Spectroscopic and Electrochemical Analysis of Cu(I) in Electroplating Solution and Evaluation of Plated Films

In this study, we investigated the behavior of the cuprous ion (Cu(I)) in a copper sulfate plating solution and the effects of Cu(I) on the quality of the resultant copper plating film. Through spectroscopic methods, two kinds of Cu(I)-containing compounds in the plating solution were identified by analyzing the kinetics of the complex forming reactions between Cu(I) and the disodium salt of bathocuproinedisulfonic acid (BCS). The first Cu(I) component reacts slowly with BCS and probably incorporated deep inside the polyethylene glycol (PEG) matrix; thus, Cu(I) is sterically hindered by PEG, preventing interactions with the BCS in the plating solution. The other Cu(I) component can instantaneously react with BCS, forming a complex. In addition, interestingly, it has been shown that the instantaneous component affects the roughness of copper plating films. These results indicate that spectroscopic measurement and analysis is effective for the management and evaluation of plating solutions for high-quality production.