Abstract:
An exposure method for manufacturing a liquid crystal display utilizes a scanning exposure apparatus to expose a pattern of a mask onto a glass plate. The exposure method includes a step of moving a mask stage that holds the mask in a scanning direction by a first electromagnetic actuator. The first electromagnetic actuator moves the mask stage associating with a guide member that extends in the scanning direction. The method also includes the step of moving the mask stage in a non-scanning direction different from the scanning direction by a second electromagnetic actuator. The second electromagnetic actuator moves the mask stage associating with no guide member, and a moving distance in the non-scanning direction by the second electromagnetic actuator is shorter than a moving distance in the scanning direction by the first electromagnetic actuator.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a stage unit having a means for limiting the moving range of a moving table on which a target positioning object is mounted, a drive table driven by a linear motor and capable of easily performing origin detection, and a scanning exposure apparatus for manufacturing semiconductor elements or the like by using the same.  
         [0003]     2. Related Background Art  
         [0004]     To manufacture semiconductor elements, liquid crystal display elements, or the like by using the photolithography technique, a projection exposure apparatus is conventionally used, in which a pattern formed on a reticle (or a photomask) is exposed, through a projection optical system, onto a wafer (or a glass plate) coated with a photoresist.  
         [0005]     In recent years, one chip pattern of a semiconductor element or the like tends to become larger. For this reason, a projection exposure apparatus for exposing a pattern on a reticle, which has a larger size, onto a wafer is required. To meet such a requirement for increasing the exposure area with a so-called step and repeat type projection exposure apparatus for performing full exposure of the entire pattern on the reticle, the projection optical system must be made larger. However, this results in an increase in manufacturing cost of a projection optical system having high imaging performance on the entire surface of the wide exposure field.  
         [0006]     Therefore, a so-called step and scan type scanning exposure apparatus has received a great deal of attention. In this apparatus, after each shot area of the wafer is moved to the scan start position, the reticle, which is being illuminated, is scanned in a direction crossing the optical axis of the projection optical system. In synchronism with this scanning, the wafer is scanned in the direction crossing the optical axis of the projection optical system, thereby exposing the pattern of the reticle onto each shot area of the wafer.  
       SUMMARY OF THE INVENTION  
       [0007]     According to the present invention, there is provided a stage unit arranged in a scanning exposure apparatus which illuminates a mask on which a transfer pattern is formed, scans the mask in the first direction (Y direction or −Y direction) as a predetermined scanning direction, and synchronously scans a photosensitive substrate in a direction corresponding to the scanning direction, thereby sequentially exposing the pattern of the mask onto the photosensitive substrate, comprising a base, a scanning stage arranged to be freely moved in the first direction on the base, a fine adjustment stage, arranged to be freely moved, with respect to the scanning stage, within predetermined ranges in the first direction of a target scanning object and a second direction perpendicular to the first direction, for mounting the target scanning object thereon, a first electromagnetic actuator for driving the fine adjustment stage in the second direction with respect to the scanning stage, and a second electromagnetic actuator for driving the fine adjustment stage in the first direction with respect to the scanning stage with a larger thrust than that of the first electromagnetic actuator.  
         [0008]     In this case, as each of the first and second electromagnetic actuators, an electromagnetic actuator of a moving magnet type in which a stationary member having a coil is fixed on the scanning stage side is used. Cooling means for cooling the stationary member of each of the first and second electromagnetic actuators by circulating a predetermined cooling fluid is preferably arranged.  
         [0009]     In addition, a movable mirror fixed on the fine adjustment stage, and an interferometer for irradiating a measurement light beam on the movable mirror to detect a displacement of the fine adjustment stage with respect to the scanning stage are provided. The cooling means preferably circulates the cooling fluid from a portion near an optical path of the light beam from the interferometer.  
         [0010]     Furthermore, one of the first and second electromagnetic actuators is preferably constituted by a pair of electromagnetic actuators which are parallelly arranged.  
         [0011]     In the scanning exposure apparatus, a large inertial force in the first direction as the scanning direction is applied to the fine adjustment stage particularly at the start and end of scanning. According to the stage unit of the present invention, however, an actuator having a small thrust is used as the electromagnetic actuator for driving the fine adjustment stage in the second direction (X direction or −X direction) because the inertial force applied to the fine adjustment stage in the second direction which is not the scanning direction can be almost neglected. With this arrangement, the shape and weight of the movable member of the electromagnetic actuator can be reduced. For this reason, the overall weight of the fine adjustment stage is reduced, thereby improving the control performance of the stage. In addition, the capacity of the coil of the electromagnetic actuator in the second direction can also be reduced. Since a heat generation amount from the coil is also decreased, heat deformation of each stage is minimized, thereby minimizing the adverse influence of heat to the measurement equipment for position measurement.  
         [0012]     When each of the first and second electromagnetic actuators is an electromagnetic actuator of a moving magnet type, and the cooling means for cooling the stationary member of each of the first and second electromagnetic actuators by circulating the predetermined cooling liquid is arranged, the fine adjustment stage is separated from the coil as a heat source. For this reason, the heat deformation of the fine adjustment stage can be minimized as compared to a case wherein an electromagnetic actuator of a moving coil type is used.  
         [0013]     When the stationary member as a heat source is liquid-cooled, the total heat generation amount is minimized. It is mechanically easy to cool the stationary member in this manner.  
         [0014]     The movable mirror fixed on the fine adjustment stage, and the interferometer for irradiating the measurement light beam on the movable mirror to detect the displacement of the fine adjustment stage with respect to the scanning stage are arranged, and the cooling fluid is circulated from the portion near the optical path of the light beam from the interferometer. In this case, when the cooling fluid has the largest cooling capability, the electromagnetic actuators are sequentially cooled from the portion near the optical path. For this reason, temperature adjustment of a gas on the optical path is stably performed, thereby maintaining a high measurement precision.  
         [0015]     When one of the first and second electromagnetic actuators is constituted by a pair of electromagnetic actuators which are parallelly arranged, driving in the rotational direction is enabled by applying thrusts to the pair of electromagnetic actuators in opposite directions.  
         [0016]     According to the present invention, there is provided a stage unit comprising a moving table for mounting a target positioning object thereon, a base for mounting the moving table thereon to be freely moved in a predetermined direction, driving means for driving the moving table in the predetermined direction with respect to the base, switch means for stopping an operation of the driving means when the moving table moves beyond an allowable movement range in the predetermined direction, and push-back means for generating a biasing force for pushing back the moving table to the allowable movement range side before the switch means operates.  
         [0017]     In this case, the biasing force of the push-back means is preferably larger than the frictional force between the moving table and the base. At the same time, the biasing force is preferably a force within a range smaller than that of the driving force in the normal operation of the driving means.  
         [0018]     An elastic member is used as an example of the push-back means.  
         [0019]     A linear motor is used as an example of the driving means.  
         [0020]     According to the present invention, when the moving table moves beyond the allowable movement range because of runaway and comes close to the switch means, the push-back means starts to apply the biasing force to the moving table to the allowable movement range side. When the moving table further moves, the switch means operates to stop the operation of the driving means. More specifically, the driving force of the driving means to the moving table is eliminated, and the moving table is stopped.  
