Illumination device for projection system and method for fabricating

Abstract

An illumination system for a microlithographic stepper has a light source that emits light of selected wavelength(s) along an optical path toward a photomask. An aperture mask is positioned in the path of the illumination light and between the light source and the photomask. The aperture mask has a dithered pattern of pixels. The intensity of the pattern controls the illumination of the photomask. The masking aperture pattern defines one or more zones of illumination. Each zone has elements that are patterned in accordance with a selected wavelength of incident light to diffract the incident light into an illumination pattern for illuminating a photomask. Each of the elements is constructed with a matrix of pixels. In the preferred embodiment the array of pixels is 8×8. The number of elements is generally greater than 3×3.

1. A method for controlling on-axis and off-axis illumination of a photomask comprising the steps of :
 directing a beam of light of a selected wavelength toward a pupil of an illumination system;  
 passing the beam of light through a fly's eye lens located near the pupil;  
 diffracting the light through a masking aperture having a half tone diffraction pattern of dithered pixels patterned for distributing  to distribute the light into two or more zones.  
 
     
     
       2. The method of  claim 1  wherein said half-tone diffraction pattern of dithered pixels comprises an array of pixels, each pixel of a clear or opaque type, said clear and opaque pixels for respectively passing and blocking incident light, wherein the number, size, and type of the pixels are chosen in accordance with:
 (a) the wavelength of light used to illuminate the photomask, and  
 (b) the  a size and shape of the  features of the photomask, for generating  to generate a continuous illumination intensity pattern on the photomask with illumination intensity at any location controlled by the half-tone dithered image .  
 
     
     
       3. The masking aperture  method of  claim 2  wherein the half-tone dithered image  masking aperture comprises an array of diffraction elements and each diffraction element is  comprises a dithered image  pattern of clear and/or opaque pixels. 
     
     
       4. The method of  claim 3  wherein each diffraction element comprise an n×n dithered matrix of pixels, the  an intensity of each element is defined by the number and type of pixels in its dithered matrix and wherein the pixels in each matrix are dithered to avoid artifacts. 
     
     
       5. The method of  claim 4  wherein the matrix of diffracting elements  pixels is selected from the group consisting of 2×2, 4×4, 8×8, 16×16, 32×32 and  64×64 pixels . 
     
     
       6. The method of  claim 3  wherein the  an intensity of each sub pixel is defined by a recursion relationship where: 
                      4   ⁢     D     n   /   2         +       D   00   2     ⁢     U     n   /   2                   4   ⁢     D     n   /   2         +       D   01   2     ⁢     U     n   /   2                       4   ⁢     D     n   /   2         +       D   10   2     ⁢     U     n   /   2                   4   ⁢     D     n   /   2         +       D   11   2     ⁢     U     n   /   2                              
 
       where 
         U   n     =                1       1       ⋯       1           1                                               ⋮                                               1                                                  .         
 
     
     
       7. The method of  claim 6  wherein the matrix of pixels comprises an 8×8 matrix and the relative intensity, D8, comprises: 
         D   8     =                0       32       8       40       2       34       10       42           48       16       56       24       50       18       58       26           12       44       4       36       14       46       6       38           60       28       52       20       62       30       54       22           3       35       11       43       1       33       9       41           51       19       59       27       49       17       57       27           15       47       7       39       13       45       5       37           63       31       55       23       61       29       53       21              .         
 
     
     
       8. The method of  claim 1  wherein the zones are arranged symmetrically about the center of the masking aperture. 
     
     
       9. The method of  claim 1  wherein the zones are arranged asymmetrically about the center of the masking aperture. 
     
     
       10. The method of  claim 1  wherein each of the zones have  has one shape selected from the group consisting of circles , squares , rectangles , ellipses , rings , circular rings , square rings  and any combinations  thereof. 
     
     
       11. The method of claim  1    10  wherein the selected shape is a stepped square. 
     
     
       12. The method of  claim 1  wherein the zone(s)  each zone is shaped in an ellipse and the major axis of each ellipse is aligned at a 45 degree angle with respect to the center of the masking aperture. 
     
     
       13. A method for controlling on-axis and off-axis illumination of a photomask comprising:
 directing a beam of light of a selected wavelength toward a pupil of an illumination system;  
 passing the beam of light through a fly's eye lens located near the pupil;  
 diffracting the light through a masking aperture having a half tone diffraction pattern of dithered pixels patterned for distributing  to distribute the light into one or more zones to form a pattern of illumination intensity in the one or more zones wherein each zone has a shape corresponding to shapes  selected from the group consisting of ellipses , square rings , stepped squares  and any combination thereof.  
 
