Abstract:
A method and apparatus for controlling plasma uniformity is disclosed. When etching a substrate, a non-uniform plasma may lead to uneven etching of the substrate. Impedance circuits may alleviate the uneven plasma to permit more uniform etching. The impedance circuits may be disposed between the chamber wall and ground, the showerhead and ground, and the cathode can and ground. The impedance circuits may comprise one or more of an inductor and a capacitor. The inductance of the inductor and the capacitance of the capacitor may be predetermined to ensure the plasma is uniform. Additionally, the inductance and capacitance may be adjusted during processing or between processing steps to suit the needs of the particular process.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Embodiments of the present invention generally relate to a method and apparatus for controlling plasma uniformity. 
         [0003]    2. Description of the Related Art 
         [0004]    When processing substrates in a plasma environment, the uniformity of the plasma will affect the uniformity of processing. For example, in a plasma deposition process, if the plasma is greater in the area of the chamber corresponding to the center of the substrates, then more deposition will likely occur in the center of the substrate as compared to the edge of the substrate. Similarly, if the plasma is greater in an area of the chamber corresponding to the edge of the substrate, more deposition will likely occur on the edge of the substrate as compared to the center. 
         [0005]    In an etching process, if the plasma is greater in the area of the chamber corresponding to the center of the substrate, more material will likely be removed or etched from the substrate in the center of the substrate as compared to the edge of the substrate. Similarly, if the plasma is greater in the area of the chamber corresponding to the edge of the substrate, more material may be removed or etched from the substrate at the edge of the substrate compared to the center of the substrate. 
         [0006]    Non-uniformity in plasma processes can significantly decrease device performance and lead to waste because the deposited layer or etched portion is not consistent across the substrate. If the plasma could be made uniform, a consistent deposition or etch is more likely to occur. Therefore, there is a need in the art for a method and an apparatus for controlling plasma uniformity in a plasma process. 
       SUMMARY 
       [0007]    Embodiments of the present invention generally comprises a method and an apparatus for controlling the uniformity of a plasma. In one embodiment, a plasma processing apparatus comprises a chamber body, a substrate support disposed within the chamber body, and a showerhead disposed within the chamber body opposite to the substrate support. A power supply is coupled with the substrate support. At least one item selected from the group consisting of a capacitor, an inductor, and combinations thereof is coupled to at least two of the chamber body, the showerhead, and the substrate support. 
         [0008]    In another embodiment, a plasma processing apparatus comprises a chamber body, a substrate support disposed within the chamber body, and a showerhead disposed within the chamber body opposite to the substrate support. A power supply is coupled with the showerhead. A cathode can is disposed within the chamber body. At least one item selected from the group consisting of a capacitor, an inductor, and combinations thereof is coupled to at least two of the chamber body, the substrate support, the showerhead, and the cathode can. The cathode can substantially encircles the substrate support. 
         [0009]    In another embodiment, an etching apparatus comprises a chamber body, a substrate support disposed within the chamber body, and a showerhead disposed within the chamber body opposite to the substrate support. A power supply is coupled with the substrate support. A first capacitor is coupled with the showerhead, and a first inductor is coupled to the showerhead. A second capacitor is coupled to the chamber body, and a second inductor is coupled to the chamber body. 
         [0010]    In another embodiment, a plasma distribution controlling method comprises applying a current to a substrate disposed within a processing chamber on a substrate support. The processing chamber has a chamber body and a showerhead disposed within the chamber body opposite to the substrate. The method further comprises coupling at least two of the showerhead, the chamber body, and the substrate support to an item selected from the group consisting of an inductor, a capacitor, and combinations thereof to adjust the plasma distribution. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0012]      FIG. 1  is a schematic cross sectional view of a plasma processing apparatus. 
           [0013]      FIG. 2  is a schematic cross sectional view of an etching apparatus according to one embodiment of the invention. 
           [0014]      FIG. 3  is a schematic cross sectional view of an etching apparatus according to another embodiment of the invention. 
