Double patterning is one of the main enabling technologies for expanding lithography beyond 45nm technology node.
Geometric pitch split and litho friendly design is the core of double patterning. There has been lot of development
recently in area of DP to minimize split errors and hot spots. In this paper we demonstrate one such application of
predictive modeling to detect hot spots. The matrix for pitch splitting is developed at higher resolution wavelengths in
design stage and the decomposed results are evaluated with different source types. This type of predictive model
confronts hot spot information and un-resolvable pitches in design stage and assists in developing restricted design rules
for litho friendly design.
As semiconductor technologies move toward 70nm
generation and below, contact-hole is one of the most
challenging features to print on wafer. There are two
principle difficulties in defining small contact-hole
patterns on wafer. One is insufficient process margin
besides poor resolution compared with line-space pattern.
The other is that contact-hole should be made through
pitches and random contact-hole pattern should be
fabricated from time to time.
PIXBAR technology is the candidate which can help
improve the process margin for random contact-holes.
The PIXBAR technology lithography attempts to
synthesize the input mask which leads to the desired
output wafer pattern by inverting the forward model from
mask to wafer. This paper will use the pixel-based mask
representation, a continuous function formulation, and
gradient-based interactive optimization techniques to
solve the problem. The result of PIXBAR method helps
gain improvement in process window with a short
learning cycle in contact-hole pattern assist-feature
testing.
Scatter Bar (SBAR) insertion is a computationally expensive operation. SBAR are usually generated rule-based. SBAR rule tables dictate the insertion of SBAR with different SBAR width dependent on the width of the printable main features and the spacing between the main features and SBAR. Optimization of the SBAR rules drives manufactures to ever more complex SBAR tables which increase the runtime. In advanced process nodes, SBAR printing issues, missing SBAR due to clean-up problems and joining SBAR of different width together remain challenging. On the other hand, pixelized inversion methods may yield optimized SBAR solutions, especially in terms of SBAR placement for contact layers, but comes at the expense of significant computational effort and increased mask writing and inspection time. Since OPC changes the spacing between SBAR and main features, an accurate and optimized SBAR solution requires OPC and SBAR optimization to run interactively.
This work focuses on both line/space and contact layers To ensure fast SBAR optimization, SBAR placement and SBAR width optimization are separated. SBAR of uniform width are placed fast driven by a simple rule-based table comprising only a single SBAR width. This intermediate SBAR layer is subject into a model-based approach, which fragments the SBAR layer based on proximity with respect to the main features or other SBAR, and assigns measurement sites to each SBAR fragment. A model is used to move each SBAR fragment inward or outward so that the image cut line shows a maximum SBAR intensity closer to a predefined SBAR printing threshold. While the main features are unchanged, several iterations are applied to converge the SBAR fragments. Keeping the SBAR fragments fixed, OPC is applied to the main features. Repeating these steps allows optimization of the SBAR width and the OPC simultaneously. Site based as well as contours based verification methods are applied to ensure that the SBAR printing margin has been significantly improved. The improved SBAR printing margin allows manufactures to apply more aggressive SBAR placement rules, which, in addition to the optimized SBAR width, helps to enlarge the depth of focus, therefore, widen the common process window of the lithography process.
Electrical failure due to incomplete contacts or vias has arisen as one of the primary modes of yield loss for 130 nm and below designs in manufacturing. Such failures are generally understood to arise from both random and systematic sources. The addition of redundant vias, where possible, has long been an accepted DFM practice for mitigating the impact of random defects. Incomplete vias are often characterized by having a diameter near the target dimension but a depth of less than 100% of target. As such, it is a difficult problem to diagnose and debug in-line, since bright and dark field optical inspection systems cannot typically distinguish between a closed, partially open and fully open contact. Advanced metrology systems have emerged in recent years to meet this challenge, but no perfect manufacturing solution has yet been identified for full field verification of all contacts. Voltage Contrast (VC) SEM metrology biases the wafer to directly measure electrical conductivity after fill / polish, and can therefore easily discern a lack of electrical connection to the underlying conductor caused by incomplete photo, etch, or fill processing. While an entire wafer can in principal be VC scanned, throughput limitations dictate very sparse sampling in manufacturing. SEM profile grading (PG) leverages the rich content of the secondary electron waveform to decipher information about the bottom of the contact. Several authors have demonstrated an excellent response of the Profile Grade to intentional defocus vectors. However, the SEM can only target discreet or single digit groupings of contacts, and therefore requires intelligent guidance to identify those contacts which are most prone to failure, enabling protection of the fab WIP. An a-priori knowledge of which specific contacts in a layout are most likely to fail would prove very useful for proactive inspection in manufacturing. Model based pre-manufacturing verification allows for such knowledge to be communicated to manufacturing. This paper will focus on 130 nm node contact patterning, and will correlate SEM Profile Grade output to the extensive suite of model-based image tags from the CalibreTM opc-verification engine. With an understanding of which image parameters are most highly correlated to the occurrence of incomplete contact formation for a given process, the process model can be used to automatically direct inspection metrology to those layout instances that pose the highest risk of patterning failure through the lithographic process window. Such an approach maximizes the value content of in-line metrology.
