Substrate holding system and lithographic apparatus

Abstract

The substrate holding system includes a substrate support configured to support a substrate, a gas source, and a plurality of conduits. The substrate support includes a first port and a plurality of second ports located radially outside the first port. The first port and the plurality of second ports are configured to be in fluid communication with the gas source. The gas source is configured to supply an inert gas to the region between the substrate and the substrate support via the first port and the plurality of second ports. The substrate holding system is configured to be able to supply an inert gas to the region between the substrate and the substrate support through the first port or the plurality of second ports. The substrate holding system is configured to extract gas from the region between the substrate and the substrate support through the plurality of second ports.

Description

Technical Field

[0001] [Cross - reference to related applications] This application claims the benefit of priority of European application No. 22183530.9, filed on Jul. 7, 2022, the entire content of which is incorporated herein by reference.

[0002] [Technical Field] The present invention relates to a substrate holding system, a lithographic apparatus including the substrate holding system, a method of supporting a substrate on a substrate support, and a method of manufacturing a device including the method of supporting a substrate on a substrate support.

Background Art

[0003] A lithographic apparatus is a machine constructed 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 project a pattern of a patterning device (e.g., a mask), often referred to as a “design layout” or “design,” onto a layer of radiation - sensitive material (resist) provided on a substrate (e.g., a wafer). Known lithographic apparatuses include so - called steppers, in which each target portion is irradiated by exposing the entire pattern at once to the target portion, and so - called scanners, in which while the pattern is scanned through a radiation beam in a predetermined direction (“scanning” direction), the substrate is scanned synchronously in this direction, either parallel or antiparallel.

[0004] As semiconductor manufacturing processes advance, the dimensions of circuit elements are continuously reduced, and the number of functional elements such as transistors per device has been steadily increasing over the decades, following a trend commonly referred to as "Moore's Law". To follow Moore's Law, the semiconductor industry pursues technologies that can create ever smaller features. For projecting a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features 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 the resolution of smaller features can be achieved by providing an immersion liquid having a relatively high refractive index, such as water, in a local region between the projection system of the lithographic apparatus and the substrate during exposure. The effect of the immersion liquid is that smaller features can be imaged because the exposure radiation has a shorter wavelength in the liquid than in the gas. The effect of the immersion liquid is also thought to lead to an increase in the numerical aperture (NA) of the system and an increase in the depth of focus.

[0006] The immersion fluid may be confined by a fluid handling structure in a local region between the projection system of the lithographic apparatus and the substrate. SUMMARY OF THE INVENTION

[0007] In a semiconductor manufacturing process, a substrate is supported on a substrate support. Specifically, the substrate is supported on a plurality of bars protruding from the surface of the substrate support.

[0008] During use in a semiconductor manufacturing process, the substrate support may be surrounded by air. Oxygen and moisture in the air oxidize the substrate support, chemically changing the upper surface of the substrate support into an oxide film. Moisture in the air around the upper surface of the substrate support may originate from the humidity of the environment surrounding the substrate support or from regions where water (as an immersion liquid) exists around the substrate support. The presence of static electricity accumulated under the substrate may accelerate the oxidation process.

[0009] The formed oxide film is usually softer than the material of the substrate support and the material of the substrate support coating. The relative movement during clamping and unclamping may grind and remove the oxide film. This tribocorrosion process reduces the flatness of the substrate support.

[0010] Furthermore, since the oxide film is hydrophilic, when the substrate support is used in combination with water as the immersion liquid, the water on the outer radial side of the substrate support is drawn into the region between the substrate and the substrate support. This can increase the adhesive capillary force and change the strain pattern of the substrate (which can be called a strain fingerprint or a wafer load grid (WLG)).

[0011] An object of the present invention is to suppress the formation of an oxide film on the upper surface of the substrate support and reduce the flatness drift of the substrate support and the change in the strain pattern of the substrate.

[0012] According to the present invention, there is provided a substrate holding system including a substrate support configured to support a substrate, a gas source, and a plurality of conduits. The substrate support includes a first port in its central region and a plurality of second ports radially outside the first port. The first port and the plurality of second ports are configured to be in fluid communication with the gas source via the plurality of conduits. The gas source is configured to supply an inert gas to the region between the substrate and the substrate support via a first conduit and the first port, and via a second conduit and the plurality of second ports. The substrate holding system is configured to be able to supply an inert gas to the region between the substrate and the substrate support through the first port or the plurality of second ports, and the substrate holding system is configured to extract gas from the region between the substrate and the substrate support through the plurality of second ports.

[0013] According to the present invention, there is also provided a lithographic apparatus including the substrate holding system.

[0014] According to the present invention, a method of supporting a substrate on a substrate support is provided. The substrate support includes a first port in a central region of the substrate support and a plurality of second ports radially outside the first port. The method includes a substrate loading step of supplying an inert gas through the plurality of second ports into the region between the substrate and the substrate support, and a subsequent substrate clamping step of supplying an inert gas through the first port into the region between the substrate and the substrate support.

[0015] According to the present invention, a method of manufacturing a device including a method of supporting a substrate is also provided.

[0016] Further embodiments, features and advantages of the present invention, and the structures and operations of various embodiments, features and advantages of the present invention will be described in detail below with reference to the accompanying drawings.

Brief Description of the Drawings

[0017] Embodiments of the present invention are described only by way of example with reference to the following accompanying schematic diagrams. Corresponding reference symbols in the drawings indicate corresponding parts.

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[0018] The features shown in the drawings are not necessarily to scale and are not limited to the sizes and / or arrangements depicted. It will be understood that the drawings may include optional features that are not essential to the present invention. Further, not all of the features of the device are depicted in each drawing, and the drawings may show only some of the components relevant to the description of a particular feature.

Embodiments for Carrying Out the Invention

[0019] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including, for example, ultraviolet radiation having a wavelength of 365, 248, 193, 157, or 126 nm.

[0020] As used in this document, the terms "reticle", "mask", or "patterning device" may be broadly construed to refer to a general patterning device that can be used to impart a patterned cross-section corresponding to a pattern created on a target portion of a substrate to an incident radiation beam. The term "light valve" may also be used in this context. In addition to classical masks (transmission or reflection, binary, phase shift, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0021] FIG. 1 schematically depicts a lithographic apparatus. The lithographic apparatus includes 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 constructed to support a patterning device (e.g., a mask) MA and connected to a first positioning device PM configured to accurately 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 positioning device PW configured to accurately 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) of the substrate W.

[0022] During operation, the illumination system IL receives the radiation beam B from the 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, and / or other types of optical components, or any combination thereof, for directing, shaping, and / or controlling the radiation. The illuminator IL can be used to adjust the radiation beam B to have a desired spatial intensity distribution and angular intensity distribution in a cross-section in the plane of the patterning device MA.

[0023] As used herein, the term "projection system" PS should be broadly construed to encompass various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, depending on other factors such as the use of exposure radiation and / or immersion liquid and the use of vacuum. Any of the terms "projection lens" used herein may also be considered synonymous with the more general term "projection system" PS.

[0024] The lithographic apparatus may be of a type in which at least a portion of the substrate W is covered by an immersion liquid having a relatively high refractive index, for example water, to fill the immersion space between the projection system PS and the substrate W, which is also referred to as immersion lithography. Detailed information on immersion techniques is described in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0025] The lithographic apparatus may be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel and / or while the preparation for the next exposure of the substrate W is being carried out on the substrate W disposed on one substrate support WT, another substrate W on the other substrate support WT may be used for the exposure of the pattern onto the other substrate W.

[0026] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not shown). The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a characteristic of the projection system PS or of the radiation beam B. The measurement stage may hold a plurality of sensors. The cleaning device may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the system that provides the immersion liquid. The measurement stage may move under the projection system PS when the substrate support WT is away from the projection system PS.

[0027] During operation, the radiation beam B is incident on a patterning device (e.g. a mask) MA held on a mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioning device PW and the position measurement system IF, the substrate support WT can be accurately moved so that, for example, different target portions C are positioned at the locations where they are focused and aligned in the path of the radiation beam B. Similarly, the first positioning device PM and optionally another position sensor (not explicitly shown in FIG. 1) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks P1, P2 are shown occupying dedicated target portions, but may be arranged in the spaces between the target portions. The substrate alignment marks P1, P2 are known as scribe line alignment marks when arranged between the target portions C.

