Modulating fluid handling system

Abstract

A fluid handling system comprising a fluid handling structure configured to at least partly confine a liquid to an immersion space between a final element and a substrate, wherein the fluid handling structure comprises: a plurality of gas knife compartments and a plurality of gas supply compartments, wherein the flow of gas to each of the gas knife compartment and gas supply compartment is individually controllable by a respective variable flow valve.

Description

MODULATING FLUID HANDLING SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23186992.6 which was filed on July 21, 2023 and of EP application 24165075.3 which was filed on March 21, 2024 which are incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The present invention relates to a fluid handling system.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 fluidhandling system. The fluid handling system may be an assembly comprising a number of component parts, some such parts having complicated and intricate structures. In particular, the fluid handling system provides an intricate system of flow channels for the fluid provided to the immersion space.

[0007] US2017363948 Al discloses an immersion system comprising a fluid handling structure configured to contain immersion fluid to a region, the fluid handling structure having, at a boundary of a space: at least one gas knife opening in a radially outward direction from the space; and at least one gas supply opening in the radially outward direction from the at least one gas knife opening relative to the space; and a gas supply system configured to supply substantially pure CO2 gas through the at least one gas knife opening and the at least one gas supply opening so as to provide an atmosphere of substantially pure CO2 gas adjacent to, and radially outward of, the space. The system may be configured such that the gas exits the at least one gas knife opening at a first gas velocity and the gas exits the at least one gas supply opening at a second gas velocity.

[0008] US20210096471 Al discloses an immersion fluid confinement structure comprising gas exits and openings which are divided into two groups, the groups being connected to two respective flow control valves.SUMMARY

[0009] In a lithographic patterning process, a fluid handling system confines a liquid to an immersion space between a final optical element and a substrate. A fluid handling structure comprising a gas knife and a gas supply is provided to reduce or prevent problems such as immersion fluid loss at the immersion fluid / air boundary and formation of gas bubbles in the immersion fluid.

[0010] In a lithographic patterning process, a substrate is moved relative to the fluid handling system. During substrate movement, the problem of immersion fluid loss is exacerbated at a receding side of the fluid handling structure, and the problem of bubble formation is exacerbated on an advancing side. However, increasing flow through the gas knife can lead to droplets being swept up at the advancing side. The selected flow through the gas knife and gas supply is therefore always a compromise between the conflicting gas flow requirements, rather the optimal gas flow being provided at different sides of the substrate.

[0011] The gas flow requirements of the gas knife and the gas supply are different at the receding and advancing sides. These problems can be reduced or prevented by increasing the gas flow through the gas knife and the gas supply, however the gas flow requirements at the advancing side and at the receding side are different. Therefore, increasing the gas flow through the gas knife and the gas supply results in an uneconomical use of gas.

[0012] It is an aim of the present invention to provide a fluid handling system which reduces immersion fluid loss and bubble formation, while ensuring that gas is used efficiently.

[0013] According to the present invention, 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 afinal element and a substrate, wherein the fluid handling structure comprises: a plurality of gas knife compartments, including at least a first gas knife compartment and a second gas knife compartment, wherein the first gas knife compartment comprising at least one opening located radially outward of the space, and the second gas knife compartment comprising at least one opening located radially outward of the space, the second gas knife compartment being fluidly separated from the first gas knife compartment, wherein each of the gas knife compartments are in fluid communication with a gas knife chamber via a gas knife variable flow valve, such that the first gas knife compartment is in fluid communication with a gas knife chamber via a first gas knife variable flow valve, and the second gas knife compartment is in fluid communication with the gas knife chamber via a second gas knife variable flow valve; a plurality of gas supply compartments, including at least a first gas supply compartment and a second gas supply compartment, wherein the first gas supply compartment comprising at least one opening located radially outward relative to the first gas knife compartment, such that the first gas knife compartment is disposed between the first gas supply compartment and the immersion space; and the second gas supply compartment comprising at least one opening located radially outward relative to the second gas knife compartment, such that the second gas knife compartment is disposed between the second gas supply compartment and the immersion space, the second gas supply compartment being fluidly separated from the first gas supply compartment, wherein each of the gas supply compartments are in fluid communication with a gas supply chamber via a gas supply variable flow valve, such that the first gas supply compartment is in fluid communication with a gas supply chamber via a first gas supply variable flow valve, and the second gas supply compartment is in fluid communication with the gas supply chamber via a second gas supply variable flow valve.

[0014] According to the present invention 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 element and a substrate, wherein the fluid handling structure comprises: a first gas knife compartment comprising at least one opening located radially outward of the space, and a second gas knife compartment comprising at least one opening located radially outward of the space, the second gas knife compartment being fluidly separated from the first gas knife compartment, a first gas knife chamber fluidly connected to the first gas knife compartment and fluidly connected to the second gas knife compartment and configured to supply a first gas to the first gas knife compartment and the second gas knife compartment, a second gas knife chamber fluidly connected to the first gas knife compartment and fluidly connected to the second gas knife compartment and configured to supply a second gas to the first gas knife compartment and the second gas knife compartment, a switching valve configured to variably direct flow of the first gas from the first gas knife chamber to the first gas knife compartment only, or to the second gas knife compartment only, or to the first gas knife compartment and the second gas knife compartment.

[0015] According to the present invention there is provided a fluid handling structure configured to at least partly confine a liquid to an immersion space between a final element and a substrate, wherein the fluid handling structure comprises: a liquid supply comprising a first liquid supply opening and a second liquid supply opening configured to supply a liquid to the immersion space through the first liquid supply opening and the second liquid supply opening; fluid extraction comprising a set of extraction openings, the fluid extraction being configured to extract immersion fluid from the immersion space through the extraction openings, wherein each of the extraction openings are fluidly connected to an underpressure, wherein the liquid supply is disposed radially inwards of the fluid extraction, wherein the first liquid supply opening and the second liquid supply opening are disposed radially inward from the gas knife, and are disposed diametrically opposite each other relative to the immersion space, and the first liquid supply opening and the second liquid supply opening are connected to a liquid supply chamber.

[0016] According to the present invention there is provided a computer program having instructions thereon which, when executed on a computer, cause the fluid handling system in which the fluid handling structure comprises a gas knife to control the flow of gas through the first gas knife compartment and the second gas knife compartment based on at least one of a number of parameters, wherein the parameters comprise: a position of the substrate relative to the fluid handling structure, a predicted volume of immersion liquid on the surface of the substrate outside of the immersion space, a predicted size of droplets of immersion liquid on the surface of the substrate outside of the immersion space, a predicted position of liquid on the surface of the substrate outside of the immersion space, distance between the bottom surface of the fluid handling structure and the surface of the substrate, a flow of gas being provided to the surface of the substrate, substrate velocity, substrate acceleration, position of resist on a substrate surface, contact angles of the resist with the substrate surface.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference symbols indicate corresponding parts, and in which:

[0018] Figure 1 depicts the schematic overview of the lithographic apparatus;

[0019] Figures 2a, 2b, 2c and 2d each depict, in cross section, two different versions of a fluid handling system 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;

[0020] Figure 3 is a schematic overview of a fluid handling system according to an embodiment of the present invention;

[0021] Figure 4 is a schematic overview of a fluid handling system according to an embodiment of the present invention;

[0022] Figure 5 is a schematic overview of a cross-section of a fluid handling system according to an embodiment of the present invention;

[0023] Figure 6 is a schematic overview of a fluid handling system according to an embodiment of the present invention;

[0024] Figure 7 is a schematic overview of a cross-section of a gas knife according to an embodiment of the present invention;

[0025] Figures 8a depicts a schematic overview of a fluid handling system according to an embodiment of the present invention, and Figure 8b depicts a schematic overview of a fluid handling system according to an embodiment of the present invention, which comprises a liquid supply having a plurality of liquid supply compartments.

[0026] Figure 9 is a schematic overview of a fluid handling system according to an embodiment of the present invention.

[0027] Figures 10a and 10b are schematic overviews of a fluid handling system according to an embodiment of the present invention.

[0028] Figures I la and 1 lb are schematic overviews of a fluid handling system according to a further embodiment of the present invention.

[0029] Figure 12 is a schematic of a fluid handling structure comprising a liquid supply opening and liquid extraction opening.

[0030] Figure 13 shows a plan view of a fluid handling structure.

[0031] Figure 14 shows a modulating liquid supply and a modulating liquid extraction supply according to the present invention.

[0032] Figure 15 is an example of an angled opening.

[0033] Figure 16 shows an example of a circular substrate which may be modelled as a number of separate regions.

[0034] Figures 17a, 17b, 17c and 17d show different examples of gas flow modulation of different regions of the substrate. Figure 17e is a schematic of gas flow states A, B and C.

[0035] Figure 18 shows an example of a fluid handling structure according to an embodiment of the present invention.

[0036] Figure 19 shows an example of a fluid handling structure according to an embodiment of the present invention.

[0037] Figure 20 shows an example of a fluid handling structure according to an embodiment of the present invention.

[0038] Figure 21 shows an example of a fluid handling structure according to an embodiment of the present invention.

[0039] 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 aredepicted in each of the figures, and the figures may only show some of the components relevant for describing a particular feature.DETAILED DESCRIPTION

[0040] 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).

[0041] 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.

[0042] Figure 1 schematically depicts a lithographic apparatus. The lithographic apparatus includes an illumination system (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.

[0043] 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 a desired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.

[0044] 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 animmersion 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.

[0045] 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 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 may have an inverted frusto-conical shape. Although a frusto-conical shape is described here, other suitable shapes may also be used. 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.

[0046] 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. The fluid handling structure 12 defines at least one slit 400 (which may more generally be referred to as an opening) through which the radiation beam B can pass. The slit 400 may define at least part of the immersion space 11.

[0047] 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 radiation beam 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 opening23 additionally reduces the ingress of bubbles into the immersion space 11. This supply of the immersion liquid may function as a liquid seal.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 to extract 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.

[0052] 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.

[0053] 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.

[0054] The left hand side of the fluid handling system 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 other figures, but could also be included with the other variations of the fluid handling system described in relation to Figures 2a, 2b, 2c, or 2d.

[0055] 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. Themeniscus 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 inner periphery 39 may define slit 400, through which radiation beam B can pass. 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.

[0060] 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 have the 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.

[0061] The two different versions of the fluid handling structure of Figure 2b thus allow for movement of the meniscus 33 in the same direction as the substrate W, enabling faster scan speedsand 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.

[0062] 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.

[0063] 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 structure 12. Alternatively or additionally, the immersion liquid may be supplied through a supply opening 20 in the inner surface of the fluid structure 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.

[0064] 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.

[0065] 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 the surrounding 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 thebottom 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 structure 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.

[0066] As shown on the left hand side of Figure 2c, a 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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 32a and 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 openings34 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.

[0071] 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.

[0072] 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).

[0073] 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.

[0074] 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 the inclined 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 thecircumference 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.

[0075] 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 41a 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.

[0076] 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.

[0077] Figures 2a-2d show examples of different configurations which can be used as part of a fluid handling system. 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 interchangeable with 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 gasinto the extraction member. The supply member may supply fluid, liquid or gas to the space by being connected to a relevant supply.

[0078] According to the present invention, 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.

[0079] As mentioned with reference to Figures 2a-2d, the fluid handling system comprises the fluid handling structure which confines the immersion fluid to an immersion space 11 between a final element 100 and a substrate W. The substrate W is moved relative to the fluid handling structure 12 during a lithographic processing step.

[0080] Loss of immersion fluid from the immersion space 11, and formation of bubbles in the immersion fluid can become exacerbated when the substrate W is moved relative to the fluid handling system. To prevent loss of immersion fluid from the immersion space 11, a gas knife which surrounds the immersion space 11 is typically provided. To prevent formation of bubbles in the immersion fluid, a gas supply which surrounds the gas knife is typically provided.

[0081] A fluid handling structure typically comprises the gas knife which surrounds the immersion space 11. Typically, the gas knife is configured to blow gas onto the substrate W through a plurality of openings, such as the gas knife opening 26, first gas knife opening 26a, second gas knife opening 26b and third gas knife opening 26c described previously in Figures 2a and 2d. This is done to firstly, prevent or minimise loss of fluid on the substrate W, and secondly, prevent or minimise creation of gas-bubbles in the immersion fluid by shielding the immersion fluid from the surrounding atmosphere. The surrounding atmosphere may be air, i.e. it may contain nitrogen and oxygen. Sometimes, a gas supply is provided which surrounds the gas knife. The gas supply is configured to blow gas onto the substrate W through a plurality of openings, such as gas supply openings 27b described previously in Figure 2c, to provide further shielding of the immersion fluid from the atmosphere surrounding the fluid handling structure 12.

[0082] When a substrate W is moved relative to the fluid handling structure 12, the substrate W has a receding side and an advancing side. The receding side of the substrate W is the part of the substrate W which is moving away from the centre of the immersion space 11, and the advancing side of the substrate W is the part of the substrate which is moving towards the centre of the immersion space 11. This also means that when the fluid handling structure 12 is moved relative to the substrate W, the fluid handling structure 12 has a receding side and an advancing side. In this case, the receding side of the fluid handling structure is the part of the fluid handling structure which is moving towards from the centre of the immersion space 11, and the advancing side is the part of the fluid handling structure which is moving away the centre of the immersion space 11.

[0083] It is desirable to shield the immersion fluid from the gas in the surrounding atmosphere. The gas flow requirements at the advancing side of the fluid handling structure and at the recedingside of the fluid handling structure may be different (e.g. gas flow at one side may need to be higher than the other).

[0084] For example, gas bubble creation in the immersion fluid is likely to be more significant at the advancing side of the fluid handling structure than at the receding side of the fluid handling structure. By providing a flow of gas to the periphery of the immersion space 11, the immersion space 11 is shielded from the surrounding atmosphere, and the likelihood of gas-bubble formation of gas from surrounding atmosphere is reduced. It might be expected that increasing the flow of gas through the gas knife would further reduce bubble creation. However, increasing gas flow at the advancing side of the gas knife does not lead to a significant reduction in bubble formation and leads to unnecessary increased gas use. Furthermore, increasing gas flow at the advancing side of the gas knife may cause droplets of immersion fluid to be swept up and pushed along in front of the leading edge of the fluid handling structure 12 which is not desirable. Thus, it is preferable to decrease flow through the gas knife at the advancing side of the fluid handling structure. Accordingly, instead it has been proposed to provide a gas supply, separate from the gas knife, to provide further shielding from the atmosphere.

[0085] Immersion fluid loss during substrate W movement is likely to be exacerbated at the receding side of the fluid handling structure relative to the advancing side of the fluid handling structure. It might be expected that increasing the flow of gas through the gas knife would further reduce immersion fluid loss at the receding side. However, if the flow of gas through the gas knife at the receding side and the flow of gas through the gas knife at the advancing side are not individually controlled, increasing the flow of gas through the gas knife at the receding side also results in increasing gas flow at the advancing side of the gas knife at the same time. This does not lead to a significant reduction in immersion fluid loss and leads to unnecessary increased gas use. Furthermore, as described above, decreasing flow through the gas knife at the advancing side further reduces droplet accumulation. However, if flow through the gas knife is reduced, the gas knife may not provide sufficient shielding of the immersion space 11 from the surrounding atmosphere at the receding side. Therefore, if flow through the gas knife is reduced in view of the problems identified above, flow through the gas supply should be increased to provide sufficient shielding of the immersion space 11 from the outside air.

[0086] References to increasing / decreasing gas flow at the advancing / receding side of the gas knife / gas supply mean increasing / decreasing gas flow through gas knife / gas supply at an advancing / receding side of the fluid handling structure relative to the receding / advancing side of the fluid handling structure.

[0087] Accordingly, there exists a challenging problem of gas flow management through the gas knife and the gas supply.

[0088] Reference is now made to Figures 3 and 4 which schematically depict a fluid handling system comprising a fluid handling structure. The fluid handling structures shown in Figure 3 andFigure 4 comprise a plurality of gas knife compartments 501, 502. The gas knife compartments 501, 502 may be referred to as “the gas knife” in the detailed description for brevity. The gas knife compartments 501, 502 include at least a first gas knife compartment 501 comprising at least one opening 508 located radially outward of the immersion space 11, and a second gas knife compartment 502 comprising at least one opening 518 radially outward from the immersion space 11. The second gas knife compartment 502 is fluidly separated from the first gas knife compartment 501, so that the flow of gas out of the openings 508 of the first gas knife compartment 501 can be different from the flow of gas out of the openings 518 of the second gas knife compartment 502. In an alternative embodiment, different flow of gas to the advancing and receding sides of the gas knife can be enabled by a single gas knife compartment extending around the immersion space 11 having a plurality of gas lines connected to different locations around the gas knife compartment, the gas lines being configured to supply gas to the gas knife compartment (not shown). For example, a first gas line may be connected to a first location and a second gas line may be connected to a second location. The plurality of gas lines (e.g. the first gas line and the second gas line) may be configured to deliver the same gas or they may be configured to deliver different gases. The locations may be arranged equidistant from each other around a circumference of the immersion space 11. In an example, the first gas line may be disposed opposite the second gas line relative to a centre of the immersion space 11. The plurality of gas lines may comprise further gas lines, such as a third gas line, fourth gas line, etc. When at least two of the plurality of gas lines provide different gases (such as air and carbon dioxide respectively), the partial pressure of each gas will vary around the gas knife compartment. When the plurality of gas lines all supply the same gas, it may be possible to vary the pressure of gas around the gas knife compartment. Accordingly, gas flow control around a circumference of the immersion space 11 may be achieved.

