Radiation source conduit system and method

Abstract

The radiation source includes a chamber, a window, and a conduit system. The chamber confines the gas and contaminants generated during radiation generation. The window isolates the gas from the environment outside the chamber and allows radiation to pass between the gas chamber and the environment. The refill path allows gas exchange. The conduit system directs the flow of the refill gas, one of the gases, or the refill gas and the gas, at least during a refill operation, to prevent contaminants from contacting the window. The conduit system may include one or more one-way valves, which may be magnetic check valves. The permanent magnet components of the magnetic check valves may be disposed outside the conduits and chamber to prevent the permanent magnet components from being corroded by the gases in the conduits or chamber.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to U.S. Application No. 63 / 424,176, filed November 10, 2022, and incorporated herein by reference in its entirety.

[0002]

[0002] This application is also related to International Application No. PCT / US2021 / 021543, filed March 9, 2021, entitled CONDUIT SYSTEM, RADIATION SOURCE, LITHOGRAPHIC APPARATUS, AND METHODS THEREOF, which is incorporated by reference in its entirety into this specification.

[0003]

[0003] The present disclosure relates to pulsed discharge radiation sources, such as ultraviolet gas discharge lasers for lithography systems. [Background technology]

[0004]

[0004] Methods of generating deep ultraviolet (DUV) radiation include, but are not limited to, using pulsed discharge radiation sources. An excimer laser is one example of a pulsed discharge radiation source. A pulsed discharge radiation source excites gas molecules confined in a chamber to generate laser radiation of a desired wavelength. The radiation may be exhausted from the chamber through a window. The gas molecules may include, but are not limited to, fluorine, neon, krypton, argon, etc. The gas molecules may be excited by applying a voltage (e.g., an electrical pulse) to the gas via electrodes. Over the lifetime of the radiation source, the gas chamber may grow contaminant particles due to interactions between the electrodes and the gas. The contaminant particles may then contaminate other photosensitive components (e.g., the window) and cause unexpected premature failure of the radiation source.

[0005] Pulsed discharge radiation sources may be used to generate radiation in a variety of applications, for example to generate DUV radiation in lithography apparatus. A lithography apparatus is a machine that applies a desired pattern onto a substrate, typically onto a target portion of the substrate. Lithography apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A patterning device, which may be a mask or reticle, may be used to generate a circuit pattern that will be formed on an individual layer of the IC. This pattern may be transferred onto a target portion (e.g. comprising part of, one, or several dies) on the substrate (e.g. a silicon wafer). 30 Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning a radiation beam across the pattern in a given direction (the ``scan'' direction) while synchronously scanning the target portion in a direction parallel or anti-parallel to the scan direction.

[0006]

[0006] Lithographic apparatus typically include an illumination system that conditions radiation generated by a radiation source before the radiation is incident on a patterning device. A patterned beam of DUV light can be used to create extremely small features on a substrate. The illumination system may include a pulsed discharge radiation source having a gas chamber that is susceptible to premature failure due to contaminants in the gas chamber. Summary of the Invention

[0007]

[0007] It is therefore desirable to protect photosensitive components or reduce the likelihood of premature failure of pulsed discharge radiation sources due to contaminants, for example by managing gas flow within the radiation source.

[0008] According to an aspect of an embodiment, an apparatus is disclosed that includes a chamber configured to hold a fluorine-containing gas, a conduit configured to circulate the fluorine-containing gas to and from the chamber during generation of radiation, the conduit being defined at least in part by a conduit wall, and a one-way check valve disposed within the conduit. The one-way check valve includes: a check valve element including a ferromagnetic material having a first magnetic field strength and a first corrosion resistance, the check valve element being disposed within the conduit and exposed to the fluorine-containing gas, the check valve element being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; and a permanent magnet including a magnetizable material having a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance, the permanent magnet being disposed outside the chamber and outside the conduit adjacent the conduit wall to avoid exposure to the fluorine-containing gas, the permanent magnet being configured to exert a biasing force on the check valve element to bias the check valve element to the first position.

[0009]

[0009] The permanent magnet may be disposed adjacent an outer surface of the conduit wall and sufficiently close to the check valve element to exert a biasing force on the check valve element. The check valve element may be a sphere. The ferromagnetic material may include nickel. The permanent magnet may include neodymium.

[0010]

[0010] The exterior, such as the outer surface, of the conduit wall may include a structure defining a recess, and the permanent magnet may be positioned at least partially in the recess in sufficient proximity to the check valve element and disposed relative to the check valve element so as to exert a biasing force on the check valve element.

[0011] According to another aspect of an embodiment, an apparatus is disclosed that includes a chamber configured to hold a fluorine-containing gas, a conduit configured to circulate the fluorine-containing gas to and from the chamber during generation of radiation, the conduit being defined at least in part by a conduit wall, and a one-way check valve disposed within the conduit. The one-way check valve includes: a nickel-containing sphere disposed within the conduit and exposed to the fluorine-containing gas, the sphere being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; and a neodymium permanent magnet disposed outside the chamber and inside the conduit adjacent the conduit wall to avoid exposure to the fluorine-containing gas, the neodymium permanent magnet configured to exert a biasing force on the sphere that biases the sphere to the first position.

[0012]

[0012] The sphere may include nickel having a first magnetic field strength and a first corrosion resistance, and the neodymium permanent magnet has a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance.

[0013] According to another aspect of an embodiment, a radiation source configured to generate radiation is disclosed, the radiation source including a chamber configured to contain a corrosive gas and contaminants generated during the generation of the radiation, a window configured to isolate the corrosive gas from an environment external to the chamber and allow radiation to pass between the chamber and the environment, and a conduit system, the conduit system including a replenishment path configured to allow exchange of the corrosive gas, a conduit configured to circulate the corrosive gas to and from the chamber during the generation of the radiation, and a one-way valve disposed intersecting the conduit and configured to prevent flow of the contaminants toward the window. The one-way check valve includes: a check valve element disposed within the conduit and exposed to the corrosive gas, the check valve element including a ferromagnetic material having a first magnetic field strength and a first corrosion resistance, the check valve element being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; and a permanent magnet disposed outside the chamber and outside the conduit adjacent the conduit wall to avoid exposure to the corrosive gas, the permanent magnet being configured to exert a biasing force on the check valve element to bias it toward the first position. The conduit system is configured to direct the flow of one of the refill gas and the corrosive gas, or the refill gas and the corrosive gas, at least during a refill operation to prevent contaminants from contacting the window, thereby extending at least the useful life of the window.

