In-situ observation of electromigration failure in AlCuSi interconnects with a passivation film

In-situ observation with an optical microscope of electromigration in a widely used Al-0.5wt%Cu-1wt%Si interconnects was conducted to study the mechanism of void formation and transportation. In the case of an interconnect covered with a passivation film, generation of voids occurred in the cathode side around a triangle shaped notch, which was introduced to be able to detect void formation. The voids accumulated in the cathode side and moved toward the cathode end. Rupture occurred in the cathode side, which was damaged by electromigration. On the other hand, in the case of an interconnect without a passivation film, generation and accumulation of voids was observed at the tip of the notch. Growth of voids was found at the tip of the notch and the rupture occurred at this damaged region. The authors analyzed the theory of void transport by electromigration and stress. The experimental results are in good agreement with the theoretical results and show that electromigration is significantly influenced by the stress in the interconnection. Moreover, the mechanism of void growth was discussed to consider nucleation theory.