Yoshitaka Mitsuda and Kenji Kobayashi

Institute of Industrial Science, The University of Tokyo
7-22-1 Roppongi, Minato-ku, Tokyo 106-8558, JAPAN
mitsuda@cc.iis.u-tokyo.ac.jp

Diamond films were generally deposited by CVD method from a hydrocarbon as a carbon source diluted with an amount of hydrogen [1,2]. Therefore, it was believed that the high density of atomic hydrogen could be present in the CVD circumstances, in evidence of the strong emission spectra of H atom Balmer series detected during the deposition. Atomic hydrogen might play an important role to inhibit the growth of graphitic carbon and/or to keep sp3 surface structure on the growth interface, making diamond growth possible [3,4]. Very recent studies, however, reveal that diamond can be deposited in Ar based plasma with a small portion of oxygen, such as Ar-10%CH4-4%O2 [5]. Therefore, in this paper, we have investigated the effect of diluent gas on diamond growth in order to clarify the deposition mechanism, especially the role of hydrogen.

Diamond particles were deposited on the (100) silicon substrates in the plasma generated by conventional MW plasma CVD equipment. Raman scattering spectroscopy and SEM characterized the crystal structure and the morphology of obtained samples, respectively.

Diamond was successfully grown in plasma with H2, Ar, or He as a diluent, which was demonstrated by Raman peak of 1333 cm-1. The parameters range of deposition for single phase of diamond, however, was dependent on diluent gas. This range was extensively narrow in case of rare gas based plasma, and was only at 6%O2, 600 ºC for He, at 4%O2, 750 ºC for Ar, compared with the wide range for H2. The deposition rates and the activation energies of total deposition reaction were equivalent for using any plasma. The activation energy was estimated to be around 59 kJ/mol. These facts said that the atomic hydrogen density could be sufficient for diamond growth using any diluent gas if needed. Moreover, the atomic hydrogen was originated by the dissociation from CH4, not from H2.

The parameters range of deposition for single phase of diamond was expanded by the addition of a small amount of hydrogen into Ar-CH4-O2 plasma. During the deposition in (Ar/H2)-CH4-O2 plasma, the emission intensity of Hb line was almost constant in spite of H2 or O2 concentration. Therefore, it was doubtful that the high population of H could be needed for diamond formation, although it was generally believed.

1. M. Kamo, Y. Sato, S. Matsumoto and N. Setaka, J. Cryst. Growth., 62 (1983) 642.
2. Y. Saito, K. Sato, K. Gomi and H. Miyadera, J. Mater. Sci., 25 (1990) 1246.
3. B. V. Spitsyn, L. L. Bouilov and B. V. Derjaguin, J. Cryst. Growth, 52 (1981) 219.
4. J. A. Mucha, D. L. Flamm and D. E. Ibbotson, J. Appl. Phys., 65 (1989) 3448.
5. K. Sobue, Y. Mitsuda, N. Masuko and H. Imai, Hyomen Gijyutsu, 45 (1994) 1126 (in Japanese).