Patent Publication Number: US-11392042-B2

Title: Exposure apparatus and exposure method, and flat panel display manufacturing method

Description:
This is a Continuation of U.S. application Ser. No. 15/763,579 filed Aug. 9, 2018, which is a 371 of International Application No. PCT/JP2016/078809 filed Sep. 29, 2016, which claims the benefit of Japanese Patent Application No. 2015-194828 filed Sep. 30, 2015. The disclosures of the prior applications are hereby incorporated by reference herein in their entireties. 
    
    
     TECHNICAL FIELD 
     The present invention relates to exposure apparatuses and exposure methods, and flat panel display manufacturing methods, and more particularly, to an exposure apparatus and an exposure method used in a lithography process for producing micro-devices such as a liquid crystal display device, and a flat panel display manufacturing method using the exposure apparatus and the exposure method. 
     BACKGROUND ART 
     Conventionally, in a lithography process for producing electronic devices (micro-devices) such as a liquid crystal display device or a semiconductor device (such as an integrated circuit), exposure apparatuses are used such as an exposure apparatus of a step-and-scan method (a so-called scanning stepper (also called a scanner)) that transfers a pattern formed on a mask irradiated with an energy beam, while a mask (photomask) or a reticle (hereinafter collectively called a “mask”) and a glass plate or a wafer (hereinafter collectively called a “substrate”) are moved synchronously along a predetermined scanning direction (scan direction). 
     As this type of exposure apparatus, an exposure apparatus equipped with an optical interferometer system is known that obtains position information within a horizontal plane of a substrate subject to exposure using a bar mirror (long mirror) that a substrate stage device has (refer to PTL 1). 
     Here, in the case of obtaining position information of the substrate using the optical interferometer system, influence of the so-called air fluctuation cannot be ignored. While the influence of air fluctuation mentioned above can be reduced using an encoder system, due to the increasing size of substrates in recent years, it is becoming difficult to prepare a scale that can cover the entire moving range of the substrate. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] U.S. Patent Application Publication No. 2010/0266961 
     SUMMARY OF INVENTION 
     According to a first aspect of the present invention, there is provided an exposure apparatus that irradiates an object with an illumination light via an optical system, comprising: a movable body arranged below the optical system that holds the object; a drive system that can move the movable body in a first direction and a second direction orthogonal to each other within a predetermined plane orthogonal to an optical axis of the optical system; a measurement system that has a grating member with a plurality of grating areas arranged mutually apart in the first direction, a plurality of heads each irradiating the grating member with a measurement beam that can move in the second direction, and a measurement device that measures position information of the plurality of heads in the second direction, in which one of the grating member and the plurality of heads is provided at the movable body, along with the other of the grating member and the plurality of heads being provided facing the movable body, and the measurement system, measuring position information of the movable body in at least directions of three degrees of freedom within the predetermined plane, based on measurement information of at least three heads of the plurality of heads irradiating at least one of the plurality of grating areas with the measurement beam and measurement information of the measurement device; and a control system that controls the drive system based on position information measured by the measurement system, wherein the measurement beam of each of the plurality of heads moves off of one of the plurality of grating areas, and moves to irradiate another grating area adjacent to the one grating area while the movable body is being moved in the first direction, and the control system acquires correction information to control movement of the movable body using, of the plurality of heads, a head whose measurement beam has moved off of the one grating area and moves to irradiate the another grating area and is a different head from the at least three heads, based on measurement information of the at least three heads, or position information of the movable body measured using the at least three heads. 
     According to a second aspect of the present invention, there is provided an exposure apparatus that irradiates an object with an illumination light via an optical system, comprising: a movable body arranged below the optical system that holds the object; a drive system that can move the movable body in a first direction and a second direction orthogonal to each other within a predetermined plane orthogonal to an optical axis of the optical system; a measurement system, having a grating member with a plurality of first grating areas arranged mutually apart in the first direction and a plurality of second grating areas arranged mutually apart in the first direction at positions different from the plurality of first grating areas in the second direction, a plurality of heads irradiating the grating member with a measurement beam from each of the heads that can move in the second direction, and a measurement device that measures position information of the plurality of heads in the second direction, in which one of the grating member and the plurality of heads is provided at the movable body, along with the other of the grating member and the plurality of heads being provided facing the movable body, and the measurement system measuring position information of the movable body in at least directions of three degrees of freedom within the predetermined plane, based on measurement information of at least three heads of the plurality of heads irradiating at least two of the plurality of first grating areas and the plurality of second grating areas with the measurement beam and measurement information of the measurement device; and a control system that controls the drive system based on position information measured by the measurement system, wherein the measurement beam of each of the plurality of heads moves off of one grating area of the plurality of first grating areas or the plurality of second grating areas, and moves to irradiate one grating area of another first grating area or another second grating area adjacent to the one grating area of the first grating area or the second grating area while the movable body is being moved in the first direction, and the control system acquires correction information to control movement of the movable body using, of the plurality of heads, a head whose measurement beam has moved off of one grating area of the plurality of first grating areas or the plurality of second grating areas and moves to irradiate the another first grating area or the another second grating area and is a different head from the at least three heads, based on measurement information of the at least three heads, or position information of the movable body measured using the at least three heads. 
     According to a third aspect of the present invention, there is provided a flat panel display manufacturing method, comprising: exposing a substrate using the exposure apparatus according to one of the first aspect and the second aspect; and developing the substrate that has been exposed. 
     According to a fourth aspect of the present invention, there is provided an exposure method irradiating an object with an illumination light via an optical system, comprising: measuring position information of a movable body that holds the object at least in directions of three degrees of freedom within a predetermined plane by a measurement system having a grating member with a plurality of grating areas arranged mutually apart in a first direction within the predetermined plane orthogonal to an optical axis of the optical system, a plurality of heads irradiating the grating member with a measurement beam from each of the heads that can move in a second direction orthogonal to the first direction within the predetermined plane, and a measurement device that measures position information of the plurality of heads in the second direction, in which one of the grating member and the plurality of heads is provided at the movable body, along with the other of the grating member and the plurality of heads being provided facing the movable body, based on measurement information of at least three heads of the plurality of heads irradiating at least one of the plurality of grating areas with the measurement beam and measurement information of the measurement device; and moving the movable body based on position information measured by the measurement system, wherein the measurement beam of each of the plurality of heads moves off of one of the plurality of grating areas, and moves to irradiate another grating area adjacent to the one grating area while the movable body is being moved in the first direction, and correction information to control movement of the movable body using a head different from the at least three heads of the plurality of heads whose measurement beams have moved off of the one grating area and move to irradiate the another grating area is acquired, based on measurement information of the at least three heads or position information of the movable body measured using the at least three heads. 
     According to a fifth aspect of the present invention, there is provided an exposure method irradiating an object with an illumination light via an optical system, comprising: measuring position information of the movable body at least in directions of three degrees of freedom within a predetermined plane orthogonal to an optical axis of the optical system by a measurement system having a grating member with a plurality of first grating areas arranged mutually apart in the first direction within the predetermined plane and a plurality of second grating areas arranged mutually apart in the first direction at positions different from the plurality of first grating areas in the second direction, a plurality of heads irradiating the grating member with a measurement beam from each of the heads that can move in the second direction, and a measurement device that measures position information of the plurality of heads in the second direction, in which one of the grating member and the plurality of heads is provided at the movable body, along with the other of the grating member and the plurality of heads being provided facing the movable body, based on measurement information of at least three heads of the plurality of heads irradiating at least two of the plurality of first grating areas and the plurality of second grating areas with the measurement beam and measurement information of the measurement device; and moving the movable body based on position information measured by the measurement system, wherein the measurement beam of each of the plurality of heads moves off of one grating area of the plurality of first grating areas or the plurality of second grating areas, and moves to irradiate one grating area of another first grating area or another second grating area adjacent to the one grating area of the first grating area or the second grating area while the movable body is being moved in the first direction, and correction information to control movement of the movable body using a head different from the at least three heads of the plurality of heads whose measurement beams have moved off of one of the first grating area and the second grating area and move to irradiate the another of the first grating area and the second grating area is acquired, based on measurement information of the at least three heads or position information of the movable body measured using the at least three heads. 
     According to a fifth aspect of the present invention, there is provided a flat panel display manufacturing method, comprising: exposing a substrate using the exposure method according to one of the fourth aspect and the fifth aspect; and developing the substrate that has been exposed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view schematically showing a structure of a liquid crystal exposure apparatus according to a first embodiment. 
         FIG. 2A  is a view schematically showing a structure of a mask encoder system, and  FIG. 2B  is an enlarged view of a part of the mask encoder system (part A in  FIG. 2A ). 
         FIGS. 3A to 3E  are views (No. 1 to No. 5) used to explain a linkage process of head outputs in the mask encoder system and a substrate encoder system. 
         FIG. 4A  is a view schematically showing a structure of a substrate encoder system, and  FIGS. 4B and 4C  are enlarged views of a part of the substrate encoder system (part B in  FIG. 4A ). 
         FIG. 5  is a schematic view of the substrate encoder system. 
         FIG. 6  is a block diagram showing an input/output relation of a main controller that mainly structures the control system of the liquid crystal exposure apparatus. 
         FIG. 7A  is a view (No. 1) showing an operation of the mask encoder system at the time of exposure operation, and  FIG. 7B  is a view (No. 1) showing an operation of the substrate encoder system at the time of exposure operation. 
         FIG. 8A  is a view (No. 2) showing an operation of the mask encoder system at the time of exposure operation, and  FIG. 8B  is a view (No. 2) showing an operation of the substrate encoder system at the time of exposure operation. 
         FIG. 9A  is a view (No. 3) showing an operation of the mask encoder system at the time of exposure operation, and  FIG. 9B  is a view (No. 3) showing an operation of the substrate encoder system at the time of exposure operation. 
         FIGS. 10A to 10C  are views (No. 1 to No. 3) used to explain a modified example (No. 1) of the linkage process of head outputs. 
         FIGS. 11A to 11F  are views (No. 1 to No. 6) used to explain a modified example (No. 2) of the linkage process of head outputs. 
         FIGS. 12A and 12B  are views (No. 1 and No. 2) used to explain a structure of a measurement system for obtaining the distance between a pair of heads. 
         FIGS. 13A and 13B  are views (No. 1 and No. 2) used to explain a structure of a measurement system for obtaining tilt amount of a Y slide table. 
         FIG. 14  is a planar view showing a substrate holder and a pair of head units of a substrate encoder system that a liquid crystal exposure apparatus according to a second embodiment has, along with a projection optical system. 
         FIGS. 15A and 15B  are views used to explain a movement range in the X-axis direction of the substrate holder when position measurement of the substrate holder is performed. 
         FIGS. 16A to 16D  are views used to explain a first state to a fourth state in a state change of positional relation between a pair of head units and a scale in the process when the substrate holder moves in the X-axis direction in the second embodiment. 
         FIGS. 17A to 17C  are views used to explain a linkage process at the time of switching heads of the substrate encoder system that measures position information of the substrate holder performed in the liquid crystal exposure apparatus according to the second embodiment. 
         FIG. 18  is a planar view showing a substrate holder and a pair of head units of a substrate encoder system that a liquid crystal exposure apparatus according to a third embodiment has, along with a projection optical system. 
         FIG. 19  is a view used to explain a characteristic structure of a liquid crystal exposure apparatus according to a fourth embodiment. 
         FIG. 20  is a view showing an irradiation point of a measurement beam on an encoder scale. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereinafter, a first embodiment will be described, using  FIGS. 1 to 11F . 
       FIG. 1  schematically shows a structure of a liquid crystal exposure apparatus  10  according to the first embodiment. Liquid crystal exposure apparatus  10  is a projection exposure apparatus of a step-and-scan method, or a so-called scanner whose exposure target is a rectangular (square-shaped) glass substrate P (hereinafter simply referred to as substrate P) used in, for example, a liquid crystal display device (flat panel display) or the like. 
     Liquid crystal exposure apparatus  10  has an illumination system  12 , a mask stage device  14  that holds a mask M on which a circuit pattern and the like is formed, a projection optical system  16 , an apparatus main section  18 , a substrate stage device  20  that holds substrate P whose surface (a surface facing a +Z side in  FIG. 1 ) is coated with a resist (sensitive agent), a control system for these parts and the like. In the description below, a direction in which mask M and substrate P are relatively scanned with respect to illumination light IL at the time of scanning exposure will be described as an X-axis direction within a predetermined plane orthogonal to an optical axis of projection optical system  16  (coincides with an optical axis of illumination system  12 ), a direction orthogonal to the X-axis within a horizontal plane will be described as a Y-axis direction, and a direction orthogonal to the X-axis and the Y-axis will be described as a Z-axis direction, and each of the rotation directions around the X-axis, the Y-axis, and the Z-axis will be described as θx, θy, and θz directions, respectively. Also, positions in the X-axis, the Y-axis, and the Z-axis directions will each be described as an X position, a Y position, and a Z position, respectively. 
     Illumination system  12  is structured similarly to the illumination system disclosed in, U.S. Pat. No. 5,729,331 and the like. Illumination system  12  irradiates mask M with a light emitted from a light source not shown (a mercury lamp) serving as an exposure illumination light (illumination light) IL, via parts not shown such as a reflection mirror, a dichroic mirror, a shutter, a wavelength selection filter, and various kinds of lenses. As illumination light IL, a light including at least one of an i-line (wavelength 365 nm), a g-line (wavelength 436 nm), and an h-line (wavelength 405 nm) (in the embodiment, a synthetic light of the i-line, the g-line, and the h-line described above) is used. Illumination system  12  has a plurality of optical systems that irradiates a plurality of illumination areas whose positions in the Y-axis direction are different with illumination light IL, respectively, and the number of this plurality of optical systems is the same as the number of a plurality of optical systems of projection optical system  16  to be described later on. 
     Mask stage device  14  includes a mask holder (also called a slider, or a movable member)  40  that holds mask M by vacuum chucking, a mask driving system  91  (not illustrated in  FIG. 1 , refer to  FIG. 6 ) that drives mask holder  40  in a scanning direction (the X-axis direction) in predetermined long strokes as well as finely drive mask holder  40  appropriately in the Y-axis direction and the θz direction, and a mask position measurement system that measures at least position information (position information in directions of three degrees of freedom including the X-axis direction, the Y-axis direction, and the θz direction, and the θz direction includes rotation (yawing) information; the same hereinafter) of mask holder  40  within the XY plane. Mask holder  40  consists of a frame shaped member in which an opening section in a rectangular shape in a planar view is formed, as is disclosed in U.S. Patent Application Publication No. 2008/0030702. Mask holder  40  is mounted on a pair of mask guides  42  fixed to an upper mount section  18   a , which is a part of apparatus main section  18 , via an air bearing (not shown). Mask drive system  91  includes a linear motor (not shown). While the description below is made with mask holder  40  being moved, a table or a stage having a holding section of mask M may be moved. That is, the mask holder holding the mask does not necessarily have to be provided separately with the mask table or the mask stage and the mask may be held by vacuum suction or the like on the mask table or the mask stage, and in such a case, the mask table or the mask stage holding the mask is to be moved in directions of three degrees of freedom within the XY plane. 
     The mask position measurement system is equipped with a mask encoder system  48  in which one of a pair of encoder head units  44  (hereinafter simply referred to as a head unit  44 ) and a plurality of encoder scales  46  (overlapping in a depth direction of the page surface in  FIG. 1 , refer to  FIG. 2A ) irradiated with a measurement beam via head unit  44  is provided at mask holder  40 , and the other of encoder heads  44  and the plurality of encoder scales  46  is provided facing mask holder  40 . In the embodiment, encoder head  44  is provided at upper mount section  18   a  via an encoder base  43 , and the plurality of encoder scales  46  is provided on the lower surface side of mask holder  40  so that the each of the encoder scales faces the pair of encoder heads  44 . Note that encoder heads  44  may be provided, not at upper mount section  18   a  but at, for example, the upper end side of projection optical system  16 . The structure of mask encoder system  48  will be described in detail, later on. 
     Projection optical system  16  is supported by upper mount section  18   a , and is placed below mask stage device  14 . Projection optical system  16  is a so-called multi-lens projection optical system having a structure similar to the projection optical system disclosed in U.S. Pat. No. 6,552,775 and the like, and is equipped with a plurality of ( 11  in the embodiment; refer to  FIG. 2A ) optical systems which forms an upright normal image with a double telecentric equal magnifying system. 
     In liquid crystal exposure apparatus  10 , when an illumination area on mask M supported by upper mount section  18   a  is illuminated with illumination light IL from illumination system  12 , by the illumination light having passed mask M, a projection image (partial upright image) of the circuit pattern of mask M within the illumination area is formed on an irradiation area (exposure area) of the illumination light on substrate P conjugate with the illumination area, via projection optical system  16 . And, by substrate P being relatively moved in the scanning direction with respect to the exposure area (illumination light IL) along with mask M being relatively moved in the scanning direction with respect to the illumination area (illumination light IL), scanning exposure of a shot area on substrate P is performed, and the pattern formed on mask M is transferred onto the shot area. 
     Apparatus main section  18  (also referred to such as a main section or a frame structure) supports mask stage device  14 , projection optical system  16 , and substrate stage device  20  described above, and is installed on a floor  11  of a clean room via a plurality of vibration isolation devices  19 . Apparatus main section  18  is structured similarly to the apparatus main section disclosed in U.S. Patent Application Publication No. 2008/0030702. In the embodiment, the apparatus main section has upper mount section  18   a  (also called an optical surface plate) that supports projection optical system  16  described above, a lower mount section  18   b  where substrate stage device  20  is arranged, and a pair of middle mount sections  18   c.    
     Substrate stage device  20  is a device used to position substrate P with high precision with respect to a plurality of partial images (exposure light IL) of the mask pattern of substrate P projected via projection optical system  16  in scanning exposure, and moves substrate P in directions of six degrees of freedom (the X-axis, the Y-axis, and the Z-axis directions, and the θx, the θy, and the θz directions). While the structure of substrate stage device  20  is not limited in particular, a stage device of a so-called coarse/fine movement structure can be used, including a gantry type two-dimensional coarse movement stage and a fine movement stage finely moved with respect to the two-dimensional coarse movement stage, as is disclosed in U.S. Patent Application Publication No. 2008/129762, U.S. Patent Application Publication No. 2012/0057140 and the like. In this case, substrate P can be moved in directions of three degrees of freedom within the horizontal plane by the coarse movement stage, and substrate P can also be finely moved in directions of six degrees of freedom by the fine movement stage. 
     Substrate stage device  20  is equipped with a substrate holder  34 . Substrate holder  34  consists of a plate-like member having a rectangular shape in a planar view, and substrate P is mounted on its upper surface. Note that the substrate holder that holds the substrate does not necessarily have to be provided separately from the table or stage where the holding section of the substrate is provided, in this case, fine movement stage  32 , and the substrate may be held by vacuum suction or the like on the table or the stage. Substrate holder  34  is moved in the X-axis direction and/or the Y-axis direction with respect to projection optical system  16  in predetermined long strokes and is also finely moved in directions of six degrees of freedom, by a plurality of linear motors (voice coil motors) structuring a part of a substrate drive system  93  (not shown in  FIG. 1 , refer to  FIG. 6 ). The structure of substrate stage device  20  described so far (however excluding the measurement system) is disclosed in U.S. Patent Application Publication No. 2012/0057140. 
     Also, liquid crystal exposure apparatus  10  has a substrate position measurement system for measuring position information of substrate holder  34  (namely, substrate P) in directions of six degrees of freedom. The substrate position measurement system includes a Z tilt position measurement system  98  for acquiring position information of substrate P in the Z-axis, the θx, and θy directions (hereinafter referred to as Z tilt direction), and a substrate encoder system  50  for acquiring position information of substrate P in the XY plane in directions of three degrees of freedom, as is shown in  FIG. 6 . While the structure of Z tilt position measurement system  98  is not limited in particular, a measurement system can be used that obtains position information of substrate P in the Z tilt direction with apparatus main section  18  (lower mount section  18   b ) serving as a reference, using a plurality of sensors attached to a system including substrate holder  34 , as is disclosed in U.S. Patent Application Publication No. 2010/0018950 and the like. The structure of substrate encoder system  50  will be described later in the description. 
     Next, the structure of mask encoder system  48  will be described, using  FIGS. 2A and 2B . As is typically shown in  FIG. 2A , in areas on the +Y side and the −Y side of mask M (more specifically, an opening section not shown for housing mask M) in mask holder  40 , a plurality of encoder scales  46  (also referred to as grating members, grating section, grid members and the like; however, will be simply referred to as scales  46  below) is placed. Although  FIG. 2A  illustrates the plurality of scales  46  in a solid line placed on the upper surface of mask holder  40  to facilitate understanding, the plurality of scales  46  is actually placed at the lower surface side of mask holder  40  so that the Z position of the lower surface of each of the plurality of scales  46  coincides with the Z position of the lower surface (pattern surface) of mask M, as is shown in  FIG. 1 . 
