Title: Inspection method and apparatus for projection optical systems
Abstract: A reference mark is formed on an under-surface of a reference mark member that is disposed on a mask stage. The mask stage can be part of a projection exposure apparatus in which a substrate and a mask are moved in respective scanning directions during scanning exposure. The projection exposure apparatus also may include a projection system disposed under the mask stage, with the mask and substrate being provided on opposite sides of projection system. The mask stage may be moved into the image field of the projection system, and the reference mark is detected.
Patent Number: 6,850,327 Issued on 02/01/2005 to Taniguchi, et al.
| Inventors:
|
Taniguchi; Tetsuo (Yokohama, JP);
Tsuji; Toshihiko (Chiba-ken, JP)
|
| Assignee:
|
Nikon Corporation (Tokyo, JP)
|
| Appl. No.:
|
237130 |
| Filed:
|
September 9, 2002 |
Foreign Application Priority Data
| Feb 21, 1995[JP] | 7-32245 |
| Feb 21, 1995[JP] | 7-32247 |
| Current U.S. Class: |
356/399 |
| Intern'l Class: |
G01B 011/00 |
| Field of Search: |
356/399-401
250/548,577
|
References Cited [Referenced By]
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| 4657379 | Apr., 1987 | Suwa.
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| 4666273 | May., 1987 | Shimizu et al.
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| 4780615 | Oct., 1988 | Suzuki.
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| 4829193 | May., 1989 | Nishi.
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| 4871237 | Oct., 1989 | Anzai et al.
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| 4880310 | Nov., 1989 | Nishi.
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| 4897553 | Jan., 1990 | Nishi.
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| 4943733 | Jul., 1990 | Mori et al.
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| 5204535 | Apr., 1993 | Mizutani.
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| 5214489 | May., 1993 | Mizutani et al.
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| 5243195 | Sep., 1993 | Nishi | 250/548.
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| 5406373 | Apr., 1995 | Kamon.
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| 5408320 | Apr., 1995 | Katagiri et al.
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| 5414514 | May., 1995 | Smith et al.
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| 5506684 | Apr., 1996 | Ota et al.
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| 5528027 | Jun., 1996 | Mizutani.
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| 5646413 | Jul., 1997 | Nishi.
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| 5661546 | Aug., 1997 | Taniguchi.
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| 5793472 | Aug., 1998 | Hori et al. | 355/53.
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| 6018384 | Jan., 2000 | Ota.
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| 6151122 | Nov., 2000 | Taniguchi et al.
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| 6169602 | Jan., 2001 | Taniguchi et al.
| |
| 6198527 | Mar., 2001 | Nishi | 355/53.
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| 6236448 | May., 2001 | Ota.
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| 6249336 | Jun., 2001 | Ota.
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| 6388735 | May., 2002 | Ota.
| |
| Foreign Patent Documents |
| A-58-8353 | Jan., 1983 | JP.
| |
| A-59-94032 | May., 1984 | JP.
| |
| A-60-18738 | Jan., 1985 | JP.
| |
| A-60-28613 | Feb., 1985 | JP.
| |
| A-60-78457 | May., 1985 | JP.
| |
| A-62-200724 | Sep., 1987 | JP.
| |
| A-63-81818 | Apr., 1988 | JP.
| |
Primary Examiner: Stafira; Michael P.
Attorney, Agent or Firm: Oliff & Berridge PLC
Parent Case Text
This is a Division of application Ser. No. 09/667,754 filed Sep. 21, 2000,
now U.S. Pat. No. 6,525,817 which in turn is a Division of application
Ser. No. 09/332,027 filed Jun. 14, 1999 (now U.S. Pat. No. 6,151,122),
which is a Division of application Ser. No. 09/253,711 filed Feb. 22, 1999
(now U.S. Pat. No. 6,169,602), which is a Continuation of application Ser.
No. 08/603,764 filed Feb. 20, 1996 (now abandoned). The entire disclosure
of the prior application(s) is hereby incorporated by reference herein in
its entirety.
Claims
What is claimed is:
1. A projection exposure apparatus in which a substrate and a mask are
moved in respective scanning directions during scanning exposure,
comprising:
a mask stage which is movable in the scanning direction;
a projection system disposed under the mask stage, the mask being provided
on one side of the projection system and the substrate being provided on
an opposite side of the projection system; and
a reference mark member disposed on the mask stage, that has an
under-surface on which a reference mark is formed, the reference mark
member being different from and adjacent to the mask.
2. The projection exposure apparatus according to claim 1, wherein the
reference mark member has a plurality of the reference marks on the
under-surface which are apart from each other in the scanning direction.
3. The projection exposure apparatus according to claim 1, wherein the
reference mark member has a plurality of the reference marks on the
under-surface which are apart from each other in a direction perpendicular
to the scanning direction.
