EFFECT OF OXYGEN ON FILAMENT ACTIVITY IN DIAMOND CHEMICAL VAPOR-DEPOSITION

Previous studies that have focused on the interactions of CH4/H2 and C2H2/H2 mixtures with the hot W filaments used for diamond chemical vapor deposition have been extended in order to determine the effect of oxygen on filament activity. The behavior of W filaments has now been studied up to 2300-degrees-C in mixtures of 3% CH4/H2, with 0.5, 1.0, and 1.5% O2, at a pressure of 25 Torr. The effects of the addition of O2 on filament resistance, emissivity, and power conumption, as well as on the partial pressures of the gases (CH4, C2H2, O2, CO, and H2O) in the reaction chamber, have been determined. The significant improvements in filament activity that are observed are shown to be due to removal of carbon from the filament surface by formation of CO. These results can be understood on the basis of our quasi-equilibrium thermodynamic model for the C-H-O system.