EP4681024A1

EP4681024A1 - Substrate support and lithographic apparatus

Info

Publication number: EP4681024A1
Application number: EP24703390.5A
Authority: EP
Inventors: Niek Jacobus Johannes ROSET; Edwin Johannes Cornelis Bos; Simon Karel RAVENSBERGEN; Frank Pieter Albert VAN DEN BERKMORTEL; Zhuangxiong HUANG; Sayyed Hamid HOSSEINI; Dipanjay DEWANJI; Dennis Johannes Franciscus HECK; Wladimir Fransiscus Gerardus Maria HERTOG; Johannes Marinus Abraham HOFMAN; Sander BLOM; Cornelius Maria ROPS
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2023-03-13
Filing date: 2024-02-08
Publication date: 2026-01-21
Also published as: CN121002449A; KR20250162539A; TW202439034A; JP2026510101A; WO2024188552A1

Abstract

A substrate support configured to support a substrate, comprising an upper component, a core component and a lower component; wherein: a first opening is formed in an upper surface of the upper component; a first passageway communicating with the first opening is defined in the upper component and the core component; a first extraction channel communicating with the first passageway is defined by the core component and the lower component; and a first conditioning channel is defined by the core component and the lower component.

Description

SUBSTRATE SUPPORT AND LITHOGRAPHIC APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23161486.8 which was filed on 13 March 2023 and of EP application 23200625.4 which was filed on 28 September 2023 and which are incorporated herein in their entirety by reference.

FIELD

[0002] The present invention relates to a substrate support configured to support a substrate, a lithographic apparatus including a substrate support, a method of supporting a substrate and a method of manufacturing a device including a method of supporting a substrate.

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, use a projection system to 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 immersion 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 between the projection system of the lithographic apparatus and the substrate by a fluid handling structure.

SUMMARY

[0007] In a semiconductor manufacturing process, a substrate is supported on a substrate support. Specifically, the substrate is supported on a plurality of burls protruding from the a surface of the substrate support.

[0008] In semiconductor manufacturing, there is an increasing trend towards integrating more functionality onto unit surfaces of substrates by shrinking, and increasing the number of, stacked film layers on the substrate. Increasing the number of layers stacked on a substrate increases the stress induced between the film and the substrate, which can cause significant substrate warpage and decrease overlay performance.

[0009] New configurations of substrate support have been proposed, with additional functionality to prevent unfavourable warpage of the substrate support. Specifically new configurations of substrate support have been proposed with additional functionality to prevent unfavourable warpage of the substrate support during loading of the substrate onto the substrate support. The new configurations of substrate supports may comprise with additional openings to provide an edge-lifting force on a radially outward region of the substrate during loading.

[0010] However, the additional openings, and their positional requirements, place constraints on other features of the substrate support, such as supply channels in fluid communication with the openings and conditioning channels configured to maintain the substrate support at a constant temperature. If these supply channels and conditioning channels are not optimally positioned within the substrate support, the temperature of the substrate support may change over time, causing transient structural deformation. Transient structural deformation can lead to a reduction in overlay performance of the lithographic apparatus including the substrate support.

[0011] The object of the present invention is to provide a substrate support which allows additional functionality to be implemented in substrate supports without resulting in a reduction in overlay performance caused by temperature-induced structural deformations.

[0012] According to the present invention, there is provided a substrate support configured to support a substrate, comprising an upper component, a core component and a lower component; wherein: a first opening is formed in an upper surface of the upper component; a first passageway communicating with the first opening is defined in the upper component and the core component; a first extraction channel communicating with the first passageway is defined by the core component and the lower component; and a first conditioning channel is defined by the core component and the lower component.

[0013] Further embodiments, features and advantages of the present invention, as well as the structure and operation of the various embodiments, features and advantages of the present invention are described in detail below with reference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0014] 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:

Figure 1 depicts a schematic overview of a lithographic apparatus.

Figure 2 depicts, in cross-section, a substrate support not in accordance with the present invention.

Figure 3 depicts, in cross-section, a portion of a substrate support in a loading state.

Figure 4 depicts, in cross-section, a portion of a substrate support in a clamp state.

Figure 5 depicts, in cross-section, a portion of a substrate support in a bypass state.

Figure 6 depicts, in cross-section, a substrate support not in accordance with the present invention (i.e., a comparative example)

Figure 7 depicts, in cross-section, a portion of a substrate support in accordance with the present invention.

Figure 8 depicts an isometric view of a substrate support in accordance with the present invention, with an upper portion removed such that channels within the substrate support are visible.

Figure 9 depicts, in plan view, a portion of a substrate support in accordance with the present invention with an upper portion removed such that passageways within the substrate support are visible.

Figure 10 depicts, in cross-section, a portion of a substrate support in accordance with the present invention and including a “stacked channels” configuration.

Figure 11 depicts, in cross-section, a portion of a substrate support in accordance with the present invention and including a “stacked channels” configuration different to the “stacked channels” configuration depicted in Figure 10.

Figure 12 depicts, in cross-section, a portion of a substrate support in accordance with the present invention and wherein a conditioning channel is in fluid communication with an extraction channel.

Figure 13 depicts, in cross-section, a portion of a substrate support in accordance with the present invention, wherein an extraction channel is fluid communication with another extraction channel.

Figure 14 depicts, in cross-section, a portion of substrate support in accordance with the present invention, wherein a conditioning channel is in fluid communication with a fluid extraction gutter. Figure 15 depicts, in cross-section, a portion of a substrate support in accordance with the present invention and wherein a conditioning channel is in fluid communication with an extraction channel.

Figure 16 depicts, in cross-section, a radially outward portion of a substrate support in accordance with the present invention, showing a first fluid extraction groove.

Figures 17A and 17B depict, in cross-section a radially outward portion of a substrate support in accordance with the present invention, wherein a flow-restricting member is provided in the first fluid extraction groove.

Figure 18 depicts, in plan view, a fluid extraction groove in which a plurality of flowrestricting members are disposed.

Figure 19 depicts, in cross-section, a radially outward portion of a substrate support in accordance with the present invention, showing a first fluid extraction groove.

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

DETAILED DESCRIPTION

[0015] 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).

[0016] 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.

[0017] 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.

[0018] 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.

[0019] The term “projection system” PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and/or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system” PS.

[0020] The lithographic apparatus is of a type wherein at least a portion of the substrate W may be covered by an immersion liquid having a relatively high refractive index, e.g., water, so as to fill an immersion space between the projection system PS and the substrate W - which is also referred to as immersion lithography. More information on immersion techniques is given in US 6,952,253, which is incorporated herein by reference.

[0021] The lithographic apparatus may be of a type having two or more substrate supports WT (also named “dual stage”). In such a “multiple stage” machine, the substrate supports WT may be used in parallel, and/or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W. [0022] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not depicted in figures). The measurement stage is arranged to hold a sensor and/or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid. The measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS.

[0023] In operation, the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position measurement system IF, the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly depicted in Figure 1) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions. Substrate alignment marks Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C.

[0024] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axis, i.e., an x-axis, a y-axis and a z-axis. Each of the three axis is orthogonal to the other two axis. A rotation around the x-axis is referred to as an Rx-rotation. A rotation around the y- axis is referred to as an Ry -rotation. A rotation around about the z-axis is referred to as an Rz- rotation. The x-axis and the y-axis define a horizontal plane, whereas the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the invention and is used for clarification only. Instead, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0025] Immersion techniques have been introduced into lithographic systems to enable improved resolution of smaller features. In an immersion lithographic apparatus, a liquid layer of immersion liquid having a relatively high refractive index is interposed in the immersion space between a projection system PS of the apparatus (through which the patterned beam is projected towards the substrate W) and the substrate W. The immersion liquid covers at least the part of the substrate W under a final element of the projection system PS. Thus, at least the portion of the substrate W undergoing exposure is immersed in the immersion liquid.

[0026] In commercial immersion lithography, the immersion liquid is water. Typically the water is distilled water of high purity, such as Ultra-Pure Water (UPW) which is commonly used in semiconductor fabrication plants. In an immersion system, the UPW is often purified and it may undergo additional treatment steps before supply to the immersion space as immersion liquid. Other liquids with a high refractive index can be used besides water as the immersion liquid, for example: a hydrocarbon, such as a fluorohydrocarbon; and/or an aqueous solution. Further, other fluids besides liquid have been envisaged for use in immersion lithography.

[0027] In this specification, reference will be made in the description to localized immersion in which the immersion liquid is confined, in use, to the immersion space between the final element and a surface facing the final element. The facing surface is a surface of substrate W or a surface of the supporting stage (or substrate support WT) that is co-planar with the surface of the substrate W. (Please note that reference in the following text to surface of the substrate W also refers in addition or in the alternative to the surface of the substrate support WT, unless expressly stated otherwise; and vice versa). A fluid handling structure IH present between the projection system PS and the substrate support WT is used to confine the immersion liquid to the immersion space. The immersion space filled by the immersion liquid is smaller in plan than the top surface of the substrate W and the immersion space remains substantially stationary relative to the projection system PS while the substrate W and substrate support WT move underneath.

[0028] Other immersion systems have been envisaged such as an unconfined immersion system (a so-called ’All Wet’ immersion system) and a bath immersion system. In an unconfined immersion system, the immersion liquid covers more than the surface under the final element. The liquid outside the immersion space is present as a thin liquid film. The liquid may cover the whole surface of the substrate W or even the substrate W and the substrate support WT co-planar with the substrate W. In a bath type system, the substrate W is fully immersed in a bath of immersion liquid.

[0029] The fluid handling structure IH is a structure which supplies the immersion liquid to the immersion space, removes the immersion liquid from the immersion space and thereby confines the immersion liquid to the immersion space. It includes features which are a part of a fluid supply system. The arrangement disclosed in PCT patent application publication no. WO 99/49504 is an early fluid handling structure comprising pipes which either supply or recover the immersion liquid from the immersion space and which operate depending on the relative motion of the stage beneath the projection system PS. In more recent designs, the fluid handling structure extends along at least a part of a boundary of the immersion space between the final element of the projection system PS and the substrate support WT or substrate W, so as to in part define the immersion space .

[0030] The fluid handing structure IH may have a selection of different functions. Each function may be derived from a corresponding feature that enables the fluid handling structure IH to achieve that function. The fluid handling structure IH may be referred to by a number of different terms, each referring to a function, such as barrier member, seal member, fluid supply system, fluid removal system, liquid confinement structure, etc..

[0031] Immersion liquid may be used as the immersion fluid. In that case the fluid handling structure IH may be a liquid handling system. In reference to the aforementioned description, reference in this paragraph to a feature defined with respect to fluid may be understood to include a feature defined with respect to liquid.

[0032] A lithographic apparatus has a projection system PS. During exposure of a substrate W, the projection system PS projects a beam of patterned radiation onto the substrate W. To reach the substrate W, the path of the radiation beam B passes from the projection system PS through the immersion liquid confined by the fluid handling structure IH between the projection system PS and the substrate W. The projection system PS has a lens element, the last in the path of the beam, which is in contact with the immersion liquid. This lens element which is in contact with the immersion liquid may be referred to as ‘the last lens element’ or “the final element”. The final element is at least partly surrounded by the fluid handling structure IH. The fluid handling structure IH may confine the immersion liquid under the final element and above the facing surface.

[0033] As depicted in Figure 1, the lithographic apparatus comprises a controller 500. The controller 500 is configured to control the substrate table WT.

[0034] Figure 2 illustrates part of a lithographic apparatus that is not in accordance with the present invention. The arrangement illustrated in Figure 2 and described below may be applied to the lithographic apparatus described above and illustrated in Figure 1. Figure 2 is a cross-section through a substrate support 20 and a substrate W. In an embodiment, the substrate support 20 comprises one or more conditioning channels 61 of a thermal conditioning system. A gap 5 exists between an edge of the substrate W and an edge of the substrate support 20. When the edge of the substrate W is being imaged or at other times such as when the substrate W first moves under the projection system PS (as described above), the immersion space filled with liquid by the fluid handling structure IH (for example) will pass at least partly over the gap 5 between the edge of the substrate W and the edge of the substrate support 20. This can result in liquid from the immersion space entering the gap 5.

[0035] The substrate W is held by a support body 21 (e.g. a pimple or burl table) comprising one or more burls 41 (i.e., projections from the surface). The support body 21 is an example of an object holder. Another example of an object holder is a mask holder. An under-pressure applied between the substrate W and the substrate support 20 helps ensure that the substrate W is held firmly in place. However, if immersion liquid gets between the substrate W and the support body 21 this can lead to difficulties, particularly when unloading the substrate W.

[0036] In order to deal with the immersion liquid entering that gap 5 at least one drain 10, 12 is provided at the edge of the substrate W to remove immersion liquid which enters the gap 5. In the example of Figure 2 two drains 10, 12 are illustrated though there may only be one drain or there could be more than two drains. In an embodiment, each of the drains 10, 12 is annular so that the whole periphery of the substrate W is surrounded.

[0037] A primary function of the first drain 10 (which is radially outward of the edge of the substrate W/support body 21) is to help prevent bubbles of gas from entering the immersion space where the liquid of the fluid handling structure IH is present. Such bubbles may deleteriously affect the imaging of the substrate W. The first drain 10 is present to help avoid gas in the gap 5 escaping into the immersion space in the fluid handling structure IH. If gas does escape into the immersion space, this can lead to a bubble which floats within the immersion space. Such a bubble, if in the path of the projection beam, may lead to an imaging error. The first drain 10 is configured to remove gas from the gap 5 between the edge of the substrate W and the edge of the recess in the substrate support 20 in which the substrate W is placed. The edge of the recess in the substrate support 20 may be defined by a cover ring 101 which is optionally separate from the support body 21 of the substrate support 20. In the x/y plane, the cover ring 101 may be shaped, as a ring that surrounds the outer edge of the substrate W. The first drain 10 extracts mostly gas and only a small amount of immersion liquid.