4. The projection exposure apparatus according to claim 1, wherein the
reference mark member is apart from the mask with respect to the scanning
direction.
5. The projection exposure apparatus according to claim 4, wherein the
reference mark member includes a first member and a second member which
are on both sides of the mask with respect to the scanning direction, each
of the first and second members having a reference mark.
6. The projection exposure apparatus according to claim 4, further
comprising an interferometer unit having a reflection surface on the mask
stage, wherein the mask stage is moved on the basis of positional
information measured by the interferometer unit, and the reference mark
member is disposed between the reflection surface of the interferometer
unit and the mask held on the mask stage.
7. The projection exposure apparatus according to claim 4, wherein the
reference mark member has a plurality of the reference marks on the
under-surface.
8. The projection exposure apparatus according to claim 7, wherein the mask
to be provided on the mask stage has a plurality of reference marks.
9. The projection exposure apparatus according to claim 7, further
comprising a reference mark detecting system.
10. The projection exposure apparatus according to claim 9, wherein the
reference mark detecting system detects the reference mark via the
projection system.
11. The projection exposure apparatus according to claim 10, further
comprising a substrate stage, and wherein the reference mark detecting
system has a light receiving portion on the substrate stage.
12. The projection exposure apparatus according to claim 9, further
comprising an image formation characteristic correction system which
operates based on information obtained by detecting the reference mark.
13. The projection exposure apparatus according to claim 12, wherein the
image formation characteristic correction system adjusts the projection
system.
14. The projection exposure apparatus according to claim 12, wherein the
reference mark member includes a first member and a second member which
are on both sides of the mask with respect to the scanning direction, each
of the first and second members having a reference mark.
15. The projection exposure apparatus according to claim 9, wherein the
reference mark member includes a first member and a second member which
are on both sides of the mask with respect to the scanning direction, each
of the first and second members having a reference mark.
16. A micro-device manufacturing method including a lithography process in
which a substrate is exposed using the projection exposure apparatus
defined in claim 1.
17. A projection exposure method in which a substrate is exposed by
projecting an image of a pattern formed on a mask via a projection system,
the method comprising:
moving a mask stage on which a reference mark member is disposed, the
projection system being under the mask stage, the reference mark member
being different from and adjacent to the mask; and
detecting the reference mark which is formed on an under-surface of the
reference mark member.
18. The projection exposure method according to claim 17, wherein the
reference mark member has a plurality of the reference marks on the
under-surface.
19. The projection exposure method according to claim 18, wherein the
plurality of reference marks are arranged on the under-surface so as to be
included in an illumination area within an effective field of the
projection system.
20. The projection exposure method according to claim 17, wherein the
reference mark is detected while the mask stage is positioned at a
predetermined position.
21. The projection exposure method according to claim 17, wherein the
reference mark is detected at the time of a mask exchange operation.
22. The projection exposure method according to claim 17, wherein the
reference mark member is illuminated to detect the reference mark using an
illumination system other than an illumination system that is used for
exposure.
23. The projection exposure method according to claim 18, further
comprising:
obtaining an image forming characteristic by detecting the reference marks
via the projection system.
24. The projection exposure method according to claim 23, wherein the image
forming characteristic includes a focus position.
25. The projection exposure method according to claim 23, wherein the image
forming characteristic includes coma.
26. The projection exposure method according to claim 17, wherein the
reference mark member includes a first member and a second member which
are on both sides of the mask, each of the first and second members having
a reference mark.
27. A micro-device manufacturing method comprising a lithography process in
which a substrate is exposed using the projection exposure method defined
in claim 17.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inspection method for a projection
optical system, which requires highly accurate image formation
characteristics, for fabricating semiconductor integrated circuits or
liquid crystal devices, and also relates to an inspection apparatus for
carrying out the inspection method and a projection exposure system
provided with the inspection apparatus. The invention is applicable to a
stepper type projection exposure apparatus but is particularly suitable
for a projection exposure apparatus of the scan exposure type, such as a
slit-scan type or step-and-scan type, where patterns of geometric shapes
on a mask are serially transferred on a photosensitive substrate while
scanning in synchronization the mask and the substrate.
2. Related Background Arts
Projection optical systems, which are mounted, for example, in a projection
exposure apparatus for fabricating semiconductor integrated circuits or
liquid crystal devices, require extremely high accuracy with respect to
image formation characteristics such as projection magnification and image
distortion. For this reason, a method for measuring projection
magnification and image distortion of the projection optical system with
high accuracy and a correction method for correcting the image formation
characteristics with high accuracy have been developed. At present, there
are roughly two methods for measuring projection magnification and image
distortion.
