Optical element unit

Abstract

An optical element unit is provided comprising an optical element group for projecting light along an optical axis of the optical element group and a housing having an inner housing part partly defining a first space and a light passageway between the inner housing part and a second space. The inner housing part receives the optical element group. The optical element group comprises an ultimate optical element located in the region of the light passageway. A load-relieving device is provided adjacent to the ultimate optical element, the load relieving device partly defining the first space and the second space and at least partly relieving the ultimate optical element from loads resulting from pressure differences between the first space.

1 . (canceled) 
     
     
         2 . An optical element unit, comprising:
 an optical element group configured to project exposure light along an optical axis of the optical element group;   a support structure comprising an inner part partly defining a first space and an exposure light passageway, the inner part receiving the optical element group; and   a cover device,   wherein:
 the optical element group comprises an ultimate optical element located in a region of the exposure light passageway; 
 the cover device extends between the support structure and a surface of the ultimate optical element so that a narrow open gap is formed between the surface of the ultimate optical element and the cover device; 
 the narrow open gap is configured to pass fluids during operation of the optical element unit; and 
 the cover device is configured so that a further exposure light passageway is defined for the exposure light passing the surface of the ultimate optical element. 
   
     
     
         3 . The optical element unit of  claim 2 , wherein the narrow open gap is configured so that, during operation of the optical element unit, a fluid passes through the narrow open gap between a first space comprising the further exposure light passageway and a second space defined between the cover device and the support structure. 
     
     
         4 . The optical element unit of  claim 2 , wherein the cover device comprises a heat exchanging element connectable to a heat exchanging device to provide at least one member selected from the group consisting of heating of the cover device and cooling of the cover device. 
     
     
         5 . The optical element unit of  claim 4 , wherein the heat exchanging element is selected from the group consisting of a heat exchange medium line, a heat conducting element, an element configured to enhance heat transfer performance, a heat transfer rib, and combinations thereof. 
     
     
         6 . The optical element unit of  claim 4 , wherein the heat exchanging element is located on a side of the cover device facing the ultimate optical element. 
     
     
         7 . The optical element unit of  claim 4 , wherein the heat exchanging element is located on a side of the cover device facing away from the ultimate optical element. 
     
     
         8 . The optical element unit of  claim 4 , wherein the heat exchanging element is integrated within a tempering device. 
     
     
         9 . The optical element unit of  claim 4 , wherein the heat exchanging element comprises a heat exchange medium line configured to be fed, by the heat exchanging device, with a member selected from the group consisting of a heating medium and a cooling medium. 
     
     
         10 . The optical element unit of  claim 4 , further comprising a tempering device which comprises a plurality of circularly arranged heat exchange medium lines. 
     
     
         11 . The optical element unit of  claim 2 , wherein an inner circumference of the cover device defines an aperture defining the further exposure light passageway. 
     
     
         12 . The optical element unit of  claim 2 , wherein the cover device has an inner circumference and an outer circumference, and the cover device is connected to the support structure at the outer circumference. 
     
     
         13 . The optical element unit of  claim 2 , wherein:
 the surface of the ultimate optical element comprises an optical surface having a surface region which is optically used when using the optical element group to project light along the optical axis; and   the cover device reaches close to the optically used surface region.   
     
     
         14 . The optical element unit of  claim 13 , wherein the optically used surface region corresponds to at least 80% of the further exposure light passageway. 
     
     
         15 . The optical element unit of  claim 11 , wherein a dimension of the further exposure light passageway is substantially identical to a dimension of the optically used surface region. 
     
     
         16 . The optical element unit of  claim 2 , wherein the cover device comprises a thin walled cover. 
     
     
         17 . The optical element unit of  claim 2 , wherein the cover device comprises a thin wall segment extending between the support structure and the ultimate optical element in a circumferential direction of the ultimate optical element. 
     
     
         18 . The optical element unit of  claim 2 , wherein the cover device comprises at least one layer, each layer comprising a material selected from the group consisting of a metal material, a sheet metal material, a composite material, a plastics material, a ceramic material and a glass material. 
     
     
         19 . The optical element unit of  claim 2 , wherein the cover device does not directly contact the ultimate optical element. 
     
     
         20 . The optical element unit of  claim 2 , further comprising an adjustment device configured to adjust a distance between the ultimate optical element and the cover device to adjust a gap width of the narrow open gap. 
     
     
         21 . The optical element unit of  claim 2 , wherein:
 the optical element group comprises a penultimate optical element located adjacent to the ultimate optical element; and   the surface of the ultimate optical element is one of facing towards the penultimate optical element and facing away from the penultimate optical element.   
     
     
         22 . The optical element unit of  claim 2 , further comprising a holding device, wherein the ultimate optical element is supported by the support structure via the holding device, and the cover device is a component separate from the holding device. 
     
     
         23 . The optical element unit of  claim 2 , further comprising a holding device, wherein the ultimate optical element is supported by the support structure via the holding device, and the holding device defines at least one duct configured to pass fluids during operation of the optical element unit between one of the first and second space and a space confined by the cover device and the ultimate optical element. 
     
     
         24 . The optical element unit of  claim 2 , wherein the cover device is supported by one of the support structure and a heat exchanger shell forming part of the heat exchanging device and surrounding at least part of the support structure. 
     
     
         25 . An apparatus having a light path, the apparatus comprising:
 an optical element unit according to  claim 2 ,   wherein the optical element unit is located within the light path, and the apparatus is an optical exposure apparatus.