3.3 Thermal Oxidation of Silicon
The oxide of silicon, or silicon dioxide (SiO2), is one of the most important ingredients in integrated circuits. Thermal SiO2 is amorphous. It has a density of 2.2 gm/cm3 and molecular Density of 2.3x1022 molecules/cm3 . The crystalline SiO2 is also possible and known as Quartz has a density of 2.65 gm/cm3. SiO2 has excellent properties which makes them necessary in every part of the integrated circuits. It is an excellent electrical insulator having energy gap ~ 9 eV with a resistivity greater than 1020 ohm-cm and breakdown electric field greater than 10MV/cm. Si technology became popular because of the stable and reproducible Si/SiO2 interface. Conformal oxide growth on exposed Si surface is easily possible. SiO2 is a good diffusion mask for common dopants such as. B, P, As, Sb. In addition there exists good etching selectivity between Si and SiO2.
The formation of SiO2 on a silicon surface is most often accomplished through a process called thermal oxidation. As its name implies, is a technique that uses extremely high temperatures (usually between 700-1200°C) to promote the growth rate of oxide layers whose thicknesses range from 20 to 10000 nm. During the process, silicon substrate is exposed to a high purity oxidizing species like oxygen gas (dry oxidation) or water vapour (wet oxidation).