Exposure apparatus including silica glass for photolithography

Abstract

A silica glass has a structure determination temperature of 1200 K or lower and an OH group concentration of at least 1,000 ppm. The silica glass is used for photolithography together with light in a wavelength region of 400 nm or shorter.

What is claimed is:  
     
         1 . A silica glass for photolithography used together with light in a wavelength region of 400 nm or shorter, said silica glass having a structure determination temperature of 1,200 K or lower and an OH group concentration of at least 1,000 ppm.  
     
     
         2 . A silica glass according to  claim 1 , wherein said silica glass has a fluorine concentration of at least 300 ppm.  
     
     
         3 . A silica glass according to  claim 1 , wherein said silica glass has a scattering loss amount of 0.2%/cm or less with respect to ArF excimer laser.  
     
     
         4 . A silica glass according to  claim 1 , wherein said silica glass has a scattering loss characteristic which is of center symmetry.  
     
     
         5 . A silica glass according to  claim 1 , wherein said silica glass has an internal absorptivity of 0.2%/cm or less at a thickness of 10 mm with respect to ArF excimer laser.  
     
     
         6 . A silica glass according to  claim 1 , wherein said silica glass has an internal transmittance of 99.6% or more at a thickness of 10 mm with respect to ArF excimer laser.  
     
     
         7 . A silica glass according to  claim 1 , wherein, after being irradiated with 1×10 6  pulses of KrF excimer laser at an average one-pulse energy density of 400 mJ/cm 2 , said silica glass exhibits an internal transmittance exceeding 99.5% at a thickness of 10 mm with respect to light having a wavelength of 248 nm.  
     
     
         8 . A silica glass according to  claim 1 , wherein, after being irradiated with 1×10 6  pulses of ArF excimer laser at an average one-pulse energy density of 100 mJ/cm 2 , said silica glass exhibits an internal transmittance exceeding 99.5% at a thickness of 10 mm with respect to light having a wavelength of 193 nm.  
     
     
         9 . A silica glass according to  claim 1 , wherein said silica glass has a birefringence amount of 2 nm/cm or less.  
     
     
         10 . A silica glass according to  claim 1 , wherein said silica glass has a polarization characteristic and a birefringence characteristic which are of center symmetry.  
     
     
         11 . An optical member used together with light in a wavelength region of 400 nm or shorter, said optical member comprising a silica glass according to  claim 1 .  
     
     
         12 . An optical member according to  claim 11 , wherein said silica glass has a fluorine concentration of at least 300 ppm.  
     
     
         13 . An exposure apparatus using light in a wavelength region of 400 nm or shorter as exposure light, which comprises: 
 a stage allowing a photosensitive substrate to be held on a main surface thereof;    an illumination optical system for emitting the exposure light of a predetermined wavelength and transferring a predetermined pattern of a mask onto said substrate;    a projection optical system provided between a surface on which the mask is disposed and said substrate, for projecting an image of the pattern of said mask onto said substrate; and    an optical member comprising the silica glass according to  claim 1 .    
     
     
         14 . An exposure apparatus according to  claim 13 , wherein said silica glass has a fluorine concentration of at least 300 ppm.  
     
     
         15 . An exposure apparatus according to  claim 13 , wherein said illumination optical system comprises said optical member.  
     
     
         16 . An exposure apparatus according to  claim 13 , wherein said projection optical system comprises said optical member.  
     
     
         17 . A method for producing a silica glass having a structure determination temperature of 1,200 K or lower and an OH group concentration of at least 1,000 ppm, said method comprising the steps of: 
 heating a silica glass ingot having an OH group concentration of 1,000 ppm or more to a temperature of 1,200 to 1,350 K;    maintaining said ingot at said temperature for a predetermined period of time; and then    cooling said ingot to a temperature of 1,000 K or lower at a temperature-lowering rate of 50 K/hr or less to anneal said ingot.    
     
     
         18 . A method according to  claim 17 , further comprising a step of hydrolyzing a silicon compound in a flame to obtain fine glass particles, and depositing and melting said fine glass particles to obtain the silica glass ingot having an OH group concentration of 1,000 ppm or more.  
     
     
         19 . A method according to  claim 18 , wherein a volume ratio of oxygen gas to hydrogen gas in said flare is 0.4 or more.  
     
     
         20 . A method according to  claim 17 , further comprising the steps of: 
 hydrolyzing a silicon compound in a flame to obtain fine glass particles, and depositing and melting said fine glass particles to obtain a silica glass ingot having an OH group concentration of 1,000 ppm or more; and then    cooling said silica glass ingot from a temperature of at least 1,373 K to a temperature not higher than 1,073 K at a temperature-lowering rate of 50 K/hr or less to pre-anneal said ingot.    
     
     
         21 . A method according to  claim 20 , wherein a volume ratio of oxygen gas to hydrogen gas in said flare is 0.4 or more.