Droplet generator nozzle

Abstract

A nozzle for a droplet generator for a laser-generated plasma radiation source is provided. The nozzle comprises a glass capillary tube used for emitting liquid drops; and a nozzle adapter, the nozzle adapter comprising a through-hole, and wherein the glass capillary is at least partially disposed in the through-hole. The nozzle further comprises a glass ferrule, the glass capillary tube is connected to the nozzle connector through the glass ferrule, and the shape of the glass ferrule is consistent with that of the through hole of the nozzle connector. A method of manufacturing a nozzle for a droplet generator is also provided.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22186633.8 filed on July 25, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a nozzle for a droplet generator of a laser-generated plasma radiation source and to a method for manufacturing the nozzle. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. For example, a lithographic apparatus may be used to manufacture integrated circuits (ICs). For example, a lithographic apparatus may project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (such as a photoresist, or simply resist) provided on a substrate.

[0005] To project a pattern on a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of a feature that can be formed on the substrate. A lithographic apparatus may use extreme ultraviolet (EUV) radiation (extreme ultraviolet (EUV) radiation has a wavelength in the range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm) to form smaller features on a substrate, compared to a lithographic apparatus that uses radiation having a wavelength greater than, for example, 4 nm to 20 nm.

[0006] EUV radiation can be generated using a plasma. A radiation system for generating EUV radiation can include a laser for exciting a fuel to provide a plasma, and a source collector module for containing the plasma. For example, a plasma can be generated by directing a laser beam to a fuel, which is a stream of particles of a suitable material, such as tin (Sn), or a suitable gas or vapor, such as Xe gas or Li vapor. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector. The radiation collector can be a mirrored normal incidence radiation collector that receives radiation and focuses the radiation into a beam. The source collector module can include an enclosure or chamber arranged to provide a vacuum environment to support the plasma. Such radiation systems are generally referred to as laser produced plasma (LPP) sources.

[0007] The fuel may be directed toward the path of the laser beam by a droplet generator. The droplet generator may include a nozzle for emitting the fuel as droplets. Such nozzles may operate in a pressurized and / or high temperature environment, and as such, may require forming a high temperature and pressure resistant seal (e.g., an airtight seal) between components of the nozzle. Existing nozzles may include seals between components that suffer from poor reliability, stability, and performance.

[0008] Figure 1 A prior art nozzle assembly 100 is depicted in . The nozzle 100 is an example of a nozzle disclosed in WO2021 / 074043 A1 (which document is incorporated herein by reference). The nozzle 100 includes a glass capillary 110 for emitting fuel droplets from a fuel emitter. The fuel emitter may be a droplet generator.

[0009] Glass capillary 110 is coupled to nozzle fitting 120, which may be integral with or coupled to a fuel emitter. Fitting 120 may include metal, and thus may be referred to as a metal fitting.

[0010] It is necessary to form a seal, such as an airtight seal, between the glass capillary 110 and the fitting 120. To this end, the glass capillary 110 is at least partially disposed in the through hole 140 of the fitting 120. The fitting 120 is heated, and pressure is applied to the glass capillary 110, so that the glass capillary 110 conforms to the shape of the through hole 140 and forms a direct glass-to-metal seal with the through hole 140. In this way, a seal is formed between the fitting 120 and the capillary 110.

[0011] However, by design, this method deforms the glass capillary 110 to contact the metal fitting 120. This deformation may not be reproducible. Therefore, the properties of the glass capillary 110, such as the transfer function, resonance characteristics (fundamental frequency), strength, and sealing of the glass to the metal, may not be reproducible. The transfer function is the ratio of the velocity modulation of the droplet leaving the nozzle to the driving force applied to the nozzle. The transfer function is preferably high at the fundamental modulation frequency (e.g., between 50 KHz and 200 KHz). The transfer function depends on the geometric aspects of the glass capillary 110, including the length and diameter. Therefore, it is not expected that the manufacturing process changes such geometric parameters. In addition, bubbles and / or high stress locations may be generated during the deformation and cooling process, which may weaken the final product. Summary of the invention

[0012] It is an object of the present disclosure to provide a nozzle for a droplet generator having a seal between a glass capillary and a fitting that overcomes one or more of the deficiencies of known nozzles.

[0013] According to one aspect of the present invention, there is provided a nozzle of a droplet generator for a laser-generated plasma radiation source, the nozzle comprising: a glass capillary for emitting droplets; a nozzle joint, the nozzle joint comprising a through hole, wherein the glass capillary is at least partially disposed in the through hole; and a glass ferrule, the glass ferrule connects the glass capillary to the nozzle joint, the glass ferrule being consistent in shape with the through hole of the nozzle joint.

[0014] Advantageously, such nozzles allow the glass capillary to retain as much of its original strength and shape as possible, limiting the structural and reproducibility issues discussed above. The glass ferrule connects the glass capillary to the nozzle joint, rather than deforming the glass capillary. The glass ferrule can be deformed under heating to provide a secure seal, including providing a direct seal of metal to glass when the nozzle joint is a metal fitting, without affecting the properties of the glass capillary. In addition, the ferrule material can be optimized for the bonding function, thereby providing an improved seal and / or improving the manufacturing process. For example, a ferrule material that softens at a lower temperature than the glass capillary material can be selected, reducing the energy required to manufacture the nozzle. Therefore, the softening temperature / firing temperature of the glass ferrule can be lower than the softening temperature / firing temperature of the glass capillary, so that the capillary is substantially not softened during the bonding process. The softening temperature of the glass ferrule is still higher than the maximum operating temperature of the nozzle / system for which the nozzle is designed. For example, the softening temperature can be higher than 300°C, or higher than 400°C, or higher than 500°C.

[0015] In some embodiments, the coefficient of thermal expansion of the glass capillary is substantially the same as the coefficient of thermal expansion of the nozzle joint, or is smaller than the coefficient of thermal expansion of the nozzle joint, or is larger than the coefficient of thermal expansion of the nozzle joint. Specifically, the coefficient of thermal expansion (CTE) of the glass capillary can be within a range of 1 PPM / K based on the coefficient of thermal expansion of the nozzle joint, or within a range of 0.5 PPM / K based on the coefficient of thermal expansion of the nozzle joint, or within a range of 0.3 PPM / K based on the coefficient of thermal expansion of the nozzle joint. Alternatively or in addition, the coefficient of thermal expansion of the glass ferrule can be within a range of 1 PPM / K based on the coefficient of thermal expansion of the nozzle joint, or within a range of 0.5 PPM / K based on the coefficient of thermal expansion of the nozzle joint. As used herein, having a CTE within the CTE value of the nozzle joint may include having a CTE that is higher or lower than the CTE of the nozzle joint. The coefficient of thermal expansion may be a coefficient of thermal expansion within a temperature range that includes the operating temperature of the nozzle and / or the manufacturing temperature range of the nozzle. Such embodiments can limit cracking and defects caused by different expansion and contraction characteristics of components of the nozzle when the nozzle is heated and cooled during manufacturing and use.

