Compaction and Cold Crucible Induction Melting of Fine Poly Silicon Powders for Economical Production of Polycrystalline
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Compaction and Cold Crucible Induction Melting of Fine Poly Silicon Powders for Economical Production of Polycrystalline Silicon Ingot Daesuk Kim1, Jesik Shin2, Byungmoon Moon2, and Kiyoung Kim1 1 Material engineering, Korea University of Technology and Education, Byung-cheon, Cheon-an, 330-708, Korea, Republic of 2 Korea Institute of Industrial Technology, Songdodong7-47, In-cheon, 406-800, Korea, Republic of ABSTRACT The consolidation and casting processes of fine silicon powders, by-product of high purity silicon rods making process in the current method, were systematically investigated for use as economical solar-grade feedstock. Morphology, size, and contamination type of the fine silicon powders were inspected by combined analysis of SEM, particle size analyzer, and FT-IR. Silicon powder compacts were tried to fabricate by a consolidation process without a binding agent and then their density ratio and strength were evaluated. Finally, the electrical resistivity of the specimens prepared by an electromagnetic casting method was examined for purity assessment. INTRODUCTION The annual world photovoltaic (PV) market entered the age of GW, in a rapid expansion with the average annual growth rate of 35% since the middle 1990s. The strongly growing PV market is based on crystalline silicon technology. More than 90% of the annual solar cell production is made of crystalline silicon wafers. The issues which the PV industry is currently facing are the cost reduction and the shortage of solar grade silicon due to strongly increasing demand; Around 70% of the production cost of solar module comes from silicon wafers, and the shortage of silicon supply is limiting the growth of the worldwide PV-industry based on silicon [1,2]. Most of the existing facilities for high purity silicon production are using the established Siemens process, as shown in figure 1. In the conventional Siemens process, purified trichlorosilane (TCS; SiHCl3) gas is reduced by hydrogen and deposited on silicon or tantalum rods. But, this technology provides highly pure but very expensive silicon due to low deposition yield into silicon rods. Therefore, in this study, the consolidation and casting processes of the low-priced silicon powders, by-product of high purity silicon making process in the current method, were systematically investigated to economically produce a multi-crystalline silicon wafer for solar cell. The characteristics of the silicon powders were inspected by combined analysis of SEM, particle size analyzer, and FT-IR. Silicon powder compacts were tried to fabricate by a consolidation process without binding agents. Also, the melting experiment and electrical resistivity examination were carried out for purity assessment.
Figure 1. Schematic of a conventional Siemens process for high purity silicon production. EXPERIMENTAL Morphology, size, and contamination type of the fine silicon powders were inspected by combined analysis of SEM, particle size analyzer, and FT-IR. In order to form the silicon powders into a disc w
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