Measurement of Anisotropic Biaxial Stresses in Si1-xGex/Si Mesa Structures by Oil-Immersion Raman Spectroscopy

Abstract

Anisotropic biaxial stress states in Si1-xGex/Si mesa structures were evaluated by oil-immersion Raman spectroscopy. Using a high-numerical-aperture lens, the electrical field component perpendicular to the surface, i.e., z-polarization, can be obtained. The z-polarization enables the excitation of the forbidden optical phonon mode, i.e., the transverse optical (TO) phonon mode, even under the backscattering geometry from (001)-oriented diamond-type crystals. The anisotropic biaxial stress evaluation of Si1-xGex was considered difficult compared with that of Si, because many unknown parameters exist for Si1-xGex, e.g., phonon deformation potentials (PDPs), the Ge concentration x, and the factor of Raman shift on x. In this study, PDPs and the Ge concentration in Si1-xGex were investigated in detail. As a result, using precise PDPs and x, a clear dependence of anisotropic biaxial stress states in Si1-xGex on the mesa structure shape was observed.