Optimization of operating conditions in abatement equipment

Abstract

A method for optimizing operating conditions in an abatement system configured to treat an effluent stream from a processing tool and an abatement system are disclosed. The method for optimizing operating conditions in an abatement system configured to treat an effluent stream from a processing tool that includes PFCs includes varying operating parameters that control the operating conditions of the abatement system, determining a change in the concentration of PFCs present in the abatement system exhaust stream, and determining whether to hold the operating parameters based on the change in the PFC concentration. In this manner, the PFC concentration in the exhaust can be used to determine whether the abatement system is operating at the correct operating conditions.

Description

[Technical field]

[0001] The field of the invention relates to methods for optimizing operating conditions in an abatement apparatus configured to treat an effluent stream from a processing tool, and to the abatement apparatus. [Background technology]

[0002] Abatement devices are known and are commonly used to treat effluent gas streams from manufacturing process tools used, for example, in the semiconductor or flat panel display manufacturing industries. During such manufacturing, residual perfluorinated compounds (PFCs) and other compounds are present in the effluent gas streams pumped from the process tools. PFCs are difficult to remove from exhaust gases and are known to have a relatively high greenhouse effect, making them undesirable to be released into the environment.

[0003] Known abatement devices, such as radiant burners, use combustion to remove PFCs and other compounds from exhaust gases to meet a specific destruction rate efficiency (DRE). Typically, the exit gas stream is a nitrogen stream containing the PFCs and other compounds. Fuel gas and oxidant gas are mixed with the exit gas stream, and the gas stream is conveyed to a combustion chamber bounded laterally by an exit face of a perforated gas burner. Fuel gas and air are simultaneously supplied to the perforated gas burner to affect flameless combustion at the exit face, and the amount of air passing through the perforated gas burner is sufficient to consume all combustibles in the mixed gas stream injected into the combustion chamber, as well as the fuel gas supplied to the burner. Summary of the Invention [Problem to be solved by the invention]

[0004] There are several techniques for treating effluent gas streams, each of which has its drawbacks, and it would therefore be desirable to provide improved techniques for treating effluent gas streams. [Means for solving the problem]

[0005] According to a first aspect, a method for optimizing operating conditions in an abatement apparatus configured to treat an exhaust flow containing PFCs from a processing tool is provided, the method including the steps of altering operating parameters controlling the operating conditions of the abatement apparatus, determining a change in PFC concentration in the exhaust flow of the abatement apparatus, and determining whether to hold the operating parameters based on the change in PFC concentration.

[0006] The first aspect recognizes that thermal abatement of PFC gases requires high temperatures, typically 1500°C or higher, for example to abate CF4. Air is typically supplied to the abatement system to aid in combustion (in the case of gas combustors) or as a reagent to aid in the abatement of the PFC gases (in the case of electrically heated abatement systems such as plasmas). The abatement system typically receives nitrogen from the pump purge along with the gas to be abated, and nitrogen and oxygen from the air. At the temperatures required for PFC abatement, NOx is thermally produced from the nitrogen and oxygen. Increasing the temperature improves the abatement of the PFCs, but also increases the amount of NOx produced, as shown in Figure 1.

[0007] Accordingly, a method is provided. The method can optimize or adjust operating conditions in an abatement system that treats an exhaust stream from a process tool. The effluent stream can include perfluorinated compounds. The method can include changing or adjusting operating parameters to control the operating conditions of the abatement system. The method can include determining or identifying a change or change in the concentration or amount of PFCs in the exhaust stream exiting the abatement system in response to the change in operating conditions. The method can include deciding or determining whether to hold the adjusted operating parameters based on the change in concentration of PFCs. In this manner, the concentration of PFCs present in the exhaust can be used to determine whether the exhaust gas cleaning system is operating at the correct operating conditions. The change in concentration can provide an indication of whether a target DRE is being achieved by the abatement system at the operating parameters.

[0008] In one embodiment, the modifying step includes adjusting the operating parameters from the initial operating parameters to the adjusted operating parameters.

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

[0010] In one embodiment, the operating conditions include one of an operating temperature and an oxidizing / reducing environment of the abatement apparatus. Thus, the operating conditions can include an operating temperature and / or an oxidizing / reducing environment within the abatement apparatus.

[0011] In one embodiment, if the resulting PFC concentration is less than the initial PFC concentration, the determining step includes retaining the adjusted operating parameters, such that if the PFC concentration in the exhaust decreases (meaning the DRE has increased), the modified operating parameters can continue to be applied to continue operating the abatement device under the modified operating conditions.

[0012] In one embodiment, if the resulting PFC concentration is less than the initial PFC concentration but equal to or greater than the threshold concentration, the determining step includes retaining the adjusted operating parameters. Thus, if the PFC concentration in the exhaust is reduced but still meets or exceeds the threshold target concentration (meaning the required DRE has not been achieved) and thus large amounts of PFC are still being discharged from the abatement device, the modified operating parameters can continue to be applied to continue operation of the abatement device at the modified operating conditions.

[0013] In one embodiment, if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is less than the initial PFC concentration, but the resulting PFC concentration is equal to or greater than the threshold concentration, the determining step includes retaining the adjusted operating parameters. Thus, if the change in the operating parameters increases the temperature within the abatement system while the PFC concentration in the exhaust decreases, but the PFC concentration in the exhaust meets or exceeds the threshold target concentration (meaning the required DRE has not been achieved) and large amounts of PFC are still being exhausted from the abatement system, the changed operating parameters can continue to be applied to continue operating the abatement system at the increased operating temperature.

[0014] In one embodiment, if the adjusted operating parameters reduce the operating temperature and the resulting PFC concentration is greater than or equal to the initial PFC concentration, but the resulting PFC concentration is greater than or equal to the threshold concentration, the determining step includes one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters to reduce the operating temperature.

[0015] In one embodiment, if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is equal to or greater than the threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, the determining step includes retaining the adjusted operating parameters. Thus, if a change in the operating parameters increases the temperature of the abatement system and the PFC concentration in the exhaust meets or exceeds the threshold target concentration (meaning the required DRE has not been achieved), and a significant amount of PFC is still being exhausted from the abatement system, but the concentration of PFC being exhausted from the abatement system is decreasing, the changed operating parameters can continue to be applied to continue operation of the abatement system at the increased operating temperature.

[0016] In one embodiment, if the resulting PFC concentration is less than the initial PFC concentration but less than the threshold concentration, the determining step includes one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters to increase the operating temperature. Thus, if the PFC concentration in the exhaust decreases but does not exceed or is below the target threshold concentration (meaning the DRE is achieved or exceeded), the change in the operating parameters can be cancelled. Alternatively, the change in the operating parameters can be maintained but further changes to the operating parameters to increase the operating temperature of the abatement device can be prevented or rejected.

