Patent Publication Number: US-2007109912-A1

Title: Liquid ring pumping and reclamation systems in a processing environment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit under 35 U.S.C. § 119(e) to provisional application No. 60/801,913, filed May 19, 2006, the entire contents of which are incorporated herein by reference. This application also claims priority from and is a continuation-in-part of U.S. patent application Ser. No. ______, filed Sep. 18, 2006 (Attorney Docket No. Serie 7132), which claims priority from U.S. Provisional Patent Application Ser. No. 60/720,597, entitled “Point of Use Process Control Blender,” and filed Sep. 26, 2005. This application is further a continuation-in-part of U.S. patent application Ser. No. 11/107,494, filed Apr. 15, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 10/939,570, filed Sep. 13, 2004, which is a divisional application of U.S. patent application Ser. No. 09/468,411, filed Dec. 20, 1999 (now U.S. Pat. No. 6,799,883), which is a continuation-in-part of U.S. patent application Ser. No. 09/051,304, filed Apr. 16,1998 (now U.S. Pat. No. 6,050,283). The disclosures of the above-identified patent applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND  
      1. Field of the Invention  
      This disclosure pertains to methods and systems for the management of chemicals in processing environments, such as semiconductor fabrication environments.  
      2. Related Art  
      In various industries, chemical delivery systems are used to supply chemicals to processing tools. Illustrative industries include the semiconductor industry, pharmaceutical industry, biomedical industry, food processing industry, household product industry, personal care products industry, petroleum industry and others.  
      The chemicals being delivered by a given chemical delivery system depend, of course, on the particular processes being performed. Accordingly, the particular chemicals supplied to semiconductor processing tools depend on the processes being performed on wafers in the tools. Illustrative semiconductor processes include etching, cleaning, chemical mechanical polishing (CMP) and wet deposition (e.g., chemical vapor deposition, electroplating, etc.).  
      Commonly, two or more fluids are combined to form a desired solution for a particular process. The solution mixtures can be prepared off-site and then shipped to an end point location or a point-of-use for a given process. This approach is typically referred to as batch processing or batching. Alternatively, and more desirably, the cleaning solution mixtures are prepared at the point-of-use with a suitable mixer or blender system prior to delivery to the cleaning process. The latter approach is sometimes referred as continuous blending.  
      In either case, accurate mixing of reagents at desired ratios is particularly important because variations in concentration of the chemicals detrimentally affect process performance. For example, failure to maintain specified concentrations of chemicals for an etch process can introduce uncertainty in etch rates and, hence, is a source of process variation.  
      In today&#39;s processing environments, however, mixing is only one of many aspects that must be controlled to achieve a desired process result. For example, in addition to mixing, it may be desirable or necessary to control removal of chemicals from a processing environment. It may also be desirable or necessary to control temperatures of chemical solutions at various stages in the processing environment. Currently, chemical management systems are not capable of adequately controlling a plurality of process parameters for certain applications.  
      Therefore, there is a need for methods and systems for managing chemical conditioning and supply in processing environments.  
     SUMMARY  
      One embodiment provides a blender system for maintaining a chemical solution at desired concentrations. The system includes a blender unit configured to receive and blend at least two chemical compounds and deliver a solution comprising a mixture of the compounds at selected concentrations to at least one tank that retains a selected volume of the delivered solution; at least one processing station having an inlet fluidly coupled to the tank and configured to perform a process on an article using solution received from the tank; a fluid reclamation system fluidly coupled to an outlet of the processing station configured to return solution removed from the processing station to a point upstream from the tank, whereby at least a portion of the solution removed from the tank is returned to the point upstream from the tank for reuse at the processing station; and a controller. The controller configured is to: control operation of the blender unit to maintain a concentration of the at least one compound in the solution delivered to the tank within a selected concentration range; and change a flow rate of the solution into and out of the tank when a concentration of the at least one compound in the volume of solution contained in the tank falls outside of a target range.  
      Another embodiment of a system for maintaining a chemical solution at desired concentrations includes a blender unit configured to receive and blend at least two chemical compounds and deliver a solution comprising a mixture of the compounds at selected concentrations to at least a first supply tank that retains a selected volume of the delivered solution; at least one processing station having an inlet fluidly coupled to the tank and configured to perform a process on an article using solution received from the first supply tank; and a vacuum pump system fluidly coupled to at least one outlet of the processing station via a vacuum line. The vacuum pump system includes a liquid ring pump having a suction port coupled to the vacuum line to receive an incoming multiphase stream formed from one or more fluids removed from the processing station via the outlet; and a sealant fluid tank coupled to an exhaust port of the liquid ring pump and comprising one or more devices configured for removing liquid from a multiphase stream output by the liquid ring pump through the exhaust port; wherein the sealant fluid tank provides the liquid ring pump sealant fluid needed for the operation of the liquid ring pump. The system further includes a controller configured to: control operation of the blender unit to maintain a concentration of the at least one compound in the solution delivered to the first supply tank within a selected concentration range; and change a flow rate of the solution into and out of the first supply tank when a concentration of the at least one compound in the volume of solution contained in the first supply tank falls outside of a target range.  
      Another embodiment provides a method of providing a chemical solution to a tank. The method includes providing at least two compounds to a blender unit to form a mixed solution of the at least two compounds at selected concentrations; providing the mixed solution from the blender unit to a tank in order to fill the tank with a predetermined volume of the solution; and maintaining a concentration of at least one compound in the solution contained in the tank within a selected concentration range. maintaining a concentration of at least one compound in the solution contained in the tank within a selected concentration range includes controlling the blender unit to maintain the at least one compound within the selected concentration range; and changing a flow rate of solution into and out of the tank when the concentration of the at least one compound in the solution contained in the tank falls outside of a target range. The method further includes flowing the solution from the tank to a processing chamber at which a process using the solution is performed; removing at least a portion of the solution from the process chamber; returning the removed portion of the solution to a point upstream from the process chamber, whereby the removed portion is available for reuse in the process chamber; and monitoring the removed portion of the solution to determine whether at least one of the chemical compounds in the removed portion of the solution is at a predetermined concentration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:  
       FIG. 1  is a diagram of a processing system illustrating onboard components, according to one embodiment of the present invention.  
       FIG. 2  is a diagram of a processing system illustrating onboard and off-board components, according to another embodiment of the present invention.  
       FIG. 3  is a diagram of a semiconductor fabrication system, according to one embodiment of the present invention.  
       FIG. 4  is a diagram of a processing system, according to one embodiment of the present invention.  
       FIG. 5  is a schematic diagram of an exemplary embodiment of a semiconductor wafer cleaning system including a cleaning bath connected with a point-of-use process control blender system that prepares and delivers a cleaning solution to the cleaning bath during a cleaning process.  
       FIG. 6  is a schematic diagram of an exemplary embodiment of the process control blender system of  FIG. 5 .  
       FIG. 7  is a diagram of a processing system having an off-board blender, according to one embodiment of the present invention.  
       FIG. 8A  is a diagram of a processing system having a reclamation system, according to one embodiment of the present invention.  
       FIG. 8B  is a diagram of a processing system having a reclamation system, according to one embodiment of the present invention.  
       FIG. 8C  is a diagram of a processing system having a reclamation system, according to one embodiment of the present invention.  
       FIG. 9  is a diagram of a vacuum pump system, according to one embodiment of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
      Embodiments of the present invention provide methods and chemical management systems for controlling various aspects of fluid delivery and/or recovery.  
      Systems Overview  
       FIG. 1  shows one embodiment of a processing system  100 . Generally, the system  100  includes a processing chamber  102  and a chemical management system  103 . According to one embodiment, the chemical management system  103  includes an input subsystem  104  and an output subsystem  106 . It is contemplated that any number of the components of the subsystems  104 ,  106  may be located onboard or off-board, relative to the chamber  102 . In this context, “onboard” refers to the subsystem (or component thereof being integrated with the chamber  102  in the Fab (clean room environment), or more generally with a processing tool of which the chamber  102  is a part; while “off-board” refers to the subsystem (or component thereof) being separate from, and located some distance away from, the chamber  102  (or tool, generally). In the case of the system  100  shown in  FIG. 1 , the subsystems  104 ,  106  are both onboard, such that the system  100  forms an integrated system which may be completely disposed in a Fab. Accordingly, the chamber  102  and the subsystems  104 ,  106  may be mounted to a common frame. To facilitate cleaning, maintenance and system modifications the subsystems may be disposed on detachable subframes supported by, for example, casters so that the subsystems may be easily disconnected and rolled away from the chamber  102 .  
      Illustratively, the input subsystem  104  includes a blender  108  and a vaporizer  110  fluidly connected to an input flow control system  112 . In general, the blender  108  is configured to mix two or more chemical compounds (fluids) to form a desired chemical solution, which is then provided to the input flow control system  112 . The vaporizer  110  is configured to vaporize a fluid and provide the vaporized fluid to the input flow control system  112 . For example, the vaporizer  110  may vaporize isopropyl alcohol and then combine the vaporized fluid with a carrier gas, such as nitrogen. The input flow control system  112  is configured to dispense the chemical solution and/or vaporized fluid to the chamber  102  at desired flow rates. To this end, the input flow control system  112  is coupled to the chamber  102 A by a plurality of input lines  114 . In one embodiment, the chamber  102 A is configured with a single processing station  124  at which one or more processes can be performed on a wafer located at the station  124 . Accordingly, the plurality of input lines  114  provide the appropriate chemistry (provided by the blender  108  via the input flow control system  112 ) required for performing a given process at the station  124 . In one embodiment, the station  124  may be a bath, i.e., a vessel containing a chemical solution in which a wafer is immersed for a period of time and then removed. However, more generally, the station  124  may be any environment in which one or more surfaces of a wafer are exposed to one or more fluids provided by the plurality of input lines  114 . Further, it is understood that while  FIG. 1  shows a single processing station, the chamber  102 A may include any number of processing stations, as will be described in more detail below with respect to  FIG. 2 .  
