Patent Publication Number: US-2023162955-A1

Title: Electrostatic chuck with detachable shaft

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/283,113, filed on Nov. 24, 2021, the entire contents of which are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     1) Field 
     Embodiments of the present disclosure pertain to the field of reactor or plasma processing chambers and, in particular, to electrostatic chucks with detachable shafts. 
     2) Description Of Related Art 
     Processing systems such as reactors or plasma reactors are used to form devices on a substrate, such as a semiconductor wafer or a transparent substrate. Often the substrate is held to a support for processing. The substrate may be held to the support by vacuum, gravity, electrostatic forces, or by other suitable techniques. During processing, the precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying a power, such as a radio frequency (RF) power, to an electrode in the chamber from one or more power sources coupled to the electrode. The excited gas or gas mixture reacts to form a layer of material on a surface of the substrate. The layer may be, for example, a passivation layer, a gate insulator, a buffer layer, and/or an etch stop layer. 
     In the semiconductor and other industries, electrostatic chucks (ESC) are used to hold a workpiece such as substrates on supports during processing of the substrate. A typical ESC may include a base, an electrically insulative layer disposed on the base, and one or more electrodes embedded in the electrically insulative layer. The ESC may be provided with an embedded electric heater, as well as be fluidly coupled to a source of heat transfer gas for controlling substrate temperature during processing. During use, the ESC is secured to the support in a process chamber. The electrode in the ESC is electrically biased with respect to a substrate disposed on the ESC by an electrical voltage source. Opposing electrostatic charges accumulate in the electrode of the ESC and on the surface of the substrate, the insulative layer precluding flow of charge there between. The electrostatic force resulting from the accumulation of electrostatic charge holds the substrate to the ESC during processing of the substrate. 
     SUMMARY 
     Embodiments of the present disclosure include electrostatic chucks (ESCs) for plasma processing chambers, and methods of fabricating ESCs. 
     In an embodiment, a substrate support assembly includes a cooling bottom plate, a ceramic top plate, and a bond layer between the ceramic top plate and the cooling bottom plate, the ceramic top plate in direct contact with the bond layer, and the bond layer in direct contact with the cooling bottom plate. A detachable shaft is coupled to the cooling bottom plate by a plurality of bolts at a side of the cooling bottom plate opposite the bond layer. 
     In an embodiment, a system includes a chamber, a plasma source within or coupled to the chamber, and an electrostatic chuck within the chamber. The electrostatic chuck includes a cooling bottom plate, a ceramic top plate, and a bond layer between the ceramic top plate and the cooling bottom plate, the ceramic top plate in direct contact with the bond layer, and the bond layer in direct contact with the cooling bottom plate. A detachable shaft is coupled to the cooling bottom plate by a plurality of bolts at a side of the cooling bottom plate opposite the bond layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  illustrates expanded views of components of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
         FIG.  1 B  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
         FIG.  1 C  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
         FIG.  1 D  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
         FIG.  1 E  illustrates a process for fabricating an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
         FIG.  1 F  illustrates an expanded view of components of an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
         FIG.  2 A  illustrates a process for fabricating an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
         FIG.  2 B  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) including a covering ring on a top ceramic plate, in accordance with an embodiment of the present disclosure. 
         FIG.  3    illustrates a cross-sectional view of an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
         FIG.  4    is a schematic cross-sectional view of a process chamber including a substrate support assembly, in accordance with an embodiment of the present disclosure. 
         FIG.  5    is a partial schematic cross-sectional view of a processing chamber including a substrate support assembly, in accordance with an embodiment of the present disclosure. 
         FIG.  6    illustrates a block diagram of an exemplary computer system, in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Electrostatic chucks (ESCs) for plasma processing chambers, and methods of fabricating ESCs, are described. In the following description, numerous specific details are set forth, such as electrostatic chuck components and material regimes, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known aspects, such as plasma enhanced chemical vapor deposition (PECVD) or plasma enhanced atomic layer deposition (PEALD) processes, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale. 
