The preparation of glass cell surfaces that are chemically functionalized with poly(ethylene glycol) (PEG) chains to reduce sample adsorption and their use in fluorescence correlation spectroscopy (FCS) is described. Optical glass coverslips were acid etched and reacted with either 750 Mr PEG (PEG-750) or 5000 Mr PEG (PEG-5000) to produce adsorption-resistant optical surfaces. FCS data for Nile red-loaded Triton X-100 micelles (NR-TX-100) and Alexa Fluor 555-labeled proteins, bovine serum albumin (BSA-A555), lipidized BSA (lipid-BSA-A555), and three low molecular weight dyes deposited on PEGylated coverslips were evaluated. Measurement artifacts due to sample adsorption on the PEG-5000 functionalized coverslips were reduced significantly for the majority of test materials. Calculations of translational diffusion coefficients and Stokes radii confirmed the effectiveness of this approach. PEG-5000 functionalized coverslips were demonstrated as more effective in inhibiting adsorption than PEG-750 functionalized coverslips. Neither of the functionalized coverslips inhibited the adsorption of one test compound, rhodamine B, a dye that adsorbs strongly on glass surfaces. The use of longer PEG chains in conjunction with chemical cross-linking is proposed for producing a denser, less porous PEG layer for the prevention of strongly glass-adsorbing fluorophores that do not interact with the PEG layer.

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.

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.

Additive-abrasive interactions in chemical-mechanical planarization (CMP) slurries are investigated using fluorescence correlation spectroscopy (FCS). The FCS technique provides quantitative determinations of the interaction between additives and abrasive particles by characterizing the competitive adsorption of the additive and a fluorescent probe molecule by an abrasive particle. Adsorption of the CMP additives glycine and benzotriazole (BTA) on precipitated and sol-gel colloidal silica abrasives are characterized. Significant differences in the fluorescent probe’s adsorption to the different silica abrasives in the presence of the additives suggest surface chemistry differences between the different types of silica. Extensions of the analysis of FCS data are proposed for improving the quantitative determination of the competitive adsorption of fluorescent probe dyes and CMP additives on abrasive particles.