Analysis of distinct scattering of extreme ultraviolet phase and amplitude multilayer defects with an actinic dark-field microscope

The authors report on experimental and simulative scattering analyses of phase and amplitude defects found in extreme ultraviolet multilayer mirrors, such as mask blanks for EUV lithography. The goal of the analyses is to develop a novel mask blank inspection procedure using one single inspection tool that allows to determine whether a defect is a surface type (amplitude) defect, or a buried type (phase) defect. The experiments were carried out with an actinic dark-field reflection microscope. Programmed defects of both types were fabricated, using different nanostructuring techniques. Analytical and rigorous scattering simulations were carried out to predict and support the experimental results.