Interfacial and bonding characteristics of low-temperature Cu–Cu joints with an Au passivation layer

As the three-dimensional (3D) integrated circuit technology advances toward finer-pitch structures, hybrid Cu bonding has emerged as a superior alternative to conventional microbumps. However, Cu oxidation and the high thermal budgets required for bonding present significant technical hurdles. This study proposes depositing a uniform Au thin film on Cu surfaces via electroless plating to act as an oxidation barrier to overcome these limitations. To enable systematic investigation of interfacial evolution, bonding was conducted at 220 °C under 30 MPa for 1.5 h. The specific activation energies of Au–Cu interdiffusion causes the Au passivation layer to remain localized at the bonding interface, effectively suppressing Cu oxidation even under atmospheric pressure. The resulting joints exhibited excellent mechanical integrity, achieving a maximum shear strength of 57.8 MPa with minimal void formation and a low surface roughness. Compared to nonpassivated joints, the Au-passivated samples demonstrated superior reliability and performance even after postbonding annealing. These findings provide mechanistic insights into thickness-dependent interfacial diffusion, void evolution, and reliability behavior in Au-passivated Cu–Cu bonding systems.