Abstract:
A match circuit includes the following: a power input circuit coupled to an RF source; an inner coil input circuit coupled between the power input circuit and an input terminal of an inner coil, the inner coil input circuit including an inductor and a capacitor coupled in series to the inductor, the inductor connecting to the power input circuit, and the capacitor connecting to the input terminal of the inner coil, a first node being defined between the power input circuit and the inner coil input circuit; an inner coil output circuit coupled between an output terminal of the inner coil and ground, the inner coil output circuit defining a direct pass-through connection to ground; an outer coil input circuit coupled between the first node and an input terminal of an outer coil; and an outer coil output circuit coupled between an output terminal of the outer coil and ground.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority as a continuation of U.S. application Ser. No. 13/751,001, filed Jan. 25, 2013, entitled “TCCT Match Circuit for Plasma Etch Chambers,” which claims priority to U.S. Provisional Application No. 61/747,919, filed on Dec. 31, 2012, and entitled “TCCT Match Circuit for Plasma Etch Chambers.” U.S. application Ser. No. 13/751,001 claims priority as a Continuation-in-Part of U.S. patent application Ser. No. 13/658,652, filed on Oct. 23, 2012, and entitled “Faraday Shield Having Plasma Density Decoupling Structure Between TCP Coiling Zones,” which claims priority as a Continuation-in-Part of U.S. patent application Ser. No. 13/198,683, filed on Aug. 4, 2011, and entitled “Internal Faraday Shield Having Distributed Chevron Patterns and Correlated Positioning Relative to External Inner and Outer TCP Coil, which claims priority to U.S. Provisional Patent Application No. 61/480,314 filed on Apr. 28, 2011 and entitled “Internal Faraday Shield Having Distributed Chevron Patterns and Correlated Positioning Relative to External Inner and outer TCP Coil.” The disclosures of these applications are incorporated herein by reference in their entirety for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to semiconductor fabrication, and more particularly, to a TCCT match circuit for plasma etch chambers. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    In semiconductor manufacturing, etching processes are commonly and repeatedly carried out. As is well known to those skilled in the art, there are two types of etching processes: wet etching and dry etching. One type of dry etching is plasma etching performed using an inductively coupled plasma etching apparatus. 
         [0004]    A plasma contains various types of radicals, as well as positive and negative ions. The chemical reactions of the various radicals, positive ions, and negative ions are used to etch features, surfaces and materials of a wafer. During the etching process, a chamber coil performs a function analogous to that of a primary coil in a transformer, while the plasma performs a function analogous to that of a secondary coil in the transformer. 
         [0005]    Existing transformer coupled capacitive tuning (TCCT) match designs suffer from a number of problems, especially when utilized to perform manufacturing processes for magneto-resistive random access memory (MRAM). Problems include a limited TCCT range, limited transformer coupled plasma (TCP) power, high coil voltages, and coil arcing. As a result, the process window of the reactor chamber can be quite limited, meaning that a variety of recipes cannot be accommodated. If a recipe out of the process window is forced to run, it may be aborted due to over voltage and/or over current interlocks, and even worse, may result in arcing of the TPC coil and destruction of the ceramic window and ceramic cross. Furthermore, a sputtering effect of the ceramic window due to capacitive coupling by the TCP coil can develop over time when terminal voltages are not well balanced. The result is sputtering of particles from the ceramic window that are subsequently deposited on the wafer, which may result in loss of yield. This effect can limit the operational longevity of the reactor to, for example, 500 RF hours of operation. 
         [0006]    In view of the foregoing, there is a need for an improved TCCT match circuit for plasma etch chambers. 
       SUMMARY 
       [0007]    Disclosed is an apparatus used in etching semiconductor substrates and layers formed thereon during the manufacturer of semiconductor devices. The apparatus is defined by TCCT match circuitry which controls the operation of TCP coils of a plasma processing chamber in which etching is performed. 
         [0008]    In one embodiment, a match circuit coupled between an RF source and a plasma chamber is provided, the match circuit including the following: a power input circuit, the power input circuit coupled to an RF source; an inner coil input circuit coupled between the power input circuit and an input terminal of an inner coil, the inner coil input circuit including an inductor and a capacitor coupled in series to the inductor, the inductor connecting to the power input circuit, and the capacitor connecting to the input terminal of the inner coil, a first node being defined between the power input circuit and the inner coil input circuit; an inner coil output circuit coupled between an output terminal of the inner coil and ground, the inner coil output circuit defining a direct pass-through connection to ground; an outer coil input circuit coupled between the first node and an input terminal of an outer coil; an outer coil output circuit coupled between an output terminal of the outer coil and ground. 
