This is to say, demands for quality is becoming strenuous because of enormous quantity of data growth with increasing of refined pattern on photo mask manufacture. In the result, massive amount of simulated error occurs on mask inspection that causes lengthening of mask production and inspection period, cost increasing, and long delivery time. In a sense, it is a trade-off between the high accuracy RET and the mask production cost, while it gives a significant impact on the semiconductor market centered around the mask business. To cope with the problem, we propose the best method of a DFM solution using two-dimensional metrology for refined pattern.

back to top

Advanced CD Metrology

Select this Article		Comparative scatterometric CD measurements on a MoSi photo mask using different metrology tools Jan Richter, Jens Rudolf, Bernd Bodermann, and John C. Lam Proc. SPIE 7122, 71222U (2008); http://dx.doi.org/10.1117/12.800732 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The demands on CD metrology techniques in terms of both reproducibility and measurement uncertainty increase with decreasing critical dimensions (CD) on lithography masks. Additionally a full 3D characterization of the mask structures becomes more and more important to understand and control the printing behavior of state of the art photomasks. Furthermore, an extension of metrology characterization including material properties can provide the final puzzle pieces for a better correlation of mask metrology to wafer metrology. Here, optical metrology systems, especially at-wavelength systems, are very well suited to characterize structure features of a photomask regarding their printing behavior on a wafer. In particular scatterometry is able to provide a better understanding of the investigated structure and allows for modeling of secondary structure parameters as well as material composition. AMTC has a commercial scatterometer from n&k Technology (n&k 5700-CDRT) in use. This system measures the spectral transmission and reflection, the 0th diffraction order. Beside thin film characterization this system is used for CD and edge profile characterization, also. The analysis of the data uses a look-up table approach in combination with a database, which has been generated and can be expanded, respectively, using a RCWA based software. At PTB we have realized a new DUV hybrid scatterometer which combines essential elements of a radiometer, an ellipsometer, and a diffractometer. These two systems are different both in terms of the measurement modes, the data evaluation method and the Maxwell-solver used. Therefore we started to compare the performance of both systems to traditional metrology system for CD metrology and phase measurement. For this purpose we performed first comparative scatterometric measurements on a MoSi phase shifting mask.

Select this Article		Mask process monitoring with optical CD measurements for sub-50-nm Kyung-Yoon Bang, Jin-Back Park, Jeong-Hun Roh, Dong-Hoon Chung, Sung-Yong Cho, Yong-Hoon Kim, Sang-Gyun Woo, and Han-Ku Cho Proc. SPIE 7122, 71222V (2008); http://dx.doi.org/10.1117/12.801416 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Process control of line width and etch depth on the photomask production is more important as the industry moves toward 50nm node and beyond. In this paper, we report the ellipsometer-based scatterometry based metrology system that provides line width and resist thickness measurements on sub 50 nm node test masks for a mask process monitoring. Measurements were made with spectroscopic rotating compensator ellipsometer system. For analysis we made up modeling libraries with a 200 nm half pitch and checked and applied them to ADI and ACI measurements of binary and phase shift mask (PSM). We characterized the CD uniformity, linearity, thickness uniformity. Results show that linearity measured from fixed-pitch, varying line/space ratio targets show good correlation to top-down CD-SEM with R2 of more than 0.99. Resist thickness results show that depth bias is about 2nm between AFM and OCD in ADI step. The data show that optical CD measurements provide a nondestructive way to monitor mask processes with relatively little time loss from measurement step.

Select this Article		Improvement in metrology on new 3D-AFM platform Ingo Schmitz, Marc Osborn, Sean Hand, and Qi Chen Proc. SPIE 7122, 71222X (2008); http://dx.doi.org/10.1117/12.803581 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract According to the 2007 edition of the ITRS roadmap, the requirement for CD uniformity of isolated lines on a binary or attenuated phase shift mask is 2.1nm (3σ) in 2008 and requires improvement to1.3 nm (3σ) in 2010. In order to meet the increasing demand for CD uniformity on photo masks, improved CD metrology is required. A next generation AFM, InSight^TM 3DAFM, has been developed to meet these increased requirements for advanced photo mask metrology. The new system achieves 2X improvement in CD and depth precision on advanced photo masks features over the previous generation 3D-AFM. This paper provides measurement data including depth, CD, and sidewall angle metrology. In addition the unique capabilities of damage-free defect inspection and Nanoimprint characterization by 3D AFM are presented.

back to top

Metrology for Placement and Optical Structure

Select this Article		Development of a 1.5D reference comparator for position and straightness metrology on photomasks J. Flügge, R. Köning, Ch. Weichert, W. Häßler-Grohne, R. D. Geckeler, A. Wiegmann, M. Schulz, C. Elster, and H. Bosse Proc. SPIE 7122, 71222Y (2008); http://dx.doi.org/10.1117/12.801251 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The so-called Nanometer Comparator is the PTB vacuum length comparator which has been developed for high precision length metrology on measurement objects with micro- and nanostructured graduations, like e.g. line scales, incremental encoders or photomasks. The Nanometer Comparator allows to achieve smallest measurement uncertainties in the nm-range by use of vacuum laser interferometry for the displacement measurement. We will report on the achieved measurement performance of this high precision vacuum length comparator and the already started developments to substantially enhance its measurement capabilities by additional straightness measurement capabilities. The enhanced Nanometer Comparator will provide traceability for photomask pattern placement measurements in industry, also facing the challenges due to the increased requirements on registration metrology as set by the introduction of new lithography techniques like double patterning methods.

Select this Article		Photomask registration and overlay metrology by means of 193 nm optics Gerd Klose, Norbert Kerwien, Michael Arnz, Dirk Beyer, and Norbert Rosenkranz Proc. SPIE 7122, 71222Z (2008); http://dx.doi.org/10.1117/12.801077 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract This paper reports on the current status of PROVE^TM - a new photomask registration and overlay metrology system currently under development at Carl Zeiss. The scope of the project is to design and build a photomask pattern placement metrology tool which is serving the 32 nm node. Performance specifications of the tool are actually driven by double exposure/ double patterning approaches which will help to extend the 193 nm lithography platforms, while keeping the semiconductor industry conform to ITRS roadmap requirements. A secondary requirement of pattern placement metrology tools is the CD measurement option for design features of interest. Combining both registration and CD measurement reduces the number of process operations a photomask has to encounter during manufacture. Optical design considerations are discussed, which led to the tool being designed for 193 nm illumination corresponding to at-wavelength metrology for most current and future photomask applications. The concept enables registration and CD metrology by transmitted or reflected light. The short wavelength together with a NA of 0.6 also provides sufficient resolution even at working distances compatible with the use of pellicles, hence enabling the tool for qualification of final, production ready masks. Imaging simulations with a rigorous Maxwell solver prove our chosen optical concept to be adequate for the various mask types (e.g. COG, MoSi, EUV) commonly used today and presumably in the future. The open concept does enable a higher NA for future, pellicle free applications.

