Optimizing operating conditions in a reduction device

Abstract

A method of optimizing operating conditions in an abatement apparatus configured to treat an effluent stream from a process tool and an abatement apparatus are disclosed. The method of optimizing operating conditions in an abatement apparatus configured to treat an effluent stream from a process tool containing PFCs includes varying an operating parameter that controls an operating condition of the abatement apparatus, determining a change in PFC concentration present in the effluent stream of the abatement apparatus, and determining whether to retain the operating parameter based on the change in PFC concentration. In this way, the concentration of PFCs present in the effluent can be used to determine whether the abatement apparatus is operating at the correct operating conditions.

Description

TECHNICAL FIELD

[0001] The field of the invention relates to a method of optimizing operating conditions in an abatement apparatus configured to treat an effluent stream from a process tool and an abatement apparatus. BACKGROUND

[0002] Abatement apparatuses are known and are commonly used to treat effluent gas streams from process tooling used in, for example, the semiconductor or flat panel display manufacturing industries. During such manufacturing, residual perfluorinated compounds (PFCs) and other compounds are present in the effluent gas stream pumped from the process tool. PFCs are difficult to remove from the effluent gas and their release into the environment is undesirable as they are known to have a relatively high greenhouse effect.

[0003] Known abatement apparatuses, such as radiant burners, use combustion to remove PFCs and other compounds from the effluent gas stream to meet a particular destruction rate efficiency (DRE). Typically, the effluent gas stream is a nitrogen gas stream containing PFCs and other compounds. A fuel gas and an oxidant gas are mixed with the effluent gas stream and the gas stream mixture is delivered to a combustion chamber which is laterally surrounded by an outlet surface of a perforated gas burner. The fuel gas and air are simultaneously supplied to the perforated burner to achieve flameless combustion at the outlet surface, with the amount of air passing through the perforated burner being sufficient to consume not only the fuel gas supplied to the burner but also all combustibles in the gas stream mixture injected into the combustion chamber.

[0004] Despite the existence of techniques for treating effluent gas streams, they each have their own drawbacks. It is therefore desirable to provide an improved technique for treating effluent gas streams. SUMMARY

[0005] According to a first aspect, there is provided a method of optimizing operating conditions in an abatement apparatus configured to treat an effluent stream containing PFCs from a process tool, the method comprising: varying an operating parameter which controls an operating condition of the abatement apparatus; determining a change in PFC concentration in the effluent stream of the abatement apparatus; and determining whether to retain the operating parameter based on the change in PFC concentration.

[0006] The first aspect recognizes that thermal abatement of PFC gases requires high temperatures, typically > 1500 °C, to abate, for example, CF4. Air is typically supplied to the abatement device, either to support combustion (in the case of a gas-fired burner) or as a reagent to assist in the abatement of PFC gases (in the case of an electrically powered abatement unit such as a plasma or other electrically heated unit). The abatement unit typically receives nitrogen gas from a pump purge as well as the gas to be abated, and nitrogen and oxygen from the air. At the temperatures required for PFC abatement, NOx is thermally generated from the nitrogen and oxygen. As shown in Figure 1 increasing the temperature improves PFC abatement, but also increases the amount of NOx generated.

[0007] Accordingly, a method is provided. The method can optimize or adjust operating conditions within an abatement device that processes an effluent stream from a process tool. The effluent stream can contain perfluorinated compounds. The method can include changing or adjusting an operating parameter to control an operating condition of the abatement device. The method can include determining or identifying a change or modification in a concentration or amount of PFCs within the effluent stream exiting the abatement device in response to a change in the operating condition. The method can include determining or deciding whether to retain the operating parameter that has been adjusted based on the change in the concentration of PFCs. In this way, the concentration of PFCs present in the effluent can be used to determine whether the abatement device is operating at the correct operating condition. This change in concentration can provide an indication of whether the abatement device is achieving a target DRE with the operating parameter.

[0008] In one embodiment, the changing includes adjusting the operating parameter from an initial operating parameter to an adjusted operating parameter.

[0009] In one embodiment, the determining the change includes determining an initial PFC concentration present in the effluent stream and a resulting PFC concentration present in the effluent stream in response to the adjusted operating parameter.

[0010] In one embodiment, the operating condition includes one of an operating temperature and an oxidizing / reducing environment of the abatement device. Accordingly, the operating condition can include an operating temperature and / or an oxidizing / reducing environment within the abatement device.

[0011] In one embodiment, the determining includes retaining the adjusted operating parameter when the resulting PFC concentration is lower than the initial PFC concentration. Accordingly, if the concentration of PFCs in the effluent is reduced (meaning that the DRE has increased), then the changed operating parameter can continue to be applied to continue operating the abatement device at the changed operating condition.

[0012] In one embodiment, when the resulting PFC concentration is below the initial PFC concentration but above the threshold concentration, the determination includes retaining the adjusted operating parameter. Thus, if the PFC concentration in the effluent is reduced, but still matches or exceeds the threshold target concentration (meaning that the desired DRE has not yet been achieved), and thus too many PFCs are still being discharged from the abatement device, the changed operating parameter can continue to be applied to continue operating the abatement device under the changed operating conditions.

[0013] In one embodiment, when the adjusted operating parameter increases the operating temperature and the resulting PFC concentration is below the initial PFC concentration, but the resulting PFC concentration is above the threshold concentration, the determination includes one of rejecting the adjusted operating parameter and preventing further changes to the operating parameter to decrease the operating temperature. Thus, if the change in operating parameter increased the temperature within the abatement device as the PFC concentration in the effluent was reduced, but still matches or exceeds the threshold target concentration (meaning that the desired DRE has not yet been achieved), and thus too many PFCs are still being discharged from the abatement device, the changed operating parameter can continue to be applied to continue operating the abatement device under the increased operating temperature.

[0014] In one embodiment, when the adjusted operating parameter decreases the operating temperature and the resulting PFC concentration is above the initial PFC concentration, but the resulting PFC concentration is above the threshold concentration, the determination includes one of rejecting the adjusted operating parameter and preventing further changes to the operating parameter to decrease the operating temperature. Thus, if the change in operating parameter decreased the temperature within the abatement device as the PFC concentration in the effluent was reduced, but still matches or exceeds the threshold target concentration (meaning that the desired DRE has not yet been achieved), and thus too many PFCs are still being discharged from the abatement device, the changed operating parameter can continue to be applied to continue operating the abatement device under the decreased operating temperature.

[0015] In one embodiment, when the adjusted operating parameter increases the operating temperature, the resulting PFC concentration is above the threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, the determination includes retaining the adjusted operating parameter. Thus, if the change in operating parameter increased the temperature within the abatement device and the PFC concentration in the effluent matches or exceeds the threshold target concentration (meaning that the desired DRE has not yet been achieved), and thus too many PFCs are still being discharged from the abatement device, but the concentration of PFCs being discharged from the abatement device is decreasing, the changed operating parameter can continue to be applied to continue operating the abatement device under the increased operating temperature.

[0016] In one embodiment, when the resulting PFC concentration is below the initial PFC concentration but below the threshold concentration, the determination includes one of rejecting the adjusted operating parameter and preventing further changes to the operating parameter to increase the operating temperature. Thus, if the PFC concentration present in the effluent is reduced, but still does not exceed or fall below the target threshold concentration (meaning that the DRE has been achieved or exceeded), the change in operating parameter can be reversed. Alternatively, the change to the operating parameter can be maintained, but further changes to the operating parameter to increase the operating temperature of the abatement device can be prevented or rejected.

