Transport phenomena in the scale-up of hot filament-assisted chemical vapor deposition of diamond

Heat transfer and fluid flow in a diamond deposition reactor were examined to identify parameters important to reactor design and scale-up. Physical and mathematical modeling of hot filament-assisted diamond deposition reactors indicated that both ordinary and thermal diffusion are equally important in the transport of nutrient species to the substrate surface. The atomic hydrogen concentration field in the reactor is established mainly by diffusive mixing of the atomic hydrogen with molecular hydrogen and other species in the gas phase. Homogeneous chemical reactions in the gas phase do not significantly affect the atomic hydrogen concentration profiles. In hot filament reactors, in addition to convection, conduction and radiation, filament-to-substrate heat transfer takes place by dissociation of molecular hydrogen at or near the filament and recombination of atomic hydrogen at the substrate surface Computer simulation of the heat transfer and fluid flow in a typical hot filament reactor for diamond deposition indicated that system geometry, filament temperature and pressure are important parameters in the design of reactors for coating large areas. The investigation clearly indicates considerable promise of science-based design and scale-up of hot filament reactors for diamond deposition.