The silicon etching that occurs during the CVD diamond growth has been
investigated as a function of the methane content in the gas phase by
SEM and AFM in the tapping mode on pristine Si(lll) surfaces. Size, d
epth, and angular distributions of the etch pits were recorded. We evi
dence the strong effect of the carbon content on the etching process.
The silicon etching is slightly increased with addition of 0.1-0.25% o
f methane in the feed gas, and depletes with larger addition of carbon
. This etching occurs easily along Si(100) directions. This is explain
ed by the better stability on (100) planes of the precursor SiH2 to re
move silane than on (111) planes. A modelization of the process points
out the balance between the drop of the atomic hydrogen concentration
in the gas phase and the inhibition of hydrogen bulk diffusion into s
ilicon when increasing the methane content and covering the surface wi
th carbon. This explains the occurrence of a maximum of silicon etchin
g. Possible consequences on the diamond nucleation process are then pu
t forward. It is thus expected that the etching of the silicon is gene
rally detrimental as generating low-density silicon surface such as Si
(100) where diamond nucleation is inhibited.