U.S. patent application number 12/884332 was filed with the patent office on 2011-01-06 for projection optical system, exposure apparatus, and exposure method.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Yasuhiro Omura.
Application Number | 20110002032 12/884332 |
Document ID | / |
Family ID | 36574679 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110002032 |
Kind Code |
A1 |
Omura; Yasuhiro |
January 6, 2011 |
PROJECTION OPTICAL SYSTEM, EXPOSURE APPARATUS, AND EXPOSURE
METHOD
Abstract
A catadioptric projection optical system for forming a reduced
image of a first surface (R) on a second surface (W) is a
relatively compact projection optical system having excellent
imaging performance as well corrected for various aberrations, such
as chromatic aberration and curvature of field, and being capable
of securing a large effective image-side numerical aperture while
suitably suppressing reflection loss on optical surfaces. The
projection optical system comprises at least two reflecting mirrors
(CM1, CM2), and a boundary lens (Lb) whose surface on the first
surface side has a positive refracting power, and an optical path
between the boundary lens and the second surface is filled with a
medium (Lm) having a refractive index larger than 1.1. Every
transmitting member and every reflecting member with a refracting
power forming the projection optical system are arranged along a
single optical axis (AX) and the projection optical system has an
effective imaging area of a predetermined shape not including the
optical axis.
Inventors: |
Omura; Yasuhiro;
(Kumagaya-shi, JP) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD, SUITE 400
MCLEAN
VA
22102
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
|
Family ID: |
36574679 |
Appl. No.: |
12/884332 |
Filed: |
September 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11513160 |
Aug 31, 2006 |
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12884332 |
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11266288 |
Nov 4, 2005 |
7348575 |
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11513160 |
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PCT/JP2004/006417 |
May 6, 2004 |
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11266288 |
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60721582 |
Sep 29, 2005 |
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Current U.S.
Class: |
359/364 |
Current CPC
Class: |
G02B 9/34 20130101; G03F
7/70225 20130101; G03F 7/7015 20130101; G02B 17/0844 20130101; G03F
7/70341 20130101; H01L 21/027 20130101 |
Class at
Publication: |
359/364 |
International
Class: |
G02B 17/08 20060101
G02B017/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2003 |
JP |
2003-128154 |
Oct 9, 2003 |
JP |
2003-350647 |
Oct 24, 2003 |
JP |
2003-364596 |
Claims
1. A catadioptric projection objective for imaging a pattern
provided in an object plane of the projection objective onto an
image plane of the projection objective comprising: a first
objective part comprising one or more refractive optical elements
for imaging the pattern provided in the object plane into a first
intermediate image; a second objective part including at least one
concave mirror for imaging the first intermediate image into a
second intermediate image; a third objective part comprising one or
more refractive optical elements for imaging the second
intermediate image onto the image surface; wherein: the projection
objective has a maximum lens diameter D.sub.max, a maximum image
field height Y', and an image side numerical aperture NA; wherein
COMP1=D.sub.max/(Y'NA.sup.2) and wherein the following condition
holds: COMP1<about 13.5.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/513,160, filed Aug. 31, 2006, which is a
continuation application of U.S. Ser. No. 11/266,288, filed Nov. 4,
2005, now U.S. Pat. No. 7,348,575, issued Mar. 25, 2008, which is a
continuation-in-part application of PCT serial no.
PCT/JP2004/006417, filed May 6, 2004. Application Ser. No.
11/266,288 also claims priority of U.S. Provisional Application No.
60/721,582, filed Sep. 29, 2005. The disclosures of these prior
applications are incorporated herein by reference in their
entireties.
FIELD OF THE INVENTION
[0002] The present invention relates to a catadioptric projection
optical system, exposure apparatus, and exposure method and, more
particularly, to a high-resolution catadioptric projection optical
system suitable for exposure apparatus used in production of
semiconductor devices, liquid-crystal display devices, etc. by
photolithography.
RELATED BACKGROUND ART
[0003] The photolithography for production of the semiconductor
devices and others is implemented using a projection exposure
apparatus for projecting a pattern image of a mask (or a reticle)
through a projection optical system onto a wafer (or a glass plate
or the like) coated with a photoresist or the like. The resolving
power (resolution) required for the projection optical system of
the projection exposure apparatus is becoming increasingly higher
and higher with increase in integration degree of the semiconductor
devices and others.
[0004] As a result, in order to satisfy the requirements for the
resolving power of the projection optical system, it is necessary
to shorten the wavelength .lamda. of illumination light (exposure
light) and to increase the image-side numerical aperture NA of the
projection optical system. Specifically, the resolution of the
projection optical system is expressed by k.lamda./NA (where k is
the process coefficient). The image-side numerical aperture NA is
represented by nsin .theta., where n is a refractive index of a
medium (normally, gas such as air) between the projection optical
system and the image plane and .theta. a maximum angle of incidence
to the image plane.
[0005] In this case, if the maximum incidence angle .theta. is
increased in order to increase the numerical aperture NA, it will
result in increasing the input angle to the image plane and the
output angle from the projection optical system, so as to increase
reflection loss on optical surfaces and thus fail to secure a large
effective image-side numerical aperture. For this reason, there is
the known technology of increasing the numerical aperture NA by
filling a medium like a liquid with a high refractive index in the
optical path between the projection optical system and the image
plane.
[0006] However, application of this technology to the ordinary
dioptric projection optical systems caused such disadvantages that
it was difficult to well correct for chromatic aberration and to
satisfy the Petzval's condition to well correct for curvature of
field, and that an increase in the scale of the optical system was
inevitable. In addition, there was another disadvantage that it was
difficult to secure a large effective image-side numerical aperture
while well suppressing the reflection loss on optical surfaces.
SUMMARY OF THE INVENTION
[0007] A first object of the embodiment is to provide a relatively
compact projection optical system having excellent imaging
performance as well corrected for various aberrations, such as
chromatic aberration and curvature of field, and being capable of
securing a large effective image-side numerical aperture while well
suppressing the reflection loss on optical surfaces.
[0008] In the case where the projection optical system is composed
of only reflecting optical members and in the case where the
projection optical system is composed of a combination of
refracting optical members with reflecting optical members, with
increase in the numerical aperture, it becomes more difficult to
implement optical path separation between a beam entering a
reflecting optical member and a beam reflected by the reflecting
optical member and it is infeasible to avoid an increase in the
scale of the reflecting optical member, i.e., an increase in the
scale of the projection optical system.
[0009] In order to achieve simplification of production and
simplification of mutual adjustment of optical members, it is
desirable to construct a catadioptric projection optical system of
a single optical axis; in this case, with increase in the numerical
aperture, it also becomes more difficult to achieve the optical
path separation between the beam entering the reflecting optical
member and the beam reflected by the reflecting optical member, and
the projection optical system increases its scale.
[0010] A second object of the embodiment is to achieve a large
numerical aperture, without increase in the scale of optical
members forming a catadioptric projection optical system.
[0011] A third object of the embodiment is to provide an exposure
apparatus and exposure method capable of performing an exposure to
transcribe a fine pattern with high accuracy through a projection
optical system having excellent imaging performance and having a
large effective image-side numerical aperture and therefore a high
resolution. In order to achieve the above-described first object, a
projection optical system according to a first aspect of the
embodiment is a catadioptric projection optical system for forming
a reduced image of a first surface on a second surface,
[0012] the projection optical system comprising at least two
reflecting mirrors, and a boundary lens whose surface on the first
surface side has a positive refracting power,
[0013] wherein, where a refractive index of an atmosphere in an
optical path of the projection optical system is 1, an optical path
between the boundary lens and the second surface is filled with a
medium having a refractive index larger than 1.1,
[0014] wherein every transmitting member and every reflecting
member with a refracting power constituting the projection optical
system are arranged along a single optical axis, and
[0015] the projection optical system having an effective imaging
area of a predetermined shape not including the optical axis.
[0016] In order to achieve the above-described second object, a
projection optical system according to a second aspect of the
embodiment is a catadioptric projection optical system for forming
an image of a first surface on a second surface, the projection
optical system comprising:
[0017] a first imaging optical system comprising two mirrors, for
forming an intermediate image of the first surface; and
[0018] a second imaging optical system for forming the intermediate
image on the second surface,
[0019] wherein the second imaging optical system comprises the
following components in order of passage of a ray from the
intermediate image side:
[0020] a first field mirror of a concave shape;
[0021] a second field mirror;
[0022] a first lens unit comprising at least two negative lenses
and having a negative refracting power;
[0023] a second lens unit having a positive refracting power;
[0024] an aperture stop; and
[0025] a third lens unit having a positive refracting power.
[0026] In order to achieve the above-described second object, a
projection optical system according to a third aspect of the
embodiment is a catadioptric projection optical system for forming
an image of a first surface on a second surface, the projection
optical system comprising:
[0027] a first unit disposed in an optical path between the first
surface and the second surface and having a positive refracting
power;
[0028] a second unit disposed in an optical path between the first
unit and the second surface and comprising at least four
mirrors;
[0029] a third unit disposed in an optical path between the second
unit and the second surface, comprising at least two negative
lenses, and having a negative refracting power; and
[0030] a fourth unit disposed in an optical path between the third
unit and the second surface, comprising at least three positive
lenses, and having a positive refracting power,
[0031] wherein an intermediate image is formed in the second unit
and wherein an aperture stop is provided in the fourth unit.
[0032] In order to achieve the above-described second object, a
projection optical system according to a fourth aspect of the
embodiment is a catadioptric projection optical system for forming
an image of a first surface on a second surface, the projection
optical system comprising:
[0033] a first imaging optical system comprising at least six
mirrors, for forming a first intermediate image and a second
intermediate image of the first surface; and
[0034] a second imaging optical system for relaying the second
intermediate image onto the second surface.
[0035] In order to achieve the above-described third object, an
exposure apparatus according to a fifth aspect of the embodiment is
an exposure apparatus for effecting an exposure of a pattern formed
on a mask, onto a photosensitive substrate, the exposure apparatus
comprising:
[0036] an illumination system for illuminating the mask set on the
first surface; and
[0037] the projection optical system according to any one of the
above-described aspects, for forming an image of the pattern formed
on the mask, on the photosensitive substrate set on the second
surface.
[0038] In order to achieve the above-described third object, an
exposure method according to a sixth aspect of the embodiment is an
exposure method of effecting an exposure of a pattern formed on a
mask, onto a photosensitive substrate, the exposure method
comprising:
[0039] an illumination step of illuminating the mask on which the
predetermined pattern is formed; and
[0040] an exposure step of performing an exposure of the pattern of
the mask set on the first surface, onto the photosensitive
substrate set on the second surface, using the projection optical
system as set forth in the above.
[0041] The present invention will be more fully understood from the
detailed description given hereinbelow and the accompanying
drawings, which are given by way of illustration only and are not
to be considered as limiting the embodiment.
[0042] Further scope of applicability of the embodiment will become
apparent from the detailed description given hereinafter. However,
it should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the invention,
are given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will be
apparent to those skilled in the art from this detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is an illustration schematically showing a
configuration of an exposure apparatus according to an embodiment
of the embodiment.
[0044] FIG. 2 is an illustration showing a positional relation
between the optical axis and an effective exposure area of arcuate
shape formed on a wafer in the embodiment.
[0045] FIG. 3 is an illustration schematically showing a
configuration between a boundary lens and a wafer in the first
example of the embodiment.
[0046] FIG. 4 is an illustration schematically showing a
configuration between a boundary lens and a wafer in the second
example of the embodiment.
[0047] FIG. 5 is an illustration showing a lens configuration of a
projection optical system according to the first example of the
embodiment.
[0048] FIG. 6 is a diagram showing the transverse aberration in the
first example.
[0049] FIG. 7 is an illustration showing a lens configuration of a
projection optical system according to the second example of the
embodiment.
[0050] FIG. 8 is a diagram showing the transverse aberration in the
second example.
[0051] FIG. 9 is an illustration showing a lens configuration of a
catadioptric projection optical system according to the third
example.
[0052] FIG. 10 is an illustration showing a lens configuration of a
catadioptric projection optical system according to the fourth
example.
[0053] FIG. 11 is an illustration showing an exposure area on a
wafer in the third and fourth examples.
[0054] FIG. 12 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system in
the third example.
[0055] FIG. 13 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system in
the fourth example.
[0056] FIG. 14 is an illustration showing a lens configuration of a
catadioptric projection optical system according to the fifth
example.
[0057] FIG. 15 is an illustration showing a lens configuration of a
catadioptric projection optical system according to the sixth
example.
[0058] FIG. 16 is an illustration showing a lens configuration of a
catadioptric projection optical system according to the seventh
example.
[0059] FIG. 17 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system in
the fifth example.
[0060] FIG. 18 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system in
the sixth example.
[0061] FIG. 19 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system in
the seventh example.
[0062] FIG. 20 is a flowchart of a method of producing
semiconductor devices as microdevices.
[0063] FIG. 21 is a flowchart of a method of producing a liquid
crystal display device as a microdevice.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0064] In the projection optical system according to the first
aspect of the embodiment, the medium having the refractive index
larger than 1.1 is interposed in the optical path between the
boundary lens and the image plane (second surface), thereby
increasing the image-side numerical aperture NA. In passing,
"Resolution Enhancement of 157-nm Lithography by Liquid Immersion"
reported in "Massachusetts Institute of Technology" in "SPIE2002
Microlithography" by Mr. M. Switkes and Mr. M. Rothschild describes
Fluorinert (Perfluoropolyethers: trade name of 3M, USA) and
Deionized Water as candidates for media having the required
transmittance for light of wavelength .lamda., of not more than 200
nm.
[0065] In the projection optical system according to the first
aspect of the embodiment, the optical surface on the object side
(first surface side) of the boundary lens is provided with the
positive refracting power, whereby the reflection loss is reduced
on this optical surface and, in turn, the large effective
image-side numerical aperture can be secured. In the optical system
having the high-refractive-index material like liquid as the medium
on the image side, it is feasible to increase the effective
image-side numerical aperture to not less than 1.0 and, in turn, to
enhance the resolution. However, where the projection magnification
is constant, the object-side numerical aperture also increases with
increase in the image-side numerical aperture; therefore, if the
projection optical system is constructed of only refracting
members, it will be difficult to satisfy the Petzval's condition
and it will result in failing to avoid the increase in the scale of
the optical system.
[0066] Therefore, the projection optical system according to the
first aspect of the embodiment adopts the catadioptric system of
the type comprising at least two reflecting mirrors, in which every
transmitting member and every reflecting member with a refracting
power (power) are arranged along the single optical axis and which
has the effective imaging area of the predetermined shape not
including the optical axis. In the projection optical system of
this type, for example, through action of a concave reflecting
mirror, it is feasible to well correct for the chromatic aberration
and to readily satisfy the Petzval's condition to well correct for
the curvature of field, and the scale of the optical system can be
reduced.
[0067] The projection optical system of this type has the
configuration wherein every transmitting member (lenses or the
like) and every reflecting member with a power (concave reflecting
mirrors or the like) are arranged along the single optical axis,
which is preferable because the degree of difficulty in production
is considerably lower than in a multi-axis configuration wherein
the optical members are arranged along multiple optical axes.
However, in the case of the single-axis configuration wherein the
optical members are arranged along the single optical axis, the
chromatic aberration tends to be difficult to well correct for, but
this problem of correction for chromatic aberration can be
overcome, for example, by use of laser light with a narrowed
spectral width like ArF laser light.
[0068] In this manner, the first aspect of the embodiment can
realize the relatively compact projection optical system having the
excellent imaging performance as well corrected for the various
aberrations such as chromatic aberration and curvature of field and
being capable of securing the large effective image-side numerical
aperture while well suppressing the reflection loss on the optical
surfaces. Therefore, an exposure apparatus and exposure method
using the projection optical system according to the first aspect
of the embodiment are able to perform an exposure of a fine pattern
to transcribe the pattern through the projection optical system
having the excellent imaging performance and the large effective
image-side numerical aperture and therefore the high
resolution.
[0069] In the first aspect of the embodiment, the projection
optical system is preferably arranged to have an even number of
reflecting mirrors, i.e., to form the image of the first surface on
the second surface through an even number of reflections. When the
projection optical system in this configuration is applied, for
example, to the exposure apparatus and exposure method, not a
mirror image (a flipped image) but an unmirrored (unflipped) image
(erect image or inverted image) of the mask pattern, is formed on
the wafer, whereby the ordinary masks (reticles) can be used as in
the case of the exposure apparatus equipped with the dioptric
projection optical system.
