Anti-oxidation property of nanotwinned copper micro-cone array for low-temperature bonding

Solid-state insertion bonding utilizing nanotwinned copper micro-cone array (nt-Cu MCA) was regarded as a potential solution to the vertical interconnection of chips. It is widely acknowledged that oxide on the Cu substrate is a hazard to the Cu/Sn bonding. However, the anti-oxidation property of nt-Cu MCA has not been evaluated, which is exactly the focus of our investigation. We measured the thickness evolution of oxide film on nt-Cu MCA during heated in air condition, which was determined to follow logarithmic law. Molecular dynamics (MD) simulation showed that the growth rate of oxide slowed down as it thickened. Surface morphology observation revealed that oxide particles segregated around the grain boundaries, while twin boundaries had little effect on the oxidation, which was verified by MD simulation. The oxygen content on nt-Cu MCA was about half that on fine-grained Cu (fg-Cu), which can be ascribed to the small amount of grain boundaries. The great anti-oxidation property of nt-Cu MCA ensures the quality of Cu/Sn bonding in the future application in low temperature solid-state bonding.