Abstract:
A projection exposure apparatus which has a projection optical system and projects a pattern onto a substrate through the projection optical system is disclosed. This apparatus includes a sensor unit which comprises a light-receiving element for detecting light incident through the projection optical system, a vessel in which the light-receiving element is arranged, and a sealing window which transmits the incident light and seals the vessel. A space between the sealing window and the light-receiving element is filled with a medium having a refractive index greater than 1.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a projection exposure apparatus, device manufacturing method, and sensor unit.  
       BACKGROUND OF THE INVENTION  
       [0002]     Along with micropatterning of a semiconductor element, an exposure light source shifts from high-pressure mercury lamp of g-line to a light source of i-line having a shorter wavelength, and further shifts to KrF and ArF excimer lasers having shorter wavelengths. Also, in order to increase a resolution, the NA (numerical aperture) of a projection lens must be increased. Hence, the depth of focus tends to be reduced. As is known well, these relationships are expressed by 
 
(resolution)= k 1·(λ/ NA ) 
 
(depth of focus)=± k 2·λ/ NA   2  
 
 where λ represents the wavelength of light used for exposure, NA represents the NA (numerical aperture) of the projection lens, and k1 and k2 represent coefficients for a process. 
 
         [0003]     Recently, the KrF and ArF excimer lasers with short wavelengths are used. Also, an F 2  excimer laser, EUV light source, and X-ray source are examined for use. Alternatively, the technique for increasing the resolution and the depth of focus by a phase-shift mask, modified illumination, or the like is practically used. However, the cost of the apparatus increases when using the F 2  excimer laser, EUV light source, and X-ray source.  
         [0004]     An immersion technique is tried to be applied to the projection exposure apparatus which uses the existing ArF excimer laser. Note that in this immersion method, the space between the projection lens and the wafer is filled with a liquid with a high refractive index to increase the resolution and the depth of focus. For example, the immersion-type projection exposure apparatus is disclosed in Japanese Patent Laid-Open No. 06-124873.  
         [0005]     More specifically, in the immersion technique, as shown in  FIG. 13 , the space between a wafer  2  and an optical element  7  which is the last stage of the projection lens is filled with a liquid  25 . Assume that the wavelength of the exposure light in the air is λ0, the refractive index of the liquid  25  used for immersion with respect to the air is n, the convergent half-angle of a light ray is α, and NA0=sinα. The resolution and the depth of focus obtained by using the immersion technique is expressed by 
 
(resolution)= k 1·(λ0/ n )/ NA 0 
 
(depth of focus)=± k 2·(λ0/ n )/( NA 0) 2  
 
 That is, the immersion effect is equivalent to setting an exposure wavelength to 1/n. In other words, when designing projection optical systems with the same NA, the depth of focus can be n times by the immersion technique. This immersion technique can be applied to all pattern shapes, and used in combination with the phase-shift mask technique, the modified illumination technique, or the like. 
 
         [0006]     In order to utilize this effect, the purity, uniformity, temperature, and the like of the liquid must be accurately managed. In the exposure apparatus which sequentially exposes the wafer in a step-and-repeat operation, it is important to minimize the flow and oscillation of the liquid during the operation, and eliminate air bubbles left on the wafer surface when loading the wafer in the liquid.  
         [0007]     In a general projection exposure apparatus which does not use the immersion technique, an illuminance unevenness sensor which measures the illuminance and the illuminance unevenness of the exposure light irradiating the wafer is generally disposed near the wafer. Also, a sensor which measures the magnification and the focal position variation of the projection lens for calibration is generally arranged near the wafer.  
         [0008]     As a sensor unit for calibration, a light-receiving element is sometimes arranged under silica glass on which a reference mark pattern is formed by chromium and the like as shown in  FIG. 4 . Such a sensor unit is used, as will be described below. That is, the pattern similar to the reference mark in  FIG. 4  is formed on a reticle. This pattern is projected on the reference mark, and the light-receiving element measures a light amount transmitted through the reference mark. When an in-focus state is set, the projection image of the pattern formed on the reticle matches the pattern of the reference mark. The light amount detected by the light-receiving element becomes maximum. In an out-of-focus state, the pattern formed on the reticle is blurred, and the blurred pattern is projected on the mark pattern. The light amount detected by the light-receiving element is reduced. Therefore, the focus varies while detecting the light amount by using the light-receiving element. The focus calibration can be performed by detecting the in-focus position where the light amount becomes maximum.  
         [0009]     When the reference mark is displaced in the X and Y directions with respect to the pattern projection image on the reticle, the detected light amount changes accordingly. Therefore, the shifts in the X and Y directions can also be detected. That is, this sensor unit can be used as an alignment sensor unit. In addition to this, for example, a line sensor which includes many pixels for measuring exposure unevenness in a shot and measuring an effective light source, and a two-dimensional CCD for measuring the aberration of the projection lens may be disposed on a wafer stage.  
         [0010]     In consideration of measurement precision and the like, this sensor unit is preferably used in a state (immersion state) wherein the space under the projection lens is filled with the liquid as in the wafer, in the immersion-type projection exposure apparatus.  
         [0011]     However, when using the above-described sensor unit in the immersion state, the following problems will occur.  
         [0012]      FIG. 12  shows a conventional illuminance unevenness sensor unit. In the illuminance unevenness sensor unit, a light-receiving element  23  is arranged in a sensor vessel  22  sealed by a sealing window  21 . A light-shielding member  28  which has a pinhole is arranged on the sealing window  21 . The light-receiving element  23  is arranged in the sealed space to prevent the characteristics of the light-receiving element  23  from degrading due to humidity and the like. When the light is applied to the sensor unit having this structure, as known as Snell&#39;s law, the light is refracted at an interface between the air and the sealing window  21 , and an interface between the sealing window  21  and the internal space of the sensor unit.  
         [0013]     Assume that the refractive index of the outer space of the sensor unit is n1, the refractive index of the sealing window  21  is n2, the refractive index of the internal space of the sensor unit is n3, the incident angle and refractive angle of the light at the interface between the outer space of the sensor unit and the sealing window  21  are θi1 and θr1, respectively, and the incident angle and refractive angle of the light at the interface between the sealing window  21  and the internal space of the sensor unit are θi2 and θr2, respectively. The following equation is established by Snell&#39;s law: 
 
 n 2·sin(θ i 2)= n 3·sin(θ r 2) 
 
