Combustible Gas Diluter and Method Thereof

Abstract

A flammable gas diluter (5) for reliably diluting a flammable gas flow to a concentration below the flammable gas's limit of flammability is disclosed. The diluter (5) includes a dilution vessel (10) having an outer envelope defining a longitudinal flow path from an inlet (11) to an outlet (12), at least one air inlet (16, 17) assembly for directing an air flow into the inlet (11) of the dilution vessel (10), a flammable gas inlet (15) arrangement positioned toward the inlet (11) end of the dilution vessel (10), and two gas flow generators positioned upstream of the flammable gas inlet (15) arrangement and configured to exhaust the air flow into the air inlet (16, 17) assemblies. The two gas flow generators are configured to operate as primary and backup gas flow generators. The combustible gas diluter (10) includes two dampers (16A, 17A), one damper (16A, 17A) associated with each of the gas flow generators, and each damper (16A) is mounted between the corresponding gas flow generator and the dilution vessel (10). The dampers (16A, 17A) are configured to conceal a passage between the corresponding gas flow generator and the dilution vessel (10) when closed and to open the passage between the gas flow generator and the dilution vessel (10) when open. A control circuit (80) is configured to control the opening and closing of the dampers (16A), and the control circuit (80) is configured to open the dampers (16A, 17A) when the corresponding gas flow generator is in an operating mode and close the dampers (16A, 17A) when the corresponding gas flow generator is shut down in a standby mode.

Description

Technical Field

[0001] The field of the present invention relates to combustible gas dilution and in some embodiments to vacuum pumping and removal systems.

Background Art

[0002] There are semiconductor manufacturing processes where the gas to be exhausted and removed is a combustible gas such as hydrogen. For example, in lithography, products are manufactured by controlled exposure to a radiation source. In this case, the radiation source is extreme ultraviolet (EUV) radiation. In this process, hydrogen is increasingly used in large quantities as a barrier gas to shield the optics and mirrors from sputtered tin excited by a laser to emit EUV light within the lithography tool. These processes are carried out in a vacuum, and the vacuum system provides the vacuum pressure required for this process to be carried out and transports the hydrogen away safely for removal.

[0003] In many removal systems, the combustible gas removed from the vacuum processing chamber is burned to remove the gas. There are environmental implications associated with this, which generally require two removal tools, namely, one in operation and one standby in case the combustor within the operating removal tool fails. This arrangement is expensive in terms of both fuel and space.

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is considered desirable to provide an alternative method for removing combustible gas from a gas stream so that the gas stream can be safely exhausted.

Means for Solving the Problems

[0005] A first aspect provides a flammable gas diluter for diluting a flow of flammable gas to a concentration below the flammable limit of the flammable gas. The diluter includes a dilution vessel having an outer envelope defining a longitudinal flow path from an inlet to an outlet, at least one air inlet assembly for directing a flow of air into the inlet of the dilution vessel, a flammable gas inlet arrangement positioned towards the inlet end of the dilution vessel, two gas flow generators configured to pump a flow of air through the air inlet assembly, the two gas flow generators being positioned upstream of the flammable gas inlet arrangement and configured to operate as operating and standby gas flow generators, two dampers, one damper being associated with each of the gas flow generators, each damper being mounted between the corresponding gas flow generator and the dilution vessel, the dampers being configured to cover a passage between the corresponding gas flow generator and the dilution vessel when closed and to open the passage between the gas flow generator and the dilution vessel when open, and a control circuit configured to control the opening and closing of the dampers, the control circuit being configured to open the dampers during an operating mode of the corresponding gas flow generator and to close the dampers when the corresponding gas flow generator is stopped in a standby mode.

[0006] Flammable gases are difficult to handle and dispose of. For these reasons, flammable gases exhausted from a system are generally treated by burning them in a combustor, optionally using methane as fuel. This method has environmental impacts, is relatively expensive in both fuel and space, and may have reliability issues. Despite the difficulties associated with handling flammable gases, if flammable gases can be safely diluted below their flammable limits, many flammable gases can be readily vented to the atmosphere.

[0007] Heretofore, when diluting flammable gases, it has been common to use nitrogen, an inert gas, at above atmospheric pressure. However, in systems with large amounts of flammable gas, the amount of nitrogen required to reduce the concentration of the flammable gas below its flammable level is often prohibitively expensive. Further, operation at high pressure has its own challenges.

[0008] If the dilution of the flammable gas can be carried out safely and reliably, it seems to be acceptable as a removal means instead of the combustion of the flammable gas. When the concentration of the flammable gas increases, not only does it affect safety, but it is also necessary to stop the system that generates the flammable gas, which can be expensive.

[0009] Embodiments address these problems using a flammable gas diluter that receives air supply from at least two gas flow generators, each configured to operate in an operating mode or as a standby. Thus, while one gas flow generator generates the required air flow, the other can function as a standby in a standby mode where it can be used at any time when the operating gas flow generator requires maintenance inspection.

[0010] One potential problem associated with providing two gas flow generators is that there may be a leakage path for the gas flow outside the dilution system through the non-operating gas flow generator. This can not only cause pressure fluctuations within the system, triggering alarms and system shutdowns, but also the flow passing through the gas flow generator in the direction opposite to its operating direction will cause it to rotate in reverse, making it difficult or impossible to start when needed. This is addressed by providing a buffer associated with each gas flow generator. These buffers are configured to open or cover the gas flow path between the gas flow generator and the dilution container and are controlled by a control circuit so that they can be automatically opened and closed as needed. In this way, when not in operation, the "reverse direction" path through the non-operating gas flow generator is at least partially blocked, suppressing the leakage of gas from the system and causing the reverse rotation of the gas flow generator.

[0011] The buffer has several forms, and in some embodiments, it includes slats that form a louver type arrangement. The slats have a narrow cross-section and a wide cross-section, and in the closed position, the wide cross-section lies parallel to and across the gas passage cross-section, and in the open position, the wide cross-section lies perpendicular to the passage cross-section. Thus, the slats are rotatably mounted such that only the narrow cross-section becomes a barrier to the gas passage in this orientation. When closed, the slats can cover more than 95% of the cross-sectional area.

