OBJECT HOLDER, TOOL, AND METHOD FOR MANUFACTURING OBJECT HOLDER - Patent application

Abstract

An object holder configured to support an object, comprising: a core body having a plurality of burls having distal ends in a support plane that supports the object; and an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers, the electrostatic sheet being bonded to the core body by a bonding material having a thickness of at least 100 nm.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[01] This application claims priority to European Application No. 20163373.2, filed March 16, 2020, which is incorporated herein by reference in its entirety.

[0002]

[02] The present invention relates to an object holder for 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 a tool for electrostatic sheet attachment and to a method for manufacturing the object holder. [Background technology]

[0003]

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

[0004]

[04] 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, can be used to form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, e.g., 193 nm.

[0005]

[05] In a conventional lithographic apparatus, the substrate to be exposed is supported by a substrate holder (i.e. an object that directly supports the substrate), which in turn is supported by a substrate table (an object such as a mirror block or stage, i.e. a table that supports the substrate holder and provides a top surface surrounding it). The substrate holder is often a flat inflexible disk whose size and shape corresponds to the substrate (but may have a different size or shape). The substrate holder has an array of protrusions, called burls or pimples, protruding from at least one face. The substrate holder may also have an array of protrusions on two opposing faces. 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 face 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 face of the substrate holder, the substrate is spaced apart from the body of the substrate holder. The purpose is to help prevent particles (i.e. contaminating particles such as dust particles) that may be present on the substrate table or substrate holder from distorting the substrate holder or substrate. Since the total surface area of ​​the burls is only a small fraction of the total area of ​​the substrate or substrate holder, it is highly likely that a particle will be located between the burls and its presence will have no effect. Often the substrate holder and substrate are received in a recess in the substrate table such that the top surface of the substrate is flush with the top surface of the substrate table.

[0006]

[06] Due to the high accelerations experienced by the substrate during use of a high throughput lithographic apparatus, it is not sufficient to simply allow the substrate to rest on the burls of the substrate holder. The substrate is clamped in place. Two methods of clamping the 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, so that the substrate is held in place by the higher pressure of the 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, e.g. for extreme ultraviolet (EUV) radiation lithography. In this case, it may not be possible to generate a sufficiently large pressure difference across the substrate (or substrate holder). Therefore, electrostatic clamping may be used. In electrostatic clamping, a potential difference is established between an electrode plated on the substrate, or on its lower surface, and an electrode provided on or in the substrate table and / or substrate holder. The two electrodes act like a large capacitor and a reasonable potential difference can generate a substantial clamping force. An electrostatic arrangement can be such that a pair of electrodes, one on the substrate table and one on the substrate, clamps the entire stack of substrate table, substrate holder and substrate together. In a known arrangement, one or more electrodes can be provided on or in the substrate holder such that the substrate holder is clamped to the substrate table and the substrate is clamped separately to the substrate holder.

[0007]

[07] There is a need for an improved substrate holder comprising one or more electrostatic clamps for clamping the substrate to a substrate table and / or a substrate to the substrate holder, or more generally an object holder such as a patterning device holder comprising one or more electrostatic clamps for holding the object holder to a table and / or holding an object relative to the object holder. Summary of the Invention

[0008]

[08] 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 comprising a plurality of burls having distal ends in a support plane for supporting an object, and an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers, the electrostatic sheet being bonded to the core body by a bonding material having a thickness of at least 100 nm.

[0009]

[09] According to a second aspect of the present invention, there is provided a tool for mounting an electrostatic sheet comprising electrodes sandwiched between dielectric layers to a core body comprising a plurality of burls having distal ends in a support plane for supporting an object, the tool comprising a plate comprising a plurality of recesses for each of the burls, the plate being configured to couple to the electrostatic sheet such that the recesses align with respective holes in the electrostatic sheet.

[0010]

[0010] According to a third aspect of the present invention, there is provided a method of manufacturing an object holder comprising: providing a core body comprising a plurality of burls having distal ends in a support plane for supporting an object; coupling an electrostatic sheet to a plate comprising a plurality of recesses for each burl such that the recesses align with respective holes in the electrostatic sheet, the electrostatic sheet comprising electrodes sandwiched between dielectric layers; and controlling movement of the plate to attach the electrostatic sheet to the core body between the burls as the electrostatic sheet is coupled, the depth of the recesses determining the height to which the electrostatic sheet is attached. [Brief description of the drawings]

[0011]

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

[0012] [Figure 1]

[0012] There is depicted a lithography system comprising a lithographic apparatus and a radiation source. [Diagram 2]

[0013] 1 is a cross-sectional view of an object holder according to one embodiment of the present invention. [Diagram 3]

[0014] 1A-1D are cross-sectional views relating to different stages in a method for manufacturing an object holder according to an embodiment of the invention; [Figure 4]

[0014] Figures 1A-1C are cross-sectional views relating to different stages in a method for manufacturing an object holder according to one embodiment of the present invention. [Diagram 5]

[0014] Figures 1A-1C are cross-sectional views relating to different stages in a method for manufacturing an object holder according to one embodiment of the present invention. [Figure 6]

[0015] 1 is a close-up view of a portion of an object holder according to one embodiment of the present invention. [Figure 7]

[0016] 11 is a diagram illustrating the variation of burrs at different positions on a core body of an object holder according to one embodiment of the present invention. [Figure 8]

[0017] 1 is a close-up view of a portion of an object holder according to one embodiment of the present invention. [Figure 9]

[0018] FIG. 9 is an enlarged view of a portion of the object holder shown in FIG. 8. [Figure 10]

[0019] 13 is a close-up view of a portion of an object holder according to an alternative embodiment of the present invention. [Figure 11]

[0019] FIG. 1 is a close-up view of a portion of an object holder according to an alternative embodiment of the present invention. [Figure 12]

[0020] 11A-11C illustrate schematic diagrams of various possible positions of an electrostatic shield on an electrostatic sheet of an object holder according to an embodiment of the present invention; [Figure 13]

[0021] 13A-13C are close-up views of alternative configurations of object holders according to one embodiment of the present invention. [Figure 14]

[0021] FIG. 1 is a close-up view of an alternative configuration of an object holder according to one embodiment of the present invention. [Figure 15]

[0021] FIG. 1 is a close-up view of an alternative configuration of an object holder according to one embodiment of the present invention. [Figure 16]

[0021] FIG. 1 is a close-up view of an alternative configuration of an object holder according to one embodiment of the present invention. [Figure 17]

[0021] FIG. 1 is a close-up view of an alternative configuration of an object holder according to one embodiment of the present invention. [Figure 18]

[0022] FIG. 2 is a plan view of a connection between electrostatic shields of an electrostatic sheet of an object holder according to one embodiment of the present invention. [Figure 19]

[0021] FIG. 1 is a close-up view of an alternative configuration of an object holder according to one embodiment of the present invention.