[0028] To clarify the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely, the x-axis, the y-axis, and the z-axis. Each of the three axes is orthogonal to the other two axes. Rotation about the x-axis is called Rx rotation. Rotation about the y-axis is called Ry rotation. Rotation about the z-axis is called Rz rotation. The x-axis and the y-axis define a horizontal plane, and the z-axis is in the vertical direction. The Cartesian coordinate system is not intended to limit the present invention and is used only for clarification. Instead, the present invention may be clarified using another coordinate system such as a cylindrical coordinate system. The directions of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0029] Immersion technology has been introduced into lithography systems to improve the resolution of smaller features. In an immersion lithography apparatus, a liquid layer of an immersion liquid having a relatively high refractive index is inserted into the immersion space between the projection system PS (which projects a patterned beam onto the substrate W) of the apparatus and the substrate W. The immersion liquid covers at least a part of the substrate W that is under the final element of the projection system PS. Thus, at least a part of the substrate W that is to be exposed is immersed in the immersion liquid.

[0030] In commercial immersion lithography, the immersion liquid is water. Usually, water is high-purity distilled water such as ultra-pure water (UPW) commonly used in semiconductor manufacturing factories. In an immersion system, the UPW is often purified and may undergo additional processing steps before being supplied as the immersion liquid to the immersion space. In addition to water, other liquids having a high refractive index, such as hydrocarbons and / or aqueous solutions such as fluorocarbons, can be used as the immersion liquid. Furthermore, other fluids other than liquids are also envisioned to be used in immersion lithography.

[0031] In this specification, local immersion is described in which, during use, the immersion liquid is confined in an immersion space between the final element and the surface facing the final element. The opposing surface is the surface of the substrate W or the surface of a support stage (or substrate support WT) that is coplanar with the surface of the substrate W. (It should be noted that in the following text, references to the surface of the substrate W, unless otherwise specified, also refer to the surface of the substrate support WT in addition to or instead of the surface of the substrate support WT. The same applies in the reverse case). The fluid handling structure IH present between the projection system PS and the substrate support WT is used to confine the immersion liquid in the immersion space. The immersion space filled with the immersion liquid is smaller in area than the upper surface of the substrate W in a plane, and the immersion space remains substantially stationary relative to the projection system PS while the substrate W and the substrate support WT move thereunder.

[0032] As other immersion systems, a non-confined immersion system (so-called "all-wet" immersion system), a bath-type immersion system, etc. are considered. In a non-confined immersion system, the immersion liquid covers a wider area than the lower surface of the final element. The liquid outside the immersion space exists as a thin liquid film. The liquid may cover the entire surface of the substrate W or may cover the substrate W and the substrate support WT that is coplanar with the substrate W. In a bath-type system, the substrate W is completely immersed in a bath of the immersion liquid.

[0033] The fluid handling structure IH is a structure that confines the immersion liquid in the immersion space by supplying the immersion liquid to the immersion space and removing the immersion liquid from the immersion space. This includes features that are part of a fluid supply system. The configuration disclosed in PCT Patent Application Publication No. WO99 / 49504 is an initial fluid handling structure, provided with piping for supplying or recovering the immersion liquid to / from the immersion space, and operates in response to the relative movement of the stage under the projection system PS. In more recent designs, the fluid handling structure at least partially defines the immersion space by extending along at least a part of the boundary of the immersion space between the final element of the projection system PS and the substrate support WT or the substrate W.

[0034] The fluid handling structure IH may have various function options. Each function may be derived from corresponding features that enable the fluid handling structure IH to implement that function. The fluid handling structure IH may be referred to by a number of different terms representing functions such as a barrier member, a seal member, a fluid supply system, a fluid removal system, a liquid confinement structure, and the like.

[0035] As a barrier member, the fluid handling structure IH is a barrier against the flow of the immersion liquid from the immersion space. As a liquid confinement structure, this structure confines the immersion liquid in the immersion space. As a seal member, the sealing feature of the fluid handling structure IH forms a seal for confining the immersion liquid in the immersion space. The sealing feature may include an additional gas flow from an opening on the surface of a seal member such as a gas knife.

[0036] The fluid handling structure IH may supply an immersion fluid and thus may be a fluid supply system.

[0037] The fluid handling structure IH may at least partially confine the immersion liquid and thus may be a fluid confinement system.

[0038] The fluid handling structure IH may provide a barrier against the immersion liquid and thus may be a fluid confinement structure.

[0039] The fluid handling structure IH may generate or use a gas flow, for example, to assist in controlling the flow and / or position of the immersion liquid.

[0040] The gas flow may form a seal for confining the immersion fluid, and for this purpose, the fluid handling structure IH may be referred to as a seal member, and such a seal member may be a fluid confinement structure.

[0041] The immersion liquid may be used as the immersion fluid. In that case, the fluid handling structure IH may be a liquid handling system. Referring to the foregoing description, references to features defined for the fluid in this paragraph may be understood to include features defined for the liquid.

[0042] The lithographic apparatus has a projection system PS. During the exposure of the substrate W, the projection system PS projects a patterned beam of radiation onto the substrate W. In order to reach the substrate W, the path of the radiation beam B passes through an immersion liquid confined by the fluid handling structure IH between the projection system PS and the substrate W. The projection system PS has a lens element that is at the end of the beam path and contacts the immersion liquid. This lens element that contacts the immersion liquid may be referred to as the "last lens element" or "final element". The final element is at least partially surrounded by the fluid handling structure IH. The fluid handling structure IH can confine the immersion liquid under and above the opposing surface of the final element.

[0043] As shown in FIG. 1, the lithographic apparatus comprises a controller 500. The controller 500 is configured to control the substrate support WT.

[0044] Figure 2 shows a part of a lithographic apparatus that does not conform to the present invention but is useful for showing the features of the present invention. The configuration shown in Figure 2 and described below can be applied to the lithographic apparatus described above and shown in Figure 1. Figure 2 is a cross-sectional view of the substrate support 20 and the substrate W. In one embodiment, the substrate support 20 comprises one or more adjustment channels 61 of a thermal adjustment device, which will be described in more detail below. There is a gap 5 between the edge of the substrate W and the edge of the substrate support 20. When an image is formed on the edge of the substrate W, or when the substrate W first moves under the projection system PS (as described above), the immersion space filled with liquid by, for example, the fluid handling structure IH at least partially passes over the gap 5 between the edge of the substrate W and the edge of the substrate support 20. Thereby, there is a possibility that the liquid enters the gap 5 from the immersion space.

[0045] The substrate W is held by a support body 21 (e.g., a pimple or a bar table) having one or more bars 41 (i.e., protrusions from the surface). The support body 21 is an example of an object holder. Another example of an object holder is a mask support. The pressure applied between the substrate W and the substrate support 20 helps to hold the substrate W firmly in place. However, if the immersion liquid enters between the substrate W and the support body 21, problems may occur, especially when removing (unloading) the substrate W.

[0046] To cope with the immersion liquid entering the gap 5, at least one drain 10, 12 is provided at the edge of the substrate W to remove the immersion liquid entering the gap 5. In the embodiment of Figure 2, two drains 10, 12 are shown, but there may be only one drain or three or more drains. In one embodiment, each of the drains 10, 12 is annular, so that the entire perimeter of the substrate W is surrounded.

[0047] The main function of the first drain 10 (which is radially outside the edge of the substrate W / support body 21) is to prevent bubbles from entering the immersion space where the liquid of the fluid handling structure IH exists. Such bubbles may have an adverse effect on the imaging of the substrate W. The first drain 10 is provided to prevent the gas in the gap 5 from leaking into the immersion space of the fluid handling structure IH. If gas leaks into the immersion space, bubbles may be generated in the immersion space. Such bubbles may lead to imaging errors if they are in the path of the projection beam. The first drain 10 is configured to remove gas from the gap 5 between the edge of the substrate W and the edge of the recess of the substrate support 20 on which the substrate W is disposed. The edge of the recess of the substrate support 20 may be defined by a covering 101, and the covering 101 is optionally separated from the support body 21 of the substrate support 20. The covering 101 may be formed in a ring shape in plan view and may surround the outer edge of the substrate W. The first drain 10 mainly extracts gas and extracts a small amount of immersion liquid.

[0048] The second drain 12 (which is radially inside the edge of the substrate W / support body 21) is provided to prevent the liquid from finding a path to flow into the lower side of the substrate W from the gap 5 and to prevent the substrate W from being inefficiently removed from the substrate table WT after imaging. By providing the second drain 12, the problems that may occur when the liquid finds a path to flow into the lower side of the substrate W are reduced or eliminated.