[0070] In the first aspect of the embodiment, the projection
optical system preferably comprises: a first imaging optical system
comprising two mirrors, which forms an intermediate image of the
first surface; and a second imaging optical system, which forms the
intermediate image on the second surface; the second imaging
optical system preferably comprises the following components in
order of passage of a ray from the intermediate image side: a first
field mirror of a concave shape; a second field mirror; a first
lens unit comprising at least two negative lenses and having a
negative refracting power; a second lens unit having a positive
refracting power; an aperture stop; and a third lens unit having a
positive refracting power.
[0071] In this configuration, the intermediate image of the first
surface is formed in the first imaging optical system, and it is
thus feasible to readily and securely achieve the optical path
separation between the beam toward the first surface and the beam
toward the second surface, even in the case where the numerical
apertures are increased of the catadioptric projection optical
system. Since the second imaging optical system comprises the first
lens unit having the negative refracting power, the total length of
the catadioptric projection optical system can be reduced, and
adjustment for satisfying the Petzval's condition can be readily
performed. Furthermore, the first lens unit relieves variation due
to the difference of field angles of the beam expanded by the first
field mirror, so as to suppress occurrence of aberration.
Therefore, the good imaging performance can be achieved throughout
the entire region in the exposure area, even in the case where the
object-side and image-side numerical apertures of the catadioptric
projection optical system are increased in order to enhance the
resolution.
[0072] In the above-described configuration, preferably, the first
imaging optical system comprises a fourth lens unit having a
positive refracting power, a negative lens, a concave mirror, and
an optical path separating mirror; and the first imaging optical
system is arranged as follows: light traveling in the first imaging
optical system passes through the fourth lens unit and the negative
lens, is then reflected by the concave mirror, and passes again
through the negative lens to be guided to the optical path
separating mirror; the light reflected by the optical path
separating mirror is reflected by the first field mirror and the
second field mirror and thereafter directly enters the first lens
unit in the second imaging optical system.
[0073] In this configuration, the projection optical system can be
telecentric on the first surface side because the first imaging
optical system comprises the fourth lens unit having the positive
refracting power. Since the first imaging optical system comprises
the negative lens and the concave mirror, adjustment for satisfying
the Petzval's condition can be readily performed by adjusting the
negative lens and the concave mirror.
[0074] In the first aspect of the embodiment, the projection
optical system preferably comprises a first imaging optical system
comprising at least six mirrors for forming a first intermediate
image and a second intermediate image of the first surface; and a
second imaging optical system, which relays the second intermediate
image onto the second surface.
[0075] Since this configuration comprises at least six mirrors, the
first intermediate image and the second intermediate image can be
formed without increase in the total length of the catadioptric
projection optical system, and the good imaging performance can be
achieved throughout the entire region in the exposure area, even in
the case where the object-side and the image-side numerical
apertures of the catadioptric projection optical system are
increased in order to enhance the resolution.
[0076] In the aforementioned configuration, preferably, the first
intermediate image is formed between a mirror that light emerging
from the first surface enters second and a mirror that the light
emerging from the first surface enters fourth, out of the at least
six mirrors in the first imaging optical system.
[0077] In this configuration, the first intermediate image is
formed between the mirror that the light emerging from the first
surface enters second and the mirror that the light emerging from
the first surface enters fourth. Therefore, even in the case where
the object-side and image-side numerical apertures of the
catadioptric projection optical system are increased in order to
enhance the resolution, it is feasible to readily and securely
achieve the optical path separation between the beam toward the
first surface and the beam toward the second surface and to achieve
the good imaging performance throughout the entire region in the
exposure area.
[0078] Incidentally, since it is necessary to form the intermediate
image near the pupil position in order to construct the
catadioptric projection optical system of the single optical axis
according to the first aspect of the embodiment, it is desirable to
construct the projection optical system as a reimaging optical
system. In order to avoid mechanical interference between optical
members while achieving the optical path separation with the
intermediate image being formed near the pupil position of the
first imaging, the pupil diameter of the first imaging needs to be
set as small as possible even in the case where the object-side
numerical aperture is large; therefore, the first imaging optical
system with the small numerical aperture is desirably a
catadioptric system.
[0079] In the first aspect of the embodiment, therefore, the
projection optical system preferably comprises: a first imaging
optical system comprising at least two reflecting mirrors, which
forms an intermediate image of the first surface; and a second
imaging optical system, which forms a final image on the second
surface on the basis of a beam from the intermediate image. In this
case, specifically, the first imaging optical system can be
constructed using a first lens unit with a positive refracting
power, a first reflecting mirror disposed in an optical path
between the first lens unit and the intermediate image, and a
second reflecting mirror disposed in an optical path between the
first reflecting mirror and the intermediate image.
[0080] Preferably, the first reflecting mirror is a concave
reflecting mirror disposed near a pupil plane of the first imaging
optical system, and at least one negative lens is disposed in
back-and-forth optical path (a double optical path) formed by the
concave reflecting mirror. By this configuration wherein the
negative lens is disposed in the back-and-forth optical path formed
by the concave reflecting mirror in the first imaging optical
system, it becomes feasible to well correct for the curvature of
field while readily satisfying the Petzval's condition, and to well
correct for the chromatic aberration as well.
[0081] The negative lens in the back-and-forth optical path is
desirably disposed near the pupil position, but the clear aperture
of the negative lens becomes smaller because the pupil diameter of
the first imaging needs to be kept as small as possible; therefore,
the fluence (=energy amount per unit area and unit pulse) tends to
become higher at the negative lens. Therefore, if the negative lens
is made of silica, a local index change or compaction will become
likely to occur due to volumetric shrinkage under irradiation with
laser light, and, in turn, the imaging performance of the
projection optical system will degrade.
[0082] Likewise, the boundary lens located in the vicinity of the
image plane also has a small clear aperture and the fluence is
likely to become high there. Therefore, if the boundary lens is
made of silica, it will result in likely causing the compaction and
degrading the imaging performance. In the first aspect of the
embodiment, the degradation of imaging performance due to the
compaction can be avoided by a configuration wherein the negative
lens disposed in the back-and-forth optical path formed by the
concave reflecting mirror in the first imaging optical system and
the boundary lens disposed in the vicinity of the image plane in
the second imaging optical system are made of fluorite.
[0083] In the first aspect of the embodiment, the projection
optical system desirably satisfies Condition (1) below. In
Condition (1), F1 is the focal length of the first lens unit, and
Y.sub.0 a maximum image height on the second surface.
5<F1/Y.sub.0<15 (1)
[0084] The range above the upper limit of Condition (1) is
undesirable because the pupil diameter of the first imaging is too
large to avoid mechanical interference between optical members as
described above. On the other hand, the range below the lower limit
of Condition (1) is undesirable because there occurs a large
difference depending upon object heights among angles of incident
light to the reflecting mirror (field angle difference) and it
becomes difficult to achieve correction for aberrations such as
coma and curvature of field. For better demonstrating the effect of
the embodiment, the upper limit of Condition (1) is more preferably
set to 13 and the lower limit thereof to 7.
[0085] In the first aspect of the embodiment, the first lens unit
preferably comprises at least two positive lenses. This
configuration permits the positive refracting power of the first
lens unit to be set to a large value to readily satisfy Condition
(1) and it is thus feasible to well correct for coma, distortion,
astigmatism, and so on.
[0086] It is difficult to produce a reflecting mirror with high
reflectance and high endurance, and use of many reflecting surfaces
will result in loss in optical quantity. In the first aspect of the
embodiment, therefore, where the projection optical system is
applied, for example, to the exposure apparatus and exposure
method, the second imaging optical system is preferably a dioptric
system comprised of only a plurality of transmitting members, in
view of improvement in throughput.
[0087] Fluorite is a crystal material having intrinsic
birefringence, and a transmitting member made of fluorite is
considerably affected by birefringence, particularly, for light of
wavelength of not more than 200 nm. For this reason, an optical
system including such fluorite transmitting members needs to
suppress the degradation of the imaging performance due to
birefringence by combining the fluorite transmitting members of
different orientations of crystal axes, but even such
countermeasures cannot completely suppress the performance
degradation due to birefringence.
[0088] Furthermore, it is known that the refractive index
distribution inside fluorite has high-frequency components, and the
variation in refractive indices including such high-frequency
components causes flare to easily degrade the imaging performance
of the projection optical system; therefore, it is preferable to
avoid use of fluorite as much as possible. For decreasing use of
fluorite as much as possible, therefore, the embodiment is
preferably arranged so that 70% or more of the transmitting members
constituting the second imaging optical system of the dioptric
system are made of silica.
[0089] In the first aspect of the embodiment, desirably, the
effective imaging area has an arcuate shape and the projection
optical system satisfies Condition (2) below. In Condition (2), R
is a radius of curvature of an arc defining the effective imaging
area, and Y.sub.0 a maximum image height on the second surface as
described previously.
1.05<R/Y.sub.0<12 (2)
[0090] In the first aspect of the embodiment, the projection
optical system has the effective imaging area of arcuate shape not
including the optical axis, whereby the optical path separation can
be readily achieved while avoiding the increase in the scale of the
optical system. However, for example, where the projection optical
system is applied to the exposure apparatus and exposure method, it
is difficult to uniformly illuminate an illumination area of
arcuate shape on the mask. Therefore, a method to be adopted is one
of limiting an illumination beam of rectangular shape corresponding
to a rectangular region including the area of the arcuate shape, by
a field stop having an aperture (light transmitting portion) of
arcuate shape. In this case, in order to reduce loss in light
quantity due to the field stop, it is necessary to keep the radius
R of curvature of the arc defining the effective imaging area as
large as possible.
[0091] Namely, the range below the lower limit of Condition (2) is
undesirable because the radius R of curvature is so small that the
beam loss due to the field stop becomes so large as to decrease the
throughput due to reduction of illumination efficiency. On the
other hand, the range above the upper limit of Condition (2) is
undesirable because the radius R of curvature is so large that the
required aberration-corrected area becomes large in order to secure
the effective imaging area in a required width for reduction in
overrun length during scan exposure, so as to result in increase in
the scale of the optical system. For better demonstrating the
effect of the embodiment, the upper limit of Condition (2) is more
preferably set to 8 and the lower limit thereof to 1.07.
[0092] In the catadioptric projection optical system of the
aforementioned type, even in the case where the optical path to the
image plane (second surface) is not filled with the medium like
liquid, when the projection optical system satisfies Condition (2),
it is feasible to avoid the reduction of throughput due to the
decrease of illumination efficiency and to avoid the increase in
the scale of the optical system due to the increase in the required
aberration-corrected area. Where the projection optical system of
the embodiment is applied to the exposure apparatus and exposure
method, it is preferable to use, for example, ArF laser light
(wavelength 193.306 nm) as the exposure light, in view of the
transmittance of the medium (liquid or the like) filled between the
boundary lens and the image plane, the degree of narrowing of the
laser light, and so on.
[0093] The projection optical system according to the second aspect
of the embodiment is a catadioptric projection optical system for
forming an image of a first surface on a second surface,
comprising: a first imaging optical system comprising two mirrors,
which forms an intermediate image of the first surface; and a
second imaging optical system, which forms the intermediate image
on the second surface, wherein the second imaging optical system
comprises the following components in order of passage of a ray
from the intermediate image side: a first field mirror of a concave
shape; a second field mirror; a first lens unit comprising at least
two negative lenses and having a negative refracting power; a
second lens unit having a positive refracting power; an aperture
stop; and a third lens unit having a positive refracting power.
[0094] Since in this configuration the intermediate image of the
first surface is formed in the first imaging optical system, it is
feasible to readily and securely achieve the optical path
separation between the beam toward the first surface and the beam
toward the second surface, even in the case where the numerical
apertures of the catadioptric projection optical system are
increased. Since the second imaging optical system comprises the
first lens unit having the negative refracting power, the total
length of the catadioptric projection optical system can be
decreased and the adjustment for satisfying the Petzval's condition
can be readily performed. Furthermore, the first lens unit relieves
the variation due to the difference of field angles of the beam
expanded by the first field mirror, so as to suppress occurrence of
aberration. Therefore, even in the case where the object-side and
image-side numerical apertures of the catadioptric projection
optical system are increased in order to enhance the resolution,
good imaging performance can be achieved throughout the entire
region in the exposure area.
[0095] In the projection optical system according to the second
aspect of the embodiment, preferably, the first imaging optical
system comprises a fourth lens unit having a positive refracting
power, a negative lens, a concave mirror, and an optical path
separating mirror; and the first imaging optical system is arranged
as follows: light traveling in the first imaging optical system
passes through the fourth lens unit and the negative lens, is then
reflected by the concave mirror, and passes again through the
negative lens to be guided to the optical path separating mirror;
the light reflected by the optical path separating mirror is
reflected by the first field mirror and the second field mirror and
thereafter directly enters the first lens unit in the second
imaging optical system.
[0096] Since in this configuration the first imaging optical system
comprises the fourth lens unit having the positive refracting
power, the projection optical system can be made telecentric on the
first surface side. Since the first imaging optical system
comprises the negative lens and the concave mirror, the adjustment
for satisfying the Petzval's condition can be readily performed by
adjusting the negative lens and the concave mirror.
[0097] In the projection optical system according to the second
aspect of the embodiment, preferably, the first field mirror
outputs light entering the first field mirror, so as to bend the
light into a direction toward the optical axis of the catadioptric
projection optical system.
[0098] In the projection optical system according to the second
aspect of the embodiment, preferably, the second field mirror has a
convex shape.
[0099] According to these configurations, a ray incident to the
first field mirror is outputted as bent into a direction toward the
optical axis of the catadioptric system, whereby the second field
mirror can be constructed in a compact size even in the case where
the numerical apertures of the catadioptric projection optical
system are increased. Accordingly, the optical path separation
between the beam toward the first surface and the beam toward the
second surface can be readily performed even in the case where the
object-side and image-side numerical apertures are increased in
order to enhance the resolution.
[0100] In the projection optical system according to the second
aspect of the embodiment, preferably, the two mirrors in the first
imaging optical system are a mirror of a concave shape and a mirror
of a convex shape which are arranged in order of incidence of light
from the first surface, and wherein the second field mirror in the
second imaging optical system is a mirror of a convex shape.
[0101] According to this configuration, the two mirrors in the
first imaging optical system are of the concave shape and the
convex shape, and the second field mirror has the convex shape;
therefore, it is feasible to readily and securely guide the beam
emerging from the first imaging optical system, to the second
imaging optical system.
[0102] In the projection optical system according to the second
aspect of the embodiment, the aperture stop is disposed between the
first field mirror and the second surface, and the projection
optical system satisfies the following condition:
0.17<Ma/L<0.6,
[0103] where Ma is a distance on an optical axis between the first
field mirror and the second surface, and L a distance between the
first surface and the second surface.
[0104] According to this configuration, Ma/L is larger than 0.17,
and it is thus feasible to avoid mechanical interference of the
first field mirror with the first lens unit and with the second
lens unit. Since Ma/L is smaller than 0.6, it is feasible to avoid
an increase in the total length and an increase in the size of the
catadioptric projection optical system.
[0105] In the projection optical system according to the second
aspect of the embodiment, preferably, the first lens unit in the
second imaging optical system has at least one aspherical lens.
[0106] According to this configuration, at least one of optical
elements constituting the first lens unit is a lens of aspherical
shape and thus good imaging performance can be achieved throughout
the entire region in the exposure area, even in the case where the
object-side and image-side numerical apertures are increased.
[0107] The projection optical system according to the third aspect
of the embodiment is a catadioptric projection optical system,
which forms an image of a first surface on a second surface,
comprising: a first unit disposed in an optical path between the
first surface and the second surface and having a positive
refracting power; a second unit disposed in an optical path between
the first unit and the second surface and comprising at least four
mirrors; a third unit disposed in an optical path between the
second unit and the second surface, comprising at least two
negative lenses, and having a negative refracting power; and a
fourth unit disposed in an optical path between the third unit and
the second surface, comprising at least three positive lenses, and
having a positive refracting power, wherein an intermediate image
is formed in the second unit and wherein an aperture stop is
provided in the fourth unit.
