Fluid handling structure

Abstract

A fluid handling structure configured to at least partly confine an immersion liquid to an immersion space between a final element of a projection system and a substrate, comprising: a gas channel configured to supply a gas flow towards the substrate via a gas channel opening; and a chamber configured to define a control volume fluidically connected to the gas channel, the chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the control volume.

Description

FLUID HANDLING STRUCTURECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23214092.1 which was filed on 4 December 2023 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The present invention relates to a fluid handling structure.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as “design layout” or “design”) of a patterning device (e.g., a mask) onto a layer of radiation- sensitive material (resist) provided on a substrate (e.g., a wafer). 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.

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually been reduced while the amount of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as ‘Moore’s law’. To keep up with Moore’s law the semiconductor industry is chasing technologies that enable to create increasingly smaller features. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm.

[0005] Further improvements in the resolution of smaller features may be achieved by providing an immersion fluid having a relatively high refractive index, such as water, on the substrate during exposure. The effect of the immersion fluid is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the fluid than in gas. The effect of the immersion fluid may also be regarded as increasing the effective numerical aperture (NA) of the system and also increasing the depth of focus.

[0006] The immersion fluid may be confined to a localized area, referred to as an immersion space, between a liquid confinement structure of the lithographic apparatus and the substrate by a fluid handling structure. The fluid handling structure may be an assembly comprising a number of component parts, some such parts having complicated and intricate structures. In particular, the fluidhandling structure provides an intricate structure of flow channels for the fluid provided to the immersion space.

[0007] US20220075264 discloses a fluid handling structure comprising a control valve, the control valve comprising a passageway having a portion defining an opening for the flow of liquid and / or gas therethrough; an obstructing member displaceable relative to the opening for obstructing the opening by differing amounts thereby to regulate a volumetric flow rate of liquid and / or gas through the opening.

[0008] In a lithographic patterning process, a fluid handling structure confines an immersion liquid to an immersion space between a final element of a projection system and a substrate. The immersion liquid is confined by the fluid handling structure by providing a gas knife configured to supply a gas towards the substrate. Immersion liquid confinement is also optionally controlled by providing gas and immersion fluid extraction means which control extraction of the immersion liquid and gas. The gas knife comprises a channel with an opening, wherein the gas is supplied towards the substrate through the opening. It may be particularly important to have precise and accurate control of gas flow from the gas knife during scanning of the substrate.

[0009] During a lithographic processing step, the substrate may be moved relative to the fluid handling structure. During substrate movement, immersion liquid may be lost from the substrate surface. This may particularly occur when the fluid handling structure crosses an edge of the substrate, but also may also occur when scanning over inner regions of the substrate. Loss of the immersion liquid can be prevented by temporarily increasing the flow of gas through the gas knife while the fluid handling structure crosses the substrate edge. In addition, it may be beneficial to temporarily reduce the flow of gas through the gas knife during a lithographic processing step under certain circumstances, to improve the effectiveness of immersion liquid handling.

[0010] Including additional components in the fluid handling structure may be undesirable, because there may be little or no free space available in the fluid handling structure. Therefore, it is desirable to provide a fluid handling structure which may modulate the flow of gas (“a gas flow modulation means”) without introducing bulky components into the fluid handling structure.

[0011] Introducing gas flow modulation means outside the fluid handling structure may also be undesirable, because there may be a time delay between the actuation of a gas flow modulation means and the resulting gas flow modulation in the fluid handling structure. Increase reaction time of the gas flow rate may result in reduces the level of control over the gas flow, which is undesirable.

[0012] Therefore, it is desirable to provide a gas flow modulation means which has a small form factor and can be easily incorporated into a fluid handling structure. In addition, the gas flow control means must be able to quickly and accurately provide a temporary change in the gas flow rate (increase or decrease). It may be desirable for the gas flow modulation means to be able to provide a predetermined increase or decrease in the gas flow, without providing complicated components.

[0013] Therefore, there is a need to provide a relatively simple configuration with a small form factor to accurately control gas flow, so that it can be easily incorporated into a fluid handling structure.SUMMARY

[0014] According to an aspect of the disclosure, there is provided a fluid handling structure configured to at least partly confine an immersion liquid to an immersion space between a final element of a projection system and a substrate, comprising: a gas channel configured to supply a gas flow towards the substrate via a gas channel opening; and a chamber configured to define a control volume fluidically connected to the gas channel, the chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the control volume.

[0015] According to a further aspect of the disclosure, there is provided a fluid handling system comprising a fluid handling structure configured to at least partly confine an immersion liquid to an immersion space between a final element of a projection system and a substrate, wherein: the fluid handling structure comprises a gas channel configured to supply a gas flow towards the substrate via a gas channel opening; and the fluid handling system comprises: a gas supply line, configured to supply gas to the gas channel; a pressure source; and an actuatable flow valve connected between the pressure source and the gas supply line upstream of the gas channel opening, wherein the fluid handling system is configured such that when the flow valve is closed a pressure in the gas supply line is different to a pressure of the pressure source, such that actuation of the flow valve to at least partially open the flow valve causes a change of gas flow in the fluid channel by changing a pressure in the gas supply line.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the disclose will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference symbols indicate corresponding parts, and in which:

[0017] Figure 1 depicts the schematic overview of the lithographic apparatus;

[0018] Figures 2a, 2b, 2c and 2d each depict, in cross section, two different versions of a fluid handling structure with different features illustrated on the left-hand side and the right-hand side of each version, which may extend around the complete circumference according to the prior art;

[0019] Figure 3 is a schematic overview of a cross-section of a fluid handling structure;

[0020] Figure 4 is a schematic overview of a cross-section of a fluid handling structure;

[0021] Figures 5a, 5b, 5c and 5d are schematic overviews of cross-sections of a fluid handling structure;

[0022] Figure 6 is a schematic overview of a cross-section of a fluid handling structure;

[0023] Figures 7a and 7b is a schematic overview of a cross-section of a of a fluid handling structure;

[0024] Figure 8 is a schematic overview of a fluid handling structure;

[0025] Figure 9 is a schematic overview of a fluid handling structure.

[0026] The features shown in the figures are not necessarily to scale, and the size and / or arrangement depicted is not limiting. It will be understood that the figures include optional features which may not be essential to the invention. Furthermore, not all of the features of the apparatus are depicted in each of the figures, and the figures may only show some of the components relevant for describing a particular feature.DETAILED DESCRIPTION

[0027] In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm).

[0028] The term “reticle”, “mask” or “patterning device” as employed in this text may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term “light valve” can also be used in this context. Besides the classic mask (transmissive or reflective, binary, phase- shifting, hybrid, etc.), examples of other such patterning devices include a programmable mirror array and a programmable LCD array.

[0029] Figure 1 schematically depicts a lithographic apparatus. The lithographic apparatus includes an illumination structure (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation), a mask support (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA in accordance with certain parameters, a substrate support (e.g., a substrate 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 support WT in accordance with certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. A controller 500 controls the overall operation of the apparatus. Controller 500 may be a centralised control system or a system of multiple separate sub-controllers within various sub-systems of the lithographic apparatus.

[0030] In operation, the illumination system IL receives the radiation beam B from a radiation source SO, e.g. via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for directing, shaping, and / or controlling radiation. The illuminator IL may be used to condition the radiation beam B to have adesired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.

[0031] The term “projection system” PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and / or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system” PS.

[0032] The lithographic apparatus is of a type wherein at least a portion of the substrate W may be covered by an immersion liquid having a relatively high refractive index, e.g., water, so as to fill an immersion space 11 between the projection system PS and the substrate W - which is also referred to as immersion lithography. More information on immersion techniques is given in US 6,952,253, which is incorporated herein by reference.

[0033] The lithographic apparatus may be of a type having two or more substrate supports WT (also named “dual stage”). In such “multiple stage” machine, the substrate supports WT may be used in parallel, and / or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W.

[0034] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not depicted in figures). The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid. The measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS.

[0035] In operation, the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position measurement system IF, the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly depicted in Figure 1) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be locatedin spaces between target portions. Substrate alignment marks Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C.

[0036] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axis, i.e., an x-axis, a y-axis and a z-axis. Each of the three axis is orthogonal to the other two axis. A rotation around the x-axis is referred to as an Rx-rotation. A rotation around the y- axis is referred to as an Ry -rotation. A rotation around about the z-axis is referred to as an Rz- rotation. The x-axis and the y-axis define a horizontal plane, whereas the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the invention and is used for clarification only. Instead, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0037] Immersion techniques have been introduced into lithographic systems to enable improved resolution of smaller features. In an immersion lithographic apparatus, a liquid layer of immersion liquid having a relatively high refractive index is interposed in the immersion space 11 between a projection system PS of the apparatus (through which the patterned beam is projected towards the substrate W) and the substrate W. The immersion liquid covers at least the part of the substrate W under a final element of the projection system PS. Thus, at least the portion of the substrate W undergoing exposure is immersed in the immersion liquid.

[0038] In commercial immersion lithography, the immersion liquid is water. Typically the water is distilled water of high purity, such as Ultra-Pure Water (UPW) which is commonly used in semiconductor fabrication plants. In an immersion system, the UPW is often purified and it may undergo additional treatment steps before supply to the immersion space 11 as immersion liquid. Other liquids with a high refractive index can be used besides water as the immersion liquid, for example: a hydrocarbon, such as a fluorohydrocarbon; and / or an aqueous solution. Further, other fluids besides liquid have been envisaged for use in immersion lithography.

