TW202215906A - Apparatus for and method of controlling gas flow in an euv light source - Google Patents

Abstract

Disclosed is a source for and method of generating extreme ultraviolet radiation in which a flow characteristic of a gas introduced into the source or exhausted from the source is varied at least partially in accordance with a prevailing source mode of operation such as whether the source is in an on-droplet mode of operation or an off-droplet mode of operation.

Description

Apparatus and method for controlling airflow in an EUV light source

The present invention relates to an apparatus and method for generating extreme ultraviolet ("EUV") radiation from a plasma generated by electrical discharge or laser ablation of a source or target material in a container. In such applications, optical elements are used, for example, to collect and direct radiation for use in semiconductor photolithography and inspection.

Extreme ultraviolet radiation, such as electromagnetic radiation (sometimes also referred to as soft x-rays) having a wavelength of about 50 nm or less, and including radiation with a wavelength of about 13.5 nm, can be used in photolithography processes to produce Very small features are created in a circular substrate.

Methods for generating EUV radiation include converting the target material into a plasmonic state. The target material preferably includes at least one element having one or more emission lines in the EUV portion of the electromagnetic spectrum, eg, xenon, lithium, or tin. The target material can be solid, liquid or gas. In one such method, often referred to as laser generated plasma ("LPP"), the desired plasma can be generated by using a laser beam to irradiate a target material with the desired spectral line emitting element.

One LPP technique involves generating a stream of droplets of target material and irradiating at least some of the droplets with one or more pulses of laser radiation. These LPP sources generate EUV radiation by coupling laser energy into a target material having at least one EUV emitting element, resulting in a highly ionized plasma.

For this process, a plasma is typically generated in a sealed container, such as a vacuum chamber, and the resulting EUV radiation is monitored using various types of metrology equipment. In addition to generating EUV radiation, processes used to generate plasma also typically generate unwanted by-products in the plasma chamber, which can include out-of-band radiation, high-energy ions, and debris such as residual target material. Atoms and/or clots/droplets.

High-energy radiation is emitted from the plasma in all directions. In one common configuration, a near normal incidence mirror (often referred to as a "collector mirror" or simply a "collector") is positioned to collect, direct, and (in some configurations) focus at least a portion of the radiation to an intermediate location . The collected radiation can then be forwarded from the intermediate location to a set of optics, a reticle, a detector and finally to a silicon wafer.

In the EUV portion of the spectrum, it is generally considered necessary to use reflective optics for optical elements in systems including collectors, illuminators, and projection optics boxes. Such reflective optics can be implemented as normal incidence optics as mentioned or as grazing incidence optics. At the wavelengths in question, the collector is advantageously implemented as a multilayer mirror ("MLM"). As the name suggests, this MLM typically consists of alternating layers of material (MLM stacks) over a base or substrate. System optics can also be configured as coated optical elements, even if they are not implemented as MLMs.

Optical elements and in particular collectors must be placed within the vessel with the plasma to collect and redirect EUV radiation. The environment within the chamber is detrimental to the optical element and thus limits its useful life, eg, by degrading reflectivity. Optical elements within the environment can be exposed to energetic ions or particles of the target material. Particles of the target material, essentially debris from the laser vaporization process, can contaminate the exposed surface of the optical element. Particles of the target material can also cause physical damage and localized heating of the MLM surface.

In some systems, _H2 gas at a pressure in the range of about 0.5 to about 3 mbar is used as a buffer gas in the vacuum chamber for debris mitigation. In the absence of gas, under vacuum pressure, it would be difficult to adequately protect the collector from debris of the target material ejected from the irradiation zone. Hydrogen is relatively transparent to EUV radiation having a wavelength of about 13.5 nm, and is therefore preferred to other candidate gases, such as He, Ar, or other gases that exhibit higher absorption at wavelengths of about 13.5 nm.

_H2 gas is introduced into the vacuum chamber to slow down energetic debris (ions, atoms and clusters) of the target material produced by the plasma. Debris is slowed down by collisions with gas molecules. For this purpose, a flow of H ₂ , which can also be opposed to the debris trajectory and away from the collector, is used. This is used to reduce damage to deposition, implantation and sputtering target materials on the optical coating of the collector.

Thus, the process of transforming the target material produces particles and deposits residual target material on the surface, with an unobstructed path between the irradiation site and the surface and in the exhaust path of the gas that entrains the residual target material. For example, if this gas is drawn across the tops of the vanes present in the chamber and to a mechanical pump, material will soon be deposited on all cold metal parts. If the target material is tin, this can lead to the growth of tin wool that can fall onto the collector optics and block the exhaust path.

When laser radiation is used to illuminate a target material, such as tin, to generate plasma, a portion of the target material becomes debris. For example, target material debris may include Sn vapor, _SnH4 vapor, Sn atoms, Sn ions, Sn clusters, Sn particles, Sn nanoparticles, and Sn deposits. When Sn debris accumulates on the EUV collector or on one or more of the inner vessel walls of the EUV container, EUV collector efficiency, lifetime and availability can be reduced.

Tin chips from the source container can pass from the EUV source to the scanner through the intermediate focus, which can lead to contamination of, for example, the illuminator in the scanner, expensive optics whose lifetime is critical to EUV system productivity and cost of ownership. As described above, one form of tin contamination is the spray or "spray" of molten tin from the wall in the source vessel near the middle focal point. One technique used to prevent tin chips from reaching the scanner involves the application of a dynamic air lock at the intermediate focus to suppress tin contamination, as described in US Patent issued March 28, 2017 and titled "Lithographic Apparatus and Method of Manufacturing a Device" As disclosed in No. 9,606,445, which is hereby incorporated by reference in its entirety.

The process of generating EUV light can also cause the target material to be deposited on the walls of the container. Controlling target material deposition on the vessel walls is important to achieve acceptable longevity for EUV sources placed in production. Also, managing the flux of target material from the irradiation site is important to ensure that the waste target material mitigation system works as intended.

The following presents a summary of one or more embodiments in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of all considered embodiments, and is neither intended to identify key or critical elements of all embodiments, nor to set limitations on the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

According to one aspect of an embodiment, a system for optimizing process windows by allowing dynamic changes in the characteristics of airflow into a chamber enclosing an EUV source is disclosed.

