Abstract:
An apparatus and method provide fluid for immersion lithography. A nozzle member that can move in a direction, is arranged to encircle a space under the optical element. The nozzle member can have an input to supply the immersion liquid to the space under the optical element during the exposure, and an output to remove the immersion liquid from a gap between the nozzle member and the wafer during the exposure. Immersion liquid can be supplied at a first rate to the space from a first portion of the nozzle member and at a second rate to the space from a second portion during the exposure. A wafer substrate is exposed by light through the immersion liquid.

Description:
INCORPORATION BY REFERENCE 
       [0001]    This is a divisional of U.S. patent application Ser. No. 11/579,442 filed Nov. 2, 2006, which is a National Phase of International Application No. PCT/US2005/014200 filed Apr. 27, 2005, which claims the benefit of U.S. Provisional Patent Application No. 60/568,345 filed May 4, 2004, U.S. Provisional Patent Application No. 60/623,170 filed Oct. 29, 2004 and U.S. Provisional Patent Application No. 60/623,172 filed Oct. 29, 2004. Said International Application No. PCT/US2005/014200 also is a Continuation-in-Part of International Application No. PCT/US2004/022915 filed Jul. 16, 2004. All of said above-identified applications are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    This invention relates generally to immersion lithography and, more particularly, to apparatus and methods for providing fluid for immersion lithography. Specifically, this invention relates to improving fluid flow during immersion lithography. 
         [0003]    An exposure apparatus is one type of precision assembly that is commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that retains a reticle, an optical assembly, a wafer stage assembly that retains a semiconductor wafer, a measurement system, and a control system. The resist coated wafer is placed in the path of the radiation emanating from a patterned mask and exposed by the radiation. When the resist is developed, the mask pattern is transferred onto the wafer. In microscopy, extreme ultraviolet (EUV) radiation is transmitted through a thin specimen to a resist covered plate. When the resist is developed, a topographic shape relating to the specimen structure is left. 
         [0004]    Immersion lithography is a technique which can enhance the resolution of projection lithography by permitting exposures with numerical aperture (NA) greater than one, which is the theoretical maximum for conventional “dry” systems. By filling the space between the final optical element and the resist-coated target (i.e., wafer) with immersion liquid, immersion lithography permits exposure with light that would otherwise be totally internally reflected at an optic-air interface. Numerical apertures as high as the index of the immersion liquid (or of the resist or lens material, whichever is least) are possible. Liquid immersion also increases the wafer depth of focus, i.e., the tolerable error in the vertical position of the wafer, by the index of the immersion liquid compared to a dry system with the same numerical aperture. 
         [0005]    Immersion lithography thus has the potential to provide resolution enhancement equivalent to the shift from 248 to 193 nm. Unlike a shift in the exposure wavelength, however, the adoption of immersion would not require the development of new light sources, optical materials, or coatings, and should allow the use of the same or similar resists as conventional lithography at the same wavelength. In an immersion system where the final optical element and the wafer (and perhaps the stage as well) are in contact with the immersion fluid, much of the technology and design developed for conventional tools in areas such as contamination control, carry over directly to immersion lithography. 
         [0006]    One of the challenges of immersion lithography is to design a system for delivery and recovery of an immersion fluid, such as water, between the final optical element and the wafer, so as to provide a stable condition for immersion lithography. 
         [0007]    For example, injecting immersion fluid under an optical element that is inconsistent or non-uniform throughout the immersion area can adversely affect the lithography process. In addition, as immersion fluid moves in and out of the immersion area, air can be trapped under the optical element that can also affect the lithography process. Furthermore, residue immersion fluid left over in the immersion area from a previous immersion process can raise the temperature of the immersion fluid under the optical element. That is, immersion fluid left over from a previous process, which has been exposed to light again, can raise the temperature of the immersion fluid in a subsequent process under the optical element. This can adversely affect the wafer and lithography process. Therefore, what is needed is improved immersion lithography techniques for the flow and removal of immersion fluid. 