[0012] In some embodiments, the control circuit is configured to control and start a gas flow generator in standby mode in response to a signal indicating that the currently operating gas flow generator should be stopped and the gas flow generator in the current standby mode should be started, and after a predetermined delay, control the buffer associated with the started gas flow generator to open.

[0013] When switching between gas flow generators, perhaps when the operating gas flow generator has to be replaced for maintenance, in order to suppress gas leakage through the currently non-operating gas flow generator and reverse rotation of the gas flow generator, it has been found advantageous to start this gas flow generator before opening the buffer and only open the buffer after a predetermined delay. In this way, gas leakage and the corresponding fluctuations within the system can be suppressed. Gas leakage passing through the stopped gas flow generator in the reverse direction not only makes its start difficult but also results in undesirable pressure fluctuations within the system and an increase in the concentration of combustible gas, which may trigger warning signals and the shutdown of the diluting system. The signal indicating that the currently operating gas flow generator has to be stopped can be generated in response to a signal received from a sensor that senses the operating gas flow generator. When these signals indicate, for example, an increase in temperature or vibration of the gas flow generator, the control circuit can generate a signal indicating that the gas flow generator has to be stopped and replaced with a standby gas flow generator.

[0014] The predetermined delay can be the time until the gas flow generator reaches its normal operating speed, or the time until it reaches or exceeds a fraction of its normal operating speed, such as more than 70% or in some cases more than 80% of its normal operating speed. The normal operating speed can be substantially lower than the maximum speed of the gas flow generator. The delay can be set as a time, or can be determined, for example, by a sensor that senses that the gas flow generator has reached a certain operating speed.

[0015] In some embodiments, the control circuit is configured to control to close a buffer associated with the operating gas flow generator and to control the operating gas flow generator to stop.

[0016] The control circuit can control to close the buffer of the other gas flow generator upon or shortly after the opening of the buffer associated with the newly started gas flow generator. Similarly, it can control to stop the operation of the gas flow generator upon or after the closing of the associated buffer.

[0017] In some embodiments, the control circuit is configured to control to open the buffer associated with the standby gas flow generator in response to a signal indicating that the diluter must be started, to control to close the buffer associated with the operating gas flow generator, to control to start the standby gas flow generator, to control to start the operating gas flow generator after a set test time, to control to open the buffer associated with the operating gas flow generator after a predetermined delay, to control to close the buffer associated with the standby gas flow generator, and to control to stop the operation of the standby gas flow generator.

[0018] When starting the system, it is advantageous to ensure that the preliminary gas flow generator functions before startup. Therefore, it may be advantageous to start by operating the preliminary gas flow generator for a certain test time. During this test time, the buffer associated with this gas flow generator needs to be opened, while the buffer associated with the other gas flow generator needs to be closed. After the certain test time has elapsed, the operating gas flow generator can be started. At this time, the buffer associated with it is still closed. After a predetermined delay, the buffer is opened, the buffer associated with the preliminary gas flow generator is closed, and the preliminary flow generator is turned off. The closing of the buffer associated with the preliminary gas flow generator can be substantially simultaneous with or slightly after the opening of the buffer of the operating gas flow generator. There is no problem in putting both gas flow generators into an operating state and opening both buffers in this regard. Putting one gas flow generator into a non-operating state and opening its buffer will result in gas leakage and reverse rotation.

[0019] In some embodiments, the combustible gas inlet arrangement includes a plurality of openings at least partially arranged across the cross-section of the dilution container towards the inlet end of the dilution container at different distances from the outer envelope of the dilution container, and a plurality of gas stream guiding configurations arranged between the combustible gas inlet arrangement and the outlet, each at a different position along the length of the dilution container. At least one of the plurality of gas stream configurations is an inwardly directed guiding gas stream configuration for directing the gas stream away from the outer envelope, and at least one of the gas stream configurations is an outwardly directed guiding gas stream configuration for directing the gas stream towards the outer envelope.

[0020] The diluter may advantageously have a simple design with few moving parts, since the diluter can be made robust, reliable, and less prone to failure. This can be very important in systems where a failure of the removal unit can potentially stop the combustible gas to the system, which may then, in turn, require the system to be stopped immediately, resulting in damage to the system.

[0021] The dilution of combustible gas would seem to be an acceptable alternative means of removal to the combustion of combustible gas, provided it can be done safely. The inventor recognizes that many of the hazards associated with the handling of combustible gas are related to transporting the combustible gas from the point of use to a point where it can be safely removed. Thus, many of the difficulties can be addressed by providing a diluter with a simple design, relatively compact, and few moving parts, and which can be used as a use-point diluter for diluting combustible gas at or near the point of use.

[0022] In some embodiments, the dilution vessel includes a constriction portion and the combustible gas inlet arrangement is positioned within the constriction portion such that air is accelerated before passing through the combustible gas inlet.

[0023] Combustible gas, when introduced into the diluter, may initially be above its flammable upper limit, but during dilution, it needs to be diluted below its flammable lower limit and measures taken to reduce the risk of ignition between these times. Using the constriction portion to increase the air flow at the combustible gas inlet is one way to initially dilute the gas relatively rapidly and suppress ignition, especially when the increased flow rate exceeds the flame speed of the combustible gas.

[0024] In some embodiments, the diluter is configured to dilute the combustible gas to less than a fraction of its lower flammable limit at the outlet of the system, optionally less than half, and optionally less than a quarter. For safety reasons and to provide a robust system, it may be advantageous for the system to dilute the gas to a fraction of its lower flammable limit and for the sensor to issue a warning if the outlet exceeds a fraction of its lower flammable limit.

[0025] The constriction only extends over a fraction of the length of the dilution vessel, and since the dilution vessel extends beyond the constriction, the gas stream decelerates. This aids in the mixing of the combustible gas and air within the confined space.

