Citric Acid as a Complexing Agent in CMP of Copper

Polishing slurries used in chemical-mechanical planarization (CMP) of copper typically include a complexing agent and an oxidizer. Our present work investigates the effectiveness of citric acid as a complexing agent for with employed as an oxidizer. We show that the rate of copper removal from increases when both citric acid and are used in acidic solutions () and decreases drastically in alkaline solutions (), as well as in citric acid without any in the slurry. We investigate the underlying surface reactions of these effects by using Fourier transform electrochemical impedance spectroscopy (FTEIS) in combination with potentiodynamic measurements. We analyze the relative roles of citric acid, , and solution pH in removal, and develop a reaction scheme describing the surface chemistry of in this system. The results presented here also demonstrate how FTEIS can be used for quantitative investigation of surface reactions in complex CMP systems.