Investigation of Low Temperature Cu-Cu Direct Bonding with Pt Passivation Layer in 3D 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 pre-treatment. 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 of chip and wafer level bonding process have been successful demonstrated, showing a high potential to be applied on 3D IC and heterogeneous integration.