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 radially outward of the first port. The first port and the plurality of second ports are configured to be in fluid communication with a gas source. The gas source is configured to supply an inert gas to a region between the substrate and the substrate support through the first port and the plurality of second ports. The substrate holding system is configured such that inert gas may be supplied to a 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 a region between the substrate and the substrate support through the plurality of second ports.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22183530.9, filed on July 7, 2022, and its entire contents are incorporated herein by reference. Technical Field

[0003] The invention relates to a substrate holding system, a lithographic apparatus comprising a substrate holding system, a method of supporting a substrate on a substrate support and a method of manufacturing a device comprising the method of supporting a substrate on a substrate support. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). For example, a lithographic apparatus can project a pattern (also often referred to as a "design layout" or "design") of a pattern forming device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer). Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the "scanning" direction), while simultaneously scanning the substrate parallel or antiparallel to that direction.

[0005] As semiconductor manufacturing processes continue to advance, the size of circuit elements continues to decrease, while the number of functional elements (such as transistors) per device has been steadily increasing for decades, following a trend commonly referred to as "Moore's Law." To keep up with Moore's Law, the semiconductor industry is chasing technologies that can create smaller and smaller features. To project a pattern onto a substrate, a lithography device can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently in use are 365nm (i-line), 248nm, 193nm, and 13.5nm.

[0006] The resolution of smaller features can be further improved by providing an immersion fluid with a relatively high refractive index, such as water, on the substrate during exposure. The effect of the immersion fluid is to enable imaging of smaller features, since the wavelength of the exposure radiation in the fluid is shorter than that in the gas. The effect of the immersion fluid can also be seen as increasing the effective numerical aperture (NA) of the system and increasing the depth of focus.

[0007] The immersion fluid may be confined to a localized region between the projection system and the substrate of the lithographic apparatus by the fluid handling structure. Summary of the invention

[0008] In the semiconductor manufacturing process, the substrate is supported on a substrate support, and more specifically, the substrate is supported on a plurality of protrusions protruding from the surface of the substrate support.

[0009] When used in a semiconductor manufacturing process, the substrate support may be surrounded by air. Oxygen and water in the air may cause oxidation of the substrate support, wherein the top surface of the substrate support is chemically converted into an oxide film. The water in the air around the top surface of the substrate support may come from humidity in the environment surrounding the substrate support, or from areas surrounding the substrate support where water (as an immersion fluid) is present. The oxidation process may be accelerated by the presence of static charge accumulated on the bottom surface of the substrate.

[0010] The oxide film that forms is usually softer than the material of the substrate support or the material of the substrate support coating. The relative movement during clamping and unclamping can lead to the oxide film being removed by abrasion. This tribo-corrosion process leads to a reduction in the flatness of the substrate support.

[0011] Furthermore, the oxide film is hydrophilic, so in a substrate support in combination with water used as an immersion fluid, water radially outside the substrate support is attracted into the region between the substrate and the substrate support. This increases the adhesive capillary forces, which may result in a change in the deformation pattern of the substrate (which may be referred to as a deformation fingerprint or wafer load grid (WLG)).

[0012] The object of the present invention is to suppress the formation of an oxide film on the top surface of a substrate support so as to mitigate the flatness drift of the substrate support and the change of the deformation mode of the substrate.

[0013] According to the present invention, there is provided a substrate holding system, comprising a substrate support configured to support a substrate, a gas source and a plurality of conduits, wherein:

[0014] The substrate support includes a first port located in a central region thereof and a plurality of second ports located radially outward of the first port;

[0015] The first port and the plurality of second ports are configured to be in fluid communication with a gas source via a plurality of conduits;

[0016] a gas source configured to supply an inert gas to a region between the substrate and the substrate support via a first conduit and a first port and via a second conduit and a plurality of second ports;

[0017] The substrate holding system is configured to enable an inert gas to be supplied to a region between the substrate and the substrate support through the first port or the plurality of second ports; and

[0018] The substrate holding system is configured to extract gas from a region between the substrate and the substrate support through the plurality of second ports.

[0019] According to the present invention, there is also provided a lithographic apparatus comprising a substrate holding system.

[0020] According to the present invention, there is also provided a method for supporting a substrate on a substrate support, the substrate support comprising a first port located in a central region of the substrate support and a plurality of second ports located radially outward of the first port, the method comprising:

[0021] a substrate loading step in which an inert gas is supplied to a region between the substrate and the substrate support through the plurality of second ports; and

[0022] This is followed by a substrate clamping step in which an inert gas is supplied through the first port to the region between the substrate and the substrate support.

[0023] According to the present invention, there is also provided a method for manufacturing a device, including the method of supporting a substrate.

[0024] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments, features, and advantages of the present invention are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference characters indicate corresponding parts, and in which:

[0026] Figure 1 A schematic overview of a lithographic apparatus is shown;

[0027] Figure 2 showing a cross-sectional view of a radially outer portion of a substrate support;

[0028] Figure 3A-3C shows a cross-sectional view of a substrate support of a substrate holding system not according to the present invention during a loading sequence;

[0029] Figure 4 A cross-sectional view showing a substrate support of a substrate holding system not according to the invention in a clamped state;

[0030] Figure 5 shows a cross-sectional view of a substrate support of a substrate holding system not according to the invention in an unloaded state;

[0031] Figure 6 shows a graph of the surface oxidation percentage (O) of a substrate support WT having a DLC coating versus the exposure time (t) (in hours) in an environment containing air, ultrapure water and nitrogen;

[0032] Figure 7Shown are: (i) a graph of the surface oxidation percentage (O) of a substrate support WT having a DLC coating versus exposure time (t) (in seconds) in an environment containing air; and (ii) a graph of the contact angle (CA) of a substrate support WT having a DLC coating versus exposure time (t) (in seconds) in an environment containing air.

[0033] Figure 8 A substrate support of a substrate holding system according to the present invention is shown in plan view;

[0034] Figure 9A-9C shows a cross-sectional view of a substrate support of a substrate holding system according to the present invention during a loading sequence;

[0035] Fig.10 shows a cross-sectional view of a substrate support of a substrate holding system according to the present invention in a clamped state;

[0036] Fig.11 shows a cross-sectional view of a substrate support of a substrate holding system according to the present invention in an unloaded state;

[0037] Fig.12 A schematic diagram showing a fluid management system of a substrate holding system according to the present invention is shown.

[0038] Fig.13 A tool hole with an orifice for providing an inert gas is shown.

[0039] The features shown in the figures are not necessarily drawn to scale, and the sizes and / or arrangements depicted are not limited. It should be understood that the figures include optional features that may not be required by the present invention. In addition, not all features of the device are depicted in each figure, and only some components relevant to describing a particular feature may be shown in the figure. DETAILED DESCRIPTION

[0040] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (eg, having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm).

[0041] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam that corresponds to the pattern to be created in a target portion of the substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0042] Figure 1 A lithographic apparatus is schematically shown. The lithographic apparatus comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation), a mask support (e.g., a mask table) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., a substrate table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support WT according to 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.

[0043] In operation, the illumination system IL receives a radiation beam B from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0044] The term "projection system" PS as used herein should be interpreted broadly to cover various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, depending on the exposure radiation used and / or other factors, such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0045] The lithographic apparatus is of a type in which at least a portion of the substrate W may be covered by an immersion liquid (e.g. water) having a relatively high refractive index, thereby filling an immersion space 11 between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion technology is given in US 6,952,253, which is incorporated herein by reference.

[0046] The lithographic apparatus may be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps for preparing a substrate W for subsequent exposure may be performed on a substrate W located on one substrate support WT while another substrate W on another substrate support WT is used to expose a pattern on the other substrate W.

