U.S. patent application number 11/289596 was filed with the patent office on 2006-04-13 for correcting device, exposure apparatus, device production method, and device produced by the device production method.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Eiji Sakamoto, Nobuyoshi Tanaka.
Application Number | 20060077363 11/289596 |
Document ID | / |
Family ID | 18857687 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060077363 |
Kind Code |
A1 |
Tanaka; Nobuyoshi ; et
al. |
April 13, 2006 |
Correcting device, exposure apparatus, device production method,
and device produced by the device production method
Abstract
A correcting device that properly maintains the flatness of a
mask, an exposure apparatus in which overlay accuracy is increased
by making use of the correcting device, and a device production
method. The correcting device includes a gas flow path including a
first area and a second area. The first area is formed above a
reticle having formed thereon a pattern that is projected onto a
material to be processed in order to form an image of the pattern
on the material to be processed. The second area is connected to
the first area, has a cross-sectional area that is different from
that of the first area, and is not disposed in line with the
reticle. The correcting device also includes a blowing section that
blows gas to the gas flow path.
Inventors: |
Tanaka; Nobuyoshi; (Tokyo,
JP) ; Sakamoto; Eiji; (Tochigi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
18857687 |
Appl. No.: |
11/289596 |
Filed: |
November 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11126367 |
May 11, 2005 |
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11289596 |
Nov 30, 2005 |
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10011210 |
Dec 11, 2001 |
6951766 |
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11126367 |
May 11, 2005 |
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Current U.S.
Class: |
355/30 ;
438/12 |
Current CPC
Class: |
H01L 21/682 20130101;
G03F 7/70691 20130101; G03F 7/70783 20130101; G03F 7/70875
20130101 |
Class at
Publication: |
355/030 ;
438/012 |
International
Class: |
H01L 21/00 20060101
H01L021/00; G03B 27/52 20060101 G03B027/52 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2000 |
JP |
2000-391573 |
Claims
1. A correcting device comprising: a gas flow path including a
first area and a second area, the first area being formed above a
reticle having formed thereon a pattern that is projected onto a
material to be processed in order to form an image of the pattern
on the material to be processed, and the second area being
connected to the first area, having a cross-sectional area that is
different from that of the first area, and not being disposed in
line with the reticle; and a blowing section that blows gas to the
gas flow path.
2-36. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] In general, the present invention relates to an exposure
apparatus. More particularly, the present invention relates to an
exposure apparatus used to expose a material to be processed, such
as a monocrystalline substrate for a semiconductor wafer or a glass
substrate for a liquid crystal display (LCD), a correcting device
that corrects deformation of a mask or a reticle (hereafter, these
terms are used interchangeably in the application) used in the
exposure apparatus, a device production method using the material
to be processed, and a device that is produced from the material to
be processed. The present invention is, for example, suitable for
application to an exposure apparatus which exposes a
monocrystalline substrate for a semiconductor wafer by the
step-and-scan projection method, the scan projection method, or the
step-and-repeat projection method in a photolithography
process.
[0003] Here, the step-and-scan projection method is a projection
exposure method in which a wafer is continuously scanned in
synchronism with a scanning movement of a mask or a reticle in
order to project a pattern of the mask onto the wafer by exposure,
after which, after completion of an exposure of one shot, the wafer
is moved stepwise in order to move the next shot to an exposure
area. The scan projection method is a projection exposure method in
which a portion of the mask pattern is projected onto the wafer by
a projection optical system and the mask and a material to be
processed are scanned in synchronism with each other with respect
to the projection optical system in order to project the whole mask
pattern onto the wafer by exposure. The step-and-repeat projection
method is a projection exposure method in which the wafer is moved
stepwise with each full exposure of a shot of the wafer in order to
move the next shot to the exposure area.
[0004] 2. Description of the Related Art
[0005] In recent years, the demand for smaller and thinner
electronic devices has caused an increasing demand for finer
semiconductor devices installed in the electronic devices. For
example, it is expected that design rules of a mask pattern will
become increasingly smaller in the future as a result of an attempt
to realize a line and space (L & S) of 130 nm in a mass
production line. L & S refers to an image projected onto a
wafer during exposure with the widths of the lines and spaces being
equal, so that it is a measure of exposure resolution. In the
exposure, resolution, overlay accuracy, and throughput are three
important parameters. Resolution is defined as the smallest
dimension that can be precisely transferred. Overlay accuracy is
defined as the accuracy with which several patterns are overlaid on
a material to be processed. Throughput is the number of materials
that are processed per unit time.
[0006] There are basically two types of exposure methods, a
1.times. magnification transfer method and a projection method. The
1.times. magnification transfer method includes a method in which a
mask and a material to be processed are brought into contact with
each other and a method in which they are separated slightly.
However, in the former method, although a high resolution can be
obtained, the mask gets damaged and the material to be processed
gets scratched or defective due to dust or pieces of silicon being
pressed into the mask. In the latter method, the problem that
exists in the former method is initially solved, but, when the
separation between the mask and the material to be processed
becomes smaller than the maximum size of dust particles, damage to
the mask similarly occurs.
[0007] To overcome the problem that the mask and the material to be
processed become damaged, a projection method in which the mask and
the material to be processed are further separated has been
proposed. Of the different types of projection methods, the
projection method that uses a scanning projection exposure
apparatus is in dominant use in recent years in order to improve
resolution and to increase the size of an exposure area. In this
projection method, the mask is exposed a portion at a time, and the
mask and the wafer are caused to be in synchronism with each other.
By scanning the wafer either continuously or intermittently, the
entire mask pattern is projected onto the wafer by exposure.