Select this Article		World wide matching of registration metrology tools of various generations F. Laske, A. Pudnos, L. Mackey, P. Tran, M. Higuchi, C. Enkrich, K.-D. Roeth, K.-H. Schmidt, D. Adam, and J. Bender Proc. SPIE 7122, 712230 (2008); http://dx.doi.org/10.1117/12.802941 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Turn around time/cycle time is a key success criterion in the semiconductor photomask business. Therefore, global mask suppliers typically allocate work loads based on fab capability and utilization capacity. From a logistical point of view, the manufacturing location of a photomask should be transparent to the customer (mask user). Matching capability of production equipment and especially metrology tools is considered a key enabler to guarantee cross site manufacturing flexibility. Toppan, with manufacturing sites in eight countries worldwide, has an on-going program to match the registration metrology systems of all its production sites. This allows for manufacturing flexibility and risk mitigation.In cooperation with Vistec Semiconductor Systems, Toppan has recently completed a program to match the Vistec LMS IPRO systems at all production sites worldwide. Vistec has developed a new software feature which allows for significantly improved matching of LMS IPRO(x) registration metrology tools of various generations. We will report on the results of the global matching campaign of several of the leading Toppan sites.

Select this Article		Spectroscopic ellipsometry applications in photomask technology Ron A. Synowicki and James N. Hilfiker Proc. SPIE 7122, 712231 (2008); http://dx.doi.org/10.1117/12.801861 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Development and manufacture of advanced photomasks requires understanding the optical properties of mask materials and the ability to carefully monitor and control the film thickness, refractive index, and absorption of each film layer. Spectroscopic Ellipsometry (SE), a nondestructive optical analysis technique for determination of film thickness, refractive index, absorption, and film microstructure has been applied to many applications in current and emerging areas of photomask technology. This work surveys a variety of applications including analysis of fused silica mask blanks, imprint lithography templates, free-standing pellicles, deposited films of chromium, chromium oxide, MoSi, and multiple layers of these materials. For fused silica substrates we determine the optical properties (n & k) versus wavelength as well as the surface roughness. The near-surface index and surface roughness are used as indicators of surface polishing quality, which is an issue in the use of photomask substrates as template stamps in imprint lithography. Pellicles are free-standing films stretched over a metal frame. Because these thin pellicles are much thinner than the light coherence length, spectroscopic ellipsometry can determine the thickness, refractive index, and absorbance of the pellicle versus wavelength via interference between light reflecting from the upper and lower surfaces of the film. It is also possible to measure pellicles suspended over an underlying mask. The optical constants (n & k) of MoSi films vary widely with deposition conditions due to both composition and microstructure. Films optimized for 248 nm and 193 nm wavelengths have been analyzed. Spectroscopic ellipsometry shows good sensitivity to surface roughness and index gradients through the MoSi films. Multilayer masks such as NTAR have multiple absorbing layers such as chromium and chrome oxide. It is possible to simultaneously analyze multiple data sets acquired from the front side, from the back side through the substrate, and transmitted data through the stack. This increases the information content in the data, allowing more details from the multilayer to be determined. It is also possible to measure the birefringence in mask substrates and coated masks by using ellipsometry in transmission mode. By establishing a known polarization state incident on the mask it is possible to analyze the polarization after transmission to determine the phase difference, which is used to measure the birefringence of the sample. For patterned structures such as gratings it is possible to measure polarization-dependent diffraction effects versus angle. Measurement can be made in either reflection or transmission mode. It is possible to independently measure both s- and p-polarization components and compare to theory. As photomasks become more complex, with increasing numbers of layers (such as multilayer mirrors for EUV masks) in-situ ellipsometry shows great promise, providing the ultimate characterization of each film by allowing measurement in real-time as each layer is added to the mask structure.

back to top

Poster Session: Mask Business

Select this Article		True reticle cost saving by multi level reticle approach Thomas Struck and Hendrik Kirbach Proc. SPIE 7122, 712233 (2008); http://dx.doi.org/10.1117/12.800920 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Today reticle costs become one of the main contributors in the cost of manufacturing of advanced logic products. Especially for low volume projects as of product sampling as well as design and product verifications the saving of reticle costs becomes worthwhile. Multi level reticles are the combination of more then one lithographical layer on one physical reticle. Due to this approach the physical amount of reticles per tape out will be reduced and thereby also the costs for reticles will be significantly decreased. The multi level reticle approach is implemented as standard option in the INFINEON Technologies tape out flow for advanced logic products. This means dependent on forecasted volume and chip size it could be decided to tape out a project on multi level- or single level reticle. Technical setup, reticle layout, specification, CAD flow and experience in daily work using multi level reticles in different design nodes will be shown. Reticle cost advantage versus reduced throughput will be discussed.

Select this Article		Technology interactions on reticle delivery Paul Ackmann, Scott Goad, and Craig West Proc. SPIE 7122, 712234 (2008); http://dx.doi.org/10.1117/12.801239 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Reticle cost and cycle time to deliver new circuit designs to a wafer fab remain key focus areas for advanced semiconductor manufacturing and new product development. Resolution enhancement techniques like optical proximity correction as applied to critical layers have increased the burden on mask data preparation and reticle writing steps of the mask making flow. The growing data volume and complexity of designs must be reduced to a perfect image on a reticle in the shortest time possible against computer and machine constraints. Continued dependence on 193 nm wavelength exposure in extremely low k₁ lithography exacerbates the underlying trends. Two important factors come together to drive the economics and performance of the reticle line: the complexity of the designs and the productivity of e-beam writing tools. The designs, OPC methods, and writing tool capabilities continue to evolve with each node of technology. The study builds on prior evaluations to look at fundamental pattern complexity across 90nm, 65nm, and 45nm logic designs using the gate and metal-1 critical layers. The writing tool throughput testing uses a range of standard patterns to establish shot limited performance as a calibration method for arbitrary designs. Node to node design and tool to tool generation comparisons highlight actual step changes in complexity and capability by introducing new quantitative methods, benchmarking metrics, and testing strategies. The findings are projected into the future using design complexity and writing tool trends to suggest implications about reticle cost, cycle time, or possible gaps in technology development.

back to top

Poster Session: Advanced Mask Patterning

Select this Article		Deflection unit for multi-beam mask making Florian Letzkus, Joerg Butschke, Mathias Irmscher, Michael Jurisch, Wolfram Klingler, Elmar Platzgummer, Christof Klein, Hans Loeschner, and Reinhard Springer Proc. SPIE 7122, 712235 (2008); http://dx.doi.org/10.1117/12.801401 \| Cited 1 time Online Publication Date: Oct 20, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Two main challenges of future mask making are the decreasing throughput of the pattern generators and the insufficient line edge roughness of the resist structures. The increasing design complexity with smaller feature sizes combined with additional pattern elements of the Optical Proximity Correction generates huge data volumes which reduce correspondingly the throughput of conventional single e-beam pattern generators. On the other hand the achievable line edge roughness when using sensitive chemically amplified resists does not fulfill the future requirements. The application of less sensitive resists may provide an improved roughness, however on account of throughput, as well. To overcome this challenge a proton multi-beam pattern generator is developed [1]. Starting with a highly parallel broad beam, an aperture-plate is used to generate thousands of separate spot beams. These beams pass through a blanking-plate unit, based on a CMOS device for de-multiplexing the writing data and equipped with electrodes placed around the apertures switching the beams "on" or "off", dependent on the desired pattern. The beam array is demagnified by a 200x reduction optics and the exposure of the entire substrate is done by a continuous moving stage. One major challenge is the fabrication of the required high aspect deflection electrodes and their connection to the CMOS device. One approach is to combine a post-processed CMOS chip with a MEMS component containing the deflection electrodes and to realize the electrical connection of both by vertical integration techniques. For the evaluation and assessment of this considered scheme and fabrication technique, a proof-of-concept deflection unit has been realized and tested. Our design is based on the generation of the deflection electrodes in a silicon membrane by etching trenches and oxide filling afterwards. In a 5mm x 5mm area 43,000 apertures with the corresponding electrodes have been structured and wired individually or in groups with aluminum lines. The aperture-plate for shaping the beams has been aligned and mounted on top of the blanking-plate. Afterwards this sandwich has been fixed on a base-plate with a pin plug as interface. The electrical connection has been performed with a standard chip bonding process to the aluminum pads on the blanking-plate. Finally, the proof-of-concept deflection unit was evaluated in a test bench. The results of electrical- and exposure tests are presented and discussed in detail.

