Molecular beam mass spectrometry studies of nitrogen additions to the gas phase during microwave-plasma-assisted chemical vapour deposition of diamond

In-situ molecular beam mass spectrometry has been used to study the effects of nitrogen-containing gases on the gas-phase composition during microwave plasma chemical vapour deposition (CVD) of diamond. The molecular beam mas s spectrometer used in this work extracts gas directly from the plasma bulk via a small sampling orifice inserted into the side of the plasma. The pla sma composition was examined for a variety of nitrogen-containing gases add ed to a standard 1% C:H-2 feedstock. Nitrogen was added to this mixture at a carbon-to-nitrogen ratio, C:N=1:1, in one of the following forms: N-2, NH 3, CH3NH2, or HCN. For N-2 and NH3, the carbon source was CH4, whereas CH3N H2 and HCN required no added carbon. Mass spectrometer signals from hydroca rbons, nitrogen-containing species, and the methyl radical were recorded. T hese were calibrated to give absolute mole fractions of the main carbon- an d nitrogen-containing species present at detectable levels. The content of N-2 and NH3 in the feed was also varied while holding the CH4 content at 1% . Results are compared with those found during hot-filament CVD. The releva nce of the measured abundance of various nitrogen-containing species in the plasma to attempts to create p-type diamond is discussed. (C) 1999 Elsevie r Science S.A. All rights reserved.