[0008] In general, a projection exposure apparatus comprises an
illumination optical system that illuminates a mask and a
projection optical system, disposed between the mask and a material
to be processed, which projects a circuit pattern of the mask that
has been illuminated onto the material to be processed. In the
illumination optical system, in order to obtain a uniform
illumination area, light beams from a light source are made to
enter a light integrator comprising, for example, fly's eye lenses
that are provided using a plurality of rod lenses. With a
light-exiting surface of the light integrator being used as a
secondary light source surface, these light beams that have entered
the light integrator are used to subject a mask surface to Koehler
illumination through a condenser lens.
[0009] However, when the optical axis substantially coincides with
the direction of gravitational force, the center portion of the
mask is flexed by an amount on the order of a few microns in the
direction of the gravitational force due to its own weight,
resulting in a problem that overlay accuracy is reduced during the
exposure. More specifically, the following problems arise: (1)
Distortion of a projected image of the pattern changes as a result
of distortion of the mask pattern, and (2) focal depth, which is
the focal range that allows a certain image-formation performance
to be maintained, is reduced by curvature of field. In particular,
it is expected that due to the recent demand for finer patterns,
even a slight variation in the pattern must be increasingly taken
into account in the future.
[0010] To overcome such problems, Japanese Patent Laid-Open No.
10-214780 proposes, in a first embodiment, to enclose a mask in
order to apply static pressure to a hermetically sealed space
through a pressure control device. However, when the mask is
enclosed, heat produced by exposure causes the mask to be
distorted, so that this method is not a preferable method. In
addition, the same document proposes, in a second embodiment, to
correct the distortion of the mask through a piezoelectric device
disposed around the mask. However, the use of the piezoelectric
device around the mask is not necessarily effective in removing
flexure of the center portion of the mask caused by its own
weight.
[0011] Japanese Patent Laid-Open No. 6-176408 proposes to supply
gas having a predetermined pressure to a mask from a direction
opposite to the direction in which the mask flexes. However, it is
difficult to uniformly apply pressure to the mask. In addition, it
is difficult to dispose gas blowing means while maintaining an
exposure optical system.
SUMMARY OF THE INVENTION
[0012] In general, it is an object of the present invention to
provide a novel, useful correcting device, exposure apparatus,
device production method, and device produced by the production
method, which make it possible to overcome these conventional
problems.
[0013] More specifically, it is an object of the present invention
to provide, for illustrative purposes, a correcting device that
properly maintains the flatness of a mask, and an exposure
apparatus and a device production method, which make it possible to
increase overlay accuracy by making use of the correcting
device.
[0014] It is another object of the present invention to provide, as
for different illustrative purposes, devices, such as a
high-quality semiconductor, a liquid crystal device (LCD), a
charge-coupled device (CCD), and a thin-film magnetic head, which
are produced by the device production method.
[0015] To overcome the above-described problems, according to a
first aspect, the present invention provides a correcting device
comprising a gas flow path including a first area and a second
area, the first area being formed above a reticle having formed
thereon a pattern that is projected onto a material to be processed
in order to form an image of the pattern on the material to be
processed, and the second area being connected to the first area,
having a cross-sectional area that is different from that of the
first area, and not being disposed in line with the reticle; and a
blowing section that blows gas to the gas flow path.
[0016] According to this correcting device, by blowing gas (e.g.,
air or nitrogen) to a gas flow path having two continuously formed
areas, such as a first area and a second area, having different
cross-sectional areas, a difference in pressure between the first
area and the second area can be produced by making use of
Bernoulli's theorem. By properly making use of the pressure
difference, the correcting device can correct distortion caused by
factors other than the self-weight of the reticle. In addition, the
correcting device can restrict a rise in temperature of the reticle
caused by exposure heat by cooling the reticle as a result of
blowing air onto it.
[0017] When a third area is provided upstream from the first area
in terms of the gas that is blown, and when the cross-sectional
area of the third area is greater than the cross-sectional area of
the first area, it is possible to reduce the temperature of the gas
in the first area, so that the rise in temperature of the reticle
caused by the exposure heat can be more efficiently reduced.
[0018] When the structure of the first aspect is used, the
correcting device may further comprise a smoothing section,
disposed between the first and second areas, for smoothing movement
of the gas between the first and second areas. Accordingly, the
smoothing section can prevent the gas from deviating from
Bernoulli's theorem caused by the gas swirling between the first
and second areas. The gas flow path may be provided opposite to the
material to be processed with regard to the reticle. In general,
since a pellicle film is provided at the side of the material to be
processed, by providing the gas flow path opposite to the material
to be processed with regard to the reticle, it is possible to
prevent deformation of and damage to the pellicle film caused by
air blowing across or onto the pellicle film.
[0019] When the structure of the first aspect is used, the
correcting device may further comprise a control section that
controls the blowing section so that, when the density of the gas
is .rho., the weight of the reticle is G, the area of projection of
the reticle is A.sub.R, the cross-sectional area of the first area
is A.sub.1, the pressure of the gas in the first area is P.sub.1,
the velocity is V.sub.1, the cross-sectional area of the second
area is A.sub.2, and the pressure of the gas in the second area is
P.sub.2, the following formula is satisfied:
P.sub.1-P.sub.2=0.5.rho.V.sub.1.sup.2{(A.sub.1/A.sub.2).sup.2-1}=-G/A.sub-
.R. By virtue of this structure, the correcting device can correct
the distortion caused by the self-weight of the reticle. P.sub.2
may be set at atmospheric pressure. When the second area is set at
atmospheric pressure and the space around the reticle is open, as
disclosed in the first embodiment illustrated in Japanese Patent
Laid-Open No. 10-214780, the exposure heat is no longer confined in
the area around the recticle, so that the temperature rise of the
reticle can be restricted.
