U.S. patent application number 09/287262 was filed with the patent office on 2002-01-10 for positioning stage system and position measuring method.
Invention is credited to MATSUI, SHIN.
Application Number | 20020003629 09/287262 |
Document ID | / |
Family ID | 14595793 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003629 |
Kind Code |
A1 |
MATSUI, SHIN |
January 10, 2002 |
POSITIONING STAGE SYSTEM AND POSITION MEASURING METHOD
Abstract
A positioning stage system includes a first stage movable at
least in one of a rotational direction and a tilt direction, a
second stage movable at least in X and Y directions, a measurement
mirror system fixed to the second stage, a reference mirror system
disposed on the first stage, and a measuring system for measuring
displacement of the measurement mirror system in the X or Y
direction, while using the reference mirror system as a positional
reference, wherein the reference mirror system is arranged so that
laser light incident on the reference mirror system is reflected in
the same direction as the incidence, substantially constantly.
Inventors: |
MATSUI, SHIN; (URAWA-SHI,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
14595793 |
Appl. No.: |
09/287262 |
Filed: |
April 7, 1999 |
Current U.S.
Class: |
356/614 ;
356/498; 356/509 |
Current CPC
Class: |
G03G 17/08 20130101;
G03F 7/70691 20130101; G03G 17/04 20130101; G03G 17/06 20130101;
G03G 17/10 20130101; G03G 17/02 20130101 |
Class at
Publication: |
356/614 ;
356/509; 356/498 |
International
Class: |
G03G 017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 1998 |
JP |
10-112798 |
Claims
What is claimed is:
1. A stage system, comprising: a first stage movable at least in
one of a rotational direction and a tilt direction; a second stage
movable at least in X and Y directions; a measurement mirror system
fixed to said second stage; a reference mirror system disposed on
said first stage; and a measuring system for measuring displacement
of said measurement mirror system in the X or Y direction, while
using said reference mirror system as a positional reference;
wherein said reference mirror system is arranged so that laser
light incident on said reference mirror system is reflected in the
same direction as the incidence, substantially constantly.
2. A stage system according to claim 1, wherein said reference
mirror system includes retroreflectors.
3. A stage system according to claim 2, wherein said
retroreflectors comprise a corner cube or a cat's-eye optical
system.
4. A stage system according to claim 1, wherein said reference
mirror system includes mirrors and correcting means for changing
postures of the mirrors with respect to said first stage.
5. A stage system according to claim 4, wherein said correcting
means controls the posture of said mirrors so that the posture of
said mirrors with respect to laser light, impinging thereto, is
maintained substantially constant.
6. A stage system according to claim 5, wherein said mirrors are
mounted on said first stage through said correcting means.
7. A stage system according to claim 5, wherein said correcting
means includes driving means for controlling postures of said
mirrors, respectively.
8. A stage system according to claim 1, wherein said measuring
system detects displacement information related to said measurement
mirror system, with respect to each of the X and Y directions, on
the basis of interference between laser light coming via said
reference mirror system and laser light coming via said measurement
mirror system.
9. A stage system according to claim 1, wherein said measuring
system includes a laser interferometer to be associated with said
reference mirror system and a laser interferometer to be associated
with said measurement mirror system.
10. A stage system according to claim 1, wherein said first stage
comprises a mask stage for holding a mask and being movable at
least in one of a rotational direction along the mask surface and a
tilt direction to the mask surface, and wherein said second stage
comprises a substrate stage for holding a substrate and being
movable in X and Y directions along an X-Y plane parallel so the
substrate surface.
11. A stage system according to claim 10, wherein said reference
mirror system is mounted on one of the mask and said mask
stage.
12. A position measuring method, comprising the steps of: mounting
a reference mirror system on a first stage which is movable at
least in one of a rotational direction and a tilt direction,
wherein the reference mirror system is arranged so that laser light
incident on the reference mirror system is reflected in the same
direction as the incidence substantially constantly; fixedly
mounting a measurement mirror system on a second stage which is
movable at least in X and Y directions; measuring displacement of
the measuring mirror system in X and Y directions while using the
reference mirror system as a positional reference, on the basis of
laser interference.
13. A method according to claim 12, wherein, with respect to each
of the X and Y directions, the laser light impinging on the
reference mirror system is reflected in the same direction as the
incidence substantially constantly, on the basis of use of
retroreflectors in the reference mirror system or of relatively
changing posture of mirrors with respect to the first stage.
14. An exposure apparatus, comprising: a mask stage for holding a
mask and being movable at least in one of a rotational direction
along the mask surface and a tilt direction to the mask surface; a
substrate stage for holding a substrate, to be exposed, and being
movable in X and Y directions along an X-Y plane parallel to the
substrate surface; a measurement mirror system fixed to said
substrate stage; a reference mirror system disposed on said mask
stage; and a measuring system for measuring displacement of said
measurement mirror system in the X or Y direction, while using said
reference mirror system as a positional reference, and on the basis
of laser interference; wherein the substrate on said substrate
stage can be aligned with respect to the mask on the basis of the
measurement by said measuring system, and a pattern of the aligned
mask can be transferred and printed onto the substrate; and wherein
said reference mirror system is arranged so that laser light
incident on said reference mirror system is reflected in the same
direction as the incidence, substantially constantly.
15. An apparatus according to claim 14, wherein the pattern
transfer is made by use of X-rays.
16. An apparatus according to claim 14, wherein information related
to a positional error, in X and Y directions, of said reference
mirror system due to rotation or a change in tilt of the mask stage
is detected beforehand in relation to a drive amount of said mask
stage, and wherein said measuring system has a function for
correcting a measured value in accordance with the drive amount of
said mask stage.
17. An apparatus according to claim 14, wherein said mask stage
performs mask drive for mask positioning, and wherein said
measuring system measures displacement of said measurement mirror
after completion of the mask drive.
