Novel Method to Synthesize Ceria Coated Silica particles
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1157-E08-07
Novel Method to Synthesize Ceria Coated Silica particles Myoung-Hwan Oh*, Jae-Seok Lee, Sushant Gupta, Tae-gon Kim, Aniroddh Kaanna and Rajiv K. Singh Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, 32611, U.S.A. ABSTRACT Monodispersed ceria coated silica particles were prepared by a new type of ceria precursor. The ceria precursor was synthesized by alkoxide method, which employs ethanol as solvent. The synthesized particles were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that well-crystalline ceria coatings were deposited on the surface of the silica particles without post-heat treatment. In addition, the coated particles prepared by a new precursor were uniformly dispersed without the formation of hard aggregate as compared to those obtained by conventional method. INTRODUCTION The ceria (CeO2) particles have been widely used as a slurry abrasive for the STI CMP process in the semiconductor industry. The ceria based slurries provide excellent CMP performance owing to high nitride/oxide selectivity, chip uniformity, global planarization and high polishing efficiency [1, 2]. However, the ceria-based slurries induce defects on the wafer surface because of the broader particle size distribution and agglomeration particles resulting from poor dispersion stability. In order to overcome these problems, many researchers have investigated methods for producing ceria coated silica particles because colloidal silica offer certain advantages such as monodispersed spheres, narrow size distribution and lower specific gravity [3, 4]. However, in previous works [5-7], the synthesized ceria coated silica particles undergo severe aggregation from large volume shrinkage during the drying process because cerium sources induce the wet precipitate gelatinous in precipitation process [8]. Moreover, the resulting dispersions contain both of the ceria coated silica particles and the hard aggregates of ceria particles. In addition, in some cases, certain particles need the post-heat temperature to acquire a pure ceria coating. The objective of this study is to prepare the ceria coated silica particles without hard aggregates and verify the formation of ceria coating. This study is focused on the effect of ceria precursor on the formation of ceria coating. The evidences of pure ceria coated on the surface of silica particles are examined by means of XRD, SEM, TEM, and XPS. EXPERIMENTAL DETAILS
To prepare ceria precursor, cerium (III) nitrate hexahydrate (Ce(NO3)36H2O) and sodium hydroxide (NaOH) were used as the starting materials. Cerium (III) nitrate hexahydrate (1 g) and sodium hydroxide (1 g) were separately dissolved in 20 ml ethanol and then mixed vigorously for 12 h at 50oC. Hydrogen peroxide (H2O2) was added to the mixing solution as an oxidizing agent. The precipitated ceria precursor was separated via centrifugation, and then dispersed in
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