[0020] According to a second aspect, the present invention provides
a correcting device comprising a blowing section that blows gas
onto a reticle having formed thereon a pattern to be projected onto
a material to be processed in order to form an image of the pattern
on the material to be processed; a detecting section that detects
pressure at front and back surfaces of the reticle and produces a
detection result; and a control section that controls the blowing
section so that a difference between the pressures is maintained to
be a predetermined value, after receiving the detection result
provided by the detecting section. The correcting device can
correct the distortion of the reticle because the pressure
difference at the front and back surfaces of the reticle is
controlled by the control section so that it becomes a
predetermined value (for example, a value that cancels the
deformation caused by the weight of the reticle due to
gravitational force).
[0021] According to a third aspect, the present invention provides
a correcting device comprising a blowing section that blows gas
onto a reticle having formed thereon a pattern to be projected onto
a material to be processed in order to form an image of the pattern
on the material to be projected; a detecting section that detects a
flexure amount of the reticle and produces a detection result; and
a control section that controls the blowing section so that the
flexure amount is zero after receiving the detection result
provided by the detecting section. The correcting device can
correct the distortion of the reticle because feedback is
controlled by the control section so that the flexure amount of the
reticle is zero.
[0022] The control sections of these correcting devices can, for
example, control the gas speed and the temperature of the gas at
the blowing section.
[0023] According to a fourth aspect, the present invention provides
an exposure apparatus comprising any one of the above-described
correcting devices, an illumination optical system that illuminates
the pattern, and a projection optical system that projects the
pattern onto the material to be processed in order to form an image
of the pattern on the material to be processed. The exposure
apparatus can provide the operations of any one of the
above-described correcting devices.
[0024] According to a fifth aspect, the present invention provides
a method of producing a device comprising the steps of blowing gas
to a gas flow path including a first area and a second area, the
first area being formed above a reticle having formed thereon a
pattern that is projected onto a material to be processed in order
to form an image of the pattern on the material to be processed,
and the second area being connected to the first area, having a
cross-sectional area that is different from that of the first area,
and not being disposed in line with the reticle; subjecting the
material to be processed to a projection exposure operation using
the reticle; and performing a predetermined processing operation on
the material that has been subjected to the projection exposure
operation. The device production method, which is carried out by
the same operations as those of the exposure apparatus as a result
of the blowing step, is used to provide devices, which are
intermediate or final products. The device production method may
further comprise the step of detecting distortion of the reticle
and the step of controlling the blowing of the gas so that the
distortion of the reticle is reduced based on a result provided by
the detection. By the control operation step, the distortion of the
reticle can be corrected with high precision. Examples of such
devices are semiconductor chips used, for example, for large-scale
integration (LSI) or very large-scale integration (VLSI),
charge-coupled devices (CCDs), liquid crystal devices (LCDs),
magnetic sensors, and thin-film magnetic heads.
[0025] Further objects, features and advantages of the present
invention will become apparent from the following description of
the preferred embodiments with reference to the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a block diagram of an exposure apparatus of an
embodiment of the present invention.
[0027] FIG. 2 is a schematic, sectional view used to illustrate the
principle of a correcting device of the exposure apparatus shown in
FIG. 1.
[0028] FIG. 3 is a schematic, sectional view used to illustrate the
principle of the correcting device of the exposure apparatus shown
in FIG. 1.
[0029] FIG. 4 is a graph showing the relationship between upstream
gauge pressure and upstream gas speed in the views shown in FIGS. 2
and 3.
[0030] FIG. 5 is a perspective view of a modification of the
correcting device shown in FIG. 1.
[0031] FIG. 6 is a sectional view of the correcting device shown in
FIG. 5.
[0032] FIG. 7 is an exploded perspective view used to illustrate a
method of setting a reticle usable in the correcting device shown
in FIG. 5.
[0033] FIG. 8 is a sectional view of another modification of the
correcting device shown in FIG. 1.
[0034] FIG. 9 is a perspective view of still another modification
of the correcting device shown in FIG. 1.
[0035] FIG. 10 is a sectional view of the correcting device shown
in FIG. 9.
[0036] FIG. 11 is a perspective view of still another modification
of the correcting device shown in FIG. 1.
[0037] FIG. 12 is a sectional view of still another modification of
the exposure apparatus and of the correcting device shown in FIG.
1.
[0038] FIG. 13 is a sectional view showing a state in which the
reticle has moved in the sectional view of FIG. 12.
[0039] FIG. 14 is a schematic, side view of the exposure apparatus
shown in FIGS. 12 and 13.
[0040] FIG. 15 is an external perspective view of the exposure
apparatus shown in FIG. 14.
[0041] FIG. 16 is a schematic block diagram of a detecting section
that detects distortion of the reticle used in the exposure
apparatus shown in FIG. 1.
[0042] FIG. 17 is a flowchart used to illustrate a device
production method including an exposure step in accordance with the
present invention.
[0043] FIG. 18 is a detailed flowchart of Step 4 shown in FIG.
17.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Hereafter, for illustrative purposes, an exposure apparatus
1 of the present invention will be described with reference to the
attached drawings. FIG. 1 shows an optical path of a simplified
optical system of the illustrative exposure apparatus 1 of the
present invention.
[0045] As shown in FIG. 1, the exposure apparatus 1 comprises an
illumination device 10, a reticle 20, a projection optical system
30, a plate 40, and a correcting device 100. The exposure apparatus
1 is a scanning projection exposure apparatus which, by exposure,
projects a circuit pattern formed on the reticle 20 onto the plate
40 by the step-and-repeat projection exposure method or the
step-and-scan projection exposure method.
[0046] The illumination device 10 illuminates the reticle 20 on
which the circuit pattern to be transferred is formed, and
comprises a light source 12 and an illumination optical system
14.