[0038] The second drain 12 (which is radially inward of the edge of the substrate W/support body 21) is provided to help prevent liquid which finds its way from the gap 5 to underneath the substrate W from preventing efficient release of the substrate W from the substrate table WT after imaging. The provision of the second drain 12 reduces or eliminates any problems which may occur due to liquid finding its way underneath the substrate W.

[0039] As depicted in Figure 2, the lithographic apparatus comprises a first extraction channel 102 for the passage therethrough of immersion fluid which contains a substantially two phase flow. The first extraction channel 102 is formed within support body 21 or as a separate component. The first and second drains 10, 12 are each provided with a respective opening 107, 117 and a respective extraction channel 102, 113. The extraction channel 102, 113 is in fluid communication with the respective opening 107, 117 through a respective passageway 103, 114.

[0040] As depicted in Figure 2, the cover ring 101 has an upper surface. The upper surface extends circumferentially around the substrate W on the support body 21. In use of the lithographic apparatus, the fluid handling structure IH moves relative to the substrate support 20. During this relative movement, the fluid handling structure IH moves across the gap 5 between the cover ring 101 and the substrate W. In an embodiment the relative movement is caused by the substrate support 20 moving under the fluid handling structure IH. In an alternative embodiment the relative movement is caused by the fluid handling structure IH moving over the substrate support 20. In a further alternative embodiment the relative movement is provided by movement of both the substrate support 20 under the fluid handling structure IH and movement of the fluid handling structure IH over the substrate support 20. In the following description, movements of the fluid handling structure IH will be used to mean the relative movement of the fluid handling structure IH relative to the substrate support 20. [0041] Figures 3 to 5 illustrate a section view of a portion of a substrate support 200. The section extends in vertical (i.e., x/z) plane. Figures 3 to 5 only depict a radially outward portion of the substrate support 200. The radially outward direction is the rightward direction in Figures 3 to 5.

[0042] The substrate support 200 has additional openings configured to provide functionality, which mitigates problems such as warpage during loading of the substrate W onto the substrate support 200, without contributing to a flatness drift in the substrate W or the substrate support 200. Flatness drift of the substrate W may occur when moisture travels radially inward in the region between the substrate W and the substrate support 200.

[0043] The substrate support 200 comprises a plurality of burls 241. The distal ends of the burls 241 form a plane at which the underside of the substrate W is supported. The underside of the substrate W comes into contact with the distal ends of the burls 241. The burls 241 are at the upper side of the substrate support 200. [0044] As shown in Figures 3 to 5, the substrate support 200 comprises a plurality of seals 231, 232, 233, 234. These seals 231, 232, 233, 234 are circumferential rings protruding from the substrate support 200. There may be at least four seals: an inner seal 234, an inner-middle seal 233 radially outwards of the inner seal 234; a middle seal 232 radially outwards of the inner-middle seal 233; and an outer seal 231 radially outwards of the middle seal 232.

[0045] The plurality of seals 231, 232, 233, 234 define a plurality of regions (or “gutters”) between the substrate support 200 and the substrate W. A first fluid extraction gutter 250 is a region extending circumferentially around the substrate support 200 radially outward of the outer seal 231. A second fluid extraction gutter 251 is a region extending circumferentially around the substrate support 200 between the middle seal 232 and the outer seal 231. An ambient gutter 252 is a region extending circumferentially around the substrate support 200 between the inner-middle seal 233 and the middle seal 232. A multifunctional gutter 253 is a region extending circumferentially around the substrate support 200 between the inner seal 234 and the inner-middle seal 233.

[0046] As depicted in Figures 3 to 5, the substrate support 200 further comprises a plurality of openings 261, 262, 263. These are: a multifunctional opening 263 arranged between the inner seal 234 and the inner-middle seal 233 (in the multifunctional gutter 253); an ambient opening 262 arranged between the inner-middle seal 233 and the middle seal 232 (in the ambient gutter 252); a first fluid extraction opening 260 located radially outward of the outer seal 231 (in the first fluid extraction gutter 250); and a second fluid extraction opening 261 arranged between the middle seal 232 and the outer seal 231 (in the second fluid extraction gutter 251).

[0047] The multifunctional opening 263 may be configured to supply and extract gas to and from the multifunctional gutter 253. However, the multifunctional opening 263 may be configured to only supply gas. The ambient opening 262 may be configured to be in fluid communication with ambient pressure. The ambient pressure could be provided from the atmosphere, or from another source within the system. The ambient opening 262 may also be configured to be in fluid communication with positive pressure (pressure that is greater than ambient pressure). The ambient opening 262 may also be configured to be in fluid communication with negative pressure (pressure that is less than ambient pressure), as long as the negative pressure is higher than the pressure in the second fluid extraction gutter 251 in a clamp state. The second fluid extraction opening 261 is configured to extract fluid (and, most commonly, liquids) from the second fluid extraction gutter 251. The second fluid extraction opening 261 is an example of the second opening 117 in the substrate support 20 depicted in Figure 2. The first fluid extraction opening 260 is configured to extract immersion fluid (and, most commonly, gases in the form of bubbles) from the first fluid extraction gutter 250. The first fluid extraction opening 260 is an example of the first opening 107 in the substrate support 20 depicted in Figure 2. [0048] A region radially inward of the inner seal 234 is a clamp region 254. The substrate support may further comprise a clamp opening 264 radially inward of the inner seal 234 (in the clamp region 254) that is configured to extract gas from the clamp region 254.

[0049] When a substrate W is loaded onto a substrate support 200, the substrate W is first received by a plurality of e-pins in their extended position (not shown). The e-pins are then retracted such that the substrate W is lowered towards the substrate support 200. When the underside of the substrate W comes into contact with the plurality of burls 241, the e-pins continue to retract such that the substrate W is no longer in contact with the e-pins, and the substrate W is fully supported by the plurality of burls 241.

[0050] In this “loading state” (Figure 3), gas is supplied by the multifunctional opening 263 to the multifunctional gutter 253, such that the pressure within the multifunctional gutter 253 increases. Consequently, the pressure within the multifunctional gutter 253 becomes larger than the ambient pressure. Because the pressure within the multifunctional gutter 253 is greater than the pressure above the substrate W, a force is applied to the substrate W in an upward direction (that is, in a direction away from the substrate support 200).

[0051] The substrate support 200 is configured such that the multifunctional gutter 253 is situated near to the edge of the substrate W. Consequently, the upward force applied to the substrate W is applied to an edge region of the substrate W. In a substrate W with a diameter of 300mm, the edge region may be a region where the distance to the center of the substrate W (i.e. the radial distance) is greater than 135 mm. Generally, the edge region may be a region where the distance to the center of the substrate W is greater than 45% of the substrate W diameter. Applying the upward force in this region causes the edges of the substrate W to deform upwards. This ensures that, during substrate W loading, the radially outermost circumferential ring of burls 242 is the last point of contact between the substrate support 200 and the substrate W, which may not otherwise be the case when an “umbrella”-shaped substrate W is loaded onto the substrate support 200. This reduces the variability of friction between the radially outermost circumferential ring of burls 242 and the underside of the substrate W, which improves the substrate W load reproducibility.

[0052] At a certain point, the substrate support 200 transitions from the loading state to a “clamp state”.

[0053] In the clamp state (Figure 4), the multifunctional opening 263 may extract gas from the multifunctional gutter 253, such that an under-pressure is established within the multifunctional gutter 253. This means that, as in the clamp region 254, a clamping force is exerted on the portion of the underside of the substrate W corresponding to the multifunctional gutter 253. Alternatively, the multifunctional opening 263 may be closed, such that it is not in fluid communication with any of ambient pressure, over-pressure, or under-pressure.

[0054] In the clamp state, the ambient opening 262, the first fluid extraction opening 260 and the second fluid extraction opening 261 may be open. That is, the ambient opening 262 is in fluid communication with ambient pressure and the first fluid extraction opening 260 and the second fluid extraction opening 261 extract immersion fluid from the first fluid extraction gutter 250 and the second fluid extraction gutter 251, respectively. Alternatively, the ambient opening 262 may be in fluid communication with a positive pressure source. Alternatively, the ambient opening 262 may be in fluid communication with a negative pressure (pressure that is less than ambient pressure), as long as the negative pressure is higher than the pressure in the second fluid extraction gutter 251. Figure 4 shows that, when the substrate W is in the clamp state, immersion fluid that has flowed through the gap 5 between the substrate W and the cover ring 201 may also pass between the outer seal 231 and the underside of the substrate W, and be present in the first fluid extraction gutter 250 and the second fluid extraction gutter 251. It is this immersion fluid that is extracted by the second fluid extraction opening 261. The extraction pressure of the second fluid extraction opening 261, the middle seal 232, and the ambient pressure within the ambient gutter 252 prevent the immersion fluid flowing radially inward of the middle seal 232.

[0055] In the clamp state, the clamp opening 264 may continue to extract gas, such that the magnitude of the difference in pressure between the clamp region 254 and the area above the substrate W increases. Alternatively, the clamp opening 264 may be closed, and the magnitude of the pressure within the clamp region 254 may remain substantially constant. As a further alternative, gas may be periodically extracted through the clamp opening 264 such that the magnitude of the pressure within the clamp region 254 remains substantially constant.

[0056] The substrate support 200 may also be configured to operate in a “bypass state” (see Figure 5), which is an alternative to the clamp state. In the bypass state, the clamp opening 264 and the multifunctional opening 263 operate as in the clamp state. However, the ambient opening 262 may be closed. This means that the ambient opening 262, and therefore the ambient gutter 252, are not in fluid communication with ambient pressure. Alternatively, the ambient opening 262 may remain open, but in fluid communication with a pressure source that is not sufficient to prevent immersion fluid travelling radially inward beyond the middle seal 232. Consequently the immersion fluid surrounds the middle seal 232 and the outer circumferential ring of burls 242. In the bypass state, the multifunctional opening 263 may be in fluid communication with a negative pressure source, such that fluid can be extracted from the multi-functional gutter 253. In an alternative bypass state, the multifunctional opening 263 may supply ambient or positive pressure to the multifunctional gutter 253 to prevent the immersion fluid travelling radially inward beyond the inner-middle seal 233 towards the clamp region 254. This scenario, in which the outer circumferential ring of burls 242 is “wet” may be preferable in some cases, because having a “wet” outer circumferential ring of burls 242 affects the friction between the distal ends of the burls 242 and the underside of the substrate W. [0057] The force applied to the underside of the substrate W as a result of the supply of gas to the multifunctional gutter 253 in the loading state is an edge lift force. The edge lift force is exerted on the underside of the substrate W in the region corresponding to the multifunctional gutter 253 between the inner seal 234 and the inner-middle seal 233. During the clamp state, the atmospheric pressure or overpressure needed to prevent the immersion fluid flowing radially inward of the middle seal 232 is supplied by the ambient opening 262. Between the multifunctional opening 263 and the ambient opening 262 is the inner-middle seal 233. This means that the magnitude of the edge lifting force is dependent on the distance between the inner seal 234 and the inner-middle seal 233. In the clamp state, the fluid communication of the ambient gutter 252 with ambient pressure means that an upwards force is exerted on the substrate in a region corresponding to the ambient gutter 252 (i.e., between the inner-middle seal 233 and the middle seal 232). This can cause a flatness bump in the substrate W during the clamp state. The size of the flatness bump is dependent on the distance between the inner- middle seal 233 and the middle seal 232. Consequently, the positions of the seals 232, 233, 234 and the positions of the openings 262, 263 are constrained by the edge-lift requirements of the substrate support 200 and the flatness requirements of the substrate W.

[0058] Considering this, the distance between the inner seal 234 and the inner-middle seal 233 may be larger than the distance between the inner-middle seal 233 and the middle seal 232, and the distance between the middle seal 232 and the outer seal 231.

[0059] The distance between the inner-middle seal 233 and the middle seal 232, the distance between the middle seal 232 and the outer seal 231, and the distance between the outer seal 231 and the circumferential edge of the substrate W is sufficiently small for the multifunctional gutter 253 to be sufficiently close to the edge of the substrate W. In this context, “sufficiently close” means close enough for the edge lift force exerted on the underside of the substrate W in the region corresponding to the multifunctional gutter 253 to be such that the edge region of the substrate W is deformed upwards, and it can be ensured that the outer circumferential ring of burls 242 is the last point of contact with the underside of the substrate W when the substrate support 200 is in the loading state. [0060] Preferably, the distance between the inner-middle seal 233 and the middle seal 232 is configured such that the flatness bump in the substrate W between the inner-middle seal 233 and the middle seal 232 when the substrate W is clamped to the substrate support 200 is minimised.

[0061] The distance between the centre of the middle seal 232 in a radial direction and the centre of the outer seal 231 in a radial direction is, preferably, small to ensure that the multifunctional gutter 253 is sufficiently close to the edge of the substrate W, and to ensure that the bending moments acting on the substrate W are balanced, thus ensuring optimal flatness of the substrate W.

[0062] Further, the distance between the outer seal 231 and the circumferential edge of the substrate W is preferably small to ensure that the multifunctional gutter 253 is located sufficiently close to the circumferential edge of the substrate W.

[0063] The precise locations of the seals 231, 232, 233, 234 and openings 260, 261, 262, 263 are critical to ensuring that the additional functionality provided by the openings 262, 263 is effectively implemented. Specifically, it is preferable for the multifunctional opening 263 (and, as a consequence, the ambient opening 262, the second fluid extraction opening 261 and the first fluid extraction opening 260) to be positioned in close proximity to the edge of the substrate W, so that the edges of the substrate W can be deformed upwards during loading, and umbrella-shaped deformation can be avoided.