[0017] In one embodiment, if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is less than the initial PFC concentration but less than the threshold concentration, the determining step includes one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters to increase the operating temperature. Thus, if the change in the operating parameters increases the operating temperature and reduces the PFC concentration in the exhaust but does not exceed or fall below the target threshold concentration (meaning the DRE is achieved or exceeded), the change in the operating parameters can be reversed to reduce the operating temperature. Alternatively, the changes to the operating parameters may be maintained, but further changes to the operating parameters that would increase the operating temperature of the abatement device may be prevented or denied.

[0018] In one embodiment, if the adjusted operating parameters reduce the operating temperature and the resulting PFC concentration is greater than or equal to the initial PFC concentration but less than the threshold concentration, the determining step includes retaining the adjusted operating parameters.

[0019] In one embodiment, if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is less than the threshold concentration and the resulting PFC concentration is less than the initial PFC concentration, the determining step includes one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters that would increase the operating temperature. Thus, if the change in the operating parameters decreases the concentration of PFCs present in the exhaust, the change in the operating parameters increases the operating temperature, and the concentration of PFCs present in the exhaust does not exceed or is below the target threshold (meaning the DRE has been achieved or exceeded), the change in the operating parameters can be reversed to decrease the operating temperature. Alternatively, the change in the operating parameters can be maintained, but further changes to the operating parameters to increase the operating temperature of the abatement device can be prevented or rejected.

[0020] In one embodiment, the rejecting step includes changing the operating parameters back to the initial operating parameters, such that the operating parameters can be reverted to their previous values.

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

[0022] In one embodiment, if the resulting PFC concentration is equal to or greater than the initial PFC concentration, the determining step includes one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters. Thus, if the PFC concentration in the exhaust has increased (meaning the DRE has decreased), the changed operating parameters can be reverted. Alternatively, the changes to the operating parameters can be maintained, but further changes to the operating parameters can be prevented or rejected.

[0023] In one embodiment, the abatement apparatus includes an abatement chamber, and the operating parameters include at least one of the power provided to heat the abatement chamber, the plasma provided to the abatement chamber, and the amount of oxidant / fuel provided to the abatement chamber. Thus, the power provided to heat the abatement chamber, and / or the plasma provided to the abatement chamber, and / or the amount of oxidant / fuel mixture provided to the abatement chamber can be adjusted. For example, changing the amount of power provided to a powered abatement apparatus will change the operating temperature of the abatement apparatus. Similarly, changing the amount of plasma provided to the abatement apparatus, and potentially the oxidation / reduction conditions within the abatement apparatus, will change the operating temperature of the abatement apparatus. Similarly, changing a particular oxidant / fuel mixture ratio and / or the amount of oxidant relative to fuel in the mixture can change not only the operating temperature, but also the oxidation / reduction environment within the abatement apparatus.

[0024] In one embodiment, the operating parameter includes an oxidizer / fuel amount, and the varying step includes increasing the oxidizer / fuel amount, and if the resulting PFC concentration is greater than or equal to the initial PFC concentration, the determining step includes decreasing the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum value.

[0025] In one embodiment, the operating parameters include an oxidizer / fuel amount, the varying step includes increasing the oxidizer / fuel amount, and if the resulting PFC concentration is equal to or greater than the initial PFC concentration, but the resulting PFC concentration is less than the threshold, the determining step includes decreasing the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum. This embodiment recognizes that in, for example, an internal combustor fuel combustion abatement device, fuel and oxygen are injected with the gas stream to be abated in order to generate stronger combustion and thus achieve the temperature required to abatement the PFC gases. The fuel can be methane or propane, or other gaseous hydrocarbons. For a particular injected fuel gas flow rate, increasing the injected oxygen flow rate changes the combustion efficiency and, consequently, the operating temperature. A lower oxygen flow rate results in insufficient oxygen for complete combustion, resulting in lower temperatures, less NOx production, less PFC abatement, and higher CO emissions from partially burned fuel. As the oxygen flow rate approaches the stoichiometric mixture ratio with the fuel (optimum combustion efficiency), the temperature increases, NOx emissions increase, PFC abatement improves, and CO decreases. Further increasing the oxygen flow rate initially reduces CO emissions as the excess oxygen completely burns the fuel and has little effect on PFC abatement, but then the combustion mixture becomes leaner, leading to a decrease in temperature and a decrease in PFC abatement as shown in Figure 3. Thus, if the oxidizer / fuel mixture ratio is increased to increase the operating temperature and the PFCs present in the exhaust are at or cannot exceed the target threshold concentration (meaning the DRE has been achieved or exceeded), the oxidizer / fuel mixture ratio can be reduced or decreased during the period when such a reduction would cause the PFCs present in the exhaust to achieve a minimum and begin to increase, in order to avoid a leaning of the combustion mixture due to excess oxygen causing a decrease in 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, the operating parameter includes an oxidizer / fuel amount, and the varying step includes decreasing the oxidizer / fuel amount, and if the resulting PFC concentration is less than the initial PFC concentration, the determining step includes decreasing the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum value.

[0027] In one embodiment, the operating parameter includes an oxidizer / fuel amount, the varying step is a step of decreasing the oxidizer / fuel amount, and if the resulting PFC concentration is less than the threshold concentration, and the resulting PFC concentration is less than the initial PFC concentration, the determining step includes a step of decreasing the oxidizer / fuel amount during the time period during which the resulting PFC concentration passes through a minimum. Thus, if the change in the oxidizer / fuel mixture ratio reduces the PFC present in the exhaust and fails to allow the PFC present in the exhaust to be at or above the target threshold concentration (meaning the DRE is achieved or exceeded), the oxidizer / fuel mixture ratio can be decreased or reduced during the time period during which such reduction causes the PFC present in the exhaust to achieve a minimum and begin to increase, in order to avoid leaning the combustion mixture with excess oxygen, which would cause a reduction in operating temperature and an unnecessary increase in the PFC present in the exhaust (and an associated unnecessary decrease in the DRE).

[0028] In one embodiment, the rejecting step includes reverting the operating parameters to initial operating parameters.

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

[0030] In one embodiment, where the operating parameters include the oxidant / fuel amount and the abatement device is supplied with an enriched air source augmented with at least one of an oxygen source and a nitrogen source, the modifying step includes adjusting at least one of the oxygen source and the nitrogen source to adjust the oxidant / fuel amount. Thus, an enriched air source can be provided (which generally provides air having 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), and the amount of oxygen present can be added with the oxygen source and / or diluted with the nitrogen source to arrive at the desired oxidant / fuel mix.

