Chemical mechanical polishing (CMP) is now widely used in semiconductor manufacturing. Characterizing the particle movement in CMP is essential to understanding of the complicated material removal mechanisms for CMP. In this study, an experimental system based on fluorescence technique has been designed and developed. The particle displacement and velocity in the interface between a transparent wafer and a polishing pad were observed in-situ with the system. It can be found that some particles were embedded on the polishing pad and rotated with the pad. And the others were able to move free in slurry flow. All the particles in the experiments could be classified into four groups. The counting procedure suggested that the percentage of free particles in the field of view was between 10 and 50%. By analyzing the velocity of free particles at various rotation speeds and applied pressure, it was found that some of the free particles were able to travel at a speed 12-18 times the linear speed. The uncertainty in the velocity measurements was less than 8%. The objective of this study was to offer deep insights into the material removal mechanisms by measuring the real-time particle movement in CMP. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3576139] All rights reserved.