[0049] As shown in FIG. 2, in an embodiment, the lithographic apparatus includes a first extraction channel 102 for a passage through which a two-phase flow passes. The first extraction channel 102 is formed in a block. The first drain 10 and the second drain 12 are respectively provided with openings 107, 117 and extraction channels 102, 113. The extraction channels 102, 113 are in fluid communication with the openings 107, 117 respectively through passages 103, 114.

[0050] As shown in Figure 2, the covering 101 has an upper surface. The upper surface 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 covering 101 and the substrate W. In certain embodiments, the relative movement is caused by the substrate support 20 moving under the fluid handling structure IH. In another embodiment, the relative movement is caused by the fluid handling structure IH moving over the substrate support 20. In yet another embodiment, the relative movement is caused by both the movement of the substrate support 20 under the fluid handling structure IH and the movement of the fluid handling structure IH over the substrate support 20.

[0051] <Example> Figures 3 to 5 show cross-sectional views of the substrate W and the substrate support 210. The substrate support 210 is part of a substrate holding system 200 not according to the present invention. The substrate holding system 200 may be integrated in a lithographic apparatus as shown in Figure 1. The substrate support 210 may have features similar to those shown for the substrate support 20 in Figure 2. This example of the substrate holding system 200 and the substrate support 210 is not meant to acknowledge the state of the art, but only serves to highlight some of the particular advantages of the present invention over other possible configurations.

[0052] The substrate support 210 may include a support body, as does the substrate support 20 shown in Figure 2. However, for the sake of simplicity of explanation, this support body will not be referred to. The substrate support 210 comprises a plurality of bars 241. When the substrate W is supported by the substrate support 210, the substrate W is in direct contact with the substrate support 210. The distal ends of the bars 241 form a plane on which the underside of the substrate W is supported. The underside of the substrate W is in contact with the distal ends of the bars 241. The bars 241 are on the upper side of the substrate support 210.

[0053] The substrate support 210 shown in FIGS. 3 to 5 includes a plurality of multi-functional openings 222 arranged circumferentially around the substrate support 210, and a plurality of extraction openings 223 arranged circumferentially around the substrate support 210 radially outside the plurality of multi-functional openings 222.

[0054] The substrate holding system 200 is configured to supply clean dry air (CDA) to the region 250 between the substrate support 210 and the substrate W through the plurality of multi-functional openings 222. The substrate holding system 200 is further configured to extract fluid from the region 250 between the support body 221 and the substrate W through the plurality of multi-functional openings 222 and the plurality of extraction openings 223.

[0055] The substrate support 210 shown in FIGS. 3 to 5 includes an inner seal 231 located radially inside the plurality of extraction openings 223 and an outer seal 232 located radially outside the plurality of extraction openings 223.

[0056] The sequence of loading the substrate W onto the substrate support 210 is shown in FIGS. 3A - 3C. When the substrate W descends toward the substrate support 210 (FIG. 3A), CDA is supplied to the region 250 between the substrate W and the substrate support 210 (FIG. 3B). For a short time, the substrate W is supported on a cushion of CDA. After a short time has elapsed, the substrate holding system 200 extracts gas from the plurality of multi-functional openings 222 (FIG. 3C). As a result, the pressure in the region 250 between the substrate W and the substrate support 210 becomes lower than the ambient pressure, a clamping force in the direction toward the substrate support 210 is applied to the lower side of the substrate W, and the substrate W is fixed (clamped) to the substrate support 210.

[0057] When the substrate W is loaded onto the substrate support 210 and the clamping force is established, the substrate holding system 200 transitions to the clamped state (FIG. 4). In the clamped state, the multifunctional opening 222 may stop extracting gas from the region between the substrate W and the substrate support 210. To maintain the region between the substrate W and the substrate support 210 at a pressure lower than the ambient pressure, the extraction opening 223 may extract fluid from the region between the substrate W and the substrate support 210. During this clamped state, air from the ambient environment may enter through leakage into the region 250 between the substrate W and the substrate support 210. For example, air may leak into the region 250 between the substrate W and the substrate support 210 through holes in the body of the substrate support 210. Alternatively, air from the ambient environment may move radially inward from the side of the substrate support 210 and pass through the outer seal 232, the plurality of extraction openings 223, and the inner seal 231 to reach the inner portion of the region 250 between the substrate W and the substrate support 210.

[0058] The unload process for removing the substrate W from the substrate support 210 is shown in FIG. 5. In this process, the pressure between the substrate W and the substrate support 210 is increased by the introduction of CDA through the plurality of multifunctional openings 222. At this time, the extraction opening 223 may continue to extract fluid from the region 250 between the substrate W and the substrate support 210. This may be to remove the immersion fluid around the inner seal 231 and the outer seal 232 and make the unload sequence reproducible.

[0059] As is apparent from the above, at all stages of operation, the upper surface of the substrate support 210 is exposed to air. This air contains oxygen and may contain moisture. The air may contain moisture derived from water vapor in the air that has moved radially inward of the outer seal 232 and the inner seal 231 of the substrate support 210 from the environment surrounding the substrate support 210. Further, in immersion lithography, the region radially outside the outer seal 232 may be immersed in the immersion liquid. This is shown as the region below the gap 5 in FIG. 2. This immersion liquid may be water, for example ultra-pure water (UPW). During operation, this ultra-pure water can also move radially inward toward the center of the substrate support 210 in the form of liquid or vapor through the outer seal 232, the plurality of extraction openings 223, and the inner seal 231.

[0060] If oxygen and water are present in the region between the substrate W and the substrate support 210, oxidation of the upper surface of the substrate support 210 may occur. Since the plurality of bars 241 are arranged on the upper surface of the substrate support 210, the surface of the bars 241 may be oxidized. If the substrate support 210 is coated, it may be the coating that is oxidized. Common coatings include materials comprising diamond or diamond-like carbon (DLC). These coatings are prone to oxidation in the presence of oxygen and water.

[0061] The rate of oxidation is increased by the presence of charge that can accumulate on the lower side of the substrate W. However, since the oxidation process occurs spontaneously ( "auto-oxidation") in the presence of oxygen and water, oxidation of the upper surface of the substrate support 210 cannot be prevented even by removing this charge accumulation.

[0062] The oxide film formed by the oxidation process is usually softer than the material of the substrate support 210 or its coating material. For example, the oxide film formed when DLC is oxidized is softer than the DLC itself. This means that when the surfaces move relative to each other during loading and unloading, the oxide film may be mechanically removed. This removal of material leads to a decrease in the flatness of the substrate support 210.

[0063] Furthermore, the formed oxide film is usually hydrophilic. This means that when water is used as the immersion liquid, the water on the outer radial side of the substrate support 210 may be drawn into the region 250 between the substrate W and the substrate support 210. This may increase the adhesive capillary force acting on the lower side of the substrate W and cause drift of the wafer load grid (WLG). The WLG is a measure of overlay error due to residual deformation caused by local slippage during loading.

[0064] <Embodiment> Since auto-oxidation requires the presence of oxygen and water, it can be reduced by removing these components from the region surrounding the substrate support 210. The use of CDA in the above example aims to avoid the presence of water in the region 250 between the substrate W and the substrate support 210, but as discussed above, water may still be present in the region 250. Therefore, in order to further reduce the auto-oxidation of the upper surface of the substrate support 210, the present invention is directed to ensuring that there is no or very little oxygen or water in the region 250 between the substrate W and the substrate support 210. In the present invention, this is achieved by providing a substrate holding system 300 configured to supply an inert gas to the region 350 between the substrate support 310 and the substrate W over the time that the substrate W is clamped to the substrate support 310.

[0065] Table 1 shows the difference in the oxidation rate of a substrate support coated with diamond-like carbon (DLC) in a normal environment (including water and air) and an inert gas environment (N2 gas). The oxidation rate was determined by measuring the amount of oxidation products on the surface of the DLC. This is shown as "Increase in oxygen on the surface (%)" in Table 1. The increase rate of oxygen on the surface of the DLC after 4 days is extremely lower in the N2 gas environment (1.20) than in the water and air environment (3.50). In the N2 test, the substrate support environment was flushed with N2 (flashed), and the subsequent environment was kept sealed. This means that the potential advantage of the present invention, in which an inert gas is supplied to the region 350 between the substrate support 310 and the substrate W over the time the substrate W is clamped to the substrate support 310, is not fully represented by the results. However, the results still show that providing an inert gas environment in the region between the substrate support and the substrate can potentially have a significant impact on the oxidation rate. [Table 1]

[0066] The same relationship is shown in FIG. 6. FIG. 6 shows a plot of the surface oxidation rate (O) on the DLC coating surface against the exposure time (t, in hours) of the DLC coating on a substrate in an environment containing air, ultrapure water (UPW), and nitrogen (N2). The DLC coating is a DLC coating that can be used in the substrate support WT. In this context, the surface oxidation rate means the ratio of the DLC coating that is the oxidation product. The substrate having the DLC coating used to generate the data shown in FIG. 6 (hereinafter, "sample") was plasma-treated to obtain a minimum oxidation state of about 2%. The sample was then exposed to various environments for a period ranging from 30 minutes to 4 days. Exposure of the sample to the autoxidation conditions (i.e., air or ultrapure water) was carried out in a glass Petri dish, and the opening of the Petri dish was covered with a glass cap. To expose the sample to air, the glass cap was not made to completely cover the Petri dish so that fresh air could be continuously supplied. The sample exposed to N2 was exposed in a plastic-sealed glove box-type container containing N2 gas.

