Method of unloading object from support table

Abstract

To provide an unloading method.SOLUTION: There is provided a method of unloading an object from a support table during an unloading process. During an exposure process, the object is clamped to the support table by: applying a first pressure to a central region of the support table under a central portion of the object; and applying a second pressure to a peripheral region of the support table under a peripheral portion of the object. During clamping, the first pressure and the second pressure are controlled such that liquid is retained between the object and a seal member. The seal member is positioned radially between the central region and the peripheral region at an upper surface of the support table and protrudes towards the object. The method includes: increasing the first pressure towards ambient pressure; removing at least some of the liquid retained between the object and the seal member by decreasing the second pressure; and increasing the second pressure towards the ambient pressure.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to European Patent Application Nos. 17174583.9, filed June 6, 2017, and 18152220.2, filed January 18, 2018, which are incorporated herein by reference in their entireties.

[0002] The present invention relates to a method for unloading an object from a support table during an unloading process, a lithographic apparatus, a vacuum system for a support table of a lithographic apparatus for holding an object, and a positioner. [Background technology]

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

[0004] To project a pattern onto a substrate, lithographic apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, for example, 193 nm.

[0005]

[0005] To enable improved resolution of smaller features, immersion techniques have been introduced into lithography systems. In an immersion lithography apparatus, a layer of immersion liquid, having a relatively high refractive index, is placed in the space between the apparatus's projection system (through which the patterned beam is projected towards the substrate) and the substrate. The immersion liquid eventually covers the part of the substrate that is below the final element of the projection system. Thus, at least the part of the substrate where exposure takes place is immersed in liquid. The effect of the immersion liquid is that the exposure radiation has a shorter wavelength in the immersion liquid than in a gas, allowing smaller features to be imaged. (It can also be thought that the effect of the liquid is to increase the effective numerical aperture (NA) of the system, and to increase the depth of focus.)

[0006]

[0006] In commercial immersion lithography, the immersion liquid is water. Typically, this water is highly purified distilled water, such as ultrapure water (UPW), commonly used in semiconductor manufacturing facilities. In immersion systems, the UPW is often purified and may undergo an additional thermal step before being delivered to the space as the immersion liquid. Besides water, other liquids with high refractive indices can be used as the immersion liquid. Examples include hydrocarbons, such as fluorocarbons, and / or aqueous solutions. Furthermore, other fluids besides liquids are also envisioned for use in immersion lithography.

[0007]

[0007] In this specification, reference is made to localized immersion, where, in use, the immersion liquid is confined to a space between a final element and a surface facing the final element. The facing surface is the surface of the substrate or a surface of a support table (or substrate support) that is coplanar with the surface of the substrate. (It should be noted that in the following text, references to the surface of the substrate may also or instead refer to the surface of the substrate support, and vice versa, unless otherwise stated.) A fluid handling structure present between the projection system and the stage is used to confine the immersion liquid to a space. The space filled by the immersion liquid is smaller in plan than the top surface of the substrate, and this space is kept substantially stationary relative to the projection system while the substrate and substrate stage move below.

[0008]

[0008] Other immersion systems are also envisaged, such as unconfined immersion systems (so-called "all wet" immersion systems) and bath-based immersion systems. In unconfined immersion systems, the immersion liquid covers an area larger than the surface beneath the final element. The liquid outside the space is present as a thin film. The immersion liquid covers the entire surface of the substrate, or also covers the substrate and a support table flush with the substrate. In bath-based systems, the substrate is completely immersed in a bath of immersion liquid.

[0009] A fluid handling structure is a structure that supplies immersion liquid to a space and removes immersion liquid from the space, thereby confining the immersion liquid to the space. It includes features that are part of a fluid supply system. Figures 2 and 3 show different supply devices that can be used in such a system. The fluid handling structure extends along at least part of the boundary of the space between the final element of the projection system and the support table or substrate, so as to partially define this space.

[0010]

[0010] A fluid handling structure may have a variety of selected functions, each resulting from corresponding features that enable the fluid handling structure to achieve that function. A fluid handling structure may be referred to by a number of different terms, each describing a function, for example barrier member, seal member, fluid supply system, fluid removal system, liquid confinement structure, etc.

[0011]

[0010] The fluid handling structure as a barrier member is a barrier to the flow of immersion liquid from the space. The structure as a liquid confinement structure confines the immersion liquid in the space. The sealing feature of the fluid handling structure as a seal member forms a seal that confines the immersion liquid in the space. The sealing feature may comprise an additional gas flow from an opening in the surface of the seal member, such as a gas knife.

[0012] In an immersion apparatus, a meniscus of liquid (e.g., water) is stabilized in a seal between the backside of the substrate and the top of the support table. When the substrate is removed from the support table, some of this liquid may remain on the substrate and on the support table. It is desirable to reduce the amount of liquid that remains on the substrate and / or support table when the substrate is removed from the support table. Summary of the Invention

[0013] According to one aspect of the present invention, there is provided a method for unloading an object from a support table during an exposure process, comprising: applying a first pressure to a central region of the support table beneath a central portion of the object; the object is clamped to the support table by applying a second pressure to a peripheral region of the support table beneath a periphery of the object, and during clamping, the first pressure and the second pressure are controlled to maintain liquid between the object and a seal member, the seal member being positioned radially on an upper surface of the support table between the central region and the peripheral region and protruding towards the object, and the method further comprising: increasing the first pressure toward ambient pressure; removing at least a portion of the liquid retained between the object and the seal member by reducing the second pressure; increasing the second pressure toward ambient pressure; Includes:

[0014] According to an aspect of the present invention, there is provided a lithographic apparatus comprising: A support table for holding an object, comprising: a first channel for applying a first pressure to a central region beneath a central portion of the object; a second channel for applying a second pressure to a peripheral region beneath the periphery of the object; a seal member positioned radially on the upper surface of the support table between the first channel and the second channel and protruding toward the object; a support table including: a controller, controlling the application of the first pressure and the second pressure during the exposure process such that liquid is maintained between the object and the seal member during the exposure process; increasing the first pressure toward ambient pressure; reducing the second pressure to remove at least a portion of the liquid retained between the object and the seal member; increasing the second pressure toward ambient pressure during the unloading process; a controller adapted to Equipped with.

[0015] According to one aspect of the present invention, there is provided a vacuum system for a substrate table and a support table of a lithographic apparatus, the support table being for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit including a first vacuum pressure line configured to clamp the support table to the substrate table; a second pressure circuit, a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table beneath the periphery of the object; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table; a vacuum device configured to apply pressure to the second pressure circuit; a fourth vacuum pressure line branching from the second pressure circuit; and a second pressure circuit including: a first flow controller for controlling the pressure in the second vacuum pressure line; a second flow controller for controlling the pressure in the fourth vacuum pressure line; Equipped with.

[0016] According to one aspect of the present invention, there is provided a vacuum system for a substrate table and a support table of a lithographic apparatus, the support table being for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit, a first vacuum pressure line configured to clamp the support table to the substrate table; a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table beneath the periphery of the object; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table; a first pressure circuit including: a first flow controller for controlling the pressure in the second vacuum pressure line; a fourth flow controller for controlling flow from ambient pressure to the third vacuum pressure line; Equipped with.

[0017] According to one aspect of the present invention, there is provided a vacuum system for a substrate table and a support table of a lithographic apparatus, the support table being for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit, a first vacuum pressure line configured to clamp the support table to the substrate table; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table; a first pressure circuit including: a second pressure circuit including a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table underlying the periphery of the object; a first flow controller for controlling the pressure in the second vacuum pressure line; a fifth flow controller for controlling the pressure in the third vacuum pressure line; Equipped with.

