Time-of-flight medium energy ion scattering study of epitaxial [formula omitted] superlattice structures

Abstract

The ability to determine structural and compositional information from the sub-surface region of a semiconductor material has been demonstrated using a new time-of-flight medium energy ion scattering (ToF-MEIS) system. A series of silicon-silicon/germanium ( Si Si 1 − x Ge x ) heterostructure and multilayer samples, grown using both solid source molecular beam epitaxy (MBE) and gas source chemical vapour deposition (CVD) on Si(100) substrates, have been investigated. These data indicate that each individual layer of Si 1 − x Ge x ( x ∼ 0.22) in both 2 and 3 period samples, can be uniquely identified with a resolution of approximately 3 nm. A comparison of MBE and CVD grown samples has also been made using layers with similar structures and composition. ToF-MEIS showed that the MBE grown samples exhibit a much higher Ge concentration per layer than CVD grown samples. Surface segregation of Ge was observed for the MBE grown samples, but appears to be suppressed in the case of CVD grown samples. These data indicate the ability of ToF-MEIS to probe the differences in the kinetics associated with Ge incorporation and segregation between the two techniques. The total Ge content of each sample was confirmed independently using conventional Rutherford backscattering spectrometry (RBS).