NL2023105B1 - Lithographic apparatus - Google Patents

Abstract

Disclosed herein is a lithographic apparatus, comprising: an illumination system configured to condition a radiation beam; a patterning device (601) configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a pellicle (602) configured to cover a surface of the patterning device (601); a substrate table configured to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of a substrate when the substrate is held by the substrate table, wherein the projection system comprises one or more optical elements; a first set of one or more outlets (603) for outputting a first fluid into a first region, wherein the first region abuts and/or comprises the pellicle (602); and a second set of one or more outlets (605) configured to output a second fluid into a second region that comprises the one or more optical elements of the projection system; and wherein the second fluid is different from the first fluid. Advantageously, the fluid in the first region protects the pellicle (602) from damage by the fluid in the second region. A pellicle that would otherwise be damaged by the fluid in the second region can therefore be used.

Description

LITHOGRAPHIC APPARATUS

HELD [0001] The present invention relates to a lithographic apparatus. More particularly, the techniques disclosed herein relate to the provision of pellicles in a lithographic apparatus for use with EUV radiation.

BACKGROUND [0002] 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 the manufacture of ICs, 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 oh 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. Known lithographic apparatus 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 substrate parallel or anti-parallel to this direction.

[0003] A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1 ):

CD=k_l *λ/ΝΑ (1) where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, kl 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 ofkl.

[0004] 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 4-20 nm, for example within the range of 13-14 nm, for example within the range of 4-10 nm such as 6.7 nm or 6.8 nm. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.

[0005] 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 droplets 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.

[0006] One known problem in EUV lithographic apparatus is contamination of the patterning device. In a EUV lithographic apparatus purge gas flows at high speed towards the patterning device and may carry molecules and particles up to micrometer sizes. In some lithographic apparatus a pellicle may be provided to protect the patterning device. A pellicle is a transparent membrane that covers the patterning device. However, the use of pellicles with EUV radiation is a problem due to the high absorption of EUV radiation by the pellicle reducing the efficiency of the system.

SUMMARY [0007] According to a first aspect of the invention, there is provided a lithographic apparatus, comprising: an illumination system configured to condition a radiation beam; a patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a pellicle configured to cover a surface of the patterning device; a substrate table configured to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of a substrate when the substrate is held by the substrate table, wherein the projection system comprises one or more optical elements; a first set of one or more outlets for outputting a first fluid into a first region, wherein the first region abuts and/or comprises the pellicle; and a second set of one or more outlets configured to output a second fluid into a second region that comprises the one or more optical elements of the projection system; wherein the second fluid is different from the first fluid; and, optionally, wherein the patterning device, pellicle, first set of one or more outlets, second set of one or more outlets and substrate table are arranged such that, in use, a patterned radiation beam travels from the patterning device, then through the pellicle that is abutted by and/or comprised by the first region, then through the second region and then onto a substrate held by the substrate table.

[0008] In an embodiment, the first set of one or more outlets may be configured to provide a first gaseous environment in the first region, which first gaseous environment shields the pellicle from the second region, or, in other words, which first gaseous environment prevents fluid in the second region from reaching the pellicle.

[0009] Preferably, the first fluid is a gas that is inert and/or chemically neutral with the pellicle.

[00010] Preferably, the first fluid comprises one or more of helium, neon, argon or nitrogen.

[00011] Preferably, the second fluid comprises a gas and/or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system.

[00012] Preferably, the second fluid comprises hydrogen radicals.

[00013] According to an embodiment of the invention, the second fluid may comprise a gas and/or plasma that the pellicle is degraded by.

[00014] Preferably, the lithographic apparatus further comprises a patterning device support arranged to support the patterning device, wherein the pellicle is coupled to the patterning device support.

[00015] Preferably, the second set of one or more outlets tire arranged between the first set of one or more outlets and the one or more optical elements of the projection system.

[00016] Preferably, the lithographic apparatus further comprises a first set of one or more inlets that are arranged in the first region for removing fluid from the first region.

[00017] Preferably, the first set of inlets are arranged on the opposite side of the pellicle to the first set of outlets so that, in use, there is a cross flow of the first fluid across the pellicle.

[00018] Preferably the lithographic apparatus further comprises a second set of one or more inlets that are arranged in the second region for removing fluid from the second region.

[00019] Preferably, the second set of inlets are arranged on the opposite side of the projection system to the second set of outlets so that, in use, there is a cross flow of the second fluid across the projection system.

[00020] Preferably, the pellicle is carbon based. In this embodiment, the first fluid may comprise a carbon-containing gas, i.e. a gas containing a carbon compound.

[00021] Preferably, the pellicle comprises one or more of carbon nanotubes and diamond.

[00022] Preferably, the an illumination system is configured to condition an extreme ultraviolet, EUV, radiation beam.

[00023] Preferably, one or more of the one or more optical elements are mirrors.

[00024] Preferably, the lithographic apparatus further comprises a control system that is configured to select the first fluid that is output first set of one or more outlets in dependence on the type of pellicle being used.

[00025] According to an embodiment, the lithographic apparatus may further comprise a first fluid supply containing the first fluid and a second fluid supply containing the second fluid, the first fluid supply being in fluid connection with the first set of one or more outlets and the second fluid supply being in fluid connection withy the second set of one or more outlets. The first and/or second fluid supply may, for example, comprise a first respectively second container, but may alternatively or in addition also comprise a first respectively second fluid connector for coupling a fluid supply system.

[00026] According to a second aspect of the invention, there is provided a method comprising: conditioning a radiation beam; imparting, by a patterning device with a pellicle covering its surface, the radiation beam with a pattern in its cross-section to form a patterned radiation beam; projecting, by a projection system, the patterned radiation beam onto a target portion of a substrate, wherein the projection system comprises one or more optical elements; outputting, by a first set of one or more outlets, a first fluid into a first region, wherein the first region abuts and/or comprises the pellicle; and outputting, by a second set of one or more outlets, a second fluid into a second region that comprises the one or more optical elements of the projection system; wherein the second fluid is different from the first fluid; and, optionally, wherein the patterning device, pellicle, first set of one or more outlets, second set of one or more outlets and substrate are arranged such that a patterned radiation beam travels from the patterning device, then through the pellicle that is abutted by and/or comprised by the first region, then through the second region and then onto a substrate held by the substrate table. [00027] In an embodiment, the outputting of the first fluid into the flrst region may result, in the first region, in a first gaseous environment shielding the pellicle from the second region, or, in other words, preventing fluid in the second region from reaching the pellicle.

[00028] Preferably, the method is performed by a lithographic apparatus according to the first aspect of the invention.

[00029] Preferably, the method further comprises selecting the first fluid that is output by the first set of one or more outlets in dependence on the type of pellicle being used.

[00030] In an embodiment in which the pellicle is carbon based, the first fluid may comprise a carbon-containing gas.

[00031] According to a third aspect of the invention, there is provided a lithographic apparatus, comprising: an illumination system configured to condition a radiation beam; a patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table configured to hold a substrate in a substrate region; a pellicle configured to cover a surface of the substrate; a projection system configured to project the patterned radiation beam onto a target portion of a substrate when the substrate is held by the substrate table, wherein the projection system comprises one or more optical elements; a second set of one or more outlets configured to output a second fluid into a second region that comprises the one or more optical elements of the projection system; and a third set of one or more outlets for outputting a third fluid into a third region, wherein the third region abuts and/or comprises the substrate region; and wherein the second fluid is different from the third fluid, the third set of one or more outlets may for example be configured to provide a third gaseous environment in the third region, the third gaseous environment shielding the substrate from the second region.

[00032] In an embodiment, the substrate region comprises a membrane configured to cover a surface of the substrate, and wherein the third region abuts and/or comprises the membrane. In this embodiment, the third set of one or more outlets may be configured to provide a third gaseous environment in the third region, the third gaseous environment shielding the membrane from the second region.

[00033] Optionally, the patterning device, the projection system, second set of one or more outlets, third set of one or more outlets and substrate table arc arranged such that, in use, a patterned radiation beam travels from the patterning device, through the projection system comprising the second region, through the third region and then onto a substrate held by the substrate table.

[00034] Preferably, the third fluid is a gas that is inert and/or chemically neutral with the substrate.

