Fan, fan housing, radiation source, lithographic apparatus, and methods thereof

Abstract

A pulsed-discharge radiation source is provided. The pulsed-discharge radiation source generates DUV radiation. The pulsed-discharge radiation source includes electrodes, a fan, and a fan housing. The electrodes delivers a voltage to a gas to generate radiation. The fan delivers the gas in a first direction through a gap located between the electrodes. The fan housing encloses the fan and the gas. The fan housing includes a gas inlet and a gas guiding structure. The gas inlet receives the gas. The gas guiding structure directs the gas to the gap. The gas guiding structure has a tapered shape.

Description

FAN, FAN HOUSING, RADIATION SOURCE, LITHOGRAPHIC APPARATUS, AND METHODS THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 614,258 which was filed on 22 December 2023 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to radiation sources, for example, a pulsed discharge radiation source for lithographic apparatuses and systems.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiationsensitive material (photoresist or simply “resist”) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithographic operation, different processing steps can entail different layers to be sequentially formed on the substrate. Accordingly, it can be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus can use an alignment apparatus for detecting positions of the alignment marks and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. Misalignment between the alignment marks at two different layers is measured as overlay error.

[0005] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters can include, for example, the overlay error between successive layers formed in or on the patterned substrate and critical linewidth of developed photosensitive resist. This measurement can be performed on a product substrate and / or on a dedicated metrology target. There are various techniquesfor making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. A fast and non-invasive form of a specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range. By contrast, angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0006] Such optical scatterometers can be used to measure parameters, such as critical dimensions of developed photosensitive resist or overlay error (OV) between two layers formed in or on the patterned substrate. Properties of the substrate can be determined by comparing the properties of an illumination beam before and after the beam has been reflected or scattered by the substrate.

[0007] Lithographic process can be critically dependent on the radiation source that provides radiation for exposure of wafers. In deep ultraviolet (DUV) scanners or steppers, the radiation source includes a gas circulator (e.g., a fan, a blower) that circulates a gas that is exposed to a voltage to generate the radiation. The gas circulator consumes a substantial amount of energy and requires heat exchangers to dissipate wasted energy due to loss in gas transport. In addition, it is desired to increase the repetition rate of the radiation source, which depends on a rotational speed of the gas circulator. Thus, the repetition rate is limited by the rotational speed limit of the gas circulator.SUMMARY

[0008] Accordingly, it is desirable to reduce energy waste in a radiation source and to increase a repetition rate. For example, the gas transport efficiency can be improved based on aspects described herein.

[0009] In some aspects, a pulsed-discharge radiation source is provided. The pulsed-discharge radiation source can generate deep ultraviolet (DUV) radiation. The pulsed-discharge radiation source can include electrodes, a fan, and a fan housing. The electrodes can be configured to deliver a voltage to a gas to generate radiation. The fan can be configured to deliver the gas in a first direction through a gap located between the electrodes. The fan housing is configured to enclose the fan and the gas. The fan housing includes a gas inlet and a gas guiding structure. The gas inlet receives the gas. In some aspects, the gas guiding structure directs the gas to the gap between the electrodes. The gas guiding structure can have a tapered shape.

[0010] In some aspects, a method for generating DUV radiation using a pulsed-discharge radiation source is provided. The method can include enclosing a fan in a fan housing, providing a gas from thefan to a gap located between a pair of electrodes of the radiation source, delivering the gas in a first direction through the gap located between the pair of electrodes using the fan to accelerate the gas, and energizing the electrodes to generate radiation. The fan and the fan housing can be disposed in the radiation source. The pair of electrodes can be configured to deliver a voltage to the gas to generate the radiation. The fan housing can comprise a gas inlet and a gas guiding structure. In some aspects, the gas inlet receives the gas. The gas guiding structure can have a tapered shape.

[0011] In some aspects, a lithographic apparatus is provided. The lithographic apparatus includes a pulsed-discharge radiation source and a projection system. The projection system can be configured to project an image of a pattern onto a substrate using the radiation.

[0012] In some aspects, a metrology apparatus is provided. The metrology apparatus can include a pulsed-discharge radiation source, an illumination system, and a detection system. The pulsed-discharge radiation source can be configured to generate DUV radiation. The illumination system can be configured to illuminate a target on a substrate using the radiation. The detection system can detect radiation after it interacts with the target.

[0013] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0014] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0015] FIG. 1 shows a lithographic apparatus, according to some aspects.

[0016] FIG. 2 shows a lithographic cell, according to some aspects.

[0017] FIGS. 3, 4, 5, 6A and 6B show radiation sources, according to some aspects.

[0018] FIG. 6C shows a gas flow spreader for a radiation source, according to some aspects.