[0089] According to the present disclosure, the plurality of gas knife compartments extend around a circumference of the immersion space 11. The first knife compartment 501 may extend around half of the circumference of the immersion space 11 and the second gas knife compartment 502 may extend around the other half of the circumference of the immersion space 11. In an embodiment, there may be a gap or a partition provided between the first gas knife compartment 501 and the second gas knife compartment 502. The fluid handling structure may comprise a slit 400, which enables passage of a radiation beam B to a surface of the substrate W, wherein the gas knife compartments are configured to provide the gas over a portion of the fluid handling structure which defines the slit 400.

[0090] Each of the gas knife compartments 501, 502 is in fluid communication with a gas knife chamber (not shown) via a gas knife variable flow valve. The first gas knife compartment 501 is in fluid communication with the gas knife chamber via a first gas knife variable flow valve 503, and the second gas knife compartment 502 is in fluid communication with the gas knife chamber via a second gas knife variable flow valve 504. The gas knife chamber is configured to supply gas to the gas knifecompartment 501, 502. By providing gas to each gas knife compartment 501, 502 via a variable flow valve 503, 504, the flow of gas through each compartment 501, 502 can be different. While Figure 3 shows a gap between the first gas knife compartment 501 and the second gas knife compartment 502 and a gap between the first gas supply compartment 601 and the second gas supply compartment 602, no gap may be provided. The gas knife compartments 501, 502 are fluidly isolated from each other and the gas supply compartments 601, 602 are fluidly isolated from each other, but a gap is not necessarily provided (they may be fluidly isolated by means of a wall, for example).

[0091] The fluid handling system further comprises a plurality of gas supply compartments 601, 602. The gas supply compartments 601, 602 may be referred to as “the gas supply” in the detailed description for brevity. The gas supply compartments 601, 602 include at least a first gas supply compartment 601 and a second gas supply compartment 602.

[0092] The first gas supply compartment 601 comprises at least one opening 608 located radially outward relative to the first gas knife compartment 501. The first gas knife compartment 501 is disposed between the first gas supply compartment 601 and the immersion space 11.

[0093] The second gas supply compartment 602 comprises at least one opening 618 located radially outward relative to the second gas knife compartment 502. The second gas knife compartment 502 is disposed between the second gas supply compartment 602 and the immersion space 11. The second gas supply compartment 602 is fluidly separated from the first gas supply compartment 601.

[0094] Each of the gas supply compartments 601, 602 is in fluid communication with a gas supply chamber (not shown) via a gas supply variable flow valve 603, 604. The first gas supply compartment 601 is in fluid communication with the gas supply chamber via a first gas supply variable flow valve 603, and the second gas supply compartment 602 is in fluid communication with the gas supply chamber via a second gas supply variable flow valve 604. By providing gas to each gas supply compartment 601, 602 via a variable flow valve 603, 604, the flow of gas through each compartment 601, 602 can be different.

[0095] The flow of gas through each of the variable flow valves 503, 504, 603, 604 may be set by a variable flow valve controller (not shown). Accordingly, the flow of gas out of each of the gas knife compartments 501, 502 and gas supply compartments 601, 602 can be controlled by controlling the variable flow valve 503, 504, 603, 604.

[0096] When the first gas knife compartment 501 and the first gas supply compartment 601 are on the receding side of the fluid handling structure, the variable flow valve controller is configured to set the flow of gas through the first gas knife compartment 501 to be higher than the flow through the second gas knife compartment 502, and the variable flow valve controller is further configured to set the flow through the first gas supply compartment 601 to be lower than the flow through the second gas knife compartment 602. Thus, the flow of gas through each of the gas knife compartments 501, 502 and gas supply compartments 601, 602 can be controlled independently from one another. Accordingly, the above-mentioned described problems are reduced or eliminated.

[0097] When a movement of the substrate W is reversed and the second gas knife compartment 502 and the second gas supply compartment 602 are on the receding side of the fluid handling structure, the variable flow valve controller can change the gas flow through each of the gas knife compartments 501, 502 and gas supply compartments 601, 602, such that the gas knife flow at the receding side of the fluid handling structure is higher than that through the advancing side and the gas supply flow at the receding side is lower than that through the advancing side. The variable flow valve controller can change the flow through each compartment 501, 502, 601, 602 in accordance with the movement of the substrate W, e.g. the direction and / or rate of movement of the substrate W.

[0098] One end of a first gas knife channel 505 connects to the gas knife chamber and the other end split up into a second gas knife channel 507 and a third gas knife channel 506, such that the second gas knife channel 507 is connected to the first gas knife compartment 501, with the first gas knife variable flow valve 503 disposed between its two ends, and the third gas knife channel 506 is connected to the second gas knife compartment 502, with the second gas knife variable flow valve 504 disposed between its two ends.

[0099] One end of a first gas supply channel 605 connects to the gas supply chamber (not shown) and the other end is split up into a second gas supply channel 607 and a third gas supply channel 606. The second gas supply channel 607 is connected to the first gas supply compartment 601, with the first gas supply variable flow valve 603 disposed between the two ends of the second gas supply channel 607. The third gas supply channel 606 is connected to the second gas supply compartment 602, with the second gas supply variable flow valve 604 disposed between the two ends of the third gas supply channel 606.

[0100] Accordingly, gas is provided to all gas knife compartment 501, 502 from the gas knife chamber and the flow through each of the gas knife compartments 501, 502 is modulated by the gas knife variable flow valves 503, 504. Gas is provided to all gas supply compartment 601, 602 from the gas supply chamber and the flow through each of the gas supply compartments 601, 602 is modulated by the gas supply variable flow valves 603, 604. The gas knife chamber is configured to output a flow of gas at a flow rate of up to 200 Nl / min (normal litres per minute). The gas supply chamber is configured to output a flow of gas at a flow rate of up to 200 Nl / min (normal litres per minute). The gas flow provided by the gas knife chamber is provided to the gas knife compartments. The gas flow provided by the gas supply chamber is provided to the gas supply compartments. For example, in an embodiment having two gas knife compartments (first gas knife compartment 501 and second gas knife compartment 502) the flow through each of the gas knife compartments may be up to 100 Nl / min. For example, in an embodiment having two gas supply compartments (first gas supply compartment 501 and second gas supply compartment 502) the flow through each of the gas supply compartments may be up to 100 Nl / min.

[0101] Figure 3 illustrates gas knife compartments 501, 502 which together form a circular shape, and gas supply compartments 601, 602 with together form a circular shape. As shown in Figure 4, theshape formed by the compartments 501, 502, 601, 602 in a plan view of the fluid handling structure may be substantially square. However, the shape is not limited thereto and may be any shape.

[0102] Figure 5 shows a cross section of part of a fluid handling system according to the present invention. The first gas knife compartment 501 is provided between the first gas supply compartment 601 and the immersion space 11. Figure 5 shows the relative position of the first gas knife compartment 501 and the first gas supply compartment 601. In an embodiment having two gas knife compartments and two gas supply compartments, the same arrangement in Figure 5 is also applicable to the second gas knife compartment 502 and the second gas supply compartment 602 at a different cross section of part of the fluid handling system which is omitted for the sake of simplicity. The gas knife compartments 501, 502 are configured to supply gas supplied by gas knife chamber (not shown) to the periphery of the immersion space 11. The gas supply compartments 602, 602 are is configured to supply gas supplied by the gas supply chamber (not shown) to the periphery of the gas supplied by the gas knife chamber. As can be seen from Figure 5, gas is supplied out of the first gas knife compartment 501 and the gas supplied out of the first gas supply compartments 601 towards substrate W. The present disclosure provides a plurality of embodiments having a plurality of gas knife compartments (e.g. first gas knife compartment 501, second gas knife compartment 502, third gas knife compartment 509, fourth gas knife compartment 510, and others). Any of the possible arrangements of gas knife compartments disclosed herein can be incorporated into a fluid handling system as shown in Figure 5.

[0103] The fluid handling system comprising the fluid handling structure may further comprise a third gas knife compartment 509 and a fourth gas knife compartment 510, with corresponding features to the first gas knife compartment 501 and the second gas knife compartment 502, as shown in Figure 7, for example. The fluid handling structure may further comprise a third gas supply compartment 609 and a fourth gas supply 610, with corresponding features to the first gas knife compartment 601 and the second gas knife compartment 609, as shown in Figures 8a and 8b, for example. The fluid handling structure may further comprise additional gas knife compartments and gas supply compartments.

[0104] Embodiments of the fluid handling structure shown in Figures 7, 8a and 8b show a fluid handling structure having four vertices separated by four sides. The gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 in Figures 7, 8a and 8b are disposed so that each gas knife compartment 501, 502, 509, 510 and / or each gas supply compartment601, 602, 609, 610 covers a side of the fluid handling structure. In an embodiment, partitions which fluidly separate the gas knife compartments 501, 502, 509, 510 and / or gas supply compartment 601,602, 609, 610 are disclosed at the vertices of the fluid handling structure. Other arrangements of gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 are possible, without separating from the scope of the invention. Other possible arrangements of gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 in thefluid handling structure are described with reference to Figures 18-21. Each of the plurality of gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 may be connected to a respective supply of gas, optionally, via a variable flow valve (not shown).

[0105] An alternative embodiment of the fluid handling system comprising the fluid handling structure comprising four gas knife compartments 501, 502, 509, 510 is shown in Figure 6. Gas knife variable flow valves 511, 512, 513, 514 each control the flow of gas supplied to two adjacent gas knife compartments, e.g. gas flow through first gas knife compartment 501 is controlled by setting the flow through gas knife variable flow valves 511 and 512. The implementation of this embodiment shown in Figure 6 further comprises one-way flow valves 511a-b, 512a-b, 513a-b, 514a-b disposed fluidly between the gas knife variable flow valves 511, 512, 513, 514 and the gas knife compartments 501, 502, 509, 510, which permit gas flow in one direction only, and prevent gas flow in the reverse direction.

[0106] In other words, gas flow is permitted from the gas knife variable flow valve 511 towards the third and first gas knife compartments 509 and 501, and not in the reverse direction. Gas flow is permitted from the gas knife variable flow valve 512 towards the first and second gas knife compartments 501 and 502, and not in the reverse direction. Gas flow is permitted from the gas knife variable flow valve 513 towards the second and the fourth gas knife compartments 502 and 510, and not in the reverse direction. Gas flow is permitted from the gas knife variable flow valve 514 towards the fourth and the third gas knife compartments 510 and 509, and not in the reverse direction.

[0107] For example, one-way flow valves 511a and 51 lb are provided between variable flow valve 511 and the first and third gas knife compartments 509 and 501 respectively; one-way flow valves 512a and 512b are provided between variable flow valve 512 and the first and second gas knife compartments 501 and 502 respectively; one-way flow valves 513a and 513b are provided between variable flow valve 513 and the second and fourth gas knife compartments 502 and 510 respectively; one-way flow valves 514a and 514b are provided between variable flow valve 514 and the fourth and third gas knife compartments 510 and 509 respectively. According to this example, when variable flow valve 512 is actuated, gas flow is provided to the first and the second gas knife compartments 501 and 502 via one-way flow valves 512a and 512b respectively. One-way flow valve 512a prevents flow of gas from the first gas knife compartment 501 towards variable flow valve 512, and prevents flow of gas from the first gas knife compartment 501 towards the adjacent second gas knife compartment 502. However, other means may be provided which enable gas flow set by two the variable flow valves 511, 512, 513, 514 to be combined.

[0108] According to this embodiment, the flow of gas through gas knife compartments 501, 502, 509, 510 can be dynamically controlled during movements of the substrate W. In an example, two variable flow valves which control opposing gas knife compartments (e.g. variable flow valves 512 and 514) are continuously active during substrate movement (for example, movement in the y- direction based on the coordinates in figure 7) and the remaining variable flow valves 511 and 513 arecontrolled based on the direction of movement of the substrate W (e.g. +y-direction or -y-direction). Alternatively, for substrate movement in the x-direction, variable flow valves 511 and 513 are continuously active during substrate movement in the x-direction, and flow through variable flow valves 512 and 514 is set depending on whether the substrate W is moving in the +x-direction or -x- direction. Accordingly, improved gas flow management can be provided for a substrate W which is moved in two dimensions during lithographic processing (i.e. x-direction and y- direction). The flow of gas through gas knife compartments 501, 502, 509, 510 may be dynamically controlled based on other parameters, e.g. based on a position of substrate W and / or fluid handling system.

[0109] While the example in Figure 6 refers to examples of gas knife compartments 501, 502, 509, 510, this configuration can be implemented with the gas supply compartments.

[0110] An alternative embodiment is shown in Figure 7, wherein each of the four gas knife compartments 501, 502, 509, 510 are respectively connected to a gas knife variable flow valve. According to this embodiment, the flow of gas through each gas knife compartment 501, 502, 509, 510 can be controlled individually by each gas knife carriable flow valve. The flow may be controlled based on the movement of the substrate W, to prevent the above-mentioned problems.

[0111] Figure 8a is a schematic illustration of a fluid handling structure comprising gas knife compartments 501, 502, 509, 510 and gas supply compartments 601, 602, 609, 610.

[0112] Figure 8b is a schematic illustration of a fluid handling structure further comprising liquid supply compartments 701, 702, 709, 710. Liquid supply compartments 701, 702, 709, 710 are configured to provide an additional flow of liquid to the immersion space 11. The liquid may be water. Variable control flow valves are omitted from Figures 8a and 8b for improved clarity of the figure, however the flow of gas to each of the gas knife supply compartments 501, 502, 510, 511, the flow of gas to each of the gas supply compartments 601, 602, 610, 611 and the flow of liquid to each of the gas liquid supply compartments 701, 702, 710, 711 is supplied by a respective variable flow valve. The flow may be controlled based on the movement of the substrate W, to prevent the above- mentioned problems.

[0113] The fluid handling structure comprises gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 which are configured to supply gas to the periphery of the immersion space 11. The fluid handling structure comprises at least one slit 400 (which may more generally be referred to as an opening) for the path of the radiation beam B which enables passage of radiation beam B to a surface of the substrate W, and the gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 are configured to provide the gas over a portion of the fluid handling structure which defines the at least one opening for the radiation beam B. Any of the fluid handling structures described herein may be provided with slit 400. While the slit 400 is not shown in the fluid handling structures illustrated in Figures 3-4, 6-11, 13-14, 17, these fluid handling structures may have a slit 400 incorporated therein. The slit 400 enables passage of radiation beam B to a surface of the substrate W, and the plurality of gas knife compartments 501, 502, 509,510 and / or gas supply compartments 601, 602, 609, 610 may be configured to provide the gas over a portion of the fluid handling structure which defines the slit 400. Optionally, another gas may be provided over a portion of the fluid handling structure which does not define the slit 400 (for example, as in the embodiments described with reference to Figures 18-21).

[0114] According to some embodiments, another gas, e.g., air, may be provided over a portion of the fluid handling structure which does not define the slit 400. The another gas may have a lower carbon footprint than the gas, e.g., carbon dioxide, but be suitable for confining the immersion liquid to the immersion space 11. The dimensions of each of the plurality of gas knife compartments may be selected based on dimensions of slit 400. It may be preferable to provide a gas such as carbon dioxide only over a portion of the immersion space 11 which defines the slit 400 (and optionally, over a portion of the immersion space 11 which is in the vicinity of slit 400). For example, the size of the gas knife compartment(s) and / or gas supply compartment(s) being used to provide carbon dioxide over the portion of the fluid handling structure defining the slit 400 may be selected so as to adequately provide carbon dioxide to the slit 400, whilst not providing carbon dioxide to other parts of the fluid handling structure. For example, in Figures 18, 19, 20 and 21, the size of the first gas knife compartment 521 and second gas knife compartment 522 (and the seventh gas knife compartment 527 and the eighth gas knife compartment 528 in Figure 19) may be selected to that the gas (such as carbon dioxide) is provided to areas of the immersion space 11 where the radiation beam B is incident on the substrate W. In other words, the first gas knife compartment 521 and the second gas knife compartment 522 may extend around the immersion space 11 so that they supply a gas to a region of the immersion space 11 covering the slit 400. The third gas knife compartment 523 and the fourth gas knife compartment 524 may (and the fifth gas knife compartment 525 and the sixth gas knife compartment 526 in Figure 19) extend around portions of the immersion space 11 not covered by the first gas knife compartment 521 and second gas knife compartment 522, so that they may provide another gas to regions of the immersion space 11 not defined by the slit 400.

