Abstract:
A scanning exposure apparatus includes a projection optical system for projecting a pattern of a reticle onto a wafer, a reticle stage for holding and scanningly moving the reticle relative to the projection optical system, a reticle stage actuator for moving the reticle stage and a reticle interferometer for detecting positional information related to the reticle stage, the reticle interferometer being kept separate from the reticle stage actuator with respect to vibration transmission.

Description:
This application is a continuation of Application Ser. No. 08/901,792, filed Jul. 28, 1997 now U.S. Pat. No. 6,177,978, which is a contiunation of Ser. No. 08/441,696 filed May 15, 1995 now abandoned. 
    
    
     FIELD OF THE INVENTION AND RELATED ART 
     This invention relates generally to an exposure apparatus such as a semiconductor exposure apparatus and, more particularly, to a scanning stage device suitably usable in a scanning type exposure apparatus wherein an arcuate or rectangular slit-like region of a pattern of a reticle is imaged on a substrate such as a wafer and wherein both the reticle and the substrate are scanningly moved so that the reticle pattern as a whole is exposed and transferred to the substrate. 
     In a scanning type exposure apparatus wherein both a reticle (original) and a substrate are scanningly moved so that a reticle pattern as a whole is transferred onto the substrate, it is necessary to control the scanning speed of the reticle or the substrate very precisely and stably. Generally, for this purpose, a scanning exposure apparatus is provided with linear motor means which is, as shown in FIG. 14, incorporated into driving means of a scanning stage device for holding and scanningly moving a reticle or a substrate. The illustrated device comprises a base  101 , a guide  102  fixed to the base  101  and having a U-shaped sectional shape, and a wafer stage  103  movable reciprocally in a predetermined direction (scan direction) along the guide  102 . The device further comprises a pair of linear motor stators  104  and  105  disposed at opposite sides of the movement path of the wafer stage  103 , which is movable along the guide  102 , and being provided integrally with the base  101 . The device further comprises a pair of linear motor movable elements  106  and  107  which are provided integrally with the sides  103   a  and  103   b  of the wafer stage  103 , respectively. The linear motor stators  104  and  105  and the linear motor movable elements  106  and  107  constitute a pair of linear motors E 1  and E 2  for providing acceleration and deceleration of the wafer stage  103  in the scan direction. The wafer stage  103  is guided by the guide  102  without contact thereto, through association of static pressure bearing means (not shown), for example. 
     The linear motor stators  104  and  105  have elongated loop-like yokes  104   a  and  105   a , extending along and substantially throughout the length of the guide  102 , and elongated magnets  104   b  and  105   b  fixed to the insides of the yokes  104   a  and  105   a , respectively. The magnets  104   b  and  105   b  extend through coil openings  106   a  and  107   a , respectively, of the linear motor movable elements  106  and  107 , respectively. When the linear motor movable elements  106  and  107  are energized in response to supply of drive currents from a voltage source (not shown), thrust forces are produced along the magnets  104   b  and  105   b  by which the wafer stage  103  is accelerated or decelerated. 
     Wafer W 0  is attracted to the wafer stage  103  and, above the wafer, a reticle is held by a reticle stage  203  (see FIG.  17 ). By means of slit-like exposure light L 0  (its section being depicted by a broken line) impinging on a portion of the reticle, a slit-like region of the wafer W 0  is exposed such that a portion of the reticle pattern is transferred to that region. Each exposure cycle of the scanning type exposure apparatus comprises moving both the wafer stage  103  and the reticle stage  203  so that the reticle pattern as a whole is transferred to the wafer W 0 . During movement of the wafer stage  103  which holds the wafer W 0 , the position thereof is detected by means of a laser interferometer  108  (FIG.  17 ). The reticle stage  203  has similar driving means such as described above, and it is controlled in a similar way. Speed control during acceleration and deceleration of the wafer stage  103  through the linear motors E 1  and E 2 , is performed in the following manner. 