18. A device manufacturing method, comprising the steps of:
transferring, by exposure, a pattern of a mask onto a substrate by
use of an exposure apparatus including (i) a mask stage for holding
the mask and being movable at least in one of a rotational
direction along the mask surface and a tilt direction to the mask
surface, (ii) a substrate stage for holding the substrate, to be
exposed, and being movable in X and Y directions along an X-Y plane
parallel to the substrate surface, (iii) a measurement mirror
system fixed to the substrate stage, (iv) a reference mirror system
disposed on the mask stage, and (v) a measuring system for
measuring displacement of the measurement mirror system in the X or
Y direction, while using the reference mirror system as a
positional reference, and on the basis of laser interference,
wherein the substrate on the substrate stage can be aligned with
respect to the mask on the basis of the measurement by the
measuring system, and a pattern of the aligned mask can be
transferred and printed onto the substrate, and wherein the
reference mirror system is arranged so that laser light incident on
the reference mirror system is reflected in the same direction as
the incidence, substantially constantly; and developing the exposed
substrate, whereby a device can be produced from the substrate.
Description
FIELD OF THE INVENTION AND RELATED ART
[0001] This invention relates to a positioning stage system and a
position measuring method usable in an exposure apparatus, for
example, for manufacture of semiconductor devices, for example. In
another aspect, the invention is concerned with an exposure
apparatus having such a positioning stage system.
[0002] With further miniaturization and increasing density of a
semiconductor chip due to enlargement of integration of
semiconductor device, a very narrower linewidth has bee desired.
For a semiconductor device of 1 GDRAM, for example, it should have
a linewidth of 0.18 micron. As regards registration of printed
patterns, it should be 80 nm for a semiconductor device of 256
MDRAM and 60 nm for a semiconductor device of 1 GDRAM.
[0003] Exposure apparatuses for lithographically transferring a
pattern formed on a mask to a substrate such as a wafer, are also
required to provide high precision and good linewidth precision.
While i-line or KrF laser are used as exposure light, to prevent
degradation of resolution due to diffraction, a proximity exposure
apparatus based on step-and-repeat process and using X-rays of
shorter wavelength has been proposed.
[0004] A proximity exposure apparatus performs an exposure process
while keeping a wafer, held on a wafer stage, close at a small gap
of about 10-50 microns to a mask. The wafer stage is moved in X and
Y directions to move stepwise exposure shots on the wafer to an
exposure region, opposed to the mask, sequentially. Alignment
measurement for the mask and wafer is performed by using an
alignment optical system, and then an X-ray beam (exposure light)
is projected to the mask whereby the pattern formed on the mask is
transferred to the wafer.
[0005] In such exposure apparatus, it is important to position a
mask and a wafer precisely. A high precision positioning stage
system is therefore necessary. As a measuring system for a wafer
positioning stage, a laser interferometer capable of measuring
movement amount of a movable member at high precision may be
used.
[0006] Such laser interferometer generally includes a laser
oscillator (laser head) for emitting laser light, a measuring
mirror mounted on a positioning stage to be measured, a reference
mirror which provides a measurement reference, an optical system
having a polarization beam splitter, for example, for distributing
the laser light from the laser oscillator to the measuring mirror
and the reference mirror, and a photodetector. The laser light
emitted from the laser oscillator is separated by the polarization
beam splitter, so that a portion of the laser light passes through
the polarization beam splitter and it is projected on the measuring
mirror mounted on the positioning stage which is the target to be
measured. The remaining portion of the laser light is reflected by
the polarization beam splitter toward the reference mirror. Light
reflected by this reference mirror goes through the polarization
beam splitter, while light reflected by the measuring mirror is
reflected by the polarization beam splitter, whereby both are
directed to and detected by the same photodetector. These laser
lights to be detected by the photodetector interfere with each
other to produce interference fringe. The photodetector is used to
count the fringes, on the basis of which the distance between the
reference mirror and the measuring mirror is detected. In
accordance with the result, the position or movement amount of the
positioning stage (target of measurement) having the measuring
mirror mounted thereon can be determined.
[0007] Here, the reference mirror provides a measurement reference,
and preferably it should be fixed to a base member which is
integrally connected with measuring optical components. Also, it
should be disposed close, as much as possible, to a member (e.g.,
mask) on which a reference should inherently be defined. This
reduces the effect of thermal expansion between them. For example,
in a projection exposure apparatus using g-line or i-line as
exposure light, a reference mirror for a wafer X-Y stage for moving
the wafer stepwise to the exposure station may be fixed to a base
member of a lens barrel (Japanese Laid-Open Patent Application,
Laid-Open No. 163354/1994).
[0008] In an X-ray exposure apparatus of proximity type wherein
unit-magnification exposure is performed while holding a mask and a
wafer close to each other, a measurement reference for a wafer X-Y
stage may preferably be provided by a mask itself or a mask
supporting member close to the mask.
[0009] In X-ray exposure apparatuses of proximity type, generally,
a mask which should provide a reference is mounted for small
movement in a rotational direction or tilt direction relative to an
X-Y measurement beam. For example, a mask supporting member for
holding the mask is structured to have freedom in a rotational
direction along the mask surface so that it can absorb a mask
manufacturing error or conveyance error. Alternatively, it is
structured to have freedom in a tilt direction along the mask
surface to that it can absorb a wedge component of the mask. In
such structure, if the reference mirror is provided on the mask or
mask supporting member, the mask or mask supporting member which
defines the measurement reference is displaceable in the rotational
direction or tilt direction relative to the X-Y measurement beam,
such that accurate measurement is not assured. Further, movement of
the mask produces other components in X and Y directions which,
although they are small because they are based on a cosine error,
may lead to a result that the projected measuring beam do not come
back to the photodetector. In that occasion, the wafer stage
positioning is not attainable. The reference mirror may be mounted
on any immovable member disposed outside the mask holding member in
an attempt to avoiding the above problem. However, then the
distance to the mask become long, and there arises a problem of a
non-negligible error due to thermal expansion.
