Patent Publication Number: US-9404176-B2

Title: Substrate support with radio frequency (RF) return path

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional patent application Ser. No. 61/655,737, filed Jun. 5, 2012, which is herein incorporated by reference. 
    
    
     FIELD 
     Embodiments of the present invention generally relate to substrate processing systems. 
     BACKGROUND 
     Physical vapor deposition (PVD) processes can use radio frequency (RF) energy to enhance substrate processing for certain applications. For example, RF energy may be provided to a target of a PVD chamber to facilitate sputtering of materials from the target and depositing the sputtered materials onto a substrate disposed in the PVD chamber. The inventors have observed that process non-uniformity issues, such as non-uniform film deposition, may arise in such PVD chambers under certain operating conditions. The inventors believe that conventional electrostatic chucks may be at least a part of the cause of these process non-uniformities. 
     Accordingly, the inventors have provided embodiments of improved substrate supports for use in substrate processing systems. 
     SUMMARY 
     Embodiments of substrate supports having a radio frequency (RF) return path are provided herein. In some embodiments, a substrate support may include a dielectric support body having a support surface to support a substrate thereon and an opposing second surface; a chucking electrode disposed within the support body proximate the support surface; and an RF return path electrode disposed on the second surface of the dielectric support body. 
     In some embodiments, a substrate support may include a dielectric support body having a support surface to support a substrate thereon and an opposing second surface; a chucking electrode disposed within the support body proximate the support surface; and an RF return path electrode disposed within the dielectric support body. 
     In some embodiments, a substrate processing system may include a process chamber having an inner volume; a shield to separate the inner volume into a processing volume and a non-processing volume and extending toward a ceiling of the process chamber; and a substrate support. The substrate support may include a dielectric support body having a support surface to support a substrate thereon and an opposing second surface; a chucking electrode disposed within the support body proximate the support surface; and an RF return path electrode disposed on the second surface of the dielectric support body, wherein the RF return path electrode is patterned into a plurality of sections. 
     Other and further embodiments of the present invention are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted 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. 
         FIG. 1  depicts a schematic cross sectional view of a process chamber having a substrate support in accordance with some embodiments of the present invention. 
         FIG. 1A  depicts a partial schematic cross sectional view of the substrate support of  FIG. 1  in accordance with some embodiments of the present invention. 
         FIG. 2  depicts a partial schematic cross sectional view of a process chamber having a substrate support in accordance with some embodiments of the present invention. 
         FIG. 2A  depicts a partial schematic cross sectional view of the substrate support of  FIG. 2  in accordance with some embodiments of the present invention. 
         FIGS. 3A-C  respectively depict schematic side view of a substrate support in accordance with some embodiments of the present invention. 
         FIG. 4  depicts a schematic bottom view of a substrate support in accordance with some embodiments of the present invention. 
         FIG. 5  depicts a partial side view in cross-section of a substrate support in accordance with some embodiments of the present invention. 
         FIGS. 6A-B  respectively depict top and side schematic views of a plurality of conductive elements of a substrate support in accordance with some embodiments of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Embodiments of substrate supports having a radio frequency (RF) return path are provided herein. In some embodiments, substrate supports in accordance with the present invention are configured to provide an improved RF return path between the substrate support and an adjacent chamber component, such as a process kit shield which surrounds a processing volume of a process chamber, to provide a shorter route to ground. The RF return path may advantageously provide a low impedance return path for RF currents used during processing. For example, in some embodiments, substrate supports in accordance with the present invention may include an RF return path ground plane that provides a more efficient and shorter electrical length for the RF return path, thereby reducing uncontrolled and stray losses and improving process uniformity. 
     In some embodiments, a substrate support is provided with an RF return path electrode configured to provide an RF return path to a desired chamber component for the RF energy in the process chamber. The RF return path may provide a ground plane in a plane substantially parallel to the support surface for supporting the substrate. The RF return path may provide a shorter RF return path as compared to conventional substrate supports. The RF return path may alternatively or in combination provide a more radially and/or azimuthally uniform RF return path as compared to conventional substrate supports. For example, in certain applications that use RF energy provided to an electrode in the process chamber at high or very high frequencies—such as 27 MHz or above, or 40 MHz or above, the substrate support may become an antenna that provides an RF return path for the RF energy provided to the process chamber. In such embodiments, conventional substrate supports may provide an undesirable RF return path that can cause processing non-uniformities due to stray losses or process control difficulties due to signal cross-talk between the RF energy and control signals for heaters, chucking electrodes, thermocouples, or the like that may be disposed within the substrate support. The inventors have observed that providing RF ground planes, before return RF currents start to couple uncontrollably, and in a more uniform configuration on the substrate support, results in more uniform processing results on the substrate. 
