Substrate support

Abstract

A substrate support for supporting a substrate. The substrate support comprises a main body having a surface, and a plurality of projections protruding from the surface of the main body. The distal ends of the plurality of projections define a support surface for a substrate. The substrate support also comprises a seal member of a size and / or shape to accommodate the plurality of projections. The seal member is flexible and has a fixed end attached to the surface and a free end. When the substrate is supported on the substrate support and subject to a clamping force, the seal member is at least partly disposed between the substrate support and the substrate and a distance between the free end of the seal member and the bottom surface of the substrate is smaller than a distance between the surface of the main body and the bottom surface of the substrate.

Description

SUBSTRATE SUPPORTCROSS-REFERENCE TO REEATED APPEICATIONS

[0001] This application claims priority of EP 24204537.5 which was filed on 3 October 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to a substrate support configured to support a substrate, and a system comprising the substrate support.BACKGROUND

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

[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] A lithographic apparatus may include an illumination system for providing a projection beam of radiation, and a support structure for supporting a patterning device. The patterning device may serve to impart the projection beam with a pattern in its cross-section. The apparatus may also include a projection system for projecting the patterned beam onto a target portion of a substrate.

[0006] In a lithographic apparatus, the substrate to be exposed (which may be referred to as a production substrate) may be held on a substrate support (sometimes referred to as a wafer table). The substrate support may be supported on a stage. The substrate support includes a substrate-facing surface of a main body. There may be a plurality of through holes extending to the substrate-facing side of the substrate support. The plurality of through holes enable fluid flow to provide negative pressure to aid in securing the substrate to the substrate support.

[0007] There is a desire to more effectively and efficiently secure the substrate to the substrate support. Particularly, it there is a problem that substrates which are warped may be difficult to be secured to the substrate support. This can result in a great amount of flow and pressure being requiredto secure the substrate or a situation where the substrate is not fully secured to the substrate support.SUMMARY

[0008] An object of the present invention is to provide a substrate support configured to support a substrate.

[0009] In accordance with the present invention, a substrate support for supporting a substrate. The substrate support comprises a main body having a surface, and a plurality of projections protruding from the surface of the main body. The distal ends of the plurality of projections define a support surface for a substrate. The substrate support also comprises a seal member of a size and / or shape to accommodate the plurality of projections. The seal member is flexible and has a fixed end attached to the surface and a free end. When the substrate is supported on the substrate support and subject to a clamping force, the seal member is at least partly disposed between the substrate support and the substrate and a distance between the free end of the seal member and the bottom surface of the substrate is smaller than a distance between the surface of the main body and the bottom surface of the substrate.

[0010] In accordance with another aspect of the present invention, a substrate support for supporting a substrate. The substrate support comprises a main body having a surface configured to face a substrate, the main body defining a groove recessed in the surface; and a retractable seal member. The retractable seal member comprises two flexible members, the two flexible members each having a distal end and a proximal end. At the distal ends, the two flexible members are attached together and at the proximal ends the two flexible members are attached to the main body. One of the flexible members is attached to the main body at one side of the groove and the other flexible member is attached to the main body at an opposite side of the groove. The retractable seal member is configured to change between an extended condition and a retracted condition. The retractable seal member is configured such that in the extended condition, the two flexible members extend out of the groove and form a straight wall extending towards the substrate, and a distal end of the retractable seal member contacts the substrate. The retractable seal member is configured such that in the retracted condition, the two flexible members are at least predominantly retracted into the groove.

[0011] Also in accordance with the present invention, a system comprising the substrate support.

[0012] 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, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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 schematically depicts an overview of a lithographic apparatus;Figure 2 depicts a plan view of a substrate support;Figure 3 depicts a cross-sectional view of the substrate support of Figure 2;Figure 4 depicts a cross-sectional view through a substrate support supporting a warped substrate;Figures 5A-D depict substrate supports including different arrangements of seal members as shown in cross-sectional view;Figures 6A-B depict cross-sectional views of a substrate support a seal member, having an outer diameter less than the diameter of the substrate, in an initial condition and a secured condition;Figures 7A-B depict different arrangements of seal member in plan view;Figure 8 depicts a plan view of a substrate support having a plurality of sealing members;Figure 9A-B depict a cross-sectional view of a substrate support including a retractable seal member in an extended condition and in a retracted condition;Figures 10 depicts a plan view of the substrate support of Figures 9A-B.

[0014] 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 substrate support 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 436, 405, 365, 248, 193, 157, 126 or 13.5 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 LA. The lithographic apparatus includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation or DUV radiation), a mask support (e.g., a mask table) MT constructedto 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 table (e.g., a support table or a substrate support) 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 table 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. The substrate table WT may optionally comprise a substrate support (not shown in Figure 1) constructed to hold 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 may be 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 tables WT (also named “dual stage”). In such “multiple stage” machine, the substrate tables 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 table WT while another substrate W on the other substrate table WT is being used for exposing a pattern on the other substrate W.

[0022] In addition to the substrate table WT, the lithographic apparatus may comprise a measurement stage (not shown in Figure 1). 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 projectionsystem 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 table 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 PMS, the substrate table WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B 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] In this specification, 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 axes is orthogonal to the other two axes. 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] In a lithographic apparatus it is necessary to position with great accuracy the upper surface of a substrate to be exposed in the plane of best focus of the aerial image of the pattern projected by the projection system. To achieve this, the substrate can be held on a substrate support. The surface of the substrate support that supports the substrate can be provided with a plurality of burls whose distal ends can be coplanar in a nominal support plane. The burls, though numerous, may be small in cross- sectional area parallel to the support plane so that the total cross-sectional area of their distal ends is a few percent, e.g. less than 5%, of the surface area of the substrate. The gas pressure in the space between the substrate support and the substrate may be reduced relative to the pressure above the substrate to create a force clamping the substrate to the substrate support.

[0026] A plan view of a substrate support 1 is shown in Figure 2. A partial cross section of the substrate support 1 is depicted in Figure 3. The substrate support 1 may be a part of or integral with the substrate table WT shown in Figure 1. The substrate support 1 may comprise a main body 10having an upper surface 11. The main body 10 may form a substantial portion of the substrate support 1. The upper surface 11 may be a top surface of the main body 10 when positioned as shown in Figure 3. That is, the upper surface 11 may be top surface in the Z-direction (the vertical direction).

[0027] The substrate support 1 may comprise a plurality of burls (protrusions or projections) 20 connected to, and protruding from, the upper surface 11 of the main body 10. Optionally, the substrate support 1 may comprise a plurality of burls (protrusions or projections) 20 connected to, and protruding from, the lower surface (opposite the upper surface 11) of the main body 10. The plurality of burls 20 may have proximal ends 21, which are situated near the main body 10 when in position, and distal ends 22. The distal ends 22 may be at opposite ends of the plurality of burls 20 to the proximal ends 21. That is, the distal ends 22 may be situated at an end of the burl 20 away from the main body 10.

[0028] The plurality of burls 20 may have a central longitudinal axis 23, with the proximal end 21 at one end of the burl 20 and the distal end 22 at the other end of the burl 20 along the central longitudinal axis 23. Thus, each of the plurality of burls 20 may have a central longitudinal axis 23 from the proximal end 21 to the distal end 22.

