Microbridge testing of silicon oxide/silicon nitride bilayer films deposited on silicon wafers

The present work further develops the microbridge testing method to characterize mechanical properties of bilayer thin films. We model the substrate deformation with three coupled springs and consider residual stress in each layer to formulate deflection versus load under large deformation, resulting in a closed-form formula. If the mechanical properties of one layer are available, the closed formula is able to simultaneously evaluate the Young's modulus and residual stress of the other layer, and the bending strength of the bilayer films from the microbridge test. The analytic results are confirmed by finite element calculations. Using a load and displacement sensing nanoindenter system equipped with a microwedge probe, we conduct microbridge tests on low-temperature silicon oxide/silicon nitride bilayer films prepared by the microelectromechanical technique. The experimental results verify the proposed method, yielding the Young's modulus of 41.00±3.60 GPa, the residual stress of -180.88±7.90 MPa and the bending strength of 0.903±0.111 GPa for the low-temperature silicon oxide films.