Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/552,356 filed on Oct. 27, 2011 titled “TEMPERATURE CONTROL WITH STACKED PROPORTIONING VALVE,” the content of which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention generally relate to plasma processing equipment, and more particularly to methods of controlling 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 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. To accommodate increasingly complex film stacks, many plasma processes expose a workpiece to a number of sequential plasma conditions within a same processing chamber. Operations in such in-situ recipes (performed within a single manufacturing apparatus rather than in separately tuned systems) may require temperature setpoints spanning a wide range. 
    
    
     
       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 heat transfer fluid-based heat source and a heat transfer fluid-based heat sink coupled to a workpiece supporting chuck; 
         FIG. 2  illustrates a schematic of plumbing coupling a heat transfer fluid-based heat source and a heat transfer fluid-based heat sink to a workpiece supporting chuck; 
         FIG. 3  is a schematic illustrating an embodiment of the present invention in which the function of the manifolds depicted in  FIG. 2  are integrated by two stacked proportioning valves; 
         FIG. 4  is a plan view of further illustrating a stacked proportioning valve, in accordance with an embodiment of the present invention; 
         FIGS. 5A-5E  are cross-sectional views along the transverse A-A, B-B, and C-C sections illustrating various states of three independent parallel valve stages as the angular position of a valve rotor is varied, in accordance with an embodiment; and 
         FIG. 6  illustrates a schematic of a plasma etch system including a heat transfer fluid-based heat source and a heat transfer fluid-based heat sink coupled to a workpiece supporting chuck, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the invention. However, it will be understood by those skilled in the art that other embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention. Some portions of the detailed description that follows are presented in terms of algorithms and symbolic representations of operations on data bits or binary digital signals within a computer memory. These algorithmic descriptions and representations may be the techniques used by those skilled in the data processing arts to convey the substance of their work to others skilled in the art. 
     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 etch system  300  which includes a component for which temperature is controlled. The plasma etch system  300  may be any type of high performance etch chamber known in the art, 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 may be similarly controlled. While the exemplary embodiments are described in the context of the plasma etch system  300 , it should be further noted that the temperature control system architecture described herein is also adaptable to other plasma processing systems (e.g., plasma deposition systems, etc.) which present a heat load on a temperature controlled component. 
     The plasma etch system  300  includes a grounded chamber  305 . A substrate  310  is loaded through an opening  315  and clamped to a temperature controlled electrostatic 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. 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. In the exemplary embodiment, an inner thermal zone is proximate a center of substrate  310  and an outer thermal zone is proximate to a periphery/edge of substrate  310  with a temperature sensing probe  376  disposed within each zone and communicatively coupled to a temperature controller  375 , which in the exemplary embodiment is a component of a system controller  370  responsible for automation of the system  300 . 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 an RF input  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 etch 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 a 13.56 MHz generator supplies between 500 W and 3000 W while a 2 MHz generator supplies between 0 and 7000 W of power for a total bias power (W b,tot ) of between 500 W and 10000 W. In another dual frequency bias power embodiment a 60 MHz generator supplies between 100 W and 3000 W while a 2 MHz generator supplies between 0 and 7000 W of power for a total bias power (W b,tot ) of between 100 W and 10000 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 2000 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. Notably, the system component to be temperature controlled by a temperature controller  375  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 controlled with the temperature controller  375 . For such showerhead embodiments, the showerhead may or may not be RF powered. 
     For a high bias power density (kW/workpiece area) embodiment, such as that applicable to dielectric etching, it is problematic to supply heating power to the chuck  320  via a resistive heater because of RF filtering issues. For the system  300 , the chuck heating power is provided by a heat transfer fluid loop. For such embodiments, a first heat transfer fluid loop cools the chuck  320  and a second heat transfer fluid loop heats the chuck  320 . In the exemplary embodiment, the temperature controller  375  is coupled, either directly, or indirectly to a chiller  377  (heat sink) and a heat exchanger  378  (heat source). The temperature controller  375  may acquire the temperature setpoint of the chiller  377  or the heat exchanger (HTX)  378 . A difference between the temperature of the chiller  377  and a temperature setpoint for the chuck  320  and the difference between the temperature of the heat exchanger  378  and the temperature setpoint is input into a feedforward or feedback control line along with the plasma power (e.g., total bias power). The chiller  377  is to provide a cooling power to the chuck  320  via a coolant loop thermally coupling the chuck  320  with the chiller  377 . In the exemplary embodiment therefore, two coolant loops are employed. One coolant loop has a cold liquid (e.g., Galden or Fluorinert, etc. at a temperature setpoint of −5° C. while another loop contains liquid at high temperature (e.g., Galden or Fluorinert, etc. at a temperature setpoint of 55° C.). When cooling is required a valve  385  is opened while a valve  386  for the heating loop is opened when heating is required. In preferred embodiments, only one of the heating and cooling valves  385  and  386  is open at any particular time such that a total fluid flow to the chuck  320  at any given time is delivered from either the chiller  377  or the HTX  378 . 