[0016] In some embodiments, the glass ferrule has a lower softening and / or firing temperature than the glass capillary. This means that during the manufacture of the nozzle, the glass ferrule deforms (when heated) while the glass capillary retains its original solid properties.

[0017] According to another aspect of the present invention, a method for manufacturing a nozzle for a droplet generator is provided, the method comprising positioning a glass capillary in a through hole of a nozzle joint, positioning a glass ferrule preform around the glass capillary, and heating the glass ferrule preform to form a glass ferrule that couples the glass capillary to the nozzle joint.

[0018] In some embodiments, positioning the glass ferrule preform includes positioning the glass ferrule preform in a through hole of the nozzle adapter. A force may be applied, such as using a pusher and / or a weight, to push the glass ferrule preform into the through hole.

[0019] In an alternative embodiment, positioning the glass ferrule preform includes positioning the glass ferrule preform at an end of the through hole. Then, heating the glass ferrule preform so that the glass ferrule preform flows into the through hole to form the glass ferrule. Specifically, the glass capillary may be positioned in the through hole with a gap between the glass capillary and the wall of the through hole so that when heated, the glass ferrule preform flows into the gap by capillary action. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments with reference to the accompanying drawings.

[0021] Figure 1 An example of a conventional nozzle for a droplet generator for a laser produced plasma radiation source is depicted.

[0022] Figure 2 A lithographic system comprising a lithographic apparatus and a radiation source and embodying a droplet generator is depicted.

[0023] Figure 3 A nozzle for a droplet generator is depicted.

[0024] Figures 4a to 4e Depicted Figure 3 Alternative examples of nozzles.

[0025] Figure 5 An example of a droplet generator including a nozzle is depicted.

[0026] Figure 6 A method of manufacturing a nozzle is illustrated.

[0027] Figure 7 An example of a method in which a glass ferrule preform is forced into place is depicted.

[0028] Figure 8a and Figure 8b An alternative example of a method is depicted in which a glass ferrule preform is flowed into a gap between a through-hole of a nozzle adapter and a glass capillary.

[0029] The drawings are schematic. The schematic diagrams and views show the components described below. However, the components depicted in the drawings are not drawn to scale. For clarity, the relative sizes of the components in the drawings are exaggerated. In the following description of the drawings, the same or similar reference numerals indicate the same or similar components or entities, and only the differences with respect to the various embodiments are described. DETAILED DESCRIPTION

[0030] Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, wherein, unless otherwise indicated, the same numbers in the different drawings represent the same or similar elements. The embodiments set forth in the following description of the exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, the embodiments are merely examples of devices and methods consistent with aspects related to the present invention as described in the appended claims.

[0031] Figure 2 A lithographic system is shown 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 IE, a support structure MT configured to support a patterning device MA (e.g. a mask or reticle), a projection system PS, and a substrate table WT configured to support a substrate W.

[0032] The illumination system IE is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. Furthermore, the illumination system IL may comprise a faceted field mirror arrangement 10 and a faceted pupil mirror arrangement 11. The faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11 together provide an EUV radiation beam B having a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may comprise other mirrors or arrangements in addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement.

[0033] After being so conditioned, the EUV radiation beam B interacts with the pattern forming 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 a substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14, which are configured to project the patterned EUV radiation beam B' onto a substrate W, which is held by a substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image having features that are smaller than corresponding features on the pattern forming device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is Figure 2 1. Although described in FIG. 1 as having only two mirrors 13, 14, the projection system PS may comprise a different number of mirrors (eg six or eight mirrors).

[0034] The substrate W may include a pre-formed pattern. In this case, the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B′ with the pattern previously formed on the substrate W.

[0035] A relative vacuum, ie a small amount of gas (eg 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.

[0036] Figure 2 The radiation source SO shown in is of a type that may be referred to as a laser produced plasma (LPP) source, for example. 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, such as tin (Sn), which is provided by, for example, a fuel emitter 3 (an example of a droplet generator). Although tin is mentioned 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 an alloy. The fuel emitter 3 includes a nozzle 200 configured to direct tin, for example, in the form of droplets, along a trajectory toward a plasma formation region 4. The laser beam 2 is incident on the tin at the plasma formation region 4. The deposition of laser energy into the tin generates a tin plasma 7 at the plasma formation region 4. During de-excitation and recombination of electrons with ions of the plasma, radiation including EUV radiation is emitted from the plasma 7.

[0037] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 includes, for example, a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). The collector 5 may have a multilayer mirror structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration having two focal points. As discussed below, a first of the focal points may be at the plasma formation region 4, and a second of the focal points may be at the intermediate focus 6.

[0038] The laser system 1 may be spatially separated from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable guiding mirrors and / or a beam expander, and / or other optical devices. The laser system 1, the radiation source SO and the beam delivery system may together be considered a radiation system.

[0039] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at an intermediate focus 6 to form an image at the intermediate focus 6 of a plasma present at the plasma formation region 4. The image at the intermediate focus 6 serves as a virtual radiation source for the illumination system IE. The radiation source SO is arranged so that the intermediate focus 6 is located at or near an opening 8 in an enclosure 9 of the radiation source SO.

[0040] although Figure 2 The radiation source SO is depicted as a laser produced plasma (LPP) source, but any suitable source may be used to produce EUV radiation, such as a discharge produced plasma (DPP) source or a free electron laser (EEL).

[0041] As described above, the fuel emitter 3 may include a nozzle 200 configured to direct fuel (eg, tin in the form of droplets) along a trajectory towards the plasma formation region 4 . Figure 3 An example of a nozzle according to the present disclosure is illustrated.

[0042] Figure 3 The nozzle 200 shown in is a nozzle for a droplet generator. For example, the droplet generator can be the fuel emitter 3 discussed above. The nozzle 200 includes a glass capillary 210 for emitting droplets. The glass capillary 210 is a hollow glass tube that is open at a first end 225 and at a second end 230. In use, fuel enters the first end 225 and travels along the length of the glass capillary 210 (along the axis X) to the second end 230, from which the fuel is emitted in the form of droplets.

[0043] The glass capillary 210 may include borosilicate, aluminosilicate, or quartz. The glass capillary 210 may include soda lime glass or alkali barium glass. The glass capillary 210 may include alkali barium aluminoborosilicate glass. The glass capillary 210 may be optimized or modified, such as by mixing alkali metals (Na and K) and / or alkaline earth metals (Ca and Mg), etc., to obtain desired physicochemical properties.

[0044] The glass capillary tube 210 may be a straight tube having substantially constant inner and outer diameters, at least for a portion of the glass capillary tube disposed in the nozzle adapter 230 .