[0031] In one embodiment, the method includes repeating the modifying and determining steps iteratively, such that the steps of adjusting the operating parameters and identifying the amount of PFC present in the source can be repeated using a previous change in the operating parameters as a starting point for further changes in the operating parameters.

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

[0033] In one embodiment, the method includes identifying a PFC concentration profile for the treatment cycle prior to the modifying step. Thus, the typically varying concentrations of PFCs present in the exhaust stream during a treatment cycle can be determined first to understand whether it is appropriate to adjust the operating parameters within each treatment cycle (if the treatment cycle is relatively long and the amount of PFCs present in the exhaust is relatively constant) or whether it would be more appropriate to vary the operating parameters between treatment cycles.

[0034] In one embodiment, the method provides that if the PFC concentration profile deviates significantly from the maximum deviation amount, the modifying step occurs in a subsequent processing cycle.

[0035] In one embodiment, the method includes selecting times within each treatment cycle when the PFC concentration profile deviates significantly from a maximum deviation amount to determine a change in the concentration of PFCs present in the exhaust stream.

[0036] According to a second aspect, an abatement apparatus configured to treat an exhaust flow containing PFCs from a processing tool is provided, the abatement apparatus comprising a controller operable to modify operating parameters controlling operating conditions of the abatement apparatus and a sensor operable to determine a change in the amount of PFC present in the exhaust flow of the abatement apparatus, the controller operable to determine whether to hold the operating parameters based on the change in the amount of PFC present in the exhaust flow determined by the sensor.

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

[0038] In one embodiment, the controller is operable to determine an initial concentration of PFCs present in the exhaust stream and a resultant concentration of PFCs present in the exhaust stream in response to the adjusted operating parameters.

[0039] In one embodiment, the operating conditions include one of an operating temperature and an oxidizing / reducing environment of the abatement device.

[0040] In one embodiment, the controller is operable to hold the adjusted operating parameters if the resulting PFC concentration is less than the initial PFC concentration.

[0041] In one embodiment, the controller is operable to hold the adjusted operating parameters if the resulting PFC concentration is less than the initial 8 PFC concentration but greater than or equal to the threshold concentration.

[0042] In one embodiment, the controller is operable to hold the adjusted operating parameters if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is less than the initial PFC concentration, but the resulting PFC concentration is greater than or equal to the threshold concentration.

[0043] In one embodiment, the controller is operable to one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters that would reduce the operating temperature if the adjusted operating parameters reduce the operating temperature and the resulting PFC concentration is greater than or equal to the initial PFC concentration, but the resulting PFC concentration is greater than or equal to the threshold concentration.

[0044] In one embodiment, the controller is operable to maintain the adjusted operating parameters if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is greater than or equal to the threshold concentration and the resulting PFC concentration is less than the initial PFC concentration.

[0045] In one embodiment, the controller is operable to one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters to increase the operating temperature if the resulting PFC concentration is less than the initial PFC concentration but less than the threshold concentration.

[0046] In one embodiment, the controller is operable to one of rejecting the adjusted operating parameters and preventing further modification of the operating parameters to increase the operating temperature if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is less than the initial PFC concentration but less than the threshold concentration.

[0047] In one embodiment, the controller is operable to maintain the adjusted operating parameters if the adjusted operating parameters reduce the operating temperature and the resulting PFC concentration is greater than or equal to the initial PFC concentration but less than the threshold concentration.

[0048] In one embodiment, the controller is operable to one of rejecting the adjusted operating parameters and preventing further changes to the operating parameters that would increase the operating temperature if the adjusted operating parameters increase the operating temperature and the resulting PFC concentration is less than the threshold concentration and the resulting PFC concentration is less than the initial PFC concentration.

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

[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 one of reject the adjusted operating parameters and prevent further changes to the operating parameters if the resulting PFC concentration is greater than or equal to the initial PFC concentration.

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

[0053] In one embodiment, the control device is operable such that the operating parameters include an oxidizer / fuel amount and the varying includes increasing the oxidizer / fuel amount, and if the resulting PFC concentration is greater than or equal to the initial PFC concentration, decreasing the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum value.

[0054] In one embodiment, the controller is operable to: determine whether the operating parameters include an oxidizer / fuel amount and whether the varying includes increasing the oxidizer / fuel amount; and to decrease the oxidizer / fuel amount while the resultant PFC concentration passes through a minimum if the resultant PFC concentration is greater than or equal to the initial PFC concentration but the resultant PFC concentration is less than a threshold concentration.

[0055] In one embodiment, the control device is operable to reduce the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum value, where the operating parameters include an oxidizer / fuel amount and the varying includes reducing the oxidizer / fuel amount, and if the resulting PFC concentration is less than the initial PFC concentration, the control device is operable to reduce the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum value.

[0056] In one embodiment, the control device is operable to reduce the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum value, where the operating parameters include an oxidizer / fuel amount and the varying includes reducing the oxidizer / fuel amount, and if the resulting PFC concentration is less than the initial PFC concentration, the control device is operable to reduce the oxidizer / fuel amount while the resulting PFC concentration passes through a minimum value.

[0057] In one embodiment, the control device is operable to decrease the oxidizer / fuel amount while the resultant PFC amount passes through a minimum if the operating parameter includes an oxidizer / fuel amount and the change includes decreasing the oxidizer / fuel amount, the resultant PFC concentration is less than a threshold concentration, and the resultant PFC concentration is less than an initial PFC concentration.

[0058] In one embodiment, the controller is operable to reject by changing the operating parameters back to the initial operating parameters.

[0059] 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.

[0060] In one embodiment, the control device is operable to adjust at least one of the oxygen source and the nitrogen source to adjust the oxidant / fuel amount when the operating parameters include an oxidant / fuel amount and the abatement device is supplied with an enriched air source augmented by at least one of the oxygen source and the nitrogen source.

[0061] In one embodiment, the controller is operable to iteratively cycle between changing the operating parameters and determining whether to retain the operating parameters.

[0062] In one embodiment, the sensor is operable to determine an initial PFC concentration in response to receiving an indication that a PFC is present in the effluent stream.

[0063] In one embodiment, the controller is operable to identify a PFC concentration profile for a process cycle prior to altering an operating parameter.

[0064] In one embodiment, the controller is operable to make changes to the operating parameters in subsequent process cycles if the PFC concentration profile deviates significantly from the maximum deviation amount.

[0065] In one embodiment, the controller is operable to select a time within each treatment cycle for determining a change in PFC mass concentration in the exhaust stream when the PFC concentration profile deviates significantly from a maximum deviation mass.

[0066] According to a third aspect, there is provided a computer program product operable, when executed by a computer, to control an abatement apparatus to carry out the method of the first aspect and embodiments thereof.