[0067] After a predetermined exposure time, the ratio of surface oxidation was measured using X-ray photoelectron spectroscopy (XPS). XPS can measure the elemental composition and also the chemical and electronic states of the atoms in the material.

[0068] Contact angle analysis was also performed on the sample. The contact angle (CA) is a measure of the ability of a liquid to wet the surface of a solid. The shape taken by a droplet on the surface depends on the surface tension of the fluid and the nature of the surface. The droplet has a curved shape. The angle between (i) the surface on which the droplet is formed and (ii) the tangent to the curved shape of the droplet at the edge of the droplet (i.e., the place where the surface on which the droplet is formed and the droplet are in contact) is the contact angle.

[0069] As shown in FIG. 6, the surface oxidation rate on the sample surface increases as the exposure time becomes longer. The oxidation rate of the sample was high for the sample in an environment containing air and low for the sample in an environment containing ultrapure water. The oxidation rate of the sample in an environment containing N2 was much lower than the oxidation rates of the samples of air and ultrapure water. Therefore, FIG. 6 shows that supplying an inert gas to the region between the substrate support WT and the substrate W can significantly reduce the oxidation rate of the surface of the substrate support WT facing the substrate. This means that the temporal deterioration of the flatness of the substrate support WT can be avoided. As a result, the life of the substrate support can be extended.

[0070] FIG. 7 shows (i) a plot of the surface oxidation rate (O) against the exposure time (t, seconds) of a sample (i.e., a DLC-coated substrate) in an environment containing air and (ii) a plot of the contact angle (CA) against the exposure time (t, seconds) of the sample in an environment containing air. The plots generally show that as the surface oxidation rate increases, the contact angle decreases. A large contact angle represents a highly hydrophobic surface. Therefore, FIG. 7 shows that the hydrophobicity decreases as the surface oxidation rate increases. Therefore, FIG. 7 demonstrates that as the surface of the substrate support WT is oxidized, water molecules may be more likely to be attracted. This means that the water on the outer radial side of the substrate support WT is more likely to be attracted to the region 250 between the substrate W and the substrate support WT. This means that the adhesive capillary force acting on the lower side of the substrate W may increase, which may cause drift of the wafer load grid (WLG). Therefore, the wafer load grid (WLG) can be improved by supplying an inert gas to the region between the substrate W and the substrate support WT and reducing the oxidation rate.

[0071] The substrate holding system 300 comprises a substrate support 310, a gas source 382, and a plurality of conduits. Similar to the substrate holding system 200, the substrate holding system 300 can be integrated into a lithographic apparatus as shown in FIG. 1. However, the present invention is not limited to such an implementation of the substrate holding system 300, and the substrate holding system 300 can be used in a variety of other scenarios. For example, the present invention can be implemented in a lithographic apparatus that does not utilize immersion technology.

[0072] The substrate support 310, which is part of the substrate holding system 300 according to the present invention, is shown in FIGS. 8 to 11. FIG. 8 shows a plan view of the substrate support 310. FIGS. 9 to 11 show cross-sectional views of the substrate support 310 operating in a number of states. The substrate support 310 is configured to support a substrate W. The substrate support 310 itself may be similar in structure to the substrate support 210 of the previous example, but includes an additional supply opening 321 in the central region of the substrate support 310.

[0073] Similar to the substrate support 210 of the previous example, the substrate support 310 may include a support body. However, for the sake of simplicity of explanation, this support body will not be referred to. The substrate support 310 may comprise a plurality of bars 341. When the substrate W is supported by the substrate support 310, the substrate W is in direct contact with the substrate support 310. The distal ends of the bars 341 form a plane on which the underside of the substrate W is supported. The underside of the substrate W is in contact with the distal ends of the bars 341. The bars 341 are on the upper side of the substrate support 310. The plurality of bars 341 may be arranged in a plurality of circumferential rings. However, the present invention is not limited thereto, and the plurality of bars 341 may be arranged in any suitable pattern. The diameter of each bar 341 is not particularly limited. In one embodiment, the bar may have a diameter of about 100 μm to 120 μm. In another embodiment, the bar may have a diameter of about 175 μm. The diameters of the plurality of bars 341 may be the same, or may vary across the entire substrate support 310.

[0074] The distance between each barb 341 is called the barb pitch. This may be constant throughout the substrate support 310 or may vary as known to those skilled in the art. In certain embodiments, the barb pitch may be about 1.5 mm. In another embodiment, the barb pitch may be about 2.5 mm.

[0075] The substrate support 310 includes a supply opening 321 located in a central region of the substrate support 310. For the purposes of this embodiment, the substrate W and the substrate support 310 are aligned such that the center of the substrate W and the center of the substrate support 310 are aligned in a direction perpendicular to the upper surface of the substrate support 310. This means that the supply opening 321 is located under the central region of the substrate W. The substrate support 310 includes a plurality of multi-functional openings 322 that can be circumferentially arranged around the periphery of the substrate support 310 radially outside the supply opening 321. The plurality of multi-functional openings 322 may be evenly distributed circumferentially around the supply opening 321. In a substrate support configured to support a substrate W with a diameter of 300 mm, the radial distance between each of the plurality of multi-functional openings 322 and the center of the substrate support 310 may be greater than 40 mm, preferably greater than 50 mm, and more preferably greater than 60 mm. In a substrate support configured to support a substrate W with a diameter of 300 mm, the radial distance between each of the plurality of multi-functional openings 322 and the center of the substrate support 310 may be less than 100 mm, preferably less than 80 mm, and more preferably less than 65 mm. These dimensions can be adjusted according to the diameter of the substrate W configured to be supported by the substrate support 310. For example, the radial distance between each of the plurality of multi-functional openings 322 and the center of the substrate support 310 may be greater than 13% of the diameter of the substrate W, preferably greater than 17% of the diameter of the substrate W, and more preferably greater than 20% of the diameter of the substrate W. For example, the radial distance between each of the plurality of multi-functional openings 322 and the center of the substrate support 310 may be less than 33% of the diameter of the substrate W, preferably less than 27% of the diameter of the substrate W, and more preferably less than 22% of the diameter of the substrate W.

[0076] In one embodiment, the radial distance from the center of the substrate support 310 to each multi-functional opening 322 may be the same. In another embodiment, the radial distance from the center of the substrate support 310 to some of the multi-functional openings 322 may be greater than that to other multi-functional openings 322 for some of the multi-functional openings 322. This may be the case even if the plurality of multi-functional openings 322 are arranged in a plurality of circumferential rings and the distance from the center of the substrate support 310 to the multi-functional openings is different for each circumferential ring. The supply opening 321 is an example of a first port. The plurality of multi-functional openings 322 are examples of a plurality of second ports.

[0077] The supply opening 321 and the plurality of multi-functional openings 322 are configured to be in fluid communication with a gas source 382 via a plurality of conduits 371, 372, 373. The gas source 382 may be configured to supply an inert gas to the supply opening 321 via the conduits 371, 372 and to supply an inert gas to the plurality of multi-functional openings 322 via the conduits 371, 373. The substrate holding system 300 may be further configured to extract gas from the region 350 between the substrate W and the substrate support 310 through the plurality of multi-functional openings 322.

[0078] The substrate support 310 may further include a plurality of extraction openings 323 that are radially outside the plurality of multi-functional openings 322 and are circumferentially arranged around the substrate support 310. The substrate holding system 300 may be configured to extract fluid from the region 350 between the substrate W and the substrate support 310 through the plurality of extraction openings 323. The plurality of extraction openings 323 may be provided in the edge region of the substrate support 310. The plurality of extraction openings 323 are examples of a plurality of third ports. Instead of the plurality of extraction openings 323, the present invention may include a single extraction opening 323 in the form of an annular channel that extends circumferentially around the substrate support 310 in the edge region.