[0013]

[0023] While the invention is susceptible to various modifications and alternative forms, specific embodiments have been 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, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014]

[0024] 1 shows a lithography system comprising a radiation source SO and a lithographic apparatus LA. The 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.

[0015]

[0025] 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 an EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0016]

[0026] After being so conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. 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 number 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', thus forming an image with smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4 or 8 may be applied. Although the projection system PS is shown in FIG. 1 as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (for example 6 or 8 mirrors).

[0017]

[0027] The substrate W may include a previously formed pattern. In such a case, the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the previously formed pattern on the substrate W.

[0018]

[0028] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the source SO, in the illumination system IL and / or in the projection system PS.

[0019]

[0029] 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 generating EUV radiation.

[0020]

[0030] 2 is a cross-sectional view of an object holder 20 according to an embodiment of the invention. The object holder 20 is configured to support an object. In the following description, the invention is described in the context of the object holder being a substrate holder 20 configured to support a substrate W, although 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.

[0021]

[0031] In one 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 arranged to hold the substrate W relative to the substrate stage of the substrate table WT.

[0022]

[0032] As shown in FIG. 2, in one embodiment, the substrate holder 20 includes a core body 21. The core body 21 is a plate-like disk. As shown in FIG. 2, in one embodiment, the core body 21 includes a plurality of burls 22. The burls 22 are protrusions protruding 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 plane 24 that supports the substrate W. The lower surface of the substrate W contacts the distal ends 23 of the burls 22. The position of the lower surface of the substrate W corresponds to the support plane 24. The burls 22 are arranged such that the substrate W is placed approximately flat on the substrate holder 20.

[0023]

[0033] The burls 22 are not shown to scale in FIG. 2. In a practical embodiment, hundreds, thousands or tens of thousands of burls may be distributed over a substrate holder 20 having a diameter of, for example, 200 mm, 300 mm or 450 mm. The tips of the burls 22 have a small area, for example less than 1 mm2, so that the total area of ​​all the burls 22 on one side of the substrate holder 20 is less than about 10% of the total area of ​​the total surface area of ​​the substrate holder 20. Due to the arrangement of the burls 22, particles that may be on the surface of the substrate W, the substrate holder 20 or the substrate table WT will likely fall between the burls 22 and thus not result in deformation of the substrate W or the substrate holder 20. The arrangement of the burls, which may form a pattern, may be regular or may vary as desired to provide an appropriate distribution of forces on the substrate W and the substrate table WT. The burls 22 may have any shape in plan, but are typically circular in plan. The burls 22 may have the same shape and dimensions throughout their height, but are typically tapered. The burls 22 may protrude above the remaining object-facing surface of the substrate holder 20 (i.e., the upper surface of the electrostatic sheet 25) a distance of about 1 μm to about 5 mm, desirably about 5 μm to about 250 μm, desirably about 10 μm. Thus, 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, desirably about 5 μm to about 250 μm, desirably about 10 μm. The thickness of the core body 21 of the substrate holder 20 may be in the range of about 1 mm to about 50 mm, desirably in the range of about 5 mm to 20 mm, typically 10 mm.

[0024]

[0034] The core body 21 may be made of a rigid material. Preferably, the material has a high thermal conductivity or a low coefficient of thermal expansion. Preferably, the material is electrically conductive. Preferably, the material has a high hardness. Suitable materials include SiC (silicon carbide), Si3N4 (silicon nitride), quartz, and / or various other ceramics and glass-ceramics, such as Zerodur™ glass-ceramics. The core body 21 may be fabricated by selectively removing material from a solid disk of the material to leave protruding burls 22. Suitable techniques for removing material include electrical discharge machining (EDM), etching, machining, and / or laser ablation. The core body 21 may also be fabricated by growing burls 22 through a mask. The burls 22 may be of the same material as the base and may be grown by physical vapor deposition processing or sputtering. In one embodiment, the core body 21 comprises one or more internal channels (not shown in the figures). In one embodiment, the core body 21 comprises multiple layers bonded together. In one embodiment, the layers are formed of different materials. By way of example only, in one embodiment, the core body 21 comprises a layer of SiSiC, a layer of glass, and another layer of SiSiC, in that order. Other combinations of layers are possible.

[0025]

[0035] As shown in FIG. 2, in one embodiment, the substrate holder 20 comprises one or more electrodes 26 for electrostatic clamping. To provide an electrostatic clamping force, a potential difference may be generated between the substrate W and the substrate holder 20 and / or between the substrate holder 20 and the substrate stage of the substrate table WT. In one embodiment, the electrodes 26 are enclosed between dielectric layers (also known as electrical isolation layers) 27, 28. The generated potential difference may be on the order of 10 to 5,000 volts. An arrangement for locally controlling the temperature of the substrate using one or more heaters and temperature sensors is described in US Publication No. 2011-0222033, which is incorporated herein by reference in its entirety and the techniques described therein may be applied to the techniques described herein.

