The effect of acetic acid and phosphoric acid addition on slurry for Ta CMP has been investigated. By applying dc polarization and open-circuit potential measurements, several aspects in slurry formulations, experimental variables and electrochemical mechanism such as corrosion and passivation during processes can be discussed. Electrochemical measurements indicated that Ta could be rapidly passivated in all hydrogen peroxide-based slurries. The passive film could only be partially removed under CMP condition. It has been found that the corrosion rate is enhanced with acetic acid or phosphoric acid addition as well as XPS results revealed that passive film formed on Ta surface was different when with acetic acid and phosphoric acid addition. We evaluated acetic acid and phosphoric acid addition as accelerator of Ta CMP by adsorption on Ta surface thus postponed passivation during CMP. In addition, electrochemical behaviors of Ta CMP also have been studied by impedance analysis. This approach may be useful for the development of the second step Cu CMP process.