The first method is one which transfers a pattern of a test mask to a
photosensitive substrate (e.g., wafer). This method is disclosed, for
example, in Japanese Patent Laid-Open Publication No. Sho 58-8353. In the
first method, the test mask pattern is transferred onto a photosensitive
substrate, and after the photosensitive substrate is moved a predetermined
distance in accordance with a laser interferometer, the pattern is again
transferred onto the substrate so that it overlaps with the previously
transferred pattern. After development of the substrate, the overlap error
or registration error is measured. At this time, since marks overlap one
above the other after the photosensitive substrate is moved, the marks are
patterns drawn at different places on the test mask.
The second method is one where an image of a pattern formed on a
photosensitive substrate is measured directly by a photoelectric sensor
without an actual exposure process such as the first method. This second
method is disclosed, for example, in Japanese Patent Laid-Open Publication
Nos. Sho 59-94032 or Sho 60-18738. An example of the second method will be
briefly described in reference-to FIGS. 1(a) and 1(b).
FIG. 1(a) shows a schematic structure of an example of a conventional
projection exposure apparatus. As shown in FIG. 1(a), a test reticle TR as
a test mask is provided with a plurality of light transmission portions
305A to 305B (in this example, slits) formed at predetermined intervals.
Illumination light passes through the light transmission portions 305A to
305G and forms an image thereof on the photosensitive substrate side
through a projection optical system PL. FIG. 1(a) shows the arrangement of
a pattern plate 301 and a photoelectric sensor 302 (both of which are
positioned on an image forming position of the light transmission portion
305A). The pattern plate 301 has a very small light transmission portion
306 which serves as a mark detection device. The photoelectric sensor 302
receives the illumination light from the light transmission portion 306.
The pattern plate 301 and the photoelectric sensor 302 are mounted on a
wafer stage, which has the photosensitive substrate mounted thereon and is
movable on a plane perpendicular to an optical axis of the projection
optical system PL. The position of the wafer stage is precisely measured
by a reflector 303 fixed to the wafer stage and an external laser
interferometer 304. The output of the photoelectric sensor 302 varies by
scanning the wafer stage.
FIG. 1(b) shows a graph representing the result of the output of the
photoelectric sensor 302. In the figure, the axis of abscissa represents a
position x of the scanning direction of the wafer stage, and the axis of
ordinate represents an output value I of the photoelectric sensor 302. The
image forming position of the light transmission portion 305A of the test
reticle TR can be measured by obtaining, in FIG. 1(b), a position x.sub.0
where the output value I of an output curve 307 becomes maximum. If a
similar measurement is performed with respect to a plurality of light
transmission portions of the test reticle TR, the respective image forming
positions of the light transmission portions 305A to 305G will be
obtained. Therefore, the projection magnification and the image distortion
of the projection optical system can be obtained because the positions of
the light transmission portions 305A to 305G are known in advance.
In addition to the aforementioned photoelectric sensor scanning method,
there is known a method where an image of a pattern on a reticle is
magnified with a microscope and is detected by mean of an image pick-up
device, such as two-dimensional CCD, or a method where, conversely,
illumination light is emitted from a slit provided on a wafer stage and is
received via a pattern of a test reticle TR by scanning the wafer stage
(see Japanese Patent Laid-Open Publication No. Sho 63-81818).
The image formation characteristic of the projection optical system, such
as magnification or image distortion, is required to be measured and
regulated at the time of the manufacture by a projection exposure
apparatus. The image formation characteristic also is required to be
corrected at the time of actual use, because it varies due to an
atmospheric pressure variation and illumination light absorption of a
projection optical system. As a countermeasure, a method, where a quantity
of the variation of the image formation characteristics are predicted in
advance and correction of magnification is performed by varying an air
pressure of the projection optical system, is known as disclosed, for
example, in Japanese Patent Laid-Open Publication Nos. 60-28613 or Sho
60-78457.
However, this method alone is insufficient and also there is the
possibility that magnification and image distortion vary due to long-term
fluctuations in a system. Therefore, the system should be used while
periodically checking magnification and image distortion by means of
methods such as described above. Also, since the demand for accuracy of
correction corresponding to an atmospheric pressure variation has become
increasingly severe in recent years, it is necessary to frequently check a
correction error caused by measurement. In this sense, the aforementioned
second method whose measurement time is short is superior to the first
method, and in many cases, the second method is actually used.
Also, a step-and-scan projection exposure apparatus, where a mask and each
shot area of a photosensitive substrate are scanned in synchronization
with respect to a projection optical system in order to substantially
increase an exposure area without greatly increasing the size of the
projection optical system, has been aimed at in recent years. However,
there has been provided no method for measuring an image formation
characteristic, which makes use of, in particular, the feature of a
projection exposure apparatus of a scan exposure type such as a
step-and-scan type.
