Gas-phase concentration measurements and diamond film composition from chlorine assisted CVD

Abstract

Molecular beam mass spectrometry has been used to obtain quantitative measurements of the composition of the gas-phase species prevailing during diamond chemical vapour deposition (CVD) using a variety of chlorine containing source gases. Gas mixtures used were 1% of a chlorinated methane (CH4 −n,Cln,n = 1 − 4) in H2 and 1% CH4 in H2 with added chlorine varying from 1%–4%. At filament temperatures optimum for diamond growth (≈2300 °C) the relative concentrations of the various hydrocarbon species (CH4, C2H2, C2H4) in the gas mixture are remarkably similar to those measured when the carbon precursor species is CH4. At these filament temperatures almost all the chlorine is reduced to HCl, its concentration being proportional to the chlorine fraction in the source gas, regardless of the form of the chlorine in the input mixture. Auger electron spectroscopy analysis of the as-grown diamond films indicated that no chlorine was present in the bulk of the films, though trace amounts of chlorine were detected on the film surface. These observations are consistent with the supposition that chlorine atoms are involved in the gas-surface reactions which produce active growth sites on the diamond surface.