Method for reducing the mask complexity and allowing the formation of SRAFs in inverse lithography technique

초록

Inverse lithography techniques (ILT) were proposed to design the optimized mask pattern effectively, and can effectively generate an optical proximity correction (OPC) pattern which is the one of resolution enhancement techniques (RET) [1]. Usually, the optimization in ILT has been performed by steepest decent iteration [2], Newton iteration [3] and genetic algorithm [4]. Though a desired target image can be effectively obtained from the mask pattern optimized by ILT, the mask pattern is not suitable for fabrication because of its complexity. For such a reason, some techniques to reduce the mask complexity have been proposed. First is to introduce an additional penalty term of cost function [2], and second is to use the limited pixel flipping [5]. Third is to move pattern boundary only [6]. Unfortunately, since the second and the third methods cannot essentially generate sub-resolution assist features (SRAFs), the pattern fidelity is not so good. In this paper, we propose the method of reducing the mask complexity and allowing the formation of SRAFs by using limited pixel flipping and putting seed pixels.