[0115] The plurality of gas knife compartments may extend around a circumference of the immersion space 11 defining a shape comprising four vertices separated by four sides, each of the gas knife compartments being disposed along at least one of the four sides and optionally, one or more vertices. In an embodiment, the shape defined by the gas knife compartments may be different. The shape defined by the gas knife compartments may be any appropriate shape and is not limited to those shown in the figures, e.g. the shape may have more than four sides and / or the sides may be curved.

[0116] Embodiments of the present invention having a fluid handling structure defining a shape comprising four vertices separated by four sides may comprise rounded corners disposed at the vertices (not shown). Alternatively, the shape defined by the fluid handling structure may have a greater number of sides and / or the sides may be curved (not shown). In an embodiment, the shape defined by the plurality of gas knives of the fluid handling structure may be substantially circular, or circular (not shown).

[0117] In an embodiment such as the example shown in Figures 3 and 4, the first gas knife compartment 501 extends around half of the circumference of the immersion space 11 and the second gas knife compartment 502 extends around the other half of the circumference of the immersion space. Similarly, the first gas supply compartment 601 extends around half of the circumference of the immersion space 11 and the second gas supply compartment 602 extends around the other half of the circumference of the immersion space 11.

[0118] In an embodiment, such as the example shown in Figures 18-21, a first gas knife compartment 521 and a second gas knife compartment 522 are disposed opposite each other relative to a centre of the immersion space 11, the first gas knife compartment 521 and the second gas knife compartment 522 extending around portions of the immersion space 11. In this embodiment, the fluid handling structure further comprises a third gas knife compartment 523 and a fourth gas knife compartment 524 disposed between the first and second gas knife compartments 521, 522, the third gas knife compartment 523 and the fourth gas knife compartment 524 being connected to another gas chamber configured to supply another gas; optionally, the gas comprising carbon dioxide and the another gas comprising air; optionally, the gas knife comprising further gas knife compartments configured to supply the gas or the another gas.

[0119] The fluid handling system shown in Figures 2a-2d may be implemented with a plurality of gas knife compartments 501, 502, 509, 510 and gas supply compartments 601, 602, 609, 610, so that the flow of gas out of each compartment 501, 502, 509, 510, 601, 602, 609, 610 can be modulated individually based on the movement of the substrate W. The fluid handling system shown in Figures 2a-2d may be implemented with a plurality of gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 having another arrangement, such as that shown in Figures 18-21.

[0120] The gas knife chamber may be configured to supply substantially pure carbon dioxide (CO2 through at least one opening 508, 518 of each of the respective gas knife compartments 501, 502, 509, 510. The gas supply chamber may be configured to supply substantially pure CO2 through at least one opening 608, 618 of each of the respective gas supply compartments 601, 602, 609, 610. An alternative gas be supplied by the gas knife chamber or the gas supply chamber. The gases supplied by the gas knife chamber and the gas supply chamber may be different. CO2 may be selected as the gas supplied by the gas knife compartments 501, 502, 509, 510 and the gas supply compartments 601, 602, 609, 610 when the immersion fluid is water. CO2 has higher solubility in water than oxygen or nitrogen (which may be abundant in the atmosphere surrounding the immersion space 11). By providing CO2 shielding of the immersion space 11 from the atmosphere, the likelihood of bubble formation is further reduced. This is because if a bubble of CO2 is formed in the immersion fluid, the bubble is likely to dissolve in the immersion fluid. CO2 may be selected as the supplied gas when the immersion fluid is a fluid other than water.

[0121] In Figures 7, 8a and 8b the gas knife comprises the gas knife compartments 501, 502, 509, 510 and / or the gas supply comprises the gas supply compartments 601, 602, 609, 610 which are disposed to surround the immersion space 11 in the shape of a four-sided shape (a square), with each of the gas knife compartments 501, 502, 509, 510 and / or each of the gas supply compartments 601, 602, 609, 610 being provided along a side of the shape. In other words, the gas knife and / or gas supply shown is a square, with the partition between each gas knife compartment 501, 502, 509, 510 and / or each gas supply compartment 601, 602, 609, 610 being provided at the vertex of the square.

[0122] However, other configurations of the gas knife and / or gas supply are possible. Other locations of partitions between different gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 are possible. For example, the partitions may be provided at the centre of each side of the gas knife and / or gas supply, so that each gas knife compartment 501, 502, 509, 510 and / or each gas supply compartment 601, 602, 609, 610 has an L-shape (not shown). In other words, each compartment may be disposed to cover a vertex and portions of each side adjacent to the vertex. However, the partitions are not necessarily disposed at the centre of the sides of the fluid handling structure (e.g. they may be provided off centre). In another embodiment, there may be more than four gas knife compartments and / or four gas supply compartments. A possible arrangement of the gas knife and / or gas supply includes four L-shaped gas knife compartments and / or gas supply compartments provided at the vertices of the gas knife and / or gas supply, with straight gas knife compartments and / or gas supply compartments disposed between the L-shaped gas knife compartments and / or gas supply compartments, respectively. The gas knife compartments and / or gas supply compartments are not necessarily straight, and they may be curved. While reference is made to “vertices” of the gas knife and / or gas supply, the gas knife and / or gas supply does not necessarily comprise sharp corners and may have rounded edges instead. In other words, the gas knife and / or gas supply may be of any suitable shape which extends around at least a portion of the immersion space 11, and the gas knife and / or gas supply may be split up into a plurality of compartments of any suitable shape.

[0123] Figure 9 shows an additional embodiment comprising a pressure reservoir 550 fluidly connected to each gas knife compartment, configured to provide an additional gas flow pulse to the respective gas knife compartment. The additional gas flow pulse is provided by actuating additional gas flow through pulse valves 503a, 504a. In an embodiment having two gas knife compartments, a control unit (not shown) is configured to cause at least one of the pressure reservoirs 550 to provide the additional gas flow pulse to the first gas knife compartment 501 and the second gas knife compartment 502 respectively connected to, in response to a determination that an edge of the substrate W is intersecting the first gas knife compartment 501 and the gas knife compartment 502 that the pressure reservoirs 550 are connected to, respectively. The at least one pressure reservoir 550 may be further connected to additional gas knife compartment(s). The pressure reservoir 550 may be connected to one or more of the plurality of gas knife compartments, including the first gas knifecompartment 501, the second gas knife compartment 502, the third gas knife compartment 509, the fourth gas knife compartment 510 (the third gas knife compartment 509 and the fourth gas knife compartment 510 are not shown in Figure 9), as well as any other gas knife compartments present.

[0124] According to the present disclosure, improved management of gas flow is achieved which helps alleviate the problems outlined above, such as droplet accumulation, bubble formation in the immersion fluid (also referred to as immersion liquid), and others. In addition, improved management of gas flow may lead to more efficient use of resources which may reduce any negative environmental impacts of the fluid handling system. This may be particularly advantageous if the gas which is used to at least partly confine the immersion liquid to the immersion space 11 between the final element 100 and the substrate W has a relatively high carbon footprint, when compared to other abundant gases. Carbon footprint is an index that may be used to compare the total amount of greenhouse gases that an activity or product produces. While reference is made to the fluid handling system at least partly confining the immersion liquid to the immersion space 11 between the final element 100 and the substrate W and / or substrate support WT, the fluid handling system may also fully confine the immersion liquid to the immersion space 11 between the final element 100 and the substrate W and / or substrate support WT.

[0125] For example, the gas used to at least partly confine the immersion liquid to the immersion space 11 may comprise carbon dioxide which may have a higher carbon footprint than air. Therefore, more efficient gas management may lead to a decreased carbon footprint of the fluid handling system.

[0126] Alternative embodiments of the fluid handling system which alleviate or prevent some of the problems discussed above are described with reference to Figures 10a, 10b, 1 la, and 1 lb.

[0127] As discussed previously, there exists a challenge of managing gas flow due to the opposing gas flow requirements at an advancing side and a receding side of the fluid handling structure. According to an alternative embodiment of the invention, there is provided a fluid handling system which can be used to alleviate the problems of immersion fluid loss at a receding side of the fluid handling structure and prevent droplet accumulation at an advancing side of the fluid handling structure.

[0128] A schematic plan view of this embodiment is shown on Figures 10a and 10b.

[0129] According to this embodiment, the fluid handling system comprises a fluid handling structure configured to at least partly confine a liquid to an immersion space between a final element 100 and a substrate W and / or substrate support WT, wherein the fluid handling structure comprises: the first gas knife compartment 501 comprising at least one opening located radially outward of the immersion space (not shown), and the second gas knife compartment 502 comprising at least one opening located radially outward of the immersion space. The openings of the respective gas knife compartments are not shown in Figures 10a, 10b, Ila and 11b.

[0130] The second gas knife compartment 502 is fluidly separated from the first gas knife compartment 501, so that the flow of gas from the first gas knife compartment 501 and the second gasknife compartment 502 may be independent of each other. A first gas knife channel 800 is fluidly connected to the first gas knife compartment 501 and is fluidly connected to the second gas knife compartment 502 and configured to supply a first gas (labelled Gas 1) to the first gas knife compartment 501 and / or the second gas knife compartment 502.

[0131] The first gas knife channel 800 may be fluidly connected to a source of the first gas, such as a canister with pressurised first gas or a mains supply of the first gas. The first gas may be, for example, air, e.g. extremely clean dry air (XCDA), extremely clean humidified air (XCHA) or nitrogen.

[0132] A second gas knife channel 900 is fluidly connected to the first gas knife compartment 501 and is fluidly connected to the second gas knife compartment 502 and is configured to supply a second gas (labelled Gas 2) to the first gas knife compartment 501 and / or the second gas knife compartment 502. The second gas knife channel 900 may be fluidly connected to a source of the second gas, such as a canister with pressurised gas or a mains supply of the second gas. The second gas may be, for example, carbon dioxide or other gas that readily dissolves in the immersion liquid.

[0133] A switching valve 801 is configured to variably direct flow of the first gas from the first gas knife channel 800 to the first gas knife compartment 501 only, or to the second gas knife compartment 502 only, or to the first gas knife compartment 501 and the second gas knife compartment 502. The switching valve 801 is labelled O / C valve in Figures 10a, 10b, 1 la and 1 lb meaning open / close valve. Second switching valve 901 in Figures Ila and 11b may comprise any of the features described in connection with switching valve 801.

[0134] Accordingly, the switching valve 801 may direct the flow of the first gas from the first gas knife channel 800 to the first gas knife compartment 501 via first conduit 800a or to the second gas knife compartment 502 via second conduit 800b, or both. For example, the switching valve 801 may be configured to split the flow of first gas from the gas knife channel 800 to the first conduit 800a and second conduit 800b in a proportion. For example, the switching valve 801 may direct anywhere between 0 and 100% of the first gas to the first conduit 800a, with the remaining gas directed to the second conduit 800b. For example, when 100% of the first gas is directed to the first conduit 800a, 0% is directed to the second conduit 800b; when 70% of the gas is directed to the first conduit 800a, 30% of the gas is directed to the second conduit 800b. When the switching valve 801 changes the proportion of gas directed to the first conduit 800a and the second conduit 800b (such as switching between the states shown in Figures 10a and 10b), it may be advantageous to change the flow gradually rather than abruptly. This may prevent propagation of shock waves through the first gas.

[0135] The first conduit 800a and a third conduit 900a are fluidly connected to form a first joint conduit 1000a. The first joint conduit 1000a is fluidly connected to the first gas knife chamber 501. Accordingly, the flow of gas provided to the first gas knife compartment 501 is a sum of first gas flow rate through first conduit 800a and the second gas flow rate through third conduit 900a. As a result,the mixed gas supplied to the first gas knife compartment 501 is a mixture of the first gas and the second gas.

[0136] The second gas channel 900 is configured to supply gas to the first gas knife compartment 501 via third conduit 900a and to the second gas knife compartment 502 via a fourth conduit 900b.

[0137] The second conduit 800b and the fourth conduit 900b are fluidly connected to form second joint conduit 1000b. The second joint conduit 1000b is fluidly connected to the second gas knife chamber 502.

[0138] When the switching valve 801 is configured to block gas flow to the second conduit 800b, the flow of gas provided to the first gas knife compartment 501 corresponds to the flow rate of the second gas in third conduit 900a and the flow rate of the first gas in the first conduit 800a. When the switching valve 801 is configured to block gas flow to the second conduit 800b, the flow of gas provided to the second gas knife compartment 502 corresponds to the flow rate of the second gas in fourth conduit 900b. This is shown schematically in Figure 10a.

[0139] When the switching valve 801 is configured to block gas flow to the first conduit 800a, the flow of gas provided to the first gas knife compartment 501 corresponds to the flow rate of the second gas in third conduit 900a. When the switching valve 801 is configured to block gas flow to the first conduit 800a, the flow of gas provided to the second gas knife compartment 502 corresponds to the flow rate of the first gas in the second conduit 800b and the flow rate of the second gas in fourth conduit 900b.

[0140] During movement of the substrate W with respect to the fluid handling system, the first gas knife compartment 501 may be disposed at the receding side of the fluid handling structure. In this case, the switching valve 801 may be configured to direct first gas flow to the first gas knife compartment 501 only. This may result in a higher gas flow from the first gas knife compartment 501 than from the second gas knife compartment 502, because the first gas and the second gas are supplied to the first gas knife compartment 501 and only the second gas is supplied to the second gas knife compartment 502. Accordingly, a higher gas flow rate may be provided at the receding side to reduce immersion fluid loss. The gas flow rate at the advancing side may be kept relatively low so that droplet accumulation is prevented.

[0141] The first gas knife compartment 501 and the second gas knife compartment 502 may be fluidly isolated from each other, so that when the switching valve 801 is configured to restrict flow of the first gas to the first gas knife compartment 501 only, the first gas cannot enter the second gas knife compartment 502 via third conduit 900a, fourth conduit 900b and second joint conduit 1000b. This may be achieved by means of a one-way flow valves (not shown) disposed within the first conduit 800a, second conduit 800b, third conduit 900a, fourth conduit 900b, first joint conduit 1000a and second joint conduit 1000b, so that gas flow is only permitted from the first gas knife channel 800 and the second gas knife channel 900 towards the gas knife compartments 501 and 502, and not in the opposite direction.

[0142] Figure 10a shows the embodiment in a state in which the first gas knife compartment 501 is at a receding side of the fluid handling structure and the second gas knife compartment 502 is at an advancing side of the fluid handling structure. In this case, the fluid handling structure is considered to be stationary and the substrate W is moving in a positive y direction relative to the fluid handling structure, i.e. the substrate W is moving upwards in Figure 10a relative to the fluid handling structure. In other words, the fluid handling structure may be considered to move in a negative y direction relative to the substrate W. In this case, the switching valve 801 directs first gas flow to the first gas knife compartment 501 only, and a higher gas flow rate is provided at the receding side of the fluid handling structure. In Figures 10a and 10b, gas flow is indicated by bold lines which include arrows. In the example on Figure 10a, there is no gas flow through second conduit 800b. The switching valve 801 may permit some gas flow through the second conduit 800b. For example, the switching valve 801 may permit a low flow of gas to the conduit which supplies gas to the gas knife compartment which is located at the advancing side of the fluid handling structure (which would be gas knife compartment 502 in Figure 10a, for example).

[0143] Figure 10b shows the embodiment in a state in which the second gas knife compartment 502 is at a receding side of the fluid handling structure and the first gas knife compartment 501 is at an advancing side of the fluid handling structure. In this case, the fluid handling structure is considered to be stationary and the substrate W is moving in a negative y direction relative to the fluid handling structure, i.e. the substrate W is moving downwards in Figure 10b relative to the fluid handling structure. . In other words, the fluid handling structure may be considered to move in a positive y direction relative to the substrate W. In this case, the switching valve 801 directs first gas flow to the second gas knife compartment 502 only, and a higher gas flow rate is provided at the receding side of the fluid handling structure. In the example on Figure 10b, there is no gas flow through first conduit 800a. The switching valve 801 may permit some gas flow through the second conduit 800b. For example, the switching valve 801 may permit a low flow of gas to the conduit which supplies gas to the gas knife compartment which is located at the advancing side of the fluid handling structure (which would be gas knife compartment 501 in Figure 10b, for example).

[0144] In an embodiment, the first gas knife compartment 501 extends around a first portion of the circumference of the immersion space and the second gas knife compartment 502 extends around a second portion of the circumference of the immersion space. In Figures 10a, 10b, I la and 1 lb, this means that the immersion space is located within the space defined by the first gas knife compartment 501 and the second gas knife compartment 502. In an embodiment, first gas knife compartment 501 and the second gas knife compartment 502 are not concentric. In an embodiment, first gas knife compartment 501 and the second gas knife compartment 502 do not overlap.

