Substrate support and lithographic apparatus

Abstract

A substrate support configured to support a substrate in a lithographic apparatus, the substrate support comprising: a first peripheral wall (31) having a first height; a first drain (12) located radially outward of the first peripheral wall and configured to extract a fluid; a second peripheral wall (32) having a second height and located radially outward of the first opening; a second drain (119) located radially outward of the second peripheral wall and configured to extract a fluid; a flow restriction (33) having a third height and located radially outward of the second opening; and a third drain (10) located radially outward of the flow restriction and the substrate and configured to extract a fluid, wherein the first opening, the second opening and the third opening are distributed along the circumference of the substrate support, and the third height is smaller than the first height and the second height.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to European Application No. 22206863.7, filed November 11, 2022, which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present invention relates to a substrate support configured to support a substrate in a lithographic apparatus, a lithographic apparatus including the substrate support, and a method of manufacturing a device using the substrate support. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus are used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also called a "design layout" or "design") from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate (e.g. a wafer). Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the radiation beam in a predetermined direction (the "scan" direction) while synchronously scanning the substrate parallel to or anti-parallel to this direction.

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements are continually shrinking, while the number of functional elements, such as transistors, per device has been steadily increasing for decades, following a trend commonly referred to as "Moore's Law." To keep up with Moore's Law, the semiconductor industry is pursuing technologies capable of producing increasingly fine features. To project patterns onto a substrate, lithography equipment may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm.

[0005] Further improvement in resolution of finer features can be achieved by providing an immersion liquid with a relatively high refractive index, such as water, over the substrate during exposure. The effect of the immersion liquid is to enable imaging of finer features because the exposure radiation has a shorter wavelength in the immersion liquid than in a gas. The effect of the immersion liquid may also be thought of as increasing the effective numerical aperture (NA) of the system and increasing the depth of focus.

[0006] The immersion fluid may be confined to a localized region between the projection system of the lithographic apparatus and the substrate by the fluid handling structure. Summary of the Invention [Problem to be solved by the invention]

[0007] In semiconductor manufacturing processes, a substrate is supported on a substrate support. Specifically, the substrate is supported on a plurality of burls protruding from the surface of the substrate support. The surface of the substrate that contacts the burls is often provided with a backside coating. The backside coating may be used to control friction between the substrate and the burls and / or to assist in dicing and packaging processes after device fabrication. The backside coating may vary in thickness near the edge of the substrate, causing variations in the size of the gap between the wall on the substrate support and the backside of the substrate that controls fluid flow. This variation in gap size results in variations in the time it takes to remove immersion liquid from below the edge of the substrate. This leads to variations in the heat load on the substrate (due to evaporative cooling) and ultimately to overlay errors. Therefore, it is desirable to improve the speed and consistency of removing immersion liquid from below the edge of the substrate. [Means for solving the problem]

[0008] According to the present invention, there is provided a substrate support configured to support a substrate in a lithographic apparatus, the substrate support comprising: a first peripheral wall having a first height, a first drain located radially outward of the first peripheral wall and configured to extract a fluid, a second peripheral wall having a second height located radially outward of the first opening, a second drain located radially outward of the second peripheral wall and configured to extract a fluid, a flow restriction having a third height located radially outward of the second opening, and a third drain located radially outward of the flow restriction and the substrate and configured to extract a fluid, wherein the first opening, the second opening and the third opening are distributed around the periphery of the substrate support, and the third height is smaller than the first and second heights.

[0009] According to the present invention, there is also provided a lithographic apparatus including a substrate support.

[0010] The present invention also provides a method for manufacturing a device using a substrate support.

[0011] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments, features, and advantages of the present invention, are described in detail below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0012] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: [Figure 1] 1 depicts a schematic diagram of a lithographic apparatus; [Figure 2] 1 depicts cross-sectional views of two different versions of a fluid handling system for use in a lithographic projection apparatus; [Figure 3] 1 depicts cross-sectional views of two different versions of a fluid handling system for use in a lithographic projection apparatus; [Figure 4] 1 shows a cross-sectional view of a portion of a substrate support according to the present invention; [Figure 5] 5 shows a cross-sectional view of the substrate support of FIG. 4 during extraction of immersion liquid; [Figure 6] 5 shows a cross-sectional view of the substrate support of FIG. 4 when the extraction of immersion liquid has stopped at the outer drain; [Figure 7] 5 shows a cross-sectional view of a variant of the substrate support of FIG. 4; [Figure 8] 5 shows a plan view of the substrate support of FIG. 4. [Figure 9] 1 shows a cross-sectional view of a portion of another substrate support.

[0013] The depicted features are not necessarily to scale, and the depicted size and / or arrangement is not intended to limit the present invention. It will be understood that the drawings include optional features that may not be essential to the present invention. Furthermore, not all features of a device may be shown in each drawing, and a drawing may show only some of the components relevant to the description of a particular feature. DETAILED DESCRIPTION OF THE INVENTION

[0014] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (eg, wavelengths of 365, 248, 193, 157 or 126 nm).