[0026]

[0036] As shown in FIG. 2, in one embodiment, the substrate holder 20 comprises an electrostatic sheet 25. The electrostatic sheet 25 comprises one or more electrodes 26. For the electrodes 26, in one embodiment, two halves of a continuous metal film (but separated from the distal ends 23 of the burls 22) may be deposited to form the positive and negative elements of the electrostatic clamp, spaced apart from each other at a separation distance. 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, and optionally at least about 500 μm. In one embodiment, the separation distance is at most about 2 mm, optionally at most about 1 mm, and optionally at most about 500 μm. In one embodiment, the separation distance is about 500 μm. Thus, there may be two electrodes 26. However, the number of electrodes 26 in electrostatic sheet 25 is not particularly limited and may be one, three, or more. The metal lines of electrodes 26 may have a layer thickness of greater than about 20 nm, desirably greater than about 40 nm. The metal lines desirably have a layer thickness of about 1 μm or less, desirably less than about 500 nm, desirably less than about 200 nm.

[0027]

[0037] The electrode 26 of the upper electrostatic sheet 25 may be configured to electrostatically clamp the substrate W to the substrate holder 20. The electrode 26 of the lower electrostatic sheet 25 may be configured to electrostatically clamp the substrate holder 20 to the remaining substrate table WT.

[0028]

[0038] In one embodiment, the material of the core body 21 and the burls 22 is electrically conductive. For example, in one embodiment, 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 is electrically conductive. In one embodiment, a ground layer may be provided that electrically grounds or electrically connects the distal ends 23 of two or more of the burls 22 (optionally all of the burls 22) to a common potential. The ground layer may be formed by depositing a relatively thick layer of a conductive material. The conductive material is not particularly limited. In one embodiment, the conductive material is Cr. In an alternative embodiment, the conductive material is CrN. In one embodiment, the deposited layer is then patterned to form the ground layer. The pattern may comprise a series of metal lines that connect the distal ends 23 of the burls 22. Such a pattern may be referred to as a "Manhattan" pattern. In an alternative embodiment, the deposited layer is not patterned. In one embodiment, a ground layer or another layer is disposed over the surface of the core body 21 and / or the burls 22. The ground layer or another layer may help to smooth the surface to make it easier to clean.

[0029]

[0039] As shown in FIG. 2, in one embodiment, the electrostatic sheet 25 comprises an electrode 26 sandwiched between the dielectric layers 27, 28. As shown in FIG. 2, in one embodiment, the burls 22 and the electrostatic sheet 25 are provided on both major surfaces of the substrate holder 20. In an alternative 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 between the burls 22. For example, as shown in FIG. 2, the electrostatic sheet 25 is provided with holes 34. The holes 34 are arranged such that their positions correspond to the burls 22 of the core body 21. The burls 22 protrude through the respective holes 34 of the electrostatic sheet 25 such that the electrode 26 sandwiched between the dielectric layers 27, 28 is provided in the area between the burls 22.

[0030]

[0040] As shown in FIG. 2, in one embodiment, the substrate holder 20 comprises a bonding material 29. In one embodiment, the bonding material has a thickness of at least 100 nm. The bonding material 29 fixes the position of the electrostatic sheet 25 relative to the core body 21. The bonding material 29 keeps the holes 34 of the electrostatic sheet 25 aligned with the burls 22. In one embodiment, the burls 22 are positioned in the center of each hole 34 of the electrostatic sheet 25. By specifying that the bonding material 29 has a thickness of at least 100 nm, a minimum level of compliance of the bonding layer is ensured. Generally, the thicker the bonding material, the more compliant it is and the less susceptible it is to stress levels caused by temperature differences at the interface between the core body 21 and the electrostatic sheet 25. In one embodiment, the bonding material 29 has a thickness of at least 200 nm, optionally at least 500 nm, optionally at least 1 μm, optionally at least 2 μm, optionally at least 5 μm, optionally at least 10 μm, optionally at least 20 μm, optionally at least 25 μm, and optionally at least 50 μm. The inventors have found that a thickness of the bonding material 29 of at least 25 μm improves the tolerance of the interface parts to temperature differences (i.e., the bonding layer is more compliant). In one embodiment, the bonding material 29 has a thickness of at most 100 μm. This ensures a minimum level of stability of the bonding material 29, which is beneficial for the electrostatic performance of the clamping function. In one embodiment, the bonding material 29 has a thickness of at most 75 μm, optionally at most 50 μm. Reducing the thickness of the bonding material 29 helps to make the bonding material 29 more stable. By way of example only, in one embodiment, bonding material 29 has a thickness in the range of about 25 μm to about 75 μm.

[0031]

[0041] As shown in FIG. 2, in one embodiment, 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 one embodiment, the separate portions of the bonding material 29 have substantially the same thickness as one another. As shown in FIG. 10, in an alternative embodiment, the bonding material 29 extends continuously to the area between the core body 21 and the electrostatic sheet 25. As shown in FIG. 10, in one embodiment, the bonding material 29 extends to the area between the electrostatic sheet 25 and the burl 22.

[0032]

[0042] Figures 3 to 5 show diagrammatically successive stages of the process of manufacturing the substrate holder 20. In particular, Figures 3 to 5 show the stage of bonding the electrostatic sheet 25 to the core body 21.

[0033]

[0043] As shown in FIG. 3, in one embodiment, a method of manufacturing a substrate holder 20 comprises providing a core body 21. The core body 21 comprises a plurality of burls 22 for supporting a substrate W. As shown in FIG. 3, in one embodiment, the method comprises applying a bonding material 29 to the core body 21. The bonding material 29 is applied to at least one of the major surfaces of the core body 21. The bonding material 29 is applied between the burls 22. As shown in FIG. 3, in one embodiment, a plurality of separate portions of the bonding material 29 are applied to the core body 21. In an alternative embodiment, the bonding material 29 is applied substantially continuously across the major surfaces of the core body 21 between the burls 22. The method of distributing the bonding material 29 is not particularly limited. By providing a plurality of separate portions of the bonding material 29, the overall volume of the bonding material 29 can be reduced. This reduces the possibility of excess bonding material 29 being present near the burls 22, which may adversely affect the clamping function of the substrate holder 20.

