Diffusion of Oxygen in Silicon Thermal Oxides

A method for comparing the oxidation rates of silicon under an initial 1000Å of thermal oxides is described. Ellipsometry is used to measure the thicknesses of a pair of samples before and after a relatively short time of additional oxide growth in dry oxygen. Excluding the known orientation effect, a large variation in growth rate at a given temperature is noted. The rate is directly related to the index of refraction of the initial oxide. As this index is known to depnd upon the initial growth temperature, the apparent oxygen diffusion "activation energy" must include this newly documented temperature factor. Parabolic and linear rate constants are presented and are compared with literature values. This study gives further evidence that silicon thermal oxides are metastable structures.