Projection exposure apparatus having compact substrate stage

The projection exposure apparatus is provided with a moving mirror (24X, 24Y) having a length Lm set so as to satisfy a relationship as represented by Lm<Dw+2BL, in which Dw is a diameter of a substrate stage (18) and BL is the distance between a projection center of an optical projection system (PL) and a detection center of a mark detection system (AS). The projection exposure apparatus having the moving mirror so set for its length Lm as to satisfy the above relationship can make the substrate stage (18) more compact in size and lighter in weight, thereby achieving improvements in performance of controlling the position of the substrate stage (18), as compared with a conventional exposure apparatus having a moving mirror set so as for its length to meet a relationship as represented by Lm>Dw+2BL.

BACKGROUND OF THE INVENTION 
The present invention relates to a projection exposure apparatus and, more 
particularly, to a projection exposure apparatus and a method for the 
exposure of a pattern of a mask onto a photosensitive substrate through an 
optical projection system, said pattern of the mask being so adapted as to 
be employed for manufacturing semiconductor elements, liquid crystal 
display elements and the like in a lithographic process. 
In a lithographic process for manufacturing micro devices such as, for 
example, semiconductor elements, liquid crystal display elements, charge 
couple devices (CCD's ), thin film magnetic heads and the like, there has 
been employed a projection exposure apparatus for projecting an image of a 
photomask or reticle (hereinafter referred to generally as "reticle") with 
a transcribing pattern formed thereon onto a substrate such as, for 
example, a wafer or a glass plate (hereinafter referred to as "wafer") 
with a photoresist material coated thereon through an optical projection 
system. 
The projection exposure apparatus of this kind requires a reticle to be 
aligned with a wafer at a high degree of precision prior to exposure. In 
order to effect the alignment, the wafer is provided thereon with a mark 
for detecting a position (an alignment mark) which has been transcribed 
thereonto by the exposure in the lithographic process previously carried 
out, whereby the projection exposure apparatus can detect the position of 
the wafer or a circuitry pattern on the wafer with high precision by 
detecting the position of the alignment mark. 
Hitherto, an alignment microscope for detecting such an alignment mark may 
be broken down roughly into an on-axis type for effecting the detection of 
the alignment mark through a projecting lens and an off-axis type for 
effecting the detection of the alignment mark without the use of a 
projecting lens, however, such an alignment microscope of an off-axis type 
will be more appropriate than that of an on-axis type for a projection 
exposure apparatus where there is employed an excimer laser light source 
which will become a mainstream for this purpose from now on. The reasons 
why the alignment microscope of such an off-axis type can be employed more 
advantageously than that of an on-axis type are because it allows a wider 
freedom of optical design without taking any chromatic aberration into 
account and it can use a variety of alignment systems due to the fact that 
it is mounted separately from the projecting lens, while the alignment 
microscope of such an on axis type cannot converge alignment light or 
cause a greater error due to chromatic aberration even if such alignment 
light would be converged, because the projecting lens is corrected for the 
chromatic aberration against exposure light. Further, for example, a 
phase-contrast microscope or a differential interference microscope may 
also be employed. 
FIG. 10 is an abbreviated plan view showing a portion nearby a wafer table 
of a conventional projection exposure apparatus with an alignment 
microscope of an off-axis type. As shown in FIG. 10, the wafer table as a 
substrate stage or which a wafer W is placed is provided thereon with a 
Y-axially moving mirror 80Y having a surface reflecting at an angle normal 
to the Y-axis and an X-axially moving mirror 80X having a surface 
reflecting at an angle normal to the X axis. The Y-axially moving mirror 
80Y is provided with a Y-axial interferometer, although not shown, and 
Y-axial interferometer beams in the measuring longitudinal axis in the 
Y-axial direction passing through a projection center of an optical 
projection system PL and a detection center of an alignment microscope 82 
allows the measurement of the Y-axial displacement from the reference 
position of the Y-axially moving mirror 80Y, thereby determining the Y 
coordinate of the wafer table. On the other hand, an interferometer for 
measuring the X-coordinate of the wafer table is provided with an exposing 
X-axial interferometer for projecting interferometer beams in a measuring 
longitudinal axis Xe in the X-axial direction passing through the 
projection center of the optical projection system and with an aligning 
X-axial interferometer for projecting interferometer beams in a measuring 
longitudinal axis Xa in the X axial direction passing through the 
detection center of the alignment microscope 82. 
As at least three interferometers are provided for measuring the positions 
of the wafer table as described hereinabove, the wafer table can be 
aligned by the aligning interferometer (the measuring longitudinal axis 
Xa, Y) at the time of alignment and the position of exposure can be 
measured and determined by the exposing interferometer (the measuring 
longitudinal axis Xe, Y) at the time of exposure, thereby allowing an 
accurate alignment and exposure so as to cause no Abbe's error due to the 
rotation of the wafer table. 
As an interferometer for managing the position of the wafer table of a 
projection exposure apparatus, there has generally been employed a 
Twyman-Green interferometer. The Twyman-Green interferometer has a fixed 
light path having an unvariable arm length (a length of the light path), 
which is a light path of interferometer beams to an unshown fixed mirror, 
and a moving light path which allows its arm length to vary in accordance 
with the position of a moving mirror. It is further arranged so as to 
determine the position of the wafer table as a relative displacement 
between the fixes mirror and the moving mirror by comparing the arm 
lengths or the fixed light path and the moving light path. However, this 
interferometer determines the position of the wafer table by sequentially 
adding signals of the positions of the moving mirror one by one so that 
the position of the moving mirror cannot be measured if the interferometer 
beams were cut and they would not strike the moving mirror. Accordingly, 
it requires the interferometer beams to always strike the moving mirror. 
At this end, the conventional projection exposure apparatus is designed in 
such a manner that in order to effect alignment measurement and exposure 
over the entire surface of the wafer W, the length Lm of the moving mirror 
located in the longitudinal length of the wafer table (the X-axially 
moving mirror 80X as in FIG. 10) should be set so as to establish the 
relationship as follows: 
EQU Lm&gt;Dw+2BL 
where Dw is the diameter of the wafer; and BL is the distance between the 
measuring longitudinal axes Xe and Xa. In other words, it is requisite for 
the length of the X-axially moving mirror to satisfy the above 
relationship. 
Moreover, a wafer size becomes larger as the time passes and the technical 
innovation develops, and a wafer may recently be as large as 300 
millimeters in diameter. Therefore, the length of the moving mirror should 
also be made longer, resulting in enlarging the size of a wafer table on 
which the moving mirror is mounted. 
Further, since an alignment system for the projection exposure apparatus of 
an off-axis type has an alignment micro-scope mounted outside the optical 
projection system, the diameter of the optical projection system should 
become larger, too, as the N.A. of the optical projection system becomes 
higher and the field thereof becomes greater. Moreover, as the distance 
between the optical projection system and the alignment micro-scope 
becomes apart to a more extent, this causes the moving mirror to becomes 
longer in length and the wafer table to become greater in size. 
The fact that the wafer table as a substrate stage becomes greater in size 
due to the various factors as described herein-above is now becoming a big 
issue to solve. In other words, the larger size and the greater weight of 
the substrate stage may cause the worsening of control and a decrease in 
throughput, thereby resulting in making the entire size of the apparatus 
larger and the entire weight thereof heavier. 
Under such circumstances, great demands have been made to develop 
technology of making a substrate stage compact in size and consequently 
lighter in weight, thereby enabling control over a movement of the 
substrate stage at a higher speed and effecting alignment at a more 
accurate way. 
SUMMARY OF THE INVENTION 
Therefore, the present invention has a primary object to provide a 
projection exposure apparatus so adapted as to achieve an improvement in 
various performance, particularly in performance of controlling a 
substrate table. 
Another object of the present invention is to provide a projection exposure 
apparatus so adapted as to manage a position of two-dimensional 
coordinates of a substrate stage with a high degree of precision at the 
time when a pattern of a mask is exposed through an optical projection 
system and when a mark on a photosensitive substrate is detected by a mark 
detection system. 
The present invention has further objects to provide a projection exposure 
apparatus capable of making a N.A. of the optical projection system higher 
and making a field thereof greater in size while retaining the substrate 
table constant in size. 
The present invention has still further objects to provide a projection 
exposure apparatus which is so adapted as to measure the position of the 
mark over the entire surface of the photo-sensitive substrate and to 
expose a pattern over the entire surface thereof through the optical 
projection system, without causing any disadvantage and difficulties even 
if the moving mirror and the substrate stage are made more compact in size 
and lighter in weight. 
The present invention has a still further object to provide a projection 
exposure apparatus that can ensure stability of a baseline. 
The present invention has a still further object to provide a projection 
exposure apparatus that makes the moving mirror and the substrate stage to 
be mounted thereon more compact in size and lighter in weight. 
Moreover, the present invention has another objects to provide a projection 
exposure method for measuring a position of a mark with respect to the 
entire surface of a photosensitive substrate and for exposing a pattern 
with respect to the entire surface thereof, without causing any 
disadvantage and difficulties even if the moving mirror and the substrate 
stage are made more compact in size and lighter in weight. 
In order to achieve the primary object as described herein above, the 
present invention provides a projection exposure apparatus for exposing an 
image of a pattern formed on a mask onto a photosensitive substrate 
through an optical projection system, which comprises a substrate stage 
disposed to move on a two-dimensional plane with the photosensitive 
substrate loaded thereon; a mark detection system disposed separately from 
the optical projection system for detecting a mark on the substrate stage 
or a mark on the photosensitive substrate; an interferometer system for 
managing a position of two-dimensional coordinates of the substrate stage; 
and a moving mirror disposed on the substrate stage for measuring a 
displacement from a reference position by the interferometer system; 
wherein a length Lm of the moving mirror is so set as to satisfy a 
relationship as follows: 
EQU Lm&lt;Dw+2BL 
where Dw is a diameter Dw of the photosensitive substrate and BL is a 
distance between a projection center of the optical projection system and 
a detection center of the mark detection system. 
