Method for unloading an object from a support table

Abstract

To provide a method of unloading an object from a support table during an unloading process.SOLUTION: An object is clamped to a support table during an exposure process 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 No. 17174583.9 filed on June 6, 2017 and No. 18152220.2 filed on January 18, 2018. These are hereby incorporated by reference in their entirety into this application.

[0002]

[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 Art

[0003]

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

[0004]

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

[0005]

[0005] To enable the improvement of the resolution of smaller features, an immersion technique has been introduced into the lithography system. In an immersion lithography apparatus, a liquid layer of an immersion liquid having a relatively high refractive index is placed in the space between the projection system of the apparatus (through which the patterned beam passes and is projected towards the substrate) and the substrate. The immersion liquid finally covers a part of the substrate under the final element of the projection system. Therefore, at least a part of the substrate on which exposure is performed is immersed in the liquid. The effect of the immersion liquid is that the imaging wavelength of the exposure radiation is shorter in the immersion liquid than in air, enabling the miniaturization of the features to be imaged. (It is also considered that the effect of the liquid is to increase the numerical aperture (NA) of the system and to increase the depth of focus.)

[0006]

[0006] In immersion lithography for the market, the immersion liquid is water. Usually, this water is high-purity distilled water such as ultrapure water (UPW) commonly used in semiconductor manufacturing factories. In the immersion system, the UPW is often purified and an additional heat step may be performed before it is supplied to the space as the immersion liquid. In addition to water, other liquids having a high refractive index can be used as the immersion liquid. Examples thereof include hydrocarbons such as fluorinated hydrocarbons and / or aqueous solutions. Furthermore, other fluids other than liquids are also envisioned for use in immersion lithography.

[0007]

[0007] The description in this specification refers to local immersion that confines the immersion liquid in the space between the final element and the surface facing the final element during use. The opposing surface is the surface of the substrate or the surface of a support table (or substrate support) that is on the same plane as the surface of the substrate. (It should be noted that when referring to the surface of the substrate in the following documents, unless otherwise specified, this also refers to the surface of the substrate support in addition to or instead of this, and vice versa.) The immersion liquid is confined in the space using a fluid handling structure existing between the projection system and the stage. The space filled with the immersion liquid is smaller than the upper surface of the substrate in plan view, and this space is maintained substantially stationary with respect to the projection system while the substrate and the substrate stage are moving below.

[0008]

[0008] Other immersion systems such as non-confined immersion systems (so-called "All Wet" immersion systems) and bath-type immersion systems are also envisioned. In a non-confined immersion system, the immersion liquid covers an area wider than the surface under the final element. The liquid outside the space exists as a thin liquid film. The immersion liquid covers the entire surface of the substrate or covers the substrate and the support table on the same plane as this substrate. In a bath-type system, the substrate is completely immersed in the immersion liquid bath.

[0009]

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

[0010]

[0010] The fluid handling structure can have various selected functions. Each function is obtained from a corresponding feature that enables the fluid handling structure to achieve that function. The fluid handling structure may be referred to by many different terms each representing a function, such as a barrier member, a seal member, a fluid supply system, a fluid removal system, a liquid confinement structure, etc.

[0011]

[0010] The fluid handling structure as a barrier member is a barrier against the flow of the 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 include an additional gas flow from the opening of the surface of the seal member such as a gas knife.

[0012]

[0011] In a liquid immersion apparatus, a liquid (e.g., water) meniscus is stabilized on a seal between the back side of a substrate and the upper part of a support table. When removing the substrate from the support table, a part of this liquid may remain on the substrate and on the support table. It is desirable to reduce the amount of liquid remaining on the substrate and / or on the support table when removing the substrate from the support table.

Summary of the Invention

[0013]

[0012] According to one aspect of the present invention, a method of unloading an object from a support table during an unloading process is provided. During an exposure process, applying a first pressure to a central region of the support table under the central part of the object, by applying a second pressure to a peripheral region of the support table under the peripheral part of the object, the object is clamped to the support table, and during the clamping, the first pressure and the second pressure are controlled such that a liquid is held between the object and a seal member, the seal member being positioned radially between the central region and the peripheral region on the upper surface of the support table and protruding towards the object, the method comprising: increasing the first pressure towards the ambient pressure, removing at least a part of the liquid held between the object and the seal member by reducing the second pressure, increasing the second pressure towards the ambient pressure, and.

[0014]

[0013] According to one aspect of the present invention, a lithographic apparatus is provided. This lithographic apparatus is a support table for holding an object, a first channel for applying a first pressure to a central region under the central part of the object, a second channel for applying a second pressure to a peripheral region under the peripheral part of the object, A seal member positioned radially between a first channel and a second channel on the upper surface of the support table and protruding towards the object, A support table including A controller, Controlling to apply a first pressure and a second pressure during the exposure process so that a liquid is retained between the object and the seal member during the exposure process, Increasing the first pressure towards the ambient pressure, Reducing the second pressure so as to remove at least a part of the liquid retained between the object and the seal member, Increasing the second pressure towards the ambient pressure during the unload process, A controller adapted as such, Comprising.

[0015]

[0014] According to one aspect of the present invention, a vacuum system for a substrate table and a support table of a lithographic apparatus is provided. The support table is for holding an object, and the vacuum system includes a flow circuit, and the flow circuit includes 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 under the peripheral portion of the object, A third vacuum pressure line configured to apply a first pressure to a central region of the support table under the central portion of the object so as 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, The 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, Comprising.

[0016]

[0015] According to one aspect of the invention, a vacuum system for a substrate table and a support table of a lithographic apparatus is provided. The support table is for holding an object, and the vacuum system includes a flow circuit, the flow circuit comprising a first pressure circuit comprising 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 under a peripheral portion of the object, a third vacuum pressure line configured to apply a first pressure to a central region of the support table under a central portion of the object so as to clamp the object to the support table, and a first flow controller for controlling the pressure in the second vacuum pressure line, and a fourth flow controller for controlling the flow from the ambient pressure to the third vacuum pressure line.