[0026] In some embodiments, the combustible gas diluter includes at least one gas flow generator for pumping an air flow into its air inlet assembly, and the at least one gas flow generator is positioned upstream of the combustible gas inlet arrangement.

[0027] As described above, the concentration of the combustible gas within the diluter is between the upper and lower flammable limits over a portion of the length of the diluter downstream of the combustible gas inlet. Thus, it is advantageous that there are no potential ignition sources over this portion of the diluter, and since the diluter is configured such that moving parts, such as those present in a gas flow generator that can be in the form of a fan, are upstream of the combustible gas inlet, there are no moving parts downstream of the combustible gas inlet that could be a potential cause of ignition.

[0028] In some embodiments, the combustible gas diluter includes two gas flow generators configured to operate as active and standby gas flow generators.

[0029] In many systems where it is necessary to extract and remove flammable gas, it is important that the concentration of the flammable gas does not exceed a certain level. That is, when diluting the flammable gas at the point of use, it is particularly important that the system can be relied upon and does not malfunction. Accordingly, in some embodiments, two gas flow generators are provided, one configured to operate as a primary gas flow generator and the other configured as a backup gas flow generator that functions in the event of a failure in the primary gas flow generator. Since the diluter has a simple design with few moving parts, a highly reliable system can be provided in the case where components with moving parts, in this case the gas flow generators, are duplicated.

[0030] In some embodiments, the air inlet assembly includes a conduit that directs air into the inlet of the dilution container, and the two gas flow generators are provided at substantially the same longitudinal position on the conduit and, in some embodiments, at different positions around the gas conduit.

[0031] In some embodiments, the two gas flow generators can be installed vertically above and below at different longitudinal positions along the conduit. In another embodiment, they can be installed on both sides of the conduit to reduce the height of the diluter and make it more compact. When installed on both sides of the conduit, one of the gas flow generators can be rotationally offset relative to the other so that the air inlets of the two gas flow generators do not directly face each other.

[0032] In some embodiments, at least one gas flow generator and the dilution container are configured such that the air flow rate at the flammable gas inlet arrangement is greater than the flame speed of the flammable gas.

[0033] As described above, when the combustible gas is in the diluter closest to the inlet of the combustible gas where its concentration is the highest, it is important to prevent the ignition of the combustible gas. Therefore, in the combustible gas inlet arrangement, by supplying air at a speed greater than the flame speed of the combustible gas, its ignition will be prevented. In this regard, for example, since the flame speed of hydrogen is 3 to 4 meters per second, the hydrogen diluter must be configured such that the air speed at the hydrogen gas inlet is greater than 3 to 4 meters per second. In some embodiments, it is configured to be greater than 20 meters per second, preferably greater than 25 or 30 meters per second.

[0034] In some embodiments, in addition to supplying this accelerated air flow, a flame confinement cone can be present at the combustible gas inlet.

[0035] In some embodiments, the combustible gas inlet arrangement is configured such that the opening faces away from the gas outlet.

[0036] It has been found that the mixing of the combustible gas with air is improved when the opening faces away from the gas outlet and in some embodiments when it faces the direction of the gas inlet.

[0037] In some embodiments, the opening of the combustible gas inlet arrangement has a diameter of 2 to 5 mm.

[0038] The selection of the size of the combustible gas opening affects the flow of the combustible gas into the diluter, especially when the opening faces the direction of the air flow for dilution. If the opening is too large, it will prevent the outflow of the combustible gas and may actually cause contamination by the air flowing into the vacuum system. If it is too small, the opening will suppress the gas flow. It has been found that an opening size of 2 to 5 mm provides a particularly effective flow of the combustible gas into the diluter.

[0039] In some embodiments, the combustible gas inlet arrangement includes an outer ring channel and a radial channel extending from the outer ring channel towards the center of the ring, the radial channel including an opening.

[0040] To supply a flow of combustible gas into an air flow in a manner that promotes mixing between the two gas flows, it has been found advantageous to provide the openings of the inlet arrangement at different radial positions across the gas flow such that instead of a single plume being formed, there are several flows of combustible gas from different openings at different radial positions. Also, the use of arms across the cross-section of the diluter has been found to provide an effective arrangement where the air flow is not overly restricted and thus the vacuum pump is not overly stressed. The collar or outer ring channel surrounding the diffuser when hydrogen is introduced from the pumping system into the diffuser is sized to allow a substantially even and unrestricted flow to the spider arms near the inner circumference. In some embodiments, the spider includes 4 to 8 arms across the inlet of the diffuser or diluter. The spider arms are sized not to restrict the air flow path of the diffuser by more than 30%. The openings of the spider arms are, in some embodiments, distributed substantially evenly along the length of the arm and are arranged to face the flow of diluent gas.

[0041] The outer ring channel may be within the dilution vessel, but in some embodiments, the outer ring is around the outer envelope of the dilution channel and the radial channel runs through the radial arms extending from the inner surface of the outer envelope, the channel extending through the dilution vessel wall and being in fluid communication with the outer ring channel.

[0042] The flammable gas diluter is suitable for diluting various flammable gases, and is particularly suitable for hydrogen. Since hydrogen is a very light gas, it becomes substantially difficult to pump. Hydrogen also tends to accumulate towards the top of the system when the flow rate is low. Therefore, there are challenges in removing hydrogen, and the diluter of the embodiment is particularly effective in addressing these challenges. In particular, due to the reliability of the system with few moving parts, the flow rate is generally maintained at a relatively constant value, and hydrogen will substantially diffuse through a plurality of openings. Furthermore, since hydrogen exists in the atmosphere, it can be released into the atmosphere when sufficiently diluted. Generally, the flammable limit of hydrogen is a concentration of 4%, so there should be no risk of ignition if it is less than 4%. However, in order to provide a robust and safe system, a dilution level limit of 1% is generally set at the outlet.

