Method for manufacturing a substrate support for a lithographic apparatus, substrate table, lithographic apparatus, device manufacturing method and method of use - Patents.com

Abstract

The present disclosure relates to a method of manufacturing a substrate table and a substrate support for a substrate table. In one arrangement, a plurality of holes are formed through a base member. A burl-forming member is bonded to the base member. A plurality of burl structures are formed in the burl-forming member. Each burl structure has a distal surface that contacts a supported substrate in use. Each burl structure has an opening for at least one hole formed through the base member.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 19214460.8, filed December 9, 2019, and European Application No. 20183998.2, filed July 3, 2020, both of which are incorporated by reference in their entirety into this specification.

[0002] The present invention relates to a method of manufacturing a substrate support for a lithographic apparatus, a substrate table having a substrate support, a lithographic apparatus having a substrate table, a device manufacturing method using a lithographic apparatus, and a method of using a substrate table. [Background technology]

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

[0004]

[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 for decades, following a trend colloquially known as "Moore's Law". To keep up with Moore's Law, the semiconductor industry is pursuing technologies that allow it to create smaller and smaller features. To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm.

[0005]

[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]

[0006] In a lithographic apparatus, a substrate to be exposed (sometimes called a product substrate) may be held on a substrate table (sometimes also called a wafer table or substrate holder). The substrate table may be moveable with respect to the projection system. A substrate-facing surface of the substrate table may be provided with a number of protrusions (called burls). The distal surfaces of the burls may conform to a flat surface and may support the substrate. The burls may provide several advantages: they do not cause deformation of the substrate, since contaminant particles on the substrate table or on the substrate are more likely to fall between the burls; it is easier to machine the burls so that their ends conform to a surface than to make the surface of the substrate table flat; and the characteristics of the burls may be adjustable, for example to control the clamping of the substrate to the substrate table.

[0007]

[0007] The product substrate may distort due to frictional forces between the burls and the substrate. These interactions can be reduced by driving a fluid through the burls to provide a lubricating effect. Driving fluid uniformly and reliably through a large number of burls has proven difficult. Summary of the Invention

[0008] It is an object of the present invention to improve the manufacture and / or performance of a substrate support.

[0009]

[0009] In accordance with one aspect of the present invention, there is provided a substrate table comprising a substrate support configured to support a substrate during a lithographic process, the substrate support comprising a plurality of holes extending through a base member of the substrate support and a plurality of burl structures, each burl structure comprising a distal surface configured to contact a substrate supported by the substrate support during use, each burl structure comprising an opening for at least two of the holes in the base member, and the substrate table configured to provide an outward flow of fluid through all of the openings in each of one or more of the burl structures.

[0010]

[0010] According to a further aspect, there is provided a method of manufacturing a substrate support for a lithographic apparatus, the method comprising forming a plurality of holes through a base member, joining a burl forming member to the base member after the holes have been formed in the base member, and after the burl forming member has been joined to the base member, forming a plurality of burl structures in the burl forming member thereby to form the substrate support, the burl structures being formed such that each burl structure has a distal surface configured to contact a substrate supported by the substrate support in use, and such that each burl structure has an opening to at least one of the holes formed through the base member.

[0011]

[0011] According to a further aspect, there is provided a method of manufacturing a substrate support for a lithographic apparatus, the method comprising forming a plurality of holes through a base member, joining a burl forming member to the base member after the holes have been formed in the base member, and forming a plurality of burl structures in the burl forming member, each burl structure being formed such that each burl structure has a distal surface configured to contact a substrate supported by the substrate support during use, and each burl structure having an opening to at least one of the holes formed through the base member.

[0012]

[0012] According to a further aspect, there is provided a method of manufacturing a substrate support for a lithographic apparatus, the method comprising forming a plurality of holes through a base member and, after at least a portion of each of the plurality of holes have been formed in the base member, forming a plurality of burl structures in the base member, the burl structures being formed such that each burl structure has a distal surface configured to contact a supported substrate during use and such that each burl structure has an opening to at least one of the holes formed through the base member.

[0013] Further embodiments, features and advantages of the present invention are described in detail below with reference to the accompanying drawings. [Brief description of the drawings]

[0014]

[0014] Embodiments of the present 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, in which:

[0015] [Figure 1] 1 depicts a schematic overview of a lithographic apparatus; [Diagram 2] 2A and 2B depict schematic diagrams of a substrate table having a substrate support with a burl structure; [Diagram 3] FIG. 2 is a cross-sectional perspective view illustrating a schematic burl structure of the substrate support. [Figure 4] 1 is a schematic cross-sectional side view showing a portion of a substrate support comprising a burl structure with sub-burls; [Diagram 5] FIG. 5 is a schematic top view showing the burl structure of FIG. 4. [Figure 6] 1 is a schematic cross-sectional side view showing a portion of a substrate support comprising a burl structure with sub-burls having holes passing therethrough. [Figure 7] FIG. 7 is a schematic top view showing the burl structure of FIG. [Figure 8] 2 is a schematic cross-sectional side view showing a portion of a substrate support having a porous layer upstream of a burl structure; [Figure 9] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 10] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 11] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 12] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 13] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 14] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 15] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 16] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, including bonding a base member to a burl-forming member; [Figure 17] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, in which hole and burr structures are formed in the same base member; [Figure 18] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, in which hole and burr structures are formed in the same base member; [Figure 19] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, in which hole and burr structures are formed in the same base member; [Figure 20]1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, in which hole and burr structures are formed in the same base member; [Figure 21] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, in which hole and burr structures are formed in the same base member; [Figure 22] 1A-1D show schematic diagrams of steps in a method of manufacturing a substrate support, in which hole and burr structures are formed in the same base member; [Diagram 23] 11 is a schematic cross-sectional side view of a portion of a further exemplary substrate support comprising a burl structure; [Figure 24] FIG. 13 is a schematic cross-sectional side view illustrating how a substrate support can be mounted within a recess formed in a part of a substrate table, with an inset showing an enlarged portion of the layered structure of the substrate support; [Diagram 25] 5A-5D show schematic steps in a method of manufacturing a base member of a substrate support; [Figure 26] 5A-5D show schematic steps in a method of manufacturing a base member of a substrate support; [Figure 27] 5A-5D show schematic steps in a method of manufacturing a base member of a substrate support; [Figure 28] 1A-1D show schematic steps in a method of manufacturing a burl-forming member of a substrate support; [Figure 29] 1A-1D show schematic steps in a method of manufacturing a burl-forming member of a substrate support; [Diagram 30] 1A-1D show schematic steps in a method of manufacturing a burl-forming member of a substrate support; [Diagram 31] 1A-1D show schematic steps in a method of manufacturing a burl-forming member of a substrate support;