[0015] The terms "reticle," "mask," or "patterning device," as used herein, may be broadly interpreted to refer to any general patterning device that can be used to impart an incident radiation beam with a patterned cross-section that corresponds to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. Beyond the classic mask (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0016] Figure 1 illustrates a schematic diagram of a lithographic apparatus comprising: an illumination system (also called an illuminator) IL configured to condition a radiation beam B (e.g. UV or DUV radiation), a mask support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to precisely position the patterning device MA according to certain parameters, a substrate support (e.g. a substrate table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to precisely position the substrate support WT according to certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) on the substrate W.

[0017] In operation, the illumination system IL receives the radiation beam B from the radiation source SO, for example via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B at the plane of the patterning device MA, so that the radiation beam B has a desired spatial and angular intensity distribution in its cross-section.

[0018] The term "projection system" PS as used herein should be interpreted broadly as encompassing various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, depending on the exposure radiation used and / or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system" PS.

[0019] The lithographic apparatus is of a type in which the substrate W is at least partially covered with an immersion liquid (e.g. water) having a relatively high refractive index, filling an immersion space 11 between the projection system PS and the substrate W, which is also known as immersion lithography. Further details about immersion techniques are found in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0020] The lithographic apparatus may be of a type having two or more substrate supports WT (also known as "dual stage") In such a "multi-stage" apparatus, the substrate supports WT may be used in parallel, and / or a substrate W placed on one substrate support WT may be undergoing preparation steps for a subsequent exposure of the substrate W, while another substrate W on another substrate support WT may be used to expose a pattern for the other substrate W.

[0021] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not shown). The measurement stage is configured to hold a sensor and / or a cleaning device. The sensor may be configured to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be configured to clean part of the lithographic apparatus, for example part of the projection system PS or part of a system for providing immersion liquid. The measurement stage may move below the projection system PS when the substrate support WT is spaced apart from the projection system PS.

[0022] In operation, a radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a mask support MT, and is patterned according to a pattern (design layout) present on the patterning device MA. Having passed through the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and the position measurement system IF, the substrate support WT can be precisely moved, for example, so that different target portions C are positioned at focused and aligned positions on the path of the radiation beam B. Similarly, the patterning device MA may be precisely positioned with respect to the path of the radiation beam B using the first positioner PM and possibly further position sensors (not explicitly shown in FIG. 1 ). The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 are illustrated as occupying dedicated target portions, they may also be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0023] For clarity of the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes: x, y, and z. Each of the three axes is orthogonal to the other two. Rotation about the x-axis is called Rx rotation, rotation about the y-axis is called Ry rotation, and rotation about the z-axis is called Rz rotation. The x- and y-axes define a horizontal plane, and the z-axis is vertical. The Cartesian coordinate system is not a limitation of the present invention and is used for clarity only. Alternatively, another coordinate system, such as a cylindrical coordinate system, may be used for clarity of the present invention. The orientation of the Cartesian coordinate system may be different, for example, the z-axis may have a component along the horizontal plane.

[0024] Immersion techniques have been introduced into lithography systems to improve the resolution of finer features. In an immersion lithography apparatus, a layer of immersion liquid, having a relatively high refractive index, is interposed in an immersion space 11 between the apparatus's projection system PS (through which a patterned beam is projected onto the substrate W) and the substrate W. The immersion liquid covers at least a portion of the substrate W that is located below the final element of the projection system PS. Thus, at least the part of the substrate W that is to be exposed is immersed in the immersion liquid.

[0025] In commercial immersion lithography, the immersion liquid is water. Typically, this water is highly pure distilled water, such as ultrapure water (UPW), which is widely used in semiconductor manufacturing facilities. In immersion systems, UPW is often purified and may undergo additional processing steps before being supplied to the immersion space 11 as the immersion liquid. Besides water, other liquids with high refractive indices can be used as immersion liquids, such as hydrocarbons, such as fluorocarbons, and / or aqueous solutions. Furthermore, fluids other than liquids are also envisioned for use in immersion lithography.

[0026] Reference is made herein to localized immersion, where, in use, immersion liquid is confined in an immersion space 11 between the final element and a surface facing the final element. The facing surface is the surface of the substrate W or a surface of the support stage (or substrate support WT) that is flush with the surface of the substrate W. (Note that in the following text, references to the surface of the substrate W will refer in addition to or instead to the surface of the substrate support WT, unless otherwise stated, and vice versa.) A fluid handling structure IH present between the projection system PS and the substrate support WT is used to confine the immersion liquid to the immersion space 11. The immersion space 11, which is filled with immersion liquid, is narrower in plan than the top surface of the substrate W, and the immersion space 11 remains substantially stationary relative to the projection system PS while the substrate W and substrate support WT move underneath.

[0027] Other immersion systems are envisaged, such as non-enclosed immersion systems (so-called "all wet" immersion systems) and bath-type immersion. In a non-enclosed immersion system, the immersion liquid covers more than the surface below the final element. The liquid outside the immersion space 11 is present as a thin film. The liquid may cover the entire surface of the substrate W, or it may cover the substrate W and a substrate support WT that is flush with the substrate W. In a bath-type system, the substrate W is completely immersed in a bath of immersion liquid.

