Patent Publication Number: US-2009225289-A1

Title: Lithographic apparatus and methods

Description:
This application claims priority and benefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 61/064,126, entitled “Lithographic Apparatus and Methods”, filed on Feb. 19, 2008. The content of that application is incorporated herein in its entirety by reference. 
    
    
     FIELD 
     The present invention relates to a lithographic apparatus and a method for providing a substrate under a projection system of an immersion lithographic apparatus as well as a method of removing a substrate from under a projection system of an immersion lithographic apparatus. 
     BACKGROUND 
     A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. 
     It has been proposed to immerse the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. The liquid may be distilled water (ultra pure water) although another liquid may be used. An embodiment of the present invention will be described with reference to liquid. However, another fluid may be suitable, particularly a wetting fluid, an incompressible fluid and/or a fluid with higher refractive index than air, desirably a higher refractive index than water. Fluids excluding gases are particularly desirable. The point of this is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid. (The effect of the liquid may also be regarded as increasing the effective numerical aperture (NA) of the system and also increasing the depth of focus.) Other immersion liquids have been proposed, including water with solid particles (e.g. quartz) suspended therein, or liquids with nano-particle suspensions (e.g. particles with a maximum dimension of up to 10 nm). The suspended particles may or may not have a similar or the same refractive index as the liquid in which they are suspended. A liquid which may be suitable is hydrocarbon or fluorohydrocarbon, or an aqueous solution. 
     However, submersing the substrate or substrate and substrate table in a bath of liquid (see, for example, U.S. Pat. No. 4,509,852 means that there is a large body of liquid that must be accelerated during a scanning exposure. This requires additional or more powerful motors and turbulence in the liquid may lead to undesirable and unpredictable effects. 
     In an immersion apparatus, immersion fluid is handled by a fluid handling system, structure or apparatus. In an embodiment the fluid handling system may supply immersion fluid and therefore be a fluid supply system. In an embodiment the fluid handling system may at least partly confine immersion fluid and thereby be a fluid confinement system. In an embodiment the fluid handling system may provide a barrier to immersion fluid and thereby be a barrier member, such as a fluid confinement structure. In an embodiment the fluid handling system may create or use a flow of gas, for example to help in controlling the flow and/or the position of the immersion fluid. The flow of gas may form a seal to confine the immersion fluid so the fluid handling structure may be referred to as a seal member; such a seal member may be a fluid confinement structure. In an embodiment, immersion liquid is used as the immersion fluid. In that case the fluid handling system may be a liquid handling system. In reference to the aforementioned description, reference in this paragraph to a feature defined with respect to fluid may be understood to include a feature defined with respect to liquid. 
     One of the arrangements proposed is for a liquid supply system to provide liquid on only a localized area of the substrate and in between the final element of the projection system and the substrate using a liquid confinement system (the substrate generally has a larger surface area than the final element of the projection system). One way which has been proposed to arrange for this is disclosed in PCT patent application publication no. WO 99/49504. As illustrated in  FIGS. 2 and 3 , liquid is supplied by at least one inlet IN onto the substrate, preferably along the direction of movement of the substrate relative to the final element, and is removed by at least one outlet OUT after having passed under the projection system. That is, as the substrate is scanned beneath the element in a −X direction, liquid is supplied at the +X side of the element and taken up at the −X side.  FIG. 2  shows the arrangement schematically in which liquid is supplied via inlet IN and is taken up on the other side of the element by outlet OUT which is connected to a low pressure source. In the illustration of  FIG. 2  the liquid is supplied along the direction of movement of the substrate relative to the final element, though this does not need to be the case. Various orientations and numbers of in- and out-lets positioned around the final element are possible, one example is illustrated in  FIG. 3  in which four sets of an inlet with an outlet on either side are provided in a regular pattern around the final element. 
     A further immersion lithography solution with a localized liquid supply system is shown in  FIG. 4 . Liquid is supplied by two groove inlets IN on either side of the projection system PL and is removed by a plurality of discrete outlets OUT arranged radially outwardly of the inlets IN. The inlets IN and OUT can be arranged in a plate with a hole in its center and through which the projection beam is projected. Liquid is supplied by one groove inlet IN on one side of the projection system PL and removed by a plurality of discrete outlets OUT on the other side of the projection system PL, causing a flow of a thin film of liquid between the projection system PL and the substrate W. The choice of which combination of inlet IN and outlets OUT to use can depend on the direction of movement of the substrate W (the other combination of inlet IN and outlets OUT being inactive). 
     In European patent application publication no. EP 1420300 and United States patent application publication no. US 2004-0136494, each hereby incorporated in their entirety by reference, the idea of a twin or dual stage immersion lithography apparatus is disclosed. Such an apparatus is provided with two tables for supporting a substrate. Leveling measurements are carried out with a table at a first position, without immersion liquid, and exposure is carried out with a table at a second position, where immersion liquid is present. Alternatively, the apparatus has only one table. 
     PCT patent application publication WO 2005/064405 discloses an all wet immersion lithography arrangement in which the immersion liquid is unconfined. In such a system the whole top surface of the substrate is covered in liquid. An advantage of such an arrangement is that the whole top surface of the substrate is exposed to substantially the same conditions. This may have an advantage for temperature control and processing of the substrate. In WO 2005/064405, a liquid supply system provides liquid to a gap between the projection system and the substrate. That liquid is allowed to leak over the remainder of the substrate. A barrier at the edge of a substrate table substantially prevents liquid from escaping so that it can be removed from the top surface of the substrate table in a controlled way. 
     SUMMARY 
     Although the system of WO 2005/064405 may improve temperature control and processing of the substrate, evaporation of the immersion liquid may occur. A way to help alleviate such a problem is described in United States patent application publication no. US 2006/0119809 in which a member is provided which covers the substrate W in substantially all positions and which is arranged to have immersion liquid extending between it and the top surface of the substrate and/or substrate table which holds the substrate. 
     It is desirable, for example, to provide an apparatus in which the whole of the top surface of the substrate is covered in immersion fluid and in which at least a deleterious effect of providing liquid on the whole of the top surface of the substrate is addressed. 
     According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising: a substrate table constructed to hold a substrate; a projection system configured to project a patterned radiation beam onto a target portion of a substrate; a member held substantially stationary relative to the projection system configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table; a fluid supply system for supplying an immersion fluid to a space between the projection system and the substrate and/or substrate table and to provide the immersion fluid to extend between the substrate table and/or substrate and the surface of the member; and a seal device for sealing between the surface of the member and the substrate table. 
     According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising: a substrate table constructed to hold a substrate; a projection system configured to project a patterned radiation beam onto a target portion of a substrate; a member held substantially stationary relative to the projection system and with a through hole for the passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table; a fluid supply system for supplying an immersion fluid to a space between a final element of the projection system and the substrate and/or substrate table and to provide immersion fluid to extend between the substrate table and/or substrate and the surface of the member; a first fluid removal system for removing fluid from the space; and a second fluid removal system for removing fluid from between the surface of the member and the substrate table at a position radially outwardly of the substrate. 
     According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising: a substrate table constructed to hold a substrate; a member with a surface facing the substrate table; a pre-wetting station for providing immersion fluid onto a surface of the substrate and/or substrate table prior to the substrate/substrate table moving under the member such that the immersion fluid extends between the surface of the substrate and/or substrate table and the surface of the member facing the substrate table. 
     According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising: a substrate table constructed to hold a substrate; a member with a surface facing the substrate table; and a fluid remover for removing fluid from a surface of the substrate and substrate table as the substrate/substrate table moves from underneath the surface of the member during movement of the substrate from under the member. 
     According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising: a first substrate table constructed to hold a substrate; and a second substrate table constructed to hold a substrate, wherein the first and second substrate tables are releasably attachable together. 
     According to an aspect of the invention, there is provided a method of providing a substrate under a projection system of an immersion lithographic apparatus, the method comprising: moving a substrate on a substrate table under an elongate pre-wetting station which provides an immersion fluid on a top surface of the substrate and/or substrate table; and moving a pre-wet portion of the substrate/substrate table under a member which is held substantially stationary relative to the projection system such that immersion fluid extends between a surface of the member facing the substrate/substrate table and the substrate/substrate table. 
