Fluorescence Correlation Spectroscopic Studies of Particle Properties for Colloidal Ceria Abrasives Used in Chemical-Mechanical Planarization

The application of fluorescence correlation spectroscopy (FCS) in the characterization of ceria abrasives used in chemical-mechanical planarization (CMP) slurries is described. A fluorescent dye, Rhodamine 110 (R110), is used for this purpose. R110 adsorption on ceria particles is found to be pH-dependent and colloidal ceria dispersions differing in mean hydrodynamic diameter are analyzed. A Langmuir isotherm is generated for R110 adsorption on ceria, and the magnitude of the Langmuir constant is found to be four-times smaller than the corresponding constant for R110 adsorption on colloidal silica CMP abrasives. R110-labeled ceria particles are generated to quantitatively determine the particle size distribution (PSD) of abrasive ceria dispersions. The Maximum Entropy Method is used reduce the FCS autocorrelation function of R110-labeled ceria particle dispersions thereby producing a PSD. These findings indicate that ceria size distributions containing particles as small as 5 to 10 nm in diameter can be readily characterized using FCS.