摘要:
本文采用射频等离子体增强化学气相沉积（rf-PECVD）技术在单晶硅衬底上沉积了两个系列的硅薄膜.通过对样品进行固定角度椭圆偏振测试,结果表明第一个系列硅薄膜为非晶硅,形成了突变的a-Si：H/c-Si异质结构,此结构在HIT电池中有利于形成好的界面特性,对于非晶硅薄膜采用通常的Tauc-Lorentz摇摆模型（Genosc）拟合结果很好;第二个系列硅薄膜为外延硅,对于外延硅薄膜,随着膜厚增加晶化率降低,当外延硅薄膜厚度为46 nm时开始非晶硅生长.对于外延硅通常采用EMA模型（即将硅薄膜体层看成由非晶硅和c-Si构成的混合层）拟合结果较好,当硅薄膜中出现非晶硅生长时,将体层分成混合层和非晶硅两层,采用三层模型拟合结果很好.本文证实了椭偏光谱分析采用不同的模型可对单晶硅衬底上不同结构的硅薄膜进行有效表征.
Abstract:
Two series of silicon films on c-Si substrates with different thicknesses are deposited by radio frequency plasma enhanced chemical vapor deposition（rf-PECVD）.The structures of samples are investigated by spectroscopic ellipsometry（SE） with fixed angle. The results show that the films are all amorphous for the first series of samples.In such a case an abrupt a-Si：H/c-Si heterojunction is formed which is beneficial for the passivation of the interface of HIT solar cell.For amorphous silicon films,the fitting result is acceptable by using Tauc-Lorentz Genosc model.For the second series,the films are of epitaxial Si at the initial deposition stages,the amorphous fraction increases with the increase of thickness.When the film thickness reaches a critical value of 46 nm,a transition to pure amorphous phase occurs.The epitaxial film shows excellent fitting by using the effective medium approximation（EMA） model under the assumption of the mixture of c-Si phases and a-Si：H.However,we obtain better fitting result by using a three-layer model, whose bulk layer is divided into EMA layer and a-Si layer after the transition to pure amorphous phase.This study indicates that the SE analysis,operated in different models,is effective to characterize different structures of silicon films on c-Si substrate.
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