[0047] For the light source 12, a laser may be used. For the laser,
an ArF excimer laser having a wavelength of approximately 193 nm, a
KrF excimer laser having a wavelength of approximately 248 nm, or
an F.sub.2 excimer laser having a wavelength of approximately 153
nm may be used. However, the types of lasers which may be used are
not limited to excimer lasers, so that, for example, a
yttrium-aluminum-garnet (YAG) laser may be used. The number of
lasers used is not limited. When a laser is used as the light
source 12, it is preferable to use a light-beam shaping optical
system that shapes parallel light beams from the laser light source
into beams having desired forms and an optical system that converts
coherent laser light beams into incoherent light beams. The types
of light sources that can be used as the light source 12 are not
limited to lasers, so that one or a plurality of mercury lamps,
xenon lamps, etc., may be used.
[0048] The illumination optical system 14 illuminates the mask 20,
and includes a lens, a mirror, a light integrator, and a stop. For
example, a condenser lens, a fly's eye lens, an aperture stop, a
condenser lens, a slit, and an image-forming optical system are
disposed in that order. The illumination optical system 14 is used
regardless of whether the light is axial or oblique light. Examples
of the light integrator include integrators formed by placing fly's
eye lenses or two sets of cylindrical lens array (or reticular
lens) plates upon each other. The light integrator may be replaced
by an optical rod or a diffracting device.
[0049] A circuit pattern (or image) to be transferred is formed on
the reticle 20. Diffraction light coming from the reticle 20 is
projected onto the plate 40 through the projection optical system
30. The plate 40 is a material to be processed, such as a wafer or
a liquid crystal substrate, and has a resist coated thereto. The
reticle 20 and the plate 40 are in a conjugate relationship. In the
embodiment, an optical axis OO' shown in FIG. 1 matches the
direction of gravitational force. The reticle 20 used in the
embodiment is formed of quartz and has a density of approximately
2200 kg/m.sup.3, a size of 152 mm in the vertical direction.times.a
size of 152 mm in the horizontal direction.times.a size of 6.35 mm
in the height direction, and a weight of 323 gf (=3.17 N), which is
approximately equivalent to a pressure of 140 Pa.
[0050] When a scanning projection exposure apparatus is used, the
pattern on the mask 20 is transferred onto the plate 40 by scanning
the mask 20 and the plate 40 in synchronism with each other. When a
stepper (or an exposure apparatus using the step-and-repeat
exposure method) is used, exposure is performed while the mask 20
and the plate 40 are stopped.
[0051] For the projection optical system 30, there may be used, for
example, an optical system comprising only a plurality of lens
elements, an optical system (catadioptric optical system) including
a plurality of lens elements and at least one concave mirror, an
optical system including a plurality of lens elements and at least
one diffracting optical element such as a saw-tooth shaped
diffracting optical element, or an optical system which is entirely
a mirror may be used. When chromatic aberration needs to be
corrected, the projection optical system 30 may be formed using a
plurality of lens elements formed of glass materials having
different variances (Abbe numbers) or the diffracting optical
element may be formed so that scattering occurs in a direction
opposite to the lens elements.
[0052] The plate 40 is coated with a photoresist. The photoresist
applying step consists of a pre-processing operation, an operation
for applying an adhesiveness increasing agent, a photoresist
applying operation, and a pre-baking operation. The pre-processing
operation includes cleaning, drying, and the like. The operation
for applying an adhesiveness increasing agent is carried out to
modify the surface of the plate 40 (that is, to increase its
hydrophobic property by applying a surface active agent), so that
the adhesiveness between the photoresist and a base is increased.
In the operation for applying an adhesiveness increasing agent, an
organic film, such as a hexamethyl-disilazane (HMDS) film, is
applied or evaporated. The pre-baking operation is a baking
operation, but provides a softer surface than that after
development, and is carried out to remove solvent.
[0053] The correcting device 100 corrects distortion or flexure of
the reticle 20. The reticle 20 is flexed due to its own weight by a
few microns in the direction of a gravitational force that is
parallel to the optical axis OO' shown in FIG. 1. Therefore, the
correcting device 100 first corrects the distortion of the reticle
20 caused by its own weight by making use of Bernoulli's theorem.
The correcting device 100 comprises a gas pipe 110, which forms a
gas flow path 111, and a blowing section 120, which blows gas to
the gas flow path 111. The gas flow path 111 comprises an area 112,
which is situated above or below the reticle 20, and an area 114,
which is not situated in line with the reticle 20.
