Method of polishing glass substrate
View Patent ↗An object of the present invention is to provide a polishing method for diminishing concave defects of a glass substrate used in a reflective mask for EUVL and the like. The invention relates to a method of polishing a glass substrate which comprises polishing a major surface of the glass substrate while feeding a polishing slurry between the glass substrate and a pad surface of a polishing pad, wherein the polishing load of the polishing pad is from 1 to 60 g/cm 2 . The pad surface of the polishing pact is preferably dressing-processed.
1. A method of polishing a glass substrate, which comprises polishing a major surface of the glass substrate while feeding a polishing slurry comprising silica having an average primary particle diameter of 60 nm or less between the glass substrate and a pad surface of a polishing pad, wherein during the polishing step the polishing pad has a polishing load of from 1 to 60 g/cm 2 and wherein the polishing slurry has a pH of 1 to 4 and a colloidal silica content of 10 to 30% by mass.
2. The method of polishing a glass substrate according to claim 1 , wherein the polishing pad is a suede-based pad having a pad surface with a maximum peak and a minimum peak wherein the difference in height between the maximum peak and the minimum peak on the surface of 50 μm or less.
3. The method of polishing a glass substrate according to claim 1 , wherein the polishing load of the polishing pad is from 1 to 25 g/cm 2 .
4. The method of polishing a glass substrate according to claim 1 , wherein the pad surface of the polishing pad is dressing-processed with a dress plate.
5. The method of polishing a glass substrate according to claim 4 , wherein the dress plate is electrodeposited diamond.
6. The method of polishing a glass substrate according to claim 1 , wherein the polishing pad has an average open pore diameter of from 5 to 50 μm.
7. The method of polishing a glass substrate according to claim 1 , wherein the polishing pad has as average open pore diameter of from 5 to 30 μm.
8. The method of polishing a glass substrate according to claim 1 , wherein the surface to be polished of the glass substrate is preliminarily polished so as to have a surface roughness Rms of 3 nm or less.
9. The method of polishing a glass substrate according to claim 1 , wherein the polishing slurry has an average primary particle diameter of 30 nm or less.
10. The method of polishing a glass substrate according to claim 1 , wherein the glass substrate is a glass substrate for a mask blank.
11. The method of polishing a glass substrate according to claim 1 , wherein the polishing slurry has an average primary particle diameter of 15 nm or less.
12. The method of polishing a glass substrate according to claim 1 , wherein the polishing slurry comprises silica.
13. The method of polishing a glass substrate according to claim 1 , wherein the polishing slurry comprises-ceria.
14. The method of polishing a glass substrate according to claim 1 , wherein the polishing slurry has a colloidal silica content of 18 to 22% by mass.