Lithographic apparatus, method for unloading substrate and method for loading substrate

Abstract

To improve flatness of the clamped substrate, and / or to reduce wear of the support table.SOLUTION: There is provided a method for unloading a substrate from a support table configured to support the substrate, the method comprising: supplying gas to a gap between a base surface of the support table and the substrate via a plurality of gas flow openings in the support table, wherein during an initial phase of unloading, the gas is supplied through at least one gas flow opening in an outer region of the support table and not through any gas flow opening in a central region of the support table radially inward of the outer region, and during a subsequent phase of unloading, the gas is supplied through at least one gas flow opening in the outer region and at least one gas flow opening in the central region.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This document claims priority to European Patent Application No. 16154599.1 and European Patent Application No. 16172678.1, filed February 8, 2016 and June 2, 2016, which are incorporated by reference in their entireties herein.

[0002] The present invention relates to a lithographic apparatus, a method for unloading a substrate and a method for loading a substrate, particularly onto a support table of a lithographic apparatus. [Background technology]

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device, alternatively called a mask or reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of one or several dies) on the substrate (e.g. a silicon wafer). The transfer of the pattern is typically by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions which are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern with a radiation beam in a given direction (the "scan" direction) while synchronously scanning the substrate parallel or anti-parallel to the given direction (the "scan" direction). It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] It has been proposed to immerse the substrate in a lithographic projection apparatus in a liquid having a relatively high refractive index, such as water, so as to fill the space between the final element of the projection system and the substrate. In an embodiment, the liquid is ultrapure water, but other liquids can be used. An embodiment of the invention has been described with reference to a liquid. However, other fluids may be suitable, in particular wetting fluids, incompressible fluids and / or fluids with a higher refractive index than air, preferably a higher refractive index than water. Fluids other than gases are particularly desirable. The point is that the exposure radiation has a shorter wavelength in the liquid, allowing smaller features to be imaged. (The effect of the liquid can be seen as increasing the effective numerical aperture (NA) of the system, and also increasing the depth of focus.) Other immersion liquids have also been proposed, such as water in which solid particles (e.g. quartz) are suspended, or a liquid in which there is a suspension of nanoparticles (e.g. particles with a maximum dimension of up to 10 nm). The suspended particles may or may not have a similar or the same refractive index as the liquid in which they are suspended. Other liquids that may be suitable are hydrocarbons, such as aromatics, fluorohydrocarbons, and / or aqueous solutions.

[0005]

[0005] Immersing the substrate or the substrate and support table in a bath of liquid (see for example US Pat. No. 4,509,852) also means that there is a large body of liquid that has to be accelerated during the scanning exposure, which requires additional or more powerful motors and turbulence in the liquid can cause undesirable and unpredictable effects.

[0006]

[0006] In an immersion apparatus, the immersion fluid is handled by a fluid handling system, device structure or apparatus. In an embodiment, the fluid handling system is capable of supplying the immersion fluid and is therefore a fluid supply system. In an embodiment, the fluid handling system is capable of at least partially confining the immersion fluid and is thereby a fluid confinement system. In an embodiment, the fluid handling system is capable of forming a barrier to the fluid and is thereby a barrier member such as a fluid confinement structure. In an embodiment, the fluid handling system is capable of generating or using a flow of gas, for example, to help control the flow and / or position of the immersion fluid. The flow of gas may form a seal that confines the immersion fluid and therefore the fluid handling structure may also be referred to as a sealing member. Such a sealing member may be a fluid confinement structure. In an embodiment, an immersion liquid is used as the immersion fluid. In this case, the fluid handling system may be a liquid handling system. With regard to the above description, references to features defined in this paragraph with respect to a fluid may be taken to include features defined with respect to a liquid. Summary of the Invention

[0007]

[0007] In both immersion or dry apparatus, the substrate is clamped to a support table during the exposure process. Clamping may be assisted by the presence of a gap between the substrate and the support table at a lower pressure compared to ambient pressure. Ambient pressure is the pressure surrounding the substrate and support table. The area surrounded by the support table and substrate may be at a near vacuum pressure such that the substrate is vacuum clamped to the support table.

[0008]

[0008] The support table includes one or more holes formed therein. The holes facilitate clamping of the substrate. Gas may be extracted through the holes from a gap enclosed by the substrate and the support table, thereby reducing pressure in the gap to clamp the substrate.

[0009]

[0009] The substrate is loaded onto the support table. During the loading of the substrate, the substrate may be deformed due to gravity. The substrate is clamped in a deformed state, which may increase the overlay.

[0010]

[0010] The substrate has areas to which near-vacuum pressure is applied during unloading and areas to which near-vacuum pressure is not applied. When the near-vacuum pressure is not applied (e.g. released) the substrate can move away from the support table. In other areas where the near-vacuum pressure is still applied the substrate can slip. This can cause wear on the support table where the substrate slips. The periphery of the top surface of the support table is particularly prone to wear.

[0011] For example, it is desirable to provide a lithographic apparatus, a method for unloading a substrate, and a method for loading a substrate that improves the flatness of a clamped substrate and / or reduces wear on the support table.

[0012]

[0011] According to one aspect of the present invention, there is provided a method of unloading a substrate from a support table configured to support the substrate, the method comprising supplying gas to a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table, wherein during an initial stage of unloading, gas is supplied from at least one gas flow opening in an outer region of the support table and no gas flow openings in a central region of the support table radially inward from the outer region, and during a later stage of unloading, gas is supplied from at least one gas flow opening in the outer region and at least one gas flow opening in the central region.

[0013]

[0012] According to one aspect of the invention there is provided a method of loading a substrate onto a support table configured to support the substrate, the method comprising extracting gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table, wherein in a first stage of loading, gas extraction is from at least one gas flow opening in a central region of the support table and no gas flow openings in a middle region of the support table radially outward of the central region and no gas flow openings in an outer region of the support table radially outward of the middle region; in a second stage of loading, gas extraction is from at least one gas flow opening in the central region and at least one gas flow opening in the middle region and no gas flow openings in the outer region; and in a third stage of loading, gas extraction is from at least one gas flow opening in the central region, at least one gas flow opening in the middle region, and at least one gas flow opening in the outer region.

[0014]

[0013] According to one aspect of the invention, there is provided a method of loading a substrate onto a support table configured to support the substrate, the method including lowering the substrate towards the support table; controlling a negative pressure source to apply negative pressure through a plurality of gas flow openings in the support table as the substrate is lowered towards the support table to extract gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table; controlling a negative pressure source in fluid communication with one of the gas flow openings in the support table to stop applying negative pressure when the substrate reaches a predetermined distance above the support table; and controlling a negative pressure source to resume applying negative pressure when the substrate lands on the support table to extract gas through the plurality of gas flow openings in the support table.

[0015]

[0014] According to one aspect of the invention there is provided a method of loading a substrate onto a support table configured to support the substrate, the method comprising extracting gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table, wherein in a first stage of loading, gas extraction is from at least one gas flow opening in an outer region of the support table and no gas flow openings in an intermediate region of the support table radially inward of the outer region and no gas flow openings in a central region of the support table radially inward of the intermediate region; in a second stage of loading, gas extraction is from at least one gas flow opening in the outer region and at least one gas flow opening in the intermediate region and no gas flow openings in the central region; and in a third stage of loading, gas extraction is from at least one gas flow opening in the outer region, at least one gas flow opening in the intermediate region, and at least one gas flow opening in the central region.

[0016]

[0015] According to one aspect of the present invention, there is provided a lithographic apparatus comprising a gas flow system, a controller configured to control the gas flow system, and a support table configured to support a substrate, the support table comprising a base surface, a central region, an outer region radially outward of the central region, and a plurality of gas flow openings configured by the gas flow system to supply gas to a gap between the base surface and the substrate, wherein when the substrate is unloaded from the support table, during an early stage of unloading, the controller is configured to control the gas flow system to supply gas from at least one gas flow opening in the outer region and not from any gas flow openings in the central region, and during a later stage of unloading, the controller is configured to control the gas flow system to supply gas from at least one gas flow opening in the outer region and from at least one gas flow opening in the central region.

[0017]

[0016] According to one aspect of the present invention, there is provided a lithographic apparatus comprising a gas flow system, a controller configured to control the gas flow system, and a support table configured to support a substrate, the support table comprising a base surface, a central region, a middle region radially outward of the central region, an outer region radially outward of the middle region, and a plurality of gas flow openings configured for use by the gas flow system to extract gas from a gap between the base surface and the substrate, wherein when the substrate is loaded onto the support table, in a first stage of loading, the controller controls extraction of gas from at least one gas flow opening in the central region and extraction of gas from at least one gas flow opening in the middle region. A lithographic apparatus is provided, wherein in a second stage of loading, the controller is configured to control the gas flow system to extract gas from at least one gas flow opening in the central region and at least one gas flow opening in the middle region, and not from any gas flow openings in the outer region; and in a third stage of loading, the controller is configured to control the gas flow system to extract gas from at least one gas flow opening in the central region, at least one gas flow opening in the middle region, and at least one gas flow opening in the outer region.

[0018]

[0017] According to one aspect of the present invention, there is provided a lithographic apparatus comprising a gas flow system with a negative pressure source, a controller configured to control the gas flow system, and a support table configured to support a substrate, wherein when the substrate is lowered towards the support table, the controller is configured to control the negative pressure source to apply negative pressure through a plurality of gas flow openings in the support table to extract gas from a gap between the support table and the substrate, when the substrate reaches a predetermined distance above the support table, the controller is configured to control the negative pressure source in fluid communication with any of the gas flow openings in the support table to stop applying negative pressure, and when the substrate lands on the support table, the controller is configured to control the negative pressure source to resume applying negative pressure to extract gas through the plurality of gas flow openings in the support table.

[0019]

[0018] According to one aspect of the present invention, there is provided a lithographic apparatus comprising a gas flow system, a controller configured to control the gas flow system, and a support table configured to support a substrate, the support table comprising a base surface, a central region, a middle region radially outward of the central region, an outer region radially outward of the middle region, and a plurality of gas flow openings configured for use by the gas flow system to extract gas from a gap between the base surface and the substrate, each region being provided with a flow path in fluid communication with the gas flow opening of that region and a pressure sensor configured to sense a pressure relative to that region, and wherein when a substrate is loaded onto the support table, the controller is configured to control the timing of extraction of gas from the gas flow openings of each region based on the sensed pressure in each region. [Brief description of the drawings]

[0020]

[0019] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which:

[0021] [Figure 1] 1 depicts a lithographic apparatus according to an embodiment of the present invention; [Diagram 2]

[0021] A liquid supply system for use in a lithographic projection apparatus is depicted. [Diagram 3]

[0022] 1 illustrates a cross-sectional side view of another liquid supply system according to an embodiment; [Figure 4]

[0023] 1 depicts a support table of a lithographic apparatus according to an embodiment of the invention in cross-section; [Diagram 5]

[0024] 1 illustrates, in plan view, a support table of a lithographic apparatus according to an embodiment of the invention; [Figure 6]

[0025] 3 illustrates, in plan view, a support table of a lithographic apparatus according to another embodiment of the invention; [Figure 7]

[0026] 2 illustrates a schematic representation of a support table and part of a gas flow system of a lithographic apparatus according to an embodiment of the invention; [Figure 8]

[0027] 2 illustrates a schematic diagram of a support table and a gas flow system of a lithographic apparatus according to an embodiment of the present invention; [Figure 9]

[0028] 2 illustrates a schematic diagram of a support table and a gas flow system of a lithographic apparatus according to an embodiment of the invention; [Figure 10]

[0029] 4 shows the vertical height of the substrate over time as the substrate is lowered onto the support table. [Figure 11]

[0030] 4 shows pressures in different parts of the lithographic apparatus when a substrate is lowered onto the support table. [Figure 12]

[0031] 2 illustrates diagrammatically how a substrate is lowered onto a support table according to an embodiment of the present invention; [Figure 13]

[0032] 1 illustrates, in plan view, a support table of a lithographic apparatus according to an embodiment of the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022]

[0033] Figure 1 depicts a schematic diagram of a lithographic apparatus according to an embodiment of the invention. a. an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation); b. a support structure (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters; c. a support table WT constructed to hold a substrate (e.g., a resist-coated substrate) W and connected to a second positioner PW configured to accurately position the table, e.g., a sensor table for supporting one or more sensors, or a support table WT, according to certain parameters; d. A projection system (eg 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 (eg comprising one or more dies) of the substrate W.

