U.S. patent application number 09/885404 was filed with the patent office on 2001-11-08 for scanning exposure methods.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Ebihara, Akimitsu.
Application Number | 20010038959 09/885404 |
Document ID | / |
Family ID | 26738921 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038959 |
Kind Code |
A1 |
Ebihara, Akimitsu |
November 8, 2001 |
Scanning exposure methods
Abstract
Since a mask stage 16 and a substrate stage 14 are supported in
a floating manner over a base member 12, the both stages are driven
in mutually opposite directions in a non-contact manner along the
scanning direction by the aid of a linear motor 13. During this
process, the movement of the both stages 16, 14 does not exert any
force on the base member 12 and other components, and thus the
momentum is conserved. The mass ratio between the stage 16 and the
stage 14 is set to be identical with a reduction magnification of
an unillustrated projection optical system. Therefore, according to
the law of conservation of momentum, the velocity ratio between the
stage 16 and the stage 14 is a reciprocal number of the reduction
magnification of the projection optical system. Thus, the both
stages 16, 14 are subjected to accurate synchronous control. It is
possible to suppress inclination and fluctuation of the entire
apparatus, and it is possible to improve the synchronization
performance of the mask stage and the substrate stage.
Inventors: |
Ebihara, Akimitsu;
(Kyoto-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
NIKON CORPORATION
|
Family ID: |
26738921 |
Appl. No.: |
09/885404 |
Filed: |
June 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09885404 |
Jun 21, 2001 |
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09749561 |
Dec 28, 2000 |
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09749561 |
Dec 28, 2000 |
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09152928 |
Sep 15, 1998 |
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60059570 |
Sep 19, 1997 |
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Current U.S.
Class: |
430/30 ;
355/18 |
Current CPC
Class: |
G03F 7/70358 20130101;
G03F 7/70716 20130101; G03F 7/70725 20130101; G03F 7/70766
20130101 |
Class at
Publication: |
430/30 ;
355/18 |
International
Class: |
G03C 005/00; G03B
027/00 |
Claims
1. An exposure apparatus for transferring a pattern formed on a
mask onto a photosensitive substrate through a projection optical
system while synchronously moving the mask and the photosensitive
substrate, the exposure apparatus comprising: a substrate stage
supported in a floating manner over a base member; a mask stage
supported in a floating manner over the base member and having a
mass corresponding to an amount obtained by multiplying a mass of
the substrate stage by a reduction magnification of the projection
optical system; and a first linear motor provided between the
substrate stage and the mask stage, for driving the substrate stage
and the mask stage so that the mask and the substrate are moved in
mutually opposite directions.
2. The exposure apparatus according to claim 1, wherein the
projection optical system is an optical system which projects an
inverted image of the pattern formed on the mask onto the
photosensitive substrate.
3. The exposure apparatus according to claim 1, wherein the
photosensitive substrate is held horizontally on the substrate
stage, the mask is held vertically on the mask stage, and the
projection optical system comprises a plurality of transmitting
optical elements, a beam splitter, and a reflecting optical
element, and wherein the optical system projects the pattern of the
mask arranged on an object plane onto the photosensitive substrate
arranged on an image formation plane at a predetermined reduction
magnification.
4. The exposure apparatus according to claim 3, further comprising
a half TTL alignment detection system which is capable of
detecting, via the beam splitter, both of an alignment mark formed
on the mask and an alignment mask formed on the photosensitive
substrate.
5. The exposure apparatus according to claim 1, wherein a second
linear motor for driving the mask stage is provided between the
base member and the mask stage.
6. The exposure apparatus according to claim 5, wherein a third
linear motor for driving the substrate stage is provided between
the base member and the substrate stage.
7. The exposure apparatus according to claim 6, wherein at least
one of the second linear motor and the third linear motor is
provided with a regenerative braking circuit for finely adjusting a
velocity ratio during synchronous movement of the both stages
effected by the first linear motor
8. The exposure apparatus according to claim 1, wherein the
substrate stage comprises a first stage which is movable in a first
direction in which the photosensitive substrate is moved
synchronously, with the mask stage and a second stage which is
movable in the first direction integrally with the first stage
while holding the photosensitive substrate and which is movable in
a second direction perpendicular to the first direction by being
guided by the first stage.
9. The exposure apparatus according to claim 1, wherein the
substrate stage is supported in the floating manner over the base
member via an air bearing.
10. The exposure apparatus according to claim 1, wherein the mask
stage is supported in the floating manner over the base member via
an air bearing.
11. A scanning exposure apparatus having a projection optical
system with an optical axis substantially perpendicular to a mask
and a substrate respectively, for transferring a pattern formed on
the mask onto the substrate through the projection optical system,
the scanning exposure apparatus comprising: a base; a first stage
for moving the mask over the base; a second stage for moving the
substrate over the base; and a driving system connected to the
first stage and the second stage, for synchronously moving the mask
and the substrate at a velocity ratio corresponding to a
magnification of the projection optical system, wherein: the
driving system drives the first stage and the second stage along
predetermined directions oppositely to one another so that a
reactive force generated by the synchronous movement is offset.
12. The scanning exposure apparatus according to claim 11, wherein
a mass ratio between the first stage and the second stage is
substantially coincident with a projection magnification of the
projection optical system.
13. The scanning exposure apparatus according to claim 11 wherein
the projection optical system comprises a refractive optical
element and at least one reflecting optical element, and the
projection optical system reduces and projects a partial inverted
image of the pattern on the mask onto the substrate.
14. The scanning exposure apparatus according to claim 11 wherein
the projection optical system comprises at least two reflecting
optical elements, and its image plane is arranged on a side of an
object plane with respect to the projection optical system.
15. The scanning exposure apparatus according to claim 13, wherein
the projection optical system comprises, as the reflecting optical
element, at least one of a mirror, a concave mirror, and a beam
splitter.
16. The scanning exposure apparatus according to claim 14, wherein
the projection optical system comprises, as the reflecting optical
element, at least one of a mirror, a concave mirror, and a beam
splitter.
17. The scanning exposure apparatus according to claim 11, wherein
an object plane and an image plane of the projection optical system
are arranged in an identical plane, and the first and second stages
move the mask and the substrate along the plane respectively.
18. The scanning exposure apparatus according to claim 14, wherein
an object plane and an image plane of the projection optical system
are arranged in an identical plane, and the first and second stages
move the mask and the substrate along the plane respectively.
19. The scanning exposure apparatus according to claim 14, further
comprising an illumination system arranged on a side opposite to
the projection optical system with respect to the base, for
irradiating the mask with a light beam.
20. The scanning exposure apparatus according to claim 17, further
comprising an illumination system arranged on a side opposite to
the projection optical system with respect to the base, for
irradiating the mask with a light beam.
21. The scanning exposure apparatus according to claim 18, further
comprising an illumination system arranged on a side opposite to
the projection optical system with respect to the base, for
irradiating the mask with a light beam.
22. A scanning exposure method for transferring a pattern formed on
a mask onto a substrate through a projection optical system, the
scanning exposure method comprising the steps of: arranging the
mask and the substrate in an identical plane perpendicular to an
optical axis of the projection optical system; projecting a partial
inverted image of the pattern formed on the mask onto the
substrate; and synchronously moving the mask and the substrate
oppositely to one another along predetermined directions on the
plane so that a reactive force generated by the synchronous
movement is substantially offset.
23. The scanning exposure method according to claim 22, wherein the
mask and the substrate are synchronously moved at a velocity ratio
corresponding to a magnification of the projection optical
system.
24. The scanning exposure method according to claim 22 wherein in
order to perform overlay transfer of the pattern on the mask onto a
pattern on the substrate, a velocity ratio between the mask and the
substrate is adjusted during the synchronous movement so that at
least one of a magnification error and a distortion error between
the pattern on the substrate and the image of the pattern on the
mask is corrected.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exposure apparatus and
an exposure method. In particular, the present invention relates to
an exposure apparatus, especially a scanning exposure apparatus and
a scanning exposure method in which a mask held by a mask stage and
a photosensitive substrate held by a substrate stage are subjected
to scanning in a synchronized manner by using an illumination light
beam, so as to transfer, onto the photosensitive substrate, a
pattern such as a semiconductor circuit pattern and a liquid
crystal circuit pattern formed on the mask via a projection optical
system.