[0043] In some embodiments, the dilution container, the flammable gas inlet configuration, and the gas guiding configuration are formed of and grounded to metal.

[0044] As described above, it may be preferable to remove ignition sources from the gas flow in the diluter. That is, in some embodiments, the flammable gas diluter is formed of a grounded metal to reduce any possibility of electrostatic sparks. In some embodiments, the metal is stainless steel. In this way, a metal diluter is provided, having no moving parts in the flammable gas flow, and in some embodiments having a flow rate exceeding the flame speed of the flammable gas, thereby substantially removing any possibility of ignition.

[0045] The inwardly directed induced gas flow configuration and the outwardly directed induced gas flow configuration can have several forms. In some embodiments, the inwardly directed induced gas flow configuration includes a ring-shaped baffle protruding inward from the outer envelope, and the outwardly directed induced gas flow configuration includes a cone-shaped baffle positioned at the center, with the apex of the cone facing the inlet of the dilution container.

[0046] These gas flow configurations, which direct gas through a dilution vessel towards the center of the gas flow path and then away from it, provide effective mixing of the gas and thus substantially dilute the combustible gas within a relatively small volume. This results in a compact dilution vessel that is advantageous for use as a use point removal system.

[0047] In some embodiments, the plurality of inward and outward induced gas flow configurations are arranged alternately along the length of the dilution vessel. Thus, an outward induced gas flow configuration follows an inward induced gas flow configuration.

[0048] In some embodiments, the dilution vessel includes a volume of less than 70 liters, and the combustible gas diluter is configured to dilute a flow of combustible gas up to 1000 SLM (standard liters per minute).

[0049] The diluter of the embodiment is compact by its design and can dilute a relatively large flow of combustible gas within a relatively small volume. Thus, a 70 - liter diluter, and in some cases a 50 - liter diluter, can dilute a flow of combustible gas up to 1000 SLM.

[0050] In some embodiments, the combustible gas diluter includes a combustible gas sampler adjacent to the outlet, the combustible gas sampler is in fluid communication with a combustible gas sensor, and the combustible gas diluter further includes a control circuit for suppressing the flow of combustible gas to the diluter in response to the combustible gas sensor indicating a concentration of combustible gas exceeding a predetermined level.

[0051] In some embodiments, the combustible gas sampler includes an outer ring channel and a radial channel extending from the outer ring channel towards the center of the ring, and the radial channel includes an opening.

[0052] To ensure the safety of the system, the concentration of the gas exiting the diluter must be below the flammable limit of that gas. Thus, in some embodiments, a sampler is present near the outlet to ensure this. If the concentration rises above the desired flammable concentration limit, a wired safety control circuit will suppress the flow of combustible gas to the diluter. In this regard, when it is a user point diluter, it may involve stopping the tool to which it is attached and generating a hydrogen flow.

[0053] In some embodiments, the gas flow generator is configured to supply atmospheric air to the combustible gas diluter.

[0054] A second aspect provides a vacuum pumping system for evacuating air from at least one vacuum chamber within a semiconductor processing tool, the vacuum pumping system including a plurality of vacuum pumps for evacuating air from at least one vacuum chamber and a removal system for receiving the exhaust from at least one of the at least one vacuum chamber, the removal system comprising a combustible gas diluter according to the first aspect.

[0055] The diluter of the first aspect provides an effective removal system that can be provided as a system integrated with a vacuum pumping system for an evacuation chamber within a semiconductor processing tool that exhausts combustible exhaust gas. That is, there is a user point removal for combustible gas, and there is no need to pipe it elsewhere or burn it within the removal system along with the drawbacks of a combustor removal system.

[0056] In some embodiments, the semiconductor processing tool includes an extreme ultraviolet lithography tool and the combustible gas comprises hydrogen.

[0057] Extreme ultraviolet lithography is a technology that uses increasing amounts of hydrogen. Thus, a removal system that can provide effective dilution of this hydrogen and safely dilute it at the point of use without piping it elsewhere or burning it is a particularly efficient way to evacuate and remove air from such a system.

[0058] In some embodiments, the vacuum pumping system further includes a housing for accommodating a plurality of pumps and an air flow duct for receiving air from the housing, the air flow duct being in fluid communication with at least one air inlet assembly for supplying air to the flammable gas diluter, such that in response to at least one operation of the gas flow generator, air passes through the housing and flows into the diluter along the air duct.

[0059] The air flow is necessary for diluting the flammable gas and may in some cases be a cabinet extraction flow that passes over a pump that is removing air from the system to remove potentially leaking gas, which can be a problem especially if the gas is flammable. Thus, in many process systems that pump flammable gases, there is already an air flow at a predetermined location and both the duct and the air flow generator can be saved because this air flow can be directed directly to the diluter. Thereby, an efficient way is provided to reuse the air flow through the housing of the pumping system to dilute the hydrogen withdrawn from the chamber.

[0060] A third aspect provides a method of controlling the operation of two gas flow generators to supply a gas flow to the flammable gas diluter of any of the preceding claims, the method comprising controlling the first of the two gas flow generators, which is currently in standby mode, to start while keeping a buffer between the first gas flow generator and the dilution vessel in a closed position, and controlling to open the buffer associated with the first gas flow generator after a predetermined delay.

[0061] When a gas flow generator that is in the current standby mode and isolated from the system through a buffer starts, if the buffer is opened while the air flow generator is inoperative, it will provide a leakage path from the diluter to the outside through the inoperative gas flow generator. Therefore, it is advantageous to start it before opening the buffer. This leakage path can cause turbulence in the flow within the diluter, trigger an alarm, and potentially stop it.

[0062] In some embodiments, the method further includes controlling to close a buffer associated with a second gas flow generator to be stopped after a predetermined delay, and controlling to stop the second gas flow generator.

