Novel Cu-to-Cu Bonding With Ti Passivation at 180 $^{\circ}{\rm C}$ in 3-D Integration

A novel CMOS-compatible bond structure using Cu-to-Cu bonding with Ti passivation is demonstrated at low temperature and investigated. With the Ti protection of inner Cu, Cu bonding temperature can be reduced to 180 °C. In addition, excellent electrical stability against humidity and temperature cycling is achieved. Diffusion behavior and mechanism of Cu and Ti are also discussed. With excellent bond results and reliability, this bonded scheme has the potential to be applied in 3-D integration.