[0017]

[0016] According to one aspect of the invention, a vacuum system for a substrate table and a support table of a lithographic apparatus is provided. The support table is for holding an object, and the vacuum system includes a flow circuit, the flow circuit comprising a first pressure circuit comprising 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 under a central portion of the object so as to clamp the object to the support table, and a second pressure circuit comprising a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table under a peripheral portion of the object, and 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, is provided.

[0018]

[0017] A vacuum system for a substrate table and a support table of a lithographic apparatus, wherein the support table is for holding an object, the vacuum system includes a flow circuit, and the flow circuit includes 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 under a peripheral portion of the object, a third vacuum pressure line configured to apply a first pressure to a central region of the support table under a central portion of the object so as to clamp the object to the support table, the third vacuum pressure line being connected to the second vacuum pressure line via a flow controller for maintaining a predetermined pressure difference between the second vacuum pressure line and the third vacuum pressure line, a second pressure circuit including another flow controller for controlling the flow from the ambient pressure to the second vacuum pressure line, A vacuum system comprising.

Brief Description of the Drawings

[0019]

[0018] Hereinafter, embodiments of the present invention will be described as an example with reference to the attached schematic diagrams. In the attached drawings, corresponding reference numerals indicate corresponding parts.

[0020]

Figure 1

[0019] A lithographic apparatus according to an embodiment of the present invention is shown.

Figure 2

[0020] A liquid supply system for use in a lithographic projection apparatus is shown.

Figure 3

[0021] It is a side sectional view showing another liquid supply system according to an embodiment.

Figure 4

[0022] A substrate supported on a support table is schematically shown according to an embodiment of the present invention.

Figure 5

[0023] A liquid meniscus fixed between the substrate shown in FIG. 4 and the support table is schematically shown in close-up.

Figure 6

[0024] What can happen to the liquid meniscus when the substrate is removed from the support table is schematically shown in close-up.

Figure 7

[0025] It is a graph showing the relationship between time and pressure in different regions during an unloading process according to an embodiment of the present invention.

Figure 8

[0026] It is a graph showing the relationship between time and pressure in different regions according to a comparative example.

Figure 9

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

Figure 10

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

Figure 11

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

Figure 12

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

Figure 13

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

Figure 14

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

Figure 15

[0028] A side sectional view of a substrate supported on a support table according to an embodiment of the present invention is schematically shown.

Figure 16

[0029] A graph showing the relationship between time and pressure in different regions during the unload process according to an embodiment of the present invention.

Figure 17

[0030] A graph showing the relationship between time and pressure in different regions according to a comparative example.

Figure 18

[0031] Schematically shows a diagram of a vacuum system according to an embodiment of the present invention.

Figure 19

[0031] Schematically shows a diagram of a vacuum system according to an embodiment of the present invention.

Figure 20

[0031] Schematically shows a diagram of a vacuum system according to an embodiment of the present invention.

Figure 21

[0031] Schematically shows a diagram of a vacuum system according to an embodiment of the present invention.

Figure 22

[0031] Schematically shows a diagram of a vacuum system according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0021]

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

[0022]

[0033] The term "reticle", "mask", or "patterning device" can be broadly interpreted, when used in this context, to refer to a general-purpose patterning device that can be used to provide a patterned cross-section to an incoming radiation beam corresponding to a pattern generated on a target portion of a substrate. Also, the term "light valve" can be used in this context. Examples of such patterning devices other than classical masks (transmission or reflection masks, binary masks, phase shift masks, hybrid masks, etc.) include programmable mirror arrays and / or programmable LCD arrays.

[0023]

[0034] Figure 1 schematically shows a lithographic apparatus. The apparatus comprises the following. 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., a mask table) MT connected to a first positioner PM configured to support a patterning device (e.g., a mask) MA and to accurately position the patterning device MA in accordance with certain parameters. c. A support table, 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, connected to a second positioner PW configured to accurately position the surface of a table, such as the substrate W, in accordance with certain parameters. 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., including one or more dies) of the substrate W.

[0024]

[0035] During operation, the illumination system IL receives a radiation beam or radiation from a radiation source SO, e.g., via a beam delivery system BD. The illumination system IL can 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. Using the illuminator IL, the radiation beam B can be adjusted to have a desired spatial and angular intensity distribution in a cross-section at the plane of the patterning device MA.

[0025]

[0036] As used herein, the term "projection system" PS should be construed broadly to include various types of projection systems, such as refractive optical systems, reflective optical systems, catadioptric optical systems, anamorphic optical systems, magneto-optical systems, electro-magneto-optical systems, and / or electro-static optical systems, or any combination thereof, as appropriate in accordance with the radiation used and / or other factors such as the use of immersion liquid or the use of a vacuum. When the term "projection lens" is used herein, this can be regarded as synonymous with the more general term "projection system".

[0026]

[0037] A lithographic apparatus can be of a type having two or more support tables, for example, a combination of two or more support tables, or one or more support tables and one or more cleaning tables, sensor tables, or measurement tables. For example, a lithographic apparatus can be a multi-stage apparatus comprising two or more tables positioned on the exposure side of the projection system, each table comprising and / or holding one or more objects. In one example, one or more of the tables can hold a radiation-sensitive substrate. In one example, one or more of the tables can hold a sensor for measuring radiation from the projection system. In one example, the multi-stage apparatus comprises a first table (i.e., a support table) configured to hold a radiation-sensitive substrate and a second table not configured to hold a radiation-sensitive substrate (hereinafter generally referred to as a measurement table, a sensor table, and / or a cleaning table). The second table can comprise and / or hold one or more objects other than the radiation-sensitive substrate. Such one or more objects can include one or more selected from a sensor for measuring 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] During operation, the radiation beam B is incident on the pattern (design layout) present on the patterning device MA held on the support structure MT and is patterned by the patterning device MA. The radiation beam B passing through the patterning device MA passes through the projection system PS, and the projection system PS focuses the beam on the target portion C of the substrate W. Using the second positioner PW and the position sensor IF (for example, an interference device, a linear encoder, a 2D encoder, or a capacitive sensor), the support table W can be accurately moved, for example, to position various target portions C at the focused and aligned positions in the path of the radiation beam B. Similarly, using the first positioner PM and another position sensor (not explicitly shown in FIG. 1), the patterning device MA can be accurately positioned with respect to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using the patterning device mask alignment marks M1, M2 and the substrate alignment marks P0, P1. The illustrated substrate alignment marks M1, M2 occupy dedicated target portions, but they can also be positioned in the space between the target portions C (known as scribe line alignment marks).

