Chemical vapor deposition
In chemical vapor deposition the thin film is formed from one or more gas phase components. Either a compound decomposes to form the film or a reactions between gas components as takes place on form, Invariably the CVD reactions are surface catalyzed, preferentially taking place on the surface of wafers inserted into the gas stream. In-use CVD processes fall into one of three general categories. They are atmospheric pressure ( APCVD or simply CVD ). low-pressure (LPCVD). and plasma-enhanced (PECVD) pro-cesses. Atmospheric pressure depositions can be performed in relatively simple systems. Low-pressure often offers comparable kinetics with improved uniformity and less gas consumption. In plasma CVD the electrons in the plasma impart energy to the reaction gases,thereby enhancing the reactions and permitting very low deposition temperatures.
CVD reactors come in a variety of shapes and configurations; an example configuration employed in AP/LPCVD depositions is pictured in Fig. 4.14. CVD processing is routinely used to produce the masking and intermetallic films required in the formation of complex ICs. Polyerystalline Si. which functions as a pseudo-metal when heavily doped. is also deposited employing atmospheric and low-pressure CVD.APCVD. LPCVD. and PECVD are all typically used at some point in an IC process flow