[0047] In addition to the substrate support WT, the lithographic apparatus may further comprise a measuring table (not shown in the figure). The measuring table is arranged to accommodate sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measuring table may accommodate a plurality of sensors. The cleaning means 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 for providing immersion liquid. The measuring table may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0048] In operation, a radiation beam B is incident on a patterning device (e.g. a mask MA) which is held on a mask support MT and is patterned by a pattern (design layout) on the patterning device MA. After passing through the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be precisely moved, for example, in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, a first positioner PM and possibly another position sensor ( Figure 1 The patterning device MA may be positioned relative to the path of the radiation beam B using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, they may be located in spaces between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe line alignment marks.

[0049] To illustrate the present invention, a Cartesian coordinate system is used. A Cartesian coordinate system has three axes, namely an x-axis, a y-axis and a z-axis. Each of the three axes is orthogonal to the other two axes. A rotation around the x-axis is called an Rx rotation. A rotation around the y-axis is called an Ry rotation. A rotation around the z-axis is called an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in a vertical direction. The Cartesian coordinate system does not limit the present invention and is only used for illustration. On the contrary, another coordinate system (such as a cylindrical coordinate system) can be used to illustrate the present invention. The direction of the Cartesian coordinate system may be different, for example, so that the z-axis has a component along the horizontal plane.

[0050] Immersion technology has been introduced into lithography systems to enable improved resolution of smaller features. In an immersion lithography apparatus, a liquid layer of an immersion liquid having a relatively high refractive index is inserted in an immersion space 11 between the apparatus's projection system PS (through which a patterned light beam is projected towards the substrate W) and the substrate W. The immersion liquid covers at least a portion of the substrate W beneath the final element of the projection system PS. Thus, at least the portion of the substrate W that is undergoing exposure is immersed in the immersion liquid.

[0051] In commercial immersion lithography, the immersion liquid is water. Typically, the water is high purity distilled water, such as ultrapure water (UPW) commonly used in semiconductor manufacturing plants. In an immersion system, the UPW is typically purified, and it may undergo additional processing steps before being supplied to the immersion space 11 as an immersion liquid. In addition to water, other liquids with a high refractive index may be used as immersion liquids, for example: hydrocarbons, such as fluorinated hydrocarbons; and / or aqueous solutions. In addition, it has been envisioned that other fluids than liquids may be used in immersion lithography.

[0052] In this specification, reference will be made in the description to partial immersion, wherein the immersion liquid is confined in use in an immersion space between a final element and a surface facing the final element. The facing surface is the surface of the substrate W or the surface of a support table (or substrate support WT) which is coplanar with the surface of the substrate W. (Note that references to the surface of the substrate W hereinafter also refer additionally or alternatively to the surface of the substrate support WT, unless otherwise expressly stated; and vice versa). The presence of a fluid handling structure IH between the projection system PS and the substrate support WT serves to confine the immersion liquid in the immersion space. The immersion space filled with the immersion liquid is smaller in plane than the top surface of the substrate W, and the immersion space remains substantially stationary relative to the projection system PS, while the substrate W and the substrate support WT move underneath.

[0053] Other immersion systems have been envisaged, such as unconfined immersion systems (so-called "all-wet" immersion systems) and bath immersion systems. In an unconfined immersion system, the immersion liquid covers more than just the surface below the final component. The liquid outside the immersion space is present in the form of a thin liquid film. The liquid may cover the entire surface of the substrate W, even the substrate W and a substrate support WT coplanar with the substrate W. In a bath system, the substrate W is completely immersed in a bath of immersion liquid.

[0054] A fluid handling structure IH is a structure that supplies immersion liquid to, removes immersion liquid from and thereby confines immersion liquid in the immersion space. It includes features that are part of a fluid supply system. The arrangement disclosed in PCT patent application publication number WO 99 / 49504 is an early fluid handling structure that includes conduits that supply immersion liquid or recover immersion liquid from the immersion space and that operate in accordance with the relative movement of the platform below the projection system PS. In newer designs, the fluid handling structure extends along at least a portion of the boundary of the immersion space between the final element of the projection system PS and the substrate support WT or substrate W so as to partially define the immersion space.

[0055] The fluid handling structure IH can have a variety of different functions. Each function can be derived from a corresponding feature that enables the fluid handling structure IH to perform that function. The fluid handling structure IH can be represented by many different terms, each of which represents a function, such as a barrier member, a sealing member, a fluid supply system, a fluid removal system, a liquid confinement structure, etc.

[0056] As a barrier member, the fluid handling structure IH is a barrier to the flow of immersion liquid from the immersion space. As a liquid confinement structure, the structure confines the immersion liquid in the immersion space. As a sealing member, the sealing features of the fluid handling structure IH form a seal to confine the immersion liquid in the immersion space. The sealing features may include additional airflow from an opening on the surface of the sealing member, such as an air knife.

[0057] The fluid handling structure IH may provide immersion liquid and is therefore a fluid supply system.

[0058] The fluid handling structure IH may at least partially confine immersion liquid and thereby be a fluid confinement system.

[0059] The fluid handling structure IH may provide a barrier to the immersion fluid, thereby being a barrier member, such as a fluid confinement structure.

[0060] The fluid handling structure IH may generate or use a gas flow, for example, to help control the flow and / or position of the immersion fluid.

[0061] The gas flow may form a seal to confine the immersion fluid and thus the fluid handling structure IH may be referred to as a sealing member; such a sealing member may be a fluid confinement structure.

[0062] An immersion liquid may be used as the immersion fluid. In this case, the fluid handling structure IH may be a liquid handling system. With reference to the above description, references in this paragraph to features defined relative to a fluid may be understood to include features defined relative to a liquid.

[0063] The lithographic apparatus has a projection system PS. During exposure of the substrate W, the projection system PS projects a patterned radiation beam onto the substrate W. In order to reach the substrate W, the path of the radiation beam B from the projection system PS passes through an immersion liquid confined by a fluid handling structure IH between the projection system PS and the substrate W. The projection system PS has a lens element, which is the last lens element in the beam path, which is in contact with the immersion liquid. This lens element in contact with the immersion liquid may be referred to as the "last lens element" or the "final element". The final element is at least partially surrounded by the fluid handling structure IH. The fluid handling structure IH may confine the immersion liquid below the final element and above the facing surface.

[0064] like Figure 1 As shown, the lithographic apparatus comprises a controller 500. The controller 500 is configured to control a substrate support WT.

[0065] Figure 2 There is shown a portion of a lithographic apparatus which is not in accordance with the present invention, but which may be used to demonstrate features of the present invention. Figure 2 The arrangement shown in and described below can be applied to the above and Figure 1 The lithographic apparatus shown in FIG. Figure 2 is a cross section through the substrate support 20 and the substrate W. In one embodiment, the substrate support 20 comprises one or more conditioning channels 61 of a thermal regulator, 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 imaging the edge of the substrate W, or at other times, such as when the substrate W is first moved under the projection system PS (as described above), the immersion space filled with liquid by the fluid handling structure IH (for example) will at least partially pass through the gap 5 between the edge of the substrate W and the edge of the substrate support 20. This may cause liquid in the immersion space to enter the gap 5.

[0066] The substrate W is held by a support 21 (e.g., a ridge or burl platform) that includes one or more burls 41 (i.e., protrusions from the surface). The support 21 is an example of an object holder. Another example of an object holder is a mask support. The negative pressure applied between the substrate W and the substrate support 20 helps to ensure that the substrate W is firmly held in place. However, if immersion liquid enters between the substrate W and the support 21, this can cause difficulties, particularly when unloading the substrate W.

