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From Electrical to Physical-Chemical Characterization of the Cu/SiO₂ Hybrid-Bonding Interface—A Cu₂O-Layer as a Cu Diffusion Barrier?

This letter discusses copper (Cu) diffusion in the framework of the development of future 3D stacked devices by means of hybrid bonding-based interconnects. Indeed, at the bonding interface, due to the bonding tool accuracy, an inherent misalignment exists between top and bottom tiers leading to a direct contact between copper and neighboring dielectrics. Our experimental studies do not evidence any copper diffusion for the analyzed hybrid bonding-based test structures. Indeed, BTS/TVS (Bias Temperature Stress/Triangular Voltage Sweep) electrical characterization does not evidence any mobile ions diffusion. Our Electron Energy Loss Spectroscopy (EELS) analysis reveals the presence of a thin layer (~3 nm) of cuprous oxide (Cu2O) at the copper/dielectric interface that most probably acts as a diffusion barrier to copper.