     FIG. 15 is a top plan view of the scanning stage device of FIG.  14 . When, for example, the wafer stage  103  is at the leftward end position in the scan direction as viewed in the drawing and the center O 0  of the width of the wafer W 0  in the scan direction is at the acceleration start position P 1 , acceleration by rightward thrust of the linear motors E 1  and E 2  as viewed in the drawing starts. Acceleration stops when the center O 0  of the wafer W 0  comes to the acceleration end position P 2 . After this, the liner motors E 1  and E 2  serve only to control and maintain a constant scanning speed of the wafer stage  103 . When the center O 0  of the wafer W 0  comes to the deceleration start position P 3 , deceleration by leftward thrust of the linear motors E 1  and E 2  as viewed in the drawing starts. When the center O 0  of the wafer W 0  comes to the deceleration end position P 4 , running of the wafer stage  103  stops. Simultaneously therewith, leftward acceleration as viewed in the drawing starts. Moving the wafer stage  103  leftwardly, as viewed in the drawing, is performed by controlling the linear motors E 1  and E 2  in a similar way but in the opposite direction. 
     In such an acceleration and deceleration cycle, if for example the wafer stage  103  runs rightwardly as viewed in the drawing, the exposure process starts just when the center O 0  of the wafer W 0  comes to the acceleration end position P 2 , such that the exposure light L 0  impinges on a rightward end slit-like region of the wafer W 0  as viewed in the drawing. When the center O 0  of the wafer W 0  comes to the deceleration start position P 3 , the exposure of the whole surface of the wafer W 0  is completed. Thus, during exposure of the wafer W 0 , the wafer stage  103  moves at a constant scanning speed, and the reticle (not shown) moves similarly. The relative position of the wafer W 0  and the reticle at the time of starting of the exposure process is controlled precisely, and the speed ratio of the wafer W 0  and the reticle is controlled so that it exactly corresponds to the reduction magnification of a projection optical system disposed between the wafer and the reticle. After completion of the exposure process, both the wafer and the reticle are decelerated appropriately. 
     For a higher productivity of a scanning type exposure apparatus, it is desirable to reduce, as much as possible, the time to be consumed by the acceleration and deceleration of the linear motors E 1  and E 2 . Also, from the viewpoint of saving space, the moving distance of the wafer stage  103  during acceleration and deceleration of the linear motors E 1  and E 2  should desirably be short. This requires that the linear motors E 1  and E 2  provide a large thrust and also that the strength of the magnetic field of the linear motor stators  104  and  105  is very large, such as about 5,000 G., for example. In order to meet this requirement, the yokes  104   a  and  105   a  may be made of a material such as iron, for example, having a high saturation magnetic flux density, but even on such an occasion it is still necessary that the opposite end portions  104   c  and  105   c  (FIG. 16) of the yokes  104   a  and  105   a , where the magnetic flux of the magnetic field is strong such as discussed above is concentrated, have a very large sectional area so as not saturate the concentrated magnetic flux. 
     In the arrangement described above, the opposite end portions of the yokes of the linear motor stators should have a very large sectional area so as to avoid saturation of the magnetic flux. Additionally, the central portion of the yoke (where acceleration or deceleration of a wafer stage, for example, is not necessary) has the same sectional size of the end portion thereof. As a result, the yoke as a whole has a very large weight. Thus, the device as a whole is very large and very heavy. Also, for producing a large magnetic field as described above, the magnet of the linear motor stator should have a large thickness, and it should be made of a rare earth magnet which is very expensive. If a thick and expensive magnet is provided along the entire running path of the scanning stage, the cost of the linear motor becomes very high. 
     Further, as shown in FIG. 17, as regards the reticle stage  203 , it is necessary that a base  201  thereof is supported by a frame  204  which is integral with the base  101  of the wafer stage  103 , and additionally that the reticle stage is accelerated to a speed, four or five times higher than the speed of the wafer stage  103 . For this reason, there occurs a problem of vibration of the reticle stage  203  due to the reactive force of the -linear motor. More specifically, since the reticle stage  203  is located in an upper portion of the exposure apparatus, structurally a vibration easily occurs. Also, since the reticle stage is driven by a large drive force as compared with that of the linear motor means of the wafer stage  103 , the exposure apparatus as a whole is swingingly vibrated to a great degree which causes a large external disturbance to a servo system of the exposure apparatus. Since such an external disturbance is a bar to synchronization of scanning of the reticle stage  203  and the wafer stage  103 , it is necessary to delay the start of the succeeding exposure cycle until the external disturbance diminishes. Thus, the throughput is low. 
