Abstract:
A pedestal assembly and method for controlling temperature of a substrate during processing is provided. In one embodiment, method for controlling a substrate temperature during processing includes placing a substrate on a substrate pedestal assembly in a vacuum processing chamber, controlling a temperature of the substrate pedestal assembly by flowing a heat transfer fluid through a radial flowpath within the substrate pedestal assembly, the radial flowpath including both radially inward and radially outward portions, and plasma processing the substrate on the temperature controlled substrate pedestal assembly. In another embodiment, plasma processing may be at least one of a plasma treatment, a chemical vapor deposition process, a physical vapor deposition process, an ion implantation process or an etch process, among others.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit of U.S. Provisional Application Ser. No. 61/016,000 filed Dec. 21, 2007 (Attorney Docket No. APPM/12975L), which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention generally relate to semiconductor substrate processing systems. More specifically, the invention relates to a method and apparatus for controlling temperature of a substrate in a semiconductor substrate processing system. 
         [0004]    2. Description of the Related Art 
         [0005]    In manufacture of integrated circuits, precise control of various process parameters is required for achieving consistent results within a substrate, as well as the results that are reproducible from substrate to substrate. As the geometry limits of the structures for forming semiconductor devices are pushed against technology limits, tighter tolerances and precise process control are critical to fabrication success. However, with shrinking geometries, precise critical dimension and etch process control has become increasingly difficult. During processing, changes in the temperature and/or temperature gradients across the substrate may be detrimental to etch rate and uniformity, material deposition, step coverage, feature taper angles, and other parameters of semiconductor devices. 
         [0006]    A substrate support pedestal is predominantly utilized to control the temperature of a substrate during processing, generally through control of backside gas distribution and the heating and cooling of the pedestal itself. Although conventional substrate pedestals have proven to be robust performers at larger critical dimension, existing techniques for controlling the substrate temperature distribution across the diameter of the substrate must be improved in order to enable fabrication of next generation, submicron structures, such as those having critical dimensions of about 55 nm and beyond. 
         [0007]    Therefore, there is a need in the art for an improved method and apparatus for controlling temperature of a substrate during processing the substrate in a semiconductor substrate processing apparatus. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention generally is a method and apparatus for controlling temperature of a substrate during processing in a semiconductor substrate processing apparatus. The method and apparatus enhances temperature control across the diameter of a substrate, and may be utilized in etch, deposition, implant, and thermal processing systems, among other applications where the control of the temperature profile of a workpiece is desirable. 
         [0009]    In one embodiment, a method for controlling a substrate temperature during processing includes placing a substrate on a substrate pedestal assembly in a vacuum processing chamber, controlling a temperature of the substrate pedestal assembly by flowing a heat transfer fluid through a radial flowpath within the substrate pedestal assembly, the radial flowpath including both radially inward and radially outward portions, and plasma processing the substrate on the temperature controlled substrate pedestal assembly. In another embodiment, plasma processing may be at least one of a plasma treatment, a chemical vapor deposition process, a physical vapor deposition process, an ion implantation process or an etch process, among others. 
         [0010]    In another embodiment of the invention, a pedestal assembly is provided that includes a base having an electrostatic chuck secured to a top surface thereof. A cooling flowpath formed in the base, the cooling flowpath configured to direct flow both radially inward and radially outward. 
         [0011]    In yet another embodiment of the invention, a pedestal assembly is provided that includes a base having an electrostatic chuck secured to a top surface thereof. A substantially toroidal flowpath formed in the base, the substantially flowpath having an inlet and outlet formed in a bottom surface of the base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    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. 
