Abstract:
An electrostatic chuck comprises a ceramic body having a first surface and a second surface that is on an opposite side of the ceramic body to the first surface, the ceramic body comprising a through-hole between the first surface and the second surface. The electrostatic chuck further comprises a thermally conductive base that supports the ceramic body and comprises a second hole that lines up with the through-hole, wherein the second hole is to fluidly couple to a source of heat transfer gas. The electrostatic chuck further comprises a bonding layer between the ceramic body and the thermally conductive base, the bonding layer comprising a space between an opening of the through-hole on the second surface and the gas introduction path.

Description:
RELATED APPLICATIONS 
       [0001]    This patent application is a continuation application of U.S. patent application Ser. No. 15/613,061, filed Jun. 2, 2017, which is a divisional application of U.S. patent application Ser. No. 13/842,044, filed Mar. 15, 2013, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/735,895, filed Dec. 11, 2012. U.S. patent application Ser. Nos. 13/842,044 and 15/613,061 are herein incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Some embodiments of the present invention relate, in general, to a substrate support assembly such as an electrostatic chuck that has a plasma resistant protective layer. Other embodiments relate to reactive multi-layer foils and the manufacture of reactive multi-layer foils. 
       BACKGROUND 
       [0003]    In the semiconductor industry, devices are fabricated by a number of manufacturing processes producing structures of an ever-decreasing size. Some manufacturing processes such as plasma etch and plasma clean processes expose a substrate support (e.g., an edge of the substrate support during wafer processing and the full substrate support during chamber cleaning) to a high-speed stream of plasma to etch or clean the substrate. The plasma may be highly corrosive, and may corrode processing chambers and other surfaces that are exposed to the plasma. 
         [0004]    Additionally, traditional electrostatic chucks include a ceramic puck silicone bonded to a metal cooling plate. The Ceramic puck in such traditional electrostatic chucks is manufactured by a multi-step manufacturing process that can be costly to form an embedded electrode and heating elements. 
         [0005]    Reactive multilayer foils (referred to herein as reactive foils) are used to form a metal bond between substrates. Traditional reactive foil is manufactured in flat featureless sheets. Traditional reactive foil is typically not appropriate for bonding substrates having non-flat surfaces. Additionally, if the traditional reactive foil is used to bond substrates having surface features, the reactive foil is machined (e.g., by laser drilling, chemical etching, etc.) to form corresponding features in the reactive foil. Such machining can induce a heat load on the reactive foil and cause the reactive foil to ignite. Moreover, traditional reactive foil has a preset size such as 9 inch squares. When the traditional reactive foil is used to bond substrates that are larger than the reactive foil, then multiple sheets of reactive foil are used to perform the bonding. This commonly introduces leakage paths such as cracks, grooves, lines, etc. between the reactive foil sheets, and causes the resultant metal bond to not be vacuum sealed. 
       SUMMARY 
       [0006]    In one embodiment, an electrostatic chuck includes a ceramic body and a thermally conductive base bonded to a lower surface of the ceramic body. The ceramic body may be bonded to the thermally conductive base by a metal bond or by a silicone bond. The electrostatic chuck is fabricated with a protective layer bonded to an upper surface of the ceramic body by a metal bond, the protective layer comprising a bulk sintered ceramic article. 
         [0007]    In another embodiment, reactive foil is manufactured. A template having one or more surface features is provided. Alternating nanoscale layers of aluminum and nickel are deposited onto the template to form a reactive foil sheet. The reactive foil sheet is removed from the template. The resultant reactive foil sheet has one or more foil features corresponding to one or more surface features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that different references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
           [0009]      FIG. 1  depicts a sectional view of one embodiment of a processing chamber; 
           [0010]      FIG. 2  depicts an exploded view of one embodiment of a substrate support assembly; 
           [0011]      FIG. 3  depicts a side view of one embodiment of a substrate support assembly; 
           [0012]      FIG. 4  depicts an exploded side view of one embodiment of a substrate support; 
           [0013]      FIG. 5  illustrates one embodiment of a process for manufacturing an electrostatic chuck; 
           [0014]      FIG. 6  illustrates another embodiment of a process for manufacturing an electrostatic chuck; and 
           [0015]      FIG. 7  illustrates one embodiment of a process for performing a metal bonding process. 
           [0016]      FIG. 8  illustrates one embodiment of a process for manufacturing reactive foil having preformed foil features. 
           [0017]      FIG. 9A  illustrates deposition of nanoscale metal layers onto a template having surface features. 
           [0018]      FIG. 9B  illustrates a reactive foil sheet having preformed foil features. 
           [0019]      FIG. 10A  illustrates deposition of nanoscale metal layers onto a non-planar template. 
           [0020]      FIG. 10B  illustrates a non-planar reactive foil sheet. 
           [0021]      FIG. 11  illustrates interlocking reactive foil sheets. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0022]    Embodiments of the present invention provide a substrate support assembly (e.g., an electrostatic chuck) having a protective layer formed over a ceramic body of the substrate support assembly. The protective layer may provide plasma corrosion resistance for protection of the ceramic body. The protective layer may be a bulk sintered ceramic article (e.g., a ceramic wafer) that is metal bonded to the ceramic body using a nano-bonding technique. Various bonding materials such as In, Sn, Ag, Au, Cu and their alloys could be used along with a reactive foil. 