[0045] Figure 3 Also shown in the figure is a nozzle joint 220. The nozzle joint 220 is attached to or can be attached to a droplet generator (e.g., a fuel emitter 3), or generally attached to or can be attached to a system in which the nozzle 200 is intended to be used. For example, the nozzle joint 220 can be integral with the droplet generator or connected to the droplet generator. The nozzle joint 220 includes a through hole 240. In the illustrated example, the through hole 240 is substantially straight and can be a uniform cylinder. As further discussed below, the through hole 240 and the nozzle joint 220 can take other forms. The glass capillary 210 is disposed in the through hole 240 of the nozzle joint 220. In the illustrated example, the glass capillary 210 protrudes from the lower end (further along the X-axis) of the nozzle joint 220. That is, the second end 230 is not disposed in the through hole 240. The first end 225 of the glass capillary 210 is flush with the upper end (earlier along the X-axis) of the nozzle joint 220. In other examples, either or both ends 225 , 230 of the glass capillary may be flush with one end of the nozzle adapter 220 , or may protrude from the respective ends of the nozzle adapter 220 .

[0046] The nozzle joint 220 may be formed of or include a metal. In such cases, the nozzle joint may be referred to as a metal fitting 220. In a specific example, for example, the nozzle joint 220 is formed of or includes molybdenum, tantalum, tungsten, and / or niobium. In some embodiments, the nozzle joint 220 may include, for example, aluminum and / or platinum. In some embodiments, the nozzle joint 220 may be formed of or include a metal alloy, such as stainless steel, TZM (molybdenum titanium), tungsten, tantalum, niobium. The nozzle joint may be formed of or include any alloy of molybdenum and tungsten, such as MoW50 (50% molybdenum and 50% tungsten), MoW30 (30% tungsten). The nozzle joint 220 may be formed of an alloy of tungsten and tantalum (e.g., WTa10 containing 10% tantalum) or any other alloy of the metals listed above, or include an alloy of tungsten and tantalum (e.g., WTa10 containing 10% tantalum) or any other alloy of the metals listed above. The nozzle joint 220 may include a metal oxide. For example, the nozzle adapter can include a metal oxide layer. The metal oxide layer can have a thickness of 1 nm or more, or 10 nm or more, or 100 nm or more. Alternatively or additionally, the metal oxide layer can have a thickness of 5 μm or less, or 1 μm or less, or 100 μm or less. The metal oxide layer can cover only a portion of the nozzle adapter 220, such as the through hole 240 or a portion of the through hole 240. In yet other examples, the nozzle adapter 220 is formed of a metal oxide, a ceramic, or a glass.

[0047] At least a portion of the nozzle adapter 220 may advantageously include an oxide layer on the surface forming the through hole 240. Such an oxide layer may provide a more robust and / or more reliable and / or more effective glass-to-metal seal. Beneficially, providing an oxide layer (e.g., a metal oxide layer) provides oxygen atoms that can be used to form an effective glass-to-metal bonding layer.

[0048] It will be appreciated that the provision of a metal oxide layer is suitable for any metal that forms a glass-to-metal seal. For example, a nozzle adapter 220 including any of molybdenum, tungsten, tantalum, and / or a metal alloy such as nickel-cobalt-iron alloy may include a metal oxide layer. In some exemplary embodiments, at least a portion of the nozzle adapter 220 (e.g., at least a portion of the through hole 240 of the nozzle adapter) may be oxidized to ensure that a sufficient and / or adequate oxide layer is present prior to forming a glass-to-metal seal.

[0049] If such an oxide layer is desired but is found to be initially absent or insufficient, the nozzle joint 220 may be treated to form an oxide layer. For example, the nozzle joint 220 may be heated in the presence of oxygen to accelerate the formation of such an oxide layer.

[0050] Advantageously, the coefficient of thermal expansion (CTE) of the nozzle adapter 220 is substantially the same as or within a predefined range relative to the CTE of the glass capillary 210. Specifically, the CTE may be an operating temperature range of the nozzle. The operating temperature range may depend on the fuel emitted or ejected by the nozzle 200. For example, liquid tin as a fuel may have an operating temperature range of approximately 300K to 530K. The approximate matching of the CTEs of the glass capillary 210 and the nozzle adapter 220 limits the likelihood of damage occurring during heating and cooling of the nozzle 200 due to the different expansion / contraction characteristics of the glass capillary 210 and the nozzle adapter 220.

[0051] Furthermore, it is also advantageous that the CTE of the nozzle joint 220 is substantially the same as the CTE of the glass capillary 210, or is within a predefined range relative to the CTE of the glass tube 210, over a temperature range that includes the temperatures required to manufacture the nozzle 200, as discussed further below. Thus, it is advantageous that the CTE of the nozzle joint 220 is substantially the same as the CTE of the glass tube 210, or is within a predefined range relative to the CTE of the glass tube 210, over a temperature range that includes the temperatures reached during manufacturing, and preferably also over an operating temperature range of the nozzle 200 that may include temperatures less than room temperature. To this end, in some examples, the coefficient of thermal expansion of the glass capillary 210 is within a range of ±1 PPM / K of the coefficient of thermal expansion of the nozzle joint 220, or within a range of ±0.5 PPM / K of the coefficient of thermal expansion of the nozzle joint 220, or within a range of ±0.3 PPM / K of the coefficient of thermal expansion of the nozzle joint 220 (i.e., the CTE of the glass capillary 210 may be higher or lower than the CTE of the nozzle joint 220 as long as the CTE is within a given range). The CTE may be the CTE at operating and / or manufacturing temperature.The CTE of the glass capillary 210 and the nozzle joint may typically be 10 PPM / K or less, or 8 PPM / K or less, or 7 PPM / K or less.

[0052] For example, a nozzle fitting 220 comprising molybdenum may have a CTE of approximately 5.5 ppm / K. Thus, the predefined range of the CTE of the glass capillary 210 may be, for example, + / - 0.5 ppm / K relative to the CTE of the nozzle fitting 220. Various borosilicate or aluminosilicate glasses include CTEs that match molybdenum within a range of + / - 0.5 PPM / K.

[0053] Furthermore, in use, the fuel provided by the droplet generator may be, for example, a tin compound, such as SnBr4, SnBr2, SnH4, or a tin alloy, such as a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy, or a combination of the foregoing. Depending on the material used, the target material may be provided by the droplet generator at various temperatures including room temperature or near room temperature (e.g., tin alloy, SnBr4), at elevated temperatures (e.g., pure tin), or at temperatures below room temperature (e.g., SnH4). Therefore, having temperature-invariant relative dimensions is particularly beneficial for the glass capillary 210 and the nozzle adapter 220 in terms of their performance over the entire operating temperature range.

[0054] By closely matching the CTE of the glass capillary 210 to the CTE of the nozzle adapter 220, cracking of the glass capillary after the nozzle is heated to operating temperature (eg, 250 K to 500 K of molten tin) can be avoided.