[0108] In the projection optical system according to the third
aspect of the embodiment, the intermediate image of the first
surface is formed in the second unit and it is thus feasible to
readily and securely achieve the optical path separation between
the beam toward the first surface and the beam toward the second
surface, even in the case where the numerical apertures of the
catadioptric projection optical system are increased. Since the
projection optical system comprises the third unit having the
negative refracting power, the total length of the catadioptric
projection optical system can be decreased and the adjustment for
satisfying the Petzval's condition can be readily performed.
Therefore, the good imaging performance can be achieved throughout
the entire region in the exposure area, even in the case where the
object-side and image-side numerical apertures of the catadioptric
projection optical system are increased in order to enhance the
resolution.
[0109] In the projection optical system according to the third
aspect of the embodiment, preferably, the second unit comprises the
following components in order of incidence of light from the first
surface: a first reflecting mirror of a concave shape; a second
reflecting mirror of a convex shape; a third reflecting mirror of a
concave shape; and a fourth reflecting mirror of a convex
shape.
[0110] According to this configuration, the second unit comprises
the concave mirror, the convex mirror, the concave mirror, and the
convex mirror in order of incidence of light from the first
surface, and it is thus feasible to readily and securely guide the
beam emerging from the first imaging optical system, to the second
imaging optical system.
[0111] In the projection optical system according to the third
aspect of the embodiment, preferably, the second unit comprises at
least one negative lens, and an optical element located nearest to
the third unit in the optical path of the second unit is the fourth
reflecting mirror or a double pass lens through which light passes
twice.
[0112] According to this configuration, since the optical element
located nearest to the third unit in the optical path of the second
unit is the fourth reflecting mirror or the double pass lens
through which the light passes twice, the adjustment for satisfying
the Petzval's condition can be readily performed by adjusting the
lens in the third unit having the negative refracting power, and
the fourth reflecting mirror or the double pass lens.
[0113] In the projection optical system according to the third
aspect of the embodiment, preferably, the third reflecting mirror
outputs light entering the third reflecting mirror, so as to bend
the light into a direction toward the optical axis of the
catadioptric projection optical system.
[0114] This configuration enables miniaturization of the fourth
reflecting mirror because a ray incident to the third reflecting
mirror is outputted as bent into a direction toward the optical
axis of the catadioptric projection optical system. Therefore, it
is feasible to readily and securely achieve the optical path
separation between the beam toward the first surface and the beam
toward the second surface, even in the case where the object-side
and image-side numerical apertures are increased in order to
enhance the resolution.
[0115] In the projection optical system according to the third
aspect of the embodiment, the aperture stop is disposed between the
third reflecting mirror and the second surface, and the projection
optical system satisfies the following condition:
0.17<Ma/L<0.6,
[0116] where Ma is a distance on an optical axis between the third
reflecting mirror and the second surface, and L a distance between
the first surface and the second surface.
[0117] In this configuration, Ma/L is larger than 0.17, and it is
thus feasible to avoid mechanical interference of the third
reflecting mirror with the second unit and with the third unit.
Since Ma/L is smaller than 0.6, it is feasible to avoid an increase
in the total length and an increase in the size of the catadioptric
projection optical system.
[0118] In the projection optical system according to the third
aspect of the embodiment, the third unit comprises at least one
aspherical lens. Since in this configuration at least one of
optical elements constituting the third unit is the aspherical
lens, good imaging performance can be achieved throughout the
entire region in the exposure area, even in the case where the
object-side and image-side numerical apertures are increased.
[0119] The projection optical system according to the fourth aspect
of the embodiment is a catadioptric projection optical system,
which forms an image of a first surface on a second surface, the
projection optical system comprising: a first imaging optical
system comprising at least six mirrors, which forms a first
intermediate image and a second intermediate image of the first
surface; and a second imaging optical system, which relays the
second intermediate image onto the second surface.
[0120] Since the projection optical system according to the fourth
aspect of the embodiment comprises at least six mirrors, the first
intermediate image and the second intermediate image can be formed,
without increase in the total length of the catadioptric projection
optical system, and good imaging performance can be achieved
throughout the entire region in the exposure area, even in the case
where the object-side and image-side numerical apertures of the
catadioptric projection optical system are increased in order to
enhance the resolution.
[0121] In the projection optical system according to the fourth
aspect of the embodiment, preferably, the first intermediate image
is formed between a mirror that light emerging from the first
surface enters second and a mirror that the light emerging from the
first surface enters fourth, out of said at least six mirrors in
the first imaging optical system.
[0122] In this configuration, the first intermediate image is
formed between the mirror that the light emerging from the first
surface enters second and the mirror that the light emerging from
the first surface enters fourth. Therefore, it is feasible to
readily and securely achieve the optical path separation between
the beam toward the first surface and the beam toward the second
surface and to obtain good imaging performance throughout the
entire region in the exposure area, even in the case where the
object-side and image-side numerical apertures of the catadioptric
projection optical system are increased in order to enhance the
resolution.
[0123] In the projection optical system according to the fourth
aspect of the embodiment, preferably, the first imaging optical
system comprises a field lens unit comprised of a transmitting
optical element and having a positive refracting power, and the at
least six mirrors are arranged so as to continuously reflect light
transmitted by the field lens unit.
[0124] Since in this configuration the first imaging optical system
comprises the field lens unit with the positive refracting power
comprised of the transmitting optical element, distortion or the
like can be corrected for by this field lens unit and the
projection optical system can be made telecentric on the first
surface side. Since no lens is disposed in optical paths between
the at least six mirrors, it is feasible to secure a region for
holding each mirror and to readily hold each mirror. Since the
light is continuously reflected by each mirror, the Petzval's
condition can be readily satisfied by adjusting each mirror.
[0125] In the projection optical system according to the fourth
aspect of the embodiment, the first imaging optical system
preferably comprises a field lens unit comprised of a transmitting
optical element and having a positive refracting power, and the
first imaging optical system preferably comprises at least one
negative lens between a mirror that light emerging from the first
surface enters first and a mirror that the light emerging from the
first surface enters sixth, out of the at least six mirrors.
[0126] Since in this configuration the first imaging optical system
comprises the field lens unit with the positive refracting power
comprised of the transmitting optical element, the projection
optical system can be made telecentric on the first surface side.
Since the optical system comprises at least one negative lens
between the mirror that the light emerging from the first surface
enters first and the mirror that the light emerging from the first
surface enters sixth, correction for chromatic aberration can be
readily made by adjusting this negative lens and it is easy to make
such adjustment as to satisfy the Petzval's condition.
[0127] In the projection optical system according to the fourth
aspect of the embodiment, preferably, every optical element
constituting the second imaging optical system is a transmitting
optical element to form a reduced image of the first surface on the
second surface.
[0128] This configuration is free of the optical path separation
load because every optical element forming the second imaging
optical system is a transmitting optical element. Therefore, the
image-side numerical aperture of the catadioptric projection
optical system can be increased and the reduced image can be formed
at a high reduction rate on the second surface. It is also feasible
to readily correct for coma and spherical aberration.
[0129] In the projection optical system according to the fourth
aspect of the embodiment, preferably, the second imaging optical
system comprises the following components in order of passage of
light emerging from the first imaging optical system: a first lens
unit having a positive refracting power; a second lens unit having
a negative refracting power; a third lens unit having a positive
refracting power; an aperture stop; and a fourth lens unit having a
positive refracting power.
[0130] According to this configuration, the first lens unit with
the positive refracting power, the second lens unit with the
negative refracting power, the third lens unit with the positive
refracting power, the aperture stop, and the fourth lens unit with
the positive refracting power constituting the second imaging
optical system advantageously function to satisfy the Petzval's
condition. It is also feasible to avoid an increase in the total
length of the catadioptric projection optical system.
[0131] In the projection optical system according to the fourth
aspect of the embodiment, a mirror disposed at a position where
light emerging from the first surface is most distant from the
optical axis of the catadioptric projection optical system, out of
the at least six mirrors is preferably a mirror of a concave shape,
and the aperture stop is preferably disposed between the mirror of
the concave shape and the second surface. Preferably, the
projection optical system satisfies the following condition:
0.2<Mb/L<0.7,
[0132] where Mb is a distance on an optical axis between the mirror
of the concave shape and the second surface and L a distance
between the first surface and the second surface.
[0133] In this configuration, since Mb/L is larger than 0.2, it is
feasible to avoid mechanical interference of the mirror of the
concave shape located at the position most distant from the optical
axis of the catadioptric projection optical system, with the first
lens unit, the second lens unit, and the third lens unit. Since
Mb/L is smaller than 0.7, it is feasible to avoid an increase in
the total length and an increase in the size of the catadioptric
projection optical system.
[0134] In the projection optical system according to the fourth
aspect of the embodiment, preferably, the second lens unit and the
fourth lens unit have at least one aspherical lens.
[0135] Since in this configuration at least one of optical elements
constituting the second lens unit and the fourth lens unit is a
lens of aspherical shape, it is feasible to readily make the
aberration correction and to avoid an increase in the total length
of the catadioptric projection optical system. Therefore, good
imaging performance can be achieved throughout the entire region in
the exposure area, even in the case where the object-side and
image-side numerical apertures are increased.
[0136] The projection optical system according to the fourth aspect
of the embodiment is preferably as follows: the catadioptric
projection optical system is a thrice-imaging (three time) optical
system, which forms the first intermediate image being an
intermediate image of the first surface, and the second
intermediate image being an image of the first intermediate image,
in an optical path between the first surface and the second
surface.
[0137] In this configuration, the projection optical system is the
thrice-imaging optical system, whereby the first intermediate image
is an inverted image of the first surface, the second intermediate
image is an erect image of the first surface, and the image formed
on the second surface is an inverted image. Therefore, in the case
where the catadioptric projection optical system is mounted on the
exposure apparatus and where an exposure is carried out with
scanning of the first surface and the second surface, the scanning
direction of the first surface can be made opposite to the scanning
direction of the second surface, and it is easy to perform such
adjustment as to decrease a change in the center of gravity of the
entire exposure apparatus. It is also feasible to reduce vibration
of the catadioptric projection optical system caused by the change
in the center of gravity of the entire exposure apparatus, and good
imaging performance can be achieved throughout the entire region in
the exposure area.
[0138] The projection optical systems according to the second
aspect to the fourth aspect of the embodiment are characterized in
that a lens surface on the first surface side of a lens located
nearest to the second surface out of lenses in the catadioptric
projection optical system has a positive refracting power, and in
that, where a refractive index of an atmosphere in the catadioptric
projection optical system is 1, a medium having a refractive index
larger than 1.1 is interposed in an optical path between the lens
nearest to the second surface, and the second surface.
[0139] In this configuration, the medium having the refractive
index larger than 1.1 is interposed in the optical path between the
lens located nearest to the second surface in the catadioptric
projection optical system and the second surface, the wavelength of
exposure light in the medium is 1/n times that in air where the
refractive index of the medium is n, and thus the resolution can be
enhanced.
[0140] The projection optical systems according to the second
aspect to the fourth aspect of the embodiment are preferably
configured so that an optical axis of every optical element with a
predetermined refracting power in the catadioptric projection
optical system is arranged substantially on a single straight line,
and so that a region of an image formed on the second surface by
the catadioptric projection optical system is an off-axis region
not including the optical axis.
[0141] According to this configuration, the optical axis of every
optical element in the catadioptric projection optical system is
arranged substantially on the single straight line, and it is thus
feasible to reduce the degree of difficulty of production in
production of the catadioptric projection optical system and to
readily perform relative adjustment of each optical member.
[0142] The exposure apparatus according to the fifth aspect of the
embodiment is an exposure apparatus for effecting an exposure of a
pattern formed on a mask, onto a photosensitive substrate,
comprising: an illumination system, which illuminates the mask set
on the first surface; and the projection optical system according
to any one of the first aspect to the fourth aspect of the
embodiment, which forms an image of the pattern formed on the mask,
on the photosensitive substrate set on the second surface.
[0143] According to this configuration, the exposure apparatus
comprises the compact catadioptric projection optical system with
the large numerical aperture, and thus the exposure apparatus is
able to suitably perform an exposure of a fine pattern on the
photosensitive substrate.
[0144] In the exposure apparatus according to the fifth aspect of
the embodiment, preferably, the illumination system supplies
illumination light which is s-polarized light with respect to the
second surface. This configuration enhances the contrast of the
image formed on the photosensitive substrate and secures a large
depth of focus (DOF). Particularly, the projection optical systems
according to the first aspect to the fourth aspect of the
embodiment permit the optical path separation to be achieved
without use of an optical path deflecting mirror (bending mirror)
having a function of deflecting the optical axis. There is a high
risk of causing a large phase difference between p-polarized light
and s-polarized light reflected by the optical path deflecting
mirror, and in use of the optical path deflecting mirror, it
becomes difficult to supply illumination light of s-polarized light
with respect to the second surface, because of this reflection
phase difference; namely, there arises a problem that the
illumination light is not s-polarized light on the second surface
even through generation of polarization in the circumferential
direction with respect to the optical axis of the illumination
optical device. In contrast to it, this problem hardly occurs in
the projection optical systems according to the first aspect to the
fourth aspect of the embodiment.
[0145] In the exposure apparatus according to the fifth aspect of
the embodiment, preferably, the projection exposure of the pattern
of the mask onto the photosensitive substrate is performed while
moving the mask and the photosensitive substrate along a
predetermined direction relative to the projection optical
system.
[0146] The exposure method according to the sixth aspect of the
embodiment is an exposure method of effecting an exposure of a
pattern formed on a mask, onto a photosensitive substrate,
comprising: an illumination step of illuminating the mask on which
the predetermined pattern is formed; and an exposure step of
performing an exposure of the pattern of the mask set on the first
surface, onto the photosensitive substrate set on the second
surface, using the projection optical system according to any one
of the first aspect to the fourth aspect of the embodiment.
[0147] In this configuration, the exposure is performed by the
exposure apparatus including the compact catadioptric projection
optical system with the large numerical aperture, whereby a fine
pattern can be suitably exposed.
[0148] Embodiments of the embodiment will be described below with
reference to the drawings.
[0149] FIG. 1 is a schematic configuration diagram showing an
embodiment of the exposure apparatus of the embodiment.
[0150] In FIG. 1, the exposure apparatus EX has a reticle stage RST
supporting a reticle R (mask), a wafer stage WST supporting a wafer
W as a substrate, an illumination optical system IL for
illuminating the reticle R supported by the reticle stage RST, with
exposure light EL, a projection optical system PL for performing a
projection exposure of an image of a pattern on the reticle R
illuminated with the exposure light EL, onto the wafer W supported
by the wafer stage WST, a liquid supply device 1 for supplying a
liquid 50 onto the wafer W, a recovery device 20 for collecting the
liquid 50 flowing out of the wafer W, and a controller CONT for
totally controlling the overall operation of the exposure apparatus
EX.
[0151] The present embodiment will be described using as an example
a case where the exposure apparatus EX is a scanning exposure
apparatus for performing an exposure of a pattern formed on the
reticle R, onto the wafer W while synchronously moving the reticle
R and wafer W along a scanning direction (so called a scanning
stepper). In the description below, a direction coinciding with the
optical axis AX of the projection optical system PL is defined as a
Z-axis direction, the synchronous movement direction (scanning
direction) of the reticle R and wafer W in the plane normal to the
Z-axis direction, as an X-axis direction, and a direction
(non-scanning direction) normal to the Z-axis direction and the
Y-axis direction as a Y-axis direction. Directions around the
X-axis, around the Y-axis, and around the Z-axis are defined as
.theta.X, .theta.Y, and .theta.Z directions, respectively. The
"wafer" encompasses a semiconductor wafer coated with a resist, and
the "reticle" encompasses a mask with a device pattern to be
projected at an enlargement, reduction, or unit magnification onto
the wafer.
[0152] The illumination optical system IL is a system for
illuminating the reticle R supported by the reticle stage RST, with
the exposure light EL, based on the exposure light from a light
source 100 for supplying the illumination light in the ultraviolet
region. The illumination optical system IL has an optical
integrator for uniformizing the illuminance of a beam emitted from
the light source 100, a condenser lens for condensing the exposure
light EL from the optical integrator, a relay lens system, a
variable field stop for defining an illumination area in a slit
shape on the reticle R with the exposure light EL, and so on. Here
the illumination optical system IL is provided with an s-polarized
light converter 110 for converting linearly polarized light from
the light source 100, into polarized light as s-polarized light
with respect to the reticle R (wafer W), without substantial loss
of light quantity. The s-polarized light converter of this type is
disclosed, for example, in Japanese Patent No. 3246615.