[0028]

[0039] FIG. 2 schematically shows a local liquid supply system or a fluid handling system. The liquid supply system is provided with a fluid handling structure IH (or a fluid confinement structure) extending along at least a part of the boundary of the space 11 between the final element of the projection system PS and the support table WT or the substrate W. The fluid handling structure IH is substantially stationary with respect to the projection system PS in the XY plane, but some relative movement can occur in the Z direction (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, which may be a non-contact seal such as a gas seal (such a system having a gas seal is disclosed in European Patent No. 1,420,298) or a liquid seal.

[0029]

[0040] The immersion liquid handling structure IH at least partially confines the immersion liquid within the space 11 between the final element of the projection system PS and the substrate W. The space 11 is at least partially formed by an immersion liquid handling structure IH positioned below and surrounding the final element of the projection system PS. The immersion liquid is introduced into the space 11 within the immersion liquid handling structure IH below the projection system PS through one of the liquid openings 13. The immersion liquid can also be removed through another one of the liquid openings 13. The immersion liquid may be introduced into the space 11 through at least two liquid openings 13. Which of the liquid openings 13 to use for supplying the immersion liquid and optionally which of the liquid openings 13 to use for removing the immersion liquid can be determined according to the moving direction of the support table WT.

[0030]

[0041] During use, the immersion liquid can be confined within the space 11 by a non-contact seal such as a gas seal 16 formed by the gas formed between the bottom of the immersion liquid handling structure IH and the surface of the substrate W. The gas within the gas seal 16 is provided under pressure through the inlet 15 into the gap between the immersion liquid handling structure IH and the substrate W. The gas is withdrawn through the outlet 14. The overpressure of the gas inlet 15, the vacuum level of the outlet 14, and the geometry of the gap are configured such that a high-speed gas flow towards the inside for confining the immersion liquid is generated. Such a system is disclosed in U.S. Patent No. 2004 / 0207824 (which is hereby incorporated by reference in its entirety). In one example, the immersion liquid handling structure IH does not have a gas seal 16.

[0031]

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

[0032]

[0043] The fluid handling structure IH confines the immersion liquid at least partially within the space 11 between the final element of the projection system PS and the substrate W. The space 11 is at least partially formed by a fluid handling structure IH positioned below and surrounding the final element of the projection system PS. In one example, the fluid handling structure IH includes a body member 53 and a porous member 33. The porous member 33 is plate-shaped and has a plurality of holes (i.e., openings or pores). In one embodiment, the porous member 33 is a mesh plate, and a large number of small holes 84 are formed in a mesh pattern. Such a system is disclosed in U.S. Patent No. 2010 / 0045949A1, which is hereby incorporated by reference in its entirety into the present application.

[0033]

[0044] The body member 53 includes a supply port 72 capable of supplying the immersion liquid to the space 11 and a recovery port 73 capable of recovering the immersion liquid from the space 11. The supply port 72 is connected to a liquid supply device 75 via a passage 74. The liquid supply device 75 can supply the immersion liquid to the supply port 72 via the corresponding passage 74. The recovery port 73 can recover the immersion liquid from the space 11. The recovery port 73 is connected to a liquid recovery device 80 via a passage 79. The liquid recovery device 80 recovers the immersion liquid recovered via the recovery port 73 through the passage 29. The porous member 33 is disposed at the recovery port 73. By performing a liquid supply operation using the supply port 72 and a liquid recovery operation using the porous member 33, the space 11 is formed on one side between the projection system PS and the fluid handling structure IH and on the other side between the substrate W.

[0034]

[0045] FIG. 4 schematically shows a cross-section of the substrate W supported on the support table WT. Hereinafter, the present 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 present invention is not limited to the situation where the substrate W is supported on the support table WT. For example, the present invention is applicable to a patterning device MA supported by a support structure MT.

[0035]

[0046] As shown in FIG. 4, the substrate W is supported by a support table WT. During use of the lithographic apparatus, the substrate W can be clamped to the support table WT. For example, during the 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 FIG. 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 under a central portion WC of the substrate W. As shown in FIG. 4, in one embodiment, the first channel 26 is provided so as to penetrate 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. Since the first pressure p1 is smaller 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. The second channel 27 is for applying a second pressure p2 to a peripheral region 22 of the support table WT under a peripheral portion WP of the substrate W. The second channel 27 is radially outside the first channel 26. In one embodiment, the second channel 27 is provided so as to penetrate 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 that radially surrounds 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 between a first channel 26 and a second channel 27 in the radial direction. The seal member 24 is positioned on the upper 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, when the substrate W is clamped to the support table WT, the seal member 24 does not come into direct contact with the substrate W. There is a small gap between the upper portion of the seal member 24 and the back side 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, when the substrate W is clamped to the support table WT, the outer seal member 25 does not come into direct contact with the substrate W. There is a small gap between the upper portion of the outer seal member 25 and the back side of the substrate W.

[0040]

[0051] During the exposure process, fluid is extracted from the peripheral region 22 through the second channel 27. The second pressure p2 applied by the second channel 27 further promotes clamping of the substrate W to the support table WT. The fluid flow through the second channel 27 helps to reduce the amount of immersion liquid reaching the back side 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 fixed on the seal member 24 between the upper portion of the seal member 24 and the bottom of the substrate W. The liquid meniscus 23 is immobilized based on capillary pressure. The first pressure p1 and the second pressure p2 are controlled such that the difference between these pressures is smaller than the capillary pressure on the seal member 24 (i.e., smaller than the force required to remove the liquid meniscus 23 from the seal member 24).

[0042]

[0053] As described above, the first channel 26 and the second channel 27 are connected to one or more pressure circuits forming part of a vacuum system 40, which will be described in more detail below. In one embodiment, the vacuum system 40 (i.e., the vacuum supply) is configured such that the pressure difference 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 region away from the seal member 24). For this reason, as shown in FIG. 5, the liquid meniscus 23 is fixed at the seal. FIG. 5 is a close-up of the liquid meniscus 23 fixed at the seal member 24 of the support table WT.