[0017] In one embodiment, when the adjusted operating parameter increases the operating temperature and the resulting PFC concentration is below the initial PFC concentration but below the threshold concentration, the determination includes one of rejecting the adjusted operating parameter and preventing further changes to the operating parameter to increase the operating temperature. Thus, if the change to the operating parameter increased the operating temperature, and if the PFC concentration present in the effluent decreased, but still exceeds or is below the target threshold concentration (meaning that the DRE has been reached or exceeded), the change to the operating parameter can be reversed to decrease the operating temperature. Alternatively, the change to the operating parameter can be maintained, but further changes to the operating parameter to increase the operating temperature of the abatement device can be prevented or rejected.

[0018] In one embodiment, when the adjusted operating parameter decreases the operating temperature and the resulting PFC concentration is above the initial PFC concentration but below the threshold concentration, the determination includes retaining the adjusted operating parameter.

[0019] In one embodiment, when the adjusted operating parameter increases the operating temperature, the resulting PFC concentration is below the threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, the determination includes one of rejecting the adjusted operating parameter and preventing further changes to the operating parameter to increase the operating temperature. Thus, if the change to the operating parameter resulted in a decrease in the concentration of PFC present in the effluent, and if the change to the operating parameter increased the operating temperature, and if the PFC concentration present in the effluent does not exceed or is below the target threshold amount (meaning that the DRE has been reached or exceeded), the change to the operating parameter can be reversed to decrease the operating temperature. Alternatively, the change to the operating parameter can be maintained, but further changes to the operating parameter to increase the operating temperature of the abatement device can be prevented or rejected.

[0020] In one embodiment, the rejecting includes changing the operating parameter back to the initial operating parameter. Thus, the operating parameter can be restored to the previous value.

[0021] In one embodiment, the rejecting includes changing the operating parameter to a value between the initial operating parameter and the adjusted operating parameter.

[0022] In one embodiment, when the resulting PFC concentration is above the initial PFC concentration, the determination includes one of rejecting the adjusted operating parameter and preventing further changes to the operating parameter. Thus, if the PFC concentration in the effluent increases (meaning that the DRE has decreased), the changed operating parameter can be reversed. Alternatively, the change to the operating parameter can be maintained, but further changes to the operating parameter can be prevented or rejected.

[0023] In one embodiment, the abatement device includes an abatement chamber, and the operating parameter includes at least one of the power supplied to heat the abatement chamber, the plasma supplied to the abatement chamber, and the oxidant / fuel amount supplied to the abatement chamber. Thus, the power supplied to heat the abatement chamber and / or the plasma supplied to the abatement chamber and / or the oxidant / fuel mixture amount supplied to the abatement chamber can be adjusted. For example, changing the amount of power supplied to an electrically powered abatement device will change the operating temperature of that abatement device. Likewise, changing the amount of plasma supplied to an abatement device will change the operating temperature of that abatement device, and can change the oxidation / reduction conditions within that abatement device. Likewise, changing the amount of a particular oxidant / fuel mixture and / or changing the amount of oxidant to fuel within the mixture can change the operating temperature within the abatement device as well as the oxidation / reduction environment.

[0024] In one embodiment, when the operating parameter includes the oxidant / fuel amount, the changing includes increasing the oxidant / fuel amount and the resulting PFC concentration is higher than the initial PFC concentration, and the determining includes decreasing the oxidant / fuel amount when the resulting PFC concentration passes through a minimum value.

[0025] In one embodiment, when the operating parameter includes the oxidant / fuel amount, the changing includes increasing the oxidant / fuel amount, the resulting PFC concentration is higher than the initial PFC concentration, but the resulting PFC concentration is lower than a threshold concentration, and the determining includes decreasing the oxidant / fuel amount when the resulting PFC concentration passes through a minimum value. This embodiment recognizes that in a fuel-fired abatement device using, for example, an inwardly firing burner, fuel and oxygen are injected along with the gas stream to be abated in order to produce a more intense combustion, and thus achieve the temperatures required to abate PFC gases. The fuel can be methane or propane, or other gaseous hydrocarbons. For a particular fuel gas stream being injected, as the oxygen flow injected increases, the combustion efficiency, and thus the operating temperature, changes. At low oxygen flow, there is not enough oxygen for complete combustion, the temperature is low, NOx production is low, PFC abatement is poor, and there are high levels of CO emissions from the partially combusted fuel. As the oxygen flow approaches the stoichiometric ratio with the fuel (for optimum combustion efficiency), the temperature increases, NOx production increases, PFC abatement improves, and CO is reduced. Since the excess oxygen ensures complete combustion of the fuel, there is little effect on the abatement of PFCs, and thus, increasing the oxygen flow further first reduces CO emissions; but then begins to dilute the combustion mixture, resulting in a decrease in temperature and a decrease in PFC abatement, as Figure 3As shown in the middle, therefore, if the oxidant / fuel mixture is increased to raise the operating temperature and the PFCs present in the exhaust are at or do not exceed the target threshold concentration (meaning that the DRE has been reached or exceeded), the oxidant / fuel mixture can be reduced or decreased for a period of time such that this reduction results in the PFCs present in the exhaust reaching a minimum and beginning to increase in order to avoid an excess of oxygen diluting the combustion mixture, which results in a decrease in the operating temperature and an unnecessary increase in the PFCs present in the exhaust (and an associated unnecessary decrease in the DRE).

[0026] In one embodiment, when the operating parameter comprises an oxidant / fuel amount, the change comprises decreasing the oxidant / fuel amount, and the resulting PFC concentration is below the initial PFC concentration, the determination comprises decreasing the oxidant / fuel amount while the resulting PFC concentration passes through a minimum. Thus, if the change in oxidant / fuel mixture results in a decrease in PFCs present in the exhaust, and the PFCs present in the exhaust are at or do not exceed the target threshold concentration (meaning that the DRE has been reached or exceeded), then the oxidant / fuel mixture can be reduced or decreased for a period of time such that this reduction results in the PFCs present in the exhaust reaching a minimum and beginning to increase in order to avoid an excess of oxygen diluting the combustion mixture, which results in a decrease in the operating temperature and an unnecessary increase in the PFCs present in the exhaust (and an associated unnecessary decrease in the DRE).

[0027] In one embodiment, when the operating parameter comprises an oxidant / fuel amount, the change comprises decreasing the oxidant / fuel amount, the resulting PFC concentration is below the threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, the determination comprises decreasing the oxidant / fuel amount while the resulting PFC concentration passes through a minimum. Thus, if the change in oxidant / fuel mixture results in a decrease in PFCs present in the exhaust, and the PFCs present in the exhaust are at or do not exceed the target threshold concentration (meaning that the DRE has been reached or exceeded), then the oxidant / fuel mixture can be reduced or decreased for a period of time such that this reduction results in the PFCs present in the exhaust reaching a minimum and beginning to increase in order to avoid an excess of oxygen diluting the combustion mixture, which results in a decrease in the operating temperature and an unnecessary increase in the PFCs present in the exhaust (and an associated unnecessary decrease in the DRE).