       FIG. 2A  illustrates a schematic of valving and plumbing manifolds  361  for the heat transfer fluid-based heat source/sink employed in the plasma etch system of  FIG. 1 , in accordance with an embodiment of the present invention. As further depicted, a pair of heat transfer fluid supply lines  381  and  382  are coupled to the chiller  377  and a heat transfer fluid channel embedded in the chuck  320  (subjacent to a working surface of the chuck upon which substrate  310  is disposed during processing) via the valves  385  (EV  4  and EV  3 , respectively). The line  381  is coupled to a heat transfer fluid channel embedded subjacent to a first, outer zone, of the chuck working surface while the line  382  is coupled to a heat transfer fluid channel embedded subjacent to a second, inner zone, of the chuck working surface to facilitate dual zone cooling. Similarly, the line  381  and  382  also couples the chuck  320  to the HTX  378  via the valves  386  (EV 2  and EV 1 , respectively) to facilitate dual zone heating. Return lines  383 A complete the coupling of each of the inner and outer zone heat transfer fluid channels to the chiller/HTX,  377 / 378  via return valves EV 3  and EV 1 . 
     During operation, because each of the hot and cold coolant loops is tapped to control the chuck temperature, differences in the amount of fluid which is returned from the chuck  320  to the reservoirs in the chiller  377  and HTX  387  may occur. Even where the individual valves  385  and  386  are operated completely out of phase, small differences in individual valve actuation rates may result in a net migration of heat transfer fluid from one of the chiller and HTX  377 , 378  to the other of the chiller and HTX  377 ,  378 . A means to neutralize that net migration would then be needed. 
       FIG. 3  is a schematic illustrating an embodiment of the present invention in which the function of the manifolds  361  are integrated by two stacked proportioning valves  461 A and  461 B for switching heat transfer fluid from the chiller  377  and HTX  378  to each of the inner and outer coolant channels of the cathode (chuck)  320 . As shown in  FIG. 3 , heat transfer fluid lines from the chiller  377  and HTX  378  feed into each of the stacked proportioning valves  461 A and  461 B, heat transfer fluid lines couple output ports of the valves  461 A and  461 B to the inputs for each zone in the chuck  320 . Temperature probes in the chuck  320  (e.g.,  376  in  FIG. 1 ) output a measured chuck temperature. In the exemplary embodiment where the temperature probes are fiber optic probes, probe output is passed through a photon converter (counter)  346  and then relayed to the temperature controller  375  and/or the controller  380  responsible for outputting a drive signal  481  to the stacked proportioning valves  461 A and  461 B. Controller  380  may be any conventional temperature controller, such as but not limited to those commercially available from Azbil/Yamatake Corporation of Japan. The temperature controller  375  may function as a two-way communication interface between the controller  380  and the temperature probe  376 , for example. 
       FIG. 4  is a plan view of further illustrating one stacked proportioning valve  461 , in accordance with an embodiment of the present invention.  FIGS. 5A-5E  are cross-sectional views along the transverse A-A, B-B, and C-C sections denoted in  FIG. 4  further illustrating states of the three parallel valve stages as the angular position of a valve rotor is varied, in accordance with an embodiment. 
     Generally, the stacked proportioning valve  461  includes an appropriately machined rotor disposed within a single stationary valve body  411  defining a plurality of fluidly independent cavities with multiple ports coupled to each cavity. As show in  FIGS. 4 and 5A , the rotor  511  is cylindrical in its simplest form with a longitudinal axis L extending through the valve body  411  to have a portion of the rotor  511  disposed in each of the fluidly independent cavities. The rotor  511  is to move in a controlled way about its axis within the stationary valve body  411  (e.g., by ±21°). It should be noted the ±21° deflection angle is illustrative, with this angle variable in alternate embodiments of the invention as a matter of design. The valve body  411  bears the fittings or ports  415  that connect the valve assembly to the hot (HTX)  378  and cold chiller  377  and to the cathode (chuck)  320 . 