       SUMMARY 
       [0008]    According to certain embodiments, a method for immersion lithography includes injecting immersion fluid into an inner cavity in a direction that is different than a direction in which the nozzle moves; and exposing light through the immersion fluid onto a wafer substrate covered with photoresist. 
         [0009]    According to certain embodiments, a nozzle for immersion lithography includes an inner cavity and an immersion fluid input. The inner cavity holds immersion fluid. The immersion fluid input injects immersion fluid into the inner cavity in a direction that is different than a direction in which a wafer substrate moves. 
         [0010]    According to certain embodiments, a method for immersion lithography includes injecting immersion fluid at a first rate; injecting immersion fluid at a second rate, the second rate being different than the first rate; and exposing light through the immersion fluid onto a wafer substrate covered with photoresist. 
         [0011]    According to certain embodiments, a nozzle for immersion lithography includes an inner cavity, a first input, and a second input. The inner cavity holds immersion fluid. The first input injects immersion fluid at a first rate. The second input injects immersion fluid at a second rate. The second rate is different than the first rate. 
         [0012]    According to certain embodiments, a method for immersion lithography includes injecting immersion fluid into an inner cavity at a first side and a second side in a direction that is different than a direction in which a wafer substrate moves, the immersion fluid being injected from the first side having a flow rate that is different from the immersion fluid being injected from the second side; and exposing light through the immersion fluid onto a wafer substrate covered with photoresist. 
         [0013]    According to certain embodiments, an apparatus includes an inner cavity, a first input, and a second input. The inner cavity holds immersion fluid. The first input is at a first side of the inner cavity and injects immersion fluid into the inner cavity at a first direction and a first rate. The second input is at a second side of the inner cavity and injects immersion fluid into the inner cavity at a second direction and a second rate. The first rate is different than the second rate, and the first and second directions are different than a scanning axis direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a simplified elevational view schematically illustrating an immersion lithography system according to certain embodiments; 
           [0015]      FIG. 2  is a perspective view of a nozzle for fluid delivery and recovery for immersion lithography according to certain embodiments; 
           [0016]      FIG. 3  is a simplified cross-sectional view of the nozzle of  FIG. 2  according to certain embodiments; 
           [0017]      FIG. 4  is a cross-sectional view of the inner part of the nozzle of  FIG. 2  according to certain embodiments; 
           [0018]      FIG. 5  is a simplified cross-sectional view of the nozzle according to certain embodiments; 
           [0019]      FIG. 6  is a simplified view schematically illustrating a pressure control system for fluid recovery in an immersion lithography system according to certain embodiments; 
           [0020]      FIG. 7  is a simplified view schematically illustrating a pressure control system for fluid recovery in an immersion lithography system according to certain embodiments; 
           [0021]      FIG. 8  is a simplified view schematically illustrating a pressure control system for fluid recovery in an immersion lithography system according to certain embodiments; 
           [0022]      FIG. 9  is a simplified view schematically illustrating a pressure control system for fluid recovery in an immersion lithography system with immersion fluid stagnation prevention according to certain embodiments; 
           [0023]      FIG. 10  is a perspective view of a nozzle for fluid delivery and recovery for immersion lithography where immersion fluid is injected on a non-scanning axis according to certain embodiments; 
           [0024]      FIG. 11  is a perspective view of a nozzle for fluid delivery and recovery for immersion lithography where immersion fluid is input from a left side faster than immersion fluid is input from a right side according to certain embodiments; 
           [0025]      FIG. 12  is a perspective view of a nozzle for fluid delivery and recovery for immersion lithography including a porous member according to certain embodiments; and 
           [0026]      FIG. 13  is a perspective view of a nozzle for fluid delivery and recovery for immersion lithography including one or more porous members according to certain embodiments. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0027]    Reference will now be made in detail to exemplary implementations and examples of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
         [0028]      FIG. 1  shows an immersion lithography system  10  including a reticle stage  12  on which a reticle is supported, a projection lens  14 , and a wafer  16  supported on a wafer stage  18 . An immersion apparatus  20 , which is sometimes referred to herein as a nozzle, is disposed around the final optical element  22  of the projection lens  14  to provide and recover an immersion fluid, which may be a liquid such as water or oil, between the final optical element  22  and the wafer  16 . In this example, the immersion lithography system  10  is a scanning exposure system in which the reticle and the wafer  16  are moved synchronously in respective scanning directions during a scanning exposure. 