[0019] FIG. 7 is a flow chart that shows method steps for performing functions of embodiments described herein, according to some embodiments.

[0020] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears.Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0021] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0022] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0023] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0024] Enumerative adjectives (e.g., “first,” “second,” “third,” or the like) can be used to distinguishing like elements without establishing an order, hierarchy, quantity, or permanent numeric assignment (unless otherwise noted). For example, the terms “first target” and “second target” can be used in a manner analogous to “i* target” and “j* target” so as to facilitate the distinguishing of two targets without specifying a particular order, hierarchy, quantity, or immutable numeric correspondence.

[0025] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can include 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 can 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 can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result fromcomputing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine -readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0026] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0027] Example Lithographic Systems

[0028] FIG. 1 shows a lithographic apparatus 100, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 can comprise one or more of the following: an illuminator IL to condition a radiation beam B (e.g., deep ultra violet (DUV) radiation); a support structure MT (e.g., a mask table) to support a patterning device MA (e.g., a mask, a reticle, or a dynamic patterning device); a first positioner PM to accurately position patterning device MA; a substrate table WT (e.g., a wafer table) to hold a substrate W (e.g., a resist-coated wafer); and a second positioner PW to accurately position substrate W. Lithographic apparatus 100 can also comprise a projection system PS to project patterned radiation onto a target portion C (e.g., comprising one or more dies) of substrate W. The pattern can be imparted to radiation beam B by patterning device MA. In lithographic apparatus 100, patterning device MA and projection system PS can be transmissive.

[0029] In some aspects, illuminator IL can comprise 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.

[0030] In some aspects, support structure MT can hold patterning device MA in a manner that depends on the orientation of patterning device MA with respect to a reference frame, a design of lithographic apparatus 100, and other conditions, such as whether or not patterning device MA is held in a vacuum environment. Support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. Support structure MT can be, for example, a frame or a table (e.g., can be fixed or movable). By using one or more positioning sensors (e.g., alignment sensor), support structure MT can ensure that patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0031] In some aspects, the term “patterning device” can refer to a device that can be used to create a pattern of radiation at a cross-section of radiation beam B, such as to create a pattern at target portion C of substrate W. The pattern imparted to radiation beam B can correspond to a particular functional layer in a device being created at target portion C to form an integrated circuit. Examples of patterning devices MA include, for example, reticles, masks, or programmable LCD panels. Masks types used in lithography can include binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types.

[0032] In some aspects, the term “projection system” can refer to any type of projection system (e.g., refractive, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof) suitable for the exposure radiation being used. Features of projection systems can account for additional factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. For example, a projection system can be designed for use in a controlled gas environment such that the beam path can be conditioned as desired.

[0033] In some aspects, lithographic apparatus 100 can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table.

[0034] In some aspects, lithographic apparatus 100 can also be of a type in which at least a portion of substrate W can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between projection system PS and substrate W. An immersion liquid can also be applied to other spaces in lithographic apparatus 100, for example, between patterning device MA and projection system PS. Immersion techniques can increase the numerical aperture (NA) of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be disposed between projection system PS and substrate W during exposure.

[0035] In some aspects, illuminator IL can receive a radiation beam from source SO (e.g., radiation source). Source SO and lithographic apparatus 100 can be separate physical entities. For example, source SO can be a detached excimer laser. In such cases, source SO is not considered to be part of the lithographic apparatus 100 and radiation beam B passes from source SO to illuminator IL with the aid of a beam delivery system BD. Beam delivery system BD can include, for example, suitable directing mirrors and / or a beam expander.

[0036] In some aspects, source SO can be an integral part of the lithographic apparatus 100. For example, source SO can be a mercury lamp integrated with lithographic apparatus 100. A radiation system (or illumination system) can comprise source SO, illuminator IL, and / or beam delivery system BD.

[0037] In some aspects, illuminator IL can comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “o-outer” and “o-inner,” respectively) of the intensity distribution in a pupil plane of illuminator IL can be adjusted. In addition, illuminator IL can comprise various other components, such as an integrator IN and a condenser CO. Illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0038] In some aspects, radiation beam B can be incident on patterning device MA, which is held on support structure MT, and is patterned by patterning device MA. Having traversed patterning deviceMA, radiation beam B can pass through projection system PS, which focuses the beam onto a target portion C of substrate W. Projection System PS has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0039] In some aspects, projection system PS can project an image of a pattern MP of patterning device MA. The image can be formed by diffracted beams produced from the pattern MP by radiation from the intensity distribution. The image can be projected on a photoresist layer coated on the substrate W. For example, pattern MP can comprise an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction can generate diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) can traverse the pattern without any change in propagation direction. The zeroth order diffracted beams can traverse an upper lens or upper lens group of projection system PS, upstream of pupil conjugate PPU of projection system PS, to reach pupil conjugate PPU. The portion of the intensity distribution in the plane of pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illuminator IL. An aperture device PD, for example, can be disposed at or substantially at a plane that includes pupil conjugate PPU of projection system PS.

