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 descri...