Abstract:
A projection exposure apparatus is provided. The projection exposure apparatus includes an illumination optical system for illuminating a portion of a mask pattern on a mask with an exposing radiation flux of a predetermined shape, a fixed support, a projection optical system fixed to the fixed support for projecting the image of the illuminated portion of the mask pattern onto a substrate, and a carriage for integrally holding the mask and the substrate, the carriage being movable in a predetermined direction with respect to the projection optical system to successively exposing the substrate with the image of the mask pattern formed by the exposing radiation flux. The projection exposure apparatus further includes a long mirror elongated in the predetermined direction and fixed to the fixed support, the length of the long mirror being at least equal to the stroke of the carriage movement in the predetermined direction, and a measurement system for measuring the position of the mask and the position of the substrate with respect to the long mirror to determine the position of the mask relative to the substrate in a direction perpendicular to the predetermined direction.

Description:
This is a continuation of application, application Ser. No. 08/888,291, filed Jul. 3, 1997, now abandoned. This application also is a continuation-in-part of application Ser. No. 08/881,902, filed Jun. 23, 1997, now U.S. Pat. No. 6,049,372 issued Apr. 11, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exposure apparatus, and more particularly, to a projection exposure apparatus in which a pattern on a mask is projected onto a photosensitive substrate and exposed by moving the mask and the photosensitive substrate in a predetermined direction with respect to a projection optical system. 
     2. Discussion of the Related Art 
     FIG. 7 illustrates the construction of a conventional projection exposure apparatus. A pattern on a mask  110  is projected onto a glass plate  114  (photosensitive substrate) at equal magnification via a projection optical system  112 . In FIG. 7, the direction of movement (scan) of the mask  110  and glass plate  114  is taken as the X axis, a direction perpendicular to the X-axis in the plane of the mask  110  is taken as the Y-axis, and a direction normal to the mask  110  (i. e., the direction of the optical axis of the projection optical system  112 ) is taken as the Z-axis. The projection optical system  112  is installed at the center of a C-shaped bridge  116  (fixed support). An illumination optical system  118  includes a light source, such as an ultra-high-pressure mercury lamp, and a fly-eye lens, etc., and is installed on one end of the bridge  116  to illuminate a predetermined portion of the mask  110  with uniform brightness. 
     The mask  110  and the glass plate  114  are held on a mask stage  120  and a plate stage  122 , respectively, such that the mask  110  and the glass plate  114  are substantially parallel to the XY plane. Furthermore, mask stage  120  and plate stage  122  are installed on a carriage  124  as an integral unit. Two Y-direction micromotion actuators  126  and  128  are installed on the carriage  124  beneath the mask stage  120  to adjust the position of the mask stage  120  in the Y direction. An X-direction micromotion actuator  130  is installed on the carriage  124  at the end portion of the mask stage  120  on the side of the projection optical system  112  to adjust the position of the mask stage  120  in the X direction. 
     The plate stage  122  is constructed in such a way as to be movable in the Z direction and tiltable about the X-axis and the Y-axis in order to substantially match the exposed region on the plate  114  with the pattern imaging plane of the mask  110  formed through the projection optical system  112  during scanning exposure. In other words, the imaging condition is adjusted by moving the plate stage  122  in the Z direction and by adjusting inclination of the glass plate  114  (i.e., tilting the glass plate  114  about the X-axis and the Y-axis). By performing such adjustments, it is possible to make corrections for thickness irregularities, inclination, and deformation, etc., which exist in the glass plate  114 . 
     The carriage  124  can slide in the X direction along guide members  132   a  and  132   b . When the carriage  124  is moved in the X direction with respect to illuminating light emitted by the illumination system  118 , the mask  110  and the glass plate  114  are synchronously scanned by the illumination light from the projection optical system  112 . This way, the pattern on the mask  110  is successively transferred onto the glass plate  114 . Thus, the entire pattern on the mask  110  is projected and exposed onto the glass plate  114  by one scanning operation. 
