Influence of aromatic functionality on quaternary ammonium levelers for Cu plating

Electrochemical and spectroscopic methods are utilized to study the interaction of three levelers - Dodecyltrimethyl ammonium bromide (DTAB), benzyldimethylhexadecyl ammonium chloride (BDAC), and thonzonium bromide (ThonB) - with Cu electrode surfaces. Electroplating Cu in the presence of 0, 10, 25, and 50 ppm concentrations of each of the levelers showed that each of the additives inhibit the onset of Cu deposition. Surface Enhanced Raman Spectroscopy (SERS) showed that DTAB exhibits no potential dependent behavior while both BDAC and ThonB exhibit potential dependent behavior. The stability of DTAB, evidenced by the gradual onset Cu deposition and lack of potential dependence in the SERS data, is possibly due to the formation of hemi or pre-micellar structures on the Cu surface. Stabilization of BDAC and ThonB is attained by the electrostatic interactions with the surface as evidenced by the potential dependent behavior exhibited in the SERS. One contributing factor to the performance of amphiphilic cationic surfactants as levelers is the concentration at which micellization occurs (cmc).