[0063] In some embodiments, the method includes controlling to open a buffer associated with a standby gas flow generator in response to a signal indicating that the diluter must be started, controlling to close a buffer associated with the operating gas flow generator, controlling to start the standby gas flow generator, controlling to start the operating gas flow generator after a set test time, controlling to open a buffer associated with the operating gas flow generator after a predetermined delay, controlling to close a buffer associated with the standby gas flow generator, and controlling to stop the operation of the standby gas flow generator.

[0064] Yet another specific and preferred aspect is presented in the appended independent and dependent claims. The features of the dependent claims can be combined with the features of the independent claims as appropriate, and can also be combined in combinations other than those explicitly shown in the claims.

[0065] When describing a device feature as being operable to provide a function, it will be recognized that this includes a device feature that provides that function or a device feature that is adapted or configured to provide that function.

[0066] Here, embodiments of the present invention will be further described with reference to the accompanying drawings.

Brief Description of the Drawings

[0067]

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Modes for Carrying Out the Invention

[0068] Before discussing the embodiments in more detail, an overview will first be given as follows.

[0069] Dilution is an acceptable option for discharging a large amount of flammable gas from the system, such as for discharging hydrogen from an EUV tool. Conventionally, dilution of flammable gas has been performed using an inert gas, but with the increase in the hydrogen flow rate, a large flow rate is required, and it brings additional risks and environmental damage, so dilution with an inert gas cannot be tolerated.

[0070] Dilution with air provides a cost-effective and environmentally friendly alternative.

[0071] Basic theory Combustible gases from systems such as hydrogen from EUV initially contain little or no oxygen, so they exceed the UFL (upper flammable limit). In the case of hydrogen, this is 75% by volume.

[0072] The embodiments aim to dilute to less than the lower flammable limit LFL (4% by volume hydrogen). To reach from a safe UFL excess to a safe LFL below, the mixture needs to pass through the flammable range (75% to 4% by volume hydrogen). Ignition of the flammable mixture will cause deflagration / explosion. The risk is scaled using the volume of the combustible gas (hydrogen) and the size and length of the duct used to transport the gas.

[0073] The properties of hydrogen are as follows. The MIE (minimum ignition energy) of H2 is 17 μJ, compared to 800 μJ for gasoline and 300 μJ for methane. The flame speed of H2 in air is 2.88 m / s, compared to 0.2 - 0.5 m / s for gasoline and 0.356 m / s for methane.

[0074] If the air velocity at the hydrogen introduction point ≫ the flame speed of hydrogen (30 m / s), the risk of backflash is avoided or at least reduced.

[0075] Hydrogen gas has high diffusivity, large buoyancy, and rapidly mixes with air.

[0076] The risks are as follows. It is very easy to ignite a hydrogen mixture. In the ignited state, the flame will propagate very fast.

[0077] To mitigate these risks, it is considered advantageous to achieve air dilution near the point of use at the earliest possible opportunity. Thereby, the locations where a flammable mixture could be ignited are reduced, the risk of explosion in the pipeline is reduced, and a design is provided that allows inspection, certification, and reproduction at any location without having to analyze the pipe route designation and environment each time.

[0078] System Embodiments of the dilution unit aim to manage the flammable zone where the flammable gas is between its LFL and UFL by diluting the flammable gas below its lower flammability limit and, in some cases, below 1 / 4 of its lower flammability limit, eliminating or at least reducing potential ignition sources.

[0079] In some embodiments, the system of the present invention utilizes cabinet extraction air as a diluent to reduce the need for an additional fan to draw air from the pumping system cabinet.

[0080] FIG. 1 shows a diluter 5 according to an embodiment. The diluter 5 includes a dilution vessel 10 extending from an inlet 11 to an outlet 12. The inlet 11 is connected to an air supply portion 14 having two air inlets 16 and 17. These are configured to receive air from a primary fan in the case of the air inlet 16 and from a standby fan in the case of the air inlet 17. Each of the air inlets has an associated buffer 16a, 17a. The buffer includes a slat that rotates between an open position where the primary fan in the case of the buffer 16a is operating and a closed position where the secondary fan in the case of the buffer 17a is in a standby mode. The closed buffer 17a prevents air from the air supply portion 14 from leaking to the outside through the secondary fan. The buffer is controlled by a control circuit (not shown) so as to open and close automatically according to the operating state of the diluter. The air from the air inlet is sent along the pipe of the air supply portion 14 to the air inlet 11 of the dilution unit. The dilution unit 10 has a constriction 18, and a combustible gas inlet arrangement 15 is provided therein. Thus, when reaching the constriction, the air is accelerated, and as a result, passes through the combustible gas inlet configuration at a high speed and at a speed greater than the flame speed of the combustible gas. Thereafter, the dilution unit 10 extends to a larger diameter where the gas decelerates and mixing is improved.

[0081] Next, the gas flows through various gas guiding configurations for directing the gas towards or away from the outer envelope, whereby they are mixed to have a uniform concentration below the lower flammable limit of the combustible gas until they reach the outlet 12. In this regard, the combustible gas entering at the inlet 15 is generally at a concentration exceeding the upper flammable limit and passes through the diluter at a concentration that is of course combustible when passing through the diluter until it reaches a concentration below the lower flammable limit before exiting at the outlet 12.

[0082] The dilution vessel 10, particularly the gas guiding configurations for promoting the mixing of the combustible gas and air, are shown in more detail in FIG. 2. In this embodiment, these gas guiding configurations take the form of cones 30, 34 for guiding the flow towards the outer wall and baffles 32, 36 for guiding the flow towards the center.

[0083] The combustible gas enters the dilution vessel at the constriction through an inlet arrangement in the form of an inlet spider 15. This takes the form of a collar or ring around the outside of the gas dilution vessel 10 into which the hydrogen gas flows. There are radial arms extending from the outer ring to the gas flow portion through the wall of the dilution vessel. These extend across the cross-section of the constriction and the openings in the arms dispense hydrogen into the air flow. These openings face towards the air inlet 11 of the gas dilution vessel 10.

