OBJECT HOLDER, ELECTROSTATIC SHEET AND METHOD FOR MANUFACTURING ELECTROSTATIC SHEET - Patent application

Abstract

An object holder configured to support an object, the object holder comprising: a core body having a plurality of burls with distal ends in a support surface for supporting the object, an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers, and a circumferential barrier for reducing the outflow of gas escaping from a space between the object and the core body.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority from European Application No. 20179524.2, filed June 11, 2020, which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present invention relates to an object holder for use in a lithographic apparatus. More particularly, the object holder comprises an electrostatic clamp arranged to clamp the object holder to a table and / or to clamp an object to the object holder. The present invention further relates to an electrostatic sheet and a method for manufacturing an electrostatic sheet. [Background technology]

[0003] A lithographic apparatus is a machine configured 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, for example, project a pattern from a patterning device (e.g. a mask or reticle) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4-20 nm, e.g., 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, for example, 193 nm.

[0005] In a conventional lithographic apparatus, the substrate to be exposed may be supported by a substrate holder (i.e., the object that directly supports the substrate), which is supported by a substrate table (i.e., an object such as a mirror block or stage, i.e., a table that supports the substrate holder and provides a top surface surrounding the substrate holder). The substrate holder is often a flat, rigid disk whose size and shape corresponds to the substrate (although it may have a different size or shape). It has an array of protrusions, called burls or pimples, protruding from at least one side. The substrate holder may also have arrays of protrusions on two opposing sides. In this case, when the substrate holder is placed on the substrate table, the body of the substrate holder is held a small distance above the substrate table while the ends of the burls on one side of the substrate holder rest on the surface of the substrate table. Similarly, when the substrate rests on top of the burls on the opposite side of the substrate holder, the substrate is spaced apart from the body of the substrate holder. The purpose of this is to help prevent particles (i.e. contaminant particles such as dust particles) that may be present on either the substrate table or substrate holder from distorting the substrate holder or substrate. Because the total surface area of ​​the burls is only a small fraction of the total area of ​​the substrate or substrate holder, it is very likely that any particle will be between the burls and its presence will have no effect. Often the substrate holder and substrate are accommodated in a recess in the substrate table so that the top surface of the substrate is substantially flush with the top surface of the substrate table.

[0006] Due to the high accelerations experienced by a substrate during use in a high-throughput lithography apparatus, simply allowing the substrate to rest on the burrs of the substrate holder is not sufficient. It must be clamped in place. Two methods for clamping a substrate in place are known: vacuum clamping and electrostatic clamping. In vacuum clamping, the space between the substrate holder and the substrate, and optionally between the substrate table and the substrate holder, is partially evacuated, and the substrate is held in place by a high-pressure gas or liquid above it. However, vacuum clamping cannot be used when the beam path and / or the environment near the substrate or substrate holder is kept at low or very low pressure, for example, in extreme ultraviolet (EUV) radiation lithography. In this case, it may not be possible to generate a pressure difference across the substrate large enough to clamp the substrate (or substrate holder). Therefore, electrostatic clamping can be used. In electrostatic clamping, a potential difference is established between an electrode plated on or on the substrate's underside and an electrode on or in the substrate table and / or substrate holder. The two electrodes act as a large capacitor, capable of generating a substantial clamping force with a reasonable potential difference. The electrostatic arrangement can be such that a single pair of electrodes, one on the substrate table and one on the substrate, clamps the entire stack of substrate table, substrate holder and substrates together. In known arrangements, one or more electrodes may be provided on or in the substrate holder so that the substrate holder is clamped to the substrate table and the substrate is separately clamped to the substrate holder. Summary of the Invention [Problem to be solved by the invention]

[0007] There is a need for improved substrate holders that include one or more electrostatic clamps for clamping the substrate holder to a substrate table and / or a substrate to the substrate holder, and more generally for improved object holders, such as patterning device holders, that include one or more electrostatic clamps for holding the object holder to a table and / or holding an object relative to the object holder. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided an object holder configured to support an object, the object holder comprising: a core body having a plurality of burls with distal ends in a support surface for supporting an object; an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers; and a circumferential barrier for reducing the outflow of gas escaping from a space between the electrostatic sheet and the core body.

[0009] According to a second aspect of the present invention, there is provided an electrostatic sheet for an object holder configured to support an object, the electrostatic sheet comprising: holes for accommodating burrs of a core for supporting the object; dielectric layers; and electrodes sandwiched between the dielectric layers; the electrostatic sheet further comprising a circumferential barrier for reducing the outflow of gas escaping from a space between the electrostatic sheet and the core.

[0010] According to a third aspect of the present invention, there is provided a method of manufacturing an electrostatic sheet for an object holder configured to support an object, the method comprising: applying electrodes to a dielectric layer; bonding the dielectric layer to another dielectric layer such that the electrodes are sandwiched between the dielectric layers; and the electrostatic sheet comprising a circumferential barrier for reducing the outflow of gas escaping from a space between the electrostatic sheet and the object. [Brief explanation of the drawings]

[0011] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which:

[0012] [Figure 1] FIG. 1 depicts a lithography system comprising a lithographic apparatus and a radiation source;

[0013] [Figure 2] 1 is a cross-sectional view of an object holder according to an embodiment of the present invention.

[0014] [Figure 3a]1 is a cross-sectional view of an object holder according to an embodiment of the present invention. [Figure 3b] 1 is a cross-sectional view of an object holder according to an embodiment of the present invention.

[0015] [Figure 4] 1A and 1B are enlarged views of portions of an object holder according to an embodiment of the present invention.

[0016] [Figure 5] 10 is a cross-sectional view showing another embodiment of an object holder according to the present invention. [Figure 6] 10 is a cross-sectional view showing another embodiment of an object holder according to the present invention.

[0017] [Figure 7] 1 is a plan view showing a cross section of an object holder according to an embodiment of the present invention.

[0018] [Figure 8] 8 is a diagram showing another view of the object holder shown in FIG. 7. FIG.

[0019] [Figure 9] 1A and 1B are enlarged views of portions of an object holder according to an embodiment of the present invention.

[0020] [Figure 10] 1A-1C illustrate different stages of parts of a method for manufacturing an object holder according to an embodiment of the present invention. [Figure 11] 1A-1C illustrate different stages of parts of a method for manufacturing an object holder according to an embodiment of the present invention. [Figure 12] 1A-1C illustrate different stages of parts of a method for manufacturing an object holder according to an embodiment of the present invention.

[0021] [Figure 13] 1A and 1B are enlarged views of portions of an object holder according to an embodiment of the present invention.

[0022] [Figure 14] 1A and 1B are enlarged views of portions of an object holder according to an embodiment of the present invention.

[0023] [Figure 15] 1A and 1B are enlarged views of portions of an object holder according to an embodiment of the present invention.

[0024] [Figure 16] 1 is a plan view of a portion of an object holder according to an embodiment of the present invention.

[0025] [Figure 17] 1 is a cross-sectional view showing an electrostatic sheet according to an embodiment of the present invention.

[0026] [Figure 18] 18A-18D illustrate different stages of a method for manufacturing the electrostatic sheet shown in FIG. 17. [Figure 19] 18A-18D illustrate different stages of a method for manufacturing the electrostatic sheet shown in FIG. 17.

[0027] [Figure 20] 1A-1D show schematic diagrams of different stages of a method for manufacturing an electrostatic sheet according to an embodiment of the present invention; [Figure 21] 1A-1D show schematic diagrams of different stages of a method for manufacturing an electrostatic sheet according to an embodiment of the present invention; [Figure 22] 1A-1D show schematic diagrams of different stages of a method for manufacturing an electrostatic sheet according to an embodiment of the present invention; [Figure 23] 1A-1D show schematic diagrams of different stages of a method for manufacturing an electrostatic sheet according to an embodiment of the present invention; [Figure 24] 1A-1D show schematic diagrams of different stages of a method for manufacturing an electrostatic sheet according to an embodiment of the present invention; [Figure 25] 1A-1D show schematic diagrams of different stages of a method for manufacturing an electrostatic sheet according to an embodiment of the present invention;

[0028] [Figure 26]1 is a cross-sectional view of an embodiment of an object holder according to the present invention;

[0029] [Figure 27] FIG. 27 is a plan view showing a portion of the electrostatic sheet shown in FIG. 26.

[0030] [Figure 28a] 3A-3D show schematic diagrams of different stages of a method for manufacturing an object holder according to an embodiment of the present invention; [Figure 28b] 3A-3D show schematic diagrams of different stages of a method for manufacturing an object holder according to an embodiment of the present invention; [Figure 28c] 3A-3D show schematic diagrams of different stages of a method for manufacturing an object holder according to an embodiment of the present invention; [Figure 28d] 3A-3D show schematic diagrams of different stages of a method for manufacturing an object holder according to an embodiment of the present invention; [Figure 28e] 3A-3D show schematic diagrams of different stages of a method for manufacturing an object holder according to an embodiment of the present invention; [Figure 28f] 3A-3D show schematic diagrams of different stages of a method for manufacturing an object holder according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0031] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may be described in detail herein. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular forms disclosed, but on the contrary, are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0032] 1 shows a lithography system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate a beam of EUV radiation B and to provide the beam of EUV radiation B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask or reticle), a projection system PS, and a substrate table WT configured to support a substrate W.

[0033] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. In addition, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together, the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. In addition to, or instead of, the facetted field mirror device 10 and the facetted pupil mirror device 11, the illumination system IL may include other mirrors or other devices.