         [0021]     Even in this state, the push-back means is operating. Since the push-back means has a biasing force larger than the frictional force between the moving table and the base, the moving table is pushed back to the allowable movement range side. The switch means is set in an inoperative state, and driving of the moving table by the driving means is enabled. When, e.g., the control system of the driving means shifts to an error sequence upon operation of the switch means, and the driving means is driven upon completion of error processing, runaway of the moving table to the switch means side is prevented.  
         [0022]     When the push-back means has an elastic member such as a coil spring or a rubber member, the biasing force can be generated by the elastic member with a simple arrangement without particularly adding a power source or the like.  
         [0023]     When the driving means is constituted by a linear motor, and the switch means operates to stop supplying the driving power to the linear motor, the linear motor has no driving force at all. Therefore, only the frictional force and the biasing force from the push-back means act on the moving table, thereby easily pushing back the moving table to the allowable movement range side.  
         [0024]     According to the present invention, there is provided a drive table comprising a driving system for two-dimensionally moving a table along an X direction and a Y direction, which are perpendicular to each other, X position detection means for detecting a position of the table along the X direction, Y position detection means for detecting the position of the table along the Y direction, θ detection means for detecting a rotation amount θ about θ axis perpendicular to the X and Y directions of the table, X reference position detection means for detecting that a predetermined first position on the table reaches a predetermined X reference position on an X reference coordinate axis, Y reference position detection means for detecting that a predetermined second position on the table reaches a predetermined Y reference position on a Y reference coordinate axis, θ reference position detection means for detecting that a predetermined third position on the table reaches a predetermined θ reference position on another X or Y reference coordinate axis, and a calculation unit for converting detection values from the X position detection means, the Y position detection means, and the θ detection means into coordinate values on an X-Y reference coordinate plane on the basis of detection signals obtained from the X reference position detection means, the Y reference position detection means, and the θ reference position detection means and detection values from the X position detection means, the Y position detection means, and the θ detection means, which are obtained upon generation of the detection signals.  
         [0025]     The driving system is preferably a non-contact type driving unit.  
         [0026]     It is preferable that the X reference position detection means have an X position detection light-shielding plate arranged at the predetermined first position on the table, and an X reference position detection sensor, arranged at the predetermined X reference position, for generating a signal when the light-shielding plate reaches the X reference position, the Y reference position detection means have a Y position detection light-shielding plate arranged at the predetermined second position on the table, and a Y reference position detection sensor, arranged at the predetermined Y reference position, for generating a signal when the light-shielding plate reaches the Y reference position, the θ reference position detection means have a θ position detection light-shielding plate arranged at the predetermined third position on the table, and a θ reference position detection sensor, arranged at the predetermined θ reference position, for generating a signal when the light-shielding plate reaches the θ reference position, and the calculation means include reference rotation amount calculation means for obtaining a reference rotation amount about an axis perpendicular to the X-Y reference coordinate plane of the table from a shift between a detection signals from the θ reference position detection sensor and a detection signal from the X reference position detection means or the Y reference position detection means.  
         [0027]     It is preferable that the X reference position detection means have X direction driving means for pressing an X direction side edge of the table against an X reference stopper provided on the reference coordinate axis in advance, and X press detection means for detecting that the X direction side edge is pressed against the X reference stopper, the Y reference position detection means have Y direction driving means for pressing a Y direction side edge of the table against a Y reference stopper provided on the reference coordinate axis in advance, and Y press detection means for detecting that the Y direction side edge is pressed against the Y reference stopper, the θ reference position detection means have θ direction driving means for pressing the X or Y direction side edge of the table against a θ reference stopper provided to be separated from the X or Y reference stopper on the reference coordinate axis by a predetermined distance, and θ press detection means for detecting that the X or Y direction side edge is pressed against the θ reference stopper, and the calculation means include rotation amount reset means for setting a detection value from rotation amount detection means to a reference rotation amount in accordance with a detection signal from the θ press detection means and a detection signal from the X or Y press detection means.  
         [0028]     The drive table of the present invention has the reference position detection means for detecting that the predetermined positions on the table reach the predetermined reference positions on the reference coordinate axes for the three displacements, displacements in the X and Y directions of the table, and the rotation amount θ about the θ axis perpendicular to the X and Y directions, and the calculation means for converting the detection values from the position detection means, which are obtained upon generation of the detection signals obtained from the reference position detection means into the coordinate values on the reference coordinates. For this reason, origin detection with respect to the reference coordinate axes of the drive table can be precisely performed.  
         [0029]     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.  
         [0030]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a view schematically showing the arrangement of a scanning exposure apparatus;  
         [0032]      FIG. 2  is a perspective View for explaining synchronous scanning in the scanning exposure apparatus shown in  FIG. 1 ;  
         [0033]      FIG. 3  is a plan view showing a reticle stage;  
         [0034]      FIG. 4  is a front view of the reticle stage shown in  FIG. 3 ;  
         [0035]      FIG. 5  is a plan view showing an embodiment of a stage unit according to the present invention;  
         [0036]      FIG. 6  is a front view of the stage unit shown in  FIG. 5 ;  
         [0037]      FIG. 7  is a sectional view of an electromagnetic actuator shown in  FIG. 6 ;  
         [0038]      FIG. 8  is a plan view showing a reticle stage as an embodiment of the stage unit according to the present invention;  
         [0039]      FIG. 9  is a front view of the reticle stage shown in  FIG. 8 ;  
         [0040]      FIG. 10  is an enlarged plan view showing a limit switch shown in  FIG. 8 ;  
         [0041]      FIG. 11  is a front view of the limit switch shown in  FIG. 10 ;  
         [0042]      FIG. 12  is a front view showing the closed state of a microswitch;  
         [0043]      FIG. 13  is an enlarged view of the main part so as to explain the relationship between a reference plate and an origin sensor shown in  FIG. 8 ;  
         [0044]      FIG. 14  is an enlarged plan view showing the first modification of the limit switch shown in  FIG. 10 ;  
         [0045]      FIG. 15  is a partially cutaway front view of the limit switch shown in  FIG. 14 ;  
         [0046]      FIG. 16  is an enlarged plan view showing the second modification of the limit switch shown in  FIG. 10 ;  
         [0047]      FIG. 17  is a front view of the limit switch shown in  FIG. 16 ;  
         [0048]      FIG. 18  is a plan view schematically showing the arrangement of a drive table;  
         [0049]      FIG. 19  is a plan view showing the arrangement of an embodiment of the drive table according to the present invention;  
         [0050]      FIG. 20  is a plan view showing an origin detection method in the drive table shown in  FIG. 19 ; and  
         [0051]      FIG. 21  is a plan view showing another origin detection method in the drive table shown in  FIG. 19 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0052]      FIG. 1  is a view schematically showing the arrangement of a scanning exposure apparatus. Referring to  FIG. 1 , an illumination light beam IL from an optical integrator (not shown) in an illumination optical system illuminates a field stop  2  through a first relay lens  1 . The illumination light beam passing through the slit-like opening of the field stop  2  illuminates a slit-like illumination area  7  on a reticle  6  at a uniform illuminance through a second relay lens  3 , a mirror  4  for deflecting the optical path, and an illumination condenser lens  5 . The arrangement surface of the field stop  2  is conjugate with the pattern formation surface of the reticle  6 . The projected image of the rectangular opening formed in the field stop  2  and having a width d s  of the short side corresponds to the slit-like illumination area  7 .  