[00035] Preferably, the third fluid comprises one or more of helium, neon, argon or nitrogen. [00036] According to an embodiment, the second fluid comprises a gas and/or plasma that the substrate is degraded by.

[00037] Preferably, the second fluid comprises a gas and/or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system.

[00038] Preferably, the second fluid comprises hydrogen radicals.

[00039] Preferably, the lithographic apparatus further comprises a third set of one or more inlets that are arranged in the third region for removing fluid from the third region.

[00040] Preferably, the third set of one or more inlets are arranged on the opposite side of the substrate to the third set of one or more outlets so that, in use, there is a cross flow of the third fluid across the substrate.

[00041] Preferably, the lithographic apparatus further comprises a second set of one or more inlets that are arranged in the second region for removing fluid from the second region.

[00042] Preferably, the second set of one or more inlets are arranged on the opposite side of the projection system to the second set of one or more outlets so that, in use, there is a cross flow of the second fluid across the projection system.

[00043] Preferably, the illumination system is configured to condition an extreme ultraviolet, EUV, radiation beam.

[00044] Preferably, one or more of the one or more optical elements are mirrors.

[00045] The lithographic apparatus may further comprise a control system that is configured to select the third fluid that is output from the third set of one or more outlets in dependence on the type of substrate or membrane being used.

[00046] According to an embodiment, the lithographic apparatus may further comprise a second fluid supply containing the second fluid and a third fluid supply containing the third fluid, the second fluid supply being in fluid connection with the second set of one or more outlets and the third fluid supply being in fluid connection with the third set of one or more outlets.

[00047] The third aspect of the invention may be applied in combination with the first and/or second aspect of the invention.

[00048] According to a fourth aspect of the invention, there is provided a method comprising: conditioning a radiation beam; imparting, by a patterning device, the radiation beam with a pattern in its cross-section to form a patterned radiation beam; projecting, by a projection system, the patterned radiation beam onto a target portion of a substrate held in a substrate region, wherein the projection system comprises one or more optical elements; outputting, by a second set of one or more outlets, a second fluid into a second region that comprises the one or more optical elements of the projection system; and outputting, by a third set of one or more outlets, a third fluid into a third region, wherein the third region abuts and/or comprises the substrate region; and wherein the second fluid is different from the third fluid, the third fluid outputted into the third region may, for example, provide a third gaseous environment in the third region, the third gaseous environment shielding the substrate from the second region.

[00049] In an embodiment, the substrate region may comprise a membrane configured to cover a surface of the substrate, and wherein the third region abuts and/or comprises the membrane. In this embodiment, the third fluid outputted into the third region may, for example, provide a third gaseous environment in the third region, the third gaseous environment shielding the membrane from the second region.

[00050] Optionally, the patterning device, pellicle, second set of one or more outlets, third set of one or more outlets and substrate are arranged such that a patterned radiation beam travels from the patterning device, through the second region, through the third region and then onto a substrate held by the substrate table.

[00051] Preferably, the method is performed by a lithographic apparatus according to the third aspect of the invention.

[00052] Preferably, the method further comprises selecting the third fluid that is output by the third set of one or more outlets in dependence on the type of substrate or membrane being used. [00053] The fourth aspect of the invention may be applied in combination with the first and/or second aspect of the invention.

[00054] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES [00055] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.

[00056] Figure 1 schematically depicts a known lithographic apparatus;

[00057] Figure 2 shows pressure zones of a known lithographic apparatus;

[00058] Figure 3 shows in side view a feature of the known lithographic apparatus;

[00059] Figure 4 shows a known arrangement of patterning device assembly and masking blades;

[00060] Figure 5 shows a known arrangement of patterning device assembly and masking blades in plan view;

[00061] Figure 6 shows the provision of a first region and a second region in a lithographic apparatus according to an embodiment of the first aspect of the invention;

[00062] Figure 7 is flowchart of a method according to an embodiment of the second aspect of the invention;

[00063] Figure 8 shows, in a side view, an arrangement of a substrate table and a third set of outlets and inlets according to tin embodiment of the third aspect of the invention;

[00064] Figure 9 shows the arrangement of figure 8 in a plan view; and [00065] Figure 10 shows the provision of a second region and a third region in a lithographic apparatus according to an embodiment of the third aspect of the invention.

[00066] The features and advantages of the present invention 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. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.

DETAILED DESCRIPTION [00067] This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.

[00068] The embodiment(s) described, and references in the specification to one embodiment, an embodiment, an example embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[00069] Embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may 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 may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[00070] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention may be implemented. [00071] Figure 1 schematically shows a lithographic apparatus LAP including a source collector module SO. 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 patterning device) 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 PB by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. [00072] 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.

[00073] The support structure MT comprises a part for receiving and holding 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. Tire 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. [00074] 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.

[00075] 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 var ious hybr id 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 minors impart a pattern in a r adiation beam which is r eflected by the minor matrix.

[00076] 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 vessel and vacuum pumps. [00077] As here depicted, the apparatus is of a reflective type (i.e., employing a reflective mask and reflective optics in the illuminator IL and projection system PS [00078] 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.

[00079] Referring to Figure 1, the illuminator IL receives an EUV radiation beam from the EUV source SO. Methods to produce EUV radiation include, but are not necessarily limited to, converting a material into a plasma state that has at least one chemical element, e.g., xenon, lithium, or tin, with one or more emission lines in the EUV range. In one such method, often termed laserproduced plasma (LPP), the required plasma can be produced by irradiating a fuel, such as a droplet of material having the required line-emitting element, with a laser beam. The EUV source SO may be part of an EUV radiation source 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 EUV source.

[00080] The laser and the EUV source may be separate entities, for example when a CO2 laser is used to provide the laser beam for fuel excitation. In such cases, the radiation beam is passed from the laser to the EUV source with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. The laser and a fuel supply may be considered to comprise an EUV radiation source.

[00081] 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.

[00082] The radiation beam PB 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. The patterning device MA may be positioned using first positioning device such as interferometer IF1 and mask alignment marks Ml, M2. After being reflected from the patterning device (e.g., mask) MA, the patterned radiation beam PB 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 positioning device such as interferometer IF2 and substrate alignment marks Pl, P2 (e.g., using interferometric devices, linear encoders or capacitive sensors), 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 PB.

[00083] The depicted apparatus could be used in at least one of the following modes: [00084] 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.

[00085] 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.

[00086] 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 a programmable patterning device, such as a programmable mirror array of a type as referred to above. [00087] Figure 2 schematically shows an known apparatus. Figures 3 to 5 show parts of this apparatus in more detail. The apparatus of Figure 2 includes a first chamber 101 that contains an illumination system IL as well as a projection system PS. The illumination system IL is configured to condition a radiation beam received from source SO, and the projection system PS is configured to project a patterned radiation beam PB onto a target portion of a substrate W. First chamber 101 also contains a patterning device support constructed to support the patterning device MA, the patterning device MA being capable of imparting a radiation beam with a pattern in its cross-section to form the patterned radiation beam. A second chamber 102 contains the wafer stage of which for clarity only the substrate W is shown.

[00088] Figure 2 shows how the apparatus may be divided into four different vacuum environments VE1 to VE4. First chamber 101 define a first vacuum environment VE1 that encloses the patterning device stage of which for clarity only the patterning device MA is shown. First chamber 101 also includes a separator construction 103 that defines two further vacuum environments: VE2 housing the illumination system IL, and VE3 housing the projection system PS. Vacuum environments VE2 and VE3 could be further divided. Separator construction 103 includes a sleeve 105 having an aperture 104 for passing the projection beam PB from the illumination system IL to patterning device MA, and for passing the patterned radiation beam from patterning device MA to the projection system PS. The sleeve 105 also serves to force the gas flow downwards (ie away from the patterning device) and to maintain the gas flow even to avoid disturbance of the EUV radiation intensity. Possibly the sleeve may taper towards the patterning device MA. Second chamber 102 defines a vacuum environment VE4 that the wafer stage (of which for clarity only substrate W is shown). Vacuum environments VE1 and VE2 are formed and maintained by respective vacuum vessels and vacuum pumps VP1 and VP2, which can also be a plurality of vacuum pumps.

