Alloy diffusion barrier layer

Abstract

A microelectronic device includes a reflow structure. The reflow structure has a copper-containing member and a solder member, and a barrier layer between them. The barrier layer has metal grains, with a diffusion barrier filler between the metal grains. The metal grains include at least a first metal and a second metal, each selected from nickel, cobalt, lanthanum, and cerium, with each having a concentration in the metal grains of at least 10 weight percent. The diffusion barrier filler includes at least a third metal, selected from tungsten and molybdenum. A combined concentration of tungsten and molybdenum in the diffusion barrier filler is higher than in the metal grains to provide a desired resistance to diffusion of copper. The barrier layer includes 2 weight percent to 15 weight percent of the combined concentration of tungsten, and molybdenum. A bump bond structure and a lead frame package are disclosed.

What is claimed is: 
     
         1 . A microelectronic device, comprising:
 a bond pad electrically connected to a semiconductor die;   copper on the bond pad;   a layer on the copper, the layer including:
 at least 10 weight percent of a first metal selected from the group consisting of nickel, cobalt, lanthanum, and cerium; 
 at least 10 weight percent of a second metal, different from the first metal, selected from the group consisting of nickel, cobalt, lanthanum, and cerium; and 
 at least 2 weight percent of a third metal selected from the group consisting of tungsten and molybdenum; and 
   solder on the layer.   
     
     
         2 . The microelectronic device of  claim 1 , wherein the third metal is in between the grains of the first metal or the grains of the second metal. 
     
     
         3 . The microelectronic device of  claim 1 , wherein the third metal is in between the grains of the first metal and the grains of the second metal. 
     
     
         4 . The microelectronic device of  claim 1  further comprising intermetallic compounds between the solder and the layer. 
     
     
         5 . The microelectronic device of  claim 1 , wherein a combined concentration of tungsten and molybdenum in the layer is greater than 2 weight percent and less than 15 weight percent. 
     
     
         6 . The microelectronic device of  claim 1 , wherein:
 the layer includes at least 10 weight percent of nickel;   the layer includes at least 10 weight percent of cobalt; and   the layer includes less than 1 weight percent lanthanum and cerium.   
     
     
         7 . The microelectronic device of  claim 1 , wherein the layer includes less than 1 weight percent molybdenum. 
     
     
         8 . The microelectronic device of  claim 1 , wherein a thickness of the layer is between 2 microns and 20 microns, and wherein the solder includes at least 25 weight percent tin. 
     
     
         9 . The microelectronic device of  claim 4 , wherein the intermetallic compound is more malleable than Ni 3 Sn 4 . 
     
     
         10 . The microelectronic device of  claim 4 , wherein the intermetallic compound does not include copper and tin. 
     
     
         11 . A microelectronic device, comprising:
 a bond pad electrically connected to a semiconductor die;   copper on the bond pad;   a layer on the copper, the layer including:
 at least 10 weight percent of a first metal selected from the group consisting of lanthanum, and cerium; 
 at least 10 weight percent of a second metal, different from the first metal, selected from the group consisting of lanthanum, and cerium; and 
 at least 2 weight percent of a third metal selected from the group consisting of tungsten and molybdenum; and 
   solder on the layer.   
     
     
         12 . The microelectronic device of  claim 11 , wherein the third metal is in between the grains of the first metal or the grains of the second metal. 
     
     
         13 . The microelectronic device of  claim 11 , wherein the third metal is in between the grains of the first metal and the grains of the second metal. 
     
     
         14 . A microelectronic device, comprising:
 a bond pad electrically connected to a semiconductor die;   copper on the bond pad;   a layer on the copper, the layer including:
 a first metal selected from the group consisting of lanthanum, and cerium; and 
 a second metal selected from the group consisting of tungsten and molybdenum in between the first metal; and 
   solder on the layer.   
     
     
         15 . The microelectronic device of  claim 11 , wherein the second metal encloses the first metal from a cross-sectional view of the microelectronic device. 
     
     
         16 . The microelectronic device of  claim 11  further comprising intermetallic compounds between the solder and the layer. 
     
     
         17 . The microelectronic device of  claim 16 , wherein the intermetallic compound does not include copper and tin.