         [0053]     The pattern image of the reticle  6  in the illumination area  7  is formed and projected in a slit-like exposure area  18  on a wafer  17  through a projection optical system  14  which is telecentric on both the sides (or telecentric on one side). The Z axis is set parallel to the optical axis of the projection optical system  14 . The X axis is set perpendicular to the sheet surface of  FIG. 1  in a plane perpendicular to the Z axis. The Y axis is set parallel to the sheet surface of  FIG. 1 . The scanning direction is parallel to the Y axis.  
         [0054]     The reticle  6  is held on a fine adjustment stage  8 . The fine adjustment stage  8  is movably and rotatably mounted on a scanning stage  9  in the X-Y plane. The scanning stage  9  is mounted on a reticle base  10  so as to be driven by a linear motor (not shown) in the Y direction (or in the −Y direction) as the scanning direction. The coordinate values of the fine adjustment stage  8  along the Y and X directions, which are measured by a movable mirror  11  fixed at the end portion on the fine adjustment stage  8  and a laser interferometer  12  arranged outside, are supplied to a main control system  13 . The main control system  13  controls the position of the fine adjustment stage  8  and the scanning speed of the scanning stage  9  on the basis of the supplied coordinate values.  
         [0055]     On the other hand, the wafer  17  is mounted on an X stage  20  through a wafer holder  19 . The X stage  20  is mounted on a Y stage  21  so as to be freely driven by a driving motor  27  in the X direction. The Y stage  21  is mounted on a unit base  22  so as to be freely driven by a driving motor  25  and a feed screw  26  in the Y direction. A Z stage for adjusting the portion of the wafer  17  along the Z direction, a leveling stage (not shown) for adjusting the inclination angle of the wafer  17 , and the like are mounted on the X stage  20 . The two-dimensional coordinate values of the X stage  20 , which are measured by a movable mirror  23  fixed on the X stage  20  and a laser interferometer  24  arranged outside, are supplied to the main control system  13 . The main control system  13  controls the operations of the driving motors  25  and  27  on the basis of the supplied coordinate values.  
         [0056]     In scanning exposure, when the projection magnification of the projection optical system  14  is defined as β, the scanning stage  9  on the reticle side is scanned in a direction indicated by an arrow B 1  at a speed V R  under the control of the main control system  13 . In synchronism with this scanning, the Y stage  21  on the wafer side is scanned in a direction indicated by an arrow C 1  at a speed V W  (=β·V R ), thereby sequentially projecting and exposing the pattern image of the reticle  6  onto the wafer  17 .  
         [0057]      FIG. 2  is a perspective view showing synchronous scanning. Referring to  FIG. 2 , a pattern area  15  of the reticle  6  is scanned in the direction indicated by the arrow B 1  with respect to the hatched slit-like illumination area  7 . In synchronism with this scanning, a shot area  16  of the wafer  17  is scanned in the direction indicated by the arrow C 1  with respect to the hatched exposure area  18 . With this operation, the pattern image in the pattern area  15  of the reticle  6  is sequentially exposed onto the shot area  16 .  
         [0058]      FIG. 3  is a plan view of the reticle stage in  FIG. 1 .  FIG. 4  is a side view of the reticle stage. As shown in  FIG. 3 , the scanning stage  9  is mounted to be moved in the Y direction along linear guides  34 A and  34 B on the reticle base  10 , which are parallel to the Y axis. A first linear motor  31 A is constituted by a stationary member  33 A and a movable member  32 A while a second linear motor  31 B is constituted by a stationary member  33 B and a movable member  32 B. The stationary members  33 A and  33 B are fixed on the reticle base  10  to be parallel to the linear guides  34 A and  34 B. The movable members  32 A and  32 B are fixed to the scanning stage  9  along the stationary members  33 A and  33 B. The scanning stage  9  is driven by the two linear motors  31 A and  31 B in the +Y or −Y direction with respect to the reticle base  10 .  
         [0059]     As shown in  FIG. 4 , the fine adjustment stage  8  is mounted on the scanning stage  9 . The fine adjustment stage  8  can be finely moved by a driving system (not shown) in the X and Y directions with respect to the scanning stage  9  and also can be finely rotated in the θ direction on the scanning stage  9 .  
         [0060]     As for a method of driving the fine adjustment stage of this type, three mechanical systems for converting the rotational movement of a servo motor into a linear movement are used, and the fine adjustment stage is moved by the three mechanical systems in the X, Y, and θ directions.  
         [0061]     A system using an electromagnetic actuator is also proposed as a two-dimensional stage driving system (e.g., Japanese Patent Laid-Open No. 2-35709). In this system, thrusts in the two driving directions are equal to each other. Additionally, the system is heavy, and no countermeasure is made against deformation due to heat generation.  
         [0062]     In the fine adjustment stage using such an electromagnetic actuator, the thrusts and shapes of two electromagnetic actuators for moving the fine adjustment stage in the two directions are equal regardless of the driving directions. Particularly, although the scanning exposure apparatus requires a smaller thrust to move the fine adjustment stage in a direction perpendicular to the scanning direction than in the scanning direction, an electromagnetic actuator having an excessive thrust is used. Therefore, the fine adjustment stage becomes heavy, and the heat generation amount also increases.  
         [0063]     When the fine adjustment stage becomes heavy, the natural frequency becomes lower, so the response speed cannot be increased. In addition, the fine adjustment stage is deformed due to heat generation of the coil of the electromagnetic actuator, resulting in a degradation in accuracy of the reticle holding surface or the reflecting mirror holding surface. Furthermore, heat generation of the coil degrades the measurement precision of the measurement system such as an interferometer for detecting the position of the fine adjustment stage. For example, when an interferometer is used, heat generation of the coil causes an increase in ambient temperature, which causes variations or fluctuations in temperature of air on the optical path of the interferometer, resulting in an error in measurement value.  
       First Embodiment  
       [0064]     The first embodiment associated with a stage unit according to the present invention will be described below with reference to FIGS.  5  to  7 . In this embodiment, the present invention is applied to the reticle stage of a step and scan type projection exposure apparatus. The same reference numerals as in FIGS.  1  to  4  denote the same parts in FIGS.  5  to  7 , and a detailed description thereof will be omitted.  
         [0065]      FIG. 5  is a plan view of the reticle stage of this embodiment. Referring to  FIG. 5 , a scanning stage  9  is mounted on a base  10  to be slidable in the Y direction along linear guides  34 A and  34 B. The scanning stage  9  is driven by linear motors  31 A and  31 B in the +Y or −Y direction with respect to the reticle base  10 . A Y axis movable mirror  45  is fixed at the end portion of the scanning stage  9  in the Y direction. A laser beam from an external laser interferometer  44  is irradiated on the movable mirror  45  to be parallel to the Y axis, as indicated by an optical path  46 . The Y coordinate of the scanning stage  9  is obtained from the measurement value from the laser interferometer  44 .  
         [0066]     A fine adjustment stage  8  is mounted on the scanning stage  9  to be finely moved by a driving system (to be described later) in the X and Y directions and in the rotational direction (θ direction). A reticle  6  ( FIG. 6 ) having an original pattern is held, by, e.g., vacuum suction, on the fine adjustment stage  8  having an opening (not shown) at the central portion. An exposure illumination light beam from an illumination optical system (not shown) is irradiated on a slit-like illumination area in the pattern formation area on the lower surface of the reticle. In scanning exposure, the reticle is scanned through the scanning stage  9  at a predetermined speed in the +Y or −Y direction as the widthwise direction of the illumination area. Position adjustment is performed by the fine adjustment stage  8  as needed.  