BACKGROUND ART
[0002] Recently, a scanning type exposure apparatus based on the
step-and-scan system (hereinafter referred to as "S&S system",
if necessary), which realizes a resolution line width of not more
than 0.5 .mu.m, has been developed as an exposure apparatus for
producing semiconductor elements. The apparatus is being actively
improved in order to realize genuine and practical use for the
semiconductor production line. The exposure apparatus based on the
S&S system is disclosed, for example, in (1) Japanese Laid-Open
Patent Publication No. 56-111218, (2) SPIE Vol. 1088 Optical/Laser
Microlithography II (1989), pp. 424-433, (3) Japanese Laid-Open
Patent Publication No. 2-229423, and (4) Japanese Laid-Open Patent
Publication No. 4-277612.
[0003] Among them, in order to use mirror projection of 1.times.
magnification in the S&S system, the above-mentioned patent
document (1) discloses a system in which the mask is linearly moved
in the scanning direction during scanning exposure, while the
semiconductor wafer is moved in the scanning direction in a
scanning manner, and it is moved in a direction perpendicular
thereto in a stepwise manner. The above-mentioned document (2)
discloses a reduction projection scanning exposure apparatus of the
S&S system which uses a 1/4 reduction projection optical system
having a circular arc-shaped slit field constructed by combining an
optical lens and a reflecting mirror so as to accurately control
the velocity ratio between the mask (or reticle) and the wafer to
be 4:1 during scanning exposure. The above-mentioned patent
document (3) discloses an apparatus in which an excimer laser is
used as an illumination light beam, and an effective projection
area is subjected to restriction to a regular hexagon which is
inscribed in a circular image field of an ordinary reduction
projection lens system to perform exposure based on the S&S
system. The above-mentioned patent document (4) discloses an
apparatus in which an effective projection area is subjected to
restriction to a linear slit-shaped (rectangular) area which is
formed along a diameter of a circular image field of an ordinary
reduction projection lens system to perform exposure based on the
S&S system.
[0004] Besides, in order to obtain a higher resolving power,
Japanese Laid-Open Patent Publication No. 6-300973 (5) discloses a
reduction projection optical system comprising a plurality of
optical lenses, a beam splitter, and a concave mirror, the system
being applied to an ArF excimer laser having a wavelength of not
more than 200 nm as an illumination light beam for exposure. A
similar projection optical system is also disclosed in Japanese
Laid-Open Patent Publication No. 5-88087 applied by the same
applicant as that of the present application.
[0005] In the respective conventional techniques described above,
the scanning type exposure apparatus based on the use of the
reduction projection optical system generally adopts the system in
which the reticle stage for holding the reticle and the wafer stage
for holding the wafer are moved in a scanning manner at a velocity
ratio which coincides with a reciprocal number of a reduction
magnification of the projection optical system. Therefore, it has
been necessary that a driving source (for example, a linear motor)
for the reticle stage and a driving source (for example, a linear
motor) for the wafer stage should be individually provided on an
apparatus body (for example, a column for fixing the projection
optical system thereon) to precisely control the both driving
sources in a synchronized manner so that the reticle and the wafer
are relatively moved while maintaining a constant velocity ratio.
Namely, such a system requires the linear motor for linearly moving
the reticle stage with respect to the projection optical system
during scanning exposure, the linear motor for linearly moving the
wafer stage with respect to the projection optical system, and a
servo control circuit for individually and precisely controlling
the respective linear motors on the basis of measured values
obtained by laser interferometers for individually measuring the
position of movement of the respective stages with respect to the
projection optical system.
[0006] In the case of the scanning type exposure apparatus based on
the use of the reduction projection optical system as described
above, a method is generally adopted in which a stage having
superior characteristics runs after a stage having inferior
characteristics, because the reticle stage (mask stage) and the
wafer stage (substrate stage) have different dynamic
characteristics respectively. However, such a scanning type
exposure apparatus has the following inconvenience. Namely, the
stage having inferior characteristics is slow in setting
adjustment, because it is affected, for example, by fluctuation of
the body so serve as a backbone of the apparatus. In order to
improve the synchronization performance, it is necessary to use a
stage having extremely excellent dynamic characteristics, as the
stage having superior characteristics. Moreover, it is necessary
and indispensable to use a special unit such as a so-call active
vibration-removing apparatus (vibration-preventive apparatus) for
reducing fluctuation of the body. Therefore, the system of the
apparatus is complicated to that extent, and the cost becomes
expensive.
[0007] Further, the scanning exposure apparatus based on the use of
the reduction projection system, in which the optical axis ranging
from the reticle to the wafer is linear, has the following
inconvenience, as in the apparatuses described in the foregoing
patent documents (3) and (4). Namely, the reticle stage and the
wafer stage are generally arranged so that both of them are moved
in the horizontal direction. Further, the reticle stage and the
wafer stage are disposed so that they are separated from each other
in the vertical direction by a distance of about 80 to 150 cm.
Accordingly, the reticle stage is arranged at an upper position of
the body of the exposure apparatus. Therefore, the entire apparatus
may be inclined due to scanning movement of the reticle stage
during scanning exposure in some cases. In other cases, excessive
stress may be applied to the respective structural components (for
example, the column, and the base plate) for constituting the
apparatus body.
[0008] The conventional apparatus has also involved the following
inconveniences. Namely, disorder occurs in synchronous control for
the linear motor for the reticle stage and the linear motor for the
wafer stage. Further, the transfer magnification becomes
non-uniform in relation to the scanning direction concerning the
pattern image transferred to the shot area on the wafer if the
interferometer suffers measurement error (count mistake).
[0009] The present invention has been made considering the
inconveniences involved in the conventional technique as described
above, an object of which is to provide an exposure apparatus and a
scanning exposure apparatus each of which has a simple structure
and makes it possible to reduce the stress generated in the
structural components for constructing the apparatus, suppress
inclination and fluctuation of the entire apparatus, and improve
the synchronization performance of the mask stage and the substrate
stage.
[0010] Another object of the present invention is to provide a
scanning exposure method which makes it possible to reduce the
stress generated in the exposure apparatus, suppress inclination
and fluctuation of the entire apparatus, and improve the
synchronization performance of the mask stage and the substrate
stage.
DISCLOSURE OF THE INVENTION
[0011] According to a first aspect of the present invention, there
is provided an exposure apparatus for transferring a pattern formed
on a mask onto a photosensitive substrate through a projection
optical system while synchronously moving the mask and the
photosensitive substrate, the exposure apparatus comprising:
[0012] a substrate stage supported in a floating manner over a base
member;
[0013] a mask stage supported in a floating manner over the base
member and having a mass corresponding to an amount obtained by
multiplying a mass of the substrate stage by a reduction
magnification of the projection optical system; and
[0014] a first linear motor provided between the both stages, for
driving the substrate stage and the mask stage so that the mask and
the substrate are moved in mutually opposite directions.
[0015] According to the exposure apparatus, the mask stage and the
substrate stage are supported in the floating manner on the base
member. Therefore, the both stages are driven by the first linear
motor in the mutually opposite directions while making no contact
along the movement direction. During this process, no force is
exerted at all on the base member and other components by the
movement of the both stages. Thus, the momentum is conserved. In
the present invention, the mass of the mask stage corresponds to
the amount obtained by magnifying the mass of the substrate stage
by the reduction magnification. Therefore, according to the law of
conservation of momentum, the velocity ratio between the mask stage
and the substrate stage is a reciprocal number of the reduction
magnification of the projection optical system, and thus the both
stages are subjected to accurate synchronous control. The position
of the center of gravity of the entire system scarcely changes, and
hence the main body including the base member is neither fluctuated
nor inclined due to the movement of the both stages (synchronous
scanning for the mask and the substrate).
[0016] The exposure apparatus of the present invention may be
constructed such that the projection optical system is an optical
system which projects an inverted image of the pattern formed on
the mask onto the photosensitive substrate. When the exposure
apparatus is constructed as described above, the photosensitive
substrate is accurately exposed by projection with the image of the
pattern when the mask stage and the substrate stage are
synchronously moved in the mutually opposite directions by the aid
of the first linear motor.
