Method of direct plating of copper on a substrate structure

Abstract

The present invention teaches a method for depositing a copper seed layer onto a substrate surface, generally onto a barrier layer. The barrier layer may include a refractory metal and/or a group 8, 9 or 10 metal. The method includes cathodically pre-treating the substrate in an acid-containing solution. The substrate is then placed into a copper solution (pH≧7.0) that includes complexed copper ions and a current or bias is applied across the substrate surface. The complexed copper ions are reduced to deposit a copper seed layer onto the barrier layer. In one aspect, a complex alkaline bath is then used to electrochemically plate a gapfill layer on the substrate surface, followed by overfill in the same bath. In another aspect, an acidic bath ECP gapfill process and overfill process follow the alkaline seed layer process.

1 . A method for depositing copper onto a substrate surface, wherein the substrate surface comprises an interlayer, comprising: 
 depositing an interlayer on a substrate surface;    pre-treating the substrate surface to remove unwanted deposits from the surface of the interlayer by a cathodic treatment in an acid-containing bath to reduce a critical current density during plating; and    depositing a first copper layer onto the interlayer, wherein the first copper layer is a continuous copper layer and wherein the process of depositing the first copper layer onto the interlayer comprises: 
 placing the substrate surface into contact with a copper solution, wherein the copper solution comprises complexed copper ions, a complexing agent and a pH equal to or greater than 7.0; and  
 applying a first plating bias to the substrate surface.  
   
   
   
       2 . The method of  claim 1 , wherein the interlayer is selected from the group consisting of cobalt, titanium, titanium nitride, titanium silicon nitride, tantalum, tantalum nitride, tantalum silicon nitride, tungsten, tungsten nitride, a Ti—W alloy, ruthenium, a ruthenium-tantalum alloy, rhodium, osmium or iridium.  
   
   
       3 . The method of  claim 1 , wherein the complexed copper ions are selected from the group consisting of copper ED, copper EDTA, copper citrate and combinations thereof.  
   
   
       4 . The method of  claim 1 , wherein the acid-containing bath is positioned on the same copper plating system as the copper solution.  
   
   
       5 . The method of  claim 1 , wherein the cathodic treatment is performed at a potential in the range of about 0 volt to about −1.0 volt.  
   
   
       6 . The method of  claim 1 , wherein the cathodic treatment is performed at a current density in the range of about 0.05 mA/cm 2  to about 5 mA/cm 2 .  
   
   
       7 . The method of  claim 1 , wherein the acid-containing bath contains sulfuric acid, wherein the concentration of the sulfuric acid is in the range between about 10 g/l to about 50 g/l.  
   
   
       8 . The method of  claim 1 , wherein the process of applying a first plating bias comprises plating copper onto the interlayer with a plating current that is at least equal to a critical current density.  
   
   
       9 . The method of  claim 8 , wherein the critical current density is less than 10 mA/cm 2 .  
   
   
       10 . The method of  claim 1 , further comprising depositing a second copper layer onto the first copper layer, wherein the process of depositing the second copper layer comprises: 
 placing the substrate surface into a second copper solution, wherein the second copper solution is acidic and includes free-copper ions; and    applying a second plating bias to the substrate surface.    
   
   
       11 . The method of  claim 10 , further comprising: 
 applying a third plating bias to the substrate surface while in contact with the second copper solution to deposit a third copper layer onto the second copper layer.    
   
   
       12 . The method of  claim 1 , further comprising: 
 applying a second plating bias to the substrate surface while in contact with the copper solution to deposit a second copper layer onto the first copper layer.    
   
   
       13 . The method of  claim 1 , further comprising: 
 applying a nucleation bias to the substrate surface after placing the substrate surface into the copper solution and prior to applying a first plating bias to the substrate surface, the nucleation bias being configured to generate a first current density across the substrate surface greater than a critical current density.    
   
   
       14 . The method of  claim 2 , wherein the interlayer is an interlayer on which a discontinuous copper film has been deposited.  
   
   
       15 . A method for depositing copper onto a substrate surface, wherein the substrate surface comprises an interlayer, comprising: 
 depositing an interlayer on a substrate surface;    pre-treating the substrate surface to remove unwanted deposits from the surface of the interlayer by a cathodic treatment in an acid-containing bath to reduce a critical current density during plating;    depositing a first copper layer onto the interlayer, wherein the first copper layer is a continuous copper layer and wherein the process of depositing the first copper layer onto the interlayer comprises: 
 placing the substrate surface into contact with a copper solution, wherein the copper solution comprises complexed copper ions, a complexing agent and a pH equal to or greater than 7; and  
 applying a first plating bias to the substrate surface; and  
   applying a second plating bias to the substrate surface while in contact with the copper solution to deposit a second copper layer onto the first copper layer.    
   
   
       16 . The method of  claim 15 , wherein the interlayer is selected from the group consisting of cobalt, titanium, titanium nitride, titanium silicon nitride, tantalum, tantalum nitride, tantalum silicon nitride, tungsten, tungsten nitride, a Ti—W alloy, ruthenium, a ruthenium-tantalum alloy, rhodium, osmium and iridium.  
   
   
       17 . The method of  claim 15 , wherein the complexed copper ions are selected from the group consisting of copper ED, copper EDTA, copper citrate and combinations thereof.  
   
   
       18 . The method of  claim 15 , further comprising: 
 applying a third plating bias to the substrate surface while in contact with the copper solution to deposit a third copper layer onto the second copper layer.    
   
   
       19 . A method for depositing copper onto a substrate surface, wherein the substrate surface comprises a ruthenium-tantalum alloy, comprising: 
 depositing a ruthenium-tantalum alloy on a substrate surface; and    depositing a first copper layer onto the ruthenium-tantalum alloy, wherein the first copper layer is a continuous copper layer and wherein the process of depositing the first copper layer onto the ruthenium-tantalum alloy comprises: 
 placing the substrate surface into contact with a copper solution, wherein the copper solution comprises complexed copper ions, a complexing agent and a pH equal to or greater than 7.0; and  
 applying a first plating bias to the substrate surface.  
   
   
   
       20 . The method of  claim 19 , wherein the ruthenium-tantalum alloy contains between about 70 atomic % and about 95 atomic % of ruthenium and the balance tantalum.  
   
   
       21 . The method of  claim 20 , wherein the thickness of the ruthenium-tantalum alloy is between about 5 Å to about 200 Å.  
   
   
       22 . The method of  claim 19 , wherein the complexed copper ions are selected from the group consisting of copper ED, copper EDTA, copper citrate and combinations thereof.  
   
   
       23 . The method of  claim 19 , further comprising depositing a second copper layer onto the first copper layer wherein the process of depositing the second copper layer comprises: 
 applying a second plating bias to the substrate surface while in contact with the copper solution to deposit a second copper layer onto the first copper layer.