Abstract:
A plasma processing system for use with a gas. The plasma processing system comprises a first electrode, a second electrode, a gas input port, a power source and a passive circuit. The gas input port is operable to provide the gas between the first electrode and the second electrode. The power source is operable to ignite plasma from the gas between the first electrode and the second electrode. The passive circuit is coupled to the second electrode and is configured to adjust one or more of an impedance, a voltage potential, and a DC bias potential of the second electrode. The passive radio frequency circuit comprises a capacitor arranged in parallel with an inductor.

Description:
[0001]    The present application claims benefit under 35 U.S.C. §119 (e) to U.S. provisional patent application 61/166,994, filed Apr. 6, 2009, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Advances in plasma processing have facilitated growth in the semiconductor industry. Plasma processing may involve different plasma generating technologies, for example, inductively coupled plasma processing systems, capacitively-coupled plasma processing systems, microwave generated plasma processing systems and the like. Manufacturers often employ capacitively-coupled plasma processing systems in processes that involve etching and/or depositing of materials to manufacture semiconductor devices. 
         [0003]    Next-generation semiconductor devices being fabricated with new advanced materials, complex stacks of dissimilar materials, thinner layers, smaller features, and tighter tolerances may require plasma processing systems with more exact control and wider operating windows for plasma process parameters. Thus, an important consideration for plasma processing of substrates involves capacitively-coupled plasma processing systems possessing capabilities to control a plurality of plasma related process parameters. Conventional methods to control plasma related process parameters may include a passive RF coupling circuit, a radio frequency (RF) generator or a DC power source. 
         [0004]      FIG. 1A  illustrates a simplified schematic of a prior art plasma processing system  100  during a plasma etching process. Plasma processing system  100  includes a confinement chamber  102 , upper electrode  104 , a lower electrode  106  and an RF driver  108 . Confinement chamber  102 , upper electrode  104  and lower electrode  106  are arranged to provide a plasma-forming space  110 . RF driver  108  is electrically connected to lower electrode  106 , while upper electrode  104  is electrically connected to ground. 
         [0005]    In operation, a substrate  112  is held on lower electrode  106  via an electrostatic force. A gas source (not shown) supplies an etching gas to plasma-forming space  110 . RF driver  108  provides a driving signal to lower electrode  106 , thus providing a voltage differential between lower electrode  106  and upper electrode  104 . The voltage differential creates an electromagnetic field in plasma-forming space  110 , wherein the gas in plasma-forming space  110  is ionized, forming plasma  114 . Plasma  114  etches the surface of substrate  112 . 
         [0006]      FIG. 1B  illustrates a magnified view of the bottom portion of plasma processing system  100  during a conventional etching process. As shown in the figure, a plasma sheath  116  is formed between plasma  114  and the surface of substrate  112 . Plasma sheath  116  bears the potential drop between the potential of plasma  114  and the potential of lower electrode  106 . Plasma ions  118  from plasma  114  are accelerated toward the surface of substrate  112  via the potential drop across plasma sheath  116 . The bombardment of substrate  112  with plasma ions  118  causes material on the surface of substrate  112  to be etched away. During the etching process, the flux of neutral species along with ions from plasma also causes a polymer layer to be deposited on substrate  112 . In this manner, plasma  114  may be used to etch and/or deposit materials onto substrate  112  in order to create electronic devices. 
         [0007]    In reality, the need to precisely control plasma processing parameters and etching/deposition behavior require that plasma processing systems be more complex than that of plasma processing system  100  of  FIGS. 1A &amp; 1B . 
         [0008]      FIG. 2  shows a simplified schematic of a prior art plasma processing system  200 . As illustrated in  FIG. 2 , plasma processing system  200  includes an upper electrode  204 , a lower electrode  206 , a grounded upper extension ring  210 , an upper insulator  212 , a grounded bottom extension ring  214 , a bottom insulator  216 , an RF matching circuit  218 , an RF generator  220 , an RF matching circuit  222  and an RF generator  224 . 
         [0009]    The basic setup of plasma processing system  200  of  FIG. 2  is similar to the aforementioned plasma processing system  100  of  FIG. 1A , but differs in that instead of upper electrode  204  being grounded, it is connected to RF generator  224  via RF matching circuit  222 . In this manner the RF bias of upper electrode  204  can be independently controlled. Also, plasma processing system  200  contains grounded upper and bottom extension rings that drain RF current from the plasma boundaries. In the example of plasma processing system  200 , lower electrode  206  is electrically isolated from grounded bottom extension ring  214  by bottom insulator  216 . Similarly, upper electrode  204  is electrically isolated from a grounded upper extension ring  210  by upper insulator  212 . 
