Title of Invention	GAS COMBUSTION APPARATUS
Abstract	A method of combusting ammonia is described, in which an exhaust gas containing varying amounts of at least ammonia and hydrogen is conveyed from a chamber to a combustion nozzle (34) connected to a combustion chamber (36). A combustion gas for forming a combustion flame within the chamber is supplied to the chamber. Depending on the relative amounts of ammonia and hydrogen exhaust from the chamber, hydrogen is added to the exhaust gas so that, when the exhaust gas contains ammonia, the gas combusted by the flame contains at least a predetermined amount of hydrogen.

Title of Invention

GAS COMBUSTION APPARATUS

Abstract

A method of combusting ammonia is described, in which an exhaust gas containing varying amounts of at least ammonia and hydrogen is conveyed from a chamber to a combustion nozzle (34) connected to a combustion chamber (36). A combustion gas for forming a combustion flame within the chamber is supplied to the chamber. Depending on the relative amounts of ammonia and hydrogen exhaust from the chamber, hydrogen is added to the exhaust gas so that, when the exhaust gas contains ammonia, the gas combusted by the flame contains at least a predetermined amount of hydrogen.

Full Text	GAS COMBUSTION APPARATUS The present invention relates to apparatus for, and a method of, combusting an exhaust gas containing at least ammonia. A primary step in the fabrication of semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of vapourjjrecursors. One known technique for depositinjg_a thin film on a substrate is chemical vapour deposition (CVD). In this technique, process gases are supplied to a process chamber housing the substrate and react to form a thin film over the surface of the substrate. An example of a material commonly deposited on to a substrate is gallium nitride (GaN). GaN, and related material alloys (such as InGaN. AIGaN and InGaAIN) are compound semiconductors used for the manufacture of green, blue and white light emitting devices (such as LEDs and laser diodes) and power devices (such as HBTs and HEMTs). These compound semiconductors are usually formed using a fomn of CVD usually known as MOCVD (metal organic chemical vapour deposition). In overview, this process involves reacting together volatile organometallic sources of the group III metals Ga, In and/or Al, such as trimethyl gallium (TMG), trimethyl indium (TMI) and trimethyl aluminium (TMA), with ammonia at elevated temperatures to form thin films of material on wafers of a suitable substrate material (such as Si, SIC, sapphire or AIN)^^^ydrogen gas is generally also present, providing a carrier gas for the organometallic precursor and the other process gases. Following the deposition process conducted within the process chamber, there is typically a residual amount of the gases supplied to the process chamber contained in the gas exhaust from the process chamber. Process gases such as ammonia and hydnDgen are highly dangerous if exhausted to the atmosphere, and so in view of this, before the exhaust gas is vented to the atmosphere, abatement apparatus is often provided to treat the exhaust gas to convert the more CONFIRMATION COFir hazardous components of the exhaust gas into species that can be readily removed from the exhaust gas, for example by conventional scrubbing, and/or can be safely exhausted to the atmosphere. One known type of abatement apparatus is described in EP-A-0 819 887. This abatement apparatus comprises a combustion chamber having an exhaust gas combustion nozzle for receiving the exhaust gas to-be treated. An annular combustion nozzle is provided outside the exhaust gas nozzle, and a gas mixture of a fuel and air is supplied to the annular combustion nozzle for forming a flame inside the combustion chamber for burning the exhaust gas received from the process chamber to destroy the harmful components of the exhaust gas. This form of abatement apparatus is generally located downstream from a pumping system for drawing the exhaust gas from the process chamber. To prevent damage to the pumping system as the exhaust gas passes therethrough, a nitrogen purge gas is typically supplied to one or more purge ports of the pumping system for pumping with the exhaust gas. As a result, the gas received by the abatement apparatus usually also contains a significant amount of nitrogen. Nitrogen is safe and requires no abatement. With the apparatus such as that described in EP-A-0 819 887, we have found that the destruction and removal efficiency (DRE) of hydrogen is very high, often exceeding 99.99%, whilst the DRE , of ammonia is highly variable depending on tfie~other gases contained within the exhaust gas entering the abatement apparatus. Ammonia is highly toxic, having a threshold limit value, or TLV, of 25 ppm, and we have found that the amount of ammonia exhaust from the abatement apparatus can be as high as 2400 ppm depending on the chemistry and the relative amounts of the gases contained within the exhaust gas. It is an aim of at least the preferred embodiment of the present invention to seek to provide a method of, and apparatus for, combusting ammonia with a consistently high DRE irrespective of the other gases, and the relative amounts thereof, present in an exhaust gas containing the ammonia. In a first aspect, the present invention provides a method of combusting ammonia, the method comprising the steps of conveying an exhaust gas containing varying^ amounts of at least ammonia andJiydrogen from_a chamber to a combustion ^nozzle connected to a combustion chamber, supplying to the chamber a combustion gas for forming a combustion flame within the chamber, and selectively adding hydrogen to the exhaust gas depending on the relative amounts of ammonia and hydrogen exhaust from the chamber so that, when the exhaust gas contains ammonia, the gas combusted by the flame contains at least a predetermined amount of hydrogen. We have found that the destruction and removal