Low temperature (<180°C) wafer-level and chip-level In-to-Cu and Cu-to-Cu bonding for 3D integration

Two bonded structures, Cu/In bonding and Cu-Cu bonding with Ti passivation, were investigated for the application of 3D interconnects. For Cu/In bonding, the bonds were achieved at 170°C due to the isothermal solidification. The intermetallic compounds formed in the joint was Cu₂In phase. For another case, Cu-Cu bonding with Ti passivation was successfully achieved at 180°C Application of Ti passivation can protect inner Cu from oxidation; therefore, the required bonding temperature can be decreased. Compared to direct Cu-Cu bonding, Cu/In bonding and Cu-Cu bonding with Ti passivation can be performed at low temperature, which can meet low thermal budget requirement for most devices. Besides, with the good electrical performance and reliability, these two bonded interconnects can be applied for 3D IC interconnects.