     According to an aspect of the invention, there is provided a method of removing a substrate table from under a projection system of an immersion lithographic apparatus, the method comprising: moving a substrate on a substrate table from under a member which is held substantially stationary relative to the projection system; and using a fluid removing device positioned over a portion of the substrate table which emerges as the substrate table is moved from under the member to remove fluid from the portion. 
     According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising: a substrate table constructed to hold a substrate; a projection system configured to project a patterned radiation beam onto a target portion of a substrate; a member held substantially stationary relative to the projection system configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table; a fluid supply system for supplying a substantially incompressible immersion fluid to a space between the projection system and the substrate and/or substrate table and between the substrate table and/or substrate and the surface of the member; and a seal device for sealing between the surface of the member and the substrate table. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 
         FIG. 1  depicts a lithographic apparatus according to an embodiment of the invention; 
         FIGS. 2 and 3  depict a liquid supply system for use in a lithographic projection apparatus; 
         FIG. 4  depicts a further liquid supply system for use in a lithographic projection apparatus; 
         FIG. 5  depicts, in cross-section, a barrier member which may be used in an embodiment of the present invention as a liquid supply system; 
         FIG. 6  illustrates, in cross-section, another barrier member which may be used in an embodiment of the present invention; 
         FIGS. 7   a - c  illustrate an embodiment of the present invention during substrate swap; 
         FIG. 8  illustrates, in plan, the embodiment of  FIG. 7 ; 
         FIG. 9   a  illustrates, in cross-section, an embodiment of the present invention during substrate swap; 
         FIG. 9   b  illustrates, in cross-section, a variation on the  FIG. 9   a  embodiment during substrate swap; and 
         FIG. 10  illustrates, in plan, the embodiment of  FIG. 9   a.    
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: 
     an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation); 
     a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; 
     a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and 
     a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. 
     The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. 
     The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which may be fixed or movable as required. The support structure MT may ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” 
     The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. 
     The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. 
     The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. The projection system may be held by a metrology frame RF. The projection system may be held by a base frame BF. The base frame RF may support the metrology frame RF. The metrology frame RF may be supported by, and dynamically isolated from, the base frame BF using, for example, one or more isolation mounts. 
     As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask). 
     The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more patterning device tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. 
     Referring to  FIG. 1 , the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus may be separate entities, for example when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source SO may be an integral part of the lithographic apparatus, for example when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system. 
     The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator IL can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator IL may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. Similar to the source SO, the illuminator IL may or may not be considered to form part of the lithographic apparatus. For example, the illuminator IL may be an integral part of the lithographic apparatus or may be a separate entity from the lithographic apparatus. In the latter case, the lithographic apparatus may be configured to allow the illuminator IL to be mounted thereon. Optionally, the illuminator IL is detachable and may be separately provided (for example, by the lithographic apparatus manufacturer or another supplier). 
     The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device MA. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in  FIG. 1 ) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M 1 , M 2  and substrate alignment marks P 1 , P 2 . Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies. 
     The depicted apparatus could be used in at least one of the following modes: 
     1. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 
     2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion C in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion C. 
     3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. 
     Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. 
     Traditional arrangements for providing liquid between a final element of the projection system PS and the substrate can be classed into two general categories. These are the bath type arrangement in which the whole of the substrate W and optionally part of the substrate table WT is submersed in a bath of liquid and the so called localized immersion system in which liquid is substantially only provided to a localized area of the substrate. In the latter category, the space filled by liquid is smaller in plan than the top surface of the substrate and the area filled with liquid remains stationary relative to the projection system PS while the substrate W moves underneath that area. A further arrangement, to which an embodiment of the present invention is mainly directed, is the all wet solution in which the liquid is unconfined. In this arrangement, substantially the whole top surface of the substrate and all or part of the substrate table is covered in immersion liquid. The depth of the liquid covering at least the substrate is small. The liquid may be a film, such as a thin film, of liquid on the substrate. Any of the liquid supply devices of  FIGS. 2-5  can also be used in such a system; however, their sealing features are not present, are not activated, are not as efficient as normal or are otherwise ineffective to seal liquid to only the localized area. Four different types of localized liquid supply systems are illustrated in  FIGS. 2-5 . The liquid supply systems disclosed in  FIGS. 2-4  were described above. 
       FIG. 5  schematically depicts a localized liquid supply system with a barrier member  12 , which extends along at least a part of a boundary of the space  11  between the final element of the projection system PS and the substrate table. The barrier member  12  is substantially stationary relative to the projection system PS in the XY plane though there may be some relative movement in the Z direction (in the direction of the optical axis). In an embodiment, a seal is formed between the barrier member  12  and the surface of the substrate W and may be a contactless seal such as a gas seal or fluid seal. 
     The barrier member  12  at least partly contains liquid in the space  11  between a final element of the projection system PS and the substrate W. A contactless seal, such as a gas seal  16 , to the substrate W may be formed around the image field of the projection system PS so that liquid is confined within the space  11  between the substrate surface and the final element of the projection system PS. The space  11  is at least partly formed by the barrier member  12  positioned below and surrounding the final element of the projection system PS. Liquid is brought into the space  11  below the projection system PS and within the barrier member  12  by liquid inlet  13  and may be removed by liquid outlet  13 . The barrier member  12  may extend a little above the final element of the projection system PS and the liquid level rises above the final element so that a buffer of liquid is provided. The barrier member  12  has an inner periphery that at the upper end, in an embodiment, closely conforms to the shape of the projection system PS or the final element thereof and may, e.g., be round. At the bottom, the inner periphery closely conforms to the shape of the image field, e.g., rectangular though this need not be the case. 
     The liquid is contained in the space  11  by the gas seal  16  which, during use, is formed between the bottom of the barrier member  12  and the surface of the substrate W. The gas seal  16  is formed by gas, e.g. air or synthetic air but, in an embodiment, N 2  or another inert gas, provided under pressure via inlet  15  to the gap between barrier member  12  and substrate W and extracted via outlet  14 . The overpressure on the gas inlet  15 , vacuum level on the outlet  14  and geometry of the gap are arranged so that there is a high-velocity gas flow inwards that confines the liquid. The force of the gas on the liquid between the barrier member  12  and the substrate W contains the liquid in a space  11 . Those inlets/outlets may be annular grooves which surround the space  11 . The annular grooves may be continuous or discontinuous. The flow of gas is effective to contain the liquid in the space  11 . Such a system is disclosed in United States patent application publication no. US 2004-0207824. 
     Other arrangements are possible and, as will be clear from the description below, an embodiment of the present invention may use any type of localized liquid supply system as the liquid supply system. 
     One or more localized liquid supply systems seal between a part of the liquid supply system and a substrate W. Relative movement of that part of the liquid supply system and the substrate W may lead to breakdown of the seal and thereby leaking of liquid. The problem may be more significant at high scan velocities. An increased scan velocity is desirable because throughput increases. 
       FIG. 6  illustrates a barrier member  12  which is part of a liquid supply system. The barrier member  12  extends around the periphery (e.g., circumference) of the final element of the projection system PS such that the barrier member (which is sometimes called a seal member) is, for example, substantially annular in overall shape. The projection system PS may not be circular and the outer edge of the barrier member  12  may also not be circular so that it is not necessary for the barrier member to be ring shaped. The barrier could also be other shapes so long as it has an opening through which the projection beam may pass out from the final element of the projection system PS. The opening may be centrally located. Thus during exposure the projection beam may pass through liquid contained in the opening of the barrier member and onto the substrate W. The barrier member  12  may be, for example, substantially rectangular and is not necessarily the same shape as the final element of the projection system PS is at the height of the barrier member  12 . 
     The function of the barrier member  12  is at least partly to maintain or confine liquid in the space between the projection system PS and the substrate W so that the projection beam may pass through the liquid. The top level of liquid is simply contained by the presence of the barrier member  12  and the level of liquid in the space is maintained such that the liquid does not overflow over the top of the barrier member  12 . A seal is provided between the bottom of the barrier member  12  and the substrate W. In  FIG. 6  a seal device is configured to provide a contactless seal and is made up of several components. Working radially outwardly from the optical axis of the projection system PS, there is provided a (optional) flow plate  50  which extends into the space (though not into the path of the projection beam) which helps maintain substantially parallel flow of the immersion liquid out of outlet  20  across the space. The flow control plate has through holes  55  in it to reduce the resistance to movement in the direction of the optical axis of the barrier member  12  relative to the projection system PS and/or substrate W. 