[0023]

[0034] The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling radiation.

[0024]

[0035] The support structure MT holds the patterning device MA. It holds the patterning device in a manner that depends on the orientation of the patterning device MA, the design of the lithographic apparatus, and other conditions, for example whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be for example a frame or a table, which may be fixed or movable as required. The support structure MT may ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS. Any use of the terms "reticle" or "mask" herein may be considered as synonymous with the more general term "patterning device".

[0025]

[0036] The term "patterning device", as used herein, should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in a target portion of a substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate if, for example, the pattern includes phase-shifting features or so-called assist features. Generally, the pattern imparted to the radiation beam corresponds to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0026]

[0037] The term "projection system" as used herein should be interpreted broadly as covering any type of projection system including, for example, refractive optical systems, catadioptric optical systems, magnetic optical systems, electromagnetic optical systems and electrostatic optical systems, or any combination thereof, as appropriate depending on, for example, the exposure radiation used or other factors such as the use of an immersion liquid or the use of a vacuum. When the term "projection lens" is used herein, it can be considered as synonymous with the more general term "projection system".

[0027]

[0038] As here depicted, the apparatus may be of a transmissive type (e.g. employing a transmissive mask) or it may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).

[0028]

[0039] The lithographic apparatus may be of a type having two or more tables (or stages or supports), for example two or more support tables or a combination of one or more support tables and one or more cleaning, sensor or measurement tables. For example, in an embodiment the lithographic apparatus is a multi-stage apparatus including two or more tables arranged at the exposure side of the projection system, each table including and / or holding one or more objects. In an embodiment, one or more of the tables may hold a radiation sensitive substrate. In an embodiment, one or more of the tables may hold a sensor for measuring radiation from the projection system. In an embodiment, the multi-stage apparatus comprises a first table (i.e. the support table) configured to hold a radiation sensitive substrate and a second table (hereinafter collectively referred to as, but not limited to, a measurement, sensor and / or cleaning table) that is not configured to hold a radiation sensitive substrate. The second table may include and / or hold one or more objects other than a radiation sensitive substrate. Such one or more objects may include one or more selected from the following: a sensor for measuring radiation from the projection system, one or more alignment marks, and / or a cleaning device (eg for cleaning the liquid confinement structure).

[0029]

[0040] In such a "multiple stage" (or "multi-stage") machine, several tables can be used in combination, or preliminary steps can be carried out on one or more tables while another one or more tables are used for exposure. A lithographic apparatus may have two or more patterning device tables (or stages or supports) that can be used in combination in a similar manner as substrate, cleaning, sensor and / or measurement tables.

[0030]

[0041] With reference to Figure 1, the illumination system IL receives a radiation beam from a radiation source SO or radiation. The radiation source SO and the lithographic apparatus may be separate entities, for example when the radiation source SO is an excimer laser. In such a case, the radiation source SO is not considered to form part of the lithographic apparatus and the radiation beam is passed from the radiation source SO to the illumination system IL with the aid of a beam delivery system BD, for example comprising suitable directing mirrors and / or beam expanders. In other cases, the radiation source SO may be an integral part of the lithographic apparatus, for example when the radiation source SO is a mercury lamp. The radiation source SO and the illumination system IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0031]

[0042] The illumination system IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. In general, the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illumination system IL may be adjusted. The illumination system IL may also comprise various other components, such as an integrator IN and a condenser CO. The illumination system IL may be used to adjust the radiation beam to have a desired uniformity and intensity distribution over its cross-section. Similar to the radiation source SO, the illumination system IL may or may not be considered to form part of the lithographic apparatus. For example, the illumination system IL may be an integral part of the lithographic apparatus or may be a separate component of the lithographic apparatus. In the latter case, the lithographic apparatus may be configured such that the illumination system IL can be mounted thereon. Optionally, the illumination system IL is detachable and may be provided separately (e.g. by the manufacturer of the lithographic apparatus or by another supplier).

[0032]

[0043] The radiation beam B is incident on the patterning device MA, which is held on the support structure MT, and is patterned by the patterning device MA. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (not explicitly shown in Figure 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during a scan. In general, movement of the support structure MT can be realised with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realised using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. The patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. As illustrated the patterning device alignment marks M1, M2 occupy dedicated target portions, but they may also be located in spaces between the target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0033]

[0044] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein may have other applications in the manufacture of components with micro-scale and even nano-scale features, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0034]

[0045] Arrangements for providing liquid between the final element of the projection system PS and the substrate can be divided into three general categories: bath-based arrangements, so-called localized immersion systems, and all-wet immersion systems. In a bath-based arrangement, substantially the whole of the substrate W, and optionally part of the support table WT, is submerged in a bath of liquid.

[0035]

[0046] A localized immersion system uses a liquid supply system in which liquid is supplied only to a localized area of ​​the substrate. The space filled with liquid is smaller than the top surface of the substrate in plan, and the area filled with liquid remains substantially stationary relative to the projection system PS, while the substrate W moves below it. Figures 2 and 3 show different supply devices that can be used in such a system. Sealing features are present to confine the liquid to a localized area. One way proposed to arrange this is disclosed in PCT Patent Application Publication WO 99 / 49504.

[0036]

[0047] A proposed arrangement is to provide a liquid supply system with a liquid confinement structure that extends along at least part of the boundary of the space between the final element of the projection system and the support table. Such an arrangement is shown in figure 2.

[0037]

[0048] 2 illustrates diagrammatically a localized liquid supply system, i.e. a fluid handling system. The liquid supply system comprises a fluid handling structure IH (or liquid confinement structure) extending along at least part of the boundary of a space 11 between a final element of the projection system PS and the support table WT or substrate W. (Note that unless stated otherwise, any description below of the surface of the substrate W additionally or alternatively refers to the surface of the support table WT as well.) The fluid handling structure IH is substantially stationary relative to the projection system PS in the XY plane, but there may be some relative movement in the Z direction (in the direction of the optical axis). In an embodiment, a seal is formed between the fluid handling structure IH and the surface of the substrate W, which may be a contactless seal, such as a gas seal (such a system with a gas seal is disclosed in European Patent Application Publication EP-A-1,420,298) or a liquid seal.

[0038]

[0049] The fluid handling structure IH at least partially confines liquid in a space 11 between the final element of the projection system PS and the substrate W. A contactless seal to the substrate W may be formed around the image field of the projection system PS such that liquid is confined in the space 11 between the surface of the substrate W and the final element of the projection system PS. The space 11 is at least partly formed by the fluid handling structure IH arranged below and surrounding the final element of the projection system PS. Liquid is drawn into the space 11 below the projection system PS and inside the fluid handling structure IH by one of the liquid openings 13. Liquid may be removed by another of the liquid openings 13. Liquid may be drawn into the space 11 from at least two liquid openings 13. Which liquid opening 13 is used to supply liquid and optionally which is used to remove liquid may depend on the direction of movement of the support table WT. The fluid handling structure IH may extend slightly above the final element of the projection system PS. The liquid level rises above the final element so that a buffer of liquid is provided. In an embodiment the fluid handling structure IH has an inner periphery which at its top closely conforms to the shape of the projection system PS or a final element thereof and which may for example be circular, and at the bottom the inner periphery closely conforms to the shape of the image field which may for example be rectangular, although this does not have to be the case.

[0039]

[0050] The liquid may be confined in the space 11 by a gas seal 16 that is formed in use between the bottom of the fluid handling structure IH and the surface of the substrate W. The gas seal 16 is formed by a gas. Gas in the gas seal 16 is supplied under pressure via an inlet 15 to the gap between the fluid handling structure IH and the substrate W. The gas is extracted via an outlet 14. The overpressure on the gas inlet 15, the vacuum level relative to the outlet 14 and the geometry of the gap are configured such that there is a high velocity gas flow inwards, which confines the liquid. The force of the gas on the liquid between the fluid handling structure IH and the substrate W confines the liquid in the space 11. The inlet / outlet may be an annular groove surrounding the space 11. The annular groove may be continuous or discontinuous. The gas flow has the effect of confining the liquid in the space 11. Such a system is disclosed in US Patent Application Publication US2004-0207824, which is incorporated herein by reference in its entirety. In an embodiment, the fluid handling structure IH does not have a gas seal 16.

[0040]

[0051] Figure 3 illustrates, in cross-section, a side view of another liquid supply system, i.e. a fluid handling system, according to an embodiment. The arrangement shown in Figure 3 and described below can be applied to the lithographic apparatus shown in Figure 1 and described above. The liquid supply system comprises a fluid handling structure IH (i.e. a liquid confinement structure) that extends along at least part of the boundary of a space 11 between the final element of the projection system PS and the support table WT or the substrate W. (Please note that, unless stated otherwise, any reference below to the surface of the substrate W may additionally or alternatively also refer to the surface of the support table WT.)

[0041]

[0052] The fluid handling structure IH at least partially confines liquid to a space 11 between the final element of the projection system PS and the substrate W. The space 11 is at least partly formed by the fluid handling structure IH arranged below and surrounding the final element of the projection system PS. In an embodiment, the fluid handling structure IH comprises a body member 53 and a porous member 33. The porous member 33 is plate-shaped and has a plurality of holes (i.e. openings or pores). In an embodiment, the porous member 33 is a mesh plate having a multitude of small holes 84 formed in a mesh. Such a system is disclosed in US Patent Application Publication US2010 / 0045949A1, which is incorporated herein by reference in its entirety.

[0042]

[0053] The body member 53 includes a supply port 72 capable of supplying liquid to the space 11 and a recovery port 73 capable of recovering liquid from the space 11. The supply port 72 is connected to a liquid supply device 75 through a passage 74. The liquid supply device 75 can supply liquid to the supply port 72. The liquid supplied from the liquid supply device 75 is supplied to each supply port 72 through the corresponding passage 74. The supply port 72 is disposed at a predetermined position facing the optical path of the body member 53 near the optical path. The recovery port 73 can recover liquid from the space 11. The recovery port 73 is connected to a liquid recovery device 80 through a passage 79. The liquid recovery device 80 includes a vacuum system and can recover liquid by sucking the liquid through the recovery port 73. The liquid recovery device 80 recovers the liquid recovered through the passage 79 via the recovery port 73. The porous member 33 is disposed in the recovery port 73.

[0043]

[0054] In an embodiment, to form a space 11 with liquid between the projection system PS and the fluid handling structure IH on the one hand and the substrate W on the other hand, liquid is supplied to the space 11 from supply port 72 and the pressure in the recovery chamber 31 in the fluid handling structure IH is adjusted to a negative pressure to recover liquid via holes 84 in the porous member 33 (i.e. recovery port 73). By performing a liquid supply operation using the supply port 72 and a liquid recovery operation using the porous member 33, the space 11 is formed between the projection system PS and the fluid handling structure IH on the one hand and the substrate W on the other hand.

[0044]

[0055] As shown in the figure, the apparatus may be of an immersion type, alternatively the apparatus may be of a dry type in which the substrate is not immersed in a liquid.

[0045]

[0056] Figure 4 shows, in cross-section, a support table WT of a lithographic apparatus according to an embodiment of the invention. The support table WT is configured to support a substrate W. The lithographic apparatus also comprises a gas flow system interacting with the support table WT.