[0055] like Figure 3 As shown in FIG. 1 , the nozzle 200 further includes a glass ferrule 250. The glass ferrule 250 connects the glass capillary 210 to the nozzle joint 220. The glass ferrule 250 is consistent in shape with the through hole 240 of the nozzle joint 220. Figure 1 Compared to the prior art example shown in , the nozzle 200 includes an additional component in the form of a glass ferrule 250 to attach the glass capillary 210 to the nozzle fitting 220. The glass ferrule 250 is deformed to conform to the shape of the through hole 240, rather than deforming the glass capillary 210. This allows the use of a direct glass-to-fitting seal (e.g., a direct glass-to-metal seal, where the nozzle fitting is a metal fitting) without the disadvantages of deforming the glass capillary 210 discussed above. The glass ferrule 250 forms a glass-to-metal seal with the nozzle fitting 220, and a glass-to-glass seal with the glass capillary 210. The glass ferrule 250 can be considered as a soldering glass that connects the nozzle fitting 250 to the glass capillary 210. Solder glasses, as well as specific examples of solder glasses that may be used to form the glass ferrule 250, are discussed in RG Frieser, "A Review of Solder Glasses," Electronic Components Science and Technology, Vol. 2, 1975, pp. 163-169, which is incorporated herein by reference.

[0056] The glass ferrule 250 is formed of a material that deforms preferentially to the glass capillary 210. For example, the glass ferrule 250 may have a lower softening and / or firing temperature than the glass capillary. By heating the glass ferrule 250 to a temperature higher than the softening temperature of the glass ferrule 250 but lower than the softening temperature of the glass capillary 210, the glass ferrule 250 may be conformed to the through hole 240 without damaging the glass capillary 210. The softening temperature or firing temperature of the glass ferrule 250 may be, for example, 50K or more lower than the corresponding temperature of the glass capillary 210, or 100K or more lower than the corresponding temperature of the glass capillary 210, or 150K or more lower than the corresponding temperature of the glass capillary 210, or 200K or more lower than the corresponding temperature of the glass capillary 210.

[0057] The coefficient of thermal expansion (CTE) of the glass ferrule 250 can be substantially equal to or lower than the CTE of the nozzle joint 220 and / or the CTE of the glass capillary 210. In some examples, the CTE of the glass ferrule 250 is within ±1 PPM / K of the CTE of the nozzle joint 220 and / or the CTE of the glass capillary 210, or within ±0.5 PPM / K of the CTE of the nozzle joint 220 and / or the CTE of the glass capillary 210 (i.e., the CTE of the glass ferrule can be higher or lower than the CTE of the nozzle joint and / or the glass capillary 210 as long as the CTE is within a given range). As with the CTE of the glass capillary 210 discussed above, approximately matching the CTE of the glass ferrule 250 to the CTE of other components can reduce failures due to different expansion and contraction characteristics. However, specifically for the glass ferrule 250, it has been found that a CTE lower than the CTE of the nozzle adapter 220 and the glass capillary 210, but still within the range of the other CTEs listed above, is advantageous. However, in the case of a thin glass ferrule 250, such as formed by capillary action, as discussed below, the ferrule 250 can be thin enough so that thermally generated expansion or contraction is negligible. Expansion of the glass ferrule 250 is unlikely to be a factor in seal failure, and therefore a glass having any CTE can be used for the glass ferrule 250.

[0058] In some examples, the glass ferrule 250 is formed of a glass having a thermal expansion coefficient of 2 PPM / K or greater, or 3 PPM / K or greater, or 4 PPM / K or greater. Alternatively or additionally, the glass ferrule 250 may be formed of a glass having a thermal expansion coefficient of 6 PPM / K or less, or 7 PPM / K or less, or 8 PPM / K or less. Preferably, the thermal expansion coefficient of the glass ferrule 250 is in the range from 3.5 PPM / K to 7 PPM / K. More preferably, the CTE of the glass ferrule is in the range of 0.5 PPM / K based on the CTE of the glass capillary 210. In addition, the glass ferrule 250 preferably has a softening temperature in the range of 500° C. to 900° C.

[0059] The material of the glass ferrule 250 should be resistant to the fuel that the nozzle 200 is intended to handle. For example, in the case where the nozzle 200 emits tin droplets, the material of the glass ferrule 250 should be resistant to tin.

[0060] In some examples, the glass ferrule 250 is formed of borosilicate, aluminosilicate, borofluorophosphate or borovanadate glass, or includes borosilicate, aluminosilicate, borofluorophosphate or borovanadate glass. In some examples, the glass ferrule 250 is formed of a mixture of materials. For example, the glass ferrule 250 may include solid particles added to the glass, such as metal particles, oxide particles or ceramic particles. Adding such particles can provide many advantages. First, by adding particles of material with very low CTE, the average CTE of the resulting glass mixture can be reduced. This provides additional flexibility when selecting the glass material while still allowing the CTE of the glass ferrule 250 to match other components. Secondly, by selecting the size of the particles, the minimum spacing of the capillary layer can be ensured. This can help center the glass capillary 210 in the nozzle joint 220. Third, the particles can help prevent cracking and make the material more stress-resistant.

[0061] exist Figure 3 In the example illustrated in , the glass ferrule 250 is shown as being relatively thick. This may be the case, for example, where the glass ferrule 250 is formed by a preformed tube around the glass capillary 210 located within the through hole 240, which is then heated to conform to the shape of the through hole 240. The thickness of the glass ferrule 250 may be 1 mm or less, or 0.7 mm or less, or 0.5 mm or less. The thickness of the glass ferrule may be 0.3 mm or more, or 0.5 mm or more. The thickness may be in the range of from 0.3 mm to 0.7 mm. As used herein, the thickness of the glass ferrule 250 refers to the thickness of the wall of the glass ferrule 250 between the wall of the through hole 240 and the outer wall of the glass capillary 210.

[0062] In other examples, a thinner glass ferrule 250 may be used. In this case, the glass may flow into the narrow space between the glass capillary 210 and the wall of the through hole 240 to form the glass ferrule 250. Therefore, in some examples, the glass ferrule may have a thickness of 0.2 mm or less and / or 0.1 mm or more. In some examples, the diameter of the glass capillary 210 and the diameter of the through hole 240 create a spacing between the glass capillary 210 and the nozzle joint 220 so that when the glass of the glass ferrule 250 is softened, the glass of the glass ferrule 250 flows by capillary action. In some examples, the spacing between the glass capillary 210 and the nozzle joint 220 is 10 μm or more, or 15 μm or more, or 20 μm or more. Alternatively or additionally, the spacing may be 30 μm or less, or 25 μm or less, or 20 μm or less. In a preferred example, the spacing is in the range of from 15 μm to 25 μm. Here, the spacing may be an average spacing, for example wherein the spacing at different points between the glass capillary 210 and the nozzle joint 220 is different.

