太陽能多晶矽晶體生長的晶粒控制及汙染改善

Abstract

現在多晶矽長晶發展所謂高效多晶矽，據有多且小的初始晶粒，重要的是晶碇缺陷生成速率低，因此多晶矽品質大幅提高，太陽能電池轉換效率提高達18%。目前高效多晶矽生長主要是藉由底部未完全熔化之矽碎料作為成核層，使矽從此成核層成核長出晶碇。然而這種生產方式有嚴重問題存在。其一為成核層在坩堝邊緣和角落處容易熔化，熱場控制困難，造成產量下降。其二為底部未溶晶種區，會造成晶碇底部汙染，紅區變大，紅區是晶碇品質低的區域必須去除，因此同樣降低了多晶矽的產量。 為解決問題目前高效多晶矽問題，吾人朝兩方向進行。第一是找出更簡單成核方法取代目前以矽碎料成核層，關於新的成核方法，本論文第一個方法是利用坩堝底部凹槽圖騰作為自身成核晶種取代目前矽碎料成核層。本論文第二個成核方法是利用矽粉混氮化矽粉塗佈層，使底部晶粒均勻成核產生小晶粒。兩種方法皆不需要控制熱場，沒有角落晶種層熔化以及未熔區晶種汙染晶碇問題。在凹槽圖騰坩堝實驗中，底部晶粒小且均勻，晶向分布平均，伴隨39.9%的non-Σ晶界。在矽粉混氮化矽粉實驗中，我們共設計三個矽粉混氮化矽粉比例，三者從縱切片和底部橫切片晶粒照皆可以清楚看到控制區具有均勻小晶粒，其中在矽粉混氮化矽粉1:1實驗中，吾人可以在晶碇底部誘導出高達51.6%的non-Σ晶界。 第二個研究方向是解決晶碇底部紅區汙染問題，晶碇污染來源主要是坩堝和塗佈層，因此吾人解決之道為利用阻障層降低來自坩堝和塗佈層的汙染，本論文作為阻障層材料有聚矽氮烷以及氧化鋇，從少數載子壽命圖能看出具有阻障層區域晶碇底部紅區變小，汙染獲得明顯改善。

In the directional solidification gowth of multicrystalline silicon, grain control was crucial to ingpt’s quality and solar cell efficiency. Recently, the development of the high performance multi-crystalline silicon based on nucleation of small and uniform grains with dominant non-coherent grain boundaries had small propogation rate of dislocation. HP-MC Si had good and more uniform quality. However, there were some serious problems in HP-Mc Si lowering the yield in the production. One is the melting of seed layer near the edges and corners and the other is the back diffusion of impurities from the contaminated seeds. In thie paper, we proposed more simple way for nucleation and used diffusion barrier layer to lower the impuritied from crucible and coating. For grian control, two methods, notch patterned crucible and silicon/silicon nitride mixed coating, were proposed. Both of them resolved the problems in HP-MC Si production. With these two methods, we can get small and uniform grains, more random orientation and high percentage of non-Σ grain boundary in the inicial stage. In this study, polysilazane and barium oxide coatings with different layer configurations were considered. With the diffusion barrier layer, the lifetime of the ingot was improved and the red zone was reduced. The wetting behaviors of these diffusion barriers in contact with silicon were also discussed.