Use of Liquid Precursors for Diamond Chemical Vapor Deposition--The Effects of Mass Transport and Oxygen

Thermal plasma chemical vapor deposition of diamond-utilizing liquidfeedstock injection has been shown to yield higher mass deposition rates,larger crystal size, and thicker films when compared to the use of gaseousfeedstock for equivalent operating conditions. Increased mass transport ofthe activated precursor species across the substrate diffusion boundarylayer and the presence of oxygen in liquid precursors are investigated aspotential reasons for the observed results. Comparisons of the variousprecursor systems investigated in this study are based on crystal size andfilm thickness as a function of radial postion, area of deposit, totalmass deposition rate, and the observed liquid precursor droplet trajectorieswithin the deposition chamber using a laser strobe video system. The resultsindicate that the mass transport in both the liquid and gaseous precursorsystems is greatly improved by the use of an inert carrier gas. Further, theuse of a liquid versus a gaseous precursor does not seem toresult in higher total deposition rates when the operating conditions forboth have been optimized. Finally, the presence of oxygen in the liquidfeedstock system is found to be at least partly responsible for theincreased growth rate, which is observed when comparing the plainhydrocarbon precursor cases with the oxygenated liquid precursorcase.