Plasma Processes and Associated Mechanisms of Hybrid Bonding for Heterogeneous Integration: A Review

Abstract

The hybrid bonding for heterogeneous integration has gained momentum for advanced applications in image sensors (IS), high performance computing (HPC), and artificial intelligence (AI). The hybrid bonding can enable the chip-to-chip interconnections at ultra-high density for increased bandwidth, energy efficiency and design feasibility with scalability beyond achievable by microbumps. The continuous improvement is yet ongoing to expand to applications requiring low hybrid bonding temperature, deep submicron hybrid bonding pad pitch and high quality of hybrid bonding with high yield and reliability performance. The multi-disciplinary research to understand the bonding mechanisms on materials and processing on metal and dielectrics with different characteristics could help to further advance the technology. This review emphasizes the roles of plasma processes on hybrid bonding especially on plasma processed dielectric characteristics, plasma surface treatment enhanced hybrid bonding quality, impact of post annealing to the plasma activated dielectric bonding, associated dielectric-dielectric bonding mechanisms, impact of plasma treatment on Cu surface, and Cu surface passivation during plasma activation. It first refreshes the fundamental technology developed from Si/SiO2 wafer bonding to lay the foundation followed by the recent progress in the understanding of mechanisms of SiCN-SiCN bonding including but not limiting to plasma damage, dangling bonds, water stress corrosion, and interfacial voids. The requirements of dielectric capping layer and a few alternative candidates for capping layer dielectrics are reviewed for feasibility. The requirements of pre-bonding Cu surface is atomically clean. However, the embedded Cu pads in dielectrics would be exposed to the same plasma conditions as the dielectrics. Concerns of Cu surface compound formation during plasma surface activation and the progresses of co-optimization plasma chemistry for both dielectric and Cu are addressed. The challenges and future development are highlighted for reaching the ultimate manufacturing goals of high yield and high reliability hybrid bonding for versatile applications.