[0028] The fluid handling structure IH is a structure that supplies immersion liquid to and removes immersion liquid from the immersion space 11, thereby confining the immersion liquid to the immersion space 11. It includes features that are part of a fluid supply system. The arrangement disclosed in PCT Patent Application Publication No. WO 99 / 49504 is an early fluid handling structure that comprises pipes that supply or remove immersion liquid to or from the immersion space 11 and that operate in response to relative movement of a stage directly below the projection system PS. In more recent designs, the fluid handling structure extends along at least part of the boundary of the immersion space 11 between the final element of the projection system PS and the substrate support WT or substrate W, and partly defines the immersion space 11.

[0029] The fluid handling structure IH may have a choice of different functions, each derived from corresponding features that enable the fluid handling structure IH to perform that function. The fluid handling structure IH may be referred to by a number of different terms to describe each function, such as barrier member, seal member, fluid supply system, fluid removal system, liquid confinement structure, etc.

[0030] As a barrier member, the fluid handling structure IH provides a barrier to the flow of immersion liquid from the immersion space 11. As a liquid confinement structure, it confines the immersion liquid to the immersion space 11. As a seal member, a sealing function of the fluid handling structure IH forms a seal to confine the immersion liquid to the immersion space 11. The sealing function may comprise an additional gas flow from openings in the surface of the seal member, such as a gas knife.

[0031] The fluid handling structure IH may supply immersion fluid and therefore may be a fluid supply system.

[0032] The fluid handling structure IH may at least partly confine the immersion fluid and thereby provide a fluid confinement system.

[0033] The fluid handling structure IH may provide a barrier to the immersion fluid and thereby be a barrier member such as a fluid confinement structure.

[0034] The fluid handling structure IH may, for example, generate or use a flow of gas to help control the flow and / or position of the immersion fluid.

[0035] The flow of gas may form a seal to confine the immersion fluid, and so the fluid handling structure IH may be referred to as a seal member, and such a seal member may be a fluid confinement structure.

[0036] An immersion liquid may be used as an immersion fluid, in which case the fluid handling structure IH may be a liquid handling system. In the context of the above 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.

[0037] The lithographic apparatus has a projection system PS. During exposure of a substrate W, the projection system PS projects a patterned beam of radiation onto the substrate W. The path of the radiation beam B passes from the projection system PS through immersion liquid confined between the projection system PS and the substrate W by a fluid handling structure IH, before reaching the substrate W. The projection system PS has a lens element at the end of the beam path that is in contact with the immersion liquid. The lens element in contact with the immersion liquid may be referred to as the "final lens element" or "final element". The final element is at least partly surrounded by a fluid handling structure IH. The fluid handling structure IH may confine immersion liquid below the final element and above a facing surface.

[0038] As shown in Figure 1, the lithographic apparatus comprises a controller 500. The controller 500 is configured to control a substrate table WT.

[0039] Figure 2 shows schematically a localised liquid supply or fluid handling system. The liquid supply system comprises a fluid handling structure IH (or liquid confinement structure) that extends along at least part of the boundary of a space 11 between the final element of the projection system PS and the support table WT or substrate W. The fluid handling structure IH is substantially stationary in the XY plane relative to the projection system PS, although there may be some relative movement in the Z direction (along the optical axis). In one example, a seal is formed between the fluid handling structure IH and the surface of the substrate W and may be a contactless seal such as a gas seal (such a system comprising a gas seal is disclosed in EP 1,420,298) or a liquid seal.

[0040] The fluid handling structure IH at least partly confines immersion liquid to a space 11 between the final element of the projection system PS and the substrate W. The space 11 is at least partly formed by the fluid handling structure IH located below and surrounding the final element of the projection system PS. Immersion liquid is introduced into the space 11 below the projection system PS and inside the fluid handling structure IH by one of the liquid openings 13. Immersion liquid may be removed by another liquid opening 13. Immersion liquid may be introduced into the space 11 through at least two liquid openings 13. Which liquid opening 13 is used to supply immersion liquid, and optionally which liquid opening 13 is used to remove immersion liquid, may depend on the direction of movement of the support table WT.

[0041] The immersion liquid may be confined in the space 11 by a contactless seal, such as a gas seal 16 formed by gas that, in use, forms between the bottom of the fluid handling structure IH and the surface of the substrate W. Gas in the gas seal 16 is supplied under pressure to the gap between the fluid handling structure IH and the substrate W via an inlet 15. The gas is extracted via an outlet 14. The overpressure at the gas inlet 15, the vacuum at the outlet 14 and the geometry of the gap are configured to provide a high velocity gas flow inward that confines the immersion liquid. Such a system is disclosed in US 2004 / 0207824, which is incorporated herein by reference in its entirety. In one example, the fluid handling structure IH does not have a gas seal 16.

[0042] Figure 3 depicts a cross-sectional side view of another liquid supply or fluid handling system. The arrangement shown in Figure 3 and described below may be applied to the lithographic apparatus shown in Figure 1 and described above. The liquid supply system comprises a fluid handling structure IH (or liquid confinement structure) that extends along at least part of the boundary of the space 11 between the final element of the projection system PS and the support table WT or substrate W.

[0043] The fluid handling structure IH at least partly confines immersion liquid to a space 11 between the final element of the projection system PS and the substrate W. The space 11 is at least partly formed by the fluid handling structure IH located below and surrounding the final element of the projection system PS. In one example, the fluid handling structure IH comprises a body member 53 and a porous member 33. The porous member 33 is plate-shaped and has a plurality of holes (i.e. openings or pores). The porous member 33 may be a mesh plate having a multitude of small holes 84 formed in a mesh pattern. Such a system is disclosed in US 2010 / 0045949 A1, the entire contents of which are incorporated herein by reference.