[0016]

[0015] Features shown in the figures are not necessarily to scale, and the sizes and / or arrangements shown are not limiting. It will be understood that the drawings include optional features that may not be essential to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017]

[0016] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 436 nm, 405 nm, 365 nm, 248 nm, 193 nm, 157 nm, 126 nm, or 13.5 nm).

[0018]

[0017] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted to refer to a general purpose patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Besides the classical mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0019]

[0018] Figure 1 illustrates diagrammatically a lithographic apparatus LA. The lithographic apparatus comprises an illumination system (also called illuminator) IL configured to condition a radiation beam B (e.g. EUV radiation or DUV radiation), a mask support (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and coupled to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate table WT configured to hold a substrate (e.g. resist coated wafer) W and coupled to a second positioner PW constructed to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0020]

[0019] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the 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 the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution across its cross-section in the plane of the patterning device MA.

[0021]

[0020] The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems including refractive optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and / or other factors such as the use of an immersion liquid or the use of a vacuum. When the term "projection lens" is used herein, this may be considered as synonymous with the more general term "projection system" PS.

[0022] The lithographic apparatus may be of a type in which at least a part of the substrate W may be covered with 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. This is also called immersion lithography. More information about immersion techniques is given in US Patent No. 6,952,253, which is incorporated herein by reference.

[0023] The lithographic apparatus may be of a type having two or more substrate tables WT (also known as "dual stage"). In such a "multi-stage" machine, the substrate tables WT may be used in parallel and / or a substrate W on one substrate table WT may be used for exposing a pattern thereon while a substrate W arranged on the other substrate table WT is being used to perform preparatory steps for a subsequent exposure of the substrate W.

[0024] In addition to the substrate table WT, the lithographic apparatus may include a measurement stage (not shown in FIG. 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 a part of the lithographic apparatus, for example a part of the projection system PS or a part of a system for providing immersion liquid. When the substrate table WT is remote from the projection system PS, the measurement stage may be moved below the projection system PS.

[0025] 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 a pattern (design layout) present on the 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. Using the second positioner PW and the position measurement system PMS, the substrate table WT can be accurately moved, for example to position the various target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the patterning device MA can be accurately positioned with respect to the path of the radiation beam B using the first positioner PM and possibly further position sensors (not explicitly shown in FIG. 1 ). The patterning device MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, it is also possible that they may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-line alignment marks.

[0026]

[0025] In this specification, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely, the x-axis, the y-axis, and the z-axis. Each of the three axes is orthogonal to the other two axes. Rotation about the x-axis is referred to as Rx rotation. Rotation about the y-axis is referred to as Ry rotation. Rotation about the z-axis is referred to as Rz rotation. The x-axis and the y-axis define a horizontal plane, and the z-axis defines a vertical direction. The Cartesian coordinate system does not limit the invention and is used merely for clarity. Alternatively, 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.

[0027]

[0026] In a lithographic apparatus, it is necessary to position with great precision the upper surface of the 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 table. The surface of the substrate table supporting the substrate can be provided with a number of burls whose distal ends can be flush in the nominal support surface. The burls are numerous but small in their cross-sectional area parallel to the support surface, so that the total cross-sectional area of ​​their distal ends is a few percent of the surface area of ​​the substrate, for example less than 5%. The gas pressure in the space between the substrate table and the substrate can be reduced compared to the pressure above the substrate to generate a force that clamps the substrate to the substrate table. Alternatively or additionally, an electrostatic clamping force can be used to clamp the substrate to the substrate table.

[0028]

[0027] When the substrate is loaded onto the substrate table, it generally does not land perfectly flat on the substrate table. This means that during the loading of the substrate, after one point of the substrate touches at least one of the burls, the remaining part of the substrate tends to touch the substrate table. The frictional forces between the substrate and the substrate table during loading can cause in-plane deformations in the substrate as the substrate touches the substrate table over its entirety. A similar effect can occur during unloading. The in-plane deformations can increase the overlay error.

[0029]

[0028] It is possible to reduce the frictional forces between the burls and the substrate by driving a fluid (e.g., gas and / or liquid) through the burls to provide a lubricating effect. Providing such a lubricating fluid flow uniformly is difficult, as undesirable variations in flow resistance between different burls will result in corresponding variations in the flow rate through the burls. A lower flow resistance will result in a higher flow rate, and vice versa.

[0030]

[0029] One approach to reducing the above problems is to provide a flow restriction within each burl to increase the flow resistance within each burl in a controlled manner. Increasing the flow resistance of the burl ensures sufficient flow from each burl without excessive flow through any one burl or excessive overall flow.

[0031]

[0030] The embodiments described below provide an efficient and / or reliable method of manufacturing a substrate support having burls with such flow restrictions (hereinafter referred to as burle structures).

[0032]

[0031] Figure 2 shows a substrate support 2 attached to an upper surface of a substrate table WT. The support table WT provides relative motion between the substrate W and a projection system PS of the lithographic apparatus LA during exposure of the substrate W in a lithographic process performed by the lithographic apparatus LA. The lithographic apparatus LA may be used in a method for manufacturing a device, such as a semiconductor device. The substrate table WT and / or the lithographic apparatus LA may be constructed and / or arranged to operate in any of the ways described above with reference to Figure 1.

