Abstract:
A thermal exchanger assembly for a wafer chuck and method of use therefor is disclosed. More particularly, complimentary manifolds, each having a plurality of fins, are positioned with respect to one another to provide interleaved spaced-apart fins. At least one thermo-electric device is disposed between alternating pairs of fins. The thermo-electric device is coupled to the fins to provide a thermally conductive path from one manifold to the other through the thermo-electric device. The thermal exchanger assembly may be located in a process chamber for processing a wafer, including but not limited to a semiconductor wafer.

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The present invention relates generally to method and apparatus for semiconductor processing, and more particularly to thermal exchanger assembly for a wafer chuck assembly. 
     2. Description of the Background Art 
     In semiconductor wafer processing, the wafer is conventionally maintained within a desired temperature range. Though this may involve regulating temperature in a process chamber, it conventionally involves controlling the temperature of the wafer. 
     Others have addressed wafer temperature control by providing chilled water through a wafer support pedestal. By cooling the wafer support pedestal, the wafer resting on a wafer chuck is cooled as well. However, this approach is time consuming, and conventionally response times are limited to approximately 2 minutes per degree. Because of the time required for chilled water to take effect, compensation times may be too long for rapid thermal processing or other processing causing rapid wafer temperature changes. 
     Others have suggested using thermo-electric devices. These devices are disposed under a support surface supporting the wafer in an oriented planar array. However, temperature gradients form between such thermo-electric devices and cause variation across the wafer. Additionally, a planar array of thermo-electric devices is limited to surface area under the support surface. 
     To address these limitations, others have suggested attaching at least one thermo-electric device to a stem, which is attached to a platen. However, stem length may be limited in some process chambers. Accordingly, it would be desirable to provide a solution having more available surface area within a confined volume for attaching at least one thermo-electric device. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention comprises a thermal exchanger assembly for a wafer chuck assembly. The thermal exchanger assembly comprises a first manifold having a first set of radially positioned fins, and a second manifold having a second set of radially positioned fins. The first and second set of radially positioned fins interleaved with one another to provide spaced-apart pairs of fins. At least one thermo-electric device is alternately located between and in thermal communication with the pairs of fins. 
     Another aspect of the present invention is a thermal exchanger assembly at least partially located in a process chamber of a processing system. These and other aspects of the present invention will be more apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 depicts a schematic and cross-sectional view of an exemplary portion of a processing system having a thermal exchanger assembly; 
     FIGS. 2A through 2C (collectively referred to as FIG. 2) depict cross-sectional views of an exemplary portion of an embodiment of a thermal exchanger assembly in accordance with aspects of the present invention; 
     FIG. 3 depicts a perspective view of a thermo-electric device that may be used in the thermal exchanger assembly of FIG. 2; 
     FIG. 3A depicts a surface plan view of an alternate embodiment of the thermo-electric device of FIG. 3; 
     FIG. 4 depicts a plan and cross-sectional view illustrating radial positioning of an exemplary portion of the thermal exchanger assembly of FIG. 2; and 
     FIG. 4A depicts a perspective view illustrating electrical connections for an exemplary portion of the embodiment of the thermal exchanger assembly of FIG.  2 C. 
    
    
     DETAILED DESCRIPTION 
     Process System 
     Referring to FIG. 1, there is illustratively shown an exemplary embodiment of a process system  99  in accordance with an aspect of the present invention. Process system  99  comprises process chamber  100 . Process chamber  100  generally houses a support pedestal  150 . Susceptor or wafer chuck assembly  10  comprises a portion of support pedestal  150 . Wafer chuck assembly  10  may be an electrostatic chuck. Wafer chuck assembly  10 , which is used to support a substrate such as a wafer  11  within process chamber  100 . Depending on process requirements, wafer  11  can be heated or cooled to some desired temperature or within some desired temperature range. For purposes of clarity, wafer  11  refers to any work piece upon which film processing is performed. Depending on processing stage, wafer  11  may be a silicon semiconductor wafer, or other material layer, which has been formed on wafer  11 . 
     In chamber  100 , wafer chuck assembly  10  is heated or cooled by applying an electric current from power supply  106  to thermo-electric devices  20  (shown in FIG.  2 ). Thermo-electric devices  20  (shown in FIG. 2) draw (subtract) or supply (add) thermal energy depending on direction of current flow of power supply  106 . Accordingly, a thermo-electric device may take advantage of a Peltier effect. Wafer  11  may be heated or cooled to within a desired process temperature range of about −40° C. to about 200° C., subject to properties of materials used in assembly  98  of FIG.  2 . 