     During operation, the rotor  511  moves within the valve body  411 , to open and close appropriate ports  415  (e.g., with particular valve states  501 ,  502 ,  503 ,  504  and  505  illustrated in  FIGS. 5A-5E , respectively) for heat transfer fluid to flow from the HTX  378  or the chiller  377  to a certain (dedicated) cooling zone (e.g., inner and outer ESC loops  381 ,  382 ). In an embodiment, when the stacked proportioning valve  461  is to pass little or no heat transfer fluid from the chiller  377  or HTX  378  to the chuck  320  (e.g., when the rotor  511  is at 0°), heat transfer liquid is diverted back to the chiller  377  or HTX  378  from which it originated (this flow is referred to herein as the “prime bypass” and replaces the function of the bypasses  383 ,  384  illustrated in  FIG. 1B . In this way, the HTX  378  and chiller  377  are always permitted to output several GPM. Conversely, according to the mechanical design of the valve, when the stacked proportioning valve  461  is appropriately positioned to send a maximum flow (e.g., 3-8 GPM) from a certain chiller to the chuck  320 , then the prime bypass is fully closed. As such, it is again noted that the stacked proportioning valve  461  not a mixing valve, but rather, at any given rotor angle, a finite flow of either hot or cold heat transfer fluid may be established through the chuck  320 , and in the preferred embodiment, never both at the same time beyond few-ml-per-min leakage as described elsewhere herein. The prime bypass flow exists so that both the chiller  377  and HTX  378  may maintain a constant pump rate even when one of them is prevented from flowing to the chuck  320 . Therefore, at any instant in time, a given zone (e.g., inner or outer) of the chuck  320  is either being heated or cooled, or neither, but not both. 
     Section views A-A, B-B and C-C in  FIGS. 5A-5E  depict the appropriate action of the stacked proportioning valve  461 . The  FIGS. 5A-5E  depict sections through the monolithic rotor  511 , thus the angular position of the sectioned heat transfer fluid flow channels  520  in each figure are nominally equal. As illustrated in section C-C, the stacked proportioning valve  461  switches flow from a given chiller back to the same chiller when that flow returns from the cathode. 
       FIG. 5A  illustrates the state of the stacked proportioning valve  461  referred to as “MV=+100” where full flow is sent between the chuck  230  and the HXT  378  while the chiller  377 , (cold) flow is fully diverted through prime bypass.  FIG. 5B  illustrates the state of stacked proportioning valve  461  associated with a control command value MV=+50% where a controlled portion of hot fluid (e.g., from HTX  378 ) is sent to the chuck  320  while all cold fluid (e.g., from chiller  377 ) is shunted away from the chuck  320  by the bypass and the return from the chuck  320  is routed only back to the hot fluid source (e.g., to HTX  378 ).  FIG. 5C  illustrates the state of stacked proportioning valve  461  associated with a control command value “MV=0” where neither the chiller  377  nor the HTX  378  is supplying the cathode (chuck  320 ) and all flow of the chiller  377  and the HTX  378  is returned to the same chiller through prime bypass.  FIG. 5D  illustrates the state of stacked proportioning valve  461  associated with a control command value MV=−50% where a controlled portion of cold fluid (e.g., from chiller  377 ) is sent to the chuck  320  while all hot fluid (e.g., from HTX  378 ) is shunted away from the chuck  320  by the bypass, and the return from the chuck  320  is routed only back to the cold fluid source (e.g., to chiller  377 ).  FIG. 5E  illustrates a state associated with MV=−100, when full cold chiller flow (e.g., from chiller  377 ) is sent to the cathode, and all the hot chiller flow (e.g., from HTX  378 ) is sent to prime bypass. 
     In embodiments, the rotor  511  has diameter in the range of 1.25″ to 3.0″. The external ports  415  are approximately 0.75″ O.D. Internal channels  520  are sized accordingly to avoid undesired fluid restrictions. The valve body  411  may be one piece or may be made of rigidly assembled sections, according to mechanical and manufacturing considerations known to those skilled in the art of valving design. In the exemplary embodiment, the rotor  511  and valve body  411  are the same or dissimilar metals. Plastics (e.g., PTFE) may also be utilized. The rotor  511  may be appropriately enclosed by journal bearings (e.g., 4 bearing) that seal the pressurized heat transfer fluid inside each section of the stacked proportioning valve  461 . Such bearings should maintain a rotating seal with acceptably low leak rate and wear-resistance. Depending on the embodiment, the journal bearings may be Teflon, Kel-F, Vespel, graphite-filled, or molybdenum-disulfide-filled analogues thereof, and the like. 
     In embodiments where the chiller  377  operates between −10° C. and 80° C., depending on the application and the HTX  378  operates between 40° C. and 130° C., the components of the stacked proportioning valve  461  are toleranced accordingly for thermal expansion over this whole range. Since the stacked proportioning valve  461  will act as an equilibration path between the dissimilar temperatures, it may incorporate thermal breaks (e.g., thermally resistive materials and/or voids) to minimize conductive heat transfer through the body  411  or rotor  511 . As further illustrated in  FIG. 4 , a motor  460  and gearbox  462  are to rigidly affixed to the rotor  511  by a drive shaft to accurately move the rotor  511  within the body  411  over the desired angular positions θ about the transverse plane, as illustrated in  FIGS. 5A-5E  (e.g., ±21°). The motor  460  and gearbox  462  may need to be thermally decoupled from the temperature of stacked proportioning valve  461  itself by appropriate mechanical design. The motor  460  may for example be a stepper motor, or servomotor. 
