Low Temperature Fine-pitch Cu-Cu Bonding Using Au Nanoparticles as Intermediate

In this paper, we propose a Cu-Cu bonding approach utilizing Au nanoparticles (NPs) fabricated by Physical Vapor Deposition (PVD) method as intermediate to realize time-saving, low-temperature and fine-pitch bonding. Confocal microscope was used to observe the morphology of electroplated Cu bumps. Moreover, atomic force microscope (AFM) measurement was employed to detect surface morphology of electroplated Cu bumps with and without modification of Au NPs. In addition, to reveal underlying bonding mechanisms, surface topography of Au NPs was also observed by transmission electron microscope (TEM). Furthermore, shear strength tests of bonded chips were carried out after the bonding process, and fracture surfaces were investigated by scanning electron microscopy (SEM) along with energy-dispersive spectrometer (EDS) analysis. Test results illustrate that average bonding strength above 10 MPa was realized, and demonstrate that the reliable Cu-Cu bonding utilizing Au NPs as a surface modification layer was accomplished at the low temperature of 200 °C for 3 mins under the pressure of 30 MPa without annealing.