An XPS comparative study on thermal oxide barrier formation on Nb and NbN thin films

Abstract

In connection with Josephson junction technology, the oxidation of both Nb and NbN thin films is comparatively investigated by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Radio frequency sputtering for cleaning the NbN surface is less efficient than for Nb. However, the nature of oxides and their thicknesses are not sensitive to the presence of contaminant for NbN film oxidation either in pure oxygen or in air. It is not the case for Nb where the oxide interface is thicker with impurity. In the range of oxygen pressure from 10 -5 to 10 -2 mbar and of temperature from 20 to 200°C, formation mainly of Nb 2 O 5 is obtained with NbO and NbO 2 at the interface between Nb 2 O 5 and NbN. The thickness of the oxide layer is thinner for NbN oxidation than for Nb and in contrast to Nb reaches a saturation value of about 20 Å. During oxidation nitrogen seems to diffuse toward the surface.