Improving the Efficiency of Pattern Extraction for Character Projection Lithography using OPC optimization

摘要

This paper proposes an approach to improving pattern extraction efficiency for character projection lithography (CPL). CPL is a promising technology for electron beam direct-write lithography. The advantage of CPL is the reduced number of electron beam (EB) shots compared to conventional variably-shaped beam lithography, because character patterns that frequently appear within a layout can be simultaneously written by a single EB shot with a CP aperture mask. This means that it is important to extract frequently-used character patterns and prepare CP aperture masks in order to reduce the number of EB shots. However, with random logic devices, each character pattern is subject to being deformed into many different patterns that have complicated optical proximity correction (OPC) features, which cannot be extracted as a unique CP aperture mask. In order to overcome this problem, we propose a method of improving the efficiency of pattern extraction for CPL with random logic devices by employing OPC optimization. Our proposed method can reduce the variety in the deformed patterns with two developed cell-based algorithms: (1) a cell grouping algorithm that categorizes differentiated cells and extracts some typical cell groups, and (2) an OPC optimization algorithm that regards the cells in a group as one typical cell and corrects for the OPC features of a typical cell to form a CP aperture mask. In conducted experiments, we successfully achieved a 30% improvement in extraction efficiency.