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MATERIALS RESEARCH

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In situ mass spectrometry during diamond chemical vapor deposition using a low pressure flat flame C. A. Wolden,a) R. F. Davis, and Z. Sitar Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7919

J. T. Prater Army Research Office, Research Triangle Park, North Carolina 27709-2211 (Received 27 September 1996; accepted 6 March 1997)

A combination of experiments and detailed kinetic modeling was used to investigate diamond deposition chemistry in low pressure combustion synthesis. Microprobe sampling was employed to provide in situ, quantitative measurements of the stable gas-phase species impinging the growth surface. The reactant gas ratio was found to be the most critical experimental variable. A detailed kinetic model was developed for the stagnation flow system. Comparison of experimental measurements showed very good agreement with model predictions. The model was then used to predict the concentration of radical species and analyze the sensitivity of predictions to g H , the probability of atomic hydrogen recombination on the surface. It was shown that g H dramatically affects the distribution of radical species near the diamond surface. The analysis also indicates that atomic carbon may be an important gas-phase precursor in this system. Comparison of mole fraction measurements and observations of film morphology were used to draw conclusions on the growth mechanism.

I. INTRODUCTION

A number of researchers1–6 have experimentally demonstrated high rate diamond synthesis using premixed flat flames. Large area uniformity has been demonstrated in both atmospheric1,2 and reduced pressure systems.3–5 Recently, we demonstrated that growth morphology can be controlled in this system, allowing the production of high quality k100l textured films.6 The stagnation-flow reactor is scaleable,2 and at reduced pressures the flames are very stable and require minimal thermal management.3–6 The stagnation flow geometry may be accurately described using a one-dimensional similarity solution,7 permitting the development of detailed chemical kinetic models. Despite their advantages, there is little or no diagnostic information available from these systems. In this paper we report on the use of in situ mass spectrometry to provide quantitative measurements of the gas species impinging the substrate. Mass spectroscopy has been used to provide insight into the chemistry of many diamond chemical vapor deposition (CVD) systems. Hsu8,9 has used molecular beam mass spectrometry (MBMS) to measure stable and radical species in both hot-filament and microwave CVD a)

Present address: Department of Chemical Engineering, Colorado School of Mines, Golden, Colorado 80401. e-mail: cwolden@ mines.edu J. Mater. Res., Vol. 12, No. 10, Oct 1997

http://journals.cambridge.org

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systems. Microprobe sampling has been used to measure stable species in a conventional oxy-acetylene torch,10 a plasma jet,11 and a hot-filame