Patent Publication Number: US-2013240144-A1

Title: Fast response fluid temperature control system

Description:
TECHNICAL FIELD 
     Embodiments of the present invention generally relate to plasma processing equipment, and more particularly to methods of controlling chamber component temperatures during processing of a workpiece with a plasma processing chamber. 
     BACKGROUND 
     In a plasma processing chamber, such as a plasma etch or plasma deposition chamber, the temperature of a chamber component is often an important parameter to control during a process. For example, a temperature of a substrate holder, commonly called a chuck or pedestal, may be controlled to heat/cool a workpiece to various controlled temperatures during the process recipe (e.g., to control an etch rate). Similarly, a temperature of a showerhead/upper electrode, chamber liner, baffle, process kit, or other component may also be controlled during the process recipe to influence the processing. Conventionally, a heat sink and/or heat source is coupled to the processing chamber to maintain the temperature of a chamber component at a desired temperature. Often, at least one heat transfer fluid loop thermally coupled to the chamber component is utilized to provide heating and/or cooling power. 
     Long line lengths in a heat transfer fluid loop, and the large heat transfer fluid volumes associated with such long line lengths are detrimental to temperature control response times. Point-of-use systems are one means to reduce fluid loop lengths/volumes. However, physical space constraints disadvantageously limit the power loads of such point-of-use systems. 
     With plasma processing trends continuing to increase RF power levels and also increase workpiece diameters (with 300 mm now typical and 450 mm systems now under development), a temperature control system capable of both a fast response time and high power loads is advantageous in the plasma processing field. 
     SUMMARY OF DESCRIPTION 
     Methods and systems for controlling temperatures in plasma processing chamber using a local heat transfer fluid loop coupled to at least one remote heat transfer fluid loop via a heat exchanger are described. 
     In an embodiment, a supply line and a return line fluidly couple a heat transfer fluid reservoir of a remote loop to a first side of a heat exchanger that is proximate to a temperature controlled chamber component, such as a chuck. A local heat transfer fluid loop is fluidly coupled to a second side of the heat exchanger and thermally couples the chamber component to the heat sink or source provided by the remote loop. 
     In embodiments, multiple supply lines and multiple heat transfer fluid reservoirs (e.g., hot and cold) are coupled to the local loop with multiple heat exchangers having their secondary sides configured in parallel. In each branch of the local loop there is a 2-way that is controlled based on a control algorithm to apportion a fixed fluid flow in the local loop between the paralleled heat exchangers. In embodiments, a 3-way or 4-way mixing valve apportions a fixed fluid flow in the local loop between the paralleled heat exchangers and/or a bypass line. 
     In embodiments where the temperature component has multiple temperature zones, a mixing valve is coupled to each of the temperature zone via multiple branches from each heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which: 
         FIG. 1  illustrates a schematic of a plasma etch system including a primary heat transfer fluid loop coupled to heat source and a primary heat transfer fluid loop coupled to a heat sink with a temperature controlled component thermally coupled to the primary loops through a local heat transfer fluid loop, in accordance with an embodiment of the present invention; 
         FIG. 2A  illustrates a block diagram of hardware in a temperature control system which may be employed in a plasma processing system, in accordance with an embodiment; 
         FIG. 2B  illustrates a block diagram of hardware in a temperature control system which may be employed in a plasma processing system, in accordance with an embodiment; 
         FIG. 3  illustrates a block diagram of hardware in a temperature control system which may be employed in a plasma processing system, in accordance with an embodiment; 
         FIG. 4  illustrates a block diagram of hardware in a temperature control system which may be employed in a plasma processing system having multiple temperature control zones, in accordance with an embodiment; 
         FIG. 5  illustrates a block diagram of a temperature control algorithm which may be employed in the temperature control systems described herein, in accordance with an embodiment; 
         FIG. 6  illustrates a method to operate the temperature control systems described herein, in accordance with an embodiment; 
         FIG. 7  is a graph illustrating temperature control response times for the temperature control system illustrated in  FIG. 2A , in accordance with an embodiment; and 
         FIG. 8  illustrates a block diagram of an exemplary computer system incorporated into the plasma etch system depicted in  FIG. 1  which is configured to automatically execute the temperature control algorithm illustrated in  FIG. 5 , in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In some instances, well-known methods and devices are shown in block diagram form, rather than in detail, to avoid obscuring the present invention. Reference throughout this specification to “an embodiment” means that a particular feature, structure, function, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, functions, or characteristics may be combined in any suitable manner in one or more embodiments. For example, a first embodiment may be combined with a second embodiment anywhere the two embodiments are not mutually exclusive. 
     Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system&#39;s registers and/or memories into other data similarly represented as physical quantities within the computing system&#39;s memories, registers or other such information storage, transmission or display devices. 
     The terms “coupled” and “connected,” along with their derivatives, may be used herein to describe structural relationships between components. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” my be used to indicated that two or more elements are in either direct or indirect (with other intervening elements between them) physical or electrical contact with each other, and/or that the two or more elements co-operate or interact with each other (e.g., as in a cause an effect relationship). 
       FIG. 1  illustrates a cross-sectional schematic view of a plasma processing system  300  which includes a component for which temperature is controlled. The plasma processing system  300  may be any type of processing chamber known in the art, including plasma etch chambers, such as, but not limited to, Enabler™, MxP®, MxP+™, Super-E™, DPS II AdvantEdge™ G3, or E-MAX® chambers manufactured by Applied Materials of CA, USA. Other commercially available etch chambers, as well as other plasma processing systems, such as plasma enhanced chemical vapor deposition (PECVD) systems, and the like, may be similarly controlled. 
     The plasma processing system  300  includes a grounded chamber  305 . A workpiece to be processed (i.e., substrate)  310  is loaded through an opening  315  and clamped to a temperature controlled chuck  320 . The substrate  310  may be any workpiece conventionally employed in the plasma processing art and the present invention is not limited in this respect. Furthermore, the dimension of the substrate may vary as known in the industry with conventional silicon substrates currently having a diameter of 300 mm and 450 mm substrates in development. In particular embodiments, temperature controlled chuck  320  includes a plurality of zones, each zone independently controllable to a temperature setpoint which may be the same or different between the zones. For example, the temperature controlled chuck  320  may include both an inner thermal zone proximate a center of substrate  310  and an outer thermal zone proximate to a periphery/edge of substrate  310 . Process gases, are supplied from gas source  345  through a mass flow controller  349  to the interior of the chamber  305 . Chamber  305  is evacuated via an exhaust valve  351  connected to a high capacity vacuum pump stack  355 . 
     When plasma power is applied to the chamber  305 , a plasma is formed in a processing region over substrate  310 . A first plasma bias power  325  is coupled to the chuck  320  (e.g., cathode) via transmission line  328  to energize the plasma. The plasma bias power  325  typically has a low frequency between about 2 MHz to 60 MHz, and in a particular embodiment, is in the 13.56 MHz band. In the exemplary embodiment, the plasma processing system  300  includes a second plasma bias power  326  operating at about the 2 MHz band which is connected to the same RF match  327  as plasma bias power  325  to provide a dual frequency bias power. In one dual frequency bias power embodiment for the exemplary 300 mm substrate, a 13.56 MHz generator supplies between 500 W and 10000 W while a 2 MHz generator supplies between 0 and 10000 W of power for a total bias power (W b,tot ) of between 500 W and 20000 W. In another dual frequency bias power embodiment a 60 MHz generator supplies between 100 W and 8000 W while a 2 MHz generator supplies between 0 and 10000 W of power for a total bias power (W b,tot ) of between 100 W and 20000 W. 
     A plasma source power  330  is coupled through a match (not depicted) to a plasma generating element  335  (e.g., showerhead) which may be anodic relative to the chuck  320  to provide high frequency source power to energize the plasma. The plasma source power  330  typically has a higher frequency than the plasma bias power  325 , such as between 100 and 180 MHz, and in a particular embodiment, is in the 162 MHz band. In particular embodiments the top source operates between 100 W and 5000 W. Bias power more directly affects the bias voltage on substrate  310 , controlling ion bombardment of the substrate  310 , while source power more directly affects the plasma density. 
