Two-step fabrication process for die-to-die and die-to-wafer Cu-Cu bonds

The scale of joints shrinks continuously due to super small and extremely fast computing devices consent to Moore's Law. Copper-to-copper direct bonding appears to be one of a solution to the limitation of scaling down into sub-micron scale. Moreover, bonding quality such as mechanical strength and electrical properties in copper bonding becoming an important topic. In this study, we examine the relationship of the bonding time and temperature on the bonding strength and bump resistance in Cu-Cu bonds with highly <111> oriented nanotwinned copper. In addition, the Cu-Cu joints were subjected to a post annealing process at the bonding strength after the second step annealing at 300 °C under 47MPa for 1 hour in vacuum ambient The bonding strength increases 3-4 folds after the post annealing. Some of the open Cu-Cu joints became connected after the post-annealing process.