EP4360408A1

EP4360408A1 - Pressure-energized ferrule for high pressure droplet generator nozzle

Info

Publication number: EP4360408A1
Application number: EP22730384.9A
Authority: EP
Inventors: Rahul Sunil KAPADIA; Bob Rollinger; Joshua Mark LUKENS; Georgiy Olegovich VASCHENKO; Sreedhar GANNA
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2021-06-23
Filing date: 2022-05-18
Publication date: 2024-05-01
Also published as: WO2022268413A1; CN117999856A; KR20240024078A; TW202307582A

Abstract

Disclosed is a capillary retention system including a pressure-energized ferrule which is double-sealing and configured and arranged so that internal target material pressure acts to increase the sealing pressure. According to another aspect of an embodiment the pressure-energized ferrule is configured and arranged so that sealing contact pressure on the capillary is closer to the capillary free face making 5 up the nozzle outlet and thus reduces the capillary free length in turn increasing the bending mode of the capillary, thereby making it less likely to be excited by system vibrations.

Description

PRESSURE-ENERGIZED FERRULE FOR HIGH PRESSURE DROPLET GENERATOR NOZZLE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63/213,804, filed June 23, 2021, titled PRESSURE-ENERGIZED FERRULE FOR HIGH PRESSURE DROPLET GENERATOR NOZZLE, which is incorporated herein in its entirety by reference.

FIELD

[0002] This disclosure relates to a nozzle apparatus. The nozzle apparatus may be used to generate targets in an extreme ultraviolet (EUV) light source.

BACKGROUND

[0003] EUV light, for example, electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays) and including light at a wavelength of about 13 nm, is used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers.

[0004] Methods for generating EUV light include, but are not limited to, altering the physical state of the target material into a plasma state. The target material includes 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 target material, for example, in the form of a droplet, stream, or cluster of target 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.

[0005] CO2 amplifiers and lasers, which output an amplified light beam at a wavelength of about 10600 nm, can deliver certain advantages as a drive laser for irradiating the target material in an LPP process. This may be especially true for certain target materials, for example, for materials containing tin. For example, one advantage is the ability to produce a relatively high conversion efficiency between the drive laser input power and the output EUV power.

[0006] In the EUV light source, EUV may be produced in a two-step process in which a droplet of target material travelling to an irradiation site is first struck by a pre-pulse that conditions the droplet for subsequent phase conversion at the irradiation site. Conditioning in this context may include altering the shape of the droplet, e.g., flattening the droplet, or the distribution of the droplet, e.g., at least partially dispersing some of the droplet as a mist. For example, a pre-pulse hits the droplet to modify the distribution of the target material and a main pulse hits the target to transform it to an EUV-emitting plasma. In some systems the pre-pulse and the main pulse are provided by the same laser and in other systems the pre-pulse and the main pulse are provided by two separate lasers. In some systems there may be one or more additional conditioning pulses ahead of the main pulse.

[0007] A nozzle apparatus may be used to produce a stream or jet of fluid material out of a capillary ending in a nozzle outlet or orifice. The nozzle apparatus must be retained in place while operating. In one implementation of a nozzle retention system, a polyimide ferrule is used to seal the glass capillary against a nozzle body. This ferrule creates the seal for containing the high pressure liquid target material. Sealing is achieved by using a tightening nut.

[0008] This implementation has some drawbacks. One drawback is that the ferrules lose sealing pressure as the internal pressure of target material is increased and also due to the fact that polyimide ferrule loses its strength as it is heated. Thus, these ferrules would not be suitable for use at higher pressures, e.g., pressures greater than 14,000 psi (lOOObar) that it is anticipated will be required in future droplet generators. Additionally, the ferrule softens at the droplet generator operating temperatures and thus adds a non-linearity to the overall nozzle system. The resulting reduction in stiffness can permit capillary tip oscillations, which can affect droplet stability.

[0009] There is therefore a need for a capillary retention system that avoids these drawbacks.

SUMMARY

[0010] The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments and is not intended to identify key or critical elements of all embodiments nor set limits on the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments as a prelude to the more detailed description that is presented later.

[0011] According to one aspect of an embodiment there is disclosed an apparatus for an extreme ultraviolet light source, the apparatus comprising a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state, a capillary having a first end and a second end; the capillary being in fluid communication with the cavity at the first end and the second end defining a nozzle outlet for emitting a stream of the target material, a ferrule having a through hole surrounding and forming a seal with at least a lengthwise portion of the capillary, the capillary extending through the through hole, a nozzle nut mechanically coupling the ferrule to the nozzle body, at least a portion of the ferrule having a conical shape wherein an outer diameter of the ferrule decreases in a direction toward the second end of the capillary. The portion of the ferrule having a conical shape is dimensioned to mate with an interior surface of a complementary cavity defined by the nozzle nut to form a seal between the portion of the ferrule having a conical shape and the interior surface. The ferrule may be formed of a polyimide, a polyamide-imide, or a polybenzimidazole. The nozzle body may be formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum. The ferrule may have an outwardly extending circumferential shoulder adjacent a portion of the conical shape having a greatest outer diameter, the shoulder being adapted to be received in a channel formed between the nozzle body and the nozzle nut, the shoulder being an annular gasket forming a seal between the nozzle body and the nozzle nut. The apparatus may further comprise an annular gasket arranged laterally adjacent to a portion of the conical shape having a greatest outer diameter, the annular gasket being adapted to be received in a channel formed between the nozzle body and the nozzle nut to form a seal between the nozzle body and the nozzle nut. The ferrule may comprise a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular flange surrounding the through hole and configured and arranged to engage the capillary. The ferrule may comprise a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular channel arranged radially adjacent outward of the through hole. The ferrule may comprise a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular flange configured and arranged to engage the capillary and an annular channel arranged radially adjacent outward of the annular flange.