     It is noted that these exemplary power ranges are for processing of a workpiece having a 300 mm diameter (e.g., 12 inch wafer) and power levels can be expected to scale with subsequent generations of the systems so as to maintain at least the same power densities (i.e., watts/unit of substrate area). For example, in an embodiment where the system  300  is configured for 450 mm substrates, the power ranges above are increased by a factor of between 2 and 2.5. 
     The system component to be temperature controlled by the control system  100  is neither limited to the chuck  320  nor must the temperature controlled component directly couple a plasma power into the process chamber. In an alternative embodiment for example, a showerhead through which a process gas is input into the plasma process chamber is the temperature controlled component. For such showerhead embodiments, the showerhead may or may not be an RF powered electrode. In still other embodiments, the temperature controlled component is a wall liner of the chamber  305  or a process kit composed of one or more of: baffles, shrouds, confinement rings, and bellows, as know in the art. 
     Referring still to  FIG. 1 , in embodiments, for the plasma processing system  300 , chuck heating power (e.g., to elevate the chuck temperature to 50° C., or more) and chuck cooling power (e.g., to reduce the chuck temperature to 20° C., or below) is provided by a local heat transfer fluid loop  115 . The use of a heat transfer fluid loop  115  is particularly advantageous for high bias power densities (kW/workpiece area) embodiments, such as that applicable to dielectric etching where application of 5 kW powers to a 300 mm substrate is not uncommon and RF filtering issues preclude embedding resistive heaters into the chuck  320  (or other temperature controlled component such as a top electrode, etc.). 
     Embodiments of the present invention include a temperature control system employing both a primary heat transfer fluid loop and a secondary heat transfer loop to thermally couple the temperature controlled component of a plasma processing system to a heat sink or heat source. As employed herein, a primary heat transfer loop is directly coupled to the heat source or heat sink and a secondary heat transfer fluid loop is directly coupled to the temperature controlled component with a primary and secondary loop coupled to each other through an intermediate heat exchanger. For clarity, the secondary heat transfer loop is also referred to herein as a “local” loop, being proximate to the temperature controlled component, while the primary heat transfer loop(s) is(are) referred to herein as “remote” loop(s). One technical advantage of the presently described system is that the local (secondary) loop can be of a short length with minimal fluid volume to increase the system response time to heat load changes (transients). As the intermediate heat exchanger can be relatively smaller than the heat source or sink, control efforts can be applied in close proximity to the control target (i.e., the intermediate heat exchanger may be within a few feet, or less, of the chamber component). 
       FIG. 1  illustrates an exemplary embodiment where a local heat transfer fluid loop  115  is coupled to a first heat exchanger  112 , which is in turn further coupled to a remote heat transfer loop  105  that places the first heat exchanger  112  in fluid communication with a heat sink (e.g., a chiller  377 ) to remove heat from the chuck  320 . As further illustrated, a temperature controller  375  is coupled, either directly, or indirectly (via the controller  370 ) to one or more actuators  120  operative in the local heat transfer fluid loop  115 , or to an actuator in the remote heat transfer loop  105  to modulate heat transfer between the local heat transfer fluid loop  115  and the remote heat transfer loop  105  and affect temperature control of the temperature controlled component (chuck  320 ). For example, in one embodiment having only one remote heat transfer loop  105 , the local heat transfer fluid loop  115  includes a bypass (not depicted) of the first heat exchanger  112  with the actuator apportioning heat transfer fluid flow within the local heat transfer fluid loop  115  between the bypass and the first heat exchanger  112 . To affect such apportionment, the temperature controller  375  may acquire the temperature setpoint of the chiller  377 , and/or a sensed component temperature output from a temperature sensor  376 . In further embodiments, as described elsewhere herein, the temperature controller  375  may further acquire a sensed local heat transfer fluid temperature output from a temperature sensor in the local heat transfer fluid loop  115 . 