[0067] In order to handle 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. Figure 2In the embodiment of, two drain pipes 10, 12 are shown, but there may be only one drain pipe, or there may be more than two drain pipes. In one embodiment, each drain pipe 10, 12 is annular so that the entire periphery of the substrate W is surrounded.

[0068] The main function of the first drain pipe 10 (which is radially outside the edge of the substrate W / support body 21) is to help prevent bubbles from entering the immersion space of the liquid in the fluid handling structure IH. Such bubbles may have an adverse effect on the imaging of the substrate W. The presence of the first drain pipe 10 helps to avoid the gas in the gap 5 from escaping into the immersion space in the fluid handling structure IH. If the gas does escape into the immersion space, it may cause bubbles to float in the immersion space. If such bubbles are located in the path of the projection beam, it may cause imaging errors. The first drain pipe 10 is configured to remove gas from the gap 5 between the edge of the substrate W and the edge of the groove in the substrate support 20 where the substrate W is located. The edge of the groove in the substrate support 20 can be defined by a cover ring 101, which is optionally separated from the support body 21 of the substrate support 20. The cover ring 101 can be shaped as a ring in a plane and surrounds the outer edge of the substrate W. The first drain pipe 10 extracts most of the gas and a small amount of immersion liquid.

[0069] A second drain 12 is provided (which is located radially inwardly of the edge of the substrate W / support 21) to help prevent liquid from entering from the gap 5 from imaging under the substrate W and preventing the substrate W from being effectively released from the substrate table WT. The provision of the second drain 12 can reduce or eliminate any problems that may arise due to liquid entering under the substrate W.

[0070] like Figure 2 As shown, in one embodiment, the lithographic apparatus comprises a first extraction channel 102 for passing a two-phase flow therethrough. The first extraction channel 102 is formed in a block. The first drain pipe 10 and the second drain pipe 12 are each provided with a corresponding opening 107, 117 and a corresponding extraction channel 102, 113. The extraction channels 102, 113 are in fluid communication with the corresponding openings 107, 117 through the corresponding channels 103, 114.

[0071] like Figure 2As shown, the cover ring 101 has an upper surface. The upper surface extends circumferentially around the substrate W on the support body 21. When the lithography equipment is used, the substrate support 20 moves relative to the fluid handling structure IH. During this relative movement, the fluid handling structure IH moves across the gap 5 between the cover ring 101 and the substrate W. In one embodiment, the relative movement is caused by the substrate support 20 moving below the fluid handling structure IH. In an alternative embodiment, the relative movement is caused by the fluid handling structure IH moving above the substrate support 20. In another alternative embodiment, the relative movement is provided by the movement of the substrate support 20 below the fluid handling structure IH and the movement of the fluid handling structure IH above the substrate support 20.

[0072] <Example>

[0073] Figure 3 to Figure 5 2 shows a cross-sectional view of a substrate W and a 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 Figure 1 In the lithographic apparatus shown in FIG. 1 , the substrate support 210 may have Figure 2 This example of substrate holding system 200 and substrate support 210 is in no way meant to be an admission of the current state of the art, but is merely intended to highlight some specific advantages of the present invention over other possible configurations.

[0074] The substrate support 210 may include a support body, such as Figure 2 2. The substrate support 210 is shown in FIG. 210. However, for simplicity, the support will not be mentioned. The substrate support 210 includes a plurality of protrusions 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 protrusions 241 form a plane supporting the bottom surface of the substrate W. The bottom surface of the substrate W is in contact with the distal ends of the protrusions 241. The protrusions 241 are located on the upper side of the substrate support 210.

[0075] Figure 3 to Figure 5 The illustrated substrate support 210 includes a plurality of multifunctional openings 222 circumferentially arranged around the substrate support 210 , and a plurality of extraction openings 223 circumferentially arranged around the substrate support 210 , the plurality of extraction openings 223 being located radially outside the plurality of multifunctional openings 222 .

[0076] The substrate holding system 200 is configured to supply clean dry air (CDA) to a region 250 between the substrate support 210 and the substrate W through the plurality of multifunctional openings 222. The substrate holding system 200 is also configured to extract fluid 223 from the region 250 between the support 221 and the substrate W through the plurality of multifunctional openings 222 and the plurality of extraction openings.

[0077] Figure 3 to Figure 5 The illustrated substrate support 210 includes an inner seal 231 located radially inwardly of the plurality of extraction openings 223 and an outer seal 232 located radially outwardly of the plurality of extraction openings 223 .

[0078] Figure 3A-3C 2 shows the sequence of loading the substrate W onto the substrate support 210. When the substrate W is lowered toward the substrate support 210 ( Figure 3A ), CDA is supplied to the region 250 between the substrate W and the substrate support 210 ( Figure 3B ). For a short period of time, the substrate W is supported on the CDA pad. After this short period of time has passed, the substrate holding system 200 extracts gas through the plurality of multi-functional openings 222 ( Figure 3C ). This reduces the pressure in the region 250 between the substrate W and the substrate support 210 to be less than the ambient pressure, and applies a clamping force to the bottom surface of the substrate W in a direction toward the substrate support 210, so that the substrate W is clamped to the substrate support 210.

[0079] Once the substrate W is loaded onto the substrate support 210 and the clamping force has been established, the substrate holding system 200 transitions to the clamping state ( Figure 4 ). In the clamped state, the multifunctional opening 222 no longer extracts gas from the area between the substrate W and the substrate support 210. In order to maintain the area between the substrate W and the substrate support 210 at a pressure less than the ambient pressure, the extraction opening 223 can extract fluid from the area between the substrate W and the substrate support 210. Throughout the clamped state, air from the surrounding environment may enter the area 250 between the substrate W and the substrate support 210 through leakage. For example, air may leak into the area 250 between the substrate W and the substrate support 210 through holes in the body of the substrate support 210. Alternatively, air from the environment may migrate radially inward from the side of the substrate support 210, passing through the outer seal 232, the plurality of extraction openings 223 and the inner seal 231, to reach the inner part of the area 250 between the substrate W and the substrate support 210.

[0080] Figure 5 The unloading process of the substrate W from the substrate support 210 is shown. During this process, CDA is introduced through the plurality of multi-function openings 222 to increase the pressure between the substrate W and the substrate support 210. At this point, the extraction openings 223 may continue to extract fluid from the region 250 between the substrate W and the substrate support 210. This may remove any immersion fluid around the inner seal 231 and the outer seal 232 and ensure that the unloading sequence is repeatable.

[0081] As is clear from the above, at all stages of operation, the top surface of the substrate support 210 is exposed to air. The air contains oxygen and may contain water. The air may contain water from water vapor in the air that migrates radially inward from the environment surrounding the substrate support 310 toward the outer seal 232 and the inner seal 231 of the substrate support 210. Furthermore, in immersion lithography, the area radially outward of the outer seal 232 may be immersed in an immersion fluid. This is particularly useful in immersion lithography. Figure 2 5 is shown as the area below the gap 5. The immersion fluid can be water, such as ultrapure water (UPW). In operation, the ultrapure water in liquid or vapor form can also migrate radially inward toward the center of the substrate support 210, passing through the outer seal 232, the plurality of extraction openings 223 and the inner seal 231.

[0082] When the area between the substrate W and the substrate support 210 contains oxygen and water, the upper surface of the substrate support 210 may be oxidized. A plurality of knobs 241 are located on the upper surface of the substrate support 210, so the surface of the knobs 241 may be oxidized. If the substrate support 210 is coated, it may be that the coating is oxidized. Common coatings include materials containing diamond or diamond-like carbon (DLC). These coatings are easily oxidized in the presence of oxygen and water.