     Next, an alignment mechanism for aligning the mask  110  with the glass plate  114  in the abovementioned projection exposure apparatus will be described. Moving mirrors  136   a ,  136   b ,  138   a , and  138   b  are fixed to bottom portions of the mask stage  120  and plate stage  122  in respective positions corresponding to the Y-direction micromotion actuators  126  and  128 . The moving mirrors  136   a  and  136   b  are arranged to reflect laser beams originating from a differential type laser interferometer  140  fixed to the carriage  124 . More specifically, a laser beam emitted by the laser interferometer  140  is split into two laser beams by a split optical system  144 , and the resultant two laser beams are guided to the moving mirrors  136   a  and  136   b . The laser beams reflected by the moving mirrors  136   a  and  136   b  return to the laser interferometer  140  through the split optical system  144 . At the interferometer  140 , the two light beams reflected by the moving mirrors  136   a  and  136   b  are coupled to produce interference. Based on the interference information, the relative positional deviation between the mask  110  and the glass plate  114  in the non-scanning direction (i.e., the Y direction) is detected at a position corresponding to Y-direction micromotion actuator  126 . 
     The moving mirrors  138   a  and  138   b  are arranged to reflect laser beams originating from a differential type laser interferometer  142  fixed to the carriage  124 . More specifically, a laser beam emitted by the laser interferometer  142  is split into two laser beams by a split optical system  146 , and the resultant laser beams are guided to the moving mirrors  138   a  and  138   b . The laser beams reflected by the moving mirrors  138   a  and  138   b  return to the laser interferometer  142  through the split optical system  146 . At the interferometer  142 , the two light beams reflected by the moving mirrors  138   a  and  138   b  are coupled to produce interference. Based on the interference information, the relative positional deviation between the mask  110  and the glass plate  114  in the non-scanning direction (i.e., the Y direction) is detected at a position corresponding to Y-direction micromotion actuator  128 . 
     Thus, the relative positional deviation between the mask  110  and the glass plate  114  in the Y direction can be detected by the laser interferometer  140  and the laser interferometer  142  at two points  126 ,  128 , which are separated by a predetermined distance in the X direction. Furthermore, the relative rotational deviation about the Z direction between the mask  110  and the glass plate  114  can be detected from the difference in the results detected at the laser interferometer  140  and laser interferometer  142 . When such deviations are detected, the Y-direction micromotion actuators  126 ,  128  are driven to offset the deviations. Furthermore, since the laser interferometers  140  and  142  utilize laser beams from light sources fixed to the carriage  124 , the relative positional deviation detected in the Y direction is unaffected by changes in the attitude of the carriage  124 . For example, even when the carriage  124  is displaced in the Y direction due to fluctuations in the X direction movement of the carriage  124 , the light sources for the laser interferometers  140  and  142  and the split optical systems  144  and  146  are also displaced together with the carriage  124 . Accordingly, no positional deviations between the mask  110  and glass plate  114  are detected in the Y direction. 
     A reflex mirror  148  and a reflex mirror  150  are disposed on the end portions of the mask stage  120  and plate stage  122 , respectively, on the negative X direction side in the positions corresponding to the X-direction micromotion actuator  130 . The reflex mirrors  148  and  150  are arranged to reflect laser beams from laser interferometers  152  and  154 , respectively. The laser interferometer  152  is a length measuring type interferometer, and emits a laser beam from a light source toward the reflex mirror  148  fixed to the mask stage  120  and toward a fixed mirror (not shown in the figures) fixed to the bridge  116 . Furthermore, this interferometer  152  detects interference (synthesis) between the laser beam reflected by the reflex mirror  148  and the laser beam reflected by the fixed mirror, and determines the position of the mask  110  in the X direction on the basis of the interference. 
     The laser interferometer  154  is also a length measuring type interferometer, and emits a laser beam from a light source fixed to a fixed system, such as the bridge  116  or the projection optical system  112 , toward the reflex mirror  150  fixed to the plate stage  122  and toward the abovementioned fixed mirror (not shown in the figures). Furthermore, the interferometer  154  detects interference between the laser beam reflected by the reflex mirror  150  and the laser beam reflected by the fixed mirror, and determine the position of the glass plate  114  in the X direction on the basis of the interference. 
     Furthermore, the relative positional deviation between the mask  110  and the glass plate  114  in the X direction is detected from the difference in the results detected at the laser interferometer  152  and laser interferometer  154 . More specifically, the relative difference between the position of the mask  110  in the X direction measured by the laser interferometer  152  and the position of the glass plate  114  in the X direction measured by the laser interferometer  154  is determined. Here, since light sources used for laser interferometers  152  and  154  are fixed to the fixed system (bridge  116  or the projection optical system  112 , etc.), changes in the attitude of the carriage  124  in the pitching direction (direction of rotation about the Y-axis), i.e., the relative positional deviation between the mask  110  and the glass plate  114  in the scanning direction (the X direction) including the pitching amount of the carriage  124 , can be detected. The output of the laser interferometer  154  at the plate stage  122  side is fed back to a carriage driving controller (not shown in the figures) to control the speed of the carriage  124  relative to the projection optical system  112  so as to produce uniform exposure across the entire area of the glass plate  114  during scanning exposure. 
