Diamond synthesis in supersonic direct-current arcjet plasma at subtorr pressures

Abstract

A new approach to diamond thin film synthesis is presented. A supersonic, direct-current (d.c.) arcjet designed for expansion into low pressures (approximately 1 Torr), operating on mixtures of methane (0.5–25%) in hydrogen and argon, was employed to produce diamond films on silicon and molybdenum substrates. At subtorr pressures, free molecular flow conditions are approached, resulting in strongly reduced boundary layer effects. Large area coatings (up to 20 cm 2) due to the wide expansion of the plasma plume were obtained. The high molecular velocity, on the order of 10 km s −1 at the arcjet exit, and the high activation energies by the thermal plasma provide a high reactive species flux, both of the above giving rise to relatively high diamond growth rates (1–20 μm h −1, despite the lower pressures. Results of parametric studies of diamond growth over ranges of substrate temperatures and reactant mixture ratios show good agreement with commonly observed trends in other vapor deposition systems.