         [0009]    In one embodiment, the capacitor is a variable capacitor having a value of between about 150 pF to about 1500 pF; and the inductor has a value of about 0.3 uH to about 0.5 uH. 
         [0010]    In one embodiment, the outer coil input circuit includes a second capacitor. 
         [0011]    In one embodiment, the second capacitor is a variable capacitor having a rating of about 150 pF to about 1500 pF. 
         [0012]    In one embodiment, the outer coil output circuit includes a second capacitor. In one embodiment, the second capacitor has a value of about 80 pF to about 120 pF. In another embodiment, the second capacitor has a value of about 100 pF+/−about 1%. 
         [0013]    In one embodiment, the power input circuit includes a second capacitor coupled to the RF source, a second inductor coupled to the inner coil input circuit, a third capacitor coupled between the second capacitor and the second inductor, a second node being defined between the second capacitor and the third capacitor, and a fourth capacitor coupled between the second node and ground. In one embodiment, the second capacitor has a rating of about 5 pF to about 500 pF; the third capacitor has a rating of about 50 pF to about 500 pF; the second inductor has a value of about 0.3 uH to about 0.5 uH; and the fourth capacitor has a value of about 200 pF to about 300 pF. In one embodiment, the fourth capacitor has a value of about 250 pF+/−about 1%. 
         [0014]    In another embodiment, a match circuit is provided, including the following: a power input circuit, the power input circuit coupled to an RF source; an inner coil input circuit coupled between the power input circuit and an input terminal of an inner coil, the inner coil input circuit including an inductor and a first capacitor coupled in series to the inductor, the inductor connecting to the power input circuit, and the first capacitor connecting to the input terminal of the inner coil, a first node being defined between the power input circuit and the inner coil input circuit; an inner coil output circuit coupled between an output terminal of the inner coil and ground, the inner coil output circuit defining a direct pass-through connection to ground; an outer coil input circuit coupled between the first node and an input terminal of an outer coil; an outer coil output circuit coupled between an output terminal of the outer coil and ground, the outer coil output circuit including a second capacitor having a value greater than about 100 pF. 
         [0015]    In one embodiment, the first capacitor is a variable capacitor having a value of between about 150 pF to about 1500 pF; and the inductor has a value of about 0.3 uH to about 0.5 uH. 
         [0016]    In one embodiment, the outer coil input circuit includes a third capacitor. In one embodiment, the third capacitor is a variable capacitor having a rating of about 150 pF to about 1500 pF. 
         [0017]    In one embodiment, the power input circuit includes a third capacitor coupled to the RF source, a second inductor coupled to the inner coil input circuit, a fourth capacitor coupled between the third capacitor and the second inductor, a second node being defined between the third capacitor and the fourth capacitor, and a fifth capacitor coupled between the second node and ground. In one embodiment, the third capacitor has a rating of about 5 pF to about 500 pF; the fourth capacitor has a rating of about 50 pF to about 500 pF; the second inductor has a value of about 0.3 uH to about 0.5 uH; and the fifth capacitor has a value of about 200 pF to about 300 pF. In one embodiment, the fifth capacitor has a value of about 250 pF+/−about 1%. 
         [0018]    In another embodiment, a match circuit is provided, including the following: a power input circuit, the power input circuit coupled to an RF source; an inner coil input circuit coupled between the power input circuit and an input terminal of an inner coil, the inner coil input circuit including an inductor and a first capacitor coupled in series to the inductor, the inductor connecting to the power input circuit, and the first capacitor connecting to the input terminal of the inner coil, a first node being defined between the power input circuit and the inner coil input circuit; an inner coil output circuit coupled between an output terminal of the inner coil and ground, the inner coil output circuit defining a direct pass-through connection to ground; an outer coil input circuit coupled between the first node and an input terminal of an outer coil, the outer coil input circuit includes a second capacitor; an outer coil output circuit coupled between an output terminal of the outer coil and ground, the outer coil output circuit including a third capacitor. 
         [0019]    In one embodiment, the first capacitor is a variable capacitor having a rating of between about 150 pF to about 1500 pF; and wherein the inductor has a value of about 0.3 uH to about 0.5 uH. 
         [0020]    In one embodiment, the second capacitor is a variable capacitor having a rating of about 150 pF to about 1500 pF. 
         [0021]    In one embodiment, the third capacitor has a value of about 80 pF to about 120 pF. In one embodiment, the third capacitor has a value of about 100 pF+/−about 1% 
