The Effect of Oxygen Partial Pressure of Ambient Atmosphere
on Mode and Velocity of Marangoni Convection
in Molten Silicon Column

T. Azami¹, S. Nakamura¹, T. Hibiya¹ and K. Mukai<sup>2

1</sup>Fundamental Research Laboratories, NEC Corporation,
34 Miyukigaoka, Tsukuba 305-8501, Japan
²Department of Materials Science and Engineering, Kyushu Institute of Technology,
1-1, Sensui-cho, Tobata-ku, Kita-Kyushu 804-8550, Japan

Crystal growth of semiconductor silicon is controlled by a heat and mass transfer process at the crystal-melt interface. The Marangoni effect at the free surface is considered to play a significant role in this process. Moreover, Niu et al. reported that surface tension and its temperature coefficient of molten silicon are sensitive to oxygen partial pressure of ambient atmosphere [1]. However, there have been few reports on these subjects. The mode of temperature oscillation of a half-zone molten silicon column 5-mm high and 5-mm in diameter changed with increasing oxygen partial pressure of ambient atmosphere: oscillation with multiple frequencies (at Po₂ = 3.5 x 10^-7 MPa) changed to that with single frequency (at Po₂ = 1.8 x 10^-5 MPa ). Also, velocity of the Marangoni flow, which was revealed by X-Ray radiography with a tracer particle under microgravity, decreased with increasing oxygen partial pressure. These experimental results can be explained by dependence of temperature coefficient of surface tension of molten silicon on oxygen partial pressure of ambient atmosphere: adsorbed oxygen atoms at the silicon melt surface significantly affect surface tension and its temperature coefficient.

[1] Z.-G. Niu, K. Mukai, Y. Shiraishi, T. Hibiya, K. Kakimoto, and M. Koyama, J. Jpn. Assoc. Crystal Growth, 24 (1997) 369.

This study was funded by a part of "Ground Research for Space Utilization" promoted by NASDA and Japan Space Forum.