Thus, all of the aforementioned conventional methods of measuring the
magnification or image distortion of the projection optical system are a
method of measuring a gap or distance between the projected images of two
(or more) different marks on a test mask. For this reason, it is necessary
to accurately grasp the mark gap or pitch of the test mask in advance.
However, normally the patterns on the mask are fabricated with an
electronic beam drawing device, and the gap or pitch between spaced marks
for measurement of magnification is not very accurate, so the gap of each
mask has to be measured in advance with a reticle pattern measuring
machine. This measurement is substantially impossible in a manufacturing
site where a plurality of masks are used. For this reason, it is
conceivable to use a reference mask, but this method has the disadvantage
that measurement cannot be performed frequently during the aforementioned
actual exposure.
Also, the above method has a problem regarding accuracy of reticle pattern
measurement. For example, when a mask is mounted in an exposure apparatus,
it is normally disposed with the pattern thereof facing downwardly, but in
the reticle pattern measuring machine the mask is mounted with the pattern
surface thereof facing upwardly. Therefore, influences of deflection
caused by self-weight are different between the two masks. This difference
results in a measurement error. In addition, even in the exposure
apparatus, deflection by self-weight varies between the masks and causes
image distortion.
Furthermore, although it is also conceivable that only some of the masks
are measured in order to perform correction of the projection optical
system, the gap or distance between the marks varies because the mask
absorbs the heat of the illumination light during measurement and
therefore the mask itself is thermally expanded. If correction, including
the thermal expansion of the mask, is made during measurement, there will
be no problem. However, if the mask is exchanged for a subsequent mask,
there will be the drawback that an error remains in the magnification of
the projection optical system, because the mask after exchange has not
been thermally expanded. Moreover, even in a method where the distance
between the marks is unknown but magnification is always held in an
initial magnification obtained at the time of exchange, if a mask is
exchanged for a subsequent one, an error will occur in the magnification
of the projection optical system, for the same reasons.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an inspection
method which is capable of accurately measuring an image formation
characteristic of a projection optical system, such as magnification and
image distortion, while overcoming drawbacks of conventional inspection
methods such as described above.
Another object of the present invention is to provide an inspection method
which could be capable of accurately measuring an image formation
characteristic of a projection optical system, such as magnification and
image distortion, even if there are drawing errors in marks for projection
magnification and image distortion measurement formed on a mask.
Still another object of the present invention is to provide an improved
inspection apparatus which is capable of accurately and quickly measuring
an image formation characteristic of a projection optical system, such as
magnification and image distortion.
A further object of the present invention is to provide a projection
exposure apparatus having an inspection apparatus which is capable of
accurately and quickly inspecting an image formation characteristic of a
projection optical system, such as magnification and image distortion.
A further object of the present invention is to provide a projection
exposure apparatus which is capable of accurately and quickly measuring an
image formation characteristic of a projection optical system, such as
magnification and image distortion, and also accurately correcting the
image formation characteristic.
A first inspection method for a projection optical system according to the
present invention comprises the steps of (1) moving a predetermined
pattern formed on a mask to a first position, (2) moving the predetermined
pattern to a second position different from the first position
perpendicularly with respect to an optical axis of the projection optical
system, (3) detecting a positional relationship between the first position
and the second position, (4) detecting a positional relationship between a
position where the image of the predetermined pattern in the first
position is projected by the projection optical system and a position
where the image of the predetermined pattern in the second position is
projected by the projection optical system, and (5) obtaining an image
formation characteristic of the projection optical system, based on the
positional relationship detected in step (3) and the positional
relationship detected in step (4).
A second inspection method for a projection optical system according to the
present invention comprises the steps of (1) detecting a positional
relationship between first and second patterns formed on a mask, (2)
detecting a positional relationship between a position where an image of
the first pattern is projected by the projection optical system and a
position where the image of the second pattern is projected by the
projection optical system, and (3) obtaining an image formation
characteristic of the projection optical system, based on the positional
relationship detected in step (1) and the positional relationship detected
in step (2).
In the aforementioned first or second inspection method of a projection
optical system according to the present invention, an example of the
projection optical system is provided in a projection exposure apparatus
which transfers the pattern formed on the mask to a photosensitive
substrate.
A third inspection method for a projection optical system according to the
present invention comprises the steps of (1) detecting a positional
relationship between a plurality of reference marks, the reference marks
being defined by a reference mark member disposed on a mask stage and also
being arranged at intervals in a moving direction of the mask stage, (2)
forming projected images of the reference marks on a wafer stage by
illuminating a collimated light beam to the reference marks of the
reference mark member, (3) moving the wafer stage and then detecting a
positional relationship between a plurality of projected images of the
reference marks, and (4) obtaining an image formation characteristic of
the projection optical system, based on the positional relationship
between reference marks and the positional relationship between projected
images detected in step (3).