         [0023]    In one embodiment, the ceramic body is a bulk sintered ceramic body (e.g., another ceramic wafer). When the ceramic body does not include a chucking electrode, the metal bond may function as a chucking electrode for the electrostatic chuck. The ceramic body may additionally be metal bonded to a thermally conductive base by another metal bond. The thermally conductive base may include heating elements as well as channels that can be used to regulate temperature by flowing liquid for heating and/or cooling. The metal bond between the thermally conductive base and the ceramic body provides a good thermal contact, and enables the thermally conductive base to heat and cool the ceramic body, the protective layer and any substrate held by the electrostatic chuck during processing. Embodiments provide an electrostatic chuck that can be as much as  4   x  cheaper to manufacture than conventional electrostatic chucks. Moreover, embodiments provide an electrostatic chuck that can adjust temperature rapidly and that is plasma resistant. The electrostatic chuck and a substrate being supported may be heated or cooled quickly, with some embodiments enabling temperature changes of 2° C./s or faster. This enables the electrostatic chuck to be used in multi-step processes in which, for example, a wafer may be processed at 20-30° C. and then rapidly ramped up to 80-90° C. for further processing. The embodiments described herein may be used for both Columbic electrostatic chucking applications and Johnson Raybek chucking applications. 
         [0024]    In another embodiment, reactive foil is manufactured that has preformed surface features. The reactive foil may be manufactured by depositing alternating nanoscale layers of two reactive materials such as aluminum and nickel onto a template that has surface features. The surface features of the template may correspond to surface features of one or more substrates that the reactive foil will be used to bond. For example, if the one or more substrates have holes in them, then the template may have steps corresponding to the holes. These steps may cause reactive foil formed on the template to have preformed holes that correspond to the holes in the substrate. 
         [0025]      FIG. 1  is a sectional view of one embodiment of a semiconductor processing chamber  100  having a substrate support assembly  148  disposed therein. The substrate support assembly  148  has a protective layer  136  of a bulk ceramic that has been metal bonded to a ceramic body of the substrate support assembly  148 . The metal bond may include a combination of metals, such as a combination of indium, tin, aluminum, nickel and one or more additional metals (e.g., such as gold or silver). The metal bonding process is described in greater detail below. 
         [0026]    The protective layer may be a bulk ceramic (e.g., a ceramic wafer) such as Y 2 O 3  (yttria or yttrium oxide), Y 4 Al 2 O 9  (YAM), Al 2 O 3  (alumina) Y 3 Al 5 O 12  (YAG), YAlO3 (YAP), Quartz, SiC (silicon carbide) Si 3 N 4  (silicon nitride) Sialon, Minn. (aluminum nitride), AlON (aluminum oxynitride), TiO 2  (titania), ZrO 2  (zirconia), TiC (titanium carbide), ZrC (zirconium carbide), TiN (titanium nitride), TiCN (titanium carbon nitride) Y 2 O 3  stabilized ZrO 2  (YSZ), and so on. The protective layer may also be a ceramic composite such as Y 3 Al 5 O 12  distributed in Al 2 O 3  matrix, Y 2 O 3 —ZrO 2  solid solution or a SiC—Si 3 N 4  solid solution. The protective layer may also be a ceramic composite that includes a yttrium oxide (also known as yttria and Y 2 O 3 ) containing solid solution. For example, the protective layer may be a ceramic composite that is composed of a compound Y 4 Al 2 O 9  (YAM) and a solid solution Y 2 -xZr x O 3  (Y 2 O 3 —ZrO 2  solid solution). Note that pure yttrium oxide as well as yttrium oxide containing solid solutions may be doped with one or more of ZrO 2 , Al 2 O 3 , SiO 2 , B 2 O 3 , Er 2 O 3 , Nd 2 O 3 , Nb 2 O 5 , CeO 2 , Sm 2 O 3 , Yb 2 O 3 , or other oxides. Also note that pure Aluminum Nitride as well as doped Aluminum Nitride with one or more of ZrO 2 , Al 2 O 3 , SiO 2 , B 2 O 3 , Er 2 O 3 , Nd 2 O 3 , Nb 2 O 5 , CeO 2 , Sm 2 O 3 , Yb 2 O 3 , or other oxides may be used. Alternatively, the protective layer may be sapphire or MgAlON. 
         [0027]    The protective layer may be a sintered ceramic article that was produced from a ceramic powder or a mixture of ceramic powders. For example, the ceramic composite may be produced from a mixture of a Y 2 O 3  powder, a ZrO 2  powder and an Al 2 O 3  powder. The ceramic composite may include Y 2 O 3  in a range of 50-75 mol %, ZrO 2  in a range of 10-30 mol % and Al 2 O 3  in a range of 10-30 mol %. In one embodiment, the HPM ceramic composite contains approximately 77% Y 2 O 3 , 15% ZrO 2  and 8% Al 2 O 3 . In another embodiment, the ceramic composite contains approximately 63% Y 2 O 3 , 23% ZrO 2  and 14% Al 2 O 3 . In still another embodiment, the HPM ceramic composite contains approximately 55% Y 2 O 3 , 20% ZrO 2  and 25% Al 2 O 3 . Relative percentages may be in molar ratios. For example, the HPM ceramic composite may contain 77 mol % Y 2 O 3 , 15 mol % ZrO 2  and 8 mol % Al 2 O 3 . Other distributions of these ceramic powders may also be used for the ceramic composite. 