Select this Article		Mask patterning for the 22nm node using a proton multi-beam projection pattern generator Joerg Butschke, Mathias Irmscher, Holger Sailer, Lorenz Nedelmann, Marcus Pritschow, Hans Loeschner, and Elmar Platzgummer Proc. SPIE 7122, 712236 (2008); http://dx.doi.org/10.1117/12.801402 Online Publication Date: Oct 20, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Decreasing throughput of high-end pattern generators and insufficient line edge roughness (LER) of chemically amplified resists (CAR) might become limitations for future mask making. An alternative could be the introduction of less sensitive resists, linked to a turning away from today's electron beam pattern generators. Moderate exposure doses of around 25μC/cm² could be achieved for non-CAR materials like HSQ by the use of 10keV protons. Targeting optimized absorber performance, Shin-Etsu has developed an Opaque-molybdenum-over-glass (OMOG) material, designed for 32mn mask technology and beyond. This hard mask concept allows using thin resist layers, as required by an ion beam exposure. Goal of this work was to assess a HSQ based non-CAR process using a multiple ion beam pattern generator including subsequent transfer into the absorber by dry etch processes. Proton exposures have been done on the IMS Nanofabrication proof of concept tool which is designed for 40,000 programmable ion beams. For comparison, an electron based reference process has been set up in parallel to the proton multi-beam approach. Hard mask opening and subsequent absorber etching have been accomplished in a state of the art mask etcher. Assessment of the process flow has been done in terms of feature profile, LER and resolution capability.

Select this Article		High accuracy jog CD control on OPC pattern by advanced laser writer Sigma7500 Tomas Chin, Wen-Bin Wu, and Chiang-Lin Shih Proc. SPIE 7122, 712237 (2008); http://dx.doi.org/10.1117/12.801414 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract With the progress of mask writer technology, 50 KV electron beam writers always perform with better pattern fidelity and critical dimension (CD) control than traditional laser raster-scan writers because laser spot size is confined by the laser longer wavelength relative to electron beam. As far as Optical Proximity Correction (OPC) pattern fidelity is concerned, critical masks with OPC process have to choose Variable-Shape-Beam (VSB) electron beam writer presently. However, the over-aggressive OPC fragmentation induces data volume abrupt explosion, longer writing time, higher mask cost and even mask quality degradation ¹. Micronic Sigma7500 laser writer introduces a novel imaging system combining partial coherent light and DUV spatial light modulation (SLM) to generate a high-quality pattern image ². The benefit of raster-scan laser writer is high throughput with consistent writing time regardless of pattern geometry, complexity and data size. However, pattern CD accuracy still needs improvement. This study is to evaluate jog CD control capability of Sigma7500 on OPC typical line-and-space test patterns with different orientations of 0°, 90°, 45° and 135°. In addition, mask CD uniformity and OPC jog height linearity will also be demonstrated.

back to top

Poster Session: Advanced Mask Processing and Materials

Select this Article		70nm DRAM intra-field CDU improvement by dose modulation on mask transmittance Tomas Chin, Wen Bin Wu, Chiang Lin Shih, Pei Cheng Fan, and Guy Ben Zvi Proc. SPIE 7122, 712238 (2008); http://dx.doi.org/10.1117/12.801417 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract DRAM intra-field CD uniformity (CDU) demand becomes more crucial with pattern size shrink and wafer die or memory size expanding. Intra-field CDU error mainly comes from mask CD error, scanner exposure and wafer process. This study makes use of a method to extract systematic CDU error from multi-field CDU results. Based on the information of the systematic CDU error, localized mask transmittance modulation is implemented to compensate the intra-field systematic CDU error on wafer. A focused ultrafast laser beam forms shading elements in mask quartz substrate. Mask transmittance modulation is controlled by the shading element density variation. This study will demonstrate the intra-field CDU improvement result, CD modulation calibration validity, CD proximity variation result and mask inspection result etc.

Select this Article		The study of CD behavior due to transmission control position change within photomask substrate Munsik Kim, Hyemi Lee, Sungha Woo, Kangjoon Seo, Yongkyoo Choi, and Changyeol Kim Proc. SPIE 7122, 712239 (2008); http://dx.doi.org/10.1117/12.801432 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As design rule of memory device is smaller and smaller, the CD uniformity of a photomask become the most important factor to satisfy wafer exposure performance. Once the photomask is made, CD uniformity of the mask can't be changed and if CD uniformity of the mask is not good to use for wafer exposure, we must reject it and make another one again. But, after applying transmission control tool for CD uniformity, we have an extra chance to control mask CD uniformity in one mask and this is very effective for wafer printing result. In this paper, we are going to evaluate the behavior of wafer CD due to transmission control position change within photomask substrate and find the optimum control position for better wafer result.

Select this Article		Effects of photo resist erosion in development on critical dimension performance for 45nm node and below Guen-Ho Hwang, Dong-Hyun Kim, Chu-bong Yu, Byeng-Sun Kang, Ik-Boum Hur, Cheol Shin, Sung-Mo Jung, and Sang-Soo Choi Proc. SPIE 7122, 71223A (2008); http://dx.doi.org/10.1117/12.802741 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In previous study, it has been reported that photo resist erosion after development gets severe as patterns size decreases. The 60nm feature requiring for SRAF(Sub Resolution Assistant Feature) of 45nm technology node, the photo resist erosion after develop on unexposed area was almost 400Å. It will be a serious problem to degrade not only the resist thickness margin for thinner resist to enhance resolution and pattern collapse, but also CD(Critical Dimension) performance capability such as CD linearity and SRAF resolution capability by proceeding dry etching. In this paper, the effects of photo resist erosion by pattern size on CD linearity performance were studied. The photo resist erosion by pattern size was simulated with the Gaussian blur model before dry etching. The effects of dosage, PEB(Post Exposure Bake) temperature and development conditions were evaluated to reduce blur value before dry etching.

back to top

Poster Session: Metrology

Select this Article		Novel CD measurement and precise pattern size extraction method for optical images Lev Faivishevsky Proc. SPIE 7122, 71223C (2008); http://dx.doi.org/10.1117/12.801434 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A new method for accurate CD measurement and precise pattern size extraction from optical images is proposed. The approach is based on the underlying field theory of optical image generation. The method demonstrates superior precision compared with traditional edge detection schemes based on the image and not on the field nature of image creation. The proposed method presents accuracy parallel to that achieved by SEM imaging. Therefore it provides an alternative to electronic microscopy measurements in certain cases. This new method may be implemented for applications of accurate mask-CD measurement, as well as for retrieving the mask model from an optical image for a die to model application.