[0028] In one embodiment, the rejecting comprises changing the operating parameter back to the initial operating parameter.

[0029] In one embodiment, the rejecting comprises changing the operating parameter to a value between the initial operating parameter and the adjusted operating parameter.

[0030] In one embodiment, when the operating parameter comprises an oxidant / fuel amount and the abatement device is supplied by an oxygen-enriched air source supplemented by at least one of an oxygen source and a nitrogen source, the changing comprises adjusting at least one of the oxygen source and the nitrogen source to adjust the oxidant / fuel amount. Thus, an enriched air source (which typically provides air with a higher oxygen concentration than ambient air in a more cost-effective manner than providing the same amount of oxygen from a pure oxygen source) can be provided, and the amount of oxygen present can be topped up using the oxygen source and / or diluted using the nitrogen source to achieve the desired oxidant / fuel mixture amount.

[0031] In one embodiment, the method comprises iteratively repeating the steps of varying and determining. Thus, the steps of adjusting the operating parameter and identifying the amount of PFC present in the source can be repeated, with the previous variation of the operating parameter being the starting point for the further variation of the operating parameter.

[0032] In one embodiment, the determining comprises determining the initial PFC concentration in response to receiving an indication that PFC is present in the effluent stream. Thus, a signal can be provided from, for example, a processing tool or from a sensor that detects the presence or possible presence of PFC.

[0033] In one embodiment, the method comprises identifying a PFC concentration profile of a processing cycle prior to varying. Thus, the generally varying concentration of PFC present in the effluent stream during a processing cycle can first be determined in order to understand whether it is appropriate to adjust the operating parameter within each processing cycle (assuming that the processing cycle is relatively long and the amount of PFC present in the effluent is relatively constant) or whether it is more appropriate to vary the operating parameter between processing cycles.

[0034] In one embodiment, the method comprises the varying occurring in a subsequent processing cycle when the PFC concentration profile deviates by more than a maximum deviation amount.

[0035] In one embodiment, the method comprises selecting a time within each processing cycle to determine the variation in PFC concentration present in the effluent stream when the PFC concentration profile deviates by more than a maximum deviation amount.

[0036] According to a second aspect, there is provided a abatement apparatus configured to treat a PFC containing effluent stream from a processing tool, the abatement apparatus comprising: a controller operable to vary an operating parameter, the operating parameter controlling an operating condition of the abatement apparatus; a sensor, the sensor operable to determine a variation in PFC concentration present in the effluent stream of the abatement apparatus, wherein the controller is operable to determine whether to retain the operating parameter based on the variation in PFC concentration present in the effluent stream determined by the sensor.

[0037] In one embodiment, the controller is operable to adjust the operating parameter from an initial operating parameter to an adjusted operating parameter.

[0038] In one embodiment, the controller is operable to determine an initial PFC concentration present in the effluent stream and a resultant PFC concentration present in the effluent stream in response to the adjusted operating parameter.

[0039] In one embodiment, the operating condition comprises one of an operating temperature and an oxidising / reducing environment of the abatement apparatus.

[0040] In one embodiment, when the resulting PFC concentration is below the initial PFC concentration, the controller is operable to retain the adjusted operating parameter.

[0041] In one embodiment, when the resulting PFC concentration is below the initial PFC concentration but above the threshold concentration, the controller is operable to retain the adjusted operating parameter.

[0042] In one embodiment, when the adjusted operating parameter increases the operating temperature and the resulting PFC concentration is below the initial PFC concentration but the resulting PFC concentration is above the threshold concentration, the controller is operable to retain the adjusted operating parameter.

[0043] In one embodiment, when the adjusted operating parameter decreases the operating temperature and the resulting PFC concentration is above the initial PFC concentration but the resulting PFC concentration is above the threshold concentration, the controller is operable to one of: reject the adjusted operating parameter, and prevent further changes to the operating parameter to decrease the operating temperature.

[0044] In one embodiment, when the adjusted operating parameter increases the operating temperature, the resulting PFC concentration is above the threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, the controller is operable to retain the adjusted operating parameter.

[0045] In one embodiment, when the resulting PFC concentration is below the initial PFC concentration but below the threshold concentration, the controller is operable to one of: reject the adjusted operating parameter, and prevent further changes to the operating parameter to increase the operating temperature.

[0046] In one embodiment, when the adjusted operating parameter increases the operating temperature and the resulting PFC concentration is below the initial PFC concentration but below the threshold concentration, the controller is operable to one of: reject the adjusted operating parameter and prevent further changes to the operating parameter to increase the operating temperature.

[0047] In one embodiment, when the adjusted operating parameter decreases the operating temperature and the resulting PFC concentration is above the initial PFC concentration but below the threshold concentration, the controller is operable to retain the adjusted operating parameter.

[0048] In one embodiment, when the adjusted operating parameter increases the operating temperature, the resulting PFC concentration is below the threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, the controller is operable to one of: reject the adjusted operating parameter, and prevent further changes to the operating parameter to increase the operating temperature.

[0049] In one embodiment, the controller is operable to reject by changing the operating parameter back to the initial operating parameter.

[0050] In one embodiment, the controller is operable to reject by changing the operating parameter to a value between the initial operating parameter and the adjusted operating parameter.

[0051] In one embodiment, the controller is operable to perform one of rejecting the adjusted operating parameter and preventing further changes to the operating parameter when the resulting PFC concentration is higher than the initial PFC concentration.

[0052] In one embodiment, the abatement device includes an abatement chamber and the operating parameter includes at least one of a power supplied to heat the abatement chamber, a plasma supplied to the abatement chamber, and an oxidant / fuel amount supplied to the abatement chamber.

[0053] In one embodiment, when the operating parameter includes the oxidant / fuel amount, the change includes increasing the oxidant / fuel amount and the resulting PFC concentration is higher than the initial PFC concentration, so as to decrease the oxidant / fuel amount when the resulting PFC concentration passes through a minimum value.

[0054] In one embodiment, when the operating parameter includes the oxidant / fuel amount, the change includes increasing the oxidant / fuel amount and the resulting PFC concentration is higher than the initial PFC concentration, but the resulting PFC concentration is lower than a threshold concentration, so as to decrease the oxidant / fuel amount when the resulting PFC concentration passes through a minimum value.

[0055] In one embodiment, when the operating parameter includes the oxidant / fuel amount, the change includes decreasing the oxidant / fuel amount and the resulting PFC concentration is lower than the initial PFC concentration, so as to decrease the oxidant / fuel amount when the resulting PFC concentration passes through a minimum value.

[0056] In one embodiment, when the operating parameter includes the oxidant / fuel amount, the change includes decreasing the oxidant / fuel amount, the resulting PFC concentration is lower than a threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, so as to decrease the oxidant / fuel amount when the resulting PFC amount passes through a minimum value.

[0057] In one embodiment, the controller is operable to reject by changing the operating parameter back to the initial operating parameter.

[0058] In one embodiment, the controller is operable to reject by changing the operating parameter to a value between the initial operating parameter and the adjusted operating parameter.

[0059] In one embodiment, when the operating parameter includes the oxidant / fuel amount and the abatement device is supplied by an oxygen-enriched air source supplemented with at least one of an oxygen source and a nitrogen source, the controller is operable to adjust at least one of the oxygen source and the nitrogen source, thereby adjusting the oxidant / fuel amount.

