Reduced striae extreme ultraviolet elements

Abstract

Titania-containing silica glass bodies and extreme ultraviolet elements having low levels of striae are disclosed. Methods and apparatus for manufacturing and measuring striae in glass elements and extreme ultraviolet elements are also disclosed.

1 - 4 . (canceled)  
     
     
         5 . A method of manufacturing an extreme ultraviolet lithography element comprising: 
 providing a silicon-containing feedstock and a titanium containing feedstock;    delivering the silicon-containing feedstock and titanium-containing feedstock to a conversion site;    converting the silicon-containing feedstock and titanium-containing feedstock into titania-containing silica soot;    consolidating the titania-containing silica soot into an inclusion-free, homogeneous titanium-containing silica glass preform; and    finishing the titanium-containing glass preform into an extreme ultraviolet lithographic element having an rms striae level less than 0.05 mega Pascals.    
     
     
         6 . The method of  claim 5 , wherein the conversion site includes a furnace having exhaust vents and the method includes maintaining said striae level by controlling exhaust vent flow during the manufacturing process.  
     
     
         7 . The method of  claim 5 , further including providing the furnace with more than six exhaust vents.  
     
     
         8 . The method of  claim 5 , wherein the striae level is modified by adjusting the distance between the preform and the burner.  
     
     
         9 . The method of  claim 5 , wherein soot is deposited into a cup mounted on an oscillating table and the striae level is decreased by increasing the rotation rate of the table.  
     
     
         10 . The method of  claim 9 , wherein the rotation rate of the boule is greater than 6 rpm.  
     
     
         11 . A method of measuring striae in an extreme ultraviolet lithographic element comprising utilizing a polariscope to measure the optical retardance in the element as a function of position and converting the optical retardance to stress values.  
     
     
         12 . The method of  claim 11 , wherein the polariscope has a sensitivity of at least 0.05 nm.  
     
     
         13 . The method of  claim 11 , wherein the polariscope utilizes light source having a beam size less than the spacing of the striae in the element.  
     
     
         14 . The method according to  claim 5 , wherein the titania-containing silica soot is deposited into a revolving collection cup and the collected soot is consolidated at a temperature above 1600° C.  
     
     
         15 . The method according to  claim 5 , wherein the oscillation and rotation is defined by the equations:  
           x ( t )= r   1  sin 2 πω 1   t+r   2  sin 2πω 2   t      y ( t )= r   1  cos 2πω 1   t+r   2  cos 2πω 2   t    wherein:    x(t) and y(t) represent the coordinates of the center of the boule as measured from the center of the furnace ringwall as a function of time (t) measured in minutes,    the sum of r1 and r2 must be less than the difference between the radius of the ringwall and radius of the containment cup;    the parameters r 1 , r 2 , ω 1 , ω 2 , and a fifth parameter, ω 3 , which represents the boule's rotation rate about its center in revolutions per minute (rpm) define the total motion of the boule; and    the values of ω 1 , ω 2  and ω 3  are each above 5.0 rpm.    
     
     
         16 . The method according to  claim 16 , wherein ω 1 , ω 2  and ω 3  are 7.0488, 7.7563 and 6.5736, respectively.  
     
     
         17 . The method according to  claim 5 , wherein the silica-containing feedstock and the titania-containing feedstock are delivered such that the titania content of the consolidated glass is in the range of 5 wt. % to 10 wt. %.  
     
     
         18 . The method according to  claim 5 , wherein the silica-containing feedstock and the titania-containing feedstock are delivered such that the titania content of the consolidated glass is in the range of 6 wt. % to 8 wt. %.  
     
     
         19 . A method for making a glass boule suitable for the manufacture of extreme ultraviolet lithography elements, said method comprising the steps of: 
 providing a silicon-containing feedstock and a titanium containing feedstock;    delivering the silicon-containing feedstock and titanium-containing feedstock to a conversion site where they are converted into titania-containing silica particles;    depositing the soot particles into a vessel located on a table having an oscillation pattern and a rotation pattern;    consolidating the titania-containing silica soot into an inclusion-free, homogeneous titanium-containing silica glass boule having an rms striae level less than 0.05 mega Pascals; and    after consolidation, removing the boule from the vessel for further processing into elements suitable for extreme ultraviolet lithography;    wherein, to say patterns are defined by the equations:        x ( t )= r   1  sin 2 πω 1   t+r   2  sin 2πω 2   t      y ( t )= r   1  cos 2πω 1   t+r   2  cos 2πω 2   t      x(t) and y(t) represent the coordinates of the center of the boule as measured from the center of the furnace ringwall as a function of time (t) measured in minutes; 
 the sum of r1 and r2 must be less than the difference between the radius of the ringwall and radius of vessel; and 
 the parameters r 1 , r 2 , ω 1 , ω 2 , and a fifth parameter, ω 3 , which represents the boule's rotation rate about its center in revolutions per minute (rpm).  
 
   
     
     
         20 . The method according to  claim 19 , wherein the values of ω 1 , ω 2  and ω 3  are each above 5.0 rpm.  
     
     
         21 . The method according to  claim 19 , wherein ω 1 , ω 2  and ω 3  are 7.0488, 7.7563 and 6.5736 rpm, respectively.  
     
     
         22 . The method according to  claim 19 , wherein the silica-containing feedstock and the titania-containing feedstock are delivered such that the titania content of the consolidated glass is in the range of 5 wt. % to 10 wt. %.  
     
     
         22 . The method according to  claim 19 , wherein the silica-containing feedstock and the titania-containing feedstock are delivered such that the titania content of the consolidated glass is in the range of 6 wt. % to 8 wt. %.  
     
     
         23 . The method according to  claim 19 , wherein the silica-containing feedstock and the titania-containing feedstock are delivered such that the titania content of the consolidated glass is in the range of 6.8 wt. % to 7.5 wt. %.  
     
     
         24 . The method according to  claim 19 , wherein the consolidation is carried out at a temperature above 1600° C.