[0084] The gas guiding configurations 30, 32, 34, 36 are arranged at different longitudinal positions along the length of the dilution vessel 10 and alternately include cones for guiding the flow towards the outer edge of the dilution vessel and baffles for returning the flow towards the center. Thus, at the lower end close to the air and hydrogen inlets, there is a cone 30 that acts to deflect the gas mixture towards the outer wall of the vessel and further to decelerate the flow accelerated at the constriction 18. Next in the gas flow path is a baffle 32 that guides air back towards the center, followed by a cone 34 and then a baffle 36. In this embodiment, there is a sampling spider 40 for sampling the gas before it exits. This is directed to a hydrogen sensor and it can be determined that the concentration of hydrogen exiting through the outlet 12 is below the lower flammable limit of hydrogen. The signal from the hydrogen sensor is then transmitted to a control circuit, which can then generate a control signal to stop the supply of hydrogen to the diluter in response to determining that the level of hydrogen concentration exceeds a predetermined limit value, which may involve stopping the process in the vacuum chamber that receives hydrogen from there.

[0085] Figure 3 shows a diluter 10 arranged to be connected to a duct and an air flow generator. The air flow generator is in the form of fans 20 and 22 and is attached to the air inlets 16 and 17 (see Figure 1) of the diluter. Fan 20 is the primary fan and fan 22 is the secondary or standby fan. The dilution container 10 is shown and the arms from the spider and the openings on the arms can be seen. These openings appear to face the outlet, but in many embodiments they will face the inlet, as it has been found that the mixing and flow of gas through these openings is increased in this arrangement. The arms themselves are designed not to unduly impede the air flow, but result in supplying the combustible gas flow to different parts of the air flow, improving mixing and suppressing the formation of fumes.

[0086] In this embodiment, there is a cabinet extraction pipe 64 that receives the air flowing around the pumping cabinet containing the vacuum pump of the system, and this air flow is used to suppress the combustible gas that may leak from the pumps or their pipes that collect in the cabinet. In this embodiment, this air flow is reused as a source of air for dilution. Thereby, the additional fan for pumping this air onto the roof as well as the additional piping are saved, of course.

[0087] Figure 4 schematically shows how the gas flow through the diluter and the velocity of the gas flow and the concentration of hydrogen change along the length of the diluter. The left figure shows the gas from the air inlet 16 and the gas from the hydrogen inlet 15, showing a manner in which the air flow speeds up and slows down at the constriction where hydrogen is added and then accelerates again towards the exhaust port 12 and slows down somewhat at each of the deflector plates 30, 32, 34, 36. Thereby, the mixing is improved and mixing can be carried out in a relatively small volume.

[0088] The right figure shows the mole fraction of hydrogen when the flow progresses in the dilution vessel and mixing occurs. Therefore, the mole fraction ranges from a high concentration exceeding the flammable upper limit to the concentration within the flammable range and then to a concentration below the flammable limit where it can be safely exhausted from the vessel. In this embodiment, there are three cones 30, 34, 38, and after the third cone, the mole concentration is about 1%, which is thus the required level. As can be seen, since the primary flow exits uniformly from the full opening of the spider, effective mixing of hydrogen occurs therein.

[0089] Figure 5 shows a vacuum pumping and removal system according to an embodiment. This embodiment is for pumping an extreme ultraviolet radiation lithography process. This arrangement includes a pump in section 50 that evacuates an exposure chamber that exposes a wafer to laser light, and a pump in section 52 that evacuates a source chamber where extreme ultraviolet radiation is generated from a laser and a tin flow and where hydrogen is used as a shield to protect various optical elements from tin sputtering. The generated extreme ultraviolet light is sent into the exposure chamber through a channel using optical elements. Therefore, the amount of hydrogen in the source chamber is significantly more than that in the exposure chamber, and the main component to be diluted is this hydrogen.

[0090] In this embodiment, there is a housing 62 that houses a plurality of pumps 60 forming pumping sections 50 and 52. There is a gas flow passing through this housing, which is a cabinet extraction flow and is used to cool the pumps and remove gases that may leak from the pumps. In this embodiment, there is a duct 64 that flows cabinet extraction gas from the cabinet towards the gas diluter 10 of the embodiment. The gas diluter 10 has fans 20, 22 that send air into the gas dilution vessel 10, and an inlet 15 into which hydrogen discharged from the foreline of the pump that evacuates the chamber is introduced. This inlet is arranged in a limited part of the diluter and includes a spider. The gas that has been mixed and diluted is discharged through an exhaust gas flow 66. In this embodiment, the fans 20 and 22 are arranged side by side, thereby reducing the height of the diluter.

[0091] In this embodiment, sensors 70 and 72 are present to sense both oxygen and hydrogen levels in different streams. Similarly, hydrogen sensors can be present near the outlet of the diluter 10, and these sensors can be used with a control circuit to inhibit the process if it is determined that the concentration levels of hydrogen or oxygen in the exhausted gas pose a flammability problem.

[0092] Figure 6 schematically shows different zones within the dilution system. In the initial zone, the drawn air is introduced from the primary and standby centrifugal fans. The drawn air is below the lower flammability limit because the internal hydrogen level is very low. The gas is received through a conduit from the scanner or exposure chamber 100 and the source chamber 120 with a composition of 132 SLM (standard liter per minute) of N2 and 12 SLM of H2 from the scanner chamber and 600 SLM of H2 from the source chamber. Inside the conduit, the hydrogen concentration exceeds the upper flammability limit while the oxygen level is below the limiting oxygen concentration. Hydrogen is introduced through the inlet spider 15, and a flame restraint cone 75 is present to prevent ignition when this gas stream encounters air. The gas stream flowing through here (zone 0) exceeds the lower flammability limit, is below the upper flammability limit, and exceeds the limiting oxygen concentration, so there is a possibility of ignition. To avoid or at least prevent ignition, there are no moving parts in this part of the diluter, the material of the diluter is formed of grounded metal, and the flow rate is maintained to exceed the flame speed of the flammable mixture.