[0044] The body member 53 is provided with supply ports 72 capable of supplying immersion liquid to the space 11, and recovery ports 73 capable of recovering immersion liquid from the space 11. The supply ports 72 are connected to a liquid supply unit 75 via passages 74. The liquid supply unit 75 is capable of supplying immersion liquid to the supply ports 72 through the corresponding passages 74. The recovery ports 73 are capable of recovering immersion liquid from the space 11. The recovery ports 73 are connected to a liquid recovery unit 80 via passages 79. The liquid recovery unit 80 recovers the immersion liquid recovered via the recovery ports 73 through the passages 79. The porous member 33 is arranged at the recovery ports 73. By performing a liquid supply operation using the supply ports 72 and a liquid recovery operation using the porous member 33, a space 11 is formed between the projection system PS and the fluid handling structure IH on one side, and between the projection system PS and the substrate W on the other side.

[0045] FIG. 4 shows part of a substrate support for a lithographic apparatus according to the present invention. The configuration shown in FIG. 4 and described below may be part of a substrate table WT and may be applied to the lithographic apparatus shown in FIG. 1 as described above. FIG. 4 shows a cross section through a substrate support 20 and a substrate W. In an embodiment, the substrate support 20 comprises one or more conditioning channels (not shown) of a thermal conditioner. The substrate W is held by a support body 21 (e.g., a pimple or burl table) comprising one or more burl 41 (i.e., protrusions from its surface). The support body 21 is an example of an object holder. Another example of an object holder is a mask holder. Negative pressure applied between the substrate W and the substrate support 20 helps to hold the substrate W firmly in place.

[0046] A gap 5 exists between the edge of the substrate W and the edge of the recess in the substrate support 20. The edge of the recess in the substrate support 20 may be defined by a cover ring 101, which is optionally separate from the support body 21 of the substrate support 20. The cover ring 101 may be ring-shaped in plan and may surround the outer edge of the substrate W. When the edge of the substrate W is being imaged, or at another time when the substrate W first moves under the projection system PS (as described above), the immersion space 11, which is filled with liquid by (for example) the fluid handling structure IH, passes at least partially over the gap 5 between the edge of the substrate W and the edge of the substrate support 20. This may allow liquid from the immersion space 11 to enter the gap 5.

[0047] Immersion liquid getting into the gap 5 can be problematic, particularly when unloading the substrate W. To deal with immersion liquid getting into this gap 5, two drains 10, 12 are provided at the edges of the substrate W to remove immersion liquid that has gotten into the gap 5. In one embodiment, each of the drains 10, 12 is annular and surrounds the entire periphery of the substrate W.

[0048] The main function of the outer drain 10 (located radially outward from the edge of the substrate W / support body 21) is to prevent the intrusion of gas bubbles into the immersion space 11 where the liquid of the fluid handling structure IH is present. Such gas bubbles could have a detrimental effect on imaging of the substrate W. The outer drain 10 is present to prevent gas in the gap 5 from leaking into the immersion space 11 of the fluid handling structure IH. If gas were to leak into the immersion space 11, air bubbles could form in the immersion space 11. Such bubbles could cause imaging errors if they were in the path of the radiation beam B. The outer drain 10 is configured to remove gas from the gap 5 between the edge of the substrate W and the edge of the recess in the substrate support 20 in which the substrate W is placed. The outer drain 10 extracts mostly gas and only a small amount of immersion liquid.

[0049] The inner drain 12 (located radially inward from the edge of the substrate W / support body 21) is provided to prevent liquid from seeping under the substrate W from the gap 5, which could make it difficult to efficiently remove the substrate W from the substrate support 20 after imaging. The provision of the inner drain 12 reduces or eliminates problems that can arise due to liquid getting under the substrate W.

[0050] As shown in Figure 4, in one embodiment, the lithographic apparatus includes a first extraction channel 102 and a second extraction channel 113. The first extraction channel 102 and the second extraction channel 113 may be configured to allow two-phase flow therethrough. The first extraction channel 102 may be formed within the support body 21 or may be formed within a separate block. The outer drain 10 and the inner drain 12 include openings 107 and 117, respectively. The extraction channels 102 and 113 are in fluid communication with the respective openings 107 and 117 through respective passages 103 and 114.

[0051] As shown in Figure 4, the cover ring 101 has a top surface, which extends circumferentially around the substrate W on the support body 21. During use of the lithographic apparatus, the substrate support 20 moves relative to the fluid handling structure IH. During this relative movement, the fluid handling structure IH moves across the gap 5 between the cover ring 101 and the substrate W. In an embodiment, this relative movement occurs by the substrate support 20 moving below the fluid handling structure IH. In another embodiment, this relative movement occurs by the fluid handling structure IH moving above the substrate support 20. In yet another embodiment, this relative movement occurs by both movement of the substrate support 20 below the fluid handling structure IH and movement of the fluid handling structure IH above the substrate support 20. In the following description, "movement of the fluid handling structure IH" means relative movement of the fluid handling structure IH with respect to the substrate support 20.

