Enforcement of curvy MRC compliance with reduced complexity in inverse lithography

Mask complexity has become a critical issue for advanced semiconductor nodes in optical proximity correction (OPC) and subsequent mask manufacturing, especially when inverse lithography technology (ILT) introduces curvy features for better imaging performance. Meanwhile, mask rule check (MRC) algorithms conceived for rectilinear designs, when applied to curvy ones, lead to false and missing violations. In this paper, we develop synthesized layouts with regional constant width sub-resolution assist features (SRAFs) for user discretion to reduce complexity and straightforward implementation of MRC and correction. Additionally, a skeleton-based distance-map approach intended for the remaining freeform features is designed and readily applied iteratively for MRC-clean layouts. Simulation results suggest that the proposed approach can effectively resolve MRC violations with negligible performance discount in terms of pattern error (PE) fidelity, with significantly reduced mask complexity.