WO2012100846A1

WO2012100846A1 - Conduit for radiation, suitable for use in a lithographic apparatus

Info

Publication number: WO2012100846A1
Application number: PCT/EP2011/066405
Authority: WO
Inventors: Naghmeh Hajhosseini; Gerardus Swinkels; Gert-Jan Brands; Richard Baaten
Original assignee: Asml Netherlands B.V.
Priority date: 2011-01-25
Filing date: 2011-09-21
Publication date: 2012-08-02
Also published as: TW201232189A

Abstract

A conduit through which radiation may pass has a longitudinal centreline and includes a first opening that circumscribes the longitudinal centreline and a second opening that circumscribes the longitudinal centreline. The second opening is narrower than the first opening. The first opening is axially offset from the second opening along the longitudinal centreline. One or more internal sidewalls extend from the first opening to the second opening to form the conduit. The one or more internal sidewalls circumscribe, or together circumscribe, the longitudinal centreline. The one or more internal sidewalls include or are provided with lips. Each lip having a leading face, facing toward the first opening, a trailing face, facing toward the second opening, and a tip having a tip face. Each lip extends away from an internal sidewall, generally toward the longitudinal centreline. Tips of the lips are located progressively nearer the longitudinal centerline from the first opening to the second opening. Each lip is axially placed along the longitudinal centerline from an adjacent lip. Each lip has the same or overlapping circumferential position about the longitudinal centreline. The lips and/or internal sidewall or sidewalls are constructed and arranged such that radiation entering the conduit through the first opening and being incident on a face of a lip will generally be prevented from leaving the conduit via the first opening, or leaving through the first opening in one or more pre-determined directions, and/or leaving via the second opening, or leaving through the second opening in one or more pre-determined directions. The conduit has one or more features selected from the group consisting of: each lip being angled toward the first opening; each tip face being non-parallel with respect to the longitudinal centerline, the tip face being at least partially angled toward the second opening; and internal sidewall portions between lips being angled in the range of 0° +/- 10° relative to the longitudinal centerline.

Description

CONDUIT FOR RADIATION, SUITABLE FOR USE IN A LITHOGRAPHIC

APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of US provisional application 61 /435,846 which was filed on January 25, 201 1 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to a conduit for radiation, suitable for use in a lithographic apparatus.

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 is alternatively referred to as a mask or a reticle, may 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 radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.

[0004] Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured.

[0005] A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1 ): where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, ki is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1 ) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of k-i .

[0006] In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 5-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Such radiation is termed extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser- produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.

[0007] EUV radiation may be produced using a plasma. A radiation system for producing EUV radiation may include a laser for exciting a fuel to provide the plasma, and a source collector module for containing the plasma. The plasma may be created, for example, by directing a laser beam at a fuel, such as particles of a suitable material (e.g. tin), or a stream of a suitable gas or vapor, such as Xe gas or Li vapor. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosing structure or chamber arranged to provide a vacuum environment to support the plasma. Such a radiation system is typically termed a laser produced plasma (LPP) source. In an alternative system, which may also employ the use of a laser, radiation may be generated by a plasma formed by the use of an electrical discharge - a discharge produced plasma (DPP) source. [0008] When a laser (e.g. an infra red laser) is used in the generation of the plasma (or more generally the generation of EUV radiation), the laser beam itself, or at least a portion thereof, may substantially follow the same or similar beam path taken by radiation emitted by the plasma. This may be problematic. For example, the optical systems in a lithographic apparatus will be designed for use with, for example, a particular wavelength of radiation, for example, a particular wavelength (or range of wavelengths) of EUV radiation. If, for example, infra red radiation constituting the laser beam is incident on these optical systems, damage may be caused to these optical systems. Even if damage is not caused, the laser beam may pass through the lithographic apparatus and have a degrading effect on patterns applied to a substrate by the lithographic apparatus.

SUMMARY

[0009] It is desirable to obviate or mitigate at least one deficiency of the prior art, whether identified herein or elsewhere, or to provide an alternative to existing apparatus.

[00010] According to an aspect of the invention, there is provided a conduit through which radiation may pass, the conduit having a longitudinal centerline, the conduit comprising: a first, relatively wide, opening that circumscribes the longitudinal centerline; a second, relatively narrow, opening that circumscribes the longitudinal centerline; the first opening being axially offset from the second opening along the longitudinal centerline; one or more internal sidewalls extending from the first opening to the second opening to form the conduit, the one or more internal sidewalls circumscribing, or together circumscribing, the longitudinal centerline; the one or more internal sidewalls comprising, or being provided with, lips, each lip having a leading face, facing toward the first opening, a trailing face, facing toward the second opening, and a tip having a tip face; each lip extending away from an internal sidewall, generally toward the longitudinal centerline, tips of the lips being located progressively nearer the longitudinal centerline from the first opening to the second opening; each lip being axially displaced along the longitudinal centerline from an adjacent lip, each lip having the same or overlapping circumferential position about the longitudinal centerline, the lips and/or internal sidewall or sidewalls being constructed and arranged such that radiation entering the conduit through the first opening and being incident on a face of a lip will, in general, be prevented from leaving the conduit via that first opening, or leaving through that first opening in one or more pre-determined directions, and/or leaving via the second opening, or leaving through that second opening in one or more pre-determined directions; and wherein the conduit has one or more of the following features, or a combination of one or more of the following features: each lip being angled toward the first opening; and/or each tip face being non-parallel with respect to the longitudinal centerline, the tip face being at least partially angled toward the second opening; and/or internal sidewall portions between lips being angled in the range of 0° +/- 10° relative to the longitudinal centerline.

