Experimental measurements and numerical simulations of the gas composition in a hot-filament-assisted diamond chemical-vapor-deposition reactor

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Abstract
Molecular‐beam mass spectroscopy was used to measure the gas composition near a growing diamondsurface in a hot‐filament‐assisted chemical‐vapor‐deposition reactor. The dependencies of the gas composition on changes in (1) the carbon mole fraction in the reactor feed X C, (2) the identity of the inlet carbon source (CH4 versus C2H2), and (3) the surface temperature T S , were studied. For X C≤0.02, the gas composition appeared to be nearly independent of the identity of the inlet hydrocarbon source and depended only on the C/H ratio in the feed gas. At higher values of X C, catalytic poisoning of the hot filament resulted in different product distributions in these two systems. Increasing the surface temperature affected changes in the hydrocarbon composition; the dependencies of the CH3 and C2H2 mole fractions on T S can each be characterized as having an activation energy of 3±1 kcal/mol. Surprisingly, the H‐atom mole fraction was independent of T S . These results suggest that reported temperature sensitivities of film growth properties are primarily due to changes in the kinetics of surface processes rather than changes in the gas composition near the surface. A numerical model of the process is presented. In the study of the compositional change as a function of X C, the code gives good prediction for the methane case but grossly underestimates the methane and methyl concentrations for the acetylene case. The H‐atom mole fraction is predicted to increase by ×7 if the H destruction probability on the diamondsurface is expected to have an activation energy of 7.3 kcal/mol. Good agreement with experimental data can be obtained, however, if H loss by lateral transport to the walls is taken into account.