       FIGS. 3A-C  respectively depict schematic side views of a portion of a substrate support  300  in accordance with some embodiments of the present invention. The substrate support  300  includes a support body  302  having a support surface  306  to support a substrate during processing and an RF return path electrode  304  (or a ground plane electrode) to provide a return path to ground for RF energy provided to the process chamber during processing. The RF return path electrode  304  may be configured to provide an RF return path to the outer edge of the substrate support  300 , for example, to facilitate coupling to another chamber component adjacent to the substrate support  300 , such as described below with respect to  FIGS. 1-1A, 2-2A, and 5 . The support body  302  may be fabricated from a suitable process-compatible dielectric material, such as a ceramic. In some embodiment, the ceramic may be a high Q, or low loss ceramic that provides a low tangent loss or loss dissipative factor. In some embodiments, the support body  302  may be fabricated from aluminum nitride (AlN). 
     The support body  302  of the substrate support  300  may also include a chucking electrode  310 , for example, when the substrate support  300  is configured as an electrostatic chuck. A first conductor  312  may be provided to couple the chucking electrode to a power source (as shown in  FIG. 1 ) to facilitate operation of the electrostatic chuck. In some embodiments, the support body  302  of the substrate support  300  may also include one or more heater electrodes  314 , as depicted in  FIGS. 3A-C . In some embodiments, the one or more heater electrodes  314  may include a plurality of heater electrodes, for example, arranged in a plurality of zones. For example,  FIGS. 3A-C  depict two heater electrodes  316 ,  318  respectively arranged in a central and outer zone, although greater numbers of zones and/or different geometric arrangements are contemplated. One or more conductors, such as conductors  320 ,  322 , are provided to coupled the one or more heater electrodes  314  to one or more heater electrode power supplies (as shown in  FIG. 1 ) to facilitate operation of the heaters. 
     In some embodiments, the RF return path electrode  304  may be disposed on a surface  308  of the support body  302  opposite the support surface  306 , such as the RF return path electrode  304 A in  FIG. 3A . In some embodiments, the RF return path electrode  304  may be disposed within the support body  302 , as depicted in  FIGS. 3B and 3C . In embodiments corresponding to  FIG. 3B , the RF return path electrode  304  may be disposed within the support body  302  proximate the surface  308  (i.e., RF return path electrode  304 B), for example within a few millimeters of the surface  308  (such as about 2 mm), and closer to the surface  308  than any other electrodes, such as the one or more heater electrodes  314 . Alternatively, in embodiments corresponding to  FIG. 3C , the RF return path electrode  304  may be disposed within the support body  302  with no other electrodes between the RF return path electrode  304  and the chucking electrode  310  (i.e., RF return path electrode  304 C). Any other electrodes that may be present, such as the one or more heater electrodes  314 , may be disposed on the opposite side of the RF return path electrode  304 , closer to the surface  308  of the body  302 . 
     The RF return path electrode  304  may comprise any suitable process-compatible conductive material that is a good conductor of RF energy. In embodiments where the RF return path electrode  304  is disposed within the support body  302 , the RF return path electrode  304  may comprise, for example, a molybdenum mesh. In embodiments where the RF return path electrode  304  is disposed on the surface  308  of the support body  302  (i.e.,  304 A), the RF return path electrode  304  may be a layer of conductive material disposed on the surface  308 , such as by deposition, printing, or the like. In some embodiments, the RF return path electrode  304  may comprise one or more of titanium, copper, nickel, composite mixtures of ceramic and metal, or the like. In some embodiments, the RF return path electrode  304  may comprise a plurality of layers, such as a layer of titanium disposed on the surface  308  (which may act as an adhesion layer), a layer of copper disposed on the titanium layer (which may act as the primary electrode layer), and a layer of nickel disposed on the copper layer (which may act as a protective layer, for example, to prevent corrosion of the copper layer). 
     The RF return path electrode  304  may be any suitable thickness, based on the skin depth for the RF frequency to be used, to provide sufficient RF conductivity and to prevent an electrical choke condition. In some embodiments, the RF return path electrode  304  may be from about 50 to about 150 micrometers in thickness. 
     In embodiments where the RF return path electrode  304  is disposed on the surface  308 , the RF return path electrode  304  may be patterned into a plurality of sections  402 , as shown in  FIG. 4 . In some embodiments, the sections  402  may be separated by open regions  404 . The open regions  404  may be thin strips between adjacent sections  402 . Adjacent sections  402  may be coupled together by a thin strip or bridge of the conductive material that forms the RF return path electrode  304 . Providing the RF return path electrode  304  in sections advantageously facilitates reducing thermal stress on the RF return path electrode  304  that may cause the electrode to separate from the support body  302  due to repeated cycling of expansion and contraction arising from use. 
     The RF return path electrode  304  may also include open regions to provide an electrical standoff for a plurality of terminals  406  that may be provided to couple power to electrodes within the support body, such as the chucking electrode and the one or more heater electrodes. In some embodiments, a conduit  408  may be provided to facilitate providing a gas to the support body  302 , for example to provide a backside gas to the support surface  306  of the support body  302  (for example via a through hole  506  in the support body  302 , as shown in  FIG. 5 ). In some embodiments, the conduit  408  may be disposed proximate a central axis of the support body  302 . As no electrical signals are being provided through the conduit  408 , there does not need to be an electrical standoff region surrounding the conduit  408 . 
