Investigation of biaxial strain in strained silicon on insulator (SSOI) using high-resolution x-ray diffraction

Intrinsic biaxial strain values of strained Si on insulator (SSOI) layers were measured using symmetric Bragg-Brentano configuration (i.e., {004} 0-20scans) and asymmetric {224} rocking curves. We confirmed that the twist angle between the layer and substrate can be incorporated into the biaxial strain equations for epitaxial layers. Moreover, as the samples were annealed up to 1200°C, the tensile parallel strains increased from 0.56% to 0.7%. 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 the increasing parallel strains after annealing.