Research on the manufacturing of high purity colloidal silica abrasive with controlled particle size

Colloidal silica is one of the most important abrasive in chemical mechanical planarization (CMP), which requires high purity and specific size distribution. Traditional ion exchange method is low cost but with high impurity metal ions such as Na+, A13+, Fe3+ which were strictly restrict in some CMP process. To further remove these impurity metal ions, a new two step ion exchange method was developed to obtain high purity silicic acid. At first, the original silica acid was acidized by strong acid such as sulfuric acid or nitric acid, the elements aluminum and iron was ionized to tri-valence, then the acidized silica acid was treated with cation exchange resin to remove the A13+. Fe3-and anion exchange resin to remove the SO42-or NO3-, the impurity content can controlled in the range of several ppm. Several factors such as temperature, stabilizing agent and solid concentration during the manufacturing process were investigated to control the growth of silica particles. A proposed model was given to the uniform growth of silica nanoparticles, the colloidal silica with different size were synthesized by controlled conditions, the particle size was measured by chemistry titration, SEM, and dynamic light scattering method, the results shows that calculated results was in accordance with the test datum.