[0039] In this specification, reference will be made in the description to localized immersion in which the immersion liquid is confined, in use, to the immersion space 11 between the final element 100 and a surface facing the final element 100. The facing surface is a surface of substrate W or a surface of the supporting stage (or substrate support WT) that is co-planar with the surface of the substrate W. (Please note that reference in the following text to surface of the substrate W also refers in addition or in the alternative to the surface of the substrate support WT, unless expressly stated otherwise; and vice versa). A fluid handling structure 12 present between the projection system PS and the substrate support WT is used to confine the immersion liquid to the immersion space 11. The immersion space 11 filled by the immersion liquid is smaller in plan than the top surface of the substrate W and the immersion space 11 remains substantially stationary relative to the projection system PS while the substrate W and substrate support WT move underneath.

[0040] Other immersion systems have been envisaged such as an unconfined immersion system (a so-called ’All Wet’ immersion system) and a bath immersion system. In an unconfined immersion system, the immersion liquid covers more than the surface under the final element 100. The liquid outside the immersion space 11 is present as a thin liquid film. The liquid may cover the whole surface of the substrate W or even the substrate W and the substrate support WT co-planar with the substrate W. In a bath type system, the substrate W is fully immersed in a bath of immersion liquid.

[0041] The fluid handling structure 12 is a structure which supplies the immersion liquid to the immersion space 11, removes the immersion liquid from the immersion space 11 and thereby confines the immersion liquid to the immersion space 11. It includes features which are a part of a fluid supply system. The arrangement disclosed in PCT patent application publication no. WO 99 / 49504 is an early fluid handling structure comprising pipes which either supply or recover the immersion liquid from the immersion space 11 and which operate depending on the relative motion of the stage beneath the projection system PS. In more recent designs, the fluid handling structure extends along at least a part of a boundary of the immersion space 11 between the final element 100 of the projection system PS and the substrate support WT or substrate W, so as to in part define the immersion space 11.

[0042] The fluid handing structure 12 may have a selection of different functions. Each function may be derived from a corresponding feature that enables the fluid handling structure 12 to achieve that function. The fluid handling structure 12 may be referred to by a number of different terms, each referring to a function, such as barrier member, seal member, fluid supply system, fluid removal system, liquid confinement structure, etc..

[0043] In an embodiment, immersion liquid is used as the immersion fluid. In that case the fluid handling structure 12 may be a liquid handling system. In reference to the aforementioned description, reference in this paragraph to a feature defined with respect to fluid may be understood to include a feature defined with respect to liquid.

[0044] A lithographic apparatus has a projection system PS. During exposure of a substrate W, the projection system PS projects a beam of patterned radiation onto the substrate W. To reach the substrate W, the path of the radiation beam B passes from the projection system PS through the immersion liquid confined by the fluid handling structure 12 between the projection system PS and the substrate W. The projection system PS has a lens element, the last in the path of the beam, which is in contact with the immersion liquid. This lens element which is in contact with the immersion liquid may be referred to as ‘the last lens element’ or “the final element”. The final element 100 is at least partly surrounded by the fluid handling structure 12. The fluid handling structure 12 may confine the immersion liquid under the final element 100 and above the facing surface.

[0045] Figures 2a, 2b, 2c and 2d show different features which may be present in variations of a fluid handling system. The designs may share some of the same features as Figures 2a, 2b, 2c and 2d unless described differently. The features described herein may be selected individually or in combination as shown or as required. The figures depict different versions of a fluid handling systemwith different features illustrated on the left hand side and the right hand side, which may extend around the complete circumference. Thus, for example, the fluid handling system may have the same features extending around the complete circumference. For example, the fluid handling system may have only the features of the left hand side of Figure 2a, or the right hand side of Figure 2a, or the left hand side of Figure 2b, or the right hand side of Figure 2b, or the left hand side of 2c, or the right hand side of 2c, or the left hand side of 2d, or the right hand side of 2d. Alternatively, the fluid handling system may be provided with any combination of features from these figures at different locations around the circumference. The fluid handling system may comprise the fluid handling structure 12 as described in the variations below.

[0046] Figure 2a shows a fluid handling system comprising a fluid handling structure 12 around the bottom surface of the final element 100. The final element 100 has an inverted frusto-conical shape. The frusto-conical shape having a planar bottom surface and a conical surface. The frusto-conical shape protrudes from a planar surface and having a bottom planar surface. The bottom planar surface is the optically active portion of the bottom surface of the final element 100, through which the radiation beam B may pass. The final element 100 may have a coating 30. The fluid handling structure 12 surrounds at least part of the frusto-conical shape. The fluid handling structure 12 has an inner-surface which faces towards the conical surface of the frusto-conical shape. The inner-surface and the conical surface may have complementary shapes. A top surface of the fluid handling structure 12 may be substantially planar. The fluid handling structure 12 may fit around the frusto-conical shape of the final element 100. A bottom surface of the fluid handling structure 12 may be substantially planar and in use the bottom surface may be parallel with the facing surface of the substrate support WT and / or substrate W. Thus, the bottom surface of the fluid handling structure 12 may be referred to as a surface facing the surface of the substrate W. The distance between the bottom surface and the facing surface may be in the range of 20 to 500 micrometers, desirably in the range of 70 to 200 micrometers.

[0047] The fluid handling structure 12 extends closer to the facing surface of the substrate W and substrate support WT than the final element 100. The immersion space 11 is therefore defined between the inner surface of the fluid handling structure 12, the planar surface of the frusto-conical portion and the facing surface. During use, the immersion space 11 is filled with immersion liquid. The immersion liquid fills at least part of a buffer space between the complementary surfaces between the final element 100 and the fluid handling structure 12, in an embodiment at least part of the space between the complementary inner-surface and the conical surface.

[0048] The immersion liquid is supplied to the immersion space 11 through an opening formed in a surface of the fluid handling structure 12. The immersion liquid may be supplied through a supply opening 20 in the inner-surface of the fluid handling structure 12. Alternatively or additionally, the immersion liquid is supplied from an under supply opening 23 formed in the bottom surface of the fluid handling structure 12. The under supply opening 23 may surround the path of the radiationbeam B and it may be formed of a series of openings in an array or a single slit. The immersion liquid is supplied to fill the immersion space 11 so that flow through the immersion space 11 under the projection system PS is laminar. The supply of the immersion liquid from the under supply opening 23 additionally reduces the ingress of bubbles into the immersion space 11. This supply of the immersion liquid may function as a liquid seal.

[0049] The immersion liquid may be recovered from a recovery opening 21 formed in the inner- surface. The recovery of the immersion liquid through the recovery opening 21 may be by application of an underpressure; the recovery through the recovery opening 21 as a consequence of the velocity of the immersion liquid flow through the immersion space 11 ; or the recovery may be as a consequence of both. The recovery opening 21 may be located on the opposite side of the supply opening 20, when viewed in plan. Additionally or alternatively, the immersion liquid may be recovered through an overflow recovery 24 located on the top surface of the fluid handling structure 12. The supply opening 20 and recovery opening 21 can have their function swapped (i.e. the flow direction of liquid is reversed). This allows the direction of flow to be changed depending upon the relative motion of the fluid handling structure 12 and substrate W.

[0050] Additionally or alternatively, immersion liquid may be recovered from under the fluid handling structure 12 through a recovery opening 25 formed in its bottom surface. The recovery opening 25 may serve to hold a meniscus 33 of the immersion liquid to the fluid handling structure 12. The meniscus 33 forms between the fluid handling structure 12 and the facing surface and it serves as border between the liquid space and the gaseous external environment. The recovery opening 25 may be a porous plate which may recover the immersion liquid in a substantially single phase flow. The recovery opening in the bottom surface may be a series of pinning openings 32 through which the immersion liquid is recovered. The pinning openings 32 may recover the immersion liquid in a two phase flow.

[0051] Optionally radially outward, with respect to the inner-surface of the fluid handling structure 12, is a gas knife opening 26. Gas may be supplied through the gas knife opening 26 at elevated speed to assist liquid confinement of the immersion liquid in the immersion space 11. The supplied gas may be humidified and it may contain substantially carbon dioxide. Radially outward of the gas knife opening 26 is a gas recovery opening 28 for recovering the gas supplied through the gas knife opening 26.

[0052] Further openings, for example open to atmosphere or to a gas source or to a vacuum, may be present in the bottom surface of the fluid handling structure 12, i.e. in the surface of the fluid handling structure 12 facing the substrate W. An example of such an optional further opening 50 is shown in dashed lines on the right hand side of Figure 2a. As shown, the further opening 50 may be a supply or extraction member, which is indicated by the double-headed arrow. For example, if configured as a supply, the further opening 50 may be connected to a liquid supply or a gas supply as with any of the supply members. Alternatively, if configured as an extraction, the further opening 50 may be used toextract fluid, and may for example, be connected to atmosphere or to a gas source or to a vacuum.For example, the at least one further opening 50 may be present between gas knife opening 26 and gas recovery opening 28, and / or between pinning openings 32 and gas knife opening 26.

