Evaluation of mechanical property of Sn-Ag bonding layer adopting Ni(P)/Cu Bi-layer diffusion barrier for 3D integration

The mechanical properties of bonding layer have a great impact on the reliability of 3D integration. In this study, to improve the mechanical properties of bonds, Sn-Ag solder layer and the Ni(P)/Cu bi-layer diffusion barrier were adopted for high reliability of 3D integration bonding. These combinations reveal noticeably high bonding strength and can be explained through their microstructures. The bonding strength increased drastically between 200°C and 250°C, which suggested that the microstructure evolution of the bonding layer influenced the bonding strength greatly. For the samples with a Sn-Ag bonding layer, the bonding strength is much higher than that of Sn bonding layer sample, in the range of 250°C and 275°C. These results can be attributed to the presence of small Ag₃Sn IMCs that had formed in high density and were dispersed throughout the bonding layer, which improved the mechanical strength. This result highlights the possibility of acquiring a control window to produce a bonding structure with a high mechanical reliability on Cu pillar bonding.