Evaluation of anisotropic biaxial stress in Si_1-xGe_x/Ge mesa-structure by oil-immersion raman spectroscopy

Si_1-xGe_x is one of the prospective materials for the next-generation transistors due to its high carrier mobility, especially for high Ge concentration Si_1-xGe_x. Inducing strain in the Si_1-xGe_x leads to transistor performance improvement, however it is difficult to evaluate strain induced in the channel region because the strained Si_1-xGe_x channel may be scaled down to nanosize and relaxed complicatedly. We adopted oil-immersion Raman spectroscopy to evaluate the stress in the Si_1-xGe_x nanostructure. In this technique, the anisotropic biaxial stress state in the Si_1-xGe_x nanostructure can be evaluated. As a result, the nanostructure size dependence of the biaxial stress states in the Si_1-xGe_x mesa structure on the Ge substrates was obtained, which was confirmed for the Si_1-xGe_x with 76, 85, 92% Ge concentrations.