back to top

Poster Session: Inspection and Repair

Select this Article		A novel approach to mask defect inspection Amir Sagiv, Yuri Shirman, and Shmoolik Mangan Proc. SPIE 7122, 71223E (2008); http://dx.doi.org/10.1117/12.802200 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Memory chips, now constituting a major part of semiconductor market, posit a special challenge for inspection, as they are generally produced with the smallest half-pitch available with today's technology. This is true, in particular, to photomasks of advanced memory devices, which are at the forefront of the "low-k₁" regime. In this paper we present a novel photomask inspection approach, that is particularly suitable for low-k₁ layers of advanced memory chips, owing to their typical dense and periodic structure. The method we present can produce a very strong signal for small mask defects, by suppression of the modulation of the pattern's image. Unlike dark-field detection, however, here a single diffraction order associated with the pattern generates a constant "gray" background image, that is used for signal enhancement. We define the theoretical basis for the new detection technique, and show, both analytically and numerically, that it can easily achieve a detection line past the printability spec, and that in cases it is at least as sensitive as high-resolution based detection. We also demonstrate this claim experimentally on a customer mask, using the platform of Applied Material's newly released Aera2^TM mask inspection tool. The high sensitivity demonstrates the important and often overlooked concept that resolution is not synonymous with sensitivity. The novel detection method is advantageous in several other aspects, such as the very simple implementation, the high throughput, and the relatively simple pre- and post-processing algorithms required for signal extraction. These features, and in particular the very high sensitivity, make this novel detection method an attractive inspection option for advanced memory devices.

Select this Article		Automated reticle inspection data analysis for wafer fabs Derek Summers, Gong Chen, Bryan Reese, Trent Hutchinson, Marcus Liesching, Hai Ying, and Russell Dover Proc. SPIE 7122, 71223F (2008); http://dx.doi.org/10.1117/12.801524 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract To minimize potential wafer yield loss due to mask defects, most wafer fabs implement some form of reticle inspection system to monitor photomask quality in high-volume wafer manufacturing environments. Traditionally, experienced operators review reticle defects found by an inspection tool and then manually classify each defect as 'pass, warn, or fail' based on its size and location. However, in the event reticle defects are suspected of causing repeating wafer defects on a completed wafer, potential defects on all associated reticles must be manually searched on a layer-by-layer basis in an effort to identify the reticle responsible for the wafer yield loss. This 'problem reticle' search process is a very tedious and time-consuming task and may cause extended manufacturing line-down situations. Often times, Process Engineers and other team members need to manually investigate several reticle inspection reports to determine if yield loss can be tied to a specific layer. Because of the very nature of this detailed work, calculation errors may occur resulting in an incorrect root cause analysis effort. These delays waste valuable resources that could be spent working on other more productive activities. This paper examines an automated software solution for converting KLA-Tencor reticle inspection defect maps into a format compatible with KLA-Tencor's Klarity Defec^TM data analysis database. The objective is to use the graphical charting capabilities of Klarity Defect to reveal a clearer understanding of defect trends for individual reticle layers or entire mask sets. Automated analysis features include reticle defect count trend analysis and potentially stacking reticle defect maps for signature analysis against wafer inspection defect data. Other possible benefits include optimizing reticle inspection sample plans in an effort to support "lean manufacturing" initiatives for wafer fabs.

Select this Article		Results from the KLA-Tencor TeraScanXR reticle inspection tool Aditya Dayal, Bo Mu, Venkat Iyer, Phillip Lim, Arosha Goonesekera, and Bill Broadbent Proc. SPIE 7122, 71223G (2008); http://dx.doi.org/10.1117/12.801831 \| Cited 3 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The new TeraScanXR reticle inspection system extends the capability of the previous TeraScanHR platform to advanced 32nm logic and 40nm Half Pitch (HP) memory technology nodes. The TeraScanXR has been designed to provide a significant improvement in image quality, defect sensitivity and throughput relative to the HR platform. Defect sensitivity is increased via a combination of improved Die-to-Die (D:D) and Die-to-Database (D:DB) algorithms, as well as enhancements to the image auto-focus (IAF). Modifications to system optics and the introduction of a more powerful image processing computer have enabled a ~2X faster inspection mode. In this paper, we describe the key features of the TeraScanXR platform and present preliminary data that illustrate the capability of this tool. TeraScanHR tools currently at customer sites are field-upgradeable to the TeraScanXR configuration.

Select this Article		Layout driven DNIR Kiyoshi Kageyama, Kohei Yanagisawa, Atsushi Kobayashi, Shinji Kunitani, and Yoji Tonooka Proc. SPIE 7122, 71223H (2008); http://dx.doi.org/10.1117/12.801940 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract With the shrinking of devices, aggressive OPC is becoming imperative. Generally, OPC must be kept within photomask manufacturing limits, but at process and OPC development stages, patterns exceeding photomask manufacturing and inspection limits are often included. To resolve this issue, MRC (Mask Rule Checking) is executed as a method to verify patterns exceeding photomask manufacturing and inspection limits. Two options are available in MRC to solve errors: (1) repair layout (or OPC) of corresponding areas; or (2) manufacture photomask including corresponding areas but with no inspection. Option (1) is generally extremely time-consuming, and if lithographically feasible, (2) would be selected. However, if detected error flags become massive, it is nearly beyond human control to take care of configurations of DNIR(Do Not Inspect Region). In addition, massive amounts of DNIR will augment inspection tool setup time almost factorial. Further, inspection tools have limitations in DNIR setup method, and DNIR settings that do not meet criteria will be considered as setting violations. Therefore, we developed TLDD (Toppan Layout Driven DNIRs), a tool that automatically generates DNIR based on detected by MRC. This tool has the following features: (1) applies limitations to the number of DNIRs; (2) follows DNIR limitations of inspection tools; and (3) follows both (1) and (2) upon which DNIR area is minimized as much as possible. By utilizing this tool, difficult-to-inspect regions can be automatically set as DNIR independent of DNIR rules of inspection tools or individual operator skills, while enabling inspection of important areas at high sensitivity.

