Epitaxical nucleation of polycrystalline silicon carbide during chemical vapor deposition
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Theodore M. Besmann, Karren L. More, and Thomas S. Moss Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (Received 17 June 1992; accepted 12 January 1993)
Polycrystalline silicon carbide was deposited from methyltrichlorosilane in cold-walled and hot-walled reactors, on (100) SiC surface layers that were formed on (100) Si wafers. The initial stages of the process were studied by electron microscopy after relatively short deposition times. Submicron surface features nucleated with a specific crystallographic orientation with respect to the substrate, where h i l l j planes in theb-SiC substrate coincided with hOOOl j planes in the a - S i C features. These a - S i C features occurred only at twins on h i l l j planes of the b - S i C substrate. This demonstrates that nucleation under these conditions is controlled by defects in the substrate. Surface contamination and the reactor configuration also had substantial effects on nucleation.
I. INTRODUCTION
II. DESCRIPTION OF EXPERIMENTS
Polycrystalline SiC produced by chemical vapor deposition (CVD) exhibits a wide range of different microstructures that have, in many cases, been empirically correlated to various processing parameters.1-2 Most of the research conducted on nucleation and growth mechanisms during CVD has focused on the epitaxical growth of single crystals, with particular emphasis on the formation of electronic materials such as Si. This previous work provides a starting point for understanding the formation of polycrystalline materials. Although the nucleation and growth of polycrystalline Si have been studied in detail,3^5 in general, the microstructure evolution of polycrystalline materials is not well understood. Because of its high strength and chemical stability at elevated temperatures, SiC produced by CVD is potentially important for protective coatings. There is also considerable interest in forming ceramic matrix composites by performing CVD in a porous structure (known as chemical vapor infiltration or CVI).6"9 Research on the deposition of polycrystalline SiC is thus primarily of interest for high-temperature coatings and structural materials. Some of the knowledge obtained may also be relevant to the formation of single-crystal SiC thin films that are currently of interest for electronic applications. The research presented here describes the CVD of SiC on SiC surfaces. This is a relatively simple system that is also the basis for related work on the development of laser light-scattering as an in situ method for monitoring nucleation and growth. Preliminary results with this optical technique are described elsewhere.10'11 1086
http://journals.cambridge.org
J. Mater. Res., Vol. 8, No. 5, May 1993
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Deposition was conducted with two different reactor configurations. Figure 1 depicts a hot-wall system, where the graphite tube surrounding the sample was heated by a radio-frequency (RF) generator operating at 455 kHz. A corresponding cold-wall configuration was also used where t
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