           [0013]      FIG. 1  is a schematic diagram of an exemplary semiconductor substrate processing apparatus comprising a substrate pedestal in accordance with one embodiment of the invention; 
           [0014]      FIGS. 2A-B  are a schematic cross-sectional view and a top view of one embodiment of a substrate pedestal illustrating a cooling flowpath; 
           [0015]      FIG. 3  is a cross sectional view of the substrate pedestal of  FIG. 1 ; 
           [0016]      FIG. 4  is a top view of the substrate pedestal of  FIG. 1  illustrating one embodiment of a cover plate disposed on a base plate; 
           [0017]      FIG. 5  is a top view of the substrate pedestal of  FIG. 1  with the cover plate removed to expose the top of the base plate; 
           [0018]      FIG. 6  is a bottom view of the substrate pedestal of  FIG. 1 ; 
           [0019]      FIGS. 6A-B  are partial sectional and an enlarged bottom views of one embodiment of a flow director; 
           [0020]      FIG. 7  is a bottom view the base plate; 
           [0021]      FIG. 8  is a top view of one embodiment of a channel separator plate; 
           [0022]      FIG. 9  is a bottom view of the channel separator plate; 
           [0023]      FIG. 10  is a bottom isometric view of the channel separator plate 
           [0024]      FIG. 11  is a partial sectional view of the substrate pedestal of  FIG. 1 ; 
           [0025]      FIG. 12  is another partial sectional view of the substrate pedestal of  FIG. 1  illustrating a connection ports for the cooling inlet and outlet; 
           [0026]      FIG. 13  is an exploded isometric view of another embodiment of a base assembly; 
           [0027]      FIGS. 14-16  are bottom, side and top view of one embodiment of a channel separator plate of the base assembly of  FIG. 13 ; 
           [0028]      FIG. 17  is a bottom isometric view of one embodiment of a inlet manifold cage; 
           [0029]      FIG. 18  is a partial side sectional view of the channel separator plate and inlet manifold cage; 
           [0030]      FIGS. 19-21  are bottom, side and top view of one embodiment of a bottom cover plate of the base assembly of  FIG. 13 ; 
           [0031]      FIG. 22  is a partial side cutaway isometric view of the base assembly of  FIG. 13 ; and 
           [0032]      FIGS. 23-26  are alternative bottom views of a base plate of the base assembly of  FIG. 13 . 
       
    
    
       [0033]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is also contemplated that elements and features of one embodiment may be beneficially incorporated on other embodiments without further recitation. 
       DETAILED DESCRIPTION 
       [0034]    The present invention generally is a method and apparatus for controlling temperature of a substrate during processing. Although invention is illustratively described in a semiconductor substrate processing apparatus, such as, e.g., a processing reactor (or module) of a CENTURA® integrated semiconductor wafer processing system, available from Applied Materials, Inc. of Santa Clara, Calif., the invention may be utilized in other processing systems, including etch, deposition, implant and thermal processing, or in other application where control of the temperature profile of a substrate or other workpiece is desirable. 
         [0035]      FIG. 1  depicts a schematic diagram of an exemplary etch reactor  100  having one embodiment of a substrate pedestal assembly  116  having an internal radial coolant flowpath. The particular embodiment of the etch reactor  100  shown herein is provided for illustrative purposes and should not be used to limit the scope of the invention. 
         [0036]    Etch reactor  100  generally includes a process chamber  110 , a gas panel  138  and a controller  140 . The process chamber  110  includes a conductive body (wall)  130  and a ceiling  120  that enclose a process volume. Process gasses from the gas panel  138  are provided to the process volume of the chamber  110  through a showerhead or one or more nozzles  136 . 
         [0037]    The controller  140  includes a central processing unit (CPU)  144 , a memory  142 , and support circuits  146 . The controller  140  is coupled to and controls components of the etch reactor  100 , processes performed in the chamber  110 , as well as may facilitate an optional data exchange with databases of an integrated circuit fab. 
         [0038]    In the depicted embodiment, the ceiling  120  is a substantially flat dielectric member. Other embodiments of the process chamber  110  may have other types of ceilings, e.g., a dome-shaped ceiling. Above the ceiling  120  is disposed an antenna  112  comprising one or more inductive coil elements (two co-axial coil elements are illustratively shown). The antenna  112  is coupled, through a first matching network  170 , to a radio-frequency (RF) plasma power source  118 . 
         [0039]    In one embodiment, the substrate pedestal assembly  116  includes a mount assembly  162 , a base assembly  114  and an electrostatic chuck  188 . The mounting assembly  162  couples the base assembly  114  to the process chamber  110 . 
         [0040]    The electrostatic chuck  188  is generally formed from ceramic or similar dielectric material and comprises at least one clamping electrode  186  controlled using a power supply  128 . In a further embodiment, the electrostatic chuck  188  may comprise at least one RF electrode (not shown) coupled, through a second matching network  124 , to a power source  122  of substrate bias. The electrostatic chuck  188  may optionally comprise one or more substrate heaters. In one embodiment, two concentric and independently controllable resistive heaters, shown as concentric heaters  184 A,  184 B, are utilized to control the edge to center temperature profile of the substrate  150 . 
         [0041]    The electrostatic chuck  188  may further comprise a plurality of gas passages (not shown), such as grooves, that are formed in a substrate supporting surface of the chuck and fluidly coupled to a source  148  of a heat transfer (or backside) gas. In operation, the backside gas (e.g., helium (He)) is provided at controlled pressure into the gas passages to enhance the heat transfer between the electrostatic chuck  188  and the substrate  150 . Conventionally, at least the substrate supporting surface of the electrostatic chuck is provided with a coating resistant to the chemistries and temperatures used during processing the substrates. 