[0083] The oxidation rate is increased by the presence of charge that may accumulate on the bottom surface of the substrate W. However, oxidation of the top surface of the substrate support 210 cannot be prevented by eliminating this charge accumulation, since the oxidation process occurs spontaneously in the presence of oxygen and water ("auto-oxidation").

[0084] The oxide film formed by the oxidation process is generally 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 the oxide film can be mechanically removed when the surfaces move relative to each other during loading and unloading. This removal of material causes the flatness of the substrate support 210 to decrease.

[0085] Furthermore, the oxide film formed is usually hydrophilic. This means that when water is used as the immersion fluid, water radially outside the substrate support 210 may be attracted into the region 250 between the substrate W and the substrate support 210. This increases the adhesive capillary forces exerted on the bottom surface of the substrate W, resulting in a drift of the wafer loading grid (WLG). The WLG is a measure of the overlay error caused by residual deformation caused by local sliding during loading.

[0086] <Example>

[0087] Since auto-oxidation requires the presence of oxygen and water, auto-oxidation can be mitigated by removing these components from the area around the substrate support 210. The use of CDA in the above example is intended to avoid the presence of water in the area 250 between the substrate W and the substrate support 210, but as mentioned above, water may still be present in the area 250. Therefore, in order to further mitigate the auto-oxidation of the top surface of the substrate support 210, the present invention is intended to ensure that there is no or little oxygen or water in the area 250 between the substrate W and the substrate support 210. In the present invention, this is achieved by providing a substrate holding system 300, which is configured to supply an inert gas to the area 350 between the substrate support 310 and the substrate W during the entire time that the substrate W is clamped to the substrate support 310.

[0088] Table 1 shows the difference in 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 is determined by measuring the amount of oxidation products on the DLC surface. This is shown in Table 1 as "Surface oxygen increase (%)". After 4 days, the oxygen increase on the DLC surface in the N2 gas environment (1.20) is much lower than that in the water and air environment (3.50). In the N2 test, the substrate support environment is flushed with N2 and then the environment is kept sealed. This means that the results cannot fully represent the potential advantages of the present invention, in which an inert gas is provided to the region 350 between the substrate support 310 and the substrate W during the entire time that the substrate W is clamped to the substrate support 310. However, the results still show that providing an inert gas environment in the region between the substrate support and the substrate can have a significant effect on the oxidation rate.

[0089] Table 1

[0090]

[0091] Figure 6 The same relationship is shown. Figure 6 A graph is depicted of the percentage of surface oxidation (O) of a DLC coating surface versus the exposure time (t) of the DLC coating on a substrate in an environment containing air, ultrapure water, and nitrogen (in hours). The DLC coating is a DLC coating that can be used on a substrate support WT. In this article, the percentage of surface oxidation refers to the percentage of the DLC coating that is an oxidation product. Figure 6The substrate with DLC coating (hereinafter referred to as "sample") for the data shown was plasma treated to obtain a minimum oxidation state of about 2%. The samples were then exposed to different environments for time periods ranging from 30 minutes to 4 days. The samples were exposed to auto-oxidation conditions (i.e., air or ultrapure water) in a glass petri dish with a glass cover covering the opening of the petri dish. For samples exposed to air, the glass cover did not completely cover the petri dish to allow for a continuous supply of fresh air. Samples exposed to N2 were exposed in a plastic sealed glove box container containing N2 gas.

[0092] After a predetermined exposure time, the percentage of surface oxidation was determined using X-ray photoelectron spectroscopy (XPS). XPS can measure the elemental composition as well as the chemical and electronic states of the atoms within the material.

[0093] The samples were also analyzed for contact angle. The contact angle (CA) is a measure of the ability of a liquid to wet a solid surface. The shape that a droplet assumes on a surface depends on the surface tension of the fluid and the properties of the surface. A droplet has a curved shape. The angle between (i) the surface on which the droplet forms and (ii) the tangent to the curved shape of the droplet at the edge of the droplet (i.e., where the droplet meets the surface on which it forms) is the contact angle.

[0094] like Figure 6 As shown in Figure 2, the surface oxidation percentage of the sample surface increases with the increase in exposure time. In the environment containing air, the oxidation rate of the sample is high, while in the environment containing ultrapure water, the oxidation rate of the sample is low. In the environment containing N2, the oxidation rate of the sample is much lower than the oxidation rate of the sample in air and ultrapure water. Therefore, Figure 6 It is shown that supplying an inert gas in the region between the substrate support WT and the substrate W can significantly reduce the oxidation rate of the substrate facing surface of the substrate support WT. This means that a degradation of the flatness of the substrate support WT over time can be avoided. Thus, the lifetime of the substrate support can be increased.

[0095] Figure 7 The following graphs are depicted: (i) the surface oxidation percentage (O) of the sample (i.e., substrate with DLC coating) in an environment containing air versus the exposure time (t) in seconds, and (ii) the contact angle (CA) of the sample in an environment containing air versus the exposure time (t) in seconds. The graphs show that, in general, as the surface oxidation percentage increases, the contact angle decreases. A high contact angle indicates that the surface is highly hydrophobic. Therefore, Figure 7 It is shown that as the percentage of surface oxidation increases, the hydrophobicity decreases. Figure 7It is shown that as the surface of the substrate support WT oxidizes, it may attract water molecules more easily. This means that water radially outside the substrate support WT is more likely to be attracted into the region 250 between the substrate W and the substrate support WT. This means that the adhesive capillary force applied to the bottom surface of the substrate W may increase, which may cause the wafer load grid (WLG) to drift. Therefore, the wafer load grid (WLG) can be improved by reducing the oxidation rate by providing an inert gas to the region between the substrate W and the substrate support WT.

[0096] The substrate holding system 300 includes a substrate support 310, a gas source 382, ​​and a plurality of conduits. Like the substrate holding system 200, the substrate holding system 300 can be integrated into a lithography apparatus, such as Figure 1 However, the present invention is not limited to this implementation of the substrate holding system 300, and the substrate holding system 300 can be used in various other scenarios. For example, the present invention can be implemented using a lithography apparatus that does not utilize immersion technology.

[0097] Figures 8 to 11 A portion of a substrate support 310 of a substrate support system 300 in accordance with the present invention is shown. Figure 8 9 to 10 show a plan view of the substrate support 310. Fig.11 A cross-sectional view of a substrate support 310 operating in a plurality of states is shown. The substrate support 310 is configured to support a substrate W. The structure of the substrate support 310 itself may be similar to the substrate support 210 in the previous example, but includes an additional supply opening 321 in a central region of the substrate support 310 .

[0098] As with the substrate support 210 in the previous example, the substrate support 310 may include a support body. However, for simplicity, the support body will not be mentioned. The substrate support 310 may include a plurality of burls 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 burls 341 form a plane that supports the bottom surface of the substrate W. The bottom surface of the substrate W is in contact with the distal ends of the burls 341. The burls 341 are located above the substrate support 310. The plurality of burls 341 may be arranged in a plurality of circumferential rings. However, the present invention is not limited thereto, and the plurality of burls 341 may be arranged in any suitable pattern. The diameter of each burl 341 is not particularly limited. In one embodiment, the diameter of the burl may be about 100 to 120 μm. In another embodiment, the diameter of the burl may be about 175 μm. The diameter of each of the plurality of burls 341 may be the same, or may vary across the substrate support 310.

[0099] The distance between each burl 341 is referred to as the burl pitch. This may be constant across the substrate support 310, or may vary, as known to those skilled in the art. In one embodiment, the burl pitch may be approximately 1.5 mm. In another embodiment, the burl pitch may be approximately 2.5 mm.

