Relationship between interfacial adhesion and electromigration in Cu metallization

Electromigration in Cu conductors differs from that in Al alloys. In Cu, it is almost exclusively via interfacial or surface diffusion whereas for Al alloys, diffusion at the temperatures of interest is primarily through the grain boundaries. It has been argued interfaces are such rapid pathways because of the poor adhesion between Cu metal and the adjacent materials from which the interface is composed. Accordingly, this study focuses on relating the electromigration induced drift velocity and the adhesion to Cu of upper surface cap materials. In addition, traditional electromigration lifetime studies were performed to correlate the results of the drift velocity measurements to device reliability. The results indicate that the adhesion of the Cu/cap interface can be directly correlated to the electromigration lifetime of copper conductors.