The present invention further provides the projection exposure apparatus 
which further comprises the interferometer system having at least a first 
measuring longitudinal axis extending in a first axial direction 
connecting between the projection center of the optical projection system 
and the detection center of the mark detection system, a second measuring 
longitudinal axis extending in a second axial direction intersecting 
perpendicularly with the first measuring longitudinal axis at the 
projection center of the optical projection system, and a third measuring 
longitudinal axis extending in a third axial direction intersecting 
perpendicularly with the first measuring longitudinal axis at the 
detection center of the mark detection system. 
Further, the present invention provides the projection exposure apparatus 
further comprising a control means for resetting an interferometer in the 
second measuring longitudinal axis in a state in which the substrate stage 
is aligned with a position in which a spatial relationship of a 
predetermined reference point on the substrate stage with a predetermined 
reference point within a projection region of the optical projection 
system is detectable within a projection region of the optical projection 
system and resetting an interferometer in the third measuring longitudinal 
axis in a state in which the substrate stage is aligned with a position in 
which a reference point on the substrate stage is located within the 
detection region of the mark detection system. 
Furthermore, the present invention provides the projection exposure 
apparatus which further comprises a position detection means for detecting 
a spatial relationship of a position of the projection center of the image 
of the pattern of the mask with a position of the reference point on the 
substrate stage is detected through the mask and the optical projection 
system, wherein the position of the projection center of the image of the 
pattern of the mask is the reference point within the projection region of 
the optical projection system. 
In addition, the present invention provides the projection exposure 
apparatus which further comprises a reference plate provided with a first 
reference mark and a second reference mark in a predetermined spatial 
relationship and loaded on the substrate stage; and a control means for 
resetting at least one of the interferometer in the second measuring 
longitudinal axis and the interferometer in the third measuring 
longitudinal axis in a state that the substrate stage is aligned with a 
predetermined position so as to locate the first reference mark of the 
reference plate within the detection region of the mark detection system 
and at the same time to locate the second reference mark of the reference 
plate in a position in which a spatial relationship with a position of a 
predetermined reference point within the projection region of the optical 
projection system is detectable. 
The present invention additionally provides the projection exposure 
apparatus which further comprises a position detection means for detecting 
a spatial relationship of the projection center of the image of the 
pattern of the mask with a position of the second reference mark of the 
reference plate via the mask and the optical projection system, wherein 
the projection center of the image of the pattern of the mask is the 
reference point of the optical projection system within its projection 
region. 
In addition, the present invention provides the projection exposure 
apparatus having the control means which is so configured as to effect the 
detection by the mark detection system and the detection by the position 
detection means simultaneously in a state that the substrate stage is 
aligned with the predetermined position. 
Moreover, the present invention provides the projection exposure apparatus 
having the control means which resets the interferometer in the second 
measuring longitudinal axis after the measurement of the mark on the 
photosensitive substrate by the mark detection system has been finished 
and resets the interferometer in the third measuring longitudinal axis 
after exposure onto the photosensitive substrate via the optical 
projection system has been finished. 
In order to further achieve the object as described herein above, the 
present invention provides a projection exposure method for exposing an 
image of a pattern formed or a mask to the photosensitive substrate 
through an optical projection system, which comprises detecting a spatial 
relationship of a predetermined reference point on a substrate stage on 
which to load the photosensitive substrate with an alignment mark on the 
photosensitive substrate loaded on the substrate stage; aligning the 
predetermined reference point on the substrate stage within a projection 
region of the optical projection system after the detection; detecting a 
deviation of a position of the predetermined reference point on the 
substrate stage with respect to the predetermined reference point within 
the projection region of the optical projection system; detecting a 
position of coordinates of the substrate stage; moving the substrate stage 
on the basis of the spatial relationship detected hereinabove, the 
deviation of the position detected hereinabove, and the position of the 
coordinates of the substrate stage detected hereinabove; and aligning the 
image of the pattern of the mask with the photosensitive substrate loaded 
on the substrate stage. 
Further, the present invention provides a projection exposure method for 
exposing an image of a pattern formed on a mask onto each of plural shot 
areas on a photosensitive substrate through an optical projection system, 
which comprises detecting the position of each of a mark for detecting a 
position of a sample shot area selected from plural shot areas on the 
photo-sensitive substrate and a predetermined reference point on a 
substrate stage with said photosensitive substrate loaded thereon; 
computing a spatial relationship of the position of the predetermined 
reference point of the substrate stage with all the shot areas on the 
photosensitive substrate by operation on the basis of a result of 
detection obtained by the previous step; aligning the predetermined 
reference point on the substrate stage within a projection region of the 
optical projection system after the operation; detecting a deviation of a 
position of the predetermined reference point on the substrate stage with 
respect to the predetermined reference point within the projection region 
of the optical projection system; detecting a position of coordinates of 
the substrate stage; controlling a movement of the substrate stage on the 
basis of the spatial relationship of the positions obtained by the 
operation, the deviation of the position detected hereinabove, and the 
position of the coordinates of the substrate stage detected hereinabove; 
and aligning each of the shot areas on the photosensitive substrate loaded 
on the substrate stage with the image of the pattern of the mask. 
Other objects, features and advantages of the present invention will become 
apparent in the course of the description of this specification with 
reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The projection exposure apparatus according to an embodiment of the present 
invention will be described in more detail with reference to the 
accompanying drawings. 
As shown in FIG. 1, the projection exposure apparatus according to the 
present invention is of a type capable of exposing an image of a pattern 
formed on a mask R to a photo-sensitive substrate W through an optical 
projection system PL. More specifically, the projection exposure apparatus 
comprises a substrate stage 18 with the photosensitive substrate W loaded 
thereon, disposed so as to move in a two-dimensional plane; a mark 
detection system AS for detecting a mark on the substrate stage 18 or on 
the photosensitive substrate W, disposed separately from the optical 
projection system PL; an interferometer system 26 for managing the 
position of two dimensional coordinates of the substrate stage 18; and 
moving mirrors 24X and 24Y located above the substrate stage 18 for 
allowing displacement from the reference position to be measured by the 
interferometer system 26; in which a length Lm of each of the moving 
mirrors 24X and 24Y establishes the relationship as follows: 
EQU Lm&lt;Dw+2BL, 
in which Dw is a diameter of the photosensitive substrate W and BL is a 
distance between the projection center of the optical projection system PL 
and the detection center of the mark detection system AS. 
On the other hand, the conventional projection exposure apparatus is 
arranged in such a fashion that the length of a moving mirror Lm is set so 
as to establish the relationship: 
EQU Lm&gt;Dw+2BL. 
Therefore, as described hereinabove, the projection exposure apparatus 
according to the present invention has the length Lm of each of the moving 
mirrors set so as to satisfy the relationship: 
EQU Lm&lt;Dw+2BL, 
as shown in FIG. 3, the substrate stage 18 on which to mount the moving 
mirrors can be made more compact in size and lighter in weight, thereby 
achieving improvements in performance of controlling the position of the 
substrate stage 18, more specifically, in alignment precision, maximal 
speed, maximal acceleration and the like. 
For the projection exposure apparatus according to the present invention, 
there may be employed any interferometer system, as the interferometer 
system 26, as long as it can manage the position of the two-dimensional 
coordinates of the substrate stage 18. It is preferred that the 
interferometer system has at least three measuring longitudinal axes, that 
is, a first measuring longitudinal axis Y extending in the first axial 
direction connecting the projection center of the optical projection 
system PL and the detection center of the mark detection system AS, a 
second measuring longitudinal axis Xe extending in the second axial 
direction and intersecting perpendicularly with the first measuring 
longitudinal axis Y at the projection center of the optical projection 
system PL, and a third measuring longitudinal axis Xa extending in the 
second axial direction and intersecting perpendicularly with the first 
measuring longitudinal axis Y at the detection center of the mark 
detection system AS. The interferometer system having the such measuring 
longitudinal axes can manage the position of the two dimensional 
coordinates of the substrate stage 18 with high precision, without causing 
a so-called Abbe's error even at the time when the pattern of the mask is 
exposed through the optical projection system PL and at the time when the 
mark on the photosensitive substrate W is detected by the mark detection 
system AS. 
The projection exposure apparatus according to the present invention is 
further provided with a control means 28 which resets an interferometer 
26Xe having the second measuring longitudinal axis Xe in such a state that 
the substrate stage 18 is aligned with a position in which the spatial 
relationship between a predetermined reference point on the substrate 
stage 18 in a projection region of the optical projection system PL and a 
predetermined reference point within a projection region of the optical 
projection system PL can be detected and which resets an interferometer 
26Xa having the third measuring longitudinal axis Xa in such a state that 
the substrate stage 18 is aligned so as to allow the reference point on 
the substrate stage 18 to locate within a detection region of the mark 
detection system AS. 
With the arrangement as described hereinabove, when the interferometer 26Xe 
having the second measuring longitudinal axis Xe is brought into an 
unmeasurable state, the control unit 28 once moves the substrate stage 18 
to a position in which the reference point on the substrate stage 18 is 
located on the first measuring longitudinal axis on the basis of measured 
value during a period of time when the interferometer 26Xa having the 
third measuring longitudinal axis Xa is still active, and then resumes a 
movement of the substrate stage 18 from this position on the basis of the 
values measured by the interferometer 26Y having the first measuring 
longitudinal axis Y, thereby resetting the interferometer 26Xe having the 
second measuring longitudinal axis Xe in the such state in which the 
substrate stage 18 is aligned with the position in which the spatial 
relationship between the position of the predetermined reference point on 
the substrate stage 18 in the projection region of the optical projection 
system PL and the position of the predetermined reference point in the 
projection region of the optical projection system PL is detectable. On 
the other hand, when the interferometer 26Xa having the third measuring 
longitudinal axis Xa is brought into an unmeasurable state, the control 
unit 28 once moves the substrate stage 18 to the position in which the 
reference point on the substrate stage is located on the first measuring 
longitudinal axis Y on the basis of the measured value during a period of 
time when the interferometer 26Xe having the second measuring longitudinal 
axis Xe is still active, and then resumes a movement of the substrate 
stage 18 from this position on the value measured by the interferometer 
26Y having the first measuring longitudinal axis Y, whereby the 
interferometer 26Xa having the third measuring longitudinal axis Xa is 
reset in the such state in which the substrate stage 18 is aligned with a 
predetermined position (i.e. the reset position of the interferometer 
having the third measuring longitudinal axis) in which the reference point 
on the substrate stage is located in the detection region of the mark 
detection system AS. 
