Target supply system

Abstract

A target supply system for a radiation source, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module. The bleed module comprises: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel; wherein the configurable connector is switchable between a number of connector configurations, comprising: an operational configuration, wherein fluid passage through the conduit is permitted and fluid passage into the vessel is not permitted; and a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel.

Description

TARGET SUPPLY SYSTEMCROSS REFERENCE TO EARLIER APPLICATIONS

[0001] This application claims priority of application No. EP 24174863.1, filed 8 May 2024.FIELD

[0002] The present invention relates to a target supply system for a radiation source, in particular an electromagnetic radiation source, such as a laser produced plasma radiation source and / or an EUV radiation source. In another aspect, the present invention relates to a method of removing liquid target material from a target supply system. The laser produced plasma radiation source may form part of an extreme ultraviolet (EUV) exposure apparatus.BACKGROUND

[0003] Light generated by means of a radiation source can be used by exposure apparatuses for semiconductor manufacturing processes. Examples of such exposure apparatuses are a lithographic apparatus, a metrology, or an inspection apparatus, more specifically a mask inspection apparatus and even more specifically an actinic mask inspection apparatus.

[0004] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (e.g., a photoresist or resist) provided on a substrate. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses EUV radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] An (actinic) mask inspection apparatus is an apparatus that is configured for measuring dimensions or detecting defects in masks or mask blanks. EUV lithography uses a reflective surfaces instead of a lenses as optics. Mask blanks used in EUV lithography generally have a multilayer structure which functions as a Bragg reflector, the multilayers may be altematingly Molybdenum and Silicon. If a defect exists in this structure, the projected pattern will be deformed in the lithographic process. Therefore, mask inspection to check whether a defect is present is considered a requirement for a massproduction process. EUV mask inspection may be used for several purposes and in several different stages. Firstly, it can be used for the detection of phase defects that may occur in mask blanks. Such phase defects may occur during the manufacturing of the multilayer stack of the mask blank. If undetected, these phase defects are printed on all chips printed with the part of a mask containing the phase defects. Such phase defects may be correctly detected by using the same or similar (13.5nm)actinic EUV wavelength as the lithography tool. Secondly, mask inspection can be used for patterned mask inspection and can be carried out for the quality control of EUV patterned masks. For example, the mask inspection can be used to measure critical dimensions on the mask blank. In addition to phase defects, absorber pattern defects on the surface can be detected. Thirdly, mask inspection can be used for simulating exposure and determining the deterioration of optical contrast of a defect detected in the actinic inspection. Forth, the mask inspection can be used for optical proximity correction (OPC) evaluation or during mask repair process so as to improve pattern transfer fidelity. Further, it can be used for inspecting optical contrast after fixing the defect. In addition to the above, mask inspection can also be used to measure small particle / amplitude effects.

[0006] In the above-mentioned applications, EUV radiation may be generated by a laser produced plasma (LPP) radiation source. LPP radiation sources comprise a system for supplying a target material (e.g. liquid tin) for plasma generation. An example of such a system is disclosed in US 2022 / 0159871 A 1. WO 2023 / 089082 A 1 discloses a hydraulic system for supplying liquid target material to a radiation source.

[0007] During servicing or modification, liquid target material may be removed or pushed out of selected portions of a target material supply system - e.g. to allow removal / installation / modification of components.

[0008] In addition, as part of servicing or modification, at least a part of the target material supply system may be subjected to a check for leaks. Gas is injected into at least a part of the target supply system, and sensors are provided to detect emission of the gas (indicating a leak). In order to carry out the aforementioned leak check, the relevant part of the target material supply system needs to have liquid target material removed or pushed out.

[0009] Typically, in existing systems the removal of liquid target material is achieved by use of a purge gas. The purge gas displaces target material out of selected components into surrounding components. The purged target material may comprise gas bubbles and or oxidized material due to exposure to the atmosphere and / or purge gas. Subsequent use of such purged target material can cause damage to the surrounding components of the target material supply system. In particular, where portions of the target material supply system comprise hydraulic components, gas in the target material is particularly detrimental. The compressibility of gas compromises hydraulic operation, by preventing effective hydraulic response.SUMMARY

[0010] According to a first aspect there is provided a target supply system for a radiation source, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module, the bleed module comprising: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel; wherein the configurable connector is switchablebetween a number of connector configurations, comprising: an operational configuration, wherein fluid passage through the conduit is permitted; and a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel.