[0064] However, in current configurations of substrate support 200, the positions of the openings 260, 261, 262, 263, 264 are constrained by the locations of channels within the body of the substrate support 200 that supply and/or receive fluids to/from the openings 260, 261, 262, 263. The locations of the channels that supply and/or receive fluids to/from the openings 260, 261, 262, 263, and the locations of conditioning channels are constrained in that they cannot overlap in the radial direction. The positions of the conditioning channels are themselves constrained the requirement for them to effectively regulate the temperature of the substrate support 200. A substrate support 200 which exhibits poor thermal performance (i.e., is incapable of maintaining a consistent temperature during use) is likely to cause an overlay error in the lithographic apparatus as a result of transient structural deformations that arise from the varying temperature. Thus, there are competing considerations: (i) positioning openings such that they effectively provide their intended functionality and (ii) positioning channels such that the substrate support 200 exhibits acceptable thermal performance. In current configurations of substrate supports, it may be difficult to satisfy these competing considerations simultaneously.

< Comparative Example >

[0065] Figure 6 depicts a section view of a substrate support 300 not in accordance with the present invention. The section view extends in a vertical (i.e., x/z plane). As in Figures 3 to 5, the radially outward direction is the rightward direction in Figure 6. Only a radially outward portion of the substrate support 300 is shown. That is, the substrate support 300 continues to the left of the portion shown in Figure 6. The substrate support 300 may further comprise a plurality of burls (not shown), such as the burls 241 described in relation to Figures 3 to 5, on an upper surface.

[0066] The substrate support 300 depicted in Figure 6 exhibits the same functionality as the substrate support 200 exhibited in Figures 3 to 5. That is, the substrate support 300 comprises a first extraction opening 360, a second extraction opening 361, an ambient opening 362 and a multifunctional opening 363. The substrate support 300 may include a clamp opening (equivalent to clamp opening 264 in the substrate support 200 depicted in Figures 3 to 5), but this is not depicted in Figure 6.

[0067] The first extraction opening 360 is in fluid communication with a first extraction channel 380, a second extraction opening 361 is in fluid communication with a second extraction channel 381, an ambient opening 362 is in fluid communication with an ambient channel 382, and a multifunctional opening 363 is in fluid communication with a multifunctional channel 383. The substrate support 300 may be configured such that each of these openings 360, 361, 362, 363 provide the same functionality as the openings 260, 261, 262, 263 described in relation to the substrate support 200 depicted in Figures 3 to 5. [0068] The substrate support 300 further comprises one or more conditioning channels 391, 392, 393 of a thermal conditioning system. The conditioning channels act as heat sinks. Conditioning fluid flowing through the conditioning channels 391, 392, 393 is maintained at a constant temperature. The temperature that the conditioning fluid may be maintained at the desired temperature of the substrate support 300. As such, if the body of the substrate support 300 becomes higher or lower than the desired temperature (i.e., higher or lower than the temperature of the conditioning fluid), heat will be transferred to or from the conditioning fluid, and the temperature of the body of the substrate support 300 will return to the desired value. The components which maintain the conditioning fluid at a constant temperature may be located in a position within the lithographic apparatus other than the substrate support 300.

[0069] The substrate support 300 is formed of a first component 310 and a second component 311. In the horizontal (i.e., x/y) plane, the first component 310 and the second component 311 may each have the same shape as the substrate support 300 as a whole. That is, if the substrate support 300 has a circular shape in the horizontal plane, the first component 310 and the second component 311 will each have a circular shape in the horizontal plane.

[0070] The first component 310 is bonded to the second component 311. This may be such that the second component 311 is positioned on top of the first component 310. That is, an upper surface of the first component 310 may be bonded with a lower surface of the second component 311. In this configuration, it may be an upper surface of the second component 311 which is configured to support the substrate W. Thus, it could be said that the substrate support 300 is formed of two layers, with the lower layer being the first component 310 and the upper layer being the second component 311. [0071] The channels 380, 381, 382, 383 and the conditioning channels 391, 392, 393 may each be formed at an interface between the first component 310 and the second component 311. That is, the channels 380, 381, 382, 383 and the conditioning channels 391, 392, 393 may each be formed at a position where the upper surface of the first component 310 is bonded to the lower surface of the second component 311. This means that the channels 380, 381, 382, 383 and conditioning channels 391, 392, 393 may be formed using standard subtractive manufacturing processes.

[0072] The configuration shown in Figure 6 suffers from a number of disadvantages. As has been explained above, the positions of the openings 360, 361, 362, 363 are constrained by the requirements of functionality which they provide. However, the positions of the openings 360, 361, 362, 363 are also constrained by the locations of the channels 380, 381, 382, 383 with which they communicate. The locations of the channels 380, 381, 382, 383 are constrained in that they cannot overlap in the radial direction. In fact, it is preferable for there to be a certain distance between channels 380, 381, 382, 383 to ensure that the channels 380, 381, 382, 383 do not cause detriment to the structural integrity of the substrate support 300. The locations of the channels 380, 381, 382, 383 are further constrained by considerations relating to the thermal performance of the substrate support 300. [0073] In the comparative example shown in Figure 6, to position the openings 361, 362, 363 and the associated channels 381, 383 in the desired locations, passageways 371, 373, which connect the openings 361, 363 with their respective channels 381, 383 are inclined, such that they are not vertical (i.e., not perpendicular to the upper surface of the second component 311). Manufacturing holes at such an inclined angle is more complex than manufacturing vertical holes (i.e., holes that extend in a direction that is perpendicular to the surface in which they are formed). Further, the angle of inclination at which a hole can be manufactured may be limited. This means that, depending on the constraints on the position of the openings 361, 363 and their respective channels 381, 383, angled passageways 371, 373 may not be feasible as a means for bringing the openings 361, 363 and the channels 381, 383 into fluid communication.

[0074] To improve the thermal performance of the substrate support 300 (that is, to ensure that all of the substrate support 300 can be maintained at the desired temperature), it may be preferable to locate one of the conditioning channels 391, 392, 393, such as the conditioning channel 391, in close proximity to the first extraction channel 380 and the second extraction channel 381. For example, it may be preferable for the first conditioning channel 391 to be located in a position that is radially outwards of the ambient channel 382 and the multifunctional channel 383, but radially inward of the first extraction channel 380 and the second extraction channel 381. This is because the first extraction channel 380 and the second extraction channel 381 are likely to contain liquid, such as immersion fluid. When this liquid evaporates, a significant thermal load acts on the first extraction channel 380 and the second extraction channel 381. However, in the arrangement depicted in Figure 6, there is insufficient space available between the second extraction channel 381 and the ambient channel 382 for the first conditioning channel 391 to be located between the second extraction channel 381 and the ambient channel 382.

< Present Invention >

[0075] Figure 7 depicts a section view of a substrate support 200 in accordance with the present invention. The section view extends in the vertical (i.e., x/z) plane. As in Figures 3 to 5, the radially outward direction is the rightward direction. Only a radially outward portion of the substrate support 200 is shown. That is, the substrate support 200 continues to the left of the portion shown. For illustrative purposes, the substrate support 200 comprises the same openings 260, 261, 262, 263 and functionality as the substrate support 200 depicted in Figures 3 to 5. However, the present invention is not limited to being implemented within a substrate support 200 with such functionality. That is, a substrate support 200 in accordance with the present invention may not necessarily have each of the openings 260, 261, 262, 263 and the seals 231, 232, 233 included in the substrate support 200 depicted in Figures 3 to 5.

[0076] The substrate support 200 depicted in Figure 7 is formed of three components: a lower component 210, a core component 211 and an upper component 212. However, the present invention is not limited to a configuration with only three components 210, 211 and 212, and a substrate support 200 in accordance with the present invention may include more components. For example, a substrate support 200 in accordance with the present invention may comprise 4, 5 or more components.

[0077] In the horizontal (i.e., x/y) plane, the lower component 210, the core component 211 and the upper component 212 may each have the same shape as the substrate support 200 as a whole. That is, if the substrate support 200 has a circular shape in the horizontal plane, the lower component 210, the core component 211 and the upper component 212 will each have a circular shape in the horizontal plane.

[0078] The lower component 210, the core component 211 and the upper component 212 are bonded together. In the substrate support 200 depicted in Figure 7, the lower component 210 is bonded to the core component 211 and the core component 211 is bonded to the upper component 212. Specifically, an upper surface of the lower component 210 is bonded to a lower surface of the core component 211 and an upper surface of the core component 211 is bonded to a lower surface of the upper component 212. Thus, it could be said that the substrate support 200 depicted in Figure 7 is formed of three layers, with a lower layer being the lower component 210, a middle layer being the core component 211 and an upper layer being the upper component 212.

[0079] The means by which the components are bonded together is not particularly limited. It is preferable that the method of bonding allows for effective heat transfer between the lower component 210 and the core component 211, and the core component 211 and the upper component 212. This is preferable because it means that features within the substrate support 200 which are responsible for regulating the temperature of the substrate support 200 can do so effectively. For instance, if conditioning channels 291, 292, 293 are formed predominantly in one of the components, such as the core component 211, their ability to regulate the temperature of the substrate support 200 is not limited to the core component 211. This is because heat can be transferred from the other components (i.e., the upper component 212 and the lower component 210) through the bond layers and to the conditioning channels 291, 292, 293 (or vice-versa). Consequently, the conditioning channels 291, 292, 293 are able to regulate the temperature of the whole substrate support 200.

[0080] The substrate support 200 may further include heaters (not shown). As with the conditioning channels 291, 292, 293, even if the heaters are contained within a single component, their ability to regulate the temperature of the substrate support 200 is not limited to this component, because heat is able to be transferred across the bond layers.

[0081] In addition to the requirement that the bonding technique allows for effective heat transfer between the components 210, 211, 212, it is preferable that the bond layer formed between the components 210, 211, 212 is able to withstand high temperatures. Specifically, it is preferable that the bond layer formed between components 210, 211, 212 is able to withstand temperatures that the substrate support 200 may be exposed to in manufacturing process that are performed after the components 210, 211, 212 are bonded together. For example, if a substrate support 200 manufacturing process includes a step of diamond coating after the components 210, 211, 212 are bonded together, it is preferable that the bonding layer is able to withstand the temperatures required for the diamond coating process.

[0082] Examples of bond techniques may include infiltration bonding and diffusion bonding, which will be discussed in further detail below.

[0083] Of the three components 210, 211, 212 of the substrate support 200 depicted in Figure 7, the upper component 212 may be configured to support the substrate W. That is, the upper surface of the upper component 210 may comprise the openings 260, 261, 262, 263, as well as any seals 231, 232, 233, 234 and burls 241 which were described in relation to the substrate support 200 in Figures 3 to 5. [0084] In accordance with the present invention, the substrate support 200 comprises a first extraction opening 260. The first extraction opening 260 is an example of a first opening. The first extraction opening 260 may be formed in an upper surface of the upper component 212. This first extraction opening 260 is in fluid communication with a first extraction channel 280. The first extraction opening 260 may be in fluid communication with the first extraction channel 280 via a first passageway 270, such that the first extraction opening 260 communicates directly with the first passageway 270 and the first passageway 270 communicates directly with the first extraction channel 280. In this context, “communicates directly” means that the features communicate without intermediary, i.e., the features adjoin.

[0085] The first extraction channel 280 may be defined by the core component 211 and the lower component 210. Specifically, the first extraction channel 280 may be defined by the core component 211 and the lower component 210 such that the first extraction channel 280 is located at an interface between the core component 211 and the lower component 210. However, exactly how the first extraction channel 280 is located at the interface between the core component 211 and the lower component 210 is not particularly limited. In the configuration shown in Figure 7, the first extraction channel 280 is formed by a channel portion 280a in the core component 211 and a channel portion 280b in the lower component 210. The substrate support 200 is configured such that, when the core component 211 is bonded to the lower component 210, the channel portion 280a in the core component 211 aligns with the channel portion 280b in the lower component 210, and the first extraction channel 280 is formed.

[0086] The channel portions 280a, 280b may be recessed portions in the components 211, 210. For example, the channel portion 280a may be a recessed portion in the core component 211 and the channel portion 280b may be a recessed portion in the lower component 210. The channel portions 280a, 280b may be voids in the components 211, 210. Specifically, the channel portions 280a, 280b may be open voids. The channel portions 280a, 280b may be cavities in the components 211, 210. Specifically, the channel portions 280a, 280b may be open cavities in the components 211, 210. That is, when the components 211, 210 are not bonded together, the channel portions 280a, 280b may be open to an environment surrounding the components 211, 210. The channel portions 280a, 280b may be regions within the components 211, 210 where the material from which the components 211, 210 are formed is not present or removed. The channel portions 280a, 280b may be cut into a surface of the components 211, 210. For example, the channel portion 280a may be cut into a lower surface of the core component 211 and the channel portion 280b may be cut into an upper surface of the lower component 210. The channel portions 280a, 280b may be rectangular in shape. Alternatively, the channel portions 280a, 280b may be U-shaped. In general, the shape of the channel portions 280a, 280b is not particularly limited.

[0087] In the substrate support 200 depicted in Figure 7, the channel portion 280a in the core component 211 is much larger than the channel portion 280b in the lower component 210, so when the first extraction channel 280 is formed, the majority of the first extraction channel 280 is within the core component 211. However, this may not be the case, and the channel portion 280a in the core component 211 may be the same size as the channel portion 280b in the lower component 210, or the channel portion 280a in the core component 211 may be smaller than the channel portion 280b in the lower component.

[0088] In fact, whilst the first extraction channel 280 is defined by both the lower component 210 and the core component 211, it may be the case that only one of the lower component 210 and the core component 211 comprises a channel portion 280a, 280b. For example, the first extraction channel 280 may be formed of a channel portion 280a in the core component 211, with the substrate support 200 being configured such that, when the core component 211 and the lower component 210 are bonded together, an upper surface of lower component 210 seals off an open end of the recess portion (i.e., channel portion 280a) in the core component 211 to fully form the first extraction channel 280. The fact that the first extraction channel 280 may be formed in the ways described above may also apply to other channels in the substrate support 200, such as the channels 281, 282, 283 and the conditioning channels 291, 292, 293 in the substrate support 200. The fact that the first extraction channel 280 may be formed in the ways described above may also apply to the horizontal portions of passageways 271, 272, 273.

