Mechanism of submonolayer oxide formation on silicon surfaces upon thermal oxidation

We present the results of an experimental and theoretical investigation of the initial oxidation of Si(100). Oxidation kinetics were measured in real time by x-ray-photoelectron spectroscopy. In the pressure and temperature regime studied, we observed the following kinetic phenomena: a decrease of the initial oxidation rate with increasing temperature, kinetic curves (i.e., coverage vs time) showing saturation with the saturation value increase for the higher temperatures, and a transition from ``passive'' to ``active'' oxidation. To account for the experimental results a phenomenological first-order phase-transition theory was used. On comparing the experimental and theoretical results, we suggested a physical mechanism for submonolayer silicon oxide formation.