Abstract:
In one embodiment of the invention, a substrate support assembly comprises an electrostatic chuck having an electrode embedded therein and having an aperture disposed therethrough, a conductive liner disposed on the surface of the electrostatic chuck within the aperture, a conductive tubing extending from a lower surface of the electrostatic chuck and axially aligned with the aperture, and a conductive coating at least partially within the aperture and at least partially within the conductive tubing, wherein the conductive coating provides a conductive path between the conductive liner and the conductive tubing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/792,480, filed Mar. 15, 2013, which is hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments of the present invention generally relate to apparatus and methods for refurbishing an electrostatic chuck. More specifically, to repairing a severed electrical connection in the balancing circuit of an electrostatic chuck. 
     2. Description of the Related Art 
     In substrate processing equipment, an electrostatic chuck is commonly used for clamping a substrate to a pedestal during processing. The electrostatic chuck clamps the substrate by creating an attractive force between the substrate and the chuck. A voltage is applied to one or more electrodes in the chuck to induce oppositely polarized charges in the substrate and the electrodes, respectively. The opposite charges pull the substrate against the chuck, thereby retaining the substrate. 
     In a bipolar, electrostatic chuck, a chuck body has a pair of coplanar electrodes embedded therein. Each electrode is respectively connected to a terminal of a dual power supply having a common terminal, which is referred to as a center tap. The center tap is connected to a substrate spacing mask provided on the surface of the chuck in order to balance any variations in the impedance between the substrate and the electrodes. Thus, a constant electrostatic attraction force between the substrate and the chuck is maintained across the surface of the chuck. 
     The electrical connection between the center tap and the substrate spacing mask is often made through the conductive wall of a gas conduit used to supply gas to the backside of the substrate during processing. The gas conduit is attached to a metalized central bore within the chuck body. This connection works well during substrate processing, but the conductive connection is sometimes disrupted or otherwise compromised over time. While the conductive connection may remain mechanically sound, the connection may not be effectual in conducting electric current, which results in improper or dysfunctional operation of the electrostatic chuck. 
     Conventional repair methods include re-establishing the conductive connection using welding techniques, such as electron beam welding or laser welding techniques. However, these methods are expensive and time consuming, which increases cost of ownership and extends chamber downtime. 
     Therefore, a need exists for apparatus and methods of restoring a compromised balancing circuit electrical connection in an electrostatic chuck. 
     SUMMARY 
     In one embodiment of the invention, a substrate support assembly comprises an electrostatic chuck having an electrode embedded therein and having an aperture disposed therethrough, a conductive liner disposed on the surface of the electrostatic chuck within the aperture, a conductive tubing extending from a lower surface of the electrostatic chuck and axially aligned with the aperture, and a conductive coating at least partially within the aperture and at least partially within the conductive tubing, wherein the conductive coating provides a conductive path between the conductive liner and the conductive tubing. 
     In another embodiment, a method for repairing a severed electrical connection within a balancing circuit of an electrostatic chuck assembly comprises applying a conductive fluid across the severed electrical connection, and curing the conductive fluid to establish a conductive path across the severed electrical connection. 
     In another embodiment, a method for repairing a severed electrical connection within a balancing circuit of an electrostatic chuck assembly comprises determining the resistance between a substrate spacing mask disposed on the upper surface of an electrostatic chuck and a conductive tubing extending from the lower surface of the electrostatic chuck and axially aligned with a metallically lined aperture extending through the electrostatic chuck, evaluating the determined resistance to determine whether the electrical connection between the conductive conduit and the substrate mask has been severed, and repairing the severed connection by restoring a conductive path between the conductive tubing and the substrate spacing mask by applying a coating comprising a nano-particle conductive material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic, cross-sectional view of an exemplary substrate support assembly, which may benefit from the present invention. 
         FIG. 2  is a schematic depiction of a substrate support assembly utilizing a method of repairing a severed electrical connection between a conductive gas conduit and a conductive passage according to one embodiment of the present invention. 
         FIG. 3  is a schematic, cross-sectional view of another substrate support assembly that may benefit from the invention. 
         FIG. 4  is a schematic, cross-sectional view of another substrate support assembly that may benefit from the invention. 
