Low Temperature Copper to Copper Direct Bonding.

We have observed that it is possible to direct bond copper to copper at low temperature. For sputtered Cu surface on silicon wafer without any further surface planarization, we determined that 100°C temperature and uniform pressure (107 N/m2) condition for three hours can produce a very strong Cu–Cu bond. A straight-pull test is completed and the results revealed that an adhesion promoter layer is required at the copper-silicon interface.