[0017] The exposure apparatus of the present invention may be
constructed such that the photosensitive substrate is held
horizontally on the substrate stage, the mask is held vertically on
the mask stage, and the projection optical system comprises a
plurality of transmitting optical elements, a beam splitter, and a
reflecting optical element, wherein the optical system projects the
pattern of the mask arranged on an object plane onto the
photosensitive substrate arranged on an image formation plane at a
predetermined reduction magnification. When the exposure apparatus
is constructed as described above, for example, it is possible to
arrange a half TTL alignment detection system on a side opposite to
the mask stage in relation to the beam splitter. By doing so, the
alignment mark formed on the mask can be detected separately from
or simultaneously with the alignment mark formed on the
photosensitive substrate by using the half TTL alignment detection
system by the aid of the beam splitter. Accordingly, the detection
of the reticle alignment mark and the detection of the wafer
alignment mark can be conveniently performed by using the single
detecting system.
[0018] The exposure apparatus of the present invention may be
constructed such that a second linear motor for driving the mask
stage is provided between the base member and the mask stage.
According to this structure, the mask stage can be driven
independently from the base member by driving the second linear
motor in a state in which the first linear motor is turned OFF.
Accordingly, it is possible to perform positional resetting and
fine adjustment for the mask stage.
[0019] The exposure apparatus of the present invention may be
constructed such that a third linear motor for driving the
substrate stage is provided between the base member and the
substrate stage. When the exposure apparatus is constructed as
described above, the substrate stage can be driven independently
from the base member by driving the third linear motor in a state
in which the first linear motor (and the second linear motor)
is/are turned OFF. Accordingly, it is possible to perform
positional resetting and fine adjustment for the substrate
stage.
[0020] The exposure apparatus of the present invention may be
constructed such that a regenerative braking circuit for finely
adjusting a velocity ratio during synchronous movement of the both
stages effected by the first linear motor is provided together with
at least one of the second linear motor and the third linear motor.
When the exposure apparatus is constructed as described above, at
least one of the second linear motor and the third linear motor is
allowed to perform the regenerative braking action by the aid of
the regenerative braking circuit. Thus, the apparent mass of at
least any one of the mask stage and the substrate stage which are
moved in the mutually opposite directions by the first linear motor
can be increased to finely adjust the velocity ratio between the
both stages during the movement. The term "regenerative braking"
refers to occurrence of the braking action brought about by
allowing the motor to function as a kind of generator. Accordingly,
the load to be driven by the first linear motor can be increased.
Namely, it is possible to increase the apparent mass of at least
one of the mask stage and the substrate stage. According to the
exposure apparatus in conformity with the foregoing construction,
when the mass ratio between the both stages is not accurately set
to be a desired value, the velocity ratio between the both stages
can be adjusted to ensure desired synchronization performance.
Besides, it is possible to ensure stable synchronization
performance even when the momentum is not completely conserved by
always making the velocity ratio between the both stages to
coincide with the reciprocal number of the reduction magnification
of the projection optical system by appropriately adjusting the
regenerative braking amount during the movement (scanning).
[0021] The exposure apparatus of the present invention may be
constructed such that the substrate stage comprises a first stage
which is movable in a first direction in which the photosensitive
substrate is synchronously moved, and a second stage which is
movable in the first direction integrally with the first stage
while holding the photosensitive substrate and which is movable in
a second direction perpendicular to the first direction by being
guided by the first stage. When the exposure apparatus is
constructed as described above, the second stage for holding the
substrate is moved in the first direction integrally with the first
stage to perform scanning exposure, and then the second stage is
moved in the second direction perpendicular to the first direction
with respect to the first stage. By repeating this process, it is
possible to easily realize exposure based on the so-called
step-and-scan system.
[0022] According to a second aspect of the present invention, there
is provided a scanning exposure apparatus including a projection
optical system having an optical axis substantially perpendicular
to a mask and a substrate respectively, for transferring a pattern
formed on the mask onto the substrate through the projection
optical system, the scanning exposure apparatus comprising:
[0023] a base;
[0024] a first stage for moving the mask over the base;
[0025] a second stage for moving the substrate over the base;
and
[0026] a driving system connected to the first stage and the second
stage, for synchronously moving the mask and the substrate at a
velocity ratio corresponding to a magnification of the projection
optical system, wherein:
[0027] the driving system drives the first stage and the second
stage along predetermined directions oppositely to one another so
that a reactive force generated by the synchronous movement is
offset.
[0028] According to a third aspect of the present invention, there
is provided a scanning exposure method for transferring a pattern
formed on a mask onto a substrate through a projection optical
system, the scanning exposure method comprising the steps of:
[0029] arranging the mask and the substrate in an identical plane
perpendicular to an optical axis of the projection optical
system;
[0030] projecting a partial inverted image of the pattern formed on
the mask onto the substrate; and
[0031] synchronously moving the mask and the substrate oppositely
to one another along predetermined directions on the plane so that
a reactive force generated by the synchronous movement is
substantially offset.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 shows a fundamental construction of the present
invention.
[0033] FIG. 2 shows a schematic arrangement illustrating an
exposure apparatus according to a first embodiment.
[0034] FIG. 3 shows a schematic plan view illustrating the
apparatus shown in FIG. 1.
[0035] FIG. 4 shows a block diagram illustrating an arrangement of
a control system of the apparatus shown in FIG. 1.
[0036] FIG. 5 shows a block diagram illustrating an arrangement of
a control system of an apparatus according to a second
embodiment.
[0037] FIG. 6A shows a schematic front view concerning a modified
embodiment of the exposure apparatus according to the present
invention.
[0038] FIG. 6B shows a right side view of the modified embodiment
of the exposure apparatus shown in FIG. 6B.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] The fundamental construction of the exposure apparatus
according to the present invention will be explained below with
reference to FIG. 1. FIG. 1 shows the fundamental construction of
the exposure apparatus 10 according to the present invention. The
exposure apparatus 10 comprises vibration-preventive pedestal 12 as
a base member, a substrate stage 14 supported in a floating manner
over the vibration-preventive pedestal 12 via an air bearing
(air-operated bearing) 13, and a mask stage 16 supported in a
floating manner over the substrate stage 14. A linear motor 18 is
provided between the substrate stage 14 and the mask stage 16.
Namely, for example, a driving coil 18A of the linear motor 18 is
disposed on a side of the mask stage 16 having a mass Mr, and a
magnet track section 18B of the linear motor 18 is disposed on a
side of the substrate stage 14 having a mass Mw. The ratio between
the mass Mr of the mask stage 16 and the mass Mw of the substrate
stage 14 corresponds to a reduction magnification of an
unillustrated projection optical system.
[0040] In the exposure apparatus 10 according to the present
invention constructed as described above, the both stages 14, 16
are supported in the floating manner. Therefore, when the linear
motor 18 is excited, only the internal force makes the action,
wherein the force of action F1 and the force of reaction F2, which
are equal to one another in magnitude and opposite in direction
(F2=-F1), are applied to the respective stages 16, 14. Assuming
that the velocities of movement of the both stages 16, 14 generated
by the forces are Vr and Vw, and air resistance or the like is
neglected, the following expression is given according to the law
of conservation of momentum:
Mr.multidot.Vr=Mw.multidot.Vw
[0041] Therefore, the velocity ratio between the both stages 16, 14
is given as follows:
Vr/Vw=Mw/Mr
[0042] However, in the present invention, the ratio Mr/Mw between
the masses of the both stages 16, 14 is set to be equal to the
reduction magnification Mp1 of the unillustrated projection optical
system as described above, and hence the following expression is
given:
Vr/Vw=Mw/Mr=1/Mp1
[0043] Accordingly, the velocity ratio between the both stages 16,
14 coincides with the reciprocal number of the reduction
magnification of the projection optical system. Therefore, in an
ideal state, when a system to conserve the momentum is constructed,
the both stages 14, 16 can be always subjected to synchronous
scanning (movement) in a reliable manner by servo-controlling the
velocity (or position) of only one of the substrate stage 14 and
the mask stage 16.
[0044] For example, when the mask stage 16 is servo-controlled, if
the mask stage 16 makes vibrative action, then the substrate stage
14 makes vibrative action similar to that of the mask stage 16 at
the same velocity ratio as the reciprocal number of the mass ratio.
