Gas-phase composition measurements during chlorine assisted chemical vapor deposition of diamond: A molecular beam mass spectrometric study

Abstract

We have constructed a molecular beam mass spectrometer designed specifically to sample gases from a diamond chemical vapor deposition (CVD) process chamber thereby enabling characterization of the gas-phase CVD environment. With this in situ diagnostic technique we have obtained quantitative measurements of the composition of the gas-phase species as a function of filament temperature for a variety of C/H/Cl gas mixtures. The precursor mixtures used were 1% of a chloromethane (CH4−nCln, n=1-4) in hydrogen and 1% CH4 in hydrogen with added Cl2 varying from 1% to 4%. At filament temperatures optimum for diamond growth (∼2300°C) the relative CH4/C2H2/C2H4 product distribution measured in the gas mixture is remarkably similar to that established when CH4 is the carbon precursor species. At these filament temperatures almost all the chlorine is reduced to HCl, its concentration being proportional to the Cl fraction in the source gas, regardless of the form of the chlorine in the source gas mixture. Compositional 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. From these observations we surmise that chlorine atoms are involved in the gas-surface reactions which produce active growth sites on the diamond surface.