[0044]

[0055] During the exposure process, the seal member 24 is wet because the liquid meniscus 23 is present. When the substrate W is unloaded (i.e., removed) from the support table WT, a part of the liquid from the liquid meniscus 23 may remain on the substrate W, and a part of the liquid of 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 on the seal member 24 while maintaining contact with the substrate W.

[0045]

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

[0046]

[0057] FIG. 6 shows the liquid from the liquid meniscus 23 that remains on the substrate W and remains 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 before unloading the substrate W, a large pressure difference is generated on the seal member 24 by increasing the vacuum level in the peripheral region 22. This will be described in more detail below.

[0048]

[0059] In one embodiment, the controller 500 is adapted to control the application of the first pressure p1 and the second pressure p2 during the exposure process such that a liquid is held between the substrate W and the seal member 24 during the exposure process. This is the situation shown in FIG. 5. The function of the controller 500 immediately before and during the unloading process will be described below.

[0049]

[0060] FIG. 7 is a graph showing the relationship between time and pressure in different regions before and during the execution of the unloading process. The lower line formed by the dashed-dotted line indicates the second pressure p2 in the peripheral region 22 during the execution of the unloading process. The upper line formed by the broken line represents the first pressure p1 in the central region 21 during the execution of the unloading process.

[0050]

[0061] The pressure fluctuations shown in FIG. 7 represent merely an example of how the first pressure p1 and the second pressure p2 vary before and during the execution of the unloading process. However, the present invention is not limited to the specific form of lines as shown in FIG. 7.

[0051]

[0062] As shown in FIG. 7, in one embodiment, the controller 500 is adapted to increase the first pressure p1 towards the ambient pressure. This is shown in the central time region (out of the three time periods) shown in FIG. 7.

[0052]

[0063] In one embodiment, the controller 500 is adapted to reduce the second pressure p2 such that at least a portion of the liquid held between the substrate W and the seal member 24 is removed. This is shown in FIG. 7 at the start of the central time period during which the second pressure p2 decreases.

[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 periphery of the support table WT. At this point (i.e., before the substrate W is unloaded), at least a portion 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 the ambient pressure during the unloading process. This is shown in the second half of the central time period and the right - hand time period shown in FIG. 7. Specifically, the second pressure p2 is increased towards the ambient pressure after reaching its minimum value. By increasing the second pressure p2 towards the 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 part of the liquid before the unloading process, the amount of liquid remaining on the back side of the substrate W after the unloading process is reduced. This reduces the undesirable problems that may occur when processing the unloaded substrate W later. For example, liquid residues on the back side of the unloaded substrate W may generate capillary forces, and as a result, scratches may occur on the substrate W. This degrades the quality of the substrate W. Specifically, some substrates W may be reused, which means that after unloading the substrate W from the support table WT, the unloaded substrate W needs to be clamped again to the same support table (or a different support table) WT later. The closing substrate is an example of such a substrate W. It is undesirable for such reusable substrate W to have liquid residues that can cause scratches, for example.

[0056]

[0067] By removing at least a part of the liquid before the unloading process, the amount of liquid remaining in contact with the seal member 24 and / or the outer seal 25 is reduced. This reduces the possibility that the substrate W will adhere unnecessarily to any specific position on the support table WT later. Also, this reduces the risk that some liquid will accidentally move to the grid used for measurement. Also, this reduces the amount of liquid that may evaporate when loading the next substrate W. When evaporation occurs, a cold spot is generated, and for this reason, the support table WT is deformed unnecessarily. Also, this reduces the amount of contamination transmitted on the support table WT.

[0057]

[0068] As described above, immediately before unloading the substrate W, a large pressure difference is generated on 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 discharge the liquid meniscus 23 during the sequence of unloading the substrate W. First, while a vacuum is maintained in the peripheral region 22, gas can be blown into the central region 21. This increases the pressure difference between the first pressure p1 and the second pressure p2 to be greater than the capillary pressure on the seal member 24. As a result, the liquid meniscus 23 is removed from the seal member 24. Thereafter, the vacuum for the second pressure p2 can be switched off so that the second pressure p2 increases and the substrate W can be released.

[0059]

[0070] An embodiment of the present invention is expected to achieve an improvement over this comparative example. Specifically stated, an embodiment of the present invention is expected to reduce the wear of the burr at the edge of the support table WT.

[0060]

[0071] This is because when an overpressure is applied under the central portion WC of the substrate W while maintaining the second pressure p2 under the peripheral portion WP of the substrate W, the substrate W bends into an umbrella shape. The edge of the substrate W slides on the burr at the edge of the substrate W. This wears the burr.

[0061]

[0072] An embodiment of the present invention is expected to achieve a reduction in the bending of the substrate W. In one embodiment of the present invention, no overpressure (i.e., increasing the first pressure p1 to be greater than the ambient pressure) is applied under the central portion WP of the substrate W. Therefore, the wear of the burr due to the 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 the ambient pressure. FIG. 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 FIG. 8, the lower line indicates the second pressure p2 and the upper line indicates the first pressure p1.

[0063]

[0074] The sequences shown in FIGS. 7 and 8 do not apply an overpressure under the central portion C of the substrate W until the vacuum applied under the peripheral portion WP of the substrate W is significantly reduced. FIGS. 7 and 8 show that the first pressure p1 can be increased to be greater than the ambient pressure at the final stage of unloading. Due to the overpressure, the substrate W deforms into an umbrella shape. As a result, the substrate W may slide on the outer burr. However, when the first pressure p1 is greater than the ambient pressure, the second pressure p2 is very close to the ambient pressure, so the vertical force applied to the burr by this sliding is minimized. As a result, the wear of the burr at the edge of the support table WT is reduced. However, in the sequence shown in FIG. 8, an undesirable amount of liquid remains on the substrate W and / or the support table WT from the liquid meniscus 23.

[0064]

[0075] One embodiment of the present invention is expected to achieve an improvement over the above-described comparative example. Specifically, one embodiment of the present invention is expected to reduce the amount of liquid returning onto the seal member 24 while avoiding bending at the edge of the substrate W during the unloading process.