[0100] The substrate support 310 includes a supply opening 321 located in a central region of the substrate support 310. For the purpose of the present embodiment, the substrate W and the substrate support 310 are aligned so 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 below the central region of the substrate W. The substrate support 310 also includes a plurality of multifunctional openings 322, which may be arranged circumferentially around the substrate support 310 radially outside the supply opening 321. The plurality of multifunctional openings 322 may be uniformly distributed around the supply opening 321 in the circumferential direction. In a substrate support configured to support a substrate W having a diameter of 300 mm, the radial distance between each of the plurality of multifunctional openings 322 and the center of the substrate support 310 may be greater than 40 mm, preferably greater than 50 mm, and further preferably greater than 60 mm. In a substrate support configured to support a substrate W having a diameter of 300 mm, the radial distance between each of the plurality of multifunctional openings 322 and the center of the substrate support 310 may be less than 100 mm, preferably less than 80 mm, and further preferably less than 65 mm. These dimensions may be scaled according to the diameter of the substrate W that the substrate support 310 is configured to support. For example, the radial distance between each of the plurality of multifunctional 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 further preferably greater than 20% of the diameter of the substrate W. For example, the radial distance between each of the plurality of multifunctional 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 further preferably less than 22% of the diameter of the substrate W.

[0101] In one embodiment, the radial distance from the center of the substrate support 310 to each multifunctional opening 322 may be the same. In another embodiment, the radial distance from the center of the substrate support 310 to some multifunctional openings 322 may be greater than the radial distance to other multifunctional openings 322. This may be that the plurality of multifunctional openings 322 are arranged in a plurality of circumferential rings, wherein the distance from the center of the substrate support 310 to the multifunctional openings is different for each circumferential ring. The supply opening 321 is an example of a first port. The plurality of multifunctional openings 322 are an example of a plurality of second ports.

[0102] The supply opening 321 and the plurality of multifunctional 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 multifunctional openings 322 via the conduits 371, 373. The substrate holding system 300 may also be configured to extract gas from the region 350 between the substrate W and the substrate support 310 through the plurality of multifunctional openings 322.

[0103] The substrate support 310 may further include a plurality of extraction openings 323, which are arranged circumferentially around the substrate support 310 radially outside the plurality of multifunctional openings 322. The substrate holding system 300 may be configured to extract fluid from a 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 disposed in an edge region of the substrate support 310. The plurality of extraction openings 323 are an example of a plurality of third ports. Instead of a plurality of extraction openings 323, the present invention may include a single extraction opening 323 in the form of an annular channel extending circumferentially around the substrate support 310 in the edge region.

[0104] The substrate support 310 may also include a plurality of seals 331, 332. The seals 331, 332 are circumferential rings protruding from the substrate support 310. In one embodiment, the substrate support 310 includes an inner seal 331 and an outer seal 332, wherein the inner seal 331 is located radially inwardly of the plurality of extraction openings 323 but still within the edge region of the substrate support 310, and the outer seal 332 is located radially outwardly of the plurality of extraction openings 323.

[0105] The edge region may be a region radially outward of the radially outermost circumferential ring of the burls 341. The combination of the outer seal 332, the plurality of extraction openings 323 and the inner seal 331 prevents air and / or immersion fluid from the surroundings of the substrate support 310 from migrating radially inwardly in 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, when the substrate W is supported on the substrate support 310, the distance to the circumferential edge of the substrate W is less than 50 mm, preferably less than 25 mm, and further preferably less than 10 mm. The distance between the plurality of extraction openings 323 and the edge of the substrate W may be less than 25 mm, preferably less than 10 mm, further preferably less than 5 mm, and greater than 1.5 mm.

[0106] These dimensions may be scaled for a substrate support 310 configured to support substrates W having alternating diameters. For example, when a substrate W is supported on the substrate support 310, the distance between each of the plurality of extraction openings 323 and the circumferential edge 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, further preferably less than 2% of the diameter of the substrate W, and greater than 0.5% of the diameter of the substrate W.

[0107] In one embodiment, when the substrate W is supported by the substrate support 310, the top 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 bottom surface of the substrate W. However, the distance between the top surfaces of the inner seal 331 and the outer seal 332 and the bottom surface of the substrate W is such that the distance between the top surfaces of the seals 331, 332 and the bottom surface of the substrate W forms at least a partial seal. That is, the seals 331, 332 themselves inhibit but do not completely prevent the flow of fluid between the region 350 between the substrate W and the substrate support 310, which is the region radially outside the substrate support 310. The distance between the top surfaces of the seals 331, 332 and the bottom surface of the substrate W may be less than 10 μm and preferably less than 5 μm, and preferably greater than 1 μm and preferably greater than 3 μm. Therefore, the inert gas flowing from the center of the substrate support 310 to the extraction opening 323 acts to strengthen the inner seal 331 and prevents air from entering the area 350 between the substrate W and the substrate support 310 from areas radially outside the substrate support 310 .

[0108] The width of the inner seal 331 and the outer seal 332 (i.e., the radial distance between the inner circumferential edge of the seal and the outer circumferential edge of the seal) may preferably be greater than 0.1 mm, and also preferably greater than 0.2 mm. The width of the inner seal 331 and the outer seal 332 may preferably be less than 1 mm, and also preferably less than 0.6 mm.

[0109] The substrate holding system 300 may be configured to perform a loading sequence, operate in a clamping state, and perform an unloading sequence.

[0110] 9A to 9C Three stages of a loading sequence of a substrate support 310 of a substrate holding system 300 are depicted. Fig.9AThe substrate W is shown 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 retractable pins in their extended position (not shown). The pins may then be retracted so that the substrate W is lowered toward the substrate support 310. When the bottom surface of the substrate W contacts the plurality of protrusions 341, the pins continue to retract so that the substrate W is no longer in contact with the pins and the substrate W is fully supported by the plurality of protrusions 341. However, the present invention is not limited to this method of lowering the substrate W toward the substrate support 310, and it should be understood that those skilled in the art may implement any known technique to lower the substrate W toward the substrate support 310.

[0111] When the substrate W approaches the substrate support 310, the inert gas is provided from the gas source 382 to the region 350 above the substrate support 310 via the plurality of conduits 371, 372, 373 and the multifunctional opening 322 (see Fig. 9B ). When the substrate W approaches the substrate support 310, the pressure in the region 350 between the substrate W and the substrate support 310 increases to be greater than the ambient pressure, and the substrate W falls on the inert gas pad. 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 can be supported in such a way that there is a small gap (h) between the substrate support 310 and the substrate W. The gap (h) can preferably be greater than 50 μm, preferably greater than 80 μm, and further preferably greater than 100 μm. The gap (h) can preferably be less than 500 μm, preferably less than 250 μm, and further preferably less than 200 μm. When the substrate W is supported on the inert gas pad, the inert gas supplied from the multifunctional opening 322 flows radially outward to the edge of the substrate W in the region 350 between the substrate W and the substrate support 310.

[0112] The substrate W may be supported on the inert gas cushion for a predetermined time. The predetermined amount of time may depend on the flow rate of the inert gas through the plurality of multifunctional openings 322. The predetermined time may be the time required to ensure that the majority of the air entering between the substrate W and the substrate support 310 from the environment during the descent of the substrate W to the substrate support 310 has been replaced by the inert gas. In one embodiment, the amount of time may be greater than 10 ms, preferably greater than 20 ms. In one embodiment, the amount of time may be less than 500 ms, preferably less than 200 ms. However, the present invention is not limited to supporting the substrate W on the inert gas cushion for a predetermined time, for example, the substrate W may be supported on the inert gas cushion until the reading of the sensor 378 reaches a predetermined threshold.

