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Eddy-current sensor systems have been employed to determine the real-time thickness distribution of metal films and the thickness at endpoint detection in metal chemical mechanical polishing (CMP) processes, to achieve global planarization and avoid overpolishing or underpolishing. However, the large lift-off distance of 3.5 mm between the sensor coil and metal film gradually decreases with continuous wear of the polishing pad, which has a strong negative impact on the sensitivity and accuracy of the thickness measurement. In this study, a double-coil eddy-current sensor system, with novel characteristic ratio detection capability, is proposed for metal film thickness measurement and compared with a traditional amplitude-based method. The linear relationship between the characteristic ratio and metal film thickness that is immune to lift-off distance is demonstrated both theoretically and experimentally. The experimental results show that the proposed method performs better than the amplitude-based method, reducing the effect of lift-off distance variation and obtaining an excellent linear measurement range from 24 to 2095 nm. The measurement accuracy is as high as 2.1 nm with an excitation frequency of 1.39 MHz and a large lift-off distance of 3.5 mm. The relative measurement error is less than 1.2% and the endpoint thickness ranges from 100 to 180 nm in the Cu-CMP process, when the lift-off distance varies from 3.6 to 3.3 mm.

Abstract: The synthesis of CeO2nanoparticles for CeO2based slurry gains continuous emphasis on improving its performance in the chemical mechanical polishing of dielectric materials. Urea was selected to dominate the growth and morphology during the calcination process. Thermogravimetry experiments were used to analyze the the decomposition behavior. Particle morphology and size were analyzed. Crystalline phase information and surface valence were used to compare the differences in surface physical and chemical properties of ceria by different synthesis process. The CeO2nanoparticles synthesized with urea were dispersed in water as slurry. The particle sizes of CeO2were measured by dynamic light scattering. The Zeta potential of CeO2dispersion were measured to show dispersing performance. The CeO2nanoparticles synthesized with urea condensation show good monodisperse properties. The material removal rate of silicon oxide and surface quality after chemical mechanical polishing were selected to evaluate the chemical mechanical polishing performance. The CeO2nanoparticles synthesized with urea condensation not only yielded better surface quality results than the commercial slurry but also showed a 153% (pH = 4) and 100% (pH = 10) increase in the material removal rate of silicon oxide compared to commercial.