Projection objective for microlithography

Abstract

A projection objective for imaging a pattern arranged in an object surface of the projection objective into an image surface of the projection objective with a demagnified imaging scale has a plurality of optical elements which are arranged along an optical axis of the projection objective and are configured in such a way that a defined image field curvature of the projection objective is set in such a way that an object surface that is curved convexly with respect to the projection objective can be imaged into a planar image surface. What can be achieved given a suitable setting of the object surface curvature is that a gravitation-dictated bending of a mask does not have a disturbing effect on the imaging quality.

What is claimed is: 
     
         1 . A projection objective for imaging a pattern arranged in an object surface of the projection objective into an image surface of the projection objective with a demagnified imaging scale, having:
 a plurality of optical elements which are arranged along an optical axis of the projection objective and are configured in such a way that a defined image field curvature of the projection objective is set in such a way that an object surface that is curved convexly with respect to the projection objective can be imaged into a planar image surface.   
     
     
         2 . The projection objective as claimed in  claim 1 , the object surface being curved in such a way that an effective object surface curvature in at least one direction perpendicular to the optical axis essentially corresponds to a surface curvature which results from a gravitation-dictated mask bending of the mask. 
     
     
         3 . The projection objective as claimed in  claim 1 , the projection objective being designed for use with a mask that can be moved in a scanning direction, and the object surface being curved in such a way that an object surface curvature which is scanner-integrated in the scanning direction corresponds to the surface curvature caused by gravitation-dictated bending of the mask. 
     
     
         4 . The projection objective as claimed in  claim 1 , wherein at least one optical element of the projection objective bears at one nonrotationally symmetrical surface. 
     
     
         5 . The projection objective as claimed in  claim 4 , the nonrotationally symmetrical surface being a toric surface designed for influencing the image field curvature. 
     
     
         6 . The projection objective as claimed in  claim 1 , the projection objective essentially being corrected with regard to all field-dependent image errors, with the exception of the image field curvature. 
     
     
         7 . The projection objective as claimed in  claim 1 , the projection objective essentially being corrected with regard to all image errors, with the exception of the image field curvature. 
     
     
         8 . The projection objective as claimed in  claim 1 , the projection objective having an image-side numerical aperture NA>0.8. 
     
     
         9 . The projection objective as claimed in  claim 1 , wherein |R p |≧0.1 DOF holds true, where |R p | is the magnitude of the Petzval sum and DOF is the depth of focus of the projection objective. 
     
     
         10 . A projection objective for imaging a pattern arranged in an object surface of the projection objective into an image surface of the projection objective with a demagnified imaging scale, having:
 a plurality of optical elements which are arranged along an optical axis of the projection objective and are configured in such a way that a defined image field curvature of the projection objective is set in such a way that an object surface that is curved convexly with respect tp the projection objective can be imaged into a planar image surface, the object surface being curved in such a way that an effective object surface curvature in at least one direction perpendicular to the optical axis essentially corresponds to a surface curvature which results from a gravitation-dictated mask bending of the mask, and |R p |≧0.1 DOF holding true, where |R p | is the magnitude of the Petzval sum and DOF is the depth of focus of the projection objective.