[0113] After the substrate W lands on the inert gas cushion and a predetermined time has passed (or after the reading of the sensor 378 reaches a predetermined threshold), the inert gas is no longer 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 During this process, the pressure in the region 350 between the substrate W and the substrate support 310 is reduced to less than the ambient pressure, and a force is applied to the bottom surface of the substrate W in a direction toward the substrate support 310 , so that the substrate W is clamped to the substrate support 310 .

[0114] By performing this loading sequence, it is ensured that when the substrate W is first clamped to the substrate support 310, the majority of the gas in the region 350 between the substrate W and the substrate support 310 is an inert gas, rather than air containing oxygen and potentially water.

[0115] Fig.10 The substrate holding system 300 is shown configured in a chucking state. In this state, an inert gas is supplied from a gas source 382 and through the supply opening 321 to the region 350 between the substrate W and the substrate support 310. In one embodiment, in the chucking 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 chucking 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 the plurality of multifunctional openings 322.

[0116] The substrate holding system 300 performs a clamped state during most of the time that the substrate W is clamped to the substrate support 310. The substrate holding system 300 may perform a clamped state during the entire time that the substrate W is supported by the substrate support 310, except during loading and unloading sequences. If the substrate holding system 300 is implemented within a lithographic apparatus, the substrate holding system 300 may operate in a clamped state during the entire time that the lithographic apparatus performs an exposure process on the substrate W. Typically, the substrate holding system 300 may operate in a clamped state for 90% of the time that the substrate holding system 300 operates, and preferably for 95% of the time that the substrate holding system 300 operates.

[0117] In the clamping 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. An inert gas environment is an environment in which the vast majority of the gas is an inert gas. In this regard, the vast majority may mean greater than 90%, preferably greater than 95%, and also preferably greater than 99%. In the clamping state, the flow rate of the inert gas through the supply opening 321 may be greater than 1NLpm (standard liters per minute, that is, if the gas is at standard temperature and pressure, the unit of the flow rate is liters per minute), preferably greater than 1.5NLpm, and also preferably greater than 1.8NLpm. In the clamping state, the flow rate of the inert gas through the supply opening 321 may be less than 10NLpm, preferably less than 5NLpm, and also preferably less than 2.5NLpm. For example, the flow rate of the inert gas may be 2NLpm. With this flow rate, an inert gas environment can be established in the region 350 between the substrate W and the substrate support 310 within approximately 350ms. This means that the time that the substrate support 310 is exposed to oxidizing conditions can be reduced by approximately 98%, depending on the timing of the loading and unloading sequences.

[0118] By providing an inert gas to the region 350 between the substrate W and the substrate support 310 for most of the time that the substrate W is clamped to the substrate support 310, it can be ensured that the majority of the gas present in the region 350 between the substrate W and the substrate support 310 is an inert gas, rather than air from the surrounding environment, which contains oxygen and may contain water, throughout the time that the substrate W is clamped to the substrate support 310. For example, even if there are leaks within the substrate support 310 so that air from the environment can enter the region 350 between the substrate W and the substrate support 310, the constant flow of inert gas from the supply openings 321 to the extraction openings 323 and the constant extraction of fluid from the extraction openings 323 means that the air is quickly removed and replaced by the inert gas before it causes any significant oxidation of the upper surface of the substrate support 310.

[0119] The supply opening 321 is located in a central region of the substrate support 310. In one embodiment, the central region may be a region whose radial distance to the center of the substrate support 310 is less than 25 mm, preferably less than 15 mm, and further preferably less than 10 mm. In one embodiment, the supply opening 321 may be located in 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 via the supply opening 321, the inert gas flows radially outward toward the edge of the substrate W. Therefore, by providing 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, it is ensured that the inert gas is distributed in the entire region 350 between the substrate W and the substrate support 310.

[0120] In the clamped state, the extraction opening 323 can extract fluid from the region 350 between the substrate W and the substrate support 310 so that 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) can be maintained throughout the time of operation in the clamped state. In one embodiment, the magnitude of the clamping pressure is greater than 100 mbar, preferably greater than 300 mbar, and more preferably greater than 350 mbar. In one embodiment, the magnitude of the clamping pressure is less than 800 mbar, preferably less than 500 mbar, and preferably less than 450 mbar. The reason why the extraction of fluid from the region 350 between the substrate W and the substrate support 310 via the extraction opening 323 occurs is that the extraction opening 323 is in fluid communication with a pressure region whose pressure is lower than the pressure in the region 350 between the substrate W and the substrate support 310. The substrate holding system 300 can be configured such that the plurality of extraction openings 323 are in fluid communication with a pressure region having a pressure of 400 mbar or more below ambient pressure, preferably 550 mbar or more below ambient pressure, more preferably 650 mbar or more below ambient pressure, 800 mbar or less below ambient pressure, and preferably 750 mbar or less below ambient pressure. The reduced pressure region with which the plurality of extraction openings 323 are in fluid communication is formed by a vacuum pressure source 381.

[0121] The substrate holding system 300 may be configured such that the plurality of extraction openings 323 are capable of extracting 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 further preferably greater than 29 NLpm.

[0122] Since the pressure at the plurality of extraction openings 323 located in the edge region of the substrate support 310 is lower than the pressure throughout the rest 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 region 350 between the substrate W and the substrate support 310. Furthermore, 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, thereby preventing air and water from migrating radially inward from the region around the substrate support 310.

[0123] Fig.11 The unloading step of the substrate W unloading sequence is shown. This step of the unloading sequence can occur after the substrate holding system 300 has been operated in the clamping state. Fig.11In the steps of the unloading sequence shown in , an inert gas is supplied to the region 350 between the substrate W and the substrate support 310 through a 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 can be increased to be the same as the ambient pressure, in which case the clamping force applied to the substrate W is completely released. The pressure in the region 350 between the substrate W and the substrate support 310 can be increased to be greater than the ambient pressure. In this case, a force in an upward direction (i.e., a direction away from the substrate support 310) is applied to the bottom surface of the substrate W.

[0124] 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 inert gas to the region 350 between the substrate W and the substrate support 310. Therefore, the pressure within the region may vary radially in the region 350 between the substrate W and the substrate support 310. Specifically, the pressure may be higher in the radially inward region and lower in the radially outward region. In the radially inward region, the pressure may be greater than the ambient pressure, while in the radially outward region, the pressure may be lower than the ambient pressure. In this case, a force is applied to the bottom surface of the substrate W, the force being directed upward in the inner region of the substrate W (i.e., in a direction away from the substrate support 310) and directed downward in the outer region of the substrate W (i.e., in a direction toward the substrate support 310). This may cause the substrate to deform into an umbrella shape, in which the substrate is bent so that the distance between the substrate W and the substrate support 310 at the center of the substrate W is greater than the distance at the edge. This may mean that the substrate W contacts the plurality of burls 341 at the edge of the substrate support 310 , but does not contact the plurality of burls 341 in the middle of the substrate support 310 .

[0125] The inert gas introduced through the plurality of multifunctional openings 322 will flow radially outwards to be extracted by the plurality of extraction openings 323. This circulating flow ensures that any immersion fluid 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 repeatable. Since the gas supplied to the plurality of multifunctional openings 322 is an inert gas, rather than, for example, air, it is ensured that the region 350 between the substrate W and the substrate support 310 does not contain any significant amount of oxygen during this stage of the unloading sequence.

[0126] The unloading sequence may continue with the plurality of retractable pins (not shown) extending from their retracted positions such that distal end portions of the retractable pins contact the bottom surface of the substrate W. As the plurality of retractable pins continue to extend, the substrate W is lifted upward (i.e., away from the substrate support 310 ) such that the substrate W is no longer in contact with the plurality of burls 341 .