[0079] The substrate support 310 may further include a plurality of seals 331, 332. The seals 331, 332 are circumferential rings protruding from the substrate support 310. In certain embodiments, the substrate support 310 includes an inner seal 331 that is located radially inward of the plurality of extraction openings 323 but still within the edge region of the substrate support 310, and an outer seal 332 that is located radially outward of the plurality of extraction openings 323.

[0080] The edge region may be a region that is radially outside the radially outermost circumferential ring of the flange 341. The combination of the outer seal 332, the plurality of extraction openings 323, and the inner seal 331 prevents air and / or immersion liquid from moving radially inward from the environment around the substrate support 310 into the region 350 between the substrate W and the substrate support 310. In an embodiment where the substrate support 310 is configured to support a substrate W having a diameter of 300 mm, the edge region of the substrate support 310 may be a region where the distance to the periphery of the substrate W is less than 50 mm, preferably less than 25 mm, and more preferably less than 10 mm when the substrate W is supported on the substrate support 310. The distance between each of the plurality of extraction openings 323 and the edge of the substrate W may be less than 25 mm, preferably less than 10 mm, more preferably less than 5 mm, and may also be greater than 1.5 mm.

[0081] These dimensions can be adjusted according to the substrate support 310 configured to support substrates W having alternating diameters. For example, when the substrate W is supported on the substrate support 310, the distance between each of the plurality of extraction openings 323 and the periphery of the substrate W may be less than 10% of the diameter of the substrate W, preferably less than 4% of the diameter of the substrate W, more preferably less than 2% of the diameter of the substrate W, and may also be greater than 0.5% of the diameter of the substrate W.

[0082] In one embodiment, when the substrate W is supported by the substrate support 310, the upper surfaces of the inner seal 331 and the outer seal 332 (i.e., the surfaces of the inner seal 331 and the outer seal 332 that are substantially parallel to the substrate W 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 inner seal 331 and the outer seal 332 and the lower surface of the substrate W is such that at least a partial seal is formed between the upper surfaces of the seals 331, 332 and the lower surface of the substrate W. That is, the seals 331, 332 themselves suppress, but do not completely prevent, the flow of fluid between the region 350 between the substrate W and the substrate support 310 and the region radially outside the substrate support 310. The distance between the upper surfaces of the seals 331, 332 and the lower surface of the substrate W may be less than 10 μm, preferably less than 5 μm, preferably greater than 1 μm, and preferably greater than 3 μm. As a result, the flow of the inert gas from the center of the substrate support 310 to the extraction opening 323 serves to strengthen the inner seal 331 and prevent air from the region radially outside the substrate support 310 from entering the region 350 between the substrate W and the substrate support 310.

[0083] The widths of the inner seal 331 and the outer seal 332 (i.e., the radial distance between the inner peripheral edge and the outer peripheral edge of the seal) may preferably be greater than 0.1 mm, more preferably greater than 0.2 mm. The widths of the inner seal 331 and the outer seal 332 may preferably be less than 1 mm, more preferably less than 0.6 mm.

[0084] The substrate holding system 300 may be configured to perform a load sequence, operate in a clamped state, and perform an unload sequence.

[0085] Figures 9A through 9C show the substrate support 310 of the substrate holding system 300 in three stages of the load sequence. Figure 9A shows the substrate W being lowered toward the substrate support 310. The method of lowering the substrate W toward the substrate support 310 is not particularly limited. As an example, the substrate W may first be received by a plurality of extensible pins (not shown) in the extended position. Next, the pins may be retracted to lower the substrate W toward the substrate support 310. When the lower side of the substrate W contacts the plurality of bars 341, the pins are continuously retracted, the substrate W no longer contacts the pins, and the substrate W is fully supported by the plurality of bars 341. However, the present invention is not limited to this method of lowering the substrate W toward the substrate support 310, and those skilled in the art will understand that any known technique for lowering the substrate W toward the substrate support 310 can be implemented.

[0086] As the substrate W approaches the substrate support 310, an inert gas is supplied from the gas source 382 through the plurality of conduits 371, 372, 373 and the multi-functional opening 322 to the region 350 above the substrate support 310 (see Figure 9B). As the substrate W approaches the substrate support 310, the pressure in the region 350 between the substrate W and the substrate support 310 becomes greater than the ambient pressure, and the substrate W lands on a cushion of inert gas. That is, the substrate W is supported by the inert gas supplied to the region 350 between the substrate W and the substrate support 310. The substrate W may be supported such that a small gap (h) exists between the substrate support 310 and the substrate W. This gap (h) may preferably be greater than 50 μm, preferably greater than 80 μm, and more preferably greater than 100 μm. This gap (h) may preferably be less than 500 μm, preferably less than 250 μm, and more preferably less than 200 μm. While the substrate W is supported on a cushion of inert gas, the inert gas supplied from the multi-functional opening 322 flows radially outward toward the edge of the substrate W in the region 350 between the substrate W and the substrate support 310.

[0087] The substrate W is supported on a cushion of inert gas for a predetermined time. The predetermined time may depend on the flow rate of the inert gas passing through the plurality of multifunctional openings 322. The predetermined time is the time required to ensure that most of the air that enters between the substrate W and the substrate support 310 from the environment while the substrate W is being lowered towards the substrate support 310 is replaced by the inert gas. In certain embodiments, this amount of time may be longer than 10 milliseconds, preferably longer than 20 milliseconds. In certain embodiments, this amount of time may be shorter than 500 milliseconds, preferably shorter than 200 milliseconds. However, the present invention is not limited to the substrate W being supported on a cushion of inert gas for a predetermined time. For example, the substrate W may be supported on a cushion of inert gas until the reading of the sensor 378 reaches a predetermined threshold value.

[0088] After the substrate W lands on a cushion of inert gas and a predetermined time has elapsed (or after the reading of the sensor 378 reaches a predetermined threshold value), the inert gas stops being supplied to the region 350 between the substrate W and the substrate support 310 via the plurality of multifunctional openings 322. Instead, the substrate support 310 switches to extract gas from the region 350 between the substrate W and the substrate support 310 via the plurality of multifunctional openings 322 (FIG. 9C). In this implementation, the pressure in the region 350 between the substrate W and the substrate support 310 becomes lower than the ambient pressure, and a force in the direction towards the substrate support 310 is applied to the lower side of the substrate W, clamping the substrate W to the substrate support 310.

[0089] By performing this load sequence, it is ensured that when the substrate W is first clamped to the substrate support 310, most of the gas in the region 350 between the substrate W and the substrate support 310 is an inert gas rather than air that may contain oxygen or water.

[0090] The state in which the substrate holding system 300 is configured to operate in the clamped state is shown in FIG. 10. In this state, an inert gas is supplied from the gas source 382 to the region 350 between the substrate W and the substrate support 31 through the supply opening 321. In certain embodiments, in the clamped state, the inert gas is supplied to the region 350 between the substrate W and the substrate support 310 only through the supply opening 321. In another embodiment, in the clamped state, the inert gas is supplied to the region 350 between the substrate W and the substrate support 310 through the supply opening 321 and a plurality of multifunctional openings 322.

[0091] The substrate holding system 300 executes the clamped state for most of the time that the substrate W is clamped to the substrate support 310. The substrate holding system 300 may execute the clamped state for the entire time that the substrate W is supported by the substrate support 310, except during the load sequence and the unload sequence. When the substrate holding system 300 is implemented within a lithographic apparatus, the substrate holding system 300 may operate in the clamped state for the entire time that the lithographic apparatus is performing an exposure process on the substrate W. Generally, the substrate holding system 300 may operate in the clamped state for 90% of the time that the substrate holding system 300 is operating, preferably 95% of the time that the substrate holding system 300 is operating.

[0092] In the clamped state, the flow rate of the inert gas is sufficient to establish or maintain an inert gas environment in the region 350 between the substrate W and the substrate support 310. The inert gas environment is an environment in which most of the gas is an inert gas. In this aspect, "most" may mean greater than 90%, preferably greater than 95%, and more preferably greater than 99%. In the clamped state, the flow rate of the inert gas through the supply opening 321 may be greater than 1 NLpm (Normal Liter per minute, i.e., the flow rate in liters per minute when the gas is at standard temperature and standard pressure), preferably greater than 1.5 NLpm, and more preferably greater than 1.8 NLpm. In the clamped state, the flow rate of the inert gas through the supply opening 321 may be less than 10 NLpm, preferably less than 5 NLpm, and more preferably less than 2.5 NLpm. For example, the flow rate of the inert gas may be 2 NLpm. Using this flow rate, the inert gas environment can establish the inert gas environment in the region 350 between the substrate W and the substrate support 310 in about 350 ms. This means that depending on the timing of the load sequence and the unload sequence, the time during which the substrate support 310 is exposed to oxidation conditions can be reduced by about 98%.