[0014]

[0014] The permanent magnet may be disposed adjacent the exterior of the conduit wall and sufficiently close to the check valve element to exert a biasing force on the check valve element. The check valve element may be a sphere. The ferromagnetic material may include nickel. The permanent magnet may include neodymium.

[0015]

[0015] The exterior of the conduit wall may include a structure defining a recess, and the permanent magnet may be positioned at least partially in the recess in sufficient proximity to the check valve element and disposed relative to the check valve element so as to exert a biasing force on the check valve element.

[0016]

[0016] Further features of the present disclosure, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the art based on the teachings contained herein. [Brief explanation of the drawings]

[0017]

[0017] The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate the present disclosure and, together with the description, serve to further explain the principles of the present disclosure and enable those skilled in the art to make and use the embodiments described in this specification.

[0018] [Figure 1A] 1 illustrates a reflective lithographic apparatus according to some embodiments; [Figure 1B]

[0019] 1 depicts a transmissive lithographic apparatus according to some embodiments; [Figure 2]

[0020] 1 illustrates a schematic of a lithographic cell according to some embodiments. [Figure 3]

[0021] 1 illustrates a radiation source according to some embodiments. [Figure 4] 1 illustrates a radiation source according to some embodiments. [Figure 5A]

[0022] 1 illustrates a portion of a radiation source according to some embodiments. [Figure 5B] 2 illustrates a portion of a radiation source according to some embodiments; [Figure 5C] 2 illustrates a portion of a radiation source according to some embodiments; [Figure 6]

[0023] 1 illustrates a one-way valve according to some embodiments. [Figure 7]

[0024] 1 illustrates a cross section of a one-way valve according to some embodiments. [Figure 8]

[0025] 1 is a flowchart illustrating method steps for carrying out the functions of embodiments described herein, according to some embodiments. [Figure 9]

[0026] 1 is a cross-sectional view of a one-way valve that may be used in implementations according to some embodiments. [Figure 10]

[0027] 1 is a cross-sectional view of a one-way valve that may be used in implementations according to some embodiments.

[0019]

[0028] Features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings. Like reference numerals identify corresponding elements throughout the drawings. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Also, the leftmost digit(s) of a reference number generally identifies the drawing in which that reference number first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as drawings to scale. DETAILED DESCRIPTION OF THE INVENTION

[0020]

[0029] This specification discloses one or more embodiments incorporating features of the present disclosure. The disclosed one or more embodiments are exemplary. The scope of the present disclosure is not limited to the disclosed one or more embodiments. The claimed features are defined by the claims appended hereto.

[0021]

[0030] References in the specification to one or more described embodiments, and to "one embodiment," "an embodiment," "exemplary embodiment," "example embodiment," etc., indicate that one or more described embodiments may include a particular feature, structure, or characteristic, but not all embodiments necessarily include that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one of ordinary skill in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly stated.

[0022]

[0031] Spatially relative terms such as "beneath," "below," "lower," "above," "on," "upper," and the like may be used herein to facilitate describing the relationship of one element or feature to another element or feature, as shown in the figures. Spatially relative terms are intended to encompass various orientations of the device in use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0023]

[0032] As used herein, the term "about" refers to a given quantity value that can vary based on a particular technique. Based on a particular technique, the term "about" can refer to a given quantity value that can vary, for example, within 10-30% of that value (e.g., ±10%, ±20%, or ±30% of that value).

[0024]

[0033] Embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may comprise any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustical, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be recognized that such description is merely for convenience and that such actions actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc.

[0025]

[0034] However, before describing such embodiments in detail, it is beneficial to present an exemplary environment in which embodiments of the present disclosure may be practiced.

[0026]

[0035] Exemplary Lithography System

[0036] 1A and 1B are schematic diagrams of lithographic apparatus 100 and lithographic apparatus 100', respectively, in which embodiments of the present disclosure may be implemented. Lithographic apparatus 100 and lithographic apparatus 100' each comprise: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet radiation or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100' also comprise a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. In lithographic apparatus 100, patterning device MA and projection system PS are reflective. In lithographic apparatus 100', patterning device MA and projection system PS are transmissive.

[0027]

[0037] The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling the radiation beam B.

[0028]

[0038] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to a reference frame, the design of at least one of lithographic apparatuses 100 and 100′, and other conditions, such as whether or not the patterning device is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be, for example, a frame or a table, and may be fixed or movable as required. By using sensors, the support structure MT may ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

[0029]

[0039] The term "patterning device" MA should be interpreted broadly to refer to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0030]

[0040] Patterning device MA may be transmissive (as in lithographic apparatus 100' in Figure 1B) or reflective (as in lithographic apparatus 100 in Figure IA). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, or attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam B in different directions. The tilted mirrors impart a pattern to a radiation beam B that is reflected by the small mirror matrix.

[0031]

[0041] The term "projection system" PS can include any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, appropriate to the exposure radiation used, or other factors such as the use of an immersion liquid or a vacuum on the substrate W. A vacuum environment can be provided throughout the beam path using a vacuum wall and vacuum pumps.

[0032]

[0042] The lithographic apparatus may also be of a type wherein at least a portion of the substrate is covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system and the substrate. Immersion liquids may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. As used herein, the term "immersion" does not mean that a structure such as the substrate must be submerged in liquid, but rather that a liquid is present between the projection system and the substrate during exposure.

[0033]

[0043] Referring to Figures 1A and 1B, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example if the source SO is an excimer laser. In this case, the source SO is not considered to form part of the lithographic apparatus 100 or 100' and the radiation beam B passes from the source SO to the illuminator IL via a beam delivery system BD (Figure 1B), which may comprise, for example, suitable directing mirrors and / or beam expanders. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example if the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, may be referred to as a radiation system.

[0034]

[0044] The illuminator IL may comprise an adjuster AD (Figure 1B) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO (Figure 1B). The illuminator IL can be used to condition the radiation beam B to obtain a desired uniformity and intensity distribution in its cross-section.

[0035]

[0045] Referring to Figure 1A, a radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometric device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IFl can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. Mask alignment marks Ml, M2 and substrate alignment marks Pl, P2 may be used to align patterning device (eg mask) MA and substrate W.

