Thermal stability and diffusion barrier performance of amorphous Ni-P layer at Sn/Ni-P/Cu interface

As chip integration increases and micro-bump size reduces in 3D integrated circuits (ICs), issues with service reliability due to electromigration and thermomigration are becoming more prevalent. This paper investigates the thermal stability of an amorphous Ni-P layer at different heating treatment temperatures and the microstructure evolution of the Sn/Ni-P/Cu interface under different soldering conditions. The study indicates that the maximum temperature for maintaining an amorphous Ni-P barrier layer is below 250 °C. The amorphous layer of Ni-P acts as an effective inhibitor of Cu atom diffusion at the Sn/Ni-P/Cu interface during soldering. However, when exposed to soldering conditions exceeding 275 °C for 5 min or more, the amorphous layer of Ni-P, with a thickness of approximately 1.8 μm, loses its ability to act as a barrier layer at the Sn/Ni-P/Cu interface. This occurs specifically under conditions of 300 °C and dwell times less than 5 min. Additionally, the consumption of the Ni-P barrier layer is mainly governed by grain boundary diffusion and bulk diffusion. The findings of this study could provide theoretical guidance for designing the structure of solder joints with barrier layers.