In the aforementioned inspection method, the reference mark member may be a
single reference mark member, and the plurality of reference marks may be
formed in the single reference mark member. Also, a center of the single
reference mark member may be aligned with an optical axis of the
projection optical system. In addition, the reference mark member may
comprise a plurality of reference mark members, and the plurality of
reference mark members may be provided around a position where the mask is
arranged.
A fourth inspection method for a projection optical system according to the
present invention comprises the steps of (1) detecting a positional
relationship between a plurality of reference marks of a reference mark
member provided in positions which are optically conjugate with patterns
of a mark arranged on a mask stage, the reference marks being arranged at
intervals in a moving direction of the mask stage, (2) forming projected
images of the reference marks on a wafer stage by illuminating a
collimated light beam to the reference marks of the reference mark member,
(3) moving the wafer stage and then detecting a positional relationship
between a plurality of projected images of the reference marks, and (4)
obtaining an image formation characteristic of the projection optical
system, based on the positional relationship between reference marks and
the positional relationship between projected images detected in step (3).
A first inspection apparatus for a projection optical system according to
the present invention comprises: a mask stage arranged on the incident
light side of the projection optical system to be inspected and movable in
a direction perpendicular to an optical axis of the projection optical
system, while holding a mask; a position measuring device for measuring
first and second positions of the mask stage; and an image position
detection device for detecting a relationship between a projected position
at which an image of a predetermined pattern formed on the mask is
projected through the projection optical system when the mask stage is in
the first position and a projected position at which an image of the
predetermined pattern formed on the mask is projected through the
projection optical system when the mask stage is in the second position.
A second inspection apparatus for a projection optical system according to
the present invention comprises: a mask stage arranged on the incident
light side of the projection optical system to be inspected and holding a
mask having first and second patterns; a pattern position detection device
for detecting a positional relationship between the first and second
patterns; and an image position detection device for detecting a
relationship between a projected position at which an image of the first
pattern is projected through the projection optical system and a projected
position at which an image of the second pattern is projected through the
projection optical system.
A third inspection apparatus for a projection optical system according to
the present invention comprises: a reference mark member provided on a
position on a mask stage or a position which is optically conjugate with
patterns held in the mask stage and formed with a plurality of reference
marks; an illumination optical system for projecting images of the
plurality of reference marks toward the projection optical system to be
inspected; and an image position detection device for detecting a position
of a projected image of at least one of the plurality of reference marks
obtained through the projection optical system.
A fourth inspection apparatus of a projection optical system according to
the present invention comprises: a reference mark member having a
plurality of reference marks formed thereon and disposed on a mask stage
adjacent to a mask in a scanning direction of the mask stage; an
illumination optical system for projecting images of the plurality of
reference marks toward the projection optical system to be inspected; and
an image position detection device for detecting a position of a projected
image of at least one of the plurality of reference marks obtained through
the projection optical system.
A first projection exposure apparatus according to the present invention
comprises: a projection optical system for projecting an image of a
pattern formed on a mask on a predetermined plane; a mask stage freely
movable in a direction perpendicular to an optical axis of the projection
optical system, while holding the mask; a position measuring device for
measuring a position of the mask stage; a stage control device for moving
the mask stage from a first position to a second position, based on an
output of the position measuring device; an image position detection
device for detecting a positional relationship between a projected
position at which an image of the predetermined pattern formed on the mask
is projected through the projection optical system when the mask stage is
in the first position and a projected position at which an image of the
predetermined pattern formed on the mask is projected through the
projection optical system when the mask stage is in the second position;
and a calculation device for calculating an image formation characteristic
of the projection optical system, based on the positions of the mask stage
measured by the position measuring device when the mask stage is in the
first and second position and based on the positional relationship
detected by the image position detection device.
A second projection exposure apparatus according to the present invention
comprises: a mask stage for holding a mask having first and second
patterns formed thereon; a projection optical system for projecting images
of the patterns on a mask onto a predetermined plane; a pattern position
detection device for measuring a positional relationship between the first
and second patterns; an image position detection device for detecting a
positional relationship between a projected position at which an image of
the first pattern is projected through the projection optical system and a
projected position of an image at which the second pattern is projected
through the projection optical system; and a calculation device for
calculating an image formation characteristic of the projection optical
system, based on the positional relationship detected by the pattern
position detection device and the positional relationship detected by the
image position detection device.
In the aforementioned projection exposure apparatuses according to the
present invention, an example of the pattern position detection device has
a pattern detection device for photoelectrically detecting the first and
second patterns of the mask, a stage control device for moving the mask
stage perpendicularly relative to an optical axis of the projection
optical system so that the first and second patterns cross an area of
detection of the pattern detection device, and a position measuring device
for measuring a position of the mask stage.
