SYSTEM AND METHOD FOR BLENDING, MONITORING AND DISPENSING CHEMICAL

MIXTURES

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001 ] This application claims priority from U.S. Provisional Application No. 61/002,894, filed November 13, 2007, entitled, "SYSTEM AND METHOD FOR BLENDING, MONITORING AND DISPENSING CHEMICAL MIXTURES," which is incorporated herein by reference for all purposes.

TECHNICAL FIELD OF THE DISCLOSURE

[0002] The present invention relates generally to liquid dispensing in semiconductor manufacturing processes and, more particularly, to a low cost system and method of blending, monitoring, and dispensing multi-component chemical mixtures in semiconductor manufacturing processes.

BACKGROUND OF THE RELATED ART

[0003] The semiconductor industry uses various chemical formulations to clean silicon wafers during the manufacturing process. Many of the formulation recipes include chemicals that have a limited lifetime due to decomposition, particularly when repeatedly pressurized and de-pressurized. Hydrogen peroxide (H ₂ O ₂ ) is one of these more unstable chemicals.

[0004] H ₂ O ₂ is a constituent of both "standard clean" formulations referred to as "SC1 " and "SC2" in the industry. SC1 is used to remove particles from wafers and SC2 is used to remove metals from wafers. SC1 is a formulation of ammonium hydroxide (NH ₄ OH), hydrogen peroxide (H ₂ O ₂ ), and ultrapure water (UPW). Hydrogen peroxide is mixed with hydrochloric acid (HCI) and UPW in the SC2 formulation.

[0005] A chemical blending system that can create these formulations is described in detail in U.S. Patent No. 6,799,883. This prior chemical blending system introduces

chemicals into a stream one at a time at discrete mixing zones. One piece of instrumentation downstream of each mixing zone is required to measure the effect of the chemical added at each mixing zone. Complex calibration methods are required when either conductivity, ultrasonic, or index of refraction based concentration metrologies are used. The complex calibration methods are necessary because no one concentration measurement can uniquely identify the composition of the output fluid. This prior chemical blending system also requires a means to simultaneously increase one fluid flow rate while reducing the other in order to maintain a constant overall flow rate.

[0006] A chemical mixing system that can mix all of the constituent chemicals for the recipes into a tank is described in U.S. Patent No. 7,281 ,840. In this prior chemical mixing system, the mixture is recirculated. The tank is heated to elevate the blend temperature. The mixture composition is monitored by a concentration measurement device and compared to a target composition using a microprocessor-based controller. The relative amounts of the component chemicals are adjusted by metering in more or less of the component chemicals.

[0007] The prior chemical mixing system described in U.S. Patent No. 7,281 ,840 requires an expensive chemical monitoring system such as near infra-red (NIR) spectroscopy that can differentiate the relative amounts of chemicals in a multi-component chemical mixture. Another drawback is that NIR tools require significant processing power, which consequently increases the time before a correction to the blend can be made. This prior chemical mixing system also heats and recirculates the entire mixture, which will tend to degrade the composition due to H ₂ O ₂ outgassing.

[0008] Dispensing chemical mixtures in semiconductor manufacturing processes requires great precision, uniformity, and consistency. Consequently, there is always room for improvement.

SUMMARY

[0009] Embodiments disclosed herein provide systems and methods of blending, monitoring, and dispensing multi-component chemical mixtures, which can be particularly useful in semiconductor manufacturing processes. In a chemical mixing system, one or more chemicals may need to be replenished from time to time. As one of ordinary skill in the art can appreciate, some chemicals are more volatile or unstable than the others. The volatility of chemicals in a mixing system can make it difficult to control and maintain the quality of the resulting mixture. Examples of volatile chemicals include hydrogen peroxide (H ₂ O ₂ ). H ₂ O ₂ is a weak acid and can readily decompose into water and oxygen. Thus, a chemical mixing system generally needs to replenish H ₂ O ₂ that cycles through the system. In some applications, some or all of the chemicals in the system are heated, which makes the situation worse as the elevated temperature may accelerate the H ₂ O ₂ decomposition process. As a result, even more H ₂ O ₂ would need to be added. In prior chemical mixing systems, replenishing H ₂ O ₂ is generally done by dosing H ₂ O ₂ into the systems based on trial and error experience.