           [0015]      FIG. 4  shows the plasma uniformity distribution according to one embodiment of the invention. 
           [0016]      FIGS. 5A and 5B  show the plasma uniformity distribution according to another embodiment of the invention. 
           [0017]      FIGS. 6A and 6B  show the plasma uniformity distribution according to another embodiment of the invention. 
           [0018]      FIGS. 7A-7D  show the plasma uniformity distribution according to another embodiment of the invention. 
           [0019]      FIGS. 8A-8F  show the plasma uniformity distribution according to another embodiment of the invention. 
           [0020]      FIGS. 9A-9D  show the plasma uniformity distribution according to another embodiment of the invention. 
           [0021]      FIGS. 10A-10B  show the plasma uniformity distribution according to another embodiment of the invention. 
           [0022]      FIGS. 11A-11E  show additional impedance circuits that may be utilized. 
       
    
    
       [0023]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
       DETAILED DESCRIPTION 
       [0024]    Embodiments of the present invention generally comprises a method and an apparatus for controlling plasma uniformity. While the embodiments will be described below in regards to an etching apparatus and method, it is to be understood that the embodiments have equal application in other plasma processing chambers and processes. One exemplary apparatus in which the invention may be practiced is the ENABLER™ etching chamber available from Applied Materials, Inc., Santa Clara, Calif. It is to be understood that embodiments of the present invention may be practiced in other chambers, including those sold by other manufacturers. 
         [0025]      FIG. 1  is a schematic cross sectional view of a plasma processing apparatus  100 . The apparatus  100  comprises a chamber  102  having a substrate  104  disposed therein on a susceptor  106 . The susceptor  106  may be movable between a lowered position and a raised position. The substrate  104  and susceptor  106  may be disposed within the chamber  102  opposite a showerhead  108 . The chamber  102  may be evacuated by a vacuum pump  110  coupled to a bottom  112  of the chamber  102 . 
         [0026]    Processing gas may be introduced to the chamber  102  from a gas source  114  through the showerhead  108 . The gas may be introduced into a plenum  116  disposed between a backing plate  118  and the showerhead  108 . The gas may then pass through the showerhead  108  where it is ignited into a plasma  122  by a current applied to the showerhead  108  by a power source  120 . In one embodiment, the power source  120  may comprise an RF power source. 
         [0027]      FIG. 2  is a schematic cross sectional view of an etching apparatus  200  according to one embodiment of the invention. The apparatus  200  comprises a processing chamber  202  having a substrate  204  disposed therein. The substrate  204  may be disposed on a susceptor  206  that is movable between a raised and a lowered position. The substrate  204  and the susceptor  206  may sit opposite to a showerhead  208  within the processing chamber  202 . A vacuum pump  210  may draw a vacuum within the processing chamber  202 . The vacuum pump  210  may be disposed under the susceptor  206 . 
         [0028]    Processing gas may be provided to the processing chamber  202  from a gas source  212  to a plenum  214  above the showerhead  208 . The processing gas may flow through gas passages  216  into the processing area  218 . The showerhead  208  may be biased with a current from a power source  230 . The current may flow to the showerhead  208  whenever the switch  228  is turned on. In one embodiment, the power source  230  may comprise an RF power source. In another embodiment, the showerhead  208  may be open or at floating potential. 
         [0029]    When the substrate  206  is biased, an RF current applied to the substrate  206  will travel to ground out of the showerhead  208  and/or through the chamber wall  220 . The easier the path to ground, the more RF current will follow the path. Hence, if both a showerhead  208  and chamber wall  220  are grounded, the plasma may be drawn closer to the chamber wall  220  due to its proximity to the RF current source. The plasma drawn to the chamber wall  220  may result in more etching at the edge of the substrate  206 . If the plasma within the chamber  202  were uniform, then the etching within the chamber  202  would be uniform. 
