Effects of electrodeposited Co–W and Co–Fe–W diffusion barrier layers on the evolution of Sn/Cu interface

Abstract

In 3D IC, a high-efficiency diffusion barrier layer is urgently required for Sn/Cu micro-bumps, to inhibit the formation of Cu–Sn intermetallic compounds (IMCs). In this work, the barrier performance of electrodeposited Ni, Co–9W, Co–20W, Co–20Fe–10W and Co–36Fe–17W were studied. After aging at 150 °C for 672 h, the thicknesses of the IMCs formed between Sn and these barriers were determined. Among the five barriers studied, Co–36Fe–17W exhibited the best barrier effect, with a thickness of 0.61 μm. At the Sn/Co–W interface, CoSn3 IMC and Co–W–Sn were formed, while at the Sn/Co–Fe–W interface, CoSn3 IMC, FeSn2 IMC, and Co–Fe–W–Sn were observed. The layered CoSn3 IMC gradually evolved into an isolated island structure as the Fe and W concentration rose at the Sn/Co–Fe–W samples. The growth of CoSn3 in the Sn/Co–W and Sn/Co–Fe–W samples involved a competition between diffusion control and interfacial reaction control. The presence of W atoms effectively inhibited Co diffusion, while the FeSn2 IMC layer acted as a barrier, suppressing the nucleation of CoSn3. The synergistic effect of these factors contributed to the excellent barrier properties of the Co–Fe–W layer. This research establishes a scientific basis for selecting barriers that exhibit superiority in advanced packaging.