Abstract:
A catadioptric projection optical system for use in photolithography used in manufacturing semiconductors having a quarter waveplate following a reticle and multiple aspheric surfaces and calcium fluoride lens elements. A quarter waveplate following the reticle eliminates asymmetry in reticle diffraction caused by polarized illumination. The use of additional aspheric surfaces reduces the number of lens elements and aids in reducing aberrations. Calcium fluoride elements are used in the lens group adjacent the wafer to help minimize compaction. In one embodiment, only calcium fluoride material is used. The present invention provides a projection optics system having a numerical aperture of 0.75 for use with wavelengths in the 248, 193, and 157 nanometer range. The object and image locations are separated by a predetermined distance, making possible retrofitting of older optical systems. The present invention is particularly suited for use in semiconductor manufacturing and has improved imaging with less aberrations, particularly at shorter wavelengths.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to projection optics used in semiconductor manufacturing equipment, and particularly to a catadioptric projection optic system having a high numerical aperture used with short wavelengths. 
     BACKGROUND OF THE INVENTION 
     In semiconductor manufacturing, photolithography techniques are often used. These photolithography techniques require the image of a reticle to be projected onto a wafer or photosensitive substrate. Relatively complicated projection optics are often used to project the image of the reticle onto the wafer or photosensitive substrate. The projection optics are required to provide a very high quality image of the reticle so that very small feature sizes on the reticle can be imaged accurately with very little aberrations. The projection optics often provide a magnification less than one resulting in a reduced image. Often, only a small portion of the image field is utilized that has the best imaging qualities. However, it is desirable to provide as large an image field as possible to enhance throughput and increase production of semiconductor devices. With the tremendous demand for decreased feature sizes in combination with higher throughput, new and improved projection optical systems are continually needed. Because of the ever decreasing feature sizes demanded by the semiconductor manufacturing industry, projection optics are needed that have higher numerical apertures and that are designed to operate at shorter wavelengths. Current optical designs cannot meet the demands of the manufacturers of semiconductors. For example, a prior optical system is disclosed in U.S. Pat. No. 4,953,960 entitled “Optical Reduction System” issuing Sep. 4, 1990 to Williamson. Therein disclosed is an optical reduction system operating in the wavelength range of 248 nanometers and having a numerical aperture of 0.45. Another projection optical system is disclosed in U.S. Pat. No. 5,089,913 entitled “High Resolution Reduction Catadioptric Relay Lens” issuing Feb. 18, 1992 to Singh et al, which is herein incorporated by reference. Therein disclosed is an optical system having a restricted spectral wavelength at 248 nanometers and having a numerical aperture of 0.6. Another projection optics system is disclosed in U.S. Pat. No. 5,537,260 entitled “Catadioptric Optical Reduction System With High Numerical Aperture” issuing Jul. 16, 1996 to Williamson, which is herein incorporated by reference. Therein disclosed is a projection optics system having a numerical aperture of 0.7 with different embodiments operating in wavelengths ranging from 360 to 193 nanometers. While these optical systems have operated adequately, there is a need for a projection optics used in semiconductor manufacturing to reproduce feature sizes substantially smaller than those of current systems. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a catadioptric optical system using multiple aspheric surfaces improving performance and reducing the number of lens elements. Calcium fluoride lens elements are used in a lens group closest to the wafer or photosensitive substrate. A zero-order quarter waveplate is positioned after the reticle and before a lens group having at least one aspheric surface prior to a beamsplitter. An aspheric concave mirror is placed adjacent the beamsplitter and adjacent a surface perpendicular to the lens group. Another lens group is positioned adjacent the beamsplitter opposing the aspheric concave mirror having a majority of the lens elements made of calcium fluoride and imaging the reticle at the wafer or photosensitive substrate. A relatively high numerical aperture of 0.75 is obtained, and in one embodiment a wavelength of 157 nanometers is utilized. 
     Accordingly, it is an object of the present invention to provide a projection optic system with a higher numerical aperture than current projection optic systems. 
     It is a further object of the present invention to decrease the lens elements of the projection optic system. 
     It is yet a further object of the present invention to prevent asymmetry in reticle diffraction caused by polarized illumination. 
     It is an advantage of the present invention that it results in reduced aberrations. 
     It is a further advantage of the present invention that reduced feature sizes can be imaged. 
     It is yet a further advantage of the present invention that it uses circular polarized electromagnetic radiation through the reticle. 
     It is a feature of the present invention that it uses calcium fluoride as a lens material in a lens group near the wafer. 
     It is another feature of the present invention that multiple aspheric lens elements are used. 
     It is yet another feature of the present invention that a zero-order quarter waveplate is positioned after the reticle. 
     These and other objects, advantages, and features will be readily apparent in view of the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically illustrates one embodiment of the present invention designed for use with 248 nanometer wavelength electromagnetic radiation. 
     FIG. 2 schematically illustrates a second embodiment of the present invention designed for use with 193 nanometer wavelength electromagnetic radiation and having two aspheric surfaces. 
     FIG. 3 schematically illustrates a third embodiment of the present invention designed for use with 193 nanometer wavelength electromagnetic radiation and having five aspheric surfaces. 
     FIG. 4 is a graph comparing the wavefront aberrations as a function of image height of the embodiment illustrated in FIG.  2  and the embodiment illustrated in FIG.  3 . 
     FIG. 5 schematically illustrates a fourth embodiment of the present invention designed for use with 157 nanometer wavelength electromagnetic radiation using calcium fluoride material. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a first embodiment of the present invention. A reticle  10  is positioned at an object location and a wafer or photosensitive surface or substrate  50  is positioned at an image location. The projection optics between the reticle  10  and wafer or photosensitive substrate  50  provides a magnification of less than one or a reduction ratio of approximately 4 to 1. The embodiment illustrated in FIG. 1 has a numerical aperture of 0.75, a 26×5 mm field at the wafer or photosensitive substrate  50  used with 248 nanometer wavelength electromagnetic radiation over a spectral bandwidth of 40 pecometers full-width-half maximum, FWHM. Following the reticle  10  is a first quarter waveplate  12 . Quarter waveplate  12  is preferably a zero-order quarter waveplate. This zero-order quarter waveplate  12  allows circularly polarized light to be used through the reticle avoiding diffraction asymmetry resulting from the relative orientation of reticle features and light polarization vector. Following the quarter waveplate  12  is a planar-convex lens  14 . Following the planar-convex lens  14  is a bi-concave lens  16 . Following lens  16  is a bi-convex lens  18 , a meniscus lens  20 , and a bi-convex lens  22 . Following this first lens group is a fold mirror  24 . Following the fold mirror  24  is a meniscus lens  26 . Following the meniscus lens  26  is an aspheric lens  28 . Aspheric lens  28  has a spherical concave surface and an aspherical convex surface. Following aspheric lens  28  is a bi-concave lens  30 . Following this lens group, after the fold mirror  24 , is a beamsplitter  31 . Beamsplitter  31  has a partially reflective surface  32 . Adjacent one surface of the beamsplitter  31  is a quarter waveplate  34  followed by a concave aspheric mirror  36 . The quarter waveplate  34  is preferably a zero-order quarter waveplate. Adjacent the opposing surface of the beamsplitter  31  is another quarter waveplate  38 , a bi-convex lens  40 , and a meniscus lens  42 . The quarter waveplate  38  is also preferably a zero-order quarter waveplate. The lens  40  and lens  42  are made of calcium fluoride. Following lens  42  is a meniscus lens  44  made of silica. Following meniscus lens  44  is a meniscus lens  46  and a meniscus lens  48 . Lenses  46  and  48  are made of calcium fluoride. Following lens  48  is a plate  49 . The third lens group between the beamsplitter  31  and the wafer or photosensitive substrate  50  have elements made form calcium fluoride, with the exception of lens  44 , the quarter waveplate  38 , and plate  49 . This embodiment uses calcium fluoride in a majority of the lens elements in this lens group after the beamsplitter  31 . This embodiment, designed for operation at 248 nanometer wavelengths, has the advantage of providing a high numerical aperture in a package that has a distance between the reticle  10  and wafer or photosensitive substrate  50  of a predetermined distance. This predetermined conjugate distance is advantageous in using this embodiment as a replacement for optical systems of earlier designs having the same predetermined conjugate distance. 
     In a preferred configuration the optical system, illustrated in FIG. 1, may be made according to the construction data of the following Tables 1 and 1A. 
     
