Objective with crystal lenses

Abstract

Objective, in particular a projection objective for a microlithography projection-exposure installation, with at least one fluoride crystal lens. A reduction in the detrimental influence of birefringence is achieved if this lens is a (100)-lens with a lens axis which is approximately perpendicular to the {100} crystallographic planes or to the crystallographic planes equivalent thereto of the fluoride crystal. In the case of objectives with at least two fluoride crystal lenses, it is favorable if the fluoride crystal lenses are arranged such that they are rotated with respect to one another. The lens axes of the fluoride crystal lenses may in this case point not only in the <100> crystallographic direction but also in the <111> crystallographic direction or in the <110> crystallographic direction. A further reduction in the detrimental influence of birefringence is achieved by the simultaneous use of groups with (100)-lenses rotated with respect to one another and groups with (111)-lenses or (110)-lenses rotated with respect to one another. A further reduction in the detrimental influence of birefringence is obtained by covering an optical element with a compensation coating.

1 - 30 . (canceled)  
     
     
         31 . An objective comprising: 
 a plurality of optical elements, each of the plurality of optical elements having optical surfaces,    wherein during use an image point in an image plane is impinged by a bundle of rays with rays which respectively have an optical path difference ΔOPL for two mutually orthogonal states of linear polarization, at least one optical surface is covered with a compensation coating, the compensation coating is designed in such a way that the optical path differences ΔOPL of the bundle of rays have significantly reduced values in comparison with an objective without a compensation coating, and the compensation coating comprises multiple layers.    
     
     
         32 . The objective as claimed in  claim 31 , wherein the optical element with the compensation coating has an element axis, and the compensation coating has an effective birefringence distribution, the effective birefringence values of which depend on azimuth angles α F  with respect to a reference direction perpendicular to the element axis and on aperture angles θ F  with respect to the element axis.  
     
     
         33 . The objective as claimed in  claim 32 , wherein the effective birefringence distribution of the compensation coating for the aperture angle θ F =0° is approximately zero.  
     
     
         34 . The objective as claimed in  claim 32 , wherein the effective birefringence distribution of the compensation coating primarily depends on the aperture angle θ F.    
     
     
         35 . The objective as claimed in  claim 32 , wherein the optical element with the compensation coating is interchangeable.  
     
     
         36 . The objective as claimed in  claim 31 , wherein at least two optical elements comprise fluoride crystal lenses are lenses or lens parts each of the lenses or the lens parts has a lens axis, and the lenses or the lens parts are arranged such that they are rotated with respect to one another about the lens axes in such a way that the distribution of the optical path differences ΔOPL (α R , θ R ) of the bundle of rays as a function of the azimuth angle α R  and of the aperture angle θ R  has significantly reduced values in comparison with lenses or lens parts of which the lens axes point in the same principal crystallographic direction and which are not arranged such that they are rotated with respect to one another about the lens axes.  
     
     
         37 . The objective as claimed in  claim 36 , wherein the optical path differences ΔOPL as a function of the azimuth angle α R  for a given aperture angle θ φ  vary less than 30%.  
     
     
         38 . The objective as claimed in  claim 36 , wherein the lenses or lens parts respectively have a birefringence distribution Δn (α L ,θ L ), the birefringence values Δn of which depend on azimuth angles α L  with respect to a reference direction perpendicular to the lens axis and on aperture angles θ R  with respect to the lens axis, the birefringence distribution Δn (α L ,θ L ) having a k-fold azimuthal symmetry, angles of rotation γ being defined between the reference directions of the individual lenses or lens parts, a number of n lenses or n lens parts forming a group within which the lens axes point in the same principal crystallographic direction or a principal crystallographic direction equivalent thereto and within which the birefringence distributions Δn (α L ,θ L ) with respect to the reference directions have the same azimuthal profile, the following applying for the angle of rotation .gamma. between respective pairs of lenses or lens parts of a group:  
       
         
           
             
               
                 γ 
                 = 
                 
                   
                     
                       360 
                       ⁢ 
                       ° 
                     
                     
                       k 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       n 
                     
                   
                   + 
                   
                     
                       m 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           360 
                           ⁢ 
                           ° 
                         
                         k 
                       
                     
                     ± 
                     
                       10 
                       ⁢ 
                       ° 
                     
                   
                 
               
               , 
             
           
         
       
       m being an integral number.  
     
