Molecular dynamic simulation of grain size and work temperature effect on mechanical properties of polycrystalline copper

Polycrystalline copper is considered by the industries to be the best TSV electroplating material and other interconnected structure material because of its ultra-low resistivity, high conductivity, low electro-migration rate and good compatibility with the multilayer interconnects process. Its mechanical properties are completely different from the bulk monocrystalline copper, these properties are critically vital to evaluate the thermomechanical reliability of TSV and interconnected structure in 3D packaging. To investigate the effect of the work temperature and grain size on the mechanical properties of polycrystalline Cu, The MD simulations of uniaxial tensile test are performed. The results showed that the elastic modulus gradually increases with the augment of the mean grain size, and the corresponding flow stress concurrently increases, and the flow stress is proportional to the square-root of the grain size, which satisfies the inverse-Hall-Petch relation. It also turned that the elastic modulus decreases with increasing of ambient temperatures, the flow stress is negatively correlated with the temperature. From all the tensile simulation tests, it was confirmed that the mechanism of plastic deformation for polycrystalline copper with 4.65-9.31nm grain sizes is mainly the grain's rotation and grain- boundary sliding, the dislocation nucleation and migration is no longer the dominant factor of plastic deformation.