         [0042]    The base assembly  114  is generally formed from aluminum or other metallic material. The base assembly  114  includes one or more cooling passages that are coupled to a source  182  of a heating or cooling fluid. A heat transfer fluid, which may be at least one gas such as Freon, Helium or Nitrogen, among others, or a liquid such as water or oil, among others, is provided by the source  182  through the passages to control the temperature of the base assembly  114 , thereby heating or cooling the base assembly  114 , thereby controlling, in part, the temperature of a substrate  150  disposed on the base assembly  114  during processing. 
         [0043]    Temperature of the pedestal assembly  116 , and hence the substrate  150 , is monitored using a plurality of sensors (not shown in  FIG. 1 ). Routing of the sensors through the pedestal assembly  116  is further described below. The temperature sensors, such as a fiber optic temperature sensor, are coupled to the controller  140  to provide a metric indicative of the temperature profile of the pedestal assembly  116 . 
         [0044]      FIGS. 2A-B  are a schematic cross-sectional view and a top view of one embodiment of a substrate pedestal assembly  116  illustrating a cooling flowpath  200  configured to provide uniform temperature control of the substrate pedestal assembly  116 . The substrate pedestal assembly  116  includes an electrostatic chuck  188  disposed on a base assembly  114 . The flowpath  200  may be routed through one or more passages formed through the base assembly  114 . The flowpath  200  has a generally radial orientation through the base assembly  114 . Although the flowpath  200  is shown in  FIG. 2A  has having a center inlet such that the heat transfer fluid provided by the source  182  flows radially outward, it is contemplated that the direction of flow may be reversed. 
         [0045]    In one embodiment, the flowpath  200  includes a first radial path  202  and a second radial path  204 . The first and second radial paths  202 ,  204  are configured to direct flow of the heat transfer fluid in substantially opposite directions. The base assembly  114  is generally larger in diameter than the electrostatic chuck  188  such that the first and second radial paths  202 ,  204  extend radially beyond the outer diameter of the chuck  188  and substrate  150  to provide good temperature control at the edge of the substrate. 
         [0046]    In the embodiment depicted in  FIGS. 2A-B , the first radial path  202  is adjacent the surface of the base assembly  114  that contacts the electrostatic chuck  188 , while the second radial path  204  is dispose below the first radial path  202 . In one embodiment the flowpath  200  has a mushroom configuration, e.g., is substantially a torus. The toroidal shape of the flowpath  200  may be comprised of a plurality of individual radial passages, or a single passage. 
         [0047]    The toroidal shape significantly reduces the length of the flowpath utilized in conventional bases. For examples, in a comparably sized base suitable for processing 300 mm substrates, the configuration of a flowpath of one embodiment of the invention reduces the flowpath length from approximately 72 inches in bases of conventional substrate supports to about 6 inches. This reduction in length greatly reduces the temperature drop between the inlet and outlet of the cooling passages, thereby significantly reducing temperature gradients in the substrate support pedestal. In one embodiment, the temperature delta between the inlet and outlet of the cooling passages is about 0.1 to about 1.0 as compared to about 7 to about 17 degrees Celsius in conventional substrate supports. The fluid inlet temperature range may be between (−)100 degrees Celsius to about (+)200 degrees Celsius, such as between (−)30 to about (+)85 degrees Celsius. This arrangement of the radial flowpath also has a significant reduction in the flow resistance, thereby allowing greater fluid flow and higher heat transfer rates at a selected operational pressure. 
         [0048]      FIG. 3  is a cross sectional view of the base assembly  114  of  FIG. 1 . In one embodiment, the base assembly  114  includes an internal coolant flowpath  300  that is substantially radial in orientation. In another embodiment, the flowpath  300  may be configured as described with reference to the flowpath  200 . 
         [0049]    In one embodiment, the base assembly  114  includes a top cover plate  302 , a base plate  304 , a channel separator plate  306  and a bottom cover plate  308 . The plates  302 ,  304 ,  306 ,  308  are generally fabricated from a good thermal conductor, for example a metal, such as stainless steel or aluminum. 
         [0050]    The top cover plate  302  is disposed in a recess  310  formed in a top  312  of the base plate  304 . The depth of the recess  310  may be selected such that a top surface  328  of the top cover plate  302  is substantially coplanar with the top  312  of the base plate  304 . The electrostatic chuck  188  (not shown in  FIG. 3 ) is supported at least one the top surface  328  of the top cover plate  302 . 
