Application of Fluorescence Correlation Spectroscopy in the Characterization of Particle Size Distributions of Colloidal Silica Abrasives Used in Chemical-Mechanical Planarization

Abstract

Particle size distribution (PSD) analysis of colloidal silica abrasives employed in chemical-mechanical planarization slurries is demonstrated using fluorescence correlation spectroscopy (FCS). FCS allows a quantitative determination of the PSD for a dispersion of abrasive silica particles through fluorescence measurements of a dye, Rhodamine 110 (R110), adsorbed to the particles. Analysis of the autocorrelation function (ACF) of the fluorescence intensity fluctuations from R110-dyed silica confirms the presence of the adsorbed dye on the particles. Application of the method of histograms to the ACF yields a detailed analysis of the shape of the PSD for silica particle dispersions. FCS is shown to reliably measure the hydrodynamic diameter of silica particles less than 20 nm in mean size, and at particle concentrations which are too dilute for PSD analysis using a widely applied method for this purpose, dynamic light scattering.