[0034]

[0044] As shown in FIG. 4 , in one embodiment, the method comprises coupling the electrostatic sheet 25 to a plate 30 of the tool. The plate 30 comprises a plurality of recesses 31 for each of the burls 22 of the core body 21. The recesses 31 align with respective holes 34 of the electrostatic sheet 25. In one embodiment, the centers of the recesses 31 are aligned with the centers of the holes 34 of the electrostatic sheet 25. The plate 30 is configured such that the pattern of the recesses 31 corresponds to the pattern of the burls 22 of the core body 21. Thus, the disclosure above regarding the number and positioning of the burls 22 applies equally to the number and positioning of the recesses 31 of the plate 30 and the holes 34 of the electrostatic sheet 25. In one embodiment, the plate 30 has a maximum of 10 recesses 31 in a direction perpendicular to the plane of the plate 30. 5 Nm -1 The plate 30 is compliantly configured to accommodate variations in the height of the burls 22.

[0035]

[0045] The manner in which the plate 30 is coupled to the electrostatic sheet 25 is not particularly limited. For example, the coupling between the plate 30 and the electrostatic sheet 25 may be by vacuum and / or electrostatic adhesion and / or temporary bonding. In one embodiment, the plate 30 is positioned relative to the core body 21, for example, using a positioner. The positioner is configured to control the movement of the plate 30 when the electrostatic sheet 25 is coupled. The positioner positions the plate 30 relative to the core body 21 such that the recesses 31 of the plate 30 (and therefore the holes 34 of the electrostatic sheet 25) are aligned with the burls 22 of the core body 21.

[0036]

[0046] The positioner is configured to control the movement of the plate 30 to attach the electrostatic sheet 25 to the core body 21 between the burls 22. For example, the positioner may lower the plate 30 downward onto the core body 21. In an alternative embodiment, the positioner is configured to move the core body 21 upward toward the plate 30 such that the burls 22 extend through the holes 34 in the electrostatic sheet 25.

[0037]

[0047] During the attachment process, the distal ends 23 of the burls 22 contact the bottom of the recesses 31, which stops the electrostatic sheet 25 and the core body 21 from getting closer to each other. The depth of the recesses 31 determines the height to which the electrostatic sheet 25 is attached. The depth of the recesses 31 controls the distance between the bottom of the electrostatic sheet 25 and the top surface of the core body 21 (where the bonding material 29 is disposed). The depth of the recesses 31 controls the height to which the burls 22 protrude above the top surface of the electrostatic sheet 25 in the manufactured substrate holder 20.

[0038]

[0048] In one embodiment, the recess 31 has a depth corresponding to the above-mentioned protruding distance of the burr 22. For example, the recess 31 has a depth of about 1 μm to about 5 mm, desirably about 5 μm to about 250 μm.

[0039]

[0049] In one embodiment, the method of manufacturing the substrate holder 20 includes curing the bonding material 29. In one embodiment, the bonding material 29 is cured under vacuum. This helps to avoid inclusions in the bonding material 29, although it is not essential that the bonding material 29 be cured. In an alternative embodiment, the bonding material 29 does not need to be cured.

[0040]

[0050] The type of bonding material used is not particularly limited. In one embodiment, bonding material 29 comprises an adhesive material, although it is not required that bonding material 29 be an adhesive material. Non-adhesive materials can also be used. For example, in an alternative embodiment, bonding material 29 is a material used in soldering or welding electrostatic sheet 25 to core body 21.

[0041]

[0051] FIG. 5 shows diagrammatically the moment when the distal end 23 of the crowbar 22 abuts against the bottom of the recess 31 .

[0042]

[0052] In one embodiment, the bonding material 29 secures the electrostatic sheet 25 to the core body 21 at a height defined by the recess 31 in the plate 30. In one embodiment, the method comprises separating the plate 30 from the electrostatic sheet 25. As shown in Figure 2, in one embodiment, an electrostatic sheet 25 is provided on each side of the core body 21. The method steps described above may be repeated for the opposite side of the core body 21 such that an electrostatic sheet 25 is provided on both surfaces of the core body 21.

[0043]

[0053] In one embodiment, at least one of the burls 22 is at most 10 mm in a direction in the support plane 24 at the distal end 23. 7 Nm -1 In normal use of the substrate holder 20, the direction in the support plane 24 is horizontal. The stiffness in the direction in the support plane 24 may be referred to as the horizontal stiffness. The horizontal stiffness refers to the amount of force that needs to be applied to the distal end 23 of the burl 22 to move the distal end 23 horizontally. For example, 7 Nm -1 A horizontal stiffness of 10 means that a force of 10 N applied horizontally at the distal end 23 will move the distal end 23 horizontally 1 μm. 7 Nm -1 By specifying that the burls 22 extend through the holes 34 in the electrostatic sheet 25, the burls 22 are longer (vertically) than the thickness of the electrostatic sheet 25. By providing longer burls 22, the horizontal stiffness of the burls 22 can be reduced. In one embodiment, most of the burls 22 are at most 10 7 Nm -1 In one embodiment, the majority of the burr 22 has a stiffness of at most 10 in a direction in the support plane 24 at the distal end 23. 7 Nm -1The horizontal stiffness of the burls 22 can be controlled by selecting the length of the burls 22. Additionally or alternatively, the horizontal stiffness of the burls 22 can be controlled by selecting the width (i.e., perimeter) of the burls 22.

[0044]

[0054] By reducing the horizontal stiffness of the burls 22, the burls 22 become more flexible in the direction of thermal expansion of the substrate W during exposure. During the exposure process, the substrate W is heated by radiation. Heating of the substrate W causes it to expand locally. The amount of expansion varies across the substrate W. The expansion of the substrate W may cause parts of the underside of the substrate W to slip relative to the distal ends 23 of some of the burls 22. Such slippage may cause undesirable overlay errors, which may be difficult to predict (and therefore difficult to compensate). By reducing the horizontal stiffness of the burls 22, the possibility of slippage of the substrate W relative to the burls 22 is reduced. The expansion of the substrate W exerts a horizontal force on the distal ends 23 of the burls 22. The burls 22 may bend to maintain contact with the substrate W. The burls 22 may act as cantilevers.