efficiency (DRE) of ammonia is significantly enhanced when a predetermined amount of hydrogen is present in the gases to be combusted by the flame. By selectively adding hydrogen to the ' exhaust gas when the exhaust gas contains ammonia but not a sufficient amount of hydrogen to achieve a high DRE of ammonia, the DRE of ammonia can be maintained at a consistently high level. In one preferred embodiment the hydrogen is conveyed to the nozzle for additien to the exhaust gas, where theliydrogen is preferably injected into the combustion chamber from a plurality of apertures extending about the combustion nozzle. In another prefen'ed embodiment, the hydrogen is added to the exhaust gas upstream from the combustion nozzle, thereby promoting mixing of the additional hydrogen with the exhaust gas. The addition of hydrogen to the exhaust gas may be timed according to the cycle of gas supply to the chamber. Alternatively, the amount of hydrogen added to the exhaust gas may be adjusted in response to the reception of data indicative of a variation of the chemistry of the gas exhaust from the chamber,. The data indicative of the variation of the chemistry of the exhaust gas being supplied by the process tool, for example when the gases supplied to the chamber do not contain sufficient hydrogen to achieve a high ammonia DRE. Alternatively, a gas sensor may be located within a conduit system for conveying the exhaust gas to the nozzle, with this sensor being configured to supply the data. Hydrogen-is preferably added to-the exhaust gas so that the ratio by volume of hydrogen to ammonia combusted by the flame is at least 1:1, We have found that mixtures of hydrogen, ammonia and nitrogen in approximate ratios of 1:1:1 and 2:1:1 respectively can be combusted below the TLV of ammonia using only a pilot flame of the combustion chamber. The pilot flame is typically formed from a mixture of fuel and oxidant, for example methane and air, in a ratio by volume of between 1:8 and 1:12. Consequently, the amount of methane or other fuel supplied to the chamber to form the combustion flame can be significantly reduced, thereby reducing operating costs. In a second aspect, the present invention provides apparatus for combusting exhaust gas;'the apparatus comprising a combustion chamberf^mean&for supplying to the chamber a combustion gas for forming a combustion flame within the chamber, a combustion nozzle connected to the combustion chamber, means for conveying an exhaust gas containing varying amounts of at least ammonia and hydrogen from a chamber to the nozzle, and means for selectiveTy adding hySrogen to the exhaust gas depending on the relative amounts of ammonia and hydrogen exhaust from the chamber. Features described above in relation to method aspects of the invention are equally applicable to apparatus aspects of the invention, and vice versa. Preferred features of the present invention will now be described with reference to the accompanying drawing, in which Figure 1 iliustrat^s a process chamber connected to a combustion appargtus according to one embodiment of the invention; Figure 2 Illustrates a cross-sectional view of a plurality of exhaust gas combustion nozzles connected to a combustion chamber of the combustion apparatus of Figure 1; Figure 3 illustrates an arrangement for supplying hydrogen to each^combustion nozzle connected to the combustion chamber of Figure 2; Figure 4 illustrates a control system for controlling the amount of hydrogen supplied to each combustion nozzle of Figure 2; and Figure 5 illustrates a process chamber connected to a combustion apparatus according to another embodiment of the Invention. With reference first to Figure 1, combustion apparatus 10 Is provided for treating gases exhausting from a process chamt)er 12 for processing> for example, semiconductor devicesvilat panel display devices or solar panel devices.^vThe chamber 12 receives various process gases for use in performing the processing within the chamber. In this example. MOCVD (metal organic chemical vapour deposition) of a layer of material such as GaN is performed within the process chamber 12. Gases comprising organometallic sources of the group III metals Ga, In and/or Al, such as trimethyl gallium (TMG), trimethyl indium (TMI) and trimethyl aluminium (TMA), ammonia and hydrogen are conveyed to the process chamber 12 from respective sources 14.16,18 thereof at elevated temperatures to form thin films of material on wafers of a suitable substrate material (such as SI, SIC, sapphire or AIN). An exhaust gas is drawn from the outlet of the process chamber 12 by a pumping system 20. During the processing within the chamber, only a portion of the process gases will be consumed, and so the exhaust gas will contain a mixture of the process gases supplied to the chamber, and by-products from the processing within the chamber. As illustrated in Figure 1, the pumping system 20 may comprise a secondary pump 22, typically in the form of a turbomolecular pump, for drawing the exhaust gas from the process chamber. The turbomolecular pump 22 can generate a vacuum of at least 10*^ mbar in the process chambei:42- The gas is typically exhausted from the tufbomolecular pump 22 at a pressure of around 1 mbar. In view of this, the pumping system also comprises a primary, or backing pump 24 for receiving the gas exhaust from the turbomolecular pump 22 and raising the pressure of the gas to a pressure around atmospheric pressure. In order to prevent damage to the pumping system 20 during pumping of the gases from the process chamber 12, a nitrogen purge gas is supplied from a source 26 thereof to one or more purge ports 28, 30 of the pumping system 20. The gas exhaust from the pumping system 22 is conveyed to an inlet 32 of the combustion apparatus 10. As illustrated in Figure 2, the inlet 32 comprises at least one exhaust gas combustion nozzle 34 connected to a combustion chamber 36rof the combustion apparatus 10. Each combustion nozzle 34 has an inlet 