[0029] The distal ends 22 of the plurality of burls 20 form a support plane for a substrate W. Specifically, the distal ends 22 of the plurality of burls 20 may support a lower surface 31 of the substrate W. An upper surface 32 of the substrate W may be a surface opposite the lower surface 31. The upper surface 32 may be a surface which is configured to receive the radiation beam B.

[0030] The support plane may be formed in a substantially flat plane. Consequently, the substrate W can be positioned on the support plane to also be substantially flat, which can reduce errors in the pattern printed onto the substrate W (i.e., defectivity).

[0031] As shown in Figure 3, the plurality of burls 20 may be substantially frusto-conical, i.e. a truncated cone, or may be conical in shape. They may instead be substantially cylindrical. A frustoconical burl 20 may be stronger than a cylindrical burl 20 and thus have less likelihood of breaking. Preferably the plurality of burls 20 have the same shape as each other.

[0032] The plurality of burls 20 may be connected to the upper surface 11 of the main body 10 in any suitable way. The plurality of burls 20 may be separate components which are attached to the upper surface 11 of the main body 10. Alternatively, the plurality of burls 20 may be integral to the main body 10. In other words, the plurality of burls 20 may be formed as protrusions from the upper surface 11 of the main body 10, i.e. the plurality of burls 20 may be formed as a single part with the main body 10.

[0033] The substrate support 1 may be configured to enable fluid to be extracted from between the substrate W supported on the support plane and the upper surface 11. Fluid at the edge of the substrate W may be drawn under the substrate W. As fluid is extracted the pressure beneath the substrate W is reduced relative to pressure above the substrate W, and the edge of the substrate W will lower towards the substrate support 1. The substrate W can be clamped by extracting fluid in thespace below the substrate W to provide a reduced relative pressure in the space between the substrate support 1 and the substrate W.

[0034] The main body 10 defines a plurality of through holes. Some of these through holes may be configured as extraction openings 12, otherwise referred to as extraction orifices, through which the fluid is extracted.

[0035] It is beneficial to reduce leakage of fluid into the space between the substrate W and the main body 10 when the substrate W is clamped. Therefore, it may be beneficial to provide a physical boundary positioned near the edge of the substrate support 1. The physical boundary could be formed towards an edge of the main body 10 as shown in Figures 2 and 3. The physical boundary could be formed by a sealing member 40. The sealing member 40 may be a wall type protrusion formed around the edge of the main body 10, for example, around the circumference of the main body 10. The sealing member 40 may be formed to provide a seal between the lower side, e.g., lower surface 31, of the substrate W and the substrate support 1 around the edge of the substrate W. The seal provided by the sealing member 40 need not be a perfect seal but may be a partial seal that reduces but does not eliminate flow of fluid into the space between the substrate support 1 and substrate W.

[0036] The sealing member 40 may surround the plurality of burls 20. The sealing member 40 may protrude from the upper surface 11 of the main body 10. The sealing member 40 may be connected to the main body 10 in any way. The sealing member 40 may be integral with the main body 10.

[0037] A pressure sensor (not shown in the drawings) may be used to measure the pressure between the substrate W and the upper surface 11 of the main body 10. Various sensors for measuring the pressure in the space below the substrate W are known. For example, a pressure sensor as disclosed in WO 2017 / 137129 Al, which is hereby incorporated by reference in its entirety, provides an example of an appropriate pressure sensor which might be used.

[0038] A flow rate sensor (not shown in drawings) may be used to measure the flow rate of the fluid extracted via the extraction orifices 12. Various sensors for measuring the flow rate from the space below the substrate W are known.

[0039] For the present invention, the exact arrangement of the substrate support 1 is not particularly limited. For example, the exact arrangement of burls 20 and sealing member 40 in the substrate support 1 is not particularly limited.

[0040] Figure 4 shows a cross-sectional view through a substrate W and substrate support 1, similar to that of Figure 3 (with corresponding features having the same reference numbers). The substrate W of Figure 4 is warped. In this example, the substrate W is warped such that the periphery of the substrate W is farther from the substrate support 1 than the central region C of the substrate W. This may be referred to as a bowl-shaped warped substrate W. In order to secure the substrate W to the substrate support 1, fluid is extracted through the extraction orifice 12, as shown by arrow E. The flow of fluid is depicted by arrows in Figure 4. At the periphery of the substrate W, the force provided by the flow is weaker due to warpage of the substrate W. In particular, the flow rate may bereduced due to the distance between the substrate W and the substrate support 1, in particular between the periphery of the substrate W and the support plane defined by the distal ends 22 of the burls 20. Furthermore, fluid may leak out at the periphery of the substrate W, as shown by the arrow L in Figure 4, therefore leading to a potentially insufficient level of suction to draw the periphery of the substrate W to the support surface provided by the distal ends 22 of the burls 20. Some substrates have different warpage, for example an umbrella-shaped warped substrate W which is farther from the substrate support 1 at the central region C of the substrate W than at the periphery of the substrate W. In these cases, the risk of fluid flow leakage may be higher near the central region C of the substrate W rather than at a periphery of the substrate W. For example, in some circumstances leakage around holes in the substrate support 1, such as for pins, may occur.

[0041] There is therefore a problem that substrates W which are warped may be difficult to be secured to the substrate support 1. This can result in a great amount of flow and pressure being required to secure the substrate W and possibly leading to overlay errors. Alternatively, the problem may result in an inability to sufficiently secure substrates W which are too warped, leading to wastage of these substrates W.

[0042] Figure 5A-D illustrates arrangements of a substrate support 1, such as that of Figure 4, further comprising a seal member 5. Similarly to the substrate supports 1 of Figures 3 and 4, the substrate supports 1 of Figure 5 A-D are each suitable for supporting a substrate W. The substrate support 1 comprises a main body 10 having a surface 11, and a plurality of projections 20 (otherwise referred to as burls) protruding from the surface 11 of the main body 10. The distal ends 22 of the plurality of projections 20 define a support surface for a substrate W. The substrate support 1 also comprises a seal member 5. The seal member 5 is provided such that leakage may be partially or fully reduced by bridging the gap between the surface 11 of the substrate support 1 and the bottom of the substrate W. In this way, the leakage L present in the arrangement of Figure 4 may be avoided.

[0043] The seal member 5 is of a size and / or shape to accommodate the plurality of projections 20. For example, the projections 20 may be disposed at a distance from each other and the seal member 5 may be small enough to fit between the projections 20. Alternatively, the seal member 5 may be shaped to accommodate the projections 20. The seal member 5 is flexible. In other words, during use, the seal member 5 may change its shape during use. The seal member 5 has a fixed end 50 attached to the surface 11 of the substrate support 1. In this way, the fixed end 50 may be held in place such that the seal member 5 does not move in an unwanted way. Furthermore, the fixed end 50 being attached to the surface 11 of the substrate support 1 may reduce a likelihood of flow leakage between the fixed end 50 and the surface 11. The seal member 5 has a free end 51 which is not directly attached to the surface 11 of the substrate support 1. In this way, the free end 51 may change position depending on the conditions.