SUMMARY OF THE INVENTION
[0010] It is accordingly an object of the present invention to
provide a positioning stage system and a position measuring method,
by which high-precision measurement and high-precision positioning
are attainable constantly regardless of displacement of a
measurement reference for a laser interferometer.
[0011] It is another object of the present invention to provide an
exposure apparatus having such stage positioning system, or a
device manufacturing method using such exposure apparatus.
[0012] These and other objects, features and advantages of the
present invention will become more apparent upon a consideration of
the following description of the preferred embodiments of the
present invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic and perspective view of an embodiment
wherein a stage positioning system according to the present
invention is incorporated into an X-ray exposure apparatus.
[0014] FIG. 2 is a schematic and perspective view of another
embodiment wherein a stage positioning system according to the
present invention is incorporated into an X-ray exposure
apparatus.
[0015] FIG. 3, (a) is a schematic and enlarged view of a main
portion of mirror posture correcting means in a stage positioning
system according to the present invention.
[0016] FIGS. 3, (b) and (c) are a schematic and front view and a
schematic and side view, respectively, of other examples of mirror
posture correcting means.
[0017] FIG. 4 is a schematic and enlarged view of a main portion of
.theta. driving means for maintaining the posture of a reference
mirror in a positioning stage system according to the present
invention.
[0018] FIG. 5 is a schematic and perspective view of another
embodiment wherein a stage positioning system according to the
present invention is incorporated into an X-ray exposure
apparatus.
[0019] FIG. 6 is a schematic and perspective view of a further
embodiment wherein a stage positioning system according to the
present invention is incorporated into an X-ray exposure
apparatus.
[0020] FIG. 7 is a flow chart of semiconductor device manufacturing
processes.
[0021] FIG. 8 is a flow chart of a wafer process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Preferred embodiments of the present invention will now be
described with reference to the accompanying drawings.
[0023] FIG. 1 is a schematic and perspective view of an embodiment
of a stage positioning system which is incorporated into an X-ray
exposure apparatus.
[0024] In FIG. 1, along a path of X-ray beam L (exposure light)
which is emitted from a light source (not shown), a mask .theta.
stage 2 for holding a mask 1 and a wafer X-Y stage 4 for holding a
wafer 3 (substrate) are disposed close to each other. The mask
.theta. stage 2 for holding the mask 1 is supported, movably in a
rotational (.theta.) direction, by a base plate 2a through leaf
spring guides 6, 6, . . . , disposed at four corners. It can be
rotationally driven in .theta. direction by .theta. driving means 7
and through an operating member 8 fixed to the mask .theta. stage
2. The angle .theta. thereof in the rotational direction can be
detected by an angle sensor 9.
[0025] The wafer X-Y stage 4 has a wafer chuck 5 for holding the
wafer 3, and it is made movable in X and Y directions along the
wafer surface. It can be moved in X and Y directions, by driving
means (not shown). At an end portion of the wafer X-Y stage 4 with
respect to the X direction, there is an X-measurement mirror 10
mounted. At an end portion with respect to the Y direction, there
is a Y-measurement mirror 11 mounted. Also, at the mask .theta.
stage side, there are an X-reference corner cube 12 and a
Y-reference corner cube 13 which function as reference mirrors with
respect to X and Y directions, respectively. These corner cubes are
disposed close to the mask 1 on the mask .theta. stage 2, or they
are mounted on the mask 1.
[0026] For precise measurement of the wafer 3 position with respect
to the mask 1, there are an X-axis laser interferometer 20x and a
Y-axis laser interferometer 20y for measuring the position or
movement amount of the wafer X-Y stage in X and Y directions. The
X-axis laser interferometer 20x serves to measure the position of
the wafer X-Y stage 4 with respect to the X direction. It comprises
a laser oscillator (laser head) 21x for emitting measurement laser
light mx, an X measuring mirror 10 mounted on the wafer X-Y stage 4
(target to be measured), an X-reference corner cube 12 for
providing a measurement reference and being mounted on the mask
.theta. stage 2, a polarization beam splitter 22x disposed between
the laser oscillator 20x and the X measuring mirror 10, a
right-angle mirror 23x for directing a portion of the laser light
mx, being divided by the polarization beam splitter 22x, toward the
X-reference corner cube 12, and a photodetector 24x. Thus, the
laser light mx emitted by the laser oscillator 21x is divided by
the polarization beam splitter 22x. A portion of the laser light mx
is transmitted through the polarization beam splitter 22x, and it
is projected on the X measurement mirror 10 on the wafer X-Y stage
4. The remaining portion of the laser light mx is reflected by the
polarization beam splitter 22x, and via the right-angle mirror 23x
it is projected onto the X-reference corner cube 12 which provides
a reference mirror. Light reflected by the X-reference corner cube
12 goes through the polarization beam splitter 22x, while light
reflected by the X measurement mirror 10 is reflected by the
polarization beam splitter 22x, and both lights are projected on
the photodetector 24x. These laser lights projected on the
photodetector 24x interfere with each other, to produce
interference fringe. By counting the fringes with the photodetector
24x, the position and movement amount of the wafer X-Y stage 4
(target to be measured), having the X measurement mirror 10 mounted
thereon, with respect to the X direction can be measured.
[0027] The Y-axis laser interferometer 20y serves to measure the
position and movement amount of the wafer X-Y stage 4 with respect
to the Y direction. Similarly, it comprises a laser oscillator
(laser head) 21y for emitting measurement laser light my, a Y
measuring mirror 11 mounted on the wafer X-Y stage 4 (target to be
measured), a Y-reference corner cube 13 for providing a measurement
reference and being mounted on the mask .theta. stage 2, a
polarization beam splitter 22y disposed between the laser
oscillator 20y and the Y measuring mirror 11, a right-angle mirror
23y for directing a portion of the laser light my, being divided by
the polarization beam splitter 22y, toward the Y-reference corner
cube 13, and a photodetector 24y. Also, there is a right-angle
mirror 25y for deflecting the laser light my, emitted from the
laser oscillator 21y, to the polarization beam splitter 22y. Thus,
the position and movement amount of the wafer X-Y stage 4 (target
to be measured), having the Y measurement mirror 11 mounted
thereon, with respect to the Y direction can be measured through
the Y-axis laser interferometer, similarly.
