WO2023110321A1

WO2023110321A1 - Apparatus for recovery of euv target material

Info

Publication number: WO2023110321A1
Application number: PCT/EP2022/082766
Authority: WO
Inventors: Shiva Kumara Thejasvi RAJAVELU MURALIDHAR; Yue Ma; Nina Vladimirovna Dziomkina; Arpit Hemantkumar GANDHI; Daniel Steven DEBRUIN; Andrei Dorobantu; Fernando BRIZUELA; Sebastian BOMMER
Original assignee: Asml Netherlands B.V.
Priority date: 2021-12-17
Filing date: 2022-11-22
Publication date: 2023-06-22
Also published as: TW202347004A

Abstract

Disclosed is a conduit structure for an EUV system in which a nonhorizontal interior surface of the conduit is provided with flow obstructions that impede the flow of molten target material across the surface so that the molten target material freezes on and is captured by the interior surface. Where the conduit is one through which droplets of target material pass out of an EUV chamber, flow obstructions on the side of the conduit ensure that molten target material that is originally caught by an upper surface of the conduit and flows to the sidewall adheres to the sidewall and stays clear of the actual droplet path. This ensures that an opening in the conduit is maintained allowing the intended flow. The conduit structure may be placed, for example, between an interior of the chamber in which the EUV radiation is generated and a target material receptacle.

Description

APPARATUS FOR RECOVERY OF EUV TARGET MATERIAL

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63/290,864, filed December 17, 2021, titled APPARATUS FOR RECOVERY OF EUV TARGET MATERIAL; and U.S. Application No. 63/407,915, filed September 19, 2022, titled APPARATUS FOR RECOVERY OF EUV TARGET MATERIAL, both of which are incorporated herein in their entireties by reference.

FIELD

[0002] The present disclosure relates to an apparatus for generating extreme ultraviolet (“EUV”) radiation from a plasma created by changing the state of a target material. In such applications optical elements are used, for example, to collect and direct the EUV radiation for use in semiconductor photolithography.

BACKGROUND

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

[0004] Methods for generating EUV radiation include converting a target material to a plasma state. The target material preferably includes at least one element, e.g., xenon, lithium, or tin, with one or more emission lines in the EUV portion of the electromagnetic spectrum. The target material can be solid, liquid, or gas. In one such method, often termed laser produced plasma (“LPP”), the required plasma can be produced by using a laser beam to irradiate a target material having the required lineemitting element.

[0005] One LPP technique involves generating a stream of target material droplets and irradiating at least some of the droplets with one or more laser radiation pulses. The stream of droplets is generated by a droplet generator.

[0006] The process of transforming the target material results in deposits of residual target material accumulating on every surface where there is an unobstructed path between the irradiation site and the surface. It also results in such deposits on the surfaces exposed to flows of gas that entrain residual target material. These surfaces include vanes, exhaust ports, and drain paths. If the target material is tin, this can lead to the growth of tin wool which can drop onto the collector optics and clog the exhaust and drain paths. Tin is used as an example of a specific target material herein with the understanding that other types of target materials may be used and may present the same or similar management issues. [0007] One technique for controlling tin accumulation involves capturing tin from vapor or particles on a collection surface heated to above the melting point of tin. On such heated collection surfaces the tin melts (or remains molten) and is caused to flow to a capture receptacle. Liquid tin, however, tends to erupt or “spit” in the presence of hydrogen radicals such as are found in an EUV chamber, and this ejected tin can strike the collector.

[0008] Also, the liquid tin typically does not flow as intended. For example, structures within the chamber such as vanes and gutters for scrubbers provided to remove some or all of the tin vapor in the chamber may drip liquid tin onto the collector. Liquid tin may also create thermal shorts i.e., unintended heat conductive paths. In addition liquid tin is highly corrosive and leads to failures of, for example, the electrical heaters used to maintain the collection surfaces above the melting point of tin. [0009] One chamber feature requiring particular attention is the tin catch or receptacle that is positioned to receive tin from unused tin droplets and store the tin for subsequent removal. Unused droplets occur, for example, in systems in which the generation of light is enabled or disabled by interrupting or redirecting the laser pulses that would otherwise convert the droplets rather than by interrupting the generation of droplets. Provision must be made for controlling and containing the unused tin, preferably without breaking the vacuum in the chamber. The structure through which the droplets pass as exiting the chamber is prone to tin accumulation in the form of tin wool or wires. This structure may be implemented as a conduit structure in an insert in a collector flow ring as described below. Eventually this tin accumulation can obstruct the exit path of the unused tin droplets.

[0010] There is thus a requirement to manage residual target material so that it does not obstruct orifices in the source chamber, including the entrance to the tin catcher. It is in this context that the need for the presently disclosed subject matter arises.

SUMMARY

[0011] The following presents a succinct summary of one or more embodiments in order to provide a basic understanding of the disclosed subject matter. This summary is not an extensive overview of all contemplated embodiments. It is not intended to single out particular elements as being key or critical to any embodiments nor set limits on the scope of implementation of any or all embodiments. Its sole purpose is to present some concepts in a streamlined form as a prelude to the more detailed description that is presented later.

[0012] According to one aspect, an interior surface of a conduit structure for an EUV system is provided with flow obstructions that impede the flow of molten target material across a nonhorizontal surface of the conduit structure so that the molten target material freezes on and is captured by the interior surface. The conduit structure may be placed, for example, between an interior of the chamber in which the EUV radiation is generated and a target material receptacle in which case the interior surface is a side surface of the conduit structure. [0013] According to another aspect of an embodiment there is disclosed a conduit structure adapted to be placed in fluid communication with an interior of a chamber for an EUV radiation source in which a target material is transformed, the conduit structure comprising at least one sidewall facing an interior of the conduit structure, at least a part of the sidewall being provided with a plurality of flow obstructions arranged to impede a flow of molten target material across the plurality of flow obstructions.

[0014] The conduit structure may comprise a plate arranged to cover the at least a part of the sidewall, the plurality of flow obstructions being arranged on the plate. The plurality of flow obstructions may comprise a plurality of codirectional ridges extending in a first direction at least partially through the conduit structure. One of the ridges may be discontinuous. The ridges may extend in a zigzag pattern with a first group of straight segments angled at a first angle with respect to the first direction alternating with a second group of straight segments angled at a second angle with respect to the first direction.

[0015] According to another aspect of an embodiment there is disclosed an EUV radiation source including a chamber in which an EUV target material is transformed, the chamber having at least one conduit structure having a surface exposed to the EUV target material, wherein a first portion of the surface is arranged at a position at which molten target material encounters the first portion of the surface and gravity tends to pull the molten target material in a first direction downward across the first portion of the surface and a second portion of the surface below the first portion provided with a plurality of flow obstructions arranged to impede a flow of molten target material across the second portion in the first direction.

[0016] The surface may comprise a plate insert including the plurality of flow obstructions. The plate insert may be maintained at a temperature lower than a melting temperature of the target material. The target material may be tin and the plate insert may be maintained at a temperature not greater than approximately 200°C.

[0017] The plurality of flow obstructions may comprise a plurality of codirectional ridges extending in a second direction substantially normal to the first direction. An uppermost one of the ridges may be discontinuous. The ridges may extend in a zigzag pattern with a first group of straight segments angled at a first angle with respect to the second direction alternating with a second group of straight segments angled at a second angle with respect to the second direction. An uppermost one of the ridges may be discontinuous defining a plurality of gaps through the uppermost ridge.