       
         
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Element 
                 Radius of 
                 Radius of 
                 Thickness 
                   
               
               
                 Number 
                 Curvature(Front)mm 
                 Curvature(Back)mm 
                 mm 
                 Glass 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 Infinite 
                 71.0257 
                   
               
             
          
           
               
                 12 
                 Infinite 
                 Infinite 
                 6.0000 
                 Silica 
               
               
                 space 
                   
                   
                 6.0000 
               
               
                 14 
                 Infinite 
                 −1637.5100 CX  
                 17.8788 
                 Silica 
               
               
                 space 
                   
                   
                 7.6907 
               
               
                 16 
                 −507.9899 CC 
                  425.0110 CC 
                 23.6604 
                 Silica 
               
               
                 space 
                   
                   
                 23.6491 
               
               
                 18 
                  482.8744 CX 
                 −334.9535 CX 
                 32.3037 
                 Silica 
               
               
                 space 
                   
                   
                 12.0839 
               
               
                 20 
                 −210.1022 CC 
                 −342.7380 CX 
                 35.5779 
                 Silica 
               
               
                 space 
                   
                   
                 1.5001 
               
               
                 22 
                  254.8364 CX 
                 −1377.8565 CX  
                 38.5079 
                 Silica 
               
               
                 space 
                   
                   
                 83.5499 
               
             
          
           
               
                 24 
                 Infinite 
                 −64.0738 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 26 
                 −200.6185 CX 
                 −294.6182 CC 
                 −30.0000 
                 Silica 
               
               
                 space 
                   
                   
                 −33.6639 
               
               
                 28 
                 A(1) 
                  207.0105 CX 
                 −30.2428 
                 Silica 
               
               
                 space 
                   
                   
                 −1.9989 
               
               
                 30 
                 2223.6648 CC 
                 −166.4311 CC 
                 −27.4282 
                 Silica 
               
               
                 space 
                   
                   
                 −21.5924 
               
               
                 31 
                 Infinity 
                 Infinity 
                 −91.0000 
                 Silica 
               
             
          