     A long reflex mirror  156  extending in the X direction is fixed to the upper surface of the carriage  124  to reflect the laser beam emitted by a laser interferometer  158 . The laser interferometer  158  is a differential type interferometer which detects changes in the attitude of the carriage  124  in the rolling direction (the direction of rotation about the X-axis). In this interferometer system, a laser beam emitted by a light source fixed to the bridge  116  is split into two beams and is guided to two points on the reflex mirror  156 , which are separated along the Z direction. The laser beams reflected by the reflex mirror  156  are coupled to yield interference at the interferometer  158 . According to the interference, the amount of rotation of the carriage  124  about the X-axis, i.e., the rolling amount, is detected. The positional deviations of the mask  110  and the glass plate  114  relative to the fixed system in the Y direction is determined on the basis of the rolling amount detected by the interferometer  158 . This deviation is corrected by driving the Y-direction micromotion actuators  126  and  128 . 
     In the conventional projection exposure apparatus described above, the laser interferometers  140  and  142  and the split optical systems  144  and  146  for the interferometers are fixed to the carriage  124 . Accordingly, if the carriage  124  is deformed due to poor straightness of the guide members  132   a  and  132   b , etc., a relative displacement is generated between the split optical system  144  and split optical system  146 . As a result, the measured values by the laser interferometers  140  and  142 , i.e., the relative positional deviation between the mask  110  and the glass plate  114  in the Y direction, may contain errors. 
     Furthermore, since the laser interferometers  140  and  142  are installed on the carriage  124 , it is necessary to apply a large driving force to drive the carriage  124 . Moreover, since the long reflex mirror  156  is fixed to the carriage  124  and the weight of the carriage  124  includes the weight of the reflex mirror  156 , the driving force to the carriage  124  needs to be increased even further. As a result, the size of the driving system becomes undesirably large. With such a large driving system, it is difficult to achieve high scanning precision (uniform speed control, etc.) for the carriage  124 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a projection exposure apparatus that substantially obviates the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a projection exposure apparatus in which the relative positional deviation between the mask and the photosensitive substrate in the nonscanning direction can be accurately detected. 
     Another object of the present invention is to provide a projection exposure apparatus which is compact and light in weight and has a stable operating precision. 
     Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a projection exposure apparatus, including an illumination optical system for illuminating a portion of a mask pattern on a mask with an exposing radiation flux of a predetermined shape; a fixed support; a projection optical system fixed to the fixed support for projecting the image of the illuminated portion of the mask pattern onto a substrate; a carriage for integrally holding the mask and the substrate, the carriage being movable in a predetermined direction with respect to the projection optical system to successively expose the substrate with the image of the mask pattern formed by the exposing radiation flux; a long mirror elongated in the predetermined direction and fixed to the fixed support, the length of the long mirror being at least equal to the stroke of the carriage movement in the predetermined direction; and a measurement system for measuring the position of the mask and the position of the substrate with respect to the long mirror to determine the position of the mask relative to the substrate in a direction perpendicular to the predetermined direction. 
     In another aspect, the present invention provides a position detector for detecting the position of a movable stage moving relative to a fixed support in a predetermined direction with a predetermined moving range, the position detector including an extended mirror fixed to the fixed support of the exposure apparatus, the extended mirror being elongated in the predetermined direction and longer than the predetermined moving range of the movable stage; an optical element installed on the movable stage; and an optical measurement system for optically measuring the positional relationship between the extended mirror and the optical element to derive the position of the movable stage relative to the fixed support in a direction perpendicular to the predetermined direction. 