[0044] When the substrate W is supported on the substrate support 1 and subject to a clamping force, the seal member 5 is at least partly disposed between the main body 10 and the substrate W. In otherwords, at least part of the seal member 5 is disposed between the main body 10 and the substrate W. In particular, the free end 51 may be disposed between the main body 10 and the substrate W. A distance between the free end 51 of the seal member 5 and the bottom surface of the substrate W is smaller than a distance between the surface 11 of the main body 10 and the bottom surface of the substrate W, in the region around the seal member 5. In other words, the seal member 5, at or towards the free end 51, is configured to approach or contact the bottom surface of the substrate W. The fixed end 50 is attached to the surface 11 of the main body 10. Therefore, the seal member 5 may span the gap between the surface 11 of the main body 10 and the bottom of the substrate W, therefore reducing a likelihood of significant leakage L, such as that shown in Figure 4. In this way, a likelihood of successfully securing a warped substrate W to the substrate support 1 is increased. Furthermore, the overall force applied to the substrate W by the fluid flow may be reduced, reducing the energy taken to generate sufficient fluid flow to secure the substrate W. In this way, a likelihood of being able to provide sufficient flow to efficiently and effectively secure a warped substrate W to the substrate support 1 is improved.

[0045] Figures 5A-C show the substrate W in its initial condition before it has been fully secured to the substrate support 1. In this condition, the free end 51 of the sealing member 5 is raised at a distance from the surface 11 of the main body 10. After this, the fluid flow may be provided by suction through the extraction orifice 12 in order to apply a clamping force to secure the substrate W to the substrate support 1. As shown, for example, in Figures 5A-C, when the substrate W is supported on the substrate support 1, prior to and / or during application of the clamping force, the free end 51 of the seal member 5 is close to, or possibly touching, the bottom surface of the substrate W. In particular, the free end 51 is desirably closer to the bottom of the substrate W than the free end 51 is to the surface 11 of the main body 10. In this way, a majority of a gap between the surface 11 of the main body 10 and the substrate W may be blocked by the seal member 5, which may improve fluid flow clamping of the substrate W to the substrate support 1.

[0046] A low friction coating may optionally be provided on the seal member 5 in a region of the seal member 5 configured to contact the bottom surface of the substrate W. The low friction coating may be made of a material having a lower coefficient of friction than a material making up a majority of the seal member 5. The low friction coating may be provided at or towards the free end 51 of the seal member 5. For example, the low friction coating may comprise polytetrafluoroethylene (PTFE), polyamide (PA), polyether ether ketone (PEEK), polyimide, polyethylene terephthalate (PET), or diamond-like carbon (DLC). In this way, the likelihood of the seal member 5 remaining in contact with the bottom of the substrate W during the clamping process may be increased. As such, a likelihood of significant leakage between the bottom surface of the substrate W and the free end 51 of the seal member 5 may be reduced. Furthermore, a lateral force on the substrate W during clamping / securing to the substrate support 1 may be reduced. This reduced force may reduce alikelihood of moving or deforming the substrate W in the lateral direction. As such, an amount of overlay error may be reduced.

[0047] Figure 5D shows the secured condition, with the substrate W in its secured position on the support surface of the distal ends 22 of the projections 20. In other words, Figure 5D shows the substrate W after the clamping force has been applied to draw the substrate W towards the substrate support 1 and to flatten the substrate W to lie on the distal ends 22 of the projections 20. As the substrate W moves towards the main body 10, the seal member 5 is also drawn towards the main body 10, for example by the force of the substrate W. When the substrate is fully in contact with the support surface of the distal ends 22 of the projections 20, the seal member 5, at least in a region between the surface 11 and the substrate W, is entirely at or below a height of the projections 20. As shown in Figures 5D and 6B, this may be achieved by the thickness of the seal member 5 being less than a height of the projections 20 above the surface 11 of the main body 10.

[0048] In the arrangement of Figure 5D, the seal member 5 defines a plurality of orifices, each configured to accommodate a respective projection 20. In this way, the seal member 5 is configured to fall between the projections 20 when the substrate W is in the secured position. The seal member 5 therefore does not prevent the bottom surface of the substrate W from contacting the distal ends 22 of the projections 20. The substrate W is therefore free to lie flat in the secured position.

[0049] In a preferred arrangement, the seal member 5 has an annular shape having an innermost edge 501 having an inner radius and an outermost edge 502 having an outer radius. This annular shape of the seal member 5 is shown, for example, in Figure 7A, which provides a plan view of a sealing member 5 according to any of Figures 5A-D and 6A-B. With this arrangement, the inner radius of the seal member 5 is desirably less than the radius of the substrate W. In an alternative arrangement, the seal member 5 may not form a complete annulus. For example, the seal member 5 may be only a segment of an annulus. Alternatively, the seal member 5 may take a different shape, such as a rectangle, having an innermost edge and an outermost edge, where the innermost edge is configured to fall under the substrate W during use.

[0050] In the arrangement of Figure 5B, when no clamping force is being applied, the seal member 5 has a substantially straight cross-sectional shape extending between the innermost edge 501 and the outermost edge 502. In other words, the seal member 5 is substantially flat between the free end 51 and the fixed end 52. This arrangement has the advantage of being simple to manufacture. With this arrangement, the angle of the seal member 5 to the surface 11 of the main body 10 may change in order to move between an initial condition, where the substrate W is warped away from the distal ends 22 of the projections 20, and a secured condition, where the substrate W is flat on the support surface.

[0051] In contrast to the arrangement of Figure 5B, in the arrangements of Figures 5A and 5C, when no clamping force is being applied, the seal member 5 has a substantially curved cross-sectional shape extending between the innermost edge 501 and the outermost edge 502. In other words, the sealmember 5 is substantially bent between the free end 51 and the fixed end 52. With this arrangement, the amount of curvature of the seal member 5 may change in order to move between an initial condition, where the substrate W is warped away from the distal ends 22 of the projections 20, and a secured condition, where the substrate W is flat on the support surface.

[0052] In the arrangement of Figure 5 A, the seal member 5 has a curved shape such that an upper or end surface of the seal member 5 is closest, or in contact with, the substrate W. For example, as shown in Figure 5A, the terminal free end 51 of the seal member 5 is in close proximity to the bottom of the substrate W. With an arrangement such as this, the seal member 5 does not have to be excessively bent in order to achieve the curved shape.

[0053] In the arrangement of Figure 5C, the seal member 5 is more curved than in the arrangement of Figure 5A. In particular, in the arrangement of Figure 5C, the seal member 5 is curved back on itself such that, when the substrate W is supported on the substrate support 1, prior to or during application of the clamping force, the bottom surface 53 of the sealing member 5 contacts the bottom surface of the substrate W. The bottom surface 53 of the seal member 5 is the surface facing the surface 11 of the main body 10 at the fixed end 50 of the seal member 5. The curvature of the seal member 5 towards the free end 51 causes the seal member 5 to be curled around such that the bottom surface 53 of the seal member 5 is facing the bottom surface of the substrate W. This arrangement may promote better contact, desirably sliding contact, between the seal member 5 and the substrate W throughout the process of securing the substrate W to the substrate support 1. Furthermore, the contact force between the seal member 5 and the substrate W may be reduced by the curved around portion of the seal member 5 being more compliant. In this arrangement, a lateral stiffness of the seal member 5 may be greater than in the arrangements where the seal member 5 is less curved. This may further reduce a likelihood of leakage due to unwanted collapsing of the seal member 5, particularly when the fluid flow is applied.