     As shown in  FIG. 5 , a plurality of terminals  502  (one shown in  FIG. 5  for clarity) may be provided to electrically couple the RF return path electrode  304  to a conductive member (e.g., second conductive member  115 , described below with respect to  FIG. 1 ). Similar terminals  504  may be provided to couple the chucking electrode and/or the one or more heater electrodes (not shown in  FIG. 5 ) to their respective conductors (e.g.,  312 ,  320 ,  322 , as described in  FIGS. 3A-C ). 
     The second conductive member extends radially outwards from the support body to couple the RF return path electrode  304  to a grounded shield (e.g., bottom shield  138  discussed below with respect to  FIG. 1 ), for example, via a plurality of conductive elements  129 . Thus, the RF return path electrode  304  provides a ground plane within the support body  302  that facilitates an RF return path to ground that may be advantageously shortened as compared to conventional substrate supports. In addition, the RF return path electrode  304  provides a ground plane that may be azimuthally more uniform and/or more symmetric, which may advantageously improve processing uniformity. 
     The above substrate support may be used in many different process chambers where RF energy is provided to the process chamber. For example,  FIG. 1  depicts a simplified, cross-sectional view of a physical vapor deposition (PVD) chamber  100  having a substrate support  106  in accordance with some embodiments of the present invention. The substrate support  106  may be similar to the substrate support  300  discussed above. Examples of PVD chambers suitable for modification in accordance with the teachings provided herein include chambers having high frequency sources, the ALPS® Plus and SIP ENCORE® PVD processing chambers, both commercially available from Applied Materials, Inc., of Santa Clara, Calif. Other processing chambers from Applied Materials, Inc. or other manufacturers, including those configured for other types of processing besides PVD, may also benefit from modifications in accordance with the inventive apparatus disclosed herein. 
     In some embodiments of the present invention, the PVD chamber  100  includes a chamber lid  101  disposed atop a process chamber  104  and removable from the process chamber  104 . The chamber lid  101  may include a target assembly  102  and a grounding assembly  103 . The process chamber  104  contains a substrate support  106  for receiving a substrate  108  thereon. The substrate support  106  may be located within a lower grounded enclosure wall  110 , which may be a chamber wall of the process chamber  104 . The lower grounded enclosure wall  110  may be electrically coupled to the grounding assembly  103  of the chamber lid  101  such that an RF return path is provided to an RF power source  182  disposed above the chamber lid  101 . Alternatively, other RF return paths are possible, such as those that travel from the substrate support  106  via a process kit shield (e.g. a bottom shield  138  as discussed below) and ultimately back to the grounding assembly  103  of the chamber lid  101 . The RF power source  182  may provide RF power to the target assembly  102  as discussed below. 
     The substrate support  106  has a material-receiving surface facing a principal surface of a target  114  and supports the substrate  108  to be sputter coated in planar position opposite to the principal surface of the target  114 . The substrate support  106  may include a dielectric member  105  having a substrate processing surface  109  for supporting the substrate  106  thereon. In some embodiments, the substrate support  108  may include one or more first conductive members  107  disposed below the dielectric member  105  and having a dielectric member facing surface  118  adjacent to the dielectric member  105 . For example, the dielectric member  105  and the one or more first conductive members  107  may be part of an electrostatic chuck, RF electrode, or the like which may be used to provide chucking or RF power to the substrate support  106 . 
     The substrate support  106  may support the substrate  108  in a first volume  120  of the process chamber  104 . The first volume  120  may be a portion of the inner volume of the process chamber  104  that is used for processing the substrate  108  and may be separated from the remainder of the inner volume (e.g., a non-processing volume) during processing of the substrate  108 . The first volume  120  is defined as the region above the substrate support  106  during processing (for example, between the target  114  and the substrate support  106  when in a processing position). 
     In some embodiments, the substrate support  106  may be vertically movable to allow the substrate  108  to be transferred onto the substrate support  106  through a load lock valve (not shown) in the lower portion of the process chamber  104  and thereafter raised to a deposition, or processing position. A bellows  122  connected to a bottom chamber wall  124  may be provided to maintain a separation of the inner volume of the process chamber  104  from the atmosphere outside of the process chamber  104 . One or more gases may be supplied from a gas source  126  through a mass flow controller  128  into the lower part of the process chamber  104 . An exhaust port  130  may be provided and coupled to a pump (not shown) via a valve  132  for exhausting the interior of the process chamber  104  and to facilitate maintaining a desired pressure inside the process chamber  104 . 