     Referring back to  FIG. 3 , the function of a controller  380  is further configured to receive the process temperature and to generate an angular MV (within ±21°) by an appropriate temperature-control algorithm and then directly actuate the motor  460  appropriately. Mechanical feedback and encoding of the rotor angle may be implemented by one of ordinary skill. These functions in the illustrated embodiment are performed by a standalone module but could also be integrated into the temperature controller  375  which also manages functions of the process chamber. Regardless of the implementation, the system  383  is to follow a process sequence of an (etch) process recipe performed by the etch system  300 . A hybrid model-based/PID temperature control algorithm is utilized in a particular embodiment. 
     Initialization and service routines for the new temperature control hardware are performed in an appropriate fashion and can be implemented by those of ordinary skill in the art. In the course of adapting the control system, the GPM flow as a function of angular position may be calibrated and may need to be subjected to software-linearization. These tasks could be done partly by simulation but ultimately be empirical laboratory measurements. Related data collection may be needed to address chamber-matching considerations, as is generally experienced with all production tools. 
     In an embodiment, the stacked proportioning valve  461  has no angular position of the rotor  511  that results in dead-tight shutoff of the (˜80 PSI) heat transfer fluid output pressure from the chiller  377  or HTX  378 . For example, even at MV=0, a few ml/min of heat transfer fluid flow to the chuck  320  may be allowable. For such embodiments, the valve action may be made less frictional and less wear will be expected. In one such embodiment, the fluid resistance for heat transfer fluid to exit from the chuck  320  back to the HTX  378 /chiller  377  reservoir through the channels depicted in section C-C are made to be slightly less than the flow resistance of (pressurized) hot and cold supply ports in sections A-A and B-B when MV=0. This will avoid a rise to ˜80 PSI of the chuck channels when the chamber is idle for a long time at MV=0. Such embodiments result in a slight mixing of hot and cold chiller liquids, but at a small enough level that may be tolerable in a manufacturing environment, or require only a nominal passive leveling means between the reservoirs of the chiller  377  and HTX  378 . 
     A leak rate of heat transfer fluid from the last journal bearing (outboard of section C-C) to an outer containment vessel may increase with wear of the stacked proportioning valve  461 . The valve  461  may be designed to be a rebuildable component assembly. Optionally, the stacked proportioning valve  461  may be designed “leaky” to simplify tolerancing and manufacturability, and to take advantage of the self-lubracating properties of the heat transfer fluid. Such a scheme is akin to pistons and bearings in internal combustion engines, where an “oil sump” and a recirculating pump circulate intentionally-leaked fluids. In such embodiments, the stacked proportioning valve  461  would be disposed in a double-containment that would not normally accumulate any heat transfer fluid. For servicing, when dead-tight isolation of the chiller  377  HTX  378  from all valve components is needed, 4 manually-actuated ball valves that can be incorporated in line with both chillers&#39; supply and return hoses. In other embodiments quick-connects may also serve an equivalent purpose at the same locations. The valve body  411  may optionally be instrumented by pressure transducers and flow transducers placed at appropriate points in the line, for example as illustrated in the schematics of  FIG. 2 . 
     Accordingly, embodiments described herein effectively emulate one half of the manifolds  361  illustrated in  FIG. 2 , and further accomplish this task in a smoothly-varying manner without fluid hammer. As such, a pair of 2 complete motor-plus-valve assemblies, as described herein, may be utilized in place of the manifolds  361  (e.g.,  461 A and  461 B) for embodiments where the chuck  320  as the separate inner and outer liquid channels.  FIG. 6  illustrates a schematic of a plasma etch system  600  including a heat transfer fluid-based heat source and a heat transfer fluid-based heat sink coupled to a workpiece supporting chuck, in accordance with an embodiment. Generally, the plasma etch system  600  includes the components sharing like reference numbers with those of the system  100  in  FIG. 1 , with like reference numbers indicating a component has a same structure and/or function between the two systems. As further illustrated in  FIG. 6 , the etch system  600  includes at least one of the stacked proportioning valves  461 , and advantageously includes at least two stacked proportioning valves  461 , one for each thermal zone of the chuck  320  (inner and outer zone illustrated). A plurality of controllers  380 - 380 N may further be provided to provide control commands to a respective one of each of the stacked proportioning valves  461  (e.g.,  461 A and  461 B as further shown in  FIG. 4 ), substantially as described elsewhere herein in the context of single temperature zone embodiments. 
     It is to be understood that the above description is 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 may not be 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.

Technology Category: 4