         [0028]    The processing chamber  100  includes a chamber body  102  and a lid  104  that enclose an interior volume  106 . The chamber body  102  may be fabricated from aluminum, stainless steel or other suitable material. The chamber body  102  generally includes sidewalls  108  and a bottom  110 . An outer liner  116  may be disposed adjacent the side walls  108  to protect the chamber body  102 . The outer liner  116  may be fabricated and/or coated with a plasma or halogen-containing gas resistant material. In one embodiment, the outer liner  116  is fabricated from aluminum oxide. In another embodiment, the outer liner  116  is fabricated from or coated with yttria, yttrium alloy or an oxide thereof. 
         [0029]    An exhaust port  126  may be defined in the chamber body  102 , and may couple the interior volume  106  to a pump system  128 . The pump system  128  may include one or more pumps and throttle valves utilized to evacuate and regulate the pressure of the interior volume  106  of the processing chamber  100 . 
         [0030]    The lid  104  may be supported on the sidewall  108  of the chamber body  102 . The lid  104  may be opened to allow excess to the interior volume  106  of the processing chamber  100 , and may provide a seal for the processing chamber  100  while closed. A gas panel  158  may be coupled to the processing chamber  100  to provide process and/or cleaning gases to the interior volume  106  through a gas distribution assembly  130  that is part of the lid  104 . Examples of processing gases may be used to process in the processing chamber including halogen-containing gas, such as C 2 F 6 , SF 6 , SiCl 4 , HBr, NF 3 , CF 4 , CHF 3 , CH 2 F 3 , Cl 2  and SiF 4 , among others, and other gases such as O 2 , or N 2 O. Examples of carrier gases include N 2 , He, Ar, and other gases inert to process gases (e.g., non-reactive gases). The gas distribution assembly  130  may have multiple apertures  132  on the downstream surface of the gas distribution assembly  130  to direct the gas flow to the surface of the substrate  144 . Additionally, the gas distribution assembly  130  can have a center hole where gases are fed through a ceramic gas nozzle. The gas distribution assembly  130  may be fabricated and/or coated by a ceramic material, such as silicon carbide, Yttrium oxide, etc. to provide resistance to halogen-containing chemistries to prevent the gas distribution assembly  130  from corrosion. 
         [0031]    The substrate support assembly  148  is disposed in the interior volume  106  of the processing chamber  100  below the gas distribution assembly  130 . The substrate support assembly  148  holds the substrate  144  during processing. An inner liner  118  may be coated on the periphery of the substrate support assembly  148 . The inner liner  118  may be a halogen-containing gas resist material such as those discussed with reference to the outer liner  116 . In one embodiment, the inner liner  118  may be fabricated from the same materials of the outer liner  116 . 
         [0032]    In one embodiment, the substrate support assembly  148  includes a mounting plate  162  supporting a pedestal  152 , and an electrostatic chuck  150 . In one embodiment, the electrostatic chuck  150  further includes a thermally conductive base  164  bonded to an electrostatic puck  166  by a metal or silicone bond  138 . Alternatively, a simple ceramic body may be used instead of the electrostatic puck  166 , as will be described in greater detail with reference to  FIG. 3 . An upper surface of the electrostatic puck  166  is covered by the protective layer  136  that is metal bonded to the electrostatic puck  166 . In one embodiment, the protective layer  136  is disposed on the upper surface of the electrostatic puck  166 . In another embodiment, the protective layer  136  is disposed on the entire surface of the electrostatic chuck  150  including the outer and side periphery of the thermally conductive base  164  and the electrostatic puck  166 . The mounting plate  162  is coupled to the bottom  110  of the chamber body  102  and includes passages for routing utilities (e.g., fluids, power lines, sensor leads, etc.) to the thermally conductive base  164  and the electrostatic puck  166 . 
         [0033]    The thermally conductive base  164  and/or electrostatic puck  166  may include one or more optional embedded heating elements  176 , embedded thermal isolators  174  and/or conduits  168 ,  170  to control a lateral temperature profile of the support assembly  148 . The conduits  168 ,  170  may be fluidly coupled to a fluid source  172  that circulates a temperature regulating fluid through the conduits  168 ,  170 . The embedded isolator  174  may be disposed between the conduits  168 ,  170  in one embodiment. The heater  176  is regulated by a heater power source  178 . The conduits  168 ,  170  and heater  176  may be utilized to control the temperature of the thermally conductive base  164 , thereby heating and/or cooling the electrostatic puck  166  and a substrate (e.g., a wafer) being processed. The temperature of the electrostatic puck  166  and the thermally conductive base  164  may be monitored using a plurality of temperature sensors  190 ,  192 , which may be monitored using a controller  195 . 