38 for receiving the exhaust gas, and an outlet 40 from which the exhaust gas enters the combustion chamber 38. Whilst Figure 2 illustrates two combustion nozzles 34 for receiving the exhaust gas, the inlet 32 may comprise any suitable number, for example four, six or more, combustion nozzles 34 for receivingThe exhaust gas. In the preferred embodiments, the Inlet 32 comprises four combustion nozzles 34. In this embodiment of the Invention, each combustion nozzle 34 includes a hydrogen inlet 42 for receiving hydrogen from a source 44 thereof (illustrated in Figure 3). An annular gap 46 defined between the outer surface of the nozzle 34 and the Inner surface of a sleeve 48 extending about the nozzle 34 allows the hydrogen to be conveyed from the Inlet 42 to a plurality of hydrogen outlets 50 surrounding the nozzle 34 and from which the hydrogen enters the combustion chamber 36 co-axially with the exhaust gas. As illustrated in Figure 2, each combustion nozzle 34 is mounted in a first annular plenum chamber 52 having an inlet 54 for receiving a first gas mixture of fuel and oxidant, for example, a mixture of methane and air, providing a combustion gas for forming combustion flames within the combustion chamber 36, and a plurality of outlets-56 from which the combustion gas is conveyed into the combustion chamber 36. As illustrated in Figure 2, the combustion nozzles 34 are mounted in the first plenum chamber 52 such that each nozzle 34 passes substantially co-axially through a respective outlet 56, such that the combustion gas is conveyed into the combustion chamber 36 about the sleeves 48 of the combustion nozzles 34, As also illustrated in Figure 2, the first plenum chamber 52 is located above a second annular plenum chamber 58 having an inlet 60 for receiving a second, pilot gas mixture of fuel and oxidant, for example, another mixture of methane and air, for forming pilot flames within the combustion chamber 36. As illustrated in Figure 2, the second plenum chamber 58 comprises a plurality of first apertures 62 coaxial with the outlets 56 from the first plenum chamber 52 and through which the combustion nozzles 34 extend into the combustion chamber 36, and a plurality of second apertures 64 surrounding the first apertures 62. The second apertures 64 allow the pilot gas mixture to enter the combustion chamber 36 to form the pilot ~Tlame for igniting the combustion gas to fonri combustion flames within the combustion chamber 36. In the event that the abatement device is operated in pilot only then the supply of combustion gas to the first plenum chamber 52 may be disconfinued. The pilot fiame formed at the apertures 64 is then used to ignite the exhaust gas and any additional hydrogen supplied to the nozzles 34. Figure 4 illustrates a control system for controlling the supply of hydrogen to each of the combustion nozzles 34, The control system comprises a controller 70 for receiving signals 72 data indicative of a variation of the chemistry of the exhaust gas output from the process chamber 12 and thus supplied to the combustion nozzles 34. Each of the signals 72 may be received directly from a process tool 74 controlling the supply of gases to the process chamber 12 using valves 75, as illustrated in Figure 1. Altematively. the signals 72 may be received from a host computer of a local area network of which the controller 70 and the controller of the process tool 74 form part, the host computer being configured to receive information from the controller of the process tool regarding the chemistry of the gases supplied to the process chamber and to output the signals 72 to the controller 70 in response thereto. As another alternative, the signals 72 may be received from a gas sensor located between the outlet of the process chamber 12 and the combustion nozzles 34. In response to the data contained in the received signals 72, the controller 70 may selectively control the supply of hydrogen to each combustion nozzle 34. With reference to Figures 3 and 4, the control system Includes a plurality of variable flow control devices 76, for example valves 76 each located between the hydrogen source 44 and a respective hydrogen inlet 42, and moveable between open and closed positions in response to a signal 78 received from the controller 70. A chocked flow orifice may be provided between each valve 76 and the respective hydrogen inlet 42 for restricting the rate of supply of hydrogen to each hydrogen inlet 42. Altematively, a single valve 76 may be used to control the supply of hydrogen to each of the combustion nozzles 34 providing the Inlet 32 of the ^combustion apparatus 10. When the valves 76 are open, hydrogen is conveyed from the hydrogen source 44 to each hydrogen inlet 42. The hydrogen passes downwards (as illustrated) within the annular gap 46, and is output from the hydrogen outlets 50 into the combustion chamber 36 for combustion with the exhaust gas.. By selectively adding hydrogen to the gas combusted within the combustion chamber 36, the controller 70 can maintain the relative amounts of ammonia and hydrogen combusted within the combustion chamber 36 at or around predetermined values, for example at least 1:1, thereby maintaining a high DRE of ammonia. We have found experimentally that mixtures of hydrogen, ammonia and nitrogen in approximate ratios of 1:1:1 and 2:1:1 respectively can be combusted below the TLV of ammonia using only a pilot flame of the combustion chamber, and it is anticipated that combustion of mixtures with lower amounts of hydrogen will be similarly achievable. As there is thus no longer any requirement to provide combustion gas to the combustion chamber 36 for the combustion of ammonia at least, fuel consumption may be significantly reduced. Retuming to Figure 1. the by-products from the combustion of the exhaust gas within the combustion chamber 36 may be conveyed to a wet scrubber, solid reaction media, or other secondary abatement device 80, as illustrated in Figure 1. After