     Each of the plurality of scales  46  has a grating area (grating section) in which a reflective two-dimensional grating or two reflective one-dimensional gratings with different (e.g. orthogonal) arrangement directions (periodic directions) are formed, and the plurality of scales  46  is provided at the lower surface side of mask holder  40  on both sides of the mounting area (including the opening section described earlier) of mask M in the Y-axis direction so that the grating areas are arranged apart in the X-axis direction. Note that while the grating may be formed in the X-axis and the Y-axis directions to cover the entire area of scales  46 , since it is difficult to form the grating with good precision at the edge of scales  46 , in the embodiment, the grating is formed so that the periphery of the grating area in scales  46  becomes a margin part. Therefore, spacing between grating areas is larger than the spacing between a pair of scales  46  adjacent in the X-axis direction, and the period while an area other than the grating areas is irradiated with the measurement beam is to be a non-measurement period (also called a non-measurement section; however, hereinafter referred to collectively as non-measurement period) in which position measurement cannot be performed. 
     In mask holder  40  of the embodiment, in the areas on the +Y side and the −Y side of the mounting area of mask M, three scales  46  are arranged in the X-axis direction at a predetermined spacing. That is, mask holder  40  has a total of six scales  46 . Each of the plurality of scales  46  is substantially identical, except for the point that the scales are arranged symmetrically in the vertical direction of the page surface on the +Y side and the −Y side of mask M. Scale  46  consists of a plate-shaped (strip-shaped) member rectangular in a planar view extending in the X-axis direction, made of quartz glass. Mask holder  40  is formed of ceramics, and the plurality of scales  46  is fixed to mask holder  40 . In the embodiment, instead of the plurality of scales  46  arranged apart in the X-axis direction, one (single) scale may be used as a mask holder scale. In this case, the grating area may also be one, or a plurality of grating areas may be formed set apart in the X-axis direction on one scale. 
     As is shown in  FIG. 2B , on the lower surface (a surface facing the −Z side in the embodiment) of scale  46  at an area on one side in the width direction (the −Y side in  FIG. 2B ), an X scale  47   x  is formed. Also, on the lower surface of scale  46  at an area on the other side in the width direction (the +Y side in  FIG. 2B ), a Y scale  47   y  is formed. X scale  47   x  is structured by a reflective diffraction grating (an X grating) having a plurality of grid lines extending in the Y-axis direction formed at a predetermined pitch in the X-axis direction (the X-axis direction serving as a periodic direction). Similarly, Y scale  47   y  is structured by a reflective diffraction grating (a Y grating) having a plurality of grid lines extending in the X-axis direction formed at a predetermined pitch in the Y-axis direction (the Y-axis direction serving as a periodic direction). In X scale  47   x  and Y scale  47   y  of the embodiment, the plurality of grid lines is formed at a spacing of 10 nm or less. Note that in  FIGS. 2A and 2B , for convenience of illustration, the spacing (pitch) between the grids is shown much wider than the actual spacing. The same applies to other drawings as well. 
     Also, as is shown in  FIG. 1 , a pair of encoder bases  43  is fixed on the upper surface of upper mount section  18   a . The pair of encoder bases  43  is placed so that one of the pair is at the −X side of mask guide  42  on the +X side, and the other is at the +X side of mask guide  42  on the −X side (that is, placed in the area between the pair of mask guides  42 ). Also, a part of projection optical system  16  described above is arranged in between the pair of encoder bases  43 . Encoder base  43 , as is shown in  FIG. 2A , consists of a member extending in the X-axis direction. Encoder head unit  44  (hereinafter simply referred to as head unit  44 ) is fixed in the center in the longitudinal direction to each of the pair of encoder bases  43 . That is, head unit  44  is fixed to apparatus main section  18  (refer to  FIG. 1 ), via encoder base  43 . Since the pair of head units  44  is substantially identical, except for the point that the head units are arranged symmetrically in the vertical direction of the page surface on the +Y side and the −Y side of mask M, the description below is on only one of the head units (on the −Y side). 
     As is shown in  FIG. 2B , head unit  44  has a plurality of heads whose position of a measurement beam, irradiated on at least one of the plurality of scales  46  arranged in the X-axis direction, is different in at least one of the X-axis direction and the Y-axis direction, and a unit base  45  consisting of a plate-shaped member having a rectangular shape in a planar view. Fixed to unit base  45  are a pair of X heads  49   x  arranged separately to each other that irradiates a measurement beam at a spacing larger than the spacing of a pair of X scales  47   x  (grating areas) adjacent in the X-axis direction, and a pair of Y heads  49   y  arranged separately to each other that irradiates a measurement beam at a spacing larger than the spacing of the pair of Y scales  47   y  (grating areas) adjacent in the X-axis direction. That is, mask encoder system  48  has a total of four X heads  49   x ; one pair each on both sides of the mounting area of mask M of mask holder  40  in the Y-axis direction, along with a total of four Y heads  49   y ; one pair each on both sides of the mounting area of mask M in the Y-axis direction. Note that the pair of X heads  49   x  or the pair of Y heads  49   y  does not necessarily have to be arranged separate larger than the spacing of the pair of X scales  49   x  or the pair of Y scales  49   y , and may be arranged at a spacing around the same or smaller scale spacing or may be arranged in contact with each other, as long as a pair of measurement beams is arranged larger than the scale spacing in the X-axis direction. Also, in  FIG. 2B , while one of X head  49   x  and one of Y head  49   y  are housed together in a housing and the other of X head  49   x  and the other of Y head  49   y  are housed together in another housing, the pair of X heads  49   x  and the pair of Y heads  49   y  may each be arranged independently. Also, in  FIG. 2B , to facilitate understanding, while the pair of X heads  49   x  and the pair of Y heads  49   y  are illustrated to be arranged above (the +Z side of) scale  46 , the pair of X heads  49   x  is actually arranged below X scale  47   y  and the pair of Y heads  49   y  is actually arranged below Y scale  47   y  (refer to  FIG. 1 ). Also, the spacing (length in the Y-axis direction) between X head  49   x  and Y head  49   y  whose X positions are the same is set shorter than the width (length in the Y-axis direction) of scale  49 . 
     The pair of X heads  49   x  and the pair of Y heads  49   y  are fixed to unit base  45  so that a position (especially the position in a measurement direction (the X-axis direction)) of at least one of the pair of X heads  49   x  (measurement beam) or head (measurement beam) spacing, and a position (especially the position in a measurement direction (the Y-axis direction)) of at least one of the pair of Y heads  49   y  (measurement beam) or head (measurement beam) spacing do not change due to vibration or the like. Also, unit base  45  itself is also formed of a material whose coefficient of thermal expansion is lower than scale  46  (or is about the same as scale  46 ), so that the position or spacing of the pair of X heads  49   x  and the position or spacing of the pair of Y heads  49   y  do not change due to temperature change or the like. 
     X head  49   x  and Y head  49   y  are encoder heads of a so-called diffraction interference method as is disclosed in U.S. Patent Application Publication No. 2008/0094592 that irradiate corresponding scales (X scale  47   x , Y scale  47   y ) with measurement beams, and by receiving the beams from the scales, supply displacement amount information of mask holder  40  (namely mask M, refer to  FIG. 2A ) to main controller  90  (refer to  FIG. 6 ). That is, in mask encoder system  48 , four X heads  49   x  and X scale  47   x  (differs depending on the X position of mask holder  40 ) facing the X heads  49   x  structure four X linear encoders  92   x  (not shown in  FIG. 2B , refer to  FIG. 6 ) for obtaining position information of mask M in the X-axis direction, and four Y heads  49   y  and Y scale  47   y  (differs depending on the X position of mask holder  40 ) facing the Y heads  49   y  structure four Y linear encoders  92   y  (not shown in  FIG. 2B , refer to  FIG. 6 ) for obtaining position information of mask M in the Y-axis direction. In the embodiment, while a head is used whose measurement direction is in one of two different directions (coincides with the X-axis direction and the Y-axis direction) within the XY plane, a head may be used whose measurement direction differs from one of the X-axis direction and the Y-axis direction. For example, a head may be used whose measurement direction is in a direction rotated by an angle of 45 degrees with respect to the X-axis direction or the Y-axis direction within the XY plane. Also, instead of a one-dimensional head (an X head or a Y head) whose measurement direction is in one of the two different directions within the XY plane, for example, a two-dimensional head (an XZ head or a YZ head) whose measurement direction is in two directions such as; one of the X-axis direction and the Y-axis direction, and the Z-axis direction, may be used. In this case, it also becomes possible to measure position information of mask holder  40  in directions of three degrees of freedom (including the Z-axis direction, the θx direction, and the θy direction, and θx direction is rolling information, θy direction is pitching information) different from the directions of three degrees of freedom described above (the X-axis direction, the Y-axis direction, and the θz direction). 
     Main controller  90 , as is shown in  FIG. 6 , obtains position information of mask holder  40  (refer to  FIG. 2A ) in the X-axis direction and the Y-axis direction, based on an output of four X linear encoders  92   x  and four Y linear encoders  92   y , at a resolution of 10 nm or less. Also, main controller  90  obtains θz position information (rotation amount information) of mask holder  40 , based on an output of at least two of the four X linear encoders  92   x  (or four Y linear encoders  92   y ). Main controller  90  controls the position in the XY plane of mask holder  40  using mask drive system  91 , based on position information in directions of three degrees of freedom within the XY plane of mask holder  40  obtained from measurement values of mask encoder system  48  described above. 
     Here, as is shown in  FIG. 2A , in mask holder  40  as is described above, in each of the areas on the +Y side and the −Y side of mask M, three scales  46  are arranged in the X-axis direction at a predetermined spacing. Also, at least in scanning exposure of substrate P, of the three scales  46  arranged in the X-axis direction at a predetermined spacing described above, mask holder  40  is moved in the X-axis direction between a position where head unit  44  (all the pair of X heads  49   x  and the pair of Y heads  49   y  (each refer to  FIG. 3B )) faces scale  46  furthest to the +X side and a position where head unit  44  faces scale  46  furthest to the −X side. Note that in at least one of an exchange operation and a pre-alignment operation of mask M, in the case mask holder  40  is moved away from the illumination area illuminated with illumination light IL in the X-axis direction and at least one head of head unit  44  moves off of scale  46 , at least one head may be provided arranged away from head unit  44  in the X-axis direction so that position measurement of mask holder  40  by mask encoder system  48  can be continued even in the exchange operation or the pre-alignment operation. 
     And, in mask stage device  14  of the embodiment, as is shown in  FIG. 2B , the spacing between each of the pair of X heads  49   x  and the pair of Y heads  49   y  that one head unit  44  has is set larger than a pair of scales  46  adjacent to each other of the plurality of scales  46 . This allows at least one head of the pair of X heads  49   x  to constantly face X scale  47   x  and at least one head of the pair of Y heads  49   y  to constantly face Y scale  47   y  in mask encoder system  48 . Accordingly, mask encoder system  48  can supply position information of mask holder  40  (refer to  FIG. 2A ) to main controller  90  (refer to  FIG. 6 ) without the position information being cut off. 
     To describe this specifically, in the case mask holder  40  (refer to  FIG. 2A ) moves to the +X side, mask encoder system  48  goes through; a first state (the state shown in  FIG. 2B ) in which the pair of heads  49   x  both face X scale  47   x  on the +X side of the adjacent pair of X scales  47   x , a second state in which X head  49   x  on the −X side faces an area between the above adjacent pair of X scales  47   x  (facing neither of the X scales  47   x ) and X head  49   x  on the +X side faces X scale  47   x  on the +X side, a third state in which X head  49   x  on the −X side faces X scale  47   x  on the −X side and X head  49   x  on the +X side faces X scale  47   x  on the +X side, a fourth state in which X head  49   x  on the −X side faces X scale  47   x  on the −X side and X head  49   x  on the +X side faces an area between a pair of X scales  47   x  (facing neither of the X scales  47   x ), and a fifth state in which the pair of heads  49   x  both face X scale  47   x  on the −X side, in the order described above. Accordingly, at least one of the X heads  49   x  constantly faces X scale  47   x.    
     Main controller  90  (refer to  FIG. 6 ), in the first state, the third state, and the fifth state described above, obtains X position information of mask holder  40 , based on an average value of the output of the pair of X heads  49   x . Also, main controller  90 , in the second state described above, obtains X position information of mask holder  40 , based on only the output of X head  49   x  on the +X side, and in the fourth state described above, obtains X position information of mask holder  40 , based on only the output of X head  49  on the −X side. Accordingly, measurement values of mask encoder system  48  are not cut off. Note that the X position information may also be obtained using the output of only one of the pair of X heads  49   x  also in the first state, the third state, and the fifth state. However, in the second state and the fourth state, in both the pair of head units  44  one of the pair of X heads  49   x  and one of the Y heads  49   y  move off of scale  46  so that position information in the θz direction (rotation information) of mask holder  40  can no longer be acquired. Therefore, it is preferable to arrange the three scales  46  arranged on the +Y side and the three scales  46  arranged on the −Y side with respect to the mounting area of mask M shifted from one another so that the spacing between adjacent pair of scales  46  do not overlap in the X-axis direction, and that even when X head  49   x  and Y head  49   y  move off of scale  46  in one of the three scales  46  arranged on the +Y side and the three scales  46  arranged on the −Y side, X head  49   x  and Y head  49   y  do not move off in the other of the scales  46 . Or, the pair of head units  44  may be arranged shifted in the X-axis direction only by a distance larger than the spacing of an adjacent pair of scales  46  (width in a non-grating area). This avoids the non-measurement period when measurement beams move off (cannot measure) the grating area of scale  46  in the X-axis direction from overlapping in a total of four heads; the pair of X heads  49   x  arranged on the +Y side and the pair of X heads  49   x  arranged on the −Y side, and makes it possible to constantly measure position information in the θz direction of mask holder  40  at least during scanning exposure. Note that in at least one of the pair of head units  44 , at least one head may be arranged which is arranged apart in the X-axis direction with respect to at least one of the pair of X heads  49   x  and the pair of Y heads  49   y , so that two heads face scale  46  in at least one of X head  49   x  and Y head  49   y , also in the second state and in the fourth state. 
     Also, with mask encoder system  48  of the embodiment, in order to avoid the measurement values of mask encoder system  48  from being cut off, a linkage process is performed on the output of the heads when the state moves between the first, the third and the fifth states described above, namely the state in which both heads of the pair face the scale and the output is supplied from each of the heads of the pair, and the second and the fourth states, namely the state in which only one of the heads of the pair faces the scale and the output is supplied from only one of the heads of the pair. The linkage process of the heads will be described below, using  FIGS. 3A to 3E . Note that to simplify the description, in  FIGS. 3A to 3E , a two-dimensional grating (grating) is to be formed on scale  46 . Also, the outputs of each of the heads  49   x  and  49   y  are to be ideal values. Also, in the description below, while the linkage process of the pair of X heads  49   x  that are adjacent (to be referred to as  49   x   1  and  49   x   2  for convenience) will be described, a similar linkage process is performed also on the pair of Y heads  49   y  that are adjacent (to be referred to as  49   y   1  and  49   y   2  for convenience). 
     As is shown in  FIG. 3A , in the case each of the pair of X heads  49   x   1  and  49   x   2  obtain X position information of mask holder  40  (refer to  FIG. 2A ) using, of the pair of scales  46  that are adjacent (referred to as  46   1  and  46   2  for convenience), scale  46   2  on the +X side, the pair of X heads  49   x   1  and  49   x   2  both output X coordinate information. Here, the outputs of the pair of X heads  49   x   1  and  49   x   2  become the same value. Next, because X head  49   x   1  moves outside the measurement range of scale  46   2  when mask holder  40  is moved in the +X direction as is shown in  FIG. 3B , the output of X head  49   x   1  is invalidated before X head  49   x   1  moves outside the measurement range. Accordingly, the X position information of mask holder  40  is obtained based only on the output of X head  49   x   2 . 
     Also, when mask holder  40  (refer to  FIG. 2A ) is moved further in the +X direction as is shown in  FIG. 3C , X head  49   x   1  faces scale  46   1  on the −X side. While X head  49   x   1  outputs the X position information of mask holder  40  immediately after measurement becomes possible using scale  46   1 , because counting is resumed from an undefined value (or zero) for the output of X head  49   x   1 , the output cannot be used for calculating the X position information of mask holder  40 . Accordingly, in this state, linkage process of each of the outputs of the pair of X heads  49   x   1  and  49   x   2  becomes required. As the linkage process, specifically, a process is performed to correct the output of X head  49   x   1  regarded as an undefined value (or zero) (so that the output becomes the same value as that of X head  49   x   2 ), using the output of X head  49   x   2 . The linkage process is completed before mask holder  40  further moves in the +X direction and X head  49   x   2  moves outside the measurement range of scale  46   2 , as is shown in  FIG. 3D . 
     Similarly, as is shown in  FIG. 3D , in the case X head  49   x   2  moves outside the measurement range of scale  46   2 , the output of X head  49   x   2  is invalidated before X head  49   2  moves outside the measurement range. Accordingly, the X position information of mask holder  40  (refer to  FIG. 2A ) is obtained based only on the output of X head  49   x   1 . Then, the linkage process using the output of X head  49   x   1  is performed with respect to X head  49   x   2 , immediately after mask holder  40  is moved further in the +X direction and measurement becomes possible with each of the pair of X heads  49   x   1  and  49   x   2  using scale  46   1  as is shown in  FIG. 3E . Hereinafter, the X position information of mask holder  40  is obtained, based on the outputs of each of the pair of X heads  49   x   1  and  49   x   2 . 
     The linkage process above described so far is performed on the premise that the positional relation of the four heads (two X heads  49   x  and two Y heads  49   y ) that one head unit  44  has is known. The positional relation between each of the heads can be obtained in a state where the four heads described above face a common scale and using the scale is the state, or by using a measurement device (such as a laser interferometer or a distance sensor) placed in between each of the heads. 
     Note that while the linkage process described above was performed based on the output of X head  49   x   2  which forms a pair with X head  49   x   1  in the case X head  49   x   1  moves into an invalidated (deactivated) state, the linkage is not limited to this, and the linkage process may be performed, based on the outputs of more heads (such as three or four). Also, the linkage process may be performed using an average value of the outputs of more heads. A modified example of the linkage process will be described specifically below, using  FIGS. 10A to 10C . Note that for convenience, in  FIGS. 10A to 10C , the description will be made with four X heads  49   x  represented by codes  49   x   1  to  49   x   4 , and four Y heads  49   y  represented by reference codes  49   y   1  to  49   y   4 . Also, the description will be made with the pair of scales  46  which are adjacent subject to the linkage process represented by codes  46   1  and  46   2 . 
     With mask encoder system  48 , since the plurality of scales  46  is arranged separately placed in the X-axis direction, when mask M is moved in the −X direction from a state shown in  FIG. 10A  where the eight heads (X heads  49   x   1  to  49   x   4 , Y heads  49   y   1  to  49   y   4 ) are in a state facing one of the scales  46   t , a state occurs in which four heads (X heads  49   x   2 ,  49   x   4  and Y heads  49   y   2 ,  49   y   4 ) of the eight heads that the pair of head units  44  has whose X positions are the same simultaneously move off of scale  49  (are deactivated), as is shown in  FIG. 10  B. As is described above, a control is performed on the outputs of each of the heads that move off of scale  49  so that the outputs become undefined values (or zero). 
     Main controller  90  (refer to  FIG. 6 ) performs a restoring process (linkage process using the output values of the other heads) of the output values of the deactivated heads before the four heads (X heads  49   x   2 ,  49   x   4 , Y heads  49   y   2 ,  49   y   4 ) that have moved into a deactivated state (a state in which the output values are undefined) described above as is shown in  FIG. 10C  face the other scale  46   2 . In the case of restoring the output value of head  49   y   2  in the deactivated state, of the four heads (X heads  49   x   1 ,  49   x   3 , Y heads  49   y ,  49   y   3 ) in an active state, by using three arbitrary outputs (of e.g., X head  49   x   1 , Y heads  49   y   1 ,  49   y   3 ), position relation between the three active heads and the deactivated head  49   y   2  subject to the linkage process is obtained. As is described above, the positional relation between these heads is to be known. Here, since the head which is intended to move into a deactivated state next can be predicted in advance from the movement direction of mask M, calculation for the linkage process described above is performed before the four heads subject to the linkage process actually move into the deactivated state (the state shown in  FIG. 10A ). Also, since the head which is intended to move into the deactivated state next can be predicted similarly in advance, in the state shown in  FIG. 10C  just before a part of the heads move into the deactivated state, measurement of position information of mask M (position control of mask M) is performed, using the outputs of the heads whose active state continue (X heads  49   x   2 ,  49   x   4 , Y heads  49   y   2 ,  49   y   4  in  FIG. 10C ), without using the outputs of the heads which are intended to move into the deactivated state (X heads  49   x   1 ,  49   x   3 , Y heads  49   y   1 ,  49   y   3  in  FIG. 10C ). 
     Main controller  90  (refer to  FIG. 6 ) obtains position information (position information in each of the X, the Y, and the θz directions) of the deactivated Y head  49   y   2  from the output values of the three active heads described above, calculates (estimates) the output value of Y head  49   y   2  based on the position information and uses this as the output value of Y head  49   y   2  that has been activated again. The same applies to the linkage process performed on other heads (X heads  49   x   2 ,  49   x   4 , Y head  49   y   4 ) shown in  FIG. 10B  which are in the deactivated state. 
     Next, a structure of substrate encoder system  50  will be described. Substrate encoder system  50 , as is shown in  FIG. 1 , is equipped with a plurality of encoder scales  52  (overlapping in the depth of the page surface in  FIG. 1 , refer to  FIG. 4A ) arranged at substrate stage device  20 , a plurality of (two, in the embodiment) encoder bases  54  fixed to the lower surface of upper mount section  18   a , a plurality of encoder scales  56  fixed to the lower surfaces of encoder bases  54 , and a plurality of (two for one encoder base  54 , in the embodiment) encoder head units  60  (hereinafter simply referred to as head units  60 ). Note that since the two encoder bases  54  are overlapping in a depth direction of the page surface (the X-axis direction) in  FIG. 1 , encoder base  54  on the +X side is hidden in the depth side of the page surface. Similarly, the two head units  60  corresponding to encoder base  54  on the −X side are hidden in the depth side of the page surface of the two head units  60  corresponding to encoder base  54  on the +X side. 
     As is shown modeled in  FIG. 4A , in substrate stage device  20  of the embodiment, in each of the areas on the +Y side and on the −Y side of substrate P (substrate mounting area), four encoder scales  52  (hereinafter simply referred to as scales  52 ) are arranged at a predetermined spacing in the X-axis direction. That is, substrate stage device  20  has a total of eight scales  52 . Each of the plurality of scales  52  is substantially identical, except for the point that the scales are arranged symmetrically in the vertical direction of the page surface on the +Y side and the −Y side of substrate P. Scale  52 , similarly to scale  46  (each refer to  FIG. 2A ) of mask encoder system  48  described above, consists of a rectangular plate-shaped (strip-shaped) member in a planar view extending in the X-axis direction, made of quartz glass. Also, each of the plurality of scales  52  has a grating area (grating section) in which a reflective two-dimensional grating or two reflective one-dimensional gratings with different (e.g. orthogonal) arrangement directions (periodic directions) are formed, and four scales  52  are provided on both sides of the substrate mounting area in the Y-axis direction so that the grating areas are arranged apart in the X-axis direction. 