[0153] A predetermined illumination area on the reticle R is
illuminated with the exposure light EL of a uniform illuminance
distribution by the illumination optical system IL. The exposure
light EL emitted from the illumination optical system IL is, for
example, deep ultraviolet light (DUV light) such as the emission
lines (g-line, h-line, and i-line) in the ultraviolet region from a
mercury lamp and KrF excimer laser light (wavelength 248 nm), or
vacuum ultraviolet light (VUV light) such as ArF excimer laser
light (wavelength 193 nm) and F2 laser light (wavelength 157 nm).
The present embodiment is assumed to use the ArF excimer laser
light.
[0154] The reticle stage RST is a stage supporting the reticle R
and is two-dimensionally movable in the plane normal to the optical
axis AX of the projection optical system PL, i.e., within the XY
plane and finely rotatable in the .theta.Z direction. The reticle
stage RST is driven by a reticle stage driving device RSTD such as
a linear motor. The reticle stage driving device RSTD is controlled
by the controller CONT. The two-dimensional position and an angle
of rotation of the reticle R on the reticle stage RST are measured
in real time by a laser interferometer, and the result of the
measurement is fed to the controller CONT. The controller CONT
drives the reticle stage driving device RSTD on the basis of the
measurement result of the laser interferometer to position the
reticle R supported by the reticle stage RST.
[0155] The projection optical system PL is one for performing a
projection exposure of a pattern on the reticle R at a
predetermined projection magnification .beta. onto the wafer W, and
is composed of a plurality of optical elements (lenses), which are
supported by a lens barrel PK as a metal member. In the present
embodiment, the projection optical system PL is a reduction system
with the projection magnification .beta. of 1/4 or 1/5, for
example. The projection optical system PL may be either of a 1:1
system and an enlarging system. An optical element (lens) 60 is
exposed from the lens barrel PK on the distal end side (wafer W
side) of the projection optical system PL of the present
embodiment. This optical element 60 is detachably (replaceably)
attached to the lens barrel PK.
[0156] The wafer stage WST is a stage supporting the wafer W, and
is provided with a Z-stage 51 holding the wafer W through the wafer
holder, an XY stage 52 supporting the Z-stage 51, and a base 53
supporting the XY stage 52. The wafer stage WST is driven by a
wafer stage driving device WSTD such as a linear motor. The wafer
stage driving device WSTD is controlled by the controller CONT. As
the Z-stage 51 is driven, the wafer W held by the Z-stage 51 is
controlled as to the position in the Z-axis direction (focus
position) and as to the position in the .theta.X and .theta.Y
directions. As the XY stage 52 is driven, the wafer W is controlled
as to the position in the XY directions (the position in the
directions substantially parallel to the image plane of the
projection optical system PL). Namely, the Z-stage 51 controls the
focus position and angle of inclination of the wafer W to match the
surface of the wafer W with the image plane of the projection
optical system PL by the autofocus method and autoleveling method,
and the XY stage 52 positions the wafer W in the X-axis direction
and in the Y-axis direction. It is needless to mention that the
Z-stage and XY stage may be integrally arranged.
[0157] A moving mirror 54 is provided on the wafer stage WST
(Z-stage 51). An interferometer 55 is disposed at the position
opposite to the moving mirror 54. The two-dimensional position and
the angle of rotation of the wafer W on the wafer stage WST are
measured in real time by the laser interferometer 55, and the
result of the measurement is fed to the controller CONT. The
controller CONT drives the wafer stage driving device WSTD on the
basis of the measurement result of the laser interferometer 55 to
position the wafer W supported by the wafer stage WST.
[0158] The present embodiment adopts the liquid immersion method,
in order to substantially shorten the exposure wavelength so as to
improve the resolution and substantially widen the depth of focus.
For this reason, the space between the surface of the wafer W and
the end surface (lower face) 7 of the optical element (lens) 60 on
the wafer W side of the projection optical system PL is filled with
a predetermined liquid 50 at least during the period of
transcribing the image of the pattern of the reticle R onto the
wafer W. As described above, the lens 60 is exposed on the end
surface side of the projection optical system PL and the liquid 50
is arranged in contact with only the lens 60. This prevents
corrosion or the like of the lens barrel PK made of metal. Since
the end surface 7 of the lens 60 is sufficiently smaller than the
lens barrel PK of the projection optical system PL and the wafer W
and since the liquid 50 is kept in contact with only the lens 60 as
described above, the liquid 50 is arranged to be locally filled on
the image plane side of the projection optical system PL. Namely,
the liquid-immersed portion between the projection optical system
PL and the wafer W is sufficiently smaller than the wafer W. The
present embodiment uses pure water as the liquid 50. Pure water can
transmit not only the ArF excimer laser light, but also the
exposure light EL if the exposure light EL is the deep ultraviolet
light (DUV light) such as the emission lines (g-line, h-line, and
i-line) in the ultraviolet region emitted from a mercury lamp and
the KrF excimer laser light (wavelength 248 nm), for example.
[0159] The exposure apparatus EX is provided with the liquid
supplying device 1 for supplying the predetermined liquid 50 to the
space 56 between the end surface (distal end face of lens 60) 7 of
the projection optical system PL and the wafer W, and a liquid
recovery device 2 as a second recovery device for collecting the
liquid 50 in the space 56, i.e., the liquid 50 on the wafer W. The
liquid supplying device 1 is a device for locally filling the space
on the image plane side of the projection optical system PL with
the liquid 50, and is provided with a tank for storing the liquid
50, a compression pump, and a temperature regulator for regulating
the temperature of the liquid 50 to be supplied to the space 56.
One end of supply tube 3 is connected to the liquid supplying
device 1 and the other end of the supply tube 3 is connected to a
supply nozzle 4. The liquid supplying device 1 supplies the liquid
50 to the space 56 through the supply tube 3 and supply nozzle
4.
[0160] The liquid recovery device 2 is provided with a suction
pump, a tank for storing the collected liquid 50, and so on. One
end of recovery tube 6 is connected to the liquid recovery device 2
and the other end of the recovery tube 6 is connected to a
collection nozzle 5. The liquid recovery device 2 collects the
liquid 50 in the space 56 through the collection nozzle 5 and
recovery tube 6. For filling the space 56 with the liquid 50, the
controller CONT drives the liquid supplying device 1 to supply the
liquid 50 in a predetermined amount per unit time through the
supply tube 3 and supply nozzle 4 to the space 56, and drives the
liquid recovery device 2 to collect the liquid 50 in a
predetermined amount per unit time through the collection nozzle 5
and recovery tube 6 from the space 56. This results in placing the
liquid 50 in the space 56 between the end surface 7 of the
projection optical system PL and the wafer W to form a
liquid-immersed portion. Here the controller CONT can arbitrarily
set the liquid supply amount per unit time to the space 56 by
controlling the liquid supplying device 1, and can also arbitrarily
set the liquid collection amount per unit time from on the wafer W
by controlling the liquid recovery device 2.
[0161] FIG. 2 is an illustration showing a positional relation
between the optical axis and an effective exposure area of arcuate
shape formed on a wafer in the present embodiment. In the present
embodiment, as shown in FIG. 2, a region well corrected for
aberration, i.e., aberration-corrected region AR is defined in an
arcuate shape by a circle with an outside radius (radius) Ro
centered around the optical axis AX, a circle with an inside radius
(radius) Ri centered around the optical axis AX, and two line
segments parallel to the X-direction, spaced by a distance H. Then
an effective exposure region (effective imaging area) ER is set in
an arcuate shape by two arcs with a radius R of curvature spaced in
the X-direction, and two line segments of the length D parallel
with the X-direction as spaced by the distance H, so as to be
substantially inscribed in the aberration-corrected region AR of
arcuate shape.
[0162] In this manner, the entire effective imaging area ER of the
projection optical system PL exists in the region off the optical
axis AX. The size along the Y-direction of the effective imaging
area ER of arcuate shape is H, and the size along the X-direction
is D. Although not shown, the illumination area of arcuate shape
(i.e., the effective illumination area) having the size and shape
optically corresponding to the effective exposure region ER of
arcuate shape is thus formed not including the optical axis AX, on
the reticle R.
[0163] The exposure apparatus of the present embodiment is arranged
so that the interior of the projection optical system PL is kept in
an airtight state between an optical member located nearest to the
reticle among the optical members forming the projection optical
system PL (which is lens L11 in the first and second examples, lens
L1 in the third and fifth examples, lens L21 in the fourth and
sixth examples, or lens L51 in the seventh example) and a boundary
lens Lb (lens L217 in the first and second examples, lens L18 in
the third example, lens L36 in the fourth example, lens L20 in the
fifth example, lens L41 in the sixth example, or lens L70 in the
seventh example) and so that the gas inside the projection optical
system PL is replaced with an inert gas such as helium gas or
nitrogen, or the inside is kept in a substantially vacuum state.
Furthermore, the members such as the reticle R and reticle stage RS
are disposed in the narrow optical path between the illumination
optical system IL and the projection optical system PL, and an
interior of a casing (not shown) for hermetically enclosing the
reticle R, the reticle stage RS, etc. is filled with an inert gas
such as nitrogen or helium gas, or kept in a substantially vacuum
state.
[0164] FIG. 3 is an illustration schematically showing a
configuration between the boundary lens and the wafer in the first
example of the present embodiment. With reference to FIG. 3, the
boundary lens Lb in the first example has a convex surface kept
toward the reticle (first surface). In other words, the
reticle-side surface Sb of the boundary lens Lb has a positive
refracting power. The optical path between the boundary lens Lb and
the wafer W is filled with a medium Lm having the refractive index
larger than 1.1. In the first example, deionized water is used as
the medium Lm.
[0165] FIG. 4 is an illustration schematically showing a
configuration between the boundary lens and the wafer in the second
example of the present embodiment. With reference to FIG. 4, the
boundary lens Lb in the second example also has a convex surface
kept toward the reticle and the reticle-side surface Sb thereof has
a positive refracting power as in the first example. However, the
second example is different from the first example in that a
plane-parallel plate Lp is detachably arranged in the optical path
between the boundary lens Lb and the wafer W and in that the
optical path between the boundary lens Lb and the plane-parallel
plate Lp and the optical path between the plane-parallel plate Lp
and the wafer W are filled with the medium Lm having the refractive
index larger than 1.1. In the second example deionized water is
also used as the medium Lm as in the first example.
[0166] The present embodiment is arranged so that during an
exposure by the step-and-scan method of performing a scanning
exposure while moving the wafer W relative to the projection
optical system PL, the liquid medium Lm is continuously filled in
the optical path between the boundary lens Lb of the projection
optical system PL and the wafer W from start to end of the scanning
exposure. Another potential configuration is such that the wafer
holder table WT is constructed in a chamber shape so as to
accommodate the liquid (medium Lm) and that the wafer W is
positioned and held by vacuum suction in the center of the inner
bottom part thereof (in the liquid), as in the technology disclosed
in Japanese Patent Application Laid-Open No. 10-303114, for
example. In this configuration, the distal end of the lens barrel
of the projection optical system PL is arranged to reach the inside
of the liquid and, consequently, the wafer-side optical surface of
the boundary lens Lb reaches the inside of the liquid.
[0167] In this manner, an atmosphere with little absorption of the
exposure light is formed throughout the entire optical path from
the light source 100 to the substrate P. As described above, the
illumination area on the reticle R and the exposure region (i.e.,
the effective exposure region ER) on the wafer W are of the arcuate
shape extending in the X-direction. Therefore, the positions of the
reticle R and substrate W are controlled using the reticle stage
controller RSTD, the substrate stage driving device, the laser
interferometers, etc. to synchronously move (scan) the reticle
stage RST and the substrate stage WS, in turn, the reticle R and
substrate (wafer) W along the X-direction, whereby the scanning
exposure of the reticle pattern is performed in the exposure region
having a width equal to the Y-directional size H of the effective
exposure region ER and a length according to a scan amount
(movement amount) of the substrate W, on the substrate W.
[0168] In each example, an aspherical surface is expressed by
mathematical expression (a) below, where y represents a height in a
direction normal to the optical axis, z a distance (sag) along the
optical axis from a tangent plane at an apex of the aspherical
surface to a position on the aspherical surface at the height y, r
a radius of curvature at the apex, .kappa. a conical coefficient,
and C.sub.n aspherical coefficients of order n. In each example, a
lens surface formed in aspherical shape is provided with mark * on
the right side to a surface number.
z=(y.sup.2/r)/[1+{1-(1+.kappa.)y.sup.2/r.sup.2}.sup.1/2]+c.sub.4y.sup.4+-
c.sub.6y.sup.6+c.sub.8y.sup.8+c.sub.10y.sup.10+c.sub.12y.sup.12+c.sub.14y.-
sup.14+c.sub.16y.sup.16+c.sub.18y.sup.18+c.sub.20y.sup.20 (a)
[0169] In the first and second examples, the values of the
aspherical coefficients C.sub.16 to C.sub.20 are 0, and thus the
description thereof is omitted.
[0170] In each example, the projection optical system PL is
composed of a first imaging optical system G1 for forming an
intermediate image (or an optically conjugate point) of the pattern
of the reticle R disposed on the object plane (first surface), and
a second imaging optical system G2 for forming a reduced image (or
an optically conjugate point) of the reticle pattern on the wafer W
disposed on the image plane (second surface) on the basis of light
from the intermediate image. Here the first imaging optical system
G1 is a catadioptric system including a first concave reflecting
mirror CM1 and a second concave reflecting mirror CM2, and the
second imaging optical system G2 a dioptric system.
First Example
[0171] FIG. 5 is an illustration showing a lens configuration of
the projection optical system according to the first example of the
present embodiment. With reference to FIG. 5, in the projection
optical system PL according to the first example, the first imaging
optical system G1 is composed of the following components arranged
in order from the reticle side along the traveling direction of
light: a biconvex lens L11 whose convex surface of aspherical shape
is kept toward the wafer; a biconvex lens L12; a negative meniscus
lens L13 whose concave surface of aspherical shape is kept toward
the reticle; and a first concave reflecting mirror CM1. In the
first imaging optical system G1, a reflecting surface of second
concave reflecting mirror CM2 for reflecting the light reflected by
the first concave reflecting mirror CM1 and transmitted by the
negative meniscus lens L13, toward the second imaging optical
system G2 is placed in a region not including the optical axis AX
between the biconvex lens L12 and the negative meniscus lens L13.
Therefore, the biconvex lens L11 and the biconvex lens L12
constitute a first lens unit having a positive refracting power.
The first concave reflecting mirror CM1 constitutes a concave
reflecting mirror disposed near the pupil plane of the first
imaging optical system G1.
[0172] On the other hand, the second imaging optical system G2 is
composed of the following components in order from the reticle side
along the traveling direction of light: a positive meniscus lens
L21 whose concave surface is kept toward the reticle; a biconvex
lens L22; a positive meniscus lens L23 whose concave surface of
aspherical shape is kept toward the wafer; a negative meniscus lens
L24 whose convex surface of aspherical shape is kept toward the
reticle; a negative meniscus lens L25 whose convex surface is kept
toward the reticle; a biconcave lens L26 whose concave surface of
aspherical shape is kept toward the reticle; a positive meniscus
lens L27 whose concave surface is kept toward the reticle; a
negative meniscus lens L28 whose convex surface of aspherical shape
is kept toward the reticle; a biconvex lens L29; a biconvex lens
L210; a positive meniscus lens L211 whose convex surface is kept
toward the reticle; an aperture stop AS; a positive meniscus lens
L212 whose concave surface is kept toward the reticle; a biconvex
lens L213; a positive meniscus lens L214 whose concave surface of
aspherical shape is kept toward the wafer; a positive meniscus lens
L215 whose convex surface is kept toward the reticle; a positive
meniscus lens L216 whose concave surface of aspherical shape is
kept toward the wafer; and a planoconvex lens L217 (boundary lens
Lb) whose plane is kept toward the wafer.