[0089] The first passageway 270 may be defined in the upper component 212 and the core component 211. The first passageway 270 may extend in a substantially vertical direction (i.e., substantially perpendicular to the upper surface of the upper component 212) from the first extraction opening 260 in the upper component 212, through the thickness of the upper component 212, through any bond layer which exists between the core component 211 and the upper component 212, and into the first extraction channel 280. However, the shape of the first passageway is not particularly limited. For example, the first passageway 270 may be an L-shape, as is to be described with references to passageways 271, 272, 273.

[0090] The substrate support 200 may further comprise a second extraction opening 261. The second extraction opening 261 is an example of a second opening. The second extraction opening 261 may be formed in the upper surface of the upper component 212. The second extraction opening 261 may be in fluid communication with a second extraction channel 281. A second passageway 271 may be disposed between the second extraction opening 261 and the second extraction channel 281, such that the second extraction opening 261 and the second extraction channel 281 are in fluid communication. Specifically, the second extraction opening 261 may communicate directly with the second passageway 271 and the second passageway may communicate directly with the second extraction channel 261.

[0091] The second extraction opening 261 may be located radially inward of the first extraction opening 260. The second extraction channel 281 may be located radially inward of the first extraction channel 280.

[0092] The second passageway 271 may be defined, by the upper component 212 and the core component 211. The second passageway 271 may be substantially L-shaped. That is, the second passageway 271 may include a first vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component 212 and communicating directly with the second extraction opening 261. The second passageway 271 may further comprise a horizontal portion extending in a direction substantially parallel to the upper surface of the upper component 212 and communicating directly with the first vertical portion of the second passageway 271. The vertical portion and the horizontal portion of the second passageway 271 may be a substantially L-shape. The second passageway 271 may further include a second vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component 212 and communicating directly with the second extraction channel 281.

[0093] The second extraction channel 281 may be located radially outward of the second extraction opening 261, so fluid flowing within the horizontal portion of the second passageway 271 in a direction that is from the second extraction opening 261 to the second extraction channel 281 will travel in a radially outward direction.

[0094] The substrate support 200 may further comprise a first conditioning channel 291. A first conditioning channel 291 may be located in a position radially inward of the first extraction channel 280 and the second extraction channel 281. If the second extraction channel 281 is not present, the first conditioning channel 291 may be located in a position radially inward of the first extraction channel 280. The first extraction channel 280 and the second extraction channel 281 are known to experience a significant thermal load. This is because the first extraction channel 280 and the second extraction channel 281 may contain two-phase fluids. For example, the first extraction channel 280 and the second extraction channel 281 may contain immersion liquid in the case that the substrate support 200 is configured for use in immersion lithography. This liquid may evaporate within the channels 280, 281, causing an evaporative load (i.e., a thermal load) on the walls of the first extraction channel 280 and the second extraction channel 281, which is transferred to the body of the substrate support 200. Consequently, it is preferable to position the first conditioning channel 291 in close proximity to the first extraction channel 280 and the second extraction channel 281, so that the evaporative load on the first extraction channel 280 and the second extraction channel 281 can be effectively mitigated by the first conditioning channel 291. Further, because the first conditioning channel 291 is located radially inward of the first extraction channel 280 and the second extraction channel 281, the evaporative thermal load from the first extraction channel 280 and the second extraction channel 281 cannot be transferred radially inward towards the centre of the substrate support 200. Consequently, the extent to which the thermal load experienced by the first extraction channel 280 and the second extraction channel 281 can adversely affect the flatness of the substrate support 200 is limited.

[0095] The radial distance between a radially inward wall of the second extraction channel 281 and a radially outward wall of the first conditioning channel 291 may be less the 5 mm, preferably less than 2 mm, and further preferably less than 1.6 mm. The radial distance between a radially inward wall of the second extraction channel 281 and a radially outward wall of the first conditioning channel 291 may greater than 1 mm, and preferably greater than 1.4 mm. For example, the radial distance between a radially inward wall of the second extraction channel 281 and a radially outward wall of the first conditioning channel 291 may be greater than 1 mm and less than 5 mm, and preferably greater than 1.4 mm and less than 2 mm, and further preferably greater than 1.4 mm and less than 1.6 mm. The radial distance between a radially inward wall of the second extraction channel 281 and a radially outward wall of the first conditioning channel 291 may be 1.5 mm. These distances ensure that the first conditioning channel 291 is sufficiently close to the second extraction channel 281 and the first extraction channel 280 for the first conditioning channel 291 to be able to effectively mitigate the thermal load experienced by the second extraction channel 281 and the first extraction channel 280, but that that the wall thickness between the second extraction channel 281 and the first conditioning channel is sufficient to ensure that the presence of the channels 280, 281, 291 does not significantly weaken the structural integrity of the substrate support 200.

[0096] The radial distance between a radially inward wall of the first extraction channel 280 and a radially outward wall of the second extraction channel 281 may be less the 5 mm, preferably less than 2 mm, and further preferably less than 1.6 mm. The radial distance between a radially inward wall of the first extraction channel 280 and a radially outward wall of the second extraction channel 281 may be greater than 1 mm, and preferably greater than 1.4 mm. For example, the radial distance between a radially inward wall of the first extraction channel 280 and a radially outward wall of the second extraction channel 281 may be less than 5 mm and greater than 1 mm, and preferably less than 2 mm and greater than 1.4 mm, and further preferably less than 1.6 mm and greater than 1.4 mm. These distances ensure that the openings 260, 261, 262, 263 can be located sufficiently close to the edge of the substrate support 200, but that that the wall thickness between the first extraction channel 280 and the second extraction channel 281 is sufficient to ensure that the presence of the first extraction channel 280 and the second extraction channel 281 does not significantly weaken the structural integrity of the substrate support 200. [0097] The radial distance between a radial edge of the substrate support 200 and a radially outward wall of the first extraction channel 280 may be less than 5 mm, preferably less than 2 mm, and further preferably less than 1.5 mm. The radial distance between a radial edge of the substrate support 200 and a radially outward wall of the first extraction channel 280 may be greater than 1 mm, and preferably greater than 1.3 mm. For example the radial distance between a radial edge of the substrate support 200 and a radially outward wall of the first extraction channel 280 may be less than 5 mm and greater than 1 mm, and preferably less than 2 mm and greater than 1.3 mm, and further preferably less than 1.5 mm and greater than 1.3 mm. These distances contribute to the first conditioning channel 291 being favourably located in a radially outward position. These distances also ensure that the plurality of channels 280, 281, 282, 283 can be favourably located in an edge region of the substrate support 200 such that the plurality of openings 260, 261, 262, 263 can be located close to the edge of the substrate W (i.e., where they must be located to provide their required functionality) without necessitating excessively long horizontal portions of the passageways 271, 272, 273. The minimum distances are such that the thickness of the body of the substrate support 200 in between the first extraction channel 280 an the edge of the substrate support 200 is sufficient to ensure that the presence of the first extraction channel 280 does not detriment the structural integrity of the substrate support 200.

[0098] The width of the first extraction channel 280 (that is, a radial distance between a radially outward wall and a radially inward wall of the first extraction channel 280) and the width of the second extraction channel 281 (that is, a radial distance between a radially outward wall and a radially inward wall of the second extraction channel 281), henceforth, the widths of the extraction channels 280, 281, may be less than 5 mm, preferably less than 2 mm, and further preferably less than 1.6 mm. The widths of the extraction channels 280, 281 may be greater than 1 mm and preferably greater than 1.4 mm. For example, the widths of the extraction channels 280, 281 may be less than 5 mm and greater than 1 mm, and preferably less than 2 mm and greater than 1.4 mm, and further preferably less than 1.6 mm and greater than 1.4 mm. These dimensions ensure that the first conditioning channel 291 can be favourably located in a radially outward location, but ensures that the channels 280, 281 are sufficiently wide for them to be able to effectively extract fluids from the region between the substrate W and the substrate support 200.

[0099] The substrate support 200 may further include an ambient opening 262. The ambient opening 262 is an example of a fourth opening. The ambient opening 262 may be formed in the upper surface of the upper component 212. The ambient opening 262 may be in fluid communication with an ambient channel 282. A fourth passageway 272 may be located between the ambient opening 262 and the ambient channel 282. The fourth passageway 272 may directly communicate with both the ambient opening 262 and the ambient channel 282 to facilitate the fluid communication between the ambient opening 262 and the ambient channel 282. [0100] As with the second passageway 271, the fourth passageway 272 may be configured to be in an L shape. That is, the fourth passageway 272 may include a first vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component 212 and directly communicating with ambient opening 262. The fourth passageway 272 may further comprise a horizontal portion extending in a direction substantially parallel to the upper surface of the upper component 212 and directly communicating with the vertical portion of the fourth passageway 272. The fourth passageway 272 may further comprise a second vertical portion directly communicating with the horizontal portion of the fourth passageway 272 and extending in a direction substantially perpendicular to the upper surface of the upper component 212 down through the core component 211 to directly communicate with the ambient channel 282.

[0101] The ambient channel 282 may be located radially inward of the first extraction channel 280, the second extraction channel 281 and the first conditioning channel 291. The ambient opening 262 may be located radially inward of the second extraction opening 261 and the first extraction opening 260.

[0102] The substrate support 200 may further comprise a multifunctional opening 263. The multifunctional opening 263 is an example of a third opening. The multifunctional opening 263 may be formed in the upper surface of the upper component 212. The multifunctional opening 263 may be in fluid communication with a multifunctional channel 283. The substrate support 200 may further comprise a third passageway 273 disposed between the multifunctional opening 263 and the multifunctional channel 283 such that the multifunctional opening 263 directly communicates with the third passageway 273 and the multifunctional channel 283 to facilitate the fluid communication between the multifunctional opening 263 and the multifunctional channel 283.

[0103] As with the second passageway 271 and the fourth passageway 272, the third passageway 273, may be in L-shape or have a dog-leg. That is, the third passageway 273 may comprise a first vertical portion extending in a direction perpendicular to the upper surface of the upper component 212 and directly communicating with the multifunctional opening 263. The third passageway 273 may further comprise a horizontal portion extending in a direction parallel to the upper surface of the upper component 212 and directly communicating with the first vertical portion of the third passageway 273. The third passageway 273 may further comprise a second vertical portion directly communicating with the horizontal portion of the third passageway 273 and extending in a direction substantially perpendicularly to the upper surface of the upper component 212 down through the core component 211 to communicate directly with the multifunctional channel 283.

[0104] The ambient channel 282 may be located radially inward of the ambient opening 262. The multifunctional channel 283 may be located radially inward of the multifunctional opening 263. Therefore, in the flow path extending from the ambient opening 262 to the ambient channel 282, immersion fluid travelling through the horizontal portion fourth passageway 272 would move in a radially inward direction, and in the flow path extending from the multifunctional opening 263 to the multifunctional channel 283, immersion fluid travelling through the horizontal portion of the third passageway 273 would move in a radially inward direction.

[0105] The substrate support 200 may comprise a plurality of further conditioning channels 292, 293. For example, in the embodiment shown in Figure 7, the substrate support 200 includes a second conditioning channel 292 and a third conditioning channel 293.

[0106] The ambient channel 282 and the multifunctional channel 283 may be located radially inward of the first conditioning channel 291. The ambient channel 282 and the multifunctional channel 283 may be located radially outward of the second conditioning channel 292. It may be preferable that the second conditioning channel 292 is not located radially outward of the ambient channel 282 and the multifunctional channel 283. This is because, if the second conditioning channel 292 were to be located radially outward of the ambient channel 282 and the multifunctional channel 283, the radial distance between the ambient channel 282 and the ambient opening 262, and the radial distance between the multifunctional channel 283 and the multifunctional opening 263 would become excessively large. If the radial distance between the ambient channel 282 and the ambient opening

262 and the radial distance between the multifunctional channel 283 and the multifunctional opening

263 become excessively large, the flow resistance between the respective channels 282, 283 and the openings 262, 263 may undesirably increase. This is caused by the additional length of the horizontal portions of the third passageway 273 and the fourth passageway 272. Further, positioning the second conditioning channel 292 radially inward of the ambient channel 282 and the multifunctional channel 283 means that any thermal (heating or cooling) load on the ambient channel 282 or the multifunctional channel 283 cannot be transferred radially inward toward the centre of the substrate support 200.

[0107] Alternatively, the second conditioning channel 292 may be located between the ambient channel 282 and the multifunctional channel 283. That is, the second conditioning channel 292 may be located radially inward of the multifunctional channel 283 and radially outward of the ambient channel 282. This may be preferable to ensuring that the second conditioning channel 292 can effectively mitigate the thermal load experienced by the ambient channel 282 and the multifunctional channel 283.

[0108] The multifunctional opening 263 may be located radially inward of the ambient opening 262. Conversely, the ambient channel 282 may be located radially inward of the multifunctional channel 283. That is, the radial arrangement of the multifunctional opening 263 and the ambient opening 262 may be the opposite of the radial arrangement of the corresponding multifunctional channel 283 and the ambient channel 282. To enable this, the horizontal portion of the fourth passageway 272 may be longer than the horizontal portion of the third passageway 273.

[0109] Channels 280, 281, 282, 283 configured to supply or extract gas in a substrate support 200 may experience stresses in response to the pressure within the channels 280, 281, 282, 283. The stresses experienced by the channels 280, 281, 282, 283 may result in deformation of the channels 280, 281, 282, 283. Radially inward channels may be more sensitive to changes in pressure. That is, a radially inward channel may exhibit a larger amount of deformation in response to a given change in pressure than that of a radially outward channel in response to the same change in pressure. In the substrate support 200, the multifunctional channel 283 may experience larger pressure changes during use than the ambient channel 282. Consequently, to minimize deformation of the substrate support 200 during use, it is preferable for the multifunctional channel 283 to be located radially inward of the ambient channel 282, as described above.