 Therefore, 
 
sin(θ r 2)=( n 2/ n 3)·sin(θ i 2) 
 
 When n2&gt;n3, the light which is applied at an incident angle of θi2′ (critical angle) or more defined by sin(θi2′)=n3/n2 is not refracted, but totally reflected. 
 
         [0014]     The NA of the projection lens is given by 
 
 NA=n 1·sin(θ i 1) 
 
         [0015]     In a general projection exposure apparatus which does not use the immersion technique, since the outer space of the sensor unit is filled with the air, the refractive index n1=1. When the refractive index is 1, the NA is less than 1.0, or at most around 0.9. When NA=0.83, the incident angle θi1=56.44°. When the material of the sealing window  21  is the silica glass, the refractive index n2=1.56. By Snell&#39;s law, the refractive angle θr1 at the interface between the outer space of the sensor unit and the sealing window  21  is 32.29°. Since θr1=θi2, the incident angle θi2 of the light at the interface between the sealing window  21  and the internal space of the sensor unit is also 32.29°. The critical angle θi2′ at the interface between the sealing window and the internal space of the sensor unit is given by 
 
sin θ i 2 ′=n 3/ n 2=1/1.56=0.64 
 
 Therefore, since θi2′=39.9° and θi2′&gt;θi2, the light is not totally reflected, but can reach the surface of the light-receiving element. 
 
         [0016]     Alternatively, in the immersion-type projection exposure apparatus, the outer space of the sensor unit is filled with the liquid. Assume that the liquid is pure water. The refractive index of the pure water is 1.44. When the refractive index n1=1.44 in the above example, the incident angle θi1=56.44°, and the refractive index n2=1.56. Hence, by Snell&#39;s law, the refractive angle θr1 at the interface between the outer space of the sensor unit and the sealing window  21  is 50.28°. Since θr1=θi2, the incident angle θi2 of the light at the interface between the sealing window  21  and the internal space of the sensor unit is also 50.28°. As described above, the critical angle θi2′ at the interface between the sealing window  21  and the internal space of the sensor unit is given by 
 
sin θ i 2 ′=n 3 /n 2=1/1.56=0.64 
 
 Therefore, since θi2′=39.9° and θi2′&lt;θi2, the light is totally reflected. The light which is applied at an incident angle of 39.9° to 50.28°is totally reflected at the interface, and cannot reach the surface of the light-receiving element. Hence, the light amount cannot be accurately measured by using a total light beam, thus posing a problem. This problem affects not only the illuminance unevenness sensor unit but also the above-descried calibration sensor unit or the like. 
 