[0054] The principle of the correcting device 100 will be described
with reference to FIGS. 2 and 3. Here, FIGS. 2 and 3 are schematic,
sectional views used to illustrate the principle of the correcting
device 100. FIG. 2 illustrates the case in which a gas flow path
111A is disposed below the reticle 20, and FIG. 3 illustrates the
case in which a gas flow path 111B is disposed above the reticle
20. In FIGS. 2 and 3, the arrows represent the directions in which
gas flows. The gas flow path 111A (in FIG. 2) comprises a wide area
112A, which is disposed below the reticle 20, and a narrow area
114A, which is not in line with the reticle 20. The gas flow path
111B (in FIG. 3) comprises a narrow area 112B, which is disposed
above the reticle 20, and a wide area 114B, which is not in line
with the reticle 20. Here, Formula 1 is established from
Bernoulli's theorem: 1 2 .times. V 1 2 + P 1 .rho. + gZ 1 = 1 2
.times. V 2 2 + P 2 .rho. + gZ 2 ( 1 ) ##EQU1## where .rho. is the
density of the gas flowing in the direction of the arrows shown in
FIGS. 2 and 3, A.sub.1 is the cross-sectional area of each of the
areas 112A and 112B that is perpendicular to the plane of the sheet
(FIGS. 2 and 3), P.sub.1 is the pressure of the gas in each of the
areas 112A and 112B, V.sub.1 is the speed of the gas, Z.sub.1 is
the height from a reference surface at the center of each of the
areas 112A and 112B, A.sub.2 is the cross-sectional area of each of
the areas 114A and 114B that is perpendicular to the plane of the
sheet (FIGS. 2 and 3), P.sub.2 is the pressure of the gas in the
areas 114A and 114B, V.sub.2 is the speed of the gas, and Z.sub.1
is the height from a reference surface at the center of each of the
areas 114A and 114B. Here, since the centers of the areas 112A and
112B and the corresponding areas 114A and 114B coincide,
Z.sub.1=Z.sub.2. Therefore, Formula 1 becomes Formula 2. When
Formula 2 is transformed, it becomes Formula 3. 1 2 .times. V 1 2 +
P 1 .rho. = 1 2 .times. V 2 2 + P 2 .rho. ( 2 ) P 1 - P 2 = 0.5
.rho. ( V 2 2 - V 1 2 ) ( 3 ) ##EQU2## Since .times. .times. V 1 A
1 = V 2 A 2 ( 4 ) and .times. .times. V 2 = A 1 A 2 .times. V 1 , (
5 ) ##EQU3## Formula 6 is established:
P.sub.1-P.sub.2=0.5.rho.V.sub.1.sup.2{(A.sub.1/A.sub.2).sup.2-1}
(6)
[0055] When the central lines of the areas 112A and 112B and the
corresponding areas 114A and 114B do not coincide, Formula 6
becomes:
P.sub.1-P.sub.2=0.5.times..rho..times.V.sub.1.sup.2.times.{(A.sub.1/A.sub-
.2).sup.2-1}+.rho..times.g.times.(Z.sub.2-Z.sub.1). However, when
P.sub.1-P.sub.2 is on the order of 100 Pa,
.rho..times.g.times.(Z.sub.2-Z.sub.1) is
12.25.times.(Z.sub.2-Z.sub.1), so that when Z.sub.2-Z.sub.1 is
equal to or less than a value on the order of 0.1 (10 cm), Formula
6 produces an error on the order of 10%, which is not a problem
from a practical standpoint.
[0056] P.sub.1-P.sub.2 is a difference in pressure between the
areas 112A and 112B and the corresponding areas 114A and 114B. When
the gas flow paths 111A and 111B are open to the atmosphere in
order to set P.sub.2 at atmospheric pressure, it is possible to
apply the pressure difference obtained by the above formula against
the weight of the reticle 20 (that is, in general, in the
embodiment, G=3.17 and A.sub.R=0.1522 when G represents the weight
of the reticle and A.sub.R is the area of projection of the reticle
20). By setting P.sub.2 at atmospheric pressure and causing the
space around the reticle 20 to be open, heat will not be confined
in the area around the reticle 20 as it is in the first embodiment
disclosed in Japanese Patent Laid-Open No. 10-214780, thereby
making it possible to prevent deformation and distortion of the
reticle 20 as a result of restricting a temperature rise in the
reticle 20.
[0057] The relationship between P.sub.1 (upstream gauge pressure)
and V.sub.1 (upstream gas speed) is shown in FIG. 4. An area ratio
which is greater than one means that the gas flow paths 111A and
111B have shrunk, whereas an area ratio less than one means that
they have expanded.
[0058] In order to apply a pressure equivalent to the self-weight
of the reticle 20 after rewriting Formula 4 using 140 Pa, which is
equivalent to the self-weight of the reticle 20, when the gas flow
path 111A is contracted (that is, when A.sub.1>A.sub.2),
V.sub.115/{(A.sub.1/A.sub.2).sup.2-1}.sup.1/2 On the other hand,
when the gas flow path 111B is expanded (that is, when
A.sub.1<A.sub.2), V.sub.1=15/{1-(A.sub.1/A.sub.2).sup.2}.sup.1/2
Referring to FIGS. 2 and 4, when A.sub.1/A.sub.2=2 in the case in
which the gas flow path 111A is disposed below the reticle 20, the
required gas speed is V.sub.1=8.7 m/sec. Similarly, referring to
FIGS. 3 and 4, when A.sub.1/A.sub.2=0.5 in the case in which the
gas flow path 111B is disposed above the reticle 20, the required
gas speed is V.sub.1=8.7 m/sec.
[0059] According to the correcting device 100, by blowing gas, such
as air or nitrogen, to the gas flow paths having two continuously
formed areas having different cross-sectional areas, a difference
in pressure can be produced between both of the areas as a result
of making use of Bernoulli's theorem. By properly making use of the
pressure difference, the correcting device 100 can correct
distortion caused by factors other than the self-weight of the
reticle 20. In addition, the correcting device 100 can restrict a
temperature rise in the reticle 20, caused by heat of exposure
light emitted from the illumination device 10, by cooling the
reticle 20 as a result of blowing gas onto the reticle 20.
[0060] In FIG. 1, the gas pipe 110, which is recessed above the
reticle 20, is used. Therefore, in FIG. 1, the area 114 is provided
not only behind the area 112 but also in front of the area 112
(that is, upstream in terms of the gas that is being blown). Since
the cross-sectional area of the area 112 is smaller than the
cross-sectional area of the upstream-side area 114, the temperature
of the gas in the area 112 can be reduced, so that the temperature
rise in the reticle 20 caused by the exposure heat can be
restricted.
[0061] In FIG. 1, the structure shown FIG. 3 can be used instead of
the structure shown in FIG. 2. More specifically, the gas pipe 110
is provided opposite to the plate 40 in relation to the reticle 20.
