4H-SiC纳米薄膜的微结构及其光电性质研究

采用新设计的电极结构的等离子体增强化学气相沉积(PECVD)技术,在高功率密度、高氢稀释比、低温、偏压及低反应气压的条件下,在衬底表面形成双等离子流,增加了衬底表面SiC的成核概率,增强成核作用,形成纳米晶.采用高H2等离子体刻蚀弱的、扭曲的、非晶Si—C及Si—Si和Si—H等键时,由于H等离子体对纳米SiC晶粒与非晶态键的差异刻蚀作用,产生自组织生长,发生晶化.Raman光谱和透射电子衍射(TEM)的测试结果表明,纳米晶SiC是4HSiC多型结构.电子显微照片表明平均粒径为16nm,形状为微柱体.实验结果指出,SiC纳米晶的形成必须经过偏压预处理成核,并且其晶化存在一个功率密度阈值;当低于这一功率密度阈值时,晶化消失;当超过这一阈值时,纳米晶含量随功率密度的提高而增加.随着晶化作用的加强,电导率增加. 关键词： 4H-SiC PECVD 纳米结构 多型薄膜 纳米电子学

Study on the structural and optic-electronical properties of 4H polytype-SiC films

Nanocrystalline (nc) 4H-silicon carbide (SiC) films were deposited by plasma-enhanced chemical vapour deposition,which anode reaction structure was redesigned,with high power density,high hydrogen dilution,pre-bias treatment,bias and low reaction pressure.The crystallization of nc-4H-SiC films could be ascribed to the above conditions,which form bi-flow of plasma on the substrate and make the probability of forming SiC nuclei large,i.e.,the function of forming nulei become strong.High hydrogen plasma etch weak,distorted bonds and amorphous Si_C,Si_Si and Si_H bonds,meanwhile the growth organized-self of nc-4H-SiC films was produced due to difference of etching different bonds.The test results of Raman spectroscopy and high resolution transmission electron microscope (TEM) indicates that the structure of nanocrystalline silicon carbide in films is for hexagonal polytype,i.e.,alpha silicon carbide.The micro-structure of films is two phases structure the nanocrystalline SiC surrounded by amorphous SiC,the mean diameter of micro-columnar nc-SiC is about 16nm.To form the nc-SiC,the pre-bias treatment must be applied and threshold of power desity of PECVD must be over 2.5W/cm 2.the content of nc-SiC increased with power density above threshold.The conductivity of films increased with strong crystallization.