硅碳比对Si(111)表面SSMBE异质外延SiC薄膜的影响

利用固源分子束外延(SSMBE)生长技术, 在不同的硅碳蒸发速率比(Si/C)条件下, 在Si(111)衬底上生长SiC单晶薄膜. 利用反射式高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)和傅立叶变换红外光谱(FTIR)等实验技术, 对生长的样品形貌和结构进行了研究. 结果表明, 在Si/C比(1.1:1.0)下生长的薄膜样品, XRDω扫描得到半高宽为2.1°; RHEED结果表明薄膜具有微弱的衍射环, 有孪晶斑点. 在Si/C比(2.3:1.0)下生长的薄膜, XRDω扫描得到的半高宽为1.5°, RHEED显示具有Si的斑点和SiC的孪晶斑点. AFM显示在这两个Si/C比下生长的样品表面都有孔洞或者凹坑, 表面比较粗糙. 从红外光谱得出 薄膜存在着比较大的应力. 但在Si/C比(1.5:1.0)下生长的薄膜样品, XRDω 扫描得到的半高宽仅为1.1°; RHEED显示出清晰的SiC的衍射条纹, 并可看到SiC的3×3表面重构, 无孪晶斑点; AFM图像表明, 没有明显的空洞, 表面比较平整. FTIR谱的位置显示, 在此Si/C比下生长的薄膜内应力比较小. 因此可以认为, 存在着一个优化的Si/C比(1.5:1.0), 在这个Si/C比下, 生长的薄膜质量较好.

Effect of Different Si/C flux Ratios on the Growth of SiC on Si (111) by SSMBE

Si films were grown on SiC (111) substrate by solid-source molecular beam epitaxy (SSMBE) at different Si/C flux ratios. The structure characteristics of SiC films were investigated by reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), atomic force microscope (AFM) and Fourier transform infrared spectroscope (FTIR). For the sample grown at Si/C flux ratio (1.1:1.0), ring patterns and twin spots are observed in RHEED and the full width at half maximum (FWHM) of the rocking curve is 2.1°. For the sample grown at Si/C flux ratio(2.3:1.0), the Si spots coexist with SiC spots in the RHEED and the FWHM of the rocking curve is 1.5°. For these two Si/C flux ratios, there are voids and rough surface observed in AFM and large strain exists shown in the FTIR spectra. However, for the sample grown at the Si/C flux ratio (1.5:1.0), besides SiC streaks, a (3×3) surface reconstruction can be observed in RHEED and no SiC twin spots are observed. The results of XRD show that the FWHM of the rocking curve is just 1.1°. The AFM results indicate that the surface of the sample is even and there are no obvious voids. While the results of FTIR show that the strain in the film is small. Therefore, the optimized Si/C flux ratio is 1.5:1.0, and the quality of the film grown at the optimized Si/C flux ratio is the best.