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October - December 2009

Volume 8, Issue 4, Articles (04xxxx)

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Special Section on Extreme-Ultraviolet Lithography

Select this Article OPEN ACCESS		Guest Editorial: Extreme Ultraviolet Lithography Kevin Cummings and Kazuaki Suzuki J. Micro/Nanolith. MEMS MOEMS 8, 040901 (Dec 22, 2009); http://dx.doi.org/10.1117/1.3272639 Online Publication Date: Dec 22, 2009 Full Text: Read Online (HTML) \| Download PDF
		Abstract Unavailable

Select this Article		Extreme ultraviolet lithography’s path to manufacturing Harry J. Levinson J. Micro/Nanolith. MEMS MOEMS 8, 041501 (Dec 22, 2009); http://dx.doi.org/10.1117/1.3273965 \| Cited 4 times Online Publication Date: Dec 22, 2009 Full Text: Read Online (HTML) \| Download PDF See Also: Erratum
	+ -	Show Abstract The origins of extreme ultraviolet (EUV) lithography and its progress toward readiness for manufacturing are recounted. Source power and reliability and mask defects are known items requiring additional improvement before EUV lithography will be suitable for use in the volume manufacturing of integrated circuits. Additional cycles of learning, as obtained from pilot line operation, will greatly accelerate the maturation of EUV lithography and enable its use in manufacturing as early as 2013.

Select this Article		Estimating the out-of-band radiation flare levels for extreme ultraviolet lithography Simi A. George, Patrick P. Naulleau, Senajith Rekawa, Eric Gullikson, and Charles Drew Kemp J. Micro/Nanolith. MEMS MOEMS 8, 041502 (Oct 02, 2009); http://dx.doi.org/10.1117/1.3238514 \| Cited 8 times Online Publication Date: Oct 02, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract For the commercialization of extreme ultraviolet lithography (EUVL), discharge or laser-produced, pulsed plasma light sources are being considered. These sources are known to emit into a broad range of wavelengths that are collectively referred to as out-of-band (OOB) radiation by lithographers. Multilayer EUV optics reflect OOB radiation emitted by the EUV sources onto the wafer plane, resulting in unwanted background exposure of the resist (flare) and reduced image contrast. The reflectivity of multilayer optics at the target wavelength of 13.5 nm is comparable to that of their reflectivity in the deep ultraviolet (DUV) and UV regions from 100 to 350 nm. The aromatic molecular backbones of many of the resists used for EUV are equally absorptive at specific DUV wavelengths as well. To study the effect of these wavelengths on imaging performance in a real system, we are in the process of integrating a DUV source into the Sematech Berkeley 0.3-NA microfield exposure tool (MET). We present the simulation-based imaging results predicting the potential impact of OOB based on known resist, mask, and multilayer conditions. It should be noted that because the projection optics work equally well as imaging optics at DUV wavelengths, OOB radiation cannot be treated simply as uniform background or DC flare.

Select this Article		Effects of plasma spatial profile on conversion efficiency of laser-produced plasma sources for EUV lithography Ahmed Hassanein, Valeryi Sizyuk, Tatyana Sizyuk, and Sivanandan Harilal J. Micro/Nanolith. MEMS MOEMS 8, 041503 (Oct 02, 2009); http://dx.doi.org/10.1117/1.3224901 \| Cited 10 times Online Publication Date: Oct 02, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Extreme ultraviolet (EUV) lithography devices that use laser-produced plasma (LPP), discharge-produced plasma (DPP), and hybrid devices need to be optimized to achieve sufficient brightness with minimum debris generation to support the throughput requirements of high-volume manufacturing lithography exposure tools with a long lifetime. Source performance, debris mitigation, and reflector system are all critical to efficient EUV collection and component lifetime. Enhanced integrated models continue to be developed using the High Energy Interaction with General Heterogeneous Target Systems (HEIGHTS) computer package to simulate EUV photon emission, debris generation, and transport in both single and multiple laser beam interaction systems with various targets. A new Center for Materials under Extreme Environments (CMUXE) was recently established to benchmark HEIGHTS models for various EUV-related issues. The models being developed and enhanced were used to study the effect of plasma hydrodynamics evolution on the EUV radiation emission for planar and spherical geometry of a tin target and explain the higher conversion efficiency of a planar target in comparison to a spherical target. HEIGHTS can study multiple laser beams, various target geometries, and pre-pulses to optimize EUV photon production. Recent CMUXE and other experimental results are in good agreement with HEIGHTS simulation.

