Method to plate C4 to copper stud

Abstract

A method for plating a second metal directly to a first metal without utilizing a mask. A semiconductor substrate is provided including at least one metal feature and at least one insulating layer covering the metal feature and the substrate. At least one recess is formed in the at least one insulating layer thereby exposing at least a portion of the metal feature. At least one conductive barrier layer is formed over the insulating layer and the exposed portion of the metal feature. A plating seed layer of a first metal is formed over the at least one barrier layer. A photoresist layer is deposited over the plating seed layer. Portions of the photoresist layer and portions of the plating seed layer outside of the at least one recess are removed. Photoresist remaining in the at least one recess is removed. A second metal is electroplated to the plating seed layer in the recess, using the barrier layer to conduct electrical current.

What is claimed is:  
     
         1 . A method for plating a second metal directly to a first metal without utilizing a mask, said method comprising the steps of: 
 providing a semiconductor substrate including at least one metal feature and at least one insulating layer covering said metal feature and said substrate;    forming at least one recess in said at least one insulating layer thereby exposing at least a portion of said metal feature;    forming at least one conductive barrier layer over said insulating layer and said exposed portion of said metal feature;    forming a plating seed layer of a first metal over said at least one barrier layer;    depositing a photoresist layer over said plating seed layer;    removing portions of said photoresist layer and portions of said plating seed layer outside of said at least one recess;    removing photoresist remaining in said at least one recess; and    electroplating a second metal to said plating seed layer in said recess.    
     
     
         2 . The method according to    claim 1   , wherein said metal feature is a metal last provided in said semiconductor substrate.  
     
     
         3 . The method according to    claim 1   , wherein said conductive barrier is provided by sputter deposition of a layer of at least one nitride of tantalum on said insulating layer and said exposed portion of said metal feature and subsequent sputter deposition of a layer of tantalum on said tantalum nitride layer, such that the layer including the nitride of tantalum is in the α-phase.  
     
     
         4 . The method according to    claim 3   , wherein said tantalum nitride layer is about 10 Å to about 1000 Å thick and said tantalum layer is about 500 Å to about 5000 Å thick.  
     
     
         5 . The method according to    claim 1   , wherein said seed layer is formed by electrolytic or electroless plating of said first metal.  
     
     
         6 . The method according to    claim 5   , wherein said seed layer is copper.  
     
     
         7 . The method according to    claim 6   , wherein said copper is sputter coated on said layer of tantalum.  
     
     
         8 . The method according to    claim 6   , wherein said copper tantalum structure is α-Ta/TaN/Cu.  
     
     
         9 . The method according to    claim 6   , wherein said copper layer is about 1000 Å to about 20,000 Å thick.  
     
     
         10 . The method according to    claim 3   , wherein said tantalum is alpha tantalum.  
     
     
         11 . The method of    claim 3   , wherein said tantalum layer is TaN/α-Ta/TaN-laminate.  
     
     
         12 . The method according to    claim 1   , wherein said portions of said photoresist layer and said seed layer outside of said recess are removed by chemical-mechanical polishing.  
     
     
         13 . The method according to    claim 1   , wherein said photoresist is spun on said plating seed layer.  
     
     
         14 . The method according to    claim 1   , wherein said barrier layer forms a conductor for said electroplating of said second metal.  
     
     
         15 . The method according to    claim 1   , wherein said second metal is a solder ball made of an alloy of lead and tin, plated lead-free solder or other platable terminal metallurgies.  
     
     
         16 . The method according to    claim 1   , further comprising the step of: 
 removing said at least one conductive barrier layer from horizontal portions between said recesses.    
     
     
         17 . The method according to    claim 16   , wherein said electroplated second metal acts as a mask for the removal of said at least one conductive barrier layer.  
     
     
         18 . The method according to    claim 1   , wherein said at least one metal feature is formed in said substrate.  
     
     
         19 . The method according to    claim 1   , wherein said insulating layer includes a layer of an oxide and a nitride and at least one layer of a polyimide.  
     
     
         20 . The method of    claim 19   , further comprising the step of: 
 forming a layer of at least one nitride or other passivation layer over the polyimide.    
     
     
         21 . The method according to    claim 1   , wherein said second metal is a solder ball.  
     
     
         22 . A method for plating a second metal directly to a first metal without utilizing a mask, said method comprising the steps of: 
 providing a semiconductor substrate including at least one metal feature and at least one insulating layer covering said metal feature and said substrate;    forming at least one recess in said at least one insulating layer thereby exposing at least a portion of said metal feature;    forming at least one conductive barrier layer over said insulating layer and said exposed portion of said metal feature;    forming a plating seed layer of a first metal over said at least one barrier layer;    providing a pad in said at least one recess for preventing removal of portions of said seed layer in said at least one recess;    removing portions of said photoresist layer and portions of said plating seed layer outside of said at least one recess;    removing said pad; and    electroplating a second metal to said plating seed layer in said recess.    
     
     
         23 . The method of    claim 22   , further comprising the step of: 
 utilizing a hard polishing pad to remove said seed layer outside of said recess.    
     
     
         24 . A semiconductor structure, comprising: 
 a semiconductor substrate;    at least one metal feature provided in said substrate;    at least one insulating layer at least partially covering said at least one metal feature;    at least one recess located in said at least one insulating layer over said at least one metal feature;    at least one conductive barrier layer located over said at least one electrical insulating layer and over a portion of said at least one metal feature under said at least one recess;    at least one plating seed layer of a first metal located over a portion of said conductive barrier layer within said recess; and    a second metal electroplated to said seed layer in said recesses.    
     
     
         25 . The method according to    claim 24   , wherein said at least one metal feature is formed of at least one metal or alloy having low resistivity.  
     
     
         26 . The method according to    claim 25   , wherein said metal or alloy includes at least one member selected from the group consisting of Al, Au, Ni, W, α-Ta, and alloys including Al, Au, Ni, W, or α-Ta.