[0033]

[0032] The substrate support 2 comprises a plurality of burl structures 6. Figure 3 shows an example burl structure 6 in more detail. Each burl structure 6 comprises a distal surface 11. In use, the distal surface 11 contacts a substrate W supported by the substrate support 2. In the case of a planar substrate, the distal surfaces 11 of the burl structures 6 may be coplanar.

[0034] In the illustrated embodiment, the burl recess 14 extends from the distal surface 11 in each burl structure 6 to the concave surface 13. In the example of FIG. 3, the burl recess 14 is substantially cylindrical. The axis of cylindrical symmetry of the burl recess 14 is perpendicular to the substrate W supported by the burl structure 6 in use. The burl recess 14 defines a channel through which a fluid (e.g., liquid and / or gas) can flow in use to provide the lubrication effect described above. In some embodiments, as illustrated in FIG. 3, each of the one or more burl structures 6 comprises a wall that surrounds the burl recess 14 in a direction parallel to the plane of the substrate W supported in use. The distal portion of the wall forms all or part of the distal surface 11 that contacts the substrate W supported in use. The wall has a radially outer surface 8 facing away from the burl recess 14. In the illustrated embodiment, the radially outer surface 8 is tapered. Tapering the radially outer surface 8 may strengthen the wall compared to an alternative configuration in which the radially outer surface 8 is not tapered. The wall has a radially inner surface 10 facing inwardly of the burl recesses 14. The surface 9 between the burl structures 6 may be substantially flat and, in use, faces towards the substrate W supported by the substrate support 2. When the radially outer surface 8 is tapered, it may meet the surface 9 at an oblique angle (rather than 90 degrees).

[0035]

[0034] The substrate table WT is configured to provide an outward flow of fluid (e.g. liquid and / or gas) via the burl structure 6. The outward flow of fluid exits the burl recesses 14 and passes towards the substrate W supported by the substrate table WT (upwards in the orientation of Figures 2 and 3). The outward flow of fluid may be provided, for example, during loading and / or unloading of the substrate W onto the substrate table WT and / or at least briefly while the substrate W is fully loaded onto the substrate table WT, to reduce frictional forces between the burl structure 6 and the substrate W. The outward flow of fluid may be provided using a fluid source 4 (e.g. a gas or liquid source) together with any combination of devices for controllably directing the fluid flow, including, for example, any combination of ducting, valves, pumps, filters, sensors and / or other suitable components.

[0036]

[0035] The substrate support 2 comprises a base member 20. The base member 20 may comprise, for example, a portion of a silicon wafer. The base member 20 comprises a plurality of holes 12 extending through the base member 20. In the example of FIG. 3, the holes 12 extend vertically through the base member 20. Each hole 12 is substantially cylindrical with a longitudinal axis of cylindrical symmetry in the illustrated example. In some embodiments, the holes 12 may have other orientations and / or shapes, such as shapes with non-circular cross-sections or with cross-sections that vary in size with depth. One or more of the holes 12 may be tapered, for example. The opening of each hole 12 at the top surface of the base member 20 faces upward. The opening of each hole 12 at the bottom surface of the base member 20 faces downward. Each hole 12 may be referred to as a channel. In one embodiment, each hole 12 is elongated (e.g., the length of each hole 12 is greater than the diameter of the hole 12). In one embodiment, each hole 12 has a diameter in the range of 0.001 to 0.2 mm, optionally in the range of 0.001 to about 0.05 mm. In one embodiment, each hole 12 has a length in the range of 0.005 to 1 mm, optionally in the range of 0.005 to about 0.2 mm.

[0037]

[0036] Each burl structure 6 comprises an opening for at least one of the holes 12. In embodiments where the burl structure 6 does not have a concave surface 13, the opening may be provided in the distal surface 11 in contact with the substrate W. In embodiments such as those shown in Figures 3 to 22 where the burl structure 6 comprises a concave surface 13, each concave surface 13 may comprise an opening for at least one of the holes 12. Each concave surface 13 partially blocks the flow of fluid compared to the absence of the concave surface 13. Thus, the combination of the concave surface 13 and the holes 12 in each burl structure 6 acts as a flow restrictor. The amount of flow restriction depends on the cross-sectional area and the number of the holes 12.

[0038] In some embodiments, burl structures 6 are provided, each comprising an opening for at least two of the holes 12 in the base member 20. Where the burl structures 6 comprise concave surfaces 13, each concave surface 13 may comprise an opening for at least two of the holes 12 in the base member 20. Providing multiple holes 12 in each of the burl structures 6 and / or concave surfaces 13 improves the robustness of the flow restriction function. Contamination is less likely to interfere with multiple holes than a single hole. In an embodiment, the substrate table WT is configured to provide an outward flow of fluid through all openings in each of the one or more burl structures 6 and / or concave surfaces 13.

[0039]

[0038] In some embodiments, as illustrated in Fig. 3, the base member 20 further comprises a plurality of base recesses 15 therein. Fig. 3 shows one such base recess 15 on the underside of the base member 20. Each base recess 15 is aligned with a different respective one of the burl structures 6 on the opposite side of the base member 20 (e.g., each base recess 15 will be aligned with a different burl structure 6). The alignment is such that an outward flow of fluid is provided by driving a flow of fluid (e.g., from a fluid source 4) through the base recess 15 and the burl recess 14 of each burl structure 6 via the holes 12 in the base member 20. When the substrate support 2 is attached to the substrate table WT (e.g., as shown in Fig. 2), the base recess 15 can form a channel leading from the burl structure 6 to further ducting in the substrate table WT.

[0040]

[0039] In some embodiments, for each of one or more burl structures 6, the cross-sectional area of ​​each hole 12 opening into the concave surface 13 in the burl recess 14, when viewed perpendicularly from the plane of the base member 20, is smaller than the cross-sectional area of ​​the respective base recess 15 aligned with the burl structure 6 and smaller than the cross-sectional area of ​​the burl recess 14. The holes 12 thus act to restrict flow through each burl structure 6 compared to the notional case where each burl structure 6 comprises a base recess 15 directly connected to a burl recess 14 with no restrictive structure provided therebetween (i.e. the concave surface 13 does not comprise a hole 12).

