Effect of substrate heating and ion beam polishing on the interface quality in Mo/Si multilayers—X-ray comparative study

Abstract

Three periodic Mo/Si multilayers were prepared by electron-beam evaporation at different conditions. An in situ polishing of amorphous Si layers with Ar+ ions of 800 eV energy and substrate heating to 170°C were used for the two of them which were designed as multilayer mirrors optimized for 13 nm wavelength at normal incidence (30 periods of nominally 6.9 nm). A third multilayer was deposited at room temperature with reduced Mo layer thicknesses and number of periods to suppress interface roughness buildup. The goal was a comparison of ion beam polishing and substrate heating in terms of the interface quality and evaluation of the merit of more sophisticated depositions. The interfaces were studied by specular X-ray reflectivity and interface diffuse scattering measured at Cu K α1 wavelength. The interface morphology parameters are very close on ion beam polishing and substrate heating indicating a similar relaxation mechanism of the growing surface. The main difference is a larger thickness of the Mo 5Si 3 interlayers with substrate heating, which has practical implications for peak reflectivities. On the other hand, a slightly worse interface replication here is appealing for the applications where a good imaging contrast is of primary importance. At room temperature deposition, the interface roughness is nearly doubled at 3 times smaller number of multilayer periods.