     Note that in the embodiment, while the case is described when the plurality of scales  52  is fixed to the upper surface of substrate holder  34 , the position arranged of the plurality of scales  52  is not limited to this and may be arranged separately (however, moving integrally with substrate holder  34  in directions of six degrees of freedom) on outer side of substrate holder  34  in a state with a predetermined gap between substrate holder  34 . Note that the plurality of scales  52  may be arranged on an upper surface of a substrate table that has substrate holder  34  and can be finely drive in at least the Z-axis direction, the θx direction, and the θy direction, or on an upper surface of a substrate stage that supports the substrate table in a finely movable manner. 
     As shown in  FIG. 4B , X scales  53   x  are formed on one side (the −Y side in  FIG. 4B ) of the width direction in areas on the upper surface of scales  52 . Also, Y scales  53   y  are formed on the other side (the +Y side in  FIG. 4B ) of the width direction in areas on the upper surface of scales  52 . Since the structure of X scales  53   x  and Y scales  53   y  is the same as X scales  47   x  and Y scales  47   y  (each refer to  FIG. 2B ) formed on scales  46  (each refer to  FIG. 2A ) of mask encoder system  48  described above, the description thereabout will be omitted. Note that in the embodiment, while X scales  53   x  and Y scales  53   y  are formed in the same length in the X-axis direction within scales  52  formed on substrate holder  34 , the X scales and Y scales may be made to have a length different from each other. Also, the X scales  53   x  and Y scales  53   y  may be arranged, relatively shifted in the X-axis direction. 
     Referring back to  FIG. 4A , the two encoder bases  54  (and the corresponding two head units  60 ) are placed apart in the X-axis direction. Since the structure of the two encoder bases  54  is substantially the same except for the point that the arrangement is different, in the description below, one of the encoder base  54  and the pair of head units  60  corresponding to encoder base  54  will be described. 
     Encoder base  54  consists of a plate-like member extending in the Y-axis direction, and as is shown in  FIG. 1 , is fixed to the lower surface of upper mount section  18   a . In the embodiment, as is shown in  FIG. 4A , while the X positions of the two encoder bases  54  partly overlap the X position of projection optical system  16 , encoder bases  54  and projection optical system  16  are arranged mechanically separated (in a non-contact state). Note that encoder bases  54  may be arranged separately on the +Y side and the −Y side of projection optical system  16 . 
     To the lower surfaces of encoder bases  54 , a plurality of encoder scales  56  (hereinafter simply referred to as scales  56 ) is fixed. In the embodiment, as is shown in  FIG. 4A , two scales  56  are arranged in an area further to the +Y side of projection optical system  16  and two scales  56  are arranged in an area further to the −Y side of projection optical system  16 , with the two scales each arranged separately in the Y-axis direction. That is, to encoder base  54 , a total of four scales  56  are fixed. Scales  56 , which consist of plate-like (strip-shaped) members with a rectangular-shape in a planar view extending in the Y-axis direction, are made of quartz glass, similarly to scales  52  arranged on substrate stage device  20 . Each of the plurality of scales  56  has a grating area (grating section) in which a reflective two-dimensional grating or two reflective one-dimensional gratings with different (e.g. orthogonal) arrangement directions (periodic directions) are formed, and in the embodiment, similar to scale  46  and scale  52 , scale  56  has an X scale on which a one-dimensional grating whose arrangement direction (periodic direction) is in the X-axis direction is formed and a Y scale on which a one-dimensional grating whose arrangement direction (periodic direction) is in the Y-axis direction is formed, and two scales each are arranged on both sides of projection optical system  16  in the Y-axis direction, with the grating areas of the two scales set apart from each other in the Y-axis direction. Note that to facilitate understanding, while the plurality of scales  56  illustrated in solid lines are illustrated as if the scales were arranged on the upper surface of encoder base  54  in  FIG. 4A , the plurality of scales  56  are actually arranged at the lower surface side of encoder base  54 , as shown in  FIG. 1 . Note that while two each of scales  56  are provided at the +Y side and the −Y side of projection optical system  16  in the embodiment, the number of scales  56  provided does not have to be two, but may be one, three, or more. Also, while scale  56  is to be provided with the grating surface facing downward (so that the grating area becomes parallel to the XY plane) in the embodiment, scale  56  may be provided, for example, so that the grating area becomes parallel to the YZ plane. 
     As shown in  FIG. 4C , X scales  57   x  are formed in areas on one side (the +X side in  FIG. 4C ) in the width direction at the lower surface of scales  56 . Also, Y scales  57   y  are formed in areas on the other side (the −X side in  FIG. 4C ) in the width direction at the lower surface of scales  56 . Since the structure of X scales  57   x  and Y scales  57   y  is the same as X scales  47   x  and Y scales  47   y  (each refer to  FIG. 2B ) formed on scales  46  (each refer to  FIG. 2A ) of mask encoder system  48  described above, the description thereabout will be omitted. 
     Referring back to  FIG. 1 , the two head units  60  are arranged apart in the Y-axis direction below encoder base  54 . Since each of the two head units  60  is substantially the same except for the point that the units are placed symmetrically in the lateral direction f the page surface in  FIG. 1 , hereinafter only one of the units (at the −Y side) will be described. Head unit  60 , as it can be seen from  FIGS. 4B and 4C , is equipped with Y slide table  62 , a pair of X heads  64   x , a pair of Y heads  64   y , a pair of X heads  66   x , and a pair of Y heads  66   y . Note that the pair of head units  60  in the embodiment has the same structure as the pair of head units  44  of mask encoder system  48 , except for the point that the pair of head units is rotated by 90 degrees. 
     Y slide table  62 , which consists of a plate-like member having a rectangular-shape in a planar view, is placed below encoder base  54  via a predetermined clearance with respect to encoder base  54 . Also, the Z position of Y slide table  62  is set to be on the +Z side than that of substrate holder  34  which substrate stage device  20  has (each refer to  FIG. 1 ), regardless of the Z tilt position of substrate holder  34 . 
     Y slide table  62  is moved in long strokes in the Y-axis direction by head unit drive system  86  (refer to  FIG. 6 ) that includes an actuator such as a linear motor. A mechanical linear guide device is provided for guiding Y slide table  62  straightly in the Y-axis direction, in between Y slide table  62  and encoder base  54 . Also, relative movement in the X-axis direction of Y slide table  62  is limited with respect to encoder base  54  by the operation of the linear guide device described above. 
     Main controller  90  (refer to  FIG. 6 ) synchronously moves, as appropriate, one of the head units  60  (the +Y side) placed further to the +Y side than projection optical system  16  below two scales  56 , and the other of the head units  60  (the −Y side) placed further to the −Y side than projection optical system  16  below two scales  56 , in predetermined strokes in the Y-axis direction. Here, while the pair of head units  60  may be moved synchronously with the movement of substrate stage device  20  in the Y-axis direction, in the embodiment, the pair of head units  60  is moved so that with each of the pair of head units  60 , not all measurement beams of the pair of X heads  66  and the pair of Y heads  66   y  move off of the grating area of scale  52  (at least irradiation of one measurement beam on the grating area is maintained) in the Y-axis direction. Note that while a linear motor is used as the actuator for moving Y slide table  62  in the embodiment, the embodiment is not limited to this, and the actuator may be other driving devices such as a belt driver, a feed screw device or the like. Note that in the embodiment, while the structure is employed in which Y slide table  62  is provided at the lower surface (refer to  FIG. 4 ) of upper mount section  18   a  of apparatus main section  18 , Y slide table  62  may be provided at lower mount section  18   b  or at middle mount section  18   b.    
     X head  64   x , Y head  64   y , X head  66   x , and Y head  66   y  are each an encoder head of the so-called diffraction interference method similar to X head  49   x  and Y head  49   y  (each refer to  FIG. 2B ) that mask encoder system  48  describe above has, and are fixed to Y slide table  62 . Here, with head units  60 , the pair of Y heads  64   y , the pair of X heads  64   x , the pair of Y heads  66   y , and the pair of X heads  66   x  are fixed to Y slide table  62 , so that the distance between the heads of each pair does not change due to vibration or the like. Also, Y slide table  62  itself is formed of a material having a thermal expansion coefficient lower than scales  52  and  56  (or equal to scales  52  and  56 ), so that the mutual distance between; the pair of Y heads  64   y , the pair of X heads  64   x , the pair of Y heads  66   y , and the pair of X heads  66   x , does not change due to temperature change or the like. Also, the spacing (length in the X-axis direction) between X head  64   x  and Y head  64   y  whose Y positions are the same is set shorter than the width (length in the X-axis direction) of scale  56 . Similarly, the spacing (length in the Y-axis direction) between X head  66   x  and Y head  66   y  whose X positions are the same is set shorter than the width (length in the Y-axis direction) of scale  52 . 
     As shown in  FIG. 5 , each of the pair of X heads  64   x  irradiates two places (two points) separate from each other in the Y-axis direction on X scale  57   x  with a measurement beam, and each of the pair of Y heads  64   y  irradiates two places (two points) separate from each other in the Y-axis direction on Y scale  57   y  with a measurement beam. At substrate encoder system  50 , by receiving beams from scales corresponding to the X heads  64   x  and Y heads  64   y  described above, information on displacement quantity of Y slide table  62  (not shown in  FIG. 5 ; refer to  FIGS. 4B and 4C ) is supplied to main controller  90  (refer to  FIG. 6 ). 
     That is, in substrate encoder system  50 , by eight (2×4) X heads  64   x  and X scales  57   x  (different depending on the Y position of Y slide table  62 ) facing the X heads  64   x , eight X linear encoders  96   x  (not shown in  FIG. 5 ; refer to  FIG. 6 ) are structured, used for acquiring position information in the Y-axis direction of each of the four Y slide tables  62  (that is, the four head units  60  (refer to  FIG. 1 )), and by eight (2×4) Y heads  64   y  and Y scales  57   y  (different depending on the Y position of Y slide table  62 ) facing the Y heads  64   y , eight Y linear encoders  96   y  (not shown in  FIG. 5 ; refer to  FIG. 6 ) are structured, used for acquiring position information in the Y-axis direction of each of the four Y slide tables  62 . 
     Main controller  90 , as shown in  FIG. 6 , acquires position information of each of the four head units  60  (refer to  FIG. 1 ) in the X-axis direction and the Y-axis direction, based on the output of the eight X linear encoders  96   x  and the eight Y linear encoders  96   y , at a resolution of 10 nm or less. Also, main controller  90  obtains θz position information (rotation amount information) of one head unit  60 , based on outputs of the two X linear encoders  96   x  (or the two Y linear encoders  96   y ) corresponding to the one head unit  60 . Main controller  90  controls the position of head units  60  in the XY plane using head unit drive system  86  (refer to  FIG. 6 ), based on the position information of each of the four head units  60  within the XY plane. 
     Now, as shown in  FIG. 4A , at encoder base  54 , two scales  56  are arranged at a predetermined spacing in the Y-axis direction in areas at the +Y side and −Y side of projection optical system  16 , as is described above. 
     Similarly to the above mask encoder system  48 , also in substrate encoder system  50 , the spacing between each head of the pair of X heads  64   x  and each head of the pair of Y head  64   y  that one head unit  60  has is set wider than the spacing between the adjacent scales  56 , as shown in  FIG. 4C . This allows at least one head of the pair of X heads  64   x  to constantly face X scale  57   x  and at least one head of the pair of Y heads  64   y  to constantly face Y scale  57   y , in substrate encoder system  50 . Substrate encoder system  50 , therefore, is able to acquire position information of Y slide table  62  (head units  60 ) without interrupting the measurement values. Accordingly, linkage process (refer to  FIGS. 3A to 3E , or to  FIGS. 10A to 10C ) of the outputs of the heads similar to the linkage process of the outputs of the heads in mask encoder system  48  described above is performed here as well. 
     Main controller  90 , as is shown in  FIG. 6 , obtains position information in the X-axis direction and the Y-axis direction of substrate holder  34  (refer to  FIG. 1 ) with respect to apparatus main section  18  (refer to  FIG. 1 ) at a resolution of 10 nm or less, based on outputs of the eight X linear encoders  94   x , the eight Y linear encoders  94   y , and outputs of the eight X linear encoders  96   x , and the eight Y linear encoders  96   y  (that is, position information of each of the four head units  60  in the XY plane). Also, main controller  90  obtains Oz position information (rotation quantity information) of substrate holder  34 , based on at least two outputs of eight X linear encoders  94   x  (or, eight Y linear encoders  94   y ). Main controller  90  controls the position of substrate holder  34  within the XY plane using substrate driving system  93 , based on position information of substrate holder  34  within the XY plane obtained from the measurement values of the above substrate encoder system  50 . 
     Also, since substrate P is moved rotationally at a fine angle in the θz direction also during exposure operation, to make obtaining position information of substrate P in the Oz direction possible, in substrate encoder system  50 , of the total of 16 heads facing downward (eight X heads  66   x  and eight Y heads  66   y ), spacing between each of the heads and spacing between each of the scales are set so that at least three heads constantly face either of the scales. This allows a state to be maintained in which position information in directions of three degrees of freedom (X, Y,  8   z ) within the horizontal plane of substrate holder  34  can be obtained constantly during the exposure operation. 
     Also, as is shown in  FIG. 3A , substrate holder  34 , as is described above, has four scales  52  which are placed at a predetermined spacing in the X-axis direction in each of the areas on the +Y side and the −Y side of substrate P. 
     Similarly to the above mask encoder system  48 , the spacing between the heads of the pair of X heads  66   x  and heads of the pair of Y heads  66   y  that one head unit  60  has is set wider than the spacing between adjacent scales  52 , as shown in  FIG. 4B . This allows at least one head of the pair of X heads  66   x  to constantly face X scale  53   x  and at least one head of the pair of Y heads  66   y  to constantly face Y scale  53   y , in substrate encoder system  50 . Substrate encoder system  50 , therefore, is able to obtain position information of substrate holder  34  (refer to  FIG. 4A ) without interrupting the measurement values. Accordingly, linkage process (refer to  FIGS. 3A to 3E , or to  FIGS. 10A to 10C ) of the outputs of the heads similar to the linkage process of the outputs of the heads in mask encoder system  48  described above is performed here as well. 
     Note that all descriptions (including explanatory notes) on heads and scales structuring mask encoder system  48  previously described may be applied similarly, as for the pair of Y heads  64   y , the pair of X heads  64   x , the pair of Y heads  66   y , and the pair of X heads  66   x  that each of the pair of head units  60  of substrate encoder system  50  has and scales  56  and  52  irradiated with the measurement beams from these heads. 
     Note that in the first modified example (refer to  FIGS. 10A to 10C ) of the linkage process described above, while the linkage process was performed using the four heads (that is, a total of eight heads) that each of the pair of head units  44  (or head units  60 ) has arranged on the +Y side and the −Y side of mask M (or substrate P), as for the linkage process of the heads facing downward (X heads  66   x , Y heads  66   y ) for obtaining position information of substrate holder  34 , a linkage process shown in  FIGS. 11A to 11F  can also be performed. A second modified example of the linkage process will be described specifically below, using  FIGS. 11A to 11F . Note that for convenience, in  FIGS. 11A to 11F , the description will be made with the four heads facing downward represented by codes X heads  66   x   1 ,  66   x   2 , and Y heads  66   y   1 ,  66   y   2 , along with the four heads facing upward represented by reference codes X heads  64   x   1 ,  64   x   2 , and Y heads  64   y   1 ,  64   y   2 . Also, the description will be made with the pair of scales  52  which are adjacent subject to the linkage process represented by codes  52   1  and  52   2 . Also,  FIGS. 11B, 11D, and 11F  are views corresponding to  FIGS. 11A, 11C, and 11E , respectively. 
     Also in the second modified example of the linkage process, head unit  60  has four encoder heads facing downward (X heads  66   x   1 ,  66   x   2 , and Y heads  66   y ,  66   y   2 ) as is shown in  FIG. 11A , and the linkage process is performed on the assumption that the positional relation between these four heads is known. Furthermore, head unit  60 , as is shown in  FIG. 11B , also has four encoder heads facing upward (X heads  64   x   1 ,  64   x   2 , and Y heads  64   y   1 ,  64   y   2 ), and the linkage process is performed on the assumption that the positional relation between these four heads is also known. Positional relation between these heads can be obtained in a state by using corresponding scales (scales  52  or scales  56 ) when each of the four heads facing upward or each of the four heads facing downward faces the corresponding scales, or by using a measurement device (such as a laser interferometer) arranged between each of the heads. Here, in the linkage process of the modified example, the linkage process is performed on the assumption that during the linkage process, the four heads facing upward (X heads  64   x   1 ,  64   x   2 , and Y heads  64   y   1 ,  64   y   2 ) do not move off of scale  56  fixed to apparatus main section  18  (refer to  FIG. 1 ). Furthermore, the linkage process is performed also on the assumption that grid error between scale  56  (fixed) and scale  52  (movable) on the substrate holder (refer to  FIG. 4A ) is known. 
     In the first modified example (refer to  FIGS. 10A to 10C ) described above, while output values of heads that have been deactivated are restored of the total of eight heads, using the total of eight heads that the pair of head units  44  has, in the second modified example, in the case two heads move into a deactivated state of the four heads facing downward (X heads  66   x   1 ,  66   x   2 , and Y heads  66   y   1 ,  66   y   2 ) that one head unit  60  has, output values of the deactivated heads described above are restored, using output values of the four heads (X heads  64   x   1 ,  64   x   2 , and Y heads  64   y   1 ,  64   y   2 ) facing upward. 
     To describe this specifically, with substrate encoder system  50 , as is shown in  FIG. 11A , since scales  52   1  and  51   2  are arranged separately placed in the X-axis direction, when substrate P is moved in the −X direction from a state where the four heads (X heads  66   x   1 ,  66   x   2 , and Y heads  66   y ,  66   y   2 ) face one of the scales  52   1 , a state occurs in which of the four heads that head unit  60  has, two heads (X head  49   x   2  and Y head  49   y   2 ) whose X positions are the same simultaneously move off of scales  52   1  and  51   2  (are deactivated), as is shown in  FIG. 11C . As is described above, a control is performed on the outputs of each of the heads that move off of scales  52   1  and  52   2  so that the outputs become undefined values (or zero). Also, as is described above, when substrate P is moved in the X-axis direction, head unit  60  is controlled (refer to  FIGS. 11B, 11D, and 11F ), so that the position within respect to scale  56  which is fixed does not change. 
     Main controller  90  (refer to  FIG. 6 ) performs a restoring process (linkage process using the output values of the other heads) of the output values of the deactivated heads before the two heads (X head  66   x   2  and Y head  66   y   2 ) that have moved into a deactivated state (a state in which the output values are undefined) described above as is shown in  FIG. 11E  face the other scale  52   2 . In the case of restoring the output value of head  66   y   2  in the deactivated state, of the six heads (X heads  66   x   1 ,  64   x   1 ,  64   x   2  and Y heads  66   y ,  64   y   1 ,  64   y   2 ) in an active state, by using three arbitrary outputs (of e.g., X head  66   x   1 , Y heads  66   y   1 ,  64   y   1 ), position relation between the three active heads and the deactivated head  66   y   2  subject to the linkage process is obtained. As is described above, the positional relation between these heads is to be known. Also, the active three heads used in the linkage process described above includes at least one head (one of X head  66   x   1 , X heads  64   x   1 , and  64   x   2  in the example above) whose measurement direction is in the X-axis direction and at least one head (one of Y head  66   y   1 , Y heads  64   y   1 , and  64   y   2  in the example above) whose measurement direction is in the Y-axis direction. 
     Main controller  90  (refer to  FIG. 6 ) obtains position information (position information in each of the X, the Y, and the θz directions) of the deactivated Y head  66   y   2  from the output values of the three active heads described above, calculates (estimates) the output value of Y head  66   y   2  based on the position information, and uses this as the output value of Y head  66   y   2  that has been activated again. The same applies to the linkage process performed on X head  66   x   2  shown in  FIG. 11C  which is in the deactivated state. 
       FIG. 6  is a block diagram showing an input/output relation of main controller  90 , which mainly structures a control system of liquid crystal exposure apparatus  10  (refer to  FIG. 1 ) and has overall control over each section. Main controller  90 , which includes a work station (or a microcomputer) or the like, has overall control over each section of liquid crystal exposure apparatus  10 . 
     In liquid crystal exposure apparatus  10  (refer to  FIG. 1 ) having the structure described above, under the control of main controller  90  (refer to  FIG. 6 ), a mask loader not shown performs loading of mask M onto mask stage device  14 , and a substrate loader not shown performs loading of substrate P onto substrate stage device  20  (substrate holder  34 ). Main controller  90  then executes alignment measurement (detection of a plurality of alignment marks on substrate P) using an alignment detection system not shown, and then, when the alignment measurement has been completed, sequentially performs an exposure operation of a step-and-scan method on a plurality of shot areas set on substrate P. Note that position information of substrate holder  34  is measured by substrate encoder system  50  also in the alignment measurement operation. 
     Next, an example of an operation of mask stage device  14  and substrate stage device  20  at the time of exposure operation will be described, using  FIGS. 7A to 9B . Note that, in the description below, while the case of setting four shot areas on one substrate P (in the case of a four-piece setting) will be described, the number and placement of the shot areas set on one substrate P can be appropriately changed. 
       FIG. 7A  shows mask stage device  14  which has completed alignment operation, and  FIG. 7B  shows substrate stage device  20  (members other than substrate holder  34  are not shown. The same applies to the description below) which has completed alignment operation. Exposure processing, as an example, is performed from a first shot area S1 which is set at the −Y side and also the +X side of substrate P, as shown in  FIG. 7B . In mask stage device  14 , positioning of mask M is performed based on the output of mask encoder system  48  (refer to  FIG. 6 ), so that the edge at the +X side of mask M is positioned slightly to the −X side than the illumination area (in the state shown in  FIG. 7A , however, illumination light IL is not irradiated yet on mask M) of illumination light IL irradiated from illumination system  12  (refer to  FIG. 1  for each section), as shown in  FIG. 7A . 
     To be more specific, the edge at the +X side of mask M is placed to the −X side with respect to the illumination area, only by an entrance length necessary to perform scanning exposure at a predetermined speed (that is, acceleration distance necessary to reach the predetermined speed), and at the position, scales  46  are arranged so that the position of mask M can be measured with mask encoder system  48 . Main controller  90  (refer to  FIG. 6 ) also performs position control of mask holder  40  within a range in which at least three heads (three heads of four heads  49   x  and four heads  49   y ) do not move off (do not move outside the measurement range) of scales  46 . 
     Also, in substrate stage device  20 , positioning of substrate P is performed based on the output of substrate encoder system  50  (refer to  FIG. 6 ), so that the edge at the +X side of the first shot area  81  is positioned slightly to the −X side than the exposure area (in the state shown in  FIG. 7B , however, illumination light IL is not irradiated yet on substrate P) on which illumination light IL (refer to  FIG. 1 ) from projection optical system  16  is irradiated, as shown in  FIG. 7B . To be more specific, the edge at the +X side of the first shot area S1 of substrate P is placed to the −X side with respect to the exposure area, only by an entrance length necessary to perform scanning exposure at a predetermined speed (that is, acceleration distance necessary to reach the predetermined speed), and at the position, scales  52  are arranged so that the position of substrate P can be measured with substrate encoder system  50 . Main controller  90  (refer to  FIG. 6 ) also performs position control of substrate holder  34  within a range in which at least three (three of eight heads  66   x  and eight heads  66   y ) heads do not move off (do not move outside the measurement range) of scales  52 . 
     Note that also when scanning exposure of the shot areas has been completed and mask M and substrate P are decelerated, scales  46  and  52  are arranged similarly so that mask encoder system  48  and substrate encoder system  50  can measure the position of mask M and substrate P, respectively, until mask M and substrate P has finished moving further by a deceleration distance necessary for deceleration to a predetermined speed from the speed at the time of scanning exposure. Alternatively, the position of mask M and substrate P may each be measured by measurement systems different from mask encoder system  48  and substrate encoder system  50 , during at least one of the operations of acceleration and deceleration. 
