RECYCLING OF SILICON POWDER RETRIEVED FROM DIAMOND WIRE SLICING KERF Marwan Dhamrin, Tadashi Saitoh and Koichi Kamisako Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan, Toshinori Mori and Naohisa Iwamoto, Japan Fine Steel, 1-19-1, Ishide, Sanyoonoda, Yamaguchi 756-0063, Japan
ABSTRACT: Recycling procedure to retrieve the Silicon from the diamondwire saw sludge is proposed and examined. In order to clarify the impact of common impurities in the silicon sludge. The resulting evolution curves from the TDPMS measurement indicate that most of the organic gases will have high evolution intensity at temperatures below 200 oC. However, CO and N2 have almost the same evolution all over the range of temperatures between 100 and 1000oC. Modelexperiment was performed to investigate the impact of nickel and carbon on multicrystalline ingot quality. The diffusion length distribution was normal in the nickel contaminated ingot and comparable non-contaminated ingots while the carbon contaminated ingot have poor quality if compared with non-contaminated ingots. The Total oxygen measurement was used to evaluate the oxygen contents in our swarfmaterial and the total oxygen contents were found to be below 5 %. We succeeded to melt the silicon swarf in small scale experiment and the impurity concentration was compared to the initial impurity concentrations in the silicon swarf. Keyword: Silicon Feedstock, Recycle, Diamond Wire, Sludge, Swarf
Photovoltaics became one of the most promising technologies to supplyworld-wide clean energy. The number of solar cell fabrication companies has increased massively in the recent few years leading to a strong demand of the poly silicon required for the solar cell production in which about 90 % is based on crystalline silicon ingots. These ingots are sliced using multi-wiresaw machines with steel wires of 120-150 m diameters which therefore loses at least 40 % of theingot in a powder form. Additionally, there is a strong interest toward thinner wafers with thicknesses below 160 m which will requires a thinner slicing wires or it will lead directly to more silicon waste. The poly silicon prices have increased rapidly in recent years and it would be rather hard to reach grid parity without reducing the poly silicon cost. The current slicing technologies usesloose abrasives (e.g., SiC) carried by oil or water slurry and during the slicing process, the wire moves at deferent speeds depending on slice recipe with respect to the silicon ingot surface. The abrasives in the slurry are caught between the wire and the ingot surface. The forces applied by the moving wire tension together with the slurry particles resulted in fast and nice slicing. However, inaddition to the huge thickness variation and environmental impacts of slurries and chemicals used to clean the wafer surfaces after slicing, these technologies has a big disadvantage of silicon swarf that contains fine SiC particles mixed with silicon powder and other organic coolants. Several attempts to recycle the silicon swarf retrieved from the SiC based wire saw machines. However, so farthere no highly successful attempts reported so far. The reason is the fine SiC particles size that cannot be filtered so easily nor separated by centrifuges. On the other hand, fixed abrasive diamond wire saw slicing of mono- and multicrystalline silicon ingots have a very high potential for both, using thinner wires for thinner wafer slicing and higher possibilities of recycling the silicon swarfafter diamond wire slicing due to the absence of Silicon SiC
particles. In addition, diamond wire slicing will reduces the usage of oil based slurries and wafer cleaning chemicals and will bring a new horizon for cheap silicon based solar cells. In this work, recycling procedure to retrieve the Silicon from the diamond wire saw sludge is proposed and examined.
2 GENERAL CONCEPT OF RECYCLING...
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