Select this Article		Improving cost of ownership on KLA-Tencor wafer fab reticle inspections by implementing pixel migration via new STARlight2+ capability Yung-Feng Cheng, Wei-Cyuan Lo, Ming-Jui Chen, Peter Huang, Chunlin Chen, Swapnajit Chakravarty, Paul Yu, and Russell Dover Proc. SPIE 7122, 71223J (2008); http://dx.doi.org/10.1117/12.802331 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In the ever-changing semiconductor industry, wafer fabs and mask shops alike are adding low cost of ownership (CoO) to the list of requirements for inspections tools. KLA-Tencor has developed and introduced STARlight2+ (SL2+) to satisfy this need. This new software algorithm is available on all TeraScanHR and TeraFab models. KLA-Tencor has cooperated with United Microelectronics Corporation (UMC) to demonstrate and improve SL2+, including its ability to lower CoO, on 65nm and below photomasks. These improvements are built on the rich history of STARlight. Over the years, STARlight has become one of the industry standards for reticle inspection. Like its predecessors, SL2+ uses only transmitted and reflected light images from a reticle to identify defects on the reticle. These images along with plate-specific information are then processed by SL2+ to generate reference images of how the patterns on the reticle should appear. These reference images are then compared with the initial optical images to identify the defects. The new and improved SL2+ generates more accurate reference images. These images reduce background noise and increase the usable sensitivity. With the results from controlled engineering tests, a fab or mask shop can then decide to inspect reticles at a given technology node with a large pixel; this is sometimes referred to as pixel migration. The larger pixel with SL2+ can then perform the inspections at similar sensitivity settings and higher throughput, thus lowering CoO.

back to top

Poster Session: Contamination Control and Cleaning

Select this Article		An effective haze monitoring method Shih-Ping Lu, Shean-Hwan Chiou, and Wen-Jui Tseng Proc. SPIE 7122, 71223L (2008); http://dx.doi.org/10.1117/12.801429 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Monitoring and controlling of haze defect is becoming important more than ever before [1]. Regular and frequent mask inspection is expected to reduce the risk of defect print on wafer [2]. However, such frequent inspection requires longer inspection time and additional cost, which should lead to worsening of productivity. It is known that haze defect grows from non-killer defect at its infant stage to killer defect as time advances. And such haze growth process is dependent on the haze size in its infant stage, location of haze generation and such. If the haze inspection procedure were customized in a most suited way to optimally monitor the growth characteristics of haze, the inspection throughput would become higher without sacrificing the performance and reliability of mask inspection itself. For such a purpose, we have studied an effective haze monitoring method that ensures both sensitivity and throughput high enough. We will show that a variable scan method using a DUV mask inspection tool is quite effective in cutting down inspection time and cost.

Select this Article		Results of new mask contamination inspection capability STARlight2+ 72nm pixel with cell-to-cell HiRes5 for qualifying memory masks in wafer fabs Raj Badoni, Jinggang Zhu, Russell Dover, Norbert Schmidt, Michael Lang, Andreas Jahnke, and Florian Uhlig Proc. SPIE 7122, 71223M (2008); http://dx.doi.org/10.1117/12.802332 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As the industry embarks on sub 50nm half pitch design nodes, higher resolution and advanced photomask inspection algorithm are needed to resolve shrinking features and find critical yield limiting defects. In this paper, we evaluate the detection capability of STARlight2+ 72nm pixel on sub-50nm memory masks. The mask sets targeted for this evaluation were focused on critical layers. Although memory mask sets are dominated by multi-die layout, single die layout masks were also inspected because of their significance during research and development. Inspection results demonstrated the performance of STARlight2+ based on its sensitivity to contamination defects and the inspectability of masks with this detection method. The most common plan of record for mask inspection in a wafer fab is die-to-die transmitted pattern inspection modes, which limits the inspection area to the die region only and cannot be used for single-die reticle inspections. However, STARlight2+ has single die inspection capability, which is also needed in order to inspect scribe-lines and frame areas. The primary defects of interest are photo induced crystal defects or haze. Haze continues to be the primary reason for mask returns at 193nm exposure across the industry. The objective of this paper is to demonstrate STARlight2+ 72nm capability to support memory wafer fab mask qualification requirements.

Select this Article		SL2+: H5 use case Kosuke Ito, Steven Liu, Isaac Lee, Russell Dover, and Paul Yu Proc. SPIE 7122, 71223N (2008); http://dx.doi.org/10.1117/12.802333 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Photomask contamination inspections, whether performed at maskshops as an outgoing inspection or at wafer fabs for incoming shipping and handling or progressive defect monitoring, have been performed by KLA-Tencor STARlight systems for a number of design nodes. STARlight has evolved since it first appeared on the 3xx generation of KLA-Tencor mask inspection tools. It was improved with the TeraStar (also known as SLF) based tools with the SL1 algorithm. SL2 first appeared on the TeraScan systems (also known as 5xx) and has been widely adopted in both mask shops and wafer fabs. Design rules continue to advance as do inspection challenges. Advances in computer processing power have enabled more complex and powerful algorithms to be developed and applied to the STARlight technology. The current generation of STARlight, which is known as SL2+, implements improved modeling fidelity as well as a completely new paradigm to the existing STARlight technology known as HiRes5, or simply "H5". H5 is integrated seamlessly within SL2+ and provides die-to-die-like performance in both transmitted and reflected light, in addition to the STARlight detection, in unit time. It achieves this by automatically identifying repeating structures in both X and Y directions and applying image alignment and difference threshold. A leading mask shop partnered with KLA-Tencor in order to evaluate SL2+ at its facility. SL2+ demonstrated a high level of sensitivity on all test reticles, with good inspectability on advanced production reticles. High sensitivity settings were used for 45 nm HP and smaller design rule masks and low false detections were achieved. H5 provided additional sensitivity on production plates, demonstrating the ability to extend the use of SL2+ to cover 32 nm DR plate inspections. This paper reports the findings and results of this evaluation.

back to top

Poster Session: EUV Mask Processing and Substrates

Select this Article		Evaluation of backside particle contamination and electrostatic chuck design on the cleanliness of EUV reticle mask blanks in a multilayer Mo/Si ion beam deposition system A. V. Hayes, R. Randive, I. Reiss, J. Menendez, P. Kearney, and T. Sugiyama Proc. SPIE 7122, 71223O (2008); http://dx.doi.org/10.1117/12.801870 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A key requirement for the success of EUV lithography is a high volume supply of defect-free Mo/Si multilayer (ML)- coated mask blanks. The process of fabricating mask blanks is particularly sensitive to particle contamination because decoration by the deposition of the reflective stack on sub-lithographic (< 22 nm) particles can create larger, printable defects. One possible source of added defects is the mask substrate fixturing method, which, in the Veeco ion beam deposition (IBD) system used to deposit our ML coatings, must allow tilt and rotation of a vertically oriented substrate. As commonly practiced, an electrostatic chuck (ESC) is used instead of a mechanical clamping fixture to avoid transferring particles to the front surface of the mask by mechanical clamping and declamping operations. However, a large number of particles can be introduced to the backside of the mask by electrostatic clamping. Up to now, there has been little concern about such backside particles, except for relatively large particles (> 1 micron) that may affect out-of-plane distortion of the mask in an EUV lithography tool. As the cleanliness of the EUV masks and mask blank fabrication approaches perfection, however, there is more concern that particles transferred from the backside to the frontside of the mask may be a significant issue. Such transfer may occur in the deposition chamber, in the substrate cassette, or in the transfer module and may be indirect. In this paper, we present data from characterizing the amount, size, shape, composition, and location of the backside particle defects generated by electrostatic clamping, using a particle counter and scanning electron microscope (SEM), and compare results for a pin-type e-chuck, which has a small contact area, with the standard flat e-chuck. The key result is a 10X to 30X reduction in the total number of backside particles for the pin chuck. Also, preliminary data indicates that the pin chuck stays cleaner under service conditions than the flat chuck. The exact elemental composition of the defects is sensitive to the clamping method and type of backside Cr coating. In general, for the flat chuck, Al defects, attributed to particles from the alumina chuck surface, are dominant. For the pin chuck, Si,Cr,N,O defects from the mask surface are mainly observed.

