生長多晶矽之熱流場與雜質傳輸控制數值分析;Investigation of thermal-fluid and impurity concentration distributions for growing multicrystalline Silicon

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题名:	生長多晶矽之熱流場與雜質傳輸控制數值分析;Investigation of thermal-fluid and impurity concentration distributions for growing multicrystalline Silicon
作者:	黃柏翔;Huang,Bo-siang
贡献者:	機械工程研究所
关键词:	數值模擬;多晶矽;導流裝置;multicrystalline silicon (mc-Si);numerical simulation;gas guidance device
日期:	2012-07-18
上传时间:	2012-09-11 18:17:17 (UTC+8)
出版者:	國立中央大學
摘要:	直接固化法(DS)生長多晶矽常被用於光電產業。多晶矽太陽能電池的品質與晶碇內的雜質濃度有高度的相關性。在本研究中，採用數值模擬多晶矽固化生長之暫態熱流場生長過程，來探討導流板的安裝位置在固化過程對氧濃度與碳濃度的影響。導流板裝置會影響氣體與熔湯的流動型態，並且影響熔湯內氧雜質與碳雜質的分佈情形。晶碇固化時隨著固化分率增加，熔湯與坩堝接觸面積減少，使熔湯內氧濃度降低。結果顯示將導流板裝置到自由液面的距離降低導可減少熔湯內氧濃度但卻增加熔湯內碳濃度。導流板高度分別為2.7cm、5.5cm、8.3cm、11cm、13.8cm。晶碇內氧濃度於導流板高度2.7cm時會有最低的氧濃度結果，與導流板高度13.8cm相比可降低氧濃度約30%。晶碇內碳濃度隨著導流板高度降低而逐漸降低，但當導流板高度從5.5cm降低到2.7cm後，晶碇內碳濃度反而增加。因此，導流板的最佳安裝高度為5.5cm，可得到降低晶碇內氧雜質與碳雜質的結果。Directional solidification (DS) method is frequently used to produce the mc-Si ingots in the PV wafer industrial. The efficiency of an mc-Si solar cell depends strongly on the impurity content and level of the mc-Si wafers. In this study, numerical simulation of the transient temperature, velocity and concentration of oxygen and carbon and silicon carbide has been carried out in order to clarify the influence of gas shield on impurity transport of oxygen, carbon and silicon carbide in a directional solidification system furnace during the growth process. The installation of such a gas flow guidance device changes the gas and melt flow pattern in the furnace, which would affect the transport of carbon oxide and silicon oxide in the gas and oxygen and carbon in the melt. As the solidification fraction enlarges, the oxygen concentration in the melt decreases, because of the reduction in the amount of crucible surface immersed below the silicon melt. Results show that a decrease of the relative position of gas shield and gas-melt interface reduces the oxygen concentration in the melt but enlarges the carbon impurity. The distance between gas guidance device and free surface are presented using 2.7cm, 5.5cm, 8.3cm, 11cm, 13.8cm. The distance with 2.7cm can reduce oxygen concentration about 30% and show the minimum oxygen concentration in the ingot. Carbon concentration decreases with reducing height in the ingot, but carbon concentration increases when the height of gas shield changes from 5.5cm to 2.7cm. Thus, the optimum position to install the gas flow guidance device for obtaining the best carbon and oxygen levels in the ingot during the solidification process is 5.5cm.
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