     One or more embodiments are directed to an electrostatic chuck (ESC) with a detachable shaft. Embodiments can be implemented to fabricate an ESC with a detachable shaft. 
     Embodiments described herein can include a bevel edge, bonded, detachable shaft design for an ESC. Embodiments can include an organic bonded mushroom design. In an embodiment, an ESC design includes a shaft that is detachable, is purgeable, and can provide a heat and cool design for a mushroom or bevel ESC. In an embodiment, an O ring is used to protect the bond. 
     To provide context, stat-of-the art designs to not provide for a detachable shaft design for both heat and cool applications. Embodiments described herein can include provide for heat and/or cool for a mushroom or bevel ESC, and/or provide for a detachable shaft, and/or provide for allowing for the edge of the wafer to be purged. Embodiments can be implemented to reduce the cost of a heater and to provide robust manufacturing of an ESC. 
     Advantages to implementing one or more embodiments described herein can include one or more of: (1) providing an ESC with both heat and cool capabilities, (2) enabling application of RF, edge purge, backside gas, (3) providing an O-ring that protects a bond if required such as silicone, and/or (4) a detachable metal shaft that can render fabrication that is cost effective. 
     In an embodiment, a manufacturing operation can include one or more of: (1) a ceramic ESC is manufactured with high voltage (HV) electrode, RF mesh and heater elements, a cooling plate is produced and bonded with an organic bond, and a detachable shaft is attached by bolts. (2) A bond is made between the ceramic and a metal plate to make it cost effective. (3) A detachable metal shaft renders facile assembly. A shaft provides conduit for HV, coolant, gas, purge and RF sourcing. (4) Heat and cool operations can both be accessible with a same ESC design. 
       FIG.  1 A  illustrates expanded views of components of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
     Referring to both views (a) and (b) of  FIG.  1 A , an ESC  100  includes a cooling plate  102  (e.g., a metal cooing plate, such as an aluminum cooling plate), which can have cooling channels therein. A detachable shaft  106 , such as a detachable metal shaft (or, alternatively, a detachable ceramic shaft) is coupled to the backside of the cooling plate  102 . In one embodiment, the detachable shaft  106  is coupled to the backside of the cooling plater  102  with a plurality of bolts (e.g., such as shown in  FIGS.  1 E and  1 F ). A ceramic top plate  108  (such as an aluminum nitride top plate) is bonded to the top side of the cooling plate  102  with a bonding layer  112  (such as a silicone bond layer or an organic bond layer or, alternatively, an aluminum foil). In one embodiment, the ceramic top plate  108  has a bevel, as is depicted. In one embodiment, the ceramic top plate  108  has purge holes  107 , as is depicted. In an embodiment, the ESC  100  can be referred to as a bevel edge, bonded, detachable shaft design. 
       FIG.  1 B  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  1 B , an ESC includes a cooling plate  102  (e.g., a metal cooing plate), which can have cooling channels  103  therein. A detachable shaft  106 , such as a detachable metal shaft (or, alternatively, a detachable ceramic shaft) is coupled to the backside of the cooling plate  102 . In one embodiment, the detachable shaft  106  is coupled to the backside of the cooling plater  102  with a plurality of bolts (e.g., such as shown in  FIG.  1 E and  1 F , which fit into openings  118 ). The shaft  106  can include one or more openings or conduits therein to include facilities lines  120 . A ceramic top plate  108  (such as an aluminum nitride top plate) is bonded to the top side of the cooling plate  102  with a bonding layer  112  (such as a silicone bond layer or an organic bond layer or, alternatively, an aluminum foil), which can be protected by an O-ring  122 . In one embodiment, the ceramic top plate  108  has a bevel, as is depicted. The bevel can accommodate an edge ring  124 . Thus, in an embodiment, an ESC can include an edge ring, a protection O-ring, a bond layer, a cooling plate, and a detachable shaft. 