      Illustratively, the output subsystem  106  includes an output flow control system  116 , a vacuum tanks subsystem  118  and a vacuum pumps subsystem  120 . A plurality of output lines  122  fluidly couple the chamber  102 A to the output flow control system  116 . In this way, fluids are removed from the chamber  102 A via the plurality of output lines  122 . The removed fluids may then be sent to drain, or to the vacuum tanks subsystem  118  via fluid lines  117 . In one embodiment, some fluids are removed from the vacuum tanks subsystem  118  and routed to the vacuum pump subsystem  120  for conditioning (e.g., neutralization or dilution) as part of a waste management process.  
      In one embodiment, the input subsystem  104  and the output subsystem  106  independently or cooperatively effect a plurality of process control objectives. For example, solution concentration may be monitored and controlled at various stages from the blender  108  to the chamber  102 A. In another embodiment, the output flow control system  116 , the vacuum tanks subsystem  118  and/or the vacuum pumps subsystem  120  cooperate to control a desired fluid flow over a surface of a wafer disposed in the chamber  102 A. In another embodiment, the output flow control system  116  and a vacuum pumps subsystem  120  cooperate to condition fluids removed from the chamber  102 A by the output flow control system  116  and then return the conditioned fluids to the blender  108 . These and other embodiments are described in more detail below.  
      In one embodiment, transfer means (e.g., robots) are disposed inside and/or proximate the chamber  102 A to move wafers into, through and out of the chamber  102 . The chamber  102 A may also be part of a larger tool, as will be described below.  
      In one embodiment, the various controllable elements of the system  100  are manipulated by a controller  126 . The controller  126  may be any suitable device capable of issuing control signals  128  to one or more controllable elements of the system  100 . The controller  126  may also receive a plurality of input signals  130 , which may include concentration measurements of solution in the system at different locations, level sensor outputs, temperature sensor outputs, flow meter outputs, etc. Illustratively, the controller  126  may be a microprocessor-based controller for a programmable logic controller (PLC) program to implement various process controls including, in one embodiment, a proportional-integral-derivative (PID) feedback control. An exemplary controller that is suitable for use in the process control blender system is a PLC Simatic S 7 -300 system commercially available from Siemens Corporation (Georgia). Although the controller  126  is shown as a singular component, it is understood that the controller  126  may in fact be a plurality of control units collectively forming the control system for the processing system  100 .  
      As noted above, one or more of the components of the system  100  may be located off-board relative to the chamber  102 A (or the overall tool of which the chamber  102 A is a part).  FIG. 2  shows one such configuration of a processing system  200  having off-board components relative to a chamber  102 B. Like numerals refer to components previously described with respect to  FIG. 1 . Illustratively, the blender  108 , the vacuum tanks subsystem  118  and the vacuum pumps subsystem  120  are located off-board. In contrast, the vaporizer  110 , the input flow control system  112 , and the output flow control system  116  are shown as onboard components, as in  FIG. 1 . The off-board components may be located in the Fab with the processing tool (i.e., a processing chamber  102 B and any other integrated components which may form a processing tool) or in a sub-fab. It should be understood that the configuration of the system  200  in  FIG. 2  is merely illustrative and other configurations are possible and contemplated. For example, the system  200  may be configured such that the vacuum tanks subsystem  118  is onboard, while the vacuum pumps subsystem  120  is off-board. Collectively, the blender  108 , the vaporizer  110 , the input flow control subsystem  112 , the output flow control subsystem  116 , the vacuum tanks subsystem  118  and a vacuum pumps subsystem  120  make up the chemical management system  103 , according to one embodiment of the present invention. It should be noted, however, that the chemical management systems described with respect to  FIG. 1  and  FIG. 2  are merely illustrative. Other embodiments within the scope of the present invention may include more or less components and/or different arrangements of those components. For example, in one embodiment of the chemical management system the vaporizer  110  is not included.  
      The system  200  of  FIG. 2  also illustrates an embodiment of a multi-station chamber  102 B. Accordingly,  FIG. 2  shows the processing chamber  102 B having five stations  204   1-5  (individually(collectively) referred to as station(s)  204 ). More generally, however, the chamber  102 B may have any number of stations (i.e., one or more stations). In one embodiment, the stations can be isolated from one another by sealing means (e.g., actuatable doors disposed between the processing stations). In a particular embodiment, the isolation means are vacuum tight so that the processing stations may be kept at different pressure levels.  
      Each station  204  may be configured to perform a particular process on a wafer. The process performed at each station may be different and, therefore, require different chemistry provided by the blender  108  via the input flow control system  112 . Accordingly, the system  200  includes a plurality of input line sets  206   1-5 , each set corresponding to a different station. In the illustrative embodiment of  FIG. 2 , five sets  206   1-5  of input lines are shown for each of the five processing stations. Each input line set is configured to provide an appropriate combination of chemicals to a given station. For example, in one embodiment, the chamber  102 B is a cleaning module for cleaning wafers before and between, e.g., etching processes. In this case, the input line set  206   1  for a first processing station  204   1  may provide a combination of a SC-1 type solution (which includes a mixture of ammonium hydroxide and hydrogen peroxide in deionized water) and deionized water (DIW). The input line set  206   2  for a second processing station  204   2  may provide one or more of deionized water (DIW) and isopropyl alcohol (IPA). The input line set  206   3  for a third processing station  204   3  may provide one or more of deionized water, diluted hydrogen fluoride, and isopropyl alcohol. The input line set  206   4  for a fourth processing station  204   4  may provide one or more of deionized water, known mixed chemical solutions, proprietary chemical solutions of a specific nature and isopropyl alcohol. The input line set  206   5  for a fifth processing station  204   5  may provide one or more of deionized water, SC-2 type solution (which includes an aqueous mixture of hydrogen peroxide with hydrochloric acid) and isopropyl alcohol. As in the case of the system  100  described with respect to  FIG. 1 , the stations  204  may be any environment in which one or more surfaces of a wafer are exposed to one or more fluids provided by the plurality of input lines  114 .  
      It is contemplated that fluid flow through the input lines in a given set  206  (as well as the lines  114  of  FIG. 1 ) may be individually controlled. Accordingly, the timing and a flow rate of fluids through the individual lines of a given set may be independently controlled. Further, while some of the input lines provide fluids to a wafer surface, other fluids may be provided to the internal surfaces of a processing station  204  for the purpose of cleaning the surfaces, e.g., before or after a processing cycle. Further, the input lines shown in  FIG. 2  are merely illustrative and other inputs may be provided from other sources.  
      Each of the processing stations  204   1-5  has a corresponding output line or set of output lines, whereby fluids are removed from the respective processing stations. Illustratively, the first processing stations  204   1  is coupled to a drain  208 , while the second through the fourth processing stations  204   2-4  are shown coupled to the output flow control system  116  via respective output line sets  210   1-4 . Each set is representative of one or more output lines. In this way, fluids are removed from the chamber  102 A via the plurality of output lines  122 . The fluids removed from the processing stations via the output line sets  210   1-4  coupled to the output flow control system  116  may be routed to the vacuum tanks subsystem  118  via a plurality of fluid lines  117 .  
      In one embodiment, transfer means (e.g., robots) are disposed inside and/or proximate the chamber  102 B to move wafers into, through, and out of the chamber  102 B. The chamber  102 B may also be part of a larger tool, as will now be described below with respect to  FIG. 3 .  
      Referring now to  FIG. 3 , a plan view of a processing system  300  is shown, according to one embodiment of the present invention. The processing system  300  includes a front end section  302  for receiving wafer cassettes. The front end section  302  interfaces with a transfer chamber  304  housing a transfer robot  306 . Cleaning modules  308 ,  310  are disposed on either side of the transfer chamber  304 . The cleaning modules  308 ,  310  may each include a processing chamber (single station or multi-station), such as those cleaning chambers  102 A-B described above with respect to  FIG. 1  and  FIG. 2 . The cleaning modules  308 ,  310  include and/or are coupled to the various components of the chemical management system  103  described above. (The chemical management system  103  is shown in dashed lines to represent the fact that some components of the chemical management system may be located onboard the processing system  300  and other components may be located off-board; or all components can be located onboard.) Opposite the front end section  302 , the transfer chamber  304  is coupled to a processing tool  312 .  
      In one embodiment, the front and section  302  may include load lock chambers which can be brought to a suitably low transfer pressure and then opened to the transfer chamber  304 . The transfer robot  306  then withdraws individual wafers from the wafer cassettes located in the load lock chambers and transfers the wafers either to the processing tool  312  or to one of the cleaning modules  308 ,  310 . During operation of the system  300 , the chemical management system  103  controls the supply and removal of fluids to/from the cleaning modules  308 ,  310 .  
      It is understood that the system  300  is merely one embodiment of a processing system having the chemical management system of the present invention. Accordingly, embodiments of the chemical management system are not limited to configurations such as that shown in  FIG. 3 , or even to semiconductor fabrication environments.  
      Systems and Process Control  
      Referring now to  FIG. 4 , a processing system  400  is shown with respect to which additional embodiments of a chemical management system will now be described. For convenience, the additional embodiments will be described with respect to a multi-station chamber system, such as the system  200  shown in  FIG. 2  and described above. It is understood, however, that the following embodiments also apply to the system  100  shown in  FIG. 1 . Further, it is noted that the order of the processing stations  204  in  FIG. 4  is not necessarily reflective of the order in which processing is performed on a given wafer, but rather is arranged for convenience of illustration. For convenience, like reference numbers correspond to like components previously described with respect to  FIG. 1  and/or  2  and will not be described in detail again.  
