Surface studies of amorphous W75Si25 oxidation

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 0C for times of 10 min to 30 h. Angle resolved XPS measurements indicated that the surface region consisted of a thin layer (/similar to/16 A) of primarily SiO2 above a layer of mainly WO3 for oxidation temperatures up to 425 0C. At oxidation temperatures between 150 and 425 0C 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 0C, 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 0C. The kinetics were parabolic and displayed an Arrhenius-type temperature dependence with rates similar to W oxidation