     Next, mask holder  40  is moved in the +X direction (acceleration, constant speed drive, and deceleration) as shown in  FIG. 8A , and synchronously with mask holder  40 , substrate holder  34  is moved in the +X direction (acceleration, constant speed drive, and deceleration) as shown in  FIG. 8B . When mask holder  40  is moved, main controller  90  (refer to  FIG. 6 ) performs position control of mask M based on the output of mask encoder system  48  (refer to  FIG. 6 ) as well as perform position control of substrate P based on the output of substrate encoder system  50  (refer to  FIG. 6 ). When substrate holder  34  is moved in the X-axis direction, the four head units  60  are to be in a stationary state. While mask holder  40  and substrate holder  34  are moved at a constant speed in the X-axis direction, illumination light IL (refer to  FIG. 1  for each part) that has passed through mask M and projection optical system  16  is irradiated on substrate P, and by this operation, the mask pattern that mask M has is transferred to shot area S1. Note that since substrate holder  34  is moved in fine strokes in the Y-axis direction at the time of scanning exposure, in the case measurement beams from each of the heads  66   s  and  66   y  may possibly move off of the corresponding scales  53   x  and  53   y , head unit  60  may be moved in fine strokes in the Y-axis direction synchronously with substrate holder  34  at the time of scanning operation. 
     When transfer of the mask pattern to the first shot area on substrate P is been completed, in substrate stage device  20 , substrate holder  34  is moved (Y step) based on the output of substrate encoder system  50  (refer to  FIG. 6 ) in the −Y direction by a predetermined distance (a distance almost half of the dimension in the width direction of substrate P), for exposure operation of a second shot area S2 set at the +Y side of the first shot area S1, as shown in  FIG. 9B . In the above Y stepping operation of substrate holder  34 , mask holder  40  is stationary in a state where the edge of mask M at the −X side is positioned slightly to the +X side than the illumination area (in the state shown in  FIG. 9A , however, mask M is not illuminated), as shown in  FIG. 9A . 
     In the above Y stepping operation of substrate holder  34 , as shown in  FIG. 9B , at substrate stage device  20 , the four head units  60  are moved in the Y-axis direction synchronously with substrate holder  34 . That is, as is shown in  FIG. 6 , main controller  90 , of substrate encoder system  50 , moves the four head units  60  in the Y-axis direction via the head unit drive system  86 , based on the output of Y linear encoders  96   y , while moving substrate holder  34  in the Y-axis direction to a target position via substrate driving system  93 , based on the output of Y linear encoders  94   y . On this operation, main controller  90  moves the four of head units  60  synchronously with substrate holder  34  (so that the four head units  60  follow substrate holder  34 ). Also, main controller  90  performs position control of Y slide table  62  within a range in which at least one head of the plurality of heads  64   x  and  64   y  does not move off (does not move outside the measurement range) of scales  56 . 
     Accordingly, each of the measurement beams irradiated from X heads  66   x  and Y heads  66   y  (refer to  FIG. 5  for each head) does not move away from X scales  53   x  and Y scales  53   y  (refer to  FIG. 5  for each scale), regardless of the Y position of substrate holder  34  (including when substrate holder  34  is moving). In other words, the four head units  60  should move synchronously with substrate holder  34  in the Y-axis direction, at a degree in which each of the measurement beams irradiated from X heads  66   x  and Y heads  66   y  while substrate holder  34  is moved in the Y-axis direction (during the Y stepping operation) do not move away from X scales  53   x  and Y scales  53   y , that is, at a degree in which measurement by the measurement beams from X heads  66   x  and Y heads  66   y  is not interrupted (measurement can be continued). 
     On this operation, movement of Y slide table  62  (X heads  64   x ,  66   x , Y heads  64   y ,  66   y ) in the step direction may be started prior to substrate holder  34 , before movement of substrate holder  34  in the step direction (the Y-axis direction) is started. This allows acceleration of each of the heads to be suppressed, and furthermore, allows tilt (inclining forward in the advancing direction) of each of the heads to be suppressed. Also, instead of this, movement of Y slide table  62  in the step direction may be started later than substrate holder  34 . 
     In the description below, although it is not illustrated, when the Y stepping operation of substrate holder  34  is completed, mask holder  40  is moved in the −X direction based on the output of mask encoder system  48  (refer to  FIG. 6 ), and synchronously with mask holder  40 , substrate holder  34  is moved in the −X direction based on the output of substrate encoder system  50  (refer to  FIG. 6 ). This allows the mask pattern to be transferred to the second shot area S2. The four head units  60  is to be in a stationary state also on this operation. Hereinafter, by appropriately repeating the scanning operation of mask holder  40 , the Y stepping operation of substrate holder  34 , and the scanning operation of substrate holder  34  described above, the mask pattern is sequentially transferred with respect to the plurality of shot areas on substrate P. In the exposure operation described above, the pair of head units  60  is moved in the same direction by the same distance as substrate holder  34  each time substrate holder  34  is stepped in the +Y direction and the −Y direction, so that the state facing scales  56  is maintained. 
     Here, as is described above, at the time of Y stepping operation of substrate holder  34  described above, in substrate stage device  20 , four Y sliders  76  are moved in the Y-axis direction synchronously with substrate holder  34 . That is, main controller  90  (refer to  FIG. 6 ), moves Y sliders  76  in the Y-axis direction based on an output of a Y slider position measurement system  80  (refer to  FIG. 4 ; an encoder system in this case), while moving substrate holder  34  in the Y-axis direction to a target position based on the output of the encoder system. On this operation, main controller  90  moves Y sliders  76  synchronously with substrate holder  34  (so that Y sliders  76  follow substrate holder  34 ). Also, main controller  90  performs position control of Y sliders  76  within a range in which at least one head of a plurality of heads  384   x  and  384   y  does not move off (does not move outside the measurement range) of a scale plate  340 . 
     Accordingly, each of the measurement beams irradiated from X heads  384   x  and Y heads  384   y  (refer to  FIG. 20  for each head) does not move away from X scales  342   x  and Y scales  342   y  (refer to  FIG. 20  for each scale), regardless of the Y position of substrate holder  34  (including when substrate holder  34  is moving). In other words, for example, two Y sliders  76  should move synchronously with substrate holder  34  in the Y-axis direction, at a degree in which each of the measurement beams irradiated from X heads  384   x  and Y heads  384   y  while substrate holder  34  is moved in the Y-axis direction (during the Y stepping operation) do not move away from X scales  342   x  and Y scales  342   y , that is, at a degree in which measurement by the measurement beams from X heads  384   x  and Y heads  384   y  is not interrupted (measurement can be continued). That is, the movement of the pair of head units  60  and substrate holder  34  in the Y-axis direction does not have to be synchronous, or a follow-up movement. 
     On this operation, movement of Y slider  76  (X heads  384   x ,  386   x , Y heads  384   y ,  386   y ) in the step direction may be started prior to substrate holder  34 , before movement of substrate holder  34  in the step direction (the Y-axis direction) is started. This allows acceleration of each of the heads to be suppressed, and furthermore, allows tilt (inclining forward in the advancing direction) of each of the heads to be suppressed. Also, instead of this, movement of Y slider  76  in the step direction may be started later than substrate holder  34 . 
     Also, when the Y stepping operation of substrate holder  34  is completed, mask M (refer to  FIG. 1 ) is moved in the −X direction based on the output of mask stage position measurement system  54  (refer to  FIG. 4 ), and synchronously with mask M, by substrate holder  34  being moved in the −X direction based on the output of a position measurement system within the horizontal plane of the substrate stage (refer to  FIG. 4 ; encoder system in this case), the mask pattern is transferred onto the shot area of substrate P. On this operation, for example, the two sliders  76  are to be in a stationary state. With liquid crystal exposure apparatus  10 , by appropriately repeating the scanning operation of mask M, the Y stepping operation of substrate holder  34 , and the scanning operation of substrate holder  34  described above, the mask pattern is sequentially transferred with respect to the plurality of shot areas on substrate P. In the exposure operation described above, for example, the two Y sliders  76  are moved in the same direction by the same distance as substrate holder  34  each time substrate holder  34  is stepped in the +Y direction and the −Y direction, so that the state facing target  338  (scale plate  340 ) is maintained. 
     Here, as is described above, Y scale  53   y  has a plurality of grid lines extending in the X-axis direction. Also, as is shown in  FIG. 20 , an irradiation point  66   y  (the same code as the Y head is used for convenience) of the measurement beam from Y head  66   y  irradiated on Y scale  53   y  is elliptic, with the long axis direction being in the Y-axis direction. With Y linear encoder  94   y  (refer to  FIG. 6 ), when Y head  66   y  and Y scale  53   y  are relatively moved in the Y-axis direction and the measurement beam crosses over the grid lines, the output from Y head  66   y  changes, based on phase change of ±1 st  order diffracted light from the irradiation point. 
     Meanwhile, main controller  90  (refer to  FIG. 6 ) controls position (Y position) in the step direction of head unit  60  during the scanning exposure operation described above, so that Y head  66   y  that head unit  60  (refer to  FIG. 4B ) has does not cross over the plurality of grid lines forming Y scale  53   y , that is, the output from Y head  66   y  does not change (the change remains zero), when substrate holder  34  is moved in the scanning direction (the X-axis direction). 
     Specifically, the Y position of Y head  66   y  is measured by a sensor having resolution higher than the pitch between the grid lines that structure Y scale  53 , and just before the irradiation point of the measurement beam from Y head  66   y  crosses the grid lines (when the output of Y head  66   y  is about to change), the Y position of Y head  66   y  is controlled via head unit drive system  86  (refer to  FIG. 6 ). Note that this is not limited, and for example, in the case the output of Y head  66   y  changes by the measurement beam from Y head  66   y  crossing over the grid lines, by controlling the drive of Y head  66   y  according to the change, the change of the output from Y head  66   y  may be substantially canceled. In this case the sensor to measure the Y position of Y head  66   y  is not required. 
     As is described so far, with liquid crystal exposure apparatus  10  according to the present embodiment, because mask encoder system  48  for acquiring the position information of mask M within the XY plane and substrate encoder system  50  for acquiring the position information of substrate P within the XY plane (refer to  FIG. 1  for each system) each has a short optical path length of the measurement beams irradiated on the corresponding scales, the influence of air fluctuation can be reduced when compared to conventional interferometer systems. Therefore, the positioning accuracy of mask M and substrate P improves. Also, since the influence of air fluctuation is small, partial air-conditioning unit which is indispensable when using a conventional interferometer system can be omitted, which allows cost reduction. 
     Furthermore, in the case of using the interferometer system, large and heavy bar mirrors had to be equipped in mask stage device  14  and substrate stage device  20 , however, with mask encoder system  48  and substrate encoder system  50  according to the present embodiment, the above bar mirrors will not be necessary; therefore, the system including mask holder  40  (e.g. mask stage device) and the system including substrate holder  34  (e.g. substrate stage device) each becomes more compact and light, as well as the weight balance being improved, which improves position controllability of mask M and substrate P. Also, places that require adjustment are less than the case using the interferometer system, which allows cost reduction of mask stage device  14  and substrate stage device  14 , and furthermore improves maintainability. Adjustment at the time of assembly also becomes easy (or unnecessary). 
     Also, in substrate encoder system  50  according to the embodiment, since the structure is employed of measuring the Y position information of substrate P by moving the four head units  60  in the Y-axis direction on movement (e.g. stepping operation) of substrate P in the Y-axis direction, there is no need to place a scale extending in the Y-axis direction or to increase the width in the Y-axis direction of the scale extending in the X-axis direction at the substrate stage device  20  side (or no need to arrange a plurality of heads in the Y-axis direction at the apparatus main section  18  side). This simplifies the structure of the substrate position measurement system, which allows cost reduction. 
     Also, in mask encoder system  48  according to the present embodiment, since the structure is employed of acquiring the position information of mask holder  40  in the XY plane while appropriately switching the output of the pair of adjacent encoder heads (X head  49   x , Y head  49   y ) according to the X position of mask holder  40 , the position information of mask holder  40  can be acquired without interruption, even if a plurality of scales  46  are arranged at a predetermined spacing (spaced apart from one another) in the X-axis direction. Accordingly, there is no need to prepare a scale having a length equal to the moving strokes of mask holder  40  (a length around three times of scale  46  of the present embodiment) in the system, which allows cost reduction, and this makes it suitable especially for liquid crystal exposure apparatus  10  that uses a large mask M as in the present embodiment. Also similarly, in substrate encoder system  50  according to the present embodiment, since a plurality of scales  52  are placed in the X-axis direction and a plurality of scales  56  are placed in the Y-axis direction each at a predetermined spacing, scales having a length equal to the moving strokes of substrate P do not have to be prepared, which makes it suitable for application in liquid crystal exposure apparatus  10  which uses a large substrate P. 
     Note that in the first embodiment described above, while the case has been described in which each of the four head units  60  has four heads (a pair of X heads  66   x  and a pair of Y heads  66   y ) used to measure the position of substrate holder  34 , and a total of 16 heads are provided for position measurement of the substrate holder, the number of heads for position measurement of the substrate holder may be less than 16. Hereinafter, such an embodiment will be described. 
     Second Embodiment 
     Next, a second embodiment will be described, based on  FIGS. 14 to 17C . Since the structure of the liquid crystal exposure apparatus according to the second embodiment is the same as the above first embodiment, except for the structure of a part of substrate encoder system  50 , only the difference will be described below, and components having the same structure and function as the first embodiment will have the same reference signs as the first embodiment, and the descriptions thereabout will be omitted. 
       FIG. 14  shows a planar view of substrate holder  34  and a pair of head units  60  of substrate encoder system  50  according to the second embodiment, along with projection optical system  16 . In  FIG. 14 , to facilitate understanding of the description, illustration of encoder base  54  or the like is omitted. Also, in  FIG. 14 , head units  60  (Y slide table  62 ) are illustrated in dotted lines, while illustration of X head  64   x  and Y head  64   y  provided on the upper surface of Y slide table  62  is omitted. Here, while substrate encoder system  50  in the first embodiment described above has a pair of encoder bases  54 , along with a total of four head units  60  (refer to  FIG. 4  and the like) corresponding to the pair of encoder bases  54 , with substrate encoder system  50  according to the second embodiment, only one encoder base  54  (not shown in  FIG. 14 ) is provided and head units  60  are arranged one each on the +Y side and the −Y side of projection optical system  16 . 
     In the liquid crystal exposure apparatus according to the second embodiment, as is shown in  FIG. 14 , in each of the areas on the +Y side and the −Y side with substrate mounting area of substrate holder  34  arranged in between, five encoder scales  152  (hereinafter simply referred to as scales  152 ) are arranged in the X-axis direction at a predetermined spacing so that grating areas are spaced apart from one another in the X-axis direction. With the five scales  152  arranged on the +Y side of the substrate mounting area and the five scales  152  arranged on the −Y side, the spacing between adjacent scales  152  (grating area) is the same, however, the arrangement positions of the five scales  152  on the −Y side, as a whole, are shifted to the +X side by a predetermined distance D (a distance slightly larger than the spacing between adjacent scales  152  (grating area)) with respect to the five scales  152  on the +Y side. This arrangement is employed to avoid a state from occurring in which of the total of four heads; two X heads  66   x  and two Y heads  66   y  to be described later on for measuring position information of substrate holder  34 , two or more of the heads do not face any of the scales (that is, a non-measurement period in which the measurement beam moves off of the scale does not overlap among the four heads). 
     Each of the scales  152  consists of a plate-shaped (strip-shaped) member rectangular in a planar view extending in the X-axis direction, made of quartz glass. On the upper surface of each of the scales  152 , a reflective two-dimensional diffraction grating (two-dimensional grating) RG is formed whose periodic direction is in the X-axis direction and the Y-axis direction in a predetermined pitch (1 μm). Hereinafter, the grating area described earlier will also be called simply as two-dimensional grating RG. Note that in  FIG. 14 , the spacing (pitch) between the grids of two-dimensional grating RG is illustrated remarkably wider than the actual spacing, for convenience of illustration. The same applies also to other drawings that will be described below. In the description below, the five scales  152  arranged in the area on the +Y side of substrate holder  34  will be referred to as a first grating group, and the five scales  152  arranged in the area on the −Y side of substrate holder  34  will be referred to as a second grating group. 
     To the lower surface (surface on the −Z side) of Y slide table  62  of one of the head units  60  positioned at the +Y side, X head  66   x  and Y head  66   y  are fixed apart by a predetermined distance (a distance slightly larger than the spacing between adjacent scales  152 ) in the X-axis direction, in a state facing scales  152 , respectively. Similarly, to the lower surface (surface on the −Z side) of Y slide table  62  of the other head unit  60  positioned at the −Y side, Y head  66   y  and X head  66   x  are fixed apart by a predetermined distance in the X-axis direction, in a state facing scales  152 , respectively. That is, X head  66   x  and Y head  66   y  facing the first grating group and X head  66   x  and Y head  66   y  facing the second grating group each irradiates scales  152  with a measurement beam at a spacing wider than the spacing of the grating area of adjacent scales  152 . In the description below, for convenience of explanation, X head  66   x  and Y head  66   y  that one of the head units  60  has will be referred to as head  66   a  and head  66   b , and X head  66   x  and Y head  66   y  that the other head unit  60  has will be referred to as head  66   c  and head  66   d.    
     In this case, head  66   a  and head  66   c  are arranged at the same X position (on the same straight line parallel to the Y-axis direction), and head  66   b  and head  66   d  are arranged at the same X position (on the same straight line parallel to the Y-axis direction) which is different from the X position of head  66   a  and head  66   c . By heads  66   a  and  66   d  and two-dimensional grating RG facing each of the heads, a pair of X linear encoders is structured, and by heads  66   b  and  66   c  and two-dimensional grating RG facing each of the heads, a pair of Y linear encoders is structured. 
     In the liquid crystal exposure apparatus according to the second embodiment, the structure of other parts including the remaining parts of head unit  60  is similar to liquid crystal exposure apparatus  10  according to the first embodiment described earlier, except for drive control (position control) of substrate holder  34  using the substrate encoder system by main controller  90 . 
     In the liquid crystal exposure apparatus according to the second embodiment, between a first position where a pair of head units  60  faces the +X edge of substrate holder  34  as is shown in  FIG. 15A  and a second position where a pair of head units  60  faces the −X edge of substrate holder  34  as is shown in  FIG. 15B  within a range in which substrate holder  34  moves in the X-axis direction, position measurement of substrate holder  34  can be performed by heads  60   a  to  60   d  of the pair of head units  60 , that is, by the pair of X linear encoders and the pair of Y linear encoders.  FIG. 15A  shows a state in which only head  66   b  faces none of scales  152 , and  FIG. 15B  shows a state in which only head  66   c  faces none of scales  152 . 
     In the process in which substrate holder  34  is moved in between the first position shown in  FIG. 15A  and the second position shown in  FIG. 15B , positional relation between the pair of head units  60  and scales  152  shifts between five states; between a first state to a fourth state shown in  FIGS. 16A to 16D , respectively, and a fifth state in which all four heads  66   a  to  66   d  face two-dimensional grating RG of any one of the scales  152  (that is, the measurement beam of all four heads  66   a  to  66   d  irradiates two-dimensional grating RG. Hereinafter, instead of using the expressions; face two-dimensional grating RG of the scale, or the measurement beam is irradiated on two-dimensional grating RG of scale  152 , these will be expressed simply as; heads face the scales. 
     Here, the six scales  152  will be taken up for convenience of explanation, and codes a to f are to be used to identify each scale, using the expressions scales  152   a  to  152   f  (refer to  FIG. 16A ). 
     The first state shown in  FIG. 16A  shows a state in which head  66   a  faces scale  152   b , heads  66   c ,  66   d  face scale  152   e , and only head  66   b  faces none of the scales, and the second state shown in  FIG. 16B  shows a state in which substrate holder  34  moves in the +X direction by a predetermined distance from the state shown in  FIG. 16A  so that heads  66   a ,  66   b  face scale  152   b , head  66   d  faces scale  152   e , and only head  66   c  no longer faces any of the scales. In the process of shifting from the state in  FIG. 16A  to the state in  FIG. 16B , the heads go through the fifth state in which heads  66   a ,  66   b  face scale  152   b  and heads  66   c ,  66   d  face scale  152   e.    
     The third state in  FIG. 16C  shows a state in which substrate holder  34  has been moved in the +X direction by a predetermined distance from the state in  FIG. 16B , and only head  66   a  no longer faces any of the scales. In the process of shifting from the state in  FIG. 16B  to the state in  FIG. 16C , the heads go through the fifth state in which heads  66   a ,  66   b  face scale  152   b , head  66   c  faces scale  152   d , and head  66   d  faces scale  152   e.    
     The fourth state in  FIG. 16D  shows a state in which substrate holder  34  has been moved in the +X direction by a predetermined distance from the state in  FIG. 16C , and only head  66   d  no longer faces any of the scales. In the process of shifting from the state in  FIG. 16C  to the state in  FIG. 16D , the heads go through the fifth state in which head  66   a  faces scale  152   a , head  66   b  faces scale  152   b , head  66   c  faces scale  152   d , and head  66   d  faces scale  152   e.    
     When substrate holder  34  is moved in the +X direction by a predetermined distance from the state in  FIG. 16D , after going through the fifth state in which head  66   a  faces scale  152   a , head  66   b  faces scale  152   b , and heads  66   c ,  66   d  face scale  152   d , the heads then move into the first state in which head  66   a  faces scale  152   a , heads  66   c ,  66   d  face scale  152   d , and only head  66   b  faces none of the scales. 
     While the description above is on the shift of the state (positional relation) between three each of scales  152  of the five scales  152  each arranged on the ±Y sides of substrate holder  34  and the pair of head units  60 , also between the ten scales  152  and the pair of head units  60 , when looking at three each of scales  152  that are adjacent of the five scales arranged each on the ±Y sides of substrate holder  34 , the positional relation with the pair of head units shifts in a similar order as is described above. 
     In this way, in the second embodiment, at least three heads of the total of four heads; two X heads  66   x , that is  66   a ,  66   d , and two Y heads  66   y , that is  66   b ,  66   c , constantly face any of the scales  152  (two-dimensional grating RG) even when substrate holder  34  is moved in the X-axis direction. Furthermore, even when substrate holder  34  is moved in the Y-axis direction, since the pair of Y slide table  62  is moved in the Y-axis direction so that the measurement beams of the four heads do not move off of scales  152  (two-dimensional grating RG) in the Y-axis direction, at least three of the four heads face any of the scales  152 . Accordingly, main controller  90  can constantly control position information of substrate holder  34  in the X-axis direction, the Y-axis direction, and the θz direction, using three heads of heads  66   a  to  66   d . This point will be described further below. 
     When measurement values of X head  66   x  and Y head  66   y  are to be CX and CY, respectively, measurement values CX and CY can be expressed in the following equations (1a) and (1b), respectively.
 