           
               
                 32 
                 Infinity 
                   
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 31 
                 Infinity 
                 Infinity 
                 91.0000 
                 Silica 
               
               
                 space 
                   
                   
                 1.7156 
               
               
                 34 
                 Infinity 
                 Infinity 
                 6.000 
                 Silica 
               
               
                 space 
                   
                   
                 23.3211 
               
             
          
           
               
                 36 
                 A(2) 
                 −23.3211 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 34 
                 Infinity 
                 Infinity 
                 −6.000 
                 Silica 
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 31 
                 Infinity 
                 Infinity 
                 −91.0000 
                 Silica 
               
               
                 31 
                 Infinity 
                 Infinity 
                 −68.0000 
                 Silica 
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 38 
                 Infinity 
                 Infinity 
                 −4.4503 
                 Silica 
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 40 
                 −627.6194 CX 
                  211.4176 CX 
                 −21.5127 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 42 
                  −87.2228 CX 
                 −200.3029 CC 
                 −19.1435 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 44 
                  −91.9856 CX 
                  −59.4578 CC 
                 −27.1671 
                 Silica 
               
               
                 space 
                   
                   
                 −2.9551 
               
               
                 46 
                  −73.3403 CX 
                 −160.4650 CC 
                 −21.3988 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.4194 
               
               
                 48 
                 −126.8033 CX 
                 −368.0257 CC 
                 −5.2755 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.0000 
               
               
                 49 
                 Infinity 
                 Infinity 
                 −0.9000 
                 Silica 
               
             
          
           
               
                   
                 Image Distance = 
                 −2.3000 
                   
               
               
                 50 
                 Infinity 
               
               
                   
               
             
          
         
       
     
     The aspheric constants are provided according to the following equation and Table 1A 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1A 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           
                             
                               z 
                               = 
                               
                                 
                                   
                                     
                                       ( 
                                       curv 
                                       ) 
                                     
                                      
                                     
                                       y 
                                       2 
                                     
                                   
                                   
                                     1 
                                     + 
                                     
                                       
                                         ( 
                                         
                                           1 
                                           - 
                                           
                                             
                                               ( 
                                               
                                                 1 
                                                 + 
                                                 K 
                                               
                                               ) 
                                             
                                              
                                             
                                                 
                                             
                                              
                                             
                                               
                                                 ( 
                                                 curv 
                                                 ) 
                                               
                                               2 
                                             
                                              
                                             
                                               y 
                                               2 
                                             
                                           
                                         
                                         ) 
                                       
                                       
                                         1 
                                         / 
                                         2 
                                       
                                     
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     A 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     4 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     B 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     6 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     C 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     8 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     D 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     10 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     E 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     12 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     F 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     14 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     G 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     16 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     H 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     18 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     J 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     20 
                                   
                                 
                               
                             
                           
                         
                       
                     
                             
                     
                         
                     
                   
                 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Aspheric 
                 Curv 
                 K 
                 A 
                 B 
                 C 
                 D 
               
               
                   
               
               
                 A(1) 
                 0.00497390 
                 0.000000 
                 2.35640E−08 
                 −7.81654E−14 
                 −4.40789E−17 
                 2.12263E−20 
               
               
                 A(2) 
                 −0.00289239 
                 0.000000 
                 2.36370E−09 
                 1.65324E−13 
                 7.69607E−18 
                 9.96953E−23 
               
               
                   
               
               
                   
                   
                 E 
                 F 
                 G 
                 H 
                 J 
               
               
                   
               
               
                 A(1) 
                   
                 −6.05312E−24 
                 9.94327E−28 
                 −8.75026E−28 
                 3.18657E−36 
                 0.00000E+00 
               
               
                 A(2) 
                   
                 4.61249E−26 
                 −3.24220E−30 
                 2.06573E−34 
                 −4.86011E−40 
                 0.00000E+00 
               
               
                   
               
             
          
         
       
     
     FIG. 2 illustrates a second embodiment of a projection optics system having a numerical aperture of 0.75, a 26×5 mm field at the wafer, using 193 nanometer wavelength electromagnetic radiation over a spectral bandwidth of 25 picometers full-width-half maximum. Following reticle  10  is a zero-order quarter waveplate  112 , a planar convex lens  114 , a bi-concave lens  116 , a meniscus lens  118 , a meniscus lens  120 , and a bi-convex lens  122 . After this lens group a fold mirror  124  is positioned. Following fold mirror  124  is a meniscus lens  126 , an aspheric lens  128  and a meniscus lens  130 . The aspheric lens  128  has an aspheric concave surface and a spherical convex surface. Following this lens group, after fold mirror  124 , is a beamsplitter  131 . Beamsplitter  131  has a partially reflective surface  132 . Adjacent one side of the beamsplitter  131  is a second quarter waveplate  134 . The second quarter waveplate  134  is preferably a zero-order quarter waveplate. Following second quarter waveplate  134  is an aspheric concave mirror  136 . Adjacent an opposing surface of the beamsplitter  131  is a third quarter waveplate  138 . This third quarter waveplate  138  is also preferably a zero-order quarter waveplate. Following the third quarter waveplate  138  is a bi-convex lens  140 , a meniscus lens  142 , a meniscus lens  144 , a meniscus lens  146 , a meniscus lens  148 , and a plate  149 . Lenses  18 ,  19 ,  20 ,  21 , and  22  are made of calcium fluoride. Adjacent the plate  149  is wafer  50  positioned at the image location. In this embodiment, the use of calcium fluoride lenses or elements between the second quarter waveplate  138  and the plate  149  greatly minimizes compaction or radiation induced change in the refractive index. This lens group is particularly susceptible to compaction due to the relatively small beam sizes and high flux density. This embodiment utilizes two aspheric surfaces. The use of aspheric surfaces is advantageous in that the number of lens elements is reduced. 
     In a preferred configuration the optical system, illustrated in FIG. 2, may be made according to the construction data of the following Tables 2 and 2A. 
     