[0010] Embodiments disclosed herein provide a new solution to blend, monitor, and dispense multi-component chemical mixtures in a controlled and efficient manner. This new solution can prevent a volatile chemical from decomposing prematurely by introducing that chemical at the very last stage before dispensing. Within this disclosure, H ₂ O ₂ is used as an example of a volatile chemical. However, one of ordinary skill in the art can appreciate that embodiments disclosed herein may be implemented or otherwise adapted for chemical mixing systems that utilize various volatile chemicals. Within this disclosure, "volatile chemicals" may refer to chemicals that are unstable, readily decomposable, or easily dissociated due to a change in the environment such as temperature, pressure, etc.

[001 1 ] In embodiments disclosed herein, H ₂ O ₂ is introduced into a mixture of two or more chemicals right before dispensing. These two or more chemicals are considered relatively more stable than H ₂ O ₂ . In embodiments disclosed herein, chemicals that are not as volatile as H ₂ O ₂ are introduced into a recirculation loop. In some embodiments, the recirculation loop is heated or cooled to a desired target temperature. In some embodiments, the mixture of chemicals is directed from the recirculation loop to a mixing manifold. H ₂ O ₂ may be introduced into the heated

mixture of chemicals in the mixing manifold. The final multi-component chemical mixture may then be dispensed through a plurality of dispense points. In some embodiments where the final mixture is a SC1 formulation, hydrogen peroxide (H ₂ O ₂ ) is introduced into a mixture of ammonium hydroxide (NH ₄ OH) and ultrapure water (UPW). In some embodiments where the final mixture is a SC2 formulation, H ₂ O ₂ is mixed with hydrochloric acid (HCI) and UPW before dispensing.

[0012] In some embodiments, a chemical mixing system may comprise a mixing manifold, a first flow path to the mixing manifold and a second flow path to the mixing manifold. The first flow path may comprise a first flow controller coupled to a pressurized source of a first chemical for supplying a first controlled flow of the first chemical to the mixing manifold. The second flow path may comprise a recirculation loop and a flow meter for supplying a second controlled flow of a mixture of two or more chemicals to the mixing manifold. In some embodiments, the recirculation loop may comprise a heat exchanger for heating or cooling the mixture to a target temperature and a conductivity sensor for sensing a conductivity of the mixture.

[0013] In some embodiments, a chemical mixing system may comprise a tank, a recirculation loop, a mixing manifold, and a dispense manifold. In some embodiments, the tank is coupled to a first flow controller, a second flow controller, and the recirculation loop. In some embodiments, the recirculation loop comprises a pump, a heat exchanger coupled to the pump, and a recirculation flow controller. In some embodiments, the first flow controller, the second flow controller, and the recirculation flow controller are inline flow controllers. In embodiments disclosed herein, all chemicals except the volatile chemical(s) are mixed before entering the recirculation tank. In some embodiments, the fluid dispense rate, concentration, and temperature can be controlled by the pump speed, flow controller flow rates, and heat exchanger flow rates and temperature. In some embodiments, the heat exchanger is in fluidic communication with the mixing manifold. In some embodiments, the mixing manifold is coupled to the dispensing manifold. In some embodiments, the dispensing manifold is coupled to a plurality of point of use (POU) dispense points.