[0041] 4 to 7 show an embodiment in which one or more burl structures 6 each comprise one or more sub-burls 32 in the burl recess 14 of the burl structure 6. Each sub-burl 32 has a distal tip 11B. The distal tip 11B forms part of the distal surface of the burl structure 6 that, in use, contacts the substrate W supported by the substrate support 2. The part of the distal surface provided by the distal tip 11B is less than all of the distal surface of the burl structure 6. In this type of embodiment, one or more burl structures 6 each may comprise a wall that, in use, surrounds the burl recess 14 in a direction parallel to the plane of the supported substrate W (e.g., in all horizontal directions in the orientation shown in the figures). The distal portion 11A of the wall forms part of the distal surface that, in use, contacts the supported substrate W. The distal tip 11B of each of the sub-burls 32 is, in use, spaced from the distal portion 11A of the wall in all directions parallel to the plane of the supported substrate W. In the example shown, a single sub-burl 32 is provided in the centre of the burl recess 14 when viewed from above. In other embodiments, the sub-burl 32 may be provided in other locations. In other embodiments, a plurality of sub-burls 32 may be provided in each of one or more burl structures 6, each having a distal tip 11B, and spaced from the distal portion 11A of the respective wall in all directions parallel to the plane of the supported substrate W.

[0042]

[0041] The provision of sub-burls 32 as described above can improve the mechanical robustness of the burl structure 6. Improving the robustness of the burl structure 6 improves the freedom to adjust other properties of the burl structure 6, such as the width of the distal portion 11A of the wall, without compromising the overall robustness. The provision of sub-burls 32 also provides an opportunity to have different topographies or roughness in different parts of the individual burls (e.g. between the distal portion 11A of the wall and the distal tip 11B of the sub-burls 32 within the wall). This approach also provides an opportunity to provide different top coatings in different parts of the individual burl structure 6. For example, to improve the robustness of the burl structure 6 during landing or wrist-off of the substrate W, where mechanical sliding contact may be present, the distal tip 11B may be configured to have a surface that has a relatively low surface energy (e.g., lower than the surface energy of the distal portion 11A of the wall), is relatively rough (e.g., rougher than the distal portion 11A of the wall), and / or provides relatively low friction (e.g., lower friction than the distal portion 11A of the wall).

[0043] In an embodiment of the type shown in Figures 4 and 5, all holes 12 passing through the portion of the base member 20 corresponding to each burl structure 6 have an opening in the concave surface 13 of the burl structure 6. The holes 12 do not pass through any of the sub-burls 32. In another embodiment, as illustrated in Figures 6 and 7, at least one hole 12 formed through the base member 20 passes through at least one sub-burl 32. In the example shown, a single sub-burl 32 is provided in the illustrated burl structure 6, with one of the holes 12 passing through the sub-burl 32 of the burl structure 6 along the axis of cylindrical symmetry of the sub-burl 32. By arranging the holes 12 to pass through the sub-burl 32, frictional forces between the sub-burl 32 and the supported substrate W can be reduced. The holes 12 passing through the sub-burl 32 can also be periodically cleaned and / or reconditioned (e.g., by driving a fluid through the sub-burl 32) the surface near the opening of the hole 12 in the sub-burl 32.

[0044]

[0043] In some embodiments, it may be desirable to provide a filtering function upstream of one or more of the burl structures 6. The filtering may be configured, for example, to prevent contaminant particles larger than a predefined size from reaching the burl structures 6 and / or any area downstream of the burl structures 6 (e.g., between the substrate support 2 and the substrate W). In some embodiments, a porous layer 36 is provided upstream of the openings in each of the at least one burl structure 6, for example upstream of the holes 12 passing through the concave surface 13 of the at least one burl structure 6. The porous layer 36 may be formed in the base member 20 or in a separation member 40 attached to the base member 20, as shown in FIG. 8. In some embodiments, the holes 12 and the burl structures 6 are formed in the base member 20. Alternatively, the substrate support 2 may further comprise a burl-forming member 30 bonded to the base member 20. The burl-forming member 30 may comprise, for example, a portion of a silicon wafer. In embodiments having a burl forming member 30, as described further below with reference to Figures 9-16, the burl structures 6 may be formed exclusively within the burl forming member 30. Forming the holes 12 and the burl structures 6 within different members provides manufacturing advantages, as described below with reference to Figures 9-16.

[0045]

[0044] In one embodiment, as illustrated in FIG. 8, the porous layer 36 comprises a plurality of holes formed in a solid member (separation member 40 in the illustrated example), such as a portion of a silicon wafer. In one embodiment, the size of each of the holes in the porous layer 36 and / or the average size of the holes in the porous layer 36 is smaller than each of the holes 12 formed in the base member 20. In one embodiment, the number of holes per unit area in the porous layer 36 is greater than the number of holes 12 per unit area in the concave surface 13 of each burl structure 6. The holes in the porous layer 36 may be formed using any known technique for forming holes of suitable size, including, for example, deep reactive ion etching or focused ion beam milling. Thus, the holes in the porous layer 36 may be substantially cylindrical, with an axis of cylindrical symmetry aligned with the axis of cylindrical symmetry of one or more holes 12 through the concave surface 13 of the burl structure 6.

[0046]

[0045] Figures 9 to 16 show steps in an exemplary method for manufacturing a substrate support 2 for a lithographic apparatus LA. The substrate support 2 may take any of the suitable forms described above with reference to Figures 2 to 8.

[0047] In one embodiment, an initial step in the method is to provide a base member 20. Optionally, a hard mask layer 16 is provided on the base member 20 to provide the arrangement of FIG.

[0048]

[0047] In one embodiment, in a subsequent step, the arrangement of Figure 9 is processed to form a pattern in the hard mask layer 16. A removal process, such as deep reactive ion etching or focused ion beam milling, is then applied to form holes 12 in the base member 20, thereby forming the arrangement of Figure 10. The holes 12 are formed in the pattern defined by the patterned hard mask layer 16. At this stage, the holes 12 may be blind (as shown) or may extend all the way through the base member 20.