Further, the position of the center of gravity of the system is
always constant, because the momentum is conserved. Accordingly,
the vibration-preventive pedestal 12 is not fluctuated. Therefore,
the synchronization error during scanning is always zero between
the both stages 16, 14 (between the mask and the substrate held by
the both stages 16, 14 respectively).
EMBODIMENTS
First Embodiment
[0045] The first embodiment of the present invention will be
explained with reference to FIGS. 2 to 4. FIGS. 2 and 3 show the
arrangement of main components of an exposure apparatus 100 of the
step-and-scan system according to the first embodiment.
[0046] The exposure apparatus 100 comprises a base structure 200 as
a base member held horizontally on an unillustrated
vibration-preventive pad, a wafer stage 14 as a substrate stage
supported in a floating manner over the base structure 200, a
reticle stage body 206 as a mask stage supported in a floating
manner over the base structure 200, a projection optical system PL
held by an unillustrated main column body over the wafer stage 14
and fixed to the base structure 200, and an illumination optical
system 212 also held by the unillustrated main column body and
fixed to the base structure 200. In this embodiment, the wafer
stage 14 comprises a first wafer stage body 208 as a first stage
which is movable in the X direction (scanning direction), and a
second wafer stage body 220 as a second stage which is guided by
the first stage body 208 and which is movable in the Y direction
perpendicular to the X direction. Specified arrangement of these
components will be described in detail later on.
[0047] Two prism-shaped fixed guide rails 202, 204, which extend in
parallel to one another in the X direction (direction perpendicular
to the plane of the paper) perpendicular to the Y direction, are
provided to protrude at a portion of a first end (left end) in the
Y direction in FIG. 2, on the upper surface of the base structure
200. Other portions of the upper surface of the base structure 200
are polished to be flat to support the respective movable bodies
(stages) in the Z direction and smoothly move them in the XY plane.
One of the fixed guide rails 202 is formed with a guide surface
202A for restricting, in the Z direction, the reticle stage body
206 which is movable in the X direction, and a guide surface 202B
for restricting the reticle stage body 206 in the Y direction. The
other fixed guide rail 204 is formed with a guide surface 204A for
restricting, in the Y direction, the first wafer stage body 208
which is movable in the X direction.
[0048] As shown in FIG. 2, this embodiment uses the reticle stage
body 206 of the vertical type for vertically holding a reticle R as
a mask. The reticle stage body 206 is provided with a reticle fine
movement stage 210 for vertically holding the reticle R to perform
translational fine movement and rotational fine movement in a plane
(XZ plane in FIG. 2) perpendicular to the optical axis AX of the
projection optical system PL.
[0049] The illumination optical system 212 is disposed on a side
opposite to the projection optical system PL in relation to the
reticle R, which radiates a rectangular pattern area on the reticle
R with an illumination light beam having an intensity distribution
extending in a form of slit (or a rectangular form) in the
direction perpendicular to the scanning direction (X direction)
during scanning exposure. The portion of the pattern on the reticle
R, which is irradiated with the linear slit-shaped illumination
light beam, is disposed at the center of a circular field on the
side of the object plane which is perpendicular to the horizontal
optical axis AX of the projection optical system PL. The pattern is
projected onto the wafer W at a resolving power of, for example,
not more than 0.35 .mu.m via the projection optical system PL
having a predetermined reduction magnification Mp1 (1/4 in this
embodiment) which is constructed to be telecentric on both sides by
a first lens group G1, a second lens group G2, and a third lens
group G3 to serve as transmitting optical elements, a beam splitter
BS as a beam-splitting unit, and a concave mirror MR as a
reflecting optical element. This embodiment uses the projection
optical system which projects, onto the wafer W, an inverted image
(inverted on the X axis) of the unillustrated circuit pattern
formed on the pattern plane on the reticle R. Detailed arrangement
of such a projection optical system PL is particularly disclosed,
for example, in Japanese Laid-open Patent Publication Nos. 5-88087
and 6-300973 referred to above. Accordingly, further detailed
explanation will be omitted herein.
[0050] Those fixed at the bottom of the reticle stage body 206 are
a pad PDA for air bearing (air-operated bearing) for supporting the
self-weight of the reticle stage body 206 opposing to the guide
surface 202A of the fixed guide rail 202, a pad PDB for air bearing
for restricting displacement in the Y direction of the reticle
stage body 206 opposing to the guide surface 202B of the fixed
guide rail 202, and a pad PDC for air bearing for supporting the
self-weight of the reticle stage body 206 opposing to the surface
200A of the base structure 200 located between the fixed guide
rails 202 and 204. Among these pads, the pad PDB for restricting
displacement in the Y direction is composed of an air
pressure/vacuum combination type pad (vacuum pre-loaded air
bearing) constructed by combining a plurality of air pad sections
for ejecting pressurized air, and a plurality of vacuum pad
sections arranged alternately therewith in the X direction
(direction perpendicular to the plane of the paper) for sucking
air. The air pressure/vacuum combination type pad functions such
that the reticle stage body 206 is supported in a floating manner
while being separated from the guide surface by a predetermined
clearance owing to the balance between the suction force
(pre-loaded pressure) exerted by the vacuum pad sections and the
pressure of air ejected from the air pad sections. In the case of
the pad PDA and the pad PDC, the self-weight of the reticle stage
body 206 acts as a pre-loaded pressure. Accordingly, the reticle
stage body 206 is supported in a floating manner while being
separated from the guide surface by a predetermined clearance owing
to the balance between the self-weight and the pressure of air
ejected from the pad PDA and the pad PDC. In the following
description, the phrase "the pad supports the self-weight" will be
also used in this meaning.
[0051] The wafer stage 14, which comprises the first wafer stage
body 208 and the second wafer stage body 220, is supported in a
floating manner over the upper surface of the base structure 200 at
a second end portion in the Y direction of the fixed guide rail
204.
[0052] The first wafer stage body 208 is formed to have a
rectangular frame-shaped configuration extending over the XY plane
over the base structure 200 (see FIG. 3). The self-weight of the
first wafer stage body 208 is supported by pads PDD, PDE which
serve as air bearings arranged at four corners opposing to the
upper surface of the base structure 200. Displacement of the first
wafer stage body 208 in the Y direction (right and left directions
in the plane of the paper) is restricted by an air pressure/vacuum
combination type pad PDF which is fixed to the first wafer stage
body 208 opposing to the vertical guide surface 204A of the fixed
guide rail 204. Accordingly, the first wafer stage body 208 is
movable in a friction-less manner in the X direction by being
guided by the guide surface 204A and the surface of the base
structure 200.
[0053] A first linear motor 216, which is arranged along the X
direction, is provided between the first wafer stage body 208 and
the reticle stage body 206. The first linear motor 216 comprises a
magnet track section 216A fixed on a side of the first wafer stage
body 208 and extending over a movement stroke in the X direction
(the magnet track section 216A comprises a yoke having a ]-shaped
cross section extending in the X axis direction, and a pair of
magnets fixed to upper and lower surfaces of the yoke), and a
driving coil section 216B fixed on a side of the reticle stage body
206. Thus, the first linear motor 216 generate the thrust force in
the X direction. Namely, in the first embodiment, for example, when
the reticle stage section 206 is driven toward the front of the
plane of the paper integrally with the driving coil section 216B by
driving the linear motor 216, the reaction of the foregoing
operation is generated to drive the wafer stage 14 toward the back
of the plane of the paper integrally with the magnet track section
216A.
[0054] The reticle stage body 206 is movable singly in the X
direction by the aid of a second linear motor 214 provided along
the X direction. The linear motor 214 comprises a magnet track
section 214A fixed on a side of the base structure 200 and
extending over a movement stroke in the X direction of the reticle
stage body 206 (the magnet track section 214A comprises a yoke
having a U-shaped cross section fixed on the guide surface 200A,
and a pair of magnets fixed to right and left inner surfaces of the
yoke), and a driving coil section 214B fixed on a side of the
reticle stage body 206. Thus, the second linear motor 214 generate
the thrust force in the X direction. The second linear rotor 214 is
used to restore the reticle stage body 206 to a predetermined reset
position. Besides, the second linear motor 214 has various other
roles which will be described later on.