         [0051]    Referring additionally to the top view of the base assembly  114  depicted in  FIG. 4 , the top cover plate  302  includes a plurality of apertures. The apertures are utilized for lift pins and routing of various heaters, sensor, gas and power utilities through the base assembly  114  to the electrostatic chuck  188 . In the embodiment depicted in  FIG. 4 , apertures  314  are provided for lift pins, aperture  316  is provided for chuck power utilities, apertures  318  are provided for heater elements, apertures  320  are provide for temperature sensors, and apertures  324 ,  326  are provide for delivery of a heat transfer gas between the top cover plate  302  and the electrostatic chuck  188 . The same reference numerals may be used to identity apertures in other components of the base assembly  114  utilized for routing the same. 
         [0052]    The base plate  304  includes a step  330  through which a plurality of mounting holes  332  are formed through. The mounting holes  332 , one of which is shown for sake of clarity, are generally arranged on a bolt circle on the step  330 . The step  330  is disposed outward and below the top  312  of the base plate  302 , and therefore, is also beyond the edge of the substrate  150 . 
         [0053]      FIG. 5  is a top view of the substrate pedestal  114  with the cover plate  302  removed to expose a recessed surface  340  of the base plate  304 . The recessed surface  340  includes a plurality of cooling channels formed therein. In the embodiment depicted in  FIG. 5 , an inner cooling channel  502  and an outer cooling channel  504  are provided. Helium, or other heat transfer gas or fluid, is provided to the cooling channels  502 ,  504  through respective inlets  506 ,  508 . The heat transfer gas is distributed through the channels  502 ,  504  to the plurality of apertures  324 ,  326  in the cover plate  302  (shown in  FIG. 4 ), through which the heat transfer gas is distributed between the electrostatic chuck  188  and base assembly  114 . The temperature of the fluids in the channels  502 ,  504  may have their temperature independently regulated to assist in providing center to edge substrate temperature control. 
         [0054]    Referring back to  FIG. 3 , the base plate  304  includes a cavity  334  formed in a bottom  336  of base plate  304 . The bottom cover plate  308  is sealingly coupled to the bottom  336  of the base plate  304  to seal the channel separator plate  306  within the cavity  334 . In one embodiment, the bottom cover plate  308  is disposed a step  338  formed in the bottom  336  of the base plate  304 , and sealed to the base plate  304  by a continuous weld or other suitable technique. 
         [0055]    The channel separator plate  306  bifurcates the cavity  334  into two disc-shaped plenums  342 ,  344 . The plenums  342 ,  344  are vertically stacked and fluidly coupled through a gap  346  defined between an outer sidewall  346  of the cavity  344  and an outside edge of the channel separator plate  306 . In the embodiment depicted in  FIG. 3 , the radial coolant flowpath is defined through the upper plenum  342  into the lower plenum  344  though the gap  348 . It is also contemplated that the direction of flow through the flowpath may be reversed. 
         [0056]    In one embodiment, the channel separator plate  306  maintained in a spaced-part relation from a top wall  352  of the cavity  334  by a plurality of spacers  354 . The spacers  354  are part of the base plate  304 . At least some of the spacers  354  may have a radial orientation such that the flow through the upper plenum  342  is directed radially. 
         [0057]      FIG. 6  depicts a bottom view of the base plate  304  illustrating the spacers  354  projecting form the top wall  352 . Only a small number of spacers  354  are shown in  FIG. 6  for the sake of clarity, as the spacers  354  are distributed 360 degrees around the centerline of the base plate  304 . At least some of the spacers  354  bridge the space between the top wall  352  and the channel separator plate  306 . The number, orientation, distribution and size of the spacers  354  may be selected to provide a desired profile of heat transfer from the base plate  304  to the fluid disposed in the upper plenum  342 . In the embodiment depicted in  FIG. 6 , the spacers  354  are elongated and have a major axis aligned with the radial flow direction. The spacers  354  may also be staggered so that flow passing between two adjacent spacers  354  positioned at the same radius from the centerline of the base plate  304  will be directed towards the next outward spacer  354 , thereby causing some lateral movement and mixing of the cooling fluid as it mores outward towards the gap  348 . 
         [0058]    Additionally shown in  FIG. 6  are a plurality of bosses  602  through which the various apertures  314 ,  316 ,  318 ,  320 ,  322 ,  324 ,  326  extend. The bosses  602  provide a barrier between the apertures and the plenum  342 . The bosses  602  align with bosses  702  (shown in  FIG. 7 ) present on the outside of the base cover plate  308  to facilitate routing of utilities, sensors, heaters, fluids, and the like through the pedestal assembly  116 . The joint between the bottom cover plate  308  and base plate  304  may be brazed or sealed in another suitable fashion to prevent entry of fluids into the apertures. 
