An Intensive Study of Effects of Orientations of Cu Bumps on Cu-Cu Direct Bonding for 3D Integration by Molecular Dynamics Simulation

In this paper, the bonding process of (100)- and (111)-oriented single crystal Cu bumps as well as (111)-oriented nanotwinned Cu (nt-Cu) bumps is studied intensively by molecular dynamics simulation. The influence of bonding temperature (473, 523 and 573 K) and bonding stress (0.5, 1 and 1.5 MPa) on the bonding process of the above three Cu bumps are characterized. It is found that the bonding degree of (111)-oriented single crystal Cu bumps is better than that of (100)-oriented ones, the shear strength of (111)-oriented Cu bump interconnects obtained under the condition of bonding temperature 473 K without bonding stress is about 22% higher than that of (100)-oriented ones. The bonding degree of (111)-oriented nt-Cu bump interconnects is slightly better than that of (111)-oriented ones, at bonding temperature 473 K and without bonding stress whose shear strength is about 18% higher than that of the latter. The use of (111)-oriented nt-Cu bumps can effectively improve the plasticity of Cu-Cu direct bonding interconnects. Moreover, the increase in bonding temperature can significantly improve the bonding degree of Cu bump interconnects, but the influence of bonding stress on the bonding degree of Cu bump interconnects is not completely positive.