[0067] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate and in combinations other than those explicitly set out in the claims.

[0068] Where a device feature is described as operable to provide a certain functionality, this should be understood to include device features that provide that functionality or that are adapted or configured to provide that functionality.

[0069] Embodiments of the present invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0070] [Figure 1] 1 is a graph illustrating the amount of NOx generated and the amount of CF4 destroyed relative to temperature. [Diagram 2] 1 illustrates an internal combustion abatement device according to one embodiment. [Diagram 3] 1 is a graph showing the amount of NOx generated and the amount of CF4 destroyed relative to the oxygen injection flow rate. [Figure 4] 4 is a flow chart illustrating the main process steps performed by a controller according to one embodiment. [Diagram 5] 1 shows typical DRE and NOx emissions as a function of injected O2 from a single nozzle abatement device. [Figure 6] FIG. 2 is a plot of the concentration of CF4 in the exhaust as a function of O2 injection flow rate from the data of FIG. 1 (solid line), with the secondary Y-axis being the rate of change of CF4 concentration with respect to O2 injection flow rate (dashed line). [Figure 7] 13 is a plot showing O2 infusion flow rate versus computer algorithm iteration number at different starting points to solve for optimal infusion flow rate at 95% DRE for 1 SLM of CF4 with a dilution factor of 1000. [Figure 8] 13 is a plot of the CF4 flow rate (solid line) and O2 injection flow rate tracking (dashed line) from the tool by the algorithm (1000x dilution, pure O2). [Figure 9] As in FIG. 8, but showing DRE (solid line) and NOx emissions (dashed line). [Figure 10]1 is a plot showing O2 injection flow rate versus computer algorithm iterations at different O2 purities to determine the optimal injection flow rate at 95% DRE for 1 SLM of CF4 with a dilution factor of 1000. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] Before describing the embodiments in detail, an overview is provided. The embodiments provide an apparatus for controlling operating conditions within an abatement apparatus to reduce the presence of PFCs in the exhaust stream while controlling the production of unwanted by-products occurring within the abatement apparatus and / or controlling resources consumed by the abatement apparatus. For example, the operating temperature and / or the oxidizing / reducing environment within the abatement apparatus can be controlled to achieve target operating conditions, selected as known appropriate trade-off conditions that control the amount of reactive by-products produced and / or control resources consumed by the abatement apparatus while achieving a desired goal for PFC reduction. For example, emission regulations may require a certain minimum DRE of PFC gases, such as DRE>95% for CF4. Emission regulations may also specify limits on the emission of combustion by-products, such as NOx.

[0072] Abatement device 2 illustrates an internal combustion abatement system 10 according to one embodiment. The abatement system 10 includes an internally fired perforated burner 20 that is fed with a hydrocarbon fuel (typically methane or propane) / air mixture that provides a hot zone and ignition source for chemical destruction of target compounds in the effluent stream that is introduced into a combustion chamber 30 in the center of the burner using inlet piping 40 terminating in a nozzle 50. Generally, fuel is provided through a fuel inlet 100 into a plenum 90 for delivery to the perforated burner 20 under the control of a controller 120.

[0073] Nozzle 50 includes auxiliary ports arranged as a central lance 60 or a coaxial annulus 70 (fed from a shared plenum 80) used for the introduction of a fuel gas or oxidizer, which is provided under the control of a controller 120 to aid in the destruction of the compounds to be treated. Generally, an oxidizer / fuel mixture is fed into plenum 90 via central lance 60 and oxidizer / fuel inlet 110, and fed into the coaxial annulus 70 under the control of controller 120.

[0074] A sensor 130 is provided that measures the concentration of PFCs in the exhaust from the combustion chamber 30. The PFC concentration in the abatement exhaust can be measured by infrared absorption at a characteristic frequency of the PFC gas of interest. Fourier transform infrared (FTIR) spectrometers or mass spectrometers are known and can be used, but are expensive and can be damaged by prolonged exposure to acids and particulates in the exhaust stream. Inexpensive non-dispersive infrared (NDIR) sensors can also be used, but have a wide frequency response and can exhibit cross-sensitivity to other gases. Photoacoustic IR sensors may be more suitable, as they have a narrow frequency response, high sensitivity, and are resistant to corrosion.

[0075] Downstream of the combustion chamber 30 are a water weir and cooling section (not shown) for cooling the exhaust gas, and a packed tower (not shown) for absorbing water-soluble gases.

[0076] Example of operation Determining Operating Characteristics Although not required in all embodiments, the relationship between operating temperature, PFC DRE, and NOx production is first determined to improve the performance of the abatement system 10. Specifically, by measuring the change in PFC concentration in the abatement exhaust versus changes in injected oxygen, an operating region on a graph describing the relationship between oxygen flow rate, resulting NOx production, and PFC DRE can be determined, as shown in FIG. 3, and the oxygen injection flow rate can be optimized. This relationship can then be used to set the initial operating conditions (in this example, the initial oxygen flow rate) selected by the controller 120 and how the 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 required, as the controller 120 can alternatively implement a simpler relationship, as illustrated in FIG. 1, that assumes that an increase in operating temperature reduces the amount of PFC and increases the amount of NOx, and vice versa.

[0077] Control device operation The main steps performed by the controller 120 are described below: The controller 120 operates to control the operating conditions within the combustion chamber 30, in this example by adjusting the flow of injected oxygen (or fuel) to exactly achieve the required PFC DRE level, thereby controlling the operating temperature within the combustion chamber 30, thereby minimizing NOx production and emissions.

[0078] The main considerations for the controller in response to the PFC measured by sensor 130 are as follows: As the oxygen flow rate increases, the DRE increases (meaning the concentration of PFC in the exhaust decreases), and if the DRE is below the desired level, then the abatement system 10 is currently operating in region A shown in Figure 3 with too much PFC and too little NOx, and the oxygen flow rate must be increased until the DRE increases to the desired level (meaning the amount of PFC decreases).

[0079] As the oxygen supply flow rate increases, the DRE increases (meaning a decrease in the amount of PFC). If the DRE is equal to or greater than the required level, the abatement device is operating in a manner that causes too little PFC to be emitted and too much NOx to be generated in region B shown in Figure 3, so the oxygen supply flow rate must be reduced until the DRE decreases to the required level (meaning an increase in the amount of PFC).

