Sub-resolution assist feature placement for contact hole symmetry
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Solution Overview
Problem
Current resolution enhancement techniques in photolithography, such as off-axis illumination and sub-resolution assist features, fail to produce symmetric contact holes, leading to asymmetrical printed critical dimensions that do not meet design rules, causing issues in subsequent processing steps.
Innovation Solution
A method of designing masks with sub-resolution assist features positioned at varying distances relative to mask features, based on their spacing, to control the aspect ratio and achieve symmetric contact holes by adjusting the placement of sub-resolution assist features according to specific relationships and using a look-up table for optimal placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sub-resolution assist features are positioned at equal distances from mask features, then the mask design is simple and easy to manufacture, but the printed contact holes become asymmetrical and do not meet design rules
Solution Approach 1:
The patent applies local quality by positioning sub-resolution assist features at different distances from mask features based on local spacing requirements. Specifically, when mask features are spaced closer together, SRAFs are positioned at a first distance, and when mask features are spaced farther apart, SRAFs are positioned at a second distance. This local adaptation ensures symmetric contact hole printing while maintaining manufacturing feasibility.
Solution Approach 2:
The patent implements dynamics by making the SRAF positioning adaptable and variable rather than fixed. The positioning distance is dynamically adjusted based on the spacing between adjacent mask features, allowing the mask design to optimize for symmetry in different local contexts while remaining manufacturable.
2Manufacturing precision
If sub-resolution assist features are positioned at varying distances to achieve symmetric contact holes, then contact hole symmetry and design rule compliance are improved, but the mask design complexity and positioning precision requirements increase
Solution Approach 1:
The patent applies parameter changes by systematically varying the positioning distance of sub-resolution assist features based on the spacing parameter of adjacent mask features. Two distinct positioning distances are defined: a first distance for closely-spaced mask features and a second distance for widely-spaced mask features. This parameter-based approach achieves contact hole symmetry while managing design complexity through clear, rule-based positioning criteria.
3Measurement precision
If conventional sub-resolution assist features are used, then resolution enhancement is achieved, but the critical dimension control and aspect ratio control are insufficient
Solution Approach 1:
The patent applies local quality by making the SRAF positioning locally optimized for each mask feature based on its specific spacing to adjacent features. This local optimization ensures that each contact hole achieves the correct aspect ratio and critical dimension, rather than using a uniform approach that cannot accommodate varying local geometries.
Solution Approach 2:
The patent uses parameter changes to control critical dimension by systematically adjusting the SRAF positioning distance parameter. By defining different positioning distances (first distance and second distance) based on mask feature spacing, the method achieves precise control over the printed contact hole critical dimensions and aspect ratios, enhancing resolution while maintaining manufacturing precision.
Data Source
AI summary
A method of making a mask design having optical proximity correction features is provided. The method can include obtaining a target pattern comprising a plurality of target pattern features corresponding to a plurality of features to be imaged on a substrate. The method can also comprise generating a mask design comprising mask features corresponding to the plurality of features to be imaged on the substrate and controlling the aspect ratio of at least one of the features of the plurality of features to be imaged on the substrate by positioning a sub-resolution assist feature proximate to the corresponding mask feature.