Lithographic Pattern Splitting for Image Quality and Depth of Focus
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Solution Overview
Problem
Current lithographic processes face challenges in achieving optimal image quality and process latitude when printing dense feature patterns, as existing resolution enhancement techniques can diminish image quality and reduce depth of focus, especially when splitting patterns into sub-patterns with increased pitch.
Innovation Solution
A method is introduced to split lithographic patterns into sub-patterns by generating test structures, varying their dimensions, and analyzing image quality metrics to determine optimal splitting ranges, allowing for improved image quality and process latitude through a double or multi-exposure process, while incorporating design rule checks and graph theory algorithms to ensure features are spaced at least twice the critical dimension apart.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pattern splitting is applied to improve image quality of dense features, then image quality metric improves, but depth of focus decreases
Solution Approach 1:
The lithographic pattern is divided into multiple sub-patterns (first sub-pattern and second sub-pattern) with different pitch characteristics. Dense features are separated into one sub-pattern while sparse features form another sub-pattern, allowing each to be optimized independently for image quality without compromising depth of focus
Solution Approach 2:
Different pitch values are assigned to different sub-patterns based on their specific feature density requirements. The first sub-pattern uses a first pitch value optimized for dense features, while the second sub-pattern uses a second pitch value optimized for sparse features, enabling local optimization of image quality for each region type
2Reliability
If features are spaced at least twice the critical dimension apart in sub-patterns, then process latitude improves, but manufacturing complexity increases
Solution Approach 1:
The manufacturing process is segmented into multiple exposure steps, with each sub-pattern being printed separately. This segmentation allows each exposure to use optimized pitch values that ensure features are spaced at least twice the critical dimension apart, improving process latitude while managing complexity through systematic process division
Solution Approach 2:
The pattern splitting and sub-pattern generation are performed in advance during the design stage, before actual manufacturing. This preliminary action establishes the spacing requirements (features spaced at least twice the critical dimension apart) and prepares the optimized sub-patterns, reducing the complexity burden on the manufacturing stage
Data Source
AI summary
A method of splitting a lithographic pattern into two sub-patterns, includes generating test structures corresponding to structures of interest in the lithographic pattern, varying the test structures through a selected range of dimensions, simulating an image of the test structures, determining an image quality metric for the simulated image, analyzing the determined image quality metric to determine pitch ranges for which split improves the image quality metric and ranges for which split does not improve the image quality metric, and generating the two sub-patterns in accordance with the determined pitch ranges.