      The blender  108  of the system  400  is configured with a plurality of inputs  402   1-N  (collectively inputs  402 ) each receiving a respective chemical. The inputs  402  are fluidly coupled to a primary supply line  404 , wherein the respective chemicals are mixed to form a solution. In one embodiment, the concentrations of the various chemicals are monitored at one or more stages along the supply line  404 . Accordingly,  FIG. 4  shows a plurality of chemical monitors  406   1-3  (three shown by way of illustration) disposed in-line along the supply line  404 . In one embodiment, a chemical monitor is provided at each point in the supply line  404  where two or more chemicals are combined and mixed. For example, a first chemical monitor  406   1  is disposed between a point where the first and second chemicals (inputs  402   1-2 ) are mixed and a point (i.e., upstream from) where a third chemical (input  402   3 ) is introduced into the supply line  404 . In one embodiment, the concentration monitors  406  used in the system are electrode-less conductivity probes and/or Refraction Index (RI) detectors including, without limitation, AC toroidal coil sensors such as the types commercially available under the model 3700 series from GLI International, Inc. (Colorado), RI detectors such as the types commercially available under the model CR-288 from Swagelok Company (Ohio), and acoustic signature sensors such as the types commercially available from Mesa Laboratories, Inc. (Colorado).  
      The blender  108  is selectively fluidly coupled via the primary supply line  404  to a plurality of point of use destinations (i.e., processing stations  204 ). (Of course, it is contemplated that in another embodiment the blender  108  services only one point of use destination.) In one embodiment, the selectivity of which processing station to service is controlled by a flow control unit  408 . The flow control unit  408  is representative of any number of devices suitable for controlling aspects of fluid flow between the blender and downstream destinations. For example, the flow control unit  408  may include a multi-way valve for controlling the routing of the solution from the blender  108  to a downstream destination. Illustratively, the flow control unit  408  can selectively (e.g., under the control of the controller  126 ) route the solution from the blender  108  to a first point of use supply line  410 , a second point of use supply line  412  or a third point of use supply line  414 , where each point of use supply line is associated with a different processing station. The flow control unit  408  may also include flow meters or flow controllers.  
      In one embodiment, a vessel is disposed in-line with respect to each of the point of use supply lines. For example,  FIG. 4  shows a first vessel  416  fluidly coupled to the first point of use supply line  410 , between the flow control unit  408  and the first processing station  204   1 . Similarly, a second vessel  418  is fluidly coupled to the second point of use supply line  412 , between the flow control unit  408  and the second processing station  204   2 . The vessels are suitably sized to provide a sufficient volume for supplying the respective processing stations during a time when the blender  108  is servicing a different processing station (or when the blender  108  is otherwise unavailable, such as for maintenance). In a particular embodiment, the vessels have a capacity of 6 to 10 liters, or specific volumes required for given processing requirements. The fluids levels of each vessel may be determined by the provision of respective level sensors  421 ,  423  (e.g., high and low sensors). In one embodiment, the vessels  416 ,  418  are pressure vessels and, accordingly, each include a respective inlet  420 ,  422  for receiving a pressurizing gas. In one embodiment, the contents of the vessels  416 ,  418  are monitored for concentration. Accordingly, the vessels  416 ,  418  shown in  FIG. 4  include active concentration monitoring systems  424 ,  426 . These and other aspects of the system  400  will be described in more detail below with respect to  FIGS. 5-6 .  
      In operation, the vessels  416 ,  418  dispense their contents by manipulating respective flow control devices  428 ,  430 . The flow control devices  428 ,  430  may be, for example, pneumatic valves under the control of the controller  126 . The solution dispensed by the vessels  416 ,  418  is then flowed to the respective processing station  204  via the respective input lines  206 . Further, the vaporized fluid from the vaporizer  110  may be flowed to one or more processing station  204 . For example, in the present illustration, vaporized fluid is input to the second processing station  204   2.    
      Each of the individual input lines  206  may have one or more fluid management devices  432   1-3  (for convenience, each set of input lines is shown having only one associated fluid management device). The fluid management devices  432  may include, for example, filters, flow controllers, flow meters, valves, etc. In a particular embodiment, one or more of the flow management devices  432  include heaters for heating the fluids being flowed through the respective lines.  
      Removal of fluids from the respective processing chambers is then performed by operation of the output flow control subsystem  116 . As shown in  FIG. 4 , each of the respective plurality of output lines  210  of the output flow control subsystem  116  includes its own associated one or more flow management devices  434   1-3  (for convenience, each set of output lines is shown having only one associated fluid management device). The fluid management devices  434  may include, for example, filters, flow controllers, flow meters, valves, etc. In one embodiment, the fluid management devices may include active pressure control units. For example, a pressure control unit may be made up of a pressure transducer coupled to a flow controller. Such active pressure control units may operate to effect a desired process control with respect to wafers and the respective processing stations, such as by controlling the interface of fluid and a wafer surface. For example, it may be necessary to control the pressure in the output lines relative to the pressure and the processing stations to ensure a desired fluid/wafer interface.  
      In one embodiment, fluids removed by the output flow control subsystem  116  are flowed into one or more vacuum tanks of the vacuum tanks subsystem  118 . Accordingly, by way of illustration, the system  400  includes two vacuum tanks. A first tank  436  is coupled to the output lines  210   1  of the second processing chamber  204   2 . A second tank  438  is coupled to the output lines  210   3  of the third processing chamber  204   3 . In one embodiment, a separate tank may be provided for each different chemistry input to the respective processing stations. Such an arrangement may facilitate reuse of the fluids (reclamation will be described in more detail below) or disposal of the fluids.  
      The fluid levels in each of the tanks  436 ,  438  may be monitored by one or more level sensors  437 ,  439  (e.g., high and low level sensors). In one embodiment, the tanks  436 ,  438  are selectively pressurized by the input of a pressurizing gas  440 ,  442  and may also be vented to depressurize the tanks. Further, each tank  436 ,  438  is coupled to the vacuum pump subsystem  120  by a respective vacuum line  444 ,  446 . In this way, vapors can be removed from the respective tanks and processed at the vacuum pump subsystem  120 , as will be described in more detail below. In general, the contents of the tanks may either be sent to drain or be reclaimed and returned to the blender for reuse. Accordingly, the second tank  438  is shown emptying to a drain line  452 . In contrast, the first tank  436  is shown coupled to a reclamation line  448 . The reclamation line  448  is fluidly coupled to the blender  108 . In this way, fluids may be returned to the blender  108  from the processing station(s) and reused. The reclamation of fluids will be described in more detail below with respect to  FIG. 8 .  
      In one embodiment, fluid delivery in the system  400  is facilitated by establishing a pressure gradient. For example, with respect to the system  400  shown in  FIG. 4 , a decreasing pressure gradient may be established beginning with the blender  108  and ending with the processing stations  204 . In one embodiment, the blender  108  and vaporizer  110  are operated at a pressure of about 2 atmospheres, the input flow control subsystem  112  is operated at about 1 atmosphere and the processing stations  204  are operated at about 400 Torr. Establishing such a pressure gradient motivates fluid flow from the blender  108  to the processing stations  204 .  
      During operation, the vessels  416 ,  418  will become depleted and must be periodically refilled. According to embodiment, the management (e.g., filling, dispensation, repair and/or maintenance) of the individual vessels occurs asynchronously. That is, while a given vessel is being serviced (e.g., filled), the other vessels may continue to dispense solution. A filling cycle for a given vessel may be initiated in response to a signal from a low fluid level sensor (one or the sensors  420 ,  423 ). For example, assume that the sensor  421  of the first vessel  416  indicates a low fluid level to the controller  126 . In response, the controller  126  causes the first vessel  416  to depressurize (e.g. by opening a vent) and causes the flow control unit  408  to place the first vessel  416  in fluid communication with the blender  108 , while isolating the blender from the other vessels. The controller  126  then signals the blender  108  to mix and dispense the appropriate solution to the first vessel  416 . Once the first vessel  416  is sufficiently filled (e.g., as indicated by a high-level fluid sensor), the controller  126  signals the blender  108  to stop dispensing solution and causes the flow control unit  408  to isolate the blender  108  from the first vessel  416 . Further, the first vessel  416  may then be pressurized by injecting a pressurizing gas into the gas inlet  420 . The first vessel  416  is now ready to begin dispensation of solution to the first processing station. During this filling cycle, each of the other vessels may continue to dispense solution to their respective processing stations.  
      In one embodiment, it is contemplated that servicing the respective vessels is based on a prioritization algorithm implemented by the comptroller  126 . For example, the prioritization algorithm may be based on volume usage. That is, the vessel dispensing the highest volume (e.g., in a given period of time) is given highest priority, while the vessel dispensing the lowest volume is given lowest priority. In this way, the prioritization of the vessels can be ranked from highest volume dispensed to lowest volume dispensed.  
      Blenders  
      In various embodiments, the present invention provides a point-of-use process control blender system which includes at least one blender to receive and blend at least two chemical compounds together for delivery to one or more vessels or tanks including chemical baths that facilitate processing (e.g., cleaning) of semiconductor wafers or other components. The chemical solution is maintained at a selected volume and temperature within the tank or tanks, and the blender can be configured to continuously deliver chemical solution to one or more tanks or, alternatively, deliver chemical solution to the one or more tanks only as necessary (as mentioned above and described further below), so as to maintain concentrations of compounds within the tank(s) within desirable ranges.  
      The tank can be part of a process tool, such that the blender provides chemical solution directly to a process tool that includes a selected volume of a chemical bath. The process tool can be any conventional or other suitable tool that processes a semiconductor wafer or other component (e.g., via an etching process, a cleaning process, etc.), such as the tool  312  described above with respect to  FIG. 3 . Alternatively, the blender can provide chemical solution to one or more holding or storage tanks, where the storage tank or tanks then provide the chemical solution to one or more process tools.  
      In one embodiment, a point-of-use process control blender system is provided that is configured to increase the flow rate of chemical solution to one or more tanks when the concentration of one or more compounds within the solution falls outside of a selected target range, so as to rapidly displace undesirable chemical solution(s) from the tank(s) while supplying fresh chemical solution to the tank(s) at the desired compound concentrations.  
      Referring now to  FIG. 5 , a blender system  500  including the blender  108  is shown, according to one embodiment of the invention. The blender  108  is shown coupled to a tank  502 , and in combination with monitoring and recirculation capabilities, according to one embodiment. In one embodiment, the tank  502  is the pressure vessel  416  or  418  shown in  FIG. 4 . Alternatively, the tank  502  is a cleaning tank (e.g., in one of the cleaning modules  308 ,  310  of the processing system  400 ) in which semiconductor wafers or other components are immersed and cleaned.  