[0028] As described above, the corner cubes 12 and 13 which are
reference mirrors for providing measurement references for the
laser interferometer means 20 (20x and 20y), measuring the position
or movement amount of the wafer X-Y stage 4 with respect to X or Y
direction, are disposed adjacent to the mask 1 on the rotatable
mask .theta. stage or provided on the mask 1 itself. As a result,
when the mask .theta. stage 2 is rotationally driven through the
.theta. driving means 7 so as to absorb a manufacturing error or
conveyance error of the mask 1, even though the corner cubes 12 and
13 (reference mirrors) are rotated together therewith, it is
assured that the corner cubes 12 and 13 reflect the incident laser
light in the same direction. This assuredly prevents failure of
impingement of reflected measurement laser light on the
photodetector means 24 (24x and 24y) and thus failure of
measurement. Therefore, even if the mask .theta. stage 2 is rotated
in the rotational direction along the mask surface, the position or
movement amount of the wafer X-Y stage 4 with respect to the X or Y
direction can be measured precisely, on the basis of the
measurement reference provided by the corner cubes 12 and 13
(reference mirrors) which are disposed adjacent the mask 1 or on
the mask 1 itself.
[0029] While this embodiment uses a corner cube for the reference
mirror, in place of it, a cat's-eye having a reference mirror
disposed at the lens focal point position may be used with similar
advantageous effects. Further, this embodiment uses an optical
system for distributing laser light, emitted from a laser
oscillator, to reference mirrors, so that reflected lights from
these mirrors are detected by one and the same photodetector.
However, a laser interferometer having a reference mirror
accommodated therein may be used. More specifically, with regard to
the two reference mirrors, there may be two such laser
interferometers independent, to measure the position or movement
amount of the wafer X-Y stage.
[0030] Referring now to FIGS. 2 and 3, another embodiment of
positioning stage system according to the present invention will be
described.
[0031] FIG. 2 is a perspective view schematically showing a stage
positioning system according to another embodiment of the present
invention. This embodiment differs from the embodiment of FIG. 1 in
that a reference mirror to be provided on a mask .theta. stage is
mounted through mirror posture correcting means. In this
embodiment, the elements corresponding to those of the FIG. 1
embodiment are denoted by like numerals. Detailed description
therefor will be omitted.
[0032] In FIG. 2, an X-reference mirror 30x and a Y-reference
mirror 30y are mounted on a mask .theta. stage 2 through X-mirror
posture correcting means 31x and Y-mirror posture correcting means
31y, respectively. The positions of the X-mirror posture correcting
means 31x and Y-mirror posture correcting means 31y mounted on the
mask .theta. stage 2 are different, but they are structured with
similar components. Like numerals are assigned to corresponding
elements, with suffixes x and y.
[0033] Details of the Y-mirror posture correcting means 31y will
now be explained, also in conjunction with FIG. 3A. The Y-mirror
posture correcting means 31y comprises a Y-mirror fixing table 32y
for fixing the Y-reference mirror 30y, a hinge 33y mounted at a
middle portion of one side face, in Y direction, of the mask
.theta. stage 2 and being rotatably connected to the mask .theta.
stage 2, and a pair of urging force producing means 34y and 34y,
each having an urging force producing member 35y such as a
compressed spring, for example, and a rod 36y. The paired urging
force producing means 34y and 34y are disposed at symmetrical
positions on the opposite sides of the hinge 33y. The paired urging
force producing members 35y and 35y each has an end fixed to a base
plate 2a and another end urging the rod 36y against the surface of
the mirror fixing table 32y to press it. The hinge 33y has no or
very small rotation rigidity, but a large rigidity in its axial
direction, such that it functions to rotate freely relative to the
mask .theta. stage 2 and to confine its motion in axial direction.
Thus, the pair of urging force producing means 34y and 34y function
to press the surface of the mirror fixing table 32y at the
symmetrical positions on the opposite sides of the hinge 33y, to
thereby keep the posture of the mirror fixing table 32y constant.
With use of such mirror posture correcting means 31y having paired
urging force producing means 34y and 34y, it is assured that, even
if the mask .theta. stage 2 is rotated in .theta. direction as
depicted by a broken line in FIG. 3A, the mirror fixing table 32y
keeps its original posture without being moved through the hinge
33y, since the opposite side faces thereof are pressed by the
urging force producing means 34y and 34y. As a result, the
Y-reference mirror 39y fixed to the mirror fixing table 32y can be
kept in constant posture with respect to the measurement laser
light. In place of compressed coil spring, the urging force
producing means 34y may use an air cylinder, a linear motor, a
magnetic force producing member, or an elastmeric member such as a
rubber, for example. The hinge 33y may be modified such as shown in
FIG. 3B or 3C. More specifically, a rotation bearing may be used at
the hinge, that is, a rotation bearing 33o may be disposed between
the mirror fixing table 32 and the mask .theta. stage 2 so that
they can be freely moved relative to each other while any motion
along its axial direction is confined.
[0034] With the structure, as described, that the reference mirror
means 30 (30x and 30y) is mounted on the mask .theta. stage 2 with
intervention of mirror posture correcting means 31 (31x and 31y),
the reference mirror 30 (30x and 30y) fixed to the mirror fixing
table 32 (32x and 32y) can be kept in constant posture with respect
to the measurement laser light even if the mask .theta. stage 2 is
rotationally moved in rotational direction along the mask surface.
Thus, the measurement laser light from the laser interferometer 20
(20x and 20y) can be reflected constantly in a predetermined
direction. This avoids the possibility of failure of detection of
the measurement laser light by the photodetector 24 (24x and 24y)
and failure of measurement. It is assured therefore that,
regardless of rotation of the mask .theta. stage 2 in the
rotational direction along the mask surface, the position or
movement amount of the wafer X-Y stage 4 can be measured precisely
on the basis of the measurement reference defined by the reference
mirror 30, disposed adjacent to the mask 1.