Also, the aforementioned first and second projection exposure apparatuses
of the present invention further comprise a substrate stage for mounting a
photosensitive substrate to which a predetermined pattern of the mask is
transferred. In addition, an example of an object to be detected by the
image position detection device is an image of the predetermined pattern
or first and second patterns transferred to the photosensitive substrate.
Furthermore, it is preferable that the aforementioned first and second
projection exposure apparatuses of the present invention are a projection
exposure apparatus of the scan exposure type where a photosensitive
substrate is exposed while scanning the photosensitive substrate and a
mask in synchronization with each other.
A third projection exposure apparatus according to the present invention is
suitable for projecting a pattern on a mask mounted on a mask stage onto a
photosensitive substrate through a projection optical system and
comprises: a reference mark member formed with a plurality of reference
marks and disposed in a position on the mask stage or a position which is
nearly optically conjugate with the pattern; an image position detection
device for detecting a position of a projected image of at least one of
the plurality of reference marks under illumination light in the same
wavelength band as illumination light for exposure; a calculation device
for obtaining an image formation characteristic of the projection optical
system, based on the result of the detection of the image position
detection device; and a correction device for correcting an image
formation characteristic of the projection optical system, based on the
image formation characteristic obtained by the calculation device.
A fourth projection exposure apparatus according to the present invention
is suitable for projecting a transfer pattern formed on a mask onto a
photosensitive substrate through a projection optical system by scanning
the photosensitive substrate in a direction (-X direction or +X direction)
corresponding to a predetermined scanning direction (+X direction or -X
direction) in synchronization as the mask formed with a pattern to be
transferred is scanned in the predetermined scanning direction through the
mask stage and comprises: a reference mark member having a plurality of
reference marks formed thereon and disposed on a mask stage adjacent to a
mask in a scanning direction of the mask stage; an image position
detection device for detecting a position of a projected image of at least
one of the plurality of reference marks under illumination light in the
same wavelength band as illumination light for exposure; a calculation
device for obtaining an image formation characteristic of the projection
optical system, based on the result of the detection of the image position
detection device; and a correction device for correcting an image
formation characteristic of the projection optical system, based on the
image formation characteristic obtained by the calculation device.
In the aforementioned projection exposure apparatus according to the
present invention, it is preferable that the reference mark member be
arranged within an approach run section of the mask stage where the
illumination light for exposure is illuminated, at the time of
acceleration or deceleration during scan and exposure.
Also, in the aforementioned third and fourth projection exposure systems
according to the present invention, an example of an object of detection
of the image position detection device is an image projected on a test
photosensitive substrate or a test thermosensitive substrate through the
projection optical system.
In accordance with the aforementioned first inspection method of the
present invention, the image formation characteristics of the projection
optical system, such as magnification and image distortion, could be
accurately detected even if there is a drawing error in the mask on the
mask for measuring a projection magnification or an image distortion.
That is, the principles of measuring the projection magnification or the
image distortion of the projection optical system is to measure how a
given length on the mask side varies through the projection optical
system. Therefore, it is necessary that a length which becomes a single
reference on the mask side is accurately known. In the first inspection
method of the present invention, a predetermined pattern on the mask is
moved. To obtain the positional relationship (distance of movement), a
distance that this pattern is moved becomes a single strict length
standard on the mask side. And, to obtain the positional relationship
between the images of this predetermined pattern obtained on a
predetermined plane through the projection optical system before and after
the movement of the predetermined pattern, the relation between a length
which becomes a single standard on the mask side and a variation in the
length through the projection optical system, i.e., the image formation
characteristics of the projection optical system is strictly obtained.
Also, in accordance with the aforementioned second inspection method for
the projection optical system of the present invention, a length which
becomes a single standard on the mask side is strictly known by obtaining
the positional relationship (gap) between the first and second patterns
formed on the mask. This method, as with the aforementioned first
inspection method of the present invention, could accurately detect the
image formation characteristics of the projection optical system, such as
magnification and image distortion, even if there is a drawing error in
the mark on the mask for measuring projection magnification or an image
distortion.
In addition, in the first and second inspection methods for the projection
optical system of the present invention, in a case where the projection
optical system is provided in a projection exposure apparatus where a
pattern formed on a mask is transferred onto a photosensitive substrate,
the image formation characteristics of the projection optical system can
be accurately detected. If correction is performed based on the detection,
the mask pattern can be transferred with a high degree of overlap or
registration accuracy to the photosensitive substrate.
