Method and apparatus for etching silicon wafer and method for analysis of impurities

Abstract

A wafer etching and impurity analysis method is presented where a wafer is held in a vessel having gas introduction and exhaust ports, a solution including a mixture of hydrofluoric acid and nitric acid alone or together with sulfuric acid is bubbled with a carrier gas without being heated, which generates a gas containing vaporized hydrofluoric acid and nitric acid, and the inside of the vessel is purged so that the amount of gas supplied is kept constant at all times. The molar ratio of the hydrofluoric acid and nitric acid (and sulfuric acid if used) in the solution is set to a specific value. The amount of gas introduced is specified. All or a specific portion of the wafer is cooled to a specific temperature between 0 and 20° C. Consequently, the gas is condensed on the surface of the wafer, which allows the required portion of the wafer to be etched and the amount of required in-plane etching to be uniform. The method produces a wafer surface with good smoothness after etching, reduces the amount of recovery liquid needed, and reduces the amount of admixed silicon during impurity analysis, the concentration time, and so forth.

1 . A silicon wafer etching method, comprising: 
 applying a carrier gas through a mixed solution of hydrofluoric acid and nitric acid or of hydrofluoric acid, nitric acid, and sulfuric acid to obtain an etching gas;    introducing the etching gas obtained by bubbling and containing vaporized hydrofluoric acid and nitric acid into a vessel equipped with an inlet and an outlet; and    cooling said vessel to a specific tmperature,    wherein the etching gas is condensed on the surface of a silicon wafer that is held inside said vessel and that has been cooled, thereby etching the silicon wafer surface.    
     
     
         2 . The silicon wafer etching method according to  claim 1 , wherein the mixed solution comprises hydrofluoric acid and nitric acid, and the nitric acid is used in an amount of 0.351 to 2.805 mol per mole of hydrofluoric acid.  
     
     
         3 . The silicon wafer etching method according to  claim 1 , wherein the mixed solution comprises hydrofluoric acid, nitric acid, and sulfuric acid, and the nitric acid is used in an amount of 0.351 to 2.805 mol and the sulfuric acid in an amount of 0.163 to 0.490 mol per mole of hydrofluoric acid.  
     
     
         4 . The silicon wafer etching method according to  claim 1 , wherein the cooling temperature of the silicon wafer is 0 to 20° C.  
     
     
         5 . The silicon wafer etching method according to  claim 1 , wherein the cooled portion of the silicon wafer is the entire wafer, the outer periphery of the wafer, the middle part of the wafer, or a specific part of the wafer.  
     
     
         6 . The silicon wafer etching method according to  claim 1 , wherein the amount of etching is 0.02 to 10.0 μm.  
     
     
         7 . A silicon wafer etching apparatus, comprising: 
 a device for generating an etching gas, which is obtained by bubbling a carrier gas through a mixed solution of hydrofluoric acid and nitric acid or of hydrofluoric acid, nitric acid, and sulfuric acid;    a vessel having a gas inlet and outlet system, said vessel configured to receive the etching gas containing vaporized hydrofluoric acid and nitric acid; and    a holding and cooling device for holding a silicon wafer in the vessel and colling the wafer to a specific temperature.    
     
     
         8 . A method for analyzing the impurities of a silicon wafer, comprising: 
 generating an etching gas by bubbling a carrier gas through a mixed solution containing hydrofluoric acid and nitric acid; introducing the etching gas containing vaporized hydrofluoric acid and nitric acid into a vessel having a system for introducing and exhausting the etching gas, wherein the etching gas is condensed on a surface of a cooled silicon wafer held inside said vessel, thereby etching said surface;    scanning the entire surface of the etched wafer with a mixed solution of hydrofluoric acid and aqueous hydrogen peroxide to recover any decomposition residue; and    concentrating the recovered mixed solution and analyzing said solution for metal impurities.    
     
     
         9 . The method for analyzing impurities of a silicon wafer according to  claim 8 , wherein the mixed solution of hydrofluoric acid and aqueous hydrogen peroxide is used in an amount of 50 to 150 μL.