     
         39 . The objective as claimed in  claim 36 , wherein the optical element with the compensation coating is one of the of fluoride crystal lenses or lens parts, and the element axis is the lens axis of the one of the fluoride crystal lenses or lens parts.  
     
     
         40 . The objective as claimed in  claim 31 , wherein a plurality of optical element are covered with compensation coatings.  
     
     
         41 . The objective as claimed in  claim 31 , wherein the objective has a numerical aperture on the image side that is greater than 0.7.  
     
     
         42 . The objective as claimed in  claim 31 , wherein the objective is designed for wavelengths less than 200 nm.  
     
     
         43 . The objective as claimed in  claim 31 , wherein the objective is designed for wavelengths less than 160 nm.  
     
     
         44 . The objective as claimed in  claim 31 , wherein the objective is a refractive objective.  
     
     
         45 . The objective as claimed in  claim 31 , wherein the objective is a catadioptric objective with lenses and at least one mirror.  
     
     
         46 . The objective as claimed in  claim 31 , wherein all the lenses are of calcium fluoride.  
     
     
         47 . A microlithography projection-exposure installation, comprising: 
 an illuminating system,    an objective as claimed in  claim 31 , which during use can project an image of a structure-bearing mask onto a light-sensitive substrate.    
     
     
         48 . A method for producing semiconductor components that comprises using a microlithography projection-exposure installation as claimed in  claim 47 .  
     
     
         49 - 81 . (canceled)  
     
     
         82 . The objective as claimed in  claim 31 , wherein at least one of the multiple layers comprises a fluoride.  
     
     
         83 . The objective as claimed in  claim 82 , wherein the fluoride is selected from the group consisting of magnesium fluoride and lanthanum fluoride.  
     
     
         84 . The objective as claimed in  claim 31 , wherein at least two of the multiple layers comprise different materials.  
     
     
         85 . The objective as claimed in  claim 31 , wherein the multiple layers comprise alternating layers of material.  
     
     
         86 . An optical system, comprising: 
 a plurality of optical elements; and    a coating comprising multiple layers,    wherein: 
 the coating is supported by one of the plurality of optical elements;  
 during use of the optical system the coating at least partially compensates for intrinsic birefringence of at least one of the plurality of optical elements; and  
 the optical system is a microlithography projection objective.  
   
     
     
         87 . The optical system of  claim 86 , wherein the coating comprises a fluoride.  
     
     
         88 . The optical system of  claim 87 , wherein the fluoride is selected from the group consisting of magnesium fluoride and lanthanum fluoride.  
     
     
         89 . The optical system of  claim 86 , wherein at least two of the multiple layers comprise different materials.  
     
     
         90 . The optical system of  claim 86 , wherein the one of the plurality of optical elements is a lens.  
     
     
         91 . The optical system of  claim 90 , wherein the lens is a calcium fluoride lens.  
     
     
         92 . The optical system of  claim 86 , wherein the material from which the one of the plurality of optical elements is formed comprises calcium fluoride.  
     
     
         93 . The optical system of  claim 86 , wherein the multiple layers comprise alternating layers of material.  
     
     
         94 . An optical system, comprising: 
 a plurality of optical elements; and    a coating,    wherein: 
 the coating is supported by one of the plurality of optical elements;  
 the coating comprises at least one material different from the material from which the one of the plurality of optical elements is formed;  
 during use of the optical system the coating at least partially compensates for intrinsic birefringence of at least one of the plurality of optical elements; and  
 the optical system is a microlithography projection objective.  
   
     
     
         95 . The optical system of  claim 94 , wherein the coating comprises a fluoride.  
     
     
         96 . The optical system of  claim 95 , wherein the fluoride is selected from the group consisting of magnesium fluoride and lanthanum fluoride.  
     
     
         97 . The optical system of  claim 94 , wherein the coating comprises multiple layers.  
     
     
         98 . The optical system of  claim 94 , wherein the one of the plurality of optical elements is a lens.  
     
     
         99 . The optical system of  claim 98 , wherein the lens is a calcium fluoride lens.  
     
     
         100 . The optical system of  claim 94 , wherein the material from which the one of the plurality of optical elements is formed comprises calcium fluoride.  
     
     
         101 . The optical system of  claim 86 , wherein the multiple layers comprise alternating layers of material.