<title>Optimization of modified illumination for 0.25-um resist patterning</title>

Abstract

In order to achieve wide focus latitude in various 0.25 micrometers patterns, the optimization of optical parameters in KrF excimer laser lithography has been investigated by means of optical intensity simulation. The accuracy of simulated DOF values was confirmed experimentally, using a chemically amplified negative resist and a KrF excimer laser stepper with NA equals 0.5 and sigma equals 0.7. The optical parameters, such as NA, sigma, and annular shield ratio in an annular illumination, were optimized for 1:1 L&S. Our results indicate that the DOF value in the conventional illumination is insufficient even under the optimum condition, but that in the annular illumination it is wide enough. To investigate the DOF value for sparse patterns the minimum contrast value, as well as the optimum optical parameters, was estimated for each defocal position. The optimum parameters set for sparse patterns was very different from that for 1:1 L&S. Moreover, the DOF value of sparse pattern was relatively small compared to that of 1:1 L&S.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.