M. Asmann et al., Use of liquid precursors for diamond chemical vapor deposition - The effects of mass transport and oxygen, PLASMA CHEM, 20(2), 2000, pp. 209-224
Thermal plasma chemical vapor deposition of diamond-utilizing liquid feedst
ock injection has been shown to yield higher mass deposition rates, larger
crystal size, and thicker films when compared to the use of gaseous feedsto
ck for equivalent operating conditions. Increased mass transport of the act
ivated precursor species across the substrate diffusion boundary layer and
the presence of oxygen in liquid precursors are investigated as potential r
easons for the observed results. Comparisons of the various precursor syste
ms investigated in this study are based on crystal size and film thickness
as a function of radial postion, area of deposit, total mass deposition rat
e, and the observed liquid precursor droplet trajectories within the deposi
tion chamber using a laser strobe video system. The results indicate that t
he mass transport in both the liquid and gaseous precursor systems is great
ly improved by the use of an inert carrier gas. Further, the use of a liqui
d versus a gaseous precursor does not seem to result in higher total deposi
tion rates when the operating conditions for both have been optimized. Fina
lly, the presence of oxygen in the liquid feedstock system is found to be a
t least partly responsible for the increased growth rate, which is observed
when comparing the plain hydrocarbon precursor cases with the oxygenated l
iquid precursor case.