On the use of illumination-source pixels in the central-obscuration area for enhancing the process window of contact printing with high-NA EUV lithography

Abstract

One of the challenges with high numerical aperture extreme ultra-violet lithography (high-NA EUVL) is the limited depth-of-focus (DOF). In this study, we demonstrate how an illumination source with the majority of pixels in the central obscuration region of the source can increase the process window of contact printing cases, especially in dynamic random access memory (DRAM) but also in logic applications, except in configurations with a center-to-center pitch smaller than ∼30 nm. We demonstrate this through full-resist model rigorous lithography simulations. For hexagonal contact configurations such as those used in DRAM, a simple qualitative explanation of the simulated DOF increase is also presented. An experimental validation of the simulated results will be presented in future work.