     While in the simplest implementation only one remote heat transfer loop and one local heat transfer loop is utilized, the exemplary embodiment employs two remote heat transfer loops: one remote loop thermally coupling the local loop to a heat sink; and a second remote loop thermally coupling the local loop to a heat source. The load may maintain a constant heat transfer fluid flow at all times through flow apportionment between the two heat exchangers to yield superior response time and predictable temperature uniformity where the temperature controlled component is to have a wider operating temperature range or faster response time than is achievable through a system employing a single remote heat transfer fluid loop. For example, in one advantageous embodiment illustrated by  FIG. 1 , the temperature controller  375  is coupled, either directly, or indirectly (via the controller  370 ) to the one or more actuators  120  to apportion variable fractions of a constant flow rate in the local heat transfer fluid loop  115  between the heat exchangers  112  and  114  which have local (secondary) sides fluidly coupled in parallel into the local heat transfer loop  115 . The heat exchangers  112  and  114  further include remote (primary) sides, the first of which is coupled to the remote heat transfer loop  105  and the second of which is coupled to the remote heat transfer loop  110 . The remote heat transfer loop  100  is further coupled to the heater  378  as a heat source. 
       FIG. 2A  illustrates a block diagram of hardware in a temperature control system  201  which may be employed in a plasma processing system, in accordance with an embodiment. The system  201  further depicts hardware components introduced in the context of  FIG. 1 . The first remote loop  110  is couples a heater  378  to the heat exchanger  114 . Generally, the heater  378  is to operate in any conventional manner to maintain a reservoir of heat transfer liquid at a high temperature setpoint. The high temperature setpoint is generally to be fixed at a constant value for all temperatures at which the control target, the electrostatic chuck (ESC)  320  in the depicted embodiment, is to be operated. In the exemplary embodiment the high temperature setpoint ranges between 80° C. and 120° C. The heat transfer liquid may be any employed in the art, for example a perfluoropolyether known under the trade names of Fluorinert (3M, Inc.) or Galden (Solvey Solexis, Inc), etc. Noting there are different formulations of such heat transfer liquids directed at specific operating temperature ranges, a high temperature formulation with an appropriately high boiling point for the high temperature setpoint may be selected, for example Galden HT200 in the exemplary embodiment where the high temperature setpoint is between 80° C. and 120° C. 
     The first remote loop  110  includes a supply line  110 A and return line  110 B coupling the heater  378  to the heat exchanger  114 , and more specifically places the heater  378  in fluid communication with a primary side  114 A. The heat exchanger  114  may generally be any known in art though smaller form factors (e.g., plate designs) are desirable where the local heat transfer fluid loop  115  is space constrained as it is in the exemplary embodiment where the temperature controlled chamber component is the chuck  320  offering limited external chamber access below a plasma processing chamber where other cabling including RF transmission lines, DC supply lines, sensor lines, and mechanical actuators (e.g., lifts, bellows, etc.) all complete for chamber access. The remote loop lines  110 A,  110 B may be of any length needed to accommodate space constraints proximate to the chamber component (ESC  320 ) and facilitization. In the exemplary embodiment, lines  110 A and  110 B are on the order of 75 feet and of a diameter to accommodate moderate circulation pressures such that fluid volume of the first remote loop  110  may range from 1 to 5 liters while the heat transfer fluid reservoir in the heater  378  typically being 8-10 liters for a total fluid volume of 9-15 liters. This relatively large volume provides a good static heat source. 
     As further illustrated in  FIG. 2A , the second remote heat transfer fluid loop  105  couples the chiller  377  to the heat exchanger  112 , and more specifically places the chiller  377  in fluid communication with a primary side  112 A. Similar to the heater  378 , the chiller  377  may be of any conventional design and manufacture (e.g., commercially available from SMC Corp.) and also is to maintain heat transfer fluid in a reservoir of similar capacity as that of the heater  378  with a pump to circulate the fluid in the loop  105 . The loop lines  105 A,  105 B may again be of any length needed to accommodate space constraints proximate to the chamber component and accommodate facilities. In the exemplary embodiment, lines  105 A and  105 B are also on the order of 75 feet with a fluid volume of the first remote loop  110  again being in the range of 1 to 5 liters for a total fluid volume of 9-15 liters. While the first and second remote heat transfer fluid loop  105  and  110  are therefore of approximately the same thermal mass, embodiments are not limited in this respect beyond serving as a good static heat source/heat sink. 
