In this study, the abrasive size distribution of ceria-based slurry below wafer and its effect on in-wafer uniformity were examined. Based on our observation, the abrasive size varies depending on the location on the wafer. Hence process parameters such as pad surface morphology and slurry viscosity were thoroughly investigated to observe their effect on the distribution on the wafer surface. It was found that the small size particles were considerably reduced near the center location of the wafer surface during the pad lifetime with reduced slurry viscosity and high polishing pressure. Hence, the contact conditions and the characteristic of fluid should be simultaneously considered in order to obtain the stable in-wafer uniformity. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3562559] All rights reserved.