使用單向固化法生長1.6噸級太陽能多晶矽晶碇之數值模擬分析;Numerical Simulation Analysis of 1.6 ton Solar Multicrystalline Silicon Ingots by Directional Solidification Process

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Title:	使用單向固化法生長1.6噸級太陽能多晶矽晶碇之數值模擬分析;Numerical Simulation Analysis of 1.6 ton Solar Multicrystalline Silicon Ingots by Directional Solidification Process
Authors:	侯致中;Hou, Zhi-Zhong
Contributors:	機械工程學系
Keywords:	單向固化法;多晶矽晶碇;熱應力;界面形狀;暫態數值模擬;Directional Solidification System;Multi-crystalline silicon;Thermal stress;Interface shape;Transient numerical simulation
Date:	2017-08-22
Issue Date:	2017-10-27 16:20:52 (UTC+8)
Publisher:	國立中央大學
Abstract:	單向固化系統法(Directional Solidification System，簡稱DSS)為目前生長大尺寸多晶矽的主要生產方式，其優勢為成本低、製造過程簡單、品質佳及晶碇尺寸大等優點。而目前由美國設備商GT advanced technologies所開發之第八代機台(Generation 8，簡稱G8)，已成功的進入噸級晶碇的生產，然而單以加大爐體以生產更大尺寸的矽晶仍有其需要面對的挑戰。長晶過程與晶碇的品質有極大的關係，為了得到更好的晶碇品質，針對界面形狀、雜質、差排密度及熱應力等指標進行優化，其中加熱器功率比是影響長晶動力的關鍵之一。藉由調控不同的加熱器功率比，控制上及側加熱器之功率，並且在不同固化分率之下，會有不同的影響。在固化初期時，使用較大功率之上加熱器可提高長率，而在固化末期時則會抑制長率，當我們能得到理想的界面形狀，就能夠有效控制缺陷的產生。另外，熱應力的問題也是影響品質的關鍵之一。在固化過程中，絕緣籠會向上提升進行取熱，由於G8的爐體較大，爐體內部具有相當大的熱能，為了使大量的熱能夠散失，設備商設計了較大的絕緣籠開度，以維持固化過程中的長晶動能。然而當絕緣籠在開始固化的瞬間開度過大時，晶碇內的熱應力也會隨之變大，而這在設備商所交給中美矽晶G8爐體及製程參數所做的實驗中，正好也應證了這個問題。為了解決熱應力之問題，在絕緣籠的開度上必須重新設計，以達到更好的製程良率。除了熱應力之問題外，改善晶碇品質也是很重要的一環，要兼顧長率與熱應力，使兩者之間取得平衡。 ;Directional Solidification System (DSS) is the main method for growing the large-sized multi-crystalline silicon. The advantages of this method are lower production cost, simple manufacturing process, good quality and large crystal size. At present, the eighth generation (G8) furnace, developed by the US equipment maker GT advanced technologies, has been used to grow crystal with 1600 kg silicon feedstock capacity. However, enlarging the furnace to grow the large-sized ingot with the high quality still faces to some challenges In order to improve crystal quality measured by the crystal-melt interface shape, impurities, dislocation density and thermal stress, the furnace geometry and crystal growth conditions should be optimized. The heating power ratio defined as the power on the top heater to the side one is one of key parameters affecting crystal quality and energy saving. By adjusting the heating power ratio, the power between top and side heater can be controlled. Different heating power ratios will cause different effects on the solidification process. The growth rate is increased at the early stages and reduced at the end of the solidification process when heating power on the top heater is higher than the side one. As a result, the crystal-melt interface will be modified and hence, the formation of defects can be controlled. In addition, thermal stress is one of the factors affecting the crystal quality significantly. During the solidification process, the side insulation of furnace will be lifted up to take heat out. For large furnace, it is difficult to release heat quickly. Hence, higher raising velocity of the side insulation is designed to maintain the kinetic energy of solidification process. However, when the side insulation is upwardly moved too fast at the early stages, the thermal stress of silicon ingot will get larger. This agrees with the experimental growth of G8 provided by Sino-American silicon Products (SAS). In sum, the opening of the insulation cage should be re-designed to obtain the lower thermal stress and a better process yield. Besides the improvement of crystal quality, shortening the growth time is also a very important part in this study.
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