Ultrapure colloidal silica for use in chemical mechanical polishing applications

Abstract

An ultrapure colloidal silica dispersion comprising colloidal silica particles having a mean or aggregate particle size from about 10 to about 200 nm, wherein the colloidal silica dispersion has less than 200 ppb of each trace metal impurity disposed therein, excluding potassium and sodium, and have less than 2 ppm residual alcohol.

1 . An ultrapure colloidal silica dispersion comprising colloidal silica particles having a mean or aggregate particle size from about 10 to about 200 nm, wherein said colloidal silica dispersion has less than 200 ppb of each trace metal impurity disposed therein, excluding potassium and sodium, and have less than 2 ppm residual alcohol.  
   
   
       2 . The ultrapure colloidal silica dispersion of  claim 1 , wherein the colloidal silica dispersion is prepared by a method comprising the steps of: 
 dissolving a fumed silica in an aqueous solvent comprising an alkali metal hydroxide to produce an alkaline silicate solution;    removing the alkali metal via ion exchange to generate a silicic acid solution; and    adjusting temperature, concentration and pH of said silicic acid solution to values sufficient to initiate nucleation and particle growth; and    cooling said silicic acid solution at a rate sufficient to produce said colloidal silica dispersion.    
   
   
       3 . The ultrapure colloidal silica dispersion of  claim 1 , wherein said colloidal silica dispersion is prepared by a method comprising the step of: 
 suspending said colloidal silica particles in an aqueous solvent.    
   
   
       4 . The ultrapure colloidal silica dispersion of  claim 1 , wherein each said trace metal is present in said dispersion in a range from about 5 to about 200 ppb, excluding potassium and sodium.  
   
   
       5 . The ultrapure colloidal silica dispersion of  claim 1 , wherein the cumulative trace metal concentration of said dispersion, excluding potassium and sodium, is in the range from about 0.5 to about 5 ppm.  
   
   
       6 . A potassium silicate solution having less than 200 ppb of each trace metal impurity selected from the group consisting of: Li, Rb, Cs, Fr, Fe, and Al, excluding potassium and sodium, and less than 2 ppm residual alcohol.