Robust source and polarization joint optimization for thick-mask lithography imaging

Background: Optical lithography is a key technology to fabricate very large-scale integrated circuits. As the critical dimension of integrated circuits approaches the diffraction resolution limit, thick-mask effects have begun to significantly influence the lithography image quality. Aim: We develop a computational lithography approach, dubbed source and polarization joint optimization (SPO), to compensate for image distortion in the thick-mask lithography process. Approaches: SPO manipulates the intensity distribution and polarization angles of the pixelated light source to modulate the diffracted light field off the photomask, thus improving the lithography image quality over the variation of process conditions. The thick-mask effects are accounted for in the imaging model using the rigorous three-dimensional diffraction simulator. The SPO framework is established to consider the image errors on both focal and defocus imaging planes with exposure variation. Two kinds of gradient-based optimization algorithms, namely, simultaneous SPO (SiSPO) and sequential SPO (SeSPO), are developed. Result: The superiority of the proposed methods is verified by a set of numerical experiments. Conclusion: The SeSPO algorithm outperforms the SiSPO algorithm in terms of image fidelity, process window, and computational efficiency.