[0173] In the first example, all the transmitting members (lenses)
and all the reflecting members with a power (the first concave
reflecting mirror CM1 and the second concave reflecting mirror CM2)
constituting the projection optical system PL are arranged along
the single optical axis AX. Specifically, 100% of the transmitting
members forming the second imaging optical system G2 are made of
silica. The optical path between the planoconvex lens L217 as the
boundary lens Lb and the wafer W is filled with the medium Lm
consisting of deionized water. In the first example, the light from
the reticle R passes through the lenses L11 to L13 to enter the
first concave reflecting mirror CM1. The light reflected by the
first concave reflecting mirror CM1 travels via the lens L13 and
the second concave reflecting mirror CM2 to form an intermediate
image of the reticle R near the first concave reflecting mirror
CM1. The light reflected by the second concave reflecting mirror
CM2 travels through the lenses L21 to L217 (Lb) to form a reduced
image of the reticle R on the wafer W.
[0174] In the first example, all the transmitting members (lenses)
forming the projection optical system PL are made of silica
(SiO.sub.2). The lasing center wavelength of the ArF excimer laser
light being the exposure light is 193.306 nm, and the refractive
index of silica near 193.306 nm varies at a rate of
-1.591.times.10.sup.-6 per wavelength change of +1 pm, and varies
at a rate of +1.591.times.10.sup.-6 per wavelength change of -1 pm.
In other words, the dispersion (dn/d.lamda.) of the refractive
index of silica is -1.591.times.10.sup.-6/pm near 193.306 nm. The
refractive index of deionized water near 193.306 nm varies at a
rate of -2.6.times.10.sup.-6 per wavelength change of +1 pm and
varies at a rate of +2.6.times.10.sup.-6 per wavelength change of
-1 pm. In other words, the dispersion (dn/d.lamda.) of the
refractive index of deionized water is -2.6.times.10.sup.-6/pm near
193.306 nm.
[0175] In the first example, the refractive index of silica for the
center wavelength of 193.306 nm is 1.5603261, the refractive index
of silica for 193.306 nm+0.1 pm=193.3061 nm is 1.560325941, and the
refractive index of silica for 193.306 nm-0.1 pm=193.3059 nm is
1.560326259. The refractive index of deionized water for the center
wavelength of 193.306 nm is 1.47, the refractive index of deionized
water for 193.306 nm+0.1 pm=193.3061 nm is 1.46999974, and the
refractive index of deionized water for 193.306 nm-0.1 pm=193.3059
nm is 1.47000026.
[0176] Table (1) below presents values of specifications of the
projection optical system PL according to the first example. In
Table (1), .lamda. represents the center wavelength of the exposure
light, .beta. a projection magnification (imaging magnification of
the entire system), NA the image-side (wafer-side) numerical
aperture, Ro and Ri the outside radius and inside radius of the
aberration-corrected region AR, H and D the Y-directional size and
X-directional size of the effective exposure region ER, R the
radius of curvature of the arc defining the effective exposure
region ER (effective imaging area) of arcuate shape, and Y.sub.0
the maximum image height. Each surface number represents an order
of a surface from the reticle side along the traveling direction of
rays from the reticle surface being the object plane (first
surface) to the wafer surface being the image plane (second
surface), r a radius of curvature of each surface (radius of
curvature at an apex: mm in the case of an aspherical surface), d
an on-axis spacing or surface separation (mm) of each surface, and
n the refractive index for the center wavelength.
[0177] The surface separation d changes its sign every reflection.
Therefore, the sign of the surface separation d is negative in the
optical path from the first concave reflecting mirror CM1 to the
second concave reflecting mirror CM2, and positive in the other
optical paths. The radius of curvature of each convex surface kept
toward the reticle is positive, and the radius of curvature of each
concave surface kept toward the reticle is negative, regardless of
the direction of incidence of light. The notations in Table (1)
also apply to Table (2) hereinafter.
TABLE-US-00001 TABLE 1 Principal Specification .lamda. = 193.306 nm
.beta. = +1/4 NA = 1.04 Ro = 17.0 mm Ri = 11.5 mm H = 26.0 mm D =
4.0 mm R = 20.86 mm Y.sub.0 = 17.0 mm Specification of Optical
Members Surface number r d n Optical Member (reticle surface)
70.25543 1 444.28100 45.45677 1.5603261 (L11) 2* -192.24078 1.00000
3 471.20391 35.53423 1.5603261 (L12) 4 -254.24538 122.19951 5*
-159.65514 13.00000 1.5603261 (L13) 6 -562.86259 9.00564 7
-206.23868 -9.00564 (CM1) 8 -562.86259 -13.00000 1.5603261 (L13) 9*
-159.65514 -107.19951 10 3162.83419 144.20515 (CM2) 11 -389.01215
43.15699 1.5603261 (L21) 12 -198.92113 1.00000 13 3915.27567
42.01089 1.5603261 (L22) 14 -432.52137 1.00000 15 203.16777
62.58039 1.5603261 (L23) 16* 515.92133 18.52516 17* 356.67027
20.00000 1.5603261 (L24) 18 269.51733 285.26014 19 665.61079
35.16606 1.5603261 (L25) 20 240.55938 32.43496 21* -307.83344
15.00000 1.5603261 (L26) 22 258.17867 58.24284 23 -1143.34122
51.43638 1.5603261 (L27) 24 -236.25969 6.67292 25* 1067.55487
15.00000 1.5603261 (L28) 26 504.02619 18.88857 27 4056.97655
54.00381 1.5603261 (L29) 28 -283.04360 1.00000 29 772.31002
28.96307 1.5603261 (L210) 30 -8599.87899 1.00000 31 667.92225
52.94747 1.5603261 (L211) 32 36408.68946 2.30202 33 .infin.
42.27703 (AS) 34 -2053.34123 30.00000 1.5603261 (L212) 35
-514.67146 1.00000 36 1530.45141 39.99974 1.5603261 (L213) 37
-540.23726 1.00000 38 370.56341 36.15464 1.5603261 (L214) 39*
12719.40982 1.00000 40 118.92655 41.83608 1.5603261 (L215) 41
190.40194 1.00000 42 151.52892 52.42553 1.5603261 (L216) 43*
108.67474 1.12668 44 91.54078 35.50067 1.5603261 (L217:Lb) 45
.infin. 6.00000 1.47 (Lm) (Wafer surface) (Aspherical data)
2.sup.nd surface .kappa. = 0 C.sub.4 = -8.63025 .times. 10.sup.-9
C.sub.6 = 2.90424 .times. 10.sup.-13 C.sub.8 = 5.43348 .times.
10.sup.-17 C.sub.10 = 1.65523 .times. 10.sup.-21 C.sub.12 = 8.78237
.times. 10.sup.-26 C.sub.14 = 6.53360 .times. 10.sup.-30 5th
surface and 9.sup.th surface (same surface) .kappa. = 0 C.sub.4 =
7.66590 .times. 10.sup.-9 C.sub.6 = 6.09920 .times. 10.sup.-13
C.sub.8 = -6.53660 .times. 10.sup.-17 C.sub.10 = 2.44925 .times.
10.sup.-20 C.sub.12 = -3.14967 .times. 10.sup.-24 C.sub.14 =
2.21672 .times. 10.sup.-28 16th surface .kappa. = 0 C.sub.4 =
-3.79715 .times. 10.sup.-8 C.sub.6 = 2.19518 .times. 10.sup.-12
C.sub.8 = -9.40364 .times. 10.sup.-17 C.sub.10 = 3.33573 .times.
10.sup.-21 C.sub.12 = -7.42012 .times. 10.sup.-26 C.sub.14 =
1.05652 .times. 10.sup.-30 17th surface .kappa. = 0 C.sub.4 =
-6.69596 .times. 10.sup.-8 C.sub.6 = 1.67561 .times. 10.sup.-12
C.sub.8 = -6.18763 .times. 10.sup.-17 C.sub.10 = 2.65428 .times.
10.sup.-21 C.sub.12 = -4.09555 .times. 10.sup.-26 C.sub.14 =
3.25841 .times. 10.sup.-31 21st surface .kappa. = 0 C.sub.4 =
-8.68772 .times. 10.sup.-8 C.sub.6 = -1.30306 .times. 10.sup.-12
C.sub.8 = -2.65902 .times. 10.sup.-17 C.sub.10 = -6.56830 .times.
10.sup.-21 C.sub.12 = 3.66980 .times. 10.sup.-25 C.sub.14 =
-5.05595 .times. 10.sup.-29 25th surface .kappa. = 0 C.sub.4 =
-1.54049 .times. 10.sup.-8 C.sub.6 = 7.71505 .times. 10.sup.-14
C.sub.8 = 1.75760 .times. 10.sup.-18 C.sub.10 = 1.71383 .times.
10.sup.-23 C.sub.12 = 5.04584 .times. 10.sup.-29 C.sub.14 = 2.08622
.times. 10.sup.-32 39th surface .kappa. = 0 C.sub.4 = -3.91974
.times. 10.sup.-11 C.sub.6 = 5.90682 .times. 10.sup.-14 C.sub.8 =
2.85949 .times. 10.sup.-18 C.sub.10 = -1.01828 .times. 10.sup.-22
C.sub.12 = 2.26543 .times. 10.sup.-27 C.sub.14 = -1.90645 .times.
10.sup.-32 43rd surface .kappa. = 0 C.sub.4 = 8.33324 .times.
10.sup.-8 C.sub.6 = 1.42277 .times. 10.sup.-11 C.sub.8 = -1.13452
.times. 10.sup.-15 C.sub.10 = 1.18459 .times. 10.sup.-18 C.sub.12 =
-2.83937 .times. 10.sup.-22 C.sub.14 = 5.01735 .times. 10.sup.-26
(Values corresponding to Condition) F1 = 164.15 mm Y.sub.0 = 17.0
mm R = 20.86 mm (1) F1/Y.sub.0 = 9.66 (2) R/Y.sub.0 = 1.227
[0178] FIG. 6 is a diagram showing the transverse aberration in the
first example. In the aberration diagram, Y indicates the image
height, each solid line the center wavelength of 193.3060 nm, each
dashed line 193.306 nm+0.1 pm=193.3061 nm, and each chain line
193.306 nm-0.1 pm=193.3059 nm. The notations in FIG. 6 also apply
to FIG. 8 hereinafter. As apparent from the aberration diagram of
FIG. 6, though the first example secures the very large image-side
numerical aperture (NA=1.04) and the relatively large effective
exposure region ER, the chromatic aberration is well corrected for
the exposure light with the wavelength band of 193.306 nm.+-.0.1
pm.
Second Example
[0179] FIG. 7 is an illustration showing a lens configuration of
the projection optical system according to the second example of
the present embodiment. With reference to FIG. 7, in the projection
optical system PL according to the second example, the first
imaging optical system G1 is composed of the following components
in order from the reticle side along the traveling direction of
light: a biconvex lens L11 whose convex surface of aspherical shape
is kept toward the wafer; a biconvex lens L12; a negative meniscus
lens L13 whose concave surface of aspherical shape is kept toward
the reticle; and a first concave reflecting mirror CM1. In the
first imaging optical system G1, a reflecting surface of a second
concave reflecting mirror CM2 for reflecting the light reflected by
the first concave reflecting mirror CM1 and transmitted by the
negative meniscus lens L13, toward the second imaging optical
system G2 is placed in the region not including the optical axis AX
between the biconvex lens L12 and the negative meniscus lens L13.
Therefore, the biconvex lens L11 and the biconvex lens L12
constitute a first lens unit having a positive refracting power.
The first concave reflecting mirror CM1 constitutes a concave
reflecting mirror disposed near the pupil plane of the first
imaging optical system G1.
[0180] On the other hand, the second imaging optical system G2 is
composed of the following components in order from the reticle side
along the traveling direction of light: a positive meniscus lens
L21 whose concave surface is kept toward the reticle; a biconvex
lens L22; a positive meniscus lens L23 whose concave surface of
aspherical shape is kept toward the wafer; a negative meniscus lens
L24 whose convex surface of aspherical shape is kept toward the
reticle; a negative meniscus lens L25 whose convex surface is kept
toward the reticle; a biconcave lens L26 whose concave surface of
aspherical shape is kept toward the reticle; a positive meniscus
lens L27 whose concave surface is kept toward the reticle; a
negative meniscus lens L28 whose convex surface of aspherical shape
is kept toward the reticle; a biconvex lens L29; a biconvex lens
L210; a positive meniscus lens L211 whose convex surface is kept
toward the reticle; an aperture stop AS; a positive meniscus lens
L212 whose concave surface is kept toward the reticle; a biconvex
lens L213; a positive meniscus lens L214 whose concave surface of
aspherical shape is kept toward the wafer; a positive meniscus lens
L215 whose convex surface is kept toward the reticle; a positive
meniscus lens L216 whose concave surface of aspherical shape is
kept toward the wafer; and a planoconvex lens L217 (boundary lens
Lb) whose plane is kept toward the wafer.
[0181] In the second example, a plane-parallel plate Lp is disposed
in the optical path between the planoconvex lens L217 as the
boundary lens Lb and the wafer W. The medium Lm consisting of
deionized water is filled in the optical path between the boundary
lens Lb and the plane-parallel plate Lp and in the optical path
between the plane-parallel plate Lp and the wafer W. In the second
example, the transmitting members (lenses) constituting the
projection optical system PL are made of silica or fluorite
(CaF.sub.2). Specifically, the lens L13, lens L216, and lens L217
(Lb) are made of fluorite, and the other lenses and plane-parallel
plate Lp are made of silica. Namely, approximately 88% of the
transmitting members forming the second imaging optical system G2
are made of silica.
[0182] Furthermore, in the second example all the transmitting
members (lenses and plane-parallel plate) and all the reflecting
members with a power (first concave reflecting mirror CM1 and
second concave reflecting mirror CM2) forming the projection
optical system PL are arranged along the single optical axis AX. In
the second example, thus, the light from the reticle R travels
through the lenses L11 to L13 to enter the first concave reflecting
mirror CM1. The light reflected by the first concave reflecting
mirror CM1 travels via the lens L13 and the second concave
reflecting mirror CM2 to form an intermediate image of the reticle
R near the first concave reflecting mirror CM1. The light reflected
by the second concave reflecting mirror CM2 travels through the
lenses L21-L217 (Lb) and the plane-parallel plate Lp to form a
reduced image of the reticle R on the wafer W.
[0183] In the second example, the lasing center wavelength of the
ArF excimer laser light being the exposure light is 193.306 nm, and
the refractive index of silica near 193.306 nm varies at a rate of
-1.591.times.10.sup.-6 per wavelength change of +1 pm and varies at
a rate of +1.591.times.10.sup.-6 per wavelength change of -1 pm. In
other words, the dispersion (dn/d.lamda.) of the refractive index
of silica near 193.306 nm is -1.591.times.10.sup.-6/pm. The
refractive index of fluorite near 193.306 nm varies at a rate of
-0.980.times.10.sup.-6 per wavelength change of +1 pm and varies at
a rate of +0.980.times.10.sup.-6 per wavelength change of -1 pm. In
other words, the dispersion (dn/d.lamda.) of the refractive index
of fluorite near 193.306 nm is -0.980.times.10.sup.-6/pm.
[0184] Furthermore, the refractive index of deionized water near
193.306 nm varies at a rate of -2.6.times.10.sup.-6 per wavelength
change of +1 pm, and varies at a rate of +2.6.times.10.sup.-6 per
wavelength change of -1 pm. In other words, the dispersion
(dn/d.lamda.) of the refractive index of deionized water near
193.306 nm is -2.6.times.10.sup.-6/pm. In the second example, thus,
the refractive index of silica for the center wavelength of 193.306
nm is 1.5603261, the refractive index of silica for 193.306 nm+0.1
pm=193.3061 nm is 1.560325941, and the refractive index of silica
for 193.306 nm-0.1 pm=193.3059 nm is 1.560326259.
[0185] The refractive index of fluorite for the center wavelength
of 193.306 nm is 1.5014548, the refractive index of fluorite for
193.306 nm+0.1 pm=193.3061 nm is 1.501454702, and the refractive
index of fluorite for 193.306 nm-0.1 pm=193.3059 nm is 1.501454898.
Furthermore, the refractive index of deionized water for the center
wavelength of 193.306 nm is 1.47, the refractive index of deionized
water for 193.306 nm+0.1 pm=193.3061 nm is 1.46999974, and the
refractive index of deionized water for 193.306 nm-0.1 pm=193.3059
nm is 1.47000026. Table (2) below presents values of specifications
of the projection optical system PL in the second example.