         [0030]    In order to control the plasma within the processing chamber  202 , impedance circuits  222  may be coupled to the chamber wall  220  and/or the showerhead  208 . When a capacitor  224  is a part of the impedance circuit, the capacitor  224  may push the plasma from the location to which the capacitor  224  is coupled. The capacitor  224  disconnects the item from ground. The capacitor  224  impedes the current from flowing to ground. An inductor  226 , on the other hand, functions opposite to that of the capacitor  224 . The inductor pulls the plasma closer to the object coupled to the inductor  226 . The voltage drop across the inductor is out of phase with the biased object (i.e., the showerhead  208  or the substrate  206 ) and hence increases relative to ground. Thus, more current flows through the inductor  226  to ground than directly to ground. When both an inductor  226  and a capacitor  224  are present, the capacitance and/or the inductance may be tailored to meet the particular needs of the user. For multiple RF applications, various combinations of series and parallel circuit elements and/or transmission lines may be used to achieve the desired impedance.  FIGS. 11A-11E  show several impedance circuits that may be utilized. It is to be understood that other impedance circuits may be utilized as well. 
         [0031]    The processing chamber  202  may have a chamber wall  220 . The chamber wall  220  may be coupled directly to ground or coupled to an impedance circuit  222  that is coupled to ground. The impedance circuit  222  may comprise a capacitor  224  and/or an inductor  226 . The capacitor  224  may have switch  228  that couples the capacitor to the chamber wall  220  and a switch  228  that couples the capacitor  224  to ground. Similarly, the inductor  226  has a switch that couples the inductor  226  to the chamber wall  220  and a switch  228  that couples the inductor  226  to ground. In one embodiment, a capacitor  224  may be present without an inductor  226 . In another embodiment, an inductor  226  may be present without a capacitor  224 . In another embodiment, both a capacitor  224  and an inductor  226  may be present. In another embodiment, the wall  220  may be coupled directly to ground without coupling to a capacitor  224  and/or an inductor  226 . 
         [0032]    The showerhead  208  may also be coupled to ground through an impedance circuit  222 , directly to ground, to a power source  230 , or open at a floated potential. The impedance circuit  222  may comprise a capacitor  224  and/or an inductor  226 . The capacitor  224  may have switch  228  that couples the capacitor to the showerhead  208  and a switch  228  that couples the capacitor  224  to ground. Similarly, the inductor  226  has a switch  228  that couples the inductor  226  to the showerhead  208  and a switch  228  that couples the inductor  226  to ground. In one embodiment, a capacitor  224  may be present without an inductor  226 . In another embodiment, an inductor  226  may be present without a capacitor  224 . In another embodiment, both a capacitor  224  and an inductor  226  may be present. In another embodiment, the showerhead  208  may be coupled directly to ground without coupling to a capacitor  224  and/or an inductor  226 . In another embodiment, the showerhead  208  may be open at a floating potential. In another embodiment, the showerhead  208  may be coupled to a power source  230 . The showerhead  208  may be electrically isolated from the chamber wall  220  by a spacer  232 . In one embodiment, the spacer  232  may comprise a dielectric material. 
         [0033]    The susceptor  206  may be coupled to ground, coupled to a power source  238 , or open at a floating potential. In one embodiment, the power source  238  may comprise an RF power source. Switches  228  may be used to couple the susceptor  206  to the power source  238  or ground. 
         [0034]    In one embodiment, a cathode can  236  may at least partially surround the susceptor  206 . The cathode can  236  may provide additional control of the plasma uniformity. The cathode can  236  may be electrically isolated from the susceptor  206  by a spacer  234 . In one embodiment, the spacer  234  may comprise a dielectric material. The cathode can  236  may be used to control the plasma within the processing chamber  202 . The cathode can  236  may be coupled directly to ground or coupled to an impedance circuit  222  that is coupled to ground. The impedance circuit  222  may comprise a capacitor  224  and/or an inductor  226 . The capacitor  224  may have switch  228  that couples the capacitor  224  to the cathode can  236  and a switch  228  that couples the capacitor  224  to ground. Similarly, the inductor  226  has a switch  228  that couples the inductor  226  to the cathode can  236  and a switch  228  that couples the inductor  226  to ground. In one embodiment, a capacitor  224  may be present without an inductor  226 . In another embodiment, an inductor  226  may be present without a capacitor  224 . In another embodiment, both a capacitor  224  and an inductor  226  may be present. In another embodiment, the cathode can  236  may be coupled directly to ground without coupling to a capacitor  224  and/or an inductor  226 . 