[0049]

[0048] In one embodiment, in a subsequent step, the base member 20 is turned over and a plurality of base recesses 15 are formed in the base member 20, thereby forming the arrangement shown in FIG. 11. FIG. 11 shows one of the base recesses 15. The shape and depth of each base recess 15 is not particularly limited. In some embodiments, each base recess 15 is substantially cylindrical with an axis of cylindrical symmetry perpendicular to the plane of the base member 20. In the illustrated embodiment, each base recess 15 is deep enough to ensure that the hole 12 then penetrates the base member 20.

[0050]

[0049] In one embodiment, in a subsequent step, as shown in Figure 12, a coating 24 is applied. The coating 24 covers the inner surface of the base recess 15. The coating 24 also covers the inner surface of each of the holes 12. The coating 24 is applied from the side of the base member 20 opposite where the burl structures 6 should be located (the formation of the burl structures 6 is described below). The coating 24 may be configured to reduce the risk of contaminants clogging any of the holes 12 during use. In some embodiments, the coating 24 is hydrophobic and / or has antistatic properties. By providing the coating 24 before the burl structures 6 are present, possible contamination of the burl structures 6 by the material of the coating 24 is avoided.

[0051]

[0050] In one embodiment, in a subsequent step, the upper and lower surfaces of the arrangement of FIG. 12 are processed to remove the hard mask layer 16 and coating 24 in the area outside the base recess 15, as shown in FIG. 13.

[0052]

[0051] In one embodiment, in a subsequent step, the burl-forming member 30 is bonded to the base member 20, as shown in Figure 14. In this embodiment, the burl-forming member 30 is bonded to the base member 20 after the holes 12 are formed in the base member 20. Thus, the process of forming the holes 12 cannot contribute to contamination to the burl-forming layer 30. Any coating 24 provided on the base member 20 is also provided before the burl-forming member 30 is bonded to the base member 20, thereby also avoiding cross-contamination with the material of the coating 24.

[0053]

[0052] The burl-forming member 30 may be formed by thinning a silicon wafer to a desired thickness. In one embodiment, the burl-forming member 30 is bonded to the base member 20 via one or more additional layers (not shown), thereby providing a multi-layer structure having three or more layers. The one or more additional layers may provide additional desired functions. For example, the one or more additional layers may comprise an electrical insulation layer to electrically insulate an upper portion of the substrate support 2 from the remainder of the substrate support 2 and / or elements connected to the substrate support 2 from below. In some embodiments, the burl structure 6 may be electrically grounded via the burl-forming member 30. Alternatively or additionally, either or both of the burl-forming member 30 and the base member 20 may each be formed from multiple layers.

[0054]

[0053] In some embodiments, as shown in Figure 14, a burl coating 26 is provided on the burl forming member 30. The burl coating 26 is configured to be suitable for contacting the substrate W during use. The burl coating 26 may, for example, be configured to provide a lower frictional contact than would be the case without the burl coating 26. The burl coating 26 is provided on the burl forming member 30 prior to bonding the base member 20 to the burl forming member 30. The risk of clogging any holes 12 in the base member 20 with material from the burl coating 26 is thereby reduced or avoided.

[0055]

[0054] In some embodiments, multiple burl structures 6 are formed in the burl-forming member 30. Forming the burl structures 6 in separate burl-forming members 30 rather than in the base member 20 facilitates precise control of the height of the burl structures 6. The height of the burl structures 6 can be defined by the thickness of the burl-forming member 30, which can be controlled with high precision. Forming the holes 12 in the base member 20 without the presence of the burl-forming member 30 also prevents cross-contamination between the process used to form the holes 12 (e.g., deep reactive ion etching or focused ion beam milling) and the process used to form the burl structures 6.

[0056]

[0055] In one embodiment, the burl structures 6 are formed after the burl-forming members 30 are bonded to the base member 20. The combination of the burl structures 6 and the base member 20 provides the substrate support 2. An example of such a substrate support 2 is shown in FIG. 16. The burl structures 6 are formed in such a manner that each burl structure 6 has a distal surface 11 that, in use, contacts the substrate W supported by the substrate support 2. In the illustrated example, the distal surface 11 is a surface of the burl coating 26. In one embodiment, the distal surface 11 can be a surface of the burl-forming member 30 (where the burl coating 26 is not provided). Each burl structure 6 has an opening for at least one of the holes 12 formed through the base member 20. In some embodiments, as shown, each burl structure 6 has a burl recess 14. The burl recess 14 extends from the distal surface 11 to a concave surface 13 in the burl structure 6. In this type of embodiment, the concave surface 13 has an opening for at least one of the holes 12 formed through the base member 20.

[0057]

[0056] In one embodiment, the substrate support 2 of FIG. 16 is formed by starting from the arrangement of FIG. 14 and first removing material from the outside of the burl structure 6 to provide the arrangement of FIG. 15. The material may be removed using, for example, laser ablation or etching. In a subsequent step, material is removed from inside the burl structure 6 to form the concave surface 13, thereby providing the substrate support 2 of FIG. 16. The material may be removed using, for example, laser ablation or etching. In this type of embodiment, the burl structure 6 is thus formed by removing material from the outside of the burl structure 6 before removing material from the inside of the burl structure 6. This approach is advantageous because it is not necessary to protect the inside of the burl structure 6 when removing material from the outside of the burl structure 6 (which may be performed using, for example, laser ablation, which may generate a significant amount of debris). In other embodiments, material may be removed simultaneously from the inside and outside of the burl structure 6 to directly form the arrangement of FIG. 16 from the arrangement of FIG. 15 (i.e., without an intermediate step leading to the arrangement of FIG. 15). In yet another embodiment, the burl structure 6 is formed by removing material from the inside of the burl structure 6 before removing material from the outside of the burl structure 6 .

