EP4182587A1

EP4182587A1 - Apparatus for protecting fluid lines in an euv source

Info

Publication number: EP4182587A1
Application number: EP21736273.0A
Authority: EP
Inventors: Yang Shi
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2020-07-15
Filing date: 2021-06-21
Publication date: 2023-05-24
Also published as: WO2022012869A1; TW202218486A; CN115803551A

Abstract

A source material valve placed in a fluid feed line for a source material chamber such as a source material refill reservoir to prevent molten source material in the chamber from reaching and so contaminating and blocking the fluid feed lines upstream of the source material valve in the event of a pressure malfunction.

Description

APPARATUS FOR PROTECTING FLUID LINES IN AN EUV SOURCE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63/052,184 filed July 15, 2020 and titled APPARATUS FOR PROTECTING FLUID LINES IN AN EUV SOURCE, which is incorporated herein in its entirety by reference.

FIELD

[0002] This disclosure relates to protection of fluid lines used to pressurize source material chambers in a system for producing extreme ultraviolet radiation.

BACKGROUND

[0003] Extreme ultraviolet (“EUV”) radiation, e.g., electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13.5 nm, is used in photolithography to produce extremely small features on substrates such as silicon wafers. Here and elsewhere herein the term “light” is used even though it is understood that the radiation described using that term may not be in the visible part of the spectrum.

[0004] Methods for generating EUV light include converting a source material from a liquid state into a plasma state. The source material preferably includes at least one element, e.g., xenon, lithium, or tin, with one or more emission lines in the EUV range. In one such method, often termed laser produced plasma (“LPP”), the required plasma can be produced by using a laser beam to irradiate a source material having the required line-emitting element.

[0005] The source material may take one of many forms. It may be solid or a molten. If molten, it may be dispensed in several different ways such as in a continuous stream or as a stream of droplets. As an example, the source material in much of the discussion which follows is molten tin which is dispensed as a stream of droplets. It will be understood by one of ordinary skill in the art, however, that other forms of source materials, forms of source material, and delivery modes may be used.

[0006] Thus, one LPP technique involves generating a stream of source material droplets and irradiating at least some of the droplets with laser light pulses in a vacuum chamber. In more theoretical terms, LPP light sources generate EUV radiation by depositing laser energy into a source material having at least one EUV emitting element, creating a highly ionized plasma.

[0007] The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma in all directions. In one common arrangement, a near-normal-incidence mirror (often termed a “collector mirror” or simply a “collector”) is positioned to collect, direct, and, in some arrangements, focus the light to an intermediate location. The collected light is then relayed from the intermediate location to a set of scanner optics and ultimately to a substrate. [0008] The stream of droplets is generated by a source material dispenser such as a droplet generator. The portion of the droplet generator that releases the droplets, sometimes referred to as the nozzle or the nozzle assembly, is located within the vacuum chamber. The droplet generator nozzle assembly requires a constant supply of source material. This source material is typically provided from a supply of source material maintained in a source material chamber or a series of source material chambers. Source material must be transferred from the source material chambers to the nozzle assembly. This can be accomplished by pressurizing the molten source material and causing it to flow through conduits maintained above the melting point of the source material.

[0009] In the individual chambers, the molten source material is subjected to fluid under pressure to drive the source material through the heated conduits. The fluid is introduced into the reservoir through a fluid feed line. Because the molten source material is also subjected to pressure in other parts of the system, there is a possibility that the molten source material will fill the chamber and start to flow into the fluid feed line. This can cause problems such as the source material solidifying in and blocking the fluid line.

[0010] Also, in a multi-chamber system, there are different source material chambers serving different purposes. There may be a requirement for unidirectional flow between these chambers, for example, to prevent contaminated source material from flowing into and mixing with purified source material. [0011] It is in these contexts that subject matter disclosed and claimed herein may be advantageous.

SUMMARY

[0012] The following presents a simplified 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 contemplated embodiments and is not intended to identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its 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.

[0013] According to one aspect of an embodiment, there is disclosed a source material valve placed in a fluid feed line for a source material chamber such as a source material refill reservoir to prevent molten source material in the chamber from reaching and so contaminating and blocking the fluid feed lines upstream of the source material valve in the event of a pressure malfunction.

[0014] According to another aspect of an embodiment, there is disclosed an apparatus for controlling a flow of molten source material from a source material retaining chamber in an EUV source, the apparatus comprising a valve body defining a cavity, the valve body having a first valve body end adapted to be connected to a fluid feed line and a second valve body end adapted to be placed in fluid communication with the source material retaining chamber, the cavity having a seating wall at an end of the cavity closer to the first valve body end and an internal component arranged in the cavity and adapted to move from a first position in which the internal component permits a flow of fluid through the cavity to a second position in which an upper portion of the internal component seats against the seating wall to prevent a flow of molten source material through the cavity.