         [0035]    It should be understood that various embodiments discussed above may be utilized in any combination. For example, the cathode can  236  may or may not be present. If the cathode can  236  is present, the impedance circuit  222  may or may not be present. Similarly, an impedance circuit  222  may or may not be coupled to the chamber wall  220 . Similarly, an impedance circuit may or may not be coupled to the showerhead  208 . If the impedance circuit  222  is present, the capacitor  224  may or may not be present and the inductor  226  may or may not be present. The showerhead  208  may be coupled directly to ground, coupled to an impedance circuit  222 , or left open at a floating potential. The susceptor  206  may be coupled directly to ground or left open at a floating potential. Additionally, the wall  220  may be left open at a floating potential. 
         [0036]    The apparatus  200  may comprise a movable cathode (not shown) and may comprise a processing region without discontinuities. Without discontinuities may include a slit valve opening disposed at a location below the processing area. Additionally, multiple RF sources may be coupled to the apparatus  200 . Various combinations of series and parallel circuit elements and/or transmission lines may be used to achieve the desired impedance.  FIGS. 11A-11E  show several impedance circuits that may be utilized. It is to be understood that other impedance circuits may be utilized as well. 
         [0037]      FIG. 3  is a schematic cross sectional view of an etching apparatus  300  according to another embodiment of the invention. The apparatus  300  comprises a processing chamber  302  having a substrate  304  disposed therein. The substrate  304  may be disposed on a susceptor  306  opposite to a showerhead  308 . The susceptor  306  may be movable between a raised position and a lowered position. A vacuum pump  310  may evacuate the processing chamber  302  to the desired pressure. 
         [0038]    Similar to the embodiment shown in  FIG. 2 , an impedance circuit  312  may be used to control the plasma uniformity. The impedance circuit  312  may have an inductor  314  and/or a capacitor  316 . The impedance circuit  312  may have one or more switches  318  that may couple the capacitor  316  and/or the inductor  314  to ground and/or to the object. Impedance circuits  312  may be coupled to the chamber wall  320 , to the showerhead  308 , and to a cathode can  322 , if present. The cathode can  322 , if present, may be spaced form the susceptor  306  by a spacer  324 . In one embodiment, the spacer  324  may comprise a dielectric material. Similarly, the showerhead  308  may be electrically isolated from the chamber wall  320  by a spacer  326 . In one embodiment, the spacer  326  may comprise a dielectric material. 
         [0039]    The susceptor  306  may be coupled directly to ground, coupled to a power source  328 , or left open at a floating potential. The showerhead  308  may have two or more separate zones. The showerhead  308  may comprise a first zone  330  and a second zone  332 . In one embodiment, the second zone  332  may encircle the first zone  330 . Both the first zone  330  and the second zone  332  may each be coupled directly to ground, coupled to an impedance circuit  312 , or coupled to a power source  334 ,  336 . The first zone  330  may be electrically isolated from the second zone  332  by a spacer  338 . In one embodiment, the spacer  338  may comprise a dielectric material. 