         [0022]    In one embodiment, the power input circuit includes a fourth capacitor coupled to the RF source, a second inductor coupled to the inner coil input circuit, a fifth capacitor coupled between the fourth capacitor and the second inductor, a second node being defined between the fourth capacitor and the fifth capacitor, and a sixth capacitor coupled between the second node and ground. In one embodiment, the fourth capacitor has a rating of about 5 pF to about 500 pF; wherein the fifth capacitor has a rating of about 50 pF to about 500 pF; the second inductor has a value of about 0.3 uH to about 0.5 uH; and the sixth capacitor has a value of about 200 pF to about 300 pF. In one embodiment, the sixth capacitor has a value of about 250 pF+/−about 1%. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings. 
           [0024]      FIG. 1  illustrates a plasma processing system utilized for etching operations, in accordance with one embodiment of the present invention. 
           [0025]      FIG. 2  is a cross-sectional view of a plasma processing chamber, in accordance with an embodiment of the invention. 
           [0026]      FIG. 3  illustrates a top view, schematically representing the inner coil and outer coil, in accordance with one embodiment of the present invention. 
           [0027]      FIG. 4A  is a schematic diagram illustrating the circuit topology of the TCCT match circuitry, in accordance with an embodiment of the invention. 
           [0028]      FIG. 4B  is a simplified schematic illustrating components of the TCCT match circuitry, in accordance with an embodiment of the invention. 
           [0029]      FIG. 5  is a graph showing ion density versus TCP power for various top end configurations, in accordance with embodiments of the invention. 
           [0030]      FIG. 6  illustrates four graphs, each showing ion density versus radial distance, in accordance with embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Disclosed is a TCCT match circuit for use in etching semiconductor substrates and layers formed thereon during the manufacture of semiconductor devices. The TCCT match circuitry controls the operation of a TCP coil disposed over a dielectric window of a chamber in which etching is performed. 
         [0032]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well known process operations and implementation details have not been described in detail in order to avoid unnecessarily obscuring the invention. 
         [0033]      FIG. 1  illustrates a plasma processing system utilized for etching operations, in accordance with one embodiment of the present invention. The system includes a chamber  102  that includes a chuck  104 , and a dielectric window  106 . The chuck  104  can be an electrostatic chuck for supporting the substrate when present. 
         [0034]    Further shown is a bias RF generator  160 , which can be defined from one or more generators. If multiple generators are provided, different frequencies can be used to achieve various tuning characteristics. A bias match  162  is coupled between the RF generators  160  and a conductive plate of the assembly that defines the chuck  104 . The chuck  104  also includes electrostatic electrodes to enable the chucking and dechucking of the wafer. Broadly, a filter and a DC clamp power supply can be provided. Other control systems for lifting the wafer off of the chuck  104  can also be provided. Although not shown, pumps are connected to the chamber  102  to enable vacuum control and removal of gaseous byproducts from the chamber during operational plasma processing. 
         [0035]    The dielectric window  106  can be defined from a ceramic type material. Other dielectric materials are also possible, so long as they are capable of withstanding the conditions of a semiconductor etching chamber. Typically, chambers operate at elevated temperatures ranging between about 50 Celsius and about 120 Celsius. The temperature will depend on the etching process operation and specific recipe. The chamber  102  will also operate at vacuum conditions in the range of between about 1 m Torr (mT) and about 100 m Torr (mT). Although not shown, chamber  102  is typically coupled to facilities when installed in a clean room, or a fabrication facility. Facilities include plumbing that provide processing gases, vacuum, temperature control, and environmental particle control. 
         [0036]    These facilities are coupled to chamber  102 , when installed in the target fabrication facility. Additionally, chamber  102  may be coupled to a transfer chamber that will enable robotics to transfer semiconductor wafers into and out of chamber  102  using typical automation. 
         [0037]      FIG. 2  is a cross-sectional view of a plasma processing chamber, in accordance with an embodiment of the invention. The TCP coil is shown to include an inner coil (IC)  122 , and an outer coil (OC)  120 . The TCP coil is placed and arranged over the dielectric window  106 . 
         [0038]    TCCT match circuitry  124  enables dynamic tuning of power provided to the inner and outer coils. The TCP coil is coupled to the TCCT match circuitry  124  which includes connections to the inner coil  120 , and outer coil  122 . In one embodiment, the TCCT match circuitry  124  is configured to tune the TCP coil to provide more power to the inner coil  122  versus the outer coil  120 . In another embodiment, the TCCT match circuitry  124  is configured to tune the TCP coil to provide less power to the inner coil  122  versus the outer coil  120 . In another embodiment, the power provided to the inner coil and the outer coil will be to provide an even distribution of power and/or control the ion density in a radial distribution over the substrate (i.e., wafer, when present). In yet another embodiment, the tuning of power between the outer coil and the inner coil will be adjusted based on the processing parameters defined for that etching being performed on the semiconductor wafer disposed over chuck  104 . 
