Method for processing a semiconductor substrate having a copper surface disposed thereon and structure formed

Abstract

A semiconductor wafer having copper bondpads ( 17 ) that are free of voids ( 13 ) and a method for coating the copper bondpads ( 17 ) with solderable or wirebondable metals such that the copper bondpads ( 17 ) are free of the voids ( 13 ). The void free metal coatings are achieved using a dual activation process. In a first activation step ( 27 ), the copper bondpads ( 17 ) are activated by placing them in a palladium bath. In a second activation step ( 28 ), the bondpads are placed in a nickel—boron bath. After the dual activation, the copper bondpads ( 17 ) are coated with a layer of nickel—phosphorous or palladium. The nickel—phosphorous or palladium layer may be coated with a layer of gold for subsequent formation of solder balls or wirebonds thereon.

1 . A method for processing a semiconductor substrate having a copper surface disposed thereon in preparation for subsequent bonding operations, comprising the steps of: 
 providing the semiconductor substrate having copper disposed thereon, the copper having a bonding surface;    cleaning the bonding surface;    activating the bonding surface first activation process;    activating the bonding surface second activation process that is di first activation process; and    depositing one of a solderable metal on the bonding surface.    
     
     
         2 . The method of  claim 1 , wherein the step of cleaning the bonding surface includes removing organic contaminants from the bonding surface.  
     
     
         3 . The method of  claim 2 , wherein the step of removing organic contaminants from the bonding surface includes using an oxygen plasma to remove the bonding surface.  
     
     
         4 . The method of  claim 1 , wherein the step of cleaning the bonding surface includes removing inorganic contaminants from the bonding surface.  
     
     
         5 . The method of  claim 4 , wherein the step of cleaning the bonding surface includes using a buffered oxide etchant.  
     
     
         6 . The method of  claim 1 , wherein the step of activating the bonding surface a first time includes treating the bonding surface with an activation solution comprising palladium.  
     
     
         7 . The method of  claim 1 , wherein the step of activating the bonding surface a second time includes performing nickel—boron electroless plating.  
     
     
         8 . The method of  claim 7 , further including performing the step of activating the bonding surface for a first time ranging between approximately 20 seconds and approximately 50 seconds and performing the step of nickel—boron electroless plating for a time ranging between approximately 1.5 minutes and approximately 8 minutes.  
     
     
         9 . The method of  claim 7 , wherein the nickel—boron has a thickness ranging between approximately 0.1 microns and approximately 0.5 microns.  
     
     
         10 . The method of  claim 7 , wherein the step of depositing one of a solderable or a wirebondable metal on the bonding surface includes plating nickel—phosphorous on the nickel—boron.  
     
     
         11 . The method of  claim 1 , wherein the step of depositing one of a solderable or a wirebondable metal on the bonding surface includes depositing a layer of nickel—phosphorous by electroless plating.  
     
     
         12 . The method of  claim 1 , wherein the step of depositing one of a solderable or a wirebondable metal on the bonding surface includes depositing a layer of palladium by electroless plating.  
     
     
         13 . A method for forming a nickel layer on copper, wherein the copper is disposed on a semiconductor wafer, comprising the steps of: 
 cleaning a surface of the copper;    performing a first activation step;    performing a second activation step to activate the surface; and    plating one of a solderable or a wirebondable metal on the activated surface.    
     
     
         14 . The method of  claim 13 , further including the step of forming an oxidation protection layer on the one of a solderable or a wirebondable metal.  
     
     
         15 . The method of  claim 14  wherein the oxidation protection layer is gold.  
     
     
         16 . The method of  claim 13 , wherein the step of performing the first activation step includes activating the surface in a palladium activation bath and the step of performing the second activation step includes depositing a layer of nickel-boron using electroless plating.  
     
     
         17 . The method of  claim 16 , further including performing the first and second activation steps and performing the step of plating one a solderable or a wirebondable metal at temperatures less than approximately 90 degrees Celsius.  
     
     
         18 . A semiconductor wafer, comprising: 
 a semiconductor wafer having copper bond pads;    a layer of palladium disposed on the copper bond pads;    a layer of electroless nickel-boron disposed on the layer of palladium; and    one of a solderable or a wirebondable layer disposed on the electroless nickel—boron layer.    
     
     
         19 . The semiconductor wafer of  claim 18 , wherein the one of a solderable or a wirebondable layer is a layer comprising electroless nickel—palladium.  
     
     
         20 . The semiconductor wafer of  claim 18 , further including an oxidation protection layer disposed on the layer of electroless nickel—boron.  
     
     
         21 . The semiconductor wafer of  claim 20 , wherein the oxidation protection layer is a layer of gold.  
     
     
         22 . The semiconductor wafer of  claim 18 , wherein the one of a solderable or a wirebondable layer is a layer of electroless palladium.