With the arrangement of the projection exposure apparatus according to the 
present invention as described hereinabove, the length of the substrate 
stage 18 can be set so as to become approximately as long as a diameter of 
a wafer W regardless the size of an baseline amount BL because the 
substrate stage 18 can be aligned with the reset position on the basis of 
the measured value of the interferometer having the first measuring 
longitudinal axis Y even if both the interferometer having the second 
measuring longitudinal axis and the interferometer having the third 
measuring longitudinal axis would have been brought into an unmeasurable 
state during a movement of the substrate stage to the reset position of 
the interferometer. Therefore, the projection exposure apparatus according 
to the present invention can readily make the N.A. of the optical 
projection system PL higher and the field thereof larger in order to 
improve resolving power, while retaining the size of the substrate stage 
constant. 
Further, it is also possible as a matter of course that, if either one of 
the interferometers having the second and third measuring longitudinal 
axes would be kept in a measurable state over the entire period of time 
when the substrate stage is being moved to the reset position of the other 
interferometer, the substrate stage can be directly aligned with the reset 
position of the other interferometer on the basis of the measured values 
of the one interferometer and the interferometer having the first 
measuring longitudinal axis. 
In this case, it is preferred that the projection exposure apparatus 
according to the present invention further comprises position detection 
means 52A and 52B for detecting the spatial relationship between the 
position of the projection center of an image of the pattern of the mask, 
that is the reference point within the projection region of the optical 
projection system PL, and the reference position on the substrate stage 18 
via the mask R and the optical projection system PL. In such a case, the 
spatial relationship of the projection center of the image of the pattern 
of the mask R with the reference point on the substrate stage 18 can be 
detected by the position detection means 52A and 52B prior to the 
resetting of the interferometer 26Xe having the second measuring 
longitudinal axis Xe, upon alignment of the substrate stage 18 with the 
position in which the spatial relationship of the position of the 
predetermined reference point on the substrate stage 18 within the 
projection range of the optical projection system PL with the position of 
the projection center of the pattern image of the mask is detectable, that 
is, with the reset position of the interferometer having the second 
measuring longitudinal axis. 
In a preferred aspect of the present invention, the projection exposure 
apparatus having the interferometer system is further provided with a 
reference plate FP1 loaded on the substrate stage 18, which has a first 
reference mark 30-1 and second reference marks 32-1 and 32-2 formed in a 
predetermined spacial relationship; and a control means 28 so adapted as 
to reset at least one of the interferometer having the second measuring 
longitudinal axis and the interferometer having the third measuring 
longitudinal axis in such a state in which the substrate stage 18 is 
aligned with the predetermined position, i.e. with the reset position of 
the interferometer having the second measuring longitudinal axis and the 
interferometer having the third measuring longitudinal axis, so as to 
locate the first reference mark 30-1 of the reference plate FP1 within the 
detection region of the mark detection system AS and to locate the second 
reference marks 32-1 and 32-2 of the reference plate FP1 in a position in 
which the spatial relationship with the position of the predetermined 
reference point within the projection region of the optical projection 
system PL is detectable. 
With the arrangement as described hereinabove, the control means 28 aligns 
the substrate stage 18 with the predetermined position, i.e. with the 
reset position of the interferometer having the second measuring 
longitudinal axis and the interferometer having the third measuring 
longitudinal axis, so as to locate the first reference mark 30-1 of the 
reference plate FP1 within the detection region of the mark detection 
system AS and simultaneously to locate the second reference marks 32-1 and 
32-2 of the reference plate FP1 in a position in which the spacial 
relationship with the predetermined reference point within the projection 
region of the optical projection system PL is detectable. In this state, 
at least one of the interferometers having the second and third measuring 
longitudinal axes is reset. 
In other words, when one of the interferometers having the second and third 
measuring longitudinal axes be brought into an unmeasurable state, the 
control means 28 is so disposed as to align the substrate stage 18 with 
the reset position on the basis of the value measured by the other 
interferometer and the interferometer having the first measuring 
longitudinal axis and then to reset the one or both of the interferometers 
having the second and third measuring longitudinal axes. Hence, simply by 
presetting the moving region of the substrate stage so as for both of the 
interferometer in the second measuring longitudinal axis and the 
interferometer in the third measuring longitudinal axis to simultaneously 
fail to fall into an unmeasurable state, the position of the mark can be 
measured over the entire surface of the photosensitive substrate and the 
pattern can be exposed through the optical projection system without 
causing any inconvenience and difficulties even if the moving mirror and 
the substrate stage are made more compact in size and lighter in weight. 
In this case, however, it is prerequisite that the first reference mark 
30-1 and the second reference marks 32-1 and 32-2 are previously provided 
on the reference plate FP1 in such a likewise spatial relationship as 
between the optical projection system PL and the mark detection system AS. 
In the such case, too, it is preferred that the projection exposure 
apparatus according to the present invention further comprises position 
detection means 52A and 52B for detecting the spatial relationship between 
the projection center of the image of the pattern of the mask R, that is 
the reference point within the projection region of the optical projection 
system PL, and the second reference marks 32-1 and 32-2 of the reference 
plate FP1 via the mask R and the optical projection system PL. With this 
arrangement of the projection exposure apparatus according to the present 
invention, the spatial relationship of the positions between the 
projection center of the pattern image of the mask and the second 
reference marks 32-1 and 32-2 through the mask R and the optical 
projection system PL can be detected by the position detection means 52A 
and 52B, before resetting the interferometer in the second measuring 
longitudinal axis Xe or the interferometers for the second and third 
measuring longitudinal axes, upon alignment of the substrate stage 18 with 
the reset position as described hereinabove. 
In a further preferred aspect of the present invention, the projection 
exposure apparatus is provided with the control means 28 so adapted as to 
simultaneously effect the detection by the mark detection system AS and by 
the position detection means 52A and 52B, in such a state that the 
substrate stage 18 is aligned with the predetermined position. It is to be 
noted herein that the term "simultaneously" or related terms referred to 
herein are intended to mean the state in which the detection is effected 
at the same time as well as the state in which the substrate stage is 
stayed in an unmoving state after alignment with the predetermined 
position (the reset position). 
In the latter case, it is possible to measure the baseline while the 
substrate stage is stayed still in a one a position so that the 
measurement of the interferometers can be effected without undergoing any 
adverse influence by disturbance of air or for other reasons, thereby 
ensuring stability in a baseline amount that is one of the most 
significant factors for the mark detection system of an off-axis type. 
In a still further aspect of the present invention, the projection exposure 
apparatus is provided with the control means so adapted as to reset the 
interferometer in the second measuring longitudinal axis after the 
measurement of the mark on the photosensitive substrate W by the mark 
detection system AS has been finished and, on the other hand, to reset the 
interferometer in the third measuring longitudinal axis after the exposure 
of the photosensitive substrate by the optical projection system has been 
finished. 
With this arrangement as described hereinabove, if the interferometer in 
the third measuring longitudinal axis becomes in an unmeasurable state 
during the exposure of the photosensitive substrate W to the pattern 
through the optical projection system PL, the interferometer in the third 
measuring longitudinal axis can be reset after the exposure has been 
finished. On the other hand, if the interferometer in the second measuring 
longitudinal axis becomes in an unmeasurable state in the process of 
finishing the measurement of the mark on the photo-sensitive substrate by 
the mark detection system AS, the interferometer in the second measuring 
longitudinal axis can be reset after the measurement has been finished. 
Therefore, even if a situation would occur where the interferometer in the 
third measuring longitudinal axis is brought into an unmeasurable 
condition during exposure by the optical projection system PL or where the 
interferometer in the second measuring longitudinal axis becomes in an 
unmeasurable state during measuring the position-detecting mark by the 
mark detection system AS, no serious inconvenience and difficulties will 
be caused to occur so that the length of the moving mirror can be 
shortened accordingly, more specifically, to approximately a diameter of 
the photosensitive substrate W. 
Moreover, the present invention provides the projection exposure method for 
exposing an image of a pattern formed on a mask R to a photosensitive 
substrate W by projection via the optical projection system PL, which 
comprises detecting a spatial relationship between a predetermined 
reference point on the substrate stage 18 with the photosensitive 
substrate W loaded thereon and an alignment mark formed on the 
photosensitive substrate W loaded on the substrate stage 18; aligning the 
predetermined reference point on the substrate stage 18 within a 
projection region of the optical projection system PL after the above 
detection; detecting a deviation of the position of the reference point on 
the substrate stage 18 with respect to the predetermined reference point 
within the projection region of the optical projection system PL; 
detecting a position of coordinates of the substrate stage 18; controlling 
a movement of the substrate stage on the basis of the detected spatial 
relationship, the detected deviation and the detected position of the 
coordinates thereof; and aligning the image of the pattern of the mask 
with the photosensitive substrate loaded on the substrate stage 18. 
With the arrangement of the projection exposure method as described 
hereinabove, the predetermined reference point on the substrate stage 18 
is aligned within the projection region of the optical projection system 
PL after the spatial relationship of the predetermined reference point on 
the substrate stage 18 with the alignment mark on the photosensitive 
substrate W has been detected, followed by detecting a deviation of the 
position of the predetermined reference point on the substrate stage 18 
with respect to the position of the predetermined reference point within 
the projection region of the optical projection system PL and detecting 
the position of the coordinates of the substrate stage 18 upon detecting 
the deviation of the predetermined reference point on the substrate stage 
18. Further, the movement of the substrate stage is controlled on the 
basis of the detection results obtained above, and then the image of the 
pattern of the mask R is aligned with the photosensitive substrate W 
loaded on the substrate stage 18. Therefore, the projection exposure 
method according to the present invention can align the image of the 
pattern of the mask R with the photosensitive substrate W loaded on the 
substrate stage 18 with a high degree of precision without causing any 
inconvenience and difficulties, even if the interferometer or a 
coordinates system for managing the position of the substrate stage 18 to 
be employed upon detection of the spatial relationship of the 
predetermined reference point on the substrate stage 18 with the alignment 
mark on the photosensitive substrate W would be identical to or different 
from the interferometer or a coordinates system for managing the position 
of the substrate stage 18 upon detection of the such deviation and upon 
detection of the position of the coordinates of the substrate stage. 
