Plating solution for high rate electroless deposition of copper

Abstract

An electroless copper plating solution is disclosed herein. The solution includes an aqueous copper salt component, an aqueous solution of formaldehyde, an amine based complexing agent, and mixture of alkaline pH modifying substances in an amount sufficient to make the electroless plating solution alkaline. A method of preparing an electroless copper plating solution is also provided.

What is claimed is: 
     
         1 . An electroless copper plating solution, comprising:
 a copper source;   a secondary amine complexing agent;   a reducing agent; and   a pH modifying substance.   
     
     
         2 . The electroless copper plating solution, according to  claim 1 , wherein the copper source is copper sulphate (CuSO 4 ). 
     
     
         3 . The electroless copper plating solution, according to  claim 1 , wherein the secondary amine complexing agent is diisopropanolamine ((CH 3 CH(OH)CH 2 ) 2 NH). 
     
     
         4 . The electroless copper plating solution, according to  claim 1 , wherein, the reducing agent is formaldehyde (CH 2 O). 
     
     
         5 . The electroless copper plating solution, according to  claim 1 , wherein, the pH modifying substance is a mixture of disodium carbonate (Na 2 CO 3 ) and sodium hydroxide (NaOH). 
     
     
         6 . The electroless copper plating solution, according to  claim 1 , wherein, a pH of electroless copper plating solution is more than 13. 
     
     
         7 . The electroless copper plating solution, according to  claim 2 , wherein the concentration of sulphate (CuSO 4 ) is between about 0.05 mol/L to a solubility limit of the aqueous copper sulphate (CuSO 4 ) component. 
     
     
         8 . The electroless copper plating solution, according to  claim 3 , wherein the concentration of secondary amine complexing agent diisopropanolamine ((CH 3 CH(OH)CH 2 ) 2 NH) is from about 0.1 mol/L to about 3 mol/L. 
     
     
         9 . The electroless copper plating solution, according to  claim 4 , wherein the concentration of reducing agent formaldehyde (CH 2 O) is from about 0.1 mol/L to about 4 mol/L. 
     
     
         10 . The electroless copper plating solution, according to  claim 5 , wherein, the concentrations of pH modifying substances are from 0.05 mol/L to 1.0 mol/L for disodium carbonate (Na 2 CO 3 ) and from 0.1 mol/L to 3.0 mol/L for sodium hydroxide (NaOH). 
     
     
         11 . The electroless copper plating solution, according to  claim 1 , wherein the electroless copper plating solution is prepared by sequentially combining the copper source component to a volume of water, then adding the complexing agent to the aqueous copper source component/water combination, thereafter adding the pH modifying substance, and lastly adding the aqueous reducing agent component. 
     
     
         12 . The electroless copper plating solution, according to  claim 11 , wherein the electroless copper plating solution is prepared by sequentially combining the aqueous copper sulphate (CuSO 4 ) salt as copper source component to a volume of water, then adding diisopropanolamine ((CH 3 CH(OH)CH 2 ) 2 NH) as complexing agent to the aqueous copper sulphate (CuSO 4 ) salt component/water combination, thereafter adding NaOH and Na 2 CO 3  as the pH modifying substances, and lastly adding the CH 2 O as aqueous reducing agent component. 
     
     
         13 . The electroless copper plating solution, according to  claim 1 , wherein the electroless copper plating solution is operated without additional stabilizing additives. 
     
     
         14 . The electroless copper plating solution, according to  claim 13 , wherein the stabilization of the electroless copper plating solution is obtainable by means of the bubbling of air through the solution. 
     
     
         15 . The electroless copper plating solution, according to  claim 1 , wherein the electroless copper plating solution is operated at ambient temperature. 
     
     
         16 . The electroless copper plating solution, according to  claim 1 , wherein the composition of electroless copper plating solution comprises as follows: copper source is CuSO 4  and is provided at concentration 0.11 mol/L, complexing agent is diisopropanolamine and is provided at concentration 0.2 mol/L, reducing agent is formaldehyde and is provided at concentration 0.38 mol/L, pH modifying substances (Na 2 CO 3  and NaOH)-0.26 mol/L and 0.5 mol/L, respectively. 
     
     
         17 . The electroless copper plating solution, according to  claim 1 , wherein the electroless copper plating solution enables depositing at least 30 μm thick (or more) copper coatings per one hour. 
     
     
         18 . The electroless copper plating solution, according to  claim 1 , wherein the electroless copper plating solution enables reducing more than 98% of the initial copper (II) content to metallic copper coating in 1.5 hours. 
     
     
         19 . The electroless copper plating solution, according to  claim 1 , wherein the electroless copper plating solution after electroless copper deposition can be replenished and repeatedly used.