[0046]

[0057] The support table WT includes a base surface 61. In an embodiment, the base surface 61 is configured to be substantially parallel to a bottom surface of a substrate W supported by the support table WT. In an embodiment, the support table WT includes a plurality of burls 62. The burls 62 protrude above the base surface 61. Each of the plurality of burls 62 has an individual burl distal end 63. The burl distal ends 63 are disposed in a support plane to support the substrate W. When the substrate W is supported by the support table WT, the substrate W is supported by the individual burl distal ends 63 of each of the plurality of burls 62.

[0047]

[0058] In use, the substrate W is supported by the support table WT. When the substrate W is supported by the support table WT, the substrate W is supported by the respective burl distal ends 63 of each burl 62.

[0048]

[0059] A gap is defined between a base surface 61 of the support table WT and the substrate W. The width of the gap corresponds to the height of the crowbar distal ends 63 from the base surface 61.

[0049]

[0060] FIG. 7 shows a schematic cross-sectional view of a support table WT and a part of a gas flow system 97 of a lithographic apparatus according to an embodiment of the present invention. The lithographic apparatus comprises a gas flow system 97. The gas flow system 97 interacts with the support table WT. As shown in FIG. 7, in an embodiment, the support table WT comprises a number of gas flow openings 69. The gas flow openings 69 facilitate clamping of the substrate W. Gas can be extracted through the gas flow openings 69 from a gap enclosed by the substrate W and the support table WT to reduce the pressure in the gap for clamping of the substrate W. In an embodiment, an additional two-phase extractor (not shown in FIG. 7) is radially outside the outer seal 67 to extract gas and liquid bubbles from between the substrate W and the support table WT.

[0050]

[0061] In an embodiment, the gas flow system 97 is configured to supply gas through the gas flow openings 69 to the gap between the base surface 61 and the substrate W. In an embodiment, the gas flow system 97 is configured to extract gas from the gap between the base surface 61 and the substrate W via the gas flow openings 69. In an embodiment, the gas flow system 97 is configured to supply gas to and extract gas from the gap through the gas flow openings 69.

[0051]

[0062] In a method of unloading a substrate W from the support table WT, gas is supplied via gas flow openings 69 in the support table WT to a gap between the base surface 61 and the substrate W. In an embodiment, the method of unloading a substrate W includes different stages of unloading in which different pressure profiles are applied to the gap between the base surface 61 and the substrate W.

[0052]

[0063] There may be two distinct stages of unloading. In an embodiment, the method includes an early stage of unloading and a later stage of unloading. The later stage of unloading follows the early stage of unloading. In an embodiment, the later stage of unloading immediately follows the early stage of unloading. In an alternative embodiment, there are three stages of unloading. In an embodiment, a middle stage of unloading follows the early stage of unloading and before the later stage of unloading. In an embodiment, there are four or more stages of unloading.

[0053]

[0064] In an embodiment, the support table WT comprises a central region 81 and an outer region 83 as shown in Figure 4. The outer region 83 is radially outward of the central region 81.

[0054]

[0065] In an early stage of unloading, gas is supplied from at least one gas flow opening 69 in the outer region 83 and no gas flow openings in the central region 81. In a later stage of unloading, gas is supplied from at least one gas flow opening 69 in the outer region 83 and also from at least one gas flow opening in the central region 81.

[0055]

[0066] When the substrate W is clamped to the support table WT, a vacuum (or near vacuum pressure) is applied to the central region 81 and the outer region 83. When the substrate W is unloaded, the vacuum is released in the outer region 83 before it is released in the central region 81. By releasing the vacuum in the outer region 83 first and then in the central region 81, it is expected that the substrate W will be released (i.e. move away) from the edge towards the centre. An embodiment of the invention is expected to inhibit the substrate W from slipping on the burls 62 in the outer region 83 (e.g. periphery) of the support table WT. Thus, an embodiment of the invention is expected to achieve reduced wear of the burls 62 at the periphery of the support table WT.

[0056]

[0067] In some embodiments, the central region 81 is bounded by the outer region 83. However, this is not necessarily the case. For example, as shown in FIG.

[0057]

[0068] As mentioned above, in an embodiment, the method includes an intermediate stage of unloading. This may be the case in particular if the support table WT comprises an intermediate region 82. The intermediate region 82 is radially outward of the central region 81. The intermediate region 82 is radially inward of the outer region 83. In an embodiment, the intermediate region 82 borders the central region 81. In an embodiment, the intermediate region 82 borders the outer region 83.

[0058]

[0069] In one embodiment, during an early stage of unloading, gas is supplied from at least one gas flow opening 69 in the outer region 83 and from no gas flow openings in the central region 81 and the intermediate region 82. During an intermediate stage of unloading, gas is supplied from at least one gas flow opening 69 in the outer region 83 and from at least one gas flow opening 69 in the intermediate region 82 and from no gas flow opening 69 in the central region 81. During a later stage of unloading (after the intermediate stage of unloading), gas is supplied from at least one gas flow opening 69 in the outer region 83, at least one gas flow opening 69 in the intermediate region 82, and at least one gas flow opening 69 in the central region 81.

[0059]

[0070] Thus, in an embodiment, the support table WT comprises three different segments or clamping areas where the vacuum can be applied and released at different times. By providing an additional intermediate region 82 and releasing the vacuum in the intermediate region 82 followed by the central region 81 after releasing the vacuum in the outer region 83, an embodiment of the invention is expected to reduce wear on the burls 62. This is because the successive release of the vacuum starting from the periphery and ending in the central region 81 is expected to reduce the likelihood of the substrate W slipping on the burls 62, i.e. reduce the slipping force. In an embodiment, the support table WT comprises four or more different segments or clamping areas where the vacuum can be released at different times starting from the periphery and ending in the central region 81.

[0060]

[0071] In an embodiment, the gas flow system 97 is configured to provide a gas (e.g. air) jet from the gas flow openings 69 before releasing the vacuum. The gas jet is to encourage the substrate W to move away from the burls 62 so that the likelihood of slippage is reduced. In an embodiment, during an initial stage of unloading, gas is supplied from the at least one gas flow opening 69 in the outer region 83 at a first pressure greater than the ambient pressure. The gas supplied at the first pressure greater than the ambient pressure is a gas jet that encourages the substrate W to move away from the burls 62. After this gas jet, gas is supplied from the at least one gas flow opening 69 in the outer region 83 at a second pressure less than the first pressure. In an embodiment, the second pressure is greater than the ambient pressure. Thus, when the second pressure is applied, the substrate W does not reattach to the support table WT. In an alternative embodiment, the second pressure is less than the ambient pressure, so that the vacuum is released after the initial gas jet. By supplying gas at the second pressure less than the ambient pressure, the vacuum is gradually released in the outer region 83. Therefore, gas injection may be performed prior to releasing the vacuum in the outer region 83. By supplying gas at a first pressure greater than ambient pressure, the likelihood of a warped substrate W coming into unwanted contact with the burls 62 during the unload process is reduced. Generally, when a substrate W warps, it does so at its edges. Thus, the substrate W is at greatest risk of coming into unwanted contact with the burls 62 in the outer region 83 during the unload process.

[0061]

[0072] In some embodiments, gas may be supplied to any of the outer region 83, the intermediate region 82, and the central region 81 at a first pressure greater than ambient pressure. For example, in some embodiments, during an intermediate stage of unloading, gas is supplied through the at least one gas flow opening 69 in the intermediate region 82 at a first pressure greater than ambient pressure, and thereafter gas is supplied through the at least one gas flow opening 69 in the intermediate region 82 at a second pressure less than the first pressure.

[0062]

[0073] In an embodiment, in a later stage of unloading, gas is supplied from the at least one gas flow opening 69 in the central region 81 at a first pressure greater than ambient pressure, and thereafter gas is supplied from the at least one gas flow opening 69 in the central region 81 at a second pressure less than the first pressure. Thus, a jet can be applied to each region before releasing the vacuum. This reduces the force with which the substrate W slides over the burls 62, i.e. the likelihood of the substrate W sliding over the burls 62, resulting in less wear on the burls 62.

[0063]

[0074] The present invention has been described above in terms of a method of unloading a substrate W from a support table WT. The present invention is equally applicable to a method of loading a substrate W onto the support table WT.

[0064]

[0075] According to the method of loading the substrate W onto the support table WT, the method includes extracting gas from the gap via a plurality of gas flow openings 69 in the support table WT. The method of loading the substrate W includes at least three loading steps. There may be four or more steps.

[0065]

[0076] In a first stage of loading, gas is extracted from at least one gas flow opening 69 in the central region 81 and not from the gas flow openings 69 in the intermediate region 82 and the outer region 83. Then in a second stage of loading, gas is extracted from at least one gas flow opening 69 in the central region 81 and at least one gas flow opening 69 in the intermediate region 82 and not from the gas flow openings 69 in the outer region 83. Then in a third stage of loading, gas is extracted from at least one gas flow opening 69 in the central region 81, at least one gas flow opening 69 in the intermediate region 82, and at least one gas flow opening 69 in the outer region 83.

[0066]

[0077] Thus, the vacuum may be applied first to the central region 81, then to the middle region, and then to the outer region 83. An embodiment of the present invention is expected to achieve a reduction in lattice deformation remaining after loading of the substrate W. Deformation of the substrate W may increase overlay errors. For example, deformation of the substrate W may reduce the accuracy of the incidence of radiation on the substrate W. Curvature of the surface of the substrate W may cause the radiation to be slightly off-target in contact with the substrate W. In particular, if the substrate W is first clamped to the burls 62 at the periphery of the support table WT, any deformation of the substrate W may remain when the substrate W is clamped. By applying vacuum first to the central region 81 and finally to the outer region 83, it is expected that clamping of the substrate W to the burls 62 will start from the central region 81. This is expected to reduce deformation of the substrate W when the substrate W is loaded onto the support table WT. In an embodiment, the support table WT comprises four or more regions. During loading, the vacuum is applied first to the most central region and last to the outermost region.

[0067]

[0078] As explained above, gas may be supplied to the same region throughout different stages of unloading. For example, gas is supplied to the central region 81 in an early stage of unloading, a middle stage of unloading, and a later stage of unloading. The gas flow openings 69 used to supply gas in the different stages may be the same gas flow openings 69. Alternatively, different gas flow openings 69 may be used within a particular region in different stages.

[0068]

[0079] Similarly, during the loading process, gas may be extracted to one region at different stages of the loading process. For example, gas may be extracted at a central region 81 during the first, second, and third stages of loading. The gas flow openings 69 used for a particular region at different stages may be the same gas flow openings 69. Alternatively, different gas flow openings may be used for a particular region at different stages.

[0069]

[0080] In an embodiment, gas may be supplied from the gas flow openings 69 during the loading process to prevent the bowed substrate W from unnecessarily touching the burls 62, especially at the periphery of the support table WT. In an embodiment, during the first stage of loading, gas at a pressure greater than ambient pressure is supplied from at least one gas flow opening 69 in the middle region 82 and / or at least one gas flow opening 69 in the outer region 83. Thus, while a vacuum is formed in the central region 81, gas jets are supplied to the middle region 82 and the outer region 83. This prevents the substrate W from unnecessarily touching the burls 62 in the middle region 82 or the outer region 83 before the substrate W contacts the burls 62 in the central region 81.

[0070]

[0081] In one embodiment, during the second stage of loading, gas is supplied at a pressure greater than ambient pressure through at least one gas flow opening 69 in the outer region 83. Thus, a gas jet can be provided to the outer region 83 even when a vacuum is formed in the intermediate region 82.

