A low-temperature Cu-to-Cu interconnection method by using nanoporous Cu fabricated by dealloying electroplated Cu–Zn

Abstract

Cu-to-Cu interconnection has drawn increasing attention as the bump pitch is decreasing continuously. Cu-to-Cu interconnections exhibit excellent mechanical, electrical, and thermal properties without forming IMCs, which usually degrade the interconnect reliability due to their brittle nature. In this paper, Cu-to-Cu interconnection can be realized at 150 °C for 10 min under a pressure of 3 MPa. The microstructure of the nanoporous Cu coarsened significantly and the interfaces of the bondline can not be distinguished clearly after bonding at 250 °C for 30 min under a pressure of 3 MPa. The microstructure was more densified along the bonding interface than the rest part, and the degree of densification was increased with the increasing bonding temperature and pressure. The average resistivity, thermal conductivity, and shear strength of the bondlines were determined to be 4.12 μΩ cm, 176.49 W m−1 K−1, and 18.78 MPa, respectively. After aging at 200 °C for 300 h, the shear strength was increased by 44.5% due to the increased densification rate brought by the diffusion of Cu atoms, which confirmed the Cu–Cu interconnection reliability during long-term service.