利用電子迴旋共振化學氣相沉積法於低溫成長摻雜晶矽薄膜及其應用於非晶矽薄膜太陽能電池

Using electron cyclotron resonance chemical vapor deposition at low temperature growth of doped crystalline silicon thin film for amorphous silicon thin film solar cells

王冠杰(Kuan-Chieh Wang)

指導教授 ： 張正陽

國立中央大學/理學院/光電科學研究所/碩士(2012年)

摘要

本篇論文是利用電子迴旋共振化學氣相沉積法(ECR-CVD)來成長p、n型摻雜矽薄膜及薄膜太陽能電池，並探討其特性。ECR-CVD屬於高密度電漿源沉積，利用入射微波頻率與系統磁場內電子的迴旋角頻率相同時產生共振吸收達到最大能量轉換。相較於傳統PECVD，ECR-CVD有幾項特點，如較快的沉積速率、較高氣體使用率、低離子轟擊等。
利用調變外加磁場電流、微波功率、製程壓力、氬氣流量、氫氣稀釋比例及摻雜氣體流量等參數來探討其對摻雜薄膜品質之影響。利用拉曼光譜儀、紫外可見光光譜儀及霍爾量測系統等儀器分析薄膜特性。p型摻雜薄膜品質要好，需在高氫氣比例製程下，厚度可在約30nm時載子濃度控制在19至20次方，約65%的高結晶率及載子移動率控制在1.1至1.3 cm2/V-s，。
在製程上改善有下列幾項，清腔影響、退火溫度控制、背部TCO影響、透明導電膜保護、氫電漿處理及加入緩衝層影響等，經過AM1.5太陽光模擬器分析後，清腔與退火溫度影響結構明顯，背部TCO可有效增加電流吸收由5.51增加至9.32 mA/cm2，透明導電膜保護基板下也可使電流由4.74上升至6.35 mA/cm2，氫電漿處理可以提高約0.1V之開路電壓，而利用緩衝層也可提升開路電壓值。
利用以上探討之改善方式製作薄膜太陽能電池，量測後開路電壓0.32 V、短路電流密度5.4 mA/cm2、填充因子45%及轉換效率0.78%，由於機台狀況改變，使得結果並非預期中之數值，改善製程中已有效率1.2%，理論上效率可以達1.5%以上。
利用ECR-CVD製程薄膜太陽能電池效率無法大幅提升，首先面臨基板問題，SnO2(F)基板有表面結構且抗蝕刻性差，若使用電性佳且表面平坦的AZO基板可以減少氫電漿蝕刻問題及ECR-CVD高鍍率在基板結構上產生之介面缺陷。沉積速率快可能造成薄膜結構中缺陷密度高，對於摻雜層產生之開路電壓及本質層的光響應產生短路電流密度皆有影響。在高密度電漿下製程可能會破壞已沉積之薄膜，造成介面處薄膜結構差，本質層成長時破壞p型摻雜層造成開路電壓下降。因此利用ECR-CVD在高密度電漿下成長p-i-n薄膜太陽能電池之結果不如預期。

關鍵字

非晶矽 ； 摻雜晶矽薄膜 ； 電子迴旋共振化學氣相沉積法

並列摘要

This paper is based on electron cyclotron resonance chemical vapor deposition (ECR-CVD) to research the characteristics of p and n-doped silicon thin film and apply on thin film solar cell. ECR-CVD is a high density plasma system that plasma generated in the ECR system process is via resonant absorption of a microwave by electron in a magnetic field and gas ionization via subsequent electron-atom collisions. Compared with conventional PECVD, ECR-CVD has several advantages, such as the high deposition rates, high gas utilization, low ion bombardment, and so on.
This experiment we explored the film quality by modulation of the current of magnetic field, microwave power, process pressure, Ar flow rate, hydrogen dilution ratio, doping gas flow rate. Measured thin film by Raman spectrometer, UV-VIS spectrometer and Hall system. Under high hydrogen dilution condition, the film thickness about 30nm can to control the concentration 19 to 20 order, high crystallization rate to 65%, while the mobility can be control on 1.1 to 1.3 cm2/V-s.
The processes of improvement solar cell, such as chamber clean, temperature of annealing, effect of back TCO, substrate protected by TCO, hydrogen plasma treatment and effect of buffer layer. Measured by AM1.5 solar simulator, obviously effected in structure by chamber clean and anneal temperature, using back TCO can increase current density from 5.51 to 9.32 mA/cm2, protected by TCO also can improve current density from 4.74 to 6.35 mA/cm2, hydrogen plasma treatment the texture can increase open circuit voltage about 0.1V, and buffer layer also improve the open circuit voltage.
We used above all of improvement process to growth solar cell, open circuit voltage (VOC) is 0.32 V, short circuit current (JSC) is 5.4 mA/cm2, fill factor (FF) is 45%, efficiency (η) is 0.78%. The condition of ECR-CVD is change, so the measurement data is not what we expected. In the experiment of improvement process, the efficiency already had 1.2%. In theory the efficiency can reach 1.5% up.
Used ECR-CVD to deposit thin film solar cell that efficiency cannot be dramatically. First faced with the substrate problem, SnO2 substrate exist texture on surface and its etch resistance is poor. If use the AZO substrate with good electrical properties and flat surface, the problem of hydrogen plasma etching and high deposition rate of ECR-CVD cause the interface defect on substrate structure can be reduce. High deposition rate may result in high defect density in the thin film structure, it would effect the open circuit voltage of doping layer and light response current of intrinsic layer. In high density plasma process may undermine the already deposited film, cause the film structure at interface is poor, destroy the p-type doepd layer of the intrinsic layer growth resulting in decreased open circuit voltage. Therefore, the use of ECR-CVD growth of pin thin film solar cells results not as good as expected.

並列關鍵字

doped crystalline silicon thin film ； electron cyclotron resonance

參考文獻

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