Electrochemical Analysis of Surface Films on Copper in Phosphoric Acid, with a Focus on Planarization

Copper planarization is of great interest in the microelectronics industry. In this work we monitored surface film formation on a copper wire in situ by tracking the time evolution of the system impedance in aqueous phosphoric acid, a condition relevant to electrochemical mechanical planarization (eCMP). First, potentiodynamic scans (PD scans) were performed in order to characterize the active and passive behavior of copper in the solutions. Then copper was biased at various potentials obtained from the PD scans, and the impedance at high frequencies (100 and 50 kHz) was monitored to detect the formation of a surface film over the copper. A newly designed guillotined electrode was employed to create fresh copper surfaces in the solution in situ. The transient impedance response immediately following copper exposure to solution clearly shows that a resistive film, presumably either a porous salt or viscous liquid, does form over the copper surface in the passive region. These films will have implications in potential eCMP and electropolishing protocols. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3095461] All rights reserved.