[0036]

[0046] Referring to Figure 1B, the radiation beam B is incident on a patterning device (e.g., mask MA), which is held on a support structure (e.g., mask table MT), and is patterned by the patterning device. After traversing the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W.

[0037]

[0047] The projection system PS projects an image of the mask pattern MP, formed by diffracted beams generated from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP may include an array of lines and spaces. Non-zero-order diffraction of radiation at the array produces bypass diffracted beams redirected perpendicular to the lines. Non-diffracted beams (i.e., so-called zero-order diffracted beams) traverse the pattern without changing their direction of propagation. The zero-order diffracted beams traverse the upper lens or upper lens group of the projection system PS, which is upstream of the pupil conjugate PPU of the projection system PS, and reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU associated with the zero-order diffracted beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD is, for example, arranged in a plane or substantially in a plane containing the pupil conjugate PPU of the projection system PS.

[0038]

[0048] The projection system PS is arranged to capture not only the zeroth-order diffracted beam but also first or higher-order diffracted beams (not shown) by means of a lens or lens group L. In some embodiments, the resolution-enhancing effect of dipole illumination can be exploited by using dipole illumination to image a line pattern extending in a direction perpendicular to the lines. For example, a first-order diffracted beam interferes with a corresponding zeroth-order diffracted beam at the level of the wafer W to produce an image of the line pattern MP at the highest possible resolution and process window (i.e., usable depth of focus combined with an acceptable exposure dose deviation). In some embodiments, astigmatism can be reduced by providing a radial pole (not shown) in the opposite quadrant of the pupil IPU of the illumination system.

[0039]

[0049] With the aid of a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. to position different target portions C in the path of the radiation beam B). Similarly, the mask MA can be accurately positioned with respect to the path of the radiation beam B (e.g. after mechanical retrieval from a mask library or during a scan) using the first positioner PM and a further position sensor (not shown in Figure 1B).

[0040]

[0050] In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. The substrate alignment marks (as shown in the figures) occupy dedicated target portions, but may be located in spaces between the target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0041]

[0051] The mask table MT and patterning device MA may be within a vacuum chamber V, and an in-vacuum robot IVR may be used to move the patterning device, such as a mask, in and out of the vacuum chamber. Alternatively, when the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot may be used for various transport operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for smooth movement of any payload (e.g., a mask) to a fixed kinematic mount in the transfer station.

[0042]

[0052] Lithographic apparatus 100 and 100' can be used in at least one of the following modes:

[0043]

[0053] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept substantially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C in one go (i.e. a single static exposure), and the substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0044]

[0054] 2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0045]

[0055] 3. In another mode, the support structure (e.g. mask table) MT holds a programmable patterning device and is held substantially stationary, while the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be used, and the programmable patterning device is updated as required with each movement of the substrate table WT, or between successive pulses of radiation during a scan. This mode of operation is readily adaptable to maskless lithography using a programmable patterning device such as a programmable mirror array.

[0046]

[0056] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0047]

[0057] In some embodiments, lithographic apparatus 100' includes a deep ultraviolet (DUV) source configured to generate a beam of DUV radiation for DUV lithography. The DUV source may be, for example, a gas discharge laser (e.g., an excimer laser).

[0048]

[0058] Exemplary Lithography Cell

[0059] FIG. 2 illustrates a lithography cell 200, sometimes referred to as a lithocell or cluster, according to some embodiments. Lithography apparatus 100 or 100′ can form part of lithography cell 200. Lithography cell 200 can also include one or more devices for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing exposed resist, a chill plate CH, and a bake plate BK. A substrate handler, or robot RO, retrieves substrates from input / output ports I / O1, I / O2, moves them between various process tools, and delivers them to a loading bay LB of lithography apparatus 100 or 100′. These devices, often collectively referred to as a track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Accordingly, these various tools can be operated to maximize throughput and processing efficiency.

[0049]

[0060] Exemplary Radiation Sources

[0061] Pulsed discharge radiation sources have many applications, such as, for example, lithography, medical procedures, laser ablation machining, and laser imprinting. Lithography apparatus is one example where a stable illumination source may be desirable. The illumination source may comprise precision optical assemblies that are sensitive to contaminants. FIG. 3 illustrates a radiation source 300 according to some embodiments. In some embodiments, the radiation source 300 is a pulsed discharge radiation source, such as, but not limited to, a gas discharge laser. The radiation source 300 comprises a gas chamber 302, a window 304, and a conduit system 306. The radiation source 300 may further comprise one or more electrodes 310 (also referred to as "electrical connections"). The conduit system 306 may comprise a network of valves, conduits, and contaminant filters (not shown, but described in more detail with reference to FIG. 4).

[0050]

[0062] In some embodiments, the gas chamber 302 can contain a gas 308. The gas 308 can include fluorine, neon, krypton, argon, etc. A conduit system 306 is connected to the gas chamber 302. The conduit system 306 can allow for management of the gas 308 within the gas chamber 302. For example, the conduit system 306 can direct a flow (e.g., circulation) of the gas 308 through a filter within the conduit system 306 to purify the gas 308. A voltage can be applied to the gas 308 (e.g., via one or more electrodes 310) to generate radiation 312. The window 304 can allow the radiation 312 to exit the gas chamber 302.

[0051]

[0063] Figure 4 illustrates a radiation source 400 according to some embodiments. In some embodiments, the radiation source 400 illustrated in Figure 4 may represent in more detail the radiation source 300 illustrated in Figure 3. For example, Figure 4 may show a more detailed view of the conduit system 306. Unless otherwise noted, elements in Figure 4 having similar reference numbers as elements in Figure 3 (e.g., reference numbers that share the two rightmost digits) may have similar structure and function.

[0052]

[0064] In some embodiments, the radiation source 400 comprises a gas chamber 402, a window 404, and a conduit system (e.g., conduit system 306 of FIG. 3 ). The radiation source 400 may further comprise one or more electrodes 410. The radiation source 400 may further comprise a window 418. The window 418 may be similar in structure and function to the window 404. The conduit system comprises a refill conduit 414 (also referred to as a “refill path”), a conduit 416, and a contaminant filter 420 (or simply a filter). The conduit system may further comprise a one-way valve 422, a conduit 424, a one-way valve 426, and any combination thereof.