[0040] In some aspects, projection system PS can capture the zeroth order diffracted beams, first order diffracted beams, and / or higher order diffracted beams (not shown) (e.g., capture using a lens or lens group L). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first-order diffracted beams can interfere with corresponding zeroth-order diffracted beams at the level of substrate W to create an image of pattern MP at a highest possible resolution and process window (e.g., usable depth of focus in combination with tolerable exposure dose deviations). In some aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of illumination system pupil IPU. Further, in some aspects, astigmatism aberration can be reduced by blocking the zeroth order beams, at pupil conjugate PPU, that are associated with radiation poles in opposite quadrants. This is is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0041] In some aspects, with the aid of second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of radiation beam B). Similarly, first positioner PM and another position sensor (not shown) can be used to accurately position patterning device MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0042] In some aspects, movement of support structure MT can be achieved using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of first positioner PM. Similarly, movement of substrate table WT can be achieved using a long-stroke module and a short-stroke module, which form part of second positioner PW. In the case of a stepper (as opposed to a scanner), support structure MT can be connected to a short-stroke actuator or can be fixed. Patterning device MA and substrate W can be aligned using measurement targets, for example, mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although targets as illustrated (e.g., substrate alignment marks Pl, P2) can occupy dedicated target portions, targets can be located in spaces between target portions (referred to as scribe-lane targets or alignment marks). Similarly, in situations in which more than one die is provided on patterning device MA, the mask alignment marks can be located between the dies.

[0043] In some aspects, support structure MT and patterning device MA can be in a vacuum chamber V. An in-vacuum robot IVR can be used to move patterning devices, such as a mask, in and out of vacuum chamber V. Alternatively, when support structure MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0044] In some aspects, lithographic apparatus 100 can be used in at least one of the following modes:

[0045] 1. In step mode, the support structure (for example, mask table) MT and substrate table WT can be kept substantially stationary, while an entire pattern imparted to radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). Substrate table WT can then be shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0046] 2. In scan mode, support structure MT and substrate table WT can be scanned synchronously while a pattern imparted to radiation beam B is projected onto a target portion C (e.g., a single dynamic exposure). The velocity and direction of substrate table WT relative to support structure MT can be determined by the (de-)magnification and image reversal characteristics of projection system PS.

[0047] 3. In another mode, support structure MT can be kept substantially stationary holding a programmable patterning device, and substrate table WT can be moved or scanned while a pattern imparted to radiation beam B is projected onto a target portion C. A pulsed radiation source for source SO can be employed and the programmable patterning device can be updated as needed after each movement of substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0048] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0049] In some aspects, lithographic apparatuses can comprise a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.

[0050] Example Lithographic Cell

[0051] FIG. 2 shows a lithographic cell 200, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatus 100 can form part of lithographic cell 200. Lithographic cell 200 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Examples of such apparatuses can include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO can pick up substrates from input / output ports I / Ol, I / O2, move them between the different process apparatuses and deliver the substrates to a loading bay LB of lithographic apparatus 100. The different apparatuses, which are often collectively referred to as the track, can be under the control of a track control unit TCU, which can itself be controlled by a supervisory control system SCS. Supervisory control system can also control lithographic apparatus 100 via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0052] Example Radiation Sources

[0053] There are many applications of pulsed-discharge radiation sources. In some aspects, a pulsed- discharge laser can be used for lithographic processes, medical procedures, machining via laser ablation, laser imprinting, and more. A lithographic apparatus is one example in which a high repetition rate of the laser is desirable. The pulsed-discharge radiation source can comprise a gas circulator (also referred to as a blower or a fan) that transports gas molecules to a gap formed by discharge electrodes of the pulsed-discharge radiation source. Gas transport can be inefficient due to an open space between an output of the gas circulator and the electrodes. The distance from the discharge electrodes to the blades of the gas circulator is an open volume. Therefore, the gas circulator is operated at a high rotation speed. The inefficiency can increase energy waste in the radiation source. Thus, additional heat exchangers are used to dissipate the wasted energy. In addition, the inefficiency can limit repetition rate of the laser. For example, for a repetition frequency of 6000 Hz, the gas circulator in some implementations of a radiation source may operate at 5000 rpm. At this exemplary rate, the gas circulator may consume about 5-15 KW, which may represent a significant portion (e.g., about 15%-25%) of the total laser energy consumption. The repetition frequency is limited by the maximum rotational speed of the gas circulator.

