On-site generation of ultra-high-purity buffered-HF and ammonium fluoride

Abstract

Provided is a novel method and system for preparing ultra-high-purity buffered-hydrofluoric acid or ammonium fluoride controlled concentration. The method comprises bubbling purified ammonia vapor into ultra-pure hydrofluoric acid. The inventive method and system can be used as an on-site subsystem in a semiconductor device fabrication facility for supplying the buffered-hydrofluoric acid and ammonium fluoride to points of use in the semiconductor device fabrication facility.

What is claimed is:  
     
         1 . A method of preparing ultra-high-purity buffered-hydrofluoric acid or ammonium fluoride of controlled concentration, comprising bubbling purified ammonia vapor into ultra-pure hydrofluoric acid.  
     
     
         2 . The method according to  claim 1 , wherein ultra-high-purity buffered-hydrofluoric acid is prepared.  
     
     
         3 . The method according to  claim 2 , wherein said ultra-high-purity buffered-hydrofluoric acid has a concentration of 10:1, 50:1 or 200:1 as measured by volume parts of 40% ammonium fluoride to 49% HF.  
     
     
         4 . The method according to  claim 1 , wherein ultra-high-purity ammonium fluoride is prepared.  
     
     
         5 . The method according to  claim 4 , wherein the ammonium fluoride is a 40% by weight ammonium fluoride solution.  
     
     
         6 . The method according to  claim 1 , wherein the ammonia vapor bubbling is performed in a generator which is connected to a point of use.  
     
     
         7 . The method according to  claim 6 , wherein the point of use is located in a semiconductor device fabrication facility.  
     
     
         8 . The method according to  claim 1 , wherein the ultra-pure hydrofluoric acid is prepared by a process comprising the steps of: 
 removing a flow of hydrogen fluoride vapor from a source of hydrogen fluoride;    contacting said hydrogen fluoride vapor with a recirculating volume of high-purity water containing a high concentration of hydrogen fluoride in a hydrogen fluoride ionic purifier unit, wherein said hydrogen fluoride ionic purifier unit passes purified hydrogen fluoride gas; and    combining the hydrogen fluoride gas with acidic deionized water to produce the ultra-pure hydrofluoric acid.    
     
     
         9 . The method according to  claim 8 , wherein the source of hydrogen fluoride is an anhydrous hydrogen fluoride source.  
     
     
         10 . The method according to  claim 8 , wherein the source of hydrogen fluoride is essentially arsenic-free.  
     
     
         11 . The method according to  claim 8 , wherein the source of hydrogen fluoride is ultra-pure arsenic-free aqueous hydrogen fluoride.  
     
     
         12 . The method according to  claim 8 , wherein the ammonia vapor is prepared by a process comprising the steps of: 
 removing a flow of ammonia vapor from a source of liquid ammonia;    contacting said flow of ammonia vapor with a recirculating volume of high-purity water containing a high concentration of ammonium hydroxide in an ammonia ionic purifier unit, wherein said ammonia ionic purifier unit passes said purified ammonia vapor.    
     
     
         13 . The method according to  claim 12 , wherein said recirculating volume of high-purity water in said hydrogen fluoride ionic purifier and said recirculating volume of high-purity water in said ammonia ionic purifier are free of additives.  
     
     
         14 . The method according to  claim 1 , wherein the ammonia vapor is prepared by a process comprising the steps of: 
 removing a flow of ammonia vapor from a source of liquid ammonia;    contacting said flow of ammonia vapor with a recirculating volume of high-purity water containing a high concentration of ammonium hydroxide in an ammonia ionic purifier unit, wherein said ammonia ionic purifier unit passes said purified ammonia vapor.    
     
     
         15 . The method according to  claim 1 , wherein the step of bubbling the purified ammonia vapor into the ultra-pure hydrofluoric acid is performed in a generator, and wherein the ultra-pure hydrofluoric acid is formed by introducing a 49% by weight hydrogen fluoride solution into the generator, and diluting said hydrogen fluoride solution with high-purity water.  
     