       FIG.  1 C  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  1 C , an ESC includes a cooling plate  102  (e.g., a metal cooing plate), which can have cooling channels therein. A detachable shaft  106 , such as a detachable metal shaft (or, alternatively, a detachable ceramic shaft) is coupled to the backside of the cooling plate  102 . In one embodiment, the detachable shaft  106  is coupled to the backside of the cooling plater  102  with a plurality of bolts (e.g., such as shown in  FIGS.  1 E and  1 F ). The shaft  106  can include one or more openings or conduits therein to include facilities lines  120 . A ceramic top plate  108  (such as an aluminum nitride top plate) is bonded to the top side of the cooling plate  102 . In one embodiment, the ceramic top plate  108  has a bevel, as is depicted. The bevel can accommodate an edge ring  124 . Thus, in an embodiment, an ESC can include an edge ring, a protection O-ring, a bond layer, a cooling plate, and a detachable shaft. 
       FIG.  1 D  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) having a detachable shaft, in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  1 D , an ESC includes a cooling plate  102  (e.g., a metal cooing plate), which can have cooling channels  103  therein. A detachable shaft  106 , such as a detachable metal shaft (or, alternatively, a detachable ceramic shaft) is coupled to the backside of the cooling plate  102 . In one embodiment, the detachable shaft  106  is coupled to the backside of the cooling plater  102  with a plurality of bolts (e.g., such as shown in  FIGS.  1 E and  1 F , which fit into openings  118 ). The shaft  106  can include one or more openings or conduits therein to include facilities lines  120 . A ceramic top plate  108  (such as an aluminum nitride top plate) is bonded to the top side of the cooling plate  102  with a bonding layer  112  (such as a silicone bond layer or an organic bond layer or, alternatively, an aluminum foil). In an embodiment, the ceramic top plate  108  includes dimples  109 , as is depicted. In one embodiment, the ceramic top plate  108  has a bevel, as is depicted. 
     With reference again to  FIGS.  1 A- 1 D , in accordance with one or more embodiments of the present disclosure, an organic bonded ceramic ESC is provided with a metal cooling plate. A detachable metal shaft is attached at the bottom of cooling plate. The ESC has bevel purge on the side and an edge ring is used to purge gas to the edge of the wafer. A second gas connection through metal shaft goes through a cooling plate bond and ceramic to provide gas behind a supported wafer. In one embodiment, the bond is silicone, T412 acrylic or FFKM. In one embodiment, a ceramic ESC has high voltage electrodes and/or RF mesh and/or one or more heaters. O-rings can be used to protect a bond such as a silicone bond. 
     It is to be appreciated that the above embodiments can be directed to the coupling of a detachable metal shaft to a metal plate, such as a cooling plate. In other embodiments, a detachable metal shaft is coupled to a ceramic plate. For example, in accordance with one or more embodiments of the present disclosure, inserts are included inside ceramic portions of an ESC to hold a clamp ring and shaft. The shaft and ceramic plate are separate and, in one embodiment, the shaft is a detachable shaft. Embodiments can be implemented to provide a detachable metal shaft with a ceramic plate. Embodiments can be implemented to address cost and/or the need for edge purge. Particular embodiments can include a ceramic (such as a metal oxide or metal nitride) for use as an ESC on top of a metal shaft separated with one or more O-rings. A temperature range of the ESC can be adjusted by changing properties of the top plate. The top plate can be configured to hold a clamp ring on a top thereof. 
     In an embodiment, a ceramic part is made separate in two parts and then metal bonded with inserts inside and then attached to a shaft and clamp ring. In one embodiment, an edge ring is bolted to an insert. In a particular embodiment, the use of three locator pins is implemented to precisely maintain the position on top of the ESC. A cover ring of ceramic or metal can be used on top of the ESC. In one embodiment, the ring creates gap so gas is purged to the back edge of the ESC and is bolted to the insert and aligned with the three precise pins. 