[0060] In one embodiment, the controller is operable to iteratively repeat changing the operating parameter and determining whether to retain the operating parameter.

[0061] In one embodiment, the sensor is operable to determine the initial PFC concentration in response to receiving an indication that PFC is present in the effluent stream.

[0062] In one embodiment, the controller is operable to identify a PFC concentration profile of the processing cycle prior to changing the operating parameter.

[0063] In one embodiment, the controller is operable to make the change to the operating parameter in a subsequent processing cycle when the PFC concentration profile deviates by more than the maximum deviation amount.

[0064] In one embodiment, the controller is operable to select a time within each processing cycle to determine the change in PFC amount concentration in the effluent stream when the PFC concentration profile deviates by more than the maximum deviation amount.

[0065] According to a third aspect, there is provided a computer program product operable, when executed by a computer, to control an abatement device to perform the method of the first aspect and embodiments thereof.

[0066] Further specific and preferred aspects are set out in the appended dependent and independent claims. Features of dependent claims can be combined with features of the independent claims as appropriate and can be combined with other than those explicitly set out in the claims.

[0067] Where device features are described as being operable to provide functionality, it will be understood that this includes device features which provide that functionality, or which are adapted or constructed to provide that functionality. BRIEF DESCRIPTION OF DRAWINGS

[0068] Embodiments of the application will now be further described with reference to the drawings in which:

[0069] Figure 1 is a graph showing NOx production and CF4 destruction versus temperature;

[0070] Figure 2 shows an inwardly fired combustion abatement device according to one embodiment;

[0071] Figure 3 is a graph of NOx production and CF4 destruction versus oxygen injection flow rate;

[0072] Figure 4 is a flow chart showing the main processing steps performed by the controller according to one embodiment;

[0073] Figure 5 shows typical DRE and NOx emissions as a function of O2 injected from a single nozzle abatement device;

[0074] Figure 6 shows CF4 concentration in effluent as a function of O2 flow injected according to data in Figure 1

[0075] Figure 7 is a plot showing O2 injection flow vs. number of iterations of computer algorithm to find solution for optimal injection flow at 95% DRE for 1 SLM of CF4 at a dilution factor of 1000 in the case of pure O2 with different starting points;

[0076] Figure 8 is a plot of CF4 flow from the tool (solid line) and injected O2 flow trace (dashed line) according to algorithm (1000x dilution, pure O2);

[0077] Figure 9 is the same as Figure 8 but shows DRE (solid line) and NOx emissions (dashed line); and

[0078] Figure 10 is a plot showing O2 injection flow vs. number of iterations of computer algorithm to find solution for optimal injection flow at 95% DRE for 1 SLM of CF4 at a dilution factor of 1000, with different purities of O2 shown. DETAILED DESCRIPTION

[0079] Before any embodiments are discussed in more detail, first an overview will be provided. The embodiments provide an apparatus that controls operating conditions within an abatement device to reduce the presence of PFCs in an effluent stream, while also controlling the production of unwanted byproducts produced within the abatement device and / or controlling resources consumed by the abatement device. For example, the operating temperature and / or oxidizing / reducing environment within the abatement device can be controlled to achieve a target operating condition that has been selected as a known suitable trade-off condition that achieves a desired goal of PFC abatement, while also controlling the amount of reaction byproducts produced and / or controlling resources consumed by the abatement device. For example, emissions regulations can require a particular minimum DRE for PFC gases, such as DRE > 95% for CF4. The regulations can also specify limits on emissions of combustion byproducts such as NOx.

[0080] Abatement device

[0081] Figure 2 ​An inwardly fired combustion abatement device 10 is shown according to one embodiment. The abatement device 10 includes an inwardly fired perforated burner 20 that is supplied with a hydrocarbon fuel (typically methane or propane) / air mixture that provides a hot zone and ignition source for the chemical destruction of target compounds within an effluent stream that is introduced into a combustion chamber 30 at the core of the burner through an inlet piping system 40 that terminates at a nozzle 50. Typically, fuel is supplied from a fuel inlet 100 to a plenum 90 for supply to the perforated burner 20 under the control of a controller 120.

[0082] The nozzle 50 is provided with an auxiliary port that is positioned for a central lance 60 or coaxial annulus 70 (supplied from a common plenum 80) for the introduction of a fuel gas or oxidant supplied under the control of the controller 120 in order to assist in the destruction of these compounds to be treated. Typically, an oxidant / fuel mixture is supplied to the plenum 90 via a central lance 60 and an oxidant / fuel inlet 110 for supply to the coaxial annulus 70 under the control of the controller 120.

[0083] A sensor 130 is provided that measures the concentration of PFCs in the effluent from the combustion chamber 30, the concentration of PFCs in the effluent can be measured by infrared absorption at the characteristic frequency of the PFC gas of interest. Fourier transform infrared (FTIR) spectrometers and mass spectrometers are known and can be used, but are expensive and can be damaged by long term exposure to the acid and dust in the effluent stream. Low cost non-dispersive infrared (NDIR) sensors can be used, but are likely to be cross sensitive to other gases due to their broader frequency response. Photoacoustic IR sensors can be more suitable due to their narrow frequency response, high sensitivity and resistance to corrosion.

[0084] A water weir and quench zone (not shown) is provided downstream of the combustion chamber 30 to cool the effluent, and a packed tower (not shown) is provided to absorb water soluble gases.

[0085] Example operation

[0086] Operation characteristic determination

[0087] While not necessary in every embodiment, in order to improve the performance of the abatement device 10, the relationship between operating temperature, PFC DRE and NOx production is initially determined. In particular, by measuring the change in PFC concentration in the abatement effluent in response to changes in the injected oxygen, the operating region on a graph depicting the relationship between oxygen flow and the produced NOx production and PFC DRE can be determined, and the oxygen injection flow can be optimized, as Figure 3As shown in the diagram. This relationship can then be used to set the initial operating conditions selected by controller 120 (in this example, the initial oxygen flow rate), and to determine how controller 120 should respond to changes in the amount of PFC present in the exhaust as the operating conditions change. As mentioned above, a detailed understanding of this relationship is not necessary, as controller 120 can instead implement a simpler relationship that assumes an increase in operating temperature should decrease the amount of PFC and increase the amount of NOx, and vice versa, as shown in the diagram. Figure 1 As shown in the image.

[0088] Controller operation

[0089] The main steps performed by controller 120 will now be described. Controller 120 operates to control the operating conditions within combustion chamber 30, and in this example, by controlling the operating temperature within combustion chamber 30, NOx formation and emissions can be minimized by adjusting the flow rate of injected oxygen (or fuel) to just achieve the desired PFC DRE level.

[0090] The controller's response to the PFC measured by sensor 130 is primarily based on the following considerations. If the DRE increases in response to an increase in oxygen flow (meaning a decrease in the concentration of PFC in the exhaust), and the DRE is less than or equal to the desired level, then the oxygen flow should be increased until the DRE increases (meaning a decrease in the amount of PFC) to the desired level, because the reduction device 10 is currently... Figure 3 The operation in region A shown results in excessive PFC emissions and insufficient NOx production.

