Microbridge Tests on Bilayer Thin Films

In the present work, we report a microbridge testing method for a bilayer microbridge beam initially buckled by a residual compressive resultant force and a residual moment. A theoretical formula is derived in closed form with the consideration of substrate deformation. Measuring the profile of the initial buckling, one can evaluate the Young's modulus and residual stress of each layer of the bilayer beam. Alternatively, the Young's modulus and residual stress can be evaluated also from the loaddeflection curve of the microbridge. Experimentally, Si₃N₄(200 nm)/SiO₂(400 nm) microbridge samples were fabricated on a silicon wafer by the micromachining technique. The Young's modulus and residual stress were determined from the microbridge test to be 35 ± 2 GPa and –380 ± 20 MPa for the silicon oxide layer and 250 ± 7 GPa and 470 ± 15 MPa for the silicon nitride layer.