Abstract:
An immersion liquid confinement apparatus recovers an immersion liquid from an immersion area that includes a gap between a projection system and an object of exposure in an immersion lithography system. The apparatus includes a confinement member that includes an outlet and an aperture through which a patterned image is projected onto the object. A first liquid-permeable member covers the outlet and has a first surface that faces the object and a second surface opposite the first surface, the second surface contacting a first chamber. A second liquid-permeable member has first and second oppositely-facing surfaces, the first surface of the second liquid-permeable member contacts the first chamber, the second surface of the second liquid-permeable member contacts a second chamber that is different from the first chamber. A hydrophobic porous member is provided between the first chamber and a vacuum system that supplies a low pressure to the first chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation-in-Part of application Ser. No. 12/573,356 filed Oct. 5, 2009 (now U.S. Pat. No. 8,477,284), which claims the benefit of U.S. Provisional Patent Application No. 61/193,019 filed Oct. 22, 2008 and claims the benefit of U.S. Provisional Patent Application No. 61/272,292 filed Sep. 9, 2009. This application claims the benefit of U.S. Provisional Application No. 61/272,292 filed Sep. 9, 2009 and of U.S. Provisional Application No. 61/272,422 filed Sep. 23, 2009. The disclosures of each of the above-identified applications is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The invention relates to immersion lithography apparatus and methods, and particularly to apparatus and methods for recovering immersion fluid. 
     A typical lithography apparatus includes a radiation source, a projection optical system and a substrate stage to support and move a substrate to be imaged. A radiation-sensitive material, such as a resist, is coated onto the substrate surface before the substrate is placed on the substrate stage. During operation, radiation energy from the radiation source is used to project an image defined by an imaging element through the projection optical system onto the substrate. The projection optical system typically includes a plurality of lenses. The lens or optical element closest to the substrate can be referred to as the last or final optical element. 
     The projection area during exposure is typically much smaller than the surface of the substrate. The substrate therefore is moved relative to the projection optical system in order to pattern the entire surface of the substrate. In the semiconductor industry, two types of lithography apparatus are commonly used. With so-called “step-and-repeat” apparatus, the entire image pattern is projected at one moment in a single exposure onto a target area of the substrate. After the exposure, the substrate is moved or “stepped” in the X and/or Y direction(s) and a new target area is exposed. This step-and-repeat process is performed multiple times until the entire substrate surface is exposed. With scanning type lithography apparatus, the target area is exposed in a continuous or “scanning” motion. For example, when the image is projected by transmitting light through a reticle or mask, the reticle or mask is moved in one direction while the substrate is moved in either the same or the opposite direction during exposure of one target area. The substrate is then moved in the X and/or Y direction(s) to the next scanned target area. The process is repeated until all of the desired target areas on the substrate have been exposed. 
     Lithography apparatus are typically used to image or pattern semiconductor wafers and flat panel displays. The word “substrate” as used herein is intended to generically mean any workpiece that can be patterned including, but not limited to, semiconductor wafers and flat panel displays. 
     Immersion lithography is a technique that can enhance the resolution of lithography exposure apparatus by permitting exposure to take place with a numerical aperture (NA) that is greater than the NA that can be achieved in conventional “dry” lithography exposure apparatus having a similar optical system. By filling the space between the final optical element of the projection system and the resist-coated substrate, immersion lithography permits exposure with light that would otherwise be internally reflected at the optic-air interface. Numerical apertures as high as the index of the immersion fluid (or of the resist or lens material, whichever is least) are possible in immersion lithography systems. Liquid immersion also increases the substrate depth-of-focus, that is, the tolerable error in the vertical position of the substrate, by the index of the immersion fluid compared to a dry system having the same numerical aperture. Immersion lithography thus can provide resolution enhancement without actually decreasing the exposure light wavelength. Thus, unlike a shift in the exposure light wavelength, the use of immersion would not require the development of new light sources, optical materials (for the illumination and projection systems) or coatings, and can allow the use of the same or similar resists as conventional “dry” lithography at the same wavelength. In an immersion system in which only the final optical element of the projection system and its housing and the substrate (and perhaps portions of the stage as well) are in contact with the immersion fluid, much of the technology and design developed for dry lithography can carry over directly to immersion lithography. 
