Accurate, non-time-intensive evaluation of the stress-migration endurance for layered Al interconnects

A new method has been developed to evaluate the stress-migration (SM) endurance of layered Al interconnects stacked with refractory metals. The stress-migration endurance of layered interconnects has so far been evaluated in a manner similar to that for single layer interconnects, by monitoring the resistance change. However, in the case of layered interconnects it is hard to detect the resistance change by the conventional electrical method since the resistance change arising from void generation in the Al portion of the layered interconnect is negligibly small. In this work, a new method for monitoring stress relaxation characteristics in layered Al interconnects has been developed. A stress relaxation model based on creep deformation theory was applied and coupled with the Tezaki model to predict SM lifetime. The stress in interconnects was directly measured by the X-ray diffraction method. The stress relaxation ratio and SM lifetime were derived from the stress relaxation characteristics in the layered interconnect. The SM endurance of layered interconnects in multilevel interconnection structures was evaluated utilizing the new method. It was found for the first time that the SM endurance of the lower-most interconnect is the best in a multilevel interconnection structure.<>