Systematic defects have drawn a lot of focus from the semiconductor industry, especially in the technology development and early technology ramp. However, random defects are still dominant when the technology is mature and in highvolume manufacturing. Historically, foundries have run critical area analysis on incoming designs in order to identify the yield-limiting failure modes and estimate the yield loss. However, with growing design complexity in advanced technology nodes, the calculation runtime of critical area has increased from hours to days and even week(s). Also FINFET brings their own challenges and new failure modes such as transistor-related defectivity and inter-layer interactions. Meanwhile, it has become more and more challenging to obtain accurate defect density by failure mode. In this paper, GlobalFoundries and Cadence describe the motivations that drove their partnership to develop a new generation of critical area analysis with adaptive sampling to reduce runtime while maintaining accuracy, especially while taking into account connectivity and transistor defectivity. After reviewing the principle and challenges of critical area calculation and yield estimation, two new methodologies of yield modeling using critical area analysis are given to address these challenges. The first methodology avoids the costly and complicated process of defect density calibration. The second methodology fulfills the wafer-based yield projection with critical area normalization and machine learning.
Process and reliability risks have become critically important during mass production at advanced technology nodes even with Extreme Ultraviolet Lithography (EUV) illumination. In this work, we propose a design-for-manufacturability solution using a set of new rules to detect high risk design layout patterns. The proposed methods improve design margins while avoiding area overhead and complex design restrictions. In addition, the proposed method introduces an in-design pattern replacement with automatically generated fixing hints to improve all matched locations with identified patterns.
Continuous scaling of CMOS process technology to 7nm (and below) has introduced new constraints and challenges in determining Design-for-Yield (DFY) solutions. In this work, traditional solutions such as improvements in redundancy and in compensating target designs for low process window margins are extended to meet the additional constraints of complex 7nm design rules. Experiments conducted on 7nm industrial designs demonstrate that the proposed solution achieves 9.1%-41% redundant-via-rate improvements while ensuring all 7nm design rule constraints are met.
Design-process weakpoints also known as hotspots cause systematic yield loss in semiconductor manufacturing. One of the main goals of DFM is to detect such hotspots. For the application of AI in hotspot detection, a variety of machine learning-based techniques have been proposed as an alternative to time expensive process simulations. Related research works range from finding efficient layout representations and features and developing reliable machine learning models. Main stream layout representations include density-based feature, pixel-based feature, frequency domain feature, concentric circle sampling (CCS) and squish pattern. However most of them are either suffering from information loss (e.g. density-based feature, and CCS), or not storage efficient (e.g. images). To address these problems, we propose a convolutional neural network called Squish-Net where the input pattern representation is in an adaptive squish form. Here, the squish pattern representation is modified to handle variations in the topological complexity across a pattern catalog, which still allows no information loss and high data compression. We show that different labeling strategies and pattern radius contribute to the trade-offs between prediction accuracy and model precision. Two imbalance-aware training strategies are also discussed with supporting experiments.
Layout-pattern-based approaches for physical design analysis and verification have become mainstream in recent years and are enabling many new applications. Prior work introduced the ability to collect all patterns from multiple layouts into a catalog as well as to use machine learning techniques to score and filter patterns to identify which ones are critical. In this paper, data mined from a library of scored patterns from established designs is applied to the analysis of diagnosis results from a new design to improve defect root cause analysis (RCA).
The flow for this approach is as follows: patterns interacting with nets reported in diagnosis callouts are selected as patterns of interest (POIs) from the catalog of all patterns. Next, features of interest (FOIs) are extracted from all POIs to build a dataframe. Finally, volume diagnosis results identifying nets with likely open or short defects are added to the dataframe. RCA is performed using the dataframe to identify likely root cause(s) for failures and suggest refined failure locations for targeted inspection, physical failure analysis, or other electrical failure analysis.
The approach described above is applied to products in high-volume manufacturing using a leading-edge technology node. Silicon validation results will be included for example applications.
