Thermal Oxide or SiO2 is one of the “building block” films used in making both simple and complex semiconductor devices. If grown correctly using a high purity, low defect silicon substrate, it can be an excellent dielectric (insulating) thin film. It is normally found on a device as “field oxide” electrically isolating polysilicon, metal, or other conductive thin film(s) from the silicon substrate or “bulk” of the device. It is also found on the device as a “gate oxide”.
Silicon wafers are oxidized in furnaces ranging from 800°C to 1050°C. The furnaces consist of a quartz tube in which the wafers are placed on a carrier made of quartz glass. The quartz glass has a very high melting point (above 1500°C) providing a stable carrier for high temperature processes. To prevent cracks and/or warping, the quartz tube is heated slowly (e.g. +10°C per minute). Individual heating zones provide optimal tempering throughout the tube.