     Additionally, wafer chuck assembly  10  may be heated or cooled by supplying a thermal medium, such as a liquid through piping  421  from pump and reservoir  420 . Pump and reservoir  420  may be coupled via piping  423  to a heater or chiller  422  for supplying or removing thermal energy to such a thermal medium. 
     Temperature sensor  29 , such as a thermocouple, may be attached to or embedded in wafer chuck assembly  10  to monitor temperature in a conventional manner. For example, measured temperature may be used in a feedback loop to control electric current applied to thermo-electric devices  20  from power supply  106 , such that wafer temperature can be maintained or controlled at a desired temperature or within a desired temperature range suitable for a process application. Control unit  110  may be used to receive a signal from temperature sensor  29  and control power supply  106  in response. 
     Vacuum pump  102  is used to evacuate process gases from process chamber  100  and to help maintain a desired pressure or desired pressure within a pressure range inside chamber  100 . Orifice  120  through a wall of chamber  100  is used to introduce process gases into process chamber  100 . Sizing of orifice  120  conventionally depends on the size of process chamber  100 . 
     Chamber  100  is coupled to gas panel  130  via orifice  120  in part by valve  125 . Gas panel  130  is configured to receive and then provide a resultant process gas from two or more gas sources  135 ,  136  to process chamber  100  through orifice  120  and valve  125 . Gas panel  130  is further configured to receive and then provide a purge gas from purge gas source  138  to process chamber  100  through orifice  120  and valve  125 . 
     Control unit  110 , such as a programmed personal computer, work station computer, and the like, is configured to control flow of various process gases through gas panel  130  as well as valve  125  during different stages of a wafer process sequence. Illustratively, control unit  110  comprises central processing unit (CPU)  112 , support circuitry  114 , and memory  116  containing associated control software  113 . In addition to control of process gases through gas panel  130 , control unit  110  may be configured to be responsible for automated control of other activities used in wafer processing—such as wafer transport, temperature control, chamber evacuation, among other activities, some of which are described elsewhere herein. 
     Control unit  110  may be one of any form of general purpose computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. CPU  112  may use any suitable memory  116 , such as random access memory, read only memory, floppy disk drive, hard disk, or any other form of digital storage, local or remote. Various support circuits may be coupled to CPU  112  for supporting system  10 . Software routines  113  as required may be stored in memory  116  or executed by a second computer processor that is remotely located (not shown). Bi-directional communications between control unit  110  and various other components of wafer processing system  10  are handled through numerous signal cables collectively referred to as signal buses  118 , some of which are illustrated in FIG.  1 . 
     Process system  99  comprises RF power supplies  410  and  412 , showerhead  400 , gas source  405 , and matching network(s)  411 . Notably, process system  99  may be configured for physical vapor deposition (PVD) or chemical vapor deposition (CVD). More particularly, process system  99  may be used for PVD “subzero” deposition of copper, where wafer chuck assembly  10  is cooled for cooling substrate structure  11  to temperatures from about −20° C. to about 0° C. 
     Showerhead  400  and wafer support pedestal  150  provide in part spaced apart electrodes. An electric field may be generated between these electrodes to ignite a process gas introduced into chamber  100  to provide plasma  405 . 
     Conventionally, pedestal  150  is coupled to a source of radio frequency (RF) power source  412  through a matching network  411 , which in turn may be coupled to control unit  110 . Alternatively, RF power source  410  may be coupled to showerhead  400  and matching network  411 , which in turn may be coupled to control unit  110 . Moreover, matching network  411  may comprise different circuits for RF power sources  410  and  412 , and both RF power sources  410  and  412  may be coupled to showerhead  400  and pedestal  150 , respectively. 
     Wafer Chuck Assembly 
     Referring to FIG. 2, there is illustratively shown several exemplary embodiments of wafer chuck assembly  10 . Wafer chuck assembly  10  comprises a platen  12 , a thermal exchanger assembly  98 , and a manifold  15 . 
