In this paper, an in-situ interfacial fluid pressure measurement system had been developed for 12 '' CMP equipment. Using this system, the interfacial fluid behavior is studied during the polishing process of 12-inch silicon wafer. The effects of the basic polishing variables, including the slurry injection position, the down force, the rotational speed, and the slurry flow rate, on the fluid pressure are investigated systematically. The results suggest that all of these polishing variables have obvious effects on the fluid pressure: the slurry injection position with suitable center distance between the pad and angular distance to the wafer leading edge is good for uniform slurry dispersion and the fluid pressure building; the increasing down force can increase the ratio of the positive pressure and the average fluid pressure significantly; the fluid pressure increases with the rotational speed till a critical speed and then decreases; the fluid pressure increases with the slurry flow rate slightly, the slurry injection position with larger center distance has lower critical speed and has greater dependence on the slurry flow rate due to the lower slurry utilization efficiency caused by larger centrifugal spraying effect. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.063203jes] All rights reserved.