         [0017]     The above discussion is related to the problem in the immersion-type projection exposure apparatus. Alternatively, the projection exposure apparatus having a high NA has a factor which degrades the measurement precision of the conventional sensor unit which does not use the immersion technique. Generally, a photo-sensor has a characteristic to change the sensitivity in accordance with the incident angle of the light at the light-receiving surface. Hence, in the conventional projection exposure apparatus, the total light beam reaches the light-receiving element without total reflection. However, since light having a large incident angle at the light-receiving surface of the sensor is present, the light amount cannot be accurately measured upon reception of the influence of the angle characteristic of the sensitivity, thus posing a problem.  
         [0018]     A complex optical system arranged on the sensor can cope with these problems. However, in consideration of the sensor unit disposed on the stage which moves at high speed while holding the wafer, it is very difficult to implement the complex optical system in terms of weight and space.  
       SUMMARY OF THE INVENTION  
       [0019]     The present invention has been made on the basis of the recognition of the above problems, and has as its exemplified object to detect, at high precision, a wide-angle light beam which exits from an optical system having a high NA.  
         [0020]     The first aspect of the present invention is directed to a projection exposure apparatus which has a projection optical system and projects a pattern onto a substrate through the projection optical system, and the apparatus comprises a sensor unit which comprises a light-receiving element for detecting light incident through the projection optical system, a vessel in which the light-receiving element is arranged, and a sealing window which transmits the incident light and seals the vessel. A space between the sealing window and the light-receiving element is filled with a medium having a refractive index which is greater than 1.  
         [0021]     According to a preferable embodiment of the present invention, the sensor unit can be arranged not to include an interface at which total reflection of the incident light entering the sensor unit occurs.  
         [0022]     According to a preferable embodiment of the present invention, the medium can comprise a liquid, preferably an inert liquid.  
         [0023]     According to a preferable embodiment of the present invention, the liquid can include one of PFE (perfluoroether), PFPE (perfluoropolyether), HFE (hydrofluoroether), and HFPE (hydrofluoropolyether).  
         [0024]     According to a preferable embodiment of the present invention, the sensor unit can comprise a member covering the light-receiving element. The member can comprise one of fluoroplastic and glass.  
         [0025]     According to a preferable embodiment of the present invention, the apparatus can further comprise a supply unit which supplies the liquid to the sensor unit.  
         [0026]     According to a preferable embodiment of the present invention, the apparatus can further comprises a recovery unit which recovers the liquid from the sensor unit.  
         [0027]     According to a preferable embodiment of the present invention, the apparatus can further comprises a liquid supply unit which supplies the liquid to a space between the projection optical system and one of the substrate and the sensor unit.  
         [0028]     According to a preferable embodiment of the present invention, the apparatus can further comprises a liquid supply unit which supplies the liquid to a space between the projection optical system and one of the substrate and the sensor unit, and a tank which stores the liquid, wherein the liquid in the tank is supplied to both the sensor unit and the liquid supply unit.  
         [0029]     According to a preferable embodiment of the present invention, the apparatus can further comprise driving means for aligning the substrate, wherein the liquid also serves as a coolant for cooling the driving means.  
         [0030]     According to a preferable embodiment of the present invention, the medium can comprise a solid material such as fluoroplastic or glass.  
         [0031]     According to a preferable embodiment of the present invention, the sensor unit can comprise a light-shielding member with a predetermined shape at an incident portion for the incident light. The sealing window can comprise a predetermined light-shielding pattern.  
         [0032]     The second aspect of the present invention is directed to a projection exposure apparatus which has a projection optical system and projects a pattern onto a substrate through the projection optical system, and the apparatus comprises a sensor unit which comprises a light-receiving element for detecting light incident through the projection optical system, and a vessel in which the light-receiving element is arranged. The vessel is filled with a solid which has a refractive index greater than 1 and transmits the incident light.  
         [0033]     The third aspect of the present invention is directed to a sensor unit comprising a light-receiving element which detects light, and the unit comprises a vessel in which the light-receiving element is arranged, and a sealing window which transmits light incident thereon and seals the vessel. A space between the sealing window and the light-receiving element is filled with a medium having a refractive index which is greater than 1.  
         [0034]     According to a preferable embodiment of the present invention, the unit can be arranged not to include an interface at which total reflection of the incident light entering the unit occurs.  
         [0035]     According to a preferable embodiment of the present invention, the medium can comprise a liquid or solid. The solid material can comprise fluoroplastic or glass.  
         [0036]     The fourth aspect of the present invention is directed to a sensor unit comprising a light-receiving element which detects light, and the unit comprising a vessel in which the light-receiving element is arranged. The vessel is filled with a solid which has a refractive index greater than 1 and transmits the light.  
