Diamond CVD by microwave plasmas in argon-diluted methane without or with 2% hydrogen additive

Many research groups have reported that when methane was diluted by argon for microwave plasma-enhanced chemical vapor deposition (CVD) of diamond, growth of large-grain microcrystalline diamond (MCD) was suppressed, while nanocrystalline diamond (NCD) was deposited. We report for the first time the growth of well-faceted MCD by microwave plasma CVD in argon-diluted methane without molecular hydrogen additive or with only little (2%) hydrogen additive. High-density C₂ radicals generated in the plasmas might be responsible for both the promotion of secondary nucleation of diamond for the growth of NCD in atomic hydrogen deficient environments and the promotion of the growth of large-grain diamond at the presence of adequate atomic hydrogen leading to the deposition of MCD. A nonuniform plasma ball was applied to grow both MCD and MCD simultaneous on the same silicon substrate in the same gas mixture.