The chemical reactions describing the thermal oxidation of silicon in oxygen or water vapor are given by the following equations:


Si(solid) + O2 SiO2 (solid) -------------------DRY OXIDATION

Si(solid) + 2H2O SiO2(solid) +2H2 -----------WET OXIDATION


For growth of an oxide of thickness d, a layer of silicon with thickness of 0.44d is consumed. Oxidation proceeds by the diffusion of the oxidizing species through the oxide to the Si-SiO2 interface, where the oxidation reaction occurs.


When bare silicon is exposed to the atmosphere, it reacts almost immediately with oxygen or moisture present in the air and forms a thin (about 10 to 20A) layer of silicon dioxide, called the native oxide. The thickness of the native oxide is sufficient to stop further oxidation of the silicon at room temperature. [1]


Fig. 1 Silicon Oxidation Process [2]


Uses of silicon dioxide