[0015] According to another aspect of an embodiment, there is disclosed an apparatus for controlling a flow of molten source material from a chamber in an EUV source, the apparatus comprising a valve body which when arranged vertically defines a vertical cavity, the valve body having an upper valve body end adapted to be connected to a fluid feed line and a lower valve body end adapted to be placed in fluid communication with the chamber, the cavity having a seating wall at an upper end of the cavity and an internal component arranged in the cavity and adapted to be moved vertically by molten source material entering the cavity through the lower valve body end from a first position in which the internal component permits a flow of fluid through the cavity to a second position in which an upper portion of the internal component is moved toward and into sealing contact against the seating wall to prevent a flow of molten source material through the cavity.

[0016] According to another aspect of an embodiment, there is disclosed an apparatus for controlling a flow of molten source material from a chamber in an EUV source, the apparatus comprising a valve body defining a cavity, the valve body having an first valve body end adapted to be connected to a fluid feed line and a second valve body end adapted to be placed in fluid communication with the chamber, the cavity having a seating wall at an end of the cavity closer to the valve body end; and an internal component arranged in the cavity, the apparatus being adapted to have a first state in which the internal component permits a flow of fluid through the cavity and a second state in which the cavity is partially filled with molten source material and in which the internal component prevents a flow of molten source material through the cavity due to the molten source material in the cavity.

[0017] According to another aspect of an embodiment, there is disclosed an apparatus for controlling a flow of molten source material between a first source material retaining chamber and a second source material retaining chamber in an EUV source, the apparatus comprising a valve body defining a cavity, the valve body having a first valve body end adapted to be placed in fluid communication with the first source material retaining chamber connected and a second valve body end adapted to be placed in fluid communication with the second source material retaining chamber, the cavity having a seating wall at an end of the cavity closer to the first valve body end, and an internal component arranged in the cavity and adapted to move from a first position in which the internal component permits a flow of source material through the cavity from the first source material retaining chamber to the second source material retaining chamber to a second position in which an upper portion of the internal component seats against the seating wall to prevent a flow of molten source material through the cavity from the second source material retaining chamber to the first source material retaining chamber.

[0018] According to additional aspects of embodiments, the internal component may comprise a generally cylindrical body and a plurality of wing members arranged around a lower periphery of the generally cylindrical body. The plurality of wing members may comprise at least three wing members arranged around a lower periphery of the generally cylindrical body in a rotationally symmetric pattern, for example, the plurality of wing members may comprise six wing members arranged around a lower periphery of the generally cylindrical body at 60 degree intervals. The outer face of the wing members may be rounded.

[0019] According to additional aspects of embodiments, the internal component may be solid and comprise a material having a density less than a density of the molten source material. If the molten source material is molten tin the internal component may comprise, for example, titanium or a titanium alloy. The internal component may have a spherical upper surface with a radius R and the seating wall may have a complementary spherical surface with a radius R. The internal component may have a tapered lower portion. The apparatus may further comprise a heater in thermal contact with the valve body and adapted to maintain a temperature of the valve body and the internal component above a melting point of the source material. The valve body may comprise molybdenum.

[0020] Further embodiments, features, and advantages of the subject matter of the present disclosure, as well as the structure and operation of the various embodiments are described in detail below with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows a schematic, not-to-scale view of an overall broad conception for a laser-produced plasma EUV light source system according to an aspect of an embodiment.

[0022] FIG. 2 is a plan view of a droplet dispenser such as could be used in an EUV light source such as that shown in FIG. 1.

[0023] FIG. 3 is a conceptual diagram of a source material supply system having multiple source material chambers.

[0024] FIG. 4A is a plan view of an internal component for a source material valve according to an aspect of an embodiment.

[0025] FIG. 4B is a bottom view of the internal component of FIG. 4A.

[0026] FIG. 5 is a plan view of an alternative configuration for an internal component for a source material valve according to an aspect of an embodiment.

[0027] FIG. 6 is a cross sectional view of a source material valve according to one aspect of an embodiment in a first state.

[0028] FIG. 7 is a cross sectional view of a source material valve of FIG. 6 in a second state.

[0029] FIG. 8 is a diagram of a multichamber system in which a source material valve establishes unidirectional flow according to an aspect of an embodiment.

[0030] Further 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 is noted that the 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 persons skilled in the relevant art based on the teachings contained herein.

DETAILED DESCRIPTION

[0031] 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 promote a thorough understanding of one or more embodiments. It may be evident in some or all instances, however, that any embodiment described below can be practiced without adopting the specific design details described below.