[0014] In some embodiments, a method of mixing chemicals for dispensing in a semiconductor manufacturing process may comprise mixing ultra pure water and a chemical solution in a recirculation loop. In some embodiments, the recirculation

loop is temperature-controlled and conductivity controlled to produce a first mixture having a first temperature and a first conductivity. The method may further comprise directing the first mixture to a mixing chamber via a first flow path and directing a second chemical having a second temperature and a second conductivity to the mixing chamber via a second flow path. In some embodiments, the method may further comprise directing one or more additional chemicals to the mixing chamber. In some embodiments, the mixing chamber is pressured. In some embodiments, the mixing chamber is part of a mixing manifold. In some embodiments, the mixing manifold is coupled to a dispensing manifold. In some embodiments, the method may further comprise dispensing a final mixture onto a plurality of wafers via a plurality of point of use dispensing points coupled to the dispense manifold. In some embodiments, the second chemical is hydrogen peroxide. In some embodiments, the final mixture is a SC1 formulation. In some embodiments, the final mixture is a SC2 formulation.

[0015] Embodiments disclosed herein can provide many advantages. For example, in prior chemical mixing systems, a near-infrared (NIR) sensor may be utilized to monitor the conductivity of the chemical mixture. Horiba CS-150 Series Concentration Monitors are examples of NIR systems using NIR sensors. By isolating H ₂ O ₂ from the rest of the chemicals, a low cost conductivity sensor can be utilized in embodiments disclosed herein to monitor the conductivity of the mixture of chemicals that are not as volatile. Horiba HE-480C Conductivity Meter is an example system using conductivity sensors. This can mean a significant saving because a NIR sensor may cost ten times more than a conductivity sensor. By isolating H ₂ O ₂ from the rest of the chemicals, the cost of heating the chemicals can also be reduced. This has an additional benefit of preventing H ₂ O ₂ from being affected by temperature disturbances. The recirculation loop can provide accurate concentration and temperature control which can lead to the use of less chemicals which, in turn, means embodiments disclosed herein can generate less waste. Some embodiments may be coupled to a facility supplied line, which can be unregulated. In embodiments disclosed herein, the flow and concentration can be advantageously isolated from the facility supplied line pressure disturbances. Furthermore, some embodiments may provide a wide range of flow rates in a single configuration.

[0016] These, and other, aspects will be better appreciated and understood when considered in conjunction with the following description and the accompanying

drawings. The following description, while indicating various embodiments and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions or rearrangements may be made within the scope of the disclosure, and the disclosure includes all such substitutions, modifications, additions or rearrangements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the inventive aspects of this disclosure will be best understood with reference to the following detailed description, when read in conjunction with the accompanying drawings, in which:

[0018] FIGURE 1 depicts a simplified block diagram of one embodiment of a chemical mixing system;

[0019] FIGURE 2 depicts a representative configuration of one embodiment of a chemical mixing system; and

[0020] FIGURE 3 depicts a representative configuration of one embodiment of a chemical mixing system with flow paths and electronic paths.

DETAILED DESCRIPTION

[0021 ] The invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well known starting materials, processing techniques, components and equipment are omitted so as not to unnecessarily obscure the disclosure in detail. Skilled artisans should understand, however, that the detailed description and the specific examples, while disclosing preferred embodiments, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions or rearrangements within the scope of the underlying inventive concept(s) will become apparent to those skilled in the art after reading this disclosure.

[0022] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, product, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0023] Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized encompass other embodiments as well as implementations and adaptations thereof which may or may not be given therewith or elsewhere in the specification and all such embodiments are intended to be included within the scope of that term or terms. Language designating such non-limiting examples and illustrations includes, but is not limited to: "for example," "for instance," "e.g.," "in one embodiment," and the like.

[0024] Reference is now made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts (elements).