[0034] After being conditioned in this manner, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B' is produced. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. To that end, the projection system PS may comprise a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by a substrate table WT. The projection system PS may apply a demagnification factor to the patterned EUV radiation beam B' to form an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4x or 8x may be applied. Although the projection system PS is shown in Figure 1 as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (e.g. 6 or 8 mirrors).

[0035] The substrate W may include a previously formed pattern, in which case the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B' to the previously formed pattern on the substrate W.

[0036] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided within the source SO, illumination system IL and / or projection system PS.

[0037] The source SO may be a laser-produced plasma (LPP) source, a discharge-produced plasma (DPP) source, a free-electron laser (FEL), or any other source capable of producing EUV radiation.

[0038] 2 is a cross-sectional view of an object holder 20 according to an embodiment of the present invention. The object holder 20 is configured to support an object. In the following description, the present invention is described in the context of the object holder being a substrate holder 20 configured to support a substrate W. However, the object holder is not limited to such a substrate holder 20. For example, the object holder may be configured to support a patterning device MA.

[0039] In an embodiment, the substrate table WT comprises a substrate holder 20 and a substrate stage. The substrate stage comprises a recess in which the substrate holder 20 is held. The substrate holder 20 is configured to hold the substrate W relative to the substrate stage of the substrate table WT.

[0040] As shown in FIG. 2, in one embodiment, the substrate holder 20 includes a core body 21. The core body 21 is a plate-shaped disk. As shown in FIG. 2, in one embodiment, the core body 21 includes a plurality of burls 22. The burls 22 are protrusions that protrude from the surface of the core body 21. As shown in FIG. 2, in one embodiment, the burls 22 have distal ends 23. The core body 21 is configured such that the distal ends 23 are within a support surface 24 for supporting the substrate W. The lower surface of the substrate W comes into contact with the distal ends 23 of the burls 22. The position of the lower surface of the substrate W corresponds to the support surface 24. The burls 22 are arranged so that the substrate W is approximately flat on the substrate holder 20.

[0041] The burls 22 are not shown to scale in Figure 2. In a practical embodiment, there may be hundreds, thousands, or tens of thousands of burls distributed throughout a substrate holder 20 of, for example, 200 mm, 300 mm, or 450 mm diameter. The tips of the burls 22 may be, for example, 1 mm 2Because the burls 22 have a small area, the total area of ​​all of the burls 22 on one side of the substrate holder 20 is less than about 10% of the total surface area of ​​the substrate holder 20. The burls 22 are arranged so that any particles that may be present on the surface of the substrate W, substrate holder 20, or substrate table WT fall between the burls 22 and are therefore unlikely to cause deformation of the substrate W or substrate holder 20. The burl arrangement, which may form a pattern, may be regular or may vary as needed to provide an appropriate force distribution on the substrate W and substrate table WT. The burls 22 may have any shape in a plan view, but are generally circular in a plan view. The burls 22 may have the same shape and dimensions throughout their entire height, but are generally tapered. The burls 22 may protrude above the remainder of the object-facing surface of the substrate holder 20 (i.e., the upper surface of the electrostatic sheet 25) by a distance of about 1 μm to about 5 mm, preferably about 5 μm to about 250 μm, and preferably about 10 μm. Therefore, the vertical distance between the distal ends 23 of the burls 22 and the upper surface of the electrostatic sheet 25 is about 1 μm to about 5 mm, preferably about 5 μm to about 250 μm, and preferably about 10 μm. The thickness of the core 21 of the substrate holder 20 can be in the range of about 1 mm to about 50 mm, preferably in the range of about 5 mm to 20 mm, and typically 10 mm.

[0042] The core 21 may be made of a hard material. The material preferably has high thermal conductivity and a thermal expansion coefficient close to that of the object being held. Preferably, the material is electrically conductive. Preferably, the material has high hardness. Suitable materials include SiC (silicon carbide), SiSiC (silicon carbide), Si3N4 (silicon nitride), quartz, and / or various other ceramics and glass-ceramics, such as Zerodur® glass-ceramic. The core 21 can be fabricated by selectively removing material from a solid disk of associated material, leaving protruding burls 22. Suitable techniques for removing material include electrical discharge machining (EDM), etching, machining, and / or laser ablation. The core 21 can also be fabricated by growing burls 22 through a mask. The burls 22 may be the same material as the substrate and can be grown by a physical vapor deposition process or sputtering. In some embodiments, the core 21 includes one or more internal channels (not shown). In some embodiments, the core 21 comprises multiple layers bonded together. In some embodiments, the multiple layers are formed of different materials. By way of example only, in some embodiments, the core 21 comprises, in order, a layer of SiSiC, a layer of glass, and another layer of SiSiC. Other combinations of layers are possible.

[0043] As shown in FIG. 2 , in one embodiment, the substrate holder 20 includes one or more electrodes 26 for electrostatic clamping. A potential difference may be generated to provide an electrostatic clamping force between the substrate W and the substrate holder 20, and / or between the substrate holder 20 and a substrate stage of the substrate table WT. In one embodiment, the electrodes 26 are encapsulated between dielectric layers (also known as electrical insulating layers) 27, 28. The generated potential difference may be on the order of 10 volts to on the order of 5,000 volts. An arrangement using one or more heaters and temperature sensors to locally control the temperature of a substrate is described in U.S. Publication No. 2011-0222033, the entire contents of which are incorporated herein by reference, and the teachings thereof may be applied to the teachings herein.

[0044] As shown in FIG. 2 , in one embodiment, the substrate holder 20 includes an electrostatic sheet 25. The electrostatic sheet 25 includes one or more electrodes 26. For the electrodes 26, in one embodiment, two halves of a continuous metal film (separated from the distal ends 23 of the burls 22) can be deposited a certain separation distance from each other to form the positive and negative elements of the electrostatic clamp. The separation distance is not particularly limited. In one embodiment, the separation distance is at least about 20 μm, optionally at least about 50 μm, optionally at least about 100 μm, optionally at least about 200 μm, or optionally at least about 500 μm. In one embodiment, the separation distance is at most about 2 mm, optionally at most about 1 mm, or optionally at most about 500 μm. In one embodiment, the separation distance is about 500 μm. Thus, two electrodes 26 can be present. However, the number of electrodes 26 of the electrostatic sheet 25 is not particularly limited and may be one, three, or more. The metal lines of electrode 26 may have a thickness greater than about 20 nm, preferably greater than about 40 nm. Preferably, the metal lines have a thickness of about 1 μm or less, preferably less than about 500 nm, preferably less than about 200 nm.

[0045] The electrodes 26 of the upper electrostatic sheet 25 may be configured to electrostatically clamp the substrate W to the substrate holder 20. The electrodes 26 of the lower electrostatic sheet 25 may be configured to electrostatically clamp the substrate holder 20 to the remainder of the substrate table WT.

[0046] In some embodiments, the material of the core body 21 and the burls 22 is electrically conductive. For example, in some embodiments, the material of the burls 22 is SiSiC. However, it is not necessary that the material of the core body 21 and the burls 22 be electrically conductive. In some embodiments, a ground layer may be provided that electrically connects the distal ends 23 of two or more burls 22 (optionally all of the burls 22) to a ground or common potential. The ground layer may be formed by depositing a relatively thick layer of an electrically conductive material. The electrically conductive material is not particularly limited. In some embodiments, the electrically conductive material is Cr. In some other embodiments, the electrically conductive material is CrN. In some embodiments, the deposited layer is then patterned to form the ground layer. The pattern may include a series of metal lines connecting the distal ends 23 of the burls 22 together. Such a pattern may be referred to as a "Manhattan" pattern. In some other embodiments, the deposited layer is not patterned. In some embodiments, the ground layer or another layer is disposed to cover the surface of the core body 21 and / or the burls 22. The ground layer or other layer can help smooth the surface, making it easier to clean.

[0047] As shown in FIG. 2 , in one embodiment, the electrostatic sheet 25 includes an electrode 26 sandwiched between dielectric layers 27 and 28. As shown in FIG. 2 , in one embodiment, burls 22 and the electrostatic sheet 25 are provided on both major surfaces of the substrate. In another embodiment, the burls 22 and the electrostatic sheet 25 are provided on only one of the two major surfaces of the substrate holder 20. As shown in FIG. 2 , in one embodiment, the electrostatic sheet 25 is located between the burls 22. For example, as shown in FIG. 2 , holes 34 are provided in the electrostatic sheet 25. The holes 34 are positioned to correspond to the burls 22 of the core 21. The burls 22 protrude through each hole 34 in the electrostatic sheet 25 such that the electrode 26, sandwiched between the dielectric layers 27 and 28, is located in the region between the burls 22.

[0048] 2, in one embodiment, the substrate holder 20 includes a bonding material 29. In one embodiment, the bonding material has a thickness of at least 100 nm, for example, about 50 μm. The bonding material 29 fixes the position of the electrostatic sheet 25 relative to the core 21 so that it does not move. The bonding material 29 maintains the state in which the holes 34 in the electrostatic sheet 25 are aligned with the burls 22. In one embodiment, the burls 22 are positioned in the center of each hole 34 in the electrostatic sheet 25.

[0049] 2, in some embodiments, the bonding material 29 is formed in separate portions that do not connect to one another. There may be some variation in the thickness of the different portions of the bonding material 29. In some embodiments, the separate portions of the bonding material 29 have substantially the same thickness as one another.