[0053]

[0065] In some embodiments, the gas chamber 402 can contain the gas 408. A conduit system can be connected to the gas chamber 402 to allow circulation of the gas 408, for example, during operation to generate radiation 412. For example, the conduit system can circulate the gas 408 to a contaminant filter 420 connected to the gas chamber 402 (gas flow direction indicated by arrow 428). The contaminant filter 420 can remove contaminant particles 432 from the gas chamber 402. A conduit 416 reconnects the contaminant filter 420 to the gas chamber 402, and the gas flow is such that clean, filtered gas can blow against a window 404 (gas flow direction indicated by arrow 430). The window 404 can contain the gas 408 from the environment outside the gas chamber 402. A differential pressure device (not shown) can be used to induce gas flow in the radiation source 400. For example, there can be a blower inside the gas chamber 402. Contaminant filter 420 may block a portion of the flow circulating through gas chamber 402 and redirect the flow to windows 404 and 418 after removing contaminant particles 432. Gas 408 may be supplied or exhausted using a refill conduit 414 connected to gas chamber 402. That is, refill conduit 414 may allow for replacement of gas 408. It should be appreciated that the piping configuration shown in FIG. 4 is provided as a non-limiting example. For example, piping configurations using more or fewer conduits, T-junctions, valves, etc. may be envisioned to achieve cleanliness of sensitive optical components such as windows 404 and 418.

[0054]

[0066] In some embodiments, arrows 428, 430, and 434 represent gas flow during operation of radiation source 400, for example, when generating radiation 412. To generate radiation 412, a voltage can be applied to gas 408, for example, via one or more electrodes 410. The radiation 412 can have characteristics that depend on the applied voltage (e.g., an electrical pulse of radiation). Windows 404 and 418 can allow radiation 412 to pass between gas chamber 402 and an environment external to gas chamber 402. In some embodiments, radiation source 400 is a gas discharge laser. Radiation source 400 can include an optical reflector 436 and a partial optical reflector 438. Optical reflector 436 and partial optical reflector 438 together function as an optical resonator. The optical resonator, in combination with a gain medium (e.g., gas 408), allows amplification of radiation 412 as it travels back and forth between optical reflector 436 and partial optical reflector 438. The radiation source 400 can then output a radiation beam 440 via transmission in a partial optical reflector 438 .

[0055]

[0067] In some embodiments, the expected life of the gas chamber 402 depends on the first critical component becoming inoperable due to wear. One example of a wear-prone component is the one or more electrodes 410. During operation of the radiation source 400, the one or more electrodes 410 interact with the gas 408. The interaction causes electrode material to bond with the gas 408 and separate from the one or more electrodes 410, essentially eroding the one or more electrodes 410. Such corrosion is expected, and the rate of corrosion is predictable. The longer the radiation source 400 operates, the more the electrodes erode. A criterion for the life of at least one or more electrodes 410 may be determined as the time it takes for the one or more electrodes to erode from a new state beyond the point of operable operation (e.g., measured by the number of pulses generated over their lifetime). An undesirable behavior of the radiation source 400 is for a component to unexpectedly fail before its specified life.

[0056]

[0068] In some embodiments, one or more of the contaminant particles 432 may be deposited on the window 404 by an unintended gas flow. For example, as described above, arrows 428, 30, and 434 represent the gas flow during operation of the radiation source 400. As the radiation source 400 operates, the quality of the gas 408 deteriorates (e.g., it becomes used up). Therefore, the gas 408 can be replaced with fresh, fresh gas (also referred to as a "refill gas") by accessing the gas chamber 402 using the refill conduit 414. The refill gas may be the same type of gas as the fresh gas 408, or may be a different, fresh gas. In some embodiments, replacing the gas 408 includes evacuating the gas 408 using the refill conduit 414 and then injecting the refill gas again using the refill conduit 414. Replacing the gas 408 can agitate the contaminant particles 432 that would normally settle at the bottom of the gas chamber 402. The agitated contaminant particles 432 may have a higher probability of adhering to the windows 404 and 418. Also, the exhaust of gas 408 may draw contaminant particles 432 into the refill conduit 414, and the subsequent injection of refill gas through the same conduit may blow the contaminant particles 432 into the gas chamber 402, some of which may adhere to the windows 404 and 418.

[0057]

[0069] In some embodiments, the window 404 is transparent, allowing the radiation 412 to pass through. However, contaminant particles may absorb a significant amount of energy from the radiation 412, heating contaminant particles 432 deposited on the window 404 and transferring that heat to the window 404. The energy density of the radiation 412 may be high enough to damage the window 404 by heating the contaminant particles 432 on the window 404. Failure of the window 404 may occur unexpectedly long before the life of one or more electrodes 410 is exhausted. In high-volume IC production, unexpected machine downtime (e.g., unplanned maintenance) can be very detrimental due to the unexpected loss of production time. In scenarios where failures are predictable (e.g., occurring during a predetermined lifespan or scheduled maintenance), spare parts and procedures can be prepared. The structures and functions described in the embodiments herein can improve the average lifespan and reliability of pulsed discharge radiation sources by reducing the probability of unexpected premature failure of the pulsed discharge radiation source.

[0058]

[0070] In some embodiments, the conduit system is configured to direct the flow of the make-up gas, the gas 408, or both the make-up gas and the gas 408. The direction of the gas flow can change depending on the operating state of the radiation source 400 (e.g., during operation or during a make-up procedure) based on the piping configuration of the conduit system. The gas flow can be manipulated to avoid stirring up or directing contaminant particles 432 toward the windows 404 and 418. By manipulating the gas flow in this manner, the conduit system can extend the useful life of the windows 404 and 418. The useful life of the gas chamber 402, radiation source 400, etc. can also be improved by avoiding unexpected and costly disassembly (whereas the useful life of the radiation source can be dictated by a simple window failure, since it may be more efficient to simply replace the radiation source immediately rather than disassembling it).

[0059]

[0071] In some embodiments, one-way valve 422 may be disposed across conduit 416. One-way valve 422 may include a check valve, such as a ball check valve, a flap check valve, a spring check valve, a gravity check valve, or the like. A check valve is a valve that closes to prevent backflow. One-way valve 422 may represent a check valve mechanism that combines the structures and / or features of the check valves described above. For example, a ball check valve may be used in a vertical orientation, where a ball is depressed and closed by gravity (e.g., a gravity check valve). While the check valve self-shuts using the pressure of gas moving in the “wrong” direction, the excess force (e.g., from gravity) on the shutoff mechanism may provide a crack pressure threshold that allows gas to push open the check valve. In some embodiments, one-way valve 422 may be a user-adjustable valve (e.g., an electrically actuated valve, a ball valve with an adjustable angle relative to gravity, a pneumatic valve, etc.).