[0018]

[0017] A vacuum system for a substrate table and a support table of a lithographic apparatus, the support table being for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit, a first pressure circuit including a first vacuum pressure line configured to clamp the support table to the substrate table; a second pressure circuit, a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table beneath the periphery of the object; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table, the third vacuum pressure line connected to the second vacuum pressure line via a flow controller to maintain a predetermined pressure differential between the second vacuum pressure line and the third vacuum pressure line; a second pressure circuit including: another flow controller for controlling flow from ambient pressure to the second vacuum pressure line; A vacuum system comprising: [Brief explanation of the drawings]

[0019]

[0018] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0020] [Figure 1] 1 depicts a lithographic apparatus according to one embodiment of the present invention; [Figure 2] 1 depicts a liquid supply system for use in a lithographic projection apparatus; [Figure 3]

[0021] 1 illustrates a cross-sectional side view of another liquid supply system according to an embodiment; [Figure 4]

[0022] 1 illustrates a schematic representation of a substrate supported on a support table in accordance with one embodiment of the present invention; [Figure 5]

[0023] 5 shows a schematic close-up of a liquid meniscus clamped between the substrate and support table shown in FIG. 4; [Figure 6]

[0024] 10 shows a close-up schematic of what may happen to the liquid meniscus when the substrate is removed from the support table; [Figure 7]

[0025] 10 is a graph illustrating pressure versus time in different regions during the unloading process according to one embodiment of the present invention. [Figure 8]

[0026] 10 is a graph showing pressure versus time in different regions according to a comparative example. [Figure 9]

[0027] 1 shows a schematic diagram of a vacuum system according to an embodiment of the present invention; [Figure 10]

[0027] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 11]

[0027] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 12]

[0027] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 13]

[0027] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 14]

[0027] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 15]

[0028] 1A and 1B schematically illustrate a cross-sectional side view of a substrate supported on a support table in accordance with one embodiment of the present invention; [Figure 16]

[0029] 10 is a graph illustrating pressure versus time in different regions during the unloading process according to one embodiment of the present invention. [Figure 17]

[0030] 10 is a graph showing pressure versus time in different regions according to a comparative example. [Figure 18]

[0031] 1 shows a schematic diagram of a vacuum system according to an embodiment of the present invention; [Figure 19]

[0031] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 20]

[0031] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 21]

[0031] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. [Figure 22]

[0031] A diagram of a vacuum system according to an embodiment of the present invention is shown schematically. DETAILED DESCRIPTION OF THE INVENTION

[0021]

[0032] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (eg, having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm).

[0022]

[0033] The terms "reticle," "mask," or "patterning device," as used herein, may be broadly interpreted as referring to a general-purpose patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. Besides the classic mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and / or programmable LCD arrays.

[0023]

[0034] Figure 1 schematically depicts a lithographic apparatus comprising: a. Optionally, 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 configured 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 connected to a second positioner PW configured to accurately position the surface of the table, e.g., a substrate W, according to certain parameters, such as a sensor table supporting one or more sensors or a support table WT configured to hold a substrate (e.g., a resist-coated wafer) W. d. a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0024]

[0035] In operation, the illumination system IL receives a radiation beam or radiation from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0025]

[0036] The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems, including refractive optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate depending on the radiation used and / or other factors such as the use of an immersion liquid or a vacuum. Where the term "projection lens" is used herein, this may be considered as synonymous with the more general term "projection system".

[0026]

[0037] The lithographic apparatus may be of a type having two or more support tables, for example two or more support tables, or a combination of one or more support tables with one or more cleaning tables, sensor tables, or measurement tables. For example, the lithographic apparatus may be a multi-stage apparatus comprising two or more tables positioned on the exposure side of the projection system, each comprising and / or holding one or more objects. In one example, one or more of the tables may hold a radiation-sensitive substrate. In one example, one or more of the tables may hold a sensor that measures radiation from the projection system. In one example, 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 generally, but without limitation, referred to as a measurement table, sensor table, and / or cleaning table) that is not configured to hold a radiation-sensitive substrate. The second table may comprise 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 a sensor that measures radiation from the projection system, one or more alignment marks, and / or a cleaning device (e.g., for cleaning a liquid confinement structure).

[0027]

[0038] In operation, the radiation beam B is incident on a pattern (design layout) present 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. Using the second positioner PW and position sensor IF (e.g., an interferometric device, a linear encoder, a 2D encoder, or a capacitive sensor), the support table W can be accurately moved, for example, to position different target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (not explicitly shown in FIG. 1 ) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W can be aligned using patterning device mask alignment marks M1, M2 and substrate alignment marks P0, P1. Although the substrate alignment marks M1, M2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions C (these are known as scribe-lane alignment marks).

[0028]

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

[0029]

[0040] The fluid handling structure IH at least partly confines immersion liquid in 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, which is positioned below and surrounding the final element of the projection system PS. Immersion liquid is introduced into the space 11 in the fluid handling structure IH below the projection system PS by one of the liquid openings 13. Immersion liquid can also be removed by another of the liquid openings 13. Immersion liquid may be introduced into the space 11 via at least two liquid openings 13. Which of the liquid openings 13 is used to supply immersion liquid, and optionally which of the liquid openings 13 is used to remove immersion liquid, can depend on the direction of movement of the support table WT.

[0030]

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

[0031]

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

[0032]

[0043] The fluid handling structure IH at least partly confines immersion liquid in 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 positioned below and surrounding the final element of the projection system PS. In one example, the fluid handling structure IH comprises a body member 53 and a porous member 33. The porous member 33 is plate-like and has a plurality of holes (i.e. openings or pores). In one 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 2010 / 0045949 A1, which is incorporated herein by reference in its entirety.

[0033]

[0044] The body member 53 is provided with supply ports 72 capable of supplying immersion liquid to the space 11, and recovery ports 73 capable of recovering immersion liquid from the space 11. The supply ports 72 are connected to liquid supply apparatuses 75 via passages 74. The liquid supply apparatuses 75 are capable of supplying immersion liquid to the supply ports 72 via the corresponding passages 74. The recovery ports 73 are capable of recovering immersion liquid from the space 11. The recovery ports 73 are connected to liquid recovery apparatuses 80 via passages 79. The liquid recovery apparatus 80 recovers the immersion liquid recovered via the recovery ports 73, via the passages 29. The porous member 33 is arranged at the recovery ports 73. By performing a liquid supply operation using the supply ports 72 and performing a liquid recovery operation using the porous member 33, a space 11 is formed between the projection system PS and the fluid handling structure IH on the one side, and the substrate W on the other side.

[0034]

[0045] 4 shows a schematic cross-section of a substrate W supported on a support table WT. In the following, the invention will be described with reference to the substrate W as an example of an object and the support table WT as an example of a support table. However, the invention is not limited to situations in which the substrate W is supported on the support table WT. For example, the invention is applicable to a patterning device MA supported by a support structure MT.

[0035]

[0046] As shown in Figure 4, the substrate W is supported by the support table WT. During use of the lithographic apparatus, the substrate W may be clamped to the support table WT. For example, during an exposure process, the substrate W is clamped to the support table WT. Between exposure processes, the substrate W may be unloaded from the support table WT. For example, during a substrate exchange sequence, the substrate W may be removed from the substrate WT.

[0036]

[0047] As shown in Figure 4, in one embodiment, the support table WT includes a first channel 26. The first channel 26 is for applying a first pressure p1 to a central region 21 of the support table WT below a central portion WC of the substrate W. As shown in Figure 4, in one embodiment, the first channel 26 is provided through the body 20 of the support table WT. In one embodiment, the first channel 26 is connected to a pressure circuit configured to apply the first pressure p1 to the central region 21. Because the first pressure p1 is less than the ambient pressure above the substrate W, the substrate W is clamped to the support table WT.

[0037]

[0048] In one embodiment, the support table WT includes a second channel 27 for applying a second pressure p2 to a peripheral region 22 of the support table WT underlying a peripheral portion WP of the substrate W. The second channel 27 is radially outward of the first channel 26. In one embodiment, the second channel 27 is provided through the body 20 of the support table WT. In an alternative embodiment, the second channel 27 is provided as a gap between the body 20 and an extraction body radially surrounding the body 20. In one embodiment, the second channel 27 is connected to a pressure circuit configured to apply the second pressure p2 to the peripheral region 22.

[0038]

[0049] In one embodiment, the support table WT includes a seal member 24. The seal member 24 is positioned radially between the first channel 26 and the second channel 27. The seal member 24 is positioned on the top surface of the support table WT. The seal member 24 is annular in plan view. The seal member 24 protrudes toward the substrate W. However, the seal member 24 does not come into direct contact with the substrate W when the substrate W is clamped to the support table WT. There is a small gap between the top of the seal member 24 and the backside of the substrate W.

[0039]

[0050] In one embodiment, the support table WT includes an outer seal 25. The outer seal 25 is positioned radially outside the second channel 27. The outer seal 25 is positioned on the upper surface of the support table WT. The outer seal member 25 is annular in plan view. The outer seal member 25 protrudes toward the substrate W. However, the outer seal member 25 does not come into direct contact with the substrate W when the substrate W is clamped to the support table WT. There is a small gap between the top of the outer seal member 25 and the backside of the substrate W.

[0040]

[0051] During the exposure process, fluid is extracted from the peripheral region 22 via the second channel 27. The second pressure p2 applied by the second channel 27 further facilitates clamping the substrate W to the support table WT. The fluid flow through the second channel 27 helps to reduce the amount of immersion liquid that reaches the backside of the substrate W.

