Materials And Fabrication Processes For Highly Accurate X-Ray Masks

Abstract

AbstractThis paper discusses the properties of materials for x-ray masks used in synchrotron radiation lithography system. Through computer simulations and experimental analysis, we evaluate three kinds of membranes (Si, SiN, SiC) in terms of mechanical distortions, surface smoothness and optical transmittance. SiC exhibits the smallest distortion, but SiN has the best characteristics in the surface smoothness and the optical transmittance. By virtue of their high x-ray absorption coefficient and dry etching capabilities, Ta, W and Re are selected as potential absorber materials. We study their stress control characteristics, etching characteristics and the relation between their Young's modulus and distortions. We find that Ta is an excellent absorber because of its good stress controllability and good etching characteristics, such as a high etch rate and etch selectivity. By adopting a Ta/SiN structure, highly accurate masks can be fabricated by a process in which patterning the absorber is carried out before removing the bulk Si.