      An inlet of cleaning tank  502  is connected with the blender  108  via a flow line  512 . The flow line  512  may correspond to one of the point of use lines  410 ,  412 ,  414  shown in  FIG. 4 , according to one embodiment. In the illustrative embodiment, the cleaning solution formed in the blender unit  108  and provided to cleaning tank  502  is an SC-1 cleaning solution, with ammonium hydroxide (NH 4 OH) being provided to the blender unit via a supply line  506 , hydrogen peroxide (H 2 O 2 ) being provided to the blender unit via a supply line  508 , and de-ionized water (DIW) being provided to the blender unit via a supply line  510 . However, it is noted that the blender system  500  can be configured to provide a mixture of any selected number (i.e., two or more) of chemical compounds at selected concentrations to any type of tool, where the mixtures can include chemical compounds such as hydrofluoric acid (HF), ammonium fluoride (NH 4 F), hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 ), acetic acid (CH 3 OOH), ammonium hydroxide (NH 4 OH), potassium hydroxide (KOH), ethylene diamine (EDA), hydrogen peroxide (H 2 O 2 ), and nitric acid (HNO 3 ). For example, the blender  108  may be configured to dispense solutions of dilute HF, SC-1, and/or SC-2. In a particular embodiment, it may be desirable to input hot diluted HF. Accordingly, the blender  108  may be configured with an input for hot DIW. In a particular embodiment, the hot DIW may be maintained from about 25° C. to about 70° C.  
      In addition, any suitable surfactants and/or other chemical additives (e.g., ammonium peroxysulfate or APS) can be combined with the cleaning solutions to enhance the cleaning effect for a particular application. A flow line  514  is optionally connected with flow line  512  between the blender unit  108  and the inlet to tank  502  to facilitate the addition of such additives to the cleaning solution for use in the cleaning bath.  
      Tank  502  is suitably dimensioned and configured to retain a selected volume of cleaning solution within the tank (e.g., a sufficient volume to form the cleaning bath for cleaning operations). As noted above, the cleaning solution can be continuously provided from blender unit  108  to tank  502  at one or more selected flow rates. Alternatively, cleaning solution can be provided from the blender unit to the tank only at selected time periods (e.g., at initial filling of the tank, and when one or more components in the cleaning solution within the tank falls outside of a selected or target concentration range). Tank  502  is further configured with an overflow section and outlet that permits cleaning solution to exit the tank via overflow line  516  while maintaining the selected cleaning solution volume within the tank as cleaning solution is continuously fed and/or recirculated to the tank in the manner described below.  
      The tank is also provided with a drain outlet connected with a drain line  518 , where the drain line  518  includes a valve  520  that is selectively controlled to facilitate draining and removal of cleaning solution at a faster rate from the tank during selected periods as described below. Drain valve  520  is preferably an electronic valve that is automatically controlled by a controller  126  (previously described above with respect to  FIGS. 1-4 ). The overflow and drain lines  516  and  518  are connected to a flow line  522  including a pump  524  disposed therein to facilitate delivery of the cleaning solution removed from tank  502  to a recirculation line  526  and/or a collection site or further processing site as described below.  
      A concentration monitor unit  528  is disposed in flow line  522  at a location downstream from pump  524 . The concentration monitor unit  528  includes at least one sensor configured to measure the concentration of one or more chemical compounds in the cleaning solution (e.g., H 2 O 2  and/or NH 4 OH) as the cleaning solution flows through line  522 . The sensor or sensors of concentration monitor unit  528  can be of any suitable types to facilitate accurate concentration measurements of one or more chemical compounds of interest in the cleaning solution. In some embodiments, the concentration sensors used in the system are electrode-less conductivity probes and/or Refraction Index (RI) detectors including, without limitation, AC toroidal coil sensors such as the types commercially available under the model 3700 series from GLI International, Inc. (Colorado), RI detectors such as the types commercially available under the model CR-288 from Swagelok Company (Ohio), and acoustic signature sensors such as the types commercially available from Mesa Laboratories, Inc. (Colorado).  
      A flow line  530  connects an outlet of concentration monitor unit  528  with an inlet of a three-way valve  532 . The three-way valve may be an electronic valve that is automatically controlled by controller  126  in the manner described below based upon concentration measurements provided by unit  528 . A recirculation line  526  connects with an outlet of valve  532  and extends to an inlet of tank  502  to facilitate recirculation of solution from the overflow line  516  back to the tank during normal system operation (as described below). A drain line  534  extends from another outlet of valve  532  to facilitate removal of solution from tank  502  (via line  516  and/or line  522 ) when one or more component concentrations within the solution are outside of the target ranges.  
      Recirculation flow line  526  can include any suitable number and types of temperature, pressure and/or flow rate sensors and also one or more suitable heat exchangers to facilitate heating, temperature and flow rate control of the solution as it recirculates back to the tank  502 . The recirculation line is useful for controlling the solution bath temperature within the tank during system operation. In addition, any suitable number of filters and/or pumps (e.g., in addition to pump  524 ) can be provided along flow line  526  to facilitate filtering and flow rate control of the solution being recirculated back to tank  502 . In one embodiment, the recirculation loop defined by the drain line  518 , the valve  520 , the pump  524 , the line  522 , the concentration monitor unit  528 , the  3 -way valve  532  and the recirculation line  526  defines the one of the concentration monitoring systems  424 ,  426  described above with reference to  FIG. 4 .  
      The blender system  500  includes a controller  126  that automatically controls components of the blender unit  108  as well as drain valve  520  based upon concentration measurements obtained by concentration monitor unit  528 . As described below, the controller controls the flow rate of cleaning solution from blender unit  108  and draining or withdrawal of cleaning solution from tank  502  depending upon the concentration of one or more compounds in the cleaning solution exiting tank  502  as measured by concentration monitor unit  528 .  
      Controller  126  is disposed in communication (as indicated by dashed lines  536  in  FIG. 5 ) with drain valve  520 , concentration monitor unit  528 , and valve  532 , as well as certain components of blender unit  108  via any suitable electrical wiring or wireless communication link to facilitate control of the blender unit and drain valve based upon measured data received from the concentration monitor unit. The controller can include a processor that is programmable to implement any one or more suitable types of process control, such as proportional-integral-derivative (PID) feedback control. An exemplary controller that is suitable for use in the process control blender system is a PLC Simatic S7-300 system commercially available from Siemens Corporation (Georgia).  
      As noted above, the blender unit  108  receives independently fed streams of ammonium hydroxide, hydrogen peroxide and de-ionized water (DIW), which are mixed with each other at suitable concentrations and flow rates so as to obtain an SC-1 cleaning solution having a desired concentration of these compounds. The controller  126  controls the flow of each of these compounds within blender unit  108  to achieve the desired final concentration and further controls the flow rate of SC-1 cleaning solution to form the cleaning bath in tank  502 .  
      An exemplary embodiment of the blender unit is depicted in  FIG. 6 . In particular, each of the supply lines  506 ,  508  and  510  for supplying NH 4 OH, H 2 O 2  and DIW to blender unit  108  includes a check valve  602 ,  604 ,  606  and an electronic valve  608 ,  610 ,  612  disposed downstream from the check valve. The electronic valve for each supply line is in communication with controller  126  (e.g., via electronic wiring or wireless link) to facilitate automatic control of the electronic valves by the controller during system operation. Each of the NH 4 OH and H 2 O 2  supply lines  506  and  508  respectively connects with an electronic three-way valve  614 ,  616  that is in communication with controller  126  (via electronic wiring or a wireless link) and is disposed downstream from the first electronic valve  608 ,  610 .  
      The DIW supply line  510  includes a pressure regulator  618  disposed downstream from electronic valve  612  to control the pressure and flow of DIW into system  108 , and line  510  further branches into three flow lines downstream from regulator  618 . A first branched line  620  extending from main line  510  includes a flow control valve  621  disposed along the branched line and which is optionally controlled by controller  126 , and line  620  further connects with a first static mixer  630 . A second branched line  622  extends from main line  510  to an inlet of the three-way valve  614  that is also connected with NH 4 OH flow line  506 . In addition, a third branched line  624  extends from main line  510  to an inlet of the three-way valve  616  which is also connected with H 2 O 2  flow line  508 . Thus, the three-way valves for each of the NH 4 OH and H 2 O 2  flow lines facilitate the addition of DIW to each of these flows to selectively adjust the concentration of ammonium hydroxide and hydrogen peroxide in distilled water during system operation and prior to mixing with each other in the static mixers of the blender unit.  
      An NH 4 OH flow line  626  is connected between an outlet of the three-way valve  614  for the ammonium hydroxide supply line and the first branch line  620  of the de-ionized water supply line at a location between valve  621  and static mixer  630 . Optionally, flow line  626  can include a flow control valve  628  that can be automatically controlled by controller  126  to enhance flow control of ammonium hydroxide fed to the first static mixer. The ammonium hydroxide and de-ionized water fed to the first static mixer  630  are combined in the mixer to obtain a mixed and generally uniform solution. A flow line  634  connects with an outlet of the first static mixture and extends to and connects with a second static mixer  640 . Disposed along flow line  634  is any one or more suitable concentration sensors  632  (e.g., one or more electrode-less sensors or RI detectors of any of the types described above) that determines the concentration of ammonium hydroxide in the solution. Concentration sensor  632  is in communication with controller  126  so as to provide the measured concentration of ammonium hydroxide in the solution emerging from the first static mixer. This in turn facilitates control of the concentration of ammonium hydroxide in this solution prior to delivery to the second static mixer  640  by selective and automatic manipulation of any of the valves in one or both of the NH 4 OH and DIW supply lines by the controller.  
