Anchoring sulfur migration to mitigate Kirkendall voids in nano-twinned copper interconnections for robust and reliable packaging

Abstract

Nano-twinned copper (nt-Cu), with a preferred orientation, is highly promising as interconnect materials in high-density advanced packaging due to its considerable mechanical strength, excellent electrical conductivity, and resistance to thermal migration. However, its application is impeded by sulfur-containing byproducts from the electroplating process, exacerbating the formation of Kirkendall voids within solder joints during thermal aging. Herein, through the incorporation of Zinc (Zn) into the nt-Cu layer, we develop a nt-Cu/Zn composite structure. Our findings provide the first definitive confirmation of the mechanism by which sulfur atoms migrate to the Cu₃Sn/nt-Cu interface through interstitial diffusion, thereby reducing the activation energy for vacancy formation. We further demonstrate that Zn effectively anchoring sulfur atoms, forming ZnS within the nt-Cu layer during heat treatment, which increases the vacancy formation energy and inhibits the development of Kirkendall voids. Remarkably, no Kirkendall voids are observed in the modified interconnects even after prolonged aging at 150°C for 1000 h. The nt-Cu/Zn composite metallization layers significantly decrease the growth rate of interfacial intermetallic compounds by 33.6% and enhance the shear strength of solder interconnections to 228.9%. This research underscores the potential of nt-Cu in advanced electronic packaging, offering new pathways for improving the power density and reliability of electronic devices.