     In a further aspect, the present invention provides an exposure apparatus for projecting a mask pattern on a mask onto a substrate at equal magnification, including a fixed support; an illumination optical system fixed to the fixed support for emitting an exposing radiation flux to illuminate a portion of the mask pattern on the mask; a projection optical system fixed to the fixed support for projecting the image of the illuminated portion of the mask pattern onto the substrate at equal magnification; a carriage for integrally holding the mask and the substrate in parallel, the carriage being movable in a predetermined moving direction substantially parallel to the surfaces of the mask and the substrate with a predetermined moving range to successively exposing the substrate with the image of the mask pattern formed by the exposing radiation flux; a first optical element adjacent the mask; a second optical element adjacent the substrate; a first extended mirror optically coupled to the first optical element, the first extended mirror being fixed to the fixed support and extending in the predetermined moving direction of the carriage, the first extended mirror being longer than the predetermined moving range of the carriage; a second extended mirror optically coupled to the second optical element, the second extended mirror being fixed to the fixed support and extending in the predetermined moving direction of the carriage, the second extended mirror being longer than the predetermined moving range of the carriage; and an optical measurement system for optically measuring the position of the first optical element relative to the first extended mirror and the position of the second optical element relative to the second extended mirror to determine the position of the mask relative to the substrate in a direction perpendicular to the predetermined moving direction of the carriage. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
     In the drawings: 
     FIG. 1 is a perspective view illustrating an equal-magnification upright image type projection exposure apparatus according to an embodiment of the present invention; 
     FIG. 2 is a schematic side view of the projection exposure apparatus of FIG. 1; 
     FIG. 3 is a front view showing the schematic construction (layout) of an interferometer system for the projection exposure apparatus of FIG. 1; 
     FIG. 4 is a front view showing the schematic construction (layout) of a modified interferometer system for the projection exposure apparatus of FIG. 1; 
     FIG. 5A is a front view showing the schematic construction (layout) of another modified interferometer system for the projection exposure apparatus of FIG. 1; 
     FIG. 5B is a front view showing the schematic construction (layout) of another modified interferometer system for the projection exposure apparatus of FIG. 1; 
     FIG. 6 is a front view showing the schematic construction (layout) of a further modified interferometer system for the projection exposure apparatus of FIG. 1; and 
     FIG. 7 is a perspective view showing the construction of a conventional projection exposure device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 1 shows the construction of the projection exposure apparatus according to a preferred embodiment of the present invention. In this embodiment, the present invention is applied to a scan type projection exposure apparatus. A pattern on a mask  10  is projected onto a glass plate  14  (photosensitive substrate) via a projection optical system  12  at equal magnification. In FIG. 1, the direction of movement (scanning) of the mask  10  and glass plate  14  is taken as the X axis, a direction perpendicular to the X-axis in the plane of the mask  10  is taken as the Y-axis, and a direction normal to the mask  10  (i. e., the direction of the optical axis of the projection optical system  12 ) is taken as the Z-axis. The projection optical system  12  is fixed at the center of a C-shaped bridge  16  (fixed support). An illumination optical system  18  including a light source, such as an ultra-high-pressure mercury lamp, and a fly-eye lens, etc., is fixed to one end of the bridge  16 , to illuminate a predetermined portion of a mask  10  with uniform brightness. 
     The mask  10  and the glass plate  14  are held on a mask stage  20  and a plate stage  22 , respectively, such that the mask  10  and glass plate  14  are substantially parallel to the XY plane. Furthermore, the mask stage  20  and plate stage  22  are integrally held by a common carriage  24 . Two Y-direction micromotion actuators  26  and  28  are fixed to the carriage  24  beneath the mask stage  20  to adjust the position of the mask stage  20  in the Y direction. An X-direction micromotion actuator  30  is installed on the carriage  24  at the end portion of the mask stage  20  at the projection optical system  12  side to adjust the position of the mask stage  20  in the X direction. 
     The plate stage  22  is constructed to be movable in the Z direction and tiltable about the X-axis and the Y-axis in order to substantially match the exposure region on the plate  14  with the pattern imaging plane of the mask  10  formed through the projection optical system  12  during scanning exposure. In other words, the imaging conditions are adjusted by moving the plate stage  22  in the Z direction and by adjusting inclination of the glass plate  14  (i.e., tilting about the X-axis and the Y-axis). By performing such adjustments, it is possible to make corrections for thickness irregularities, inclination and deformation, etc., which may exist in the glass plate  14 . 
