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.
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