Assessment of mechanical properties of metallic thin-films through micro-beam testing

Abstract

Microelectronic industry is driven by the continuous miniaturization process conducing to the introduction of materials with better performance. These materials are subjected to stresses mainly due to thermal mismatch, microstructural changes or process integration which can be in the origin of mechanical reliability issues. To study these phenomena and even electromigration a good mechanical characterization of the materials is needed. This work aims at developing tests to assess fracture and elastoplastic behavior of thin Cu films. The tests developed are based on the deflection of microbeams (micromachined using a focused ion beam) using a nanoindenter. Different test geometries for microbeams have been evaluated and quantitative data have been obtained combining experimental results with analytical or numerical models, depending on the property under study. Microbeam response shows a strong dependence on the orientation of the grains close to the fixed end. Grain orientation has been measured by electron backscatter diffraction and the plastic behavior has been modeled by the finite element method using an in-house crystal plasticity subroutine. The effect of film thickness on fracture energy has been determined from tests of notched beams.