[0055] As shown in FIGS. 2 and 3, a second wafer stage body 220,
which carries a wafer holder 218 for vacuum-sucking the wafer W,
and fiducial mark plate FM, is held movably in the Y direction at
the inside of the frame of the first wafer stage body 208. FIG. 3
shows the arrangement of the wafer stage body as viewed on the XY
plane. As shown in FIG. 2, a plurality of pads PDI, PDG for air
bearings for supporting the self-weight of the second wafer stage
body 220, are attached to lower portions of the second wafer stage
body 220 opposing to the upper surface of the base structure
200.
[0056] As also shown in FIG. 3, a guide surface 222 for guiding the
second wafer stage body 220 in the Y direction (or for restricting
displacement in the X direction) is formed on any one of inner
surfaces of two straight frame sections of the first wafer stage
body 208 extending in the Y direction and interposing the second
wafer stage body 220. A pair of air pressure/vacuum combination
type pads PDH, which are opposed to the guide surface 222, are
fixed to first end portions of the second wafer stage body 220.
[0057] Further, as shown in FIG. 3, a pair of linear motors 240,
242 for moving the second wafer stage body 220 in the Y direction
with respect to the first wafer stage body 208 are provided between
the second wafer stage body 220 and the respective two straight
frames of the first wafer stage 208 extending in the Y direction.
Respective driving coil sections 240A, 242A of the pair of linear
motors 240, 242 are fixed on both sides of the second wafer stage
body 220. Accordingly, the second wafer stage body 220 can be
finely rotated (in an order of second) on the surface of the base
structure 200 by delicately changing the driving amounts of the
respective linear motors 240, 242.
[0058] Now, the mesial conformation concerning the reticle R and
the first and second wafer stage bodies 208, 220 on the XY plane
will be further explained with reference to FIG. 3. In FIG. 3, the
movement position of the reticle R in the X direction (scanning
direction) in the XZ plane and the minute rotation amount (yawing
error) of the reticle R in the XZ plane are successively measured
by radiating a length-measuring laser beam onto a reflecting mirror
CMx fixed to a portion of the fine movement stage 210 provided on
the reticle stage body 206, and receiving a reflected beam
therefrom by using laser interferometers RIFx, RIF.theta.. Although
not illustrated in any of FIGS. 2 and 3, a laser interferometer
RIFy is also provided for successively measuring the position
concerning the reticle fine movement stage 210 in the Z direction
(the vertical direction in the plane of the paper in FIG. 2 or the
direction perpendicular to the plane of the paper in FIG. 3). In
this embodiment, the laser interferometer RIFy measures the
position in the Z direction of the reticle fine movement stage 210.
However, considering the wafer stage coordinate system, the
position in the Z direction corresponds to the position in the Y
direction, and hence the reference symbol "laser interferometer
RIFy" is consciously used. Therefore, the measured value obtained
by using the laser interferometer RIFy is expressed as PY in the
following description.
[0059] The coordinate position of the wafer W in the XY plane is
successively measured by a laser interferometer WIFy for radiating
a length-measuring laser beam onto a movement mirror My provided at
the second end (right end) in the Y direction of the second wafer
stage body 220 to extend in the X axis direction and receiving a
reflected light beam therefrom, and a laser interferometer WIFx for
radiating a length-measuring laser beam onto a movement mirror Mx
provided at the first end in the X direction of the second wafer
stage body 220 to extend in the Y axis direction and receiving a
reflected light beam therefrom. The respective interferometers
WIFx, WIFy simultaneously measure, in a successive manner, the
minute rotation amount (yawing error) of the second wafer stage
body 220. The movement mirrors and the interferometers are omitted
from the illustration in FIG. 2.
[0060] Plane mirrors and corner prisms (any of which are not
shown), which serve as references for any of the respective
interferometers RIFx, RIF.theta., RIFy, WIFx, WIFy, are fixed to
the base structure 200 so that the coordinate positions of the
reticle R and the wafer W are measured on the basis of the base
structure 200.
[0061] One shot area SA is illustrated on the wafer W shown in FIG.
3. The state shown in FIG. 3 represents a moment at which the
central point of the shot area SA is just coincident with the
vertical optical axis AX of the projection optical system PL (the
optical axis of the lens group G3 shown in FIG. 2). At this point
of time, the central point of the pattern area on the reticle R is
also just coincident with the horizontal optical axis AX (the
optical axis of the lens groups G1, G2 shown in FIG. 2).
[0062] The exposure apparatus 100 according to the first embodiment
further comprises an alignment optical system 230 of the TTL
(through-the-lens) system for photoelectrically detecting an
alignment mark formed on the wafer W or the fiducial mark plate FM
from a position located between the projection optical system PL
and the reticle R via a peripheral portion in the projection field
of the projection optical system PL, and an alignment optical
system 232 of the half TTL system for detecting an alignment mark
on the wafer W or the fiducial mark plate FM via the beam splitter
BS and the third lens group G3, and for detecting an alignment mark
on the reticle R via the beam splitter BS and the first and second
lens groups G1, G2.
[0063] In the exposure apparatus 100 constructed as described
above, the ratio between the total value Mr of the masses of both
of the reticle stage body 206 and the reticle fine movement stage
210 and the mass of the wafer stage 14, i.e., the total value Mw of
the masses of both of the first wafer stage body 208 and the second
wafer stage body 220 is designed to be equal to the reduction
magnification Mp1 of the projection optical system PL. In the case
of this embodiment, the magnification Mp1 of the projection optical
system is 1/4 as described above. Accordingly, the mass ratio Mr/Mw
is also set to be 1/4. Specifically, for example, although the
situation greatly depends on the diameter of the wafer W to be
used, it is possible to set the total mass Mw of the wafer stage
body to be about 40 to 100 Kg, and it is possible to set the total
mass Mr of the reticle stage body to be about 10 to 25 Kg.
[0064] FIG. 4 shows an arrangement of a control system for the
exposure apparatus 100 according to the first embodiment. The
control system comprises, for example, an alignment control system
259, a main stage control system 260, a driving circuit 253, a
driving system 254, a main scanning driving system 255, and a
driving circuit 256. Now, the respective constitutive components of
the control system will be explained together with the function
thereof.
[0065] The detection information from the TTL alignment detection
system 230 and the detection information from the half TTL
alignment detection system 232 are inputted into the alignment
control system 259 which is operated to determine the coordinate
position and the positional discrepancy error of the alignment
marks on the wafer W, the reticle R, or the fiducial mark plate
FM.
[0066] The main stage control system 260 is interfaced with an
unillustrated operating microcomputer, which is connected to the
driving system 254, the main scanning driving system 255, the
driving circuit 256, and the driving circuit 253 for driving and
controlling the respective linear motors 214, 216, 240, 242, and
the reticle fine movement stage 210 respectively.
[0067] Among them, the driving circuit 253 servo-controls the
reticle fine movement stage 210 on the basis of the command
information from the main control system 260 and the respective
pieces of positional information PX, PY, P.theta. in the X
direction, the Y direction, and the rotational (yawing) direction
measured by the interferometers RIFx, RIF.theta., RIFy disposed on
the side of the reticle so that the reticle R is finely moved
during alignment and scanning exposure.
[0068] The driving system 254 servo-controls the driving of the
second linear motor 214 on the basis of the command information
from the main control system 260 and the positional information PX
(and the velocity information Vx) measured by the interferometer
RIFx disposed on the side of the reticle.
[0069] The main scanning driving system 255 is principally operated
during scanning exposure. The main scanning driving system 255
servo-controls the first linear motor 216 so that the absolute
velocity of at least one of the reticle stage body 206 and the
first wafer stage body 208 is equal to the velocity command
information supplied from the main control system 260, while
monitoring any one of or both of the velocity information Vx (or
the positional information PX) measured by the interferometer RIFx
disposed on the side of the reticle and the velocity information Vx
(or the positional information PX) measured by the interferometer
WIFx disposed on the side of the wafer.
[0070] The driving circuit 256 servo-controls the driving of the
pair of linear motors 240, 242 on the basis of the command
information from the main control system 260 and the positional
information PX, PY, P.theta. measured by the interferometers WIFx,
WIFy disposed on the side of the wafer.