[0080] If the DRE decreases (meaning that the amount of PFC increases) in response to an increase in the amount of oxygen supplied, the abatement device 10 will operate in region C shown in Figure 3, and the excess supply of oxygen will cause the operating temperature of the abatement device to drop, resulting in a decrease in DRE (increase in the amount of PFC) and excessive generation of NOx, so it is necessary to reduce the supplied oxygen flow rate so that the DRE passes through its maximum value (the amount of PFC passes through its minimum value - since the DRE passes through its maximum value, there are two points where 95% DRE can be obtained, and the point with the lowest oxygen utilization rate is the point where the least NOx is generated) and reduce the DRE to the required level (the PFC concentration increases to the required level).

[0081] It should be understood that embodiments contemplate other types of abatement devices, such as electrically heated or plasma fed abatement devices, which will generally exhibit similar characteristics to those shown in FIG.

[0082] FIG. 5 is a plot of DRE and NOx emissions as a function of premixed oxygen injection flow rate to the inlet from the abatement device in one embodiment. In this embodiment, the DRE reaches a maximum value between 20 and 25 SLM O2. Note that the curve passes through 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 beyond this will lead to increased NOx emissions and waste resources. Therefore, it is desirable to use the minimum oxygen flow rate that meets this standard.

[0083] Figure 6 (left plot) shows the residual CF4 in the exhaust gas, calculated from the DRE performance curve shown in Figure 5, assuming a CF4 flow rate of 1 SLM and a dilution factor of 1000 (this condition will be used to explain various examples in the following studies). Figure 6 (right plot) also shows the rate of change of the steady-state CF4 concentration with respect to the change in O2 injection flow rate. Above the minimum value of CF4 (i.e. at maximum DRE), the abatement worsens with increasing O2 injection flow rate. This characteristic can be used to establish the optimum of two possible solutions to achieve, for example, a DRE of 95%.

[0084] Control unit processing steps Figure 4 is a flow chart illustrating in greater detail the major steps performed by the controller 120 in one exemplary implementation described with reference to Figure 3. In this implementation, the target concentration in the exhaust is P0 (which may be set, for example, based on achieving 95% DRE), which will result in approximately 0.0065 lbs / hr of NOx.

[0085] In step S1, PFC gas enters the exhaust stream, which may be signaled from the process tool to controller 120, or may be detected by a mass flow controller (not shown) at the inlet to the abatement system 10, or may be detected by sensor 130. The process then proceeds to S2.

[0086] In step S2, the oxygen injection flow rate is set to a flow rate of F1 standard liters per minute (SLM) as an initial flow rate set point expected to achieve the required DRE. For example, as shown in Figure 3, the flow rate F1 can be set to 17.6 SLM. The process then proceeds to step S3.

[0087] In step S3, the sensor 130 measures an initial PFC concentration P1 in the exhaust gas. Then, the process proceeds to step S4.

[0088] In step S4, the oxygen injection flow rate into the FN SLM is increased by ΔF. Typically, the flow rate is increased by, for example, 5%. Then, the process proceeds to step S5.

[0089] In step S5, the resulting PFC concentration PN is measured using sensor 130. The process then proceeds to step S6.

[0090] In step S6, it is determined whether DRE has increased (meaning that PN is smaller than P1). If DRE has not increased, the process proceeds to step S7. If DRE has increased, the process proceeds to step S8.

[0091] In step S7, it is determined that the oxygen flow rate is excessive and the abatement system is operating in region C shown in Figure 3. Therefore, the oxygen injection flow rate is reduced by a predetermined percentage amount (e.g., 33%) and the process returns to step S3.

[0092] In step S8, the resulting concentration P N If the resulting concentration P is greater than the target concentration P0, the abatement device is operating in region A shown in FIG. 3, meaning that the DRE is too low, and the process returns to step S4. N If is less than the target concentration P0, which means the abatement system is operating in region B shown in Figure 3, the DRE is too high, the oxygen injection flow rate is reduced by ΔF, and the process returns to step S5. If the concentration matches the target concentration, it means the DRE has been achieved, and no further changes to the oxygen injection flow rate are necessary at this point.

[0093] If at a future time it is desired to re-evaluate whether the abatement system 10 is operating optimally, the process can return to step S3 and repeat.

[0094] In an alternative approach to the characteristics shown in Figures 5 and 6, the search strategy is as follows. (1) Using the provided parameters (required DRE, CF4 inflow to the abatement system, dilution factors for the system and pump purge), determine the desired CF4 concentration in the exhaust. (2) Measure the CF4 concentration in the exhaust when injection begins. (3) Increase the injection flow rate by a given step size, remeasure the CF4 concentration, and if it is below the target value and the CF4 concentration decreases with increasing O2 injection, accept the new conditions and repeat. (4) If the new concentration is lower than the target value, decrease the injection flow rate until it exceeds the target value, decrease the step size of (3), and repeat (3). (5) If the new concentration is higher than the target value and the CF4 concentration is increasing with increasing injection flow rate, reduce the injection rate and repeat (5) until the CF4 concentration is lower than the target value, then perform (4) until it is higher than the target value, and then proceed to (3). (6) Continue executing (3) until either the target value is reached or the step size reaches a lower bound (this covers the case where the target DRE cannot be reached, and ends with the best solution that can be found). (7) Once a solution is found, the optimal history value is used as the starting point for initiating injection, allowing future searches to find a solution faster.

[0095] A BASIC computer program to perform this search (i.e., curve fit to the DRE performance in Figure 5) using model data as a proxy for measured values ​​of CF4 in the exhaust is provided in the Appendix.

[0096] An example of the search for the optimal injection flow rate starting from different initial conditions is shown in Fig. 7. It shows that the algorithm is stable even at extreme starting points and copes well with finding the desired solution combining a target DRE of 95% and the lowest possible NOx.

[0097] Optimizing processing cycles It is not expected that PFC gas will flow to the abatement system 10 at all times. In practice, the PFC flow will be intermittent corresponding to one or two processing steps on each wafer. The PFC gas flow to the abatement system 10 may also vary within a processing step, for example, generated by consumption of gas in etching a layer of material on the wafer and then increasing as the layer is etched (known as overetch). Thus, embodiments account for this variation by learning the optimal injection flow rate for a series of wafers undergoing the same process. Once the presence of PFC gas is detected, the sensor 130 can then be monitored during this period and a profile indicative of the amount of PFC generated over time can be identified for evaluation. If the amount of PFC is relatively constant, a processing step can be performed within each processing period, in other words, intra-processing period optimization typically occurs. However, if the PFC amount varies more than a particular amount, then an average PFC amount for each processing step can be calculated and the processing steps can be performed at times when the PFC amount most closely matches that average amount; in other words, inter-processing period optimization typically occurs.

