We examined a real-time coefficient of friction (COF) monitoring to evaluate the correlation between the pad surface response during polishing and material removal rate for metal chemical-mechanical polishing (CMP) applications. The results showed that a correlation of the removal rate and COF in tungsten (W) CMP was contrary to that in copper (Cu) CMP. Polishing by-products generated during CMP affects the friction force between the probing tip and the pad surface. The balance between the chemical and mechanical factors indicates the different frictional behavior between W CMP and Cu CMP. Furthermore, we detected the failures in the CMP process, which extracts an out-of-range deviation of the continuously monitored COF in product wafers, and reveal them in tantalum CMP. These results demonstrated the usefulness of an in situ CMP process monitor. (C) 2008 The Electrochemical Society.