         [0037]     The fifth aspect of the present invention is directed to a projection exposure apparatus which has a projection optical system and projects a pattern onto a substrate through the projection optical system, and the apparatus comprises a sensor unit which icomprises a light-receiving element which detects light incident through the projection optical system, a vessel in which the light-receiving element is arranged, and a sealing window which transmits the incident light therethrough and seals the vessel. A space between the sealing window and the light-receiving element is filled with a liquid.  
         [0038]     The sixth aspect of the present invention is directed to a projection exposure apparatus which has a projection optical system and projects a pattern onto a substrate through the projection optical system, and the apparatus comprises a sensor unit which includes a light-receiving element which detects light incident through the projection optical system, and a vessel in which the light-receiving element is arranged. The vessel is filled with a solid which transmits the incident light.  
         [0039]     According to a preferable embodiment of the present invention, the solid material can comprise fluoroplastic or glass.  
         [0040]     The seventh aspect of the present invention is directed to a sensor unit comprising a light-receiving element which detects light, and the unit comprises a vessel in which the light-receiving element is arranged, and a sealing window which transmits the incident light and seals the vessel. A space between the sealing window and the light-receiving element is filled with a liquid.  
         [0041]     The eighth aspect of the present invention is directed to a sensor unit comprising a light-receiving element which detects light, and the unit comprises a vessel in which the light-receiving element is arranged, and a solid which fills the vessel and transmits the light.  
         [0042]     According to a preferable embodiment of the present invention, the solid material can comprise fluoroplastic or glass.  
         [0043]     The present invention can detect, at high precision, the wide-angle light beam which exits from the optical system having the high NA.  
         [0044]     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0045]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0046]      FIG. 1  is a view showing the schematic arrangement of an immersion-type projection exposure apparatus according to the first embodiment of the present invention;  
         [0047]      FIG. 2  is a view schematically showing the arrangement of a sensor unit;  
         [0048]      FIG. 3  is a view showing an example of a pinhole pattern applied to the sensor unit;  
         [0049]      FIG. 4  is a view showing an example of a pattern including a plurality of bars applied to the sensor unit;  
         [0050]      FIG. 5  is a view schematically showing another arrangement of the sensor unit;  
         [0051]      FIG. 6  is a view showing the schematic arrangement of a sensor unit according to the second embodiment of the present invention;  
         [0052]      FIG. 7  is a view showing the schematic arrangement of a sensor unit according to the third embodiment of the present invention;  
         [0053]      FIG. 8  is a view showing the schematic arrangement of a sensor unit according to the fourth embodiment of the present invention;  
         [0054]      FIG. 9  is a view showing the schematic arrangement of a sensor unit according to the fifth embodiment of the present invention;  
         [0055]      FIG. 10  is a view showing the schematic arrangement of the immersion-type projection exposure apparatus according to the first embodiment of the present invention;  
         [0056]      FIG. 11  is a view schematically showing a projection exposure apparatus according to the sixth embodiment of the present invention;  
         [0057]      FIG. 12  is a view schematically showing the arrangement of a conventional light amount sensor unit;  
         [0058]      FIG. 13  is a sectional view of the sensor unit for explaining an immersion effect;  
         [0059]      FIG. 14  is a flowchart showing the flow of a manufacturing process of a semiconductor device; and  
         [0060]      FIG. 15  is a flowchart showing a wafer process in detail. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0061]     First, the principle of the present invention will be described below.  FIG. 2  is a view showing the schematic arrangement of a sensor unit (e.g., illuminance unevenness sensor unit) to which the present invention is applied. In the sensor unit shown in  FIG. 2 , a light-receiving element  23  is arranged in a sensor vessel  22  sealed by a sealing window  21 . The internal space of the sensor unit, i.e., the space between the sealing window  21  and the light-receiving element  23  is filled with a liquid, e.g., a liquid  24  having the refractive index almost equal to that of a liquid used for immersion in wafer exposure. A light-shielding member  28  which has a pinhole is arranged on the sealing window  21 . When the light is applied to the sensor unit having this structure, the light is refracted at an interface between the air and the sealing window  21 , and an interface between the sealing window  21  and the internal space of the sensor unit.  
         [0062]     Assume that the refractive index of the outer space of the sensor unit is n1, the refractive index of the sealing window  21  is n2, the refractive index of the internal space of the sensor unit is n3, the incident angle and refractive angle of the light at the interface between the outer space of the sensor unit and the sealing window  21  are θi1 and θr1, respectively, and the incident angle and refractive angle of the light at the interface between the sealing window  21  and the internal space of the sensor unit are θi2 and θr2, respectively.  
         [0063]     In the immersion-type projection exposure apparatus, the outer space of the sensor unit is filled with the liquid. Assume that the liquid is pure water (refractive index=1.44). If the refractive index n1=1.44 and NA=0.83, the incident angle θi1 is 56.44°, and the refractive index n2 is 1.56. Hence, by Snell&#39;s law, the refractive angle θr1 at the interface between the outer space of the sensor unit and the sealing window  21  is 50.28°. Since θr1=i2, the incident angle θi2 at the interface between the sealing window  21  and the internal space of the sensor unit is also 50.28°. When the internal space of the sensor unit is filled with the inert liquid having a refractive index n3 of 1.34, the critical angle θi2′ at the interface between the sealing window and the internal space of the sensor unit is expressed by 
 
