Copper-metallized integrated circuits having electroless thick copper bond pads

Abstract

A metal structure ( 100 ) for a contact pad of a semiconductor device, which has interconnecting traces of a first copper layer ( 102 ). The substrate is protected by an insulating overcoat ( 104 ). In the structure, the first copper layer of first thickness and first crystallite size is selectively exposed by a window ( 110 ) in the insulating overcoat. A layer of second copper ( 105 ) of second thickness covers conformally the exposed first copper layer. The second layer is deposited by an electroless process and consists of a transition zone, adjoining the first layer and having copper crystallites of a second size, and a main zone having crystallites of the first size. The second thickness is selected so that the distance a void from the second layer can migrate during the life expectancy of the structure is smaller than the combined thicknesses of the first and second layers. A layer of nickel ( 106 ) is on the second copper layer, and a layer of noble metal ( 107 ) is on the nickel layer.

1 . A method for fabricating a metal structure for a contact pad of a semiconductor device having interconnecting traces of a first copper layer of a first thickness, the device protected by an insulating overcoat, comprising the steps of: opening a window in the insulating overcoat to selectively expose a portion of the first copper layer;
 depositing a layer of second copper on the exposed portion of the first copper layer by an electroless plating technique, the second layer having a second thickness; selecting the second thickness so that the distance a void from the second layer can migrate within the life expectancy of the metal structure is smaller than the combined thicknesses of the first and second layers;   activating the second copper by exposing the second copper to an acetic palladium chloride solution so that a controlled portion of the second copper is substituted by palladium;   depositing a layer of nickel on the second copper layer; and   depositing a layer of noble metal on the nickel layer.   
     
     
         2 . The method according to  claim 1  wherein the step of depositing the nickel layer uses an electroless plating technique. 
     
     
         3 . The method according to  claim 1  wherein the noble metal is palladium. 
     
     
         4 . The method according to  claim 3  wherein the step of depositing a palladium layer uses an electroless plating technique. 
     
     
         5 . The method according to  claim 1  wherein the step of depositing a noble metal layer comprises first a step of electrolessly plating a layer of palladium on the nickel layer and then forming an outermost layer of gold by an immersion technique. 
     
     
         6 . The method according to  claim 1  wherein the noble metal is gold. 
     
     
         7 . The method according to  claim 6  wherein the step of depositing the layer of gold uses an electroless plating technique.