     As an exemplary fabrication scheme,  FIG.  1 E  illustrates a process for fabricating an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
     Referring to part (a) of  FIG.  1 E , fabrication of a substrate support assembly includes coupling a ceramic bottom plate  132  (which can be a groove plate and can include a heater) and a ceramic top plate  138  (which can include a heater) with a bond layer  142 . In one embodiment, the bond layer  142  is a metal layer between the ceramic top plate  138  and the ceramic bottom plate  132 , the ceramic top plate  138  in direct contact with the bond layer  142 , and the bond layer  142  in direct contact with the ceramic bottom plate  132 . Inserts  152  and  154  can be included within the ceramic bottom plate  132 , the ceramic top plate  138 , and the bond layer  142 . The ceramic bottom plate  132  can include facilities lines  150  coupled to a bottom surface thereof. 
     Referring to part (b) of  FIG.  1 E , a metal shaft  136  is coupled to an assembly  160  by the ceramic bottom plate  132  at a side of the ceramic bottom plate  132  opposite the bond layer  142 . It is also to be appreciated that the ceramic top plate may include other features  162 , such as top grooves (or channels) for accommodating cooling gas flow which match through passage for gas in bond layer and top ceramic so gas is delivered behind wafer or for edge purge. The metal shaft  136  can include an O-ring  164  and openings  166  to accommodate bolts  156 . Referring to part (c) of  FIG.  1 E , an ESC  170  results from the coupling of part (b) of  FIG.  1 E . In an embodiment, the metal shaft  136  is a detachable metal shaft. 
     As an exemplary structure,  FIG.  1 F  illustrates an expanded view of components of an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  1 F , the structures of  FIG.  1 E  are shown relative to one another. Expanded views of inserts  152  and  154  and bolts  156  are depicted. The inserts  152  can be a helicoil configured to hold a clamp ring or cover ring. The inserts  154  can be a helicoil configured to hold shaft  136  to the bottom plate  132 , e.g., by bolts  156 . 
     As an exemplary fabrication scheme,  FIG.  2 A  illustrates a process for fabricating an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
     Referring to part (a) of  FIG.  2 A , a clamp ring, cover ring or edge ring  172  is provided above the structure  170  of  FIG.  1 E . Bolts  174  are used to couple the clamp ring, cover ring or edge ring  172  to the structure  170  to form an ESC. 
     As an exemplary fabrication scheme,  FIG.  2 B  illustrates a cross-sectional view of a portion of an electrostatic chuck (ESC) including a covering ring on a top ceramic plate, in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  2 B , clamp ring, cover ring or edge ring  172  provides a gap  180  between the clamp ring, cover ring or edge ring  172  and the ceramic top plate  138 . The gap  180  can enable edge purge of a substrate supported by the electrostatic chuck. 
     To provide further context, generally, diffusion bonding is a costly process and heating to such high temperatures affects thermal and or electrical properties of ceramics. State-of-the-art ESCs are typically fabricated with two diffusion bonds: one diffusion bond between a top plate and a bottom plate, and a second diffusion bond between the bonded plates and a shaft. It is to be appreciated that the use of too many diffusion bonds formed at high temperature can affect ceramic resistivity. Embodiments described herein can be implemented to eliminate the need for diffusion bonding. Embodiments can be implemented to ensure that a top plate does not change (or only minimally changes) resistivity during fabrication of an ESC. Embodiments may be implemented to advantageously reduce the cost of ESC fabrication since at least one high temperature operation is removed from the fabrication scheme. Embodiments can be implemented to preserve or retain an as-sintered resistivity of a top ceramic material. 
     Advantages to implementing one or more embodiments described herein can include use of a low cost metal shaft in place of a high cost ceramic shaft. In one embodiment, the metal shaft is a detachable metal shaft. Embodiments can enable fabrication of an ESC without resistivity change. Advantages can include reduced fabrication cost for an ESC. Advantages can include enabling the possibility of fabricating an ESCs to maintain the electrical properties of the components included in the ESC. 
     In comparison to state-of-the-art approaches which can include two diffusion bonds, in accordance with an embodiment of the present disclosure, an aluminum bond is used in place of one of the typical diffusion bonds. For example, an aluminum bond can be used between a top plate and a bottom plate. A metal shaft with an O-ring can be used to replace a ceramic bond between a ceramic shaft and a ceramic bottom plate. 