         [0010]    Plasma processing system  200  may be a single, double (DFC), or triple frequency RF capacitively discharge system. Non-limiting examples of radio frequencies provided by RF generator  224  include 2, 27 and 60 MHz. In plasma processing system  200 , a substrate  208  may be disposed above lower electrode  206  for processing. 
         [0011]    Consider the situation wherein, for example, substrate  208  is being processed. During plasma processing, RF generator  220  with a path to ground may supply a low power RF bias to lower electrode  206  through RF matching circuit  218 . As an example, RF matching circuit  218  may be used to maximize power delivery to plasma processing system  200 . The driving signal from RF generator  220  provided to lower electrode  206  provides a voltage differential between lower electrode  206  and upper electrode  204 . The voltage differential creates an electromagnetic field which causes a gas to become ionized, thereby generating a plasma between upper electrode  204  and lower electrode  206  (the gas and the plasma are not shown to simplify schematic). The plasma may be used to etch and/or deposit materials onto substrate  208  to create electronic devices. 
         [0012]    Consider the situation, wherein, for example, a manufacturer may want to adjust the voltage of upper electrode  204  during the etching process to provide additional control over plasma processing parameters. The voltage of upper electrode  204  may be adjusted by RF generator  224  through RF matching circuit  222  with a path to ground. RF generator  224 , in the example of  FIG. 2 , may be high powered. 
         [0013]    Another type of prior art plasma processing system will now be described with reference to  FIG. 3 . 
         [0014]      FIG. 3  shows a simplified schematic of a prior art plasma processing system  300 . As illustrated in  FIG. 3 , plasma processing system  300  includes upper electrode  204 , lower electrode  206 , grounded upper extension ring  210 , upper insulator  212 , grounded bottom extension ring  214 , bottom insulator  216 , RF matching circuit  218 , RF generator  220 , an RF filter  322  and a DC power source  324 . In plasma processing system  300 , substrate  208  may be disposed above lower electrode  206  for processing. 
         [0015]    Plasma processing system  300  of  FIG. 3  is similar to the aforementioned multi-frequency capacitively-couple plasma processing system  200  of  FIG. 2 , but differs in the extent that in the example of  FIG. 3 , DC power source  324  is coupled to upper electrode  204  through RF filter  322  with a path to ground. RF filter  322  is generally used to provide attenuation of unwanted harmonic RF energy without introducing losses to DC power source  324 . Unwanted harmonic RF energy is generated when the plasma discharges and may be kept from being returned to the DC power source by RF filter  322 . 
         [0016]    Consider the situation wherein, for example, a manufacturer may want to adjust the DC potential of upper electrode  204  during plasma processing to provide additional control over plasma processing parameters. The DC potential of upper electrode  204 , in the example of  FIG. 3 , may be adjusted by employing DC power source  324 . Typically the purpose of applying a DC bias on upper electrode  204  would be to prevent electrons from going to upper electrode  204 , therefore keeping them captured in the plasma. In this manner, the plasma density can be increased, which thereby increases the etch rate of the material of substrate  208 . 
         [0017]    The aforementioned plasma processing systems require employing an external RF and/or DC power supply to adjust the voltage on the upper electrode to attain additional control over plasma-related parameters. Since the requirement of external power sources may be expensive to implement, plasma processing systems that use an RF coupling circuit with a DC current path to ground in order to achieve RF coupling and DC bias have been developed. This type of prior art plasma processing system will now be described with reference to  FIGS. 4 and 5 . 
         [0018]      FIG. 4  shows a simplified schematic of a conventional plasma processing system  400 . As illustrated in  FIG. 4 , plasma processing system  400  includes upper electrode  204 , lower electrode  206 , a grounded upper extension ring  404 , upper insulator  212 , a grounded bottom extension ring  412 , bottom insulator  216 , RF matching circuit  218 , RF generator  220 , a conductive coupling member  410  and an RF coupling circuit  402 . In plasma processing system  400 , substrate  208  may be disposed above lower electrode  206  for processing. 
