Patent ID: 8211193
Filing Date: 2012-07-03
Classification: C01B,C01P,C09G,C09K,C23F,H01L

Abstract:
1. A method of chemical mechanical polishing a surface of a substrate comprising the step of: contacting said substrate with a composition, said composition comprising: (i) a plurality of colloidal silica particles; and (ii) a medium for suspending said particles; wherein said composition has less than 200 ppb of each trace metal impurity, excluding potassium and sodium, less than 2 ppm residual alcohol, and wherein the cumulative trace metal concentration, excluding potassium and sodium, is in the range from about 0.5 to about 5 ppm; wherein said composition is an ultrapure colloidal silica dispersion; and wherein said contacting is carried out at a temperature and for a period of time sufficient to planarize said substrate; wherein said colloidal silica particles have a surface area from about 20 m wherein said colloidal silica particles are prepared by a process comprising the steps of: dissolving a fumed silica in an aqueous solvent comprising an alkali metal hydroxide to produce a alkaline silicate solution; removing said alkali metal via ion exchange to convert said alkaline silicate solution to a silicic acid solution; adjusting temperature, concentration and pH of said silicic acid solution to values sufficient to initiate nucleation and particle growth; cooling said silicic acid solution at a rate sufficient to produce a colloidal silica dispersion; and isolating said colloidal silica particles from said colloidal silica dispersion to produce colloidal silica particles having a mean or aggregate particle size about 10 nm to about 200 nm.