[0145] In an embodiment, the switching valve 801 is configured to direct the flow of first gas from the first gas knife channel 800 to either the first gas knife compartment 501, or to the second gas knife compartment 502, or to the first gas knife compartment 501 and the second gas knife compartment501 based on the direction of movement of the substrate W. Accordingly, a higher gas flow may be provided to the receding side of the fluid handling structure at any moment during its movement, as described above.

[0146] Alternatively, the switching valve 801 may direct equal proportions of first gas flow to the first gas knife compartment 501 and to the second gas knife compartment 502, so that the flow of gas from each of the compartments is the same. Alternatively, the switching valve 801 may direct gas flow to the gas knife compartment which is at the advancing side of the fluid handling structure, so that a higher gas flow may be provided to the advancing side of the fluid handling structure, should that be required.

[0147] In an embodiment during movement of the substrate W, the switching valve 801 is configured to direct first gas flow from the first gas knife channel 800 to the first gas knife compartment 501 only when the first gas knife compartment 501 is at a receding side of the fluid handling structure, and the switching valve 801 is configured to direct first gas flow from the first gas knife channel 800 to the second gas knife compartment 502 only when the second gas knife compartment 502 is at a receding side of the fluid handling structure. The switching valve 801 may be configured so that it does not allow gas flow from the first gas knife channel 800 to a plurality of gas knife compartments. For example, the switching valve 801 may be switched between two states only, wherein a first state permits gas flow through the first gas knife compartment 501 only and a second state permits gas flow through the second gas knife compartment 502 only. In an alternative embodiment permitting gas flow through both gas knife compartments 501, 502 , the switching valve 801 may have further intermediate states.

[0148] The switching valve 801 may be set and controlled by a control unit (or controller).

[0149] A further embodiment according to the present invention is illustrated by Figures Ila and 11b.

[0150] According to the embodiments shown on Figures 1 la and 1 lb, the switching valve 801 is a first switching valve 801, and the fluid handling system further comprises a second switching valve 901 configured to direct flow of the second gas (labelled Gas 2 on Figure I la and 1 lb) from the second gas knife channel 900 to the first gas knife compartment 501, or the second gas knife compartment 502, or the first gas knife compartment 501 and the second gas knife compartment 502.

[0151] Accordingly, gas flow control of the second gas can be performed in a similar manner to gas flow control of the first gas, described with reference to Figures 10a and 10b.

[0152] The second switching valve 901 may comprise some or all of the features described with reference to the switching valve 801 or the first switching valve 801.

[0153] Accordingly, the second switching valve 901 may direct the flow of the second gas from the second gas knife channel 900 to the first gas knife compartment 501 via third conduit 900a or to the second gas knife compartment 502 via second conduit 900b, or both.

[0154] During movement of the substrate W with respect to the fluid handling system, the second switching valve 901 may be configured to direct second gas flow from the second gas knife channel 900 to the first gas knife compartment 501 only when the first gas knife compartment 501 is at an advancing side of the fluid handling structure, and the second switching valve 901 is configured to direct second gas flow from the second gas knife channel 900 to the second gas knife compartment 502 only when the second gas knife compartment 502 is at an advancing side of the fluid handling structure.

[0155] In Figure Ila, gas flow is indicated by bold lines and bold arrows. In the example of Figure Ila, the first switching valve 801 is in a state which permits first gas flow to the first gas knife compartment 501 only. Figure 1 la shows the embodiment in a state in which the first gas knife compartment 501 is at a receding side of the fluid handling structure and the second gas knife compartment 502 is at an advancing side of the fluid handling structure. In this case, if the fluid handling structure is considered to be stationary and the substrate W is moving in a positive y direction relative to the fluid handling structure, i.e. the substrate W is moving upwards in figure Ila relative to the fluid handling structure. In other words, the fluid handling structure may be considered to move in a negative y direction relative to the substrate W.

[0156] In the example of Figure Ila, the second switching vale 901 is in a state which permits second gas flow to the second gas knife compartment 502 only. This mode of operation may be employed when the first gas knife compartment 501 is at a receding side of the fluid handling structure and the second gas knife compartment 502 is at an advancing side of the fluid handling structure. Figure 1 lb shows the embodiment in a state in which the first gas knife compartment 501 is at a receding side of the fluid handling structure and the second gas knife compartment 502 is at an advancing side of the fluid handling structure. In both cases, if the fluid handling structure is considered to be stationary and the substrate W is moving in a positive y direction relative to the fluid handling structure, i.e. the substrate W is moving upwards in Figures 1 la and 1 lb relative to the fluid handling structure. In other words, the fluid handling structure may be considered to move in a negative y direction relative to the substrate W.

[0157] The direction of movement of the substrate W may change during lithographic processing, meaning that the gas flow requirements of the fluid handling structure at the advancing and at the receding side of the fluid handling structure may be reversed.

[0158] The first switching valve 801 may switch the direction of permitted direction of flow of the first gas, so that the first gas can flow to the second gas knife compartment 502 and cannot flow to the first gas knife compartment 501. The second switching valve 901 may switch the direction of permitted direction flow of the second gas, so that the second gas can flow to the first gas knife compartment 501 and cannot flow to the second gas knife compartment 502, Figure 1 lb. The first switching valve 801 and the second switching valve 901 may be switched simultaneously. For example, the flow of the first gas and the second gas is shown schematically with bold arrows inFigure I la when the first gas knife compartment 501 is at a receding side, and the fluid handling system may switch to the configuration on Figure 1 lb when the substrate W direction is switched. This may be done in response to a determination that the substrate W has switched directions. The state of each valve 801, 901 may be set and controlled by a control unit (or controller).

[0159] The first gas knife channel 800 may be configured to output a flow of first gas at a flow rate of up to 200 Nl / min (normal litres per minute), or preferably, in the range of 50-150 Nl / min (normal litres per minute). The second gas knife channel 900 may be configured to output a flow of first gas at a flow rate of up to 200 Nl / min (normal litres per minute), or preferably, in the range of 100-150 Nl / min (normal litres per minute). The flow rate of each chamber may be varied to facilitate different gas flows from each of the gas knife compartments. The flow rate from the gas knife compartments may need to be adjusted based on the settings of the lithographic process, such as substrate speed. For example, the system may be configured such that the gas knife compartment at the receding side of the fluid handling structure outputs the mixed gas at a rate of 90 normal litres per minute through its opening(s), and the gas knife compartment at the advancing side of the fluid handling structure outputs the second gas or the mixed gas at a rate of 60 normal litres per minute through its opening(s).

[0160] The solubility of the first gas in the immersion fluid may be lower than the solubility of the second gas in the immersion fluid. Thus, the second gas may lead to reduced bubble occurrence in the immersion fluid. This is because any bubbles of second gas may dissolve faster than bubbles of the first gas. It may be advantageous to provide a flow of second gas on a side of the substrate W at which bubble formation may be exacerbated. The immersion fluid may be water.

[0161] The first gas may comprise a gas which does not have a negative environmental impact, e.g. it may be a gas that has a low carbon-footprint. The first gas may comprise air.

[0162] The second gas may comprise carbon dioxide. Carbon dioxide may have a higher carbon footprint than air. Therefore, it may be advantageous to avoid unnecessary use of the second gas to lower the carbon footprint of a lithographic process.

[0163] Thus, provision of a high flow of the first gas at a receding side of the fluid handling structure may provide effective shielding against immersion liquid loss while keeping the carbon footprint low.

[0164] The second gas may be a gas which provides shielding against bubble creation in the immersion fluid. In some embodiments, the second gas may have a higher carbon footprint than the first gas. Through this advanced management of gas flow, sufficient shielding against fluid loss may be provided while keeping the carbon footprint low, as the additional gas shield required for immersion fluid loss prevention is provided by the first gas which has a lower carbon footprint.

[0165] The rate of bubble formation at an advancing side of the fluid handling structure may by higher than the rate of bubble formation at a receding side of the fluid handling structure. The size of the bubbles formed at an advancing side of the fluid handling structure may be higher than the size of bubbles formed at a receding side of the fluid handling structure. Therefore, shielding of theimmersion fluid with the second gas may be most favourable at the advancing side of the fluid handling structure.

[0166] At a receding side of the fluid handling structure, there may be a greater rate of immersion fluid loss than at the advancing side. The solubility of gas in immersion fluid does not necessarily have an effect on prevention of the immersion fluid loss. Immersion fluid loss may be effectively prevented by providing a gas flow rate.

[0167] In view of the above-description problems, the second gas may confine the immersion liquid at an advancing side of the fluid handling structure during movement and the first gas may be used at a receding side of the fluid handling structure. Accordingly, the second gas is only provided around a portion of the circumference of the immersion space, while the first gas can be provided to the remaining portion of the circumference of the immersion space. The total carbon footprint of a lithographic process may be reduced, when compared with a known fluid handling system which provides the second gas around the entire circumference of the immersion space.

[0168] Other gases could be selected for the first gas and / or the second gas. The first gas and second gas may be switched so that the first gas comprises carbon dioxide and the second gas comprises air.

[0169] As discussed with reference to Figures 7, 8a and 8b, the arrangement of the plurality of gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 around the immersion space 11 may vary, without departing from the scope of the present invention. The various arrangements of the gas knife compartments 501, 502, 509, 510 and / or gas supply compartments 601, 602, 609, 610 can be incorporated into the fluid handling systems as described with reference to Figures 3-15. In other words, the gas knife compartments 501, 502, 509, 510 and gas supply compartments 601, 602, 609, 610 of the embodiments described with reference to Figures 3-15 may surround the immersion space 11 in variety of configurations disclosed herein.

[0170] An alternative arrangement of four gas knife compartment surrounding an immersion space 11 is shown in Figure 18. This embodiment may comprise the first gas knife channel 800 configured to supply the first gas and the second gas knife channel 900 configured to supply the second gas (not shown in Figure 18).

[0171] According to an embodiment, the fluid handling system comprising the fluid handling structure comprises a first gas knife compartment 521, a second gas knife compartment 522, a third gas knife compartment 523 and a fourth gas knife compartment 524.

[0172] The first gas knife compartment 521 and the second gas knife compartment 522 may be connected to the second gas knife channel 900 (which may be configured to supply carbon dioxide), and optionally, connected to the second gas knife channel 900 via respective variable flow valves.

[0173] The third gas knife compartment 523 and the fourth gas knife compartment 524 may be connected to the first gas knife channel 800 (which may be configured to supply air), and optionally, connected to the first gas knife channel 800 via respective variable flow valves .

[0174] The first gas knife compartment 521 and the second gas knife compartment 522 may be disposed opposite each other relative to the centre of the immersion space 11. The third gas knife compartment 523 and the fourth gas knife compartment 524 may be disposed between the first gas knife compartment 521 and the second gas knife compartment 522.

[0175] The fluid handling structure may comprise a slit 400 which enables passage of radiation beam B from the projection system PS to the substrate surface. Gas bubbles formed at an edge of the immersion space 11 may enter a central portion of the immersion space 11, including a portion of the immersion space 11 below the slit 400. Presence of gas bubbles below the slit 400 may be particularly detrimental to the lithographic process, as the bubbles may interfere with radiation beam B. It may be particularly preferable to avoid gas bubbles from entering an area of the immersion space 11 where the radiation beam B travels. It may be preferable to reduce the use of gases having a high carbon footprint, to reduce the carbon footprint of a lithographic process.

[0176] The gas knife compartments may be arranged so that the second gas (such as carbon dioxide) is provided to the area portion of the fluid handling structure which defines the slit 400 and optionally, the first gas (such as air) is provided over a portion of the fluid handling structure which does not define the slit 400.

[0177] The dimensions of the gas knife compartments may be selected in accordance with the dimensions of the slit 400. For example, the first gas knife compartment 521 and the second gas knife compartment 522 may have a width (measured along the x-direction in Figures 18-21) which is equal to or greater than the width of the slit 400 (measured along the x-direction in Figures 18-21). This is beneficial when the substrate W is moved relative to the fluid handling structure in the orthogonal direction (i.e. in the y-direction) because the gas supplied by the first gas knife compartment 521 and / or second gas knife compartment 522 is supplied across the width of the slit 400. In some embodiments, the substrate W may be moved in a direction parallel to the width of the slit 400, e.g. in the x direction. In such a case, the fluid handling structure as shown in Figure 19 may be used, with the seventh gas knife compartment 527 and the eighth gas knife compartment 528. The seventh gas knife compartment 527 and the eighth gas knife compartment 528 may have a height (measured along the y-direction in Figure 19) which is equal to or greater than the height of the slit 400 (measured along the y-direction in Figure 19). This is beneficial when the substrate W is moved relative to the fluid handling structure in the parallel direction (i.e. in the x-direction) because the gas supplied by the seventh gas knife compartment 527 and / or eighth gas knife compartment 528 is supplied across the height of the slit 400. In all these embodiments, the dimensions of the third gas knife compartment 523 and the fourth gas knife compartment 524 (and the fifth gas knife compartment 525 and sixth gas knife compartment 526 if relevant) may be selected, so that the first gas (e.g. air) is provided over a portion of the fluid handling structure which does not define the slit 400.Accordingly, the second gas (such as carbon dioxide) may be provided to cover a portion of the fluidhandling portion 12 which defines the slit 400. The dimensions of the slit 400 referred to herein are the width and height of the slit 400 in plan view of the fluid handling structure 12.

[0178] According to an embodiment of the present invention, the first gas knife compartment 521, the second gas knife compartment 522, the third gas knife compartment 523 and the fourth gas knife compartment 524 are disposed to cover a respective vertex of the gas knife and at least a portion of sides adjacent to said respective vertex.

[0179] A vertex of the gas knife is a corner of the gas knife formed by two sides of the gas knife. For example, when the gas knife is in the shape of a square, rectangle, rhombus or kite in plan view, the corners of the shape correspond to four vertices of the gas knife. When two sides of a gas knife meet to form a rounded portion, the vertex is defined as a point of the rounded portion which is furthest away from a centre of the gas knife.

[0180] A vertex covered by the first gas knife compartment 521 and a vertex covered by the second gas knife compartment 522 may define a line. During a lithographic process, the substrate W may be moved substantially parallel to the line defined by the vertices.

[0181] The second gas (such as carbon dioxide) may be provided to portions of the fluid handling structure defined by the first gas knife compartment 521, the second gas knife compartment 522. The second gas (such as air) may be provided to portions of the fluid handling structure defined by the third gas knife compartment 523, the fourth gas knife compartment 524. Accordingly, the second gas may be provided to a region of the immersion space 11 where gas bubble prevention is most desirable, i.e. the area which is disposed below the slit 400. The third gas knife compartment 523 and the fourth gas knife compartment 524 disposed to provide a first gas (such as air) provide a flow of gas which confines the immersion liquid to the immersion space 11, while reducing the carbon footprint of the fluid handling structure.

[0182] The first gas may be air, or another gas which is suitable for confining an immersion liquid to the immersion space 11 and having a relatively low carbon footprint. The second gas may be carbon dioxide, or another gas with high solubility in the immersion liquid.

[0183] The second gas knife channel 900 may provide a flow of the second gas to the first gas knife compartment 521 and the second gas knife compartment 522, and optionally, the first gas knife channel 800 is configured to supply air and / or the second gas knife channel 900 is configured to supply carbon dioxide. In an embodiment, the second gas (e.g. carbon dioxide) may be provided only to an advancing side of the substrate W during a lithographic process, where bubble prevention may be most critical. Thus, the second gas may be provided to the first gas knife compartment 521 and the first gas may be provided to the second gas knife compartment 522, the third gas knife compartment 523 and the fourth gas knife compartment 524 (when the first gas knife compartment 521 is at an advancing side). This is illustrated schematically in Figure 20. The arrow A shows possible movement of the substrate W relative to the fluid handling structure. The gas provided to the compartments may be changed depending on the direction of movement.

[0184] In an embodiment, each of the third gas knife compartment 523 and fourth gas knife compartment 524 may be connected via variable flow valves (not shown). This enables variable gas flow which may be advantageous during movement of the substrate W.

[0185] The flow of gas may be modulated as described with reference to Figures 10-11. Namely, the first gas knife compartment 521 and the second gas knife compartment 522 may be configured so that the second gas is only provided on a receding side of the substrate W during substrate movement.

[0186] According to an embodiment, the plurality of gas knife compartments may include further gas knife compartments, such as the example shown on Figure 19. These gas knife compartments may be arranged so that the second gas (such as carbon dioxide) is provided to the area of the fluid handling structure which defines the slit 400 and optionally, the first gas (such as air) is provided over the portion of the fluid handling structure which does not define the slit 400.