         FIG. 5  is a schematic top plan view of a substrate support assembly showing the center tap structure described in  FIGS. 3 and 4 . 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     The present invention includes methods and apparatus for testing and repairing an electrical connection between bipolar electrodes contained within an electrostatic chuck and a conductive mask disposed atop the electrostatic chuck, particularly after removal of the electrostatic chuck. This connection is known as a balancing circuit because it balances the electrostatic forces applied to a substrate positioned atop the electrostatic chuck. 
     In one embodiment, the electrostatic chuck is tested to determine whether the balancing circuit electrical connection has been disrupted. In one embodiment, if the electrical connection has been disrupted, the electrical connection is repaired via a conductive coating process. 
       FIG. 1  is a schematic, cross-sectional view of an exemplary substrate support assembly  100 , which may benefit from the present invention. The substrate support assembly  100  includes an electrostatic chuck  105  for supporting and retaining a substrate  102  during processing. The electrostatic chuck  105  may comprise aluminum (Al) or an aluminum containing ceramic material, such as Al/Al 2 O 3 /AlN, or other material. 
     The electrostatic chuck  105  has a substrate spacing mask  107  disposed on the upper surface thereof. The substrate spacing mask  107  may comprise a material such as titanium, titanium nitride, or diamond-like carbon, and the like. The substrate spacing mask  107  is deposited to a pre-defined thickness that maintains the substrate  102  slightly above the surface of the electrostatic chuck  105 . The electrostatic chuck  105  further contains a conductive passage  103  disposed therethrough. In one embodiment, the conductive passage  103  electrically couples the substrate spacing mask  107  to the bottom region of the electrostatic chuck  105 . 
     In one embodiment, a heat transfer fluid is transported from a gas source  130  to a conductive gas conduit  132  through a gas conduit  135 . The conductive gas conduit  132  is mechanically and electrically coupled to the conductive passage  103 , such as by brazing. In one embodiment, the conductive gas conduit  132  is conductive tubing, such as stainless steel tubing. In one embodiment, the conductive gas conduit is axially aligned with the conductive passage  103 . Heat transfer fluid is transported through the conductive gas conduit  132  to the passage  103  extending through the electrostatic chuck  105 . The gas is further transported through the conductive passage  103  to the backside of the substrate  102 . The flow of gas may provide heating or cooling to the backside of the substrate  102 . The heat transfer gas may be helium, argon, hydrogen, among others. 
     The electrostatic chuck  105  includes one or more chucking electrodes  110  embedded therein. The chucking electrodes  110  are fabricated from a conductive material, such as tungsten, graphite, copper, or the like. The chucking electrodes  110  are disposed in an upper region of the electrostatic chuck  105  to provide the necessary electrostatic force to retain the substrate  102  when energized. The chucking electrodes  110  may be configured in any manner necessary to electrostatically retain the substrate  102 . However, in the embodiment depicted in  FIG. 1 , the chucking electrodes  110  are in a bipolar configuration. 
     The chucking electrodes  110  are connected to a power supply  140  comprising a pair of dual terminal DC voltage supplies  162  and  164  with a center tap  166 . The cathode on the voltage supply  162  is coupled to one of the bipolar chucking electrodes  110  via an electrode lead  163 , and the anode from the other voltage supply  164  is coupled to the other bipolar chucking electrode  110  via an electrode lead  165 . The cathode of the voltage supply  164  is coupled to the anode of the voltage supply  162  with a center tap  166  coupled therebetween. The center tap  166  is further coupled to the substrate spacing mask  107  via the conductive gas conduit  132  and the conductive passage  103 . A first brazed joint  170  may be used to electrically and mechanically couple the conductive gas conduit  132  to the conductive passage  103 . A metalized layer  175  may be used to electrically and mechanically couple the substrate spacing mask  107  to the conductive passage  103 . The first brazed joint  170  and the metalized layer  175  may comprise a conductive metallic material, such as gold (Au), silver (Ag) or aluminum (Al) or other conductive material. In one embodiment, the metalized layer  175  may be a tungsten (W) paste that is sintered to form a metallic layer and electrically connect the substrate spacing mask  107  to the conductive passage  103 . The electrical connection between the substrate spacing mask  107  and the conductive passage  103  comprising the metalized layer  175  can also include carbon nano tubes or graphene sheet or foils. The metalized layer  175  can also comprise multiple layers of the conductive metallic material, nano tube, sheets or foil as described herein, that include a corrosion resistant upper layer and a conductive inner metal contact made of nano ink or paste. Thus, a mechanically and electrically stable connection is formed between the center tap  166  and the substrate spacing mask  107 . As such, variations in the electrostatic force due to physical variations in the distance between the substrate  102  and the chucking electrode  110  may be balanced. Therefore, changes in the electrostatic force are balanced by having the center tap  166  of the power supply  140  coupled to the substrate spacing mask  107  in a balancing circuit. 