[0053] The two different versions of the fluid handling structure 12 of the left and right sides of Figure 2a pin the meniscus 33. The version of the fluid handling structure 12 on the right hand side of Figure 2a may pin the meniscus 33 at a position that is substantially fixed with respect to the final element 100, due to the fixed position of the pinning opening 32. The version of the fluid handling structure 12 on the left hand side of Figure 2a may pin the meniscus 33 below the recovery opening 25, and thus the meniscus 33 may move along the length and / or width of the recovery opening 25. For the radiation beam B to be directed to a full side of the substrate W under exposure, the substrate support WT supporting the substrate W is moved relative to the projection system PS. To maximize the output of substrates W exposed by the lithographic apparatus, the substrate support WT (and so substrate W) is moved as fast as possible. However, there is a critical relative speed (often referred to as a critical scan speed) above which the meniscus 33 between the fluid handling structure 12 and the substrate W becomes unstable. An unstable meniscus 33 has a greater risk of losing immersion liquid, for example in the form of one or more droplets. Furthermore, an unstable meniscus 33 has a greater risk of resulting in the inclusion of gas bubbles in the immersion liquid, especially when the confined immersion liquid crosses the edge of the substrate W.

[0054] A droplet present on the surface of the substrate W may apply a thermal load and may be a source of defectivity. The droplet may evaporate leaving a drying stain, it may move transporting contamination such as a particle, it may collide with a larger body of immersion liquid introducing a bubble of gas into the larger body and it may evaporate, applying the thermal heat load to the surface on which it is located. Such a thermal load could be a cause of distortion and / or a source of a positioning error if the surface is associated with positioning of components of the lithographic apparatus relative to the substrate W being imaged. A formation of a droplet on a surface is therefore is undesirable. To avoid formation of such a droplet, the speed of the substrate support WT is thus limited to the critical scan speed at which the meniscus 33 remains stable. This limits the throughput of the lithographic apparatus.

[0055] The left hand side of the fluid handling structure 12 in Figure 2a may comprise a spring 60. The spring 60 may be an adjustable passive spring configured to apply a biasing force to the fluid handling structure 12 in the direction of the substrate W. Thus, the spring 60 can be used to control the height of the fluid handling structure 12 above the substrate W. Such adjustable passive springs are described in US 7,199,874 which is herein incorporated by reference in its entirety. Other bias devices may also be appropriate, for example, using an electromagnetic force. Although the spring 60 is shown with the left hand side of Figure 2a, it is optional and does not need to be included with the other features of the left hand side of Figure 2a. The spring 60 is not shown on any of the otherfigures, but could also be included with the other variations of the fluid handling structure 12 described in relation to Figures 2a, 2b, 2c, or 2d.

[0056] Figure 2b shows two different versions of the fluid handling structure 12 on its left side and on its right side, which allow movement of the meniscus 33 with respect to the final element 100. The meniscus 33 may move in the direction of the moving substrate W. This decreases the relative speed between the meniscus 33 and the moving substrate W, which may result in improved stability and a reduced risk of breakdown of the meniscus 33. The speed of the substrate W at which the meniscus 33 breaks down is increased so as to allow faster movement of the substrate W under the projection system PS. Throughput is thus increased.

[0057] Features shown in Figure 2b which are common to Figure 2a share the same reference numbers. The fluid handling structure 12 has an inner surface which complements the conical surface of the frusto-conical shape. The bottom surface of the fluid handling structure 12 is closer to the facing surface than the bottom planar surface of the frusto-conical shape.

[0058] Immersion liquid is supplied to the immersion space 11 through supply openings 34 formed in the inner surface of the fluid handling structure 12. The supply openings 34 are located towards the bottom of the inner surface, perhaps below the bottom surface of the frusto-conical shape. The supply openings 34 are located around the inner surface, spaced apart around the path of the radiation beam B.

[0059] Immersion liquid is recovered from the immersion space 11 through recovery openings 25, in the bottom surface of the fluid handling structure 12. As the facing surface moves under the fluid handling structure 12, the meniscus 33 may migrate over the surface of the recovery opening 25 in the same direction as the movement of the facing surface. The recovery openings 25 may be formed of a porous member. The immersion liquid may be recovered in single phase. The immersion liquid may be recovered in a two phase flow. The two phase flow is received in a chamber 35 within the fluid handling structure 12 where it is separated into liquid and gas. The liquid and gas are recovered through separate channels 36, 38 from the chamber 35.

[0060] An inner periphery 39 of the bottom surface of fluid handling structure 12 extends into the immersion space 11 away from the inner surface to form a plate 40. The inner periphery 39 forms a small aperture which may be sized to match the shape and size of the radiation beam B. The plate 40 may serve to isolate the immersion liquid at either side of it. The supplied immersion liquid flows inwards towards the aperture, through the inner aperture and then under the plate 40 radially outwardly towards the surrounding the recovery openings 25.

[0061] The fluid handling structure 12 may be in two parts as shown on the right hand side of Figure 2b: an inner part 12a and an outer part 12b. The inner part 12a and the outer part 12b may move relatively to each other, mainly in a plane parallel to facing surface. The inner part 12a may have the supply openings 34 and it may have the overflow recovery 24. The outer part 12b may havethe plate 40 and the recovery opening 25. The inner part 12a may have an intermediate recovery 42 for recovering the immersion liquid which flows between the inner part 12a and the outer part 12b.

[0062] The two different versions of the fluid handling structure 12 of Figure 2b thus allow for movement of the meniscus 33 in the same direction as the substrate W, enabling faster scan speeds and increased throughput of the lithographic apparatus. However, the migration speed of meniscus 33 over the surface of the recovery opening 25 in the fluid handling structure 12 of the left side of Figure 2b may be slow. The fluid handling structure 12 of the right side of Figure 2b allows for quicker movement of the meniscus 33, by moving the outer part 12b with respect to the inner part 12a and the final element 100. However, it may be difficult to control the intermediate recovery 42 so as to ensure that enough immersion liquid is provided between the inner part 12a and the outer part 12b to prevent contact therebetween.

[0063] Figure 2c shows two different versions of the fluid handling structure 12 on its left side and on its right side, which may be used to pin the meniscus 33 of the immersion liquid to the fluid handling structure 12 as described above in relation to Figures 2a and / or 2b. Features shown in Figure 2c which are common to Figures 2a and / or 2b share the same reference numbers.

[0064] The fluid handling structure 12 has an inner surface which compliments the conical surface of the frusto-chronical shape. The bottom surface of the fluid handling structure 12 is closer to the facing surface than the bottom planar surface of the frusto-chronical shape. Immersion liquid is supplied to the immersion space 11 delivered through an opening formed in a surface of the fluid handling structure 12. The immersion liquid may be supplied through a supply opening 34 in the inner surface of the fluid system 12. Alternatively or additionally, the immersion liquid may be supplied through a supply opening 20 in the inner surface of the fluid system 12. Alternatively or additionally, the immersion liquid is supplied through the under supply opening 23. The immersion liquid may be recovered via an extraction member, for example, via recovery opening 21 formed in the inner-surface and / or overflow recovery 24 and / or one or more openings in a surface of the fluid handling structure 12 as described below.

[0065] The two different versions of the fluid handling structure 12 of the left and right sides of Figure 2c pin the meniscus 33. The version of the fluid handling structure 12 on the right hand side of Figure 2c may pin the meniscus 33 at a position that is substantially fixed with respect to the final element 100, due to the fixed position of the recovery opening 32a. The version of the fluid handling structure 12 on the left hand side of Figure 2c may pin the meniscus 33 below the recovery opening 25, and thus the meniscus 33 may move along the length and / or width of the recovery opening 25.

[0066] As described above in relation to Figure 2b, an inner periphery of the bottom surface of fluid handling structure 12 may extends into the immersion space 11 away from the inner surface to form a plate 40 as shown on the left hand side. As described above, this may form a small aperture, and may isolate the immersion liquid at either side and / or cause immersion liquid to flow inwards towards the aperture, through the inner aperture and then under the plate 40 radially outwardly towards thesurrounding the recovery openings 25. Although this features is shown on the left hand side in Figure 2c, it is optional in combination with the other features shown. Preferably, as shown on the left hand side, immersion liquid is supplied to the immersion space 11 through supply openings 34 formed in the inner surface of the fluid handling structure 12. The supply openings 34 are located towards the bottom of the inner surface, perhaps below the bottom surface of the frusto-conical shape. The supply openings 34 are located around the inner surface, spaced apart around the path of the radiation beam B. Alternatively or additionally, the immersion liquid may be supplied through a supply opening 20 in the inner surface of the fluid system 12. Alternatively or additionally, the immersion liquid is supplied through the under supply opening 23. Although the supply openings 34 are the preferred liquid supply, any combination of supply openings 34, supply openings 20 and / or under supply openings 23 may be provided.

[0067] As shown on the left hand side of Figure 2c, the fluid handling system may comprise the fluid handling structure 12 as described above and a further device 3000. The fluid handling structure 12 may have an extraction member, such as recovery opening 25, and a liquid supply opening, such as the under supply opening 23. It will be understood that the fluid handling structure 12 may comprise any configuration as disclosed in relation to the left hand of Figure 2a, the right hand side of Figure 2a, the left hand side of Figure 2b, the right hand side of Figure 2b or (as described below) the right hand side of Figure 2c, in combination with the further device 3000.

[0068] The further device 3000 may otherwise be referred to as a droplet catcher. The further device 3000 is provided to reduce occurrence of liquid on the surface of the substrate W after the fluid handling structure 12 has moved over the surface. The further device 3000 may comprise a liquid supply member 3010 and at least one extraction member 3020. The at least one extraction member 3020 may be formed in a shape surrounding the at least one supply member 3010 in plan. The at least one liquid supply member 3010 may be configured to provide a further liquid to a space 3110 between at least a part of the further device 3000 and the surface of the substrate W. The further device 3000 may be configured to recover at least some of the liquid via the at least one extraction member 3020. The further device 3000 may be used to incorporate any liquid left on the surface of the substrate W with the liquid in the space 3110 and then use the further device 3000 to extract the liquid such that the amount of liquid remaining on the surface of the substrate W is reduced.