Building on previous work for cataloging unique topological patterns in an integrated circuit physical design, a new process is defined in which a risk scoring methodology is used to rank patterns based on manufacturing risk. Patterns with high risk are then mapped to functionally equivalent patterns with lower risk. The higher risk patterns are then replaced in the design with their lower risk equivalents. The pattern selection and replacement is fully automated and suitable for use for full-chip designs. Results from 14nm product designs show that the approach can identify and replace risk patterns with quantifiable positive impact on the risk score distribution after replacement.
Topological pattern-based methods for analyzing IC physical design complexity and scoring resulting patterns to
identify risky patterns have emerged as powerful tools for identifying important trends and comparing different designs.
In this paper, previous work is extended to include analysis of layouts designed for the 7nm technology generation. A
comparison of pattern complexity trends with respect to previous generations is made. In addition to identifying
topological patterns that are unique to a particular design, novel techniques are proposed for scoring those patterns based
on potential yield risk factors to find patterns that pose the highest risk.
At advanced technology nodes (sub-22 nm), design rules become very complicated as interactions between multiple layers become more complex, while the number of design elements within the optical radius increases. As a result, one may possibly encounter novel yield limiters in the 2D/3D design space with every new product taping out to the fab. Key to fast yield ramp is identifying novel constructs that may become yield detractors, and to address the challenge in the DFM space before actual Silicon is run. A comprehensive methodology to find such geometric constructs is proposed.
KEYWORDS: Metals, Databases, Digital electronics, Manufacturing, Raster graphics, Logic, System on a chip, Optical lithography, Optical proximity correction, Product engineering
In order to maximize yield, IC design companies spend a lot of effort to analyze what types of design styles are needed and used in their layouts (standard cells, macros, routing layers, and so forth). This paper introduces a novel methodology for full chip high performance topological pattern analysis and the applications of this methodology towards analyzing design styles in order to quantify and measure design changes and the degree of layout regularization. This new approach allows engineers to perform a full profiling across all patterns that exist in design and without needing to explicitly specify what patterns to analyze.
Design rule checks (DRC) are the industry workhorse for constraining design to ensure both physical and electrical manufacturability. Where DRCs fail to fully capture the concept of manufacturability, pattern-based approaches, such as DRC Plus, fill the gap using a library of patterns to capture and identify problematic 2D configurations. Today, both a DRC deck and a pattern matching deck may be found in advanced node process development kits. Major electronic design automation (EDA) vendors offer both DRC and pattern matching solutions for physical verification; in fact, both are frequently integrated into the same physical verification tool.
In physical verification, DRCs represent dimensional constraints relating directly to process limitations. On the other hand, patterns represent the 2D placement of surrounding geometries that can introduce systematic process effects. It is possible to combine both DRCs and patterns in a single topological pattern representation. A topological pattern has two separate components: a bitmap representing the placement and alignment of polygon edges, and a vector of dimensional constraints. The topological pattern is unique and unambiguous; there is no code to write, and no two different ways to represent the same physical structure. Furthermore, markers aligned to the pattern can be generated to designate specific layout optimizations for improving manufacturability.
In this paper, we describe how to do systematic physical verification with just topological patterns. Common mappings between traditional design rules and topological pattern rules are presented. We describe techniques that can be used during the development of a topological rule deck such as: taking constraints defined on one rule, and systematically projecting it onto other related rules; systematically separating a single rule into two or more rules, when the single rule is not sufficient to capture manufacturability constraints; creating test layout which represents the corners of what is allowed, or not allowed by a rule; improving manufacturability by systematically changing certain patterns; and quantifying how a design uses design rules. Performance of topological pattern search is demonstrated to be production full-chip capable.
Pattern-based approaches to physical verification, such as DRC Plus, which use a library of patterns to identify problematic 2D configurations, have been proven to be effective in capturing the concept of manufacturability where traditional DRC fails. As the industry moves to advanced technology nodes, the manufacturing process window tightens and the number of patterns continues to rapidly increase. This increase in patterns brings about challenges in identifying, organizing, and carrying forward the learning of each pattern from test chip designs to first product and then to multiple product variants. This learning includes results from printability simulation, defect scans and physical failure analysis, which are important for accelerating yield ramp.