back to top

Poster Session: Nano-Imprint

Select this Article		UV NIL template making and imprint evaluation Shiho Sasaki, Takaaki Hiraka, Jun Mizuochi, Akiko Fujii, Yuko Sakai, Takanori Sutou, Satoshi Yusa, Koki Kuriyama, Masashi Sakaki, Yasutaka Morikawa, Hiroshi Mohri, and Naoya Hayashi Proc. SPIE 7122, 71223P (2008); http://dx.doi.org/10.1117/12.802746 \| Cited 2 times Online Publication Date: Oct 20, 2008 Full Text: \| Download PDF
	+ -	Show Abstract UV NIL shows excellent resolution capability with remarkable low line edge roughness, and has been attracting pioneers in the industry who were searching for the finest patterns. We have been focused on the resolution improvement in NIL template making with a 100keV acceleration voltage spot beam EB writer process, and have established a template making process to meet the requirements of the pioneers. Usually such templates needed just a small field (several hundred microns square or so). Now, for several semiconductor devices, the UV NIL is considered not only as a patterning solution for R&D purpose but eventually as a potential candidate for production, and instead of a small field, a full chip field mask is required. Although the 100kV EB writers have excellent resolution capability, they are adopting spot beams (SB) to generate the pattern and have a fatally low throughput if we need full chip writing. In this paper, we are focusing on the 50keV variable shaped beam (VSB) EB writers, which are used in current 4X photomask manufacturing. The 50keV VSB writers can generate full chip pattern in a reasonable time, and by choosing the right patterning material and process, we achieved resolution down to 28nm.

Select this Article		Development status of back-end process for UV-NIL template fabrication Yuichi Inazuki, Kimio Itoh, Sho Hatakeyama, Kouichirou Kojima, Masaaki Kurihara, Yasutaka Morikawa, Hiroshi Mohri, and Naoya Hayashi Proc. SPIE 7122, 71223Q (2008); http://dx.doi.org/10.1117/12.803615 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Nano-imprint lithography (NIL) is eminently suitable for low cost patterning for nanostructures. As feature sizes of the UV-NIL templates are the same as the wafer patterns, there are enormous challenges such as writing and inspecting smaller patterns for NIL template fabrication. In our previous works, we achieved less than 16nm resolution with a 100keV spot beam writer and non CAR. We also reported optimization of metrology for NIL templates and the characterization of anti-sticking layers with scanning probe microscopies. Normally the template is made from a 6025 photomask blank. After the blank undergoes a process similar to the photomask process, it is diced into 65 mm x 65 mm size and four pieces, and then each piece is polished into its final shape. Therefore it becomes difficult to inspect and clean them, because 65 mm substrates are unfamiliar in photomask industry. In order to reach the step for mass-production of the templates, the development of "back-end process", which includes not only cleaning and inspection but also repair, dicing, polishing, and coating anti-sticking layers, is essential. Especially keeping low contamination level during dicing and polishing processes is one of the critical issues. In this paper, we report our development status of "back-end process" for NIL templates. Especially, we focus on the techniques of reducing adder defects during dicing process and improving cleaning capability.

back to top

Poster Session: DFM

Select this Article		Non-uniform yield optimization for integrated circuit layout considering global interactions J. Andres Torres and Fedor G. Pikus Proc. SPIE 7122, 71223R (2008); http://dx.doi.org/10.1117/12.801144 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract In a previous work we have shown a yield optimization metric and a technique that considers the effects of several types of yield enhancement methods for a given layout. Those findings suggested that it is important to consider two types of yield tradeoffs, local tradeoffs where addressing one yield loss mechanism degrades others in the immediate vicinity of the correction (local optimization window), and global tradeoffs where the net effect of the correction can be fully accounted only when considering neighboring optimization windows. Such conclusion was derived from the fact that the locally optimized layouts did not completely realize the theoretically optimal yield, which was obtained from the assumption that global tradeoffs could be fully resolved. This work focuses in the contribution that such global tradeoffs have on the final yield score when accounted properly during the optimization. While the previous work focused only in selecting the corrections that locally improved the yield score1, this work evaluates the global interactions before and after a change, and the correction is only accepted if it improves the global score. While the global optimization requires a more expensive computational process, the intention of this work is to determine how close the optimal layout can be from its theoretical limit. Since the optimization is performed and evaluated under four different types of processes in which the failure mechanisms vary in relative importance, it is possible to derive conclusions as to the need of considering global effects when trading off runtime requirements with quality of the correction.

Select this Article		Fast and simple modeling of non-rectangular transistors Jen-Yi Wuu, Fedor G. Pikus, and Malgorzata Marek-Sadowska Proc. SPIE 7122, 71223S (2008); http://dx.doi.org/10.1117/12.801541 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As CMOS feature size scales down to 65nm and below, challenges for device and circuit manufacturability are emerging. As commonly seen in real designs, devices with distorted gate shapes and rough line-edges are manufactured despite the applications of aggressive resolution enhancement techniques (RET). It has been shown that such irregular gates could introduce significant extra leakage current. Existing tools and device models cannot handle non-rectangular geometries. Therefore, it is critical that a modeling flow capable of handling such irregular devices is developed and smoothly integrated into the post-lithography delay and leakage circuit analysis process. Previously proposed methods either model an irregular transistor as two different rectangular devices, one for on and the other for off state analyses; or they are difficult to be implemented. In this paper, we propose a new modeling approach that serves as a fast and simple solution to this problem and overcomes these drawbacks. We found that by adjusting both gate length and width of the equivalent device, a single equivalent rectangular device can be determined. Through TCAD and SPICE simulation experiments, we demonstrate that our model can accurately capture both on and off currents of the modeled nonrectangular gate device. The average error of our modeling approach is 1.6% for I_on and 7.5% for I_off.

Select this Article		Study of influence to transistor properties on the change of OPC pattern Kazuya Sugawa, Norimasa Nagase, Takahisa Itoh, Mitsuo Sakurai, and Tomoyuki Okada Proc. SPIE 7122, 71223T (2008); http://dx.doi.org/10.1117/12.801547 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Slight change of OPC pattern shape may influence transistor characteristics. So inputting the result of Litho- Simulation, Contour, to SPICE-simulator, we investigated the change of the transistor characteristic. First of all, we investigated the sensitivity of the transistor characteristics to OPC pattern change. We found that the difference of shape with Isolated, Dense pattern, and a different OPC tool caused difference after SPICE-simulation. In this investigation, we report focusing on the transient and DC analysis of transistor characteristics. Contour data was measured and averaged before input to SPICE and a change of transistor characteristic was able to be detected. We came to the conclusion that this investigation method is effective to check the influence of the transistor characteristics due to OPC pattern change. And we can adopt this method as one technique for deciding the applicability of the OPC tool and its upgrade, which were issues for MASK data processing.