[0060]

[0072] In some embodiments, during the evacuation of gas 408, one-way valve 422 can prevent gas flow (represented by arrow 430) from going backward. For example, gas 408 from gas chamber 402 is prevented from proceeding toward window 404. In this manner, the probability of contaminant particles 432 contacting window 404 is reduced.

[0061]

[0073] As described above, the refill conduit 414 may become contaminated with contaminant particles 432. To avoid the spread of contaminant particles 432, in some embodiments, the conduit system may include a separate exhaust conduit 442 (also referred to as an "exhaust path") dedicated to the exhaust of gas 408. In this scenario, the refill conduit 414 may be dedicated to the injection of make-up gas. Because the exhaust and make-up of gas are handled in separate conduits, this configuration may avoid contaminants in the exhaust conduit 442 being blown back into the gas chamber 402. It should be appreciated that the locations of the refill conduit 414 and the exhaust conduit 442 are not limited to those depicted in FIG. 4 and that their locations may be selected to minimize the likelihood of spreading contaminant particles 432 throughout the gas chamber 402 (e.g., the locations of the refill conduit 414 and the exhaust conduit 442 may be interchanged).

[0062]

[0074] In some embodiments, the conduit system may include additional elements that allow for manipulation of the flow of gas 408 and / or the makeup gas. The structure of the additional elements is shown in FIG. 4, while their function is described in more detail with reference to FIG. 5. The conduit system may further include a conduit 444 (also referred to as a "bypass conduit"), a one-way valve 446, a conduit 448 (also referred to as a "bypass conduit"), and a one-way valve 450. A one-way valve 452 may be disposed to intersect with makeup conduit 414. The one-way valve 452 may prevent gas from entering the gas chamber 402 via makeup conduit 414. Any combination of the above structures may be used to achieve the desired flow direction of gas 408 and makeup gas.

[0063]

[0075] It should be appreciated that in some embodiments, conduit 424, conduit 448, one-way valve 426, one-way valve 450, and window 418 may be structured and configured similarly to conduit 416, conduit 444, one-way valve 422, one-way valve 446, and window 404, respectively. For example, the similarity may be exact or approximate structural and / or functional symmetry.

[0064]

[0076] Figures 5A, 5B, and 5C show a portion of a radiation source 500 according to some embodiments. In some embodiments, radiation source 500 may also represent radiation source 300 (Figure 3) and / or radiation source 400 (Figure 4) in more detail. For example, Figure 5 may show a more detailed view of conduit system 306 and its functionality. Unless otherwise noted, elements in Figure 5 having similar reference numbers as elements in Figures 3 and 4 (e.g., reference numbers that share the two rightmost digits) may have similar structure and function.

[0065]

[0077] Referring to Figure 5A, there is shown a flow of gas 508 (indicated by arrows, also shown as gas particles, not to be confused with contaminant particles 432 in Figure 4). The radiation source 500 comprises a gas chamber 502, a window 504, and a conduit system (e.g., conduit system 306 in Figure 3). The radiation source 500 may further comprise a window 518. The conduit system may comprise a contaminant filter 520, a refill conduit 514, a conduit 516, a conduit 524, a one-way valve 522, and a one-way valve 526. The conduit system may further comprise a conduit 544, a conduit 548, a one-way valve 546, a one-way valve 550, and a one-way valve 552. Some of these elements have already been described with reference to their counterparts in Figure 4 (e.g., referenced by numbers sharing two right-most digits).

[0066]

[0078] In some embodiments, the flow of gas 508 (represented by arrows) during operation of radiation source 500 (e.g., generating radiation) is as shown in FIG. 5A . Contaminant filter 520 can remove contaminants (e.g., contaminant particles 432 ( FIG. 4 )) from gas chamber 502. Conduit 516 reconnects contaminant filter 520 to gas chamber 502, and the gas flow is such that clean, filtered gas can be blown onto window 504. To facilitate flow direction, one-way valve 522 is shown in an open state, allowing filtered gas to blow onto window 504. Conversely, one-way valve 522 can be closed to prevent gas flow from reversing and attracting contaminants from gas chamber 502 to window 504. It should be appreciated that while functionality is described with respect to contaminants on the window 504 side, a similar or symmetrical process is used for window 518 using corresponding conduits and valves.

[0067]

[0079] 5B, in some embodiments, the flow of gas 508 during evacuation of gas 508 is represented by the illustrated arrows. Where gas flow is shown in both directions away from one-way valves (e.g., one-way valves 546 and 550), such valves may close if the gas flow is in a direction opposite to that of the one-way valve or if the pressure of the gas flow is insufficient to overcome the cracking pressure threshold of the one-way valve. To facilitate evacuation of gas 508, one-way valve 552 is shown in an open state allowing gas 508 to exit gas chamber 502 while preventing gas 508 and contaminants from flowing toward window 504.

[0068]

[0080] Referring to FIG. 5C , in some embodiments, the flow of refill gas during refilling of gas chamber 502 is represented by the illustrated arrows. To facilitate refilling gas chamber 502, one-way valve 546 is shown in an open state, allowing refill gas to enter gas chamber 502. One-way valve 552 is in a closed state, preventing gas flow from gas chamber 502 toward window 504 (preventing contaminants present in gas chamber 502 from flowing toward window 504). In this configuration, (pure, contaminant-free) refill gas enters gas chamber 502 via conduit 544. Conduit 544 may be a bypass conduit that bypasses the orifice connecting gas chamber 502 and refill conduit 514. That is, conduit 544 directly connects conduit 516 and refill conduit 514. Uncontaminated refill gas (or filtered gas 508 in FIG. SA) can flow through windows 504 and 518 without depositing dust on windows 504 and 518. The uncontaminated make-up gas can also exert pressure on the window 504 that can blow away any contaminants present on the window 504. In this manner, at least the useful life of the window 504 may be extended due to a reduced probability that contaminants on the window 504 will absorb radiant energy.