         [0039]    In one implementation, the TCCT match circuitry having variable capacitors (as discussed in further detail below) can be configured to be adjusted automatically to achieve a predetermined ratio of currents in the two coils. It should be understood that the circuits illustrated herein provide tuning and adjustment to the desired ratio of currents. In one embodiment, the ratio of currents can range from 0.1 to 1.5. Commonly, this ratio is referred to as the transformer coupled capacitive tuning (TCCT) ratio. The setting of the TCCT ratio, however, is based on the process that is desired for a particular wafer or wafers. 
         [0040]    It should be appreciated that by providing a tunable TCP coil, the chamber  102  can provide flexibility for controlling ion density versus TCP power, and radial ion density profiles, depending on the processing operations being performed. 
         [0041]    Additionally, it should be noted that although reference is made throughout the present disclosure to a TCCT match circuitry, the use of this terminology should not limit the scope of the circuitry defined to achieve the desired match function and provide for tuning. In other embodiments, it is contemplated that match circuitry in accordance with the principles and embodiments described herein can be applied to achieve a desired match function for plasma processing systems without TCCT functionality, or having a fixed TCCT ratio. 
         [0042]      FIG. 3  illustrates a top view, schematically representing the inner coil  122  and outer coil  120 , in accordance with one embodiment of the present invention. The top view shown represents the connections to the coil as previously described to include outer coil  120  and inner coil  122 , as one example. The inner coil  122  will include an inner coil  1  (IC 1 ) and inner coil  2  (IC 2 ). The outer coil  120  includes an outer coil  1  (OC 1 ) and an outer coil  2  (OC 2 ). The connections between the coil ends are illustrated relative to the circuitry provided in the TCCT match circuitry  124 . The illustration in  FIG. 3  is provided to show the circular winding associated with each of the inner and outer coils of the TCP coil utilized in chamber  102 , in accordance with one embodiment of the present invention. As shown, the inner coils IC 1  and IC 2  are arranged as parallel spirals that are interleaved with one another. As shown, IC 1  and IC 2  resemble a pair of arithmetic or Archimedean spirals of substantially the same shape but with one rotated by about 180 degrees about its axis relative to the other. An input terminal  300  of IC 1  is situated diametrically opposite input terminal  302  of IC 2 . Additionally, an output terminal  304  of IC 1  is situated diametrically opposite output terminal  306  of IC 2 . The configuration of the outer coils OC 1  and OC 2  is similar to that of the inner coils IC 1  and IC 2 , defining substantially similar parallel spirals, interleaved with one another, and rotated by approximately 180 degrees relative to each other. An input terminal  308  of OC 1  is diametrically opposite input terminal  310  of OC 2 , whereas output terminal  312  of OC 1  is diametrically opposite output terminal  314  of OC 2 . In one embodiment, the input and output terminals of the inner coils and the outer coils are arranged in a substantially linear configuration. It should be appreciated that other types of coil configurations are possible. For example, it is possible to have a dimensional coil that provides a dome type structure, and other coil type structures other than flat coil distributions. 
         [0043]    As has been noted, the TCP coil is coupled to the TCCT match circuitry  124  which includes connections to the inner coil  120 , and outer coil  122 . As shown, the outer coil  120  input terminals  308  and  310  are coupled to node  146 , which in turn connects to TCCT input circuitry  320 . The output terminals of the outer coil  120  are connected to node  142 , which connects to TCCT output circuitry  324 . The inner coil  122  has its input terminals  300  and  302  connected to node  140 , which then connects to TCCT input circuitry  320 . The output terminals  304  and  306  of the inner coil  122  are connected to node  148 , which connects to TCCT output circuitry  324 . The TCCT input circuitry receives power from an RF power source  322 . The TCCT output circuitry is connected to ground. 
         [0044]      FIG. 4A  is a schematic diagram illustrating the circuit topology of the TCCT match circuitry, in accordance with an embodiment of the invention. The RF source  322  provides power to a power input circuit  400 . A variable capacitor C 1  is coupled between the RF source  322  and a node  410 . Node  410  connects to a capacitor C 2 , that in turn is connected to ground. Node  410  also connects to a variable capacitor C 3 , which in turn connects to an inductor L 5 . Inductor L 5  is coupled to a node  412 . In one embodiment, the power input circuit  400  is defined by the variable capacitor C 1 , node  410 , capacitor C 2  coupled to ground, the variable capacitor C 3  and the inductor L 5 , arranged as has been described. 