passing through the abatement device 80, the exhaust gas may be safely vented to the atmosphere. Figure 5 illustrates a second embodiment, in which the additional hydrogen is conveyed to the exhaust gas upstream from the inlet 32 of the combustion apparatus 10. In this embodiment, a first conduit system 82 conveys the hydrogen from the hydrogen source 44 to a second conduit system 84 for conveying the exhaust gas from the pumping system 20 to the inlet 32 of the combustion apparatus 10. As illustrated, a single valve 76 may be provided in the first conduit system 82 and controlled by the controller 70 in response to signals 72 received from the controller of the process tool 74 to selectively convey hydrogen frohi the hydrogen source 74 to the exhaust gas within the second conduit system 84. A chocked flow orifice may be provided between the valve 78 and the second conduit system 84 for restricting the rate of supply of hydrogen to exhaust gas. In this embodiment, therefore, the hydrogen inlet 42 and sleeve 48 of each combustion nozzle 34 may be omitted. CLAIMS A method of combusting ammonia, the method comprising the steps of conveying an exhaust gas containing varying amounts of at least ammonia and hydrogen from a chamber to a combustion nozzle connected to a combustion chamber, supplying to the chamber a combustion gas for forming a combustion flame within the chamber, and selectively adding hydrogen to the exhaust gas depending on the-relative amounts of ammonia and-hydrogen exhaust from the chamber so that, when the exhaust gas contains ammonia, the gas combusted by the flame contains at least a predetemiined amount of hydrogen. A method according to Claim 1, wherein the hydrogen is conveyed to the nozzle for addition to the exhaust gas. A method according to Claim 1 or Claim 2, wherein the hydrogen is injected into the combustion chamber from a plurality of apertures extending about the combustion nozzle. A method according to Claim 1, wherein the hydrogen is added to the exhaust gas upstream from the combustion chamber. A moth's? according to any preceding claim, wherein the amount of hydrogen added to the exhaust gas is adjusted in response to the reception of data indicative of a variation of the chemistry of the gas exhaust from the chamber. A method according to Claim 5, wherein the exhaust gas is exhaust from a chamber of a process tool, the data indicative of the variation of the chemistry of the exhaust gas being supplied by the process tool. A method according to any preceding clairn.. wherein hydrogen Is added to the exhaust gas so that the ratio by volume of hydrogen to ammonia combusted by the flame is at least 1:1. A method according to any preceding claim, wherein the combustion gas comprises a mixture of a fuel and an oxidant. A method according to Claim &,jfl^herein the fuel comprises a hydrocarbon, _ preferably methane. A method according to Claim 8 or Claim 9, wherein the oxidant comprises air. A method according to any of Claims 8 to 10, wherein the ratio by volume of fuel and oxidant within the combustion gas is between 1:8 and 1:12. A method according to any preceding claim, wherein the combustion gas is supplied to the chamber substantially co-axially with the exhaust gas. A method according to any preceding claini, wherein the exhaust gas comprises at least one of ammonia, hydrogen and nitrogen. Apparatus for combusting exhaust gas, the apparatus comprising a combustion chamber, meBns for supplying to the chamber a combustion gas for forming a combustion flame within the chamber, a combustion nozzle connected to the combustion chamber, means for conveying an exhaust gas containing varying amounts of at least ammonia and hydrogen from a chamber to the nozzle, and means for selectively adding hydrogen to the exhaust gas depending on the relative amounts of ammonia and hydrogen exhaust from the chamber. Apparatus according to Claim 14, wherein the tiydrogen adding means is configured to convey the additional hydrogen to the combustion nozzle for addition to the exhaust gas. Apparatus according to Claim 15, wherein the hydrogen adding means comprises a sleeve extending about the nozzle for receiving the additional hydrogen and conveying the-additlonal hydrogen to the combustion chamber. Apparatus according to any of Claims 14 to 16, wherein the hydrogen adding means comprises a plurality of apertures extending about the combustion nozzle from which the additional hydrogen is injected into the combustion chamber. Apparatus according to Claim 14, wherein the hydrogen adding means is configured to add hydrogen to the exhaust gas upstream from the combustion chamber. Apparatus according to any of Claims 14 to 18, wherein the hydrogen adding means comprises means for receiving data indicative of a variation of the chemistry of the gas exhaust from the chamber, and for adjusting the amount of hydrogen added to the exhaust gas In response thereto. Apparatus according to Claim 19, wherein the exhaust gas is exhaust frorn a chamber of a process tool, the data indicative of the variation of the chemistry of the exhaust gas being supplied by the process tool. Apparatus according to any of Claims 14 to 20, wherein the hydrogen adding means is configured to add hydrogen to the exhaust gas so that the ratio by volume of hydrogen to ammonia combusted by the flame is at least 1:1. Apparatus according to any of Claims 14 to 21, xArti^rein the combustion gas comprises a mixture of a fuel and an oxidant. Apparatus according to Claim 22, wherein the fuel comprises a hydrocarbon, preferably methane. Apparatus according to Claim 22 or Claim 23, wherein the oxidant comprises air. Apparatus according to any of Claims 22 to 24, wherein the ratio by volume of fuel and oxidant within the combustion gas is between 1:8 and 1:12. Apparatus according to any of Claims 14 to 25, wherein the combustion gas supply means is configured to supply the combustion gas to the chamber substantially co-axially with the exhaust gas.