         [0067]     Y axis movable mirrors  48 A and  48 B are fixed at the end portion of the fine adjustment stage  8  in the Y direction. Laser beams from external laser interferometers  47 A and  47 B are irradiated on the movable mirrors  48 A and  48 B to be parallel to the Y axis, as indicated by optical paths  49 A and  49 B. The Y coordinate of the fine adjustment stage  8  is obtained from the average value of the measurement values from the interferometers  47 A and  47 B. The rotation angle of the fine adjustment stage  8  is obtained from the difference between the measurement values from the interferometers  47 A and  47 B. An X axis movable mirror  51  is fixed at the end portion of the fine adjustment stage  8  in the X direction. A laser beam from an external laser interferometer  50  is irradiated on the movable mirror  51  to be parallel to the X axis, as indicated by an optical path  52 . The X coordinate of the fine adjustment stage  8  is obtained from the measurement value from the laser interferometer  50 . The position of the scanning stage  9  along the Y direction and the scanning speed are controlled on the basis of the X coordinate, the Y coordinate, and the rotation angle, which are obtained in the above manner, and the position and the rotation angle of the fine adjustment stage  8  are simultaneously controlled.  
         [0068]     As shown in  FIG. 6 , a plurality of spherical rollers (only rollers  43 A and  43 B are illustrated in  FIG. 6 ). are arranged between the fine adjustment stage  8  and the scanning stage  9 . The fine adjustment stage  8  is smoothly moved on the plane of the scanning stage  9  through these rollers  43 A and  43 B.  
         [0069]     The driving system of the fine adjustment stage  8  will be described below in detail.  
         [0070]     As shown in  FIGS. 5 and 6 , electromagnetic actuators  39 A and  39 B each constituted by a moving magnet type (MM type) linear motor for mainly driving the fine adjustment stage  8  in the Y direction as the scanning direction in scanning exposure are provided on the side surfaces of the fine adjustment stage  8  in the +X and −X directions, respectively. The electromagnetic actuator  39 A is constituted by a movable member  37 A fixed on the side surface of the fine adjustment stage  8  in the +X direction and a stationary member  38 A fixed to the scanning stage  9 . When a current flows through the stationary member  38 A incorporating a coil, a linear force is applied to the movable member  37 A incorporating a magnet, thereby moving the movable member  37 A in the Y or −Y direction. When the current inversely flows, the moving direction is reversed. All electromagnetic actuators used to drive the fine adjustment stage  8  in this embodiment are MM type linear motors and similarly operate.  
         [0071]     The fine adjustment stage  8  is driven in the +Y, the −Y, or the rotational direction by the electromagnetic actuator  39 B constituted by a movable member  37 B fixed on the side surface of the fine adjustment stage  8  in the −X direction and a stationary member  38 B fixed to the scanning stage  9 , and the above electromagnetic actuator  39 A. Driving in the rotational direction is performed within a range not to bring the movable members  37 A and  37 B into contact with the stationary members  38 A and  38 B.  
         [0072]     Electromagnetic actuators  42 A and  42 B for mainly driving the fine adjustment stage  8  in the X direction as a direction perpendicular to the scanning direction are arranged on the side surfaces of the fine adjustment stage  8  in the −Y and +Y directions, respectively. The electromagnetic actuator  42 A is constituted by a movable member  40 A fixed on the side surface of the fine adjustment stage  8  in the −Y direction and a stationary member  41 A fixed to the scanning stage  9 . The electromagnetic actuator  42 B is constituted by a movable member  40 B fixed on the side surface of the fine adjustment stage  8  in the +Y direction and a stationary member  41 B fixed to the scanning stage  9 . The fine adjustment stage  8  is driven by the electromagnetic actuators  42 A and  42 B in the +X, the −X, or the rotational direction.  
         [0073]     Both of the electromagnetic actuators  42 A and  42 B have a thrust smaller than that of the electromagnetic actuators  39 A and  39 B used for the scanning direction.  
         [0074]     The operations of the electromagnetic actuators and the fine adjustment stage  8  will be briefly described below. While the scanning stage  9  is moving in the scanning direction at a constant speed, the fine adjustment stage  8  can be driven in the X direction by applying a thrust to the two electromagnetic actuators  42 A and  42 B in the same direction. Similarly, the fine adjustment stage  8  can be driven in the Y direction by applying a thrust to the two electromagnetic actuators  39 A and  39 B in the same direction.  
         [0075]     In addition, the fine adjustment stage  8  can be rotated by applying thrusts in the opposing directions to the two electromagnetic actuators  42 A and  42 B for driving the fine adjustment stage  8  in the X direction. The electromagnetic actuators  39 A and  39 B in the Y direction also similarly operate.  
         [0076]     When the scanning stage  9  is accelerated/decelerated in the scanning direction (Y direction) in scanning exposure, a large inertial force is generated to the fine adjustment stage  8  in the Y direction by this acceleration. However, this inertial force can be canceled by the thrusts of the electromagnetic actuators  39 A and  39 B, thereby setting the relative speed between the fine adjustment stage  8  and the scanning stage  9  to zero. A thrust required to cancel the inertial force in the scanning direction (Y direction) is larger than that required in the direction (X direction) perpendicular to the scanning direction. As the electromagnetic actuators  39 A and  39 B, large actuators having larger thrusts are used.  
         [0077]     In this embodiment, a cooling means for removing heat generated from the electromagnetic actuators  39 A,  39 B,  42 A, and  42 B are provided. This cooling means will be described below with reference to  FIGS. 5 and 7 .  
         [0078]     Referring to  FIG. 5 , the stationary members  38 A,  38 B,  41 A, and  41 B of the electromagnetic actuators  39 A,  39 B,  42 A, and  42 B are arranged in a circulating cooling path (to be described later), adjusted to a predetermined temperature by a liquid cooling temperature adjustment unit  53 , and cooled by a cooling fluid supplied from an internal circulating pump. The circulating cooling path starting from the liquid cooling temperature adjustment unit  53  is sequentially serially constituted by a cooling fluid circulating tube  54 , the stationary member  41 B, a cooling fluid circulating tube  56   a,  the stationary member  38 B, a cooling fluid circulating tube  56   b,  the stationary member  41 A, a cooling fluid circulating tube  56   c,  the stationary member  38 A, a cooling fluid circulating tube  55 , returning to the liquid cooling temperature adjustment unit  53 . The cooling fluid starts to flow from the cooling fluid circulating tube  54  near the optical path  49 A of the laser interferometer, and passes through the cooling fluid circulating tube  56   a  near the optical path  49 B of the laser interferometer and immediately through the stationary member  38 B near the optical path  52  of the laser interferometer. Therefore, the temperature in the optical paths  49 A,  49 B, and  52  of the laser interferometers is precisely maintained at a predetermined level.  
         [0079]      FIG. 7  is a sectional view of the electromagnetic actuator  42 B in  FIG. 6  along a plane parallel to the sheet surface of  FIG. 6 . As shown in  FIG. 7 , the stationary member  41 B is constituted by a base  60 , a hollow cover  61  fixed on the base  60 , and a coil  62  accommodated in the cover  61 . In this case, to cool the coil  62 , a cooling fluid  63  flows between the coil  62  and the cover  61 . If the coil  62  has satisfactory insulating properties, e.g., water can be used as the cooling fluid  63 . However, as the cooling fluid  63 , a chemically inert fluid having no corrosiveness against the coil  62  and the cover  61  and no conductivity is preferable. In this embodiment, therefore, e.g., a fluorine-based inert fluid is used as the cooling fluid  63 .  