[0052] The support body 21 includes a plurality of burls 41. When the substrate W is supported by the support body 21, the substrate W comes into direct contact with the burls 41 of the support body 21. The support body 21 is a portion of the substrate support 20 that physically supports the back surface of the substrate W. The tips of the burls 41 define a support surface that supports the back surface of the substrate W. The back surface of the substrate W comes into contact with the tips of the burls 41. The burls 41 are located on the upper surface of the support body 21.

[0053] When the substrate W is loaded onto the substrate support 20, it is first received by the e-pins (not shown) in the extended position. The e-pins then retract and the substrate W moves down towards the substrate support 20. When the underside of the substrate W comes into contact with the burls 41, the e-pins continue to retract, and the substrate W no longer comes into contact with the e-pins, and the substrate W is fully supported by the burls 41.

[0054] During the loading process, the gas pressure between the substrate W and the substrate support 20 may be controlled to control the loading process. For example, a relatively high pressure may be generated during the loading process, generating an upward force that deforms the edge of the substrate W upward. This may reduce or completely eliminate umbrella-shaped deformation of the substrate W. After the loading process is completed, gas may be extracted through one or more clamp openings (not shown) to establish a negative pressure (a pressure lower than atmospheric pressure) below the substrate W. Thus, a force is applied to the substrate W in a direction toward the substrate support 20, and the substrate W is clamped to the substrate support 20.

[0055] To remove the substrate W from the substrate support 20 after exposure of the substrate W is complete, the pressure beneath the substrate W is gradually increased towards ambient pressure, reducing the clamping force acting on the substrate W. The e-pins (not shown) extend from their retracted position. As the e-pins extend, their tips contact the underside of the substrate W. As the e-pins continue to extend, the substrate W is lifted off the multiple burls 41.

[0056] As shown in FIG. 4, the substrate support 20 further includes a plurality of seals 31, 32. The seals 31, 32 are peripheral walls that protrude from the substrate support 20. In this example, there are at least two seals: an inner seal 31 and an outer seal 32 located radially outside the inner seal 31. The inner drain 12 is located between the inner seal 31 and the outer seal 32. When the substrate W is supported by the substrate support 20, the upper surfaces of the plurality of seals 31, 32 (i.e., the surfaces of the plurality of seals 31, 32 that are substantially parallel to and closest to the substrate W) do not contact the lower surface of the substrate W. However, the distance between the upper surfaces of the plurality of seals 31, 32 and the lower surface of the substrate W is set so that at least a partial seal is formed between the upper surfaces of the seals 31, 32 and the lower surface of the substrate W. In other words, the plurality of seals 31, 32 suppress, but do not completely prevent, the flow of fluid.

[0057] The distance between the top surface of the seals 31, 32 and the back surface of the substrate W is preferably less than 10 μm, more preferably less than 5 μm, and preferably greater than 1 μm, more preferably greater than 3 μm. In an embodiment, the distance between the top surface of the seals 31, 32 and the back surface of the substrate W may not be the same for each seal 31, 32.

[0058] For a substrate support 20 configured to support a substrate W having a diameter of 300 mm, the following dimensions are preferred: For a substrate W not having a diameter of 300 mm, the dimensions may be similar or may be adjusted (scaled) to the diameter of the substrate W. The distance between the outer seal 32 and the periphery of the substrate W is preferably less than 5 mm, more preferably less than 3 mm, and even more preferably less than 2.5 mm. The distance between the outer seal 32 and the periphery of the substrate W is preferably greater than 1 mm.

[0059] The width of each of the plurality of seals 31, 32 (i.e., the radial distance between the inner circumferential edge of the seal and the outer circumferential edge of the seal) is preferably 0.1 mm or more, more preferably 0.2 mm or more. The width of each of the plurality of seals 31, 32 is preferably less than 1 mm, more preferably less than 0.6 mm.

[0060] The widths of the seals 31, 32 do not have to be the same. The width of one of the seals 31, 32 may be wider to allow a ring-shaped burl 42 (not shown) to be placed on the upper surface of the seal 32. In one embodiment, the width of the outer seal 32 is wider than the width of the inner seal 31. Preferably, the width of the outer seal 32 is greater than 0.4 mm and less than 0.6 mm, for example, 0.5 mm. The width of the inner seal 31 is preferably less than 0.3 mm and greater than 0.2 mm, for example, 0.25 mm.

[0061] In one embodiment, the burls 41 are arranged in a circumferential ring. The burls 42 of the radially outermost circumferential ring may be arranged between the inner seal 31 and the outer seal 32. When the substrate support 20 supports the substrate W, the burls 42 of the outer ring are preferably in a dry state, i.e., not in contact with the immersion liquid, in order to reduce wear on the burls 42 of the outer ring.

[0062] In one embodiment, when a substrate W having a diameter of 300 mm is clamped on the substrate support 20, the burls 42 of the radially outermost circumferential ring are preferably less than 10 mm from the peripheral edge of the substrate W, more preferably less than 5 mm from the peripheral edge of the substrate W, more preferably less than 4 mm from the peripheral edge of the substrate W, and even more preferably less than 3.5 mm from the peripheral edge of the substrate W. When a substrate W having a diameter of 300 mm is clamped on the substrate support 20, the burls 42 of the radially outermost circumferential ring are preferably spaced more than 1 mm from the peripheral edge of the substrate W.