     However, because the substrate moves rapidly in a typical lithography system, the immersion liquid in the immersion area including the space between the projection system and the substrate tends to be carried away from the immersion area. If the immersion liquid escapes from the immersion area, that liquid can interfere with operation of other components of the lithography system. One way to recover the immersion liquid and prevent the immersion liquid from contaminating the immersion lithography system is described in US2006/0152697 A1, the disclosure of which is incorporated herein by reference in its entirety. Also see US2007/0222967 A1, the disclosure of which is incorporated herein by reference in its entirety. 
     The systems described in US2006/0152697 A1 and US2007/0222967 A1 include an immersion liquid confinement member. The immersion liquid confinement member includes an outlet through which immersion liquid is recovered (collected) from the immersion area. The outlet is covered by a liquid-permeable member such as a mesh or porous member. A vacuum control unit applies suction to a chamber associated with the outlet so as to draw the immersion liquid on the substrate through the liquid-permeable member and the outlet. It is important to control the suction force applied to the liquid-permeable member. 
     SUMMARY 
     In the systems described above, a lengthy pathway of liquid exists between the vacuum control system and the liquid-permeable member that is disposed to face the substrate (see, for example, FIGS. 6-9 of US2006/0152697). The length of the liquid-filled pathway may cause delays in liquid sucking when liquid on the substrate (and/or the substrate-holding table) first touches the lower surface of the liquid-permeable member. A long liquid pathway also may cause a large pressure pulse to occur at the liquid-permeable member when the flow rate in the pathway abruptly changes. 
     U.S. patent application Ser. No. 12/573,356 describes an immersion liquid confinement apparatus that includes first and second liquid-permeable members to remove liquid from an immersion area that includes a gap between a projection system and an object (such as a substrate, a substrate holding table or both) in an immersion lithography system. The first liquid-permeable member covers an outlet in the confinement member and has a first surface that faces the object and a second surface opposite the first surface and which is in contact with a first chamber. The second liquid-permeable member is disposed in the first chamber and includes a first surface that is spaced from and opposes the second surface of the first liquid-permeable member. The second liquid-permeable member also includes a second surface opposite its first surface. The second surface of the second liquid-permeable member contacts a second chamber that is different from the first chamber. 
     In the apparatus of U.S. patent application Ser. No. 12/573,356, first and second vacuum systems are respectively coupled to the first and second chambers. The first vacuum system, coupled to the first chamber, draws the immersion liquid from the immersion area into the first chamber through the first liquid-permeable member so that the liquid flows from the first surface of the first liquid-permeable member to the second surface of the first liquid-permeable member. Preferably, liquid is not conveyed from the first chamber to the first vacuum system. Therefore, there is no lengthy liquid pathway between the first liquid-permeable member and the first vacuum system. The second vacuum system is coupled to the second chamber and draws liquid from the first chamber through the second liquid-permeable member into the second chamber such that the liquid flows through the second liquid-permeable member from its first surface to its second surface. 
     The second vacuum system also draws the immersion liquid from the second chamber so that the liquid can be disposed of and/or recycled and resupplied to the immersion area through, for example, an immersion liquid supply system. Although there may be a lengthy liquid pathway between the second vacuum system and the second liquid-permeable member, because the second liquid-permeable member does not directly face the object (substrate, substrate table, etc.), the pressure fluctuation caused by the change in flow through the second liquid-permeable member would not affect the pressure in the first chamber. 
     As noted above, it is preferable, in fact highly desirable, that liquid is not conveyed from the first chamber to the first vacuum system. If liquid enters the connecting path between the first chamber and the first vacuum system, the vacuum regulator of the first vacuum system would not be able to accurately control the vacuum pressure within the first chamber. One way to avoid or inhibit liquid entering the connecting path, which typically is a tube or a channel connecting the first chamber to the first vacuum system, is to design the connecting path with a relatively large cross-section so that any liquid entering the path could easily fall back into the first chamber. Another option is to place the port where the connecting path communicates with the first chamber high up within the chamber and to carefully control the liquid level within the first chamber so that the liquid never touches the port. Both of these options limit the design of the confinement member and tend to increase its size. 
