Method of direct plating of copper on a ruthenium alloy

Abstract

A method is disclosed for depositing a copper seed layer onto a substrate surface, generally onto a barrier layer that is an alloy of a group VIII metal and a refractory metal. In one aspect, the alloy consists of at least 50% ruthenium and the balance a copper diffusion barrier material. A copper layer is electroplated on the alloy directly. In one aspect, the surface of the barrier layer is conditioned prior to plating to improve adhesion and reduce the critical current density for plating on the barrier layer. The conditioning may include cathodic pre-treatment or a plasma pre-treatment in a hydrogen or hydrogen/helium mixture. In one aspect, the substrate surface is immersed in an acidic plating bath and a nucleation waveform is applied to form a seed layer. In another aspect, the substrate is immersed in a neutral or alkaline copper solution that includes complexed copper ions.

1 . A method of processing a substrate, comprising: 
 providing a dielecric layer on a substrate;    forming features into the surface of the dielectric layer;    depositing an electrically continuous barrier/adhesion layer onto the surface of the dielectric layer, wherein the barrier/adhesion layer comprises an alloy, wherein at least 50 atomic % of the alloy comprises a metal from the group consisting of ruthenium, rhodium, palladium, cobalt, nickel, osmium, iridium, platinum and combinations thereof and wherein the balance of the alloy is selected from the group consisting of tantalum, titanium, zirconium, hafnium, niobium, molybdenum, tungsten and combinations thereof; and    directly plating a first copper layer onto the barrier/adhesion layer, the first copper layer being an electrically continuous layer, wherein the process of directly plating a first copper layer comprises: 
 placing the barrier/adhesion layer into contact with a copper solution, wherein the copper solution comprises copper ions; and  
 applying a first plating waveform to the barrier/adhesion layer.  
   
   
   
       2 . The method of  claim 1 , further comprising conditioning the surface of the electrically continuous barrier/adhesion layer prior to plating the first copper layer.  
   
   
       3 . The method of  claim 2 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises: 
 placing the substrate in a plasma-etch chamber;    flowing a process gas into the chamber, wherein the process gas comprises at least one of the group consisting of hydrogen, a helium-hydrogen mixture and combinations thereof; and    generating a plasma in the chamber.    
   
   
       4 . The method of  claim 2 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises cathodically pre-treating the barrier/adhesion layer in an acid-containing bath.  
   
   
       5 . The method of  claim 4 , wherein the acid-containing bath contains sulfuric acid, wherein the concentration of the sulfuric acid is in the range between about 10 g/l and about 50 g/l.  
   
   
       6 . The method of  claim 4 , wherein cathodically pre-treating the barrier/adhesion layer further comprises performing the cathodic pre-treatment at a current density in the range of about 1 mA/cm 2  to about 5 mA/cm 2 .  
   
   
       7 . The method of  claim 4 , wherein the cathodic pre-treatment is performed at a potential in the range of about 0 volt to about −1.0 volt vs. AgCl.  
   
   
       8 . The method of  claim 2 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises cathodically pre-treating the barrier/adhesion layer in an alkaline or neutral bath.  
   
   
       9 . The method of  claim 2 , wherein the process of directly plating a first copper layer onto the barrier/adhesion layer occurs less than about 150 minutes after the process of conditioning the surface of the barrier/adhesion layer.  
   
   
       10 . The method of  claim 1 , wherein the process of applying a first plating waveform to the barrier/adhesion layer further comprises: 
 applying a nucleation waveform to the barrier/adhesion layer, the nucleation waveform being configured to generate a first current density across the barrier/adhesion layer greater than a critical current density.    
   
   
       11 . The method of  claim 1 , further comprising applying a second plating waveform to the first copper layer while in contact with the copper solution to deposit a second copper layer onto the first copper layer.  
   
   
       12 . The method of  claim 1 , wherein the copper solution further comprises a complexing agent and a pH equal to or greater than 7.0.  
   
   
       13 . The method of  claim 12 , further comprising depositing a second copper layer onto the first copper layer, wherein the process of depositing the second copper layer comprises: 
 placing the first copper layer into a second copper solution, wherein the second copper solution is acidic and includes free-copper ions; and    applying a second plating waveform to the first copper layer.    
   
   
       14 . The method of  claim 1 , wherein the barrier/adhesion layer comprises a Ru—Ta alloy of at least about 50 atomic % ruthenium and wherein the balance of the alloy is tantalum.  
   
   
       15 . The method of  claim 14 , wherein the features have sidewalls and the thickness of the barrier/adhesion layer is between about 10 Å and about 50 Å on the sidewalls.  
   
   
       16 . The method of  claim 2  wherein the process of conditioning the surface of the barrier/adhesion layer and the process of plating the first copper layer take place on the same copper plating system.  
   
   
       17 . A method of processing a substrate, comprising: 
 providing a dielecric layer on a substrate;    forming features into the surface of the dielectric layer;    depositing an electrically continuous barrier/adhesion layer onto the surface of the dielectric layer, wherein the barrier/adhesion layer comprises a Ru—Ta alloy of between about 70 atomic % and 95 atomic % ruthenium and wherein the balance of the alloy is tantalum;    conditioning the surface of the electrically continuous barrier/adhesion layer prior to plating the first copper layer; and    directly plating a first copper layer onto the barrier/adhesion layer, the first copper layer being an electrically continuous layer wherein the process of directly plating a first copper layer comprises: 
 placing the barrier/adhesion layer into contact with a copper solution, wherein the copper solution comprises copper ions; and  
 applying a first plating waveform to the barrier/adhesion layer.  
   
