Reactive Deposition

Reactive deposition is the formation of a film of a compound, either by codeposition and reaction of the constituents or by the reaction of a deposited species with the ambient gaseous environment. If the reacting species form a volatile compound, etching results. If the reaction results in a nonvolatile species, a compound film is formed (Ref 40).

Codeposition of reactive species does not necessarily mean that they will chemically react to form a compound. For example, a mixture of titanium and carbon may not have any TiC, or it may be partially TiC and the rest an unreacted mixture of titanium and carbon, substoichiometric TiCi_x, or TiC with excess titanium or carbon, each of which will have different properties. Generally, for low-temperature deposition, the best situation for reactive deposition is where one of the reacting species is condensable and the other is gaseous (e.g., titanium plus nitrogen). If both are condensable (e.g., titanium plus carbon), the best deposition condition is to have a high substrate temperature to promote reaction or use postdeposition heat treatment to promote reaction. Reactively deposited films of oxides and nitrides are commonly used in the optics, electronics, decorative, and mechanical applications, with TiN being one of the more common film materials.

There are a number of techniques for performing reactive atomistic film deposition. The simplest way is to thermally evaporate the material in a partial pressure of a reactive gas in the process called reactive evaporation (see the article "Vacuum Deposition, Reactive Evaporation, and Gas Evaporation" in this Volume). This generally gives poor-quality films because the materials are not completely reacted and the high gas pressures necessary for reaction result in gas phase collision and vapor phase nucleation, giving a low-density deposit. Better-quality films are obtained by promoting the chemical reaction by some means, such as activating the reactive gas or using concurrent energetic particle bombardment to promote the chemical reaction (Ref 13).

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