Effect of Nitrous Oxide Gas on Cvd Diamond Film Deposition
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EFFECT OF NITROUS OXIDE GAS ON CVD DIAMOND FILM DEPOSITION T. SAWAOKA, A. B. Y. TAKAGI, YOSHIMOTO, KOINUMA, HAHT*, T M. AA** * and T. SHIRAISHI T. NAGAI Research Laboratory of Engineering Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 227 Japan Department of Industrial Chemistry, Faculty of Engineering, Tokyo University, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113 Japan ** Department of Communications, Faculty of Engineering, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa, 259-12 Japan H.
HASHIMOTO
ABSTRACT The addition of nitrous oxide (N 2 0) gas in the hot-filament chemical vapor deposition of carbon film from mixtures of methane and hydrogen was found to increase remarkably the content of diamond structure in the film. Increased particle size and crystal orientation parallel to the (111) direction were also obtained by the N20 addition. Mass spectrometry revealed that the vapor phase reaction was scarcely affected by the N2 0 addition.
INTRODUCTION Diamond film preparation from the gas phase has been achieved by various chemical vapor depositions using rf plasma[1], microwave plasma[2l, dc arc[3] and hot filament[4]. Among them, hot-filament CVD is a simple and low cost prc---s and can be a practically useful method if the formation of adiamond phase could be accelerated and purified by a catalytic effect of additives. Kawato and Kondo reported that the addition of oxygen to a mixture of methane and hydrogen was effective for increasing the diamond phase fraction in the film, although significant amount of amorphous phase still remained[5]. In this study, the effect of nitrous oxide gas (N 2 0) addition was examined in the hot-filament CVD of carbon films from mixtures of methane and hydrogen. The oxygen radical which could be easily generated by the decomposition of N2 0 was presumed to be more effective than molecular oxygen for the production of diamond phase. N2 0 has the N-O bond dissociation energy (197.6kJ/mol) lower than the 0-0 bond dissociation energy (490.4kJ/mol) of molecular oxygen. An attempt was made to investigate the gas phase reaction by mass spectroscopy. EXPERIMENTAL Figure
1
shows
the schematic
diagram
of
hot-filament
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
CVD
862
. f ' Diffusion pump Figure 1 Schematic diagram of hot-filament CVD apparatus.
1700
1600 1500 1400 1300 Wave Number (cm-1)
1200
Figure 2 Raman spectra of the films prepared at various N2 0/CH4 ratios.
apparatus used in this study.
Typically, a mixture of 1.5sccm of methane and 50sccm of hydrogen was introduced to the chamber. The molar ration of N2 0 to CH4 was varied from 0 to 10%. The temperature of tungsten filament was kept at 2300 C, as measured by a two-color band-type pyrometer (Chino Works, Ltd.,
IR-AQ model). The substrate, Si(lll), was placed -2mm below the filament and heated at 750 0 C. The reaction was carried out at 100 Torr for 4 hours. The gas phase species between the substrate and filament can be introduced into a quadrupole mass s
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