[0011] Provision of a bleed module avoids the re-introduction of contaminated target material along with gas into the target supply system after servicing or modification. This particularly advantageous in systems where the pressure module is hydraulic, due to the sensitivity of hydraulic systems to gas.

[0012] Additionally, in the operational configuration fluid passage into the vessel may not be permitted.

[0013] The radiation source may be an electromagnetic radiation source, configured to produce electromagnetic radiation. In particular, the (electromagnetic) radiation source may be a laser produced plasma radiation source. The (electromagnetic) radiation may comprise EUV radiation.

[0014] The target supply system may further comprise a vacuum source connectable to the vessel at a vessel side of the configurable connector. For example, the bleed module may comprise a vacuum source, in fluid communication with the vessel. Alternatively, the bleed module may comprise a connector, configured to connect to an external vacuum source.

[0015] The conduit may be an outlet conduit of the pressure module. This way, the bleed vessel can receive target material which is being removed from components in the target supply system downstream of the pressure module, without a need to bring the target material (and / or gas) back into the pressure module.

[0016] The target supply system may further comprise a fuel generator connected to the outlet conduit.

[0017] The conduit may be an inlet conduit of the pressure module. This way, the bleed vessel can receive target material which is being removed from components in the target supply system upstream of the pressure module, without a need to bring that target material (and / or gas) into the pressure module.

[0018] The target supply system may further comprise a refill module, configured to supply liquid target material to the pressure module, connected to the inlet conduit.

[0019] The pressure module may be hydraulically pressurised.

[0020] The configurable connector may comprise a freeze valve, the freeze valve comprising: a valve conduit, configured to carry liquid target material; and a heat exchange device disposed adjacent to the valve conduit; wherein the heat exchange device is configured to selectively solidify liquid target material in the valve conduit so as to stop flow through the valve conduit.

[0021] Advantageously, the freeze valve does not comprise moving parts, which would be liable to damage during target material phase changes.

[0022] The configurable connector may comprise three freeze valves joined at a 3-way junction, wherein a first and a second freeze valve connect to the conduit and a third freeze valve connects to the vessel.

[0023] The valve conduit may comprise a change in cross section.

[0024] The change in cross-section allows a solid plug formed during valve closure to more effective resist pressure.

[0025] The freeze valve may further comprise a gas connection, configured to selectively permit passage of gas in or out of the freeze valve.

[0026] The vessel of the bleed module may comprise a heating system, configured to melt any target material contained in the vessel.

[0027] The vessel may be substantially composed of a stainless steel.

[0028] The vessel may be coated on an interior surface with a tin-phobic coating.

[0029] Advantageously a coated stainless steel construction reduces the production cost of the vessel and allows compliance with well-known pressure vessel standards.

[0030] According to a second aspect there is provided a method of removing liquid target material from a target supply system for a laser produced plasma source, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module, the bleed module comprising: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel; wherein the method comprises: switching the configurable connector from an operational configuration, permitting fluid passage though the conduit, to a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel; purging the target material in a portion of the conduit into the vessel with a gas.

[0031] Said method of removing liquid target material may be comprised in a method of disassembling the target supply system.

[0032] The target supply system may further comprise one or more components in fluid communication with the conduit; and the method may further comprise: purging the target material in at least one of the one or more components into the vessel with a gas; and detaching the at least one of the one or more components.

[0033] According to a third aspect there is provided a laser produced plasma radiation source comprising a target supply system according to the first aspect. The target supply system may comprise any of the optional features above.

[0034] According to a fourth aspect there is provided an exposure apparatus comprising a laser produced plasma radiation source according to the third aspect.BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2 depicts a system for (actinic) mask inspectionFigure 3 schematically illustrates a target material supply system;Figure 4 schematically illustrates a bleed module suitable for use in the target material supply system of Figure 3;Figure 5A is a schematic cross-section of a freeze valve;Figure 5B is a schematic cross-section of a another freeze valve; and Figure 6 is a schematic cross-section of a service freeze valve.DETAILED DESCRIPTION

[0036] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[0037] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0038] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13,14 in Figure 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0039] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[0040] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and / or in the projection system PS.