TABLE-US-00002 TABLE 2 (Principal Specifications) .lamda. = 193.306
nm .beta. = +1/4 NA = 1.04 Ro = 17.0 mm Ri = 11.5 mm H = 26.0 mm D
= 4.0 mm R = 20.86 mm Y.sub.0 = 17.0 mm (Specifications of Optical
Members) Surface Number r d n Optical member (reticle surface)
72.14497 1 295.66131 46.03088 1.5603261 (L11) 2* -228.07826 1.02581
3 847.63618 40.34103 1.5603261 (L12) 4 -207.90948 124.65407 5*
-154.57886 13.00000 1.5014548 (L13) 6 -667.19164 9.58580 7
-209.52775 -9.58580 (CM1) 8 -667.19164 -13.00000 1.5014548 (L13) 9*
-154.57886 -109.65407 10 2517.52751 147.23986 (CM2) 11 -357.71318
41.75496 1.5603261 (L21) 12 -196.81705 1.00000 13 8379.53651
40.00000 1.5603261 (L22) 14 -454.81020 8.23083 15 206.30063
58.07852 1.5603261 (L23) 16* 367.14898 24.95516 17* 258.66863
20.00000 1.5603261 (L24) 18 272.27694 274.16477 19 671.42370
49.62123 1.5603261 (L25) 20 225.79907 35.51978 21* -283.63484
15.10751 1.5603261 (L26) 22 261.37852 56.71822 23 -1947.68869
54.63076 1.5603261 (L27) 24 -227.05849 5.77639 25* 788.97953
15.54026 1.5603261 (L28) 26 460.12935 18.83954 27 1925.75038
56.54051 1.5603261 (L29) 28 -295.06884 1.00000 29 861.21046
52.50515 1.5603261 (L210) 30 -34592.86759 1.00000 31 614.86639
37.34179 1.5603261 (L211) 32 39181.66426 1.00000 33 .infin.
46.27520 (AS) 34 -11881.91854 30.00000 1.5603261 (L212) 35
-631.95129 1.00000 36 1465.88641 39.89113 1.5603261 (L213) 37
-542.10144 1.00000 38 336.45791 34.80369 1.5603261 (L214) 39*
2692.15238 1.00000 40 112.42843 43.53915 1.5603261 (L215) 41
189.75478 1.00000 42 149.91358 42.41577 1.5014548 (L216) 43*
107.28888 1.06533 44 90.28791 31.06087 1.5014548 (L217:Lb) 45
.infin. 1.00000 1.47 (Lm) 46 .infin. 3.00000 1.5603261 (Lp) 47
.infin. 5.00000 1.47 (Lm) (wafer surface) (Aspherical data) 2nd
surface .kappa. = 0 C.sub.4 = 9.57585 .times. 10.sup.-9 C.sub.6 =
7.09690 .times. 10.sup.-13 C.sub.8 = 1.30845 .times. 10.sup.-16
C.sub.10 = -5.52152 .times. 10.sup.-22 C.sub.12 = 4.46914 .times.
10.sup.-25 C.sub.14 = -2.07483 .times. 10.sup.-29 5th surface and
9th surface (same surface) .kappa. = 0 C.sub.4 = 1.16631 .times.
10.sup.-8 C.sub.6 = 6.70616 .times. 10.sup.-13 C.sub.8 = -1.87976
.times. 10.sup.-17 C.sub.10 = 1.71587 .times. 10.sup.-20 C.sub.12 =
-2.34827 .times. 10.sup.-24 C.sub.14 = 1.90285 .times. 10.sup.-28
16th surface .kappa. = 0 C.sub.4 = -4.06017 .times. 10.sup.-8
C.sub.6 = 2.22513 .times. 10.sup.-12 C.sub.8 = -9.05000 .times.
10.sup.-17 C.sub.10 = 3.29839 .times. 10.sup.-21 C.sub.12 =
-7.46596 .times. 10.sup.-26 C.sub.14 = 1.06948 .times. 10.sup.-30
17th surface .kappa. = 0 C.sub.4 = -6.69592 .times. 10.sup.-8
C.sub.6 = 1.42455 .times. 10.sup.-12 C.sub.8 = -5.65516 .times.
10.sup.-17 C.sub.10 = 2.48078 .times. 10.sup.-21 C.sub.12 =
-2.91653 .times. 10.sup.-26 C.sub.14 = 1.53981 .times. 10.sup.-31
21st surface .kappa. = 0 C.sub.4 = -7.97186 .times. 10.sup.-8
C.sub.6 = -1.32969 .times. 10.sup.-12 C.sub.8 = -1.98377 .times.
10.sup.-17 C.sub.10 = -4.95016 .times. 10.sup.-21 C.sub.12 =
2.53886 .times. 10.sup.-25 C.sub.14 = -4.16817 .times. 10.sup.-29
25th surface .kappa. = 0 C.sub.4 = -1.55844 .times. 10.sup.-8
C.sub.6 = 7.27672 .times. 10.sup.-14 C.sub.8 = 1.90600 .times.
10.sup.-18 C.sub.10 = 1.21465 .times. 10.sup.-23 C.sub.12 =
-7.56829 .times. 10.sup.-29 C.sub.14 = 1.86889 .times. 10.sup.-32
39th surface .kappa. = 0 C.sub.4 = -6.91993 .times. 10.sup.-11
C.sub.6 = 7.80595 .times. 10.sup.-14 C.sub.8 = 3.31216 .times.
10.sup.-18 C.sub.10 = -1.39159 .times. 10.sup.-22 C.sub.12 =
3.69991 .times. 10.sup.-27 C.sub.14 = -4.01347 .times. 10.sup.-32
43rd surface .kappa. = 0 C.sub.4 = 8.30019 .times. 10.sup.-8
C.sub.6 = 1.24781 .times. 10.sup.-11 C.sub.8 = -9.26768 .times.
10.sup.-16 C.sub.10 = 1.08933 .times. 10.sup.-18 C.sub.12 =
-3.01514 .times. 10.sup.-22 C.sub.14 = 5.41882 .times. 10.sup.-26
(Values corresponding to Condition) F1 = 178.98 mm Y.sub.0 = 17.0
mm R = 20.86 mm (1) F1/Y.sub.0 = 10.53 (2) R/Y.sub.0 = 1.227
[0186] FIG. 8 is a diagram showing the transverse aberration in the
second example. It is also apparent from the aberration diagram of
FIG. 8, as was the case with the first example, that the second
example also secures the very large image-side numerical aperture
(NA=1.04) and the relatively large effective exposure region ER,
while the chromatic aberration is well corrected for the exposure
light with the wavelength band of 193.306 nm.+-.0.1 pm.
[0187] In each example, as described above, the high image-side
numerical aperture of 1.04 is secured for the ArF excimer laser
light with the wavelength of 193.306 nm, and the effective exposure
region (stilt exposure region) of arcuate shape of 26.0
mm.times.4.0 mm can be secured; therefore, the scanning exposure of
the circuit pattern can be performed at high resolution within the
exposure region of rectangular shape of 26 mm.times.33 mm, for
example.
[0188] Next, the third example of the embodiment will be described.
FIG. 9 is an illustration showing a lens configuration of the
catadioptric projection optical system according to the third
example of the embodiment. The catadioptric projection optical
system PL1 according to the third example is composed of the
following optical systems in order from the object side (i.e., the
reticle R1 side): a first imaging optical system G1 for forming an
intermediate image of the reticle R1 located on the first surface;
and a second imaging optical system G2 for forming an intermediate
image of the reticle R1 on a wafer (not shown) located on the
second surface.
[0189] The first imaging optical system G1 is composed of a lens
unit with a positive refracting power (fourth lens unit or first
unit) G11, after-described lens L5, and two reflecting mirrors M1,
M2. The lens unit G11 functions for making the optical system
telecentric on the reticle R1 side. The second imaging optical
system G2 is composed of after-described two reflecting mirrors M3,
M4, a lens unit with a negative refracting power (first lens unit
or third unit) G21, a lens unit with a positive refracting power
(second lens unit) G22, an aperture stop AS1, and a lens unit with
a positive refracting power (third lens unit) G23. The lens unit
G21 functions to adjust the magnification and to relieve the
variation due to the difference of field angles of the beam
expanded by the reflecting mirror M3, so as to suppress occurrence
of aberration. The lens unit G22 functions to converge the
diverging beam. The lens unit G23 functions to condense the beam so
as to achieve the large numerical aperture on the wafer side.
[0190] Here the lens unit G11 is composed of the following
components in order of passage of rays from the object side
(reticle R1 side): a plane-parallel plate L1; a negative meniscus
lens L2 whose concave surface of aspherical shape is kept toward
the object side; a biconvex lens L3; and a positive meniscus lens
L4 whose concave surface of aspherical shape is kept toward the
wafer.
[0191] The beam transmitted by the positive meniscus lens L4
travels through the negative meniscus lens (negative lens) L5 with
the concave surface kept toward the object, is reflected by the
concave reflecting mirror (concave mirror or first reflecting
mirror) M1 with the concave surface kept toward the object, passes
again through the negative meniscus lens L5, and is reflected by
the convex reflecting mirror (optical path separating mirror or
second reflecting mirror) M2 with the convex surface kept toward
the wafer. The negative meniscus lens L5 functions for satisfying
the Petzval's condition.
[0192] The beam reflected by the convex reflecting mirror M2 forms
an intermediate image of the reticle R1 at the position a shown in
FIG. 9, in order to securely achieve the optical path separation
between the beam toward the reticle R1 and the beam toward the
wafer. Here the position a is located on or near a plane whose
normal is the optical axis AX1 where the concave reflecting mirror
M1 is placed.
[0193] Next, the beam reflected by the convex reflecting mirror M2
is incident to the concave reflecting mirror (first field mirror or
third reflecting mirror) M3 with the concave surface kept toward
the object, to be bent into a direction toward the optical axis AX1
of the catadioptric projection optical system PL1, and is outputted
from the concave reflecting mirror M3. The beam emerging from the
concave reflecting mirror M3 is quickly converged, is reflected by
the convex reflecting mirror (second field mirror or fourth
reflecting mirror) M4 with the convex surface kept toward the
wafer, and is directly incident to the negative meniscus lens L6
forming the lens unit G21. The convex reflecting mirror M4 relieves
the variation of the beam due to field angles expanded by the
concave reflecting mirror M3, so as to suppress occurrence of
aberration. The negative meniscus lens L5, concave reflecting
mirror M1, convex reflecting mirror M2, concave reflecting mirror
M3, and convex reflecting mirror M4 constitute a second unit.
[0194] The lens unit G21 is composed of the following components in
order of passage of rays: a negative meniscus lens L6 whose convex
surface of aspherical shape is kept toward the object; and a
biconcave lens L7 whose concave surface of aspherical shape is kept
toward the wafer. Since the negative meniscus lens L6 and the
biconcave lens L7 have the lens surfaces of aspherical shape, good
imaging performance can be achieved throughout the entire region in
the exposure area, while securing the large numerical aperture on
the image side of the catadioptric projection optical system PL1.
The lens unit G22 is composed of the following components in order
of passage of rays: a positive meniscus lens L8 whose concave
surface of aspherical shape is kept toward the object; a biconvex
lens L9; a positive meniscus lens L10 whose concave surface of
aspherical shape is kept toward the object; a biconvex lens L11;
and a biconvex lens L12. The lens unit G23 is composed of the
following components in order of passage of rays: a positive
meniscus lens L13 whose convex surface is kept toward the object; a
positive meniscus lens L14 whose convex surface is kept toward the
object; a positive meniscus lens L15 whose convex surface is kept
toward the object; a positive meniscus lens L16 whose concave
surface of aspherical shape is kept toward the wafer; a positive
meniscus lens L17 whose concave surface of aspherical shape is kept
toward the wafer; and a planoconvex lens L18 with a positive
refracting power whose convex surface is kept toward the object.
The lens unit G22, aperture stop AS1, and lens unit G23 constitute
a fourth unit.
[0195] The catadioptric projection optical system PL1 is
constructed to satisfy the condition of 0.17<Ma/L<0.6, where
Ma is a distance on the optical axis AX1 between the reflecting
mirror M3 and the aperture stop AS1, and L a distance between the
reticle RI and the wafer. When Ma/L satisfies the lower limit, it
is feasible to avoid mechanical interference of the concave
reflecting mirror M3 with the lens unit G21 and the lens unit G22.
When Ma/L satisfies the upper limit, it is feasible to avoid an
increase in the total length and an increase in the size of the
catadioptric projection optical system PL1. For securely avoiding
the mechanical interference and securely avoiding the increase in
the total length and the increase in the size of the projection
optical system, the projection optical system is further preferably
constructed to satisfy the condition of 0.2<Ma/L<0.5.
[0196] When this catadioptric projection optical system PL1 of the
present example is applied to the exposure apparatus, pure water
with the refractive index of about 1.4 is interposed in the optical
path between the lens L18 and the wafer, where the refractive index
of the atmosphere in the catadioptric projection optical system PL1
is 1. Therefore, the wavelength of the exposure light in pure water
is about 0.71 (1/1.4) times that in the atmosphere, whereby the
resolution can be enhanced.
[0197] The optical axis AX1 of every optical element included in
the catadioptric projection optical system PL1 and having the
predetermined refracting power is placed substantially on the
single straight line, and the region of the image formed on the
wafer by the catadioptric projection optical system PL1 is the
off-axis region not including the optical axis AX1. Therefore, it
is feasible to reduce the degree of difficulty of production in
production of the catadioptric projection optical system PL1 and to
readily achieve relative adjustment of each optical member.
[0198] In the catadioptric projection optical system PL1 of the
third example, since the intermediate image of the reticle R1 is
formed in the first imaging optical system G1, it is feasible to
readily and securely achieve the optical path separation between
the beam toward the reticle R1 and the beam toward the wafer, even
in the case where the numerical apertures of the catadioptric
projection optical system PL1 are increased. Since the second
imaging optical system G2 has the lens unit G21 with the negative
refracting power, it is feasible to shorten the total length of the
catadioptric projection optical system PL1 and to readily achieve
the adjustment for satisfying the Petzval's condition. Furthermore,
the lens unit G21 relieves the variation due to the difference of
field angles of the beam expanded by the concave reflecting mirror
M3, so as to suppress occurrence of aberration. Therefore, good
imaging performance can be achieved throughout the entire region in
the exposure area, even in the case where the reticle R1-side and
wafer-side numerical apertures of the catadioptric projection
optical system PL1 are increased in order to enhance the
resolution.
[0199] Next, the fourth example of the embodiment will be described
with reference to the drawing. FIG. 10 is an illustration showing a
lens configuration of the catadioptric projection optical system
according to the fourth example of the embodiment. The catadioptric
projection optical system PL2 of the fourth example is composed of
the following optical systems in order from the object side (i.e.,
the reticle R2 side): a first imaging optical system G3 for forming
an intermediate image of reticle R2 located on the first surface;
and a second imaging optical system G4 for forming an intermediate
image of the reticle R2 on a wafer (not shown) located on the
second surface.
[0200] The first imaging optical system G3 is composed of a lens
unit with a positive refracting power (fourth lens unit or first
unit) G31, after-described lens L24, and two reflecting mirrors
M21, M22. The lens unit G31 functions for making the optical system
telecentric on the reticle R2 side. The second imaging optical
system G4 is composed of after-described two reflecting mirrors
M23, M24, a lens unit with a negative refracting power (first lens
unit or third unit) G41, a lens unit with a positive refracting
power (second lens unit) G42, an aperture stop AS2, and a lens unit
with a positive refracting power (third lens unit) G43. The lens
unit G41 functions to adjust the magnification and to relieve the
variation due to the difference of field angles of the beam
expanded by the reflecting mirror M23, so as to suppress occurrence
of aberration. The lens unit G42 functions to converge the
diverging beam. The lens unit G43 condenses the beam so as to
achieve a large numerical aperture on the wafer side.
[0201] Here the lens unit G31 is composed of the following
components in order of passage of rays from the object side
(reticle R2 side): a plane-parallel plate L21; a positive meniscus
lens L22 whose concave surface of aspherical shape is kept toward
the object; and a biconvex lens L23. The beam transmitted by the
biconvex lens L23 passes through the negative meniscus lens
(negative lens) L24 with the concave surface kept toward the
object, is reflected by the concave reflecting mirror (concave
reflecting mirror or first reflecting mirror) M21 with the concave
surface of aspherical shape kept toward the object, passes again
through the negative meniscus lens L24, and is then reflected by
the convex reflecting mirror (optical path separating mirror or
second reflecting mirror) M22 with the convex surface of aspherical
shape kept toward the wafer. The negative meniscus lens L24
functions for satisfying the Petzval's condition.
