Thermal wave imaging of misfit dislocations and correlation with minority carrier lifetime

Abstract

It has recently been demonstrated that oxidation-induced stacking faults in silicon can be imaged in a non-contact manner using a modulated optical reflectance method associated with the propagation of thermal waves and plasma waves in the material. We applied the high spatial resolution capability of this imaging technique to the observation of epitaxial misfit dislocations at the interfaces of a layer of germanium-doped silicon buried within a silicon structure. The samples were angle-lapped and polished to allow the inspection over the whole depth of the structure. The misfit dislocation images dramatically demonstrate the capability of the technique for the detection of defects beneath the silicon surface. The minority carrier lifetime of such structures, which has been determined previously using a depth-dependent technique, is correlated with the intensity of the modulated optical reflectance signal. Using a stack of epitaxial Si/Si(Ge) layers with various Ge concentrations, the modulated optical reflectance is shown to be proportional to the concentration of germanium.