Using pattern classification technology and a relational database, GLOBALFOUNDRIES has constructed a pattern database (PDB) of more than one million potential yield detractor patterns. In PDB, 2D geometries are clustered based on similarity criteria, such as radius and edge tolerance. Each cluster is assigned a representative pattern and a unique identifier (ID). This ID is then used as a persistent reference for linking together information such as the failure mechanism of the patterns, the process condition where the pattern is likely to fail and the number of occurrences of the pattern in a design. Patterns and their associated information are used to populate DRC Plus pattern matching libraries for design-for-manufacturing (DFM) insertion into the design flow for auto-fixing and physical verification. Patterns are used in a production-ready yield learning methodology to identify and score critical hotspot patterns. Patterns are also used to select sites for process monitoring in the fab.
In this paper, we describe the design of PDB, the methodology for identifying and analyzing patterns across multiple design and technology cycles, and the use of PDB to accelerate manufacturing process learning. One such analysis tracks the life cycle of a pattern from the first time it appears as a potential yield detractor until it is either fixed in the manufacturing process or stops appearing in design due to DFM techniques such as DRC Plus. Another such analysis systematically aggregates the results of a pattern to highlight potential yield detractors for further manufacturing process improvement.
Pattern matching tools have become increasingly common in physical design flows for verification and layout analysis.
Recently developed topological-based pattern matching engines offer several advantages over conventional three-value logic implementations. In this paper the use of such topological engines is explored for measuring physical design regularity, driving improvements in overall regularity, and for implementing targeted enhancements for suboptimal layout configurations.
As technology processes continue to shrink, standard design rule checking (DRC) has become insufficient to guarantee
design manufacturability. DRCPlus is a powerful technique for capturing yield detractors related to complex 2D
situations1,2. DRCPlus is a pattern-based 2D design rule check beyond traditional width and space DRC that can identify
problematic 2D configurations which are difficult to manufacture. This paper describes a new approach for applying
DRCPlus in a router, enabling an automated approach to detecting and fixing known lithography hotspots using an
integrated fast 2D pattern matching engine. A simple pass/no-pass criterion associated with each pattern offers designers
guidance on how to fix these problematic patterns. Since it does not rely on compute intensive simulations, DRCPlus can
be applied on fairly large design blocks and enforced in conjunction with standard DRC in the early stages of the design
flow. By embedding this capability into the router, 2D yield detractors can be identified and fixed by designers in a
push-button manner without losing design connectivity. More robust designs can be achieved and the impact on
parasitics can be easily assessed.
This paper will describe a flow using a fast 2D pattern matching engine integrated into the router in order to enforce
DRCPlus rules. An integrated approach allows for rapid identification of hotspot patterns and, more importantly, allows
for rapid fixing and verification of these hotspots by a tool that understands design intent and constraints. The overall
flow is illustrated in Figure 1. An inexact search pattern is passed to the integrated pattern matcher. The match locations
are filtered by the router through application of a DRC constraint (typically a recommended rule). Matches that fail this
constraint are automatically fixed by the router, with the modified regions incrementally re-checked to ensure no additional DRCPlus violations are introduced.
Unwanted scattered light affects image-quality, OPC behavior and becomes increasingly problematic with decreasing wavelength. A software system has been written that incorporates a pattern-matching algorithm to locate regions in the mask geometry that closely resemble a problematic shape. Our goal is to improve manufacturing of a full-chip layout by identifying locations worst impacted by flare. The Pattern Matcher match factor shows good agreement in predicting flare sensitivity for several flare measurement layouts. The software is able to generate and process patterns capturing short-range, mid-range and long-range flare effects.
Layout test patterns are being pursued that are more sensitive than circuit patterns in detecting and quantifying residual processing effects. These patterns permit the rapid searching of layouts for the locations of worst-case process impacts, and may facilitate layout compensation at OPC speeds. These patterns have been taped-out along with snippets of circuits in preparation for experimental verification of the ability to link residual process effects to electronic design. The collection includes pattern-and-probe-based targets for measuring aberrations, illumination non-uniformity and etch-depth errors in phase-shifting masks, plasma etching with loading effects related to area and perimeter factors, and patterns for CMP orientation and feature proximity. The goal is to use these test patterns to develop maximum lateral impact functions for each individual process effect for use in fast-CAD techniques capable of inspecting large layouts.
