Use of perfluoroalkanes in vacuum ultraviolet applications

Abstract

This invention concerns liquid perfluoro-n-alkanes for use in applications demanding high transparency at UV wavelengths ranging from about 150 to 165 nm, especially 157 nm. Uses include optical couplants, optical cements, optical elements, optical inspection media for photolithography at 157 nm exposure wavelength.

1 . A process comprising a light source emitting light in the wavelength range from 155 to 160 nm, a surface illuminated over at least a portion thereof by said emitted light, and a perfluoro-n-alkane liquid disposed between said light source and said suface in such manner that at least a portion of said emitted light illuminating said surface is caused to be transmitted through said liquid, said liquid consisting essentially of perfluoro-n-pentane, perfluoro-n-hexane, of a mixture thereof. 
   
   
       2 . The process of  claim 1  wherein said perfluoro-n-alkane liquid is characterized by an oxygen concentration of <10 ppm, a water concentration of <10 ppm and absorbance of 0.1 to 10 cm−1. 
   
   
       3 . The process of  claim 2  wherein said oxygen concentration is less than 5 ppm and said absorbance is in the range of 0.1 to 2 cm−1. 
   
   
       4 . The process of  claim 3  wherein said oxygen concentration is less than 1 ppm and said absorbance is in the range of 0.1 to 1 cm−1. 
   
   
       5 . The process of  claim 1  wherein said light source is a laser, emitting light at 157 nm. 
   
   
       6 . The process of  claim 1  wherein said surface comprises a photoresist polymer. 
   
   
       7 . The process of  claim 6  wherein said photoresist surface is immersed in said liquid. 
   
   
       8 . The process of  claim 1  or  claim 4  wherein said light source is a laser which emits light at 157 nm, said surface comprises a photoresist polymer, said surface is immersed in said liquid and wherein said light illuminating said surface causes an imagewise exposure of said surface. 
   
   
       9 . The process of  claim 8  further comprising the steps of extracting oxygen, water and organic contaminants from said liquid prior to immersion of said photoresist surface in said liquid. 
   
   
       10 . The process of  claim 9  further comprising handling and maintaining said extracted liquid in an oxygen-minimized atomsphere. 
   
   
       11 . The process of  claim 9  wherein said extraction is effected by fractional distillation in a greese-free still followed by contacting the heart cut of the condensate thereof with a solid absorbant selected from the group consisting of silica gel, 3A zeolite molecular sieves, 4A zeolite molecular sieves, 5A zeolite molecular sieves, and mixtures thereof. 
   
   
       12 . The process of  claim 11  wherein said solid absorbant is a mixture. 
   
   
       13 . An apparatus comprising a light source capable of emitting light in the wavelength range from 150 to 165 nm, a surface disposed so that upon activation of said light source said surface will be illuminated by the light emitted form said light source over at least a portion thereof by said emitted light, and a perfluoro-n-alkane liquid disposed between said light source and said surface in such manner that at least a portion of said emitted light illuminating said surface is caused to be transmitted through said liquid, said liquid consisting essentially of perfluoro-n-pentane, perfluoro-n-hexane, of a mixture thereof. 
   
   
       14 . The apparatus of  claim 13  wherein said perfluoro-n-alkane liquid is characterized by an oxygen concentration of <10 ppm, a water concentration of <10 ppm and absorbance of 0.1 to 10 cm−1. 
   
   
       15 . The apparatus of  claim 14  wherein said oxygen concentration is less than 5 ppm and said absorbance is in the range of 0.1 to 2 cm−1. 
   
   
       16 . The apparatus of  claim 15  wherein said oxygen concentration is less than 1 ppm and said absorbance is in the range of 0.1 to 1 cm−1. 
   
   
       17 . The apparatus of  claim 13  wherein said light source is a laser, which is capable of emitting, light at 157 nm. 
   
   
       18 . The apparatus of  claim 3  wherein said surface comprises a photoresist polymer. 
   
   
       19 . The apparatus of  claim 18  wherein said photoresist surface is immersed in said liquid. 
   
   
       20 . The apparatus of  claim 13  or  claim 16  wherein said light source is a laser capable of emitting light at 157 nm, said surface comprises a photoresist polymer, said surface is immersed in said liquid and said apparatus is provided with a means for accomplishing imagewise exposed of said surface. 
   
   
       21 . The apparatus of  claim 20  further comprising an oxygen-minimized atmosphere.