Selective electrochemical deposition methods using pyrophosphate copper plating baths containing ammonium salts, citrate salts and/or selenium oxide

Abstract

An electrochemical fabrication process and apparatus are provided that can form three-dimensional multi-layer structures using pyrophosphate copper plating solutions that contain citrate salts, selenium oxide, and/or excess ammonium salts. In some embodiments the citrate salts are provided in concentrations that yield improved anode dissolution, reduced formation of pinholes on the surface of deposits, reduced likelihood of shorting between anode and cathode during deposition processes, and reduced plating voltage throughout the period of deposition. A preferred citrate salt is ammonium citrate in concentrations ranging from somewhat more that about 10 g/L for 10 mA/cm 2 current density to as high as 200 g/L or more for a current density as high as 40 mA/cm. In some embodiments deposits having enhanced ductility and/or reduced tendency to crack are provided.

We claim:  
     
         1 . An electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process comprises: 
 (A) selectively depositing at least a portion of a layer onto a substrate, wherein the substrate may comprise previously deposited material; and    (B) forming a plurality of layers such that each successive layer is formed adjacent to and adhered to a previously deposited layer, wherein said forming comprises repeating operation (A) a plurality of times;    wherein at least a plurality of the selective depositing operations comprise 
 (1) contacting the substrate and a pattern mask;  
 (2) in presence of a plating solution, conducting an electric current through the at least one opening in the selected mask between an anode and the substrate such that a selected deposition material is deposited onto the substrate to form at least a portion of a layer; and  
 (3) removing the mask from the substrate; and  
   wherein the selected deposition material is copper; and wherein the plating solution comprises pyrophosphate copper in combination with at least one of the following (a) an ammonium ion concentration greater than about 1.5 g/l, (b) ammonium ions and citrate ions, or (c) ammonium ions and tartrate ions.    
     
     
         2 . The process of  claim 1  additionally comprising supplying a plurality of preformed masks, wherein each mask comprises a patterned dielectric material that includes at least one opening through which deposition can take place during the formation of at least a portion of a layer, and wherein each mask comprises a support structure that supports the patterned dielectric material, and wherein the contacting of the substrate and a patterned mask comprises contacting a selected one of the preformed masks to the substrate.  
     
     
         3 . The process of  claim 2  wherein the dielectric comprises a conformable material.  
     
     
         4 . The process of  claim 1  wherein a source of citrate ions comprises a citrate salt.  
     
     
         5 . The process of  claim 4  wherein the citrate salt comprises at least one of (1) potassium citrate, (2) sodium citrate, (3) potassium sodium citrate, or (4) ammonium citrate, (5) ammonium hydrogen citrate.  
     
     
         6 . The process of  claim 4  wherein the citrate salt is supplied in a concentration that is effective in holding the plating voltage at a reduced level substantially during the entire duration of a plating operation.  
     
     
         7 . The process of  claim 4  wherein the citrate salt is supplied in a concentration that is effective in substantially reducing the occurrence of shorting during plating operations that achieve the desired thickness of deposition.  
     
     
         8 . The process of  claim 7  wherein the citrate salt is supplied in a concentration that is effective in achieving a uniformity of deposit that has a minimum thickness which is no less than 50% of a maximum thickness.  
     
     
         9 . The process of  claim 1  wherein a source of tartrate ions comprises a tartrate salt.  
     
     
         10 . The process of  claim 4  wherein the tartrate salt comprises at least one of (1) potassium tartrate, (2) sodium tartrate, (3) potassium sodium tartrate, or (4) ammonium tartrate, or (5) ammonium hydrogen tartrate.  
     
     
         11 . The process of  claim 1  wherein the selenium oxide is supplied in a concentration that is effective in reducing cracking to an acceptable level.  
     
     
         12 . The process of  claim 11  wherein the reduction in cracking substantially eliminates cracking that contacts patterned features.  
     
     
         13 . The process of  claim 11  wherein the reduction in cracking substantially eliminates cracking.  
     
