Low-Temperature Cu-Cu Bonding using Nanocrystalline Grains

The nanocrystalline copper (NC-Cu) has been considered a promising candidate in novel heterogeneous interconnects since fine grains can not only serve as diffusion paths but also contribute high internal energy for grain growth during the bonding process. Moreover, the equiaxed grain makes it a potential candidate to overcome the sidewall effect that the nanotwinned copper (NT -Cu) has faced recently in fine-pitched via. In this study, we successfully fabricated a random-oriented NC-Cu with its average grain size at about 120 nm. N on-destructive tests and cross-sectional images were taken after a bonding process operated at 200°C under 22 MPa for 1 hour and 0.5 hour. The results concluded that NC-Cu films are able to eliminate the bonding interface and form a robust joint whose bonding strength exceeds 28 MPa, indicating that the nanocrystalline grains are indeed an available approach for heterogeneous interconnects.