[0187] In an embodiment, the fluid handling system further comprises a fifth gas knife compartment 525, a sixth gas knife compartment 526 which are each connected to the first gas knife channel 800, optionally, via respective variable flow valves (not shown). In the embodiment (such as shown in Figure 19), the gas knife compartments connected to the first gas supply channel 800 are disposed along the sides of the fluid handling structure. The embodiment further comprises a seventh gas knife compartment 527, an eighth gas knife compartment 528 which are each connected to the second gas knife channel 900, optionally, via respective variable flow valves (not shown),

[0188] Each of the first, second, seventh and eighth gas knife compartments 521, 522, 527, 528 may be disposed to cover a respective vertex of the gas knife and at least a portion of the adjacent sides adjacent to said vertex, and each of the third, fourth, fifth and sixth gas knife compartments 523, 524, 525, 526 may be disposed to cover a respective side of the gas knife between the vertices.

[0189] The dimensions of the each of the first, second, third, fourth, fifth, sixth, seventh and eighth gas knife compartments 521, 522, 523, 524, 525, 526, 527, 528 may be selected so that the second gas is provided over a portion of the fluid handling structure 12 which defines the slit 400. For example, dimensions may be selected such that the second gas (e.g. carbon dioxide) is provided over the portion of the fluid handling structure which defines the slit 400, and the first gas (e.g. air) is provided over portions of the fluid handling structure 12 which do not define the slit 400 (and are not aligned with the slit 400 during relative movement of the substrate W and fluid handling structure 12). Selecting dimensions of each of the plurality of gas knife compartments in this way may reduce the carbon footprint of the fluid handling structure 12, as the second gas is preferentially provided to a portion of the fluid handling structure 12 where prevention of gas bubbles is over relatively high importance (i.e. the portion defined by the slit 400). For example, with reference to Figure 18-21, dimensions of the gas knife compartments are selected so that, during relative movement of the substrate W and the fluid handling structure 12 in y direction (and in the x direction for Figure 19 as well), the second gas is provided over a region defined by the slit 400 and to the periphery of that region.

[0190] The flow of gas through each of the gas knife compartments may be based on a direction of movement of the substrate W. If the fluid handling structure is moved with any of the vertices in the leading or trailing direction relative to the substrate W, the second gas (such as carbon dioxide) may be provide over the slit 400 for the radiation beam B. For example, if the substrate W is moved in Figure 19 to the left or right, the seventh gas knife compartment 527 and / or the eighth gas knife compartment 528 may provide gas over the slit 400.

[0191] The flow of gas may be controlled so that a total flow of gas may be higher at a receding side of the substrate W than at an advancing side of the substrate W.

[0192] According to an embodiment, further gas knife compartments may be provided which are concentric with the gas knife compartments disposed to surround the immersion space 11. The concentric gas knife compartments may be connected to a different gas supply than the gas knife compartment they are concentric to, so that additional control over the composition and flow of gas provided over a portion of the fluid handling structure is provided.

[0193] For example, Figure 21 shows an example of a fluid handling structure similar to that shown in Figure 19, except that instead of the second gas knife compartment 522, two concentric gas knife compartments 522a and 522b are provided. Inner second gas knife compartment 522a is connected to the second gas supply channel 900 and the outer second gas knife compartment 522b is connected to the first gas supply channel 800. The flow of gas through each of these channels may be modulated to provide the optimum gas flow speed and composition. The dimensions of concentric compartments may be varied so that a flow of second gas is provided over a portion of the fluid handling structure which defines the slit 400. For example, dimensions of two concentric gas knife compartments 522a and 522b may be selected such that the second gas may be provided over a region defined by the slit 400, e.g. based on the width of the slit 400 as described above for Figures 18-21.

[0194] Any of the plurality of gas knife compartments can be provided with a further concentric gas knife compartment.

[0195] In an alternative embodiment, different flows of gas to different regions of the immersion space 11 may be enabled by a single gas knife compartment extending around the immersion space 11 having a plurality of gas lines connected to different locations around the gas knife compartment.

[0196] For example, the possible modes of gas flow described with reference to Figures 18-21 may be achieved by a single gas knife compartment comprising a plurality of gas lines connected to the single gas knife compartment, instead of providing a plurality of gas knife compartments which are fluidly separated. Controlling the type and pressure of gas provided by each of the gas lines may provide a flow of gas such as carbon dioxide over a portion of the fluid handling structure 12 which defines a slit 400, and air over portion(s) of the fluid handling structure which do not define / are not aligned with the slit 400 during relative movement.

[0197] It will be appreciated by the skilled person that the first and second gas knife channel 800, 900 may comprise a thermal control unit (not shown). The thermal control unit may be arranged tocontrol the temperature of the gas provided by the channels 800, 900 before reaching the gas knife compartments 501, 502. The thermal control unit may be arranged upstream or down stream the valves 801, 901.

[0198] As described previously with reference to Figure 2a, the fluid handling structure 12 may comprise an under supply opening 23 which is configured to supply an immersion liquid to the immersion space 11. The fluid handling structure 12 may comprise other openings which are configured to supply an immersion liquid to the immersion space 11 (such as supply opening 20 as shown in Figure 2a or supply opening 34 as shows in Figure 2b). The fluid handling structure 12 may also comprise extraction members (such as recovery openings 32a and / or 32b e.g. as shown in Figure 2c, and / or gas recovery openings 28 and / or pinning opening 32 e.g. as shown in Figure 2a) or other openings configured to extract the immersion liquid and / or gas. The extraction members may recover immersion liquid and gas in a two phase flow.

[0199] During movement of the substrate W relative to the fluid handling structure 12, the immersion liquid may move in the same direction as the substrate W. This may be due to a non-slip boundary condition between the substrate W and the immersion liquid. The non-slip boundary condition is a boundary condition which enforces that at a solid boundary a fluid (such as the immersion liquid) attains zero velocity relative to the solid. This means that there is a portion of immersion liquid which may adhere to the substrate surface during scanning, meaning that the immersion liquid may not be effectively extracted / recovered by the extraction members.

[0200] An example of a fluid handling structure 12 comprising a liquid supply opening 2000 and fluid extraction opening 2001 is shown schematically on Figure 12. In Figure 12, the substrate W is moved relative to the fluid handling structure 12, for example the substrate W is being moved to the right hand side of the figure. Immersion liquid may be supplied to immersion space 11 via the liquid supply opening 2000. The immersion liquid may be extracted via fluid extraction opening 2001. The direction of immersion liquid flow is shown by arrows towards and away from the liquid supply opening 2000 and the fluid extraction opening 2001 in Figure 12.

[0201] The fluid extraction opening 2001 is an example of an extraction member. The fluid extraction opening 2001 may be configured to recover the immersion liquid and gas via two-phase flow extraction. The gas extracted by the fluid extraction opening 2001 may be a gas which is supplied by a gas knife (not shown in Figure 12) which is configured to confine the immersion liquid to the immersion space 11. The gas knife may comprise an opening similar to the gas knife opening 26 of Figure 2a.

[0202] The portion of the immersion liquid which may be left behind on the substrate surface at the receding side of the fluid handling structure is illustrated schematically on Figure 12. The portion of the immersion liquid which is left behind is shown schematically as a liquid film having thickness di. This portion of the immersion liquid may be left behind on the surface of the substrate W because it is not successfully extracted by the fluid extraction opening 2001. The thickness di may affect thevolume of liquid which is left behind on the substrate surface. For example, a greater thickness di may lead to a greater volume of liquid being left on the substrate surface and / or droplets of immersion liquid of greater size being left on the substrate surface. It may be advantageous to avoid immersion liquid droplet formation.

[0203] Figure 13 shows a plan view of a fluid handling structure 12. The fluid handling structure 12 may comprise two liquid supply openings, such as the liquid supply opening 2000, disposed in the fluid handling structure 12 at angular positions labelled 90° and 270° in Figure 13 (the liquid supply openings are not shown in Figure 13). These liquid supply openings may be connected to a liquid supply chamber (not shown), and the liquid supply openings may be configured to supply liquid to an immersion space 11 at an equal flow rate. When the substrate W is stationary, this may result in approximately uniform immersion liquid supply around the circumference of the immersion space 11, as immersion liquid is supplied at an equal rate through each of the liquid supply openings. However, this provision of an equal supply of liquid from each of the liquid supply openings may be disadvantageous during substrate movement, as described below.

[0204] The fluid handling structure 12 may further comprise a fluid extraction comprising at least one fluid extraction openings, such as the fluid extraction opening 2001. Preferably the fluid handling structure 12 comprises multiple fluid extraction openings. Preferably the fluid handling structure 12 comprises at least four fluid extraction openings, for example disposed in the fluid handling structure 12 at angular positions of 45°, 135°, 225°, 315° in Figure 13 (the liquid extraction openings are not shown in Figure 13). The fluid extraction openings may be equidistant from a centre of the immersion space 11 and they may be disposed further away from the centre of the immersion space 11 than each of the liquid supply openings. These fluid extraction openings may be connected to an underpressure and may be configured to extract immersion liquid and gas. For example, the fluid extraction openings may extract / recover the immersion liquid, as well as gas which is supplied to the substrate surface by a gas knife (this may be referred to as fluid extraction, for brevity). As the liquid extraction openings may each be connected to the same underpressure source, the rate of fluid extraction through each opening may be the same. When the substrate W is stationary, this may result in approximately uniform fluid extraction around the circumference of the immersion space 11, as immersion liquid is extracted at an equal rate through each of the fluid extraction openings. However, this may be disadvantageous during substrate movement, as described below.

[0205] Figure 13 shows a plan view of the fluid handling structure 12. During movement of the substrate W, the unrecovered immersion liquid 300 may form a substantially triangular shape, as shown in Figure 13. When the substrate speed exceeds a predetermined critical speed, immersion liquid may be lost from the tip of the substantially triangular unrecovered immersion liquid 300, i.e. at the lowermost point of the y-axis in Figure 13. In Figure 13, the substrate W is moving in the negative y-direction with respect to the fluid handling structure 12 (i.e. opposite to the direction y- axis), the unrecovered immersion liquid 300 forming a substantially triangular shape in the negativey -direction. This may result in immersion liquid being lost at the receding side of the fluid handling structure (e.g. negative y-direction in Figure 13). Additionally, or alternatively, this may lead to the formation of immersion liquid droplets on the substrate surface which is a source of defectivity. It may be preferable to avoid this.

[0206] Any lost droplets of immersion liquid on the substrate W may (subsequently) collide with an advancing meniscus during subsequent substrate movement. This may result in the formation of gas bubbles inside the immersion liquid. These gas bubbles may move in the direction of the receding side of the fluid handling structure due to shear exerted by the substrate W on the immersion liquid. If the gas bubbles are too large (for example, larger than 70 pm), they may not be dissolved in the immersion liquid by the time they reach the centre of the immersion space 11, meaning that these bubbles may interfere with a radiation beam B which is incident on the substrate W which may lead to defects on the substrate W due to the change of refractive index in the path of radiation beam B. It is noted that the gas bubbles being problematic at 70 pm is only an example and, depending on settings of the system, gas bubbles at other sizes, e.g. larger than 50 pm may be problematic.

[0207] The unrecovered immersion liquid 300 may undesirably lead to formation of a wave of immersion liquid travelling along the outer edge of the immersion space 11 towards a receding side of the fluid handling structure. This may disrupt the stability of the substantially triangular unrecovered immersion liquid 300 which may lead to further loss of immersion liquid even when the substrate speed does not exceed a predetermined critical speed. Thus, this may further increase loss of immersion liquid, even when the substrate W is moving relatively slowly.

[0208] The problems identified above may be solved by providing a modulating immersion liquid supply which can supply immersion liquid at different rates at an advancing side and a receding side. Additionally, or alternatively, a modulating fluid extraction may be provided which can extract immersion fluid at different rates at the advancing side and the receding side. By modulating the rate of liquid supply and / or the rate of fluid extraction at the advancing and the receding side of the fluid handling structure, the problems identified above may be alleviated or prevented.

[0209] A fluid handling system comprising a modulating liquid immersion supply and / or a modulating fluid extraction may be used in combination with a modulating gas knife and / or a modulating gas supply, such as those described in the present disclosure. Alternatively, modulating liquid immersion supply and / or a modulating fluid extraction may be implemented in a fluid handling system which does not comprise a modulating gas knife or a modulating gas supply. The term modulating gas knife may be used to refer to a gas knife comprising a plurality of gas knife compartments, wherein gas can be supplied at different rates through each of the compartments. The term modulating gas supply may be used to refer to a gas supply comprising a plurality of gas supply compartments, wherein gas can be supplied at different rates through each of the compartments.

[0210] Figure 14 shows a modulating liquid supply 700 and a modulating fluid extraction 700a according to the present invention. A fluid handling structure 12 comprising at least one of themodulating liquid supply 700 and the modulating fluid extraction 700a may alleviate or prevent the problems identified above.

[0211] According to this embodiment, there may be provided a fluid handling system comprising a fluid handling structure 12 configured to at least partly confine a liquid to an immersion space 11 between a final element 100 and a substrate W and / or substrate support WT. The fluid handling system may further comprise a fluid extraction 700a comprising a set of extraction openings. The fluid extraction 700a is configured to extract immersion liquid from the immersion space 11 through the extraction openings. Each of the extraction openings are fluidly connected to an underpressure. The fluid handling structure 12 may comprise a liquid supply 700 comprising a first liquid supply opening 2000a and a second liquid supply opening 2000b configured to supply a liquid to the immersion space 11 through the first liquid supply opening 2000a and the second liquid supply opening 2000b. The first liquid supply opening 2000a and the second liquid supply opening 2000b are disposed radially inward from the gas knife, and are disposed diametrically opposite each other relative to the immersion space 11. The first liquid supply opening 2000a and the second liquid supply opening 2000b are connected to a liquid supply chamber (not shown). The liquid supply 700 is disposed radially inwards of the fluid extraction 700a. The liquid supply chamber may be a source of immersion liquid.

[0212] The fluid handling structure 12 may comprise a gas knife (not shown) configured to supply gas to a surface of the substrate W via at least one gas knife opening (not shown) of the gas knife. The at least one gas knife opening may be similar to the gas knife opening 26 of Figure 2a. The gas knife (not shown) may be a modulating gas knife, such as the modulating gas knife comprising at least a first gas knife compartment 501 and a second gas knife compartment 502 according to the present disclosure, e.g. illustrated schematically in Figure 4.

[0213] In Figure 14, a first liquid supply opening 2000a and a second liquid supply opening 2000b are diametrically opposite each other, i.e. they are located at angular positions of 90° and 270°. Optionally, further liquid supply openings may be disposed in liquid supply 700 surrounding the centre of the immersion space 11. These further liquid supply openings may be configured to supply immersion liquid supply 700. The number of openings in liquid supply 700 shown in Figure 14 is illustrative, not prescriptive.

[0214] The fluid extraction 700a may also extract gas via the extraction openings via a two-phase flow. The set of extraction openings are disposed radially outward from the liquid supply 700 and radially inward from the gas knife (not shown), and the extraction openings are disposed around a perimeter (e.g. around a circumference or periphery) of the immersion space 11 wherein each of the extraction openings are fluidly connected to an underpressure. The pitch and / or size of holes of the extraction openings may vary. In an embodiment, the extraction openings are disposed equidistantly from each other around the perimeter.

[0215] The set of extraction openings may comprise a first extraction opening 2001a, a second extraction opening 2001b, a third extraction opening 2001c and a fourth extraction opening 2001d. The first extraction opening 2001a, second extraction opening 2001b, third extraction opening 2001c and fourth extraction opening 2001d may be disposed at angular positions of 45°, 135°, 225°, 315° in the fluid extraction 700a.

[0216] The fluid extraction 700a may comprise at least one other set of extraction openings. For example, two further sets of extraction openings may be provided. The set of extraction openings is concentric to the at least one other set of extraction openings. Each set of extraction openings may be concentric to another set.

[0217] In an embodiment, the fluid handling system may further comprise a fluid extraction variable flow valve (not shown), i.e. for two phase extraction, between the underpressure and at least one of the extraction openings. Alternatively, fluid extraction variable flow valves may be provided between the underpressure and each of the extraction openings. In an embodiment comprising multiple sets of extraction openings, one or more of these sets may comprise extraction openings connected to the underpressure via a respective fluid extraction variable flow valve. This may provide improved control of the fluid extraction rate on an advancing side and on a receding side of the fluid handling structure.

[0218] In an embodiment, the fluid handling system may further comprise a first fluid extraction variable flow valve provided between the underpressure and the first extraction opening 2001a, and / or a second fluid extraction variable flow valve provided between the underpressure and the second extraction opening 2001b, and / or a third fluid extraction variable flow valve provided between the underpressure and the third extraction opening 2001c, and / or a fourth fluid extraction variable flow valve provided between the underpressure and the fourth extraction opening 2001d. These fluid extraction variable flow valves are not shown in the figures. These fluid extraction variable flow valves are disposed downstream of the respective extraction opening. For example, a fluid extraction variable flow valve may be disposed downstream of fluid extraction 2001 in Figure 12 such that the rate of fluid extraction may be modulated.

[0219] Accordingly, the rate of fluid extraction may be controlled at each of the extraction openings.

