Semi In-Situ Observation on Void Formation in Electromigrated Sn-Ag Film and its Prediction by Random-Walk Simulation

In this study a thin metallic film composed of Sn-3.5Ag (wt.%) was subjected to a current density of 7.77×104 A/cm2 at room temperature, in order to test the ability of existing models of electromigration (EM) to predict the nucleation and evolution of voids generated by the resulting atomic migration. The computer simulation used to compute the coupled current distribution, thermal distribution and atomic migration problems relied on a Random Walk (RW) method that has not previously been applied to this problem but is particularly well suited to modelling a domain which is undergoing changes due to the formation of voids. Comparison of the experimental results and computer simulations provide proof of concept that the RW method can be successfully applied to this class of problem, but also that imperfections in the film can lead to deviations from the predicted patterns.