Molecular beam mass spectrometry studies of the gas-phase chemistry occurring during microwave plasma assisted chemical vapour deposition of diamond

A molecular beam mass spectrometer has been used for in-situ studies of the gas-phase composition during microwave plasma chemical vapour deposition o f diamond, in a way that decouples the gas-phase reactions from those occur ring near the substrate surface. The system has been used to examine the plasma composition for a variety of hydrocarbon precursor-in-H, feedstock gas mixtures. Stable hydrocarbon spe cies, and the methyl radical signal, were recorded and calibrated to give m ole fractions of all the carbon-containing species present at detectable le vels. The plasma composition has been studied with varying chemical vapour deposition process parameters such as applied microwave power, and concentr ation of hydrocarbon in the feed gas. Molecular beam mass spectrometry has also been used to determine the plasma gas temperature, yielding results in good agreement with non-invasive methods. (C) 1999 Elsevier Science S.A. A ll rights reserved.