     According to aspects of the invention, a hydrophobic porous member is placed at the connecting path to prevent liquid from traveling from the first chamber to the first vacuum system. Preferably the hydrophobic porous member is placed at the entrance port of the connecting path so that the liquid remains in the first chamber. The expression “hydrophobic” as used herein is intended to mean “repels liquid”, and is not limited to materials that repel water (that is, “hydro” is intended to encompass many liquids, not only water). 
     The size of the pores and the hydrophobicity of the hydrophobic material of the hydrophobic porous member are selected such that the low pressure (vacuum) provided by the first vacuum system will be insufficient to pull (suck) the immersion liquid through the hydrophobic porous member. Thus, only gas passes through the hydrophobic porous member. Liquid will not pass through the hydrophobic porous member when the first vacuum system applies its vacuum through the connecting path to the first chamber. 
     Using the hydrophobic porous member will permit the cross-section of the connecting path between the first chamber and the first vacuum system to be minimized, which can enable the size of the confinement member to be reduced. The size of the confinement member also can be reduced because the hydrophobic porous member (and thus the entrance port of the connecting path) can be located at many more places within the first chamber, including places that may become submerged in the liquid within the first chamber. 
     Other aspects of the invention relate to an immersion lithography apparatus having a projection system, a movable stage that is movable to a position below the projection system and that holds an object such as a substrate, and a confinement member according to aspects of the invention. 
     Other aspects of the invention relate to methods of manufacturing devices using the immersion lithography apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in conjunction with the following drawings of exemplary embodiments in which like reference numerals designate like elements, and in which: 
         FIG. 1  is a simplified elevational view schematically illustrating an immersion lithography system according to some embodiments of the invention; 
         FIG. 2  is a simplified side cross-sectional view of a liquid confinement member and its fluid removal system according to a first embodiment of the invention; 
         FIG. 3  is a simplified side cross-sectional view of a liquid confinement member and its fluid removal system according to a second embodiment of the invention; 
         FIG. 4  is a simplified side cross-sectional view of a liquid confinement member and its fluid removal system according to a third embodiment of the invention; 
         FIG. 5  is a flowchart that outlines a process for manufacturing a device in accordance with the invention; and 
         FIG. 6  is a flowchart that outlines device processing in more detail. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows an immersion lithography system  10  including a reticle stage  12  on which a reticle is supported, a projection system  14  having a last or “final” optical element  16 , and a fine-movement stage  22  on which a substrate  26  is supported, which in turn is movable over a coarse-movement stage  20 . An immersion liquid supply and recovery apparatus  18 , which is sometimes referred to herein as a liquid confinement member  18 , is disposed around the final optical element  16  of the projection system  14  so as to supply and recover an immersion fluid, which may be a liquid such as, for example, water, to/from a gap  28  between the final optical element  16  and the substrate  26 . In the present embodiment, the immersion lithography system  10  is a scanning lithography system in which the reticle and the substrate  26  are moved synchronously in respective scanning directions during a scanning exposure operation. The fine-movement stage  22  controls the position of the substrate  26  in one or more (preferably all) of the X, Y, Z, θX, θY and θZ directions with a higher degree of precision than the coarse-movement stage  20 , which is primarily used for moving the substrate  26  over longer distances, as is well known in the art. The upper surface of the fine movement stage  22  includes a substrate holder that preferably has a recess that holds the substrate  26 . In addition, a portion of the upper surface of the fine movement stage  22  that surrounds the held substrate has an upper surface that is substantially level with the upper surface of the held substrate so that when the immersion area is located near the edge of the substrate, liquid is still maintained between the liquid confinement member  18  and the upper surfaces of the substrate  26  and of the substrate holder. 
     The illumination source of the lithography system can be a light source such as, for example, a mercury g-line source (436 nm) or i-line source (365 nm), a KIT excimer laser (248 nm), an ArF excimer laser (193 nm) or a F 2  laser (157 nm). The projection system  14  projects and/or focuses the light passing through the reticle onto the substrate  26 . Depending upon the design of the exposure apparatus, the projection system  14  can magnify or reduce the image illuminated on the reticle. It also could be a 1× magnification system. 
