Investigation on Electromigration-Induced Failure and Reservoir Effect in AlCu Interconnects

Aluminum-copper alloy (AlCu) is commonly utilized as interconnect material in low-power devices. However, as the size of electronic devices continues to decrease and current density increases, electromigration (EM) has emerged as a significant reliability concern for AlCu interconnects in the microelectronics industry. In this study, two-level AlCu interconnect structures with a Ti/TiN barrier layer were fabricated using 0.18 μm technology to perform accelerated EM tests. The test samples were subjected to three current levels (1.45 mA, 2.40 mA and 5.30 mA) at three ambient temperatures (200 °C, 225 °C and 250 °C) to investigate the nucleation and evolution of voids during EM degradation and then obtain the mean time to failure (MTTF). The numerical simulation method of atomic density integral (ADI) was used to simulate experimental observations based on the ANSYS platform, considering the coupled effects of electron wind force, stress gradient, temperature gradient, and atomic density gradient. A comparison of the experimental results and numerical simulations proves that the ADI method can be applied successfully to EM failure prediction of AlCu interconnects. Finite element models with different reservoir lengths were built to demonstrate the mechanism of the reservoir effect. The results show that the reservoir can improve the EM lifetime of the interconnect, but there is a critical extension length beyond which increasing extension sizes have no effect on EM lifetime.