         [0029]      FIGS. 2 and 3  show the apparatus or nozzle  20  for delivery and recovery of the fluid between the final optical element  22  and the wafer  16  for immersion lithography.  FIG. 2  shows the bottom perspective view of the nozzle  20 , which includes an outer part  30  and an inner part  32 . The inner part  32  defines an inner cavity  34  to receive the fluid between the final optical element  22  and the wafer  16 . The inner part  32  includes apertures  38  for fluid flow into and out of the inner cavity  34 . For example, in certain embodiments, the apertures  38  can act as an immersion fluid input into the inner cavity  34 . As seen in  FIG. 3 , there are apertures  38  disposed on both sides of the final optical element  22  in a direction intersecting with the scanning direction. The inner part  32  has a flat portion  33  surrounding the inner cavity  34 . The flat portion  33  is substantially parallel to the wafer  16 . The distance D 1  between the end surface of the final optical element  22  and the wafer  16  is greater than the distance D 2  between the flat portion  33  and the wafer  16 . The distance D 1  can be 1.0-5.0 mm, and the distance D 2  could be 0.5-2.0 mm. In certain embodiments, the distance D 1  is substantially equal to the distance D 2 . The inner part  32  further includes a pair of buffers or buffer slots  40  with purge holes  42 . The buffers  40  are arranged at or near the flat portion  33 . The buffers  40  are disposed on opposite sides of the final optical element  22  in the scanning direction. A cross-sectional view of the inner part  32  in the direction of scan  44  is illustrated in  FIG. 4 . 
         [0030]    The outer part  30  is spaced from the inner part  32  by an intermediate spacing or groove  48 . In certain embodiments, the outer part  30  can include one fluid recovery opening  50  disposed on a side of the final optical element  22 . In certain embodiments, the fluid recovery openings  50  are disposed on opposite sides of the final optical element  22 . A porous member  51  can be disposed in a slot or outer cavity  53  which extends around the inner part  32  and fluidicly communicates with the pair of fluid recovery openings  50 . In certain embodiments, nozzle  20  can comprise a plurality of porous members in various locations, as is described in further detail below. The porous member  51  may be a mesh or may be formed of a porous material having holes typically in the size range of about 50-200 microns. For example, the porous member  51  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, or a sheet of material having chemically etched holes (e.g., by photo-etching). The outer part  30  further includes a fluid buffer outlet  56  and a fluid recovery outlet  58 . In certain embodiments of the nozzle  20 ′ as seen in  FIG. 5 , the inner part  32  does not contact or form a seal with the final optical element  22 , but is spaced from the final optical element  22 . The gap prevents nozzle vibrations from being transmitted to the final optical element  22 . However, the gap may allow the fluid to be exposed to air. 
         [0031]    One feature of the nozzle  20  is that it is made in two pieces, namely, the outer part  30  and the inner part  32 . The inner part  32  keeps the fluid between the lens and the wafer surface, and the outer part  30  is mainly provided for fluid recovery. Vibration can be introduced during fluid recovery from the outer part  30  through the porous member  51  to the other components of the lithography system, including the inner part  32  which may be used to direct an autofocus beam to the wafer  16 . A damping material can be mounted between the outer part  30  and the mounting piece to which the outer part  30  is mounted to minimize the transmission of vibration from the outer part  30 . In addition, the outer part  30  that includes the porous member may be prone to contamination and thus needs to be replaced for maintenance. Making the outer part  30  as a separate part facilitates easier maintenance. It can also minimize readjustment and recalibration time after replacement of the outer part as opposed to replacing the entire nozzle  20 . Manufacturability of the nozzle  20  can also be improved if the nozzle  20  is made in two separate parts. It is understood that the nozzle  20  may be made of a single piece in alternative examples. 