[0110] It is preferable for the first conditioning channel 291 to be located radially outward of the ambient channel 282 and the multifunctional channel 283 so that the first conditioning channel 291 can be positioned in close proximity to the second extraction channel 281, as discussed above.

[0111] Figure 8 depicts a substrate support 200 in accordance with the present invention. The view of the substrate support 200 in Figure 8 is from above the substrate support 200. The substrate support 200 has had an upper portion removed, so that features within the core component 211, such as the channels 280, 281, 282, 283 and the conditioning channels 291, 292, 293, are visible.

[0112] In accordance with the present invention, the channels 280, 281, 282, 283 may be cavities within the substrate support 200. The cross-section of each channel 280, 281, 282, 283 may be rectangular. As can be seen in Figure 8, each of the channels 280, 281, 282, 283 extend circumferentially around the entirety of the substrate support 200.

[0113] Whilst the conditioning channels 291, 292, 293 have previously been referred to as distinct channels (i.e., the first conditioning channel 291, the second conditioning channel 292, the third conditioning channel 293), the substrate support 200 depicted in Figure 8 has a single conditioning channel 290 in a spiral configuration. That is, the conditioning channel 290 begins in a radially inward position. As the conditioning channel 290 extends around the substrate support 200, the distance between the conditioning channel 290 and the center of the substrate support 200 increases. When such a spiral configuration is implemented, a section view of the substrate support 200, such as the view shown in Figure 7, will show distinct conditioning channels 291, 292, 293. Consequently, in the substrate support 200 shown in Figure 7, the first conditioning channel 291, the second conditioning channel 292 and the third conditioning channel 293 may be part of a single, spiralling conditioning channel 290.

[0114] The passageways 270, 271, 272, 273 may not extend circumferentially around the substrate support 200. For example, the passageways 270, 271, 272, 273 may be holes. The holes may have a circular cross-section.

[0115] Like the passageways 270, 271, 272, 273 with which they communicate, the openings 260, 261, 262, 263 may not extend circumferentially around the substrate support 200. The openings 260, 261, 262, 263 may have the same cross-section of the corresponding passageways 270, 271, 272, 273. For example, the openings 260, 261, 262, 263 may be circular. A plurality of each of the openings 260, 261, 262, 263 may be circumferentially distributed around the substrate support 200. For example, there may be a plurality of multifunctional openings 263 distributed circumferentially around the substrate support 200.

[0116] Figure 9 shows a portion of a substrate support 200 in accordance with the present invention. The view of the portion of the substrate support 200 in Figure 9 is from a position above the substrate support 200. The substrate support 200 has had an upper portion removed, so that features, within the upper component 212, such as the horizontal portions of the passageways 270,

271, 272, 273, are visible.

[0117] As shown in Figure 9, the passageways 270, 271, 272, 273 may be located at different circumferential positions. This is such that, even when the horizontal portions of the passageways 270, 271, 272, 273 overlap in the radial direction (such as passageways 272 and 273), the horizontal portions of the passageway do not interfere with each other.

[0118] If there are a plurality of openings 260, 261, 262, 263, there may be a passageway 270, 271,

272, 273 for each of the openings 260, 261, 262, 263. For example, where there are a plurality of ambient openings 262 (e.g., ambient opening A, ambient opening B, ambient opening C, etc.), there may be a fourth passageway 272 for each of the ambient openings 262 (e.g., fourth passageway A 272a corresponding to ambient opening A, fourth passageway B 272b corresponding to ambient opening B, fourth passageway C 273c corresponding to ambient opening C, etc.).

[0119] The horizontal portions of the passageways 270, 271, 272, 273 may be located at the interface between the core component 211 and the upper component 212. In the embodiment depicted in Figure 7, the horizontal portion of the passageways 271, 272, 273 are formed by a passageway portion in the upper component 212, such that when the core component 211 is bonded to the upper component 212, the core component 211 provides a closing face so that the recess in the upper component 212 becomes a complete passageway 271, 272, 273. However, in accordance with the present invention, the horizontal portions of the passageways 271, 272, 273 may not be formed in this manner. For example, each of the horizontal portions of the passageways 271, 272, 273 may be formed by a passageway portion in both the upper component 212 and the core component 211, such that when the core component 211 is bonded to the upper component 212, the passageway portions align to form the passageways 271, 272, 273.

[0120] The second extraction channel 281, the multifunctional channel 283 and the ambient channel 282 may all be in communication with a fluid control unit 201. The first extraction channel 280 may also be in communication with the fluid control unit 201, though this is not depicted in Fig. 7.

[0121] Figure 10 depicts another substrate support 400 in accordance with the present invention. In the substrate support 400 depicted in Figure 10, the channels 480, 481, 482, 483 are arranged in a stacked configuration. Apart from the arrangement of the channels 480, 481, 482, 483, the substrate support 400 may comprise the same features as the substrate support 200 described above. That is, the substrate support 400 depicted in Figure 10 includes a lower component 410, a core component 411 and an upper component 412. The substrate support 400 further includes channels 480, 481, 482, 483, openings 461, 462, 463, and passageways 470, 471, 472, 473.

[0122] In the substrate support 200 depicted in Figure 7, all of the channels 280, 281, 282, 283 are formed at the interface between the lower component 210 and the core component 211. In the substrate support 400, the first extraction channel 480 and the ambient channel 482 are formed at the interface between the lower component 410 and the core component 411, but the second extraction channel 481 and the multifunctional channel 483 are formed at the interface between the core component 411 and the upper component 412. As a result of this configuration, the channels 480, 481, 482, 483 can overlap in the radial direction without physically interfering with each other. For instance, in the substrate support 400, a radially inward portion of the first extraction channel 480 is located below a radially outward portion of the second extraction channel 481. Similarly, a radially inward portion of the ambient channel 482 may be located below a radially outward portion of the multifunctional channel 483, though this is not depicted in Fig. 10. Consequently, each of the channels 480, 481, 482 and 483 can be located in a radially outer region of the substrate support 400, in the proximity of where the openings 460, 461, 462, 463 must be located to provide their required functionality. As such, the horizontal portions of passageways 470, 471, 472, 473 can be shortened, and so undesirably large flow resistance avoided.

[0123] Figure 11 depicts another substrate support 500 in accordance with the present invention. Like the substrate support 400, in the substrate support 500, the channels 480, 481, 482, 483 are arranged in a stacked configuration. Specifically, the first extraction channel 580 and the multifunctional channel 583 are located at the interface between the lower component 510 and the core component 511, and the second extraction channel 581 and the ambient channel 582 are located at the interface between the core component 511 and the upper component 512. The first conditioning channel 591 is located radially inward of the first extraction channel 580 and the second extraction channel 581 and radially outward of the ambient channel 582 and the multifunctional channel 583. As has been described earlier in the present disclosure, locating the first conditioning channel 591 such that it is in close proximity to the first extraction channel 580 and the second extraction channel

581 means that the thermal load at the first extraction channel 580 and the second extraction channel

582 can be effectively mitigated.

[0124] In general, the “stacked channels” concept means that it is possible to compress the positions of the various channels in the radial direction. That is, it is possible to fit all of the channels 580, 581, 582, 583 into a smaller region. This means that each of the channels 580, 581, 582, 583 can be arranged closer to the radial edge of the substrate support 500. As described above, this is beneficial, because the openings 560, 561, 562, 563 must be located close to the edge in order to provide their functionality. By providing the channels 580, 581, 582, 583 closer to the openings 560, 561, 562, 563 in the radial direction, the lengths of the horizontal portion of the passageways 571, 572, 573 can be reduced. [0125] In general, the presence of two bond layers means that the channels 280, 281, 282, 283 and the conditioning channels 291, 292, 293 can be formed at one of the interfaces (e.g., the interface between a lower component 210 and the core component 211) and horizontal portions of passageways 270, 271, 272, 273 can be formed at the other interface (e.g., the interface between the core component 211 and the upper component 212). Consequently, the locations of the openings 260, 261, 262, 263 are uncoupled (i.e., made independent of) the locations of the channels 280, 281, 282, 283. Additionally or alternatively, the presence of two bond layers means that channels 280, 281, 282, 283 can be “stacked” on top of each other, which reduces size of the region of the components 210, 211, 212 required to accommodate them. The increased design freedom provided by the provision of two bond layers means that the substrate support 200 can be configured such that the functionality of the additional openings 262, 263 can be effectively provided and the substrate support 200 can exhibit favourable thermal performance.

[0126] The example substrate supports 200, 400, 500 described above have all comprised three components and two bond layers. However, the present invention is not limited to this configuration. In general, increasing the number of components bonded together increases the design freedom, because there are positions within the thickness (i.e., the dimension in the vertical, z, direction) at which features such as channels (e.g., the channels 280, 281, 282, 283 and the conditioning channels 291, 292, 293) horizontal portions of passageways (e.g., passageways 271, 272, 273) can be located. [0127] However, it should be recognized that increasing the number of components 210, 211, 212 within the substrate support 200 may contribute to increasing the complexity of the required manufacturing process. Forming a substrate support 200 with three components 210, 211, 212 and two bond layers offers a good balance between providing design freedom for the positioning of features within the substrate support 200 whilst avoiding any unnecessary increase in the complexity of the manufacturing process.

[0128] As explained above, a heat load (i.e. the cooling load) is applied to the surfaces of the various channels 280, 281, 282, 283 as a result of the evaporation of immersion fluid on the surfaces. The heat load may be dependent on the presence or absence of immersion fluid in the channels 280, 281, 282, 283. When fluid is present on the surfaces of the channels 280, 281, 282, 283 evaporation will occur, and a cooling load will be applied to the surfaces of the channels 280, 281, 282, 283. When fluid is not present in the channels 280, 281, 282, 283, evaporation will not occur and so a cooling load may not be applied to the surfaces of the channels 280, 281, 282, 283. If fluid is present in the channels 280, 281, 282, 283, the magnitude of the cooling load may dependent on a rate of evaporation of the fluid from the surfaces of the channels 280, 281, 282, 283. The rate of evaporation may be dependent on the relative humidity (RH) of the gas (e.g. air) which flows through the channels 280, 281, 282, 283. When the relative humidity is 100%, no evaporation will take place.

[0129] To ensure that the temperature of the substrate support 200 remains substantially uniform, and remains within acceptable limits, the substrate support 200 may comprise a thermal conditioning system. The thermal conditioning system may include the conditioning channels 291, 292, 293. The thermal conditioning system may further comprise a plurality of heaters (not shown) distributed around a surface of the substrate support 200. For example, there may be 6 or more heaters distributed around the surface of the substrate support 200. The heaters may be actively controlled. That is, the thermal conditioning system may comprise one or more temperature sensors (not shown), and a control system (not shown) may control the operation of the thermal conditioning system (e.g. the heaters) based on data recorded by the temperature sensors.

[0130] During operation, the first extraction channel 280 may contain immersion fluid for a majority of the time that the substrate support 200 is in operation. This may be because the first extraction channel 280 is primarily responsible for extracting immersion fluid from the area between the substrate W and the substrate support 200. That is, the first extraction channel 280 may extract the majority of the immersion fluid. The second extraction channel 281 may extract less immersion fluid than the first extraction channel 280. Consequently, the second extraction channel 281 may not contain immersion fluid for a majority of the time that the substrate support 200 is in operation. This means that, during the operation of the substrate support 200, the second extraction channel 281 may “dry out”. That is, during operation of the substrate support 200, it may be likely that all of the immersion fluid within the second extraction channel 281 may be extracted and/or evaporate, to leave the second extraction channel 281 dry. Consequently, the cooling load applied to the surfaces of the second extraction channel 281 may vary as a function of time.

[0131] If the cooling loads applied to the surfaces of a channel 280, 281, 282, 283 vary over time, it may be difficult for the thermal conditioning system to effectively regulate the temperature of the substrate support 200. For instance, if a cooling load on a surface of a channel 280, 281, 282, 283 were to change (e.g. increase), the operation of a heater in the vicinity of the channel 280, 281, 282, 283 would need to change (i.e. heat up) so the overall temperature of the substrate support 200 in the vicinity of the channel 280, 281, 282, 283 remains substantially constant. However, it may take some time for the change in cooling load to be detected and for the operation of the heater to be changed. Thus, for a time, the temperature of the substrate support 200 may become variable (i.e. not constant). As explained above, if a temperature of all or parts of the substrate support 200 varies over time, the substrate support 200 may undergo transient structural deformation, which can result in an increase in overlay error. Further, if the thermal conditioning system is required to regulate the temperature of the substrate support 200 whilst fluctuating cooling loads are applied to the channels 280, 281, 282, 283, a complex control system may be required.

[0132] In some embodiments, the substrate support 200 may comprise additional features which improve the temporal uniformity of the cooling load applied to the surfaces of the second extraction channel 281. The additional features may achieve this by one or more of: (i) ensuring that immersion fluid is present on the surfaces of the second extraction channel 281 for substantially all of the time that the substrate support 200 is in operation; and (ii) ensuring that the air flowing into the second extraction channel 281 is substantially saturated (i.e. that the relative humidity of the air flowing into the second extraction channel 281 is at or near 100%). In the embodiments described below, this is achieved by bringing the second extraction channel 281 and/or the second fluid extraction gutter 251 into fluid communication with a reliable (i.e. substantially constant) source of immersion fluid. [0133] Figure 12 depicts a cross-section view of a substrate support 200 in accordance with the present invention. The cross-section view extends in the vertical plane (i.e. the x/z plane). The substrate support 200 may be similar to the substrate support 200 depicted in Figure 7, except as described below. In the depiction of the substrate support 200 shown in Figure 12, the radially outward direction is the rightward direction. Only a radially outward portion of the substrate support 200 is shown. That is, the substrate support 200 may continue of the left of the portion shown in Figure 12. The cross-section view of the substrate support 200 shown in Figure 12 is a different cross-section view to the substrate support 200 depicted in Figure 7. Whilst the cross-section views shown in Figures 7 and 12 each pass through a diameter of the substrate support 200, the planes along which the cross-section is taken may be rotationally offset, e.g. by an angle of 15 degrees.

