Copper forms three silicides which are stable at room temperature, with compositions of Cu5Si, Cu15Si4, and Cu3Si. The sequence of formation of these phases in Cu-Si bilayers is described. Cu3Si is always the first phase formed by annealing to 200 CC, and is the stable phase on bulk Si. We show that Cu3Si has a dramatic effect on the oxidation of (100) silicon. While thermal oxidation of Si is normally carried out at temperatures above 700 °C, the process described here produces a thick layer of SiO2at room temperature. The SiO2 layer grows spontaneously to over one micrometer in thickness in several weeks in air, beneath most of the original Cu3Si layer. Analysis by Rutherford backscattering, Auger electron spectroscopy, cross-sectional transmission electron microscopy, and scanning electron microscopy reveals the presence of Cu3Si particles at the buried SiO2/Si interface. These Cu3Si particles catalyze the room temperature oxidation of silicon. © 1991, American Vacuum Society. All rights reserved.