[0065]

[0076] Specifically, in the sequence shown in FIG. 8, as soon as the second pressure p2 is increased, the liquid returns onto the seal member 24. As a result, the seal member 24 remains wet, so that the next substrate W adheres to the support table WT unnecessarily.

[0066]

[0077] As shown in FIG. 7, in one embodiment, the controller 500 is adapted to increase the first pressure p1 while reducing the second pressure p2 to remove at least a portion of the liquid held between the substrate W and the seal member 24. This is shown at the start of the central time period in FIG. 7. The second pressure p2 is reduced while the first pressure p1 is increased. As a result, the pressure difference between the first pressure p1 and the second pressure p2 increases more rapidly, whereby the liquid meniscus 23 is removed more rapidly. This means that the substrate W can be unloaded from the support table WT more rapidly, which can increase throughput.

[0067]

[0078] As shown in FIG. 7, in one embodiment, the second pressure p2 reaches the ambient pressure level (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 with respect to the ambient pressure during the unloading process. Thus, throughout the unloading process, the liquid is moved from the central region 21 towards the second channel 27. As a result, the liquid in the vicinity of the seal member 24 is moved away from the central region 21. For example, by removing the liquid through the second channel 27, the amount of liquid remaining on the support table WT after the completion of the unloading process can be reduced.

[0068]

[0079] Each of FIGS. 9 to 12 schematically shows a vacuum system 40 according to an embodiment of the present invention. The pressure sequence (e.g., the pressure sequence shown in FIG. 7) described above can be implemented using the vacuum system 40 shown in FIGS. 9 to 12.

[0069]

[0080] The vacuum system 40 is for a support table WT for holding the substrate W. The vacuum system 40 includes 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 (as shown in FIG. 15, for example). In one embodiment, the flow circuit of the vacuum system 40 includes 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 of the support table WT under the central portion WP of the substrate W so as to clamp the substrate W to the support table WT. For example, in one embodiment, the third vacuum pressure line 54 is connected to a first channel 26.

[0070]

[0081] As shown in FIG. 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 lower than the ambient pressure between the support table WT and the substrate table 65. In one embodiment, the second positioner (shown in FIG. 1) includes the substrate table 65. Generally, the movement of the support table WT can be realized 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 a pressure for clamping 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 under 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] As shown in each of FIGS. 9 to 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 so as 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 branched from the second pressure circuit 42.

[0073]

[0084] As shown in each of FIGS. 9 to 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 opened, the second vacuum pressure line 41 is connected to the vacuum supply of the second pressure circuit 42.

[0074]

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

[0075]

[0086] In the embodiment shown in FIGS. 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. Therefore, by switching the first flow controller 44 and the second flow controller 45, the pressure in the second vacuum pressure line 41 can be switched from the supply by the vacuum supply of the second pressure circuit 42 to the supply by the vacuum supply of the first pressure circuit 43. For this reason, the second pressure p2 can be controlled by switching the first flow controller 44 and the second flow controller 45.

[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) compared to the vacuum supply of the second pressure circuit 42. Therefore, during the exposure process, by opening the first flow controller 44 and closing the second flow controller 45, the second pressure p2 is controlled by the vacuum supply of the second pressure circuit 42. Immediately before the start of the unload process, 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 supplied by the vacuum supply of the pressure circuit 43.

[0077]

[0088] The support table WT is clamped to the substrate table 65 by a vacuum pressure. The substrate W is clamped to the support table WT by a 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] In the embodiment shown in FIGS. 9 to 12, during the exposure process, the first vacuum pressure line 49 is configured to provide a lower pressure compared to the second vacuum pressure line 41 or the third vacuum pressure line 54. The first pressure circuit 43 can supply 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 (for example, for the unloading process), the negative pressure source for the second pressure line 41 and the third vacuum pressure line 54 is switched. In the embodiments 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] As shown in FIGS. 9 to 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 the 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 the 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 becomes greater than the second pressure p2 applied to the peripheral region 22. The fourth flow controller 58 is configured such that the difference between the first pressure p1 and the second pressure p2 remains within a predetermined range during the exposure operation.

[0081]

[0092] As shown in FIGS. 9 to 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 a 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 the ambient pressure to the third vacuum pressure line 54 via the fourth flow controller 58.

[0082]

[0093] As shown in FIGS. 9 to 11, in one embodiment, the vacuum system 40 includes a sixth flow controller 56. The sixth flow controller 56 is provided in a connection line 55 that connects 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 restricting portion configured to restrict the 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 the pressure difference between the second vacuum pressure line 41 and the third vacuum pressure line 54. As described above, there is also a flow from the ambient pressure to the third vacuum pressure line 54. The sixth flow controller 56 is configured to restrict the flow from the ambient pressure to the second vacuum pressure line 41.

[0083]

[0094] As shown in FIGS. 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. By closing the seventh flow controller 59, the first pressure p1 can be increased.

[0084]

[0095] As shown in each of FIGS. 9 to 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 the flow from the vacuum chamber 47 to the first pressure circuit 43. As shown in FIGS. 9 and 10, in one embodiment, the third flow controller 48 is in a fourth vacuum pressure line 50. Alternatively, as shown in FIG. 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 restricting portion configured to restrict the 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 opened, the second vacuum pressure line 41 is in fluid communication with the vacuum chamber 47. As a result, the second pressure p2 drops towards the pressure in the vacuum chamber 47.

[0086]

[0097] This drop in the second pressure p2 can be carried out in less than 1 second, optionally less than 0.5 second, optionally less than 0.2 second, optionally less than 0.1 second. The second pressure p2 is decreased to remove the liquid meniscus 23 from between the seal member 24 and the substrate W.

[0087]

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

[0088]

[0099] Whenever the second flow controller 45 is opened, the negative pressure applied 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 rapidly increases 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 applied by the second vacuum pressure line 41, the initial vacuum level supplied by the first pressure circuit 43 is restored. The vacuum chamber 47 stores the vacuum pressure and releases the stored vacuum pressure when increasing the negative pressure applied by the second vacuum pressure line 41. By configuring the vacuum device to include the vacuum chamber 47, the initial vacuum level can be restored even more rapidly. This is useful for increasing the throughput of the substrate W. Specifically, this shortens the waiting time between uses that is necessary to restore the vacuum level supplied by the first pressure circuit 43. The restoration of the vacuum level in the vacuum chamber 47 can be performed at a low flow rate during measurement and exposure processes (i.e., between substrate exchange sequences) so as not to interfere with other vacuum levels.