[0071] Next, explanation will be made for the operation during
scanning exposure of the exposure apparatus 100 according to the
first embodiment constructed as described above. In this
explanation, it is assumed that previous preparation has been
completed, for example, for the reticle alignment performed by the
half TTL alignment detection system 232, the global alignment for
the reticle R and the wafer W performed by the TTL alignment
detection system 230, and the baseline measurement based on the use
of the fiducial plate FM.
[0072] At first, in order that a first end in the X axis direction
of a predetermined shot area on the wafer W is positioned in the
exposure field of the projection optical system PL, the main stage
control system 260 gives a command to the main scanning driving
system 254 and the driving circuit 256 to drive the linear motor
216 and the linear motors 240, 242. Accordingly, the second wafer
stage body 220 is moved in the X direction integrally with the
first wafer stage body 208 oppositely to the reticle stage body
206, and it is driven in the Y direction with respect to the first
wafer stage body 208. Thus, the first end of the shot area in the X
direction is positioned in the exposure field of the projection
optical system PL. Next, the main stage control system 260 drives
the second linear motor 214 by the aid of the driving system 254 to
restore the reticle stage body 206 to the predetermined reset
position. Accordingly, the second end of the reticle in the X axis
direction coincides with the exposure field of the projection
optical system PL. In this procedure, in order to prevent the
reticle stage body 206 from change in position in the X direction,
the following operation may be performed. Namely, the first linear
motor 216 is driven while servo-controlling the second linear motor
214 on the basis of the measured value obtained by the reticle
interferometer 250, so that the first and second wafer stage bodies
208, 220 are integrally and singly moved in the X direction over
the base structure 200. After that, only the second linear motor
214 is servo-controlled on the basis of the measured value obtained
by the reticle interferometer 250, so that the reticle stage body
206 is moved singly in the X direction over the base structure
200.
[0073] Next, the main stage control system 260 gives a command to
the main scanning driving system 255 to drive the linear motor 216
so that exposure for the shot area is started. In the first
embodiment, both of the wafer stage 14 and the reticle stage body
206 are supported in the floating manner over the base structure
200 via the air bearings (air-operated bearings). Accordingly, when
a driving current is supplied to the driving coil section 216B of
the first linear motor 216, the first wafer stage body 208 and the
second wafer stage body 220 are moved, for example, in the +X
direction at a velocity Vw in an integrated manner over the upper
surface of the base structure 200 in accordance with the law of
conservation of momentum, while the reticle stage body 206 is moved
in the -X direction at a velocity Vr over the upper surface of the
base structure 200. In this process, as described above, the ratio
between the total value Mr of the masses of both of the reticle
stage body 206 and the reticle fine movement stage 210 and the
entire mass Mw of the wafer stage 14 is set to be equal to the
reduction magnification 1/4 of the projection optical system PL.
Therefore, according to the law of conservation of momentum, the
velocity ratio between the reticle stage body 206 and the wafer
stage 14 is 4:1, regardless of the state of acceleration, constant
velocity, or deceleration. Namely, the velocity ratio is equal to
the reciprocal number of the reduction magnification Mp1.
Therefore, when only one of the velocities (or positions) or the
wafer stage 14 and the reticle stage body 206 is servo-controlled,
the both can be always reliably subjected to synchronous
scanning.
[0074] In this procedure, the absolute values of the respective
scanning velocities Vw, Vr (velocities with respect to the base
structure 200) determine the amount of exposure light given onto
the wafer W during scanning exposure. Therefore, it is necessary
for the main scanning driving system 255 to servo-control the
driving of the first linear motor 216, while monitoring the
velocity information outputted from any one of the interferometer
RIFx for measuring the position in the X direction of the reticle
stage body 206 and the interferometer WIFx for measuring the
position in the X direction of the first wafer stage body 208, so
that the velocity thereof becomes a designated constant value.
[0075] For example, when the reticle stage body 206 is
servo-controlled, even if the reticle stage body 206 makes
vibrative movement, the wafer stage 14 makes vibrative movement
similar to the reticle stage body 206 while maintaining the same
velocity ratio as the reciprocal number of the mass ratio. Further,
the position of the center of gravity of the system is always
constant, because the momentum is conserved. Accordingly, the base
structure 200 is never fluctuated. Therefore, the synchronization
error between the both is always zero during scanning exposure.
[0076] When the exposure for one shot area on the wafer W is
completed as described above, the main stage control system 260
drives the linear motors 240, 242 by the aid of the driving circuit
256 to position a shot area adjacent to the shot area which has
been exposed on the wafer W, in the exposure field of the
projection optical system PL (the stepping is performed). After the
positioning, the main stage control system 260 drives the linear
motor 216 by the aid of the main scanning driving system 255 to
scan the reticle stage body 206 in the direction opposite to the
previous direction so that exposure for the shot is started. In
this procedure, the wafer stage 14 is scanned in the -X direction
at a velocity which is 1/4 of the velocity of the reticle stage
body 206.
[0077] Thereafter, the shot areas on the wafer are subjected to
exposure in accordance with the step-and-scan system in the same
manner as described above.
[0078] As explained above, according to the first embodiment, the
following effect is obtained. Namely, the reticle structure 206 and
the wafer stage 12 can be always subjected to scanning with no
synchronization error of zero by using the simple structure on the
basis of the law of conservation of momentum only by setting the
mass ratio Mr/Mw between the stage body on the reticle side and the
stage body on the wafer side to be equal to the reduction
magnification Mp1 of the projection optical system PL, without
providing any complicated synchronization control circuit or the
like and without using neither stage especially excellent in
dynamic characteristics nor special vibration-preventive apparatus
such as an active vibration-preventive apparatus. Further, since
the reticle stage body 206 and the wafer stage 14 (wafer stage
bodies 208, 220) are moved in the mutually opposite directions in
accordance of the law of conservation of momentum, the position of
the center of gravity in the X direction concerning the entire body
including the base structure 200 scarcely changes. Accordingly, the
fluctuation of the apparatus is reduced.
[0079] In the first embodiment as described above, the linear motor
216, which extends in the scanning direction (X direction), is
arranged between the reticle stage body 206 and the substrate stage
(wafer stage bodies 208, 220). The wafer stage 14 is supported by
the air bearings so that it is moved linearly in the X direction in
the non-contact manner over the base structure 200. The reticle
stage body 206 is supported by the air bearings so that it is moved
linearly in the X direction in the non-contact manner over the base
structure 200.
[0080] Therefore, the relative positional relationship in the X
direction between the reticle R and the wafer W is controlled in
accordance with the law of conservation of momentum during the
period in which the driving current is supplied to the driving coil
section 216B of the linear motor 216. However, when the electric
power supply to the linear motor 216 is interrupted, the system
loses the restricting force for retaining the relative positional
relationship in the X direction between the reticle stage body 206
and the wafer stage 14.
[0081] For this reason, there is a possibility that the relative
positional relationship in the X direction between the reticle
stage body 206 and the wafer stage 14 may be gradually discrepant
due to, for example, vibration from vibration sources (other motors
or the like) in the exposure apparatus, which would appear when the
electric power supply to the linear motor 216 is interrupted,
vibration from, for example, an air conditioner disposed outside
the exposure apparatus, vibration of the floor on which the
exposure apparatus is installed, and slight inclination of the
entire exposure apparatus.
[0082] In this context, the linear motor 216 may be a linear motor
which is allowed to perform servo-control so that the relative
displacement in the X direction between the reticle stage body 206
and the wafer stage 14 is maintained to be zero, by modifying, for
example, the coil arrangement of the linear motor 216, the winding
structure of the respective coils, and the supply control for the
driving current. In such an arrangement, it is possible to easily
obtain a stationary relative positional relationship in the X
direction between the reticle R and the wafer W only by controlling
the supply current to the linear motor 216. However, even in such a
case, there is a possibility that the reticle stage body 206 and
the wafer stage 14 make discrepancy in the X direction over the
base structure 200 in an integrated manner due to, for example,
various vibrations and inclination of the exposure apparatus.
[0083] In any case, it is a fact for the reticle stage body 206
that the wafer stage 14 is discrepant with respect to the base
structure 200. This fact means that a change occurs in the relative
positional relationship in the X direction to be set upon the start
of scanning exposure between the reticle R and the optical axis (or
the illumination light beam) of the illumination system 212 fixed
to the base structure 200. Such a change may seriously affect the
exposure sequence based on the step-and-scan system.