[0050] Figure 3a is a cross-sectional view of a substrate holder 20 according to one embodiment of the present invention. For simplicity, features shown in Figure 3a that are common to the configuration shown in Figure 2 will not be described below. Instead, the following description will focus on features that are shown in Figure 3a but not in Figure 2.

[0051] As shown in FIG. 3a, in an embodiment, the substrate holder 20 includes a thermal regulator. The thermal regulator is configured to thermally regulate the core 21 and / or the electrostatic sheet 25 and / or the substrate W. The thermal regulator can be used to control the temperature of the substrate W, for example, during an exposure process. As shown in FIG. 3a, in an embodiment, the thermal regulator includes a circuit 30 through which a thermal regulation fluid flows. The thermal regulation fluid may be a gas or a liquid (e.g., water). In an embodiment, the circuit 30 includes one or more channels that are connected to each other. As shown in FIG. 6, in an embodiment, the channels of the circuit 30 are provided within the core 21. In an embodiment, the thermal regulator includes a heater and a sensor that are controlled to control the thermal regulation function.

[0052] As shown in Figure 3a, in one embodiment, core body 21 is manufactured in two parts, which are then attached to each other at joint 31. The channel for circuit 30 can be formed in one of the two parts of core body 21. Circuit 30 is surrounded by the other part of core body 21. Manufacturing the core body in two parts makes it easier to manufacture core body 21.

[0053] As shown in FIG. 3 a, in some embodiments, a coating is provided on the distal end 23 of the burr 22. In some embodiments, the coating on the distal end 23 is configured to resist corrosion and wear and to provide a desirable coefficient of friction against the substrate W. In some embodiments, the coating comprises chromium nitride. In some embodiments, the coating comprises diamond-like carbon (DLC). In some embodiments, the coating comprises a layer of chromium nitride on a layer of diamond-like carbon (DLC). Other materials can also be used as the coating on the distal end 23 of the burr 22.

[0054] As shown in FIG. 3a, in one embodiment, the substrate holder 20 includes multiple temperature sensors 222. The temperature sensors 222 can measure the temperature distribution within the substrate holder 20. EUV light heats the wafer and may also heat the substrate holder 20, causing deformation of both the wafer and the substrate holder 20 and resulting in overlay errors. By knowing the (3D) temperature distribution throughout the substrate holder 20, exposure parameters may be modified to reduce overlay errors. The temperature sensors 222 may be located on the core 21 and / or the electrostatic sheet 25. The temperature sensors 222 may be negative temperature coefficient sensors (lengths on the order of 1 mm). The temperature sensors 222 may be spatially distributed within the substrate holder 20. The temperature sensors 222 may be located closer to the object-facing surface of the substrate holder 20 than the circuit 30. The temperature sensors 222 may be located radially or axially relative to the substrate holder 20.

[0055] 3a, in one embodiment, the temperature sensor 222 is disposed in a hole 220 having a radial opening. The hole 220 is located at the outer edge of the core 21 between the circuit 30 and the electrostatic sheet 25. A wire 224 is connected to the temperature sensor 222.

[0056] FIG. 3b is a cross-sectional view of substrate holder 20 according to one embodiment of the present invention. For simplicity, features shown in FIG. 3b that are common to the configuration shown in FIG. 3a will not be described below. Instead, the following description focuses on features not shown in FIG. 3a but shown in FIG. 3b. As shown in FIG. 3b, temperature sensor 222 is disposed in hole 226 having an axial opening. Hole 226 is disposed between circuit 30 and electrostatic sheet 25. Wiring 224 is connected to temperature sensor 222. Compared to the sensor configuration of FIG. 3a, the sensor configuration of FIG. 3b has more flexibility because temperature sensor 222 can be disposed over a wider area.

[0057] Figure 4 is an enlarged view of a portion of the substrate holder 20 according to an embodiment of the present invention. As shown in Figure 4, in an embodiment, the core body 21 includes at least one gas supply passage 38. The gas supply passage 38 is configured to supply gas to a radial gap 39 between the electrostatic sheet 25 and a radially outer surface 41 of at least one burl 22 via a vertical gap 40 between the core body 21 and the electrostatic sheet 25. In Figure 8, double arrows represent gas flow.

[0058] As shown in FIG. 3A above, in one embodiment, the substrate holder 20 includes a thermal conditioner configured to thermally condition the substrate W. By providing a gas supply passage 38, gas can be supplied between the substrate W and the substrate holder 20 to increase heat transfer between the substrate W and the substrate holder 20. This helps control the temperature of the substrate W. As shown in FIG. 4 , gas is supplied through the gas supply passage 38 directly below the electrostatic sheet 25. The gas supply passage 38 terminates at an opening in the object-facing surface 37 of the core 21 directly below the electrostatic sheet 25. The gas flows through a vertical gap 40 between the core 21 and the electrostatic sheet 25 and reaches a radial gap 39. The gas then fills the gap between the substrate W and the upper surface of the electrostatic sheet 25, thereby improving heat transfer between the substrate W and the substrate holder 20.

[0059] FIG. 5 is a cross-sectional view of a portion of a substrate holder 20 according to an embodiment of the present invention. As shown in FIG. 5 , in one embodiment, the substrate holder 20 includes circumferential barriers 81 and 82. The circumferential barriers 81 and 82 are for reducing the outflow of fluid escaping from the space between the electrostatic sheet 25 and the core 21. As described above, gas may be supplied below the electrostatic sheet 25. The gas can flow under the electrostatic sheet 25 toward the substrate W and reside in the gap between the substrate W and the electrostatic sheet 25. The circumferential barriers 81 and 82 are configured to enclose a volume of gas that improves thermal conduction between the core 21 and the substrate W. The circumferential barriers 81 and 82 are configured to help maintain fluid pressure between the substrate W and the substrate holder 20. The circumferential barriers 81 and 82 are located radially outward of holes in the substrate holder 20 through which pins pass for controlled lowering of the substrate W onto the substrate holder 20. In one embodiment, the circumferential barriers 81 and 82 are located radially inward of the edges of the substrate W on the substrate holder 20. Certain embodiments of the present invention are expected to improve the uniformity of heat transfer between the substrate W and the substrate holder 20. Certain embodiments of the present invention are expected to improve the accuracy of temperature control of the substrate W during the exposure process.

[0060] The circumferential barriers 81, 82 form a circumferential gas flow constriction. In some embodiments, the circumferential barriers 81, 82 do not completely seal the volume of gas between the substrate W and the substrate holder 20. In some embodiments, the circumferential barriers 81, 82 are configured to allow leakage of fluid (e.g., gas such as hydrogen) from the space between the substrate W and the core 21. By allowing some leakage of fluid through the circumferential barriers 81, 82, the gas pressure below the substrate W can be reduced more quickly. This allows the substrate W to be unclamped from the substrate holder 20 more quickly. This allows the substrate W to be replaced with another substrate more quickly. Certain embodiments of the present invention are expected to improve throughput.

[0061] 5 , in some embodiments, a circumferential barrier 82 is located between the electrostatic sheet 25 and the core body 21. In some embodiments, the circumferential barrier 82 between the electrostatic sheet 25 and the core body 21 is formed by a bonding material, such as an adhesive material. For example, in some embodiments, the material used to form the circumferential barrier 82 is the same as the bonding material 29 used to attach the electrostatic sheet 25 to the core body 21. The circumferential barrier 82 helps to maintain the connection between the electrostatic sheet 25 and the core body 21. Some embodiments of the present invention are expected to make the substrate holder 20 more rigid.

[0062] In some embodiments, the circumferential barrier 82 between the electrostatic sheet 25 and the core 21 extends around the entire circumference. In some embodiments, the circumferential barrier 82 between the electrostatic sheet 25 and the core 21 extends the complete vertical gap between the electrostatic sheet 25 and the core 21. In some embodiments, the circumferential barrier 82 between the electrostatic sheet 25 and the core 21 substantially prevents gas from passing through. In some other embodiments, the circumferential barrier 82 between the electrostatic sheet 25 and the core 21 is configured to allow some gas to leak through. In some embodiments, gas is allowed to leak through the gap between the bottom surface of the substrate W and the top surface of the electrostatic sheet 25.

[0063] As shown in FIG. 5 , in one embodiment, a circumferential barrier 81 is provided above the electrostatic sheet 25. As shown in FIG. 5 , in one embodiment, the circumferential barrier 81 is formed by the electrostatic sheet 25. The circumferential barrier 81 may be integrally formed as part of the electrostatic sheet 25. For example, in one embodiment, the circumferential barrier 81 is formed as an integral part of the upper dielectric layer 28 of the electrostatic sheet 25. The circumferential barrier 81 is configured to extend around the entire circumference. As shown in FIG. 5 , in one embodiment, the circumferential barrier 81 is configured to protrude toward the substrate W to a height that is lower than the protruding height of the burls 22. As shown in FIG. 5 , in one embodiment, the circumferential barrier 81 is positioned such that a gap exists between the underside of the substrate W and the top 84 of the circumferential barrier 81. Gas can leak out through a small gap above the top 84 of the circumferential barrier 81. By providing a small gap, the circumferential barrier 81 does not directly contact the substrate W. The circumferential barrier 81 does not adversely affect the flatness of the substrate W.