Consequently, some of the features of the substrate support 200 which are visible in Figure 7 (e.g. the passageways, 271, 272, 273) may not be visible. The gutters 250, 251, 252, 253, which are schematically depicted, are still visible in Figure 12, because the gutters 250, 251, 252, 253 extend circumferentially around the substrate support 200, so will be visible irrespective of the angular position of the vertical cross-section view.

[0134] In the substrate support 200 depicted in Figure 12, the second extraction channel 281 is in fluid communication with the first conditioning channel 291. The first conditioning channel 291 may contain conditioning fluid permanently during the operation of the substrate support 200. By bringing the second extraction channel 281 into fluid communication with the first conditioning channel 291, conditioning fluid may be able to flow from the first conditioning channel 291 to the second extraction channel 281. Thus, even if immersion fluid within the second extraction channel 281 has evaporated, the second extraction channel 281 will not become dry, because a steady supply of conditioning fluid may be supplied to the second extraction channel 281.

[0135] The second extraction channel 281 may be brought into fluid communication with the first conditioning channel 291 via a first connecting passageway 275. The configuration of the first connecting passageway 275 is not particularly limited, as long as it brings the second extraction channel 281 and the first conditioning channel 291 into fluid communication. In the substrate support 200 depicted in Figure 12, the first connecting passageway 275 comprises a horizontal portion at an interface between the upper component 212 and the core component 211. The first connecting passageway 275 further comprises two vertical portions. One of the vertical portions connects the horizontal portion to the first conditioning channel 291 and the other one of the vertical portions connects the horizontal portion to the second extraction channel 281. [0136] Figure 13 depicts a cross-section view of a substrate support 200 in accordance with the present invention. The view depicted in Figure 13 may be substantially the same as the view depicted in Figure 12. The substrate support 200 depicted in Figure 13 may be substantially the same as the substrate support 200 depicted in Figure 7, except as described below.

[0137] In the substrate support 200 depicted in Figure 13 the second extraction channel 281 is in fluid communication with the first extraction channel 280. As explained above, the first extraction channel 280 may contain immersion fluid for a majority of the time that the substrate support 200 is in operation. By bringing the second extraction channel 281 into fluid communication with the first extraction channel 280, immersion fluid is able to flow from the first extraction channel 280 to the second extraction channel 281. Consequently, the second extraction channel 281 can be prevented from drying out.

[0138] The first extraction channel 280 may be brought into fluid communication with the second extraction channel 281 via a second connecting passageway 276. The second connecting passageway 276 may be similar to the first connecting passage away 275, except from the fact that it brings the first extraction channel 280 and the second extraction channel 281 into fluid communication, rather than the second extraction channel 281 and the first conditioning channel 291.

[0139] In the embodiments depicted in Figures 12 and 13, the fact that fluid can be supplied to the second extraction channel 281 means that the second extraction channel 281 can be prevented from drying out. That is, fluid may be present on the surfaces of the extraction channel 281 for a majority of the time that the substrate support 200 is in operation. Thus, the cooling load applied to the surfaces of the second extraction channel 281 may be made to be more temporally uniform. In some embodiments, the fluid that is supplied to the second extraction channel 281 may be sufficient for all of the surfaces of the second extraction channel 281 to remain wet. In this case, the relative humidity within the second extraction channel 281 may be at (or near) 100% . In this case, no evaporation (or a very small amount of evaporation) occurs. Thus, no thermal load (or a very small thermal load) is applied to the surfaces of the second extraction channel 281. This means that the thermal conditioning system is not required to make large compensations for the cooling load applied to the second extraction channel 281, and the temperature of the substrate support 200 can be made to be more temporally.

[0140] In the case that the first conditioning channel 291 is in fluid communication with the second extraction channel 281 (Figure 12), conditioning fluid within the first conditioning channel 291 may be drawn into the second extraction channel 281 by virtue of the fact that the pressure within the second extraction channel 281 is lower than the pressure within the first conditioning channel 291. If this is not the case, fluid may be drawn from the first conditioning channel 291 and into the second extraction channel 281 by capillary forces in the first connecting passageway 275. Similarly, in the case that the first extraction channel 280 is in fluid communication with the second extraction channel 281 (Figure 13), immersion fluid may be drawn from the first extraction channel 280 to the second extraction channel 281 by virtue of the fact that the pressure within the second extraction channel 281 may be less than the pressure within the first extraction channel 280. If this is not the case, fluid may be drawn from the first extraction channel 280 to the second extraction channel 281 by capillary forces in the second connecting passageway 276.

[0141] In some cases, the transfer of fluid to the second extraction channel 281 may be actively controlled. For example, an active controller (not shown) may comprise a valve and/or pressure gradient generating means. The active controller may be configured to drive the flow of fluid to the second extraction channel 281 (from the first extraction channel 280 or from the first conditioning channel 291). The active controller may also be configured to block the flow of fluid to the second extraction channel 281.

[0142] Figure 14 depicts a cross-section view of a substrate support 200 in accordance with the present invention. Figure 14 is the same cross-section view as the cross-section view in Figures 12 and 13. The substrate support 200 depicted in Figure 14 may be substantially the same as the substrate support 200 depicted in Figure 7, except as described below. In the substrate support 200 depicted in Figure 14, the first conditioning channel 291 is in fluid communication with the second fluid extraction gutter 251. The second fluid extraction gutter 251 may be referred to simply as a fluid extraction gutter. By bringing the first conditioning channel 291 into fluid communication with the second fluid extraction gutter 251, conditioning fluid can flow from the first conditioning channel 291 to the second fluid extraction gutter 251, thus ensuring that the second fluid extraction gutter 251 remains wet (i.e. has fluid on surfaces thereof) for a majority of the time that the substrate support 200 is in operation.

[0143] The first conditioning channel 291 may be brought into fluid communication with the second fluid extraction gutter 251 by a third connecting passageway 277. The third connecting passageway 277 may comprise first portion 277a in the core component 211 and second portion 277b in the other component, such as the upper component 212 .

[0144] The second extraction channel 281 is configured to extract immersion fluid from the second fluid extraction gutter 251 (via the second extraction opening 261 and the second passageway 271). If the surfaces of the second fluid extraction gutter 251 are consistently wet, the air that is drawn through the second extraction opening 261 may be substantially saturated. That is, a relative humidity of the fluid (i.e. air) that enters the second extraction channel 281 may be high (e.g. greater than 90% preferable greater than 95%, and preferably greater than 98%). This may mean that the rate of evaporation within the second extraction channel 281 may be low. Consequently, the cooling load that is applied to the surfaces in the second extraction channel 281 may be very low, irrespective of whether or not fluid is present on the surfaces of the second extraction channel 281. If the air is substantially saturated, the rate of evaporation may be approximately zero, irrespective of whether or not fluid is present on the surfaces of the second extraction channel 281. Consequently, by bringing the first conditioning channel 291 into fluid communication with the second fluid extraction gutter 251, the cooling load applied to the surfaces of the second extraction channel 281 can be made to be substantially constant over time.

[0145] Figure 15 depicts a cross-section view of a portion of a substrate support 200. The substrate support 200 may be substantially the same as the substrate support 200 depicted in Figure 7. The cross-section view depicted in Figure 15 may also be the same or substantially the same as the crosssection view depicted in Figure 7, except as described below. Because the cross-section view depicted in Figure 15 is substantially the same as the cross-section view depicted in Figure 7, the second passageway 271 (i.e. the passageway which connects the second extraction opening 261 and the second extraction channel 281) can be seen. Some features, such as the first, third and fourth passageways 270, 272, 273 have been removed from the figure to improve the clarity of the features which are to be described.

[0146] The substrate support 200 depicted in Figure 15 is a modification of the substrate support 200 depicted in Figure 12 in that, like the substrate support 200 depicted in Figure 12, the first conditioning channel 291 and the second extraction channel 281 are in fluid communication. This fluid communication is provided by a fourth connecting passageway 278 which connects the first conditioning channel 291 to the second passageway 271. Thus, fluid communication between the first conditioning channel 291 and the second extraction channel 281 is enabled via the fourth connecting passageway 278 and the second passageway 271. Whilst not shown, it will be understood that the same could be done for bringing the first extraction channel 280 into fluid communication with the second extraction channel 281. That is, the first extraction channel 280 could be brought into fluid communication with the second extraction channel 281 by connecting the first extraction channel 280 to the first passageway 271.

[0147] The structure of the connecting passageways 275, 276, 277, 278 is not particularly limited. Whilst the first connecting passageway 275 and the second connecting passageway 276 have been shown to comprise a horizontal portion with small vertical portions connecting the horizontal portion to the various channels, this may not always necessarily be the case. For example, the first and second connecting passageways 275, 276 may be substantially vertical. This may be the case in a “stacked channels” configuration, such as the “stacked channels” configuration described above. [0148] A plurality of the connecting passageways may be provided. For example, a plurality of first connecting passageways 275 may be provided in the case that the first conditioning channel 291 is in fluid communication with the second extraction channel 281. The plurality of connecting passageways may be distributed circumferentially around the substrate support 200. The number of connecting passageways (e.g. the number of first connecting passageways 275 in the case that the first conditioning channel 291 is in fluid communication with the second extraction channel 281) may be greater than 10 and less than 100. Increasing the number of connecting passageways may increase the uniformity of the fluid transfer to the second extraction channel 281. [0149] The diameter of the first, second and third and fourth connecting passageways 275, 276, 277, 278 (and particularly, the first, third and fourth connecting passageways 275, 277, 278) may be small. Specifically, the diameter of the first and third connecting channels 275, 277 may be sufficiently small to provide a flow resistance. The flow resistance may ensure that the volume of fluid that flows to the second extraction channel 281 or second fluid extraction gutter 251 is not excessive. This may be particularly important in the embodiment depicted in Figure 14: if an excessive amount of fluid flows from the first conditioning channel 291 and into the second fluid extraction gutter 251, the second fluid extraction gutter 251 may overflow. The diameter of the first, second third and fourth connecting passageways 275, 276, 277, 278 may be sufficiently small that that the flow resistance in the connecting passageways 275, 276, 277, 278 is contributed to by capillary forces. Flow resistance within the first, second, third and fourth connecting passageways 275, 276, 277, 278 may be increased by providing additional components therein. The additional components may comprise a porous media or a micro-sieve (not shown). Additionally, or alternatively, the additional components may comprise a water-permeable membrane (not shown). The water-permeable membrane may allow the passage of water vapour through the connecting passageway, whilst keeping the majority of the fluid in the different channels separate.

[0150] A substrate support 200 in which an extraction channel and/or an extraction gutter are in fluid communication with a fluid source within the substrate support (e.g. another extraction channel or a conditioning channel) may be implemented in substrate supports 200 which have different features to those of the substrate support 200 depicted in Figure 7 and described above.

[0151] In some embodiments, the first fluid extraction opening 260, the first passageway 270 and the first extraction channel 280 (which may be referred to collectively as a first drain system) may be arranged as described below in relation to Figures 16 to 19. For instance, in the embodiments depicted in Figures 7 to 15, first drain system may be as described below in relation to Figures 16 to 19. The arrangement of the first drain system described below and depicted in Figures 16 to 19 may also be implemented in substrate supports other than those depicted in Figures 7 to 15, e.g. in the substrate support 20 depicted in Figure 2 (where the first drain system is equivalent to the first drain 10 of the substrate support 20 depicted in Figure 2).

[0152] As has been explained above, in some embodiments the first fluid extraction opening 260 is located radially outward of the outer seal 231 (i.e. in the first fluid extraction gutter 250), and radially outward of the edge of the substrate W. The first fluid extraction opening 260 is in fluid communication with the first extraction channel 280, such that fluid (i.e. immersion liquid and gas) can be extracted from the first fluid extraction gutter 250 via the first fluid extraction opening 260 and the first extraction channel 280. The first fluid extraction opening 260 may be in fluid communication with the first extraction channel 280 via the first passageway 270.

[0153] As has also been explained above, a fluid handling structure IH present between the projection system PS and the substrate support WT is used to confine the immersion liquid to an immersion space between a final element of the projection system PS and the substrate W. In use of the lithographic apparatus, the substrate support WT moves relative to the fluid handling structure IH. During this relative movement, the fluid handling structure IH moves across a gap 5 between the cover ring 101, 201 and the substrate W.

[0154] A primary function of the first drain system is to help prevent bubbles of gas from entering the immersion space where the liquid of the fluid handling structure IH is present. Such bubbles may deleteriously affect the imaging of the substrate W. The first drain system is present to help avoid gas in the gap 5 escaping into the immersion space dbetween the projection system PS and the substrate support WT, 200. If gas does escape into the immersion space, this can lead to a bubble which floats within the immersion space. Such a bubble, if in the path of the radiation beam B, may lead to an imaging error. The first drain system is configured to extract gas from the gap 5 between the edge of the substrate W and the edge of a surface of the substrate support WT, 200, e.g., an upper surface of cover ring 101, 201. Another function of the first drain system is to extract immersion fluid from between the substrate W and the substrate support 200, 300, 400, 500 (i.e. from the first fluid extraction gutter 250).

[0155] After the fluid handling structure IH has relatively moved across the gap 5 between the cover ring 101, 201 and the substrate W, a small amount of immersion fluid may remain on the surface of the substrate W, in the region which the fluid handling structure IH has moved over. This can lead to the presence of bubbles and watermarks on the surface of the substrate W, which can lead to defectivity (i.e. errors in the pattern that is imparted to the surface of the substrate W). To minimise the amount of liquid that remains on a region of the surface of the substrate W after the fluid handling structure IH has passed over that region of the surface of the substrate W, the first drain system should extract fluid from the first fluid extraction gutter 250 efficiently and uniformly (spatially uniformly and temporally uniformly).

