Synthesis of Size-controllable Copper Nanoparticles: Electrochemical Behaviors and Sintering Property

With the fast development of electronic packaging technology, the chip integration density becomes higher, and the interconnecting trace pitch becomes smaller. The 3D stacked packaging technology has become an important route for the continuation of "Moore's law". However, the traditional interconnect materials such as Sn and Ag can hardly meet the requirement for the interconnection of 3D ultra-narrow pitch due to their low melting point, high cost and electromigration under high electric field. As an alternative material, the Cu nanoparticles (CuNPs) can obtain interconnecting performance similar to Ag, with only one-tenth of cost. CuNPs are not susceptible to electromigration under electric fields, and can be sintering at low temperature to realize the interconnection of ultra-narrow pitch. In this paper, size-controllable and antioxidative CuNPs were prepared via wet-chemical redox method, with the selections of copper hydroxide as the main salt, ascorbic acid as the reducing agent, and polyvinylpyrrolidone (PVP-K30) as the coating agent. The as-synthesized CuNPs showed near spherical shape, high dispersibility, uniform size distribution of 102±36 nm, and were not oxidized after 30 days storage in air. The formation process of these CuNPs were also investigated by electrodeposition method. The results revealed that with the addition of PVP coating agent, the over-potential for the reduction of Cu
²⁺
to CuNPs will increase, and the nucleation/growth rate of Cu will be restricted. As a result, finer CuNPs can be obtained.