Asymmetrical RF Drive for Electrode of Plasma Chamber

Abstract

RF power is coupled to one or more RF drive points ( 50 - 56 ) on an electrode ( 20 - 28 ) of a plasma chamber such that the level of RF power coupled to the RF drive points ( 51 - 52,55 - 56 ) on the half ( 61 ) of the electrode that is closer to the workpiece passageway ( 12 ) exceeds the level of RF power coupled to the RF drive points ( 53 - 54 ), if any, on the other half ( 62 ) of the electrode. Alternatively, RF power is coupled to one or more RF drive points on an electrode of a plasma chamber such that the weighted mean of the drive point positions is between the center ( 60 ) of the electrode and the workpiece passageway. The weighted mean is based on weighting each drive point position by the time-averaged level of RF power coupled to that drive point position. The invention offsets an increase in plasma density that otherwise would exist adjacent the end of the electrode closest to the passageway.

1 - 9 . (canceled) 
     
     
         10 . Apparatus for coupling RF power to a plasma chamber comprising:
 a plasma chamber having a workpiece passageway;   one or more RF power supplies; and   an electrically undivided electrode positioned so as to couple electrical power from the electrode to a plasma within the plasma chamber;   wherein:   a first half of the electrode is closer to the workpiece passageway than a second half of the electrode;   the first half of the electrode includes one or more RF drive points that are connected to receive RF power from the one or more RF power supplies;   the second half of the electrode includes no RF drive points that are connected to receive RF power; and   the plasma chamber includes no other electrode that is connected to receive RF power.   
     
     
         11 . The apparatus of  claim 10 , wherein the electrode further comprises:
 an RF drive point, located at the center of the electrode, connected to receive RF power from the one or more RF power supplies.   
     
     
         12 . The apparatus of  claim 10 , wherein the electrode further comprises:
 one or more RF drive points that are connected to receive RF power from the one or more RF power supplies and that are positioned on the geometric boundary between the first and second halves of the electrode.   
     
     
         13 . The apparatus of  claim 10 , wherein the electrode comprises:
 a back wall;   a showerhead; and   a suspension connected between the perimeter of the showerhead and the back wall;   wherein the RF drive points are on the back wall.   
     
     
         14 - 25 . (canceled) 
     
     
         26 . A method of coupling RF power to a plasma chamber, comprising the steps of:
 providing a plasma chamber having a workpiece passageway;   providing an electrically undivided electrode positioned so as to couple electrical power from the electrode to a plasma within the plasma chamber, wherein a first half of the electrode is closer to the workpiece passageway than a second half of the electrode; and   supplying RF power to one or more RF drive points on the first half of the electrode;   wherein the second half of the electrode includes no RF drive points that are connected to receive RF power; and   wherein the plasma chamber includes no other electrode that is connected to receive RF power.   
     
     
         27 . The method of  claim 26 , further comprising the step of:
 supplying RF power to an RF drive point located at the center of the electrode.   
     
     
         28 . The method of  claim 26 , further comprising the step of:
 supplying RF power to one or more RF drive points that are positioned on the geometric boundary between the first and second halves of the electrode.   
     
     
         29 . The method of  claim 26 , wherein the electrode comprises:
 a back wall;   a showerhead; and   a suspension connected between the perimeter of the showerhead and the back wall;   wherein the RF drive points are on the back wall.   
     
     
         30 - 32 . (canceled)