     Because the second remote heat transfer fluid loop  105  is isolated from the first remote heat transfer fluid loop  110 , the heat transfer fluid formulation utilized in the second remote heat transfer fluid loop  105  may be optimized for a desired, constant second temperature setpoint (e.g., low temperature), independent from that employed by the first remote heat transfer fluid loop  110 . In certain embodiments, multiple remote heat transfer fluid loops employ heat transfer fluids of different composition, with typically different specific gravity, different boiling points, etc. For example, where the first remote heat transfer fluid loop  110  is a heat source employing Galden HT200 for operation in the range of 80° C.-120° C., the second remote heat transfer fluid loop  105  employs Galden HT135 for operation in the range of 0° C.-20° C. (or even a −15° C.-0° C.). 
     In alternative embodiments, for at least one of the remote heat transfer fluid loops, the heat transfer fluid undergoes a phase change at a temperature of the heat exchanger, at a temperature of the heat source/sink or at a temperature there between. For example, in one embodiment the chiller  377  is replaced with any conventional vapor-compression refrigeration unit thermally coupled to the remote heat transfer fluid loop  105 . For such an embodiment, heat is removed at the heat exchanger  112  with direct expansion a constant pressure and temperature phase change of the heat transfer fluid at the primary side  112 A. As such, the heat transfer fluid is not necessarily a liquid, but may also be in a gas phase or a vapor. A similar technique may also be employed for remote heat transfer loop  110 , though the cycle is reversed with condensation of a hot gas or vapor (e.g., steam, etc.) occurring at the primary side  114 A. 
     The heat exchangers  112 ,  114  include secondary sides  112 B,  114 B respectively that are in fluid communication with the local heat transfer fluid loop  115 . As shown the local heat transfer fluid loop  115  includes a branch  216  in fluid communication with the heat exchanger secondary side  112 B to thermally couple the local heat transfer fluid loop  115  to the second remote heat transfer fluid loop  105 . Similarly, the local heat transfer fluid loop  115  includes a branch  217  in fluid communication with the heat exchanger secondary side  114 B to thermally couple the local heat transfer fluid loop  115  to the first remote heat transfer fluid loop  110 . Because the local heat transfer fluid loop  115  is not in fluid communication with either of the remote heat transfer fluid loops  105 ,  110 , the heat transfer fluid formulation utilized in the local heat transfer fluid loop  115  may also be independently optimized for a desired operating temperature range. For example, in one embodiment the heat transfer fluid employed by the local heat transfer fluid loop  115  is of a different composition than that employed by one or both of the remote heat transfer fluid loops  105 ,  110 . In the exemplary embodiment, the heat transfer fluid is a liquid, such as Galden HT135, HT200, etc. and is circulated via the pump  240 . Alternatively, the heat transfer fluid undergoes a phase-change at some point within the local heat transfer fluid loop  115  and so a gas or vapor phase is also contemplated for particular embodiments. 
     In embodiments, the local heat transfer fluid loop  115  is to be of significantly shorter line length than that of the remote heat transfer fluid loop(s) because the local heat transfer fluid loop  115  is to have a temperature setpoint which is to fluctuate during processing as a process recipe calls for different operating temperatures. With the architecture of the system  201 , the local heat transfer fluid loop  115  in essence becomes part of the load that is to be temperature controlled by modulating thermal exposure of the load to the heat sink and source provided by the remote loops  110 ,  105 . This thermal load remains well mixed with a uniform temperature through circulation of the heat transfer fluid with the local loop  115 , for example in  FIG. 2A , as motivated in a clockwise circulation by the pump  240 . Minimal line length therefore advantageously reduces thermal mass of the load, reducing transient response times. With short line lengths, line diameters may also be smaller than those employed in the remote loop lines  110 A,B and  105 A,B for reduced heat transfer fluid volumes. The local heat transfer fluid loop  115  advantageously has less than half the volume of the first remote loop  110 , and preferably no more than 10 to 30% of the remote loop volume. In one exemplary embodiment where a remote loop has total fluid volume of 9-15 liters, the local heat transfer fluid loop  115  has a volume of about 2 liters. 
