Measurements of residual stresses in thin films using micro-rotating-structures

In the present study, micro-rotating-structures for local measurements of residual stresses in a thin film were simulated by the finite element method (FEM). A sensitivity factor - the ratio of the deflection of the micro-structure to the normalized residual stress is introduced and tabulated from the FEM results. Thereafter, a formula to calculate the residual stress is given so that the residual stress can be easily evaluated from the deflection of the rotating beam. A variety of optimized micro-rotating-structures were then designed and fabricated to verify the FEM results. Residual stresses in both silicon nitride and polysilicon thin films were determined by this technique and compared with measurements by the wafer-curvature method. The two methods lead to comparable results. In addition, the micro-rotating-structures have the ability to measure spatially and locally a large range of residual tensile or compressive stresses.