Optical imaging properties of dense phase shift feature patterns

Abstract

Optical lithography resolution enhancement methods are continuing to develop, driven by the semiconductor industry’s requirements for imaging subwavelength feature sizes. In the phase shift area, pattern decomposition into multiple exposures has been found to be useful and is finding its way into production. Recently, layout construction based on dense fine-pattern imaging has received increasing interest. This type of approach can minimize the proximity and other spatial frequency effects that otherwise limit strong phase shift technologies. Simple fine-feature template masks are easier and cheaper to fabricate and inspect as well as offering the potential to be reused for multiple designs. In this article, imaging and process issues specific to dense phase shift patterns are explored both experimentally and through simulation. Progress is reported in applying our gratings of regular arrays and trim exposures for ultralarge scale integrated circuit lithography (GRATEFUL) imaging method to fine features in both x and y orientations. The use of a graytone trim mask to vary fine-feature dimensions in a dual-exposure, strong phase shift process has been explored. We have also studied multiple-exposure lithography using one mask and varying illumination between exposures.