Abstract:
A substrate holding apparatus contacts an undersurface of a substrate and holds the substrate. At least a portion of a top surface of the substrate is to be immersed in liquid. The apparatus includes a chuck unit to attract the substrate and a preventing system to prevent the liquid from reaching the undersurface of the substrate.

Description:
[0001]     This application is a divisional application of copending U.S. patent application Ser. No. 11/002,900, filed Dec. 3, 2004.  
         [0002]     This application claims foreign priority based on Japanese Patent Application No. 2003-409446, filed Dec. 8, 2003, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to a substrate holding technique adapted, for example, to exposure apparatuses used for fabricating devices having micropattems, such as LSIs (large-scale integrations). In particular, the present invention relates to a substrate-holding technique used in, for example, a liquid-immersion exposure apparatus for projecting a pattern of an original onto a photosensitive substrate via a liquid layer.  
         [0005]     2. Description of the Related Art  
         [0006]     A typical liquid-immersion exposure apparatus is provided with a light source and an optical projection unit to achieve higher resolution or high focal depth. Japanese Patent Laid-Open Nos. 6-124873 and 6-168866 disclose examples of such a liquid-immersion exposure apparatus.  
         [0007]     A conventional technique related to the present invention will now be described with reference to FIGS.  9  to  13 .  
         [0008]      FIG. 9  illustrates a typical liquid-immersion exposure apparatus, which includes an illumination unit  1 ; a reticle stage  2 ; a step-and-repeat lens  3 ; a main body  4 ; and a wafer stage  5 . The illumination unit  1  receives a light beam from a light source, not shown in the drawing, and emits the light beam towards a reticle, which is not shown in the drawing, provided in the reticle stage  2 . The reticle includes an exposure pattern of an original. The reticle stage  2  photoscans the reticle against a wafer  12  shown in  FIG. 10 , i.e., a photosensitive substrate, at a predetermined reduction rate. The step-and-repeat lens  3  projects the original pattern included in the reticle towards the wafer  12  at a reduced rate. The main body  4  supports the reticle stage  2 , the step-and-repeat lens  3 , and the wafer stage  5 . The wafer stage S shifts the wafer  12  to an exposure position in a step-by-step manner, and scans the wafer  12  in synchronization with the scanning of the reticle.  
         [0009]     Referring to  FIG. 10 , the wafer stage  5  includes a stage base  5 S, a wafer chuck  5 C, and a slider  5 B. The wafer chuck  5 C is disposed on the slider  5 B. The wafer chuck  5 C holds the wafer  12  in place and also contains immersion liquid. The wafer chuck  5 C is movable while holding the wafer  12  in place, and moreover, the wafer chuck  5 C can be detached from the slider  5 B.  
         [0010]     The exposure apparatus further includes an alignment scope  6 ; a focus scope  7 ; an x-axis mirror bar  8 ; and a y-axis mirror bar  9 .  
         [0011]     The alignment scope  6  is a microscope which measures an alignment mark on the wafer  12  and an alignment reference mark on the wafer stage  5  so as to determine the alignment position of the wafer  12  with respect to a reference point and the alignment position between the reticle and the wafer  12 . The focus scope  7  determines the surface structure of the wafer  12  and performs a focus measurement in an optical-axis direction (positional) measurement on the surface of the wafer  12  with respect to the optical-axis direction.  
         [0012]     The x-axis mirror bar  8  functions as a target for determining the position of the slider  5 B in the x-axis direction via a laser interferometer. On the other hand, the y-axis mirror bar  9  functions as a target for determining the position of the slider  5 B in the y-axis direction.  
         [0013]     The upper surface of the slider  5 B is provided with a stage reference marker  10  and a light-intensity sensor  1   1 . The stage reference marker  10  is provided with a target used for stage alignment. The light-intensity sensor  11  calibrates the intensity of light before an exposure operation so as to compensate for the light intensity. The pattern in the reticle is projected and transferred to the wafer  12  via the step-and-repeat lens  3 . Thus, the wafer  12 , i.e., a single-crystal silicon substrate, has a resist pattern disposed thereon.  