[0041] The lithographic apparatus LA and radiation source SO described herein can be used in method for performing a circuit layout patterning process. A circuit layout patterning method comprises receiving a substrate with a photoresist layer. The method further comprises directing EUV radiation from radiation source to the photoresist layer to form a patterned photoresist layer. The method further comprises developing and etching the patterned photoresist layer to form a circuit layout.

[0042] Figure 2 depicts a system for (actinic) mask inspection. A mask inspection system can be used to identify or inspect defects in a mask to be used in a lithographic process by means of an apparatus described in figure 1. The mask inspection system comprises a radiation source SO (which may be equivalent to the radiation source of Figure 1 ) and an illumination system 22 and a detection system 24. A mask MA is placed on a mask stage 26 and illuminated by the illumination system 22 reflecting radiation incident from the radiation source SO. The radiation coming from the illuminated mask MA is reflected by the detection system 24. In this way an image is formed on a detector 28.

[0043] The radiation source SO shown in Figure 1 and / or Figure 2 may be examples of a type which may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel (i.e., a target material), such as tin (Sn) which is provided from, e.g., a fuel generator 3. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form, and may, for example, be a metal or alloy. The fuel generator 3 may comprise a nozzle configured to direct the fuel, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the fuel at the plasma formation region 4. The deposition of laser energy into the tin creates a plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of electrons with ions of the plasma 7.

[0044] The EUV radiation from the plasma 7 is collected and focused by a collector 5. Collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes referred to more generally as a normal -incidence radiation collector). The collector 5 may have a multilayer mirror structure which is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two focal points. A first one of the focal points may be at the plasma formation region 4, and a second one of the focal points may be at an intermediate focus 6, as discussed below.

[0045] The laser system 1 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and / or a beam expander, and / or other optics. The laser system 1, the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[0046] Radiation that is reflected by the collector 5 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image at the intermediate focus 6 of theplasma present at the plasma formation region 4. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9 of the radiation source SO.

[0047] Figure 3 schematically illustrates a target supply system 30 for a laser produced plasma source. The target supply system comprises: a pressure module 32, an inlet conduit 34, an outlet conduit 36, and a bleed module 40. Target supply system may form a part of the radiation source SO of the lithographic system of Figure 1 and / or the radiation source SO of the mask inspection system of Figure 2, or any other type of (EUV) exposure apparatus.

[0048] The pressure module 32 is configured to pressurize a liquid target material. The target material may be tin (Sn). Target material entering an inlet of pressure module 32 exits at an outlet of pressure module 32 at a required pressure.

[0049] The inlet conduit 34 and the outlet conduit 36 are both configured to carry liquid target material, and are fluidly connected to the pressure module 32. The inlet conduit 34 is connected to the inlet of the pressure module 32. The outlet conduit 36 is connected to the outlet of the pressure module 32.

[0050] The outlet conduit may comprise an upstream component 36a, connected to the pressure module 32, and a downstream component 36b, connected to the fuel generator 3. The upstream component 36a and the downstream component 36b are configured to disconnect - for example, during maintenance.

[0051] The terms ‘downstream’ and ‘upstream’ are used here with reference to the orientation of fluid flow in normal operation of target supply system 30 - that is, from the pressure module 32 toward the fuel generator 3.

[0052] In some embodiments, the pressure module 32 comprises a hydraulic bellows system, configured to pressurize the liquid target material. A nonlimiting example is disclosed in WO 2023 / 089082 Al.

[0053] The bleed module 40 comprises a vessel 42, a configurable connector 44, and a vacuum source 46.

[0054] Configurable connector 44 is provided inline with the outlet conduit 36. Configurable connector 44 is connected with the vessel 42. The configurable connector 44 is provided adjacent to the disconnection point of the upstream component 36a and the downstream component 36b. The configurable connector may be provided upstream or downstream of the disconnection point of the upstream component 36a and the downstream component 36b, because tin may be pushed in either direction, pulling a vacuum from the upstream or downstream direction, respectively.