     Periodic service and maintenance of the substrate support assembly  100  is required during the lifetime of a processing chamber housing the electrostatic chuck  105 . Accordingly, the electrostatic chuck  105  may be periodically removed from its processing chamber for refurbishing. 
     However, it has been discovered that the electrical connection between the conductive gas conduit  132  and the conductive passage  103  may become severed during use and/or during removal of the electrostatic chuck  105 . Thus, the balancing circuit between the substrate spacing mask  107  and the chucking electrodes  110  is rendered non-functional. 
     One embodiment for repairing a severed electrical connection in the balancing circuit of the substrate support assembly  100  involves first testing the assembly to detect whether the connection has been severed and then repairing the severed connection through the use of various techniques and/or devices. First, the substrate support assembly is tested to determine whether the electrical connection between the conductive gas conduit  132  and the conductive passage  103  has been disrupted. In one embodiment, the resistance across the connection may be tested via an ohmmeter. If the resistance is equal to or less than a specified resistance, the connection is intact. If the resistance is greater than the specified resistance, the connection must be repaired. In one embodiment, the required resistance is 200 kilo ohms (kΩ). If the required resistance is not present, the connection is repaired. 
       FIG. 2  is a schematic depiction of a method of repairing the connection between the conductive gas conduit  132  and the conductive passage  103  according to one embodiment of the present invention. The conductive passage  103  may be repaired by applying a coating  200  on the inside of the conductive passage  103 . Heat may then be applied to the coating  200  for a specified time period to cure the coating and re-establish electrical continuity for the balancing circuit between the substrate spacing mask  107  and the chucking electrodes  110 . In one aspect, the coating  200  bridges and electrically connects the substrate spacing mask  107  to the conductive gas conduit  132 . 
     The coating  200  may comprise a nano-particle based metal coating, such as a silver coating. The coating  200  may be in the form of an ink or a paste that may be applied by a brush, a spray coating technique, or other suitable coating method. Suitable silver materials that may be used to coat the temperature sensor include a material sold under the trade name TEC-PA-030 (or other materials sold under the trade name TEC-PA-XXX, such as TEC-PA-010, TEC-PA-020, etc.), all available from InkTec® Co., LTD of South Korea, or any other suitable conductive nano inks that can be easily cured using IR heating, flame heating, induction heating or furnace heating. 
     The coating  200  provides good adhesion with the various materials of the electrostatic chuck  105 . Thus, the coating  200  may be easily deposited on the surfaces of the first brazed joint  170 , the metalized layer  175 , and the surfaces of the conductive gas conduit  132 . In one embodiment, the coating  200  may be a conductive nano coating/nano ink that is sintered on the electrostatic chuck  105  comprising an Al/Al 2 O 3 /AlN, or other material. The coating  200  is used to establish proper electrical contact with the center tap circuit. In one embodiment, the coating  200  comprises a nano silver material that maintains conductivity even when an exposed surface of the coating  200  is oxidized during curing. 
     The coating  200  includes particles having a size of about 10 nanometers to about 100 nanometers. The coating  200  may be deposited by numerous techniques including spray coating, brush coating, and a printing and firing process. The application process may comprise coating transparent silver nano-particles in the form of an ink onto the surface. Then, the ink is heated to evaporate and dry, leaving a silver organic transparent film to form a self assembled silver monolayer that forms the coating  200 . In one embodiment, the coating  200  includes an electrical resistivity at room temperature (about 27 degrees C.) that is less than about 0.002 micro Ohms per centimeter (μΩ cm). 