[0041]

[0052] During the exposure process, a seal is formed between the seal member 24 and the substrate W. Specifically, a liquid meniscus 23 is pinned on the seal member 24 between the top of the seal member 24 and the bottom of the substrate W. The liquid meniscus 23 is pinned based on capillary pressure. The first pressure p1 and the second pressure p2 are controlled so that the difference between these pressures is less than the capillary pressure above the seal member 24 (i.e., less than the force required to remove the liquid meniscus 23 from the seal member 24).

[0042]

[0053] As mentioned above, the first channel 26 and the second channel 27 are connected to one or more pressure circuits that form part of a vacuum system 40, which is described in more detail below. In one embodiment, the vacuum system 40 (i.e., the vacuum supply) is configured such that a pressure differential between the first pressure p1 and the second pressure p2 is maintained even when the supply pressure fluctuates.

[0043]

[0054] The pressure difference between the first pressure p1 and the second pressure p2 is controlled to be greater than the capillary pressure in the gap between the substrate W and the support table WT (i.e., the area away from the seal member 24). This causes the liquid meniscus 23 to pin at the seal, as shown in Figure 5. Figure 5 is a close-up of the liquid meniscus 23 pinned at the seal member 24 of the support table WT.

[0044]

[0055] During the exposure process, the seal member 24 is wetted due to the presence of the liquid meniscus 23. When the substrate W is unloaded (i.e. removed) from the support table WT, some of the liquid from the liquid meniscus 23 may remain on the substrate W, and some of the liquid from the liquid meniscus 23 may remain in contact with the seal member 24. It is desirable to reduce the amount of liquid from the liquid meniscus 23 that remains in contact with the substrate W and on the seal member 24.

[0045]

[0056] 1, in one embodiment, the lithographic apparatus includes a controller 500. The controller 500 is configured to control a vacuum supply connected to the first channel 26 and the second channel 27. The controller 500 is configured to control a first pressure p1 and a second pressure p2 applied to the central region 21 and the peripheral region 22, respectively.

[0046]

[0057] Figure 6 shows liquid from the liquid meniscus 23 remaining on the substrate W and in contact with the seal member 24 after the substrate W has been unloaded from the support table WT. This residual liquid is undesirable.

[0047]

[0058] In one embodiment, immediately prior to unloading the substrate W, a large pressure differential is created across the seal member 24 by increasing the vacuum level in the peripheral region 22, as will be described in more detail below.

[0048]

[0059] In one embodiment, the controller 500 is adapted to control the application of a first pressure p1 and a second pressure p2 during the exposure process, such that liquid is maintained between the substrate W and the seal member 24 during the exposure process. This is the situation illustrated in Figure 5. The function of the controller 500 just prior to and during the unload process will now be described.

[0049]

[0060] 7 is a graph showing pressure versus time in different regions before and during the unloading process. The lower dashed line represents the second pressure p2 in the peripheral region 22 during the unloading process. The upper dashed line represents the first pressure p1 in the central region 21 during the unloading process.

[0050]

[0061] The pressure fluctuations shown in Figure 7 are merely an example of how the first pressure p1 and the second pressure p2 may fluctuate before and during the unloading process, however, the present invention is not limited to the particular form of the lines shown in Figure 7.

[0051]

[0062] 7, in one embodiment, the controller 500 is adapted to increase the first pressure p1 toward ambient pressure, which is shown in the middle time region (of the three time periods) shown in FIG.

[0052]

[0063] In one embodiment, the controller 500 is adapted to reduce the second pressure p2 so as to remove at least some of the liquid retained between the substrate W and the seal member 24. This is shown in Figure 7 at the beginning of the central time period during which the second pressure p2 is reduced.

[0053]

[0064] This is done before the substrate W is removed from the support table WT. Thus, the second pressure p2 is reduced (and the first pressure p1 is increased) while the substrate W remains supported on the burls of the support table WT. At this point (i.e. before the substrate W is unloaded), at least some of the liquid from the liquid meniscus 23 is removed. The liquid can be removed via the second channel 27.

[0054]

[0065] In one embodiment, the controller 500 is adapted to increase the second pressure p2 towards ambient pressure during the unloading process. This is shown in the latter part of the central time period and the right-hand time period shown in Figure 7. Specifically, the second pressure p2 is increased towards ambient pressure after reaching a minimum value. By increasing the second pressure p2 towards ambient pressure, the clamping pressure is reduced so that the substrate W can be removed from the support table WT.

[0055]

[0066] By removing at least a portion of the liquid before the unloading process, the amount of liquid remaining on the backside of the substrate W after the unloading process is reduced. This reduces undesirable problems that may occur during subsequent processing of the unloaded substrate W. For example, liquid residue on the backside of the unloaded substrate W may generate capillary forces, which may result in scratches on the substrate W. This reduces the quality of the substrate W. Specifically, some substrates W may be reused, which means that after the substrate W is unloaded from the support table WT, the unloaded substrate W must later be clamped again to that support table (or a different support table) WT. A closing substrate is an example of such a substrate W. It is undesirable for such a reusable substrate W to have liquid residue that may cause scratches, for example.

[0056]

[0067] By removing at least some of the liquid before the unloading process, the amount of liquid remaining in contact with the seal member 24 and / or outer seal 25 is reduced. This reduces the likelihood that a subsequent substrate W will undesirably adhere to any particular location on the support table WT. This also reduces the risk that some liquid will accidentally transfer to a grid used for measurement. This also reduces the amount of liquid that may evaporate when loading the next substrate W. Evaporation can cause cold spots that cause undesirable deformation of the support table WT. This also reduces the amount of contamination that can be transferred onto the support table WT.

[0057]

[0068] As mentioned above, just prior to unloading the substrate W, a large pressure differential is created across the seal member 24 by increasing the vacuum level in the peripheral region 22 and decreasing the vacuum level in the central region 21 .

[0058]

[0069] As a comparative example, an alternative method for reducing the amount of liquid is to evacuate the liquid meniscus 23 during the sequence for unloading the substrate W. First, gas can be blown into the central region 21 while a vacuum is maintained in the peripheral region 22. This increases the pressure difference between the first pressure p1 and the second pressure p2 to exceed the capillary pressure on the seal member 24. This results in the liquid meniscus 23 being removed from the seal member 24. The vacuum for the second pressure p2 can then be switched off so that the second pressure p2 can increase to release the substrate W.

[0059]

[0070] An embodiment of the present invention is expected to achieve improvements over this comparative example, specifically, to reduce burl wear on the edge of the support table WT.

[0060]

[0071] This is because if an overpressure is applied under the central portion WC of the substrate W while maintaining a second pressure p2 under the peripheral portion WP of the substrate W, the substrate W will bend into an umbrella shape. The edge of the substrate W will slide over the burls at the edge of the substrate W. This will wear the burls.

[0061]

[0072] An embodiment of the present invention is expected to achieve reduced bending of the substrate W. In an embodiment of the present invention, no overpressure (i.e., increasing the first pressure p1 above ambient pressure) is applied below the central portion WP of the substrate W. Thus, wear on the burls due to bending of the substrate W is reduced.

[0062]

[0073] As another comparative example, the substrate W can be unloaded by gradually increasing both the first pressure p1 and the second pressure p2 towards ambient pressure. Figure 8 is a graph showing the relationship between time and pressure in different regions when unloading the substrate W according to such a comparative example. In Figure 8, the lower line shows the second pressure p2 and the upper line shows the first pressure p1.

[0063]

[0074] The sequence shown in Figures 7 and 8 does not apply overpressure under the central portion C of the substrate W until the vacuum applied under the peripheral portion WP of the substrate W has been significantly reduced. Figures 7 and 8 show that the first pressure p1 can be increased above ambient pressure during the final stages of unloading. The overpressure causes the substrate W to deform into an umbrella shape, which can cause the substrate W to slip on the outer burls. However, because the second pressure p2 is very close to ambient pressure when the first pressure p1 is greater than ambient pressure, this slippage exerts minimal normal force on the burls. This results in reduced burl wear at the edges of the support table WT. However, the sequence shown in Figure 8 leaves an undesirable amount of liquid from the liquid meniscus 23 on the substrate W and / or support table WT.

[0064]

[0075] An embodiment of the present invention is expected to achieve improvements over the comparative examples described above, specifically by reducing the amount of liquid that backs up onto the seal member 24 while avoiding buckling at the edge of the substrate W during the unload process.

