Si + O2 → SiO2
Or a "wet" oxidation process:
Si + 2H2O → SiO2 + 2H2
Dry oxidations are typically performed at 900°C - 1200°C at high oxygen pressures. Dry oxidations exhibit the lowest oxide growth rate of the thermal oxidation processes used in semiconductor device manufacture, typically around 14 - 25 nm/hr. Because of this, dry oxidation processes are normally used only for processes that require silicon dioxide film thicknesses of less than 100 nm. Dry oxidation processes tend to produce silicon dioxide films with the highest quality electrical and material characteristics. "Wet" oxidations can be performed using either entrained water or in situ generated steam produced by the reaction of hydrogen and water:
2H2 + O2 . 2H2O + Si → SiO2 + 2H2
Historically, wet oxidation was used in the LOCOS (LOCal Oxidation of Silicon) process for the production of electrically isolating "field oxide" in older device designs. The use of TEOS oxides and new flowable CVD films has largely supplanted this process in advanced device fabrication.
Silicon dioxide has been, arguably, the most important material of the different thin films employed for semiconductor device fabrication for more than a half century. Indeed, the fact that silicon forms a stable and adherent oxide with good electrical properties is probably the reason why. As a consequence, many studies are available in the literature that deal with the growth and characterization of thermal silicon dioxide thin films and the interested reader is referred to these works and references contained therein for an in-depth understanding of such aspects as the oxide growth mechanism and interface characteristics. Practically, thermal silicon oxides can be grown using a variety of equipment configurations and the best approach depends on the particular device requirements. In this section we will describe those equipment configurations that would most likely be encountered in the semiconductor fab.
Steam oxidation using a vertical batch furnace proceeds similar to dry oxidations but uses pyrogenic steam as the oxidizing gas. Pyrogenic steam is generated outside of the furnace in a quartz chamber where hydrogen and oxygen are combusted and the product steam is fed to the process tube.
While MKS does not directly produce thermal processing equipment for the semiconductor industry, we act as an OEM supplier for producers of thermal processing products.