A numerical model was developed and used to study the near-surface gas-phase chemistry during atmospheric-pressure radio-frequency (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 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, CH3, C2H2 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 1230K) but less well for lower (~1000K) and higher (~1300K) 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 H/CH3 and C2H2/CH3.
Bibliographical noteFunding Information:
This work was partially supported by the National Science Foundation (CTS-9424271), by the Engineering Research Center on Plasma-Aided Manufacturing (NSF ECD-8721545) and by the Minnesota Supercomputer Institute.
- Chemical vapor deposition
- Radio-frequency plasmas
- Thermal plasmas