         [0059]    Referring additionally to the detailed views of  FIGS. 6A-B , a flow director  604  may be provided on the downstream side of each of the bosses  604  to promote wrapping of the heat transfer fluid flowing through the plenum  342  around the backside of the boss. In one embodiment, the flow director  604  has an orientation substantially orthogonal to the orientation of the spacers  354 . The flow director  604  may additionally include one or more slots  606  that allow the fluid directed between the boss  602  and director  604  to escape, thus maintaining flow between the boss  602  and director  604 , as shown by the arrows depicted in  FIG. 6A . Alternatively, the flow director  604  may not bridge the space between the channel separator plate  306  and the top wall  352  of the base plate  304 , thereby functioning as a weir such that a portion of the fluid between the boss  602  and director  604  may escape over the director  604 . The wrapping of the fluid promotes good heat transfer from the bosses  604 , thus compensating for the low heat transfer rate through the voids of the apertures. 
         [0060]      FIG. 8  is a top view of one embodiment of the channel separator plate  306 . The channel separator plate  306  includes a plurality of holes  802  through with the bosses  602  of the base plate  304  extend. The channel separator plate  306  also includes one or more inlet holes  804 , which allow entry of the coolant fluid into the cavity  334 , as further described below. 
         [0061]      FIGS. 9-10  are a bottom and bottom isometric views of the channel separator plate  306 . The channel separator plate  306  includes a lateral feed  908  for providing heat transfer fluid to the inlet holes  804 . The lateral feed  908  allows the heat transfer fluid inlet of the pedestal assembly  116  to be offset from the center of the pedestal, thereby allowing more efficient space utilization for routing electrical utilities, lift pins, gas channels and the like. In the embodiment depicted in  FIG. 9 , the lateral feed  908  is defined by a wall  916  that projects from the bottom of the channel separator plate  306 . The wall  916  has a generally hollow, dog-bone shape, surrounding an outer plenum  910  at a first end of the lateral feed  908 , an inner plenum  912  at a second end of the lateral feed  908 , and a channel fluidly coupling the plenums  910 ,  912 . The outer plenum  910  is generally positioned outward from the center of the channel separator plate  306 . The outer plenum  910  is positioned to align with a fluid inlet hole  398  formed in the bottom cover plate  308  (as shown in  FIGS. 3 and 12 ). The inner plenum  912  is generally positioned at the center of the channel separator plate  306 . The portion of the wall  916  surrounding the inner plenum  912  is wide enough to surround the inlet holes  804  so that fluid from the lateral feed  908  is directed through holes  804  in the channel separator plate  306  and into a center distribution plenum defined on the upper side of the channel separator plate  306 . 
         [0062]      FIG. 11  is an enlarged sectional view of the base assembly  114  illustrating one embodiment a center distribution plenum  1102 . The center distribution plenum  1102  is bounded by the channel separator plate  306  on the bottom and the base plate  304  on the top. A wall  1106  extends downward from the base plate  304  to provide an outer boundary of the center distribution plenum  1102 . The wall  1106  is positioned outward of the holes  804  so as to allow the holes  804  to provide a fluid passage between the plenums  912 ,  1102 . The wall  1106  is configured to allow fluid to escape radially from the center distribution plenum  1102  into the upper plenum  342 , as shown by arrows  1104 . 
         [0063]    In one embodiment, the wall  1106  includes one or more passages  1110 , such as holes or slots, through which the fluid may escape into the upper plenum  342  from the center distribution plenum  1102 . In one embodiment, the passages  1110  are through holes. In the embodiment depicted in  FIG. 11 , the wall  1106  has a generally cylindrical shape, having passages  1110  formed in a distal end. The passages  1110  may be spaced equidistantly along the wall  1106 . Alternatively, the one or more passages  1110  may be configured as a continuous weir that allows the flow of fluid to be directed equally in all radial directions. Optionally, the number and spacing of the passages  1110  may be selected to direct more flow to one region of the upper plenum  342  relative to another region of the upper plenum  342 , if desired. 
         [0064]    Also shown in  FIG. 11 , the base plate  306  includes a center boss  1108  which isolates a center passage  1112  from the fluids in the plenums  912 ,  1102 . The center passage  1112  is aligned with the aperture  316  formed through the top cover plate  302  and a hole  1118  formed through the bottom cover plate  308 . The passage  1112 , aperture  316  and hole  1118  facilitate routing of utilities to the electrostatic chuck  118  through the pedestal assembly  116 . The joint between the bottom cover plate  308  and boss  1108  may be brazed or sealed in another suitable fashion to prevent entry of fluids into the passages. One of the bosses  702  of the bottom cover plate  308 , shown as boss  1114  in  FIG. 11 , has a port  1116  formed therein to facilitate coupling of the utility conduit. The other bosses  702  are similarly configured. 
