Method to analyze the concentrations of Cu+-related species in Cu plating bath is suggested.
•
The concentrations of Cu+-related species in a bath aged under open-circuit condition are evaluated.
•
The Cu+ ion in the bath is stabilized by forming a complex with organic additives.
Abstract
Cu+-related species formed under electrolytic and open circuit conditions (e.g., Cu+ and Cu+-3-mercapto-1-propane sulfonate (MPS)) are important intermediates that influence the performance of Cu-plating baths. However, trace amounts of Cu+-related species in the aged bath are difficult to analyze, thus making it increasingly difficult to ensure the performance of the bath. Here, an in-line and simple electrochemical method—based on a diffusion-limited current analysis of a 2-channel flow cell—was proposed to detect Cu+-related species in a bulk solution. Based on the voltammogram, in the range of 0.5–1.0 V, the aged bath possesses anodic currents related to the oxidation of Cu+-related complexes. The aged bath containing PEG revealed a single diffusion-limited current plateau at 0.5–1.0 V due to the oxidation of Cu+. In the presence of bis (3-sulfopropyl) disulfide, three current plateaus were observed, corresponding to the three-electron oxidation of the Cu(I)MPS complex. The concentrations of Cu+ and Cu(I)MPS in the aged bath were evaluated using master calibration curves that were prepared based on simulation and experiment. The proposed method could be effectively utilized for the automated in-line monitoring of Cu electroplating baths.