[0091] If the DRE increases in response to an increase in the supplied oxygen flow rate (meaning a decrease in the PFC amount), and the DRE is greater than or equal to the required level, then the supplied oxygen flow rate should be reduced until the DRE decreases (meaning an increase in the PFC amount) to the required level, because the reduction device... Figure 3 The operation in region B, as shown, resulted in insufficient PFC emissions and excessive NOx production.

[0092] If the DRE decreases in response to an increase in the supplied oxygen flow rate (meaning an increase in the PFC concentration), then the oxygen flow rate supply should decrease so that the DRE passes through its peak (the PFC concentration passes through its minimum – since the DRE passes through its maximum, there may be two points where 95% DRE is achieved, and the point with the lowest oxygen utilization is the point that produces the least NOx), and then the DRE decreases to the desired level (the PFC concentration increases to the desired level), because the reduction device 10 is in... Figure 3 The system operates in region C as shown, and the excessive supply of oxygen causes the operating temperature of the depletion device to drop, resulting in a reduction in DRE (the amount of PFC) and an excessive production of NOx.

[0093] It will be appreciated that embodiments contemplate other types of abatement devices, such as electrically heated or plasma-supplied abatement devices. Those embodiments will generally exhibit similar characteristics to those shown in Figure 3

[0094] Figure 5 is a plot of DRE and NOx emissions as a function of pre-mixed oxygen injection flow rate from the abatement device to the inlet in one embodiment. In this embodiment, DRE reaches a maximum between 20 and 25 SLM of O2. Note that the curve passes 95% DRE at two points - 20 SLM and 40 SLM. NOx emissions rise linearly after an initial plateau. Generally, 95% DRE is required to meet environmental standards, and any improvement on this results in increased NOx emissions and wasted resources. Thus, it is desirable to use the lowest oxygen flow rate that achieves this standard.

[0095] Figure 6 (left plot) shows the calculated residual CF4 in the effluent resulting from the DRE performance curve shown in Figure 5 (right plot) for the conditions of 1 SLM of CF4 flow and a dilution factor of 1000 (these conditions will be used for illustration of various examples throughout the remainder of this discussion). Above the minimum in CF4 (i.e. at maximum DRE), as the O2 injection increases, the abatement gets worse. This feature can be used to establish the optimal solution among two possible solutions to achieve, for example, 95% DRE.

[0096] Controller processing steps

[0097] Figure 4 is a flow chart showing in more detail the main steps performed by the controller 120 in one example implementation described with reference to Figure 3 In this target concentration, the production of NOx is expected to be approximately 0.0065 lb / hr.

[0098] At step SI, PFC gas enters the effluent stream, which can be signaled from the processing tool to the controller 120, detected by a mass flow controller (not shown) at the inlet of the abatement device 10, or can be detected by the sensor 130. Processing then proceeds to step S2.

[0099] ​At step S2, the oxygen injection inlet flow rate is set to a flow rate of F1 standard litres per minute (SLM) as an initial flow rate setting expected to achieve the required DRE. For example, the flow rate F1 can be set to 17.6 SLM as shown in Figure 3. The process then proceeds to step S3. Figure 3

[0100] At step S3, the sensor 130 measures the initial PFC concentration P1 in the effluent. The process then proceeds to step S4.

[0101] At step S4, the oxygen injection flow rate is increased to F N SLM. Typically, the flow rate is increased by, for example, 5%. The process then proceeds to step S5.

[0102] At step S5, the resulting PFC concentration P N is measured using the sensor 130. The process then proceeds to step S6.

[0103] At step S6, it is determined whether the DRE has increased (meaning that P N is less than P1). If the DRE has not increased, the process proceeds to step S7. If the DRE has increased, the process proceeds to step S8.

[0104] At step S7, it is determined that the oxygen flow rate is too high, and the abatement device is operating in region C as shown in Figure 4. Accordingly, the oxygen injection flow rate is reduced by a percentage amount (for example, 33%) and the process returns to step S3. Figure 3 At step S8, if the resulting concentration P N is greater than the target concentration P0, the abatement device is operating in region A as shown in Figure 4, meaning that the DRE is too low, and so the process returns to step S4. If the resulting concentration P N is less than the target concentration P0, this means that the abatement device is operating in region B as shown in Figure 4, meaning that the DRE is too high, and so the oxygen injection flow rate is reduced

[0105] and the process returns to step S5. If the resulting concentration matches the target concentration, meaning that the DRE has been achieved, then no further changes to the oxygen injection flow rate are required at this time. Figure 3 Figure 3 If it is desired to re-evaluate whether the abatement device 10 is operating optimally at a future point, the process can return to step S3 and repeat. In an alternative approach to the features shown in Figures 3 and 4, the search strategy is therefore:

[0106] In an alternative approach to the features shown in Figures 3 and 4, the search strategy is therefore:

[0107] Figure 5 In an alternative approach to the features shown in Figures 3 and 4, the search strategy is therefore: Figure 6 In an alternative approach to the features shown in Figures 3 and 4, the search strategy is therefore:​​​

[0108] (1) Use the provided parameters to establish the desired CF4 concentration in the effluent: the required DRE, the CF4 input into the abatement, and the dilution factor and pump purge of the device.

[0109] (2) Measure the CF4 concentration in the effluent at the start of the injection.

[0110] (3) Increase the injection flow by a step size and re-measure the CF4 concentration. If this is at or below the target, and the CF4 concentration decreases with increasing O2 injection, accept the new conditions and repeat.

[0111] (4) If the new concentration is less than the target, decrease the injection flow until it is above the target, decrease the step size in (3), and repeat (3).

[0112] (5) If the new concentration is greater than the target concentration and the CF4 concentration increases with increasing injection flow, decrease the injection, repeat (5) until the CF4 concentration is less than the target concentration, then proceed with (4) until it is above the target and proceed with (3).

[0113] (6) Continue until either the target is reached when (3) is executed or the step size reaches a lower limit (this accommodates the case where the desired DRE cannot be reached and a best solution that can be found is stabilized).

[0114] (7) Once a solution has been found, the optimal history value is used as the starting point for the start of the injection, allowing a faster solution to be found in future searches.

[0115] A BASIC computer program is listed in the Appendix for performing this search using model data as a proxy for the measurement of CF4 in the effluent (i.e., the curve fit DRE performance). Figure 5

[0116] Figure 7 An example of the search for the optimal injection flow starting from different initial conditions is shown, which demonstrates that the algorithm is robust even at extreme starting points and manages to find the desired solution that combines 95% of the target DRE and the lowest possible NOx.

[0117] Processing cycle optimisation

[0118] ​It is not possible for the PFC gas to flow to the abatement device 10 constantly. In practice, the PFC flow will be intermittent, corresponding to one or more processing steps on each wafer. The PFC gas flow to the abatement device 10 can also vary during a processing step, for example, by being generated in the process of etching a layer of material onto the wafer, then increasing once that layer has been etched (known as over-etching). Embodiments therefore address this variation by learning the optimum injection flow over a series of wafers subjected to the same process. When PFC gas is detected as being present, then the sensor 130 can be monitored during this period, and a curve showing the amount of PFC generated over time can be determined for evaluation. If the PFC amount is relatively constant, then the processing step can be performed within each processing cycle, in other words, the processing cycle will generally be optimised. However, if the PFC amount varies by more than a certain amount, then an average PFC amount can be calculated for each processing step, and the processing step described above can be performed when the PFC amount most closely matches this average amount, in other words, the processing during optimisation will generally occur.