In general, a pellicle or a film (not shown) is provided at the
plate 40 side. The pellicle is a transparent protective film (or a
structural member thereof) provided within a certain distance from
the reticle 20 in order to prevent foreign matter from adhering
onto the reticle 20. Therefore, by providing the gas pipe 110
opposite to the plate 40 in relation to the reticle 20, it is
possible to prevent the reticle 20 from deforming and breaking,
when gas flows, by using the pellicle, so that the reticle 20 can
be indirectly protected.
[0062] The structures of the gas pipe 110 and the reticle 20 shown
in FIG. 1 are merely examples. For example, as shown in FIGS. 5 and
6, a correcting device 100C, including a gas pipe 110C defined by a
gas flow path 111C, having areas 112C and 114C, may be formed by a
pair of cross-sectionally parallel surfaces 116C and 118C in order
to cause the reticle 20 to protrude from a bottom surface 118C (or
a reticle table) of the gas pipe 110. Here, FIG. 5 is a perspective
view of a modification of the correcting device shown in FIG. 1,
and FIG. 6 is a sectional view thereof. As shown in FIG. 7, the
reticle 20 is secured to a reticle chuck 22 through a vacuum hole
23 formed at the reticle chuck 22, which is accommodated in a
rectangular hole 25 formed in the center of a rectangular reticle
stage 24. By properly setting a height H of the reticle stage 24, a
cross-sectional area A.sub.1 of the area 112C shown in FIG. 5 is
determined. A cross-sectional area A.sub.2 of the area 114C is
defined by the pair of parallel surfaces 116C and 118C of the gas
pipe 110C.
[0063] The blowing section 120 shown in FIG. 1 blows gas, whose
temperature is controlled at a certain temperature, towards the
scanning direction of the reticle stage 24. For example, as shown
in FIG. 5, the blowing section 120 includes a filter 122 and a duct
124. For the gas, air may be used when the light source 12 is a
mercury lamp, while nitrogen or the like may be used when the light
source 12 is a laser. The filter 122 is provided at the exit of the
blowing section 120 and cleans the gas that blows from the blowing
section 120. For the filter 122, a HEPA (manufactured by Nippon
Cambridge Filter Co., Ltd.) may be used. The duct 124 is connected
to an external gas source (not shown) in order to cause the gas to
flow into the blowing section 120.
[0064] The gas pipe 110 shown in FIG. 1 includes a transmission
window 117, formed of a material such as glass that passes exposure
light from the illumination optical system 14, at a top surface 116
thereof.
[0065] As shown in FIG. 6, it is preferable for the correcting
device 100 to further include a smoothing section 130, disposed
between the areas 112C and 114C, which smooths the movement of the
gas flowing therebetween. The smoothing section 130 can prevent the
gas from deviating from Bernoulli's theorem, which would be caused
by the gas swirling between the areas 112C and 114C. Although in
the embodiment the smoothing section 130 is formed by a triangular
column that is provided at the upstream side and the downstream
side of the reticle stage 24, an inclined portion does not have to
take the form of a straight line as in the embodiment. It may take
any form, such as a curved form or an arcuate form, as long as it
can smooth the movement of the gas.
[0066] FIG. 8 illustrates a correcting device 100D, which is a
modification of the correcting device shown in FIG. 1, in which,
similar to the gas pipe 110 shown in FIG. 1, a gas pipe 110D, which
is recessed above the reticle 20, is formed at a top surface 116D.
In the modification, due to the depth of the recess in the top
surface 116D, the cross-sectional area of an area 112D can be
adjusted. Accordingly, this modification has the feature that a
height H of the reticle stage 24 shown in FIG. 7 does not have to
be set at so high a value.
[0067] FIGS. 9 and 10 illustrate a correcting device 100E, which is
still another modification of the correcting device shown in FIG.
1. More specifically, a gas pipe 110E is formed so that the reticle
stage 24 is accommodated in a recess 119 formed in a bottom surface
118E (reticle table), and so that the top surface of the reticle
stage 24 and the top surface of the other portions of the bottom
surface 118E are at the same height. A cross-sectional area A.sub.1
of an area 112E and a cross-sectional area A.sub.2 of an area 114E,
both of which are illustrated in FIG. 9, are defined by a stepped
portion of a top surface 116E of the gas pipe 110.
[0068] The correcting device 100E further comprises a control
section 140, a memory 142, and a pressure sensor 150. The blowing
section 120, the control section 140, the memory 142, and the
pressure sensor 150 form a (feedback) control system. In this
modification, the control section 140 causes the difference in
pressure between the front and back surfaces of the reticle 20 to
be detected through the pressure sensor 150 in order to control the
blowing section 120 (or a driver (not shown) of the blowing section
120) so that the pressure difference becomes a predetermined value
(for example, so that it becomes a value required to cancel the
deformation of the reticle 20 caused by its own weight due to
gravity, or, more specifically, so that it satisfies
P.sub.1-P.sub.2=0.5.rho.V.sub.1.sup.2{(A.sub.1/A.sub.2).sup.2-1}=-G/A.sub-
.R. Therefore, the correcting device 100E can correct the
distortion of the reticle caused by its own weight.
[0069] The control section 140 is connected to the pressure sensor
150 in order to control, for example, the blast volume, and the gas
speed and the gas temperature at the blowing section 120 based on
the detection results of the pressure sensor 150. The control
section 140 is also connected to the memory 142, so that the memory
142 can store the method of controlling the blowing section 120
carried out by the control section 140 and/or the data used for the
method. The memory 142 may be a read-only memory (ROM), a
random-access memory (RAM), other such storage devices. In this
modification, the control section 140 is a control section of the
exposure apparatus 1. However, if necessary, this control section
140 may be a control section of an external device, the
illumination device 10, and the projection optical system 30. In
addition, separate control sections may be provided for these
component parts.
