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PSM design for inverse lithography with partially coherent illumination
1Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 19716, USA. maxu@udel.edu
Optics Express
|November 26, 2008
Summary
This study introduces a new framework for optimizing phase-shifting masks (PSM) in semiconductor lithography, specifically addressing partially coherent illumination. The method enhances pattern fidelity and manufacturability for advanced chip production.
Area of Science:
- Semiconductor Manufacturing
- Optical Lithography
- Computational Imaging
Background:
- Phase-shifting masks (PSM) are crucial resolution enhancement techniques (RET) in optical lithography.
- Existing gradient-based PSM optimization methods primarily focus on coherent illumination.
- Partially coherent illumination, common in practical systems, introduces complexities not fully addressed by prior methods.
Purpose of the Study:
- To develop a novel framework for gradient-based PSM optimization that accurately accounts for partially coherent illumination.
- To improve pattern fidelity and manufacturability in semiconductor lithography.
- To enable the design of PSMs for projecting extremely sparse patterns.
Main Methods:
- Utilized singular value decomposition (SVD) to decompose the partially coherent imaging equation into a sum of coherent systems (SOCS).
- Employed a first-order coherent approximation based on the largest eigenvalue for PSM optimization.
- Introduced a post-processing step using 2D discrete cosine transformation (DCT) for enhanced pattern manufacturability and fidelity.
- Incorporated photoresist tone reversing techniques for designing PSMs capable of projecting sparse patterns.
Main Results:
- Successfully developed a PSM optimization framework for partially coherent illumination, addressing its inherent nonlinearities.
- Demonstrated improved pattern fidelity and manufacturability through DCT post-processing.
- Showcased the ability to design PSMs for projecting extremely sparse patterns using tone reversing.
Conclusions:
- The proposed framework effectively optimizes phase-shifting masks under partially coherent illumination, a significant advancement for semiconductor lithography.
- The integration of SVD, DCT, and tone reversing offers a robust approach to tackle complex lithography challenges.
- This research contributes to achieving higher resolution and better pattern control in advanced chip manufacturing.