[00011] The conduit has been described as having "one or more of the following features, or a combination of one or more of the following features". These features have been described as constituting an aspect of the invention. Alternatively, each feature could, in isolation, or in combination with one or more other of such features, form another and/or independent aspect of the invention.

[00012] Each lip may be angled toward the first opening by being angled with respect to a normal of the longitudinal centerline by: >0° - 40°; or 10° - 40°; or 20° - 30°.

[00013] Each tip face may be angled toward the second opening by being angled with respect to the longitudinal centerline by: >0°, or 5° - 15°; or substantially 10°.

[00014] An angle between a trailing face of a lip and an internal sidewall portion adjacent to that trailing face may be substantially equal to or greater than 100°.

[00015] Each lip may circumscribe the longitudinal centerline.

[00016] The first and/or second openings may be defined by the internal sidewall or sidewalls or the lips.

[00017] The internal sidewalls may be angled to ensure that the conduit is tapered (internally), and/or the lips may extend from those sidewalls by a substantially equal amount.

[00018] The lips may together define a tapering sub-conduit through the conduit. [00019] The tapering conduit or tapering sub-conduit may be substantially conical in shape, or a shape that matches or accommodates an intended, desired or pre-existing cross-sectional shape of a radiation beam that is to pass through the conduit.

[00020] The lips may extend progressively nearer the longitudinal centerline, and/or are progressively longer, (as progression is made along the centerline) from the first opening to the second opening.

[00021] The lips and/or internal sidewall or sidewalls may be constructed and arranged such that radiation entering the conduit through the first opening and being incident on a leading face of a lip will, in general, be prevented from leaving the conduit via that first opening, or leaving through that first opening in one or more pre-determined directions, and/or via the second opening, or leaving through that second opening in one or more pre-determined directions, by being: trapped in a region define between: a leading face of a first lip, a trailing face of an adjacent second lip that faces that leading face of the first lip, and/or a portion of an internal sidewall extending between the first and second lips; and/or by being deflected out through the first or second opening in a direction not equal to the one or more pre-determined direction.

[00022] One or more faces of the lips, and/or the internal sidewall or sidewalls, may be formed from a material, or are coated with a material, that is substantially absorbent with respect to a particular wavelength, or range of wavelengths, of radiation (e.g. infra red radiation, commonly used in an EUV source in the generation of EUV radiation).

[00023] According to an aspect of the invention, there is provided a conduit through which radiation may pass. The conduit has a longitudinal centreline and includes a first opening that circumscribes the longitudinal centreline, and a second opening that circumscribes the longitudinal centreline. The second opening is narrower than the first opening. The first opening is axially offset from the second opening along the longitudinal centreline. One or more internal sidewalls extend from the first opening to the second opening to form the conduit. The one or more internal sidewalls circumscribe, or together circumscribe, the longitudinal centreline. The one or more internal sidewalls include, or are provided with, lips. Each lip has a leading face facing toward the first opening, a trailing face facing toward the second opening, and a tip having a tip face. Each lip extends away from an internal sidewall, generally toward the longitudinal centreline. The tips of the lips are located progressively nearer the longitudinal centerline from the first opening to the second opening. Each lip is axially displaced along the longitudinal centerline from an adjacent lip. Each lip has the same or overlapping circumferential position about the longitudinal centreline. The lips and/or internal sidewall or sidewalls are constructed and arranged such that radiation entering the conduit through the first opening and being incident on a face of a lip will generally be prevented from leaving the conduit via the first opening, or leaving through the first opening in one or more pre-determined directions, and/or leaving via the second opening, or leaving through the second opening in one or more pre-determined directions. The conduit has one or more features selected from the group consisting of: each lip being angled toward the first opening; each tip face being non-parallel with respect to the longitudinal centerline, the tip face being at least partially angled toward the second opening; and internal sidewall portions between lips being angled in the range of 0° +/- 10° relative to the longitudinal centerline.

[00024] According to another aspect of the invention, there is provided lithographic apparatus having one or more conduits according to the previously described aspects, wherein the or each conduit is located: upstream of an intermediate focus, or a focus point, of the apparatus; and/or upstream of an aperture between a radiation source and an illuminator of the apparatus; upstream of a site at which a radiation emitting plasma may be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

[00025] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[00026] Figure 1 depicts a lithographic apparatus according to an embodiment of the invention;

[00027] Figure 2 is a more detailed example of a view of the apparatus of Figure 1 ;

[00028] Figure 3 is a more detailed view of an embodiment of a source collector module of the apparatus of Figures 1 and 2; [00029] Figure 4 schematically depicts two separate components or modules of a lithographic apparatus, and a structure linking the components or modules;

[00030] Figure 5 depicts a conduit for use in conjunction with the structure shown in and described with reference to Figure 4;

[00031] Figure 6 schematically depicts the conduit of Figure 5 in more detail;

[00032] Figure 7 schematically depicts an expanded view of a part of the conduit shown in Figure 6;

[00033] Figure 8 schematically depicts a conduit for use in conjunction with the structure shown in Figure 4, in accordance with an embodiment of the present invention; and

[00034] Figure 9 schematically depicts an expanded view of a part of the conduit shown in Figure 8.

DETAILED DESCRIPTION

[00035] Figure 1 schematically depicts a lithographic apparatus 100 including a source collector module SO according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask or a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g. a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[00036] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. [00037] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system.

[00038] The term "patterning device" should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[00039] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and 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 in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.