According to another aspect of an embodiment, an apparatus for generating EUV radiation by laser irradiation of a droplet of a target material is disclosed, the apparatus comprising: a container; an inlet structure defining at least one inlet path , the at least one inlet path is adapted and configured to connect a source of a gas to an interior of the vessel to add the gas to the vessel in a flow along the inlet path; an outlet structure defining at least one an outlet path adapted and configured to connect to an interior of the vessel to permit gas in the vessel to flow out of the vessel along the outlet path; a variable flow regulator optionally configured at in one of the inlet path and the outlet path and adapted to adjust a characteristic of the flow of the gas into or out of the vessel based at least in part on a mode in which the device is operating; and a controller that is Configured to control the operation of this flow controller. The controller can be adapted to operate using a look-ahead control process. The apparatus may further comprise a second variable flow regulator selectively disposed in the other of the inlet path and the outlet path and the apparatus may further comprise a second variable flow regulator a variable flow regulator, the second variable flow regulator selectively configured in the other of the inlet path and the outlet path and adapted to regulate entry or A characteristic of the flow of the gas leaving the vessel.

The device may have a droplet-on mode of operation, in which the droplets generate EUV radiation when irradiated by a laser while the device is in one mode; and a droplet-out mode of operation, in which the droplets are in another mode A mode is not used to generate EUV radiation when not irradiated by a laser. The variable flow regulator is selectively disposed partially or completely or not at all in the inlet path, and is adapted to adjust the amount of gas entering the vessel based at least in part on the mode in which the device is operating a characteristic of the flow. The characteristic can be any one or a combination of flow rate, flow velocity, flow profile, and flow composition. The flow composition may be such that it does not contain a reactive gas during the droplet up mode and contains a reactive gas during the droplet off mode. The reactive gas may contain oxygen. The inlet structure may include a collector cone.

The variable flow regulator may include a flow obstruction and a motor mechanically coupled to the flow obstruction and adapted to move the flow obstruction at least partially into the flow path. "Motor" as used herein and elsewhere includes any device used to generate motive power. The motor may comprise a linear motor. The motor may include a solenoid. The flow obstruction may present a solid cross-section to the flow or a cross-section having at least one aperture when placed in the flow path. The flow obstruction may have an open tubular shape and be oriented such that the flow obstruction redirects a portion of the gas when placed in the flow path. The flow obstruction may have an aerodynamic shape. The variable flow regulator may include a mass flow controller.

The variable flow regulator may include: a valve adapted to be in fluid communication with the gas source; and a manifold including a plurality of fluid conduits respectively connecting the valve to the inlet, in the plurality of fluid conduits each has a respective flow restrictor that limits a flow rate through the respective conduit to a respective value, the valve is configured to permit the gas to flow through the plurality of flow conduits one of them.

According to another aspect of an embodiment, an apparatus for generating EUV radiation by laser irradiation of a droplet of a target material is disclosed, the apparatus comprising: a container having at least one inlet, the at least one The inlet is adapted to connect to a source of a gas and add the gas to the vessel in a flow along a flow path; a droplet generator configured to introduce the droplets into the vessel to reach an irradiation site within the container, wherein the droplets are used to generate EUV radiation when irradiated by a laser when the device is in droplet-on mode, and wherein the droplets are in a droplet outside mode not used to generate EUV radiation when not irradiated by a laser; and a variable flow regulator selectively disposed in the flow path and adapted to be based at least in part on the device A characteristic that regulates the flow of the gas into the vessel in either the droplet on mode or the droplet off mode.

According to another aspect of an embodiment, a flow regulator for regulating a characteristic of the flow of a gas from a gas source into a container in a device for generating EUV radiation is disclosed, the flow regulator comprising : an inlet adapted to be in fluid communication with the gas source; an outlet adapted to be in fluid communication with an inlet to the vessel; and a flow restrictor based at least in part on an operating mode of the device A flow of the gas through the regulator along a flow path from the inlet to the outlet can be selectively blocked. The flow restrictor may include a flow obstruction and a motor mechanically coupled to the flow obstruction and adapted to move the flow obstruction fully outside, fully within, or partially within the flow path in one of the flow paths. The flow restrictor may include: a valve adapted to be in fluid communication with the gas source; and a manifold including a plurality of fluid conduits respectively connecting the valve to the inlet, each of the plurality of fluid conduits One has a respective flow restrictor that limits a flow rate through the respective conduit to a respective value, the valve configured to permit the gas to flow through one of the plurality of flow conduits one.

According to another aspect of an embodiment, a method of controlling the operation of an apparatus for generating EUV radiation by laser irradiation of droplets of a target material in a container is disclosed, the method comprising: in the operating the device in an out-of-droplet mode that is not used to generate EUV radiation; consistent with the operating steps, regulating at least one of entering and leaving the vessel based at least in part on the device operating in the out-droplet mode a characteristic of a flow of a gas of the same; switching to operating the device in a droplet-up mode used by the droplets to generate EUV radiation; and consistent with the switching step, based at least in part on the device operating in the droplet A characteristic of a flow of a gas into and out of at least one of the container is adjusted by operating in the drop-on mode. The method may be carried out under the control of a controller operating according to a preview process. The characteristic can be any one or a combination of flow rate, flow velocity, flow profile, and flow composition. The flow composition may be a flow composition that does not contain a reactive gas during the droplet up mode and contains a reactive gas during the droplet off mode. The reactive gas may contain oxygen. The device may include a flow obstruction and a motor for moving the flow obstruction, and the device that regulates a characteristic of a flow of a gas into the vessel based at least in part on the device operating in the out-of-droplet mode Steps include moving the flow obstruction at least partially into a flow path of the gas entering the vessel. The device may comprise: a valve adapted to be in fluid communication with a source of the gas; and a manifold comprising a plurality of fluid conduits respectively connecting the valve to the vessel, each of the plurality of fluid conduits One has a respective flow restrictor that limits a flow rate through the respective conduit to respective values, the valve configured to permit the gas to flow through one of the plurality of flow conduits or, and the step of modulating a characteristic of a flow of a gas into the vessel based at least in part on the device operating in the out-of-droplet mode includes operating the valve to select a conduit of the one of the plurality of conduits is placed in fluid communication with the source of the gas.

Further embodiments, features and advantages of the present invention, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings.

Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to enhance a thorough understanding of one or more embodiments. It may be apparent, however, in some or all instances that any of the embodiments described below may be practiced without employing the specific design details described below. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate the description of one or more embodiments.

Before describing such embodiments in greater detail, however, it is instructive to present an example environment in which embodiments of the invention may be implemented. In the following embodiments and within the scope of the patent application, the terms "upward," "downward," "top," "bottom," "vertical," "horizontal," and similar terms may be used. Unless otherwise specified, these terms are only intended to show relative orientation and are not intended to show any orientation with respect to gravity.

Referring initially to FIG. 1, there is shown a schematic diagram of an exemplary EUV radiation source, such as a laser-generated plasma EUV radiation source 10, in accordance with one aspect of an embodiment of the present invention. As shown, EUV radiation source 10 may include a pulsed or continuous laser source 22, which may be, for example, a pulsed radiation beam 12 that produces a beam of radiation 12 at 10.6 μm or 1 μm focused to the main focus PF Gas discharge _CO2 laser source. The pulsed gas discharge _CO2 laser source can have DC or RF excitation operating at high power and high pulse repetition rate.

EUV radiation source 10 also includes a target delivery system 24 for delivering the target material in the form of droplets or a continuous stream of liquid. In this example, the target material is a liquid, but it could also be a solid or a gas. The target material may consist of tin or tin compounds, but other materials may be used. In the depicted system, target material delivery system 24 introduces droplets 14 of target material into the interior of vacuum chamber 26 up to the irradiation zone at the PF of collector 30, where the target material may be irradiated to generate plasma. The vacuum chamber 26 may be provided with a liner. In some cases, an electrical charge is placed on the target material to permit turning the target material toward or away from the irradiation area. It should be noted that, as used herein, an irradiation area is an area where irradiation of the target material can or is intended to occur, and is an irradiation area even when irradiation does not actually occur. The EUV light source may also include a beam steering system 32 .

In the system shown, the components are configured such that the droplets 14 travel substantially horizontally. The direction from the laser source 22 toward the irradiation area (ie, the nominal propagation direction of the beam 12 ) can be considered as the Z-axis. The path taken by the droplets 14 from the target material delivery system 24 to the irradiation area can be considered as the X-axis. The view of Figure 1 is thus perpendicular to the XZ plane. The orientation of the EUV radiation source 10 is preferably rotated relative to gravity as shown, with arrow G showing a preferred orientation downward relative to gravity. This orientation applies to EUV sources, but not necessarily to optical downstream components, such as scanners and the like. Also, although a system is depicted in which the droplets 14 travel substantially horizontally, those of ordinary skill in the art will appreciate that other configurations may be used in which the droplets travel vertically or at 90 degrees relative to gravity (horizontal ) and 0 degrees (vertical) at an angle (including 90 and 0 degrees).

EUV radiation source 10 may also include EUV light source controller system 60 , laser ignition control system 65 , and beam steering system 32 . EUV radiation source 10 may also include a detector such as a target position detection system, which may include one or more droplet imagers 70 that generate droplets indicative of the target For example, an output relative to the absolute or relative position of the irradiated region and this output is provided to the target position detection feedback system 62 .

As shown in FIG. 1 , the target material delivery system 24 may include a target delivery control system 90 . The target delivery control system 90 may operate in response to a signal (eg, the target error described above, or some amount derived from the target error provided by the system controller 60) to adjust the path of the target droplet 14 through the irradiation area . This can be accomplished, for example, by repositioning the point at which the target delivery mechanism 92 releases the target droplet 14 . For example, the droplet release point can be repositioned by tilting the target delivery mechanism 92 or by translating the target delivery mechanism 92 laterally. The target delivery mechanism 92 extends into the chamber 26 and is preferably externally supplied with target material and a gas source to place the target material in the target delivery mechanism 92 under pressure.

Continuing with FIG. 1, radiation source 10 may also include one or more optical elements. In the following discussion, collector 30 is used as an example of such an optical element, but the discussion applies to other optical elements as well. Collector 30 may be a normal incidence reflector, eg implemented with an additional thin barrier layer (eg _B4C , ZrC, _Si3N4 or C ₎ deposited at each interface to effectively block thermally induced interlayer diffusion The MLM. Other substrate materials such as aluminum (Al) or silicon (Si) may also be used. The collector 30 may be in the form of a prolate spheroid with a central aperture to allow the laser radiation 12 to pass through and reach the irradiation area. The collector 30 may, for example, be in the shape of an ellipsoid, which as mentioned has a primary focus PF at the irradiation area and an intermediate focus IF on the optical axis OA of the collector 30, where EUV radiation may be output from the EUV radiation source 10 It is input, for example, to an IC lithography scanner 50, which uses the radiation to process a silicon wafer workpiece 52, for example, using a reticle or mask 54 in a known manner. The silicon wafer workpiece 52 is then additionally processed in a known manner to obtain integrated circuit devices.

The solid double arrows in Figure 2 show the direction of debris propagation. Contoured arrows show favorable configurations of _H2 flow. Outlet 42 acts as an exhaust port through which H ₂ exits chamber 26 . Arrow G indicates the direction of gravity in one embodiment.

Figure 3A is a schematic representation of a configuration for generating such a stream. As shown in FIG. 3A , the hydrogen gas flows into the chamber 26 through a conical inlet 44 (conical flow) positioned in the central aperture of the collector 30 and from the top of the chamber 26 from a location near the intermediate focus IF. The position of the principal focus PF of the collector 30 on its optical axis OA is also shown. Hydrogen flows away from collector 30 and through outlet 42 . Hydrogen entering from the top of chamber 26 also flows through outlet 42 . A fan module 46 for forcing gas into the chamber 26 is also shown in FIG. 3A. The fan module 46 , which may be a fan filter unit, is connected to the gas source 48 through the conduit 56 . Additionally, a shower head including a plurality of nozzles that introduce gas into the vessel may be positioned along at least a portion of the inner vessel wall. See International Application Publication No. WO 2018/127565, filed on January 5, 2018 and published on July 12, 2018, entitled "Guiding Device and Associated System", the entire specification of which is hereby incorporated by reference manner is incorporated herein.

