Atomic-scale perspectives on plastic deformation in homogenous Au bonding: Unraveling the role of diverse material defects

Gold homogeneous bonding is a promising technique for next-generation 3D-IC interconnects, offering low resistivity, favorable parasitic characteristics, and resistance to oxidation. However, the plastic deformation of gold during thermal cycling under service conditions, driven by various material defects, has not been extensively studied. This work investigates the mechanisms of plastic deformation in Au-Au thermosonic flip-chip joints through a comprehensive characterization of defects at the bonding interface, including basal-plane dislocations and their behaviors, stacking faults, and deformation twins (specifically barrier twin T1 and incoming twin T2). Notably, the incoherent twin boundary (ITB) of T1 dissociated into a 9R structure, comprising two distinct 9R phases with varying tilt angles, driven by the glide of Shockley partial dislocations (SPDs). This study provides quantitative analysis, revealing that a higher proportion of the edge component within the mixed dislocation requires increased stress for SPD emission. Finite element analysis indicates that the stress required for the emission of SPDs from the ITB dissociation is achievable during thermal cycling, with a maximum shear stress of approximately 354.25 MPa. This study offers new insights into the role of atomic-scale defects in the plastic deformation of Au-Au joints, contributing to a deeper understanding of deformation mechanisms in homogeneous gold bonding.