         [0080]     On the other hand, the movable member  40 B is constituted by fixing a pair of magnets  64  and  65  to a fixing plate  65  above the stationary member  41 B such that the stationary member  41 B is sandwiched therebetween. That is, the electromagnetic actuator  42 B of this embodiment is of a moving magnet type having magnets incorporated in the movable member  41 B. In this case, since the coil  62  as a main heat source is incorporated on the stationary member  41 B side, the coil  62  can be easily cooled. The remaining electromagnetic actuators  39 A,  39 B, and  42 A also have the same arrangement.  
         [0081]     As described above, when electromagnetic actuators having the same thrust regardless of the scanning direction and the direction perpendicular to this direction are used, an actuator having an excessive thrust is used as the electromagnetic actuator for applying a thrust in the direction perpendicular to the scanning direction. As a result, the entire stage becomes heavy to cause an increase in cost. In this embodiment, however, electromagnetic actuators having appropriate thrusts in the scanning direction and in the direction perpendicular to this direction are used. As a result, the weight of the entire stage is decreased, the heat generation amount is decreased, and cost is reduced.  
         [0082]     According to this embodiment, cooling is efficiently performed by circulating the heat absorption fluid without leaking the heat mainly generated in the coil in the stationary member of the electromagnetic actuator to the scanning stage  9 , the fine adjustment stage  8 , and the like as radiated heat, or conducted heat. In addition, the influence of the temperature or the fluctuation of air with respect to the laser beams can be minimized.  
         [0083]     In this embodiment, a linear motor is used as the electromagnetic actuator. Even if a voice coil motor is used in place of the linear motor, the same effect can be obtained. In this embodiment, the electromagnetic actuators are serially connected and cooled. However, the electromagnetic actuators can also be parallelly cooled. The parallel cooling method is advantageous in that the electromagnetic actuators can be cooled under the same conditions. However, this method has a difficulty in control because piping becomes complex, and if a single temperature adjustment unit is used, the cooling fluid flows toward a lower pressure.  
         [0084]     In this embodiment, the stage unit of the present invention is applied to the reticle stage used in a step and scan type projection exposure apparatus. However, the stage unit of the present invention can also be applied to the wafer stage in addition to the reticle stage.  
         [0085]     As shown in  FIGS. 3 and 4 , a pair of microswitches  36 A and  36 B serving as limit switches are fixed on the reticle base  10  along the linear guide  34 A so as to sandwich the scanning stage  9 . In correspondence with the microswitches  36 A and  36 B, a pair of operation plates  35 A and  35 B are attached to the scanning stage  9  in this case, while the two microswitches  36 A and  36 B are open, a driving power is supplied to the linear motors  31 A and  31 B. As shown in  FIG. 4 , when the scanning stage  9  is moved in the −Y direction, and the operation plate  35 A is brought into contact with the microswitch  36 A to close the microswitch  36 A, the driving power to the linear motors  31 A and  31 B is stopped, and the scanning stage  9  stops in the closed state of the microswitch  36 A. To supply the driving power to the linear motors  31 A and  31 B again, the scanning stage  9  must be manually pushed back in the movable range (a range to supply the driving power to the linear motors  31 A and  31 B) in the +Y direction to open the microswitch  36 A.  
         [0086]     Similarly, the scanning stage  9  is moved in the +Y direction, and the operation plate  35 B is brought into contact with the microswitch  36 B to close the microswitch  36 B, the driving power to the linear motors  31 A and  31 B is stopped. To supply the driving power to the linear motors  31 A and  31 B again, the scanning stage  9  must be manually pushed back in the movable range in the −Y direction.  
         [0087]     As described above, in the reticle stage shown in  FIGS. 3 and 4 , the movable range of the scanning stage  9  is set by the microswitches  36 A and  36 B. To return the scanning stage  9  in the movable range again after the microswitches  36 A and. 36 B are closed, the scanning stage  9  must be manually pushed back in the movable range. For this purpose, if the scanning stage  9  is moved beyond the movable range during the exposure process, the operator must open the chamber for accommodating the exposure apparatus and interrupt the exposure process to manually move the scanning stage  9 . In this case, the temperature in the exposure apparatus changes upon opening/closing the chamber. Until the temperature is stabilized, the exposure process must be interrupted, resulting in a decrease in throughput (productivity) of the exposure process.  
         [0088]     Similarly, in, e.g., the wafer stage of the scanning exposure apparatus, or in a normal full exposure type exposure apparatus (e.g., a stepper), when the movable range of the stage is limited by a microswitch, and the driving power to the driving unit is stopped if the stage is moved beyond the movable range, the stage must be manually pushed back in the movable range. For this reason, the throughput of the exposure process is decreased.  
       Second Embodiment  
       [0089]     The second embodiment associated with the stage unit according to the present invention will be described below with reference to FIGS.  8  to  13 . In this embodiment, the present invention is applied to the reticle stage of a step and scan type projection exposure apparatus. The same reference numerals as in FIGS.  1  to  4  denote the same parts in  FIGS. 8 and 9 , and a detailed description thereof will be omitted.  
         [0090]      FIG. 8  is a plan view of the reticle stage of this embodiment. Referring to  FIG. 8 , a scanning stage  9  is mounted on a base  10  to be slidable in the Y direction along linear guides  34 A and  34 B. The scanning stage  9  is driven by linear motors  31 A and  31 B in the +Y or −Y direction with respect to the base  10 . A sliding portion  9   a  ( FIG. 9 ) is formed on the lower surface of the scanning stage  9  so as to oppose one linear guide  34 A while a sliding portion  9   b  ( FIG. 13 ) is formed to oppose the other linear guide  34 B. Bearings  90  are interposed between the linear guides  34 A and  34 B and the sliding portions  9   a  and  9   b.    
         [0091]     A Y axis movable mirror  11 Y is fixed at the end portion of a fine adjustment stage  8  in the Y direction. Laser beams from two external laser interferometers  12 YB and  12 YA are irradiated on the movable mirror  11 Y to be parallel to the Y axis. The Y coordinate of the fine adjustment stage  8  is obtained from the average value of the measurement values from the laser interferometers  12 YB and  12 YA, and the rotation angle of the fine adjustment stage  8  is obtained from the difference between the measurement values from the laser interferometers  12 YB and  12 YA. An X axis movable mirror  11 X is fixed at the end portion of the fine adjustment stage  8  in the X direction. A laser beam from an external laser interferometer  12 X is irradiated on the movable mirror  11 X to be parallel to the X axis. The X coordinate of the fine adjustment stage  8  is obtained from the measurement value from the laser interferometer  12 X. The position and the scanning speed of the scanning stage  9  along the Y direction are controlled on the basis of the X coordinate, the Y coordinate, and the rotation angle, which are measured in the above manner, and the position and rotation angle of the fine adjustment stage  8  are simultaneously controlled.  
         [0092]     A reference plate  72  is fixed to the side surface portion of the scanning stage  9  in the X direction. An origin sensor  73  is fixed at a position where the reference plate  72  on the base  10  passes.  