         [0014]     In  FIG. 9 , the wafer chuck  5 C and the wafer  12  on the slider  5 B are illustrated in cross section so as to provide an easier understanding of the relationship among the step-and-repeat lens  3 , a light beam from the focus scope  7 , and the wafer  12 .  
         [0015]     The exposure apparatus further includes a wafer-shifting robot  13  for supplying and retrieving the wafer  12 ; an immersion-liquid tank  14  for storing the immersion liquid; and a liquid supplying/retrieving unit  15  for supplying the immersion liquid to the wafer chuck  5 C from the immersion-liquid tank  14  or retrieving the immersion liquid from the wafer chuck  5 C back to the immersion-liquid tank  14 .  
         [0016]      FIGS. 11 A  to  11 H illustrate the liquid-immersion exposure operation performed on the wafer  12 .  
         [0017]     Referring to  FIG. 11A , an alignment operation is performed in the wafer stage  5  so that an alignment measurement and a focus measurement can be performed on the wafer  12  disposed on the wafer stage  5 . In this state, the immersion liquid is not present between the wafer  12  and the step-and-repeat lens  3 . If the immersion liquid is present, the measurements become difficult, since the difference in the index of refraction between the resist and the immersion liquid is small. For this reason, the alignment measurement and the focus measurement are performed without any of the immersion liquid being supplied.  
         [0018]     Referring to  FIG. 11B , after the alignment operation is completed, the wafer  12  on the wafer stage  5  is shifted to a position directly below the liquid supplying/retrieving unit  15 . After this shifting process, the immersion-liquid tank  14  supplies immersion liquid having a refraction of index of more than one to the liquid supplying/retrieving unit  15 . The liquid supplying/retrieving unit  15  then supplies droplets of the immersion liquid to the wafer chuck  5 C until the liquid layer on the surface of the wafer  12  reaches a predetermined thickness. Accordingly, liquid having a refraction of index greater than the air fills a space provided between the step-and-repeat lens  3  and the wafer  12  such that the numerical aperture of the step-and-repeat lens  3  is enlarged. This contributes to higher resolution.  
         [0019]     Referring to  FIG. 11C , the wafer  12  is shifted to an exposure position in a state where the immersion liquid is disposed on the wafer  12 . Subsequently, referring to  FIG. 11D , a step-and-repeat exposure process or a step-and-scan exposure process is performed. Referring to  FIG. 11E , after the exposure process is completed, the slider  5 B is shifted to a retrieving position of the wafer-shifting robot  13  such that the wafer  12  is retrieved. Referring to  FIG. 11F , after the retrieving process, the retrieved wafer  12  is ejected from the exposure apparatus in order to perform the subsequent step.  
         [0020]     Referring to  FIG. 11G , a subsequent wafer  12  is transferred to the wafer chuck  5 C on the wafer stage  5  via the wafer-shifting robot  13 . Referring to  FIG. 11H , the subsequent wafer  12  is shifted to the initial position for the alignment and focus measurements. Thus, the exposure operation illustrated in  FIGS. 11A  to  11 F is repeated. Accordingly, the liquid-immersion exposure operation is performed on each wafer  12  in the manner described above.  
         [0021]      FIGS. 12A, 12B , and  13  illustrate detailed examples of the wafer chuck  5 C shown in  FIGS. 9 and 10 . Specifically,  FIGS. 12A, 12B , and  13  illustrate how immersion liquid  16  may leak into a space between the undersurface of the wafer  12  and a wafer suction unit.  
         [0022]     In the example shown in  FIGS. 12A and 12B , a vacuum-chuck component  5 D provided in the wafer chuck  5 C vacuums the wafer  12  so as to support the wafer  12 . A circumferential projection (a ring-shaped projection)  5 P is provided around the outer periphery of the vacuum-chuck component  5 D. If foreign matter attaches to the circumferential projection  5 P or if a scratch is present on the circumferential projection  5 P, a leakage  105 F may occur. Such a leakage  105 F may cause the immersion liquid  16  to enter the openings provided in the vacuum-chuck component  5 D, and may thus lead to vacuum errors. Moreover, such a leakage  105 F may, for example, lower the liquid level of the layer of the immersion liquid  16 .  
