Selective etching of silicon wafer

Abstract

An apparatus that includes a solution bath of a seasoned solution, the seasoned solution containing a mixture of hydrofluoric acid, nitric acid, and acetic acid; and one or more silicon wafers being suspended in a position above the solution bath, wherein at least a portion of the mixture having been used in thinning the one or more silicon wafers.

What is claimed is: 
     
         1 . An apparatus comprising:
 a solution bath of a seasoned solution, the seasoned solution comprising a mixture of hydrofluoric acid, nitric acid, and acetic acid; and   one or more silicon wafers being suspended in a position above the solution bath, wherein at least a portion of the mixture is used in thinning the one or more silicon wafers.   
     
     
         2 . The apparatus of  claim 1 , wherein the at least a portion of the mixture is at least 10% in a volume of a total volume of the mixture. 
     
     
         3 . The apparatus of  claim 2 , wherein the mixture having a ratio among hydrofluoric acid, nitric acid and acetic acid between about 1:3:3 and about 1:3:5. 
     
     
         4 . The apparatus of  claim 3 , wherein the solution bath having a re-circulation port, the mixture inside the solution bath being re-circulated through the re-circulation port and a chemical cabinet to be re-applied in thinning the one or more silicon wafers. 
     
     
         5 . The apparatus of  claim 4 , wherein the chemical cabinet is adapted to periodically add a fresh mixture of hydrofluoric acid, nitric acid, and acetic acid onto the solution bath in a volume of about 10 to about 20% of the total volume of the mixture. 
     
     
         6 . The apparatus of  claim 1 , further comprising:
 a spraying element to apply the mixture onto the one or more silicon wafers.   
     
     
         7 . The apparatus of  claim 1 , wherein the portions of the one or more silicon wafers being thinned are heavily boron doped with a level of at least 1×10 19  atoms/cm 3 .