[0025] Embodiments disclosed herein provide a low cost system and method of blending, monitoring, and dispensing multi-component chemical mixtures in semiconductor manufacturing processes. FIG. 1 is a simplified diagrammatical representation of one embodiment of system 10 for blending, monitoring, and dispensing chemical mixtures useful in a semiconductor manufacturing process. As FIG. 1 exemplifies, Fluid 1 and Fluid 2 are mixed in Recirculation Loop 60 to produce Mixture 70 of Fluid 1 and Fluid 2. Mixture 70 is directed to Mixing Manifold 80 via a first flow path. Fluid 3 is directed to Mixing Manifold 80 via a second flow path that is separate from the first flow path. Fluid 1 , Fluid 2, and Fluid 3 are then mixed in Mixing Manifold 80 to

produce Mixture 85. Fluid 1 and Fluid 2 contain chemicals that are considered relatively stable than Fluid 3. One example of a volatile chemical contained in Fluid 3 is hydrogen peroxide (H ₂ O ₂ ). One example of Fluid 1 is ultra pure water (UPW). Depending upon what final formulation is desired, Fluid 2 may contain NH ₄ OH, HCI, HF, or other chemicals that are less volatile than H ₂ O ₂ . Exemplary components of system 10 are described in detail below with reference to FIG. 2.

[0026] In some embodiments, system 10 comprises components located in separate locations. In the example of FIG. 1 , Recirculation Loop 60 is located at Location A and Mixing Manifold 80 is located at Location B. This is possible because, in some embodiments, hydrogen peroxide is isolated and handled separately from the rest of the chemicals that are considered relatively more stable. In some embodiments, Location A can house components of system 10 that handle relatively more stable chemicals and be remote from Location B. Location B can house components of system 10 that handle relatively more volatile chemicals and be local to dispensing points. As an example, Location A might be in the subfab area and Location B might be in the fab area such as a semiconductor manufacturing cleanroom. The separation of system 10 components can be significant and can provide additional advantages over prior chemical systems. For example, system 10 can significantly reduce the footprint required in the fab area/cleanroom, which can be very expensive to construct and/or maintain.

[0027] As one skilled in the art can appreciate, the setup of system 10 shown in FIG. 1 can be implemented in various ways. For example, in some embodiments, additional one or more volatile chemicals may be directed via additional flow path(s) directly to Mixing Manifold 80 prior to dispensing.

[0028] FIG. 2 is a diagrammatical representation of one embodiment of system 10 for blending, monitoring, and dispensing chemical mixtures. In the example shown in FIG. 2, system 10 includes a closed loop with temperature and concentration control in which all chemicals except volatile chemical(s) are mixed into and pumped from a recirculation tank. In FIG. 2, Fluid 1 is supplied by Pressurized Source 1 1 to Tank 20 and Fluid 2 is supplied by Pressured Source 12 to Tank 20. Tank 20 may be coupled to Level Sensor 35, Vent Valve 24 and to Drain 40 via Drain Valve 41 . Level Sensor 35, Vent Valve 24 and Drain Valve 41 may operate in a manner known to those skilled in the art and thus are not further described herein.

[0029] In some embodiments, Mixture 70 of Fluid 1 and Fluid 2 are directed to Mixing

Manifold 80 via a first flow path. In some embodiments, the first flow path includes Recirculation Loop 60. In some embodiments, Recirculation Loop 60 comprises Conductivity Sensor 25 positioned between Tank 20 and Pump 30 for sensing a conductivity of Mixture 70 of Fluid 1 and Fluid 2. Sensing the conductivity of a mixture and not the concentration of individual chemicals in the mixture can be useful if only one chemical contributes to the conductivity of the mixture.

[0030] In some embodiments, Pump 30 is positioned between Tank 20 and Heat Exchanger 50 for pumping Mixture 70 of Fluid 1 and Fluid 2 from Tank 20 to Heat Exchanger 50. In some embodiments, Heat Exchanger 50 implements a flow arrangement in which Heat Transfer Fluid 54 enters Heat Exchanger 50 via inlet 52 and exits Heat Exchanger 50 via outlet 53 as controlled by Throttling Valve 51 . In this arrangement, Heat Transfer Fluid 54 does not mix with Mixture 70 of Fluid 1 and Fluid 2. One example of Heat Transfer Fluid 54 is water, which may be cold or hot. Other types of liquids may also be used to heat or cool Mixture 70 of Fluid 1 and Fluid 2. As one skilled in the art can appreciate, other types of heat exchangers may be utilized. For example, Heat Exchanger 50 may be an electric heater with coils. In this case, Heat Transfer Fluid 54, inlet 52, outlet 53, and Throttling Valve 51 would not be necessary. In some embodiments, Heat Exchanger 50 may have its own flow rate and temperature controls.