[0032] With initial reference to FIG. 1 there is shown a schematic view of an exemplary EUV light source, e.g., a laser produced plasma EUV light source 20 according to one aspect of an embodiment of the present invention. As shown, the EUV light source 20 may include a pulsed or continuous laser source 22, which may for example be a pulsed fluid discharge CO2 laser source producing radiation at 10.6 pm or other suitable wavelengths. The pulsed fluid discharge CO2 laser source may have DC or RF excitation operating at high power and high pulse repetition rate.

[0033] The EUV light source 20 also includes a source delivery system 24 for delivering source material in the form of liquid droplets or a continuous liquid stream. The source material may be made up of tin or a tin compound, although other materials could be used. The source delivery system 24 introduces the source material into the interior of a chamber 26 to an irradiation region 28 where the source material may be irradiated to produce plasma. In some cases, an electrical charge is placed on the source material to permit the source material to be steered toward or away from the irradiation region 28. It should be noted that as used herein an irradiation region is a region where source material irradiation may occur and is an irradiation region even at times when no irradiation is actually occurring. [0034] Continuing with FIG. 1, the light source 20 may also include one or more optical elements such as a collector 30. The collector 30 may be a normal incidence reflector, for example, implemented as a multilayer mirror or “MLM,” that is, a SiC substrate coated with a Mo/Si multilayer with additional thin barrier layers deposited at each interface to effectively block thermally-induced interlayer diffusion. Other substrate materials, such as A1 or Si, can also be used. The collector 30 may be in the form of a prolate ellipsoid, with an aperture to allow the laser light to pass through and reach the irradiation region 28. The collector 30 may be, e.g., in the shape of a ellipsoid that has a first focus at the irradiation region 28 and a second focus at a so-called intermediate point 40 (also called the intermediate focus) where the EUV light may be output from the EUV light source 20 and input to, e.g., an integrated circuit lithography tool 50 which uses the light, for example, to process a silicon wafer work piece 52 in a known manner. The silicon wafer work piece 52 is then additionally processed in a known manner to obtain an integrated circuit device. [0035] The EUV light source 20 may also include an EUV light source controller system 60, which may also include a laser firing control system 65, along with, e.g., a laser beam positioning system (not shown). The EUV light source 20 may also include a source position detection system which may include one or more droplet imagers 70 that generate an output indicative of the absolute or relative position of a source droplet, e.g., relative to the irradiation region 28, and provide this output to a source position detection feedback system 62. The source position detection feedback system 62 may use this output to compute a source position and trajectory, from which a source error can be computed. The source error may then be provided as an input to the light source controller 60. In response, the light source controller 60 can generate a control signal such as a laser position, direction, or timing correction signal and provide this control signal to a laser beam positioning controller (not shown). The laser beam positioning system can use the control signal to control the laser timing circuit and/or to control a laser beam position and shaping system (not shown), e.g., to change the location and or focal power of the laser beam focal spot within the chamber 26.

[0036] As shown in FIG. 1, the light source 20 may include a source delivery control system 90. The source delivery control system 90 is operable in response to a signal, for example, the source error described above, or some quantity derived from the source error provided by the system controller 60, to correct for errors in positions of the source droplets within the irradiation region 28. This may be accomplished, for example, by repositioning the point at which the source delivery mechanism 92 releases the source droplets. The source delivery mechanism 92 extends into the chamber 26 and is also externally supplied with source material and a fluid source to place the source material in the source delivery mechanism 92 under pressure.

[0037] FIG. 2 shows in greater detail a source delivery mechanism 92 for delivering source material into the chamber 26. For the generalized embodiment shown in FIG. 2, the source delivery mechanism 92 may include a reservoir 94 holding a molten source material such as tin. Heating elements (not shown) controllably maintain the source delivery mechanism 92 or selected sections thereof at a temperature above the melting temperature of the source material. The molten source material 95 may be placed under pressure by using an inert fluid such as argon introduced through a feed line 96. The pressure forces the source material 95 to pass through a supply conduit 98 which conveys the molten source material to valve 100 and nozzle 102. The supply conduit 98 is heated and may include one or more filters. Conventionally, as mentioned above, this supply conduit 98 may be made of a tantalum tungsten alloy and is connected to maintain a liquid tight seal with other components in the system with compression fittings which may be made of molybdenum. The supply conduit line 98 is preferably flexible to permit relative motion of the reservoir 94 and the nozzle 102.

[0038] The valve 100 may be a thermal valve. A thermoelectric device such as a Peltier device may be employed to establish the valve 100, freezing source material between the reservoir 94 and nozzle 102 to close the valve 100 and heating the solidified source material to open the valve 100. FIG. 2 also shows that the source delivery mechanism 92 is coupled to a movable member 104 such that motion of the movable member 104 changes the position of the point at which droplets are released from the nozzle 102. Motion of the movable member 104 is controlled by a droplet release point positioning system.