Select this Article		Performance results of laser-produced plasma test and prototype light sources for EUV lithography Norbert R. Böwering, Igor V. Fomenkov, David C. Brandt, Alexander N. Bykanov, Alex I. Ershov, William N. Partlo, David W. Myers, Nigel R. Farrar, Georgiy O. Vaschenko, Oleh V. Khodykin, Jerzy R. Hoffman, Christopher P. Chrobak, Shailendra N. Srivastava, Imtiaz Ahmad, Chirag Rajyaguru, et al. J. Micro/Nanolith. MEMS MOEMS 8, 041504 (Oct 05, 2009); http://dx.doi.org/10.1117/1.3224942 \| Cited 3 times Online Publication Date: Oct 05, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Improved performance and specific results are reported for several test and prototype extreme ultraviolet (EUV) light sources developed for next-generation lithography. High repetition rate and high-power CO₂ laser-produced plasma sources operating on tin droplet targets are described. Details of laser architecture, source chambers and system operation are given. Stable output power, efficient light collection, and clean EUV transmission could be achieved for hours of operation. We review progress during integration of light sources with collector mirrors reaching EUV power levels at intermediate focus of 60 W and 45 W, respectively, with duty cycles of 25% and 40%. Far-field EUV images of the collected light were recorded to monitor the source output performance during extended tests of collector longevity and debris protection with system operation time exceeding 50 h. Development results on EUV spectra, out-of-band (OOB) radiation, and ion debris obtained with dedicated metrology setups are also described. Angle-resolved measurements with ion energy analyzer and Faraday cups reveal the contributions of individual ion charge states in related spectra. Our laser-produced EUV light source technology has now reached a level of maturity in full integration where prototype sources can be delivered and pilot line introduction can be prepared.

Select this Article		Flare in extreme ultraviolet lithography: metrology, out-of-band radiation, fractal point-spread function, and flare map calibration Gian F. Lorusso, Frieda Van Roey, Eric Hendrickx, Germain Fenger, Michael Lam, Christian Zuniga, Mohamed Habib, Hesham Diab, and James Word J. Micro/Nanolith. MEMS MOEMS 8, 041505 (Oct 05, 2009); http://dx.doi.org/10.1117/1.3238515 \| Cited 8 times Online Publication Date: Oct 05, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The critical role of flare in extreme ultraviolet (EUV) lithography is well known. In this work, the implementation of a robust flare metrology is discussed, and the proposed approach is qualified both in terms of precision and accuracy. The flare measurements are compared to full-chip simulations using a simplified single fractal point-spread function (PSF), and the parameters of the analytical PSF are optimized by comparing the simulation output to the experimental results. After flare map calibration, the matching of simulation and experiment in the flare range from 4 to 12% is quite good, clearly indicating an offset of about 3%. The origin of this offset is attributed to the presence of DUV light. An experimental estimate of the DUV component is found in good agreement with the predicted value.

Select this Article		Analysis of Coulomb and Johnsen-Rahbek electrostatic chuck performance in the presence of particles for extreme ultraviolet lithography Michael R. Sogard, Andrew R. Mikkelson, Vasu Ramaswamy, and Roxann L. Engelstad J. Micro/Nanolith. MEMS MOEMS 8, 041506 (Nov 02, 2009); http://dx.doi.org/10.1117/1.3238518 \| Cited 2 times Online Publication Date: Nov 02, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The successful implementation of extreme ultraviolet lithography (EUVL) requires the use of an electrostatic chuck to both support and flatten the mask during scanning exposure. The EUVL Mask Standard, SEMI P37, specifies the nonflatness of the mask frontside and backside, as well as the thickness variation, to be 30 to 100 nm peak-to-valley, dependent on the class of substrate. Thus, characterizing and predicting the capability of the electrostatic chuck to reduce mask nonflatness to meet these specifications are critical issues. In this research, the ability of such chucks to deal with the presence of particles trapped between the substrate and chuck is investigated. Analytical and finite element modeling are used to identify the forces needed to fully embed or deform a particle during electrostatic chucking. Simulation results (using an elastic analysis) show that the forces generated by both Coulomb and Johnsen-Rahbek chucks should be able to sufficiently deform, or flatten, particles that are nearly 1.0 μm in size.

Select this Article		Development progress of optics for extreme ultraviolet lithography at Nikon Katsuhiko Murakami, Tetsuya Oshino, Hiroyuki Kondo, Masayuki Shiraishi, Hiroshi Chiba, Hideki Komatsuda, Kazushi Nomura, and Jin Nishikawa J. Micro/Nanolith. MEMS MOEMS 8, 041507 (Oct 05, 2009); http://dx.doi.org/10.1117/1.3238522 \| Cited 5 times Online Publication Date: Oct 05, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The full-field extreme ultraviolet (EUV) exposure tool named EUV1 is integrated and exposure experiments are started with a numerical aperture of the projection optics of 0.25, and conventional partial coherent illumination with a coherence factor of 0.8. 32-nm elbow patterns are resolved in a full arc field in static exposure. In a central area, 25-nm line-and-space patterns are resolved. In scanning exposure, 32-nm line-and-space patterns are successfully exposed on a full wafer. Wavefront error of the projection optics is improved to 0.4-nm rms. Flare impact on imaging is clarified, dependent on flare evaluation using the Kirk test. Resolution enhancement technology (RET) fly-eye mirrors and reflection-type spectral purity filters (SPFs) are investigated to increase throughput. High-NA projection optics design is also reviewed.