[0058] In some embodiments, removing material inside the burl structure 6 includes removing material down to at least the upper surface of the base member 20 below the burl-forming members 30. In this type of embodiment, the concave surfaces 13 each comprise a surface of the base member 20 (as shown in FIG. 16).

[0059] In the exemplary method described above with reference to Figures 9 to 16, the substrate support 2 is manufactured by bonding a base member 20 to a burl-forming member 30. The holes 12 are formed in the base member 20 and the burl structures 6 are formed in the burl-forming member 30. Figures 17 to 22 show an alternative approach, in which both the holes 12 and the burl structures 6 are formed in the base member 20.

[0060]

[0059] In an initial step, as shown in Figure 17, a base member 20 is provided. In the illustrated example, a burl coating 26 is provided on the base member 20. The burl coating 26 may be configured in any of the manners described above for the burl coating 26 in Figures 14-16.

[0061] In one embodiment, in a subsequent step, a removal process is used to form holes 12 through the base member 20 and burl coating 26 to provide the arrangement shown in Figure 18. The removal process may include, for example, deep reactive ion etching or focused ion beam milling. At this stage the holes 12 may be blind (as shown) or may extend all the way through the base member 20.

[0062]

[0061] In one embodiment, in a subsequent step, the arrangement of FIG. 18 is turned over and a removal process is applied to form a plurality of base recesses 15, thereby providing the arrangement of FIG. 19. Thus, in this embodiment, the base recesses 15 are formed before the burl structures 6 (formed as described below). Forming the base recesses 15 before the burl structures 6 is desirable because it avoids having to support structures on the delicate burl structures 6 during the formation of the base recesses 15. The manufacturing process is thus simplified and / or the risk of damage to the burl structures 6 is reduced or avoided. The shape and depth of each base recess 15 is not particularly limited. In some embodiments, each base recess 15 is substantially cylindrical with an axis of cylindrical symmetry perpendicular to the plane of the base member 20. In the illustrated embodiment, each base recess 15 is deep enough to ensure that the holes 12 then penetrate the base member 20.

[0063]

[0062] In one embodiment, in a subsequent step, a coating 24 is applied, as shown in Figure 20. The coating 24 covers the inner surface of the base recess 15. The coating 24 also covers the inner surface of each of the holes 12. In some embodiments, the coating 24 is hydrophobic and / or has antistatic properties.

[0064]

[0063] In one embodiment, as shown in Fig. 22, starting from the arrangement of Fig. 20, the substrate support 2 is formed by first removing material from the outside of the burl structure 6 to provide the arrangement of Fig. 21. In a subsequent step, material is removed from the inside of the burl structure 6 to form the concave surface 13, thereby providing the substrate support 2 of Fig. 22. In this type of embodiment, the burl structure 6 is thus formed by removing material from the outside of the burl structure 6 before removing material from the inside of the burl structure 6. The advantages associated with this approach are discussed above. In other embodiments, material may be removed simultaneously from the inside and outside of the burl structure 6 to directly form the arrangement of Fig. 22 from the arrangement of Fig. 20 (i.e. without the intermediate step leading to the arrangement of Fig. 21). In yet other embodiments, the burl structure 6 is formed by removing material from the inside of the burl structure 6 before removing material from the outside of the burl structure 6.

[0065] In embodiments of the type described above, at least a portion of each hole 12 through the base member 20 is formed (e.g., to form at least a blind hole as shown in FIG. 18), and optionally, all of each hole 12 is formed prior to the burl structure 6. Forming all or at least a portion of the holes 12 at an early stage may facilitate manufacturing by protecting existing structures or reducing the extent to which considerations must be made during a removal process (e.g., deep reactive ion etching or focused ion beam milling), e.g., by requiring special arrangements to hold the base member 20 during the removal process and / or to otherwise protect existing structures from mechanical damage and / or contamination.

[0066]

[0065] In other embodiments, the order described above with reference to Figures 17 to 22 may be varied. For example, in some embodiments, the formation of the plurality of base recesses 15 as shown in Figure 19 is performed after one or more steps described above with reference to Figures 20 to 22 (e.g., after removal of material from the exterior and interior of the burl structure 6). Alternatively or additionally, the order of the material removal process used to form the burl structure 6 as described above with reference to Figures 21 and 22 may be reversed. In such embodiments, material is thus removed from the interior of the burl structure 6 (with the base recesses 15 formed before or after) to form the concave surface 13 before material is removed from the exterior of the burl structure 6. Alternatively or additionally, in some embodiments, the hole 12 is formed through the base member 20 after one or more steps described above with reference to Figures 19 to 22 (e.g., after formation of the plurality of base recesses 15, after removal of material from the exterior of the burl structure 6, and / or after removal of material from the interior of the burl structure 6 to form the concave surface 13). For example, in one embodiment, the removal of material from the inside of the burl structure 6 to form the concave surface 13 is performed before the holes 12 are formed through the base member 20, and the removal of material from the outside of the burl structure 6 is performed after the holes 12 are formed through the base member 20. In a first variation of this example, the base recess 15 is formed after the holes 12 are formed through the base member 20 and before the removal of material from the outside of the burl structure 6. In a second variation of this example, the base recess 15 is formed after the removal of material from the outside of the burl structure 6.

[0067] 23 shows part of a further exemplary substrate support 2 mounted on a substrate table WT. In this example, the substrate support 2 comprises a base member 20 and a burl forming member 30 joined to the base member 20. The burl forming member 30 comprises a plurality of burl structures 6. The base member 20 comprises a plurality of holes 12 extending through it. The burl structures 6 and holes 12 may take any of the forms described in relation to the substrate support 2 above.

[0068]

[0067] Each burl structure 6 comprises an opening 41 to at least one hole 12 in the base member 20. In the illustrated example, an elongated intermediate passage 42 and an intermediate chamber 43 are provided in the flow path between the opening 41 and the hole 12 in the base member 20. The opening 41 is thus fluidly connected to the hole 12 by the intermediate passage 42 and the intermediate chamber 43. As will be described below, for example, if the elongated intermediate passage 42 is sufficiently tapered, the intermediate chamber 43 can be omitted. In the examples of Figures 3 to 22, the openings are directly connected to each of the holes 12 in the base member 20.