Furthermore, according to the first projection exposure apparatus of the
present invention, the aforementioned first inspection method for the
projection optical system can be carried out. That is, accurate
measurement of magnification and image distortion can be performed with
respect to not only a test mask where a gap or distance between marks is
measured in advance but also all masks that are used in actual exposure.
Moreover, according to the fourth projection exposure apparatus of the
present invention, the aforementioned second inspection method for the
projection optical system can be carried out. That is, the positional
relationship between the first and second patterns formed on the mask is
accurately detected as needed by means of the pattern position detection
device. Therefore, the second projection exposure apparatus of the present
invention, as with the first projection exposure apparatus of the present
invention, could accurately detect the image formation characteristics of
the projection optical system even if masks were different.
In the aforementioned second projection exposure apparatus of the present
invention, the pattern position detection device has a pattern detection
device for photoelectrically detecting the patterns on the mask, a stage
control device for moving the mask stage perpendicularly relative to an
optical axis of the projection optical system so that the first and second
patterns cross an area of detection of the pattern detection device, and a
position measuring device for measuring a position of the mask stage. In
such a case, the mask stage is moved by the stage control device, and the
first and second patterns on the mask are detected by the pattern
detection device. At this time, the position of the mask stage is detected
by the position measuring device. In this way, the positional relationship
between the first and second patterns can be detected.
Also, in the third and fourth projection exposure apparatuses of the
present invention, when the apparatuses further comprise a substrate stage
for mounting a photosensitive substrate to which a pattern of the mask is
transferred and also an object to be detected by the image position
detection device is an image of the predetermined pattern or first and
second patterns transferred to the photosensitive substrate, the image
formation characteristics of the projection optical system can be
accurately detected in the same state as actual exposure.
In addition, when the third and fourth projection exposure apparatuses of
the present invention are a projection exposure apparatus of the scan
exposure type where a photosensitive substrate is exposed while scanning
the photosensitive substrate and a mask in synchronization with each
other, the apparatus do not need to be newly modified because normally
there is provided a mask stage and a position measuring device which are
the constitutional elements of the present invention.
Furthermore, according to the third projection exposure apparatus, the
image formation characteristics of the projection optical system is
accurately measured without suffering the influence of a drawing error on
the mask and is corrected by the correction device.
In the prior art, the image formation characteristics, such as
magnification or image distortion, has been measured with the reference
mark for measurement of the mask. On the other hand, in the present
invention, the reference mark member has a plurality of reference marks
whose positions are accurately measured in advance, and when the image
formation characteristics of the projection optical system is measured,
the reference mark member is moved, for example, up to a position where
the mask is held during exposure, and the image formation characteristic,
such as projection magnification or image distortion, is measured with the
reference marks of the reference mark member. Therefore, unlike the prior
art, the image formation characteristics of the projection optical system
can be measured and accurately corrected without suffering the influence
of a drawing error of the reference mark for measurement on the mask, a
picture position measurement error, or thermal expansion of the mask.
According to the fourth projection exposure apparatus of the present
invention, in the scan-exposure type projection exposure apparatus, as
with the first projection exposure system, the image formation
characteristics of the projection optical system can be measured without
suffering the influence of a drawing error on the mask and can be
corrected by the correction device. Also, since the reference mark member
has been arranged on the mask stage in the scanning direction with respect
to the mask, the reference mark member can be quickly arranged in a
position where the mask is exposed, by moving the mask stage.
In addition, in the fourth projection exposure apparatus of the present
invention, when the reference mark member is arranged within an approach
run section of the mask stage where the illumination light for exposure is
illuminated, at the time of acceleration or deceleration during scan and
exposure, there is no need to provide an additional place for the
reference mark member. Since the reference mark member is arranged within
the approach run section during scan and exposure, illumination light for
exposure can be used as illumination light for illuminating the reference
mark. Therefore, a measurement error of the image formation
characteristics, which is caused due to a difference between illumination
light beams, does not occur.