[00040] The projection system, like the illumination system, may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desired to use a vacuum for EUV radiation since other gases may absorb too much radiation. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[00041] As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). [00042] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such "multiple stage" machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

[00043] Referring to Figure 1 , the illuminator IL receives an extreme ultra violet radiation beam from the source collector module SO. Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., xenon, lithium or tin, with one or more emission lines in the EUV range. In one such method, often termed laser produced plasma ("LPP") the required plasma can be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam. The source collector module SO may be part of an EUV radiation system including a laser, not shown in Figure 1 , for providing the laser beam exciting the fuel. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector, disposed in the source collector module. The laser and the source collector module may be separate entities, for example when a CO₂ laser is used to provide the laser beam for fuel excitation.

[00044] In such cases, the laser is not considered to form part of the lithographic apparatus and the radiation beam is passed from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the source collector module, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.

[00045] The illuminator IL may comprise an adjuster 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 can be adjusted. In addition, the illuminator IL may comprise various other components, such as facetted field and pupil mirror devices. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. [00046] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. After being reflected from the patterning device (e.g. mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor PS2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. Patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks M1 , M2 and substrate alignment marks P1 , P2.

[00047] The depicted apparatus could be used in at least one of the following modes:

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

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 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 may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

3. In another mode, the support structure (e.g. mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the 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 programmable patterning device, such as a programmable mirror array of a type as referred to above.

[00048] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[00049] Figure 2 shows an example of the lithographic apparatus 100 in more detail, including the source collector module SO, the illumination system IL, and the projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector module SO. An EUV radiation emitting plasma 210 may be formed by a discharge produced plasma source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is created by, for example, an electrical discharge causing an at least partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for efficient generation of the radiation. In an embodiment, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[00050] The radiation emitted by the hot plasma 210 is passed from a source chamber 21 1 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap) which is positioned in or behind an opening in source chamber 21 1 . The contaminant trap 230 may include a channel structure. Contamination trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure, as known in the art.

[00051] The collector chamber 212 may include a radiation collector CO which may be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near an opening 221 in the enclosing structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[00052] Subsequently the radiation traverses the illumination system IL, which may include a facetted field mirror device 22 and a facetted pupil mirror device 24 arranged to provide a desired angular distribution of the radiation beam 21 , at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 21 at the patterning device MA, held by the support structure MT, a patterned beam 26 is formed and the patterned beam 26 is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by the wafer stage or substrate table WT.

[00053] More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 may optionally be present, depending upon the type of lithographic apparatus. Further, there may be more mirrors present than those shown in the Figures, for example there may be 1 - 6 additional reflective elements present in the projection system PS than shown in Figure 2.

[00054] Collector optic CO, as illustrated in Figure 2, is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are disposed axially symmetrically around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[00055] Alternatively, the source collector module SO may be part of an LPP radiation system as shown in Figure 3. A laser LA is arranged to deposit laser energy into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li) provided by a supply (not shown in the drawings), creating the highly ionized plasma 210 with electron temperatures of several 10's of eV. The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma, collected by a near normal incidence collector optic CO and focused onto the opening 221 in the enclosing structure 220.

[00056] Figure 3 shows that the radiation that is emitted by the plasma 210 propagates along the optical axis O. However, it will be also be appreciated from Figure 3 that the laser beam radiation provided by the laser LA may also propagate directly along that optical axis O, depending on the nature of the interaction (e.g. the degree of scattering and/or the degree of the laser beam that remains) when or after the laser beam has interacted with (e.g. vaporised) the fuel. This situation may largely be overcome by providing an obscuration on the optical axis, downstream of the plasma 210. However, this obscuration may not be sufficient to prevent laser beam radiation from passing from the radiation source SO and onto, into and through the lithographic apparatus. For instance, scattering or the like of the radiation beam off the fuel can cause the laser beam, or portions thereof, to be directed around or past the obscuration.

[00057] Figure 4 schematically depicts two components or modules of a lithographic apparatus. The first module is the source SO, and the second module is the illuminator IL. Radiation leaving the source is generally depicted by arrows 300, 302.

[00058] A structure 304 is shown as providing a guide out of the source SO and into the illuminator IL. This guide 304 may for example be disposed about an intermediate focus IF of radiation 302 that is to be passed in to the illuminator IL. Due to the shape of the guide, for example being conical or the like, tapering towards the intermediate focus IF, radiation 300 having a beam path that is not as desired will be will be incident on the guide, and will not pass through the guide 304. This undesired radiation 300 may, for example, be EUV radiation which is not propagating in a desired direction. In this instance, the structure 304 could be described as an aperture, defining a cross- sectional shape of an EUV beam 302. Alternatively or additionally, the undesired radiation 300 may be radiation from the aforementioned laser that has been scattered or reflected or the like from a fuel used in the generation of the EUV radiation. Together with the obscuration located on the optical axis (not shown), as described above, the guide of the structure 304 may prevent laser beam radiation from passing onto, into and through the illuminator IL or the lithographic apparatus in general.

[00059] Figure 5 shows a conduit 310 which may be, or which may form part of, the structure, or guide of that structure, discussed in relation to Figure 4. The conduit 310 comprises sidewalls which extend from a first, relatively wide, opening 312 that circumscribes a longitudinal centerline of the conduit 310 (which in this case, corresponds to the optical axis O), to a second, relatively narrow, opening 314 that also circumscribes the longitudinal centre line (optical axis O). The conduit as a whole thus takes the form of a part conical-shell (which may be referred to as a frustoconical shell or the like).

[00060] Depending on the incoming angle or direction of the radiation, radiation entering the conduit 310 through the first, relatively wide opening 312 may either emerge from the conduit 310 through the second, relatively narrow, opening 314 or be incident on and substantially absorbed by sidewalls of the conduit 310. Figure 5 shows examples of radiation 316 that pass through the conduit 310, and also an example of radiation 318 that does not pass through the conduit 310.