[0093] When the combustible mixture flows through the dilution vessel, mixing occurs by means of baffles and cones until the concentration of the combustible substance in Zone 2 drops below one quarter of the lower flammable limit, at which point the gas can be safely released into the air. To confirm that the mixed gas is substantially below the lower flammable limit, combustible gas sensors 72 are present both at the outlet and further inside the dilution vessel. There is a control circuit 80 associated with the sensors 72, which is configured to receive signals from the sensors and activate an alarm and / or stop the system in response to the lower flammable limit or a predetermined percentage of the lower flammable limit being exceeded. The control circuit 80 is also configured to control the fans 20, 22 and dampers 16a, 17a (see Figure 1) during start-up, during shutdown, and when replacing the fans, thereby enabling continuous operation during such replacement.

[0094] There are primary and secondary or standby fans 20, 22, which in this embodiment are centrifugal fans with speed control capable of providing flow rates up to 4000 m 3 / h. Thereby, an inlet air velocity of approximately 14 m / s is obtained and, accelerated in the constriction 18, increases to over 30 m / s, which is approximately 10 times the flame speed of hydrogen.

[0095] The distribution of hydrogen into the air flow also prevents flashback, and the cones and baffles promote the mixing of hydrogen into the air flow such that the hydrogen concentration is less than 1 v / v% by the time it reaches the final baffle plate.

[0096] Figure 7 shows the fans 20, 22 with dampers 16a, 17a, which are shown in the closed position separating the fans 20, 22 from the air supply portion 14 of the diluter. In this embodiment, the two fans are mounted one above the other.

[0097] Figure 8 shows an alternative arrangement of the two fans 22, 22, where they are mounted at the same height to provide a compact arrangement. This figure shows that the air outlets of the fans provide an air flow to the corresponding air inlets 16, 17 of the air supply portion 14 of the hydrogen diluter. Since the fans are mounted in different rotational directions, the air inlet 17 from fan 22 to the diluter is offset with respect to the air inlet 16 from fan 20, and the two openings do not directly face each other.

[0098] The air fan inlets 21, 23 for each of the fans 20, 22 are also shown. There is a guillotine valve (not shown) separating the air fan inlets 21, 23 from the hydrogen diluter, allowing the fans to be removed from the system. This arrangement is particularly compact but requires careful control of the fans and dampers to suppress air leakage from a non-operating fan very close to an operating fan. This will be described in more detail with reference to Figure 10.

[0099] Figure 9 shows the fan 20 and the positions of the fan air inlet 21 and the fan air outlet or diluter air inlet 16.

[0100] Figure 10 shows the steps of a fan replacement method according to an embodiment. Thus, when replacement or maintenance inspection of an operating fan is required, at step S10, a standby fan in standby mode is started, and when it is determined that a high rotational speed has been reached after a predetermined delay such that leakage in the reverse direction through the fan is suppressed (step D5), at step S20, the fan damper associated with this fan is opened. At this point, the primary fan damper associated with the fan to be maintained or replaced is closed (step S30), and then this fan can be stopped at step S40. In this way, by careful control of the dampers associated with the fan, any path for leakage out through the non-operating fan is suppressed.

[0101] As an example, when the primary fan is operating and needs to be replaced due to a temperature rise or an increase in vibration of the winding or bearing, the following procedure is used to maintain the OK signal to the tool and prevent this signal from being cancelled; otherwise, the hydrogen flow will be blocked and the system may be stopped. · The primary fan operates with the primary buffer open. · Start the secondary fan and wait for 5 seconds (the time from 0 rpm to the default speed), then · Release the secondary buffer and close the primary buffer, · Turn off the primary fan.

[0102] Note that the fan replacement cannot be performed for at least 80 seconds at this point due to the torque generated by the fan during deceleration.

[0103] If the secondary fan fails, the primary fan needs to be restarted after waiting for 80 seconds.

[0104] Similar precautions are required at startup to avoid excessive leakage of air from the dilution system. Fan startup test sequence: When the fan performs its startup test, the air flow rate can be maintained in the following sequence: · Release the secondary buffer, · Start the secondary fan, · Timer... Orbit the fan for 1 minute to check its operation, · Start the primary fan and wait for 5 seconds, then · Release the primary buffer and close the secondary buffer, · Turn off the secondary fan.

[0105] Note that the fan replacement cannot be performed for at least 80 seconds at this point due to the torque generated by the fan during deceleration.

[0106] If the primary fan fails, the secondary fan needs to be restarted after waiting for 80 seconds.

[0107] In summary, the embodiment uses cabinet extraction air as dilution air, collects air from parallel paths by using a multi-aperture inlet spider, and supplies power from an integrated blower, that is, provides a system that provides a predetermined combustible zone. By monitoring important parameters such as combustible gas concentration, air flow, and temperature and linking them with control signals, it is possible to provide control of the system and / or shutdown of the system in response to these signals.

[0108] A secondary fan is available as a backup for the primary fan. Since H2 does not flow through the fan, the fan can be serviced and maintained during tool operation.

[0109] Embodiments of the diluter provide a highly reliable and common-mode failure-insensitive system because they have few moving parts and use redundancy and diversity in most of their monitoring and control systems. In particular, there is a standby fan, and the air flow comes from a cabinet extraction section that provides flow balance across the pump module.

[0110] In some embodiments, one 4kW inverter-driven fan is sufficient to provide both cabinet extraction and dilution. The secondary fan is in a standby state and detects when it is necessary to operate the standby fan using a preventive maintenance monitor for the operating fan. When a performance degradation of the primary fan is detected, the secondary fan starts and the primary fan is isolated and stopped. For each fan, the bearings and the motor can be maintained in place. The inlet and outlet of the fan are separated independently.

[0111] In some embodiments, it takes 5 seconds for the secondary fan to ramp up to its maximum speed. This is significantly more cost and power efficient than those having an oil-fired burner where both the primary unit and the standby unit operate.