[0018] The EUV radiation source may further comprise a cooling flow ring arranged at least partially around a circumference of a collector mirror positioned in the chamber, the conduit structure being positioned in the cooling flow ring to provide a pathway between the interior of the chamber and a target material receptacle.

[0019] The plurality of flow obstructions may comprise a plurality of substantially circular indentations. The plurality of flow obstructions may comprise a plurality of substantially rectangular indentations. The plurality of substantially rectangular indentations may be coextensive with a length of the second portion of the surface. The plurality of substantially rectangular indentations may be arranged in rows and columns in an array.

[0020] The plurality of flow obstructions may comprise a plurality of angled vanes located on the second portion. The plurality of flow obstructions may comprise a plurality of elongated slits extending normal to the first direction with each slit having an associated gutter portion. At least a portion of the surface may be roughened.

[0021] The EUV radiation source may further comprise a top surface element adjacent the surface and angled with respect to the surface and adapted and arranged to permit molten target material collecting on the top surface element to flow off of the top surface element and onto the surface. [0022] According to another aspect of an embodiment there is disclosed an EUV radiation source including a chamber and a target material receptacle in fluid communication with an interior of the chamber through a conduit, the conduit comprising a target material collection plate positioned to at least partially cover an interior surface of the conduit, the target material collection plate including a plurality of structures impeding a flow of molten target material across the plurality of structures thus causing the molten target material to solidify on the target material collection plate.

[0023] According to another aspect there is disclosed an EUV radiation source including a chamber, the chamber including a surface at a position exposed to residual target material during generation of EUV radiation, the source comprising a target material collection plate at least partially covering the surface, the target material collection plate being maintained at a temperature below a melting temperature of the target material, the target material collection plate including a plurality of flow obstructions, the target material collection plate being oriented so that gravity pulls molten target material across the flow obstructions and the flow obstructions being oriented to arrest a flow of molten target material.

[0024] According to another aspect of an embodiment there is disclosed a conduit structure adapted to be placed in fluid communication with an interior of a chamber for an extreme ultraviolet (EUV) radiation source in which a target material is transformed, the conduit structure comprising at least one sidewall facing an interior of the conduit structure, the at least one sidewall having a first sidewall edge extending in a first direction and at least a part of the sidewall being provided with a plurality of flow obstructions extending substantially in the first direction and arranged to impede a flow of molten target material across the part of the sidewall in a second direction different from the first direction. The conduit structure also comprises a top wall facing an interior of the conduit structure, the top wall being arranged to have a top wall edge extending in the first direction substantially parallel to the first sidewall edge, the top wall edge having a plurality of edge features arranged to inhibit a flow of target material along the top wall edge in the first direction.

[0025] The top wall may be in thermal contact with a source of heat such that the top wall reaches a temperature greater than a melting temperature of the target material. The plurality of edge features may comprise a plurality of depressions. The plurality of depressions may be arranged in a linear array. The depressions may be substantially triangular with a base of the depression being positioned at the top wall edge.

[0026] Each depression may be provided with a layer of tinphobic material. At least part of a surface of the top wall exclusive of the surfaces of the depressions is provided with a layer of tinphilic material. The entire surface of the top wall exclusive of the surfaces of the depressions may be covered with a layer of tinphilic material.

[0027] The conduit structure may further comprise a heating element in thermal contact with at least part of the top wall and arranged to maintain at least part of the top wall at a first temperature. The heating element may be arranged to maintain a first portion of the top wall at the first temperature and to maintain a second portion of the top wall at a second temperature different from the first temperature.

[0028] According to another aspect of an embodiment there is disclosed an extreme ultraviolet (EUV) radiation source including a chamber in which an EUV target material is transformed, the chamber having at least one conduit structure, the conduit structure comprising a lateral side surface exposed to the EUV target material, wherein a first portion of the lateral side surface is arranged at a position at which molten target material encounters the first portion of the lateral side surface and arranged with an orientation so that gravity would tend to pull the molten target material in a first direction downward across the first portion of the lateral side surface, and a second portion of the lateral side surface below the first portion provided with a plurality of flow obstructions arranged to impede a flow of molten target material across the second portion in the first direction, the lateral side surface having a first lateral side surface edge extending in a second direction. The conduit structure further comprises a top wall facing an interior of the conduit structure, the top wall being arranged to have a top wall edge extending in the second direction substantially parallel to first lateral side surface edge, the top wall edge having a plurality of edge features arranged to inhibit a flow of target material along the top wall edge in the second direction.

[0029] The plurality of edge features may comprise a plurality of depressions. The plurality of depressions may be arranged in a linear array. Each depression may be substantially triangular with a base of the depression being positioned at the top wall edge. A surface of each depression may be provided with a layer of tinphobic material. At least part of a surface of the top wall exclusive of the surfaces of the depressions may be provided with a layer of tinphilic material.

[0030] The conduit structure may further comprise a heating element in thermal contact with at least part of the top wall and arranged to maintain at least part of the top wall at a first temperature. The heating element may be arranged to maintain a first portion of the top wall at the first temperature and to maintain a second portion of the top wall at a second temperature different from the first temperature.

[0031] Further embodiments, features, and advantages of the presently disclosed subject matter, as well as the structure and operation of the various embodiments are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a schematic, not-to-scale view of an overall broad conception for a laser-produced plasma EUV radiation source system.

[0033] FIG. 2 is a not-to-scale diagram showing a possible arrangement of a chamber and gas flow systems used in a laser-produced plasma EUV radiation source system.

[0034] FIG. 3A is a schematic not-to-scale plan view of a part of a possible arrangement of a laser- produced plasma EUV radiation source system.

[0035] FIG. 3B is a schematic not-to-scale plan view of a part of a possible arrangement of a laser- produced plasma EUV radiation source system according to an aspect of an embodiment of the presently disclosed subject matter.

[0036] FIG. 4 is a not-to-scale perspective view showing a possible arrangement of a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0037] FIG. 5 is a not-to-scale perspective view showing a possible structure for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0038] FIG. 6A is a not-to-scale plan view showing a possible arrangement of flow obstructions on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0039] FIG. 6B is a not-to-scale cutaway side view taken along line BB of FIG. 6A showing a possible arrangement of an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0040] FIG. 6C is a not-to-scale cutaway side view showing another possible arrangement of an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0041] FIG. 7 is a cutaway side view of target material capture and retention for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0042] FIGS. 8 A and 8B are not-to-scale plan views showing other possible arrangements of flow obstructions on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0043] FIGS. 9 A and 9B are not-to-scale plan views showing other possible arrangements of flow obstructions on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter. [0044] FIGS. 10A and 10B are not-to-scale plan views showing other possible arrangements of flow obstructions on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0045] FIG. 11 A is a not-to-scale diagram of an insert plate for a target material control system according to an aspect of an embodiment of the presently disclosed subject matter.

[0046] FIGS. 1 IB - 1 IE are cross sections of embodiments of tin arresting structures on the insert plate of FIG. 11 taken along line C-C of FIG. 11 according to aspects of an embodiments of the presently disclosed subject matter.