         [0040]    It should be understood that various embodiments discussed above may be utilized in any combination. For example, the cathode can  322  may or may not be present. If the cathode can  322  is present, the impedance circuit  312  may or may not be present. Similarly, an impedance circuit  312  may or may not be coupled to the chamber wall  320 . Similarly, an impedance circuit  312  may or may not be coupled to the first zone  330  of the showerhead  308 . An impedance circuit  312  may or may not be coupled to the second zone  332  of the showerhead  308 . If the impedance circuit  312  is present, the capacitor  316  may or may not be present and the inductor  314  may or may not be present. The first and second zones  330 ,  332  of the showerhead  308  may be coupled directly to ground, coupled to an impedance circuit  312 , or left open at a floating potential. The susceptor  306  may be coupled directly to ground or left open at a floating potential. Additionally, the wall  320  may be left open at a floating potential. 
         [0041]    The apparatus  300  may comprise a movable cathode (not shown) and may comprise a processing region without discontinuities. Without discontinuities may include a slit valve opening disposed at a location below the processing area. Additionally, multiple RF sources may be coupled to the apparatus  300 . Various combinations of series and parallel circuit elements and/or transmission lines may be used to achieve the desired impedance.  FIGS. 11A-11E  show several impedance circuits that may be utilized. It is to be understood that other impedance circuits may be utilized as well. 
         [0042]    Examples shown below will discuss various arrangements of impedance circuits coupled with a plasma processing chamber and the how the impedance circuits affect the plasma uniformity. In general, the operating range for the pressure may be between a few mTorr to several thousand mTorr. 
       COMPARISON EXAMPLE 1 
       [0043]      FIG. 4  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead is coupled directly to ground, and the chamber wall is coupled directly to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 4 , the plasma density is high near the edge of the substrate. 
       EXAMPLE 1 
       [0044]      FIG. 5A  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead is coupled to ground through a capacitor having a capacitance of 70 pF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 5A , the plasma density near the edge of the substrate is increased compared to the plasma density shown in  FIG. 4 . The capacitor functions to push the plasma towards the chamber wall. 
       EXAMPLE 2 
       [0045]      FIG. 5B  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The chamber wall is coupled to ground through a capacitor having a capacitance of 70 pF. The showerhead is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 5B , the plasma density near the edge of the substrate is decreased compared to the plasma density shown in  FIG. 4 . The capacitor functions to push the plasma towards the showerhead. 
       EXAMPLE 3 
       [0046]      FIG. 6A  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead is coupled to ground through an inductor having an inductance of 10 nH and a capacitor having a capacitance of 0.36 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 6A , the plasma density near the edge of the substrate is decreased compared to the plasma density shown in  FIG. 4 . The capacitor and inductor together function to pull the plasma towards the showerhead. 
       EXAMPLE 4 
       [0047]      FIG. 6B  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The chamber wall is coupled to ground through an inductor having an inductance of 10 nH and a capacitor having a capacitance of 0.36 nF. The showerhead is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 6B , the plasma density near the edge of the substrate is increased compared to the plasma density shown in  FIG. 4 . The capacitor and inductor together function to pull the plasma towards the chamber wall. 
       COMPARISON EXAMPLE 2 
       [0048]      FIG. 7A  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the inner zone and the outer zone are coupled directly to ground. The chamber wall is also directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 7A , the plasma density near the edge of the substrate is substantially the same as the plasma density shown in  FIG. 4 . 
       EXAMPLE 5 
       [0049]      FIG. 7B  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the inner zone and the outer zone are coupled to an impedance circuit having an inductor and a capacitor. The inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 7B , the plasma density is pulled closer towards the center of the substrate and away from the wall as compared to  FIG. 7A . 
       EXAMPLE 6 
       [0050]      FIG. 7C  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. The outer zone is directly coupled to ground while the inner zone is coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. The inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is also directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 7C , the plasma density is pulled closer towards the center of the substrate and away from the wall as compared to both  FIG. 7A  and  FIG. 7B . 
       EXAMPLE 7 
       [0051]      FIG. 7D  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. The inner zone is directly coupled to ground while the outer zone is coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. The inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is also directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 7D , the plasma density is pulled closer towards the outer zone as compared to  FIG. 7A ,  FIG. 7B , and  FIG. 7C . 