[0093] By supplying an inert gas to the region 350 between the substrate W and the substrate support 310 for most of the time when the substrate W is clamped to the substrate support 310, it is ensured that for the entire time the substrate W is clamped to the substrate support 310, most of the gas present in the region 350 between the substrate W and the substrate support 310 is an inert gas and not air from the surrounding environment that may contain oxygen or moisture. For example, even if there is a leak in the substrate support 310 and air from the environment may enter the region 350 between the substrate W and the substrate support 310, a constant flow of inert gas from the supply opening 321 to the extraction opening 323, and a constant extraction of fluid from the extraction opening 323 mean that the air is quickly removed and replaced with an inert gas before the air can cause significant oxidation of the upper surface of the substrate support 310.

[0094] The supply opening 321 is located in the central region of the substrate support 310. In certain embodiments, the central region may be a region where the radial distance to the center of the substrate support 310 is less than 25 mm, preferably less than 15 mm, and more preferably less than 10 mm. In certain embodiments, the supply opening 321 may be located at the center of the substrate support 310. The substrate holding system 300 and the substrate support 310 may be configured such that after the inert gas is supplied through the supply opening 321, the inert gas flows radially outward toward the edge of the substrate W. Thus, by supplying the inert gas to the region 350 between the substrate W and the substrate support 310 through the supply opening 321 located in the central region of the substrate support 310, the inert gas can be reliably distributed throughout the region 350 between the substrate W and the substrate support 310.

[0095] In the clamped state, the extraction opening 323 may maintain the clamping pressure (i.e., the difference between the pressure in the region 350 between the substrate W and the substrate support 310 and the ambient pressure) over the time the clamping state is operative by extracting fluid from the region 350 between the substrate W and the substrate support 310. In certain embodiments, the magnitude of the clamping pressure is greater than 100 mbar, preferably greater than 300 mbar, and more preferably greater than 350 mbar. In certain embodiments, the magnitude of the clamping pressure is less than 800 mbar, preferably less than 500 mbar, and more preferably less than 450 mbar. Fluid extraction from the region 350 between the substrate W and the substrate support 310 through the extraction opening 323 occurs because the extraction opening 323 is in fluid communication with a pressure region that is lower than the pressure in the region 350 between the substrate W and the substrate support 310. The substrate holding system 300 may be configured such that the plurality of extraction openings 323 are in fluid communication with a pressure region that is more than 400 mbar lower than the ambient pressure, preferably more than 550 mbar lower than the ambient pressure, and more preferably more than 650 mbar lower than the ambient pressure, and less than 800 mbar lower than the ambient pressure, preferably less than 750 mbar lower than the ambient pressure. The low-pressure region with which the plurality of extraction openings 323 are in fluid communication is formed by the vacuum pressure source 381.

[0096] The substrate holding system 300 may be configured such that the plurality of extraction openings 323 can extract fluid from the region 350 between the substrate W and the substrate support 310 at a rate greater than 10 NLpm, preferably greater than 25 NLpm, and more preferably greater than 29 NLpm.

[0097] Since the pressure of the plurality of extraction openings 323 located in the edge region of the substrate support 310 is lower than the pressure of the remaining portion of the region 350 between the substrate W and the substrate support 310, the inert gas supplied to the central region of the substrate support 310 flows radially from the central region of the region 350 between the substrate W and the substrate support 310 toward the plurality of extraction openings 323. This ensures that the inert gas is distributed throughout the entire region 350 between the substrate W and the substrate support 310. Further, the flow of the inert gas toward the edge of the region 350 between the substrate W and the substrate support 310 strengthens the inner seal 331 and the outer seal 332 and prevents air and water from moving radially inward from the region around the substrate support 310.

[0098] The unloading process of the unloading sequence of the substrate W is shown in FIG. 11. This process of the unloading sequence may be executed after the substrate holding system 300 operates in a clamped state. To transition from the clamped state to the process of the unloading sequence shown in FIG. 11, an inert gas is supplied to the region 350 between the substrate W and the substrate support 310 through the plurality of multifunctional openings 322. This means that the pressure in the region 350 between the substrate W and the substrate support 310 increases. The pressure in the region 350 between the substrate W and the substrate support 310 may increase until it is the same as the ambient pressure, in which case the clamping force acting on the substrate W is completely released. The pressure in the region 350 between the substrate W and the substrate support 310 may increase until it is higher than the ambient pressure. In this case, an upward (i.e., away from the substrate support 310) force acts on the lower side of the substrate W.

[0099] In this step of the unloading sequence, the plurality of extraction openings 323 may extract fluid from the region 350 between the substrate W and the substrate support 310. This may occur simultaneously with the supply of an inert gas to the region 350 between the substrate W and the substrate support 310. As a result, in the region 350 between the substrate W and the substrate support 310, the pressure within the region may vary radially. Specifically, the pressure may be higher in the radially inner region and lower in the radially outer region. In the radially inner region, the pressure may be higher than the ambient pressure, and in the radially outer region, the pressure may be lower than the ambient pressure. In this case, the force applied to the lower side of the substrate W is in the upward direction (i.e., away from the substrate support 310) in the inner region of the substrate W and in the downward direction (i.e., toward the substrate support 310) in the outer region of the substrate W. As a result, the substrate W may deform into an umbrella shape in which the distance between the substrate W and the substrate support 310 is larger at the center than at the edge of the substrate W. This may mean that the substrate W is in contact with the plurality of beads 341 at the edge of the substrate support 310 but not in contact with the plurality of beads 341 at the center of the substrate support 310.

[0100] The inert gas introduced through the plurality of multi-functional openings 322 flows radially outward and is extracted by the plurality of extraction openings 323. This circulating flow ensures that the immersion liquid around the inner seal 331 and the outer seal 332 is removed before the substrate W is unloaded from the substrate support 310. This ensures that the loading sequence is reproducible. Since the gas supplied to the plurality of multi-functional openings 322 is an inert gas rather than, for example, air, it is ensured that a large amount of oxygen is not contained in the region 350 between the substrate W and the substrate support 310 during this stage of the unloading sequence.

[0101] The unloading sequence is continued with a plurality of telescopic pins (not shown) extended from the retracted position such that the distal portions of the telescopic pins contact the underside of the substrate W. As the plurality of telescopic pins continue to extend, the substrate W is lifted upward (i.e., away from the substrate support 310), and the substrate W no longer contacts the plurality of burls 341.

[0102] When an inert gas is supplied during the clamping state and the unloading sequence, the inert gas may be extracted by the plurality of extraction openings 323. These extraction openings 323 are necessary regardless of the supply of the inert gas for the purpose of maintaining the clamping pressure in the region 350 between the substrate W and the substrate support 310. Therefore, according to the present invention, no additional extraction openings for extracting the inert gas are necessary.

[0103] The substrate support 310 is provided with a supply opening 321 and a plurality of multifunctional openings 322, and since the substrate holding system 300 can be configured to supply the inert gas to one side but not to the other side, the inert gas can be supplied to the supply opening 321 during the clamping state and to the multifunctional openings 322 during the loading sequence and the unloading sequence. It is important that the inert gas is supplied to the central region of the substrate support 310 during the clamping state because once the inert gas is supplied to the region 350 between the substrate W and the substrate support 310, the inert gas flows radially outward, ensuring that the entire region 350 between the substrate W and the substrate support 310 is surrounded by the inert gas. Conversely, during the loading sequence and the unloading sequence, it is important that the inert gas is supplied to the region radially outside the central region. This is because if the inert gas is supplied to the central region during the loading sequence and the unloading sequence, unevenness (bumps) in flatness may occur in the central region of the substrate W due to the pressure distribution generated under the substrate W.

[0104] An example of the configuration of the fluid management system of the substrate holding system 300 is shown in FIG. 12. In the illustrated configuration, the gas source 382 is connected to the multi-functional opening 322 and the supply opening 321 via the inert gas supply valve 361. The inert gas supply valve 361 may be a three-way valve having a first opening corresponding to the inert gas supply conduit 371, a second opening corresponding to the supply opening conduit 372, and a third opening corresponding to the multi-functional opening conduit 373. The inert gas supply valve 361 may be configured to supply the inert gas only to the supply opening conduit 372, not to supply the inert gas to either the supply opening conduit 372 or the multi-functional opening conduit 373, and to supply the inert gas only to the multi-functional opening conduit 373. The inert gas supply valve 361 may be further configured to supply the inert gas to the supply opening conduit 372 and the multi-functional opening conduit 373 simultaneously. Thus, only the inert gas supply valve 361 is required to provide the inert gas supply function of the present invention. This means that the system is simple, easy to assemble, and easy to maintain.