     An RF bias power source  134  may be coupled to the substrate support  106  in order to induce a negative DC bias on the substrate  108 . In addition, in some embodiments, a negative DC self-bias may form on the substrate  108  during processing. For example, RF energy supplied by the RF bias power source  134  may range in frequency from about 2 MHz to about 60 MHz, for example, non-limiting frequencies such as 2 MHz, 13.56 MHz, or 60 MHz can be used. In other applications, the substrate support  106  may be grounded or left electrically floating. Alternatively or in combination, a capacitance tuner  136  may be coupled to the substrate support  106  for adjusting voltage on the substrate  108  for applications where RF bias power may not be desired. Alternatively, or in combination, as indicated by the dashed box, the power source  134  may be a DC power source and may be coupled to a chucking electrode disposed in the substrate support  106  when the substrate support  106  is configured as an electrostatic chuck. 
     The process chamber  104  further includes a process kit shield, or shield, to surround the processing, or first volume of the process chamber  104  and to protect other chamber components from damage and/or contamination from processing. In some embodiments, the shield may include a grounded bottom shield  138  connected to a ledge  140  of an upper grounded enclosure wall  116  of the process chamber  104 . As illustrated in  FIG. 1 , the chamber lid  101  may rest on the ledge  140  of the upper grounded enclosure wall  116 . Similar to the lower grounded enclosure wall  110 , the upper grounded enclosure wall  116  may provide a portion of the RF return path between the lower grounded enclosure wall  110  and the grounding assembly  103  of the chamber lid  101 . However, other RF return paths are possible, such as via the grounded bottom shield  138 . 
     The bottom shield  138  extends downwardly and may include one or more sidewalls  139  configured to surround the first volume  120 . The bottom shield  138  extends along the walls of the upper grounded enclosure wall  116  and the lower grounded enclosure wall  110  downwardly to below a top surface of the substrate support  106  and returns upwardly until reaching a top surface of the substrate support  106  (e.g., forming a u-shaped portion at the bottom of the shield  138 ). A first ring  148  (e.g., a cover ring) rests on the top of the u-shaped portion (e.g., a first position of the first ring  148 ) when the substrate support  106  is in its lower, loading position (not shown) but rests on the outer periphery of the substrate support  106  (e.g., a second position of the first ring  148 ) when the substrate support  106  is in its upper, deposition position (as illustrated in  FIG. 1 ) to protect the substrate support  106  from sputter deposition. Although discussed above as the substrate support  106  being moveable relative to the shield  138  and the first ring  148 , in some embodiments, it may be possible that the substrate support  106  is stationary and the shield  138  and the first ring  148  are moveable relative to the substrate support  106 . 
     An additional dielectric ring  111  (e.g., a deposition ring) may be used to shield the periphery of the substrate  108  from deposition. For example, the dielectric ring  111  may be disposed about a peripheral edge of the substrate support  106  and adjacent to the substrate processing surface  109  as illustrated in  FIG. 1 . In some embodiments, the dielectric ring  111  may shield exposed surfaces of the one or more first conductive members  107  as shown. 
     In some embodiments, the substrate support  106  may include a second conductive member  115  to facilitate an RF return path between the substrate support  106  and the bottom shield  138 . The second conductive member  115  may include any suitable conductive materials, such as including one or more of stainless steel, copper (Cu), nickel (Ni), any suitable metal alloys, and/or any conductive flexible materials available in thin sheets, or the like. For example, as illustrated in  FIG. 1 , the second conductive member  115  may be disposed about and in contact with the one or more first conductive members  107  such that RF energy provided to the substrate  108  by an RF source (e.g., an RF power source  182  as discussed below) returns to the RF source by traveling radially outward from the substrate support along the dielectric member facing surface  118  of the one or more first conductive members  107  and along a first surface  119  of the second conductive member  115  disposed substantially parallel to a peripheral edge surface  117  of the one or more first conductive members  107  after travelling along the dielectric member facing surface  118 . 
     Providing the second conductive member  115  advantageously provides a low impedance return path for RF currents generated during processing. In some embodiments, the second conductive member  115  may be flexible to permit compression or expansion of a gap between the second conductive member  115  and a bottom of the shield  138 . Such flexibility may allow optimization of a spacing between the source material  113  of the target  114  and the substrate  108  without having to alter the RF return path from the substrate support  106  to the shield  138  via the second conductive member  115 . 
     In some embodiments, such as those illustrated in  FIG. 1 , the second conductive member  115  may include a body  121  disposed about the one or more first conductive members  107 . For example, in some embodiments, the body  121  may have a cylindrical tubular form. The body  121  may include the first surface  119 , where the first surface  119  is disposed on a peripheral edge surface opposing side of the body  121 . A first lip  123  may extend radially outward from a lower end of the body  121  and includes a second surface  125 . The second surface  125  is a radially outward extending surface, wherein RF energy travels along the second surface  125  after travelling along the first surface  119 . The second conductive member  115  may further include a second lip  127  extending radially inward from an upper end of the body  121  and covering a peripheral edge of the dielectric member facing surface  118  of the one or more first conductive members  107 . 