     As shown, the branches  216  and  217  couple the secondary sides of the two heat exchangers  114  and  112  in parallel within the local heat transfer fluid loop  115 . At least one end of the branches  216  and  217  are coupled together through one or more actuators controllable to apportion the heat transfer fluid circulated within the local heat transfer fluid loop  115  between the heat exchangers  112 ,  114 . In the exemplary embodiment, the actuator is a mixer  220 A entailing either set of valves (i.e., a valve manifold with one valve per exchanger) or a multi-way mixing valve with an input side coupled to each of the heat exchangers  112 ,  114 . As shown, the mixer  220 A includes three sides, two in fluid communication with outlets of the secondary sides  112 B,  114 B and the third side being an outlet in fluid communication with the inlet to the ESC  320 . Depending on the position of a valve relative to the two input sides in the mixer  220 A, between 0 and 100% of a fluid flow through the local heat transfer fluid loop  115  passes through a first of the secondary sides  112 B,  114 B with the remainder passing through the secondary of the secondary sides. In certain such embodiments, the fluid flow through the local heat transfer fluid loop  115  is maintained at a constant, fixed rate by the pump  240  with only apportionment of that fixed rate varying in response to a control operator&#39;s output signal. 
     In the exemplary embodiment, the mixer  220 A coupled to a downstream end of the heat exchangers  112 ,  114  disposed between the heat exchangers  112 ,  114  and ESC  320  as the temperature controlled chamber component to place the control actuator as close to the control target as possible. Of course, an alternate embodiment may have the mixer  220 A coupled to an upstream end of the heat exchangers, for example to be disposed either between the heat exchangers  112 ,  114  and the pump  240  or to remain disposed between the heat exchangers  112 ,  114  and the ESC  320  but with the recirculation direction reversed to be counterclockwise. 
     In an embodiment, both the chamber component to be controlled and the local heat transfer fluid loop are temperature sensed via separate temperature sensors. As illustrated in  FIG. 2A , temperature of the heat transfer fluid in the local loop  115  is sensed with a sensor (e.g., thermocouple)  230  disposed at the outlet of the mixer  220 A for immediate feedback to a controller of the mixer  220 A. The ESC  320  is similarly sensed with the sensor  376 . As described elsewhere herein, temperature control algorithms may employ one or more of these separate temperature sensors. 
       FIG. 2B  illustrates a block diagram of hardware in a temperature control system  202  which may be employed in a plasma processing system, in accordance with an embodiment Like the system  201 , the system  202  further depicts hardware components introduced in the context of  FIG. 1  with like reference numbers applied to those components already described. As shown the system  202  is substantially the same as that of system  201  with the addition of a bypass line  218  enabling the local heat transfer fluid loop  115  to circulate at a constant flow rate while concurrently apportioning 0% of the flow through both the heat exchangers  112 , and  114 . As such, the branches  217  and  216  may be rendered stagnant for a time. In the system  202 , the flow proportioning is between the branches  216 ,  217  and bypass  218 , all in parallel, with flow via a four-way mixer  220 B having three inlet sides, each coupled to one of the branches and one outlet side coupled to the ESC  320  (or other temperature controlled chamber component). Advantages of the system  202  over the system  202  include an ability to reduce the thermal load on the system, for example during a idle time of the processing chamber when there is relatively little external perturbation of the system. 
     In an alternate embodiment, at least one of the heat source and heat sink are provided by a heater or chiller in-situ to local heat transfer fluid loop  115 .  FIG. 3  illustrates a block diagram of hardware in a temperature control system  301  which may be employed in a plasma processing system, in accordance with such an embodiment. As shown, the first remote heat transfer fluid loop  110  is replaced with an in-situ heater  345  positioned on the local heat transfer fluid branch  217 . The in-situ heater  345  may for example be an in-line resistive heater. As with the system  201 , the actuator  120  couples the outputs of the in-situ heater  345  and heat exchanger  112  to apportion a constant flow rate with the local loop between the two. As such, the system  301  may be considered intermediate between systems employing only one remote heat transfer loop and those employing two remote heat transfer fluid loops (e.g.,  201 ,  202 ) to the extent that active heating is applied to the branch  217 . However, as most in-line heaters (or chillers) are not capable of power loads as high as those achievable with larger ex-situ systems (e.g., heater  378 ), the system  301  is best suited for moderate response times and/or moderately low ESC temperatures (e.g., below 30° C.). In one embodiment, in the system  301  the actuator  120  may be implemented with a three-way valve (e.g., like mixer  220 A) or equivalent set of 2-way valves mixing two input sides into one outlet side. In another embodiment where the local heat transfer fluid loop  115  includes the bypass  218  (denoted in  FIG. 3  with a dashed line), the actuator  120  may be implemented with a four-way valve (e.g., like mixer  220 B) or a functionally equivalent set of 2-way valves. 