Select this Article		Process liability evaluation for extreme ultraviolet lithography Hajime Aoyama, Kazuo Tawarayama, Yuusuke Tanaka, Daisuke Kawamura, Yukiyasu Arisawa, Taiga Uno, Takashi Kamo, Toshihiko Tanaka, Toshiro Itani, Hiroyuki Tanaka, Yumi Nakajima, Ryoichi Inanami, Kosuke Takai, Koji Murano, Takeshi Koshiba, et al. J. Micro/Nanolith. MEMS MOEMS 8, 041508 (Oct 05, 2009); http://dx.doi.org/10.1117/1.3238542 \| Cited 2 times Online Publication Date: Oct 05, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This work concerns the readiness of extreme ultraviolet lithography (EUVL) for high-volume manufacturing based on accelerated development in critical areas, and the construction of a process liability (PL) test site that integrates results in these areas. Overall lithography performance is determined from the performance of the exposure tool, the printability obtainable with the resist, mask fabrication with accurate critical dimension (CD) control, and correction technology for mask data preparation. The EUV1 exposure tool can carry out exposure over the full field (26 × 33 mm) at a resolution high enough for 32-nm line-and-space patterns when Selete Standard Resist 3 (SSR3) is used. The effect of flare on CD variation is a critical issue in EUVL, so flare is compensated for based on the point spread function for the projection optics of the EUV1 and aerial simulations that take resist blur into account. Production readiness of EUVL based on the integration of results in these areas is evaluated by electrical tests on low-resistance tungsten wiring. We find the PL test site to be very useful for determining where further improvements need to be made and for evaluating the production readiness of EUVL.

Select this Article		Imaging budgets for extreme ultraviolet optics: ready for 22-nm node and beyond Marc Bienert, Aksel Göhnemeier, Oliver Natt, Martin Lowisch, Paul Gräupner, Tilmann Heil, Reiner Garreis, Koen van Ingen Schenau, and Steve Hansen J. Micro/Nanolith. MEMS MOEMS 8, 041509 (Oct 05, 2009); http://dx.doi.org/10.1117/1.3238543 \| Cited 2 times Online Publication Date: Oct 05, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We derive an imaging budget from the performance of extreme ultraviolet (EUV) optics with NA = 0.32, and demonstrate that the requirements for 22-nm applications are met. Based on aerial image simulations, we analyze the impact of all relevant contributors, ranging from conventional quantities like straylight or aberrations, to EUV-specific topics, namely the influence of 3-D mask effects and faceted illumination pupils. As test structures we consider dense to isolated lines, contact holes, and 2-D elbows. We classify the contributions in a hierarchical order according to their weight in the critical dimension uniformity (CDU) budget and identify the main drivers. The underlying physical mechanisms causing different contributions to be critical or less significant are clarified. Finally, we give an outlook for the 16- and 11-nm nodes. Future developments in optics manufacturing will keep the budgets controlled, thereby paving the way to enable printing of these upcoming nodes.

Select this Article		Recent progress in developing an extreme ultraviolet full-field exposure tool at Selete Kazuo Tawarayama, Hajime Aoyama, Shunko Magoshi, Yuusuke Tanaka, Seiichiro Shirai, and Hiroyuki Tanaka J. Micro/Nanolith. MEMS MOEMS 8, 041510 (Dec 29, 2009); http://dx.doi.org/10.1117/1.3275786 \| Cited 2 times Online Publication Date: Dec 29, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The Selete full-field EUV exposure tool, EUV1, manufactured by Nikon, is being set up at Selete. Its lithographic performance was evaluated in exposure experiments with a static slit using line-and-space (L&S) patterns, Selete Standard Resist 03 (SSR3), a numerical aperture of 0.25, and conventional illumination (σ = 0.8). The results show that 25-nm L&S patterns were resolved. Dynamic exposure experiments demonstrate that the resolution is 45 nm across the exposure field. The CD uniformity across a shot is 3 nm. Evaluation of the overlay performance of the EUV1 using alignment marks on a processed wafer revealed the repeatability to be better than 1 nm. The overlay accuracy obtained with enhanced global alignment was less than 4 nm (3σ) after linear correction. These results show that the EUV1 has attained the quality level of a typical alpha-level lithography tool and is suitable for test site verification.

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Articles

Select this Article		Inverse lithography for 45-nm-node contact holes at 1.35 numerical aperture Monica Laurel Kempsell, Eric Hendrickx, Alexander Tritchkov, Kyohei Sakajiri, Kenichi Yasui, Susuki Yoshitake, Yuri Granik, Geert Vandenberghe, and Bruce W. Smith J. Micro/Nanolith. MEMS MOEMS 8, 043001 (Nov 18, 2009); http://dx.doi.org/10.1117/1.3263702 \| Cited 2 times Online Publication Date: Nov 18, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Inverse lithography technology (ILT) is a procedure that optimizes the mask layout to produce an image at the wafer with the targeted aerial image. For an illumination condition optimized for dense pitches, ILT inserts model-based subresolution assist features (AF) to improve the imaging of isolated features. ILT is ideal for random contact hole patterns, in which the AF are not at intuitive locations. The raw output of ILT consists of very complex smooth shapes that must be simplified for an acceptable mask write time. It is challenging for ILT to quickly converge to the ideal pattern as well as to simplify the pattern to one that can be manufactured quickly. ILT has many parameters that effect process latitude, background suppression, conversion run time, and mask write time. In this work, an optimization procedure is introduced to find the best tradeoff between image quality and run time or write time. A conversion run time reduction of 4.7× is realized with the outcome of this optimization procedure. Simulations of mask write time quantify the ability of ILT to be used for full chip applications. The optimization procedure is also applied to alternate mask technologies to reveal their advantages over commonly used 6% attenuated phase shift masks.

