AN RF PLASMA-JET APPLIED TO DIAMOND, GLASSY-CARBON AND SILICON-CARBIDE FILM SYNTHESIS

An r.f.-generated plasma jet (RPJ) has been used for thin film growth. A hydrogen-methane plasma jet stream, supersonically supplied from a graphite nozzle, produced carbon films on heated (800-900-degrees-C) silicon and graphite substrates. The gas pressure in the reactor was 4-90 Torr. The film growth rate and the properties of the films depend strongly on the CH4-to-H-2 mass flow ratio and the gas pressure. At 4 Torr and a CH4-to-H-2 ratio of about 0.1 the maximum growth rate may exceed 1 mm h-1. At such high deposition rates, however, glassy carbon deposition dominates over diamond film growth. For CH4-to-H-2 ratios of 0.03 or less diamond films were grown in a limited peripheral area on the graphite substrate. Under identical processing conditions the jet stream produced SiC films on Si substrates. The process is controlled by plasma chemical etching of both the graphite nozzle and the substrate surface by the hydrogen content in the plasma jet. At gas pressures above 15 Torr, diamond films may be grown on silicon substrates at rates greater than 1 mum h-1. At pressures above 50 Torr, diamond film growth was found also in the central substrate area.