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 IOW vacuum bonding, and another is in N-2 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 degrees C for 90 min at 1 MPa in vacuum bonding. The size was as large as 40 mu m in width and 10 mu m in height. For non-vacuum conditions, the nt-Cu bumps can be bonded to nt-Cu films at the 250 degrees 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.