[0054] FIG. 3 shows a radiation source 300, according to some aspects. In some aspects, radiation source 300 is a pulsed-discharge radiation source. A gas discharge laser is an example of a pulsed- discharge radiation source. Source SO of lithographic apparatuses 100 (FIG. 1) can use implement radiation source 300. Radiation source 300 can comprise a gas chamber 302, a window 304, conduit system 306, and one or more electrodes 310 (also “electrical connection”). Conduit system 306 can comprise a network of valves, conduits, and contaminant filters (not shown).

[0055] In some aspects, gas chamber 302 can confine a gas 308. Gas 308 can comprise fluorine, neon, krypton, argon, and the like. Gas 308 can be rarified via a pressure control system (e.g., vacuum system) that controls a pressure within gas chamber 302. Conduit system 306 is connected to gas chamber 302. Conduit system 306 can allow management of gas 308 in gas chamber 302. For example, conduit system 306 can direct a flow (e.g., circulation) of gas 308 to a filter within conduit system 306 to purify gas 308. A voltage / current can be supplied to gas 308 (e.g., via one or more electrodes 310) to generate radiation 312. The voltage / current can be in the form of pulse with sufficient power to create a plasma of gas 308 in a region between electrodes 310. The plasma can generate radiation with a set of wavelengths that depend on energy states of the plasma. The type of gas 308 (e.g., fluorine) can determine the wavelengths that are produced (e.g., DUV wavelengths). Window 304 can allow radiation 312 to exit gas chamber 302.

[0056] FIG. 4 shows a radiation source 400, according to some aspects. In some aspects, the view in FIG. 4 can represent a more detailed and / or different view of a portion of radiation source 300 (FIG. 3) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 3 and 4 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include gas chamber 402, gas 408, and electrodes 410.

[0057] In some aspects, radiation source 400 can comprise gas chamber 402, one or more electrodes 410, and a gas circulator 414. Gas circulator 414 can be a blower (or a fan) or an external pressure system that is connected to gas chamber 402 via ducting. Gas chamber 402 can confine a gas. The gas can comprise fluorine, neon, krypton, argon, or other similar species (for example, argon fluoride). To generate radiation 312 (FIG. 3), an electrical pulse can be supplied to gas 408 via electrodes 410, thereby igniting a plasma of gas 408 at plasma-generation region 416 (between electrodes 410) of gas chamber 402. The generated plasma can release DUV radiation, thereby operating as a DUV radiation source. The perspective in FIG. 4 can be considered as being 90 degrees with respect to the perspective of FIG. 3 (e.g., whereas radiation 312 is shown in FIG. 3 traveling to the right of the page (can also be left of the page), radiation can travel in / out of the page in FIG. 4).

[0058] In various implementations of radiation source 400, after a volume of gas has been converted to plasma, it may not be immediately suitable for another conversion to plasma for producing DUV radiation. For example, in the process of generating radiation, gas 408 and electrodes 410 can interact chemically. For example, a materials within electrodes 410 (e.g., copper) can chemically interact with a chemical content of gas 408 (e.g., fluorine) to create a dust-like byproduct (e.g., metal-fluoride by product). The byproduct can become a contaminant that absorbs radiation in subsequent radiation pulses. Therefore, a gas flow 418 (indicated by arrows) can be implemented in order to optimize the production of radiation by circulating the spent portion of gas 408 and contaminants out of the plasmageneration region 416 while supplying unspent gas for the next plasma ignition. Gas circulator 414 can generate gas flow 418. Gas circulator 414 can include a plurality of blades 424. In some aspects, theplurality of blades 424 can extend parallel to one another along the length of the gas chamber 402. Radiation source 402 can include one or more heat exchangers (not shown) configured to dissipate energy. Additional details about blower functions are described in WO 2022 / 140074, published on June 30, 2022, which is incorporated by reference herein in its entirety.

[0059] In some aspects, to make the gas transport be more efficient, gas circulator 414 and an area from gas circulator 414 to electrodes 410 can be a confined or closed volume. In some aspects, gas circulator 414 can be enclosed in an enclosure 420 (also referred to as fan housing). In some aspects, enclosure 420 can have a shape corresponding to an external shape of gas circulator 414. For example, enclosure 420 can have a shape similar to gas circulator 414.

[0060] In some aspects, a gas guiding structure 422 can be attached to enclosure 420 of gas circulator 414. Gas guiding structure 422 can have a converged flow channel. That is, a gas volume can be gradually reduced from gas circulator 414 to a discharge area (e.g., area or gap between electrodes 410). Gas guiding structure 414 can have a tapered shape such as to gradually reduce a gas volume from gas circulator 414 to the discharge area.

