The ability of silicon to form a silicon dioxide layer is one of the key factors in silicon technology. Silicon dioxide (SiO2) is one silicon atom and two oxygen atoms. This is the chemical composition of ordinary window glass, but the form of SiO2 used for semiconductors is much more pure. Layers of SiO2 are grown into a bare silicon surface. This process is called thermal oxidation.

Silicon wafers enter the diffusion furnace and are exposed to oxygen gas. The oxygen atoms combine with silicon atoms during what is called the linear stage. After a layer of 500 Angstroms is grown, the oxygen is no longer in direct contact with the silicon surface. At this point the oxide vapor migrates through the already existing layer of oxide until it reaches silicon and the layer keeps growing.

There are two primary methods to grow oxide onto a wafer, dry and wet oxide. Dry oxide is the preferred method for layers less than 1000 Angstroms thick.

Thermal oxide is a “building block” film used to make both simple and complex semiconductors. It is a good dielectric or insulating film when grown onto high quality silicon wafers.