FEM simulation of micro-rotating-structures and their applications in measurement of residual stresses in thin films

FEM simulation of micro-rotating-structures was performed for local measurement of residual stresses in thin films. A sensitivity factor is introduced, studied and tabulated from the simulation results. The residual stress can be evaluated from the rotating deflection, the lengths of rotating and fixed beams, and the sensitivity factor. The micro-structure technique was applied to measure residual stresses in both silicon nitride and polysilicon thin films, before and after rapid thermal annealing (RTA), and further confirmed by wafer curvature method. Residual stresses in polysilicon films at different RTA stages were also characterized by micro-Raman spectroscopy (MRS). The experimental results indicate that micro-rotating-structures indeed have the ability to measure spatially and locally residual stresses in MEMS thin films with appropriate sensitivities.