Copper Plating Solutions and Method of Making and Using Such Solutions

Abstract

The present technology generally relates to copper plating solutions. Specifically, the present technology includes a copper plating solution comprising a source of copper ions and a conductivity salt wherein the copper plating solution has a pH between 1.7 and 3.5 as is essentially free of chloride ions. The present technology also relates to a method of using such copper plating solutions.

What is claimed is: 
     
         1 . A method of plating copper onto a substrate comprising:
 providing a substrate; and   contacting said substrate with a copper plating solution comprising a source of copper ions and a conductivity salt wherein said copper plating solution has a pH between about 1.7 and about 3.5 as is essentially free of chloride ions.   
     
     
         2 . The method of  claim 1  wherein said substrate is a metal seed layer on a silicon solar cell wafer. 
     
     
         3 . The method of  claim 1  wherein said source of copper ions is copper sulfate. 
     
     
         4 . The method of  claim 1  wherein said conductivity salt is lithium sulfate. 
     
     
         5 . The method of  claim 1  wherein said pH is between about 2.3 and about 3.0. 
     
     
         6 . The method of  claim 1  further comprising an additive selected from the group of imidazoles and imidazole derivatives, thiazoles and thiazole derivatives, compounds that contain a quaternary nitrogen atom such as thiazolium compounds and polymeric quaternary compounds. 
     
     
         7 . The method of  claim 6  wherein said additive is selected from the group of 2 mercaptoimidazole, 2 mercaptothiazole, 3-(carboxymethyl)benzothiazolium bromide, 2 mercapto-1-methylimidazole, 2 aminothiazole and Cyastat SN. 
     
     
         8 . A copper plating solution comprising:
 a source of copper ions; and   a conductivity salt   
       wherein said copper plating solution has a pH between about 1.7 and about 3.5 as is essentially free of chloride ions. 
     
     
         9 . The solution of  claim 8  wherein said source of copper ions is copper sulfate. 
     
     
         10 . The solution of  claim 8  wherein said conductivity salt is lithium sulfate. 
     
     
         11 . The solution of  claim 8  wherein said conductivity salt is sodium sulfate. 
     
     
         12 . The solution of  claim 8  wherein said pH is between about 2.3 and about 3.0. 
     
     
         13 . The solution of  claim 8  further comprising an additive selected from the group of imidazoles and imidazole derivatives, thiazoles and thiazole derivatives, compounds that contain a quaternary nitrogen atom such as thiazolium compounds and polymeric quaternary compounds. 
     
     
         14 . The solution of  claim 13  wherein said additive is selected from the group of 2 mercaptoimidazole, 2 mercaptothiazole, 3-(carboxymethyl)benzothiazolium bromide, 2 mercapto-1-methylimidazole, 2 aminothiazole and Cyastat SN.