[0063] Note that in such examples where a thinner glass ferrule 250 is used, the CTE of the glass ferrule 250 itself may not have a significant effect on the stability of the nozzle 200. The expansion of the thin material in such examples is small compared to the expansion of the nozzle adapter 220 and the glass capillary 210. Therefore, only the CTE of the nozzle adapter 220 and the glass capillary 210 can be matched (as discussed above). This allows for more choices in the material of the glass ferrule 250 because the CTE of the glass ferrule 250 is not a factor in selecting the material. For example, the material of the glass ferrule 250 can be selected to optimize properties such as softening / firing temperature, wetting, and / or capillary action.

[0064] exist Figure 3In the example illustrated in , the glass ferrule 250 extends through only a portion of the through hole 240. The glass ferrule 250 of this example is flush with the upper end of the through hole 240 at one end. The through hole 240 is shaped to provide a lip 245 for limiting the extension of the glass ferrule 250 further along the through hole 240. Thus, for example, a glass ferrule preform can be pushed into the through hole 240 from the upper end of the through hole 240 and will be stopped by the lip 245 to properly position the glass ferrule within the through hole 240. Although in this example, the lip 245 is toward the droplet outlet end of the through hole 240, in other examples, the lip 245 can be toward the liquid supply inlet side of the through hole 240 (e.g., the location where the ferrule 240 is inserted from the droplet outlet end). In addition, in the illustrated example, the portion of the through hole 240 through which the glass ferrule 240 passes is substantially cylindrical. However, in other examples, the glass ferrule 250 extends through the through hole 240 to different lengths, and the through hole 240 may have different shapes.

[0065] 4A to 4E illustrate some examples of alternative forms of the nozzle 200 .

[0066] In FIG. 4A , the first end 225 of the glass capillary 210 is no longer flush with the upper end of the through hole 240, but instead extends beyond the upper end. In addition, the lip 245 of the through hole 240 is wedge-shaped. The lip 245 tapers from the maximum diameter of the through hole 240 to the minimum diameter of the through hole 240, and the minimum diameter of the through hole 240 is in the portion of the through hole 240 into which the glass ferrule 250 does not extend. The end of the glass ferrule 250 that cooperates with the lip 245 is similarly wedge-shaped.

[0067] In FIG. 4B , the through hole 240 is substantially in the shape of a truncated cone. That is, the through hole 240 has a substantially conical surface. The diameter of the through hole 240 tapers from the upper end of the through hole 240 to the lower end of the through hole 240. Such a truncated cone / conical shape can be formed, for example, by machining the nozzle joint 220 with a conical reamer. The glass ferrule 250 is consistent with the shape of the through hole 250 and is therefore also substantially in the shape of a truncated cone. In this example, the glass ferrule 250 extends the entire length of the through hole 240. In other examples, the glass ferrule 250 may only partially extend through the through hole 240. In such examples, only a portion of the through hole 240 (the portion into which the glass ferrule 250 extends) may be substantially in the shape of a truncated cone.

[0068] Figure 34A and 4B have a partially truncated cone-shaped outer shape. However, the outer shape of the nozzle joint 220 can take any form. Specifically, the outer shape of the nozzle joint can be configured for assembly into the droplet generator 3. FIG. 4C shows examples of nozzles 220 with different outer shapes. In this case, the nozzle joint 220 has a substantially cylindrical outer portion. In other examples, the outer shape (or a portion of the outer shape) can be a cube or any other shape.

[0069] In the nozzles 200 discussed thus far, the glass ferrule 250 has extended from the upper end of the through hole 240 (i.e., the end through which the fuel is introduced into the nozzle 200). However, any of the examples discussed in the present invention may alternatively have the glass ferrule 250 extending from the lower end of the through hole 240 (i.e., the end opposite the upper end). FIG. 4D shows such a nozzle 200. The nozzle 200 is substantially similar to the nozzle 200 except that the glass ferrule 250 extends from the lower end of the through hole 240 to the lip 245. Figure 3 The nozzle shown in .

[0070] 4E illustrates yet another example of a nozzle 200, wherein the glass ferrule 250 extends completely through the through hole 240. In this example, the through hole 240 is substantially cylindrical in shape.

[0071] Figure 5 An example of a nozzle 200 coupled to a droplet generator 3 is shown. The droplet generator 3 may be a fuel emitter 3, as described above with respect to Figure 2 As discussed. The droplet generator 3 includes a body 31 to which the nozzle 200 is attached. A nut couples the body 31 to the nozzle 200. Specifically, the nut extends at least around the upper portion of the nozzle joint 220 to secure the nozzle 200 to the body 3. A seal 33 is provided between the upper surface of the nozzle joint 220 and the body 3. In use, fuel is provided to the first end 225 of the glass capillary 210 via the body 31. The fuel passes through the glass capillary 210 to the sending end 230, where the fuel is emitted in the form of droplets. As shown in Figure 5 As shown in , the second end 230 of the glass capillary 210 can be configured to launch a droplet. For example, as shown, the second end 230 can be shaped to provide a narrow opening through which the droplet leaves the glass capillary 210.

[0072] Figure 6 Illustrated is a method 300 of manufacturing a nozzle 200 for a droplet generator 3. The method 300 may be used to manufacture any of the nozzles 200 discussed above.

[0073] The method 300 begins at 301 where a glass capillary 210 is positioned in a through hole 240 of a nozzle adapter 220. The outer diameter of the glass capillary 210 is slightly smaller than the inner diameter of the through hole 240. In this way, the glass capillary 210 can be inserted into the through hole 240. For example, the difference between the outer diameter of the glass capillary 210 and the inner diameter of the through hole 240 can be about 1 mm, 0.1 mm, or less, but other differences in corresponding diameters can be used in other embodiments. The characteristics of the glass capillary 210, the nozzle adapter 220, and the through hole 240 can be the same as those discussed above.

[0074] With the glass capillary 210 in place, the method 300 proceeds to 302 where a glass ferrule preform 400 is positioned around the glass capillary 210. The glass ferrule preform is the same material as the glass ferrule 250 discussed above, but has not yet been formed to conform to the shape of the through hole 240. Note that in some examples, 302 of the method 300 is the reverse of 301. In other words, the glass ferrule preform 400 is positioned around the glass capillary 210, and then the glass capillary 210 (and the preform 400) are positioned in the through hole 240.