[0065]

[0076] 8, as soon as the second pressure p2 is increased, the liquid moves back onto the seal member 24. As a result, the seal member 24 remains wet, causing the next substrate W to undesirably stick to the support table WT.

[0066]

[0077] 7, in one embodiment, the controller 500 is adapted to increase the first pressure p1 while decreasing the second pressure p2 to remove at least some of the liquid retained between the substrate W and the seal member 24. This is shown at the beginning of the central time period in FIG. 7. The first pressure p1 is increased while the second pressure p2 is decreased. As a result, the pressure difference between the first pressure p1 and the second pressure p2 increases more quickly, thereby removing the liquid meniscus 23 more quickly. This means that the substrate W can be unloaded from the support table WT more quickly, thereby increasing throughput.

[0067]

[0078] As shown in FIG. 7 , in one embodiment, the second pressure p2 reaches the ambient pressure level (the zero line on the Y-axis) at a later time than the first pressure p1. The second pressure p2 is maintained lower than the first pressure p1 throughout the process of unloading the substrate W from the support table WT. As shown in FIG. 7 , in one embodiment, the second pressure p2 is applied at a level lower than the first pressure p1 relative to ambient pressure during the unload process. Thus, throughout the unload process, liquid is moved from the central region 21 toward the second channel 27. As a result, liquid near the seal member 24 is moved away from the central region 21. For example, by removing liquid through the second channel 27, the amount of liquid remaining on the support table WT after the unload process is completed can be reduced.

[0068]

[0079] 9-12 each schematically illustrate a vacuum system 40 according to one embodiment of the present invention. The vacuum systems 40 illustrated in FIGS. 9-12 can be used to implement the pressure sequences described above (e.g., the pressure sequence illustrated in FIG. 7).

[0069]

[0080] The vacuum system 40 is for a support table WT to hold a substrate W. The vacuum system 40 comprises a flow circuit including a first pressure circuit 43. The first pressure circuit 43 includes a first vacuum pressure line 49. The first vacuum pressure line 49 is for clamping the support table WT to a substrate table 65 (e.g., as shown in FIG. 15 ). In one embodiment, the flow circuit of the vacuum system 40 comprises a second pressure circuit 42. The second pressure circuit 42 includes a second vacuum pressure line 41 and a third vacuum pressure line 54. The third vacuum pressure line 54 is configured to apply a first pressure p1 to a central region 21 of the support table WT below a central portion WP of the substrate W to clamp the substrate W to the support table WT. For example, in one embodiment, the third vacuum pressure line 54 is connected to the first channel 26.

[0070]

[0081] As shown in Figure 15, in one embodiment, the support table WT is supported by the substrate table 65. The support table WT is clamped to the substrate table 65 by applying a pressure between the support table WT and the substrate table 65 that is less than ambient pressure. In one embodiment, the second positioner (shown in Figure 1) includes the substrate table 65. In general, movement of the support table WT can be achieved using a long-stroke module and a short-stroke module that form part of the second positioner PW. In one embodiment, the short-stroke module includes the substrate table 65. The first pressure circuit 43 is configured to apply pressure to clamp the support table WT to the second positioner PW.

[0071]

[0082] In one embodiment, the flow circuit of the vacuum system 40 includes a second pressure circuit 42. The second pressure circuit 42 is configured to apply a second pressure p2 to the peripheral region 22 of the support table WT below the peripheral portion WP of the substrate W. In one embodiment, the second pressure circuit 42 includes a vacuum device. The vacuum device is configured to supply pressure to the second pressure circuit 42.

[0072]

[0083] 9-12, in one embodiment, the second pressure circuit 42 includes a second vacuum pressure line 41. For example, in one embodiment, the second vacuum pressure line 41 is connected to the second channel 27 to apply a second pressure p2 to the peripheral region 22. In one embodiment, the second pressure circuit 42 includes a third vacuum pressure line 50 branching off from the second pressure circuit 42.

[0073]

[0084] 9-12, the flow circuit of the vacuum system 40 includes a first flow controller 44. The first flow controller 44 is configured to control the pressure in the second vacuum pressure line 41. For example, in one embodiment, the first flow controller 44 is a valve that can be opened and closed. When the first flow controller 44 is open, the second vacuum pressure line 41 is connected to the vacuum supply of the second pressure circuit 42.

[0074]

[0085] 9-12, in one embodiment, the flow circuit of vacuum system 40 includes a second flow controller 45. Second flow controller 45 is configured to control the pressure in fourth vacuum pressure line 50. For example, in one embodiment, second flow controller 45 is a valve that can be opened and closed.

[0075]

[0086] 9 to 11, when the second flow controller 45 is opened, the fourth vacuum pressure line 50 is in fluid communication with the first pressure circuit 43. Thus, by switching between the first flow controller 44 and the second flow controller 45, the pressure in the second vacuum pressure line 41 can be switched from being supplied by the vacuum supply of the second pressure circuit 42 to being supplied by the vacuum supply of the first pressure circuit 43. Thus, by switching between the first flow controller 44 and the second flow controller 45, the second pressure p2 can be controlled.

[0076]

[0087] For example, in one embodiment, the vacuum supply of the first pressure circuit 43 provides a lower pressure (i.e., a stronger vacuum) than the vacuum supply of the second pressure circuit 42. Thus, during the exposure process, the second pressure p2 is controlled by the vacuum supply of the second pressure circuit 42 by opening the first flow controller 44 and closing the second flow controller 45. Just before the unloading process begins, the first flow controller 44 can be closed and the second flow controller 45 can be opened to reduce the second pressure p2 to the pressure provided by the vacuum supply of the pressure circuit 43.

[0077]

[0088] The support table WT is clamped to the substrate table 65 by vacuum pressure. The substrate W is clamped to the support table WT by vacuum pressure. In one embodiment, the pressure applied to the region between the support table WT and the substrate table 65 is lower than the pressure applied to the region between the substrate W and the support table WT.

[0078]

[0089] 9-12, during the exposure process, the first vacuum pressure line 49 is configured to provide a lower pressure than the second vacuum pressure line 41 or the third vacuum pressure line 54. The first pressure circuit 43 can provide a lower pressure (i.e., a deeper vacuum) than the second pressure circuit 42.

[0079]

[0090] As shown in each of FIGS. 9 to 12 , in one embodiment, the second vacuum pressure line 41 is connected to the third vacuum pressure line 54. A connection line 55 is provided to connect the second vacuum pressure line 41 to the third vacuum pressure line 54. The same vacuum pressure source supplies negative pressure to both the second vacuum pressure line 41 and the third vacuum pressure line 54. For example, during the exposure process, the second pressure circuit 42 supplies negative pressure to both the second pressure line 41 and the third vacuum pressure line 54. When it is necessary to remove the liquid meniscus 23 (e.g., for an unloading process), the negative pressure source for the second pressure line 41 and the third vacuum pressure line 54 is switched. In the embodiment shown in FIGS. 9 to 11 , the negative pressure source is switched from the second pressure circuit 42 to the first pressure circuit 43. In the embodiment shown in FIG. 12 , the negative pressure source is switched from the second pressure circuit 42 to the third pressure circuit 63.

[0080]

[0091] 9-12, in one embodiment, the vacuum system 40 includes a fourth flow controller 58. The fourth flow controller 58 is for controlling the flow from ambient pressure to the third vacuum pressure line 54. For example, in one embodiment, the fourth flow controller 58 is a restriction. The flow from ambient pressure to the third vacuum pressure line 54 increases the pressure provided to the central region 21 by the third vacuum pressure line 54. As a result, the first pressure p1 supplied to the central region 21 is greater than the second pressure p2 applied to the peripheral region 22. The fourth flow controller 58 is configured to maintain a difference between the first pressure p1 and the second pressure p2 within a predetermined range during an exposure operation.

[0081]

[0092] 9-12, in one embodiment, the vacuum system 40 includes a first ambient pressure line 57. The first ambient pressure line 57 is in fluid communication with the third vacuum pressure line 54. A fourth flow controller 58 is provided in the first ambient pressure line 57. The first ambient pressure line 57 connects ambient pressure to the third vacuum pressure line 54 through the fourth flow controller 58.

