Homoepitaxial Growth Rate Studies on Diamond (110), (111), and (100) Surfaces in a Hot-Filament Reactor
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HOMOEPITAXIAL GROWTH RATE STUDIES ON DIAMOND (110), (111), AND (100) SURFACES IN A HOT-FILAMENT REACTOR C. JUDITH CHU*, BENJAMIN J. BAI, NORMA J. KOMPLIN, DONALD E. PATTERSON* MARK P. D'EVELYN, ROBERT H. HAUGE, AND JOHN L. MARGRAVE* Rice University, Department of Chemistry, P. 0. Box 1892, Houston, TX 77251 *also affiliated with Houston Advanced Research Center, 4802 Research Forest Dr., The Woodlands, TX 77381 ABSTRACT 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 order for 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/mole 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/mole for the three crystal-orientations studied.
Introduction It is well known in the chemical vapor deposition of polycrystalline diamond films that the final film morphology is very sensitive to growth conditions such as substrate temperature and methane concentration. There have been reports of changes in the crystal faces from (11) to (100) as well as from (100) to (111) with increasing substrate temperature. 1- 3 With increasing methane concentration, the morphology changes from predominantly (111) at low concentrations, to cubo-octahedron ((111) and (100)), to predominantly (100) at high concentrations (3-6% CH4). 1-2,4-6 Clearly a detailed study of the growth kinetics is needed. Due to the complexity of polycrystalline diamond growth, and the fact that the modeling of diamond growth has all been performed on single faces of diamond such as (110),7 (111),8- 10 and (100),1 1-12 a study of the growth kinetics of homoepitaxial (100), (111), and (110) diamond films is therefore warranted. We have previously reported the growth of homoepitaxial (111), (100), and (110) diamond films in our hot filament reactor in identifying the precursor for diamond growth. 13 ,1 4 We now present the results of our growth rate studies on (110), (111), and (100) diamonds. Experimental The hot-filament chemic
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