As can be appreciated, the EUV source as described in the previous row relies on a flow of hydrogen gas to protect the collector, metrology optics and interior surfaces of the vessel from target material debris. Because such systems are currently configured, the hydrogen flow recipe (including, for example, specific selection of flow rates for collector cone flow, collector peripheral flow, shower jets on the liner, etc.) does not change during operation of the recipe It is static in the sense.

Due to this situation, the flow recipe may not be optimized for changes in EUV power or exposure pattern. This can result in an undesirably small process window. For example, high collector cone flow rates can be beneficial for collector protection to better overcome momentum transfer from ions exiting the plasma, and thus also improve droplet/plasma stability. A disadvantage of higher collector conical flow rates is that the entrained tin overtakes the outgassing, resulting in high deposition rates inside the vessel, which affects vessel and collector life.

Static flow formulations can become particularly problematic for anisotropic ion distributions. Under these conditions, the flow recipe needs to rebalance the total flow to increase the flow to the collector cone, thereby protecting the collector and vessel walls from excessive tin deposition. The desired conical flow can be high so that in the absence of plasma (ie, outside the droplet), the flow overtakes the exhaust (asymmetric exhaust in this example) and recirculates back to the vessel , thereby making the droplet unstable. This is an example of a situation where there may not be a single static process window while maintaining tin deposition below acceptable limits while maintaining satisfactory droplet stability.

Thus, according to one aspect of the embodiment, the process window for the EUV source is optimized by varying the hydrogen flow rate based on the particular use case. For example, it is contemplated that for some future applications, the angular ion distribution is rather anisotropic for some plasmonic formulations. These plasmonic formulations can be used at current and higher EUV power levels. For some ion distributions, there is no process window that meets both the droplet on and off droplet requirements. According to one aspect of an embodiment, the flow rate can be varied to optimize the process window. More specifically, the collector cone flow can be varied. This can be achieved by using a fast actuation throttle element to control the rate of the conical flow.

Increased ion momentum towards the collector may require rebalancing of the flow to meet collector and vessel protection requirements. In particular, there may be a need for increased conical flow. However, the conical flow cannot be increased without limit, since excess conical flow can lead to recirculation flow and unstable droplets when plasma is not present, eg, before or after EUV exposure.

Therefore, based on the total hydrogen flow available, it is not possible to simultaneously satisfy the droplet-outside-droplet stability requirements with a single flow setting while also meeting the tin deposition limits on the vessel and collector. Essentially, the center of the process window is shifted based on the presence or absence of plasma. According to one aspect of the embodiment, the problem associated with the shifting process window is addressed by setting the collector cone flow to be dynamically adjusted lower when outside the droplet and higher when on the droplet question. The time frame for any such adjustment in cone flow needs to be approximately the flow resequencing time scale in the vessel. Based on droplet pushback measurements, the time scale for flow resequencing is approximately 20 ms. Therefore, actuators for flow governors must also be able to operate with at least similar response times/bandwidths.

Referring now to FIG. 3B, according to one aspect of the embodiment, the configuration for controlling the flow rate and flow characteristics of the composition, such as the gas entering and/or exiting the chamber 26, may include a fan module 46 that The module includes a variable flow regulator such as will be described below in connection with FIGS. 4A , 4B, 5 and 6 . The variable flow regulator in fan module 46 operates under the control of controller 47, which may be a dedicated hardware controller or may be a control system distributed across several components and consisting of both hardware and software . The controller 47 also controls a controllable mixing valve 64 which is in controllable fluid communication with the first gas source 48 and the second gas source 49 . The controllable mixing valve 64 may be used to control the composition of the gas flowing into the chamber 26 through the fan module 46 . The composition of the gas flowing into chamber 26 may vary depending on the mode of operation of the system. For example, there may be one type of gas, which may be a single species of gas from the first gas source 48 flowing into the chamber 26 or a mixture of two or more gases during operation on the droplet, and A second type of gas is introduced into chamber 26 from second gas source 49 during out-of-droplet operation. For example, reactive gases, such as oxygen, which can produce undesired side effects during plasma generation, can be introduced to shut down droplet operation for purposes such as collector surface repair.

Also shown in FIG. 3B is an exhaust flow modifier 66 positioned in the outlet flow path from one of the outlets 42 . The exhaust flow modifier 66 is shown disposed in one of the outlet flow paths, it will be apparent to those of ordinary skill in the art that the exhaust flow modifier 66 may also be placed in additional outflow paths. Exhaust flow regulator 66 operates under the control of controller 47 to vary the rate at which gas exits chamber 26 through outlet port 42 . The variable flow of the structure can be used, for example, to drag the vessel pressure. For example, vessel pressure can undesirably vary during the droplet on-droplet transition. Control of the exhaust flow regulator 66 can be used to compensate for this pressure variation and thus contribute to process stability.

Also, in general, the hydrogen flow is configured for use cases where the EUV source operates at full power. However, there may be applications where operating the source at less than full power would be beneficial. At low dose targets, the gas flow is contaminated with target materials such as tin, but the momentum transfer from the ions is not sufficient to decelerate the cone sufficiently so that the gas in the cone discharges into the exhaust. Therefore, tin contamination occurs in the container above the exhaust gas. This can be mitigated by reducing the collector cone flow. The reduced collector cone flow is acceptable for collector protection because the power load from the ions is greatly reduced. When the scanner requests a low dose target, then the flow setting of the cone flow can be reduced in an automated fashion.

In some cases, there may also be potential benefits to varying the flow during droplet generator startup and shutdown. It may also be useful for the airflow across the face of the collector ("umbrella flow") to vary over time to prevent stagnation zones from forming. As mentioned, in addition to controlling the volume and sweep of the flow itself, it may also be advantageous to use mechanical means to modify the shape of the flow.

As mentioned, during operation on the droplet (ie, the operation when the plasma is generated), the plasma essentially behaves as a rock in the water flow in a similar manner to the physical elements that impede the flow, thereby diverting the flow and Reduce velocity, especially at the center of the plume. To control this effect, a blockage in the form of a mechanical flow block, for example, can be moved into the center of the conical flow between the collector mirror and the bottom of the container, in position in the fan filter unit (FFU). This mechanical block can be constructed so that it is not so large that it cannot be moved rapidly using known techniques (such as the type of linear motors used to move hard disk read/write heads), and cannot operate at frequencies up to 50 to 80 kHz. Actuation at frequency. Such typical voice coil linear motors with magnetic heads are rated for full range actuation times of 15 to 20 milliseconds. Enterprise work motors are even faster.