     When far ultraviolet radiation such as from the excimer laser is used, glass materials such as silica glass and calcium fluoride that transmit far ultraviolet rays can be used in the projection system  14 . The projection system  14  can be catadioptric, completely refractive or completely reflective. 
     With an exposure device, use of the catadioptric type optical system can be considered. Examples of the catadioptric type of optical system are shown in U.S. Pat. Nos. 5,668,672 and 5,835,275. In these cases, the reflecting optical device can be a catadioptric optical system incorporating a beam splitter and concave mirror. U.S. Pat. No. 5,689,377 also uses a reflective-refracting type of optical system incorporating a concave mirror, etc., but without a beam splitter, and also can be employed with this invention. The disclosures of the above-mentioned U.S. patents are incorporated herein by reference in their entireties. 
       FIG. 2  is a cross-section view of an embodiment of a liquid confinement member  18 . As shown in  FIG. 2 , the liquid confinement member  18  maintains immersion liquid  80  in an immersion area, which includes the gap or space between the final optical element  16  of the projection system  14  and a portion of the upper surface of the substrate  26 . The immersion liquid  80  in  FIG. 2  can be seen as occupying only a portion of the upper surface of the substrate  26 . That is, the size of the immersion area is smaller than the size of the upper surface of the substrate  26  such that only part of the upper surface of the substrate is covered. Depending on the relative position of the substrate  26  with respect to the projection system  14  (and the liquid confinement member  18 ) the immersion area can be disposed over the substrate, over a portion of the substrate and a portion of the substrate holder that surrounds the substrate, or over only a portion of the substrate holder (for example, when the substrate is moved such that it no longer is disposed below the projection system  14 ). In addition, if the exposure apparatus includes a measurement stage that is used to take measurements regarding the projection system  14 , the immersion area can be formed between an upper surface of the measurement stage and the final optical element  16  (there would be no substrate holder on the measurement stage). 
     The liquid confinement member  18  includes at least one (and preferably more than one) liquid supply inlets  30  through which the immersion liquid  80  is supplied to the immersion area. The liquid is supplied to the supply inlets  30  through a supply path, one end of which is connected to a liquid supply  15  and the other end of which is connected to an inlet manifold of the liquid confinement member  18 . The liquid supplied to the supply inlets  30  reaches the substrate  26  after passing through aperture  35  disposed centrally in the confinement member  18 . As shown in  FIG. 2 , the supply and recovery of the immersion liquid is controlled so that the level of the immersion liquid between the liquid confinement member  18  and the final optical element  16  is maintained above the lower surface of the final optical element  16  so that the exposure light transmitted through the projection system  14  travels only through the immersion liquid (that is, the exposure light does not travel through any air or gas) before reaching the substrate  26 . 
     In the  FIG. 2  embodiment, the liquid confinement member  18  includes an outlet  40 . In the  FIG. 2  embodiment, the outlet  40  is an annular groove that surrounds aperture  35 , and thus also surrounds the immersion area. Liquid is removed from the immersion area and from the surface of the substrate  26  (and/or the surface of the substrate holder) via the outlet  40 . The outlet  40  is covered by a first liquid-permeable member  52  such that a first chamber  42  is disposed at least partially within the liquid confinement member  18 . A first (lower) surface of the first liquid-permeable member  52  faces toward the substrate  26 , whereas a second (upper) surface of the first liquid-permeable member  52  contacts the chamber  42 . Liquid that passes through the first liquid-permeable member  52  from its first surface to its second surface thus enters the first chamber  42 . 
     Although the outlet  40  (and thus also the first liquid-permeable member  52 ) is a continuous groove in  FIG. 2 , the outlet  40  (and thus the first liquid-permeable member  52  covering the outlet) could be a series of arc-shaped portions, straight portions or angled portions that collectively surround the immersion area and communicate with first chamber  42 . Furthermore, the outlet could be circular in plan view, rectangular or any other shape in plan view. 