         [0093]      FIG. 13  is a view showing the positional relationship between the reference plate  72  and the origin sensor  73 . Referring to  FIG. 13 , the origin sensor  73  is constituted by a light-emitting portion and a light-receiving portion. When the reference plate  72  passes between the light-emitting portion and the light-receiving portion in the Y direction, an origin signal is generated from the light-receiving portion. In this embodiment, e.g., at the start of use the reticle stage, the origin signal is used to reset the measurement values from the laser interferometers  12 YA and  12 YB.  
         [0094]     Referring back to  FIG. 8 , a pair of limit switch units  71 A and  71 B are fixed on the base  10  to sandwich the scanning stage  9  in the Y direction.  
         [0095]      FIG. 9  is a front view of  FIG. 8 . As shown in  FIG. 9 , when the scanning stage  9  is moved in the −Y or +Y direction, the bottom portion of the scanning stage  9  is brought into contact with the limit switch unit  71 A or  71 B, and the driving power to the linear motors  31 A and  31 B is stopped, as will be described later. More specifically, the allowable movement range of the scanning stage  9  in the Y direction is defined by the limit switch units  71 A and  71 B.  
         [0096]      FIG. 10  is an enlarged plan view of the limit switch unit  71 A in  FIG. 8 .  FIG. 11  is an enlarged front view of the limit switch unit  71 A. In the limit switch unit  71 A shown in  FIGS. 10 and 11 , a linear guide  75  is formed in the Y direction in a frame  74  having a U-shaped section in the Y-Z plane. A movable member  76  is slidably mounted along the linear guide  75 . Tensile coil springs  77  and  78  are mounted between projecting portions  76   a  and  76   b  on both the side surfaces of the movable member  76  and a side wall  74   a  of the frame  74  in the +Y direction, respectively. The movable member  76  is pressed against the side wall  74   a  side by the tensile coil springs  77  and  78 . When the movable member  76  is in contact with the side wall  74   a,  the total biasing force of the tensile coil springs  77  and  78  is set to be larger than the frictional force between the scanning stage  9  and the base  10  and at the same time smaller than the average driving force of the linear motors  31 A and  31 B.  
         [0097]     An operation plate  79  is fixed on the side surface of the movable member  76 , and a microswitch  80  is fixed at a position where the operation plate  79  passes on the frame  74 . Two circuits are parallelly arranged in the microswitch  80 . Each of these two circuits is connected in a corresponding one of the driving current supply cables of each of the linear motors  31 A and  31 B. When the microswitch  80  is brought into contact with the operation plate  79  and closed, the microswitch  80  is set in an operative state, and the internal circuits are turned off, thereby stopping supply of the driving current to the linear motors  31 A and  31 B. When the operation plate  79  is separated to open the microswitch  80 , the microswitch  80  is set in an inoperative state, and the internal circuits are turned on, thereby driving the linear motors  31 A and  31 B. The other limit switch unit  71 B in  FIG. 8  has a structure symmetrical with that of the limit switch unit  71 A in  FIG. 10 .  
         [0098]     The operation of this embodiment will be described below. Referring to  FIG. 11 , an area in the Y direction, which is sandwiched between the movable member  76  and the movable member of the limit switch unit  71 B ( FIG. 8 ) is defined as an allowable movement range  81 . At this time, the scanning stage  9  is moved in a direction indicated by an arrow  82  (−Y direction) upon runaway of the linear motors  31 A and  31 B in  FIG. 8  beyond the allowable movement range  81 , the scanning stage  9  starts to press the movable member  76 . Thereafter, as shown in  FIG. 12 , the movable member  76  is pressed by the scanning stage  9  and moved in the −Y direction along the linear guide  75 . The operation plate  79  fixed to the movable member  76  closes the microswitch  80 . In this state, supply of the driving current to the linear motors  31 A and  31 B is stopped, and the driving force of the scanning stage  9  is eliminated. In this case, since the tensile coil springs  77  and  78  have a sufficient biasing force F for pushing back the scanning stage  9  in the +Y direction, the movable member  76  pushes back the scanning stage  9  in the +Y direction. In addition, the microswitch  80  is opened to allow to supply the driving current to the linear motors  31 A and  31 B.  
         [0099]     In this embodiment, however, when the microswitch  80  is closed to stop the driving current, the driving system (not shown) of the linear motors  31 A and  31 B sets the driving current to the linear motors  31 A and  31 B to, e.g., zero, thereby informing error occurrence to the host computer (not shown). Thereafter, when the error is restored, supply of the driving current to the linear motors  31 A and. 31 B is started. The scanning stage  9  is returned in the allowable movement range  81  by the movable member  76 .  
         [0100]     The measurement values from the laser interferometers  12 YA and  12 YB in  FIG. 8  may have an error because of runaway or the like. For this reason, when the error is restored, the linear motors  31 A and  31 B are driven to move the scanning stage  9  in the −Y direction such that the reference plate  72  moves across the origin sensor  73 . At this time, an origin signal obtained from the origin sensor  73  is used to reset the measurement values from the laser interferometers  12 YA and  12 YB. With this operation, the Y coordinate of the scanning stage  9  is always accurately measured.  
         [0101]     As described above, according to this embodiment, after the microswitch  80  is closed to stop the driving current to the linear motors  31 A and  31 B, the movable member  76  serving as a push-back means pushes back the scanning stage  9  to the allowable movement range  81 . For this reason, the operator need not manually push back the scanning stage  9 . Therefore, the exposure process of the scanning exposure apparatus using the reticle stage in  FIG. 8  is not interrupted for a long time, resulting in an increase in throughput of the exposure process.  
         [0102]     The first modification of the limit switch  71 A on the left side of  FIG. 8  will be described below with reference to  FIGS. 14 and 15 . The same reference numerals as in FIGS.  8  to  13  denote the same parts in  FIGS. 14 and 15 , and a detailed description thereof will be omitted.  
         [0103]      FIG. 14  is an enlarged plan view of the limit switch unit of this modification.  FIG. 15  is an enlarged partially cutaway front view of the limit switch unit. In this limit switch unit, through holes  74   c  and  74   d  are formed in the side walls  74   a  and  74   b  of the frame  74  in the Y direction. A columnar movable member  83  is inserted into the through holes  74   c  and  74   d  to be parallel to the Y axis. A stopper  84  is fixed on the surface of the movable member  83  in the side walls  74   a  and  74   b,  and a compression coil spring  85  is interposed between the stopper  84  and the side wall  74   b  while surrounding the movable member  83 . Therefore, when the scanning stage  9  is kept separated from the movable member  83 , the stopper  84  is pressed against the side wall  74   a  side by the biasing force of the compression coil spring  85  in the +Y direction. The end portion of the movable member  83  in the +Y direction projects from the side wall  74   a  in the +Y direction. When the stopper  84  is in contact with the side wall  74   a,  the biasing force of the compression coil spring  85  is set to be larger than the frictional force between the scanning stage  9  and the base  10  in  FIG. 8  and at the same time smaller than the average driving force between the linear motors  31 A and  31 B.  
         [0104]     The operation plate  79  is fixed on the side surface of the stopper  84 , and the microswitch  80  is fixed at a position where the operation plate  79  passes on the frame  74 . When the microswitch  80  is brought into contact with the operation plate  79  and closed, supply of the driving current to the linear motors  31 A and  31 B is stopped. When the operation plate  79  is kept separated to open the microswitch  80 , the linear motors  31 A and  31 B are driven.  
