Growth of electromigration-induced hillocks in Al interconnects

Electromigration-induced hillock growth in polycrystalline Al segments was extensively investigated. Hillocks composed of columnar grains grew near the anode by epitaxial Al addition at the interface between the Al and underlying TiN layer, which pushed up the original Al film. The hillocks rotated away from their initial (111) out-of-plane orientation in a manner consistent with the physical rotation of the hillock surface. Wedgelike and rounded hillocks were observed, and their formation is explained by the interaction between grain extrusion and grain growth. Trends elucidated by review of both thermal- and electromigration-induced hillock studies can be explained by the mechanisms identified in this work.