In ICs, silicon dioxide is used for several purposes, ranging from serving as a mask
against dopant introduction into silicon to serving as the most critical component in
the metal-oxide-semiconductor transistor, the subject of Chapters 5–7.
SiO2 layers of precisely controlled thickness are produced during IC
fabrication by reacting Si with either oxygen gas or water vapor at an elevated
temperature. In either case the oxidizing species diffuses through the existing oxide
and reacts at the Si–SiO2 interface to form more SiO2. The relevant overall
reactions are