[0070] The pressure sensor 150 comprises a sensor 152, disposed at
the front side of the reticle 20 inside a gas flow path 111E, and a
sensor 154, disposed at the back side of the reticle 20 below a
bottom surface 118E of the gas pipe 110E. For the pressure sensor
150, sensors of any structure known in the industrial field, such
as a strain gauge, a load cell, a piezoelectric device, a pressure
electrically conductive sheet, a pressure sensitive polymer, a
photodiode, an electrostatic capacitive (differential pressure)
sensor, a Bourdon tube, a bellows, a diaphragm, or a torsion bar
may be used. The structures and operations of these types of
sensors are well known, and will not be described in detail
below.
[0071] FIG. 11 is an external perspective view of a correcting
device 100F, which is still another modification of the correcting
device 100 shown in FIG. 1. The correcting device 100F is similar
to the correcting device 100E, but differs from it in that, unlike
the area 114E that spreads vertically with respect to the area
112E, an area 114F spreads towards the left and right with respect
to an area 112F. In other words, a top surface 116F of a gas flow
path 110F (not shown) is maintained horizontally with respect to
the areas 112F and 114F. By combining the structures shown in FIGS.
9 and 11, the area 114F may spread in the upward and downward
directions and towards the left and right with respect to the area
112F.
[0072] In the present invention, it does not matter what scanning
method is used on the reticle 20, so that, for example, as shown in
FIGS. 12 to 15, the present invention may be applied to a scanning
exposure apparatus 200. Referring to FIGS. 12 and 13, the
correcting device 100F is used with the reticle 20 that is scanned
in synchronism by a pair of linear motors 204 and 227, which can
move perpendicular to each other. FIG. 13 shows a state in which
the reticle 20 has moved towards the left from its position shown
in FIG. 12.
[0073] Hereafter, with reference to FIGS. 14 and 15, the exposure
apparatus 200 will be described. FIG. 14 is a schematic side view
of the exposure apparatus 200, and FIG. 15 is an external
perspective view of the exposure apparatus 200. Through a
projection optical system 202, the exposure apparatus 200 projects
a portion of the circuit pattern of the reticle 20 disposed on a
reticle stage 201, which holds the reticle 20 and which can be used
for performing a scanning operation in the Y direction, onto a
wafer W disposed on an XY stage 203. The exposure apparatus 200 is
a step-and-scan exposure apparatus which is used to project the
pattern of the reticle 20 onto the wafer W by exposure as a result
of scanning the reticle 20 and the wafer W in the Y direction in
synchronism with each other with respect to the projection optical
system 202 and which interposes stepwise movements in order to
apply scanning exposure light to a plurality of shots on the wafer
W.
[0074] The reticle stage 201 is driven in the Y direction by the
linear motors 204 and 227. An X stage 203a of the wafer stage 203
is constructed so that it is driven in the X direction by a linear
motor 205, and a Y stage 203b is constructed so that it is driven
in the Y direction by a linear motor 206. The synchronized scanning
operation of the reticle 20 and the wafer W is carried out by
driving the reticle stage 201 and the Y stage 203b in the Y
direction at a fixed speed ratio (for example, 4:-1, where the -
sign means opposite direction) while laser interferometers 222 and
223 monitor the locations of the reticle stage 201 and the Y stage
203b in the Y direction. The wafer W is moved stepwise in the X
direction by the X stage 203a.
[0075] The wafer stage 203 is provided on a stage table 207, which
is supported on, for example, the floor at three points through
three dampers 208. The reticle stage 201 and the projection optical
system 202 are provided on a telescopic surface plate 209, which is
supported through three dampers 211 and column supports 212 on a
base frame 210 disposed on, for example, the floor. Although the
dampers 203 are active dampers that actively deaden or isolate
vibration in six axial directions, they may be passive dampers. In
addition, dampers do not need to be used to support the telescopic
surface plate 209.
[0076] At three points between the telescopic surface plate 209 and
the stage table 207, the exposure apparatus 200 includes
distance-measuring means, such as measurement laser interferometers
or microcomputers. Light projecting means 221 and light-receiving
means 222 form a focus sensor for detecting whether or not the
wafer W on the wafer stage 203 is positioned at a focal plane of
the projection optical system 202. More specifically, the
light-projecting means 221, secured to the telescopic surface plate
209, projects light onto the wafer W from an oblique direction, and
the light-receiving means 222 detects the location of the reflected
light in order to detect the location of the surface of the wafer W
in the optical axis direction of the projection optical system
202.
[0077] In the structure, transporting means (not shown) transports
the wafer W onto the wafer stage 203 via a transportation path
between the two column supports 212 at the front portion of the
exposure apparatus 200. When a predetermined alignment is
completed, the exposure apparatus 200 transfers the pattern of the
reticle 20 onto a plurality of exposure areas of the wafer W by
exposure while it repeats scanning exposure operations and causes
stepwise movements to be repeated. In the scanning exposure
operation, the reticle stage 201 and the Y stage 203b are moved at
a predetermined speed ratio in the Y direction (scanning
direction). Using slit-shaped exposure light, the pattern on the
reticle 20 is scanned, and the wafer W is scanned using the
projection image of the pattern in order to project the pattern of
the reticle 20 onto a predetermined exposure area of the wafer W by
exposure. During the scanning exposure operation, the height of the
surface of the wafer W is measured by the focus sensor. Based on
the measured value, the height and tilt of the wafer stage 203 are
controlled in real time in order to correct the focus. After
completion of a scanning exposure operation on one exposure area,
by driving the X stage 203a in the X direction in order to move the
wafer W stepwise, another exposure area is positioned at a scanning
exposure starting location and is, then, subjected to scanning
exposure. By combining the stepwise movements in the X direction
and the movements for performing scanning exposure in the Y
direction, in order to allow the exposure operations to be
successively performed efficiently with respect to the plurality of
exposure areas on the wafer W, the location of each of the exposure
areas, scanning in the +Y or -Y direction, the order in which each
exposure area is exposed, and the like, are set.