     
     
       14. The method of  claim 13  further comprising diffracting the light beam through a masking aperture having a half tone diffraction pattern of dithered pixels patterned for distributing  to distribute the light into one or more zones to form one or more additional patterns of light intensity selected from the group consisting of circles , squares , rectangles  and circular rings . 
     
     
       15. A method for controlling on- axis and off - axis illumination of a photomask comprising:      providing a beam of light;        homogenizing the light with an optical element; and        diffracting the light with a half tone diffraction pattern of dithered pixels patterned to distribute the light into two or more zones.     
     
     
       16. The method of  claim 15  wherein said half- tone diffraction pattern of dithered pixels comprises an array of pixels, each pixel of a clear or opaque type, said clear and opaque pixels for respectively passing and blocking incident light, wherein the number, size, and type of the pixels are chosen in accordance with:    ( a )  a wavelength of light used to illuminate the photomask, and      ( b )  a size and shape of features of the photomask, to generate a continuous illumination intensity pattern on the photomask.     
     
     
       17. The method of  claim 16  wherein a masking aperture used in the diffracting comprises an array of diffraction elements and each diffraction element comprises a dithered pattern of clear and/or opaque pixels. 
     
     
       18. The method of  claim 17  wherein each diffraction element comprises an n×n dithered matrix of pixels, an intensity of each element is defined by the number and type of pixels in its dithered matrix and wherein the pixels in each matrix are dithered to avoid artifacts. 
     
     
       19. The method of  claim 18  wherein the matrix of pixels is selected from the group consisting of  2 × 2 ,  4 × 4 ,  8 × 8 ,  16 × 16 ,  32 × 32  and  64 × 64  pixels. 
     
     
       20. The method of  claim 17  wherein an intensity of each pixel is defined by a recursion relationship where:          D   n     =                  4   ⁢     D     n   /   2         +       D   00   2     ⁢     U     n   /   2                   4   ⁢     D     n   /   2         +       D   01   2     ⁢     U     n   /   2                       4   ⁢     D     n   /   2         +       D   10   2     ⁢     U     n   /   2                   4   ⁢     D     n   /   2         +       D   11   2     ⁢     U     n   /   2                            
       
         where:  
         
           
             
               
                 U 
                 n 
               
               = 
               
                 
                    
                   
                     
                       
                         1 
                       
                       
                         1 
                       
                       
                         ⋯ 
                       
                       
                         1 
                       
                     
                     
                       
                         1 
                       
                       
                         
                             
                         
                       
                       
                         
                             
                         
                       
                       
                         
                             
                         
                       
                     
                     
                       
                         ⋮ 
                       
                       
                         
                             
                         
                       
                       
                         
                             
                         
                       
                       
                         
                             
                         
                       
                     
                     
                       
                         1 
                       
                       
                         
                             
                         
                       
                       
                         
                             
                         
                       
                       
                         
                             
                         
                       
                     
                   
                    
                 
                 . 
               
             
           
         
       
     
     
       21. The method of  claim 20  wherein the matrix of pixels comprises an  8 × 8  matrix and the relative intensity, D 8   , comprises:            D   8     =                0       32       8       40       2       34       10       42           48       16       56       24       50       18       58       26           12       44       4       36       14       46       6       38           60       28       52       20       62       30       54       22           3       35       11       43       1       33       9       41           51       19       59       27       49       17       57       25           15       47       7       39       13       45       5       37           63       31       55       23       61       29       53       21              .           
     
     
       22. The method of  claim 15  wherein the zones are arranged symmetrically about the center of a masking aperture used in the diffracting. 
     
     
       23. The method of  claim 15  wherein the zones are arranged symmetrically about the center of a masking aperture used in the diffracting. 
     
     
       24. The method of  claim 15  wherein each of the zones has a shape selected from the group consisting of circle, square, rectangle, ellipse, ring, circular ring, square ring and any combination thereof. 
     
     
       25. The method of  claim 24  wherein the selected shape is a stepped square. 
     
     
       26. The method of  claim 15  wherein each zone is shaped in an ellipse and the major axis of each ellipse is aligned at a  45  degree angle with respect to the center of a masking aperture used in the diffracting. 
     
     
       27. A method for controlling on- axis and off - axis illumination of a photomask comprising:      providing a beam of light;        homogenizing the light with an optical element; and        diffracting the light with a half tone diffraction pattern of dithered pixels patterned to distribute the light into one or more zones to form a pattern of illumination intensity in the one or more zones wherein each zone has a shape selected from the group consisting of ellipse, square ring, stepped square and any combination thereof.     
     
     
       28. The method of  claim 27  further comprising diffracting the light beam with a half tone diffraction pattern of dithered pixels patterned to distribute the light into one or more zones to form one or more additional patterns of light intensity selected from the group consisting of circle, square, rectangle and circular ring.