Micro-Raman study of thermoelastic stress distribution in oxidized silicon membranes and correlation with finite element modeling

Silicon on insulator (SOI) pressure sensors show potential applications in high temperature environment. However, as a result of thermal mismatch, large stresses usually exist in the composite SiO2/Si membranes which would provide an otherwise promising substrate for such sensors. These stresses can significantly influence the long term reliability of such membranes. In this work a high spatial resolution (10 μm2) Raman spectroscopy method has been used to measure the localized stresses over an oxidized membrane, thus yielding stress maps. The method is based on the frequency shift of the Raman line at 520 cm−1. Shift between 0.05 and 1 cm−1 are observed. A three-dimensional commercially available finite element modeling (FEM) software (ANSYS) has been used to modelize the thermal stress distribution over the complete micromachined bilayer membrane. Its validity has been checked out through optical profilometer deflection measurements. The experimental Raman shifts were compared with those calculated using stresses from FEM and a biaxial stress hypothesis. Finally, the sensitivity of Raman stress mapping method for high temperature SOI pressure sensors is discussed.