[0069]

[0068] The flow resistance to flow through the holes 12 in the base member 20 is greater than the flow resistance to flow through the intermediate passage 42 and the intermediate chamber 43. Thus, the portion of the base member 20 providing the holes 12 acts as a flow restrictor. The amount of flow restriction depends on the cross-sectional area and number of the holes 12. The relative dimensions of the elements shown in FIG. 23 can vary depending on the details of the implementation context. In one class of implementations, the diameter of the intermediate passage 42 can be approximately 10 to 100 times the diameter of each hole 12 in the base member 20. The overall height (labeled 45) of the combination of the base member 20 and the burl forming member 30 can be, for example, approximately 0.5 to 1.5 mm.

[0070] In some embodiments, the substrate support 2 may fit onto the underlying substrate table WT within a recess 50 (e.g. having a depth of about 0.5 mm to 1 mm) formed in the substrate table WT, as shown in Figure 24. The substrate support 2 may therefore easily be retrofitted onto an existing substrate table WT without changing the overall height of the substrate table WT.

[0071]

[0070] Figures 25 to 27 show stages in an exemplary process for manufacturing a base member 20 of the type described above with reference to Figures 23 and 24. The process is applicable both to the case where multiple holes 12 are provided per bour structure 6 and to the case where a single hole 12 is provided per bour structure 6. The process may use a silicon-on-insulator (SOI) substrate to achieve accurate layer thicknesses for providing the flow restriction holes 12, to accommodate wafer fab manufacturing processes, and / or to provide a good thermal expansion coefficient to match a substrate table WT formed from SiSiC.

[0072] In a first step, a SOI substrate (e.g., 300 mm in diameter) is provided, as shown in FIG. 25. Layer 20A is the handle Si substrate layer of the SOI substrate. Layer 20B is the buried SiO2 layer of the SOI substrate. Layer 20C is the device layer of the SOI substrate, which is made of Si.

[0073]

[0072] In a second step, as shown in Fig. 26, a base recess 15 is formed in the base member 20. The base recess 15 may take any of the forms described above with reference to Figs. 3 to 24. The base recess 15 may be formed by selective etching. Alternatively or additionally, the base recess 15 may be formed using laser processing. Laser processing is inherently less clean than selective etching and care may be needed to maintain the thickness of the layer in which the hole 12 is formed. The difference in threshold fluence between Si and SiO2 may not be sufficient to use SiO2 as an inherent process stop (e.g., by arranging for the laser process fluence to be higher than the threshold fluence for Si but lower than the threshold fluence for SiO2, so that the laser process automatically stops when it reaches SiO2). However, SiO2 may be used as a visual process stop (e.g., by arranging the process to stop when SiO2 becomes visible).

[0074]

[0073] In a third step, as shown in Figure 27, a hole 12 is formed. In the illustrated example, only a single hole 12 is formed, but this technique can also be used to form multiple holes 12. One or more holes 12 can be formed using deep reactive ion etching (DRIE) or laser micro-drilling. The most uniform and clean results can be obtained using DRIE, but this technique is relatively complex and expensive. Laser micro-drilling offers a less expensive alternative.

[0075] 28 to 31 show stages in an exemplary process for manufacturing a burl forming member 30. The process can use a SiC substrate to provide suitable mechanical robustness and to match the thermal expansion coefficient of the substrate table WT and base member 20 (e.g. formed from a SOI substrate) which are formed from SiSiC. The process shown in the figures relies on laser processing which is compatible with techniques used to manufacture other aspects of the substrate table WT.

[0076] In a first step, a piece of SiC (eg, 300 mm in diameter) is provided, as shown in FIG.

[0077]

[0076] In a second step, as shown in Figure 29, the material outside the burl structure 6 is removed using laser structuring.

[0078]

[0077] In a third step, as shown in Figure 30, laser drilling is used to form the elongated intermediate passage 42. The laser drilling is performed from the bottom side, which provides an advantageous tapering. The tapering makes it easier to achieve proper alignment between the intermediate passage 42 and corresponding structures in the base member 20, such as the holes 12. The tapering may mean, for example, that an intermediate chamber 43 is not required.

[0079] In a fourth step, the burl recesses 14 are formed using laser ablation, as shown in Fig. 31. A roughening process may also be applied to prevent optical adhesion between the substrate support 2 and the substrate W during use. Various techniques may be used to achieve roughening, including, for example, one or more of ion beam figuring (IBF), laser treatment, mechanical abrasive roughening, chemical abrasive roughening, applying a coating with inherent roughness, and starting only with a single-sided polished SiC substrate.

[0080]

[0079] Other processing techniques may be used to form the burl-forming member 30. These may include one or more of electrical discharge machining (EDM), milling, grinding, and etching. For example, etching may be used instead of laser drilling to form the intermediate passage 42 in the third step. The burl recess 14 may be formed by EDM or etching instead of laser ablation in the fourth step.

[0081] In one embodiment, the burl-forming member 30 is attached to the base member 20 after the base member 20 has been processed to provide holes 12 (e.g., as shown in FIG. 27). One or more processing steps may be performed on the burl-forming member 30 before or after the burl-forming member 30 is attached to the base member 20 to provide the arrangement shown in FIG. 31, such as to form a plurality of burl structures 6.

[0082]

[0081] Although particular reference is made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein has other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like. In light of these alternative applications, those skilled in the art will recognize that the use of the terms "wafer" or "die" herein may be considered synonymous with the more general terms "substrate" or "target portion", respectively. The substrates described herein may be processed, before or after exposure, for example in a track (a tool that typically applies a layer of resist to the substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, the substrate may be processed multiple times, for example to produce a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0083]

[0082] Although specific reference has been made above to the use of embodiments of the present invention in relation to optical lithography, it will be appreciated that the present invention may be used in other applications.