[0039] For the source delivery mechanism 92, one or more modulating or non-modulating source material dispensers may be used. For example, a modulating dispenser may be used having a capillary tube formed with an orifice. The nozzle 102 may include one or more electro-actuatable elements, e.g. actuators made of a piezoelectric material, which can be selectively expanded or contracted to deform the capillary tube and modulate a release of source material from the nozzle 102.

[0040] For some applications it is potentially advantageous to provide for an inline droplet generator refilling system and procedure which do not require powering the system down in order to refill the reservoir and then bringing the system back online. Thus, this inline refill system enables tin refill without stopping the generation of droplets, greatly increasing overall system availability. Such a system may use multiple source material chambers, e.g., a primary reservoir, a refill reservoir, a refill tank, and a prime tank. An example of a two chamber system, including a reservoir and a vessel, is disclosed in U.S. Patent No. 8,816,305, titled “Filter for Material Supply Apparatus” and issued August 26, 2014, the entire disclosure of which is hereby incorporated by reference. Tin transfer between these reservoirs is driven by applying different pressures to the chambers. Molten tin responds strongly to pressure differentials. A one psi pressure difference can result in a 100 mm tin height difference. Typically, a droplet generator operates at a pressure on the order of 4000 psi. Here and elsewhere, the term “fluid” is used in its conventional sense as referring both to a gas and to a liquid.

[0041] In performing a tin refill while the droplet generator is operating, any one of several malfunctions can permit the molten tin to enter the fluid inlet line. For example, a pressure control glitch, a data communication error, or miscalibration or drifting of the pressure controller can all cause the fluid line to be flooded with liquid tin. Because there is no heating mechanism in the fluid line, the liquid tin can solidify and severely clog the fluid line. Remedying this can require an extended down time and even a module swap.

[0042] One way to attempt to reduce the possibility of tin clogging the fluid feed lines involves the use of interlocks to protect the fluid lines. These interlocks, however, can add substantial complexity to the system. They can also cause unexpected depressurizations of the inline refill system. They also do not entirely prevent fluid line contamination due, for example, to pressure sensor drifting or software bugs, or simple communication errors or delays.

[0043] According to one aspect of an embodiment, a more reliable and robust system for preventing source material from entering the fluid feed line is provided by interposing a source material valve between source material path and fluid line. Such a measure is in principle essentially error-proof and robust against all malfunctions caused by errors such as software/hardware failures, network communication errors, power outages, sensor drift, and so on. Such a system also simplifies machine and material damage control design, which in turn improves overall system availability and robustness. [0044] FIG. 3 is a conceptual diagram of such a system. FIG. 3 shows two chambers for retaining molten source material, a primary reservoir 300 and a refill reservoir 310. Primary reservoir 300 contains liquid source material 305 and refill reservoir 310 contains liquid source material 315. Primary reservoir 300 is pressurized with a fluid from fluid feed line 307. Refill reservoir 310 is pressurized with a fluid from fluid feed line 317. The fluid may be any suitable inert fluid such as argon gas. Typically, the primary reservoir 300 and refill reservoir 310 are pressurized to a pressure on the order of 4000 psi.

[0045] In a typical conventional system, there is nothing that prevents the source material in the chamber from rising, filling the chamber, and reaching the fluid feed line, resulting in all of the problems mentioned above. According to an aspect of an embodiment, a liquid source material valve is used to prevent source material from entering the fluid fill line. Specifically, a source material valve 320 is placed between the chamber 300 and fluid feed line 307. The source material valve 320 is in fluid communication with the chamber 300. Fluid communication in this context means that there is a path fluid can flow between source material valve 320 and the chamber 300. Conceptually this may equivalently be regarded as placing the source material valve 320 in fluid line 307. Also, a source material valve 330 is placed between the chamber 310 and fluid feed line 317. Each source material valve allows fluid to flow freely in both directions even if there is pressure difference as long as there is no incoming source material flow. If, however, the source material 305 rises and enters the source material valve 320, then the source material valve 320 will close. Similarly, if the source material 315 rises and enters the source material valve 330, then the source material valve 330 will close.

