沉积温度对等离子体化学气相沉积制备硅氧薄膜微结构的影响

利用13.56 MHz的射频等离子体化学气相沉积设备(RF-PECVD)在不同沉积温度(50~400 ℃)下制备了一系列氢化硅氧(SiO_x:H)薄膜材料,并研究了薄膜材料性能与微结构的变化规律。随着沉积温度的增加,薄膜内的氧含量(C_O)下降,晶化率(X_C)也下降,折射率(n)上升,此外,薄膜的结构因子(R)下降,氢含量(C_H)先上升后下降,由此在合适的中间温度下可以获得最大的氢含量。通过实验结果分析提出了不同沉积温度下制备硅氧薄膜的内在微结构模型:低温下沉积的硅氧薄膜是以氢化非晶硅氧(a-SiO_x:H)相为主体并嵌入氢化纳米晶硅(nc-Si:H)的复合材料,而在高温下沉积的硅氧薄膜则是以氢化非晶硅(a-Si:H)相为主体并嵌入越来越少的nc-Si:H相和a-SiO_x:H相的复合材料。由上可知,要制备太阳电池通常采用的晶化率X_C高、氧含量C_O高的氢化纳米晶硅氧(nc-SiO_x:H)材料,需要采用相对较低的沉积温度。

Effect of Deposition Temperature on Microstructure of Silicon Oxide Film Prepared by Plasma Enhanced Chemical Vapor Deposition

Hydrogenated silicon oxide (SiO_x:H) films were prepared by 13.56 MHz radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The effect of the deposition temperature (T) variation (from 50 ℃ to 400 ℃) on the film performance and microstructure were investigated. The T increases could induce the decreases of oxygen content (C_O) in the SiO_x:H film and at the same time make the film transform from nanocrystalline state to amorphous state gradually, which resulted in the film crystallinity (X_C) decreases and the film refractive index (n) increases. Further, it was found that the microstructure factor (R) decreases and the hydrogen content (C_H) in the SiO_x:H film increases first and then decreases with the T increases. A maximum of C_H could be obtained with an intermediate T. Based on the above results, the low-temperature formed film is considered as a typical composite with hydrogenated nanocrystalline silicon (nc-Si:H) inserted in the hydrogenated amorphous silicon oxide (a-SiO_x:H) matrix, however, the high-temperature deposited film consists of hydrogenated amorphous silicon (a-Si:H) matrix with nc-Si:H and a-SiO_x:H phases less and less diluted inside. The results show that excellent hydrogenated nanocrystalline silicon oxide (nc-SiO_x:H) film with high X_C and C_O for solar cell application should be deposited at a relatively low temperature.