Full Text

GAS COMBUSTION APPARATUS
The present invention relates to apparatus for, and a method of, combusting an exhaust gas containing at least ammonia.
A primary step in the fabrication of semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of vapourjjrecursors. One known technique for depositinjg_a thin film on a substrate is chemical vapour deposition (CVD). In this technique, process gases are supplied to a process chamber housing the substrate and react to form a thin film over the surface of the substrate.
An example of a material commonly deposited on to a substrate is gallium nitride (GaN). GaN, and related material alloys (such as InGaN. AIGaN and InGaAIN) are compound semiconductors used for the manufacture of green, blue and white light emitting devices (such as LEDs and laser diodes) and power devices (such as HBTs and HEMTs). These compound semiconductors are usually formed using a fomn of CVD usually known as MOCVD (metal organic chemical vapour deposition). In overview, this process involves reacting together volatile organometallic sources of the group III metals Ga, In and/or Al, such as trimethyl gallium (TMG), trimethyl indium (TMI) and trimethyl aluminium (TMA), with ammonia at elevated temperatures to form thin films of material on wafers of a suitable substrate material (such as Si, SIC, sapphire or AIN)^^^ydrogen gas is generally also present, providing a carrier gas for the organometallic precursor and the other process gases.
Following the deposition process conducted within the process chamber, there is typically a residual amount of the gases supplied to the process chamber contained in the gas exhaust from the process chamber. Process gases such as ammonia and hydnDgen are highly dangerous if exhausted to the atmosphere, and so in view of this, before the exhaust gas is vented to the atmosphere, abatement apparatus is often provided to treat the exhaust gas to convert the more
CONFIRMATION COFir

hazardous components of the exhaust gas into species that can be readily removed from the exhaust gas, for example by conventional scrubbing, and/or can be safely exhausted to the atmosphere.
One known type of abatement apparatus is described in EP-A-0 819 887. This abatement apparatus comprises a combustion chamber having an exhaust gas combustion nozzle for receiving the exhaust gas to-be treated. An annular combustion nozzle is provided outside the exhaust gas nozzle, and a gas mixture of a fuel and air is supplied to the annular combustion nozzle for forming a flame inside the combustion chamber for burning the exhaust gas received from the process chamber to destroy the harmful components of the exhaust gas.
This form of abatement apparatus is generally located downstream from a pumping system for drawing the exhaust gas from the process chamber. To prevent damage to the pumping system as the exhaust gas passes therethrough, a nitrogen purge gas is typically supplied to one or more purge ports of the pumping system for pumping with the exhaust gas. As a result, the gas received by the abatement apparatus usually also contains a significant amount of nitrogen.
Nitrogen is safe and requires no abatement. With the apparatus such as that described in EP-A-0 819 887, we have found that the destruction and removal efficiency (DRE) of hydrogen is very high, often exceeding 99.99%, whilst the DRE , of ammonia is highly variable depending on tfie~other gases contained within the exhaust gas entering the abatement apparatus. Ammonia is highly toxic, having a threshold limit value, or TLV, of 25 ppm, and we have found that the amount of ammonia exhaust from the abatement apparatus can be as high as 2400 ppm depending on the chemistry and the relative amounts of the gases contained within the exhaust gas.

It is an aim of at least the preferred embodiment of the present invention to seek to provide a method of, and apparatus for, combusting ammonia with a consistently high DRE irrespective of the other gases, and the relative amounts thereof, present in an exhaust gas containing the ammonia.
In a first aspect, the present invention provides a method of combusting ammonia,
the method comprising the steps of conveying an exhaust gas containing varying^
amounts of at least ammonia andJiydrogen from_a chamber to a combustion ^nozzle connected to a combustion chamber, supplying to the chamber a combustion gas for forming a combustion flame within the chamber, and selectively adding hydrogen to the exhaust gas depending on the relative amounts of ammonia and hydrogen exhaust from the chamber so that, when the exhaust gas contains ammonia, the gas combusted by the flame contains at least a predetermined amount of hydrogen.
We have found that the destruction and removal efficiency (DRE) of ammonia is significantly enhanced when a predetermined amount of hydrogen is present in the gases to be combusted by the flame. By selectively adding hydrogen to the ' exhaust gas when the exhaust gas contains ammonia but not a sufficient amount of hydrogen to achieve a high DRE of ammonia, the DRE of ammonia can be maintained at a consistently high level.
In one preferred embodiment the hydrogen is conveyed to the nozzle for additien to the exhaust gas, where theliydrogen is preferably injected into the combustion chamber from a plurality of apertures extending about the combustion nozzle. In another prefen'ed embodiment, the hydrogen is added to the exhaust gas upstream from the combustion nozzle, thereby promoting mixing of the additional hydrogen with the exhaust gas.
The addition of hydrogen to the exhaust gas may be timed according to the cycle of gas supply to the chamber. Alternatively, the amount of hydrogen added to the exhaust gas may be adjusted in response to the reception of data indicative of a