         [0019]    Plasma processing system  400  of  FIG. 4  is similar to the aforementioned multi-frequency capacitively-coupled plasma processing systems  200  and  300  of  FIG. 2  and  FIG. 3 , but differs in that in the example of  FIG. 4 , upper electrode  204  is connected to a passive circuit (RF coupling circuit  402 ) instead of an external RF or DC source. Specifically, RF coupling circuit  402  is coupled to upper electrode  204  with a path to DC ground. Instead of using external power sources as done in the examples of in  FIG. 2  and  FIG. 3 , in  FIG. 4 , RF coupling and DC bias to upper electrode  204  is achieved by providing a DC current return to ground and RF coupling circuit  402 . 
         [0020]    Plasma processing system  400  of  FIG. 4  also differs from the examples of  FIG. 2  and  FIG. 3  in that in plasma processing system  400 , the various extension rings are different, as will be further discussed below. 
         [0021]    In plasma processing system  400 , upper electrode  204  is electrically isolated from grounded upper electrode extension ring  404  by upper insulator  112 . Grounded upper electrode extension ring  404  may be constructed of a conductive aluminum material that is covered with a quartz layer  414  on the surface. Similarly, lower electrode  206  is electrically isolated from DC grounded bottom extension ring  412  by bottom insulator  216 . Grounded bottom extension ring  412  may be constructed of conductive aluminum material that may be covered with a quartz layer  416  on the surface. Other conductive materials may also be employed in the construction of lower electrode extension ring  412 . 
         [0022]    Conductive coupling member  410  is disposed above the aluminum portion of lower electrode extension ring  412  to provide a path for DC current return to ground. Conductive coupling member  410  may be constructed of silicon. Alternatively, conductive coupling member  410  may also be constructed of other conductive materials. In plasma processing system  400 , conductive coupling member  410  is a ring shape. The ring shape advantageously provides radial uniformity for DC current return to ground at the bottom of the plasma processing chamber. However, conductive coupling member  410  may be formed into any appropriate shape, e.g., a circular disc shape, a doughnut shape and the like, that may provide uniformity for DC current return to ground. 
         [0023]    Upper electrode  204  is provided with RF coupling circuit  402  that controls the RF coupling to ground. RF coupling circuit  402  does not require a power supply, i.e., RF coupling circuit  402  is a passive circuit. RF coupling circuit  402  may be configured with a circuit to vary the impedance and/or the resistance to change the RF voltage potential and/or the DC bias potential on upper electrode  204 , respectively. A prior art example RF coupling circuit  402  will now be described with reference to  FIG. 5 . 
         [0024]      FIG. 5  is an exploded view of an example RF coupling circuit  402 . As illustrated in  FIG. 5 , RF coupling circuit  402  includes an inductor  502 , a variable capacitor  504 , an RF filter  506 , a variable resistor  508  and a switch  510 . RF coupling circuit  402  is configured with inductor  502  in series with variable capacitor  504  with a path to ground for generating a variable impedance output. Non-limiting example capacitance values of variable capacitor  504  include between about 20 pF to about 4,000 pF, when the operating frequency is about 2 MHz. A non-limiting example of an inductance value of inductor  502  is about 14 nH. 
         [0025]    RF filter  506  is connected to variable resistor  508  and switch  510  for generating a variable resistance output. When switch  510  is open, upper electrode  204  of  FIG. 4  is floating and there is no DC current path. When switch  510  is closed, a current path tends to flow from upper electrode  304  through the plasma (not shown) to DC grounded bottom extension ring  412  via conductive coupling member  410  of  FIG. 4 . 
         [0026]    Variable capacitor  504  and inductor  502  are disposed in the current path thereby providing the impedance to the current flow. The impedance of RF coupling circuit  402  may be adjusted by changing the value of variable capacitor  504 . The RF voltage potential of upper electrode  204  of  FIG. 4  may be controlled by changing the impedance through inductor  502  and variable capacitor  504  of RF coupling circuit  402 . As mentioned previously, RF coupling circuit  302  is a passive circuit and therefore does not require a power supply. 
         [0027]    Furthermore, variable resistor  508  is disposed in the current path to provide resistance to the current flow. The resistance of RF coupling circuit  402  may be adjusted by changing the value of variable resistor  508 . Thus, the DC potential of upper electrode  204  of  FIG. 4  may be controlled to provide gradation in the DC potential values between DC floating, in which switch  510  of  FIG. 5  is opened, and DC ground, in which switch  510  of  FIG. 5  is closed. 
         [0028]    RF coupling circuit  402  provides methods and arrangements for controlling plasma process parameters (e.g., plasma density, ion energy, and chemistry) by adjusting the RF impedance and/or the DC bias potential on upper electrode  204  by employing RF coupling with a DC current path to ground. Control may be achieved without employing any external power supply source. 