[0089]

[0100] As shown in each of FIGS. 10 to 12, in one embodiment, the vacuum system 40 includes a separation chamber 60. The separation chamber 60 is for separating a two-phase flow. The two-phase flow is a flow containing 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] The liquid is output from the separation chamber 60 through the liquid outlet 62. The gas is output from the separation chamber 60 through the gas outlet 61. The liquid outlet 62 is positioned at the bottom of the separation chamber 60. The liquid from the two-phase flow accumulates at the bottom of the separation chamber 60 due to gravity. As shown in FIGS. 10 and 12, in one embodiment, when the first flow controller 44 is opened, the liquid can be extracted from the separation chamber 60. Alternatively, as shown in FIG. 11, in one embodiment, a fifth flow controller 52 is provided in the fourth vacuum pressure line 50. When the fifth flow controller 52 is opened, the liquid can be extracted from the separation chamber 60. However, when the first flow controller 44 (see FIGS. 10 or 12) or the fifth flow controller 52 (see FIG. 11) is closed, the liquid remains in the separation chamber 60. In one embodiment, when the second pressure p2 is being reduced (for example, when the second flow controller 45 is opened), liquid extraction is blocked. Then, when the second flow controller 45 is closed and the first flow controller 44 is opened, liquid extraction resumes. This is performed after the substrate W is 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, the elements of the first pressure circuit 43 are protected from the liquid. A second advantage is that the pressure in the first vacuum pressure line 49 becomes even more stable because a single-phase flow flows through the first pressure circuit 43. This is because a two-phase flow usually causes undesirable pressure fluctuations.

[0092]

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

[0093]

[0100] In one embodiment, the separation chamber 60 has a volume of at least 1 milliliter, optionally at least 2 milliliters, and optionally at least 5 milliliters. In one embodiment, the separation chamber 60 has a volume of up to 10 milliliters, optionally up to 5 milliliters, and optionally up to 2 milliliters.

[0094]

[0101] As shown in FIGS. 10 and 12, the separation chamber 60 is upstream of the first flow controller 44 and the second flow controller 45. As shown in FIGS. 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]

[0102] The fourth vacuum pressure line 50 is connected to the 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 immediately before the unloading process.

[0096]

[0103] In one embodiment, the second vacuum pressure line 41 is configured for the flow of liquid, and the fourth vacuum pressure line 50 is configured for the flow of gas (see FIGS. 10 and 12). Therefore, when the first flow controller 44 is opened, the liquid flows from the separation chamber 60 into the second vacuum pressure line 41 and further through the first flow controller 44. During this time, substantially no liquid flows through the fourth vacuum pressure line 50. This is because the liquid is separated from the two-phase flow by the separation chamber 60. As a result, the first pressure circuit 43 that provides the lowest pressure can be kept in a dry state.

[0097]

[0104] As shown in each of FIGS. 9 to 12, in one embodiment, the vacuum devices 46, 47 are downstream of the second flow controller 45 and are configured to apply pressure to the fourth vacuum pressure line 50. When the second flow controller 45 is closed, a low pressure is not applied to the peripheral region 22. When the second flow controller 45 is opened (and the first flow controller 44 is closed), a low pressure is applied to the peripheral region 22.

[0098]

[0105] As shown in each of FIGS. 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 is used not only to clamp the support table WT to the substrate table 65, but can also be used to apply a low pressure to the peripheral region 22 immediately before the unloading 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 FIGS. 9 to 11). In the embodiment shown in FIGS. 9 to 11, the third flow controller 48 is a restriction that allows, for example, the pressure in the vacuum chamber 47 to be reduced at a low speed during exposure and measurement operations.

[0100]

[0107] As shown in FIG. 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, a fourth vacuum pressure line 50 is in fluid communication with a third pressure circuit 63. The third pressure circuit 63 has a vacuum generated by a Venturi pump 46. The Venturi pump 46 is an alternative way to generate the deep vacuum necessary to reduce the second pressure p2 before the unload process. The Venturi pump 46 can be made quite small for a small vacuum flow. In one embodiment, the third pressure circuit 63 includes a supply of compressed dry air. The supply of compressed dry air is provided to the Venturi pump 46, which causes a Venturi effect to generate a 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 further used to activate a flow controller.

[0104]

[0111] Hereinafter, the differences between the embodiment of FIG. 11 and the embodiments of FIGS. 9 and 10 will be specifically described. As shown in FIG. 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 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 in fluid communication with 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 flow. Accordingly, the fourth vacuum pressure line 50 is connected to the separation chamber 60 for inputting two-phase flow. The 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] Accordingly, in one embodiment as shown in FIG. 11, the vacuum chamber 47 includes the separation chamber 60. The vacuum system 40 includes a third flow controller 48 for controlling the pressure in the fifth vacuum pressure line 51. The third flow controller 48 in this embodiment operates in the same manner as the third flow controller 48 in the embodiments of FIGS. 9 and 10. That is, the third flow controller 48 includes a restriction configured to limit the continuous flow from the vacuum chamber 47 to the vacuum supply of the first pressure circuit 43.

[0109]

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

[0110]

[0117] In each of the embodiments shown in FIGS. 9 to 12, by switching which vacuum source is connected to the second vacuum pressure line 41, the second pressure p2 supplied by the second vacuum pressure line 41 can be temporarily reduced. For two alternative embodiments that do not require this function, reference is made to FIGS. 13 and 14 for description.

[0111]

[0118] Some of the components in the embodiments of FIGS. 13 and 14 are the same as those in the embodiments of FIGS. 9 to 12. When this is the case, the same reference numerals are used in these drawings, and detailed description is omitted.

[0112]

[0119] In the embodiment shown in FIG. 13, the first pressure circuit 43 includes each of 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 necessary. The first pressure circuit 43 is configured to provide a deep vacuum for clamping the support table WT to the substrate table 65. Therefore, in the embodiment of FIG. 13, the pressure applied between the substrate W and the support table WT can be made closer to the pressure applied to the region between the support table WT and the substrate table 65. This is different from the case in the embodiments shown in FIGS. 9 to 12, where the pressure for clamping the support table WT to the substrate table 65 is significantly smaller than the pressure for clamping the substrate W to the support table WT.