[0031 ] In some embodiments, Temperature Sensor 65 is positioned in Recirculation Loop 60 downstream from Heat Exchanger 50 for sensing the temperature of Mixture 70 coming from Heat Exchanger 50. In some embodiments, Filter 60 may be positioned in Recirculation Loop 60 between Heat Exchanger 50 and Temperature Sensor 65. In some embodiments, Recirculation Flow Controller 31 is positioned in Recirculation Loop 60 downstream from Temperature Sensor 65 for controlling the flow of Mixture 70 circulating back to Tank 20.

[0032] In some embodiments, the first flow path further includes a series of valves, including Check Valve 71 and Pneumatic Valve 72, and Flow Meter 73. As Mixture 70 is directed to Mixing Manifold 80 via the first flow path, Fluid 3 is directed to Mixing Manifold 80 via the second flow path as controlled by Flow Controller 23. In some embodiments, Fluid 3 is supplied by Pressured Source 13 separate from Pressurized Sources 1 1 and 12. Mixture 70 and Fluid 3 are then mixed in Mixing Manifold 80 to

produce Mixture 85. Additional teachings on a mixing manifold can be found in U.S. Patent No. 5,839,828 by Glanville, which is incorporated herein by reference. In some embodiments, Mixture 85 is directed to Dispense Manifold 90 for dispensing onto wafers via Dispense Valves 92 and Point of Use (POU) Dispense Points 93 and regulated using measurements taken from Pressure Sensor 95. In some embodiments, Vent Valve 91 may be coupled to Dispense Manifold 90 and Drain 40.

[0033] In some embodiments, system 10 can mix three fluids (Fluid 1 , Fluid 2, and Fluid 3) to supply one to twelve POU Dispense Points 93. As a specific example, Fluid 1 may be ultra pure water (UPW), Fluid 3 may be H ₂ O ₂ , and Fluid 2 may contain NH ₄ OH, HCI, HF, or other chemical(s) depending upon a formulation of Mixture 85 desired. In some embodiments, system 10 may be useful for mixing SC1 , SC2, and dilute HF chemistries in a wide range of mix ratios. In some embodiments, the fluid dispense rate, concentration and temperature can be controlled via the pump speed, the flow controller flow rates, and the heat exchanger flow rates and temperature.

[0034] FIG. 2 exemplifies a combination tank recirculation loop and inline flow controlled configuration where blending of chemicals with various levels of volatility can be accomplished. More specifically, chemicals that are the least likely to decompose due to outgassing (e.g., NH ₄ OH, HCI, HF) can be blended and heated or cooled within the recirculation loop. Chemicals that are more likely to decompose due to outgassing (e.g., H ₂ O ₂ ) can be blended inline to the distribution point. Two factors drive isolating the dilution of H ₂ O ₂ from a tank recirculation loop. First, H ₂ O ₂ readily decomposes in a recirculation loop. Second, H ₂ O ₂ does not readily dissociate in UPW. For additional discussion on H ₂ O ₂ decomposition, readers are directed to an article by Terri Couteau et al., "Dilute RCA Cleaning Chemistries," Semiconductor International, October 1998, which is incorporated herein by reference.

[0035] In one embodiment of system 10, H ₂ O ₂ can be isolated from long exposures to elevated temperatures and pressurization cycles that would cause H ₂ O ₂ to outgass. The flow through the pump and heat exchanger returning back into the tank represents a recirculation loop with repeated pressurization and de-pressurization cycles. In embodiments disclosed herein, the heat exchanger can be an efficient, high surface area heat exchanger, requiring low energy consumption. Moreover, the heat exchanger can use readily available facility supplied hot water as the heating medium, which has an additional benefit of reducing the overall cost of ownership.