     Radially outwardly along the bottom of the barrier member  12  there may be provided an outlet  60  which provides a flow of liquid in a direction substantially parallel to the optical axis towards the substrate. This flow of liquid is used to help fill a gap between the edge of the substrate W and the substrate table WT which supports the substrate. If the gap is not filled with liquid, bubbles may be included in the liquid in the space between the projection system PS and the substrate W when an edge of the substrate W is passed under the seal. This is undesirable as it may lead to deterioration of the image quality. 
     Radially outwardly of the outlet  60  may be an extractor assembly  70  to extract liquid from between the barrier member  12  and the substrate W and/or the substrate table WT. The extractor  70  will be described in more detail below and forms part of the contactless seal which is created between the barrier member  12  and the substrate W. 
     Radially outwardly of the extractor assembly  70  may be a recess  80 . The recess is connected through an inlet  82  to the atmosphere. The recess if connected via an outlet  84  to a low pressure source. Radially outwardly of the recess  80  may be a gas knife  90 . An arrangement of the extractor, recess and gas knife is disclosed in detail in United States patent application publication no. US 2006/0158627. However, in that document the arrangement of the extractor assembly is different. 
     The extractor assembly  70  comprises a liquid removal device or extractor or inlet  100  such as the one disclosed in United States patent application publication no. US 2006-0038968, incorporated herein its entirety by reference. Any type of liquid extractor may be used. In an embodiment, the liquid removal device  100  comprises an inlet which is covered in a porous material  110  which is used to separate liquid from gas to enable single-liquid phase liquid extraction. A chamber  120  downstream of the porous material  110  is maintained at a slight under pressure and is filled with liquid. The under pressure in the chamber  120  is such that the meniscuses formed in the holes of the porous material prevent ambient gas from being drawn into the chamber  120  of the liquid removal device  100 . However, when the porous surface  110  comes into contact with liquid there is no meniscus to restrict flow and the liquid can flow freely into the chamber  120  of the liquid removal device  100 . The porous surface  110  extends radially inwardly along the barrier member  12  (as well as around the space). The rate of extraction through the porous surface  110  varies according to how much of the porous material  110  is covered by liquid. 
     During scanning of the substrate W (during which the substrate moves under the barrier member  12  and projection system PS) the meniscus can be drawn either towards or away from the optical axis by a drag force applied by the moving substrate. This can lead to liquid loss which may result in evaporation of the liquid, cooling of the substrate, and consequent shrinkage and overlay errors as described above. Liquid stains may also or alternatively be left behind from interaction between the liquid droplets and resist photochemistry. A plate  200  may be provided between the liquid removal device  100  and the substrate W so that the function of liquid extraction and the function of meniscus control can be separated from one another. The barrier member  12  may be optimized for each. 
     The plate  200  is a divider, or any other element, which has the function of splitting the space between the liquid removal device  100  and the substrate W into two channels. The two channels are: an upper channel  220  and a lower channel  230 . The upper channel  220  is between the upper surface of the plate  200  and the liquid removal device  100 . The lower channel  230  is between the lower surface of the plate  200  and the substrate W. Each channel is open, at its radially innermost end, to the space  11 . The thickness of the plate is not critical. Although as illustrated in  FIG. 6  the upper channel  220  extends horizontally, this is not necessarily the case. The reason for the upper channel  220  extending horizontally in  FIG. 6  is because of the structural arrangement of the components. However, the upper channel  220  could also extend vertically or any where between horizontally and vertically. The gravitational pressure on the liquid in the upper channel  220  is very low and, if necessary, can be counteracted by applying an under pressure, for example through liquid removal device  100  itself or through another passage such as breathing holes  250  described below. 
     In an embodiment, the upper channel  220  between the liquid removal device  100  and the plate  200  is narrower than the lower channel  230  between the plate  200  and the substrate W. The lower channel is between 250 mm and 50 μm high, or between 100 and 60 μm. The height of the lower channel depends, in a non-limiting list, on design (for example for viscous drag length from flow pattern), fluid parameters (such as viscosity, density, surface tension) and surface properties (which may include the contact angle resulting from binding energy surface/liquid and liquid surface tension). The upper channel  220  has a stronger capillary action, for instance by making it 2 to 3 times narrower than the lower channel. Alternatively or additionally, the upper channel  220  may have a surface (for example a coating) which is more liquidphillic than a surface of the lower channel  230 . However, the upper channel  220  may be higher than the lower channel  230 . If the upper channel  220  is too narrow, liquid does not flow in that channel because the frictional resistance is too large. The meniscus may be pinned because it is fully loaded with hydrodynamic forces. Thus, if the upper channel  220  is made higher, for example in the region of 150 μm, than the lower channel  230  which could be perhaps 60 μm, these difficulties may be overcome. Above a channel height of 250 μm the capillary action is reduced. In order to promote capillary action, the upper channel  220  could be made liquidphillic or a height step close to the meniscus between the plate  200  and the liquid removal device  100  may be made such that the channel radially inwardly is higher than radially outwardly. 
     An under pressure may be applied in the upper channel  220 , rather than leaving it open to the atmosphere through breathing holes  250  e.g. through the holes  250 . In this way the upper channel  220  may be made wider. 
     With the plate  200 , there are two meniscuses  310 ,  320 . A first meniscus  310  is positioned above the plate  200 . It extends between the porous surface  110  and the top surface of the plate  200 . A second meniscus  320  is positioned underneath the plate  200 . It extends between the plate  200  and the substrate W. In this way the extractor assembly  70  may be optimized for control of the first meniscus  310  for optimum extraction of liquid and/or for positional control of the second meniscus  320 . Thus the viscous drag length for the second meniscus  320  is reduced. The characteristics, in particular of the plate  200 , are optimized to make it energetically favorable for the second meniscus  320  to remain adhered to the plate  200 . So, the scan speed of the substrate W beneath the barrier member  10  may be increased. Capillary forces acting on the second meniscus  320  are outwards and are balanced by an under pressure in the liquid adjacent the second meniscus  320  so that the second meniscus  320  stays substantially still. Higher loading on the second meniscus  320 , for example by viscous drag and inertia, results in a lowering of the contact angle of the second meniscus  320  with the surface. 
     One or more breathing holes  250  are provided at the radially outward most end of the plate  200 . The first meniscus  310  is free to move inwardly and outwardly beneath the porous material  110  so that the extraction rate of the liquid removal device  100  may vary according to how much of the porous material  110  is covered by liquid. As illustrated in  FIG. 6  the second meniscus  320  adheres to a lower inward edge of the plate  200 . 
     In  FIG. 6  the inner most bottom edge of the plate  200  is provided with a sharp edge so as to pin the second meniscus  320  substantially in place. The radius of the edge is, in an embodiment, less than 0.1 mm, less than 50 μm, less than 20 μm or about 10 μm. 
     An alternative or additional way of pinning the second meniscus  320  is to change the surface properties of the surface of the plate  200  to which the second meniscus  320  adheres. For example, a change from a liquidphilic to a liquidphobic surface in a radially outward direction on the plate  200  could also result in pinning of the second meniscus  320  at that change because the shape of the meniscus will need to invert for it to pass from the liquidphilic to the liquidphobic surface. Additionally or alternatively, the second meniscus  320  may be pinned by changing the surface of the plate  200  from a rough to a smooth surface. When fully wetted the rough surface can act as a meniscus trap. If the surface is not fully wetted and the liquid is only on the peaks of the roughness, a rough surface can be liquidphobic such as in the so called lotus effect. Additionally, electro wetting could be used to locally trap the meniscus. This has an advantage in that it can be turned on and off. 
     Although not specifically illustrated in  FIG. 6 , the liquid supply system has an arrangement to deal with variations in the level of the liquid. This is so that liquid which builds up between the projection system PS and the barrier member  12  can be dealt with and does not spill. Such a build-up of liquid might occur during relative movement of the barrier member  12  to a projection system PS described below. One way of dealing with this liquid is to provide the barrier member  12  so that it is very large so that there is hardly any pressure gradient over the periphery (e.g., circumference) of the barrier member  12  during movement of the barrier member  12  relative to the projection system PS. In an alternative or additional arrangement, liquid may be removed from the top of the barrier member  12  using, for example, an extractor such as a single phase extractor similar to the extractor  120 . An alternative or additional feature is a liquidphobic or hydrophobic coating formed in a band around the top of the barrier member  12  surrounding the opening and/or around the last optical element of the projection system PS, radially outward of the optical axis of the projection system. The liquidphobic or hydrophobic coating helps keep the immersion liquid in the space. 