       FIG. 4  illustrates a block diagram of hardware in a temperature control system  401  which may be employed in a plasma processing system where a chamber component includes multiple temperature control zones, in accordance with one embodiment. In  FIG. 4 , the ESC  320  includes a control zone A and a control zone N. While it is contemplated that any of the systems described elsewhere herein may simply be replicated for each control zone present in a multi-zone component, multiplication of the remote loops may be prohibitive on a basis of cost or space constraints. As such, in the exemplary embodiment, a plurality of mixers, one for each control zone are fluidly coupled to each heat exchanger or in-situ source/since present with control of the zones made independent through independent actuation of the mixers. 
     The ESC zone A has an inlet in fluid communication with a first mixer  120 A (e.g., a 3-way mixing valve), that is in parallel fluid communication with a downstream (or upstream) end of each of the first heat exchanger  112  and a second heat exchanger  114  (or inline heater, chiller) via the branches  216 A and  217 A, respectively. Similarly, the ESC zone N has an inlet in fluid communication with a second mixer  120 N (e.g., a second 3-way mixing valve) that is in parallel fluid communication with a downstream (or upstream) end of each of the first heat exchanger  112  and the second heat exchanger  112  (or inline heater, chiller) via the branches  216 N and  217 N, respectively, which are tapped of the branches  216 A and  217 A. The thermal zones A-N each include an outlet in fluid communication with the upstream (or downstream) end of each of the first and second heat exchangers  112 ,  114  (or inline heater, chiller). For example, the outlets from each zone A, N may be joined and returned to supply a low pressure side of the pump  240 . 
     As shown, each zone further includes a independent primary temperature sensor  376 A,  376 N and an independent second temperature sensor  230 A,  230 N. Separate control algorithms may be implemented to independently control each mixer  120 A through  120 N substantially as described elsewhere herein in the context of a single thermal zone. In further embodiments, each mixer may be further coupled to a bypass substantially as described elsewhere herein in the context of a single temperature zone. 
       FIG. 5  illustrates a block diagram of a temperature control algorithm  501  which may be employed in the temperature control systems described herein, in accordance with an embodiment. In the exemplary embodiment, the control algorithm  501 , or the like, is implemented by the temperature controller  375 , as further illustrated in  FIG. 1  during processing of a workpiece. 
     While any conventional single level control algorithm may be utilized to affect temperature control based on an sensed temperature of the control target (e.g., ESC  320 ), in the exemplary embodiments where both a temperature of the control target and temperature of heat transfer fluid in the local heat transfer fluid loop are sensed, the control algorithm may have a cascaded control architecture, such as that depicted in  FIG. 5 . 
     As illustrated, a primary controller  510  receives as an input a setpoint temperature  512  for the chamber component to which the component is to be controlled. The setpoint temperature  512  for example is defined in a process recipe step within a process recipe filed specifying a sequence of process recipe steps. The primary controller  510  further receives as an input a primary sensed temperature provided by the primary temperature sensor  376 . The primary sensed temperature is the actual temperature of the control target. A control operator  515  then output a primary control output  516  to counteract a deviation determined between the setpoint temperature  512  and the primary sensed temperature. Any conventional means of determining a control effort based on this deviation may be utilized (e.g., PID control). 
     A secondary controller  520  receives as an input the control output  516  and performs a comparison to a secondary sensed temperature provided by the secondary temperature sensor  230 . From the resulting deviation, the control operator  525  generates a secondary control output  516  which is output as the basis for driving an actuator  530 , such as a mixing valve actuator where a mixing valve is employed. Resulting changes to the system are then fed back through the temperature sensors. 
