MEMS-based microstructures for nanomechanical characterization of thin films

Abstract

The measurement of mechanical properties of thin films is a major issue for the designof reliable microelectronic devices, microsensors or thin coatings. New simplemicrostructures actuated through the release of internally stressed long beamsmade of high temperature, low pressure chemical vapour deposition silicon nitridehave been developed to test under uniaxial tension submicron thin film materialspecimens. The relative displacement between a fixed and a moving cursor is used todetermine the strain applied to the specimen. The stress is inferred based onthe mismatch strain and Young’s modulus of the silicon nitride actuator beam.By multiplying the tensile test microstructures with different lengths, the fullstress–strain curve characterizing the thin material sample is generated fromwhich the elastic stiffness, yield strength, ductility and fracture stress can beextracted. The potential of the method is demonstrated through applicationson both brittle and ductile thin films. The Young’s modulus of 238 GPa for a373 nm thick silicon nitride film is extracted and size effects are observed for theyield strength of pure aluminium with a value of 220 and 550 MPa, respectively,for 373 and 205 nm thick films. An original variant of the procedure based onthis new test microstructure for measuring Young’s modulus is also presented.