Equal amounts of carbon-12 methyl halides and carbon-13 methane, along with hydrogen, have been introduced into a hot-filament diamond CVD chamber. The isotopic ratios of the as-deposited diamond films on tantalum have been measured by Raman spectroscopy. It was found that methyl chloride yielded carbon-12 enriched diamond films, while the other methyl halides resulted in equal amounts of carbon-13 and carbon-12 in the films. Furthermore, the carbon-12 enrichment was more enhanced as the substrate temperature was lowered. Matrix-isolation FTIR analyses of the gas samples collected during the deposition indicated that there was no straightforward agreement between the 12C/13C ratios of the gas phase species, methane and acetylene, and that of the diamond films. The results imply the presence of a new chlorocarbon radical such as CH2Cl, which is postulated as a more effective growth species than the methyl radical.

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Prepared for publication in Materials Research Society Symposium ProceedingsRice University Department of Chemistry Houston, TX 77251-1892 92-18875 May29,1992Reproduction, in whole or in part, is permitted for any purpose of the United States Government.This document has been approved for public release and sale; its distribution is unlimited. Y2 7Form Approved REPORT DOCUMENTATION PAGE Approved for public release; distribution is unlimited. ABSTRACT (Maximum 200 words)Growth rates of homoepitaxial (110), (111), and (100) diamond films were experimentally determined, for the first time, in a hot filament reactor using methane and carbon tetrachloride as the carbon source. Methane concentrations from 0.07% to 1.03% in H2 were studied at a substrate temperature of 970 C. Growth rates were found to be crystal-face dependent with respect to methane concentration, being linear or first orderfor the (100) orientation, sublinear for (110), and sigmoidal for (111). The observed growth kinetics of (111) suggest the viability of an acetylene mechanism for (111), along with the methyl radical mechanism at methane concentrations above 0.73%. CC14 concentrations from 0.06% to 0.69% in H2 were also investigated at a substrate temperature of 970 C. Growth rate behavior was similar to that of methane for all three crystal faces. The temperature dependence of the growth rates was also crystal-orientation dependent At substrate temperatures above 730 "C, growth rates are thought to be mainly transport limited, yielding effective activation energies of 8±3, 18±2, and 12±4 kcal/mol for (100), (110), and (111) orientations, respectively. At substrate temperatures below 730 "C, growth rates are thought to be surface reaction rate-limited, with an overall effective activation energy of 50±19 kcal/mol for the three crystal-orientations studied.14. (110), (111), and (100) diamond films were experimentally determined, for the first time, in a hot filament reactor using methane and carbon tetrachloride as the carbon source. Methane concentrations from 0.07% to 1.03 % in H2 were studied at a substrate temperature of 970 0 C. Growth rates were found to be crystal-face dependent with respect to methane concentration, being linear or first order for the (100)-orientation, sublinear for (110), and sigmoidal for (11). The observed growth kinetics of (111) suggest the viability of an acetylene mechanism for (111), along with the methyl radical mechanism at methane concentrations above 0.73%. CC14 concentrations from 0.06% to 0.69% in H2 were also investigated at a substrate temperature of 970 0 C. Growth rate behavior was similar to that of methane for all three crystal faces.The temperature dependence of the growth rates was also crystal-orientation dependent. At substrate temperatures above 730°C, growth rates are thought to be mainly transport limited, yielding effective activation energies of 8.3, 18±2, and 12±4 kcal/mole for (100), (110), and (111) orientations, respectively. At substrate temperatures below 730*C, growth rates are thought ...

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The incorporation of methane into low-pressure CVD diamond thin films has been compared to that of acetylene. 13CH4 and 12C2 H2 were used as the hydrocarbon sources in a heated-filament CVD diamond growth process at a total concentration of 0.5% hydrocarbon in 99.5% hydrogen. Results indicated that methane and/or methyl radical is the dominant carbon source for diamond growth in a hot filament reactor under steady state conditions and that acetylene is rapidly hydrogenated to methane. Results also indicated that diamond surface reactions play an important role in determining the relative methane to acetylene ratios.