Furthermore, in the aforementioned third and fourth projection exposure
systems of the present invention, when an object to be detected by the
image position detection device is an image projected on a test
photosensitive substrate or a test thermosensitive substrate through the
projection optical system, the image formation characteristics of the
projection optical system can be accurately detected in the same state as
actual exposure.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described in further detail with reference to
the accompanying drawings, in which:
FIGS. 1(a) and 1(b) are diagrams of a conventional inspection method for a
projection optical system, FIG. 1(a) showing the schematic structure of
the system and FIG. 1(b) showing an output curve of a photoelectric
sensor;
FIG. 2 is a flowchart showing a first embodiment of an inspection method
for a projection optical system according to the present invention;
FIG. 3 is a schematic view, partly in section, showing a projection
exposure apparatus for carrying out the inspection method for the
projection optical system of FIG. 2;
FIGS. 4(a) to 4(d) are diagrams used to concretely explain the inspection
method for the projection optical system of FIG. 2, FIG. 4(a) being a plan
view showing a reference mark formed on the reticle, FIG. 4(b) being an
elevational view showing the essential section of the exposure system of
FIG. 2, FIG. 4(c) being a plan view of a pattern plate used in the
constitution of FIG. 4(b), and FIG. 4(d) being a graph showing an output
curve of a photoelectric sensor;
FIG. 5(a) is an elevational view showing the essential section of a
modification of the first embodiment, and FIG. 5(b) is a plan view of the
pattern plate shown in FIG. 5(a);
FIGS. 6(a) and 6(b) are diagrams showing a modification of the pattern
plate used in the exposure system of FIG. 3, and FIGS. 6(c) and 6(d) are
graphs showing the output waveform and the differentiated value of a
photoelectric sensor obtained when the pattern plate of FIGS. 6(a) and
6(b) is used;
FIG. 7(a) is a schematic view showing the essential section of a projection
exposure apparatus for explaining a second embodiment of the inspection
method for the projection optical system according to the present
invention, and FIG. 7(b) is a diagram showing a resist image formed by
exposure in the second embodiment;
FIG. 8 is a flowchart showing a third embodiment of the inspection method
for the projection optical system according to the present invention;
FIGS. 9(a) to 9(c) are diagrams used to explain a projection exposure
apparatus for carrying out the inspection method for the projection
optical system of FIG. 8, FIGS. 9(a) and 9(b) showing the location
detection operation of a reference mark formed on a reticle and FIG. 9(c)
showing the essential section of the exposure system;
FIG. 10 is a schematic view showing, partly in cross section, a projection
exposure apparatus for carrying out another inspection method for the
projection optical system according to the present invention;
FIGS. 11(a) to 11(d) are diagrams used to concretely explain the inspection
method for the projection optical system of FIG. 10, FIG. 11(a) being a
plan view showing reference marks formed on a reference plate provided on
a reticle stage, FIG. 11(b) being an elevational view showing the
essential section of the exposure apparatus of FIG. 10, FIG. 11(c) being a
plan view of a pattern plate used in the constitution of FIG. 11(b), and
FIG. 11(d) being a graph showing an output curve of a photoelectric
sensor;
FIG. 12(a) is a schematic view showing the essential part of a projection
exposure apparatus for explaining another embodiment of the inspection
method for the projection optical system according to the present
invention, and FIG. 12(b) is a view showing a resist image formed by
exposure in the second embodiment;
FIGS. 13(a) to 13(c) are views showing the periphery of a reticle stage for
explaining another embodiment of the projection exposure apparatus of the
present invention, FIGS. 13(a) and 13(b) being cross-sectional views and
FIG. 13(c) being a plan view;
FIG. 14 is a view showing the peripheral constitution of a reticle stage
for explaining still another embodiment of the projection exposure
apparatus of the present invention;
FIG. 15 is a view showing the peripheral constitution of a reticle stage
for explaining a further embodiment of the projection exposure apparatus
of the present invention; and
FIG. 16 is a view showing a modification of the reference plates used in
the projection exposure apparatus of the embodiments of FIGS. 14 and 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of an inspection method for a projection optical system
according to the present invention and a projection exposure apparatus for
carrying out the inspection method will hereinafter be described in
reference to FIG. 2 and FIGS. 4(a) to 4(d). The embodiment of the present
invention is applied to a step-and-scan projection exposure apparatus
where patterns on a reticle (photomask) are serially transferred on shot
areas of a semiconductor wafer (photosensitive substrate) while scanning
the reticle and the wafer in synchronization with each other.
FIG. 3 schematically illustrates the projection exposure apparatus of this
embodiment. In the figure, reference character IL denotes illumination
light (e.g., bright-line such as a g-line or an i-line in a ultraviolet
spectral region) emitted from a light source 1 comprising an extra-high
pressure mercury vapor lamp. The illumination light IL passes through a
shutter (not shown) and is converted to luminous flux whose illuminance
distribution is substantially uniform by means of an illuminance
uniforming illumination system 2A comprising a collimator lens, a fly-eye
lens, and a reticle blind. In addition to the bright-line of the
extra-high pressure mercury-vapor lamp, a KrF excimer laser beam, an ArF
excimer laser beam, copper vapor laser beam or harmonics of YAG laser beam
is employed as illumination light IL. Also, the reticle blind comprises a
plurality of movable light shielding portions so that an area on a reticle
R which is illuminated can be optionally set.
The illuminance uniforming illumination system 2A is further provided with
a variable diaphragm for varying an illumination state of the reticle R.
With this variable diaphragm, the numerical aperture (.sigma.-value which
is a coherence factor of the illumination system) of th