[0069]

[0081] 6 illustrates a one-way valve 600 according to some embodiments. The one-way valve 600 comprises a conduit portion 602 and a flap 604. The one-way valve 600 may further comprise a hinge 606. The hinge 606 may attach the flap 604 to the conduit portion 602. If the hinge 606 is omitted, the flap 604 may be a flexible (e.g., flexure) flap and may attach directly to the conduit portion 602. The hinge 606 may be spring-loaded to define a cracking pressure threshold (e.g., the valve opens only when the flow pressure exceeds a predetermined amount). A flexure flap may also define a cracking pressure threshold. An arrow 608 represents the direction of flow permitted by the one-way valve 600.

[0070]

[0082] 7 shows a cross section of a one-way valve 700 according to some embodiments. The one-way valve 700 comprises a conduit portion 702 and a ball 704. The ball 704 can be spring-loaded to define a crack pressure threshold. The one-way valve 700 can also define a crack pressure threshold without a spring (e.g., using gravity and the weight of the ball 704). Arrow 708 represents the direction of flow allowed by the one-way valve 700.

[0071]

[0083] FIG. 8 illustrates method steps for performing the functions described herein, according to some embodiments. The method steps of FIG. 8 may be performed in any conceivable order, and not all steps need be performed. Additionally, the method steps of FIG. 8 described below reflect only example steps and are not limiting. That is, additional method steps and functions may be envisioned based on the embodiments described with reference to FIGS. 1 through 7.

[0072]

[0084] In step 802, radiation is generated using a pulsed discharge radiation system.

[0073]

[0085] In step 804, a gas is used to trap the gas and any contaminants created during generation.

[0074]

[0086] In step 806, a window is used to separate the gas from the environment outside the gas chamber.

[0075]

[0087] In step 808, a window is used to allow radiation to pass between the gas chamber and the environment.

[0076]

[0088] In step 810, the gas is replaced using the refill path.

[0077]

[0089] In step 812, the flow of the refill gas, one of the gases, or the refill gas and the gas is directed during the refill operation to prevent contaminants from contacting the window.

[0078]

[0090] In some embodiments, any one or all of the one-way valves described above, e.g., one-way valves 422, 426, 442, 446, 450, 452, 522, 526, 546, 550, and 552, may include check valves, such as ball check valves, flap check valves, spring check valves, gravity check valves, and the like. The ball check valve may be implemented as a magnetic check valve, as shown in FIG. 9. One-way magnetic check valve 900 is disposed within conduit section 910, which includes conduit wall 920, and includes ball 930. In a first position, as shown, ball 930 contacts valve stop 940. In this position, ball 930 blocks flow in a downward direction, which may or may not coincide with gravity. Gas flow from below can open one-way valve 900. Thus, as shown, one-way valve 900 may be configured to allow filtered gas to flow through a window (not shown), while preventing backflow of contaminated gas, for example.

[0079]

[0091] Ball 930 may be made of a ferromagnetic material, such as nickel, that is resistant to corrosion by the gas within conduit portion 910. The ferromagnetic material may be magnetized. Ball 930 is shown biased against valve stop 940 by permanent magnet 950, which may be made of a rare earth material, such as neodymium. Permanent magnet 950 is positioned close enough to ball 930 so that it can exert a magnetic force on ball 930. While permanent magnet 950 is positioned relative to ball 930 such that the magnetic force exerted by permanent magnet 950 on ball 930 urges ball 930 to the closed position, the magnetic force is weak enough that upward gas pressure in the illustration will move ball 930 upward, opening one-way magnetic check valve 900 and allowing flow in that direction. However, ball 930 prevents flow in the opposite direction because pressure from that direction will tend to seat ball 930 more firmly against valve stop 940, closing one-way magnetic check valve 900.

[0080]

[0092] Materials suitable for making strong permanent magnets, such as neodymium, can have very low corrosion resistance. Corrosion leads to metal loss due to reaction with gas, measured as weight loss. Because the gases within the conduit section 910 tend to be corrosive, permanent magnets made from materials with low corrosion resistance, such as neodymium, tend to corrode even if plated with a material such as nickel. To prevent this, in some embodiments, the permanent magnets are located outside the conduit section 910, where they are not exposed to the corrosive gases.

[0081]

[0093] 10, similar to the arrangement described above, a one-way magnetic check valve 1000 is disposed within a conduit section 910, including a conduit wall 920, and includes a ball 930. As such, in the first position shown, ball 930 contacts a valve stop 940. Ball 930 may again be made of a ferromagnetic material, such as nickel, that is resistant to corrosion by the gas within conduit section 910.

[0082]

[0094] Ball 930 is shown in a position where it is biased against valve stop 940 by permanent magnet 1010, which may be made of a rare earth material such as neodymium. In the embodiment shown in Figure 10, permanent magnet 1010 is positioned outside of conduit section 910 and is therefore not exposed to corrosive gases within conduit section 910. As shown, in some embodiments, conduit wall 920 is provided with a groove or recess 1020, and permanent magnet 1010 is positioned within the recess. In some embodiments, there is no recess, and permanent magnet 1010 is simply positioned adjacent to the exterior surface of conduit wall 910.

[0083]

[0095] In these embodiments, conduit wall 920 is made of a material that is magnetically permeable, i.e., a material through which magnetic field lines can pass. As can be seen, permanent magnet 1010 is positioned sufficiently close to ball 930 so that permanent magnet 1010 can exert a magnetic force on ball 930. The arrangement of permanent magnet 1010 relative to ball 930 is such that the magnetic force exerted by permanent magnet 1010 on ball 930 biases ball 930 to a closed position, but is not so strong that gas flow in the upward direction in the illustration cannot move ball 930 upward, thus opening one-way valve 900 and allowing flow in that direction.

[0084]

[0096] In some embodiments, the material of ball 930 is not magnetized or has only weak magnetization that generates a weaker magnetic field, while the permanent magnet has a stronger magnetic field strength. At the same time, the material of ball 930 has a higher corrosion resistance than the material that makes up permanent magnet 1010.

[0085]

[0097] Although specific reference is made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, etc. Those skilled in the art will recognize that when the terms "wafer" or "die" are used herein in connection with these alternative applications, they may be considered synonymous with the more general terms "substrate" or "target portion," respectively. Substrates referred to herein may be processed, before or after exposure, in, for example, a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit, and / or an inspection unit. Where appropriate, the disclosure herein may apply to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce a multi-layer IC, and thus the term substrate, as used herein, may also refer to a substrate that already includes multiple processed layers.