[0063] The diameters of the burls 41, 42 do not have to be the same. For example, the burls 41, 42 in each circumferential ring may have different diameters. The diameter of the burls 41, 42 within a circumferential ring may depend on the radial distance from the center of the substrate support 20. This is because the contact stiffness of a burl is proportional to its diameter. Therefore, by varying the diameter of the burls 41, 42, the amount of deformation at the burl-substrate interface can be adjusted. This means that the diameters of the burls 41, 42 can be controlled so that the substrate W is maintained within the required flatness tolerance despite complex pressure profiles at the backside of the substrate W. The required diameters of the burls 41, 42 in each ring can be determined by experimentation or optimization through simulation.

[0064] Preferably, the diameter of the burls 42 in the radially outermost circumferential ring (or rings) is between 200 μm and 350 μm, and the diameter of the burls 41 in the innermost ring is between 150 μm and 250 μm. Even more preferably, the diameter of the burls 42 in the radially outermost circumferential ring is between 250 μm and 330 μm, and the diameter of the burls 41 in the remaining circumferential rings is between 190 μm and 240 μm. Even more preferably, the diameter of the burls 42 in the radially outermost circumferential ring is between 260 μm and 280 μm, for example 270 μm, and the diameter of the burls 41 in the remaining rings is between 200 μm and 220 μm, for example 210 μm.

[0065] The smaller the diameter of the burls, the faster they will wear and the more frequently the substrate support 20 (or support body 21) will need to be replaced. To prevent the burls 41, 42 from wearing out too quickly, the diameter of all of the burls 41, 42 should be greater than 150 μm.

[0066] Other techniques, such as changing the material or applying a coating such as diamond or DLC, can also be used to adjust the stiffness of the burls 41, 42. However, because the substrate W typically has a lower stiffness than the burls 41, 42, deformation at the interface between the substrate and the burls is not significantly affected by the burl material or coating. As a result, these techniques are not very effective in controlling the flatness of the substrate W.

[0067] In the above-described embodiment, the pitch of the burls (the distance between the burls 41, 42) is preferably greater than 0.5 mm, more preferably greater than 1 mm, and even more preferably greater than 1.4 mm. The pitch of the burls is preferably less than 3 mm, more preferably less than 2 mm, and even more preferably less than 1.6 mm, for example 1.5 mm.

[0068] The burls 41 may have a height (i.e., the length from the surface of the support body 21 to the tip of the burl) of about 150 μm. However, the burls 41 may have any suitable height.

[0069] The material of the substrate support 20 is not particularly limited, and any suitable material known in the art can be used. Preferably, the substrate support 20 may be made of silicon carbide (SiSiC).

[0070] Fabrication of the substrate support 20 may involve standard techniques known in the art. Some openings may be too small for methods such as electrical discharge machining (EDM). In such cases, laser drilling may be used.

[0071] In an embodiment of the invention, the intermediate drain 119 is provided outside the outer seal 32 and within the outer drain 10. The intermediate drain 119 is preferably located inside the outer edge of the substrate W. The flow restriction 33 is provided between the intermediate drain 119 and the outer drain 12. The intermediate drain 119 and the flow restriction 33 cooperate to increase the extraction rate of the immersion liquid and make the extraction of immersion liquid more consistent even when variations in the thickness of the backside coating on the substrate W cause variations in the size of the gap between the backside of the substrate W and the top surface of the substrate support 20.

[0072] The intermediate drain 119 has an opening 121 located in the upper surface of the support body 21 and is connected via a passage 118 to a negative pressure source, for example the extraction channel 102. The first extraction channel 102 is preferably connected to a negative pressure source in order to provide efficient extraction of immersion liquid via the intermediate drain 119 and the outer drain 10.

[0073] The flow restricting portion 33 may comprise a raised portion of the support body 21 or a porous member mounted on the support body 21. Desirably, the height of the flow restricting portion 33 is less than the height of the inner seal 31 and the outer seal 32, such that the gap between the substrate W and the upper surface of the flow restricting portion 33 is greater than the gap between the substrate W and the upper surfaces of the inner seal 31 and the outer seal 32. Desirably, the gap between the substrate W and the flow restricting portion 33 is at least 10 μm, preferably at least 20 μm, and more preferably at least 30 μm. Desirably, the distance between the support surface and the upper surface of the flow restricting portion 33 is less than 100 μm, preferably less than 70 μm, and more preferably less than 50 μm. The flow restricting portion 33 has a radial width of at least 0.1 mm, preferably at least 0.25 mm. Desirably, the flow restricting portion 33 has a radial width of less than 2 mm, more desirably less than 0.25 mm. The flow restricting portion 33 can have several functions. For example, the flow restriction 33 can ensure that the extraction flow rate through the intermediate drain 119 is not too high, thereby reducing excessive evaporation and the associated cooling load that can result from high gas flow rates. The flow restriction 33 can also make the pressure in the vicinity of the intermediate drain 119 more consistent, helping to provide a more uniform extraction of immersion liquid. The flow restriction 33 can prevent situations where only air is extracted, leaving liquid remaining in some areas.