      A H 2 O 2  flow line  636  connects with an outlet of the three-way valve  616  that is connected with the H 2 O 2  supply line. Flow line  636  extends from three-way valve  616  to connect with flow line  634  at a location that is between concentration sensor(s)  632  and second static mixer  640 . Optionally, flow line  636  can include a flow control valve  638  that can be automatically controlled by controller  126  to enhance flow control of hydrogen peroxide fed to the second static mixer. The second static mixer  640  mixes the DIW diluted NH 4 OH solution received from the first static mixer  630  with the H 2 O 2  solution flowing from the H 2 O 2  feed line to form a mixed and generally uniform SC-1 cleaning solution of ammonium hydroxide, hydrogen peroxide and de-ionized water. A flow line  642  receives the mixed cleaning solution from the second static mixture and connects with an inlet of an electronic three-way valve  648 .  
      Disposed along flow line  642 , at a location upstream from valve  648 , is at least one suitable concentration sensor  644  (e.g., one or more electrode-less sensors or RI detectors of any of the types described above) that determines the concentration at least one of hydrogen peroxide and ammonium hydroxide in the cleaning solution. Concentration sensor(s)  644  is also in communication with controller  126  to provide measured concentration information to the controller, which in turn facilitates control of the concentration of ammonium hydroxide and/or hydrogen peroxide in the cleaning solution by selective and automatic manipulation of any of the valves in one or more of the NH 4 OH, H 2 O 2  and DIW feed lines by the controller. Optionally, a pressure regulator  646  can be disposed along flow line  642  between sensor  644  and valve  648  so as to control the pressure and flow of cleaning solution.  
      A drain line  650  connects with an outlet of three-way valve  648 , while flow line  652  extends from another outlet port of three-way valve  648 . The three-way valve is selectively and automatically manipulated by controller  126  to facilitate control of the amount of cleaning solution that emerges from the blender unit for delivery to tank  502  and the amount that is diverted to drain line  650 . In addition, an electronic valve  654  is disposed along flow line  652  and is automatically controlled by controller  126  to further control flow of cleaning solution from the blender unit to tank  502 . Flow line  652  becomes flow line  512  as shown in  FIG. 5  for delivery of SC-1 cleaning solution to tank  502 .  
      The series of electronic valves and concentration sensors disposed within blender unit  108  in combination with controller  126  facilitate precise control of the flow rate of cleaning solution to the tank and also the concentrations of hydrogen peroxide and ammonium peroxide in the cleaning solution at varying flow rates of the cleaning solution during system operation. Further, the concentration monitor unit  528  disposed along the drain line  522  for tank  502  provides an indication to the controller when the concentration of one or both the hydrogen peroxide and ammonium peroxide falls outside of an acceptable range for the cleaning solution.  
      Based upon concentration measurements provided by concentration monitor unit  528  to controller  126 , the controller may be programmed to implement a change in flow rate of cleaning solution to the tank and to open drain valve  520  so as to facilitate a rapid displacement of SC-1 cleaning solution in the bath while supplying fresh SC-1 cleaning solution to the tank, thus bringing the cleaning solution bath within compliant or target concentration ranges as quickly as possible. Once cleaning solution has been sufficiently displaced from the tank such that the hydrogen peroxide and/or ammonium hydroxide concentrations fall within acceptable ranges (as measured by concentration monitor unit  528 ), the controller is programmed to close drain valve  520  and to control the blender unit so as to reduce (or cease) the flow rate while maintaining the desired compound concentrations within the cleaning solution being delivered to the tank  502 .  
      An exemplary embodiment of a method of operating the system described above and depicted in  FIGS. 5 and 6  is described below. In this exemplary embodiment, cleaning solution can be continuously provided to the tank or, alternatively, provided only at selected intervals to the tank (e.g., when cleaning solution is to be displaced from the tank). An SC-1 cleaning solution is prepared in blender unit  108  and provided to tank  502  with a concentration of ammonium hydroxide in a range from about 0.01-29% by weight, preferably about 1.0% by weight, and a concentration of hydrogen peroxide in a range from about 0.01-31% by weight, preferably about 5.5% by weight. The cleaning tank  502  is configured to maintain about 30 liters of cleaning solution bath within the tank at a temperature in the range from about 25° C. to about 125° C.  
      In operation, upon filling the tank  502  with cleaning solution to capacity, the controller  126  controls blender unit  108  to provide cleaning solution to tank  502  via flow line  512  at a first flow rate from about 0-10 liters per minute (LPM), where the blender can provide solution continuously or, alternatively, at selected times during system operation. When the solution is provided continuously, an exemplary first flow rate is about 0.001 LPM to about 0.25 LPM, preferably about 0.2 LPM. Ammonium hydroxide supply line  506  provides a feed supply of about 29-30% by volume NH 4 OH to the blender unit, while hydrogen peroxide supply line  508  provides a feed supply of about 30% by volume H 2 O 2  to the blender unit. At a flow rate of about 0.2 LPM, the flow rates of the supply lines of the blender unit can be set as follows to ensure a cleaning solution is provided having the desired concentrations of ammonium hydroxide and hydrogen peroxide: about 0.163 LPM of DIW, about 0.006 LPM of NH 4 OH, and about 0.031 LPM of H 2 O 2 .  
      Additives (e.g., APS) can optionally be added to the cleaning solution via supply line  514 . In this stage of operation, a continuous flow of fresh SC-1 cleaning solution can be provided from the blender unit  108  to tank  502  at the first flow rate, while cleaning solution from the cleaning bath is also exiting tank  502  via overflow line  516  at generally the same flow rate (i.e., about 0.2 LPM). Thus, the volume of the cleaning solution bath is maintained relatively constant due to the same or generally similar flow rates of cleaning solution to and from the tank. The overflow cleaning solution flows into drain line  522  and through concentration monitor unit  528 , where concentration measurements of one or more compounds (e.g., H 2 O 2  and/or NH 4 OH) within the cleaning solution are determined continuously or at selected time intervals, and such concentration measurements are provided to controller  126 .  
      Cleaning solution can optionally be circulated by adjusting valve  532  such that cleaning solution flowing from tank  502  flows through recirculation line  526  and back into the tank at a selected flow rate (e.g., about 20 LPM). In such operations, blender unit  108  can be controlled such that no cleaning solution is delivered from the blender unit to the tank unless the concentrations of one or more compounds in the cleaning solution are outside of selected target ranges. Alternatively, cleaning solution can be provided by the blender unit at a selected flow rate (e.g., about 0.20 LPM) in combination with the recirculation of cleaning solution through line  526 . In this alternative operating embodiment, three-way valve  532  can be adjusted (e.g., automatically by controller  126 ) to facilitate removal of cleaning solution into line  534  at about the same rate as cleaning solution being provided to the tank by the blender unit, while cleaning solution still flows through recirculation line  526 . In a further alternative, valve  532  can be closed to prevent any recirculation of fluid through line  526  while cleaning solution is continuously provided to tank  502  by blender unit  108  (e.g., at about 0.20 LPM). In this application, solution exits the tank via line  516  at about the same or similar flow rate as the flow rate of fluid into the tank from the blender unit.  
      For applications in which cleaning solution is continuously provided to the tank, controller  126  maintains the flow rate of cleaning solution from blender unit  108  to tank  502  at the first flow rate, and the concentrations of hydrogen peroxide and ammonium hydroxide within the selected concentration ranges, so long as the measured concentrations provided by the concentration monitor unit  528  are within acceptable ranges. For applications in which cleaning solution is not continuously provided from the blender unit to the tank, controller  126  maintains this state of operation (i.e., no cleaning solution from blender unit to tank) until a concentration of hydrogen peroxide and/or ammonium hydroxide are outside of the selected concentration ranges.  
      When the concentration of at least one of hydrogen peroxide and ammonium hydroxide, as measured by concentration monitor unit  528 , deviates outside of the acceptable range (e.g., the measured concentration of NH 4 OH deviates from the range of about 1% relative to a target concentration, and/or the measured concentration of H 2 O 2  deviates from the range of about 1% relative to a target concentration), the controller manipulates and controls any one or more of the valves in blender unit  108  as described above to initiate or increase the flow rate of cleaning solution from the blender unit to tank  502  (while maintaining the concentrations of NH 4 OH and H 2 O 2  in the cleaning solution within the selected ranges) to a second flow rate.  
      The second flow rate can be in a range from about 0.001 LPM to about 20 LPM. For continuous cleaning solution operations, an exemplary second flow rate is about 2.5 LPM. The controller further opens drain valve  520  in tank  502  to facilitate a flow of cleaning solution from the tank at about the same flow rate. At the flow rate of about 2.5 LPM, the flow rates of the supply lines of the blender unit can be set as follows to ensure a cleaning solution is provided having the desired concentrations of ammonium hydroxide and hydrogen peroxide: about 2.04 LPM of DIW, about 0.070 LPM of NH 4 OH, and about 0.387 LPM of H 2 O 2 .  
      Alternatively, cleaning solution that is being recirculated to the tank at a selected flow rate (e.g., about 20 LPM) is removed from the system by adjusting three-way valve  532  so that cleaning fluid is diverted into line  534  and no longer flows into line  526 , and the blender unit adjusts the second flow rate to a selected level (e.g., 20 LPM) so as to compensate for the removal of fluid at the same or similar flow rate. Thus, the volume of cleaning solution bath within tank  502  can be maintained relatively constant during the increase in flow rate of cleaning solution to and from the tank. In addition, the process temperature and circulation flow parameters within the tank can be maintained during the process of replacing a selected volume of the solution within the tank.  
      The controller maintains delivery of the cleaning solution to tank  502  at the second flow rate until concentration monitor unit  528  provides concentration measurements to the controller that are within the acceptable ranges. When the concentration measurements by concentration monitor unit  528  are within the acceptable ranges, the cleaning solution bath is again compliant with the desired cleaning compound concentrations. The controller then controls blender unit  108  to provide the cleaning solution to tank  502  at the first flow rate (or with no cleaning solution being provided to the tank from the blender unit), and the controller further manipulates drain valve  520  to a closed position so as to facilitate flow of cleaning solution from the tank only via overflow line  516 . In applications in which the recirculating line is used, the controller manipulates three-way valve  532  such that cleaning solution flows from line  522  into line  526  and back into tank  502 .  