sin θ i 2 ′=n 3 /n 2=1.34/1.56=0.86 
 
 Therefore, since θi2′=59.20° and θi2′&gt;θi2, the light is not totally reflected. The total incident light reaches the surface of the light-receiving element  23 . 
 
         [0064]      FIG. 7  is a view showing the schematic arrangement of another illuminance unevenness sensor unit to which the present invention is applied. In the sensor unit shown in  FIG. 7 , the light-receiving element  23  is arranged in the sensor vessel  22 . The light-receiving element  23  is coated with a coating member (solid material)  33 , and the light-shielding member  28  having a pinhole is arranged on the coating member  33 . Preferably, the coating member  33  protects the light-receiving element  23  from the liquid used for immersion, and has a refractive index almost equal to or more than that of the liquid used for immersion. The coating member  33  can also serve as a light-shielding window arranged not to form a space in the sensor unit.  
         [0065]     When the light is applied to the sensor unit having this structure, the light is refracted at the interface between the air and the coating member  33 . Assume that the refractive index of the outer space of the sensor unit is n1, the refractive index of the coating member  33  is n2, the incident angle and refractive angle of the light at the interface between the outer space of the sensor unit and the coating member  33  are θi1 and θr1, respectively. In the immersion-type projection exposure apparatus, the outer space of the sensor unit is filled with the liquid. Assume that the liquid is pure water (refractive index=1.44). When the refractive index n1=1.44 and the NA=0.83, the incident angle θi1=56.44°. When the refractive index n2 of the coating member  33  is larger than 1.30, the total incident light can be guided into the coating member, and reach the surface of the light-receiving element.  
         [0066]     Since the sensor unit exemplified in  FIGS. 2 and 7  is incorporated in the immersion-type projection exposure apparatus, even when using the wide-angle incident light which is applied from the optical system having the high NA to the sensor unit, the incident light can be detected at high precision in the illuminance unevenness and calibration measurements.  
         [0067]     Also, when the sensor unit exemplified in  FIGS. 2 and 7  is incorporated in the projection exposure apparatus which does not use the immersion technique, the incident light can be detected at high precision in the illuminance unevenness and calibration measurements.  
         [0068]     Preferred embodiments will be described below.  
       First Embodiment  
       [0069]      FIG. 1  is a view showing the schematic arrangement of an immersion-type projection exposure apparatus according to the first embodiment of the present invention. The exposure apparatus shown in  FIG. 1  illuminates a reticle  1  by using an illumination optical system  3 . A circuit pattern formed on the reticle  1  is projected and transferred onto a wafer  2  coated with a photosensitive agent via a projection optical system  4 . The illumination optical system  3  can include a modified illumination forming apparatus, light amount control apparatus, and the like for projecting the circuit pattern of the reticle  1  onto the wafer  2 . The reticle  1  is held on the reticle stage  5 , and aligned at a predetermined position. The position of the reticle  1  is measured by a laser interferometer  16  using a reference mirror  14  arranged on the reticle stage  5 . A driving motor  18  drives the reticle stage  5 .  
         [0070]     Information used for aligning the circuit pattern of the reticle  1  and the pattern already formed on the wafer  2  is acquired by using an alignment optical system  6 .  
         [0071]     The projection optical system  4  includes a plurality of optical elements, and has an optical element  7  which is the last one of these optical elements. Preferably, the lower surface of the optical element  7 , i.e., the surface opposing the surface of the wafer  2  is flat, or convex toward the surface of the wafer  2 . This contributes to elimination of an air layer or air bubbles left on the surface of the optical element  7  when filling (immersing) the space between the optical element  7  and the wafer  2  or the space between the optical element  7  and a sensor unit  27  with the liquid. The surfaces of the optical element  7  and the photosensitive-agent light-amount sensor unit  27  on the wafer  2  which are to be immersed are preferably coated with a lyophilic agent for a liquid  25  used for immersion.  
         [0072]     A liquid supply device  12  supplies the liquid  25  into the space between the optical element  7  and the wafer  2  (or the sensor unit  27 ) to perform the immersion. This liquid  25  is recovered by a liquid recovery device  11 .  
         [0073]     A wafer chuck  8  holds the wafer  2 . This wafer chuck  8  (wafer  2 ) is driven by an X-Y stage  10  driven by a driving motor  17 , and a fine adjustment stage  9  arranged on the X-Y stage  10 . The fine adjustment stage  9  includes a tilt function for correcting the position of the wafer  2  in the θ direction, adjusting its position in a Z direction, and correcting its tilt.  
         [0074]     The fine adjustment stage  9  has a reference mirror  13  (not shown in the Y direction) for measuring the position in the X and Y directions. By using this, a laser interferometer  15  measures the position of the fine adjustment stage  9  in the X and Y directions. Focus measurement devices  19  and  20  measure the position in the Z direction and the tilt of the wafer  2 .  
         [0075]     A controller  26  controls the X-Y stage  10 , reticle stage  5 , focus measurement devices  19  and  20 , and the like.  
         [0076]     The sensor unit  27  serves as a light amount sensor unit which measures the light amount of the exposure light in the first embodiment. The sensor unit  27  has a light-receiving element  23  arranged in a sensor vessel  22  sealed by a sealing window  21 . The internal space of the sensor vessel  22  is filled with an inert liquid  24 . The sensor unit  27  may be arranged on the wafer chuck  8 , fine adjustment stage  9 , or another place as long as the light amount of the exposure light can be measured. The sealing window  21  on the surface of the sensor unit  27  has a pattern with a pinhole. For example, the sensor unit  27  can be used for measuring the absolute illuminance and illuminance unevenness of the exposure apparatus. Also, the sensor unit  27  can be used for alignment or calibration by changing the shape (mask shape) of the portion through which the light passes on the surface of the sensor unit  27 .  
         [0077]     Then, the operation of the exposure apparatus shown in  FIG. 1  will be described. When measuring the illuminance of the exposure light, the sensor unit  27  serving as the light amount sensor unit is aligned at the central portion under the projection optical system  4  by driving the X-Y stage  10 . Next, the liquid supply device  12  supplies the liquid  25  in the space between the optical element  7  and the sensor unit  27 . In this state, the illumination optical system  3  measures the illuminance of the exposure light while exposing the sensor unit  27  via the projection optical system  4 . The liquid  25  used for immersion is supplied from the liquid supply device  12  into the space between the optical element  7  and the sensor unit  27 , and recovered by the liquid recovery device  11 .  
         [0078]     The sensor vessel  22  of the sensor unit  27  is filled with the inert liquid  24  having the refractive index almost equal to that of, e.g., the liquid  25  used for immersion. Therefore, even when the exposure light is applied from the projection optical system  4  having the high NA, the total exposure light can reach the light-receiving element  23 , thereby measuring the luminance at high precision.  