     The carriage  24  is constructed to be slidable in the X direction along guide members  32   a  and  32   b  by a driving system  36 . When the carriage  24  is moved in the X direction with respect to the illuminating light emitted by the illumination system  18 , the mask  10  and the glass plate  14  are synchronously scanned with respect to the projection optical system  12  (i e., the illuminating light). This way, the pattern on the surface of the mask  10  is successively transferred onto the glass plate  14 . Thus, the entire pattern region on the mask  10  is projected and exposed onto the glass plate  14  (i.e., transferred onto the glass plate  14 ) by one scanning operation 
     Next, the alignment mechanism for aligning the mask  10  with the glass plate  14  in the abovementioned projection exposure apparatus will be described with reference to FIGS. 1,  2 , and  3 . In this embodiment, the positions of the mask  10  and glass plate  14  are measured using six laser interferometers  40 ,  42 ,  44 ,  46 ,  48 ,  50 , which are fixed to the bridge  16 . The laser interferometers  40  and  42  emit measurement-use laser beams toward reflex mirrors  54  and  56 , respectively, disposed on the side edge of the mask stage  20  facing the projection optical system  12 . The reflex mirrors  54  and  56  are disposed with a predetermined spacing in the Y direction, and the reflecting surfaces of the mirrors are parallel to the YZ plane. The laser interferometers  40  and  42  measure the position of the mask  10  in the X direction on the basis of the laser beams reflected by the reflex mirrors  54  and  56 . Furthermore, the rotational displacement of the mask  10  about the Z-axis can be determined from the measured values obtained by the laser interferometers  40  and  42 . More specifically, the rotational displacement of the mask  10  about the Z-axis can be determined from the relative displacement between the position of the reflex mirror  54  (i. e., the position of the mask  10 ) measured by the laser interferometer  40  and the position of the reflex mirror  56  (i. e., the position of the mask  10 ) measured by the laser interferometer  42 . 
     The laser interferometers  44  and  46  emit measurement-use laser beams toward reflex mirrors  58  and  60 , respectively, disposed on the side edge of the plate stage  22  facing the projection optical system  12 . The reflex mirrors  58  and  60  are disposed with a predetermined spacing in the Y direction, and the reflecting surfaces of the mirrors are parallel to the YZ plane. The laser interferometers  44  and  46  measure the position of the glass plate  14  in the X direction on the basis of the laser beams reflected by the reflex mirrors  58  and  60 . Furthermore, the rotational displacement of the glass plate  14  about the Z-axis can be determined from the measured values obtained by the laser interferometers  44  and  46 . More specifically, the rotational displacement of the glass plate  14  about the Z-axis can be determined from the relative displacement between the position of the reflex mirror  58  (i. e., the position of the glass plate  14 ) measured by the laser interferometer  44  and the position of the reflex mirror  60  (i. e., the position of the glass plate  14 ) measured by the laser interferometer  46 . 
     The laser interferometer  48  measures the position of the mask  10  in the Y direction. This interferometer  48  illuminates a long reflex mirror  62  (one end of which is fixed to the ceiling portion of the bridge  16 ) with a measurement-use laser beam through a split optical system  64  fixed to the mask stage  20 . The reflex mirror  62  has a length which is equal to or larger than the movement stroke of the carriage  24 . One end of this mirror  62  is fixed to the bridge  16 , whereas the other end extends in the direction of the mask stage  20  (X direction). Furthermore, the reflecting surface (bottom surface) of the reflex mirror  62  is oriented perpendicular to the Y axis (i.e., parallel to the XZ plane). The split optical system  64  guides the laser beam emitted by the laser interferometer  48  in a direction perpendicular to the reflecting surface of the reflex mirror  62 . The laser interferometer  48  receives the laser beam reflected from the reflecting mirror  62  to measure the position of the mask  10  in the Y direction with respect to the reflex mirror  62 . More specifically, the displacement of the mask  10  in the Y direction is measured using a fixed system (bridge  16 , projection optical system  12 , etc.) as a reference. 
     The laser interferometer  50  measures the position of the glass plate  14  in the Y direction. This interferometer  50  illuminates a long reflex mirror  66  (one end of which is fixed to the ceiling portion of the bridge  16 ) with a measurement-use laser beam through a split optical system  68  fixed to the plate stage  22 . Like the abovementioned reflex mirror  62 , the reflex mirror  66  has a length which is equal to or larger than the movement stroke of the carriage  24 . One end of the mirror  66  is fixed to the bridge  16 , whereas the other end is extending in the direction of the plate stage  22  (X direction). Furthermore, the reflecting surface (bottom surface) of the reflex mirror  66  is oriented perpendicular to the Y axis (i. e., parallel to the XZ plane). The split optical system  68  guides the laser beam emitted by the laser interferometer  50  in a direction perpendicular to the reflecting surface of the reflex mirror  66 . The laser interferometer  50  receives the laser beam reflected from the reflecting mirror  66  to measure the position of the glass plate  14  in the Y direction with respect to the reflex mirror  66 . More specifically, the displacement of the glass plate  14  in the Y direction is measured using the fixed system (bridge  16 , projection optical system  12 , etc.) as a reference. 