[0054] In the arrangements of Figures 5A-D, the outer radius of the seal member 5 is greater than the radius of the substrate W. In other words, an outer region of the seal member 5 is configured to sit radially outwards of the substrate W. This arrangement may be implemented for example where the substrate support 1 has an outer dimension greater than the diameter of the substrate W. Furthermore, in the arrangements of Figures 5A-D, the free end 51 is towards the inner radius of the seal member 5. In this way, the seal member 5 is configured such that the free end 51 sits between the substrate W and the main body 10 during use.

[0055] Figure 6A-B illustrates a substrate support 1, such as that of Figure 4, further comprising a seal member 5 according to another arrangement. In Figure 6A, the substrate W is in the initial condition before it has been fully secured to the substrate support 1. In Figure 6B, the substrate W is in the secured position on the substrate support 1. The arrangement of Figure 6A is largely the same as that of Figure 5A, except that in the arrangement of Figure 6A, the free end 51 is towards outermost edge 502 of the seal member 5. With this arrangement, the outer radius of the seal member5 is equal to or less than the radius of the substrate W. In this way, the seal member 5 is configured such that the free end 51 sits between the substrate W and the main body 10 during use. Although the arrangement of Figure 6A shows a partially curved seal member 5, any suitable cross-sectional shape of seal member 5 may be used. For example, the arrangement of Figure 6A could be adapted to include a substantially flat seal member 5, like that of Figure 5B, or a curled seal member 5, like that of Figure 5C. The arrangement, such as that of Figure 6A-B, wherein the free end 51 is at the outermost edge 502 of the seal member 5, is desirable because when the fluid flows, pressure aids in holding the seal member 5 towards the bottom surface of the substrate W to maintain the seal, shown by the force arrows F in Figure 6A.

[0056] The fixed end 50 of the seal member 5 may be attached to the main body 10 of the substrate support 1 using any suitable method. For example, the fixed end 50 may be bonded or adhered to the surface 11 of the main body 10. In a preferred arrangement, the fixed end 50 of the seal member 5 may be attached to the surface via an adhesive 55, as shown for example in Figures 5D and 6A-B. The adhesive 55 preferably allows electrical conductivity between the surface 11 of the main body 10 and the sealing member 5. In this way, a risk of electrostatic discharge may be reduced. The sealing member 5 and the main body 10 may have the same electrical potential. The adhesive 55 may, for example be tape, such as carbon tape, or glue.

[0057] The substrate support 1 may optionally include a spacer 54 disposed between the surface 11 of the main body 10 and the sealing member 5. The spacer 54 may aid in achieving a desired position of the sealing member 5 in the initial condition, with the substrate W in place over the substrate support 1 but not yet secured to the substrate support 1. For example, the spacer 54 may raise the sealing member 5 to increase a distance between the sealing member 5 and the surface 11 of the main body 10, and decrease a distance between the seal member 5 and the substrate W. In other words, the spacer 54 is desirably configured to elevate the free end 51 of the sealing member 5 compared to the fixed end 50 of the sealing member 5. The spacer 54 is desirably disposed at or towards the fixed end 50 of sealing member 5. The fixed end 50 of the seal member 5 may be attached to the surface 11 of the main body 10 via the spacer 54. The spacer 54 may be used to raise the free end 51 of the sealing member 5 by increasing an angle between the surface 11 of the main body 10 and the sealing member 5. In this way, the spacer 54 may be relatively small compared to the resulting elevation of the free end 51. This is advantageous because the free end 51 can be elevated by the spacer 54 without the spacer 54 being so large as to inhibit the seal member 5 from lying sufficiently flat to enable to the substrate W to be secured flat on the support surface on the distal ends 22 of the projections 20.

[0058] As shown in Figure 5B, the spacer 54 may have a wedge shape, having a greater height towards the free end 51 of the sealing member 5. The spacer 54 may be particularly useful in arrangements where the sealing member 5 has a straight cross-sectional shape, such as shown in Figure 5B. This is because the spacer 54 can be used to raise the free end 51 of the seal member 5 towards the substrate W. A spacer 54 may be used in a configuration having a seal member 5 with acurved cross-sectional shape in order to aid in positioning the free end 51 of the seal member 5 close to, or in contact with, the seal member 5.

[0059] The seal member 5 may be formed of any suitable material. In particular, the seal member 5 may be formed of a material suitable for use in a vacuum environment. For example, the seal member 5 may comprise silicone, nitrile rubber (otherwise known as NBR), urethane and / or polyether ether ketone (otherwise known as peek). In a preferred arrangement the seal member 5 comprises metal. In a preferred arrangement, the seal member 5 may comprise peek and / or metal in a region configured to contact the substrate W. In this way, a likelihood of contamination or damage to the substrate W may be reduced. For example, a coating of metal or peek may be provided in the region of the seal member 5 expected to contact the substrate W. In another preferred arrangement, the seal member 5 may be predominantly or entirely formed of metal. The metal may, for example, comprise or consist of nickel or stainless steel.

[0060] Figure 7A, which provides a plan view of a sealing member 5 according to any of Figures 5A-D and 6A-B. In the arrangement of Figure 7A, the seal member 5 has a continuous, annular ring shape.

[0061] Figure 7B provides a plan view of a sealing member 5 comprising a plurality of segments 510. In this arrangement, each segment 510 may be configured to move independently. For example, the free end 51 in one segment may be at a different height over the surface 11 of the main body 10 than the free end 51 in another segment. This may be useful in reducing a likelihood of leakage in a scenario where the substrate W has asymmetrical warpage.

[0062] As shown in Figure 7B, the plurality of segments 510 may be separated by radially extending slits 511 in the seal member 5. In particular, in the arrangement of Figure 7B, the slits 511 extend from the inner radius 510 of the seal member 5 partially towards the outermost edge 502 of the seal member 5. In the arrangement of Figure 7B the slits 511 extend only partially across the seal member 5, such that the seal member 5 is circumferentially continuous at the outermost edge 502. In an alternative arrangement, one or more of the slits 511, optionally all of the slits 511, may extend fully between the innermost edge 501 and the outermost edge 502 such that adjacent segments 510 are entirely separated from each other by the slits 511.

[0063] The main body 10 may define one or more additional holes 13, in addition to the one or more extraction orifices 12. The holes 13 may extend through the surface 11 of the main body 10. The holes 13 may, for example, be provided to accommodate pins (not shown). The seal member 5 may define one or more openings (not shown) configured to surround a corresponding one or more of the holes 13. In this way, the seal member 5 may not impede the function of the holes 13.