[0064] In any embodiment, the dimensions of the circumferential barrier 81, which forms a small gap (for gas leakage), are selected to control the rate of gas escaping from the region between the substrate W and the core 21. In one embodiment, the circumferential barrier 81 is configured so that the vertical gap between the top 84 of the circumferential barrier 81 and the underside of the substrate W (which corresponds to the vertical distance between the top 84 of the circumferential barrier 81 and the distal end 23 of the burl 22) is greater than 2 μm. In another embodiment, as shown in FIG. 26 , the circumferential barrier 81 above the electrostatic sheet 25 is not provided (but a circumferential barrier 82 is provided below the electrostatic sheet 25). In one embodiment, the vertical gap is at least 3 μm, and optionally at least 5 μm. Providing a larger vertical gap allows for greater manufacturing tolerances in the vertical position of the circumferential barrier 81 while preventing the circumferential barrier 81 from undesirably affecting the flatness of the substrate W. It is expected that an embodiment of the present invention will facilitate the manufacture of the substrate holder 20. As described above, bonding material 29 is used to connect electrostatic sheet 25 to core 21. By increasing manufacturing tolerances, bonding material 29 can be used without excessively reducing manufacturing yield. The use of bonding material can reduce the accuracy with which the vertical position of electrostatic sheet 25 can be determined. Furthermore, if an adhesive is used, the adhesive may drift over time, potentially resulting in a vertical shift of approximately 0.1 μm. It is expected that certain embodiments of the present invention will enable the use of adhesive while maintaining manufacturing yield.

[0065] In one embodiment, the circumferential barrier 81 is configured to have a width (radial to the substrate holder 20) greater than 0.5 mm. In one embodiment, the circumferential barrier 81 has a radial width of at least 0.6 mm, optionally at least 1 mm, for example 1.2 mm. By increasing the radial width of the circumferential barrier 81, the vertical gap to the substrate W can be increased (as explained above) without unduly increasing the flow rate of gas leaking out of the space between the substrate W and the substrate holder 20.

[0066] 5, in one embodiment, bonding material 29 is used to bond electrostatic sheet 25 to core body 21 radially outward of a circumferential barrier 82 between electrostatic sheet 25 and core body 21. In one embodiment, this radially outer bonding material 29 extends around the entire circumference, similar to circumferential barrier 82. In another embodiment, radially outer bonding material 29 is formed from individual dots of bonding material, similar to bonding material 29 between the central portion of electrostatic sheet 25 and core body 21.

[0067] As shown in FIG. 5 , in one embodiment, the electrostatic sheet 25 extends radially beyond the substrate W. As shown in FIG. 5 , in one embodiment, the substrate holder 20 includes a gap 83 in one of the dielectric layers 27, 28. The gap 83 allows the electrode 26 to be connected to a power source. For example, the electrode 26 may be connected to a high-voltage power supply. In one embodiment, the electrode 26 is configured to be connected to an external power source. As shown in FIG. 5 , in one embodiment, the gap 83 is radially outward of the circumferential barriers 81, 82. In the configuration shown in FIG. 5 , the gap 83 is provided in the upper dielectric layer 28. In another embodiment, the gap 83 is provided in the lower dielectric layer 27.

[0068] The substrate holder 20 is designed to allow the electrode 26 to be electrically connected to a power source while sealing the gas volume between the substrate W and the substrate holder 20. As shown in FIG. 5 , in one embodiment, the electrode 26 passes under a circumferential barrier 81 that allows gas to escape. In one embodiment, the electrostatic sheet 25 includes an electrostatic shield 45. The electrostatic shield 45 is formed from a conductive material. In one embodiment, the electrostatic shield 45 is grounded. The electrostatic shield 45 is configured to shield other components from the electrostatic sheet 25. In one embodiment, the electrostatic shield 45 is configured to shield the substrate W and / or the rest of the core 21 and the burl 22 from charges in the dielectric layers 28, 27. The electrostatic shield 45 may be provided at one or more different locations around the electrostatic sheet 25. As shown in FIG. 5 , in one embodiment, the electrostatic shield 45 is provided to cover the top 84 of the circumferential barrier 81.

[0069] In some embodiments, electrostatic shield 45 comprises a conductive plating on the surface of electrostatic sheet 25. In some embodiments, electrostatic shield 45 is applied by chemical vapor deposition. In some embodiments, electrostatic shield 45 is applied by sputtering. In some embodiments, electrostatic shield 45 is applied by physical vapor deposition. In some embodiments, electrostatic shield 45 has a thickness of at least 50 nm, optionally at least 100 nm, optionally at least 200 nm, and optionally at least 500 nm. In some embodiments, electrostatic shield 45 has a thickness of at most 1000 nm, optionally at most 500 nm, optionally at most 200 nm, and optionally at most 100 nm. In some embodiments, the thickness of electrostatic shield 45 may vary in different sections of the electrostatic shield.

[0070] 5, in one embodiment, the electrostatic shield 45 is provided to cover the circumferential barrier 81. The electrostatic shield 45 is configured to prevent discharge in the gap between the top 84 of the circumferential barrier 81 and the substrate W. As shown in FIG. 5, in one embodiment, the electrostatic shield 45 is provided on the top surface of the electrostatic sheet 25 radially outward from the circumferential barrier. The electrostatic shield 45 is configured to prevent discharge between the electrode 26 in the gap 83 and the substrate W.

[0071] Providing gap 83 in dielectric layer 28 and extending electrostatic sheet 25 radially beyond substrate W makes it relatively simple to make connections between electrode 26 and a power supply. Furthermore, core 21 is relatively easy to manufacture.

[0072] In one embodiment, electrostatic sheet 25 is configured to extend radially beyond the radial extent of substrate W by at least 3 mm, optionally at least 5 mm, and optionally at least 10 mm. For example, in one embodiment, substrate W has a diameter of 300 mm. Electrostatic sheet 25 may have a diameter of, for example, at least 306 mm, optionally at least 310 mm, and optionally at least 320 mm. By providing electrostatic sheet 25 that is larger than substrate W, the surface of electrostatic sheet 25 may be used as space for providing, for example, fiducial markers.

[0073] Figure 26 is a cross-sectional view of a portion of a substrate holder 20 according to an embodiment of the present invention. Only the differences from the embodiment shown in Figure 5 will be described below.

[0074] 26, in one embodiment, electrostatic sheet 25 does not include circumferential barrier 81 on the substrate-facing surface of electrostatic sheet 25. Circumferential barrier 82 is provided on the core-facing surface of electrostatic sheet 25.

[0075] As shown in FIG. 26 , in one embodiment, electrostatic sheet 25 includes at least one gas vent 262. Gas vent 262 penetrates electrostatic sheet 25 and connects the substrate-facing surface to the core-facing surface. Gas vent 262 is configured to allow gas flow between the substrate-facing surface and the core-facing surface of electrostatic sheet 25. The dimensions of gas vent 262 are not particularly limited. In one embodiment, gas vent 262 extends further in the radial direction of electrostatic sheet 25 rather than in the circumferential direction of electrostatic sheet 25. In one embodiment, gas vent 262 extends further in the radial direction of electrostatic sheet 25 than holes 34 through which burrs 22 protrude.

[0076] In one embodiment, the multiple gas vents 262 are provided at different circumferential positions around the electrostatic sheet 25. When the substrate holder 20 holds the substrate W, the gas pressure under the central portion of the substrate W is higher than the gas pressure under the edge of the substrate W. This is due, at least in part, to backfill gas provided to increase the thermal connection between the substrate holder 20 and the substrate W. Under the peripheral region of the substrate W, the gas pressure decreases in a direction toward the edge of the substrate W. The pressure gradient depends on factors such as the shape of the substrate W.

[0077] 26, in some embodiments, the gas vent 262 has a radially inner edge that is radially inward of the edge of the substrate W. When gas flows from under the central portion of the substrate W, the gas can flow through the gas vent 262 before reaching the edge of the substrate W. Some embodiments of the present invention are expected to reduce the dependency of the pressure gradient on the shape of the substrate W. Some embodiments of the present invention are expected to facilitate control of the pressure gradient of the backfill gas toward the vacuum.

[0078] Figure 27 is a plan view of the portion of the electrostatic sheet 25 shown in Figure 26. As shown in Figure 27, the gas vent 262 is radially outward of the holes 34 for the burls 22. As shown in Figure 27, in one embodiment, the gas vent 262 extends across the edge 261 of the substrate W.

[0079] Figure 6 is a cross-sectional view of a portion of a substrate holder 20 according to an embodiment of the present invention. As shown in Figure 6, in an embodiment, a circumferential barrier 81 is formed by the core body 21. The circumferential barrier 81 may be integrally formed as part of the core body 21. The dimensions of the circumferential barrier 81 shown in Figure 6 may be the same as the dimensions of the circumferential barrier 81 shown in Figure 5 above. Therefore, for brevity, these dimensions will not be repeated here.

[0080] In some embodiments, the gap between the top 84 of the circumferential barrier 81 and the substrate W may be smaller than that shown in FIG. 5 . For example, in some embodiments, the vertical gap between the top 84 and the substrate W is at most 10 μm, optionally at most 5 μm, and optionally at most 2 μm. By forming the circumferential barrier 81 from the core 21, the vertical distance between the top 84 of the circumferential barrier 81 and the distal end 23 of the burl 22 can be more precisely controlled. Some embodiments of the present invention are expected to achieve tighter manufacturing tolerances. If the vertical gap above the top 84 of the circumferential barrier 81 is smaller, the radial width of the circumferential barrier 81 may be smaller. This helps maintain a relatively constant flow of gas through the gap above the circumferential barrier 81. For example, in some embodiments, the radial width of the circumferential barrier 81 is at most 2 mm, optionally at most 1 mm, and optionally at most 0.5 mm.