[00089] As is shown in Figure 2 vacuum pump VP1 maintains vacuum environment VE1 at a lower pressure than vacuum environments VE2 and VE3. Clean gas (e.g., hydrogen, helium, nitrogen, oxygen or argon) is injected into vacuum environments VE2 and VE3 using gas injectors (not shown). The vacuum pumps VP1 , VP2 as such are known to the skilled person, and may be coupled to the apparatus in various ways.

[00090] The separator construction 103 can be arranged in various ways, and may include, for example, a sleeve 105 extending towards the patterning device MA at the end of which sleeve 105 is provided the projection beam aperture 104 extend towards the patterning device MA. The sleeve 105 bearing the aperture 104 may have a tapered cross-section.

[00091] The apparatus also includes a radiation beam shaping device comprising patterning device masking blades REB for controlling the dimensions of the projection beam PB. As shown in

Figure 4 such blades REB extend at least partially between the patterning device MA and the aperture 104 of the separator construction 103 during use.

[00092] Figure 3 schematically shows the mask table MT holding the patterning device MA, and blades REB-X and blades REB-Y which are located near the patterning device MA for controlling the shape of the projection beam in the X and Y directions, respectively. The Y-blades REB-Y are positioned nearer to the patterning device MA than the X-blades REB-X, when viewed in the Z-direction but of course the blades could be arranged the other way around. The patterning device stage metrology frame RS-MF is provided with an aperture 4 for allowing the radiation beam to reach and be reflected by the patterning device MA.

[00093] The X-blades REB-X are located at a small distance 10a from the projection beam aperture 4 measured in the Z-direction. This last-mentioned distance is not more than about 5 mm, and not more than about 2 mm.

[00094] Also, the Y-blades REB-Y are located at small distances 10b from the patterning device MA. The last-mentioned distance is also no more than about 5 mm, measured in the Zdirection.

[00095] The smallest distance 10c between the X-blades and Y-blades may be about 5mm, when measured in the Z-direction.

[00096] Figures 4 and 5 show respectively schematic side and plan views of the patterning device assembly in more detail. As shown in Figure 4 gas injection means comprising gas supply conduits 121 having respective gas outlets 120 are provided on either side of the patterning device MA and are arranged such that gas (in particular hydrogen, helium, nitrogen, oxygen or argon) may be injected in a direction parallel to the surface of the patterning device MA, in the direction of the arrows in the figure, and substantially in the space between the patterning device MA and the blades REB-X, REB-Y. By injecting gas close to the patterning device surface and in particular into the confined space between the patterning device surface and the blades the possibility of contamination from components such as the blades themselves and other components is substantially reduced. It may further also be advantageous to provide the support structure for holding the patterning device in a partially enclosed environment, at least in the vicinity of the confined space between the patterning device surface and the blades. In such configuration an even more effective gas transport towards the projection optics compartment may be achieved due to the pressure created in the partially enclosed environment.

[00097] One or more gas supply conduits are provided coupled to the support structure. For example, the gas supply conduits are provided such that they extend downwards through the support structure MT at a vertical direction (i.e., in the z direction) or at an inclination defining an angle with the z direction. The outlets of the gas supply conduits are preferably oriented towards the patterning device surface, for example horizontally (i.e., in the X-Y plane). Figure 5 shows in particular three gas outlets 120 which are provided equispaced on each lateral side of the patterning device. Gas supply conduits 121 are provided that extend vertically (i.e., in the z direction) through the patterning device assembly with the outlets of the gas supply conduits being oriented horizontally (i.e.. in the X-Y plane) such that hydrogen gas is supplied parallel to the surface of the patterning device MA in the space between the patterning device MA and the blades REB-Y. It will be understood that other numbers of gas supply conduits and other arrangements may be provided that achieve the same objective of supplying gas in a direction parallel to the surface of the patterning device MA and between the patterning device and the blades. However, the gas supply conduits are formed as part of the patterning device stage so that they move with the patterning device stage even in large movements of the patterning device.

[00098] For example, the gas could be injected in the X direction, or in the Y direction (as shown in the Figures the gas is injected in the X direction). The gas is injected in the X direction because in this case the conduits 121 interfere less with the movement of the patterning device stage. The gas is injected between the blades that are closest to the patterning device (in this case the REB-Y blades), but could be injected between the REB-Y and the REB-X blades. In general terms, the gas conduits are located no more than about 10mm from the surface of the patterning device MA.

[00099] Within the projection system PS, there are optical elements, such as mirrors, for directing and/or conditioning the EUV radiation beam. In order to provide an environment prevents oxidation and contamination of the optical elements, it is known to feed hydrogen gas into the projection system PS. The hydrogen gas, under the influence of EUV radiation, may at least in part be ionised and contain hydrogen radicals. This environment is referred to herein as a hydrogen plasma and may comprise only hydrogen gas, a mixture of hydrogen gas and hydrogen radicals or only hydrogen radicals.

[000100] Described above, with reference to Figures 1 to 5, are components of a known lithographic apparatus that performs lithographic processes with EUV radiation. The patterning device MA used in the above-described known lithographic apparatus is not covered by a pellicle. [000101] Known pellicles for use with EUV radiation are based on a poly-silicon core. These pellicles show good resistance to the operating conditions, in particular the plasma environment. However, a problem with these pellicles is that the transmission of EUV radiation through these pellicles is only about 75%-85%. Another problem is that the pellicles have a large spurious reflection of DUV radiation. Resists are sensitive to DUV radiation and so an additional spectral purity membrane is required to suppress the effects of DUV reflection. The use of such a known pellicle therefore causes the total transmission of an EUV radiation beam to be reduced by about 50%. [000102] An additional problem is that DUV radiation is used for the inspection of patterning devices. A patterning device can therefore not be inspected when a poly-silicon pellicle is in place due to the poor transmission of DU V radiation through the pellicle. In order for it to be possible for patterning devices to be inspected it is therefore necessary for the pellicle to be easily removable and this complicates the mounting of the pellicle and compromises on other implementation aspects.

[000103] The above identified problems with poly-silicon based pellicles can be avoided by alternatively using carbon based pellicles. Carbon based pellicles have a high EUV transmission, that may be over 95%, a low DUV reflectance and the transmittal of DUV radiation through the pellicle is sufficient for an inspection of a patterning device to be performed when a pellicle is in place. Some of the advantages of carbon based pellicles are described in ‘CNTs in the context of EUV pellicle history’. E. Gallagher et al, Proc.SPlE, 2018.

[000104] A problem with using carbon based pellicles is that is that they are unable to withstand the operating conditions. In particular, the carbon based pellicles are severely degraded by the very reductive hydrogen plasma environment. The resistance of the carbon based pellicles to the operating conditions can improved by coating the pellicles with molybdenum or zirconium. However, when such a coating is applied the transmission through the pellicle is decreased, and the EUV scattering and reflection is increased, to the extent that the imaging properties and transmission of the radiation beam are significantly worsened.

[000105] Embodiments provide a lithographic apparatus that performs lithographic processes with EUV radiation. The patterning device used in the lithographic apparatus according to embodiments is covered by a pellicle.

[000106] The pellicle advantageously protects the patterning device by shielding the patterning device from any particles and gas flows.

[000107] The pellicle is preferably thin and substantially transparent to the radiation beam so that the pellicle does not substantially reduce the power of the radiation beam. Tire pellicle should also be able to withstand the operating conditions, i.e. the power of the radiation beam and the use of a plasma environment, without being quickly degraded.

[000108] Embodiments solve the above problems with the use of pellicles in an EUV lithographic apparatus by providing at least first and second regions in the path of the radiation beam with each region having different characteristics.

[000109] The first region is substantially only the local environment of the pellicle. The first region at least abuts a surface of the pellicle and preferably comprises the pellicle. In the first region a gaseous environment is provided that is suitable for a carbon based pellicle to be used without a molybdenum or zirconium coating of the pellicle being required.

[000110] The second region is within the projection system PS but does not comprise the local environment of the pellicle. The second region comprises the optical elements of the projection system PS where a plasma environment, such as a hydrogen plasma, is provided so that oxidation and contamination of the mirrors is prevented.