      Thus, the point-of-use process control blender system described above is capable of effectively and precisely controlling the concentration of at least two compounds in a cleaning solution delivered to a chemical solution tank (e.g., a tool or a solution tank) during an application or process despite potential decomposition and/or other reactions that may modify the chemical solution concentration in the tank. The system is capable of continuously providing fresh chemical solution to the tank at a first flow rate, and rapidly displacing chemical solution from the tank with fresh chemical solution at a second flow rate that is faster than the first flow rate when the chemical solution within the tank is determined to have undesirable or unacceptable concentrations of one or more compounds.  
      The point-of-use process control blender systems are not limited to the exemplary embodiments described above and depicted in  FIGS. 5 and 6 . Rather, such systems can be used to provide chemical solutions with mixtures of any two or more compounds such as the types described above to any semiconductor processing tank or other selected tool, while maintaining the concentrations of compounds within the chemical solutions within acceptable ranges during cleaning applications.  
      In addition, the process control blender system can be implemented for use with any selected number of solution tanks or tanks and/or semiconductor process tools. For example, a controller and blender unit as described above can be implemented to supply chemical solution mixtures with precise concentrations of two or more compounds directly to two or more process tools. Alternatively, the controller and blender unit can be implemented to supply such chemical solutions to one or more holding or storage tanks, where such storage tanks supply chemical solutions to one or more process tools (such as in the system  400  shown in  FIG. 4 ). The process control blender system provides precise control of the concentrations of compounds in the chemical solutions by monitoring the concentration of solution(s) within the tank or tanks, and replacing or replenishing solutions to such tanks when the solution concentrations fall outside of target ranges.  
      The design and configuration of the process control blender system facilitates placement of the system in substantially close proximity to the one or more chemical solution tanks and/or process tools which are to be provided with chemical solution from the system. In particular, the process control blender system can be situated in or near the fabrication (fab) or clean room or, alternatively, in the sub-fab room but proximate where the solution tank and/or tool is located in the clean room. For example, the process control blender system, including the blender unit and controller, can be situated within about 30 meters, preferably within about 15 meters, and more preferably within about 3 meters or less, of the solution tank or process tool. Further, the process control blender system can be integrated with one or more tools so as to form a single unit including the process blender system and tool(s).  
      Off-Board Blenders  
      As mentioned above, the blender  108  may be located off-board, according to one embodiment. That is, the blender  108  may be decoupled from the processing station(s) being serviced by the blender  108 , in which case the blender  108  may then be remotely located, e.g., in a sub-fab.  
      In a particular embodiment of an off-board blender, a centralized blender is configured for servicing a plurality of tools. One such centralized blender system  700  is shown in  FIG. 7 . In general, the blender system  700  includes a blender  108  and one or more filling stations  702   1-2 . In the illustrative embodiment two filling stations  702   1-2  (collectively filling stations  702 ) are shown. The blender  108  may be configured as in any of the embodiments previously described (e.g., as described above with respect to  FIG. 6 ). The blender  108  is fluidly coupled to the filling stations  702  by a primary supply line  404  and a pair of flow lines  704   1-2  coupled at their respective ends to one of the filling stations  702   1-2 . A flow control unit  706  is disposed at the junction of the primary supply line and the flow lines  704   1-2 . The flow control unit  706  is representative of any number of devices suitable for controlling aspects of fluid flow between the blender  108  and the filling stations  702 . For example, the flow control unit  706  may include a multi-way valve for controlling the routing of the solution from the blender  108  to a downstream destination. Accordingly, the flow control unit  408  can selectively (e.g., under the control of the controller  126 ) route the solution from the blender  108  to the first filling station  702   1  via the first flow line  704   1  and to the second filling station  702   2  via the second flow line  704   2 . The flow control unit  706  may also include flow meters or flow controllers.  
      Each of the filling stations  702  is coupled to one or more processing tools  708 . In the illustrative embodiment, the filling stations are each coupled to four tools (Tools  1 - 4 ), although more generally the filling stations may be coupled to any number of points of use. Routing (and/or metering, flow rate, etc.) of the solutions from the filling stations  702  may be controlled by flow control units  710   1-2  disposed between the respective filling stations and the plurality of tools  708 . In one embodiment, filters  712   1-2  are disposed between the respective filling stations and the plurality of tools  708 . The filters  712   1-2  are selected to remove debris from the solution prior to being delivered to the respective tools.  
      In one embodiment, each filling station  702  supplies a different chemistry to the respective tools  708 . For example, in one embodiment the first filling station  702   1  supplies diluted hydrofluoric acid, while the second filling station  702   2  supplies a SC-1 type solution. Flow control devices at the respective tools may be operated to route the incoming solutions to appropriate processing stations/chambers of the tools.  
      In one embodiment, each of the filling stations may be operated asynchronously with respect to the blender  108 . That is, each filling station  702   1-2  may be filled while simultaneously dispensing a solution to one or more of the tools  708 . To this end, each filling station is configured with a filling loop having at least two vessels disposed therein. In the illustrative embodiment, the first filling station has a first filling loop  714   A-D  with two vessels  716   1-2 . The filling loop is defined by a plurality of flow line segments. A first flow line segment  714   A  fluidly couples the flow line  704  with the first vessel  716   1 . A second flow line segment  714   B  fluidly couples the first vessel  716   1  to the processing tools  708 . A third flow line segment  714   c  fluidly couples the flow line  704  with the second vessel  716   2 . A fourth flow line segment  714   D  fluidly couples the second vessel  716   2  to the processing tools  708 . A plurality of valves  720   1-4  are disposed in the filling loop to control fluid communication between the blender  108  and the vessels  716 , and between the vessels  716  and the plurality of tools  708 .  
      Each of the vessels  716  have an appropriate number of level sensors  717   1-2  (e.g., a high level sensor and a low level sensor) in order to sense a fluid level within the respective vessel. Each of the vessels also has a pressurizing gas input  719   1-2 , whereby the respective vessel may be pressurized, and a vent  721   1-2 , whereby the respective vessel may be depressurized. Although not shown, the filling loop  714   A-D  of the first processing station  702   1  may be equipped with any number of flow management devices, such as pressure regulators, flow controllers, flow meters, etc.  
      The second filling station  702  is likewise configured. Accordingly, the second filling station  702  of  FIG. 7  is shown having two vessels  722   1-2  disposed in a filling loop  724   A-D  having a plurality of valves  726   1-4  for controlling fluid communication.  
      In operation, the controller  126  may operate the flow control unit  706  to establish communication between the blender  108  and the first filling station  702   1 . The controller  126  may also operate the first filling loop valve  720   1  to establish fluid communication between the first flow line  704   1  and the first flow line segment  714   A  of the filling loop  714   A-D , thereby establishing fluid communication between the blender  108  and the first vessel  716   1 . In this configuration, the blender  108  may flow a solution to the first vessel  716   1  until an appropriate one of the sensors  717   1  (i.e., a high level sensor) indicates that the vessel is full, at which point the first filling loop valve is closed  720   1  and the vessel  716   1  may be pressurized by application of a gas to the pressurizing gas input  719   1 . Prior to and during filling the first vessel, the respective vent  721   1  may be open to allow the vessel to depressurize.  
      While the first vessel  716   1  is being filled, the filling station  702   1  may be configured such that the second vessel  716   2  is dispensing solution to one or more of the tools  708 . Accordingly, the second valve  720   2  is closed, the third valve  720   3  is open, and the fourth valve  720   2  is set to a position allowing fluid communication between the second vessel  716   2  and the processing tools  708  via the fourth flow line segment  714   D . During dispensation of solution, the second vessel may be under pressure by application of a pressurizing gas to the respective gas input  721   2.    
      Upon determining that the fluid level in second vessel  716   2  has reached a predetermined low level, as indicated by an appropriate low level sensor  717   2 , the filling station  702  may be configured to halt dispensation from the second vessel  716   2  and begin dispensation from the first vessel  716   1  by setting the valves of the first filling loop to appropriate positions. The second vessel  716   2  may then be depressurized by opening the respective vent  721   2 , after which the second vessel  716   2  may be filled by solution from the blender  108 .  
      The operation of the second filling station  702   2  is identical to the operation of the first filling station  702   1  and, therefore, will not be described in detail.  
      After filling a vessel in one of the filling stations  702   1-2 , the filling station will be capable of dispensing a solution to one or more of the tools  708  for a period of time. During this time, the flow control unit  706  may be operated to place the blender  108  in fluid communication with the other filling station. It is contemplated that the vessels of the filling stations may be sized in capacity such that, for given flow rates into and out of the filling stations, the blender  108  may refill one of the vessels of one of the filling stations before the standby vessel of the other filling station is depleted. In this way, solution dispensation from the filling stations may be maintained with no interruption, or substantially no interruption.  
      Reclamation Systems  
      As noted above, in one embodiment of the present invention, fluids removed from processing stations (or, more generally, points of use) are reclaimed and reused. Referring now to  FIG. 8A , one embodiment of a reclamation system  800 A is shown. The reclamation system  800 A includes a number of components previously described with respect to  FIG. 4 , and those components are identified by like numbers and will not be described again in detail. Further, for clarity a number of items previously described have been removed. In general, the reclamation system  800 A includes the blender  108  and a plurality of tanks  802   1-N  (collectively tanks  802 ). The tanks  802  correspond to the tank  436  shown in  FIG. 4  and, therefore, each tank is fluidly coupled to a respective processing station (not shown) and may also be fluidly coupled to the vacuum pump subsystem  120  (not shown).  
