Electromigration modelling of void nucleation in open Cu-TSVs

Recently, Through Silicon Vias (TSVs) have attracted much attention in three-dimensional (3D) integration technology due to their function as vertical connections of the different stacked semiconductor dies. Since electromigration (EM) will continue to be a key reliability issue in modern structures, the prediction of the EM failure behavior is a crucial necessity. Traditionally, Black´s equation has been used from the early times of EM investigations for the estimation of the interconnect time to failure. In this work we investigate the applicability of Black´s equation to open copper TSV structures using TCAD. TCAD can significantly contribute to the comprehension of EM failure mechanisms, in particular for the understanding of the early failure mode dominated by the void nucleation mechanism. The simulation procedure is applied to an open copper TSV technology in order to find the sites where void formation is most likely to occur. The time to failure is determined as the time needed to reach the stress threshold for void nucleation. Simulations are carried out for different current densities and successfully fitted to Black´s equation. In this way, we have shown that failure development in studied TSV structures obeys Black´s equation.