[000111] According to embodiments, a carbon based pellicle is used. The carbon based pellicle has a high transmittance, a high heat capacity, and is not degraded by the gaseous environment provided in the first region. The carbon based pellicle may be constructed in any of a number of known ways and from a range of carbon based materials. For example, it may be formed for any of carbon nanotubes, graphene or diamond.

[000112] Advantageously, the pellicle according to embodiments does not require a molybdenum or zirconium coating. The overall transmission of the EUV radiation beam is therefore improved over that achieved when either poly-silicon based pellicles or molybdenum or zirconium coated carbon-based pellicles are used.

[000113] Figure 6 shows how the first and second regions may be provided according to embodiments.

[000114] Shown in Figure 6 are a patterning device 601, a pellicle 602 that covers the patterning device 601, a first set of one or more outlets 603, a second set of one or more outlets 605, a first set of one or more inlets 604, a second set of one or more inlets 606, a first fluid supply 607, such as a container or connector, in fluid connection with the first set of one or more outlets 603 and a second fluid supply 607, such as a container or connector, in fluid connection with the second set of one or more outlets 605.

[000115] Figure 6 may comprise a number of other components that are not shown. In particular, the optical elements in the second region are not shown. There may be a physical separation sheet between the patterning device 601 part and the optical elements. Blades may be provided, such as the blades as shown in Figures 3 and 4, as well as other components. Although not fully shown in Figure 6, there is also a patterning device support that holds the patterning device 601. [000116] The first set of one or more outlets 603 may be a plurality of outlets arranged along a side of the pellicle 602, such as shown along the side of the patterning device 601 in Figure 5.

[000117] A gas is output from the first set of one or more outlets 603 into the local environment of the pellicle 602. The gas output from the first set of one or more outlets 603 comprises an inert and/or chemically neutral gas that the carbon based pellicle 602 is not degraded by. For example, the gas may be any of helium, neon, argon or nitrogen. Advantageously, the carbon based pellicle 602 is able to withstand the conditions in the local environment of the pellicle 602.

[000118] A first set of one or more inlets 604 are preferably also provided next to the pellicle 602 for removing the gas in the first region 609, i.e. the local environment of the pellicle 602. The first set of one or more outlets 603 are preferably provided on the opposite side of the pellicle 602 to the first set of one or more inlets. The first region 609 therefore comprises a cross-flow of gas across the pellicle 602.

[000119] The second set of one or more outlets output a gas and/or plasma, such as a hydrogen plasma as known for use in a lithographic apparatus with EUV radiation, into the second region 610. [000120] A second set of one or more inlets 606 are preferably also provided for removing the gas and/or plasma in the projection system PS. The second set of one or more gas inlets are preferably provided on the opposite side of the projection system PS to the second set of one or more inlets so that there is a cross-flow of the gas and/plasma through the second region 610.

[000121] Although not shown in Figure 6, the second region 610 comprises the optical elements of the projection system PS and the second sets of one or more outlets and inlets are arranged between the first sets of one or more outlets and inlets and the optical elements of the projection system PS.

[000122] Although not shown in Figure 6, the lithographic apparatus also comprises a control system and one or more of any of conduits, valves and pumps for both providing a controlling the fluid flows into, and preferably also out of, the first and second regions 609,610.

[000123] The first 609 and second 610 regions are not separated by a physical barrier that prevents fluid in the second region from flowing into the first region and reaching the pellicle 602. The boundary between the first and second regions is therefore approximately defined as the places at which the concentration of fluid from the second region is large enough to cause substantial damage to the carbon based pellicle. The boundary is dependent on how the fluid flows are controlled by the control system as well as the environment of the pellicle and in the projection system.

[000124] However, the positioning of the first sets of one or more outlets and inlets next to the pellicle 602, the directing of the gas output from the one or more outlets across the pellicle 602 and the positioning of the second sets of one or more outlets and inlets further away from the pellicle 602 than the first sets of one or more outlets and inlets, all cause the local environment of the pellicle 602 to substantially be comprised of gas from the first set of one or more outlets 603 so that a carbon based pellicle 602 in, or abutting, the first region is not substantially degraded. The first region may be comprised of at least 80%-90% of gas from the first set of one or more outlets 603 and this is sufficient to prevent a carbon based pellicle 602 from being substantially degraded by fluid from the second region.

[000125] The control system can control the width of first region 609 in the direction of the radiation beam by controlling the rate at which fluid flows out of the one or more first and/or second one or more outlets and/or by controlling the rate at which fluid flows out of the one or more first and/or second inlets.

[000126] The first region 609 may cover the entire surface of the pellicle 602 and preferably covers the entire pellicle 602. The first region 609 should also be thin in the direction of the radiation beam through the pellicle 602 so that there is only a short path distance of the radiation beam through the first region. The width of first region 609 in the direction of the radiation beam should be large enough to ensure that the amount fluid, i.e. gas and/or plasma, from the second region 610 that is likely to reach the pellicle 602 is not large enough to substantially damage the pellicle 602. However, the first region 609 is preferably also controlled by the control system to be substantially no wider than necessary to achieve this so as to minimise the distance that the radiation beam travels through the first region 609. Any degrading effects that the gas in the first region 609 has on the radiation beam, such as EUV radiation being absorbed, is therefore minimised.

[000127] The amount of absorption of EUV radiation by the gas in the first region 609 is relatively small. Due to the high transmittance of the carbon based pellicles 602, and relatively small amount of absorption in the first region 609, an overall performance gain is provided over the known techniques with poly-silicon based pellicles or molybdenum or zirconium coated carbon based pellicles.

[000128] In the lithographic apparatus according to embodiments, a beam of EUV radiation that has been patterned by the patterning device 601 travels from the surface of the patterning device 601 and through a carbon based pellicle 602 that has a high transmittance of EUV radiation. The pellicle 602 is abutted by, and/or comprised by, a the first region 609 that provides a gaseous environment that does not degrade the pellicle 602. The radiation beam then travels out of the first region 609 and into a second region 610 that comprises the optical elements of the projection system PS. The second region 610 provides a gaseous and/or plasma environment, such as a hydrogen plasma, as required by the optical elements. The radiation beam then travels out of the projection system PS and onto a substrate.

[000129] Figure 7 is a flowchart of a process according to an embodiment.

[000130] In step 701, the process begins.

[000131] In step 703, a radiation beam is conditioned.

[000132] In step 705, a patterning device (601) with a pellicle (602) covering its surface imparts the radiation beam with a pattern in its cross-section to form a patterned radiation beam. [000133] In step 707, a projection system projects the patterned radiation beam onto a target portion of a substrate, wherein the projection system comprises one or more optical elements. [000134] In step 709, a first set of one or more outlets (603) outputs a first fluid into a first region, wherein the first region abuts and/or comprises the pellicle (602).

[000135] In step 711, a second set of one or more outlets (605) outputs a second fluid into a second region that comprises the one or more optical elements of the projection system; wherein the second fluid is different from the first fluid; and, optionally, wherein the patterning device (601), pellicle (602), first set of one or more outlets, second set of one or more outlets and substrate are arranged such that a patterned radiation beam travels from the patterning device (601), then through the pellicle (602) that is abutted by and/or comprised by the first region, then through the second region and then onto a substrate held by the substrate table.

[000136] In step 713, the process ends.

[000137] Embodiments include a number of modifications to the above-described techniques. [000138] In particular, it is not necessary for the first and/or second sets of one or more inlets to be provided. In addition, the above-described first set of one or more inlets may instead be a set of one or more outlets of the same gas output from the first set of one or more outlets 603. The arrangement of outlets for gas of the first region would therefore be substantially as shown in Figure 5. Advantageously, such an arrangement of outlets forces a flow of the gas in the first region away from the pellicle 602 and thereby reduces the likelihood of gas and/or plasma from the second region reaching the pellicle 602.

[000139] As an alternative to what is described above shown in Figure 1, the lithographic apparatus may be used with an alternative type of patterning device 601 that imparts a pattern on the radiation beam when the radiation beam passes through the patterning device 601, rather than reflecting off the patterning device 601. The patterning device 601 would still be covered by a carbon based pellicle 602 that is made possible due to the provision of a first region as described above. [000140] Preferably, the gas output from the first set of one or more outlets 603 is neon, argon or nitrogen. These comprise atoms/molecules that are relatively heavy and, due to their higher inertia than helium, it is easier to maintain the first region when one of these gasses is used.