     A second liquid-permeable member  54  is disposed within first chamber  42  and includes a first (lower) surface that is spaced from and faces the second (upper) surface of the first liquid-permeable member  52 . The second liquid-permeable member  54  also includes a second (upper) surface opposite its first surface and that contacts a second chamber  60 . The second chamber  60  thus is defined by the second liquid-permeable member  54  and walls or other structure. 
     The first chamber  42  communicates with a first vacuum system V 1  that applies a suction force to the first chamber  42 . The suction force is sufficient to draw immersion liquid through the first liquid-permeable member  52  into the first chamber  42 . The first vacuum system V 1  is controlled so that the suction force applied to the first liquid-permeable member  52  is maintained below the bubble point of the first liquid-permeable member  52 . That is, the first vacuum system V 1  controls a pressure in the first chamber  42  such that substantially only liquid is removed from the immersion area and/or from the surface of the substrate  26  (and/or the surface of the substrate holder) through the first liquid-permeable member  52 , but not gas from the surface of the substrate  26  (and/or the surface of the substrate holder). However, the first vacuum system V 1  does not cause the liquid to be removed from first chamber  42 . 
     Rather, a second vacuum system V 2  that communicates with the second chamber  60  causes liquid within the first chamber  42  to be drawn through the second liquid-permeable member  54  into the second chamber  60 . The liquid within the second chamber  60  is then removed from the second chamber  60  via the suction force caused by second vacuum system V 2 . The second vacuum system V 2  is controlled so that the suction force applied to the second liquid-permeable member  54  is maintained below the bubble point of the second liquid-permeable member  54 . That is, the second vacuum system V 2  controls a pressure in the second chamber  60  such that substantially only liquid is removed from the first chamber  42  through the second liquid-permeable member  54 , but not gas from the first chamber  42 . The vacuum systems V 1  and V 2  can be systems for controlling a vacuum force as described, for example, in US2006/0152697 A1 and US2007/0222967 A1, the disclosures of which are incorporated herein by reference in their entireties. 
     As noted above, it is highly desirable that liquid is not conveyed from the first chamber  42  to the first vacuum system V 1 . If liquid enters the connecting path  90  between the first chamber  42  and the first vacuum system V 1 , the vacuum regulator (not shown) of the first vacuum system V 1  would not be able to accurately control the vacuum pressure within the first chamber  42 . One way to avoid or inhibit liquid entering the connecting path  90 , which typically is a tube or a channel connecting the first chamber  42  to the first vacuum system V 1 , is to design the connecting path  90  with a relatively large cross-section so that any liquid entering the path  90  could easily fall back into the first chamber  42 . For example, the cross-section of the connecting path, when no hydrophobic porous member is provided, should be at least 8 mm. Another option is to place the port  92  where the connecting path  90  communicates with the first chamber  42  high up within the chamber  42  and to carefully control the liquid level within the first chamber  42  so that the liquid never touches the port  92 . Both of these options limit the design of the confinement member  18  and tend to increase its size. 
     Accordingly, a hydrophobic porous member  96  is placed at the connecting path  90  to prevent liquid from traveling from the first chamber  42  to the first vacuum system V 1 . Preferably the hydrophobic porous member  96  is placed at the entrance port  92  of the connecting path  90  so that the liquid remains in the first chamber  42 . The expression “hydrophobic” as used herein is intended to mean “repels liquid”, and is not limited to materials that repel water (that is, “hydro” is intended to encompass many liquids, not only water). 
     According to one embodiment, the hydrophobic porous member  96  is a porous body of polytetrafluoroethylene (Teflon™), or is a porous body having surfaces coated with polytetrafluoroethylene, although other materials that are hydrophobic with respect to the immersion liquid  80  can be used. Other hydrophobic materials include, for example, perfluoroalkoxy (PFA) and fluorinated ethylene propylene (FEP). The size of the pores could range from 1-150 μm in diameter, for example. Because of the hydrophobicity and the small diameter of the pores, immersion liquid  80  would not be able to enter the pores unless the pressure controlled by first vacuum system V 1  is lower than the pressure caused by the repulsive capillary force between the hydrophobic pores and the immersion liquid  80 . The pressure caused by the repulsive capillary force can be calculated by the following equation:
 
Bubble point pressure=2γ cos θ/ r,  
         where γ=surface tension of the immersion liquid,   θ=contact angle of immersion liquid on the hydrophobic member,   r=radius of the largest pore in the hydrophobic member.       