[0071]

[0082] As noted above, in some embodiments, vacuum is first applied to the central region 81, then to the intermediate region 82, and then to the outer region 83. However, in alternative embodiments, the loading sequence is reversed. In some embodiments, in a first stage of loading, gas is extracted from at least one gas flow opening 69 in the outer region 83 of the support table WT, and not from the gas flow openings 69 in the intermediate region 82 of the support table WT and not from the gas flow openings 69 in the central region 81 of the support table WT. In a second stage of loading, gas is extracted from at least one gas flow opening 69 in the outer region 83 and at least one gas flow opening 69 in the intermediate region 82, and not from the gas flow openings 69 in the central region 81. In a third stage of loading, gas is extracted from at least one gas flow opening 69 in the outer region 83, at least one gas flow opening 69 in the intermediate region 82, and at least one gas flow opening 69 in the central region 81.

[0072]

[0083] This embodiment of the invention is expected to be advantageous for clamping a bowed substrate W having a bowl shape (ie the outer periphery of the substrate W is higher than the central portion of the substrate W).

[0073]

[0084] In one embodiment, gas flow is restricted between the central region 81 and the intermediate region 82. Restricting gas flow between the central region 81 and the intermediate region 82 allows for substantially independent extraction or supply of gas to each of the gaps in the central region 81 and the intermediate region 82.

[0074]

[0085] For example, Figure 4 shows a central region wall 64. The central region wall 64 protrudes above the base surface 61. The central region wall 64 restricts the flow of gas between the intermediate region 82 and the central region 81. In an embodiment, the central region wall 64 is configured to restrict the flow of gas between the central region 81 and the intermediate region 82. The top of the central region wall 64 does not contact the substrate W when the substrate W is clamped to the support table WT. The central region wall 64 acts as a seal. The central region wall 64 is not as tall as the burls 62. There is a small gap between the substrate W and the top of the central region wall 64.

[0075]

[0086] FIG. 5 illustrates in plan view the support table WT shown in FIG. 4. The burls 62 have been omitted from FIG. 5 for simplicity. In one embodiment, the central region wall 64 is continuous. There is no break in the central region wall 64 through which gas can flow between the intermediate region 82 and the central region 81. As shown in FIG. 5, in one embodiment, the central region wall 64 is circular in plan. However, other shapes are possible. For example, the central region wall 64 can be square or rectangular.

[0076]

[0087] As shown in FIG. 5, in an embodiment, the intermediate region 82 surrounds the central region 81. The intermediate region 82 surrounds the central region 81 in a plan view. As shown in FIG. 5, in an embodiment, the intermediate region 82 is defined at its radial periphery by an intermediate region wall 65. The intermediate region wall 65 protrudes above the base surface 61. The intermediate region wall 65 is configured to restrict gas flow between the intermediate region 82 and the outer region 83. This allows for substantially independent supply or extraction of gas to each of the gaps in the intermediate region 82 and the outer region 83. The intermediate region wall 65 acts as a seal. The intermediate region wall 65 is not as tall as the burls 62. There is a small gap between the substrate W and the top of the intermediate region wall 65.

[0077]

[0088] By allowing substantially independent gas flow to each region, the loading and unloading processes can be more precisely controlled. As shown in Figure 5, in one embodiment, outer region 83 surrounds middle region 82. Outer region 83 surrounds middle region 82 in plan view.

[0078]

[0089] 5, in one embodiment, the outer region 83 is defined at its radial periphery by an outer region wall 66. The outer region wall 66 protrudes above the base surface 61. The outer region wall 66 is configured to restrict gas flow between the outer region 83 and a region radially outward of the outer region 83. The outer region wall 66 acts as a seal. The outer region wall 66 is not as tall as the burls 62. A small gap exists between the substrate W and the top of the outer region wall 66.

[0079]

[0090] In an embodiment, the support table WT comprises one or more outer seals 67. The outer zone wall 66 and the outer seal 67 may form a double seal. The double seal may be for a water extraction system. For example, fluid extraction openings 88 (see FIG. 7) may be provided for extracting liquid (and also gas) from the space between the outer zone wall 66 and the outer seal 67.

[0080]

[0091] In some embodiments, each region has its own inlet passage. This means that the gas pressure in each region can be controlled separately. In some embodiments, the gas flow system 97 comprises a flow passage 98 for each region. For example, in some embodiments, the gas flow system 97 comprises a central flow passage connected to at least one gas flow opening 69 in the central region 81, a middle flow passage connected to at least one gas flow opening 69 in the middle region 82, and an outer flow passage connected to at least one gas flow opening in the outer region 83. The central flow passage, the middle flow passage, and the outer flow passage are independent of each other. The central flow passage, the middle flow passage, and the outer flow passage are depicted as double-headed arrows in FIG. 7.

[0081]

[0092] Figure 6 shows in plan view a support table WT that is an alternative to the support table WT shown in Figure 5. However, the functionality of the invention in the embodiment shown in Figure 6 is substantially the same as in the embodiment shown in Figure 5. Crowbar 62 has been omitted from Figure 6 for simplicity.

[0082]

[0093] As shown in FIG. 6, in an embodiment, the central region 81 includes a number of non-overlapping central sub-regions 91. Each central sub-region 91 is defined by a central sub-region wall 94. Each central sub-region wall 94 protrudes above the base surface 61. Each central sub-region wall 94 is configured to restrict gas flow between the central region 81 and any other region (e.g., the outer region 83 or the intermediate region 82). This allows gas to be supplied to or extracted from the gaps in the central region 81 substantially independently of the other regions. Each central sub-region wall 94 acts as a seal. Each central sub-region wall 94 is not as tall as the burls 62. A small gap exists between the substrate W and the top of each central sub-region wall 94.

[0083]

[0094] 6, in one embodiment the central sub-regions 91 are spaced apart from one another. The central sub-region walls 94 of adjacent central sub-regions 91 are spaced apart and do not touch one another. This means that there is space between the central sub-regions 91 (i.e. outside the central sub-region walls 94) that does not belong to either the central region 81, the intermediate region 82, or the outer region 83. It is therefore not necessary for the intermediate region 82 or the outer region 83 to completely surround the central region 81.

[0084]

[0095] Alternatively, adjacent central sub-regions 91 may abut each other. A central sub-region wall 94 may be shared by adjacent central sub-regions 91. This means that the central sub-region wall 94 may be a dividing line between adjacent central sub-regions 91. One central sub-region 91 may be on one side of the central sub-region wall 94 and another central sub-region 91 may be on the other side of the central sub-region wall 94.

[0085]

[0096] As shown in FIG. 6, the intermediate region 82 and the outer region 83 may be arranged similarly to the central region 81. In particular, the invention may be implemented by using islands of seals (formed by the sub-region walls). The sub-regions may be referred to as islands of seals because in plan view the edges of the sub-regions look like islands defined by seals (i.e. the sub-region walls). In particular, in an embodiment, the intermediate region 82 includes a number of non-overlapping intermediate sub-regions 92. Each intermediate sub-region 92 is defined by an intermediate sub-region wall 95. Each intermediate sub-region wall 95 protrudes above the base surface 61. Each intermediate sub-region wall 95 is configured to restrict the flow of gas between the intermediate region 82 and any other region. This means that the supply or extraction of gas to or from the gap of the intermediate region 82 can be performed substantially independently from the other regions. Each intermediate sub-region wall 95 acts as a seal. Each intermediate sub-region wall 95 is not as high as the burl 62. There is a small gap between the substrate W and the top of each intermediate sub-region wall 95.

[0086]

[0097] 6, in some embodiments, the intermediate subregions 92 are spaced apart from one another. However, this is not necessarily the case. In some embodiments, the intermediate subregions 92 are directly adjacent to one another without gaps. For example, the intermediate subregion wall 95 of one intermediate subregion 92 may be joined to the intermediate subregion wall 95 of an adjacent intermediate subregion 92 such that no gaps exist between adjacent intermediate subregions 92.

[0087]

[0098] As shown in FIG. 6, in an embodiment, the outer region 83 includes a number of non-overlapping outer sub-regions 93 that restrict gas flow therebetween. Each outer sub-region 93 is defined by an outer sub-region wall 96. Each sub-region wall 96 protrudes above the base surface 61. The outer region 83 is made up of outer sub-regions 93. The spaces between the outer sub-regions 93 (through which gas can flow freely) do not form part of the outer region 83. Each outer sub-region wall 96 is configured to restrict gas flow between the outer region 83 and any other region. This means that gas can be supplied to or extracted from the outer region 83 substantially independently of any other region. Each outer sub-region wall 96 acts as a seal. Each outer sub-region wall 96 is not as high as the burl 62. There is a small gap between the substrate W and the top of each outer sub-region wall 96.

[0088]

[0099] 6, in one embodiment, the outer sub-regions 93 are spaced apart from one another. However, this is not necessarily the case. In alternative embodiments, the outer sub-regions 93 are directly adjacent to one another with no gaps.

[0089]

[0100] Figure 5 shows concentric regions of the support table WT, whereas Figure 6 shows regions formed by using islands of seals (formed by sub-region walls). In an embodiment, at least one of the regions may be formed as shown in Figure 5 and at least one of the regions may be formed as shown in Figure 6. For example, in an embodiment, the central region 81 is formed from a central sub-region 91 as shown in Figure 6, while the outer regions 83 are defined by intermediate region walls 65 and outer region walls 66. Other combinations of the embodiments shown in Figures 5 and 6 are also possible.

[0090]

[0101] In one embodiment, different regions of the support table WT are separated from one another by walls, for example as shown in Figures 5 to 7 and described above. However, the presence of walls is not essential. In alternative embodiments, walls are not provided.

[0091]

[0102] Figure 13 illustrates, in plan view, a schematic representation of a support table according to an embodiment of the present invention. In an embodiment, the support table WT comprises a plurality of independently controllable flow passages 98 (see Figure 9), each connected to a gas flow opening 69 in a different region of the support table WT. Figure 13 illustrates three sets of gas flow openings 69. Each set of gas flow openings 69 is in fluid communication with a flow passage 98. The flow passages 98 are independently controllable from each other. This allows the pressure in each set of gas flow openings 69 to be controlled independently from each other.

[0092]

[0103] Each set of gas flow openings 69 includes a plurality of gas flow openings 69. As shown in FIG. 13, in one embodiment, a set of gas flow openings 69 is arranged in a ring. Other arrangements are possible, such as a square or diamond shape. As shown in FIG. 13, in one embodiment, each set has 12 gas flow openings 69. However, the number of gas flow openings 69 in each set is not particularly limited and may be, for example, 6, 10, or 16.

[0093]

[0104] Each set of gas flow openings 69 is disposed at a different radial distance from the center of the support table WT. FIG. 13 illustrates a configuration in which a first set of gas flow openings 69 is disposed at a radial distance r1 from the center of the support table WT. A second set of gas flow openings 69 is disposed at a radial distance r2 from the center of the support table WT. A third set of gas flow openings 69 is disposed at a radial distance r3 from the center of the support table WT. In FIG. 13, one dashed line represents a boundary between a central region 81 and a middle region 82 of the support table. Another dashed line represents a boundary between a middle region 82 and an outer region 83 of the support table. As shown in FIG. 13, the first set of gas flow openings 69 is disposed in the central region 81 of the support table WT. The second set of gas flow openings 69 is disposed in the middle region 82 of the support table WT. The third set of gas flow openings 69 is disposed in the outer region 83 of the support table WT.

[0094]

[0105] The flow of each set of gas flow openings 69 can be controlled to provide the loading or unloading sequence described above. For example, in one embodiment, gas is extracted first through a first set of gas flow openings 69, and additionally through a second set of gas flow openings 69, and additionally through a third set of gas flow openings 69. The number of sets of gas flow openings 69 is not particularly limited and may be, for example, two, four, or more.

[0095]

[0106] FIG. 13 primarily shows the burl plate 21 of the support table WT (see FIGS. 5 and 6 for differences between the burl plate 21 and the chuck 22 of the support table WT). As shown in FIG. 13, the burl plate 21 has a radius r0. In some embodiments, the first set of gas flow openings 69 are positioned such that r1:r0 is at least 0.2. In some embodiments, the first set of gas flow openings 69 are positioned such that r1:r0 is at most 0.5. In some embodiments, the first set of gas flow openings 69 are positioned such that r1:r0 is around 0.4.

