An Ellipsometric Study of Oxide Growth on Nb, Al and Nb3Al Films by rf Plasma

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Abstract
The rf-oxidation process on Nb, Al and Nb3Al films has been investigated by in-situ ellipsometry. The Nb3Al cleaned surface has a refractive index of n=2.98–i3.50 which is close to the Nb-index of n=2.98–i3.41. The Nb, Al and Nb3Al oxide-layers have refractive indices of n≃2.5, n≃1.7 and n≃2.3, respectively. The oxide growth on Nb3Al films obeyed the logarithmic law, the same as with Nb, and was gaverned by the Nb-behavior in the rf discharge rather than by the Al-behavior. The oxygen partial pressure, rather than the rf voltage, was an effective parameter with which to control the thin oxide-layer thicknesses.