[0098] A method to account for such flow rate variations is to "learn" the optimum injection flow rate for a series of wafers undergoing the same process. If a digital signal is available indicating when the PFC gas is flowing, the sensor 130 readings can be monitored during this period and an average calculated. The oxygen injection flow rate is increased for the next wafer processing, and the sensor 130 readings are averaged for this next wafer. The same method described above is then used to determine if the injection flow rate needs to be further increased or decreased for each subsequent wafer until the optimum setting is obtained.

[0099] Figure 8 shows a typical time profile of the inlet CF4 from a series of etching processes and the corresponding tracking of the O2 injection flow rate using the control algorithm (by storing the last best historical value, which can be used to speed up finding the solution). After finding the solution in the first etching cycle, the injection flow rate of the subsequent steps can be quickly set to its optimal flow rate, and the resulting 95% CF4 DRE and low NOx can be obtained in a timely manner, as shown in Figure 9.

[0100] Many semiconductor manufacturing plants derive their oxygen supply from an air separation unit (usually a pressure swing adsorption unit). The oxygen purity is typically 90-95% and is of unknown and variable quality. If the abatement unit was always supplied with oxygen of constant purity, the system could be configured to inject the same amount of oxygen every time CF4 flows to obtain the desired performance, and exhaust monitoring to obtain the optimal flow rate would not be necessary. In practice this rarely occurs, and this method helps to solve this problem by adjusting the O2 injection flow rate (impurities) in response to the CF4 concentration in the exhaust. By way of example, FIG. 10 shows the results resulting from various input levels into a search for O2 purity to achieve a DRE of 95% for CF41SLM at 1000 times system dilution from an initial flow rate of zero.

[0101] Also, in another embodiment, rather than adjusting the oxygen injection rate for a constant fuel injection rate, the oxygen injection rate can be kept constant and the fuel injection rate adjusted.

[0102] A similar method can also be applied to plasma abatement devices: instead of adjusting oxygen or fuel injection rates to adjust combustion conditions, the injection rate of a reagent such as air, and / or the power to the plasma can be adjusted in response to PFC exhaust sensor measurements.

[0103] If a PFC flow "on" digital signal is not available, to train a series of wafers, the presence of a PFC exhaust gas sensor signal (above some background noise level) can be used to detect when PFC gas is flowing and, consequently, to determine when to start and stop measuring PFC emission levels.

[0104] Oxygen supply The oxidant supplied to the abatement system 10 can come from a pure oxygen source, although in some embodiments, an "oxygen-enriched air source" is provided. Specifically, oxygen-enriched air is typically composed of 85% to 95% oxygen with the remainder being nitrogen. It can be produced from air at lower cost and is safer than having a pure oxygen source. In this case, instead of adjusting the oxygen injection flow rate, the "oxygen-enriched air" injection flow rate can be kept constant and the oxygen concentration can be adjusted by dilution with nitrogen (or enrichment with pure oxygen).

[0105] In one embodiment, to obtain CF4DRE>95% and minimum NOx, pure oxygen injection is found to have an optimum flow rate of 17 slm per nozzle.

[0106] If the premix injection flow rate is set at 20 SLM per nozzle (using standard flow regulators) and the oxygen supply is always diluted to a concentration of 85%, this will achieve optimal conditions.

[0107] Then, using the oxygen concentration measurements and knowing how many times it needs to be injected, a single 20 SLM nitrogen mass flow controller (MFC) can be used to add the desired amount of nitrogen and dilute the oxygen enriched air for the six nozzles to 85% O (rather than using six MFCs).

[0108] Example: Required oxygen concentration per nozzle is 17 SLM, measured oxygen concentration is 95%, target concentration is 85%, 6 injection operations in this case, Set the premix injection flow rate per nozzle to 17 / 0.85=20 SLM 6 nozzles require 6x17=102 SLM of oxygen This requires 102 / 0.95=107.4 SLM of 95% oxygen-enriched air. · Therefore, add 120-107.4=13.6 SLM of nitrogen.

[0109] General: Required oxygen concentration per nozzle is A SLM, measured oxygen concentration is y%, target concentration is x%, n injection operations in this case, Set the premix injection flow rate per nozzle to A / x SLM (constant) n nozzles require nA SLM oxygen This requires nA / y SLM of oxygen-enriched air at a concentration of y%. · Hence, (nA / x-nA / y)=(nA / x).(1-x / y) SLM of nitrogen is added.

[0110] Assume the accuracy of the MFC is 1% full scale (0.2 SLM of N2). The worst case error is for only one injection running when only 0.2 SLM = 1.1% of the oxygen can escape (17 SLM). Thus the error is no worse than using a separate MFC for each injection (it is better if multiple injections are turned on).

[0111] Thus, embodiments provide a method for optimizing PFC abatement using exhaust gas sensors. Sensors in the exhaust of a thermal abatement system can measure the concentration of the PFC gas being abated, and can also measure other by-products. The sensor signals are used to adjust the condition of the abatement equipment, and the sensor response to the adjustments is used to determine optimal settings that achieve sufficient abatement while minimizing the generation of undesirable by-products such as NOx.

[0112] Although exemplary embodiments of the present invention are disclosed in detail herein with reference to the accompanying drawings, it should be understood that the present invention is not limited to the detailed embodiments, and various changes and modifications may be made therein by those skilled in the art without departing from the scope of the present invention as defined by the appended claims and their equivalents.

