Study on the microstructure and rheological behavior of colloidal dispersions

Abstract

In this thesis, the microstructure and rheological behavior of silica suspensions were examined experimentally. The silica particles synthesized by sol-gel method were dispersed in either aqueous or organic phase and stabilized by sterically and electrostatically. We begin with silica particles dispersed in aqueous medium for wafer polishing. In this case, the silica particles were prepared by sol-gel reaction of silicon alkoxide utilizing commercial silica particles as seeds that were grown through stepwise additions of the silicone precursor. Before the growth reaction, the commercial silica particles were pre-treated by vibratory mill with zirconia balls and by sonication to ensure well-dispersed state. When the growth reaction was completed, the silica particles were dispersed in alcohol medium. The alcohol was removed by vacuum distillation, and repeated washings with distilled water followed by centrifugations. Then, the cleaned silica particles were redispersed in water. The dispersion stability of the silica slurries was examined by measuring surface charge of silica particles and rheological properties. Wafer-polishing performance of the prepared silica slurries was evaluated by measuring the polishing (or removal) rate, and average root mean square (RMS) roughness of the polished wafer surface using monoethanolamine (MEA) and tetramethylammonium hydroxide (TMAH) as polishing accelerators. The polishing result showed that the removal rate was nearly independent of the concentrations of MEA and TMAH in the range of 0.3 ~ 0.5 wt% and 100 ~ 500 ppm, respectively. Among the most interesting features is that hydrothermal treatment of the prepared silica slurries in autoclave increased the removal rate as high as ten times. Although the removal rate was increased as the abrasive particle size increased, surface roughness of the polished wafer surface was deteriorated. Then, we considered the stability of silica suspensions which were stabilized either by a...