       FIG. 1A  depicts the substrate support  106  and second conductive member  115  originally illustrated in  FIG. 1  in a further magnified view. In operation, as illustrated by the dotted line in  FIG. 1A , an RF current may travel radially outward along the dielectric member facing surface  118  of the one or more first conductive members  107 . Next, the RF current may continue to travel radially outward along a surface of the second lip  127  disposed adjacent to the dielectric member facing surface  118 . The RF current may continue from the surface of the second lip  127  to the first surface  119  of the body, and then to the second surface  125  of the first lip  123 . From the second surface  125 , the RF current may travel along a plurality of conductive elements  129  disposed on the second surface  125 . The conductive elements  129  may be disposed about the body  121  on the second surface, and are discussed in further detail below. From the plurality of conductive elements  129 , the RF current may then travel along the bottom shield  138  toward the grounding assembly  103  and ultimately to the RF power source  182 . 
       FIG. 2  depicts alternative embodiments of a second conductive member of a substrate support. The substrate support of  FIG. 2  may be generally similar to the substrate support described above except as noted below. As shown in  FIG. 2 , a substrate support  200  may include a dielectric member  205  having a surface  209  for supporting the substrate  108  thereon. The substrate support  200  may include one or more first conductive members  207  disposed below the dielectric member  205  and having a dielectric member facing surface  213  adjacent to the dielectric member  205 . As illustrated in  FIG. 2 , the dielectric member  205  may extend in radially outward direction beyond a peripheral edge surface  217  of the one or more first conductive members  207 . 
     The substrate support  200  may include a second conductive member  215  to facilitate an RF return path between the substrate support  200  and the bottom shield  138 . The second conductive member  215  may include any suitable conductive materials, such as including those discussed above for the second conductive member  115 . For example, as illustrated in  FIG. 2 , the second conductive member  215  may be disposed about and contacting the one or more first conductive members  207  such that RF energy provided to the substrate  108  by an RF source (e.g., the RF power source  182  as discussed below) returns to the RF source by traveling radially outward from the substrate support along the dielectric layer facing surface  213  of the one or more first conductive members  207  and along the peripheral edge surface  217  on the one or more first conductive members  207  and a first surface  219  of the second conductive member  215  disposed along a peripheral edge surface  217  of the one or more first conductive members  207  after travelling along the dielectric member facing surface  213 . 
     In some embodiments, such as those illustrated in  FIG. 2 , the second conductive member  215  may include a body  221  disposed about the one or more first conductive members  207 . The body  221  may include the first surface  219 , where the first surface  119  is disposed on a peripheral edge surface facing side of the body  221 . The second conductive member  215  may further include a first lip  223 , a third lip  231 , and a fourth lip  233 , and other elements as discussed below. 
     The fourth lip  233  may extend radially inward from a lower end of the body  221  and below the one or more first conductive members  207 . For example, the fourth lip  233  may be used to at least partially secure the second conductive member  215  to the substrates support  200 , such as by way of fasteners, bolts, or the like disposed through the fourth lip  233  and into a lower side of the one or more first conductive members  207 . The fourth lip  233  may facilitate the formation of a gap  235  between the first surface  219  and the peripheral edge surface  217  of the one or more first conductive members  207 . In operation, RF energy may traverse the gap by traveling from the peripheral edge surface  217  to a fourth surface  234  of the fourth lip  233  to the first surface  219  of the body  221 . 
     The third lip  231  may extending radially outward from an upper end of the body  221  and further may extend at least partially along a lower surface of the dielectric member  205 . The third lip  231  may include a third surface  236 , wherein RF energy travels from the first surface  219  to the third surface  236 . The third surface  236  may be disposed on a dielectric member facing side of the third lip  231 . 
     The second conductive member  215  may include a protrusion  238  which extends downward from a body opposing end of the third lip  231 . The protrusion may include a surface  240 , wherein RF energy travels from the third surface  236  to the surface  240 . 
     The first lip  223  may extend radially outward from a lower end of the protrusion  238 . The first lip  223  may include a second surface  225 . The second surface  225  may be a radially outward extending surface, wherein RF energy travels along the second surface  225  after travelling along the surface  240  of the protrusion  238 . 
       FIG. 2A  depicts the substrate support  200  and second conductive member  215  originally illustrated in  FIG. 2  in a further magnified view. In operation, as illustrated by the dotted line in  FIG. 2A , an RF current may travel radially outward along the dielectric member facing surface  213  of the one or more first conductive members  207 . Next, the RF current may continue to travel along the peripheral edge surface  217  of the one or more first conductive members  207  and then radially outward along the fourth surface  234  of the fourth lip  233 . The RF current may continue from the fourth surface  234  to the first surface  219  of the body  221 , and then to the third surface  236  of the third lip  231 . From the third surface  236 , the RF current may travel downward along the surface  240  of the protrusion and then radially outward along the second surface  225  of the first lip  223 . From the second surface  225 , the RF current may travel along the plurality of conductive elements  129  disposed on the second surface  225 . The conductive elements  129  may be disposed about the body  221  on the second surface  225 , and are discussed in further detail below. From the plurality of conductive elements  129 , the RF current may then travel along the bottom shield  138  toward the grounding assembly  103  and ultimately to the RF power source  182 . 