         [0065]    The fluid outlet of the flowpath through the pedestal assembly  116  is shown in the partial sectional view of  FIG. 12 . A fluid outlet hole  1202  is formed through the bottom cover plate  308  to drain the lower plenum  344 . The outlet hole  1202  is generally positioned near the inlet hole  398 . Two of the bosses  702  formed on the bottom cover plate  308 , shown as inlet boss  1204  and outlet boss  1206  in  FIG. 12 , are utilized to provide fluid connection to the flowpath  300  through the holes  398 ,  1202 . In one embodiment, the boss  1204  is coupled to the heat transfer fluid source  182  while the boss  1206  is coupled to a drain or recirculated back through the fluid source  182 . The pressure, flow rate, temperature, density and composition of the heat transfer medium of cooling fluid provided through the flowpath  300  provides enhanced control of the heat transfer profile through the pedestal assembly  116 . Moreover, as the density, pressure and flow rate of fluid in the flowpath  300  may be controlled in-situ during processing of substrate  150 , the temperature control of the substrate  150  may be changed during processing to further enhance processing performance. 
         [0066]    In operation, a substrate  150  is provided on the pedestal assembly  116 . Power is provide to the electrostatic chuck  188  to secure the substrate. Power is provided to the heaters within the electrostatic chuck  188  to provide control of the lateral temperature provide of the substrate  150 . Coolant fluid, which may be liquid and/or gas, such as Freon, is provided through the radial cooling path defined in the base assembly  114  to enable precise temperature control of the substrate. 
         [0067]    In one embodiment, coolant is provided to the center distribution plenum  1102  from which the coolant is distributed radially through the one or more passages  1110  into the disk shaped upper plenum  342 . Flow directors  604  are utilized to promote wrapping of the heat transfer fluid flowing through the upper plenum  342  around the various bosses  604  extending through the plenum  342 . The coolant then flows from the upper  342  through gap  348  into the lower disk shaped platen  344 , from which the coolant is ultimately removed. The radial configuration of the coolant flowpath, along with the cross flow orientation, reduces coolant path length and pressure drop, beneficially contribute to the enhanced cooling uniformity of the pedestal assembly  116 , thereby enabling improved process control within the reactor  100 . 
         [0068]    For example, the above mentioned substrate temperature control may be beneficially employed during an etch process wherein a plasma is formed within the reactor  100  from gases provided from the gas panel  138 . Other substrate fabrication processes, such as those mentioned above and performed in a vacuum chamber and/or requiring precise temperate control may also benefit from the use of the temperature control methods and apparatuses described therein. 
         [0069]      FIG. 13  is an exploded isometric view of another embodiment of a base assembly  1300  through which heat transfer fluid flows from an upper disc-shaped plenum into a lower disc-shaped plenum from which the fluid is ultimately removed. The base assembly  1300  includes a base plate  1302 , a channel separate plate  1304  and a bottom cover plate  1306 . The base plate  1302  and the bottom cover plate  1306  are sealingly coupled together capturing the channel separator plate  1304  therebetween such that coolant fluid introduced between the channel separator plate and the base plate flows outward and over an outer diameter  1314  of the channel separator plate  1304  into a bottom plenum defined between the channel separator plate  1304  and the bottom cover plate  1306 . The base plate  1302 , channel separator plate  1304  and the bottom cover plate  1306  all include a central aperture  1308  which provides a conduit for routing power and other utilities to the electrostatic chuck  188  (shown in  FIG. 1 ) which is coupled to a top  1316  of the base plate  1302 . 
         [0070]    The base plate  1302  and the bottom cover plate  1306  also include a plurality of lift pin holes  1310 . The channel separator plate  1304  includes a plurality of notches  1312  formed in the outer diameter  1314  which are aligned with the lift pin holes  1310  such that the channel separator plate  1304  does not interfere with the operation of the lift pins. 
         [0071]    The top  1316  of the base plate  1302  additionally includes an inner channel  1318  and an outer cooling channel  1320 . The inner channel  1318  is fed through an inlet  1322  formed through the base plate  1302 . The outer channel  1320  is fed fluid through an inlet  1324  formed through the base plate  1302 . Cooling fluid feeds  1328 ,  1330  are provided in the bottom cover plate  1306  and aligned with the inlets  1320 ,  1322  to allow a fluid, such as He, Nitrogen or other fluids, to be routed through the base assembly to the cooling channels  1318 ,  1322  to enhance heat transfer between the assembly  1300  and the electrostatic chuck  118 . An aperture  1326  is provided in the channel separator plate  1304  to facilitate coupling of the cooling feeds  1328 ,  1330  to the inlets  1322 ,  1324 . 