[0096]

[0107] In some embodiments, the second set of gas flow openings 69 are positioned such that r2:r0 is at least 0.5. In some embodiments, the second set of gas flow openings 69 are positioned such that r2:r0 is at most 0.8. In some embodiments, the second set of gas flow openings 69 are positioned such that r2:r0 is around 0.6.

[0097]

[0108] In some embodiments, the third set of gas flow openings 69 are positioned such that r3:r0 is at least 0.5. In some embodiments, the third set of gas flow openings 69 are positioned such that r3:r0 is at most 0.95. In some embodiments, the third set of gas flow openings 69 are positioned such that r3:r0 is around 0.9.

[0098]

[0109] As indicated above, other arrangements of the gas flow openings 69 are possible, for example square or diamond shaped. Any of the above walls can be provided with other configurations, for example non-radial opening configurations. This is useful because the substrate W may not warp symmetrically, i.e. rotationally symmetrically, e.g. the substrate W may warp in a saddle shape.

[0099]

[0110] As shown in FIG. 13, in some embodiments, the support table includes an outer seal 67, although the walls depicted in FIG.

[0100]

[0111] As shown in Figure 13, in one embodiment, the support table WT includes a number of pinholes 71. Although six pinholes 71 are depicted in Figure 13, any suitable number of pinholes 71 may be used, i.e., the number of pinholes 71 is not limited to six. The pinholes 71 allow the pins 70 (shown in Figure 12 and described below) to extend vertically through the support table WT. In one embodiment, one of the sets of gas flow openings WT is located at substantially the same radial distance from the center of the support table WT as the pinholes 71. In the configuration shown in Figure 13, a second set of gas flow openings 69 and the pinholes 71 are located at a radial distance r2 from the center of the support table WT.

[0101]

[0112] Figure 8 illustrates generally the support table WT and a gas flow system 97 according to one embodiment of the invention. Figure 8 illustrates flow paths 98 of the gas flow system 97. The flow paths 98 are in fluid communication with the gas flow openings 69 of the support table WT. Figure 8 illustrates only one flow path 98 by way of example only. The gas flow system 97 includes multiple flow paths 98 for independently controlling the application and release of vacuum to each region of the support table WT.

[0102]

[0113] As shown in Figure 8, in one embodiment, the gas flow system 97 includes at least one piezoelectric valve 99. The piezoelectric valve 99 is configured to vary the flow rate through a flow path 98, which may be a central flow path, an intermediate flow path, or an outer flow path. However, it is not necessary to use a piezoelectric valve. Other valves may be used to vary the flow rate. For example, a solenoid valve may be used.

[0103]

[0114] In an embodiment, the piezoelectric valve 99 is used to control pressure and flow during a substrate load sequence and / or a substrate unload sequence. The use of the piezoelectric valve 99 is expected to make it easier to create load / unload sequences for various applications. For example, the sequence may depend on the type of layer formed on the substrate W during an exposure operation. This allows for reduction of lattice errors of the substrate W during the substrate loading process.

[0104]

[0115] By providing a variable valve, such as a piezoelectric valve 99, a closed loop feedback control can be used to improve the loading sequence for any shape of the substrate W. For example, in an embodiment, the support table WT includes at least one pressure sensor 85. The pressure sensor 85 is configured to sense a pressure near the substrate W. For example, the pressure sensor 85 is configured to sense a pressure in the flow passage 98 as shown in FIG. 8 . Alternatively, the pressure sensor may be located elsewhere. The pressure sensor 85 may be configured to sense a pressure between the support table WT and the substrate W. In an embodiment, the controller of the gas flow system 97 is configured to vary the flow rate in the flow passage 98 based on the pressure sensed by the pressure sensor 85.

[0105]

[0116] In one embodiment, the gas flow system 97 includes a valve pressure sensor 86. The valve pressure sensor 86 is configured to sense pressure in a flow passage 98 proximate a piezoelectric valve 99. In one embodiment, the gas flow system 97 includes a negative pressure source 87. The negative pressure source 87 may be, for example, a vacuum generator.

[0106]

[0117] In an embodiment, the pressure sensor 85 is as close as possible to the substrate W. For example, the pressure sensor 85 is part of the support table WT. In an embodiment, the support table WT comprises a chuck 22 and a burl plate 21 (see, for example, Figures 5 and 6). The burl plate 21 comprises a base surface 61 and a burl 62. The burl plate 21 is attached to the chuck 22. In an embodiment, the pressure sensor 85 is provided on the burl plate 21 so as to be as close as possible to the substrate W. This helps to better measure what is happening at the substrate W. The valve pressure sensor 86 is provided near the outlet of the piezoelectric valve 99. The valve pressure sensor 86 can be used to keep the control stable.

[0107]

[0118] The relationship between the setting of the piezoelectric valve 99 and the pressure response of the substrate W can be measured by the pressure sensor 85. This measurement can be used as a feed-forward correction for the next substrate W, especially if the deformation (e.g. warpage) can be compared for all substrates in a batch.

[0108]

[0119] The piezoelectric valve 99 (or any other type of valve) can be controlled based on the output from the pressure sensor 85. A pressure sensor 85 may be provided at each area of ​​the support table WT to provide feedback. By using the pressure sensor 85 in combination with the piezoelectric valve 99 (or any other type of valve), the load / unload sequence can be made more robust.

[0109]

[0120] In one embodiment, the gas flow system 97 comprises a mass flow controller for each region of the support table WT. Each mass flow controller is configured to measure and control gas flow through a passage 98 associated with one of the central region 81, the intermediate region 82, and the outer region 83.

[0110]

[0121] In an embodiment, each region comprises a channel 98 and a pressure sensor 85. The channel 98 is in fluid communication with the gas flow openings 69 of that region. The pressure sensor 85 is configured to sense the pressure for that region, i.e. the central region 81, the middle region 82 or the outer region 83. This may include sensing the pressure between the substrate W and the support table WT in that region and / or sensing the pressure in the channel 98. This allows the suction flow for each region to be determined independently, such that an optimal pressure profile in time can be applied for each region. Measuring the pressure between the substrate W and the support table WT may be beneficial in that the pressure affecting the substrate W may be more accurate and can be used as a parameter to control clamping more precisely.

[0111]

[0122] In an embodiment, when the substrate W is loaded onto the support table WT, the controller 500 is configured to control the timing of extraction of gas from the gas flow openings 69 in each region based on the sensed pressure in each passage 98.

[0112]

[0123] It is expected that certain embodiments of the present invention will achieve improved loading sequences without the need for prior knowledge of the bow of the substrate W. By determining the suction flow for each region, the controller 500 can automatically determine the optimal loading sequence. For example, the controller 500 can determine the sequence of turning on the vacuum from the center region 81 or from the outer region 83.

[0113]

[0124] FIG. 9 illustrates a schematic diagram of a zone arrangement of a support table WT with a gas flow system 97 according to an embodiment of the present invention. The zone arrangement illustrated in FIG. 9 is an example of a hybrid between the concentric circle arrangement of FIG. 5 and the island seal arrangement of FIG. 6. In the arrangement of FIG. 9, a central region 81 is defined by a central region wall 64 in a manner similar to that illustrated in FIG. 5 above, while an intermediate region 82 includes a number of intermediate sub-regions 92 defined by intermediate sub-region walls 95 in a manner similar to that illustrated in FIG. 6 above. An outer region 83 includes a number of outer sub-regions 93 defined by outer sub-region walls 96 in a manner similar to that illustrated in FIG. 6 above.

[0114]

[0125] FIG. 9 is an example of a non-circular seal island (i.e., sub-region). The intermediate sub-regions 92 and the outer sub-regions 93 have the shape of a portion of an annulus rather than a circle. In the arrangement shown in FIG. 9, each intermediate sub-region 92 corresponds to a quarter of an annulus. There are four intermediate sub-regions 92. However, the number of intermediate sub-regions 92 may be less than or greater than four. As shown in FIG. 9, in one embodiment, the support table WT comprises eight outer sub-regions 93, each of which corresponds to half a quarter of an annulus. However, the number of outer sub-regions 93 may be less than or greater than eight.

[0115]

[0126] As explained above, in an embodiment, the vacuum pressure can be controlled substantially independently for regions at different radial positions (i.e., different distances from the center of the support table WT), and the support table WT has a radial degree of freedom for controlling the clamping pressure.

[0116]

[0127] In an embodiment, the lithographic apparatus has a tangential (or rotational) degree of freedom to control the clamping pressure. In particular, in an embodiment, the clamping pressure of different sub-regions (at different tangential positions) of the same region can be controlled independently. For example, in an embodiment, the gas flow between the intermediate sub-regions 92 is restricted to allow substantially independent extraction or supply of gas to each gap of the intermediate sub-regions 92.

[0117]

[0128] 9, in an embodiment at least one of the regions includes a plurality of tangentially distributed subregions. Each subregion comprises a flow channel 98 and a pressure sensor 85. The flow channel 98 is in fluid communication with the gas flow openings 69 of that subregion. The pressure sensor 85 is configured to sense a pressure relative to the subregion, for example the pressure sensor 85 may be configured to sense the pressure between the support table WT and the substrate W in that subregion, or the pressure in the flow channel 98.

[0118]

[0129] When the substrate W is loaded onto the support table WT, the controller 500 is configured to control the timing of extraction of gas from the gas flow openings 69 of each sub-region based on the sensed pressure in each flow passage 98. The controller 500 can determine an optimal loading sequence to independently control the sub-regions at different tangential positions. This can be particularly beneficial when clamping a substrate W that has varying tangential bowing.

[0119]

[0130] In some embodiments, gas flow between the middle subregions 92 is restricted by middle subregion walls 95. In some embodiments, gas flow is restricted between the outer subregions 93 to allow substantially independent extraction or supply of gas to each gap in the outer subregions 93. For example, gas flow between the outer subregions may be restricted by outer subregion walls 96.

[0120]

[0131] In embodiments in which the central region 81 includes multiple non-overlapping central sub-regions 91, gas flow between the central sub-regions 91 may be restricted to allow substantially independent extraction or supply of gas to each gap in the central sub-regions 91. For example, gas flow may be restricted by central sub-region walls 94.

[0121]

[0132] In an embodiment, the gas flow system 97 comprises a separate flow passage 98 for each sub-region within a region of the support table WT. Figure 9 shows a flow passage 98 diagrammatically connected to at least one gas flow opening 69 of one outer sub-region 93. This only represents one flow passage 98 for one sub-region. A separate flow passage 98 may be provided for each of the outer sub-regions 93. Similarly, a separate flow passage 98 may be provided for each of the intermediate sub-regions 92. If the central region 81 comprises multiple central sub-regions 91, a separate flow passage 98 may be provided for each of the central sub-regions 91. The flow passages 98 are independent of each other.

[0122]

[0133] 9 , in an embodiment, a pressure sensor 85 is associated with the outer sub-region 93. The pressure sensor 85 is configured to sense pressure in the outer sub-region 93. The pressure sensor 85 therefore provides a measure of the clamping pressure in the gap between the base surface 61 and the substrate W in the outer sub-region 93.

[0123]

[0134] In an embodiment, the gas flow system 97 comprises a piezoelectric valve 99 (or another type of valve, such as a solenoid valve) configured to control the pressure applied to the outer sub-regions 93. The piezoelectric valve 99 may be controlled based on information from the pressure sensor 85. In an embodiment, the controller 500 controls the piezoelectric valve 99 based on information from the pressure sensor 85. Thus, the controller 500 can substantially independently control the pressure in each of the outer sub-regions 93. Similarly, in an embodiment, the controller 500 can substantially independently control the pressure in each of the middle sub-regions 92. In an embodiment, the controller 500 can substantially independently control the pressure in each of the central sub-regions 91.

