CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63/356,610 which was filed on 29 June 2022, and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] The disclosed subject matter relates to a freeze valve for a target material generator.

BACKGROUND

[0003] Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of 100 nanometers (nm) or less (also sometimes referred to as soft x-rays), and including light at a wavelength of, for example, 20 nm or less, between 5 and 20 nm, or between 13 and 14 nm, can be used in photolithography processes to produce extremely small features in or on substrates, for example, silicon wafers, by initiating polymerization in a resist layer. Methods for generating EUV light include, but are not limited to, altering the physical state of a source material to a plasma state. The source material includes a compound or an element, for example, xenon, lithium, or tin, with an emission line in the EUV range. In one such method, often termed laser produced plasma (“LPP”), the required plasma is produced by irradiating a source material, for example, in the form of a droplet, stream, or cluster of source material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment. The source material, such as xenon, lithium, or tin, which emits in the EUV range when in the plasma state, is commonly referred to as a target material since it is targeted and irradiated by the drive laser. The droplet, stream, or cluster of target material is produced by a target material generator within which the target material is transported.

SUMMARY

[0004] In some general aspects, a freeze valve includes: a valve body defining an axial opening extending along an axial direction; and a wire within the axial opening of the valve body. The wire includes a plurality of strands that define a plurality of continuous fluid pathways through the axial opening of the valve body.

[0005] Implementations can include one or more of the following features. For example, the valve body can have a cylindrical shape. The wire can be configured to prevent material that is in solid form from extruding through the axial opening at a pressure greater than 10,000 PSI, 20,000 PSI, 30,000 PSI, 100,000 PSI, 200,000 PSI, 300,000 PSI, 400,000 PSI, 500,000 PSI, 600,000 PSI, 700,000 PSI or 725,000 PSI. The strands of the plurality of strands can be arranged helically within the axial opening and the continuous fluid pathways can be helical pathways through the axial opening.

[0006] Each strand can have a diameter in the range of 0.2-0.3 millimeters (mm), and a diameter of the wire can be in the range of 4-6 mm. The regions between the plurality of strands can have a cross- sectional area between 0.785-7.069 mm ² .

[0007] The axial opening of the valve body can be defined by a constant diameter along the length of the wire. The axial opening of the valve body can include a step feature, and the wire can be seated between a fixed stop at a first end of the wire and the step feature at a second end of the wire. The fixed stop can be or can include a solid disk having a central axial opening, the central opening having a diameter that is smaller than an outer diameter of the wire and the outer diameter of the solid disk being larger than the outer diameter of the wire. The central axial opening of the fixed stop can be fluidly coupled to a source of gas. The fixed stop can also include a fixed stop body extending from the solid disk and into the axial opening of the valve body. The fixed stop body includes a central opening in fluid communication with the central opening of the solid disk and also in fluid communication with the axial opening of the valve body. The freeze valve can also include a first fluid port and a second fluid port, the first fluid port being defined at the fixed stop. The axial opening can include a primary axial opening and a smaller-diameter axial opening. The primary axial opening is between the fixed stop and the step feature and the smaller-diameter axial opening is between the step feature and the second fluid port. The primary axial opening has a diameter that is larger than the diameter of the smaller-diameter axial opening.

[0008] The valve body can be made of molybdenum or a refractory metal, and the plurality of wire strands can be made of tungsten or a refractory metal.

[0009] The freeze valve can also include a temperature controller in thermal communication with the valve body. The temperature controller can be configured to adjust a temperature of target material within the axial opening within a range of temperatures that includes the freezing point and the thawing point of the target material to thereby adjust the flow of target material through or within the axial opening.

[0010] Each gap between the wire and an inner surface of the valve body can have an area taken along a direction perpendicular to the axial direction that is less than or equal to regions formed between the strands of the wire. The axial opening can include a smaller-diameter axial opening adjacent a primary axial opening, and the wire can be placed or disposed in the primary axial opening, and target material in a solid state can be formed in the smaller-diameter axial opening when a temperature of the target material is held below the freezing point of the target material.

[0011] The wire can include a first wire and a second wire arranged in series within the axial opening of the valve body, each of the first wire and the second wire including a plurality of strands that define a plurality of continuous fluid pathways through the axial opening of the valve body. The strands of the first wire can be arranged helically within the axial opening to thereby define first helical pathways through the axial opening and the strands of the second wire can be arranged helically within the axial opening to thereby define second helical pathways through the axial opening.

[0012] The strands of the plurality of strands can be arranged linearly within the axial opening and the continuous fluid pathways can be linear pathways through the axial opening.

[0013] The axial opening of the valve body can include a first step feature and a second step feature, and wherein the wire is seated between the first step feature and the second step feature.

[0014] In other general aspects, a target generator includes: an exiting nozzle in fluid communication with at least one target material reservoir; and at least one freeze valve in fluid communication with a fluid pathway defined between the exiting nozzle and the at least one target material reservoir. The freeze valve includes: a valve body defining an axial opening extending along an axial direction; and a wire within the axial opening of the valve body. The wire includes a plurality of strands that define a plurality of continuous fluid pathways through the axial opening of the valve body.

[0015] Implementations can include one or more of the following features. For example, the valve body can have a cylindrical shape. The freeze valve can include a fluid port that is, during a purging operation, fluidly coupled to a source of gas. The freeze valve can include a second fluid port that is, at all times, in fluid communication with the fluid pathway defined between the exiting nozzle and the at least one target material reservoir. The freeze valve can include first and second fluid ports interposed within the fluid pathway defined between the exiting nozzle and the at least one target material reservoir.

[0016] The target generator can also include target material within the fluid pathway defined between the exiting nozzle and the at least one target material reservoir. The freeze valve can include a temperature controller configured to, during operation of the exiting nozzle, maintain the target material within a smaller-diameter axial opening of the axial opening at a temperature below its freezing temperature to thereby maintain the target material in solid form such that the solid target material within the smaller-diameter axial opening is a stopping mechanism configured to reduce or prevent the flow of material through a primary axial opening of the axial opening. The primary axial opening is adjacent to the smaller-diameter axial opening. The target material can include tin and the valve body of the freeze valve can be made of molybdenum or a refractory metal, and the strands can be made of tungsten or a refractory metal.

[0017] In other general aspects, a method of controlling fluid includes: freezing a target material within a smaller-diameter axial opening of a valve body of a freeze valve to thereby prevent the frozen target material from axially extruding through a plurality of regions formed from wire strands of a wire seated within a primary axial opening of the valve body when an axial pressure in a range of 10,000 to 765,000 PSI is applied to the frozen target material; thawing the target material within the smaller-diameter axial opening of the valve body of the freeze valve; and, once thawed, enabling a fluid to flow through one or more of the regions of the primary axial opening and the smaller-diameter axial opening of the valve body of the freeze valve. The primary axial opening has a larger diameter than the smaller-diameter axial opening.

