Model-Based SRAF Guidance Map for Lithography
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Solution Overview
Problem
Current methods for generating Sub-Resolution Assist Features (SRAFs) in photolithography are inefficient, leading to high costs and long development cycles due to their inability to account for all pattern shapes and line widths, and they often converge to local optima or require complex iterative processes.
Innovation Solution
The development of a model-based SRAF guidance map that computes an image gradient map and uses Fourier Transform operations to determine SRAF placement rules, allowing for efficient and rule-free placement of SRAFs that optimize the process window by enhancing edge slopes and improving robustness against focus and dose changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional iterative methods are used to generate SRAFs, then the process can converge to a solution, but the computational expense is high and development cycles are long
Solution Approach 1:
The patent applies preliminary action by pre-computing the SRAF guidance map using Fourier Transform operations before the actual SRAF placement process. This guidance map contains pre-calculated information about optimal SRAF locations and their impact on process window robustness, eliminating the need for time-consuming iterative simulations during the placement process itself.
Solution Approach 2:
The patent replaces the mechanical iterative optimization process with a mathematical Fourier Transform approach. Instead of repeatedly simulating lithography processes and adjusting SRAF placements iteratively, the system uses frequency-domain analysis to directly compute optimal SRAF configurations, substituting computational mechanics with mathematical transformation.
2Reliability
If traditional SRAF generation methods are used, then SRAFs can be placed to improve process window robustness, but the methods converge to local optima and require complex iterative processes
Solution Approach 1:
The patent substitutes complex iterative optimization algorithms with a direct Fourier Transform-based calculation. The SRAF guidance map is computed once using frequency-domain analysis, providing a straightforward lookup process for placement decisions without requiring complex iterative adjustments or convergence checks.
Solution Approach 2:
The patent creates a computational copy of the lithography process behavior in the form of the SRAF guidance map. This guidance map replicates the essential information needed for optimal SRAF placement without requiring repeated simulations, allowing rapid placement decisions based on pre-computed frequency-domain data.
3Ease of operation
If rule-based SRAF placement is used, then the process is simpler, but it cannot account for all pattern shapes and line widths
Solution Approach 1:
The patent achieves universality by computing a general SRAF guidance map that applies to all pattern types and configurations through Fourier Transform analysis. This single guidance map generation process accommodates various pattern shapes, line widths, and densities, making the system universally applicable without requiring separate rules for each pattern type.
Solution Approach 2:
The patent changes the approach from fixed placement rules to parameter-based guidance. The SRAF guidance map is generated by analyzing the frequency content of the pattern, allowing the system to automatically adapt to different pattern characteristics. The guidance map incorporates information about pattern shape, size, and spacing through its frequency-domain representation, enabling flexible placement decisions for any pattern configuration.
Data Source
AI summary
Methods are disclosed to create efficient model-based Sub-Resolution Assist Features (MB-SRAF). An SRAF guidance map is created, where each design target edge location votes for a given field point on whether a single-pixel SRAF placed on this field point would improve or degrade the aerial image over the process window. In one embodiment, the SRAF guidance map is used to determine SRAF placement rules and/or to fine tune already-placed SRAFs. In another embodiment the SRAF guidance map is used directly to place SRAFs in a mask layout.