[0124]

[0135] Therefore, different pressures can be applied to different tangential positions of the support table WT. This means that the support table WT has a tangential degree of freedom for controlling the clamping pressure. In an embodiment, the pressure set point does not differ for different tangential positions. In an embodiment, each sub-region has its own pressure control loop. This is useful for processing tangentially warped or curved substrates. This allows, for example, to apply the same pressure to different tangential (i.e. rotational) positions even if the curvature of the substrate W is different at different tangential positions.

[0125]

[0136] Embodiments of the present invention are expected to improve the flatness of clamped substrates W having non-circularly symmetric warpage (e.g., saddle-shaped warpage) without requiring a priori knowledge of the warpage of the substrate W to be clamped.

[0126]

[0137] As explained above, the gas flow system 97 is capable of delivering a pressure (i.e., gas jet) above ambient pressure to a particular region. In an embodiment, the gas flow system 97 is configured to apply gas at a pressure above ambient pressure to each sub-region independently. Thus, the delivery of the gas jet can be controlled depending on the tangential position within the support table WT. Tangential position means the position along the tangential (azimuth) direction.

[0127]

[0138] In an alternative embodiment, the gas extraction system 97 is controlled to stop extracting gas when the substrate W is at a predetermined distance above the support table WT. The predetermined distance may vary depending on the lithographic apparatus. The predetermined distance can be calibrated for a particular lithographic apparatus. More specifically, in an embodiment, a method of loading the substrate W onto the support table WT includes lowering the substrate W towards the support table WT. In an embodiment, for example, the substrate W is supported by a number of pins 70 (shown in FIG. 12 ) that contact a lower surface of the substrate W. The pins 70 extend vertically through the support table WT. The controller 500 is configured to control the pins 70 (e.g., via actuators) such that the pins 70 move vertically downward. As the pins 70 move vertically downward, the substrate W moves down towards the support table WT.

[0128]

[0139] In one embodiment, the substrate W is supported

[0140] As the substrate W is lowered towards the support table WT, the negative pressure source 87 is controlled to apply negative pressure via a number of gas flow openings 69 in the support table WT (shown in Figures 8 and 9) to extract gas from the gap between the base surface 61 of the support table WT and the substrate W. The negative pressure source 87, which may be a vacuum supply, for example, is turned on as the substrate W is lowered towards the support table WT.

[0129]

[0141] In an embodiment, the controller 500 is configured to turn on the negative pressure source 87 when it determines that the pins 70 are descending vertically. In an embodiment, the highest possible gas extraction flow rate is turned on as soon as the pins 70 move down with the substrate W towards the support table WT. This is to reduce air resistance between the substrate W and the support table WT while the substrate W moves towards the support table WT. This also results in faster throughput.

[0130]

[0142] In an embodiment, the negative pressure source 87 in fluid communication with the gas flow openings 69 in the support table WT is controlled to stop applying negative pressure when the substrate W reaches a predetermined distance above the support table WT. The vacuum is turned off when the pins 70 are just above the height of the support table WT.

[0131]

[0143] In an embodiment, the controller 500 is configured to monitor the vertical height of the pins 70 supporting the substrate W. As shown in FIG. 12, in an embodiment, the lithographic apparatus comprises a height sensor 60. The height sensor 60 is configured to measure the vertical position of the pins 70. The height sensor 60 is configured to output a value representative of the height of the substrate W from the support table WT. The height sensor 60 is connected to the controller 500. The height sensor 60 is configured to output a signal indicative of the height of the pins 70 to the controller 500. In particular, the height sensor 60 is configured to output a signal indicative of the height of the top of the pins 70 from the support table WT to the controller 500. The controller 500 is configured to control the negative pressure source 87 based on the signal received from the height sensor 60. In an embodiment, the controller 500 is configured to control the negative pressure source 87 by controlling a piezoelectric valve 99 (shown in FIGS. 8 and 9).

[0132]

[0144] In one embodiment, the height sensor 60 is located near the support table WT. In one embodiment, the height sensor 60 is connected to, in or on the support table WT. In an alternative embodiment, the height sensor 60 is remote from the support table WT, as shown in FIG.

[0133]

[0145] According to an embodiment, the substrate W lands on the support table WT without the application of vacuum, which improves the positional accuracy enabling clamping of the substrate W onto the support table WT.

[0134]

[0146] In an embodiment, when the substrate W lands on the support table WT, the negative pressure source 87 is controlled to resume applying negative pressure to extract gas from the gap via the plurality of gas flow openings 69 in the support table WT. After the substrate W lands on the support table WT with no vacuum formed, the vacuum is reapplied.

[0135]

[0147] In an embodiment, the vacuum is gradually increased in steps from a low flow rate to a high flow rate. In particular, in an embodiment, when the substrate W lands on the support table WT, the negative pressure source 87 is controlled to gradually increase the negative pressure in multiple steps such that the flow rate of gas extracted from the gap through the multiple gas flow openings 69 is gradually increased.

[0136]

[0148] 10 shows the vertical height of the substrate W above the support table WT when the substrate W is loaded. The Y-axis represents the vertical height in the Z direction. The X-axis represents the time when the substrate W is loaded.

[0137]

[0149] FIG. 11 shows the pressures measured in different parts of the lithographic apparatus over the same period of time for loading the substrate W. The solid line represents the pressure on the pins 70. When the pins 70 are supporting the substrate W, they are subjected to a negative pressure (i.e. a downward force) due to the weight of the substrate W. When the pins 70 no longer support the substrate W (because the substrate W is fully supported by the support table WT instead of the pins 70), the negative pressure disappears. This can be seen on the right hand side of FIG. 11 where the solid line rises to a zero pressure value on the Y-axis of the graph. This corresponds to the time when the substrate W is fully supported by the support table WT. This is because once the substrate W is fully supported by the support table WT, the weight of the substrate W no longer presses down on the pins 70.

[0138]

[0150] The dashed lines in Figure 11 represent the pressure applied to the fluid extraction openings 88 (shown in Figure 7) at the periphery of the support table WT. When the substrate W is fully supported by the support table WT, the vacuum is turned on to the fluid extraction openings 88. In Figures 10 and 11, time t0 represents the time when the pins 70 start to move downwards with the substrate W. Time t1 represents the time when the substrate W lands on the support table WT. Time t2 represents the time when the substrate W is fully supported by the support table WT.

[0139]

[0151] The dashed and dotted line in Figure 11 represents the negative pressure relative to the gas flow openings 69 in the support table WT. The magnitude of the negative pressure gradually increases after the substrate W lands on the support table WT.

[0140]

[0152] It is expected that embodiments of the present invention will improve the clamping accuracy of the substrate W while also improving throughput. It is expected that embodiments of the present invention will enable clamping of a wide variety of substrates W. For example, some substrates W are flat, while others are more warped (i.e. less flat). As described above, after the substrate W lands on the support table WT, the vacuum is gradually increased in stages from a low flow rate to a high flow rate. Flat and low / moderately warped substrates W can be clamped at the lowest possible flow rate, thus improving the positional accuracy of the substrate W relative to the support table WT. Highly warped substrates W, which cannot be clamped at the lowest flow rate, can be clamped at a later point when the flow rate is increased.

[0141]

[0153] Embodiments of the present invention are expected to improve the positional accuracy of clamping a substrate W onto the support table WT, particularly for new substrates W (i.e. substrates W that have not yet been used). It has been found that commonly used substrates W are somewhat less sensitive to positional inaccuracies when clamping.

[0142]

[0154] An embodiment of the present invention includes a loading sequence for substrate W utilizing several different pre-clamp flows. This results in dynamic substrate loading that allows different types of substrate W to be clamped as well as the possibility to optimize positional accuracy and throughput. It is possible to turn the pre-clamped vacuum on and off at certain vertical positions of the pins 70. In an alternative embodiment, the controller 500 is configured to control the negative pressure source 87 to vary the negative pressure based on a certain pressure level. For example, the pressure level can be measured by a pressure sensor 85 (shown in FIG. 8 ).

[0143]

[0155] The load sequence in which the vacuum is turned off when the pins 70 are just above the level of the support table WT can be combined with the load sequence described above in which gas is extracted from different regions of the gas flow openings 69 in different stages of loading. In particular, in one embodiment, the first stage of loading, the second stage of loading, and the third stage of loading described above are performed when the substrate W lands on the support table WT. In this way, the flow rate is gradually increased when the substrate W lands on the support table WT. However, before the substrate W lands on the support table WT, gas is extracted during the descent of the substrate W, and the vacuum is turned off when the substrate W reaches a predetermined distance above the support table WT.

[0144]

[0156] A load sequence in which the vacuum is turned off when the pins 70 are just above the level of the support table WT can be performed with any type of support table WT. The support table shown in Figure 5 above with three separate vacuum areas is only one example of a type of support table WT that can be used. Other support tables WT that can be used may have, for example, only one or two vacuum areas.

[0145]

[0157] In an embodiment, the lithographic apparatus comprises a controller 500 configured to control the gas flow system 97. The controller 500 is capable of implementing the above-mentioned applied pressure sequences.

[0146]

[0158] Many of the above examples have been described in the context of an immersion lithography apparatus. However, the invention is equally applicable to dry lithography apparatus. It will be appreciated that any of the above features may be used in conjunction with other features, and the present application covers more than just the combinations specified.

[0147]

