Measurement of Surface Tension for Molten Silicon by Electromagnetic Levitation Combined with Static Magnetic Field
- Paper number
IAC-06-A2.2.09
- Author
Mr. Noriaki Takenaga, University of Tokyo, Japan
- Coauthor
Dr. Shumpei Ozawa, University of Tokyo, Japan
- Coauthor
Prof. Taketoshi Hibiya, University of Tokyo, Japan
- Coauthor
Dr. Hidekazu Kobatake, Tohoku University, Japan
- Coauthor
Dr. Hiroyuki Fukuyama, Tohoku University, Japan
- Coauthor
Prof. Masahito Watanabe, Japan
- Coauthor
Dr. Satoshi Awaji, Tohoku University, Japan
- Year
2006
- Abstract
During silicon single crystal growth, Marangoni convection, which becomes dominant in microgravity condition, causes defects in crystals such as growth striation. This convection is originated from a difference of surface tension at the melt surface. Therefore, it is crucial to measure surface tension and its temperature coefficient accurately to control the Marangoni convection. Furthermore, the accurate value of surface tension and its temperature coefficient for molten silicon is required from the view point of optimization of the manufacturing process of silicon ingot by computer simulation. Recently the surface tension of molten silicon has been measured using the electromagnetic levitation (EML) technique; surface tension can be estimated from the oscillation frequency of the levitated droplet. In this method, the molten silicon can be kept free from container that is pollution source, and it is easy to control the atmosphere of oxygen partial pressure and to prepare the undercooled condition. However, motion of center of gravity, rotation, and convection within droplets cause errors when determining oscillation frequency. In the present investigation, the EML technique was combined with static magnetic field. It is expected that the applied static magnetic field can suppress motion of the center of gravity, rotation, and convection of droplets [1]. The objective of this study is to explore the possibility that application of the static magnetic force can improve the measurement of surface tension of molten silicon by the EML technique. Cubical silicon ingot (600mg) was levitated and melted in levitation coil with an applied magnetic field of 0.1T to 1.0T. The oxygen partial pressure around the sample was well controlled by 99.9999The oscillation and rotation of the molten silicon can be suppressed by applying magnetic field. Although the oscillation mode of m=2 can still remain, those of m=0, and 1 become inappreciable at a magnetic field of 0.5-0.8T. The estimated surface tension at a magnetic field of 0.5 – 0.8 T using the Cummings-Blackburn equation showed an agreement with that measured by the conventional sessile drop method.
[1] H. Yasuda, I. Ohnaka, Y. Ninomiya, R. Ishii, S. Fujita, K. Kishio, J. Crystal Growth 260 (2004) 475.
- Abstract document
- Manuscript document
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