Electrical and Reliability Investigation of Cu-to-Cu Bonding With Silver Passivation Layer in 3-D Integration

In this article, low-temperature Cu-Cu bonding with the Ag passivation layer was accomplished at 180 °C for 3 min without a postannealing process. The Ag passivation layer effectively prevents Cu from oxidation and assists Cu diffusion to realize low-temperature bonding. The small grain size of the Ag passivation layer controlled by sputtering working pressure is observed to improve bonding quality. Different plasma treatment parameters and bonding conditions were executed to evaluate bonding quality. The diffusion behavior of passivation bonding is investigated, and the corresponding mechanism is discussed as well. In addition, reliability assessments, including thermal cycling, high-temperature storage, and unbiased highly accelerated stress test, indicate excellent stability of this bonding structure, showing the potential for low-temperature bonding technology in 3-D integration applications.