         [0023]     On the other hand, in the example shown in  FIG. 13 , an electrostatic-chuck component  5 E provided in the wafer chuck  5 C supports the wafer  12  with an electrostatic suction force. Such a technique is also problematic in that the immersion liquid  16  may enter the electrostatic-chuck component  5 E so as to cause, for example, a leakage of voltage or lowering the liquid level of the layer of the immersion liquid  16 .  
       SUMMARY OF THE INVENTION  
       [0024]     It is an exemplified object of the present invention to provide a substrate-holding technique which prevents liquid from reaching the undersurface of a substrate.  
         [0025]     According to the present invention, the foregoing object is attained by providing a substrate holder, in which a substrate is immersed in liquid and an undersurface of the substrate is in contact with the substrate holder so as to be held by the substrate holder. Such a substrate holder includes a chuck unit to which the substrate is attracted; and a blocking unit for preventing the liquid from entering a space between the undersurface of the substrate and the chuck unit.  
         [0026]     According to the present invention, a substrate-holding technique that prevents immersion liquid from entering the undersurface of a substrate is provided.  
         [0027]     Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments (with reference to the attached drawings). In the description, reference is made to the accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such an example, however, is not exhaustive of the various embodiments of the invention, and therefore, reference is made to the claims which following the description for determining the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the invention.  
         [0029]      FIGS. 1A and 1B  are cross-sectional views each illustrating a wafer chuck provided with a vacuum-chuck component and a sealing unit for preventing immersion-liquid leakage according to a first embodiment of the present invention.  
         [0030]      FIG. 2  is a cross-sectional view illustrating a wafer chuck provided with an electrostatic-chuck component and the sealing unit shown in  FIG. 1 .  
         [0031]      FIGS. 3A  to  3 C are cross-sectional views each illustrating a wafer chuck provided with a sealing unit for preventing immersion-liquid leakage according to a second embodiment of the present invention.  
         [0032]      FIGS. 4A  to  4 C are cross-sectional views each illustrating a wafer chuck provided with a sealing unit for preventing immersion-liquid leakage according a third embodiment of the present invention.  
         [0033]      FIGS. 5A and 5B  are schematic diagrams each illustrating a local-fill liquid-immersion exposure apparatus according to a fourth embodiment of the present invention.  
         [0034]      FIGS. 6A  to  6 C are cross-sectional views each illustrating a wafer chuck provided with a sealing unit for preventing immersion-liquid leakage according to a fifth embodiment of the present invention.  
         [0035]      FIG. 7  is a flow chart illustrating a method for fabricating a device according to the present invention.  
         [0036]      FIG. 8  is a flow chart illustrating a wafer-processing step, which is one of the steps included in the method shown in  FIG. 7 .  
         [0037]      FIG. 9  is a schematic diagram of a typical liquid-immersion exposure apparatus of a movable-pool type, to which the present invention can be applied.  
         [0038]      FIG. 10  is a schematic perspective view of a wafer stage included in the exposure apparatus shown in  FIG. 9 .  
         [0039]      FIGS. 11A  to  11 H are diagrams illustrating an exposure operation performed by the exposure apparatus shown in  FIG. 9 .  
         [0040]      FIGS. 12A and 12B  are cross-sectional views illustrating an example of a typical wafer chuck provided in the exposure apparatus shown in  FIG. 9 .  
         [0041]      FIG. 13  is a cross-sectional view illustrating another example of a typical wafer chuck provided in the exposure apparatus shown in  FIG. 9 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]     Preferred embodiments of the present invention will now be described with reference to the drawings.  