[0018] Implementations can include one or more of the following features. For example, once thawed, the fluid can be enabled to flow through the regions having a transverse extent that is in the range of 2.0 - 0.5 mm between the strands of the wire at a conductance of 0.03 - 0.001 L/s. The target material can be frozen by maintaining the target material at a temperature below the freezing point of the target material for a sufficient duration to solidify the target material. The fluid can be enabled to flow through the one or more regions of the primary axial opening and the smaller-diameter axial opening of the valve body of the freeze valve by enabling a purge gas to flow into the primary axial opening from a gas source and through the primary axial opening. The method can further include, while enabling the purge gas to flow, applying a pressure to the purge gas to push liquid target material present within and out of the primary axial opening and the smaller-diameter axial opening and back to a target material reservoir.

DESCRIPTION OF DRAWINGS

[0019] Fig. 1A is a side cross-sectional view of a freeze valve including a valve body defining an axial opening and a wire including wire strands within the axial opening;

[0020] Fig. IB provides an axial cross-sectional view of the freeze valve of Fig. 1A taken along the line 1B-1B (which is in the XY plane), this view showing details of the wire strands and fluid pathways within the axial opening defined by the wire strands;

[0021] Fig. 1C is a perspective view of another implementation of the wire that can be implemented in the freeze valve of Figs. 1 A and IB, showing details of the wire strands and fluid pathways within the axial opening defined by the wire strands;

[0022] Fig. 2A is a side cross-sectional view of a portion of the freeze valve of Fig. 1 A when the freeze valve is in a closed state;

[0023] Fig. 2B is a side cross-sectional view of the portion of the freeze valve of Fig. 1 A when the freeze valve is in an open state;

[0024] Fig. 3 is a schematic diagram showing the freeze valve of Figs. 1A and IB in a target material nozzle assembly;

[0025] Fig. 4A is close-up perspective view of an implementation of a wire including parallel wire strands that can be used within the axial opening of the valve body of the freeze valve of Figs. 1 A and IB;

[0026] Fig. 4B is close-up perspective view of an implementation of a wire including helical wire strands that can be used within the axial opening of the valve body of the freeze valve of Figs. 1 A and IB;

[0027] Fig. 5 A is a top plan view of an implementation of a fixed stop that can be used in the freeze valve of Figs. 1A and IB; [0028] Fig. 5B is a side perspective view of the fixed stop of Fig. 5A;

[0029] Fig. 5C is a side cross-sectional view of an implementation of the freeze valve of Figs. 1 A and IB and including the fixed stop of Figs. 5A and 5B;

[0030] Fig. 5D is a side cross-sectional view of a freeze valve designed like the freeze valve of Figs. 1 A and IB, with the fixed stop of Figs. 5A and 5B and two wires in series within the axial opening; [0031] Fig. 6 is a flow chart showing a procedure for controlling fluid using any of the freeze valves of Figs. 1A-5C;

[0032] Fig. 7A-7F are schematic diagrams showing the freeze valve of Figs. 1 A and IB in a target material nozzle assembly during the procedure of Fig. 6;

[0033] Fig. 8A is a side cross-sectional view of a double-wetted implementation of the freeze valve of Figs. 1 A and IB, in which target material fluid can flow through both fluid ports of the freeze valve;

[0034] Fig. 8B is a schematic diagram showing the double-wetted freeze valve of Fig. 8A implemented in a target material nozzle assembly; and

[0035] Fig. 9 is a schematic block diagram showing an implementation of the target material nozzle assembly of Fig. 3 integrated within a target generator that supplies targets to an EUV light source.

DESCRIPTION

[0036] Referring to Figs. 1A and IB, a freeze valve 100 includes a valve body 128 that defines an axial opening 135 (or primary axial opening 135) that generally extends along an axial direction that is parallel with the Z axis. The freeze valve 100 includes a wire 140 within the axial opening 135. The wire 140 is fixed within the axial opening 135 such that it touches an inner surface 122 of the valve body 128. The wire 140 includes a plurality of wire strands 141 (Fig. IB). A plurality of continuous fluid pathways are defined in regions 160 between adjacent wire strands 141 and in gaps 161 between the wire strands 141 and the inner surface 122 of the valve body 128. The wire 140 (and each of the wire strands 141), and the continuous fluid pathways (defined by the regions 160 and the gaps 161) extend along the axial opening 135 and specifically along the axial direction (which is parallel with the Z axis). The axial opening 135 is interposed within the valve body 128 and extends between a fixed stop 105 and a step feature 132 formed in the valve body 128 (and specifically at the inner surface 122). The fixed stop 105 defines a central axial opening 110 that enables fluid communication between the axial opening 135 and a first fluid port 103A. The step feature 132 is the location at which the axial opening 135 is in fluid communication with a smaller-diameter axial opening 150. The axial opening 135 that is formed within the valve body 128 is in fluid communication with the first fluid port 103 A and a second fluid port 103B.

[0037] The freeze valve 100 can be configured to perform two different functions. The first function occurs when the freeze valve 100 is in a closed state, in which the freeze valve 100 holds or maintains (solid) target material, thereby reducing or preventing flow of any solid material through the freeze valve 100. The freeze valve 100 is able to perform the first function when the target material within the smaller-diameter axial opening 150 of the freeze valve 100 is sufficiently cooled for a duration of time, thus making any target material within the smaller-diameter axial opening 150 a solid. When the target material is in a solid form, the solid target material acts as a plug that reduces or prevents fluid flow through the freeze valve 100. The second function occurs when the freeze valve 100 is in an open state, in which the freeze valve 100 enables or permits a fluid to flow. For fluid to flow without being impeded through the freeze valve 100, the target material within the smaller-diameter axial opening 150 and any target material that makes its way into the axial opening 135 must be sufficiently warmed, such that any target material within the smaller-diameter axial opening 150 and the axial opening 135 becomes a fluid. The fluid that is able to flow through the freeze valve 100, could be a gas, a liquid or a combination of gas and liquid.

[0038] Referring to Fig. 2 A, the freeze valve 100 is closed and is performing the first function in which the target material is a solid target material 201 S. While closed, the freeze valve 100 needs to be able to reduce or prevent retain the extrusion of solid target material 20 IS from within the smaller- diameter axial opening 150 under anticipated operating pressures P applied along the Z direction (for example, along the -Z direction) and out of the freeze valve 100. In general, in prior freeze valves, the pressure P that can be applied along the -Z direction typically can reach up to a maximum valve Pmax of 10,000 pounds per square inch (PSI) before the solid target material begins to extrude along the -Z direction out of the freeze valve. The “punch pressure” (as represented by Equation (1) below) is defined as the pressure at which the solid target material within the smaller-diameter axial opening of a freeze valve extrudes out of that freeze valve. On the other hand, the freeze valve 100 is designed such that, when closed (during performance of the first function), the solid target material 201 S within the smaller-diameter axial opening 150 is prevented from extruding along the -Z direction into the axial opening 135 and out of the freeze valve 100, even at punch pressures that reach up to a maximum value Pmax of 725,000 PSI. The punch pressure PPioo of the freeze valve 100 is increased by decreasing a diameter or extent of the opening (along a plane that is perpendicular to the Z axis) through which the solid target material 20 IS within the smaller-diameter axial opening 150 can be extruded (along the -Z direction). This is because the punch pressure PPioo of the freeze valve 100 is inversely proportional to the square of the diameter or extent of the opening positioned axially along the -Z direction from the smaller-diameter opening 150. And, because the wire strands 141 are seated within the axial opening 135, the solid target material 201 S within the smaller-diameter axial opening 150 therefore is pushed against much smaller openings (specifically and primarily, the regions 160 and, secondarily and less likely, the gaps 161) along the axial direction (the -Z direction) upon application of axial pressure P along the -Z direction.

