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 occurred in the Cu/Si3N4 interface at locations which were 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 were discussed.

In situ Observation of Electromigration-Induced Void Migration in Dual-Damascene Cu Interconnect Structures. A.V.Vairagar, S.G.Mhaisalkar, A.Krishnamoorthy, K.N.Tu, A.M.Gusak, M.A.Meyer, E.Zschech: Applied Physics Letters, 2004, 85[13], 2502-4