         [0029]    Future generations of plasma etchers will require scaling of geometrical dimensions of hardware and good transferability of current processes for large substrate diameters. Unfortunately, the aforementioned plasma processing systems do not offer sufficient scaling and transferability of current processes for large substrate diameters. What is needed is a plasma processing system that provides scaling and transferability of current processes for large substrate diameters while allowing control over plasma related parameters. 
       BRIEF SUMMARY 
       [0030]    It is an object of the present invention to provide a capacitively coupled plasma processing system which provides scaling and transferability of current processes, control of plasma uniformity, density, and radial distribution for large substrate diameters. 
         [0031]    An aspect of the present invention is drawn to a plasma processing system for use with a gas. The plasma processing system comprises a first electrode, a second electrode, a gas input port, a power source and a passive circuit. The gas input port is operable to provide the gas between the first electrode and the second electrode. The power source is operable to ignite plasma from the gas between the first electrode and the second electrode. The passive circuit is coupled to the second electrode and is configured to adjust one or more of an impedance, a voltage potential, and a DC bias potential of the second electrode. The passive radio frequency circuit comprises a capacitor arranged in parallel with an inductor. 
         [0032]    Additional objects, advantages and novel features of the invention are set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         [0033]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate an exemplary embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
           [0034]      FIG. 1A  illustrates a simplified schematic of a prior art plasma processing system during a plasma etching process; 
           [0035]      FIG. 1B  illustrates a magnified view of the bottom portion of plasma processing system of  FIG. 1A  during a conventional etching process; 
           [0036]      FIG. 2  shows a simplified schematic of a prior art plasma processing system with an RF generator coupled to an upper electrode; 
           [0037]      FIG. 3  illustrates a prior art plasma processing system with a DC power source connected to an upper electrode; 
           [0038]      FIG. 4  illustrates a prior art plasma processing system with an RF circuit arrangement coupled to an upper electrode with a path to DC ground; 
           [0039]      FIG. 5  illustrates a simplified schematic of an RF circuit arrangement; 
           [0040]      FIG. 6  shows, in accordance with an embodiment of the present invention, a simplified schematic for a plasma processing system containing an upper electrode coupled to a resonant filter circuit arrangement with a path to DC ground through an inductor; 
           [0041]      FIG. 7  illustrates, in accordance with an embodiment of the present invention, a graph representing data showing the measured effects of etch rate on a substrate versus the radius or distance away from the center of the substrate compared to the etch rate for a similarly configured system except with a floating upper electrode; 
           [0042]      FIG. 8  illustrates, in accordance with an embodiment of the present invention, a graph representing data showing the impedance of a resonant filter circuit with a path to DC ground versus the capacitance value of a variable capacitor, a component of resonant filter; 
           [0043]      FIG. 9  illustrates, in accordance with an embodiment of the present invention, a graph representing data showing the DC voltage of a lower electrode and the RF voltage of an upper electrode versus the capacitance value of a variable capacitor, a component of the resonant RF circuit. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]      FIG. 6  illustrates a plasma processing system  600  in accordance with an example embodiment of the present invention. As illustrated in  FIG. 6 , plasma processing system  600  includes upper electrode  204 , lower electrode  206 , RF matching circuit  218 , RF generator  220 , upper insulator  212 , bottom insulator  216 , grounded bottom extension ring  214 , grounded upper extension ring  210 , a set of confinement rings  602 , an RF ground device  604  and a resonant filter  606 . Resonant filter  606  includes an inductor  608 , a variable capacitor  610  and a stray capacitance  612 . In plasma processing system  600 , a substrate  208  may be disposed above lower electrode  206  for processing. 
         [0045]    RF generator  220  provides RF power to lower electrode  206  through RF matching circuit  218 . Non-limiting examples of radio frequencies supplied by RF generator  220  include 2, 27 and 60 MHz. 
         [0046]    Upper electrode  204  opposes lower electrode  206  and is capacitively coupled thereto. Upper electrode  204  is additionally coupled to ground and electrically isolated from grounded upper extension ring  210  by upper insulator  112 . Lower electrode  206  is coupled to ground and electrically isolated from grounded bottom extension ring  214  by bottom insulator  216 . 
         [0047]    Upper electrode  204  is able to couple to resonant filter  606 . Upper electrode  104  is also able to be grounded via RF ground device  604 . Stray capacitance  612  is defined as parasitic capacitance of electrode  204  to ground. Inductor  608  and variable capacitor  610  are arranged in parallel with one another and are each connected to ground. 