         [0072]    A passage  1332  is also provided through the base plate  1302 , channel separator plate  1304  and bottom cover plate  1306  to allow passage of a thermal couple. The bottom cover plate  1306  additionally includes a pair of apertures  1334 ,  1336  to facilitate the flow of cooling fluid into and out of the base assembly  1300  as further described below. 
         [0073]      FIGS. 14-16  are bottom, top and side views of the channel separator plate  1304 . The channel separator plate  1304  includes a bottom  1402  and a top  1602 . A first boss  1404  extends from the bottom  1402  such that a recess is formed in the top  1602  of the channel separator plate  1304 . The recess formed in the first boss  1404  accepts a portion of an inlet manifold cage  1502  which extends from the top  1602  of the channel separator plate  1304 . A second boss  1406  extends from the first boss  1404  from the bottom  1402  of the channel separator plate  1304 . The second boss  1406  includes a passage  1408  formed through the channel separator plate  1304 . The passage  1408  allows fluid entering the base assembly  1300  to flow through the inlet manifold cage  1502  and into the upper plenum defined between the channel separator plate  1304  and the base plate  1302 . 
         [0074]    The inlet manifold cage  1502  includes sides  1504  and a top  1506 . A plurality of windows  1508  are formed through the sides  1504  of the inlet manifold cage  1502  to facilitate the flow of fluid entering the base assembly  1300  through the passage  1408  to the upper plenum defined between the channel separator plate  1304  and the base plate  1302 . The windows  1508  may be holes, slot or other features suitable for allowing fluid to flow therethrough. 
         [0075]    The inlet manifold cage  1502  includes a ring  1604  which circumscribes the center aperture  1308 . An extension  1606  is formed on the outer diameter of the ring  1604  and is aligned with the passage  1408  formed through the second boss  1406  such that fluid directed through the second boss  1406  enters the volume defined within the inlet manifold cage  1502 . 
         [0076]      FIG. 17  is a bottom isometric view of one embodiment of the inlet manifold cage  1502 . The inlet manifold cage  1502  includes an annular inner wall  1702  which is circumscribed by the side  1504 . The inner wall  1702 , the side  1504  and the top  1506  of the inlet manifold cage  1504  define a fluid passage  1704  within the manifold cage  1502 . 
         [0077]      FIG. 18  is a partial side sectional view of the channel separator plate  1304  and the inlet manifold cage  1502 . As depicted in the embodiment of  FIG. 18 , the inlet manifold cage  1502  sits partially within the recess formed in the first boss  1404 . The windows  1508  are arranged along the sides  1504  of the inlet manifold cage  1502  proximate the top  1506 , such that the windows  1508  are positioned to provide fluid to the top  1602  of the channel separator plate  1304 . Thus, fluid entering the fluid passage  1704  through the passage  1408  defined through the boss  1406  can readily flow into the upper plenum in a direction radially outward from the sides  1504 . 
         [0078]      FIGS. 19-21  are bottom, side and top views of one embodiment of the bottom cover plate  1306 . A bottom  1902  of the bottom cover plate  1306  includes a plurality of cavities  1904  formed therein to reduce the thermal mass of the bottom cover plate  1306 , thereby allowing the assembly  1300  to be heated and cooled more rapidly. The bottom cover plate  1306  additionally includes two holes  1906 ,  1908  formed therethrough which facilitates routing of the cooling fluid entering and exiting the base assembly  1300 . The hole  1906  is sufficiently large enough to accept the boss  1406  extending from the channel separator plate  1304 . The hole  1908  facilities draining the lower plenum defined between the bottom cover plate  1306  and the channel separator plate  1304 . The hole  1908  may include a counter bore  2158  on the bottom  1902  to facilitate alignment with mating components. 
         [0079]    A top  2002  of the bottom cover plate  1306  includes a first boss  2004  and a second boss  2006 . The first boss  2004  circumscribes the center aperture  1308 . The second boss  2006  has the passage  1332  formed therethrough which is utilized for temperature sensing. The bottom cover plate  1306  may also include a second hole  1910  for accommodating a temperature probe utilized to sense the temperature of the bottom cover plate  1306 . 