 CX =( pi−X )cos θ z +( qi−Y )sin θ z   (1a)
 
 CY =−( pi−X )sin θ z +( qi−Y )cos θ z   (1b)
 
     Here, X, Y, and θx show the position of substrate holder  34  in the X-axis direction, the Y-axis direction, and the Oz direction, respectively. Also, pi and qi are the X position coordinate values and the Y position coordinate values of each of the heads  66   a  to  66   d . In the embodiment, the X coordinate values and the Y coordinate values (pi, qi) (i=1, 2, 3, 4) of each of the heads  66   a ,  66   b ,  66   c , and  66   d  can be calculated easily from the position information in the X-axis direction and the Y-axis direction (position of the center of Y slide table  62  in the X-axis direction and the Y-axis direction) of each of the pair of head units  60  (refer to  FIG. 1 ) calculated from the output of the four X linear encoders  96   x  and the four Y linear encoders  96   y , based on a known relation of each head with respect to the center of Y slide table  62 . 
     Accordingly, when substrate holder  34  and the pair of head units  60  have a positional relation as is shown in  FIG. 15A  and the position of substrate holder  34  within the XY plane in directions of three degrees of freedom is (X, Y, θz), then measurement values of the three heads  66   a ,  66   c , and  66   d  can theoretically be expressed by the following equations, (2a) to (2c) (also called an affine transformation relation).
 
 C 1=( p 1− X )cos θ z +( q 1− Y )sin θ z   (2a)
 
 C 3=−( p 3− X )sin θ z +( q 3− Y )cos θ z   (2b)
 
 C 4=( p 4− X )cos θ z +( q 4− Y )sin θ z   (2c)
 
     In a reference state where substrate holder  34  is at a coordinate origin (X, Y, θz)=(0, 0, 0), by simultaneous equations (2a) to (2c), C1=p1, C3=q3, and C4=p4. The reference state is a state in which the center of substrate holder  34  (almost coincides with the center of substrate P) coincides with the center of the projection area by projection optical system  16  and the θz rotation is zero. Accordingly, in the reference state, the Y position of substrate holder  34  can also be measured by head  66   b , and measurement value C2 by head  66   b , according to equation (1b), is C2=q2. 
     Accordingly, when the measurement values of the three heads  66   a ,  66   c , and  66   d  are to be initially set to p1, q3, and p4 in the reference state, hereinafter, the three heads  66   a ,  66   c , and  66   d  are to present theoretical values given by the equations (2a) to (2c) with respect to displacements (X, Y, θz) of substrate holder  34 . 
     Note that in the reference state, instead of one of the heads  66   a ,  66   c , and  66   d , such as  66   c , measurement value C2 of head  66   b  may be initially set as q2. 
     In this case, hereinafter, the three heads  66   a ,  66   b , and  66   d  are to present theoretical values given by the equations (2a), (2c), and (2d) with respect to displacements (X, Y, θz) of substrate holder  34 .
 
 C 1=( p 1− X )cos θ z +( q 1− Y )sin θ z   (2a)
 
 C 4=( p 4− X )cos θ z +( q 4− Y )sin θ z   (2c)
 
 C 2=−( p 2− X )sin θ z +( q 2− Y )cos θ z   (2d)
 
     In simultaneous equations (2a) to (2c) and simultaneous equations (2a), (2c), and (2d), three equations are given with respect to three variables (X, Y, θz). Therefore, conversely, if dependent variables C1, C3, and C4 in simultaneous equations (2a) to (2c), or dependent variables C1, C4, and C2 in simultaneous equations (2a), (2c), and (2d) are given, variables X, Y, and θz can be obtained. Here, the equations can be solved easily when an approximate sin θz≈θz is applied, or when a higher approximate is applied. Accordingly, positions (X, Y, θz) of wafer stage WST can be calculated from measurement values C1, C3, and C4 (or C1, C2, and C4) of heads  66   a ,  66   c , and  66   d  (or heads  66   a ,  66   b , and  66   d ). 
     Next, a linkage process, namely, initial setting of measurement values, at the time when switching heads of the substrate encoder system that measures position information of substrate holder  34  performed in the liquid crystal exposure apparatus according to the second embodiment, will be described centering on the operation of main controller  90 . 
     In the second embodiment, as is previously described, three encoders (X heads and Y heads) are constantly measuring the position information of substrate holder  34  in an effective stroke range of substrate holder  34 , and on performing the switching process of the encoders (X head or Y head), as is shown in  FIG. 17B , each of the four heads  66   a  to  66   d  faces any of the scales  52  and moves into a state (the fifth state described earlier) so that the position of substrate holder  34  can be measured.  FIG. 17B  shows an example of the fifth state that appears during the change of state from the state shown in  FIG. 17A  in which the position of substrate holder  34  is measured with heads  66   a ,  66   b , and  66   d  and then substrate holder  34  is moved in the +X direction to the state shown in  FIG. 17C  in which the position of substrate holder  34  is measured with heads  66   b ,  66   c , and  66   d . That is,  FIG. 17B  shows a state in which the three heads used for measuring position information of substrate holder  34  are being switched, from heads  66   a ,  66   b , and  66   d  to heads  66   b ,  66   c , and  66   d.    
     At the moment when the switching process (linkage) of heads (encoders) used for position control (measurement of position information) of substrate holder  34  within the XY plane, heads  66   a ,  66   b ,  66   c , and  66   d  are facing scales  152   b ,  152   b ,  152   d , and  152   e , respectively, as is shown in  FIG. 17B . When taking a look at  FIGS. 17A to 17C , it may appear that head  66   a  is about to be switched to head  66   c  in  FIG. 17B , however, as it is obvious from the point that the measurement direction is different in head  66   a  and head  66   c , it is meaningless to give the measurement value (count value) of head  66   a  without any changes to head  66   c  as an initial value of the measurement value at the timing when linkage is performed. 
     Therefore, in the embodiment, main controller  90  is to perform switching from the measurement of position information (and position control) of substrate holder  34  using the three heads  66   a ,  66   b , and  66   d  to the measurement of position information (and position control) of substrate holder  34  using the three heads  66   b ,  66   c , and  66   d . That is, in this method, the concept is different from a normal encoder linkage and the linkage is not from one head to another head, but is a method of linking a combination of three heads (encoders) to another combination of three heads (encoders). 
     Main controller  90 , first of all, solves simultaneous equations (2a), (2c), and (2d) based on measurement values C1, C4, and C2 of heads  66   a ,  66   d , and  66   b , and calculates position information (X, Y, θz) of the substrate holder within the XY plane. 
     Next, main controller  90  substitutes X and θz calculated above into the following affine transformation equation (equation (3)), and obtains the initial value (the value that should be measured by head  66   c ) of the measurement value of head  66   c.  
 