     Furthermore, if the exposure apparatus as a whole is swingingly vibrated, it may cause deformation of the frame  204  which supports the reticle stage  203  and the projection optical system  205 , which may result in a large error in detected values of the laser interferometers  108  and  208 , for example, for detecting the positions of the wafer stage  103  and the reticle stage  203 , respectively. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a solution for at least one of the problems described above. 
     It is another object of the present invention to provide a stage device by which reduction in size, reduction in weight, reduction in heat generation or reduction of cost is assured. 
     It is a further object of the present invention to provide an exposure apparatus having such a stage device. 
     It is a still further object of the present invention to provide a stage device by which vibration due to drive can be reduced considerably. 
     It is yet a further object of the present invention to provide an exposure apparatus having such a stage device as discussed above. 
     It is yet a further object of the present invention to provide a device manufacturing method for manufacturing high-precision microdevices by using an exposure apparatus such as described above. 
     In accordance with an aspect of the present invention, there is provided a stage device, comprising: a movable stage being movable along a path having a constant speed movement region and an acceleration region; first thrust producing means for accelerating and moving said movable stage in said acceleration region of said path; and second thrust producing means, separate from said first thrust producing means, for moving said movable stage at a constant speed in said constant speed movement region of said path. 
     As compared with the first thrust producing means which provides positive or negative acceleration of the movable stage, the second thrust producing means for moving the movable stage at a constant speed can be made considerably light in weight and small in size. Thus, the driving means portion of the stage device can be small in size, light in weight, low in heat generation and small in cost. 
     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a scanning stage device according to a first embodiment of the present invention. 
     FIG. 2 is a fragmentary enlarged perspective view of a portion of the stage device of FIG. 1, as depicted by a circle T in FIG.  1 . 
     FIG. 3 is a top plan view of the stage device of FIG.  1 . 
     FIG. 4 is a perspective view of a scanning stage device according to a second embodiment of the present invention. 
     FIG. 5 is a schematic view of an embodiment of a scanning type exposure apparatus having a stage device according to one of the first and second embodiments of the present invention. 
     FIG. 6 is a schematic view for explaining another embodiment of a scanning type exposure apparatus having a stage device according to one of the first and second embodiments of the present invention. 
     FIG. 7 is a perspective view of a scanning stage device according to a third embodiment of the present invention. 
     FIG. 8 is a fragmentary perspective view of a secondary linear motor of the stage device of FIG.  7 . 
     FIG. 9 is a perspective view of a modified form of the scanning stage device of the third embodiment of the present invention. 
     FIG. 10 is a schematic view for explaining an elliptic coil and a fluctuation preventing magnet unit of the stage device of FIG.  9 . 
     FIG. 11 is an elevational view, showing an exposure apparatus as a whole, having a stage device according to the third embodiment of the present invention. 
     FIG. 12 is a flow chart-of microdevice manufacturing processes for manufacturing microdevices such as semiconductor devices, for example. 
     FIG. 13 is a flow chart of a wafer process. 
     FIG. 14 is a perspective view of a known type scanning stage device. 
     FIG. 15 is a top plan view of the stage device of FIG.  14 . 
     FIG. 16 is a schematic view for explaining a magnetic field of linear motor stators of the stage device of FIG.  14 . 
     FIG. 17 is an elevational view of a known type exposure apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some preferred embodiments of the present invention will be described in conjunction with the drawings. 
     Embodiment 1 
     FIG. 1 is a perspective view of a scanning stage device according to a first embodiment of the present invention. The stage device comprises an anti-vibration base  1 , a guide  2  having a pair of guide rails  2   a  and  2   b  fixed to the base  1 , a scanning stage  3  being reciprocally movable in a predetermined direction along the guide  2 , two pairs of linear motor stators  4  and  5  disposed along and at the opposite sides of the running path of the scanning stage  3 , and linear motor movable elements  6  and  7  provided at the opposite side faces  3   a  and  3   b  of the scanning stage  3  integrally therewith. 
     Each pair of linear motor stators  4  ( 5 ) has a structure which may correspond to the structure that: a long linear motor stator such as illustrated in FIG. 14 is provided along the entire length of the running path of the scanning stage  3 , and after this, the central portion thereof is removed such that the opposite end portions of the stator remain. The stators  4  ( 5 ) are disposed at those positions corresponding to the positions of the “remaining” stator end portions. 
