Electroplated lead-free bump deposition

Abstract

A method of forming a metal feature on a workpiece with deposition is provided. The method includes providing an under bump metal layer for solder of an electronic device on the workpiece, depositing a substantially pure tin layer directly to the under bump metal layer, and depositing a tin silver alloy layer onto the substantially pure tin layer.

1 . A method of forming a metal feature on a workpiece with deposition, the method comprising: 
 providing an under bump metal layer for solder of an electronic device on the workpiece;    depositing a substantially pure tin layer directly to the under bump metal layer; and    depositing a tin silver alloy layer onto the substantially pure tin layer.    
     
     
         2 . The method of  claim 1 , wherein substantially all of the substantially pure tin plating chemistry from the workpiece is rinsed.  
     
     
         3 . The method of  claim 1 , wherein the deposition is accomplished by electrodeposition.  
     
     
         4 . The method of  claim 1 , wherein the under bump metal comprises either copper or nickel.  
     
     
         5 . The method of  claim 1 , wherein the workpiece is thermally treated.  
     
     
         6 . An apparatus for forming a substantially lead free solder bump on a workpiece having an electrically conducting seed layer, the electrically conducting seed layer being covered by a patterned resist mask layer having a plurality of feature openings is provided, the apparatus comprising: 
 a first plating bath with a metal ion content configured to deposit a substantially pure tin layer in the resist pattern features;    a second plating bath with a metal ion content configured to deposit a tin-silver alloy layer in the resist pattern features.    
     
     
         7 . The apparatus of  claim 6 , further comprising a rinse tank configured to rinse substantially all of the substantially pure tin plating chemistry from the workpiece; and.  
     
     
         8 . The apparatus of  claim 6 , further comprising a copper electrodeposition module.  
     
     
         9 . The apparatus of  claim 6 , further comprising a copper electrodeposition module and a nickel electrodeposition module.  
     
     
         10 . The apparatus of  claim 6 , further comprising a cleaning module.  
     
     
         11 . A method for forming an electronic device having a lead free solder feature, the method comprising: 
 depositing a substantially pure tin layer directly to a layer of under bump metal for solder of the electronic device; and    depositing a tin silver alloy layer onto the pure tin layer.    
     
     
         12 . The method of  claim 11 , wherein the deposition is accomplished by electrodeposition.  
     
     
         13 . The method of  claim 11 , wherein the under bump metal comprises either copper or nickel.  
     
     
         14 . The method of  claim 11 , further comprising rinsing substantially all of the substantially pure tin plating chemistry from the electronic device.  
     
     
         15 . A method for forming a lead free solder bump on a workpiece, the method comprising: 
 providing the workpiece with an electrically conducting seed layer, the electrically conducting seed layer being covered by a patterned resist mask layer having a plurality of feature openings;    immersing the workpiece in a first plating bath, the first plating bath having a metal ion content;    providing electrical contact to the seed layer and providing an electrical potential through the metal ion content of the first plating bath to cause between about 2 and about 150 microns of substantially pure tin to deposit in the resist pattern features;    immersing the workpiece in a second plating bath with a metal ion content; and    forming a electrical contact to the seed layer to form an electrical potential through the metal ion content of the second plating bath to cause between about 2 and about 150 microns of a tin-silver alloy to deposit in the resist pattern features.    
     
     
         16 . The method of  claim 15 , further comprising removing the photoresist patterning layer.  
     
     
         17 . The method of  claim 15 , wherein substantially all of the seed layer not covered by the plated tin and tin-silver alloy is removed.  
     
     
         18 . The method of  claim 15 , further comprising thermally treating the workpiece at between about 210 to about 230 degrees centigrade to cause the substantially pure tin and tin-silver layers to intermix and form a substantially uniform tin-silver alloy feature.  
     
     
         19 . The method of  claim 15 , wherein the substantially pure tin layer is about 30 microns and the tin-silver alloy layer is about 030 microns, and wherein the tin-silver alloy composition is between about 1% and about 7% silver by weight before thermal treatment and about 0.5% to about 3.5% silver by weight after thermal treatment.  
     
     
         20 . The method of  claim 15 , wherein the substantially pure tin layer is about 10 microns and the tin-silver alloy layer is about 10 microns, and wherein the tin-silver alloy composition is between about 1% and about 7% silver by weight before thermal treatment and about 0.5% to about 3.5% silver by weight after thermal treatment.  
     
     
         21 . The method of  claim 15 , wherein the substantially pure tin layer is about 1 micron or about 10 microns and the tin-silver alloy layer is between about 20 microns to about 120 microns.  
     
     
         22 . The method of  claim 15 , wherein the substantially pure tin layer is about one-fourth the thickness of the tin-silver layer.  
     
     
         23 . The method of  claim 15 , further comprising moving the workpiece to a rinse tank, rinsing substantially all of the substantially pure tin plating chemistry from the workpiece, and removing the workpiece from the rinse tank.  
     
     
         24 . An apparatus for forming a lead free solder bump on a workpiece having an electrically conducting seed layer, the electrically conducting seed layer being covered by a patterned resist mask layer having a plurality of feature openings, the apparatus comprising: 
 a first process module disposed to support a first plating bath having a metal ion content adapted to deposit a substantially pure tin layer on the workpiece;    a second process module disposed to support a second plating bath with a metal ion content adapted to deposit a tin and silver layer on the workpiece; and    a controller programmable to plate the workpiece with the substantially pure tin layer in the first process module and to plate the workpiece with the tin and silver layer in the second process module.    
     
     
         25 . The apparatus of  claim 24 , further comprising a rinse tank disposed to support rinsing substantially all of the pure tin plating chemistry from the workpiece, wherein the controller is further programmable to rinse the workpiece in the rinse tank.  
     
     
         26 . The apparatus of  claim 24 , further comprising a copper electrodeposition module, wherein the controller is further programmable to deposit copper on the workpiece with the copper electrodeposition module.  
     
     
         27 . The apparatus of  claim 24 , further comprising a nickel electrodeposition module, wherein the controller is further programmable to deposit nickel on the workpiece with the nickel electrodeposition module.  
     
     
         28 . The apparatus of  claim 24 , further comprising a cleaning module, wherein the controller is further programmable to clean the workpiece with the cleaning module.