GAS-PHASE CONCENTRATION MEASUREMENTS AND DIAMOND FILM COMPOSITION FROM CHLORINE ASSISTED CVD

Molecular beam mass spectrometry has been used to obtain quantitative measurements of the composition of the gas-phase species prevailing du ring diamond chemical vapour deposition (CVD) using a variety of chlor ine containing source gases. Gas mixtures used were 1% of a chlorinate d methane (CH4-nCln, n=1-4) in H-2 and 1% CH4 in H-2 with added chlori ne varying from 1%-4%. At filament temperatures optimum for diamond gr owth (approximate to 2300 degrees C) the relative concentrations of th e various hydrocarbon species (CH4, C2H2, C2H4) in the gas mixture are remarkably similar to those measured when the carbon precursor specie s is CH4. At these filament temperatures almost all the chlorine is re duced to HCl, its concentration being proportional to the chlorine fra ction in the source gas, regardless of the form of the chlorine in the input mixture. Auger electron spectroscopy analysis of the as-grown d iamond films indicated that no chlorine was present in the bulk of the films, though trace amounts of chlorine were detected on the film sur face. These observations are consistent with the supposition that chlo rine atoms are involved in the gas-surface reactions which produce act ive growth sites on the diamond surface.