[0047] FIG. 12 is a not-to-scale perspective view showing another possible arrangement of flow obstructions on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0048] FIG. 13A is a not-to-scale perspective view showing a possible arrangement of flow obstructions on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0049] FIG. 13B is a not-to-scale cutaway side view taken along line FF of FIG. 13 A showing a possible arrangement of an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter. [0050] FIG. 13C is a not-to-scale perspective view showing another possible arrangement of flow obstructions on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0051] FIGS. 14A - 14F are plan views of surface roughening that may be used on an insert plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0052] FIG. 15 is a plan view schematic of a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter. [0053] FIG. 16 is a bottom perspective view of a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0054] FIG. 17A is a plan view of the bottom of a top plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0055] FIG. 17B is an edge-on view of a top plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0056] FIG. 18A is an enlargement of a portion of FIG. 17 A.

[0057] FIG. 18B is an enlargement of a portion of FIG. 17B.

[0058] FIG. 19 is a perspective view of a portion of an edge of a top plate for a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0059] FIG. 20 is a front view of a target material control system for an entrance of a target material receptacle according to an aspect of an embodiment of the presently disclosed subject matter.

[0060] 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. The 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

[0061] 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, specific details are set forth to promote a thorough understanding of all described 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 ascribed to it below. In other instances, well-known structures and devices are shown in schematic or block diagram form in order to facilitate description of one or more embodiments.

[0062] Before describing such embodiments in more detail, however, it is instructive to describe an example environment in which embodiments of the presently disclosed subject matter may be implemented. In the description that follows and in the claims the terms “up,” “down,” “top,” “bottom,” “vertical,” “horizontal,” and like terms may be employed. These terms are intended to show relative orientation only and not any orientation with respect to gravity unless otherwise indicated or clear from context.

[0063] With initial reference to FIG. 1 there is shown a schematic view of an exemplary EUV radiation source, e.g., a laser produced plasma EUV radiation source 10 according to one aspect of an embodiment of the presently disclosed subject matter. As shown, the EUV radiation source 10 may include a pulsed or continuous laser source 22, which may for example be a pulsed gas discharge CO2 laser source producing a beam 12 of radiation at 10.6 pm or 1 pm. The pulsed gas discharge CO2 laser source may have DC or RF excitation operating at high power and at a high pulse repetition rate.

[0064] The EUV radiation source 10 also includes a target delivery system 24 for delivering target material in the form of liquid droplets or a continuous liquid stream. In this example, the target material is a liquid, but it could also be a solid or gas. Tin is used as a nonlimiting example of a target material in the description which follows with the understanding that other materials could be used. Also, droplets are used as a nonlimiting example of the form of the tin with the understanding that other forms could be used [0065] In the system depicted the target material delivery system 24 introduces droplets 14 of the target material into the interior of a vacuum chamber 26 having a chamber wall 27. The vacuum chamber 26 includes an irradiation region 28 where the target material may be irradiated to produce plasma. It should be noted that as used herein an irradiation region is a region where target material irradiation may or is intended to occur and is an irradiation region even at times when no irradiation is actually occurring. The EUV light source may also include a beam steering system 32.

[0066] In the system shown, the components are arranged so that the droplets 14 travel substantially horizontally. The direction from the laser source 22 towards the irradiation region 28, that is, the nominal direction of propagation of the beam 12, may be taken as the Z axis. The path the droplets 14 take from the target material delivery system 24 to the irradiation region 28 may be taken as the X axis. The view of FIG. 1 is thus normal to the XZ plane. The orientation of the EUV radiation source 10 may be rotated with respect to gravity as shown, with the arrow G showing the orientation with respect to gravitationally down. While a system in which the droplets 14 travel substantially horizontally is depicted, it will be understood by one having ordinary skill in the art that other arrangements can be used in which the droplets travel vertically or at some angle with respect to gravity between and including 90° (horizontal) and 0° (vertical).

[0067] The EUV radiation source 10 may also include an EUV light source controller system 60 and a laser firing control system 65. The EUV radiation source 10 may also include a detector such as a target position detection system 70 that generates an output indicative of the absolute or relative position of a target droplet, e.g., relative to the irradiation region 28, and provide this output to a target position detection feedback system 62.

[0068] 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 adjusts the path of the target droplets 14 through the irradiation region 28. This adjustment may be accomplished, for example, by repositioning the point at which a droplet generator 92 releases the target droplets 14. The droplet release point may be repositioned, for example, by tilting the droplet generator 92 or by laterally translating the droplet generator 92. The droplet generator 92 extends into the chamber 26 and is preferably externally supplied with target material. A gas source (not shown) places the target material in droplet generator 92 under pressure. Droplets 14 that pass through the irradiation region 28 without being transformed continue to a target material receptacle 34, also referred to as tin catch 34 herein.

[0069] Continuing with FIG. 1, the radiation source 10 may also include one or more optical elements. In the following description, a collector 30 is used as an example of such an optical element, but the description applies to other optical elements as well. The collector 30 may be a normal incidence reflector, for example, implemented as a multilayer mirror. The collector 30 may be in the form of a prolate ellipsoid, with a central aperture to allow the laser radiation 12 to pass through and reach the irradiation region 28. The collector 30 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 40) where the EUV radiation may be output from the EUV radiation source 10 and input to, e.g., an integrated circuit lithography scanner 50. The scanner 50 uses the radiation, for example, to process a silicon wafer workpiece 52 in a known manner using a reticle or mask 54. The silicon wafer workpiece 52 is then additionally processed in a known manner to make an integrated circuit device.

[0070] As mentioned, management of residual target material is a critical technical challenge. Residual tin has a tendency to collect on the surfaces of the chamber 26 in a process known as tin writing. This tin can fall and contaminate the collector 30. The tin can also block various portals and conduits intended to permit a flow of a buffer gas inside the chamber 26 or serving as an exit for unused droplets. This residual tin must be managed to extend the lifetime of the source.

[0071] FIG. 2 shows several modules directed to the mitigation of tin contamination. In the orientation shown, the droplet generator is positioned directly behind the chamber 26 so that the droplet path is out of the plane of the figure to a conduit structure including a tin catch entrance 110. In the embodiment shown the tin catch entrance 110 is positioned in a collector flow ring (“CFR”) 100 surrounding the circumferential periphery of the collector 30. The CFR 100 is provided to establish gas flows in the vicinity of the collector 30. The CFR 100 can include a cooling flow channel configured to transport a fluid provided to remove heat from at least a portion of the CFR 100 during EUV radiation generation. Further details on the construction and operation of a CFR such as the CFR 100 are available from International Publication No. WO 2021/130017, titled “Collector Flow Ring” and published July 1, 2021.

[0072] All patent applications, patents, and printed publications cited herein are incorporated herein by reference in their entireties, except for any definitions, subject matter disclaimers or disavowals, and except to the extent that the incorporated material is inconsistent with the express disclosure herein, in which case the language in this disclosure controls.

[0073] The CFR 100 introduces a flow of a buffer gas tending to carry tin away from the surface of the collector 30. Gas is also introduced through a collector flow cone 120 arranged at the central aperture of the collector 30. The laser radiation 12 also passes through this aperture. Further along the optical axis of the chamber 26 between the primary focus and the intermediate focus 40 of the collector 30 there is a section 130 with surfaces having a series of flow vanes directing the flow of gas in patterns intended to keep tin away from critical surfaces. This section 130 may also include vanes 36 for collecting tin. A high flow scrubber 140 may also be employed to control tin. Exhaust ports 125 are provided to exhaust buffer gas from the chamber 26 and must also be kept clear of residual target material.

