Hot-filament diamond CVD with forced convection - diagnostic and growth experiments

Diagnostic and growth experiments were performed in a multi-filament CVD reactor using forced convection for the feed gas supply in order to investigate kinetic and gas dynamic effects during diamond deposition. An insight in these effects seems to be a prerequisite for large-area deposition of diamond by hot-filament CVD. Conditions of forced convection were attained by injecting the feed gas compositions via a jet vertically to the substrate and multi- filament array into the reaction region. Under these conditions the residence time of species in the reaction zone is 1 to 2 orders of magnitude shorter than under diffusion-controlled conditions leading to a change in the kinetically controlled gas phase composition. According to kinetic modelling and mass spectrometry measurements acetylene formation can be suppressed for the benefit of methane and methyl radicals. The maximum growth rate detected at the stagnation point of the jet indicates an enhanced transport of relevant growth s pecies to the film growth front. As hot-filament CVD with forced convection also presents a simplified process where diffusion effects in the gas jet as well as heterogeneous reactions at the filaments - except from hydrogen dissociation - are suppressed, in situ growth rate measurements are discussed in terms of a kinetic model describing the temporal development of gas composition in the jet.