Select this Article		Speckle in optical lithography and its influence on linewidth roughness Oscar Noordman, Andrey Tychkov, Jan Baselmans, James Tsacoyeanes, Gary Politi, Michael Patra, Vladan Blahnik, and Manfred Maul J. Micro/Nanolith. MEMS MOEMS 8, 043002 (Dec 04, 2009); http://dx.doi.org/10.1117/1.3256131 \| Cited 4 times Online Publication Date: Dec 04, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In recent years speckle in optical projection microlithography received increasing interest because of its potential contribution to linewidth roughness (LWR). Speckle is a light interference effect that causes the dose delivered to the reticle to be nonuniform, causing a linewidth variation of the patterns imaged in the resist. The contrast of the speckle pattern is shown to be caused by a combination of temporal and spatial coherence effects of the light. The temporal part, determined by the bandwidth of the laser light and the duration of the laser pulse, is found to be the dominant contributor to speckle in today’s ArF optical lithography. The spatial distribution of the speckle pattern depends on the intensity distribution of the light in the pupil. Consequently, the spatial frequencies of the LWR induced by speckle depend on the illumination condition, which is confirmed experimentally by exposing wafers with different amounts of speckle contrast. The experiments demonstrate that the amplitude of the LWR induced by speckle is consistent with theory and simulations. Its amplitude is small compared to other sources of LWR, but it is clearly present and should not be ignored when extending ArF optical lithography into future technology nodes.

Select this Article		Residual speckle in a lithographic illumination system Gregg M. Gallatin, Naonori Kita, Tomoko Ujike, and Bill Partlo J. Micro/Nanolith. MEMS MOEMS 8, 043003 (Nov 25, 2009); http://dx.doi.org/10.1117/1.3256007 \| Cited 4 times Online Publication Date: Nov 25, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Finite bandwidth and finite exposure time place a fundamental limit on dose uniformity. We evaluate the amplitude and spatial distribution of this residual speckle in a given type of lithographic illumination system. For nominal bandwidths and exposure times, the level of dose nonuniformity is on the order of several percent. We argue that this effect actually makes only a small contribution to line edge roughness.

Select this Article		Line-edge-roughness transfer during plasma etching: modeling approaches and comparison with experimental results Vassilios Constantoudis, George Kokkoris, Panagiota Xydi, Evangelos Gogolides, Erwine Pargon, and Mickaël Martin J. Micro/Nanolith. MEMS MOEMS 8, 043004 (Dec 01, 2009); http://dx.doi.org/10.1117/1.3268365 \| Cited 4 times Online Publication Date: Dec 01, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Both modeling and experimental results for the effects of plasma etching on photoresist line edge roughness and linewidth roughness (LER/LWR) and their transfer to underlayer films are presented and compared. In particular, we investigate the roughness formation on both photoresist and underlayer sidewalls during (1) isotropic trimming of photoresist, and (2) anisotropic plasma etching and LER transfer to substrate. The trimming process is modeled with an isotropic movement of the resist sidewall. In the anisotropic plasma etching process, the resist sidewall is used as a mask to anisotropically transfer the pattern to the underlying film. Experiments include trimming of a photoresist patterned with 193-nm photolithography in O₂ plasma with no bias voltage and anisotropic etching of BARC and Si underlayers in CF₄ and HBr/Cl₂/O₂ with bias. Both model and experimental results show that resist trimming causes reduction of resist LER and increase of the correlation length and roughness exponent with trimming time. This means that surface nano-protrusions versus trimming time become shorter and wider. In the case of anisotropic etching, the model predicts noticeable reduction of LWR, whereas correlation length and roughness exponent remain almost unaffected. The first experimental results seem to confirm these predictions.

Select this Article		Study of the contour-based optical proximity correction methodology Liang Zhu, Xiaohui Kang, Yili Gu, and Steve Yang J. Micro/Nanolith. MEMS MOEMS 8, 043005 (Oct 02, 2009); http://dx.doi.org/10.1117/1.3238544 Online Publication Date: Oct 02, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract As design rule continues to shrink, resolution enhancement techniques (RET) such as optical proximity correction (OPC) become more and more complex to enable design printability. As we know, typically integrated circuit (IC) layouts are simple shapes such as rectangles. However, high spatial frequency components of the mask spectrum that are not captured by the low-pass pupil result in a rounded image. In addition, the diffusion process in the postexposure bake (PEB) step makes the wafer rounding effects worse. This means that it is difficult to get the wafer image to match the design exactly at corners, even with the most aggressive OPC methodology. Therefore, pre-OPC site placement optimization is necessary to achieve high quality wafer images. In this work, a contour-based OPC methodology is proposed to minimize the time consumption in pre-OPC simulation site placement optimization and OPC job running. Rounded target contours that best describe the real intended wafer result are used as the target during OPC correction. By comparing classical OPC recipe-driven target point placement and contour-based OPC methodology, it is found that contour-based OPC methodology can achieve comparable image quality in a shorter turn around time (TAT) with fewer engineer resources.