       FIGS. 6A-B  depict the conductive elements  129  in accordance with some embodiments of the present invention. The embodiments of the conductive elements as illustrated in  FIGS. 6A-B  may be utilized with any embodiments of the second conductive member (e.g.,  115  or  215 ) as discussed above. For example, as illustrated in  FIG. 6A  in top down view of the substrate support ( 106  or  200 ), the plurality of conductive elements  129  may be disposed about the second surface ( 125  or  225 ) of the first lip ( 123  or  223 ) of the second conductive member ( 115  or  215 ). The size and number of the plurality of conductive elements  129  may vary as desired to provide a desired RF return path for RF currents generated during processing. The plurality of conductive elements  129  may be symmetrically disposed about the substrate support  106  ( 200 ) as illustrated. However, other arrangements, such as non-symmetrical arrangements of the conductive elements  129  may be possible, for example, depending on how RF current is being supplied to the system  100 . As discussed herein, the RF current may be provided symmetrically through an electrode coincident with a central axis of the system. However, in other embodiments, the RF source may be coupled asymmetrically to the target (or other electrode) in the processing system. 
       FIG. 6B  depicts an exemplary conductive element  129 . In some embodiments, the conductive element  129  may be in the shape of a loop, such as a circle, oval, or the like, wherein a bottom side of the loop contacts the second surface ( 125  or  225 ) and an upper side of the loop contacts the u-shaped portion of the bottom shield  138 . Other embodiments of the conductive elements  129  may be possible, such as a continuous element, for example, such as one or more of a continuous spiral seal or gasket, a ball seal, or the like. 
     Returning to  FIG. 1 , and in some embodiments, a magnet  152  may be disposed about the process chamber  104  for selectively providing a magnetic field between the substrate support  106  and the target  114 . For example, as shown in  FIG. 1 , the magnet  152  may be disposed about the outside of the chamber wall in a region just above the substrate support  106  when in processing position. In some embodiments, the magnet  152  may be disposed additionally or alternatively in other locations, such as adjacent the upper grounded enclosure wall  116 . The magnet  152  may be an electromagnet and may be coupled to a power source (not shown) for controlling the magnitude of the magnetic field generated by the electromagnet. 
     The chamber lid  101  generally includes the grounding assembly  103  disposed about the target assembly  102 . The grounding assembly  103  may include a grounding plate  156  having a first surface  157  that may be generally parallel to and opposite a backside of the target assembly  102 . A grounding shield  112  may extending from the first surface  157  of the grounding plate  156  and surround the target assembly  102 . The grounding assembly  103  may include a support member  175  to support the target assembly  102  within the grounding assembly  103 . 
     In some embodiments, the support member  175  may be coupled to a lower end of the grounding shield  112  proximate an outer peripheral edge of the support member  175  and extends radially inward to support a seal ring  181 , the target assembly  102  and optionally, a dark space shield  179 . The seal ring  181  may be a ring or other annular shape having a desired cross-section. The seal ring  181  may include two opposing planar and generally parallel surfaces to facilitate interfacing with the target assembly  102 , such as the backing plate  162 , on a first side of the seal ring  181  and with the support member  175  on a second side of the seal ring  181 . The seal ring  181  may be made of a dielectric material, such as ceramic. The seal ring  181  may insulate the target assembly  102  from the ground assembly  103 . 
     The dark space shield  179  is generally disposed about an outer edge of the target  114 , such about an outer edge of a source material  113  of the target  114 . In some embodiments, the seal ring  181  is disposed adjacent to an outer edge of the dark space shield  179  (i.e., radially outward of the dark space shield  179 ). In some embodiments, the dark space shield  179  is made of a dielectric material, such as ceramic. By providing a dielectric dark space shield  179 , arcing between the dark space shield and adjacent components that are RF hot may be avoided or minimized. Alternatively, in some embodiments, the dark space shield  179  is made of a conductive material, such as stainless steel, aluminum, or the like. By providing a conductive dark space shield  179  a more uniform electric field may be maintained within the process chamber  104 , thereby promoting more uniform processing of substrates therein. In some embodiments, a lower portion of the dark space shield  179  may be made of a conductive material and an upper portion of the dark space shield  179  may be made of a dielectric material. 
     The support member  175  may be a generally planar member having a central opening to accommodate the dark space shield  179  and the target  114 . In some embodiments, the support member  175  may be circular, or disc-like in shape, although the shape may vary depending upon the corresponding shape of the chamber lid and/or the shape of the substrate to be processed in the process chamber  100 . In use, when the chamber lid  101  is opened or closed, the support member  175  maintains the dark space shield  179  in proper alignment with respect to the target  114 , thereby minimizing the risk of misalignment due to chamber assembly or opening and closing the chamber lid  101 . 