[0055] The vacuum source 46 is in fluid communication with the vessel. The vacuum source 46 may be a utility provided by the broader lithographic system or exposure apparatus.

[0056] The configurable connector 44 is switchable between a number of connector configurations, comprising an operational configuration and a bleed configuration. In the operational configuration fluid passage through the outlet conduit 36 is permitted. Additionally, in the operational configurationfluid passage into the vessel 42 is not permitted. In the bleed configuration a portion of the conduit 36 is in fluid communication with the vessel 42. In an example, in the operational configuration, the portion 36b of the outlet conduit 36 downstream of the configurable connector 44 may be in fluid communication with the vessel 42.

[0057] The target supply system 30 further comprises a fuel generator 3 connected to the outlet conduit 36. The fuel generator 3 may also be referred to as the fuel generator. Fuel generator 3 is connected at the downstream end of the outlet conduit 36.

[0058] The target supply system 30 further comprises a refill module 38, configured to supply liquid target material to the pressure module 32, connected to the inlet conduit 34.

[0059] Additionally, or alternatively, a bleed module 41 may be provided at the inlet conduit 34. The bleed module 41 is substantially the same as the bleed module 40 described above, differing only in that the configurable connector 44 is provided inline with the inlet conduit 34. In some embodiments, a bleed module may be provided adjacent to the pressure module 32 at its inlet and / or outlet. A bleed module may be placed at any suitable location along a fluid path of the target supply system 30.

[0060] In some embodiments, target material may be fed into the target supply system 30 in the form of solid ingots at the refill module 38. The refill module may be configured to melt the target material and condition it for use downstream (e.g. in the pressure module 32).

[0061] Figure 4 shows a schematic cross-section of the bleed module 40. The bleed module 40 comprises a vessel 42, a configurable connector 44, a vacuum source 46 and a heating system 48.

[0062] The vessel 42 may be substantially composed of stainless steel. The vessel 42 may be coated on an interior surface with a tin-phobic coating 43. The term tin-phobic here is intended to denote materials which are not easily wetted by liquid tin. The aforementioned coated stainless steel construction reduces the production cost of the vessel, without unduly compromising resistance to tin corrosion, and allows ready compliance with well-known pressure vessel standards (e.g. American Society of Mechanical Engineers standards).

[0063] In an example, the vessel 42 may be able to contain at least around 100ml of target material. The vessel 42 may be able to contain up to around 200ml of target material.

[0064] The vessel 42 of the bleed module comprises a heating system 48, configured to melt any target material (e.g. tin) contained in the vessel 42. In an example, the heating system 48 may comprise an electrical heating jacket or any other type of heating element, such as a rod heater or wire element.

[0065] The possible modes of fluid flow (described in relation to Figure 3) in the bleed module 40 and adjacent portions of the conduit 36 are indicated by arrows in Figure 4.

[0066] The configurable connector comprises freeze valves. The configurable connector comprises three freeze valves 50a, 50b, 50c. The freeze valves 50a, 50b, 50c are joined at a 3 -way junction. A first freeze valve 50a and a second freeze valve 50b connect to the conduit 36 and a third freeze valve 50c connects to the vessel 42. The first freeze valve 50a connects to the downstream component 36b. The second freeze valve 50b connects to the upstream component 36a.

[0067] In some embodiments, the bleed module may be provided at the end of a line or conduit instead of inline with a line or conduit. For example, the bleed module may be provided at one of the ends of a junction. In such embodiments, the configurable connector may comprise only a single freeze valve. In other embodiments, the configurable connector may comprise two, four, five or any other number of freeze valves.

[0068] Freeze valves are configured to selectively stop or permit flow. In an alternative any valve capable of selectively stopping or permitting flow may be used. Freeze valves will be described in more detail below.

[0069] The vacuum source 46 may be used to draw target material into the vessel 42, and / or to assist evacuating the target supply system of gas.

[0070] The bleed module 41 provided at the inlet conduit 34 is substantially the same as bleed module 40, differing only in its placement along the inlet conduit 34, as opposed to the outlet conduit 36. Reference will be made to sub-components of bleed module 41 using the same reference numerals as those used with reference to bleed module 40.

