A Low-Cost Passivation for Low Temperature Cu-Cu Bonding Using PVD-Deposited Cu₃N

Abstract

PVD-deposited Cu3N has been demonstrated for Cu-Cu bonding as a low-cost passivation material. Cu3N exhibits stability at room temperature but undergoes decomposition upon heating, making it an attractive candidate for Cu bonding passivation. XRD analysis reveals that the decomposition of PVD-deposited Cu3N primarily occurs within the temperature range of 200℃~250℃. Cu3N-Cu3N bonding, relying on the decomposition reaction, is successfully demonstrated, and TEM analysis confirms the presence of Cu grains at the bonding interface. Moreover, Cu bonding using Cu3N passivation has been demonstrated as well. The bonding capability at low temperatures is found to be influenced by the thin film properties of Cu3N. For wafer level bonding, the N2 flow rate during Cu3N deposition requires careful adjustment to balance the antioxidation capability and the N2 outgassing phenomenon. For chip level bonding, the N2 outgassing phenomenon poses no significant issue. By demonstrating the potential of Cu3N as a passivation material, this study suggests a promising method for achieving lower temperature requirements in Cu bonding through the adjustment of Cu3N thin film properties.