[0159] Below are listed clauses which represent alternative configurations of the lithography according to the present invention. Clause 1. A method of unloading a substrate from a support table configured to support a substrate, the method comprising: supplying gas to a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table; During an initial stage of unloading, gas is supplied from at least one gas flow opening in an outer region of the support table and not from a gas flow opening in a central region of the support table that is radially inward of the outer region; A method in which in a later stage of unloading, gas is supplied from at least one gas flow opening in the outer region and at least one gas flow opening in the central region. Clause 2. In the initial stage of unloading, the gas supply is performed from at least one gas flow opening in the outer region, and not from the gas flow openings in the central region and from the gas flow openings in the intermediate region of the support table, which is located radially inside the outer region and radially outside the central region; During an intermediate stage of unloading, gas is supplied from at least one gas flow opening in the outer region and at least one gas flow opening in the intermediate region, but not from any gas flow opening in the central region; 2. The method according to claim 1, wherein in a later stage of unloading, gas is supplied from at least one gas flow opening in the outer region, at least one gas flow opening in the middle region, and at least one gas flow opening in the central region. Clause 3. The method according to clause 2, wherein during an intermediate stage of unloading, gas is supplied from at least one gas flow opening in the intermediate region at a first pressure greater than ambient pressure, and thereafter gas is supplied from at least one gas flow opening in the intermediate region at a second pressure less than the first pressure. Clause 4. A method according to any of clauses 1 to 3, wherein in an initial stage of unloading, gas is supplied from at least one gas flow opening in the outer region at a first pressure greater than ambient pressure, and thereafter gas is supplied from at least one gas flow opening in the outer region at a second pressure less than the first pressure. Clause 5. A method according to any of clauses 1 to 4, wherein in a later stage of unloading, gas is supplied from at least one gas flow opening in the central region at a first pressure greater than ambient pressure, and thereafter gas is supplied from at least one gas flow opening in the central region at a second pressure less than the first pressure. Clause 6. A method of loading a substrate onto a support table configured to support the substrate, the method comprising: extracting gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table; During a first stage of loading, gas is extracted from at least one gas flow opening in a central region of the support table, but not from a gas flow opening in an intermediate region of the support table radially outside the central region, and not from a gas flow opening in an outer region of the support table radially outside the intermediate region; During a second stage of loading, gas is extracted from at least one gas flow opening in the central region and at least one gas flow opening in the intermediate region, but not from any gas flow opening in the outer region; A method in which in a third stage of loading, gas extraction occurs from at least one gas flow opening in the central region, at least one gas flow opening in the intermediate region, and at least one gas flow opening in the outer region. Clause 7. The method according to clause 6, wherein in a first stage of loading, a supply of gas at a pressure greater than ambient pressure is provided from at least one gas flow opening in the intermediate region and / or at least one gas flow opening in the outer region. Clause 8. The method according to clause 6 or 7, wherein in the second stage of loading, the supply of gas is performed through at least one gas flow opening in the outer region at a pressure greater than ambient pressure. Clause 9. When the substrate is lowered toward the support table, gas is extracted from at least one gas flow opening in the central region, at least one gas flow opening in the middle region, and at least one gas flow opening in the outer region; when the substrate reaches a predetermined distance above the support table, no gas is extracted from the central region gas flow openings, the intermediate region gas flow openings, or the outer region gas flow openings; 9. The method of any of clauses 6 to 8, wherein the first stage of loading, the second stage of loading, and the third stage of loading occur when the substrate lands on the support table. Clause 10. The method of any of clauses 2 to 9, comprising restricting gas flow between the central region and the intermediate region to allow substantially independent extraction or supply of gas to each gap in the central region and intermediate region. Clause 11. The method of any of clauses 2-10, wherein the intermediate region surrounds the central region. Clause 12. The method of any of clauses 2-11, wherein the intermediate region is defined at its radial periphery by an intermediate region wall that projects above the base surface and restricts gas flow between the intermediate region and the outer region. Clause 13. The method of any of clauses 2 to 11, wherein the intermediate region includes a plurality of non-overlapping intermediate sub-regions restricting gas flow therebetween. Clause 14. The method of clause 13, wherein each intermediate sub-region is defined by an intermediate sub-region wall that projects above the base surface and restricts gas flow between the intermediate region and the central region or the outer region. Clause 15. The method of clause 13 or 14, wherein the intermediate sub-regions are spaced apart from one another. Clause 16. The method of clauses 13 to 15, wherein gas can be extracted or supplied to each gap in the intermediate sub-region substantially independently of each other. Clause 17. A method according to any of clauses 2 to 16, comprising restricting gas flow between the intermediate region and the outer region so as to provide substantially independent extraction or supply of gas to each gap in the intermediate region and the outer region. Clause 18. The method of any of clauses 2 to 17, wherein the outer region surrounds the intermediate region. Clause 19. The method of any of clauses 1 to 18, comprising restricting gas flow between the central region and the outer region to provide substantially independent extraction or supply of gas to each gap in the central region and the outer region. Clause 20. The method of any of clauses 1 to 19, wherein the central region is defined by a central region wall that projects above a base surface of the support table and restricts gas flow between the central region and the outer region. Clause 21. The method of any of clauses 1 to 19, wherein the central region includes a plurality of non-overlapping central sub-regions that restrict gas flow therebetween. Clause 22. The method of clause 21, wherein each central subregion is defined by a central subregion wall that projects above the base surface and restricts gas flow between the central region and the outer region. Clause 23. The method of clause 21 or 22, wherein the central sub-regions are spaced apart from one another. Clause 24. The method of any one of clauses 21 to 23, wherein gas can be extracted or supplied to each gap in the central sub-region substantially independently of each other. Clause 25. The method of any of clauses 1 to 24, wherein the outer region is defined at its radial periphery by an outer region wall that projects above the base surface and restricts gas flow between the outer region and a region radially outward of the outer region. Clause 26. The method of any of clauses 1 to 24, wherein the outer region includes a plurality of non-overlapping outer sub-regions that restrict gas flow therebetween. Clause 27. The method of clause 26, wherein each outer subregion is defined by an outer subregion wall that projects above the base surface and restricts gas flow between the outer region and a region radially outward of the outer region. Clause 28. The method of clause 26 or 27, wherein the outer sub-regions are spaced apart from one another. Clause 29. The method of any one of clauses 26 to 28, wherein gas can be extracted or supplied to each gap in the outer sub-region substantially independently of each other. Clause 30. Gas flow system; a controller configured to control the gas flow system; a support table configured to support a substrate, The support table is A base surface; A central region; an outer region radially outward of the central region; a plurality of gas flow openings configured for use with the gas flow system to supply gas to a gap between the base surface and the substrate; When the substrate is unloaded from the support table, During an initial stage of unloading, the controller is configured to control the gas flow system to supply gas through at least one gas flow opening in the outer region and not through the gas flow opening in the central region; The lithographic apparatus, wherein during a later stage of unloading, the controller is configured to control the gas flow system to supply gas through at least one gas flow opening in the outer region and through at least one gas flow opening in the central region. Clause 31. The support table includes an intermediate region radially outward of the central region and radially inward of the outer region; When the substrate is unloaded from the support table, During an initial stage of unloading, the controller is configured to control the gas flow system to supply gas through at least one gas flow opening in the outer region and not through the gas flow opening in the central region and not through the gas flow opening in the intermediate region; During an intermediate stage of unloading, the controller is configured to control the gas flow system to supply gas through at least one gas flow opening in the outer region and at least one gas flow opening in the intermediate region, but not through the gas flow opening in the central region; A lithographic apparatus as described in clause 30, wherein during a later stage of unloading, the controller is configured to control the gas flow system to supply gas from at least one gas flow opening in the outer region, at least one gas flow opening in the middle region, and at least one gas flow opening in the central region. Clause 32. A lithographic apparatus as described in Clause 31, wherein during an intermediate stage of unloading, the controller is configured to control the gas flow system to supply gas from at least one gas flow opening in the intermediate region at a first pressure greater than ambient pressure, and then to supply gas from at least one gas flow opening in the intermediate region at a second pressure less than the first pressure. Clause 33. A lithographic apparatus according to any of clauses 30 to 32, wherein during an initial stage of unloading, the controller is configured to control the gas flow system to supply gas from at least one gas flow opening in the outer region at a first pressure greater than ambient pressure, and then to supply gas from at least one gas flow opening in the outer region at a second pressure less than the first pressure. Clause 34. A lithographic apparatus according to any of clauses 30 to 33, wherein during a later stage of unloading, the controller is configured to control the gas flow system to supply gas from at least one gas flow opening in the central region at a first pressure greater than ambient pressure and then to supply gas from at least one gas flow opening in the central region at a second pressure less than the first pressure. Article 35. Gas flow system; a controller configured to control the gas flow system; a support table configured to support a substrate, the support table comprising: A base surface; A central region; an intermediate region radially outward of the central region; an outer region radially outward of the intermediate region; a gas flow system configured to extract gas from a gap between the base surface and the substrate; and a plurality of gas flow openings configured for use in extracting gas from the gap between the base surface and the substrate; When the substrate is loaded onto the support table During a first stage of loading, the controller is configured to control the gas flow system to extract gas from at least one gas flow opening in the central region and not from the gas flow openings in the intermediate region and not from the gas flow openings in the outer region; During a second stage of loading, the controller is configured to control the gas flow system to extract gas from at least one gas flow opening in the central region and at least one gas flow opening in the middle region, but not from any gas flow opening in the outer region; A lithographic apparatus, wherein during a third stage of loading, the controller is configured to control the gas flow system to extract gas from at least one gas flow opening in the central region, at least one gas flow opening in the middle region, and at least one gas flow opening in the outer region. Clause 36. A lithographic apparatus as described in Clause 35, wherein during a first stage of loading, the controller is configured to control the gas flow system to supply gas at a pressure greater than ambient pressure from at least one gas flow opening in the intermediate region and / or at least one gas flow opening in the outer region. Clause 37. A lithographic apparatus according to clause 35 or 36, wherein during the second stage of loading, the controller is configured to control the gas flow system to supply gas from at least one gas flow opening in the outer region at a pressure greater than ambient pressure. Clause 38. When the substrate is lowered towards the support table, the controller is configured to control the gas flow system to extract gas from at least one gas flow opening in the central region, at least one gas flow opening in the middle region, and at least one gas flow opening in the outer region; when the substrate reaches a predetermined distance above the support table, the controller is configured to control the gas flow system to not extract gas from any of the gas flow openings in the central region, the gas flow openings in the middle region, and the gas flow openings in the outer region; 38. A lithographic apparatus according to any of clauses 35 to 37, wherein the controller is configured to control the gas flow system to perform a first stage of loading, a second stage of loading, and a third stage of loading when the substrate lands on the support table. Clause 39. A lithographic apparatus according to any of clauses 31 or 37, wherein the central region is defined by a central region wall protruding above the base surface and configured to restrict gas flow between the central region and the intermediate region so as to allow substantially independent supply or extraction of gas to each of the gaps in the central region and the intermediate region. Clause 40. A lithographic apparatus according to any of clauses 31 to 39, wherein the intermediate region surrounds the central region. Clause 41. A lithographic apparatus according to any of clauses 31 to 40, wherein the intermediate region is defined at its radial periphery by an intermediate region wall projecting above the base surface and restricting gas flow between the intermediate region and the outer region. Clause 42. The lithographic apparatus of any of clauses 31 to 40, wherein the intermediate region comprises a plurality of non-overlapping intermediate sub-regions, each intermediate sub-region being defined by an intermediate sub-region wall projecting above the base surface and restricting gas flow between the intermediate region and the outer region such that gas can be substantially independently supplied to or extracted from each gap in the intermediate region and the outer region. Clause 43. The lithographic apparatus of clause 42, wherein the intermediate sub-regions are spaced apart from one another. Clause 44. A lithographic apparatus according to clause 42 or 43, wherein the gas flow system is configured to extract or supply gas to each gap in the intermediate sub-region substantially independently of each other. Clause 45. A lithographic apparatus according to any of clauses 31 to 44, wherein the outer region surrounds the intermediate region. Article 46. Gas flow systems: a central passage connected to at least one gas flow opening in the central region; an outer flow passage connected to the at least one gas flow opening in the outer region; 46. ​​A lithographic apparatus according to any of clauses 30 to 45, wherein the central flow channel is independent of the outer flow channels. Article 47. If the gas flow system: a central passage connected to at least one gas flow opening in the central region; an intermediate flow passage connected to at least one gas flow opening in the intermediate region; an outer flow passage connected to the at least one gas flow opening in the outer region; 46. ​​The lithographic apparatus of any of clauses 31 to 45, wherein the central channel, the intermediate channel and the outer channel are independent of each other. Clause 48. A lithographic apparatus according to clause 46 or 47, wherein the gas flow system comprises at least one piezoelectric valve configured to vary a flow rate in the central flow path, the intermediate flow path and / or the outer flow path. Clause 49. At least one pressure sensor configured to sense pressure in the central flow path, the intermediate flow path, and / or the outer flow path; 49. The lithographic apparatus of any of clauses 46 to 48, wherein the controller is configured to vary a flow rate in the central channel, the intermediate channel and / or the outer channel based on a pressure sensed by the pressure sensor. Clause 50. A lithographic apparatus according to any of clauses 30 to 49, wherein the central region is defined by a central region wall protruding above the base surface and configured to restrict gas flow between the central region and the outer region so as to allow substantially independent supply or extraction of gas to each gap in the central region and the outer region. Clause 51. A lithographic apparatus as described in any of clauses 30 to 49, wherein the central region includes a plurality of non-overlapping central sub-regions, each central sub-region being defined by a central sub-region wall protruding above the base surface and restricting gas flow between the central region and the outer region so as to allow substantially independent supply or extraction of gas to each gap in the central region and the outer region. Clause 52. A lithographic apparatus according to clause 51, wherein the central sub-regions are spaced apart from one another. Clause 53. A lithographic apparatus according to clause 51 or 52, wherein the gas flow system is configured to extract or supply gas to each gap in the central sub-region substantially independently of each other. Clause 54. A lithographic apparatus according to any of clauses 30 to 53, wherein the outer region is defined at its radial periphery by an outer region wall protruding above the base surface and restricting gas flow between the outer region and a region radially outward of the outer region. Clause 55. A lithographic apparatus according to any of clauses 30 to 54, wherein the outer region includes a plurality of non-overlapping outer subregions restricting gas flow therebetween, each outer subregion being defined by an outer subregion wall protruding above the base surface and restricting gas flow between the central region and the outer region. Clause 56. A lithographic apparatus according to clause 55, wherein the outer sub-regions are spaced apart from one another. Clause 57. A lithographic apparatus according to clause 55 or 56, wherein the gas flow system is configured to extract or supply gas to each gap in the outer sub-region substantially independently of each other. Clause 58. A method of loading a substrate onto a support table configured to support the substrate, the method comprising: Lowering the substrate towards the support table; controlling a negative pressure source to apply negative pressure to extract gas from a gap between a base surface of the support table and the substrate via a plurality of gas flow openings in the support table as the substrate is lowered toward the support table; controlling a negative pressure source in fluid communication with any of the gas flow openings in the support table to stop applying negative pressure when the substrate reaches a predetermined distance above the support table; and and controlling the negative pressure source to resume applying negative pressure to extract gas through a plurality of gas flow openings in the support table when the substrate lands on the support table. Clause 59. The method of clause 58, wherein the negative pressure source is controlled to gradually increase the negative pressure in multiple steps such that when the substrate lands on the support table, the gas flow extracted from the gap through the multiple gas flow openings gradually increases. Clause 60. A gas flow system having a negative pressure source; a controller configured to control the gas flow system; a support table configured to support a substrate, a controller configured to control the negative pressure source to apply negative pressure to extract gas from a gap between the support table and the substrate via a plurality of gas flow openings in the support table when the substrate is lowered towards the support table; a controller configured to control a negative pressure source in fluid communication with any of the gas flow openings in the support table to stop applying negative pressure when the substrate reaches a predetermined distance above the support table; The lithographic apparatus is configured such that, when the substrate lands on the support table, the controller resumes controlling the negative pressure source to apply negative pressure to extract gas through a plurality of gas flow openings in the support table. Clause 61. A method of loading a substrate onto a support table configured to support a substrate, the method comprising: extracting gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table; During a first stage of loading, gas is extracted from at least one gas flow opening in an outer region of the support table, but not from a gas flow opening in an intermediate region of the support table radially inward of the outer region and not from a gas flow opening in a central region of the support table radially inward of the intermediate region; During a second stage of loading, gas is extracted from at least one gas flow opening in the outer region and at least one gas flow opening in the intermediate region, but not from any gas flow opening in the central region; A method in which in a third stage of loading, gas extraction occurs from at least one gas flow opening in the outer region, at least one gas flow opening in the middle region, and at least one gas flow opening in the central region. Article 62. Gas flow system; a controller configured to control the gas flow system; a support table configured to support a substrate, the support table comprising: A base surface; A central region; an intermediate region radially outward of the central region; an outer region radially outward of the intermediate region; a gas flow system configured to extract gas from a gap between the base surface and the substrate; and a plurality of gas flow openings configured for use in extracting gas from the gap between the base surface and the substrate; Each area is a flow passage in fluid communication with the gas flow openings in the region; a pressure sensor configured to sense a pressure in the flow path; The lithographic apparatus is configured such that, when a substrate is loaded onto the support table, the controller controls the timing of extracting gas from the gas flow openings in each region based on the sensed pressure in each flow path. Clause 63. At least one of the regions includes a plurality of tangentially distributed subregions, each of which comprises: a flow passage in fluid communication with the gas flow openings of the sub-region; a pressure sensor configured to sense a pressure in the flow path; 63. A lithographic apparatus as described in clause 62, wherein when the substrate is loaded onto the support table, the controller is configured to control the timing of extracting gas from the gas flow openings of each sub-region based on the sensed pressure of each flow path.