Select this Article		Design-specific variation in pattern transfer by via/contact etch process: full-chip analysis Valeriy Sukharev, Ara Markosian, Armen Kteyan, Levon Manukyan, Nikolay Khachatryan, Jun-Ho Choy, Hasmik Lazaryan, Henrik Hovsepyan, Seiji Onoue, Takuo Kikuchi, and Tetsuya Kamigaki J. Micro/Nanolith. MEMS MOEMS 8, 043007 (Dec 04, 2009); http://dx.doi.org/10.1117/1.3268422 \| Cited 1 time Online Publication Date: Dec 04, 2009 Full Text: Read Online (HTML) \| Download PDF See Also: Erratum
	+ -	Show Abstract A novel model-based algorithm provides a capability to control full-chip design-specific variation in pattern transfer caused by via/contact etch (VCE) processes. This physics-based algorithm is capable of detecting and reporting etch hot spots based on the fabrication-defined thresholds of acceptable variations in critical dimension (CD) of etched shapes. It can be used also as a tool for etch process optimization to capture the impact of a variety of patterns presented in a particular design. A realistic set of process parameters employed by the developed model allows using this novel VCE electronic design automation tool for design-aware process optimization in addition to the “standard” process-aware design optimization.

Select this Article		Nonionic photoacid generator behavior under high-energy exposure sources Richard A. Lawson, David E. Noga, Laren M. Tolbert, and Clifford L. Henderson J. Micro/Nanolith. MEMS MOEMS 8, 043010 (Nov 06, 2009); http://dx.doi.org/10.1117/1.3259205 \| Cited 2 times Online Publication Date: Nov 06, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A series of nonionic photoacid generators (PAGs) are synthesized and their acid generation efficiency measured under deep ultraviolet (DUV) and electron beam exposures. The acid generation efficiency is determined with an on-wafer method that uses spectroscopic ellipsometry to measure the absorbance of an acid sensitive dye (Coumarin 6). Under DUV exposures, common ionic onium salt PAGs show excellent photoacid generation efficiency, superior to most nonionic PAGs tested in this work. In contrast, when under 100-keV high energy e-beam exposures, almost all of the nonionic PAGs show significantly better acid generation performance than the ionic onium salt PAGs tested. In particular, one nonionic PAG shows almost an order of magnitude improvement in the Dill C acid generation rate constant compared to a triarylsulfonium PAG. The high energy acid generation efficiency is found to correlate well with the electron affinity of the PAGs, suggesting that improvements in PAG design can be predicted. Nonionic PAGs merit further investigation as a means for producing higher sensitivity resists under high energy exposure sources.

Select this Article		Fluorinated polymethacrylates as highly sensitive nonchemically amplified e-beam resists Jeffrey R. Strahan, Jacob R. Adams, Wei-Lun Jen, Anja Vanleenhove, Colin C. Neikirk, Timothy Rochelle, Roel Gronheid, and C. Grant Willson J. Micro/Nanolith. MEMS MOEMS 8, 043011 (Dec 30, 2009); http://dx.doi.org/10.1117/1.3274005 \| Cited 3 times Online Publication Date: Dec 30, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In an effort to improve on the sensitivity of commercial nonchemically amplified e-beam resists, four polyacrylates functionalized with α-CF₃ and/or CH₂CF₃ alkoxy substituents were studied. The α-CF₃ substituent is known to increase backbone-scission efficiency while simultaneously eliminating acidic outgassing and cross-linking known to occur in α-halogen substituted polyacrylates. Contrast curves for the polymeric α-CF₃ acrylates, generated through e-beam exposure, showed that the resists required an order of magnitude less dose than the current industry standards, poly(methyl methacrylate) (PMMA) and ZEP. The fundamental sensitivity of these materials to backbone scissioning was determined via ⁶⁰Co γ-ray irradiation. The chain scissioning, G(s), and cross-linking, G(x), values calculated from the resulting change in molecular weight demonstrated that all fluorinated resists possess higher G(s) values than either PMMA or ZEP and have no detectable G(x) values. Utilizing e-beam and EUV interference lithographies, the photospeed of poly(methyl α-trifluoromethacrylate) (PMTFMA) was found to be 2.8× and 4.0× faster, respectively, than PMMA.

Select this Article		Chalcogenide glass e-beam and photoresists for ultrathin grayscale patterning Andriy Kovalskiy, Jiri Cech, Miroslav Vlcek, Christopher M. Waits, Madan Dubey, William R. Heffner, and Himanshu Jain J. Micro/Nanolith. MEMS MOEMS 8, 043012 (Dec 22, 2009); http://dx.doi.org/10.1117/1.3273966 \| Cited 3 times Online Publication Date: Dec 22, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are demonstrated. It is shown that the ChG films can be used to make ultrathin ( ∼ 600 nm), high-resolution grayscale patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent ChG patterns can be useful as such on the surface or can be used to transfer the etched pattern into silicon or other substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater etch selectivity than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale lithography for microelectromechanical systems (MEMS) applications is also shown. A substrate to ChG/silver thickness etching ratio of ∼ 10 is obtained for the transfer of patterns into silicon using reactive ion etching (RIE), more than a fivefold increase compared to traditional polymer photoresist.