     The target assembly  102  may include a source distribution plate  158  opposing a backside of the target  114  and electrically coupled to the target  114  along a peripheral edge of the target  114 . The target  114  may comprise a source material  113  to be deposited on a substrate, such as the substrate  108  during sputtering, such as a metal, metal oxide, metal alloy, or the like. In some embodiments, the target  114  may include a backing plate  162  to support the source material  113 . The source material  113  may be disposed on a substrate support facing side of the backing plate  162  as illustrated in  FIG. 1 . The backing plate  162  may comprise a conductive material, such as copper-zinc, copper-chrome, or the same material as the target, such that RF and DC power can be coupled to the source material  113  via the backing plate  162 . Alternatively, the backing plate  162  may be non-conductive and may include conductive elements (not shown) such as electrical feedthroughs or the like. 
     A conductive member  164  may be disposed between the source distribution plate and the backside of the target  114  to propagate RF energy from the source distribution plate to the peripheral edge of the target  114 . The conductive member  164  may be cylindrical, with a first end  166  coupled to a target-facing surface of the source distribution plate  158  proximate the peripheral edge of the source distribution plate  158  and a second end  168  coupled to a source distribution plate-facing surface of the target  114  proximate the peripheral edge of the target  114 . In some embodiments, the second end  168  is coupled to a source distribution plate facing surface of the backing plate  162  proximate the peripheral edge of the backing plate  162 . 
     The target assembly  102  may include a cavity  170  disposed between the backside of the target  114  and the source distribution plate  158 . The cavity  170  may at least partially house a magnetron assembly  196  as discussed below. The cavity  170  is at least partially defined by the inner surface of the conductive member  164 , a target facing surface of the source distribution plate  158 , and a source distribution plate facing surface (e.g., backside) of the target  114  (or backing plate  162 ). In some embodiments, the cavity  170  may be at least partially filled with a cooling fluid  192 , such as water (H 2 O) or the like. In some embodiments, a divider  194  may be provided to contain the cooling fluid  192  in a desired portion of the cavity  170  (such as a lower portion, as shown) and to prevent the cooling fluid  192  from reaching components disposed on the other side of the divider  194 , as discussed below. 
     An insulative gap  180  is provided between the grounding plate  156  and the outer surfaces of the source distribution plate  158 , the conductive member  164 , and the target  114  (and/or backing plate  162 ). The insulative gap  180  may be filled with air or some other suitable dielectric material, such as a ceramic, a plastic, or the like. The distance between the grounding plate  156  and the source distribution plate  158  depends on the dielectric material between the grounding plate  156  and the source distribution plate  158 . Where the dielectric material is predominantly air, the distance between the grounding plate  156  and the source distribution plate  158  should be between 5 mm and 40 mm. 
     The grounding assembly  103  and the target assembly  102  may be electrically separated by the seal ring  181  and by one or more of insulators  160  disposed between the first surface  157  of the grounding plate  156  and the backside of the target assembly  102 , e.g., a non-target facing side of the source distribution plate  158 . 
     The target assembly  102  has the RF power source  182  connected to an electrode  154  (e.g., a RF feed structure). The RF power source  182  may include an RF generator and a matching circuit, for example, to minimize reflected RF energy reflected back to the RF generator during operation. For example, RF energy supplied by the RF power source  182  may range in frequency from about 13.56 MHz and to about 162 MHz or above. For example, non-limiting frequencies such as 13.56 MHz, 27.12 MHz, 60 MHz, or 162 MHz can be used. 
     In some embodiments, a second energy source  183  may be coupled to the target assembly  102  to provide additional energy to the target  114  during processing. In some embodiments, the second energy source  183  may be a DC power source to provide DC energy, for example, to enhance a sputtering rate of the target material (and hence, a deposition rate on the substrate). In some embodiments, the second energy source  183  may be a second RF power source, similar to the RF power source  182 , to provide RF energy, for example, at a second frequency different than a first frequency of RF energy provided by the RF power source  182 . In embodiments where the second energy source  183  is a DC power source, the second energy source may be coupled to the target assembly  102  in any location suitable to electrically couple the DC energy to the target  114 , such as the electrode  154  or some other conductive member (such as the source distribution plate  158 , discussed below). In embodiments where the second energy source  183  is a second RF power source, the second energy source may be coupled to the target assembly  102  via the electrode  154 . 