     For example, polarizing beam splitters may be used as the split optical systems  64 ,  68  for guiding the laser beams from the laser interferometers  48  and  50  to the reflex mirrors  62  and  66 , respectively. FIG. 3 illustrates the construction of such an interferometer system, which measures the displacement of the mask  10  (glass plate  14 ) in the Y direction. Here, a reference mirror  65  is disposed on the rear side of a polarizing beam splitter  64  installed on the mask stage  20 . This reference mirror  65  reflects the laser beam that passes through the polarizing beam splitter  64 . In the present embodiment, a portion of the light emitted by the laser interferometer  48  is directed to the reflex mirror  62  by the polarizing beam splitter  64 , while the remaining light passes through the polarizing beam splitter  64  and impinges on the reference mirror  65 . 
     The laser interferometer  48  measures the position of the mask  10  in the Y direction with respect to the reflex mirror  62  from the difference in optical path length between the laser beam reflected by the reflex mirror  62  and the laser beam reflected by the reference mirror  65 . That is, when the mask  10  is displaced in the Y direction with respect to the reflex mirror  62 , the length of the optical path from the polarizing beam splitter  64  to the reflex mirror  62  changes. Therefore, a relative difference in optical path length is generated between the laser beam returning from the reflex mirror  62  and the laser beam returning from the reference mirror  65 . Accordingly, the position of the of the mask  10  in the Y direction can be measured on the basis of interference between the two laser beams received by the laser interferometer  48 . The split optical system  68  for the plate stage  22  may have a similar construction. 
     In the present embodiment, relative translational displacements ΔX, ΔY in the X and Y directions and relative rotational displacement ΔXθ, ΔYθ, ΔZθ about the X, Y, and Z axes between the mask  10  and the glass plate  14  can be detected on the basis of the measured values obtained by the six laser interferometers  40 ,  42 ,  44 ,  46 ,  48 ,  50  above. In detail, the position MX of the mask  10  in the X direction is determined on the basis of the measured value MX1 obtained by the laser interferometer  40  and the measured value MX2 obtained by the laser interferometer  42  by taking an average, for example. Furthermore, the rotational displacement MZθ of the mask  10  about the Z axis is determined from the difference between the measured value MX1 obtained by the laser interferometer  40  and the measured value MX2 obtained by the laser interferometer  42 . In addition, the position MY of the mask  10  in the Y direction is determined from the measured value obtained by the laser interferometer  48 . 
     As for the glass plate  14 , the position PX of the glass plate  14  in the X direction is determined on the basis of the measured value PX1 obtained by the laser interferometer  44  and the measured value PX2 obtained by the laser interferometer  46  by taking an average, for example. The rotational displacement PZθ of the glass plate  14  about the Z axis is determined from the difference between the measured value PX1 obtained by the laser interferometer  44  and the measured value PX2 obtained by the laser interferometer  46 . In addition, the position PY of the glass plate  14  in the Y direction is determined from the measured value obtained by the laser interferometer  50 . 
     Furthermore, the relative deviation ΔX between the mask  10  and the glass plate  14  in the X axis including pitching (rotation about the Y-axis) of the carriage  24  is determined from the difference between the position MX of the mask  10  in the X direction and the position PX of the glass plate  14  in the X direction determined above. Moreover, the relative deviation ΔY between the mask  10  and the glass plate  14  in the Y direction including rolling (rotation about the X-axis) of the carriage  24  is determined from the difference between the position MY of the mask  10  in the Y direction and the position PY of the glass plate  14  in the Y direction. In addition, the relative rotational deviation ΔZθ between the mask  10  and the glass plate  14  about the Z-axis is determined from the rotational displacement MZΔ of the mask  10  about the Z axis and the rotational displacement PZΔ of the glass plate  14  about the Z direction. 
