Surface Finish Requirements for SXPL Optics

Abstract

In order for soft X-ray projection lithography to become a viable candidate for the mass production of integrated circuits having 0.1-μm design rules, it will be necessary to satisfy an array of technical performance requirements. Among these requirements is system throughput (i.e. wafers/hour.) For SXPL exposure tools operating at 14 nm using multilayer X-ray mirrors, the system throughput depends sensitively on the peak reflectance of the multilayers. The peak reflectance, in turn, can be deleteriously affected by the surface finish of the mirror substrates. That is, the roughness of the substrate can propagate through the multilayer during growth, resulting in reduced reflectance. Therefore, it is imperative to use X-ray mirror substrates with low surface roughness.