 C 3=−( p 3− X )sin θ z +( q 3− Y )cos θ z   (3)
 
     In equation (3) above, p3 is the X coordinate value and q3 is the Y coordinate value of head  66   c . In the embodiment, as is described earlier, as for coordinate values (p3, q3), the values are used that are calculated from the position of the center of Y slide table  62  in the X-axis direction and the Y-axis direction of each of the pair of head units  60  calculated from the output of the four X linear encoders  96   x  and the four Y linear encoders  96   y , based on the known positional relation of head  66   c  with respect to the center of Y slide table  62 . 
     By giving initial value C3 described above as the initial value of head  66   c , linkage is to be completed without contradictions while maintaining the positions (X, Y, θz) of substrate holder  34  in directions of three degrees of freedom. Thereinafter, the position coordinates (X, Y, θz) of wafer stage WST are calculated by solving the following simultaneous equations (2b) to (2d), using the measurement values C2, C3, and C4 of heads  66   b ,  66   c , and  66   d  which are used after the switching.
 
 C 3=−( p 3− X )sin θ z +( q 3− Y )cos θ z   (2b)
 
 C 4=( p 4− X )cos θ z +( q 4− Y )sin θ z   (2c)
 
 C 2=−( p 2− X )sin θ z +( q 2− Y )cos θ z   (2d)
 