[0039] Fig. IB shows the cross-section 1B-1B taken through the valve body 128 and intersecting the axial opening 135. Also visible in Fig. IB is the smaller-diameter axial opening 150 positioned beyond the step feature 132. Under the axial pressure P along the -Z direction, the solid target material 201S within the smaller-diameter axial opening 150 is pushed against the solid ends of the portions of the wire strands 141 that fall within the diameter Diso of the opening 150. Additionally, under axial pressure P along the -Z direction, the solid target material 201 S within the smaller- diameter opening 150 is also pushed into the regions 160 when the punch pressure PPioo is exceeded. The punch pressure would normally be calculated based on the assumption that the opening in which the solid target material 20 IS is held and the opening through which the solid target material 201 S would be extruded are cylindrical. Here, however, the openings (the regions 160) are not cylindrical but rather are closer in shape to polygons such as triangles. Nevertheless, it is evident that the extent or diameter Dieo of each region 160 is much smaller than that the diameter D135 of the axial opening 135. Moreover, because the smaller-diameter axial opening 150 is axially centered with the wire 140, solid target material 20 IS within the smaller-diameter axial opening 150 generally is not in direct fluid communication with the gaps 161, which are blocked by the step feature 132. Any solid target material 201 S that is pushed somehow into the gaps 161 would be traveling along a path that is not parallel with the Z direction, and because of this, would be subjected to even greater friction. For these reasons, a greater amount of force is applied to the solid target material 20 IS along the +Z direction in response to the pressure P being applied along the -Z direction. This greater amount of friction is due to the plurality of wire strands 141 within the axial opening 135 forming much smaller openings (via the regions 160) through which the solid target material 201 S within the smaller- diameter axial opening 150 could be extruded. Accordingly, the punch pressure PPioo that would force the solid target material 20 IS to flow along the -Z direction through the axial opening 135 in which the wire 140 is seated is much greater than the punch pressure PPo that would force the solid target material 201 S through the axial opening 135 that lacks the wire 140. For example, the punch pressure PPioo can be twice as large as, three times as large as, four times as large as, ten times as large as, twenty times large as, thirty times as large as, forty times as large as, fifty times as large as, sixty times as large as, seventy times as large as, or greater than seventy one times as large as the punch pressure PPo. As such, the punch pressure PPioo of the freeze valve 100 is at least 10,000 PSI, at least 20,000 PSI, at least 30,000 PSI, at least 100,000 PSI, at least 200,000 PSI, at least 300,000 PSI, at least 400,000 PSI, at least 500,000 PSI, at least 600,000 PSI, at least 700,000 PSI or about 725,000 PSI.

[0040] The calculation for the punch pressure PPioo discussed next assumes that the openings are cylindrical, and thus, these calculations are a rough estimate of the actual punch pressure PPioo for the freeze valve 100.

[0041] The punch pressure PPioo of the freeze valve 100 as discussed above, can be approximated by calculating the punch pressure PPieo for extrusion through a single region 160 in accordance with the following punch pressure extrusion Equation (1):

In Equation (1), the variable Do is the extent of the area within the diameter Diso of the smaller - diameter axial opening 150 that is extruded into a particular region 160 (as shown in Fig. IB); Df is the extent Dieo of that particular region 160 (as shown in Fig. IB); E is the length Liso of the smaller- diameter axial opening 150 (as shown in Fig. 1 A) taken along the Z axis; a and b are constants that are determined by angles A150-1 and A150-2 (as shown in Fig. 1A) at the region of the step feature 132 at which the smaller-diameter axial opening 150 connects to the axial opening 135; and K is a strength coefficient and n is an elasticity of the valve body 128. As evident from Equation (1), the punch pressure PPieo depends on the number of wire strands 141 within the wire 140 since the number of wire strands 141 affects size of the smaller diameter Dieo, and thereby affects the value of Df. The calculation of the overall punch pressure PP100 of the freeze valve 100 is determined based on the value of the punch pressure PPieo for a single region 160.

[0042] For example, with reference to Fig. 1C, the punch pressure PPieo can be calculated for a wire 140C within the axial opening 135 of the valve body 128C that includes a total of 337 wire strands 141C. The wire 140C also includes a plurality of continuous fluid pathways defining the regions 160C between adjacent wire strands 141C, and the gaps 161C between the wire strands 141C and the inner surface 122C of the valve body 128C. For simplicity, the following calculation assumes that the wire strands 141C are straight and therefore extend axially along the Z direction only. If the wire 140C has an overall diameter of 5 millimeter (mm) (and the diameter D135 of the axial opening 135 is also about 5 mm or slightly larger), and the wire 140C includes 337 wire strands 141C, then the diameter Df (Dieo) of each region 160C is about 0.056 mm, the diameter Do is about 0.185 mm. If the length L150 is 34 mm, and a = 0.8, b = 1.5, K = 69 bar, and n = 0.05, then the punch pressure PPieo is on the order of 300,000 PSI. As mentioned, the calculation above assumes that the wire strands 141C and the regions 160C are linear. However, the wire 140C can be designed with helical strands 141C and thus the regions 160C are also helical. Because of this design, any extruding solid target material 201 S would experience even more friction because it would be extruding along a direction that includes a component that is perpendicular to the +Z direction, and the actual punch pressure PPieo would be even higher.

[0043] Referring to Fig. 2B, the freeze valve 100 is open and performing the second function in which any target material within the freeze valve 100 is liquid. While open, the freeze valve 100 needs to be able to conduct a fluid 202F within the axial opening 135 of the freeze valve 100 and do so at an acceptable rate. The fluid 202F can be or can include target material in fluid or liquid form. The fluid 202F can also or alternatively include fluid material such as purging gas 204G, or a combination of a gas and liquid. The rate at which the fluid 202F is conducted through the axial opening 135 of the freeze valve 100, is referred to as the “conductance” of the freeze valve 100. The conductance needs to be at or above an acceptable rate for the freeze valve 100 to conduct fluid 202F through the axial opening 135 effectively. The freeze valve 100 is designed such that the conductance of fluid 202F through the freeze valve 100 during the performance of the secondary function is not adversely impacted by the design that enables the freeze valve 100 to perform the first function (Fig. 2A) in which the punch pressure PPioo can be at least 725,000 PSI. The freeze valve 100 is designed such that the conductance of fluid flow 202F through the freeze valve 100, when performing the second function, is improved, when compared to prior freeze valves designs. In particular, the conductance of the flow of fluid 202F through the freeze valve 100 is proportional (for example, linearly) to the number of regions 160 and gaps 161 that are defined within the axial opening 135, and such regions 160 and gaps 161 are present due to fact that the wire 140 is held within the axial opening 135, and the wire 140 includes the plurality of wire strands 141. The conductance of the fluid 202F flow through the valve body 128 depends on the total cross-sectional area of the continuous pathway between the first fluid port 103A and the second fluid port 103B.