[000141] The provision of the first region with a different composition from the second region according to embodiments provides further advantages to those described above. These may include improving the particle protection of the patterning device 601 and/or pellicle 602 due to the use of a relatively heavy gas in the first region and reducing the shear force at the walls. The resistance to electric breakdown may also be increased, which may be necessary due to potentially high electrostatic fields around the patterning device support. In this case, a suitable gas for use in the first region would be nitrogen.

[000142] Embodiments also include the use of a known poly-silicon pellicle with a first region comprising tin inert and/or chemically neutral gas as described above. Such a first region would reduce the generation of hydrogen sulphide at the pellicle, which can cause deposits in the projection system PS.

[000143] Embodiments also include a lithographic apparatus in which at the gas output through at least the first set of one or more outlets 603 can be changed. For example, if a carbon based pellicle 602 is being used then the output gas should be an inert and/or chemically neutral gas as described above. However, if a poly-silicon based pellicle is used then the gas output from first set of one or more outputs may be a hydrogen plasma (or there may be no gas output). The output gas is therefore chosen in dependence on the type of pellicle being used. The time required to change a pellicle, or patterning device 601 together with a pellicle, is about 20-30 seconds.

[000144] Embodiments can generally be used to provide an environment of a pellicle that protects the pellicle from all other environments in the system. In particular, the first region may not just be the local environment of the pellicle. For example, when the first region is provided for pellicle of a patterning device in the system as shown in Figure 2, the first region may include all of region VE1 and protect the pellicle from the gasses/plasmas in regions VE2 and VE3.

[000145] Figures 8 and 9 show respectively schematic side and plan views of the substrate table WT constructed to hold the substrate W in a substrate region 223. According to the third aspect of the invention gas supply conduits 221 feeding a third set of one or more gas outlets 220 are provided on either side of the substrate region 223. The third set of one or more outlets 220 is arranged such that gas may be injected in a direction parallel to the surface of the substrate W, in the direction of the arrow in the figure. The outlets 220 output the gas into a third region 224, which in this embodiment abuts the substrate region 223. By injecting gas close to the substrate, the substrate is shielded from the second region 225, which shielding prevents the substrate from being deteriorated like damaged, etched or contaminated - by the fluid present in the second region 225.

[000146] Figure 9 shows particularly three gas outlets 220 and associated gas supply conduits which are provided equispaced on each lateral side of the substrate region 223. It will be understood that other numbers of gas outlets and/or gas supply conduits as well as other arrangements of gas outlets and/or gas supply conduits may be provided that achieve the same objective of supplying gas. Preferably supplying gas in a direction parallel to the surface of the substrate.

[000147] Although not shown in figures 8 and 9, the substrate may be covered by a membrane configured to cover a surface of the substrate. The third region may abut and/or comprise the substrate.

[000148] A schematic example of a substrate W having one surface covered by a membrane 502 is shown in figure 10. Figure 10 additionally shows a third set of one or more outlets 503 for outputting the third fluid into the third region 224; a third set of one or more inlets 504 for discharging fluid from the third region 224; a third fluid supply 507, such as a connector or container, in fluid connection with the third set of one or more outlets 503; a second set of one or more outlets 505 for outputting the second fluid into the second region 225; a second set of one or more inlets 506 for discharging fluid from the second region 225; and a second fluid supply 508, such as a connector or container, in fluid connection with the second set of one or more outlets 505.

[000149] Figure 10 may comprise a number of other components that are not shown. In particular, the optical elements in the second region 225 are not shown. There may be a physical separation sheet between the substrate W and the optical elements. Although not shown in Figure 10, there is also a substrate support that holds the substrate W and a membrane support that holds the membrane 502.

[000150] The third set of one or more outlets 503 may be a plurality of outlets arranged along a side of the substrate W, such as shown along the side of the substrate W in Figure 9.

[000151] A gas is output from the third set of one or more outlets 503 into the local environment of the membrane 502. The gas output from the third set of one or more outlets 503 comprises an inert and/or chemically neutral gas that the substrate W and/or membrane 502 is not degraded by. For example, the gas may be any of helium, neon, argon or nitrogen. Advantageously, the membrane 502 is able to withstand the conditions in the local environment of the membrane 502.

[000152] A third set of one or more inlets 504 are preferably also provided next to the membrane 502 for removing the gas in the third region, i.e. the local environment of the membrane

502. The third set of one or more outlets 503 are preferably provided on the opposite side of the membrane 502 to the third set of one or more inlets 504. The third region therefore comprises a cross-flow of gas across the membrane 502.

[000153] The second set of one or more outlets output a gas and/or plasma, such as a hydrogen plasma as known for use in a lithographic apparatus with EUV radiation, into the second region 225. [000154] A second set of one or more inlets 506 are preferably also provided for removing the gas and/or plasma in the projection system PS. The second set of one or more gas outlets 505 are preferably provided on the opposite side of the projection system PS to the second set of one or more inlets 506 so that there is a cross-flow of the gas and/plasma through the second region 225.

[000155] Although not shown in Figure 10, the second region 225 comprises the optical elements of the projection system PS and the second sets of one or more outlets and inlets are arranged between the third sets of one or more outlets and inlets and the optical elements of the projection system PS.

[000156] Although not shown in Figure 10, the lithographic apparatus also comprises a control system and one or more of any of conduits, valves and pumps for both providing a controlling of the fluid flows into, and preferably also out of, the second 225 and third 224 regions.

[000157] The third 224 and second 225 regions are not separated by a physical barrier that prevents fluid in the second region 225 from flowing into the third region 224 and reaching the membrane 502 or substrate W. The boundary 226 between the third 224 and second 225 regions is therefore approximately defined as the places at which the concentration of fluid from the second region 225 is large enough to cause substantial damage to the substrate or membrane. The boundary 226 is dependent on how the fluid flows are controlled by the control system as well as the environment of the pellicle and in the projection system.

[000158] However, the positioning of the third sets of one or more outlets and inlets next to the membrane 502 and/or substrate W, the directing of the gas output from the one or more outlets across the membrane 502 and/or substrate W and the positioning of the second sets of one or more outlets and inlets further away from the membrane 502 or substrate W than the third sets of one or more outlets and inlets, all cause the local environment of the membrane 502 and/or substrate W to substantially be comprised of gas from the third set of one or more outlets 503 so that a membrane 502 (or substrate W) in, or abutting, the third region 224 is not substantially degraded. The third region 224 may be comprised of at least 80%-90% of gas from the third set of one or more outlets 503 and this is sufficient to prevent a membrane 502 and/or substrate W from being substantially degraded by fluid from the second region 225.

[000159] The control system can control the width of third region 224 in the direction of the radiation beam by controlling the rate at which fluid flows out of the one or more third and/or second one or more outlets and/or by controlling the rate at which fluid flows out of the one or more third and/or second inlets.

[000160] The third region 224 may cover the entire surface of the membrane 502 and/or substrate W and preferably covers the entire membrane 502 and/or substrate W. The third region 224 should also be thin in the direction of the radiation beam through the membrane 502 so that there is only a short path distance of the radiation beam through the third region 224. The width of third region 224 in the direction of the radiation beam should be large enough to ensure that the amount fluid, i.e. gas and/or plasma, from the second region 225 that is likely to reach the membrane 502 and/or substrate W is not large enough to substantially damage the membrane 502 and/or substrate W. However, the third region 224 is preferably also controlled by the control system to be substantially no wider than necessary to achieve this so as to minimise the distance that the radiation beam travels through the third region 224. Any degrading effects that the gas in the third region 224 has on the radiation beam, such as EUV radiation being absorbed, is therefore minimised.

[000161] The amount of absorption of EUV radiation by the gas in the third region is relatively small. Due to the high transmittance of the membrane 502, and relatively small amount of absorption in the third region, an overall performance gain is provided over the known techniques.