      In one embodiment, the tanks  802  are configured to separate liquids from gases in the incoming liquid-gas streams. To this end, the tanks  802  may each include an impingement plate  828   1-N  at an inlet of the respective tanks. Upon encountering the impingement plate  828 , liquid is condensed out of the incoming fluid streams by operation of blunt force. The tanks  802  may also include demisters  830   1-N . The demisters  830  generally include an array of surfaces positioned at angles (e.g., approximately 90 degrees) relative to the fluid being flowed through the demister  830 . Impingement with the demister surfaces causes further condensation of liquid from the gas. Liquid condensed from the incoming stream is captured in a liquid storage area  832   1-N  at a lower portion of the tanks, while any remaining vapor is removed to the vacuum pump subsystem  120  (shown in  FIG. 1 ). In one embodiment, a degassing baffle  834   1-N  is positioned below the demisters, e.g., just below the impingement plates  828 . The degassing baffle extends over the liquid storage area  832  and forms an opening  836   1-N  at one end. In this configuration the degassing baffle allows liquid to enter the liquid storage area  832  via the opening  836 , but prevents moisture from the liquid from being reintroduced with the incoming liquid-gas stream.  
      Each of the tanks  802  is fluidly coupled to the blender  108  via a respective reclamation line  804   1-N  (collectively reclamation lines  804 ). Fluid flow is motivated from the tanks through their respective reclamation lines  804  by the provision of a respective pump  806   1-N  (collectively pump  806 ). Fluid communication between the tanks  802  and their respective pumps  806  is controlled by operation of pneumatic valves  808   1-N  (collectively valves  808 ) disposed in the reclamation lines  804 . In one embodiment, the pumps  806  are centrifugal pumps or suitable alternatives such as air operated diaphragm or bellows pumps.  
      In one embodiment, filters  810   1-N  (collectively filters  810 ) are disposed in each of the reclamation lines. The filters  810  are selected to remove debris from the reclaimed fluids prior to being introduced into the blender  108 . Although not shown, the filters may each be coupled to a flushing system configured to flow a flushing fluid (e.g., DIW) through the filters to remove and carry away the debris caught by the filters. Fluid flow into the filters and into the blender  108  may be managed (e.g., controlled and/or monitored) by the provision of one or more flow management devices. Illustratively, flow management devices  812   1-N ,  814   1-N  are disposed in the respective reclamation lines upstream and downstream of the filters. For example, in the illustrative embodiment, the upstream devices  812   1-N  are pneumatic valves (collectively valves  812 ) are disposed upstream of each of the filters  810 . Accordingly, the flow rates of the reclamation fluids may be controlled by operation of the pneumatic valves  812 . Further, the downstream devices  814   1-N  include pressure regulators and flow control valves to ensure a desired pressure and flow rate of the fluids being introduced to the blender  108 . Each of the flow management devices may be under the control of the controller  126  (shown in  FIG. 4 ).  
      Each of the reclamation lines  804  terminate at the primary supply line  404  of the blender  108 . Accordingly, each of the fluids flowed from the respective tanks may be streamed into and mixed with the solution being flowed through the primary supply line  404 . In one embodiment, the reclamation fluids are introduced upstream from a mixing station (e.g., mixer  642  described above with respect to  FIG. 6 ) disposed in line with the primary supply line  404 . Further, one or more concentration monitors  818  may be disposed along the primary supply line  404  downstream from the mixer  642 . Although only one concentration monitor is shown for convenience, it is contemplated that a concentration monitor is provided for each different chemistry being reclaimed, in which case the reclamation streams may be introduced into the primary supply line  404  at an appropriate point upstream from a respective concentration monitor for the particular stream. In this way, the concentration of a respective chemistry may be monitored at the respective concentration monitor. If the concentration is not within a target range, the blender  108  may operate to inject calculated amounts of the appropriate chemical(s) from the various inputs  402 . The resulting solution is then mixed at the mixer  642  and again monitored for concentration at the concentration monitor  818 . This process may be continued, while diverting the solution to drain, until the desired concentrations are achieved. The solution may then be flowed to the appropriate point of use.  
      In some configurations, the chemistries being used at each of the respective processing stations may always be the same. Accordingly, in one embodiment, the various reclamation lines  804  may be input to the appropriate point of use supply lines  410 ,  412 ,  414 , as is illustrated by the reclamation system  800 B shown in  FIG. 8B . Although not shown, concentration monitors may be disposed along each of the reclamation lines to monitor the respective concentrations of the reclamation streams being input to the point of use supply lines. Although not shown, mixing zones may be disposed along the point of use supply lines  410 ,  412 ,  414  to mix the incoming reclamation streams with the stream from the blender  108 . Also, suitable mixing of streams may be achieved by delivering the stream from the blender  108  and the respective reclamation streams at 180 degrees relative to each other. The incoming streams may be mixed at a T-junction coupling, whereby the resulting mixture is flowed toward the respective points of use at 90 degrees relative to the flow paths of the incoming streams.  
      Alternatively, it is contemplated to flow each of the reclamation fluids to a point upstream of the appropriate concentration monitor in the blender  108 , as is illustrated by the reclamation system  800 C shown in  FIG. 8C . For example, a reclaimed solution of diluted hydrofluoric acid from the first reclamation line  804   1  may be input downstream of a hydrofluoric acid input  402   1  and upstream of the first concentration monitor  406   1  configured to monitor the concentration of hydrofluoric acid. A reclaimed solution of SC-1 type chemistry from the second reclamation line  804   2  may be input downstream of the ammonium hydroxide input  402   2  and hydrogen peroxide input  402   3 , and upstream of the second and third concentration monitors  406   2 ,  406   N  configured to monitor the concentration of SC-1 type solution constituents. And so on. In one embodiment, distinguishing between various constituents in a mixture of multiple constituents, such as ammonium hydroxide and hydrogen peroxide, is possible by deriving an equation from process modeling using metrology signals and analytical results from titrations. The incoming chemical concentration to the process must be known; more specifically, the concentration of the fluid must be known before decompositions, escape of the NH 3  molecule, or formation of any resultant salts or by-products from the chemical processes occurring. In this way, the changing metrology can be observed and the change in components typical for that process can be predicted.  
      In each of the foregoing embodiments, the reclamation fluids may be filtered and monitored for appropriate concentrations. However, after some amount of time and/or some number of process cycles the reclaimed fluids will no longer be viable for their intended use. Accordingly, and the one embodiment, the solutions from the tanks  804  are only recirculated and reused for a limited time and/or a limited number of process cycles. In one embodiment, the process cycles are measured in number of wafers processed. Thus, in a particular embodiment, a solution of a given chemistry for a given process station is reclaimed and reused for N wafers, where N is some predetermined integer. After N wafers have been processed, the solution is diverged to drain.  
      It should be understood that the reclamation systems  800 A-C shown in FIGS.  8 A-C are merely illustrative of one embodiment. Persons skilled in the art will recognize other embodiments within the scope of the present invention. For example, in another embodiment of the reclamation systems  800 A-C, fluids may be alternatively routed from the tanks  802  to an off-board reclamation facility located, e.g., in the sub-fab. To this end, appropriate flow control devices (e.g., pneumatic valves) may be disposed in the respective reclamation lines  804 .  
      Vacuum Pump Subsystem  
      Referring now to  FIG. 9 , one embodiment of the vacuum pump subsystem  120  is shown. In general, the vacuum pump subsystem  120  may operate to collect waste fluids and separate gases from fluids to facilitate waste management. Accordingly, the vacuum pump subsystem  120  is coupled to each of the vacuum tanks  436 ,  438  (shown in  FIG. 4 ) and vacuum tank  802  (shown in  FIG. 8 ) by a vacuum line  902 . Thus, the vacuum line  902  may be coupled to the respective vacuum lines  444  and  446  shown in  FIG. 4 . Although not shown in  FIG. 9 , one or more valves may be disposed in the vacuum line  902  and/or the respective vacuum lines (e.g., lines  444  and  446  shown in  FIG. 4 ) of the vacuum tanks, whereby a vacuum may be selectively placed on the respective tanks. Further, a vacuum gauge  904  may be disposed in the vacuum line  902  in order to measure the pressure in the vacuum line  902 .  
      In one embodiment, an active pressure control system  908  is disposed in the vacuum line  902 . In general, the active pressure control system  908  operates to maintain a desired pressure in the vacuum line  902 . Controlling the pressure in this way may be desirable to ensure process control over processes being performed in the respective processing stations  204  (shown in  FIG. 4 , for example). For example, assuming a process being performed in a given processing station  204  requires that a pressure of 400 Torr be maintained in the vacuum line  902 , the active pressure control system  908  is operated under PID control (in cooperation with the controller  126 ) to maintain the desired pressure.  
      In one embodiment, the active pressure control system  908  includes a pressure transmitter  910  and a pressure regulator  912 , which are an electrical communication with each other. The pressure transducer  910  measures the pressure in the vacuum line  902  and then issues a signal to the pressure regulator  912 , causing the pressure regulator  912  to open or close a respective variable orifice, depending on a difference between the measured pressure and the set (desired) pressure.  
      In one embodiment, the vacuum placed on the vacuum line  902  is generated by a pump located downstream from the active pressure control system  908 . In a particular embodiment, the pump  914  is a liquid ring pump. A liquid ring pump may be particularly desirable because of its ability to safely handle surges and steady streams of liquids, vapors and mists. While the operation of liquid ring pumps is well-known, a brief description is provided here. It is understood, however, that embodiments of the present invention are not limited to the particular operational or structural aspects of liquid ring pumps.  
      In general, a liquid ring pump operates to remove gases and mists by the provision of an impeller rotating freely in an eccentric casing. The vacuum pumping action is accomplished by feeding a liquid, usually water (called sealant fluid), into the pump. In the illustrative embodiment, the sealant fluid is provided by a tank  906 , which is fluidly coupled to the pump  914  by a feed line  913 . Illustratively, a valve  958  is disposed in the feed line  913  in order to selectively isolate the tank  906  from the pump  914 . As the sealant fluid enters the pump during operation, the sealant fluid is urged against the inner surface of the pump  914  casing by the rotating impeller blades to form a liquid piston which expands in the eccentric lobe of the pump&#39;s casing, thereby creating a vacuum. When gas or vapor (from the incoming stream) enters the pump  914  at a suction port  907  of the pump  914 , to which the vacuum line  902  is coupled, the gas/vapor is trapped by the impeller blades and the liquid piston. As the impeller rotates, the liquid/gas/vapor is pushed inward by the narrowing space between the rotor and casing, thereby compressing the trapped gas/vapor. The compressed fluid is then released through a discharge port  909  as the impeller completes its rotation.  
