An ellipsometric study of surface films on copper electrodes undergoing electropolishing

Simultaneous current-potential and in situ steady-state ellipsometric measurements were carried out in order to study the electropolishing of vertical copper electrodes in a 65% aqueous solution of phosphoric acid. A technique was developed for displacing the visible, viscous film with glycerol and examining whether a second film was sandwiched between the copper surface and the viscous film. By using this technique, it was demonstrated that the electropolishing process involves the formation of two films on the electrode: (i) an adherent sandwiched solid film at least 40Å in thickness, and (ii) a displaceable viscous layer of highly concentrated electrolyte about 2000-3500Å thick. The solid film was either completely or partially destroyed when the electrode undergoing polishing was removed from the electrolyte, washed, and dried