[0074] FIG. 3A is a plan view of an arrangement such as that shown in FIG. 2 from the perspective of the intermediate focus 40 of the collector 30. As can be seen, a droplet generator 92 generates a stream of droplets 14. Also shown is the CFR 100 surrounding the periphery or circumference of the collector 30. Droplets 14 may be irradiated in the irradiation region 28 at the primary focus of the collector 30 or they may pass through the primary focus without transformation to the tin catch entrance 110 and then through a conduit 112 to a tin catch 34. The tin catch 34 collects the molten tin and passes it to a tin bucket (not shown). A freeze valve (not shown) may be provided to permit draining of the tin catch 34 without interrupting operation of the source.

[0075] Conventionally, the walls of the conduit 112 beyond the tin catch entrance 110 are smooth planar surfaces. This undesirably allows stray residual tin to accumulate on the walls in the form of, for example, tin whiskers or wires. The accumulated tin can eventually partially or wholly block the conduit 112 so that the tin droplets 14 can no longer pass through unimpeded.

[0076] To address this issue, according to an aspect of an embodiment, at least one sidewall of the conduit 112 is provided with an engineered surface having obstructions that capture residual tin by arresting the flow of tin across the engineered surface and freezing it in place. The engineered surface may be provided in the form of a thin plate-shaped insert positioned adjacent to the sidewall of the conduit 112 or may be integral with the sidewall of the conduit 112. In the description that follows, a plate-shaped insert will be used as an example of an implementation. The plate-shaped insert may be constructed as a liner that can be easily swapped out during maintenance after it has accumulated its capacity of tin. The stray tin may be tin entrained in a flow of gas through the tin catch entrance 110 and conduit 112 or may be tin that flows down to the sidewall of the conduit 112 from an upper surface of the conduit 112 as described below.

[0077] The flow obstructions on the sidewall ensure that molten target material that is originally caught by an upper surface of the conduit 112 and flows to the sidewall is frozen on the sidewall and stays clear of the intended droplet path. This ensures that an opening in the conduit 112 is maintained allowing the intended flow.

[0078] According to one aspect of an embodiment, as shown in FIG. 3B, stray tin entering the tin catcher entrance 110 is captured and stored on a plate 200 maintained at a temperature below the melting point of tin. According to another aspect of an embodiment, the plate 200 is heated to, for example, a temperature in a range of approximately 70°C to approximately 200°C, e.g., approximately 100°C (approximately here and elsewhere being +/- 10%). In the example where the material comprising the surface includes aluminum, a temperature of greater than 70°C unexpectedly appears to increase the surface tension of tin and aluminum thus reducing flow speed downward across the plate 200.

[0079] Maintaining the plate 200 at a temperature in the range of approximately 80°C to approximately 200°C causes tin to freeze on the surface of the plate 200. The plate 200 may be maintained at the desired temperature by active means, i.e., provision of a temperature control plate 215 (FIG. 6 A and FIG. 15)), or by passive means, i.e., by heat transfer from sufficiently proximate heated elements.

[0080] FIG. 4 provides a closer perspective view of the conduit 112 with the plate 200 in relation to the collector 30, the CFR 100, the tin catch 34, and the flow of droplets as indicated by the arrow A. FIG. 4 also shows a roof element 210 arranged to cover the conduit 112. FIG. 5 shows the plate 200 in relation to the roof element 210 and in particular the lateral extent of the plate 200 in the same direction as and parallel to the droplet exit flow path.

[0081] FIG. 6A is a plan view of the plate 200 according to an aspect of an embodiment. In the embodiment of FIG. 6 A the plate 200 is shaped as a trapezoid. It will be understood, however, that this shape is arbitrary and may be selected to at least partially cover the sidewall of the conduit 112. The broken dotted line 300 indicates the lower edge of a tin landing zone where molten tin comes into contact with the plate 200 when the plate 200 is in place adjacent to the sidewall of the conduit 112. After molten tin impinges on the plate 200 the tin flows generally downward (in the figure and gravitationally) and encounters a series of tin arresting structures or flow obstructions 310 that resist the flow of the tin, eventually slowing the tin flow long enough for the tin to freeze and be captured as solidified tin on the plate 200.

[0082] In the embodiment shown, the obstructions 310 are in the form of a vertical series of zigzag walls or ridges 320, 330, and 340 establishing troughs or grooves between them. While in the example of FIG. 6A there are three such grooves, it will be appreciated that fewer or more grooves may be used. The angle between segments of the zigzag walls or ridges 320, 330, and 340 is selected to enhance stoppage of molten tin by, for example, permitting the molten tin to flow without excessively overtopping the ridges 320, 330, and 340.

[0083] According to another aspect of an embodiment, the top ridge 320, that is, the ridge first encountered by the molten tin after impinging and flowing on the landing zone 300, is broken with gaps 350 between at least some of its segments. These gaps 350 also serve to prevent molten tin from overtopping the top ridge 320 and instead direct the flow of molten tin through the grooves between the ridges 320, 330, and 340. This design allows for the possibility that the tin flow acquires momentum because the gaps in the groove wall provide a low resistance path to the next groove while dissipating some of the momentum of the tin flow due to the viscosity of the molten tin.

[0084] According to an aspect of an embodiment, the geometry of the obstructions on the plate 200 is determined so that the tin freezes on the plate 200 within the extent of the plate 200 in the gravitationally downward direction, e.g., about 30 mm. The surface thus configured can retain a substantial amount of tin in a low profile, i.e., a profile that does not impede the path of droplets transiting the conduit 112. It is preferable for some applications to configure the obstructions so that the tin does not build up in a single spot thermally shorting the plate 200 to proximate hot surfaces. According to another aspect of an embodiment the surface is configured to prevent tin from flowing along a path that avoids, i.e., “walks around” or meanders around the surface features intended to capture the tin.

[0085] FIG. 6B is a side cutaway view of the plate 200 taken along line BB of FIG. 6A. The plate 200 has a plate body 205 from which the ridges 320, 330, and 340 project. Representative dimensions for the plate are a plate body thickness C of approximately 1 mm, a ridge thickness D of approximately 0.5 mm, and a ridge projection length E of about 3 mm. It will be understood that these dimensions are representative only and that the dimensions employed in any given implementation will be selected according to the technical requirements of that implementation. In some embodiments the groove pitch may be 8 mm. In embodiments having one or more gaps between ridge wall segments, the width of the gap may be, for example, 3 mm.

[0086] The ridges may be configured as steps. The steps may be angled with respect to gravitationally horizontal. This may be achieved by angling the steps with respect to the plate 200 or by steps that project orthogonally from an angled plate, or by introducing angles in some combination of these arrangements. For example, FIG. 6C is a side cutaway view which is the same as the arrangement in FIG. 6B except that in FIG. 6C the plate body 205 is angled at an angle 0 with respect to vertical. For some implementations this enhances the ability of the ridges 320, 330, and 340 to arrest the flow of molten target material across the face of the plate body 200. The angle 0 may be, for example, in the range of approximately 5° to approximately 45° and more specifically in the range of approximately 10° to approximately 30°.

[0087] FIG. 7 shows an example of an arrangement in which both the plate 200 is angled with respect to vertical and the ridges 360 and 365 are angled with respect to the plate 200. This forms a hook-like arrangement as shown in FIG. 7. Molten tin flowing over the ridges of the plate 200 will solidify into a mass 370 and tend to form a complementary hook-like structure mechanically latched to the plate 200, thus additionally securing the mass 370.