[0078] In the exposure apparatus 200 shown in FIG. 14, light that
has been emitted from a laser interferometer light source (not
shown) is caused to enter the Y-direction laser interferometer 224.
The light that has entered the Y-direction laser interferometer 224
is divided by a beam splitter (not shown) inside the laser
interferometer 224 into light that is directed towards a fixed
mirror (not shown) disposed inside the laser interferometer 224 and
light that is directed towards a Y-direction moving mirror (not
shown). The light that is directed towards the Y-direction moving
mirror passes through a Y-direction length measurement optical path
(not shown), and, then, impinges upon the Y-direction moving mirror
secured to the reticle stage 201. Here, the light that is reflected
passes again through the Y-direction length measurement optical
path, returns to the beam splitter inside the laser interferometer
202, and is superimposed on the light reflected at the fixed
mirror. At this time, by detecting changes in the interference of
light, the distance of movement in the Y direction is measured. The
information regarding the distance of movement measured in this way
is fed back to a scanning control device (not shown), which
controls the positioning operation of a scanning location of the
reticle stage 201.
[0079] The reticle 20 is deformed as a result of being heated by
the exposure light from the illumination device 10. In the present
invention, it is possible to correct both thermal deformation of
the reticle 20 and flexure of the reticle 20 caused by its own
weight. Hereafter, an example of correcting the deformations of the
reticle 20 will be given with reference to FIG. 16. FIG. 16 is a
schematic block diagram of a detecting section 150 that detects any
distortion of the reticle 20. The reticle 20 is secured to the
reticle chuck 22 through a suction pad 21. The reticle 20 is
distorted by a flexure amount .delta. caused by its own weight,
heat, and other factors. The detecting section 150 comprises a
light-emitting section 152, lenses 154 and 156, and a
light-receiving section 158. In this example, the light-emitting
section 152 and the light-receiving section 158 form a
light-reflective photo-interrupter. A light-emitting diode (LED), a
laser diode (LA), or the like may be used for the light-emitting
section 152. A photodiode, phototransistor, a photo IC, or the like
may be used for the light-receiving section 158. The light-emitting
section 152 illuminates a pattern formed on the surface of the
reticle 20. Light reflected therefrom is detected by the
light-receiving section 158 in order to detect the flexure amount
.delta. of the reticle 20. The detection results provided by the
light-receiving section 158 is transmitted to, for example, the
control section 140 shown in FIG. 10. The control section 140 makes
use of such results to control the blowing section 120. The control
section 140 controls feedback of the blowing section 120 so that
the flexure amount .delta. of the reticle 20 becomes zero in order
to correct the distortions of the reticle 20.
[0080] In the exposure, light beams emitted from the light source
12 are used to subject the recticle 20 to, for example, Koehler
illumination by the illumination optical system 14. Since the
exposure apparatus 1 makes it possible to reduce or remove the
distortions of the reticle 20, the pattern of the reticle 20 can be
transferred onto the resist with high precision, so that a
high-quality device (such as a semiconductor device, a liquid
crystal display (LCD) device, an image pickup device (including a
charge-coupled device (CCD)), and a thin-film magnetic head) can be
provided.
[0081] Referring to FIGS. 17 and 18, an embodiment of a device
production method using the above-described exposure apparatus 1
will be described. FIG. 17 is a flowchart used to illustrate the
production of a device (such as a semiconductor chip of, for
example, an integrated circuit (IC) or a large-scale integrated
circuit (LSI), an LCD, and a CCD). Here, an example of producing a
semiconductor chip will be described. In Step 1, a circuit pattern
is designed for the device. In Step 2, a mask having the designed
circuit pattern formed thereon is produced. In Step 3, a wafer is
produced, using silicon or other materials. In Step 4 (wafer
process or pre-processing step), the mask and the wafer are used to
actually form the circuit on the wafer using lithography
techniques. Then, in the following step, Step 5, (post-processing
step), the wafer produced in Step 4 is formed into a semiconductor
chip, wherein assembly (dicing, bonding), packaging (of the chip),
and the like are performed. In Step 6, the semiconductor device
produced in Step 5 is inspected by conducting operation
confirmation tests, durability tests, and the like. Thereafter, in
Step 7, the finished semiconductor device is shipped.
[0082] FIG. 18 is a detailed flowchart of Step 4 (the wafer
process). In Step 11, the surface of the wafer is oxidized. Then,
in Step 12 (chemical-vapor deposition (CVD) step), an insulation
film is formed on the wafer surface. In Step 13, an electrode is
formed on the wafer by, for example, evaporation. In Step 14, ions
are implanted into the wafer. In Step 15, a photosensitization
agent is coated onto the wafer. In Step 16, the mask circuit
pattern is printed onto the wafer by exposure using the exposure
apparatus 1. In Step 17, the exposed portion of the wafer is
developed. In Step 18, portions other than where the developed
resist image is formed are etched. In Step 19, unwanted resist is
removed from the wafer after etching. Multiple circuit patterns are
formed on the wafer by repeating the above-described steps. By
virtue of this embodiment of the device production method, devices
having a higher quality than conventional devices can be
produced.
[0083] Except as otherwise discussed herein, the various components
shown in outline or in block form in the Figures are individually
well known and their internal construction and operation are not
critical either to the making or using or to a description of the
best mode of the invention.
[0084] While the present invention has been described with
reference to what are presently considered to be the preferred
embodiments, it is to be understood that the invention is not
limited to the disclosed embodiments. On the contrary, the
invention is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims. The scope of the following claims is to be accorded the
broadest interpretation so as to encompass all such modifications
and equivalent structures and functions.
* * * * *