Dissolution and electrochemical impedance spectroscopy studies of thin copper oxide films on copper in semi-aqueous fluoride solutions

The selective dissolution of thin copper oxide films grown on copper in semi-aqueous formulations containing dimethyl sulfoxide (DMSO), ammonium fluoride (NH4F) and water was studied. Optimization of the formulations was carried out by systematic evaluation of the effect of solvent content and pH on the removal rates of copper oxide films and selectivity towards copper and carbon doped oxide (CDO) low k dielectric film. Copper oxide removal rate of ∼180 Å/min with a selectivity of ∼130:1 towards copper and ∼20:1 selectivity towards CDO was obtained in a formulation containing 29% DMSO, 1% NH4F and 70% H2O at pH 4. Electrochemical impedance spectroscopy studies were performed on this system and the data were analyzed to characterize the copper oxide/electrolyte interface with the ultimate objective of developing an end point detection technique for copper oxide removal.