[0044] Referring to Fig. 1C, as discussed above, the wire 140C includes a total of 337 wire strands 141C. The wire 140C also includes a plurality of continuous fluid pathways defining the regions 160C between adjacent wire strands 141C, and the gaps 161C between the wire strands 141C and the inner surface 122C of the valve body 128C. As discussed above, the conductance of the fluid 202F through the freeze valve 100 in which the wire 140C is seated is proportional to the number of regions 160C and gaps 161C defined by the wire 140C and its relationship within the valve body 128C, and also proportional to the total cross-sectional area of the continuous pathway between the first fluid port 103A and the second fluid port 103B (Fig. 1 A). Thus, a rough estimate of the conductance through the freeze valve 100 that includes the wire 140C can be calculated as follows. It should be noted that the wire strands 141C have a helical shape and because of this, the regions 160C and the gaps 161C are helically-shaped. For simplicity, the following calculation assumes that the wire strands 141C are straight and therefore extend axially along the Z direction only. If the wire 140C has an overall diameter of 5 millimeter (mm) (and the diameter D135 of the axial opening 135 is also about 5 mm or slightly larger), and the wire 140C includes 337 wire strands 141C, then the diameter Dieo of each region 160 is about 0.056 mm, the diameter Diei of each gap 161 is about 0.34 mm, and there are about 265 regions 160 and 61 gaps 160. In this example, then the conductance through the freeze valve 100 can be about 0.0326 liters/s (L/s). A comparably-sized freeze valve that lacks the wire 140C arranged in a valve body 128C can have a conductance of about 0.0001 L/s under similar operating conditions.

[0045] The freeze valve 100, when functioning in the open state (as shown in Fig. 2B), allows flow of fluid 202F through the valve body 128. The fluid 202F is compatible with the valve body 128, and can be or include a gas 204G such as a purge or forming gas that is pumped in from a gas system 312 (such as shown in Fig. 3). Such a purge or forming gas can be a gas that is non-reactive with the target material and the materials of features that are fitted to or within the valve body 128, such as the fixed stop 105, and the axial opening 135 that holds the wire 140 that includes the plurality of wire strands 141. The purge or forming gas can include, for example, inert gases such as argon and hydrogen. The fluid 202F can also include target material that is in liquid form that remains within the freeze valve 100. The fluid 202F can be conducted from an external gas system 312 (Fig. 3), through the first fluid port 103A the central axial opening 110 of the fixed stop 105, through the axial opening 135 within the valve body 128, and through the second fluid port 103B.

[0046] Thus, the improvements to the punch pressure PPioo as well as the maintenance (and improvement) of the conductance of the freeze valve 100 are the result of fixing the wire 140 including the plurality of wire strands 141 in the axial opening 135, as discussed in more detail below. [0047] Referring again to Figs. 1A and IB, the valve body 128 extends in an axial direction that is parallel with the Z axis. The axial opening 135 generally is defined by a constant diameter (D135) along the length Luo of the wire 140. The valve body 128 can be cylindrical in shape and therefore defines a cylindrical outer surface 125. The valve body 128 is made up of material that is continuous in form and is rigid enough to withstand pressures applied to the freeze valve 100 (such as when the pressure P is applied to the solid target material 20 IS or the pressure at which the gas 204G is supplied). The diameter of the cylindrical outer surface 125 can vary as it extends parallel to the Z axis. For example, the valve body 128 can have a larger diameter at the position at which the fixed stop 105 is fitted (as shown in Fig. 1 A), and can have a smaller diameter at the location at which the valve body 128 contains the smaller-diameter axial opening 150 (as shown in Fig. 1A).

[0048] The valve body 128 and the wire strands 141 of the wire 140 are each made of a material that is compatible with and non-reactive with materials that come in contact with the valve body 128 and the wire strands 141, including materials such as the target material (in solid or fluid form), and the gas 204G. For example, if the freeze valve 100 is used in a target material nozzle assembly 334 that is configured to supply targets to an EUV light source (shown in Fig. 9), then the target material can include tin or a tin alloy. In this example, the valve body 128 can be made of a refractory metal such as molybdenum, tungsten, niobium, rhenium, or an alloy of these metals. And, the wire strands 141 can also be made of a refractory metal such as tungsten.

[0049] As shown in Fig. 1 A, the valve body 128 includes the inner surface 122 that defines the axial opening 135, and the wire 140 is interposed between (or seated between) the fixed stop 105 and the step feature 132. The fixed stop 105 is seated at a first end 108 of the valve body 128. The fixed stop 105 can have a cylindrical disk shape that complements the shape of the first end 108 of the valve body 128. The fixed stop 105 is made of a solid rigid material that is able to withstand pressures that can be applied from the solid target material 201 S or the fluid 202F. The solid disk form of the fixed stop 105 defines the central axial opening 110 that, when seated, fluidly couples the first fluid port 103A to the axial opening 135. The central axial opening 110 of the fixed stop 105 has a diameter Duo that is smaller than the diameter D135 of the axial opening 135 so that the wire 140 is stopped from moving along the -Z direction. The step feature 132 within the valve body 128 is adjacent to a smaller-diameter axial opening 150 that is in fluid communication with the axial opening 135, and therefore the smaller-diameter axial opening 150 extends parallel with the Z axis. The step feature 132 forms the intersection between the smaller-diameter axial opening 150 and the axial opening 135, which has a larger diameter than the smaller-diameter axial opening 150. The step feature 132 and the fluidly connected smaller-diameter axial opening 150 are formed such that fluid 202F (such as target material or purging gas) can flow between the axial opening 135 and the smaller-diameter axial opening 150. The smaller-diameter axial opening 150 is configured with a smaller diameter Diso than the diameter D135 of the axial opening 135. Thus, the wire 140 with the plurality of wire strands 141 is held within, confined within, and statically held inside the valve body 128 between the fixed stop 105 and the step feature 132. Moreover, the wire 140 with the plurality of wires 141, when interposed between fixed stop 105 and the step feature 132 within the axial opening 135 of the valve body 128, remains fixed in position when the freeze valve 100 is configured to function in either the closed or open state (as shown in Fig. 2A and 2B).