[0061] FIG. 5 is a schematic of a radiation source 500 according to some aspects. In some aspects, the view in FIG. 5 can represent a more detailed and / or different view of a portion of radiation source 300 (FIG. 3) and radiation source 400 (FIG. 4) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 3, 4, and 5 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include a gas chamber 502, a gas 508, electrodes 510, a fan 514, a fan housing 520, and a guiding structure 522.

[0062] In some aspects, fan 514 rotates about an axis 526. In some aspects, fan 514 can include a plurality of blades 524. The plurality of blades 524 can be elongated in the direction of gas chamber 502 (in a second direction B). In some aspects, a blower rotor (not shown) may be coupled to the plurality of blades. The blower rotor can be configured to rotate at a varied rotation speed.

[0063] In some aspects, fan housing 520 can enclose fan 514. Fan housing 520 can be configured such as axis 526 intersects a side of fan housing 520. Fan housing (also referred to as enclosure) 520 can comprise an inlet 528 and an outlet 530. In some aspects, inlet 528 can be included in the side of fan housing that intersects with axis 526. In various implementations, fan housing 520 can form a closed volume inside of gas chamber 502, fluidly communicating with the remainder of gas chamber 502 through inlet 528 and outlet 530. Inlet 528 is configured to receive gas 508. Outlet 530 can deliver gas 508 to a gap between electrodes 510 via guiding structure 522. Fan housing 520 can deliver gas 508 in a first direction A via outlet 530 and can receive gas 508 via inlet 528 in second direction B. In some aspects, first direction A can be substantially perpendicular to second direction B. First direction A may correspond to the direction of the flow of gas 508 into fan housing 520.

[0064] In some aspects, guiding structure 522 can be connected to fan housing 520. Guiding structure 522 can direct the gas flow towards the gap between electrodes 510. Guiding structure 522 can delivergas 508 through the gap in first direction A. Electrodes 510 can deliver a voltage to gas 508 to generate radiation. In some aspects, guiding structure 522 can be connected to outlet 530 of fan housing 520. For example, guiding structure 522 can comprise an inlet 532 and an outlet 534. Inlet 532 can have a size and shape that match the size and shape of outlet 530.

[0065] In some aspects, guiding structure 522 can have a tapered shape. Guiding structure 522 can be a convergent nozzle. Guiding structure 522 can gradually converge to a size that substantially corresponds to the height of the gap formed by electrodes 510 (e.g., from about 5 mm to about 15 mm). For example, outlet 534 can have a size and a shape that match the size and shape of the gap between electrodes 510. In some aspects, guiding structure 522 can widen in second direction B to correspond to the length of the gap in the second direction B (e.g., length from about 500 mm to about 750 mm). In a non-limiting example, a size of outlet 530 of fan 514 in second direction B (e.g., from 250 mm to about 450 mm) direction may be less than the length of the gap formed by electrodes 510 in second direction B.

[0066] In some aspects, a gas flow spreader (not shown) is disposed at outlet 534 of guiding structure 522 that works as a homogenizer.

[0067] In some aspects, fan housing 520 can be made of the same metal as the blades 524 of fan 514. In some aspects, fan housing 520 can be made of a dielectric. The dielectric can be selected such as it can withstand the chamber gas environment.

[0068] In some aspects, fan housing 520 can have a shape corresponding to the shape of fan 514. In a non-limiting example, fan housing 520 can have a circular shape. In some aspects, a diameter of fan 514 can be substantially equal to the diameter of fan housing 520 (e.g., from about 100 mm to about 160 mm).

[0069] The fan and fan housing described herein may provide many advantages. In some implementations, there is an increase in the gas flow velocity near the electrodes (e.g., an increase from about 50 m / s to about 100 m / s). Thus, the fan and fan housing may improve the efficiency of radiation source. In some implementations, a lowered rotation speed is sufficient for maintaining the desired gas flow velocity. Thus, energy consumption may be decreased. In some implementations, when operating the fan at a low speed (e.g., 3000 rpm instead of 5000 rpm), an improved laser energy stability is obtained. In some implementations, a blower with a reduced length may be used while maintaining the desired gas flow velocity near the electrodes. For example, a blower having a length less the electrode length may be used.

[0070] In some aspects, it is desired to increase the gas flow efficiency. One or more centrifugal fans may be used instead or in addition to the fan described above. In addition, a cross flow fan may limit a size of the gas chamber (e.g., gas chamber 402). Using one or more centrifugal fans provide the advantage of flexibility in designing a length of the gas chamber.

