The dependence of chemical mechanical planarization (CMP) performance on both composite polymer core and colloidal silica shell particle sizes is examined. The highest removal rate is observed for the largest diameter cores combined with the smallest silica particles. The model used to explain the results takes into account both the total number of active silica particles still bonded to the polymer core but at the same time pressed against the wafer surface and the indentation depth of each single particle. A contact-area-based mechanism is dominant at the large core (600 nm)-small shell (15 nm) particle sizes, and an indentation mechanism takes over as the shell particle size increases (90 nm). Larger cores elastically deform and gently transfer the applied downforce to a higher number of silica particles with respect to smaller cores. (C) 2008 The Electrochemical Society.