     When choosing the material of the hydrophobic member  96 , the properties of the member (pore size and hydrophobicity) should be considered so that the required pressure inside the first chamber  42  is higher than the pressure caused by the repulsive capillary force between the liquid and the hydrophobic member  96 . That is, the size of the pores and the hydrophobicity of the hydrophobic material of the hydrophobic porous member  96  are selected such that the low pressure (vacuum) provided by the first vacuum system V 1  will be insufficient to pull (suck) the immersion liquid through the hydrophobic porous member  96 . Thus, only gas passes through the hydrophobic porous member  96 . Liquid will not pass through the hydrophobic porous member  96  when the first vacuum system V 1  applies its vacuum through the connecting path  90  to the first chamber  42 . 
     The manner in which the liquid confinement member  18  is controlled to remove liquid now will be described. 
     For context, a system such as the system described in US2006/0152697 A1 will be described. The system of US2006/0152697 A1 is similar to what is shown in  FIG. 2  of the present application except that there is no second chamber  60 , second liquid-permeable member  54 , second vacuum control system V 2 , or hydrophobic porous member  96 . The system of US2006/0152697 A1 simply draws immersion liquid through a single liquid-permeable member such as the first liquid-permeable member  54  shown in Applicants&#39;  FIG. 2 . The liquid fills a single chamber, such as first chamber  42 , and the liquid is drawn from chamber  42  by a single vacuum system such as system V 1  of Applicants&#39;  FIG. 2 . Accordingly, there is a lengthy liquid pathway between the vacuum system and the liquid-permeable member that faces the substrate. Therefore, as mentioned earlier, when liquid initially contacts the lower surface of the liquid-permeable member, there is a delay in the recovery of that liquid due to the time required to accelerate the liquid in the lengthy liquid pathway. In addition, the long liquid pathway causes a large pressure pulse to occur when the flow rate in the pathway changes abruptly, which occurs, for example, when exposure begins and ends for each substrate and when rapid movements of the substrate occur, for example, between the exposure of different shot areas on the substrate. Accordingly, to avoid exceeding the bubble point at the liquid-permeable member, the suction force provided by the vacuum control system typically is reduced substantially below the suction force that would exceed the bubble point of the liquid-permeable member. Thus, even when there are pressure pulses, the vacuum force will not exceed the bubble point of the liquid-permeable member. Reducing the suction force, however, further reduces the responsiveness of the liquid recovery system, for example, when liquid initially touches the liquid-permeable member. This can cause liquid to escape from below the liquid confinement member. Reducing the suction force also reduces the maximum flow rate by which the liquid can be collected. For example, in a system where the bubble point of the liquid-permeable member is 2 KPascal, the vacuum control system may be controlled so that the steady state suction force applied to the liquid-permeable member is about 1 KPascal. 
     In the system described in Applicants&#39;  FIG. 2 , a suction force much closer to the bubble point of the first liquid-permeable member can be applied to the first-liquid permeable member by first vacuum control system V 1  because there is a very short liquid path above the first liquid-permeable member  52  in the first chamber  42 . In particular, the length of the liquid path is approximately equal to the distance between the lower surface of the second liquid-permeable member  54  and the upper surface of the first liquid-permeable member  52 . This distance can be as small as 3 mm. 
     Because there is a short liquid path formed above the first liquid-permeable member  52 , there is substantially no delay in liquid sucking when liquid first touches the lower surface of the first liquid-permeable member  52 . Furthermore, the short liquid pathway formed above the first liquid-permeable member  52  will not cause large pressure pulse to occur when the flow rate in that pathway changes abruptly. Accordingly, the first vacuum control system V 1  can be controlled so as to apply a suction force to the first liquid-permeable member that is very close to the bubble point of the first liquid-permeable member  52 . Thus, the conditions occurring at the first liquid-permeable member  52  are very stable regardless of the rate of liquid flow through the first liquid-permeable member  52 . 