[0127] When the inert gas is supplied in the clamping state and the unloading sequence, the inert gas can be extracted through the plurality of extraction openings 323. Regardless of whether the inert gas is supplied, these extraction openings 323 are required to maintain 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 are required to extract the inert gas.

[0128] Since the substrate support 310 is provided with a supply opening 321 and a plurality of multifunctional openings 322, and the substrate holding system 300 can be configured so that the inert gas can be provided to one of them but not to the other, the inert gas is supplied to the supply opening 321 during the clamping state, and the inert gas is supplied to the multifunctional opening 322 during the loading and unloading sequence. It is important to supply the inert gas to the central area of ​​the substrate support 310 during the clamping state, because once the inert gas is supplied to the area 350 between the substrate W and the substrate support 310, the inert gas flows radially outward, which ensures that the entire area 350 between the substrate W and the substrate support 310 is surrounded by the inert gas. In contrast, it is important to supply the inert gas to the area radially outside the central area during the loading and unloading sequence. This is because, if the inert gas is supplied to the central area during the loading and unloading sequence, the pressure distribution generated on the bottom surface of the substrate W may cause the central area of ​​the substrate W to have a flatness bulge.

[0129] Fig.12 An example of a fluid management system configuration of a substrate holding system 300 is shown. In the configuration shown, a gas source 382 is connected to a multifunctional opening 322 and a supply opening 321 via an inert gas supply valve 361. The inert gas supply valve 361 may be a three-way valve, wherein a first opening corresponds to an inert gas supply conduit 371, a second opening corresponds to a supply opening conduit 372, and a third opening corresponds to a multifunctional opening conduit 373. The inert gas supply valve 361 may be configured to supply inert gas neither to the supply opening conduit 372 nor to the multifunctional opening conduit 373, but only to the supply opening conduit 372 and the multifunctional opening conduit 373. The inert gas supply valve 361 may also be configured to supply inert gas to the supply opening conduit 372 and the multifunctional opening conduit 373 at the same time. In this way, only the inert gas supply valve 361 is required to provide the inert gas supply function of the present invention, which means that the system is simple, easy to assemble, and easy to maintain.

[0130] Alternatively, the inert gas supply valve 361 may be a 4-way valve. The 4-way inert gas supply valve 361 may include the same three ports as the 3-way inert gas supply valve 361, and have an additional port configured to exhaust the inert gas to the external environment or other parts of the substrate holding system 300. The valve type used for the inert gas supply valve 361 is not particularly limited, and any suitable valve known to those skilled in the art may be used.

[0131] The present invention is not limited to such a configuration of supplying inert gas to the supply opening 321 and the plurality of multifunctional openings 322. For example, the flow of 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 inert gas to the supply opening 321 may be controlled by a first 2-way valve, the inlet opening of which is connected to the first inert gas supply conduit, and the outlet opening is connected to the supply opening conduit. The flow of inert gas to the plurality of multifunctional openings 322 may be controlled by a second 2-way valve, the inlet opening of which is connected to the second inert gas supply conduit, and the outlet opening is connected to the multifunctional opening conduit.

[0132] like Fig.12 As shown, the plurality of multifunctional openings 322 and the plurality of extraction openings 323 are in fluid communication with a vacuum pressure source 381. The vacuum pressure source 381 provides a pressure region lower than the ambient pressure. Therefore, the vacuum source 381 allows gas to be extracted through the multifunctional openings 322 and the plurality of extraction openings 323. Fig.12 In the configuration shown, the flow path between the vacuum source 381 and the multi-function opening 322 is different from the flow path between the vacuum pressure source 381 and the plurality of extraction openings 323. Each flow path may include a valve to control the extraction of fluid from the corresponding opening. The valve may be a simple 2-way valve, with its inlet opening connected to the vacuum source conduit 374 and its outlet opening connected to the conduits 373, 375 corresponding to the multi-function 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 2-way valve 365.

[0133] A flow restrictor 370 (also referred to as a control valve) may be included in the fluid management system. The flow restrictor 370 may be configured to control the flow of fluid through conduits 371, 372, 373, 374. The type of flow restrictor 370 used is not particularly limited. For example, the flow restrictor 370 may be a needle valve, a solenoid valve, or any other suitable type of control valve known to those skilled in the art. Each flow restrictor 370 does not have to be identical. In fact, each flow restrictor 370 may have different characteristics so that the flow of fluid through the system may be adjusted in different parts of the pipeline. In this way, the rate of fluid supply / extraction may become different at different openings or at different times. Fig.12 The restrictor 370 shown in FIG. 3 is an example, and additional restrictions may be included, or some restrictions may be omitted, to provide desired flow characteristics.

[0134] The fluid management system may include a plurality of additional valves, such as check valves (non-return valves), pressure relief valves, isolation valves, and the like.

[0135] In the fluid management system, there may be multiple paths between the vacuum pressure source 381 and the multiple multifunctional openings 322. Each path may include valves 362, 363, 364 and a flow restrictor 370. Each flow restrictor 370 may be configured in different ways. For example, each flow restrictor 370 may be configured to allow fluid to flow through at different volume flow rates. Therefore, the extraction flow from the multiple multifunctional openings 322 may be controlled by changing the valve opened in the valves 362, 363, 364. However, this is merely an example configuration of the present invention, and the flow extraction path is not limited to this configuration. For example, the branch between the vacuum pressure source 381 and the multiple multifunctional openings 322 may not be divided into multiple paths. The flow rate of the fluid may be controlled by a variable flow restrictor valve.

[0136] 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; volume flow; pressure; temperature; flow rate; fluid composition. These sensed characteristics may be communicated to a monitoring system. The monitoring system may be configured to change functional aspects of the flow system in response to the measurements. The monitoring system may be included in the substrate holding system 300, or may be located external to the substrate holding system 300.

[0137] Throughout the specification, the term "conduit" is used to refer to channels that fluidly connect the various components in the substrate holding system 300. The term "conduit" is not limited to fixed rigid pipes, but is intended to encompass all suitable fluid channels and connections known to those skilled in the art.

[0138] In the above embodiment, a single supply opening 321 is mentioned. However, the present invention is not limited thereto, and the substrate support 310 includes a plurality of supply openings 321, each of which is configured in the same manner as the above-mentioned single supply opening 321. The plurality of supply openings 321 may all be located in the central region. Alternatively, some supply openings 321 may be located in the central region, but other supply openings 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 cause effects such as a pressure drop or turbulence 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, as well as the number of supply openings 321.

[0139] 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, further preferably greater than 1 mm, and further preferably greater than 1.1 mm. In an embodiment with multiple supply openings 321, the diameter of each supply opening 321 may be greater than 0.4 mm, and preferably greater than 0.6 mm.

[0140] In order for the supply opening 321 not to interfere with the plurality of burls 341, the diameter of the supply opening 321 may be smaller than the sum of the burl pitch and the burl radius. For example, if the burl pitch is 1.5 mm, the diameter of the (multiple) supply openings may be smaller than 1.2 mm. If the burl pitch is 2.5 mm, the diameter of the (multiple) supply openings may be smaller than 2.1 mm.

[0141] In one embodiment of the present invention, the upper surface of the substrate support 310 may include a plurality of additional openings ( Figures 8 to 11 310 ). These openings may be used to provide an entry point to a tool, or to accommodate a plurality of retractable pins used to lower and / or raise the substrate W toward and away from the substrate support 310 during loading and unloading sequences. Fig.13 An example of a tool opening 390 is shown. It may be the case that the area within the tool opening 390 needs to be maintained at ambient pressure. In previous configurations of the substrate support 310, the gas within a hole such as the tool opening 390 would be air at ambient pressure. Although the tool opening 390 may have been provided with a seal 392 to inhibit air from flowing from the area within the tool opening 390 to the area 350 between the substrate W and the substrate support 310, a leak at the seal 392 would mean that the area around the tool opening 390 would be exposed to air. Oxygen and possible moisture in the leaking air may cause the upper surface of the substrate support W to oxidize in the area around the tool opening 390. This may cause a local flatness drift.