       
         
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Element 
                 Radius of 
                 Radius of 
                 Thickness 
                   
               
               
                 Number 
                 Curvature(Front)mm 
                 Curvature(Back)mm 
                 mm 
                 Glass 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  10 
                 Infinite 
                 71.0257 
                   
               
             
          
           
               
                 112 
                 Infinity 
                 Infinity 
                 6.0000 
                 Silica 
               
               
                 space 
                   
                   
                 6.0014 
               
               
                 114 
                 Infinity 
                 −1637.5100 CX 
                 17.8788 
                 Silica 
               
               
                 space 
                   
                   
                 9.1702 
               
               
                 116 
                 −433.0968 CC 
                 2598.0412 CC 
                 29.3027 
                 Silica 
               
               
                 space 
                   
                   
                 28.9382 
               
               
                 118 
                 −5578.3482 CC  
                 −382.9273 CX 
                 29.8579 
                 Silica 
               
               
                 space 
                   
                   
                 16.6017 
               
               
                 120 
                 −189.0676 CC 
                 −239.8621 CX 
                 18.0000 
                 Silica 
               
               
                 space 
                   
                   
                 1.5014 
               
               
                 122 
                  259.603 CX 
                 −2163.768 CX 
                 37.8249 
                 Silica 
               
               
                 space 
                   
                   
                 86.0743 
               
             
          
           
               
                 124 
                 Infinity 
                 −64.0738 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 126 
                 −200.8102 CX 
                 −363.2248 CC 
                 −28.2406 
                 Silica 
               
               
                 space 
                   
                   
                 −48.5160 
               
               
                 128 
                 A(1) 
                  215.5519 CX 
                 −30.2428 
                 Silica 
               
               
                 space 
                   
                   
                 −2.0011 
               
               
                 130 
                 −718.0642 CX 
                 −142.9228 CC 
                 −12.1060 
                 Silica 
               
               
                 space 
                   
                   
                 −23.8197 
               
               
                 131 
                 Infinity 
                 Infinity 
                 −91.0000 
                 Silica 
               
             
          
           
               
                 132 
                 Infinity 
                   
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 131 
                 Infinity 
                 Infinity 
                 91.0000 
                 Silica 
               
               
                 space 
                   
                   
                 1.7156 
               
               
                 134 
                 Infinity 
                 Infinity 
                 6.0000 
                 Silica 
               
               
                 space 
                   
                   
                 25.1737 
               
             
          
           
               
                 136 
                 A(2) 
                 −25.1737 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 134 
                 Infinity 
                 Infinity 
                 −6.0000 
                 Silica 
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 131 
                 Infinity 
                 Infinity 
                 −91.0000 
                 Silica 
               
               
                 131 
                 Infinity 
                 Infinity 
                 −68.000 
                 Silica 
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 138 
                 Infinity 
                 Infinity 
                 −4.4503 
                 Silica 
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 140 
                 −366.1837 CX 
                  259.6264 CX 
                 −22.6130 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 142 
                  −85.8999 CX 
                 −176.3075 CC 
                 −19.0232 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 144 
                  −86.4495 CX 
                  −64.6738 CC 
                 −15.3239 
                 CaF 2   
               
               
                 space 
                   
                   
                 −5.5180 
               
               
                 146 
                 −100.7188 CX 
                 −180.9651 CC 
                 −31.1363 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.2329 
               
               
                 148 
                 −138.0675 CX 
                 −502.9595 CC 
                 −5.2755 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.0000 
               
               
                 149 
                 Infinity 
                 Infinity 
                 −0.9000 
                 Silica 
               
             
          
           
               
                   
                 Image Distance = 
                 −2.3000 
                   
               
               
                  50 
                 Infinity 
               
               
                   
               
             
          
         
       
     
     The aspheric constants are provided according to the following equation and Table 2A 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2A 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           
                             
                               z 
                               = 
                               
                                 
                                   
                                     
                                       ( 
                                       curv 
                                       ) 
                                     
                                      
                                     
                                       y 
                                       2 
                                     
                                   
                                   
                                     1 
                                     + 
                                     
                                       
                                         ( 
                                         
                                           1 
                                           - 
                                           
                                             
                                               ( 
                                               
                                                 1 
                                                 + 
                                                 K 
                                               
                                               ) 
                                             
                                              
                                             
                                                 
                                             
                                              
                                             
                                               
                                                 ( 
                                                 curv 
                                                 ) 
                                               
                                               2 
                                             
                                              
                                             
                                               y 
                                               2 
                                             
                                           
                                         
                                         ) 
                                       