Select this Article		Predicting distortions and overlay errors due to wafer deformation during chucking on lithography scanners Kevin T. Turner, Sathish Veeraraghavan, and Jaydeep K. Sinha J. Micro/Nanolith. MEMS MOEMS 8, 043015 (Nov 06, 2009); http://dx.doi.org/10.1117/1.3247857 \| Cited 2 times Online Publication Date: Nov 06, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Chucking of substrates with wafer shape and thickness variations results in elastic deformation that can cause significant in-plane distortions that lead to overlay errors in lithographic patterning. As feature sizes shrink, overlay errors due to the combination of wafer geometry and chucking become a larger fraction of the error budget and must be controlled. We use a finite element model and a lithographic correction postprocessing scheme to predict in-plane distortions that result from chucking wafers with shape variations. We then use the predictions of in-plane distortions at two different patterning steps to calculate the component of overlay error that arises from localized shape variations. Using the model, in-plane distortion and overlay errors due to chucking are examined for multiple wafers with different geometries. The results show that long spatial wavelength shape variations cause significant distortion, but can largely be mitigated through the use of simple first-order corrections that are applied in typical lithography scanners. In contrast, high-frequency spatial variations cause distortions that cannot be corrected and hence lead to meaningful overlay errors. The results provide fundamental insight into chucking-induced overlay errors and can serve as a basis for the development of higher order scanner correction schemes that explicitly account for the wafer geometry through high-density wafer shape measurements.

Select this Article		Thick-membrane-operated radio frequency switches with wafer-level package using gold compressive bonding Jongseok Kim, Sangwook Kwon, Youngtack Hong, Insang Song, Heemoon Jeong, Hyung Choi, and Byeongkwon Ju J. Micro/Nanolith. MEMS MOEMS 8, 043020 (Oct 02, 2009); http://dx.doi.org/10.1117/1.3238545 Online Publication Date: Oct 02, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An electrostatically actuated radio frequency (rf) switch is fabricated using a thick silicon membrane, and the device is packaged using a high resistivity silicon cap wafer with a gold (Au) thermocompressive bonding method. To achieve an rf switch that can operate at low voltage, a thick membrane with a pivot under the membrane is used. This design makes it possible to maintain the very small gap between the electrodes and the membrane without bending. A cavity with a pivot-patterned silicon wafer and a coplanar waveguide (CPW) signal-line-formed glass wafer is bonded using an anodic bonding method. After a mechanical polishing process, a deep reactive ion etcher is used to fabricate the membrane structure with a spring and a spring bar. To package the fabricated rf switch, an Au thermocompressive bonding process is used. A 1-μm-thick sputtered Au layer is used as intermediate bonding material. The bonding temperature and pressure are 350 °C and 63 MPa, respectively, and the time duration of the bonding is set to 30 min. The electrodes of the switch and the electrical contact pads on the cap wafers are interconnected via a hole and a sputtered Au metal layer. The total size of the complete packaged rf switch is 2.2 × 1.85 mm, and its rf characteristics have been measured using a Hewlett−Packard (HP) 8510C network analyzer. The measured driving voltage is approximately 16 V, the isolation is approximately −38.4 dB, and the insertion loss is approximately −0.43 dB at 2 GHz.

Select this Article		In situ measurement of gas diffusion properties of polymeric seals used in MEMS packages by optical gas leak testing Changsoo Jang, Arindam Goswami, Bongtae Han, and Suk-Jin Ham J. Micro/Nanolith. MEMS MOEMS 8, 043025 (Oct 02, 2009); http://dx.doi.org/10.1117/1.3227904 Online Publication Date: Oct 02, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A novel inverse approach is proposed for in situ measurement of gas diffusion properties of polymeric seals used in microelectromechanical systems (MEMS) packages. The cavity pressure evolution of a polymer-sealed MEMS package subjected to a constant bombing pressure is documented as a function of time using classical interferometry, and the diffusion properties of the polymeric seal are subsequently determined from the measured pressure history. A comprehensive numerical procedure for the inverse analysis is established considering three diffusion regimes that characterize the leak behavior through a polymeric seal. The method is implemented to determine the helium diffusivity and solubility of a polymeric seal.

Select this Article		Effects of layers and vias on continuous-wave laser heating and damage of surface-micromachined structures Justin R. Serrano and Leslie M. Phinney J. Micro/Nanolith. MEMS MOEMS 8, 043030 (Oct 22, 2009); http://dx.doi.org/10.1117/1.3249657 Online Publication Date: Oct 22, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The response of microsystem components to laser irradiation is relevant to processes and applications such as laser processing, optical diagnostics, and optical microelectromechanical systems (MEMS) device design and performance. The dimensions of MEMS, which are on the order of several micrometers, are on the same order as infrared laser wavelengths, which results in interference phenomena when the parts are partially transparent. Four polycrystalline silicon structures were designed and irradiated with 532 and 808 nm continuous wave laser light to determine the effects of layers, air gaps, and the presence of a substrate via on the threshold laser power for damage. The presence of a substrate via resulted in lower damage thresholds, and a single-layer structure had the highest damage threshold for structures irradiated with infrared light. Structures irradiated with visible wavelength light exhibited less sensitivity to the underlying via. Optical interference calculations are carried out to evaluate the absorptance of these structures as a feasible explanation for the observed results.