[0012] According to another aspect of an embodiment there is disclosed an apparatus for an extreme ultraviolet light source, the apparatus comprising a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state, a glass capillary having a first end extending into the cavity and a second end defining a nozzle outlet for emitting target material that has passed inside and along a length of the glass capillary, a ferrule having a central through hole adapted to receive the glass capillary, the ferrule surrounding and forming a seal with at least a lengthwise portion of the glass capillary, the glass capillary extending through the central through hole, a portion of the ferrule having a fmstoconical shape with a first diameter towards the first end of the glass capillary and a second diameter towards the second end of the glass capillary, the first diameter being greater than the second diameter, and a threaded nozzle nut arranged to mechanically couple with the nozzle body to capture the ferrule between the nozzle nut and the nozzle body, the nozzle nut having a fmstoconical cavity dimensioned to receive the portion of the ferrule having the fmstoconical shape. The ferrule may be formed of a polyimide, a polyamide-imide, or a polybenzimidazole. The nozzle body may be formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum. The ferrule may have an outwardly extending circumferential shoulder received in a channel formed between the nozzle body and the nozzle nut. The ferrule may have a disc-like portion facing the cavity and comprising an annular flange surrounding the through hole and configured and arranged to engage the glass capillary. The ferrule may have a disc-like portion facing the cavity and comprising an annular channel arranged radially adjacent outward of the through hole. The ferrule may have a disc like portion facing the cavity and comprising an annular flange configured and arranged to engage the glass capillary and an annular channel arranged radially adjacent outward of the annular flange.

[0013] According to another aspect of an embodiment there is disclosed an apparatus for an extreme ultraviolet light source, the apparatus comprising a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state, a cylindrical glass capillary having a first end extending into the cavity and a second end defining a nozzle outlet for emitting target material that has passed through the cylindrical glass capillary, a ferrule having a central through hole dimensioned to receive the cylindrical glass capillary to permit the cylindrical glass capillary to pass through and extend from a back end of the ferrule disposed towards the cavity and a front end of the ferrule disposed towards the nozzle outlet, the ferrule surrounding and forming a seal with at least an intermediate lengthwise portion of the cylindrical glass capillary, a portion of the ferrule axially between the front end of the ferrule and the back end of the ferrule having a frustoconical shape with a first diameter towards the back end of the ferrule and a second diameter towards the front end of the ferrule, the first diameter being greater than the second diameter, and a threaded nozzle nut arranged to mechanically couple with the nozzle body to capture the ferrule between the nozzle nut and the nozzle body, the nozzle nut having a frustoconical space dimensioned to receive the portion of the ferrule having the frustoconical shape. The ferrule may be formed of a polyimide, a polyamide-imide, or a poly benzimidazole. The nozzle body may be formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum. The ferrule may have outwardly extending circumferential shoulder received in a channel formed between the nozzle body and the nozzle nut. The back end of the ferrule may have a disc-like portion facing the cavity and comprising an annular flange surrounding the through hole and configured and arranged to engage the cylindrical glass capillary. The ferrule may have a disc-like portion facing the cavity and comprising an annular channel arranged radially adjacent outward of the through hole. The ferrule may have a disc-like portion facing the cavity and comprising an annular flange configured and arranged to engage the capillary and an annular channel arranged radially adjacent outward of the annular flange.

[0014] According to another aspect of an embodiment there is disclosed an apparatus for an extreme ultraviolet light source, the apparatus comprising a tubular structure disposed in a support structure and having a first end and a second end, an actuator mechanically coupled to an exterior wall of the tubular structure, the first end of the tubular structure extending into a cavity configured to receive target material that emits extreme ultraviolet (EUV) light when in a plasma state, at least a portion of the tubular structure being surrounded by a ferrule, and a ferrule nut adapted to be mechanically coupled to the support structure, the ferrule being received between the support structure and the ferrule nut, at least a portion of the ferrule having a conical shape wherein an outer diameter of the ferrule decreases in a direction toward the second end of the tubular structure. The ferrule may be formed of a material comprising polyimide. The support structure may be formed of a material comprising molybdenum. The ferrule may have an outwardly extending circumferential rib received in a channel formed between the support structure and the ferrule nut. [0015] Further embodiments, features, and advantages of the subject matter of the present disclosure, as well as the structure and operation of the various embodiments are described in detail below with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a block diagram of an implementation of an extreme ultraviolet (EUV) light source. [0017] FIG. 2A is a side-cross sectional view of a target formation apparatus.