The material selection and construction techniques of the block and its supports can be chosen to be extremely light. The minimum amount of embossing of the support arm and block can be such that it is stiff enough that it will not experience excessive deflection when placed in a conical flow.

The obstruction can have any of a variety of shapes. For example, it can be solid to present a solid face to the flow, and aerodynamically shaped to modify the redirection of the flow to achieve the desired result. Additional shapes of flow blocks can be used, such as thin hollow shaped blocks, blockages with hollow centers, and shapes that divert the flow or portions of the flow to specific locations. As another option, a membrane or knife edge can be used to restrict flow in or near the container. As another option, the flow rate can be maintained constant, but the gas velocity can be modified by changing the flow pattern (eg, from a narrow jet to a wider flow).

FIG. 4A shows a configuration in which a flow blocker 100 is placed in the flow path feeding gas to the collector cone 44 . The obstruction 100 may be placed in the fan module 46 . The obstruction 100 is attached by an arm 110, which in turn is attached to a motor 120 that can move the obstruction 100 into and out of the flow path. It will be appreciated that the blockage can be caused to move completely out of the flow path, partially into the flow path, or completely into the flow path. As used herein and elsewhere, the term "motor" is used to mean any device that provides, imparts, or produces motion. In the example shown, motor 120 is a voice coil linear motor. In addition to the mechanisms described above for moving the occlusion 100, other mechanisms for moving the occlusion 100 in and out of the conical flow can also be used, such as solenoids, brushes and brushless motors, pneumatic actuators actuators, piezoelectric elements and the like. Furthermore, all such mechanisms can be tuned to have dynamic properties through the use of blocks, springs, dampers, and proportional, integral, and derivative ("PID") parameters, which enhance the frequency-specific performance required for a given application. Response time and overrun.

Figure 4B shows a configuration similar to that in Figure 4A, except that the obstruction 100 has an aerodynamic shape. Figure 5 shows a configuration similar to that of Figure 4A, except that the obstruction 100 has a tubular shape and is oriented so as to be able to direct flow to a specific location. The obstruction 100 may also have other shapes depending on the particular use case. Such an embodiment may have additional benefits in that it may be used to reduce or eliminate the overshoot in a more efficient manner rather than just turning the flow upwards. Figure 6 shows a configuration in which mass flow controller 130 is used as a variable flow regulator. A sufficiently fast flow controller can be implemented using any of several possible configurations. As one example, a fast mass flow controller (MFC) may be placed closer to the source than it would be in conventional configurations. MFCs are commercially available with response times as low as 25 ms.

In another configuration, flow control is by switching between two or more preset orifices or flow restrictors to modulate between two or more of the chamber flow rates A quick turnaround is achieved. This orifice configuration can be placed in close proximity to the container to ensure rapid changes in flow delivered to the EUV volume. FIG. 7 shows a configuration in which flow to chamber 26 is regulated by switching valve 150 selectively connected to one of flow restrictors 170 , 180 and 190 . More specifically, gas from mass flow controller 160 flows in conduit 56 to switch or valve 150, which selectively connects conduit 56 to one of the flow controllers 170, 180, and 190 in the manifold one. Valve 150 may operate under the control of a signal generated elsewhere in the system (eg, in a scanner). The flow restrictors 170, 180, 190 may advantageously have different flow impedances. The flow rate along conduit 200 into chamber 26 will therefore depend on which of the flow restrictors valve 150 connects to conduit 56 . In this way, the flow rate can be changed rapidly. In an alternative configuration, the switching valve 150 may be connected to separate gas sources, each of which is at a different pressure. Valve 150 will selectively connect one of these sources to chamber 26 through conduit 200 .

Thus, according to one aspect of the embodiment, the use of time-varying hydrogen flow rates can be used to optimize process windows for tin management performance, droplet stability, and plasma stability based on the specific use case of power and/or exposure pattern change. A time-varying hydrogen flow was used within the burst to meet both droplet on- and off-droplet process window requirements for tin management performance, droplet stability, and plasma stability. A mechanical flow block positioned inside the central conical flow can be used to modify the flow for time outside the droplet to limit or eliminate the difference between the _H2 flow on the droplet inside the chamber and outside the droplet. The flow block can also be used to physically redirect a portion of the central cone flow to enhance the tin mitigation effect of the liner flow by modifying the direction and location of the additional flow inside the module that produces the liner flow. Mechanical blocks can be used to modify the flow emanating from the central cone to reduce or eliminate droplet instability between on-droplet and off-droplet conditions. Mechanical flow blocks can also be used to reduce or eliminate the amount of tin driven into the chamber by the flow of target material outside the droplet.

8 shows a process according to an aspect of an embodiment in which dynamic flow control may be used in the presence of anisotropic ions. The process will start with an initial state S10 in which the source is operating outside the droplet, ie, EUV plasma is not being produced. In step S20, the conical flow can be set to a value such as 100 slm, which maintains the stability of the droplets. In step S30, EUV exposure is initiated, ie the source begins to operate in droplet-on mode. In step S40, which may begin at the same time as step S30 or even before step S30, if the system is using feedforward control, the cone flow is set not to be optimized for droplet stability, but instead to A value that minimizes the build-up of tin chips, such as 120 slm. This operation continues until the EUV exposure is stopped in step S50. Next, in step S60, which may begin at the same time as step S50 or even before the stop decision is made in step S50, if the system is using feedforward control, the conical flow is set to optimize for droplet stability instead of The value that minimizes the build-up of tin chips.

9 is a flowchart showing a process for changing the gas composition depending on the operating mode of the system. It should be understood that the process of FIG. 9 may be used alone or in conjunction with the process described in connection with FIG. 8 . In step S10, start the system by operating outside the droplet. During out-of-droplet operation, in step S70, the flow composition is set to include a reactive gas such as oxygen. This may be the type of gas that will interfere with the plasma generation during operation on the droplet. In step S30, it is determined whether the system switches to the droplet operation. If the system switches to operating on droplets, in step S80, the flow composition is established as a flow composition that does not include reactive gas. In step S50, it is determined whether the system switches back to the out-of-droplet operation. If not, the gas composition that does not include active gas is maintained in step S60. Otherwise, the system reverts to the droplet out-of-drop operation in step S10.