     A difficulty with a localized area liquid supply system is that it is difficult to contain all of the immersion liquid. Thus, avoiding leaving some liquid behind on the substrate as the substrate moves under the projection system is difficult. In order to avoid liquid loss, the speed at which the substrate moves under the liquid supply system should be limited due to potential bubble entrapment at the advancing meniscus. This is particularly so with an immersion liquid capable of generating high values of NA in the immersion lithography apparatus because they tend to have a lower surface tension than water as well as a higher viscosity. Breakdown speed of a meniscus scales with surface tension over viscosity so that a high NA liquid may be far harder to contain. Leaving liquid behind on the substrate in only certain areas may lead to a temperature variation throughout the substrate due to evaporation of the immersion liquid left behind and thus leading to overlay errors. Also or alternatively, as the immersion liquid evaporates, it is possible that a drying stain can be left behind on the substrate W. Also or alternatively, the liquid may diffuse into the resist on the substrate leading to inconsistencies in the photochemistry of the top surface of the substrate. Although a bath type solution (i.e. where the substrate is submerged in a container of liquid) may alleviate many of these problems, substrate swap in the immersion apparatus may be particularly difficult with a bath type solution. An embodiment of the present invention addresses one or more of these issues, or other issues not mentioned here, as will be described below. 
     In an embodiment of the present invention, substantially the whole of the top surface of the substrate W is covered in immersion liquid throughout imaging of the substrate. Furthermore, a member is positioned above the substrate. The member has a surface which faces the substrate and substrate table. Immersion fluid (in particular fluid which is not a gas, such as an incompressible fluid) extends between the top surface of the substrate and/or substrate table and the surface of the member facing the substrate and/or substrate table. This ensures that no evaporation of liquid can take place from the surface of the substrate. It also ensures that no surface waves can develop on the liquid, thereby causing deleterious vibrations. Furthermore contaminants may be prevented from entering the system and may be flushed out by an outward flow of liquid. Furthermore no gas knife is needed and which can be a source of contamination. 
     Liquid is removed from between the member and the substrate table by one or more extractors positioned either in the substrate table, the carrier of the substrate table or in the member itself. Due to limited flow rate, an extensive drain at the edge of the substrate table, or formed in the surface of the substrate table WT surrounding the substrate (when present on the substrate table WT), is not required. This may result in a smaller footprint of the substrate table. The extractor could be a single phase extractor, with or without a gas knife, or a gas drag principle extractor such as used in the barrier member disclosed in U.S. patent application Ser. No. 11/987,569, filed Nov. 30, 2007. 
     In an embodiment illustrated in  FIGS. 7 and 8 , the member is fixed in position relative to the substrate and substrate table during imaging. The projection beam passes through the member onto the substrate. Therefore, at least part of the member  1000  is transparent to radiation with a wavelength of the projection beam. In the embodiment illustrated in  FIGS. 9 and 10 , the member is substantially stationary in position relative to the projection system PS. The projection beam passes through a through hole  1075  in the member  1000  onto the substrate W. As will become clear, the two systems have similarities, particularly in the way in which replacement of a first substrate underneath the projection system with a second substrate is accomplished. Also as will become clear, the types of barrier member illustrated in  FIGS. 2-6  and other types of liquid supply system can be used in these embodiments. 
     As illustrated in cross-section in  FIG. 7   a,  a member  1000  is used. The member  1000  is in the form of a plate. The member  1000  is fixed relative to the substrate table WT (so called chuck or mirror block) during imaging of the substrate W. In an embodiment, a clamping mechanism is provided to attach the member  1000  to the substrate table WT during imaging. This can be accomplished, for example, by using a clamping mechanism mounted on the substrate table WT or mounted on the member  1000 . The clamping mechanism may be in the form of a vacuum or electrostatic attachment device, for example. 
     A gap exists between the member  1000  and the substrate table WT and substrate W. This gap is filled with immersion liquid. The immersion liquid therefore extends between the top surface of the substrate table WT and substrate W and the surface of the member  1000  facing the substrate table WT and substrate W. Therefore, the member  1000  can be thought of as floating on a film of liquid. 
     A barrier member  12  is used to provide liquid between a final element of the projection system PS and a surface of the member  1000  opposite to the surface of the member  1000  which faces the substrate table WT and substrate W. The barrier member  12  can be of any type. In particular the barrier member  12  can be of the types illustrated in  FIGS. 5 and 6 . However, any type of barrier member  12  can be used. Particularly suitable barrier members are those which provide liquid to a localized area. That is, the barrier members provide liquid to an area, in plan, which is smaller than the area, in plan, of the substrate W. 
     In an embodiment, the immersion liquid provided by the barrier member  12  and the immersion liquid between the member  1000  and substrate table WT is the same. The transparent part of the member  1000  may have a refractive index which closely matches to within 0.05-0.1% that of the immersion liquid provided by the barrier member  12  and/or between the member  1000  and substrate table WT. The member  1000  may have a width equal to or less than the substrate table WT or the distance between a seal device (as further discussed below) located at opposing sides of the substrate table WT. 
     The member  1000  may, for example, be or comprise a glass or quartz plate with a thickness of selected from between about 100 μm and about 1000 μm. In an embodiment, the thickness of member  100  is selected from the range of 500 μm to 800 μm. The plate is desirably made as thin as possible but does need to have some thickness so as to avoid major deflection and handling issues. The member  1000  must be transparent to the radiation used. If radiation with a wavelength of 193 nm is used, the plate could be made, for example, from quartz. 
     An advantage of providing the member  1000  in the embodiment of  FIG. 7  is that the top surface of the member  1000  (i.e. that which faces the projection system PS) can be provided with a surface (for example with a coating) which is ideally suited for the barrier member  12 . In particular, a coating can be chosen which is advantageous in terms of containment of liquid by the barrier member  12 . For example, the top surface of the member  1000  could be coated with a liquidphobic material (i.e. a material with which the immersion liquid has a contact angle of more than 70°, more than 90°, more than 100°, more than 110°, more than 120° or more than 130°). As the bottom surface of the member  1000  is in contact with immersion fluid, it may have a surface with a high contact angle (i.e. more than 70°, more than 90°, more than 100°, more than 110°, more than 120° or more than 130°). It is desirable for the bottom surface of the member to be liquidphobic as this reduces friction between the immersion liquid and the bottom surface of the member  1000 . 
     A liquid supply device (separate from the barrier member  12 ) may be provided to supply liquid to the gap between the member  1000  and the substrate table WT for use during imaging. Such a liquid supply device may provide liquid through the member  1000  or through the substrate table WT. In an embodiment, a radially outward flow is caused during imaging. Such a radially outward flow is advantageous from a defectivity point of view. This may be particularly so if the top surface of the substrate table WT and/or the substrate W are not all co-planar. For instance, the substrate W may be placed in a recess in the substrate table WT. In that instance a liquid supply device may be provided to provide liquid to that recess. Such a liquid supply device could be capable of generating a flow of liquid across the surface of the substrate W. This has an advantage in terms of temperature control, leaching of resist and/or top coat from the substrate W, etc. Particularly in the case of the top surface of the substrate table WT and substrate W being co-planar, a liquid supply device to provide liquid during imaging to the gap may not be necessary. The gap may be filled with liquid during substrate swap as described below. 
     A seal device may be provided between the substrate table WT and the member  1000 . Such a seal device is provided around the periphery (e.g., circumference) of the substrate W. The seal device may be arranged, for example, to provide a contactless seal. The contactless seal device may, for example, be similar to the contactless seal device on the bottom of the barrier member  12  described above in relation to  FIG. 5 . It is not necessary to have a seal device. This is because the film of liquid between the member  1000  and the top surface of the substrate table WT is relatively thin. Therefore, the liquid may be held in place by capillary forces (depending on contact angle). Also during imaging there is substantially no relative movement between the member  1000  and the substrate table WT. 
     If a liquid supply system is used to provide liquid to the gap between the substrate table WT and the member  1000 , then a liquid removal system may be necessary to remove liquid from the gap. The liquid removal system may be incorporated into the above seal device or may be totally separate. The contactless seal device used in the barrier members of  FIGS. 5 and 6  is suitable for the dual purpose of sealing and removing liquid. 