[0050] Fig. 3 shows an implementation 300 of the freeze valve 100 that is used in the target material nozzle assembly 330. The target material nozzle assembly 330 includes a nozzle 334 in fluid communication with a reservoir 338. The reservoir 338 is configured to hold liquid target material 331. A fluid flow path 337 is formed between the reservoir 338 and the nozzle 334 to thereby supply liquid target material 331 stored in the reservoir 338 to the nozzle 334. While not shown in Fig. 3, the fluid flow path 337 can include other components, such as additional valves (such as the additional valve shown in Fig. 8A) and reservoirs, to allow additional control of the liquid target material 337. The nozzle 334 can be made of a capillary tube 336 extending generally along a longitudinal direction and defining an opening 335. The opening 335 is at an end of the capillary tube 336. The capillary tube 336 can be made of, for example, glass in the form of fused silica, borosilicate, aluminosilicate, or quartz. The liquid target material 331 flows through the capillary tube 336 and is ejected through the opening 335. When the pressure applied at the reservoir 338 is greater than a certain pressure (such as the Laplace pressure), the liquid target material 331 exits the opening 335 as a stream of targets (as shown below in Fig. 7C).

[0051] In the location shown in Fig. 3, the freeze valve 300 is a purging or service freeze valve that is in fluid communication with the fluid flow path 337 between the nozzle 335 and the reservoir 338.

The freeze valve 300 is an implementation of the freeze valve 100, and includes a first fluid port 303A and a second fluid port 303B and a valve body 328 between the first fluid port 303A and the second fluid port 303B. The first fluid port 303 A including a fixed stop 305 with a central axial opening 310 that is fluidly coupled to a gas system 312, while the second fluid port 303B is in fluid communication with the fluid flow path 337.

[0052] The freeze valve 300 also includes a temperature control apparatus 313 configured to control the temperature at which the freeze valve 300 can perform the functions of opening and closing the freeze valve 300. For example, the temperature control apparatus 313 can be a cartridge heater in thermal communication with the valve body 328 of the freeze valve 300. If the temperature control apparatus 313 maintains the temperature of the valve body 328 significantly below the melting point of the liquid target material 331, then any liquid target material 331 within the smaller-diameter axial opening 350 of the freeze valve 300 solidifies (changing from a liquid to a solid state), and this solid target material within the smaller axial opening 350 acts as a plug, thereby reducing or preventing fluid (such as the liquid target material 331 or the gas from the gas system 313) from flowing through the freeze valve 300. If the temperature control apparatus 311 maintains the temperature of the valve body 328 above the melting point of the liquid target material 331, then any solid target material within the smaller-diameter axial opening 350 melts to form the liquid target material 331. Moreover, the liquid target material 331 and gas from the gas system 331 would thereby be free to flow through the freeze valve 300.

[0053] The freeze valve 100 (in Figs. 1A and IB) as discussed previously, includes the valve body 128 with the wire 140 defining a plurality of wire strands 141. The wire 140 including the wire strands 141 can each be formed to collectively create different axial geometries (as shown in Figs. 4A and 4B) that extend parallel to the Z axis within the axial opening 135 of the freeze valve 100. The collective axial geometries formed by the wire strands 141 seated within the valve body 128 can change the form and cross-sectional area of the continuous fluid pathways defined by the regions 160 and the gaps 161 between the adjacent wire strands 141 and wire strands 141 and the axial opening 135 inner surface 122. Additionally, because the conductance of a fluid through the valve body 128 depends on the total cross-sectional area of the continuous pathways (such as the regions 160 and the gaps 161) the collective axial geometries created by the wires strands 141 can change the conductance of the fluid flow, and thereby the punch pressure.

[0054] In Figs. 4A and 4B, example axial geometries formed by wires (which include a plurality of wire strands) that can be seated within the axial opening 135 of the valve body 128 of the freeze valve 100 is shown.

[0055] In the implementation of Fig. 4A, a wire 440-1 including a plurality of wire strands 441-1 is shown. Specifically, the wire 440-1 includes 19 wire strands 441-1. Each wire strand 441-1 maintains a linear form along the Z axis, and collectively the wire strands 444- 1 extend closely together and touching each other in parallel, thereby creating a larger radial shape forming the wire 440-1. The wire 440-1 includes linearly extending gaps 461-1 that are defined by the radially extending parallel wire strands 441-1. When seated within the axial opening 135, the wire strands 441-1 additionally define linearly extending regions 461-1 between the wire strands 441-1 and the inner surface 122 within the valve body 128 of the freeze valve 100.

[0056] Referring to the implementation of Fig. 4B, a wire 440-2 includes a plurality of wire strands 441-2. Each of the wires strands 441-2 extends in a spiral form together along the Z axis and in the same direction or angle, creating a helically shaped wire 440-2. The wire 440-2 includes gaps 461-2 that are formed by pathways created by the spiral shaped wire strands 441-2 that extend together in the same direction close in proximity. The pathways of the gaps 462-2 are also spiral shaped. Additionally, the wire 440-2, when implemented, for example, within the valve body 128 including an inner surface 122 of the freeze valve 100, also defines extending regions 461-2 between the wire strands 441-2 and the inner surface 122 further allowing fluid to flow.

[0057] Referring to Figs. 5A and 5B, an implementation 505 of the fixed stop 105 is shown. The fixed stop 505 includes a disk 506 and a fixed stop body 507 axially extending from the disk 506. Similar to that of the fixed stop 105 (shown in Fig.lA), the fixed stop 505 has a central axial opening 510 having a diameter D510 that extends through the disk 506 and the fixed stop body 507. Additionally, the fixed stop body 507 has a smaller outer diameter relative to an outer diameter of the disk 506. The fixed stop body 507 extends axially at a length L507 from the disk 506.

[0058] Referring to Fig. 5C, an implementation 500 of a freeze valve 100 includes the fixed stop 505. In this implementation, the fixed stop body 507 extends within a portion of the valve body 528. The valve body 528 of the freeze valve 500 (similarly to the freeze valve 100 shown in Fig. 1A) includes an axial opening 535. The freeze valve 500 also includes a wire 540 within the axial opening 535, the wire 540 seated between an end 518 of the fixed stop body 507 and a step feature 532 formed in the valve body 528. The wire 540 extends a length L540 along the Z direction. Beyond the step feature 523 along the Z direction, a smaller-diameter axial opening 550 is fluidly connected to a second fluid port 503B, the smaller-diameter axial opening 550 also fluidly connected with the axial opening 535. Additionally, the axial opening 535 is fluidly connected with the central axial opening 510 of the fixed stop 505, and the central axial opening 510 of the fixed stop 505 is in fluid communication with a first fluid port 503 A. The fixed stop 505 extends a total length L507 along the Z direction within the axial opening 535 of the valve body 528. The diameter D510 of the central axial opening of the fixed stop 505 is smaller than the diameter D535 of the axial opening 535 of the valve body 528. In this way, the wire 540 remains in place between the fixed stop 505 and the step feature 532. Moreover, the length L507 of the fixed stop body 507 can be any suitable length and can be selected depending on the length L ₅₄ oof the wire 540. For example, if the total length (sum of length L507 and L540) of the axial opening 535 is 34 mm, with the fixed stop body 507 length L507 being 10 mm, then the wire 540 length L540 would be 24 mm. As another example, if the total length (sum of the length L507 and L540) of the axial opening 535 is 60 mm, the length L540 of the wire is 30 mm, then the length L507 of the fixed stop body 507 needs to be 30 mm.