[0084] The second linear motor 214 functions in order to dissolve
the inconvenience as described above. Namely, in the exposure
apparatus 100 according to the first embodiment, in addition to the
first linear motor 216 for controlling the relative positional
relationship between the reticle stage body 206 and the wafer stage
14 (wafer stage bodies 208, 220) at the velocity ratio in
accordance with the law of conservation of momentum, there is
provided the second linear motor 214 for controlling the absolute
position of the reticle stage body 206 with respect to the base
structure 200. Accordingly, the electric power supply terminal of
the driving coil section 214B of the second linear motor 214 may be
opened to give a no-loaded state when the reticle stage body 206
and the wafer stage 14 (wafer stage bodies 208, 220) are moved in
the opposite directions during scanning exposure in accordance with
the law of conservation of momentum. On the other hand, when the
absolute position of the reticle stage body 206 is controlled, the
second linear motor 214 may be servo-controlled on the basis of the
positional information and the velocity information from the
interferometer RIFx for measuring the position of the reticle stage
body 206 in the X direction with respect to the base structure
200.
[0085] Therefore, the position of the reticle R with respect to the
illumination light beam can be always managed accurately by
controlling the respective linear motors in an associated manner in
accordance with a wafer exposure sequence based on the S&S
system.
[0086] Further, the positional relationship of the reticle R and
the wafer W with respect to the base structure 200 after completion
of the exposure process can be made unchanged from the positional
relationship established when the exposure process is started.
Accordingly, the present invention is also advantageous in that the
discrepancy in the receiving position is avoided, for example,
between the apparatus and an arm of an automatic conveying
mechanism when the reticle is exchanged or when the wafer is
exchanged.
[0087] The first embodiment has been illustrated by using the case
based on the use of the inverting type optical system as the
projection optical system in which the inverted image of the
pattern on the reticle R is projected onto the wafer W. However,
for example, when a vertically symmetrical circuit pattern is
subjected to exposure, it is possible to use, as the projection
optical system, an erecting type optical system in which an
erecting image of a circuit pattern is formed on a photosensitive
substrate.
[0088] Further, the first embodiment has been exemplified by the
case in which the reduction magnification of the projection optical
system is 1/4. However, any of magnifications may be used as the
reduction magnification of the projection optical system. For
example, even when the reduction magnification is one-fold
(1.times. magnification), the present invention has a great merit
because of the following reason. Namely, according to the present
invention, the position of the center of gravity of the system is
not moved due to any movement of the stage, because the momentum is
conserved. Therefore, the body is not fluctuated by the reaction
force caused by the movement of the stage. Accordingly, it is
unnecessary to use any expensive vibration-preventive apparatus or
the like, such as an active vibration-preventive apparatus.
Moreover, even when one of the stages is moved in a vibrative
manner, the other stage is moved in the same vibrative manner in
accordance therewith. Thus, no synchronization error occurs.
Second Embodiment
[0089] Next, a second embodiment according to the present invention
will be explained with reference to FIG. 5. In this embodiment, the
same or equivalent components as those described in the first
embodiment are designated by the same reference numerals,
explanation of which will be simplified or omitted. As shown in
FIG. 5, the second embodiment is characterized in that a
power-generating coil 257 and a load circuit 258 for regenerative
braking for consuming the current supplied from the coil 257, which
are operatively linked to the linear motor 214, are additionally
provided. The other components of the control system and the other
apparatus system and arrangement are the same as those described in
the first embodiment.
[0090] In the second embodiment, the second linear motor 214 is
utilized to provide a regenerative braking circuit for finely
adjusting the velocity ratio between the reticle stage body 206 and
the wafer stage 14 (wafer stage bodies 208, 220) during scanning
exposure, for example, within a range of about .+-.0.1% at a
resolving power of an order of p.p.m. Specifically, the
power-generating coil 257 and the load circuit 258 are provided as
shown in FIG. 5 to finely change the transfer magnification
concerning the scanning direction (assuming that the designed
dimension in the scanning direction on the wafer W is 35 mm,
expansion or contraction is made therefor only by about several
hundreds nm as a whole).
[0091] This arrangement will be described in further detail below.
The power-generating coil 257 is constructed by providing a special
power-generating coil in the second linear motor 214, or by using
the driving coil also for power generation. The load circuit 258
(including an appropriate load resistor) is connected to the
terminal of the power-generating coil during the period in which
the reticle stage and the wafer stage are moved in the opposite
directions by means of the first linear motor 216 so that the
regenerative control is performed. Thus, the dynamic load in the X
direction of the reticle stage body 206 is increased to minutely
change the amount of the velocity ratio between the reticle stage
body 206 and the wafer stage 14.
[0092] In order to control the amount of regenerative braking, the
load circuit 258 may be constructed such that the current from the
power-generating coil 257 is allowed to flow to the load resistor
via a high-speed switching element or the like to vary, in a wide
range, the ON/OFF frequency of the switching element, the duty
ratio of the ON time and the OFF time or the like.
[0093] In this embodiment, in order to precisely make fine
adjustment for the velocity ratio Vw/Vr with respect to the
reduction magnification Mp1, the power-generating coil 257 (see
FIG. 5), which is integrated with the driving coil section 214B of
the second linear motor 214, and the load circuit 258 are utilized
to make control so that a dynamic load is applied to the movement
direction of the reticle stage body 206. The load circuit 258 acts
as a variable load resistor for the power-generating circuit 257,
and it has a function to substantially continuously change the
current obtained from the power-generating coil 257 in accordance
with a control command supplied from the main scanning driving
circuit 255.
[0094] During the scanning exposure, the reticle stage body 206 may
be primarily moved at the velocity Vr. However, when the
appropriate load resistor is connected to the terminal of the
power-generating coil 257, then the momentum, which corresponds to
the energy consumed by the load resistor, is added to the reticle
stage body 206. The addition corresponds to the increase in
apparent mass Mr of the reticle stage body 206 by a minute amount.
Accordingly, the velocity ratio Vw/Vr between the wafer stage 14
and the reticle stage body 206 is finely adjusted.
[0095] In such a situation, the action is made only in the
direction to increase the apparent mass of the reticle stage body
206. Accordingly, the mass ratio Mr/Mw is increased, and the
velocity ratio Vw/Vr is adjusted in a direction to achieve
Mp1<(Vw/Vr). Therefore, the velocity ratio may be matched with
the reduction magnification by previously setting the masses of the
respective stage bodies so that the mass ratio Mr/mw in the
stationary state is slightly smaller than the reduction
magnification Mp1, and always adjusting the regenerative braking
amount appropriately during scanning exposure.
[0096] On the other hand, when the wafer stage 14 and the reticle
stage body 206 are subjected to scanning movement in the mutually
opposite directions in accordance with the law of conservation of
momentum, if the electric power is supplied to the driving coil
section 214B of the second linear motor 214 to be simultaneously
used for the driving of the reticle stage body 206, then the
apparent dynamic mass of the reticle stage body 206 can be slightly
decreased. Accordingly, it is also possible to adjust the velocity
ratio Vw/Vr in a direction to achieve Mp1>(Vw/Vr).
[0097] According to the second embodiment of the present invention
as described above, the scanning velocity ratio between the reticle
R and the wafer W during scanning exposure can be finely adjusted
extremely easily by controlling the regenerative braking amount
(the current value from the power-generating coil). Accordingly,
when the velocity ratio between the reticle R and the wafer W is
detected from the results of measurement performed by the
interferometers to apply feedback control for the regenerative
braking amount so that the detected value is a previously set
value, then the transfer magnification concerning the scanning
direction can be evenly subjected to fine adjustment. Moreover, it
is also possible to adjust the transfer strain (distortion) by
delicately changing the velocity ratio at the scanning start
portion and the velocity ratio at the scanning end portion of a
shot area on the wafer W, and the velocity ratio at the central
portion of the shot area.
