| 摘要 |
A method for converting fumed silica into colloidal silica is provided to minimize the surface defects of substrates or semiconductor wafers. T-30 particles made by Wacker Chemicals are used as the fumed silica source. T-30 is dissolved in KOH. At around 90 degree in centigrade, silica is dissolved quickly. Filtration is optional to remove the undissolved silica and prevent gel forming. The final solid content is about 21% and it contains about 15% SiO2. That is suitable to ion exchange process to make perc for particle growth. The fumed silica powder, e.g., S-13 or T-30, supplied by Wacker, is added under high speed mixing to a solution of the deionized water mixed with an electronic grade of KOH. After the powder is fully dispersed, the mixture is charged into a reactor and heated up to 95-100 degree in centigrade under mixing. The silica powder dissolves gradually into a water clear K silicate solution at 5-25% SiO2 solid with KOH/SiO2 weight ratio ranging from 0.3-0.5. The final pH of the solution at room temperature was around 11.0-13.3.
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