微晶矽薄膜製程之電漿放射光譜分析與其在太陽能電池之應用

Optical Emission Spectroscopic in PECVD of Microcrystalline Silicon and its Application in Soar cell Process

潘彥妤(YEN-YU PAN)

指導教授 ： 魏大欽

中原大學/工學院/化學工程學系/碩士(2008年)

https://doi.org/10.6840/cycu200900594

摘要

本研究以高頻(80MHz)電漿輔助化學氣相沉積儀製備微晶矽薄膜，在鍍膜的同時利用電漿放射光譜儀(Optical Emission Spectroscopy , OES)技術在不同電漿功率、氣體配比、操作壓力下，探討電漿物種改變對膜材性質之影響。第一部分以SiH4/H2/Ar電漿沉積微晶矽薄膜，再量測其鍍膜速率、結晶率以及薄膜鍵結，配合光譜分析將物種濃度和薄膜性質做連結。
實驗結果發現電漿功率的提升可使非晶矽轉為微晶矽，且成膜速率增加，但在高功率下膜材較不緻密。而氫原子的蝕刻機制有助於結晶率的提升，但過多的氫原子會使結晶率持平，且鍍膜速率下降。壓力的增加則造成結晶率的下降，鍍膜速率先升後降。因此，為取得高沉積速率和高結晶率，可藉由調整電漿功率、氣體配比以及壓力變化來得到。而OES當中發現SiH強度與鍍膜速率有相同的趨勢，H/SiH相對強度可代表結晶率大小，並可利用物種濃度的變化來解釋薄膜性質改變的原因。
第二部份為製作微晶矽薄膜太陽能電池，改變本質層的鍍膜條件來探討其對太陽能表現參數的影響，壓力在0.5Torr時所製作之元件光電流密度較高，且由暗電導得知氧含量較少，而無添加Ar的情況下有助於Voc的提升。研究結果顯示結晶率的上升會提升光電流及光電轉換效率，配合OES得知H/SiH < 1.5時所沉積之薄膜較接近非晶矽，H/SiH >2.5以上較有可能沉積出結晶率>60%之薄膜，因此利用電漿放射光譜可作為監控微晶矽薄膜之即時分析系統。

關鍵字

微晶矽薄膜太陽能電池 ； 電漿輔助化學氣相沉積儀 ； 電漿放射光譜儀(OES)

並列摘要

Deposition of microcrystalline silicon using VHF-GD (Very High Frequency-Glow Discharge) method was investigated. OES (Optical Emission Spectroscopy) was used to do real-time analysis on the Microcrystalline Si PECVD Process. The effects of operating parameters (power, gas ratio, pressure) on the thin film properties are discussed. The relation between species concentration from OES and thin film properties like deposition rate and crystalline fraction is linked.
The results show the deposited film turns from amorphous to microcrystalline and deposition rate increases when plasma power increases. But in higher power, thin film is not compact. Etch model of hydrogen atom will help crystalline fraction increases but too much hydrogen atom will keep crystalline fraction stop changing. When pressure increases, crystalline fraction will decrease. The deposition rate first increases and then decreases when total pressure increases. In OES spectrum, we can find that SiH intensity has the same trend with deposition rate. It is also shown that the H/SiH ratio is a powerful parameter to correlate to the crystalline fraction of the deposited film.
The second part of this study is silicon thin film solar cells. The search for
solar cell performance parameters was studied under various deposition conditions of intrinsic layer. The thin film photo current is higher at lower pressure and has less oxygen content. If there is no Ar addition, open voltage will increase. According to the OES experiment results, the thin film is more like amorphous when H/SiH < 1.5. If H/SiH ratio >2.5, it is possible to deposit silicon film of crystalline fraction >60%. In conclusion, OES is an efficient and easy-to-handle in-situ tool that will contribute in monitoring the deposition process.

並列關鍵字

microcrystall silicon thin film solar cell ； Optical emission spectroscopy ； Plasma Enhanced Chemical Vapor Deposition

參考文獻

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