         [0048]    In operation, a gas  614  is provided, by a gas source (not shown) into a plasma forming space  618 . A driving signal is provided by RF generator  220  through RF matching circuit  218  to lower electrode  206 . The driving signal creates an electromagnetic field between upper electrode  204  and lower electrode  206 , which turns gas  614  within plasma forming space  618  into plasma  622 . Plasma  622  may then be used to etch substrate  208  for creating electronic devices. 
         [0049]    The impedance of resonant filter  606  can be controlled by varying the capacitance of variable capacitor  610 . By adjusting the impedance of resonant filter  606 , the low frequency RF current path between upper electrode  604  and grounded upper extension ring  610  can be controlled. Also, modifying the impedance of resonant filter  606  modifies upper electrode  204 &#39;s RF voltage and phase relationship between the upper and lower sheaths of plasma  622 . In this manner, plasma processing parameters such as the shape and density of plasma  622  can be controlled by simply adjusting the impedance of resonant filter  606 . 
         [0050]    For example, if the impedance of the resonant filter  606  is high, low frequency RF current is blocked from going into upper electrode  204 , developing large electrode DC self-bias. In this case with provided DC current path through plasma between upper electrode  204  and grounded upper ( 210 ) and lower ( 214 ) grounded extension rings, plasma sheath may not collapse at upper electrode  204  during rf cycle. Therefore, the electrons approaching electrode  204  can be reflected back into plasma and remain captured in plasma, producing more ionization and, therefore, increasing plasma density. Also by tuning the resonant filter, both top and bottom plasma sheaths can be run at nearly in-phase condition, resulting in trapping of electrons in the plasma bulk, and, therefore, plasma density enhancement. The local increase in plasma density will therefore cause a local increase in the etch rate of substrate  208 . Thus, in this fashion, a properly tuned resonant filter  606  may have the same effect of applying a DC bias to upper electrode  204 , as done in prior art plasma processing system  300  in  FIG. 3 . 
         [0051]    In this manner, by simply tuning the impedance of resonant filter  606 , it is possible to control the radial distribution of plasma  622  above substrate  208 , and therefore control the radial distribution of plasma processing parameters such as etch rate. This will be discussed further below in reference to  FIG. 7 . 
         [0052]      FIG. 7  compares the etch rate as a function of substrate radius for a plasma processing system with a floating upper electrode  204  and for an example plasma processing system in accordance with the present invention (in which upper electrode  204  is coupled to resonant filter  606 ). The figure includes a graph  700 , wherein the x-axis is substrate radius (in mm), and the y-axis is the etch rate of substrate  208  (in Å/min). Graph  700  includes a dotted function  702  and a dashed function  704 . Dotted function  702  represents an etch rate as a function of substrate radius for a plasma processing system in which upper electrode  204  is floating. Dashed function  704  represents an etch rate as a function of wafer radius in accordance with an aspect of the present invention, in which upper electrode  204  is coupled to resonant filter  606 . 
         [0053]    Dotted function  702  features a maximum etch rate of approximately 3950 Å/min, indicated by point  706 , at the center of the substrate, i.e., a substrate radius of 0 mm. Dotted function  702  decreases as the radius increases, to a minimum etch rate of approximately 3750 Å/min at ±147 mm from the center of the substrate, indicated by points  712  and  714 . 
         [0054]    Dashed function  704  features a maximum etch rate of approximately 4750 Å/min, indicated by point  708 , at the center of the substrate, i.e., a wafer radius of 0 mm. Dashed function  704  decreases as the radius increases, to a minimum etch rate of approximately 3850 Å/min at ±147 mm from the center of the substrate, indicated by points  710  and  716 . 
         [0055]    It is clear from graph  700  that the maximum etch rates for the plasma processing system with floating upper electrode and the example plasma processing system in accordance with the present invention are achieved at the center of the substrate. It is further clear from graph  700  that the etch rates for the plasma processing system with floating upper electrode  204  and the example plasma processing system in accordance with the present invention decrease as the distance from the center of the substrate increases. However, the key point here is how the radial distribution of the etch rate changes as a result of implementing resonant filter  606  to upper electrode  204 . 
         [0056]    The etch rate at the center of the substrate, i.e., point  708 , of the example plasma processing system in accordance with the present invention is approximately 20% more than the etch rate at the center of the substrate, i.e., point  706 , of the plasma processing system with floating upper electrode  204 . The etch rate at the substrate edges, radius off 147 mm, i.e., points  716  and  710 , of the example plasma processing system in accordance with the present invention is approximately 2.7% more than the etch rate at a substrate radius of ±147 mm, i.e., points  712  and  714 , of the plasma processing system with upper electrode  204  floating. Therefore, it is clear that here, the effect of resonant filter  606  coupled to upper electrode  204  was mainly to increase the etch rate in the center of substrate. 