       EXAMPLE 8 
       [0052]      FIG. 8A  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. The outer zone is directly coupled to ground while the inner zone is coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. The inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is also directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. As shown in  FIG. 8A , the plasma density is pulled closer towards the center of the substrate and away from the wall. 
       EXAMPLE 9 
       [0053]      FIG. 8B  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is evenly distributed between the inner and outer zones as compared to  FIG. 8A . 
       EXAMPLE 10 
       [0054]      FIG. 8C  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 35 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pulled closer towards the outer zone. 
       EXAMPLE 11 
       [0055]      FIG. 8D  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 40 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pulled closer towards the outer zone as compared to  FIG. 8A . 
       EXAMPLE 12 
       [0056]      FIG. 8E  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 45 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is more evenly distributed as compared to  FIG. 8D . 
       EXAMPLE 13 
       [0057]      FIG. 8F  shows the plasma distribution for a processing chamber in which the substrate is biased with 1 kW RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 400 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pulled closer towards the inner zone. 
       EXAMPLE 14 
       [0058]      FIG. 9A  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. The inner zone is coupled directly to ground while the outer zone is coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. The inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pulled closer towards the outer zone. 
       EXAMPLE 15 
       [0059]      FIG. 9B  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density substantially evenly distributed between the inner and outer zones. 
       EXAMPLE 16 
       [0060]      FIG. 9C  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 35 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pulled closer towards the inner zone. 
       EXAMPLE 17 
       [0061]      FIG. 9D  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises both an inductor and a capacitor. For the inner zone, the inductor has an inductance of 40 nH and the capacitor has a capacitance of 0.1 nF. For the outer zone, the inductor has an inductance of 30 nH and the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pulled closer towards the inner zone. 
       EXAMPLE 18 
       [0062]      FIG. 10A  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises only a capacitor. For the inner zone, the capacitor has a capacitance of 0.1 nF. For the outer zone, the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pushed closer towards the outer zone. 
       EXAMPLE 19 
       [0063]      FIG. 10B  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises only a capacitor. For the inner zone, the capacitor has a capacitance of 0.1 nF. For the outer zone, the capacitor has a capacitance of 1.0 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pushed closer towards the outer zone. 
       EXAMPLE 20 
       [0064]      FIG. 10C  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises only a capacitor. For the inner zone, the capacitor has a capacitance of 1.0 nF. For the outer zone, the capacitor has a capacitance of 0.1 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pushed closer towards the inner zone. 
       EXAMPLE 21 
       [0065]      FIG. 10D  shows the plasma distribution for a processing chamber in which the substrate is biased with RF current. The showerhead has both an inner zone and an outer zone circumscribing the inner zone. Both the outer zone and the inner zone are coupled to an impedance circuit. The impedance circuit comprises only a capacitor. For the inner zone, the capacitor has a capacitance of 1.0 nF. For the outer zone, the capacitor has a capacitance of 1.0 nF. The chamber wall is directly coupled to ground. The showerhead is spaced a few centimeters from the substrate. The plasma is an argon plasma at a pressure of about 100 mTorr. The plasma density is pushed closer towards the inner zone. 
         [0066]    The impedance circuit may be preselected to control the plasma uniformity. For example, if an inductor is present, the inductance may be preselected prior to processing. During processing, the inductance may be changed to suit the needs of the process. The inductance change may occur at any time during processing. Similarly, the capacitance of the capacitor, if present, may be preselected to control the plasma uniformity. For example, the capacitance may be preselected prior to process. During processing, the capacitance may be changed to suit the needs of the process. The capacitance change may occur at any time during processing. 
         [0067]    By selectively utilizing impedance circuits coupled to the chamber wall and/or the showerhead and/or a cathode can (if present), the plasma uniformity may be controlled to suit the needs of the user. Additionally, splitting the showerhead into at least two separate zones may provide an additional level of control over the plasma uniformity. By controlling the plasma uniformity, an etching process may be performed while reducing undesired over or under etching. 
         [0068]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.