Illuminating apparatus

Abstract

An illuminating apparatus is disclosed which comprises a light source, an optical system for condensing light emitted from the light source and illuminating an object with the condensed light, and an optical member which absorbs light having wavelengths from 260 to 340 nm among the light emitted from the light source, wherein the optical member is made of glass or crystalline material to which metal is doped.

What is claimed is:  
     
         1 . An illuminating apparatus comprising: 
 a light source;    an optical system disposed in an optical path of a light emitted from said light source to condense the light emitted from the light source and illuminate an object with the condensed light; and    an optical member disposed in said optical path, and exhibiting an absorbing property for light having wavelength from 260 to 340 nm among the light emitted from the light source, to suppress formation of ammonium sulfate that would otherwise form in the absence of said optical member,    wherein said optical member is made of glass or crystalline material doped with an impurity that has said absorbing property.    
     
     
         2 . An apparatus according to  claim 1 , wherein said impurity comprises at least one of Na, Fe, Pb, Al, Rb and Cs.  
     
     
         3 . An illuminating apparatus according to  claim 1 , wherein said object is a mask on which a pattern is formed, and the illuminating apparatus is provided in an apparatus for transferring the pattern on the mask onto a photosensitive substrate.  
     
     
         4 . An illuminating apparatus comprising: 
 a light source;    an optical system for condensing light emitted from the light source and illuminating an object with condensed light; and    an optical member in which fluid absorbing light having wavelength from 260 to 340 nm among the light emitted from the light source is filled.    
     
     
         5 . An illuminating apparatus according to  claim 4 , wherein said fluid is one of gaseous rubidium, gaseous caesium and ozone gas.  
     
     
         6 . An illuminating apparatus according to  claim 4 , wherein said object is a mask on which a pattern is formed, and the illuminating apparatus is provided in an apparatus for transferring the pattern on the mask onto a photosensitive substrate.  
     
     
         7 . An apparatus according to  claim 1 , wherein said optical member is made of crystalline material doped as aforesaid, and said crystalline material is one of fluorite (CaF 2 ) and magnesium fluoride (MgF 2 ).  
     
     
         8 . An apparatus according to  claim 1 , wherein said light source comprises a discharge lamp and a light reflecting-condensing member to reflect and condense the light from the discharge lamp so as to direct the light to said object.  
     
     
         9 . An apparatus according to  claim 8 , wherein said optical system includes a wavelength selecting element which selects a light of a predetermined wavelength band among the light emitted from said light source, and wherein said optical member is disposed between said reflecting-condensing member and said wavelength selecting element.  
     
     
         10 . An exposure apparatus for transferring a pattern formed on a mask onto a substrate with a light emitted from a light source, comprising: 
 an illumination optical system disposed between said light source and said mask, and which illuminates said mask with the light emitted from the light source; and    an optical member disposed in said optical path, and exhibiting an absorbing property for light having wavelength from 260 to 340 nm among the light emitted from the light source, to suppress formation of ammonium sulfate that would otherwise form in the absence of said optical member,    wherein said optical member is made of glass or crystalline material doped with an impurity that has said absorbing property.    
     
     
         11 . An apparatus according to  claim 10 , wherein said light source comprises a discharge lamp and a light reflecting-condensing member to reflect and condense the light from the discharge lamp.  
     
     
         12 . An apparatus according to  claim 11 , wherein said illumination optical system includes a wavelength selecting element which selects a light of predetermined wavelength band among the light emitted from said light source, and wherein said optical member is disposed between said reflecting-condensing member and said wavelength selecting element.  
     
     
         13 . An apparatus according to  claim 12 , wherein said impurity is at least one of Na, Fe, Pb, Al, Rb and Cs.