Hot filament assisted diamond growth at low temperatures with oxygen addition
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Hot filament assisted diamond growth at low temperatures with oxygen addition Z. Li Tolt, L. Heatherly, and R. E. Clausing Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6093
C. S. Feigerle Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996-1600 (Received 22 April 1996; accepted 16 December 1996)
Addition of a small amount of oxygen to the CH4 and H2 feed gas permits hot filament assisted chemical vapor deposition (HFCVD) of diamond at significantly lower filament and substrate temperatures. The former can be reduced to as low as 1400 ±C and the latter to 450 ±C. The amount of oxygen required is much lower than what has been used in most studies of the oxygen effect. For each CH4 %, there is a narrow window in the OyC ratio, where diamond can be deposited at low temperature. This window shifts to higher OyC ratios as the CH4 % increases and expands with increases in filament temperature. The effect of changing substrate and filament temperatures on growth rate and film quality are often not consistent with previous experiences with HFCVD of diamond. Increasing the filament temperature does not always improve the growth rate and film quality, and the non-diamond carbon content in the film is dramatically reduced at lower substrate temperatures. Optimum conditions were found that gave reasonable growth rates (,0.5 mmyh) with high film quality at filament temperatures below 1750 ±C and substrate temperatures below 600 ±C. With these reductions in operating temperatures, power consumption can be significantly reduced and the filament lifetime extended indefinitely.
I. INTRODUCTION
It is commonly accepted that diamond deposition in a hot filament assisted chemical vapor deposition (HFCVD) reactor requires a filament temperature higher than 1900 ±C to activate the gas. Production of atomic hydrogen, along with activated growth species, is considered vital to this technology.1,2 The growth rate reaches a maximum at a substrate temperature around 950 ±C, and 700 ±C is the typical lower limit below which significant amounts of non-diamond carbon codeposits on the substrate. One exception to this is the low substrate temperature growth using unusually high filament temperatures (2300–2700 ±C).3–5 The high filament and high substrate temperatures required for HFCVD diamond film growth impose certain limitations on this technique. Diamond films can be grown only on those high temperature materials which can withstand the extreme conditions of growth. Moreover, cooling from the temperatures at which the films were grown introduces differential thermal contraction between the film and the substrate, creating substantial stress within the film. The harsh conditions present in a HFCVD reactor also produce undesirable effects on the process. The combined effects of high temperature and carburization of the filament result in frequent breaking and severe distortion of filaments, limiting their lifetime 1344
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