Shot noise and process window study for printing small contact holes using EUV lithography

Abstract

A theoretical analysis of the capability of Extreme Ultra-violet Lithography (EUVL) to print contacts in the range of 30-50 nm with acceptable yield is presented. We study the problem from the viewpoint of two issues: the effects of shot noise and the available process window. Shot noise is modeled as a simple statistical fluctuation of the number of photons absorbed in a given contact. The process windows for various size contacts are simulated for a representative 0.25-NA EUV tool. We find that EUVL should be able to print 30 nm contacts with a reasonable exposure latitude, and we also conclude that the effects of shot noise will not significantly decrease yield at this exposure latitude for a resist with a dose-to-clear value of ~5 mJ/cm2. A dose-to-clear value becomes ~2 mJ/cm2 for 50 nm contacts. In addition, a comparison at the same node shows that 50-nm contacts have a greater process window than 30-nm lines.