A web-based tool is presented that analyzes the worst-case effect of lens aberrations on projection printed layouts. These effects are important to the designer since they can be half as large as those of OPC. They can easily be detected by scanning through the layout and matching the inverse Fourier transform of the aberration function to the local layout geometry at each location of interest. The software system for detecting and quantifying these effects is based on a client/server model, where the user interface runs on the client side as a Java applet and the server has access to the binaries and performs all of the heavy numerical processing. The online system provides direct access to this lithography tool, allowing the user to create custom aberration patterns with Zernike polynomials and input custom mask layouts in either CIF or GDS II formats. As a result of the simulation run, the user is provided with a JPEG image of the match results as well as a text file listing match statistics including coordinate locations of the best matches and the match factors.
A prototype system is proposed for incorporating fast process models with EDA management of layout to identify and help arbitrate locations in a chip that are likely subject to less than ideal process effects. The approach uses pattern matching to find those locations in a layout that have the greatest impact from residual imperfections in manufacturing. For each process under study, the maximal lateral test pattern that maximizes the spillover from the surrounding pattern is first determined. The quantitative impact of the spillover for an actual layout is then assessed through comparing the degree of similarity of the actual pattern in a neighborhood about a critical point to the maximal lateral test pattern and scaling the impact accordingly. This fast-CAD pattern-matching approach is shown to be applicable for analysis of yield reduction due to combined effects of defects and alignment tolerances among mask levels as well as for identifying layout areas affected by reflective notching, CMP dishing and, with less accuracy, heating in laser assisted processing.
This paper validates the pattern matching methodology for locating and quantifying worst-case aberration-distortion of patterns through the comparison of theoretically predicted and simulated images. The matching process identifies those pattern element that will be most affected by the aberrations specific to the given lens. Once the highly impacted layout structures are identified, the region is extracted and simulated with and without aberrations using SPLAT to observe the induced pattern distortions. It is shown that even for good quality lenses, the resulting line- edge and line-end perturbations of PSM layouts for residual amounts of aberrations can exceed half those of optical proximity effects and may be quantified as additional input into the OPC process. The resulting feature edge shift is large and linear with aberration level for odd aberrations and much smaller for even aberrations whose electric fields add in quadrature. The effects of aberrations on binary marks are about half as large as the effects on phase-shift and phase-edge masks. The goal of the system is to allow measurements of aberrations across the field and among tools to be utilized int eh design process to inform designers of problematic features and to apply appropriate compensation on the mask.
A prototype CAD system for rapidly determining locations in large layouts that are most impacted by aberrations in projection printing is described. Aberrations are accurately modeled as producing spillover between mask openings with a localized pattern that is the inverse Fourier transform (IFT) of the optical path difference (OPD) function in the pupil. The novel function in the CAD system then quickly rank orders all pattern edges and corners according to the degree of similarity of their surrounding layout to the IFT function. The prototype is based on the Cadence Design Framework II CAD system and adds procedures for evaluating the spillover function, fast pattern matching, and extraction of local layout regions for further user aerial image simulation with SPLAT. Speed and memory limitations prompted the creation of a new C++ binary that incorporates the core data structures and algorithms for pattern matching. A pattern-matching sweep of a mask can now be accomplished in roughly the time it takes to flatten and merge the mask layout in Cadence. Results are presented in current technologies using both binary and phase-shifting masks.
The Lithography Analysis using Virtual Access (LAVA) web site at http://cuervo.eecs.berkeley.edu/Volcano/ has been enhanced with new optical and deposition applets, graphical infrastructure and linkage to parallel execution on networks of workstations. More than ten new graphical user interface applets have been designed to support education, illustrate novel concepts from research, and explore usage of parallel machines. These applets have been improved through feedback and classroom use. Over the last year LAVA provided industry and other academic communities 1,300 session and 700 rigorous simulations per month among the SPLAT, SAMPLE2D, SAMPLE3D, TEMPEST, STORM, and BEBS simulators.
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