     The coating  200  may be cured by heating. The coating  200  may be heated by numerous techniques including infrared (IR) light, convection heating, microwaves, a flame-treatment, and combinations thereof. In one embodiment, the curing comprises heating the coating  200  to a temperature of about 150 degrees Celsius (° C.) to about 200° C., and maintaining the temperature for about 15 minutes to 30 minutes. After heating the coating  200 , a very thin layer (e.g., having a thickness of about 500 nanometers (nm) to about 5 microns, such as about 20 nm to about 100 nm) of electrically conductive material is formed between the conductive gas conduit  132  and the substrate spacing mask  107 , which provides electrical continuity between the substrate spacing mask  107  and the center tap  166  (shown in  FIG. 1 ). 
       FIG. 3  is a schematic, cross-sectional view of another substrate support assembly  300  that may benefit from the invention. The substrate support assembly  300  includes an electrostatic chuck  105  disposed on a conductive gas conduit  132  similar to the embodiment shown in  FIG. 1 . The electrostatic chuck  105  includes chucking electrodes (not shown) and is electrically coupled to a power source and gas source (both not shown) similar to the configuration shown in  FIG. 1 . The electrostatic chuck  105  has a substrate spacing mask  107  disposed on the upper surface thereof. A center tap structure  305  is disposed in the conductive passage  103 . The center tap structure  305  includes the center tap  166  that is coupled to the conductive passage  103  by an extended member  310 . The center tap structure  305  also includes a conductive member  315  that extends away from the center of the conductive passage  103  and is in contact with the backside of the substrate  102 . The center tap structure  305  forms the balancing circuit as described in  FIG. 1 . 
     Similar to the substrate support assembly  100  of  FIG. 1 , the electrical connection between the conductive gas conduit  132  and the conductive passage  103  may become severed during use and/or during removal of the electrostatic chuck  105 . To repair the electrical connection, the coating  200  as described in  FIG. 2  is utilized. 
     Additionally, the electrostatic chuck  105  is modified to include a chamfer  320  at corner regions thereof adjacent the conductive passage  103 . The chamfer  320  may be a beveled region that is utilized to reduce stress between the conductive passage  103 , and the first brazed joint  170  and the metalized layer  175 . The chamfer  320  may also be used to increase surface area available for bonding with the braze material utilized in the first brazed joint  170  and the metalized layer  175 . The chamfer  320  thus may be used to reduce stresses on the center tap structure  305  and/or the conductive passage  103  to prevent or minimize damage to the electrical connection between the conductive gas conduit  132  and the conductive passage  103  during use and/or during removal of the electrostatic chuck  105 . 
       FIG. 4  is a schematic, cross-sectional view of another substrate support assembly  400  that may benefit from the invention. The substrate support assembly  400  includes an electrostatic chuck  105  disposed on a conductive gas conduit  132  similar to the embodiment shown in  FIG. 1 . The electrostatic chuck  105  includes chucking electrodes (not shown) and is electrically coupled to a power source and gas source (both not shown) similar to the configuration shown in  FIG. 1 . The substrate support assembly  400  is identical to the substrate support assembly  300  of  FIG. 3  with the exception of a radius  405  at corner regions of the electrostatic chuck  105  adjacent the conductive passage  103 . The radius  405  may be utilized to reduce stress between the conductive passage  103 , and the first brazed joint  170  and the metalized layer  175 . The radius  405  may also be used to increase surface area available for bonding with the braze material utilized in the first brazed joint  170  and the metalized layer  175 . The radius  405  thus may be used to reduce stresses on the center tap structure  305  and/or the conductive passage  103  to prevent or minimize damage to the electrical connection between the conductive gas conduit  132  and the conductive passage  103  during use and/or during removal of the electrostatic chuck  105 . 
       FIG. 5  is a schematic top plan view of a substrate support assembly  500  showing the center tap structure  305  described in  FIGS. 3 and 4 . The center tap structure  305  includes the conductive member  315  having ends  505  that define an open region therebetween. 
     Embodiments described herein provide apparatus and methods for repairing a broken electrical circuit in an electrostatic chuck. The coating and method as described herein provides a more economical and faster repair of the electrical connection as compared to laser and e-beam welding techniques, which greatly reduces cost of ownership. The coating  200  also extends the lifetime of the electrostatic chuck  105  by providing improved electrical contact that is uniform and more robust. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.