                                       
                                         1 
                                         / 
                                         2 
                                       
                                     
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     A 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     4 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     B 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     6 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     C 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     8 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     D 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     10 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     E 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     12 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     F 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     14 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     G 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     16 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     H 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     18 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     J 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     20 
                                   
                                 
                               
                             
                           
                         
                       
                     
                             
                     
                         
                     
                   
                 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Aspheric 
                 Curv 
                 K 
                 A 
                 B 
                 C 
                 D 
               
               
                   
               
               
                 A(1) 
                 0.00576125 
                 0.000000 
                 3.60293E−09 
                 −4.18487E−13 
                 −4.80164E−17 
                 1.86225E−20 
               
               
                 A(2) 
                 −0.00288476 
                 0.000000 
                 1.74269E−09 
                 1.17255E−13 
                 6.94898E−18 
                 −2.48358E−22 
               
               
                   
               
               
                   
                   
                 E 
                 F 
                 G 
                 H 
                 J 
               
               
                   
               
               
                 A(1) 
                   
                 −5.22691E−24 
                 8.72143E−28 
                 −7.89947E−32 
                 2.97093E−36 
                 0.00000E+00 
               
               
                 A(2) 
                   
                 7.10580E−26 
                 −5.86680E−30 
                 3.49595E−34 
                 −6.83625E−39 
                 0.00000E+00 
               
               
                   
               
             
          
         
       
     
     FIG. 3 illustrates a third embodiment of the present invention. This embodiment has a numerical aperture of 0.75, 26×5 mm field at the wafer, and is designed for use with 193 nanometer wavelength electromagnetic radiation over a spectral bandwidth of 25 picometers full-width-half maximum. This, the third embodiment, has five aspheric surfaces for reducing aberrations. Adjacent or following reticle  10  is a quarter waveplate  212 . Following quarter waveplate  212  is a planar convex lens  214 , and an aspheric lens  216 . Aspheric lens  216  has a concave surface and an aspheric surface. Following aspheric lens  216  is a bi-convex lens  218 , a meniscus lens  220 , and a bi-convex lens  222 . Following this first lens group is a fold mirror  224 . Following fold mirror  224  is a meniscus lens  226  and an aspheric lens  228 . Aspheric lens  228  has a concave aspheric surface and aspherical convex surface. Following aspheric lens  228  is a meniscus lens  230 . Following this lens group after the fold mirror  224  is a beamsplitter  231 . Beamsplitter  231  has a partially reflective surface  232 . Adjacent one side of the beamsplitter  231  is a second quarter waveplate  234 . Following the second quarter waveplate  234  is a concave aspheric mirror  236 . Adjacent an opposing surface of the beamsplitter  231  is a third quarter waveplate  238  followed by a bi-convex lens  240 , a meniscus lens  242 , an aspheric lens  244 . Aspheric lens  244  has a concave aspheric surface. Following aspheric lens  244  is an aspheric lens  246 . Aspheric lens  246  is placed adjacent meniscus lens  248 . Lenses  240 ,  242 ,  244 , and  246  and  248  are made of calcium fluoride. Adjacent lens  248  is a plate  249 . Wafer  50  is placed at the image plane following plate  249 . In this embodiment, the third embodiment, five aspheric surfaces are used. One in a lens group between the reticle  10  and the fold mirror  224 , aspheric lens  216 , a second in the lens group between the fold mirror  224  and the beamsplitter  231 , aspheric lens  228 . The third aspheric surface is located on the concave mirror  236 . A fourth aspheric surface is located on aspheric lens  244 , with a fifth aspheric surface located on lens  246 , both of which are in the lens group between the beamsplitter  231  and the wafer or photosensitive substrate  50 . The use of the five aspheric surfaces in this, the third embodiment of the present invention, greatly reduces aberrations. 
     In a preferred configuration the optical system, illustrated in FIG. 3, may be made according to the construction data of the following Tables 3 and 3A. 
     
       
         
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Element 
                 Radius of 
                 Radius of 
                 Thickness 
                   
               
               
                 Number 
                 Curvature(Front)mm 
                 Curvature(Back)mm 
                 mm 
                 Glass 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  10 
                 Infinite 
                 71.0257 
                   
               
             
          
           
               
                 212 
                 Infinite 
                 Infinite 
                 6.0000 
                 Silica 
               
               
                 space 
                   
                   
                 5.9995 
               
               
                 214 
                 Infinite 
                 −1637.5100 CX  
                 17.8788 
                 Silica 
               
               
                 space 
                   
                   
                 4.5575 
               
               
                 216 
                 −1237.3096 CC 
                 A(1) 
                 19.5803 
                 Silica 
               
               
                 space 
                   
                   
                 7.4171 
               
               
                 218 
                  364.2097 CX 
                 −674.5230 CX 
                 25.6054 
                 Silica 
               
               
                 space 
                   
                   
                 25.3077 
               
               
                 220 
                 −185.3015 CC 
                 −283.9553 CX 
                 30.8746 
                 Silica 
               
               
                 space 
                   
                   
                 1.5004 
               
               
                 222 
                  332.0965 CX 
                 −480.2185 CX 
                 42.1200 
                 Silica 
               
             
          
           
               
                 224 
                 Infinite 
                 −64.0738 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 226 
                 −197.3304 CX 
                 −362.9388 CC 
                 −30.0000 
                 Silica 
               