[0075] Figure 7 An example of positioning a glass ferrule preform 400 that can be used for method 300 is illustrated. In this example, positioning the glass ferrule preform 400 includes positioning the glass ferrule preform 400 in the through hole 240 of the nozzle adapter. The glass ferrule preform 400 can be positioned so that the glass ferrule preform 400 is completely located within the through hole 240. In this example, the glass ferrule preform 400 is approximately located at the position where the glass ferrule 250 is intended to be located. The glass ferrule preform 400 can be inserted into the through hole 240 by initially positioning the glass ferrule preform at one end (here, the upper end) of the through hole 240, and applying a force F to push the glass ferrule preform into the through hole. In the illustrated example, the glass ferrule preform 400 is pushed into the through hole 240 using a pusher 410. The pusher 240 can be formed of or include graphite. In other examples, gravity may be used to push the glass ferrule preform 400 into the through hole 240. For example, one or more weights may be placed on the upper end of the glass ferrule preform 400 (or pusher 410) so that gravity forces the glass ferrule into the through hole.

[0076] Figure 8aAn alternative example of positioning a glass ferrule preform 400 that may be used for 302 of method 300 is illustrated. In this example, the glass ferrule preform 400 is a ring of material located at the upper end of the through hole 240. It will be appreciated that in other examples, the glass ferrule preform 400 may be located at the lower end (i.e., the end through which fuel exits in use) of the through hole 240. In such cases, the nozzle adapter 220 may be rotated for the manufacturing step so that the lower end of the through hole 240, as defined above, is located above the upper end under the action of gravity.

[0077] During heating (discussed further below with respect to method 300), Figure 8a The glass ferrule preform softens and flows into the through hole 240. When cooled, this forms a glass ferrule 250 that connects the nozzle adapter 220 to the glass capillary 210, as shown in FIG. Figure 8b In a particularly advantageous embodiment, the glass capillary 210 is positioned in the through hole 240 with a gap between the glass capillary 210 and the wall of the through hole 240 so that upon heating, the glass ferrule preform 400 flows into the gap by capillary action.

[0078] Despite Figure 8b 240, but it will be appreciated that in other examples, the glass ferrule preform 400 may only partially flow through the through hole 240. For example, as discussed above, the through hole 240 may include a lip 245 to prevent the glass ferrule preform 400 from flowing further along the through hole 240.

[0079] In some examples, the glass ferrule preform 400 may include glass powder dispersed with a polymer. Such a glass ferrule preform 400 may be manufactured by compressing the glass particles and heating them so that the polymer binder binds the glass particles together to form a desired shape. Then, for example, using Figure 7 20. The method illustrated in FIG. 20 positions such a glass ferrule preform 400 about the glass capillary 210. Once in place, the glass ferrule preform 400 is heated to remove polymer from the preform 400. This can be part of the heating to deform the preform 400 discussed further below, or can be an initial heating step, heating to a lower temperature to remove polymer before heating to a higher temperature to deform the preform 400.

[0080] With the glass ferrule preform 400 already positioned, the method 300 proceeds to 303 . At 303 , the glass ferrule preform 400 is heated to form the glass ferrule 250 that couples the glass capillary 210 to the nozzle adapter 220 .

[0081] Heating the glass ferrule preform 400 may include placing the nozzle adapter 220, the glass capillary 210, and the glass ferrule preform 400 in a temperature controlled oven or chamber such as a vacuum oven. The heating may include inductively heating the nozzle adapter 220. The glass ferrule preform 400 may be heated by the nozzle adapter 220 by heating the nozzle adapter 220 by induction. Using a vacuum oven for heating may be particularly advantageous because it may allow batch processing of the nozzles 200 and provide an inert environment to prevent oxidation of the heated components.

[0082] The glass ferrule preform 400 may be heated to a temperature higher than the softening temperature of the glass ferrule preform 400 but lower than the softening temperature of the glass capillary. The glass ferrule preform 400 may be heated to a temperature of 500° C. or higher, or 650° C. or higher. The glass capillary preform 400 may be heated to a temperature of 800° C. or lower, or 750° C. or lower. Such temperatures are easily achieved in a vacuum oven.

[0083] By heating the glass ferrule preform 400 above its softening temperature, the glass ferrule preform 400 is transformed from a rigid state to a softened state, such as a relatively flexible or partially melted state. That is, the glass ferrule preform 400 may be heated directly or through the nozzle adapter 220 until the viscosity of the glass forming the glass ferrule preform 400 is reduced to the point where the glass becomes relatively flexible. Figure 7 In the example of FIG. 4 , where the glass ferrule preform 400 is substantially located at the desired final position of the glass ferrule 250, the viscosity of the glass may only need to be reduced so that the glass conforms to the shape of the through hole. Figure 8a In the example of , a lower viscosity may be required to allow the material to flow into and along the through-holes 240 .

[0084] In some examples, heating is performed in a relatively inert atmosphere or vacuum. For example, the nozzle 200 can be disposed in a shield, container, chamber, housing, etc., and exposed to a relatively inert gas, such as nitrogen or argon. A gas mixture containing hydrogen, such as a mixed gas (approximately 98% Ar and 2% H2), can also be used. Beneficially, such a relatively inert gas can prevent oxidation of one or more surfaces of the glass ferrule 250, the glass capillary 210, or the nozzle joint 220. For example, a nozzle joint 220 comprising molybdenum may be particularly subject to oxidation when heated in the presence of oxygen. In the case of a hydrogen-containing gas mixture, the hydrogen can reduce the surface of a refractory metal such as a Mo or W-based metal, thereby removing oxygen from the surface of the refractory metal. Therefore, heating the nozzle joint 220 in the presence of a relatively inert gas can prevent or at least minimize such oxidation on the surface of the nozzle joint 220 and / or the glass capillary 210 where an undesirable oxide layer is located. For example, it may be desirable to have the oxide layer only on the portion of the surface of the nozzle joint 220 where the seal between the glass and the metal is formed.

[0085] In some examples, during heating, a gas may flow through the glass capillary 210. The gas may be an inert gas, such as argon. This may prevent oxidation of the inner surface of the glass capillary 210. The gas flows at a low pressure that does not deform the glass capillary 210.

[0086] Yet another step in the method 300 of manufacturing the nozzle 200 for a droplet generator may include cooling the nozzle 200. Such cooling may be active cooling, for example, by refrigeration or with the aid of a cooling gas flow, or by natural cooling, for example, by allowing the components to cool to ambient temperature. Such cooling may follow or adhere to a predefined temperature profile. Beneficially, such cooling may at least partially anneal the glass ferrule 250 and / or the glass capillary 210, thereby reducing internal stresses within the glass components.

[0087] The method may include the step of annealing the glass ferrule 250 and / or the glass capillary 210. The specific temperature and / or heating and / or cooling rate required to anneal the glass capillary 210 may depend on the specific glass type and / or the composition of the glass. For example, the glass capillary 210 may be heated to about 600K to 800K before cooling to ambient temperature, although other temperatures may be used in other embodiments. Such annealing steps may be repeated one or more times.