         [0057]    Although maintaining radial uniformity of etch rate is typically the goal in most plasma processing applications, having the ability to increase the etch rate preferentially in the center of the substrate may be useful in many cases. For instance, in the cases where plasma processing system  600  nominally provides an etch rate that results in lower etch rate in the center, by implementing a properly tuned resonant filter  606 , one can compensate for this effect and thereby produce an end result that has uniform etch rate over the entire substrate. 
         [0058]    In essence, in plasma processing system  600 , one has the ability to modify the shape of the graph for the etch rate versus radius simply by tuning resonant filter  606 . This capability allows the etch rate to be tuned or matched with the remainder of plasma processing system  600  in order to provide a processed substrate with an increased etch rate and uniform etch profile across the entire diameter. 
         [0059]      FIG. 8  illustrates a graph of the impedance of resonant filter  606  as a function  800  of the capacitance of variable capacitor  610 . As illustrated in  FIG. 8 , the x-axis of the graph represents the capacitance of variable capacitor  610  (0 pF, 1450 pf), whereas the y-axis of the graph represents the impedance of resonant filter  606  (−2000Ω, 2500Ω). The RF frequency in this case here is around 2 MHz. 
         [0060]    As illustrated in the figure, the impedance of resonant filter  606  gradually increases from point  802 , where variable capacitor  610  has close to no capacitance, to point  804 , where variable capacitor  610  has approximately a 800 pF capacitance. Then the impedance of resonant filter  606  increases more drastically from point  804 , to point  806 , where variable capacitor  610  has approximately a 1000 pF capacitance. Then the impedance of resonant filter  606  asymptotically increases from point  806 , to point  808 , where variable&#39;capacitor  610  has approximately 1200 pF capacitance. 
         [0061]    As discussed previously, the effect of high impedance of resonant filter  606  is to increase plasma density and substrate etch rate, mostly in the center of substrate. Therefore, in order to be able to increase the etch rate preferentially in the center (as done in the case of dashed function  704  of  FIG. 7 ), one can configure variable capacitor  610  to result in the maximum impedance which allows a stable plasma  622  to be maintained. In  FIG. 8 , it is clear that point  808  (corresponding to a capacitance value of 1200 pF) gives the maximum possible impedance for resonant filter  606 ; however, since it is a very unstable point it may be difficult to maintain plasma  622  under that condition. A more suitable choice would be one which results in less impedance value but still allows plasma  622  to be maintained. An example of a suitable choice here could be point  806 , which corresponds to capacitor value of approximately 1000 pF. 
         [0062]      FIG. 9  is a graph of potential as a function of the capacitance of variable capacitor  610 . As illustrated in  FIG. 8 , the x-axis of the graph represents the capacitance of variable capacitor  610  (0 pF, 1450 pf), whereas the y-axis of the graph represents potential (−1000 V, 1500 V). 
         [0063]    As illustrated in  FIG. 9 , dashed line  902  represents the DC bias of lower electrode  206  as a function of the capacitance of variable capacitor  610 , whereas dotted line  904  represents the peak-to-peak rf voltage of upper electrode  204  as a function of the capacitance of variable capacitor  610 . The graph illustrates how the DC voltage of lower electrode  206  and the peak-to-peak voltage of upper electrode  204  can be modified by simply varying the value of variable capacitor  610 . It also shows how the capacitance value corresponding to point  806  in  FIG. 8  (where variable capacitor  610 =1000 pF) results in maximum peak-to-peak voltage on upper electrode while also maintaining relatively high value of DC bias on lower electrode  206 . 
         [0064]    As may be appreciated from the foregoing, embodiments of the invention provide methods and arrangements for controlling plasma parameters (e.g., plasma density, ion energy, and chemistry) by adjusting the RF impedance on upper electrode  204  employing resonant filter  606  circuit with a DC current path to ground via inductor  608 . Resonant filter  606  circuit and the DC ground path are relatively simple to implement. Also, control may be achieved without employing a DC power supply source. By eliminating the need for a power source, cost saving may be realized while maintaining control of plasma processing in a capacitively-coupled plasma processing chamber. 
         [0065]    The foregoing description of various preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments, as described above, were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.