     Note that while the case has been described above when the switching is from three heads to another three heads including one head different from the three heads, it was described in this way because the values to be measured using the another heads after switching is calculated based on the principle of affine transformation, using the positions (X, Y, θz) of substrate holder  34  obtained from the measurement values of the three heads used before switching, and the calculated values are set as initial values of the another heads used after switching. However, when focusing only on the two heads serving as direct targets of switching and linkage process, without referring to the procedure of calculation and the like of the values to be measured using the another heads used after switching, it may also be said that one head of the three heads used before switching is switched to a different head. In any case, the switching of the heads is performed in a state where the head used for measurement of position information and position control of the substrate holder before switching and the head used after switching both simultaneously face any of the scales  152 . 
     Note that while the description above is an example of switching of heads  66   a  to  66   d , in switching from any three heads to another three heads, or switching from one of the heads to another head, switching of heads is performed in a procedure similarly to the procedure described above. 
     The liquid crystal exposure apparatus according to the second embodiment described so far has a working effect equivalent to the liquid crystal exposure apparatus according to the first embodiment described earlier. Adding to this, with the liquid crystal exposure apparatus according to the second embodiment, while substrate holder  34  is moved, position information (including θz rotation) of substrate holder  34  within the XY plane is measured by three heads (encoders) including at least one each of X head  66   x  (X linear encoder) and Y head  66   y  (Y linear encoder) of substrate encoder system  50 . Then, by main controller  90 , the head (encoder) used for measuring position information of substrate holder  34  within the XY plane is switched from one of the heads (encoders) of the three heads (encoders) used for position measurement and position control of substrate holder  34  before switching to another head (encoder), so that the position of substrate holder  34  within the XY plane is maintained before and after the switching. Therefore, the position of substrate holder  34  within the XY plane is maintained before and after the switching and an accurate linkage becomes possible, even though switching of the encoders used for controlling the position of substrate holder  34  has been performed. Accordingly, substrate holder  34  (substrate P) can be moved along the XY plane accurately along a predetermined moving route while switching and linkage (linkage process of measurement values) of the heads are performed among a plurality of heads (encoders). 
     Also, with the liquid crystal exposure apparatus according to the second embodiment, during exposure of the substrate, substrate holder  34  is moved within the XY plane by main controller  90 , based on measurement results of position information of substrate holder  34  and position information ((X, Y) coordinate values) within the XY plane of the three heads used for measuring the position information. In this case, main controller  90  moves substrate holder  34  within the XY plane while calculating the position information of substrate holder  34  within the XY plane using the affine transformation relation. This allows the movement of substrate holder  34  (substrate P) to be controlled with good accuracy while switching the heads (encoders) used for control of the movement of substrate holder  34  using the encoder system having each of a plurality of Y heads  66   y  or a plurality of X heads  66   x.    
     Note that in the second embodiment described above, while the correction information (initial value of the another head previously described) for controlling the movement of the substrate holder using the head (corresponding to the another head described above) whose measurement beam moves off from one of the adjacent pair of scales and moves to irradiate the other scale was acquired, based on the position information measured by the three heads facing at least one scale  152 , this correction information should be acquired by the time one of the three heads facing at least one scale  152  moves off of two-dimensional grating RG, after the measurement beam of the another head is moved to irradiate the other scale. Also, in the case of performing position measurement or position control of the substrate holder by switching the three heads facing at least one scale  152  to three different heads including the another head described above, this switching should be performed by the time one of the three heads facing at least one scale  152  moves off of two-dimensional grating RG, after the correction information described above has been acquired. Note that acquiring the correction information and the switching may substantially be performed at the same time. 
     Note that in the second embodiment described above, each of the five scales  152  of the first grating group and the second grating group is arranged on substrate holder  34  so that the area that has no two-dimensional grating RG of the first grating group (non-grating area) does not overlap the area that has no two-dimensional grating RG of the second grating group (non-grating area) in the X-axis direction (first direction), or in other words, so that the non-measurement period in which the measurement beam moves off of two-dimensional grating RG does not overlap in the four heads. In this case, heads  66   a  and  66   b  that head unit  60  on the +Y side has, are arranged at a spacing wider than the width of the area that has no two-dimensional grating RG of the first group in the X-axis direction, and heads  66   c  and  66   d  that head unit  60  on the −Y side has, are arranged at a spacing wider than the width of the area that has no two-dimensional grating RG of the second group in the X-axis direction. However, the combination of the grating section including the plurality of two-dimensional gratings and the plurality of heads that can face the grating section is not limited to this. The point is, spacing between heads  66   a  and  66   b  and spacing between heads  66   c  and  66   d , position, position and length of the grating section of the first and second grating groups, spacing between the grating sections and their positions should be set, so that the (non-measurable) non-measurement period in which the measurement beam moves off of two-dimensional grating RG does not overlap in the four heads  66   a ,  66   b ,  66   c , and  66   d  during the movement of the movable body in the X-axis direction. For example, even if the position and the width of the non-grating area in the X-axis direction is the same in the first grating group and the second grating group, two heads facing at least one scale  152  (two-dimensional grating RG) of the first grating group and two heads facing at least one scale  152  (two-dimensional grating RG) of the second grating group may be arranged shifted only by a distance wider than the width of the non-grating area in the X-axis direction. In this case, the spacing between the head arranged on the +X side of the two heads facing the first grating group and the head arranged on the −X side of the two heads facing the second grating group may be set wider than the width of the non-grating area, or the two heads facing the first grating and the two heads facing the second grating may be arranged alternately in the X-axis direction, with the spacing between adjacent pair of heads being be set wider than the width of the non-grating area. 
     Also, in the second embodiment described above, while the case has been described in which the first grating group is arranged in an area on the +Y side of substrate holder  34 , and the second grating group is arranged in an area on the −Y side of substrate holder  34 , instead of one of the first grating group and the second grating group, such as the first grating group, a single scale member on which a two-dimensional grating extending in the X-axis direction is formed, may be used. In this case, one head may be made to constantly face the single scale member. In this case, a structure may be employed in which three heads may be provided to face the second grating group, and by making the spacing (spacing between irradiation positions of the measurement beams) in the X-axis direction of the three heads wider than the spacing between two-dimensional grating RG on adjacent scales  152 , at least two of the three heads facing the second grating group can face at least one two-dimensional grating RG of the second grating group regardless of the position of substrate holder  34  in the X-axis direction. Or, a structure may be employed in which at least two heads constantly face the single scale member described above regardless of the position of substrate holder  34  in the X-axis direction, together with at least one head facing at least one two-dimensional grating RG of the second grating group. In this case, each of the measurement beams of the at least two heads moves off of one of the plurality of scales  152  (two-dimensional grating RG) during the movement of substrate holder  34  in the X-axis direction, and is moved to irradiate another scale  152  (two-dimensional grating RG) adjacent to the one scale  152  (two-dimensional grating RG). However, by making the spacing between the at least two heads in the X-axis direction wider than the spacing of two-dimensional grating RG of adjacent scales  152 , the non-measurement period does not overlap in the at least two heads, that is, the measurement beam of at least one head constantly irradiates scale  152 . In these structures, at least three heads constantly face at least one scale  152 , allowing position information in directions of three degrees of freedom to be measured. 
     Note that the number of scales, spacing between adjacent scales and the like may be different in the first grating group and the second grating group. In this case, in at least two heads facing the first grating group and at least two heads facing the second grating group, spacing between the heads (measurement beams), position and the like may be different. 
     Note that in the second embodiment described above, the position of heads  66   a  to  66   d  in the X-axis direction and the Y-axis direction are calculated from the position of the center of Y slide table  62  in the X-axis direction and the Y-axis direction of each of the pair of head units  60  calculated from the output of the four X linear encoders  96   x  and the four Y linear encoders  96   y , based on the known positional relation of each head with respect to the center of Y slide table  62 . That is, the encoder system was to be used for measuring the position of heads  66   a  to  66   d  in the X-axis direction and the Y-axis direction. However, the embodiment is not limited to this, and the encoder system and the like may be used to measure position information only in the Y-axis direction of heads  66   a  to  66   d , since heads  66   a  to  66   d  (the pair of head units  60 ) can be moved only in the Y-axis direction. That is, in the second embodiment described above, the four X linear encoders  96   x  do not necessarily have to be provided. In this case, for heads  66   a  to  66   d , on applying equations (2a) to (2d) described earlier, design values (fixed values) are used for p1 to p4 (X position), and for q1 to q4 (Y position), values calculated from the output of the four linear encoders  96   y  are used. Note that in the case the affine transformation relation is not used, on measuring position information in the Y-axis direction of substrate holder  34  by heads  66   b  and  66   c , measurement information of the four linear encoders  96   y  is used, and on measuring position information in the X-axis direction of substrate holder  34  by heads  66   a  and  66   d , measurement information of the four Y linear encoders  96   y  do not have to be used. 
     Note that in the second embodiment described above, while the plurality of scales  152  having a single two-dimensional grating RG (grating area) formed on each scale was used, the present invention is not limited to this, and at least one of the first grating group or the second grating group may include a scale  152  that has two or more grating areas formed apart in the X-axis direction. 
     Note that in the second embodiment described above, while the case has been described in which to measure and control the positions (X, Y, θz) of substrate holder  34  constantly by three heads, the first grating group and the second grating group including five scales  152  each having the same structure are arranged shifted by a predetermined distance in the X-axis direction, the embodiment is not limited to this, and one of the head units  60  and the other of the head units  60  may have heads (heads  66   x ,  66   y ) used for measurement of substrate holder  34  arranged differently in the X-axis direction, without the first grating group and the second grating group being shifted in the X-axis direction (the line of scales  152  arranged almost completely facing each other). Also in this case, the positions (X, Y, θz) of substrate holder  34  can constantly be measured and controlled by the three heads. 
     Note that in the second embodiment described above, while the case of using a total of four heads, heads  66   a  and  66   b  and heads  66   c  and  66   d  has been described, the embodiment is not limited to this, and five or more heads may also be used. That is, to one of the two heads each facing the first grating group and the second grating group, at least one redundant head may be added. This structure will be described in a third embodiment below. 
     Third Embodiment 
     Next, a third embodiment will be described, based on  FIG. 18 . Since the structure of the liquid crystal exposure apparatus according to the third embodiment is the same as the first and the second embodiments previously described except for the structure of a part of substrate encoder system  50 , only the different points will be described below, and for elements having the same structure and function as the first and the second embodiments will have the same reference code as the first and the second embodiments, and the description thereabout will be omitted. 
       FIG. 18  shows substrate holder  34  and the pair of head units  60  of substrate encoder system  50  according to the third embodiment in a planar view, along with projection optical system  16 . In  FIG. 18 , to make the description comprehensive, illustration of encoder base  54  and the like is omitted. Also, in  FIG. 18 , along with head unit  60  (Y slide table  62 ) illustrated in a dotted line, illustration of X head  64   x  and Y head  64   y  provided on the upper surface of Y slide table  62  is also omitted. 
     With the liquid crystal exposure apparatus according to the third embodiment, as is shown in  FIG. 18 , in each of the areas on the +Y side and the −Y side of substrate holder  34  with the substrate mounting area in between, five scales  152  are arranged at a predetermined spacing in the X-axis direction. With the five scales  152  arranged on the +Y side of the substrate mounting area and the five scales  152  arranged on the −Y side, the spacing between adjacent scales  152  is the same, and the five scales  152  on the +Y side of the substrate mounting area and the five scales  152  on the −Y side are arranged at the same X position, facing each other. Accordingly, the position of the spacing between adjacent scales is located on almost the same straight line in the Y-axis direction that has a predetermined width. 
     To the lower surface (surface on the −Z side) of Y slide table  62  of one of the head units  60  positioned on the +Y side, a total of three heads, Y head  66   y , X head  66   x , and Y head  66   y  are fixed apart by a predetermined spacing (a distance larger than the spacing between adjacent scales  152 ) in the X-axis direction from the −X side, in a state each facing scale  152 . To the lower surface (surface on the −Z side) of Y slide table  62  of the other head unit  60  positioned on the −Y side, Y head  66   y  and X head  66   x  are fixed apart by a predetermined spacing in the X-axis direction, in a state each facing scale  152 . In the description below, for convenience of explanation, three heads that one of the head units  60  has will be referred to as head  66   e , head  66   a , and head  66   b  from the −X side, and Y head  66   y  and X head  66   x  that the other head unit  60  has will be referred to as head  66   c  and head  66   d , respectively. 
     In this case, head  66   a  and head  66   c  are arranged at the same X position (on the same straight line in the Y-axis direction), and head  66   b  and head  66   d  are arranged at the same X position (on the same straight line in the Y-axis direction). Heads  66   a ,  66   d  and the two-dimensional gratings RG that face each head structure a pair of X linear encoders, and heads  66   b ,  66   c , and  66   e  and the two-dimensional gratings RG that face each head structure three Y linear encoders. 
     With the liquid crystal exposure apparatus according to the third embodiment, the structure of other parts is similar to the liquid crystal exposure apparatus according to the second embodiment described earlier. 
     In the third embodiment, although the arrangement of scales  152  lined on the +Y side and the −Y side is not shifted in the X-axis direction, as long as the pair of head units  60  moves (or the Y position of substrate holder  4  is maintained at a position where the pair of head units  60  faces the line of scale  152 ) in the Y-axis direction synchronously with substrate holder  34 , three heads of heads  66   a  to  66   e  constantly face scale  152  (two-dimensional grating RG) regardless of the X position of substrate holder  34 . 
     The liquid crystal exposure apparatus according to the third embodiment described so far has a working effect equivalent to the liquid crystal exposure apparatus according to the second embodiment described earlier. 
     Note that in the third embodiment described above, the plurality of heads for measuring position information of substrate holder  34  can also be regarded to include one head  66   a  in addition to, e.g. heads  66   e ,  66   b ,  66   c , and  66   d  necessary for switching of the heads, whose non-measurement period partly overlaps one head  66   c  of the four heads. And, in the third embodiment, on measuring position information (X, Y, θz) of substrate holder  34 , of the five heads including the four heads  66   e ,  66   b ,  66   c , and  66   d  and the one head  66   c , measurement information is used of at least three heads irradiating at least one of the plurality of grating areas (two-dimensional grating RG) with a measurement beam. 
     Fourth Embodiment 
     Next, a fourth embodiment will be described, based on  FIG. 19 . While the structure of the liquid crystal exposure apparatus according to the fourth embodiment is different from the structure of the liquid crystal exposure apparatus according to the second embodiment described earlier on the points that scales  152  lined in each of the areas on both the +Y side and the −Y side of the substrate mounting area of substrate holder  34  are arranged facing each other similarly as in the third embodiment, and that one of the head units  60  positioned on the −Y side has two each of X heads  66   x  and Y heads  66   y  similarly to the first embodiment, as is shown in  FIG. 19 , the structure of other parts is similar to the liquid crystal exposure apparatus according to the second embodiment. 
     To the lower surface (surface on the −Z side) of Y slide table  62  of one of the head units  60 , X head  66   x  (hereinafter appropriately called head  66   e ) is provided arranged adjacent to Y head  66   y  (head  66   c ) on the −Y side, along with Y head  66   y  (hereinafter appropriately called head  66   f ) provided arranged adjacent to X head  66   x  (head  66   d ) on the −Y side. 
     With the liquid crystal exposure apparatus according to the embodiment, in a state when the pair of head units  60  is moving in the Y-axis direction (or when the Y position of substrate holder  34  is maintained at a position where the pair of head units  60  face the scales  152  lined), a case may occur when one of three heads  66   a ,  66   c , and  66   e  (to be referred to as heads of a first group) and three heads  66   b ,  66   d , and  66   f  (to be referred to as heads of a second group) do not face any of the scales due to substrate holder  34  moving in the X-axis direction, and when this occurs, the other of the heads of the first group and the heads of the second group face scale  152  (two-dimensional grating RG) without fail. That is, in the liquid crystal exposure apparatus according to the fourth embodiment, although the arrangement of scales  152  lined on the +Y side and the −Y side is not shifted in the X-axis direction, as long as the pair of head units  60  moves (or the Y position of substrate holder  4  is maintained at a position where the pair of head units  60  faces the line of scales  152 ) in the Y-axis direction, the positions (X, Y, θz) of substrate holder  34  can be measured regardless of the X position of substrate holder  34 , by the three heads included in at least one of the heads of the first group and the heads of the second group. 
     Here, a case will be considered, for example, of restoring (re-start measurement of) the heads of the first group (heads  66   a ,  66   c , and  66   e ) when the heads face scale  152  again, after heads  66   a ,  66   c , and  66   e  no longer face any of the scales and have become non-measurable. In this case, at the point before measurement is re-started by the heads of the first group (heads  66   a ,  66   c , and  66   e ), the positions (X, Y, θz) of substrate holder  34  is being continuously measured and controlled by the heads of the second group (heads  66   b ,  66   d , and  66   f ). Therefore, main controller  90 , as is shown in  FIG. 19 , at the point when the pair of head units  60  crosses over adjacent two scales  152  arranged on each of the +Y side and the −Y side and the heads of the first group and the heads of the second group face one and the other of the adjacent two scales  152 , respectively, calculates the positions (X, Y, θz) of substrate holder  34  by the method described in detail in the second embodiment based on measurement values of the heads of the second group (heads  66   b ,  66   d , and  66   f ), and by substituting the positions (X, Y, θz) of the substrate holder into the formula of affine transformation described earlier, initial values of the heads of the first group (heads  66   a ,  66   c , and  66   e ) are calculated and set at the same time. This allows the heads of the first group to be restored and to re-start measurement and control of the position of substrate holder  34  with these heads easily. 
     With the liquid crystal exposure apparatus according to the fourth embodiment described so far, the apparatus exhibits a working effect equivalent to the liquid crystal exposure apparatus according to the second embodiment described earlier. 
     Modified Example of the Fourth Embodiment 
     This modified example describes a case when a head unit having an identical structure (or a structure symmetrical in the vertical direction of the page surface) as one of the head units  60  is used as the other head unit  60  positioned on the +Y side, in the liquid crystal exposure apparatus according to the fourth embodiment. 
     In this case, similarly to the description above, eight heads are grouped into four heads each being arranged on the same straight line in the Y-axis direction; heads of a first group, and heads of a second group. 
     A case will be considered of restoring the heads of a first group and re-starting measurement with these heads when the heads face scale  152  again, after the heads of the first group no longer face any of the scales and can no longer perform measurement. 
     In this case, at the point before measurement is re-started by the heads of the first group, the positions (X, Y, θz) of substrate holder  34  are being continuously measured and controlled by three heads of the heads of the second group. Therefore, main controller  90 , as is described earlier, at the point when the pair of head units  60  crosses over adjacent two scales  152  arranged on each of the +Y side and the −Y side and the heads of the first group and the heads of the second group face one and the other of the adjacent two scales  152 , respectively, calculates initial values of each of the heads of the first group, however, in this case, the main controller cannot calculate the initial values of all four heads of the first group at the same time. This is because if the heads to be restored for measurement were three (the number of X heads and Y heads added), when the initial values of the measurement values of the three heads are set in the procedure described earlier, by solving the simultaneous equations described earlier using the initial values as measurement values C1, C2, C3 and the like, the positions (X, Y, θ) of the substrate holder is uniquely decided, which causes no problems in particular. However, simultaneous equations using the affine transformation relation that can uniquely decide the positions (X, Y, θ) of the substrate holder using measurement values of four heads cannot be conceived. 
     Therefore, in the modified example, the first group to be restored is to be grouped into two groups, each having three heads including different heads and the initial values are calculated and set simultaneously for the three heads for each group in the method described earlier. After the initial values have been set, the measurement values of the three heads of either of the groups may be used for position control of substrate holder  34 . Position measurement of substrate holder  34  by the heads of the group not used for position control may be executed in parallel with position control of substrate holder  34 . Note that the initial values of each head of the first group to be restored can be sequentially calculated individually, by the method described earlier. 
     Note that the structures described so far in the first to fourth embodiments can be changed as appropriate. In mask encoder system  48  and substrate encoder system  50  of the first embodiment described above, the arrangement of encoder heads and scales may be reversed. That is, X linear encoder  92   x  and Y linear encoder  92   y  for obtaining position information of mask holder  40  may be structured so that encoder heads are attached to mask holder  40  and scales are attached to encoder base  43 . Also, X linear encoder  94   x  and Y linear encoder  94   y  for obtaining position information of substrate holder  34  may have encoder heads attached to substrate holder  34  and scales attached to Y slide table  62 . In this case, the encoder heads attached to substrate holder  34  may be arranged along the X-axis direction in a plurality of numbers, and are preferably structured switchable with one another. Also, the encoder heads provided at substrate holder  34  may be made movable and sensors to measure position information of the encoder heads may be provided, and the scales may be provided at encoder base  43 . In this case, the scales provided at encoder base  43  are fixed. Similarly, X linear encoder  96   x  and Y linear encoder  96   y  for obtaining position information of Y slide table  62  may have scales attached to Y slide table  62  and encoder heads attached to encoder base  54  (apparatus main section  18 ). In this case, the encoder heads attached to encoder base  54  may be arranged along the Y-axis direction in a plurality of numbers, and are preferably structured switchable with one another. In the case the encoder heads are fixed to substrate holder  34  and encoder base  54 , the scales fixed to Y slide table  62  may be used in common. 
     Also, in substrate encoder system  50 , while the case has been described where a plurality of scales  52  are fixed extending in the X-axis direction on the substrate stage device  20  side and a plurality of scales  56  are fixed extending in the Y-axis direction on the apparatus main section  18  (encoder base  54 ) side, the substrate encoder system is not limited to this, and a plurality of scales extending in the Y-axis direction may be fixed on the substrate stage device  20  side and a plurality of scales extending in the X-axis direction may be fixed on the apparatus main section  18  side. In this case, head unit  60  is moved in the X-axis direction while substrate holder  34  is being moved in exposure operation and the like of substrate P. 
     Also, while the case has been described in which in mask encoder system  48 , threes scales  46  are arranged separate in the X-axis direction, and in substrate encoder system  50 , two scales  52  are arranged separate in the Y-axis direction and five scales  56  are arranged separate in the X-axis direction, the number of scales is not limited to this, and may be appropriately changed according to the size of mask M and substrate P, or movement strokes. Also, the plurality of scales may not necessarily have to be arranged separate, and a longer single scale (in the case of the embodiment above, a scale about three times the length of scale  46 , a scale about two times the length of scale  52 , and a scale about five times the length of scale  56 ) may be used. Also, in a scale group (row of scales) in which a plurality of scales arranged in the X-axis direction is continuously arranged with gaps of a predetermined spacing in between on substrate holder  34 , the length in the X-axis direction of one scale (pattern for X-axis measurement) may be a length that can be continuously measured only by a length of one shot area (the length in which a device pattern is irradiated and formed on a substrate when exposure is performed while moving the substrate on the substrate holder in the X-axis direction). This makes position measurement (position control) of substrate P (substrate holder) during scanning exposure easy, since relay control of heads with respect to the plurality of scales does not have to be performed during the scanning exposure of one shot area. Also, a plurality of scales having different lengths may be used, and the number of scales structuring the grating section does not matter, as long as each of the grating sections includes a plurality of grating areas arranged side by side in the X-axis direction or the Y-axis direction. 
     Also, in the case of arranging a scale group (row of scales) in which a plurality of scales arranged in the X-axis direction is continuously arranged with gaps of a predetermined spacing in between on substrate holder  34  in a plurality of rows at different positions (e.g. a position on one side (+Y side) and a position on the other side (−Y side) with respect to projection optical system  16 ) separate from each other in the Y axis direction, a structure may be employed so that the plurality of scale groups (plurality of rows of scales) can be used differently depending on arrangement of shots (shot map) on the substrate. For example, by making the whole length of the plurality of rows of scales different from one another between the rows of scales, the scales are applicable to different shot maps, and are also applicable to changes in the number of shot areas formed on the substrate, as in the case of a four-piece setting and the case of a six-piece setting. Also, the scales arranged on one side of projection optical system  16  and the scales arranged on the other side may have different lengths. Also, along with this arrangement, if position of gaps of each row of scales are made to be at different positions in the X-axis direction, the heads corresponding to each of the plurality of rows of scales do not move off away from the measurement range simultaneously, which allows the number of sensors considered as an undefined value in linkage process to be reduced and the linkage process to be performed with high precision. 
     Also, in the first embodiment described above, while the case has been described where X scales and Y scales are formed independently on the surface of each of the scales  46 ,  52 , and  56 , the embodiment is not limited to this, and a scale having a two-dimensional grating formed may be used, similarly to the second or fourth embodiments described earlier. In this case, an XY two-dimensional head can also be used as the encoder head. Also, while the case has been described where the encoder system of a diffraction interference method is used, the encoder is not limited to this, and other encoders such as the so-called pick-up system or a magnetic system may also be used, and the so-called scan encoder whose details are disclosed in, for example, U.S. Pat. No. 6,639,686 may also be used. Also, position information of Y slide table  62  may be obtained by a measurement system other than the encoder system (an optical interferometer system). 
     Note that in the second to fourth embodiments and the modified example (hereinafter shortly referred to as the fourth embodiment) described above, while the case has been described in which at least four heads are provided, in such a case, the number of scales  152  structuring the grating section does not matter, as long as the grating section includes a plurality of grating areas arranged side by side in the first direction. The plurality of grating areas does not necessarily have to be arranged on both one side and the other side in the Y-axis direction with substrate P of substrate holder  34  in between, and may be arranged only on one side. To continuously control the positions (X, Y, θz) of substrate holder  34  during the exposure operation of substrate P, the following conditions need to be satisfied. 
     That is, while a measurement beam of one head of the at least four heads moves off of the plurality of grating areas (two-dimensional grating RG described earlier), along with at least the three heads remaining irradiate at least one of the plurality of grating areas with the measurement beams, by movement of substrate holder  34  in the X-axis direction (the first direction), the one head described above whose measurement beam moves off of the plurality of grating areas is switched in the at least four heads described above. In this case, the at least four heads include; two heads whose positions (irradiation positions) of the measurement beams in the X-axis direction (the first direction) are different from each other, and two heads whose positions of the measurement beams in the Y-axis direction (the second direction) are different from at least one of the two heads along with positions (irradiation positions) of the measurement beams in the X-axis direction (the first direction) being different from each other, and the two heads irradiate measurement beams in the X-axis direction at a spacing wider than the spacing of a pair of adjacent grating areas of the plurality of grating areas. 
     Note that the grating areas (two-dimensional grating RG) arranged side by side in the X-axis direction may be arranged in the Y-axis direction in three or more rows. In the fourth embodiment described above, instead of the five scales  152  on the −Y side, a structure may be employed in which two rows of grating areas (two-dimensional gratings RG) adjacent in the Y-axis direction are provided, consisting of 10 grating areas (two-dimensional gratings RG) having an area which is half of each of the five scales  152  in the Y-axis direction, and heads  66   e  and  66   f  can be made to face two-dimensional grating RG at one of the rows, and heads  66   c  and  66   d  can be made to face two-dimensional grating RG at the other of the rows. Also, in the modified example of the fourth embodiment described above, also for the five scales  152  on the +Y side, a structure may be employed in which two rows of grating areas (two-dimensional gratings RG) adjacent in the Y-axis direction are provided, consisting of 10 grating areas similar to the description above, and a pair of heads can be made to face two-dimensional grating RG at one of the rows, and the remaining pair of heads can be made to face two-dimensional grating RG at the other of the rows. 
