In this study, the corrosion between the copper (Cu) seed and the TaNx films with various Ar-sputtering amounts is investigated in acidic chemical mechanical polishing (CMP) slurries. The results show that the intrinsic corrosion of the TaNx films increases with increasing the Ar-sputtering amount because Ar sputtering causes the grain boundary of the TaNx film increase. The galvanic corrosion of the TaNx film increases with increasing the Ar-sputtering amount because the N-rich surface of the TaNx film is removed by Ar bombardment. The equivalent circuit, simulated using data from electrochemical analysis, reveals changes in resistance and capacitance elements of the Cu-TaNx electrochemical system. In the acidic CMP slurry, the charge-transfer resistance of the TaNx corrosion decreases with increasing the Ar-sputtering amount, whereas the resistance of a tantalum-oxide layer shows the opposite trend because decreasing the N content of the TaNx films enhances the oxidation rate of the Ta metals.