[0064] Figure 8 shows a plan view of a substrate support 1 defining additional holes 13. The substrate support 1 of Figure 8 includes a seal member 5 disposed on the surface 11 of the main body 10. As shown, for example, in Figure 8, the substrate support 1 optionally further comprises one or more additional seal member 6. The additional seal member 6 is desirably flexible and configured toat least partially block or restrict a gap between the projections 20 and the substrate W when the substrate W is being secured to the substrate support 1. The additional seal member 6 may have an annular shape similarly to the seal member 5. The additional seal member 6 desirably has a smaller outer radius than an outer radius of the seal member 5. The additional seal member 6 may otherwise by configured to perform in the same way as the seal member 5, for example as described in Figures 5A-D and 6A-B. For example, the additional seal member 6 may comprise a fixed end and a free end. The additional seal member 6 may be configured to move between an initial condition and a secured condition. In the initial condition, the free end is elevated such that the free end is in close proximity to, or in contact with, the bottom surface of the substrate W. In the secured condition, the free end is at or below the height of the distal end 22 of the projections 20 above the surface 11 of the main body 10.

[0065] The additional seal members 6 of Figure 8 are each disposed in a region surrounding a corresponding additional hole 13. The additional seal member 6 comprises an opening configured to surround the hole 13. In other words, an innermost edge of the additional seal member 6 surrounds the hole 13 during use. The free end of the additional seal member 6 may be closer to the hole 13 than the fixed end of the additional seal member 6. In other words, the free end of the additional seal member 6 may be an innermost edge of the additional seal member 6. The fixed end of the additional seal member 6 may be towards an outermost edge of the additional seal member 6.

[0066] Figure 9A-B depict a cross-sectional view of a substrate support 1 including a retractable seal member 7. Figure 9A shows the seal member 7 in an extended condition and Figure 7B shows the seal member 7 in a retracted condition. The retractable seal member 7 is retractable because it is able to move, passively and / or actively, from the extended condition to the retracted condition and vice versa. In other words, the retractable seal member 7 is both retractable and extendable. In the extended condition, the seal member 7 extends across a gap between the main body 10 of the substrate support 1 and the bottom surface of the substrate W. In this way, similarly to the seal member 5 as described above, the retractable seal member 7 may reduce a likelihood of leakage L as shown in Figure 4.

[0067] The substrate support 1 of Figure 9A-B comprises a main body 10 having a surface 11 configured to face a substrate W. The main body 10 defines a groove 70 recessed in the surface 11. The groove 70 is configured to receive the retractable seal member 7 when the retractable seal member 7 is in the retracted condition. In this way, in the retracted condition, the retractable seal member 7 may sit below the distal ends 22 of the projections 20. This means, the retractable seal member 7 allows the substrate W to he flat on the support surface of the distal ends 22 when the retractable seal member 7 is in the retracted condition.

[0068] The retractable seal member 7 comprises two flexible members 71, 72. The two flexible members 71, 72 have a proximal end 702. The two flexible members 71, 72 have a distal end 701. At, or towards, the distal end 701, the two flexible members 71, 72 are attached together. At theproximal ends 702 the two flexible members 71, 72 are attached to the main body 10. One of the flexible members 71 is attached to the main body 10 at one side of the groove 70. The other flexible member 72 is attached to the main body 10 at an opposite side of the groove 70. The two flexible members 71, 72 may be formed of two separate members connected together towards the distal end 701. Alternatively, the two flexible members 71, 72 could be manufactured as a single body having the two flexible members 71, 72 extending towards the proximal end 702 from a joined portion at the distal end 701. The retractable seal member 7 may optionally be bi-stable. In other words, the retractable seal member 7 may be stable in both the extended condition and the retracted condition. Alternatively, the retractable seal member 7 may be monostable at a position between the extended condition and the retracted condition. The retractable seal member 7 may be designed and manufactured to have the desired stability characteristic, based for example on the chosen initial position, stress and stiffness of the retractable seal member 7.

[0069] The retractable seal member 7 is configured to change between an extended condition, as shown in Figure 9A, and a retracted condition, as shown in Figure 9B. As shown in Figure 9A, the retractable seal member 7 is configured such that in the extended condition, the two flexible members 71, 72 extend out of the groove 70 and form a wall extending towards the substrate W. The wall extending out of the groove 70 is desirably substantially straight, as compared to a curved region of the flexible members 71, 72 towards a proximal end 702 in the extended condition. The wall may extend in a direction perpendicular to the surface 11 of the main body 10, as shown in Figure 9A. The direction perpendicular to the surface 11 may be the vertical direction. In an alternative arrangement, the wall may extend at an angle to the perpendicular.

[0070] The retractable seal member 7 is configured to contact the substrate W in the extended condition. In the arrangement of Figure 9A, the wall extends such that a region towards the distal end 701 of the retractable seal member 7 contacts the bottom surface of the substrate W. The retractable seal member 7 is configured such that in the retracted condition, the two flexible members 71, 72 are at least predominantly retracted into the groove 70. In particular, the two flexible members 71, 72 sit at or below the distal ends 22 of the projections 20 such that the substrate W can lie on the support surface. In some arrangements, as shown in Figure 9B, the retractable seal member 7 may be configured such that, in the retracted condition, the two flexible members 71, 72, are entirely retracted into the groove 70. In other words, in some arrangements, the two flexible members 71, 72 sit at or below the surface 11 of the main body 10.

[0071] Figures 10 shows a plan view of a main body 10 of a substrate support 1 suitable for accommodating the retractable seal member 7 described above with reference to Figures 9A-B. The groove 70 is a circular groove having an outer diameter less than an outer diameter of the substrate W (where the outer diameter of the substrate W is shown by a dotted line in Figure 10). In this way, the groove 70 is arranged such that the retractable seal member 7 is directly below the substrate W when the substrate W is being secured to the substrate support 1.

[0072] The retractable seal member 7 may also have an annular shape, such that the retractable seal member 7 is configured to be received by the groove 70 in a retracted condition. With this arrangement, when the retractable seal member 7 is in the extended condition, the wall forms a cylindrical or frustoconical shape. This shape makes it unlikely that the wall will buckle in a lateral direction. The retractable seal member 7 is therefore robust, while having a principal vertical compliance. In other words, the stiffness of the retractable seal member 7 is low enough that the substrate W is able to move closer to the substrate support 1 without being hindered by the retractable seal member 7.

[0073] As shown for example in Figure 10, the main body 10 optionally defines a plurality of grooves 70, each configured to receive a respective retractable seal member 7. The plurality of grooves 70 are desirably concentrically arranged circular grooves 70, as shown in Figure 10. With a plurality of retractable seal members 7, a risk of leakage may be further reduced. Furthermore, an extraction flow rate and therefore a clamping force in each concentric region may optionally be controlled separately in order to apply clamping force at a desired magnitude and / or timing in different concentric regions individually.

[0074] In the arrangement of Figures 9A-B, one of the flexible members 72 is attached on a radially outward side of the groove 70 and the other flexible member 71 is attached on radially inward side of the groove 70. The flexible members 71, 72 may each be attached to the main body 10 at the respective sides of the groove 70. The flexible members 71, 72 may be attached at the surface 11 in a region radially inward and outward of the groove 70. Alternatively, the flexible members 71, 72 may be attached to the opposing sides of the groove 70.

[0075] The two flexible members 71, 72 may be attached to the main body 10 via any suitable means. For example, a bead (not shown) may be provided at the proximal end 702 of each flexible member 71, 72 and the main body 10 may be configured to receive the bead. Alternatively, or additionally the flexible member 71, 72 may, for example, be attached to the main body 10 by gluing, clamping or vulcanising.