     Next, the overall operation of the present embodiment will be described. First, an alignment mark on the mask  10  and an alignment mark on the glass plate  14  are simultaneously observed using a microscope (not shown in the figures) to perform initial alignment of the mask  10  with glass plate  14 . Then, the laser interferometers  40 ,  42 ,  44 ,  46 ,  48 ,  50  are calibrated; the measured values output from the respective laser interferometers  40 ,  42 ,  44 ,  46 ,  48 ,  50  are set to zero. Next, scanning exposure is initiated by driving the carriage  24  in the X direction via the driving system  36 . During the scanning exposure, the relative positional deviations ΔX, ΔY, ΔZθ between the mask  10  and the glass plate  14  are determined through the laser interferometers  40 ,  42 ,  44 ,  46 ,  48 ,  50  using the procedures described above. The driving amounts (adjustment amounts) of the micromotion actuators  26 ,  28 , and  30  installed on the mask stage  20  are determined in accordance with the positional deviations ΔX, ΔY and ΔZθ thus determined. Accordingly, positional adjustments of the mask  10  and glass plate  14  in the X direction, Y direction, and the rotational direction about the Z-axis are accomplished by feedback control of the micromotion actuators  26 ,  28  and  30 . 
     In the embodiment above, since the reflex mirrors  62  and  66  are fixed to the bridge  16 , relative positional deviations between the mask  10  and glass plate  14  including relative positional deviations caused by changes in the attitude or local deformation of the carriage  24  can be detected. Accordingly, even if the carriage  24  itself is deformed due to insufficient straightness of the guide members  32   a ,  32   b  of the carriage  24 , etc., the positions of the mask  10  and glass plate  14  can be accurately detected and corrected using the projection optical system  12  as a reference. As a result, the desirable positional relationship of the mask  10  and the glass plate  14  with respect to the projection optical system  12  can be maintained regardless of the guidance precision (movement performance) of the mechanical system for the carriage  24  or deformation of the carriage  24  itself. Therefore, high exposure precision (transfer precision) can be maintained. 
     Furthermore, since the reflex mirrors  62 ,  66  are not installed on the carriage  24 , the weight of the carriage  24  can be reduced as compared with the conventional exposure apparatus above. As a result, the size of the driving system  36  can be reduced and the constant-speed characteristics during scanning exposure can be improved, leading to stable exposure operation. 
     FIGS. 4,  5 A,  5 B, and  6  illustrate various modifications of the interferometer system for measuring the relative positional deviation ΔY between the mask  10  and the glass plate  14  in the Y direction. The constituent elements similar to those mentioned above are labeled with the same reference numerals and the descriptions thereof are not repeated below. 
     The interferometer system illustrated in FIG. 4 is equipped with a laser interferometer  69 , a trapezoidal mirror  70  disposed on the mask stage  20 , and a reference mirror  72  disposed on a fixed system including the bridge  16 , etc. Although not shown in the figure, a trapezoidal mirror and a reference mirror are similarly provided for the glass plate  14 . The laser interferometer  69  is arranged such that a single laser beam is split into two laser beams and is guided toward the side edge of the mask  10  and the side edge of the glass plate  14 , respectively. On the side of the mask  10 , one of the light beams emitted by the laser interferometer  69  is reflected by the trapezoidal mirror  70  toward the reflex mirror  62 . The light reflected by the reflex mirror  62  is reflected by the other side of the trapezoidal mirror  70  and impinges on the reference mirror  72 . Such configuration is also employed for the glass plate  14 . In the laser interferometer  69 , the respective light beams returning from the mask  10  and the glass plate  14  are coupled (synthesized), and interference between the two light beams are observed. This way, the relative positional deviation ΔY between the mask  10  and the glass plate  14  in the Y direction is measured. 
     FIG. 5A shows the construction of another modification of the interferometer system for measuring the positional deviations of the mask  10  and the glass plate  14  in the Y direction according to the present invention. Although FIG. 5A shows the interferometer system only for the mask  10 , a similar arrangement may be constructed for the glass plate  14 . This interferometer system is equipped with a laser interferometer  48 , a polarizing beam splitter  74  for splitting a laser beam from the laser interferometer  48  into two laser beams, a λ/4 plate  76  for altering the phase of the laser beam, a reference mirror  78  disposed on the mask stage  20 , and a corner cube  80  disposed beneath the polarizing beam splitter  74 . This example uses a so-called “double-beam interferometer” which utilizes two light beams. The system is arranged such that the distance from the reflecting surface of the polarizing beam splitter  74  to the reflecting surface of the reference mirror  78  is equal to the distance from the reflecting surface of the polarizing beam splitter  74  to the reflex mirror  62 . 