     In addition, the hydrophobic porous member  96  will prevent the first vacuum system V 1  from becoming fouled with immersion liquid, and will permit the cross-section of the connecting path  90  between the first chamber  42  and the first vacuum system V 1  to be minimized, which can enable the size of the confinement member  18  to be reduced. The size of the confinement member  18  also can be reduced because the hydrophobic porous member  96  (and thus the entrance port  92  of the connecting path  90 ) can be located at many more places within the first chamber  42 , including places that may become submerged in the liquid within the first chamber  42 . 
     The control of flow through the second liquid-permeable member  54  is similar to what was described above with respect to the control of flow through a system having a single liquid-permeable member. In particular, the suction force applied by second vacuum control system V 2  to the second liquid-permeable member  54  maintains the suction force at the second liquid-permeable member  54  far enough below the bubble point of the second liquid-permeable member  54  so that large pressure pulses that may occur at the second liquid-permeable member  54  when there are abrupt changes in liquid flow do not exceed the bubble point of the second liquid-permeable member  54 . When there are large changes in flow, however, the excess liquid, which cannot initially be drawn fast enough through the second liquid-permeable member  54  is accommodated within the first chamber  42  (that is, the liquid level within first chamber  42  will rise when there is a sudden increase in flow through the first liquid-permeable member  52 ). However, once that surge in flow reduces and the flow through the second liquid-permeable member  54  reaches a more steady state, the level of liquid within the first chamber  42  will gradually decrease until it reaches the steady condition shown in  FIG. 2 . 
     Although the second liquid-permeable member  54  in  FIG. 2  is shown as arranged substantially horizontal, it is preferable that the second liquid-permeable member  54  be arranged so that it is not horizontal along its entire surface because air bubbles may get trapped under the lower surface of a flat horizontal member  54  when the liquid flow is low. Accordingly, alternative embodiments shown in  FIGS. 3 and 4  provide a second liquid-permeable member in which a distance between the lower surface of the second liquid-permeable member and the upper surface of the first liquid-permeable member varies for different portions of the second liquid-permeable member. 
       FIG. 3  shows an embodiment in which the second liquid-permeable member  54   a  is slanted so that one portion of it is closer to the first liquid-permeable member  52  than is another portion of the second liquid-permeable member  54   a.    
       FIG. 4  shows an embodiment in which the second liquid-permeable member  54   b  is convex so that different portions of it are spaced different distances from the first liquid-permeable member  52 . In addition,  FIG. 4  shows a modification in which the connecting path  90  between the first chamber  42  and the first vacuum system V 1  is at least partially placed within the connecting path between the second chamber  60  and the second vacuum system V 2 . This modification reduces the number of connections between the confinement member  18  and the vacuum systems because a single (dual lumen) connection passage is provided between the confinement member  18  and the vacuum systems. Such a modification is facilitated by the hydrophobic member  96  because the hydrophobic member  96  enables the diameter of the connecting path  90  to be reduced. The modification shown in  FIG. 4  also can be applied to the embodiments shown in  FIGS. 2 and 3 . 
     The embodiments of  FIGS. 3 and 4  also are advantageous in that they can more readily accommodate changes in flow through the first liquid-permeable member  52  because, as the flow rate increases, more area of the second liquid-permeable member  54   a  or  54   b  will come into contact with the liquid in chamber  42 , thereby increasing the flow rate capacity through the second liquid-permeable member  54   a / 54   b.    
     In certain embodiments, the immersion fluid is a liquid having a high index of refraction. In different embodiments, the liquid may be pure water, or a liquid including, but not limited to, cedar oil, fluorin-based oils, “Decalin” or “Perhydropyrene.” 
