In-situ SEM electromigration studies were performed atfully embedded via/line interconnect structures to visualize thetime-dependent void evolution in inlaid copper interconnects. Voidformation, growth and movement, and consequently interconnect degradation,depend on both interface bonding and copper microstructure. Two phases aredistinguished for the electromigration-induced interconnect degradationprocess: In the first phase, agglomerations of vacancies and voids areformed at interfaces and grain boundaries, and voids move along weakinterfaces. In the second phase of the degradation process, they merge intoa larger void which subsequently grows into the via and eventually causesthe interconnect failure. Void movement along the copper line and voidgrowth in the via are discontinuous processes, whereas their step-likebehavior is caused by the copper microstructure. Directed mass transportalong inner surfaces depends strongly on the crystallographic orientation ofthe copper grains. Electromigration lifetime can be drastically increased bychanging the copper/capping layer interface. Both an additional CoWP coatingand a local copper alloying with aluminum increase the bonding strength ofthe top interface of the copper interconnect line, and consequently,electromigration-induced mass transport and degradation processes arereduced significantly.
