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;   an 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   one or more RF power supplies;   wherein 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; and   wherein the second half of the electrode includes no RF drive points that are 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 showerhead and the back wall;   wherein the RF drive points are on the back wall.   
     
     
         14 - 16 . (canceled) 
     
     
         17 . A method of coupling RF power to a plasma chamber, comprising the steps of:
 providing a plasma chamber having a workpiece passageway;   providing an 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;   supplying a first time-averaged level of RF power to the first half of the electrode; and   supplying a second time-averaged level of RF power to the second half of the electrode;   wherein the second time-averaged level of RF power is greater than or equal to zero; and   wherein the first time-averaged level of RF power is greater than the second time-averaged level of RF power.   
     
     
         18 - 20 . (canceled) 
     
     
         21 . The method of  claim 17 , further comprising the steps of:
 providing a power splitter having an input and a plurality of outputs;   providing one or more RF drive points on the first half of the electrode and zero or more RF drive points on the second half of the electrode;   supplying RF power to the input of the power splitter; and   connecting each output of the power splitter to supply RF power to one or more of the RF drive points;   wherein the power splitter supplies a greater level of RF power to the RF drive points on the first half of the electrode than to the zero or more RF drive points on the second half of the electrode.   
     
     
         22 . The method of  claim 21 , wherein:
 the power splitter comprises one or more attenuators such that each attenuator is connected between the input of the power splitter and one of the outputs of the power splitter.   
     
     
         23 . The method of  claim 22 , wherein:
 a plurality of the attenuators have a time-varying reactance such that the reactance of at least a first one of the attenuators increases when the reactance of at least a second one of the attenuators decreases so that the total reactance of the attenuators connected between the input of the power splitter and the electrode remains constant.   
     
     
         24 . The method of  claim 17 , further comprising the step of:
 connecting one or more attenuators between one of the one or more RF power supplies and one or more RF drive points on the electrode.   
     
     
         25 . The method of  claim 17 , wherein the electrode comprises:
 a back wall having one or more RF drive points;   a showerhead; and   a suspension connected between the showerhead and the back wall;   wherein the one or more RF power supplies are connected to supply RF power to the RF drive points on the back wall.   
     
     
         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 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.   
     
     
         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 showerhead and the back wall;   wherein the RF drive points are on the back wall.   
     
     
         30 . (canceled) 
     
     
         31 . A method of coupling RF power to a plasma chamber, comprising the steps of:
 providing a plasma chamber having a workpiece passageway;   providing an electrode positioned so as to couple electrical power from the electrode to a plasma within the plasma chamber; and   supplying RF power to a plurality of RF drive points on the electrode;   wherein the weighted mean position of the RF drive points, based on weighting each drive point position by the time-averaged level of RF power coupled to that drive point position, is between the center of the electrode and the workpiece passageway.   
     
     
         32 . The method of  claim 31 , wherein the electrode comprises:
 a back wall;   a showerhead; and   a suspension connected between the showerhead and the back wall;   wherein the RF drive points are on the back wall.