Method for improving an Optical Imaging Property of a Projection Objective of a Microlithographic Projection Exposure Apparatus

Abstract

A method is disclosed for improving an optical imaging property, for example spherical aberration or the focal length, of a projection objective of a microlithographic projection exposure apparatus. First, an immersion liquid is introduced into an interspace between a photosensitive surface and an end face of the projection objective. Then an imaging property of the projection objective is determined, for example using an interferometer or a CCD sensor arranged in an image plane of the projection objective. This imaging property is compared with a target imaging property. Finally, the temperature of the immersion liquid is changed until the determined imaging property is as close as possible to the target imaging property.

1 . A method of operating an immersion-type microlitho-graphic projection exposure apparatus, said method comprising the following steps: 
 a) applying an immersion liquid on a photosensitive surface;    b) heating or cooling the immersion liquid to a first target temperature;    c) forming an image of a reticle through a projection objective on the photosensitive surface; and    d) heating or cooling the immersion liquid to a second target temperature, which differs from the first target temperature.    
   
   
       2 . The method of  claim 1 , wherein the second target temperature is determined such that the immersion liquid at least partially compensates for a time-variant change of an optical imaging property of the projection objective.  
   
   
       3 . The method of  claim 2 , wherein the optical imaging property is a spherical aberration present in the projection objective.  
   
   
       4 . The method of  claim 2 , wherein the optical imaging property is the focal length of the projection objective.  
   
   
       5 . A method of operating an immersion-type microlitho-graphic projection exposure apparatus, said method comprising the following steps: 
 a) applying an immersion liquid on a photosensitive surface; and    b) varying a target temperature of the immersion liquid.    
   
   
       6 . A microlithographic projection exposure apparatus, comprising: 
 a) a projection objective which is configured for projecting a reticle onto a photosensitive surface;    b) a filling device for applying an immersion liquid onto the photosensitive surface;    c) a temperature control device which is configured to selectively set the temperature of the immersion liquid to different target temperatures.    
   
   
       7 . A microlithographic projection exposure apparatus, comprising: 
 a) a projection objective which is configured to project a reticle onto a photosensitive surface; and    b) an immersion liquid which contacts the photosensitive surface and has a time-variant temperature which is, at a given time, set during operation of the apparatus such that the immersion liquid reduces a time-variant aberration of the projection objective.    
   
   
       8 . The apparatus of  claim 7 , wherein the aberration is a spherical aberration.