Wafer Scale Testing of MEMS Structural Films

Abstract

AbstractBiaxial modulus and residual stress of silicon-rich silicon nitride (Si3 + xN4−x) films on silicon substrates were measured at multiple discrete locations across wafer surfaces using a versatile bulge testing method. An array of 0.2 μm thick silicon nitride membranes were fabricated across the surface of 100 mm diameter wafers. The membranes were 1 mm square. Material properties of the film were extracted by measuring the deflection of the silicon nitride membranes under controlled pressure loading conditions. Pressures from 0 to 12 psi were applied across the membranes, while their deflected shapes were measured with a white light interferometer. Numerical analysis of the measured pressure-deflection behavior of the membranes enabled the biaxial modulus and residual stress of the film to be mapped over the wafer surface. These initial results indicated that the technique was able to determine biaxial modulus to within ±1 % and residual stress within ±4 %. Furthermore, the technique can be applied to composite membranes, enabling the determination of biaxial modulus and residual stress of an additional film subsequently deposited upon the membrane film.