         [0045]    Node  412  is coupled to each of an inner coil input circuit  402  and an outer coil input circuit  404 . In one embodiment, the inner coil input circuit  402  is defined by an inductor L 3  and a variable capacitor C 5 , coupled to each other. The inductor L 3  is coupled between the node  412  and the variable capacitor C 5 . The variable capacitor C 5  connects to node  140  (shown at  FIG. 3 ), which in turn connects to the input terminals of the inner coils. 
         [0046]    With continued reference to  FIG. 4A , node  412  also connects to the outer coil input circuit  404 . In one embodiment, the outer coil input circuit  404  is defined by a variable capacitor C 4  that couples to node  412 . The variable capacitor C 4  also connects to node  146  (shown at  FIG. 3 ), which in turn connects to the input terminals of the outer coils. 
         [0047]    Additionally shown at  FIG. 4A  is the TCCT output circuitry  324 , which is defined by inner coil output circuit  406  and outer coil output circuit  408 . The inner coil output circuit  406  is connected to node  148  (shown at  FIG. 3 ), which in turn connects to the output terminals of the inner coils. In one embodiment, the inner coil output circuit  406  is defined by a ground pass through. The outer coil output circuit  408  connects to node  142  (shown at  FIG. 3 ), which in turn connects to the output terminals of the outer coils. In one embodiment, the outer coil output circuit is defined by a capacitor C 7  that is coupled between the node  142  and ground. 
         [0048]    In one embodiment, the variable capacitor C 1  is rated at approximately 5 to 500 pF. In one embodiment, the capacitor C 2  is rated at approximately 250 pF. In one embodiment, the variable capacitor C 3  is rated at about 5 to 500 pF. In one embodiment, the inductor L 5  is rated at approximately 0.3 uH. In one embodiment, the variable capacitor C 4  is rated at approximately 150 to 1500 pF. In one embodiment, the inductor L 3  is rated at approximately 0.55 uH. In one embodiment, the variable capacitor C 5  is rated at approximately 150 to 1500 pF. In one embodiment, the capacitor C 7  is rated at approximately 100 pF. 
         [0049]    TCCT match circuitry  124  enables dynamic tuning of variable capacitors C 1 , C 3 , C 4 , and C 5  to tune the power provided to the inner and outer coils. In one embodiment, the variable capacitors C 1 , C 3 , C 4 , and C 5  are controlled by processing controllers, connected to an electronics panel of chamber  102 . The electronics panel can be coupled to networking systems that will operate specific processing routines that depend on the processing operations desired during specific cycles. The electronics panel can therefore control the etching operations performed in chamber  102 , as well as control the specific settings of variable capacitors C 1 , C 3 , C 4 , and C 5 . 
         [0050]      FIG. 4B  is a simplified schematic illustrating components of the TCCT match circuitry, in accordance with an embodiment of the invention. As shown, the power input circuit  400  receives power from the RF power source  322 . The power input circuit  400  connects to node  412 . The inner coil input circuit  402  is coupled between the node  412  and the inner coil  122 . The outer coil input circuit  404  is coupled between the node  412  and the outer coil  120 . The inner coil  122  connects to inner coil output circuit  406 , which is connected to ground. The outer coil  120  connects to outer coil output circuit  408 , which is connected to ground. 
         [0051]    Broadly speaking, the presently described TCCT match circuitry design provides for improvements in power efficiency. This is believed to be due to design optimization to minimize the effect of stray capacitance on the coil with respect to plasma. The effects of stray capacitance on RF power efficiency have been studied and described in “Power Efficiency Oriented Optimal Design of High Density CCP and ICP Sources for Semiconductor RF Plasma Processing Equipment,” by Maolin Long, IEEE Transactions on Plasma Science, Vol. 34, No. 2, April 2006, which is incorporated herein by reference. 
         [0052]    With respect to the inner coil, prior TCCT match circuit designs have included output-side inductors that increase stray capacitance and therefore reduce power efficiency. However, in embodiments presented herein, the inner coil output circuit is configured as a ground pass-through, whereas the inner coil input circuit is configured to include an inductor L 3 . This reduces stray capacitance, therefore improving power efficiency and facilitating lower voltage on the inner coil. 
         [0053]    With respect to the outer coil, prior TCCT match circuit designs have provided for relatively low output-side capacitance. However, in embodiments presented herein, the outer coil output circuit is configured to provide higher capacitance, which reduces impedance for a given frequency and provides for a lower voltage drop. 
         [0054]    Table 1 shown below provides RF characterization data comparing an original top end RF design to a modified top end RF design in accordance with embodiments of the invention. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 R_conjugate 
                 X_conjugate 
               