     The position of a substrate table in lithographic apparatus may be measured in two conventional ways. One way is to provide one or more mirrors on the edge of the substrate table and to use one or more laser interferometers to judge the position of the substrate table. Such a position measurement system is well suited to an embodiment of the present invention because the presence of the member  1000  does not interfere with such a system. A different position measurement system to measure the position of the substrate table WT is to use one or more grid plates which are positioned above the substrate table. One or more sensors and/or lasers mounted on the top surface (desirably at an outer edge) of the substrate table WT then interacts with the grid plate above the substrate table thereby to derive the position of the substrate table relative to the grid plate (such a system generally known as an encoder). The relative position of the grid plate to the projection system PS is known so that the position of the substrate table relative to the projection system PS can then be calculated. The grid plate may be part of a grid plate measurement system. The grid plate measurement system may have an associated controller and actuating system. Together these features may operate as a positing system to detect the position of the substrate table relative to the projection system and control the relative movement and/or position of the substrate table relative to the projection system. 
     With the presence of the member  1000  on top of the substrate table it is desirable, when the grid plate measurement system is used, to ensure that this can still function. As is illustrated in  FIG. 8 , it is possible to optimize the shape of the member  1000  in plan view and/or the length and/or width of the member  1000  so that the member  1000  is small enough so that it does not interfere with the laser and/or sensor  1010  of the grid plate measurement system. That is, the member  1000  may be made small enough so that it covers one or more other sensors such as a transmission image sensor (TIS), an interferometric wavefront measurement sensor (ILIAS) and/or spot sensor  1015  but that it does not block the laser and/or sensor  1010  of the grid plate measurement system. That is, the grid plate measurement system laser and/or sensor  1010  can be positioned at the outer edge of the substrate table WT at a position which is not covered by the member  1000 . A suitable location for the grid plate measurement system is each of the ears at the corners of the substrate table WT. Alternatively or additionally, the member  1000  may be transparent to the wavelength of radiation used by the grid plate measurement system. Then the beam of laser  1010  and the beam detected by sensor  1010  of the grid plate measurement system can pass through the member  1000 . In that case the presence of the member  1000  should be taken into account when calculating the position of the substrate table WT relative to the projection system PS. 
     In use, once the member  1000  is in position above the substrate table WT and clamped in place, the substrate table WT moves in unison with the member  1000  beneath the projection system PS. Imaging of the substrate W is then possible as normal by movement of the substrate W under the projection system PS. Substantially the whole of the top surface of the substrate W is covered in immersion liquid (which is present in the gap). Thereby the substrate W has substantially the same and constant conditions applied over its surface. Furthermore, because it is possible to have a coating on the top surface of the member  1000  the substrate W can move quickly under the projection system PS without substantial leaking of immersion liquid from the barrier member  12 . Thus, all areas of the substrate W can be imaged. A high velocity between the projection system PS and the substrate W is possible without substantial leaking of immersion liquid. Thus, throughput may be increased. At the same time, as processing conditions between different parts of the substrate remain substantially constant, overlay performance may be improved. 
     As will be clear from  FIGS. 7   a - 7   c,  the same member  1000  is used for imaging of different substrates W positioned on different substrate tables.  FIGS. 7   a - 7   c  illustrate how the substrate swap is achieved.  FIGS. 7   a - 7   c  should be considered in conjunction with  FIG. 8 . The location of the member  1000 , substrate tables and other structures in  FIG. 8  is similar to their position in  FIG. 7   b  in that a first substrate table WT 1  is moving away from under the projection system PS and a second substrate table WT 2  is moving into position to replace the first substrate table WT 1 . 
     As is illustrated in  FIG. 7   a,  the second substrate WT 2  (or carrier  1702  of the second substrate table WT 2 ) which is holding the second substrate W 2  is coupled to the first substrate WT 1  (or carrier  1701  of the first substrate table WT 1 ). This can occur prior to movement of substrate WT 1  from under the projection system PS. A releasable coupling system  1050  is used. The coupling system fixes the two substrate tables WT 1 , WT 2  together so that they move in unison. The coupling system is optional and movement in unison may in addition or alternatively be accomplished by careful positional control of the two substrate tables WT 1 , WT 2 . The coupling system  1050  can comprise components on both the first and second substrate tables WT 1 , WT 2  or only on the first substrate WT 1  or only on the second substrate table WT 2 . Any type of coupling system may be used. For example, a mechanical interlock may be involved or an electromagnetic or vacuum suction actuated interlock may be used. Any other type of coupling system can be used. Any combination of these coupling systems may used. The coupling system desirably includes a damping system so that any collision or hard coming together between the two substrate tables WT 1 , WT 2  is dampened. Thus the risk of damage may be reduced. More generally, the coupling system may be an actuating system comprising one or more actuators. 
     Before or after the two substrate tables WT 1 , WT 2  are coupled together the member  1000  is gripped so that its position relative to the projection system PS is substantially stationary. This gripping can be done by a gripper  1100 , for example a vacuum chuck, which is attached, for example, to the metrology frame RF. Alternatively or additionally, the gripper  1100  can be attached to other items, for example to the barrier member  12 , to the projection system PS or to the base frame BF or the pre-wetter  1200  and/or dryer  1300  (further described below). Once the member  1000  has been gripped, the first substrate table WT 1  can release the member  1000  (if it had previously held it) and can move from under the member  1000 . 
     As is illustrated in  FIGS. 7 and 8 , a pre-wetter  1200  and a dryer (fluid or liquid remover)  1300  are provided on either side of the member  1000  in a plane substantially co-planar to the top surface of the substrate W. The pre-wetter  1200  and/or dryer  1300  may be fixed in position. Alternatively the pre-wetter  1200  and/or dryer  1300  may be moveable in and out of position during substrate swap and during exposure. The pre-wetter  1200  and/or dryer  1300  may be independently moveable. In order to avoid cabling issues (e.g. entanglement) the first and second substrate tables will each travel in their own loop. For example, the first substrate table will make a loop which first passes under the pre-wetting station  1200 , then under the projection system PS and then under the drying station  130  and then move to a first side of the projection system (i.e. out of the paper in  FIG. 7  towards the viewer of the paper). The second substrate table will make a similar loop except that after passing under the dryer  1300 , the substrate table will move to a second side of the projection system opposite to the first side (i.e. into the paper in  FIG. 7  away from the viewer). In this way entanglement of cables of the first and second substrate tables which provide services to those tables should not occur. Furthermore, the x-y position of the pre-wetter  1200  and/or dryer  1300  can be the same for both substrate tables. 
     In an embodiment, the pre-wetter  1200  and/or dryer  1300  is elongate and has a length equal to (or more than) the width of the member  1000  and/or the substrate table WT. 
     During substrate swap the pre-wetter  1200  applies immersion liquid to the top surface of the new substrate table (the second substrate table WT 2  as illustrated) as it is moved under the member  1000  which has been fixed relative to the projection system PS. The liquid is provided at a flow rate (which may be adjustable or adaptable) and/or the speed of the substrate table WT is adjusted, to fill the gap with liquid. Thus, a film of liquid is already present on the substrate table and substrate as the substrate table WT 2  moves under the member  1000 . Thus, immersion liquid can be provided which extends between the top surface of the second substrate table WT 2  and the substrate W 2  and the surface of the member  1000  which faces the substrate table WT 2  and the substrate W 2 . 
     The pre-wetter  1200  provides liquid both to the top surface of the substrate table WT 2  as well as substrate W 2  and any sensor  1015  or other component present under the member  1000 . In an embodiment, the pre-wetter  1200  may provide liquid to components which will be under the member  1000  during imaging. 
     At the other end of the member  1000 , where the first substrate table WT 1  is moving out from under the member  1000 , the dryer  1300  dries the top surface of the substrate table WT 1 , the substrate WI and any sensor  1015  or other component present under the member  1000 . At the end of substrate swap, the pre-wetter  1200  and/or the dryer  1300  may be positioned in preparation for the next substrate swap. 
     The dryer  1300  and the pre-wetter  1200  can take any form. For example, the dryer  1300  can take the form of a gas drag principle dryer for example, a dryer such as that disclosed in U.S. Ser. No. 11/708,686 filed on Feb. 21, 2007. That document also describes a wetting system which may be used for the pre-wetter  1200 . 
