In manufacturing microelectronic and optoelectronic devices, thin solid films of various sorts are routinely deposited and etched using low pressure, weakly ionized plasmas. The term “plasma” in this context implies an ionized gas with nearly equal numbers of positive and negative charges. This definition is not very restrictive, so. there are an enormous number of phenomena that are termed plasmas. For example, very hot, magnetized, fully ionized plasmas exist in stellar environments and thermonuclear fusion experiments. High temperature electric arcs are a form of plasma as well. In contrast, the plasmas used in electronic materials processing are near room temperature and the gas is usually weakly ionized. Indeed, due to the sensitivity of electronic devices to high temperatures, their low operating temperature is one of the major advantages of plasma processes.Plasma processing is attractive because of two important physiochemical effects: energetic free electrons in the plasma (heated by applied electric fields) dissociate the neutral gas in the plasma to create chemically reactive species; and free positive ions are accelerated by the plasma electric fields to surfaces bounding the plasma. Reactive species created in the plasma diffuse to surfaces and adsorb; wafers to be processed are typically placed on one of these surfaces.The combination of neutral species adsorption and positive ion bombardment results in surface chemical reaction. If the products of the surface reaction are volatile, they leave the surface and etching results. If the products are involatile, a surface film grows.
Application of weakly ionized plasmas for materials sampling and analysis
