Chemical vapor deposition

Chemical vapor deposition (CVD) is a chemical process used to produce high quality, high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.

Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon (SiO₂, germanium, carbide, nitride, oxynitride), carbon (fiber, nanofibers, nanotubes, diamond and graphene), fluorocarbons, filaments, tungsten, titanium nitride and various high-k dielectrics.

Types

CVD is practiced in a variety of formats. These processes generally differ in the means by which chemical reactions are initiated.

Cryogenics

In physics, cryogenics is the study of the production and behaviour of materials at very low temperatures.

It is not well-defined at what point on the temperature scale refrigeration ends and cryogenics begins, but scientists assume it starts at or below −150 °C (123 K; −238 °F). The National Institute of Standards and Technology has chosen to consider the field of cryogenics as that involving temperatures below −180 °C or −292.00 °F or 93.15 K. This is a logical dividing line, since the normal boiling points of the so-called permanent gases (such as helium, hydrogen, neon, nitrogen, oxygen, and normal air) lie below −180 °C while the Freon refrigerants, hydrogen sulfide, and other common refrigerants have boiling points above −180 °C. (above −150 °C, −238 °F or 123 K).

A person who studies elements that have been subjected to extremely cold temperatures is called a cryogenicist.

Cryogenicists use the Kelvin or Rankine temperature scales.

Definitions and distinctions

Etymology

The word cryogenics stems from Greek kρύο (cryo) – "cold" + genic – "having to do with production".