[0156] Figure 16 depicts a cross-section view of a radially outward portion of a substrate support 200 showing the first drain system (including the first fluid extraction opening 260, the first passageway 270, and the first fluid extraction channel 280, which have already been described). [0157] In the embodiment depicted in Figure 16, the first fluid extraction opening 260 extends circumferentially around the substrate support 200. The first fluid extraction opening 260 is formed in the upper surface of the substrate support 200. The first fluid extraction opening 260 may be defined by an upper portion of a first fluid extraction groove 220. The first fluid extraction groove 220 is recessed into the upper surface of the substrate support 200. The upper portion of the fluid extraction groove 220 is the portion of the first fluid extraction groove 220 on the same level as the upper surface of the substrate support 200.

[0158] The first fluid extraction groove 220 may extend circumferentially around the substrate support 200. The cross-sectional shape of the first fluid extraction groove 220 is not particularly limited. As depicted in Figure 16, the cross-sectional shape of the first fluid extraction groove 220 is substantially rectangular. The cross-sectional shape of the first fluid extraction groove 220 may alternatively be circular (i.e. rounded), V-shaped or L-shaped. In some embodiments, edges between the first fluid extraction groove 220 and the upper surface of the substrate support 200 are chamfered. [0159] The first fluid extraction channel 280 is in fluid communication with the first fluid extraction opening 260 via the first passageway 270 and the first fluid extraction groove 220. To flow from the first fluid extraction gutter 250 to the first fluid extraction groove 220, the immersion fluid flows through a slit 202. The slit 202 is defined by the upper surface of the substrate support 200 and a lower surface the cover ring 201. Specifically, the slit 202 is the gap between the upper surface of the substrate support 200 and the lower surface of the cover ring 201. The height of the slit 202 is denoted by the dimension, dj. The slit 202 extends from a radially inward end 202a (which may be defined by an edge of the cover ring 201) to a radially outward end 202b (which may be defined by an edge of the first fluid extraction opening 260). To be extracted from the first fluid extraction gutter 250, immersion fluid flows from the first fluid extraction gutter 250, through the slit 202 (from the radially inward end 202a to the radially outward end 202b), through the first fluid extraction opening 260 and into the first fluid extraction groove 220, through the first passageway 270, and through the first fluid extraction channel 280.

[0160] When the immersion fluid enters the first fluid extraction gutter 250, the extraction pressure (a pressure less than the pressure around the substrate W) in the first fluid extraction gutter 250 draws the immersion fluid into the slit 202. This may be such that the slit 202 becomes blocked by the immersion fluid. For a period of time after the immersion fluid first enters the first fluid extraction gutter 250, the first passageway 270 and the first fluid extraction groove 220 are substantially empty. When the slit 202 is blocked with the immersion fluid and the first passageway 270 and the first fluid extraction groove 220 are substantially empty, the pressure at the radially outward end 202b of the slit 202 is substantially the same as the extraction pressure in the first extraction channel 280. Thus, the pressure difference over the slit 202 (i.e. between the radially inward end 202a of the slit 202 and the radially outward end 202b of the slit 202) is relatively high. As such, a flow-rate through the slit 202 is relatively high. Consequently, immersion fluid is extracted from the first fluid extraction gutter 250 relatively quickly.

[0161] As the first drain system continues to extract the immersion fluid from the first fluid extraction gutter 250, the first passageway 270 and/or the first fluid extraction groove 220 may become filled with the immersion fluid. This may be such that the first passageway 270 and/or the first fluid extraction groove 220 is blocked by the immersion fluid. This means that the pressure at the radially outward end 202b of the slit 202 may be greater than the extraction pressure in the first extraction channel 280. Consequently, the pressure difference over the slit 220 may be relatively low (i.e. lower than in the case where the first passageway 270 and the first fluid extraction groove 220 are not blocked by the immersion fluid). As such, immersion fluid may be extracted from the first fluid extraction gutter 250 more slowly. This means that, after the fluid handling structure IH passes over the gap 5, some immersion fluid may remain on the surface of the substrate W adjacent to the gap 5. This may introduce defectivity, as described above.

[0162] To ensure that immersion fluid is extracted from the first fluid extraction gutter 250 efficiently and uniformly, the first fluid extraction groove 220 may be configured such that the time at which first passageway 270 is filled with immersion fluid is delayed. Preferably, the first fluid extraction groove 220 is configured such that the time at which first passageway 270 is filled with immersion fluid is after a time at which substantially all the immersion fluid has been extracted from the first fluid extraction gutter 250.

[0163] To delay the time at which first passageway 270 is filled with immersion fluid, a volume of the first fluid extraction groove 220 may be relatively large. Consequently, more immersion fluid must accumulate in the first fluid extraction groove 220 before the immersion fluid fills the first passageway 270. To achieve a relatively large volume for the first fluid extraction groove 220, a cross-sectional area of the first fluid extraction groove 220 may be greater than 1 mm², preferably greater than 3 mm², and further preferably greater than 5 mm². The cross-sectional area of the first fluid extraction groove 220 may be less than 10 mm². The depth (ds) of the first fluid extraction groove 220 may be greater than 0.5 mm, preferably greater than 1 mm, and further preferably greater than 1.5 mm. The depth (ds) of the first fluid extraction groove 220 should be less than approximately 5 mm and preferably less than approximately 2 mm.. When the depth of the first fluid extraction gutter 220 is less than 5 mm (and preferably less than 2 mm), flow within the first fluid extraction gutter 220 is driven by capillary forces, with the effect of gravity on the flow being less dominant (e.g. insignificant). This means that the immersion fluid is prevented from dripping within the first fluid extraction groove 220. Dripping within the first fluid extraction gutter 220 would mean that the bottom of the first fluid extraction groove 220 would be filled up before other parts of the first fluid extraction groove 220, and thus the first passageway 270 would become blocked by the immersion fluid after a shorter amount of time. The depth (ds) of the first fluid extraction groove 220 is a dimension in a direction perpendicular to the upper surface of the substrate support 200. A maximum width (dr) of the first fluid extraction groove 220 may be greater than 0.5 mm, preferably greater than 1.5 mm, and further preferably greater than 3 mm. The width (dr) of the first fluid extraction groove 220 may be less than 5 mm. The width (dr) of the first fluid extraction groove 220 is a dimension in a direction that is parallel to the upper surface of the substrate support 200. The width (dr) of the first fluid extraction groove 220 is a dimension between a radially inward wall of the first fluid extraction groove 220 and a radially outward wall of the first fluid extraction groove 220.

[0164] To ensure that the structural integrity of the substrate support 200 is not compromised by the presence of the first fluid extraction groove 220, the first fluid extraction groove 220 may be separated from other passageways and channels within the substrate support 200, and separated from the edge of the substrate support 200. For instance, a distance between the first fluid extraction groove 220 and the edge of the substrate support (and, specifically, a distance between a radially outward wall of the first fluid extraction groove 220 and a radially outward wall of the substrate support 200) may be greater than 0.1 mm, preferably greater than 0.3 mm, and further preferably greater than 0.5 mm. A distance between a bottom wall of the first fluid extraction groove 220 and a top wall of the first fluid extraction channel 280 may be greater than 0.1 mm, preferably greater than 0.3 mm, and further preferably greater than 0.5 mm. In the case that the first fluid extraction groove 220 is formed in an upper component (e.g. upper component 212), a distance between the bottom wall of the first fluid extraction groove 220 and an interface between the upper component 212 and the core component 211 may be greater than 0.1 mm, preferably greater than 0.3 mm, and further preferably greater than 0.5 mm.

[0165] A length of the slit 202 (i.e. a distance between the radially inward end 202a of the slit 202 and a radially outward end of the slit 202b of the slit 202) may be greater than 0.3 mm and preferably greater than 0.5 mm. The length of the slit 202 may be greater than the height of the slit 202 multiplied by 5, preferably greater than the height of the slit multiplied by 15, and preferably greater than the height of the slit multiplied by 20. An increase in the length of the slit 202 may increase the magnitude of the under pressure within the first fluid extraction groove 220, the first passageway 270 and the first fluid extraction channel 280. It may be preferable for a length of the slit 202 to sufficiently short such that the under pressure within the first fluid extraction groove 220, the first passageway 270 and the first fluid extraction channel 280 does not become undesirably large.

[0166] The first passageway 270 may be connected to the first fluid extraction groove 220 at a downstream-most point within the first fluid extraction groove 220 (i.e. such that a length of the flowpath between an entrance to the first passageway 270 and the radially outward end 202b of the slit 202 is maximised). This may be to further delay the filling of the first passageway 270 with immersion fluid after the first drain system begins extracting immersion fluid from the first extraction gutter 250. In the substrate support 200 depicted in Figure 16, the downstream-most point is at the radially outer edge of the first fluid extraction groove 220.

[0167] The first passageway 270 may be angled (i.e. not perpendicular to the upper surface of the substrate support 200). For example, the entrance to the first passageway 270 (i.e. where the first passageway 270 meets the first fluid extraction groove 220) may be radially outward of the exit of the first passageway 270 (i.e. where the first passageway 270 meets the first extraction channel 280). This may allow the position of the entrance to the first passageway 270 to be independent of the position of the first extraction channel 280.

[0168] It may be preferable for flow resistance within the first fluid extraction groove 220 to be relatively high in the circumferential (i.e. azimuthal) direction. When the fluid handling structure IH passes over the gap 5, immersion liquid may enter a circumferential portion of the first fluid extraction gutter 250 (e.g. immersion fluid may be present around 30° of the fluid extraction gutter 250). When being extracted by the first drain system, immersion fluid will flow into a corresponding circumferential portion of the slit 202. As explained above, the resulting blockage of this circumferential portion of the slit 202 produces a relatively high pressure difference over the slit 202, and so a relatively high rate of immersion fluid extraction from the first fluid extraction gutter 250. However, the portion of the slit 202 other than the circumferential portion containing the immersion fluid (e.g. the remaining 330°) will not be blocked. Consequently, if the flow resistance in the circumferential direction in the first fluid extraction groove 220 is low, the pressure at the radially outward end 202b of the slit 202 in the circumferential portion corresponding to where immersion fluid is present in the fluid extraction gutter 250 may be greater than the extraction pressure in the first fluid extraction channel 280. That is, a low flow-resistance within the first fluid extraction groove 220 may weaken the pressure difference over the slit 202. Thus, the rate of extraction of the immersion fluid from the first fluid extraction gutter 250 may be reduced. This may be particularly significant when the cross-sectional area of the first fluid extraction groove 220 is large. In the above description, the examples of 30° and 330° are used solely to aid the explanation.

[0169] Considering the above, a plurality of flow-restricting members may be provided inside the first fluid extraction groove 220. The plurality of flow-restricting members may be distributed circumferentially around the first fluid extraction groove 220. The plurality of flow-restricting members may be configured to increase the flow-resistance in the circumferential direction within the first fluid extraction groove 220.

[0170] Figure 17A and 17B depict a cross-section view of a radially outward portion of a substrate support 200 in which a flow-restricting member 225, 226 is disposed within the first fluid extraction groove 220. Figure 18 depicts a schematic representation of a plan view of the first fluid extraction groove 220. As shown in Figure 18, the substrate support 200 may comprise a plurality of first passageways 270 distributed circumferentially along the first fluid extraction groove 220. The flowrestricting members 225, 226 may be positioned between adjacent first passageways 270. The flowrestricting members 225, 226 may define distinct circumferential portions of the first fluid extraction groove 220. Each first passageway 270 may be in its own distinct circumferential portion.

[0171] The flow-restricting members 225, 226 may completely isolate the distinct circumferential portions of the first fluid extraction groove 220 from each other. By completely isolating the distinct circumferential portions, it is ensured that the pressure difference over the slit 202 is not be weakened by the circumferential portion of the slit 202 which is not filled with immersion fluid.

[0172] The distinct circumferential portions may be partially isolated from each other by the flowrestricting members 225, 226 (i.e. fluid can flow between the distinct circumferential portions, but the flow is restricted compared to the flow within one of the distinct circumferential portions). By partially (rather than completely) isolating the distinct circumferential portions of the first fluid extraction groove 220, immersion fluid in one distinct circumferential portion of the fluid extraction groove 220 can still be extracted therefrom if the first passageway 270 corresponding to that distinct circumferential portion is blocked. This is because the immersion fluid in the distinct circumferential portion would be able to flow to the neighbouring distinct circumferential portions, where it could then be extracted. Thus, by partially (rather than completely) isolating the distinct circumferential portions of the first fluid extraction groove 220, the robustness of the first drain system may be improved.

[0173] In the embodiment depicted in Figures 17A and 17B, the flow-restricting member 225, 226 is a vertical wall. The vertical wall may be referred to as a partition. The partition may extend across some of the cross-sectional area of the first fluid extraction groove 220. In some embodiments, the partition extends across a majority (e.g. greater than 50%, preferably greater than 80%, and further preferably greater than 90%) of the cross-sectional area of the first fluid extraction groove 220. Such a partition may decrease the flow-resistance within the first fluid extraction groove 220 in the circumferential direction. In some embodiments, the partition may extend across all of the cross- sectional area of the first fluid extraction groove 220, preventing flow in the first fluid extraction groove 220 in the circumferential direction.

[0174] In the embodiment depicted in Figure 17A, the flow-restricting member 225 is connected to a bottom surface of the cover ring 201. That is, the flow-restricting member 225 extends downward into the first fluid extraction groove 220 from the bottom surface of the cover ring 201.

[0175] Additionally or alternatively, the flow-restricting member 226 may be connected to the first fluid extraction groove 220. For example, in the embodiment depicted in Figure 17B, the flowrestricting member 226 is connected to a bottom surface of the first fluid extraction groove 220. That is, the flow-restricting member 226 extends from the bottom surface of the first fluid extraction groove 220.

[0176] The flow-restricting members 225, 226 may be integrally formed with the body of the substrate support 200. Alternatively, the flow-restricting members 225, 226 may be inserts that are configured to be attached to the body of the substrate support 200.