     Shown more generically, as an exemplary fabricated ESC,  FIG.  3    illustrates a cross-sectional view of an electrostatic chuck (ESC), in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  3   , an ESC  300  includes a ceramic bottom plate  302  having heater coils  304  therein. The heater coils  304  can be coupled to a heater connection  305  (it is to be appreciated that in another embodiment, a heater electrode is screen printed in case of tape casted A1N or A1N plate material used for the ESC fabrication). A metal shaft  306  is coupled to a bottom surface of the ceramic bottom plate  302 . In one embodiment, the metal shaft  306  is a detachable metal shaft. An O-ring may be included between the metal shaft  306  and the bottom surface of the ceramic bottom plate  302 . The ESC  300  also includes a ceramic top plate  308 . The ceramic top plate  308  has an ESC (clamping) electrode  310  or electrode assembly therein. A metal layer  312  bonds the ceramic top plate  308  to a top surface of the ceramic bottom plate  302 . A thermocouple  314  extends through an opening  315  in the ceramic bottom plate  302  and in metal layer  312 . A high voltage insulation  316  extends through the opening  315  in the ceramic bottom plate  302  and in metal layer  312  and houses an ESC high voltage connection  318 . A cover ring  399  can be coupled to the ceramic top plate  308 , such as described in association with  FIGS.  2 A- 2 B . 
     With reference again to  FIG.  3   , in accordance with an embodiment of the present disclosure, a substrate support assembly  300  includes a ceramic bottom plate  302  having heater elements  304  therein. The substrate support assembly  300  also includes a ceramic top plate  308  having an electrode  310  therein. A metal layer  312  is between the ceramic top plate  308  and the ceramic bottom plate  302 . The ceramic top plate  308  is in direct contact with the metal layer  312 , and the metal layer  312  is in direct contact with the ceramic bottom plate  302 . 
     It is to be appreciated that embodiments described herein involve bonding of upper and lower plates of a support using silicone or organic layer bonds (e.g., for ceramic to metal bonding). In other embodiments, a metal fold is used for ceramic to ceramic bonding or for metal to ceramic bonding. For example, in an embodiment, metal layer  312  provides for the incorporation of a metal bond in place of a ceramic to ceramic diffusion bond that can otherwise change a resistivity of a top ceramic during diffusion bond formation. In one embodiment, metal layer  312  is a metal foil, such as an aluminum foil. In one such embodiment, metal layer  312  is an aluminum foil impregnated with about 2% to 20% Si (e.g., as atomic % of total foil composition), with the remainder being aluminum or essentially all aluminum (i.e., the aluminum foil includes silicon having an atomic concentration in the range of 2%-20% of the aluminum foil). In an embodiment, metal layer  312  is pre-patterned, e.g., to include opening  315  and/or additional openings to accommodate lift pins, etc. In one embodiment, the metal layer  312  is an aluminum foil having a thickness in the range of 50-500 microns, and may be about 250 microns. In an embodiment, the metal layer  312  is an aluminum foil and is cleaned prior to inclusion in an ESC manufacturing process, e.g., to remove a passivation layer prior to bonding. In an embodiment, metal layer  312  is an aluminum foil and can sustain corrosive processes such as chlorine based process without etch or degradation of the metal layer  312  when the ESC is in use. However, if used for non-chlorine based processes, metal layer  312  may be composed of silver copper alloy, with or without addition of titanium, for example. In an embodiment, metal layer  312  is bonded to top plate  308  and bottom plate  302  at a temperature less than 600 degrees Celsius and, more particularly, less than 300 degrees Celsius. It is to be appreciated that higher ESC usage temperatures such as 650 degrees Celsius can be used if metal bonding is performed with a high temperature metal bond such as silver copper or gold nickel temperatures much lower than 1400 degrees Celsius but much above a 650 degrees Celsius usage temperature. 
