ILD CMP with Silica Abrasive Particles: Effect of Pore Size of CMP Pad on Removal Rate Profiles

The influence of pad intrinsic properties on the removal rate profiles of ILD CMP with fumed silica abrasive slurry was studied by changing pad's polymer hardness, porosity, and pore size. Of these intrinsic properties, pore size is found to be most critical to removal rate profiles. By systematically changing the pore size from <1 mu m to >100 mu m, with porosity from 5% to 50%, of pad made of thermal-plastic urethane (TPU), removal rate profile of oxide polishing was studied. A flat removal rate profile cross wafer is desired for ILD CMP. It was found that when the pore size was larger than a certain threshold, flat removal rate profiles could be achieved. Below the threshold, severe edge-fast/center-slow removal rate profiles were observed and such profiles cannot be remedied by changing pad's other properties like porosity or polishing process conditions. A model is proposed to explain the non-flat removal rate profiles associated with the small pore size (<20 mu m). (C) 2013 The Electrochemical Society.