Reactive Species

Molecular Species. Typically gaseous reactive species are in the molecular form (i.e., N2, O2, H2, etc.). The molecular species is less chemically reactive than the atomic species of the gas.

Activated Reactive Species. The gaseous reactive species can be "activated" to make them more chemically reactive and/or more readily adsorbed on surfaces (Ref 13). The reactivity of the species can be increased by adding internal energy to form "excited species," by fragmenting the species to form uncharged "radicals," such as O, N, or F, by forming ions, which are charged species such as O+, N+, or N+, or by forming a new volatile reactive species, such as ozone (O3) from O2 + O or Si2H6 from SiH^ Activation is most often done in a direct current, radio frequency, or microwave plasma, in a plasma arc, or by radiation adsorption (e.g., "photoexcitation") from a source such as a mercury vapor lamp or an excimer laser. Such activation is done in reactive sputter deposition, reactive ion plating, PECVD, and activated reactive evaporation. Activation of the gaseous species can also be done using other means, such as the hot filament decomposition of NH4, F2, and H2.

A plasma provides a very complicated chemical environment that can give reactive deposition processes that are not normally expected. For example, the sputter deposition of gold on oxide surfaces in an oxygen-containing plasma gives rise to very adherent gold films. It has been shown that the deposition of gold in an oxygen plasma gives rise to Au-O bonding. This may be due to the formation of activated oxygen species in the plasma or the formation of a more readily adsorbed reactive species (i.e., O3) (Ref 41, 42).

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