[0071] Returning to Figure 3 - in use, target supply system 30 may need to be serviced or modified. For example, during the lifetime of the tin supply system 30, the fuel generator 3 may require replacement multiple times. During servicing actions of a component, the residual tin in adjacent connections (e.g. inlet conduit 34 or outlet conduit 36) is purged by means of a purge gas. The gas may be substantially composed of argon and / or hydrogen.

[0072] In an example, during a swap of the fuel generator 3, the residual tin in the outlet conduit 36 between disconnection point / configurable connector 44 of the bleed module 40 and the fuel generator 3 may be pushed by means of a purge gas through the conduit into the vessel 42 of the bleed module 40. In order to push the residual tin into the vessel 42, the vessel and conduit 36 are in fluid communication. Put alternatively, the configurable connector 44 is switched to the bleed configuration and the target material in a portion of the conduit 36 is purged with a gas into the vessel 42. In this example, in the bleed configuration, first and third freeze valves 50a, 50c are open and second freeze valve 50b is blocked.

[0073] Alternatively, or additionally, the refill module 38 may need to be serviced or modified, the residual tin in the inlet conduit 34 between the bleed module 41 and the refill module 38 may be pushed by means of a purge gas through (an upstream portion of) the inlet conduit into the vessel 42 of the bleed module 41. The configurable connector 44 is switched to the bleed configuration and the target material in a portion of the conduit 34 is purged with a gas into the vessel 42. In this example, in the bleed configuration, second and third freeze valves 50b, 50c are open and first freeze valve 50a is blocked, such that tin upstream of the bleed module 41 can enter the vessel 42.

[0074] In some embodiments, purging the target material as described above, will also purge target material in at least one of the one or more components in fluid communication with the conduit 36 (e.g. fuel generator 3) into the vessel with a gas.

[0075] By purging at least, a portion of the target supply system upstream or downstream of the purge module 40 (or purge module 41), the target supply system can be conditioned fortesting, removal and / or replacement of components.

[0076] By purging the residual tin into the vessel 42 of the bleed module 40, the reintroduction of potentially contaminated residual tin into (components of) the target supply system may be avoided. Instead, pure tin may be replenished through the normal procedure via the refill module 38.

[0077] Figure 5A schematically shows a cross-section through a freeze valve 51. The freeze valve 51 comprises a valve conduit 52, configured to carry liquid target material, and a heat exchange device 54 disposed adjacent to the valve conduit. The heat exchange device 54 is configured to selectively change the phase of liquid target material 56 in the valve conduit 52. The liquid target material 56 in the valve conduit 52 is solidified so as to stop flow through the valve conduit, and solidified target material in the valve conduit may be liquefied (e.g. by adding heat to the solid plug) to enable flow through the valve conduit.

[0078] In use, liquid target material 56 can freely flow through the valve conduit 52. When it is desired to stop flow through the valve conduit 52, the heat exchange device 54 is actuated, lowering the temperature of, and solidifying liquid target material in an adjacent region 58 of the conduit into a solid plug. The solid plug at region 58 blocks the valve conduit 52, stopping flow.

[0079] In some embodiments heat exchange device 54 may comprise a heater. As such, when flow is stopped, the heater is turned off.

[0080] Additionally, or alternatively, heat exchange device 54 may comprise a cooler. As such, when flow is stopped, the cooler is turned on. The cooler may comprise both an air cooling (e.g. cooling fins) and water cooling system - the cooling system can reduce the lag time for the freeze valve to block flow, by increasing the rate at which heat is removed, reducing the time to block flow.

[0081] Figure 5B schematically shows a cross-section through an alternative freeze valve 60. Freeze valve 60 is very similar to freeze valve 51 - in the interests of brevity, only the differences between freeze valve 51 and 60 will be described. Freeze valve 51 of Figure 5A has a substantially constant cross section. Freeze valve 60 of Figure 5B differs in that the cross-section of the valve conduit 52 changes at section X-X near the heater adjacent region 58. The upstream side is larger in cross section than the downstream side, such that a solid plug formed at adjacent region 58 resists displacement due a shoulder interface 59 and resists leaks.

[0082] The freeze valve does not comprise moving parts, which would be liable to damage during target material phase changes.

