Electromigration characteristics of copper interconnects

The electromigration characteristics of electroless plated copper interconnects have been investigated under dc and time-varying current stressing. A novel scheme was reported for selective electroless Cu plating by using 150-A Co as the seeding layer. The Cu dc and pulse-dc lifetimes are found to be one and two orders of magnitude longer than that of Al-4%Cu/TiW and Al-2%Si interconnects at 275°C, and the extracted Cu lifetime at 75°C is about three and five orders of magnitude longer than that of Al-4%Cu/TiW and Al-2%Si, respectively. As previously reported for Al metallization, the Cu bipolar lifetimes were found to be orders of magnitude longer than their dc lifetimes under the same peak stressing current density because of the partial recovery of electromigration damage during the opposing phases of bipolar stressing.