Particle size distribution determination is conducted using density gradient stabilized centrifugal sedimentation in a disc centrifuge. Resulting particle diameter distribution determinations for cerium oxide, colloidal silica, fumed silica and alumina are shown to be highly repeatable and reproducible; and in many instances the measured diameter distributions exhibit resolved multimodal features. A detailed investigation of the experimental parameters used in the analysis revealed that the chemistry of the sample and the gradient e.g. pH of the slurry formulation, is the key parameter controlling the reliability of the measurement. For example, the diameter distribution of the particles in a cerium oxide slurry at pH 4.2 had a lower weight-average diameter than a cerium oxide slurry prepared at pH 5.2. the control of pH was also found to be critical for successful particle diameter analyses of the abrasive particles in colloidal silica slurries, fumed silica and alumina slurries. The adsorption of organic substances onto abrasive slurry particles altered the slurry's particle diameter distribution. The observed dependence of changes in particle diameter on the amount and type of the polymeric additive employed in the formulation points to adsorption of polymer onto abrasive particles; and indicates a high degree of sensitivity in the measurement to binding interactions between abrasive particles and the non-particulate chemical components in CMP slurries.
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