     The electrode  154  may be cylindrical or otherwise rod-like and may be aligned with a central axis  186  of the PVD chamber  100  (e.g., the electrode  154  may be coupled to the target assembly at a point coincident with a central axis of the target, which is coincident with the central axis  186 ). The electrode  154 , aligned with the central axis  186  of the PVD chamber  100 , facilitates applying RF energy from the RF power source  182  to the target  114  in an axisymmetrical manner (e.g., the electrode  154  may couple RF energy to the target at a “single point” aligned with the central axis of the PVD chamber). The central position of the electrode  154  helps to eliminate or reduce deposition asymmetry in substrate deposition processes. The electrode  154  may have any suitable diameter, however, the smaller the diameter of the electrode  154 , the closer the RF energy application approaches a true single point. For example, although other diameters may be used, in some embodiments, the diameter of the electrode  154  may be about 0.5 to about 2 inches. The electrode  154  may generally have any suitable length depending upon the configuration of the PVD chamber. In some embodiments, the electrode may have a length of between about 0.5 to about 12 inches. The electrode  154  may be fabricated from any suitable conductive material, such as aluminum, copper, silver, or the like. 
     The electrode  154  may pass through the grounding plate  156  and is coupled to a source distribution plate  158 . The grounding plate  156  may comprise any suitable conductive material, such as aluminum, copper, or the like. The open spaces between the one or more insulators  160  allow for RF wave propagation along the surface of the source distribution plate  158 . In some embodiments, the one or more insulators  160  may be symmetrically positioned with respect to the central axis  186  of the PVD chamber  100  Such positioning may facilitate symmetric RF wave propagation along the surface of the source distribution plate  158  and, ultimately, to a target  114  coupled to the source distribution plate  158 . The RF energy may be provided in a more symmetric and uniform manner as compared to conventional PVD chambers due, at least in part, to the central position of the electrode  154   
     One or more portions of a magnetron assembly  196  may be disposed at least partially within the cavity  170 . The magnetron assembly provides a rotating magnetic field proximate the target to assist in plasma processing within the process chamber  104 . In some embodiments, the magnetron assembly  196  may include a motor  176 , a motor shaft  174 , a gearbox  178 , a gearbox shaft  184 , and a rotatable magnet (e.g., a plurality of magnets  188  coupled to a magnet support member  172 ). 
     In some embodiments, the magnetron assembly  196  is rotated within the cavity  170 . For example, in some embodiments, the motor  176 , motor shaft  174 , gear box  178 , and gearbox shaft  184  may be provided to rotate the magnet support member  172 . In conventional PVD chambers having magnetrons, the magnetron drive shaft is typically disposed along the central axis of the chamber, preventing the coupling of RF energy in a position aligned with the central axis of the chamber. To the contrary, in embodiments of the present invention, the electrode  154  is aligned with the central axis  186  of the PVD chamber. As such, in some embodiments, the motor shaft  174  of the magnetron may be disposed through an off-center opening in the grounding plate  156 . The end of the motor shaft  174  protruding from the grounding plate  156  is coupled to a motor  176 . The motor shaft  174  is further disposed through a corresponding off-center opening through the source distribution plate  158  (e.g., a first opening  146 ) and coupled to a gear box  178 . In some embodiments, one or more second openings  198  may be disposed though the source distribution plate  158  in a symmetrical relationship to the first opening  146  to advantageously maintain axisymmetric RF distribution along the source distribution plate  158 . The one or more second openings  198  may also be used to allow access to the cavity  170  for items such as optical sensors or the like. 
     The gear box  178  may be supported by any suitable means, such as by being coupled to a bottom surface of the source distribution plate  158 . The gear box  178  may be insulated from the source distribution plate  158  by fabricating at least the upper surface of the gear box  178  from a dielectric material, or by interposing an insulator layer  190  between the gear box  178  and the source distribution plate  158 , or the like. The gear box  178  is further coupled to the magnet support member  172  via the gear box shaft  184  to transfer the rotational motion provided by the motor  176  to the magnet support member  172  (and hence, the plurality of magnets  188 ). 
     The magnet support member  172  may be constructed from any material suitable to provide adequate mechanical strength to rigidly support the plurality of magnets  188 . For example, in some embodiments, the magnet support member  172  may be constructed from a non-magnetic metal, such as non-magnetic stainless steel. The magnet support member  172  may have any shape suitable to allow the plurality of magnets  188  to be coupled thereto in a desired position. For example, in some embodiments, the magnet support member  172  may comprise a plate, a disk, a cross member, or the like. The plurality of magnets  188  may be configured in any manner to provide a magnetic field having a desired shape and strength. 
     Alternatively, the magnet support member  172  may be rotated by any other means with sufficient torque to overcome the drag caused on the magnet support member  172  and attached plurality of magnets  188 , for example due to the cooling fluid  192 , when present, in the cavity  170 . For example, in some embodiments, (not shown), the magnetron assembly  196  may be rotated within the cavity  170  using a motor  176  and motor shaft  174  disposed within the cavity  170  and directly connected to the magnet support member  172  (for example, a pancake motor). The motor  176  must be sized sufficiently to fit within the cavity  170 , or within the upper portion of the cavity  170  when the divider  194  is present. The motor  176  may be an electric motor, a pneumatic or hydraulic drive, or any other process-compatible mechanism that can provide the required torque. 
     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.