[0076] In the arrangement of Figures 9A-B, the substrate support 1 further comprises two flanges 81, 82. Each flange 81, 82 is configured to secure a corresponding flexible member 71, 72 to the main body 10. The flanges 81, 82 include an inner flange 81 disposed at a radially inward side of the groove 70 and an outer flange 82 disposed at a radially outward side of the groove 70. The flanges 81, 82 are optionally embedded within the main body 10. The flanges 81, 82 may extend under one or more projections 20. In this way, a risk of the flexible members 71, 72 becoming detached from the main body 10 may be reduced.

[0077] The retractable seal member 7 is configured to move from the extended condition towards the retracted condition when a clamping force is applied which attracts the substrate W towards the surface 11 of the main body 10. In other words, the retractable seal member 7 is configured to be more compliant in a direction perpendicular to the surface 11 than the substrate W. In this way, theforce of the substrate W as it moves towards the distal ends 22 is sufficient to deform the retractable seal member 7. In other words, the retractable seal member 7 does not hinder the substrate W from moving towards the distal ends 22 of the projections 20 to be secured in position on the substrate support 1. The risk of damage to the substrate W due to force exerted by the retractable seal member 7 on the substrate W is therefore low. Furthermore, with the retractable seal member 7 as described herein with respect to Figure 9A-B, a resistance of the retractable seal member 7 to retracting does not increase as the retractable seal member 7 moves towards the retracted condition. This means the forces exerted on the substrate W by the retractable seal member 7 when moving from the extended condition to the retracted condition may be more constant than with other seal member arrangements.

[0078] As explained above, the retractable seal member 7 may be passively extended and retracted. For example, the retractable seal member 7 may be configured such that it moves from an extended condition to the retracted condition due to the force of the substrate W as the substrate W moves toward the substrate support 1, for example due to a pressure difference above and below the substrate W generated by fluid flow.

[0079] The retractable seal member 7 is optionally further configured to be actively actuated to move between the retracted condition and the extended condition. In this way, the retractable seal member 7 may be easily re-set from the retracted condition to the extended condition, for example when one substrate W has been removed and the next substrate W is ready to be placed on the substrate support 1. Furthermore, the substrate support 7 may be configured such that the retractable seal member 7 may be actively actuated to aid the retractable seal member 7 in retracting without hindering the substrate W.

[0080] The retractable seal member 7 is optionally be configured to be pneumatically actuated to move between the retracted condition and the extended condition. According to one arrangement, as shown for example in Figures 9A-B, the main body 10 comprises a flow supply conduit 14 in direct fluid communication with the groove 70. In this arrangement, the retractable seal member 7 is configured to be actuated by fluid flow supply through the flow supply conduit 14. For example, fluid may be extracted from the groove 70 through the fluid supply conduit 14 to aid in retracting the retractable seal member 7 and / or fluid may be supplied to the groove 70 through the fluid supply conduit to aid in extending the retractable seal member 7.

[0081] As shown in Figure 9A-B, the distal end 701 of the retractable seal member 7 comprises a lip 73. The lip 73 may be angled to receive the bottom surface of the substrate W on an upper surface of the lip 73. The lip 73 is configured to contact the substrate W when fluid is extracted from the extraction orifice 12. In particular, a pressure difference may draw the lip 73 towards the substrate W when fluid is extracted from the extraction orifice 12 to move the substrate W between the initial condition (as shown in Figure 9A) and the secured position on the distal ends 22 of the projections 20 (as shown in Figure 9B). There may be contact layer 75 disposed on the lip 73 for contact with the substrate W. The contact layer 75 may comprise a material unlikely to damage or contaminate thesubstrate W. For example, the contact layer 75 may comprise polytetrafluoroethylene (PTFE), polyamide (PA), polyether ether ketone (PEEK), polyimide, polyethylene terephthalate (PET), or diamond-like carbon (DLC).

[0082] The flexible members 71, 72 may be formed of any suitable material. The flexible members 71, 72 desirably comprise, or are formed of, a polymer material. For example, the flexible members 71, 72 may comprise thermoplastic elastomer (TPE), fluoropolymer elastomer (e.g., viton), nitrile butadiene rubber (NBR), polyurethane, silicone.

[0083] A reinforcement structure 74 may optionally be provided towards the distal end 701 of the retractable seal member 7. For example, as shown in Figure 9A-B, the reinforcement structure 74 may be provided at the lip 73. The reinforcement structure 74 may be additional material intended to reinforce the retractable seal member 7 such that it is not subjected to excessive deformation in a region, such as the lip 73, configured to contact the substrate W. The reinforcement structure 74 is preferably on an opposite side of the retractable seal member 7 than the side configured to contact the substrate W. In this way, a material of the reinforcement structure 74 may be selected for structural reinforcement properties without needing to compromise on a material also having low likelihood to damage or contaminate the substrate W with contact.

[0084] As described above with reference to Figures 9A-B, the flexible members 71, 72 each comprise a proximal end 702 attached to the main body 10. In a preferred arrangement, the proximal ends 702 of the two flexible members 71, 72 are attached at opposing sides of the groove 70. The flexible members 71, 72 are configured such that in the extended condition, the flexible members 71, 72 are each curved at a first position on the flexible member 71, 72. The first position is between the proximal end 702 and where the flexible members 71, 72 meet to form the wall. The flexible members 71, 72 are configured such that in the retracted condition, the flexible members 71, 72 are each curved at a second position on the flexible member 71, 72. The second position is closer to a distal end 701 of the flexible member 71, 72 than the first position.

[0085] In other words, in both the extended condition and the retracted condition the flexible members 71, 72 extend from the proximal end 702 and are curved towards each other such that the two flexible members 71, 72 meet. The curved portion of each flexible member 71, 72 may form a semi-circular shape, as shown in Figures 9A-B. The flexible members 71, 72 may be symmetrically curved and meet at a central radial location, between the inner and outer sides of the groove 70. In an alternative arrangement, the flexible members 71, 72 may be symmetrically curved and meet at a noncentral radial location, between the inner and outer sides of the groove 70. The two flexible members 71,72 preferably have the same thickness but may have different thicknesses. The thickness of each flexible member 71, 72 may be between 0.1 mm and 1.2 mm, preferably 0.2 mm and 0.6 mm , more preferably 0.3 mm to 0.5 mm, for example 0.4 mm.

[0086] In the extended condition, the flexible members 71, 72 are curved and meet each other at a position along the flexible members 71, 72 that is closer to the proximal end 702 than the distal end701. In the retracted condition, the flexible members 71, 72 are curved and meet each other at a position along the flexible members 71, 72 that is not as close to the proximal end 702 than in the extended condition. In this way, the flexible members 71, 72 contact each other closer to the proximal end 702 in the extended condition than in the retracted condition. This means that the wall formed by the two flexible members 71, 72 contacting each other is longer in the extended condition than in the retracted condition. In the retracted condition, there may optionally be no wall.

[0087] Furthermore, as the retractable seal members 7 move between the extended condition and the retracted condition, the flexible members 71, 72 may roll along the sides of the groove 70, such that in the retracted condition, a part of the flexible members 71, 72 towards a proximal end 702 extends downwards into the groove 70. Therefore, in the retracted condition, the flexible members 71, 72 may extend from the proximal end 702 downwards into the groove 70 before curving such that the two flexible members 71, 72 meet each other. In this way, the flexible members 71, 72 meet at a lower height, deeper within the groove 70, in the retracted condition than in the extended condition.

