Electrochemical SERS study of Benzotriazole and 3-mercapto-1-propanesulfonate in Acidic Solution on Copper Electrode

Abstract

Since the development of acid copper plating technology, the role of additives is indispensable. In addition to the main salt copper sulfate and supporting electrolyte sulfuric acid, suppressors, accelerators, levelers and chlorine ions (Cl^-) are also required to be added into the plating solution. Appropriate additive system can have a significant impact on the coating or the plating solution, which can help improve the quality of the coating and increase the brightness of the coating. Through electrochemical measurement, vibrational spectroscopy, scanning probe microscopy, molecular dynamics simulation and other methods, researches have a deeper understanding in the adsorption configuration of some additives on the copper electrode surface and the changes in the electroplating process. Surface-enhanced Raman spectroscopy (SERS) is a powerful technique that yields vibrational information with ultra-high sensitivity. Enhancements of up to 10¹⁰ have been achieved in some systems, which provides sensitivity up to single molecule level. Therefore, SERS technique is one of the main methods to study the adsorption structure and mechanism of additives. In this paper, the competitive adsorption behaviors of benzotriazole (BTAH), 3-mercapto-1-propanesulfonate (MPS) and Cl^- in an acidic solution on the copper electrode were investigated by in-situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS). It was found that in the positive potential range, the adsorption behavior of BTAH molecules was mainly through the formation of [Cu(BTA)]_n polymer film on the copper electrode surface by the triazole ring; with the negative shift of the potential, the polymer film was gradually transformed into the BTAH molecular. The MPS was mainly adsorbed on the copper electrode by the sulfhydryl end. Cl^- mainly existed in the form of Cu-Cl, and the active sites occupying the surface of the electrode had a synergistic effect with MPS. The electroplating process on the copper foil also verified the strong adsorption of BTAH, and the presence of small copper particles on the copper foil also confirmed that MPS and Cl^- have a synergistic effect, which promotes the local deposition of copper. As the only technical method that can realize nano-level electronic interconnection, electronic electroplating is the main direction of future research. Related additive basic research is also indispensable. In the process of copper electroplating, the interfacial competitive adsorption of additives and their mechanism of action need more in-depth study. It is hoped that this study will play an important guiding role in the development of electroplating additives and the improvement of electroplating technology in the future.

Keywords

benzotriazole / 3-mercapto-1-propane sulfonate / surface enhanced Raman spectroscopy / adsorption

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