[00061] The radiation 318 that does not pass through the conduit 310 does not do so due to the radiation being incident upon a sidewall of the conduit 310. It will be appreciated that there are angular relationships which will determine whether radiation can pass through the conduit, those relationships involving the incoming angles of radiation in combination with angular relationships inherent in the structure of the conduit 310, for example the degree of tapering of the sidewalls from the first opening 312 to the second opening 314, and the size of those openings, and the like.

[00062] Figure 5 is a somewhat simplified view of a conduit that might be used in practice. For instance, referring to Figure 5, radiation 318 may not simply be incident on and absorbed by the sidewalls of the conduit 310. Instead, or at least sometimes, and at certain angles, radiation may reflect off the sidewalls and out through the second opening 314, potentially onto, into, and/or through later apparatus, for example an illuminator or the like. Figure 6 shows a more accurate representation of a proposed conduit, which is designed to minimize radiation that leaves the conduit (through either opening) after having been incident on a sidewall.

[00063] Figure 6 shows substantially the same conduit as shown in and described with reference to Figure 5. However, in contrast to the conduit shown in Figure 5, the conduit 310 in Figure 6 has now been provided with lips 320, which may also be considered to be ribs or baffles. Although not visible in the Figure, due to the way in which the Figure is provided, the lips 320 circumscribe the longitudinal centerline (optical axis O) of the conduit 310. The lips extend away from the internal sidewall and toward the longitudinal centerline (optical axis O) such that the lips 320 extend perpendicularly with respect to the longitudinal centerline. Each lip 320 has a leading face, facing towards the first opening 312, a trailing face, facing toward the second opening 314, and also a tip which has a tip face. The lips 320 are substantially equally spaced axially along the conduit 310. Since the lips 320 circumscribe the longitudinal centerline, the lips by definition have the same circumferential position (although axially displaced) relative to the longitudinal centerline. As will be discussed in more detail, this allows radiation trapping regions 322 to be formed between a leading face of a first lip 320, a trailing face of an adjacent second lip 320 that faces that leading face of the first lip, and/or a portion of an internal sidewall extending between the first and second lips 320.

[00064] Radiation having a certain propagation direction 318 enters the conduit 310 and is incident upon a leading face of a lip 320 which reflects or otherwise deflects the radiation 318 into the radiation trapping region 322, where the radiation is then reflected off an opposing trailing face of a lip 320 and onto an internal sidewall portion. The radiation 318 is thus prevented from being deflected out of the conduit via the second opening 314. The lips 320, and the associated radiation trapping regions 322, also prevent the radiation 318 from leaving the conduit 310 through the first opening 312 through which there radiation 318 initially entered the conduit 310. Depending on the nature of radiation, this may be a particular useful feature of the conduit 310. For example, if laser beam radiation was directed back towards the laser itself, this may affect the operation of the laser. For example, the radiation directed back toward the laser might inadvertently cause the triggering of a laser pulse or the like, which may reduce the output of the laser as a whole or at least degrade its performance.

[00065] Although the conduit shown in Figure 6 is potentially useful, there are potential design flaws and issues associated with its structure. Figure 7 shows an expanded view of a part of the conduit shown in Figure 6. Figure 7 shows two lips 320 extending away from the sidewall 324 of the conduit, the lips 320 extending perpendicularly with respect to the longitudinal centerline (in this case, optical axis O). Three examples of incident radiation are shown as 326, 328, and 330.

[00066] In a first example, radiation 326 that has entered the conduit is incident upon a leading face of a lip 320. Due to the angle of incidence, and the structure of the conduit as a whole, the radiation 326 is deflected (e.g. reflected) onto the sidewall 324, where the radiation is then reflected again back towards the opening in the conduit via which the radiation 326 entered that conduit. The radiation 326 is not trapped, and instead leaves the conduit through the opening via which the radiation entered that conduit. If this radiation 326 is, for example, laser beam radiation, the radiation 326 may interfere with the operation of the laser, as described above.

[00067] In a second example, radiation 328 enters the conduit in a direction substantially parallel (+/- a few degrees) to the longitudinal centerline (optical axis O) and is then incident on the leading face of the lip 320 in a substantially normal (e.g. perpendicular) manner. Since the leading face of the lip 320 extends perpendicularly with respect to the longitudinal centerline (optical axis O) of the conduit, the radiation 328 will thus be deflected (e.g. reflected) back in the same general direction from which the radiation 328 initially came. Again, this may result in the radiation 328 leaving the conduit through the first opening, via which the radiation 328 initially entered the conduit. If the radiation 328 is laser beam radiation, the radiation 328 may be directed back towards the laser, and interfere with its operation.

[00068] In a third example, radiation 330 enters the conduit, and is incident on a tip face of the lip 320. The tip face is parallel to the longitudinal centerline (optical axis O). The radiation 330 is thus deflected towards and possibly through, the second opening of the conduit. As discussed above, this is undesirable since the radiation 330 may be laser beam radiation which could damage optical components within downstream apparatus, for example an illuminator or the like of a lithographic apparatus. Alternatively or additionally, such radiation may negatively affect the application of patterns to a substrate using such lithographic apparatus. Even if the radiation 330 is EUV radiation, which would not damage optical systems within the lithographic apparatus, the EUV radiation may be directed in an undesirable manner, for example not passing through an intermediate focus. This might result in the EUV radiation 330 being incident on surfaces not treated or prepared for EUV radiation, which could cause contamination to be generated in the form of outgassing or material degradation or the like. Alternatively, this radiation might cause the EUV beam as a whole to have an undesirable angular intensity distribution. [00069] It is desirable to obviate or mitigate at least one issue noted above, for example, the issues associated with the conduit as shown in and described with reference to Figures 5, 6 and 7. This may be achieved in accordance with an embodiment of the present invention.