[0046] According to an aspect of an embodiment, the source material valve comprises a valve body defining an internal cavity and an internal component which occupies a normal operational position within the cavity in which fluid flows through the valve (a first state) but which can be moved by source material entering the cavity to a second position in which the fluid line entering the cavity is sealed (a second state). Specifically, with reference to FIG. 4A, there is shown an internal component 400 designed to move within a cavity as described below. The internal component 400 has a main body 405 with gaps 417 that permit fluid to pass the internal component. The main body 405 may be generally cylindrical with wings 410 arranged around a lower periphery of the main body 405 to establish the gaps and help stabilize the position of the internal component 400 within the cavity. Wings 410 may alternatively be referred to as fins or as spacing elements, the latter because they help maintain a spacing between the main body 405 and the walls of the cavity in the source material valve in which the internal component 400 is positioned. In general, there are preferably at least three wing members 410 arranged around a lower periphery of the generally cylindrical body 405 in a rotationally symmetric pattern, that is, symmetric about the axis of rotation of the generally cylindrical body 405. In the arrangement shown there are six wings 410 arranged spaced 60 degrees apart around the lower periphery of the generally cylindrical body 405, but one of ordinary skill will readily appreciate that a different number of wings may be used and that the wings can be arranged in a different pattern. The outer faces 415 of the wings 410 may be provided with round edges in all directions to prevent jamming. FIG. 4B is a view of the internal component 400 of FIG. 4 A from the bottom showing the orientation of the wings 410. FIG. 5 shows an internal component 450 having another possible configuration in which the bottom portion of the component body 455 is tapered in order to facilitate passage of fluid past the internal component. Wings 410 are shaped and spaced to have spaces or voids therebetween to allow fluid to flow freely past the cylindrical body 405 and through the voids between the wings 410 as long as there is not also an incoming source material flow.

[0047] FIG. 6 is a cross sectional view of a source material valve 320 according to one aspect of an embodiment. The source material valve 320 includes a valve body 500 defining within it a cavity 510. The internal component 400 is positioned within the cavity 510. In the position shown in FIG. 6, the internal component 400 is resting on the base of the cavity 510. This would be a normal operating position or first state when there is no source material surge in which fluid flows in form fluid feed line 307 through the cavity 510 and then out through the bottom of cavity 510. Also shown in FIG. 6 is a heater 530 which is in thermal contact with the valve body 500 and heats the source material valve 320 to a temperature above the melting point of the source material.

[0048] For some embodiments, the cavity 510 has a substantially uniform width and the internal component main body 405 has a width less than the cavity width to establish a gap between the cavity wall and the internal component through which fluid may flow. The gap is maintained by wings 410 that serve as spacing elements adapted to maintain the main body 405 laterally spaced away from the walls of the cavity 510. As described above, the spacing elements may comprise at least one pair of protrusions extending laterally in opposite directions from the main body 405, the protrusions having a lateral width such that the width of the protrusions together with the main body width is just slightly less than the cavity width. In some embodiments the cavity 510 is cylindrical with a first diameter and the main body 405 is cylindrical with a second diameter less than the first diameter. The spacing elements, i.e. wings 410 may be wing-like members extending radially from the main body.

[0049] FIG. 7 is a cross sectional view of the source material valve 320 of FIG. 6 in a second state which the internal component 400 has been pushed to the top of the cavity 510 by molten source material 540 when there is a tin flow surge due to pressure variations. In this position, the tin 540 is blocked from moving further into the cavity 510 and out into the fluid feed line 307 attached to the top of the source material valve 320. The top of the internal component 400 and the top of the cavity 510 contact to seal the surface so no source material can pass through to fluid line 307.

[0050] Referring again to FIG. 6, the internal component 400 includes a main body which is configured to seat itself against the top of the cavity 510 to seal the top of the cavity 510. The internal component 400 also has wings or fins 410 that maintain the internal component 400 in the proper orientation and permit fluid to flow past the internal component 400.

[0051] According to an aspect of an embodiment, in use the source material valve 320 is oriented vertically and the internal component 400 is preferably constructed so as to be buoyant with respect to the molten source material. This can be accomplished by making the internal component 400 with internal spaces or by making the internal component solid and of a material this is lighter than the molten source material. The internal component 400 is also preferably made of a material that is chemically and thermally thermal stable in the presence of liquid source material, and be mechanically robust at the prevailing pressures, e.g., 4000 psi. In the example in which the source material is tin, the main body 405 of the internal component 400 can be made for example of titanium or a titanium alloy such as Ti-Mn or Ti-V but other suitable materials may be used in other embodiments. The materials for the wings 410 should have the same chemical and mechanical stability against the liquid tin environment as the main body 405 and could be formed of the same material as the main body 405 in some embodiments. Because the wings 410 make up a smaller part of the combined volume of the wings 410 and the main body 405, the wings 410 may be made of heavier materials with sufficient robustness such as titanium, molybdenum, tungsten, and their alloys but other suitable materials may be used in other embodiments. The interior surface of the cavity 510 of the valve body 500 is preferably made of a material that is chemically and thermally stable in the presence of liquid source material, such as molybdenum if the source material is tin, but other suitable materials may be used in other embodiments.

[0052] According to another aspect of an embodiment, the top surface of the internal component 400 is a portion of a surface of a sphere with radius R. This is referred to herein as a “spherical” surface. The upper wall of the cavity 510 has a complementary spherical surface with radius R. Matching the curvature of these two mating surfaces in this manner allows for formation of a good seal even when the internal component 400 is not perfectly vertical.