         [0034]    The electrostatic puck  166  and/or protective layer may further include multiple gas passages such as grooves, mesas and other surface features, that may be formed in an upper surface of the puck  166  and/or the protective layer. The gas passages may be fluidly coupled to a source of a heat transfer (or backside) gas, such as He via holes drilled in the puck  166 . In operation, the backside gas may be provided at controlled pressure into the gas passages to enhance the heat transfer between the electrostatic puck  166  and the substrate  144 . 
         [0035]    In one embodiment, the electrostatic puck  166  includes at least one clamping electrode  180  controlled by a chucking power source  182 . In alternative embodiments, the metal bond may function as the clamping electrode. Alternatively, the protective layer may include an embedded clamping electrode (also referred to as a chucking electrode). The electrode  180  (or other electrode disposed in the puck  166  or protective layer) may further be coupled to one or more RF power sources  184 ,  186  through a matching circuit  188  for maintaining a plasma formed from process and/or other gases within the processing chamber  100 . The sources  184 ,  186  are generally capable of producing an RF signal having a frequency from about 50 kHz to about 3 GHz and a power of up to about 10,000 Watts. In one embodiment, an RF signal is applied to the metal base, an alternating current (AC) is applied to the heater and a direct current (DC) is applied to the chucking electrode. 
         [0036]      FIG. 2  depicts an exploded view of one embodiment of the substrate support assembly  148 . The substrate support assembly  148  depicts an exploded view of the electrostatic chuck  150  and the pedestal  152 . The electrostatic chuck  150  includes the electrostatic puck  166  or other ceramic body, as well as the thermally conductive base  164  attached to the electrostatic puck  166  or ceramic body. The electrostatic puck  166  or other ceramic body has a disc-like shape having an annular periphery  222  that may substantially match the shape and size of the substrate  144  positioned thereon. In one embodiment, the electrostatic puck  166  or other ceramic body may be fabricated by a ceramic material. Suitable examples of the ceramic materials include aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), titanium oxide (TiO), titanium nitride (TiN), silicon carbide (SiC) and the like. In one embodiment, the ceramic body is a bulk sintered ceramic, which may be in the form of a wafer. 
         [0037]    The thermally conductive base  164  attached below the electrostatic puck  166  or ceramic body may have a disc-like main portion  224  and an annular flange  220  extending outwardly from a main portion  224  and positioned on the pedestal  152 . In one embodiment, the thermally conductive base  164  may be fabricated by a metal, such as aluminum or stainless steel or other suitable materials. Alternatively, the thermally conductive base  164  may be fabricated by a composite of ceramic, such as an aluminum-silicon alloy infiltrated SiC or Molybdenum to match a thermal expansion coefficient of the ceramic body. The thermally conductive base  164  should provide good strength and durability as well as heat transfer properties. An upper surface of the protective layer  136  may have an outer ring  216 , multiple mesas  210  and channels  208 ,  212  between the mesas. 
         [0038]      FIG. 3  illustrates a cross sectional side view of the electrostatic chuck  150 . Referring to  FIG. 3 , the thermally conductive base  164  is coupled to a ceramic body  302  by a first metal bond  304 . The ceramic body  302  may be a bulk sintered ceramic such as aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), titanium oxide (TiO), titanium nitride (TiN), silicon carbide (SiC) and the like. The ceramic body  302  may be provided, for example, as a thin ceramic wafer. In one embodiment, the ceramic body has a thickness of about 1 mm. The ceramic body  302  may have an electrode connection  306  formed therein (e.g., by drilling a hole through the ceramic body and filling the hole with an electrically conductive material. The electrode connection  306  may connect a metal bond that functions as a clamping electrode to a chucking power source and/or to an RF source. 
         [0039]    The first metal bond  304  facilitates thermal energy exchange between the ceramic body  302  and the thermally conductive base  164  and may reduce thermal expansion mismatch therebetween. The metal base  164  may include multiple conduits (e.g., an inner conduit  168  and an outer conduit  170 ) through which fluids may be flowed to heat or cool the electrostatic chuck  150  and a substrate  144 . The metal base  164  may additionally include one or more embedded heaters  176 , which may be resistive heating elements. 
         [0040]    The first metal bond  304  mechanically bonds the thermally conductive base  164  to the ceramic body  302 . In one embodiment, the metal bonding material  304  includes tin and/or indium. Alternatively, other metals may be used. Additionally, the first metal bond  304  may include a thin layer of aluminum and nickel (e.g., having a thickness of about 2-4 mil in one embodiment) between two layers of other metals (e.g., between two layers of tin). In one embodiment, the thin layer is initially a reactive multi-layer foil (referred to herein as a reactive foil) composed of alternating nanoscale layers of reactive materials such as aluminum and nickel. During a room temperature metal bonding process, the reactive foil may be activated (e.g., ignited), creating a near instantaneous reaction generating upwards of 1500 degrees C. This may cause upper and lower layers of metal, which act as a solder, to melt and reflow to bond the thermally conductive base  164  to the ceramic body  302 . In one embodiment, the reactive foil is NanoFoil®, manufactured by Indium Corporation of America. 
