Electrochemical mechanical planarization (ECMP) has become increasingly important in recent years. The ECMP is superior over conventional CMP due to its low force, high controllability, and improved planarization through electrochemical reactions. In particular, the precision control of the removal of different surface materials has been made possible at the molecular level with assistance of an electrical potential and various nano-abrasive particles. Yet fundamental understanding in interactions between nanoparticles and polishing wafers and their effects on removal mechanisms has to be further achieved. This presentation will start with a brief review of abrasive particles on CMP. Detailed discussions will focus on the tribo-electrochemical removal mechanisms of copper and tantalum. The electrochemical and tribological behaviors are investigated using a hybrid system that is able to carry out electrochemical-mechanical polishing (ECMP). Through the measurement of potentiodynamic and electrochemical impedance spectroscopy (EIS), we are able to compare the corrosive removal verses that induced through mechanical parameters such as surface sliding speed and down force. Being able to pinpoint the reactions of mechanical verses electrochemical is beneficial to understand ECMP and will lead to its optimization.