[0018] FIG. 2B is a top cross-sectional view of the target formation apparatus of FIG. 2A.

[0019] FIG. 3 is a cross-sectional diagram of a capillary retention system.

[0020] FIG. 4A is a cross-sectional diagram of a capillary retention system according to an aspect of an embodiment.

[0021] FIG. 4B is a perspective view of a component of the embodiment of FIG. 4A according to an aspect of an embodiment.

[0022] FIG. 4C is an end-on and partly cross-sectional view of the embodiment of FIG. 4A according to an aspect of an embodiment .

[0023] FIG. 5A is a cross-sectional diagram of a capillary retention system according to an aspect of an embodiment.

[0024] FIG. 5B is a perspective view of a component of the embodiment of FIG. 5A according to an aspect of an embodiment .

[0025] FIG. 5C is an end-on and partly cross-sectional view of a component of the embodiment of FIG. 5 A.

[0026] FIG. 5D is an end-on and partly cross-sectional view of a component of the embodiment of FIG. 5 A.

[0027] FIG. 6A is a cross-sectional diagram of a capillary retention system according to an aspect of an embodiment.

[0028] FIG. 6B is an end-on and partly cross-sectional view of a component of the embodiment of FIG. 6A.

[0029] FIG. 7A is a cross-sectional diagram of a capillary retention system according to an aspect of an embodiment.

[0030] FIG. 7B is an end-on and partly cross-sectional view of a component of the embodiment of FIG. 7 A.

[0031] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art based on the teachings contained herein. DETAILED DESCRIPTION

[0032] Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to promote a thorough understanding of one or more embodiments. It may be evident in some or all instances, however, that any embodiment described below can be practiced without adopting the specific design details described below.

[0033] An overview of the EUV light source 100 and a supply system 110 is provided prior to discussing the various implementations of the nozzle apparatus 140. The EUV light source 100 is an example of a system in which the nozzle apparatus 140 may be used. However, the nozzle apparatus 140, and any of its various implementations, may be used in systems other than an EUV light source. [0034] Referring to FIG. 1, a block diagram of an EUV light source 100 that includes a supply system 110 is shown. The supply system 110 emits a stream of targets 121 such that a target 121p is delivered to a plasma formation location 123 in a vacuum chamber 109. The target 121p includes target material, which is any material that emits EUV light when in a plasma state. For example, the target material may include water, tin, lithium, and/or xenon. The plasma formation location 123 receives a light beam 106. The light beam 106 is generated by an optical source 105 and delivered to the vacuum chamber 109 via an optical path 107. An interaction between the light beam 106 and the target material in the target 121p produces a plasma 196 that emits EUV light. The supply system 110 includes a capillary tube 114 that is fluidly coupled to a reservoir 112. The capillary tube 114 is held by a nozzle apparatus 140. The capillary tube 114 defines an orifice 119 through which a material flows to form the stream of targets 121

[0035] In the example of FIG. 1, the capillary tube 114 is mechanically coupled to an actuator 193, which is connected to a control system 190 via a control link 192. The control system 190 may include a function generator, an electronic processor (not shown), and an electronic storage (not shown) to carry out the functions of the control system 190. The control link 192 is any type of connection capable of transferring an electronic signal from the control system 190 to the actuator 193. For example, the control link 192 may be a wired and/or wireless connection configured to transmit electronic signals and commands from the control system 190 to the actuator 193.

[0036] The control system 190 generates signals that, when applied to the actuator 193 or to an element associated with the actuator 193, cause the actuator 193 to move. For example, the actuator 193 may be a piezoelectric ceramic material that changes shape based on an applied voltage. The magnitude and or polarity of the voltage applied to the actuator 193 is based on the signals from the control system 190. Due to the mechanical coupling between the capillary tube 114 and the actuator 193, when the actuator 193 moves or vibrates, the capillary tube 114 experiences a corresponding motion or vibration. The vibrations imparted by the actuator 193 are generally intentional vibrations. More specifically, a radial contraction of the actuator results in a local contraction of the capillary and the expansion of the actuator results in the local expansion of the capillary. This expansion and contraction results in a creation of acoustic waves at the frequency of the applied electrical signal in the target material that is located inside of the capillary.

[0037] The reservoir 112 contains target material under pressure P. The target material is in a molten state and is able to flow, and the pressure in the vacuum chamber 109 is lower than the pressure P. The molten state may include melted metallic target material. Thus, the target material flows through the capillary tube 114 and is emitted into the chamber 109 through the orifice 119. The target material exits the orifice 119 as a jet or continuous stream 124 of target material. The jet of target material breaks up into individual droplets. The break-up of the jet 124 may be controlled such that the individual droplets coalesce into larger droplets that arrive at the plasma formation location 123 at a desired rate by vibrating the capillary tube 114 and creating acoustic waves inside of the capillary tube 114.

