Facilitating High-Reliability Cu-to-Cu Direct Bonding via Tunable Cu-selective Oxide suppression Coating 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 major 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 such as 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. RAIRS analysis confirmed ~52% oxidation suppression after 1-hour annealing at 300°C in air. Bonding tests on 5 nm passivated Cu at 300°C, 40 MPa for 1 hour showed strong Cu–Cu bonds with a shear strength of 40.7 ± 4.2 KgF, exceeding MIL-standard. STEM-EDX confirmed a defect-free interface and effective oxidation suppression without hindering bonding. This work establishes the developed coating has strong potential 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.