Impact of Working-Gas Pressure on Formation of Intermixed Zones in Mo/Si Multilayer X-Ray Mirrors Fabricated by Magnetron Sputtering

Dependence of structure of amorphous intermixed zones (AIZ) in Mo/Si x-ray multilayer mirrors (XMM) on Ar pressure within the range of 1-2.8 mTorr is studied by small-angle x-ray scattering with modelling of small-angle spectra, x-ray phase analysis, and cross-sectional electron microscopy. Original method for measurement of XMM contraction caused by AIZ formation is proposed. The method is based on precise measurement of XMM periods in samples with three multilayer stacks and different nominal Mo and Si thicknesses. Decrease of the XMM contraction when working pressure of sputtering gas increases is determined. This effect is specified with a change of AIZ composition from MoSi2 to Mo5Si3 at Mo-on-Si interface. Herewith some small decrease by 0.2 nm of this AIZ thickness is observed. The change of AIZ composition is conditioned by an energy reduction of Mo atoms incoming on silicon layer surface.