[0083] The section shown in Figure 5B is shown only for illustration, different changes in cross section may be employed to achieve an equivalent effect. For example, the valve conduit could incorporate a converging - diverging section.

[0084] In the embodiments of target supply system above, purge gas is used to purge residual target material. In addition, gas may be used to check for leaks in the target supply system. In order to introduce gas into the system, service freeze valves may be provided.

[0085] Figure 6 schematically illustrates a service freeze valve 70. Freeze valve 70 is very similar to previously-described freeze valves 51, 60- in the interests of brevity, only the differences between freeze valve 70 and 51 / 60 will be described. Freeze valve further comprises a gas section 62. The gas section comprises a gas connection 63, a heat exchange system 64 and (optionally) cooling fins 66. The gas connection allows the introduction of gas, such as purge gas, into the target supply system via the valve conduit 52. The heat exchange system 64 allows the gas connection 63 to be blocked in a similar to fashion to the heat exchanger system 54 adjacent to the valve conduit 52. The cooling fins 66 increase the speed of heat removal, allowing faster formation of a solid plug to block the gas section 62. The gas connection 63 may be also used to introduce gas into the target supply system in order to check for leaks.

[0086] In some embodiments, the above-described freeze valves may be substantially composed of a tin corrosion-resistant material such as tantalum-tungsten alloys or tungsten.

[0087] In general, freeze valves may be configured to resist pressures of up to around 1400bar.

[0088] Clauses1. A target supply system for a radiation source, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module, the bleed module comprising: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel; wherein the configurable connector is switchable between a number of connector configurations, comprising: an operational configuration, wherein fluid passage through the conduit is permitted; and a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel.2. The target supply system of clause 1, further comprising a vacuum source connectable to the vessel at a vessel side of the configurable connector.3. The target supply system of clause 1, wherein the bleed module further comprises a vacuum source, in fluid communication with the vessel.4. The target supply system of clause 1, wherein the bleed module comprises a connector configured to connect to an external vacuum source.5. The target supply system of any of clauses 1 to 4, wherein the conduit is an outlet conduit of the pressure module.6. The target supply system of clause 5, wherein the target supply system further comprises a fuel generator connected to the outlet conduit.7. The target supply system of any of clauses 1 to 4, wherein the conduit is an inlet conduit of the pressure module.8. The target supply system of clause 7, wherein the target supply system further comprises a refill module, configured to supply liquid target material to the pressure module, connected to the inlet conduit.9. The target supply system of any preceding clause, wherein the pressure module is hydraulically pressurised.10. The target supply system of any preceding clause, wherein the configurable connector comprises a freeze valve, the freeze valve comprising: a valve conduit, configured to carry liquid target material; and a heat exchange device disposed adjacent to the valve conduit; wherein the heat exchange device is configured to selectively solidify liquid target material in the valve conduit so as to stop flow through the valve conduit.11. The target supply system of any preceding clause, wherein the configurable connector comprises three freeze valves joined at a 3 -way junction, wherein a first and a second freeze valve connect to the conduit and a third freeze valve connects to the vessel.12. The target supply system of clause 10 or 11, wherein the valve conduit comprises a change in cross section.13. The target supply system of any preceding clause, wherein the vessel of the bleed module comprises a heating system, configured to melt any target material contained in the vessel.14. The target supply system of any preceding clause, wherein the vessel is substantially composed of a stainless steel.15. The target supply system of clause 14, wherein the vessel is coated on an interior surface with a tinphobic coating.16. The target supply system of any of the preceding clauses, wherein in the operational configuration fluid passage into the vessel is not permitted.17. The target supply system of any of the preceding clauses, wherein the radiation source is an electromagnetic radiation source.18. The target supply system of any of the preceding clauses, wherein the radiation source is a laser produced plasma radiation source.19. A method of disassembling a target supply system for a laser produced plasma source, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module, the bleed module comprising: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel;wherein the method comprises: switching the configurable connector from an operational configuration, permitting fluid passage though the conduit, to a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel; purging the target material in a portion of the conduit into the vessel with a gas.20. The method of disassembling a target supply system according to clause 19, wherein the target supply system further comprises one or more components in fluid communication with the conduit; and the method further comprises: purging the target material in at least one of the one or more components into the vessel with a gas; and detaching the at least one of the one or more components.21. The method of clause 19 or 20, wherein in the operational configuration fluid passage into the vessel is prohibited.22. A method of removing liquid target material from a target supply system, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module, the bleed module comprising: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel; wherein the method comprises: switching the configurable connector from an operational configuration, wherein permitting fluid passage though the conduit, to a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel; purging the target material in the portion of the conduit into the vessel with a gas.23. The method of clause 22, wherein the target supply system further comprises one or more components in fluid communication with the conduit; and the method further comprises: purging the target material in at least one of the one or more components into the vessel with a gas; and detaching the at least one of the one or more components.24. The method of clause 22 or 23, wherein in the operational configuration fluid passage into the vessel is prohibited.25. The method of any of clauses 22 to 24, wherein the target supply system is for a radiation source.26. The method of any clause 25, wherein the radiation source is an electromagnetic radiation source.27. The method of clause 25 or 26, wherein the radiation source is a laser produced plasma radiation source.28. A laser produced plasma radiation source comprising a target supply system according to any of clauses 1 to 18.29. An exposure apparatus comprising a laser produced plasma radiation source according to clause 28.