[0088] In some examples, the method 300 also includes forming a nozzle outlet in the second end 230 of the glass capillary 200. The nozzle outlet can be configured to launch droplets. Forming the nozzle outlet can include heating and / or machining the second end 230 to shape the outlet as desired, such as providing a narrow opening for launching droplets.

[0089] As used herein, the term "glass to metal" seal refers to a seal that is, for example, an airtight seal between glass and metal, wherein metal is interpreted to include metals, metal alloys, and / or metal oxides. That is, the term "glass to metal seal" should be understood to include a seal between glass and metal, wherein the metal may include an oxide layer. For example, in a specific embodiment of the present disclosure, wherein the nozzle joint 220 includes molybdenum, the term "glass to metal seal" includes a seal between a glass ferrule 250 and a surface of the nozzle joint 220, wherein the surface of the nozzle joint 220 to be sealed to the glass ferrule 250 may already include an oxide layer before the seal is formed.

[0090] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Other possible 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 has been made above to the use of embodiments of the present invention in the context of a droplet generator for a laser-generated plasma radiation source, it will be appreciated that nozzles manufactured according to the claimed and described method(s) may find utility and / or be adapted for use in a variety of other applications. For example, such nozzles may be generally adapted for use in any fluid delivery application, and may be particularly adapted for use in any fluid delivery application in which the fluid to be delivered is under pressure.

[0092] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications such as imprint lithography where the context permits.

[0093] Further aspects of the invention are set out in the following numbered aspects.

[0094] 1. A nozzle for a droplet generator for a laser-generated plasma radiation source, the nozzle comprising:

[0095] A glass capillary tube, the glass capillary tube being used for launching droplets;

[0096] a nozzle adapter, the nozzle adapter comprising a through hole, wherein the glass capillary is at least partially disposed in the through hole; and

[0097] A glass ferrule connects the glass capillary to the nozzle joint, the glass ferrule conforming to the shape of the through hole of the nozzle joint.

[0098] 2. A nozzle as described in aspect 1, wherein the thermal expansion coefficient of the glass capillary is within a range of 1 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.5 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.3 PPM / K based on the thermal expansion coefficient of the nozzle joint.

[0099] 3. A nozzle as described in aspect 1 or aspect 2, wherein the thermal expansion coefficient of the glass ring is within a range of 1 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.5 PPM / K based on the thermal expansion coefficient of the nozzle joint.

[0100] 4. The nozzle of any one of aspects 1 to 3, wherein the coefficient of thermal expansion of the glass ferrule is less than the coefficient of thermal expansion of the nozzle joint and less than the coefficient of thermal expansion of the glass capillary.

[0101] 5. The nozzle of any preceding aspect, wherein the glass ferrule has a lower softening temperature than the glass capillary.

[0102] 6. The nozzle of any of the preceding aspects, wherein the glass ferrule has been coupled to the glass capillary and nozzle joint by positioning a glass ferrule preform in the through hole and heating the glass ferrule preform.

[0103] 7. The nozzle of any one of clauses 1 to 5, wherein the glass ferrule has been coupled to the glass capillary and nozzle adapter by flowing a glass ferrule preform into the through hole by capillary action.

[0104] 8. The nozzle of any preceding aspect, wherein the glass ferrule has a thickness of 1 mm or less, or 0.7 mm or less, or 0.5 mm or less, or 0.2 mm or less.

[0105] 9. The nozzle of any preceding aspect, wherein the glass ferrule has a thickness of 0.1 mm or more, or 0.3 mm or more, or 0.5 mm or more.

[0106] 10. The nozzle of any preceding aspect, wherein the glass ferrule has a thickness in the range of 0.3 mm to 0.7 mm, or a thickness in the range of 0.1 mm to 0.2 mm.

[0107] 11. The nozzle of any preceding aspect, wherein the diameter of the glass capillary and the diameter of the through hole create a spacing between the glass capillary and the nozzle joint such that when the glass of the glass ferrule is softened, the glass of the glass ferrule flows by capillary action.

[0108] 12. The nozzle of any preceding aspect, wherein the glass ferrule extends the full length of the through hole.

[0109] 13. The nozzle of any one of clauses 1 to 11, wherein the glass ferrule extends a portion of the length of the through hole.

[0110] 14. The nozzle of clause 13, wherein the through hole is shaped to provide a lip for limiting the extension of the glass ferrule along the through hole.

[0111] 15. The nozzle according to any one of the preceding aspects, wherein the glass capillary protrudes from one or both ends of the through hole.

[0112] 16. The nozzle of any preceding aspect, wherein the end of the glass capillary is flush with the end of the through hole.

[0113] 17. The nozzle of any preceding aspect, wherein the nozzle connector comprises molybdenum, tantalum, tungsten, or a metal alloy.

[0114] 18. The nozzle of any preceding aspect, wherein the nozzle connector comprises a metal oxide layer.

[0115] 19. The nozzle of any preceding aspect, wherein the glass capillary comprises borosilicate, aluminosilicate, or quartz.

[0116] 20. The nozzle of any preceding aspect, wherein the glass ferrule comprises a borosilicate, an aluminosilicate, a borofluorophosphate, or a borovanadate.

[0117] 21. A method of manufacturing a nozzle for a droplet generator, the method comprising:

[0118] Position the glass capillary in the through hole of the nozzle adapter;

[0119] positioning a glass ferrule preform around the glass capillary;

[0120] The glass ferrule preform is heated to form a glass ferrule that couples the glass capillary to the nozzle adapter.

[0121] 22. The method of clause 21, wherein positioning the glass ferrule preform comprises positioning the glass ferrule preform in the through hole of the nozzle adapter.

[0122] 23. The method of clause 22, comprising applying a force to push the glass ferrule preform into the through hole.

[0123] 24. The method of clause 23, wherein applying the force comprises: using a pusher to push the glass ferrule preform into the through hole.

[0124] 25. The method of aspect 23 or aspect 24, comprising: applying a weight to the glass ferrule preform and / or the pusher so that gravity forces the glass ferrule to enter the through hole.

[0125] 26. The method of aspect 21, wherein positioning the glass ferrule preform comprises positioning the glass ferrule preform at an end of the through hole, and wherein the glass ferrule preform is heated to cause the glass ferrule preform to flow into the through hole to form the glass ferrule.

[0126] 27. A method as described in any one of aspects 21 to 26, wherein the glass capillary is positioned in the through hole in a manner with a gap between the glass capillary and the wall of the through hole, so that when heated, the glass ferrule preform flows into the gap by capillary action.

[0127] 28. The method of clause 27, wherein the gap has a thickness of 0.2 mm or less, and / or wherein the gap has a thickness of 0.1 mm or more.

[0128] 29. The method of any one of clauses 21 to 28, wherein the glass capillary preform is heated using an induction heater configured to heat the nozzle joint.

[0129] 30. The method of any one of aspects 21 to 29, wherein the glass capillary preform is heated using a vacuum oven.