[0142] In one embodiment of the invention, each of these tool openings 390 may include a small orifice 391. The substrate holding system 300 may be configured to supply an inert gas to the area inside the tool opening 390 through the small orifice 391, so that the pressure inside the tool opening 390 is ambient pressure, but the tool opening 390 contains an inert gas, rather than air. This means that any gas flowing from the area inside the tool opening 390 out of the seal 392 to the main area 350 between the substrate W and the substrate support 310 is inert and does not contain oxygen. This means that oxidation of the areas around the openings used for purposes such as processing and providing retractable pins is avoided, and there is no local flatness drift in these areas.

[0143] In the present invention, only the gas source 382 and the substrate support 310 are required to be included in the substrate holding system 300. However, the present invention is not limited to the precise locations of these components within the substrate holding system 300. If the substrate holding system 300 includes other components, the locations of these other components within the substrate holding system 300 are 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 one embodiment, the inert gas supply valve 361 can be located within the substrate support 310 itself. However, the inert gas supply valve 361 can also be located within the gas source 382, ​​or at a location between the substrate support 310 and the gas source 382.

[0144] The structure of the gas source 382 is not particularly limited, and any suitable configuration known to those skilled in the art may be used in the embodiments of the present invention. The gas source 382 itself may have a storage component configured to store an inert gas, or the gas source may be connected to an external system configured to supply a constant flow of inert gas to the gas source 382. The structure of the vacuum pressure source 381 is also not particularly limited, and any suitable configuration known to those skilled in the art may be used in the embodiments of the present invention.

[0145] Inert gas can be mainly composed of nitrogen (N2). That is to say, the vast majority of inert gas can be nitrogen. Specifically, the proportion of nitrogen in the inert gas can be greater than 90%, preferably greater than 95%, preferably greater than 99%, and also preferably greater than 99.5%. The proportion of other components in the inert gas should be low enough so that they do not cause any significant oxidation of the substrate support 310. Nitrogen is particularly advantageous because it is relatively cheap and easy to obtain, and comes from abundant resources (air). There is no safety problem in the amount of nitrogen used in the present invention. However, the inert gas of the present invention is not limited to nitrogen, but can also be any gas that does not contain oxygen or water, and is known not to react with the material of the substrate support and / or coating. For example, helium (H2) and argon (Ar) can also be used.

[0146] In addition to preventing oxidation of the surface of the substrate support 310, when an inert gas is provided to the region 350 between the substrate W and the substrate support 310, it can be ensured that the gas is clean and does not contain debris. Debris can adversely affect the operation of the substrate holding system 300. For example, the debris may cause a reduction in the flatness of the substrate W or may cause damage to sensitive components.

[0147] The substrate support 310 may be formed of any material known in the art. For example, the substrate support 310 may be formed of SiSiC. The substrate support 310 may be coated. The type of coating is not particularly limited and may be any coating suitable for the application known to those skilled in the art. For example, the substrate support 310 may be coated with diamond or diamond-like carbon (DLC).

[0148] In the claims, the term "port" is used to mean "an opening for passage of a fluid". The term "port" does not imply any geometrical constraints on the opening for passage of a fluid. For example, although throughout the drawings, ports are shown as holes having a cylindrical cross-section, the present invention is not limited to this configuration, and ports may be other shapes.

[0149] The present invention may provide a lithographic apparatus. The lithographic apparatus may have any / all other features or components of the lithographic apparatus described above. For example, the lithographic apparatus may optionally include one or more of the following: a source SO, an illumination system IL, a projection system PS, a substrate support WT, etc.

[0150] In particular, the lithographic apparatus may include a projection system PS configured to project a radiation beam B towards a surface area of ​​a substrate W. The lithographic apparatus may further include a substrate holding system 300 as described in any of the embodiments and variations above.

[0151] Although the application of lithography equipment in integrated circuit manufacturing may be specifically mentioned herein, it should be understood that the lithography equipment described herein may have other applications. Possible other applications include manufacturing integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0152] Where context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented by instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and that such actions are actually generated by a computing device, processor, controller, or other device that executes firmware, software, routines, instructions, etc., and in doing so may cause an actuator or other device to interact with the physical world.

[0153] Although specific reference may be made herein to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These apparatuses may generally be referred to as lithography tools.

[0154] Although specific reference may have been made above to using embodiments of the present invention in the context of optical lithography, it will be appreciated that the present invention is not limited to optical lithography where the context permits.

[0155] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be implemented in a manner other than that described. The above description is intended to be illustrative, not restrictive. Therefore, it will be understood by those skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims described 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 comprises a first port located in a central region thereof and a plurality of second ports located radially outward of 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 being 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 being configured to enable the inert gas to be supplied 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.

2. The substrate holding system of claim 1 , wherein the first port and the plurality of second ports are fluidly connected to the gas supply device via at least one valve in the substrate holding system, wherein the valve is configured to enable the inert gas to be supplied to the area between the substrate and the substrate support through the first port or the plurality of second ports.

3. The substrate holding system of claim 2, wherein the valve is further configured to exhaust the inert gas to an external environment or other portion of the substrate holding system.

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

5. A substrate holding system according to claim 4, wherein the plurality of third ports are configured to be connected to a pressure region fluid, the pressure of the pressure region being less than 400 mbar of the ambient pressure, preferably less than 550 mbar of the ambient pressure, further preferably less than 650 mbar of the ambient pressure, less than 800 mbar of the ambient pressure, and preferably less than 750 mbar of the ambient pressure.

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

7. The substrate holding system according to any one of claims 1 to 6, wherein 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, and also preferably greater than 60 mm, less than 100 mm, preferably less than 80 mm, and also preferably less than 65 mm, and / or wherein 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, and also 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, and also preferably less than 22% of the diameter of the substrate.

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

9. A substrate support system according to any one of claims 1 to 8, wherein the central area of ​​the substrate support has only one first port, and the diameter of the first port is greater than 0.6 mm, preferably greater than 0.8 mm, further preferably greater than 1 mm, further preferably greater than 1.1 mm, or wherein the central area of ​​the substrate support has multiple first ports.

10. The substrate support system of any one of claims 9, wherein the diameter of the plurality of first ports is greater than 0.4 mm, and preferably greater than 0.6 mm.

11. A substrate support system according to any one of claims 1 to 10, wherein the substrate support further comprises a plurality of protrusions protruding from the upper surface of the substrate support, and / or wherein the inert gas is mainly composed of nitrogen, and / or wherein the substrate support is formed of SiSiC, and / or wherein the substrate support is coated with diamond or diamond-like carbon.

12. The substrate support system of claim 11, wherein a diameter of the first port(s) is smaller than a sum of a distance between each of the plurality of burls and a radius of each burl.

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

14. A method of supporting a substrate on a substrate support, the substrate support comprising a first port located in a central region of the substrate support and a plurality of second ports located radially outward of the first port, the method comprising: a substrate loading step in which an inert gas is supplied to a region between the substrate and the substrate support through the plurality of second ports; as well as A subsequent substrate clamping step is performed in which the inert gas is supplied to the region between the substrate and the substrate support through the first port.

15. The method of claim 14, wherein 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 wherein the substrate clamping step is performed more than 90% of the time that the substrate is clamped to the substrate support.

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