Direct evidence of Cu/cap/liner edge being the dominant electromigration path in dual damascene Cu interconnects

In this investigation, Cu/dielectric-cap interface and Cu/cap/liner edge were studied in detail to identify the dominant path in electromigration stressed via-fed test structures that represent the dual damascene architectures in Cu metallization. The impact of the electron wind force on void evolution, agglomeration at the Cu/cap/liner edges, and interface diffusion was investigated based on morphological examinations. The investigations presented here show direct evidence of preferential accumulation of voids at the Cu/cap/liner edges. This preferential void accumulation towards Cu/cap/liner edge is analyzed and explained by means of a simplified Monte Carlo simulation.