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Three types of bonding, including Cu-In, Sn/In-Cu, and Cu/Ti-Ti/Cu, are investigated for the application of 3D interconnects. Cu-In bonding and Sn/In-Cu bonding can form intermetallic compounds at the bonding temperature lower than 180 °C. In addition, for Cu/Ti-Ti/Cu bonding, Cu can be protected from oxidation by capping Ti on Cu surface before bonding. This method can further decrease bonding temperature. All bonded structures have shown excellent electrical performance and reliability characteristics. Based on bond results, these structures can be applied for low temperature bonding in 3D interconnects.

A low temperature bonding technology of Sn/In composite solder bonded to Cu interconnect is proposed and investigated. The intermetallic compounds formed in the bonded interconnects can survive well in the following process. The Sn/In-Cu interconnects bonded at low temperature all exhibit excellent electrical performance and high resistance to multiple current stressing, showing a great potential in 3D applications.

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.