[0059] Referring to Fig. 5D, the freeze valve 500 of the axial opening 535, in additional implementations, can include a wire that is made up of two or more wires, such as a first wire 540-1 and a second wire 540-2. When two or more wires (such as the first wire 540-1 and the second wire 540-2) are arranged in series within the axial opening 535, the combined or totally length of the wires extend parallel to the Z axis, and can be seated in the same manner as that of the single wire 540 within the axial opening 535 (Fig. 5C). For example, if the length L535 of the axial opening 535 is 34 mm with the fixed stop body 507 length L507 extending 14 mm into the axial opening 535, the first and second wires 540-1 and 540-2 can be arranged in series each extending 10 mm at lengths L540-1 and L540-2, and having a combined length of 20 mm. Furthermore, if the axial opening 535 includes two wires such as the first and second wires 540-1 and 540-2 arranged in series, a discontinuity (or break) exists at the point at which the first wire 540-1 meets the second wire 540-2. This break created by the first and second wires 540-1 and 540-2 interrupts the fluid pathway within the axial opening 535. The interruption in the fluid pathway behaves as a grain boundary that interrupts dislocation motion, and thereby increases the punch pressure P applied along the Z direction of the freeze valve 500.

[0060] Referring to Fig. 6, a procedure 670 is performed by a freeze valve 700 (which can be the freeze valve 100, 300 or 500) that is used in a target material nozzle assembly 730. The steps of the procedure 670 are shown with reference to the freeze valve 700 in the target material nozzle assembly 740 of Figs. 7A-7F. In order to show the operation of the freeze valve 700, features shown (such as the wire 740 including wire strands 741) are exaggerated and not to scale. Moreover, for simplicity, only three separated wire strands 741 are shown and the regions 760 and gaps 761 between the wire strands 741 are depicted between the strands 741 and the inner surface 722 of the valve body 728. But, as noted above, additional wire strands 741 can be formed (making more regions 760 and gaps 761), the wire strands 741 can be in contact with each other, depending on the cross-sectional view through the valve body 728. As discussed above, the number of regions 760 and gaps 761 within the axial opening 735 of the valve body 728 impacts the conductance through the freeze valve 700. Additionally, when the procedure 670 refers to the target material in a solid form, it is designated as solid target material 701S in Figs. 7A-7F. When the procedure 670 refers to target material in a fluid form (such as a liquid) form, it is designated as a liquid target material 701L in Figs. 7A-7F. The purging or forming gas is designated as gas 704G in Figs. 7A-7F.

[0061] The procedure 670 begins by cooling target material that is present in the smaller-diameter axial opening 750 of the valve body 728 (671). As shown in Fig. 7 A, target material that is present in the smaller-diameter axial opening 750 can include liquid target material 701L at the start of step 671. At the start of step 671, the liquid target material 701L has already entered the smaller-diameter axial opening 750 through the second fluid port 703B, which is in fluid communication with a fluid path way 737 between a reservoir 738 and a nozzle 734. Additionally, it is possible at this time for the gas system 712 to apply a pressure Pp along the +Z direction (of the valve 700) to reduce or prevent the liquid target material 701L within the smaller-diameter axial opening 750 from flowing (or leaking) through the axial opening 735, the first fluid port 703 A, and through the central axial opening 710 of the fixed stop 705. At the start of step 671, the nozzle 734 is frozen, which means the nozzle 734 is maintained at a temperature below the freezing point of the target material thus freezing the target material and thereby only solid target material 701S is present in the nozzle 734 and the nozzle 734 is effectively closed. Thus, liquid target material 701L is not flowing to the nozzle 734. [0062] In some implementations, or in order to speed up the cooling process, the liquid target material 70 IL can be actively cooled (671) by the temperature control apparatus 713. In other implementations in which the liquid target material 701 S has a melting point higher than ambient temperatures, for example, if the target material includes tin, which has a melting point of approximately 232 °C, then the liquid target material 701L can be passively cooled (671) by removing a source of heat applied to the valve body 728 (such as by turning off the temperature control apparatus 713).

[0063] Once the liquid target material 701L within the smaller-diameter axial opening 750 of the freeze valve 700 is fully frozen (672), then the freeze valve 700 can operate in the closed state, which is shown in Fig. 7B. In the closed state, the froze valve 700 holds or maintains the solid target material 701S. Specifically, due to the design of the freeze valve 700, the solid target material 701S is prevented from axially extruding from the valve body 728 even at pressures P applied along the -Z direction of the freeze valve 700 (Fig. 7B) through the second fluid port 703B, such pressure P being at as high as 725,000 PSI (673). In particular, the solid target material 70 IS flow is significantly reduced or prevented from moving axially along the -Z direction of the freeze valve 700 (Fig. 7B) and through the axial opening 735 and to the first fluid port 703A with the solid target material 701S acting as a plug within the smaller-diameter axial opening 750 if the pressure P remains below the punch pressure of 725,000 PSI.

[0064] At this time in the procedure 670, and with reference to Fig. 7C, because the freeze valve 700 is closed, the target material nozzle assembly 730 can operate in supply mode, at which time the nozzle 734 is unfrozen (such that the solid target material 701S that was in the nozzle 734 thaws), and the liquid target material 701L that is stored within the reservoir 738 can be supplied to the nozzle 734 under pressure P. The liquid target material 701L exits through the nozzle 734 as a stream 780 of targets 782 due to the geometry of the nozzle 734 when pressure P is increased to a value that is greater than a pre-determined minimum nozzle pressure. For example, the pre-determined minimum nozzle pressure can be about 100 PSI.

[0065] When the nozzle 734 needs to be serviced or replaced, an instruction to purge is received (674). At this point, the gas system 712, the freeze valve 700, and the nozzle 734 work together to clear any liquid target material 70 IL from the fluid flow path 737 between the nozzle 734 and the reservoir 738. In order to do this, the nozzle 734 is frozen (in the manner discussed above), and then the freeze valve 700 needs to go from being closed (as shown in Fig. 7B) to being open. The temperature control apparatus 713 begins to actively warm the solid target material 701 S within the freeze valve 700 (675). Figs. 7D show this active warming while some of the solid target material 701S has melted into liquid target material 701L. During this time, the pressure P applied to the liquid target material 70 IL is reduced and liquid target material 70 IL is no longer being actively supplied to the nozzle 734 since the target material (now solid target material 701S) within the nozzle 734 is frozen. Thus, the nozzle 734 stops producing the stream 780 of the targets 782. When the nozzle 734 stops producing the stream 780 of the targets 782, some of the liquid target material 701L may remain in the fluid flow path 737 between the nozzle 734 and the reservoir 738.

