Method of sputtering a nickel silicon alloy, especially useful for forming a solder bump barrier

Abstract

A nickel silicon alloy barrier layer formed between a metal bonding pad on an integrated circuit and a tin-based solder ball, for example, a lead-free solder. The nickel silicon alloy contains at least 2 wt % silicon and preferably less than 20 wt %. An adhesion layer may be formed between the barrier layer and the bonding pad. For copper metallization, the adhesion layer may contain titanium or tantalum; for aluminum metallization, it may be aluminum. The nickel silicon alloy may be deposited by magnetron sputtering. Commercially available NiS 4.5% sputter targets have provided a superior under-bump metallization (UBM) with lead-free tin solder bumps. Dopants other than silicon/may be used to reduce the magnetic permeability and provide other advantages of the invention.

1 . A method of solder bump bonding, comprising a first step of depositing by magnetron sputtering a nickel silicon alloy layer on a metallic contact pad of an integrated circuit. 
   
   
       2 . The method of  claim 1 , further comprising a second step of depositing a solder layer comprising tin on said nickel silicon alloy layer. 
   
   
       3 . The method of  claim 2 , further comprising bonding said solder layer to metallic contact regions formed in a support substrate. 
   
   
       4 . The method of  claim 1 , wherein said nickel silicon alloy layer comprises at least 2 wt % silicon and no more than 20 wt % silicon. 
   
   
       5 . The method of  claim 1 , wherein said first step includes applying a predetermined level of bias to a pedestal electrode supporting a substrate including said contact pad. 
   
   
       6 . The method of  claim 5 , wherein said predetermined level is selected to achieve a predetermined amount of compressive stress in said nickel silicon alloy layer. 
   
   
       7 . The method of  claim 1 , further comprising sputter depositing an adhesion layer between said metallic contact pad and said nickel silicon alloy layer. 
   
   
       9 . A method of solder bump bonding, comprising a first step of depositing by magnetron sputtering an alloy comprising nickel and a dopant lacking an unfilled d-shell of electrons to form a layer on a metallic contact pad of an integrated circuit, wherein said alloy comprises at least 90 wt % nickel and sufficient amount of said dopant to produce a magnetic permeability of said layer to be less than that of a layer consisting of nickel. 
   
   
       10 . The method of  claim 9 , wherein said dopant is chosen from the group consisting of magnesium, silicon, aluminum, gallium, and germanium.