[0081] 6, in one embodiment, the substrate holder 20 includes at least one connection wire 91. The connection wire 91 extends through the core 21. The connection wire 91 is for electrically connecting the electrode 26 to a power source. In one embodiment, the connection wire 91 is a high-voltage connection wire. In one embodiment, the connection wire 91 is configured to connect the electrode 26 to an external power source. The power source may be a high-voltage power source.

[0082] 6, in one embodiment, the core body 21 includes at least one connection line channel 93. The connection line channel 93 is configured to allow the connection line 91 to extend through the core body 21. In one embodiment, the connection line 91 is a conductor such as a wire. In one embodiment, the wire has an insulating material around it to reduce the possibility of electrical breakdown between the connection line 91 and other components such as the core body 21.

[0083] As shown in FIG. 6 , in one embodiment, the connecting wire 91 is connected to the underside of the electrode 26. In one embodiment, an insulating material 92 is provided where the connecting wire 91 connects to the electrode 26. The insulating material 92 is configured to reduce the possibility of the connecting wire 91 coming into contact with a vacuum (or near-vacuum). In one embodiment, the connecting wire 91 is flexible. In one embodiment, the connecting wire 91 is connected to the electrode 26 by an adhesive. The connecting wire 91 in the connecting wire channel 93 forms an electrical feedthrough through the core 21.

[0084] In another embodiment, connecting wires 91 form electrical leads that pass through core 21 and are exposed at a location below electrostatic sheet 25. Conductive epoxy may be used to mechanically and electrically connect the electrical leads to electrodes 26.

[0085] By having the circumferential barrier 81 be part of the core 21, the gap above the circumferential barrier 81 is independent of the height of the electrostatic sheet 25. This means that the gap is independent of assembly tolerances and, for example, bonding materials drifting over time.

[0086] In some embodiments, electrostatic sheet 25 is perfectly circular when viewed in plan view. Some embodiments of the present invention are expected to facilitate the manufacture of electrostatic sheet 25. Some embodiments of the present invention are expected to provide an electrostatic sheet having a more uniformly distributed stress.

[0087] Figure 7 is a cross-sectional plan view of a portion of substrate holder 20 according to another embodiment of the present invention. Figure 8 is a cross-sectional view of substrate holder 20 shown in Figure 7. Figure 7 shows circumferential barrier 81 and electrode 26. As shown in Figure 7, in one embodiment, electrode 26 penetrates circumferential barrier 81 to form a terminal that allows electrode 26 to be connected to a power source. In one embodiment, the power source is external to substrate holder 20. In one embodiment, the power source is a high voltage power supply.

[0088] As shown in Figure 7, in one embodiment, the electrostatic sheet 25 includes multiple electrodes 26. For example, two electrodes 26 are shown in Figure 7. In one embodiment, the electrostatic sheet 25 includes a barrier 101 that separates the electrodes 26. The barrier 101 is made of an electrically insulating material so as to electrically insulate the electrodes 26 from one another. Each electrode 26 is individually connected to a power source.

[0089] As shown in FIG. 8 , in one embodiment, circumferential barrier 81 is formed on core body 21. As shown in FIG. 8 , circumferential barrier 81 includes one or more openings 107. Electrode 26 extends through opening 107. As shown in FIG. 8 , in one embodiment, electrostatic sheet 25 (including dielectric layers 27, 28 and electrode 26) extends through opening 107 in circumferential barrier 81. Electrode 26 penetrates to an outer region of circumferential barrier 81. Electrode 26 can be electrically connected to a power source radially outside of circumferential barrier 81.

[0090] As shown in FIGS. 7 and 8 , in some embodiments, the electrical connection between the electrode 26 and the power supply includes one or more intermediate plates 104. The intermediate plates 104 provide a stronger connection. In some embodiments, the intermediate plate 104 includes an insulating substrate (e.g., a glass plate) on which the power supply lines are mounted. For example, as shown in FIG. 7 , in some embodiments, the intermediate plate 104 includes high-voltage traces 102 and ground traces 103. The intermediate plate 104 is configured to electrically connect the terminals of the electrode 26 to a power connector 105. In some embodiments, the power connector 105 is flexible so that movement of the power supply is damped before reaching the electrostatic sheet 25. In some embodiments, the power connector 105 has a fixed position. Some embodiments of the present invention are expected to be backward compatible with existing lithography equipment. In some embodiments, the intermediate plate 104 reduces forces that may be applied to the electrostatic sheet 25 of the substrate holder 20 due to movement of the power connector 105. By providing intermediate plate 104, the distance that the terminals of electrode 26 extend beyond circumferential barrier 81 can be reduced (or minimized), which makes electrostatic sheet 25 easier to manufacture and makes electrostatic sheet 25 stronger.

[0091] By having the electrodes 26 pass through the openings 107 in the circumferential barrier 81, it is not necessary to fabricate connecting wire channels inside the core 21. It is expected that certain embodiments of the present invention will make the core 21 easier to manufacture.

[0092] As shown in FIG. 8 , in some embodiments, the circumferential barrier 81 is first formed as a separate component from the core body 21. The circumferential barrier 81 is connected to the core body 21 by an adhesive seal 108. As shown in FIG. 8 , in some embodiments, the middle plate 104 is connected to the core body 21 by an adhesive seal 108. As shown in FIG. 8 , in some embodiments, the electrical connection between the electrode 26 and the middle plate 104 is insulated by the adhesive seal 108 on the top surface of the electrostatic sheet 25. As shown in FIG. 8 , in some embodiments, the electrical connection between the middle plate 104 and the power connector 105 is electrically insulated by the adhesive seal 108 on the top surface of the power connector 105.

[0093] As shown in FIG. 8, in one embodiment, conductive material 106 penetrates electrostatic sheet 25 in a manner that forms an electrical connection between electrode 26 and high voltage trace 102 of middle plate 104 .

[0094] 9 is a cross-sectional view of a portion of substrate holder 20 according to one embodiment of the present invention. As shown in FIG. 9, in one embodiment, electrostatic sheet 25 is bonded to core body 21 by bonding material 29. In one embodiment, multiple volumes of bonding material 29 across the top surface of core body 21 connect core body 21 to electrostatic sheet 25. Bonding material 29 may be, for example, an adhesive or a welding material. Bonding material 29 is provided between burls 22.

[0095] As shown in FIG. 9 , in some embodiments, the object-facing surface of the core 21 between the burls 22 includes an upper step 121 and a lower step 122. The upper step 121 is vertically higher than the lower step 122 (i.e., a smaller gap exists between the electrostatic sheet 25). As shown in FIG. 9 , in some embodiments, the bonding material 29 is disposed on the upper step 121. The lower step 122 is adjacent to the upper step 121. As shown in FIG. 9 , in some embodiments, there is a step-like change (i.e., a sudden, discontinuous change in height) between the lower step 122 and the upper step 121. In some other embodiments, the change in height between the lower step 122 and the upper step 121 may be more gradual. As shown in FIG. 9 , in some embodiments, the upper step 121 is vertically lower than the lower surface 123 of the electrostatic sheet 25. 9 , in one embodiment, at least a portion of lower step 122 is vertically below lower surface 123 of electrostatic sheet 25. A portion of lower step 122 is not directly below electrostatic sheet 25. For example, a portion of lower step 122 may directly surround crowbar 22, but electrostatic sheet 25 may not be directly above that portion of lower step 122. However, a portion of lower step 122 is directly below electrostatic sheet 25.

[0096] In one embodiment, the upper step 121 forms the upper surface of the bond pad 124. The bond pad 124 is a raised portion of the core 21 on which the bonding material 29 is disposed. The height of the upper step 121 on the upper surface of the bond pad 124 affects the diameter of the volume of bonding material 29. However, the height of the lower step 122 does not affect the height of the electrostatic sheet 25 of the substrate holder 20. The height of the electrostatic sheet 25 is affected by the amount of bonding material 29 between the electrostatic sheet 25 and the core 21. The diameter of the volume of bonding material 29 depends on the amount of bonding material 29. By providing a larger gap between the lower step 122 and the electrostatic sheet 25 outside the bond pad 124, the diameter of the volume of bonding material 29 is less affected by the amount of bonding material 29. The stiffness of the bond is less affected by the volume of bonding material 29. The stiffness and shape of the volume of bonding material 29 can be more precisely controlled by controlling the shape of the bond pad 124. Certain embodiments of the present invention are expected to improve the consistency of the bond properties between the electrostatic sheet 25 and the core 21 throughout the substrate holder 20. The bond pad design is also used for the gas seal adhesive ring around the periphery of the clamp and around the holes through which the pins pass for controlled lowering of the substrate W onto the substrate holder 20.

[0097] 10 to 12 are schematic diagrams illustrating different stages in the manufacturing process of the core body 21. FIG. 13 is a cross-sectional view of the substrate holder 20 at the time when the electrostatic sheet 25 is connected to the core body 21. As shown in FIG. 13, in one embodiment, the upper step 121 has a smoother surface than the lower step 122. The lower step 122 has a greater surface roughness than the top of the bond pads 124.