               
                 space 
                   
                   
                 −38.3129 
               
               
                 228 
                 A(2) 
                  303.6930 CX 
                 −30.2428 
                 Silica 
               
               
                 space 
                   
                   
                 −2.0000 
               
               
                 230 
                 −686.9764 CX 
                 −140.3749 CC 
                 −19.1575 
                 Silica 
               
               
                 space 
                   
                   
                 −25.2130 
               
               
                 231 
                 Infinite 
                 Infinite 
                 −91.000 
                 Silica 
               
             
          
           
               
                 232 
                 Infinite 
                   
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 231 
                 Infinity 
                 Infinite 
                 91.0000 
                 Silica 
               
               
                 space 
                   
                   
                 1.7156 
               
               
                 234 
                 Infinite 
                 Infinite 
                 6.0000 
                 Silica 
               
               
                 space 
                   
                   
                 23.4104 
               
             
          
           
               
                 236 
                 A(3) 
                 −23.4104 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 234 
                 Infinite 
                 Infinite 
                 −6.0000 
                 Silica 
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 231 
                 Infinite 
                 Infinite 
                 −91.0000 
                 Silica 
               
               
                 231 
                 Infinity 
                 Infinite 
                 −68.0000 
                 Silica 
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 238 
                 Infinite 
                 Infinite 
                 −4.4503 
                 Silica 
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 240 
                 −294.3870 CX 
                  285.2516 CX 
                 −22.3559 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 242 
                  −90.0227 CX 
                 −143.4682 CC 
                 −15.3841 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 244 
                  −86.3937 CX 
                 A(4) 
                 −16.8094 
                 CaF 2   
               
               
                 space 
                   
                   
                 −4.2386 
               
               
                 246 
                  −91.3982 CX 
                 A(5) 
                 −35.1077 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.2404 
               
               
                 248 
                 −193.8008 CX 
                 −584.4706 CC 
                 −5.2755 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.0000 
               
               
                 249 
                 Infinite 
                 Infinite 
                 −0.9000 
                 Silica 
               
             
          
           
               
                   
                 Image Distance = 
                 −2.3000 
                   
               
               
                  50 
                 Infinite 
               
               
                   
               
             
          
         
       
     
     The aspheric constants are provided according to the following equation and Table 3A 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3A 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           
                             
                               z 
                               = 
                               
                                 
                                   
                                     
                                       ( 
                                       curv 
                                       ) 
                                     
                                      
                                     
                                       y 
                                       2 
                                     
                                   
                                   
                                     1 
                                     + 
                                     
                                       
                                         ( 
                                         
                                           1 
                                           - 
                                           
                                             
                                               ( 
                                               
                                                 1 
                                                 + 
                                                 K 
                                               
                                               ) 
                                             
                                              
                                             
                                                 
                                             
                                              
                                             
                                               
                                                 ( 
                                                 curv 
                                                 ) 
                                               
                                               2 
                                             
                                              
                                             
                                               y 
                                               2 
                                             
                                           
                                         
                                         ) 
                                       
                                       
                                         1 
                                         / 
                                         2 
                                       
                                     
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     A 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     4 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     B 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     6 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     C 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     8 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     D 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     10 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     E 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     12 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     F 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     14 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     G 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     16 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     H 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     18 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     J 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     20 
                                   
                                 
                               
                             
                           
                         
                       
                     
                             
                     
                         
                     
                   
                 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Aspheric 
                 Curv 
                 K 
                 A 
                 B 
                 C 
                 D 
               
               
                   
               
               
                 A(1) 
                 0.00383949 
                 0.000000 
                 −5.74812E−09 
                 1.78952E−13 
                 3.56502E−18 
                 −4.29928E−22 
               
               
                 A(2) 
                 0.00408685 
                 0.000000 
                 3.46415E−09 
                 −2.46236E−13 
                 2.98339E−21 
                 3.46678E−21 
               
               
                 A(3) 
                 −0.00290152 
                 0.000000 
                 1.61839E−09 
                 1.11129E−13 
                 5.08685E−18 
                 −5.96371E−23 
               
               
                 A(4) 
                 −0.01476551 
                 0.000000 
                 6.79788E−08 
                 2.28037E−11 
                 4.76211E−15 
                 2.35042E−18 
               
               
                 A(5) 
                 −0.00407592 
                 0.000000 
                 −1.85475E−07 
                 −5.95105E−11 
                 2.46369E−14 
                 −3.41676E−17 
               
               
                   
               
               
                   
                   
                 E 
                 F 
                 G 
                 H 
                 J 
               
               
                   
               
               
                 A(1) 
                   
                 1.07476E−25 
                 −7.13558E−30 
                 0.00000E+00 
                 0.00000E+00 
                 0.00000E+00 
               
               
                 A(2) 
                   
                 −1.14760E−24 
                 1.97684E−28 
                 −1.74440E−32 
                 6.27538E−37 
                 0.00000E+00 
               
               
                 A(3) 
                   
                 5.45877E−23 
                 −5.30479E−30 
                 3.27535E−34 
                 −5.74203E−39 
                 0.00000E+00 
               
               
                 A(4) 
                   
