Effect of Graphene Interlayer on the Structural and Mechanical Integrity of Ni/Cu Contacts

Abstract

Copper (Cu) remains a key material for advanced microelectronic interconnects due to its high electrical conductivity, scalability to nanoscale dimensions, and compatibility with established fabrication processes. However, its susceptibility to oxidation and interdiffusion with capping layers such as Ni poses significant challenges for the long-term thermal stability and mechanical reliability of Ni/Cu structures. The development of ultrathin and effective diffusion barriers is therefore critical for next-generation Cu-based contact technologies. In this context, graphene has emerged as a promising candidate owing to its atomic thickness, high chemical stability, and exceptional resistance to atomic diffusion. The effect of a graphene interlayer on the thermal stability, diffusion behavior, and tribological performance of Ni/Cu contacts was investigated. Graphene was deposited onto bulk Cu using chemical vapor deposition (CVD), followed by physical vapor deposition (PVD) of a 20 nm Ni film, and the resulting Ni/graphene/Cu structures were subjected to vacuum annealing at 450 °C. Auger electron spectroscopy revealed that graphene effectively suppresses bulk diffusion of Cu and Ni atoms, while limited diffusion along grain boundaries remains, with Cu concentration in the Ni layer not exceeding 5–10 at. %. Quantitative analysis using the Hall–Morabito and Fisher–Whipple models enables separation of bulk and grain-boundary diffusion contributions, demonstrating that residual transport occurs predominantly along grain-boundary pathways and defect sites within the graphene layer. In addition to enhancing compositional stability, graphene reduces surface roughness by nearly 50% at room temperature and by approximately 55% after annealing, significantly improves wear resistance, and prevents the formation of deep microcracks. A modest reduction in tribological performance at elevated temperatures is attributed to wrinkle formation and defect-mediated transport. Overall, these findings demonstrate that graphene acts as an effective diffusion barrier, improves surface morphology, and contributes to the mechanical reliability of Ni/Cu contacts, offering a viable pathway to improved performance and durability of microelectronic metal contacts.