     With reference to ceramic top plate  308  having the ESC (clamping) electrode  310  therein, in an embodiment, a body of the top plate may be formed by sintering a ceramic material, such as aluminum nitride (A1N) or aluminum oxide powder or other suitable material. An RF mesh can be is embedded in the body. The RF mesh can have electrical connections extending through a bottom surface of the body. The RF mesh may include molybdenum or another suitable metal material mesh about. In one embodiment, the mesh is an about 125 micron diameter mesh. The materials can be sintered to form a unitary structure. In one embodiment, the electrode  310  is fabricated from a metallic material, for example molybdenum, which may have a coefficient of thermal expansion similar to the body. In an embodiment, the ceramic top plate  308  is targeted for sustaining temperatures below 350 degrees Celsius, e.g., between 150-300 degrees Celsius, and may include dopants for optimizing such a targeted temperature range operation. 
     A clamping electrode  310  can include at least first and second electrodes. During operation, a negative charge may be applied to the first electrode and a positive charge may be applied to the second electrode, or vice versa, to generate an electrostatic force. During chucking, the electrostatic force generated from the electrodes holds a substrate disposed thereon in a secured position. As a power supplied from a power source is turned off, the charges present in an interface between the electrodes may be maintained over a long period of time. To release the substrate held on the electrostatic chuck, a short pulse of power in the opposite polarity may be provided to the electrodes to remove the charge present in the interface. 
     An electrode assembly may be formed by metallic bars, sheet, sticks, foil, and may be pre-molded, pre-casted and pre-manufactured and placed onto a surface of an insulating base during fabrication of the electrostatic chuck. Alternatively, a metal deposition process may be performed to deposit and form the electrode assembly directly on a top surface of an insulating base. Suitable deposition process may include PVD, CVD, plating, ink jet printing, rubber stamping, screen printing or aerosol print process. Additionally, metal paste/metal lines may be formed on a top surface of an insulating base. The metal paste/metal lines may initially be a liquid, paste or metal gel that may be patterned on to the object surface in a pattern to form electrode fingers with different configurations or dimensions on the top surface of the insulating base. 
     Ceramic top plate  308  or ceramic bottom plate  302  may include, but is not limited to, aluminum nitride, glass, silicon carbide, aluminum oxide, yttrium containing materials, yttrium oxide (Y 2 O 3 ), yttrium-aluminum-garnet (YAG), titanium oxide (TiO), or titanium nitride (TiN). With reference to ceramic bottom plate  302 , in an embodiment, the ceramic bottom plate  308  is targeted for sustaining temperatures up to 650 degrees Celsius, and may include dopants for optimizing such a targeted temperature range operation. In one embodiment, the ceramic bottom plate  302  has a different aluminum nitride composition than an aluminum nitride composition of the ceramic top plate  308 . Heating elements  304  included in the ceramic bottom plate  302  may use any suitable heating techniques, such as resistive heating or inductive heating. The heating elements  304  may be composed of a resistive metal, a resistive metal alloy, or a combination of the two. Suitable materials for the heating elements may include those with high thermal resistance, such as tungsten, molybdenum, titanium, or the like. In one embodiment, heating elements  304  are composed of a molybdenum wire. The heating elements  304  may also be fabricated with a material having thermal properties, e.g., coefficient of thermal expansion, substantially matching at least one or both the aluminum nitride body to reduce stress caused by mismatched thermal expansion. 
     In an embodiment, ceramic top plate  308  is fabricated and then bonded to the ceramic bottom plate by the metal layer  312  (which may already include one or more openings patterned therein). In an embodiment, the metal layer  312  bonded to the ceramic top plate  308  at the same time as the metal layer  312  is bonded to ceramic bottom plate  302 . In another embodiment, the metal layer  312  is first bonded to the ceramic top plate  308  and then the ceramic top plate/metal layer  312  pairing is bonded to ceramic bottom plate  302 . In another embodiment, the metal layer  312  is first bonded to the ceramic bottom plate  302  and then the ceramic bottom plate/metal layer  312  pairing is bonded to ceramic top plate  308 . In any case, in one particular embodiment, the ceramic top plate is formed from aluminum nitride (A1N) or aluminum oxide (Al 2 O 3 ) powder and a metal mesh which are sintered. 
