Engineering a Tunable Cu-Selective Oxide-Suppressing Coating to Enable Reliable Cu-to-Cu Direct Bonding for Advanced Interconnects

The continuous scaling of semiconductor devices, driven by Moore’s Law, demands advancements in interconnect technologies. Cu-to-Cu direct bonding has emerged as a critical solution for enabling ultra-fine pitch, high-density interconnections with superior electrical and thermal performance compared to traditional Cu-to-solder joints. This bonding method is pivotal for applications such as 3D integration, FOWLP, and 2.5D/3D packaging, supporting miniaturization, high-speed data transfer, and improved thermal management. However, Cu oxidation during processing presents a significant barrier, degrading bond integrity, increasing interfacial resistance, and complicating backend-of-line (BEOL) packaging integration. To address these challenges, we developed an ultra-thin (2–5 nm) Cu-selective oxide-suppression coating using standard industry-compatible techniques, including chemical vapor deposition (CVD) and liquid-phase deposition (LPD). The coating effectively prevents Cu oxidation during high-temperature thermal compression bonding (TCB) without requiring high-vacuum equipment or costly metal coatings, enabling scalability for heterogeneous packaging. RAIRS-QCM metrology validated the coating’s chemical stability and persistent oxidation resistance even after two months of ambient storage. Oxidation suppression efficiency of ~53% was confirmed by RAIRS characterization following an annealing at ~300°C in ambient air for 1 hour. Bonding evaluations were performed on 5 nm passivated Cu substrates under optimized bonding conditions. Shear testing revealed an average force of 40.7 ± 4.2 kgf/cm 2 , exceeding MIL-STD-883 requirements. Cross-sectional STEM confirmed a defect-free Cu-Cu bonded interface, while STEM-EDX analysis verified that the coating effectively suppressed oxidation without impeding Cu-to-Cu bonding. This work establishes the developed coating as a scalable, high-throughput solution to enhance Cu-to-Cu bonding reliability, enabling next-generation semiconductor packaging with improved electrical, mechanical, and thermal performance.