Crystal-direction dependence of uniaxial tensile strain in ultra-thin SOI

The magnitude of uniaxial strain, which depends on the direction of crystal orientation in ultra-thin SOI structure, was described. The crystal-direction dependence was derived from the anisotropic elastic constants of silicon and SiGe. The initial strain of 1.2% in SiGe and zero in silicon, was maintained in the layers during the investigation. For the bi-layer case with 1-2nm Si/30nm SiGe, the asymmetry contribution dominates relaxation of rectangular islands, generating tension in the short direction, while the long direction remains compressively strained. The results show that uniaxial tensile strain as large as 1.0% in the 〈100〉direction can be achieved in 10-nm silicon films.