       First Embodiment  
       [0043]      FIG. 1A  illustrates a detachable wafer chuck  5 C, i.e., a substrate holder, according to a first embodiment of the present invention.  FIG. 1 B  is an enlarged view of section A in  FIG. 1A . The wafer chuck  5 C of the first embodiment corresponds to the structure shown in  FIG. 12 , but is additionally provided with an O-ring sealant  17 , i.e., an elastic sealing member, which is in contact with the undersurface of the wafer  12 . Specifically, the O-ring sealant  17  is disposed along the periphery of the undersurface of the wafer  12  while being in contact with an inner peripheral portion of the undersurface of the wafer  12 .  
         [0044]     A structure for preventing a leakage of immersion liquid to a wafer suction unit will now be described with reference to  FIGS. 1A and 1B . In  FIGS. 1A and 1B , a vacuum-chuck component  5 D provided in the wafer chuck  5 C vacuums the wafer  12  so as to fixedly support the wafer  12 . As shown in  FIG. 1B , the O-ring sealant  17  is disposed adjacent to a circumferential projection (a ring-shaped projection)  5 P provided along the outermost portion of the vacuum-chuck component  5 D. By providing the O-ring sealant  17 , the leakage  105 F shown in  FIG. 12B  is prevented even if foreign matter attaches to the surface of the wafer chuck  5 C and/or the undersurface of the wafer  12 , or if a scratch is present on the surface of the wafer chuck  5 C and/or the undersurface of the wafer  12 . Thus, the O-ring sealant  17  prevents the immersion liquid  16  from entering the openings provided in the vacuum-chuck component  5 D or prevents vacuum errors from occurring. Consequently, this prevents problems, such as lowering of the liquid level of the layer of the immersion liquid  16 .  
         [0045]     The first embodiment may additionally be provided with a detector which detects a leakage through the O-ring sealant  17 , i.e., the elastic sealing member, based on, for example, air pressure or air volume in a case in which a leakage occurs through the O-ring sealant  17 . If the detector detects such a leakage, the wafer  12  or the wafer chuck  5 C holding the wafer  12  may be ejected from, for example, the wafer stage  5  or the exposure apparatus without supplying any immersion liquid  16  to the wafer  12 . Alternatively, the first embodiment may additionally be provided with a detector for detecting a leakage through the O-ring sealant  17  just after the start of the supply of the immersion liquid  16 ; and a drier for drying the interior of the wafer chuck  5 C. In such a case, if a leakage is detected, the drier dries the interior of the wafer chuck  5 C.  
       Second Embodiment  
       [0046]      FIGS. 3A  to  3 C illustrate a second embodiment of the present invention. In place of the elastic O-ring sealant  17  provided in the first embodiment, the second embodiment is provided with a differential exhaust unit. Specifically, the differential exhaust unit is disposed along a periphery of a wafer-suction surface of the wafer chuck  5 C while facing the inner peripheral portion of the undersurface of the wafer  12 .  
         [0047]     Referring to  FIG. 3C , the differential exhaust unit is disposed along the outermost portion of the vacuum-chuck component  5 D in a ring-like manner. The differential exhaust unit includes an exhaust duct A ( 5 F), an exhaust duct B ( 5 G), and an exhaust duct C ( 5 H), which are independent of one another.  
         [0048]     According to the second embodiment, the exhaust duct A ( 5 F) is used for atmopsheric pressure, the exhaust duct B ( 5 G) is used for low vacuum pressure (intermediate pressure), and the exhaust duct C ( 5 H) is used for suction-holding pressure. Consequently, by gradually decreasing the exhaust pressure towards the exterior of the wafer chuck  5 C using multiple differential exhaust ducts, a leakage is thoroughly prevented from occurring. This prevents the immersion liquid  16  from entering the vacuum-chuck component  5 D or prevents vacuum errors from occurring even if foreign matter attaches to the surface of the wafer chuck  5 C and/or the undersurface of the wafer  12 , or if a scratch is present on the surface of the wafer chuck  5 C and/or the undersurface of the wafer  12 . As a result, the leakage  105 F shown in  FIG. 12B  is prevented from occurring, meaning that the immersion liquid  16  is prevented from entering the openings provided in the vacuum-chuck component  5 D or that vacuum errors are prevented from occurring. Consequently, this prevents problems, such as lowering of the liquid level of the layer of the immersion liquid  16 .  
