Surface studies of amorphous W75Si25 oxidation

Abstract

The surface composition and oxide growth kinetics of amorphous W75Si25 sputter-deposited thin films were examined using x-ray photoelectron spectroscopy (XPS), ellipsometry, and thermogravimetric analysis (TGA). These films have been proposed as metallization layers on compound semiconductors for high-temperature applications. The 1-μm-thick films were oxidized in air at temperatures of 30 to 600 °C for times of 10 min to 30 h. Angle resolved XPS measurements indicated that the surface region consisted of a thin layer (∼16 Å) of primarily SiO2 above a layer of mainly WO3 for oxidation temperatures up to 425 °C. At oxidation temperatures between 150 and 425 °C the WO3 signal from the surface region was enhanced. In this range the SiO2 layer was thinner resulting in a larger detected signal from the underlying WO3 layer. For oxidation temperatures above 450 °C, the two oxides appeared to coexist although the surface region was enhanced in SiO2. Ellipsometry and TGA measurements did not indicate a change in oxide growth kinetics in the temperature range 150–550 °C. The kinetics were parabolic and displayed an Arrhenius-type temperature dependence with rates similar to W oxidation.