2.5 Oxidation

Silicon dioxide is widely used as an insulator in integrated circuits: as gate oxide in MOS transistors, as field oxide between devices, as mask against dopant implantation (padding oxide) as well as insulator between the interconnection wires (note that here it is chemically vapor deposited).

In the oxidation process, oxygen or $H_2O$ molecules are used to convert silicon on the surface of the wafer in silicon dioxide. Although this reaction exists at room temperatures, the oxidation rate is increased at elevated temperatures. Other factors that influence the oxidation rate are the pressure inside the furnace and silicon properties (as doping levels, contamination, ...). Thermal oxide has also good mechanical properties and a good sticking coefficient with the underlying silicon, making it one of the most important materials in integrated circuits.