         [0079]     Next, the wafer exposure will be described with reference to  FIG. 10 . When exposing the wafer, the wafer  2  which is coated with a photosensitive agent in advance is loaded onto the wafer chuck  8  by using a wafer loading apparatus (not shown). The wafer  2  on the wafer chuck  8  is fixed in a chuck method such as vacuum chuck to perform its surface leveling. The focus measurement devices  19  and  20  then perform focus and tilt measurements of the entire surface of the wafer  2 .  
         [0080]     In accordance with the focus and tilt measurement information, while the position of the fine adjustment stage  9  is controlled, the liquid supply device  12  supplies the liquid  25  into the space between the optical element  7  and the wafer  2 , and the liquid recovery device  11  recovers the supplied liquid  25 . The pattern of the reticle  1  is projected on the wafer  2 , thereby exposing the wafer  2 . After the wafer  2  is completely exposed, the wafer loading apparatus (not shown) recovers the wafer  2  from the fine adjustment stage  9 . Then, a series of exposure operations are terminated.  
         [0081]     The sensor unit  27  will be described in detail below with reference to  FIG. 2 . When the sensor unit  27  serves as the light amount sensor unit, the sensor vessel  22  is sealed by the sealing window  21  on which the light-shielding member  28  having a pattern with a pinhole is formed by chromium and the like as exemplified in  FIG. 3 . The light-receiving element  23  is arranged in the sensor vessel  22 , and the sensor vessel  22  is filled with the liquid such as the inert liquid  24 .  
         [0082]     As the material of the sealing window  21 , for example, the material (e.g., quartz) through which the exposure light is efficiently transmitted. As the inert liquid  24 , for example, a fluorine-based inert liquid such as PFE (perfluoroether), PFPE (perfluoropolyether), HFE (hydrofluoroether), HFPE (hydrofluoropolyether), or the like are preferably available. As the criterion for selecting the material, it is important to have a refractive index almost equal to that of the liquid  25  used for immersion, have a high transmittance for the exposure light, be hardly degraded by the exposure light, and cause no degradation of the characteristic of the light-receiving element  23 .  
         [0083]     The light-shielding member  28  which forms the pattern with the pinhole can use, e.g., a thin plate having a through hole. This thin plate can be arranged on the surface of or near the sealing window  21 . Also, the sensor unit which is suitable for measuring the alignment or calibration includes the pattern where a plurality of bars are arrayed as exemplified in  FIG. 4 , in place of the pattern having the pinhole. Of course, when the sensor unit is used in another application, the pattern which is suitable for the application may be used.  
         [0084]     Desirably, in the sealing window  21  and the sensor vessel  22 , the inert liquid  24  in the sensor unit is not volatilized. As shown in  FIG. 5 , an O-ring  29  may be arranged at a coupling portion between the sealing window  21  and the sensor vessel  22  to seal the sensor unit, thereby easily separating the sealing window  21  and the sensor vessel  22  as needed. For example, in the structure where the sensor unit  27  is fixed to the wafer chuck  8 , when the wafer chuck  8  is to be detached from the exposure apparatus, it may be difficult to disconnect the electrical wiring between the light-receiving element  23  and another unit (e.g., controller  26 ). Thus, in the sensor unit as shown in  FIG. 5 , for example, the sealing window  21  is attached to the wafer chuck  8 , and the sensor vessel  22  is attached to the fine adjustment stage  9 . Hence, the wafer chuck  8  can be detached from the exposure apparatus independently of the electrical wiring from the light-receiving element  23 .  
       Second Embodiment  
       [0085]      FIG. 6  is a view showing the schematic arrangement of a sensor unit in an immersion-type projection exposure apparatus according to the second embodiment of the present invention. The arrangement and operation of the overall apparatus except for the sensor unit are the same as those in the first embodiment. In  FIG. 6 , a sealing window  21  on which a light-shielding member  28  having a pattern with a pinhole as in  FIG. 3  is formed on a surface by chromium and the like, and a sensor vessel  32  having a circulation ports  32   a  and  32   b  separate an internal space from an outer space of a light amount sensor unit  27 . A light-receiving element  23  is arranged in the internal space. In this arrangement, an inert liquid  24  is supplied to the internal space of the circulation port  32  to circulate the supplied inert liquid.  
         [0086]     In the outer space, a tank  30  which stores the inert liquid  24 , and a liquid feeding pump  31  which supplies the inert liquid  24  in the tank  30  to the sensor vessel  32  can be arranged. The pump  31  can always circulates the inert liquid  24  in the sensor vessel  32 . Alternatively, the liquid feeding pump  31  may stop in the state where the sensor vessel  32  is filled with the inert liquid  24 , and be driven to circulate the inert liquid  24  as needed.  
         [0087]     As described above, in the arrangement wherein the inert liquid  24  can be supplied to the sensor vessel  32 , the sensor vessel  32  can be refilled with the inert liquid  24 , for example, even when the sensor vessel  32  is not filled with a liquid  25  because the inert liquid  24  is volatilized from a gap unintendedly generated at the coupling portion (an O-ring  29  may be arranged as shown in  FIG. 5 ) between the sealing window  21  and the sensor vessel  32 . Also, even when the composition of the inert liquid  24  is changed and degraded by illuminating the exposure light for a long time, the liquid can be easily changed. Also, even when the inert liquid  24  is contaminated by an impurity generated from the inner wall of the sensor vessel  32  or the light-receiving element  23 , the liquid can be easily changed.  
         [0088]     Since a certain amount of the inert liquid  24  is stored and circulated in the tank  30 , for example, the total amount of the inert liquid  24  used is larger than that in the first embodiment. Hence, the degradation of the inert liquid  24  caused by the exposure light irradiation or the impurity can be suppressed.  
         [0089]     Furthermore, a coolant used for cooing an X-Y stage  10  can serve as the inert liquid  24 . When the liquid can serve as the both inert liquid and coolant, the liquid feeding pump and the tank only for the sensor unit are not needed.  
         [0090]     In the sensor unit shown in  FIG. 6 , the pattern shape of the light-shielding member  28  can be changed in accordance with the application as exemplified in  FIGS. 3 and 4 . For example, the arrangement of the coupling portion between the sealing window  21  and the sensor vessel  32  can change to the arrangement exemplified in  FIG. 5 .  
       Third Embodiment  
       [0091]      FIG. 7  is a view showing the schematic arrangement of a sensor unit in an immersion-type projection exposure apparatus according to the third embodiment of the present invention. The arrangement and operation of the overall apparatus except for the sensor unit are the same as those in the first embodiment.  
