Etchant solution for removing a thin metallic layer

Abstract

An etchant solution is provided for essentially eliminating undercutting in a thin metallic layer such as a seed layer in a magnetic recording head. The etchant solution has a suitable solvent additive such as glycerol or methyl cellulose. With a suitable solvent additives, which generally increase solvent viscosity, lateral etching rates are similar to surface etch rates and undercutting is essentially eliminated.

I claim:  
     
         1 . An etchant solution for removing a thin metallic layer, comprising: 
 ferric ammonium sulfate dissolved in a solvent; and, said solvent including water and glycerol.    
     
     
         2 . An etchant solution as in  claim 1  wherein the etchant solution has a pH value of about 1.  
     
     
         3 . An etchant solution as in  claim 1  wherein the concentration of said ferric ammonium sulfate is about 0.7 M ferric.  
     
     
         4 . An etchant solution as in  claim 1  wherein said glycerol is about 20% to about 50% by weight.  
     
     
         5 . An etchant solution as in  claim 1  wherein said solution has a viscosity of about 2 to 10 times greater than the viscosity of water.  
     
     
         6 . An etchant solution for removing a thin metallic layer, comprising: 
 ferric ammonium sulfate dissolved in a solvent; and,    said solvent including water and methyl cellulose.    
     
     
         7 . An etchant solution as in  claim 6  wherein the etchant solution has a pH value of about 1.  
     
     
         8 . An etchant solution as in  claim 6  wherein the molecular weight of said methyl cellulose is about 14,000.  
     
     
         9 . A etchant solution as in  claim 6  wherein the concentration of said methyl cellulose is about 1%.  
     
     
         10 . A method for removing a thin metallic layer, comprising: 
 depositing a thin metallic layer;    forming a first photoresist layer over said thin metallic layer;    forming a pattern in said first photoresist layer exposing a portion of said thin metallic layer;    electrodepositing a material onto exposed portion of said thin metallic layer;    removing said first photoresist layer;    forming a second photoresist layer over desired electrodeposited material leaving an exposed portion of said thin metallic layer; and,    using an etchant solution to remove said exposed portion of said thin metallic layer wherein said etchant solution includes ferric ammonium sulfate dissolved in a solvent including water and glycerol.    
     
     
         11 . A method as in  claim 10  wherein the concentration of said ferric ammonium sulfate is about 0.7 M ferric.  
     
     
         12 . A method as in  claim 10  wherein the etchant solution has a pH value of about 1.  
     
     
         13 . A method as in  claim 10  wherein said glycerol is about 20% to about 50% of said solvent.  
     
     
         14 . A method as in  claim 10  wherein said solution has a viscosity of about 2 to 10 greater than water.  
     
     
         15 . An etchant solution for removing a thin metallic layer, comprising: 
 ferric ammonium sulfate dissolved in a solvent; and,    said solvent including water and a solvent additive,    wherein said etchant solution has a viscosity in the range of about 2 to about 10 times the viscosity of water.    
     
     
         16 . An etchant solution as in  claim 15  wherein said solvent additive is glycerol.  
     
     
         17 . An etchant solution as in  claim 15  wherein said glycerol is in the range of about 20% to about 50% by weight of solvent.  
     
     
         18 . An etchant solution as in  claim 15  wherein said solvent additive is methyl cellulose.  
     
     
         19 . An etchant solution as in  claim 18  wherein said methyl cellulose has a molecular weight of about 14,000 and is about 1% by weight of solvent.  
     
     
         20 . An etchant solution as in  claim 15  wherein the etchant solution has a pH value of about 1.