Electromigration and Temperature Cycling Tests of Cu-Cu Joints Fabricated by Instant Copper Direct Bonding

Because Cu-Cu bonding is the key technique in 3D IC packaging, its reliabilities will become issues in the future. In this study, Cu-Cu joints with underfill was fabricated by using instant bonding process, in which bonding conditions were under 31∼90 MPa at 300 °C for 10∼30 s. Several samples underwent two reliability tests: temperature cycling test (TCT) and electromigration (EM) test. These samples passed 1000 cycles TCT, and the measured EM life time was least 3 times longer than that of solder joints with similar dimension. Failure mechanisms of reliability tests were examined by cross-section images and finite element analysis. In TCT, cracks were formed at bonding interface because it is relative weak compared to the neighboring structures. For EM tests, voids were formed at passivation opening of joints with current crowding. The current study provides a fundamental understanding in the reliabilities of Cu/organic dielectric hybrid bonding structures.