[0089] Although specific reference has been made to use of the above -de scribed bleed module and target supply system in the context of LPP radiation sources, the above-described bleed module and target supply system may also be used in a discharge produced plasma (DPP) radiation source.

[0090] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.

[0091] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrates) or mask (or other patterning devices). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[0092] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A target supply system for a radiation source, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module, the bleed module comprising: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel; wherein the configurable connector is switchable between a number of connector configurations, comprising: an operational configuration, wherein fluid passage through the conduit is permitted and fluid passage into the vessel is not permitted; and a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel.

2. The target supply system of claim 1, further comprising a vacuum source connectable to the vessel at a vessel side of the configurable connector.

3. The target supply system of claim 1 or 2, wherein the conduit is an outlet conduit of the pressure module.

4. The target supply system of claim 3, wherein the target supply system further comprises a fuel generator connected to the outlet conduit.

5. The target supply system of claim 1 or 2, wherein the conduit is an inlet conduit of the pressure module.

6. The target supply system of claim 5, wherein the target supply system further comprises a refill module, connected to the inlet conduit, configured to supply liquid target material to the pressure module.

7. The target supply system of any preceding claim, wherein the pressure module is hydraulically pressurised.

8. The target supply system of any preceding claim, wherein the configurable connector comprises a freeze valve, the freeze valve comprising: a valve conduit, configured to carry liquid target material; and a heat exchange device disposed adjacent to the valve conduit; wherein the heat exchange device is configured to selectively solidify liquid target material in the valve conduit so as to stop flow through the valve conduit.

9. The target supply system of claim 8, wherein the valve conduit comprises a change in cross section.

10. The target supply system of any preceding claim, wherein the configurable connector comprises three freeze valves joined at a 3 -way junction, wherein a first and a second freeze valve connect to the conduit and a third freeze valve connects to the vessel.

11. The target supply system of any preceding claim, wherein the vessel of the bleed module comprises a heating system, configured to melt any target material contained in the vessel.

12. The target supply system of any preceding claim, wherein the vessel is substantially composed of a stainless steel.

13. A method of removing liquid target material from a target supply system, wherein the target supply system comprises: a pressure module, configured to pressurise a liquid target material; a conduit, configured to carry liquid target material, fluidly connected to the pressure module; and a bleed module, the bleed module comprising: a vessel; a configurable connector, provided inline with the conduit and connected with the vessel; wherein the method comprises: switching the configurable connector from an operational configuration, wherein permitting fluid passage though the conduit and prohibiting fluid passage into the vessel, to a bleed configuration, wherein a portion of the conduit is in fluid communication with the vessel; purging the target material in the portion of the conduit into the vessel with a gas.

14. The method of claim 13, wherein the target supply system further comprises one or more components in fluid communication with the conduit; and the method further comprises:purging the target material in at least one of the one or more components into the vessel with a gas; and detaching the at least one of the one or more components.

15. A laser produced plasma radiation source comprising a target supply system according to any of claims 1-12.

16. An exposure apparatus comprising a laser produced plasma radiation source according to claim 15.

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