[0038] For example, the control system 190 may provide a signal that has at least a first frequency and a second frequency via the control link 192 to thereby drive the actuator 193 to vibrate at the first and second frequencies. The first frequency may be in the megahertz (MHz) range. Vibrating the capillary tube 114 at the first frequency causes the jet 124 to break into relatively small droplets of desired sizes and speeds. The second frequency is lower than the first frequency. For example, the second frequency may be in the kilohertz (kHz) range. The second frequency is used to modulate the velocity of the droplets in the stream and to encourage target coalescence. Driving the capillary tube 114 at the second frequency causes groups of droplets to form. In any given group of droplets, the various droplets travel at different velocities. The droplets with higher velocities may coalesce with the droplets with lower velocities to form larger coalesced droplets that make up the stream of targets 121 for the EUV source. [0039] By causing the capillary tube 114 to vibrate in this manner, the final targets may be generated at frequencies of, for example, between 40 to 300 kHz and may travel toward the plasma formation location 123 at a velocity of, for example, between 40 and 120 meters per second (m/s) or up to 500 m/s but other frequencies and speeds may also be used. . The spatial separation between two adjacent targets in the stream of targets 121 may be, for example, between 1 and 3 millimeters (mm). Between 50 and 300 initial droplets (also called Rayleigh droplets) may coalesce to form a single larger target but other spatial separations may b used and may result in other coalescence characteristics.

[0040] Thus, the capillary tube 114 is intentionally moved or vibrated, and this intentional motion or vibration is controlled to promote coalescence of target material and to control the rate of target production. The intentional vibrations and or environmental effects may lead to other, unintentional, cantilever type vibrations of the capillary tube 114. The nozzle assembly 140 reduces or eliminates the unintentional vibrations while allowing the intentional vibrations. An example of the capillary tube 114 and actuator 193 are discussed prior to discussing examples of the nozzle assembly 140 in more detail. [0041] FIG. 2A is a side cross-sectional view of a target formation apparatus 216 in an X-Z plane. FIG. 2B is a top cross-sectional view of the target formation apparatus 216 in a Y-Z plane taken along the line 2B’ — 2B’ of FIG. 2A. [0042] The target formation apparatus 216 may be used in the EUV light source 100 (FIG. 1). The target formation apparatus 216 includes a capillary tube 214 that is mechanically coupled to an actuator 293 by an adhesive 234 (shown in cross-hatch shading). For example, the adhesive 234 may be an epoxy, a benzoxazine resin, a resin containing benzoxazines, a bismaleimide resin, a cyanate ester resin, or a resin containing cyanate esters. Although the example of FIGS. 2A and 2B includes the adhesive 234, the actuator 293 and the capillary tube 214 may be coupled by direct contact (for example, an interference fit or by using fasteners) and without using an adhesive.

[0043] The capillary tube 214 includes a sidewall 230 that extends along the X direction from a first end 231 to a second end 232. The sidewall 230 is a three-dimensional object that is generally cylindrical. The sidewall 230 includes an inner surface 233 and an outer surface 239. The inner surface 233 defines an interior region 238 (FIG. 2B) that is in fluid communication with a nozzle 235 at the first end 231. The nozzle 235 narrows along the -X direction to define an orifice 219. In operational use, the interior region 238 is fluidly coupled to a reservoir of target material (such as the reservoir 112 of FIG. 1), and molten target material flows in the interior region 238 of the capillary tube 214 and through the orifice 219 in the -X direction.

[0044] In the example of FIGS. 2A and 2B, the actuator 293 is a cylinder with an outer actuator surface 295 and an inner actuator surface 236. The inner actuator surface 236 defines an open central region that extends along the X direction. The inner actuator surface 236 completely surrounds a portion 237 (FIG. 2A) of the outer surface 239. The portion 237 includes any part of the outer surface 239 that is surrounded by the actuator 293. The portion 237 may extend from the first end 231 to the second end 232, or the portion 237 may extend along the X direction over less than the entire length of the sidewall 230. In the example of FIG. 2A, the portion 237 extends in the X direction over less than the entire length of the sidewall 230. The actuator 293 is mechanically coupled to the portion 237 with the adhesive 234.

[0045] The actuator 293 is made of any material that is capable of causing the sidewall 230 to move. The actuator 293 may be an electro-mechanical actuator. For example, the actuator 293 may be a piezoelectric ceramic material such as lead zirconate titanate (PZT) that changes shape in response to the application of voltage. By changing shape, the PZT also causes the capillary tube 214 to move. The actuator 293 causes symmetrical displacement of the wall of the capillary tube 214 by periodical radial contraction and expansion.

[0046] In the example shown, the targets 121 are in the form of a stream of droplets released by the orifice 119. The targets can be ionized by a main pulse in this form. Alternatively, the targets 121 can be preconditioned for ionization with one or more conditioning pulses that can, for example, change the geometric distribution of the targets 121. In one implementation, a polyimide ferrule is used to seal the glass capillary against a nozzle body.

[0047] This ferrule participates in creating the seal for containing the high pressure liquid target material. Sealing is achieved by using a tightening nut. Such a capillary retention system 300 is shown in FIG. 3. In FIG. 3, a capillary 304 with its piezoelectric ceramic actuator 305 is retained in a nozzle body 310 by a ferrule 315 and a nozzle nut 320. Also shown is a thickened portion 306 of the portion of the capillary 304 that protrudes into a cavity 330. The thickened portion 306 may be a fused glass ring as shown or may be formed integrally with the capillary 304. Liquid target material is retained in the cavity 330 and exerts pressure in the direction indicated by the arrows. The liquid target material flows down the capillary 304 to the nozzle outlet at the end.