Device performance is highly associated with the line end performance of critical layers. Poly line end shortening (LES) or bridging can result in leakage or short circuit. Model-based optical proximity correction (OPC) prioritized to fit one-dimensional pitch structures can also improve two-dimensional line end performance. However, it may still fail without meeting the line end bridging margin or minimum line end length requirements. A leakage problem has been observed, when poly gate line end shortening occurs, following the use of an OPC recipe chosen to be a compromise for the line end bridging problem. In this paper, several approaches related to OPC are studied on poly layer, in terms of line end bridging margin and line end shortening, to optimize line end performance. The OPC minimum external constraint is optimized to meet both line end bridging and shortening requirements. Serif type line end provides the OPC model with more flexibility to pull back the center segment between line end serifs and improves the bridging margin by 2%, with negligible sacrifice on line end length under overexposure conditions. No effect is seen on the bridging margin with different segment lengths of center pull back at the serif line end. Bridging margin can be improved dramatically (6%) by adding SRAF, due to the increase of aerial image intensity in the line end space. Finally, the OPC model fitting for line end shortening is briefly described and a post-correction rule-based OPC is introduced to improve the line end shortening. Handcrafted OPC is also used for this case study for few structures that need extra correction to achieve enough line end length.
The continuing shrinkage of device size will result in stringent demands on high precision CD control. For example, at 0.13um technology node a typical poly gate size variation should be controlled within +/- 8nm or even smaller. This tight CD budget includes all possible variations which can be from different modules of resist coating track, optical and mechanical parts of exposure tool, non-uniformity of wafer substrate, CD metrology, mask making and so on. Particularly, the residual swing effect after applying an inorganic anti-reflection layer (SiON) still can claim a significant CD budget if not properly optimized. Therefore, how to minimize the residual swing effect still plays important role in CD control. Simulation of reflectivity is considered analytically rigorous and is therefore frequently employed to aid in process development. However, since in manufacturing environments people usually pay more attention to the repeatability of optical metrology tools rather than their accuracies, it is not surprising if some significant discrepancies exist between theoretical and experimental results. Instead of discussing the detail error sources and the tool calibrations, a quick and convenient experimental methodology is introduced to account for such differences and to optimize the film stack composition effectively. In this paper, with the CD variations on metal and poly substrates as examples, an effective combination between the calculations and the experiments is presented in order to minimize the CD swing. We also demonstrate that with the "single wafer swing curve" technique, the residual swing effect can be easily detected and minimized. This methodology provides a possibility to determine the best anti-reflection layer not only from theoretical but also from experimental point of view in manufacturing environments. Since the residual swing effect is a common issue, the results of this paper can be widely used in either manufacturing fabs or experimental labs.
As transistor engineering continues to well below 100 nm length devices, ion implantation process tolerances are making these formerly "non-critical" lithography levels more and more difficult. In order to minimize the channeling effect and to obtain a controllable profile of dopant, an angled implantation is often required. However, a shadow area of resist pattern is always accompanied with an angled implantation. This shadowing effect consumes silicon real estate, and reduces the line edge placement (LEP) tolerances. Therefore, methodologies to reduce the shadowing effect in angled implantation become a critical consideration not only for device engineering but also for photolithography. Based on the model analysis, simulation and experiments, this paper presents an effective novel process utilizing dual-wavelength exposure (DWE) to reduce the shadowing effect. The DWE process is realized by two consecutive exposures for an I-line resist with a DUV stepper/scanner and an I-line stepper. The process leverages the high absorption coefficient of novalak-DNQ resist at 248 nm, and results in a tunable post-develop resist thickness to minimize the shadowing effect. It is effective in satisfying the junction requirements and also is helpful in minimizing the number of photoresists in a manufacturing fab. A repeatable resist profile and an excellent CD uniformity across wafer also indicated that the DWE is a potentially manufacturable process.
Resist critical dimensions (CD) and thickness are usually obtained by in-line CD SEM or in-line optical metrology measurements but varification or calibration of these is typically achived by cross sectional SEM. As we push CDs to 100nm and beyound, descrepencies between these two sources data can constitute a large percentage of the target dimension. Particularly for 193nm resists, the CD shrinkage under SEM has been well characterized, but the vertical and horizontal compaction behavior in across sectional SEM has not been explored. In this paper, the discussion is divided into two parts. One is for bulk resist and another is for patterned resist. For bulk case, the the only variable is vertical thickness. The experiments for I-line, 248nm and 193nm resist indicated that the resist thickness from the cross sectional image is strongly dependent on the resist polymer structure, the SEM conditions and the interrogration time under SEM E-beam. Therefore, the thickness comparison between optical and electronic is not always meaningful because the cross sectional thickness often shows a low thickness than the optically determined value. We have determined the optimum SEM condition to minimize vertical compaction. There are two variables for patterned resist, vertical thickness and lateral CD size. Our experiments for I-line and 248nm resists exhibited that the patterned resist thickness can be 30% lower than the optical thickness. However, the lateral CD sizes showed less variation relative to the different SEM conditions. The unique behaviors of 193nm patterned resist are also displayed and discussed in this paper. Based on all experimental data, different SEM conditions are recommended based on different purposes to generate accurate cross sectional resist images.
Photolithography on reflective surfaces with topography can cause exposure in unwanted areas, resulting in the phenomenon of reflective notching. Solutions to this problem are known within the industry, including the use of bottom anti-reflective coatings (ARCs) and dyed photoresist. In certain situations, such as on implant layers, the use of a BARC may be impractical. One potential solution to this problem lies in optimization of the illumination settings. It is known that changes in the illumination settings NA and sigma have an impact on the swing curve amplitude. It will be shown that for certain situations, reflective notching can be virtually eliminated through proper selection of the illumination settings.
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