         [0041]    The electrostatic chuck  150  additionally includes a protective layer  136  that is coupled to the ceramic body  302  by a second metal bond  308 . The protective layer  136  may be provided, for example, as a thin ceramic wafer. Mesas (not shown) may be formed on a surface of the protective layer, and the protective layer and ceramic body may include holes for the flow of helium and holes for lift pins. Such holes may be formed before or after the protective layer  136  is bonded to the ceramic body. The second metal bond  308  may be substantially similar to the first metal bond  304 , and may have been generated using a room temperature bonding process (e.g., using an ignitable reactive foil). In one embodiment, the reactive foil has preformed foil features that correspond to surface features of the protective layer and/or the ceramic body. For example, the reactive foil may have preformed holes that correspond to helium holes and lift pin holes in the protective layer. Reactive foil having preformed foil features is described in greater detail below with reference to  FIGS. 8A-11 . 
         [0042]    In one embodiment, both the first metal bond  304  and the second metal bond  308  are formed at the same time. For example, the entire structure may be pressed together in a fixture, and reactive foil between the thermally conductive base and ceramic body may be activated at approximately the same time as reactive foil between the protective layer and the ceramic body to form both metal bonds in parallel. Bond thickness may be approximately 25 microns to 500 microns (e.g., 150 to 250 microns in one embodiment). 
         [0043]    The thickness of protective layer  136  may be selected to provide desired dielectric properties such as a specific breakdown voltage. In one embodiment, when the electrostatic chuck is to be used in a Columbic mode, the protective layer has a thickness of between about 150-500 microns (and about 200-300 microns in one example embodiment). If the electrostatic chuck is to be used in a Johnson Raybek mode, the protective layer may have a thickness of around 1 mm. 
         [0044]    As mentioned above, the protective layer  136  is a bulk sintered ceramic. In one embodiment, the protective layer is a ceramic composite as described above, which has a high hardness that resists wear (due to relative motion because of thermal property mismatch between substrate &amp; the puck) during plasma processing. In one embodiment, the ceramic composite provides a Vickers hardness (5 Kgf) between about 5 GPa and about 11 GPa. In one embodiment, the ceramic composite provides a Vickers hardness of about 9-10 GPa. Additionally, the ceramic composite may have a density of around 4.90 g/cm3, a flexural strength of about 215 MPa, a fracture toughness of about 1.6 MPa·m 1/2 , a Youngs Modulus of about 190 GPa, a thermal expansion of about 8.5×10 −6 /K (20-900° C.), a thermal conductivity of about 3.5 W/mK, a dielectric constant of about 15.5 (measured at 20° C. 13.56 MHz), a dielectric loss tangent of about 11×10-4 (20° C. 13.56 MHz), and a volume resistivity of greater than 10 15  Ω·cm at room temperature in one embodiment. 
         [0045]    In another embodiment, the protective layer is YAG. In another embodiment, the protective layer is sapphire. In still another embodiment, the protective layer is yttrium aluminum oxide (Y x Al y O z ). 
         [0046]    A gasket  310  may be disposed at a periphery of the electrostatic chuck  150  between the protective layer  136  and the ceramic body  302 . In one embodiment, the gasket  310  is a fluoro-polymer compressible o-ring. In another embodiment, the gasket is a liquid polymer that cures under pressure to form the gasket. The gasket  310  provides a protective seal that protects the metal bond  308  from exposure to plasma or corrosive gases. A similar gasket may encircle and protect the first metal bond  304 . Note also that a similar type of gasket  314  may be used to seal off and separate the electrode connection  306  from the first metal bond  304 . 
         [0047]    A quartz ring  146 , or other protective ring, surrounds and covers portions of the electrostatic chuck  150 . The substrate  144  is lowered down over the electrostatic puck  166 , and is held in place via electrostatic forces. 
         [0048]    If the electrostatic chuck  150  is to be used for Columbic chucking, then the thickness of the protective layer (dielectric above the electrode) may be about 200 microns to about 1 mm. If the electrostatic shuck  150  is to be used for Johnson Raybek chucking, then the thickness of the protective layer may be about 1 mm to about 1.5 mm. 
         [0049]      FIG. 4  illustrates a cross sectional side view of one embodiment of an electrostatic chuck  400 . The electrostatic chuck  400  has a ceramic body  410  metal bonded to a protective layer  415  by a metal bond  420  and further bonded to a metal plate  455  by a silicone bond or other bond  496 . In one embodiment, the ceramic body has a thickness of about 3 mm. The ceramic body  410  may include one or more heating elements  418 . In one embodiment, the ceramic body  410  includes an electrode embedded therein. In another embodiment (as shown), an electrode  485  may be embedded in the protective layer  415 . In yet another embodiment, a metal bond  420  may at as an electrode. In one embodiment, an upper portion  492  of the protective layer  415  that lies above the electrode  485  has a thickness of greater than 200 micron (e.g., 5 mil in one embodiment). The thickness of the upper portion  492  of the protective layer  415  may be selected to provide desired dielectric properties such as a specific breakdown voltage. 
