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Chemical-mechanical polishing (CMP) has been recognized indispensable to achieve the global planarity in removal of metal overlay across the wafer, when the number of interconnecting metal layers and the size of wafer increase and the line rule reduces to nano scale. CMP has to stop at the endpoint when the overlay metal has been removed, or dishing will occur which affects the subsequent lithography in IC manufacturing. An effective in situ endpoint monitoring method essentially improves the yield rate and throughput of CMP. One notices the coefficient of friction between the pad and dielectric layer is distinguishably lower than the one between the pad and the copper overlay, based on that an endpoint monitoring method using acoustic emissions during the chemical mechanical polishing is feasible. The proposed method is tested in the experiment, and the comparison with the previous thermal monitoring technique shows consistent results.