The above description has mainly been in terms of controlling conical flow, but it will be apparent that the principles apply to controlling the flow of gas into the chamber through other inlets.

Embodiments thus have the potential to provide several benefits, including reducing the amount of tin deposited on the vessel walls, reducing the amount of tin deposited on the collector, increasing the size of the process window for plasma control, and increasing the amount of tin used for droplets The size of the process window for stability.

The above description includes examples of one or more embodiments. Of course, it is not possible to describe every conceivable combination of components or methods for purposes of describing the foregoing embodiments, but those of ordinary skill in the art will recognize that many other combinations and permutations of the various embodiments are possible. Accordingly, the described embodiments are intended to encompass all such changes, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, insofar as the term "comprising" is used in an embodiment or in the scope of a claim, this term is intended to be inclusive in a manner similar to how the term "comprising" is interpreted when "comprising" is used as a transition word in a technical solution sexual. Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and/or embodiment may be utilized in conjunction with all or a portion of any other aspect and/or embodiment, unless otherwise stated.

Other aspects of the invention are set forth in the numbered clauses below. 1. A device for generating EUV radiation by laser irradiation of droplets of a target material, the device comprising: a container; An inlet structure defining at least one inlet path adapted and configured to connect a source of a gas to an interior of the vessel to add the gas in a flow along the inlet path to the container; an outlet structure defining at least one outlet path adapted and configured to connect to an interior of the container to permit gas in the container to flow out of the container along the outlet path; a variable flow regulator selectively disposed in one of the inlet path and the outlet path and adapted to regulate the gas entering or leaving the vessel based at least in part on a mode in which the device is operating a characteristic of the flow; and a controller configured to control the operation of the flow controller. 2. The apparatus of clause 1, wherein the controller is adapted to operate using a look-ahead control process. 3. The device of clause 1, further comprising a second variable flow regulator selectively disposed in the other of the inlet path and the outlet path and adapted to adjust a characteristic of the flow of the gas into or out of the vessel based at least in part on a mode in which the device is operating. 4. The device of clause 1, wherein the device has: a droplet-on mode of operation, wherein the droplet produces EUV radiation when irradiated by a laser when the device is in a mode; and a droplet-off-operating mode mode in which the droplets are not used to generate EUV radiation when not irradiated by a laser in another mode. 5. The device of clause 1, wherein the variable flow regulator is selectively disposed in the inlet path and adapted to regulate the amount of the gas entering the vessel based at least in part on the mode in which the device is operating A characteristic of flow. 6. The device of clause 5, wherein the characteristic is a flow rate. 7. The device of clause 5, wherein the characteristic is a flow velocity. 8. The device of clause 5, wherein the characteristic is a flow profile. 9. The device of clause 5, wherein the characteristic is a first-class composition. 10. The device of clause 9, further comprising a mixing valve, a first gas source in fluid communication with the mixing valve, and a second gas source in fluid communication with the mixing valve, the mixing valve configured to communicate with the mixing valve An inlet structure is in fluid communication and operates under the control of the controller to provide one of the first gas, the second gas and a mixture of the first gas and the second gas to the inlet structure. 11. The device of clause 9, wherein the flow composition does not contain a reactive gas during the droplet on mode and contains a reactive gas during the droplet off mode. 12. The device of clause 11, wherein the reactive gas comprises oxygen. 13. The device of clause 1, wherein the inlet structure comprises a collector cone. 14. The device of clause 1, wherein the variable flow regulator comprises a flow obstruction and a motor mechanically coupled to the flow obstruction and adapted to move the flow obstruction at least partially to the flow obstruction in the flow path. 15. The device of clause 14, wherein the motor comprises a linear motor. 16. The device of clause 14, wherein the motor comprises a solenoid. 17. The device of clause 14, wherein the flow obstruction presents a solid cross-section to the flow when placed in the flow path. 18. The device of clause 14, wherein the flow obstruction presents to the flow a cross-section having at least one aperture when placed in the flow path. 19. The device of clause 14, wherein the flow obstruction has an open tubular shape and is oriented such that the flow obstruction redirects a portion of the gas when placed in the flow path. 20. The device of clause 14, wherein the flow obstruction has an aerodynamic shape. 21. The device of clause 1, wherein the variable flow regulator comprises a mass flow controller. 22. The device of clause 1, wherein the variable flow regulator comprises a valve adapted to be in fluid communication with the gas source, and a manifold comprising a plurality of fluid conduits respectively connecting the valve to the inlet, each of the plurality of fluid conduits having a respective flow restrictor through which the respective flow restrictor will pass a flow rate limited to a respective value, The valve is configured to permit the gas to flow through one of the plurality of flow conduits. 23. A device for generating EUV radiation by laser irradiation of droplets of a target material, the device comprising: a vessel having at least one inlet adapted to connect to a source of a gas and add the gas to the vessel in a flow along a flow path; A droplet generator configured to introduce the droplets into the container to an irradiation site within the container, wherein the droplets are generated by a when irradiated by a laser to generate EUV radiation, and wherein the droplets are not used to generate EUV radiation when not irradiated by a laser when the device is in a droplet out-mode; and a variable flow regulator selectively disposed in the flow path and adapted to regulate the gas entering the vessel based at least in part on whether the device is in the droplet on mode or the droplet off mode a characteristic of the flow. 24. A flow regulator for regulating a characteristic of the flow of a gas from a gas source into a container in a device for generating EUV radiation, the flow regulator comprising: an inlet adapted to be in fluid communication with the gas source; an outlet adapted to be in fluid communication with an inlet to the container; and A flow restrictor that selectively blocks a flow of the gas through the regulator along a flow path from the inlet to the outlet based at least in part on an operating mode of the device. 25. The flow regulator of clause 24, wherein the flow restrictor comprises a flow obstruction and a motor mechanically coupled to the flow obstruction and adapted to move the flow obstruction fully within the flow One of the locations outside the path, entirely within the flow path, or partially within the flow path. 26. The flow regulator of clause 24, wherein the flow restrictor comprises a valve adapted to be in fluid communication with the gas source, and a manifold comprising a plurality of fluid conduits respectively connecting the valve to the inlet, each of the plurality of fluid conduits having a respective flow restrictor through which the respective flow restrictor will pass A flow rate is limited to the respective value, The valve is configured to permit the gas to flow through one of the plurality of flow conduits. 27. A method of controlling the operation of an apparatus for generating EUV radiation by laser irradiation of droplets of a target material in a container, the method comprising: operating the device in an out-droplet mode in which the droplets are not used to generate EUV radiation; Consistent with the operating steps, adjusting a characteristic of a flow of a gas into and out of at least one of the container based at least in part on the device operating in the out-of-droplet mode; switching to operating the device in a droplet-on mode in which the droplets are used to generate EUV radiation; and Consistent with the switching step, a characteristic of a flow of a gas into and out of at least one of the container is adjusted based at least in part on the device operating in the droplet-up mode. 28. The method of clause 27, wherein the method is performed under the control of a controller operating according to a preview process. 29. The method of clause 27, wherein the characteristic is a flow rate. 30. The method of clause 27, wherein the characteristic is a flow velocity. 31. The method of clause 27, wherein the characteristic is a flow profile. 32. The method of clause 27, wherein the property is a first-class composition. 33. The method of clause 32, wherein the flow composition does not contain a reactive gas during the droplet on mode and contains a reactive gas during the droplet off mode. 34. The method of clause 33, wherein the reactive gas comprises oxygen. 35. The method of clause 27, wherein the device comprises a flow blocker and a motor for moving the flow blocker, and wherein the flow into the container is adjusted based, at least in part, on the device operating in the extra-droplet mode. The step of a characteristic of a flow of a gas includes moving the flow obstruction at least partially into a flow path of the gas entering the vessel. 36. The method of clause 27, wherein the device comprises: a valve adapted to be in fluid communication with a source of the gas; and a manifold comprising a plurality of fluid conduits respectively connecting the valve to the vessel , each of the plurality of fluid conduits has a respective flow restrictor that limits a flow rate through the respective conduit to a respective value, the valve configured to permit the gas flow through one of the plurality of flow conduits, and wherein the step of adjusting a characteristic of a flow of a gas into the vessel based at least in part on the device operating in the out-of-droplet mode includes operating the valve to put A selected conduit of the plurality of conduits is placed in fluid communication with the source of the gas.