[000162] In the lithographic apparatus according to embodiments, a beam of EUV radiation that has been patterned by the patterning device travels from the surface of the patterning device and through a pellicle that has a high transmittance of EUV radiation. The radiation beam then travels from the pellicle into a second region 225 that comprises the optical elements of the projection system PS. The second region 225 provides a gaseous and/or plasma environment, such as a hydrogen plasma, as required by the optical elements. The radiation beam then travels out of the projection system PS and second region 225, into the third region 224, through the optionally present membrane, and onto a substrate.

[000163] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device 601). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions. [000164] The term EUV radiation” may be considered to encompass electromagnetic radiation having a wavelength within the range of 4-20 nm, for example within the range of 13-14 nm. EUV radiation may have a wavelength of less than 10 nm, for example within the range of 4-10 nm such as 6.7 nm or 6.8 nm.

[000165] 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. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin film magnetic heads, etc.

[000166] Where in this application the terms first, second, and third are used, this is done to create a distinction between the one and the other and not to say anything about the number. For example, talking about 'second region' and 'third region' does not mean that there is also a 'first region'.

[000167] Embodiments of the first, second, third and fourth aspect of the invention may be worded in accordance with one or more of the next following clauses:

1) A lithographic apparatus, comprising:

an illumination system configured to condition a radiation beam;

a patterning device (601) configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam;

a pellicle (602) configured to cover a surface of the patterning device (601);

a substrate table configured to hold a substrate;

a projection system configured to project the patterned radiation beam onto a target portion of a substrate when the substrate is held by the substrate table, wherein the projection system comprises one or more optical elements;

a first set of one or more outlets (603) for outputting a first fluid into a first region, wherein the first region abuts and/or comprises the pellicle (602); and a second set of one or more outlets (605) configured to output a second fluid into a second region that comprises the one or more optical elements of the projection system; and wherein the second fluid is different from the first fluid.

2) The lithographic apparatus according to clause 1, wherein the patterning device (601), pellicle (602), first set of one or more outlets (603), second set of one or more outlets (605) and substrate table are arranged such that, in use, a patterned radiation beam travels from the patterning device (601), then through the pellicle (602) that is abutted by and/or comprised by the first region, then through the second region and then onto a substrate held by the substrate table.

3) The lithographic apparatus according to any preceding clause, wherein the first set of one or more outlets (603) is configured to provide a first gaseous environment in the first region, the first gaseous environment shielding the pellicle (602) from the second region or preventing fluid in the second region from reaching the pellicle (602),

4) The lithographic apparatus according to any preceding clause, wherein the first fluid is a gas that is inert and/or chemically neutral with the pellicle (602).

5) The lithographic apparatus according to any preceding clause, wherein the first fluid comprises one or more of helium, neon, argon or nitrogen.

6) The lithographic apparatus according to any preceding clause, wherein the second fluid comprises a gas and/or plasma that the pellicle is degraded by.

7) The lithographic apparatus according to any preceding clause, wherein the second fluid comprises a gas and/or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system.

8) The lithographic apparatus according to clause 7, wherein the second fluid comprises hydrogen radicals.

9) The lithographic apparatus according to any preceding clause, further comprising a patterning device support arranged to support the patterning device (601), wherein the pellicle (602) is coupled to the patterning device support.

10) The lithographic apparatus according to any preceding clause, wherein one or more of the second set of one or more outlets (605) are arranged between the first set of one or more outlets (603 ) and the one or more optical elements of the projection system.

11) The lithographic apparatus according to any preceding clause, further comprising a first set of one or more inlets (604) that are arranged in the first region for removing fluid from the first region.

12) Tire lithographic apparatus according to clause 11, wherein the first set of one or more inlets (604) are arranged on the opposite side of the pellicle (602) to the first set of one or more outlets (603) so that, in use, there is a cross flow of the first fluid across the pellicle (602).

13) The lithographic apparatus according to any preceding clause, further comprising a second set of one or more inlets (606) that are arranged in the second region for removing fluid from the second region.

14) The lithographic apparatus according to clause 13, wherein the second set of one or more inlets (606) are arranged on the opposite side of the projection system to the second set of one or more outlets (605) so that, in use, there is a cross flow of the second fluid across the projection system.

15) The lithographic apparatus according to any preceding clause, wherein the pellicle (602) is carbon based.

16) The lithographic apparatus according to clause 15, wherein the first fluid comprises a carboncontaining gas.

17) Tire lithographic apparatus according to clause 15 or 16, wherein the pellicle (602) comprises one or more of carbon nanotubes and diamond.

18) The lithographic apparatus according to any preceding clause, wherein the an illumination system is configured to condition an extreme ultraviolet, EUV, radiation beam.

19) The lithographic apparatus according to any preceding clause, wherein one or more of the one or more optical elements are mirrors.

20) The lithographic apparatus according to any preceding clause, further comprising a control system that is configured to select the first fluid that is output from the first set of one or more outlets (603) in dependence on the type of pellicle being used.

21) The lithographic apparatus according to any preceding clause, further comprising a first fluid supply containing the first fluid and a second fluid supply containing the second fluid, the first fluid supply (607) being in fluid connection with the first set of one or more outlets (603) and the second fluid supply (608) being in fluid connection with the second set of one or more outlets (605).

22) A method comprising: conditioning (703) a radiation beam;

imparting (705), by a patterning device (601) with a pellicle (602) covering its surface, the radiation beam with a pattern in its cross-section to form a patterned radiation beam;

projecting (707), by a projection system, the patterned radiation beam onto a target portion of a substrate, wherein the projection system comprises one or more optical elements;

outputting (709), by a first set of one or more outlets (603), a first fluid into a first region, wherein the first region abuts and/or comprises the pellicle (602); and outputting (711), by a second set of one or more outlets (605), a second fluid into a second region that comprises the one or more optical elements of the projection system;

wherein the second fluid is different from the first fluid.

23) The method according to clause 22, wherein the patterning device (601), pellicle (602), first set of one or more outlets, second set of one or more outlets and substrate are arranged such that a patterned radiation beam travels from the patterning device (601), then through the pellicle (602) that is abutted by and/or comprised by the first region, then through the second region and then onto a substrate held by the substrate table.

24) The method according to clause 22 or 23. wherein the method is performed by a lithographic apparatus according to any of clauses 1 to 21.

25) The method according to any of clauses 22 to 24, further comprising selecting the first fluid that is output by the first set of one or more outlets (603) in dependence on the type of pellicle being used.

26) The method according to any of clauses 22 to 25, wherein the outputting of the first fluid into the first region results, in the first region, in a first gaseous environment shielding the pellicle (602) from the second region.

27) The method according to any of clauses 22 to 25, wherein the outputting of the first fluid into the first region results, in the first region, in a first gaseous environment preventing fluid in the second region from reaching the pellicle (602).

28) The method according to any of clauses 22 to 27, wherein the first fluid is a gas that is inert and/or chemically neutral with the pellicle (602).

29) The method according to any of clauses 22 to 28, wherein the first fluid comprises one or more of helium, neon, argon or nitrogen.

30) The method according to any of clauses 22 to 29, wherein the second fluid comprises a gas and/or plasma that the pellicle is degraded by.

31) The method according to any of clauses 22 to 30, wherein the second fluid comprises a gas and/or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system.

32) The method according to clause 31, wherein the second fluid comprises hydrogen radicals.

33) The method according to any of clauses 22-32, wherein the pellicle (602) is carbon based, and wherein the first fluid comprises a carbon-containing gas.

34) A lithographic apparatus, comprising:

an illumination system configured to condition a radiation beam;

a patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam;

a substrate table (WT) configured to hold a substrate (W) in a substrate region (223);

a projection system configured to project the patterned radiation beam onto a target portion of a substrate (W) when the substrate (W) is held by the substrate table (WT), wherein the projection system comprises one or more optical elements;

a second set of one or more outlets (505) configured to output a second fluid into a second region (225) that comprises the one or more optical elements of the projection system; and a third set of one or more outlets (220, 503) for outputting a third fluid into a third region ((224), wherein the third region abuts and/or comprises the substrate region (223); and wherein the second fluid is different from the third fluid.

35) The lithographic apparatus according to clause 34, wherein the third set of one or more outlets (220, 503) is configured to provide a third gaseous environment in the third region (224), the third gaseous environment shielding the substrate (W) from the second region (225).