               
                   
                   
                   
                 (ohm):[looking at 
                 (ohm):[looking at 
               
               
                   
                 no 
                   
                 output of T match 
                 output of T match 
               
               
                   
                 plasma_R_load 
                 no plasma_X_load 
                 with input being 
                 with input being 
               
               
                 TCP = 2 kW 
                 (ohm):[looking at 
                 (ohm):[looking at 
                 terminated by 
                 terminated by 
               
               
                 TCCT ratio: 
                 input of splitter] 
                 input of splitter] 
                 50 ohm] 
                 50 ohm] 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Original top end w/ SF6 = 120 sccm at 10 mT 
               
             
          
           
               
                 1 
                 0.44 
                 24.624 
                 1.2698 
                 −8.4143 
               
               
                 0.5 
                 0.42977 
                 23.274 
                 1.2997 
                 −8.6419 
               
               
                 1.3 
                 0.43723 
                 23.917 
                 1.2544 
                 −7.5901 
               
             
          
           
               
                   
                 Modified top end w/ SF6 = 125 sccm at 10 mT 
               
             
          
           
               
                 1 
                 0.39092 
                 47.363 
                 1.5062 
                 −28.044 
               
               
                 0.5 
                 0.45115 
                 48.718 
                 1.855 
                 −30.524 
               
               
                 1.3 
                 0.37336 
                 43.506 
                 1.3897 
                 −24.143 
               
               
                   
               
             
          
         
       
     
         [0055]    As demonstrated by the data of Table 1, the Q value of the inner coil in an unloaded case (no plasma) for the modified top end is improved over that of the original top end. Therefore, the RF power efficiency is also improved. Thus in the unloaded case, the overall Q value of the TCP coil is improved at higher TCCT, as the outer coil dominates at lower TCCT. Additionally, the data demonstrate that the overall RF power efficiency increase in the loaded case (with plasma) is significant. 
         [0056]    Broadly speaking, the presently disclosed TCCT match circuitry provides for high power efficiency, meaning that for a given amount of power, a higher density plasma is achieved. Furthermore, by achieving high power efficiency, the disclosed TCCT match circuitry allows for voltage levels at the coil terminals to be relatively low. The ability to run at lower voltages at the coil terminals reduces the acceleration of ions that can strike the surface of the dielectric window. The result is to reduce the particle generation caused by sputtering of particles from the dielectric window. Table 2 below shows a comparison of terminal voltages between an existing TCCT match circuit design and a TCC match circuit design in accordance with embodiments of the invention. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
                 New TCCT 
                   
                 Existing TCCT 
                   
               
               
                   
                 match w/ 
                   
                 match w/ 
               
               
                   
                 SF6 = 125 
                   
                 SF6 = 120 
               
               
                 TCP = 2 kW 
                 sccm at 10 mT 
                   
                 sccm at 10 mT 
               
             
          
           
               
                 TCCT ratio: 
                 V 3  (V) 
                 V 4  (V) 
                 V 3  (V) 
                 V 4  (V) 
               
               
                   
               
             
          
           
               
                 1 
                 2135 
                 2535 
                 4596 
                 3169 
               