[0045]

[0055] In one embodiment, at least one (or most or all) of the burls 22 have a maximum of 7×10 6 Nm -1 , optionally up to 5×10 6 Nm -1 , optionally up to 3×10 6 Nm -1 , optionally up to 2×10 6 Nm -1 , and optionally up to 10 6 Nm -1 By reducing the horizontal stiffness of the burls 22, the variation in contact stiffness of the burls 22 across the substrate holder 22 is advantageously reduced.

[0046]

[0056] In one embodiment, at least one (or most or all) of the burls 22 has at least 10 mm diameter at the distal end 23. 5Nm -1 , optionally at least 2×10 5 Nm -1 , optionally at least 5×10 5 Nm -1 and optionally at least 10 6 Nm -1 This provides the crowbar 22 with a minimum of robustness.

[0047]

[0057] In one embodiment, the core body 21 including the burls 22 is made of a material having a high Young's modulus. For example, SiSiC has a high Young's modulus. In one embodiment, the burls 22 have a modulus of at least 10 7 Nm -1 , optionally at least 2×10 7 Nm -1 , and optionally at least 3×10 7 Nm -1 For example, the vertical stiffness is about 3.4×10 7 Nm -1 By increasing the vertical stiffness, the focusing performance can be improved.

[0048]

[0058] There is no particular limitation on the method of manufacturing the core body 21 including the burls 22. For example, laser ablation, electric discharge machining, and / or powder jet machining may be used to produce the burls 22.

[0049]

[0059] FIG. 6 is a close-up view of a portion of a substrate holder 20 according to an embodiment of the present invention. As shown in FIG. 6, in one embodiment, at least one of the burls 22 is surrounded by a trench 35. The trench 35 is formed in the object-facing surface 37 of the core body 21. In one embodiment, the burls 22 are directly surrounded by the trench 35. By providing the trench 35, the length of the burls 22 is increased without having to increase the thickness of the electrostatic sheet 25 or the height that the distal ends 23 of the burls 22 protrude above the upper surface of the electrostatic sheet 25. By increasing the length of the burls 22, the horizontal stiffness of the burls 22 can be reduced. The length of the burls 22 is the vertical distance between the distal ends 23 and the trench floor 36. The depth of the trench 35 is the vertical distance between the trench floor 36 and the object-facing surface 37 of the core body 21. The object-facing surface 37 of the core body 21 is the surface on which the bonding material 29 is disposed.

[0050]

[0060] The diameter of the distal end 23 of the burl 22 is not particularly limited. In one embodiment, the diameter of the distal end 23 is at least 100 μm, optionally at least 200 μm. In one embodiment, the diameter at the distal end 23 is at most 500 μm. For example, in one embodiment, the diameter at the distal end 23 is about 210 μm. The length of the burl 22 is not particularly limited. In one embodiment, the length of the burl 22 is at least 200 μm, optionally at least 500 μm, and optionally at least 1000 μm. In one embodiment, the length of the burl 22 is at most 2000 μm, optionally at most 1000 μm. For example, in one embodiment, the burl 22 not surrounded by the trench 35 has a length of about 560 μm. In one embodiment, the burl 22 surrounded by the trench 35 has a length of about 1000 μm. In one embodiment, the core body 21 comprises at least one burl 22 surrounded by a trench 35 and at least one burl 22 not surrounded by such a trench. There may be a mixture of burls 22 surrounded by a trench 35 and burls 22 not surrounded by a trench.

[0051]

[0061]

[0062] FIG. 7 is a schematic diagram illustrating how the horizontal stiffness of the burls 22 may vary depending on their position on the substrate holder 20. In one embodiment, at least one of the burls 22c in the peripheral region of the substrate holder 20 has a lower horizontal stiffness than at least one of the burls 22a in the central region of the substrate holder 20. In one embodiment, the horizontal stiffness of the burls 22 gradually increases in the radial direction away from the center of the substrate holder 20. As mentioned above, there are various ways to control the horizontal stiffness of the burls 22. FIG. 7 illustrates diagrammatically that the horizontal stiffness is varied by varying the length of the burls 22. For example, as shown in FIG. 7, in one embodiment, the length H of the burls 22 increases as the distance R from the center of the substrate holder 20 increases. Additionally or alternatively, the depth of the trench 35 surrounding the burls 22 may increase as the distance R from the center of the substrate holder 20 increases. Additionally or alternatively, the width of the burls 22 may decrease as the distance R increases from the center of the substrate holder 20. As shown in Figure 7, in one embodiment, the intermediate burls 22b may have an intermediate height that is less than the height of the peripheral burls 22c and greater than the length of the central burls 22a.

[0052]

[0063] When the substrate W expands relative to the core body 21, the relative movement of the substrate W varies depending on the radial position of the substrate W. In general, it can be expected that the relative movement between the substrate W and the core body 21 will be greatest at the periphery of the substrate holder 20 and least at the center. This means that the risk of the substrate W slipping relative to the distal ends 23 of the burls 22 is greater in the peripheral regions of the substrate holder 20. By varying the horizontal stiffness of the burls 22 depending on the radial position, the burls 22 can be made flexible as required for that position. This makes it possible to balance the benefits of flexible burls with the manufacturing complexity of the core body 21. For example, it may be more difficult to manufacture a burl 22 with a lower horizontal thickness. The manufacturing complexity of the core body 21 may be increased and there may also be a need to reduce the possibility of slipping between the substrate W and the substrate holder 20.

[0053]

[0064]

[0065] FIG. 8 is a close-up view of a portion of the substrate holder 20 according to an embodiment of the present invention. As shown in FIG. 8, in one 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 a radially outer surface 41 (shown in FIG. 9) of at least one of the burls 22 and the electrostatic sheet 25 through a vertical gap 40 between the core body 21 and the electrostatic sheet 25. FIG. 9 is a close-up view of the radial gap 39 between the radially outer surface 41 of the burl 22 and a wall 42 of the electrostatic sheet 25 that defines the hole 34 in the electrostatic sheet 25. In FIGS. 8 and 9, the double-headed arrows represent gas flow.

