Oxidation is the process of converting silicon on the wafer surface into silicon dioxide. The chemical reaction already starts at room temperature, and the resulting very thin oxide film is called native oxide. The oxidation rate can be accelerated by subjecting the wafer to oxygen or water vapor at elevated temperature. The growth rate of the thermally grown oxide depends, beside the temperature, on the pressure, the crystal orientation, the doping level and the impurity contamination of the silicon substrate as well as on the stress due to a non-planar wafer topography. The thermally grown silicon dioxide has excellent mechanical and electrical properties. It is commonly used as insulation technique between single devices, to act as gate oxide in Metal Oxide Semiconductor (MOS) structures and to serve as mask against dopant implantation. The ability of silicon to form a high quality silicon dioxide is still a crucial factor in the development of ICs.