         [0105]     In this modification, when the scanning stage  9  is moved in a direction indicated by an arrow  81  (−Y direction) to start pressing the movable member  83 , the movable member  83  and the stopper  84  are moved in the −Y direction. Thereafter, when the operation plate  79  fixed to the stopper  84  comes close to the microswitch  80 , the driving force from the linear motors  31 A and  31 B to the scanning stage  9  is eliminated. At this time, since the compression coil spring  85  has a sufficient force for pushing back the scanning stage  9 , the compression coil spring  85  pushes back the scanning stage  9  in the +Y direction through the stopper  84  and the movable member  83 . In addition, the microswitch  80  is opened to allow to supply the driving current to the linear motors  31 A and  31 B. The subsequent operation is the same as in the example shown in FIGS.  10  to  12 .  
         [0106]     The second modification of the limit switch unit  71 A on the left side of  FIG. 8  will be described below with reference to  FIGS. 16 and 17 . The same reference numerals as in FIGS.  8  to  13  denote the same parts in  FIGS. 16 and 17 , and a detailed description thereof will be omitted.  
         [0107]      FIG. 16  is an enlarged plan view of the limit. switch unit of this modification.  FIG. 17  is an enlarged front view of the limit switch unit. In this limit switch unit, a rotating pin  87  is inserted into through holes in two projecting portions  86   a  an  86   b  on a base  86  to be perpendicular to the Y axis. A movable member  88  is rotatably supported about the rotating pin  87 . A tensile coil spring  89  extends between the side surface of the movable member  88  in the −Y direction and a projecting portion  86   d  at the upper end of the base  86  in the −Y direction. A clockwise rotational force is applied to the movable member  88  by the tensile coil spring  89 . However, the left side surface of the movable member  88  is in contact with a stepped portion  86   c  on the base  86 , so that the movable member  88  is supported not to further rotate in the clockwise direction. When the movable member  88  is in contact with the stepped portion  86   c,  the biasing force by the tensile coil spring  89  is set to be larger than the frictional force between the scanning stage  9  and the base  10  in  FIG. 8  and at the same time smaller than the average driving force of the linear motors  31 A and  31 B.  
         [0108]     The microswitch  80  is fixed on the base  86  in the rotational direction of an inclined surface  88   b  on the lower right side of the movable member  88 . When the microswitch  80  is brought into contact with the inclined surface  88   b  and closed, supply of the driving current to the linear motors  31 A and  31 B in  FIG. 8  is stopped. When the inclined surface  88   b  is kept separated to open the microswitch  80 , the linear motors  31 A and  31 B are driven.  
         [0109]     In this modification, when the scanning stage  9  is moved in the direction indicated by the arrow  81  (−Y direction) to press a right side surface  88   a  of the movable member  88 , the movable member  88  is rotated counterclockwise (θ direction) about the rotating pin  87 . Thereafter, when the inclined surface  88   b  of the movable member  88  closes the microswitch  80 , the driving force from the linear motors  31 A and  31 B to the scanning stage  9  is eliminated. At this time, since the tensile coil spring  89  has a sufficient force for pushing back the scanning stage  9 , the tensile coil spring  89  pushes back the scanning stage  9  in the +Y direction through the movable member  88 . In addition, the microswitch  80  is opened to allow to supply the driving current to the linear motors  31 A and  31 B. The subsequent operation is the same as in the example shown in FIGS.  10  to  12 .  
         [0110]     In the above embodiment, as shown in  FIG. 8 , the limit switch unit  71 A is fixed on the base  10 . However, the limit switch unit  71 A may be attached to the scanning stage  9  side, and a member contacting the movable member  76  may be attached to the base  10  at a position opposing the limit switch unit  71 A.  
         [0111]     In addition, an elastic member such as a rubber member may be used in place of the tensile coil springs  77  and  78  in  FIG. 10 . Furthermore, instead of forming a through hole in the side wall  74   b  in  FIG. 15 , the movable member  83  may be formed of an elastic member such as a rubber member, and the scanning stage  9  may be pushed back by this elastic member.  
         [0112]     In the above embodiment, the linear motors  31 A and  31 B are used as the driving unit of the scanning stage  9 . However, the present invention can also be applied even when another electromagnetic driving unit such as a voice coil motor (VCM) is used. However, it is particularly preferable to use a driving unit such as a linear motor or a VCM, which allows the scanning stage  9  to freely move when the driving current is stopped.  
         [0113]     In the above embodiment, the present invention is applied to the reticle stage of the scanning exposure apparatus. However, the present invention may also be applied to the wafer stage side. Even in a full exposure type exposure apparatus (e.g., a stepper), when the allowable movement range of the stage is defined by a limit switch, the stage can be automatically returned in the allowable movement range by applying the present invention.  
         [0114]     To measure the coordinate position of a micropattern such as a VLSI at a high precision and manage its size, a mechanism for reading the position of a sample pattern on a wafer at a high resolving power and a high precision is needed. At the same time, the system of the entire apparatus must stably operate for a long time while guaranteeing the absolute measurement value to some extent. For example, when a 16M DRAM with a design rule of 0.5 μm is to be manufactured, the coordinate position precision of a mask to be used must be smaller than 0.05 μm. Assume a corresponding stable and highly precise measurement device. In this case, pattern edge detection can be probably performed using a light or electron beam. However, to realize the precision and reproducibility of coordinate position measurement, it is essential to make the system of the entire apparatus constituted by a drive table, an interferometer, and the like highly precise and stable.  
         [0115]     To make the system of the entire apparatus highly precise, a drive table using a linear motor as a driving source is used. This drive table is of a direct drive type using the linear motor. The linear motor drive table need not a mechanism for converting rotational movement of a ball screw into a linear movement, so that the structure is simplified, a backlash caused by the ball screw is prevented, and the speed limit caused by the DN value of the ball screw is eliminated. With these characteristic features, a highly precise high-speed table stage can be realized.  
         [0116]     To make the drive table highly precise, it is important to detect the accurate position of the drive table by using a laser interferometer and the like. For this purpose, the drive table must accurately perform origin detection at a predetermined position of the absolute coordinate system. Otherwise, data obtained from the interferometer becomes inaccurate.  
         [0117]     A method for detecting the origin of the drive table in the apparatus of this type is as follows.  FIG. 18  is a plan view for schematically explaining the arrangement of the drive table. As shown in  FIG. 18 , a total of three link mechanisms  141  are provided to a stage  140  of the drive table, i.e., two of them are provided on the wall in the X direction, and the remaining one is provided on the wall in the Y direction.  
         [0118]     Each of the link mechanisms  141  is constituted by a link  143  having one end coupled to the stage  140  by a ball joint  142 , a ball joint  146  coupled to the distal end of a ball screw  145  driven by a uniaxial actuator  144 , a sensor light-shielding plate  147  attached to the ball joint  146 , and a position detection sensor  148  for detecting the position of the sensor light-shielding plate  147 .  
         [0119]     With the link mechanisms  143 , the stage  140  can be freely moved on the reference coordinates. In addition, the small movement of the stage  140  is detected by the position detection sensor  148  as an apparent movement of the sensor light-shielding plate  147 . Therefore, a measurement value from each position detection sensor  148  is reset to a predetermined value, e.g., zero when the drive table is initialized. The X-Y coordinate values and a rotation amount θ of the drive table are detected using the reset value as a reference position.  
