Influence of the substrate finish and thin film roughness on the optical performance of Mo/Si multilayers

Scattering resulting from interface imperfections critically affects the image contrast and optical throughput of multilayer coatings for 13.5 nm. To investigate the scattering mechanisms, at-wavelength scattering measurements in combination with atomic force microscopy are analyzed for an in-depth characterization of the roughness properties. The different impacts of substrate finish and intrinsic thin film roughness on the scattering distribution are separated and analyzed in detail. Furthermore, a novel approach to characterize the roughness of large extreme ultraviolet substrates is presented, based on light scattering measurements at 442 nm.