[0054]

[0066] In one embodiment, the substrate holder 20 comprises a thermal regulator configured to thermally regulate the substrate W. The thermal regulator can be used to control the temperature of the substrate W, for example, during an exposure process. In one embodiment, the thermal regulator comprises a circuit through which a thermal regulation fluid flows. In one embodiment, the thermal regulator comprises a heater and a sensor that are controlled to control a thermal regulation function.

[0055]

[0067] By providing a gas supply passage 38, gas can be supplied between the substrate W and the substrate holder 20 to enhance heat transfer between the substrate holder 20 and the substrate W. This helps to control the temperature of the substrate W. As shown in FIG. 8, gas is supplied through the gas supply passage 38 directly below the electrostatic sheet 25. The gas supply passage 38 terminates in an opening in the object-facing surface 37 of the core body 21 directly below the electrostatic sheet 25. The gas flows through the vertical gap 40 between the core body 21 and the electrostatic sheet 25 and reaches the radial gap 39. The gas then fills the gap between the substrate W and the upper surface of the electrostatic sheet 25, thereby enhancing the heat transfer between the substrate W and the substrate holder 20.

[0056]

[0068] By providing the gas supply passage 38 directly under the electrostatic sheet 25, the flatness of the substrate W can be improved. This is because the gas passage between the core body 21 and the lower dielectric layer 27 of the electrostatic sheet 25 allows the gas to reach under the substrate W without needing a hole at that location in the electrostatic sheet 25. By not having a hole in the electrostatic sheet 25, it is unnecessary to have a hole in the high voltage electrode 26. By not having a hole in the high voltage electrode 26, it is unnecessary to have a ground layer at the hole to shield the electrode 26. By not having a hole in the high voltage electrode 26, there is no local reduction in electrostatic clamping force that would reduce flatness. The electrostatic sheet 25 is positioned between the gas supply passage 38 and the substrate W. In one embodiment, multiple such gas supply passages 38 are provided across the core body 21. There is no particular limit to the location and number of the gas supply passages 38. One embodiment of the present invention is expected to improve the uniformity of the pressure under the substrate W without excessively reducing the flatness of the substrate W. The vertical gap 40 is present in the area between the portions of the bonding material 29. By increasing the uniformity of the pressure under the substrate W, the average pressure can be reduced without unduly increasing the likelihood of excessively low pressure under some parts of the substrate W. By reducing the average pressure under the substrate W, the effective clamping force holding the substrate W to the substrate holder 20 is increased. The gas release time can be reduced. The type of gas used is not particularly limited. In one embodiment, the gas comprises hydrogen. In one embodiment, the electrostatic sheet 25 comprises holes directly vertically above the gas supply passages 38.

[0057]

[0069] FIG. 10 is a close-up view of a portion of the substrate holder 20 according to an embodiment of the present invention. As shown in FIG. 10, in one embodiment, the bonding material 29 substantially fills the area between the lower surface of the electrostatic sheet 25 and the facing surface of the core body 21. As shown in FIG. 10, in one embodiment, the bonding material 29 substantially covers the object-facing surface 37 of the core body 21 below the electrostatic sheet 25. As shown in FIG. 10, in one embodiment, the bonding material 29 surrounds the burls 22. As shown in FIG. 10, in one embodiment, the bonding material 29 has an upper surface that is lower than the upper surface of the electrostatic sheet 25. In an alternative embodiment, the upper surface of the bonding material 29 is substantially flush with the upper surface of the electrostatic sheet 25. The embodiment shown in FIG. 10 is in contrast to the other embodiments described above in which the bonding material 29 is provided in sparse locations (rather than the entirety of the electrostatic sheet 25).

[0058]

[0070] In one embodiment, the electrode 26 is connected to a high voltage potential (e.g., about 3200 kV). The electric field generated between the substrate W and the electrostatic sheet 25 results in an electrostatic adhesion force between the substrate holder 20 and the substrate W. In one embodiment, the core body 26 and its burls 22 are electrically grounded (or held at another controlled potential). An electric field exists in the region between the electrostatic sheet 25 and the burls 22, as well as in the region between the electrostatic sheet 25 and the core body 21. An electric field exists in the bonding material 29.

[0059]

[0071] 10, in one embodiment, the electrostatic sheet 25 includes an electrical insulator 44. The electrical insulator 44 is non-conductive and acts as a high voltage barrier. The electrical insulator 44 surrounds the electrode 26 in the plane of the electrode 26. The electrical insulator 44 reduces the possibility of electrical breakdown between the electrode 26 and the crowbar 22.

[0060]

[0072] Charges can flow through the electrical insulator 44, which can undesirably affect the clamping force when the electrode 26 is at a high voltage. Charge flow can also undesirably lead to a residual clamping force when the substrate holder 20 is not used to clamp a substrate W. In an embodiment where the bonding material 29 is on the entire surface of the electrostatic sheet 25 (e.g., as shown in FIG. 10), the surface conductivity of the bonding material 29 can undesirably affect the electrostatic field and the clamping force.

[0061]

[0073] FIG. 11 is a close-up view of a portion of the substrate holder 20 according to an embodiment of the present invention. The arrows represent the electric field. As shown in FIG. 11, in one embodiment, the electrostatic sheet 25 comprises an electrostatic shield 45. The electrostatic shield 45 is configured to separate the electrostatic sheet 25 from other components. In one embodiment, the electrostatic shield 45 is configured to shield the charge of the electrical insulator 44 from the substrate W and / or from the remaining core body 21 and the burls 22. The electrostatic shield 45 may be provided at one or more different locations around the electrostatic sheet 25. In one embodiment, the electrostatic shield 45 comprises a conductive plating on the surface of the electrostatic sheet 25. In one embodiment, the electrostatic shield 45 is applied by chemical vapor deposition. In one embodiment, the electrostatic shield 45 is applied by sputtering. In one embodiment, the electrostatic shield 45 is applied by physical vapor deposition. In one embodiment, 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 one embodiment, 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 one embodiment, the thickness of electrostatic shield 45 may be different for different areas of the electrostatic shield.

[0062]

[0074] FIG. 12 is a schematic cross-sectional view of a portion of the electrostatic sheet 25 according to an embodiment of the present invention. As shown in FIG. 12, in one embodiment, the electrostatic sheet 25 comprises an electrostatic shield 45a on a major surface of the electrostatic sheet 25 facing the core body 21. In the example shown in FIG. 11, this is the bottom surface of the electrostatic sheet 25. The electrostatic shield 45a is configured to separate the electrode 26 from the object-facing surface 37 of the core body 21. In one embodiment, the electrostatic shield 45a covers substantially the entire bottom surface of the electrostatic sheet 25. However, this is not necessarily the case. In an alternative embodiment, the electrostatic shield 45a covers only a portion of the bottom surface of the electrostatic sheet 25.

[0063]

[0075] As shown in FIG. 12, in one embodiment, the electrostatic sheet 25 comprises an electrostatic shield 45b on a hole-defining surface of the electrostatic sheet 25. The electrostatic shield 45b is configured to separate the electrostatic sheet 25 from the radially outer surface 41 of at least one of the burls 22. As shown in FIG. 12, in one embodiment, the electrostatic sheet 25 comprises an electrostatic shield 45c on a major surface of the electrostatic sheet 25 facing away from the core body 21. In the example shown in FIG. 11, this is the upper surface of the electrostatic sheet 25. The electrostatic shield 45c is configured to at least partially separate the electrostatic sheet 25 from a region of the substrate W vertically above the electrical insulator 44. In one embodiment, the electrostatic shield is electrically grounded (or held at another controlled potential). The electrostatic shield 45 can be present in several locations. In one embodiment, the electrostatic shield 45c is provided as a ring on the electrostatic sheet 25 around the hole 34 in the electrostatic sheet 25. In one embodiment, different sections 45a, 45b, 45c of the electrostatic shield have different thicknesses.

[0064]

[0076] For example, in one embodiment, the holes 34 in the electrostatic sheet 25 are substantially cylindrical, as shown in FIG. 11 . However, this is not necessarily the case. FIGS. 13 to 17 are schematic diagrams of alternative embodiments in which the holes 34 are not perfectly cylindrical. For example, as shown in FIG. 13 , in one embodiment, the holes 34 are hourglass shaped. This may be easier to manufacture, especially if powder jet machining is used to shape the dielectric layers 27, 28. In one embodiment, the electrostatic sheet 25 includes an upper dielectric layer 28 between the electrode 26 and the substrate W. The upper dielectric layer 28 tapers toward the substrate W. That is, the holes 34 increase in diameter toward the substrate W through the thickness of the upper dielectric layer 28. As shown in FIG. 13 , in one embodiment, the electrostatic sheet 25 includes a lower dielectric layer 27. The lower dielectric layer 27 is between the electrode 26 and the core body 21. In one embodiment, the lower dielectric layer tapers toward the core body 21. That is, the diameter of the hole 34 increases toward the core body 21 through the thickness of the lower dielectric layer 27. An embodiment of the present invention with hourglass-shaped walls 34 is expected to be easier to manufacture. In FIG. 13, both the upper and lower dielectric layers 28 and 27 are tapered. In an alternative embodiment, only one of the two dielectric layers 27 and 28 is tapered. In FIG. 13, the dielectric layers 27 and 28 are tapered from both sides of the electrostatic sheet 25. As shown in FIG. 19, in an alternative embodiment, the electrostatic sheet 25 is tapered from only one side. For example, both the upper and lower dielectric layers 28 and 27 may be tapered toward the substrate W. Alternatively, both the upper and lower dielectric layers 28 and 27 may be tapered toward the core body 21. In an embodiment, the hole 34 is formed in the electrostatic sheet 25 by powder blasting from only one side.

[0065]

[0077] As shown in Figures 13 to 16, the choice of where to provide electrostatic shield 45 is not particularly limited. As shown in Figure 13, in one embodiment, electrostatic shield 45 is provided on the bottom surface of electrostatic sheet 25 and inside holes 34, but not on top of electrostatic sheet 25.

[0066]

[0078] As shown in Figure 14, in one embodiment, an electrostatic shield 45 is provided between at least one of the burls 22 and only one of the two dielectric layers 27, 28 that sandwich the electrode 26. For example, as shown in Figure 14, in one embodiment, an electrostatic shield is provided on the bottom surface of the electrostatic sheet 25 and on the lower dielectric layer 27 inside the hole 34 (but not on the upper dielectric layer 28).

[0067]

[0079] As shown in FIG. 15, in one embodiment 22, electrostatic shield 45 is provided on the bottom surface of electrostatic sheet 25, inside holes 34, and on top of electrostatic sheet 25 around holes 34.

[0068]

[0080] By providing the electrostatic shield 45, the possibility of undesired electrical breakdown is reduced. This is especially important when the size of the gap between the electrode 26 and the burl 22 may not be well controlled due to manufacturing tolerances. The electrostatic shield 45 helps to reduce electrical breakdown that may be caused by charge flowing through the electrical insulator 44 or through the dielectric layers 27, 28. When the bonding material 29 is provided on the entire surface of the electrostatic sheet 25 (e.g., as shown in FIG. 10), the electrode magnetic shield 45 reduces the possibility of electrical breakdown due to the surface conductivity of the bonding material 29. The electrostatic shield 45 reduces the possibility of undesired electrostatic discharge across the gaps around the electrostatic sheet 25 that may be caused by material entering those gaps.

[0069]

[0081] As shown in FIG. 16, in one embodiment, electrostatic shield 45b is provided only on the upper dielectric layer 28 (not the lower dielectric layer 27) inside hole 34 and on top of electrostatic sheet 25 around hole 34.