[0035] Another example of reference mirror posture maintaining
means will be explained, in conjunction with FIG. 4. A mirror
fixing table 32 for fixedly holding a reference mirror 30 is
mounted at a central portion on one side face of the mask .theta.
stage 2, through a hinge 33. Like the described example, the hinge
33 has no or very small rotational rigidity, but a large rigidity
in its axial direction, such that it can rotate freely relative to
the mask .theta. stage 2 while restricting motion thereof in its
axial direction. There are a pair of mirror posture maintaining
.theta. driving means 38 and 38 disposed between the mask .theta.
stage 2 and the mirror fixing table 32, for fixedly holding the
reference mirror 30. These .theta. driving means are placed at
symmetrical positions on the opposite sides of the hinge 33. They
are actuated in accordance with the result of measurement by an
angle sensor 39 which measures the rotational angle of the mask
.theta. stage 2, so that they are expanded or contracted to
maintain the posture of the mirror fixing table 32 and the
reference mirror 31 constant. The mirror posture maintaining
.theta. driving means may comprise a piezoelectric device, a
straight-motion cylinder, an air cylinder or a magnetic driving
means, for example.
[0036] With the structure described above, when the mask .theta.
stage 2 is rotationally adjusted for mask alignment, for example,
the angle sensor 39 measures the rotational angle of the mask
.theta. stage 2 and, in accordance with the result of measurement
by the angle sensor 39, the mirror posture maintaining .theta.
driving means 38 and 38 are independently actuated to be expanded
or contracted, by which the posture of the mirror fixing table 32
and the reference mirror 30 can be maintained constant. For
example, in FIG. 4, the left-hand side mirror posture maintaining
.theta. driving means 38 may be actuated to be expanded to enlarge
the spacing between the mirror fixing table 32 and the mask .theta.
stage 2, while the right-hand side mirror posture maintaining
.theta. driving means 38 may be actuated to be contracted to
decrease the spacing between the mirror fixing table 32 and the
mask .theta. stage 2. By using the paired mirror posture
maintaining .theta. driving means in this manner, the reference
mirror 30 and the mirror fixing table 32 can be held in constant
posture regardless of rotation of the mask .theta. stage 2, and, as
a result, they can be kept in the same posture with respect to the
measurement laser light m.
[0037] Referring back to FIG. 2, measurement of the position
(movement amount) of the wafer X-Y stage 4 with respect to X and Y
directions by means of the X-axis laser interferometer 20x and
Y-axis laser interferometer 20y will be explained. Laser light my
emitted from the laser oscillator 21y of the Y-axis laser
interferometer 20y is deflected by the right-angle mirror 25y
toward the polarization beam splitter 22y, and it is divided by
this beam splitter. A portion of the laser light my is transmitted
through the polarization beam splitter 22y, and it is projected on
the Y measurement mirror 11 on the wafer X-Y stage 4 (target to be
measured). The remaining portion of the laser light my is reflected
by the polarization beam splitter 22y and, via the right-angle
mirror 23y, it is projected on the Y-reference mirror 31y. Light
reflected by this Y-reference mirror 31y goes through the
polarization beam splitter 22y, while light reflected by the Y
measurement mirror 11 is reflected by the polarization beam
splitter 22y. Both of these laser lights are projected on the
photodetector 24y. The laser lights impinging on the photodetector
24y interfere with each other to produce interference fringe. By
counting the fringes with the photodetector 24y, the position
(movement amount) of the wafer X-Y stage 4 (target to be measured)
having the Y measurement mirror 11 mounted thereon, with respect to
the Y direction can be measured. Measurement of the position
(movement amount) of the wafer X-Y stage 4 with respect to the X
direction can be measured similarly, by means of the X-axis laser
interferometer 20x.
[0038] As described above, the X or Y reference mirror 30 (30x and
30y) for providing a measurement reference for the laser
interferometer means 20 (20x and 20y), measuring the position or
movement amount of the wafer X-Y stage 4 with respect to X or Y
direction, is mounted on the mask .theta. stage 2 through the
mirror posture correcting means 31 (31x and 31y) or mirror posture
maintaining .theta. driving means 38. As a result, even when the
mask .theta. stage 2 is rotationally driven through the .theta.
driving means 7 so as to absorb a manufacturing error or conveyance
error of the mask 1, it is rotated relatively to the mask .theta.
stage 2 and keeps the same posture with respect to the measurement
laser light. Thus, the laser light impinging on the reference
mirror 30 (30x and 30y) can be reflected constantly in the same
direction as the impingement thereof. This assuredly prevents
failure of impingement of reflected measurement laser light on the
photodetector means and thus failure of measurement. Therefore, the
position or movement amount of the wafer X-Y stage 4 with respect
to the X or Y direction can be measured precisely, on the basis of
the measurement reference defined by reference mirror 30 (30x and
30y).
[0039] Next, an X-ray exposure apparatus having a stage positioning
system with a structure as having been described with reference to
FIGS. 1 and 2, will be explained. A mask 1 having a pattern formed
thereon is placed on the mask .theta. stage 2, and alignment
thereof is performed. Here, the mask .theta. stage 2 is drivingly
adjusted by the .theta. driving means 7 in rotational direction
along the mask surface, so as to absorb any mask manufacturing
error or conveyance error. A wafer 3 is held by the wafer X-Y stage
4 through the wafer chuck 5, and it is moved by the wafer X-Y stage
4 so that a predetermined exposure shot is placed at the exposure
region, opposed to the mask 1. Here, the position of the wafer 3
with respect to X and Y directions is measured by means of the
laser interferometer 20 (20x and 20y), and the wafer X-Y stage 4 is
driven in accordance with the result of measurement. The position
of the wafer X-Y stage 4 is thus controlled. The X-ray beam L of
exposure light, which may be a synchrotron radiation beam emitted
from a light source such as an electron accumulation ring (not
shown), for example, serves to lithographically transfer the
pattern of the mask 1 held by the mask .theta. stage 2 onto the
wafer 3 held by the wafer X-Y stage 4. The position of the wafer 3
with respect to X and Y directions is measured continuously even
during the exposure process, by means of the laser interferometer
20 (20x and 20y), and the wafer X-Y stage 4 is driven in accordance
with the result of measurement. This enables accurate control of
the alignment between the wafer 3 and the mask 1.
