Enhanced Diamond Film Growth by Hot-Filament CVD Using Forced Convection

Diamond film growth in hot filment CVD can be enhanced by applying forced convection. This method facilitates an increase of deposition rates up to about 5 μm/h. In the presented HFCVD system growth rates reach a maximum of about 3.3 μm/h at gas velocities of about 1000 m/s and diminish rapidly for higher velocities. Measurements of atomic hydrogen generation by determination of electrical power consumption by the filaments in hydrogen and helium show that this effect is not caused by a kinetic limitation of H generation at the filaments. The generation of H is an approximately linear function of gas velocity and filament diameter for the considered gas velocity range. Measured H generation rates were used as input for a simple one-dimensional model developed to describe the transport of atomic hydrogen and methyl, the assumed main diamond growth species, to the substrate. The calculations show a kinetic limitation of methyl concentration in the vicinity of the substrate surface due to too high convective transport velocities and can qualitatively explain the observed growth rate minimum.