[0112] Furthermore, since the dilution unit is a use point unit, it is not necessary to extract it from a system that is not operating or is operating only the scanner hydrogen flow.

[0113] Even in the event of an NOK signal, the diluter continues to operate and perform dilution. In the case of a system shutdown, the pumping system removes the OK signal, which stops the H2 supply to the tool.

[0114] In the case of an unexpected stop, the residual H2 is equalized within the pumping system, and part of the gas remains in the system and part enters the diluter, diffuses with air, and enters the exhaust of the facility. Following the restart of the diluter, the pumping system starts, and after an unexpected stop, purging is performed in the same manner as currently being done.

[0115] Exemplary embodiments of the present invention have been disclosed herein in detail with reference to the accompanying drawings, but the present invention is not limited to those embodiments, and it is understood that various modifications and variations can be achieved by those skilled in the art without departing from the scope of the invention defined by the claims and their equivalents.

[0116] Reference symbol 5 Diluter 10 Dilution container 11 Inlet to the dilution container 12 Outlet 14 Air supply pipe 15 Combustible gas inlet spider 16 Air inlet 16a Buffer 17 Auxiliary air inlet 17a Buffer 18 Constriction 20, 22 Air fans 21, 23 Fan air inlets 30, 34 Cones 32, 36 Baffles 40 Sampling spider 50 Exposed chamber pumping section 52 Source Chamber Pumping Section 60 Vacuum Pump 62 Pump Chamber 64 Conduit 66 Exhaust Port 70, 72 Sensor 75 Flame Retention Cone 80 Control Circuit 100 Scanner Chamber 120 Source Chamber

Claims

Claim 1 A flammable gas diluter for diluting a flow of flammable gas to a concentration below the flammable limit of the flammable gas, comprising: A dilution container having an outer envelope defining a longitudinal flow path from an inlet to an outlet; At least one air inlet assembly for directing a flow of air into the inlet of the dilution container; A flammable gas inlet arrangement positioned towards the inlet end of the dilution container; Two gas flow generators configured to pump a flow of air through the air inlet assembly, positioned upstream of the flammable gas inlet arrangement, and configured to operate as an operating and standby gas flow generator; Two buffers, one buffer being associated with each of the gas flow generators, each of the buffers being mounted between the corresponding gas flow generator and the dilution container, the buffer being configured to cover the passage between the corresponding gas flow generator and the dilution container when closed and to open the passage between the gas flow generator and the dilution container when open; A control circuit configured to control the opening and closing of the buffer, the control circuit being configured to open the buffer during the operating mode of the corresponding gas flow generator and to close the buffer when the corresponding gas flow generator is stopped in the standby mode; A flammable gas diluter characterized by comprising the above. Claim 2 The control circuit responds to a signal indicating that the currently operating gas flow generator is to be stopped and the currently standby mode gas flow generator is to be started, Controls to start the gas flow generator in the standby mode, and after a predetermined delay, Controls to open the buffer associated with the started gas flow generator. The flammable gas diluter according to claim 1, characterized in that it is configured as described above. Claim 3 The predetermined delay comprises the time for the gas flow generator in the standby mode to achieve a rotational speed of at least 70% of the normal operating speed. The flammable gas diluter according to claim 2, characterized in that it is configured as described above. Claim 4 The control circuit is configured to control to close the buffer associated with the gas flow generator to be stopped after the predetermined delay and to control to stop the gas flow generator. The flammable gas diluter according to claim 2 or 3, characterized in that it is configured as described above. Claim 5 In response to a signal indicating that the combustible gas diluter is to be started, the control circuit controls so that the buffer associated with the standby gas flow generator is opened and the buffer associated with the working gas flow generator is closed, and controls to start the standby gas flow generator, controls to start the working gas flow generator after a set test time, after a predetermined delay, controls to open the buffer associated with the working gas flow generator and close the buffer associated with the standby gas flow generator, and controls to stop the operation of the standby gas flow generator, The combustible gas diluter according to any one of claims 1 to 4, characterized in that it is configured as described above.

6. A vacuum pumping system for evacuating air from at least one vacuum chamber in a semiconductor processing tool, comprising the combustible gas diluter according to any one of claims 1 to 5, a plurality of vacuum pumps for evacuating the at least one vacuum chamber, a housing for accommodating the plurality of vacuum pumps, an air flow duct for receiving air from the housing, which is in fluid communication with at least one air inlet assembly for supplying the air to the combustible gas diluter, whereby the air is configured to flow through the housing along the air flow duct into the combustible gas diluter in response to the operation of at least one of the two gas flow generators, a path for supplying combustible gas discharged from the foreline of the plurality of vacuum pumps to the combustible gas inlet arrangement of the combustible gas diluter, A vacuum pumping system characterized by comprising.

7. The semiconductor processing tool includes an extreme ultraviolet lithography tool, and the combustible gas includes hydrogen. The vacuum pumping system according to claim 6.

8. A method of controlling the operation of two gas flow generators to supply a gas flow to the combustible gas diluter according to any one of claims 1 to 5, comprising controlling to start the first of the two gas flow generators in the current standby mode while keeping the buffer between the first gas flow generator and the dilution container in the closed position, after a predetermined delay, controlling to open the buffer associated with the first gas flow generator; A method characterized by comprising the above. **Claim 9** controlling to close the buffer associated with the second gas flow generator that is to be stopped after the predetermined delay; controlling to stop the second gas flow generator; The method according to claim 8, further comprising the above. **Claim 10** In response to a signal indicating that the combustible gas diluter is to be started, controlling to open the buffer associated with the standby gas flow generator and to close the buffer associated with the working gas flow generator; controlling to start the standby gas flow generator; controlling to start the working gas flow generator after a set test time; controlling to open the buffer associated with the working gas flow generator after a predetermined delay; controlling to close the buffer associated with the standby gas flow generator; controlling to stop the operation of the standby gas flow generator; The method according to claim 8 or 9, characterized by comprising the above.

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