[0040] In mask alignment adjustment in which the mask .theta. stage
2 is rotationally moved in rotational direction along the mask
surface so as to absorb any mask manufacturing error or conveyance
error, there is a possibility that the rotation of the mask 1 and
the mask .theta. stage produces other components in X and Y
directions which in turn cause displacement of the reference of the
wafer X-Y stage 2. This may result in failure of accurate
measurement of the position or movement amount of the wafer X-Y
stage 4 or of the wafer 3 with respect to X and Y directions. A
correcting method therefor, as other components in measurement
direction are produced in the reference mirror being mounted on the
mask .theta. stage 2, will be explained below in conjunction with
FIGS. 1 and 2.
[0041] The mask .theta. stage 2 is rotated by the .theta. driving
means 7 in .theta. direction so as to adjust the posture of the
mask 1, and the rotational angle .theta. thereof is detected by the
.theta. angle sensor 9. In consideration of it, other components in
X and Y directions to be produced in response to the rotational
angle caused by rotational drive are measured beforehand. On the
basis of this, the relationship between the angle .theta. and the
other components is detected and the correction amounts
corresponding to these angles are calculated beforehand. In actual
exposure process, when the position (movement amount) of the wafer
X-Y stage 4 is measured by using the laser interferometer 20 (20x
and 20y), the rotational angle .theta. of the mask .theta. stage 2
is also detected by using the .theta. angle sensor 9, and the
correction amount corresponding to the thus detected angle .theta.
is read out. Then, the measured value obtained through the laser
interferometer 20 (20x and 20y) is corrected on the basis of the
correction value and, in accordance with the result of correction,
the driving means (not shown) for the wafer X-Y stage 4 in X and Y
directions is actuated to move the wafer X-Y stage 4 in X and Y
directions. This enables higher precision positioning of the wafer
X-Y stage 4, regardless of other components in measurement
direction of the reference mirror.
[0042] Another correction method may be that the mask positioning
is completed prior to the exposure so that no mask drive is
performed in the exposure process, avoiding other components in X
and Y directions in the exposure process. More specifically, the
mask alignment adjustment may be performed before the exposure
process, and any .theta. displacement of the mask produced there is
measured and corrected. Although this adjustment may produce other
components and, as a result, the reference position of the wafer
X-Y stage 4 may displace, the position or movement amount of the
wafer X-Y stage 4 may be measured in this state and then the
positioning of the wafer X-Y stage 4 may be performed. In that
occasion, the wafer X-Y stage 4 is positioned on the basis of the
reference position being deviated due to .theta. motion of the mask
1, so that it follows the thus deviated reference position. As
regards such positional deviation, however, in the wafer alignment
operation where alignment marks of the wafer 3 and alignment marks
of the mask 1 are brought into alignment with each other, the
position correction may be performed also to correct the other
component deviation produced during the mask alignment. During the
exposure process, the exposure is performed without mask driving
adjustment. By correcting the other component deviation produced by
the mask alignment, in the procedure of wafer alignment operation,
higher precision positioning of the wafer X-Y stage is assured
similarly.
[0043] An alternative correction method may be that the mask
positioning is completed prior to the exposure process, such that
the exposure is performed without mask drive. The position
measurement for the wafer X-Y stage may be made after completion of
the mask positioning, so that on other component in X and Y
direction may be produced during the exposure process. More
specifically, the mask alignment adjustment may be made before the
exposure, and a rotational angle of the mask produced there may be
measured and corrected. While this adjustment causes other
components, the position measurement for the wafer X-Y stage may be
made after completion of the mask positioning and by using the mask
position as a reference. Then, alignment marks of the wafer and
alignment marks of the mask may be brought into alignment, and the
exposure may be performed. The exposure may be done without mask
driving adjustment. This enables higher precision positioning of
the wafer X-Y stage.
[0044] Next, another embodiment of positioning stage system
according to the present invention will be described. This
embodiment is directed to a positioning stage system with a mask
tilt stage having freedom in tilt direction along the mask surface.
Description will be made in conjunction with FIG. 5.
[0045] In FIG. 5, along a path of X-ray beam L (exposure light)
which is emitted from a light source (not shown), a mask tilt stage
52 for holding a mask 51 and a wafer X-Y stage 54 (partially
illustrated) for holding a wafer or substrate (not shown) are
disposed close to each other. The mask tilt stage 52 for holding
the mask 51 is mounted on a base plate 52a through four leaf spring
guides 56, 56, . . . , disposed at four corners, so that it can
absorb a wedge component of the mask 51. Disposed between the base
plate 52a and the mask tilt stage 52 are a plurality of tilt
driving means 57, 57, . . . , each comprising a piezoelectric
device. By actuating these tilt driving means 57 appropriately, the
mask tilt stage 52 can be tilted. The tilt of the mask tilt stage
52 is detected by means of tilt sensors 59 and 59.
[0046] At the mask tilt stage side, there are an X-reference corner
cube 62 and a Y-reference corner cube 63 which function as
reference mirrors with respect to X and Y directions, respectively.
These corner cubes are disposed close to the mask 51 on the mask
tilt stage 52, or they are mounted on the mask 51 itself. The wafer
X-Y stage 54 is provided with an X measurement mirror 60 and a Y
measurement mirror 61.
