Enhancing lithographic process latitude: a powerful approach using inverse lithography technology for depth of focus improvement

As semiconductor technology continues to scale down, maintaining the fidelity of lithographic patterns becomes increasingly challenging due to limitations in the common Depth of Focus (DOF) for considering all the critical patterns. However, the DOF of exposure patterns is related to Sub-Resolution Assistant Feature (SRAF), including its intensity and position. This study investigates the application of Inverse Lithography Technology (ILT) to optimize the placement of SRAF, which are crucial for improving image fidelity and process window. Unlike the traditional Optical Proximity Correction (OPC) which relies on rule-based SRAF and limited iterations to optimize mask. ILT has emerged as an effective and powerful computational lithography approach to address the critical challenges posed by advanced semiconductor manufacturing, particularly in improving the DOF of exposure patterns through complex, non-intuitive mask patterns. This article will present a comprehensive analysis of how ILT-generated masks can adjust the aerial image to enhance DOF, reducing the impact of focus variations on critical dimension uniformity. The proposed ILT approach is validated through simulation and experimental results, showing a significant increase in the process tolerance compared to conventional OPC methods. The improved DOF achieved with ILT not only enhances pattern fidelity but also contributes to the overall robustness and yield of semiconductor manufacturing. These findings demonstrate the efficacy of ILT in addressing DOF limitations, highlighting its role as a critical tool for future lithographic advancements.