Atomic and radical densities in a hot filament diamond deposition system

The gas phase densities of atomic carbon, atomic hydrogen, and methyl radicals are measured in a hot filament diamond deposition system by the use of absorption spectroscopy in the vacuum ultraviolet. The ratio of atomic to molecular hydrogen is also determined using the measured C and CH3 densities and the equilibrium constant for the hydrogen abstraction and recombination reactions that link the C and CH3 densities. The flux of C to the diamond surface is inadequate to explain the total growth rate, though C could have an important role in initiating growth. A model indicates that the hydrogen is dissociated at the filament and diffuses quickly throughout the rest of the system; gas phase reactions only have a small effect on the degree of dissociation. An increased input CH4 mole fraction results in lower hydrogen dissociation by poisoning the catalytic properties of the filament. (C) 1996 American Institute of Physics.