ANGULAR AND ENERGY-DEPENDENCE OF ION-BOMBARDMENT OF MO SI MULTILAYERS/

The process of ion bombardment is investigated for the fabrication of Mo/Si multilayer x-ray mirrors using e-beam evaporation. The ion treat ment is applied immediately after deposition of each of the Si layers to smoothen the layers by removing an additional thickness of the Si l ayer. In this study the parameters of Kr+ ion bombardment have been op timized within the energy range 300 eV-2 keV and an angular range betw een 20 degrees and 50 degrees. The optical performance of the Mo/Si mu ltilayers is determined by absolute measurements of the near-normal-in cidence reflectivity at 14.4 nm wavelength. The multilayer structures are analyzed further with small-angle reflectivity measurements using both specular reflectivity and diffuse x-ray scattering. The optimal s moothening parameters are obtained by determining the effect of ion bo mbardment on the interface roughness of the Si layer. The optimal cond itions are found to be 2 keV at 50 degrees angle of incidence with res pect to the surface. These settings result in 47% reflectivity at 85 d egrees (lambda = 14.4 nm) for a 16-period Mo/Si multilayer mirror, cor responding to an interface roughness of 0.21 nm rms. Analysis shows th at the interface roughness is determined by ion induced viscous flow, an effect which increases with ion energy as well as angle of incidenc e. In order to determine the effect of intermixing of the Si and Mo at oms, the penetration depth of the Kr+ ions is calculated as a function of ion energy and angle of incidence. Furthermore, the angular depend ence of the etch yield, obtained from the in situ reflectivity measure ments, is investigated in order o determine the optimal ion beam param eters for the production of multilayer mirrors on curved substrates. ( C) 1997 American Institute of Physics.