[00070] In accordance with an embodiment of the present invention, there is provided a conduit through which radiation may pass. The conduit has a longitudinal centerline, which may, or will usually, coincide with an optical axis either of the conduit itself, or of other apparatus with which the conduit is to be used. The conduit comprises a first, relatively wide, opening that circumscribes the longitudinal centerline. The term 'circumscribes' as used herein does not necessarily mean that the opening is circular. The term 'circumscribes' as used herein means that the opening (in this case, but in general any object to which the term is applied) extends around that centerline. For example the opening may extend around the longitudinal centerline in a rectilinear manner or an elliptical manner, or in any other suitable manner. The conduit further comprises a second, relatively narrow, opening that also circumscribes the longitudinal centerline. The first opening is axially offset from the second opening along the longitudinal centerline.

[00071] One or more internal sidewalls extend from the first opening to the second opening to form the conduit. The one or more internal sidewalls circumscribe, or together circumscribe, the longitudinal centerline. The term 'one or more internal sidewalls' is intended to cover the situation where one wall may extend in a circumferential and circular/elliptical manner around the centerline, or where one or more straight or curved sidewalls are together in some way brought together (e.g. joined together) to circumscribe the centerline.

[00072] The one or more internal sidewalls comprise, or are provided with lips. Each lip of the lips has a leading face that faces towards the first opening, a trailing face that faces towards the second opening, and a tip having a tip face. Each lip extends away from an internal sidewall, generally toward the longitudinal centerline. Tips of the lips are located progressively nearer the longitudinal centerline from the first opening to the second opening. This may be visualized by travelling through the conduit from the first opening to the second opening along the longitudinal centerline, the tips of the lips being located progressively nearer the longitudinal centerline as progression along the centerline takes place. It will be appreciated that this may be achieved in one of two approaches. Firstly, the sidewall(s) may taper from the first opening to the second opening, and the lips may extend substantially by the same amount from the sidewalls. Alternatively, in a second approach, the tapering or otherwise of the sidewalls may be largely irrelevant, and the lips may extend towards the centerline by different amounts to achieve much the same effect.

[00073] Each lip is axially displaced along the longitudinal centerline from an adjacent lip, for example the lips may be axially distributed in an equidistant manner from one another relative to the centerline. Each lip will have the same or overlapping circumferential position about the longitudinal centerline (i.e. as an adjacent lip). Due to the axial displacement of the lips, and the circumferential positioning, radiation trapping regions may be formed in between adjacent lips.

[00074] The lips and/or internal sidewall(s) may, in functional terms, be described as being constructed and arranged such that radiation entering the conduit through the first opening and being incident on a face of a lip (e.g. a leading face or a tip face) will, in general, be prevented from leaving the conduit via the first opening (or the second opening).

[00075] The features described above might arguably be present in the proposed conduit shown in and described with reference to Figures 5 to 7. However, in contrast to the features of that conduit, the present invention has one or more of the following additional features, or a combination of one or more of the following features: each lip is angled towards the first opening; and/or each tip face is non-parallel with respect to the longitudinal centerline, the tip face being at least partially angled toward the second opening; and/or internal sidewall portions between adjacent lips are angled at 0° +/- 10° relative to the longitudinal centerline.

[00076] It has been found that each one of the distinguishing features, in isolation, improve the performance of a conduit. In combination, the use of more than one feature further improves the performance of the conduit. 'Performance' in this context means the reduction of radiation which is incident upon a face of a lip and which would otherwise subsequently leave the conduit through the opening via which the radiation ended that conduit, and/or a reduction in radiation that is incident on a lip face and which subsequently passes through the second opining in the conduit.

[00077] Figure 8 shows a conduit 400 in accordance with an embodiment of the present invention. The conduit 400 comprises a first, relatively wide, opening 402 that circumscribes the longitudinal centerline 404 (which may coincide with an optical axis of the conduit 400). The conduit also comprises a second, relatively narrow, opening 406 that also circumscribes longitudinal centerline 404. The first opening 402 is axially offset from the second opening 406 along the longitudinal centerline 404. One or more sidewalls extend from the first opening 402 to the second opening 406 to, effectively, form the conduit 400 (or at least an internal surface thereof). The one or more sidewalls circumscribe, or together circumscribe, the longitudinal centerline 404.

[00078] The internal sidewalls comprise, or are provided with, lips 408. The lips have a leading face, facing towards the first opening 402, a trailing face, facing towards the second opening 406, and a tip which has a tip face. Each lip 408 extends away from an internal sidewall, generally towards the longitudinal centerline 404. Tips of the lips 408 are located progressively nearer the centerline 404 from the first opening 402 to the second opening 406. Each lip 408 is axially displaced along the longitudinal centerline 402 from an adjacent lip 408. Furthermore, each lip has the same or overlapping circumferential position about the longitudinal centerline 404. This allows radiation trapping regions 410 to be formed between adjacent lips. The lips 408 and/or internal sidewall or sidewalls are thus constructed and arranged such that radiation 412 entering the conduit 400 through the first opening 402 and being incident on a face of a lip 410 will in general, be prevented from leaving the conduit, via that first opening and/or via the second opening. Radiation 414 that enters the conduit 400, but which is not incident on a face of a lip 408, will leave the conduit 400 via the second opening 406, and will, for example, pass through an intermediate focus point IF.

[00079] In contrast to the conduit shown in Figures 5 to 7, the conduit in accordance with an embodiment of the present invention as shown in Figure 8 may provide improved performance in three independent, but readily combinable, features. Two of these features are visible in Figure 8. The first feature is that each lip 408 is angled towards the first opening 402. The second feature is that internal sidewall portions 416 between adjacent lips 408 are substantially parallel to the longitudinal centerline 404, in that the lips are angled in the range of 0° +/-10⁰ (inclusive) relative to the longitudinal centerline 404. A third feature, not readily apparent from Figure 8, is that each tip face is non-parallel with respect to the longitudinal centerline 404, the tip face being at least partially angled towards the second opening 406. All of these features will be described in more detail in relation to Figure 9.