36) The lithographic apparatus according to clause 34 or 35, wherein the substrate region (223) comprises a membrane (502) configured to cover a surface of the substrate (W), and wherein the third region (224) abuts and/or comprises the membrane (502).

37) Tire lithographic apparatus according to clause 36, wherein the third set of one or more outlets (220, 503) is configured to provide a third gaseous environment in the third region (224), the third gaseous environment shielding the membrane (W) from the second region (225).

38) The lithographic apparatus according to any of clauses 34-37, wherein the patterning device (601), the projection system, second set of one or more outlets (505), third set of one or more outlets (220, 503) and substrate table (WT) are arranged such that, in use, a patterned radiation beam travels from the patterning device, through the projection system comprising the second region (225), through the third region (224) and then onto a substrate (W) held by the substrate table (WT).

39) The lithographic apparatus according to any of clauses 34-38, wherein the third fluid is a gas that is inert and/or chemically neutral with the substrate (W).

40) The lithographic apparatus according to any of clauses 34-39, wherein the third fluid comprises one or more of helium, neon, argon or nitrogen.

41) The lithographic apparatus according to any of clauses 34-40, wherein the second fluid comprises a gas and/or plasma that the substrate (W) is degraded by.

42) Tire lithographic apparatus according to any of clauses 34-41, wherein the second fluid comprises a gas and/or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system.

43) The lithographic apparatus according to clause 42, wherein the second fluid comprises hydrogen radicals.

44) The lithographic apparatus according to any of clauses 34-43, further comprising a third set of one or more inlets (504) that are arranged in the third region (224) for removing fluid from the third region (224).

45) The lithographic apparatus according to clause 44, wherein the third set of one or more inlets (504) are arranged on the opposite side of the substrate (W) to the third set of one or more outlets (220, 503) so that, in use, there is a cross flow of the third fluid across the substrate (W).

46) The lithographic apparatus according to any of clauses, further comprising a second set of one or more inlets (506) that are arranged in the second region (225) for removing fluid from the second region (225).

47) The lithographic apparatus according to clause 46, wherein the second set of one or more inlets (506) are arranged on the opposite side of the projection system to the second set of one or more outlets (505) so that, in use, there is a cross flow of the second fluid across the projection system.

48) The lithographic apparatus according to any of clauses 34-47, wherein the illumination system is configured to condition an extreme ultraviolet, EUV, radiation beam.

49) The lithographic apparatus according to any of clauses 34-48, wherein one or more of the one or more optical elements are mirrors.

50) The lithographic apparatus according to any of clauses 34-49, further comprising a control system that is configured to select the third fluid that is output from the third set of one or more outlets (220,503) in dependence on the type of substrate or membrane being used.

51) The lithographic apparatus according to any preceding clause, further comprising a second fluid supply (508) containing the second fluid and a third fluid supply (507) containing the third fluid, the second fluid supply (508) being in fluid connection with the second set of one or more outlets (505) and the third fluid supply (508) being in fluid connection with the third set of one or more outlets (503).

52) A method comprising:

conditioning a radiation beam;

imparting, by a patterning device, the radiation beam with a pattern in its cross-section to form a patterned radiation beam;

projecting, by a projection system, the patterned radiation beam onto a target portion of a substrate held in a substrate region, wherein the projection system comprises one or more optical elements;

outputting, by a second set of one or more outlets, a second fluid into a second region that comprises the one or more optical elements of the projection system; and outputting, by a third set of one or more outlets, a third fluid into a third region, wherein the third region abuts and/or comprises the substrate region; and wherein the second fluid is different from the third fluid.

53) The method according to clause 52, wherein the third fluid outputted into the third region provides a third gaseous environment in the third region, the third gaseous environment shielding the substrate from the second region.

54) Tire method according to clause 52 or 53, wherein the substrate region comprises a membrane configured to cover a surface of the substrate, and wherein the third region abuts and/or comprises the membrane.

55) The method according to clause 54, wherein the third fluid outputted into the third region provides a third gaseous environment in the third region, the third gaseous environment shielding the membrane from the second region.

56) The method according to any of clauses 52 to 55, wherein the patterning device, pellicle, second set of one or more outlets, third set of one or more outlets and substrate are arranged such that a patterned radiation beam travels from the patterning device, through the second region, through the third region and then onto a substrate held by the substrate table.

57) The method according to any of clauses 52 to 56, wherein the method is performed by a lithographic apparatus according to any of clauses 34 to 51.

58) The method according to any of clauses 52 to 57, further comprising selecting the third fluid that is output by the third set of one or more outlets in dependence on the type of substrate or membrane being used.

59) The method according to any of clauses 52 to 58, wherein the third fluid is a gas that is inert and/or chemically neutral with the substrate.

60) The method according to any of clauses 52 to 59, wherein the third fluid comprises one or more of helium, neon, argon or nitrogen.

61) The method according to any of clauses 52 to 60, wherein the second fluid comprises a gas and/or plasma that the substrate is degraded by.

62) The method according to any of clauses 52 to 61, wherein the second fluid comprises a gas and/or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system.

63) The method according to clause 62, wherein the second fluid comprises hydrogen radicals.

[000168] 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 (63)