[0177] The flow-restricting members 225, 226 may be impermeable (i.e. fluid may not be able to flow therethrough). Alternatively, the flow-restricting members 225, 226 may be permeable. For example, the flow-restricting members 225, 226 may be porous, or may contain small holes.

[0178] Figure 19 depicts a cross-section view of a radially outer portion of a substrate support 200 showing the first drain system. The substrate support 200 depicted in Figure 19 comprises an upper layer 212, a core layer 211 and a lower layer 210, as has been described above.

[0179] In the substrate support 200 depicted in Figure 19, the first fluid extraction groove 220 has a more complex cross-sectional shape than that of the substrate support 200 depicted in Figure 16. This shape will be described in further detail below.

[0180] The cross-sectional shape of the first fluid extraction groove 220 may vary as a function of height within the substrate support 200. For instance, the first fluid extraction groove 220 may have a first width at the upper surface, and a second width below the upper surface. The first width may be less than the second width. This may allow the volume of the first fluid extraction groove 220 to be increased without decreasing the length of the slit 202. [0181] The cross-sectional shape of the first fluid extraction groove 220 is formed of three simple shapes: a first shape 220a, a second shape 220b and a third shape 220c. The first, second and third shapes 220a, 220b, 220c may be rectangles. The first shape 220a and the second shape 220b may be defined in the upper layer 212. The third shape 220c may be defined in the core layer 211.

[0182] The first shape 220a may be radially outward of the second shape 220b. The first shape 220a may extend from the upper surface of the upper component 212 to the interface between the upper component 212 and the core component 211. The second shape 220b may extend upward from the interface between the core component 211 and the upper component 212, but may not extend up to the upper surface of the upper component 212. The third shape 220c may extend downward from the interface between the upper layer 212 and the core layer 211.

[0183] By composing the cross-sectional shape of the first fluid extraction groove 220 of multiple simple shapes, it may be possible to maximise the volume of the first fluid extraction groove 220 whilst maintaining a required separation from, e.g. the circumferential edge of the substrate support 200 and other channels and passageways within the substrate support 200.

[0184] The material of the substrate support 200 is not particularly limited, and could be any suitable material known in the art. Preferably, the substrate support 200 may be made out of silicon infiltrated silicon carbide (SiSiC). Alternatively, the substrate support may be formed of Zerodur™ (a lithium-aluminosilicate glass-ceramic, cordierite, silicon carbide (SiC) or diamond SiSiC.

[0185] Next, a manufacturing process which may be utilized to manufacture the substrate support 200 is described. First, the lower component 210 and the core component 211 are prepared. For example, recesses for internal channels such as channels 280, 281, 282, 283, and conditioning channels 291, 292, 293 (or conditioning spiral 290) may be formed. This may be achieved using standard manufacturing techniques, such as CNC machining.

[0186] Next, the lower component 210 may be bonded to the core component 211. The bonding process may involve infiltration bonding or diffusion bonding.

[0187] Diffusion bonding relies on the principle of solid state diffusion, in which, when two components are held together with a sufficient pressure at a sufficient temperature, atoms from one component migrate to the other component and vice-versa, such that the two components become bonded together. To join two components, such as the lower component 210 and the core component 211, where the two components are formed of SiSiC, a pressure of approximately 2000 kN and a temperature of approximately 1350 °C may be required. In general, the temperature required may be close to, but less than, the melting temperature of Silicon. To aid the diffusion bonding process, a layer of a coating may be applied to a surface that is to be bonded. For example, prior to the bonding of the lower component 210 and the core component 211, a coating may be applied to the lower surface of the core component 211. The coating may be applied through physical vapour deposition (PVD). The coating may comprise at least one of Titanium, Silicon and Aluminium. The composition of the coating may be such that it includes more than a trace amount of Titanium, Silicon and Aluminium. For example, the coating may be formed substantially of at least one of Titanium, Silicon and Aluminium. That is, the coating may consist essentially of at least one of Titanium, Silicon and Aluminium. Preferably, the coating may comprise Titanium. The Titanium coating may be approximately 500 nm in thickness. An anti-oxidation protection layer may be provided to the Titanium coating. The anti-oxidation may comprise Silicon. The anti-oxidation layer may be approximately 10 nm in thickness.

[0188] After the first bonding step, vertical holes, such as the second vertical portions of the second passageway 271, the third passageway 273 and the fourth passageway 271 may be formed in the core component 211. These second vertical portions may be formed by electrical discharge machining (EDM).

[0189] Next, the upper component 212 may be prepared. For example, the horizontal portions of the channels 271, 272, 273 may be formed using an advanced structuring process (ASP).

[0190] Next, an upper surface of the core component 211 may be bonded to a lower surface of the upper component 212. Again, this bonding process may be diffusion bonding or infiltration bonding [0191] Once all of the components 210, 211, 212 have been bonded together, several structuring processes may be performed to form the desired features on the upper surface of the upper component 212. For example, an advanced structuring process may be used to form a plurality of burls 241 and seals 231, 232, 233, 234 which are located on the upper surface of the upper component 212. Further, electrical discharge machining may be used to form various holes in the upper surface of the upper component 212 that extend down into the substrate support 200, such as the first extraction opening 260 and first passageway 270. Electric discharge machining may also be used to form other holes in the substrate support 200, such as clamp openings 264.

[0192] Once the structuring processes have been completed, other holes such as the ambient opening 262, the second extraction opening 261 and the multifunctional opening 263 may be formed. These openings 261, 262, 263 may be formed using a technique such as laser drilling.

[0193] Next, a number of finishing processes may be performed to ensure that the flatness of the substrate support 200 satisfies the required tolerances. Such finishing processes may include polishing.

[0194] Once the finishing processes have been performed, 3D measurements of the substrate support 200 may be made to evaluate its geometry and to ensure that its dimensions are within the tolerances set out by the specification.

[0195] To conclude the manufacturing process, any final coating and assembly steps may be performed.

[0196] This manufacturing process is just one example of how a substrate support 200, 400, 500 in accordance with the present invention could be manufactured, and other techniques could instead be utilized, or the steps could be performed in a different order. For example, each of the hard machining processes (i.e., CNC, electrical discharge machining, and advanced structuring processes ) may be performed before the various components are bonded together.

[0197] The gas that is supplied through the openings, for example, through the multifunctional opening 263 in the loading state and through the ambient opening 262 in the clamp state is not particularly limited. For example, clean-dry air (CD A), humidified air, or Nz could be supplied. Preferably, humidified air is supplied, particularly through the ambient opening 262 in the loading state. This is because CDA with very low humidity can cause the evaporation of any immersion fluid on the outer seal 231, which creates a large thermal load on the outer seal 231. This can cause transient structural deformation to the substrate support 200, which can lead to overlay penalty. Humidified air means that less immersion fluid is evaporated from the around the outer seal 231, and the thermal load is reduced.

[0198] 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, a substrate table WT, etc..

[0199] 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. The lithographic apparatus may further comprise the substrate support 200 as described in any of the above embodiments and variations.

[0200] In the present disclosure, the terms “immersion liquid” and “immersion fluid” are used interchangeably.

[0201] 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.

[0202] 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.

[0203] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools.

[0204] 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.

[0205] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. A substrate support configured to support a substrate, comprising an upper component, a core component and a lower component; wherein: a first opening is formed in an upper surface of the upper component; a first passageway communicating with the first opening is defined in the upper component and the core component; a first extraction channel communicating with the first passageway is defined by the core component and the lower component; and a first conditioning channel is defined by the core component and the lower component.

2. The substrate support according to claim 1, wherein the upper component is bonded to the core component and the core component is bonded to the lower component, and/or wherein the upper component is bonded to the core component by diffusion bonding or infiltration bonding, and/or wherein the core component is bonded to the lower component by diffusion bonding or infiltration bonding, and/or further comprising a second extraction channel radially inwards of the first extraction channel and configured to extract fluid.

3. The substrate support according to claim 2, wherein: a second passageway communicating with the second extraction channel is defined in the upper component and the core component; and a second opening communicating with the second passageway is formed in an upper surface of the upper component, and/or wherein the second extraction channel is defined by the core component and the lower component, or wherein the second extraction channel is defined by the upper component and the core component, desirably wherein the first extraction channel and the second extraction channel are configured such that they overlap in the radial direction.

4. The substrate support according to claim 3, wherein the second opening is radially inward of the first opening, and/or wherein the second passageway forms a substantially L-shape, and/or wherein the second passageway comprises: a first vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component and communicating with the second opening; and a horizontal portion extending in a direction substantially parallel to the upper surface of the upper component and communicating with the vertical portion of the second passageway; a second vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component and communicating with the horizontal portion of the second passageway and the second extraction channel, desirably wherein the horizontal portion of the second passageway has a first wall formed by the upper component and a second wall formed by the core component.

5. The substrate support according to any claims 2-4, further comprising a multifunctional channel configured to supply or extract gas, desirably wherein the horizontal portion of the second passageway has a first wall formed by the upper component and a second wall formed by the core component, and/or wherein: a third passageway communicating with the multifunctional channel is defined in the upper component and the core component; and a third opening communicating with the third passageway is formed in the upper surface of the upper component, and/or wherein the multifunctional channel is defined by the core component and the lower component, and/or wherein the third opening is radially inwards of the second opening, and/or wherein the third passageway forms a substantially L-shape, and/or wherein the third passageway comprises: a first vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component and communicating with the third opening; a horizontal portion extending in a direction substantially parallel to the upper surface of the upper component and communicating with the vertical portion of the third passageway a second vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component and communicating with the horizontal portion of the third passageway and the multifunctional channel, desirably wherein the horizontal portion of the third passageway has a first wall formed by the upper component and a second wall formed by the core component.

6. The substrate support according to claim 5, wherein the first conditioning channel is radially outward of the multifunctional channel and radially inward of the second extraction channel, and/or further comprising an ambient channel in fluid communication with ambient pressure, desirably wherein the ambient channel is radially inwards of the multifunctional channel, and/or further comprising: a fourth passageway communicating with the ambient channel and defined in the upper component and the core component; a fourth opening communicating with the fourth passageway and formed in the upper surface of the upper component, desirably wherein the ambient channel is defined by the core component and the lower component, or wherein the ambient channel is defined by the core component and the upper component, desirably wherein the multifunctional channel and the ambient channel are configured such that they overlap in the radial direction.

7. The substrate support according to claim 6, wherein the fourth opening is radially inward of the second opening and radially outward of the third opening, and/or wherein the fourth passageway forms a substantially L-shape, and/or wherein the fourth passageway comprises: a first vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component and communicating with the fourth opening; a horizontal portion extending in a direction substantially parallel to the upper surface of the upper component and communicating with the vertical portion of the fourth passageway a second vertical portion extending in a direction substantially perpendicular to the upper surface of the upper component and communicating with the horizontal portion of the fourth passageway and the ambient channel, desirably wherein the horizontal portion of the fourth passageway has a first wall formed by the upper component and a second wall formed by the core component, and/or further comprising a second conditioning channel radially inwards of the ambient channel, and/or further comprising a second conditioning channel radially inwards of the multifunctional channel and radially outwards of the ambient channel.

8. The substrate support according to any of claims 2-7, wherein the radial distance between a radially inward wall of the second extraction channel and a radially outward wall of the first conditioning channel is less the 5 mm, preferably less than 2 mm, and further preferably less than 1.6 mm, but greater than 1 mm, and preferably greater than 1.4 mm, and/or wherein the radial distance between a radially inward wall of the first extraction channel and a radially outward wall of the second extraction channel is less than 5 mm, preferably less than 2 mm, and further preferably less than 1.6 mm, but greater than 1 mm, and preferably greater than 1.4 mm, and/or wherein the second extraction channel is in fluid communication with the first conditioning channel, and/or wherein the second extraction channel is in fluid communication with the first extraction channel, or further comprising a fluid extraction gutter extending circumferentially around the substrate support, wherein the second extraction opening is configured to extract fluid from the fluid extraction gutter, and wherein the first conditioning channel is in fluid communication with the fluid extraction gutter.

9. The substrate support according to any of the preceding claims, wherein the radial distance between a radial edge of the substrate support and a radially outward wall of the first extraction channel is less than 5 mm, preferably less than 2 mm, and further preferably less than 1.5 mm, but greater than 1 mm, and further preferably greater than 1.3 mm, and/or wherein the channel(s) are cavities extending circumferentially around the substrate support, and/or wherein the first opening is defined by a groove extending circumferentially around the substrate support, wherein the groove is recessed into the upper surface of the substrate support.

10. The substrate support according to claim 8, wherein the second extraction channel is in fluid communication with the first conditioning channel via a first connecting passageway, and/or wherein the second extraction channel is in fluid communication with the first extraction channel via a second connecting passageway, and/or wherein the first conditioning channel is in fluid communication with the fluid extraction gutter via a third connecting passageway, desirably wherein the first conditioning channel is in fluid communication with the fluid extraction gutter via a third connecting passageway y-

11. The substrate support according to claim 9 or 10, wherein the substrate support is configured such that, when a substrate is supported by the substrate support, the groove is radially outwards of a radial edge of the substrate, and/or wherein a cross-sectional area of the groove is greater than 1 mm², preferably greater than 3 mm² and further preferably greater than 5 mm², and/or wherein the first passageway is connected to the first fluid extraction groove at a downstream-most point within the first fluid extraction groove, and/or wherein a plurality of flow-restricting members are disposed within the groove.

12. The substrate support according to any of the preceding claims, wherein the lower component comprises a plurality of projections configured to support the substrate support on a stage, and/or wherein a plurality of flow-restricting members are disposed within the groove, and/or wherein the upper component, the core component, and the lower component are formed of SiSiC, and/or wherein the substrate support is configured for use in a lithographic apparatus.

13. A lithographic apparatus comprising the substrate support according to any of the preceding claims.

14. A method for supporting a substrate, comprising use of the substrate support according to any of claims 1-12.

15. A method of manufacturing a device comprising the method of supporting a substrate according to claim 14.