Soft X‐ray multilayer beam splitters

A semitransparent Mo/Si multilayer beam splitter with a completely self‐standing active area (10 × 10 mm) and a flatness of 1.1 nm (r.m.s.) was fabricated. The influence of the roughness of the membrane substrate on the reflectivity of a beam splitter was investigated for different materials and deposition schemes. Precise control of multilayer stress to give a slightly tensile state not only enables the fabrication of a large and flat reflection surface, but also makes it possible to etch away the supporting membrane and obtain a completely self‐standing structure. The performance evaluation using synchrotron radiation revealed that the fabricated beam splitter works as a one‐to‐one beam splitter whose reflectivity and transmittance are both 27% ( s ‐polarization, 45°, λ = 13.4 nm).