Resonance measurements of stresses in Al/Si3N4 microribbons

Film stresses in doubly-supported bi-layer micro-ribbons have been determined by measurement of their resonant vibration frequency. The composite aluminum/silicon-nitride ribbons constitute a programmable diffraction grating in which ribbon stresses play an important role in device behavior. To determine the intrinsic film stresses in each layer, special ribbon arrays were fabricated in which the coverage of aluminum was systematically varied from end toward the center of each ribbon. With increasing aluminum coverage, the ribbons exhibit a characteristic roll-off in resonant frequency which can be used to refine longitudinal film stresses. An analytical expression describing resonant frequency as a function of partial layer coverage is derived. By least-squares fitting this function to the observed roll-off, the film stresses in each layer are determined. It is found that the silicon-nitride stresses are large and tensile (approximately 800 MPa), while those in the aluminum are small and compressive (approximately -100 MPa).; This paper reviews the relevant theory behind the approach, demonstrates its application to wafer- level data and discusses its repeatability and accuracy.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.