[0082]

[0093] As shown in FIGS. 9-11 , in one embodiment, the vacuum system 40 includes a sixth flow controller 56. The sixth flow controller 56 is disposed in the connecting line 55 connecting the second vacuum pressure line 41 to the third vacuum pressure line 54. The sixth flow controller 56 is configured to control the flow between the second vacuum pressure line 41 and the third vacuum pressure line 54. For example, in one embodiment, the sixth flow controller 56 is a restriction configured to restrict flow. In one embodiment, the sixth flow controller 56 restricts the flow from the third vacuum pressure line 54 to the second vacuum pressure line 41. This helps to maintain a pressure differential between the second vacuum pressure line 41 and the third vacuum pressure line 54. As mentioned above, there is also flow from ambient pressure to the third vacuum pressure line 54. The sixth flow controller 56 is configured to restrict the flow from ambient pressure to the second vacuum pressure line 41.

[0083]

[0094] 9 to 12, in one embodiment, the vacuum system 40 includes a seventh flow controller 59. The seventh flow controller 59 is provided in the third vacuum pressure line 54. The seventh flow controller 59 is configured to control the pressure in the third vacuum pressure line 54. In one embodiment, the seventh flow controller 59 is a valve that can be opened and closed. During the exposure process, the seventh flow controller 59 is opened, and the first flow controller 44 is also opened. The first pressure p1 can be increased by closing the seventh flow controller 59.

[0084]

[0095] As shown in each of Figures 9-11, in one embodiment, the vacuum system includes a vacuum chamber 47. The vacuum chamber 47 is upstream of a third flow controller 48. The third flow controller 48 is configured to control flow from the vacuum chamber 47 to the first pressure circuit 43. As shown in Figures 9 and 10, in one embodiment, the third flow controller 48 is in a fourth vacuum pressure line 50. Alternatively, as shown in Figure 11, in one embodiment, the third flow controller 48 is in a fifth vacuum pressure line 51 (which will be described in more detail below). In one embodiment, the third flow controller 48 includes a restriction configured to limit continuous flow from the vacuum chamber 47 to the vacuum supply of the first pressure circuit 43.

[0085]

[0096] When the first flow controller 44 is closed and the second flow controller 45 is open, the second vacuum pressure line 41 is in fluid communication with the vacuum chamber 47. As a result, the second pressure p2 drops toward the pressure in the vacuum chamber 47.

[0086]

[0097] This reduction in the second pressure p2 may be carried out for less than 1 second, optionally less than 0.5 seconds, optionally less than 0.2 seconds, optionally less than 0.1 seconds. The second pressure p2 is reduced so as to remove the liquid meniscus 23 from between the seal member 24 and the substrate W.

[0087]

[0098] After the second pressure p2 is reduced, the second pressure is again increased toward ambient pressure, as shown in Figure 7. At this time, the second flow controller 45 can be closed and the pressure in the vacuum chamber 47 can again be reduced toward the pressure provided by the vacuum supply of the first pressure circuit 43.

[0088]

[0099] Whenever the second flow controller 45 is opened, the negative pressure provided by the second vacuum pressure line 41 increases. This means that the second pressure p2 temporarily drops. When this occurs, the vacuum pressure in the first pressure circuit 43 increases quickly because the first pressure circuit 43 is exposed to the high vacuum pressure in the second vacuum pressure line 41. After the temporary drop in the negative pressure provided by the second vacuum pressure line 41, the initial vacuum level provided by the first pressure circuit 43 is restored. The vacuum chamber 47 stores vacuum pressure and releases the stored vacuum pressure when the negative pressure provided by the second vacuum pressure line 41 is increased. By configuring the vacuum device to include the vacuum chamber 47, the initial vacuum level can be restored more quickly. This is useful for increasing the throughput of substrates W. Specifically, this reduces the waiting time between uses required for the vacuum level provided by the first pressure circuit 43 to be restored. Restoring the vacuum level in the vacuum chamber 47 can be performed at a low flow rate during the measurement and exposure processes (ie, between substrate exchange sequences) so as not to disturb other vacuum levels.

[0089]

[0100] As shown in each of Figures 10-12, in one embodiment, the vacuum system 40 includes a separation chamber 60. The separation chamber 60 is for separating a two-phase flow. A two-phase flow is a flow that contains both a liquid and a gas. The separation chamber 60 is provided in the second pressure circuit 42. The two-phase flow enters the separation chamber 60 from the second vacuum pressure line 41 (e.g., from the second channel 27).

[0090]

[0101] Liquid exits the separation chamber 60 through the liquid outlet 62. Gas exits the separation chamber 60 through the gas outlet 61. The liquid outlet 62 is positioned at the bottom of the separation chamber 60. Liquid from the two-phase flow collects at the bottom of the separation chamber 60 due to gravity. As shown in FIGS. 10 and 12, in one embodiment, liquid can be extracted from the separation chamber 60 when the first flow controller 44 is opened. Alternatively, as shown in FIG. 11, in one embodiment, a fifth flow controller 52 is provided on the fourth vacuum pressure line 50. When the fifth flow controller 52 is opened, liquid can be extracted from the separation chamber 60. However, when the first flow controller 44 (see FIG. 10 or FIG. 12) or the fifth flow controller 52 (see FIG. 11) is closed, liquid remains in the separation chamber 60. In one embodiment, liquid extraction is prevented when the second pressure p2 is reduced (e.g., when the second flow controller 45 is opened). Liquid extraction is then resumed by closing the second flow controller 45 and opening the first flow controller 44. This is performed after the substrate W has been unloaded.

[0091]

[0102] By providing the separation chamber 60, the amount of liquid output to the first pressure circuit 43 is reduced or eliminated, thereby protecting the components of the first pressure circuit 43 from liquid. A second advantage is that single-phase flow through the first pressure circuit 43 provides a more stable pressure in the first vacuum pressure line 49, as two-phase flow would normally result in undesirable pressure fluctuations.

[0092]

[0103] The separation chamber 60 does not require a deeper vacuum level to extract the liquid than that used for gas extraction, so the gas outlet 61 can be connected to the first pressure circuit 43, which has the lowest pressure (see Figures 10 and 11).

[0093] In one embodiment, separation chamber 60 has a volume of at least 1 milliliter, optionally at least 2 milliliters, optionally at least 5 milliliters. In one embodiment, separation chamber 60 has a volume of at most 10 milliliters, optionally at most 5 milliliters, optionally at most 2 milliliters.

[0094] 10 and 12, the separation chamber 60 is upstream of the first flow controller 44 and the second flow controller 45. As shown in Figures 10 and 12, in one embodiment, the separation chamber 60 is in fluid communication with the second vacuum pressure line 41 and the fourth vacuum pressure line 50.

[0095] The fourth vacuum pressure line 50 is connected to a gas outlet 61 of the separation chamber 60. The first flow controller 44 is configured to control the liquid extraction from the separation chamber 60. The second flow controller 45 is configured to control whether the second vacuum pressure line 41 is connected to the lowest pressure used just before the unloading process.

[0096]

[0103] In one embodiment, the second vacuum pressure line 41 is configured for liquid flow, and the fourth vacuum pressure line 50 is configured for gas flow (see Figures 10 and 12). Thus, when the first flow controller 44 is opened, liquid flows from the separation chamber 60 into the second vacuum pressure line 41 and through the first flow controller 44. Meanwhile, substantially no liquid flows through the fourth vacuum pressure line 50 because the liquid is separated from the two-phase flow by the separation chamber 60. As a result, the first pressure circuit 43, which provides the lowest pressure, can be kept dry.

[0097]

[0104] 9-12, in one embodiment, vacuum devices 46, 47 are downstream of second flow controller 45 and are configured to apply pressure to fourth vacuum pressure line 50. When second flow controller 45 is closed, no reduced pressure is applied to peripheral region 22. When second flow controller 45 is open (and first flow controller 44 is closed), reduced pressure is applied to peripheral region 22.

[0098]

[0105] 9 to 11, in one embodiment, the fourth vacuum pressure line 50 is in fluid communication with the first pressure circuit 43. This means that the first pressure circuit 43 can be used not only to clamp the support table WT to the substrate table 65, but also to apply low pressure to the peripheral region 22 just prior to the unload process, and to the vacuum chamber 47 during the exposure process.

[0099]

[0106] In one embodiment, the third flow controller 48 is configured to control the amount of flow from the second pressure circuit 42 into the first pressure circuit 43 (see Figures 9-11). In the embodiment shown in Figures 9-11, the third flow controller 48 is a restriction that allows the pressure in the vacuum chamber 47 to be slowly reduced, for example, during exposure and measurement operations.

[0100]

[0107] 12, in one embodiment, the vacuum device includes a venturi pump 46. The venturi pump 46 generates a vacuum by the Venturi effect. In one embodiment, the venturi pump 46 is an ejector-jet pump type aspirator.