     The linear motor stators  4  and  5  cooperate with the linear motor movable elements  6  and  7  being integral with the scanning stage  3 , to provide linear motors A 1  and A 2  (first thrust producing means) which serve to produce a first thrust for accelerating (with positive acceleration) or decelerating (with negative acceleration) the scanning stage  3  in each of the opposite end portions (acceleration or deceleration region) of the running path. 
     The scanning stage  3  movement is guided by the guide  2  without contact thereto, through static pressure bearing pads (not shown), for example. As the scanning stage  3  moves in the end portion of the running path, portions of yokes  4   a  and  5   a  of the linear motor stators  4  and  5  as well as magnets  4   b  and  5   b  held thereby penetrate through openings  6   a  and  7   a  of the linear motor movable elements  6  and  7 , respectively. As the linear motor movable elements  6  and  7  are energized by drive currents supplied thereto, they produce a thrust for accelerating or decelerating the scanning stage  3 . 
     Disposed between the guide rails  2   a  and  2   b  of the guide  2  is a secondary linear motor stator  8  which comprises, as shown in an enlarged view of FIG. 2, a small loop-like secondary yoke  8   a  and a secondary magnet  8   b  fixed to the inside of the secondary yoke  8   a . Also, there is a secondary linear motor movable element  9  which cooperates with the secondary linear motor stator  8  to provide a secondary linear motor A 3  (second thrust producing means). The secondary linear motor stator  8  is fixed to the anti-vibration base  1 , and the secondary linear motor movable element  9  is fixed to the bottom face of the scanning stage  3 . 
     The secondary linear motor A 3  is energized after the scanning stage  3  is accelerated up to a predetermined speed by means of the linear motors A 1  and A 2 , and it serves to produce a second thrust effective to maintain the scanning speed of the scanning stage  3  constant. Thus, the secondary linear motor A 3  serves to produce a thrust only in a period in which-the scanning stage  3  runs through the central portion (constant speed scanning region) of the running path, to thereby maintain the scanning speed of the scanning stage  3  constant. Therefore, it is not necessary for the secondary linear motor A 3  to produce a large thrust as by the linear motors A 1  and A 2  which serve to accelerate or decelerate the scanning stage  3 . Consequently, the secondary linear motor A 3  can be made small in size and light in weight as compared with the linear motors A 1  and A 2 . 
     Wafer W 1  is attracted to the scanning stage  3  through a wafer chuck mechanism (not shown). Above the wafer, a reticle (not shown) is held by a reticle stage (not shown). A slit-like region of the wafer W 1  is exposed with slit-like exposure light L 1  (as depicted by a broken line in FIG.  3 ), having been projected to a portion of the reticle, such that a portion of a pattern of the reticle is transferred to this portion of the wafer. By scanningly moving both the scanning stage  3  and the unshown reticle stage, the whole reticle pattern is transferred to the whole surface of the wafer W 1 . The exposure of the wafer W 1  is performed during the period in which the scanning stage  3  moves through the central portion of its running path at a constant speed. 
     In this embodiment as described, linear motor stators of linear motor means for acceleration and deceleration of the scanning stage are provided only in the opposite end portions of the running path of the scanning stage. Therefore, it is not necessary to use a long magnet or yoke as in a case where a linear motor stator is provided along the entire length of the running path. Also, the thickness of the yoke sufficient for prevention of saturation of magnetic flux at the end portion, can be made small. Additionally, since what is required for the secondary linear motor is to prevent reduction in scanning speed of the scanning stage only, it is sufficient for the stator thereof to provide a magnetic flux of a few tens or hundreds gausses. Thus, the secondary linear motor as a whole can be made very small in size. This is very effective to reduce in size and weight the stage device as well as to reduce heat generation in the stage device. Even if a rare earth magnet which is expensive is used, the cost can be reduced considerably. Furthermore, there is an additional advantage that, when the scanning stage moves in the central portion of the running path, the scanning speed of the scanning stage can be controlled very precisely with the small-size secondary linear motor. 