[0069] The further device 3000 is shown as a separate device from the fluid handling structure 12 in Figure 2c. The further device 3000 may be positioned adjacent to the fluid handling structure 12. Alternatively, the further device 3000 may be part of, i.e. integral to, the fluid handling structure 12.

[0070] The further device 3000 may be configured to provide a liquid to the space 3110 which is separate from the liquid provided by the fluid handling structure 12.

[0071] Additionally or alternatively, the fluid handling structure 12 may have the components as shown on the right hand side of Figure 2c. More specifically, the fluid handling structure 12 may comprise the at least one liquid supply member, two extraction members (e.g., recovery openings 32aand 32b) and two gas supply members (e.g., gas supply openings 27a and 27b) formed on the surface of the fluid handling structure 12. Gas supply opening 27a can be omitted, i.e. is optional. The at least one liquid supply member may be the same as the under supply opening 23 in the bottom surface of the fluid handling structure 12 described above or the supply opening 20 or liquid supply openings 34 formed on the inner surface of the fluid handling structure 12 described in relation to left hand side of Figure 2b. The liquid supply member, the extraction members and the gas supply members may be formed on the surface of the fluid handling structure 12. Specifically, these components may be formed on a surface of the fluid handling structure 12 facing the substrate W, i.e. the bottom surface of the fluid handling structure 12.

[0072] At least one of the two extraction members may comprise a porous material 37 therein. The porous material 37 may be provided within an opening, e.g., recovery opening 32a through which fluid handling structure 12 extracts fluid from below the fluid handling structure 12 and may recover the immersion liquid in a single phase flow. The other of the two extraction members, e.g., recovery opening 32b may recover the immersion fluid as a dual phase extractor. The porous material 37 does not need to be flush with the bottom surface of the fluid handling structure 12.

[0073] Specifically, the fluid handling structure 12 may comprise the liquid supply member (e.g., under supply opening 23), with a first extraction member (e.g., recovery opening 32a) radially outwards of the liquid supply member, and a first gas supply member (e.g., gas supply opening 27a) radially outwards of the first extraction member, and the second extraction member (e.g., recovery opening 32b) radially outwards of the first gas supply member, and a second gas supply member (e.g., gas supply opening 27b) radially outwards of the second extraction member. Similar to Figure 2a, further openings, for example open to atmosphere or to a gas source or to a vacuum, may be present in the bottom surface of the fluid handling structure 12 as described previously (in relation to the fluid handling structure 12).

[0074] For example, at least one further opening (not shown) may be provided in the bottom surface of the fluid handling structure 12. The further opening is optional. The further opening may be arranged between the first extraction member (e.g., recovery opening 32a) and the first gas supply member (e.g., gas supply opening 27a) as described in the arrangement above. Alternatively or additionally, the further opening may be arranged between the second extraction member (e.g., recovery opening 32b) and the second gas supply member (e.g., gas supply opening 27b) as described in the arrangement above. The further opening may be the same as further opening 50 described above.

[0075] Optionally, the fluid handling structure 12 comprises a recess 29. The recess 29 may be provided between the recovery opening 32a and recovery opening 32b or gas supply opening 27a and recovery opening 32b. The shape of the recess 29 may be uniform around the fluid handling structure 12 and may optionally contain an inclined surface. In the case of the recess 29 provided between the recovery opening 32a and recovery opening 32b, the gas supply opening 27b may be provided on theinclined surface as shown in Figure 2c. In the case of the recess 29 provided between the supply opening 27a and recovery opening 32b, the gas supply opening 27b may be provided on the inclined surface or a part of the bottom surface of the fluid handling structure 12 which is parallel to the surface of the substrate W. Alternatively, the shape of the recess 29 may vary around the circumference of the fluid handling structure 12. The shape of the recess 29 may be varied to alter the impact of gas supplied from the gas supply members on the fluid below the fluid handling structure 12.

[0076] Figure 2d shows, in its left and right halves, two different versions of the fluid handling structure 12. The fluid handling structure 12 of the left half of Figure 2d has a liquid injection buffer 41a, which holds a buffer amount of immersion liquid, and liquid injection holes 41 which supply immersion liquid from the liquid injection buffer to the immersion space 11. Outwardly of the liquid injection holes 41 are inner liquid recovery apertures 43 for conducting liquid to an inner recovery buffer 43a which is provided with a porous member. A recess 29 similar to that described relating to Figure 2c is provided outward of the inner liquid recovery apertures 43. Outward of the recess 29, in the lower face of the fluid handling structure 12 is a gas guiding groove 44 into which open outer recovery holes 44a. The outer recovery holes 44a lead a two-phase recovery flow to outer recovery buffer 44b which is also provided with a porous member. Outermost are gas sealing holes 45 which communicate between a gas sealing buffer volume 45a and the space underneath the fluid handling structure 12 to provide a gas flow to contain the immersion liquid.

[0077] The fluid handling structure 12 of the right half of Figure 2d has a liquid supply opening 20 in the inner inclined face thereof. In the underside of the fluid handling structure 12 there are (from inner side to outer side) an extraction opening 25 provided with a porous member 37; a first gas knife opening 26a, a second gas knife opening 26b and a third gas knife opening 26c. Each of these openings opens into a groove in the underside of the fluid handling structure 12 that provides a buffer volume. The outermost part of the fluid handling structure 12 is stepped so as to provide a greater separation between the fluid handling structure 12 and the substrate W.

[0078] Figures 2a-2d show examples of different configurations which can be used as part of a fluid handling structure 12. It will be understood that the examples provided above refer to specific extraction members and recovery members, but it is not necessary to use the exact type of extraction member and / or recovery member. In some cases different terminology is used to indicate the position of the member, but the same functional features may be provided. Examples of the extraction member referred to above include recovery opening 21, overflow recover 24, recovery opening 25 (possibly comprising a porous plate and / or the chamber 35), gas recovery opening 28, pinning opening 32, recovery opening 32a, recovery opening 32b and / or the intermediate recovery 42. Examples of the supply member referred to above include supply opening 20, under supply opening 23, gas knife opening 26, gas supply opening 27a, gas supply opening 27b, and / or supply openings 34. In general, an extraction member used to extract / recover fluid, liquid or gas is interchangeablewith at least any of the other examples used which extract / recover fluid, liquid or gas respectively. Similarly, a supply member used to supply fluid, liquid or gas is interchangeable with at least any of the other examples used which supply fluid, liquid or gas respectively. The extraction member may extract / recover fluid, liquid or gas from a space by being connected to an underpressure which draws the fluid, liquid or gas into the extraction member. The supply member may supply fluid, liquid or gas to the space by being connected to a relevant supply.

[0079] As mentioned in the introductory part of the description, there is a need to provide a relatively simple configuration with a small form factor to accurately control gas flow, so that it can be easily incorporated into a fluid handling structure 12.

[0080] The following embodiments described below address these issues. There is provided a fluid handling structure 12 which reduces or prevents these problems.

[0081] According to the present disclosure, there is provided a fluid handling system comprising a fluid handling structure configured to at least partly confine a liquid to an immersion space between a final optical element and a substrate.

[0082] According to the present disclosure, there is provided a fluid handling structure 12 configured to at least partly confine a gas to an immersion space 11 between a final element 100 of a projection system PS and a substrate W, comprising: a gas knife 60 comprising a gas channel configured to supply a gas flow towards the substrate W via a gas channel opening or a gas knife opening 61; and a chamber 71 configured to define a control volume 70 fluidically connected to the gas knife 60, the chamber 71 being actuatable to vary a flow rate of the gas via the gas knife opening 61 by varying a size of the control volume 70. According to the present disclosure, a simple configuration for providing a temporary increase / decrease of gas is provided.

[0083] An example embodiment is shown on Figure 3. The structure shown in Figure 3 may be configured to be used in combination with embodiments of fluid handling structures 12 shown in Figures 2a-2d, for example, gas knife 60 comprising gas knife opening 61 shown on Figure 3 may correspond to gas knife comprising the gas knife opening 26 on Figure 2a.

[0084] The chamber 71 defines a control volume 70. The chamber 71 is actuatable to vary a flow rate of the gas via the as knife opening 61 by varying a size of the control volume 70. The change in control volume 70 corresponds to the change in gas flow in the gas knife 60. By actuating the chamber 71 so that the control volume 70 is changed, the flow rate of the gas can be controlled with a high level of precision.

[0085] The chamber 71 has a small form factor and may be easily incorporated into a fluid handling structure 12. The chamber 71 may be incorporated such that it is relatively close to the gas knife opening 61. When chamber 71 is actuated, a time delay in the change of gas flow out of the gas knife opening 61 is low. This is advantageous over systems in which a gas flow control means is located further away from the gas knife opening 61. Furthermore, better management of gas can be achieved, as no additional external reservoir of gas is needed to provide an additional flow of gas.

[0086] According to an embodiment, the chamber 71 is actuatable to reduce the size of the control volume 70 to cause a temporary increase in the flow rate.

[0087] According to an embodiment, the chamber 71 is actuatable to increase the size of the control volume 70 to cause a temporary decrease in the flow rate.

