Bonding Mechanisms and Interfacial Stress in Cu–Cu Direct Bonding
As semiconductor integration advances toward high-density 3D architectures, Cu–Cu direct bonding is emerging as an important approach for enabling ultrafine-pitch interconnects beyond conventional solder-based microbumps. By eliminating the solder and forming a direct Cu–Cu interface, this approach can provide low electrical and thermal resistance while supporting much finer interconnect dimensions. However, reliable bonding at low temperatures and increasingly small dimensions requires a fundamental understanding of Cu surface and grain-boundary diffusion, interfacial contact, and microstructural evolution. Our research investigates the mechanisms that govern Cu–Cu bonding and how processing conditions, surface structure, and interface characteristics influence bond formation.
A particular focus is on the role of interfacial diffusion in promoting atomic-scale contact and strengthening across the Cu–Cu interface. We study how surface morphology, crystallographic orientation, grain structure, and bonding temperature affect diffusion and interfacial evolution, with the goal of enabling robust bonding at reduced thermal budgets. This work aims to establish scaling and process–structure–property relationships for Cu–Cu direct bonding, providing design principles for reliable ultrafine-pitch interconnects in next-generation 3D heterogeneous integration, including logic, memory, and advanced chiplet architectures.