     The immersion liquid between the member  1000  and the substrate table WT and/or substrate W may be stationary (zero flow) relative to the substrate table WT or there may be a liquid flow. The immersion liquid is substantially without gas atmosphere between the member  1000  and the substrate table WT 1  and substrate W 1 . This eliminates splashing and sloshing as well as evaporation and condensation issues and improves reproducability of shear forces among others in the liquid. 
     A swap bridge such as that described in US Patent publication number US 2007-0216881 A1 may be present between the two substrate tables WT 1 , WT 2 . The two substrate tables WT 1 , WT 2  move underneath the member  1000  together. The barrier member  12  may remain activated during substrate swap. This is because the outlet to the barrier member  12  is always blocked by the member  1000 . This is advantageous because it is then not necessary to provide a separate shutter member to block the aperture or to provide other means for maintaining the final element of the projection system wet during substrate swap. 
     Compared with systems on which only a localized area of the substrate is covered in liquid at any one time, the heat load on the substrate and substrate table is reduced. This is because such other systems require extraction of liquid along with gas from a gap between the substrate W and the substrate table WT. This is not required in this present system thereby reducing evaporation heat load. 
     In an embodiment, the member  1000  is positioned at a distance selected from about 100 μm to 500 μm or larger above the top surface of the substrate table WT 1 . In an embodiment, the gap is greater than 100 μm high, greater than 200 μm high, greater than 300 μm high, greater than 400 μm high, greater than 500 μm high or greater than 700 μm high. This is achieved for instance by providing one or more protrusions on the top surface of the substrate table WT on which the member  1000  sits thereby to space it away from the top surface of the substrate table WT. The protrusion may include the above described clamping mechanism. 
     Thickness uniformity of the member  1000  may be significant to avoid overly complicated compensation for thickness variation of the member  1000 . Furthermore, it may be necessary to carefully match the refractive index of the transparent material of the member  1000  with the refractive index of the immersion liquid. An embodiment illustrated with reference to  FIGS. 9   a  and  10  may overcome one or more of these difficulties, or other difficulty not mentioned herein, while maintaining one or more of the advantages of the embodiment of  FIGS. 7 and 8 . 
     The embodiment of  FIGS. 9   a  and  10  is the same as the embodiment of  FIGS. 7 and 8  except as described below. Features described in relation to the embodiment of  FIGS. 9   a  and  10  may also be applied to the embodiment of  FIGS. 7 and 8 . 
     As described above, the member  1000  and the substrate table WT move relative to each other in  FIGS. 9   a  and  10 . In an embodiment, the substrate table is moved with respect to the member  1000 . For example, the member  1000  is substantially stationary relative to the projection system PS. The member  1000  may be connected to a barrier member  12  or may be held substantially stationary relative to the barrier member  12  by being connected to the metrology frame RF or the base frame BF. Some actuation may be present so that the position of the member  1000  may be moved relative to the projection system PS and/or the barrier member  12  and/or metrology frame RF and/or base frame BF. This movement may be parallel and/or perpendicular to the optical axis of the projection system. The barrier member  12  may be of any type which provides liquid to the space between the projection system PS and the substrate. For example, any of the types of liquid supply systems illustrated in  FIGS. 2-6  are suitable. 
     The member  1000  has a through hole  1075  through which the projection beam passes. Positioned within the through hole is a liquid supply system to provide immersion liquid to a space between a final element of the projection system PS and the substrate W and/or the substrate table WT. Therefore, the beam PB of the projection system PS travels through the through hole of the member  1000 . In an embodiment, the liquid supply system is in the form of a barrier member, for example barrier member  12  of  FIGS. 5  or  6  optionally without liquid confinement. The barrier member  12  sits in the through hole  1075 . The barrier member  12  blocks the through hole. The barrier member  12  may be an integral part of the member  1000 . The liquid supply system is sealed to the inner periphery of the through hole  1075  in the member  1000 . Thereby the liquid in the gap between the member  1000  and the top surface of the substrate table WT and substrate W is not open to the atmosphere. As with the embodiment of  FIGS. 7 and 8 , the gap between the member  1000  and the substrate table WT and/or substrate W is entirely filled with immersion liquid. Desirably no gas is present in that gap. The immersion liquid extends between the top surface of the substrate table WT and substrate W and the surface of the member  1000  facing the top surface of the substrate table WT and substrate W. 
     Liquid may be provided to the gap between the member  1000  and the substrate table WT and substrate W by a separate liquid supply system. Alternatively or additionally, the barrier member  12  may be used to provide liquid to that gap. Liquid may only be provided to the gap by a pre-wetter  1200 , as discussed above. Liquid may be provided to the gap by a pre-wetter  1200  and during operation liquid is provided to the gap by the barrier member and/or the separate liquid supply system. 
     As will be appreciated, the barrier member  12  does not need to have perfect sealing characteristics between itself and the top surface of the substrate table WT and/or substrate W because any liquid which leaks between the barrier member  12  and the top surface of the substrate table WT or substrate W simply enters the gap where immersion liquid is present in any case and for which thermal requirements are less stringent. Indeed, in an embodiment it is desirable that the liquid is provided to the gap between the member  1000  and the substrate table WT and/or substrate W by the barrier member  12 . 
     The barrier member  12  provides a liquid to the space between the final element of the projection system and the substrate and/or substrate table. A further liquid supply system is provided to supply liquid to the gap between the member  1000  and the substrate table WT and substrate W. This liquid supply system may be part of the barrier member  12 . For example, the outlet  60  illustrated in  FIG. 6  could be used to provide liquid to the gap. In that case the sealing and extractor system and features radially outwardly of the outlet  60  illustrated in  FIG. 6  are not necessary. In this embodiment the top surface of the substrate W may or may not be co-planar with the top surface of the substrate table WT. In an embodiment, the member  1000  is at least two times the size, in plan, of the substrate table WT. That is, the width and depth (x, y) dimensions of the member  1000  are at least twice the corresponding dimensions of the substrate table WT to accommodate a full scan of the substrate W. 
     In an embodiment, a first flow of liquid is provided across the space between the final element of the projection system PS and the substrate and/or substrate table WT. This can be provided by inlet  20  in the barrier member  12  of  FIG. 6 . An outlet in the barrier member, for example outlet  13  or  20 , may be provided on the opposite side of the space so that a flow of liquid across the space  11  is present. A second flow of liquid in the gap between the member  1000  and the substrate table WT and/or substrate W can then be provided radially outward of the barrier member  12 . The radially outward flow may be provided by supplying liquid to the gap through outlet  60  in the barrier member  12 . A liquid flow radially outwardly of the barrier member  12  can be generated by removing the liquid from the gap radially outwardly of the barrier member  12 , as will be described below in more detail. The two liquid flows may be kept separate, so desirably liquid from one liquid flow does not substantially mix with liquid from the other liquid flow. The two flows are kept separate because the liquid in the flows may have different physical requirements. For example, the liquid in the first liquid flow is used as in optical component between the last optical element of the projection system and the substrate W. A patterned projection beam may pass through it during exposure. It is desirable for the liquid in the first liquid flow to have good optical qualities to optimally reduce a source of imaging defects. The liquid in the second liquid flow may be used to condition the surface of the substrate, for example, for exposure, and not be used as an optical component. Thus, the same level of control of the physical properties of the liquid in the second liquid flow as for the first liquid flow may be unnecessary. As the liquid in the second liquid flow may be unsuitable for use as an optical component, the two flows should be kept separate. 
     As with the embodiment of  FIGS. 7 and 8 , in the instance where the position of the substrate table WT is measured by an interferometer interacting with a mirror attached to the edge of the substrate table, this embodiment provides substantially no problems. However, if the grid plate measurement system is used, this embodiment may provide difficulties. However, different from the embodiment of  FIGS. 7 and 8 , an error associated with, for example, thickness non-uniformity in the embodiment of  FIG. 9   a  is a measurement error that can be corrected through calibration as opposed to an exposure error in the former embodiment. One way of alleviating this is to provide the grid plate (or plates) as the actual member  1000 . Alternatively it may be necessary to measure through the member  1000  onto the grid plate  1500  above the substrate table WT. This is the circumstance illustrated in  FIG. 9 . The one or more grid plates are attached to the member  1000  via one or more links  1505 . One or more actuators  1510  may be provided to help keep the member  1000  in place and/or dynamically decouple member  1000  from the grid plate  1500  and/or metrology frame RF. The member  1000  may experience a large force on it from the moving substrate table transmitted by liquid in the gap. 