     
         16 . The method according to  claim 1 , wherein additional hydrofluoric acid is added to the solution after the ammonia bubbling step, thereby forming said ultra-high-purity buffered-hydrofluoric acid.  
     
     
         17 . The method according to  claim 16 , wherein the ammonia bubbling step forms a 40% ammonium fluoride solution product.  
     
     
         18 . The method according to  claim 1 , wherein the ultra-pure hydrofluoric acid is formed by introducing anhydrous hydrogen fluoride into high purity water in a generator, and the ammonia vapor is bubbled into the ultra-pure hydrofluoric acid in the generator.  
     
     
         19 . The method according to  claim 1 , wherein the concentration of the buffered-hydrofluoric acid or ammonium fluoride is controlled by a step for detecting an endpoint of chemical mixing.  
     
     
         20 . The method according to  claim 19 , wherein the step for detecting an endpoint of chemical mixing is performed by acoustic velocity measurement.  
     
     
         21 . A system for preparing ultra-high-purity buffered-hydrofluoric acid or ammonium fluoride of controlled concentration, comprising a source of purified ammonia vapor, a source of ultrapure hydrofluoric acid and a generator which combines said ammonia vapor with said ultra-pure hydrofluoric acid to produce said ultra-high-purity buffered-hydrofluoric acid or ammonium fluoride.  
     
     
         22 . The system according to  claim 21 , wherein the generator is connected to a point of use through piping.  
     
     
         23 . The system according to  claim 22 , wherein the point of use is located in a semiconductor device fabrication facility.  
     
     
         24 . The system according to  claim 23 , wherein the source of ultrapure hydrofluoric acid comprises a reservoir connected to receive a hydrogen fluoride source and to provide a flow of hydrogen fluoride vapor therefrom, said flow of hydrogen fluoride vapor being connected to pass through a hydrogen fluoride ionic purifier unit which provides a recirculating volume of high-purity water containing a high concentration of hydrogen fluoride in contact with said flow of hydrogen fluoride vapor, wherein said purifier passes purified hydrogen fluoride gas, and a hydrogen fluoride generator unit, connected to receive said flow of hydrogen fluoride gas from said purifier and to combine said hydrogen fluoride gas with high-purity acidic deionized water to produce said ultra-pure hydrofluoric acid.  
     
     
         25 . The system according to  claim 24 , wherein the source of hydrogen fluoride is an anhydrous hydrogen fluoride source.  
     
     
         26 . The system according to  claim 24 , wherein the source of hydrogen fluoride is essentially arsenic-free.  
     
     
         27 . The system according to  claim 24 , wherein the source of hydrogen fluoride is ultra-pure arsenic-free aqueous hydrogen fluoride.  
     
     
         28 . The system according to  claim 24 , wherein the source of purified ammonia vapor comprises a reservoir connected to receive a liquid source of ammonia and to provide a flow of ammonia vapor therefrom, said flow of ammonia vapor being connected to pass through an ammonia ionic purifier unit which provides a recirculating volume of high-purity water, containing a high concentration of ammonium hydroxide, in contact with said flow of ammonia vapor, wherein said ammonia purifier passes said purified ammonia vapor.  
     
     
         29 . The system according to  claim 24 , wherein said recirculating volume of high-purity water in said hydrogen fluoride ionic purifier and said recirculating volume of high-purity water in said ammonia ionic purifier are free of additives.  
     
     
         30 . The system according to  claim 21 , wherein the source of purified ammonia vapor comprises a reservoir connected to receive a liquid source of ammonia and to provide a flow of ammonia vapor therefrom, said flow of ammonia vapor being connected to pass through an ammonia ionic purifier unit which provides a recirculating volume of high-purity water, containing a high concentration of ammonium hydroxide, in contact with said flow of ammonia vapor, wherein said ammonia purifier passes said purified ammonia vapor.  
     
     
         31 . The system according to  claim 21 , further comprising means for detecting an endpoint of chemical mixing.  
     
     
         32 . The system according to claim  31 , wherein the means for detecting an endpoint of chemical mixing comprises an acoustic velocity measurement sensor.