     In an embodiment, bonding the ceramic top plate  308  to the ceramic bottom plate  302  with the metal layer  312  includes heating the ceramic bottom plate  302 , the metal layer  312 , and the ceramic top plate  308  to a temperature less than 600 degrees Celsius. In an embodiment, the metal layer  312  is an aluminum foil, and the method includes cleaning a surface of the aluminum foil to remove a passivation layer of the aluminum foil prior to bonding the ceramic top plate  308  to the ceramic bottom plate  302  with the metal layer  312 . 
     In another aspect,  FIG.  4    is a schematic cross-sectional view of a process chamber  400  including a substrate support assembly  428 , in accordance with an embodiment of the present disclosure. In the example of  FIG.  4   , the process chamber  400  is a plasma enhanced chemical vapor deposition (PECVD) chamber. As shown in  FIG.  4   , the process chamber  400  includes one or more sidewalls  402 , a bottom  404 , a gas distribution plate  410 , and a cover plate  412 . The sidewalls  402 , bottom  404 , and cover plate  412 , collectively define a processing volume  406 . The gas distribution plate  410  and substrate support assembly  428  are disposed in the processing volume  406 . The processing volume  406  is accessed through a sealable slit valve opening  408  formed through the sidewalls  402  such that a substrate  405  may be transferred in and out of the process chamber  400 . A vacuum pump  409  is coupled to the chamber  400  to control the pressure within the processing volume  406 . 
     The gas distribution plate  410  is coupled to the cover plate  412  at its periphery. A gas source  420  is coupled to the cover plate  412  to provide one or more gases through the cover plate  412  to a plurality of gas passages  411  formed in the cover plate  412 . The gases flow through the gas passages  411  and into the processing volume  406  toward the substrate receiving surface  432 . 
     An RF power source  422  is coupled to the cover plate  412  and/or directly to the gas distribution plate  410  by an RF power feed  424  to provide RF power to the gas distribution plate  410 . Various RF frequencies may be used. For example, the frequency may be between about 0.3 MHz and about 200 MHz, such as about 13.56 MHz. An RF return path  425  couples the substrate support assembly  428  through the sidewall  402  to the RF power source  422 . The RF power source  422  generates an electric field between the gas distribution plate  410  and the substrate support assembly  428 . The electric field forms a plasma from the gases present between the gas distribution plate  410  and the substrate support assembly  428 . The RF return path  425  completes the electrical circuit for the RF energy prevents stray plasma from causing RF arcing due to a voltage differential between the substrate support assembly  428  and the sidewall  402 . Thus the RF return path  425  mitigates arcing which causes process drift, particle contamination and damage to chamber components. 
     The substrate support assembly  428  includes a substrate support  430  and a stem  434 . The stem  434  is coupled to a lift system  436  that is adapted to raise and lower the substrate support assembly  428 . The substrate support  430  includes a substrate receiving surface  432  for supporting the substrate  405  during processing. Lift pins  438  are moveably disposed through the substrate support  430  to move the substrate  405  to and from the substrate receiving surface  432  to facilitate substrate transfer. An actuator  414  is utilized to extend and retract the lift pins  438 . A ring assembly  433  may be placed over periphery of the substrate  405  during processing. The ring assembly  433  is configured to prevent or reduce unwanted deposition from occurring on surfaces of the substrate support  430  that are not covered by the substrate  405  during processing. 
     The substrate support  430  may also include heating and/or cooling elements  439  to maintain the substrate support  430  and substrate  405  positioned thereon at a desired temperature. In one embodiment, the heating and/or cooling elements  439  may be utilized to maintain the temperature of the substrate support  430  and substrate  405  disposed thereon during processing to less than about 800 degrees Celsius or less. In one embodiment, the heating and/or cooling elements  439  may be used to control the substrate temperature to less than 650 degrees Celsius, such as between 300 degrees Celsius and about 400 degrees Celsius. In an embodiment, the substrate support  430 /substrate support assembly  428  is as described above in association with  FIGS.  1 A- 1 F,  2 A- 2 B and  3   . 