[0088] Control volume 70 may be changed by actuation of the chamber 71 to provide a temporary increase in gas flow rate (such as an extra gas pulse) or a temporary decrease in gas flow rate. A change in the control volume 70 corresponds to the additional volume of gas temporarily supplied to the gas knife 60. For example, a decrease in the control volume 70 provides an extra “pulse” of gas. For example, an increase in the control volume 70 provides a temporary decrease in the flow of gas. By actuating the chamber 71 so that the control volume 70 is changed, the volume of gas which is temporarily introduced into / removed from the gas flow can be controlled with precision. By disposing chamber 71 in the gas channel of the gas knife 60, improved management of gas flow can be achieved without the need for an external reservoir.

[0089] It is possible to repeatedly actuate the chamber 71 to provide an oscillatory gas flow.During a lithographic processing step, it may be desirable to provide an additional pulse of gas flow out of the gas knife opening 61 for a short period of time. This may be advantageous when the fluid handling structure 12 crosses an edge of the substrate W, to reduce or prevent loss of the immersion liquid (referred to as “liquid” for brevity) from the immersion space 11 onto other regions of the substrate W. By providing an additional pulse of gas flow when the fluid handling structure 12 crosses an edge of substrate W, immersion liquid is confined to the immersion space 11 even when the fluid handling structure 12 crosses an edge of substrate W. This may prevent loss of immersion liquid from the immersion space 11 onto other regions of the substrate W. Furthermore, it may be advantageous to provide an additional pulse of gas flow during substrate processing, when the fluid handling structure 12 does not cross an edge of the substrate W. According to the present disclosure, this can be easily achieved by actuating the chamber 71 to reduce the control volume 70.

[0090] During a lithographic processing step, it may be desirable to temporarily reduce the flow of gas for a short period of time. According to the present disclosure, this can be easily achieved by actuating chamber 71 to increase the control volume 70. It may be suitable to provide a temporary reduction in gas flow, if droplets of immersion liquid have been formed on the surface of substrate W. As explained above, formation of droplets of immersion liquid on the substrate surface is undesirable for a number of reasons. Providing a temporary precise reduction in gas flow may allow the droplets to merge with the immersion liquid in the immersion space 11, thereby reducing the presence of droplets of immersion liquid, thereby alleviating the problems above. Accordingly, the throughput of the lithographic apparatus is improved and immersion liquid handling is more efficient.

[0091] It may be desirable to oscillate the flow of gas out of the gas knife opening 61. This can be done by period actuation of the chamber 71. This may be advantageous during a lithographicprocessing step in which the substrate W moves relative to the fluid handling structure 12 in a meandering motion.

[0092] Actuation of the chamber 71 can be performed by any suitable means, and examples of actuation of the chamber 71 are described below. The fluid handling structure 12 may comprise a moveable member and the fluid handling structure 12 may be configured to actuate the chamber 71 by driving movement of the moveable member. The moveable member may be within the chamber 71. The moveable member may comprise a piston 80 driveable along an axis of the chamber 71.

[0093] An example of an embodiment of the present disclosure is shown schematically on Figure 3. This embodiment comprises a piston 80. Movement of the piston 80 within chamber 71 causes a change in the control volume 70.

[0094] Another example of an embodiment of the present disclosure is shown on Figure 4. In the example shown on Figure 4, the moveable member comprises an inflatable balloon 81.

[0095] In another embodiment, the chamber 71 comprises a membrane (not shown) configured such that deformation of the membrane causes a change in the volume of the control volume 70. The chamber 71 may have parts of its wall defined by a membrane, one of the walls may be define by a membrane, or multiple regions of the chamber 71 may be defined by a membrane. According to this embodiment, actuation of the chamber 71 may be performed by applying a different pressure to a region outside the chamber 71 than the pressure inside the control volume 70. For example, applying a higher pressure outside of the chamber 71 than inside the chamber 71 will cause the control volume 70 to reduce.

[0096] The membrane may be actuated by an actuator (not shown) disposed outside the chamber 71.

[0097] The moveable member may be an inflatable balloon 81, which may be disposed inside the chamber 71 as shown on Figure 4. According to this embodiment, when the balloon 81 is inflated, the size of the control volume 70 is reduced. This embodiment may be particularly advantageous when a relatively slow additional pulse of gas flow is required, because the balloon 81 may be inflated at a relatively slow rate. The balloon 81 may nevertheless be configured to be inflatable to a predetermined volume, so that the additional pulse of gas flow is of a predetermined total volume. After inflation, chamber 71 may be actuated to reduce the control volume 70, by deflating the balloon 81 at an appropriate time to temporarily decrease the gas flow rate. The rate of inflation and / or deflation of balloon 81 may be predetermined. Alternatively, the rate of inflation and / or deflation of balloon 81 may be variable, based on parameters of a lithographic processing step.

[0098] Reference is now made to Figures 5a, 5b, 5c and 5c. These figures show some possible locations of the chamber 71 relative to the gas knife 60, however, other possible configurations are available which are not shown in Figures 5a-5d.

[0099] Further embodiments of the present disclosure may comprise one or more additional chambers disposed in the gas knife channel (for example, a second chamber, a third chamber, asexplained below). Any of these additional chambers may comprise the same features described above with reference to the chamber 71.

[0100] According to an embodiment of the present disclosure the chamber is a first chamber and the control volume is a first control volume, and the fluid handling structure 12 further comprises a second chamber configured to define a second control volume fluidically connected to a gas channel of the gas knife 60 upstream of the first control volume, the second chamber being actuatable to vary a flow rate of the gas via the gas channel opening (also may be referred to as “gas knife opening” 61) by varying a size of the second control volume. An example of this embodiment is shown on Figure 6.

[0101] The embodiment on Figure 6 shows an example comprising a first chamber 71a and a second chamber 71b disposed along the length of the gas channel of the gas knife 60. In the embodiment shown on Figure 6, the maximum size of the control volumes 70a and 70b is different. Therefore, actuation of first chamber 71a may increase the flow of gas in the gas knife 60 by a first amount and actuation of the second chamber 7 lb may increase the flow of gas by a second amount. This provides a convenient way to provide additional pulses of two predetermined amounts.

[0102] Alternatively, a chamber (such as a first chamber, second chamber or a third chamber, as defined later) may be configured such that the chamber is actuated partially. For example, a piston 80 may only be moved half-way when a chamber is actuated. Accordingly, an additional pulse of gas may be provided which corresponds to half of the maximum control volume.

[0103] The first chamber 71a and the second chamber 71b may have different maximum sizes of the respective control volumes 70a, 70b, such as in the example shown on Figure 6. Alternatively, the first chamber 71a and the second chamber 71b may have the same maximum size of the respective control volumes 70a, 70b.

[0104] The number of chambers disposed along the length of the gas channel of the gas knife 60is not limited and may be greater than two. The fluid handling structure 12 may further comprise a plurality of further chambers (not shown) arranged upstream of the second chamber 7 lb, wherein each of the plurality of further chambers defines a respective control volume, each of the plurality of further chambers being actuatable to vary a flow rate of the gas via the gas channel opening or gas knife opening 61 by varying a size of the respective control volume of the further chamber. The total number of chambers disposed along the length of the gas channel of the gas knife 60 may be four, for example.

[0105] In an embodiment, the chamber is a first chamber 71a and the control volume is a first control volume 71a, and the fluid handling structure 12 further comprises a third chamber 71c configured to define a third control volume 70c fluidically connected to the gas channel of the gas knife 60, the third chamber 71c being actuatable to vary a flow rate of the gas fluid via the gas channel opening or gas knife opening 61 by varying a size of the third control volume 70c, wherein the first chamber 70a has a first chamber opening facing into the gas channel, and the third chamber71c has a third chamber opening facing into the gas channel; and the third chamber opening at least partially faces the first chamber opening. The first chamber 71a and the third chamber 71c may be referred to as opposing chambers for brevity. Examples of this configuration are shown on Figure 7a and Figure 7b.

[0106] The terms first chamber, second chamber and third chamber are used as labels and do not necessarily imply consecutive numbering of chambers. For example, in an embodiment the fluid handling structure 12 comprises a first chamber and a third chamber but no second chamber.

[0107] The first chamber 71a and the third chamber 71c may be actuated one at a time, or may be actuated simultaneously. Actuating any one chamber 71a, 71c may generate disturbance forces due to movement of the moveable member relative to the fluid handling structure 12, which may be undesirable. This is because disturbance forces may affect movement of the fluid handling structure 12 relative to the substrate W.

[0108] The first chamber 71c may be actuatable by driving movement of a first chamber moveable member 80a along a first chamber actuation axis and the third chamber 71c is actuatable by driving movement of a third chamber moveable member 80c along a third chamber actuation axis, wherein the third chamber actuation axis is substantially parallel to the first chamber actuation axis, wherein optionally the directions of movement of the first chamber moveable member 80a and the third chamber moveable member 80c are opposite to each other.

[0109] According to an embodiment comprising opposing chambers (such as the embodiments shown on Figure 7a and 7b), facing chambers may be actuated simultaneously so that the generated disturbance forces are equal and opposite. Accordingly, the opposing forces cancel each other out and no disturbance is generated in the fluid handling structure 12.

[0110] The embodiment on Figure 7a shows that the opening of the first chamber 71a and the opening of the third chamber 71c are centred along a vertical axis. The disturbance forces generated by actuation of the opposing chambers are generated in the vertical direction. When these opposing chambers are actuated simultaneously, the disturbance forces generated by the first chamber 71a cancels out the disturbance forces generated by the third chamber 71c.

