Fabrication and testing of Au- and multilayer Mo/Si-coated diffraction gratings with high-order brilliance in high orders in the soft X-ray and EUV ranges

Glazed and low-roughness diffraction gratings ruled at 500 lines·mm^-1, designed for operation in high orders in the soft X-ray and extreme ultraviolet radiation ranges and having Au- and multilayer Mo/Si-coatings, are made by liquid anisotropic etching of Si(111)4° vicinal plates and studied by atomic force and scanning electron microscopy. The diffraction efficiency of the gratings is determined both using a laboratory reflectometer and by modelling based on a rigorous method of boundary integral equations in the PCGrate™ program, taking into account realistic groove profiles. The values of the diffraction efficiency measured in unpolarized radiation with wavelengths of 13.5 and 4.47 nm and the calculated ones, obtained with allowance for random roughness, practically coincide. For a grating with a multilayer (five Mo/Si bilayers) coating with a period of 20 nm, the absolute efficiency is ∼40% in the –8th diffraction order at an incidence angle of 70.5°, which is a record for a mid-frequency grating operating in a high order.