         [0049]      FIG. 3B  illustrates an example in which the wafer suction unit according to the second embodiment includes the electrostatic-chuck component  5 E in place of the vacuum-chuck component  5 D. Even in this case, like the structure described above, the differential exhaust unit used in the electrostatic technique prevents the immersion liquid  16  from entering the undersurface of the wafer  12  so as to prevent problems related to the leakage of the immersion liquid  16 .  
       Third Embodiment  
       [0050]      FIGS. 4A  to  4 C illustrate a third embodiment of the present invention. In place of the elastic O-ring sealant  17  in the first embodiment, the third embodiment is provided with a liquid-sealant pool disposed along an outer peripheral portion of the wafer chuck  5 C.  
         [0051]     Referring to  FIG. 4C , a circumferential liquid-sealant groove  5 K is disposed around the outer periphery of the vacuum-chuck component  5 D. Moreover, a liquid-sealant supplier for supplying a liquid sealant  5 J to the liquid-sealant groove  5 K is also provided. The liquid sealant  5 J should be formed of a material that cannot be easily diffused into the immersion liquid  16  while still having sealability. For this reason, the liquid sealant  5 J may be a fluorinated inert refrigerant, fluorinated oil, or a gelatinous polymer material.  
         [0052]      FIG. 4B  illustrates an example in which the wafer suction unit according to the third embodiment includes the electrostatic-chuck component  5 E in place of the vacuum-chuck component  5 D. Even in this case, as with the structure described above, the liquid-sealant groove  5 K and the liquid-sealant supplier used in the electrostatic technique prevent the immersion liquid  16  from entering the undersurface of the wafer  12  so as to prevent problems related to the leakage of the immersion liquid  16 .  
       Fourth Embodiment  
       [0053]     In the first to third embodiments, the entire wafer  12  is immersed in the immersion liquid  16  during the liquid-immersion exposure operation. On the other hand, a fourth embodiment of the present invention shown in  FIGS. 5A and 5B  provides a liquid-immersion exposure apparatus in which the immersion liquid  16  from the immersion-liquid tank  14  is supplied only to an area directly below the step-and-repeat lens  3 , which is the area subject to the exposure operation. According to such a technique, the immersion liquid  16  is supplied via a liquid-supplying nozzle  18  to the area on the top surface of the wafer  12  directly below the step-and-repeat lens  3 . The immersion liquid  16  is continuously supplied via the liquid-supplying nozzle  18  and is continuously retrieved from a liquid-retrieving nozzle  19 .  
         [0054]     The liquid-immersion exposure apparatus of the fourth embodiment, which supplies the immersion liquid  16  only to the area on the wafer  12  subject to the exposure operation, achieves the same effect as that achieved by the liquid-blocking sealant structure according to the first to third embodiments. The fourth embodiment is advantageous, especially in a case in which an outer region of the wafer  12  is subject to the exposure operation.  
       Fifth Embodiment  
       [0055]      FIGS. 6A  to  6 C illustrate a fifth embodiment of the present invention. The fifth embodiment is provided with the circumferential liquid-sealing groove  5 K around the outer periphery of the vacuum-chuck component  5 D in the wafer chuck  5 C as in the third embodiment, but unlike the third embodiment, the entire wafer  12  is not immersed in the immersion liquid  16 . Instead, like the fourth embodiment, the immersion liquid  16  is supplied only to the area subject to the exposure operation, which is directly below the step-and-repeat lens  3 .  