[0053] According to another aspect of an embodiment, the diameter of the main portion of the internal component 400, designated D2 in FIG. 6, is made larger than the diameter D4 of the aperture at the top of the cavity 510. This again enables the formation of good sealing even if the internal component 400 is not perfectly vertical.

[0054] According to another aspect of an embodiment, the width between outside edges of opposing wings 410, the “wingspan” designated as D1 in FIG. 6, is set to be slightly less than the diameter of the cavity 510, designated D3 in FIG. 6. The vertical extent of the wings 410 is selected to prevent the internal component 400 from being flipped and becoming j ammed in cavity 510. D 1 can be seen as the maximum outer diameter of internal component 400 which includes gaps 417 between the outermost portions formed by wings 410. [0055] As some nonlimiting examples of dimensions, D4 may be made equal typical fluid line inner diameter of .25 inches. D3 may be made to be about twice D4, i.e., .5 inches. D2 may be (V3)/4 inches to make the fluid passage cross section consistent along the length of the cavity 510. D1 is preferably just slightly less than D3, for example, .04 inches shorter than D3. R may be in the range of 10 inches to 40 inches. The height of the internal component 400, designated as H2, in general can be in the range of 1 to 2 inches. The height difference between HI and H2 is preferably less than .5 inches, and more preferably less than .25 inches. These are just examples of dimensions, and it will be apparent to one of ordinary skill in the art that other dimensions may be used.

[0056] As mentioned, in a multi-chamber system there may be a requirement for unidirectional flow of molten source material from a first chamber to a second chamber with no flow permitted from the second chamber back to the first chamber. This may be the case, for example, when the first chamber contains purified molten source material while the second chamber contains contaminated or less pure molten source material. A source material valve may be deployed to advantage in such an arrangement as well. For example, in FIG. 8, a first reservoir 800 contains essentially pure source material 805. A second reservoir 810 contains less pure source material 815. There may be situations in which it is desirable to permit flow from the first chamber 800 to the second chamber 810 but not in the reverse direction. To accommodate these situations, a source material valve 820 can be interposed between the two chambers. Source material 805 will have essentially the same density as source material 815 so the internal component 825 in source material valve 820 will tend to be neutrally buoyant. However, in the event of a malfunction causing a higher pressure in chamber 810 than in chamber 800, an internal component 825 shaped such as internal component 400 in FIGS. 6 and 7 will present more flow resistance in the direction from chamber 810 to chamber 800 and will tend to move to seat against the top of the cavity 830 and so block flow.

[0057] While the above description is in terms of the use of the novel source material valve in an arrangement for supplying source material in an EUV source, one of ordinary skill in the art will readily appreciate that the principles disclosed herein can also be advantageously exploited in other applications where prevention of molten material flow is needed.

[0058] The above description includes examples of multiple embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is construed when employed as a transitional word in a claim. 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 with all or a portion of any other aspect and or embodiment, unless stated otherwise.

[0059] Other aspects of the invention are set out in the following numbered clauses.

1. Apparatus for controlling a flow of molten source material from a source material retaining chamber in an EUV source, the apparatus comprising: a valve body defining a cavity, the valve body having a first valve body end adapted to be connected to a fluid feed line and a second valve body end adapted to be placed in fluid communication with the source material retaining chamber, the cavity having a seating wall at an end of the cavity closer to the first valve body end; and an internal component arranged in the cavity and adapted to move from a first position in which the internal component permits a flow of fluid through the cavity to a second position in which an upper portion of the internal component seats against the seating wall to prevent a flow of molten source material through the cavity.

2. The apparatus as in clause 1 wherein the cavity has a substantially uniform cavity width and wherein the internal component comprises a main body having a main body width less than the cavity width and a plurality of spacing elements adapted to maintain the main body laterally spaced away from a side wall of the cavity.

3. The apparatus as in clause 2 wherein the spacing elements comprise at least one pair of protrusions extending laterally in opposite directions from the main body, the protrusions having a lateral width such that the width of the protrusions together with the main body width is less than the cavity width.

4. The apparatus as in clause 2 wherein the cavity is cylindrical with a first diameter and the main body is cylindrical with a second diameter less than the first diameter.

5. The apparatus as in clause 4 wherein the spacing elements are wing-like members extending radially from the main body.

6. The apparatus as in clause 1 wherein the internal component comprises a generally cylindrical body and a plurality of wing members extending radially outward from the main body and arranged around a lower periphery of the generally cylindrical body.

7. The apparatus as in clause 6 wherein the plurality of wing members comprises at least three wing members arranged around a lower periphery of the generally cylindrical body in a rotationally symmetric pattern.

8. The apparatus as in clause 7 wherein the plurality of wing members comprises six wing members arranged around a lower periphery of the generally cylindrical body at 60 degree intervals.