     As an example, if the total amount of the magnetic fluxes by the linear motor stators of all the linear motors of this embodiment is about one half of the total amount of the magnetic fluxes of all the linear motors used in the FIG. 14 arrangement, the thickness of the yoke of the linear motor stator of this embodiment can be about one half of that of the FIG. 14 arrangement. Also, the necessary amount of the expensive magnet or yoke can be about one half of that of the FIG. 14 arrangement. Therefore, the present embodiment is very effective to reduce the size and weight of the stage device, to reduce the heat generation, and to reduce the cost of the stage device. This advantage is more significant in a stage device having a larger scanning region of a scanning stage. 
     Embodiment 2 
     FIG. 4 is a perspective view of a scanning stage device according to a second embodiment of the present invention. Similarly in the scanning stage  3  of the first embodiment, a scanning stage  23  is reciprocally movable along a guide  22  which comprises a pair of guide rails  22   a  and  22   b . Second thrust producing means similar to the secondary linear motor A 3  of the first embodiment, comprises small-size secondary linear motors B 1  and B 2  which are disposed at the opposite ends of the scanning stage  23 . Acceleration and deceleration of the scanning stage  23  is provided by first thrust producing means which comprises a pair of thrust producing devices C 1  and C 2  having a pair of springs. 
     The thrust producing devices C 1  and C 2  comprise: coiled springs  24  and  25  having ends which are engageable with the opposite end faces  23   c  and  23   d  of the scanning stage  23 , respectively; spring bases  24   a  and  25   a  for holding the other ends of the coiled springs  24  and  25 , respectively; spring base guides  26   b  and  27   b  which have guide surfaces  26   a  and  26   b  for guiding the spring base  24   a  and  25   a  and which have clamps (not shown) disposed therein and being able to fixedly hold the spring bases  24   a  and  25   a  at desired positions, respectively, along the guide surfaces  26   a  and  27   a , respectively; and motors  26   d  and  27   d  for rotating screws  26   c  and  27   c  to move the spring bases  24   a  and  25   a  along the guide surfaces  26   a  and  27   a , respectively. 
     For rightward movement of the scanning stage as viewed in the drawing, for example, the scanning stage  23  is first clamped at its leftward end position of its running path by means of the unshown clamps. Then, the motors  26   d  and  27   d  are driven to displace the spring bases  24   a  and  25   a  toward and close to the scanning stage  23  by the same amounts, respectively, and the left-hand side coiled spring  24  is compressed between the scanning stage  23  and the spring base. After this, the spring bases  24   a  and  25   a  are clamped to the spring base guides  24   b  and  25   b , respectively, and subsequently the clamping of the scanning stage  23  is released. 
     The scanning stage  23  moves rightwardly while being accelerated until the left-hand side coiled spring  24  expands back to its initial length and, after subsequent constant speed movement, the scanning stage engages with the right-hand side coiled spring  25 . The scanning stage  23 , while being decelerated thereby, reaches the rightward end of its running path. 
     For opposite rightward movement of the scanning stage  23 , the right-hand side coiled spring is compressed and the returning force thereof is used. 
     In this embodiment, acceleration and deceleration of the scanning stage is provided by means of a thrust producing device having springs which are light in weight and low in cost as compared with a linear motor. Thus, reduction in weight, cost and heat generation of the stage device are enhanced. 
     FIG. 5 is a schematic view of a model of a scanning type exposure apparatus which uses a scanning stage device according to the first or second embodiment described above. The exposure apparatus comprises an anti-vibration base  51 , a scanning stage  53  supported by the anti-vibration base  51 , and a unit-magnification imaging optical system  52  for imaging exposure light, being projected from a light source  50  and through a reticle L 2  supported by the scanning stage  53 , upon a wafer W 2  similarly supported by the scanning stage  53 . Similar to the scanning stages  3  and  23  of the scanning stage devices of the first and second embodiments, the scanning stage  53  comprises first and second thrust producing means (not shown) by which the scanning stage  53  can be reciprocally moved along a predetermined running path to thereby move the reticle L 2  and the wafer W 2  at the same speed. As they move through a central portion of the scanning path, the exposure process with the exposure light is performed. The scanning stage  53  is provided with a mirror  53   a  being integral therewith, and the position of the scanning stage  53  can be monitored by means of an interferometer  54  which receives light reflected by the mirror  53   a.    