Therefore, for instance, when an alignment system of an off-axis type is 
employed as a mark detection system for detecting an alignment mark, it is 
not required to measure a spatial relationship of the predetermined 
reference point within the projection region of the optical projection 
system, i.e. the projection center of the pattern image of the mask, with 
the detection center of the alignment system, that is, to measure a 
baseline amount, thereby resulting in the situation that no inconvenience 
will be caused even if the optical projection system would be provided in 
a position remote from the position of the alignment system and as a 
consequence that the size of the substrate stage can be set regardless of 
the magnitude of the baseline amount. Further, even if the substrate stage 
is made more compact in size and lighter in weight, the mark can be 
measured over the entire surface of the photosensitive substrate and the 
pattern can be exposed to the entire surface thereof via the optical 
projection system without causing any inconvenience and disadvantage. 
Further, in this case, the measurement of the position of the mark and the 
exposure to the pattern undergo any adverse influence from a deviation in 
the baseline amount. 
Further, the present invention provides a projection exposure method for 
exposing an image of a pattern formed on a mask R to each of plural shot 
areas formed on a photosensitive substrate W by projection through the 
optical projection system PL, which comprises detecting a position of a 
predetermined reference point on a substrate stage with the photosensitive 
substrate W loaded thereon and a position of a mark for detecting a 
position of a sample shot area selected from the plural shot areas formed 
thereon; calculating and determining a spatial relationship between the 
predetermined reference point on the substrate stage and all the plural 
shot areas on the photosensitive substrate on the basis of the detection 
results obtained above; aligning the predetermined reference point on the 
substrate stage within a projection region of the optical projection 
system after calculation; detecting a deviation of the position of the 
predetermined reference point on the substrate stage with respect to a 
projection center of the image of the pattern formed on the mask R; 
detecting a position of coordinates of the substrate stage; controlling a 
movement of the substrate stage on the basis of the calculated spatial 
relationship, the detected deviation and the detected position of the 
coordinates thereof; and aligning the image of the pattern thereof with 
the photosensitive substrate loaded on the substrate stage. 
With the arrangement of the projection exposure method according to the 
present invention as described hereinabove, the position of the 
predetermined reference point on the substrate stage 18 and the position 
of the alignment mark for measuring the position of the sample shot area 
on the photosensitive substrate W are detected, and the spatial 
relationship of all the shot areas on the photosensitive substrate with 
the predetermined reference point on the substrate stage is then 
calculated and determined on the basis of the results detected above. 
Thereafter, the predetermined reference point on the substrate stage 18 is 
aligned within the projection region of the optical projection system PL, 
followed by detecting a deviation of the predetermined reference point on 
the substrate stage from the projection center of the image of the pattern 
of the mask by the optical projection system and detecting the position of 
the coordinates of the substrate stage upon detection of the such 
deviation. Based on these detection results, the movement of the substrate 
stage is controlled, thereby aligning the image of the pattern of the mask 
with each of the shot areas on the photosensitive substrate loaded on the 
substrate stage. In this case, too, likewise, the image of the pattern of 
the mask can be aligned with the photosensitive substrate loaded on the 
substrate stage with a high degree of precision without causing any 
inconvenience and difficulties, even if the interferometer or a 
coordinates system for managing the position of the substrate stage 18 
upon detection of the spatial relationship of the predetermined reference 
point or the substrate stage with the alignment mark on the photosensitive 
substrate W would be identical to or different from the interferometer or 
a coordinates system for managing the position of the substrate stage upon 
detection of the such deviation and upon detection of the position of the 
coordinates of the substrate stage. 
Therefore, in this preferred aspect of the projection exposure method 
according to the present invention as described hereinabove, the size of 
the substrate stage can be set regard-less of the magnitude of the 
baseline amount in a manner similar to the another aspect of the 
projection exposure method as described hereinabove, thereby enabling 
measurement of the mark over the entire surface of the photosensitive 
substrate and exposing the pattern to the entire surface thereof through 
the optical projection system without causing any inconvenience and 
difficulties even if the substrate stage is made more compact in size and 
lighter in weight. 
The present invention will be described in more detail with reference to 
the accompanying drawings. 
FIG. 1 shows the configuration of a projection exposure apparatus 100 
according to an embodiment of the present invention, which is an exposure 
apparatus of a reduced projection type in a step-and-repeat system (a 
so-called "stepper"). 
As shown in FIG. 1, the projection exposure apparatus 100 comprises an 
illumination system IOP, a reticle stage RST for holding a reticle R as a 
mask, an optical projection system PL for projecting an image of a pattern 
formed on the reticle R onto a wafer W as a photosensitive substrate, an 
XY-stage 20 for holding the wafer W so as to move in a two-dimensional 
plane, i.e. an XY plane, a drive system 22 for driving the XY-stage 20, 
and a main control unit 28 as a control means for controlling the entire 
system of the apparatus, which consists of a mini-computer or a 
microcomputer containing a CPU, a ROM, a RAM, an I/O interface and the 
like. 
The illumination system IOP comprises a light source, such as a mercury 
lamp or an excimer laser, and an optical illumination system, such as a 
fly-eye lens, a relay lens, a condenser lens and the like. The 
illumination system IOP is disposed so as for an illuminating light IL for 
use in exposure from the light source to illuminate a pattern of the 
reticle R from its bottom plane with the pattern formed thereon at a 
uniform distribution rate of illuminance. As the illuminating light IL, 
there may be employed bright line such as i-rays of a mercury lamp or 
excimer laser beams, such as KrF, ArF or the like. 
On the reticle stage RST is fixed the reticle R via a fixing means, 
although not shown in the drawings. The reticle stage RST is so disposed 
as to be minutely driven by a drive system, although not shown, in an 
X-axial direction (in the direction perpendicular to the paper plane of 
FIG. 1), a Y-axial direction (in the direction extending lengthwise 
(toward the right and the left) on the paper of FIG. 1) and a q direction 
(in the direction of rotation in the XY plane). This allows the reticle 
stage RST to align the reticle R in such a state that the center of the 
pattern of the reticle R, i.e. the reticle center, coincides substantially 
with the light axis Ae of the optical projection system PL. FIG. 1 shows 
the state in which the alignment of the reticle is effected. 
The optical projection system PL has the light axis Ae extending in the 
Z-axial direction intersecting with the plane on which the reticle stage 
RST moves. The optical projection system PL used herein may be of a type 
having both sides made telecentric and having a predetermined reduction 
ratio b, in which b may be 1/5. With this arrangement as described 
herein-above, when the reticle R is illuminated at a uniform rate of 
illuminance with the illuminating light IL in the state that the pattern 
of the reticle R is aligned with the shot area on the wafer W, the pattern 
on the pattern-formed plane of the mask is reduced at the reduction ratio 
b and projected onto the wafer W on which a photoresist coating is formed, 
thereby forming a reduced image of the pattern in each of the shot areas 
on the wafer W. 
The XY-stage 20 comprises a Y-stage moving in the Y-axial direction on a 
base, although not shown, and an X-stage moving in the X-axial direction 
on the Y-stage thereon. In FIG. 1, the Y-stage and the X-stage are 
referred to collectively as the XY-stage 20. On the XY-stage 20 is loaded 
a wafer table 18 as the substrate table, and the wafer W is held on the 
wafer table 18 through a wafer holder, although not shown, by means of 
vacuum adsorption or for other means. 
The wafer table 18.is so configured as to minutely move in the Z-axial 
direction integrally with the wafer holder with the wafer W held thereon. 
Therefore, the wafer table 18 may also be referred to as "Z-stage". The 
position of the two-dimensional XY-coordinates of the wafer table 18 is 
managed by an interferometer system 26 through moving mirror 24. 
As shown in FIG. 2, the wafer table 18 is provided thereon with an 
X-axially moving mirror 24X having a reflecting plane intersecting at a 
right angle with the X-axis and a Y-axially moving mirror 24Y having a 
reflecting plane intersecting at a right angle with the Y-axis. The wafer 
table 18 is further provided with laser interferometers 26Xe and 26Xa for 
measuring the positions in the X axial direction and with a laser 
interferometer 26Y for measuring the position in the Y-axial direction, 
respectively, which are disposed to measure a relative displacement of 
each of the moving mirrors 24X and 24Y from the reference positions 
located in the direction of their respective measuring longitudinal axes 
by projecting laser beams to the moving mirrors 24X and 24Y and receiving 
the light reflected therefrom. In FIG. 1, in this embodiment, these 
elements are referred to collectively as the moving mirror 24 and the 
interferometer system 26. In other words, in this embodiment, the 
interferometer system 26 is constituted by the laser interferometers 26Xe, 
26Xa and 26Y. 
It is to be noted herein that the measuring longitudinal axis Y of the 
laser interferometer 26Y intersects perpendicularly with one of the 
measuring longitudinal axes of the X-axial laser interferometers, i.e. the 
measuring longitudinal axis Xe of the X axial laser interferometer 26Xe, 
at the center of the light axis Ae (the projection center) of the optical 
projection system PL. Further, it is to be noted herein that the measuring 
longitudinal axis Y of the laser interferometer 26Y intersects 
perpendicularly with the other of the measuring longitudinal axes of the 
X-axial laser interferometers, i.e. the measuring longitudinal axis Xa of 
the X-axial laser interferometer 26Xa, at the center of the light axis Aa 
(the detection center) of an alignment sensor As, as will be described 
herein-after. This arrangement can measure the position of the wafer table 
18 in the measuring axial direction with high precision without undergoing 
any influence from the Abbe's error to be otherwise caused by yawing of 
the wafer table 18 or for other reasons upon exposure of the pattern onto 
the wafer W as well as upon measurement of the mark (alignment mark) for 
detecting the position on the wafer W, as will be described in more detail 
hereinafter. 
