Polishing composition

Abstract

To provide a technique with which in a case where sulfonic acid-modified aqueous anionic sol is used as abrasive grain, in a polishing composition for polishing an object to be polished that contains SiN, the stability of the SiN polishing rate with time can be improved, and the content of hydrogen peroxide can be decreased. In a polishing composition having a pH of 6 or less, sulfonic acid-modified colloidal silica obtained by immobilizing sulfonic acid on surfaces of silica particles, and water are allowed to be contained, at this time, as the sulfonic acid-modified colloidal silica, the one derived from sulfonic acid-modified aqueous anionic silica sol produced by a production method including a first reaction step of obtaining a reactant by heating raw colloidal silica having a number distribution ratio of 10% or less of microparticles having a particle diameter of 40% or less relative to a volume average particle diameter based on Heywood diameter (equivalent circle diameter) as determined by image analysis using a scanning electron microscope in the presence of a silane coupling agent having a functional group chemically convertible to a sulfonic acid group; and a second reaction step of converting the functional group to a sulfonic acid group by treating the reactant is used.

1 . A polishing composition having a pH of 6 or less, comprising:
 sulfonic acid-modified colloidal silica obtained by immobilizing sulfonic acid on surfaces of silica particles; and   water, wherein   the sulfonic acid-modified colloidal silica is derived from sulfonic acid-modified aqueous anionic silica sol produced by a production method comprising:   a first reaction step of obtaining a reactant by heating raw colloidal silica having a number distribution ratio of 10% or less of microparticles having a particle diameter of 40% or less relative to a volume average particle diameter based on Heywood diameter (equivalent circle diameter) as determined by image analysis using a scanning electron microscope in the presence of a silane coupling agent having a functional group chemically convertible to a sulfonic acid group; and   a second reaction step of converting the functional group to a sulfonic acid group by treating the reactant.   
     
     
         2 . The polishing composition according to  claim 1 , wherein the production method further comprises a step of distilling off an organic solvent coexisting with colloidal silica under a condition of pH 7 or more so that a residual organic solvent concentration in colloidal silica having an organic solvent concentration of 1% by mass or more becomes less than 1% by mass to obtain the raw colloidal silica. 
     
     
         3 . The polishing composition according to  claim 1 , wherein the functional group is a mercapto group. 
     
     
         4 . The polishing composition according to  claim 3 , wherein the treatment is an oxidation treatment using hydrogen peroxide. 
     
     
         5 . The polishing composition according to  claim 4 , wherein an addition amount of the hydrogen peroxide is 3 to 5 mol times relative to an addition amount of the silane coupling agent, and a residual hydrogen peroxide concentration in the obtained aqueous anionic silica sol is 500 ppm by mass or less. 
     
     
         6 . The polishing composition according to  claim 1 , wherein the production method further comprises a step of lowering a viscosity of the raw colloidal silica by adding an alkaline solution or an organic solvent to the raw colloidal silica before the first reaction step. 
     
     
         7 . The polishing composition according to  claim 1 , wherein in the production method, the first reaction step is performed under a condition that a temperature condition of 90° C. or more is continued for 30 minutes or more. 
     
     
         8 . The polishing composition according to  claim 1 , wherein the polishing composition is used for an application of polishing silicon nitride. 
     
     
         9 . A polishing composition having a pH of 6 or less, and used for an application of polishing silicon nitride, comprising:
 sulfonic acid-modified colloidal silica obtained by immobilizing sulfonic acid on surfaces of silica particles, wherein   the sulfonic acid-modified colloidal silica is derived from sulfonic acid-modified aqueous anionic silica sol in which when a SiN wafer is subjected to an immersion treatment under a pH 2 condition and then washed with pure water, the number of particles having a particle diameter of less than 40% of a volume average particle diameter adhering to a surface of the SiN wafer is 50% or less relative to the number of particles having a particle diameter of 40% or more of a volume average particle diameter adhering similarly.   
     
     
         10 . The polishing composition according to  claim 9 , wherein the total content of metal impurities in the sulfonic acid-modified colloidal silica is 1 ppm by mass or less. 
     
     
         11 . The polishing composition according to  claim 9 , wherein the sulfonic acid-modified colloidal silica is produced by the production method comprising:
 a first reaction step of obtaining a reactant by heating raw colloidal silica having a number distribution ratio of 10% or less of microparticles having a particle diameter of 40% or less relative to a volume average particle diameter based on Heywood diameter (equivalent circle diameter) as determined by image analysis using a scanning electron microscope in the presence of a silane coupling agent having a functional group chemically convertible to a sulfonic acid group; and   a second reaction step of converting the functional group to a sulfonic acid group by treating the reactant.