         [0120]     However, in the origin detection mechanism using such a link mechanism, when a table driving system using a uniaxial actuator and having no link mechanism is used, the position of the drive table cannot be detected, so origin detection cannot be performed.  
         [0121]     In addition, as described above, the drive table uses a linear motor as a driving source to realize a highly precise high-speed table stage. However, when this drive table is used, and a large error occurs in origin detection, high precision cannot be achieved at all.  
       Third Embodiment  
       [0122]      FIG. 19  is a plan view for explaining the arrangement of the third embodiment associated with the drive table of the present invention.  FIG. 20  is a plan view for explaining the arrangement of origin detection in  FIG. 19 . As shown in  FIG. 19 , the two-dimensional position (including the rotational direction) of a stage  110  of the drive table is always detected by an interferometer unit consisting of three interferometers at a resolving power of, e.g., 0.02 μm.  
         [0123]     The interferometer unit is constituted by an X interferometer  101 A, a Y interferometer  101 B, and a θ interferometer  101 C. A plane including the three measuring axes (e.g., the central lines of laser beams) is arranged to be parallel to the stage  110  of the drive table. The measuring axis of the X interferometer  101 A and that of the Y interferometer  101 B are arranged to be accurately perpendicular to each other. The θ interferometer  101 C is arranged to be symmetrical with respect to the Y axis of an orthogonal coordinate system X-Y.  
         [0124]     The stage  110  is constituted by an X stage moved by an X linear motor  102 A in the X direction, and a Y stage moved by a Y linear motor  102 B provided on the X stage in the Y direction. A movable mirror  103 A for the X interferometer and a movable mirror  103 B for the Y and θ interferometers are provided at the end portions of the Y stage to extend along the X and Y directions, respectively.  
         [0125]     The X, Y, and θ interferometers  101 A to  101 C irradiate laset beams to the movable mirrors  103 A and  103 B. The light beams reflected by the movable mirrors  103 A and  103 B are coaxially synthesized with light beams from fixed mirrors (not shown). With this operation, a change in interference fringes generated on the light-receiving surface is detected, and a signal according to a change in position of the movable mirror  103 A or  103 B is generated and output to a coordinate converter  104 .  
         [0126]     The coordinate converter  104  calculates correction coordinate values in the X and Y directions, and a θ rotation correction amount of the stage  110  on the basis of the measurement values from the interferometers  101 A to  101 C. The values and amount are output to an alignment signal processing circuit (ASC)  105  and a stage controller  106  for outputting a predetermined driving command to the X and Y linear motors  102 A and  102 B. A main control unit  107  controls the stage controller  106  while communicating with the ASC  105 .  
         [0127]     The stage controller  106  drives the stage through the X and Y linear motors  102 A and  102 B in accordance with the correction coordinate values, thereby positioning the stage at a predetermined position. The θ rotation amount is corrected by finely adjusting the moving amounts of the X and Y linear motors  102 A and  102 B.  
         [0128]     In the drive table  110 , the measurement values from the X, Y, and θ interferometers  101 A to  101 C must be measurement values with respect to reference positions. Otherwise, data obtained from each interferometer becomes inaccurate. Therefore, the reference positions of the interferometers  101 A to  101 C must be accurately determined by a reference position detection means.  
         [0129]     As shown in  FIG. 20 , as the reference position detection means for detecting the origin of the interferometer unit for measuring the coordinate value of the table stage  110  freely moved in an area surrounded by a broken line, X, Y, and θ photosensors  108 A to  108 C arranged on the reference coordinates of the drive table, and X, Y, and θ light-shielding plates  109 A to  109 C arranged at the three corners of the stage  110  of the drive table in correspondence with the photosensors are provided.  
         [0130]     The photosensors  108 A to  108 C generate signals when the corresponding X, Y, and θ light-shielding plate  109 A to  109 C shield light to the X, Y, and θ photosensors  108 A to  108 C. The signals are output to the coordinate converter  104 .  
         [0131]     Therefore, the coordinate converter  104  resets the measurement values from the X and Y interferometers  101 A and  101 B to, e.g., zero when the X and Y light-shielding plates  109 A and  109 B shield light to the X and Y photosensors  108 A and  108 B upon movement of the stage  110 . A shift between the detection value from the Y photosensor  108 B with respect to the Y light-shielding plate  109 B and the detection value from the θ photosensor  108 C with respect to the θ light-shielding plate  109 C arranged to be separated from the Y light-shielding plate  109 B by a predetermined distance is calculated, thereby obtaining the reference rotation amount with respect to an axis perpendicular to the X-Y reference coordinates of the stage  110 .  
         [0132]     In this manner, by only operating the drive table in the X and Y directions, the origin with respect to the reference coordinates can be precisely detected without impairing the characteristic features of the linear motor drive table, i.e., high speed and high precision.  
         [0133]      FIG. 21  is a plan view for explaining the arrangement of another origin detection. As shown in  FIG. 21 , a stage  130  of the drive table is a drive table having an interferometer unit consisting of X, Y, and θ interferometers, as in  FIG. 19 . To detect the origin of the interferometer unit for measuring the coordinate value of the table stage  130  freely moved in an area surrounded by a broken line, an X air cylinder  131 A for pressing the table stage in the X direction, a Y air cylinder  131 B for pressing the table stage  130  in the Y direction, a θ air cylinder  131 C for pressing the table stage  130  in the Y direction in synchronism with the Y air cylinder, and X, Y, and θ reference stoppers  132 A to  132 C arranged to be oppose the X, Y, and θ air cylinders, respectively, are provided.  
         [0134]     Origin detection is performed in detail in the following manner. The table stage  130  is pressed against the X reference stopper  132 A by the X air cylinder  131 A in accordance with, e.g., a command from a control means (not shown) for controlling driving of the air cylinders. When the table stage is pressed against the stopper  132 A, and the operation of the X air cylinder  131 A is completed, the control means detects it and sends a signal to the coordinate converter  104 . The measurement value from the X interferometer at this time is set to a predetermined value, thereby detecting the origin of the X coordinate. The origin of the Y coordinate is detected in the same manner.  
         [0135]     As for the rotation amount θ of the stage, the stage  130  is pressed against the θ reference stopper  132 C by the θ air cylinder  131 C in synchronism with the Y air cylinder  131 B, thereby canceling the small rotation amount with respect to the Y coordinate (i.e., X coordinate). Upon completion of the operation of the θ air cylinder  131 C, the measurement value from the θ interferometer is set to a predetermined value, thereby detecting the origin of θ.  
         [0136]     In this manner, when the stage  130  is pressed against the reference stoppers  132 A to  132 C provided at positions opposing the air cylinders  131 A to  131 C by the air cylinders  131 A to  131 C, origin detection can be satisfactorily performed. Completion of pressing of each air cylinder is determined by the operation of the air cylinder. However, it may be detected by a press sensor arranged to the reference stopper.  
         [0137]     As described above, according to the drive table of the present invention, a position detection sensor or a mechanism for forcibly moving the drive table is provided to the drive table with this arrangement, even when the drive table and the driving actuator do not constitute a link mechanism, origin detection can be performed. In this embodiment, a non-contact type driving system such as a linear motor is used. However, a contact type driving system may also be used.  
         [0138]     From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.  
         [0139]     The basic Japanese Application Nos. 156429/1994 filed on Jun. 16, 1994, 153458/1994 filed on Jul. 5, 1994 and 268546/1994 filed on Nov. 1, 1994 are hereby incorporated by reference.