Double-dipole mask-synthesis using inverse lithography technology

Double-dipole lithography (DDL) uses two orthogonal dipole illuminations and one or two masks to print the desired wafer pattern. The main challenge of using such IC-manufacturing technique remains how to properly synthesize the proper mask patterns for the arbitrarily given target pattern. This paper presents a gradient-based inverse lithography technology (ILT) addressing the problem above. This approach properly models the partially coherent imaging system by employing the double-dipole lithography, and then uses the steepest descent method to automatically synthesize the masks required to print the desired wafer pattern. We also present results for various kinds of masks for printing 45-nm critical dimension (CD) features. The results show that our algorithm automatically generates the synthesized masks and that the synthesized masks reduce the pattern distortion error (PDE) by 85–90%. The comparison with a single-exposure case indicates a superior improvement.