     FIG. 6 is a schematic view of another model of a scanning type exposure apparatus, in which a wafer W 3  is held by a wafer stage  61  supported by a first anti-vibration base  61   a  while a reticle R 3  is held by a reticle stage  63  supported by a second anti-vibration base  62   a , such that the wafer stage  61  and the reticle stage  63  can be driven separately. The wafer stage  61  and the reticle stage  63  each includes first and second thrust producing means (not shown). A reduction imaging lens system  62  (exposure means) is disposed between the reticle stage and the wafer stage. Exposure light emitted by a light source  64  first passes through the reticle R 3  and, after being reduced by the reduction imaging lens system  62  at a predetermined reduction magnification N, it is projected on the wafer W 3 . Similar to the FIG. 5 apparatus, the exposure of the wafer W 3  is performed as the wafer stage  61  and the reticle stage  62  move through the central portions of their running paths, respectively. Here, the scanning speed V 1  of the reticle stage  62  and the scanning speed V 2  of the wafer stage  61  are controlled to satisfy the following relation: 
     V 2 /V 1 =N. 
     Embodiment 3 
     FIG. 7 is a perspective view of a scanning stage device according to a third embodiment of the present invention. The stage device comprises a reticle stage base  71   a  (scanning stage supporting means), a guide  72  having a pair of guide rails  72   a  and  72   b  fixed to the reticle stage base  71   a , a reticle stage  73  movable reciprocally in a predetermined direction along the guide  72 , two pairs of linear motor stators  74  and  75  disposed along and at the opposite sides of the running path of the reticle stage  73 , and linear motor movable elements  76  and  77  disposed on the opposite sides of the reticle stage  73  and provided integrally therewith. 
     Each pair of linear motor stators  74  ( 75 ) has a structure which may correspond to the structure that: a long linear motor stator such as illustrated in FIG. 14 is provided along the entire length of the running path of the scanning stage  73 , and after this, the central portion thereof is removed such that the opposite end portions of the stator remain. The stators  74  ( 75 ) are disposed at those positions corresponding to the positions of the “remaining” stator end portions. 
     The linear motor stators  74  and  75  cooperate with the linear motor movable elements  76  and  77  being integral with the scanning stage  73 , to provide linear motors A 4  and A 5  (first thrust producing means) which serve to produce a first thrust for accelerating or decelerating the scanning stage  73  in each of the opposite end portions (acceleration or deceleration region) of the running path. 
     The scanning stage  73  movement is guided by the guide  72  without contact thereto, through static pressure bearing pads (not shown), for example. As the scanning stage  73  moves in the end portion of the running path, portions of yokes  74   a  and  75   a  of the linear motor stators  74  and  75  as well as magnets  74   b  and  75   b  held thereby penetrate through openings  76   a  and  77   a  of the linear motor movable elements  76  and  77 , respectively. As the linear motor movable elements  76  and  77  are energized by drive currents supplied thereto, they produce a first thrust for accelerating or decelerating the scanning stage  73 . 
     The linear motor stators  74  and  75  of the linear motors A 4  and A 5  are supported by a linear motor base  71   b  (thrust producing means supporting means) which is separate from and independent of the reticle stage base  71   a . This effectively prevents vibration of the wafer stage  93  (see FIG. 11) of the exposure apparatus due to any reactive force of the drive force (thrust) of the linear motors A 4  and A 5 . 
     Disposed between the guide rails  72   a  and  72   b  of the guide  72  is a secondary linear motor stator  78  which comprises, as shown in an enlarged view of FIG. 8, a small loop-like secondary yoke  78   a  and a secondary magnet  78   b  fixed to the inside of the secondary yoke  78   a . Also, there is a secondary linear motor movable element  79  which cooperates with the secondary linear motor stator  78  to provide a secondary linear motor A 6  (second thrust producing means). The secondary linear motor stator  78  is fixed to the reticle stage base  71   a , and the secondary linear motor movable element  79  is fixed to a supporting member  79   a  which protrudes from the bottom face of the reticle stage  73 . 
