Room Temperature Cu-Cu Direct Bonding Using Wetting/Passivation Scheme for 3D Integration and Packaging

Ultra-low temperature wafer-level Cu-Cu direct bonding with wetting/passivation scheme has been successfully demonstrated at (1) room temperature with post-annealing at 100 ℃, or (2) 40 ℃ bonding without the post-annealing process. In this bonding structure, a wetting layer and a passivation layer were deposited on the Cu surface to improve the surface conditions and enhance the diffusion behavior of Cu atoms. In addition, the wetting layer can prevent formation of AuCu
3
between passivation and Cu, which is beneficial for Cu bonding at a lower temperature. The proposed bonding structure provides the breakthrough to realize wafer-level Cu-Cu direct bonding with an almost thermal stress-free process, which is key to improve reliability and broaden applications of 3D integration and advanced packaging.