Select this Article		Mask data prioritization based on design intent Kokoro Kato, Masakazu Endo, Tadao Inoue, and Masaki Yamabe Proc. SPIE 7122, 71223U (2008); http://dx.doi.org/10.1117/12.801561 \| Cited 2 times Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract MaskD2I and STARC have been working together to build efficient data flow based on the information transition from the design to the manufacturing level. By converting design level information called as "Design Intent" to the priority information of mask manufacturing data called as "Mask Data Rank (MDR)", MDP or manufacturing process based on the importance of reticle patterns is possible. Our main purpose is to build a novel data flow with the priority information of mask patterns extracted from the design intent. In EMCL2008, we introduced the idea of MDR and showed its potential effectiveness. Then we addressed an additional idea called DIF(Design Intent File) instead of RAF (Rank Assign File) in PMJ2008. Since DIF contains all the coordinate information necessary for mask data prioritization, it has been proved that mask engineers do not need to access the design information any more. Recently the necessity of information linkage between mask processes and wafer processes has been pointed out and we have started to build a new flow to share the mask data priority information. In this presentation, we will address two new progresses of MaskD2I. One is a new rank assignment method to inspection tools and the other is information feed forward to wafer process.

back to top

Poster Session: Simulation and Modeling

Select this Article		Extracting mask error function from intensity slices David Ziger Proc. SPIE 7122, 71223W (2008); http://dx.doi.org/10.1117/12.801821 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A new method to calculate Mask Error Enhancement Function, or MEEF, from the intensity slope of the unperturbed geometry and intensity offset of the perturbed mask is derived. In the limit of small perturbations, the intensity slope technique is predicted to be the same as MEEF values calculated from the ratio of wafer to mask CD differences scaled by the magnification. Full chip process window simulations were done to compare the accuracy of this new approach for 45 to 90nm mask designs for line, space and contact features. The standard deviation was less than 0.11 and the largest deviation was only 12% for over 5200 MEEF calculations. Below MEEF values of 20, the standard deviation was less 0.065 and all simulations were within ±0.5. A significant discovery in this work is the inverse relationship between image intensity slope rather than NILS or ILS at the location of the printed feature edge and MEEF. Since the image slope decreases closer to the intensity extrema, high MEEF regions are predicted to be those that print closest to the minimum and maximum intensities.

Select this Article		Focus blur model to enhance lithography model for optical proximity correction Qiaolin Zhang, Hua Song, and Kevin Lucas Proc. SPIE 7122, 71223Y (2008); http://dx.doi.org/10.1117/12.802509 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The concept of focus blur encompasses the effect of laser bandwidth longitudinal chromatic aberration and scanner stage vertical vibration. The finite bandwidth of excimer laser source causes a corresponding finite distribution of focal planes in a range of 100nm or larger for the optical lithography system. Similarly, scanner vertical stage vibration puts the wafer in a finite distribution of focal planes. Both chromatic aberration and vertical stage vibration could introduce significant CD errors, hence can no longer be ignored in current lithography processes development and OPC development that require CD control within a few nanometers. We developed several methodologies to model the laser chromatic aberration and vertical stage vibration in OPC (Optical Proximity Correction) modeling tool. Extensive simulations were done to calculate chromatic aberration and vertical stage vibration focus blur's impact on lithography patterning for a variety of test structures. Chromatic aberration and vertical stage vibration focus blur effect was further included as an regression term in experimental OPC model calibration to capture its impact on litho patterning, and significant benefit to OPC model calibration was observed.

back to top

Poster Session: RET and OPC/ORC

Select this Article		32nm design rule and process exploration flow Yunqiang Zhang, Jonathan Cobb, Amy Yang, Ji Li, Kevin Lucas, and Satyendra Sethi Proc. SPIE 7122, 71223Z (2008); http://dx.doi.org/10.1117/12.801593 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Semiconductor manufacturers spend hundreds of millions of dollars and years of development time to create a new manufacturing process and to design frontrunner products to work on the new process. A considerable percentage of this large investment is aimed at producing the process design rules and related lithography technology to pattern the new products successfully. Significant additional cost and time is needed in both process and design development if the design rules or lithography strategy must be modified. Therefore, early and accurate prediction of both process design rules and lithography options is necessary for minimizing cost and timing in semiconductor development. This paper describes a methodology to determine the optimum design rules and lithography conditions with high accuracy early in the development lifecycle. We present results from the 32nm logic node but the methodology can be extended to the 22nm node or any other node. This work involves: automated generation of extended realistic logic test layouts utilizing programmed teststructures for a variety of design rules; determining a range of optical illumination and process conditions to test for each critical design layer; using these illumination conditions to create a extrapolatable process window OPC model which is matched to rigorous TCAD lithography focus-exposure full chemically amplified resist models; creating reticle enhancement technique (RET) recipes which are flexible enough to be used over a variety of design rule and illumination conditions; OPC recipes which are flexible enough to be used over a variety of design rule and illumination conditions; and OPC verification to find, categorize and report all patterning issues found in the different design and illumination variations. In this work we describe in detail the individual steps in the methodology, and provide results of its use for 32nm node design rule and process optimization.

Select this Article		Accelerate OPC convergence with new iteration control methodology Ching-Heng Wang, Qingwei Liu, and Liguo Zhang Proc. SPIE 7122, 712240 (2008); http://dx.doi.org/10.1117/12.800598 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract A dilemmatic trade-off that all OPC engineers are facing everyday is the convergence of the OPC result and the control of the OPC iteration times. Theoretically, infinite times of OPC iterations are needed to achieve a convergent and stable correction result. But actually there should always be a cut-off for the iteration time, for turnaround- time is always an important criteria for IC fabs. But considering the design layout becomes more complicated and pattern density becomes higher with the shrinkage of the critical dimension, fragmentation control during the OPC procedure is also becoming more and more sophisticated. Thus, to achieve a convergent correction result for all OPC fragments within limited correction iteration times now becomes a big challenge to OPC engineers. This work presents our study in a new OPC iteration control methodology. It can help to find an algorithm that always converges, and reduce the excessive use of parameter setting, commands and other involvement by the user. With this, we can reduce the run time required to obtain a convergent OPC solution.

Select this Article		Enhanced DCT2-based inverse mask synthesis with initial SRAF insertion Shanhu Shen, Peng Yu, and David Z. Pan Proc. SPIE 7122, 712241 (2008); http://dx.doi.org/10.1117/12.801409 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Inverse mask synthesis, or Inverse Lithography Technology, as a next generation resolution enhancement technology, is drawing pretty much attention after years of development. However, the existing optimized mask usually is too complex such that the pattern simplifying procedures have to be applied as a post processing step. But the post processing step may lead to pattern degradation and unwanted side lobe printing. In this paper, we first implement a new inverse mask synthesis system using two dimensional discrete cosine transform(DCT2) of the target mask, where the low frequency components are used in the optimization. As the high frequency components are discarded, the resulted optimal pattern is similar in shape to that of using the level set method in the published papers. Moreover, as inverse mask synthesis is an ill-posed problem, there are some local minimum locations. Previous algorithms usually use the desired pattern as an initial iteration point, in the sense that optimized pattern shall be a perturbation of the desired pattern. A common fact is that initial solution is critical to the optimization procedure and final result. In this paper, we apply an initial SRAF insertion around the main features before starting the existing inverse engine. The SRAF insertion does not need to be as accurate as that in the traditional SRAF+main feature OPC flow. Therefore, it does not add higher time burden on the whole mask synthesis flow. We implement the SRAF insertion based on computed mask electric field distribution. The experimental results show that using the initial fast SRAF insertion, the inverse engine is able to take advantage of a better initial high contrast image distribution, and the optimized pattern can be much simpler while the pattern fidelity is still in good control. We also observe that better optimized patterns can be achieved with fewer iterations.

