In situ observation of electromigration-induced void migration in dual-damascene Cu interconnect structures

In situ electromigration experiments were carried out to study electromigration-induced failure in the upper and lower layers in dual-damascene Cu test structures. The observations revealed electromigration-induced void movement along the Cu/dielectric cap interface. It supports the premise that Cu∕Si3N4 interface acts as the dominant electromigration path. However, the observed void nucleation occurs in the Cu∕Si3N4 interface at locations which are far from the cathode, and void movement along the Cu∕Si3N4 interface in opposite direction of electron flow eventually causes void agglomeration at the via in the cathode end. The different electromigration behaviors of the upper and lower layer dual-damascene structures are discussed.