(510e) Electrochemical Study on Surface Film Formation on Copper In Phosphoric and Nitric Acid

This work focuses on the reactions of copper in phosphoric and nitric-acid based solutions. Potentiodynamic (PD) scans, electrochemical impedance spectroscopy (EIS), and studies of the time-evolution of impedance at different DC potentials are used to characterize copper's reactivity. The observed changes in impedance at a high-limit frequency (~100 kHz) can be interpreted to be the result of the formation of a porous salt/viscous liquid layer at the electrode surface. In order to fully characterize the formation of this layer, a copper wire is cut in an electrolyte solution using a guillotined-electrode apparatus. This exposes a bare copper surface on which a reaction can occur without any influence of a pre-existing oxide layer. This mimics the way that copper is exposed to solution during Chemical Mechanical Planarization (CMP) and Electrochemical Mechanical Planarization (ECMP).

Using the guillotine electrode, impedance was measured as a function of time at 100 kHz, with different applied DC potentials. The experiments were performed with Cu wire in H3PO4 and HNO3 solutions with/without benzotriazole acid (BTA). The results are interpreted in terms of the nature of the surface layer formed in each system. In addition, the rate of formation of the porous salt and copper-BTA films on copper in the presence of BTA is compared to provide insight into the method of protection of copper during CMP.