CONCLUSIONS Lithographic device, comprising: a lighting system configured to condition a radiation beam; a modeling device (601) configured to pattern the radiation beam in its cross-section to form a modeled radiation beam; a web (602) configured to cover a surface of the modeling device (601); a substrate table configured to hold a substrate; a projection system configured to project the modeled radiation beam onto a target portion of a substrate when the substrate is held by the substrate table, the projection system comprising one or more optical elements; a first set of one or more outlets (603) for outputting a first fluid into a first region, the first region touching and / or comprising the web (602); and a second set of one or more outlets (605) configured to output a second fluid in a second region comprising the one or more optical elements of the projection system; and wherein the second fluid is different from the first fluid. The lithographic device of claim 1, wherein the modeling device (601), the web (602), the first set of one or more outlets (603), the second set of one or more outlets (605), and the substrate table are arranged that, in use, a modeled radiation beam travels from the modeling device (601), then through the web (602) hit and / or contained by the first region, then through the second region, and then onto a substrate passed through the substrate table being held. The lithographic device of any preceding claim, wherein the first set of one or more outlets (603) is configured to provide a first gaseous environment in the first region, the first gaseous environment shielding the web (602) from the second area. Lithographic device according to any of the preceding claims, wherein the first fluid is a gas which is inert and / or chemically neutral with the web (602). Lithographic device according to any of the preceding claims, wherein the first fluid comprises one or more of helium, neon, argon or nitrogen. Lithographic device according to any of the preceding claims, wherein the second fluid comprises a gas and / or plasma through which the membrane is attacked. Lithographic device according to any of the preceding claims, wherein the second fluid comprises a gas and / or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system. The lithographic device of claim 7, wherein the second fluid comprises hydrogen radicals. The lithographic device according to any of the preceding claims, further comprising a modeling device support adapted to support the modeling device (601), the web (602) being coupled to the modeling device support. The lithographic apparatus according to any of the preceding claims, wherein one or more of the second set of one or more outlets (605) are disposed between the first set of one or more outlets (603) and the one or more optical elements of the projection system. The lithographic device of any preceding claim, further comprising a first set of one or more inlets (604) disposed in the first region for removing fluid from the first region. The lithographic device of claim 11, wherein the first set of one or more inlets (604) is disposed on the side of the web (602) opposite the first set of one or more outlets (603) so that, in use, a cross flow of the first fluid over the web (602). The lithographic device of any preceding claim, further comprising a second set of one or more inlets (606) disposed in the second region for removing fluid from the second region. The lithographic apparatus of claim 13, wherein the second set of one or more inlets (606) is disposed on the side of the projection system opposite the second set of the one or more outlets (605) so that, in use, there is a cross flow of the second fluid over the projection system. Lithographic device according to any of the preceding claims, wherein the nonwoven (602) is carbon based. The lithographic device of claim 15, wherein the first fluid comprises a carbonaceous gas. The lithographic device of claim 15 or 16, wherein the web (602) comprises one or more of carbon hano tubes and diamond. Lithographic device according to any of the preceding claims, wherein the lighting system is configured to condition an EUV radiation beam (extreme ultraviolet). Lithographic device according to any of the preceding claims, wherein one or more of the one or more optical elements are mirrors. The lithographic device of any of the preceding claims, further comprising a control system configured to select the first fluid, which is output from the first set of one or more outlets (603), depending on the type of fleece used. The lithographic apparatus according to any of the preceding claims, further comprising a first fluid supply containing the first fluid and a second fluid supply containing the second fluid, the first fluid supply (607) in fluid communication with the first set of one or more outlets (603) and the second fluid supply (608) is in fluid communication with the second set of one or more outlets (605). 22. Method comprising: conditioning (703) a radiation beam; providing the radiation beam (705), by a modeling device (601) with a web (602) covering its surface, with a pattern in its cross-section to form a modeled radiation beam; projecting (707), by a projection system, the modeled radiation beam onto a target portion of a substrate, the projection system comprising one or more optical elements; performing (709), through a first set of one or more outlets (603), a first fluid in a first region, the first region touching and / or comprising the web (602); and outputting (711), through a second set of one or more outlets (605), a second fluid in a second region comprising the one or more optical elements of the projection system; wherein the second fluid is different from the first fluid. The method of claim 22, wherein the modeling device (601), the web (602), the first set of one or more outlets, the second set of one or more outlets, and the substrate are arranged such that a modeled radiation beam travels from the modeling device (601), then through the web (602) touched and / or contained by the first region, then through the second region, and then onto a substrate held by the substrate table. The method of claim 22 or 23, wherein the method is performed by a lithographic device according to any of claims 1 to 21. The method of any one of claims 22 to 24, further comprising selecting the first fluid to be outputted from the first set of one or more outlets (603) depending on the type of fleece used. The method of any one of claims 22 to 25, wherein outputting the first fluid in the first region results, in the first region, in a first gaseous environment shielding the web (602) from the second region. The method of any one of claims 22 to 25, wherein outputting the first fluid in the first region results, in the first region, in a first gaseous environment that prevents fluid in the second region from forming the web (602 ) reached. The method of any one of claims 22 to 27, wherein the first fluid is a gas that is inert and / or chemically neutral with the web (602). The method of any of claims 22 to 28, wherein the first fluid comprises one or more of helium, neon, argon or nitrogen. A method according to any of claims 22 to 29, wherein the second fluid comprises a gas and / or plasma through which the web is attacked. The method of any one of claims 22 to 30, wherein the second fluid comprises a gas and / or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system. The method of claim 31, wherein the second fluid comprises hydrogen radicals. The method of any one of claims 22-32, wherein the web (602) is carbon based, and wherein the first fluid comprises a carbonaceous gas. 34. Lithographic device, comprising: a lighting system configured to condition a radiation beam; a modeling device (601) configured to pattern the radiation beam in its cross-section to form a modeled radiation beam; a substrate table (WT) configured to hold a substrate (W) in a substrate region (223); a projection system configured to project the modeled radiation beam onto a target portion of a substrate (W) when the substrate (W) is held by the substrate table (WT), the projection system comprising one or more optical elements; a second set of one or more outlets (505) for outputting a second fluid in a second region (225) comprising the one or more optical elements of the projection system; and a third set of one or more outlets (220, 503) for outputting a third fluid into a third region (224), the third region touching and / or comprising the substrate region (223); and wherein the second fluid is different from the third fluid. The lithographic apparatus of claim 34, wherein the third set of one or more outlets (220, 503) is configured to provide a third gaseous environment in the third region, the third gaseous environment shielding the substrate (W) from the second area (225). The lithographic device of claim 34, wherein the substrate region (223) comprises a membrane (502) configured to cover a surface of a substrate, and wherein the third region (224) contacts and / or comprises the membrane (502) . The lithographic device of claim 36, wherein the third set of one or more outlets is configured to provide a third gaseous environment in the third region (224), the third gaseous environment shielding the membrane (W) from the second region (224). 225). The lithographic device according to any one of claims 34 to 37, wherein the modeling device (601), the projection system, the second set of one or more outlets (505), the third set of one or more outlets (220, 503) and the substrate table (WT) is arranged such that, in use, a modeled radiation beam moves from the modeling device, through the projection system comprising the second region (225), through the third region (224) and then onto the substrate (W) which is held by the substrate table (WT). Lithographic device according to any of claims 34 to 38, wherein the third fluid is a gas which is inert and / or chemically neutral with the substrate (W). The lithographic device of any one of claims 34 to 39, wherein the third fluid comprises one or more of helium, neon, argon or nitrogen. Lithographic device according to any one of claims 34 to 40, wherein the second fluid comprises a gas and / or plasma through which the substrate (W) is attacked. The lithographic apparatus according to any one of claims 34 to 41, wherein the second fluid comprises a gas and / or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system. The lithographic device of claim 42, wherein the second fluid comprises hydrogen radicals. The lithographic device of any one of claims 34 to 43, further comprising a third set of one or more inlets (504) disposed in the third region (224) for removing fluid from the third region. The lithographic apparatus of claim 44, wherein the third set of one or more inlets (504) is disposed on the side of the substrate (W) opposite the third set of one or more outlets (220, 503) so that, in use , is a cross flow of the third fluid over the substrate (W). The lithographic device of any preceding claim, further comprising a second set of one or more inlets (506) disposed in the second region (225) for removing fluid from the second region (225). The lithographic apparatus of claim 46, wherein the second set of one or more inlets (506) is disposed on the side of the projection system opposite the second set of the one or more outlets (505) so that, in use, there is a cross flow of the second fluid over the projection system. The lithographic apparatus according to any one of claims 34 to 47, wherein the illumination system is configured to condition an ELTV (extreme ultraviolet) radiation beam. The lithographic device according to any one of claims 34 to 48, wherein one or more of the one or more optical elements are mirrors. The lithographic device of any one of claims 34 to 49, further comprising a control system configured to select the third fluid, which is output from the third set of one or more outlets (220, 503), depending on the type of substrate or membrane used. The lithographic apparatus according to any of the preceding claims, further comprising a second fluid supply (508) containing the second fluid and a third fluid supply (507) containing the third fluid, the second fluid supply (508) in fluid communication with the second set of one or more outlets (603) and the third fluid supply (508) is in fluid communication with the third set of one or more outlets (503). 52. A method comprising: conditioning a radiation beam; providing the radiation beam, by a modeling device, with a pattern in its cross-section to form a modeled radiation beam; projecting, by a projection system, the modeled radiation beam onto a target portion of a substrate held in a substrate region, the projection system comprising one or more optical elements; outputting, by a second set of one or more outlets, a second fluid in a second region comprising the one or more optical elements of the projection system; and outputting, by a third set of one or more outlets, a third fluid in a third region, the third region touching and / or comprising the substrate region; wherein the second fluid is different from the third fluid. The method of claim 52, wherein outputting the third fluid in the third region results, in the third region, in a third gaseous environment, the third gaseous environment shielding the substrate from the second region. The method of claim 52, wherein the substrate region comprises a membrane configured to cover a surface of the substrate, and wherein the third region contacts and / or comprises the membrane. The method of claim 54, wherein outputting the third fluid in the third region results, in the third region, in a third gaseous environment, the third gaseous environment shielding the membrane from the second region. The method of any one of claims 52 to 55, wherein the modeling device, the web, the second set of one or more outlets, the third set of one or more outlets, and the substrate are arranged to displace a modeled radiation beam from the modeling device, through the second region, through the third region, and then onto a substrate held by the substrate table. A method according to any of claims 52 to 56, wherein the method is performed by a lithographic apparatus according to any of claims 34 to 51. The method of any of claims 52 to 57, further comprising selecting the third fluid to be performed by the third set of one or more outlets, depending on the type of substrate or membrane used. A method according to any of claims 52 to 58, wherein the third fluid is a gas that is inert and / or chemically neutral with the substrate. The method of any of claims 52 to 59, wherein the third fluid comprises one or more of helium, neon, argon or nitrogen. A method according to any of claims 52 to 60, wherein the second fluid comprises a gas and / or plasma through which the substrate is attacked. A method according to any of claims 52 to 61, wherein the second fluid comprises a gas and / or plasma, such as a hydrogen plasma, for preventing oxidation and contamination of the one or more optical elements of the projection system. The method of claim 62, wherein the second fluid comprises hydrogen radicals.