Effects of absorber topography and multilayer coating defects on reflective masks for soft x-ray/EUV projection lithography

Abstract
The effects of mask topography and multilayer coating defect on areal images of reflective masks for soft x-ray projection lithography is studied using electromagnetic simulation. Masks made by depositing and patterning an absorber layer over the multilayer coating was found to be insensitive to variations in incidence angle and absorber layer edge profile. 100 nm of gold, germanium or carbon absorber is sufficient for high image contrast. Masks made by etching patterns into the multilayer stack is more sensitive to variations in incidence angle and edge profile. Defects on the substrate severely degrade the areal image. Different coverage profiles results in widely different areal image.