[0119] A method to address this variation in flow is to "learn" the optimum injection flow over a series of wafers subjected to the same process. If a digital signal is available to indicate when PFC gas is flowing, then the sensor 130 readings can be monitored during this period, and an average taken. For the next wafer processing, the oxygen injection flow is increased, and for this next wafer, the sensor 130 readings are averaged. Then, the same method as previously described is followed to determine whether the injection flow should be further increased or decreased for each subsequent wafer, until the optimum setting is achieved.

[0120] Figure 8 A typical time profile of inlet CF4 from a series of etch processes is shown, and the O2 injection flow tracked accordingly using a control algorithm - by storing the last best historical value, this can be used to speed up finding the solution. After the solution has been found in the first etch cycle, the injection flows for subsequent steps are quickly set to their optimum flows, and the resulting 95% CF4 DRE and low NOx are obtained in a timely manner as shown in Figure 9

[0121] Many semiconductor manufacturers obtain their oxygen supply from an air separation plant - typically a pressure swing adsorption system. The purity of the oxygen is typically 90-95%, and the quality is unknown and variable. If the abatement device is always supplied with a constant purity of oxygen, then the system can be arranged to inject the same amount of O2 each time CF4 flows to achieve the desired performance, and there would be no need to employ effluent monitoring to obtain the optimum flow. This almost never happens in practice, so this method of adjusting the injection of (impure) O2 flow in response to the concentration of CF4 in the effluent helps to overcome this problem. As an illustration, Figure 10 ​Results are shown for different levels of O2 purity input to the search to achieve 95% DRE for 1 SLM of CF4 starting from no initial flow at 1000x system dilution.

[0122] Furthermore, in another embodiment, instead of adjusting the oxygen injection flow rate for a fixed fuel injection flow rate, the oxygen injection flow rate can be fixed and the fuel injection flow rate adjusted.

[0123] Similar methods can also be applied to plasma abatement devices. Instead of adjusting the oxygen or fuel injection flow rate to adjust the combustion conditions, the injection flow rate of a reagent such as air and / or the electrical power of the plasma can be adjusted in response to PFC exhaust sensor measurements.

[0124] To learn over a range of wafers, if the digital signal for PFC flow "on" is not available, the presence of the PFC exhaust sensor signal (above any background noise level) can be used to detect when the PFC gas is flowing, and thus determine when to start and stop measuring the PFC emission levels.

[0125] Oxidant supply

[0126] While the oxidant provided to the abatement device 10 can come from a pure oxygen source, in one embodiment a "rich oxygen air source" is provided. In particular, rich oxygen air typically includes 85% - 95% oxygen, with the remainder being nitrogen. This can be produced from air at lower cost, and is safer than having a pure oxygen supply. In this case, instead of adjusting the oxygen injection flow rate, the "rich oxygen air" injection flow rate can be fixed, and the oxygen concentration adjusted by dilution with nitrogen (or enrichment with pure oxygen).

[0127] In one embodiment, it is determined that the pure oxygen injection quantity has an optimal flow rate per nozzle to have CF4 DRE > 95% and to minimize NOx to 17 slm per nozzle.

[0128] If the premix injection flow rate is set to 20 SLM per nozzle (using a standard flow regulator), and the oxygen supply is always diluted to 85% concentration, this should achieve the optimal conditions.

[0129] Then, using a measurement of the oxygen concentration, and knowing how much injection is needed, a single 20 SLM nitrogen mass flow controller (MFC) can be used to add the required amount of nitrogen to dilute the rich oxygen air to 85% O2 for the 6 nozzles (instead of using 6 MFCs).

[0130] Example: required O2 per nozzle 17 SLM, measured oxygen concentration 95%, target concentration 85%, 6 injections active:

[0131] • Set the pre-mix injection flow rate for each nozzle to 17 / 0.85 = 20 SLM

[0132] • 6 nozzles require 6x17 = 102 SLM of oxygen

[0133] • This requires 102 / 0.95 = 107.4 SLM of 95% enriched oxygen air

[0134] • So add 120-107.4 = 13.6 SLM of nitrogen

[0135] More generally: the O2 required for each nozzle is A SLM, the measured oxygen concentration is y%, the target concentration is x%, and n injections are active:

[0136] • Set the pre-mix injection flow rate for each nozzle to A / x SLM (constant)

[0137] • n nozzles require nA SLM of oxygen

[0138] • This requires nA / y SLM of y% enriched oxygen air

[0139] • So add (nA / x - nA / y) = (nA / x).(1 - x / y) SLM of nitrogen

[0140] Assuming MFC accuracy is 1% full scale (0.2 SLM of N2): the worst case error is if only one injection is active, when the oxygen flow can be off by 1.1% = 0.2 SLM of 17 SLM. So the error is no worse than using a separate MFC for each injection (and better when multiple injections are on).

[0141] Thus, embodiments provide a method of optimising PFC abatement using exhaust gas sensors. Sensors in the exhaust of a thermal abatement system measure the concentration of the PFC gas being abated, and can also measure other by-products. The sensor signals are used to adjust the conditions in the abatement unit, and the response of the sensors to the adjustments are used to determine the optimum settings to achieve sufficient abatement, while minimising the production of undesirable by-products such as NOx.

[0142] While the illustrative embodiments of the application have been disclosed in detail herein with reference to the attached drawings, it is to be understood that the application is not limited to the precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the application as defined by the appended claims and their equivalents.

[0143] Appendix - list of procedures for finding the optimum abatement conditions

[0144] 10 REM program to demonstrate optimisation of oxygen inject for CF4 abatement

[0145] 20 REM using (simulated) measurement of CF4 concentration in exhaust

[0146] 30 REM with lowest use of resources and emissions of NOx (simulated) 40

[0148] 50 REM control algorithm requires CF4 flow (from tool) and

[0149] 60 REM knowledge of the dilution factor of the gas leaving the exhaust

[0150] 70 REM in order to calculate desired CF4 concentration there

[0151] 80 REM which achieves specified destruction rate efficiency (DRE) 90

[0153] 100 REM input conditions

[0154] 110 REPEAT

[0155] 120 REM only accept values 0-100%

[0156] 130 INPUT "Target DRE (%)"; DRE% (Enter "Target DRE (%)")

[0157] 140 UNTIL (DRE% >= 0) AND (DRE% <= 100) (until (DRE% >= 0) and (DRE% <= 100)) 150

[0159] 160 INPUT "Dilution factor"; dilution_factor (Enter "dilution factor") 170

[0161] 180 REM initialise historic best value (of inject flow to store for future use)

[0162] 190 LET last_best_inject = 0 (so that last_best_inject = 0) 200

[0164] 210 REPEAT 220

[0166] 230 REM get CF4 flow (this would be from tool)

[0167] 240 INPUT "CF4 flow (slm)"; CF4_flow (Enter "CF4 flow (slm)") 250

[0169] 260 REM calculate CF4 concentration in ppm at required DRE (Note: Calculate CF4 concentration in ppm at the required DRE)

[0170] 270 LET target% = (CF4_flow * (100-DRE% ) / 100 / dilution_factor *1E6) 280