[0048] As mentioned, this implementation has drawbacks. Pressure from the cavity 330 tends to urge the ferrule 315 out of sealing engagement with the nozzle body 310. This can be seen down for example, in the area shown in the broken circle which shows the ceiling on between the capillary and the nozzle body. Also, the ferrules lose sealing pressure as the internal pressure of target material is increased and also due to the fact that polyimide polymer loses its strength as it is heated. Additionally, the ferrule softens at the droplet generator operating temperatures and thus adds a non-linearity to the overall nozzle system. For example, this low stiffness support can permit capillary tip oscillations, which can have a negative effect on droplet stability.

[0049] To overcome these drawbacks, in accordance with an aspect of an embodiment, a double sealing, pressure energized ferrule is arranged and configured such that the internal target material pressure acts to increase the sealing pressure. This feature permits the ferrule to be used for higher pressure applications. Additionally, the ferrule also moves the sealing contact pressure on the capillary closer towards the capillary free face and thus reduces the capillary free length which would help to increase the bending mode frequency of the capillary, thereby making it less likely to be excited by system vibrations. In addition, the pressure applied to the nozzle shifts the capillary into firmer engagement with the ferrule, until a widened portion of the capillary is stopped by the ferrule from sliding any further.

[0050] The ferrule material choice depends on the specific implementation and application, but materials such as polyimide (for example Vespel® SP-1), polyamide-imides (for example Torlon^® PAI) and polybenzimidazoles (PBI) may be used.

[0051] According to an aspect of an embodiment, at least a lengthwise portion of the ferrule is in the form of a truncated cone, i.e., fmstoconical.

[0052] Additionally, the use of such a ferrule would reduce the high frequency vibrations of the capillary by moving the first mode frequency of the complete assembly higher.

[0053] FIG. 4A shows a capillary retention system 400 in accordance with certain aspects of an embodiment. The capillary retention system 400 of FIG. 4 A includes a ferrule 405 and a threaded nozzle nut 410 that attaches the ferrule 405 to the nozzle body 420. The nozzle body may be formed of a refractory metal that is compatible with molten tin such as one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum.

[0054] A cavity 430 retains liquid target material under pressure. Liquid target material flows down the capillary 304. In the arrangement shown, the pressure of the target material in cavity 430 tends to improve the seal between the ferrule 405 and the capillary 304 and the seal between the ferrule 405 and the nozzle body and the nozzle nut 410. For example, the area enclosed by broken circle 440 indicates how the pressure from the cavity 430 tends to urge the ferrule 405 into closer contact with the nozzle nut 410 and the nozzle body 420. The smaller broken circle, broken circle 445, shows how the pressure from the cavity 430 urges the ferrule 405 into closer contact with the nozzle nut 410 and the capillary 304.

[0055] The ferrule 405 has outwardly extending circumferential shoulder received in a channel formed between the nozzle body 420 and the nozzle nut 410. Also, the frustoconical portion of the ferrule 405 is dimensioned to be received in a matching frustoconical portion of the nozzle nut 410. This is also true of other embodiments.

[0056] It will be noted that the portion of the ferrule 405 which faces the cavity 430 may be provided with additional structure to improve the self-energizing aspect of the capillary retention system 400. In the example shown in FIG. 4A, the ferrule 405 has an annular channel 450 and an annular flange 460. This arrangement helps permit the pressure to force the ferrule 405 into closer contact with adjacent mating surfaces.

[0057] FIG. 4B is a perspective view of the ferrule 405 shown in FIG. 4A. It can be seen that the ferrule has a back end with a disc-like structure 470 having a shoulder 475 and a front end 466 through which the end of the capillary 304 serving as the nozzle outlet will protrude in use. The ferrule 405 also includes an intermediate frustoconical section 485 which will be received in a complementarily dimensioned space in the nozzle nut 410. Again, this is also true of other embodiments.

[0058] FIG. 4C is an end-on view of the ferrule 405. As can be seen, there is a disc-like member 470 having central aperture 465 for receiving the capillary 304, an annular channel 450, an annular flange 460, and an annular shoulder 475 for the ferrule 405. The annular shoulder 475 surrounds, i.e. is radially outward and adjacent the annular channel 450 which in turn surrounds, i.e. is radially outward and adjacent the annular flange 460 in the end-on view of FIG. 4C.

[0059] Also, it should be noted that according to an aspect of an embodiment, the pressure applied to the ferrule 405 by the molten target material in the cavity 430 tends to urge and shift the capillary 304 further into the ferrule 405, all the way to the right in the figure, until the widened or thickened portion 306 of the capillary 304 is stopped by the ferrule 405 from sliding any further. This is another aspect of the self-energizing seal according to the embodiment and is true for other embodiments as shown. [0060] FIG. 5A shows another capillary retention system 500 in accordance with certain aspects of an embodiment. The capillary retention system 500 of FIG. 5A is similar to that just described in that it includes a ferrule 505 which does not have a shoulder or flange as shown in FIG. 5B. The ferrule 505 achieves a seal between the capillary 305 and the compression fitting nut 410 while a separate gasket 480 achieves a seal between the nozzle body 420 and the nut 410. In accordance with an aspect of an embodiment, this configuration eliminates mechanical coupling between two seals that may otherwise interfere with the proper sealing action during assembly. It will be understood by one of ordinary skill in the art that this configuration may be used for other embodiments disclosed herein. FIG. 5C is a view of the gasket 480. FIG. 5D is an end on view and partially cutaway view of the section of the ferrule 505.

