Fluorine-containing silica glass and its method of manufacture

Abstract

The invention relates to fluorine-containing silica glasses, and methods of their production. The silica glass may be used for an ultraviolet light optical system in which light in a wavelength region of 200 mn or less, such as an ArF (193 nm) excimer laser, is used The invention also relates to a projection exposure apparatus containing fluorine-containing glass of the invention.

What is claimed is:  
     
         1 . An optical, fluorine-containing silica glass having a weight ratio of fluorine to sulfur of no less than 100.  
     
     
         2 . An optical, fluorine-containing silica glass of  claim 1 , wherein the silica glass has a transmittance of 99.9% or higher for ultraviolet light of wavelength 193 nm.  
     
     
         3 . An optical, fluorine-containing silica glass of  claim 1 , wherein the fluorine concentration contained in the silica glass is less than 100 ppm.  
     
     
         4 . A projection exposure apparatus, which projects and exposes a pattern image of a mask onto a substrate using ultraviolet light, comprising an optical, fluorine-containing silica glass of  claim 1 .  
     
     
         5 . A projection exposure apparatus, which projects and exposes a pattern image of a mask onto a substrate, comprising an illumination optical system for illuminating the mask using ultraviolet light as exposure light and a projection optical system comprising the fluorine-containing silica glass of  claim 1  for forming the pattern image of the mask on a substrate.  
     
     
         6 . A direct flame hydrolysis method of producing a fluorine-containing silica glass comprising the steps of: 
 hydrolyzing a silicon-containing gas in a flame and in the presence of a fluorine-containing gas to form a fluorine-containing, silica glass powder, 
 wherein the silicon-containing gas, the fluorine-containing gas, a carrier gas, and a combustion gas are expelled through a burner having a circular center pipe and at least one concentric circular ring pipe surrounding the center pipe, and wherein the silicon-containing gas is expelled through the center pipe and the fluorine-containing gas is expelled through the center pipe or a ring pipe adjacent to the center pipe; and  
   allowing the glass powder to accumulate on a target and melt to form a fluorine-containing silica glass.    
     
     
         7 . A method of  claim 6 , wherein the burner and the target are moved relative to each other in a plane.  
     
     
         8 . A fluorine-containing silica glass manufactured by the method of  claim 7 , wherein the silica glass comprises between 50 and 1000 ppm fluorine with the difference between the minimum fluorine concentration and the maximum fluorine concentration in the silica glass being no more than about 15 ppm.  
     
     
         9 . A method of  claim 6 , further comprising, during the hydrolyzing step, the step of: 
 rocking the target relative to the vertical direction of growth of the silica glass on the target.    
     
     
         10 . A method of  claim 6 , further comprising, during the hydrolysis step, the step of: 
 rotating, rocking, or lowering the target with respect to the burner.    
     
     
         11 . A method of  claim 6 , wherein the burner comprises four concentric ring pipes and the fluorine-containing gas is expelled from the first ring pipe adjacent to the center pipe.  
     
     
         12 . A method of  claim 6 , wherein the burner comprises four concentric ring pipes and the fluorine-containing gas is expelled from the center pipe and from the first ring pipe adjacent to the center pipe.  
     
     
         13 . A method of  claim 12 , wherein the fluorine-containing gas is selected from a group comprising SiF 4 , SF 6 , F 2  or mixtures thereof.  
     
     
         14 . A method of  claim 6 , wherein the silicon-containing gas is a mixture of SiF 4  and SiCl 4 .  
     
     
         15 . A method of manufacturing of  claim 14 , wherein the SiCl 4  is expelled at a flow rate ranging from about 5 g/min.  
     
     
         16 . A method of manufacturing of  claim 6 , wherein both the fluorine-containing gas and the silicon-containing gas are SiF 4 .  
     
     
         17 . A method of  claim 16 , wherein the flame is a hydrogen/oxygen flame and the ratio of oxygen to hydrogen expelled from the burner ranges from about 0.2 to 0.5.  
     
     
         18 . A fluorine-containing silica glass manufactured by the method of  claim 17 , wherein the hydrogen molecule concentration in the silica glass ranges from about 2×10 17  to 5×10 18  molecules/cm 3  and the hydroxyl group concentration ranges from about 600 ppm to 1300 ppm.  
     
     
         19 . A projection exposure apparatus, which projects and exposes a pattern image of a mask onto a substrate using ultraviolet light, comprising a fluorine-containing silica glass manufactured by the method of  claim 6 .  
     
     
         20 . A projection exposure apparatus, which projects and exposes a pattern image of a mask onto a substrate, comprising an illumination optical system for illuminating the mask using ultraviolet light as exposure light and a projection optical system comprising a fluorine-containing silica glass manufactured by the method of  claim 6 .  
     
     
         21 . A fluorine-containing silica glass manufactured by the method of  claim 6 , wherein the silica glass is substantially free of chlorine and has a structure determination temperature ranging from 900 K to 1200 K.  
     
     
         22 . A silica glass of  claim 21 , wherein the fluorine concentration ranges from 10 to 1000 ppm.  
     
     
         23 . A silica glass of  claim 21 , wherein the hydroxyl concentration glass ranges from 600 to 1300 ppm and the hydrogen molecule concentration ranges from 2×10 17  to 5×10 18  molecules/cm 3 .  
     
     
         24 . A direct flame hydrolysis method of producing a fluorine-containing silica glass substantially free of chlorine, the method comprising the steps of: 
 hydrolyzing a silicon-containing gas in a flame and in the presence of a fluorine-containing gas to form a fluorine-containing, silica glass powder, 
 wherein the silicon-containing gas, the fluorine-containing gas, a carrier gas, and a combustion gas are expelled through a burner and wherein the silicon-containing gas is a silane alkoxide or silicon tetrafluoride; and  
   allowing the glass powder to accumulate on a target and melt to form a fluorine-containing silica glass.    
     
     
         25 . A method of  claim 24 , wherein the silicon-containing gas, the fluorine-containing gas, a carrier gas, and a combustion gas are expelled through a burner having a circular center pipe and at least one concentric circular ring pipe surrounding the center pipe, and wherein the silicon-containing gas is expelled through the center pipe and the fluorine-containing gas is expelled through the center pipe or a ring pipe adjacent to the center pipe.  
     
     
         26 . A method of  claim 24 , further comprising the steps of: 
 heating the resulting silica glass to a temperature of at least 1200 K for a minimum of five hours; and cooling the silica glass at a rate of 10 K per hour to a temperature of 773 K or lower.    
     
     
         27 . A projection exposure apparatus, which projects and exposes a pattern image of a mask onto a substrate using ultraviolet light, comprising a fluorine-containing silica glass of  claim 21 .  
     
     
         28 . A projection exposure apparatus, which projects and exposes a pattern image of a mask onto a substrate, comprising an illumination optical system for illuminating the mask using ultraviolet light as exposure light and a projection optical system comprising the fluorine-containing silica glass of  claim 21.