Method and apparatus for dynamic current distribution control during electroplating

Abstract

A method of electroplating a metal on a cathodically biased wafer substrate employs an electroplating apparatus having a main anode, an auxiliary electrode and an ionic current collimator, where the ionic current collimator is configured to direct ionic current that is generated by the main anode from a periphery of a plating vessel to its center. During electroplating, in a first electroplating stage (e.g., when terminal effect is pronounced), the metal is plated onto the wafer while the auxiliary electrode is cathodically biased; and in a second electroplating stage (e.g., when terminal effect subsides), the metal is plated onto the wafer while the auxiliary electrode is anodically biased. In some embodiments the auxiliary electrode is located between the ionic current collimator and the wafer, and is configured to redistribute ionic current that has passed through the collimator. The method is useful for improving the uniformity of electroplating.

1 . A method of electroplating a metal on a wafer substrate, the method comprising:
 (a) providing the wafer substrate to an electroplating apparatus having a wafer holder, and a plating vessel containing a main anode, an auxiliary electrode, and an ionic current collimator, wherein the ionic current collimator is configured to direct ionic current from the periphery to the center of the plating vessel;   (b) in a first electroplating stage, electroplating metal onto the wafer substrate while cathodically biasing the auxiliary electrode; and   (c) in a second electroplating stage, electroplating metal onto the wafer substrate while anodically biasing the auxiliary electrode.   
     
     
         2 . The method of  claim 1 , wherein the second electroplating stage is performed after the first electroplating stage, and wherein during the first electroplating stage a cathodic current initially applied to the auxiliary electrode is at least about 300% of a cathodic current applied to the wafer substrate at the same time. 
     
     
         3 . The method of  claim 1 , wherein in the second electroplating stage, the auxiliary electrode is anodically biased to a greater extent than the main anode at least during a portion of the second electroplating stage. 
     
     
         4 . The method of  claim 1 , further comprising cathodically biasing the main anode during at least a portion of the second electroplating stage. 
     
     
         5 . The method of  claim 1 , further comprising moving the ionic current collimator and the auxiliary electrode in a direction perpendicular to a plating surface of the wafer substrate, during the electroplating. 
     
     
         6 . The method of  claim 1 , further comprising the steps of:
 applying photoresist to the wafer substrate;   exposing the photoresist to light;   patterning the photoresist and transferring the pattern to the wafer substrate;   and selectively removing the photoresist from the wafer substrate.   
     
     
         7 . The method of  claim 1 , wherein the ionic current collimator comprises:
 (i) a central portion in the form of an open cylinder extending in a direction that is perpendicular to a plating surface of the wafer substrate, wherein the openings of the cylinder provide a route for the ionic current; and   (ii) a current restricting portion connected to the central portion, the current restricting portion extending in a direction that is parallel to the plating surface of the wafer substrate.   
     
     
         8 . The method of  claim 7 , wherein the current restricting portion of the ionic current collimator extends to sidewalls of the plating vessel, and is configured to block ionic current at the periphery of the plating vessel. 
     
     
         9 . The method of  claim 8 , wherein the current restricting portion of the ionic current collimator is attached to the sidewalls of the plating vessel. 
     
     
         10 . The method of  claim 1 , wherein the ionic current collimator is made of a dielectric material that is not permeable to electrolyte and is selected from the group consisting of polycarbonate, polyethylene, polypropylene, polyvinylidene difluoride (PVDF), polytetrafluoroethylene, and polysulphone. 
     
     
         11 . The method of  claim 1 , wherein the ionic current collimator does not contact the main anode and is spaced from the main anode by a distance of at least about 15% of the wafer substrate radius. 
     
     
         12 . The method of  claim 1 , wherein the auxiliary electrode resides over the main anode and between the ionic current collimator and the wafer substrate holder. 
     
     
         13 . The method of  claim 1 , wherein the ionic current collimator serves as a platform supporting the auxiliary electrode. 
     
     
         14 . The method of  claim 1 , wherein the auxiliary electrode comprises copper at least on the surface of the auxiliary electrode. 
     
     
         15 . The method of  claim 1 , wherein a footprint of the auxiliary electrode onto the main anode is at least about 40% of a total anode area. 
     
     
         16 . The method of  claim 1 , wherein the auxiliary electrode has a generally toroidal shape and a thickness of at least about 20 mm. 
     
     
         17 . The method of  claim 1 , wherein the auxiliary electrode has a working surface of at least about 600 cm 2 . 
     
     
         18 . The method of  claim 1 , wherein the apparatus further includes a thief cathode, which is cathodically biased during a portion of electroplating. 
     
     
         19 . The method of  claim 1 , wherein the apparatus further includes a thief cathode, which is cathodically biased during the first electroplating stage and during a portion of the second electroplating stage. 
     
     
         20 . The method of  claim 1 , wherein the auxiliary electrode changes polarity from cathodic to anodic after a defined sheet resistance of the electroplated layer on the wafer substrate is reached.