Other embodiments are within the scope of the claims.

10: Laser-generated plasma extreme ultraviolet (EUV) radiation source 12: Beam 14: Droplets 22: Pulsed or continuous laser source 24: Targeted Delivery Systems 26: Vacuum Chamber 30: Collector 32: Beam steering system 42: Exit/Exit port 44: Conical Inlet/Collector Cone 46: Fan module 47: Controller 48: First gas source 49: Second gas source 50: IC Lithography Scanner 52: Silicon Wafer Workpiece 54: Multiplier or mask 56: Pipes 60: Extreme Ultraviolet (EUV) Light Source Controller System 62: Target position detection feedback system 64: Controllable mixing valve 65: Laser ignition control system 66: Exhaust flow regulator 70: Droplet Imager 90: Target Delivery Control System 92: Target Delivery Agency 100: Obstruction 110: Arm 120: Motor 130: Mass flow controller 150: switch valve 160: Mass Flow Controller 170: Flow Limiter 180: Flow Limiter 190: Flow Limiter G: Arrow/Gravity Direction IF: Intermediate focus OA: Optical axis PF: Primary focus S10: Steps S20: Steps S30: Step S40: Steps S50: Steps S60: Steps S70: Steps S80: Steps S90: Steps X: axis Z: axis

1 is a schematic, not-to-scale view of a general broad concept of a laser-generated plasma EUV radiation source system according to an aspect of an embodiment.

2 is a not-to-scale diagram showing a possible configuration of a vessel and exhaust system for use in a laser-generated plasma EUV radiation source system.

3A is a schematic, not-to-scale, cross-sectional schematic view of a possible configuration of a system for introducing gas into a vessel, according to an aspect of an embodiment.

3B is a schematic, not-to-scale, cross-sectional schematic diagram of a possible configuration of a system for controlling the flow of gas into and/or out of a vessel, according to an aspect of an embodiment.

4A is a schematic, not-to-scale, cross-sectional view of a possible configuration of a container and gas inlet according to an aspect of an embodiment.

4B is a schematic, not-to-scale, cross-sectional view of a possible configuration of a container and gas inlet according to an aspect of an embodiment.

5 is a schematic, not-to-scale, cross-sectional schematic view of a possible configuration of a container and gas inlet according to an aspect of an embodiment.

6 is a schematic, not-to-scale, cross-sectional schematic view of a possible configuration of a container and gas inlet according to an aspect of an embodiment.

7 is a schematic, not-to-scale, cross-sectional schematic view of a possible configuration of a system for introducing gas into a container, according to an aspect of an embodiment.

8 is a flow diagram of a process for introducing gas into a vessel, according to an aspect of an embodiment.

9 is a flow diagram of a process for introducing gas into a vessel according to another aspect of an embodiment.

Additional features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein.

26: Vacuum Chamber

30: Collector

42: Exit/Exit port

44: Conical Inlet/Collector Cone

46: Fan module

47: Controller

48: First gas source

49: Second gas source

56: Pipes

64: Controllable mixing valve

66: Exhaust flow regulator

IF: Intermediate focus

OA: Optical axis

PF: Primary focus

Claims (36)