Select this Article		Novel approach for microassembly of three-dimensional rotary MOEMS mirrors Lidai Wang, James K. Mills, and William L. Cleghorn J. Micro/Nanolith. MEMS MOEMS 8, 043035 (Oct 29, 2009); http://dx.doi.org/10.1117/1.3256006 Online Publication Date: Oct 29, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present a novel approach to construct 3-D 1×N rotary micromirrors, which are fundamental components in optical switching systems. A rotary micromirror consists of two microparts: a rotary micromotor and a micromirror. Both of the two microparts are fabricated with PolyMUMPs,^™ (MEMSCAP, Research Triangle Park, North Carolina), a surface micromachining process. A sequential robotic microassembly process is developed to join the two microparts together to construct the 3-D device. To achieve high positioning accuracy and strong mechanical connection, the micromirror is joined to the micromotor using an adhesive mechanical fastener. The mechanical microjoint has self-alignment capability and provides a temporary joint between the two microparts. The adhesive bonding creates a strong permanent connection between the two microparts. The adhesive mechanical fastener does not require extra supporting plates to fix the micromirror, which simplifies the microassembly process and makes it possible to automatically assemble the rotary micromirror. A hybrid manipulation strategy, which includes pick-and-place and pushing-based micromanipulations, is utilized to assemble the micromirror onto the micromotor. The pick-and-place manipulation has the ability to globally position the micromirror with multiple degrees of freedom. The pushing-based manipulation can achieve high positioning accuracy. This novel approach provides great flexibility and high accuracy for assembling the complex micromirror.

Select this Article		Feedback-stabilized deformable membrane mirrors for focus control Sarah J. Lukes, Phillip A. Himmer, Eric J. Moog, Steven R. Shaw, and David L. Dickensheets J. Micro/Nanolith. MEMS MOEMS 8, 043040 (Oct 27, 2009); http://dx.doi.org/10.1117/1.3249659 \| Cited 2 times Online Publication Date: Oct 27, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This paper describes a method to extend the range of motion of a deformable, continuous membrane mirror beyond the limit of open-loop electrostatic instability through feedback control. The feedback scheme employs capacitive sensing directly at the mirror actuation electrodes and is based on frequency modulation of a coupled ring oscillator using a differential measurement technique. Analysis of the system shows that the range of stable deflection depends on the relative dynamics of the device and the feedback control circuitry. Experimental results demonstrate stable closed-loop deflection of our silicon nitride membrane test device to 69% of the air gap and confirm the dependence of the maximum stable displacement on overall loop dynamics.

Select this Article		Gap regulation for suspended rotating disk used for microgyroscopes Nan-Chyuan Tsai, Bing-Hong Liou, and Chih-Che Lin J. Micro/Nanolith. MEMS MOEMS 8, 043045 (Oct 29, 2009); http://dx.doi.org/10.1117/1.3256005 Online Publication Date: Oct 29, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An innovative magnetic module that is concurrently capable of performing as an actuator and a sensor is proposed and analyzed. The magnetic module is basically similar to a microscale linear variable differential transformer (LVDT), which is employed to actively adjust the height of a rotating seismic disk used in a gyroscope so that the pitch rate induced by Coriolis effect, due to exerted angular excitation, can be accurately measured. On one hand, the micromagnetic module acts like an actuator for height regulation on the seismic proof mass by applying appropriate electric current to the primary winding of the LVDT unit. On the other hand, the secondary winding pair of the LVDT acts like a sensor that can detect the gap change between the seismic rotating disk and the micromagnetic LVDT module, and the rotation speed (i.e., frequency) by the induced current.

Select this Article		Analysis and fabrication of reciprocal motors applied for microgyroscopes Nan-Chyuan Tsai, Jiun-Sheng Liou, Chih-Che Lin, and Tuan Li J. Micro/Nanolith. MEMS MOEMS 8, 043046 (Dec 15, 2009); http://dx.doi.org/10.1117/1.3274611 Online Publication Date: Dec 15, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract For microgyroscopes, the angular rate detection components have to oscillate forward and backward, alternatively. An innovative design of a microelectromagnetic drive module is proposed to make a Π-type thin disk reciprocally and efficiently rotate within a certain of angular interval. Twelve electromagnetic (EM) poles, with iron cores at the center and wound by electroplated copper wires, enclosing the thin disk are designed to provide the magnetic drive power. An isotropic etching technique is employed to fabricate the high-aspect-ratio trench, housing of the follow-up electroplated copper, so that the contact angle of wire against the trench can be increased and the potential defect of cavities and pores within the wire can be prevented. On the other hand, a Π-type thin disk, with a central bearing and a set of auxiliary bushings, is designed to conduct the pitch motion as an angular excitation, in addition to spinning, is exerted on the gyroscope. That is, the angular motion of the disk is two-dimensional: spinning, driven by the EM poles, and tilting, to respond to the exerted angular rate due to Coriolis effect. The efficacy of the micromagnetic drive module is verified by theoretical analysis and computer simulations by the commercial software, Ansoft Maxewll. In comparison to the conventional planar windings in microscale systems, the magnetic drive force is increased by 150%.