[0111] The embodiment on Figure 7a shows that the opening of the first chamber 71a and the opening of the third chamber 71c are centred along the same axis. However, this is not necessarily the case. The opening of the first chamber 71a and the opening of the third chamber 71c may be centred along parallel vertical axes. The opposing chambers are not necessarily aligned along a vertical axis, and may be aligned along a different axis.

[0112] The embodiment shown on Figure 7b shows an alternative configuration, in which the opening of the first chamber 71a and the opening of the third chamber 71c are centred along a horizontal axis. The disturbance forces generated by actuation of the opposing chambers are generated in the horizontal direction. When these opposing chambers are actuated simultaneously, thedisturbance forces generated by the first chamber 71a cancels out the disturbance forces generated by the third chamber 71c.

[0113] The embodiment on Figure 7a shows that the opening of the first chamber 71a and the opening of the third chamber 71c are centred along the same axis. However, this is not necessarily the case. The opening of the first chamber 71a and the opening of the third chamber 71c may be centred along parallel horizontal axes. The opposing chambers are not necessarily aligned along a horizontal axis, and may be aligned along a different axis.

[0114] The embodiments shown on Figures 7a and Figures 7b comprise a first moveable member (e.g., piston) 80a disposed in the first chamber 71a and a third moveable member (piston) 80c disposed in the third chamber 71c. However, other moveable members may be used, such as the examples described to the chamber 70.

[0115] For example, a first moveable member 80a and / or a third moveable member 80c may each be configured to actuate the chamber by driving movement of the first / third moveable member 80a, 80c, as shown in Figure 7a and Figure 7b. The first / third moveable member 80a, 80c may be within the chamber. The first / third moveable member 80a, 80c may comprise a piston driveable along an axis of the first / third chamber 71a, 71c respectively.

[0116] In an embodiment, the first chamber 71a and the third chamber 71c are configured such that the first control volume 70a and the third control volume 70c have substantially the same maximum size. According to this configuration, when the chambers 71a, 71c are actuated, the generated forces are equal and opposite, so there are no net disturbance forces acting on the fluid handling structure 12. However, the maximum size of the respective control volumes 70a, 70c of the opposing chambers 71a, 71c need not be the same to achieve the effect of reducing or eliminating the disturbance forces. The opposing chambers may have a different size and shape, however, they may be configured such that actuation of each chamber 71a, 71c results in equal and opposite disturbance forces which cancel each other out.

[0117] In an embodiment (not shown in the figures), there may be more than two opposing chambers disposed in a plane perpendicular to a longitudinal axis of the gas channel of the gas knife 60. The longitudinal axis of the gas channel of the gas knife 60 is an axis along which gas is transported. For example, three opposing chambers may be disposed, optionally, the chambers may be the same size and disposed at 120 ° intervals around the gas channel of the gas knife 60. When the opposing chambers are actuated, the generated forces balance, so there are no net disturbance forces acting on the fluid handling structure 12. Alternatively, the chambers may be arranged at intervals other than 120 °, and may have different respective volumes. Furthermore, the opposing chambers are not necessarily disposed in a plane perpendicular to a longitudinal axis of the gas channel of the gas knife 60, because the opposing chambers may be distributed along the length of the gas channel of the gas knife 60. The number of opposing chambers is not particularly limited and may be three, four, five, six, seven or more. Regardless of the number of opposing chambers, the opposing chambersmay be arranged such that when the opposing chambers are actuated, the generated forces balance so there are no net disturbance forces acting on the fluid handling structure 12.

[0118] Additionally or alternatively, it is possible to actuate each of the opposing chambers one at a time.

[0119] The first moveable member 80a and the third moveable member 80c may be configured to vary the volume of the first chamber 71a and third chamber 71c simultaneously in such a way that the first control volume 70a and the third control volume 70c are the same during a range of degrees of actuation of the first chamber 71a and third chamber 71c.

[0120] The number of opposing chambers disposed along the length of the gas channel of the gas knife 60 is not particularly limited, and a plurality of further opposing chambers may be provided along the gas channel of the gas knife 60. For example, the embodiment shown on Figure 6 may comprise additional chambers (not shown) disposed along the gas channel of the gas knife 60, wherein each of the additional chambers have a respective opening facing into the gas channel and at least partially facing an opening of the opposing first chamber 71a and second chamber 71b.

[0121] The number of opposing chambers is not particularly limited and may comprise more than two sets of opposing chambers.

[0122] Opposing chambers 71a, 71c may be configured such that disturbance forces generated when the first chamber 71a and the third chamber 71c are actuated are equal and opposite. The configuration of the opposing chambers 71a, 71c may not be limited to the examples shown on Figures 7a and 7b.

[0123] Each of the one or more of the chamber, the first chamber 71a, the second chamber 71b, the third chamber 71c and the plurality of further chambers may be configured to be actuated in an oscillatory manner, optionally sinusoidally.

[0124] The fluid handling structure 12 may be configured to actuate the chamber 71, or each of one or more of the first chamber 71a, the second chamber 71b, the third chamber 71c and the plurality of further chambers to increase the gas flow through each of the said chambers, when the opening of the chamber 71 is adjacent to a peripheral edge of the substrate W during movement of the substrate W relative to the fluid handling structure 12. This may lead to a reduction of immersion liquid loss at the substrate edge when the fluid handling structure 12 crosses an edge of the substrate W.

[0125] The fluid handling structure 12 may further comprise a variable flow valve 91 disposed between the chamber 71 and the gas channel of the gas knife 60. In other words, the variable flow valve 91 may be disposed upstream of the chamber 71. In embodiments of the invention comprising the first chamber 71a, the second chamber 71b, the third chamber 71c or the plurality of further chambers a variable flow vale 91 may be disposed between the first chamber 71a, the second chamber 71b, the third chamber 71c or the plurality of further chambers and the gas channel of the gas knife 60. In other words, the variable flow valve 91 may be disposed upstream of each of the first chamber71a, the second chamber 71b, the third chamber 71c and each of the plurality of further chambers. Accordingly, precise control of gas flow can be achieved and immersion liquid loss may be prevented.

[0126] Reference is now made to Figure 8.

[0127] A fluid handling system may comprise a fluid handling structure 12 configured to at least partly confine an immersion liquid to an immersion space 11 between a final element 100 of a projection system PS and a substrate W, wherein: the fluid handling structure 12 comprises a gas channel configured to supply a gas flow towards the substrate W via a gas channel opening 61; and the fluid handling system comprises: a gas supply line, configured to supply gas to the gas channel; a pressure source 90; and an actuatable flow valve 91 connected between the pressure source 90 and the gas supply line upstream of the gas channel opening 61, wherein the fluid handling system is configured such that when the flow valve 91 is closed a pressure in the gas supply line is different to a pressure of the pressure source 90, such that actuation of the flow valve 91 to at least partially open the flow valve 91 causes a change of gas flow in the gas channel by changing a pressure in the gas supply line. While Figure 8 shows that the gas supply line, the pressure source 90 and the flow valve 91 are disposed outside the fluid handling structure 12, these components may be disposed inside the fluid handling structure 12. The fluid handling structure 12 of the fluid handling system may be the fluid handling structure 12 according to the present disclosure. Accordingly, further control over the flow of gas can be provided.

[0128] According to this embodiment, it is possible to control the gas flow by controlling flow valve 91. This is a relatively simple configuration with a small form factor which may be used to accurately control gas flow, so that it can be easily incorporated into a fluid handling structure 12.

[0129] Figure 8 shows the fluid handling system in a state wherein the flow valve 91 is open. Accordingly, Flow 2 provided by pressure source 90 (when variable flow valve 91 is open) is provided to the gas supply line having Flow 1, so that the total flow out the gas channel opening 61 corresponds to the sum of Flow 1 and Flow 2.

[0130] For example, the flow valve 91 may be opened when the fluid handling structure 12 crosses an edge of the substrate W during a lithographic processing step.

[0131] The pressure source 90 may comprise an overpressure source having a pressure that is higher than the pressure in the gas supply line. By providing an overpressure source and variable flow valve 91, a temporary increase in the gas flow rate can be provided. The overpressure source may have a higher pressure than a pressure in the gas supply line, meaning that opening the variable gas flow valve 91 provides a quick temporary increase in the gas flow in the gas supply line. Accordingly, gas flow in the gas channel 60 can be increased at a quick time scale, with high accuracy (as the difference in pressure may be known).

[0132] In another embodiment, the pressure source 90 may be an underpressure source having a pressure that is lower than the pressure in the gas supply line. According to this embodiment, opening the flow valve 91 causes a decrease in the gas flow in the gas supply line. Providing theunderpressure source may enable the gas flow to be decreased in the gas channel on a short timescale, and allow to control the gas flow in the gas channel with high accuracy.

[0133] The fluid handling system may be configured to recover gas redirected towards the underpressure source during actuation of the flow valve 91 for subsequent use in the gas supply line. Accordingly, the gas may be recycled which prevents gas being unnecessarily wasted. An example of this embodiment is shown on Figure 9. In a further embodiment, the redirected gas may be discarded (labelled “drain” in Figure 9).

[0134] In an embodiment not shown in the figures, the fluid handling system may further comprise a fluid channel configured to supply a fluid flow towards the substrate W via a fluid channel opening; and a fluid chamber configured to define a fluid control volume fluidically connected to the fluid channel, the fluid chamber being actuatable to vary a flow rate of the fluid via the fluid channel opening by varying a size of the fluid control volume. Accordingly, the inventive concept of a chamber defining a control volume may be applied to a channel which supplies a fluid such as a liquid to the substrate W, for example, to liquid supply having under supply opening 23 shown on Figure 2a. The liquid may be water, for example. A control chamber connected to a fluid supply channel may be configured to have the same features as any of the control chambers connected to a gas supply channel described in the present disclosure.

