HIGHLY PURIFIED LIQUID PERFLUORO-n-ALKANES AND METHOD FOR PREPARING

Abstract

Provided are liquid perfluoro-n-alkanes that are highly transparent to UV wavelengths ranging from about 150 nm to 165 nm, and to the method by which high transparency may be obtained. The liquid, perfluoro-n-alkanes are useful in optical couplants, optical cements, optical elements, optical inspection media for semiconductor wafers and devices, and immersion photolithography at 157 nm exposure wavelength.

1 . A composition consisting essentially of a perfluoro-n-alkane liquid characterized by a water concentration of less than 10 ppm, an oxygen concentration of less than 10 ppm, and an absorbance at 157 nanometers in the range of 0.1 to 10 cm-1, said perfluoro-n-alkane selected from perfluoro-n-pentane, perfluoro-n-hexane, and mixtures thereof. 
     
     
         2 . The composition of  claim 1  wherein said perfluoro-n-alkane liquid is characterized by an oxygen concentration of less than 5 ppm, a water concentration of less than 5 ppm, and an absorbance at 157 nm in the range of 0.1 to 2 cm-1. 
     
     
         3 . The composition of  claim 2  wherein said perfluoro-n-alkane liquid is characterized by an oxygen concentration of less than 1 ppm, a water concentration of less than 5 ppm, and an absorbance at 157 nm of 0.1 to 1 cm-1. 
     
     
         4 . A process for preparing a perfluoro-n-alkane liquid characterized by a water concentration of less than 10 ppm, an oxygen concentration of less than 10 ppm, and an absorbance at 157 nanometers in the range of 0.1-10 cm-1, the process comprising subjecting a perfluoro-n-alkane liquid to at least one extraction step, wherein said perfluoroalkane liquid is selected from perfluoro-n-pentane, perfluoro-n-hexane, and mixtures thereof. 
     
     
         5 . The process of  claim 4  wherein said process is carried out in an oxygen-minimized atmosphere. 
     
     
         6 . The process of  claim 4  or  5  further comprising fractional distillation in a grease-free distillation system of a perfluoro-n-alkane liquid of at least 99% purity, contacting a heart cut condensate obtained therefrom with an absorbent, said absorbent being selected from silica gel, zeolite molecular sieves, and mixtures thereof. 
     
     
         7 . The process of  claim 6  further comprising purifying and activating said absorbent prior to contacting said condensate therewith by heating said absorbent in an oxidizing atmosphere to a temperature sufficient to remove substantially all water from said absorbent, then cooling and sealing the absorbent in an oxygen-minimized atmosphere. 
     
     
         8 . The process of  claim 6  wherein said absorbent is a mixture of absorbents. 
     
     
         9 . The process of  claim 6  wherein said absorbent comprises one or more zeolite molecular sieves. 
     
     
         10 . The process of  claim 9  wherein said zeolite molecular sieves are selected from 3A, 4A, and 5A zeolite molecular sieves. 
     
     
         11 . A process comprising exposing a photoresist surface to ultraviolet light at 157 nm emitted by a light source, wherein
 said photoresist surface is immersed in a perfluoro-n-alkane liquid having a water concentration of less than 10 ppm, an oxygen concentration of less than 10 ppm, and an absorbance at 157 nanometers in the range of 0.1 to 10 cm-1, said perfluoro-n-alkane liquid being selected from perfluoro-n-pentane, perfluoro-n-hexane, and mixtures thereof, and wherein said perfluoro-n-alkane liquid is disposed between said light source and said photoresist surface; and   developing said photoresist to produce an image.   
     
     
         12 . The process of  claim 11  wherein said perfluoro-n-alkane liquid has an oxygen concentration of less than 5 ppm, a water concentration of less than 5 ppm, and an absorbance at 157 nm in the range of 0.1 to 2 cm-1. 
     
     
         13 . The process of  claim 12  wherein said perfluoro-n-alkane liquid has an oxygen concentration of less than 1 ppm, a water concentration of less than 5 ppm, and an absorbance at 157 nm of 0.1 to 1 cm-1.