The surface coverage of particles between pad and wafer has been studied as a function of down load, particle size, and concentration in order to investigate oxide chemical mechanical polishing ( CMP) mechanism. In situ friction force measurements have been conducted to investigate the interfacial contact behavior during polishing. In the absence of particles, friction force increased with increasing down load. In the presence of particles, friction force increased with an increase in down load and solids loading. An equation derived from Amonton's second law was used to determine the fraction of abrasive particles that actually come into contact with the wafer. The fractional surface coverage of abrasive particles was independent of down load and increased with increasing solids loading and decreasing particle size. Determination of the amount of abrasive particles effectively involved in polishing will make clearer the oxide CMP polishing mechanisms improving slurry design leading to further optimization of the CMP process. (C) 2004 The Electrochemical Society.