Plasma-Surface Interactions in Plasma-Enhanced Chemical Vapor Deposition

Abstract

The promotion of chemical reactions by glow discharges (plasmas) has been practiced for many years (I, 2). Recent interest has focussed on the use of radio frequency (rf ) glow discharges to form thin films of insulators, semiconductors, and conductors in the fabrication of electrical and optical devices. For example, numerous organic polymers (3-5) and inorganic elemental and compound materials (6-12) have been deposited by plasma­ enhanced chemical vapor deposition (PECVD). This technique takes advantage of the high energy electrons present in glow discharges to dissociate and ionize gaseous molecules, thereby forming chemically active radicals and ions. Since thermal energy is not needed to break chemical bonds, a variety of film materials can be formed on temperature-sensitive substrates (e.g. polymers or low melting point metals). The plasma environment in PECVD performs two basic functions. First, reactive chemical species are generated by electron impact collisions, thereby overcoming kinetic limitations that may exist in CVD processes. Second, the discharge supplies energetic radiation, primarily positive ions, but also neutral and metastable species, electrons, and photons, that bombard surfaces immersed in the plasma and thereby alter surface chemistry. Specifically, ion bombardment of growing film surfaces plays