Membrane-limited selective electroplating of a conductive surface

Abstract

This invention relates to processes and apparati for selectively electroplating a metal layer or layers into recessed topographic features on a conductive surface. The processes and apparati of the invention are useful for fabricating metal circuit patterns, for example for creating copper interconnects between integrated circuit elements embedded in a thin layer of dielectric material on the surface of a semiconductor wafer.

1 . A process of electroplating metal onto a conductive surface, wherein the conductive surface comprises plateaus and trenches, the method comprising: 
 (a) contacting the conductive surface with an electroplating solution comprising platable metal ions;    (b) providing an ion-conducting membrane comprising a first surface and an opposing second surface, wherein the membrane is substantially impermeable to the platable metal ions in the electroplating solution;    (c) providing an anolyte composition which contacts an anode and the first surface of the membrane;    (d) positioning the second surface of the membrane in close proximity to, or in sensible contact with, the conductive surface; and    (e) applying a voltage between the anode and the conductive surface to electroplate at least a portion of the metal ions in the electroplating solution onto the conductive surface to form metal layers on the plateaus and in the trenches, wherein the thickness of metal electroplated in the trenches is greater than the thickness of the metal layer electroplated on the plateaus.    
   
   
       2 . The process of  claim 1 , wherein the anolyte composition comprises water, an aqueous solution, a low-conductivity fluid, a conductive solution, a conductive fluid, a conductive slurry, or a conductive gel.  
   
   
       3 . The process of  claim 1 , wherein substantially all of the platable metal ions in the electroplating solution are cations, or complexes having a positive net charge, and the membrane is an anion-selective ion-conducting membrane.  
   
   
       4 . The process of  claim 1 , wherein substantially all of the platable metal ions in the electroplating solution are anions, or complexes having a negative net charge, and the membrane is a cation-selective ion-conducting membrane.  
   
   
       5 . The process of  claim 1 , wherein the membrane comprises a polymeric ionomer functionalized with acid groups having a pKa less than 5.  
   
   
       6 . The process of  claim 5 , wherein the polymeric ionomer is a perfluorosulfonic acid/PTFE copolymer.  
   
   
       7 . The process of  claim 1 , wherein the conductive surface and the membrane are moved relative to each other in such a way that the area of contact of the membrane moves across the conductive surface.  
   
   
       8 . The process of  claim 1 , wherein the platable metal ions comprise a metal selected from silver, nickel, cobalt, tin, aluminum, copper, lead, tantalum, titanium, iron, chromium, vanadium, manganese, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, hafnium, tungsten, rhenium, osmium, iridium, and combinations thereof.  
   
   
       9 . The process of  claim 8 , wherein the platable metal ions comprise silver, nickel, cobalt, tin, copper, or aluminum.  
   
   
       10 . The process of  claim 1 , wherein the voltage is applied in such a way as to generate a constant current.  
   
   
       11 . The process of  claim 1 , wherein the voltage is varied with time between selected voltage values.  
   
   
       12 . The process of  claim 1 , wherein the trenches have lateral dimensions in the range of from about 0.01 micron to about 100 microns.  
   
   
       13 . An apparatus for electroplating metal onto a conductive surface, the conductive surface comprising plateaus and trenches, the apparatus comprising: 
 (a) a fluid source providing the conductive surface with an electroplating solution comprising platable metal ions;    (b) a charge-selective ion-conducting membrane comprising a first surface and an opposing second surface, wherein the membrane is substantially impermeable to the platable metal ions in the electroplating solution, and is adapted for the second surface to be placed in close proximity to or in sensible contact with the conductive surface;    (c) an anode in electrical contact with the first surface of the membrane; and    (d) a power source capable applying a voltage between the anode and the conductive surface to generate a flow of electrical current in an amount sufficient to electroplate at least a portion of the metal ions in the electroplating solution onto the conductive surface.    
   
   
       14 . The electroplating apparatus of  claim 13 , wherein the anode is in sensible contact with the first surface of the charge-selective ion-conducting membrane.  
   
   
       15 . The electroplating apparatus of  claim 13 , wherein the anode comprises a porous electrochemically inactive material with at least one surface that is flat and smooth.  
   
   
       16 . The electroplating apparatus of  claim 13 , further comprising a porous non-conducting spacer that is disposed between the membrane and the anode, wherein the porous non-conducting spacer comprises a material selected from open-cell polymeric foams, open-cell polymeric gels, woven fabrics, non-woven fabrics, paper, felt, and porous ceramics.  
   
   
       17 . The electroplating apparatus of  claim 13 , further comprising an electrically insulating mask covering a portion of the first or second surface of the membrane, wherein the electrically insulating mask comprises a polyolefin or a halogenated polyolefin.