Void Growth Modeling Upon Electromigration Stressing In Narrow Copper Lines

A simple three-dimensional void growth model is presented that can be used to simulate the resistance behavior in narrow copper lines upon thermo-electrical stressing. The output of the model is compared with experimental results obtained from electromigration tests carried out on single damascene copper lines encapsulated by a physical vapor deposition tantalum nitride-tantalum barrier. The electromigration resistance profiles are found to depend on different line and barrier parameters. The simulations yield a better understanding of the physical phenomena responsible for changes in the resistance profiles. The effect of a void cutting a copper line is seen as an asymptotic increase or "jump" in the measured resistance profile. At that moment, the barrier shunts the current and the void does not necessarily induce a catastrophic failure. Therefore, more voids can be formed in the line upon electromigration (EM) stress; every void spanning the line initiates a "jump" in the resistance profile. The described model approximates the experimental results with sufficient accuracy. The model can be used to predict the height of the jumps, setting adequate failure criteria beforehand for the EM experiments. The simplicity and sufficient accuracy of this model allow for easy prediction and interpretation of the EM resistance traces. (c) 2007 American Institute of Physics.