[0088] In this way, the retractable seal member 7 may make efficient use of limited space. In particular, a significant change of height of the distal end 701 can be achieved between the extended condition and the retracted condition without the groove 70 having to be excessively deep or wide.

[0089] A vertical distance between a position of the distal end 701 of the retractable seal member 7 in the retracted condition and a position of the distal end 701 of the retractable seal member 7 in the extended condition may be between 0.5 mm and 5 mm, preferably between 1 mm and 3 mm, more preferably between 1.5 mm and 2.5 mm, for example 2 mm. The depth of the groove 70 is desirably at least half of the vertical distance between a position of the distal end 701 of the retractable seal member 7 in the retracted condition and a position of the distal end 701 of the retractable seal member 7 in the extended condition. The depth of the groove 70 may be between 0.25 mm and 2.5 mm, preferably between 0.5 mm and 1.5 mm, more preferably between 0.75 mm and 1.25 mm, for example 1 mm. A width of the groove 70 between the opposing sides, may be between 0.5 mm and 5 mm, preferably between 1 mm and 3 mm, more preferably between 1.5 mm and 2.5 mm, for example 2 mm.

[0090] Structures on the substrate-facing surface, for example burls 20 and sealing member 40 may be formed by any suitable method - for example, by using a process such as electrical discharge machining, laser structuring or sand blasting. A high wear resistance coating, e.g., DLC, diamond or CrN, may be provided to protect exposed surfaces of the substrate support 1. For example, the burls 20 may be provided with the high wear resistance coating.

[0091] It will also be appreciated that the principles of the present invention can be applied to metrology or lithographic tools and clamping systems that employ electrostatic clamps.

[0092] Although specific reference may be made in this text to the use of a metrology system in the context of the manufacture of ICs, it should be understood that the metrology system described herein may have other applications, such as in the manufacture of integrated optical systems, guidance anddetection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin fdm magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and / or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains one or multiple processed layers.

[0093] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications.

[0094] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0095] Embodiments include the following numbered clauses:1. A substrate support for supporting a substrate, the substrate support comprising: a main body having a surface; a plurality of projections protruding from the surface of the main body, distal ends of the plurality of projections defining a support surface for a substrate; and a seal member of a size and / or shape to accommodate the plurality of projections, the seal member being flexible and having a fixed end attached to the surface and a free end; and wherein when the substrate is supported on the substrate support and subject to a clamping force, the seal member is at least partly disposed between the substrate support and the substrate and a distance between the free end of the seal member and the bottom surface of the substrate is smaller than a distance between the surface of the main body and the bottom surface of the substrate.2. The substrate support according to clause 1, wherein the seal member defines a plurality of openings, wherein at least one of plurality of openings accommodates the corresponding one of the plurality of projections.3. The substrate support according to clause 1 or 2, wherein when the substrate is supported on the substrate support and subject to the clamping force, the free end of the seal member is closer to the bottom surface of the substrate than the free end of the seal member is to the surface of the main body.4. The substrate support according to any one of clauses 1 to 3, wherein when the substrate is supported on the substrate support and subject to the clamping force, the free end of the seal member contacts the bottom surface of the substrate.5. The substrate support according to clause 4, further comprising a low friction coating on the seal member in a region of the seal member configured to contact the bottom surface of the substrate.6. The substrate support according to any preceding clause, wherein the seal member has an annular shape having an inner radius and an outer radius, wherein the inner radius of the seal member is less than the radius of the substrate.7. The substrate support according to clause 6, wherein, when no clamping force is being applied, the seal member has a substantially straight cross-sectional shape extending between the inner radius and the outer radius.8. The substrate support according to clause 6, wherein, when no clamping force is being applied, the seal member has a substantially curved cross-sectional shape extending between the inner radius and the outer radius.9. The substrate support according to clause 8, wherein the seal member has a substantially curved cross-sectional shape such that, when the substrate is supported on the substrate support and subject to the clamping force, the bottom surface of the sealing member contacts the bottom surface of the substrate.10. The substrate support according to any one of clauses 4 to 9, wherein the outer radius of the seal member is greater than the radius of the substrate.11. The substrate support according to clause 10, wherein the free end is towards the inner radius of the seal member.12. The substrate support according to any one of clauses 4 to 9, wherein the outer radius of the seal member is equal to or less than the radius of the substrate.13. The substrate support according to clause 12, wherein the free end is towards outer radius of the seal member.14. The substrate support according to any preceding clause, wherein the fixed end of the seal member is attached to the surface via an adhesive allowing electrical conductivity between the surface and the sealing member.15. The substrate support according to any preceding clause, wherein a spacer is disposed between the surface of the main body and the fixed end of the sealing member, wherein the spacer is configured to elevate the free end of the sealing member compared to the fixed end of the sealing member.16. The substrate support according to clause 15, wherein the spacer has a wedge shape, having a greater height towards the free end of the sealing member.17. The substrate support according to any preceding clause, wherein the seal member comprises a plurality of segments.18. The substrate support according to clause 17, wherein the plurality of segments are separated by radially extending slits in the seal member.19. The substrate support according to clause 18 when dependent on clause 4, wherein the slits extend from the inner radius of the seal member partially or fully to the outer radius of the seal member.20. The substrate support according to any preceding clause, wherein the thickness of the seal member is less than a height of the projections.21. The substrate support according to clause 20, wherein, when the substrate is fully in contact with the support surface, the seal member is entirely at or below a height of the projections.22. The substrate support according to any preceding clause, wherein the seal member comprises metal.23. The substrate support according to clause 22, wherein the seal member is predominantly or entirely formed of metal.24. The substrate support according to clause 22 or 23, wherein the metal comprises stainless steel.25. The substrate support according to any preceding clause, wherein the main body defines a hole through the main body, wherein the hole extends through the surface of the main body.26. The substrate support according to clause 25, wherein one of the openings of the seal member is configured to surround the hole on the surface of the main body.27. The substrate support according to clause 25, further comprising an additional flexible seal member disposed in a region surrounding the hole on the surface of the main body, wherein the additional flexible seal member comprises an opening configured to surround the hole, the additional flexible seal member having a fixed end attached to the surface and a free end towards the orifice.28. A substrate support for supporting a substrate, the substrate support comprising: a main body having a surface configured to face a substrate, the main body defining a groove recessed in the surface; and a retractable seal member comprising two flexible members, the two flexible members each having a distal end and a proximal end, wherein at the distal ends the two flexible members are attached together and at the proximal ends the two flexible members are attached to the main body, wherein one of the flexible members is attached to the main body at one side of the groove and the other flexible member is attached to the main body at an opposite side of the groove; wherein the retractable seal member is configured to change between an extended condition and a retracted condition, wherein the retractable seal member is configured such that, in the extended condition, the two flexible members extend out of the groove and form a straight wall extending towards the substrate, and a distal end of the retractable seal member contacts the substrate; in the retracted condition, the two flexible members are at least predominantly retracted into the groove.29. The substrate support of clause 28, wherein the groove is a circular groove having an outer diameter less than an outer diameter of the substrate.30. The substrate support of clause 29, wherein one of the flexible members is attached at a radially outward side of the groove and the other flexible member is attached at radially inward side of the groove.31. The substrate support of any of the any of clauses 28 to 30, wherein the retractable seal member is configured to move from the extended condition towards the retracted condition when a clamping force is applied which attracts the substrate towards the surface of the main body.32. The substrate support of any of the any of clauses 28 to 31, wherein the retractable seal member is configured to be pneumatically actuated to move between the retracted condition and the extended condition.33. The substrate support of clause 32, wherein the main body comprises a flow supply conduit in direct fluid communication with the groove, wherein the retractable seal member is configured to be actuated by fluid flow supply through the flow supply conduit.34. The substrate support of any of clauses 28 to 33, wherein the distal end of the retractable seal member comprises a lip and a contact layer is disposed on the lip for contact with the substrate.35. The substrate support of any of clauses 28 to 34, wherein the flexible members comprise or are formed of a polymer material.36. The substrate support of any of clauses 28 to 35, wherein a reinforcement structure is provided at the distal end of the retractable seal member.37. The substrate support of clause 36, wherein the reinforcement structure is on an opposite side of the retractable seal member than the side configured to contact the substrate.38. The substrate support of any of clauses 28 to 37, wherein the flexible members each comprise a proximal end attached to the main body, and a distal end towards a distal end of the retractable seal member, wherein the proximal ends of the two flexible members are attached at opposing sides of the groove, wherein the flexible members are configured such that in the extended condition, the flexible members are each curved at a first position on the flexible member; and in the retracted condition, the flexible members are each curved at a second position on the flexible member, wherein the second position is closer to a distal end of the flexible member than the first position.39. The substrate support of clause 38, wherein the first position is at a proximal end of the flexible member.40. The substrate support of any of clause 38 or 39, wherein the curved portion of each flexible member forms a semi-circular shape.41. The substrate support of any of clauses 28 to 40, further comprising at least two flanges, wherein each flange is configured to secure a corresponding flexible member to the main body.42. The substrate support of clause 41, when dependent on clause 29, wherein the at least two flanges includes an inner flange disposed at a radially inward side of the groove and an outer flange disposed at a radially outward side of the groove.43. The substrate support of any of clauses 28 to 42, wherein a vertical distance between a position of the distal end of the retractable seal member in the retracted condition and a position of the distal end of the retractable seal member in the extended condition is between 1 mm and 3mm.44. The substrate support of any of clauses 28 to 43, wherein a depth of the groove is equivalent to at least half of the vertical distance between a position of the distal end of the retractable seal member in the retracted condition and a position of the distal end of the retractable seal member.45. The substrate support of any of clauses 28 to 44, wherein a thickness of each flexible member is between 0.2 and 0.6 mm.46. The substrate support of any of clauses 28 to 45, wherein a width of the groove, between the opposing sides, is between 1.5 and 3 mm.47. The substrate support of any of clauses 28 to 46, wherein the substrate support defines a plurality of grooves, and at least one additional retractable seal such that each groove is associated with a corresponding retractable seal.48. The substrate support of clause 47, wherein the plurality of grooves are concentrically arranged circular grooves.49. A system comprising the substrate support according to any preceding clause.50. The system of clause 49, wherein the system is a metrology system or a lithographic system.