[0172] 290 REM step size for changing inject

[0173] 300 LET step_inject = 4 310

[0175] 320 REM get starting inject

[0176] 330 INPUT "Initial O2 inject flow (slm)"; old_inject 340

[0178] 350 REM use last_best_inject if starting point negative

[0179] 360 REM back it off by the step size to force search to converge after one iteration

[0180] 370 IF (old_inject < 0) THEN LET old_inject = last_best_inject -step_inject 380

[0182] 390 REM get O2 purity in range 80-100%

[0183] 400 REM (this would be unknown in practice -

[0184] 410 REM ca.90-95% from industrial pressure swing adsorption generators

[0185] 420 REPEAT

[0186] 430 INPUT "O2 purity (80-100%)"; O2_purity

[0187] 440 UNTIL (O2_purity >=80) AND (O2_purity <=100) 450

[0189] 460 REM initialise starting CF4 concentration in exhaust

[0190] 470 LET old_conc% = FNmeasure_CF4(old_inject)

[0191] 480 PRINT "current inject (slm): ";old_inject;", CF4 (ppm): ";old_conc%;", inject step (slm): ";step_inject;" NOx (g / hr): "+STR$(FNmeasure_NOx(inject)) 490

[0193] 500 REM main loop to find solution

[0194] 510 REPEAT 520

[0196] 530 REM done% is a Boolean flag to denote that we've already dealt with each case (it avoids GOTO statements).

[0197] 540 LET done% = FALSE (makes done% = FALSE) 550

[0199] 560 IF (CF4_flow = 0) THEN (If (CF4_flow = 0), then)

[0200] 570 REM turn inject off, no CF4 to treat (Note: Turn off injection, no CF4 to treat)

[0201] 580 LET old_inject = 0 (make old_inject = 0)

[0202] 590 REM make step_inject zero (Note: Makes step_inject zero)

[0203] 600 LET step_inject = 0 (making step_inject = 0)

[0204] 610 PRINT "Inject off" (outputs "Injection off")

[0205] 620 REM sets a flag to show we've accepted new conditions.

[0206] 630 LET done% = TRUE (makes done% = TRUE)

[0207] 640 ENDIF 650

[0209] 660 REM measure CF4 concentration at provisionally better inject

[0210] 670 LET new_inject = old_inject + step_inject

[0211] 680 REM trap negative values

[0212] 690 IF (new_inject < 0) THEN LET new_inject = 0

[0213] 700 REM measure at new inject setting

[0214] 710 LET new_conc% = FNmeasure_CF4(new_inject)

[0215] 720 REM display result

[0216] 730 PRINT "CF4 new (ppm): ";new_conc%;", target (ppm): ";target% 740

[0218] 750 IF (done% = FALSE) THEN

[0219] 760 REM we are too low but going the right way

[0220] 770 IF (new_conc% >= target%) AND (new_conc% < old_conc%) THEN

[0221] 780 REM accept new inject

[0222] 790 REM: Set a flag to show we've accepted new conditions.

[0223] 800 LET done% = TRUE

[0224] 810 ENDIF

[0225] 820 ENDIF 830

[0227] 840 IF (done% = FALSE) THEN

[0228] 850 REM is too high, but it's going the right way.

[0229] 860 IF (step_inject < 0) AND (new_conc% =< target%) THEN

[0230] 870 REM accept new inject (Note: Accepts new injection amount)

[0231] 880 REM sets a flag to show we've accepted new conditions.

[0232] 890 LET done% = TRUE

[0233] 900 ENDIF

[0234] 910 ENDIF 920

[0236] 930 REM check to see if either of the above changes has reached the target.

[0237] 940 REM: Do not make any further changes to the injection volume in that case.

[0238] 950 IF (done% = TRUE) AND (new_conc% = target%) THEN

[0239] 960 IF (step_inject > 0) AND (new_conc% < old_conc%) THEN LET step_inject = 0

[0240] 970 IF (step_inject < 0) AND (new_conc% > old_conc%) THEN LET step_inject = 0

[0241] 980 ENDIF 990

[0243] 1000 IF (done% = FALSE) THEN

[0244] 1010 REM We are much too high but going right way.

[0245] 1020 IF (step_inject < 0) AND (new_conc% < old_conc%) THEN

[0246] 1030 REM accept new inject (Note: Accepts new injection amount)

[0247] 1040 REM: Set a flag to show that we've accepted the new conditions.

[0248] 1050 LET done% = TRUE

[0249] 1060 ENDIF

[0250] 1070 ENDIF 1080

[0252] 1090 REM If we've accepted the change in inject so far, then store new_conc.

[0253] in old_conc

[0254] 1100 IF (done% = TRUE) THEN

[0255] 1110 LET old_conc% = new_conc%

[0256] 1120 LET old_inject = new_inject

[0257] 1130 REM print status on screen (Note: Output status on the screen)

[0258] 1140 PRINT "Change accepted!" (Output "The change has been accepted")

[0259] 1150 ENDIF 1160

[0261] 1170 REM Now consider cases where we are changing the injection in the wrong direction. 1180

[0263] 1190 IF (done% = FALSE) THEN

[0264] 1200 REM abatement too good; in the region, DRE is better than required.

[0265] 1210 IF (new_conc% < target%) THEN

[0266] 1220 REM decrease injection by making step_inject negative (Note: This reduces the injection amount by making step_inject negative)

[0267] 1230 LET step_inject = ABS(step_inject) * -1

[0268] 1240 REM print status on screen (Note: Output status on the screen)

[0269] 1250 PRINT "Change rejected! Decreasing inject" (outputs "Change rejected! Decreasing inject")

[0270] 1260 REM set flag to show we've accepted new conditions (comment: sets flag to show that new conditions have been accepted)

[0271] 1270 LET done% = TRUE

[0272] 1280 ENDIF

[0273] 1290 ENDIF 1300

[0275] 1310 IF (done% = FALSE) THEN

[0276] 1320 REM much too high, abatement getting worse again as inject is increased (comment: too high, abatement getting worse again as inject is increased)

[0277] 1330 IF (step_inject > 0) AND (new_conc% > old_conc%) THEN

[0278] 1340 REM decrease inject by making step_inject negative (comment: decrease inject by making step_inject negative)

[0279] 1350 LET step_inject = ABS(step_inject) * -1

[0280] 1360 REM print status on screen (comment: print status on screen)

[0281] 1370 PRINT "Change rejected! Decreasing inject" (outputs "Change rejected! Decreasing inject")

[0282] 1380 REM: Set a flag to show that we've accepted new conditions.

[0283] 1390 LET done% = TRUE

[0284] 1400 ENDIF

[0285] 1410 ENDIF 1420

[0287] 1430 IF (done% = FALSE) THEN

[0288] 1440 REM We are too low and going the wrong way.

[0289] 1450 IF (step_inject < 0) AND (new_conc% > old_conc%) AND (new_conc%> target%) THEN

[0290] 1460 REM increases injection more slowly by reducing the size of step_inject.

[0291] 1470 LET step_inject = ABS(step_inject / 2)

[0292] 1480 REM print status on screen (Note: Output status on the screen)

[0293] 1490 PRINT "Change rejected! Increasing inject more slowly" (output: "Change has been rejected! Increasing injection more slowly")

[0294] 1500 REM sets a flag to show that we have accepted the new conditions.

[0295] 1510 LET done% = TRUE

[0296] 1520 ENDIF

[0297] 1530 ENDIF 1540

[0299] 1550 IF (done% = FALSE) THEN

[0300] 1560 REM none of the above apply.