         [0032]    In certain embodiments, the nozzle  20  can comprise a groove  48  between the inner part  32  and the outer part  30 . This groove  48  functions as a breaking edge to prevent fluid in the inner part  30  from being drawn out by the porous member  51  on the outer part  30  if the fluid recovery rate is faster than the fluid supply rate. In the situation when there is no breaking edge, a balance between the fluid recovery rate and the fluid supply rate has to be maintained so that fluid can be kept within the inner part  32  at all times during scanning. Having the groove  48  allows the recovery rate to be set at a maximum to minimize fluid leakage out of the outer part  30  during scanning. The groove  48  also acts as a buffer for fluid to go in and out during scanning, minimizing immersion fluid supply and recovery requirements. 
         [0033]    In the process of immersion lithography, a fluid is to be filled between the projection lens  14  and the wafer  16  from a dry state and, at other times, the fluid is to be recovered. For example, in the beginning of exposure of a new wafer, the fluid is to completely fill the inner cavity  34  of the inner part  32  before starting exposure. During this process, ideally no air bubbles can exist between the projection lens  14  and wafer  16  or other optical paths such as the auto focus beam. The fluid supply in the inner cavity of the inner part  32  is designed to be at the highest point in the cavity (via apertures  38 ) so that the fluid is filled from top down, allowing air bubbles to be pushed out of the inner cavity during the filling process. The fluid desirably is initially supplied from one side in this embodiment (the set of apertures  38  on one side), so that the fluid is filled from one side to the other, again allowing air bubbles to be pushed out to avoid trapping air therein. Other arrangements are also possible, as long as the fluid is being filled from the inside out. 
         [0034]    On occasion, the fluid has to be fully recovered from the inner cavity of the inner part  32 . In  FIG. 4 , there are small holes  42  in each of the buffers  40  in the inner cavity. These holes  42  are provided for fast fluid recovery or fluid purge when the fluid has to be fully recovered. Sucking the fluid out from these holes  42  using high vacuum with the combination of some movement in the wafer stage  18  allows all the fluid to be recovered within a reasonable time. 
         [0035]    The inner part  32  has two groups or rows of holes  38  for supplying or recovering the fluid. Each row can be independently controlled to either supply or recover the fluid. In the case where both rows are chosen for fluid supply, all the fluid is recovered through the porous member  51  in the outer part  30 . Since both rows are supplying fluid, a pressure can build up in the inner cavity causing deformation of the final optical element  22  of the projection lens  14  or the wafer  16  or both. The fluid flow across the final optical element  22  may also be limited, and thus the temperature of the fluid between the final optical element  22  and the wafer  16  may eventually rise, causing adverse effects. On the other hand, if one row is chosen for supply and the other for recovery, a fluid flow will be driven across the final optical element  22 , minimizing temperature rise. It can also reduce the pressure otherwise created by supplying fluid from both rows. In this case, less fluid needs to be recovered through the porous member  51 , lowering the fluid recovery requirement in the porous member. In other nozzle configurations, multiple fluid supplies and recoveries may be provided so as to optimize the performance. 
         [0036]    During scanning motion of the wafer stage  18  (in the direction of scan  44  in  FIG. 2 ), the fluid may be dragged in and out of the inner cavity of the inner part  32 . When the fluid is dragged out, it is recovered through the porous member  51  in the outer part  30 . When the wafer stage  18  is moved in the opposite direction, air may be dragged into the inner cavity of the inner part  32 . During this time, the fluid in the buffers  40 , as well as the fluid supplied from within the inner cavity, helps to refill the fluid that is dragged along the scanning direction, preventing air from getting into the inner cavity. The buffers  40  and the porous member  51  work together to minimize fluid leaking out from the outer part  30 , and air dragging into the inner cavity of the inner part  32  during scanning motion of the wafer stage  18 . 