     Note that in the second to fourth embodiments described above, when substrate holder  34  moves in the X-axis direction (the first direction), it is important to set position or spacing, or position and spacing and the like of at least one of scales and heads, so that at least among the four heads mutually, measurement beams not being irradiated on (move off of the grating areas of) any of the two-dimensional grating RG, that is, measurement with the heads being non-measurable (non-measurement section) does not overlap for any two heads. For example, in a scale group (row of scales) in which a plurality of scales arranged in the X-axis direction is continuously arranged with gaps of a predetermined spacing in between on substrate holder  34 , the distance between the plurality of scales (in other words, the length of gap), the length of one scale, and two heads (heads arranged opposed to each other in one head unit  60 , e.g. two heads  66   x  as is shown in  FIG. 5 ) that relatively move with respect to the row of scales are arranged to satisfy a relation of “length of one scale&gt;distance between heads arranged opposed to each other&gt;distance between scales.” This relation is satisfied not only by the scales provided on substrate holder  34  and the corresponding head units  60 , but also by scales  56  provided on encoder base  54  and the corresponding head units  60 . Also, in each of the embodiments described above (e.g., refer to  FIG. 5 ), while the pair of X heads  66   x  and the pair of Y heads  66   y  are each arranged lined in the X-axis direction to form pairs (X heads  66   x  and Y heads  66   y  are arranged at the same position in the X-axis direction), the pairs may be arranged so that the heads are relatively shifted in the X-axis direction. Also, in a scale group (row of scales) in which a plurality of scales arranged in the X-axis direction is continuously arranged with gaps of a predetermined spacing in between on substrate holder  34 , while the length of the scale was the same for each of the scales continuously arranged in the embodiment above, scales having a length different from one another may be continuously arranged. For example, in a row of scales on substrate holder  34 , the scales arranged in the center may be physically longer than the scales (scales arranged at each edge in the row of scales) arranged at both ends in the X-axis direction. 
     Note that in the second and the fourth embodiment described above, instead of each X head  66   x  measuring position information of substrate holder  34 , an encoder head (XZ head) whose measurement direction is in the X-axis direction and the Z-axis direction may be used, together with an encoder head (YZ head) whose measurement direction is in the Y-axis direction and the Z-axis direction. As these heads, a sensor head having a structure similar to the displacement measurement sensor head disclosed in U.S. Pat. No. 7,561,280 can be used. In such a case, on switching and linkage process of the heads described earlier, adding to the linkage process performed to secure continuity of measurement results of the position of substrate holder  34  in directions of three degrees of freedom (X, Y, θz) in the XY plane by performing a predetermined calculation using measurement values of three heads used for position control of substrate holder  34  before switching, main controller  90  may also perform the linkage process to secure continuity of measurement results of the position of substrate holder  34  in the remaining directions of three degrees of freedom (Z, θx, θy) by a similar method described earlier. Specifically, taking the second embodiment representatively as an example, main controller  90  may acquire correction information for controlling the movement of substrate holder  34  in the remaining directions of three degrees of freedom (Z, θx, θy) using one head whose measurement beam moves off of one two-dimensional grating RG (grating area) and moves to irradiate another two-dimensional grating RG (grating area) of the four heads  66   a ,  66   b ,  66   c , and  66   d , based on measurement information in the Z-axis direction (a third direction) by the remaining three heads or position information of substrate holder  34  in the remaining directions of three degrees of freedom (Z, θx, θy) measured by the remaining three heads. 
     Note that in the second and the fourth embodiment, while the initial value of another head to be switched is to be set when a measurement beam moves off of one scale and moves to irradiate another scale, the embodiment is not limited to this, and correction information for controlling the substrate holder may be acquired using another head, such as correction information of the measurement values of another head. In the correction information to control the movement of the substrate holder using another head, the initial value is naturally included, but the information is not limited to this, and as long as the information may be used so that the another head can start the measurement again, the information may also be an offset value from the values to be measured after re-starting the measurement. 
     Also, in the first to fourth embodiments described above, the XZ head described earlier may be used instead of each X head of mask encoder system  48 , along with using the YZ head described earlier instead of each Y head. Or, in the first to fourth embodiments described above, mask encoder system  48  may be structured so that a plurality of heads can move relatively with respect to scales  46  in the Y-axis direction, similar to the encoder for position measurement of substrate holder  34  of substrate encoder system  50 . Also, instead of scales  46 , a scale on which a two-dimensional grating RG similar to scale  152  described earlier is formed may be used. 
     Similarly, in the first to fourth embodiments described above, the XZ head described earlier may be used instead of each X head  64   x , along with using the YZ head described earlier instead of each Y head  64   y . In such a case, also instead of scales  56 , a scale may be used, having a two-dimensional grating RG formed similar to scale  152  described earlier. In such a case, with a pair of XZ heads and a pair of YZ heads and an encoder system that these heads can face, position information of at least one of rotation (θz) and tilt (at least one of θx and θy) of a plurality of heads  66   x  and  66   y  may be measured. 
     Note that while a grating is formed (the surface is a grating surface) on the surface of scales  46 ,  52 ,  56 ,  152  and the like, for example, a cover member (such as glass or a thin film) that covers the grating may be provided so that the grating surface is provided inside the scale. 
     Note that in the description so far, while the case has been described in which the measurement direction within the XY plane of each head that the mask encoder system and the substrate encoder system are equipped with is the X-axis direction or the Y-axis direction, the embodiments are not limited to this, and in the case of the second to fourth embodiments, instead of the two-dimensional grating RG, a two-dimensional grating may be used that intersects in the X-axis direction and the Y-axis direction and also has periodic directions in two directions (called αdirection and β direction for convenience) orthogonal to each other, and corresponding to this, as each head described earlier, heads with measurement directions in the αdirection (and the Z-axis direction) or the β direction (and the Z-axis direction) may be used. Also, in the first embodiment described earlier, instead of each X scale and Y scale, for example, a one-dimensional grating whose periodic direction is in the αdirection or β direction may be used, and corresponding to this, as each head described earlier, heads with measurement directions in the αdirection (and the Z-axis direction) or the (direction (and the Z-axis direction) may be used. 
     Note that in the second to fourth embodiments described above, the first grating group may be structured by the row of X scales described earlier and the second grating group may be structured by the row of Y scales described earlier, and corresponding to this, a plurality of X heads (or XZ heads) that can face the X scales may be arranged at a predetermined spacing (spacing wider than the spacing between adjacent X scales) along with a plurality of Y heads (or YZ heads) that can face the Y scales being arranged at a predetermined spacing (spacing wider than the spacing between adjacent Y scales). 
     Note that in the first to fourth embodiments described above, as each scale arranged side by side in the X-axis direction or the Y-axis direction, a plurality of scales of different lengths may naturally be used. In this case, when two or more rows of scales having the same or orthogonal periodic directions are provided side by side, scales may be chosen with lengths that can be set so that the spacing between the scales do not overlap one another. That is, the arrangement spacing of the space between the scales structuring one row of scales does not have to be an equal spacing. 
     Note that in the first to fourth embodiments described above, while encoders for movable heads only have to measure position information of at least the movement direction (the Y-axis direction in the embodiments described above), the encoders may also measure position information of at least one direction (at least one of X, Z, θx, θy, and θz) different from the movement direction. For example, position information in the X-axis direction of a head (X head) whose measurement direction is in the X-axis direction may also be measured, and with this X information and measurement information of the X head, position information in the X-axis direction may be obtained. However, with the head (Y head) whose measurement direction is in the Y-axis direction, position information in the X-axis direction orthogonal to the measurement direction does not have to be used. Similarly, with the X head, position information in the Y-axis direction orthogonal to the measurement direction does not have to be used. In short, position information of substrate holder  34  in the measurement direction may be obtained, measuring position information in at least one direction different from the measurement direction of the heads, and by using this measurement information and measurement information of the heads. Also, for example, position information (rotation information) of the movable head in the θz direction may be measured using two measurement beams having different positions in the X-axis direction, and by using this rotation information with measurement information of the X head and the Y head, position information in the X-axis direction and the Y-axis direction may be obtained. In this case, by arranging two of one of the X heads and Y heads and one of the other of the X heads and Y heads so that the two heads having the same measurement direction are not arranged at the same position in the direction orthogonal to the measurement direction, position information in the X direction, the Y direction, and the θz direction can be measured. The other head preferably irradiates a position different from the two heads with the measurement beam. Moreover, if the heads of encoders for movable heads is an XZ head or a YZ head, by arranging, for example, two of one of the XZ heads and the YZ heads and the other of the XZ heads and the YZ heads so that the heads are not located on the same straight line, not only Z information but also position information (tilt information) in the θx direction and the θy direction can be measured. Position information in the X-axis direction and the Y-axis direction may be obtained by at least one of the position information in the θx direction and the θy direction and the measurement information of the X heads and Y heads. Similarly, with XZ heads or YZ heads, position information in a direction different from the Z-axis direction of the movable heads may also be measured, and position information in the Z-axis direction may be obtained with this measurement information and measurement information of the movable heads. 
     Note that when the scales of the encoders measuring the position information of the movable heads is a single scale (grating area), XYθz and Zθxθy may be measured by three heads, however, in the case a plurality of scales (grating areas) are arranged separately, two each of X heads and Y heads, or two each of XZ heads and YZ heads should be arranged and the spacing in the X-axis direction should be set so that the non-measurement period among the four heads do not overlap one another. While this explanation was made on the premise that the grating area is arranged parallel to the XY plane, this also can be applied similarly to a scale having a grating area parallel to the YZ plane. 
     Also, in the first to fourth embodiments described above, while the encoder was used as the measurement device for measuring position information of the movable heads, devices other than the encoder, such as, for example, an interferometer, a laser distance meter, or an ultrasonic range meter may also be used. In this case, for example, a reflection surface may be provided at the movable head (or its holding section) and a measurement beam parallel to the Y-axis direction should be irradiated on the reflection surface. Especially when the movable head is moved only in the Y-axis direction, the reflection surface does not have to be large, which makes it easy to locally air-condition the optical path of the interferometer beam to reduce air fluctuation. 
     Also, in the first to fourth embodiments described above, while the movable heads that irradiate the scales of the substrate holder with measurement beams are arranged one each in the Y-axis direction on both sides of the projection system, a plurality of movable heads may each be arranged. For example, if adjacent movable heads (measurement beams) are arranged so that the measurement period of a plurality of movable heads partly overlaps in the Y-axis direction, the plurality of movable heads can continue to measure position information even when the substrate holder moves in the Y-axis direction. In this case, linkage process becomes necessary among the plurality of movable heads. Therefore, measurement information of a plurality of heads arranged only on one side of the ±Y side of the projection system irradiating measurement beams on at least one scale may be used to acquire correction information related to another head whose measurement beam is within the scale, or measurement information of not only the heads arranged on only one side of the ±Y side but at least one head arranged on the other side may also be used. In short, of the plurality of heads each arranged on the ±Y side, measurement information of at least three heads irradiating measurement beams on the scale may preferably be used. 
     Also, with substrate encoder system  50  of the first to fourth embodiments described above, while a plurality of scales (grating areas) is arranged separately in the scanning direction (the X-axis direction) in which substrate P is moved on scanning exposure, along with a plurality of heads being movable in the stepping direction (the Y-axis direction), conversely, the plurality of scales may be arranged in the stepping direction (the Y-axis direction) along with the plurality of heads being movable in the scanning direction (the X-axis direction). 
     Also, in the first to fourth embodiments described above, the heads of mask encoder system  48  and encoder system  50  do not necessarily have to have the whole optical system that irradiates a scale with a beam from the light source, and may have a part of the light source, such as for example, only the light-emitting section. 
     Also, in the second to fourth embodiments described above, the heads of the pair of head units  60  are not limited to the arrangement in  FIG. 17  (X heads and Y heads are arranged on the ±Y sides, respectively, and the arrangement of the X head and Y head is opposite in the X-axis direction on one side and the other side of the ±Y sides), and for example, X heads and Y heads may be arranged on the ±Y sides, respectively, and on one side and the other side of the ±Y sides, the arrangement of the X head and Y head may be the same in the X-axis direction. However, in the case the X position of two Y heads is the same, when measurement of one of the two X heads is cut off, then the θz information can no longer be measured, therefore, the X position of the two Y heads should preferably be different. 
     Also, in the first to fourth embodiments described above, when the scales (scale members, grating section) irradiated with the measurement beams from the heads of the encoder system are provided at the projection optical system  16  side, the scales provided are not limited to only a part of apparatus main section  18  (frame member) supporting projection optical system  16 , and may be provided at the barrel part of projection optical system  16 . 
     Also, as is shown in  FIGS. 12A and 12B , the distance between the pairs of encoder heads that head unit  60  has (namely, each of the pair of X heads  64   x , the pair of X heads  66   x , the pair of Y heads  64   y , and the pair of Y heads  66   y ) may be measured with sensors  164  and  166 , and the output of substrate encoder system  50  may be corrected using the measurement values. While the type of sensors  164  and  166  is not limited in particular, a laser interferometer or the like can be used. In substrate encoder system  50 , while the linkage process of the outputs of the pair of encoder heads is performed as is described above, in this linkage process, the premise is that the spacing between the pair of encoder heads is known and is invariable. Therefore, while Y slide table  62  to which each of the heads is attached is formed of a material that is scarcely affected by thermal expansion or the like, as in the modified example, even if Y slide table  62  is deformed (spacing between the pair of encoder heads change) due to measuring the spacing between the encoder heads, position information of substrate P can be obtained with high precision. Similarly, also in mask encoder system  48 , the distance between the pair of encoder heads (namely, the pair of X heads  49   x  and the pair of Y heads  49   y ) may be calculated, and the output of mask encoder system  48  may be corrected using the measurement values. Also, relative positional relation may be measured for all heads (a total of eight heads in the embodiment) that head unit  60  has (the pair of heads  66   x  and the pair of heads  66   y  facing downward, and the pair of heads  64   x  and the pair of heads  64   y  facing upward), and the measurement values may be corrected. 
     Also, a calibration operation may be performed as appropriate (each time substrate exchange is performed) to measure the distance between the pairs of encoder heads that head unit  60  has (namely, each of the pair of X heads  64   x , the pair of X heads  66   x , the pair of Y heads  64   y , and the pair of Y heads  66   y ) may be calculated, as is described above. Also, aside from the calibration point for performing measurement of the spacing between the heads described above, a calibration point may be provided to perform origin positioning of the output of each of mask encoder system  48  and substrate encoder system  50 . The mark used for positioning on performing the origin positioning may be arranged on an extended line (outer side) of the plurality of scales  46  and  52 , or may be formed within scales  46  and  52 . 
     Also, tilt (tilt in the θx and θy directions) amount of Y slide table  62  to which each of the encoder heads  64   x ,  64   y ,  66   x , and  66   y  is attached with respect to the horizontal plane may be obtained, and the output of substrate encoder system  50  may be corrected according to the tilt amount (namely, inclining amount of the optical axis of each of the heads  64   x ,  64   y ,  66   x , and  66   y ). As the measurement system, as is shown in  FIG. 13A , a measurement system can be used in which a plurality of Z sensors  64   z  is attached to Y slide table  62 , and the tilt amount of Y slide table  62  is obtained with encoder base  54  (or upper mount section  18 A) serving as a reference. Z sensor  64   z  may be a laser interferometer, a TOF sensor, or a sensor used for measuring distance. Also, as is shown in  FIG. 13B , a two-axis laser interferometer  264  may be provided so that tilt amount of Y slide table  62  (amount of inclination in the θx and θy directions) and rotation amount (rotation amount in the θz direction) may be obtained. Also, tilt amount of each of the heads  64   x ,  64   y ,  66   x , and  66   y  may be measured individually, using a gyro sensor or the like. 
     Also, while encoder base  54  having the plurality of scales  56  was structured to be directly attached to the lower surface of upper mount section  18   a  (optical surface plate), the structure is not limited to this, and a predetermined base member may be arranged in a suspended manner in a state arranged separate to the lower surface of upper mount section  18   a , and encoder base  54  may be attached to the base member. 
     Also, substrate stage device  20  only has to drive at least substrate P along a horizontal plane in long strokes, and in some cases, does not have to perform fine positioning in directions of six degrees of freedom. The substrate encoder system according to each of the embodiments described above can be suitably applied, even to such a two-dimensional stage device. 
     Also, while the linkage process of heads in the first embodiment described above was performed using the output (measurement information) itself of the heads, the embodiment is not limited to this, and the linkage process may be performed using position information of the measurement target (mask stage  40 , head unit  60 , substrate holder  34 ) obtained based on the output of the heads. 
     Also, in the embodiment above, while the two rows of scales were formed by the plurality of scales  46  provided on one side and the other side of mask M in the Y-axis direction, the embodiment is not limited to this, and the row of scales may be a single row (a structure in which scales  46  are provided only on one side of mask M in the Y-axis direction). In this case, while only one head unit  44  has to be provided, the number and arrangement of the plurality of heads that the one head unit  44  has should be set so that even when a measurement beam from a part of the plurality of heads moves off of the scales, at least three heads of the remaining heads constantly face the scales. Also, each of the heads should be arranged so that in the at least three heads, a head whose measurement direction is different is included (so that two X heads and one Y head, or one X head and two Y heads constantly face the scales). Similarly with substrate holder  34 , the row of scales may be a single row. In this case, only one head unit  60  has to be provided, corresponding to the single row of scales. Specifically, in  FIG. 18 , a structure may be employed in which five scales  152  are arranged at a predetermined spacing in the X-axis direction only on the +Y side of substrate P, along with all heads  66   a  to  66   e  fixed to one head unit  60  arranged above scales  152  so that all the heads can face scales  152 . 
     Also, while mask stage device  14  in the embodiment described above employed a structure of moving in long strokes only in the X-axis direction, the embodiment is not limited to this, and the stage device may be structured to move also in predetermined long strokes in the Y-axis direction, along with the X-axis direction. In this case, similarly to head unit  60  (refer to  FIG. 4A  and the like) used for position measurement of the substrate, head unit  44  (refer to  FIG. 2B ) is preferably structured so that head unit  44  can move synchronously with mask holder  40  in the Y-axis direction so that the measurement beams from heads  49   x  and  49   y  do not move off from the corresponding scales  47   x  and  47   y . In this case, position information of head unit  44  within the XY plane should be measured by an encoder system having a structure (including linkage process of heads between scales) similar to the position measurement system of head unit  60 . 
     Also, in the embodiment described above, while scales  52  extending in the X-axis direction were fixed to substrate holder  34  and scales  56  extending in the Y-axis direction were fixed to encoder base  54 , the directions may be opposite. Specifically, an example is given in which a structure may be employed where scales extending in the Y-axis direction are fixed to substrate holder  34 , and head unit  60  moves in long strokes in the X-axis direction synchronously with substrate holder  34  at the time of scanning operation. In this case, at the time of Y stepping operation of substrate holder  34 , head unit  60  is to be in a stationary state. 
     Also, in the embodiment described above, while the structure of providing scales  52  on substrate holder  34  is employed, the scales may be formed directly on substrate P on exposure processing. For example, the scales may be formed on scribe lines between shot areas. This allows measurement of scales formed on the substrate to be performed, and based on the results of position measurement, nonlinear component errors for each of the shot areas on the substrate can be obtained, and overlay accuracy upon exposure can also be improved, based on the errors. 
     Also, in the embodiment described above, while there is a case when head unit  60  is described to move synchronously with substrate holder  34 , this means that head unit  60  is moved in a state where relative positional relation with respect to substrate holder  34  is basically maintained, and is not limited to the case in which head unit  60  and substrate holder  34  are moved in a state where positional relation, movement direction, and movement speed between head unit  60  and substrate holder  34  are strictly coincident. 
     Also, in substrate encoder system  50  according to each of the embodiments, scales used for substrate exchange may be provided at substrate stage device  20  or at another stage device to acquire position information of substrate stage device  20  moving to a substrate exchange position between the substrate loader, and heads facing downward (such as X head  66   x ) may be used to acquire position information of substrate stage device  20 . Also, heads facing upward (such as X head  64   x ) may be used to measure scales used for substrate exchange provided at encoder base  54  and to acquire position information of substrate stage device  20 . Or, position information of substrate stage device  20  may be acquired by providing heads used for substrate exchange at substrate stage device  20  or another stage device and measuring scales  56  or the scales used for substrate exchange. Note that the heads used for substrate exchange may be provided movable or fixed, with respect to substrate stage device  20  or to the another stage device. 
     Also, in mask encoder system  48  according to each of the embodiments, scales used for mask exchange may be provided at mask stage device  14  or at another stage device to acquire position information of mask stage device  14  moving to a mask exchange position between the mask loader, and head unit  44  may be used to acquire position information of mask stage device  14 . 
     Note that in the first to fourth embodiments described above, while the substrate position measurement system was structured with Z-tilt position measurement system  98  and substrate encoder system  50 , for example, the substrate position measurement system may be structured only by substrate encoder system  50  by using XZ, YZ heads instead of X, Y heads. 
     Also, in the first to fourth embodiments described above, separately from the pair of head units  60  of substrate encoder system  50 , at least one head arranged away from head unit  60  in the X-axis direction may be provided. For example, movable head units the same as each of the head units  60  may be provided at the ±Y side with respect to the mark detection system (alignment system) arranged apart from projection optical system  16  in the X-axis direction that detects alignment marks of substrate P, and in the detection operation of substrate marks, position information of substrate holder  34  may be measured using the pair of head units arranged at the ±Y side of the mark detection system. In this case, it becomes possible to continue measurement of position information of substrate holder  34  by substrate encoder system  50  (another pair of head units), even if all measurement beams from the pair of head units  60  move off of scales  152  in the mark detection operation, and the degree of freedom on designing the exposure apparatus, such as the position of the mark detection system, can be increased. Note that by arranging the substrate position measurement system for measuring position information of substrate P in the Z-axis direction near the mark detection system, measurement of position information of substrate holder  34  by substrate encoder system  50  becomes possible also in the detection operation of the Z position of the substrate. Or, the substrate position measurement system may be arranged near projection optical system  16 , and position information of substrate holder  34  may be measured with the pair of head units  60  in the detection operation of the Z position of the substrate. Also, in the embodiment, when substrate holder  34  is arranged at a substrate exchange position set away from projection optical system  16 , the measurement beams of all heads of the pair of head units  60  move off of scales  152 . Therefore, at least one head facing at least one scale of the plurality of scales  152  of substrate holder  34  arranged at the substrate exchange position may be provided, and position information of substrate holder  34  can be measured by substrate encoder system  50  also on the substrate exchange operation. Here, before substrate holder  34  reaches the substrate exchange position, or in other words, in the case the measurement beams of all heads of the pair of head units  60  move off of scales  152  before at least one head arranged at the substrate exchange position faces scale  152 , at least one head may be added and arranged along the moving route of substrate holder  34  so that measurement of position information of substrate holder  34  by substrate encoder system  50  can be continued. Note that in the case of using the at least one head provided separately from the pair of head units  60 , the linkage process described earlier may be performed using the measurement information of the pair of head units  60 . Also, the position of the at least one head facing at least one scale of the plurality of scales  152  of substrate holder  34  arranged at the substrate exchange position described above may be fixed (a fixed type head), or may be provided movable (a movable type head) so that the measurement beam does not move off of the scale similarly to each of the embodiments described above. 
     Also, the illumination light may be an ultraviolet light such as an ArF excimer laser beam (wavelength 193 nm) or a KrF excimer laser beam (wavelength 248 nm), or a vacuum ultraviolet light such as an F2 laser beam (wavelength 157 nm). Also, as the illumination light, a harmonic wave may be used, which is a single-wavelength laser beam in the infrared or visual region oscillated from a DFB semiconductor laser or a fiber laser as vacuum ultraviolet light that is amplified by a fiber amplifier doped by, e.g. erbium (or both erbium and ytterbium), and then is subject to wavelength conversion into ultraviolet light using a nonlinear crystal. Also, a solid laser (wavelengths: 355 nm, 266 nm) may also be used. 
     Also, while the case has been described where projection optical system  16  is a projection optical system of a multiple lens method equipped with a plurality of optical systems, the number of projection optical systems is not limited to this, and one or more will be fine. Also, the projection optical system is not limited to the projection optical system of a multiple lens method, and may also be an Offner type projection optical system which uses a large mirror. Also, as projection optical system  16 , a magnifying system or a reduction system may also be used. 
     Also, the exposure apparatus is not limited to the exposure apparatus for liquid crystals which transfers the liquid crystal display device pattern onto a square-shaped glass plate, and may also be widely applied to an exposure apparatus for manufacturing organic EL (Electro-Luminescence) panels, an exposure apparatus for manufacturing semiconductors, or to an exposure apparatus for manufacturing thin film magnetic heads, micromachines, and DNA chips. Also, the above embodiments can be applied not only to an exposure apparatus for manufacturing microdevices such as semiconductors, but also to an exposure apparatus that transfers a circuit pattern onto a glass substrate or a silicon wafer to manufacture a reticle or a mask used in an optical exposure apparatus, an EUV exposure apparatus, an X-ray exposure apparatus, and an electron-beam exposure apparatus. 
     Also, the object subject to exposure is not limited to a glass plate, and may also be other objects such as a wafer, a ceramic substrate, a film member, or a mask blanks. Also, in the case the exposure object is a substrate for a flat panel display, the thickness of the substrate is not limited in particular, and includes a film-like substrate (a sheet-like member having flexibility). Note that the exposure apparatus of the embodiment is especially effective in the case when the exposure object is a substrate whose length of a side or diagonal length is 500 mm or more. 
     Electronic devices such as liquid crystal display devices (or semiconductor devices) are manufactured through the steps such as; a step for performing function/performance design of a device, a step for making a mask (or a reticle) on the basis of this design step, a step for making a glass substrate (or a wafer), a lithography step for transferring a pattern of a mask (reticle) onto the glass substrate by the exposure apparatus and the exposure method described in each of the above embodiments, a development step for developing the glass substrate which has been exposed, an etching step for removing by etching an exposed member of an area other than the area where the resist remains, a resist removing step for removing the resist that is no longer necessary since etching has been completed, a device assembly step, and an inspection step. In this case, in the lithography step, because the device pattern is formed on the glass substrate by carrying out the exposure method previously described using the exposure apparatus of the embodiments described above, a highly integrated device can be manufactured with good productivity. 
     Note that the disclosures of U.S. Patent Application Publications and U.S. Patents related to the exposure apparatus and the like quoted in each of the embodiments above, in their entirety, are incorporated herein by reference as a part of the present specification. 
     INDUSTRIAL APPLICABILITY 
     As is described so far, the exposure apparatus and the exposure method of the present invention is suitable for performing exposure by irradiating and object with an illumination light in a lithography process. Also, the flat panel display manufacturing method of the present invention is suitable for producing flat panel displays. 
     REFERENCE SIGNS LIST 
     
         
           10  . . . liquid crystal exposure apparatus, 
           14  . . . mask stage device, 
           20  . . . substrate stage device, 
           34  . . . substrate holder, 
           40  . . . mask holder, 
           44  . . . head unit, 
           46  . . . scale, 
           48  . . . mask encoder system, 
           50  . . . substrate encoder system, 
           52  . . . scale, 
           56  . . . scale, 
           60  . . . head unit, 
           90  . . . main controller, 
         M . . . mask, 
         P . . . substrate.