Roughness studies of ion beam processed molybdenum surfaces

Abstract

Mechanically polished molybdenum samples have been irradiated with 150 keV molybdenum ions at fluences from zero to 16×1015 ions/cm2 to study the effects on surface smoothing. Both fluence and substrate temperature during irradiation (25, 250, and 500 °C) had considerable effects on the optical properties. Ellipsometry, profilometry, and Nomarski photography were used to characterize the surfaces. Multiple wavelength, multiple angle of incidence ellipsometry results were analyzed using effective medium approximation models, with molybdenum, molybdenum oxide, and voids as the principal constituents. Generally, we find that the reflectance calculated from the ellipsometric measurements increases continuously as a function of fluence. However, for high substrate temperature and short wavelength the reflectance as a function of fluence reaches a maximum and then decreases. Effective medium calculations indicate that there is a corresponding change in the surface roughness with fluence, and that effects due to oxides are minimal.