[0098] By providing the bond pads 124, the characteristics of the bond between the core 21 and the electrostatic sheet 25 can be controlled by controlling the characteristics of the bond pads 124. The bond characteristics are less affected by the characteristics of the surface of the core 21 beyond the bond pads 124. Some embodiments of the present invention are expected to provide greater manufacturing flexibility for portions of the surface of the core 21. In some embodiments, different manufacturing techniques are used for different steps in preparing the lower tier 122 compared to the upper tier 121.

[0099] As shown in Figure 10, in one embodiment, the burls 22 are formed by removing material 131 from the top surface of the core 21. The material 131 may be removed in a rough material removal step. The rough material removal step may have a large tolerance, which means that the surface between the burls may have a relatively large roughness immediately after the rough material removal step.

[0100] 11 , the method for manufacturing the core body 21 may include a subsequent step of removing additional material 131 in a localized rough material removal step. The localized rough material removal step forms the bond pads 124. Material 131 is removed where the lower tiers 122 are to be formed. Material 131 is not locally removed where the pads 124 are intended to be placed. After the localized rough material removal step, the upper tiers 121 and the lower tiers 122 may have a rough surface. In one embodiment, the rough material removal step is performed by laser ablation. However, other methods may be used.

[0101] As shown in FIG. 12 , in some embodiments, the method for manufacturing the core 21 includes a subsequent step of removing additional material 151 from the top of the bond pads 124. In some embodiments, the additional material 151 is removed in a fine material removal step. The fine material removal step has tighter tolerances than the coarse material removal step. After the fine material removal step, the surface of the top of the bond pads 124 is smoother than the surface of the lower portion 122 of the core 21. The smoother surface improves the consistency of the bond characteristics between the electrostatic sheet 25 and the core 21.

[0102] In one embodiment, the method for manufacturing the core body 21 includes a step of grinding the distal ends 23 of the burls 22. In one embodiment, after the step of grinding the distal ends 23 of the burls 22, a fine material removal step is performed. This means that the height of the upper steps 121 in the bond pads 124 can be precisely controlled so that the electrostatic sheet 25 has a desired vertical position. Different burls 22 may have different lengths (i.e., different vertical distances between the distal ends 23 and the object-facing surface of the core body 21 between the burls 22). The lengths of the burls 22 may be different to ensure that all of the distal ends 23 lie in a flat plane. The fine material removal step allows the height of the bond pads 124 to be adjusted so that the vertical gap filled by the bonding material 29 between the electrostatic sheet 25 and the core body 21 is carefully controlled. The lower steps 122 may have different heights throughout the substrate holder 20.

[0103] FIG. 14 is a cross-sectional view of a portion of a substrate holder 20 according to an embodiment of the present invention. As shown in FIG. 14 , in an embodiment, the object-facing surface of the core 21 includes a raised step 171. The raised step 171 surrounds the burls 22. The raised step 171 is raised relative to the lower step 122. In an embodiment, the raised step 171 is at the same height as the upper step 121. However, this is not necessarily the case. In another embodiment, the raised step 171 is higher than the upper step 121. In yet another embodiment, the raised step 171 is lower than the upper step 121. By providing the raised step 171 surrounding the burls 22, the burls 22 can be made more rigid (compared to when the raised step 171 is replaced by the lower step 122). The rigidity of the burls 22 can be controlled by controlling the height of the raised step 171. The lower step 122 between the raised step 171 and the upper step 121 reduces the sensitivity of the bond between the electrostatic sheet 25 and the core 21 to the amount of bonding material 29 .

[0104] FIG. 15 is a schematic diagram of the top surface of the core 21 between three burls 22. As shown in FIG. 15, in some embodiments, the upper step 121 is non-circular. As can be seen from FIG. 15, by making the bond pads 124 non-circular, the horizontal extent (i.e., the shape in a plan view) of the bonding material 29 between the burls 22 can be controlled. A larger area of ​​bonding material 29 can be provided between the burls 22 without the bonding material being too close to the burls 22. Some embodiments of the present invention are expected to improve the strength of the connection between the electrostatic sheet 25 and the core 21.

[0105] FIG. 16 shows a plan view of substrate holder 20 according to an embodiment of the present invention. In FIG. 16, electrostatic sheet 25 is shown transparent so that bonding material 29 underneath electrostatic sheet 25 is visible in FIG. 16. As shown in FIG. 16, in an embodiment, the volume of bonding material 29 has a non-circular shape in plan view. The shape of the bonding material corresponds to the shape of bond pads 124. Bond pads 124 are non-circular. As shown in FIG. 16, in an embodiment, bond pads 124 and bonding material 29 have recessed edges 191 facing burls 22. The size of the bond in the region between the burls is larger without decreasing the distance between the bond and burls 22.

[0106] In one embodiment, the height of the upper tier 121 is configured so that the vertical gap between the bottom of the electrostatic sheet 25 and the upper tier 121 is at least 5 μm, optionally at least 10 μm, optionally at least 20 μm, and optionally at least 50 μm. This provides sufficient manufacturing tolerance to allow for the gap to be filled by the bonding material 29. In one embodiment, the vertical gap between the electrostatic sheet 25 and the upper tier 121 is at most 200 μm, optionally at most 100 μm, and optionally at most 50 μm. A smaller gap allows for more precise control of the characteristics of the bond formed by the bonding material 29. In one embodiment, the vertical gap between the electrostatic sheet 25 and the lower tier 122 is at least 50 μm, optionally at least 100 μm, and optionally at least 200 μm. A larger gap reduces the sensitivity of the diameter of the bond formed by the bonding material 29 to the amount of bonding material used.

[0107] FIG. 17 is a cross-sectional view of an electrostatic sheet 25 according to one embodiment of the present invention. As shown in FIG. 17, in one embodiment, an electrically insulating bonding layer 32 is sandwiched between dielectric layers 27 and 28. By being electrically insulating, bonding layer 32 is configured to electrically insulate electrode 26. In one embodiment, bonding layer 32 surrounds electrode 26 within the plane of electrode 26. Bonding layer 32 electrically insulates electrode 26. Bonding layer 32 electrically insulates electrode 26 from holes 34 through which burrs 22 protrude. Bonding layer 32 is configured to bond dielectric layers 27 and 28 to one another.

[0108] In some embodiments, the bonding layer 32 is deposited in a formable state. Once bonded, the bonding layer 32 is stable (permanent). In some embodiments, the electrically insulating bonding layer 32 comprises an adhesive. In some embodiments, the bonding layer 32 comprises a polymer. In some embodiments, the bonding layer 32 comprises an organic polymer. In some embodiments, the bonding layer 32 comprises benzocyclobutene (BCB). Other materials, such as parylene, may also be used for the bonding layer 32.

[0109] In some embodiments, the upper dielectric layer 28 comprises a glass. In some embodiments, the upper dielectric layer 28 comprises an oxide. In some embodiments, the glass is a borosilicate glass, such as Corning® Eagle XG®. In some other embodiments, the upper dielectric layer 28 comprises a titania silicate glass, such as ULE®.

[0110] In some embodiments, the lower dielectric layer 27 comprises the same material as the upper dielectric layer 28. In other embodiments, the lower dielectric layer 27 is formed of a different material than the upper dielectric layer 28. For example, in some embodiments, the lower dielectric layer 27 is formed of a material having a lower resistivity than the material used for the upper dielectric layer 28. In some embodiments, the lower dielectric layer 27 comprises a borosilicate glass such as BOROFLOAT® 33 or another dielectric material.

[0111] 18 and 19 schematically illustrate different stages of a method for manufacturing electrostatic sheet 25. As shown in FIG. 18 , in one embodiment, the method comprises providing an upper dielectric layer 28 and a lower dielectric layer 27. As shown in the top of FIG. 18 , in one embodiment, the method comprises applying an electrode 26 to the upper dielectric layer 28. By applying the electrode 26 to the upper dielectric layer 28, the electrode 26 is closer to the top of the electrostatic sheet 25. As shown in FIG. 18 , in one embodiment, an adhesive layer 32 is provided on only one of the two major surfaces of the electrode 26. The electrode 26 is applied directly onto the dielectric layer 28. The adhesive layer 32 is not present between the electrode 26 and the top of the electrostatic sheet 25. This allows for better control of the electric field strength above the electrostatic sheet 25 generated by the electrode 26. While FIG. 18 shows the electrode 26 applied to the upper dielectric layer 28, in another embodiment, the electrode 26 is applied to the lower dielectric layer 27.

[0112] 18, in one embodiment, the method comprises applying an electrically insulating bonding layer 32 to the lower dielectric layer 27. The electrically insulating bonding layer 32 is applied before the dielectric layers 27, 28 are bonded to one another. In one embodiment, the bonding layer 32 is applied to the dielectric layer 27 by a spin coating process; however, other processes may be used.

[0113] In the configuration shown in Figure 18, the bonding layer 32 is applied to the lower dielectric layer 27. In another embodiment, the bonding layer 32 is applied to the upper dielectric layer 28. As shown in Figure 18, in some embodiments, the electrode 26 and the bonding layer 32 are applied to different dielectric layers 27, 28. In some other embodiments (e.g., as shown in Figures 20-25 described below), both the electrode 26 and the bonding layer 32 are applied to the same dielectric layer (which may be either the lower dielectric layer 27 or the upper dielectric layer 28).