[0086]

[0098] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, and thus, the terminology or terminology of the present disclosure should be interpreted by one of ordinary skill in the art in light of the teachings herein.

[0087]

[0099] As used herein, terms such as "radiation," "beam," "light," "illumination," and the like may encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 248 nm, 193 nm, or 157 nm). DUV generally refers to radiation having a wavelength ranging from 130 nm to 428 nm, and in some embodiments, excimer lasers can generate DUV radiation for use in lithography apparatus. For example, it should be recognized that radiation having a wavelength in the range 130-428 nm relates to radiation having a particular wavelength band, at least a portion of which is within the range 130-428 nm.

[0088]

[0100] As used herein, the term "substrate" describes a material onto which a layer of material is added. In some embodiments, the substrate itself may be patterned, and the material added on top of it may also be patterned or may remain unpatterned.

[0089]

[0101] Although specific reference may be made herein to the use of the apparatus and / or systems according to the present disclosure in the manufacture of ICs, it should be expressly understood that such apparatus and / or systems have many other possible applications. For example, they could be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD panels, thin film magnetic heads, etc. Those skilled in the art will recognize that when the terms "reticle," "wafer," or "die" are used herein in connection with these alternative applications, they should be considered interchangeable with the more general terms "mask," "substrate," and "target portion," respectively.

[0090]

[0102] While specific embodiments of the present disclosure have been described above, it will be recognized that embodiments of the present disclosure may be practiced otherwise than as described. The description is intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that changes can be made to the disclosure as described without departing from the scope of the following claims.

[0091]

[0103] It should be recognized that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. While the Summary and Abstract sections may describe one or more exemplary embodiments of the present disclosure contemplated by the inventors, they do not describe every exemplary embodiment and therefore are not intended to limit the scope of the disclosure and the appended claims in any way.

[0092]

[0104] The present disclosure has been described above using functional building blocks that illustrate examples of specific functions and their relationships. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of description. Other boundaries can be defined as long as the specific functions and their relationships are appropriately performed.

[0093]

[0105] The foregoing description of specific embodiments fully reveals the overall nature of the present disclosure, such that those skilled in the art can readily modify and / or adapt such specific embodiments to various uses without undue experimentation and without departing from the general concept of the present disclosure. Accordingly, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0094]

[0106] Other aspects of the invention are set forth in the following numbered clauses: 1. A chamber configured to hold a fluorine-containing gas; a conduit configured to circulate a fluorine-containing gas to and from the chamber during generation of radiation, the conduit being defined at least in part by a conduit wall; and a one-way check valve disposed in the conduit, the one-way check valve comprising: a check valve element disposed within the conduit and exposed to the fluorine-containing gas, the check valve element including a ferromagnetic material having a first magnetic field strength and a first corrosion resistance, the check valve element being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; an apparatus including a magnetized material having a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance, the permanent magnet disposed outside the chamber and outside the conduit adjacent to the conduit wall to avoid exposure to the fluorine-containing gas, the permanent magnet configured to exert a biasing force on the check valve element that biases the check valve element to a first position. 2. The apparatus of clause 1, wherein the permanent magnet is positioned adjacent the outer surface of the conduit wall and in sufficient proximity to the check valve element and is disposed relative to the check valve element so as to exert a biasing force on the check valve element. 3. The apparatus of clause 2, wherein the check valve element is a sphere. 4. The apparatus of clause 2, wherein the ferromagnetic material comprises nickel. 5. The apparatus of clause 2, wherein the permanent magnet comprises neodymium. 6. The apparatus of clause 1, wherein the exterior of the conduit wall includes a structure defining a recess, and wherein a permanent magnet is positioned at least partially in the recess in sufficient proximity to the check valve element and disposed relative to the check valve element so as to exert a biasing force on the check valve element. 7. The apparatus of clause 6, wherein the check valve element is a sphere. 8. The apparatus of clause 6, wherein the ferromagnetic material comprises nickel. 9. The apparatus of clause 6, wherein the permanent magnet comprises neodymium. 10. The device of clause 1, wherein the check valve element is a sphere. 11. The apparatus of clause 1, wherein the ferromagnetic material comprises nickel. 12. The apparatus of clause 1, wherein the permanent magnet comprises neodymium. 13. A chamber configured to hold a fluorine-containing gas; a conduit configured to circulate a fluorine-containing gas to and from the chamber during generation of radiation, the conduit being defined at least in part by a conduit wall; and a one-way check valve disposed in the conduit, the one-way check valve comprising: a nickel-containing sphere disposed within the conduit and exposed to the fluorine-containing gas, the sphere being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; a neodymium permanent magnet disposed outside the chamber and inside the conduit adjacent the conduit wall to avoid exposure to the fluorine-containing gas, the neodymium permanent magnet configured to exert a biasing force on the sphere that biases the sphere into a first position. 14. The apparatus of clause 13, wherein the nickel-containing sphere has a first magnetic field strength and a first corrosion resistance, and the neodymium permanent magnet has a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance. 15. A radiation source configured to generate radiation, comprising: a chamber configured to contain the corrosive gas and contaminants generated during the generation of radiation; a window configured to isolate the corrosive gas from the environment outside the chamber and to allow radiation to pass between the chamber and the environment; a refill path configured to allow for exchange of the corrosive gas; a conduit configured to circulate a corrosive gas to and from the chamber during generation of radiation; a one-way valve disposed to intersect the conduit and configured to prevent the flow of contaminants toward the window, the one-way check valve a check valve element disposed within the conduit and exposed to the corrosive gas, the check valve element including a ferromagnetic material having a first magnetic field strength and a first corrosion resistance, the check valve element being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; a permanent magnet including a magnetized material having a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance, the permanent magnet being disposed outside the chamber and outside the conduit adjacent the conduit wall to avoid exposure to the corrosive gas, the permanent magnet being configured to exert a biasing force on the check valve element that biases the check valve element to the first position; A radiation source, wherein the conduit system is configured to direct a flow of the refill gas, one of the corrosive gas, or the refill gas and the corrosive gas during at least a refill operation in a manner that prevents contaminants from contacting the window, such that the conduit system extends at least the useful life of the window. 16. The apparatus of clause 15, wherein a permanent magnet is positioned adjacent the exterior of the conduit wall and in sufficient proximity to the check valve element and is disposed relative to the check valve element to exert a biasing force on the check valve element. 17. The device of clause 16, wherein the check valve element is a sphere. 18. The apparatus of clause 16, wherein the ferromagnetic material comprises nickel. 19. The apparatus of clause 16, wherein the permanent magnet comprises neodymium. 20. The apparatus of clause 15, wherein the exterior of the conduit wall includes a structure defining a recess, and wherein a permanent magnet is positioned at least partially in the recess in sufficient proximity to the check valve element and disposed relative to the check valve element to exert a biasing force on the check valve element. 21. The device of clause 20, wherein the check valve element is a sphere. 22. The apparatus of clause 20, wherein the ferromagnetic material comprises nickel. 23. The apparatus of clause 20, wherein the permanent magnet comprises neodymium. 24. The device according to clause 15, wherein the check valve element is a sphere. 25. The apparatus of clause 15, wherein the ferromagnetic material comprises nickel. 26. The apparatus of clause 15, wherein the permanent magnet comprises neodymium.

