Preparations of silica slurry for wafer polishing via controlled growth of commercial silica seeds

Abstract

Silica slurry in aqueous medium for wafer polishing was prepared by sol-gel reaction of silicon alkoxide utilizing commercial silica particles as seeds that were grown stepwise through intermittent additions of tetraethylorthosilicate (TEOS) as a silica precursor. Before the growth reaction, the commercial silica particles were pre-treated in the vibratory mill partially filled with zirconia ball and the sonicator to ensure good dispersion. The alcohol left after growth reaction was removed by vacuum distillation and repeated washings with distilled water followed by centrifugations. Then, the alcohol-free 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. Finally, wafer-polishing performance of the prepared silica slurries was considered by measuring the polishing (or removal) rate, and RMS (root mean square) roughness of the polished wafer surface. For the polishing, MEA (monoethanolamine) and TMAH (tetramethylammonium hydroxide) were used 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. One of 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 by the increased size of the abrasive particle, surface roughness of the polished wafer surface was deteriorated.