Comparison of Diffusion Barrier Properties of Ni–Fe and Ni–Fe–W Layer at the Cu/Sn Interface

Abstract

Bump is a pivotal technology in 3D IC. However, with the reduction in bump size, there is an urgent need for a high-performance barrier layer material to retard the growth of intermetallic compounds (IMCs) at the interface. The study investigated the diffusion barrier properties and mechanical properties of electrodeposited Ni, Ni–15Fe, Ni–44Fe, Ni–42Fe–16W, and Ni–41Fe–28W. Ni–41Fe–28W demonstrated superior barrier properties, with a thickness of 0.42 μm after aging at 150 °C for 720 h. During the early stages of aging, FeSn₂ were formed at the interface, followed by the later generation of blocky Ni₃Sn₄. With a rise in Fe content, the nucleation of Ni₃Sn₄ was suppressed and the wettability and shear strength of the interface were also enhanced. As for Cu/Ni–Fe–W/Sn, a thin layer of FeSn₂ was also formed, and a whitish Ni–Fe–W–Sn layer was developed at the interface. After aging for 720 h, no significant Ni–Sn IMCs were observed. As W content increased, FeSn₂ converted from layered type to island type. The introduction of W significantly inhibited the diffusion of IMCs nucleation at the interface, endowing Ni–Fe–W with excellent barrier properties. Although W reduced the interface wettability, it enhanced shear strength at lower concentrations, with SAC305/Ni–42Fe–16W achieving the highest strength of 34.8 MPa. While as W content increased, the fracture mode shifted from ductile fracture within the solder to mixed ductile–brittle fracture, leading to decrease in interface reliability. This study provided valuable insights for the design of high-performance barrier layers in advanced packaging.

Graphical Abstract