Design calculations and characterization of C/Cr multilayer mirrors in the 6 nm BEUV

This paper focuses on the design, fabrication and characterization of the reflectivity and bandwidth of C/Cr multilayer mirrors of variable layer numbers (N = 30, 40, 100, 150 and 200) in order to exploit them as efficiently as possible at a wavelength of 6 nm. Magnetron sputtering technique was used with high base vacuum and high purity working gas (Argon 99.99%) together with a stable deposition rate during the fabrication process. The multilayers were probed using a hard X-ray diffraction method (Cu Kα radiation, λ = 0.154 nm) to characterize their reflectivity, bi-layers structure and surface roughness. An atomic force microscope was used to determine the surface topography and to analyze the surface structure imperfections such as roughness and stress induced damage. These were believed to occur during the preparation of the substrate or fabrication process. Various imperfections may also have developed due to oxidization after post production exposure to air. The surface roughness values obtained using X-ray scattering and atomic force microscopy were found to be in good agreement with each other.