   
   
       18 . The method of  claim 17 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises: 
 placing the substrate in a plasma-etch chamber;    flowing a process gas into the chamber, wherein the process gas comprises at least one of the group consisting of hydrogen, a helium-hydrogen mixture and combinations thereof; and generating a plasma in the chamber.    
   
   
       19 . The method of  claim 17 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises cathodically pre-treating the barrier/adhesion layer in an acid-containing bath.  
   
   
       20 . The method of  claim 19 , wherein cathodically pre-treating the barrier/adhesion layer further comprises performing the cathodic pre-treatment at a current density in the range of about 1 mA/cm 2  to about 5 mA/cm 2 .  
   
   
       21 . The method of  claim 19 , wherein the cathodic pre-treatment is performed at a potential in the range of about 0 volt to about −1.0 volt vs. AgCl.  
   
   
       22 . The method of  claim 17 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises cathodically pre-treating the barrier/adhesion layer in an alkaline or neutral bath.  
   
   
       23 . The method of  claim 17 , wherein the process of directly plating a first copper layer onto the barrier/adhesion layer occurs less than about 150 minutes after the process of conditioning the surface of the barrier/adhesion layer.  
   
   
       24 . The method of  claim 17 , wherein the process of applying a first plating waveform to the substrate surface further comprises: 
 applying a nucleation waveform to the substrate surface, the nucleation waveform being configured to generate a first current density across the substrate surface greater than a critical current density.    
   
   
       25 . The method of  claim 17 , further comprising applying a second plating waveform to the substrate surface while in contact with the copper solution to deposit a second copper layer onto the first copper layer.  
   
   
       26 . The method of  claim 17 , wherein the copper solution further comprises a complexing agent and a pH equal to or greater than 7.0.  
   
   
       27 . The method of  claim 26 , further comprising depositing a second copper layer onto the first copper layer, wherein the process of depositing the second copper layer comprises: 
 placing the first copper layer into a second copper solution, wherein the second copper solution is acidic and includes free-copper ions; and    applying a second plating waveform to the first copper layer.    
   
   
       28 . The method of  claim 17 , wherein the composition of the Ru—Ta alloy is not homogeneous through the thickness of the alloy.  
   
   
       29 . The method of  claim 28 , wherein the Ru—Ta alloy is ruthenium-rich adjacent the interface between the barrier/adhesion layer and the first copper layer and is tantalum-rich adjacent the interface between the barrier/adhesion layer and the dielectric layer.  
   
   
       30 . The method of  claim 17  wherein the features have sidewalls and the thickness of the barrier/adhesion layer is between about 10 Å and about 50 Å on the sidewalls.  
   
   
       31 . A method of plating an adherent copper layer onto a barrier layer, comprising: 
 depositing an electrically continuous barrier/adhesion layer onto a substrate surface, wherein the barrier/adhesion layer comprises a Ru—Ta alloy of between about 70 atomic % and 95 atomic % ruthenium and wherein the balance of the alloy is tantalum;    conditioning the surface of the electrically continuous barrier/adhesion layer prior to plating the first copper layer; and    directly plating a first copper layer onto the barrier/adhesion layer, the first copper layer being an electrically continuous layer wherein the process of directly plating a first copper layer comprises: 
 placing the substrate surface into contact with a copper solution, wherein the copper solution comprises copper ions; and  
 applying a first plating waveform to the substrate surface.  
   
   
   
       32 . The method of  claim 31 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises: 
 placing the substrate in a plasma-etch chamber;    flowing a process gas into the chamber, wherein the process gas comprises at least one of the group consisting of hydrogen, a helium-hydrogen mixture and combinations thereof; and    generating a plasma in the chamber.    
   
   
       33 . The method of  claim 31 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises cathodically pre-treating the barrier/adhesion layer.  
   
   
       34 . The method of  claim 31 , wherein the process of conditioning the surface of the barrier/adhesion layer comprises cathodically pre-treating the barrier/adhesion layer in an acid-containing bath at a current density in the range of about 1 mA/cm 2  to about 5 mA/cm 2 .  
   
   
       35 . The method of  claim 31 , wherein the cathodic pre-treatment is performed at a potential in the range of about 0 volt to about −1.0 volt vs. AgCl.  
   
   
       36 . The method of  claim 31 , wherein the process of directly plating a first copper layer onto the barrier/adhesion layer occurs less than about 150 minutes after the process of conditioning the surface of the barrier/adhesion layer.  
   
   
       37 . The method of  claim 31 , wherein the process of applying a first plating waveform to the substrate surface further comprises: 
 applying a nucleation waveform to the substrate surface, the nucleation waveform being configured to generate a first current density across the substrate surface greater than a critical current density.    
   
   
       38 . The method of  claim 31 , wherein the copper solution further comprises a complexing agent and a pH equal to or greater than 7.0.  
   
   
       39 . The method of  claim 31 , wherein the Ru—Ta alloy is ruthenium-rich adjacent the interface between the barrier/adhesion layer and the first copper layer and is tantalum-rich adjacent the interface between the barrier/adhesion layer and the dielectric layer.