Symmetric Assist Feature Pattern Generation for Photomask OPC
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Solution Overview
Problem
The optical proximity correction (OPC) process in semiconductor manufacturing introduces asymmetric assist features, making it difficult to inspect defects in photomasks and verify the accuracy of semiconductor devices, especially when critical dimensions are below 65 nm, due to reduced depth of focus and light intensity variations.
Innovation Solution
A method is developed to generate a symmetric assist feature pattern during the OPC process, where assist features are inserted into the photomask layout and remain unchanged, allowing for easier defect inspection and accuracy verification by maintaining symmetry throughout the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If asymmetric assist features are added to the photomask pattern through optical simulation, then the transferred pattern accuracy is improved, but the difficulty of defect inspection and verification increases
Solution Approach 1:
The patent applies asymmetry in reverse - it intentionally creates symmetric assist feature patterns despite the optical simulation naturally producing asymmetric results. This is achieved by generating multiple candidate assist feature patterns, evaluating their symmetry properties, and selecting those that maintain symmetry. The symmetric patterns are then used in the photomask, resolving the contradiction by prioritizing inspection ease while maintaining adequate pattern transfer accuracy through optimized symmetric configurations.
2Manufacturing precision
If asymmetric assist features are added to the photomask pattern, then the optical proximity effect is corrected, but the light intensity distribution becomes uneven affecting verification
Solution Approach 1:
The patent applies local quality by creating assist feature patterns with specific symmetric properties in different regions of the photomask. Each region's assist features are optimized to maintain symmetry while providing the necessary optical proximity correction locally. This allows the overall pattern to maintain symmetry for verification purposes while still achieving effective OPC in each local region through carefully designed symmetric assist feature configurations.
3Difficulty of detecting and measuring
If the assist feature pattern is made symmetric, then the inspection and verification processes are simplified, but the optical proximity correction effectiveness may be reduced
Solution Approach 1:
The patent applies parameter changes by systematically varying the geometric parameters of assist features (such as width, spacing, and position) while maintaining symmetry constraints. The optimization process adjusts these parameters to achieve the best possible OPC effectiveness within the symmetric configuration. This allows the system to find optimal symmetric solutions that maintain adequate correction effectiveness while enabling simplified inspection and verification processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the inspection of defects in photomasks and verification of semiconductor devices by ensuring the assist feature pattern remains symmetric, facilitating accurate assessment and reducing complexity in the semiconductor manufacturing process.
Implementation Method 1
diffraction and interference of the light will occur, which results in deviations in the transferred pattern
Implementation Method 2
diffraction and interference of the light will occur, which results in deviations in the transferred pattern
Data Source
AI summary
A method of forming a photomask is provided. A first layout pattern is first provided to a computer system and followed by generating an assist feature pattern by the computer system based on the first layout pattern and adding the assist feature pattern into the first layout pattern to form a second layout pattern. Thereafter, an optical proximity correction process is performed with reference to both the first layout pattern and the assist feature pattern to the second layout pattern without altering the assist feature pattern to form a third layout pattern by the computer system. Then, the third layout pattern is output to form a photomask.