Sn ALLOY PLATING APPARATUS AND METHOD

Abstract

An Sn alloy plating apparatus includes: a plating bath having a cathode chamber for holding therein an Sn alloy plating solution in which the substrate is to be immersed and an anode chamber for holding therein an anolyte containing Sn ions and an acid; an Sn anode located in the anode chamber; and an electrolytic solution supply line configured to supply an electrolytic solution containing the acid into the anode chamber such that a Sn ion concentration of the anolyte in the anode chamber is kept not less than a predetermined value and a concentration of the acid in the anolyte is kept not less than a predetermined acceptable value. The electrolytic solution supply line supplies the electrolytic solution into the anode chamber to increase an amount of the anolyte in the anode chamber and supply the anolyte into the Sn alloy plating solution by the increased amount.

What is claimed is: 
     
         1 . An Sn alloy plating apparatus for electrodepositing an alloy of Sn and a metal which is nobler than Sn on a surface of a substrate, the apparatus comprising:
 a plating bath whose interior is separated by an anion exchange membrane into a cathode chamber for holding therein an Sn alloy plating solution in which the substrate, serving as a cathode, is to be immersed and an anode chamber for holding therein an anolyte containing Sn ions and an acid that forms a complex with a divalent Sn ion;   an Sn anode located in the anode chamber; and   an electrolytic solution supply line configured to supply an electrolytic solution containing the acid into the anode chamber such that a Sn ion concentration of the anolyte in the anode chamber is kept not less than a predetermined value and a concentration of the acid in the anolyte is kept not less than a predetermined acceptable value,   the electrolytic solution supply line being configured to supply the electrolytic solution into the anode chamber to increase an amount of the anolyte in the anode chamber and supply the anolyte into the Sn alloy plating solution by the increased amount.   
     
     
         2 . The Sn alloy plating apparatus according to  claim 1 , wherein the electrolytic solution supply line is configured to supply the electrolytic solution into the anode chamber to increase an amount of the anolyte in the anode chamber to thereby cause the anolyte to overflow the anode chamber into the Sn alloy plating solution. 
     
     
         3 . The Sn alloy plating apparatus according to  claim 1 , further comprising:
 an overflow bath configured to store the Sn alloy plating solution that has overflowed the cathode chamber; and   a plating solution circulation line configured to return the Sn alloy plating solution in the overflow bath to the cathode chamber to thereby circulate the Sn alloy plating solution.   
     
     
         4 . The Sn alloy plating apparatus according to  claim 1 , further comprising:
 a pure water supply line configured to supply pure water into the anode chamber.   
     
     
         5 . The Sn alloy plating apparatus according to  claim 1 , further comprising:
 an acid concentration measuring device configured to measure the concentration of the acid in the anolyte in the anode chamber.   
     
     
         6 . The Sn alloy plating apparatus according to  claim 1 , further comprising:
 a dialysis cell configured to draw out a part of the Sn alloy plating solution from the cathode chamber, remove at least a part of the acid from the Sn alloy plating solution, and then return the Sn alloy plating solution to the cathode chamber.   
     
     
         7 . The Sn alloy plating apparatus according to  claim 1 , further comprising:
 an N 2  gas supply line configured to supply nitrogen gas into the anolyte in the anode chamber to form nitrogen gas bubbles in the anolyte.   
     
     
         8 . The Sn alloy plating apparatus according to  claim 1 , further comprising:
 an auxiliary electrolytic cell configured to supply an anolyte having an increased concentration of Sn ions to the Sn alloy plating solution,   the auxiliary electrolytic cell including
 an auxiliary anode chamber for holding an anolyte therein, 
 an auxiliary cathode chamber for holding a catholyte therein, 
 an anion exchange membrane separating the auxiliary anode chamber and the auxiliary cathode chamber from each other, 
 an auxiliary Sn anode located in the auxiliary anode chamber, 
 an auxiliary cathode located in the auxiliary cathode chamber, and 
 an auxiliary power source configured to apply a voltage between the auxiliary Sn anode and the auxiliary cathode when the auxiliary Sn anode is immersed in the anolyte and the auxiliary cathode is immersed in the catholyte to produce the anolyte having the increased concentration of Sn ions. 
   
     
     
         9 . An Sn alloy plating method of electrodepositing an alloy of Sn and a metal which is nobler than Sn on a surface of a substrate, the method comprising:
 providing a plating bath whose interior is separated by an anion exchange membrane into a cathode chamber and an anode chamber;   supplying an Sn alloy plating solution into the cathode chamber;   immersing the substrate in the Sn alloy plating solution;   supplying an anolyte, containing Sn ions and an acid that forms a complex with a divalent Sn ion, into the anode chamber to immerse an Sn anode in the anolyte;   supplying an electrolytic solution containing the acid into the anode chamber such that a Sn ion concentration of the anolyte in the anode chamber is kept not less than a predetermined value and a concentration of the acid in the anolyte is kept not less than a predetermined acceptable value; and   applying a voltage between the Sn anode and the substrate serving as a cathode to plate the surface of the substrate, while supplying the electrolytic solution into the anode chamber to increase an amount of the anolyte in the anode chamber and supplying the anolyte into the Sn alloy plating solution by the increased amount.   
     
     
         10 . The Sn alloy plating method according to  claim 9 , wherein the supplying the electrolytic solution into the anode chamber to increase an amount of the anolyte in the anode chamber and the supplying the anolyte into the Sn alloy plating solution by the increased amount comprises supplying the electrolytic solution into the anode chamber to increase an amount of the anolyte in the anode chamber to thereby cause the anolyte to overflow the anode chamber into the Sn alloy plating solution. 
     
     
         11 . The Sn alloy plating method according to  claim 9 , further comprising:
 circulating the Sn alloy plating solution in the cathode chamber.   
     
     
         12 . The Sn alloy plating method according to  claim 9 , further comprising:
 controlling an amount of the electrolytic solution or pure water to be supplied into the anode chamber based on the concentration of the acid in the anolyte held in the anode chamber.   
     
     
         13 . The Sn alloy plating method according to  claim 9 , further comprising:
 determining the concentration of the acid in the anolyte from an initial acid concentration of the anolyte, a quantity of electricity and a current efficiency at the Sn anode, an amount of the electrolytic solution supplied, and a permeability of the anion exchange membrane with respect to methanesulfonic acid that passes through the anion exchange membrane and migrates from the cathode chamber into the anode chamber.   
     
     
         14 . The Sn alloy plating method according to  claim 9 , further comprising:
 drawing out a part of the Sn alloy plating solution from the cathode chamber;   removing at least a part of the acid from the Sn alloy plating solution that has been drawn out; and then   returning the Sn alloy plating solution to the cathode chamber.   
     
     
         15 . The Sn alloy plating method according to  claim 9 , further comprising:
 supplying nitrogen gas into the anolyte in the anode chamber to form nitrogen gas bubbles in the anolyte.   
     
     
         16 . The Sn alloy plating method according to  claim 9 , further comprising:
 immersing an auxiliary Sn anode in an anolyte held in an auxiliary anode chamber;   immersing an auxiliary cathode in a catholyte held in an auxiliary cathode chamber that is separated from the auxiliary anode chamber by an anion exchange membrane;   applying a voltage between the auxiliary Sn anode and the auxiliary cathode to produce the anolyte having an increased concentration of Sn ions; and   supplying the anolyte having the increased concentration of Sn ions into the Sn alloy plating solution.