Diamond synthesis from vapor phase and its growth process
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1. INTRODUCTION
II. EXPERIMENTAL RESULTS
The earliest substantial work to grow diamond from gaseous phase at low pressure was presented by Eversole of Union Carbide Corp. in 19621 and independently by a Russian team of Derjaguin et al.2 This work was confirmed by Angus3 later. Recently, diamond film and particles with a well-defined crystal habit were synthesized by the Russian team with a chemical transport process in a closed system. The experimental results and the mechanism were reported principally in the Russian literature.4'5 Independently, we have shown that the diamond deposition is feasible by using the hot filament assisted CVD. The method has been extended to microwave plasma assisted CVD on the basis of the results obtained from the hot filament assisted CVD. Recently, diamond synthesis has been carried out by the modified methods of the HFACVD and various plasma techniques. Diamond synthesis has been carried out in the region where diamond is metastable. Therefore, non-diamond carbon co-deposits together with diamond. In order to continue the diamond growth, it is necessary to suppress the deposition of non-diamond carbon. The deposition process has been considered as the method that may proceed by simultaneous deposition etching processes. The most important feature of the metastable synthesis of diamond is to utilize the gas mixture that diluted the compounds containing carbon with hydrogen. The atomic hydrogen created from the hydrogen gas either by thermal energy or by electric energy has been considered as etching agent for non-diamond carbon. But the role of atomic hydrogen is not yet clear. This paper aims to elucidate the role in relation to the diamond synthesis.
A. Hot filament assisted CVD
664
http://journals.cambridge.org
J. Mater. Res., Vol. 4, No. 3, May/Jun 1989
Downloaded: 29 Mar 2015
A schematic illustration of the apparatus is shown in Fig. I.6 The main differences from the usual CVD methods are that a heated tungsten filament is set above a substrate and that a gas mixture of CH4 diluted with H2 is used. The distance between the substrate and tungsten filament is about 10 mm. The diamond growth was feasible on vari-
Tungsten filament Needle valve
I Electric furnace
I Quartz tube •Substrate
Flow meter -Thermocouple
CH 4
H2
Power source for filament
Pressure gauge
Oil pump
_L
OX) FIG. 1. Schematic drawing of hot filament assisted CVD apparatus. © 1989 Materials Research Society
IP address: 138.251.14.35
N. Setaka: Diamond synthesis from vapor phase
ous substrates: silicon, molybdenum, tungsten, various carbides, and quartz glass. The typical growth conditions that deposit diamond having well-defined habit were as follows: methane concentration (CH4/H2): < 1 vol.%; substrate temperature: 850-900 °C; total pressure: 20-40 Torr; total gas flow rate: 2H, 13.5 eV for H -» H + , and 15.4 eV for H2 -> H2+.20 In order to produce a lot of atomic hydrogen, it is necessary to accelerate the electron to 8.5 eV-13.5 eV. The above experimental results indicate that atomic hyd
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