       FIG. 6  illustrates a method  600  for operating the temperature control systems described herein, in accordance with an embodiment. After system initialization at operation  605 , a first heat transfer fluid, for example having a high boiling point, is pumped through a first primary (remote) heat transfer fluid (heater) loop at operation  610  while a second heat transfer fluid, for example having a low boiling point, is pumped through a second primary (remote) heat transfer fluid (chiller) loop concurrently at operation  615 . 
     At operation  620 , a third heat transfer fluid is pumped through a local heat transfer fluid loop that includes for example first and second local heat exchangers thermally coupling the plasma process chamber to the primary heater and chiller loops. 
     At operation  625 , mechanical valves (analog or digital) are actuated based on a control algorithm to vary a flow rate of the third heat transfer fluid between the first and second local heat exchangers. In one embodiment operation  625  further entails sensing a temperature of a chamber component, outputting a primary control signal based on a deviation between the sensed component temperature and a component temperature setpoint, sensing a temperature of the third heat transfer fluid, outputting a secondary control signal based on a deviation between the sensed third heat transfer fluid temperature and the primary control signal, and driving a multi-way valve based on the secondary control signal. Concurrent with operation  625 , a workpiece is processed in the plasma processing chamber at operation  630  while the temperature controlled chamber component is controlled to a setpoint temperature. 
       FIG. 7  is a graph illustrating temperature control response times for the temperature control system illustrated in  FIG. 2A , in accordance with an embodiment. The temperature setpoint for the control target (“ESC SP”) is plotted as a function of time (sec). The plot “CONTROL OUT” represents the secondary control output  526  generated by the cascaded control algorithm  501  as a function of time (sec) while a sensed temperature of the control target (“ESC TEMP”) is also plotted. As shown, with a change in setpoint from 60° C. to 20° C., the system stabilizes at the new setpoint in less than 90 seconds with similar performance achieved when the setpoint is returned. 
       FIG. 8  illustrates a diagrammatic representation of a machine in the exemplary form of a computer system  800  which may be utilized to perform the valve control operations described herein (e.g., to execute the method  600  and/or algorithm  501 ). In one embodiment, the computer system  800  may be provisioned as the controller  370  in the plasma etch system  300 . In alternative embodiments, the machine may be connected (e.g., networked) to other machines in a Local Area Network (LAN), an intranet, an extranet, or the Internet. The machine may operate in the capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC), a server, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines (e.g., computers) that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. 
     The exemplary computer system  800  includes a processor  802 , a main memory  804  (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory  806  (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory  818  (e.g., a data storage device), which communicate with each other via a bus  830 . 
     The processor  802  represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. The processor  802  may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. The processor  802  is configured to execute the processing logic  826  for performing the valve control operations discussed elsewhere herein. 
     The computer system  800  may further include a network interface device  808 . The computer system  800  also may include a video display unit  810  (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device  812  (e.g., a keyboard), a cursor control device  814  (e.g., a mouse), and a signal generation device  816  (e.g., a speaker). 
     The secondary memory  818  may include a machine-accessible storage medium (or more specifically a computer-readable storage medium)  831  on which is stored one or more sets of instructions (e.g., software  822 ) embodying any one or more of the valve control algorithms described herein (see e.g.,  501  in  FIG. 5 ). The software  822  may also reside, completely or at least partially, within the main memory  804  and/or within the processor  802  during execution thereof by the computer system  800 , the main memory  804  and the processor  802  also constituting machine-readable storage media. The software  822  may further be transmitted or received over a network  820  via the network interface device  808 . 
     The machine-accessible storage medium  831  may further be used to store a set of instructions for execution by a processing system and that cause the system to perform any one or more of the methods described herein (e.g., method  600 ). Embodiments of the present invention may further be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to control a plasma processing chamber temperature according to the present invention as described elsewhere herein. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices, and other such non-transitory storage media. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, while flow diagrams in the figures show a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is not required (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present invention has been described with reference to specific exemplary embodiments, it will be recognized that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. 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.