     In the present example, when the mask stage  20  is displaced with respect to the reflex mirror  62  in the Y direction, the length of the optical path of the reflected laser beam returning from the reflex mirror  62  changes. Accordingly, a difference in optical path length is generated between the laser beam returning from the reflex mirror  62  and the reflected laser beam returning from the reference mirror  78  (the latter has a fixed optical path length). The position of the mask  10  in the Y direction is detected by the laser interferometer  48  from interference between the two returning laser beams. Here, the measurements above can also be performed using a single light beam. 
     FIG. 5B shows a modification of the interferometer system of FIG.  5 A. In this modification, a corner cube  80  is used instead of the reference mirror  78  and a λ/4 plate  76  is disposed between the polarizing beam splitter  74  and the reflex mirror  62 . 
     FIG. 6 shows a further modification of the interferometer system for measuring the relative positional deviation between the mask  10  and the glass plate  14  in the Y direction according to the present invention. This interferometer system is equipped with a laser interferometer  81  and a pentaprism  82  disposed on the mask stage  20 . Furthermore, although not shown in the figures, a similar pentaprism is also provided for the glass plate  14 . The laser interferometer  81  is arranged such that a single laser beam is split into two beams and is guided toward the respective pentaprisms for the mask  10  and the glass plate  14 . At the mask  10  side, one of the laser beams is reflected by the pentaprism  82  and is directed toward the reflex mirror  62 . The light reflected by the reflex mirror  62  then returns to the laser interferometer  81  after reflected by the pentaprism  82  for the second time. At the laser interferometer  81 , the respective light beams returning from the mask  10  and the glass plate  14  are coupled (synthesized), and interference between the two laser beams is observed. This way, the relative positional deviation ΔY between the mask  10  and the glass plate  14  in the Y direction is measured. 
     In the embodiment above, the reflex mirrors  62  and  66  were fixed to the bridge  16 . However, it is also be possible to dispose these mirrors in some other locations on the fixed system (bridge  16 , projection optical system  12 , etc.). For example, these mirrors may be fixed to the projection optical system  12 . 
     In the present invention, as described above, measurement-use light (or laser beam) is projected onto long mirrors fixed to a fixed system (bridge, projection optical system, etc.) and the relative positional deviation ΔY between the mask and the photosensitive substrate (glass substrate) in a direction (Y direction) perpendicular to the scanning direction (X direction) is measured on the basis of the measurement-use lights reflected from the long mirrors. Accordingly, the desirable positional relationship of the mask and the photosensitive substrate with respect to the projection optical system can be maintained regardless of the guidance precision (movement performance) of the mechanical system for the carriage or deformation of the carriage itself. Therefore, high exposure precision (transfer precision) is maintained. Furthermore, the size of the driving system, which drives the carriage, can be reduced, and the constant-speed characteristics during scanning exposure can be improved, yielding stable exposure operation. 
     In the present invention, as described above, the long mirrors are fixed not to the carriage of the mask and photosensitive substrate, but to a fixed system (bridge  16 , projection optical system, etc.). Accordingly, the weight of the carriage can be reduced. Therefore, the size and/or load of the driving system including actuators, etc., for adjusting the relative position of the mask and photosensitive substrate, can be reduced. As a result, the constant-speed characteristics during scanning exposure can be improved, resulting in stable exposure performance. 
     Furthermore, according to the present invention, the rotational deviation about the direction of movement of the carriage (i.e., rotation about the X direction) can also be measured. In other words, relative positional deviations between the mask and the photosensitive substrate including relative positional deviations caused by changes in the attitude and/or local deformation of the carriage can be detected. Accordingly, even if the carriage is deformed as a result of poor straightness of the guide surfaces of the carriage, etc., the positions of the mask and photosensitive substrate can be accurately detected and corrected using the projection optical system (or the fixed system) as a reference. As a result, the positional relationship of the mask and the photosensitive substrate with respect to the projection optical system can be accurately maintained regardless of the guidance precision (movement performance) of the mechanical system for the carriage or deformation of the carriage itself. Therefore, high exposure precision (transfer precision) can be maintained. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the projection exposure apparatus of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.