Polishing composition

Abstract

A polishing composition containing an α-alumina, an intermediate alumina, an oxidizing agent and water; a method for reducing waviness of a substrate to be polished, including the step of applying the polishing composition to the substrate to be polished; and a method for manufacturing a substrate, including the step of polishing a substrate to be polished with the polishing composition. The polishing composition is suitable for polishing substrates for precision parts such as substrates for magnetic recording media for magnetic discs, optical discs, opto-magnetic discs, and the like; photomask substrates; glass for liquid crystals; optical lenses; optical mirrors; optical prisms; and semiconductor substrates.

1 . A polishing composition comprising an α-alumina, an intermediate alumina, an oxidizing agent and water.  
     
     
         2 . The polishing composition according to  claim 1 , further comprising an acid.  
     
     
         3 . The polishing composition according to  claim 1  or  2 , wherein the pH is less than 7.  
     
     
         4 . The polishing composition according to  claim 1  or  2 , wherein the weight ratio of the α-alumina to the intermediate alumina, α-alumina/intermediate alumina, is from 99/1 to 30/70.  
     
     
         5 . The polishing composition according to  claim 3 , wherein the weight ratio of the α-alumina to the intermediate alumina, α-alumina/intermediate alumina, is from 99/1 to 30/70.  
     
     
         6 . The polishing composition according to  claim 1  or  2 , wherein the α-alumina has a secondary average particle size of from 0.01 to 2 μm and a specific surface area of from 0.1 to 50 m 2 /g, and the intermediate alumina has a secondary average particle size of from 0.01 to 5 μm and a specific surface area of from 30 to 300 m 2 /g.  
     
     
         7 . The polishing composition according to  claim 3 , wherein the α-alumina has a secondary average particle size of from 0.01 to 2 μm and a specific surface area of from 0.1 to 50 m 2 /g, and the intermediate alumina has a secondary average particle size of from 0.01 to 5 μm and a specific surface area of from 30 to 300 m 2 /g.  
     
     
         8 . The polishing composition according to  claim 4 , wherein the α-alumina has a secondary average particle size of from 0.01 to 2 μm and a specific surface area of from 0.1 to 50 m 2 /g, and the intermediate alumina has a secondary average particle size of from 0.01 to 5 μm and a specific surface area of from 30 to 300 m 2 /g.  
     
     
         9 . The polishing composition according to  claim 2 , wherein the acid is a polyvalent acid.  
     
     
         10 . The polishing composition according to  claim 3 , wherein the acid is a polyvalent acid.  
     
     
         11 . The polishing composition according to  claim 4 , wherein the acid is a polyvalent acid.  
     
     
         12 . The polishing composition according to  claim 6 , wherein the acid is a polyvalent acid.  
     
     
         13 . The polishing composition according to  claim 2 , wherein the acid comprises an acid having a pK1 of less than 2.5 and an acid having a pK1 of 2.5 or more.  
     
     
         14 . The polishing composition according to  claim 3 , wherein the acid comprises an acid having a pK1 of less than 2.5 and an acid having a pK1 of 2.5 or more.  
     
     
         15 . The polishing composition according to  claim 4 , wherein the acid comprises an acid having a pK1 of less than 2.5 and an acid having a pK1 of 2.5 or more.  
     
     
         16 . The polishing composition according to  claim 6 , wherein the acid comprises an acid having a pK1 of less than 2.5 and an acid having a pK1 of 2.5 or more.  
     
     
         17 . The polishing composition according to  claim 9 , wherein the acid comprises an acid having a pK1 of less than 2.5 and an acid having a pK1 of 2.5 or more.  
     
     
         18 . A method for reducing waviness of a substrate to be polished, comprising the step of applying the polishing composition of  claim 1  or  2  to the substrate to be polished.  
     
     
         19 . A method for manufacturing a substrate, comprising the step of polishing a substrate to be polished with the polishing composition of  claim 1  or  2 .