         [0056]     Referring to  FIG. 6C , in the fifth embodiment, the liquid-sealant supplier (including a liquid-sealant supplying duct) and the circumferential liquid-sealing groove  5 K are disposed around the outer periphery of the vacuum-chuck component  5 D. Moreover, a circumferential liquid-sealant-exhaust groove  5 L is disposed around the outer periphery of the liquid-sealant groove  5 K. The liquid sealant  5 J is supplied to the liquid-sealant groove  5 K, and is then discharged into a liquid-sealant exhaust duct  5 M via the liquid-sealant exhaust groove  5 L. In this case, the liquid sealant  5 J is supplied at a constant rate of flow so as to maintain a predetermined liquid level of the liquid sealant  5 J. An excess amount of the liquid sealant  5 J is transferred to the liquid-sealant exhaust groove  5 L, and is then discharged into the liquid-sealant exhaust duct  5 M connected to the liquid-sealant exhaust groove  5 L.  
         [0057]     Furthermore, in order to completely remove the liquid sealant  5 J, both the liquid-sealant supplier of the liquid sealant  5 J (including the liquid-sealant supplying duct) and the liquid-sealant exhaust duct  5 M may be vacuumed.  
         [0058]     According to the first to fifth embodiments, the elastic O-ring sealant  17 , the differential exhaust unit, or the liquid-sealant groove  5 K is provided between the undersurface of the wafer  12  and the wafer chuck  5 C, i.e., the wafer suction unit. Thus, a substrate-holding technique that prevents the immersion liquid  16  from entering the undersurface of the wafer  12 , i.e., a substrate, is provided. This prevents leakages of the immersion liquid  16  into the wafer suction unit, and can prevent problems that may occur in the liquid-immersion exposure apparatus, such as a substrate suction error, an error in the wafer chuck  5 C caused by a leakage of voltage, or an error due to lack of immersion liquid  16 . Accordingly, a liquid-immersion exposure apparatus with high reliability and productivity can be provided.  
       Sixth Embodiment  
       [0059]     Referring to  FIG. 7 , a sixth embodiment of the present invention will now be described.  FIG. 7  is a flow chart illustrating a method for fabricating a micro-device using the above-mentioned liquid-immersion exposure apparatus. Such a micro-device may include, for example, a semiconductor chip, such as an IC and an LSI, a liquid-crystal panel, a CCD, a thin-film magnetic head, or a micro-machine. In step  1 , pattern designing (circuit designing) of a micro-device is performed. In step  2 , a mask of the designed pattern is fabricated (mask fabrication). In step  3 , a wafer is fabricated using, for example, silicon or glass (wafer fabrication). Step  4  is called a former step in which an actual circuit is formed on the wafer by lithography using the mask fabricated in step  2  (wafer processing). Step  5  is called a latter step in which the wafer processed in step  4  is made into a semiconductor chip (assembly process). Specifically, step  5  includes sub-steps, such as an assembly sub-step (dicing, bonding) and a packaging sub-step (chip enclosing). Subsequently, a step  6  is an inspection step in which the semiconductor micro-device formed in step  5  is inspected for, for example, operability and durability. The fabrication process of the micro-device is thus completed, and in step  7 , the micro-device is shipped.  
         [0060]      FIG. 8  is a flow chart illustrating the wafer processing step, i.e., step  4 , in further detail. In step  11 , the surface of the wafer is oxidized (oxidization). In step  12 , an insulating layer is formed over the wafer (CVD). In step  13 , an electrode is formed on the wafer by vapor deposition (electrode formation). In step  14 , ions are embedded into the wafer (ion embedding). In step  15 , a sensitizer is applied over the wafer (resist processing). In step  16 , the circuit pattern of the mask is exposed and printed onto the wafer by using the exposure apparatus described above (exposure process). In step  17 , the wafer having the circuit pattern disposed thereon is developed (development process). In step  18 , segments on the wafer other than the developed resist segments are etched (etching process). In step  19 , the resist segments no longer needed after the etching process are removed (resist removal). By repeating these steps, a multilayer circuit pattern is formed on the wafer. By using the fabrication method according to the sixth embodiment, a highly-integrated micro-device can be manufactured at a low cost.  
         [0061]     Other aspects of the present invention will now be described.  