[0061] FIG. 6A shows another capillary retention system 600 in accordance with certain aspects of an embodiment. A nozzle nut 510 that attaches the ferrule 605 to the nozzle body 520. The cavity 430 retains liquid target material under pressure. Liquid target material flows down the capillary 304. In the arrangement shown, as above, the pressure of the target material in cavity 430 tends to improve the seal between the ferrule 605 and the capillary 304 and the seal between the ferrule 605 and the nozzle body 520 and the nozzle nut 510. The ferrule 605, however, differs from ferrule 405 in that the portion of the ferrule 605 which faces the cavity 430 has an annular channel 550. This arrangement also helps permit the pressure to force the ferrule 505 into closer contact with adjacent surfaces.

[0062] FIG. 6B is an end-on view of the ferrule 605. As can be seen, there is a central aperture 565 for receiving the capillary 304, an annular step 550, and an annular shoulder 570 for the ferrule 505. [0063] FIG. 7A also shows a capillary retention system 700 in accordance with certain aspects of an embodiment. The capillary retention system 700 of FIG. 7A is similar to those just described in that it includes a ferrule 705 and a threaded nozzle nut 610 that attaches the ferrule 705 to the nozzle body 620. The cavity 430 retains liquid target material under pressure. Liquid target material flows down the capillary 304. In the arrangement shown, as above, the pressure of the target material in cavity 430 tends to improve the seal between the ferrule 705 and the capillary 304 and the seal between the ferrule 705 and the nozzle body 620 and the nozzle nut 610. The ferrule 705, however, differs from ferrules 405 and 605 in that the portion of the ferrule 705 which faces the cavity 430 has an annular channel 640 and a flange 645. This arrangement also helps permit the pressure to force the ferrule 705 into closer contact with adjacent surfaces.

[0064] FIG. 7B is an end-on and partially cutaway view of the ferrule 705. As can be seen, there is a central aperture 665 for receiving the capillary 304, an annular flange 645, and an annular shoulder 670 for the ferrule 705.

[0065] One of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is construed when employed as a transitional word in a claim. Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise.

[0066] The embodiments can be further described using the following clauses: 1. An apparatus for an extreme ultraviolet light source, the apparatus comprising: a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state; a capillary having a first end and a second end; the capillary being in fluid communication with the cavity at the first end and the second end defining a nozzle outlet for emitting a stream of the target material; a ferrule having a through hole surrounding and forming a seal with at least a lengthwise portion of the capillary, the capillary extending through the through hole; and a nozzle nut mechanically coupling the ferrule to the nozzle body; at least a portion of the ferrule having a conical shape wherein an outer diameter of the ferrule decreases in a direction toward the second end of the capillary.

2. Apparatus as in clause 1 wherein the portion of the ferrule having a conical shape is dimensioned to mate with an interior surface of a complementary cavity defined by the nozzle nut to form a seal between the portion of the ferrule having a conical shape and the interior surface.

3. Apparatus as in clause 1 wherein the ferrule is formed of a polyimide, a polyamide-imide, or a polybenzimidazole.

4. Apparatus as in clause 1 wherein the nozzle body is formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum.

5. Apparatus as in clause 1 wherein the ferrule has an outwardly extending circumferential shoulder adjacent a portion of the conical shape having a greatest outer diameter, the shoulder being adapted to be received in a channel formed between the nozzle body and the nozzle nut, the shoulder being an annular gasket forming a seal between the nozzle body and the nozzle nut.

6. Apparatus as in clause 1 further comprising an annular gasket arranged laterally adjacent to a portion of the conical shape having a greatest outer diameter, the annular gasket being adapted to be received in a channel formed between the nozzle body and the nozzle nut to form a seal between the nozzle body and the nozzle nut.

7. Apparatus as in clause 1 wherein the ferrule comprises a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular flange surrounding the through hole and configured and arranged to engage the capillary.

8. Apparatus as in clause 1 wherein the ferrule comprises a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular channel arranged radially adjacent outward of the through hole.

9. Apparatus as in clause 1 wherein the ferrule comprises a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular flange configured and arranged to engage the capillary and an annular channel arranged radially adjacent outward of the annular flange.

10. An apparatus for an extreme ultraviolet light source, the apparatus comprising: a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state; a glass capillary having a first end extending into the cavity and a second end defining a nozzle outlet for emitting target material that has passed inside and along a length of the glass capillary; a ferrule having a central through hole adapted to receive the glass capillary, the ferrule surrounding and forming a seal with at least a lengthwise portion of the glass capillary, the glass capillary extending through the central through hole, a portion of the ferrule having a fmstoconical shape with a first diameter towards the first end of the glass capillary and a second diameter towards the second end of the glass capillary, the first diameter being greater than the second diameter; and a threaded nozzle nut arranged to mechanically couple with the nozzle body to capture the ferrule between the nozzle nut and the nozzle body, the nozzle nut having a fmstoconical cavity dimensioned to receive the portion of the ferrule having the fmstoconical shape.