[0101]

[0108] As shown in FIG. 12, in one embodiment, the fourth vacuum pressure line 50 is in fluid communication with a third pressure circuit 63. The third pressure circuit 63 includes a vacuum generated by a venturi pump 46. The venturi pump 46 is an alternative method of generating the deep vacuum necessary to reduce the second pressure p2 prior to the unloading process. The venturi pump 46 can be fairly small due to its small vacuum flow. In one embodiment, the third pressure circuit 63 includes a supply of compressed dry air. The compressed dry air supply is provided to the venturi pump 46, which creates a venturi effect to generate the vacuum.

[0102]

[0109] By configuring the vacuum device to include a venturi pump 46, the vacuum supply of the first pressure circuit 43 is not affected by reducing the second pressure p2.

[0103]

[0110] In one embodiment, the supply of compressed dry air in the third pressure circuit 63 can also be used to blow air towards the substrate W during unloading of the substrate W. In one embodiment, the compressed dry air is also used to activate a flow controller.

[0104]

[0111] The differences between the embodiment of Figure 11 and the embodiments of Figures 9 and 10 will be particularly described below. As shown in Figure 11, in one embodiment, the vacuum chamber 47 and the separation chamber 60 can be combined. In one embodiment, the vacuum system 40 includes a fifth vacuum pressure line 51. The fifth vacuum pressure line 51 branches off from the fourth vacuum pressure line 50. The fifth vacuum pressure line 51 is for connecting the combined vacuum chamber 47 and separation chamber 60 to the first pressure circuit 43.

[0105]

[0112] As shown in FIG. 11, in one embodiment, the separation chamber 60 is downstream of the second flow controller 45 and upstream of the fifth flow controller 52 in the fourth vacuum line 50, and is fluidly connected to the fourth vacuum pressure line 50 and the fifth vacuum pressure line 51.

[0106]

[0113] As shown in FIG. 11, in one embodiment, the fourth vacuum pressure line 50 is in fluid communication with the second pressure circuit 42 and the fifth vacuum pressure line 51 is in fluid communication with the first pressure circuit 43.

[0107]

[0114] In one embodiment, the fourth vacuum pressure line 50 is configured for liquid and gas flows, and the fifth vacuum pressure line 51 is configured for gas flows. Accordingly, the fourth vacuum pressure line 50 is connected to the separation chamber 60 for inputting the two-phase flow. A downstream section of the fourth vacuum pressure line 50 is connected to the liquid outlet 62 of the separation chamber 60. The fifth vacuum pressure line 51 is connected to the gas outlet 61 of the separation chamber 60.

[0108]

[0115] 11, in one embodiment, vacuum chamber 47 includes separation chamber 60. Vacuum system 40 includes a third flow controller 48 for controlling the pressure in fifth vacuum pressure line 51. Third flow controller 48 in this embodiment operates similarly to third flow controller 48 in the embodiment of FIGS. 9 and 10. That is, third flow controller 48 includes a restriction configured to restrict continuous flow from vacuum chamber 47 to the vacuum supply of first pressure circuit 43.

[0109]

[0116] In one embodiment, at any point during unloading of the substrate W, the second pressure p2 is configured to be lower than the first pressure p1 relative to ambient pressure. This is also shown in Figure 7. Furthermore, at any point during unloading of the substrate W, the second pressure p2 is configured to decrease.

[0110]

[0117] 9 to 12, the second pressure p2 supplied by the second vacuum pressure line 41 can be temporarily reduced by switching which vacuum source is connected to the second vacuum pressure line 41. Two alternative embodiments that do not require this feature are described with reference to FIGS.

[0111]

[0118] Some of the components in the embodiment of Figures 13 and 14 are the same as components in the embodiment of Figures 9 to 12. Where this is the case, the same reference numerals are used in these figures and a detailed description will not be given.

[0112]

[0119] 13, the first pressure circuit 43 includes a first vacuum pressure line 49, a second vacuum pressure line 41, and a third vacuum pressure line 54. The second pressure circuit 42 is not required. The first pressure circuit 43 is configured to provide a deep vacuum to clamp the support table WT to the substrate table 65. Thus, in the embodiment of FIG. 13, the pressure applied between the substrate W and the support table WT can more closely resemble the pressure applied to the region between the support table WT and the substrate table 65. This differs from the examples shown in FIGS. 9 to 12, where the pressure to clamp the support table WT to the substrate table 65 is significantly less than the pressure to clamp the substrate W to the support table WT.

[0113]

[0120] During the unloading process, the seventh flow controller 59 is closed. This increases the first pressure p1 applied to the central region 21 towards ambient pressure. This increases the difference between the first pressure p1 and the second pressure p2. If this difference is large enough, at least some of the liquid in the meniscus 23 is removed. Subsequently, the first flow controller 44 is closed. This increases the second pressure p2 towards ambient pressure. The substrate W can then be lifted from the support table WT.

[0114]

[0121] 13 embodiment can follow a similar pattern to that shown in FIG. 8. However, the second vacuum pressure line 41 and the third vacuum pressure line 54 are connected to a deeper vacuum source in the first presser circuit 43. As a result, when the seventh flow controller 59 is closed, the pressure difference between the first pressure p1 and the second pressure p2 can be increased. This increased pressure difference helps to remove the meniscus 23 so that the remaining liquid on the backside of the substrate W and on the seal member 24 is reduced.

[0115]

[0122] As shown in FIG. 14 , in one embodiment, the first pressure circuit 43 includes a third vacuum pressure line 54. Therefore, during the exposure process, a deep vacuum is applied to the central region 21 as the first pressure p1. As shown in FIG. 14 , in one embodiment, a second pressure circuit 42 is provided. The second pressure 42 includes a second vacuum pressure line 41. In the embodiments shown in FIGS. 9 through 12 , the first pressure circuit 43 is configured to apply a deeper vacuum than the second pressure circuit 42. However, in the embodiment of FIG. 14 , the second pressure circuit 42 is configured to apply a vacuum of a similar depth to the first pressure circuit 43. This allows for a small pressure difference between the first pressure p1 (applied by the third vacuum pressure line 54) and the second pressure p2 (applied by the second vacuum pressure line 41) during the exposure process. A small pressure difference during the exposure process is desirable to form a seal on the seal member 24. If the pressure difference during the exposure process is too large, the liquid that forms the seal will be removed, and the seal will no longer exist.

[0116]

[0123] During the unloading process, the seventh flow controller 59 is closed so that the first pressure p1 increases. This increases the pressure difference between the first pressure p1 and the second pressure p2, thereby removing the meniscus 23. The first flow controller 44 is then closed so that the second pressure p2 increases towards ambient pressure. The substrate W can then be removed from the support table WT.

[0117]

[0124] 14, during the exposure process, both the first pressure p1 and the second pressure p2 correspond to a deep vacuum. Thus, when the seventh flow controller 59 is closed, a large pressure difference between the first pressure p1 and the second pressure p2 is created. This pressure difference can be large enough to remove the meniscus 23 and reduce the amount of liquid remaining on the substrate W and / or support table WT after the unload process.

[0118]

[0125] 16 is a graph showing pressure versus time in different regions before and during the unloading process. The lower dashed line shows the second pressure p2 in the peripheral region 22 during the unloading process. The upper dashed line shows the first pressure p1 in the central region 21 during the unloading process.

[0119]

[0126] The pressure variations shown in Figure 16 are only schematic and represent an example of how the first pressure p1 and the second pressure p2 may vary before and during the unloading process, however, the present invention is not limited to the particular form of the lines shown in Figure 16.

[0120]

[0127] As shown in Figure 16, in one embodiment, the controller 500 is adapted to increase the first pressure p1 toward ambient pressure. As shown in Figure 16, the controller 500 is further adapted to increase the second pressure p2 toward ambient pressure while increasing the first pressure p1 toward ambient pressure. In one embodiment, while increasing the first pressure p1 and the second pressure p2 toward ambient pressure, the pressure difference between the first pressure p1 and the second pressure p2 remains substantially constant.

[0121]

[0128] After the first pressure p1 and the second pressure p2 are increased toward the ambient pressure, the first pressure p1 and the second pressure p2 reach a substantially constant level, which can be called a steady state. In the steady state, the pressure difference between the first pressure p1 and the second pressure p2 is substantially equal to the pressure difference during the exposure process.

[0122]

[0129] In one embodiment, the controller 500 is adapted to reduce the second pressure p2 so as to remove at least some of the liquid retained between the substrate W and the seal member 24. This is shown in Figure 16 where the second pressure p2 is reduced at the end of the steady state value.