[0113]

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

[0114]

[0121] Therefore, the unloading process using the embodiment of FIG. 13 can follow the same pattern as 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 of 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 increase in the pressure difference helps to remove the meniscus 23 so that the liquid remaining on the back side 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 as the first pressure p1 to the central region 21. 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 to 12, the first pressure circuit 43 is configured to provide a deeper vacuum than the second pressure circuit 42. However, in the embodiment of FIG. 14, the second pressure circuit 42 is configured to provide a vacuum of the same depth as the first pressure circuit 43. Thereby, during the exposure process, the pressure difference between the first pressure p1 (provided by the third vacuum pressure line 54) and the second pressure p2 (provided by the second vacuum pressure line 41) can be reduced. In order to form a seal on the seal member 24, it is desirable that the pressure difference during the exposure process be small. If the pressure difference during the exposure process is too large, the liquid forming the seal is removed, so that the seal disappears.

[0116]

[0123] During the unloading process, the seventh flow controller 59 is closed so that the first pressure p1 increases. As a result, the pressure difference between the first pressure p1 and the second pressure p2 increases, and the meniscus 23 is removed. After that, the first flow controller 44 is closed, so the second pressure p2 increases toward the ambient pressure. Thereafter, the substrate W can be removed from the support table WT.

[0117]

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

[0118]

[0125] FIG. 16 is a graph showing the relationship between time and pressure in different regions before and during the execution of the unloading process. The lower line formed by the dashed-dotted line indicates the second pressure p2 in the peripheral region 22 during the unloading process. The upper line formed by the broken line indicates the first pressure p1 in the central region 21 during the unloading process.

[0119]

[0126] The pressure fluctuations shown in FIG. 16 are only schematic and represent an example of how the first pressure p1 and the second pressure p2 vary before and during the execution of the unloading process. However, the present invention is not limited to the specific form of the lines as shown in FIG. 16.

[0120]

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

[0121]

[0128] After increasing the first pressure p1 and the second pressure p2 towards the ambient pressure, the first pressure p1 and the second pressure p2 reach a substantially constant level. This 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 such that at least a portion of the liquid held between the substrate W and the seal member 24 is removed. This is shown in FIG. 16 at the point where the second pressure p2 decreases at the end of the steady state value.

[0123]

[0130] This is done before removing the substrate W from the support table WT. Thus, the second pressure p2 is reduced while the substrate W remains supported on the bar of the support table WT. At this point, i.e., before unloading the substrate W, at least a portion 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 so as to raise the substrate W. When the substrate W is raised, the shape of the substrate W is deformed into an upside-down bowl shape. When the substrate W is raised, the substrate W no longer contacts the bead in the central region 21. However, the substrate W maintains contact with the support table WT at the peripheral portion. The raising of the substrate W helps to widen the gap between the seal member 24 and the substrate W. The widening of the gap between the seal member 24 and the substrate W helps to remove the liquid held between the substrate W and the seal member 24. One embodiment of the present invention is expected to increase the amount of liquid discharged from between the substrate W and the seal member 24.

[0125]

[0132] In one embodiment, before reducing the second pressure p2, an overpressure is applied to the central region 21 so as to raise the substrate W. Reducing the second pressure p2 is after widening the gap between the seal member 24 and the substrate W. When the second pressure p2 is reduced, a larger amount of liquid can be removed from between the seal member 24 and the substrate W.

[0126]

[0133] FIG. 16 shows that an overpressure is applied to the central region 21. This is shown in the section highlighted by the elliptical boundary line in FIG. 16. As shown in the highlighted elliptical section of FIG. 16, the first pressure p1 is increased to be greater than the ambient pressure. The substrate W will soon rise after the overpressure is applied.

[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 the exposure pressure, an overpressure is applied at any point in time after the step of increasing the first pressure p1 towards the 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 will be described in more detail below. Accordingly, an overpressure is applied to the central region 21 to raise the substrate W when the first pressure p1 and the second pressure p2 (and their difference) have known values. These known values are closer to the 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. The overpressure is applied when the clamping pressure is significantly reduced.

[0128]

[0135] When the overpressure is applied, the substrate W bulges. When the substrate W bulges, the edge of the substrate W slides on the outermost bead on the support table WT. This sliding can cause wear of the bead. However, this sliding occurs when the clamping pressure is significantly reduced. For this reason, the frictional energy that may wear the outer bead is significantly reduced. The frictional force that may wear the bead is directly proportional to the clamping force when the sliding occurs.

[0129]

[0136] According to the present invention, it is possible to control when the bulge of the substrate W occurs. It is considered that the bulge occurs when the deformation of the substrate W is completed, the shape of the substrate W no longer changes, and it becomes an upside-down bowl shape. One embodiment of the present invention is expected to achieve a reduction in wear of the outer bead of the support table WT.

[0130]

[0137] FIG. 17 is a graph showing the relationship between time and pressure in different regions during the unload process according to a comparative example. In this comparative example, an overpressure is applied to the central region 21 at any point in time when the pressure difference between the first pressure p1 and the second pressure p2 is increasing. An overpressure is applied to the central region 21 at any point in time when the second pressure p2 that clamps the peripheral portion of the substrate W is smaller than that in the embodiment shown in FIG. 16. As a result, the substrate W bulges at any point in time when there is a larger clamping pressure than in the present invention. This means that when the edge of the substrate W slides on the outer bead of the support table WT, there is a greater force that may wear the outer bead. This is because there is a larger clamping pressure when the overpressure is applied to the central region 21.

[0131]

[0138] As shown in FIG. 16, the controller 500 is adapted to increase the second pressure p2 towards the ambient pressure during the unload process. Specifically, after reducing the second pressure p2 to remove a part of the liquid, the second pressure p2 is increased towards the ambient pressure. By increasing the second pressure p2 towards the ambient pressure, the clamping pressure is reduced so that the substrate W can be removed from the support table WT.

