Design of phase–shifting masks for enhanced–resolution optical lithography

As integrated circuit (IC) technology continues to push further into the submicrometer regime, considerable effort has been devoted to finding new approaches for extending the resolution limits of optical lithographic systems. The idea of using phase–shifting masks in optical lithography is one of such resolution–enhancing techniques and is commonly attributed to Levenson.1 The problem of the design of phase–shifting mask is how to determine the phase of the mask that produces a predesignated image. There are several approaches to deal with this problem such as simulated annealing algorithm2 and optimal coherent approximations.3 In this paper we present an approach of the design of the phase–shifting mask for the enhancement of optical resolution in lithography based on general theory of amplitude–phase retrieval in optical system and an iteration algorithm. For several model objects the numerical investigating results are given.