     In order to help optimize the system where the grid plates  1500  and member  1000  are separated, a flow of gas  1550  is provided (radially inwardly) in the gap between the top of the member  1000  and the grid plate  1500 . This flow of gas is advantageous because it helps maintain the gap between the member  1000  and the grid plate  1500  clear of contaminants and also helps ensures that the gas in that gap has constant properties (e.g. temperature, pressure, composition, etc.). 
     The grid plate could be secured, e.g. glued, to the member  1000 . The grid plate could be positioned (e.g. attached) relatively to the metrology frame RF or to the base frame BF. If the position of the grid plate relative to the metrology frame RF is measured then the position of the substrate table WT relative to the metrology frame RF may be calculated. Thus, the projection system PS position can also be calculated. 
     During imaging, the substrate table WT moves under the projection system PS, the barrier member  12  and the member  1000 . The projection system PS, barrier member  12  and member  1000  are substantially stationary relative to one another. Therefore, the positions of the member  1000  and substrate table WT relative to each other changes as they move relative to each other. As a consequence the surfaces of the substrate table WT and the member  1000  that define the gap move relative to each other. For this reason a sealing device  1600  is provided which seals between the substrate table WT and the member  1000  radially outwardly of the substrate W. The sealing device confines immersion liquid between the surfaces of the member  1000  and substrate table WT and/or substrate W. In an embodiment, the sealing device  1600  is provided in the substrate table WT. Alternatively or additionally, the sealing device  1600  may be provided on the substrate table carrier  1701  and/or on the member  1000 . However, in the latter option this is at the expense of a larger substrate table WT. As can be seen from  FIGS. 9   a  and  10 , the sealing device  1600  is desirably mounted adjacent the outermost edge of the substrate table WT. The sealing device  1600  should be mounted such that it encloses all objects on the substrate table WT exposed through immersion liquid and surfaces that may come in contact with immersion liquid. Such objects include the substrate W, sensor  1015 , etc. 
     The sealing device  1600  may be in the form of sealing device such as that illustrated in the bottom of the barrier members  12  of  FIG. 5  or  6 , in which a meniscus is confined between member  1000  and the sealing device  1600 . The sealing device  1600  may be a contactless sealing device. The sealing device  1600  may be a liquid removal device. If the sealing device  1600  is a liquid removal device this helps in creating the radially outward flow of immersion liquid from the barrier member  12 . 
     Therefore, the system is provided with a first liquid removal device to remove liquid from the space between the final element of the projection system and the substrate. That liquid is provided by a first liquid supply device through inlet  20 ,  13 . A second liquid removal system is present to remove liquid from the gap between the surface of the member  1000  facing the substrate table and/or substrate i.e. the (sealing) liquid removal device. The second liquid removal system removes liquid radially outwardly of the substrate W. 
     The under surface of the member  1000  can be liquidphobic, for example treated, for example with a coating. This makes the task of the sealing device  1600  on the substrate table WT easier. This may be the same as the top surface of the member  1000  of  FIGS. 7 and 8 . 
     The gap between the member  1000  and the substrate table WT and/or substrate W is desirably selected from the range of 100 μm to 500 μm or smaller than 100 μm. For example the gap maybe less than 100 μm or less than 50 μm. The distance between the final element of the projection system PL and the substrate is desirably about 3 mm. The distance of the barrier member  12  from the substrate W and/or substrate table WT can be less than the distance between the member  1000  and the substrate W or substrate table WT to create a flow resistance for the optical immersion liquid between the last element of the projection system PS and the substrate table WT and/or substrate W. For example, the barrier member  12  may be only 0.15 mm from the top surface of the substrate W and/or substrate table WT. The member  1000  maybe transparent to the wavelength of radiation used in the grid plate measurement system. 
     During substrate swap of the embodiment of  FIGS. 9 and 10 , a pre-wetting station  1200  is used like in the embodiment of  FIGS. 7 and 8 . This can be done because the member  1000  is stationary relative to the projection system PS. The liquid removal system under the pre-wetting station  1200  is turned off during substrate swap. The first and second substrate tables WT 1 , WT 2  are also coupled together as in the embodiment of  FIGS. 7 and 8 , desirably through carriers  1701 ,  1702  of the substrate tables WT 1 , WT 2 . The liquid removal system  1600  on the substrate table WT itself can be used to remove the liquid from member  1000 . It is advantageous to have a drying station like in the embodiment of  FIGS. 7 and 8  to dry the top surfaces of the substrate table WT and substrate W because as the substrate table WT moves from under the member  1000  the liquid in the gap between the member  1000  and the substrate table WT is not necessarily dragged all the way to the liquid removal device  1600  at the edge of the substrate table WT. For this purpose a dryer may be provided, for example such as one or more dryers  1350  in  FIG. 10 . 
     In  FIG. 10  the grid plate  1500  of  FIG. 9   a  has been omitted for clarity. However, a grid plate would be provided above the member  1000  as well as to the right hand side of the member  1000  as illustrated. The grid plate on the right hand side of the member  1000  is for accurate positioning of the second substrate table WT 2 . A dryer  1350  is seen as peripherally (e.g., circumferentially) surrounding the member  1000  except for at a portion where the pre-wetter  1200  is located. The dryer  1350  may dry the top surface of the substrate table WT. It will be appreciated that it is not necessary for the dryer  1350  to completely surround the member  1000 . For example, the dryer may be provided only part way around the member  1000 . In that case the controller of the apparatus controls the substrate table WT such that it only emerges from under the member  1000  at the position where the dryer  1350  is located. The dryer is positioned adjacent an edge of the member  1000 . The dryer may even be mounted in or on the member  1000 . There may be two pre-wetters  1200  and/or dryers, one for each stage/substrate table. 
       FIG. 9   b  illustrates a variation on the embodiment of  FIG. 9   a  in which the member  1000  is the same as the grid plate  1500 .  FIG. 9   b  illustrates how forces may be applied to the member  1000 /grid plate  1500 . The principles and arrangement can be used equally in the embodiment of  FIG. 9   a.    
     Because there is a large area of liquid between the member  1000  and the top surface of the substrate table WT, large drag forces can be applied onto the member  1000  by movement of the substrate table WT beneath it. In order to compensate for these forces an actuator  1700  is provided. This actuator acts between the base frame BF (or the metrology frame RF) and the member  1000 . A controller  1800  controls the force applied to the member  1000  through actuator  1700 . The controller may apply the force to the member  1000  in either a feed-forward or a feed-back manner. Force compensation will generally be by applying a force in a plane substantially parallel to the plane of the member  1000 . Height actuation may also be provided. One or more actuators may be provided to activate the barrier member  12  in height. The barrier member  12  may be fixed in a plane perpendicular to the optical axis of the projection system relative to the metrology frame RF. 
     As is illustrated in  FIG. 10 , the substrate table WT (or at least the portion that is wetted) is, in plan, smaller, e.g. a great deal smaller, than the member  1000 . This is so that the substrate table WT can be moved into a position to allow imaging of all areas of the substrate W and sensor  1015 . 
