Electrolytic method for photoresist stripping

Abstract

Photoresist stripping is performed by having a piecepart with a conductive layer that patterned by the photoresist immersed in a neutral solution. A voltage potential is applied to induce a current between the conductive layer and a counter electrode in neutral solution bath at a specified current density. After a short period of time, on the order of minutes, the photoresist is lifted off the piecepart. The piecepart is then removed from the bath, rinsed and dried.

1 . A method of stripping a photoresist from a piecepart having a conductive layer under said photoresist, comprising: 
 immersing said piecepart in a neutral solution;    generating hydrogen gas bubbles in said neutral solution for a period of time to lift said photoresist from said piecepart; and    removing said piecepart for rinsing and drying after said photoresist is lifted.    
     
     
         2 . The method of  claim 1  including applying a voltage potential across said conductive layer and a counter electrode, while both are in said neutral solution.  
     
     
         3 . The method of  claim 2  including applying said voltage potential such that said conductive layer is a cathode and said counter electrode is an anode.  
     
     
         4 . The method of  claim 1  including said neutral solution of sodium citrate, sodium orthophosphate, sodium sulfate, sodium nitrate, ammonium acetate, sodium acetate, or a water-based ionic conductive chemical.  
     
     
         5 . A method of stripping a photoresist from a piecepart having a conductive layer under said photoresist, comprising: 
 immersing said piecepart in a neutral solution;    immersing an inert counter electrode in said neutral solution;    electrically applying a potential difference across said piecepart and said counter electrode such that said piecepart acts as a cathode and said counter electrode acts as an anode;    generating hydrogen gas in said neutral solution to lift said photoresist off said piecepart; and    removing said piecepart from said solution for rinsing and drying.    
     
     
         6 . The method of  claim 5  wherein said piecepart includes a circuit board, substrate, metal mask, semiconductor wafer, or magnetic head.  
     
     
         7 . The method of  claim 5  including said neutral solution of sodium citrate, sodium orthophosphate, sodium sulfate, sodium nitrate, ammonium acetate, sodium acetate, or a water-based ionic conductive chemical.  
     
     
         8 . The method of  claim 5  including said counter electrode comprising a conductive non-corrosive material.  
     
     
         9 . The method of  claim 8  wherein said counter electrode includes stainless steel meshes or platinum covered titanium.  
     
     
         10 . The method of  claim 5  wherein said step of generating hydrogen gas comprises inducing a current between said cathode and said anode.  
     
     
         11 . The method of  claim 5  including a neutral solution incapable of stripping resist.  
     
     
         12 . The method of  claim 10  wherein said photoresist includes Riston 4840.  
     
     
         13 . The method of  claim 12  including said photoresist having a thickness of 2 mils.  
     
     
         14 . The method of  claim 12  including said photoresist having a thickness on the order of 4 mils.  
     
     
         15 . The method of  claim 13  including inducing said current having a current density on the order of 50 mA/cm 2 .  
     
     
         16 . The method of  claim 15  including immersing said piecepart in said neutral solution at a concentration on the order of 50 g/l at room temperature.  
     
     
         17 . The method of  claim 14  including inducing said current having a current density on the order of 100 mA/cm 2 .  
     
     
         18 . The method of  claim 17  including immersing said piecepart in said neutral solution at a concentration on the order of 150 g/l at 30° C.  
     
     
         19 . The method of  claim 5  including maintaining said piecepart in said neutral solution with said voltage potential applied for approximately three to fifteen minutes.  
     
     
         20 . An apparatus for electrolytic stripping of a photoresist from a piecepart having a conductive layer under said photoresist, comprising: 
 an electrolytic cell containing a neutral water-based ionic conductive solution, said piecepart, and an electrode; and    a power supply having a negative terminal electrically attached to said conductive layer and a positive terminal electrically attached to said electrode, and generating a potential difference between said conductive layer and said electrode;    such that hydrogen gas is generated in said solution when said potential difference is applied.