In this embodiment, as the three interferometers, there may be employed 
each the interferometer of a type so designed as to measure the 
displacement of the moving mirrors with respect to the fixed mirror on the 
basis of the interference state in which reference beams (not shown) are 
projected onto the fixed mirror, although not shown, and the measuring 
longitudinal beams for measuring the longitudinal distance are projected 
onto the moving mirrors, and the two beams reflected therefrom are united 
together into one resulting in interference with each other. It is 
preferred accordingly that there are employed heterodyne interferometers 
having two wavelengths as the such interferometers in order to improve 
precision in measurement. 
Turning back to FIG. 1, the measured value of the interferometer system 26 
is fed to the main control unit 28 which in turn effects alignment of the 
wafer table 18 by driving the XY-stage 20 through the drive system 22 
while monitoring the values to be measured by the interferometer system 
26. In addition, an output of a focus sensor (not shown) is also fed to 
the main control unit 28 to drive the wafer table 18 in the Z-axial 
direction (in the focusing direction) via the drive system 22 on the basis 
of the output from the focus sensor. In other words, the wafer W is 
aligned in the three directions, that is, in the X-, Y- and Z-axial 
directions, through the wafer table 18 in the manner as described 
hereinabove. 
Further, the reference plate FP is fixed on the wafer table 18 so as for 
its upper surface to become substantially on a level with the upper 
surface of the wafer W. The reference plate FP is formed on its surface 
with a variety of reference marks. Such specific examples will be 
described hereinafter. 
Furthermore, in this embodiment, the optical projection PL is provided on 
its side surface with the alignment sensor AS of an off axis type as a 
mark detection system for detecting the mark for detecting the position 
formed on the wafer W. It is to be noted herein that the wafer W is 
provided with steps by means of exposure and process treatments for the 
previous layers. Among the such steps, there may be included the 
position-detecting mark (the alignment mark) for measuring the position of 
each shot area on the wafer, and the alignment mark can be measured by the 
alignment sensor AS. 
In this embodiment, as the alignment sensor AS, there may be employed an 
alignment sensor of a so-called field image alignment (FIA) type of an 
image processing system, as disclosed in U.S. Pat. No. 5,493,403. With 
this alignment sensor AS, an illuminating light emitted from a light 
source (not shown) sending out a broad-banded illuminating light, such as 
a halogen lamp or the like, has first passed through an objective lens, 
although not shown, and then irradiated upon the wafer W or the reference 
plate FP. The light irradiated thereupon is then reflected from the wafer 
mark region (not shown) on the surface of the wafer W, and the reflected 
light passes through the objective lens and then through the reference 
plate, followed by forming an image of the wafer mark on an image-forming 
surface of a charge couple device (CCD) or other substrate, not shown, and 
at the same time by forming an index image on an index plate (not shown). 
The photo-electrically converting signals of these images are then 
processed by a signal processing circuit (not shown) disposed in a signal 
processing unit 16, and a position of the wafer mark relative to the index 
is calculated by an operation circuit, although not shown, and the 
relative position is then transmitted to the main control unit 28. Then, 
the main control unit 28 computes and determines the position of the 
alignment mark on the wafer W on the basis of the relative position and 
the measured value of the interferometer system 26. 
In addition to the alignment sensor of the FIA type, as alignment sensors, 
there may also be employed an optical alignment type including, for 
example, an alignment sensor of a laser interferometric alignment (LIA) 
type or of a laser step alignment (LSA) type, as disclosed in U.S. Pat. 
No. 5,151,750, other optical devices such as a phase microscope or a 
differential interference microscope, and a non-optical device such as a 
scanning tunnel microscope (STM) for detecting a deviation of atomic 
levels on the plane of a sample by taking advantage of the tunnel effect 
or an atomic force microscope (AFM) for detecting a deviation of atomic or 
molecular levels on the plane of a sample by taking advantage of the force 
between atoms (attracting and repelling forces). 
Further, as disclosed in U.S. Pat. No. 5,243,195, the projection exposure 
apparatus according to this embodiment of the present invention is 
provided above the reticle R with reticle alignment microscopes 52A and 
52B as a position detection means for monitoring an image of the reference 
mark on the reference plate FP simultaneously with the mark on the reticle 
R via the optical projection system PL. The detected signals S1 and S2 
from the respective reticle alignment microscopes 52A and 52B are fed to 
the main control unit 28. In this case, in order to lead the detection 
light from the reticle R to the reticle alignment microscopes 52A and 52B, 
polarizing mirrors 54A and 54B are united integrally with the respective 
reticle alignment microscopes 52A and 52B into a unit so as to form a pair 
of microscope units 56A and 56B, respectively. The microscope units 56A 
and 56B are so disposed as to be evacuated by a mirror drive unit (not 
shown) to the position in which the light does not strike the pattern 
plane of the reticle, once the exposure sequence starts, upon an 
instruction by the main control unit 28. 
In this embodiment, as shown in FIG. 3, as each of the moving mirrors 24X 
and 24Y, there is employed a moving mirror having a length Lm slightly 
longer than a diameter Dw of the wafer W. 
With this arrangement as described hereinabove, on the one hand, measuring 
longitudinal beams extending in the measuring longitudinal axis Xe do not 
strike the moving mirror 24X in such a state as shown in FIG. 4A in which 
the measured value by the interferometer 26Y becomes maximal within the 
moving scope of the wafer table 18, i.e. in which the measuring 
longitudinal beams extending in the measuring longitudinal axis Xe are 
maximal, and, on the other hand, measuring longitudinal beams extending in 
the measuring longitudinal axis Xa do not strike the moving mirror 24X in 
such a state as shown in FIG. 4B in which the measured value by the 
interferometer 26Y becomes minimal within the moving scope of the wafer 
table 18, i.e. in which the measuring longitudinal beams extending in the 
measuring longitudinal axis Xe are minimal. In other words, the state of 
FIG. 4A is a state in which an outline of an upper side of the wafer W, as 
shown in FIG. 4A, overlaps with the detection center of the alignment 
sensor AS and the state of FIG. 4B is a state in which an outline of a 
lower side of the wafer W, as shown in FIG. 4B, overlaps with the 
projection center of the optical projection system PL. 
In these cases, if the position of the wafer table 18 would be managed in a 
conventional manner by using a conventional interferometer, the former 
state makes it difficult to control the position of the wafer table 18 
during exposure and the latter makes it difficult to control the position 
of the wafer table 18 during alignment. Accordingly, in this embodiment, 
in order to avoid such difficulties, the main control unit 28 is provided 
with a reset function for the interferometers as will be described 
hereinafter. 
On the other hand, measuring longitudinal beams extending in the measuring 
longitudinal axis Y are employed for controlling the Y axial position of 
the wafer table 18. Hence, if the length of the moving mirror 24Y is 
longer tha the diameter of the wafer W, no particular problems may arise 
because the position of the wafer table 18 can be managed or monitored 
over the entire scope of the exposure region of the optical projection 
system PL and of the alignment measurement region of the alignment sensor 
AS. 
A description of a first reset function of the interferometer will now be 
made. In this embodiment, a control operation of the main control unit 28 
will be described by focusing on the first reset function of the 
interferometer. 
The first reset function of the main control unit 28 is the function of 
aligning the wafer table 18 with a predetermined reset position and 
resetting one of the interferometers 26Xe and 26Xa in the respective 
measuring longitudinal axes Xe and Xa with the predetermined reset 
position on the basis of the measured values of the interferometer 26Y in 
the measuring longitudinal axis Y and one of the interferometers 26Xe and 
26Xa, if the measuring longitudinal beams of the other of the 
interferometers 26Xe and 26Xa would run out and the involved 
interferometer would become in an unmeasurable state while the wafer table 
18 has been moving in the XY-plane. The measuring beams emitting from the 
interferometer 26Y is so disposed as to be always emitted without being 
cut. 
On the upper surface of the wafer table 18 is provided the reference plate 
FP so as for its upper surface to become on a level as substantially high 
as with the upper surface of the wafer W, as described hereinabove. As the 
reference plate FP, there may be herein employed a reference plate FP1 as 
called a great FM, as shown in FIGS. 5A and 5B and as disclosed in U.S. 
Pat. No. 5,243,195. Further, on the reference plate FP1 are provided marks 
30-1 and 30-1 for the alignment sensor as first reference marks, as shown 
in FIG. 6A, which are formed apart longitudinally at a predetermined 
interval in the lengthwise middle portion thereof. This interval is so set 
as to correspond to the designed value of the distance BL between the 
projection center of the optical projection system PL and the detection 
center of the alignment sensor AS. Further, as a pair of second reference 
marks, marks 32-1 and 32-2 for the reticle microscopes are formed 
symmetrically on the left and right sides of the first reference mark 
30-2. In other words, the reference marks 30-1 and 30-2 and the reference 
marks 32-1 and 32-2 on the reference plate FP1 are each formed in a 
predetermined spatial relationship. 
With the arrangements as described hereinabove, if the wafer table 18 is 
located in the position, for example, as indicated in FIG. 5A, in the 
state that exchange for wafers has been finished, the situation exists in 
which the measuring longitudinal beams in the measuring longitudinal axis 
Xe are cut, on the one hand, while the measuring longitudinal beams 
extending in the measuring longitudinal axis Y are kept turned on and the 
measuring longitudinal beams in the measuring longitudinal axis Xa are not 
cut, on the other. Therefore, in this state, the values measured by the 
interferometers 26Y and 26Xa are fed to the main control unit 28 and the 
main control unit 28 can recognize the position of the XY axially 
two-dimensional coordinates of the wafer table 18 at this point on the 
basis of the values measured by the interferometers 26Y and 26Xa. Further, 
on the basis of recognition of the Y-coordinate, the main control unit 28 
can also recognize with high precision that the measuring longitudinal 
beams in the measuring longitudinal axis Xe is cut. It is to be noted 
herein, however, that at this point the interferometer 26Xa is reset as 
will be described hereinafter and that the wafer table 18 is managed by a 
(Xa, Y) coordinates system. 