         [0080]      FIG. 22  is a partial cutaway respective view of the face assembly  1300 . In the embodiment depicted in  FIG. 22 , the base plate  1302  includes a lip  2250  extending from the bottom side of the base plate  1302 . The lip  2250  has an inside wall  2254  which bounds a pocket  2256  in which the channel separator plate  1304  and the bottom cover plate  1306  are accommodated. The lip  2250  of the bottom cover plate  1306  is sealed to the base plate  1302 , for example, by a continuous weld, brazing or other suitable technique, to retain the fluid flowing through the upper and lower plenums within the assembly  1300 . The pocket  2256  has a bottom  2258  on which the channel separator plate  1304  is disposed. The bottom  2258  additionally includes a plurality of fins  2206  separating a plurality of channels  2208  formed therein. The fins  2206  and channels  2208  are described in greater detail with reference to  FIGS. 23-26  below. The channels  2208  define the majority of an upper plenum  2220  defined between the channel separator plate  1304  and the bottom  2258  of the base plate  1302 . Fluid enters the upper plenum  2220  via the windows  1508  formed in the inlet manifold cage  1502 . The fluid flows from the inlet manifold cage  1502  through the channels  2208  of the upper plenum  2220  and around the edge  1314  into a gutter  2114  defined between the edge  1314  of the channel separator plate  1304  and the inside wall  2254  of the base plate  1302 . Fluid flows from the gutter  2114  into a bottom plenum  2222  and out the hole  1908  formed through the bottom cover plate  1308 . Thus, the flow pattern through the plenums  2220 ,  2222  of the base assembly  1300  is substantially similar to the base assembly  114  described with reference to  FIGS. 2A-2B . 
         [0081]    The bottom cover plate  1306  is seated on a pair of steps  2252 ,  2262  formed in the inside wall  2254  and a boss  2260  extending from the bottom  2258  and circumscribing the center aperture  1308 . The steps  2252 ,  2262  maintain the channel separator plate  1304  and the bottom cover plate  1306  in a spaced-apart relation, thus providing ample room for fluid flowing through the lower plenum  2222 . 
         [0082]      FIGS. 23-26  are alternative bottom views of the base plate  1302  of the base assembly  1300 . Common to the embodiments of  FIGS. 23-26  is the substantially radial orientation of the channels  2208  and the opposing radial direction of flow through the plenums  2220 ,  2222 . 
         [0083]    A plurality of pads  2210  extend from the bottom surface of the base plate  1302 . In one embodiment, seven pads are shown extending above the fins  2206 . The pads  2210  space the channel separator plate  1304  from the base plate  1302 , thereby creating a small gap between the channel separator plate  1304  and the fins  2206  such that minimal heat transfer is directly conducted between the base plate  1302  and the channel separator plate  1304 . 
         [0084]    In the embodiment depicted in  FIG. 23 , the channels  2208  have a substantially uniform width and/or sectional area along its radial length outward across the bottom of the base plate  1302 . To accommodate the substantially uniform channel width, the fins  2206  are flared, becoming increasingly wider as the fin nears the outside edge of the base plate  1302 . The channels  2208  may be linear, curved or have another orientation. In the embodiment depicted in  FIG. 23 , the channels  2208  are curved such that the fluid flowing through the channels  2208  has a longer residual time within the upper plenum  2220 , thereby increasing the heat transfer efficiency. 
         [0085]    In the embodiment depicted in  FIG. 24 , the channels  2208  include a main channel  2402  and a plurality of sub-channels  2404  branching therefrom. In the embodiment depicted in  FIG. 24 , at least two sub-channels are shown. However, the main channel  2402  may have in excess of three sub-channels  2404 , and the sub-channels themselves may be branched into two or more secondary channels (not shown). The sub-channels are separated by an inter-channel fin  2406 . 
         [0086]    In the embodiment depicted in  FIG. 25 , a plurality of channels  2502  are shown separated by a plurality of fins  2504 . The channels  2502  may have a uniform sectional area and/or width as the channel  2502  extends radially outward. Alternatively, the sectional area and/or width of the channels  2502  may flare as the channel  2502  nears the outer diameter of the base plate  1302 . In the embodiment depicted in  FIG. 25 , the fins  2504  separating the channels  2502  have a substantially boomerang shape, being thicker at the center of the fin  2504  as opposed to each fin end. The boomerang shape allows for a deeply curved channel  2502 , thereby substantially increasing the residence time of the fluid in the upper plenum  2220 . 
         [0087]    In the embodiment depicted in  FIG. 26 , a plurality of channels  2602  are shown separated by a plurality of fins  2604 . Each fin  2604  is substantially uniform in sectional area and/or width as the fin  2604  extends radially outward. Correspondingly, the channels  2602  are flared as they move outward toward the edge of the base plate  1302 . The fins  2604  may extend linearly in a radial direction, or they may be curved to increase the residual time of the cooling fluid in the channels  2602  defining the upper plenum  2220 . 
         [0088]    Thus, a pedestal assembly has been provided that includes a radial coolant flowpath. The radial coolant flowpath through pedestal assembly provides improved temperature control, thereby enabling the temperature profile of the substrate to be controlled. 
         [0089]    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.