     Manifold  15  comprises at least one conduit  16  having at least one inlet and at least one outlet. However, manifold  15  may comprise one or more inlets and a plurality of outlets and conduits  16 . Manifold  15  may be a separate work piece as illustratively shown in FIGS. 2A and 2B, or integrally formed with manifold  14 , as illustratively shown in FIG.  2 C. 
     Thermal exchanger assembly  98  comprises a manifold  14 , a plurality of thermo-electric devices  20 , and a manifold  13 . Manifold  14  comprises base  14 B and a plurality of fins  14 F. Manifold  13  comprises base  13 B and a plurality of fins  13 F. Fins  13 F and  14 F mate with one another in an interleaving of fins to provide spaced-apart pairs of fins  13 F and  14 F. Disposed at least partially in alternating regions between fins  13 F and  14 F is at least one thermo-electric device  20 . Accordingly, a plurality radially disposed thermo-electric devices  20  may be located in alternating gaps between fins  13 F and  14 F. Between combinations of fins  13 F,  14 F and at least one thermo-electric device  20  are gaps  21 . Gaps  21  provide thermal conductivity separation regions between such combinations for channeling thermal exchange between manifold  13  and manifold  14 . 
     Thermo-electric device  20  may be sufficiently tall to prevent manifolds  13  and  14  from touching one another, as illustratively shown in FIG. 2C; otherwise, manifolds  13  and  14  may be in direct thermal communication and thermal energy channeling through thermo-electric devices  20  would quantitatively be reduced. Because of such height of thermo-electric devices  20 , gaps  17  form between base member portions of manifolds  13  and  14  and upper fin portions of fins  14 F and  13 F, respectively, separating manifolds  13  and  14  from touching one another. Gaps  17  may be considered as a portion of gaps  21 . However, having thermo-electric devices  20  sufficiently tall to prevent manifolds  13  and  14  from touching may provide an unwanted thermal conduction path longitudinally through thermo-electric devices  20 . Accordingly, thermo-electric devices  20  in this embodiment should have thermal insulation at distal longitudinal ends. Arrows  18 , in FIG. 2C, illustratively show a thermal conduction path for heating platen  12  and thus heating wafer  11 . Arrows  18 , in FIG. 2B, illustratively show a thermal conduction path for removing heat from platen  12  and thus cooling platen  12  and in turn wafer  11 . 
     In FIG.  2 B and in FIG. 2A, thermo-electric devices  20  are not so tall as to prevent direct contact between manifolds  13  and  14 . Temporary spacers  17 T may be used for positioning manifold  13  with respect to manifold  14 , and later those temporary spacers  17 T may be removed. 
     Referring to FIG. 3, there is illustratively shown a perspective view of thermo-electric device  20 . Thermo-electric device  20  comprises plates  31  and Peltier device  22 . Peltier device  22  may be coupled to a power supply via wires  24  and  25 . Thermo-electric device  20  has upper and lower surfaces  28 , side surfaces  26 , and inner surface  27 . Thermally conductive material  23  is disposed on side surfaces  26 . Thermally conductive material  23  may be selected from a thermally conductive adhesive or a brazing alloy. With respect to a brazing alloy, a brazing foil may be used. Such a brazing foil may be pressure sensitive so less temperature is needed to braze thermo-electric device  20  to fins  13 F and  14 F. A suitable brazing alloy may comprise indium. Thermo-electric device  20  may be shaped for radial disposition, as is illustratively shown in the top view of FIG.  3 A. 
     Referring to FIG. 4, there is illustratively shown a cross-sectional and top plan view of an exemplary portion of thermal exchanger assembly  98 . As illustratively shown, fins  13 F, gaps  21 , fins  14 F, and thermo-electric devices  20  alternate in sequence and are radially disposed on or over manifold base  14 B. Thermo-electric devices  20  may be wired together, as illustratively shown with respect to wire  24 . Alternatively, tubular core  14 C, shown in FIG. 4A, may be disposed in region  97  of manifold base  14 B. 
     Referring to FIG. 4A, there is illustratively shown a perspective view of tubular core  14 C. Tubular core  14 C comprises conductive rings  34  and  35 . Electrical contacts  24  and  25  of thermo-electric devices  20  may be put in contact with an exterior surface of conductive rings  34  and  35 , respectively, and wires  24  and  25  may be in contact with an interior surface of conductive rings  34  and  35  for electrical connection to a power supply. 
     Although several preferred embodiments, which incorporate the teachings of the present invention, have been shown and described in detail, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.