Hot-Zone Design and Analysis of Highly Efficient Czochralski Silicon Growth for Photovolatic Application
|關鍵字:||柴式法;缺陷;界面;質傳;矽;輻射;熱傳;電腦模擬;heat trans;computer simulation;silicon;Czochralski||公開日期:||2004||摘要:||本篇論文展示數種柴式法生長太陽能矽晶棒的熱場設計與分析，並在中美矽晶公司的Kayex CG6000機台做生長實驗。結果發現在沒有犧牲晶體品質的前提下，長晶時所使用的必v以及氬氣使用量明顯地降低，而晶體拉速卻可以大幅地增加。值得注意的是，經由適當的熱場設計，晶體的氧含量大為降低，造成載子壽命增長。氧的軸向濃度分佈不均，也藉由模擬與實驗的結果發現，可以將石英坩堝的轉速設定成隨著時間逐漸增快的方式加以改進。
本論文的主要工作就是進行熱場設計和電腦模擬，實驗部分則是由中美矽晶進行驗證。這些熱場設計包含了輻射熱帷幕（鉬材質、在石墨上鍍其他材質或是複合式材質）、額外側保溫(碳纖材質)、底保溫(石墨或碳纖材質)和上保溫(碳纖材質)。本論文針對各熱場元件對能耗、界面凹陷、坩堝和加熱器溫度分別模擬分析。新式熱場設計的實驗也由中美矽晶完成。電腦模擬結果與實驗量測數據在使用必v以及靠近加熱器的參考溫度，十分吻合。目前經由實驗所獲得的結果，整體所使用的必v由原先實驗的59.1kWh/kg下降至17.4kWh/kg；拉速由0.8mm/min提升至1.32mm/min；釋氧量由原設備的平均約17ppma，最低可以降低至6.3ppma；氬氣使用量更是由93.3c.f./kg大幅地降低至27.1c.f./kg；長晶爐內部的石墨元件的衰退速度明顯降低；而其界面凹陷由模擬結果可知，仍維持在原有的凹陷範圍之內。由生產力、成本以及晶棒品質而言，已經超越Siemens Solar Industries(簡稱SSI)的水平。
Several hot-zone designs are presented for Czocharlski silicon growth for photovoltaic applications. Without sacrificing the crystal quality, a significant reduction of power and argon consumption was achieved, while the pulling rate was significantly increased. More importantly, the oxygen content was greatly reduced leading to longer minority lifetime of the wafers. According to the results of experiments and simulations, the variation of the axial oxygen distribution could be improved by gradually increasing the crucible rotation speed during the growth.. The major works of the thesis were hot-zone design and computer simulation. The experiments to prove the results of the designs were carried out by SAS. The design reported here included the radiation shield (molybdenum, graphite with different coatings, and composite cone) additional side and bottom insulations (graphite and graphite-felt), and upper side insulation. This thesis made simulations on the power consumption, interface concavity, the crucible and the heater temperature. Then, the growth experiments with the new hot-zone design were carried by SAS. Good agreement was found in the power consumption and a reference temperature near the heater between computer modeling and experimental measurements. The best hot zone design so far has let to a power consumption reduced from 59.1 kWh/kg to 17.4 kWh/kg, the pulling rate was increased from 0.8 mm/min to 1.32 mm/min, the average oxygen content was decreased from 17 ppma to 6.3 ppma, the consumption of argon was also reduced from 93.3 c.f../kg to 27.1 c.f./kg, the degradation rate of the graphite elements was greatly reduced, while, the interface concavity was still remained the same. According to the comparison of productivity, cost, and quality, our design has overtaken that by Siemens Solar Inustries(SSI).
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