[0047] An X-axis laser interferometer 70x serves to measure the
position or movement amount of the wafer X-Y stage 54 with respect
to the X direction. It comprises a laser oscillator 71x for
emitting measurement laser light mx, the X measuring mirror 60
mounted on the wafer X-Y stage 54 (target to be measured), an
X-reference corner cube 62 for providing a measurement reference
and being mounted on the mask tilt stage 52, a polarization beam
splitter 72x disposed between the laser oscillator 71x and the X
measuring mirror 60, a right-angle mirror 73x for directing a
portion of the laser light mx, being divided by the polarization
beam splitter 72x, toward the X-reference corner cube 62, and a
photodetector 74x. Thus, the laser light mx emitted by the laser
oscillator 71x is divided by the polarization beam splitter 72x. A
portion of the laser light mx is transmitted through the
polarization beam splitter 72x, and it is projected on the X
measurement mirror 60 on the wafer X-Y stage 54. The remaining
portion of the laser light mx is reflected by the polarization beam
splitter 72x, and via the right-angle mirror 73x it is projected
onto the X-reference corner cube 62 which provides a reference
mirror. Light reflected by the X-reference corner cube 62 goes
through the polarization beam splitter 72x, while light reflected
by the X measurement mirror 60 is reflected by the polarization
beam splitter 72x, and both lights are projected on the
photodetector 74x. These laser lights projected on the
photodetector 74x interfere with each other, to produce
interference fringe. By counting the fringes with the photodetector
74x, the position and movement amount of the wafer X-Y stage 54
(target to be measured), having the X measurement mirror 60 mounted
thereon, with respect to the X direction can be measured.
[0048] A Y-axis laser interferometer 70y serves to measure the
position and movement amount of the wafer X-Y stage 54 with respect
to the Y direction. It has a similar structure, and functions
similarly to measure the position and movement amount of the wafer
X-Y stage 54 (target to be measured), having the Y measurement
mirror 61 mounted thereon, with respect to the Y direction.
[0049] As described above, the reference corner cubes 62 and 63
which provide measurement references for the laser interferometer
means 70 (70x and 70y), measuring the position or movement amount
of the wafer X-Y stage 54 with respect to X or Y direction, are
disposed on the tiltable mask tilt stage 52. As a result, even when
the mask tilt stage 52 tilts in tilt direction along the mask
surface to cause inclination of the corner cubes 62 and 63
(reference mirrors), it is assured that the corner cubes 62 and 63
reflect the incident laser light in the same direction. This
assuredly prevents failure of impingement of reflected measurement
laser light on the photodetector means 74 and thus failure of
measurement.
[0050] Referring now to FIG. 6, a further embodiment of positioning
stage system according to the present invention will be described.
The embodiment shown in FIG. 6 differs from the embodiment of FIG.
5 in that a reference mirror to be provided on a mask tilt stage is
mounted through mirror posture correcting means. In this
embodiment, the elements corresponding to those of the FIG. 5
embodiment are denoted by like numerals. Detailed description
therefor will be omitted.
[0051] In FIG. 6, an X-reference mirror 80x and a Y-reference
mirror 80y are mounted on a mask tilt stage 52 through X-mirror
posture correcting means 81x and Y-mirror posture correcting means
81y, respectively. The positions of the X-mirror posture correcting
means 81x and Y-mirror posture correcting means 81y mounted on the
mask tilt stage 52 are different, but they are structured with
similar components. Like numerals are assigned to corresponding
elements, with suffixes x and y.
[0052] Details of the Y-reference mirror 80y and the Y-mirror
posture correcting means 81y will now be explained. The Y-reference
mirror 80y is held by the Y-mirror posture correcting means 81y
disposed at a central portion on one side face, in Y direction, of
the mask tilt stage 52. The Y-mirror posture correcting means 81y
comprises a Y-mirror fixing table 82y for fixing the Y-reference
mirror 80y, a hinge 83y mounted at a middle portion of one side
face, in Y direction, of the mask tilt stage 52 and being rotatably
connected to the mask tilt stage 52, and a pair of urging force
producing means 84y and 84y for pressing the surface of the Y
mirror fixing table 82y in Y direction. The paired urging force
producing means 84y and 84y are disposed at symmetrical positions
on the opposite sides of the hinge 83y. They engage with the
surface of the mirror fixing table 82y to press the respective
engagement positions downwardly along the Y direction, whereby the
posture of the mirror fixing table 82y can be held constant. As a
result, the Y-reference mirror 80y fixed to the mirror fixing table
82y can also be kept in constant posture, and it is held constantly
in posture perpendicular to the measurement laser light.
[0053] Thus, by using the mirror posture correcting means 81y such
as described above, the mirror fixing table 83y can be held in
constant posture even if the mask tilt stage 52 tilts in tilt
direction along the mask surface, since the mirror fixing table 83y
is pressed at its opposite sides by the paired urging force
producing means 84y and 84y. Thus, the Y-reference mirror 80y also
can be held in constant posture.
[0054] With the structure, as described, that the reference mirror
means 80 (80x and 80y) which provides a measurement reference for
the laser interferometer 70 (70x and 70y) for measuring the
position or movement amount of the wafer X-Y stage 54, are mounted
on the mask tilt stage 52 with intervention of mirror posture
correcting means 81 (81x and 81y), the reference mirror 80 can be
kept in constant posture. This is because, even if the mask tilt
stage 52 tilts in tilt direction along the mask surface, the
reference mirror 80 rotates relatively to the mask tilt stage 52.
Thus, the measurement laser light impinging on the reference mirror
can be reflected constantly in a predetermined direction. This
avoids the possibility of failure of detection of the measurement
laser light by the photodetector 74 and failure of measurement. It
is assured therefore that, regardless of tilt of the mask tilt
stage 52 in the tilt direction along the mask surface, the position
or movement amount of the wafer X-Y stage 54 can be measured
precisely on the basis of the measurement reference defined by the
reference mirror 80.