[0301] 1570 REM print status on screen (Note: Output status on the screen)

[0302] 1580 PRINT "Something amiss! Reducing search window" (Output: "Something amiss! Reducing search window")

[0303] 1590 REM reduced step size (Note: reduced step size)

[0304] 1600 LET step_inject = step_inject / 2

[0305] 1610 ENDIF 1620

[0307] 1630 REM print status of algorithm on screen and to file (Note: Outputs the algorithm status to both the screen and a file)

[0308] 1640 PRINT "current inject: ";old_inject;" slm, CF4: ";old_conc%;"ppm, inject step: ";step_inject;" slm, NOx: ";FNmeasure_NOx(old_inject);" g / hr" 1650

[0310] 1660 REM wait for a second (Note: wait one second)

[0311] 1670 WAIT(100) 1680

[0313] 1690 REM stop when either we've found a solution or the step_size is very small.

[0314] 1700 UNTIL (ABS(step_inject) < 0.01) (until (ABS(step_inject) < 0.01)) 1710

[0316] 1720 REM check to see if target achieved (Note: Check to see if the target has been achieved)

[0317] 1730 IF (old_conc% = target%) THEN

[0318] 1740 REM solution found (Note: Solution found)

[0319] 1750 PRINT "Target DRE achieved!"

[0320] 1760 REM store this in last_best_inject (Note: Store this in last_best_inject)

[0321] 1770 LET last_best_inject = old_inject

[0322] 1780 ENDIF 1790

[0324] 1800 REM check to see if target not achieved.

[0325] 1810 IF (old_conc% <> target%) THEN

[0326] 1820 PRINT "Failed to achieve target!"

[0327] 1830 ENDIF 1840

[0329] 1850 REM asks if another condition needs to be tested.

[0330] 1860 REPEAT

[0331] 1870 INPUT "Do another (Y / N)"; reply$

[0332] 1880 REM concentate to first character (Note: Concentrate on the first character)

[0333] 1890 LET reply$ = LEFT$(reply$,1)

[0334] 1900 REM only accepts Y / y or N / n (Note: Only Y / y or N / n is accepted)

[0335] 1910 UNTIL (reply$ = "N") OR (reply$ = "n") OR (reply$ = "Y") OR(reply$ = "y") (until (reply$ = "N") or (reply$ = "n") or (reply$ = "Y") or (reply$= "y")) 1920

[0337] 1930 UNTIL (reply$ = "N") OR (reply$ = "n") (until (reply$ = "N") or (reply$ = "n")) 1940

[0339] 1950 END 1960

[0341] 1970 DEF FNmeasure_CF4(inject)

[0342] 1980 REM This is a proxy for actual measurement on exhaust.

[0343] 1990 PRINT "Inject: ";inject; (outputs "injection amount")

[0344] 2000 REM accomodate purity of oxygen

[0345] 2010 LET inject = inject*O2_purity / 100

[0346] 2020 PRINT;" slm, O2 content: ";inject;" slm"

[0347] 2030 REM calculate DRE from model

[0348] 2040 LET DRE_actual = -0.000000292*inject^4 + 0.0000525*inject^3 -0.003520833*inject^2 + 0.09925*inject

[0349] 2050 REM print DRE rounded up to nearest whole number

[0350] 2060 PRINT "DRE: ";INT(DRE_actual*100 + 0.5)"% "

[0351] 2070 REM calculate amount of CF4 in slm in exhaust

[0352] 2080 LET CF4_out = CF4_flow * (1 - DRE_actual)

[0353] 2090 REM return concentration in exhaust in ppm

[0354] 2100 REM rounded to nearest whole number

[0355] 2110 = INT((CF4_out / dilution_factor * 1E6) + 0.5) 2120

[0357] 2130 DEF FNmeasure_NOx(inject)

[0358] 2140 REM This is a proxy for actual measurement on exhaust.

[0359] 2150 REM accomodate purity of oxygen (Note: Provides the purity of oxygen)

[0360] 2160 LET inject = inject*O2_purity / 100 (so that inject = inject*O2_purity / 100)

[0361] 2170 REM calculate NOx from model (Note: calculate NOx in the model)

[0362] 2180 IF (inject < 10) THEN LET NOx = 5

[0363] 2190 IF (inject >= 10) THEN LET NOx = 5*(inject - 10) + 5 (If (inject >= 10), then NOx = 5*(inject - 10) + 5)

[0364] 2200 REM round to nearest whole number (Note: round to the nearest integer)

[0365] 2210 = INT(NOx + 0.5)

[0366] Reference numerals

[0367] Elimination device 10

[0368] Perforated burner 20

[0369] Combustion chamber 30

[0370] Inlet piping system 40

[0371] nozzle 50

[0372] central lance 60

[0373] coaxial ring 70

[0374] plenum 80, 90

[0375] fuel inlet 100

[0376] fuel / oxidant inlet 110

[0377] controller 120

[0378] sensor 130

Claims

1. A method for optimizing operating conditions in a reduction device configured to process a PFC-containing discharge stream from a treatment vehicle, the method comprising: (a) Set the oxygen injection inlet flow rate to the initial flow rate setting; (b) Determine the initial PFC concentration present in the discharge stream of the reduction device; (c) Increase the oxygen injection inlet flow rate by ΔF; (d) Determine the concentration of the resulting PFC present in the discharged stream; (e) If the resulting PFC concentration is greater than the initial PFC concentration, reduce the oxygen injection inlet flow rate by one percentage point and then return to step (a). (f) If the resulting PFC concentration is less than the initial PFC concentration but greater than the target concentration, return to step (c); (g) If the resulting PFC concentration is less than the initial PFC concentration and less than the target concentration, then reduce the oxygen injection inlet flow rate by ΔF and return to step (d); and (h) If the resulting PFC concentration is less than the initial PFC concentration but equal to the target concentration, keep the oxygen injection inlet flow rate unchanged.

2. The method according to claim 1, wherein, The initial flow rate was set to 17.6 standard liters per minute.

3. The method according to claim 2, wherein, ΔF is 5%.

4. The method according to claim 3, wherein, The percentage is 33%.

5. A reduction device configured to treat a PFC-containing discharge stream from a processing vehicle, the reduction device comprising: A controller operable to change operating parameters, which control the operating conditions of the reduction device; A sensor operable to determine the concentration of PFCs present in the discharge stream of the reduction device, wherein the controller is operable to: (a) Set the oxygen injection inlet flow rate to the initial flow rate setting; (b) Determine the initial PFC concentration present in the discharge stream of the reduction device; (c) Increase the oxygen injection inlet flow rate by ΔF; (d) Determine the concentration of the resulting PFC present in the discharged stream; (e) If the resulting PFC concentration is greater than the initial PFC concentration, reduce the oxygen injection inlet flow rate by one percentage point and then return to step (a). (f) If the resulting PFC concentration is less than the initial PFC concentration but greater than the target concentration, return to step (c); (g) If the resulting PFC concentration is less than the initial PFC concentration and less than the target concentration, then reduce the oxygen injection inlet flow rate by ΔF and return to step (d); and (h) If the resulting PFC concentration is less than the initial PFC concentration but equal to the target concentration, keep the oxygen injection inlet flow rate unchanged.

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