Quantifying thiolated chemical additives for copper electroplating process

Copper foil, a thin layer of high-purity metallic copper, having excellent conductivity, ductility, and corrosion resistance, is extensively applied in various electronic applications. Thiolated (SH-containing) chemical additives (i.e., accelerator and inhibitor) in copper electroplating solution are known to be critical for optimizing the copper foil manufacturing processes. Due to the high ionic strength and acidity of copper electroplating solution, proper and accurate characterization of the thiolated chemical additives is a critical concern. In this study, a facile, accurate approach is developed for quantitative characterization of thiolated additives in the copper electroplating solution. Firstly, gold nanoparticles (AuNPs) were employed as an adsorbent for separating the thiolated chemical additives, namely, poly(ethylene glycol) thiol (PEG-SH) as inhibitor, and 3-mercaptopropionic acid (MPA) as accelerator from other interfering chemicals present in the copper electroplating solution. Subsequently, quantitative analysis of the AuNPs in the form of thin particle film was performed using attenuated total reflection-Fourier transform infrared spectroscopy. Electrospray-differential mobility analyzer was employed orthogonally for the quantitative analysis of the amount of thiolated additives adsorbed on AuNP. Interestingly, the results indicated that the detection concentration ranges of 5 μM to 100 μM for PEG-SH and 10 μM to 200 μM for MPA, respectively. Overall, this work demonstrates a successful separation and analysis methodology for the thiolated chemical additives in copper electroplating solution which enables the precise control over the copper foil manufacturing process.