Surface Roughness Healing Of Substrates For XUV Multi Layer Coatings

The roughness of interfacial surfaces of multilayer coatings contributes significantly to the degradation of normal incidence reflectivity for the XUV wavelengths. Sub-nanometer rms roughness of the interfacial surfaces is required to appreciably reduce interfacial scattering of XUV radiation. The goal of the present work is to measure the amount of surface roughness healing which can be achieved by the deposition of thin silicon films, using dc triode sputtering, upon candidate substrates for figured XUV optics. The substrates used in the present work are float glass, semiconductor grade silicon wafers, and diamond turned aluminum flats. The surface roughness profiles are measured with a WYKO TOPO-3D phase shifting interferometer and a Scanning Tunneling Microscope (STM). This paper describes initial rms roughness measurements and autocovariance calculations for the above-mentioned substrates.