[0135] Furthermore, the fluid handling system may comprise a fluid supply line, configured to supply fluid to the fluid channel; a pressure source 90; and an actuatable flow valve 91 connected between the pressure source 90 and the fluid supply line upstream of the fluid channel opening, wherein the fluid handling system is configured such that when the flow valve 91 is closed a pressure in the fluid supply line is different to a pressure of the pressure source, such that actuation of the flow valve 91 to at least partially open the flow valve 91 causes a change of fluid flow in the gas channel by changing a pressure in the fluid supply line. The fluid may be a liquid, such as water.

[0136] Accordingly, a temporary increase or decrease in fluid / liquid flow can be applied to the substrate.

[0137] The fluid channel opening may be disposed between the immersion space 11 and the gas channel opening.

[0138] The present invention may provide a lithographic apparatus. The lithographic apparatus may have any / all of the other features or components of the lithographic apparatus as described above. For example, the lithographic apparatus may optionally comprise at least one or more of a source SO, an illumination system IL, a projection system PS, etc.

[0139] Specifically, the lithographic apparatus may comprise the projection system PS configured to project the radiation beam B towards the region of the surface of a substrate W.

[0140] Although specific reference may be made in this text to the use of a 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 opticalsystems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[0141] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented by 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 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. and in doing that may cause actuators or other devices to interact with the physical world.

[0142] 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 W) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use ambient (non-vacuum) conditions.

[0143] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention, where the context allows, is not limited to optical lithography.

[0144] Embodiments include the following numbered clauses:1. A fluid handling structure configured to at least partly confine an immersion liquid to an immersion space between a final element of a projection system and a substrate, comprising: a gas channel configured to supply a gas flow towards the substrate via a gas channel opening; and a chamber configured to define a control volume fluidically connected to the gas channel, the chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the control volume.2. The fluid handling structure of clause 1, wherein the chamber is actuatable to reduce the size of the control volume to cause a temporary increase in the gas flow rate.3. The fluid handling structure of clause 1 or 2, wherein the chamber is actuatable to increase the size of the control volume to cause a temporary decrease in the gas flow rate.4. The fluid handling structure of clause 2 or 3, wherein the fluid handling structure comprises a moveable member and is configured to actuate the chamber by driving movement of the moveable member.5. The fluid handling structure of clause 4, wherein the moveable member is within the chamber.6. The fluid handling structure of clause 4 or 5, wherein the moveable member comprises a piston drivable along an axis of the chamber.7. The fluid handling structure of clause 4 or 5, wherein the moveable member comprises an inflatable balloon.8. The fluid handling structure of any of clauses 4 to 7, wherein the chamber comprises a membrane configured such that deformation of the membrane causes a change in the volume of the control volume.9. The fluid handling structure of clause 8, wherein the chamber is actuated by deformation of the membrane such that the control volume is reduced.10. The fluid handling structure of clause 9, wherein at least part of the chamber is defined by the membrane, and the membrane is deformed by an actuator disposed outside the chamber.11. The fluid handling structure of clause 9, wherein the membrane is disposed within the chamber, and the membrane is deformed by an actuator disposed within the chamber.12. The fluid handling structure of any preceding clause, wherein the chamber is a first chamber and the control volume is a first control volume, and wherein the fluid handling structure further comprises: a second chamber configured to define a second control volume fluidically connected to the gas channel upstream of the first control volume, the second chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the second control volume.13. The fluid handling structure of clause 12, wherein the first control chamber and the second control chamber are configured such that the first control volume and the second control volume have different maximum sizes.14. The fluid handling structure of clause 12, wherein the first control chamber and the second control chamber are configured such that the first control volume and the second control volume have the same maximum size.15. The fluid handling structure of any of clauses 12 to 14, further comprising a plurality of further chambers arranged upstream of the second chamber, wherein each of the plurality of further chambers defines a respective control volume, each of the plurality of further chambers being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the respective control volume of the further chamber.16. The fluid handling structure of clause 15, wherein the plurality of further chambers comprises between one and two inclusive.17. The fluid handling structure of any of clauses 1 to 16, wherein the chamber is a first chamber and the control volume is a first control volume, the structure further comprising: a third chamber configured to define a third control volume fluidically connected to the gas channel, the third chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the third control volume, wherein: the first chamber has a first chamber opening facing into the gas channel, and the third chamber has a third chamber opening facing into the gas channel; and the third chamber opening at least partially faces the first chamber opening.18. The fluid handling structure of clause 17, wherein the third chamber is actuatable to reduce the size of the third control volume to cause a temporary increase in the flow rate.19. The fluid handling structure of clause 18, wherein the third chamber has substantially the same size and shape as the first chamber.20. The fluid handling structure of any of clauses 17 to 19, wherein the first chamber is actuatable by driving movement of a first chamber moveable member along a first chamber actuation axis and the third chamber is actuatable by driving movement of a third chamber moveable member along a third chamber actuation axis, wherein the third chamber actuation axis is substantially parallel to the first chamber actuation axis, wherein optionally the directions of movement of the first chamber moveable member and the third chamber moveable member are opposite to each other.21. The fluid handling structure of any of clauses 17 to 20, wherein the first chamber and the third chamber are configured such that the first control volume and the third control volume have substantially the same maximum size.22. The fluid handling structure of any of clauses 17 to 21, wherein the structure comprises a first moveable member which is configured to actuate the first chamber by driving movement of the first member, and a third moveable member which is configured to actuate the third chamber by driving movement of the third member.23. The fluid handling structure of any of clauses 17 to 22, wherein the first moveable member and the third moveable member are configured to vary the volume of the first chamber and third chamber simultaneously in such a way that the first control volume and the third control volume are the same during a range of degrees of actuation of the first chamber and third chamber.24. The fluid handling structure of any of the preceding clauses, wherein the chamber, or each of one or more of the first chamber, the second chamber, the third chamber and the plurality of further chambers, is or are configured to be actuated in an oscillatory manner, optionally sinusoidally.25. The fluid handling structure of any of the preceding clauses, further configured to actuate the chamber, or each of one or more of the first chamber, the second chamber, the third chamber and the plurality of further chambers, when the gas chamber opening is adjacent to a peripheral edge of the substrate during movement of the substrate relative to the structure.26. The fluid handling structure of any of clauses 1 to 11, further comprising a variable flow valve disposed between the chamber and the gas channel.27. A fluid handling system comprising a fluid handling structure configured to at least partly confine an immersion liquid to an immersion space between a final element of a projection system and a substrate, wherein: the fluid handling structure comprises a gas channel configured to supply a gas flow towards the substrate via a gas channel opening; and the fluid handling system comprises: a gas supply line, configured to supply gas to the gas channel; a pressure source; and an actuatable flow valve connected between the pressure source and the gas supply line upstream of the gas channel opening, wherein the fluid handling system is configured such that when the flow valve is closed a pressure in the gas supply line is different to a pressure of the pressure source, such that actuation of the flow valve to at least partially open the flow valve causes a change of gas flow in the fluid channel by changing a pressure in the gas supply line.28. The fluid handling system according to clause 27, wherein the pressure source comprises an overpressure source having a pressure that is higher than the pressure in the gas supply line.29. The fluid handling system according of clause 27, wherein the pressure source is an underpressure source having a pressure that is lower than the pressure in the gas supply line.30. The fluid handling system according of clause 29, wherein the fluid handling system is configured to recover gas redirected towards the underpressure source during actuation of the flow valve for subsequent use in the gas supply line.31. The fluid handling structure according to any of clauses 1 to 26, wherein the fluid handling system further comprises: a fluid channel configured to supply a fluid flow towards the substrate via a fluid channel opening; and a fluid chamber configured to define a fluid control volume fluidically connected to the fluid channel, the fluid chamber being actuatable to vary a flow rate of the fluid via the fluid channel opening by varying a size of the fluid control volume.32. The fluid handling system according to clause 31, wherein the fluid channel opening is disposed between the immersion space and the gas channel opening.33. The fluid handling system according to any of clauses 12 to 14 or 24 to 25, wherein the second chamber is actuatable to reduce the size of the second control volume to cause a temporary increase in the gas flow rate.34. The fluid handling system according to any of clauses 12 to 14 or 24 to 25 or 33, wherein the second chamber is actuatable to increase the size of the second control volume to cause a temporary decrease in the gas flow rate.35. The fluid handling structure according to any of clauses 12 to 14 or 24 to 25 or 33 to 34, wherein the fluid handling structure comprises a second moveable member which is configured to actuate the second chamber by driving movement of the second moveable member.36. The fluid handling structure according to any of clauses 12 to 14 or 24 to 25 or 33 to 35, wherein the second moveable member is within the second chamber.37. The fluid handling structure according to any of clauses 12 to 14 or 24 to 25 or 33 to 36, wherein the second moveable member comprises a piston drivable along an axis of the second chamber.38. The fluid handling structure according to any of clauses 12 to 14 or 24 to 25 or 33 to 37, wherein the second moveable member comprises an inflatable balloon.39. The fluid handling structure according to any of clauses 12 to 14 or 24 to 25 or 33 to 38, wherein the second chamber comprises a membrane configured such that deformation of the membrane causes a change in the volume of the second control volume.40. The fluid handling structure according to clause 24 to 25 or 39, wherein the second chamber is actuated by deformation of the membrane such that the second control volume is reduced.41. The fluid handling structure of any one of clauses 24 to 25 or 40, wherein at least part of the second chamber is defined by the membrane, and the membrane is deformed by an actuator disposed outside the second chamber.42. The fluid handling structure of any one of clauses 24 to 25 or 40, wherein the membrane is disposed within the second chamber, and the membrane is deformed by an actuator disposed within the second chamber.43. The fluid handling system according to any of clauses 17 to 25 or 33 to 42, wherein the third chamber is actuatable to reduce the size of the third control volume to cause a temporary increase in the gas flow rate.44. The fluid handling system according to any of clauses 17 to 25 or 33 to 43, wherein the third chamber is actuatable to increase the size of the third control volume to cause a temporary decrease in the gas flow rate.45. The fluid handling structure according to any of clauses 17 to 25 or 33 to 44, wherein the fluid handling structure comprises a third moveable member which is configured to actuate the third chamber by driving movement of the third moveable member.46. The fluid handling structure according to any of clauses 17 to 25 or 33 to 45, wherein the third moveable member is within the third chamber.47. The fluid handling structure according to any of clauses 17 to 25 or 33 to 46, wherein the third moveable member comprises a piston drivable along an axis of the third chamber.48. The fluid handling structure according to any of clauses 17 to 25 or 33 to 47, wherein the third moveable member comprises an inflatable balloon.49. The fluid handling structure according to any of clauses 17 to 25 or 33 to 48, wherein the third chamber comprises a membrane configured such that deformation of the membrane causes a change in the volume of the third control volume.50. The fluid handling structure according to clause 49, wherein the third chamber is actuated by deformation of the membrane such that the third control volume is reduced.51. The fluid handling structure of clause 50, wherein at least part of the third chamber is defined by the membrane, and the membrane is deformed by an actuator disposed outside the third chamber.52. The fluid handling structure of clause 51, wherein the membrane is disposed within the third chamber, and the membrane is deformed by an actuator disposed within the third chamber.53. The fluid handling structure according to any one of clauses 31 or 32, wherein the fluid chamber is actuatable to reduce the size of the fluid control volume to cause a temporary increase in the fluid flow rate.54. The fluid handling system according to any one of clauses 31 or 32 or 53, wherein the fluid chamber is actuatable to increase the size of the fluid control volume to cause a temporary decrease in the gas flow rate.55. The fluid handling structure according to any of clauses 31 or 32 or 53 to 54, wherein the fluid handling structure comprises a fluid chamber moveable member which is configured to actuate the fluid chamber by driving movement of the fluid chamber moveable member.56. The fluid handling structure according to any of clauses 31 or 32 or 53 to 55, wherein the fluid chamber moveable member is within the fluid chamber.57. The fluid handling structure according to any of clauses 31 or 32 or 53 to 56, wherein the fluid chamber moveable member comprises a piston drivable along an axis of the fluid chamber.58. The fluid handling structure according to any of clauses 31 or 32 or 53 to 57, wherein the fluid chamber moveable member comprises an inflatable balloon.59. The fluid handling structure according to any of clauses 31 or 32 or 53 to 58, wherein the fluid chamber comprises a membrane configured such that deformation of the membrane causes a change in the volume of the fluid control volume.60. The fluid handling structure according to clause 31 or 32 or 53 to 59, wherein the fluid chamber is actuated by deformation of the membrane such that the fluid control volume is reduced.61. The fluid handling structure of any one of clauses 31 or 32 or 53 to 60, wherein at least part of the fluid chamber is defined by the membrane, and the membrane is deformed by an actuator disposed outside the fluid chamber.62. The fluid handling structure of any one of clauses 31 or 32 or 53 to 61, wherein the membrane is disposed within the fluid chamber, and the membrane is deformed by an actuator disposed within the fluid chamber.63. A fluid handling system comprising a fluid handling structure according to any of the preceding clauses, wherein the fluid handling system comprises: a gas supply line, configured to supply gas to the gas channel; a pressure source; and an actuatable flow valve connected between the pressure source and the gas supply line upstream of the gas channel opening, wherein the fluid handling system is configured such that when the flow valve is closed a pressure in the gas supply line is different to a pressure of the pressure source, such that actuation of the flow valve to at least partially open the flow valve causes a change of gas flow in the fluid channel by changing a pressure in the gas supply line.64. The fluid handling system according to clause 64, wherein the pressure source comprises an overpressure source having a pressure that is higher than the pressure in the gas supply line.65. The fluid handling system according to any one of clauses 63 or 64, wherein the pressure source is an underpressure source having a pressure that is lower than the pressure in the gas supply line.66. The fluid handling system according to any one of clauses 63 or 65, wherein the fluid handling system is configured to recover gas redirected towards the underpressure source during actuation of the flow valve for subsequent use in the gas supply line.