     In another aspect,  FIG.  5    is a partial schematic cross-sectional view of a processing chamber  500  including the substrate support assembly  300 , in accordance with an embodiment of the present disclosure. The processing chamber  500  has a body  501 . The body has sidewalls  502 , a bottom  504  and a showerhead  512 . The sidewalls  502 , bottom  504  and showerhead  512  define an interior volume  506 . In an embodiment, a substrate support assembly  300 , such as described in association with  FIGS.  1 A- 1 F,  2 A- 2 B,  3   , is disposed within the interior volume  506 . A RF generator  580  may be coupled an electrode  582  in the showerhead  512 . The RF generator  580  may have an associated RF return path  588  for completing the RF circuit when plasma is present. Advantageously, an RF ground path for maintaining the plasma can be maintained and provide a long service life for the substrate support assembly  300 . 
     In an embodiment, a semiconductor wafer or substrate supported by substrate support assembly  300  is composed of a material suitable to withstand a fabrication process and upon which semiconductor processing layers may suitably be disposed. For example, in one embodiment, a semiconductor wafer or substrate is composed of a group IV-based material such as, but not limited to, crystalline silicon, germanium or silicon/germanium. In a specific embodiment, the semiconductor wafer includes is a monocrystalline silicon substrate. In a particular embodiment, the monocrystalline silicon substrate is doped with impurity atoms. In another embodiment, the semiconductor wafer or substrate is composed of a III-V material. 
     Embodiments of the present disclosure may be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to embodiments of the present disclosure. In one embodiment, the computer system is coupled with process chamber  400  and substrate support assembly  428  described above in association with  FIG.  4    or with processing chamber  500  and substrate support assembly  300  described in association with  FIG.  5   . A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices, etc.), a machine (e.g., computer) readable transmission medium (electrical, optical, acoustical or other form of propagated signals (e.g., infrared signals, digital signals, etc.)), etc. 
       FIG.  6    illustrates a diagrammatic representation of a machine in the exemplary form of a computer system  600  within which a set of instructions, for causing the machine to perform any one or more of the methodologies described herein, may be executed. In alternative embodiments, the machine may be connected (e.g., networked) to other machines in a Local Area Network (LAN), an intranet, an extranet, or the Internet. The machine may operate in the capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC), a tablet PC, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines (e.g., computers) that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies described herein. 
     The exemplary computer system  600  includes a processor  602 , a main memory  604  (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory  606  (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory  618  (e.g., a data storage device), which communicate with each other via a bus  630 . 
     Processor  602  represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processor  602  may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processor  602  may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processor  602  is configured to execute the processing logic  626  for performing the operations described herein. 
     The computer system  600  may further include a network interface device  608 . The computer system  600  also may include a video display unit  610  (e.g., a liquid crystal display (LCD), a light emitting diode display (LED), or a cathode ray tube (CRT)), an alphanumeric input device  612  (e.g., a keyboard), a cursor control device  614  (e.g., a mouse), and a signal generation device  616  (e.g., a speaker). 
     The secondary memory  618  may include a machine-accessible storage medium (or more specifically a computer-readable storage medium)  632  on which is stored one or more sets of instructions (e.g., software  622 ) embodying any one or more of the methodologies or functions described herein. The software  622  may also reside, completely or at least partially, within the main memory  604  and/or within the processor  602  during execution thereof by the computer system  600 , the main memory  604  and the processor  602  also constituting machine-readable storage media. The software  622  may further be transmitted or received over a network  620  via the network interface device  608 . 
     While the machine-accessible storage medium  632  is shown in an exemplary embodiment to be a single medium, the term “machine-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable storage medium” shall also be taken to include any medium that is capable of storing or encoding a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. The term “machine-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media. 
     Thus, electrostatic chucks (ESCs) for plasma processing chambers, and methods of fabricating ESCs, have been disclosed.