[0113] Appendix: Program list for finding optimal abatement conditions 10 REM program to demonstrate optimization of oxygen inject for CF4 abatement 20 REM using (simulated) measurement of CF4 concentration in exhaust 30 REM with lowest use of resources and emissions of NOx (simulated) 40 50 REM control algorithm requires CF4 flow (from tool) and 60 REM knowledge of the dilution factor of the gas leaving the exhaust 70 REM in order to calculate desired CF4 concentration there 80 REM which achieves specified destruction rate efficiency (DRE) 90 100 REM input conditions 110 REPEAT 120 REM only accept values ​​0-100% 130 INPUT "Target DRE (%)"; DRE% 140 UNTIL (DRE% >= 0) AND (DRE% <= 100) 150 160 INPUT "Dilution factor"; dilution_factor 170 180 REM initialise historic best value (of inject flow to store for future use 190 LET last_best_inject = 0 200 210 REPEAT 220 230 REM get CF4 flow (this would be from tool) 240 INPUT "CF4 flow (slm)"; CF4_flow 250 260 REM calculate CF4 concentration in ppm at required DRE 270 LET target% = (CF4_flow * (100 - DRE% ) / 100 / dilution_factor * 1E6) 280 290 REM step size for changing inject 300 LET step_inject = 4 310 320 REM get starting inject 330 INPUT "Initial O2 inject flow (slm)"; old_inject 340 350 REM use last_best_inject if starting point negative 360 REM back it off by the step size to force search to converge after one iteration 370 IF (old_inject < 0) THEN LET old_inject = last_best_inject - step_inject 380 390 REM get O2 purity in range 80-100% 400 REM (this would be unknown in practice - 410 REM ca.90-95% from industrial pressure swing adsorption generators) 420 REPEAT 430 INPUT "O2 purity (80-100%)"; O2_purity 440 UNTIL (O2_purity >=80) AND (O2_purity <=100) 450 460 REM initialise starting CF4 concentration in exhaust 470 LET old_conc% = FNmeasure_CF4(old_inject) 480 PRINT "current inject (slm): ";old_inject;", CF4 (ppm): ";old_conc%;", inject step (slm): ";step_inject;" NOx (g / hr): "+STR$(FNmeasure_NOx(inject)) 490 500 REM main loop to find solution 510 REPEAT 520 530 REM done% is Boolean flag to denote that we've already dealt with each case (it avoids GOTO statements) 540 LET done% = FALSE 550 560 IF (CF4_flow = 0) THEN 570 REM turn inject off, no CF4 to treat 580 LET old_inject = 0 590 REM make step_inject zero 600 LET step_inject = 0 610 PRINT "Inject off" 620 REM set flag to show we've accepted new conditions 630 LET done% = TRUE 640 ENDIF 650 660 REM measure CF4 concentration at provisionally better inject 670 LET new_inject = old_inject + step_inject 680 REM trap negative values 690 IF (new_inject < 0) THEN LET new_inject = 0 700 REM measure at new inject setting 710 LET new_conc% = FNmeasure_CF4(new_inject) 720 REM display result 730 PRINT "CF4 new (ppm): ";new_conc%;", target (ppm): ";target% 740 750 IF (done% = FALSE) THEN 760 REM we are too low but going the right way 770 IF (new_conc% >= target%) AND (new_conc% < old_conc%) THEN 780 REM accept new inject 790 REM set flag to show we've accepted new conditions 800 LET done% = TRUE 810 ENDIF 820 ENDIF 830 840 IF (done% = FALSE) THEN 850 REM are too high but going the right way 860 IF (step_inject < 0) AND (new_conc% =< target%) THEN 870 REM accept new inject 880 REM set flag to show we've accepted new conditions 890 LET done% = TRUE 900 ENDIF 910 ENDIF 920 930 REM check to see if either of the above changes have reached the target 940 REM don't make any further changes to the inject in that case 950 IF (done% = TRUE) AND (new_conc% = target%) THEN 960 IF (step_inject > 0) AND (new_conc% < old_conc%) THEN LET step_inject = 0 970 IF (step_inject < 0) AND (new_conc% > old_conc%) THEN LET step_inject = 0 980 ENDIF 990 1000 IF (done% = FALSE) THEN 1010 REM we are much too high but going right way 1020 IF (step_inject < 0) AND (new_conc% < old_conc%) THEN 1030 REM accept new inject 1040 REM set flag to show we've accepted new conditions 1050 LET done% = TRUE 1060 ENDIF 1070 ENDIF 1080 1090 REM if we've accepted the change in inject so far then store new_conc in old_conc 1100 IF (done% = TRUE) THEN 1110 LET old_conc% = new_conc% 1120 LET old_inject = new_inject 1130 REM print status on screen 1140 PRINT "Change accepted!" 1150 ENDIF 1160 1170 REM now consider cases where we are changing the inject in the wrong d irection 1180 1190 IF (done% = FALSE) THEN 1200 REM abatement too good, in region DRE better than required 1210 IF (new_conc% < target%) THEN 1220 REM decrease inject by making step_inject negative 1230 LET step_inject = ABS(step_inject) * -1 1240 REM print status on screen 1250 PRINT "Change rejected! Decreasing inject" 1260 REM set flag to show we've accepted new conditions 1270 LET done% = TRUE 1280 ENDIF 1290 ENDIF 1300 1310 IF (done% = FALSE) THEN 1320 REM much too high, abatement getting worse again as inject is increased 1330 IF (step_inject > 0) AND (new_conc% > old_conc%) THEN 1340 REM decrease inject by making step_inject negative 1350 LET step_inject = ABS(step_inject) * -1 1360 REM print status on screen 1370 PRINT "Change rejected! Decreasing inject" 1380 REM set flag to show we've accepted new conditions 1390 LET done% = TRUE 1400 ENDIF 1410 ENDIF 1420 1430 IF (done% = FALSE) THEN 1440 REM we are too low and going the wrong way 1450 IF (step_inject < 0) AND (new_conc% > old_conc%) AND (new_conc% > target%) THEN 1460 REM increase inject more slowly by reducing size of step_inject 1470 LET step_inject = ABS(step_inject / 2) 1480 REM print status on screen 1490 PRINT "Change rejected! Increasing inject more slowly" 1500 REM set flag to show we've accepted new conditions 1510 LET done% = TRUE 1520 ENDIF 1530 ENDIF 1540 1550 IF (done% = FALSE) THEN 1560 REM none of the above apply 1570 REM print status on screen 1580 PRINT "Something amiss! Reducing search window" 1590 REM reduced step size 1600 LET step_inject = step_inject / 2 1610 ENDIF 1620 1630 REM print status of algorithmn on screen and to file 1640 PRINT "current inject: ";old_inject;" slm, CF4: ";old_conc%;" ppm, inject step: ";step_inject;" slm, NOx: ";FNmeasure_NOx(old_inject);" g / hr" 1650 1660 REM wait for a second 1670 WAIT(100) 1680 1690 REM stop when either we've found a solution or the step_size is very small 1700 UNTIL (ABS(step_inject) < 0.01) 1710 1720 REM check to see if target achieved 1730 IF (old_conc% = target%) THEN 1740 REM solution found 1750 PRINT"Target DRE achieved!" 1760 REM store this in last_best_inject 1770 LET last_best_inject = old_inject 1780 ENDIF 1790 1800 REM check to see if target not achieved 1810 IF (old_conc% <> target%) THEN 1820 PRINT "Failed to achieve target!" 1830 ENDIF 1840 1850 REM ask if another condition to be tested 1860 REPEAT 1870 INPUT "Do another (Y / N)"; reply$ 1880 REM concentate to first character 1890 LET reply$ = LEFT$(reply$,1) 1900 REM only accept Y / y or N / n 1910 UNTIL (reply$ = "N") OR (reply$ = "n") OR (reply$ = "Y") OR (reply$ = "y") 1920 1930 UNTIL (reply$ = "N") OR (reply$ = "n") 1940 1950 END 1960 1970 DEF FNmeasure_CF4(inject) 1980 REM this is a proxy for actual measurement on exhaust 1990 PRINT "Inject: ";inject; 2000 REM accomodate purity of oxygen 2010 LET inject = inject*O2_purity / 100 2020 PRINT;" slm, O2 content: ";inject;" slm" 2030 REM calculate DRE from model 2040 LET DRE_actual = -0.000000292*inject^4 + 0.0000525*inject^3 - 0.003520833*inject^2 + 0.09925*inject 2050 REM print DRE rounded up to nearest whole number 2060 PRINT "DRE: ";INT(DRE_actual*100 + 0.5)"% "; 2070 REM calculate amount of CF4 in slm in exhaust 2080 LET CF4_out = CF4_flow * (1 - DRE_actual) 2090 REM return concentration in exhaust in ppm 2100 REM rounded to nearest whole number 2110 = INT((CF4_out / dilution_factor * 1E6) + 0.5) 2120 2130 DEF FNmeasure_NOx(inject) 2140 REM this is a proxy for actual measurement on exhaust 2150 REM accomodate purity of oxygen 2160 LET inject = inject*O2_purity / 100 2170 REM calculate NOx from model 2180 IF (inject < 10) THEN LET NOx = 5 2190 IF (inject >= 10) THEN LET NOx = 5*(inject - 10) + 5 2200 REM round to nearest whole number 2210 = INT(NOx + 0.5) [Explanation of symbols]

