Investigation of Low-Temperature Cu–Cu Direct Bonding With Pt Passivation Layer in 3-D Integration

Pt has been investigated as a metal passivation material to achieve low-temperature Cu-Cu direct bonding process. With 10-nm Pt passivation layer capping on Cu surface, a good bonding surface with no oxides and small grain size can be obtained. During the low-temperature bonding process, Cu atoms diffuse through the passivation layer and form a new layer without any pretreatment. This bonding scheme with Pt passivation layer provides a solution for Cu low-temperature bonding, with excellent bonding strength, good electrical performance, and ability to endure temperature variation. In addition, both chip- and wafer-level bonding process have been successfully demonstrated, showing a high potential to be applied on 3-D integrated circuit (IC) and heterogeneous integration.