Prevention of contamination on plated wafer surfaces

Abstract

In order to prevent salt precipitation after plating a wafer surface, the described cleaning process applied to the wafer covered with a plating solution uses a complex former solution or the solution of an acid. The presence of a suitable complex former enhances the solubility of heavy metal ions typically by orders of magnitudes. Hereby a precipitation of salts is avoided. After plating, the wafer is necessarily covered with a plating solution. In a first cleaning step, the solution of the complex former is applied on the wafer surface. This procedure reduces the amounts of plating salts in the solution and keeps the solubility of the remaining salts high at the same time due to a formation of soluble metal complexes. After that step, the wafer is completely covered with clean complex solution. This solution is removed in a following step by a stream of de-ionized water, leading to a clean, water-covered wafer. The drying of the wafer can be performed in a conventional procedure (e.g. spin dryer) resulting in a clean, dry wafer. In particular, the following aqueous solutions of different complex formers are applied in various concentrations: Citrate (concentration 0.5-1.0 mol/kg); Acetate (concentration 0.5 mol/kg); EDTA (concentration 0.2-0.5 mol/kg); Ammonia (concentration 0.1-1.0 mol/kg); Hydrochloric acid; Phosphoric Acid.

What is claimed is:  
     
         1 . A method for preventing contamination after plating a metal or an alloy on a surface of a substrate comprising: 
 a) providing a plating solution on the surface of the substrate;    b) electroplating or electrolysis plating the metal or alloy on the surface of the substrate; and,    c) introducing a stabilizing agent which keeps metal or alloy ions in the plating solution.    
     
     
         2 . Method according to  claim 1 , wherein in said introducing step (c) the stabilizing agent prevents formation of precipitated salts on the surface of the substrate.  
     
     
         3 . Method according to  claim 1 , wherein the stabilizing agent comprises an aqueous solution of a complexing agent for the plating metals.  
     
     
         4 . Method according to  claim 3 , wherein the complexing agent comprises an organic or inorganic compound.  
     
     
         5 . Method according to  claim 3 , wherein the complexing agent comprises a mixture of an organic compound and an inorganic compound.  
     
     
         6 . Method according to  claim 3 , wherein the aqueous solution of the complexing agent for the plating metals comprises Citrate, Acetate, EDTA, or Ammonia.  
     
     
         7 . Method according to  claim 6 , wherein in said introducing step (c) at least one of the aqueous solutions of the complexing agent is introduced in the following concentrations: 
 Citrate in a preferred concentration of about 0.5 to about 1.0 mol/kg,    Acetate in a preferred concentration of about 0.5 mol/kg,    EDTA in a preferred concentration of about 0.2 to about 0.5 mol/kg, and/or    Ammonia in a preferred concentration of about 0.1 to about 1.0 mol/kg.    
     
     
         8 . Method according to  claim 1 , wherein the stabilizing agent comprises an acid.  
     
     
         9 . Method according to  claim 8 , wherein the acid does not form a low-soluble salt with the plated metals.  
     
     
         10 . Method according to  claim 8 , wherein the acid comprises an organic or inorganic compound.  
     
     
         11 . Method according to  claim 8 , wherein the acid comprises a mixture of an organic compound and an inorganic compound.  
     
     
         12 . Method according to  claim 8 , wherein the acid comprises aqueous solutions of Hydrochloric Acid, Sulfuric Acid, or Phosphoric Acid.  
     
     
         13 . Method according to  claim 12 , wherein in said introducing step (c) at least one of the aqueous solutions is introduced in the following concentrations: 
 Hydrochloric Acid in a preferred concentration of about 0.1 mol/kg,    Hydrochloric Acid in a preferred concentration of about 0.01 mol/kg,    Sulfuric Acid in a preferred concentration of about 0.05 mol/kg, and/or    Phosphoric Acid in a preferred concentration of about 0.1 mol/kg.    
     
     
         14 . Method according to  claim 1 , wherein the stabilizing agent comprises a mixture of an aqueous solution of a complexing agent for the plating metals and an acid.  
     
     
         15 . Method according to  claim 1 , wherein the stabilizing agent is contained in the plating solution.  
     
     
         16 . Method according to  claim 1 , wherein the substrate comprises a semiconductor wafer.  
     
     
         17 . A solution for preventing contamination after plating a metal or an alloy on a surface of a substrate comprising: 
 a plating solution; and    a stabilizing agent which keeps metal or alloy ions in the plating solution.    
     
     
         18 . The solution according to  claim 17 , wherein the stabilizing agent prevents formation of precipitated salts on the surface of the substrate.  
     
     
         19 . The solution according to  claim 17 , wherein the stabilizing agent comprises an aqueous solution of a complexing agent for the plating metals.  
     
     
         20 . The solution according to  claim 19 , wherein the complexing agent comprises an organic or inorganic compound.  
     
     
         21 . The solution according to  claim 19 , wherein the complexing agent comprises a mixture of an organic compound and an inorganic compound.  
     
     
         22 . The solution according to  claim 19 , wherein the aqueous solution of the complexing agent for the plating metals comprises Citrate, Acetate, EDTA, or Ammonia.  
     
     
         23 . The solution according to  claim 22 , wherein at least one of the aqueous solutions of the complexing agent comprises: 
 Citrate in a preferred concentration of about 0.5 to about 1.0 mol/kg,    Acetate in a preferred concentration of about 0.5 mol/kg,    EDTA in a preferred concentration of about 0.2 to about 0.5 mol/kg, and/or    Ammonia in a preferred concentration of about 0.1 to about 1.0 mol/kg.    
     
     
         24 . The solution according to  claim 17 , wherein the stabilizing agent comprises an acid.  
     
     
         25 . The solution according to  claim 24 , wherein the acid does not form a low-soluble salt with the plated metals.  
     
     
         26 . The solution according to  claim 24 , wherein the acid comprises an organic or inorganic compound.  
     
     
         27 . The solution according to  claim 24 , wherein the acid comprises a mixture of an organic compound and an inorganic compound.  
     
     
         28 . The solution according to  claim 24 , wherein the acid comprises aqueous solutions of Hydrochloric Acid, Sulfuric Acid, or Phosphoric Acid.  
     
     
         29 . The solution according to  claim 28 , wherein at least one of the aqueous solutions of the acid comprises: 
 Hydrochloric Acid in a preferred concentration of about 0.1 mol/kg,    Hydrochloric Acid in a preferred concentration of about 0.01 mol/kg,    Sulfuric Acid in a preferred concentration of about 0.05 mol/kg, and/or    Phosphoric Acid in a preferred concentration of about 0.1 mol/kg.    
     
     
         30 . The solution according to  claim 17 , wherein the stabilizing agent comprises a mixture of an aqueous solution of a complexing agent for the plating metals and an acid.  
     
     
         31 . The solution according to  claim 17 , wherein the stabilizing agent is contained in the plating solution.  
     
     
         32 . The solution according to  claim 17 , wherein the substrate comprises a semiconductor wafer.  
     
     
         33 . In a method for plating a metal alloy on a surface of a substrate by electrolytic activity using a plating solution on the surface wherein the improvement comprises introducing a stabilizing agent onto the substrate surface in order to keep metal alloy ions in the plating solution.