Reactive deposition activation, plasma

In reactive deposition, the reactive species can be activated in a plasma. 

In reactive deposition, bombardment aids chemical reactions on the surface and the presence of a plasma activates reactive species. The bombardment may also preferentially remove unreacted species from the growing deposit. 

These gases can be premixed but often they are mixed in the gas manifolding systems and the partial flow of each gas is measured separately. In reactive deposition, the reactive gas availability and plasma activation can be important variables that are sensitive to the fixture/ system geometry. If this is the case, the injection of gas into the system is an important design consideration (Ch. 4). Often gas manifolding with multiple inlets is used to obtain uiuform gas distribution in the deposition system. 

Auxiliary plasma (plasma technology) A plasma established in a processing system to assist in some aspect of the processing separate from the main processing event. Examples Plasma cleaning in a vacuum deposition system plasma activation of the reactive gas near the substrate in a reactive magnetron sputter deposition system. 

Plasma activation (film formation) Making gaseous species more chemically reactive in a plasma by excitation, ionization, fragmentation or by the production of new chemical species. See also Reactive deposition. 

Thermal CVD, reviewed above, relies on thermal energy to activate the reaction, and deposition temperatures are usually high. In plasma CVD, also known as plasma-enhanced CVD (PECV) or plasma-assisted CVD (PACVD), the reaction is activated by a plasma and the deposition temperature is substantially lower. Plasma CVD combines a chemical and a physical process and may be said to bridge the gap between CVD andPVD. In this respect, itis similar to PVD processes operating in a chemical environment, such as reactive sputtering (see Appendix). 

In some cases, the deposition rate can be increased by the action of a plasma in a process known as activated reactive evaporation (ARE). PI The plasma enhances the reactions and modifies the growth kinetics of the deposit. 

Reactive sputter deposition is a useful technique not only for coating but also for obtaining metastable phases, especially nitrides. Nitrogen gas is activated in a plasma to enhance nitride formation and heating at high temperature is not required. It is possible to obtain metastable nitrides by sputter deposition in which species in the plasma are quenched on substrates. Compounds with different crystal structures normally do not form solid solutions, but by co-sputter deposition metastable solid solutions may form. 

Plasma-enhanced chemical vapour deposition has gained importance rapidly in recent years, because this technique provides some unique advantages over conventional CVD. The important advantages include lower deposition temperatures, deposition of non-epuilibrium phases and a better control of stoichiometry and purity of deposits. In this technique, the activation energy for the breakdown of reactive species, and their subsequent interaction with other species to form a deposit, is provided by the high kinetic energy of electrons in the plasma (figure 13.2). 

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