[00080] Figure 9 is an expanded view of a part of the conduit shown in and described with reference to Figure 8. Specifically, Figure 9 shows a first lip 408a axially separated along the longitudinal centerline 404 from a second lip 408b by an internal sidewall portion 416a. The lips 408a and are angled towards the first opening (which may be described as the lips 408a, 408b being backswept). It has been found that performance of the conduit is particularly improved if the lips 408a, 408b are angled towards the first opening by being angled with respect to a normal of the longitudinal centerline 404 (e.g. perpendicular to that centerline 404) by an angle of greater than 0°, to 40° (inclusive). Performance may be improved further if the angle with respect to that normal is between 10° and 40° inclusive. Performance may increase further still if the angle is between 20° and 30° inclusive. Radiation 422 entering the conduit in a direct substantially parallel to the longitudinal centerline 404 is now, due to the angling of the lips 408a, 408b, directed downwards towards the internal sidewall portion 416a, thus improving the trapping of the radiation 422. This is in stark contrast to the conduit shown in Figures 5 to 7, where, due to the lips extending normally with respect to the longitudinal centerline, normally (i.e. perpendicularly) incident radiation would be reflected back out of the conduit through the opening via which that radiation originally entered that conduit.

[00081] The performance of the conduit may alternatively or additionally be improved by ensuring that each tip face 424 is angled with respect to the longitudinal centerline 404, the tip face 424 being at least partially angled towards the second opening. It has been found that performance can be improved when any angling takes place, such that the angle 426 with respect to the longitudinal centerline 404 is greater than 0°. A particularly desired range of angles for performance reasons have been found as being between 5° and 15° inclusive, and with optimal performance shown at substantially (e.g. +/- 1 ° or +/- 2 °) 10 °. Radiation 428 entering the conduit and incident upon a tip face 424 is, due to the angling on the tip face, angled towards a leading face of an adjacent lip 408b, where the radiation is then deflected towards the internal wall portion 416a. The radiation 428 is thus trapped, and prevented from leaving the conduit. The angling of the tip face may also allow radiation to more readily enter a radiation trapping region. This is in contrast with the conduit shown in Figures 5 to 7, where radiation incident on a tip face had a greater chance of been deflected out of the conduit, for example toward and through the second opening.

[00082] In Figure 9, the internal sidewall portion 416a is shown as being substantially parallel with respect to the longitudinal centerline 404. Performance benefits have been found to exist when the internal sidewall portion 416a is angled, represented by line 430, within a range of 0° +/- 10° (inclusive) with respect to the longitudinal centerline 404. Performance benefits may be attributable to one of a number of reasons. One reason may be that radiation 432 entering a conduit and deflected by a lip onto the internal wall portion 416a is now directed at that internal wall portion 416a with an angle of incidence which is closer to normal (e.g. perpendicular) than would be the case in the conduit of Figures 5 to 7, where the angle of the sidewalls would be far greater than 0° +/- 10°. Such an angle of incidence might increase the absorption of radiation into that sidewall portion 416a as an opposed to the radiation reflected off the sidewall portion 416a at a glancing angle. Alternatively or additionally, radiation that is incident on the sidewall 416a and which does (for whatever reason) leave the region defined between adjacent lips in the vicinity of that internal sidewall portion 416a will most likely be reflected to an opposite side of the conduit and into another radiation trapping region, as opposed to being directed back out of the conduit through the through the first opening, via which the radiation entered the conduit initially.

[00083] A further performance benefit has been found when the angle 434 between trailing faces of the lips and the internal sidewall portion adjacent to that trailing face is substantially equal to or greater than 100°. It will be appreciated that this angle 432 is a combination of the angle of the lips and angle of the internal sidewall portions previously discussed. [00084] The actual dimensions of the conduit, and its constituent lips and the like, will vary depending on the required use of the conduit, for example the desired angular intensity distribution of radiation entering the conduit and leaving the conduit. Typically, each lip may have the same width, and/or have a width (i.e. thickness) of between greater than 0 mm and less than or equal to 15 mm. Alternatively or additionally, each lip may have the same length, and/or a length of between greater than 0 mm and less than or equal to 20 mm (the lips may only have the same length when the internal sidewall or internal sidewalls, as opposed to the lips themselves, form and/or taper toward the first and second openings). Alternatively or additionally, the lips may be equally spaced apart from one another, in an axial direction along the longitudinal centerline, and/or may be spaced apart from one another by distance of between greater than 0 mm and less than or equal to 50 mm. In one example, where the lips are angled toward the first opening by substantially 30°, a suitable thickness of the lip might be 3 mm (+/- 0.1 mm). A distance between adjacent lips might be 12 mm (+/- 0.1 mm). Where the walls are tapered from the first opening to the second opening, and the lips are thus substantially the same length, the lips may have a length of 1 1 .36 mm (+/- 0.1 mm). Of course, these dimensions may be different in different embodiments, for example where the lips are angled toward the first opening by an angle other than 30°.

[00085] In the Figures described herein, the lips have been shown in a side profile. In an embodiment, the lips will circumscribe the longitudinal centerline to provide radiation trapping regions that also circumscribes the longitudinal centerline, thereby leaving no circumferential gaps in the trapping regions in a given axial position.