[0066] Once all of the solid target material 701 S has thawed (676), then fluid is enabled to flow between the first fluid port 703A through the axial opening 735 of the valve body 728 and to the second port 703B. Because a purge is being performed, the gas system 712 supplies a purge or forming gas 704G (under a pressure Pp) along the +Z direction of the valve 700 (Fig. 7E) through the first port 703A of the freeze valve 700. In the beginning, as shown in Fig. 7E, the gas 704G that is fluidly coupled through the fixed stop 705, enters the first fluid port 703A and the central axial opening 710 within the fixed stop 705, and then the gas 704G enters the axial opening 735 that includes a plurality the continuous fluid pathways (defined by the regions 760 and gaps 761) between the adjacent wire strands 741 and the inner surface 722 of then axial opening 735, before the gas 704G enters the smaller-diameter axial opening 750 and flows through the second fluid port 703B. The gas 704G pushes the liquid target material 701L out of the freeze valve 700, and also out of fluid flow path 737. The gas 704G is pushed through the freeze valve 700 at a conductance rate, and the conductance increases with the number of regions 760 and gaps 761 defined between the adjacent wire strands 741 and the inner surface 722 of then axial opening 735 in the valve body 728.

Eventually, all of the liquid target material 701L that was within the freeze valve 700 and in the fluid flow path 737 is pushed back into the reservoir 738 by the gas 704G. Moreover, this moment can happen more quickly with a higher conductance of the gas 704G through the freeze valve 700.

[0067] Fig. 7F shows the state of the freeze valve 700 and the target material nozzle assembly 730 when the purge is complete (678). With the purge complete (678), the nozzle 734 can be serviced or removed.

[0068] The procedure 670 can further include the additional step of determining whether the servicing or replacement of nozzle 734 is complete and an instruction to operate the nozzle 734 under normal operating conditions is received. At this time, the liquid target material 701L can be resupplied into the fluid flow path 737 and also the valve body 728 of the freeze valve 700 from the reservoir 738, as shown in Fig. 7A.

[0069] Referring to Figs. 8A and 8B, an implementation 800 of a freeze valve 100 is shown, the freeze valve 800 can be implemented similarly to and function at least partly similarly with the freeze valves (100, 300, 500, and 700) discussed above. The freeze valve 800 can be considered as a doublewetted target material valve in that liquid target material can, at certain moments during operation, flow through both the first fluid port 803A and the second fluid port 803B. In this way, the freeze valve 800 can be placed within a fluid flow path 337 through which the target material flows between the reservoir 338 and the nozzle 334, as shown in Fig. 8B.

[0070] The freeze valve 800 includes a valve body 828 that extends parallel with the Z axis. The valve body 828 defines an axial opening 835 that includes a wire 840. The wire 840 is designed similarly to the wires 140, 340, 540, 750 described above. In particular, the wire 840 includes a plurality of wire strands 841 that form a plurality of continuous fluid pathways defined by regions 860 that are between adjacent wire strands 841, and gaps 861 that are between the wire strands 841 and the inner surface 822 of the valve body 828. The wire 840 is held within the axial opening 835 between a first smaller-diameter axial opening 850-1 and a second small er-diameter axial opening 850-2 by a first step feature 832-1 and a second step feature 832-2, respectively. The first smaller- diameter axial opening 850-1 is in fluid communication with the first fluid port 803 A and the second smaller-diameter axial opening 850-2 is in fluid communication with the second fluid port 803B. Thus, a continuous fluid pathway exists in the valve body 828 between the first fluid port 803A and the second fluid port 803B via the first smaller axial opening 850-1, the axial opening 835, and the second smaller axial opening 850-2.

[0071] The freeze valve 800 can perform the function of controlling fluid flow of target material through a closed and open operations, in the same manner as the freeze valves (such as 100, 300, 500, and 700) discussed above. The freeze valve 800 in the closed state, can retain within the first and second smaller-diameter axial openings 850-1 and 850-2 sufficiently cooled target material that is in a solid state under applied pressures up to 725,000 PSI along the +Z direction or the -Z direction (of the freeze valve 800, Fig. 8A) without extruding into and through the axial opening 835. The freeze valve 800 can also function in the open state allowing target material that is thawed (by an external temperature control apparatus such as the 713 shown in Figs. 7A-7E), such that the target material is in a liquid state, to flow in both directions (the +Z direction and the -Z direction of the freeze valve 800, Fig. 8A) through the freeze valve 800.

[0072] As shown in Fig. 8B, the freeze valve 800 with an external temperature control (such as external temperature control 313) enables the target material to change states (such as from a solid to liquid), and enables further control of the flow of target material through the fluid flow path 337. In more complex target material nozzle assemblies 330 that include additional components, and additional fluid flow paths and reservoirs, more than one freeze valve 800 can implemented at different locations to control the flow of target material within the assembly.

[0073] Referring to Fig. 9, the target material nozzle assembly 730 (or 330) can be integrated within a target generator 990 that includes fluid flow paths and further reservoirs, in addition to other fluid regulation devices or valves (such as the freeze valve 800 shown in Figs. 8A and 8B). The target generator 990 can also include a priming system that is configured to receive a solid matter that includes target material. An example of such a target 990 is shown in WO 2020/187617, which is incorporated herein by reference in its entirety.

[0074] The target generator 990 supplies the liquid target material 70 IL in the form of the stream 780 of targets 782 to an external system 992. If the system 992 is an EUV light source, then each target 782 is delivered to a plasma formation location 993 in a vacuum chamber 994. The plasma formation location 993 can receive at least one light beam 995 (which can be a pulsed light beam) that has been generated by an optical source 995 and delivered to the vacuum chamber 994 through an optical path 996. An interaction between a pulse of the light beam 995 and the target material in the target 782 within the plasma formation location 993 produces a plasma that emits EUV light 997, which is collected 998 and supplied to a lithography exposure apparatus 999. In this example, the liquid target material 701L can be any material that emits EUV light 998 when in a plasma state, such as water, tin, lithium, and/or xenon.

[0075] Other implementations are within the scope of the following claims. The features of the freeze valve (100, 300, 500, 700, or 800) can be of other geometric shapes or forms, and also be made of other materials than what is described. For example, the valve body 128 of the freeze valve 100 can be formed in a shape other than a cylindrical shape, such that a cross-section of the valve body taken in the XY plane is not circular, but can be polygonal, such as a hexagonal shape. The valve body 128 and the wire 140 can be made of materials other than the refractory metals (as discussed above), such as stainless steel, polymers (such as plastics and resins), or even wood. The geometric form and the material of the freeze valve 100, depend on the operating parameters (such as pressure and temperature) and environment in which the freeze valve 100 is used, in addition to manufacturing cost and methods.

[0076] The embodiments can be further described using the following clauses:

1. A freeze valve comprising: a valve body defining an axial opening extending along an axial direction; and a wire within the axial opening of the valve body, the wire comprising a plurality of strands that define a plurality of continuous fluid pathways through the axial opening of the valve body.