         [0092]     In the arrangement shown in  FIG. 7 , a sensor unit  27  includes a light-shielding member  28  having a pattern with a pinhole as in  FIG. 3 , a sensor vessel  22 , a light-receiving element  23 , and a coating member  33  (solid material) filled in the sensor vessel  22  to cover the light-receiving element  23 . Preferably, the coating member  33  is made of the material which has the refractive index almost equal to or more than that of a liquid  25  used for immersion, has a high transmittance for the exposure light, is hardly degraded by the exposure light, causes no degradation of the characteristic of the light-receiving element  23 , and has a resistance to the liquid  25  used for immersion, e.g., a fluoroplastic or glass. In the sensor unit as shown in  FIG. 7 , the pattern shape of the light-shielding member  28  can change in accordance with the application as exemplified in  FIGS. 3 and 4 .  
       Fourth Embodiment  
       [0093]      FIG. 8  is a view showing the schematic arrangement of a sensor unit in an immersion-type projection exposure apparatus according to the fourth embodiment of the present invention. The arrangement and operation of the overall apparatus except for the sensor unit are the same as those in the first embodiment. A sensor unit  27  shown in  FIG. 8  includes a sealing window  21  on which a light-shielding member  28  having a pattern with a pinhole as in  FIG. 3  is formed on the surface by chromium and the like, a sensor vessel  22 , a light-receiving element  23 , a coating member  33  which covers the light-receiving element  23 , and a liquid  34  filled in the sensor vessel.  
         [0094]     Preferably, the coating member (solid material)  33  is made of the material which has the refractive index almost equal to or more than that of a liquid  34  in the sensor vessel  22 , has a high transmittance for the exposure light, is hardly degraded by the exposure light, causes no degradation of the characteristic of the light-receiving element  23 , and has a resistance to the liquid  34  in the sensor vessel, e.g., a fluoroplastic or glass.  
         [0095]     As the liquid  34  for filling the sensor vessel  22 , for example, an inert liquid described in the first and second embodiments may be used, or the liquid  25  used for immersion may be directly used. In the sensor unit shown in  FIG. 8 , the pattern shape of the light-shielding member  28  can change in accordance with the application as exemplified in  FIGS. 3 and 4 . The arrangement of the coupling portion between the sealing window  21  and the sensor vessel  32  can change as exemplified in  FIG. 5 .  
       Fifth Embodiment  
       [0096]      FIG. 9  is a view showing the schematic arrangement of a sensor unit and its environment in an immersion-type projection exposure apparatus according to the fifth embodiment of the present invention. The matters except for those described in this embodiment are the same as those in the first embodiment. In  FIG. 9 , a sealing window  21  on which a light-shielding member  28  having a pattern with a pinhole as in  FIG. 3  is formed on a surface by chromium and the like, and a sensor vessel  32  having a circulation ports  32   a  and  32   b  separates an internal space from an outer space of a light amount sensor unit  27 . A light-receiving element  23  is arranged in the internal space, and the light-receiving element  23  is coated with a coating member  33 . The internal space is filled with a liquid  25  which is the same as that supplied to the space between an optical element  7  and a wafer  2  or the sensor unit.  
         [0097]     The liquid  25  is stored in a tank  30 , supplied to a liquid supply device  12  by a liquid feeding pump  31  through liquid feeding pipes  40  and  42 , and then supplied into the sensor vessel  32  through the liquid feeding pipe  40 , a liquid feeding pipe  41 , and a port  32   b . The liquid  25  supplied into the space between the optical element  7  and the wafer  2  or sensor unit by the liquid supply device  12  is recovered by a liquid recovery device  11 . Then, the recovered liquid is fed to a liquid feeding pipe  52 . After that, the liquid  25  supplied to the sensor vessel  32  through the port  32   b  is fed to a liquid feeding pipe  51  through a port  32   a . The fed liquid is returned to the tank  30  through the liquid feeding pipe  50 . With this operation, the liquid  25  circulates in the two channels.  
         [0098]     Preferably, the coating member  33  is made of the material which has the refractive index almost equal to or more than that of a liquid  25  in the sensor vessel  32 , has a high transmittance for the exposure light, is hardly degraded by the exposure light, causes no degradation of the characteristic of the light-receiving element  23 , and has a resistance to the liquid  25  used for immersion in the sensor vessel, e.g., a fluoroplastic or glass.  
         [0099]     Effectively, the liquid feeding pipes  41  and  51  have valves which can close in the state where the sensor vessel  32  is filled with the liquid  25 . In this case, the valves can open as needed, e.g., when the liquid  25  in the sensor vessel  32  is changed.  
         [0100]     As described above, in the arrangement wherein the liquid  25  can be supplied to the sensor vessel  32 , the sensor vessel  32  can be refilled with the liquid  25 , for example, even when the sensor vessel  32  is not filled with the liquid  25  because the liquid  25  is volatilized from the coupling portion between the sealing window  21  and the sensor vessel  32 . Also, even when the composition of the liquid  25  is changed and degraded by illuminating the exposure light for a long time, the liquid can be easily changed. Also, even when the liquid  25  is contaminated by an impurity generated from the inner wall of the sensor vessel  32  or the coating member  33 , the liquid can be easily changed.  
         [0101]     Since a certain amount of the liquid  25  is stored and circulated in the tank  30 , the total amount of the liquid  25  used is larger than that in the fourth embodiment. Hence, the degradation of the liquid  25  caused by the exposure light irradiation or the impurity can be suppressed.  
         [0102]     In the sensor unit shown in  FIG. 9 , the pattern shape of the light-shielding member  28  can be changed in accordance with the application as exemplified in  FIGS. 3 and 4 . For example, the arrangement of the coupling portion between the sealing window  21  and the sensor vessel  32  can change to the arrangement exemplified in  FIG. 5 .  
         [0103]     The liquid filled in the sensor vessel  32  may be an inert liquid as described in the first and second embodiments. In this case, the liquid feeding pipes  42  and  52  which respectively communicate with the liquid supply device  12  and the liquid recovery device  11  are generally omitted. Furthermore, a coolant used for cooing an X-Y stage  10  can also serve as the inert liquid. When the liquid can serve as the both inert liquid and the coolant, the feeding pump and the tank only for the sensor unit are not needed.  
       Sixth Embodiment  
       [0104]      FIG. 11  shows the arrangement of a projection exposure apparatus according to the sixth embodiment of the present invention. This projection exposure apparatus is not an immersion-type projection exposure apparatus, but serves as a projection exposure apparatus which exposes a wafer under the condition where the space between an optical element  7  and the wafer is filled with a gas, or under a pressure-reduced condition.  