variation of the chemistry of the gas exhaust from the chamber,. The data indicative of the variation of the chemistry of the exhaust gas being supplied by the process tool, for example when the gases supplied to the chamber do not contain sufficient hydrogen to achieve a high ammonia DRE. Alternatively, a gas sensor may be located within a conduit system for conveying the exhaust gas to the nozzle, with this sensor being configured to supply the data.
Hydrogen-is preferably added to-the exhaust gas so that the ratio by volume of hydrogen to ammonia combusted by the flame is at least 1:1, We have found that mixtures of hydrogen, ammonia and nitrogen in approximate ratios of 1:1:1 and 2:1:1 respectively can be combusted below the TLV of ammonia using only a pilot flame of the combustion chamber. The pilot flame is typically formed from a mixture of fuel and oxidant, for example methane and air, in a ratio by volume of between 1:8 and 1:12. Consequently, the amount of methane or other fuel supplied to the chamber to form the combustion flame can be significantly reduced, thereby reducing operating costs.
In a second aspect, the present invention provides apparatus for combusting exhaust gas;'the apparatus comprising a combustion chamberf^mean&for supplying to the chamber a combustion gas for forming a combustion flame within the chamber, a combustion nozzle connected to the combustion chamber, means for conveying an exhaust gas containing varying amounts of at least ammonia and hydrogen from a chamber to the nozzle, and means for selectiveTy adding hySrogen to the exhaust gas depending on the relative amounts of ammonia and hydrogen exhaust from the chamber.
Features described above in relation to method aspects of the invention are equally applicable to apparatus aspects of the invention, and vice versa.
Preferred features of the present invention will now be described with reference to the accompanying drawing, in which

Figure 1 iliustrat^s a process chamber connected to a combustion appargtus according to one embodiment of the invention;
Figure 2 Illustrates a cross-sectional view of a plurality of exhaust gas combustion nozzles connected to a combustion chamber of the combustion apparatus of Figure 1;
Figure 3 illustrates an arrangement for supplying hydrogen to each^combustion nozzle connected to the combustion chamber of Figure 2;
Figure 4 illustrates a control system for controlling the amount of hydrogen supplied to each combustion nozzle of Figure 2; and
Figure 5 illustrates a process chamber connected to a combustion apparatus according to another embodiment of the Invention.
With reference first to Figure 1, combustion apparatus 10 Is provided for treating gases exhausting from a process chamt)er 12 for processing> for example, semiconductor devicesvilat panel display devices or solar panel devices.^vThe chamber 12 receives various process gases for use in performing the processing within the chamber. In this example. MOCVD (metal organic chemical vapour deposition) of a layer of material such as GaN is performed within the process chamber 12. Gases comprising organometallic sources of the group III metals Ga, In and/or Al, such as trimethyl gallium (TMG), trimethyl indium (TMI) and trimethyl aluminium (TMA), ammonia and hydrogen are conveyed to the process chamber 12 from respective sources 14.16,18 thereof at elevated temperatures to form thin films of material on wafers of a suitable substrate material (such as SI, SIC, sapphire or AIN).

An exhaust gas is drawn from the outlet of the process chamber 12 by a pumping system 20. During the processing within the chamber, only a portion of the process gases will be consumed, and so the exhaust gas will contain a mixture of the process gases supplied to the chamber, and by-products from the processing within the chamber. As illustrated in Figure 1, the pumping system 20 may comprise a secondary pump 22, typically in the form of a turbomolecular pump, for drawing the exhaust gas from the process chamber. The turbomolecular pump 22 can generate a vacuum of at least 10*^ mbar in the process chambei:42- The gas is typically exhausted from the tufbomolecular pump 22 at a pressure of around 1 mbar. In view of this, the pumping system also comprises a primary, or backing pump 24 for receiving the gas exhaust from the turbomolecular pump 22 and raising the pressure of the gas to a pressure around atmospheric pressure. In order to prevent damage to the pumping system 20 during pumping of the gases from the process chamber 12, a nitrogen purge gas is supplied from a source 26 thereof to one or more purge ports 28, 30 of the pumping system 20.
The gas exhaust from the pumping system 22 is conveyed to an inlet 32 of the combustion apparatus 10. As illustrated in Figure 2, the inlet 32 comprises at least one exhaust gas combustion nozzle 34 connected to a combustion chamber 36rof the combustion apparatus 10. Each combustion nozzle 34 has an inlet 38 for receiving the exhaust gas, and an outlet 40 from which the exhaust gas enters the combustion chamber 38. Whilst Figure 2 illustrates two combustion nozzles 34 for receiving the exhaust gas, the inlet 32 may comprise any suitable number, for example four, six or more, combustion nozzles 34 for receivingThe exhaust gas. In the preferred embodiments, the Inlet 32 comprises four combustion nozzles 34.
In this embodiment of the Invention, each combustion nozzle 34 includes a hydrogen inlet 42 for receiving hydrogen from a source 44 thereof (illustrated in Figure 3). An annular gap 46 defined between the outer surface of the nozzle 34 and the Inner surface of a sleeve 48 extending about the nozzle 34 allows the hydrogen to be conveyed from the Inlet 42 to a plurality of hydrogen outlets 50

