硼掺雜固相磊晶法應用於太陽能電池背面電場和射極之研究

Boron Doped Solid Phase Epitaxy on Mono-Crystalline Si for BSF and n-type emitter fabrication in Solar Cells by Aluminum-Induced Crystallization

林泓希(Hung-Hsi Lin)

指導教授 ： 蔡春鴻 ； 陳福榮

國立清華大學/原子科學院/工程與系統科學系/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00617

摘要

p型矽薄膜的應用在IC產業或是太陽能電池領域中佔有相當的比重，製造p型矽層的方法有許多種類，而在工業界較廣為利用的是離子佈植以及擴散的方式。離子佈植過程中會造成基板表面形成許多因離子轟擊造成的缺陷，必須以高溫熱退火(800oC)來將其修補。而擴散的方式也必須經由高溫的催化(硼約900oC)，使掺雜物在基板表面反應形成後，再利用熱擴散的方式達到預期的深度，這兩種製造p型矽薄膜的製程都有著因高溫造成的熱預算問題，對於後製程有很大的影響。
若利用鋁誘發結晶方式成長p型矽薄膜，可在較低溫(400oC)的溫度下完成。但載子濃度相較離子佈植和擴散法低(3x1018cm-3,後者約1019-1020cm-3)，導致可利用的價值相對下降。本實驗利用硼共濺鍍於鋁膜內的方式使硼存在於成長後的p型矽薄膜內，並提供電洞。在一定溫度下，硼在矽中的固相溶解度較鋁高，因此可以在低溫情況下(400oC)得到較傳統鋁誘發結晶高的載子濃度(1019cm-3)。
低溫達高掺雜的技術可應用的層面很廣，對以離子佈植和擴散方式製造的太陽能電池射極部份來說，此硼共濺鍍的方式可使高溫造成的熱預算問題降至最低。此外，太陽能電池中的背面電場部份是由網印方式形成，一樣必須經過700oC以上的熱處理才可完成背面電場的製作，由於鋁和矽的熱膨脹係數不同，高溫時易導致因熱膨脹造成的表面應變殘留，甚至使晶圓變形破裂。
因此本研究將硼共濺鍍應用於固相磊晶法上，使得在400oC即可達1019cm-3的掺雜濃度，不但突破了傳統鋁誘發結晶的載子濃度限制，也有機會將鋁誘發結晶法應用於現今太陽能電池或IC產業中製造p型矽薄膜的製程。

關鍵字

硼 ； 鋁誘發結晶 ； 固相磊晶 ； 背面電場 ； 射極

並列摘要

The Back-Surface-Field structure is usually fabricated by screen-printing technology, and the emitter is produced by ion implantation or diffusion in solar cell. Although all of these methods obtain continuous and high carrier concentration p-type silicon film, the processes must undergo a heat treatment above 800oC. It causes some critical issues such as thermal budget problem and residual strain energy results from different thermal expansion coefficient between silicon and aluminum.
In this research, we produced a continuous and p-type silicon film by aluminum induced crystallization (AIC) process to work as BSF or emitter. The advantages that fabricating p-type silicon film by AIC is the low temperature process. However, the carrier concentration obtained by AIC is only 3x1018cm-3 which is lower than other methods. It must surpass 1019cm-3, or the efficiency would decrease because of reduction of carrier lifetime caused by low carrier concentration.
We co-sputter with boron into aluminum film at first, and then boron atoms dissolve into silicon and provide holes after AIC process completes. It results in increase of carrier concentration while the annealing temperature keeps the same at 400oC. We expect the technology that produces high carrier concentration silicon film at low temperature can be used as BSF and emitter, and then gets better performance compared to conventional AIC process.

並列關鍵字

boron ； Aluminum induced crystallization ； solid phase epitaxy ； Back-Surface-Field ； emitter

參考文獻

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