シリコン融液におけるマランゴ二対流の不安定性と雰囲気酸素分圧効果(<小特集>微小重力環境を利用した結晶成長)

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Marangoni convection, which is one of mechanisms of heat and mass transfer during crystal growth, was investigated by using a liquid-bridge configuration under microgravity and on earth. Using microgravity is a convenient way to study Marangoni convection, because buoyancy flow can be suppressed so that only Marangoni flow can be distinguished. In the liquid-bridge configuration, which corresponds to floating-zone growth, flow instability and its three-dimensional structure were investigated through measurement of temperature-oscillation, flow visualization, optical pyrometry of the melt surface, observation of oscillation of the melt/crystal interface, and observation of surface oscillation by phase-shift interferometry. Azimuthal wave number m for instability structure depends on the aspect ratio of the bridge, T, which is defined as the ratio of height h to radius r. Marangoni flow was found to be affected by oxygen partial pressure of the ambient atmosphere, which corresponds to concentration of oxygen in Si melt. This is very important finding, because for the Czochralski growth system, oxygen dissolves into melt from a crucible wall made of SiO_2 It was also found that surface tension and its temperature coefficient strongly depend on oxygen partial pressure. Above the equilibrium oxygen partial pressure for SiO_2, where the total droplet system behaves as a liqund but the melt surface is coated with a SiO_2 film, surface stress and its temperaTokyo Institute of Technology ture coeflicient can be measured. Previously reported smalltemperature coefficients of surface tension, ∂σ/∂T<0.2×10^<-3> N・m_<-1>・K^<-1> would correspond to this unique behavior of Si melt above the equilibrium oxygen partial pressure for the SiO_2 phase, because these measurements have been carried out without taking account of the effect of oxygen partial pressure. A cellular pattern was observed at a surface of 20 cm deep Czochralski melt, whereas we found a hydrothermal wave at a surface of 8-mm-thick thin melt. Observed patterns are discussed in light of driving force of surface-tension-driven flow in the Czochralski melt.
日本結晶成長学会の論文
2002-10-05

シリコン融液におけるマランゴ二対流の不安定性と雰囲気酸素分圧効果(<小特集>微小重力環境を利用した結晶成長)

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