An Ellipsometric Study of Surface Films on Copper Electrodes Undergoing Electropolishing

Abstract

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 40Aå in thickness, and (ii) a displaceable viscous layer of highly concentrated electrolyte about 2000–3500Aå thick. The solid film was either completely or partially destroyed when the electrode undergoing polishing was removed from the electrolyte, washed, and dried.

Periodic Phenomena during Anodic Dissolution of Copper at High Current Densities

“…This linearity and the greater-than-unity values of BE tend to support the high field strength ionic conduction mechanism proposed for the growth phase of the potential cycle. The slope is the same (6.8 • 10 -6 cm/V) as that estimated by Kojima (32) from impedance data and a film thickness value of 60A estimated by ellipsometry (27) for electropolishing films produced in the copper/phosphoric acid system. The proposed mechanism is further supported by the relative magnitudes of field strength, slope, and intercept, as discussed in Appendix B.…”

“…To understand the role of the chlorate or chloride we first examine two conditions of ionic conduction in thin cuprous oxide films: with the chlorate electrolyte and in phosphoric acid solutions. On the basis of impedance data collected from numerous publications, Kojima (32) showed that the thickness of cuprous oxide films in orthophosphoric acid was in the range of 15-125A, with a most probable thickness of 60~k as determined by ellipsometry (27). For the typical voltage drop through such films of 1.OV, field strengths are in the range of 106-107 V/cm and, therefore, the high field ionic conduction Eq.…”

Electrochemical planarization of interconnect metallization

“…In situ studies to check for the formation of a solid film on the electrode surface (evidence for a salt-film mechanism) during electropolishing, either via optical methods or electrochemical measurements, appear to have had more success in distinguishing between mechanisms [42,43].…”

Surface chemistry and topographical changes of an electropolished NiTi shape memory alloy

“…As reported in literature, it is difficult to isolate and analyze the anodic film formed under limiting current conditions, but still there are certain reports about attempts that have been made. Novak et al 15 used ellipsometry to investigate anodic films formed during electropolishing of copper in phosphoric acid. A report by Fang et al describes that the composition of the viscous liquid film in the electropolishing of Cu can be studied using XPS and AES 16.…”