Chemical vapor deposition (CVD) is a chemical process that uses a chamber of reactive gas to synthesize high-purity, high-performance solid materials, such as electronics components. Certain components of integrated circuits require electronics made from the materials polysilicon, silicon dioxide, and silicon nitride. An example of a chemical vapor deposition process is the synthesis of polycrystalline silicon from silane (SiH4), using this reaction:
SiH4 -> Si + 2H2
In the silane reaction, the medium would either be pure silane gas, or silane with 70-80% nitrogen. Using a temperature between 600 and 650 °C (1100 - 1200 °F), and pressure between 25 and 150 Pa — less than a thousandth of an atmosphere — pure silicon can be deposited at a rate of between 10 and 20 nm per minute, perfect for many circuit board components, whose thickness is measured in microns. In general, temperatures inside a chemical vapor temperature deposition machine are high, while pressures are very low. The lowest pressures, under 10−6 pascals, are called ultrahigh vacuum. This is different than the use of the term "ultrahigh vacuum" in other fields, where it usually refers to a pressure below 10−7 pascals instead.
Some products of chemical vapor deposition include silicon, carbon fiber, carbon nanofibers, filaments, carbon nanotubes, silicon dioxide, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, and diamond. Mass-producing materials using chemical vapor deposition can get very expensive due to the power requirements of the process, which partially accounts for the extremely high cost (hundreds of millions of dollars) of semiconductor factories. Chemical vapor deposition reactions often leave byproducts, which must be removed by a continuous gas flow.
There are several main classification schemes for chemical vapor deposition processes. These include classification by the pressure (atmospheric, low-pressure, or ultrahigh high vacuum), characteristics of the vapor (aerosol or direct liquid injection), or plasma processing type (microwave plasma-assisted deposition, plasma-enhanced deposition, remote plasma-enhanced deposition).
By Michael Anissimov