熱退火對太陽能多晶矽影響之研究

Effect of Thermal Annealing On Multicrystalline Silicon For Photovoltaic Applications

費致傑(Chih-Chieh Fei)

指導教授 ： 藍崇文

國立臺灣大學/工學院/化學工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.10330

摘要

本論文提供一個簡便的方式減少影響多晶矽太陽能電池轉換效率的差排。隨著退火溫度與時間的增加，差排密度的下降比例也隨之上昇，直接利用接近0.95Tm的高溫將晶片在氬氣的氣氛中進行六小時的退火，差排密度最高可以得到約97.5%的下降比例。實驗結果指出，溫度與時間為退火程序中兩樣最重要的操作參數。差排消除的機制不單由滑移模式主導，其消除的過程是屬於退火中的回復過程，因此差排的移動也有使用攀移與交滑移。在進行完高溫退火後，亦觀察到晶片內部，原在長晶過程中析出的鐵沉澱物因高溫而溶解形成Fei，因而導致少數載子壽命的下降。而在添加磷擴散去疵的手續後，雖然具有減少Fei的效果，但並沒有辦法完全的移除因退火而溶解出來的金屬雜質。而最後利用內部聚集去疵法雖能夠讓因退火溶解出的Fei重新聚集，但是因為操作溫度僅能讓移動速度較快的鐵聚集，晶片的少數載子壽命也因為難以聚集的低移動性金屬而無法提升。

關鍵字

多晶矽 ； 差排密度 ； 退火 ； 少數載子壽命

並列摘要

We propose and demonstrate an easy method to remove dislocation limited solar cell performance in multicrystalline silicon solar material. Over 97.5% dislocation density reduction was achieved after annealing at 1350℃ for 6 hours with controlled ambient. The results show that reduction increases with increasing annealing temperature and time. According to the experiment results, the time and temperature factors are the two most important parameters for annealing processes. The mechanism of dislocation reduction is based on pair-wise annihilation which has been categorized as a mechanism of recovery. Moreover, it is evident that the rate limited step is not governed only by thermal activated glide but also by two other modes, cross slip and climb. Lifetime of minority carriers and Fe-B pair concentration are examined by μ-PCD for the case before and after annealing. Minority carrier lifetime decays conspicuously after annealing process because of the increasing concentration of Fei. The reason of Fe-B pair increased should be the precipitate of iron being dissolved during annealing process. Phosphorous gettering process for reducing metal concentration was applied for solving metal dissolving problem. The amount of Fei can be reduced by phosphorous gettering, however, it is still higher than the original level. Internal gettering is found effective only for reducing metal point defects with high mobility in silicon. The existence of metal with low mobility could also deteriorate the lifetime of silicon solar material.

並列關鍵字

multicrystalline silicon ； dislocation density ； anneal ； lifetime

參考文獻

4. Cottrel A. H., “Theory of dislocations”, Progress of Metal Physics, chapter 5 (1953) pp.205-262.

5. Secco F., and D. Aragona,”Dislocation etch for <100> planes in silicon”, Journal of Electrochemistry Society: Solid-State Science and Technology, 119 (1972) pp.948-951.

6. Umeno S., M. Okui, M. Hourai, M. Sano, and H. Tsuya, “Relationship between grown-in defects in Czochralski silicon crystals “, Japanese Journal of Applied Physics, 36 (1997) pp. L591-L594.

7. Jenkins M. W., “A new preferential etch for defects in silicon crystals”, Journal of Electrochemistry Society: Solid-State Science and Technology, 124 (1977) pp.757-762.

8. Yang K. H., “An etch for delineation of defects in silicon”, Journal of Electrochemistry Society: Solid-State Science and Technology, 131 (1984) pp.1140-1145.