[0105] Alternatively, the inert gas supply valve 361 may be a four-way valve. The four-way inert gas supply valve 361 includes the same three ports as the three-way inert gas supply valve 361 and may have an additional port configured to discharge the inert gas to the external environment or other parts of the substrate holding system 300. The type of valve used for the inert gas supply valve 361 is not particularly limited, and any suitable valve known to those skilled in the art can be used.

[0106] The present invention is not limited to this configuration in which an inert gas is supplied to the supply opening 321 and the plurality of multifunctional openings 322. For example, the flow of the inert gas from the gas source 382 to the supply opening 321 and the plurality of multifunctional openings 322 may not be controlled by a single inert gas supply valve 361. In this case (not shown), the flow of the inert gas to the supply opening 321 may be controlled by a first two-way valve having an inlet opening connected to the first inert gas supply conduit and an outlet opening connected to the supply opening conduit. The flow of the inert gas to the plurality of multifunctional openings 322 may be controlled by a second two-way valve having an inlet opening connected to the second inert gas supply conduit and an outlet opening connected to the multifunctional opening conduit.

[0107] As also shown in FIG. 12, the plurality of multifunctional openings 322 and the plurality of extraction openings 323 are in fluid communication with a vacuum pressure source 381. This vacuum pressure source 381 provides a region of pressure lower than the ambient pressure. As a result, the vacuum pressure source 381 causes gas to be extracted through the multifunctional openings 322 and the plurality of extraction openings 323. In the configuration shown in FIG. 12, the flow path between the vacuum pressure source 381 and the multifunctional openings 322 is separate from the flow path between the vacuum pressure source 381 and the plurality of extraction openings 323. Each flow path may include a valve for controlling the extraction of fluid from the corresponding opening. The valve may be a simple two-way valve having an inlet opening connected to the vacuum pressure source conduit 374 and an outlet opening connected to the conduits 373, 375 corresponding to the multifunctional opening 322 or the extraction opening 323. For example, the flow path between the vacuum pressure source 381 and the extraction opening 323 may include a two-way valve 365.

[0108] A flow rate limiting section 370 (also referred to as a control valve) may be included in the fluid management system. The flow rate limiting section 370 may be configured to control the flow rate of fluid passing through conduits 371, 372, 373, 374. The type of flow rate limiting section 370 used is not particularly limited. For example, the flow rate limiting section 370 may be a needle valve, a solenoid valve, or other suitable type of control valve known to those skilled in the art. Each of the flow rate limiting sections 370 does not have to be the same. In fact, each of the flow rate limiting sections 370 may have different characteristics so as to be able to adjust the flow rate of fluid passing through the system in different sections of the conduit. This may also enable the speed of fluid supply / extraction to be varied at different openings or at different times. The flow rate limiting section 370 shown in FIG. 12 is an example, and additional limiting sections may be included or some of the limiting sections may be omitted in order to provide the required flow rate characteristics.

[0109] The fluid management system may include a plurality of additional valves such as check valves (non-return valves), relief valves, shut-off valves, etc.

[0110] In the fluid management system, there may be a plurality of paths between the vacuum pressure source 381 and the plurality of multi-functional openings 322. Each path may include valves 362, 363, 364 and a flow rate limiting section 370. Each flow rate limiting section 370 may be configured by different means. For example, each flow rate limiting section 370 may be configured such that fluid flows at different volumetric flow rates. As a result, the extraction flow rate from the plurality of multi-functional openings 322 can be controlled by changing the open valves among valves 362, 363, 364. However, this is only one configuration example of the present invention, and the extraction flow path is not limited to this configuration. For example, the branch between the vacuum pressure source 381 and the plurality of multi-functional openings 322 does not have to branch into a plurality of paths. Instead, the flow rate of the fluid may be controlled by a variable flow rate limiting valve.

[0111] The substrate holding system 300 may include a plurality of sensors 378. The plurality of sensors 378 may be distributed throughout the fluid management system. These sensors 378 may measure a plurality of fluid characteristics such as mass flow rate, volume flow rate, pressure, temperature, flow velocity, fluid composition, etc. These sensed characteristics may be relayed to a monitoring system. This monitoring system may be configured to change aspects of the function of the flow system according to the measured values. The monitoring system may be included in the substrate holding system 300 or may be external to the substrate holding system 300.

[0112] The term "duct" is used throughout this description to refer to the passageways that fluidly connect the various components of the substrate holding system 300. The term "duct" is not limited to fixed rigid pipes and is intended to encompass all suitable fluid passageways and fluid connections known to those skilled in the art.

[0113] In the above embodiment, a single supply opening 321 has been described. However, the present invention is not limited to this, and the substrate support 310 may include a plurality of supply openings 321, each of which may be configured in the same manner as the single supply opening 321 described above. The plurality of supply openings 321 may all be located in the central region. Alternatively, some of the supply openings 321 may be located in the central region and other supply openings 321 may be located radially outside the central region. The diameter of each supply opening 321 may be such that the supply opening 321 itself does not induce effects such as pressure drop or turbulent flow in the flow of the inert gas from the gas source 382 to the region 350 between the substrate W and the substrate support 310. Therefore, the diameter of each supply opening 321 may depend on the flow rate of the inert gas supplied to the region 350 between the substrate W and the substrate support 310 and the number of supply openings 321.

[0114] In an embodiment with only a single supply opening 321, the diameter of the supply opening 321 may be greater than 0.6 mm, preferably greater than 0.8 mm, more preferably greater than 1 mm, and even more preferably greater than 1.1 mm. In an embodiment with a plurality of supply openings 321, the diameter of each supply opening 321 may be greater than 0.4 mm, preferably greater than 0.6 mm.

[0115] To prevent the supply opening 321 from interfering with a plurality of beads 341, the diameter of the supply opening 321 may be smaller than the sum of the bead pitch and the bead radius. For example, when the bead pitch is 1.5 mm, the diameter of the supply opening may be smaller than 1.2 mm. When the bead pitch is 2.5 mm, the diameter of the supply opening may be smaller than 2.1 mm.

[0116] In an embodiment of the present invention, the upper surface of the substrate support 310 may include a plurality of other openings (not shown in FIGS. 8 to 11). These openings may exist to provide an entry point for a jig tool, or may be provided to accommodate a plurality of expandable pins used to lower the substrate W towards the substrate support 310 or raise it away from the substrate support 310 during the load sequence and the unload sequence. An example of the tooling opening 390 is shown in FIG. 13. The area inside the tooling opening 390 may need to be kept at ambient pressure. In a previous configuration of the substrate support 310, the gas inside a hole such as the tooling opening 390 was air at ambient pressure. The tooling opening 390 may be provided with a seal 392 to suppress the flow of air from the area inside the tooling opening 390 to the area 350 between the substrate W and the substrate support 310, but leakage at this seal 392 may mean that the area around the tooling opening 390 may be exposed to air. Oxygen or water that may be contained in the leaked air may cause oxidation of the upper surface of the substrate support 310 in the area around the tooling opening 390. This may result in a local flatness drift.

[0117] In certain embodiments of the present invention, each of these tooling openings 390 may comprise a small orifice 391. The substrate holding system 300 may be configured to supply an inert gas through the small orifice 391 to the area inside the tooling opening 390. The pressure inside the tooling opening 390 is atmospheric pressure, but the tooling opening 390 may contain an inert gas rather than air. This means that the gas flowing from the area inside the tooling opening 390 across the seal 392 into the main area 350 between the substrate W and the substrate support 310 is inert and does not contain oxygen. This avoids oxidation in the areas around the openings used for purposes such as providing tooling and telescopic pins, meaning there is no local flatness drift in these areas.

[0118] In the present invention, only the gas source 382 and the substrate support 310 need to be included in the substrate holding system 300. However, the present invention is not limited to these components being located precisely in the substrate holding system 300. If the substrate holding system 300 includes other components, the location of these other components within the substrate holding system 300 is not limited. For example, if the substrate holding system 300 includes an inert gas supply valve 361, the location of the inert gas supply valve 361 is not limited. In certain embodiments, the inert gas supply valve 361 may be disposed within the substrate support 310 itself. However, the inert gas supply valve 361 may instead be disposed within the gas source 382 or at a location between the substrate support 310 and the gas source 382.

