Methods for reducing spherical aberration effects in photolithography

Abstract

Methods to at least partially compensate for photoresist-induced spherical aberration that occurs during mask imaging used for photolithographic processing of semiconductor devices, LCD elements, thin-film magnetic heads, reticles and other substrates including photo-defined structures thereon. A photoresist or other photosensitive material may be irradiated with a mask pattern image including a selected nonzero spherical aberration value to compensate for photoresist-induced spherical aberration.

1 . A method of producing a pattern on a photoresist, comprising: 
 providing a mask having a pattern defined thereon;    disposing the mask between an illumination source and a substrate having a photoresist disposed thereon; and    irradiating the mask with light from the illumination source to produce a mask pattern image on the photoresist altered with a nonzero spherical aberration value selected to at least partially compensate for spherical aberration induced by the photoresist.    
     
     
         2 . The method of  claim 1 , further comprising selecting the nonzero spherical aberration value of the altered mask pattern image to a value approximately equal to a photoresist-induced spherical aberration of the photoresist when the photoresist is irradiated with light having a spherical aberration of zero.  
     
     
         3 . The method of  claim 1 , further comprising selecting the nonzero spherical aberration value of the altered mask pattern image using the equation:  
       
         
           
             
               a 
               = 
               
                 
                   
                     ( 
                     
                       
                         n 
                         2 
                       
                       - 
                       1 
                     
                     ) 
                   
                   · 
                   t 
                 
                 
                   8 
                   · 
                   
                     n 
                     3 
                   
                   · 
                   
                     s 
                     4 
                   
                 
               
             
           
         
       
       where a is the nonzero spherical aberration value of the mask pattern image, n is a refractive index of the photoresist, t is a thickness of the photoresist, and s is a focal distance into the photoresist.  
     
     
         4 . The method of  claim 1 , further comprising experimentally determining the nonzero spherical aberration value for the altered mask pattern image.  
     
     
         5 . The method of  claim 1 , further comprising focusing the altered mask pattern image at approximately a mid-depth of the photoresist on the substrate.  
     
     
         6 . The method of  claim 1 , wherein providing the mask comprises forming the mask to include a pellicle.  
     
     
         7 . The method of  claim 6 , wherein forming the mask to include a pellicle includes forming the mask to include a hard pellicle.  
     
     
         8 . The method of  claim 7 , further including selecting the nonzero spherical aberration value to at least partial compensate for spherical aberration introduced by the hard pellicle.  
     
     
         9 . The method of  claim 1 , further comprising projecting the mask pattern image onto the photoresist.  
     
     
         10 . The method of  claim 1 , further comprising altering the nonzero spherical aberration value of the mask pattern image by at least one of using a projection lens apparatus, varying an optical path between the mask and a projection lens apparatus and disposing a transparent plate between the mask and a projection lens apparatus.  
     
     
         11 . A method of producing a pattern on a photoresist, comprising: 
 disposing a mask having a pattern defined thereon between an illumination source and a substrate having a photoresist disposed thereon;    irradiating the mask with light from the illumination source to produce a mask pattern image;    introducing a nonzero spherical aberration value to the mask pattern image; and    irradiating the photoresist with the mask pattern image including the nonzero spherical aberration value.    
     
     
         12 . The method of  claim 11 , further comprising selecting the introduced nonzero spherical aberration value as a value approximately equal to a photoresist-induced spherical aberration of the photoresist when the photoresist is irradiated with light having a spherical aberration of zero.  
     
     
         13 . The method of  claim 11 , further comprising selecting the introduced nonzero spherical aberration value using the equation:  
       
         
           
             
               a 
               = 
               
                 
                   
                     ( 
                     
                       
                         n 
                         2 
                       
                       - 
                       1 
                     
                     ) 
                   
                   · 
                   t 
                 
                 
                   8 
                   · 
                   
                     n 
                     3 
                   
                   · 
                   
                     s 
                     4 
                   
                 
               
             
           
         
       
       where a is the nonzero spherical aberration value of the mask pattern image, n is a refractive index of the photoresist, t is a thickness of the photoresist, and s is a focal distance into the photoresist.  
     
     
         14 . The method of  claim 11 , further comprising experimentally determining the introduced nonzero spherical aberration value.  
     
     
         15 . The method of  claim 11 , further comprising focusing the mask pattern image at approximately a mid-depth of the photoresist on the substrate.  
     
     
         16 . The method of  claim 11 , further including forming the mask to include a pellicle.  
     
     
         17 . The method of  claim 16 , wherein forming the mask to include a pellicle includes forming the mask to include a hard pellicle.  
     
     
         18 . The method of  claim 17 , further including selecting the introduced nonzero spherical aberration value to at least partially compensate for spherical aberration introduced by the hard pellicle.  
     
     
         19 . The method of  claim 11 , further comprising projecting the mask pattern image onto the photoresist.  
     
     
         20 . The method of  claim 11 , further comprising introducing the nonzero spherical aberration value by at least one of using a projection lens apparatus, varying an optical path between the mask and a projection lens apparatus and disposing a transparent plate between the mask and a projection lens apparatus.  
     
     
         21 . A method of patterning a photoresist, comprising: 
 irradiating a mask with light to produce a mask pattern image therefrom;    adding a nonzero spherical aberration value to the mask pattern image; and    irradiating a photoresist with the mask pattern image including the nonzero spherical aberration value.    
     
     
         22 . The method of  claim 21 , further comprising selecting the added nonzero spherical aberration value of the mask pattern image to a value approximately equal to a photoresist-induced spherical aberration of the photoresist when the photoresist is irradiated with light having a spherical aberration of zero.  
     
     
         23 . The method of  claim 21 , further comprising selecting the added nonzero spherical aberration value using the equation:  
       
         
           
             
               a 
               = 
               
                 
                   
                     ( 
                     
                       
                         n 
                         2 
                       
                       - 
                       1 
                     
                     ) 
                   
                   · 
                   t 
                 
                 
                   8 
                   · 
                   
                     n 
                     3 
                   
                   · 
                   
                     s 
                     4 
                   
                 
               
             
           
         
       
       where a is the nonzero spherical aberration value of the mask pattern image, n is a refractive index of the photoresist, t is a thickness of the photoresist, and s is a focal distance into the photoresist.  
     
     
         24 . The method of  claim 21 , further comprising experimentally determining the added nonzero spherical aberration value.  
     
     
         25 . The method of  claim 21 , further comprising focusing the mask pattern image including the added nonzero spherical aberration value at approximately a mid-depth of the photoresist.  
     
     
         26 . The method of  claim 21 , further including forming the mask to include a pellicle.  
     
     
         27 . The method of  claim 26 , wherein forming the mask to include a pellicle includes forming the mask to include a hard pellicle.  
     
     
         28 . The method of  claim 27 , further comprising selecting the added nonzero spherical aberration value to at least partial compensate for spherical aberration introduced by the hard pellicle.  
     
     
         29 . The method of  claim 21 , further comprising projecting the mask pattern image onto the photoresist.  
     
     
         30 . The method of  claim 21 , further comprising providing the added nonzero spherical aberration value of the mask pattern image by at least one of using a projection lens apparatus, varying an optical path between the mask and a projection lens apparatus and disposing a transparent plate between the mask and a projection lens apparatus.