Microbridge testing of silicon nitride thin films deposited on silicon wafers

A novel microbridge testing method for thin films is proposed. Theoretic analysis and finite element calculation are conducted on microbridge deformation to provide a closed formula of deflection vs load, considering both substrate deformation and residual stress in the film. Using the formula, one can simultaneously evaluate the Young's modulus, residual stress and bending strength of thin films from experimental load-deflection curves. The microbridge test is conducted with a load and displacement sensing nanoindenter system equipped with a microwedge probe. Samples for the microbridge test are prepared by the microelectromechanical fabrication technique such that they are easy to handle. Silicon nitride films fabricated by low pressure chemical vapor deposition on silicon substrates are tested to demonstrate the proposed method. The present work shows that the Young's modulus, residual stress and bending strength for the annealed silicon nitride films are 202.57 ± 15.80 GPa, 291.07 ± 56.17 MPa, and 12.26 ± 1.69 GPa, respectively.