9. The apparatus as in clause 6 wherein an outer face of each of the wing members is rounded.

10. The apparatus as in clause 1 wherein the internal component is solid and comprises a material having a density less than a density of the molten source material. 11. The apparatus as in clause 2 wherein the main body is solid and comprises a material having a density less than a density of the molten source material.

12. The apparatus as in clause 2 wherein the internal component comprises titanium or a titanium alloy.

13. The apparatus as in clause 2 wherein each of the spacing elements comprise titanium, molybdenum, tungsten, or their alloys.

14. The apparatus as in clause 1 wherein the internal component has a spherical upper surface with a radius R and wherein the seating wall has a complementary spherical surface with a radius R.

15. The apparatus as in clause 1 wherein the internal component has a tapered lower portion.

16. The apparatus as in clause 1 further comprising a heater in thermal contact with the valve body and adapted to maintain a temperature of the valve body and the internal component above a melting point of the source material.

17. The apparatus as in clause 1 wherein an internal surface of the cavity comprises molybdenum.

18. Apparatus for controlling a flow of molten source material from a chamber in an EUV source, the apparatus comprising: a valve body which when arranged vertically defines a vertical cavity, the valve body having an upper valve body end adapted to be connected to a fluid feed line and a lower valve body end adapted to be placed in fluid communication with the chamber, the cavity having a seating wall at an upper end of the cavity; and an internal component arranged in the cavity and adapted to be moved vertically by molten source material entering the cavity through the lower valve body end from a first position in which the internal component permits a flow of fluid through the cavity to a second position in which an upper portion of the internal component is moved toward and into sealing contact against the seating wall to prevent a flow of molten source material through the cavity.

19. The apparatus as in clause 18 wherein the internal component comprises a generally cylindrical body and a plurality of wing members extending radially outward from the generally cylindrical body and arranged around a lower periphery of the generally cylindrical body.

20. The apparatus as in clause 19 wherein the plurality of wing members comprises at least three wing members arranged around a lower periphery of the generally cylindrical body in a rotationally symmetric pattern.

21. The apparatus as in clause 20 wherein the plurality of wing members comprises six wing members arranged around a lower periphery of the generally cylindrical body at 60 degree intervals.

22. The apparatus as in clause 20 wherein an outer face of each of the wing members is rounded.

23. The apparatus as in clause 18 wherein the internal component is solid and comprises a material having a density less than a density of the molten source material.

24. The apparatus as in clause 18 wherein the internal component comprises titanium or a titanium alloy. 25. The apparatus as in clause 18 wherein the internal component has a spherical upper surface with a radius R and wherein the seating wall has a complementary spherical surface with a radius R.

26. The apparatus as in clause 18 further comprising a heater in thermal contact with the valve body and adapted to maintain a temperature of the valve body and the internal component above a melting point of the source material.

27. Apparatus for controlling a flow of molten source material from a chamber in an EUV source, the apparatus comprising: a valve body defining a cavity, the valve body having an first valve body end adapted to be connected to a fluid feed line and a second valve body end adapted to be placed in fluid communication with the chamber, the cavity having a seating wall at an end of the cavity closer to the valve body end; and an internal component arranged in the cavity, the apparatus being adapted to have a first state in which the internal component permits a flow of fluid through the cavity and a second state in which the cavity is at least partially filled with molten source material and in which the internal component prevents a flow of molten source material through the cavity due to the molten source material in the cavity.

28. Apparatus for controlling a flow of molten source material between a first source material retaining chamber and a second source material retaining chamber in an EUV source, the apparatus comprising: a valve body defining a cavity, the valve body having a first valve body end adapted to be placed in fluid communication with the first source material retaining chamber connected and a second valve body end adapted to be placed in fluid communication with the second source material retaining chamber, the cavity having a seating wall at an end of the cavity closer to the first valve body end; and an internal component arranged in the cavity and adapted to move between a first position in which the internal component permits a flow of source material through the cavity from the first source material retaining chamber to the second source material retaining chamber and a second position in which an upper portion of the internal component seats against the seating wall to prevent a flow of molten source material through the cavity from the second source material retaining chamber to the first source material retaining chamber.

29. The apparatus as in clause 28 wherein the internal component comprises a generally cylindrical body and a plurality of wing members arranged around a lower periphery of the generally cylindrical body.

30. The apparatus as in clause 29 wherein the plurality of wing members comprises at least three wing members arranged around a lower periphery of the generally cylindrical body in a rotationally symmetric pattern.

31. The apparatus as in clause 30 wherein the plurality of wing members comprises six wing members arranged around a lower periphery of the generally cylindrical body at 60 degree intervals.

32. The apparatus as in clause 29 wherein an outer face of each of the wing members is rounded. 33. The apparatus as in clause 28 wherein the internal component comprises titanium or a titanium alloy.