               
                 0.5 
                 1392 
                 2946 
                 3040 
                 3980 
               
               
                 1.3 
                 2409 
                 2283 
                 5000 
                 2785 
               
               
                   
               
             
          
         
       
     
         [0057]    The data in Table 2 shows a measured RF voltage comparison between a TCCT match circuitry in accordance with embodiments of the invention and an existing TCCT match circuitry. The voltage V 3  (shown at  FIG. 4A ) is measured between the variable capacitor C 5  and the node  140 , and is indicative of the voltage at the input terminals of the inner coils. The voltage V 4  (also shown at  FIG. 4A ) is measured between the output terminals of the outer coils and the capacitor C 7 , and is indicative of the voltage at the output terminals of the outer coils. 
         [0058]    As the data shown at Table 2 demonstrate, coil terminal voltage is significantly reduced in the TCCT match circuitry design according to embodiments of the invention. Because coil terminal voltage is reduced, embodiments of the present invention can be utilized across various conductor etch chambers to minimize dielectric window sputtering and also eliminate coil arcing caused by terminal-to-ground over voltage. 
         [0059]      FIG. 5  is a graph showing ion density versus TCP power for various top end configurations, in accordance with embodiments of the invention. In the graph, plots for different top end configurations are represented by different shapes. Circles correspond to a plot of an original top end having a coil-window gap of 0.1 inches. The experimental conditions are as follows: TCCT=1, SF6=50 sccm, Ar=200 sccm, Ch.P=9mT, tip=160 mm Diamonds correspond to a plot of a modified top end having a TCCT match circuitry in accordance with embodiments described herein, also having a coil-window gap of 0.1 inches. Squares correspond to a plot of an original top end having a coil-window gap of 0.4 inches. Triangles correspond to a plot of an original top end having no Faraday shield, also with a coil-window gap of 0.4 inches. 
         [0060]    Comparing the plot for the original top end with a 0.1 inch coil-window gap (represented by circles) against the plot for the modified top end with a 0.1 inch coil-window gap (represented by diamonds), it can be seen that the modified top end RF design provides for a significantly higher power efficiency than the original top end RF design. That is, for a given TCP power, the modified top end provides for a significantly higher ion density. By providing for greater power efficiency, it is possible to achieve equivalent amounts of plasma density as prior top end TCCT match designs, but at lower power. This ability provides for improved longevity of the TCCT match circuitry, as components are subject to lower power, and also reduces particle generation from sputtering of the dielectric window as previously described. 
         [0061]      FIG. 6  illustrates four graphs, each showing ion density versus radial distance. In the graph shown at the upper right of  FIG. 6 , plots are shown for various TCCT values as applied to an original top end having a coil-window gap of 0.1 inches. For each plot, TCP power=1000 W. The plot indicated by diamonds corresponds to TCCT=1. The plot indicated by squares corresponds to TCCT=0.5. The plot indicated by triangles corresponds to TCCT=1.3. 
         [0062]    In the graph shown at the upper left of  FIG. 6 , plots are shown for various TCCT values as applied to a modified top end having TCCT match circuitry in accordance with embodiments of the invention, and having a coil-window gap of 0.1 inches. For each plot, TCP power=1000 W. The plot indicated by diamonds corresponds to TCCT=1. The plot indicated by squares corresponds to TCCT=0.5. The plot indicated by triangles corresponds to TCCT=1.3. 
         [0063]    In the graph shown at the lower right of  FIG. 6 , plots are shown for various TCCT values as applied to an original top end having a coil-window gap of 0.4 inches. The plot indicated by diamonds corresponds to TCCT=1. The plot indicated by squares corresponds to TCCT=0.5. The plot indicated by triangles corresponds to TCCT=1.3. 
         [0064]    In the graph shown at the lower left of  FIG. 6 , plots are shown for various TCCT values as applied to a baseline top end with no Faraday shield, and having a coil-window gap of 0.4 inches. The plot indicated by diamonds corresponds to TCCT=1. The plot indicated by squares corresponds to TCCT=0.5. The plot indicated by triangles corresponds to TCCT=1.3. 
         [0065]    The plots shown at  FIG. 6  demonstrate that the gained plasma density resulting from incorporation of TCCT match circuitry in accordance with embodiments of the invention is more uniformly distributed across the wafer. 
         [0066]    While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. It is therefore intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention.