Substrate holder, substrate support and method of clamping a substrate to a clamping system

Abstract

A substrate holder for use in a lithographic apparatus and configured to support a substrate on a substrate support. The substrate holder includes a body having a first body surface and a second body surface, where the first body surface and the second body surface are on opposite sides of the body; a plurality of first tabs protruding from the first body surface, where each first tab has a distal surface configured to support the substrate; and a plurality of second tabs protruding from the second body surface, where each second tab has a distal surface for supporting the substrate holder on the substrate support, where the distal surfaces of the plurality of first tabs of a first subset are a first distance from the first body surface, and where the distal surfaces of the plurality of first tabs of a second subset are a second distance from the first body surface. Distal end surfaces of the first plurality of burls of a second subset are a second distance from the first body surface, the first distance being greater than the second distance.

Description

[0001] This application is a divisional application with application number 201880075157.7, entry date May 20, 2020, and invention name “Substrate holder, substrate support and method for clamping a substrate to a clamping system”. Technical Field

[0002] The invention relates to a method of clamping a substrate to a clamping system, a substrate holder for use in a lithographic apparatus and configured to support a substrate on a substrate support, and a substrate support. Background Art

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

[0004] As semiconductor manufacturing processes continue to improve, the size of circuit elements has continued to decrease for decades, while the number of functional elements (such as transistors) per device has steadily increased, following a trend commonly referred to as "Moore's Law." To keep up with Moore's Law, the semiconductor industry is pursuing technologies that can create smaller and smaller features. To project a pattern onto a substrate, a lithography device can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently used are 365nm (i-line), 248nm, 193nm, and 13.5nm. Lithography equipment using extreme ultraviolet (EUV) radiation (whose wavelength is in the range of 4nm to 20nm, such as 6.7nm or 13.5nm) can be used to form smaller features on a substrate than lithography equipment using, for example, radiation with a wavelength of 193nm.

[0005] In a lithographic apparatus, a substrate is held on a substrate holder. It is desirable that the substrate be as flat as possible to minimize imaging errors that may result from any deviation from perfect flatness. One difficulty is that when the substrate is initially placed on the substrate holder, the substrate may be uneven. Once on the substrate holder, there are in-plane stresses in the substrate, and the burls of the substrate holder supporting the substrate deform elastically. These in-plane shear stresses in the substrate result in in-plane deformations in the substrate, which themselves result in overlay errors. Summary of the invention

[0006] It is an object of the present invention to provide a method, a substrate holder and a substrate support comprising a substrate holder, wherein measures are taken to promote relaxation of a substrate placed on the substrate holder.

[0007] In an embodiment of the present invention, a method for clamping a substrate to a clamping system is provided, the method comprising the following steps: providing a substrate holder, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; and a plurality of first protrusions protruding from the first body surface, wherein each first protrusion has a distal surface configured to support the substrate; providing a supporting surface for supporting the substrate holder; providing a plurality of second protrusions, the plurality of second protrusions being used to support the substrate holder on the supporting surface by contacting the supporting surface with distal surfaces of the plurality of second protrusions; generating a first force to attract the substrate holder to the supporting surface; placing the substrate on the substrate holder so that the substrate contacts the plurality of first protrusions; generating a second force to attract the substrate to the substrate holder; and controlling at least one of the first force and the second force in a release step so that the body is deformed between the second protrusions, thereby generating a gap between the distal surfaces of the plurality of first protrusions of the first subset and the substrate, and so that the substrate is supported on the distal surfaces of the plurality of first protrusions of the second subset.

[0008] In an embodiment of the present invention, a substrate holder is provided for a lithography device and configured to support a substrate on a substrate support, the substrate holder comprising: a main body having a first main body surface and a second main body surface, wherein the first main body surface and the second main body surface are on opposite sides of the main body; a plurality of first protrusions protruding from the first main body surface, wherein each first protrusion has a distal surface configured to support the substrate; and a plurality of second protrusions protruding from the second main body surface, wherein each second protrusion has a distal surface for supporting the substrate holder on the substrate support, wherein the distal surfaces of the plurality of first protrusions of a first subset are at a first distance from the first main body surface, and the distal surfaces of the plurality of first protrusions of a second subset are at a second distance from the first main body surface, and the first distance is greater than the second distance.

[0009] In an embodiment of the present invention, a substrate support is provided, comprising: a substrate holder, comprising: a main body having a first main body surface and a second main body surface, wherein the first main body surface and the second main body surface are on opposite sides of the main body; and a plurality of first protrusions protruding from the first main body surface, wherein each first protrusion has a distal surface configured to support the substrate; and a supporting surface for supporting the substrate holder by contacting the distal surfaces of the plurality of second protrusions protruding from the supporting surface; wherein the distal surfaces of the plurality of first protrusions of the first subset are a first distance from the first main body surface, and the distal surfaces of the plurality of first protrusions of the second subset are a second distance from the first main body surface, and the first distance is greater than the second distance.

[0010] In an embodiment of the present invention, a substrate holder is provided for a lithography device and configured to support a substrate on a substrate support, the substrate holder comprising: a main body having a first main body surface and a second main body surface, wherein the first main body surface and the second main body surface are on opposite sides of the main body; a plurality of first protrusions protruding from the first main body surface, wherein each first protrusion has a distal surface configured to support the substrate; a plurality of electrodes to which a voltage can be applied so as to fix the substrate holder to the substrate support; wherein the plurality of electrodes are configured so that: depending on the applied voltage, the force between the plurality of portions of the main body of the substrate holder below the plurality of first protrusions in a first subset and the substrate support can be controlled independently of the force between the plurality of portions of the main body of the substrate holder below the plurality of first protrusions in a second subset and the substrate support. BRIEF DESCRIPTION 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 depicts a schematic overview of a lithography apparatus;

[0013] - Figure 2a and 2b depicts cross-sections of two different variations of a fluid handling structure, illustrated on the left and right sides with different features of the fluid handling structure, which may extend around the entire circumference;

[0014] - Figure 3 illustrates a cross section of a substrate holder, substrate, and substrate support of an embodiment;

[0015] - Figure 4 illustrates an alternative embodiment of a substrate holder and substrate support in a relaxed state;

[0016] - Figures 5 to 7The substrate is placed on the Figure 3 or Figure 4 the step of supporting the substrate holder on the substrate support;

[0017] - Figure 8 Pictured Figure 3 Cross-sections of alternative embodiments of substrate holders, substrates, and substrate supports;

[0018] - Fig. 9 and Fig.10 Pictured Figure 3 Cross-sections of alternative embodiments of substrate holders, substrates, and substrate supports;

[0019] - Fig.11 The pattern of the first burl and the second burl is schematically illustrated, which does not fall within the scope of the present invention. DETAILED DESCRIPTION

[0020] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365nm, 248nm, 193nm, 157nm or 126nm) and extreme ultraviolet radiation (EUV, e.g., having a wavelength in the range of about 5-100nm).

[0021] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a superpositioned patterning device that can be used to impart a patterned cross-section to an incident radiation beam that corresponds to the pattern to be produced in a target portion of the substrate. The term "light valve" can also be used in this context. In addition to classical masks (transmissive or reflective; binary, phase-shift, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0022] Figure 1 A lithographic apparatus is schematically depicted. The lithographic apparatus comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation), a mask support (e.g. a mask table) MT configured to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to specific parameters, a substrate support (e.g. a substrate table) WT configured to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support WT according to specific parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0023] In operation, the illumination system IL receives a radiation beam B from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape and / or control the radiation. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0024] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation used and / or for other factors such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0025] The lithographic apparatus may be of a type in which at least a portion of the substrate may be covered by an immersion liquid having a relatively high refractive index, such as water, so as to fill the space 11 between the projection system PS and the substrate W - this is also referred to as immersion lithography. More information on immersion techniques is given in US 6,952,253, which is incorporated herein by reference.

[0026] The lithographic apparatus may also be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps to prepare a substrate W for subsequent exposure may be performed on a substrate W located on one substrate support WT while another substrate W on another substrate support WT is used to expose a pattern on another substrate W.

[0027] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning means may be arranged to clean a part of the lithographic apparatus, e.g. a part of the projection system PS, or a part of a system for providing immersion liquid. The measurement platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0028] In operation, the radiation beam B is incident on the patterning device (e.g. mask) MA held on the mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam PB passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example, in order to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor ( Figure 1 The patterning device MA is positioned relative to the path of the radiation beam B (not explicitly depicted). The mask alignment marks M1, M2 and the substrate alignment marks P1, P2 may be used to align the patterning device MA with the substrate W. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, they may be located in spaces between multiple target portions. When the substrate alignment marks are located between multiple target portions C, the substrate alignment marks P1, P2 are referred to as scribe line alignment marks.

[0029] To illustrate the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, i.e., an x-axis, a y-axis, and a z-axis. Each of the three axes is orthogonal to the other two axes. Rotation around the x-axis is called an Rx rotation. Rotation around the y-axis is called an Ry rotation. Rotation around the z-axis is called an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in a vertical direction. The Cartesian coordinate system does not limit the present invention and is only used for illustrative purposes. On the contrary, another coordinate system, such as a cylindrical coordinate system, may be used to illustrate the present invention. The direction of the Cartesian coordinate system may be different, for example, so that the z-axis has a component along the horizontal plane.

[0030] Immersion technology has been introduced into lithography systems to achieve improved resolution of smaller features. In an immersion lithography apparatus, a liquid layer of an immersion liquid having a relatively high refractive index is inserted in the space 11 between the projection system PS of the apparatus (by which a patterned beam is projected towards the substrate W) and the substrate W. The immersion liquid covers at least a portion of the substrate W below the final element of the projection system PS. Thus, the at least a portion of the substrate W that undergoes exposure is immersed in the immersion liquid. The effect of the immersion liquid is to enable imaging of smaller features, because the exposure radiation will have a shorter wavelength in the liquid than in a gas. (The effect of the immersion liquid can also be thought of as increasing the effective numerical aperture (NA) of the system and also increasing the depth of focus.)

[0031] In commercial immersion lithography, the immersion liquid is water. Typically, the water is high purity distilled water, such as ultrapure water (UPW) commonly used in semiconductor manufacturing plants. In an immersion system, the UPW is often purified and it may undergo additional processing steps before being supplied to the immersion space 11 as an immersion liquid. In addition to using water as the immersion liquid, other liquids with a high refractive index may also be used, for example: hydrocarbons, such as fluorinated hydrocarbons; and / or aqueous solutions. In addition, it has been envisioned that other fluids besides liquids may be used in immersion lithography.

[0032] In this specification, reference will be made in the description to local immersion, wherein in use immersion liquid is confined to a space 11 between the final element 100 and a surface facing the final element 100. The facing surface is the surface of the substrate W or a surface of the supporting platform (or substrate support WT) which is coplanar with the surface of the substrate W. (Note that in addition or in the alternative, references hereinafter to the surface of the substrate W also refer to the surface of the substrate support WT, and vice versa, unless expressly stated otherwise). A fluid handling structure 12 is present between the projection system PS and the substrate support WT for confining the immersion liquid in the immersion space 11. The space 11 filled by the immersion liquid is smaller in plan than the top surface of the substrate W and remains substantially stationary relative to the projection system PS as the substrate W and substrate support WT move beneath.

[0033] Other immersion systems have been envisaged, such as unconfined immersion systems (so-called "all wet" immersion systems) and bath immersion systems. In an unconfined immersion system, the immersion liquid covers more than the surface below the final element 100. The liquid outside the immersion space 11 exists as a thin liquid film. The liquid may cover the entire surface of the substrate W, or may even cover the substrate W and a substrate support WT coplanar with the substrate W. In a bath type system, the substrate W is completely immersed in a bath of immersion liquid.

[0034] The fluid handling structure 12 is a structure that supplies immersion liquid to the immersion space 11, removes immersion liquid from the space 11, and thereby confines the immersion liquid to the immersion space 11. It includes features that are part of a fluid supply system. An early fluid handling structure is the arrangement disclosed in PCT patent application publication no. WO 99 / 49504, which includes a plurality of conduits that supply immersion liquid or withdraw immersion liquid from the space 11, the conduits operating in dependence on relative movement of a platform beneath the projection system PS. In more recent designs, the fluid handling structure extends along at least a portion of a boundary of the space 11 between the final element 100 of the projection system PS and the substrate support WT or substrate W, so as to partially define the space 11.

[0035] The fluid handling structure 12 may have a selection of different functions. Each function may be derived from a corresponding feature that enables the fluid handling structure 12 to perform the function. The fluid handling structure 12 may be referred to by a number of different terms, each of which refers to a function such as a barrier member, a sealing member, a fluid supply system, a fluid removal system, a liquid confinement structure, etc.

[0036] As a barrier member, the fluid handling structure 12 is a barrier to the flow of the immersion liquid from the space 11. As a liquid confinement structure, the structure confines the immersion liquid to the space 11. As a sealing member, the sealing features of the fluid handling structure form a seal to confine the immersion liquid to the space 11. The sealing features may include additional gas flow from an opening in the surface of the sealing member, such as an air knife.

[0037] In an embodiment, the fluid handling structure 12 may supply immersion fluid and is therefore a fluid supply system.

[0038] In an embodiment, the fluid handling structure 12 may at least partially confine an immersion fluid, thereby being a fluid confinement system.

[0039] In an embodiment, the fluid handling structure 12 may provide a barrier to the immersion fluid, thereby being a barrier member, such as a fluid confinement structure.

[0040] In an embodiment, the liquid handling structure 12 may generate or use a gas flow, for example to help control the flow and / or position of the immersion fluid.

[0041] The gas flow may form a seal to confine the immersion fluid and thus the fluid handling structure 12 may be referred to as a sealing member; such a sealing member may be a fluid confinement structure.

[0042] In an embodiment, an immersion liquid is used as the immersion fluid. In that case, the fluid handling structure 12 may be a liquid handling system. With reference to the preceding description, references in this paragraph to features defined with respect to a fluid may be understood to include features defined with respect to a liquid.

[0043] The lithographic apparatus has a projection system PS. During exposure of the substrate W, the projection system PS projects a patterned radiation beam onto the substrate W. In order to reach the substrate W, the path of the radiation beam B passes from the projection system PS through an immersion liquid, which is confined by a fluid handling structure 12 located between the projection system PS and the substrate W. The projection system PS has a lens element in contact with the immersion liquid, which is the last element in the path of the beam. This lens element in contact with the immersion liquid may be referred to as a "last lens element" or a "final element". The final element 100 is at least partially surrounded by the fluid handling structure 12. The fluid handling structure 12 may confine the immersion liquid below the final element 100 and above the facing surface.

[0044] Figure 2a and Figure 2b The different features that may be present in the variations of the fluid handling structure 12 are shown. Unless otherwise described, the designs may share the same Figure 2a and Figure 2b Some of the same features. The features described herein may be selected individually or in combination as shown or as desired.

[0045] Figure 2a A fluid handling structure 12 is shown surrounding the bottom surface of the final element 100. The final element 100 has an inverted frustoconical shape. The frustoconical shape has a flat bottom surface and a conical surface. The frustoconical shape protrudes from the flat surface and has a flat bottom surface. The flat bottom surface is an optically active portion of the bottom surface of the final element 100 through which the radiation beam B can pass. The final element 100 may have a coating 30. The fluid handling structure 12 surrounds at least part of the frustoconical shape. The fluid handling structure 12 has an inner surface facing the conical surface of the frustoconical shape. The inner surface and the conical surface have complementary shapes. The top surface of the fluid handling structure 12 is substantially flat. The fluid handling structure 12 can be assembled around the frustoconical shape of the final element 100. The bottom surface of the fluid handling structure 12 is substantially flat and, in use, can be parallel to the facing surface of the substrate support WT and / or the substrate W. The distance between the bottom surface and the facing surface may be in the range of 30 microns to 500 microns, desirably in the range of 80 microns to 200 microns.

[0046] The fluid handling structure 12 extends closer to the facing surface of the substrate W and substrate support WT than the final element 100. Thus, a space 11 is defined between the inner surface of the fluid handling structure 12, the flat surface of the frustoconical portion and the facing surface. During use, the space 11 is filled with immersion liquid. The immersion liquid fills at least part of the buffer space between the complementary surfaces between the final element 100 and the fluid handling structure 12, and in one embodiment fills at least part of the space between the complementary inner surface and the conical surface.

[0047] Immersion liquid is supplied to the space 11 through openings formed in the surface of the fluid handling structure 12. The immersion liquid may be supplied through supply openings 20 in the inner surface of the fluid handling structure 12. Alternatively or additionally, the immersion liquid is supplied from lower supply openings 23 formed in the lower surface of the fluid handling structure 12. The lower supply openings 23 may surround the path of the radiation beam B and may be formed by a series of openings in the form of an array. Immersion liquid is supplied to fill the space 11 so that the flow through the space 11 below the projection system PS is laminar. Supplying immersion liquid from the openings 23 below the fluid handling structure 12 additionally prevents air bubbles from entering the space 11. This immersion liquid supply acts as a liquid seal.

[0048] Immersion liquid may be recovered from recovery openings 21 formed in the inner surface. Immersion liquid recovery through the recovery openings 21 may be performed by applying a negative pressure; recovery through the recovery openings 21 may be a result of the speed of the immersion liquid flow through the space 11; or recovery may be a result of both. When viewed in plan, the recovery openings 21 may be located on the opposite side of the supply openings 20. Additionally or alternatively, immersion liquid may be recovered through overflow openings 24 located on the top surface of the fluid handling structure 12. In an embodiment, the supply openings 20 and the recovery openings 21 are capable of swapping their functions (i.e., the flow direction of the liquid is reversed). This allows the flow direction to be changed depending on the relative movement of the fluid handling structure 12 and the substrate W.

[0049] Additionally or alternatively, immersion liquid may be recovered from beneath the fluid handling structure 12 via recovery openings 25 formed in its bottom surface. The recovery openings 25 may be used to hold (or "pin") a meniscus 33 of the immersion liquid to the fluid handling structure 12. The meniscus 33 is formed between the fluid handling structure 12 and the facing surface and serves as a boundary between the liquid space and the gaseous external environment. The recovery openings 25 may be a porous plate that may recover the immersion liquid in the form of a single-phase flow. The recovery openings in the bottom surface may be a series of pinning openings 32 through which the immersion liquid is recovered. The pinhole openings 32 may recover the immersion liquid in the form of a two-phase flow.

[0050] Optionally, radially outward relative to the inner surface of the fluid handling structure 12 is an air knife opening 26. Gas can be supplied through the air knife opening 26 at an increased rate to assist in confining the immersion liquid in the space 11. The supplied gas may be humidified and may substantially contain carbon dioxide. Radially outward of the air knife opening 26 is a gas recovery opening 28 for recovering the gas supplied through the air knife opening 26. Additional openings (e.g., to the atmosphere or to a gas source) may be present in the bottom surface of the fluid handling structure 12. For example, additional openings may be present between the air knife opening 26 and the gas recovery opening 28 and / or between the pinning opening 32 and the air knife opening 26.

[0051] Figure 2b Shown with Figure 2a Common features share the same reference numerals.The fluid handling structure 12 has an inner surface that is complementary to the conical surface of the frustoconical shape.The lower surface of the fluid handling structure 12 is closer to the facing surface than the flat bottom surface of the frustoconical shape.

[0052] Immersion liquid is supplied to the space 11 through supply openings 34 formed in the inner surface of the fluid handling structure 12. The supply openings 34 are located towards the bottom of the inner surface, possibly below the bottom surface of the frustoconical shape. The supply openings 34 are located around the inner surface and are spaced around the path of the radiation beam B.

[0053] The immersion liquid is recovered from the space 11 through the recovery opening 25 in the lower surface of the fluid handling structure 12. When the facing surface moves below the fluid handling structure 12, the meniscus 33 may migrate above the surface of the recovery opening 25 in the same direction as the direction of movement of the facing surface. The recovery opening 25 can be formed by a porous member. The immersion liquid can be recovered in the form of a single phase. In an embodiment, the immersion liquid can be recovered in the form of a two-phase flow. The two-phase flow is received in a chamber 35 within the fluid handling structure 12, in which the two-phase flow is separated into liquid and gas. The liquid and gas are recovered from the chamber 35 through separate channels 36, 38.

[0054] The inner periphery 39 of the lower surface of the fluid handling structure 12 extends away from the inner surface into the space 11 to form a plate 40. The inner periphery 39 forms a small hole, the size of which can be set to match the shape and size of the radiation beam B. The plate 40 can be used to isolate the immersion liquid on both sides of it. The supplied immersion liquid flows inwardly through the inner hole to the hole, and then flows radially outwardly under the plate 40 to the surrounding recovery openings 25.

[0055] In an embodiment, the fluid handling structure 12 may be Figure 2bTwo parts are shown on the right: an inner part 12a and an outer part 12b. The inner part 12a and the outer part 12b may be movable relative to each other in a plane parallel to the facing surface. The inner part 12a may have a supply opening 34, and the inner part 12a may have an overflow recovery structure 24. The outer part 12b may have a plate 40 and a recovery opening 25. The inner part 12a may have an intermediate recovery structure 42 for recovering immersion liquid flowing between the inner part 12a and the outer part 12b.

[0056] The present invention will be described below with reference to an immersion lithography apparatus. In such an apparatus, the imaging of the substrate W is carried out in a state where most of the components of the apparatus are surrounded by a gas atmosphere. As described below, the substrate support WT in such an apparatus can use one or more negative pressures in order to apply a force to the substrate W to hold the substrate in an appropriate position. However, the present invention is applicable to other types of lithography apparatus. For example, the present invention is suitable for any apparatus in which the imaging of the substrate W is carried out in a gas atmosphere. In addition, the present invention can be applied to EUV lithography apparatus in which the imaging of the substrate W is carried out in a vacuum. In that case, instead of using a negative pressure to generate a holding force on the substrate W, an electrostatic force is used to hold the substrate W in an appropriate position. This will be described with reference to Fig. 9 , Fig.10 and Fig.11 Give a description.

[0057] The substrate support WT comprises a substrate holder 200 which is configured to support a substrate W. Figure 3 A cross section of a substrate holder 200 and associated substrate W and substrate support WT is illustrated according to an embodiment. Figure 3 The substrate W is shown clamped in preparation for imaging. The substrate holder 200 comprises a body 210 having a first body surface 212. The first body surface 212 faces the lower surface of the substrate W in use.

[0058] In a central region of the first body surface 212, a plurality of first burls 220 protrude from the first body surface 212. Each first burl 220 has a distal surface configured to support a substrate W. The first burls 220 are arranged relative to each other in a first regular pattern in a plane. The first regular pattern serves to support the substrate W and reduce any bending of the substrate W toward or away from the body surface 212 to an acceptable amount.

[0059] The area in the plane of each first burl 220 is relatively small compared to the area in the plane of the substrate W. Therefore, the first burl 220 only contacts a small area of ​​the lower surface of the substrate W. This reduces the chance of contaminants being transferred from the substrate holder 200 to the substrate W.

[0060] The body 210 has a second body surface 214. The second body surface 214 is on an opposite side of the body 210 to the first body surface 212. In use, the second body surface 214 faces the supporting surface 300 of the substrate support WT.

[0061] In a central region of the second body surface 214, a plurality of second protuberances 240 protrude from the second body surface 214. Each second protuberance 240 has a distal surface configured to support the substrate holder 200 on the support surface 300 by contacting the support surface 300 of the substrate support WT. The second protuberances 240 are arranged relative to each other in a second regular pattern in a plane. The second regular pattern is used to support the substrate holder 200.

[0062] The substrate holder 200 and the substrate support WT together constitute a clamping system 1000. The clamping system 1000 is adapted to be able to extract gas from between the first body surface 212 and the substrate W and from between the second body surface 214 and the support surface 300 under the control of the clamping system controller 110. The clamping system controller 110 is configured to control the gas pressure between the first body surface 212 and the substrate W independently of the gas pressure between the second body surface 214 and the support surface 300.

[0063] Similarly, a pressure differential may be created across the substrate holder 200. For example, the space between the body 210 of the substrate holder 200 and the supporting surface 300 of the substrate support WT is evacuated to a negative pressure below the higher pressure above the substrate W. The pressure differential results in a first force that holds the substrate holder 200 to the substrate support WT.

[0064] A pressure difference is generated across the substrate W. For example, the space between the body 210 of the substrate holder 200 and the substrate W is evacuated to a negative pressure lower than the higher pressure above the substrate W. The pressure difference results in a second force that holds the substrate W to the substrate holder 200 .

[0065] The precise arrangement of the first burl 220 and the second burl 240 will be described below. Figure 3 It will be clear that in an embodiment, the number of second burls 240 is less than the number of first burls 220. The first burls 220 are separated into two or more subsets. For simplicity, the present invention is described with respect to a plurality of first burls 220 having a first subset 220a and a plurality of first burls 220 having a second subset 220b. However, the present invention can be extended to a plurality of first burls 220 having other subsets.

[0066] The substrate holder 200 is arranged so that the plurality of first burls 220 of the first subset 220a can be moved in the z-direction towards and away from the substrate W relative to the plurality of first burls 220 of the second subset 220b. Two general ways of achieving this will be described. The first way is Figure 3 and Figure 4 The method shown in FIG. 1 uses negative pressure to generate a force between the substrate holder 200 and the substrate support WT and between the substrate holder 200 and the substrate W. The second method refers to Figure 8 , Fig. 9 and Fig.10 An illustration is made in which electrodes are used to generate electrostatic forces between the substrate holder 200 and the substrate support WT and between the substrate holder 200 and the substrate W. A hybrid system using one or both of negative pressure and electrostatic forces is also possible.

[0067] exist Figure 3 In the embodiment of the invention, each of the plurality of first burls 220 of the second subset 220 has an axis 230 that is a distance 237 from an axis 235 of one of the plurality of second burls 240 that is less than a distance 239 between an axis of a burl in the plurality of first burls 220 of the first subset 220a and a nearest axis 235 of one of the plurality of second burls 240. In other words, each burl in the plurality of first burls 220 of the second subset 220b has a corresponding second burl 240. In embodiments such as, for example Figure 3 In the embodiment shown in FIG. 2 , the central axis 235 of each second burl 240 is coaxial with the central axis 230 of a corresponding one of the first burls 220 (this is not seen because 240 is in Figure 3 20a). The axes 235 and 230 may be coplanar. Other ways of achieving this stiffness difference are possible, for example by varying the thickness of the body 210 and / or varying the size of the second burls 240 (smaller second burls 240 providing lower stiffness).

[0068] In an embodiment, the number of burls in the second subset 220 b is substantially equal to the number of the plurality of second burls 240 .

[0069] In addition to what is described below, Figure 4 Examples and Figure 3 The same as the embodiment of Figure 4 In the embodiment of FIG. 3 , the second burl 240 is part of the substrate support WT and protrudes from the support surface 300 . Figure 4 The substrate holder 200 and the substrate support WT of the embodiment are used with Figure 3 The embodiments work in the same way. Figure 3 Embodiments of the invention may also have the second burl 240 protruding from the support surface 300 instead of from the second body surface 214 .

[0070] like Figure 4 As shown in FIG. 2 , the substrate holder 200 is in a relaxed state in which no force is applied to the substrate holder. Figure 3 The substrate holder 200 of the embodiment of is similar in a relaxed state. In this configuration, the distal ends of the burls in the first subset 220a protrude from the first body surface 212 a less than the corresponding distance that the burls in the second subset 220b protrude from the first body surface 212. The distance difference is given by Figure 4 220a. The reason for this difference in distance is the property mentioned above: the stiffness of the substrate holder 200 at the locations corresponding to the burls in the first subset 220a is lower than at the locations corresponding to the burls in the second subset 220b. Therefore, if the same force is applied over the entire area to attract the substrate W to the substrate holder 200, the body 210 will bend towards the substrate W at the locations corresponding to the burls 220a of the first subset. If the burls in the first subset 220a and the second subset 220b are at the same distance from the first body surface 212, this will result in the burls in the first subset 220a protruding beyond the burls in the second subset 220b. To ensure that the substrate W is clamped in a position ready for imaging with the distal surfaces of all first burls 220 in the same plane, the distal surfaces of the burls in the first subset 220a protrude from the first body surface 212 less than the distal surfaces of the burls in the second subset 220b by an amount illustrated by the gap 222. As a result, the substrate W can remain flat and in contact with all first burls 220 in the clamped state, as shown in FIG. Figure 3 In the figure. Figure 7 In the case illustrated in FIG. 1 and described below, the bending of the body 210 at the location corresponding to the burls in the first subset 220a is schematically illustrated, while Figure 3 , the bend is not shown.

[0071] If a lower pressure is applied between the body 210 and the substrate support WT than between the body 210 and the substrate W, deformation of the body 210 towards the substrate support WT may occur between the second burls 240. As a result, the burls in the first subset 220a will move slightly downwards towards the substrate support WT and away from the substrate W. Figure 3 This allows the substrate W to be supported by fewer first burls 220 (i.e., by the burls in the second subset 220b) under this condition, compared to the situation that would occur if each of the first burls 220 had a corresponding second burl 240, as shown in the figure. This principle is used in the present invention related to a method of clamping a substrate, as described below with reference to Figures 5 to 7 First, we will discuss Figure 3 , a substrate W is loaded onto the substrate support 200 in the manner illustrated in . The substrate W may initially be bent (upwards (umbrella shape) or downwards (bowl shape)). In this configuration, there is an elastic deformation of the first burls 220 in the xy plane due to the high friction between the distal surfaces of the first burls 220 and the substrate W. This elastic deformation results in an in-plane deformation of the substrate W. By continuing to hold the substrate W but releasing one of the two subsets 220a, 220b of the plurality of first burls 220, any elastic deformation of the burls in the released subsets 220a, 220b can relax. The burls in the released subset of burls can then reengage with the substrate W. In Figures 3 to 7 In the particular configuration illustrated in FIG. 1 , it is then possible to release another subset of the burls 220a, 220b from contact with the substrate W so that the burls can also relax. This process can be repeated as many times as desired, with each repetition resulting in lower in-plane stresses in the substrate W. Finally, the substrate W can be sufficiently clamped ready for imaging by engaging the distal surfaces of all first burls 220 with the substrate W, as shown in FIG. Figure 7 As shown in the figure.

[0072] Figure 3 and Figures 5 to 7 It shows how the clamping system 1000 can be used during loading of a substrate W onto the substrate holder 200 to achieve a more complete relaxation of the substrate W than would occur if the body 210 was not bent between the second burls 240. The same principle can be applied to Figure 4 Clamping system.

[0073] A negative pressure is generated between the body 210 and the support surface 300 to generate a first force, thereby attracting the substrate holder 200 to the support surface 300. A second force is generated by generating a negative pressure between the substrate W and the substrate holder 200 to attract the substrate W to the substrate holder 200. Then, the substrate W is loaded onto the substrate holder 200, as shown in FIG. Figure 3 As shown in the figure.

[0074] The magnitudes of the first force and the second force are controlled to cause a release step in which the distal surfaces of the burls in the first subset 220a of the body 210 (the central first burl 220a, such as the central first burl 220a, and the substrate W) produce a gap 225 between the distal surfaces of the burls in the first subset 220a and the substrate W. Figure 5 20a) towards the support surface 300. The absence of second burls 240 below the burls in the first subset 220a means that when the force attracting the substrate holder 200 to the substrate support WT increases, the relatively thin body 210 will deform between the burls in the second subset 220b and the matching set of second burls 240. The body 210 deforms downwardly away from the substrate W towards the substrate support WT. As a result, the distal surfaces of the burls in the first subset 220a positioned above the less rigid portion of the body 210 deforming towards the substrate support WT move out of contact with the lower surface of the substrate W. This means that it is possible to support the substrate W on the substrate holder 200 under the condition that not all of the first burls 220 are in contact with the lower surface of the substrate W.

[0075] As a result of the burls in the first subset 220a being out of contact with the substrate W, the in-plane stresses in the burls in the first subset 220a are relaxed. Similarly, any in-plane stresses in the substrate W caused by contact between the burls in the first subset 220a and the substrate W are relaxed in the substrate W. As a result, in-plane deformation of the substrate W is reduced, resulting in better overlay performance.

[0076] After the substrate W has been released, as Figure 5 As shown in FIG. 2 , the burls in the first subset 220 a without corresponding second burls 240 are still far away from the lower surface of the substrate W. That is, there are gaps 225 between the distal end surfaces of the burls in the first subset 220 a and the lower surface of the substrate W.

[0077] At this stage, the controller 110 starts the reengagement step by increasing the negative pressure between the first body surface 212 and the substrate W (i.e., reducing the absolute pressure). This effectively increases the second force to attract the substrate W to the substrate holder 200, because the pressure below the substrate W is lower than the pressure above the substrate W. Alternatively or in addition, the negative pressure between the second body surface 214 and the support surface 300 may be reduced (i.e., increasing the absolute pressure), thereby reducing the first force. Both the first force and the second force may be changed. Thus, the situation moves to a situation where all the first burls 220 contact the lower surface of the substrate W.

[0078] In the separation step, the negative pressure between the first body surface 212 and the substrate W is increased and / or the negative pressure between the second body surface 214 and the support surface 300 is reduced. That is, in the separation step, the first force is reduced and / or the second force is increased. This results in the formation of a gap 226 between the distal surfaces of the burls in the second subset 220b and the substrate W. This is because the body 210 is bent away from the support surface 300 at the location corresponding to the burls in the first subset 220a, and the bending is the result of the change in the first force and / or the second force. That is, the substrate W is then supported only by the burls in the first subset 220a, as shown in FIG. Figure 6 In this position, any in-plane elastic deformation of the burls in the second subset 220b can relax, as can any associated in-plane stresses in the substrate W at the locations of the burls in the second subset 220b.

[0079] The final stage (i.e. another rejoining step) is Figure 7 . Here, a step is performed of controlling the first force and / or the second force so that the burls in the first subset 220a and the second subset 220b contact the substrate W and keep it flat in preparation for imaging. For example, the pressure between the body 210 and the support surface 300 is the same as the pressure between the body 210 and the substrate W. During another re-engagement step, the first force is increased and / or the second force is reduced. As a result, due to the lower stiffness of the body 210 at the location of the burls in the first subset 220a, the body 210 is deformed toward the substrate W between the second burls 240. Due to the height difference, i.e., the gap 222 between the burls in the first subset 220a and the second subset 220b in the relaxed state of the substrate holder 200, the bending causes the distal surfaces of the burls in both the first subset 220a and the second subset 220b to terminate in substantially the same plane, so that the substrate W can remain flat while being in contact with all the first burls 220. In this way, the in-plane stress in the substrate W is relaxed. Therefore, in Figure 7 In the position illustrated in , the entire lower surface of the substrate W can be supported at the position of each of the first burls 220 , and the substrate W can be imaged.

[0080] As desired Figure 5 The release steps shown in the figure, Figure 5 and Figure 6 The rejoining steps that occur between Figure 6 The separation steps shown in the figure and Figure 7 The further rejoining step illustrated in is performed multiple times, each repetition resulting in a further reduction of the in-plane stress in the substrate W.

[0081] Although described above with reference to increasing and decreasing negative pressure, the first force and / or the second force may be generated in other ways, such as electrostatically, for example using Coulomb clamping or using Johnson-Rahbek clamping, for example by applying a voltage to one or more electrodes. In another embodiment, the first force and / or the second force may be generated or at least controlled by a combination of applying negative pressure and using electrostatic means.

[0082] In order to enable the clamping system 1000 to independently generate pressure in the space between the second body surface 214 and the support surface 300 and between the first body surface 212 and the substrate W, it is desirable to prevent gas from reaching the second side of the substrate holder 200 through the body 210 from the first side of the substrate holder 200. Therefore, if any through holes are provided through the body 210, it must be possible to block these through holes. For example, an actuatable pin (not depicted in the figure) may be provided in the substrate support WT. The pin can be actuated so that the pin protrudes further away from the substrate support WT than the first protrusion 220. During loading and unloading of the substrate W, the pin is extended, by which the substrate W is supported. Thereby, the pin is then retracted to place the substrate W on the distal surface of the first protrusion 220 with the corresponding second protrusion 240. A seal must be provided to ensure that different vacuum pressures can be generated on both sides of the body 210.

[0083] Passages are provided to generate negative pressure. Passages having openings in the support surface 300 are provided in the substrate support WT to generate negative pressure between the substrate holder 200 and the substrate support WT. In order to generate negative pressure between the substrate holder 200 and the substrate W, one or more passages having openings in the first body surface 212 are provided in the body 210. The opposite ends of these passages are connected to a negative pressure source using, for example, hoses.

[0084] Prior art substrate holders have required that the distal surfaces of all first burls be substantially in the same plane. Previously, it was only possible to achieve within-specification flatness if each of the first burls 220 had a corresponding second burl 240. This is because the distal surfaces of the first burls 220 are polished in order to achieve the desired level of flatness. The amount of material removed during polishing depends on the force between the polishing stone and the first burls 220. In the case where the first burls 220 do not have corresponding second burls 240, the polishing stone will press the first burls 220 and bend the body 210 slightly, so less material is removed from the first burls 220 than in the case where they are supported by the corresponding second burls 240 directly below. However, due to the introduction of new flattening techniques, such as ion beam milling / polishing, photolithography etching, etc., the change in the stiffness of the body 210 below the first burl 220 no longer introduces such a defect, because the amount of material removed in ion beam milling is independent of the stiffness of the body 210 below the burl being milled. The introduction of these new planarization technologies has enabled the introduction of Figure 4 0 , wherein the burls in different subsets of the first burls may be manufactured to have different heights.

[0085] In an embodiment, the gap 222 is 3 nm or more, preferably 10 nm or more, more preferably 30 nm or more, desirably 50 nm or more, or even 100 nm or more. During imaging, the gap 222 is selected in use according to the stiffness of the body 210 and the magnitude of the first force and the second force. For example, the gap is equal to the difference in stiffness of the body 210 between the burls in the first subset 220a and the second subset 220b multiplied by the total force applied to the body 210 by the first force and the second force during imaging of the substrate.

[0086] The above description is explained based on the use of negative pressure to generate the force between the substrate W, the substrate holder 200 and the substrate support WT. However, this is not necessarily the case and the force can be generated in any other way including by using electrostatic force. Figure 8 To describe this situation.

[0087] exist Figure 8 In the embodiment, electrodes 500, 510, 600, 610 are provided for generating a first force and a second force between the substrate W, the substrate holder 200 and the substrate support WT. The magnitude of the force depends on the voltage applied to the electrodes.

[0088] exist Figure 8In an embodiment, one or more substrate electrodes 500 are deposited on the bottom surface of the substrate W. One or more first substrate holder electrodes 510 embedded in the body 210 of the substrate holder 200 are also provided. By providing a potential difference between the substrate electrode 500 and the first substrate holder electrode 510, a force can be generated to attract the substrate W towards the substrate holder 200. Similarly, one or more substrate support electrodes 600 are arranged in the substrate support WT. One or more second substrate holder electrodes 610 are arranged in the body 210 of the substrate holder 200. The potential difference between the substrate support electrode 600 and the second substrate holder electrode 610 generates a force between the substrate holder 200 and the substrate support WT. In addition to the way of generating force, Figure 8 The clamping system 1000 is similar to the above reference Figures 3 to 7 The system described is the same.

[0089] In an embodiment only one or more first substrate holder electrodes are provided in the substrate holder 200 which are at the same potential and are used to generate both forces between the substrate W and the substrate holder 200 and between the substrate holder 200 and the substrate support WT.

[0090] Fig. 9 and Fig.10 Another embodiment is shown. Fig. 9 and Fig.10 In the embodiment of Fig. 9 and Fig.10 In the diagram, electrostatically or as shown, for example Figure 3 The second force between the substrate holder 200 and the substrate W is generated using negative pressure as illustrated in FIG. 1 or by a different means or by a combination of two of those means.

[0091] exist Fig. 9 and Fig.10 In an embodiment, the stiffness of the body 210 at locations corresponding to the burls in the first subset 220a and at locations corresponding to the burls in the second subset 220b are the same, but this is not necessarily the case. However, at least two sets of substrate holder electrodes 620, 630 are provided so that the first force at the portion of the body 210 of the substrate holder 200 below the first subset 220a can be controlled independently of the first force at the portion of the body 210 of the substrate holder 200 below the second subset 220b of the plurality of first burls 220. Fig. 9 and Fig.10In an embodiment of the present invention, this is arranged by ensuring that the relative positions of the first burls 220 and the second burls 240 alternate such that each first burl 220 is positioned in a plane in a gap between corresponding second burls 240. Thus, each of the first burls 220 is at a position where considerable deformation of the body 210 is possible (i.e. the body 210 is not rigid). By providing the first substrate holder electrode 630 at a position below the burls in the first subset 220a and the second substrate holder electrode 620 at a position below the burls in the second subset 220b, it is possible to independently control the height of the distal end surfaces of the burls in the first subset 220a relative to the support surface 300 compared to the height of the distal end surfaces of the burls in the second subset 220b relative to the support surface 300.

[0092] For example, Fig. 9 As shown in FIG. 1 , an electrostatic force is generated between the second substrate holder electrode 620 corresponding to the burls in the second subset 220b and the electrode 310 of the substrate support WT. Due to this attractive force, the burls in the second subset 220b are retracted away from the substrate W, so that the substrate W is supported by the burls in the first subset 220a. In this position, any in-plane stress in the burls in the second subset 220b can relax.

[0093] On the contrary, Fig.10 , the electrostatic force generated between the first substrate holder electrode 630 and the electrode 310 as part of the substrate support WT effectively retracts the burls in the first subset 220a away from the substrate W. The substrate W is then supported by the burls in the second subset 220b. Any in-plane stresses in the burls in the first subset 220a are allowed to relax. This process may be repeated any number of times. Then, in order to clamp the substrate W for imaging, the distal surfaces of all the first burls 220 are allowed to contact the lower surface of the substrate W. In this embodiment, the distal surfaces of all the first burls 220 are substantially coplanar, even when there is no force on the substrate holder 200.

[0094] Fig.11 The diagram shows an embodiment of the arrangement of the first burl 220 and the second burl 240 according to the present invention. In the schematic diagram, the solid dots represent the areas without corresponding second burl 240 (e.g., similar to Figures 5 to 8 The circles without shading represent the first burls 220 (the first subset 220a) of the central burl of the embodiment, while the circles without shading represent the corresponding second burls 240 (i.e., similar to Figures 5 to 7 The first burls 220 (the second subset 220b) are shown on the right and left sides of the embodiment shown in FIG.

[0095] exist Fig.11In the embodiment of the present invention, only one of every four first burls 220 has a corresponding second burl 240. The supported area of ​​each first burl 220 (i.e., the supporting area of ​​the second burl 240) is similar. The rotational symmetry of the first pattern and the second pattern (four) is the same for the first pattern and the second pattern. This desirably results in a substantially symmetrical deformation of the body 210 around each of the second burls 240.

[0096] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include integrated optical systems, for the manufacture of guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0097] Where the context allows, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be recognized that such descriptions are merely for convenience, and such actions are actually generated by a computing device, a processor, a controller, or other devices that execute firmware, software, routines, instructions, etc., which may cause an actuator or other device to interact with the physical world when performing the action.

[0098] Although specific reference may be made herein to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0099] 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, such as imprint lithography, where the context permits.

[0100] Although specific embodiments of the present invention have been described above, it should be understood that the present invention can be practiced in different ways than described above. The above description is intended to be illustrative rather than restrictive. Therefore, it will be understood by those skilled in the art that the described invention can be modified without departing from the scope of the claims set forth below.

Claims

1. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; and a plurality of second protrusions protruding from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, wherein a first imaginary line extending through a central portion of the first burl along a protruding direction of the first burl does not coincide with a second imaginary line extending through central portions of all burls protruding from a surface of the second body along a protruding direction of the burls, and The plurality of first burls are arranged such that when the body is deformed, the substrate is supported only by the first burls of the first subset or the first burls of the second subset.

2. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; and a plurality of second protrusions protruding from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, wherein an imaginary line extending through a central portion of one or more of the second burls along a protruding direction of the one or more second burls passes through one or more gaps between the first burls; The plurality of first burls are arranged such that when the body is deformed, the substrate is supported only by the first burls of the first subset or the first burls of the second subset.

3. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; and a plurality of second protrusions protruding from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, wherein in the vertical direction, the one or more second protuberances do not overlap with the one or more first protuberances; The plurality of first burls are arranged such that when the body is deformed, the substrate is supported only by the first burls of the first subset or the first burls of the second subset.

4. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; a plurality of second protrusions protruding from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, wherein a first imaginary line extending through a central portion of the first burl along a protruding direction of the first burl does not coincide with a second imaginary line extending through central portions of all burls protruding from a surface of the second body along a protruding direction of the burls; as well as An electrode is provided between two of the second imaginary lines for generating an electrostatic force between the substrate holder and the substrate support to retract corresponding ones of the first protrusions away from the substrate.

5. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; a plurality of second protrusions protruding from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, wherein an imaginary line extending through a central portion of one or more of the second burls along a protruding direction of the one or more second burls passes through one or more gaps between the first burls, and An electrode is provided between two of the second imaginary lines for generating an electrostatic force between the substrate holder and the substrate support to retract corresponding ones of the first protrusions away from the substrate.

6. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; a plurality of second protrusions protruding from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, wherein in a vertical direction, the one or more second burls do not overlap with the one or more first burls, and An electrode is used to generate an electrostatic force between the substrate holder and the substrate support so as to retract a first burl of the first burls that does not overlap with the second burls away from the substrate.

7. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; a plurality of second protrusions projecting from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, and at least one electrode disposed below the plurality of first burls and extending along the second body surface of the body between adjacent second burls, the at least one electrode being configured to apply a force to the substrate holder, A first imaginary line extending through a central portion of the first burl along a protruding direction of the first burl does not coincide with a second imaginary line extending through central portions of all burls protruding from the second body surface along a protruding direction of the first burl.

8. A substrate holder for a lithographic apparatus and configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal end configured to support the substrate; and a plurality of second protrusions projecting from the second body surface, wherein each second protrusion has a distal end for supporting the substrate holder on the substrate support, and at least one electrode disposed below the plurality of first burls and extending along the second body surface of the body between adjacent second burls, the at least one electrode being configured to apply a force to the substrate holder, Wherein an imaginary line extending through a central portion of one or more of the second burls along a protruding direction of the one or more second burls passes through one or more gaps between the first burls.

9. A clamping system for clamping a substrate, comprising: A substrate holder configured to support a substrate on a substrate support, the substrate holder comprising: a body having a first body surface and a second body surface, wherein the first body surface and the second body surface are on opposite sides of the body; a plurality of first burls protruding from the first body surface, wherein each first burl has a distal surface configured to support the substrate; and a plurality of second burls for supporting the substrate holder on the support surface by bringing the support surface into contact with distal end surfaces of the plurality of second burls, wherein the clamping system is configured to generate a first force to attract the substrate holder to the support surface, and to generate a second force to attract the substrate to the substrate holder; and In the releasing step, at least one of the first force and the second force is controlled so that the body is deformed between the second burls, thereby generating a gap between the distal surfaces of the plurality of first burls of the first subset and the substrate, and so that the substrate is supported on the distal surfaces of the plurality of first burls of the second subset.

10. A lithographic apparatus comprising a clamping system comprising a substrate holder according to any one of claims 1-8, the substrate holder being configured to hold a substrate.

Images