A device for generating EUV radiation by laser irradiation of droplets of a target material, the device comprising: a container; An inlet structure defining at least one inlet path adapted and configured to connect a source of a gas to an interior of the vessel to add the gas in a flow along the inlet path to the container; an outlet structure defining at least one outlet path adapted and configured to connect to an interior of the container to permit gas in the container to flow out of the container along the outlet path; a variable flow regulator selectively disposed in one of the inlet path and the outlet path and adapted to regulate the gas entering or leaving the vessel based at least in part on a mode in which the device is operating a characteristic of the flow; and a controller configured to control the operation of the flow controller. The apparatus of claim 1, wherein the controller is adapted to operate using a look-ahead control process. The apparatus of claim 1, further comprising a second variable flow regulator selectively disposed in the other of the inlet path and the outlet path and adapted to at least A characteristic of the flow of the gas entering or leaving the vessel is adjusted based in part on a mode in which the device is operating. The device of claim 1, wherein the device has: a droplet on mode of operation, wherein the droplet generates EUV radiation when irradiated by a laser when the device is in a mode; and a droplet off mode of operation, Wherein the droplets are not used to generate EUV radiation in another mode when not irradiated by a laser. The device of claim 1, wherein the variable flow regulator is selectively disposed in the inlet path and adapted to regulate the flow of the gas into the vessel based at least in part on the mode in which the device is operating a feature. The apparatus of claim 5, wherein the characteristic is a flow rate. The apparatus of claim 5, wherein the characteristic is a flow velocity. The device of claim 5, wherein the characteristic is a flow profile. The apparatus of claim 5, wherein the characteristic is a first-class composition. The apparatus of claim 9, further comprising a mixing valve, a first gas source in fluid communication with the mixing valve, and a second gas source in fluid communication with the mixing valve, the mixing valve configured to communicate with the inlet structure in fluid communication and operating under the control of the controller to provide one of the first gas, the second gas and a mixture of the first gas and the second gas to the inlet structure. 9. The device of claim 9, wherein the flow composition does not contain a reactive gas during the droplet up mode and contains a reactive gas during the droplet off mode. The apparatus of claim 11, wherein the reactive gas comprises oxygen. The apparatus of claim 1, wherein the inlet structure includes a collector cone. The device of claim 1, wherein the variable flow regulator comprises a flow obstruction and a motor mechanically coupled to the flow obstruction and adapted to move the flow obstruction at least partially to the flow path middle. The apparatus of claim 14, wherein the motor comprises a linear motor. The apparatus of claim 14, wherein the motor includes a solenoid. The device of claim 14, wherein the flow obstruction presents a solid cross-section to the flow when placed in the flow path. 14. The device of claim 14, wherein the flow obstruction presents a cross-section with at least one aperture to the flow when placed in the flow path. The device of claim 14, wherein the flow obstruction has an open tubular shape and is oriented such that the flow obstruction redirects a portion of the gas when placed in the flow path. The device of claim 14, wherein the flow obstruction has an aerodynamic shape. The apparatus of claim 1, wherein the variable flow regulator comprises a mass flow controller. The apparatus of claim 1, wherein the variable flow regulator comprises a valve adapted to be in fluid communication with the gas source, and a manifold comprising a plurality of fluid conduits respectively connecting the valve to the inlet, each of the plurality of fluid conduits having a respective flow restrictor through which the respective flow restrictor will pass a flow rate limited to a respective value, The valve is configured to permit the gas to flow through one of the plurality of flow conduits. A device for generating EUV radiation by laser irradiation of droplets of a target material, the device comprising: a vessel having at least one inlet adapted to connect to a source of a gas and add the gas to the vessel in a flow along a flow path; A droplet generator configured to introduce the droplets into the container to an irradiation site within the container, wherein the droplets are generated by a droplet while the device is in a droplet-on mode. when irradiated by a laser to generate EUV radiation, and wherein the droplets are not used to generate EUV radiation when not irradiated by a laser when the device is in a droplet out-mode; and a variable flow regulator selectively disposed in the flow path and adapted to regulate the gas entering the vessel based at least in part on whether the device is in the droplet on mode or the droplet off mode a characteristic of the flow. A flow regulator for regulating a characteristic of the flow of a gas from a gas source into a container in a device for generating EUV radiation, the flow regulator comprising: an inlet adapted to be in fluid communication with the gas source; an outlet adapted to be in fluid communication with an inlet to the container; and A flow restrictor that selectively blocks a flow of the gas through the regulator along a flow path from the inlet to the outlet based at least in part on an operating mode of the device. The flow regulator of claim 24, wherein the flow restrictor comprises a flow obstruction and a motor mechanically coupled to the flow obstruction and adapted to move the flow obstruction completely out of the flow path , either completely within the flow path or partially within the flow path. The flow regulator of claim 24, wherein the flow limiter comprises a valve adapted to be in fluid communication with the gas source, and a manifold comprising a plurality of fluid conduits respectively connecting the valve to the inlet, each of the plurality of fluid conduits having a respective flow restrictor through which the respective flow restrictor will pass one flow rate is limited to the respective value, The valve is configured to permit the gas to flow through one of the plurality of flow conduits. A method of controlling the operation of an apparatus for generating EUV radiation by laser irradiation of droplets of a target material in a container, the method comprising: operating the device in an out-droplet mode in which the droplets are not used to generate EUV radiation; Consistent with the operating steps, adjusting a characteristic of a flow of a gas into and out of at least one of the container based at least in part on the device operating in the out-of-droplet mode; switching to operating the device in a droplet-on mode in which the droplets are used to generate EUV radiation; and Consistent with the switching step, a characteristic of a flow of a gas into and out of at least one of the container is adjusted based at least in part on the device operating in the droplet-up mode. The method of claim 27, wherein the method is performed under the control of a controller operating in accordance with a preview process. The method of claim 27, wherein the characteristic is a flow rate. The method of claim 27, wherein the characteristic is a flow velocity. The method of claim 27, wherein the characteristic is a flow profile. The method of claim 27, wherein the property is a first-rate composition. The method of claim 32, wherein the flow composition does not contain a reactive gas during the droplet up mode and contains a reactive gas during the droplet off mode. The method of claim 33, wherein the reactive gas comprises oxygen. The method of claim 27, wherein the device comprises a flow obstruction and a motor for moving the flow obstruction, and wherein a gas entering the container is regulated based at least in part on the device operating in the out-of-droplet mode The step of a characteristic of a flow includes moving the flow obstruction at least partially into a flow path of the gas entering the vessel. The method of claim 27, wherein the device comprises: a valve adapted to be in fluid communication with a source of the gas; and a manifold comprising a plurality of fluid conduits respectively connecting the valve to the vessel, the Each of the plurality of fluid conduits has a respective flow restrictor that limits a flow rate through the respective conduit to a respective value, the valve configured to permit the gas to flow through the respective conduit one of a plurality of flow conduits, and wherein the step of adjusting a characteristic of a flow of a gas into the vessel based at least in part on the device operating in the out-of-droplet mode comprises operating the valve to the plurality of A selected one of the conduits is placed in fluid communication with the source of the gas.

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