surrounding the nozzle 34 and from which the hydrogen enters the combustion chamber 36 co-axially with the exhaust gas.
As illustrated in Figure 2, each combustion nozzle 34 is mounted in a first annular plenum chamber 52 having an inlet 54 for receiving a first gas mixture of fuel and oxidant, for example, a mixture of methane and air, providing a combustion gas for forming combustion flames within the combustion chamber 36, and a plurality of outlets-56 from which the combustion gas is conveyed into the combustion chamber 36. As illustrated in Figure 2, the combustion nozzles 34 are mounted in the first plenum chamber 52 such that each nozzle 34 passes substantially co-axially through a respective outlet 56, such that the combustion gas is conveyed into the combustion chamber 36 about the sleeves 48 of the combustion nozzles 34,
As also illustrated in Figure 2, the first plenum chamber 52 is located above a second annular plenum chamber 58 having an inlet 60 for receiving a second, pilot gas mixture of fuel and oxidant, for example, another mixture of methane and air, for forming pilot flames within the combustion chamber 36. As illustrated in Figure 2, the second plenum chamber 58 comprises a plurality of first apertures 62 coaxial with the outlets 56 from the first plenum chamber 52 and through which the combustion nozzles 34 extend into the combustion chamber 36, and a plurality of second apertures 64 surrounding the first apertures 62. The second apertures 64 allow the pilot gas mixture to enter the combustion chamber 36 to form the pilot ~Tlame for igniting the combustion gas to fonri combustion flames within the combustion chamber 36. In the event that the abatement device is operated in pilot only then the supply of combustion gas to the first plenum chamber 52 may be disconfinued. The pilot fiame formed at the apertures 64 is then used to ignite the exhaust gas and any additional hydrogen supplied to the nozzles 34.
Figure 4 illustrates a control system for controlling the supply of hydrogen to each of the combustion nozzles 34, The control system comprises a controller 70 for receiving signals 72 data indicative of a variation of the chemistry of the exhaust

gas output from the process chamber 12 and thus supplied to the combustion nozzles 34. Each of the signals 72 may be received directly from a process tool 74 controlling the supply of gases to the process chamber 12 using valves 75, as illustrated in Figure 1. Altematively. the signals 72 may be received from a host computer of a local area network of which the controller 70 and the controller of the process tool 74 form part, the host computer being configured to receive information from the controller of the process tool regarding the chemistry of the gases supplied to the process chamber and to output the signals 72 to the controller 70 in response thereto. As another alternative, the signals 72 may be received from a gas sensor located between the outlet of the process chamber 12 and the combustion nozzles 34.
In response to the data contained in the received signals 72, the controller 70 may selectively control the supply of hydrogen to each combustion nozzle 34. With reference to Figures 3 and 4, the control system Includes a plurality of variable flow control devices 76, for example valves 76 each located between the hydrogen source 44 and a respective hydrogen inlet 42, and moveable between open and closed positions in response to a signal 78 received from the controller 70. A chocked flow orifice may be provided between each valve 76 and the respective hydrogen inlet 42 for restricting the rate of supply of hydrogen to each hydrogen inlet 42. Altematively, a single valve 76 may be used to control the supply of hydrogen to each of the combustion nozzles 34 providing the Inlet 32 of the ^combustion apparatus 10.
When the valves 76 are open, hydrogen is conveyed from the hydrogen source 44 to each hydrogen inlet 42. The hydrogen passes downwards (as illustrated) within the annular gap 46, and is output from the hydrogen outlets 50 into the combustion chamber 36 for combustion with the exhaust gas..
By selectively adding hydrogen to the gas combusted within the combustion chamber 36, the controller 70 can maintain the relative amounts of ammonia and hydrogen combusted within the combustion chamber 36 at or around

predetermined values, for example at least 1:1, thereby maintaining a high DRE of ammonia. We have found experimentally that mixtures of hydrogen, ammonia and nitrogen in approximate ratios of 1:1:1 and 2:1:1 respectively can be combusted below the TLV of ammonia using only a pilot flame of the combustion chamber, and it is anticipated that combustion of mixtures with lower amounts of hydrogen will be similarly achievable. As there is thus no longer any requirement to provide combustion gas to the combustion chamber 36 for the combustion of ammonia at least, fuel consumption may be significantly reduced.
Retuming to Figure 1. the by-products from the combustion of the exhaust gas within the combustion chamber 36 may be conveyed to a wet scrubber, solid reaction media, or other secondary abatement device 80, as illustrated in Figure 1. After passing through the abatement device 80, the exhaust gas may be safely vented to the atmosphere.
Figure 5 illustrates a second embodiment, in which the additional hydrogen is conveyed to the exhaust gas upstream from the inlet 32 of the combustion apparatus 10. In this embodiment, a first conduit system 82 conveys the hydrogen from the hydrogen source 44 to a second conduit system 84 for conveying the exhaust gas from the pumping system 20 to the inlet 32 of the combustion apparatus 10. As illustrated, a single valve 76 may be provided in the first conduit system 82 and controlled by the controller 70 in response to signals 72 received from the controller of the process tool 74 to selectively convey hydrogen frohi the hydrogen source 74 to the exhaust gas within the second conduit system 84. A chocked flow orifice may be provided between the valve 78 and the second conduit system 84 for restricting the rate of supply of hydrogen to exhaust gas. In this embodiment, therefore, the hydrogen inlet 42 and sleeve 48 of each combustion nozzle 34 may be omitted.