     The secondary linear motor A 6  is energized mainly after the reticle stage  73  is accelerated up to a predetermined speed by means of the linear motor A 4  or A 5 , and it serves to produce a second thrust effective to compensate for a change in the scanning speed of the reticle stage  73 . Thus, the secondary linear motor A 6  serves to produce a thrust only in a period in which the reticle stage  73  runs through the central portion (constant speed scanning region) of the running path, to thereby maintain the scanning speed of the reticle stage  3  constant. Therefore, it is not necessary for the secondary linear motor A 6  to produce a large thrust as by the linear motor A 4  or A 5  which serves to accelerate or decelerate the reticle stage  73 . Consequently, the secondary linear motor A 6  can be made small in size and light in weight as compared with the linear motors A 4  and A 5 . 
     In this embodiment as described, the linear motor stators  74  and  75  of the linear motors A 4  and A 5  for acceleration and deceleration of the reticle stage  73  are provided only in the opposite end portions of the running path of the reticle stage  73 . Therefore, it is not necessary to use a long magnet or yoke as in a case where the linear motor stators  74  and  75  are provided along the entire length of the running path. Also, the thickness of the yoke sufficient for prevention of saturation of the magnetic flux at the end portion, can be made small. This is very effective to reduce in size and weight the stage device as well as to reduce heat generation in the stage device. Even if a rare earth magnet which is expensive is used, the cost can be reduced considerably. Furthermore, there is an additional advantage that, when the reticle stage  73  moves in the central portion of the running path, the scanning speed of the reticle stage  73  can be controlled very precisely with the secondary linear motor A 6 . 
     In a case when the external disturbance to the reticle stage is small, since the necessary drive amount of the secondary linear motor A 6  is relatively small, the secondary linear motor stator  78  may be fixed to any one of the reticle stage base  71   a  and the linear motor base  71   b . If the external disturbance to the reticle stage is large, the linear motor stator may preferably be fixed to the linear motor base. This effectively prevents transmission, to the reticle stage, of any reactive force of the force of the secondary linear motor that acts against the external disturbance. 
     Generally, it is difficult to assure exact registration between the position where the thrust of the linear motors A 4  and A 5  act on the reticle stage  73  and the gravity center position of the reticle stage  73 , with respect to the vertical direction. Usually, there is a small deviation between these positions. Thus, as the linear motors A 4  and A 5  operate, the drive force of them may cause a moment for rotating the reticle stage  73 . This moment may cause a swinging motion of the reticle stage base  71   a  and, as a result of it, the exposure apparatus as a whole may swingingly vibrate or the frame  94  (see FIG. 11) may be deformed. 
     In order to avoid such a problem, a fluctuation preventing device (third thrust producing means) such as illustrated in FIG. 9 may preferably be added. This fluctuation preventing device comprises two pairs of flattened or elliptical coils  81   a  and  81   b  integrally provided with and disposed at the right-hand and left-hand sides of the guide rails of the guide  72 , respectively, as well as two, right-hand side and left-hand side pairs of fluctuation preventing magnet units  82   a  and  82   b  being supported by the linear motor base  71   b.    
     As illustrated in an enlarged view of FIG. 10, each of the coils  81   a  and  81   b  comprises a vertical type coil being held vertically. Each of the fluctuation preventing magnet units  82   a  or  82   b  comprises two magnets  83   a  having different properties and a yoke  83   b  for holding these magnets in an accumulated position with respect to the vertical direction. During operation of the linear motors A 4  and A 5 . the right-hand or left-hand coils  81   a  and  81   b  are in the position penetrating into the opening of the fluctuation preventing magnet units  82   a  and  82   b . By electric currents supplied to the coils  81   a  and  81   b , a third thrust in the vertical direction is produced such that the moment resulting from this thrust serves to cancel the rotational moment produced in the reticle stage base  71   a  by the drive forces of the linear motors A 4  and A 5 . 
     The control of the electric currents to be supplied to the coils  81   a  and  81   b  may be performed by measuring the acceleration of the reticle stage  73  and by feeding back the amount of fluctuation of the reticle stage  73 , for example, as calculated on the basis of the measurement. Alternatively, an electric current pattern having been programmed beforehand in the timed relation with the currents to be supplied to the linear motors A 4  and A 5 , may be used. 