     
         14 . The process of  claim 1  wherein the concentration of ammonium ions is sufficient to allow plating to occur at a current density of about 20 mA/cm 2  or greater in achieving a desired plating thickness.  
     
     
         15 . The process of  claim 1  wherein the concentration of ammonium ions is sufficient to allow plating to occur at a current density of about 30 mA/cm 2  or greater in achieving a desired plating thickness.  
     
     
         16 . The process of  claim 1  wherein the concentration of ammonium ions, in combination with any citrate or tartrate ions, is sufficient to allow a desired plating thickness to be achieved without the voltage increasing by a factor of two or more prior to a desired plating thickness or plating time to be reached.  
     
     
         17 . The process of  claim 1  wherein the concentration of ammonium ions, in combination with any citrate or tartrate ions, is sufficient to allow a desired plating thickness or plating time to be reached without the occurrence of shorting on at least an average of 50% of attempts to form depositions of desired thickness during the formation of a given structure.  
     
     
         18 . The process of  claim 1  wherein the concentration of ammonium ions, in combination with any citrate or tartrate ions, is sufficient to allow a desired plating thickness or plating time to be reached without the occurrence of shorting on at least 80% of attempts to form depositions of desired thickness during the formation of a given structure.  
     
     
         19 . The process of  claim 1  wherein the formation of each of a number of layers comprise at least one blanket deposition as well as the selective deposition wherein for a given layer the selectively deposited material is different from a material deposited by blanket deposition.  
     
     
         20 . The process of  claim 1  wherein the plurality of selective depositions comprise the deposition of a plurality of different materials.  
     
     
         21 . The process of  claim 1  wherein at least a portion of one layer is formed by a non-electroplating deposition process.  
     
     
         22 . The process of  claim 1  wherein a plurality of depositions occur during the formation of each of a number of layers wherein at least one of the depositions on each of the number of layers deposits copper and at least one of the other depositions on the number of layers deposits nickel.  
     
     
         23 . The process of  claim 1  wherein the selective depositing for each of a number of layers comprises at least two selective depositions.  
     
     
         24 . The process of  claim 1  wherein a number of the plurality of layers are each formed by depositing at least one structural material using at least one deposition and by depositing at least one sacrificial material by using at least one other deposition.  
     
     
         25 . The process of  claim 24  wherein at least a portion of the at least one sacrificial material is removed after formation of a plurality of layers to reveal a three-dimensional structure comprised of at least one structural material.  
     
     
         26 . The process of  claim 2  wherein, for each of a plurality of masks, the support for the conformable material for a mask comprises the anode involved in the deposition associated with the use of the mask.  
     
     
         27 . The process of  claim 3  wherein, for each of a plurality of masks, the support for the conformable material of a mask comprises a porous medium which does not act as the anode during the deposition associated with the use of the mask.  
     
     
         28 . The process of  claim 2  where a thickness of the dielectric material of at least one selected mask is less than 100 μm and is more preferably less than 50 μm.  
     
     
         29 . The process of  claim 1  wherein the formation of at least a plurality of layers additionally comprises removing a portion of the deposited material from the substrate such that a desired surface level is obtained.  
     
     
         30 . A conformable contact masking process for producing a structure, wherein the process comprises: 
 (A) supplying at least one preformed mask that comprises a patterned dielectric material that includes at least one opening through which deposition can take place during the formation of at least a portion of a layer, and wherein the at least one mask comprises a support structure that supports the patterned dielectric material; and    (B) selectively depositing at least a portion of a layer onto a substrate, comprising 
 i) contacting the substrate and the dielectric material of the preformed mask;  
 ii) in presence of a plating solution, conducting an electric current through the at least one opening in the selected mask between an anode and the substrate such that the selected deposition material is deposited onto the substrate to form at least a portion of a layer; and  
 iii) separating the selected preformed mask from the substrate;  
   wherein the selected deposition material is copper; and wherein the plating solution comprises pyrophosphate copper in combination with at least one of the following (a) an ammonium ion concentration greater than about 1.5 g/l, (b) ammonium ions and citrate ions, or (c) ammonium ions and tartrate ions.