[0088] The zigzag ridges of the embodiment just described are one example of a surface structure to capture tin. FIG. 8A shows an arrangement of circular indentations 400 arranged to capture tin flowing over the surface of the plate 200. The circular indentations 400 may have a larger or smaller radius than that of the circular indentations shown in the example of FIG. 8A. The circular indentations 400 as shown in FIG. 8A are arranged in a periodic array but a random arrangement may also be used. This is true for all of the periodic arrangements disclosed herein. FIG. 8B shows an arrangement of oblong indentations 420. Again, the oblong indentations 420 may have a larger or smaller height and/or width than shown in the example of FIG. 8B.

[0089] FIG. 9A shows an example of an arrangement of linear indentations 430 arranged to capture tin flowing over the surface of the plate 200. The indentations 430 can have various widths and depths. The indentations 430 may extend entirely across the length of the plate 200. Alternatively, the indentations 430 may be divided into segments 440 separated by gaps 445 as shown in FIG. 9B. The ga[s may be aligned as shown or may be unaligned, i.e., staggered with respect to each other. FIG. 10A shows an arrangement of ridges 460 back slanted from vertical by an angle 0’. The ridges may be back slanted as shown in FIG. 10A or forward slanted as shown as ridges 465 in FIG. 10B. The angle 0’ may be, for example, in the range of approximately 5° to approximately 45° and more specifically in the range of approximately 10° to approximately 30°. [0090] The arresting structures may have any one of a number of cross sectional shapes. For example, as shown in FIG. 1 IB, which is a cross section taken along line C-C of FIG. 11 A, each of the troughs 470 may have a square cross sectional profile. As shown in FIG. 11C, each of the troughs 480 may have an open (base up) trapezoidal cross section. As shown in FIG. 11D, each of the troughs 490 may have a triangular cross section separated by plateaus or flat portions. As shown in FIG. HE, each of the troughs 495 may have a triangular cross section with no intervening flat portions. It will be apparent that many other configurations are possible, and that these configurations may be combined according to the design considerations of a given application.

[0091] These engineered surface textures or topographies can be created using, for example, drilling, milling, or indentation techniques. The overall effect of engineering these surface topographies is to deliberately introduce structures that will slow and arrest the flow of molten tin across the surface. [0092] Other arrangements are possible. FIG. 12 is a perspective view of a portion of a plate 200 provided with an array of cylindrical structures 510. The spacing or pitch of the cylindrical structures 510 may be, for example, in a range of approximately .5 mm to approximately 7 mm.

[0093] FIG. 13A shows an arrangement having a vertical series of slits 520 with a gutter section 530 below each slit 520 raised from the surface in a “cheese grater” arrangement in which tin can flow through the slit 520 and down the back of the plate 200. FIG. 13B is a cutaway side view along line FF of the arrangement FIG. 13 A with the arrow indicating a possible direction of flow of tin encountering the tin landing above the broken line on the plate 200. FIG. 13C shows an arrangement similar to that FIG. 13 A except that the slits 540 of FIG. 13C are not continuous but instead broken up horizontally creating channels between the slits 540 for the flow of tin. It should be noted that the body 200 in the arrangements of FIGS. 13 A and 13C may be slanted similarly to the orientation of plate body 205 in FIG. 6C.

[0094] In addition to providing these structures of ridges and/or indentations on the surface of the plate 200 across which the tin flows, the surface can also be roughened to enhance the ability of the surface to slow the flow of tin. The roughening may be made by filing or etching and may be random or in a pattern. FIGS. 14A - 14F show various patterns which may be created. Thus, FIG. 14A shows a diagonal pattern for the surface of the plate 200. FIG. 14B shows a cross hatched pattern. Again, any of these patterns may be periodic and evenly spaced as shown, or may be more randomly distributed if, for example, they are formed by filing or scratching the surface of the plate 200. FIG. 14C shows a pattern running parallel to the length of the plate 200. FIG. 14D shows a pattern running transverse to the length of the surface of the plate 200. FIG. 14E shows a dense pattern of tracks running parallel to length of the surface of the plate 200. FIG. 14F shows a dense diamond pattern on the plate 200.

[0095] The plate 200 may be made of or coated with a material that rapidly forms an intermetallic bond with tin to promote the spreading of tin on the surface. These materials include aluminum, molybdenum, nickel, silver, and austenitic nickel-chromium-based superalloys such as Inconel® alloys. [0096] The plate 200 is described above primarily as being configured as an insert in a conduit. The plate 200 and conduit 112 may be configured to permit easy removal of the insert and replacement with a clean insert during servicing of the source. As mentioned, however, the obstructions may alternatively be integral with the sidewall of the conduit 112.

[0097] The plate 200 is also described above primarily as being used in a target material receptacle conduit. It will be apparent to one of ordinary skill in the art, however, that the benefits of the insert can also be obtained by placing a plate such as the plate 200 in other ports, conduits, apertures, and the like in which the uncontrolled accumulation of tin on interior surfaces could cause a blockage or other unwanted forms of tin accumulation. It will also be apparent to one of ordinary skill in the art that the benefits of the insert can also be obtained by placing the insert on other surfaces in which the uncontrolled accumulation of tin on the interior surfaces could cause tin spitting or tin breaking free of the surface and hitting the collector.

[0098] FIG. 15 shows another aspect of an embodiment. As can be seen, the conduit 112 can be tilted with respect to gravity (arrow G). According to an aspect of an embodiment, this angle may be in the range of approximately 20° to approximately 40°, e.g., 28°. Also shown in FIG. 15 is the temperature control plate 215 arranged to maintain the plate 200 at a temperature below the melting point of the target material. This permits the target material to flow along the direction of the arrow T but the target material will solidify on the plate 200 and be captured.

[0099] The conduit top element 225 is maintained above the target material melting temperature (for tin, 232°C) which prevents solidification of tin on the exposed roof surface to maintain a liquid tin layer. Tin debris impacting a bottom surface of the roof element 210 will join the liquid tin layer. After the liquid tin layer has accumulated a critical weight for tin flow, the tin starts flowing towards the edge of the roof plate 210 in the direction of arrow R. After accumulating enough tin on the edge at one location, the liquid tin drips off onto the landing zone on the plate 200 which captures the tin. [0100] Thus, as is also shown in FIG. 15, a conduit top element 225 is positioned below the roof element 210. According to an aspect of an embodiment, the top element 225 may have a bottom surface disposed at an angle with respect to the roof element 210 which adds to the angle with respect to gravity already present if the conduit 112 has a slanted orientation. The final angle 0” may be in the range of approximately 20° to approximately 40°, e.g., 32.5° with respect to horizontal. The angle permits molten target material collecting on the exposed surface of the top element 225 to flow off of the top element 225 and onto the plate 200. The top element 225 may be actively heated with its own heater or, as shown the top element may be heated passively by thermal contact with another heated surface, that is, the surface heated by temperature control plate 215. For the purposes of the discussion which follows, the sidewall with the plate 200 is referred to as the left sidewall 217 and the opposite sidewall is referred to as the right sidewall 219, “right” and “left” being viewed from the perspective of the entrance on the collector side of the conduit 112. Thus tin flow through the conduit from the vessel to the tin catch is into the plane of the figure. These references are supplied purely for the purpose of promoting clarity in the description that follows. One of ordinary skill in the art will appreciate that the designations are arbitrary. For example, the plate 200 could be provided on the right sidewall in some embodiments.