[0130] 31. The method of any one of clauses 21 to 30, wherein the glass ferrule preform is heated to a temperature above a softening temperature of the glass ferrule preform but below a softening temperature of the glass capillary.

[0131] 32. The method of any one of aspects 21 to 31, wherein the glass capillary preform is heated to a temperature of 500°C or higher, or 650°C or higher.

[0132] 33. The method of any one of aspects 21 to 32, wherein the glass capillary preform is heated to a temperature of 800°C or less, or 750°C or less.

[0133] 34. The method of any one of aspects 21 to 33, further comprising: flowing a gas through the glass capillary.

[0134] 35. The method of any one of clauses 21 to 34, further comprising: forming a nozzle outlet in an end of the glass capillary.

[0135] 36. A method as described in any one of aspects 21 to 35, wherein the thermal expansion coefficient of the glass capillary is within a range of 1 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.5 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.3 PPM / K based on the thermal expansion coefficient of the nozzle joint.

[0136] 37. A method as described in any of aspects 21 to 36, wherein the thermal expansion coefficient of the glass ferrule is within a range of 1 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.5 PPM / K based on the thermal expansion coefficient of the nozzle joint.

[0137] 38. The method of any one of aspects 21 to 37, wherein the coefficient of thermal expansion of the glass ferrule is less than the coefficient of thermal expansion of the nozzle adapter and less than the coefficient of thermal expansion of the glass capillary.

[0138] 39. The method of any one of clauses 21 to 38, wherein the glass ferrule, when formed, extends the full length of the through hole.

[0139] 40. The method of any one of clauses 21 to 38, wherein the glass ferrule, when formed, extends a portion of the length of the through hole.

[0140] 41. The method of any one of clauses 1 to 40, wherein the through hole is shaped to provide a lip for limiting the extension of the glass ferrule along the through hole.

[0141] 42. The method of any one of aspects 21 to 41, wherein the glass capillary is located in the through hole such that the glass capillary protrudes from one or both ends of the through hole.

[0142] 43. The method of any one of clauses 21 to 42, wherein the glass capillary is positioned in the through hole such that an end of the glass capillary is flush with an end of the through hole.

[0143] 44. The method of any one of aspects 21 to 43, wherein the nozzle joint comprises molybdenum, tantalum, tungsten, or a metal alloy.

[0144] 45. The method of any one of aspects 21 to 44, wherein the nozzle joint comprises a metal oxide layer.

[0145] 46. ​​The method of any one of aspects 21 to 45, wherein the glass capillary comprises borosilicate, aluminosilicate, or quartz.

[0146] 47. The method of any one of aspects 21 to 46, wherein the glass ferrule preform comprises a borosilicate, an aluminosilicate, a borofluorophosphate, or a borovanadate.

[0147] 48. A droplet generator for a laser-generated plasma radiation source, the droplet generator comprising a nozzle as described in any one of aspects 1 to 20.

[0148] 49. A lithography system comprising a radiation source, the radiation source comprising the droplet generator according to clause 48.

[0149] Although the present invention has been described in conjunction with various embodiments, other embodiments of the present invention will be apparent to those skilled in the art who consider this specification and practice the invention disclosed herein. It is intended that this specification and examples be considered exemplary only, with the true scope and spirit of the present invention being indicated by the appended claims and aspects.

Claims

1. A nozzle for a droplet generator for a laser-generated plasma radiation source, the nozzle comprising: A glass capillary tube, the glass capillary tube being used for launching droplets; a nozzle connector, the nozzle connector comprising a through hole, wherein the glass capillary is at least partially disposed in the through hole; as well as A glass ferrule connects the glass capillary to the nozzle joint, the glass ferrule conforming to the shape of the through hole of the nozzle joint.

2. The nozzle according to claim 1, wherein The thermal expansion coefficient of the glass capillary is within a range of 1 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.5 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.3 PPM / K based on the thermal expansion coefficient of the nozzle joint; and / or The thermal expansion coefficient of the glass ferrule is within a range of 1 PPM / K based on the thermal expansion coefficient of the nozzle joint, or within a range of 0.5 PPM / K based on the thermal expansion coefficient of the nozzle joint.

3. The nozzle according to claim 1 or claim 2, wherein: The coefficient of thermal expansion of the glass ferrule is smaller than the coefficient of thermal expansion of the nozzle adapter and smaller than the coefficient of thermal expansion of the glass capillary.

4. A nozzle as claimed in any preceding claim, wherein: The glass ferrule has a lower softening temperature than the glass capillary.

5. A nozzle as claimed in any preceding claim, wherein: The glass ferrule has a thickness of 1 mm or less, or 0.7 mm or less, or 0.5 mm or less, or 0.2 mm or less; and / or Wherein, the glass ferrule has a thickness of 0.1 mm or more, or 0.3 mm or more, or 0.5 mm or more.

6. A nozzle as claimed in any preceding claim, wherein: The diameter of the glass capillary and the diameter of the through hole create a spacing between the glass capillary and the nozzle joint such that the glass of the glass ferrule flows by capillary action when the glass of the glass ferrule is softened.

7. A nozzle as claimed in any preceding claim, wherein: The through hole is shaped to provide a lip for limiting extension of the glass ferrule along the through hole.

8. A nozzle as claimed in any preceding claim, wherein: The nozzle connector comprises molybdenum, tantalum, tungsten, or a metal alloy; and / or The glass capillary comprises borosilicate, aluminosilicate, or quartz; and / or The glass ferrule includes borosilicate, aluminosilicate, borofluorophosphate, or borovanadate.

9. A method for manufacturing a nozzle for a droplet generator, the method comprising: Position the glass capillary in the through hole of the nozzle adapter; positioning a glass ferrule preform around the glass capillary; as well as The glass ferrule preform is heated to form a glass ferrule that couples the glass capillary to the nozzle adapter.

10. The method of claim 9, wherein: Positioning the glass ferrule preform includes positioning the glass ferrule preform in the through hole of the nozzle adapter.

11. The method of claim 10, comprising: A force is applied to push the glass ferrule preform into the through hole.

12. The method of claim 11, comprising: A weight is applied to the glass ferrule preform and / or the pusher so that gravity forces the glass ferrule into the through hole.

13. The method of claim 9, wherein: Positioning the glass ferrule preform includes positioning the glass ferrule preform at an end of the through hole, and wherein the glass ferrule preform is heated to flow the glass ferrule preform into the through hole to form the glass ferrule.

14. The method according to any one of claims 9 to 13, wherein: The glass capillary is positioned in the through hole with a gap between the glass capillary and a wall of the through hole so that upon heating, the glass ferrule preform flows into the gap by capillary action.

15. The method according to any one of claims 9 to 14, wherein: The glass ferrule preform is heated to a temperature that is higher than a softening temperature of the glass ferrule preform but lower than a softening temperature of the glass capillary.

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