Raman Scattering Characterization of Residual Stresses in Silicon-on-Sapphire

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Abstract
In order to characterize the residual stresses in silicon-on-sapphire wafers, polarized Raman scattering measurements were made by probing both from the silicon-free surface side and from the silicon/sapphire interface (sapphire substrate) side at three different wavelengths. These measurements are described here. A theoretical consideration of the Raman tensors and frequency shifts in silicon crystals stressed by unknown forces is also given in this paper. It is found that the residual stresses are not uniform, but are distributed in the direction normal to the silicon film plane. The residual compressive stress is relaxed from the interface toward the silicon-free surface with an accompanying shear stress. The residual compressive stress is estimated to be 6.0×108∼13.0×108 N/m2 at the silicon/sapphire interface and 5.5×108∼7.5×108 N/m2 at the silicon-free surface.