| 摘要: | 本實驗是以電子迴旋共振化學氣相沉積法(ECR-CVD)來成長硼摻雜氫化氧化矽薄膜，並分析其結構與光電特性。ECR-CVD屬於高密度電漿，相較於傳統的PECVD，ECR-CVD具備良好的沉積速率、無電極汙染、較高氣體使用率與低離子轟擊效應等優點。本實驗使用ECR-CVD通入矽甲烷、氫氣、二氧化碳、與乙硼烷來製備寬能隙與低電阻率的硼摻雜氫化氧化矽薄膜，並且期望應用於異質接面矽晶太陽能電池上。以此薄膜做為太陽能電池的射極層，可以減少入射光的損耗進而提升電池的短路電流。
本實驗將調變二氧化碳流量、工作壓力、乙硼烷流量、微波功率與氫氣稀釋比等參數對硼摻雜氫化氧化矽薄膜特性的影響，並利用橢圓儀、傅里葉變換紅外光光譜儀、紫外光-可見光-近紅外光光譜儀、霍爾量測、電子能譜化學分析儀量測薄膜結構與光電性質。研究結果顯示，硼摻雜氫化氧化矽薄膜中的氧原子雖然可以調製光學性質，但是過多的氧原子相對會導致雜質濃度提升，而犧牲其導電特性，所以如何在氧含量與導電特性上取得平衡是相當重要的關鍵。在調變工作壓力與微波功率下，薄膜結晶率愈高則導電特性愈好，但太小的工作壓力與太高的微波功率會不利於矽氧鍵結的形成。在調變乙硼烷流量下，過多的硼原子也會導致雜質濃度過高，使導電特性變差，然而適量的硼原子也有助於矽氧鍵結的形成。在調變氫氣稀釋比下，高氫稀釋比則有助於氧含量與導電特性的提升。我們可成功在二氧化碳對矽甲烷流量比為0.8且氫稀釋比為60的環境下，製備出硼摻雜氫化氧化矽薄膜之光學能隙可達1.88 eV且電阻率為9.76 × 10^-3 ohm-cm。
;This experiment is based on electron cyclotron resonance chemical vapor deposition (ECR-CVD) to deposit boron-doped hydrogenated silicon oxide (SiO:H) films ,and investigating the structural as well as optoelectronic properties of the doping films. Furthermore, compared with conventional PECVD, ECR-CVD has several advantages, such as the excellent deposition rates, no electrode contamination, high gas utilization, low energy ion bombardment due to the property of high-density plasma. The boron-doped hydrogenated silicon oxide films with wide-gap and low resistivity were fabricated by ECR-CVD process by using SiH4 and CO2 gas mixture. In addition, this material will be applied to amorphous silicon / crystalline silicon heterojunction solar cells. Using p-SiO:H films as emitter layer can reduce the loss of the incident light and improved the short-circuit current of solar cells.
In this study, we modulated the CO2 flow rate, process pressure, B2H6 flow rate, microwave power, and hydrogen dilution ratio to investigate the thin films quality. Furthermore, the structural and optoelectronic properties of the p-SiO:H films have been characterized by using spectroscopy ellipsometry, Fourier transform infrared spectrometer, UV-Vis-NIR spectrometer, Hall measurement, and X-ray photoelectron spectrometer. The results of experiments shown that the excess oxygen atoms in the films will increase the defect and degrade the electronic properties. Thus, the control of oxygen content in the films is very important to obtain a high electronic properties. Under the modulation of working pressure and microwave power, the electronic properties were increased with the high crystallinity of the p-Si:O film. But the Si-O bonding will be broken in the condition of lower working pressure and higher microwave power. Under the modulation of B2H6 flow rate, the excess boron atoms in the films will increase the defect and degrade the electronic properties. However, the suitable amount of the boron atom can help the formation of Si-O bonding. Under the modulation of hydrogen dilution, the optical bandgap and electronic properties of p-SiO:H films can be increased in the condition of high hydrogen dilution. Under the condition of [CO2] / [SiH4] = 0.8 and [H2] / [SiH4] = 60, we obtained the optical bandgap and resistivity of the film were 1.88 eV and 9.76 × 10^-3 ohm-cm, respectively. |