[0202] The beam reflected by the convex reflecting mirror M22 forms
an intermediate image of the reticle R2 at the position b shown in
FIG. 10, in order to securely achieve the optical path separation
between the beam toward the reticle R2 and the beam toward the
wafer. Here the position b is located on or near a plane whose
normal is the optical axis AX2 where the concave reflecting mirror
M21 is placed.
[0203] Next, the beam reflected by the convex reflecting mirror M22
is incident to the concave reflecting mirror (first field mirror or
third reflecting mirror) M23 with the concave surface kept toward
the object, to be bent into a direction toward the optical axis AX2
of the catadioptric projection optical system PL2, and is reflected
by the concave reflecting mirror M23. The beam reflected by the
concave reflecting mirror M23 is quickly converged, is reflected by
the convex reflecting mirror (second field mirror or fourth
reflecting mirror) M24 with the convex surface of aspherical shape
kept toward the wafer, and is directly incident to the biconcave
lens L25 forming the lens unit G41. The convex reflecting mirror
M24 relieves the variation of the beam due to the field angles
expanded by the concave reflecting mirror M23, so as to suppress
occurrence of aberration. The negative meniscus lens L24, concave
reflecting mirror M21, convex reflecting mirror M22, concave
reflecting mirror M23, and convex reflecting mirror M24 constitute
a second unit.
[0204] The lens unit G41 is composed of the following components in
order of passage of rays: a biconcave lens L25 whose concave
surface of aspherical shape is kept toward the object; and a
biconcave lens L26 whose concave surface of aspherical shape is
kept toward the wafer. Since the biconcave lens L25 and the
biconcave lens L26 have the lens surfaces of aspherical shape, it
is feasible to achieve good imaging performance throughout the
entire region in the exposure area, while achieving the large
numerical aperture on the image side of the catadioptric projection
optical system PL2.
[0205] The lens unit G42 is composed of the following components in
order of passage of rays: a biconvex lens L27 whose convex surface
of aspherical shape is kept toward the object; a negative meniscus
lens L28 whose convex surface is kept toward the object; a positive
meniscus lens L29 whose concave surface is kept toward the object;
and a negative meniscus lens L30 whose convex surface of aspherical
shape is kept toward the wafer. The lens unit G43 is composed of
the following components in order of passage of rays: a positive
meniscus lens L31 whose convex surface is kept toward the object; a
positive meniscus lens L32 whose convex surface is kept toward the
object; a positive meniscus lens L33 whose convex surface is kept
toward the object; a positive meniscus lens L34 whose concave
surface of aspherical shape is kept toward the wafer; a positive
meniscus lens L35 whose concave surface of aspherical shape is kept
toward the wafer; and a planoconvex lens L36 whose convex surface
is kept toward the object. The lens unit G42, aperture stop AS2,
and lens unit G43 constitute a fourth unit.
[0206] The catadioptric projection optical system PL2 is
constructed so as to satisfy the condition of
0.17<M2a/L2<0.6, where M2 is a distance on the optical axis
AX2 between the reflecting mirror M23 and the aperture stop AS2,
and L2 the distance between the reticle R2 and the wafer. When
M2a/L2 satisfies the lower limit, it is feasible to avoid
mechanical interference of the concave reflecting mirror M23 with
the lens unit G41 and the lens unit G42. When M2a/L2 satisfies the
upper limit, it is feasible to avoid an increase in the total
length and an increase in the size of the catadioptric projection
optical system PL2. For securely avoiding the mechanical
interference and securely avoiding the increase in the total length
and the increase in the size of the projection optical system, the
projection optical system is more preferably constructed to satisfy
the condition of 0.5<M2a/L2<0.2.
[0207] When the catadioptric projection optical system PL2 of this
example is applied to the exposure apparatus, pure water having the
refractive index of about 1.4 is interposed in the optical path
between the lens L36 and the wafer, where the refractive index of
the atmosphere in the catadioptric projection optical system PL2 is
1. Therefore, the wavelength of the exposure light in pure water
becomes about 0.71 (1/1.4) times that in the atmosphere, whereby
the resolution can be enhanced.
[0208] The optical axis AX2 of every optical element included in
the catadioptric projection optical system PL2 and having the
predetermined refracting power is placed substantially on the
single straight line, and the region of the image formed on the
wafer by the catadioptric projection optical system PL2 is the
off-axis region not including the optical axis AX2. Therefore, it
is feasible to reduce the degree of difficulty of production in
production of the catadioptric projection optical system PL2 and to
readily achieve relative adjustment of each optical member.
[0209] Since the catadioptric projection optical system PL2 of the
fourth example forms the intermediate image of the reticle R2 in
the first imaging optical system G3, the optical path separation
can be readily and securely achieved between the beam toward the
reticle R2 and the beam toward the wafer, even in the case where
the numerical apertures of the catadioptric projection optical
system PL2 are increased. Since the second imaging optical system
G4 has the lens unit G41 with the negative refracting power, it is
feasible to shorten the total length of the catadioptric projection
optical system PL2 and to readily achieve the adjustment for
satisfying the Petzval's condition. Furthermore, the lens unit G41
relieves the variation due to the difference of field angles of the
beam expanded by the concave reflecting mirror M23, so as to
suppress occurrence of aberration. Therefore, good imaging
performance can be achieved throughout the entire region in the
exposure area, even in the case where the reticle R2-side and
wafer-side numerical apertures of the catadioptric projection
optical system PL2 are increased in order to enhance the
resolution.
[0210] The catadioptric projection optical system PL1 of the third
example described above is arranged so that the light reflected by
the convex reflecting mirror M4 is incident to the lens unit G21,
but the optical system may also be arranged so that a double pass
lens is disposed between the convex reflecting mirror M4 and the
lens unit G21. In this case, the light reflected by the concave
reflecting mirror M3 passes through the double pass lens, is
reflected by the convex reflecting mirror M4, passes again through
the double pass lens, and then enters the lens unit G21. Similarly,
the catadioptric projection optical system PL2 of the fourth
example is arranged so that the light reflected by the convex
reflecting mirror M24 is incident to the lens unit G41, but the
optical system may also be arranged so that a double pass lens is
disposed between the convex reflecting mirror M24 and the lens unit
G41.
[0211] In the catadioptric projection optical systems PL1, PL2 of
the respective examples described above, pure water was interposed
between the lens located nearest to the wafer, and the wafer, and
it is also possible to adopt a configuration wherein another medium
having a refractive index larger than 1.1 is interposed, where the
refractive index of the atmosphere in the catadioptric projection
optical system PL1 or PL2 is 1.
[0212] Presented below are values of specifications of the
catadioptric projection optical system PL1 according to the third
example. In the specifications, as shown in FIG. 11, A represents a
radius of a portion where the exposure light is blocked by the
optical elements constituting the catadioptric projection optical
system PL1, with the center on the optical axis AX1 of the
catadioptric projection optical system PL1, B a radius of the
maximum image height with the center on the optical axis AX1 of the
catadioptric projection optical system PL1, H a length along the
Y-direction of the effective exposure region, and C a length along
the X-direction of the effective exposure region. In the
specifications, NA represents the numerical aperture, d the surface
separation, n the refractive index, and .lamda. the center
wavelength. Furthermore, in the specifications M represents the
distance on the optical axis AX1 between the reflecting mirror M3
and the unrepresented wafer, and L the distance between the reticle
R1 and the wafer.
[0213] Table 3 presents the specifications of the optical members
of the catadioptric projection optical system PL1 according to the
third example. In the specifications of the optical members in
Table 3, each surface number in the first column indicates an order
of a surface along the traveling direction of rays from the object
side, the second column a radius of curvature of each surface (mm),
the third column an on-axis spacing or surface separation (mm) of
each surface, and the fourth column a glass material of each
optical member.
[0214] Table 4 presents the aspherical coefficients of the lenses
with a lens surface of aspherical shape and the reflecting mirrors
used in the catadioptric projection optical system PL1 in the third
example. In the aspherical coefficients of Table 4, aspherical
surface numbers in the first column correspond to the surface
numbers in the specifications of the optical members in Table 1.
The second column represents the curvature of each aspherical
surface (1/mm), the third column the conical coefficient k and the
12th-order aspherical coefficient, the fourth column the 4th-order
and 14th-order aspherical coefficients, the fifth column the
6th-order and 16th-order aspherical coefficients, the sixth column
the 8th-order and 18th-order aspherical coefficients, and the
seventh column the 10th-order and 20th-order aspherical
coefficients.
[0215] In the third and fourth examples, each aspherical surface is
expressed by the aforementioned Eq (a).
Third Example
Specifications
[0216] Image-side NA: 1.20
[0217] Exposure area: A=14 mm B=18 mm [0218] H=26.0 mm C=4 mm
[0219] Imaging magnification: 1/4
[0220] Center wavelength: 193.306 nm
[0221] Refractive index of silica: 1.5603261
[0222] Refractive index of fluorite: 1.5014548
[0223] Refractive index of liquid 1: 1.43664
[0224] Dispersion of silica (dn/d.lamda.): -1.591E-6/pm
[0225] Dispersion of fluorite (dn/d.lamda.): -0.980E-6/pm
[0226] Dispersion of liquid 1 (dn/d.lamda.): -2.6E-6/pm
[0227] Values corresponding to Condition Ma=374.65 mm L=1400 mm
TABLE-US-00003 TABLE 3 (Specifications of Optical Members) #2 #3 #4
#1 .infin. 50.0000 1: .infin. 8.0000 #5 2: .infin. 33.0000 3: ASP1
25.0422 #5 4: -163.96521 1.0000 5: 355.31617 60.7391 #5 6:
-261.84115 1.0000 7: 277.33354 29.0109 #5 8: ASP2 224.5285 9:
-176.61872 20.0000 #5 10: -515.60710 10.4614 11: ASP3 -10.4614 #6
12: -515.60710 -20.0000 #5 13: -176.61872 -204.5285 14: ASP4
518.3706 #6 15: -517.39842 -241.3807 #6 16: -652.07494 171.3807 #6
17: ASP5 20.0000 #5 18: 171.59382 41.4743 19: -245.94525 20.0000 #5
20: ASP6 95.1415 21: ASP7 28.3218 #5 22: -273.72261 1.0000 23:
578.31684 49.6079 #5 24: -908.96420 1.0000 25: ASP8 23.1140 #5 26:
-713.30127 1.0000 27: 1494.96847 33.6453 #5 28: -1392.26668
100.2723 29: 1382.10341 24.7691 #5 30: -2944133.03600 5.3079 31:
.infin. 6.0869 #7 32: 596.90080 37.1298 #5 33: 524859.29548 1.0000
34: 367.83725 41.0495 #5 35: 1341.09674 1.0000 36: 180.61255
61.4605 #5 37: 464.28786 1.0000 38: 125.76761 49.2685 #5 39: ASP9
1.0000 40: 89.27467 40.3615 #5 41: ASP10 1.1254 42: 79.35451
37.7011 #5 43: .infin. 1.0000 #8 #9 .infin. #1: 1st surface #2:
Radius of curvature #3: Surface spacing #4: Medium #5: silica glass
#6: reflecting mirror #7: aperture stop #8: pure water #9: 2nd
surface
TABLE-US-00004 TABLE 4 (Aspherical Coefficients) k c4 c6 c8 c10 #
12 # 13 c12 c14 c16 c18 c20 ASP1 -0.00714775 0.00000E+00
3.70121E-08 4.46586E-13 1.04583E-17 6.87573E-21 -5.81072E-25
5.12589E-29 0.00000E+00 0.00000E+00 0.00000E+00 ASP2 0.00091632
0.00000E+00 2.33442E-08 -7.41117E-13 5.08507E-17 -4.32871E-21
1.56850E-25 -1.33250E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP3
-0.00346903 0.00000E+00 -1.67447E-09 -6.49516E-14 -5.93050E-19
-8.10217E-23 3.21506E-27 -6.92598E-32 0.00000E+00 0.00000E+00
0.00000+00 ASP4 -0.00076630 0.00000E+00 3.06327E-10 4.69465E-14
-6.39759E-19 2.45900E-23 -8.28832E-28 1.58122E-32 0.00000E+00
0.00000E+00 0.00000E+00 ASP5 0.00125662 0.00000E+00 1.03544E-08
-1.28243E-12 -3.97225E-17 -8.03173E-21 3.90718E-25 1.64002E-30
0.00000E+00 0.00000E+00 0.00000E+00 ASP6 0.00507634 0.00000E+00
1.00543E-08 -3.32807E-12 -1.38706E-17 2.64276E-21 1.41136E-25
-6.70515E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP7 -0.00253727
0.00000E+00 -3.94919E-10 9.50312E-14 -1.02153E-18 -1.22660E-22
3.11154E-27 -4.99394E-31 0.00000E+00 0.00000E+00 0.00000E+00 ASP8
-0.00025661 0.00000E+00 -9.13443E-09 -8.61174E-14 4.52406E-19
-2.29061E-23 5.86934E-28 -7.10478E-33 0.00000E+00 0.00000E+00
0.00000E+00 ASP9 0.00458263 0.00000E+00 2.66745E-08 -3.15468E-13
7.16318E-17 1.41053E-21 -2.22512E-25 1.68093E-20 0.00000E+00
0.00000E+00 0.00000E+00 ASP10 0.01117107 0.00000E+00 2.45701E-07
4.19793E-11 4.83523E-15 2.02242E-18 -1.59072E-22 1.41579E-25
0.00000E+00 0.00000E+00 0.00000E+00 #12: Aspherical surface number
#13: Curvature
[0228] FIG. 12 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system
PL1 according to the present example. In FIG. 12, Y indicates the
image height, each dashed line the transverse aberration at the
wavelength of 193.3063 nm, each solid line the transverse
aberration at the wavelength of 193.3060 nm, and each chain line
the transverse aberration at the wavelength of 193.3057 nm. As
shown in the transverse aberration diagram of FIG. 12, the
catadioptric projection optical system PL1 of the present example
has the large numerical aperture and is corrected in a good balance
for aberration throughout the entire exposure area though it has no
large optical element.
[0229] The values of specifications of the catadioptric projection
optical system PL2 according to the fourth example will be
presented below. Table 5 presents the specifications of the optical
members of the catadioptric projection optical system PL2 in the
fourth example. Table 6 presents the aspherical coefficients of the
lenses with a lens surface of aspherical shape and the reflecting
mirrors used in the catadioptric projection optical system PL2
according to the fourth example. The specifications, the
specifications of the optical members, and the aspherical
coefficients will be described with use of the same reference
symbols as those used in the description of the specifications of
the catadioptric projection optical system PL1 in the third
example.