                 −3.36512E−22 
                 2.71804E−25 
                 0.00000E+00 
                 0.00000E+00 
                 0.00000E+00 
               
               
                 A(5) 
                   
                 2.68515E−25 
                 1.36619E−30 
                 0.00000E+00 
                 0.00000E+00 
                 0.00000E+00 
               
               
                   
               
             
          
         
       
     
     FIG. 4 graphically illustrates wavefront aberrations as a function of image height for the embodiments of the present invention illustrated in FIG.  2  and FIG.  3 . Waveform or line  52  illustrates the aberrations as a function of image height for the embodiment illustrated in FIG. 2 having two aspheric surfaces. The waveform or dashed line  54  illustrates the wavefront aberrations as a function of image height for the embodiment having five aspheric surfaces illustrated in FIG.  3 . As can readily be appreciated by FIG. 4, the wavefront aberrations are significantly reduced in the embodiment having five aspheric surfaces. 
     FIG. 5 illustrates a fourth embodiment of the present invention having a numerical aperture of 0.75, 26×5 mm field at the wafer, and designed for use with 157 nanometer wavelength electromagnetic radiation over a spectral bandwidth of 1.5 picometers fill-width-half maximum. This embodiment uses two aspheric surfaces and is made entirely of calcium fluoride. Following reticle  10  is a quarter waveplate  312 , a planar convex lens  314 , a bi-concave lens  316 , a bi-convex lens  318 , a meniscus lens  320 , and a bi-convex lens  322 . Following this lens group is a fold mirror  324 . Following fold mirror  324  is a meniscus lens  326 , an aspheric lens  328 , and a meniscus lens  330 . Aspheric lens  328  has a concave aspheric surface. Following this lens group after the fold mirror  324  is a beamsplitter  331 . Beamsplitter  331  has a partially reflective surface  332 . Adjacent one side of the beamsplitter  331  is a second quarter waveplate  334 . Following the second quarter waveplate  334  is an aspherical concave mirror  336 . Adjacent a side of the beamsplitter  331  opposing the second quarter waveplate  334  is positioned a third quarter waveplate  338 . Following the quarter waveplate  338  is a bi-convex lens  340 , a meniscus lens  342 , a meniscus lens  344 , a meniscus lens  346 , and a meniscus lens  348 . Adjacent meniscus lens  348  is positioned a plate  349 . Plate  349  is adjacent the image plane where a wafer or photosensitive substrate  50  is positioned. 
     A preferred configuration of the optical system, illustrated in FIG. 5, may be made according to the construction data in the following Tables 4 and 4A. 
     
       
         
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Element 
                 Radius of 
                 Radius of 
                 Thickness 
                   
               
               
                 Number 
                 Curvature(Front)mm 
                 Curvature(Back)mm 
                 mm 
                 Glass 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  10 
                 Infinite 
                 71.0257 
                   
               
             
          
           
               
                 312 
                 Infinite 
                 Infinite 
                 6.0000 
                 CaF 2   
               
               
                 space 
                   
                   
                 5.9971 
               
               
                 314 
                 Infinite 
                 −1637.5100 CX  
                 17.8788 
                 CaF 2   
               
               
                 space 
                   
                   
                 6.8555 
               
               
                 316 
                 −601.0743 CC 
                  337.2385 CC 
                 19.3530 
                 CaF 2   
               
               
                 space 
                   
                   
                 39.1414 
               
               
                 318 
                  372.9672 CX 
                 −444.4615 CX 
                 35.0514 
                 CaF 2   
               
               
                 space 
                   
                   
                 17.5760 
               
               
                 320 
                 −238.7418 CC 
                 −374.7892 CX 
                 33.5080 
                 CaF 2   
               
               
                 space 
                   
                   
                 1.5026 
               
               
                 322 
                  271.2372 CX 
                 −2141.5952 
                 41.9745 
                 CaF 2   
               
               
                 space 
                   
                   
                 85.7471 
               
             
          
           
               
                 324 
                 Infinite 
                 −64.0738 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 326 
                 −218.7966 CX 
                 −378.3046 CC 
                 −30.0000 
                 CaF 2   
               
               
                 space 
                   
                   
                 −41.2869 
               
               
                 328 
                 A(1) 
                  331.4015 CX 
                 −30.2428 
                 CaF 2   
               
               
                 space 
                   
                   
                 −2.0021 
               
               
                 330 
                 −473.0920 CX 
                 −138.9426 CC 
                 −15.0066 
                 CaF 2   
               
               
                 space 
                   
                   
                 −25.4542 
               
               
                 331 
                 Infinite 
                 Infinite 
                 −91.9338 
                 CaF 2   
               
             
          
           
               
                 332 
                 Infinite 
                   
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 331 
                 Infinite 
                 Infinite 
                 91.9338 
                 CaF 2   
               
               
                 space 
                   
                   
                 1.7156 
               
               
                 334 
                 Infinite 
                 Infinite 
                 6.0000 
                 CaF 2   
               
               
                 space 
                   
                   
                 23.9891 
               
             
          
           
               
                 326 
                 A(2) 
                 −23.2891 
                 Reflec- 
               
               
                   
                   
                   
                 tor 
               
             
          
           
               
                 334 
                 Infinite 
                 Infinite 
                 −6.0000 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 331 
                 Infinite 
                 Infinite 
                 −91.9336 
                 CaF 2   
               