[0123]

[0130] This is done before removing the substrate W from the support table WT. Thus, while the substrate W remains supported on the burls of the support table WT, the second pressure p2 is reduced. At this point, i.e., before unloading the substrate W, at least some of the liquid from the liquid meniscus 23 is removed. The liquid can be removed via the second channel 27.

[0124]

[0131] In one embodiment, an overpressure is applied to the central region 21 to cause the substrate W to rise. As the substrate W rises, the shape of the substrate W is deformed to resemble an upside-down bowl. As the substrate W rises, the substrate W loses contact with the burls in the central region 21. However, the substrate W maintains contact with the support table WT at its periphery. The rise of the substrate W serves to widen the gap between the seal member 24 and the substrate W. The widened gap between the seal member 24 and the substrate W serves to remove liquid retained between the substrate W and the seal member 24. One embodiment of the present invention is expected to increase the amount of liquid that is expelled from between the substrate W and the seal member 24.

[0125]

[0132] In one embodiment, before the second pressure p2 is reduced, an overpressure is applied to the central region 21 to raise the substrate W. The second pressure p2 is reduced after increasing the gap between the seal member 24 and the substrate W. Reducing the second pressure p2 allows a greater amount of liquid to be removed from between the seal member 24 and the substrate W.

[0126]

[0133] Figure 16 shows that an overpressure is applied to the central region 21. This is shown in the highlighted oval border section of Figure 16. As shown in the highlighted oval section of Figure 16, a first pressure p1 is increased above ambient pressure. Shortly after applying the overpressure, the substrate W bulges.

[0127]

[0134] As shown in FIG. 16 , in one embodiment, when the first pressure p1 is substantially constant and the pressure difference between the first pressure p1 and the second pressure p2 is substantially equal to that during the exposure process, overpressure is applied at any time after the step of increasing the first pressure p1 toward ambient pressure. The overpressure is applied when the first pressure p1 and the second pressure p2 are in a steady state. In the steady state, the first pressure p1 and the second pressure p2 have predetermined known values. These values ​​can be controlled, as described in more detail below. Thus, when the first pressure p1 and the second pressure p2 (and their difference) have known values, overpressure is applied to the central region 21 to raise the substrate W. These known values ​​are closer to ambient pressure than the first pressure p1 and the second pressure p2 during the exposure process. In other words, the clamping pressure is significantly reduced in the steady state. When the clamping pressure is significantly reduced, overpressure is applied.

[0128]

[0135] When overpressure is applied, the substrate W will lift. As the substrate W lifts, its edge will slip on the outermost burls on the support table WT. This slippage can result in burl wear. However, this slippage occurs when the clamping pressure is significantly reduced. This significantly reduces the frictional energy that can wear the outer burls. The frictional force that can wear the burls is directly proportional to the clamping force at which slippage occurs.

[0129]

[0136] In accordance with the present invention, it is possible to control when bulging of the substrate W occurs. Bulging is believed to occur when deformation of the substrate W is complete and the shape of the substrate W no longer changes and becomes an upside-down bowl shape. One embodiment of the present invention is expected to achieve reduced wear on the outer burls of the support table WT.

[0130]

[0137] FIG. 17 is a graph showing the relationship between time and pressure in different regions during an unloading process according to a comparative example. In this comparative example, overpressure is applied to the central region 21 at any time when the pressure difference between the first pressure p1 and the second pressure p2 is increasing. Overpressure is applied to the central region 21 at any time when the second pressure p2 clamping the periphery of the substrate W is smaller compared to the embodiment shown in FIG. 16. This results in the substrate W lifting at any time when there is a greater clamping pressure than in the present invention. This means that if the edge of the substrate W slips on the outer burls of the support table WT, there is a greater force that can wear the outer burls. This is because there is a greater clamping pressure when overpressure is applied to the central region 21.

[0131]

[0138] 16, the controller 500 is adapted to increase the second pressure p2 towards ambient pressure during the unloading process. Specifically, the second pressure p2 is reduced to remove some of the liquid, and then the second pressure p2 is increased towards ambient pressure. By increasing the second pressure p2 towards ambient pressure, the clamping pressure is reduced so that the substrate W can be removed from the support table WT.

[0132]

[0139] Figure 18 shows a schematic diagram of a vacuum system 40 according to one embodiment of the present invention. The vacuum system 40 shown in Figure 18 can be used to implement the pressure sequence described above (the pressure sequence shown in Figure 16).

[0133]

[0140] The vacuum system 40 is for the support table WT to hold the substrate W. The vacuum system 40 comprises a flow circuit including a first pressure circuit 43. The first pressure circuit 43 includes a first vacuum pressure line 49. The first vacuum pressure line 49 is for clamping the support table WT to the substrate table 65.

[0134]

[0141] In one embodiment, the flow circuit of the vacuum system 40 comprises a second pressure circuit 42. The second pressure circuit 42 includes a second vacuum pressure line 41 and a third vacuum pressure line 54. The third vacuum pressure line 54 is configured to apply a first pressure p1 to the central region 21 to clamp the substrate W to the support table WT. The second vacuum pressure line 41 is connected to the second channel 27 to apply a second pressure p2 to the peripheral region 22.

[0135]

[0142] Some of the components in the embodiment of Figures 18 to 22 are the same as components in the embodiment of Figures 9 to 14. Where this is the case, the same reference numbers are used in these figures and a detailed description will not be given.

[0136]

[0143] 18 , in one embodiment, the vacuum system 40 includes a sixth flow controller 56. The second vacuum pressure line 41 is connected to the third vacuum pressure line 54 via the sixth flow controller 56. The sixth flow controller 56 is configured to control the flow between the second vacuum pressure line 41 and the third vacuum pressure line 54.

[0137]

[0144] The first ambient pressure line 57 provides flow from ambient pressure to the third vacuum pressure line 54. The sixth flow controller 56 is configured to restrict flow from ambient pressure to the second vacuum pressure line 41, which helps to maintain a pressure difference between the second vacuum pressure line 41 and the third vacuum pressure line 54. By maintaining a pressure difference (i.e., a small pressure difference) between the second vacuum pressure line 41 and the third vacuum pressure line 54, liquid can be retained between the seal member 24 and the substrate W. Alternatively, if a small pressure difference cannot be maintained between the second vacuum pressure line 41 and the third vacuum pressure line 54, liquid may be removed unnecessarily, increasing the risk of breaking the seal, for example, during an exposure process.

[0138]

[0145] 18 , in one embodiment, vacuum system 40 includes a second ambient pressure line 81. Second ambient pressure line 81 fluidly connects second vacuum pressure line 41 to ambient pressure. An eighth flow controller 82 is configured to control flow from ambient pressure to second vacuum pressure line 41. For example, in one embodiment, eighth flow controller 82 is a restriction configured to restrict flow.

[0139]

[0146] In one embodiment, the vacuum system 40 includes a ninth flow controller 83. The ninth flow controller 83 is a valve that can be opened and closed. During the exposure process, the ninth flow controller 83 is closed. However, the ninth flow controller 83 is opened for the unloading process.

[0140]

[0147] As described above and shown in FIG. 16, before unloading the substrate W, both the first pressure p1 and the second pressure p2 are increased toward ambient pressure (i.e., a small pressure difference between the first pressure p1 and the second pressure p2 is maintained). The first pressure p1 and the second pressure p2 are increased to their steady-state values. This is achieved by opening the ninth flow controller 83. When the ninth flow controller 83 is opened, the second vacuum pressure line 41 is connected to ambient pressure along the second ambient pressure line 81 via the eighth flow controller 82. This allows flow from ambient pressure to the second vacuum pressure line 41. This increases the second pressure p2. Simultaneously, the pressure increase in the second vacuum pressure line 41 increases the pressure in the third vacuum pressure line 54 so that the first pressure p1 increases at the same rate.

[0141]

[0148] With the ninth flow controller 83 open, the first pressure p1 and the second pressure p2 continue to increase toward ambient pressure until they reach a steady-state value. The steady-state value depends on the configuration of the eighth flow controller 82. The greater the flow that the eighth flow controller 82 allows from ambient pressure to the second vacuum pressure line 41, the closer the steady-state value will be to ambient pressure. Therefore, the steady-state values ​​of the first pressure p1 and the second pressure p2 can be controlled by selecting the size of the orifice in the restriction of the eighth flow controller 82. In one embodiment, the steady-state value of the first pressure p1 is in the range of about 1 kPa to about 20 kPa below ambient pressure. Optionally, the steady-state value of the first pressure p1 is in the range of about 5 kPa to about 10 kPa below ambient pressure.

