High temperature electromigration behavior of cobalt lines observed by in situ transmission electron microscopy.

This article focuses on the in situ transmission electron microscopy (TEM) analysis of electromigration (EM) behavior in cobalt (Co) microelectronic interconnects as a potential replacement for copper (Cu) in back-end-of-line (BEOL) applications. The study examines void nucleation, growth, and migration under high current densities (∼5 × 10^6 A/cm²) and temperatures ranging from 300 to 1000 °C, particularly around the effective valence (Z*) inversion temperature where EM flux direction changes. Results indicate that failure mechanisms and times are relatively insensitive to temperature within 600–900 °C, with line width and grain structure playing a more significant role in EM damage evolution; narrower lines tend to fail via growth of single voids forming slit failures, while wider lines fail through the intersection of multiple voids. Additionally, devices with uniform temperature profiles exhibit longer lifetimes than those with large thermal gradients, and the findings provide insights relevant for designing EM-resistant Co interconnects in advanced semiconductor devices.