[0220] For example, at least one of the first fluid extraction variable flow valve, the second fluid extraction variable flow valve, the third fluid extraction variable flow valve and fourth fluid extraction variable flow valve may be configured to extract fluid through one of the extraction openings at a higher rate than another one of the extraction openings. For example, at least two of the first fluid extraction variable flow valve, the second fluid extraction variable flow valve, the third fluid extraction variable flow valve and fourth fluid extraction variable flow valve may be configured to extract fluid through two of the extraction openings at a higher rate than another at least one of the extraction openings. Alternatively, all of the fluid extraction variable flow valves may be individuallymodulated to set a different fluid extraction rate (i.e. rate of extraction of immersion liquid and gas) via the respective extraction opening.

[0221] For example, actuating one of the fluid extraction variable flow valves to achieve a larger under-pressure at least one extraction opening on the receding side may lead to an increased rate of immersion liquid extraction and gas extraction. Due to a higher shear of the gas flowing over the unrecovered immersion liquid 300, the thickness di may decrease, meaning that less immersion liquid is lost. In addition, any droplets which are formed may be smaller.

[0222] Additionally, on the advancing side of the fluid handling structure, a fluid extraction variable flow may be modulated such that the effective applied underpressure is smaller. As a result, more liquid and gas is extracted at the receding side than the liquid and gas extracted at the advancing side. This may be beneficial for maintaining the overall flow balance.

[0223] In an embodiment, liquid supply variable flow valves (not shown) may be provided between a liquid supply and one or more of the liquid supply openings. For example, in Figure 12 a liquid supply variable flow valve (not shown) may be provided upstream of liquid supply 2000. The liquid supply variable flow valve may modulate the flow of liquid which is provided to the immersion space 11 via the liquid supply opening.

[0224] In an embodiment, a first liquid supply variable flow valve (not shown) is provided between the liquid supply chamber (not shown) and the first liquid supply opening 2000a The first liquid supply variable flow valve is configured to control a liquid flow rate from the first liquid supply opening 2000a.

[0225] In an embodiment, a second liquid supply variable flow valve (not shown) is provided between the liquid supply chamber and the second liquid supply opening 2000b. The second liquid supply variable flow valve is configured to control a liquid flow rate from the second liquid supply opening 2000b.

[0226] The flow of liquid from the first liquid supply opening 2000a may be greater than a flow of liquid from the second liquid supply opening 2000b, or a flow of liquid from the first liquid supply opening 2000a may be the same as a flow of liquid from the second liquid supply opening 2000b, or a flow of liquid from the first liquid supply opening 2000a may be less than a flow of liquid from the second liquid supply opening 2000b. This may be selected depending on movement of the substrate W with respect to the fluid handling system.

[0227] By controlling the rate at which liquid is supplied through the first liquid supply opening 2000a and the second liquid supply opening 2000b, a non-uniform distribution of liquid supply may be achieved. By modulating the liquid supply variable flow valves, less liquid may be supplied at the receding side of the fluid handling structure, and / or more liquid may be supplied at the advancing side of the fluid handling structure. It may be particularly beneficial to provide a system which can switch the flow rate at each side of the substrate W, as the substrate W may switch direction of movement.

[0228] If less immersion liquid is supplied at the receding side, the immersion liquid volume in the unrecovered immersion liquid 300 is also less, leading to the reduction in the thickness di, i.e. a reduction in the thickness of the height of the film of unrecovered immersion liquid 300.

[0229] Provision of immersion liquid at a higher rate at the advancing side of the fluid handling structure may reduce the likelihood of any of the liquid supply openings on an advancing side becoming dry, which might result in the meniscus 33 from becoming detached from the substrate surface.

[0230] In an embodiment, control of immersion liquid supply and recovery of the fluid handling structure is modulated by providing the first liquid supply variable flow valve, the second liquid supply variable flow valve, and at least one of the first fluid extraction variable flow valve, the second fluid extraction variable flow valve, the third fluid extraction variable flow valve and the fourth fluid extraction variable flow valve. Accordingly, improved modulation of immersion liquid supply and immersion fluid extraction may be achieved.

[0231] Immersion liquid loss at the receding side may be further improved by reducing the rate of immersion liquid supply to the receding side of the fluid handling structure, and by increasing a rate of fluid extraction (i.e. immersion liquid and gas extraction) at the receding side. On the advancing side, the rate of immersion liquid supply may be increased and the rate of fluid extraction may be decreased.

[0232] Modulation of immersion liquid supply and / or immersion fluid extraction via a variable flow valve may be applied to any of the members configured to supply or extract the immersion fluid. For example, a supply variable flow may modulate the rate of liquid flow through the supply opening 20 in Figures 2a, 2c and 2d or supply opening 34 in Figure 2b. For example, a recovery variable flow may modulate the rate of liquid recovery through the recovery opening 21 in Figures 2a, 2c and 2d.

[0233] According to the present disclosure, any of the openings for supplying or extracting the immersion liquid and / or gas may be angled. An example an angled opening is shown in Figure 15. As shown, a passage 70a may have a first major axis FMA. The first major axis FMA may pass through the center of a cross-sectional area of a first entrance 65a and the center of a cross-sectional area of a first exit 60a. The angle 0 of walls 74a of the passage 70a may be determined relative to the first major axis FMA through the passage 70a. Opposite walls 74a may have the same angle 0 relative to the FMA as shown in Figure 15. The angle 0 may preferably be between approximately 0° and 30°, desirably approximately 0° and 20°, desirably approximately 0° and 15°, desirably approximately 1° and 10°, desirably approximately 5° and 7°. Alternatively, any of the openings for supplying or extracting the immersion liquid and / or gas may be straight. Alternatively, the respective openings have walls 74a at opposite sides that are parallel and have the same angle 0 to the first major axis FMA. The openings may have a circular cross section or a non-circular cross-section. For example, the cross-section of the openings may be an oval. A cross-section of the opening taken is not necessarily symmetric.

[0234] Certain extraction or supply members referred to herein may comprise an angled opening, i.e. may have walls which are angled as described above. For example, the following extraction or supply members may have be an angled opening: overflow recovery 24, recovery opening 25, gas knife opening 26, first gas knife opening 26a, second gas knife opening 26b, third gas knife opening 26c, gas supply openings 27a and 27b, gas recovery opening 28, recovery opening 32a, recovery opening 32b, supply openings 34, liquid injection hole 41, liquid recovery aperture 43, outer recovery hole 44a, gas sealing hole 45, further opening 50, first liquid supply opening 2000a, second liquid supply opening 2000b, first fluid extraction opening 2001a, second fluid extraction opening 2001b, third fluid extraction opening 2001c, and / or fourth fluid extraction opening 2001d.

[0235] Reduction of immersion liquid supply at the receding side of the fluid handling structure may increase the immersion liquid uniformity at the receding side of the fluid handling structure. This may further reduce problems such as immersion liquid loss.

[0236] Problems which are caused by opposing fluid supply requirements at the advancing and receding sides of the fluid handling structure, such as liquid loss, droplet generation and others, may be alleviated by providing a modulating gas knife and optionally, a modulating gas supply. To further reduce the occurrence of problems such as immersion liquid loss and bubble formation, while ensuring efficient use of gas, it may be desirable to provide a fluid handling structure which can control gas flow through the modulating gas knife and / or modulating gas supply based on a number of parameters which may affect behaviour of the immersion liquid at the receding and advancing sides of the fluid handling structure.

[0237] By taking into account a number of parameters which affect the immersion liquid behaviour during substrate movement, the flow of gas through the first gas knife compartment 501 and the second gas knife compartment 502 may be selected so that gas is used efficiently, while preventing the problems associated with immersion liquid loss. Optionally, the gas flow through the first gas supply compartment 501 and the second gas supply compartment 502 may also be controlled based on a number of parameters which affect the immersion liquid behaviour during substrate movement.

[0238] In some embodiments, a fluid handling structure 12 may comprise more than two gas knife compartments and / or gas supply compartments (such as the embodiment in Figure 6). In such embodiments, gas flow from each of the plurality of gas knife compartments and / or gas supply compartments may be modulated based on a number of parameters which may affect behaviour of the immersion liquid at the receding and advancing sides of the fluid handling structure. The values of parameters which affect immersion liquid behaviour, discussed below, or the combination of values of these parameters may affect the gas knife and gas supply modulation

[0239] It may also be desirable to provide a computer program having instructions thereon which, when executed on a computer, can cause the fluid handling system to control the flow of gas through each of the gas knife compartments, and optionally, through each of the gas supply compartments, based on the direction of movement of the substrate with respect to the fluid handling system.Alternatively the flow of gas may be controlled by without using a computer program, e.g. by using a trigger signal.

[0240] According to the present disclosure, a fluid handling system comprising the first gas knife compartment 501 and the second gas knife compartment 502 may set a gas flow through each of the gas knife compartments based on at least one of the number of parameters. The flow of gas through the first gas knife compartment 501 may be set to be greater than, equal to or less than the flow of gas through the second gas knife compartment 502.

[0241] According to the present disclosure, a fluid handling system further comprising the first gas supply compartment 601 and the second gas supply compartment 602 (such as, but not limited to the system shown in Figures 8a and 8b) may set a gas flow through each of the gas supply compartments based on one of the number of parameters. The flow of gas through the first gas supply compartment 601 may be set to be greater than, equal to or less than the flow of gas through the second gas supply compartment 602.

[0242] Modulation of gas flow through the gas knife compartments, and optionally, the gas supply compartments may be based on one of the following number of parameters.

[0243] The parameters may include position of the substrate W relative to the fluid handling structure 12.

[0244] The parameters may include a predicted volume and / or size of immersion liquid droplets on the surface of the substrate W outside of the immersion space 11. The parameters may include a predicted position of liquid on the surface of the substrate W outside of the immersion space 11. The predicted volume and / or size and / or position of immersion liquid droplets may be predicted based on a water-loss model. The water-loss model may predict the amount and the volume of droplets being left on the substrate W based on the speed of the substrate W, direction of substrate movement, a model of the immersion liquid behaviour exhibited when an edge of the substrate W crosses the confined immersion liquid, and / or other factors. By taking into account the position and / or size of any liquid droplets which may be present on the substrate surface that may interfere with the meniscus 33, gas flow may be modulated to reduce the likelihood of said droplets causing problems such as bubble creation. If the position and size of any liquid droplets is not taken into account, the gas flow provided may be too low or too high, which may result in reduced efficiency and efficacy of gas use.

[0245] The parameters may include settings of the fluid handling structure 12, such as the distance between the bottom surface of the fluid handling structure 12 and the facing surface of the substrate W, a total flow rate of gas from the gas knife, the flow of gas from the first gas knife compartment 501, the flow of gas from the second gas knife compartment 502, a total flow rate of gas from the gas supply, the flow of gas from the first gas supply compartment 601, and / or the flow of gas from the second gas supply compartment 602. By taking into account the distance between the bottom surface of the fluid handling structure 12 and the facing surface of the substrate W the meniscus profile may be modelled with improved accuracy, and gas flow through the gas knife and the gas supply may bemodulated such that disturbance of the meniscus 33 due to any liquid droplets is reduced. By taking into account the gas flow rate provided, immersion liquid loss may be predicted with improved accuracy.

[0246] The parameters may include substrate motion parameters, such as information on motion in the x-direction and y-direction, and / or speed. Information on direction and speed of motion may be referred to as substrate velocity. The substrate motion parameters may include substrate acceleration. This may lead to identification of critical positions on the substrate W where modulation of the gas flow (i.e. an increase or a decrease in the gas flow) may be most important for reducing immersion liquid loss.

[0247] The parameters may further include process-settings, such as information on the position of the resist on the substrate W, as well as contact angles of the resist regions with the substrate W. Regions of the substrate W comprising resists disposed thereon may have different gas flow requirements from other regions of the substrate W having resist disposed in a different pattern or other regions having no resist disposed thereon.

[0248] The computer program may model the substrate W as having a number of regions. The regions may be of the same size. Figure 16 shows an example of a circular substrate W which may be modelled as a number of separate regions. Each of these regions may have different gas flow requirements based on the parameters above. The fluid handling system may be configured to switch between different gas flow settings between the different regions, based on the gas flow requirements of each region. By providing a fluid handling system which can accommodate the individual gas flow requirements of each region, problems such as immersion liquid loss and bubble formation may be alleviated.

[0249] In the example shown on Figure 16, two left-most lower-most regions may have different gas flow requirements. In the specific example on Figure 16, the lower-left-most region has requirement “A”, namely, a low gas flow through a gas compartment (either the gas knife compartment or the gas supply compartment) located at the top of the region and a high gas flow through a gas compartment located at the bottom of the region. The adjacent lower-most second-left- most region has requirement “B”, namely, a high gas flow through a gas compartment (either the gas knife compartment or the gas supply compartment) located at the top of the region and a low gas flow through a gas compartment located at the bottom of the region. The computer program has instructions thereon which, when executed on a computer, cause the fluid handling system to provide the required gas flow to each region of the substrate W.

[0250] A fluid handling system comprising the first gas knife compartment 501, the second gas knife compartment 502, the first gas supply compartment 601 and the second gas supply compartment 602 may be set the flow through each of the compartments in accordance with Table 1. In Table 1, GK Y+ refers to the flow of the gas knife compartment located one side of the substrate W in the y- direction and GK Y- refers to the flow of the gas knife compartment located on the opposite side ofthe substrate W in the y-direction. GS Y+ refers to the flow of the gas supply compartment located one side of the substrate W in the y-direction and GK Y- refers to the flow of the gas supply compartment located on the opposite side of the substrate in the y-direction.

[0251] [Table 1]0252] According to the present disclosure, the gas flow requirements of each region of the substrate W may be met by selecting the appropriate gas flow settings from Table 1 for each of the regions.

[0253] Some example situations of gas flow modulation of different regions of the substrate W are shown in Figures 17a, 17b, 17c and 17d.

[0254] Figure 17e is a schematic showing gas flow states A, B and C. It will be noted that medium flow (as in table 1 above) is labelled in Figure 17e as “Mid flow”. While Figure 17e shows an embodiment of the gas knife comprising two variable flow valves each configured to modulate the flow of gas through a respective gas knife compartment, gas flow modulation based on the parameters identified above may be performed with another modulating gas knife, such as the gas supply shown in Figures 10a, 10b, Ila and 1 lb. In Figures 17a-17d, a region of the substrate W having gas flow requirement A is labelled “A”, a region of the substrate W having gas flow requirement B is labelled “B” and a region of the substrate W having gas flow requirement C is labelled “=” (meaning that a moderate equal flow is provided at both sides of the gas knife). The gas flow modulation may, for example, be based on the substrate position.

[0255] Figure 17a shows an example of gas flow modulation where in the gas flow requirements of each region of the substrate W are switched based on scanning direction of a substrate W. This may reduce droplet accumulation on the substrate surface. This may also reduce the length and thickness of unrecovered immersion liquid portion 300.

[0256] Figure 17b shows another example of gas flow modulation. This may also reduce the length and thickness of unrecovered immersion liquid portion 300.

[0257] Figures 17c and 17d show examples of modulating gas flow for specific regions of the substrate W. This mode may be implemented when a defectivity model predicts the locations of regions which are most susceptible to bubble formation, liquid loss, and / or other problems.

[0258] By providing an intelligent model which can accurately predict regions where switching of gas modulation may be beneficial, unnecessary modulation of the gas flow may be avoided. This may improve the lifetime of the apparatus.

[0259] It will be appreciated by the skilled person that the portions of the fluid supply and or extraction channels or openings may be provided with a coating. The coating may be a hydrophobic coating or a hydrophilic coating. Depending on the functionality of the fluid channel (or opening) a suitable coating may be selected.

[0260] Each of the fluid channels (or openings) may be provided with chamfers. Providing chamfers at an exit or entrance of a channels may be advantageous for the flow behaviour of the fluid.

[0261] 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.

[0262] 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.

[0263] 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 optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[0264] 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.

[0265] 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.

[0266] 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.