[0148]

[0160] It will be appreciated that any of the above features may be used in conjunction with other features, and the present application does not cover only the combinations specified. Certain embodiments of the invention may be applied, for example, to the embodiment of Figure 3. Also, although embodiments of the invention have been described for convenience in relation to an immersion lithography apparatus, it will be appreciated that embodiments of the invention may be used with any form of lithography apparatus.

[0149]

[0161] In light of these alternative applications, those skilled in the art will recognize that when the terms "wafer" or "die" are used herein, they may be considered synonymous with the more general terms "substrate" or "target portion", respectively. The substrates described herein may be processed, before or after exposure, in, for example, a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0150]

[0162] As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths at or about 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm). The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive and reflective optical components.

[0151]

[0163] While specific embodiments of the invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The above description is illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. 1. A method of unloading a substrate from a support table configured to support the substrate, comprising the steps of: supplying gas to a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table; During an initial stage of unloading, the gas is supplied through at least one gas flow opening in an outer region of the support table and not through a gas flow opening in a central region of the support table that is radially inward of the outer region; A method according to claim 1, wherein in a later stage of unloading, the gas supply is effected from at least one gas flow opening in the outer region and from at least one gas flow opening in the central region.

2. During an initial stage of the unloading, the gas is supplied from at least one gas flow opening in the outer region, but not from any gas flow opening in the central region and not from any gas flow opening in an intermediate region of the support table that is radially inside the outer region and radially outside the central region; During an intermediate stage of unloading, the gas is supplied through at least one gas flow opening in the outer region and at least one gas flow opening in the intermediate region, but not through any gas flow opening in the central region; 2. The method of claim 1, wherein in a later stage of the unloading, the gas is supplied from at least one gas flow opening in the outer region, at least one gas flow opening in the intermediate region, and at least one gas flow opening in the central region.

3. 3. The method of claim 2, wherein during an intermediate stage of the unloading, gas is supplied from at least one gas flow opening in the intermediate region at a first pressure greater than ambient pressure, and thereafter gas is supplied from at least one gas flow opening in the intermediate region at a second pressure less than the first pressure.

4. 1. A method of loading a substrate onto a support table configured to support the substrate, comprising the steps of: extracting gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table; During a first stage of loading, the gas is extracted from at least one gas flow opening in a central region of the support table, but not from a gas flow opening in an intermediate region of the support table radially outside the central region and not from a gas flow opening in an outer region of the support table radially outside the intermediate region; During a second stage of loading, the gas is extracted from at least one gas flow opening in the central region and at least one gas flow opening in the intermediate region, but not from any gas flow opening in the outer region; The method wherein in a third stage of loading, the gas is extracted from at least one gas flow opening in the central region, at least one gas flow opening in the intermediate region, and at least one gas flow opening in the outer region.

5. 5. The method according to claim 4, wherein in the first stage of loading, a supply of gas at a pressure greater than ambient pressure is provided from at least one gas flow opening in the intermediate region and / or from at least one gas flow opening in the outer region.

6. when the substrate is lowered towards the support table, the gas is extracted from at least one gas flow opening in the central region, at least one gas flow opening in the middle region, and at least one gas flow opening in the outer region; when the substrate reaches a predetermined distance above the support table, no gas is extracted from any of the gas flow openings in the central region, the gas flow openings in the middle region, and the gas flow openings in the outer region; The method according to claim 4 or 5, wherein the first stage of loading, the second stage of loading, and the third stage of loading occur when the substrate lands on the support table.

7. the intermediate region surrounds the central region; or the intermediate region includes a plurality of non-overlapping intermediate sub-regions restricting gas flow therebetween; and / or The method of claim 2 , wherein the outer region surrounds the intermediate region.

8. The method of claim 1 , wherein the outer region comprises a plurality of non-overlapping outer sub-regions restricting gas flow therebetween.

9. 1. A method of loading a substrate onto a support table configured to support the substrate, comprising the steps of: lowering the substrate towards the support table; controlling a negative pressure source to apply a negative pressure to extract gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table as the substrate is lowered towards the support table; controlling the negative pressure source in fluid communication with any of the gas flow openings of the support table to stop applying negative pressure when the substrate reaches a predetermined distance above the support table; and and when the substrate lands on the support table, controlling the negative pressure source to resume applying negative pressure to extract the gas through a plurality of gas flow openings in the support table.

10. 10. The method of claim 9, wherein when the substrate lands on the support table, the negative pressure source is controlled to gradually increase the negative pressure in multiple steps such that a flow rate of gas extracted from the gap through the multiple gas flow openings gradually increases.

11. 1. A method of loading a substrate onto a support table configured to support the substrate, comprising the steps of: extracting gas from a gap between a base surface of the support table and the substrate through a plurality of gas flow openings in the support table; During a first stage of loading, the gas is extracted from at least one gas flow opening in an outer region of the support table, but not from a gas flow opening in an intermediate region of the support table radially inward of the outer region and not from a gas flow opening in a central region of the support table radially inward of the intermediate region; during a second stage of loading, the gas is extracted from at least one gas flow opening in the outer region and at least one gas flow opening in the intermediate region, but not from any gas flow opening in the central region; The method according to claim 1, wherein in a third stage of loading, the gas is extracted from at least one gas flow opening in the outer region, at least one gas flow opening in the intermediate region, and at least one gas flow opening in the central region.

12. A gas flow system; a controller configured to control the gas flow system; a support table configured to support a substrate, the support table comprising: A base surface, A central region; an outer region radially outward of the central region; a plurality of gas flow openings configured for use in the gas flow system to supply gas to a gap between the base surface and the substrate; When the substrate is unloaded from the support table, during an initial stage of unloading, the controller is configured to control the gas flow system to supply the gas through at least one gas flow opening in the outer region and not through any gas flow opening in the central region; A lithographic apparatus, wherein during a later stage of unloading, the controller is configured to control the gas flow system to supply the gas through at least one gas flow opening in the outer region and through at least one gas flow opening in the central region.

13. A gas flow system; a controller configured to control the gas flow system; a support table configured to support a substrate, the support table comprising: A base surface, A central region; an intermediate region radially outward of the central region; an outer region radially outward of the intermediate region; a plurality of gas flow openings configured for use in the gas flow system to extract gas from a gap between the base surface and the substrate; When the substrate is loaded onto the support table, During a first stage of loading, the controller is configured to control the gas flow system to extract the gas from at least one gas flow opening in the central region and from no gas flow openings in the intermediate region and no gas flow openings in the outer region; During a second stage of loading, the controller is configured to control the gas flow system to extract the gas from at least one gas flow opening in the central region and at least one gas flow opening in the intermediate region, but not from any gas flow opening in the outer region; A lithographic apparatus, wherein during a third stage of loading, the controller is configured to control the gas flow system to extract the gas from at least one gas flow opening in the central region, at least one gas flow opening in the middle region, and at least one gas flow opening in the outer region.

14. a gas flow system having a negative pressure source; a controller configured to control the gas flow system; a support table configured to support a substrate, the controller is configured to control the negative pressure source to apply negative pressure to extract gas from a gap between the support table and the substrate via a plurality of gas flow openings in the support table when the substrate is lowered towards the support table; the controller is configured to control the negative pressure source in fluid communication with any of the gas flow openings in the support table to stop applying negative pressure when the substrate reaches a predetermined distance above the support table; A lithographic apparatus, wherein when the substrate lands on the support table, the controller is configured to control the negative pressure source to resume applying negative pressure to extract the gas through a plurality of gas flow openings in the support table.

15. A gas flow system; a controller configured to control the gas flow system; a support table configured to support a substrate, the support table comprising: A base surface, A central region; an intermediate region radially outward of the central region; an outer region radially outward of the intermediate region; a plurality of gas flow openings configured for use in the gas flow system to extract gas from a gap between the base surface and the substrate; Each area is: a flow passage in fluid communication with the gas flow openings in the region; a pressure sensor configured to sense pressure relative to the region; A lithographic apparatus, wherein when the substrate is loaded onto the support table, the controller is configured to control a timing of extracting gas from the gas flow openings in each region based on the sensed pressure in each region.

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