Acid etching mixture having reduced water content

Abstract

Acid etching mixtures having water content, reduced by the addition of fluorosulfonic acid. The preparation and the use of said acid etching mixtures, particularly in etching silicon, are also disclosed.

1 . A method for preparing an acid etching mixture having reduced water content comprising adding fluorosulfonic acid to an aqueous acid-containing composition.  
     
     
         2 . The method as claimed in  claim 1 , characterized in that said water content is reduced from a higher concentration to an amount from 0 to about 40% by weight, wherein the total amount of all components of said etching mixture is 100% by weight.  
     
     
         3 . The method as claimed in  claim 1 , characterized in that said fluorosulfonic acid is added to said acid-containing composition containing water in an amount from about 0.1 to about 60% by weight, wherein the total amount of all components of the etching mixture is 100% by weight.  
     
     
         4 . The method as claimed in  claim 1 , characterized in that said acid etching mixture comprises sulfuric acid, hydrofluoric acid, and one or more acids selected from the group consisting of fluorosulfonic acid, nitric(v) acid and orthophosphoric acid, and said aqueous acid-containing composition comprises one or more acids selected from the group consisting of hydrofluoric acid, sulfuric, nitric(v) acid and orthophosphoric acid.  
     
     
         5 . In a process for etching silicon or a silicon substrate using an aqueous acid etching mixture comprising hydrofluoric acid, sulfuric acid and either or both nitric(v) acid or orthophosphoric acid, wherein during said process the concentration of said hydrofluoric acid decreases and the concentration of water increases, the improvement comprising replenishing said hydrofluoric acid and simultaneously decreasing said water concentration.  
     
     
         6 . The process of  claim 5 , wherein said hydrofluoric acid is replenished while decreasing said water concentration by adding fluorosulfonic acid to said acid etching mixture, so that said fluorosulfonic acid hydrolyzes to form hydrofluoric acid and sulfuric acid, thereby consuming water to reduce the concentration thereof while increasing said concentration of hydrofluoric acid.  
     
     
         7 . The process of  claim 6 , wherein said fluorosulfonic acid is added periodically in quantity that maintains the water content of said acid etching mixture essentially constant.  
     
     
         8 . The process of  claim 5 , wherein said process is a continuous process.  
     
     
         9 . An acid etching mixture prepared by adding fluorosulfonic acid to an aqueous acid-containing composition.  
     
     
         10 . The acid etching mixture as claimed in  claim 9 , characterized in that the water content is reduced from a higher concentration to an amount from about 15 to about 35%, and said mixture further comprises nitric(v) acid in an amount from about 20 to about 40%, sulfuric acid in an amount from about 5 to about 35%, hydrofluoric acid in an amount from about 5 to about 25%, and orthophosphoric acid in an amount from about 5 to about 20%, wherein the total amount of all components present in said etching mixture is 100% (by weight).  
     
     
         11 . The acid etching mixture as claimed in  claim 9 , characterized in that the water content is reduced from a higher concentration to an amount from about 0.1 to about 15%, and said etching mixture further comprises nitric(v) acid in an amount from about 0.1 to about 10%, sulfuric acid in an amount from about 70 to about 95%, and hydrofluoric acid in an amount from about 1 to about 15%, wherein the total amount of all components present in said etching mixture is 100% (by weight).  
     
     
         12 . The acid etching mixture as claimed in  claim 9 , characterized in that the water content is reduced from a higher concentration to an amount from about 0.01 to about 0.05%, and said etching mixture further comprises fluorosulfonic acid in an amount from about 0.1 to about 30%, nitric(v) acid in an amount from about 0.1 to about 50%, sulfuric acid in an amount from about 5 to about 90%, hydrofluoric acid in an amount from about 5 to about 30%, and orthophosphoric acid in an amount from 0 to 30%, wherein the total amount of all components present in said etching mixture is 100% (by weight).  
     
     
         13 . A method for etching silicon or a silicon substrate comprising contacting said silicon or silicon substrate with an acid etching mixture prepared according to the process as claimed in  claim 6 .  
     
     
         14 . The method as claimed in  claim 13 , characterized in that said method is a spray etching or a spin etching process.