         [0105]     The exposure apparatus shown in  FIG. 11  illuminates a reticle  1  by using an illumination optical system  3 . A circuit pattern formed on the reticle  1  is projected and transferred onto a wafer  2  coated with a photosensitive agent via a projection optical system  4 . The illumination optical system  3  can include a modified illumination forming apparatus, light amount control apparatus, and the like for projecting the circuit pattern of the reticle  1  onto the wafer  2 . The reticle  1  is held on the reticle stage  5 , and aligned at a predetermined position. The position of the reticle  1  is measured by a laser interferometer  16  using a reference mirror  14  arranged on the reticle stage  5 . Also, a driving motor  18  drives the reticle stage  5 .  
         [0106]     Information used for aligning the circuit pattern of the reticle  1  and the pattern already formed on the wafer  2  is acquired by using an alignment optical system  6 .  
         [0107]     A wafer chuck  8  holds the wafer  2 . This wafer chuck  8  (wafer  2 ) is driven by an X-Y stage  10  driven by a driving motor  17 , and a fine adjustment stage  9  arranged on the X-Y stage  10 . The fine adjustment stage  9  includes a tilt function for correcting the position of the wafer  2  in the θ direction, adjusting its position in a Z direction, and correcting its tilt.  
         [0108]     The fine adjustment stage  9  has a reference mirror  13  (not shown in the Y direction) for measuring the position in the X and Y directions. By using this, a laser interferometer  15  measures the position of the fine adjustment stage  9  in the X and Y directions. Focus measurement devices  19  and  20  measure the position in the Z direction and the tilt of the wafer  2 .  
         [0109]     A controller  26  controls the X-Y stage  10 , reticle stage  5 , focus measurement devices  19  and  20 , and the like.  
         [0110]     A sensor unit  27  serves as a light amount sensor unit which measures the light amount of the exposure light in the first embodiment. The sensor unit  27  has a light-receiving element  23  arranged in a sensor vessel  22  sealed by a sealing window  21 . The internal space of the sensor vessel  22  is filled with an inert liquid  24 . The sensor unit  27  may be arranged on the wafer chuck  8 , fine adjustment stage  9 , or another place as long as the light amount of the exposure light can be measured. The sealing window  21  on the surface of the sensor unit  27  has a pattern with a pinhole. For example, the sensor unit  27  can be used for measuring the absolute illuminance and illuminance unevenness of the exposure apparatus. Also, the sensor unit  27  can be used for alignment or calibration by changing the shape (mask shape) of the portion through which the light passes on the surface of the sensor unit  27 .  
         [0111]     Then, the operation of the exposure apparatus shown in  FIG. 11  will be described. When measuring the illuminance of the exposure light, the sensor unit  27  serving as the light amount sensor unit is aligned at the central portion under the projection optical system  4  by driving the X-Y stage  10 . Next, the illumination optical system  3  measures the illuminance of the exposure light while exposing the sensor unit  27  via the projection optical system  4 .  
         [0112]     The sensor vessel  22  of the sensor unit  27  is filled with the liquid  25  having the refractive index which is larger than 1. Therefore, even when the exposure light is applied from the projection optical system  4  having the high NA, the total exposure light can reach the light-receiving element  23 , thereby measuring the luminance at high precision.  
         [0113]     Next, the wafer exposure will be described with reference to  FIG. 11 . When exposing the wafer, the wafer  2  which is coated with a photosensitive agent in advance is loaded onto the wafer chuck  8  by using a wafer loading apparatus (not shown). The wafer  2  on the wafer chuck  8  is fixed in a chuck method such as vacuum chuck to perform surface leveling of the wafer  2 . Next, while the focus measurement devices  19  and  20  perform focus and tilt measurements of the entire surface of the wafer  2 , and the position of the fine adjustment stage  9  is controlled, the wafer is exposed.  
         [0114]     After the wafer  2  is completely exposed, the wafer loading apparatus (not shown) recovers the wafer  2  from the fine adjustment stage  9 . Then, a series of exposure operations are terminated. The operation of the sensor unit  27  is the same as that described in the first embodiment. The sensor unit  27  can have the arrangement exemplified in the first to fourth embodiments. Also, in the fifth embodiment, the channels (liquid feeding pipes  42  and  52 ) respectively connected to the liquid supply device  12  and the liquid recovery device  11  can be eliminated.  
       Seventh Embodiment  
       [0115]     The pattern or structure of the light-shielding member  28  of the sensor unit exemplified in the first to the sixth embodiments can change in accordance with an application, or may be eliminated in accordance with a specific application. Also, the sealing window may include a pattern such as a reference mark pattern. That is, in place of setting a light-shielding member in addition to the sealing window, the sealing window itself may have a pattern (light-shielding member). Also, the sealing window may have various shapes in addition to a plate shape.  
         [0116]     The type of the light-receiving element used in the sensor unit is not limited to a specific one. The light-receiving element may include a single photodiode, a linear sensor or area sensor such as one- or two-dimensional CCD, or the like.  
         [0000]     [Application] 
         [0117]     A semiconductor device manufacturing process using the above-described exposure apparatus will be explained.  FIG. 14  is a view showing the flow of the whole manufacturing process of a semiconductor device. In step  1  (circuit design), a semiconductor device circuit is designed. In step  2  (mask formation), a mask is created on the basis of the designed circuit pattern. In step  3  (wafer formation), a wafer is formed using a material such as silicon. In step  4  (wafer process) called a pre-process, an actual circuit is formed on the wafer by lithography using the above-described mask and wafer. Step  5  (assembly) called a post-process is the step of forming a semiconductor chip by using the wafer formed in step  4 , and includes an assembly process (dicing and bonding) and packaging process (chip encapsulation). In step  6  (inspection), the semiconductor device manufactured in step  5  undergoes inspections such as an operation confirmation test and durability test. After these steps, the semiconductor device is completed and shipped (step  7 ).  
         [0118]      FIG. 15  shows the detailed flow of the wafer process. In step  11  (oxidation), the wafer surface is oxidized. In step  12  (CVD), an insulating film is formed on the wafer surface. In step  13  (electrode formation), an electrode is formed on the wafer by vapor deposition. In step  14  (ion implantation), ions are implanted in the wafer. In step  15  (resist processing), a photosensitive agent is applied to the wafer. In step  16  (exposure), a circuit pattern is transferred onto the wafer by the above-mentioned exposure apparatus. In step  17  (developing), a photosensitive agent on the exposed wafer is developed. In step  18  (etching), the resist is etched through an opening portion of the developed resist image. In step  19  (resist removal), an unnecessary resist after etching is removed. These steps are repeated to form multiple circuit patterns on the wafer.  
         [0119]     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the claims.  
       CLAIM OF PRIORITY  
       [0120]     This application claims priority from Japanese Patent application No. 2004-032450 filed on Feb. 9, 2004, the entire contents of which is hereby incorporated by reference herein.