In this state, the alignment measurement (hereinafter referred to sometimes 
as "EGA measurement") is effected, as disclosed in U.S. Pat. No. 
4,780,617, in which the main control unit 28 measures the position of the 
mark (alignment mark) for detecting the position of a particular sample 
shot area predetermined out of the plural shot areas on the wafer W on the 
(Xa, Y) coordinates system on the basis of the output of the alignment 
sensor AS by moving the wafer table 18 integrally with the XY-stage 20 one 
after another by the drive system 22 while monitoring the values measured 
by the interferometers 26Y and 26Xa. Thereafter, data on the entire 
sequence of the plural shot areas on the wafer is computed by effecting a 
statistical operation using the position of the wafer mark of each sample 
shot area measure in the manner as described hereinabove and the data on 
the sequence of the designed shot areas in accordance with the least 
square method as disclosed, for example, in U.S. Pat. No. 4,780,617 
(Japanese Patent Unexamined Publication No. 61-44,429). It is provided, 
however, that the position of the first reference mark 30-1 is measured on 
the coordinates (Xa, Y) system by detecting the reference mark 30-1 with 
the alignment sensor AS when resetting the interferometer 26Xa prior to 
the alignment measurement and the calculation results are converted into 
data based on the first reference mark 30-1 on the reference plate FP1. 
After the alignment measurement has been finished, the sequence of the shot 
areas is processed by exposure. In this state, it is assumed that the 
beams via the interferometer 26Xe is cut. This processing will now be 
described in more detail. 
In this processing, the main control unit 28 aligns the wafer table 18 with 
the position (the reset position) in which the preset reference mark 30-1 
on the reference plate FP1 is located within the detection region of the 
alignment sensor AS while monitoring the values measured by the 
interferometers 26Y and 26Xa. In the state that the wafer table 18 is 
aligned with the reset position, as shown in FIG. 5B, the measuring 
longitudinal beams in the measuring longitudinal axis Xe strikes the 
X-axially moving mirror 24X and the second reference marks 32-1 and 32-2 
and the first reference mark 30-2 on the reference plate FP1 are located 
within the projection region of the optical projection system PL. This can 
occur because the distance BL between the measuring longitudinal axis Xe 
and the measuring longitudinal axis Xa is designed so as to become equal 
to the distance between the first reference marks 30-1 and 30-2, as 
described hereinabove. 
In this state, the main control unit 28 can simultaneously monitor an image 
of each of the second reference marks 32-1 and 32-2 on the reference plate 
FP1 and each of the reticle marks on the reticle R corresponding to the 
respective second reference marks, by using the reticle alignment 
microscopes 52A and 52B, thereby detecting a deviation of the position of 
each of the second reference marks 32-1 and 32-2 from the position of each 
of the reticle marks corresponding to the marks, on the basis of the 
detection signals of the reticle alignment microscopes 52A and 52B. More 
specifically, the interferometer 26Xe in the measuring longitudinal axis 
Xe is reset at the same time as the spatial relationship of the positions 
of the second reference marks 32-1 and 32-2 of the reference plate FP1 
with the position of the projection center of the optical projection 
system PL can be detected. In this case, the projection center of the 
optical projection system PL coincides substantially with the projection 
center of the pattern image of the reticle R. The interferometer 26Xe is 
reset when the position of the wafer table 18 is detected using the 
alignment microscopes 52A and 52B and the second reference marks 32-1 and 
32-2 on the reference plate FP1 in the manner as described hereinabove. In 
other words, the interferometer 26Xe is reset when the position of the 
wafer table 18 with respect to the projection center of the optical 
projection system PL is detected. It can be noted herein that, although 
the resetting is usually effected by setting a count value of a counter 
for counting the value measured by the interferometer 26Xe to zero, it is 
also possible to set the initial count to any optional numeral other than 
zero. 
The operations as described hereinabove can manage the position of the 
wafer table 18 on the coordinates (Xe, Y) system. 
Moreover, the main control unit 28 can effect the detection of the position 
of the first reference mark 30-1, that is, the detection of the spatial 
relationship of the position of the first reference mark 30-1 relative to 
the position of the detection center (the index center) of the alignment 
sensor AS, by the alignment sensor AS, in accompaniment with the detection 
of the spatial relationship of the positions of the respective second 
reference marks 32-1 and 32-2 of the reference plate FP1 with the position 
of the projection center of the optical projection system PL by the 
reticle alignment microscopes 52A and 52B. This allows an accurate 
measurement of the distance between the projection center of the pattern 
image of the reticle by the optical projection system PL (i.e. the 
projection center of the optical projection system PL) and the detection 
center of the alignment sensor AS, that is, the baseline amount, 
immediately after the alignment, thereby ensuring stability in the 
baseline that is of the most significance to the off-axis system as 
described hereinabove. Further, an influence of disturbance of air upon 
the interferometers can be avoided because the measurement of the baseline 
can be effected in the state in which the wafer table 18 is stayed still. 
Moreover, the angle of rotation of the reticle R can also be detected on 
the basis of the results of the simultaneous detection of the reference 
marks on the reference plate FP1 by the reticle alignment microscopes 52A 
and 52B as well as by the alignment sensor AS. 
It is to be noted herein that the first reference mark 30-2 on the 
reference plate FP1 is disposed for the purpose to correct an error of 
rotation of the reference plate FP1 at the time of measurement of the 
baseline, if it is caused to occur, for example, due to an error of 
mounting of the reference plate FP1 on the wafer table 18 or an error of 
manufacturing. More specifically, as described hereinabove, the main 
control unit 28 aligns the first reference mark 30-2 within the detection 
region of the alignment sensor AS by moving the wafer table 18 in the 
+Y-axial direction after the measurement of the baseline has been 
finished, and the position of the mark 30-2 is measured on the basis of 
the detection signals of the alignment sensor AS. When this mark is to be 
measured, it is requisite that the measuring longitudinal axis Xe does not 
deviate from the mirror. If it is found as a result of measurement by the 
alignment sensor AS that the X-coordinate of the first reference mark 30-1 
is different from that of the first reference mark 30-2, although the 
values of the measuring longitudinal axes Xa and Xe for effecting this 
measurement should not vary, when the wafer table 18 is being moved for 
effecting the measurement, an error of rotation of the reference plate FP1 
is given on the basis of the difference between the X-coordinates of the 
marks 30-1 and 30-2, whereby the measured values of the baseline and the 
like can be corrected by that error portion. 
Further, it is possible to correct the rotation of the reticle by the 
rotational error portion given as a result of the simultaneous detection 
of the reference marks on the reference plate FP1. However, as an angle of 
rotation or a magnification of each shot area or an error of an angle of 
intersection at a right angle can be found, if a so-called in-shot, 
multi-point EGA measurement is effected in a manner as disclosed in U.S. 
patent application Ser. No. 08/569,400 (for example, as disclosed in 
Japanese Patent Unexamined Publication No. 6-275,496), which is so 
designed as to measure two or more points within the identical shot area 
upon the EGA measurement as described hereinabove, it is further possible 
to make a correction by rotating the reticle R integrally with the reticle 
stage RST in accordance with the result of the above-mentioned EGA 
measurement or to adjust a magnification of the optical projection system 
PL by a magnification correction mechanism (not shown). As such a 
magnification correction mechanism to be used herein, there may be 
employed, for example, a mechanism for driving a particular lens element 
constituting the optical projection system PL in upward and downward 
directions, as disclosed in U.S. Pat. No. 5,117,255, or a mechanism for 
adjusting an inner pressure within an airtight sealing chamber interposed 
between particular lens elements. 
Furthermore, the main control unit 28 exposes the pattern of the reticle 
onto the wafer W one after another in a step-and-repeat system while 
opening and closing a shutter of the optical illumination system, after 
each of the shot area on the wafer W is aligned with the exposure position 
while monitoring the values measured by the interferometers 26Y and 26Xe 
on the basis of the result of measurement of the deviation of the 
positions of the marks, the data on the sequence of the shot areas 
previously calculated on the basis of the first reference mark 30-1, and 
the baseline amount (the spatial relationship of the position of the first 
reference mark 30-1 relative to the second reference marks 32-1 and 32-2. 
After the exposure of the reticle pattern to all the shot areas on the 
wafer W have been finished, the wafer table 18 is returned to the position 
in which to exchange for wafers, as shown in FIG. 5A. Before the return of 
the wafer table to that position, the interferometer 26Xa is reset in a 
manner as will be described hereinafter. 
In this case, the measuring longitudinal beams in the measuring 
longitudinal axis Xa may deviate from the moving mirror 24X during the 
exposure onto the wafer W. On the other hand, however, the position of the 
wafer table 18 is managed by the coordinates (Xe, Y) system during the 
exposure so that the wafer table 18 is aligned with the predetermined 
reset position by the main control unit 28 so as to be located in the 
position in which the spatial relationship of the preset positions of the 
second reference marks 32-1 and 32-2 on the reference plate FP1 with the 
projection center of the optical projection system PL within its 
projection region can be detected, while monitoring the values measured by 
the interferometers 26Y and 26Xe. It is to be noted herein that this 
projection center of the optical projection system PL coincides 
substantially with the projection center of the pattern image of the 
reticle R. In the state that the wafer table 18 is aligned with the 
predetermined reset position, as shown in FIG. 5B, the measuring 
longitudinal beams in the measuring longitudinal axis Xa strike the moving 
mirror 24X and the first reference mark 30-1 on the reference plate FP1 is 
located within the detection region of the alignment sensor AS. This is 
allowed to occur because the mutual distance BL between the measuring 
longitudinal axes Xe and Xa is designed so as to be equal to the distance 
between the first reference marks 30-1 and 30-2 in the manner as described 
hereinabove. 
By using the alignment sensor AS in this state, the main control unit 28 
detects the position of the first reference mark 30-1 on the reference 
plate FP1 as well as resets the interfero-meter 26Xa. As described 
hereinabove, the interferometer 26Xa is reset when the position of the 
wafer table 18 with respect to the detection center of the alignment 
sensor AS is detected. Further, the position of the reference mark 30-1 of 
the reference plate FP1 is measured on the coordinates (Xa, Y) system. 