[0084]

[0083] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0085]

[0084] The above description is intended to be illustrative and not limiting. Thus, those skilled in the art will appreciate that modifications can be made to the present invention without departing from the scope of the claims set forth below.

Claims

1. a substrate table configured to support a substrate during a lithographic process, a substrate support, the substrate support comprising: a plurality of holes extending through a base member of the substrate support; and a plurality of burl structures; each burl structure comprising a distal surface configured to contact a substrate supported by said substrate support during use, each burl structure comprising an opening for at least two of the holes in said base member; the substrate table is configured to provide an outward flow of fluid through all the openings in each of one or more of the burl structures; Board table.

2. 2. A substrate table according to claim 1, wherein each burl structure comprises a burl recess extending from the distal surface to a concave surface within the burl structure, the concave surface comprising the openings for at least two of the holes in the base member.

3. each of the one or more burl structures comprises a wall surrounding the burl recess in a direction parallel to the plane of a supported substrate in use, a distal portion of the wall forming all or part of the distal surface that contacts the supported substrate in use; and / or the base member further comprises a plurality of base recesses in the base member, each base recess being aligned with a different respective one of the burl structures on an opposite side of the base member, the alignment being such that an outward flow of fluid drives a flow of fluid through the base recess and the burl recess of the respective burl structure via the holes in the base member; 3. A substrate table according to claim 2, wherein: one or more of the bur structures each comprise one or more sub-burls in the bur recess of the bur structure, each sub-burl having a distal tip forming a part of the distal surface of the bur structure that, in use, contacts the substrate supported by the substrate support, said part being less than all of the distal surface of the bur structure; and / or further comprising a porous layer upstream of the opening in each of at least one of the bur structures; and / or the bur structures are formed in a bur forming member joined to the base member.

4. for each of one or more of the burl structures, when viewed perpendicularly from the plane of the base member, a cross-sectional area of ​​each hole in the burl recess opening into the concave surface is less than a cross-sectional area of ​​the respective base recess aligned with the burl structure and less than a cross-sectional area of ​​the burl recess; each of the one or more bour structures comprises a wall surrounding the bour recess in a direction parallel to a plane of a supported substrate in use, a distal portion of the wall forming part of the distal surface which, in use, contacts the supported substrate; the distal tip of each of the sub-bars is, in use, spaced from the distal portion of the wall in all directions parallel to the face of the supported substrate. A substrate table according to claim 3.

5. A substrate table according to claim 4 , wherein at least one of the holes formed through the base member passes through at least one of the sub-vars.

6. 6. A lithographic apparatus comprising the substrate table of claim 1 , wherein the support table is configured to provide relative movement between the substrate and a projection system of the lithographic apparatus during exposure of the substrate in a lithographic process performed by the lithographic apparatus.

7. 1. A method of manufacturing a substrate support for a lithographic apparatus, comprising the steps of: forming a plurality of holes through a base member; joining a burl-forming member to the base member after the hole is formed in the base member; and forming a plurality of burl structures within said burl-forming member; Including, The burl structure is each burl structure having a distal surface configured to contact a substrate supported by the substrate support in use, and each burl structure having an opening for at least two of the holes formed through the base member; Formed, method.

8. forming the plurality of burl structures within the burl-forming member after the burl-forming member is bonded to the base member, thereby forming the substrate support; and / or each burl structure includes a burl recess extending from the distal surface to a concave surface within the burl structure, the concave surface including the openings for at least two of the holes formed through the base member; the concave surface comprises a surface of the base member; The method of claim 7.

9. 1. A method of manufacturing a substrate support for a lithographic apparatus, comprising the steps of: forming a plurality of holes through a base member; and After at least a portion of each of the plurality of holes is formed in the base member, forming a plurality of burl structures within the base member; Including, The burl structure is each burl structure having a distal surface configured to contact a substrate against which it is supported in use, and each burl structure having an opening to at least one of the holes formed through the base member; Formed, method.

10. 10. The method of claim 9, wherein each burl structure comprises a burl recess extending from the distal surface to a concave surface within the burl structure, the concave surface comprising the opening for at least one of the holes formed through the base member.

11. 11. The method of claim 10, wherein each of the one or more burl structures comprises a wall surrounding the burl recess in a direction parallel to a plane of a supported substrate, a distal portion of the wall forming all or part of the distal surface that, in use, contacts the supported substrate, and / or further comprising forming a plurality of base recesses in the base member, each base recess being positioned to align with a different respective one of the burl structures on an opposite side of the base member, the alignment being such that, in use, fluid flow is provided through the base recess and the burl recess of the respective burl structure via one or more holes formed through the base member.

12. 12. The method of claim 11, wherein for each of one or more of the burl structures, when viewed perpendicularly from the plane of the base member, a cross-sectional area of ​​each hole in the burl recess opening into the concave surface is smaller than a cross-sectional area of ​​the respective base recess aligned with the burl structure and smaller than a cross-sectional area of ​​the burl recess.

13. 13. The method of any of claims 10 to 12, wherein the burl structures are formed by removing material from an exterior of the burl structures before removing material from an interior of the burl structures to form the concave surface, and / or the concave surface of each of one or more of the burl structures comprises an opening for at least two of the holes formed through the base member, and / or each of the one or more burl structures comprises one or more sub-burls in the burl recess of the burl structure, each sub-burl having a distal tip forming a part of the distal surface of the burl structure that, in use, contacts the substrate supported by the substrate support, the part being less than all of the distal surface of the burl structure, and / or further comprising applying a coating to the inner surface of the hole formed through the base member, and / or comprising mounting the substrate support to a substrate table, the substrate table being configured to provide relative motion between the substrate and a projection system of a lithographic apparatus during exposure of the substrate in a lithographic process.

14. 14. A method according to claim 13 when dependent on claim 11, wherein the distal tip of each of the sub-bars is, in use, spaced from the distal portion of the wall in all directions parallel to the face of the supported substrate, and / or wherein at least one of the holes formed through the base member passes through at least one of the sub-bars.

15. The method of claim 14 , wherein the coating is applied from a side of the base member opposite where the burl structure is to be located.

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