連續式電漿輔助化學氣相沉積之微晶矽薄膜製程研究與電漿放射光譜量測分析

Optical Emission Spectroscopy Diagonostics of In-line Plasma Enhanced Chemical Vapor Deposition for Microcrystalline Silicon Thin Films Deposition

吳哲瑋(Zhe-Wei Wu)

指導教授 ： 柳克強

國立清華大學/原子科學院/工程與系統科學系/碩士(2012年)

摘要

微晶矽薄膜太陽能電池可以減少矽原料的使用，且能沉積在價格低廉的玻璃、不鏽鋼和塑膠基板上，因此能大幅降低材料成本。微晶矽在近紅外光的吸收係數較低，所以需要較厚的薄膜厚度(1~3 m) 來增加吸收，如何提升微晶矽薄膜的沉積速率並維持良好的結晶度與光敏性是重要的議題。而薄膜成長特性與其材料結構與光電特性，主要由製程時電漿中的粒子、自由基等所掌控，因此電漿特性之量測分析對了解電漿變化與薄膜特性之關聯性極有助益。
　　本研究主旨為發展連續式電漿輔助化學氣相沉積(In-line PECVD) 成長微晶矽薄膜之相關製程技術，作為矽薄膜太陽能電池的I-layer之應用。同時藉由光學放射光譜儀(OES) 量測電漿放射光譜，建立電漿光譜隨製程參數如射頻功率、氫稀釋比及氣體壓力變化的關係。並量測沉積薄膜的材料結構與電特性，探討電漿中反應物種濃度變化對於薄膜材料結構及電特性之影響。
　　研究發現不論是改變矽甲烷硫量、射頻功率或氣體壓力，c-Si:H薄膜結晶度都隨OES-ratio(H/SiH*, H/SiH*) 上升而增加，且光敏性與OES-ratio有相反趨勢。說明了氫原子濃度比例越高，薄膜會趨向高結晶，然而暗電導的提升也造成光敏性下降。另一方面，薄膜沉積速率與前驅物SiH3濃度有密切關係，OES以特徵譜線SiH*代表SiH3之變化。在改變氫稀釋比及氣體壓力的實驗，沉積速率與SiH*之強度變化有相同趨勢。然而在改變射頻功率時，沉積速率與SiH*並無明顯規律。經由上述研究分析，In-line PECVD可以在高功率(600 W)、高壓(4 torr) 及高矽甲烷流量(2.44 %) 的條件下成長c-Si:H薄膜，且結晶度38 %、光敏性3.94 × 102，已達到元件要求。N-P layer在商業機台ULVAC成長，搭配In-line PECVD之c-Si:H薄膜最佳化條件所製作的電池效率為1.68 %；然而若N-I-P layer皆在In-line PECVD製作，效率可達2.27 %。由結果推論在In-line PECVD製作可以避免薄膜接觸到空氣，減少氧化的機率，因此電池效率可以獲得較大的提升。

關鍵字

微晶矽薄膜 ； 電漿放射光譜 ； 薄膜太陽能電池

並列摘要

The hydrogenated microcrystalline silicon(c-Si:H) thin film solar cells can reduce silicon material, and deposited on low-cost substrate like glass, stainless steel or plastics. Therefore it significantly reduce the material cost. The absorption of c-Si:H thin films at near-infrared light is lower, so c-Si:H need thicker film(1~3 m) to enhance absorption. How to increase deposition rate c-Si:H thin films, simultaneously maintain good crystalline volume fraction(XC) and photosensitivity is very importance problem. The free radicals and particles in plasma will affect the material and photoelectric properties of c-Si:H thin films. Thus the correlation between process parameters and properties of films are demonstrated in this thesis.
　　Purpose of this study is develop process for c-Si:H thin films by In-line plasma enhanced chemical vapor deposition(In-line PECVD). The glow of the plasma associated with properties of films is detected by optical emission spectroscopy(OES). The experiment results found that whether it is varying the silane concentration, RF power or gas pressure, the XC increase with OES-ratio(H/SiH*, H/SiH*), and the photosensitivity decrease as OES-ratio increase. It is say that higher hydrogen atom density will increase XC of films, but dark conductivity enhancement also cause photosensitivity decreased. Currently, In-line PECVD can deposited c-Si:H thin film which XC = 38% and photosensitivity = 3.94 × 102 at high power(600 W), high pressure(4 torr) and high silane concentration(2.44%). The N-P layer deposited in ULVAC and c-Si:H I-layer in In-line PECVD, the cell efficiency is 1.68%. But if the N-I-P layer all deposited in In-line PECVD, the cell efficiency achieve 2.27%. From the result, all in In-line PECVD manufacture can prevent air contamination, therefore the cell efficiency can be large improve.

並列關鍵字

microcrystalline silicon thin films ； optical emission spectroscopy ； thin film solar cells

參考文獻

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