多晶矽定向固化數值模擬之熱流場與雜質分佈

Abstract

多晶矽太陽能電池目前仍是市佔率最高的太陽能電池。太陽能電池發電為達到市電平價（grid parity）的目標，必須提升晶片品質並降低生產成本。在多晶矽晶片中常見高濃度的碳與氧成分，會造成差排與熱施體，碳與氧是主要影響晶錠品質的雜質。 本研究以有限體積法（FVM）模擬定向固化系統（DSS）爐體內熱流場、氧雜質、碳雜質、磷雜質與硼雜質濃度場等。而且模擬預估碳與氧雜質濃度，與長晶業者提供實驗量測多晶矽晶錠內的碳與氧雜質濃度相當一致。模擬結果顯示熔湯對流主要由浮力所造成，隨著生長過程對流形態會改變。修改熱場爐體長成晶片製作之太陽能電池，其效率較原設計爐體所製成太陽能電池效率提昇1.8%。 本研究將針對熱流場與雜質濃度場進行分析與探討，並比較初始濃度、邊界條件、偏析效應與雜質擴散係數四者交互作用影響下，最終雜質的分佈結果，最後探討如何讓最終各項雜質分佈狀況更均勻，更趨近於實際的狀況。

Manufactures of multi-crystalline silicon ingots by means of the directional solidification system (DSS) is important to the solar photovoltaic (PV) cell industry. The quality of the ingots is highly related to the shape of the crystal-melt interface and the distributions of dopants during the crystal growth process. We performed numerical simulations to thoroughly analyze the transient thermo-fluid field and its effects to the shape evolution of the crystal-melt interface as well as the transportation of dopants, including oxygen, carbon, boron and phosphorous in transient processes. In addition, the transportation of dopants also is affected by segregation effect. Accuracy of the results is supported by comparing the evolutions of crystal heights with the benchmark experimental measurements. The excellent agreements demonstrate the applicability of the present numerical methods in capturing the key features for a practical and complex system of directional solidification system.