Select this Article		Empirical study of OPC metrology requirements for 32-nm node logic Brian S. Ward, Lena Zavylova, Peter de Bisschop, and Jeroen van de Kerkhove Proc. SPIE 7122, 712242 (2008); http://dx.doi.org/10.1117/12.801458 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract We evaluate the relationship between the number of measurements used to create each data point in an OPC model data set and resulting model quality for target 32-nm logic node applications. Generated data sets will range from singlemeasurement, unfiltered data sets to many-measurement averages based on filtered results. Intermediate measurementcount averages will also be evaluated in an attempt to quantify the tradeoff between raw measurements per data point and resulting model quality. Finally, other variations will also be considered, such as automated versus manual data filtering. The auto-fitted OPC models will be compared to identify metrology recommendations for 32-nm logic node modeling.

Select this Article		Adaptive automatic fragmentation Mohamed Serag El-Din Habib Proc. SPIE 7122, 712243 (2008); http://dx.doi.org/10.1117/12.801508 \| Cited 1 time Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract As more aggressive Resolution Enhancement Techniques (RET) are applied, the problem of correctly fragmenting edges of an OPC mask is becoming more complex. OPC recipes contain more lines devoted to control of fragmentation than anything else. This paper introduces a new Automatic Adaptive Fragmentation method that decreases the complexity of OPC recipes while providing the same or better quality of results. The adaptive fragmentation is guided by just a few simple rules that provide flexible fragmentation while adhering to mask manufacturing rule constraints.

Select this Article		Enhancing OPC model stability and predictability using SEM image contours Mohamed Serag El-Din Habib Proc. SPIE 7122, 712244 (2008); http://dx.doi.org/10.1117/12.801513 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract The process model is a major factor affecting the quality of the Model Based Optical Proximity Correction (OPC). Better process model directly leads to better OPC, hence better yield and more profit. While the traditional way in calibrating these process models is using CD measurements at sample locations in the test chip, however, the use of Scanning Electron Microscope (SEM) image contours for process model calibration and optimization has been recently introduced in trial to build more predictable models. In this study, we characterize the traditional flow models versus the contour calibrated models and study the effect of using different combinations and weighting schemes on the quality of the resulting process models, its stability and its ability to correctly predict the process.

Select this Article		Characterizing OPC model accuracy versus lens induced polarization effects in hyper NA immersion lithography Tamer M. Tawfik and Edita Tejnil Proc. SPIE 7122, 712245 (2008); http://dx.doi.org/10.1117/12.801516 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Immersion lithography is extending the lifetime of optical lithography by enabling numerical aperture (NA) greater than unity. Along with scanner hardware improvements, modeling of hyper-NA lithography systems for optical proximity correction (OPC) is also continuing to be necessary in improving photolithography capability. With the use of hyper-NA immersion lithography and polarized illumination, the assumption of scalar optical pupil in optical system modeling may no longer be valid. To fully describe the transmission of any polarization state through the optical system, Jones matrix is necessary. It has been shown that Jones matrix can be described as a combination of apodization loss, birefringence, diattenuation, scalar phase aberrations, and rotation effects. In this work, the impact of such effects on calibration and accuracy of OPC models is characterized in terms of the model fit quality, model predictability, and changes to OPC results.

Select this Article		Toward faster OPC convergence: advanced analysis for OPC iterations and simulation environment Mohamed Bahnas, Mohamed Al-Imam, and Tamer Tawfik Proc. SPIE 7122, 712248 (2008); http://dx.doi.org/10.1117/12.801878 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Achieving faster Turn-Around-Time (TAT) is one of the most attractive objectives for the silicon wafer manufacturers despite the technology node they are processing. This is valid for all the active technology nodes from 130nm till the cutting edge technologies. There have been several approaches adopted to cut down the OPC simulation runtime without sacrificing the OPC output quality, among them is using stronger CPU power and Hardware acceleration which is a good usage for the advancing powerful processing technology. Another favorable approach for cutting down the runtime is to look deeper inside the used OPC algorithm and the implemented OPC recipe. The OPC algorithm includes the convergence iterations and simulation sites distribution, and the OPC recipe is in definition how to smartly tune the OPC knobs to efficiently use the implemented algorithm. Many previous works were exposed to monitoring the OPC convergence through iterations and analyze the size of the shift per iteration, similarly several works tried to calculate the amount of simulation capacity needed for all these iterations and how to optimize it for less amount. The scope of the work presented here is an attempt to decrease the number of optical simulations by reducing the number of control points per site and without affecting OPC accuracy. The concept is proved by many simulation results and analysis. Implementing this flow illustrated the achievable simulation runtime reduction which is reflected in faster TAT. For its application, it is not just runtime optimization, additionally it puts some more intelligence in the sparse OPC engine by eliminating the headache of specifying the optimum simulation site length.

Select this Article		OPC cycle time reduction and accuracy improvement by early access to advanced Tachyon modeling of TWINSCAN XT:1900i scanner Peter Nikolsky, Tjitte Nooitgedagt, Paul van Adrichem, Jeroen Meessen, Carsten Kohler, Baukje Wisse, and Stefan Hunsche Proc. SPIE 7122, 712249 (2008); http://dx.doi.org/10.1117/12.802204 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Double Patterning (DP), Spacers and other advanced Litho technologies require an enormous amount of CD and tool data collection and development time for Optical Proximity Correction (OPC) modeling. Unfortunately this process could be started typically only when the Litho and Etch process development for the OPC'ed layer is done. This leads to significant (a month and more) delays with the mask tape-outs and final chip readiness for production. In this paper we discussed a way to reduce the overall OPC and MDP preparation and product-to-market time and increase the OPC accuracy by early collection of the OPC measurements, automatic CD-SEM recipe generation and CD data analysis and model calibration with Tachyon software. We reviewed the design of the OPC test chip, OPC exposures, data analysis and OPC modeling on the advanced and accurate Tachyon T2.0 OPC platform and ways to improve modeling cycle time. Another critical parameter of the OPC modeling is accuracy as one of the main parts of the CD error budget. We investigated approaches to OPC modeling accuracy and achieved RMS below 1nm for critical features by using module data of the respective ASML TWINSCAN XT:1900i scanner and advanced Tachyon software.

Select this Article		Sizing algorithm with continuous customizable clipping Domingo Morales, Felipe Baytelman, and Hugo Araya Proc. SPIE 7122, 71224A (2008); http://dx.doi.org/10.1117/12.805595 Online Publication Date: Oct 17, 2008 Full Text: \| Download PDF
	+ -	Show Abstract Polygon sizing is required during Mask Data Preparation in order to generate derived layers and as process bias to account for edge effects of etching. Two main features are required for polygon sizing algorithms to be useful in Mask Data Preparation software: correctness to avoid data corruption and clipping of the projection of acute angle vertices to limit connectivity modifications. However, current available solutions are either based on heuristics, producing corrupted results for certain input, or based on algorithms which may fail to maintain original design's connectivity for certain input. A novel algorithm including customizable clipping is presented.

View presentations in solar, OLEDs, and more

Field Guide to Geometrical Optics

Join SPIE