11. Apparatus as in clause 10 wherein the ferrule is formed of a polyimide, a polyamide-imide, or a polybenzimidazole.

12. Apparatus as in clause 10 wherein the nozzle body is formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an ahoy including one or more of molybdenum, tungsten, and tantalum.

13. Apparatus as in clause 10 wherein the ferrule has outwardly extending circumferential shoulder received in a channel formed between the nozzle body and the nozzle nut.

14. Apparatus as in clause 10 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular flange surrounding the through hole and configured and arranged to engage the glass capillary.

15. Apparatus as in clause 10 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular channel arranged radially adjacent outward of the through hole.

16. Apparatus as in clause 10 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular flange configured and arranged to engage the glass capillary and an annular channel arranged radially adjacent outward of the annular flange.

17. An apparatus for an extreme ultraviolet light source, the apparatus comprising: a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state; a cylindrical glass capillary having a first end extending into the cavity and a second end defining a nozzle outlet for emitting target material that has passed through the cylindrical glass capillary; a ferrule having a central through hole dimensioned to receive the cylindrical glass capillary to permit the cylindrical glass capillary to pass through and extend from a back end of the ferrule disposed towards the cavity and a front end of the ferrule disposed towards the nozzle outlet, the ferrule surrounding and forming a seal with at least an intermediate lengthwise portion of the cylindrical glass capillary, a portion of the ferrule axially between the front end of the ferrule and the back end of the ferrule having a fmstoconical shape with a first diameter towards the back end of the ferrule and a second diameter towards the front end of the ferrule, the first diameter being greater than the second diameter; and a threaded nozzle nut arranged to mechanically couple with the nozzle body to capture the ferrule between the nozzle nut and the nozzle body, the nozzle nut having a fmstoconical space dimensioned to receive the portion of the ferrule having the fmstoconical shape.

18. Apparatus as in clause 17 wherein the ferrule is formed of a polyimide, a polyamide-imide, or a polybenzimidazole.

19. Apparatus as in clause 17 wherein the nozzle body is formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum.

20. Apparatus as in clause 17 wherein the ferrule has outwardly extending circumferential shoulder received in a channel formed between the nozzle body and the nozzle nut.

21. Apparatus as in clause 17 wherein the back end of the ferrule has a disc-like portion facing the cavity and comprising an annular flange surrounding the through hole and configured and arranged to engage the cylindrical glass capillary.

22. Apparatus as in clause 17 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular channel arranged radially adjacent outward of the through hole.

23. Apparatus as in clause 17 wherein the has a disc-like portion facing the cavity and comprising an annular flange configured and arranged to engage the capillary and an annular channel arranged radially adjacent outward of the annular flange.

24. An apparatus for an extreme ultraviolet light source, the apparatus comprising: a tubular structure disposed in a support structure and having a first end and a second end; an actuator mechanically coupled to an exterior wall of the tubular structure, the first end of the tubular structure extending into a cavity configured to receive target material that emits extreme ultraviolet (EUV) light when in a plasma state, at least a portion of the tubular structure being surrounded by a ferrule; and a ferrule nut adapted to be mechanically coupled to the support structure, the ferrule being received between the support structure and the ferrule nut, at least a portion of the ferrule having a conical shape wherein an outer diameter of the ferrule decreases in a direction toward the second end of the tubular structure.

25. The apparatus of clause 24, wherein the ferrule is formed of a material comprising polyimide.

26. The apparatus of clause 24, wherein the support structure is formed of a material comprising molybdenum.

27. The apparatus of clause 24, wherein the ferrule has outwardly extending circumferential rib received in a channel formed between the support structure and the ferrule nut. [0067] The above described implementations and other implementations are within the scope of the following claims.

Claims

1. An apparatus for an extreme ultraviolet light source, the apparatus comprising: a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state; a capillary having a first end and a second end; the capillary being in fluid communication with the cavity at the first end and the second end defining a nozzle outlet for emitting a stream of the target material; a ferrule having a through hole surrounding and forming a seal with at least a lengthwise portion of the capillary, the capillary extending through the through hole; and a nozzle nut mechanically coupling the ferrule to the nozzle body; at least a portion of the ferrule having a conical shape wherein an outer diameter of the ferrule decreases in a direction toward the second end of the capillary.

2. The apparatus as in claim 1 wherein the portion of the ferrule having a conical shape is dimensioned to mate with an interior surface of a complementary cavity defined by the nozzle nut to form a seal between the portion of the ferrule having a conical shape and the interior surface.

