Chemical factors for chemical-mechanical and electrochemical-mechanical planarization of silver examined using potentiodynamic and impedance measurements

Ag may eventually replace Cu (like Cu has replaced Al) in sub-micron interconnects used for integrated circuits. Fabrication of such Ag lines would typically involve damascene structures patterned by chemical-mechanical planarization (CMP). Our present work focuses on certain chemical aspects of CMP of Ag in alkaline polishing slurries. Specifically, we study the oxidation and dissolution reactions of Ag that are relevant for CMP of this metal in KOH (pH 10) solutions, and we investigate the role of O2 in these reactions. The surface reactions are probed with Fourier transform electrochemical impedance spectroscopy in combination with potentiodynamic measurements. The reaction steps are discussed in terms of circuit models, and the possibility of incorporating electro-activated reactions in CMP through electrochemical-mechanical planarization (ECMP) of Ag is briefly discussed.