         [0037]    Recovering fluid through the porous member  51  by maintaining the pressure in the porous member  51  under the bubble point can eliminate noise and/or vibration created by mixing air with the fluid during fluid recovery. For example, in certain embodiments, by maintaining a negative pressure on the upper side of the wet porous member  51  in a predetermined pressure range, the gas (e.g., air) on the lower side of the wet porous member  51  can be prevented from passing through the wet porous member  51  while the immersion fluid on the lower side of the wet porous member  51  is recovered through the wet porous member  51 . The bubble point is a characteristic of the porous member  51  which depends on the size of the holes in the porous member  51  (the largest hole) and the contact angle which the fluid forms with the porous member  51  (as a parameter based on the property of the porous material and the property of the fluid). Due to the fact that the bubble point is typically a very low pressure (e.g., about 1000 pascal), the control of this low pressure becomes an important issue.  FIGS. 6 and 7  illustrate three specific ways of maintaining the pressure below the bubble point during fluid recovery. 
         [0038]    In the pressure control system  100  of  FIG. 6 , a pressure under bubble point is maintained at the surface of the porous member  51  using a vacuum regulator  102  with the assistance of an overflow container or tank  104  fluidicly coupled to the porous member  51  by a recovery flow line  106  (which is connected to the fluid buffer outlet  56 ). The pressure at the surface of the porous member  51  is equal to the pressure maintained by the vacuum regulator  102  subtracting the pressure created by the height of the fluid above the porous member  51 . Maintaining a constant height of fluid above the porous member  51  using the overflow tank  104  allows easy control of the pressure at the surface of the porous member  51 . The fluid that is recovered through the porous member  51  will overflow and be siphoned down along a siphon line  108  to a collection tank  110 , which is disposed below the overflow tank  104 . An optional flow path  112  is connected between the overflow tank  104  and the collection tank  110  to assist in equalizing the pressure between the overflow tank  104  and the collection tank  110  and facilitate flow along the siphon line  108 . One feature of this pressure control system  100  is that it is a passive system without the necessity of control. 
         [0039]    In the pressure control system  120  of  FIG. 7 , the pressure at the surface of the porous member  51  is maintained below the bubble point using a vacuum regulator  122  at an immersion fluid level buffer  124  which is fluidicly coupled with the porous member  51  by a buffer flow line  126  (which is connected to the fluid buffer outlet  56 ). A pressure transducer or an immersion fluid level sensor  128  is used to measure the pressure or fluid level at the fluid level buffer  124 . The sensor signal is then used for feedback control  130  to a valve  132  that is disposed in a recovery flow line  134  (which is connected to the fluid recovery outlet  58 ) connected between the porous member  51  and a collection tank  136 . The valve  132  may be any suitable valve, such as a proportional or variable valve. The variable valve  132  is adjusted to control the fluid flow through the fluid recovery line  134  to the collection tank  136  to maintain the pressure or fluid level of the fluid level buffer  124  at a preset value. The collection tank  136  is under a relatively higher vacuum controlled by a high vacuum regulator  138  for fluid recovery. In this fluid control system  120 , no overflow tank is needed and the collection tank  136  can be placed anywhere in the system and need not be disposed below an overflow tank. An on/off valve  140  is desirably provided in the fluid recovery line  134  and is switched off when fluid recovery is not required. 
