Strain characterization of strained silicon on insulator including the effects of rotational misalignment

Abstract

High resolution x-ray diffraction (XRD) techniques were used to characterize the perpendicular and parallel strains in strained Si-on-insulator (SSOI) layers. XRD profiles generated from the crystalline SSOI layer provided a direct measurement of the layer’s strain components. Calculated strain values, such as the compressive perpendicular and tensile parallel strains, were consistent with expected values. In addition, we have demonstrated that the rotational misalignment (Δϕ) between the layer and the substrate can be incorporated within the biaxial strain equations for epitaxial layers. Strain components calculated using the modified equations showed 1%–5% increase with respect to values obtained using typical strain relations. We observed an interesting phenomenon in that the tensile parallel strains increased from 0.56% to 0.7% upon annealing. This behavior was contrary to unconstrained strain relaxation but was consistent with layer constraint and the existence of finite stresses at the Si∕SiO2 interface, resulting from the difference in coefficients of thermal expansion between Si and SiO2. Since both the overlying strained Si and underlying substrate maintained a stressed state in the buried SiO2, the compressively strained oxide retained the lattice expansion of the overlying strained Si and resulted in increasing parallel strains after annealing. These results are consistent with a balanced strain structure between the strained Si overlayer and the underlying thermally grown oxide and with the related strain evolution during heat treatment.