[0114] 10 Abatement equipment 20 Perforated Burner 30 Combustion chamber 40 Inlet pipe 40 50 nozzles 60 Central Lance 70 Coaxial Annulus 80, 90 Plenum 100 Fuel inlet 110 Fuel / Oxidizer Inlet 120 Control device 130 Sensors

Claims

1. 1. A method of optimizing operating conditions in an abatement apparatus configured to treat an effluent stream containing PFCs from a processing tool, comprising: Varying operating parameters that control operating conditions of the abatement device; determining a change in PFC concentration by measuring the PFC concentration present in the exhaust stream of the abatement device; determining whether to hold the operating parameters based on the change in PFC concentrations; Including, the modifying step includes adjusting the operating parameters from initial operating parameters to adjusted operating parameters; determining the change includes determining an initial concentration of PFCs present in the exhaust stream and a resultant concentration of PFCs present in the exhaust stream in response to the adjusted operating parameters; the operating conditions include one of an operating temperature and an oxidizing / reducing environment of the abatement device; if the adjusted operating parameters increase the operating temperature and the resultant PFC concentration is less than the initial PFC concentration but the resultant PFC concentration is equal to or greater than a threshold concentration, the determining step includes maintaining the adjusted operating parameters. method.

2. 2. The method of claim 1, wherein if the adjusted operating parameters decrease the operating temperature and the resulting PFC concentrations are greater than or equal to the initial PFC concentrations, but the resulting PFC concentrations are greater than or equal to the threshold concentration, the determining step comprises one of rejecting the adjusted operating parameters and preventing further modification of the operating parameters to decrease the operating temperature; if the adjusted operating parameters increase the operating temperature and the resulting PFC concentrations are less than the initial PFC concentrations, but the resulting PFC concentrations are less than the initial PFC concentrations, the determining step comprises one of rejecting the adjusted operating parameters and preventing further modification of the operating parameters to increase the operating temperature; and if the adjusted operating parameters decrease the operating temperature and the resulting PFC concentrations are greater than or equal to the initial PFC concentrations, but the resulting PFC concentrations are less than the threshold concentration, the determining step comprises retaining the adjusted operating parameters.

3. The abatement apparatus comprises an abatement chamber, and the operating parameters include at least one of power supplied to heat the abatement chamber, a plasma supplied to the abatement chamber, and an amount of oxidant / fuel supplied to the abatement chamber, the operating parameters include the amount of oxidant / fuel and the modifying step includes increasing the amount of oxidant / fuel, and if the resultant PFC concentration is greater than or equal to the initial PFC concentration, the determining step includes decreasing the amount of oxidant / fuel while the resultant PFC concentration passes through a minimum value, or the operating parameters include the amount of oxidant / fuel and the modifying step includes increasing the amount of oxidant / fuel.

3. The method of claim 1 or 2, wherein the operating parameter includes the oxidizer / fuel amount and the varying includes decreasing the oxidizer / fuel amount, and if the resultant PFC concentration is greater than or equal to the threshold, the determining includes decreasing the oxidizer / fuel amount while the resultant PFC concentration passes through a minimum value; or wherein the operating parameter includes the oxidizer / fuel amount and the varying includes decreasing the oxidizer / fuel amount, and if the resultant PFC concentration is less than the initial PFC concentration, the determining includes decreasing the oxidizer / fuel amount while the resultant PFC concentration passes through a minimum value.

4. 4. The method of claim 3, wherein the operating parameter includes the oxidizer / fuel amount, and the varying step includes decreasing the oxidizer / fuel amount, and if the resultant PFC concentration is less than the threshold concentration and the resultant PFC concentration is less than the initial PFC concentration, the determining step includes decreasing the oxidizer / fuel amount while the resultant PFC concentration passes through a minimum value.

5. 5. The method of claim 3 or 4, wherein the rejecting step includes the step of returning the operating parameter to the initial operating parameter, and / or the rejecting step includes the step of modifying the operating parameter to a value between the initial operating parameter and the adjusted operating parameter, and / or, if the operating parameter includes the oxidizer / fuel amount and the abatement device is supplied by a source of enriched air augmented by at least one of an oxygen source and a nitrogen source, the modifying step includes the step of adjusting at least one of the oxygen source and the nitrogen source to adjust the oxidizer / fuel amount.

6. The method of claim 1 , comprising repeating the modifying and determining steps iteratively.

7. 7. The method of claim 1, wherein the determining step comprises determining the initial PFC concentration in response to receiving an indication that PFCs are present in the effluent stream.

8. 8. The method of claim 1, further comprising identifying a PFC concentration profile for the treatment cycle prior to said modifying step.

9. The method of claim 8 , wherein if the PFC concentration profile deviates significantly from a maximum deviation amount, the modifying occurs in a subsequent processing cycle.

10. 10. The method of claim 9, comprising selecting a time within each treatment cycle to determine the change in the PFC concentration present in the exhaust stream when the PFC concentration profile deviates significantly from the maximum deviation amount.

11. An abatement apparatus configured to perform the method of any one of claims 1 to 10 to treat an exhaust stream containing PFCs from a process tool, comprising: a controller operable to vary operating parameters that control operating conditions of the abatement device; a sensor operable to determine a change in the amount of PFCs present in the exhaust stream of the abatement device; Equipped with The abatement system, wherein the controller is operable to determine whether to hold the operating parameters based on a change in the amount of PFCs present in the exhaust stream as determined by the sensor.

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