[0142]

[0149] As shown in Figure 18, the vacuum system 40 is equipped with a bleed (i.e., second ambient pressure line 81 with eighth flow controller 82) with a valve (i.e., ninth flow controller 83). In normal clamping operation, the bleed is closed (by ensuring the ninth flow controller 83 is closed) to fully clamp the substrate W. During unloading of the substrate W, the bleed is opened (by opening the ninth flow controller 83) to reduce the clamping pressure on the substrate W. Once the steady-state reduced clamping pressure is achieved, an overpressure is applied to the central region 21 so that the substrate W rises. While the clamping at the edge of the substrate W is at a steady-state reduced level, the edge of the substrate W slides on the outer burls. This reduces the frictional energy of the outer burls.

[0143]

[0150] As will be appreciated, the above-described features can be used with other embodiments. For example, FIG. 16 shows the second pressure p2 being reduced to approximately the same level as during the exposure operation (i.e., the leftmost side of the graph in FIG. 16). However, the second pressure p2 may also be reduced to a lower level than during the exposure process. This helps remove liquid from between the seal member 24 and the substrate W. This can be achieved using a vacuum system 40, for example, as shown in any of FIGS. 19-22.

[0144]

[0151] FIG. 19 schematically illustrates the vacuum system 40 in which the second ambient pressure line 81, the eighth flow controller 82, and the ninth flow controller 83 are applied to the vacuum system 40 shown in FIG. 9 . The ninth flow controller 83 is opened to increase the first pressure p1 and the second pressure p2 to their steady-state values ​​(i.e., reduced clamping pressure). Overpressure is then applied to the central region 21 to deform the substrate W and form a raised shape. Once the raised shape is achieved, the second flow controller 45 is opened to reduce the second pressure p2 to a level lower than that during the exposure process. Once the raised shape is achieved, the third vacuum pressure line 54 is disconnected from the second vacuum pressure line 41. For example, the sixth flow controller 56 may be closed. The sixth flow controller 56 may be a variable restriction.

[0145]

[0152] 20 schematically illustrates the vacuum system 40 in which the second ambient pressure line 81, the eighth flow controller 82, and the ninth flow controller 83 are applied to the vacuum system 40 shown in FIG. 10. The ninth flow controller 83 is opened to increase the first pressure p1 and the second pressure p2 to their steady-state values ​​(i.e., reduced clamping pressures). An overpressure is then applied to the central region 21 to deform the substrate W and form a raised shape. Once raised, the second flow controller 45 is opened to reduce the second pressure p2 to a level lower than that during the exposure process.

[0146]

[0153] 21 schematically illustrates the vacuum system 40 in which the second ambient pressure line 81, the eighth flow controller 82, and the ninth flow controller 83 are applied to the vacuum system 40 shown in FIG. 11. The ninth flow controller 83 is opened to increase the first pressure p1 and the second pressure p2 to their steady-state values ​​(i.e., reduced clamping pressures). An overpressure is then applied to the central region 21 to deform the substrate W and form a raised shape. Once raised, the second flow controller 45 is opened to reduce the second pressure p2 to a level lower than during the exposure process.

[0147]

[0154] 22 schematically illustrates the vacuum system 40 in which the second ambient pressure line 81, the eighth flow controller 82, and the ninth flow controller 83 are applied to the vacuum system 40 shown in FIG. 12. The ninth flow controller 83 is opened to increase the first pressure p1 and the second pressure p2 to their steady-state values ​​(i.e., reduced clamping pressures). An overpressure is then applied to the central region 21 to deform the substrate W and form a raised shape. Once raised, the second flow controller 45 is opened to reduce the second pressure p2 to a level lower than during the exposure process.

[0148]

[0155] As will be appreciated, any of the features described above can be used with any other feature, and the present application encompasses more than just the combinations explicitly described. For example, one embodiment of the present invention could be applied to the example of FIG.

[0149]

[0156] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that lithographic apparatus herein may have other applications in the manufacture of microscale or nanoscale components or 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.

[0150]

[0157] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it will be recognized that such descriptions are merely for convenience and that such actions actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., and that in doing so, actuators or other devices may interact with the physical world.

[0151]

[0158] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. 1. A method for unloading an object from a support table during an unloading process, comprising the steps of: applying a first pressure to a central region of the support table beneath a central portion of the object; the object is clamped to the support table by applying a second pressure to a peripheral region of the support table beneath a periphery of the object, and during clamping, the first pressure and the second pressure are controlled to maintain liquid between the object and a seal member, the seal member being positioned radially on an upper surface of the support table between the central region and the peripheral region and protruding towards the object, the method further comprising: increasing the first pressure toward ambient pressure; removing at least a portion of the liquid retained between the object and the seal member by reducing the second pressure; increasing the second pressure toward the ambient pressure; A method comprising:

2. The method of claim 1 , wherein the step of removing at least a portion of the liquid comprises reducing the second pressure below that during the exposure process.

3. 3. The method of claim 1 or 2, wherein an overpressure is applied to the central region to raise the object before reducing the second pressure.

4. 4. The method of claim 3, wherein the overpressure is applied any time after the step of increasing the first pressure toward ambient pressure when the first pressure is substantially constant and the pressure difference between the first pressure and the second pressure is substantially equal to that during the exposure process.

5. A support table for holding an object, comprising: a first channel for applying a first pressure to a central region beneath a central portion of the object; a second channel for applying a second pressure to a peripheral region underlying the periphery of the object; a seal member positioned radially on the upper surface of the support table between the first channel and the second channel and protruding toward the object; a support table including: a controller, controlling the application of the first pressure and the second pressure during the exposure process such that liquid is maintained between the object and the seal member during the exposure process; increasing the first pressure toward ambient pressure; reducing the second pressure to remove at least a portion of the liquid retained between the object and the seal member; increasing the second pressure toward the ambient pressure during an unloading process; a controller adapted to 1. A lithographic apparatus comprising:

6. 1. A vacuum system for a substrate table and a support table of a lithographic apparatus, the support table for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit including a first vacuum pressure line configured to clamp the support table to the substrate table; a second pressure circuit, a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table beneath a periphery of the object; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table; a vacuum device configured to apply pressure to the second pressure circuit; a fourth vacuum pressure line branching from the second pressure circuit; and a second pressure circuit including: a first flow controller for controlling the pressure in the second vacuum pressure line; a second flow controller for controlling the pressure in the fourth vacuum pressure line; A vacuum system comprising:

7. The vacuum system of claim 6 further comprising a separation chamber for separating two-phase flow in the second pressure circuit.

8. 8. The vacuum system of claim 6 or 7, wherein the vacuum device includes a vacuum chamber upstream of a third flow controller in the fourth vacuum pressure line.

9. The vacuum system of claim 8 , wherein the fourth vacuum pressure line is in fluid communication with the first pressure circuit.

10. 8. The vacuum system of claim 6 or 7, wherein the vacuum device comprises a venturi pump.

11. 1. A vacuum system for a substrate table and a support table of a lithographic apparatus, the support table for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit, a first vacuum pressure line configured to clamp the support table to the substrate table; a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table beneath a periphery of the object; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table; a first pressure circuit including: a flow controller for controlling the pressure in the second vacuum pressure line; another flow controller for controlling flow from ambient pressure to the third vacuum pressure line; A vacuum system comprising:

12. 1. A vacuum system for a substrate table and a support table of a lithographic apparatus, the support table for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit, a first vacuum pressure line configured to clamp the support table to the substrate table; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table; a first pressure circuit including: a second pressure circuit including a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table underlying a periphery of the object; a flow controller for controlling the pressure in the second vacuum pressure line; another flow controller for controlling the pressure in the third vacuum pressure line; A vacuum system comprising:

13. 1. A vacuum system for a substrate table and a support table of a lithographic apparatus, the support table for holding an object, the vacuum system comprising a flow circuit, the flow circuit comprising: a first pressure circuit, a first pressure circuit including a first vacuum pressure line configured to clamp the support table to the substrate table; a second pressure circuit, a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table beneath a periphery of the object; a third vacuum pressure line configured to apply a first pressure to a central region of the support table beneath a central portion of the object to clamp the object to the support table, the third vacuum pressure line connected to the second vacuum pressure line through a flow controller to maintain a predetermined pressure differential between the second vacuum pressure line and the third vacuum pressure line; a second pressure circuit including: another flow controller for controlling flow from ambient pressure to the second vacuum pressure line; A vacuum system comprising:

14. A positioner for positioning a support table of a lithographic apparatus, the positioner comprising a vacuum system according to any one of claims 6 to 13.

15. A lithographic apparatus comprising a positioner according to claim 14.

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