寬能隙本質氫化非晶氧化矽(a-SiOx:H)薄膜光電特性與鈍化品質之關聯探討

The investigation between photoelectric characteristics and passivation quality of wide band gap intrinsic hydrogenated amorphous silicon oxide (a-SiOx:H) thin films

劉憲明(Shian-ming Liu)

指導教授 ： 利定東

國立中央大學/工學院/光機電工程研究所/碩士(2014年)

摘要

本研究利用電子迴旋共振化學氣相沉積(Electron cyclotron resonance chemical vapor deposition, ECR-CVD)製備本質氫化非晶氧化矽薄膜，相較於傳統電漿輔助化學氣相沉積(Plasma enhanced chemical vapor deposition, PECVD)其沉積速率較慢導致製程成本與時間增加，而ECR-CVD屬於高密度電漿具有較快沉積速率、無電極汙染、低離子轟擊等特點。本實驗調變微波功率、不同二氧化碳流量、氫稀釋比例、基板溫度等製程參數對a-SiOx:H薄膜特性影響，並且使用傅氏轉換紅外線光譜儀(FTIR)、橢圓偏光儀(Ellipsometer)、紫外可見光譜儀(UV-visible)量測薄膜結構特性與光電性質，最後以少數載子生命週期來判斷薄膜品質好壞。未來期望應用於異質接面太陽能電池上，以提升電池開路電壓。
本實驗選用磁場45/12/22 A與製程壓力5 mTorr條件下，使用FZ n-type單晶矽基板通入製程氣體為H2、SiH4、Ar與CO2來沉積雙面氫化非晶氧化矽薄膜。藉由少數載子生命週期(Lifetime)與表面載子複合速率(SRV)結果得知鈍化效果好壞，通入適當二氧化碳流量其氧含量可減少部份磊晶現象進而提升少數載子生命週期，但過多氧含量造成缺陷，增加薄膜中複合中心的產生。氧含量從0.14 at.(%)增加到10.91 at.(%)，薄膜光學能隙從1.81 eV上升到2.32 eV。從實驗結果得知於H2/SiH4=0、微波功率500W、基板溫度140℃條件下得到較佳鈍化效果，且熱退火200℃-120sec情形下，少數載子生命週期從153.12 μsec提高到1.5 msec，表面複合速率從97.96 cm/s下降至10 cm/s。

關鍵字

本質氫化非晶氧化矽薄膜 ； 電子迴旋共振化學氣相沉積 ； 少數載子生命週期 ； 表面載子複合速率

並列摘要

In this study, the intrinsic hydrogenated amorphous silicon oxide (a-SiOx:H) thin films was prepared by Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD). High plasma density of ECR-CVD had many advantages: (1) faster deposition rate, (2) no electrode contamination, (3) low ion bombardment. However, conventional Plasma Enhanced Chemical Vapor Deposition (PECVD) had slower deposition rate caused the increase of costs and time. The process parameters effect of a-SiOx:H thin films such as microwave power, the flow of carbon dioxide, dilution ratio and substrate temperature were investigated. The thin films structure and optical properties were analyzed by Fourier transform infrared spectroscopy, Ellipsometer, and UV-visible. Finally, we determined the thin films quality by photo conductance lifetime tester. In addition, this material will be applied to amorphous silicon / crystalline silicon heterojunction solar cells and improved the open-circuit voltage of solar cells.
This experiment chose magnetic field configuration of 45/12/22 A and process pressure 5 mTorr to deposit sandwich a-SiOx:H thin films using H2, SiH4, Ar and CO2 as reactant gases. The carrier lifetime and Surface Recombination Velocity (SRV) of Si wafer could determine the passivation quality on FZ n-type silicon substrate. We found that by accessing appropriate carbon dioxide flow could improve lifetime because the oxide atoms decreased the phenomenon of partial epitaxy. However, the overflowing oxygen content caused to increase recombination center.
The experiment results showed that low dilution ratio, microwave power of 500W, substrate temperature of 140℃ had better passivation quality. The thin films optical band gap changed from 1.81 to 2.32 eV by increasing oxygen concentration from 0.14 to 10.91 at.(%). Thin films properties at H2/SiH4=0 could be optimized after annealing process under the temperature 200℃ for 120sec. The carrier lifetime 153.12 μsec increased to 1.5 msec and SRV 97.96 cm/s decreased to 10 cm/s.

並列關鍵字

a-SiOx:H ； ECR-CVD ； Lifetime ； SRV

參考文獻

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