[0071] Example array of fans

[0072] FIGS. 6A and FIGS. 6B show a radiation source 600, according to some aspects. FIG. 6A shows a cross sectional view of radiation source 600. FIG. 6B shows a perspective view of radiation source 600. In some aspects, the view in FIGS. 6A and 6B can represent a more detailed and / or different view of a portion of radiation source 300 (FIG. 3), radiation source 400 (FIG. 4), and radiation source 500 (FIG. 5) (some omissions may be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 3, 4, and 5 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include a gas chamber 602, gas 608, and electrodes 610.

[0073] In some aspects, radiation source 600 can comprise a gas chamber 602, one or more electrodes 610, and a gas circulator 614. Gas circulator 614 can comprise one or more centrifugal fans. For example, gas circulator 614 can comprise an array of centrifugal fans (e.g., fan 614a, fan 614b, fan 614c in FIG. 6B). In some aspects, gas circulator 614 may be enclosed in an enclosure 620. For example, each centrifugal fan may have a respective enclosure. In some aspects, the plurality of centrifugal fans (and respective enclosures) are disposed in a row adjacent to each other in a direction parallel to a plasma region 616 formed between electrodes 610 (e.g., in a second direction B as shown in FIG. 6B). Enclosure 620 can include an inlet 628. Gas circulator 614 can receive gas 608 via inlet 628 in a third direction C and output gas 608 in direction A.

[0074] In some aspects, gas circulator 614 can be a centrifugal fan. In some aspects, each centrifugal fan can be run by a separate and independent motor. Centrifugal fan can comprise a stator 638 (e.g., an axial flux stator), a bearing 640 (e.g., foil bearing), and a centrifugal impeller 636. In some aspects, centrifugal impeller 636 can comprise a rare earth magnet. In some aspects, the rare earth magnet is a samarium cobalt (SmCo) or neodymium (NdFeB) magnets. In some aspects, centrifugal impeller 636 can be made from ferrite (ceramic) or alnico.

[0075] In some aspects, each centrifugal fan may be coupled to a guiding structure 622. For example, centrifugal fan 614a is coupled to guiding structure 622a. Similarly, centrifugal fan 614b and centrifugal fan 614c can be coupled to respective guiding structures (not shown in FIG. 6B). For example, enclosure 620 can be coupled to guiding structure 622. An outlet of enclosure 620 can have a form and a size that match an inlet of enclosure 620. The plurality of guiding structures are a plurality of nozzles. The nozzle may be a convergent nozzle. Guiding structure 622 can guide a flow of the gas towards a plasma region 616 (e.g., an outlet of guiding structure 622 is close to plasma region 616). For example, a shape of guiding structure 622 can be designed to alter a direction of the flow of gas 608 towards plasma region 616. In some aspects, a gas flow spreader 642 (shown in FIGS. 6B and 6C) may be disposed at an outlet 644 of guiding structure 622. Gas flow spreader 624 may be a part of an interior surface of gas chamber 602.

[0076] In some aspects, gas flow spreader 642 can comprise a plurality of grooves. The grooves can facilitate a laminar-flow like gas flow or a homogeneous-flow like gas flow (e.g., homogenizer). In some aspects, gas flow spreader 642 is configured to vary the path of gas 608 inside the grooves toachieve uniformity. In some aspects, gas flow spreader 642 can include a plurality of scalloped-shaped grooves. The scalloped-shaped grooves can be open ended channels arranged side by side. The grooves may be arranged in a divergent fashion from the outlet of guiding structure towards plasma region 616. Gas flow spreader 642 can act as a heat exchanger. Gas flow spreader 642 may be designed to achieve a desired flow shape and heat transfer (e.g., gas flow spreader may be fabricated using a three dimensional printing process).

[0077] In some aspects, the array of centrifugal fans provide many advantages. The centrifugal fan provides high efficiency that leads to an increase in a clearing ratio of undesired contaminants. A high laser pulse repetition rate may be achieved (e.g., greater than 8 KHz). In addition, a length of the gas chamber can be increased by adding one or more centrifugal fans to the array of centrifugal fans.

[0078] FIG. 7 shows method steps for performing functions described herein, according to some embodiments. The method steps of FIG. 7 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 7 described below merely reflect an example of steps and are not limiting. That is, further method steps and functions may be envisaged based upon embodiments described in reference to FIGS. 1-6B.

[0079] At step 702, a fan is enclosed in a fan housing. The fan and the fan housing are disposed in a pulsed-discharge radiation source.

[0080] At step 704, a gas is provided from the fan to a gap located between a pair of electrodes of the pulsed-discharge radiation sources.

