Nickel plating process having controlled hydrogen concentration

Abstract

A flexible plating method by continuously controlling the hydrogen concentration of the plating bath by adding controlled amounts of hydrogen gas. The control of the hydrogen concentration is provided by selected distribution and number of nozzles and size of orifices; and predetermined pressure and duration of hydrogen gas flowing through the nozzles, wherein pressure and duration may be variable with time. The control of the hydrogen concentration is selected so that the concentration provides a ramp-up phase, needed for a rapid plating start, followed by a saturation phase, needed for consistent plating stability. With the metal layer plating process under control, the present invention discloses a robust, reliable and low-cost metal structure enabling electrical wire connections to the interconnecting copper metallization of ICs. The structure comprises a layer of barrier metal, preferably nickel, that resists copper diffusion, deposited on the non-oxidized copper surface. The structure further comprises an outermost bondable metal layer, preferably gold, unto which a metal wire is bonded for metallurgical connection.

We claim:  
     
         1 . A method for forming metallurgical connections between metal wires and bond pads positioned on integrated circuits having copper interconnecting metallization, comprising the steps of: 
 activating the surface of said copper metallization by creating a non-oxidized copper surface;    depositing a layer of seed metal;    providing a barrier metal plating bath;    continuously controlling the hydrogen concentration of said bath by adding hydrogen gas, whereby the plating process is controlled for improving metal deposition;    plating a layer of barrier metal that resists copper diffusion by electroless deposition in said bath, under continuously controlled hydrogen concentration;    plating an outermost layer of bondable metal by electroless or immersion deposition; and    bonding one of said metal wires onto said outermost metal.    
     
     
         2 . The method according to  claim 1  further including the steps of: 
 providing selected distribution and number of nozzles and size of orifices; and  
 controlling the pressure and duration of hydrogen gas flowing through said nozzles, and varying said pressure and duration with time.  
 
     
     
         3 . The method according to  claim 2  wherein said control of said hydrogen concentration is selected so that said concentration provides a ramp-up phase, needed for a rapid plating start, followed by a saturation phase, needed for consistent plating stability.  
     
     
         4 . The method according to  claim 1  wherein said barrier metal is selected from a group consisting of nickel, cobalt, chromium, molybdenum, titanium, tungsten, and alloys thereof.  
     
     
         5 . The method according to  claim 4  wherein said barrier layer has a thickness between 0.5 and 1.5 μm.  
     
     
         6 . The method according to  claim 1  wherein said bondable metal is selected from a group consisting of gold, platinum, and silver.  
     
     
         7 . The method according to  claim 1  further comprising the plating of an additional barrier layer directly over the plated barrier metal, including palladium, platinum, cobalt, or osmium, before the deposition of said bondable metal.  
     
     
         8 . The method according to  claim 1  wherein said seed metal is palladium or tin.  
     
     
         9 . The method according to  claim 1  wherein said metal wires are selected from a group consisting of gold, copper, aluminum, and alloys thereof.  
     
     
         10 . The method according to  claim 1  further comprising the step of bonding said metal wire to said outermost bondable metal.