Polishing method for extreme ultraviolet optical elements and elements produced using the method

Abstract

The invention is directed to polished glass substrates suitable for extreme ultraviolet lithography. The elements are silica-titania glass elements having a coefficient of thermal expansion of 0±30×10 −9 /° C. or less, and containing 5-10 wt. % titania. The polished elements have a mid-spatial frequency peak-to-valley roughness of <10 nm and a high-spatial frequency roughness of <0.20 nm average roughness. The invention is further directed to a method of for producing optical elements suitable for extreme ultraviolet lithography (“EUVL”), the method having at least the steps of providing a glass substrate in the shape of the desired optical element and polishing the shaped substrate using a high abrasive slurry flow rate of >2.0 ml/cm 2 /min. Generally the flow rates are in the range of 2.0-10 ml/cm 2 /min. Glass substrates suitable for extreme ultraviolet lithography element have a coefficient of thermal expansion of 0±30×10 −9 /° C. or less. A particular glass suitable for EUVL use is silica-titania glass containing 5-10 wt. % titania.

1 . An element suitable for extreme ultraviolet lithography, said element comprising a silica-titania glass having a mid-spatial frequency roughness of <10 nm and a high-spatial frequency roughness of <0.20 nm average roughness;
 wherein said silica-titania glass contain 5-10 wt.% titania and has a coefficient of thermal expansion of 0±30×10 −9 /° C.   
     
     
         2 . The element according to  claim 1 , wherein said element a high-spatial frequency roughness of <0.17 nm average roughness. 
     
     
         3 . The element according to  claim 2 , wherein said element is selected from the group consisting of lenses, prisms, mirror and image masks. 
     
     
         4 . The element according to  claim 1 , wherein said element has a mid-spatial frequency roughness peak-to-valley value in the range of 6-8 nm. 
     
     
         5 . An optical element suitable, said element comprising a glass selected from the group consisting of silica-titania glass having a titania content in the range of 5-10 wt.%; silica-germania glasses' silica-alumina-germania glasses; and a silica-titania glass containing one or a plurality of additional metal oxide components and having a titania content in the range of 2-20 wt. %;
 wherein said element has a mid-spatial frequency roughness of <10 nm and a high-spatial frequency roughness of <0.20 nm average roughness.   
     
     
         6 . The optical element according to  claim 4 , wherein said element is selected from the group consisting of lenses, prisms, mirrors, display screens and masks. 
     
     
         7 . A method of for producing optical elements suitable for extreme ultraviolet lithography, said method comprising at least the steps of:
 providing a glass substrate in the shape of the desired optical element; and   polishing the shaped substrate using a high abrasive slurry flow rate of >2.0 ml/cm 2 /min.   wherein said glass substrate has a coefficient of thermal expansion of 0±30×10 −9 /° C.   
     
     
         8 . The method according to  claim 7 , wherein said abrasive slurry flow rate is in the range of 2-10 ml/cm 2 /min. 
     
     
         9 . The method according to  claim 7 , wherein said abrasive slurry flow rate is in the range of 3.1-4.5 ml/cm 2 /min. 
     
     
         10 . A method of for producing optical elements suitable for extreme ultraviolet lithography, said method comprising the steps of
 providing a glass substrate suitable for making extreme ultraviolet lithographic element;   shaping the glass substrate into said element; and   polishing the surfaces of the optical element using a high abrasive slurry flow rate, said flow rate being >2.0 ml/cm 2 /min.   
     
     
         11 . The method according to  claim 10 , wherein said flow rate is in the range of 2.0-10 ml/cm 2 /min. 
     
     
         12 . The method according  claim 10 , wherein the flow rate is in the range of 3.1-5.4 ml/cm 2 /min. 
     
     
         13 . The method according to  claim 10 , wherein said slurry contains a polishing abrasive selected from the group consisting of cerium oxide, alumina, silicon carbide, colloidal silica and diamond. 
     
     
         14 . The method according to  claim 13 , wherein the abrasive is cerium oxide. 
     
     
         15 . The method according to  claim 10 , wherein providing a glass substrate means providing a silica-titania substrate contain 5-10 wt. titania. 
     
     
         16 . A method of for producing optical elements suitable for extreme ultraviolet lithography, said method comprising the steps of
 providing boule of a silica-titania glass containing 5-10 wt. % titania,   obtaining from said boule glass substrates of size suitable for forming the desired optical elements,   shaping said substrates into said optical elements blanks; and   grinding, lapping and/or polishing said blanks into the shape of the desired optical elements;   wherein said polishing is carrier out using a high abrasive slurry flow rate, said flow rate being in the range of 2.0 ml/cm 2 /min.   
     
     
         17 . The method according to  claim 16 , wherein said flow rate is in the range of 2.0-10 ml/cm 2 /min. 
     
     
         18 . The method according to  claim 16 , wherein said flow rate is in the range of 3.1-4.5 ml/cm 2 /min. 
     
     
         19 . The method according to  claim 16 , wherein polishing means polishing the surfaces of said element to a mid-spatial frequency roughness of <10 nm. 
     
     
         20 . The method according to  claim 16 , wherein polishing means polishing the surfaces of said element to a high-spatial frequency roughness of <0.20 nm average roughness. 
     
     
         21 . The method according to  claim 20 , wherein the high-spatial frequency roughness of <0.20 nm average roughness is 0.17 nm average roughness. 
     
     
         22 . The method according to claim  160 , wherein said abrasive slurry contains an abrasive selected from the group consisting of alumina, diamond, silicon carbide, colloidal silica and cerium oxide. 
     
     
         23 . The method according to  claim 22 , wherein the abrasive in said abrasive slurry is cerium oxide.