[0036] Isolating H ₂ O ₂ from the tank recirculation loop prevents the lower cost conductivity metrology from measuring the H ₂ O ₂ concentration via the tank recirculation loop. However, this is acceptable in some applications as the low dissociation of H ₂ O ₂ in UPW prevents effective measurement of the concentration of H ₂ O ₂ through fluid conductivity. More likely, the conductivity measured in H ₂ O ₂ is the result of additives and contaminants in the H ₂ O ₂ , not the dissociated H ₂ O ₂ . The remaining chemicals of SC1 and SC2 (NH ₄ OH and HCI, respectively) more readily dissociate in UPW. Thus, the measured conductivity of the solution in the recirculation loop can correlate directly to the concentration of the more conductive species resulting from NH ₄ OH and HCI.

[0037] FIG. 3 depicts a representative configuration of one embodiment of a chemical mixing system with flow paths and electronic paths. As FIG. 3 illustrates, Controller 100 can be programmed to control the concentration of H ₂ O ₂ by the relative flow rates of the H ₂ O ₂ via Flow Controller 23 and the fluid leaving the recirculation loop via Flow Meter 73. For example, an SC2 recipe is typically defined in terms of a volumetric ratio of chemicals as received by the customer. HCI and H ₂ O ₂ are typically delivered as 37% and 30% by weight dilutions in UPW, respectively. An SC2 recipe of 1 :1 :5 would require mixing 1 part 37% HCI to 1 part 30% H ₂ O ₂ to 5 parts UPW by volume. Flow Controller 23 for Fluid 3 (H ₂ O ₂ in this example) would then be set to 1/6 ^th of the flow rate indicated by Flow Meter 73 upstream of Mixing Manifold 80. In this example, the sum of the HCI and UPW mixture would be 6 parts in 7 of the total volumetric flow and the H ₂ O ₂ flow rate would be 1 part in 7. Therefore, the H ₂ O ₂ flow rate relative to the HCI and UPW mixture would be (1/7) divided by (6/7). This flow rate weighted methodology may potentially reduce the accuracy of the H ₂ O ₂ proportion in the blend stream with respect to a more direct measurement of H ₂ O ₂ concentration such as NIR. However, at least one published research by M. M. Heyns et. al., "Cost Effective Cleaning and High Quality Thin Gate Oxides," IBM Journal of Research and Development, Vol. 43, No. 3, May 1999, which is incorporated herein by reference, has indicated that H ₂ O ₂ levels are not as critical as HCI in SC2, and NIR tools are both slower and more costly than conductivity based tools. According to M. M. Heyns et. al., particle cleaning effectiveness may be independent to H ₂ O ₂ concentration levels.

[0038] Embodiments disclosed herein provide many advantages over prior chemical mixture dispensing systems. For example, temperature of the chemical mixture can be

controlled via a low-cost, high efficiency heat exchanger in a closed, recirculation loop, which agitates the base chemical and keeps the fluid well-mixed. The combination of a high efficiency heat exchanger with readily available hot water and a recirculation loop prevents the installation of a significantly overcapacity electric heater, normally used in single pass applications. The recirculation loop serves to control pressure and temperature, allowing the fluid to warm up in a relatively short time (e.g., several minutes) to a desired temperature (e.g., 70 ^< €). Isolating H ₂ O ₂ from the recirculation loop allows the use of a conductivity sensor for measuring the conductivity of the base chemical. In addition to costing significantly less than an NIR sensor, a conductivity sensor has an additional benefit of fast response time once the fluid is brought to the desired temperature.