[0119] The structure of the gas source 382 is not particularly limited, and any configuration known to those skilled in the art as suitable can be utilized in embodiments of the present invention. The gas source 382 may have a storage element configured to store the inert gas itself, or the gas source may be connected to an external system configured to supply a constant flow rate of inert gas to the gas source 382. The structure of the vacuum pressure source 381 is also not particularly limited, and any configuration known to those skilled in the art as suitable can be utilized in embodiments of the present invention.

[0120] The inert gas may be essentially composed of nitrogen (N2). That is, most of the inert gas may be nitrogen. Specifically, the proportion of nitrogen in the inert gas may be greater than 90%, preferably greater than 95%, preferably greater than 99%, and more preferably greater than 99.5%. The proportion of other components in the inert gas must be low enough not to contribute to significant oxidation of the substrate support 310. Nitrogen is particularly preferred because it is relatively inexpensive, readily available, and obtained from a rich resource (air). The amount of nitrogen used in the present invention does not cause safety problems. However, the inert gas of the present invention is not limited to nitrogen and can be replaced with any gas known not to contain oxygen or water and not to react with the materials of the substrate support and / or the coating. For example, helium (He) or argon (Ar) can also be used.

[0121] In addition to preventing oxidation of the surface of the substrate support 310, when an inert gas is supplied to the region 350 between the substrate W and the substrate support 310, it is ensured that the gas is clean and does not contain debris. Debris can potentially affect the operation of the substrate holding system 300. For example, debris may reduce the flatness of the substrate W or damage sensitive components.

[0122] The substrate support 310 can be formed from any material known in the art. For example, the substrate support 310 may be formed from SiSiC. The substrate support 310 may be coated. The type of coating is not particularly limited, and any coating known to those skilled in the art to be suitable for the application may be used. For example, the substrate support 310 may be coated with diamond or diamond-like carbon (DLC).

[0123] In the claims, the term "port" is used to mean "an opening for fluid passage". The term "port" does not imply any geometrical constraints on the opening for fluid passage. For example, throughout the drawings the port is shown as a hole having a cylindrical cross-section, but the present invention is not limited to this configuration and the port may have other shapes.

[0124] The present invention may provide a lithographic apparatus. The lithographic apparatus may have 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 support WT, etc.

[0125] Specifically, the lithographic apparatus may comprise a projection system PS configured to project a radiation beam B towards an area on the surface of a substrate W. The lithographic apparatus may further comprise the substrate holding system 300 described in any of the above embodiments and variations.

[0126] It will be appreciated that the lithographic apparatus described in this document, which specifically refers to the use of a lithographic apparatus in the manufacture of ICs, may have other applications. Other applications include the manufacture of integrated optical systems, magnetic domain memories for induction and detection patterns, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0127] As long as the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may be implemented by instructions stored on a machine-readable medium, which may be read and executed by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (such as a computing device). For example, the 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 (such as carrier waves, infrared signals, digital signals, etc.). Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, such descriptions are for convenience only, and such actions actually occur when a computing device, processor, controller, or other device executes firmware, software, routines, instructions, etc., and at that time, an actuator or other device may interact with the physical world.

[0128] In this document, embodiments of the present invention may be specifically referred to in the context of a lithographic apparatus, but embodiments of the present invention may also be used in other apparatuses. Embodiments of the present invention may form part of any apparatus for measuring or processing an object such as a mask inspection apparatus, a metrology apparatus, or a wafer (or other substrate) or a mask (or other patterning device). These apparatuses may generally be referred to as lithography tools.

[0129] Although the use of embodiments in the context of optical lithography may have been specifically mentioned above, it will be understood that the present invention is not limited to optical lithography as long as the context permits.

[0130] Although specific embodiments of the present invention have been described above, it will be understood that the present invention may be practiced otherwise than as described above. The above description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications may be made to the present invention as described above without departing from the scope of the claims set forth below.

Claims

1. A substrate holding system comprising a substrate support configured to support a substrate, a gas source, and a plurality of conduits, wherein the substrate support includes a first port in its central region and a plurality of second ports radially outside the first port, the first port and the plurality of second ports are configured to be in fluid communication with the gas source via the plurality of conduits, the gas source is configured to supply an inert gas to a region between the substrate and the substrate support via a first conduit and the first port and via a second conduit and the plurality of second ports, the substrate holding system is configured to be able to supply the inert gas to the region between the substrate and the substrate support through the first port or the plurality of second ports, the substrate holding system is configured to extract gas from the region between the substrate and the substrate support through the plurality of second ports, A substrate holding system.

2. The first port and the plurality of second ports are in fluid communication with the gas source via at least one valve within the substrate holding system, and the valve is configured to be able to supply the inert gas to the region between the substrate and the substrate support. The substrate holding system according to claim 1.

3. The valve is further configured to discharge the inert gas to an external environment or another part of the substrate holding system. The substrate holding system according to claim 2.

4. The substrate support further includes a plurality of third ports radially outside the plurality of second ports, and the plurality of third ports are configured to extract fluid from the region between the substrate and the substrate support. The substrate holding system according to any one of claims 1 to 3.

5. The plurality of third ports are at a pressure more than 400 mbar lower than ambient pressure, preferably more than 550 mbar lower than ambient pressure, more preferably more than 650 mbar lower than ambient pressure, and less than 800 mbar lower than ambient pressure, preferably less than 750 mbar lower than ambient pressure, and are configured to be in fluid communication with a pressure region lower than ambient pressure. The substrate holding system according to claim 4.

6. The central region of the substrate support is a region where the radial distance to the center of the substrate support is less than 25 mm, preferably less than 15 mm, more preferably less than 10 mm. The substrate holding system according to any one of claims 1 to 5.

7. The radial distance between each of the plurality of second ports and the center of the substrate support is greater than 40 mm, preferably greater than 50 mm, more preferably greater than 60 mm, less than 100 mm, preferably less than 80 mm, more preferably less than 65 mm, and / or The radial distance between each of the plurality of second ports and the center of the substrate support is greater than 13% of the diameter of the substrate, preferably greater than 17% of the diameter of the substrate, more preferably greater than 20% of the diameter of the substrate, less than 33% of the diameter of the substrate, preferably less than 27% of the diameter of the substrate, more preferably less than 22% of the diameter of the substrate. The substrate holding system according to any one of claims 1 to 6.

8. When the substrate is supported on the substrate support, the distance between each of the plurality of third ports and the periphery of the substrate is less than 25 mm, preferably less than 10 mm, more preferably less than 5 mm, greater than 1.5 mm, or When the substrate is supported on the substrate support, the distance between each of the plurality of third ports and the periphery of the substrate is less than 10% of the diameter of the substrate, preferably less than 4% of the diameter of the substrate, more preferably less than 2% of the diameter of the substrate, greater than 0.5% of the diameter of the substrate. The substrate holding system according to any one of claims 4 to 7.

9. There is only one first port in the central region of the substrate support, and the diameter of the first port is greater than 0.6 mm, preferably greater than 0.8 mm, more preferably greater than 1 mm, more preferably greater than 1.1 mm, or There are a plurality of first ports in the central region of the substrate support. The substrate holding system according to any one of claims 1 to 8.

10. The diameter of the plurality of first ports is greater than 0.4 mm, preferably greater than 0.6 mm. The substrate holding system according to claim 9.

11. The substrate support further includes a plurality of bars protruding from the upper surface of the substrate support, and / or the inert gas is essentially composed of nitrogen, and / or the substrate support is formed of SiSiC, and / or the substrate support is coated with diamond or diamond-like carbon. The substrate holding system according to any one of claims 1 to 10.

12. The diameter of the first port is smaller than the sum of the distance between each of the plurality of bars and the radius of each bar. The substrate holding system according to claim 11.

13. A lithographic apparatus comprising the substrate holding system according to any one of claims 1 to 12.

14. A method of supporting a substrate on a substrate support, wherein the substrate support includes a first port in a central region of the substrate support and a plurality of second ports radially outside the first port, the method comprising: a substrate loading step of supplying an inert gas through the plurality of second ports to a region between the substrate and the substrate support; and a subsequent substrate clamping step of supplying the inert gas through the first port to the region between the substrate and the substrate support. Method.

15. In the substrate loading step, the inert gas is supplied only to the plurality of second ports, and / or in the substrate clamping step, the inert gas is supplied only to the first port, and / or the substrate clamping step is performed for a time longer than 90% of the time during which the substrate is clamped to the substrate support. The method according to claim 14.

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