               
                 331 
                 Infinite 
                 Infinite 
                 −68.0000 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.7156 
               
               
                 328 
                 Infinite 
                 Infinite 
                 −4.4503 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 340 
                 −379.1353 CX 
                  304.9678 CX 
                 −21.8077 
                 CaF 2   
               
               
                 space 
                   
                   
                 −0.5000 
               
               
                 342 
                  −94.2814 CX 
                 −162.6972 CC 
                 −17.3319 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.0800 
               
               
                 344 
                 −115.8596 CX 
                  −73.3964 CC 
                 −20.5225 
                 CaF 2   
               
               
                 space 
                   
                   
                 −3.8075 
               
               
                 346 
                  −92.2350 CX 
                 −218.2297 CC 
                 −42.4471 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.1466 
               
               
                 348 
                 −155.2317 CX 
                 −656.3405 CC 
                 −5.2755 
                 CaF 2   
               
               
                 space 
                   
                   
                 −1.0000 
               
               
                 349 
                 Infinite 
                 Infinite 
                 −0.9000 
                 CaF 2   
               
             
          
           
               
                   
                 Image Distance = 
                 −2.3000 
                   
               
               
                  50 
                 Infinite 
               
               
                   
               
             
          
         
       
     
     The aspheric constants are provided according to the following equation and Table 4A 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 4A 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           
                             
                               z 
                               = 
                               
                                 
                                   
                                     
                                       ( 
                                       curv 
                                       ) 
                                     
                                      
                                     
                                       y 
                                       2 
                                     
                                   
                                   
                                     1 
                                     + 
                                     
                                       
                                         ( 
                                         
                                           1 
                                           - 
                                           
                                             
                                               ( 
                                               
                                                 1 
                                                 + 
                                                 K 
                                               
                                               ) 
                                             
                                              
                                             
                                                 
                                             
                                              
                                             
                                               
                                                 ( 
                                                 curv 
                                                 ) 
                                               
                                               2 
                                             
                                              
                                             
                                               y 
                                               2 
                                             
                                           
                                         
                                         ) 
                                       
                                       
                                         1 
                                         / 
                                         2 
                                       
                                     
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     A 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     4 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     B 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     6 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     C 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     8 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     D 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     10 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     E 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     12 
                                   
                                 
                                 + 
                                 
                                     
                                 
                                  
                                 
                                   
                                     ( 
                                     F 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     14 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     G 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     16 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     H 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     18 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     J 
                                     ) 
                                   
                                    
                                   
                                     y 
                                     20 
                                   
                                 
                               
                             
                           
                         
                       
                     
                             
                     
                         
                     
                   
                 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Aspheric 
                 Curv 
                 K 
                 A 
                 B 
                 C 
                 D 
               
               
                   
               
               
                 A(1) 
                 0.00475685 
                 0.000000 
                 8.25386E−09 
                 −1.36412E−13 
                 −4.41072E−17 
                 2.29567E−20 
               
               
                 A(2) 
                 −0.00272498 
                 0.000000 
                 1.82601E−09 
                 9.56998E−14 
                 6.16098E−18 
                 −4.25832E−22 
               
               
                   
               
               
                   
                   
                 E 
                 F 
                 G 
                 H 
                 J 
               
               
                   
               
               
                 A(1) 
                   
                 −6.72654E−24 
                 1.13058E−27 
                 −1.00992E−31 
                 3.72128E−36 
                 0.00000E+00 
               
               
                 A(2) 
                   
                 8.51395E−26 
                 −7.80032E−30 
                 4.75429E−34 
                 −1.14164E−38 
                 0.00000E+00 
               
               
                   
               
             
          
         
       
     
     Accordingly, all of the embodiments of the present invention, from a long conjugant end at reticle  10  to a short conjugate end at wafer or photosensitive substrate  50 , provide a quarter waveplate following the reticle and a first lens group positioned between the quarter waveplate and a first fold mirror, and a second lens group between the fold mirror and a beamsplitter. In each embodiment, the lens group before the fold mirrors  24 ,  124 ,  224 , and  324  may be considered a first lens group and the lens group between the fold mirrors  24 ,  124 ,  224 , and  324  and the beamsplitters  31 ,  131 ,  231 , and  331  may be considered a second lens group. Alternatively, this first and second lens group may be considered a single lens group. The partially reflective surface on the beamsplitter reflects electromagnetic radiation to a second quarter waveplate and an aspheric concave mirror which reflects electromagnetic radiation back through the beamsplitter and through the partially reflective surface to a third quarter waveplate and through a third lens group to the photosensitive substrate or wafer  50 . All of the embodiments provide for the quarter waveplate following the reticle and have a lens with an aspheric surface between the fold mirror and the beamsplitter cube, and have lens elements between the beamsplitter cube and the photosensitive substrate, a majority of which are made of calcium fluoride. Accordingly, the present invention provides a projection optical system having a relatively high numerical aperture with improved imaging characteristics that forms well at wavelengths as short as 157 nanometers. Therefore, the present invention advances the optical arts and greatly facilitates the manufacture of semiconductor devices. 
     Although the preferred embodiments have been illustrated and described, it should be appreciated by those skilled in the art that various modifications may be made without departing from the spirit and scope of this invention.