Low-temperature Cu-to-Cu direct bonding enabled by highly (111)- oriented and nanotwinned Cu

Abstract

In this study, a low temperature diffusion bonding enabled by (111) highly oriented nanotwinned Cu (nt-Cu) was proposed. Two different bonding atmospheres, one is in low vacuum bonding, and another is in N2 bonding were carried out. Both of the two bonding atmospheres show good bonding interfaces after microstructure observation. For vacuum ambient, large-grained structure was found after 250°C for 90 min at 1 MPa in vacuum bonding. The size was as large as 40 μm in width and 10 μm in height. For non-vacuum conditions, the nt-Cu bumps can be bonded to nt-Cu films at the 250°C for 20 min under 40.6 MPa. Accordingly, it is believed that low temperature bonding in low vacuum or non-vacuum ambients can be accomplished by using highly (111)-oriented nt-Cu.