Patent ID: 7712333

Claim:
A method for smoothing a surface of a glass substrate for an EUV mask blank, comprising: providing a glass substrate having a surface on which a concave defect with a depth of more than 3 nm exists after polishing the glass substrate to have a surface roughness of 0.15 nm or below in Rms; forming a film comprising a glass material on the surface of the glass substrate having the concave defect by a vacuum deposition method, the glass material having a fluid point Tf of 150° C. or above and of not higher than a strain point Ts (° C.) of the glass substrate; heating the film of the glass material at a temperature of not lower than Tf and not higher than Ts such state such that the film of the glass material flows and buries the concave defect; and cooling the film of the glass material, thereby to reduce the depth of the concave defect to 3 nm or below.