         [0040]    In  FIG. 8 , the pressure control system  160  is similar to the system  120  of  FIG. 7 , and like reference characters are used for like parts. Instead of using the valve  132  for the feedback control of fluid recovery, this system  160  employs a controllable vacuum regulator  162  for the feedback control of fluid recovery. The vacuum regulator  162  is typically electronically controllable to adjust the vacuum pressure in the collection tank  136  based on the sensor signal from the pressure transducer or an immersion fluid level sensor  128 . The vacuum regulator  162  is adjusted to control the fluid flow through the fluid recovery line  134  to the collection tank  136  to maintain the pressure or fluid level of the fluid level buffer  124  at a preset value. The on/off valve  140  in the fluid recovery line  134  is switched off when fluid recovery is not required. 
         [0041]      FIG. 9  shows a pressure control system for fluid recovery in an immersion lithography system with immersion fluid stagnation prevention according to certain embodiments. The pressure control system  180  is similar to the system  120  of  FIG. 7  having the same components with the same reference characters. In addition, the immersion fluid level buffer  124  is fluidicly coupled with an immersion fluid supply or immersion fluid recovery  182  to supply immersion fluid to or recover immersion fluid from the immersion fluid level buffer  124  to prevent stagnation. An optional pump or a similar moving part may be used to induce flow between the immersion fluid level buffer  124  and the immersion fluid supply or immersion fluid recovery  182 . There is a possibility of bacteria/fungus growth in stagnated immersion fluid over time. Under normal operation, the immersion fluid at the immersion fluid level buffer  124  is stagnated because immersion fluid recovered from the mesh  51  will go through the small tube at the mesh level to the collection tank  136 . By inducing flow into or out of the immersion fluid level buffer  124  during normal operation, the bacteria/fungus growth problem can be prevented. 
         [0042]      FIGS. 10 and 11  are exemplary perspective views of a nozzle  20  for fluid delivery and recovery for immersion lithography where immersion fluid is injected on a non-scanning axis and immersion fluid is input from a left side faster than from a right side, respectively. Referring to  FIG. 10 , nozzle  20  includes an immersion fluid input  70  that provides immersion fluid in a non-scanning axis direction. The scanning axis is the axis in which the nozzle  20  can move to perform the immersion lithography. The nozzle  20  can move in a positive (e.g., upward) or negative (e.g., downward) direction along the scanning axis. The immersion fluid inputs  70  are located laterally on opposite sides of the projection lens  22  and can run substantially parallel to the scanning axis direction. Each immersion fluid input  70  includes one or more apertures or openings that allow immersion fluid to flow in and out of the inner cavity of the nozzle  20  under the projection lens  22 . 
         [0043]    As the nozzle  20  moves in either the positive or negative scanning axis directions, immersion fluid input  70  injects immersion fluid into the inner cavity in a non-scanning direction. In this example, the non-scanning axis direction can be substantially perpendicular or orthogonal to the scanning axis direction. In this manner, the immersion fluid flow under the projection lens  22  can be more consistent and uniform as the nozzle  20  moves in the positive or negative directions. The immersion lithography process can thus be improved by the even flow of immersion fluid under the projection lens  22 . 
         [0044]      FIG. 11  illustrates certain embodiments of improving immersion lithography. The nozzle  20  is substantially similar to the one in  FIG. 10 , except that immersion fluid input  70  can input immersion fluid on one side at a faster rate than the opposite side. In particular, immersion fluid input  70  can inject immersion fluid in a non-scanning axis direction that can be perpendicular or orthogonal to the scanning axis direction. In other examples, the only requirement is that the directions are different. In the example of  FIG. 11 , the immersion fluid input  70  on the left side of the projecting lens  22  injects immersion fluid into the inner cavity at a faster rate than the immersion fluid input on the right side of the projection lens  22 . Alternatively, the right side immersion fluid input  70  can also inject immersion fluid at a faster rate than the immersion fluid input on the left side. By injecting immersion fluid at different flow rates at opposite sides of the projection lens  22 , the nozzle  20  can prevent air from being trapped in the inner cavity during the initial filling process of the nozzle  20 . 