      The pump  914  is connected at its discharge port  909  to a fluid flow line  915  which terminates at the tank  906 . In one embodiment, the tank  906  is configured to further separate liquids from gases in the incoming liquid-gas streams. To this end, the tank  906  may include an impingement plate  916  at an inlet of the tank  906 . Upon encountering the impingement plate  916 , liquid is condensed out of the incoming fluid streams by operation of blunt force. The tank  906  may also include a demister  920 . The demister  920  generally includes an array of surfaces positioned at angles (e.g., approximately 90 degrees) relative to the fluid being flowed through the demister  920 . Impingement with the demister surfaces causes further condensation of liquid from the gas. Liquid condensed from the incoming stream is captured in a liquid storage area  918  at a lower portion of the tank  906 , while any remaining vapor is removed through an exhaust line  924 . In one embodiment, a degassing baffle  922  is positioned below the demister, e.g., just below the impingement plate  916 . The degassing baffle  922  extends over the liquid storage area  918  and forms an opening  921  at one end. In this configuration the degassing baffle  922  allows liquid to enter the liquid storage area  918  via the opening  921 , but prevents moisture from the liquid from being reintroduced with the incoming liquid-gas stream.  
      In one embodiment, the sealant fluid contained in the tank  906  is heat exchanged to maintain a desired sealant fluid temperature. For example, in one embodiment it may be desirable to maintain the sealant fluid at a temperature below 10° C. To this end, the vacuum pump subsystem  120  includes a cooling loop  950 . A pump  937  (e.g., a centrifugal pump) provides the mechanical motivation to flow the fluid through the cooling loop  950 . The cooling loop  950  includes an outlet line  936  and a pair of return lines  962 ,  964 . The first return line  962  fluidly couples the outlet line  936  to an inlet of a heat exchanger  954 . The second return line  964  is coupled to an outlet of the heat exchanger  954  and terminates at the tank  906 , where the cooled sealant fluid is dispensed into the liquid storage area  918  of the tank  906 . Illustratively, a valve  960  is disposed in the second return line  964 , whereby the cooling loop  950  may be isolated from the tank  906 . In this way, the temperature controlled sealant fluid causes some vapor/mist to condense out of the incoming fluid and into the liquid of the sealant pump  914 .  
      In one embodiment, the heat exchanger  954  is in fluid communication with an onboard cooling system  952 . In particular embodiment, the onboard cooling system  952  is a Freon-based cooling system, which flows Freon through the heat exchanger  954 . In this context, “onboard” refers to the cooling system  953  being physically integrated with the heat exchanger  954 . In another embodiment, the cooling system  953  may be an “off-board” component, such as a stand-alone chiller.  
      During operation, sealant fluid may be circulated from the tank  906  through the cooling loop  950  on a continual or periodic basis. As the sealant fluid is flowed through the heat exchanger  954 , the fluid is cooled and then returned to the tank  906 . The heat exchange effected by the heat exchanger  954  (i.e., the temperature to which the sealant fluid is brought) may be controlled by operating the cooling system  952 . To this end, a temperature sensor  953  may be placed in communication with the sealant fluid contained in the liquid storage area  918  of the tank  906 . Measurements made by the temperature sensor  953  may be provided to the controller  126 . The controller  126  may then issue appropriate control signals to the cooling system  952 , thereby causing the cooling system  952  to adjust the temperature of the Freon (or other cooling fluid being used). It is also contemplated that the sealant fluid in the liquid storage area  918  may in part be cooled by thermal exchange with the ambient environment of the tank  906 . In this way, the sealant fluid may be maintained at a desired temperature.  
      In one embodiment, cooled sealant fluid from the cooling loop  950  may be injected into the vacuum line  902  upstream from the liquid ring pump  914 . Accordingly, the vacuum pump subsystem  120  includes a feed line  957  shown branching from the second return line  964 . A valve  956  is disposed in the feed line  957 , whereby fluid communication between the cooling loop  950  and the vacuum line  902  may be established or disconnected. While the valve  956  remains open, a portion of the cooled sealant fluid flows from the cooling loop  950  into the vacuum line  902 , via the feed line  957 . Thus, the cooled sealant fluid enters a stream of gas/liquid flowing through the vacuum line  902  towards the liquid ring pump  914 . In this way, the relatively low temperature cooled sealant fluid causes some vapor or mist to condense out of the incoming gas/liquid stream prior to entering the pump  914 . In one embodiment, for a temperature of the incoming stream (from the vacuum tanks via the vacuum line  902 ) between about 80° C. and about 10° C., the temperature of the cooled sealant fluid may be between about 5° C. and about 10° C.  
      In one embodiment, the vacuum pump subsystem  120  is configured to monitor one more concentrations of constituents in the sealant fluid. Monitoring chemical concentrations may be desirable, for example, to protect any (e.g., metal) components of the liquid ring pump  914 , and/or other components of the vacuum pump subsystem  120 . To this end, the system  120  shown in  FIG. 9  includes an active chemical concentration control system  940  disposed in the cooling loop  950 . In the illustrative embodiment, the concentration control system  940  includes a chemical monitor  942  in electrical communication with a pneumatic valve  944 , as shown by the bidirectional communication path  945 . It should be appreciated, however, that the pneumatic valve  944  may not communicate directly with one another, but rather through the controller  126 . During operation, the chemical monitor  942  checks the concentration of one or more constituents of the sealant fluid flowing through the outlet line  936 . If a set point of the chemical monitor  942  is exceeded, the chemical monitor  942  (or the controller  126  in response to the signal from the chemical monitor  942 ) issues a signal to the pneumatic valve  944 , whereby the pneumatic valve  944  opens communication to a drain line  938  in order to allow at least a portion of the sealant fluid to drain. In the illustrative embodiment, a check valve  939  is disposed in the drain line  938  to prevent backflow of fluids. Further, a back pressure regulator  946  is disposed in the drain line  938 , or at a point upstream from the drain line. The back pressure regulator  946  ensures that a sufficient pressure is maintained in the cooling loop  950 , thereby allowing continued flow of sealant fluid through the cooling loop  950 .  
      In one embodiment, the tank  906  is selectively fluidly coupled to one of a plurality of different drains. A particular one of the plurality of drains is then selected on the basis of the make-up (i.e., constituents or concentrations) of the sealant fluid. For example, in the case of a sealant fluid containing a solvent the sealant fluid may be directed to a first drain, while in the case of a non-solvent the sealant fluid may be directed to a second drain. In at least one aspect, this embodiment may serve to avoid deposits being built up in a given drain line that might otherwise occur where, for example, solvents and non-solvents are disposed of through the same drain. Accordingly, it is contemplated that the sealant fluid can be monitored for independent formations of chemical solution such as HF, NH3, HCL or IPA. Each of these chemical solutions can be directed a separate drain (or, some combinations of the solutions may be directed separate drains). In one embodiment, this can be accomplished using a sound velocity sensor to measure the changing density of the solution in the tank  906 .  
      While the tank  906  is being drained (and, more generally, at any time during operation of the system  120 ), a sufficient level of sealant fluid may be maintained in the tank  906  by provision of an active level control system  928 . In one embodiment, the active level control system  928  includes a pneumatic valve  944  disposed in an input line  926 , and a plurality of fluid level sensors  934   1-2 . The fluid level sensors may include, for example, a high level fluid sensor  934   1  and a low level fluid sensor  934   2 . The pneumatic valve  944  and the plurality of fluid level sensors  934   1-2  are in electrical communication with each other via the controller  126 , as indicated by the dashed communication path  932 . In operation, the fluid level in the tank  906  may fall sufficiently to trip the low fluid level sensor  934   2 . In response, the comptroller  126  issues a control signal causing the pneumatic valve  930  to open and allow communication between a first sealant fluid source  970  (e.g., a source of deionized water (DIW)) with the tank  906  via the inlet line  926 . Once the fluid in the tank  906  is returned to a level between the high and low level sensors  934   2 , the pneumatic valve  930  is closed.  
      In addition to maintaining a sufficient level of sealant fluid in the tank  906  while the tank is being drained, the active level control system may also initiate a drain cycle in response to a signal from the high fluid level sensor  934   2 . In other words, should the fluid level in the tank  906  rise sufficiently high to trip the high fluid level sensor, the sensor then issues a signal to the controller  126 . In response, the controller  126  issues a signal causing the pneumatic valve  944  to open and allow sealant fluid flow to the drain line  938 .  
      Further, it is contemplated that the tank  906  may be coupled to any number of sealant fluids or additives. For example, in one embodiment the tank  906  is coupled to a neutralizer source  972 . The neutralizer may be selected to neutralize various constituents of the incoming steam from the vacuum tanks via the vacuum line  902 . In a particular embodiment, the neutralizer is acidic or basic, and is capable of neutralizing bases or acids, respectively. The neutralizer from the neutralizer source  972  may be selectively introduced to the tank  906  by coupling the source  972  to the inlet line  926  at a valve  974 . The valve  974  may be configured such that one or both of the sources  970 ,  972  may be placed in fluid communication with the tank  906 .  
      Various embodiments of a chemical management system have been described herein. However, the disclosed embodiments are merely illustrative and persons skilled in the art will recognize other embodiments within the scope of the invention. For example, a number of the foregoing embodiments provide for a blender  108  which may be located onboard or off-board relative to a processing tool; however, in another embodiment, the blender  108  may be dispensed with altogether. That is, the particular solutions required for a particular process may be provided in ready to use concentrations that do not require blending. In this case, source tanks of the particular solutions may be coupled to the input flow control subsystem  112 , shown in  FIG. 1  for example.  
      Accordingly, it is apparent that the present invention provides for numerous additional embodiments, which will be recognized by those skilled in the art, and all of which are in the scoped of the present invention.