Measurement of Young's modulus on microfabricated structures using a surface profiler

Abstract

A point-force, load-deflection method using a stylus-type surface profiler to determine the Young's moduli (E_Y) of thin-film microstructural materials is introduced. In this method both force and deflection in microstructures are measured simultaneously by the profiler to provide a convenient and accurate means to obtain Young's modulus directly. Measurements on two types of micromechanical structures are described: a doubly supported bridge and a bridge-slider (a beam with one fixed end and one end that can slide in a flanged housing). The influence of residual stress in the doubly supported beam is described and accounted for theoretically to interpret measurements made on low-stress silicon-nitride films. For this material E_Y is 373 GPa. In the bridge-slider structure, residual strain is relaxed to zero. Measurements on a polycrystalline-silicon bridge slider show a value for E_Y of 123 GPa in unannealed material that is doped heavily with phosphorous, and grown at 650°C.

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