[0098] In the first and second embodiments described above, the
linear motor 214 is provided in order to move the reticle stage
body 206 singly in the scanning direction over the base structure
200. However, in place of the linear motor 214 or together with the
linear motor 214, a third linear motor for generating the thrust
force in the X direction may be provided between the base structure
200 and the first wafer stage body 208 in order to reliably rest
the first and second wafer stage bodies 208, 220 at certain
positions in the X direction, and singly move the first and second
wafer stage bodies 208, 220 over the base structure 200. In this
arrangement, the third linear motor may be servo-controlled on the
basis of a measured value obtained by the wafer interferometer 252
(WIFx).
[0099] Next, concerning the case in which the unillustrated third
linear motor is added to the apparatus according to the second
embodiment, explanation will be made for a series of sequences to
perform scanning exposure by making alignment for the pattern area
on the reticle R and the shot area on the wafer W.
[0100] (1) The reticle stage body is moved to the loading position,
and the reticle R is installed on the stage. At this time, the
wafer stage 14 may be moved in the opposite direction in accordance
with the law of conservation of momentum associated with the
movement of the reticle stage body. Alternatively, the wafer stage
14 may be forcedly rest at a predetermined position by
servo-controlling the third linear motor.
[0101] (2) The respective stage bodies 206, 208, 220 are moved so
that the reticle stage body 206 and the wafer stage body 220 are
set at predetermined positions in relation to the image field of
the projection optical system. The reference mark fixed on the
wafer stage body 220 and the alignment mark formed on the reticle R
are mutually photoelectrically detected by using the alignment
detection system 232 via the projection optical system PL. The fine
movement stage 210 on the reticle stage body 206 is controlled so
that the reticle R is consistently adjusted in the respective
directions of X, Y, .theta. with respect to the movement coordinate
system of the wafer stage body 220. At the point of time at which
the reticle R is adjusted consistently with the movement coordinate
system of the wafer stage body 220, the X, Y measured value
obtained from the reticle interferometer 250 and the X, Y measured
value obtained from the wafer interferometer 252 are stored as the
achievement position for primary consistent adjustment. Thereafter,
the system is managed so that the positional relationship is
immediately reproduced.
[0102] (3) In order to place the wafer W on the wafer stage body
220, the wafer stage body 220 is moved to a predetermined loading
position. After that, the wafer stage body 220 is moved so that the
respective alignment marks, which are formed in association with
several shot areas on the wafer W, are arranged one by one in the
field of the projection optical system PL. The respective alignment
marks are successively detected by using the alignment detection
system 230 by the aid of the projection optical system PL. The
relative positional relationship (in the X, Y, .theta. directions)
between the arrangement coordinate system of the shot area on the
wafer W and the pattern area on the reticle R is determined on the
basis of results of the foregoing detection.
[0103] (4) If the determined positional relationship involves
positional discrepancy in the X direction, the first linear motor
216 is driven to move the reticle stage body 206 in the X direction
with respect to the wafer stage 14 in a state in which the third
linear motor is driven to make servo-lock so that the wafer stage
14 is not displaced with respect to the base structure. The
relative positional error in the Y direction between the shot array
coordinate system on the wafer W and the pattern area on the
reticle R is corrected by the wafer stage body 220 or by the fine
movement stage 210 disposed on the reticle stage body 206. The
relative positional error in the .theta. direction is corrected by
minute rotation of the wafer stage body 220 effected by the linear
motors 240, 242. It is noted that a .theta. stage may be
additionally provided on the wafer stage body 220.
[0104] (5) At the point of time at which the pattern area on the
reticle R and the shot array coordinate system on the wafer W are
subjected to precise consistent adjustment in relation to the X, Y,
.theta. directions, the relative positional relationship in the X,
Y directions between the reticle stage body 206 and the wafer stage
body 220 is read by using the interferometers, and it is stored as
a secondary consistent arrangement achievement position. The
secondary consistent arrangement achievement position is utilized
as a management reference for the movement positions of the
respective stage bodies during the period of exposure process for
the wafer W.
[0105] (6) Next, the reticle stage body 206 is positioned in the X
direction so that the pattern area on the reticle R is located at
the position to start irradiation with the illumination light beam.
The wafer stage 14 is positioned in the X direction so that one
shot area on the wafer W is located at the position to start
exposure.
[0106] (7) The first linear motor 216 is driven to move the reticle
stage body 206 and the wafer stage 14 in the opposite directions at
the predetermined velocity ratio corresponding to the image
formation magnification Mp1 of the projection optical system PL in
accordance with the law of conservation of momentum. During this
process, if it is necessary to make suppression to be within an
allowable range concerning variation in the velocity ratio between
the both stages, the fine adjustment for the transfer magnification
in relation to the scanning direction may be performed such that
the second linear motor 214 and the third linear motor are actively
controlled on the basis of a precise result of measurement for the
change in velocity ratio (or the change in relative positional
relationship) to continuously and finely adjust the apparent
dynamic mass of the reticle stage body 206 or the wafer stage
14.
Modified Embodiment
[0107] Next, a modified embodiment will be explained with reference
to FIGS. 6A and 6B.
[0108] An exposure apparatus according to this modified embodiment
is characterized in that not only the wafer W as a photosensitive
substrate is held horizontally, but also the reticle R as a mask is
held horizontally on the reticle stage 16.
[0109] The exposure apparatus comprises a reticle stage 16 and a
substrate stage 14 supported in a floating manner over a pedestal
12 via an air bearing (air-operated bearing) 13, a projection
optical system PL composed of a reflecting optical system for
reduction-projecting a circuit pattern, and a light source 20.
[0110] In the exposure apparatus according to this modified
embodiment, the substrate stage 14 has a first stage 14A which is
supported in a floating manner over the pedestal 12 and which is
movable in the X axis direction, and a second stage 14B which is
driven on the first stage 14A in the Y axis direction by the aid of
a linear motor. The wafer W is held on the second stage 14B.
[0111] As shown in FIG. 6B, the reticle stage 16 is arranged such
that it rides on a first stage 14A. Linear motors 18, 18, each of
which is composed of a coil 18A and a magnet 18B, are interposed
between the both stages 16, 14A.
[0112] When the reticle R is illuminated with an exposure light
beam radiated from the underlying light source 20 via an
unillustrated illumination optical system, an image of a circuit
pattern located in a slender illumination area (corresponding to an
exposure field of the projection optical system) is
reduction-projected onto the wafer W via the projection optical
system PL.
[0113] Therefore, the same effect as described above is also
obtained in the case of the modified embodiment such that the
circuit pattern is subjected to scanning exposure while maintaining
the synchronization error between the both stages 16, 14 to be
always zero in the same manner as the foregoing respective
embodiments, provided that the ratio of the masses of the reticle
stage 16 and the substrate stage 14 is set to be identical with the
reduction magnification Mp1 of the projection optical system
PL.
[0114] The first and second embodiments described above have been
exemplified by the case in which the photosensitive substrate is
held horizontally on the substrate stage, i.e., the lateral type
substrate stage is used. However, the present invention is
applicable to an exposure apparatus which uses a substrate stage in
which the photosensitive substrate is held vertically on the
substrate stage, i.e., a vertical type substrate stage is used.
[0115] The first and second embodiments described above have been
exemplified by the case in which the linear motor is used as the
driving means for driving the second stage in the non-scanning
direction. However, the present invention is not limited thereto.
The exposure apparatus may be constructed such that the second
stage is driven in the non-scanning direction by using a feed screw
mechanism.
[0116] As described above, the projection optical system PL used in
the first embodiment is disclosed and described in detail in
Japanese Laid-Open Patent Publication Nos. 5-88087 and 6-300973 and
in U.S. patents corresponding thereto, the disclosure of which are
incorporated herein by reference. Exposure apparatuses and exposure
methods based on the step-and-scan system, to which the present
invention is applicable, are disclosed in Japanese Laid-Open Patent
Publication Nos. 56-111218, 2-229423, and 4-277612 and in U.S.
patents corresponding thereto, the disclosures of which are
incorporated herein by reference.
[0117] As described above, according to the present invention, the
following excellent effects, which have not been obtained by the
conventional techniques, are obtained by using the simple
structure. Namely, the stress generated in the structural
components of the apparatus is reduced, the inclination and the
fluctuation of the entire apparatus are suppressed, and the
synchronization performance can be improved for the mask stage and
the substrate stage.
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