The structural characteristics of nanosized ceria particles were investigated to clarify the relationship between the structural characteristics of abrasives and the problem of residual particles in shallow trench isolation chemical mechanical planarization (STI CMP). The ceria particles were synthesized via a solid-state displacement reaction method, and their crystalline structure was controlled by regulating the oxygen partial pressure at the reaction site on the precursor. In a calcination process with a high oxygen concentration, the synthesized ceria particles had a cubic fluorite structure (CeO2) because of the decarbonation of the cerium precursor at a high oxygen partial pressure. The particles calcined with a low oxygen partial pressure had an included hexagonal structure (Ce2O3). The ceria slurry prepared with the cubic CeO2 yielded a higher removal rate than the slurry prepared with the hexagonal Ce2O3. Furthermore, the ceria slurry with the cubic structured particles had less residual particles on the oxide film than the slurry with the hexagonal structured particles. The resulting residual particles originated because Ce2O3 is easily agglomerated and adsorbed on the wafer surface due to the high surface activity resulting from the oxygen vacancy on the particle surface. (C) 2007 The Electrochemical Society.