Characterization of Particle Size and Surface Adsorption for SiO₂Abrasives Used in Chemical Mechanical Planarization via Fluorescence Correlation Spectroscopy

Abstract

Fluorescence correlation spectroscopy (FCS) is shown to be an effective characterization tool in the analysis of silica abrasives used in CMP slurries. Tagging of silica particles via non-covalent adsorption of a highly fluorescent dye is the key step in applying the technique to these materials. FCS is shown to have ample analytical sensitivity to detect and analyze the smallest fraction (< 20 nm) of an abrasive silica dispersion. Fractionation of abrasive silica dispersions using preparative ultracentrifugation allows a direct comparison of FCS and dynamic light scattering (DLS) methods for sizing particles with diameters less than 20 nm in the dispersion. The sensitivity of FCS measurements of this type exceeded the sensitivity of DLS determinations in this size range. Non-covalent adsorption of a fluorescent dye by the silica particle enables the characterization of adsorption behaviors of CMP slurry additives, such as benzotriazole (BTA) and amino acids, on abrasive silica particles. Different adsorption behaviors are observed and the use of one specific fluorescent dye, Rhodamine 110, afforded a determination of a quantitative isotherm for dye adsorption. Future applications of the FCS method for sizing abrasive nano-particles and adsorption isotherm analysis of other CMP abrasives, such as alumina and ceria, are proposed.

Ceria coated silica particles: One step preparation and settling behaviour under the influence of colloidal and hydrodynamic interactions

“…Although DLS is an inherently low-resolution technique (also see [22]) and has limited capability of resolving particles of different size in a mixture, it can still provide some information on the short-term behaviour of MCPs of silica and ceria. Figs.…”

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

“…Preliminary reports of the adsorption of R110 on colloidal ceria have been published recently (9,13). A more comprehensive analysis of the dye's adsorption on colloidal ceria was performed in the present study by first considering the pH-dependent fractional composition of R110 relative to the isoelectric point, pI, of colloidal ceria.…”

“…The characterization of physical properties for colloidal CMP abrasives has been achieved using a host of analytical techniques (3)(4)(5)(6). One method in particular, fluorescence correlation spectroscopy (FCS), has been demonstrated in the analysis of both the surface chemistry and particle diameter distribution of nano-sized silica CMP abrasives (7)(8)(9). In the present study, the capabilities of the FCS technique in the analysis of the physical properties of colloidal ceria CMP abrasives are described.…”