This arrangement of the main control unit 28 allows a management of the 
wafer table 18 by the coordinates (Xa, Y) system. Then, the exchanges for 
the wafers and the alignment measurement are carried out on the 
coordinates (Xa, Y) system of the interferometer 26Xa. 
Then, a description will be made of a second reset function of the 
interferometer. In this embodiment, a control operation by the main 
control unit 28 will be described by focusing on the second reset function 
of the interferometer. 
The second reset function of the main control unit 28 is the function of 
aligning the wafer table 18 so as to allow each of the reference marks of 
the wafer table 18 to be located in the respective reset positions on the 
basis of the value measured by the interferometer 26Y in the measuring 
longitudinal axis Y and resetting the corresponding interferometer in the 
measuring longitudinal axis at the reset position, when either or both of 
the measuring longitudinal beams in the measuring longitudinal axes Xe and 
Xa is or are cut during the migration of the wafer table 18 on the 
XY-plane and the corresponding interferometer or interferometers is or are 
brought into an unmeasurable state. It is to be noted herein that the 
measuring longitudinal beams Y of the interferometer 26Y are so arranged 
as to be always emitted without being cut. 
On the upper plane of the wafer table 18 is provided the reference plate FP 
so as to set its upper surface on a level as substantially high as the 
upper surface of the wafer W in the manner as described hereinabove, as 
disclose in U.S. Pat. No. 5,003,342. As the reference plate FP, there may 
be herein employed a reference plate FP2 called a small FM, as shown in 
FIGS. 7A and 7B. On the reference plate FP2 is provided a reference mark 
30-3 for the alignment sensor at its middle portion, as shown in FIG. 6B, 
and a pair of reference marks 32-3 and 32-4 are provided symmetrically on 
the longitudinally extending, left and right sides of the reference mark 
30-3. The reference mark 30-3 and the reference marks 32-3 and 32-4 on the 
reference plate FP2 are disposed in a predetermined spatial relationship 
with respect to each other. 
In the state where exchange for the wafers have been finished, the 
situation occurs where the measuring longitudinal beams in the measuring 
longitudinal axis Y are not cut and the measuring longitudinal beams in 
the measuring longitudinal axis Xa are not cut, although the measuring 
longitudinal beams in the measuring longitudinal axis Xe are cut. 
Therefore, the values measured by the interferometers 26Y and 26Xa are fed 
to the main control unit 28 so that the main control unit 28 can recognize 
the position of the XY axial, two-dimensional coordinates of the wafer 
table 18 on the basis of the values measured by the inter-ferometers 26Y 
and 26Xa and it can further recognize the situation with high precision on 
the basis of the recognition of the Y-coordinate that the measuring 
longitudinal beams in the measuring longitudinal axis Xe are cut. It is 
further to be noted herein that the interferometer 26Xa is reset in a 
manner as will be described hereinafter and that the wafer table 18 is 
managed by a (Xa, Y) coordinates system. 
In this state, the alignment measurement is effected as disclosed in U.S. 
Pat. No. 4,780,617, in which the main control unit 28 measures the 
position of the mark (alignment mark) for detecting the position of the 
particular sample shot area predetermined among the plural shot areas on 
the wafer W on the (Xa, Y) coordinates system on the basis of the output 
of the alignment sensor AS by moving the wafer table 18 integrally with 
the XY-stage 20 via the drive system 22 while monitoring the values 
measured by the interferometers 26Y and 26Xa. Thereafter, data on the 
entire sequence of the plural shot areas on the wafer is computed by 
effecting a statistical operation using the position of the wafer mark of 
each sample shot area measured in the manner as described hereinabove and 
using the data on the sequence of the designed shot areas in accordance 
with the least square method as disclosed in U.S. Pat. No. 4,780,617 (for 
example, in Japanese Patent Unexamined Publication No. 61-44,429). It is 
desired, however, that the calculation results are converted into data 
based on the reference mark 30-3 on the reference plate FP2. This can give 
a spatial relationship between the position of each of the shot areas with 
respect to the position of the reference mark 30-3, as indicated by the 
arrow in FIG. 8. It is further noted herein that the position of the 
reference mark 30-3 is measured on the (Xa, Y) coordinates system at the 
time of resetting the interferometer 26Xa prior to the alignment 
measurement by detecting the reference mark 30-3 by the alignment sensor 
AS, in a manner as will be described hereinafter. 
After the alignment measurement has been finished, the operation is shifted 
to an sequence of the exposure processes. It is assumed herein that in 
this state the interferometer beams of the interferometer 26Xe is cut. 
In the exposure processing, the main control unit 28 drives the wafer table 
18 in the -X-axial direction or in the +X-axial direction, as shown in 
FIG. 2, so as to make the Xa coordinate to become zero while monitoring 
the value measured by the interferometer 26Xa. It is to be noted herein 
that the direction in this case may be determined in accordance with the 
setting of the position in which to finish the alignment measurement. This 
can lead to the state in which the central reference mark 30-3 of the 
reference plate FP2 coincides substantially with the measuring 
longitudinal axis Y. Thereafter, the main control unit 28 aligns the wafer 
table 18 with the predetermined position, i.e. the reset position of the 
interferometer 26Xe, so as to locate the reference plate FP2 in the 
position immediately under the optical projection system PL, that is, in 
the position in which the position of the reference marks 32-3 and 32-4 
relative to the projection center of the optical projection system PL can 
be detected, by moving the wafer table 18 in the +Y-axial direction while 
monitoring the values measured by the interferometer 26Y in accordance 
with the preset Y-coordinate value (e.g. zero) of the optical projection 
system PL. The state at this time is indicated in FIG. 7B. 
In this state, the main control unit 28 can simultaneously monitor an image 
of each of the reference marks 32-3 and 32-4 on the reference plate FP2 
and the reticle marks on the reticle R corresponding to the second 
reference marks, using the reticle alignment microscopes 52A and 52B, 
thereby detecting a deviation of the position of each of the reference 
marks 32-3 and 32-4 from the position of the reticle mark corresponding to 
each of the marks, on the basis of the detection signals of the reticle 
alignment microscopes 52A and 52B. More specifically, the interferometer 
26Xe in the measuring longitudinal axis Xe is reset at the same time as 
the spatial relationship of the position of each of the reference marks 
32-3 and 32-4 of the reference plate FP2 with the position of the 
projection center of the optical projection system PL can be detected. In 
this case, the projection center of the optical projection system PL 
corresponds substantially to the projection center of the pattern image of 
the reticle R. As described hereinabove, the interferometer 26Xe is reset 
when the position of the wafer table 18 is detected using the alignment 
microscopes 52A and 52B and the second reference marks 32-3 and 32-4 on 
the reference plate FP2. In other words, the interferometer 26Xe is reset 
in such a state that the position of the wafer table 18 with respect to 
the projection center of the optical projection system PL is detected. It 
can be noted herein that, although the resetting is usually effected by 
setting a count value of a counter for counting the values measured by the 
interferometer 26Xe to zero, it is also possible to set the initial count 
to any optional numeral other than zero. 
Thus, the position of the wafer table 20 can be managed on the (Xe, Y) 
coordinates system. 
In the case of FIG. 7B, the interferometer beams of the interferometer 26Xa 
are not cut in the reset position of the interferometer 26Xe so that it is 
also possible to move the interferometer 26Xe along a straight line on the 
basis of the values measured by the interferometers 26Xa and 26Y to its 
reset position from the position in which the alignment measurement of the 
wafer table 18 has been finished. 
For instance, however, where the measuring longitudinal axes Xe and Xa are 
apart to a more extent, the interferometer beams in the measuring 
longitudinal axis Xa may be cut during the movement of the wafer table 18 
so that the position of the wafer table 18 cannot be controlled. At this 
time, the interferometer beams in the measuring longitudinal axis Xe are 
also cut. Hence, if the wafer table 18 is allowed to move in the +Y-axial 
direction after it has once been moved in the -X-axial or +X-axial 
direction in the manner as described hereinabove, the interferometer 26Xe 
can be reset in the predetermined reset position, that is, in the position 
in which the reference plate FP2 is located in the position immediately 
below the optical projection system PL, without causing an occurrence of 
the state in which the position control cannot be conducted. 
Therefore, the second reset function of the interferometer allows the 
length of the moving mirror 24X to be set as substantially long as the 
diameter of the wafer W even if whatever long the distance between the 
measuring longitudinal axes Xe and Xa would be, that is, the baseline 
amount BL would be. 
During movement of the wafer table 18 in the Y-axial direction when the 
measuring longitudinal beams in both of the measuring longitudinal axes Xa 
and Xe are cut, it is preferred that the position of the X-stage 
constituting the XY-stage 20 is set to fail to move. Hence, it is 
preferred that the servo control of the position in the X-axial direction 
be conducted by using an alternative sensor or by locking the X-stage 
itself, while the X axial interferometer cannot be employed. 
Moreover, the main control unit 28 can effect the exposure of the reticle 
pattern onto the wafer one after another in the step and-repeat system by 
opening and closing a shutter of the optical illumination system by 
aligning each shot area on the wafer W with the exposure position, while 
monitoring the values measured by the interferometers 26Y and 26Xe on the 
basis of the measured result of the deviation of the position and the data 
of the sequence of the shot areas (FIG. 8) previously computed on the 
basis of the reference mark 30-3, and the spatial relationship of the 
position of the reference mark 30-3 with the positions of the reference 
marks 32-3 and 32-4. 
When the exposure of the reticle pattern to all the shot areas on the wafer 
W has been finished, the wafer table 18 is returned to the position in 
which to exchange wafers. Before return of the wafer table to the exchange 
position, the interferometer 26Xa is reset in a manner as will be 
described hereinafter. 