[0096] 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

CLAIMS1. A substrate support for supporting a substrate, the substrate support comprising: a main body having a surface; a plurality of projections protruding from the surface of the main body, distal ends of the plurality of projections defining a support surface for a substrate; and a seal member of a size and / or shape to accommodate the plurality of projections, the seal member being flexible and having a fixed end attached to the surface and a free end; and wherein when the substrate is supported on the substrate support and subject to a clamping force, the seal member is at least partly disposed between the substrate support and the substrate and a distance between the free end of the seal member and the bottom surface of the substrate is smaller than a distance between the surface of the main body and the bottom surface of the substrate.

2. The substrate support according to claim 1, wherein the seal member defines a plurality of openings, wherein at least one of plurality of openings accommodates the corresponding one of the plurality of projections.

3. The substrate support according to claim 1 or 2, wherein when the substrate is supported on the substrate support and subject to the clamping force, the free end of the seal member is closer to the bottom surface of the substrate than the free end of the seal member is to the surface of the main body, and / or wherein when the substrate is supported on the substrate support and subject to the clamping force, the free end of the seal member contacts the bottom surface of the substrate, desirably further comprising a low friction coating on the seal member in a region of the seal member configured to contact the bottom surface of the substrate.

4. The substrate support according to any preceding claim, wherein the seal member has an annular shape having an inner radius and an outer radius, wherein the inner radius of the seal member is less than the radius of the substrate.

5. The substrate support according to claim 4, wherein, when no clamping force is being applied, the seal member has a substantially straight cross-sectional shape extending between the inner radius and the outer radius, or wherein, when no clamping force is being applied, the seal member has a substantially curved cross-sectional shape extending between the inner radius and the outer radius, desirably wherein the seal member has a substantially curved cross-sectional shape such that, when the substrate is supported on the substrate support and subject to the clamping force, the bottom surface of the sealing member contacts the bottom surface of the substrate.

6. The substrate support according to any of claims 3-5, wherein the outer radius of the seal member is greater than the radius of the substrate, desirably wherein the free end is towards the inner radius of the seal member, or wherein the outer radius of the seal member is equal to or less than the radius of the substrate, desirably wherein the free end is towards outer radius of the seal member.

7. The substrate support according to any preceding claim, wherein the fixed end of the seal member is attached to the surface via an adhesive allowing electrical conductivity between the surface and the sealing member, desirably wherein a spacer is disposed between the surface of the main body and the fixed end of the sealing member, wherein the spacer is configured to elevate the free end of the sealing member compared to the fixed end of the sealing member, desirably wherein the spacer has a wedge shape, having a greater height towards the free end of the sealing member.

8. The substrate support according to any preceding claim, wherein the seal member comprises a plurality of segments.

9. The substrate support according to claim 8, wherein the plurality of segments are separated by radially extending slits in the seal member, desirably when dependent on claim 3, wherein the slits extend from the inner radius of the seal member partially or fully to the outer radius of the seal member.

10. The substrate support according to any preceding claim, wherein the thickness of the seal member is less than a height of the projections, desirably wherein, when the substrate is fully in contact with the support surface, the seal member is entirely at or below a height of the projections.

11. The substrate support according to any preceding claim, wherein the seal member comprises metal, desirably wherein the seal member is predominantly or entirely formed of metal, and / or wherein the metal comprises stainless steel.

12. The substrate support according to any preceding claim, wherein the main body defines a hole through the main body, wherein the hole extends through the surface of the main body.

13. The substrate support according to claim 12, wherein one of the openings of the seal member is configured to surround the hole on the surface of the main body, or further comprising an additional flexible seal member disposed in a region surrounding the hole on the surface of the main body, wherein the additional flexible seal member comprises an opening configured to surround the hole, the additional flexible seal member having a fixed end attached to the surface and a free end towards the orifice.

14. A system comprising the substrate support according to any preceding claim.

15. The system of claim 14, wherein the system is a metrology system or a lithographic system.

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