     FIG. 11 shows an exposure apparatus as a whole, in which a reticle stage  73  according to the third embodiment is incorporated. As described hereinbefore, the reticle stage base  71   a  for supporting the reticle stage  73  is made integral with a frame  94  which is mounted on a base table  92  for supporting a wafer stage  93  of the exposure apparatus. On the other hand, the linear motor base  71   b  is supported by a supporting frame  90  which is directly fixed to the floor F, separately from the base table  92 . The exposure light for exposing a wafer W 4  on the wafer stage  93  is produced by a light source device  95 , as depicted by a broken line. 
     The frame  94  supports the reticle stage base  71   a  as well as a projection optical system  96  at a position between the reticle stage  73  and the wafer stage  93 . Since the linear motor stators  74  and  75  of the linear motors A 4  and A 5  for acceleration and deceleration of the reticle stage  73 , are supported by the supporting frame  90  which is separate from the frame  94  as described hereinbefore, there is no possibility that a reactive force of the drive force of the linear motors A 4  and A 5  of the reticle stage  73  is transmitted to the wafer stage  93  to cause external disturbance to its driving means or that it produces vibration of the projection optical system  96 . 
     By avoiding the problem due to the reactive force of the drive force of the linear motors A 4  and A 5  of the reticle stage  73  in the manner described, it is possible to reduce the wait time for a start of the subsequent exposure cycle and thereby to improve the throughput of the exposure apparatus. 
     The wafer stage  93  is scanningly moved by driving means (not shown) similar to that of the reticle stage  73 , in a timed relation with the reticle stage  73 . During the scan of their reticle stage  73  and the wafer stage  93 , the positions are uninterruptedly detected by means of interferometers  97  and  98 , and the detected positions are fed back to the driving means of the reticle stage  73  and the wafer stage  93 , respectively. Thus, it is assured to synchronize the scanning start positions of these stages exactly and also to control the scanning speed in the constant-speed scan region very precisely. 
     When a fluctuation preventing device such as described hereinbefore is added to the reticle stage  73 , it is possible to cancel the rotational moment attributable to the drive force of the linear motors A 4  and A 5  of the reticle stage  73  to thereby prevent fluctuation of the exposure apparatus as a whole during acceleration or deceleration of the reticle stage  73 . Thus, it is possible to avoid large swinging vibration of the exposure apparatus and resultant deformation of the frame  94  which causes deviation in relative position of the interferometer  97  or  98  relative to the reticle stage  73  or the wafer stage  93 . 
     Embodiment 4 
     Now, an embodiment of a device manufacturing method which uses an exposure apparatus such as described above, will be explained. 
     FIG. 12 is a flow chart of the sequence of manufacturing a semiconductor device such as a semiconductor chip (e.g., IC or LSI), a liquid crystal panel or a CCD, for example. Step  1  is a design process for designing the circuit of a semiconductor device. Step  2  is a process for manufacturing a mask on the basis of the circuit pattern design. Step  3  is a process for manufacturing a wafer by using a material such as silicon. 
     Step  4  is a wafer process which is called a pre-process wherein, by using the so prepared mask and wafer, circuits are practically formed on the wafer through lithography. Step  5  subsequent to this is an assembling step which is called a post-process wherein the wafer processed by step  4  is formed into semiconductor chips. This step includes assembling (dicing and bonding) and packaging (chip sealing). Step  6  is an inspection step wherein operability check, durability check and so on of the semiconductor devices produced by step  5  are carried out. With these processes, semiconductor devices are finished and they are shipped (step  7 ). 
     FIG. 13 is a flow chart showing details of the wafer process. Step  11  is an oxidation process for oxidizing the surface of a wafer. Step  12  is a CVD process for forming an insulating film on the wafer surface. Step  13  is an electrode forming process for forming electrodes on the wafer by vapor deposition. Step  14  is an ion implanting process for implanting ions to the wafer. Step  15  is a resist process for applying a resist (photosensitive material) to the wafer. Step  16  is an exposure process for printing, by exposure, the circuit pattern of the mask on the wafer through the exposure apparatus described above. Step  17  is a developing process for developing the exposed wafer. Step  18  is an etching process for removing portions other than the developed resist image. Step  19  is a resist separation process for separating the resist material remaining on the wafer after being subjected to the etching process. By repeating these processes, circuit patterns are superposedly formed on the wafer. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.