[0081] At step 706, the gas is delivered in a first direction through the gap located between the pair of electrodes using the fan to accelerate the gas. The pair of electrodes are configured to deliver a voltage to the gas to generate radiation. The fan housing comprises a gas inlet configured to receive the gas and a gas guiding structure configured to direct the gas to the gap. In some aspects, the gas guiding structure has a tapered shape.

[0082] At step 708, the electrodes are energized to generate radiation.

[0083] In some aspects, the gap with elongated shape is provided in a second direction perpendicular to the first direction. The fan with a plurality of blades is provided. The plurality of blades are coupled to a fan shaft. The plurality of blades are elongated in the second direction.

[0084] In some aspects, a path of the gas is altered using grooves disposed inside the fan to achieve uniformity of gas flow.

[0085] The method steps of FIG. 7 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 7 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-6.

[0086] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength I of 365, 248, 193, 157 or 126 nm). Generally, radiation having wavelengthsbetween about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 180-200 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 180-200 nm.

[0087] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in 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 appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate can 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) and / or a metrology unit. Where applicable, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0088] Furthermore, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0089] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0090] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. The foregoing description of specific aspects will so fully reveal the generalnature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0091] Other aspects of the invention are set out in the following numbered clauses:1. A pulsed-discharge radiation source configured to generate DUV radiation, comprising: electrodes configured to deliver a voltage to a gas to generate radiation; a fan configured to deliver the gas in a first direction through a gap located between the electrodes; and a fan housing configured to enclose the fan and the gas, wherein the fan housing comprises a gas inlet configured to receive the gas and a gas guiding structure configured to direct the gas to the gap, wherein the gas guiding structure has a tapered shape.2. The radiation source of clause 1, wherein the gap comprises an elongated shape in a second direction perpendicular to the first direction, and the fan comprises a plurality of blades coupled to a fan shaft, wherein the plurality of blades are also elongated in the second direction.3. The radiation source of clause 1, wherein the gap is elongated in a second direction perpendicular to the first direction and the fan comprises a plurality of centrifugal fans disposed in a row adjacent to each other and wherein the row is disposed substantially parallel to the second direction.4. The radiation source of clause 3, wherein each centrifugal fan comprises an axial flux motor with a magnetically levitated impeller.5. The radiation source of clause 3, wherein each centrifugal fan motor comprises a rare earth magnet.6. The radiation source of clause 5, wherein the rare earth magnet is a samarium cobalt magnet.7. The radiation source of clause 3, wherein the gas guiding structure is a series of centrifugal fan nozzles corresponding to the centrifugal fans and a series of gas flow spreaders comprising grooves that are disposed at an outlet of the gas guiding structure, which facilitates a laminar-flow like gas flow or homogenous-flow like gas flow.8. The radiation source of clause 1, wherein the gas guiding structure comprises a convergent nozzle.9. The radiation source of clause 1, wherein a fan axis of rotation intersects a side of the fan housing and the gas inlet is disposed at the side.10. The radiation source of clause 9, wherein the gas inlet receives the gas substantially perpendicular to a flow of the gas within the fan.11. The radiation source of clause 1 , further comprising a gas flow spreader disposed at an outlet of the gas guiding structure that works as a homogenizer.12. A method for generating DUV radiation using a pulsed-discharge radiation source, comprising: enclosing a fan in a fan housing, wherein the fan and fan housing are disposed in the radiation source; providing a gas from the fan to a gap located between a pair of electrodes of the radiation source;delivering, using the fan to accelerate the gas, the gas in a first direction through the gap located between the pair of electrodes that are configured to deliver a voltage to the gas to generate the radiation, wherein the fan housing comprises a gas inlet configured to receive the gas and a gas guiding structure configured to direct the gas to the gap, wherein the gas guiding structure has a tapered shape; and energizing the electrodes to generate the radiation.13. The method of clause 12, further comprising: providing the gap with elongated shape in a second direction perpendicular to the first direction, and providing the fan with a plurality of blades coupled to a fan shaft, wherein the plurality of blades are also elongated in the second direction.14. The method of clause 12, further comprising: providing the gap with elongated shape in a second direction perpendicular to the first direction, and providing a plurality of centrifugal fans disposed in a row adjacent to each other and wherein the row is disposed substantially parallel to the second direction.15. The method of clause 14, further comprising configuring the gas guiding structure as a series of centrifugal fan nozzles corresponding to the centrifugal fans and providing a series of gas flow spreaders comprising grooves that are disposed at an outlet of the gas guiding structure.16. The method of clause 12, further comprising providing the gas guiding structure as a convergent nozzle.17. The method of clause 12, further comprising orienting the fan along an axis of rotation that intersects a side of the fan housing, and arranging the gas inlet at the side.18. The method of clause 12, wherein the providing the gas comprises providing the gas at a gas inlet configured to deliver the gas substantially perpendicular to a flow of the gas within the fan.19. The method of clause 12, further comprising varying a path of the gas using groves disposed inside the fan to achieve uniformity of gas flow.20. The method of clause 12, further comprising: disposing the fan and the fan housing in a DUV laser chamber of the radiation source.21. A lithographic apparatus comprising: a pulsed-discharge radiation source configured to generate DUV radiation according to any of clauses 1-11; and a projection system configured to project an image of a pattern onto a substrate using the radiation.22. A metrology apparatus comprising: a pulsed-discharge radiation source configured to generate DUV radiation according to any of clauses M l; an illumination system configured to illuminate a target on a substrate using the radiation; and a detection system to detect radiation after it interacts with the target.