[0074] Preferably, the flow restriction 33 is an outermost feature of the support body 21 located within the periphery of the substrate W. In other words, the flow restriction 33 is a feature on the top surface of the substrate body 21 located within the footprint of the substrate W and closest to the edge of the substrate W. This allows the flow restriction 33 to be located opposite the portion of the backside of the substrate W where the thickness of the backside coating varies most. Meanwhile, the inner seal 31 and the outer seal 32 can be located at a position where the thickness of the backside coating of the substrate W is relatively uniform. Because the flow restriction 33 is relatively wide and the gap between the top surface of the flow restriction 33 and the backside of the substrate W is relatively large compared to the variation in the thickness of the backside coating, the effect of the flow restriction 33 is sufficiently uniform regardless of the variation in the thickness of the backside coating of the substrate W. It should be noted that at the outermost portion of the substrate W, the thickness of the backside coating may vary between substrates and around the circumference of the substrate. The thickness of the backside coating of the substrate W at the location of the flow restriction 33 may vary due to variations in the coverage of the backside of the substrate W. The dimensions of the flow restriction 33, in particular its height and width, can be optimized based on simulations or empirical evidence, taking into account expected variations in the thickness of the backside coating, in particular in the outer parts of the substrate W.

[0075] 4, 5 and 6 show the operation of the substrate support 20 to remove immersion liquid. FIG. 4 shows a situation in which the immersion space 11 containing immersion liquid is positioned above the gap 5 between the substrate W and the substrate support 20. The gap 5 and the space below the substrate W and outside the inner drain 12 quickly fill with immersion liquid. The first extraction channel 102 and the second extraction channel 113 are connected to a negative pressure, so that the immersion liquid is extracted through them. After the immersion space 11 moves away from above the gap 5, the immersion liquid in the vicinity of the gap 5 and the outer drain 10 is quickly removed, as shown in FIG. 5. However, immersion liquid may still remain in the vicinity of the intermediate drain 119 and the inner drain 12. Therefore, extraction of immersion liquid continues until the situation shown in FIG. 6 is reached. As shown in FIG. 6, only a thin film of immersion liquid may remain in most of the various conduits and passages of the substrate support 20. Immersion liquid may remain in the first extraction channel 102 when the extraction of the outer drain 10 is turned off when no exposure is being performed. It is desirable to minimize the remaining thin film of immersion liquid in order to minimize the cooling load due to evaporation of the immersion liquid. Compared to a similar substrate support without the intermediate drain 119 and flow restriction 33, the immersion liquid extraction process is faster and more consistent in one embodiment of the invention.

[0076] The inner drain 12, intermediate drain 119 and outer drain 10 may comprise grooves or gutters formed in the top surface of the support body 21. The openings 107, 117, 121 through which immersion liquid is extracted may each comprise a continuous slit around the entire periphery of the body 21, or a series of individual openings. Such individual openings may comprise circular holes which are easier to manufacture, or elongated slits which may provide a higher fluid flow rate.

[0077] FIG. 8 shows a top plan view of the substrate support 20. As shown, the inner drain 12, intermediate drain 119, and outer drain 10 preferably extend along the entire periphery of the support body 21. Any or all of the inner drain 12, intermediate drain 119, and outer drain 10 may be divided into individual segments that can be independently and selectively connected to a negative pressure to extract fluid only from selected areas of the periphery of the substrate W. By not extracting fluid from areas where no immersion liquid is present, power consumption and the capacity of the pump that generates the negative pressure can be reduced. In some cases, it may not be necessary to provide the intermediate drain 119 along the entire periphery of the support body 21. For example, if edge crossing by immersion liquid occurs only at certain locations, it may be sufficient to provide the intermediate drain 119 only near the location where the edge crossing occurs.

[0078] Figure 7 shows a variation of the substrate support 21 of Figure 4. In the configuration of Figure 7, the intermediate drain 119 is connected to the intermediate extraction channel 120 rather than the first extraction channel 102. In this variation, the pressure in the intermediate extraction channel 120 can be controlled independently of the pressure in the first extraction channel 102 and the second extraction channel 113, providing additional control over the rate of extraction of fluid from below the substrate W.

[0079] An alternative substrate support 200 is shown in Figure 9. The substrate support 200 comprises three main parts: a support body 221 that supports the substrate W but has a slightly smaller diameter; a cover ring 211 that provides an upper surface that is flush with the upper surface of the substrate W; and an extraction ring 231 that surrounds the support body 221 and supports the cover ring 211. The cover ring 211 is optionally separate from the extraction ring 231. In the substrate support 200, the functions of supporting the substrate W and removing immersion liquid are separated between the support body 221 and the extraction ring 231. The support body 221 and the extraction ring 231 may be thermally and / or mechanically isolated from each other by a gap 240. The gap 240 may comprise a vacuum or a gas. A seal (not shown) may optionally be provided to seal the gap 240.