3. The apparatus as in claim 1 wherein the ferrule is formed of a polyimide, a polyamide- imide, or a polybenzimidazole.

4. The apparatus as in claim 1 wherein the nozzle body is formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum.

5. The apparatus as in claim 1 wherein the ferrule has an outwardly extending circumferential shoulder adjacent a portion of the conical shape having a greatest outer diameter, the shoulder being adapted to be received in a channel formed between the nozzle body and the nozzle nut, the shoulder being an annular gasket forming a seal between the nozzle body and the nozzle nut.

6. The apparatus as in claim 1 further comprising an annular gasket arranged laterally adjacent to a portion of the conical shape having a greatest outer diameter, the annular gasket being adapted to be received in a channel formed between the nozzle body and the nozzle nut to form a seal between the nozzle body and the nozzle nut.

7. The apparatus as in claim 1 wherein the ferrule comprises a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular flange surrounding the through hole and configured and arranged to engage the capillary.

8. The apparatus as in claim 1 wherein the ferrule comprises a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular channel arranged radially adjacent outward of the through hole.

9. The apparatus as in claim 1 wherein the ferrule comprises a disc-like portion having a circular surface facing the cavity, wherein the disc-like portion comprises an annular flange configured and arranged to engage the capillary and an annular channel arranged radially adjacent outward of the annular flange.

10. An apparatus for an extreme ultraviolet light source, the apparatus comprising: a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state; a glass capillary having a first end extending into the cavity and a second end defining a nozzle outlet for emitting target material that has passed inside and along a length of the glass capillary; a ferrule having a central through hole adapted to receive the glass capillary, the ferrule surrounding and forming a seal with at least a lengthwise portion of the glass capillary, the glass capillary extending through the central through hole, a portion of the ferrule having a frustoconical shape with a first diameter towards the first end of the glass capillary and a second diameter towards the second end of the glass capillary, the first diameter being greater than the second diameter; and a threaded nozzle nut arranged to mechanically couple with the nozzle body to capture the ferrule between the nozzle nut and the nozzle body, the nozzle nut having a frustoconical cavity dimensioned to receive the portion of the ferrule having the frustoconical shape.

11. The apparatus as in claim 10 wherein the ferrule is formed of a polyimide, a poly amide - imide, or a polybenzimidazole.

12. The apparatus as in claim 10 wherein the nozzle body is formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum.

13. The apparatus as in claim 10 wherein the ferrule has outwardly extending circumferential shoulder received in a channel formed between the nozzle body and the nozzle nut.

14. The apparatus as in claim 10 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular flange surrounding the through hole and configured and arranged to engage the glass capillary.

15. The apparatus as in claim 10 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular channel arranged radially adjacent outward of the through hole.

16. The apparatus as in claim 10 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular flange configured and arranged to engage the glass capillary and an annular channel arranged radially adjacent outward of the annular flange.

17. An apparatus for an extreme ultraviolet light source, the apparatus comprising: a nozzle body including structure defining a cavity for holding a liquid target material under pressure that emits extreme ultraviolet (EUV) light when in a plasma state; a cylindrical glass capillary having a first end extending into the cavity and a second end defining a nozzle outlet for emitting target material that has passed through the cylindrical glass capillary; a ferrule having a central through hole dimensioned to receive the cylindrical glass capillary to permit the cylindrical glass capillary to pass through and extend from a back end of the ferrule disposed towards the cavity and a front end of the ferrule disposed towards the nozzle outlet, the ferrule surrounding and forming a seal with at least an intermediate lengthwise portion of the cylindrical glass capillary, a portion of the ferrule axially between the front end of the ferrule and the back end of the ferrule having a frustoconical shape with a first diameter towards the back end of the ferrule and a second diameter towards the front end of the ferrule, the first diameter being greater than the second diameter; and a threaded nozzle nut arranged to mechanically couple with the nozzle body to capture the ferrule between the nozzle nut and the nozzle body, the nozzle nut having a frustoconical space dimensioned to receive the portion of the ferrule having the frustoconical shape.

18. The apparatus as in claim 17 wherein the ferrule is formed of a polyimide, a polyamide - imide, or a polybenzimidazole.

19. The apparatus as in claim 17 wherein the nozzle body is formed of a material comprising one or more of molybdenum, tungsten, and tantalum, or an alloy including one or more of molybdenum, tungsten, and tantalum.

20. The apparatus as in claim 17 wherein the ferrule has outwardly extending circumferential shoulder received in a channel formed between the nozzle body and the nozzle nut.

21. The apparatus as in claim 17 wherein the back end of the ferrule has a disc-like portion facing the cavity and comprising an annular flange surrounding the through hole and configured and arranged to engage the cylindrical glass capillary.

22. The apparatus as in claim 17 wherein the ferrule has a disc-like portion facing the cavity and comprising an annular channel arranged radially adjacent outward of the through hole.

23. The apparatus as in claim 17 wherein the has a disc-like portion facing the cavity and comprising an annular flange configured and arranged to engage the capillary and an annular channel arranged radially adjacent outward of the annular flange.

25. The apparatus as in claim 24, wherein the ferrule is formed of a material comprising polyimide.

26. The apparatus as in claim 24, wherein the support structure is formed of a material comprising molybdenum.

27. The apparatus as in claim 24, wherein the ferrule has outwardly extending circumferential rib received in a channel formed between the support structure and the ferrule nut.