[0267] Embodiments include the following numbered clauses:1. A fluid handling system comprising a fluid handling structure configured to at least partly confine a liquid to an immersion space between a final element and a substrate, wherein the fluid handling structure comprises: a plurality of gas knife compartments, including at least a first gas knife compartment and a second gas knife compartment, wherein the first gas knife compartment comprising at least one opening located radially outward of the space, and the second gas knife compartment comprising at least one opening located radially outward of the space, the second gas knife compartment being fluidly separated from the first gas knife compartment, wherein each of the gas knife compartments are in fluid communication with a gas knife chamber via a gas knife variable flow valve, such that the first gas knife compartment is in fluid communication with a gas knife chamber via a first gas knife variable flow valve, and the second gas knife compartment is in fluid communication with the gas knife chamber via a second gas knife variable flow valve; a plurality of gas supply compartments, including at least a first gas supply compartment and a second gas supply compartment, wherein the first gas supply compartment comprising at least one opening located radially outward relative to the first gas knife compartment, such that the first gas knife compartment is disposed between the first gas supply compartment and the immersion space; and the second gas supply compartment comprising at least one opening located radially outward relative to the second gas knife compartment, such that the second gas knife compartment is disposed between the second gas supply compartment and the immersion space, the second gas supply compartment being fluidly separated from the first gas supply compartment, wherein each of the gas supply compartments are in fluid communication with a gas supply chamber via a gas supply variable flow valve, such that the first gas supply compartment is in fluid communication with a gas supply chamber via a first gas supply variable flow valve, and the secondgas supply compartment is in fluid communication with the gas supply chamber via a second gas supply variable flow valve.2. The fluid handling system according to clause 1, wherein the gas knife compartments are configured to supply gas to the periphery of the immersion space, and / or wherein the fluid handling structure further comprises a slit which enables passage of a beam to a surface of the substrate, wherein the gas knife compartments are configured to provide the gas over a portion of the fluid handling structure which defines the slit and optionally, another gas is provided over a portion of the fluid handling structure which does not define the slit and / or the plurality of gas knife compartments extend around a circumference of the immersion space defining a shape comprising four vertices separated by four sides, each of the gas knife compartments being disposed along at least one of the four sides and optionally, one or more vertices and wherein optionally:(i) the first gas knife compartment extends around half of the circumference of the immersion space and the second gas knife compartment extends around the other half of the circumference of the immersion space, or(ii) the first gas knife compartment and the second gas knife compartment are disposed opposite each other relative to a centre of the immersion space, the first gas knife compartment and the second gas knife compartment extending around portions of the immersion space, the fluid handling structure further comprising a third gas knife compartment and a fourth gas knife compartment disposed between the first and second gas knife compartments, the third gas knife compartment and the fourth gas knife compartment being connected to another gas chamber configured to supply another gas; optionally, the gas comprising carbon dioxide and the another gas comprising air; optionally, the gas knife comprising further gas knife compartments configured to supply the gas or the another gas.3. The fluid handling system according to clauses 1 or 2, wherein the gas supply compartments are configured to supply gas to the periphery of the gas supplied by the gas knife compartments.4. The fluid handling system according to any of the preceding clauses, further comprising a variable flow valve controller, wherein the variable flow valve controller is configured to individually control the flow rate through each of the first gas knife compartment, second gas knife compartment, first gas supply compartment and second gas supply compartment.5. The fluid handling system according to any of the preceding clauses, wherein the variable flow valve controller is configured to set the flow of gas through the first gas knife compartment to be higher than the flow through the second gas knife compartment, and the variable flow valve controller is further configured to set the flow through the first gas supply compartment to be lower than the flow through the second gas knife compartment.6. The fluid handling system according to any of the preceding clauses, wherein the variable flow valve controller is configured to set the flow of gas through each of the gas knife compartments and gas supply compartments based on a direction of movement of the substrate.7. The fluid handling system according to any of the preceding clauses, wherein the gas knife chamber is configured to output a flow of gas at a flow rate of up to 200 Nl / min.8. The fluid handling system according to any of the preceding clauses, wherein the gas supply chamber is configured to output a flow of gas at a flow rate of up to 200 Nl / min.9. The fluid handling system according to any of the preceding clauses, further comprising first gas knife channel having one end connected to the gas knife chamber and having a second gas knife channel and a third gas knife channel extending from the other end of the first gas knife channel, the second gas knife channel having the other end connected to the first gas knife compartment, having the first gas knife variable flow valve disposed between its two ends, and the third gas knife channel having the other end connected to the second gas knife compartment, having the second gas knife variable flow valve disposed between its two ends.10. The fluid handling system according to any of the preceding clauses, further comprising a first gas supply channel having one end connected to the gas supply chamber and having a second gas supply channel and a third gas supply channel extending from the other end of the first gas supply channel; the second gas supply channel having the other end connected to the first gas supply compartment, having the first gas supply variable flow valve disposed between its two ends, and the third gas supply channel having the other end connected to the second gas supply compartment, having the second gas supply variable flow valve disposed between its two ends.11. The fluid handling system according to any of the preceding clauses wherein the first gas knife compartment and the second gas knife compartment are fluidly separated from each other.12. The fluid handling system according to any of the preceding clauses wherein the first gas supply compartment and the second gas supply compartment are fluidly separated from each other.13. The fluid handling system according to any of the preceding clauses, wherein the fluid handling structure further comprises: a third gas knife compartment comprising at least one opening radially outward from the space; a fourth gas knife compartment comprising at least one opening radially outward from the space, wherein the third gas knife compartment is in fluid communication with a gas knife chamber via a third gas knife variable flow valve, and the fourth gas knife compartment is in fluid communication with the gas knife chamber via a fourth gas knife variable flow valve, and the third gas knife compartment and the fourth gas knife compartment are disposed in a space between the gas supply compartments and the immersion space.14. The fluid handling system according to any of the preceding clauses, wherein the fluid handling structure further comprises:a third gas supply compartment comprising at least one opening radially outward from the at least one opening of each of the gas knife compartments relative to the immersion space; a fourth gas supply compartment comprising at least one opening radially outward from the at least one opening of each of the gas knife compartments relative to the immersion space, wherein the third gas supply compartment is in fluid communication with a gas supply chamber via a third gas supply variable flow valve, and the fourth gas supply compartment is in fluid communication with the gas supply chamber via a fourth gas supply variable flow valve, and the third gas supply compartment and the fourth gas supply compartment are disposed such that the gas knife compartments are disposed in a space between the gas supply compartments and the immersion space.15. The fluid handling system according to clause 14, which comprises the variable flow valve controller of clause 4, wherein the variable flow valve controller is further configured to individually control the flow rate through the third gas knife compartment and third gas supply compartment.16. The fluid handling system according to clause 15, wherein the variable flow valve controller is configured to individually control the flow rate through the fourth gas knife compartment and the fourth gas supply compartment.17. The fluid handling system according to clause 15 or 16, wherein the variable flow valve controller is configured to individually control the flow rate through each of the gas knife compartments and gas flow compartment based on a movement of the substrate relative to the fluid handling structure.18. The fluid handling system according to any of the preceding clauses wherein the first gas knife compartment, the second gas knife compartment, the third gas knife compartment and the fourth gas knife compartment are fluidly separated from each other.19. The fluid handling system according to any of the preceding clauses, wherein the fluid handling structure further comprises: a first liquid supply compartment comprising at least one opening radially outward from the immersion space and radially inward from the first gas knife compartment and the first gas supply compartment; second liquid supply compartment comprising at least one opening radially outward from the immersion space and radially inward from the second gas knife compartment and the second gas supply compartment; wherein the first liquid supply compartment is in fluid communication with a liquid supply chamber via a first liquid supply variable flow valve, and the second liquid supply compartment is in fluid communication with the liquid supply chamber via a second liquid supply variable flow valve.20. The fluid handling system according to clause 19, wherein the variable flow valve controller is configured to individually control the flow rate through the first liquid supply compartment and the second liquid supply compartment.21. The fluid handling system according to any of the preceding clauses, further comprisinga pressure reservoir fluidly connected to each gas knife compartment, configured to provide an additional gas flow pulse to the respective gas knife compartment.22. The fluid handling system according to any of the preceding clauses, further comprising a control unit configured to cause at least one of the pressure reservoirs to provide an additional gas flow pulse to the gas knife compartment it is connected to, in response to a determination that, in plan view of the substrate, an edge of the substrate is intersecting the gas knife compartment that the at least one of the pressure reservoirs are connected to.23. The fluid handling system according to any of the preceding clauses, wherein the gas knife chamber is configured to supply substantially pure CO2 through at least one opening of each of the respective gas knife compartments.24. The fluid handling system according to any of the preceding clauses, wherein the gas supply chamber is configured to supply substantially pure CO2 through at least one opening of each of the respective gas supply compartments.25. A fluid handling system comprising a fluid handling structure configured to at least partly confine a liquid to an immersion space between a final element and a substrate, wherein the fluid handling structure comprises: a first gas knife compartment comprising at least one opening located radially outward of the immersion space, and a second gas knife compartment comprising at least one opening located radially outward of the immersion space, the second gas knife compartment being fluidly separated from the first gas knife compartment, a first gas knife channel fluidly connected to the first gas knife compartment and fluidly connected to the second gas knife compartment and configured to supply a first gas to the first gas knife compartment and the second gas knife compartment, a second gas knife channel fluidly connected to the first gas knife compartment and fluidly connected to the second gas knife compartment and configured to supply a second gas to the first gas knife compartment and the second gas knife compartment, a switching valve configured to variably direct flow of the first gas from the first gas knife channel to the first gas knife compartment only, or to the second gas knife compartment only, or to the first gas knife compartment and the second gas knife compartment.26. The fluid handling system according to clause 25, wherein the first gas knife compartment extends around a first portion of the circumference of the immersion space and the second gas knife compartment extends around a second portion of the circumference of the immersion space.27. The fluid handling system according to clause 25 or 26, wherein the switching valve is configured to direct the flow of first gas from the first gas knife channel to either the first gas knife compartment, or to the second gas knife compartment, or to the first gas knife compartment and the second gas knife compartment based on the direction of movement of the substrate.28. The fluid handling system according to any one of clauses 25 to 27, wherein during movement of the substrate, the switching valve is configured to direct first gas flow from the first gas knife channel to the first gas knife compartment only when the first gas knife compartment is on a receding side of the fluid handling structure, and the switching valve is configured to direct first gas flow from the first gas knife channel to the second gas knife compartment only when the second gas knife compartment is on a receding side of the fluid handling structure.29. The fluid handling system according to any one of clauses 25 to 28, wherein the switching valve is a first switching valve, the fluid handling system further comprising: a second switching valve configured to direct flow of the second gas from the second gas knife channel to the first gas knife compartment, or the second gas knife compartment, or the first gas knife compartment and the second gas knife compartment.30. The fluid handling system according to clause 29, wherein during movement of the substrate, the second switching valve is configured to direct second gas flow from the second gas knife channel to the first gas knife compartment only when the first gas knife compartment is on an advancing side of the fluid handling structure, and the second switching valve is configured to direct second gas flow from the second gas knife channel to the second gas knife compartment only when the second gas knife compartment is on an advancing side of the fluid handling structure.31. The fluid handling system according to any one of clauses 25 to 30, wherein the first gas knife channel and the second gas knife channel are each configured to output a flow of gas at a flow rate of up to 200 Nl / min.32. The fluid handling system according to any one of clauses 25 to 31, wherein the first gas comprises air and the second gas comprises carbon dioxide.33. The fluid handling system according to any one of clauses 25-32, wherein the gas knife compartments extend around a circumference of the immersion space defining a shape comprising four vertices separated by four sides.34. The fluid handling system according to clause 33, wherein the first gas knife compartment extends around half of the circumference of the immersion space and the second gas knife compartment extends around the other half of the circumference of the immersion space.35. The fluid handling system according to clause 25-33, wherein the gas knife further comprises a third gas knife compartment and a fourth gas knife compartment connected to the first gas knife channel, optionally, each of the third gas knife compartment and fourth gas knife compartment being connected via variable flow valves, wherein, optionally, the second gas knife channel provides a flow of the second gas to the first gas knife compartment and the second gas knife compartment or the second gas knife channel provides a flow of the second gas to the first gas knife compartment and thefirst gas knife channel provides a flow of the first gas to the second, third and fourth gas knife compartments, and optionally, the first gas knife channel is configured to supply air and / or the second gas knife channel is configured to supply carbon dioxide.36. The fluid handling system according to clause 35, wherein each of the first gas knife compartment, second gas knife compartment, third gas knife compartment and fourth gas knife compartment are disposed to cover a respective vertex of the gas knife and at least a portion of sides adjacent to said respective vertex, optionally wherein the first gas knife compartment and the second gas knife compartment are disposed opposite each other relative to a centre of the immersion space and / or the third gas knife compartment and the fourth gas knife compartment are disposed opposite each other relative to a centre of the immersion space.37. The fluid handling system according to clause 35, wherein the gas knife further comprises: a fifth gas knife compartment and a sixth gas knife compartment which are each connected to the first gas knife channel, optionally, via respective variable flow valves, and a seventh gas knife compartment and an eighth gas knife compartment which are each connected to the second gas knife channel, optionally, via respective variable flow valves, each of the first, second, seventh and eighth gas knife compartments being disposed to cover a respective vertex of the gas knife and at least a portion of the adjacent sides adjacent to said vertex, and each of the third, fourth, fifth and sixth gas knife compartments being disposed to cover a respective side of the gas knife between the vertices.38. The fluid handing system according to clauses 33-37, wherein the flow of gas through each of the gas knife compartments is based on a direction of movement of the substrate and / or the total flow of gas is higher at a receding side of the substrate than at an advancing side of the substrate.39. The fluid handling structure according to any one of clauses 25-38, wherein there is provided at least one further gas knife compartment which is concentric with any of the gas knife compartments, the at least one further gas knife compartment being connected to first gas knife supply and / or the second gas knife supply.40. The fluid handing system according to clauses 25-39, wherein the fluid handling structure further comprises a slit which enables passage of a beam to a surface of the substrate, wherein the gas knife compartments are configured to provide the gas over a portion of the fluid handling structure which defines the slit and optionally, another gas is provided over a portion of the fluid handling structure which does not define the slit.41. A fluid handling system comprising a fluid handling structure configured to at least partly confine a liquid to an immersion space between a final element and a substrate, wherein the fluid handling structure comprises:a liquid supply comprising a first liquid supply opening and a second liquid supply opening configured to supply a liquid to the immersion space through the first liquid supply opening and the second liquid supply opening; fluid extraction comprising a set of extraction openings, the fluid extraction being configured to extract immersion fluid from the immersion space through the extraction openings, wherein each of the extraction openings are fluidly connected to an underpressure, wherein the liquid supply is disposed radially inwards of the fluid extraction, wherein the first liquid supply opening and the second liquid supply opening are disposed radially inward from the gas knife, and are disposed diametrically opposite each other relative to the immersion space, and the first liquid supply opening and the second liquid supply opening are connected to a liquid supply chamber.42. The fluid handling system of clause 41, comprising a gas knife configured to supply gas to a surface of the substrate via at least one gas knife opening of the gas knife43. A fluid handling system comprising the fluid handling structure according to any one of clauses 1 to 40, wherein the first gas knife compartment and the second gas knife compartment define a gas knife, and fluid handling structure further comprises: a liquid supply comprising a first liquid supply opening and a second liquid supply opening configured to supply a liquid to the immersion space through the first liquid supply opening and the second liquid supply opening, wherein the first liquid supply opening and the second liquid supply opening are disposed radially inward from the gas knife, and are disposed diametrically opposite each other relative to the immersion space, and the first liquid supply opening and the second liquid supply opening are connected to a liquid supply chamber.44. The fluid handling system of clause 43, comprising fluid extraction comprising a set of extraction openings, the fluid extraction being configured to extract immersion fluid from the immersion space through the extraction openings, wherein each of the extraction openings are fluidly connected to an underpressure, wherein the liquid supply is disposed radially inwards of the fluid extraction.45. The fluid handling system according to any one of clauses 41, 42 and claim 44, wherein the set of extraction openings are disposed radially inward from the gas knife, and the extraction openings are disposed around a perimeter of the immersion space.46. The fluid handling system according to clause 45, further comprising a fluid extraction variable flow valve provided between the underpressure and each corresponding extraction opening.47. The fluid handling system according to clause 45, wherein the set of extraction opening comprises a first extraction opening, a second extraction opening, a third extraction opening and a fourth extraction opening, and the fluid extraction further comprises:a first fluid extraction variable flow valve provided between the underpressure and the first fluid extraction opening, and / or a second fluid extraction variable flow valve provided between the underpressure and the second fluid extraction opening, and / or a third fluid extraction variable flow valve provided between the underpressure and the third fluid extraction opening, and / or a fourth fluid extraction variable flow valve provided between the underpressure and the fourth fluid extraction opening.48. The fluid handling system according to clause 47, wherein at least one of the first fluid extraction variable flow valve, the second fluid extraction variable flow valve, the third fluid extraction variable flow valve and fourth fluid extraction variable flow valve are configured to extract fluid through one of the extraction openings at a higher rate than another one of the extraction openings.49. The fluid handling system according to any one of clauses 44 to 46, wherein the fluid extraction comprises at least one other set of extraction openings, wherein the set of extraction openings is concentric to the at least one other set of extraction openings.50. The fluid handling system according to any one of clauses 41 to 49, further comprising a first liquid supply variable flow valve provided between the liquid supply chamber and the first liquid supply opening, wherein the first liquid supply variable flow valve is configured to control a liquid flow rate from the first liquid supply opening.51. The fluid handling system according to any one of clauses 41 to 50, further comprising a second liquid supply variable flow valve provided between the liquid supply chamber and the second liquid supply opening, wherein the second liquid supply variable flow valve is configured to control a liquid flow rate from the second liquid supply opening.52. The fluid handling system according to any one of clauses 41 to 51, wherein the flow of liquid from the first liquid supply opening is greater than a flow of liquid from the second liquid supply opening, or a flow of liquid from the first liquid supply opening is the same as a flow of liquid from the second liquid supply opening, or a flow of liquid from the first liquid supply opening is less than a flow of liquid from the second liquid supply opening.53. The fluid handling system according to any of the preceding clauses, wherein the fluid handling structure comprises a supply opening on its inner surface and a supply variable flow valve, wherein liquid is supplied to the immersion space through the supply opening and the supply variable flow valve modulates the rate of liquid flow through the supply opening.54. The fluid handling system according to any of the preceding clauses, wherein fluid handling structure comprises a recovery opening on its inner surface and a recovery variable flow valve, wherein immersion liquid is recovered from the immersion space through the recovery opening and the recovery variable flow valve modulates the rate of liquid recovery through the recovery opening.55. The fluid handling system according to any one of the preceding clauses in which the fluid handling structure comprises a gas knife, wherein the fluid handling system is configured to modulate a flow of gas through the first gas knife compartment and the second gas knife compartment based on at least one of a number of parameters, wherein the parameters comprise: a position of the substrate relative to the fluid handling structure, a predicted volume of immersion liquid on the surface of the substrate outside of the immersion space, a predicted size of droplets of immersion liquid on the surface of the substrate outside of the immersion space, a predicted position of liquid on the surface of the substrate outside of the immersion space, a distance between the bottom surface of the fluid handling structure and the surface of the substrate facing the fluid handling structure, a flow of gas being provided to the surface of the substrate, substrate velocity, substrate acceleration, position of resist on a substrate surface, and contact angle of the resist with the substrate surface.56. The fluid handling system according to any of clauses 1 to 24, wherein the fluid handling system is configured to modulate a flow of gas through the first gas knife compartment, the second gas knife compartment, the first gas supply compartment and the second gas supply compartment based on at least one of a number of parameters, wherein the parameters comprise: a position of the substrate relative to the fluid handling structure, a predicted volume of immersion liquid on the surface of the substrate outside of the immersion space, a predicted size of droplets of immersion liquid on the surface of the substrate outside of the immersion space, a predicted position of liquid on the surface of the substrate outside of the immersion space, a distance between the bottom surface of the fluid handling structure and the surface of the substrate facing the fluid handling structure, a flow of gas being provided to the surface of the substrate, substrate velocity, substrate acceleration, position of resist on a substrate surface, contact angle of the resist with the substrate surface.57. A lithographic apparatus comprising the fluid handling system according to any of the preceding clauses.58. A computer program having instructions thereon which, when executed on a computer, cause the fluid handling system according to any one of the preceding clauses in which the fluid handling structure comprises a gas knife to control the flow of gas through the first gas knife compartment and the second gas knife compartment based on at least one of a number of parameters, wherein the parameters comprise: a position of the substrate relative to the fluid handling structure, a predicted volume of immersion liquid on the surface of the substrate outside of the immersion space, a predicted size of droplets of immersion liquid on the surface of the substrate outside of the immersion space, a predicted position of liquid on the surface of the substrate outside of the immersion space, distance between the bottom surface of the fluid handling structure and the surface of the substrate, a flow of gas being provided to the surface of the substrate, substrate velocity, substrate acceleration, position of resist on a substrate surface, contact angles of the resist with the substrate surface.59. A computer program having instructions thereon which, when executed on a computer, cause fluid handling system according to any one of clauses 1-24, to control the flow of gas through the first gas knife compartment, the second gas knife compartment, the first gas supply compartment and the second gas supply compartment based on at least one of a number of parameters, wherein the parameters include: a position of the substrate relative to the fluid handling structure, a predicted volume of immersion liquid on the surface of the substrate outside of the immersion space, a predicted size of droplets of immersion liquid on the surface of the substrate outside of the immersion space, a predicted position of liquid on the surface of the substrate outside of the immersion space, distance between the bottom surface of the fluid handling structure and the surface of the substrate, a flow of gas being provided to the surface of the substrate, substrate velocity, substrate acceleration, position of resist on a substrate surface, contact angles of the resist with the substrate surface.

