Enhanced Cu-to-Cu Bonding by Using Sn Passivation Layer

This study discusses the advantage of Sn-passivated Cu-to-Cu bonding compared to Cu-to-Cu direct bonding. However, Sn-capped Cu bonding in the semiconductor industry has been studied since 15 years ago, and seldom research indicated that the Sn passivate layer can tolerate surface height difference in the Cu-to-Cu bonding. Moreover, in the previous related study, the Sn layer thickness was thicker than 1.2 μm, and the bonding temperature was higher than 250°C. In this experiment, 1 μm Sn is electroplated over the Cu to compensate for the Cu surface height difference and lower the bonding temperature and pressure. Furthermore, the process was done by thermal compressive bonding (TCB), and two temperatures, 250°C and 220°C, were conducted in the experiment. Furthermore, 1 MPa and 1-minute bonding condition is used in the experiment to meet the low-pressure and high-efficient bonding process. To conclude, by passivating Sn over Cu, severe condition is not required.