Rs. Tsang et al., GAS-PHASE CONCENTRATION MEASUREMENTS AND DIAMOND FILM COMPOSITION FROM CHLORINE ASSISTED CVD, DIAMOND AND RELATED MATERIALS, 5(3-5), 1996, pp. 359-365
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.