Thermal oxidation is a way to produce a thin layer of oxide (usually silicon dioxide) on the surface of a wafer (semiconductor). The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. The rate of oxide growth is often predicted by the Deal-Grove model Thermal oxidation may be applied to different materials, but this article will only consider oxidation of silicon substrates to produce silicon dioxide.

http://en.wikipedia.org/wiki/Thermal_oxidation