[0114] As shown in FIG. 18 , in one embodiment, a method for fabricating electrostatic sheet 25 comprises patterning electrode 26 before bonding dielectric layers 27, 28 together. In one embodiment, electrode 26 comprises a metal such as chromium. In one embodiment, electrode 26 has a thickness of at least 29 nm, optionally at least 50 nm, and optionally at least 100 nm. In one embodiment, electrode 26 has a thickness of at most 500 nm, optionally at most 200 nm, and optionally at most 100 nm. In one embodiment, electrode 26 is patterned by an etching process. In another embodiment, electrode 26 is patterned by a lift-off process.

[0115] In some embodiments, the dielectric layer 28 to which the electrode 26 is applied has a thickness of at least 100 μm, optionally at least 200 μm, and optionally at least 500 μm. A thicker dielectric layer 28 is more robust for handling during the process of manufacturing the electrostatic sheet 25. In some embodiments, the dielectric layer 28 to which the electrode 26 is applied has a thickness of at most 2 mm, optionally at most 1 mm, and optionally at most 500 μm. A thinner dielectric layer 28 reduces the amount of thinning that may be required after the dielectric layers 27, 28 are bonded. The thickness of the dielectric layer 27 to which the bonding layer 32 is applied may be selected in the same manner as the thickness of the dielectric layer 28 to which the electrode 26 is applied. Therefore, possible thicknesses will not be repeated here.

[0116] 19 , in one embodiment, a method for manufacturing an electrostatic sheet 25 includes bonding an upper dielectric layer 28 to a lower dielectric layer 27. The dielectric layers 27, 28 are bonded together. In one embodiment, the method includes heating the bonded dielectric layers 27, 28, for example, to polymerize a bonding layer 32. For example, the bonded dielectric layers 27, 28 can be heated to a temperature of 250° C., although the temperature used is not particularly limited. The bonding layer 32 forms a bond between the upper dielectric layer 28 and the lower dielectric layer 27.

[0117] In some embodiments, the method for manufacturing electrostatic sheet 25 includes thinning upper dielectric layer 28 and / or lower dielectric layer 27. For example, in some embodiments, the upper dielectric layer of the finished electrostatic sheet has a thickness of up to 200 μm, optionally up to 100 μm. In some embodiments, the lower dielectric layer 27 of the finished electrostatic sheet 25 has a thickness of up to 500 μm, optionally up to 400 μm. In some embodiments, dielectric layers 27, 28 are thinned after they are bonded together. Dielectric layers 27, 28 may be thickened during the bonding step to make them more robust, and then thinned once the risk of breakage is reduced. In some other embodiments, dielectric layers 27, 28 are thinned to a desired thickness before being bonded together. In some embodiments, dielectric layers 27, 28 are thinned by a grinding and / or polishing process.

[0118] Contaminant particles may come into contact with the surfaces of components during the manufacture of electrostatic sheet 25. When dielectric layers 27, 28 contact each other, contaminant particles between dielectric layers 27, 28 become surrounded by formable bonding layer 32. Therefore, the presence of contaminant particles cannot adversely affect the manufacture of electrostatic sheet 25. Certain embodiments of the present invention are expected to provide a method for manufacturing electrostatic sheet 25 that is less susceptible to particles.

[0119] By providing the electrically insulating bonding layer 32, the bonding layer 32 serves both the functions of electrical insulation and mechanical / chemical bonding. Some embodiments of the present invention are expected to simplify the manufacturing process of the electrostatic sheet 25. There is no need to provide separate materials or processes to serve the functions of electrical insulation and bonding.

[0120] 20-25 schematically illustrate different stages of a method for manufacturing an electrostatic sheet 25 according to one embodiment of the present invention. As shown in FIG. 20, in one embodiment, the method comprises providing an upper dielectric layer 28 and a lower dielectric layer 27. In one embodiment, one or both of the dielectric layers 27, 28 are provided with one or more alignment markers 201. The alignment markers 201 facilitate aligning the dielectric layers 27, 28 relative to one another.

[0121] As shown in FIG. 21 , in one embodiment, the method comprises selectively irradiating the dielectric layers 27, 28 before they are bonded together. In one embodiment, the dielectric layers 27, 28 are irradiated based on the desired locations of the holes 34 for accommodating the burls 22 in the core 21 of the substrate holder 20. In one embodiment, the dielectric layers 27, 28 are irradiated in preparation for etching (e.g., selective laser etching) by applying a laser. As shown in FIG. 21 , the irradiation of the dielectric layers 27, 28 results in irradiated regions 211 and non-irradiated regions 212. In one embodiment, the irradiated regions 211 correspond to the desired locations of the holes 34 for accommodating the burls 22. In another embodiment, the non-irradiated regions 212 correspond to the desired locations of the holes 34 for the burls 22.

[0122] As shown in FIG. 22 , in one embodiment, a method for fabricating an electrostatic sheet 25 comprises applying an electrode 26 to one of the dielectric layers 27. In one embodiment, a thin electrical structure is applied to form the electrode 26. In one embodiment, a bonding layer 32 is applied over the thin electrical structure. The bonding layer 32 protects the electrical structure. In one embodiment, the bonding layer 32 comprises an organic polymer. In one embodiment, the bonding layer 32 comprises BCB or parylene. As shown in FIG. 23 , in one embodiment, an upper dielectric layer 28 is bonded to a lower dielectric layer 27. The bonding layer 32 serves to bond the dielectric layers 27, 28 to each other.

[0123] As shown in Figure 24, in one embodiment, the method comprises applying an etching step to form holes 34 for accommodating burls 22 of core body 21. In one embodiment, after bonding dielectric layers 27, 28 together, material is removed to form holes 34. The material is removed based on selected irradiation. In one embodiment, the step of removing material comprises selectively etching irradiated portions 211 of the dielectric layers, for example by applying a laser.

[0124] 25, in one embodiment, the method comprises exposing the electrostatic sheet 25 to an oxide plasma that removes the exposed portions of the bonding layer 32. Specifically, after etching away the irradiated portions 211 of the dielectric layers 27, 28, the sections of the bonding layer 32 in the holes 34 are exposed. The stack is placed in the oxide plasma to etch away the material of the bonding layer 32 from the holes 34.

[0125] FIGS. 28a-28f schematically illustrate different stages of a method for fabricating a substrate holder 20 according to an embodiment of the present invention. The substrate holder 20 is similar to that of the previous embodiment depicted in FIGS. 2-27, and the bonding material 29 comprises a solder 286 or welding material 286 with favorable thermal conductivity. The solder 286 may be metal-based. Furthermore, the solder 286 or welding material 286 may be less susceptible to creep or deformation during transition from atmosphere to vacuum, thereby providing more favorable uniformity and stability of the clamping force compared to adhesive or epoxy bonding. Optionally, adhesive layers 282, 284, such as platinum (Pt) or chromium (Cr), may be used to promote adhesion between the solder 286 and the core 21 and / or electrostatic sheet 25. This eliminates the need for flux in the soldering process and may be beneficial for compatibility with H-radicals and / or H-plasma in the scanner environment. The adhesive layers 282, 284 may be metal-based. The electrostatic sheet 25 is similar to that of the previous embodiment depicted in FIGS.

[0126] 28a, in one embodiment, the method comprises coating an adhesive layer 282 on the surface of the core 21 facing the electrostatic sheet 25. The surface is between the burls 22.

[0127] 28b, in an embodiment, the method further comprises coating an adhesive layer 284 on the surface of the electrostatic sheet 25 facing the core 21. Alternatively, the electrostatic shield 45 may comprise Pt and / or Cr, so that the electrostatic shield 45 may function as the adhesive layer 284.

[0128] As shown in FIG. 28c, in some embodiments, the method further comprises disposing solder 286 or welding material 286 on the adhesive layer 284.

[0129] 28d, in some embodiments, the method further comprises heating the solder 286 or welding material 286. This can be done using a hot plate 288. Heat may be transferred from the hot plate 288 through the core 21 to the solder 286 or welding material 286.

[0130] 28e, in certain embodiments, the method further comprises placing the electrostatic sheet 25 on the solder 286 or welding material 286 while the solder 286 or welding material 286 is being heated. The placing may comprise horizontally positioning the electrostatic sheet 25. The electrostatic sheet 25 may be turned over so that the adhesive layer 284 faces the core 21.

[0131] As shown in FIG. 28f, in an embodiment, the method further comprises cooling the substrate holder 20 so that the electrostatic sheet 25 is soldered or welded onto the core 21.

[0132] The solder 286 may be a relatively low temperature solder that may be applied to minimize deformation due to stress. Optionally, metals that are prone to hydrogen embrittlement are not preferred. Possible solder 286 candidates are listed below:

[0133] [Table 1]

[0134] The materials used to manufacture all parts of the object holder according to the embodiments may be any of the known materials used to manufacture known object holders. In particular, parts of the object holder according to the embodiments may be manufactured using the materials disclosed in WO2015 / 120923A1, WO2014 / 154428A2, and US2013 / 0094009A1, the contents of which are incorporated herein by reference in their entireties.

[0135] Specifically, the metal used for the electrode 26 may be Cr or Ti. The metal used for the distal end surface of the burr may be CrN or TiN. The insulating portion may be chromium oxide. The core may be SiSiC. The material used for the electrostatic shield 45 may be Cr, CrN, or W (although many other materials are possible).

[0136] To aid in clarity, the embodiments have been described with reference to the top and bottom surfaces of the object holder. The top and bottom surfaces are first and second surfaces of the object holder. The first surface is a surface to which an object can be clamped. The second surface is a surface to which a table can be fixed. When the object holder is oriented in a horizontal plane, the first surface is the top surface and the second surface is the bottom surface. However, the embodiments also include object holders that are not oriented in a horizontal plane.