[0132]

[0139] FIG. 18 schematically shows a vacuum system 40 according to an embodiment of the present invention. Using the vacuum system 40 shown in FIG. 18, the above-described pressure sequence (the pressure sequence shown in FIG. 16) can be implemented.

[0133]

[0140] The vacuum system 40 is for a support table WT for holding the substrate W. The vacuum system 40 includes 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 includes 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 so as to clamp the substrate W to the support table WT. The second vacuum pressure line 41 is connected to the second channel 27 so as to apply a second pressure p2 to the peripheral region 22.

[0135]

[0142] Some of the components in the embodiments of FIGS. 18 to 22 are the same as those in the embodiments of FIGS. 9 to 14. When this is the case, the same reference numerals are used in these drawings, and detailed descriptions are omitted.

[0136]

[0143] As shown in FIG. 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 a flow from the ambient pressure to the third vacuum pressure line 54. The sixth flow controller 56 is configured to limit the flow from the ambient pressure to the second vacuum pressure line 41. This helps to maintain the pressure difference between the second vacuum pressure line 41 and the third vacuum pressure line 54. By maintaining the pressure difference (i.e., a small pressure difference) between the second vacuum pressure line 41 and the third vacuum pressure line 54, a liquid can be held 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, the risk of breaking the seal, for example during an exposure process, increases due to the unnecessary removal of the liquid.

[0138]

[0145] As shown in FIG. 18, in one embodiment, the vacuum system 40 includes a second ambient pressure line 81. The second ambient pressure line 81 fluidly connects the second vacuum pressure line 41 to the ambient pressure. An eighth flow controller 82 is configured to control the flow from the ambient pressure to the second vacuum pressure line 41. For example, in one embodiment, the eighth flow controller 82 is a restricting portion configured to restrict the 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 unload process.

[0140]

[0147] As described above and as shown in FIG. 16, before unloading the substrate W, both the first pressure p1 and the second pressure p2 are increased towards the 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 the ambient pressure along the second ambient pressure line 81 via the eighth flow controller 82. Thereby, the flow from the ambient pressure to the second vacuum pressure line 41 becomes possible. This increases the second pressure p2. At the same time, the pressure increase in the second vacuum pressure line 41 increases the pressure in the third vacuum pressure line 54 such that the first pressure p1 increases at the same rate.

[0141]

[0148] When the ninth flow controller 83 is in the open state, the first pressure p1 and the second pressure p2 continue to increase towards the ambient pressure until they reach the steady-state values. The steady-state values vary depending on the configuration of the eighth flow controller 82. The greater the flow from the ambient pressure to the second vacuum pressure line 41 enabled by the eighth flow controller 82, the closer the steady-state value approaches the ambient pressure. Therefore, by selecting the size of the orifice in the restriction section of the eighth flow controller 82, the steady-state values of the first pressure p1 and the second pressure p2 can be controlled. In one embodiment, the steady-state value of the first pressure p1 is in the range of about 1 kPa to about 20 kPa lower than the ambient pressure. Optionally, the steady-state value of the first pressure p1 is in the range of about 5 kPa to about 10 kPa lower than the ambient pressure.

[0142]

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

[0143]

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

[0144]

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

[0145]

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

[0146]

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

[0147]

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

[0148]

[0155] As can be appreciated, any of the above-described features can be used in combination with any other feature, and the present application encompasses not only the explicitly described combinations. For example, it is also possible to apply an embodiment of the present invention to the example of FIG. 3.

[0149]

[0156] Although the present text can specifically refer to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus herein can have other uses in the manufacture of microscale or nanoscale components and features. Examples of other uses include 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, and the like.

[0150]

[0157] Where context permits, embodiments of the present invention can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention can also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. The machine-readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, the machine-readable medium can 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. Further, firmware, software, routines, instructions can be described herein as performing certain actions. However, such descriptions are for convenience only, and such actions are actually caused by a computing device, processor, controller, or other device executing firmware, software, routines, instructions, etc., and it will be recognized that when executing, an actuator or other device can interact with the physical world.

[0151]

[0158] Although specific embodiments of the present invention have been described above, it will be recognized that the present invention can be practiced otherwise than as described. The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the following claims.

Claims

1. 1. A vacuum system for a stage system including a support table and a substrate table, comprising: a first vacuum pressure line configured to clamp the support table configured to hold a substrate to the substrate table; a second vacuum pressure line configured to apply a second pressure to a peripheral region of the support table underlying a periphery of the substrate; 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 substrate to clamp the substrate to the support table; the vacuum system is configured to increase the first pressure and the second pressure towards ambient pressure while the second pressure remains lower than the first pressure until the first pressure reaches a first predetermined level and the second pressure reaches a second predetermined level, respectively, before unloading the substrate from the support table. Vacuum system.

2. 2. The vacuum system of claim 1, wherein the second pressure is increased toward the ambient pressure at the same time that the first pressure is increased toward the ambient pressure.

3. 3. The vacuum system of claim 1, wherein a pressure difference between the first pressure and the second pressure is maintained constant until the first pressure reaches the first predetermined level and the second pressure reaches the second predetermined level.

4. The vacuum system of claim 3 , wherein the pressure difference is substantially equal to the pressure difference during an exposure process.

5. The vacuum system of claim 3 , wherein an overpressure is provided to the central region while the substrate remains in contact with the peripheral region.

6. 6. The vacuum system of claim 5, wherein the overpressure is applied after the first pressure is maintained at the first predetermined level for a first predetermined time.

7. 6. The vacuum system of claim 5, wherein the overpressure is provided when the second pressure is maintained at the second predetermined level.

8. 6. The vacuum system of claim 5, wherein the overpressure is provided at a third predetermined level for a third predetermined time.

9. The vacuum system of claim 5 , wherein the second pressure is further reduced after the overpressure is applied.

10. 6. The vacuum system of claim 5, wherein the second pressure is further reduced after the second pressure is maintained at the second predetermined level for a second predetermined time.

11. The vacuum system of claim 10 , wherein the second pressure is maintained at a fourth predetermined level for a fourth predetermined time.

12. 12. The vacuum system of claim 11, wherein the second pressure is further increased toward the ambient pressure after the fourth predetermined time period.

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