[00086] In the embodiment shown, the internal sidewalls have, in general, defined the first and second openings of the conduit. The sidewalls have tapered from the first, larger opening to the second, narrower opening, and the lips have been substantially the same length. Such a structure may be more robust, and/or easier to manufacturer than alternatives. In an embodiment (not shown) the lips may define the openings. In this embodiment, the lips may extend by differing amounts, such that overall the location of the lip's tips progressively approaches the centerline as progression is made along the conduit, irrespective of the orientation or the like of the sidewalls. In this embodiment, the trapping of radiation may be improved, since the radiation trapping regions will be much deeper (in a direction perpendicular to the longitudinal centerline) than when the sidewalls are angled (e.g. tapered) and the lips extend by the same amount from those sidewalls. However, it may be more difficult to manufacture this embodiment, and/or the lips when manufactured may be more fragile and subject to fracture or the like.

[00087] In any embodiment, it will be appreciated that the tips of the lips (or more generally, the lips) define a sub-conduit within the main conduit. The sub-conduit defines a beam path, or beam paths, via which radiation can pass without becoming incident on the lips, and therefore being trapped in, or deflected by, the conduit as a whole. The conduit as a whole, or the sub-conduit in general, may be substantially conical in shape, as shown in the Figures. More generally, however, the conduit and/or sub-conduit may define or be another shape. The conduit and/or sub-conduit will or may be used to define, or assist in defining, the cross-sectional shape of a beam of radiation passing through the conduit/sub-conduit, and in this manner the conduit/sub- conduit also functions as an aperture. Thus, the sub-conduit/conduit may define any cross-section or shape, for example for a desired cross-sectional shape of a radiation beam. The dimensions of the cross-sectional shape defined by the sub-conduit/conduit may not equate exactly to the dimensions of the cross-sectional shape of the radiation beam, due to the need for tolerances for alignment of the beam within the conduit.

[00088] In an embodiment, the lips may circumscribe the longitudinal centerline to provide radiation trapping regions that also circumscribes the longitudinal centerline, thereby leaving no circumferential gaps in the trapping regions in a given axial position. In other embodiments, there may be discrete lips that do not extend continuously around (i.e. circumscribe) the longitudinal centreline. The lips may be distributed about that centreline, but there may, for instance, be gaps in an arrangement of lips that circumscribe the centreline. Such discrete lips may be easier to manufacture, construct, provide or implement. The discrete lips may, in an embodiment, together form a continuous lip. That continuous lip might circumscribe the centreline.

[00089] The lips may be provided by milling or routing, for example of a solid body or bodies of material used to form the conduit. However, such milling or routing may be difficult to implement, for example due to spatial restrictions, material fragility at the required dimensions, or simply due to the required dimensions. An alternative manner of providing the lips would be to use a frame (e.g. a wire frame) or the like to form the lips. The frame could then be built around to form the conduit as a whole, or the frame could be inserted into a structure to form the conduit. The frame would thus be an inlay. The frame could comprise wires or the like that have been provided with lips having the required or desired angular (more generally, dimensional) properties. The use of a frame to provide the lips might be easier, quicker, cheaper or a more reliable approach in comparison with using milling or routing of a solid structure. The use of the frame might also make it easier to implement, or lend itself toward the implementing of, the discrete lip concept of the preceding paragraph. In another embodiment, the frame might be the conduit (there being no need to provide a surrounding structure). The frame embodiment might be more open to the surrounding environment than the embodiment where the frame is located within a surrounding structure (or, indeed, other embodiments described herein). This may assist cooling of lips or the like of the frame, and/or allow gas or the like to enter and leave the frame more easily, for example to cool the frame, or to serve as a buffer gas or the like.

[00090] So far, the tips have been described as having a tip face. The tip face could, in some embodiments, be so small so as to be substantially point or line like. For example, when viewed in cross section the lips might be triangular or conical like, a point of the triangle or cone facing toward the longitudinal centreline.

[00091] In the embodiments described thus far, the lips and/or internal sidewall(s) have been described as being constructed and arranged such that radiation entering the conduit through the first opening and being incident on a leading face of a lip will, in general, be prevented from leaving the conduit via the first or second opening of that conduit. In a related but different embodiment, the radiation may instead be prevented from leaving through the first or second openings in one or more pre-determined directions. The one or more pre-determined directions may include, for example, along the optical axis, toward a radiation source, or a laser used in conjunction with that source, toward optical elements not designed for that radiation, or a direction not as desired (for example, the direction not being in accordance with a pre-determined and desired angular intensity distribution). The radiation might be prevented from leaving the openings in one or more predetermined directions by being deflected out through the first or second opening in a direction not equal to the one or more pre-determined directions. For example, such radiation might be directed to a beam dump, or toward a target or the like where the radiation has little or no impact on the operation, behaviour, integrity, or the like, of the apparatus in which, or with which, the conduit is used.

[00092] The conduit as a whole, or one or more surfaces thereof, may be formed from any appropriate material. For example, one or more faces of the lips, and/or the internal sidewall(s), may be formed from material, or be coated in a material or with a material, that is substantially absorbent with respect to a particular wavelength of radiation. That particular wavelength of radiation may be, for example, radiation of a laser beam used in the generation of EUV radiation in a radiation source. For instance, the material may be substantially absorbent with respect to infra red radiation. In an embodiment, the material forming all, or a main body of, the conduit might be aluminium, (stainless) steel, or molybdenum. A coating could be provided by applying, for example, bilatal and/or anodizing the aluminium. This results in a certain roughness of the material and high absorption / low reflection of the radiation.