[0080] The support body 221 has burls 41, 42 on its upper surface, as described above in connection with FIGS. 4 to 7. Additional burls (not shown) may optionally be provided in the extraction ring 231 to support the substrate W. The support body 221 also has inner and outer seals 31, 32, as described above. Gas supply / extraction channels 222, 223 are provided to control the pressure below the substrate W for clamping during operation and for shape control of the substrate W during loading and unloading operations. For example, gas openings may be configured to supply gas during unloading operations. The extraction ring 231 includes an outer drain 232 below the cover ring 211 and an inner drain 233 below the substrate W. In other words, the inner drain 233 is inside the gap 5 between the substrate W and the cover ring 211, and the outer drain 232 is outside the gap 5. The inner drain 233 and outer drain 232 are connected to extraction channels 234, 235 respectively. A flow control structure 236 may be provided adjacent to the inner drain 233. Desirably, the pressure in the extraction channels 234 and 235 is configured to maximise the extraction rate of immersion liquid from the gap 5 and prevent immersion liquid from reaching the support body 221.

[0081] The present invention may provide a lithographic apparatus, which may comprise any or all of the other features or components of the lithographic apparatus described above, for example, the lithographic apparatus may optionally comprise at least one or more of a source SO, an illumination system IL, a projection system PS, a substrate table WT, etc.

[0082] In particular, the lithographic apparatus may comprise a projection system PS configured to project a radiation beam B towards a region of a surface of the substrate W. The lithographic apparatus may further comprise a substrate support 20 as described in any of the embodiments and variations above.

[0083] It should be noted that although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, the lithographic apparatus described herein may have other applications, including the manufacture of integrated optical systems, induction and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0084] Where the context allows, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Also, embodiments of the present invention may 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 read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and the like. Furthermore, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such description is merely for convenience, and that such actions actually occur when a computing device, processor, controller, or other device executes the firmware, software, routines, instructions, etc., which may cause actuators or other devices to interact with the physical world.

[0085] Although embodiments of the invention are specifically referred to in this text in the context of lithographic apparatus, embodiments of the invention may also be applied to 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.

[0086] 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 understood that, where the context permits, the invention is not limited to optical lithography.

[0087] While specific embodiments of the present invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The foregoing description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that changes may be made to the invention as described without departing from the scope of the claims that follow.

Claims

1. 1. A substrate support configured to support a substrate in a lithographic apparatus, comprising: a first peripheral wall (31) having a first height; a first drain (12) located radially outward of the first peripheral wall and configured to extract fluid; a second peripheral wall (32) having a second height and positioned radially outward of the first opening; a second drain (119) located radially outward of the second peripheral wall and configured to extract fluid; a flow restriction (33) having a third height and positioned radially outward of the second opening; a third drain (10) located radially outward of the flow restriction and the substrate and configured to extract fluid; the first opening, the second opening, and the third opening are distributed around a periphery of the substrate support; the third height is less than the first height and the second height; Board support.

2. the second drain is distributed over at least 80%, preferably at least 90%, of the circumference of the substrate support; The substrate support of claim 1 .

3. the second drains are distributed over the entire periphery of the substrate support intersecting with immersion liquid confined by a liquid handling system of the lithographic apparatus. A substrate support according to claim 1 or 2.

4. the flow restriction extends around the same area of ​​the circumference of the substrate support as the second drain; A substrate support according to claim 1, 2 or 3.

5. and / or a plurality of burls defining a support surface for supporting the substrate, the distance between the support surface and an upper surface of at least one of the first peripheral wall and the second peripheral wall being between 1 μm and 10 μm, preferably between 1 μm and 5 μm, more preferably between 3 μm and 5 μm; and / or further comprising a plurality of burls defining a support surface for supporting the substrate, wherein the distance between the support surface and an upper surface of the flow restriction is between 10 μm and 100 μm, preferably between 20 μm and 70 μm, and more preferably between 30 μm and 50 μm. A substrate support according to any one of claims 1 to 4.

6. the flow restriction portion comprises a third peripheral wall, and / or the flow restriction portion comprises a porous member, and / or the flow restriction portion has a width in the range of 0.1 mm to 2 mm, preferably in the range of 0.25 mm to 0.5 mm; A substrate support according to any one of claims 1 to 5.

7. the distance between the second drain and the outer edge of the substrate is less than 3 mm; A substrate support according to any one of claims 1 to 6.

8. the second drain is located within the outer periphery of the substrate; A substrate support according to any one of claims 1 to 7.

9. the first drain is in fluid communication with a first extractor channel via at least one first passage, the second drain is in fluid communication with a second extractor channel via at least one second passage, and the third drain is in fluid communication with the second extractor channel via at least one third passage; or the first drain is in fluid communication with a first extractor channel via at least one first passageway, the second drain is in fluid communication with a second extractor channel via at least one second passageway, and the third drain is in fluid communication with a third extractor channel via at least one third passageway; A substrate support according to any one of claims 1 to 8.

10. the second passage is located within a body of the substrate support; The substrate support of claim 9.

11. at least one of the first drain and the second drain comprises a groove in a surface of the substrate support facing the substrate and a plurality of openings in the groove; A substrate support according to any one of claims 1 to 10.

12. At least one of the first drain and the second drain comprises a first segment and a second segment. A substrate support according to any one of claims 1 to 11.

13. the first segment and the second segment are individually and selectively connectable to an extractor channel; The substrate support of claim 12.

14. A lithographic apparatus comprising a substrate support according to any one of claims 1 to 13.

15. A method for manufacturing a device using a substrate support according to any one of claims 1 to 13.

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