[0092] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forthone or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above-described aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A pulsed-discharge radiation source configured to generate DUV radiation, comprising: electrodes configured to deliver a voltage to a gas to generate radiation; a fan configured to deliver the gas in a first direction through a gap located between the electrodes; and a fan housing configured to enclose the fan and the gas, wherein the fan housing comprises a gas inlet configured to receive the gas and a gas guiding structure configured to direct the gas to the gap, wherein the gas guiding structure has a tapered shape.

2. The radiation source of claim 1, wherein the gap comprises an elongated shape in a second direction perpendicular to the first direction, and the fan comprises a plurality of blades coupled to a fan shaft, wherein the plurality of blades are also elongated in the second direction.

3. The radiation source of claim 1, wherein the gap is elongated in a second direction perpendicular to the first direction and the fan comprises a plurality of centrifugal fans disposed in a row adjacent to each other and wherein the row is disposed substantially parallel to the second direction.

4. The radiation source of claim 3, wherein each centrifugal fan comprises an axial flux motor with a magnetically levitated impeller.

5. The radiation source of claim 3, wherein the gas guiding structure is a series of centrifugal fan nozzles corresponding to the centrifugal fans and a series of gas flow spreaders comprising grooves that are disposed at an outlet of the gas guiding structure, which facilitates a laminar-flow like gas flow or homogenous-flow like gas flow.

6. The radiation source of claim 1, wherein the gas guiding structure comprises a convergent nozzle.

7. The radiation source of claim 1, wherein a fan axis of rotation intersects a side of the fan housing and the gas inlet is disposed at the side.

8. The radiation source of claim 7, wherein the gas inlet receives the gas substantially perpendicular to a flow of the gas within the fan.

9. The radiation source of claim 1, further comprising a gas flow spreader disposed at an outlet of the gas guiding structure that works as a homogenizer.

10. A method for generating DUV radiation using a pulsed-discharge radiation source, comprising: enclosing a fan in a fan housing, wherein the fan and fan housing are disposed in the radiation source; providing a gas from the fan to a gap located between a pair of electrodes of the radiation source; delivering, using the fan to accelerate the gas, the gas in a first direction through the gap located between the pair of electrodes that are configured to deliver a voltage to the gas to generate the radiation, wherein the fan housing comprises a gas inlet configured to receive the gas and a gas guiding structure configured to direct the gas to the gap, wherein the gas guiding structure has a tapered shape; and energizing the electrodes to generate the radiation.

11. The method of claim 10, further comprising: providing the gap with elongated shape in a second direction perpendicular to the first direction, and providing the fan with a plurality of blades coupled to a fan shaft, wherein the plurality of blades are also elongated in the second direction.

12. The method of claim 10, further comprising: providing the gap with elongated shape in a second direction perpendicular to the first direction, and providing a plurality of centrifugal fans disposed in a row adjacent to each other and wherein the row is disposed substantially parallel to the second direction.

13. The method of claim 12, further comprising configuring the gas guiding structure as a series of centrifugal fan nozzles corresponding to the centrifugal fans and providing a series of gas flow spreaders comprising grooves that are disposed at an outlet of the gas guiding structure.

14. The method of claim 10, further comprising providing the gas guiding structure as a convergent nozzle.

15. The method of claim 10, further comprising orienting the fan along an axis of rotation that intersects a side of the fan housing, and arranging the gas inlet at the side.

16. The method of claim 10, wherein the providing the gas comprises providing the gas at a gas inlet configured to deliver the gas substantially perpendicular to a flow of the gas within the fan.

17. The method of claim 10, further comprising varying a path of the gas using groves disposed inside the fan to achieve uniformity of gas flow.

18. The method of claim 10, further comprising: disposing the fan and the fan housing in a DUV laser chamber of the radiation source.

19. A lithographic apparatus comprising: a pulsed-discharge radiation source configured to generate DUV radiation according to claim 1 ; and a projection system configured to project an image of a pattern onto a substrate using the radiation.

Images