[00093] The conduit described herein may be used in any particular application where trapping (or appropriate deflection) of radiation that does not have a desired angle of incidence with respect to the conduit is desired. The conduit may find particular use in a lithographic apparatus. For instance, a conduit may be located upstream of an intermediate focus, or a focus point, of the apparatus (e.g. the intermediate focus IF shown in Figure 2). This may prevent the EUV radiation having undesired angles of incidence (which is equivalent to undesired angles of propagation) from leaving the conduit and thus increasing the size of the focal point or the like. At the same time, radiation, or other radiation, may be prevented from passing back out of the conduit through the opening from which the radiation was initially directed into the conduit. This may prevent interference with operation of a laser beam, or other radiation source. Alternatively or additionally, and for much the same reasoning, a conduit can be located upstream of an aperture between a radiation source and an illuminator of the apparatus. Alternatively or additionally, and again for much the same reasoning, a conduit could be located upstream of a site at which a radiation emitting plasma may be formed. [00094] The conduit may be used in isolation, or may form part of another piece of equipment. For instance, the conduit may form part of a linking structure or guide located in-between components or modules of an apparatus, for example between a source module or component and an illuminator module or component of a lithographic apparatus.

[00095] Although specific reference may be made in this text 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, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered as synonymous with the more general terms "substrate" or "target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multilayer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[00096] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may 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. [00097] The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[00098] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

WHAT IS CLAIMED IS:

1 . A conduit through which radiation may pass, the conduit having a longitudinal centerline, the conduit comprising:

a first opening that circumscribes the longitudinal centerline;

a second opening that circumscribes the longitudinal centreline, the second opening narrower than the first opening;

the first opening being axially offset from the second opening along the longitudinal centerline;

one or more internal sidewalls extending from the first opening to the second opening to form the conduit, the one or more internal sidewalls circumscribing, or together circumscribing, the longitudinal centerline;

the one or more internal sidewalls comprising, or being provided with, lips, each lip having a leading face facing toward the first opening, a trailing face facing toward the second opening, and a tip having a tip face;

each lip extending away from an internal sidewall, generally toward the longitudinal centerline, the tips of the lips being located progressively nearer the longitudinal centerline from the first opening to the second opening;

each lip being axially displaced along the longitudinal centerline from an adjacent lip;

each lip having the same or overlapping circumferential position about the longitudinal centreline;

the lips and/or internal sidewall or sidewalls being constructed and arranged such that radiation entering the conduit through the first opening and being incident on a face of a lip will generally be prevented from leaving the conduit via the first opening, or leaving through the first opening in one or more pre-determined directions, and/or leaving via the second opening, or leaving through the second opening in one or more pre-determined directions;

and wherein the conduit has one or more features selected from the group consisting of: each lip being angled toward the first opening; each tip face being non- parallel with respect to the longitudinal centerline, the tip face being at least partially angled toward the second opening; and internal sidewall portions between lips being angled in the range of 0° +/- 10° relative to the longitudinal centerline.

2. The conduit of claim 1 , wherein each lip is angled toward the first opening by being angled with respect to a normal of the longitudinal centerline by >0° - 40°.

3. The conduit of claim 2, wherein each lip is angled toward the first opening by being angled with respect to the normal of the longitudinal centerline by 10° - 40°.

4. The conduit of claim 3, wherein each lip is angled toward the first opening by being angled with respect to the normal of the longitudinal centerline by 20° - 30°.

5. The conduit of any preceding claim, wherein each tip face is angled toward the second opening by being angled with respect to the longitudinal centerline by: >0°.

6. The conduit of claim 5, wherein each tip face is angled toward the second opening by being angled with respect to the longitudinal centerline by 5° - 15°.

7. The conduit of claim 6, wherein each tip face is angled toward the second opening by being angled with respect to the longitudinal centerline by about 10°.

8. The conduit of any preceding claim, wherein an angle between a trailing face of a lip and an internal sidewall portion adjacent to that trailing face is substantially equal to or greater than 100°.

9. The conduit of any preceding claim, wherein each lip circumscribes the longitudinal centerline.

10. The conduit of any preceding claim, wherein the first and/or second openings are defined by the internal sidewall or sidewalls or the lips.

1 1 . The conduit of any preceding claim, wherein the internal sidewalls are angled to ensure that the conduit is tapered, and/or the lips extend from those sidewalls by an equal amount.

12. The conduit of any preceding claim, wherein the lips together define a tapering sub-conduit through the conduit.

13. The conduit of claim 1 1 or claim 12, wherein the tapering conduit or tapering sub- conduit is substantially conical in shape.

14. The conduit of any preceding claim, wherein the lips extend progressively nearer the longitudinal centerline, and/or are progressively longer, from the first opening to the second opening.

15. The conduit of any preceding claim, wherein the lips and/or internal sidewall or sidewalls are constructed and arranged such that radiation entering the conduit through the first opening and being incident on a leading face of a lip will generally be prevented from leaving the conduit via that first opening, or leaving through the first opening in one or more pre-determined directions, and/or via the second opening, or leaving through the second opening in one or more pre-determined directions, by being

trapped in a region defined between a leading face of a first lip, a trailing face of an adjacent second lip that faces that leading face of the first lip, and/or a portion of the internal sidewall extending between the first and second lips; and/or

deflected out through the first or second opening in a direction not equal to the one or more pre-determined direction.

16. The conduit of any preceding claim, where one or more faces of the lips, and/or the internal sidewall or sidewalls, are formed from or coated with a material that is substantially absorbent with respect to infra red radiation.

17. A lithographic apparatus having one or more conduits of any preceding claim, wherein the or each conduit is located:

upstream of an intermediate focus, or a focus point, of the apparatus; and/or upstream of an aperture between a radiation source and an illuminator of the apparatus;

upstream of a site at which a radiation emitting plasma may be formed.

18. The lithographic apparatus of claim 17, wherein the first opening is located upstream with respect to the second opening.