The Effects of Microstructures on Normal and Early Failures of Interconnects Caused by Electromigration

Abstract

Microstructure plays a key role in reliability of interconnects. However, a quantitative correlation between microstructure and reliability of interconnects is lacking. This paper develops a statistical description of effective diffusivity of interconnects by considering grain boundaries, bulk lattice and line interface diffusion, and introduces a microstructure-based electromigration lifetime prediction model for normal failures of interconnects. Further, the probability of early failure of interconnects due to a severe microstructural inhomogeneity is calculated. Using the sub-population failure model, the mean time to failure of interconnects, with a range of microstructures from polycrystalline to hyper-bamboo, are simulated. The reported increase in lifetimes of wide polycrystalline lines with increasing w/d is mainly ascribed to reservoir effects of bonding pads in test structures. Reported lifetime prediction model may be used as guidance for circuit design and accelerated testing.