(Electrodeposition Division Early Career Investigator Award) Additives in Cu Electrodeposition for Through-Silicon Via Filling and the Growth of Cu Nanocrystals
Authors: Kim Myung Jun 
Published: February 2020

Additives play a key role in modulating the kinetics of electrochemical reactions. They adsorb onto metal surfaces and their surface coverage changes the charge transfer resistance of electrochemical reactions. This phenomenon is critical in a variety of electrochemical processes such as corrosion, electrochemical deposition, electrocatalysis, and colloidal synthesis of metal nanocrystals.
The use of additives in Cu electrodeposition is key to achieving defect-free interconnections for semiconductor devices. Controlling the surface coverage of additives enables Cu to selectively grow from the bottom of filling features, while Cu deposition outside of the features is effectively inhibited.1 This filling process is referred to as superfilling, superconformal deposition, or bottom-up filling. As a result of tremendous efforts to advance electrodeposition processes, nanometer-scaled Damascene features can be easily filled with Cu in the presence of polyether suppressors and accelerators.1,2 Furthermore, micrometer-scaled features including through-silicon vias (TSVs), microvias, and through-holes can also be successfully filled by adopting additional levelers.3,4 To further advance the metallization process, various experimental and theoretical studies are still on-going to develop new additives,5,6 to improve properties of Cu interconnections,7 and to gain a better understanding of the additives.8,9

Inorganic/organic additives, referred to as shape-directing agents or capping agents, are also essential in the colloidal syntheses of various nanocrystals.10 With the aid of additives, the shape of nanocrystals can be modulated from spherical nanoparticles to one-dimensional nanowires or to two-dimensional nanoplates. The growth of nanocrystals in colloidal syntheses is similar to metal electroless deposition because both processes are based on spontaneous redox reactions, i.e. the reduction of metal ions and the oxidation of reducing agents. However, in colloidal synthesis, the behavior of shape-directing agents is crystal facet-dependent, determining the final shape of nanocrystals by facilitating or inhibiting metal growth on certain crystal surfaces. Recently, electrochemical techniques using single-crystal electrodes have proven to be a powerful analytical tool that can clarify the growth mechanism of anisotropic nanocrystals by providing the metal growth rates on each single-crystal electrode.11,12 Successive research is still on-going to fully understand the facet-selective chemistry that occurs during nanocrystal growth.
This presentation summarizes my recent progress in TSV filling and the mechanistic study of Cu nanowire growth. The first part of this presentation will mainly focus on bromide and iodide ions that act as a leveler for TSV filling,13,14 and the second part will introduce how electrochemical analyses using single-crystal electrodes reveal the growth mechanism of Cu nanowires and how halide ions change the shape of Cu nanocrystals.11,12,15

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