3D simulation of the dislocation dynamics in polycrystalline metal thin films
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3D simulation of the dislocation dynamics in polycrystalline metal thin films B. von Blanckenhagen1 , E. Arzt2 , and P. Gumbsch1,3 1 University of Karlsruhe, izbs, Kaiserstr. 12, 76131 Karlsruhe, Germany 2 Max Planck Institute for Metals Research, Heisenbergstr.3, 70569 Stuttgart, Germany 3 Fraunhofer Institute for Mechanics of Materials, W¨ohlerstr. 11, 79108 Freiburg, Germany ABSTRACT The plastic deformation of polycrystalline fcc metal thin films with thicknesses of 1 µm and less is investigated by simulating the dynamics of discrete dislocations in a representative columnar grain. The simulations are based on the assumption that dislocation sources or multiplication sites are rare and that sources have to operate several times to generate appreciable plastic deformation. This model is thoroughly tested by calculating the response of randomly distributed dislocation sources to an applied stress and comparing the results with experimental data. Stress–strain curves, the influence of boundary conditions, dislocation densities, work hardening rates and their dependence on the film thickness as well as the dependence on grain orientation are studied. The agreement between simulation and experiment is good and many aspects of thin film plasticity can be understood with the assumption that small-scale plastic deformation is source controlled rather than mobility controlled. INTRODUCTION The miniaturization in microelectronics and micro-mechanics has led to a drastic reduction of the dimensions of the components in these devices. Interconnects in integrated circuits or tiny mechanical devices made from metallic materials often have thicknesses of 1 µm or below. The mechanical properties of these films differ dramatically from their bulk counterparts. Understanding the mechanical properties of thin metal films is therefore important in predicting the reliability of small scale devices. Experiments have shown that the flow stresses of thin metal films can exceed those of the corresponding bulk material by an order of magnitude and increase with decreasing film thickness [1, 2, 3, 4, 5]. To comprehend room temperature plasticity of thin films, it is necessary to study the effect of the confined geometry on the dislocation multiplication and motion. Grain size and film thickness of the films treated here are much smaller than the characteristic length scales of dislocation networks observed in bulk material after deformation. Therefore, the number of dislocations which have to be considered in order to understand thin film plasticity is rather small. A 3D discrete dislocation dynamics simulation (DDD) is used here to study thin film deformation by investigating dislocation motion in a representative columnar grain. Randomly distributed Frank–Read sources in the grain interior are used as the initial dislocation configuration. While the operation of a single Frank–Read source in the confined geometry of a thin film was investigated in previous papers [6, 7], this work includes the interaction between dislocations from different sources. S
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