CLAIMS
A method of combusting ammonia, the method comprising the steps of conveying an exhaust gas containing varying amounts of at least ammonia and hydrogen from a chamber to a combustion nozzle connected to a combustion chamber, supplying to the chamber a combustion gas for forming a combustion flame within the chamber, and selectively adding hydrogen to the exhaust gas depending on the-relative amounts of ammonia and-hydrogen exhaust from the chamber so that, when the exhaust gas contains ammonia, the gas combusted by the flame contains at least a predetemiined amount of hydrogen.
A method according to Claim 1, wherein the hydrogen is conveyed to the nozzle for addition to the exhaust gas.
A method according to Claim 1 or Claim 2, wherein the hydrogen is injected into the combustion chamber from a plurality of apertures extending about the combustion nozzle.
A method according to Claim 1, wherein the hydrogen is added to the exhaust gas upstream from the combustion chamber.
A moth's? according to any preceding claim, wherein the amount of hydrogen added to the exhaust gas is adjusted in response to the reception of data indicative of a variation of the chemistry of the gas exhaust from the chamber.
A method according to Claim 5, wherein the exhaust gas is exhaust from a chamber of a process tool, the data indicative of the variation of the chemistry of the exhaust gas being supplied by the process tool.

A method according to any preceding clairn.. wherein hydrogen Is added to the exhaust gas so that the ratio by volume of hydrogen to ammonia combusted by the flame is at least 1:1.
A method according to any preceding claim, wherein the combustion gas comprises a mixture of a fuel and an oxidant.
A method according to Claim &,jfl^herein the fuel comprises a hydrocarbon, _ preferably methane.
A method according to Claim 8 or Claim 9, wherein the oxidant comprises air.
A method according to any of Claims 8 to 10, wherein the ratio by volume of fuel and oxidant within the combustion gas is between 1:8 and 1:12.
A method according to any preceding claim, wherein the combustion gas is supplied to the chamber substantially co-axially with the exhaust gas.
A method according to any preceding claini, wherein the exhaust gas comprises at least one of ammonia, hydrogen and nitrogen.
Apparatus for combusting exhaust gas, the apparatus comprising a combustion chamber, meBns for supplying to the chamber a combustion gas for forming a combustion flame within the chamber, a combustion nozzle connected to the combustion chamber, means for conveying an exhaust gas containing varying amounts of at least ammonia and hydrogen from a chamber to the nozzle, and means for selectively adding hydrogen to the exhaust gas depending on the relative amounts of ammonia and hydrogen exhaust from the chamber.

Apparatus according to Claim 14, wherein the tiydrogen adding means is configured to convey the additional hydrogen to the combustion nozzle for addition to the exhaust gas.
Apparatus according to Claim 15, wherein the hydrogen adding means comprises a sleeve extending about the nozzle for receiving the additional hydrogen and conveying the-additlonal hydrogen to the combustion chamber.
Apparatus according to any of Claims 14 to 16, wherein the hydrogen adding means comprises a plurality of apertures extending about the combustion nozzle from which the additional hydrogen is injected into the combustion chamber.
Apparatus according to Claim 14, wherein the hydrogen adding means is configured to add hydrogen to the exhaust gas upstream from the combustion chamber.
Apparatus according to any of Claims 14 to 18, wherein the hydrogen adding means comprises means for receiving data indicative of a variation of the chemistry of the gas exhaust from the chamber, and for adjusting the amount of hydrogen added to the exhaust gas In response thereto.
Apparatus according to Claim 19, wherein the exhaust gas is exhaust frorn a chamber of a process tool, the data indicative of the variation of the chemistry of the exhaust gas being supplied by the process tool.
Apparatus according to any of Claims 14 to 20, wherein the hydrogen adding means is configured to add hydrogen to the exhaust gas so that the ratio by volume of hydrogen to ammonia combusted by the flame is at least
1:1.

Apparatus according to any of Claims 14 to 21, xArti^rein the combustion gas comprises a mixture of a fuel and an oxidant.
Apparatus according to Claim 22, wherein the fuel comprises a hydrocarbon, preferably methane.
Apparatus according to Claim 22 or Claim 23, wherein the oxidant comprises air.
Apparatus according to any of Claims 22 to 24, wherein the ratio by volume of fuel and oxidant within the combustion gas is between 1:8 and 1:12.
Apparatus according to any of Claims 14 to 25, wherein the combustion gas supply means is configured to supply the combustion gas to the chamber substantially co-axially with the exhaust gas.

Documents:

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Patent Number

268529

Indian Patent Application Number

4983/CHENP/2007

PG Journal Number

36/2015

Publication Date

04-Sep-2015

Grant Date

02-Sep-2015

Date of Filing

05-Nov-2007

Name of Patentee

EDWARDS LIMITED

Applicant Address

MANOR ROYAL CRAWLEY, WEST SUSSEX RH10 9LW

Inventors:

#	Inventor's Name	Inventor's Address
1	MENNIE, DARREN	BOC EDWARDS KENN BUSINESS PARK KENN ROAD CLEVEDON, NORTH SOMERSET BS21 6TH
2	JONES, NICHOLAS, BENJAMIN	BOC EDWARDS KENN BUSINESS PARK KENN ROAD CLEVEDON, NORTH SOMERSET BS21 6TH

PCT International Classification Number

F23G7/06

PCT International Application Number

PCT/GB06/01577

PCT International Filing date

2006-04-28

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	0509163.2	2005-05-05	U.K.