Selective solder plating

Abstract

A method provides a structure that includes a substrate having a metal layer disposed on a surface and a metal feature disposed on the metal layer. The method further includes immersing the structure in a plating bath contained in an electroplating cell, the plating bath containing a selected solder material; applying a voltage potential to the structure, where the structure functions as a working electrode in combination with a reference electrode and a counter electrode that are also immersed in the plating bath; and maintaining the voltage potential at a predetermined value to deposit the selected solder material selectively only on the metal feature and not on the metal layer. An apparatus configured to practice the method is also disclosed.

What is claimed is: 
     
         1 . A method, comprising:
 providing a structure comprised of a substrate having a metal layer disposed on a surface and a metal feature disposed on the metal layer;   immersing the structure in a plating bath contained in an electroplating cell, the plating bath comprising a selected solder material;   applying a voltage potential to the structure, where the structure functions as a working electrode in combination with a reference electrode and a counter electrode that are also immersed in the plating bath; and   maintaining the voltage potential at a predetermined value to deposit the selected solder material selectively only on the metal feature and not on the metal layer.   
     
     
         2 . The method as in  claim 1 , where the metal layer is comprised of Titanium and where the metal feature is comprised of Copper. 
     
     
         3 . The method as in  claim 1 , where the selected solder material is comprised of Indium. 
     
     
         4 . The method as in  claim 3 , where the plating bath is comprised of one of Indium Sulfate, Indium Chloride, Indium Methanesulfonate, Indium Acetate or Indium oxide and is further comprised of a conductivity salt or acid comprised of one of Sulfuric acid, Hydrochloric acid, Methane Sulfonic acid or Sulfamic acid. 
     
     
         5 . The method as in  claim 4 , where the plating bath is further comprised of a wetting agent. 
     
     
         6 . The method as in  claim 1 , where the selected solder material is comprised of one of Tin, Tin-Silver, Tin-Silver-Copper, Indium-Tin, Tin-Lead, Tin-Bismuth and Tin-Gold. 
     
     
         7 . The method as in  claim 1 , where the metal layer is comprised of Titanium, where the metal feature is comprised of Copper, where the selected solder material is comprised of Indium, and where the predetermined value of the voltage potential is in a range of about 1V to about 2V. 
     
     
         8 . The method as in  claim 1 , where the metal layer is comprised of Titanium, where the metal feature is comprised of Copper, where the selected solder material is comprised of Indium, and where the predetermined value of the voltage potential is in a range of about 1.875V to about 2V. 
     
     
         9 . The method as in  claim 1 , where the reference electrode is comprised of Ag/AgCl in 3M KCl, and where the counter electrode is comprised of a Pt mesh. 
     
     
         10 . The method as in  claim 1 , where the substrate comprises a recess made in a surface thereof, where the metal feature has a substantially circular ring shape, and where the recess is disposed within a circumference of the metal feature. 
     
     
         11 . An apparatus, comprising:
 a tank containing a plating bath of an electroplating cell, the plating bath comprising a selected solder material;   a working electrode immersed in the plating bath, the working electrode comprised of a structure that comprises a semiconductor substrate having a metal layer disposed on a surface and a metal feature disposed on the metal layer;   a reference electrode and a counter electrode immersed in the plating bath; and   a power supply connected with a potentiostat configured to maintain a voltage potential of the working electrode at a predetermined constant value with respect to the reference electrode to deposit the selected solder material selectively only on the metal feature and not on the metal layer.   
     
     
         12 . The apparatus as in  claim 11 , where the metal layer is comprised of Titanium and where the metal feature is comprised of Copper. 
     
     
         13 . The apparatus as in  claim 11 , where the selected solder material is comprised of Indium. 
     
     
         14 . The apparatus as in  claim 13 , where the plating bath is comprised of one of Indium Sulfate, Indium Chloride, Indium Methanesulfonate, Indium Acetate or Indium oxide and is further comprised of a conductivity salt or acid comprised of one of Sulfuric acid, Hydrochloric acid, Methane Sulfonic acid or Sulfamic acid. 
     
     
         15 . The apparatus as in  claim 14 , where the plating bath is further comprised of a wetting agent. 
     
     
         16 . The apparatus as in  claim 11 , where the selected solder material is comprised of one of Tin, Tin-Silver, Tin-Silver-Copper, Indium-Tin, Tin-Lead, Tin-Bismuth and Tin-Gold. 
     
     
         17 . The apparatus as in  claim 11 , where the metal layer is comprised of Titanium, where the metal feature is comprised of Copper, where the selected solder material is comprised of Indium, and where the predetermined constant value of the voltage potential is in a range of about 1V to about 2V. 
     
     
         18 . The apparatus as in  claim 11 , where the metal layer is comprised of Titanium, where the metal feature is comprised of Copper, where the selected solder material is comprised of Indium, and where the predetermined constant value of the voltage potential is in a range of about 1.875V to about 2V. 
     
     
         19 . The apparatus as in  claim 11 , where the reference electrode is comprised of Ag/AgCl in 3M KCl, and where the counter electrode is comprised of a Pt mesh. 
     
     
         20 . The apparatus as in  claim 11 , where the semiconductor substrate is comprised of Silicon having a recess made in a surface thereof, where the metal feature has a substantially circular ring shape, where the recess is disposed within a circumference of the metal feature, and where an edge of the recess is spaced apart from an inner edge of the metal feature by a distance of about 10 μm or less.