An Integrated Experimental-Theoretical Study on the Role of Additives in the Acid Electrodeposition of Copper
Authors: Bonechi Marco , Biffoli Fabio , Corsi Pierantonio , Mariani Elena , Giovani Claudia , Bazzicalupi Carla , Zangari Giovanni , Pagliai Marco , Innocenti Massimo 
Published: December 2024

Copper electroplating plays a critical role in the field of industrial processes. Copper is among the most common electrodeposited layers in both technological and decorative applications. Moreover, copper electroplating is a key step to avoid nickel layers, in fact, there is a growing trend toward Ni-free production process due to concerns about the toxicity of Ni [1,2].
Common copper electroplating solutions typically consist of CuSO4, H2SO4, NaCl, and different organic additives named suppressor, brightener, and leveller [3,4]. These types of additives are crucial for achieving shiny and adherent deposits but despite their widespread use, the mechanisms of action remain unclear. Understanding the influence of additives is important both to improve the quality of deposits and to meet environmental sustainability goals, including reducing organic pollutants in wastewater and replacing toxic additives like thiourea with eco-friendly alternatives such as L-cysteine. In this context, a comprehensive analysis using an integrated experimental and theoretical approach can provide significant benefits.
In this study, Electrochemical techniques and computational methods were used to elucidate the mechanisms behind the use of additives in industrial copper electroplating. Classical molecular dynamics simulations, following the gaff2016 protocol, were performed to study the behaviour of electrolytes under an electric field and assess the possibility of physical absorption. Additionally, ab-initio calculations using CAM-B3LYP(D3BJ) and a mixed 6-31G(d,p)-LANL2DZ basis set were employed to investigate the possibility of a chemical absorption and explain how additives influence the directional growth of copper nuclei.
The theoretical results obtained were verified experimentally by performing electrochemical depositions of copper under different conditions. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to study the surface composition and provided information on the nature of adsorption (chemical or physical) of additives on the copper surface. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were used to investigate the effect of additives on the morphology of the deposits, including grain size and roughness. Finally, X-ray diffractometry (XRD), SEM, and AFM imaging helped quantify preferential orientation caused by additives and revealed the influence in the initial growth steps, identifying a pivotal 2D structure. The innovatively interdisciplinary approach based on the integration of experimental and theoretical used in this work made the understanding of electrodeposition processes more clear, paving the way for sustainable and efficient electrochemical manufacturing practices.

References

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