In this case, although the situation may occur that the measuring 
longitudinal beams in the measuring longitudinal axis Xa are deviated from 
the moving mirror 24X and they do not strike it during the exposure onto 
the wafer W, the wafer table 18 is managed by the (Xe, Y) coordinates 
system during exposure so that the main control unit 28 moves the wafer 
table 18 to the position in which the Xe-coordinate becomes zero after the 
exposure has been finished, while monitoring the values measured by the 
interferometer 26Xe. In other words, the wafer table 18 is moved in the 
X-axial direction until the measured value of the interferometer 26Xe 
reaches the Xe-coordinate value at the time when the interferometer 26Xe 
is reset. This can lead to the state in which the reference mark 30-3 of 
the reference plate FP2 coincides substantially with the measuring 
longitudinal axis Y. There-after, the main control unit 28 moves the wafer 
table 18 in the -Y-axial direction while monitoring the values measured by 
the interferometer 26Y in accordance with the preset Y coordinate value of 
the detection center of the alignment sensor AS and then aligns the wafer 
table 18 with the predetermined position (i.e. the reset position of the 
interferometer 26Xa) in which the reference mark 32-3 of the reference 
plate FP2 is located within the detection region of the alignment sensor 
AS. This state is indicated in FIG. 7A. 
In the state where the wafer table 18 is aligned with the reset position, 
the measuring longitudinal beams extending in the measuring longitudinal 
axis Xa strike the X-axially moving mirror 24X, as shown in FIG. 7A, and 
the first reference mark 30-3 of the reference plate FP2 is located within 
the detection region of the alignment sensor AS. 
Further, in this state, the main control unit 28 detects the position of 
the reference mark 30-3 on the reference plate FP2 using the alignment 
sensor AS and simultaneously resets the interferometer 26Xa. As described 
hereinabove, the interferometer 26Xa is reset when the position of the 
wafer table 18 has been detected with the alignment sensor AS and the 
reference mark 30-3 of the reference plate FP2. In other words, the 
interferometer 26Xa is reset when the position of the wafer table 18 has 
been detected with respect to the detection center of the alignment sensor 
AS. Further, the position of the reference mark 30-3 of the reference 
plate FP2 is measured on the coordinates (Xa, Y) system. 
This enables the wafer table 18 to be managed by the (Xa, Y) coordinates 
system. Further, the wafers are exchanged and the alignment measurement 
are carried out on the coordinates (Xa, Y) system of the interferometer 
26Xa. 
With the arrangements as described hereinabove, the projection exposure 
apparatus in the embodiments according to the present invention can use 
the moving mirrors 24X and 24Y each having its length Lm that is defined 
to be shorter than Dw+2BL, where Dw is the diameter of the wafer W and BL 
is the baseline amount and to be slightly longer than the diameter Dw of 
the wafer W. On the other hand, a conventional exposure apparatus uses 
moving mirrors each having a length Lm that is longer than Dw+2BL. 
Therefore, he projection exposure apparatus according to the present 
invention can make the wafer table 18 with the moving mirror mounted 
thereon and the XY-stage 20 with the wafer table loaded thereon more 
compact in size and lighter in weight, as compared with the such 
conventional exposure apparatus. Further, this can gain improvements in 
performance of controlling the position of the wafer table 18 and the 
XY-stage 20. Moreover, as a matter of course, the projection exposure 
apparatus according to the present invention can be made more compact in 
size as a whole. 
It can be understood herein that, in order to conduct the alignment 
measurement by the alignment sensor AS or effect the exposure by the 
optical projection system PL, theoretically, the length Lm of the moving 
mirror is long enough if it is equal in length to the diameter Dw of the 
wafer; however, as a practical matter, it is required that the length Lm 
of the moving mirror is set to be slightly longer than the diameter Dw of 
the wafer because clearance should be ensured for smoothness on the both 
end portions of the reflecting plane of the moving mirror and for the 
diameter of the beams. 
Further, in the embodiments of the present invention as described 
hereinabove, the main control unit 28 is provided with the first and 
second reset functions which reset the interferometers at timings between 
alignment and exposure, so that each of operations for measuring the 
alignment mark and for conducting the exposure can be carried out without 
any problem and difficulty, even if the wafer table 18 is in a generally 
square shape greater than the diameter of the wafer. 
It is particularly noted herein that, as the baseline can be measured 
immediately after the alignment measurement by the operation of resetting 
the interferometers by means of the main control unit 28 using the 
reference plate FP1 as a reference plate, which is called a large FM, the 
projection exposure apparatus according to the present invention can 
ensure stability of the baseline amount that is of the most significance 
to the alignment sensor of an off-axis system. Moreover, as the 
measurement of the baseline can be carried out in a static state of the 
wafer table 18, the measurement thereof can be conducted with high 
precision without undergoing an error in measurement by the 
interferometers to be otherwise caused by air turbulence or for other 
reasons. 
On the other hand, it is noted herein that, as the main control unit 28 
further uses the reference plate FP2 as a reference plate, which is called 
a small FM, and it is operated to reset the interferometers, the size of 
the wafer table 18 can be set to be as small as the diameter of the wafer 
W, regardless of the magnitude of the baseline amount BL. 
Therefore, the present invention can readily make the N.A. of the optical 
projection system PL higher and the field thereof greater in size in order 
to improve resolving power, while sustaining the size of the wafer table 
18 constant. 
It is to be understood that the present invention is not restricted in any 
respect to those embodiments as described hereinabove and that it 
encompasses any modifications and variations within the spirit and scope 
of the present invention. For example, it is readily understood that the 
following embodiments are likewise encompassed within the present 
invention. 
As disclosed in U.S. Pat. No. 5,151,749, a yawing interferometer having 
measuring axes Y1 and Y2 as shown in FIG. 9 may also be employed in place 
of the Y-axial interferometer 26Y of FIG. 2. The yawing interferometer can 
readily give a yawing amount of the wafer table 18 by dividing a 
difference between the measured values of the Y1-axis and the Y2-axis by a 
distance Yy between the axes Y1 and Y2, Further, it allows a measurement 
of the Y-coordinate of the wafer table 18, which is equivalent of the 
interferometer in a measuring longitudinal axis Ya corresponding to the 
Y-axial interferometer 26Y of FIG. 2, on the basis of an average of the 
measured values of the Y1-axis and the Y2-axis. Likewise, the yawing 
interferometer ay be mounted on the X-axial side; however, in this case, 
the yawing interferometer should be mounted on the both side for each of 
the measuring longitudinal axes Xa and Xe so that the configuration may 
become complex. Therefore, in the case of FIG. 9, the yawing 
interferometer is mounted only on the Y-axis side on the condition that 
the degree of intersecting the moving mirror 24Y with the moving mirror 
24Y does not vary. Further, it is also possible to use the yawing 
interferometers on both of the X- and Y-axes, if the angle of intersecting 
the moving mirror 24Y with the moving mirror 24Y at a right angle would 
vary, or to measure a variation by storing the spatial relation-ship among 
the measuring longitudinal axes Xa, Xe and Y when none of their respective 
measuring longitudinal beams are still cut. 
In the embodiments as described hereinabove, the case is described in which 
the interferometers are reset using the reference plate FP1 or FP2 at 
timings when the operation is shifted to the exposure operation from the 
alignment measurement. It is to be noted herein that the interferometers 
may also be reset simply by defining a certain reference point on the 
wafer table 18 acting as the substrate stage and aligning the wafer table 
18 with a position in which the certain reference point is located within 
a predetermined reset position. Therefore, as the such certain reference 
point, there may be defined one point on the wafer W, for example, an 
alignment mark attached to a certain shot area. 
Further, in the embodiments as described hereinabove, the case is described 
in which the moving mirrors 24X and 24Y are fixed on the wafer table 18. 
It is also possible to use a wafer table as the moving mirror by 
mirror-finishing the side surface of the wafer table. In such a case, the 
rigidity of the wafer table 18 can be increased. In order to make the 
wafer table compact in size as in the embodiments as described 
hereinabove, the wafer table with its side surface mirror-finished can be 
readily employed as the moving mirror. 
Furthermore, in the embodiments as described hereinabove, a description is 
made of the case in which the coordinates of the sequence of the shot 
areas on the wafer W are predetermined by the so-called EGA measurement 
and the stepping of the wafer table is effected on the basis of the 
coordinates of the sequence thereof upon exposure. It is also possible to 
alternately reset the interferometers at the reset positions, as shown in 
FIGS. 7A and 7B, when the small FM (the reference plate FP2) is employed 
in the case where the alignment measurement of the alignment mark and the 
exposure are alternately carried out for each shot area. In this case, 
too, it is possible to measure the spatial relationship of the position of 
the reference mark 30-3 with each alignment mark upon alignment in a 
similar manner as with that indicated by the arrow in FIG. 8, followed by 
superimposition of the pattern image of the reticle upon the wafer upon 
exposure on the basis of the result of measurement. 
Moreover, in the embodiments as described hereinabove, the case is 
described in which the main control unit is provided with the reset 
function for resetting the interferometers. To the projection exposure 
apparatus according to the present invention, in addition to the reset 
function as described hereinabove, there may be applied, for example, a 
device for always managing the position of the substrate stage using an 
identical interferometer or a device for managing the position of the 
wafer table using different interferometers upon alignment and upon 
exposure. 
In addition, in the embodiments as described hereinabove, a description is 
made of the case in which the present invention is applied to the 
projection exposure apparatus in the step-and-repeat system. It is further 
to be noted that the scope of the application of the present invention is 
not restricted to the case and the present invention can also be 
appropriately applied to, for example a projection exposure apparatus of a 
step-and-scan system. In the case of the projection exposure apparatus of 
the step-and-scan system, it is also possible to correct an error of the 
angle of intersection at a right angle by varying an angle of scanning the 
reticle stage relative to the wafer stage, as disclosed in U.S. patent 
application Ser. No. 08/533,923 filed Sep. 26, 1995 (for example, Japanese 
Patent Unexamined Publication No. 7-57,991), when such an error of the 
angle of intersection or the like is found by the in-shot, multi-point EGA 
as described hereinabove. 
Furthermore, the present invention can be applied to an electron beam 
exposure apparatus or an X-ray exposure apparatus as well as to the 
optical exposure apparatus such as the stepper. Even when the present 
invention is applied to such an exposure apparatus, the present invention 
can enjoy the various merits by making the substrate stage more compact in 
size, such as improvements in controllability of the stages, cost 
reductions of a clean room by reducing an area for installation of the 
apparatus (a so-called foot print), and the like.