     The first liquid-permeable member  52 , or the second liquid-permeable member  54 , or both of the first and second liquid-permeable members may be a porous member such as a mesh or may be formed of a porous material having holes typically with a size smaller than 150 μm. For example, the porous member may be a wire mesh including woven pieces or layers of material made of metal, plastic or the like, a porous metal, a porous glass, a porous plastic, a porous ceramic, a sponge or a sheet of material having chemically etched holes (for example, by photo-etching). The first and second liquid-permeable members could be identical in structure or could differ in one or more of pore size, thickness and porosity. In certain embodiments, the first vacuum system V 1  may be controlled so that the suction force applied to the first liquid-permeable member  52  is maintained at or above the bubble point of the first liquid-permeable member  52 . That is, the first vacuum system V 1  may control a pressure in the first chamber  42  such that a mixture of liquid and gas is removed from the immersion area and/or from the surface of the substrate  26  (and/or the surface of the substrate holder) through the first liquid-permeable member  52 . In certain embodiments, the second vacuum system V 2  may be controlled so that the suction force applied to the second liquid-permeable member  54  is maintained at or above the bubble point of the second liquid-permeable member  54 . That is, the second vacuum system V 2  may control a pressure in the second chamber  60  such that a mixture of liquid and gas is removed from the first chamber  42  through the second liquid-permeable member  54 . 
     The use of the exposure apparatus described herein is not limited to a photolithography system for semiconductor manufacturing. The exposure apparatus, for example, can be used as an LCD photolithography system that exposes a liquid crystal display device pattern onto a rectangular glass plate, or a photolithography system for manufacturing a thin film magnetic head. 
     Semiconductor devices can be fabricated using the above described systems, by the process shown generally in  FIG. 5 . In step  801  the device&#39;s function and performance characteristics are designed. Next, in step  802 , a mask (reticle) having a pattern is designed according to the previous designing step, and in a step  803 , a wafer is made from a silicon material. The mask pattern designed in step  802  is exposed onto the wafer from step  803  in step  804  by a photolithography system described hereinabove in accordance with aspects of the invention. In step  805 , the semiconductor device is assembled (including the dicing process, bonding process and packaging process). Finally, the device is then inspected in step  806 . 
       FIG. 6  illustrates a detailed flowchart example of the above-mentioned step  804  in the case of fabricating semiconductor devices. In  FIG. 6 , in step  811  (oxidation step), the wafer surface is oxidized. In step  812  (CVD step), an insulation film is formed on the wafer surface. In step  813  (electrode formation step), electrodes are formed on the wafer by vapor deposition. In step  814  (ion implantation step), ions are implanted in the wafer. The above mentioned steps  811 - 814  form the preprocessing steps for wafers during wafer processing, and selection is made at each step according to processing requirements. 
     At each stage of wafer processing, when the above-mentioned preprocessing steps have been completed, the following post-processing steps are implemented. During post-processing, first, in step  815  (photoresist formation step), photoresist is applied to a wafer. Next, in step  816  (exposure step), the above-mentioned exposure device is used to transfer the circuit pattern of a mask (reticle) to a wafer. Then in step  817  (developing step), the exposed wafer is developed, and in step  818  (etching step), parts other than residual photoresist (exposed material surface) are removed by etching. In step  819  (photoresist removal step), unnecessary photoresist remaining after etching is removed. Multiple circuit patterns are formed by repetition of these preprocessing and post-processing steps. 
     A photolithography system (an exposure apparatus) according to the embodiments described herein can be built by assembling various subsystems in such a manner that prescribed mechanical accuracy, electrical accuracy, and optical accuracy are maintained. In order to maintain the various accuracies, prior to and following assembly, every optical system is adjusted to achieve its optical accuracy. Similarly, every mechanical system and every electrical system are adjusted to achieve their respective mechanical and electrical accuracies. The process of assembling each subsystem into a photolithography system includes providing mechanical interfaces, electrical circuit wiring connections and air pressure plumbing connections between each subsystem. Each subsystem also is assembled prior to assembling a photolithography system from the various subsystems. Once a photolithography system is assembled using the various subsystems, a total adjustment is performed to make sure that accuracy is maintained in the complete photolithography system. Additionally, it is desirable to manufacture an exposure system in a clean room where the temperature and cleanliness are controlled. 
     While the invention has been described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments or constructions. The invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the preferred embodiments are shown in various combinations and configurations, that are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.