34. The apparatus as in clause 28 wherein the internal component has a spherical upper surface with a radius R and wherein the seating wall has a complementary spherical surface with a radius R. 35. The apparatus as in clause 28 further comprising a heater in thermal contact with the valve body and adapted to maintain a temperature of the valve body and the internal component above a melting point of the source material.

36. The apparatus as in clause 28 wherein an internal surface of the cavity comprises molybdenum. [0060] The above described implementations and other implementations are within the scope of the following claims.

Claims

2. The apparatus as in claim 1 wherein the cavity has a substantially uniform cavity width and wherein the internal component comprises a main body having a main body width less than the cavity width and a plurality of spacing elements adapted to maintain the main body laterally spaced away from a side wall of the cavity.

3. The apparatus as in claim 2 wherein the spacing elements comprise at least one pair of protrusions extending laterally in opposite directions from the main body, the protrusions having a lateral width such that the width of the protrusions together with the main body width is less than the cavity width.

4. The apparatus as in claim 2 wherein the cavity is cylindrical with a first diameter and the main body is cylindrical with a second diameter less than the first diameter.

5. The apparatus as in claim 4 wherein the spacing elements are wing-like members extending radially from the main body.

6. The apparatus as in claim 1 wherein the internal component comprises a generally cylindrical body and a plurality of wing members extending radially outward from the main body and arranged around a lower periphery of the generally cylindrical body.

7. The apparatus as in claim 6 wherein the plurality of wing members comprises at least three wing members arranged around a lower periphery of the generally cylindrical body in a rotationally symmetric pattern.

8. The apparatus as in claim 7 wherein the plurality of wing members comprises six wing members arranged around a lower periphery of the generally cylindrical body at 60 degree intervals.

9. The apparatus as in claim 6 wherein an outer face of each of the wing members is rounded.

10. The apparatus as in claim 1 wherein the internal component is solid and comprises a material having a density less than a density of the molten source material.

11. The apparatus as in claim 2 wherein the main body is solid and comprises a material having a density less than a density of the molten source material.

12. The apparatus as in claim 2 wherein the internal component comprises titanium or a titanium alloy.

13. The apparatus as in claim 2 wherein each of the spacing elements comprise titanium, molybdenum, tungsten, or their alloys.

14. The apparatus as in claim 1 wherein the internal component has a spherical upper surface with a radius R and wherein the seating wall has a complementary spherical surface with a radius R.

15. The apparatus as in claim 1 wherein the internal component has a tapered lower portion.

16. The apparatus as in claim 1 further comprising a heater in thermal contact with the valve body and adapted to maintain a temperature of the valve body and the internal component above a melting point of the source material.

17. The apparatus as in claim 1 wherein an internal surface of the cavity comprises molybdenum.

19. The apparatus as in claim 18 wherein the internal component comprises a generally cylindrical body and a plurality of wing members extending radially outward from the generally cylindrical body and arranged around a lower periphery of the generally cylindrical body.

20. The apparatus as in claim 19 wherein the plurality of wing members comprises at least three wing members arranged around a lower periphery of the generally cylindrical body in a rotationally symmetric pattern.

21. The apparatus as in claim 20 wherein the plurality of wing members comprises six wing members arranged around a lower periphery of the generally cylindrical body at 60 degree intervals.

22. The apparatus as in claim 20 wherein an outer face of each of the wing members is rounded.

23. The apparatus as in claim 18 wherein the internal component is solid and comprises a material having a density less than a density of the molten source material.

24. The apparatus as in claim 18 wherein the internal component comprises titanium or a titanium alloy.

25. The apparatus as in claim 18 wherein the internal component has a spherical upper surface with a radius R and wherein the seating wall has a complementary spherical surface with a radius R.

26. The apparatus as in claim 18 further comprising a heater in thermal contact with the valve body and adapted to maintain a temperature of the valve body and the internal component above a melting point of the source material.

29. The apparatus as in claim 28 wherein the internal component comprises a generally cylindrical body and a plurality of wing members arranged around a lower periphery of the generally cylindrical body.

30. The apparatus as in claim 29 wherein the plurality of wing members comprises at least three wing members arranged around a lower periphery of the generally cylindrical body in a rotationally symmetric pattern.

31. The apparatus as in claim 30 wherein the plurality of wing members comprises six wing members arranged around a lower periphery of the generally cylindrical body at 60 degree intervals.

32. The apparatus as in claim 29 wherein an outer face of each of the wing members is rounded.

33. The apparatus as in claim 28 wherein the internal component comprises titanium or a titanium alloy.

34. The apparatus as in claim 28 wherein the internal component has a spherical upper surface with a radius R and wherein the seating wall has a complementary spherical surface with a radius R.

35. The apparatus as in claim 28 further comprising a heater in thermal contact with the valve body and adapted to maintain a temperature of the valve body and the internal component above a melting point of the source material.

36. The apparatus as in claim 28 wherein an internal surface of the cavity comprises molybdenum.