[0095]

[0107] The breadth and scope of protected subject matter should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. a chamber configured to hold a fluorine-containing gas; a conduit configured to circulate the fluorine-containing gas to and from the chamber during generation of radiation, the conduit being defined at least in part by a conduit wall; a one-way check valve disposed in the conduit, the one-way check valve comprising: a check valve element disposed within the conduit and exposed to the fluorine-containing gas, the check valve element including a ferromagnetic material having a first magnetic field strength and a first corrosion resistance, the check valve element being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; a permanent magnet disposed outside the chamber and outside the conduit adjacent to the conduit wall to avoid exposure to the fluorine-containing gas, the permanent magnet including a magnetized material having a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance, the permanent magnet configured to exert a biasing force on the check valve element to bias the check valve element into the first position.

2. 2. The apparatus of claim 1, wherein the permanent magnet is positioned adjacent an exterior surface of the conduit wall and in sufficient proximity to the check valve element to exert the biasing force on the check valve element.

3. 3. The apparatus of claim 2, wherein the check valve element is a sphere.

4. The device of claim 2 , wherein the ferromagnetic material comprises nickel.

5. The apparatus of claim 2 , wherein the permanent magnet comprises neodymium.

6. 2. The apparatus of claim 1, wherein the exterior of the conduit wall includes a structure defining a recess, and the permanent magnet is positioned at least partially in the recess in sufficient proximity to the check valve element and disposed relative to the check valve element to exert the biasing force on the check valve element.

7. 7. The apparatus of claim 6, wherein the check valve element is a sphere.

8. The device of claim 6 , wherein the ferromagnetic material comprises nickel.

9. The apparatus of claim 6 , wherein the permanent magnet comprises neodymium.

10. The device of claim 1 , wherein the check valve element is a sphere.

11. The device of claim 1 , wherein the ferromagnetic material comprises nickel.

12. The apparatus of claim 1 , wherein the permanent magnet comprises neodymium.

13. a chamber configured to hold a fluorine-containing gas; a conduit configured to circulate the fluorine-containing gas to and from the chamber during generation of radiation, the conduit being defined at least in part by a conduit wall; a one-way check valve disposed in the conduit, the one-way check valve comprising: a nickel-containing sphere disposed within the conduit and exposed to the fluorine-containing gas, the sphere being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; a neodymium permanent magnet disposed outside the chamber and inside the conduit adjacent a wall of the conduit to avoid exposure to the fluorine-containing gas, the neodymium permanent magnet configured to exert a biasing force on the sphere that biases the sphere toward the first position.

14. 14. The apparatus of claim 13, wherein the sphere comprising nickel has a first magnetic field strength and a first corrosion resistance, and the neodymium permanent magnet has a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance.

15. A radiation source configured to generate radiation, a chamber configured to contain corrosive gases and contaminants generated during the generation of said radiation; a window configured to isolate the corrosive gas from an environment outside the chamber and to allow the radiation to pass between the chamber and the environment; a refill path configured to allow replacement of the corrosive gas; a conduit configured to circulate the corrosive gas to and from the chamber during the generation of the radiation; a one-way valve disposed to intersect the conduit and configured to prevent the flow of the contaminants toward the window, the one-way check valve comprising: a check valve element disposed within the conduit and exposed to the corrosive gas, the check valve element including a ferromagnetic material having a first magnetic field strength and a first corrosion resistance, the check valve element being movable between a first position in which the one-way check valve is closed and a second position in which the one-way check valve is open; a permanent magnet including a magnetized material having a second magnetic field strength greater than the first magnetic field strength and a second corrosion resistance less than the first corrosion resistance, the permanent magnet being disposed outside the chamber and outside the conduit adjacent the conduit wall to avoid exposure to the corrosive gas, the permanent magnet being configured to exert a biasing force on the check valve element that biases the check valve element to the first position; the conduit system is configured to direct a flow of refill gas, one of the corrosive gas, or the refill gas and the corrosive gas during at least a refill operation in a manner that prevents the contaminants from contacting the window, so that the conduit system extends at least the useful life of the window.

16. 16. The apparatus of claim 15, wherein the permanent magnet is positioned adjacent an exterior of the conduit wall and sufficiently proximate to the check valve element and disposed relative to the check valve element to exert the biasing force on the check valve element.

17. 17. The apparatus of claim 16, wherein the check valve element is a sphere.

18. 17. The device of claim 16, wherein the ferromagnetic material comprises nickel.

19. 17. The apparatus of claim 16, wherein the permanent magnet comprises neodymium.

20. 16. The apparatus of claim 15, wherein the exterior of the conduit wall includes structure defining a recess, and the permanent magnet is positioned at least partially in the recess in sufficient proximity to the check valve element and disposed relative to the check valve element to exert the biasing force on the check valve element.

21. 21. The apparatus of claim 20, wherein the check valve element is a sphere.

22. 21. The device of claim 20, wherein the ferromagnetic material comprises nickel.

23. 21. The apparatus of claim 20, wherein the permanent magnet comprises neodymium.

24. 16. The apparatus of claim 15, wherein the check valve element is a sphere.

25. 16. The device of claim 15, wherein the ferromagnetic material comprises nickel.

26. The apparatus of claim 15 , wherein the permanent magnet comprises neodymium.

Images