Synthesis and Atomic Transport of CoSn3 NanoIMC by In Situ TEM

In order to optimize the interfacial properties by adding Co to the bumps of copper pillars and to overcome the strong tendency of Co to oxidize, an intermetallic compound (IMC) capsule was developed for the purpose of transporting elements through the intermetallic compound. In this study, we present a comprehensive analysis of the transformation process of CoSn2 nanoparticles into CoSn3 at the nanoscale using in situ heating transmission electron microscopy (TEM). The experimental results reveal that CoSn2 nanoparticle growth occurs through polymerization, whereas CoSn3 nanoparticle formation relies on the reaction between CoSn2 and Sn. During the initial stages of the reaction, Co dissolves and diffuses into Sn, leading to the nucleation and growth of CoSn2 in Sn via Ostwald ripening. As the input energy increases, vacancies in CoSn2 drive a reaction at the Sn/CoSn2 interface, resulting in the generation of CoSn3. In this process, Sn nanoparticles enter the CoSn2 structure through the Anti Structure Bridge (ASB) mechanism to fill vacancies. Following the codeposition process, CoSn(3 )nanoparticles were successfully plated within the Sn layer of the Cu-pillar bumps. Upon reflow heating, the CoSn3 nanoparticles exhibited a preference for precipitating the vacant sites within the Sn layer. This process facilitated the release of Co atoms from CoSn2, enabling their diffusion throughout the entire Sn layer.

Automated summary

An intermetallic compound (IMC) capsule was developed to optimize the interfacial properties of copper pillars by adding Co and overcome the oxidation tendency of Co. The transformation process of CoSn2 nanoparticles into CoSn3 at the nanoscale was comprehensively analyzed using in situ heating transmission electron microscopy (TEM). The experimental results showed that CoSn2 nanoparticle growth occurred through polymerization, while CoSn3 nanoparticle formation relied on the reaction between CoSn2 and Sn.