         [0050]    After the protective layer  415  is placed (and ground to a final thickness in some embodiments), mesas  418  are formed on an upper surface of the protective layer  415 . The mesas  418  may be formed, for example, by bead blasting or salt blasting the surface of the protective layer  415 . The mesas may be around 3-50 microns tall (about 10-15 in one embodiment) and about 200 microns in diameter in some embodiments. 
         [0051]    Additionally, multiple holes  475  are drilled through the ceramic body  410  and/or protective layer  415 . These holes  475  may be drilled before or after the protective layer  415  is bonded to the ceramic base  410 , and holes in the protective layer  415  may line up with holes in the ceramic body  410  and/or base  455 . In one embodiment, holes are drilled through the protective layer  415 , ceramic body  410  and base  455  after the bonding is performed. Alternatively, holes may be drilled separately and then aligned prior to bonding. The holes may line up with preformed holes in a reactive foil used to form the metal bond  420  between the ceramic body  410  and protective layer  415 . In one embodiment, gaskets  490  are placed or formed at a perimeter of the metal bond  420  and where the holes  475  meet the metal bond  420 . The gaskets formed around the holes  475  may be omitted in some implementations in which the metal bond  420  is not used as an electrode. In one embodiment, the holes  475  have a diameter of about 4-7 mil. In one embodiment, the holes are formed by laser drilling. The holes  475  may deliver a thermally conductive gas such as helium to valleys or conduits between the mesas  418 . The helium (or other thermally conductive gas) may facilitate heat transfer between a substrate and the electrostatic chuck  400 . It is also possible to deposit the mesas  418  on top of substrate support (e.g., onto the protective layer  415 ). Ceramic plugs (not shown) may fill the holes. The ceramic plugs may be porous, and may permit the flow of helium. However, the ceramic plugs may prevent arcing of flowed plasma. 
         [0052]      FIG. 5  illustrates one embodiment of a process  500  for manufacturing an electrostatic chuck. At block  505  of process  500 , a ceramic body is provided. The provided ceramic body may be a ceramic wafer. The ceramic wafer may have undergone some processing, such as to form an electrode connector, but may lack heating elements, cooling channels, and an embedded electrode. 
         [0053]    At block  510 , a lower surface of the ceramic body is bonded to a thermally conductive base by performing a metal bonding process to form a first metal bond. At block  515 , a bulk sintered ceramic protective layer is bonded to an upper surface of the ceramic body by the metal bonding process to form a second metal bond. The protective layer may be a ceramic wafer having a thickness of about 700 microns to about 1-2 mm. The metal bonding process is described with reference to  FIG. 7 . In one embodiment, the upper surface of the ceramic body is polished flat before bonding it to the protective layer. At block  520 , the second metal bond is coupled to a sealed electrode connection. This coupling may occur as a result of the metal bonding process that forms the second metal bond. 
         [0054]    At block  525 , a surface of the protective layer is ground down to a desired thickness. The protective layer may be a dialectic material over a clamping electrode, and so the desired thickness may be a thickness that provides a specific breakdown voltage (e.g., about 200-300 microns in one embodiment). 
         [0055]    At block  530 , mesas are formed on an upper surface of the protective layer. At block  535 , holes are formed in the protective layer and the ceramic body (e.g., by laser drilling). Note that the operations of block  530  may be performed after bonding the protective layer to the ceramic body (as shown), or may be performed prior to such bonding. Plugs may then be formed in the holes. In an alternative embodiment, the ceramic body may be bonded to the base after the mesas are formed, after the holes are formed and/or after the protective layer is bonded. 
         [0056]      FIG. 6  illustrates another embodiment of a process for manufacturing an electrostatic chuck. At block  605  of process  600 , a ceramic body is provided. The provided ceramic body may be a ceramic puck that includes one or more heating elements. The ceramic puck may or may not include an embedded electrode. 
         [0057]    At block  610 , a lower surface of the ceramic body is bonded to a thermally conductive base. The bond may be a silicone bond in one embodiment. In another embodiment, the bonding material may be a thermal conductive paste or tape having at least one of an acrylic based compound and silicone based compound. In yet another embodiment, the bonding material may be a thermal paste or tape having at least one of an acrylic based compound and silicone based compound, which may have metal or ceramic fillers mixed or added thereto. The metal filler may be at least one of Al, Mg, Ta, Ti, or combination thereof and the ceramic filler may be at least one of aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), titanium diboride (TiB 2 ) or combination thereof. 
         [0058]    At block  615 , a bulk sintered ceramic protective layer is bonded to an upper surface of the ceramic body by a metal bonding process to form a metal bond. The metal bonding process is described with reference to  FIG. 7 . 
         [0059]    At block  620 , a surface of the protective layer is ground down to a desired thickness. The protective layer may be a dialectic material over a clamping electrode, and so the desired thickness may be a thickness that provides a specific breakdown voltage. 
         [0060]    At block  625 , mesas are formed on an upper surface of the protective layer. At block  630 , holes are formed in the protective layer and the ceramic body (e.g., by laser drilling). In an alternative embodiment, the ceramic body may be bonded to the base after the mesas are formed, after the holes are formed or after the protective layer is bonded. 
