Direct Observation of Void Nucleation and Growth in a 2-µm-Wide Cu Redistribution Line During In Situ Electromigration

In this study, we reported direct observation of void nucleation and growth in a fan-out 2-µm-wide Cu redistribution line (RDL) embedded in polyimide dielectric layers using in situ scanning electron microscope (SEM) investigations. The electromigration experiment was conducted with an extremely high current density of
$1.14 \times 10^{7}\mathrm{A}/\text{cm}^{2}$
under an ambient condition. Current stressing induced the nucleation, growth, and coalescence of nanovoids on grain boundaries. Nano-scale delamination at the local Cu oxide/Cu RDL interface occurred. The electromigration-induced reliability challenge correlated with the void evolution in the Cu RDL was reported for the failure behavior and mechanism.