Method of producing a glass substrate for a mask blank and method of producing a mask blank

Abstract

A method of producing a glass substrate for a mask blank has the steps of measuring a convex/concave profile of a surface of the glass substrate, controlling a flatness of the surface of the glass substrate to a value not greater than a predetermined reference value by specifying the degree of convexity of a convex portion present on the surface of the glass substrate with reference to a result of measurement obtained in the profile measuring step and executing local machining upon the convex portion under a machining condition depending upon the degree of convexity, and polishing, after the flatness control step, the surface of the glass substrate subjected to the local machining by the action of a machining liquid interposed between the surface of the glass substrate and a surface of a polishing tool without direct contact therebetween.

What is claimed is:  
     
         1 . A method of producing a glass substrate for a mask blank, the method comprising: 
 a profile measuring step of measuring a convex/concave profile of a surface of the glass substrate for a mask blank;    a flatness control step of controlling a flatness of the surface of the glass substrate to a value not greater than a predetermined reference value by specifying the degree of convexity of a convex portion present on the surface of the glass substrate with reference to a result of measurement obtained in the profile measuring step and executing local machining upon the convex portion under a machining condition depending upon the degree of convexity; and    a non-contact polishing step of polishing, after the flatness control step, the surface of the glass substrate subjected to the local machining by the action of a machining liquid interposed between the surface of the glass substrate and a surface of a polishing tool without direct contact therebetween.    
     
     
         2 . A method according to  claim 1 , wherein the non-contact polishing step is carried out by float polishing.  
     
     
         3 . A method according to  claim 1  or  2 , wherein: 
 the machining liquid comprises:  
 an aqueous solution selected from water, an acidic aqueous solution, and an alkaline aqueous solution; or  
 a mixture of the aqueous solution and at least one kind of fine powder particles selected from colloidal silica, cerium oxide, zirconium oxide, and aluminum oxide.  
 
     
     
         4 . A method according to any one of claims  1  through  3 , wherein the local machining is carried out by plasma etching or a gas cluster ion beam.  
     
     
         5 . A method according to any one of claims  1  through  4 , wherein the reference value is not greater than 0.25 μm.  
     
     
         6 . A method of producing a mask blank, the method comprising the steps of preparing the glass substrate obtained by the method according to any one of  claims 1  to  5 , and forming a thin film as a transferred pattern on the glass substrate.  
     
     
         7 . A method of producing a transfer mask, the method comprising the steps of preparing the mask blank obtained by the method according to  claim 6  and patterning the thin film of the mask blank to form a thin film pattern on the glass substrate.  
     
     
         8 . A method of producing a semiconductor device, the method comprising the steps of preparing the transfer mask obtained by the method according to  claim 7  and transferring the thin film pattern of the transfer mask onto a semiconductor substrate by lithography.