Low-temperature, short-time, wafer-level bonding for Cu/Sn/Cu solid-state-diffusion interconnect in 3-D integration


 In this paper, Cu/Sn/Cu solid-state diffusion (SSD) under low temperature is proposed and investigated for three-dimensional (3-D) integration. Cu and Sn films were deposited by high-efficiency and low-cost physical vapor deposition to fabricate 40-µm-pitch daisy-chain structures. Subsequently, the Cu bump surface was treated with Ar (5% H2) plasma. The Cu/Sn/Cu structure was bonded face to face at 200 ℃ for 15 min. The interfacial composition of the as-bonded dies comprised five layers, Cu/Cu3Sn/Cu6Sn5/Cu3Sn/Cu, with no Sn remaining and no overflow. After annealing at 200 ℃ for 15 min under N2 atmosphere, as the Cu6Sn5 completely transformed into Cu3Sn, the microstructure changed to stable three layers: Cu/Cu3Sn/Cu. Additionally, the average bonding shear strength reached 27.0 MPa, which is higher than that for conventional Cu/Sn SSD bonding. The measured bonding resistance value was maintained at the theoretical value. Moreover, the parabolic growth constant of Cu3Sn reached 1.86×10−15 m2/s. Our study demonstrates the feasibility of using Cu/Sn/Cu SSD for low-temperature, short-time, wafer-level bonding.