[0101] As mentioned above, the top element 225 may be actively heated with a dedicated heater or the top element 225 may be heated passively by thermal contact with another heated surface, for example, the surface heated by temperature control plate 215. FIG. 16 shows an example of a tin control insert defining a conduit 112 having a heated top plate 230. The left side wall 217 is not visible in FIG. 16 but is positioned beneath the plate 200 from the perspective of FIG. 16. The right side wall 219 is at the top from the perspective of FIG. 16. The top element 225 is not visible in FIG. 16 but is positioned behind the heated top plate 230 from the perspective of FIG. 16. According to an aspect of an embodiment, the top plate 230 is provided with drip features 250 intended to control the motion of tin along a top plate edge 231 which is disposed to extend parallel and adjacent to an edge 202 of the plate 200 to a selected section to control dripping onto the side plate 200. The drip features 250 also direct the flow of tin such that the tin accumulates as drops more quickly. The view of FIG.

16 is generally upward so that the bottom surface of the heated top plate 230 is visible. In the example of FIG. 16, the heated top plate 230 is actively heated by a heating wire 236 shown in phantom positioned inside of the heated top plate 230 to be in thermal contact with the bottom surface of the heated top plate 230. Tin that accumulates on the bottom surface of the heated top plate 230 flows sideways (generally downward in the figure in the direction of the arrow) onto the side plate 200 as described above.

[0102] The edge 231 of the bottom surface of the heated top plate 230 that runs generally parallel to a lengthwise edge 202 of the side plate 200 is provided with drip features 250 that control the flow of tin along and off of the edge 231 and onto the plate 200. According to one aspect, the drip features 250 are arranged to obstruct the flow of tin parallel to the edge of the side plate 200 and so potentially back out towards the collector. According to another aspect the drop features 250 define sites where tin can agglomerate and then fall onto the side plate 200.

[0103] As shown in FIG. 16 the drip features 250 are configured as a linear array of triangular elements. The triangular elements may be formed as depressions or notches made, for example, by milling. The base of each triangular element is arranged to coincide with the edge 231of the bottom surface 233 of the top plate 230. While these triangular elements are used as an example in the description that follows, one of ordinary skill in the art will appreciate that other shapes may be used. The triangular elements may have any suitable dimensions, such as, for example, a base length of about 6 mm and a depth of about 3 mm.

[0104] FIG. 17A is a plan view of the bottom surface 233 of the heated top plate 230. In the example of FIG. 17 A, again, the edge 231 of the bottom surface 233 of the heated top plate 230 that runs generally parallel to the lengthwise edge of the side plate 200 is provided with drip features 250 that control the flow of tin. The flow of tin is generally in the direction of the arrows T. As in FIG. 16 the drip features 250 are configured as a linear array of triangular elements. According to another aspect, the heated top plate 230 of FIG. 17A has a first section 232 positioned closer to the opening of the front of the insert (the collector side of the conduit) and a second section 234 positioned towards the back of the insert (the tin catch side of the conduit). This first section 232, which in general will have a line of sight to the collector, extends about, for example, 50mm.

[0105] As is more apparent from FIG. 17B, which is a side view of the heated top plate 230 taken from the perspective of the left hand side of the conduit 112. The first section 232 is angled with the front part of the first section 232 being higher when in position than the back part of the first section 232 so that molten tin striking and accumulating a tin flowing surface 235 on the first section 232 will tend to flow away from the entrance of the conduit and so away from vulnerable elements such as the collector optics.

[0106] FIG. 18A is an enlargement of the area 18 A in FIG. 17 A. According to an aspect, the drip features 250 meet at a connecting area 256. The connecting area 256 may be a vertex or may be an arc having a radius of curvature of around 0.5 mm and an angle 0 of about 90°. The flow of tin is generally in the direction of the arrow T. The surface of the drip features 250 may have a layer 252 of a material that tends to repel tin, i.e., that is tinphobic such as titanium nitride (TiN). The tinphilic surface promotes the adhesion of tin to the surface and the flow of tin across an angled overhanging edge. The surface of the top plate 230 other than the drip features 250 may have a layer 254 of a material that tends not to repel tin, i.e., that is tinphilic such as tin itself. This contributes to the effect of the drip features 250 to agglomerate tin in the apexes 258 of the triangular features thus making the apexes 258 effectively tin agglomeration sites where tin collects before falling onto the side plate 200. The boundary of the tinphilic surface and transition from tinphilic to tinphobic surface coatings promotes the agglomeration of the tin.

[0107] FIG. 18B is an enlargement of the area 18B in FIG. 17B. According to an aspect, the drip features 250 may have a depth of about 0.5 mm. Also visible in FIG. 18B is the layer 252 of a tinphobic material and the layer 254 of a tinphilic material.

[0108] FIG. 19 is a perspective view looking up at the top plate edge 231 from the perspective of the plate edge 202 (not shown) and illustrating a portion of the arrangement of drip features 250 The flow of tin is generally in the direction of the arrow T. Similar to what is shown in FIG. 16, the drip features 250 are configured as a linear array of triangular elements formed as depressions made, for example, by milling. The drip features 250 tend to agglomerate tin in the apexes 258 of the drip features 250 thus making the apexes 258 effectively tin agglomeration sites where tin such as tin mass 260 collects before falling onto the side plate 200. Also visible in FIG. 18B is the layer 252 of a tinphobic material and the layer 254 of a tinphilic material as well as the connecting area 256.

[0109] According to another aspect, the temperature of the heated top plate 230 has a gradient, i.e., the first section 232 (FIG. 17A) which has a line of sight with the collector is caused to have a lower temperature than the second section 234. This is because the tin spitting rate is a function of temperature and so the temperature of the first section 232 is kept lower to reduce spitting of tin that may have an unobstructed path to the collector. The first section 232 accordingly may have a temperature in the range of about 235°C to about 260°C and the second section 234 may have a temperature above the temperature of the first section in the range of about 250°C to about 330°C but other temperatures and relative temperatures may be used in other arrangements. Also, as mentioned, the first section 232 has a slight gravitationally upward angle. This ensures the molten tin accumulation tends to flow away from the line of sight of the collector, again to minimize spitting onto the collector. According to an aspect of an embodiment, the first section 232 is not provided with drip features 250 to avoid the accumulation of tin in the first section 232 instead of the preferred accumulation in the second section 234 which is farther from the interior of the chamber 26.

[0110] Also, according to an aspect, and as shown in FIG. 20, the top plate 230 and the side plate 200 are spaced apart to establish a gap G of, for example, at least 5mm. The flow of tin is generally in the direction of the arrow T. The gap G prevents molten tin from bridging between the top plate 230 and the side wall 200 and thus causing a thermal short.

[0111] The above description includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing these embodiments, but one of ordinary skill in the art will 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.

[0112] The implementations can be further described using the following clauses.

1. A conduit structure adapted to be placed in fluid communication with an interior of a chamber for an extreme ultraviolet (EUV) radiation source in which a target material is transformed, the conduit structure comprising at least one sidewall facing an interior of the conduit structure, at least a part of the sidewall being provided with a plurality of flow obstructions arranged to impede a flow of molten target material across the part of the sidewall.