Claims

CLAIMS1. A fluid handling system comprising a fluid handling structure configured to at least partly confine immersion liquid to an immersion space between a final element and a substrate, wherein the fluid handling structure comprises: a plurality of gas knife compartments, including at least a first gas knife compartment and a second gas knife compartment, wherein the first gas knife compartment comprising at least one opening located radially outward of the space, and the second gas knife compartment comprising at least one opening located radially outward of the space, the second gas knife compartment being fluidly separated from the first gas knife compartment, wherein each of the gas knife compartments are in fluid communication with a gas knife chamber via a gas knife variable flow valve, such that the first gas knife compartment is in fluid communication with a gas knife chamber via a first gas knife variable flow valve, and the second gas knife compartment is in fluid communication with the gas knife chamber via a second gas knife variable flow valve; a plurality of gas supply compartments, including at least a first gas supply compartment and a second gas supply compartment, wherein the first gas supply compartment comprising at least one opening located radially outward relative to the first gas knife compartment, such that the first gas knife compartment is disposed between the first gas supply compartment and the immersion space; and the second gas supply compartment comprising at least one opening located radially outward relative to the second gas knife compartment, such that the second gas knife compartment is disposed between the second gas supply compartment and the immersion space, the second gas supply compartment being fluidly separated from the first gas supply compartment, wherein each of the gas supply compartments are in fluid communication with a gas supply chamber via a gas supply variable flow valve, such that the first gas supply compartment is in fluid communication with a gas supply chamber via a first gas supply variable flow valve, and the second gas supply compartment is in fluid communication with the gas supply chamber via a second gas supply variable flow valve.

2. The fluid handling system according to claim 1, wherein the gas knife compartments are configured to supply gas to the periphery of the immersion space, and / or wherein the gas supply compartments are configured to supply gas to the periphery of the gas supplied by the gas knife compartments, and / or wherein the fluid handling structure further comprises a slit which enables passage of a beam to a surface of the substrate, wherein the gas knife compartments are configured toprovide the gas over a portion of the fluid handling structure which defines the slit and optionally, another gas is provided over the a portion of the fluid handling structure which does not define the slit and / or the plurality of gas knife compartments extend around a circumference of the immersion space defining a shape comprising four vertices separated by four sides, each of the gas knife compartments being disposed along at least one of the four sides and optionally, one or more vertices and wherein optionally:(i) the first gas knife compartment extends around half of the circumference of the immersion space and the second gas knife compartment extends around the other half of the circumference of the immersion space, or(ii) the first gas knife compartment and the second gas knife compartment are disposed opposite each other relative to a centre of the immersion space, the first gas knife compartment and the second gas knife compartment extending around portions of the immersion space, the fluid handling structure further comprising a third gas knife compartment and a fourth gas knife compartment disposed between the first and second gas knife compartments, the third gas knife compartment and the fourth gas knife compartment being connected to another gas chamber configured to supply another gas; optionally, the gas comprising carbon dioxide and the another gas comprising air; optionally, the gas knife comprising further gas knife compartments configured to supply the gas or the another gas.

3. The fluid handling system according to any of the preceding claims, further comprising a variable flow valve controller, wherein the variable flow valve controller is configured to individually control the flow rate through each of the first gas knife compartment, second gas knife compartment, first gas supply compartment and second gas supply compartment, desirably wherein the variable flow valve controller is configured to set the flow of gas through the first gas knife compartment to be higher than the flow through the second gas knife compartment, and the variable flow valve controller is further configured to set the flow through the first gas supply compartment to be lower than the flow through the second gas knife compartment, and / or desirably wherein the variable flow valve controller is configured to set the flow of gas through each of the gas knife compartments and gas supply compartments based on a direction of movement of the substrate.

4. The fluid handling system according to any of the preceding claims, wherein the gas knife chamber is configured to output a flow of gas at a flow rate of up to 200 Nl / min, and / or wherein the gas supply chamber is configured to output a flow of gas at a flow rate of up to 200 Nl / min.

5. The fluid handling system according to any of the preceding claims, further comprising first gas knife channel having one end connected to the gas knife chamber and having a second gas knife channel and a third gas knife channel extending from the other end of the first gas knife channel,the second gas knife channel having the other end connected to the first gas knife compartment, having the first gas knife variable flow valve disposed between its two ends, and the third gas knife channel having the other end connected to the second gas knife compartment, having the second gas knife variable flow valve disposed between its two ends, and / or further comprising a first gas supply channel having one end connected to the gas supply chamber and having a second gas supply channel and a third gas supply channel extending from the other end of the first gas supply channel; the second gas supply channel having the other end connected to the first gas supply compartment, having the first gas supply variable flow valve disposed between its two ends, and the third gas supply channel having the other end connected to the second gas supply compartment, having the second gas supply variable flow valve disposed between its two ends.

6. The fluid handling system according to any of the preceding claims, wherein the first gas knife compartment and the second gas knife compartment are fluidly separated from each other, and / or wherein the first gas supply compartment and the second gas supply compartment are fluidly separated from each other.

7. The fluid handling system according to any of the preceding claims, wherein the fluid handling structure further comprises: a third gas knife compartment comprising at least one opening radially outward from the space; a fourth gas knife compartment comprising at least one opening radially outward from the space, wherein the third gas knife compartment is in fluid communication with a gas knife chamber via a third gas knife variable flow valve, and the fourth gas knife compartment is in fluid communication with the gas knife chamber via a fourth gas knife variable flow valve, and the third gas knife compartment and the fourth gas knife compartment are disposed in a space between the gas supply compartments and the immersion space, and / or wherein the fluid handling structure further comprises: a third gas supply compartment comprising at least one opening radially outward from the at least one opening of each of the gas knife compartments relative to the immersion space; a fourth gas supply compartment comprising at least one opening radially outward from the at least one opening of each of the gas knife compartments relative to the immersion space, wherein the third gas supply compartment is in fluid communication with a gas supply chamber via a third gas supply variable flow valve, and the fourth gas supply compartment is in fluid communication with the gas supply chamber via a fourth gas supply variable flow valve, and the thirdgas supply compartment and the fourth gas supply compartment are disposed such that the gas knife compartments are disposed in a space between the gas supply compartments and the immersion space.

8. The fluid handling system according to claim 7, comprising the variable flow valve controller of claim 3, wherein the variable flow valve controller is further configured to individually control the flow rate through the third gas knife compartment and third gas supply compartment, desirably wherein the variable flow valve controller is configured to individually control the flow rate through the fourth gas knife compartment and the fourth gas supply compartment, and / or wherein the variable flow valve controller is configured to individually control the flow rate through each of the gas knife compartments and gas flow compartment based on a movement of the substrate relative to the fluid handling structure.

9. The fluid handling system according to any of the preceding claims, wherein the first gas knife compartment, the second gas knife compartment, the third gas knife compartment and the fourth gas knife compartment are fluidly separated from each other, and / or wherein the fluid handling structure further comprises: a first liquid supply compartment comprising at least one opening radially outward from the immersion space and radially inward from the first gas knife compartment and the first gas supply compartment; second liquid supply compartment comprising at least one opening radially outward from the immersion space and radially inward from the second gas knife compartment and the second gas supply compartment; wherein the first liquid supply compartment is in fluid communication with a liquid supply chamber via a first liquid supply variable flow valve, and the second liquid supply compartment is in fluid communication with the liquid supply chamber via a second liquid supply variable flow valve, desirably wherein the variable flow valve controller is configured to individually control the flow rate through the first liquid supply compartment and the second liquid supply compartment.

10. The fluid handling system according to any of the preceding claims, further comprising a pressure reservoir fluidly connected to each gas knife compartment, configured to provide an additional gas flow pulse to the respective gas knife compartment, and / or further comprising a control unit configured to cause at least one of the pressure reservoirs to provide an additional gas flow pulse to the gas knife compartment it is connected to, in response to a determination that, in plan view of the substrate, an edge of the substrate is intersecting the gas knife compartment that the at least one of the pressure reservoirs are connected to, and / or wherein the gas knife chamber is configured to supply substantially pure CO2 through at least one opening of each of the respective gas knife compartments, and / or wherein the gas supply chamber is configured to supply substantially pureCO2through at least one opening of each of the respective gas supply compartments, and / or wherein the fluid handling system is configured to modulate a flow of gas through the first gas knife compartment, the second gas knife compartment, the first gas supply compartment and the second gas supply compartment based on at least one of a number of parameters, wherein the parameters comprise: a position of the substrate relative to the fluid handling structure, a predicted volume of immersion liquid on the surface of the substrate outside of the immersion space, a predicted size of droplets of immersion liquid on the surface of the substrate outside of the immersion space, a predicted position of liquid on the surface of the substrate outside of the immersion space, a distance between the bottom surface of the fluid handling structure and the surface of the substrate facing the fluid handling structure, a flow of gas being provided to the surface of the substrate, substrate velocity, substrate acceleration, position of resist on a substrate surface, contact angle of the resist with the substrate surface.

11. A fluid handling system comprising the fluid handling structure according to any of the preceding claims, wherein the first gas knife compartment and the second gas knife compartment define a gas knife, and fluid handling structure further comprises: a liquid supply comprising a first liquid supply opening and a second liquid supply opening configured to supply a liquid to the immersion space through the first liquid supply opening and the second liquid supply opening, wherein the first liquid supply opening and the second liquid supply opening are disposed radially inward from the gas knife, and are disposed diametrically opposite each other relative to the immersion space, and the first liquid supply opening and the second liquid supply opening are connected to a liquid supply chamber, desirably comprising fluid extraction comprising a set of extraction openings, the fluid extraction being configured to extract immersion fluid from the immersion space through the extraction openings, wherein each of the extraction openings are fluidly connected to an underpressure, wherein the liquid supply is disposed radially inwards of the fluid extraction.

12. The fluid handling system according to claim 11, wherein the set of extraction openings are disposed radially inward from the gas knife, and the extraction openings are disposed around a perimeter of the immersion space, desirably further comprising a fluid extraction variable flow valveprovided between the underpressure and each corresponding extraction opening, or desirably wherein the set of extraction opening comprises a first extraction opening, a second extraction opening, a third extraction opening and a fourth extraction opening, and the fluid extraction further comprises: a first fluid extraction variable flow valve provided between the underpressure and the first fluid extraction opening, and / or a second fluid extraction variable flow valve provided between the underpressure and the second fluid extraction opening, and / or a third fluid extraction variable flow valve provided between the underpressure and the third fluid extraction opening, and / or a fourth fluid extraction variable flow valve provided between the underpressure and the fourth fluid extraction opening, desirably wherein at least one of the first fluid extraction variable flow valve, the second fluid extraction variable flow valve, the third fluid extraction variable flow valve and fourth fluid extraction variable flow valve are configured to extract fluid through one of the extraction openings at a higher rate than another one of the extraction openings.

13. The fluid handling system according to claim 11 or 12, wherein the fluid extraction comprises at least one other set of extraction openings, wherein the set of extraction openings is concentric to the at least one other set of extraction openings, and / or further comprising a first liquid supply variable flow valve provided between the liquid supply chamber and the first liquid supply opening, wherein the first liquid supply variable flow valve is configured to control a liquid flow rate from the first liquid supply opening, and / or further comprising a second liquid supply variable flow valve provided between the liquid supply chamber and the second liquid supply opening, wherein the second liquid supply variable flow valve is configured to control a liquid flow rate from the second liquid supply opening, and / or wherein the flow of liquid from the first liquid supply opening is greater than a flow of liquid from the second liquid supply opening, or a flow of liquid from the first liquid supply opening is the same as a flow of liquid from the second liquid supply opening, or a flow of liquid from the first liquid supply opening is less than a flow of liquid from the second liquid supply opening.

14. The fluid handling system according to any of the preceding claims, wherein the fluid handling structure comprises a supply opening on its inner surface and a supply variable flow valve, wherein liquid is supplied to the immersion space through the supply opening and the supply variable flow valve modulates the rate of liquid flow through the supply opening, and / or wherein fluid handling structure comprises a recovery opening on its inner surface and a recovery variable flow valve, wherein immersion liquid is recovered from the immersion space through the recovery opening and the recovery variable flow valve modulates the rate of liquid recovery through the recovery opening, and / or wherein the fluid handling system is configured to modulate a flow of gas through thefirst gas knife compartment and the second gas knife compartment based on at least one of a number of parameters, wherein the parameters comprise: a position of the substrate relative to the fluid handling structure, a predicted volume of immersion liquid on the surface of the substrate outside of the immersion space, a predicted size of droplets of immersion liquid on the surface of the substrate outside of the immersion space, a predicted position of liquid on the surface of the substrate outside of the immersion space, a distance between the bottom surface of the fluid handling structure and the surface of the substrate facing the fluid handling structure, a flow of gas being provided to the surface of the substrate, substrate velocity, substrate acceleration, position of resist on a substrate surface, and contact angle of the resist with the substrate surface.

15. A lithographic apparatus comprising the fluid handling system according to any of the preceding claims.

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