Model-Based Photomask Synthesis for Lithography
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Solution Overview
Problem
In sub-wavelength optical lithography, existing methods for synthesizing photomasks fail to accurately replicate patterns on wafers due to distortions, necessitating improved techniques for optical proximity correction and subresolution assist feature insertion.
Innovation Solution
A model-based photomask synthesis method that calculates a figure-of-merit for the mask function, adjusts it by determining the Fréchet derivative, and optimizes edge movements and segmentation to enhance image quality, incorporating subresolution assist features and continuously varying phase and amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photomask synthesis methods are used, then the manufacturing process is simpler, but the manufacturing precision of the pattern on the wafer deteriorates due to optical proximity effects and distortions
Solution Approach 1:
The patent applies preliminary action by performing optical proximity correction and pattern optimization during the photomask synthesis stage before actual lithography. The method calculates proximity effects using a lithography model and adjusts the photomask pattern in advance to compensate for expected distortions, ensuring accurate pattern transfer to the wafer without requiring complex real-time corrections during manufacturing
Solution Approach 2:
The patent implements feedback by using a lithography model to simulate and calculate the actual pattern that will be formed on the wafer from the proposed photomask design. The calculated proximity effects and pattern deviations are fed back into the synthesis process to iteratively optimize the photomask pattern, creating a closed-loop system that continuously improves pattern accuracy based on simulated performance
2Manufacturing precision
If optical proximity correction and subresolution assist features are added, then the image quality improves, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the photomask pattern into different feature types: main resolution features and subresolution assist features. The synthesis method separately optimizes each category, allowing subresolution features to be added to enhance image quality and compensate for proximity effects without directly increasing the complexity of the primary pattern structure
Solution Approach 2:
The patent implements local quality by applying different design criteria and optimization parameters to different regions and feature types within the photomask. Subresolution assist features are strategically placed in specific locations where proximity effects are most problematic, while main features follow different design rules, allowing localized optimization of image quality without uniformly increasing overall complexity
Data Source
AI summary
An apparatus and method for improving image quality in a photolithographic process includes calculating a figure-of-demerit for a photolithographic mask function and then adjusting said photolithographic mask function to reduce the figure of demerit.