Structural characterization of strained silicon grown on a SiGe buffer layer

Abstract

The microstructure of about 50 nm thick strained-Si/Si0.7Ge0.3/graded-SiGe/Si-substrate layers grown by MBE (molecular beam epitaxy) was characterized using high-resolution x-ray based characterization techniques. The degree of relaxation of the Si-capping layer after a thermal anneal at 800 °C for 30 min was determined using reciprocal space map (RSM) scans recorded around the (1 1 3) diffraction plane. However, since a RSM is not suitable when the strain relaxation is very small, x-ray reflectivity (XRR) and omega rocking curves (ω-RCs) were employed for the relaxation study. XRR spectra were collected and analyzed to obtain thickness, Ge concentration and surface/interfacial roughness information of the as-grown and annealed samples. ω-RCs were performed in order to investigate the crystalline quality of the samples. It was found that the annealed strained layer showed higher Lorentzian fraction in ω-RCs and misfit defect density which were caused by strain relaxation. In addition, the results showed that after the annealing process the broadening in the tail region of the ω-RCs was indicative of a change in the coherence length distribution of the crystallite size. The misfit defects and surface morphology obtained from transmission electron microscopy (TEM) and atomic force microscopy (AFM) investigations were consistent with results obtained from the x-ray based characterization techniques.