         [0061]      FIG. 7  illustrates one embodiment for performing a metal bonding process. At block  705 , a surface of a first body is coated with a first metal layer. The metal layer may be tin, indium or another metal. At block  710 , a surface of a second body is coated with a second metal layer. The first body and second body may be, for example, a protective layer, a ceramic body or a thermally conductive base. For ceramic bodies (e.g, the ceramic body or protective layer), coating the surface with a metal layer may include first forming a titanium layer on the surface. Titanium has properties that cause it to form strong bonds with ceramics (such as by forming bonds with oxygen molecules in ceramics). A metal layer may then be formed over the titanium. 
         [0062]    The metal layer may be tin or indium, for example. If tin is used for the metal layer, then processes of below 250 degrees C. may be performed using the electrostatic chuck since tin has a melting temperature of 250 degrees C. If indium is used for the metal layer, then processes of below 150 degrees C. may be performed using the electrostatic chuck since indium has a melting temperature of 150 degrees C. If higher temperature processes are to be performed, than a metal having a higher melting temperature should be used for the metal layers. The titanium layer and the subsequent metal layer may be formed by evaporation, electroplating, sputtering, or other metal deposition or growth techniques. Alternatively, the first metal layer may be a first sheet of solder (e.g., a sheet of tin or indium) that is positioned against the first body, and the second metal layer may be a second sheet of solder that is positioned against the second body. In one embodiment, the first metal layer and second metal layer are each approximately 1-20 mils thick (e.g., 25-100 microns in one embodiment). 
         [0063]    At block  715 , a gasket is applied on a periphery of the coated surface of the first body or second body. The gasket will protect the coated surface from interaction with corrosive gases or plasmas. In one embodiment, the gasket is a compressible o-ring. Alternatively, the gasket may be a liquid that cures under pressure to form the gasket. 
         [0064]    At block  720 , the coated surface of the first body is positioned against the coated surface of the second body with a reactive foil therebetween. In one embodiment, the reactive foil is approximately 50-150 microns thick. At block  725 , pressure is applied to compress the first body against the second body. The pressure may be about 50 pounds per square inch (PSI) in one embodiment. While the pressure is applied, at block  730  the reactive foil is activated. The reactive foil may be activated by providing a small burst of local energy, such as by using optical, electrical or thermal energy sources. Ignition of the reactive foil causes a chemical reaction that produces a sudden and momentary localized burst of heat up to about 1500 degrees C., which melts the first and second metal layers, causing them to reflow into a single metal bond. This nano-bonding technique for forming a metal bond precisely delivers localized heat that does not penetrate the bodies being bonded. Since the bodies are not heated, the bodies may have a significant mismatch in coefficients of thermal expansion (CTE) without a detrimental effect (e.g., without inducing stress or warping). 
         [0065]      FIG. 8  illustrates one embodiment of a process  800  for manufacturing a reactive foil sheet having preformed foil features. At block  805  of process  800 , a template having surface features is provided. The template may be any rigid material in one embodiment. The template may have a substantially planar surface, with one or more surface features. Alternatively, the template may have a non-planar surface with or without surface features. 
         [0066]    The surface features may include positive steps (e.g., standoffs) and/or negative steps (e.g., holes or trenches) in a surface of the template. The steps may have a height or depth that is sufficient to cause a first portion of a deposited reactive foil sheet that covers the step to be discontiguous with a second portion of the reactive foil sheet that covers a remainder of the template. For example, standoffs may have a height of about 1-25 mm, and holes/trenches may have a depth of about 1-25 mm In one particular embodiment, the steps have a height or depth of about 2-10 mm Instead, deposited reactive foil may have the shape of the non-planar regions. 
         [0067]    The surface features may also include non-planar regions such as bumps, dips, curves, and so forth. These surface features may not cause any portions of a deposited reactive foil sheet to be discontiguous with other portions of the reactive foil sheet. 
         [0068]    At block  810 , alternating nanoscale layers of at least two reactive materials are deposited onto the template to form a reactive foil sheet. In one embodiment, the reactive materials are metals that are sputtered onto the template. The reactive materials may also be formed by evaporation, electroplating, or other metal deposition or growth techniques. Thousands of alternating layers of the two reactive materials may be deposited onto the template. Each layer may have a thickness on the scale of one nanometer to tens of nanometers. In one embodiment, the reactive foil is approximately 10-500 microns thick, depending on the number of nanoscale layers that the reactive foil includes. In a further embodiment, the reactive foil is about 50-150 microns thick. 
         [0069]    In one embodiment, the two reactive materials are aluminum (Al) and nickel (Ni), and the reactive foil is a stack of Al/Ni layers. Alternatively, the two reactive materials may be aluminum and titanium (Ti) (producing a stack of Al/Ti layers), titanium and boron (B) (producing a stack of Ti/B layers), copper (Cu) and nickel (producing a stack of Cu/Ni layers) or titanium and amorphous silicon (Si) (producing a stack of Ti/Si layers). Other reactive materials may also be used to form the reactive foil. 
