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

Abstract

In-situ molecular beam mass spectrometry has been used to study the eVects of nitrogen-containing gases on the gas-phase composition during microwave plasma chemical vapour deposition (CVD) of diamond. The molecular beam mass 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 plasma composition was examined for a variety of nitrogen-containing gases added to a standard 1% C:H 2 feedstock. Nitrogen was added to this mixture at a carbon-to-nitrogen ratio, C:NN1:1, in one of the following forms: N 2 ,N H 3 ,C H 3 NH 2 , or HCN. For N 2 and NH 3 , the carbon source was CH 4 , whereas CH 3 NH 2 and HCN required no added carbon. Mass spectrometer signals from hydrocarbons, nitrogen-containing species, and the methyl radical were recorded. These were calibrated to give absolute mole fractions of the main carbon- and nitrogen-containing species present at detectable levels. The content of N 2 and NH 3 in the feed was also varied while holding the CH 4 content at 1%. Results are compared with those found during hot-filament CVD. The relevance of the measured abundance of various nitrogen-containing species in the plasma to attempts to create p-type diamond is discussed. © 1999 Elsevier Science S.A. All rights reserved.