Chemical vapor deposition

Chemical Vapor Deposition (CVD) is a chemical process for depositing thin films of various materials. In a typical CVD process the 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 byproducts are also produced, which are removed by gas flow through the reaction chamber.

CVD is widely used in the semiconductor industry, as part of the semiconductor device fabrication process, to deposit various films including: polycrystalline, nanocrystalline, amorphous, and epitaxial[?] silicon, SiO₂, silicon germanium[?], tungsten, silicon nitride[?], silicon oxynitride[?], titanium nitride[?], and various high-k dielectrics.

A number of forms of CVD are in wide use and are frequently referenced in the literature. Some of these forms include:

• Metal-Organic CVD (MOCVD) - CVD processes based on metal-organic precursors, such as tantalum ethoxide[?], Ta(OC₂H₅)₅,to create Ta₂O₅ , Tetra Dimethyl amino Titanium (or TDMAT) to create TiN[?].

• Plasma Enhanced CVD (PECVD) - CVD processes that utilize a plasma to enhance chemical reaction rates of the precursors. PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semicondutors with lower melting points than silicon substrates. PECVD has allowed electronic circuits to be deposited on glasses as well as flexible plastic substrates with melting temperatures below 150 °C, ushering in a new age of flexible electronics.

• Electron Cyclotron Resonance PECVD (ECR-PECVD) - Used for depositing amorphous silicon, but mostly for oxide or nitride[?] dielectrics. This is best method of depositing silicon oxides, much better than PECVD. This is a remote technique, which means that the ions and radicals do not actually bombard the substrate, as opposed to standard PECVD.

• Rapid Thermal CVD (RTCVD) - CVD processes that use heating lamps or other methods to rapidly heat the wafer substrate. Heating only the substrate rather than the gas or chamber walls helps reduce unwanted gas phase reactions that can lead to particle formation.

• Atmospheric Pressure CVD (APCVD) - CVD processes at atmospheric pressure.

• Low Pressure CVD (LPCVD) - CVD processes at subatmospheric pressures. Reduced pressures tend to reduce unwanted gas phase reactions and improve film uniformity across the wafer. Most modern CVD process are either LPCVD or UHVCVD.

• Ultra-High Vacuum CVD (UHVCVD) - CVD processes at very low pressures, typically in the range of a few to a hundred millitorr.

• Atomic Layer CVD (ALCVD) - A CVD process in which two complementary precursors (eg. Al(CH₃)₃ and H₂O) are alternatively introduced into the reaction chamber. Typically, one of the precursors will adsorb onto the substrate surface, but cannot completely decompose without the second precursor. The precursor adsorbs until it saturates the surface and further growth cannot occur until the second precursor is introduced. Thus the film thickness is controlled by the number of precursor cycles rather than the deposition time as is the case for conventional CVD processes. In theory ALCVD allows for extremely precise control of film thickness and uniformity.