2. The conduit structure of clause 1 further comprising a plate arranged to cover the at least a part of the sidewall, the plurality of flow obstructions being arranged on the plate.

3. The conduit structure of clause 1 wherein the plurality of flow obstructions comprises a plurality of codirectional ridges extending in a first direction at least partially through the conduit structure.

4. The conduit structure of clause 3 wherein one of the ridges is discontinuous. 5. The conduit structure of clause 3 wherein the ridges extend in a zigzag pattern with a first group of straight segments angled at a first angle with respect to the first direction alternating with a second group of straight segments angled at a second angle with respect to the first direction.

6. The conduit structure of clause 5 wherein one of the ridges is discontinuous.

7. The conduit structure of clause 1 wherein the at least one sidewall has a first sidewall edge extending in a first longitudinal direction and further comprising a top wall facing an interior of the conduit structure, the top wall being arranged to have a top wall edge extending in the first longitudinal direction substantially parallel to the first sidewall edge, the top wall edge having a plurality of edge features arranged to inhibit a flow of target material along the top wall edge in the first direction.

8. An extreme ultraviolet (EUV) radiation source including a chamber in which an EUV target material is transformed, the chamber having at least one conduit structure having a surface exposed to the EUV target material, wherein a first portion of the surface is arranged at a position at which molten target material encounters the first portion of the surface and arranged with an orientation so that gravity would tend to pull the molten target material in a first direction downward across the first portion of the surface, and a second portion of the surface below the first portion provided with a plurality of flow obstructions arranged to impede a flow of molten target material across the second portion in the first direction.

9. The EUV radiation source of clause 8 wherein the surface comprises a plate insert including the plurality of flow obstructions.

10. The EUV radiation source of clause 9 wherein the plate insert is maintained at a temperature lower than a melting temperature of the target material.

11. The EUV radiation source of clause 9 wherein the target material is tin and the plate insert is maintained at a temperature not greater than approximately 200°C.

12. The EUV radiation source of clause 8 wherein the plurality of flow obstructions comprises a plurality of codirectional ridges extending in a second direction substantially normal to the first direction.

13. The EUV radiation source of clause 12 wherein an uppermost one of the ridges is discontinuous.

14. The EUV radiation source of clause 8 wherein the ridges extend in a zigzag pattern with a first group of straight segments angled at a first angle with respect to the second direction alternating with a second group of straight segments angled at a second angle with respect to the second direction.

15. The EUV radiation source of clause 14 wherein an uppermost one of the ridges is discontinuous defining a plurality of gaps through the uppermost ridge.

16. The EUV radiation source of clause 8 further comprising a cooling flow ring arranged at least partially around a circumference of a collector mirror positioned in the chamber, the conduit structure being positioned in the cooling flow ring to provide a pathway between the interior of the chamber and a target material receptacle. 17. The EUV radiation source of clause 8 wherein the plurality of flow obstructions comprises a plurality of substantially circular indentations.

18. The EUV radiation source of clause 8 wherein the plurality of flow obstructions comprises a plurality of substantially rectangular indentations.

19. The EUV radiation source of clause 18 wherein the plurality of substantially rectangular indentations are coextensive with a length of the second portion of the surface.

20. The EUV radiation source of clause 19 wherein the plurality of substantially rectangular indentations are arranged in rows and columns in an array.

21. The EUV radiation source of clause 8 wherein the plurality of flow obstructions comprises a plurality of angled vanes located on the second portion.

22. The EUV radiation source of clause 8 wherein the plurality of flow obstructions comprises a plurality of elongated slits extending normal to the first direction with each slit having an associated gutter portion.

23. The EUV radiation source of clause 8 wherein at least a portion of the surface is roughened

24. The EUV radiation source of clause 8 further comprising a top surface element adjacent the surface and angled with respect to the surface and adapted and arranged to permit molten target material collecting on the top surface element to flow off of the top surface element and onto the surface.

25. An extreme ultraviolet (EUV) radiation source including a chamber and a target material receptacle in fluid communication with an interior of the chamber through a conduit, the conduit comprising a target material collection plate positioned to at least partially cover an interior surface of the conduit, the target material collection plate including a plurality of structures configured to impede a flow of molten target material across the plurality of structures and thus to permit the molten target material to solidify on the target material collection plate.

26. The EUV radiation source of clause 25 wherein the target material collection plate has a first target material collection plate edge extending in a first longitudinal direction and further comprising a top wall facing an interior of the conduit structure, the top wall being arranged to have a top wall edge extending in the first longitudinal direction substantially parallel to the first target material collection plate edge, the top wall edge having a plurality of edge features arranged to inhibit a flow of target material along the top wall edge in the first direction.

27. An extreme ultraviolet (EUV) radiation source including a chamber, the chamber including a surface at a position exposed to residual target material during generation of EUV radiation, the source comprising a target material collection plate at least partially covering the surface, a temperature controller configured to maintain the target material collection plate at a temperature below a melting temperature of the target material, the target material collection plate including a plurality of flow obstructions, the target material collection plate being oriented so that gravity would pull molten target material across the flow obstructions and the flow obstructions being oriented to arrest a flow of molten target material.

28. A conduit structure adapted to be placed in fluid communication with an interior of a chamber for an extreme ultraviolet (EUV) radiation source in which a target material is transformed, the conduit structure comprising: at least one sidewall facing an interior of the conduit structure, the at least one sidewall having a first sidewall edge extending in a first longitudinal direction and at least a part of the sidewall being provided with a plurality of flow obstructions extending substantially in the first longitudinal direction and arranged to impede a flow of molten target material across the part of the sidewall in a second direction different from the first direction; and a top wall facing an interior of the conduit structure, the top wall being arranged to have a top wall edge extending in the first longitudinal direction substantially parallel to the first sidewall edge, the top wall edge having a plurality of edge features arranged to inhibit a flow of target material along the top wall edge in the first longitudinal direction.

29. The conduit structure of clause 28 wherein the top wall is in thermal contact with a source of heat such that the top wall reaches a temperature greater than a melting temperature of the target material.

30. The conduit structure of clause 28 wherein the plurality of edge features comprises a plurality of depressions.

31. The conduit structure of clause 30 wherein the plurality of depressions is arranged in a linear array.

32. The conduit structure of clause 31 wherein each depression is substantially triangular with a base of the depression being positioned at the top wall edge.

33. The conduit structure of clause 30 wherein a surface of each depression is provided with a layer of tinphobic material.

34. The conduit structure of clause 33 wherein at least part of a surface of the top wall exclusive of the surfaces of the depressions is provided with a layer of tinphilic material.

35. The conduit structure of clause 33 wherein a surface of the top wall exclusive of the surfaces of the depressions is covered with a layer of tinphilic material.

36. The conduit structure of clause 28 further comprising a heating element in thermal contact with at least part of the top wall and arranged to maintain at least part of the top wall at a first temperature.

37. The conduit structure of clause 36 wherein the heating element is arranged to maintain a first portion of the top wall at the first temperature and to maintain a second portion of the top wall at a second temperature different from the first temperature.

