Objective in a microlithographic projection exposure apparatus

Abstract

An objective in a microlithographic projection exposure apparatus has a first optical element that has polarization dependent properties causing intensity fluctuations in an image plane of the objective. These fluctuations may be produced by a second optical element that is arranged downstream of the first optical element. A gray filter disposed in the beam path reduces the intensity fluctuations.

1 . An objective in a microlithographic projection exposure apparatus, comprising: 
 a) a first optical element that has polarization dependent properties causing intensity fluctuations in a plane that is arranged downstream, in a propagation direction of light, of the optical element, and b) a gray filter that reduces the intensity fluctuations.    
   
   
       2 . The objective of  claim 1 , in which the first optical element disturbs the polarization state of at least one ray of light impinging on the first optical element.  
   
   
       3 . The objective of  claim 2 , further comprising a second optical element that is arranged downstream of the first optical element in the propagation direction of the light and has polarization dependent properties such that the intensity of the light emerging from the second optical element depends on the polarization state of light impinging thereon.  
   
   
       4 . The objective of  claim 3 , in which the second optical element attenuates the intensity of light rays, whose polarization state is disturbed by the first optical element, to a larger amount than the intensity of light rays, whose polarization state is less disturbed by the first optical element.  
   
   
       5 . The objective of  claim 4 , in which the gray filter attenuates the intensity of light rays, whose polarization state is disturbed by the first optical element, to a smaller degree than the intensity of light rays, whose polarization state is less disturbed by the first optical element.  
   
   
       6 . The objective of  claim 1 , in which the gray filter is a transmissive optical element having a locally varying transmittance.  
   
   
       7 . The objective of  claim 1 , in which the gray filter is a reflective optical element having a locally varying reflectance.  
   
   
       8 . The objective of  claim 1 , in which the gray filter does not modify the phase distribution of the projection light passing through.  
   
   
       9 . The objective of  claim 1 , in which the gray filter is disposed on the first optical element.  
   
   
       10 . The objective of  claim 3 , in which the gray filter is disposed in the beam path between the first optical element and the second optical element.  
   
   
       11 . The objective of  claim 1 , in which the gray filter is disposed interchangeably in a filter holder.  
   
   
       12 . A microlithographic projection exposure apparatus, having an illumination system and a projection objective, comprising: 
 a) an optical element that has polarization dependent properties causing intensity fluctuations in a plane that is arranged downstream, in a light propagation direction, of the optical element, and    b) a gray filter that reduces the intensity fluctuations.