Characterization of the near-surface gas-phase chemical environment in atmospheric-pressure plasma chemical vapor deposition of diamond

A numerical model was developed and used to study the near-surface gas-phase chemistry during atmospheric-pressure radiofrequency (RF) plasma diamond chemical vapor deposition (CVD). Model predictions of the mole fractions of CH4, 22 24 and 26 agree well with gas chromatograph measurements of those species over a broad range of operating conditions. The numerical model includes a two-dimensional analysis of the sampling disturbance in the thin boundary layer above the substrate, accounts for chemistry in the gas chromatography sampling line, and utilizes a reaction mechanism that is significantly revised from a previously reported version. The model is used to predict the concentrations of H, 3 22 and C at the diamond growth surface. It is suggested that methyl, acetylene and atomic carbon may all contribute significantly to film deposition during atmospheric-pressure RF plasma diamond CVD. The growth mechanism used in the model is shown to predict growth rates well at moderate substrate temperatures (~1100 to 1230 K ) but less well for lower (~1000 K) and higher (~1300 K) temperatures. The near-surface gas-phase chemical environment in atmospheric-pressure RF plasma diamond CVD is compared with several other diamond CVD environments. Compared with these other methods the thermal plasma is predicted to produce substantially higher concentration ratios at the surface of both 3 and 223 © 1999 Elsevier Science S.A. All rights reserved.