RBS analysis of MBE grown SiGe/(001)Si heterostructures with thin high Ge content SiGe channels for HMOS transistors

The growth of Si1-xGex quantum wells with high Ge composition (x>0.5) on Si(001) substrates by MBE is of great interest both for HMOS device applications and fundamental research. One of the possibilities to obtain a high Ge content Si1-xGex channel for mobile carriers, while retaining its strain, is to grow a relaxed Si1-yGey buffer layer on an underlying Si substrate. Such a buffer is termed a virtual substrate (VS), which is a constituent of SiGe metamorphic heterostructures. The effect of annealing on the structure of the Si(001)/VS/Si0.7Ge0.3/Si0.2Ge0.8/Si0.7Ge0.3 heterostructures was studied by grazing angle of incidence RBS. The thickness of the Si0.2Ge0.8 channel is inhomogeneous, which makes the analysis of the data by traditional means very hard. We have developed a model whereby the influence of the thickness inhomogeneity of each layer in the apparent energy resolution as a function of depth can be calculated. Automatic fits to the data were performed, and the roughness parameters, that is, the standard deviation of the thickness inhomogeneity of the relevant layers, were obtained, together with the thickness and stoichiometry of each layer. The results are compared with TEM and high resolution XRD experiments.