2. The freeze valve of clause 1, wherein the valve body has a cylindrical shape.

3. The freeze valve of clause 1, wherein the wire is configured to prevent material that is in solid form from extruding through the axial opening at a pressure greater than 10,000 PSI, 20,000 PSI, 30,000 PSI, 100,000 PSI, 200,000 PSI, 300,000 PSI, 400,000 PSI, 500,000 PSI, 600,000 PSI, 700,000 PSI or 725,000 PSI.

4. The freeze valve of clause 1, wherein the strands of the plurality of strands are arranged helically within the axial opening and the continuous fluid pathways are helical pathways through the axial opening.

5. The freeze valve of clause 1, wherein each strand has a diameter in the range of 0.2-0.3 millimeters (mm), and a diameter of the wire is in the range of 4-6 mm.

6. The freeze valve of clause 5, wherein regions between the plurality of strands have a cross- sectional area between 0.785-7.069 mm ² .

7. The freeze valve of clause 1, wherein the axial opening of the valve body is defined by a constant diameter along the length of the wire.

8. The freeze valve of clause 7, wherein the axial opening of the valve body includes a step feature, and wherein the wire is seated between a fixed stop at a first end of the wire and the step feature at a second end of the wire. 9. The freeze valve of clause 8, wherein the fixed stop includes a solid disk having a central axial opening, the central opening having a diameter that is smaller than an outer diameter of the wire and the outer diameter of the solid disk being larger than the outer diameter of the wire.

10. The freeze valve of clause 9, wherein the central axial opening of the fixed stop is fluidly coupled to a source of gas.

11. The freeze valve of clause 9, wherein the fixed stop further includes a fixed stop body extending from the solid disk and into the axial opening of the valve body, the fixed stop body including a central opening in fluid communication with the central opening of the solid disk and also in fluid communication with the axial opening of the valve body.

12. The freeze valve of clause 8, further comprising a first fluid port and a second fluid port, the first fluid port defined at the fixed stop, wherein the axial opening includes a primary axial opening between the fixed stop and the step feature and a smaller-diameter axial opening between the step feature and the second fluid port, the primary axial opening having a diameter that is larger than the diameter of the smaller-diameter axial opening.

13. The freeze valve of clause 1, wherein the valve body is made of molybdenum or a refractory metal, and the plurality of wire strands are made of tungsten or a refractory metal.

14. The freeze valve of clause 1, further comprising a temperature controller in thermal communication with the valve body, the temperature controller configured to adjust a temperature of target material within the axial opening within a range of temperatures that includes the freezing point and the thawing point of the target material to thereby adjust the flow of target material through or within the axial opening.

15. The freeze valve of clause 1, wherein each gap between the wire and an inner surface of the valve body has an area taken along a direction perpendicular to the axial direction that is less than or equal to regions formed between the strands of the wire.

16. The freeze valve of clause 1, wherein the axial opening includes a smaller-diameter axial opening adjacent a primary axial opening, the wire is disposed in the primary axial opening, and target material in a solid state is formed in the smaller-diameter axial opening when a temperature of the target material is held below the freezing point of the target material.

17. The freeze valve of clause 1, wherein the wire includes a first wire and a second wire arranged in series within the axial opening of the valve body, each of the first wire and the second wire comprising a plurality of strands that define a plurality of continuous fluid pathways through the axial opening of the valve body.

18. The freeze valve of clause 17, wherein the strands of the first wire are arranged helically within the axial opening to thereby define first helical pathways through the axial opening and the strands of the second wire are arranged helically within the axial opening to thereby define second helical pathways through the axial opening. 19. The freeze valve of clause 1, wherein the strands of the plurality of strands are arranged linearly within the axial opening and the continuous fluid pathways are linear pathways through the axial opening.

20. The freeze valve of clause 1, wherein the axial opening of the valve body includes a first step feature and a second step feature, and wherein the wire is seated between the first step feature and the second step feature.

21. A target generator comprising: an exiting nozzle in fluid communication with at least one target material reservoir; and at least one freeze valve in fluid communication with a fluid pathway defined between the exiting nozzle and the at least one target material reservoir, the freeze valve comprising: a valve body defining an axial opening extending along an axial direction; and a wire within the axial opening of the valve body, the wire comprising a plurality of strands that define a plurality of continuous fluid pathways through the axial opening of the valve body.

22. The target generator of clause 21, wherein the valve body has a cylindrical shape.

23. The target generator of clause 21, wherein the freeze valve includes a fluid port that is, during a purging operation, fluidly coupled to a source of gas.

24. The target generator of clause 23, wherein the freeze valve includes a second fluid port that is in fluid communication with the fluid pathway defined between the exiting nozzle and the at least one target material reservoir.

25. The target generator of clause 21, wherein the freeze valve includes first and second fluid ports interposed between the exiting nozzle and the at least one target material reservoir.

26. The target generator of clause 21, further comprising target material within the fluid pathway defined between the exiting nozzle and the at least one target material reservoir.

27. The target generator of clause 26, wherein the freeze valve comprises a temperature controller configured to, during operation of the exiting nozzle, maintain the target material within a smaller - diameter axial opening of the axial opening at a temperature below its freezing temperature to thereby maintain the target material in solid form such that the solid target material within the smaller - diameter axial opening is a stopping mechanism configured to reduce or prevent the flow of material through a primary axial opening of the axial opening, the primary axial opening being adjacent to the smaller-diameter axial opening.

28. The target generator of clause 26, wherein the target material includes tin and the valve body of the freeze valve is made of molybdenum or a refractory metal, and the strands are made of tungsten or a refractory metal.

29. A method of controlling fluid comprising: freezing a target material within a smaller-diameter axial opening of a valve body of a freeze valve to thereby prevent the frozen target material from axially extruding through a plurality of regions formed from wire strands of a wire seated within a primary axial opening of the valve body when an axial pressure in a range of 10,000 to 765,000 PSI is applied to the frozen target material, the primary axial opening having a larger diameter than the smaller-diameter axial opening; thawing the target material within the smaller-diameter axial opening of the valve body of the freeze valve; and once thawed, enabling a fluid to flow through one or more of the regions of the primary axial opening and the smaller-diameter axial opening of the valve body of the freeze valve.

30. The method of clause 29, wherein, once thawed, the fluid is enabled to flow through the regions having a transverse extent that is in the range of 2.0 - 0.5 mm between the strands of the wire at a conductance of 0.03 - 0.001 L/s. 31. The method of clause 29, wherein enabling the fluid to flow through the one or more regions of the primary axial opening and the smaller-diameter axial opening of the valve body of the freeze valve comprises enabling a purge gas to flow into the primary axial opening from a gas source and through the primary axial opening.

32. The method of clause 31, further comprising, while enabling the purge gas to flow, applying a pressure to the purge gas to push liquid target material present within and out of the primary axial opening and the smaller-diameter axial opening and back to a target material reservoir.

[0077] The above described implementations and other implementations are within the scope of the following claims.