         [0062]     Aspect 1. A liquid-immersion exposure apparatus according to Aspect 1 projects a pattern included in an original onto a substrate and operates a stage unit in order to move both the original and the substrate or only the substrate relatively with respect to an optical projection unit. Thus, the pattern of the original is repeatedly exposed on the substrate while an immersion-liquid layer is disposed in at least a part of a light-transmitting space between the optical projection unit and the substrate.  
         [0063]     The liquid-immersion exposure apparatus according to Aspect 1 is provided with a blocking unit disposed between the immersion-liquid layer and a substrate suction unit provided in a substrate holder. The blocking unit prevents a leakage of the immersion liquid by substantially blocking the immersion-liquid layer from the substrate suction-surface or the substrate suction unit.  
         [0064]     There are generally two types of liquid-immersion exposure apparatuses. One is a movable-pool type in which a wafer, i.e., the substrate, is completely immersed in the immersion liquid. The other is a local-fill type in which the wafer is partially immersed in the immersion liquid such that a region in the wafer with the immersion liquid can be shifted. The present invention can be applied to either type.  
         [0065]     The blocking unit is preferably ring-shaped such that the blocking unit substantially surrounds the undersurface of the substrate. In other words, if the substrate is circular, the blocking unit is circular, and if the substrate is rectangular, the blocking unit is also rectangular so that the blocking unit can be disposed along the periphery of the substrate. For example, an elastic sealing member is used as the blocking unit.  
         [0066]     The blocking unit may include at least one of the elastic sealing member, at least one circumferential exhaust duct, and a liquid-sealant supplier. Specifically, the elastic sealing member is in contact with the periphery of the substrate and/or an inner portion of the undersurface of the substrate positioned along the periphery of the substrate (referred to as an inner peripheral portion hereinafter) when the substrate is being held by the substrate holder. On the other hand, at least one circumferential exhaust duct is disposed on the substrate-holding surface of the substrate holder and faces the inner peripheral portion of the undersurface of the substrate when the substrate is being held by the substrate holder. The liquid-sealant supplier supplies liquid that does not mix with the immersion liquid along the periphery of the substrate and/or the inner peripheral portion of the undersurface of the substrate when the substrate is being held by the substrate holder.  
         [0067]     Aspect 2. According to the exposure apparatus of Aspect 1, the blocking unit is preferably the elastic sealing member, which is in contact with the substrate.  
         [0068]     Aspect 3. According to the exposure apparatus of one of Aspects 1 and 2, the blocking unit or the elastic sealing member is detachably disposed on the substrate holder.  
         [0069]     Aspect 4. According to the exposure apparatus of Aspect 1, the blocking unit may include at least one circumferential exhaust duct disposed on the substrate-holding surface of the substrate holder. At least one circumferential exhaust duct preferably includes a plurality of circumferential exhaust ducts so as to define a differential exhaust unit.  
         [0070]     Aspect 5. According to the exposure apparatus of Aspect 1, the blocking unit may include the liquid-sealant supplier for supplying a liquid sealant substantially along the outer peripheries of the substrate holder and the substrate.  
         [0071]     Aspect 6. According to the exposure apparatus of Aspect 5, the density of the liquid sealant supplied along the outer peripheries of the substrate holder and the substrate is greater than that of the immersion liquid.  
         [0072]     Aspect 7. According to the exposure apparatus of Aspect 5, the liquid sealant supplied along the outer peripheries of the substrate holder and the substrate is retrieved or discharged respectively by a retrieving unit or a drainage unit provided in the substrate holder.  
         [0073]     Aspect 8. According to the exposure apparatus of one of Aspects 1 to 7, the substrate holder is detachably disposed on the stage unit.  
         [0074]     Accordingly, by providing the blocking unit, such as the elastic sealing member, the differential exhaust unit and the liquid-sealant supplier, between the substrate holder and the substrate, the immersion liquid is prevented from entering the substrate suction unit so as to prevent leakages.  
         [0075]     While the present invention has been described with reference to what are at present considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included with the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.