[0070]

[0082] FIG. 17 shows a schematic perspective view of a portion of the substrate holder 20 according to an embodiment of the present invention. As shown in FIG. 17, in one embodiment, the electrostatic shields 45c surrounding different burls 22 are electrically connected to each other via conductive lines 46 (also shown in FIG. 16) on the object-facing surface of the upper dielectric layer 28 of the electrostatic sheet 25 between the electrode 26 and the substrate W. In one embodiment, the conductive lines 46 ground (or connect to another controlled potential) the electrostatic shields 45c around the holes 34. Therefore, it is not necessary to provide an electrostatic shield 45a on the bottom side of the electrostatic sheet 25 to ground the electrostatic shields 45c.

[0071]

[0083] 18 is a schematic plan view of an electrostatic shield 45c surrounding the distal end 23 of the burl 22 connected by a conductive line 46. The electrostatic shield 45c may be seen as a donut electrically grounded by a thin conductive line 46 on the electrostatic sheet 25.

[0072]

[0084] The materials used to make all of the parts of the object holder according to the embodiments can be any of the known materials used to manufacture known object holders. In particular, the parts of the object holder according to the embodiments can be made of the materials disclosed in WO 2015 / 120923 A1, WO 2014 / 154428 A2, and US 2013 / 0094009 A1, the entire contents of which are incorporated herein by reference.

[0073]

[0085] In particular, 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 parts may be chromium oxide. The core body 21 may be SiSiC. The material used for the electrostatic shield 45 may be Cr, CrN, or W (although many other materials are possible).

[0074]

[0086] To facilitate clarity, the embodiments have been described with reference to upper and lower surfaces of an object holder. The upper and lower surfaces are first and second surfaces of the object holder. The first surface is a surface to which an object may be clamped. The second surface is a surface to which a table may be clamped. When the object holder is oriented in a horizontal plane, the first surface is the upper surface and the second surface is the lower surface, although embodiments also include object holders that are not oriented in a horizontal plane.

[0075]

[0087] The embodiments include an object holder for use in any lithographic apparatus. Lithographic apparatus may include any apparatus used for manufacturing, testing, and inspection of substrates, such as electron beam inspection apparatus. To facilitate clearer explanation, the features of the object holder have been described primarily in the context of the upper surface of the substrate holder 20, which clamps to the substrate W. The features of the invention apply equally to the lower surface of the object holder, e.g. the lower surface of the substrate holder 20, which clamps to the remaining substrate table WT. By way of example only, the features relating to the flexible burls 22, the trenches 35, and the mounting tool may be applied at the lower surface of the substrate holder 20.

[0076]

[0088] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be appreciated that the lithographic apparatus described herein may have other applications, including the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0077]

[0089] Although particular reference is made herein to embodiments of the invention in the context of lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes 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 ambient (non-vacuum) conditions.

[0078]

[0090] Although particular reference has 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, such as, for example, imprint lithography, where the context permits.

[0079]

[0091] Although particular reference has been made above to the use of embodiments of the invention in the context of object inspection and optical lithography, it will be appreciated that the invention is not limited to these contexts and may be used in other applications, such as, for example, imprint lithography, where the context permits.

[0080]

[0092] 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 above description is intended to be illustrative rather than limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. 1. An object holder configured to support an object, comprising: a core body including a plurality of burls having distal ends in a support plane for supporting the object; an electrostatic sheet between the burls, the electrostatic sheet comprising an electrode sandwiched between dielectric layers; It is equipped with the electrostatic sheet is bonded to the core body by a bonding material having a thickness of at least 100 nm; at least one of the burls is immediately surrounded by a trench in the object-facing surface of the core body; Object holder.

2. At least one of the burrs is at its distal end oriented in a direction within the support plane. ５ ~10 ７ Nm －１ The object holder of claim 1 having a stiffness of

3. 3. The object holder of claim 1 or 2, wherein at least one of the burls in a peripheral region of the object holder has, at its distal end, a stiffness in a direction in the support plane that is lower than a stiffness of at least one of the burls in a central region of the object holder.

4. 4. The object holder of claim 1 , wherein the core body comprises at least one gas supply passage configured to supply gas to a radial gap between a radially outer surface of at least one of the burls and the electrostatic sheet through a vertical gap between the core body and the electrostatic sheet.

5. 5. The object holder of claim 1 , wherein the electrostatic sheet comprises an electrostatic shield configured to separate the electrostatic sheet from at least one of a region of the object vertically above an electrical insulator surrounding the electrode in the plane of the electrode, an object-facing surface of the core body, and a radially outer surface of at least one of the burls.

6. The object holder of claim 5 , wherein the electrostatic shield is provided between at least one of the burls and only one of two dielectric layers that sandwich the electrode.

7. 7. The object holder of claim 5 or 6, wherein the electrostatic shields surrounding different burls are electrically connected to each other via conductive lines on an object-facing surface of a top dielectric layer of the electrostatic sheet between the electrode and the object.

8. 8. The object holder of claim 1 , wherein the electrostatic sheet comprises a first dielectric layer between the electrode and the object, tapered toward the object or the core body, and a second dielectric layer between the electrode and the core body, tapered toward the object or the core body.

9. The object holder of claim 1 , wherein the joining material comprises an adhesive material.

10. A method for manufacturing an object holder according to any one of claims 1 to 9, comprising the steps of: providing a core body having a plurality of burls having distal ends in a support plane for supporting an object; connecting an electrostatic sheet to a plate comprising a plurality of recesses for respective burls such that the recesses align with respective holes in the electrostatic sheet, the electrostatic sheet comprising electrodes sandwiched between dielectric layers; controlling the movement of the plate to attach the electrostatic sheet to the core body between the burls when the electrostatic sheet is coupled, the depth of the recess determining the height to which the electrostatic sheet is attached; A method for providing the above.

11. A lithographic apparatus comprising an object holder according to any one of claims 1 to 9.

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