         [0070]    For some surface features, a height or depth of the surface feature may cause a portion of a deposited reactive foil sheet to be discontiguous with other portions of the reactive foil sheet. In many cases, this discontinuity is intended. However, if no discontinuity is desired, then an angle of the template with regards to a deposition source may be controlled to eliminate any such discontinuity. In one embodiment, the template is rotated and/or the angle of the template with relation to the deposition source is changed during the deposition process. In another embodiment, multiple deposition sources having different locations are used. The arrangement of the deposition sources may be set to maximize coverage of a non-planar surface and/or surface features while minimizing thickness variations in the alternating layers. 
         [0071]    At block  815 , the reactive foil sheet is removed from the template. The reactive foil sheet may have a weak mechanical bond to the template, enabling the reactive foil to be removed from the template without tearing. The reactive foil sheet may have foil features that correspond to surface features of the template. For example, the reactive foil sheet may have voids corresponding to the regions of the template that had steps. Additionally, the reactive foil sheet may have non-planar (e.g., three dimensional) features corresponding to three dimensional features in the template. The features may have various sizes and shapes. The preformed foil features may correspond to surface features of one or more substrates that the reactive foil is designed to bond. Accordingly, the formed reactive foil may be production worthy. For example, the reactive foil may be set in place on a substrate having surface features and energized to create a metal bond without first machining the reactive foil to accommodate the surface features. 
         [0072]      FIG. 9A  illustrates deposition of nanoscale metal layers onto a template  900  having surface features. The template  900  has a substantially planar surface  905  with three surface features  910 ,  915 ,  922 . Surface features  910  and  915  are steps having a height  920 . The height  920  is sufficiently tall to cause nanoscale metal layers deposited  925  onto the features  910 ,  915  to be discontiguous with nanoscale metal layers deposited  925  onto a remainder of the template&#39;s surface  905 . Surface feature  922  is a non-planar (e.g., three dimensional) feature. Metal layers  925  deposited onto feature  922  are contiguous with metal layers deposited onto the remainder of the template&#39;s surface  905 . 
         [0073]      FIG. 9B  illustrates a reactive foil sheet  950  having preformed foil features  960 ,  965 ,  970 . The reactive foil sheet  950  is formed by depositing alternating nanoscale metal layers onto template  900  of  FIG. 9A . The reactive foil sheet  950  is substantially planar. However, reactive foil sheet  950  includes a non-planar feature  970  caused by deposition over surface feature  922  of template  900 . Foil features  960  and  965  are voids in reactive foil sheet  950 , and correspond to surface features  910 ,  920  of template  900 . 
         [0074]      FIG. 10A  illustrates deposition of nanoscale metal layers onto a template  1000  having a non-planar surface  1005 . The template  1000  may have a three dimensional shape as shown, or may have any other three dimensional shape.  FIG. 10B  illustrates a non-planar reactive foil sheet  1050  having a three dimensional shape that matches the three dimensional shape of template  1000 . This three dimensional shape may correspond to a three dimensional shape of two substrates that the reactive foil will be used to bond together. Accordingly, the reactive foil sheet  1050  may be place onto one of the substrates in an orientation and position that causes a shape and any features of the reactive foil sheet  1050  to line up with a shape and features of the substrate. The second substrate may then be placed over the reactive foil sheet, and the reactive foil sheet may be ignited. Because the reactive foil sheet has a shape that matches the substrates that it will bond, the reactive foil sheet will not be deformed or torn. This may minimize or eliminate leakage paths that might otherwise be caused by attempting to use a planar reactive foil sheet to bond non-planar surfaces. 
         [0075]    The reactive foil sheets with preformed features described herein may be used to bond any two substrates. The reactive foil sheets may be particularly useful for applications in which a room temperature, rapid bond is to be formed without vacuum and between substrates having surface features. For example, the reactive foil may be used to bond an electrostatic puck with helium holes to a cooling base plate. The reactive foil sheets described herein may also be used to bond a protective layer over a showerhead, which may have thousands of gas distribution holes as well as divots and/or standoffs around the gas distribution holes. The reactive foil sheets may also be used to bond semiconductor devices, solar devices, and other devices. 
         [0076]      FIG. 11  illustrates a continuous reactive foil  1100  formed of interlocking reactive foil sheets  1105 ,  1110 ,  1115 ,  1120 . The perimeters of the reactive foil sheets  1105 - 1120  may have a tessellating puzzle shape that enables the reactive foil sheets  1105 - 1120  to interlock. The tessellating puzzle shape may be formed by depositing alternating nanoscale metal layers over a template having a step around a perimeter of the template with the tessellating puzzle shape. Accordingly, the above described process  800  may be used to create interlocking reactive foil sheets. These interlocking reactive foil sheets enable any sized substrate to be bonded using a metal bonding process without introducing leakage pathways. 
         [0077]    The preceding description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of several embodiments of the present invention. It will be apparent to one skilled in the art, however, that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. Particular implementations may vary from these exemplary details and still be contemplated to be within the scope of the present invention. 
         [0078]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. In addition, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” When the term “about” or “approximately” is used herein, this is intended to mean that the nominal value presented is precise within ±10%. 
         [0079]    Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent and/or alternating manner In one embodiment, multiple metal bonding operations are performed as a single step. 
         [0080]    It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.