[0039] The exemplary system configuration disclosed herein may have an additional advantage of isolating the flow and concentration measurements from UPW line pressure disturbances. It is common in semiconductor processing facilities to see large swings in UPW pressure, indicative of the intermittent demand placed on the facility UPW system. Moreover, in some embodiments, a single system configuration may cover all the required flow rates for up to twelve ports. This can be done, in one embodiment and as an example, by sizing the H ₂ O ₂ IFC based on the full range of the point of use (POU) dispense manifold (e.g., all 12 ports are open), taking into consideration whether any affect to the POU distribution manifold flow balance would be acceptable. This would be a less costly method to mix at the point of use over conventional systems that would require the use of multiple liquid flow controllers to cover the flow range and chemical concentration desired.

[0040] Embodiments disclosed herein can supply multiple POU dispense points that are intermittently turned on and off as required by the manufacturing process. Various methodologies may be implemented to accomplish this. For example, the pump speed and recirculation flow rate can be used to maintain a nearly constant pressure within the dispense manifold as POU dispense ports are open and closed. Additionally, the flow rate from each dispense port orifice can be uniquely determined by the pressure drop across the orifice. In the case where the discharge is at a constant pressure, regulating the pressure inside the manifold will maintain the flow rate nearly constant at open ports as other ports are opened and closed. The dispense points may have different conduit lengths from the manifold discharge

ports. As a result, in some embodiments, needle valves (or comparable throttling valves) may be utilized to equilibrate flow rates between POU dispense points.

[0041 ] Regulation of the manifold pressure can be achieved various ways. One approach would use a gas filled pressure reservoir coupled to the dispense manifold. The pressure within the reservoir would prevent a large drop in pressure when a dispense valve is rapidly opened or closed by absorbing the dispensed liquid displacement. FlexOber series pulsation dampers from PulseGuard, Inc. are examples of pressurized dampers.

[0042] A second approach would use a pressure sensor inside the dispense manifold as a feedback mechanism to adjust the pump speed in order to maintain constant manifold pressure. Those skilled in the art would be able to program a controller, such as a programmable logic controller (PLC) or a similar controller, to adjust the pump speed coincidently with the dispense ports opening and closing.

[0043] The prior chemical blending system described in U.S. Patent No. 6,799,883 derives concentrations from cumulative indirect measurements of species concentrations. Embodiments disclosed herein utilize a single measurement that is directly correlated to the concentration of the conductive chemical in the recirculation loop. An additional benefit is that the measurement can be obtained using a conductivity sensor, which costs significantly less.

[0044] The prior chemical blending system described in U.S. Patent No. 6,799,883 is also subject to flow disturbances if connected directly to readily available facility UPW supplies. In embodiments disclosed herein, the UPW supply is isolated from the point-of-use (POU). This arrangement advantageously reduces the flow fluctuations caused by pressure disturbances when facility UPW valves are opened and/or closed upstream of the mixing system.

[0045] U.S. Patent No. 7,281 ,840 limits the shelf life of H ₂ O ₂ by including it within a recirculation loop. Embodiments disclosed herein isolate H ₂ O ₂ outside of the recirculation loop, thus reducing H ₂ O ₂ material waste. Embodiments disclosed herein can also reduce waste of the conductive chemicals as compared to U.S. Patent No. 6,799,883 which sends the output flow to the waste drain until the required formulation of the complete mixture is achieved.

[0046] The prior chemical mixing system describe in U.S. Patent No. 7,281 ,840 requires an expensive and slow responding chemical monitoring system such as near infra-red (NIR) spectroscopy that can differentiate the relative amounts of chemicals in a multi- component chemical mixture. Embodiments disclosed herein utilize inexpensive and faster responding technology such as electrodeless conductivity sensors.

[0047] Embodiments of a system and method for blending, monitoring and dispensing chemical mixtures have now been described in detail. Further modifications and alternative embodiments of various aspects of the disclosure will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the disclosure. It is to be understood that the forms of the disclosure shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for or implemented from those illustrated and described herein, as would be apparent to one skilled in the art after having the benefit of the disclosure. Changes may be made in the elements or to the features described herein without departing from the spirit and scope of the disclosure as set forth in the following claims and their legal equivalents.