Micro Texture-Induced Variation of Mechanical Properties of Electroplated Copper Thin Films

Abstract

The mechanical properties of copper thin films formed by cold-rolling and electroplating were measured using a tensile test and nano-indentation. Both the Young’s modulus and the tensile strength of the films were found to vary drastically depending on the microstructure of the films. The Young’s modulus of the cold-rolled film was almost same as that of the bulk material. However, the Young’s modulus of the electroplated thin film was about a fourth of that of the bulk material. The microstructure of the electroplated film was polycrystalline and a columnar structure with a diameter of a few hundred-micron. The strength of the grain boundaries of the columnar grains seemed to be rather week. Such a columnar structure with porous grain boundaries caused the cooperative grain boundary sliding. As a result, the effective elasticity of the film became rather low and the superplastic deformation of the film appearred under an uni-axial tensile load. In addition, there was a sharp distribution of Young’s modulus along the thickness direction of the film. Though the modulus near the surface of the film was close to that of the bulk material, it decreased drastically to about a half at the depth of 1 μm. There was also a planar distribution of Young’s modulus near the surface of the film.