[0137] Embodiments include an object holder for use in any lithographic apparatus. Lithographic apparatus may include any apparatus used in the manufacture, testing, and inspection of substrates, such as electron beam inspection apparatus. To aid clarity, the features of the object holder have been described primarily in the context of an upper side of the substrate holder 20 being clamped to the substrate W. The features of the invention are equally applicable to the underside of the object holder, e.g., the underside of the substrate holder 20 being clamped to the remainder of the substrate table WT. By way of example only, features relating to the upper tier 121, the lower tier 122, and the bond pads 124 may be applied to the underside of the substrate holder 20.

[0138] Although specific reference may be made in this specification to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein may have other applications, including the manufacture of integrated optical systems, guide and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0139] Although specific reference may be made herein to embodiments of the invention in the context of lithography apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be generally referred to as lithography tools. Such lithography tools may use vacuum or atmospheric (non-vacuum) conditions.

[0140] 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 is not limited to optical lithography and may be used in other applications, for example imprint lithography, where the context permits.

[0141] Although specific reference may have been made above to the use of embodiments of the invention in the context of object inspection and optical lithography, it will be understood that the invention is not limited to these contexts and may, where the context permits, be used in other applications, for example imprint lithography.

[0142] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The foregoing description is intended to be illustrative, not limiting. Thus, it will be apparent to those skilled in the art that changes may be made to the invention as described without departing from the scope of the claims that follow.

[0143] Terms: (Item 1) An object holder configured to support an object, the object holder comprising: a core body having a plurality of burls having distal ends within a support surface for supporting the object; an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers; and a circumferential barrier for reducing the outflow of gas escaping from a space between the electrostatic sheet and the core body. (Item 2) The object holder according to item 1, wherein the circumferential barrier is positioned between the electrostatic sheet and the core body. (Item 3) An object holder according to item 1 or 2, wherein the circumferential barrier is formed by the electrostatic sheet. (Item 4) An object holder as described in item 2 or 3, further comprising a gap in one of the dielectric layers to allow the electrode to be connected to a power source, the gap being radially outward of the circumferential barrier. (Item 5) An object holder as described in any of the preceding items, wherein the electrostatic sheet further comprises at least one gas vent arranged radially outward of the crowbar and configured to allow gas to flow through the electrostatic sheet. (Item 6) An object holder as described in Item 5, wherein the gas vent has a radially inner edge that is radially inward of the edge of the object. (Item 7) An object holder as described in item 1, wherein the circumferential barrier is formed by the core body. (Item 8) An object holder as described in item 1, wherein the electrode penetrates the circumferential barrier and forms a terminal for allowing the electrode to be connected to a power source. (Item 9) An object holder according to any of the preceding items, comprising a high voltage connection wire extending through the core body to connect the electrode to a power source. (Item 10) An object holder according to any of the preceding items, wherein the electrode sheet is joined to the core body by a joining material. (Item 11) An object holder as described in Item 10, wherein the object-facing surface of the core body between the burls comprises an upper step portion on which the bonding material is provided, and a lower step portion adjacent to the upper step portion and vertically below the lower surface of the electrostatic sheet. (Item 12) The object holder according to item 11, wherein the upper portion has a smoother surface than the lower portion. (Item 13) An object holder according to any one of items 11 to 12, wherein the object-facing surface of the core body has a raised step portion surrounding the burl, and the raised step portion is raised relative to the lower step portion. (Item 14) The object holder according to any one of Items 11 to 13, wherein the upper portion is non-circular. (Item 15) An object holder according to any of the preceding items, wherein an electrically insulating bonding layer is sandwiched between dielectric layers, and / or the object holder is provided with multiple temperature sensors for detecting temperatures at multiple locations on the object holder. (Item 16) The object holder of item 15, wherein the bonding layer comprises a polymer. (Item 17) An object holder according to any one of items 15 to 16, wherein the bonding layer comprises benzocyclobutene. (Item 18) An object holder according to any one of items 15 to 17, wherein the bonding layer surrounds the electrode in the plane of the electrode so as to electrically insulate the electrode. (Item 19) The object holder according to any one of items 15 to 18, wherein the bonding layer is provided on only one of the two main surfaces of the electrode. (Item 20) An electrostatic sheet for an object holder configured to support an object, the electrostatic sheet comprising a hole for accommodating a burl of a core body for supporting the object, a dielectric layer, and an electrode sandwiched between the dielectric layers, the electrostatic sheet further comprising a circumferential barrier for reducing the outflow of gas escaping from the space between the electrostatic sheet and the core body. (Item 21) A method for manufacturing an electrostatic sheet for an object holder configured to support an object, the method comprising: applying an electrode to a dielectric layer; and bonding the dielectric layer to another dielectric layer so that the electrode is sandwiched between the dielectric layers, the electrostatic sheet comprising a circumferential barrier for reducing the outflow of gas escaping from a space between the electrostatic sheet and the object. (Item 22) The method of item 21, comprising patterning the electrodes before bonding the dielectric layers together. (Item 23) The method of any of items 21 to 22, wherein an electrically insulating bonding layer is applied to the other dielectric layers before bonding the dielectric layers together. (Item 24) A method according to any of items 21-23, comprising selectively irradiating the dielectric layers before bonding the dielectric layers together based on a desired position of a hole for accommodating a burl of the core body of the object holder, and removing material to form the hole after bonding the dielectric layers together based on the selective irradiation. (Item 25) The method of item 24, wherein the step of removing the material comprises selectively etching the irradiated portions of the dielectric layer. (Item 26) The method described in Item 25, wherein the step of selectively etching the irradiated portions of the dielectric layer is performed by applying a laser. (Item 27) A method according to any of items 24 to 26, wherein the step of removing the material comprises exposing the electrostatic sheet to an oxide plasma that removes the exposed portion of the bonding layer. (Item 28) A lithographic apparatus comprising an object holder according to any one of items 1 to 19. (Item 29) A lithography apparatus comprising the electrostatic sheet according to item 20.

Claims

1. 1. An object holder configured to support an object, the object holder comprising: a core body including a plurality of burls having distal ends within a support surface for supporting the object; an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers; a circumferential barrier for reducing the outflow of gas escaping from the space between the electrostatic sheet and the core; The circumferential barrier is an object holder positioned between the electrostatic sheet and the core.

2. The object holder of claim 1 , wherein the circumferential barrier is formed by the electrostatic sheet.

3. 3. An object holder as claimed in claim 1 or 2, further comprising a gap in one of the dielectric layers to allow the electrode to be connected to a power source, the gap being radially outward of the circumferential barrier.

4. An object holder configured to support an object, the object holder comprising: a core body including a plurality of burls having distal ends within a support surface for supporting the object; an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers; a circumferential barrier for reducing the outflow of gas escaping from the space between the electrostatic sheet and the core; the electrostatic sheet further comprising at least one gas vent disposed radially outward of the burl and configured to allow gas to flow through the electrostatic sheet.

5. 5. The object holder of claim 4, wherein the gas vent has a radially inner edge that is radially inward of an edge of the object.

6. An object holder configured to support an object, the object holder comprising: a core body including a plurality of burls having distal ends within a support surface for supporting the object; an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers; a circumferential barrier for reducing the outflow of gas escaping from the space between the electrostatic sheet and the core; the electrostatic sheet is joined to the core body by a joining material; The object-facing surface of the core body between the burls is an upper portion on which the bonding material is provided; a lower portion adjacent to the upper portion and vertically below the lower surface of the electrostatic sheet.

7. 7. The object holder according to claim 6, wherein the object-facing surface of the core body comprises a raised step portion surrounding the burl, the raised step portion being raised relative to the lower step portion.

8. an electrically insulating bonding layer sandwiched between said dielectric layers; and / or 8. The object holder of claim 1, wherein the object holder comprises a plurality of temperature sensors for detecting temperatures at a plurality of locations on the object holder.

9. The object holder of claim 8 , wherein the bonding layer comprises benzocyclobutene or solder.

10. 10. An object holder according to claim 8 or 9, wherein the bonding layer surrounds the electrode in the plane of the electrode so as to electrically insulate the electrode.

11. 1. An electrostatic sheet for an object holder configured to support an object, the electrostatic sheet comprising: a hole for receiving a burl of a core body for supporting the object; a dielectric layer; an electrode sandwiched between the dielectric layers; the electrostatic sheet further comprises a circumferential barrier for reducing the outflow of gas escaping from a space between the electrostatic sheet and the core; The electrostatic sheet further comprises at least one gas vent disposed radially outward of the crowbar and configured to allow gas to flow through the electrostatic sheet.

12. 1. A method of manufacturing an electrostatic sheet for an object holder configured to support an object, the method comprising: providing an electrode on the dielectric layer; bonding the dielectric layer to another dielectric layer such that the electrode is sandwiched between the dielectric layers; selectively irradiating the dielectric layers prior to bonding them together based on desired locations of holes for accommodating burrs in core bodies of the object holders; and removing material to form the hole after bonding the dielectric layers together based on the selective irradiation; the step of removing material comprises selectively etching the irradiated portions of the dielectric layer; The method of claim 1, wherein the electrostatic sheet comprises a circumferential barrier for reducing the outflow of gas escaping from a space between the electrostatic sheet and the object.

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