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-phas e chemistry during atmospheric-pressure radiofrequency (RF) plasma diamond chemical vapor deposition (CVD). Model predictions of the mole fractions of CH4, C2H2, C2H4 and C2H6 agree well with gas chromatograph measurements of those species over a broad range of operating conditions. The numerical mo del 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 sig nificantly revised from a previously reported version. The model is used to predict the concentrations of H, CH3, C2H2 and C at the diamond growth sur face. It is suggested that methyl, acetylene and atomic carbon may all cont ribute significantly to film deposition during atmospheric-pressure RF plas ma diamond CVD. The growth mechanism used in the model is shown to predict growth rates well at moderate substrate temperatures (similar to 1100 to 12 30 K)but less well for lower (similar to 1000 K) and higher (similar to 130 0 K) temperatures. The near-surface gas-phase chemical environment in atmos pheric-pressure RF plasma diamond CVD is compared with several other diamon d CVD environments. Compared with these other methods the thermal plasma is predicted to produce substantially higher concentration ratios at the surf ace of both H/CH3 and C2H2/CH3. (C) 1999 Elsevier Science S.A. All rights r eserved.