Practical Complementary Mask-Data Generation for EPL Stencil Masks by Using General Geometrical Operation Tools

摘要

Electron beam projection lithography (EPL) using stencil masks is one of the most promising techniques in 50-70-nm-node lithography. However, in most real situations, stencil masks have to be divided into two complementary masks due to the "doughnut pattern" problem as well as mechanical problems. This paper describes our complementary mask-data generation method that uses a pattern operation tool for conventional design-rule checking (DRC) and a phase-shift-mask (PSM) generation tool, both of which are made by Mentor Graphics. Layout patterns are divided into pieces with the DRC tool and the pieces are alternately distributed between two layers with the PSM generation tool. The advantages of using these commercial DA tools include a high processing speed based on the maintenance of a hierarchical data structure, high reliability, and flexibility in changing generation rules. We used this method for metal-layer data of a 14xl4-mm test chip (6 Mbytes in a hierarchical form). Although the original data included more than 3000 doughnut patterns, the obtained complementary data had no doughnut patterns. The aperture densities of the two complementary masks were almost equal. Because the CPU time required for data generation was about 20 minutes with a 500-MHz PC having 256-Mbyte memory, we believe that the proposed method is a valuable tool for complementary mask-data generation.