     In an aspect, there is provided an immersion lithographic apparatus comprising: a substrate table constructed to hold a substrate, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a fluid supply system configured to supply an immersion fluid to a space between the projection system and the substrate and/or substrate table and to provide the immersion fluid to extend between the substrate table and/or substrate and the surface of the member, and a seal device configured to seal between the surface of the member and the substrate table. Optionally, at least part of the member is transparent to electromagnetic radiation used by a position measurement system of the substrate table. Optionally, the seal device is a contactless seal device. Optionally, the seal device comprises a gas inlet and a gas outlet to generate a gas flow to form the seal. Optionally, the seal device is configured to enclose a substrate and/or a sensor on the substrate table. Optionally, the immersion lithographic apparatus further comprises a dryer configured to dry a top surface of the substrate table as it emerges from under the member. Optionally, the member has a size, in plan, greater than the size, in plan, of the substrate table, desirably at least two times. Optionally, the immersion lithographic apparatus further comprises a pre-wetting station configured to apply immersion fluid onto a top surface of the substrate table prior to the substrate table being moved under the member. Optionally, the seal device includes a fluid removal device. Optionally, the member is sized such that during exposure of the substrate, the entire top surface of the substrate is covered in immersion fluid. Optionally, an under surface of the member is liquidphobic to the immersion fluid. Optionally, the immersion lithographic apparatus further comprises a grid plate above the member for use in measuring the position of the substrate table. Desirably, the immersion lithographic apparatus further comprises an outlet configured to provide a gas flow between the grid plate and the member. Optionally, the immersion lithographic apparatus further comprises an actuator configured to apply a force to the member to compensate for a force applied to the member through the fluid. Desirably, the immersion lithographic apparatus further comprises a controller configured to control the force applied by the actuator in a feed-forward manner. Optionally, the seal device is part of the substrate table. Optionally, the substrate table is constructed to hold a substrate such that a top surface of the substrate is substantially co-planar with a top surface of the substrate table. Optionally, the member defines a through hole for the passage therethrough of the patterned radiation beam. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a fluid supply system configured to supply an immersion fluid to a space between the projection system and the substrate and/or substrate table to extend between the substrate table and/or substrate and the surface of the member, a first fluid removal system configured to remove fluid from the space, and a second fluid removal system configured to remove fluid from between the surface of the member and the substrate table at a position outward of the substrate. Optionally, the fluid supply system comprises a first fluid supply system to supply fluid to the space between the projection system and the substrate and/or substrate table and a second fluid supply system to supply fluid between the member and the substrate table and/or the substrate. Desirably, the fluid supply systems and the fluid removal systems are configured so that the fluid supplied by the first fluid supply system is substantially entirely removed by the first fluid removal system. Desirably, the fluid supply systems and the fluid removal systems are configured so that the fluid supplied by the second fluid supply system is substantially entirely removed by the second fluid removal system. Optionally, the fluid supply system and the first fluid removal system co-operate to form a flow of fluid across the space. Optionally, the fluid supply system and the second fluid removal system co-operate to generate a substantially radially outwardly flow of fluid. Optionally, the second fluid removal system is effective to seal fluid between the member and the substrate table and/or substrate. Optionally, the second fluid removal system is in the substrate table. Optionally, the second fluid removal system is in the member. Optionally, the member is transparent to radiation used by a position measurement system for the substrate table. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate, a member with a surface facing the substrate table, a pre-wetting station configured to provide immersion fluid onto a surface of the substrate and/or substrate table prior to the substrate and/or substrate table moving under the member such that the immersion fluid extends between the surface of the substrate and/or substrate table and the surface of the member facing the substrate table. Optionally, the immersion lithographic apparatus further comprises fluid remover configured to remove fluid from a surface of the substrate and/or substrate table as the substrate table moves from underneath the member. Optionally, the pre-wetting station is elongate and has a length equal to a plan width of the member or a fluid remover. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate, a member with a surface facing the substrate table, and a fluid remover configured to remove fluid from a surface of the substrate and/or substrate table as the substrate and/or substrate table moves from underneath the surface of the member during movement of the substrate from under the member. Optionally, the fluid remover is positioned in or on or adjacent the member. Optionally, the fluid remover is configured to remove fluid from the surface of the substrate and/or substrate table as the substrate and/or substrate table moves from underneath the surface of the member during movement of the substrate from under the member following exposure. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a first substrate table constructed to hold a substrate, and a second substrate table constructed to hold a substrate, wherein the first and second substrate tables are releasably attachable together. Optionally, the substrate tables each comprise a sensor. 
     In an aspect, there is provided a method of providing a substrate under a projection system of an immersion lithographic apparatus, the method comprising moving a substrate on a substrate table under an elongate pre-wetting station which provides an immersion fluid on a top surface of the substrate and/or substrate table, and moving a pre-wet portion of the substrate and/or substrate table under a member which is held substantially stationary relative to the projection system such that immersion fluid extends between a surface of the member facing the substrate and/or substrate table and the substrate and/or substrate table. 
     In an aspect, there is provided a method of removing a substrate table from under a projection system of an immersion lithographic apparatus, the method comprising moving a substrate on a substrate table from under a member which is held substantially stationary relative to the projection system, and using a fluid removing device located over a portion of the substrate table which emerges as the substrate table is moved from under the member to remove fluid from the portion. Optionally, the using includes positioning the fluid removing device over a portion of the substrate table which emerges as the substrate table is moved from under the member to remove fluid from the portion. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a fluid supply system configured to supply a substantially incompressible immersion fluid to a space between the projection system and the substrate and/or substrate table and between the substrate table and/or substrate and the surface of the member, and a seal device configured to seal between the surface of the member and the substrate table. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a fluid supply system configured to supply an immersion fluid to a space between the projection system and the member and to supply an immersion fluid to a space between the member and the substrate and/or substrate table to extend between the substrate table and/or substrate and the surface of the member, and a seal device configured to seal between the surface of the member and the substrate table. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a fluid supply system configured to supply a substantially incompressible immersion fluid to a space between the projection system and the substrate and/or substrate table and to further supply a substantially incompressible immersion fluid between the substrate table and/or substrate and the surface of the member, and a seal device configured to seal between the surface of the member and the substrate table. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate such that a top surface of the substrate is substantially co-planar with a top surface of the substrate table, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and with a through hole for the passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a fluid supply system configured to supply an immersion fluid to a space between a final element of the projection system and the substrate and/or substrate table and to provide immersion fluid to extend between the substrate table and/or substrate and the surface of the member, and a seal device in the substrate table configured to seal between the surface of the member and the substrate table. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate such that a top surface of the substrate is substantially co-planar with a top surface of the substrate table, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and with a through hole for the passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a fluid supply system configured to supply a substantially incompressible immersion fluid to a space between a final element of the projection system and the substrate and/or substrate table and between the substrate table and/or substrate and the surface of the member, and a seal device in the substrate table configured to seal between the surface of the member and the substrate table. 
     In an aspect, there is provided an immersion lithographic apparatus comprising a substrate table constructed to hold a substrate, a projection system configured to project a patterned radiation beam onto a target portion of a substrate, a member held substantially stationary relative to the projection system and configured to allow passage therethrough of the patterned radiation beam, a surface of the member facing the substrate table, a first fluid supply system to supply an incompressible fluid to a space between the projection system and the substrate and/or substrate table, a second fluid supply system to supply an incompressible fluid between the member and the substrate table and/or the substrate, a first fluid removal system configured to remove fluid from the space, and a second fluid removal system configured to remove fluid from between the surface of the member and the substrate table at a position outward of the substrate. 
     Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. 
     The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm). 
     The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive and reflective optical components. 
     While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the embodiments of the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. Further, the machine readable instruction may be embodied in two or more computer programs. The two or more computer programs may be stored on one or more different memories and/or data storage media. 
     The controllers described above may have any suitable configuration for receiving, processing, and sending signals. For example, each controller may include one or more processors for executing the computer programs that include machine-readable instructions for the methods described above. The controllers may also include data storage medium for storing such computer programs, and/or hardware to receive such medium. 
     One or more embodiments of the invention may be applied to any immersion lithography apparatus, in particular, but not exclusively, those types mentioned above and whether the immersion liquid is provided in the form of a bath, only on a localized surface area of the substrate, or is unconfined on the substrate and/or substrate table. In an unconfined arrangement, the immersion liquid may flow over the surface of the substrate and/or substrate table so that substantially the entire uncovered surface of the substrate table and/or substrate is wetted. In such an unconfined immersion system, the liquid supply system may not confine the immersion liquid or it may provide a proportion of immersion liquid confinement, but not substantially complete confinement of the immersion liquid. 
     A liquid supply system as contemplated herein should be broadly construed. In certain embodiments, it may be a mechanism or combination of structures that provides a liquid to a space between the projection system and the substrate and/or substrate table. It may comprise a combination of one or more structures, one or more liquid inlets, one or more gas inlets, one or more gas outlets, and/or one or more liquid outlets that provide liquid to the space. In an embodiment, a surface of the space may be a portion of the substrate and/or substrate table, or a surface of the space may completely cover a surface of the substrate and/or substrate table, or the space may envelop the substrate and/or substrate table. The liquid supply system may optionally further include one or more elements to control the position, quantity, quality, shape, flow rate or any other features of the liquid. 
     The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.