38. An extreme ultraviolet (EUV) radiation source including a chamber in which an EUV target material is transformed, the chamber having at least one conduit structure, the conduit structure comprising a lateral side surface exposed to the EUV target material, wherein a first portion of the lateral side surface is arranged at a position at which molten target material flowing from a top surface of the conduit drips down onto the first portion of the lateral side surface and arranged with an orientation so that gravity would tend to pull the molten target material in a first direction downward across the first portion of the lateral side surface, and a second portion of the lateral side surface below the first portion provided with a plurality of flow obstructions arranged to impede a flow of molten target material across the second portion in the first direction, the lateral side surface having a first lateral side surface edge extending in a second direction; and the top surface being arranged to have a top surface edge extending in the second direction substantially parallel to first lateral side surface edge, the top wall surface having a plurality of edge features arranged to inhibit a flow of target material along the top surface edge in the second direction.

39. The EUV radiation source of clause 38 wherein the plurality of edge features comprises a plurality of depressions.

40. The EUV radiation source of clause 39 wherein the plurality of depressions is arranged in a linear array.

41. The EUV radiation source of clause 39 wherein each depression is substantially triangular with a base of the depression being positioned at the top wall edge.

42. The EUV radiation source of clause 39 wherein a surface of each depression is provided with a layer of tinphobic material.

43. The EUV radiation source of clause 42 wherein at least part of a surface of the top wall exclusive of the surfaces of the depressions is provided with a layer of tinphilic material.

44. The conduit structure of clause 38 further comprising a heating element in thermal contact with at least part of the top wall and arranged to maintain at least part of the top wall at a first temperature.

45. The EUV radiation source of clause 44 wherein the heating element is arranged to maintain a first portion of the top wall at the first temperature and to maintain a second portion of the top wall at a second temperature different from the first temperature.

[0113] The above described implementations and other implementations are within the scope of the following claims.

Claims

23 CLAIMS

2. The conduit structure of claim 1 further comprising a plate arranged to cover the at least a part of the sidewall, the plurality of flow obstructions being arranged on the plate.

3. The conduit structure of claim 1 wherein the plurality of flow obstructions comprises a plurality of codirectional ridges extending in a first direction at least partially through the conduit structure.

4. The conduit structure of claim 3 wherein one of the ridges is discontinuous.

5. The conduit structure of claim 3 wherein the ridges extend in a zigzag pattern with a first group of straight segments angled at a first angle with respect to the first direction alternating with a second group of straight segments angled at a second angle with respect to the first direction.

6. The conduit structure of claim 5 wherein one of the ridges is discontinuous.

7. The conduit structure of claim 1 wherein the at least one side wall has a first sidewall edge extending in a first longitudinal direction and further comprising a top wall facing an interior of the conduit structure, the top wall being arranged to have a top wall edge extending in the first longitudinal direction substantially parallel to the first sidewall edge, the top wall edge having a plurality of edge features arranged to inhibit a flow of target material along the top wall edge in the first direction.

9. The EUV radiation source of claim 8 wherein the surface comprises a plate insert including the plurality of flow obstructions.

10. The EUV radiation source of claim 9 wherein the plate insert is maintained at a temperature lower than a melting temperature of the target material.

11. The EUV radiation source of claim 9 wherein the target material is tin and the plate insert is maintained at a temperature not greater than approximately 200°C.

12. The EUV radiation source of claim 8 wherein the plurality of flow obstructions comprises a plurality of codirectional ridges extending in a second direction substantially normal to the first direction.

13. The EUV radiation source of claim 12 wherein an uppermost one of the ridges is discontinuous.

14. The EUV radiation source of claim 8 wherein the ridges extend in a zigzag pattern with a first group of straight segments angled at a first angle with respect to the second direction alternating with a second group of straight segments angled at a second angle with respect to the second direction.

15. The EUV radiation source of claim 14 wherein an uppermost one of the ridges is discontinuous defining a plurality of gaps through the uppermost ridge.

16. The EUV radiation source of claim 8 further comprising a cooling flow ring arranged at least partially around a circumference of a collector mirror positioned in the chamber, the conduit structure being positioned in the cooling flow ring to provide a pathway between the interior of the chamber and a target material receptacle.

17. The EUV radiation source of claim 8 wherein the plurality of flow obstructions comprises a plurality of substantially circular indentations.

18. The EUV radiation source of claim 8 wherein the plurality of flow obstructions comprises a plurality of substantially rectangular indentations.

19. The EUV radiation source of claim 18 wherein the plurality of substantially rectangular indentations are coextensive with a length of the second portion of the surface.

20. The EUV radiation source of claim 19 wherein the plurality of substantially rectangular indentations are arranged in rows and columns in an array.

21. The EUV radiation source of claim 8 wherein the plurality of flow obstructions comprises a plurality of angled vanes located on the second portion.

22. The EUV radiation source of claim 8 wherein the plurality of flow obstructions comprises a plurality of elongated slits extending normal to the first direction with each slit having an associated gutter portion.

23. The EUV radiation source of claim 8 wherein at least a portion of the surface is roughened.

24. The EUV radiation source of claim 8 further comprising a top surface element adjacent the surface and angled with respect to the surface and adapted and arranged to permit molten target material collecting on the top surface element to flow off of the top surface element and onto the surface.

26. The EUV radiation source of claim 25 wherein the target material collection plate has a first target material collection plate edge extending in a first longitudinal direction and further comprising a top wall facing an interior of the conduit structure, the top wall being arranged to have a top wall edge extending in the first longitudinal direction substantially parallel to the first target material collection plate edge, the top wall edge having a plurality of edge features arranged to inhibit a flow of target material along the top wall edge in the first direction. 26

29. The conduit structure of claim 28 wherein the top wall is in thermal contact with a source of heat such that the top wall reaches a temperature greater than a melting temperature of the target material.

30. The conduit structure of claim 28 wherein the plurality of edge features comprises a plurality of depressions.

31. The conduit structure of claim 30 wherein the plurality of depressions is arranged in a linear array.

32. The conduit structure of claim 31 wherein each depression is substantially triangular with a base of the depression being positioned at the top wall edge. 27

33. The conduit structure of claim 30 wherein a surface of each depression is provided with a layer of tinphobic material.

34. The conduit structure of claim 33 wherein at least part of a surface of the top wall exclusive of the surfaces of the depressions is provided with a layer of tinphilic material.

35. The conduit structure of claim 33 wherein a surface of the top wall exclusive of the surfaces of the depressions is covered with a layer of tinphilic material.

36. The conduit structure of claim 28 further comprising a heating element in thermal contact with at least part of the top wall and arranged to maintain at least part of the top wall at a first temperature.

37. The conduit structure of claim 36 wherein the heating element is arranged to maintain a first portion of the top wall at the first temperature and to maintain a second portion of the top wall at a second temperature different from the first temperature.

39. The EUV radiation source of claim 38 wherein the plurality of edge features comprises a plurality of depressions. 28

40. The EUV radiation source of claim 39 wherein the plurality of depressions is arranged in a linear array.

41. The EUV radiation source of claim 39 wherein each depression is substantially triangular with a base of the depression being positioned at the top wall edge.

42. The EUV radiation source of claim 39 wherein a surface of each depression is provided with a layer of tinphobic material.

43. The EUV radiation source of claim 42 wherein at least part of a surface of the top wall exclusive of the surfaces of the depressions is provided with a layer of tinphilic material.

44. The conduit structure of claim 38 further comprising a heating element in thermal contact with at least part of the top wall and arranged to maintain at least part of the top wall at a first temperature.

45. The EUV radiation source of claim 44 wherein the heating element is arranged to maintain a first portion of the top wall at the first temperature and to maintain a second portion of the top wall at a second temperature different from the first temperature.