Select this Article		Formation of uniform nanoscale oxide layers assembled by overlapping oxide lines using atomic force microscopy Ampere A. Tseng, Taewoo Lee, Andrea Notargiacomo, and T. P. Chen J. Micro/Nanolith. MEMS MOEMS 8, 043050 (Dec 11, 2009); http://dx.doi.org/10.1117/1.3268427 \| Cited 2 times Online Publication Date: Dec 11, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Atomic force microscopy (AFM) has been widely used for creating nanoscale oxide lines on various material surfaces. The assembling technique used for overlapping an array of these oxide lines into a uniform oxide layer is analytically investigated and experimentally verified. The experimental data of the oxide lines induced at different scanning speeds are analytically correlated to provide the basic formula for the assembling technique. The superposition principle is then applied for simulating the assembling process to extract the criteria for assembling a uniform layer. Experiments have been conducted to verify the reliability of the uniformity criteria analytically obtained and the feasibility of the assembling technique developed. Indeed, a uniform oxide layer can be precisely assembled by following the uniformity criteria developed.

Select this Article		Fabrication of giant magneto resistance sensing devices with vertically grown Co/Cu nanowires on a substrate Thong C. Le, Hargsoon Yoon, Linfeng Chen, Roy C. McCann, and Vijay K. Varadan J. Micro/Nanolith. MEMS MOEMS 8, 043055 (Dec 21, 2009); http://dx.doi.org/10.1117/1.3273963 Online Publication Date: Dec 21, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We describe the fabrication and analysis of a giant magneto resistance (GMR) sensing device with multilayered magnetic nanowires containing alternating ferromagnetic and nonmagnetic layers on a silicon substrate. Multilayered nanowires with Co and Cu layers were vertically grown using pulsed electrochemical deposition to control the periodic structure of nanolayers in a nanopore template. Lithography-assisted template bonding (LATB) was applied to attach a polymer nanopore membrane and grow nanowires on silicon and polyimide substrates. For magnetic field sensing, the multilayered nanowires were electrically connected to top and bottom electrodes by overgrowing nanowires, and low contact resistance values of GMR sensing devices were achieved. The GMR effect was measured with magnetic field changes perpendicular and parallel to the axis of the nanowires. This simple fabrication process is highly favorable for the development of nanoscale electronics with magnetic nanowires at low cost and would offer large design flexibility.

Select this Article		Fabrication of silicon microring resonator with smooth sidewalls Yao Chen, Junbo Feng, Zhiping Zhou, Jun Yu, Christopher J. Summers, and David S. Citrin J. Micro/Nanolith. MEMS MOEMS 8, 043060 (Nov 13, 2009); http://dx.doi.org/10.1117/1.3258487 \| Cited 2 times Online Publication Date: Nov 13, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Fabrication of silicon microring resonators was optimized by using electron-beam lithography (EBL) and inductively coupled plasma (ICP) etching with different mask materials. Sidewall roughness of less than 10 nm was revealed by high-resolution scanning electron microscopy (SEM) without any post-etch process. The fabrication processes are described in detail, and comparisons are made in consideration of process complexity, process latitude, and sidewall roughness.

Select this Article		Development of polymer electrostatic comb-drive actuator using hot embossing and ultraprecision cutting technology Satoshi Amaya, Dzung Viet Dao, and Susumu Sugiyama J. Micro/Nanolith. MEMS MOEMS 8, 043065 (Dec 04, 2009); http://dx.doi.org/10.1117/1.3268366 \| Cited 2 times Online Publication Date: Dec 04, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We report the fabrication and evaluation of a PMMA electrostatic comb-drive microactuator using hot embossing and ultra-precision cutting technology. First, a two-step silicon mold is fabricated by bulk micromachining technology. Next, comb-drive microactuator structures are formed on a PMMA plate by hot embossing. Both finger width and gap between fingers are 5 μm, and finger thickness is larger than 70 μm. Then, the PMMA layer that remained after hot embossing is removed by ultra-precision cutting to release the movable parts. Last, the device is coated with a gold layer for the electrode. The PMMA comb-drive microactuator has been tested successfully.

Select this Article		Efficient simulation and optimization of wafer topographies in double patterning Feng Shao, Peter Evanschitzky, Tim Fühner, and Andreas Erdmann J. Micro/Nanolith. MEMS MOEMS 8, 043070 (Dec 31, 2009); http://dx.doi.org/10.1117/1.3275723 \| Cited 1 time Online Publication Date: Dec 31, 2009 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract As the technology marches toward the 32-nm node and beyond in semiconductor manufacturing, double-patterning and double-exposure techniques are currently regarded as the potential candidates to produce lines and spaces and contact holes, respectively. We employ the Waveguide method, a rigorous electromagnetic field (EMF) solver, to investigate the impact of wafer topographies on two specific double-patterning techniques. At first, the topography effects induced by the first patterning on the second lithography process in a lithography-etch-lithography-etch process are demonstrated. A new methodology of the bottom antireflective coating optimization is proposed to reduce the impact of wafer topography on resist profiles. Additionally, an optical proximity correction (OPC) of the second lithography mask is demonstrated to compensate the wafer-topography–induced asymmetric deformations of line ends. Rigorous EMF simulations of lithographic exposures are also applied to investigate wafer-topography effects in a freezing process. The difference between the optical properties of the frozen (first) resist and the second resist potentially causes linewidth variations. Quantitative criteria for tolerable refractive index and extinction differences between the two resist materials are given. The described studies can be used for the optimizations of topographic waferstacks, the OPC of the second litho mask, and for the development of resist materials with appropriate optical properties.

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