         [0045]    The different flow rates in the inner cavity can also improve immersion fluid flow across the projection lens  22  during exposure that avoids raising immersion fluid temperature under the projection lens  22 . For example, the different flow rates can prevent residue or left over immersion fluid from remaining in the inner cavity after exposure to light. When residue or left over immersion fluid remains, it can raise the immersion fluid temperature of newly injected immersion fluid into the inner cavity, which should be avoided during immersion lithography. Thus, the above examples of  FIGS. 10 and 11  thus improve immersion lithography. 
         [0046]    In certain embodiments, as illustrated in  FIG. 12 , nozzle  20  can comprise a porous member  52 . In certain embodiments, porous member  52  may be a mesh or may be formed of a porous material having holes typically in the size range of about 50-200 microns. For example, in certain embodiments, porous member  52  can 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, or a sheet of material having chemically etched holes (e.g., by photo-etching) In certain embodiments, porous member  52  can be disposed at or near flat portion  33 . 
         [0047]    In certain embodiments, porous member  52  can facilitate immersion fluid removal from inner cavity  34 . For example, during immersion fluid removal, applying a vacuum to porous member  52  can provide for a more evenly distributed vacuum across substantially all of porous member  52 . In certain embodiments, the more evenly distributed vacuum across substantially all of porous member  52  can result in removal of immersion fluid at a faster rate. In certain embodiments, the use of a porous member (e.g.,  52 ) can facilitate a more complete removal of immersion fluid from inner cavity  34 . 
         [0048]    In certain embodiments, the surface roughness of porous member  52  can affect the behavior of the immersion fluid in the inner cavity  34 . For example, in certain embodiments, a change in the surface roughness of porous member  52  can reduce immersion fluid turbulence and can reduce the amount of air incorporated into the immersion fluid. In certain embodiments, this can result in a faster stage scanning speed since less air is introduced into the exposure area. In a similar manner, in certain embodiments, the nozzle filling behavior can be manipulated by a change in the surface roughness of porous member  52 . 
         [0049]    In certain embodiments, as illustrated in  FIG. 13 , nozzle  20  can comprise one or more porous members  54 . In certain embodiments, the one or more porous members  54  can be a mesh or can be formed of a porous material having holes typically in the size range of about 50-200 microns. For example, in certain embodiments, the one or more porous members  54  can comprise 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, or a sheet of material having chemically etched holes (e.g., by photo-etching). In certain embodiments, the one or more porous members  54  can be disposed at or near the apertures  38 . 
         [0050]    In certain embodiments, the one or more porous members  54  can reduce the turbulence associated with the immersion fluid entering the inner cavity  34 . For example, in certain embodiments, immersion fluid entering the inner cavity  34  directly from the apertures  38  can cause turbulence in the immersion fluid, leading to the formation of additional air within the immersion fluid. As discussed above, this additional air can have an adverse effect upon the performance of the immersion lithography system. However, in certain embodiments, introducing immersion fluid into the inner cavity  34  through the one or more porous members  54  can reduce the turbulence generated at the immersion fluid inlet. This can result in more uniform immersion fluid flow into the inner cavity  34  which can lead to a higher stage scanning speed without introducing substantial air into the exposure area. In certain embodiments, two porous members  54  can be used on opposing sides of the final optical element  22 . In certain embodiments, one porous member  54  can be used on one side of the final optical element  22 . 
         [0051]    Additionally, the above examples can be applied to Twin-Stage-Type Lithography Systems. One Twin-Stage-Type Lithography System, for example, is disclosed in U.S. Pat. No. 6,262,796 and U.S. Pat. No. 6,341,007, the entire disclosures of which are incorporated herein by reference. 
         [0052]    Thus, apparatus and methods for providing fluid for immersion lithography have been described. Furthermore, the above description are intended to be illustrative and not restrictive. Many other examples will be apparent upon reviewing the above examples. The scope of the invention should, therefore, be determined not with reference to the above examples.