Nodular Silica Sol and Method of Producing the Same

Abstract

A novel nodular silica sol adapted to use as a polishing material for polishing, for instance, CMP. The nodular silica sol has a ratio of an average particle diameter (r) measured by the dynamic light scattering method versus a particle diameter (r′) converted to that of an equivalent sphere computed from an average specific surface area measured by means of the nitrogen absorption method (r/r′, referred to as “association ratio”) in a range from 1.2 to 10, the particle diameter (r′) in a range from 5 to 200 nm, and the specific surface area in a range from 13 to 550 m2/g. The nodular silica particles have heterogeneous forms, and contents of Ca and Mg contained in the nodular silica particles are below 1000 ppm against SiO2 respectively.

1 . A nodular silica sol prepared by dispersing nodular silica particles having heterogeneous forms in a solvent,
 wherein a ratio of an average particle diameter (r) obtained through measurement by means of the dynamic light scattering method versus a particle diameter (r′) converted to that of an equivalent sphere computed from an average specific surface area measured by the nitrogen absorption method (r/r′, referred to as “association ratio”) is in a range from 1.2 to 10, the particle diameter (r′) is in a range from 5 to 200 nm, the specific surface area is in a range from 13 to 550 m 2 /g, and contents of Ca and Mg (when calculated as those of the oxides) contained in the nodular silica particles are below 1000 ppm against SiO 2  respectively.   
     
     
         2 . The nodular silica sol according to  claim 1 ,
 wherein the nodular silica particles do not contain carbon.   
     
     
         3 . The nodular silica sol according to  claim 2 ,
 wherein contents of Na, K, Cu, Ni, and Fe in the nodular silica particles against SiO 2  are 10 ppm or below for Na, 10 ppm or below for K, 500 ppb or below for Cu, 300 ppb or below for Ni, and 150 ppm or below for Fe.   
     
     
         4 . A method of producing the nodular silica sol according to  claim 1  comprising the steps of:
 preparing a polymerized silicic acid solution with viscosity of a silicic acid in a range from 0.9 to 100 mPa·s by aging a silicic acid solution with pH in a range from 1.0 to 7.0 and silica concentration in a range from 0.05 to 3.0% by weight at a temperature in a range from 1 to 98° C.;   preparing a seed liquid by adding an alkali to the polymerized solution and heating the resultant mixture solution; and   building up the obtained seed liquid.   
     
     
         5 . A method of producing the nodular silica sol according to  claim 1  comprising the steps of:
 preparing a polymerized silicic acid solution with viscosity of a silicic acid in a range from 0.9 to 100 mPa·s by aging a silicic acid solution with pH in a range from 1.0 to 7.0 and silica concentration in a range from 0.05 to 3.0% by weight at a temperature in a range from 1 to 98° C.;   preparing a seed liquid by adding an alkali to the polymerized solution to adjust the pH to a range from 9 to 12.5 and heating the resultant mixture solution at a temperature in a range from 50 to 150° C.;   adding an alkali, according to the necessity, to the obtained seed liquid to adjust the pH in a range from 9 to 12.5; and   dropping a silicic acid solution or a highly purified silicic acid solution to the seed liquid at a temperature in a range from 20 to 98° C. continuously or intermittently for building up.   
     
     
         6 . The method of producing a nodular silica sol according to  claim 4 ,
 wherein the pH of the silicic acid solution was adjusted to a range from 1.0 to 7.0 by adding an alkali or an acid to the silicic acid solution.   
     
     
         7 . The method of a nodular silica sol according to  claim 5 ,
 wherein the highly purified silicic acid solution is highly purified by contacting a strong acidic cation exchanger or a strong basic anion exchanger separately to a silicic acid solution.   
     
     
         8 . A method of producing the nodular silica sol according to  claim 3 ,
 wherein the nodular silica sol produced by the production method according to  claim 4 , is further highly purified.   
     
     
         9 . The method of producing a nodular silica sol according to  claim 8 ,
 wherein, in the process for highly purifying the nodular silica sol, the nodular silica sol is contacted to a cation exchanger, and furthermore to an anion exchanger.   
     
     
         10 . The nodular silica sol according to  claim 1 ,
 wherein an average diameter (r) of the nodular silica particles is in a range from 10 to 200 nm measured by the dynamic light scattering method, a specific surface area is in a range from 30 to 300 m 2 /g, and an association ratio is 1.2 or more and less than 2.7.   
     
     
         11 . A silica sol for a polishing material comprising the nodular silica sol according to  claim 10 . 
     
     
         12 . The nodular silica sol according to  claim 1 ,
 wherein silica particles having the association ratio (r/r′) in a range from 1.2 to 4.0 and an average diameter measured by the dynamic light scattering method in a range from 10 to 150 nm are dispersed, and an absolute value of a difference between zeta potential at pH 5 and that at pH 9 is in a range from 1 to 9 mV.   
     
     
         13 . A method of producing the nodular silica sol according to  claim 1  comprising the steps of:
 (1) cleaning a silica hydrogel obtained by neutralizing a silicate with an acid to remove salts, adding an alkali to adjust molar ratio of SiO 2 /M 2 O (M: Na, K, NH 3 ) to a range from 30 to 500, and heating the mixture at a temperature in a range from 60 to 200° C. to obtain a silica sol; and   (2) using the silica sol as a seed sol, adding an alkali according to the necessity to adjust pH to a range from 9 to 12.5, and adding a silicic acid solution to the seed sol at a temperature in a range from 60 to 200° C. continuously or intermittently.   
     
     
         14 . The method of producing a nodular silica sol according to  claim 13 ,
 wherein the silicate is selected from a group consisting of sodium silicate, potassium silicate, and ammonium silicate.   
     
     
         15 . The method of producing a nodular silica sol according to  claim 13 ,
 wherein the seed sol in the step (2) is a sol in which silica particles having an average diameter measured by the dynamic light scattering method in a range from 5 to 80 nm are dispersed.   
     
     
         16 . The method of producing a nodular silica sol according to  claim 13 ,
 wherein the silicic acid solution used in the step (2) is an acidic silicic acid solution obtained by dealkylating an alkali silicate.   
     
     
         17 . A method of producing the nodular silica sol according to  claim 3 ,
 wherein the silicic acid solution used in the production method according to  claim 13  is prepared by highly purifying a silicic acid solution.   
     
     
         18 . A method of producing the nodular silica sol according to  claim 3 ,
 wherein the nodular silica sol obtained by the production method according to  claim 13  is furthermore highly purified.   
     
     
         19 . A polishing material containing the nodular silica sol according to  claim 1 .