Claims

CLAIMS1. A fluid handling structure configured to at least partly confine an immersion liquid to an immersion space between a final element of a projection system and a substrate, comprising: a gas channel configured to supply a gas flow towards the substrate via a gas channel opening; and a chamber configured to define a control volume fluidically connected to the gas channel, the chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the control volume.

2. The fluid handling structure of claim 1, wherein the chamber is actuatable to reduce the size of the control volume to cause a temporary increase in the gas flow rate, and / or wherein the chamber is actuatable to increase the size of the control volume to cause a temporary decrease in the gas flow rate, desirably wherein the fluid handling structure comprises a moveable member and is configured to actuate the chamber by driving movement of the moveable member.

3. The fluid handling structure of claim 2, wherein the moveable member is within the chamber, and / or wherein the moveable member comprises a piston drivable along an axis of the chamber, and / or wherein the moveable member comprises an inflatable balloon.

4. The fluid handling structure of claim 2 or 3, wherein the chamber comprises a membrane configured such that deformation of the membrane causes a change in the volume of the control volume, desirably wherein the chamber is actuated by deformation of the membrane such that the control volume is reduced, desirably wherein at least part of the chamber is defined by the membrane, and the membrane is deformed by an actuator disposed outside the chamber, or desirably wherein the membrane is disposed within the chamber, and the membrane is deformed by an actuator disposed within the chamber.

5. The fluid handling structure of any of the preceding claims, wherein the chamber is a first chamber and the control volume is a first control volume, and wherein the fluid handling structure further comprises: a second chamber configured to define a second control volume fluidically connected to the gas channel upstream of the first control volume, the second chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the second control volume.

6. The fluid handling structure of claim 5, wherein the first control chamber and the second control chamber are configured such that the first control volume and the second control volume havedifferent maximum sizes, or wherein the first control chamber and the second control chamber are configured such that the first control volume and the second control volume have the same maximum size.

7. The fluid handling structure of claim 5 or 6, further comprising a plurality of further chambers arranged upstream of the second chamber, wherein each of the plurality of further chambers defines a respective control volume, each of the plurality of further chambers being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the respective control volume of the further chamber, desirably wherein the plurality of further chambers comprises between one and two inclusive.

8. The fluid handling structure of any of the preceding claims, wherein the chamber is a first chamber and the control volume is a first control volume, the structure further comprising: a third chamber configured to define a third control volume fluidically connected to the gas channel, the third chamber being actuatable to vary a flow rate of the gas via the gas channel opening by varying a size of the third control volume, wherein: the first chamber has a first chamber opening facing into the gas channel, and the third chamber has a third chamber opening facing into the gas channel; and the third chamber opening at least partially faces the first chamber opening, desirably wherein the third chamber is actuatable to reduce the size of the third control volume to cause a temporary increase in the flow rate, desirably wherein the third chamber has substantially the same size and shape as the first chamber.

9. The fluid handling structure of claim 8, wherein the first chamber is actuatable by driving movement of a first chamber moveable member along a first chamber actuation axis and the third chamber is actuatable by driving movement of a third chamber moveable member along a third chamber actuation axis, wherein the third chamber actuation axis is substantially parallel to the first chamber actuation axis, wherein optionally the directions of movement of the first chamber moveable member and the third chamber moveable member are opposite to each other, and / or wherein the first chamber and the third chamber are configured such that the first control volume and the third control volume have substantially the same maximum size, and / or wherein the structure comprises a first moveable member which is configured to actuate the first chamber by driving movement of the first member, and a third moveable member which is configured to actuate the third chamber by driving movement of the third member, and / or wherein the first moveable member and the third moveable member are configured to vary the volume of the first chamber and third chamber simultaneously in such a way that the first control volume and the third control volume are the same during a range of degrees of actuation of the first chamber and third chamber.

10. The fluid handling structure of any of the preceding claims, wherein the chamber, or each of one or more of the first chamber, the second chamber, the third chamber and the plurality of further chambers, is or are configured to be actuated in an oscillatory manner, optionally sinusoidally, and / or further configured to actuate the chamber, or each of one or more of the first chamber, the second chamber, the third chamber and the plurality of further chambers, when the gas chamber opening is adjacent to a peripheral edge of the substrate during movement of the substrate relative to the structure.

11. The fluid handling structure of any of claims 1-4, further comprising a variable flow valve disposed between the chamber and the gas channel.

12. The fluid handling structure according to any of the preceding claims, wherein the fluid handling structure further comprises: a fluid channel configured to supply a fluid flow towards the substrate via a fluid channel opening; and a fluid chamber configured to define a fluid control volume fluidically connected to the fluid channel, the fluid chamber being actuatable to vary a flow rate of the fluid via the fluid channel opening by varying a size of the fluid control volume, desirably wherein the fluid channel opening is disposed between the immersion space and the gas channel opening.

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