[0055] The embodiments shown in FIGS. 5 and 6 use an optical system
for distributing laser light, emitted from a laser oscillator, to
reference mirrors, so that reflected lights from these mirrors are
detected by one and the same photodetector. However, a laser
interferometer having a reference mirror accommodated therein may
be used. More specifically, with regard to the two reference
mirrors, there may be two such laser interferometers independent,
to measure the position or movement amount of the wafer stage.
[0056] Next, an X-ray exposure apparatus having a stage positioning
system with a structure as having been described with reference to
FIGS. 5 and 6, will be explained. A mask 51 having a pattern formed
thereon is placed on the mask tilt stage 52, and alignment thereof
is performed. Here, the mask tilt stage 52 is drivingly adjusted by
the tilt driving means 57 in tilt direction along the mask surface,
so as to absorb any wedge component of the mask. A wafer (not
shown) is held by the wafer X-Y stage 54 through the wafer chuck,
and it is moved by the wafer X-Y stage 54 so that a predetermined
exposure shot is placed at the exposure region, opposed to the mask
51. Here, the position of the wafer with respect to X and Y
directions is measured by means of the laser interferometer 70 (70x
and 70y), and the wafer X-Y stage 54 is driven in accordance with
the result of measurement. The position of the wafer X-Y stage 54
is thus controlled. The X-ray beam L of exposure light, which may
be a synchrotron radiation beam emitted from a light source such as
an electron accumulation ring (not shown), for example, serves to
lithographically transfer the pattern of the mask 51 held by the
mask tilt stage 52 onto the wafer held by the wafer X-Y stage 54.
The position of the wafer with respect to X and Y directions is
measured continuously even during the exposure process, by means of
the laser interferometer 70 (70x and 70y), and the wafer X-Y stage
54 is driven in accordance with the result of measurement. This
enables accurate control of the alignment between the wafer and the
mask 51.
[0057] In mask alignment adjustment in which the mask tilt stage 52
is tilted in tilt direction along the mask surface so as to absorb
any wedge component of the mask, there is a possibility that the
tilt motion of the mask 51 produces other components in X and Y
directions which in turn cause displacement of the reference of the
wafer X-Y stage 54. This may result in failure of accurate
measurement of the position or movement amount of the wafer X-Y
stage 54 with respect to X and Y directions. However, the
components in the measurement direction of the reference mirror
such as described above can be corrected in a similar way as has
been described with reference to FIGS. 1 and 2. Thus, higher
precision positioning of the wafer X-Y stage can be accomplished,
regardless of any tilt of the mask tilt stage 52 in the tilt
direction along the mask surface.
[0058] Next, an embodiment of a device manufacturing method which
uses an X-ray exposure apparatus such as described above, will be
explained.
[0059] FIG. 7 is a flow chart of procedure for manufacture of
microdevices such as semiconductor chips (e.g. ICs or LSIs), liquid
crystal panels, CCDs, thin film magnetic heads or micro-machines,
for example.
[0060] Step 1 is a design process for designing a circuit of a
semiconductor device. Step 2 is a process for making a mask on the
basis of the circuit pattern design. Step 3 is a process for
preparing a wafer by using a material such as silicon. Step 4 is a
wafer process which is called a pre-process wherein, by using the
so prepared mask and wafer, circuits are practically formed on the
wafer through lithography. Step 5 subsequent to this is an
assembling step which is called a post-process wherein the wafer
having been processed by step 4 is formed into semiconductor chips.
This step includes assembling (dicing and bonding) process and
packaging (chip sealing) process. Step 6 is an inspection step
wherein operation check, durability check and so on for the
semiconductor devices provided by step 5, are carried out. With
these processes, semiconductor devices are completed and they are
shipped (step 7).
[0061] FIG. 8 is a flow chart showing details of the wafer
process.
[0062] Step 11 is an oxidation process for oxidizing the surface of
a wafer. Step 12 is a CVD process for forming an insulating film on
the wafer surface. Step 13 is an electrode forming process for
forming electrodes upon the wafer by vapor deposition. Step 14 is
an ion implanting process for implanting ions to the wafer. Step 15
is a resist process for applying a resist (photosensitive material)
to the wafer. Step 16 is an exposure process for printing, by
exposure, the circuit pattern of the mask on the wafer through the
exposure apparatus described above. Step 17 is a developing process
for developing the exposed wafer. Step 18 is an etching process for
removing portions other than the developed resist image. Step 19 is
a resist separation process for separating the resist material
remaining on the wafer after being subjected to the etching
process. By repeating these processes, circuit patterns are
superposedly formed on the wafer. With these processes, high
density microdevices can be manufactured with lower cost.
[0063] As described hereinbefore, a corner cube or a cat's-eye may
be used as a reference mirror. The reference mirror may be mounted
on a first positioning stage through mirror posture correcting
means or mirror posture maintaining driving means. This assures
that the reference mirror is held in constant posture with respect
to measurement laser light. Thus, even if the reference mirror
displaces in rotational direction or tilt direction together with
the first positioning stage, the position or movement amount of a
measurement mirror provided on a second positioning stage can be
measured constantly with good precision. As a result, the second
positioning stage can be positioned precisely.
[0064] The present invention is applicable to an X-ray exposure
apparatus, and the position or movement amount of a substrate stage
for holding a substrate such as a wafer can be measured precisely
while using a reference mirror, disposed on or adjacent a mask, as
a measurement reference, regardless of displacement of a mask stage
for holding the mask and being movable in a rotational direction or
tilt direction along the mask surface. Although displacement of the
mask or mask stage in rotational direction or tilt direction along
the mask surface may produce other components in X and Y directions
of the reference mirror which in turn may cause shift of the
positioning reference for the substrate stage, the substrate stage
can still be driven and positioned precisely by correcting, for
example, a measured of the position or movement amount of the
substrate stage on the basis of measurement of the mask stage.
Thus, the mask to substrate alignment can still be controlled very
precisely.
[0065] While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set
forth and this application is intended to cover such modifications
or changes as may come within the purposes of the improvements or
the scope of the following claims.
* * * * *