Fourth Example
Specifications
[0230] Image-side NA: 1.20
[0231] Exposure area: A=13.5 mm B=17.5 mm [0232] H=26.0 mm C=4
mm
[0233] Imaging magnification: 1/5
[0234] Center wavelength: 193.306 nm
[0235] Refractive index of silica: 1.5603261
[0236] Refractive index of fluorite: 1.5014548
[0237] Refractive index of liquid 1: 1.43664
[0238] Dispersion of silica (dn/d.lamda.): -1.591E-6/pm
[0239] Dispersion of fluorite (dn/d.lamda.): -0.980E-6/pm
[0240] Dispersion of liquid 1 (dn/d.lamda.): -2.6E-6/pm
[0241] Values corresponding to Condition Ma=424.85 mm L=1400 mm
TABLE-US-00005 TABLE 5 (Specifications of Optical Members) #2 #3 #4
#1 .infin. 74.5841 1: .infin. 8.0000 #5 2: .infin. 33.0000 3: ASP1
22.9375 #5 4: -238.83712 1.0000 5: 226.68450 59.5357 #5 6:
-908.69406 202.7480 #6 7: -165.20501 20.0000 #5 8: -669.93146
45.4417 9: ASP2 -45.4417 #6 10: -669.93146 -20.0000 #5 11:
-165.20501 -182.7480 12: ASP3 476.5531 #6 13: -410.99944 -182.7518
#6 14: ASP4 164.9642 #6 15: ASP5 28.4827 #5 16: 239.45495 38.2383
17: -497.63245 20.0000 #5 18: ASP6 89.6638 19: ASP7 48.7904 #5 20:
-290.43245 1.0000 21: 1036.93127 60.0000 #5 22: 1015.63994 19.7285
23: -2533.07822 63.4343 #5 24: -278.02969 31.4485 25: -1388.36824
40.8485 #5 26: ASP8 1.0000 27: .infin. 1.0000 #7 28: 479.05778
35.6437 #5 29: 1637.29836 1.0000 30: 329.32813 44.1312 #5 31:
1053.37530 1.0000 32: 200.35146 57.3982 #5 33: 515.50441 1.0000 34:
118.38756 60.5521 #5 35: ASP9 1.0000 36: 81.03425 37.8815 #14 37:
ASP10 1.0000 38: 81.71932 35.7388 #14 39: .infin. 1.0000 #8 #9
.infin. #1: 1st surface #2: Radius of curvature #3: Surface spacing
#4: Medium #5: silica glass #6: reflecting mirror #7: aperture stop
#8: pure water #9: 2nd surface #14: Fluorite
TABLE-US-00006 TABLE 6 (Aspherical Coefficients) k c4 c6 c8 c10 #
12 # 13 c12 c14 c16 c18 c20 ASP1 -0.00388454 0.00000E+00
2.22245E-08 1.47956E-13 -1.47977E-17 1.83827E-21 -3.79672E-26
6.22409E-31 0.00000E+00 0.00000E+00 0.00000E+00 ASP2 -0.00372368
0.00000E+00 -1.37639E-09 -9.27463E-14 -2.36568E-18 -4.78730E-22
4.14849E-26 -2.22906E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP3
-0.00090790 0.00000E+00 -4.17158E-09 1.53090E-13 -4.47592E-18
4.68099E-22 -2.64998E-26 6.12220E-31 0.00000E+00 0.00000E+00
0.00000E+00 ASP4 -0.00254948 0.00000E+00 1.56073E-09 1.95837E-14
1.84538E-18 -8.80727E-23 1.81493E-27 -1.48191E-32 0.00000E+00
0.00000E+00 0.00000E+00 ASP5 -0.00102929 0.00000E+00 -3.82817E-11
1.56504E-13 -2.89929E-16 1.68400E-20 -5.96465E-25 1.20191E-29
0.00000E-00 0.00000E+00 0.00000E+00 ASP6 0.00541154 0.00000E+00
3.81649E-08 -1.10034E-12 -3.69090E-16 1.33858E-20 6.34523E-25
-3.45549E-29 0.00000E+00 0.00000E+00 0.00000E+00 ASP7 0.00102903
0.00000E+00 -3.14004E-08 2.67908E-13 -1.32597E-17 2.02315E-22
-5.49818E-27 -4.97090E-32 0.00000E+00 0.00000E+00 0.00000E+00 ASP8
-0.00012579 0.00000E+00 -5.21260E-09 -2.97679E-14 -4.97667E-19
1.15081E-23 -9.40202E-29 5.04787E-34 0.00000E-00 0.00000E+00
0.00000E+00 ASP9 0.00403277 0.00000E+00 4.99776E-08 -8.99272E-13
6.60787E-17 4.38434E-22 -4.24581E-26 4.81058E-30 0.00000E-00
0.00000E+00 0.00000E+00 ASP10 0.01060914 0.00000E+00 2.60785E-07
4.78050E-11 5.21548E-15 1.26891E-18 1.53552E-22 4.32477E-26
0.00000E-00 0.00000E+00 0.00000E+00 #12: Aspherical surface number
#13: Curvature
[0242] FIG. 13 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system
PL2 according to the present example. In FIG. 13, Y indicates the
image height, each dashed line the transverse aberration at the
wavelength of 193.3063 nm, each solid line the transverse
aberration at the wavelength of 193.3060, and each chain line the
transverse aberration at the wavelength of 193.3057 nm. As shown in
the transverse aberration diagram of FIG. 13, the catadioptric
projection optical system PL2 of the present example has the large
numerical aperture and is corrected in a good balance for
aberration throughout the entire exposure area though it has no
large optical element.
[0243] The fifth example of the embodiment will be described below
with reference to the drawing. FIG. 14 is an illustration showing a
lens configuration of the catadioptric projection optical system
according to the fifth example of the embodiment. The catadioptric
projection optical system PL1 of the fifth example is comprised of
the following optical systems in order from the object side (i.e.,
the reticle R1 side): a first imaging optical system G1 for forming
a first intermediate image and a second intermediate image of the
reticle R1 located on the first surface; and a second imaging
optical system G2 for relaying the second intermediate image of the
reticle R1 onto a wafer (not shown) located on the second
surface.
[0244] The first imaging optical system G1 is composed of a lens
unit with a positive refracting power (field lens unit) G11, and
after-described six reflecting mirrors M1-M6. The lens unit G11
functions to correct for distortion and others and to make the
optical system telecentric on the reticle R1 side. The lens unit
G11 functions to keep the size of the image of the reticle R1
unchanged even if the reticle R1 is placed with deviation from the
desired position in the direction of the optical axis AX1;
therefore, the performance of the catadioptric projection optical
system PL1 can be maintained high.
[0245] The second imaging optical system G2 is entirely composed of
transmitting optical elements and is composed of a lens unit with a
positive refracting power (first lens unit) G21, a lens unit with a
negative refracting power (second lens unit) G22, a lens unit with
a positive refracting power (third lens unit) G23, an aperture stop
AS1, and a lens unit with a positive refracting power (fourth lens
unit) G24. Since the second imaging optical system G2 is entirely
composed of the transmitting optical elements, it is free of the
optical path separation load; therefore, the image-side numerical
aperture of the catadioptric projection optical system PL1 can be
set large and a reduced image can be formed at a high reduction
rate on the wafer located on the second surface. The lens units
G21-G24 advantageously function for satisfying the Petzval's
condition. The configuration of the lens units G21-G24 is able to
avoid an increase in the total length of the catadioptric
projection optical system PL1. The lens units G21-G23 are effective
to correction for various aberrations such as coma.
[0246] Here the lens unit G11 is composed of the following
components in order of passage of rays from the object side
(reticle R1 side): a plane-parallel plate L1; a positive meniscus
lens L2 whose concave surface of aspherical shape is kept toward
the object; a biconvex lens L3; and a biconvex lens L4. The beam
transmitted by the biconvex lens L4 is reflected by the concave
reflecting mirror M1 whose concave surface of aspherical shape is
kept toward the object, the convex reflecting mirror M2 whose
convex surface of aspherical shape is kept toward the wafer, and
the concave reflecting mirror M3 whose concave surface is kept
toward the object, to form the first intermediate image. The beam
reflected by the reflecting mirror M3 is reflected by the convex
reflecting mirror M4 whose convex surface is kept toward the wafer,
the concave reflecting mirror M5 whose concave surface of
aspherical shape is kept toward the object, and the concave
reflecting mirror M6 whose concave surface is kept toward the
wafer.
[0247] Since the beam is continuously reflected by the reflecting
mirrors M1-M6 without intervention of any lens, the Petzval's
condition can be readily met by adjustment of each reflecting
mirror M1-M6. A region for holding each reflecting mirror M1-M6 can
be secured and it is easy to hold each reflecting mirror M1-M6. The
curvature of field can be readily corrected for by changing the
radius of curvature of each reflecting mirror M1-M6. The beam
reflected by the reflecting mirror M6 forms the second intermediate
image.
[0248] In this case, the concave reflecting mirror M3 is placed at
the position most distant from the optical axis AX1 and the beam
can be focused by this concave reflecting mirror M3; therefore, the
beam can be set largely apart from the optical axis AX1 of the
catadioptric projection optical system PL1, without intervention of
any lens between the reflecting mirrors M1-M6, whereby interference
can be avoided between beams. When the beam is continuously
reflected by the four reflecting mirrors M3-M6, it is feasible to
avoid an increase in the total length of the catadioptric
projection optical system PL1.
[0249] The lens unit G21 is composed of the following components in
order of passage of rays: a positive meniscus lens L5 whose convex
surface is kept toward the object; a positive meniscus lens L6
whose concave surface of aspherical shape is kept toward the wafer;
a positive meniscus lens L7 whose convex surface is kept toward the
object; a negative meniscus lens L8 whose convex surface is kept
toward the object; and a negative meniscus lens L9 whose convex
surface of aspherical shape is kept toward the object. The lens
unit G22 is composed of a biconcave lens L10 whose concave surface
of aspherical shape is kept toward the wafer. The lens unit G23 is
composed of the following components in order of passage of rays: a
planoconvex lens L11 whose plane of aspherical shape is kept toward
the object; a negative meniscus lens L12 whose convex surface is
kept toward the object; a biconvex lens L13; a positive meniscus
lens L14 whose convex surface is kept toward the object; and a
biconvex lens L15.
[0250] The lens unit G24 is composed of: a biconvex lens L16; a
positive meniscus lens L17 whose convex surface is kept toward the
object; a positive meniscus lens L18 whose concave surface of
aspherical shape is kept toward the wafer; a positive meniscus lens
L19 whose concave surface of aspherical shape is kept toward the
wafer; and a planoconvex lens L20 whose convex surface is kept
toward the object.
[0251] The catadioptric projection optical system PL1 is
constructed to satisfy the condition of 0.2<Mb/L<0.7, where M
is a distance on the optical axis AX1 between the reflecting mirror
M3 and the aperture stop AS1, and L the distance between the
reticle R1 and the wafer. When Mb/L is smaller than the lower
limit, it becomes difficult to place and keep the lenses L5-L15
constituting the lens units G21-G23 indispensable for correction
for various aberrations, particularly, coma, at their accurate
positions. Namely, when Mb/L satisfies the lower limit, it is
feasible to avoid mechanical interference of the concave reflecting
mirror M3 with the lens units G21-G23. When Mb/L satisfies the
upper limit, it is feasible to avoid an increase in the total
length and an increase in the size of the catadioptric projection
optical system PL1. For more accurately place and keep each lens
L5-L15 and securely avoiding the increase in the total length of
the catadioptric projection optical system PL1, the projection
optical system is more preferably constructed to satisfy the
condition of 0.25<Mb/L<0.6.
[0252] In this fifth example the first intermediate image is formed
between the reflecting mirror M3 and the reflecting mirror M4, but
the first intermediate image may be formed in any optical path
between the reflecting mirror M2 and the reflecting mirror M4.
[0253] Next, the sixth example of the embodiment will be described
with reference to the drawing. FIG. 15 is an illustration showing a
lens configuration of the catadioptric projection optical system
according to the sixth example of the embodiment. The catadioptric
projection optical system PL2 of the sixth example is comprised of
the following optical systems in order from the object side (i.e.,
the reticle R2 side): a first imaging optical system G3 for forming
a first intermediate image and a second intermediate image of the
reticle R2 located on the first surface; and a second imaging
optical system G4 for relaying the second intermediate image of the
reticle R2 onto a wafer (not shown) located on the second
surface.
[0254] The first imaging optical system G3 is composed of a lens
unit with a positive refracting power (field lens unit) G31,
after-described lens L25, and six reflecting mirrors M11-M16. The
lens unit G31 functions to correct for distortion and others and to
make the optical system telecentric on the reticle R2 side. The
lens unit G31 functions to keep the size of the image of the
reticle R2 unchanged even if the reticle R2 is placed with
deviation from the desired position in the optical-axis direction;
therefore, the performance of the catadioptric projection optical
system PL2 can be maintained high.
[0255] The second imaging optical system G4 is entirely composed of
transmitting optical elements and is composed of a lens unit with a
positive refracting power (first lens unit) G41, a lens unit with a
negative refracting power (second lens unit) G42, a lens unit with
a positive refracting power (third lens unit) G43, an aperture stop
AS2, and a lens unit with a positive refracting power (fourth lens
unit) G44. The second imaging optical system G4 is free of the
optical path separation load because it is entirely composed of the
transmitting optical elements; therefore, the image-side numerical
aperture of the catadioptric projection optical system PL2 can be
set large and a reduced image can be formed at a high reduction
rate on the wafer located on the second surface. The lens units
G41-G44 advantageously function for satisfying the Petzval's
condition. The configuration of the lens units G41-G44 effectively
avoids an increase in the total length of the catadioptric
projection optical system PL2. The lens units G41-G43 can correct
for various aberrations such as coma.
[0256] Here the lens unit G31 is composed of the following
components in order of passage of rays from the object side
(reticle R2 side): a plane-parallel plate L21; a positive meniscus
lens L22 whose concave surface of aspherical shape is kept toward
the object; a biconvex lens L23; and a biconvex lens L24. The beam
transmitted by the biconvex lens L24 passes through the negative
meniscus lens (negative lens) L25 with the concave surface kept
toward the object, is reflected by the concave reflecting mirror
M11 with the concave surface of aspherical shape kept toward the
object, and passes again through the negative meniscus lens L25.
The beam transmitted by the negative meniscus lens L25 is reflected
by the convex reflecting mirror M12 with the convex surface of
aspherical shape kept toward the wafer, to form the first
intermediate image. The beam reflected by the reflecting mirror M12
is reflected by the concave reflecting mirror M13 with the concave
surface kept toward the object, the convex reflecting mirror M14
with the convex surface kept toward the wafer, the concave
reflecting mirror M15 with the concave surface of aspherical shape
kept toward the object, and the concave reflecting mirror M16 with
the concave surface kept toward the wafer. By adjusting the
negative meniscus lens L25, it is feasible to readily correct for
chromatic aberration and to readily satisfy the Petzval's
condition. By changing the radius of curvature of each reflecting
mirror M11-M16, it is feasible to readily correct for curvature of
field. The beam reflected by the reflecting mirror M16 forms the
second intermediate image.
[0257] In this case, the concave reflecting mirror M13 is placed at
the position most distant from the optical axis AX2, and the beam
can be focused by this concave reflecting mirror M13; therefore,
the beam can be set largely apart from the optical axis AX2 of the
catadioptric projection optical system PL2, without intervention of
any lens between the four reflecting mirrors M13-M16, and it is
feasible to avoid interference between beams. By continuously
reflecting the beam by the four reflecting mirrors M13-M16, it is
feasible to avoid an increase in the total length of the
catadioptric projection optical system PL2.
[0258] The lens unit G41 is composed of the following components in
order of passage of rays: a positive meniscus lens L26 whose convex
surface is kept toward the object; a positive meniscus lens L27
whose concave surface of aspherical shape is kept toward the wafer;
a positive meniscus lens L28 whose convex surface is kept toward
the object; a positive meniscus lens L29 whose concave surface of
aspherical shape is kept toward the wafer; and a negative meniscus
lens L30 whose convex surface is kept toward the object.
[0259] The lens unit G42 is composed of a biconcave lens L31 formed
in the aspherical shape on the wafer side. The lens unit G43 is
composed of the following components in order of passage of rays: a
biconvex lens L32 formed in the aspherical shape on the object
side; a negative meniscus lens L33 whose convex surface is kept
toward the object; a biconvex lens L34; a biconvex lens L35; and a
biconvex lens L36. The lens unit G44 is composed of a biconvex lens
L37; a positive meniscus lens L38 whose convex surface is kept
toward the object; a positive meniscus lens L39 whose concave
surface of aspherical shape is kept toward the wafer; a positive
meniscus lens L40 whose concave surface of aspherical shape is kept
toward the wafer; and a planoconvex lens L41 whose convex surface
is kept toward the object.
[0260] The catadioptric projection optical system PL2 is
constructed to satisfy the condition of 0.2<M2b/L2<0.7, where
M2b is a distance on the optical axis AX2 between the reflecting
mirror M13 and the aperture stop AS2, and L2 the distance between
the reticle R2 and the wafer. When M2b/L2 is smaller than the lower
limit, it becomes difficult to place and keep each of the lenses
L26-L36 constituting the lens units G41-G43 indispensable for
correction for various aberrations, particularly, coma, at an
accurate position. Namely, when M2b/L2 satisfies the lower limit,
it is feasible to avoid mechanical interference of the concave
reflecting mirror M13 with the lens units G41-G43. When M2b/L2
satisfies the upper limit, it is feasible to avoid an increase in
the total length and an increase in the size of the catadioptric
projection optical system PL2. For placing and keeping each lens
L26-L36 at a more accurate position and securely avoiding the
increase in the total length of the catadioptric projection optical
system PL2, the optical system is more preferably constructed to
satisfy the condition of 0.25<M2b/L2<0.6.
[0261] In the sixth example, the first intermediate image is formed
between the reflecting mirror M12 and the reflecting mirror M13;
but the first intermediate image may be formed in any optical path
between the reflecting mirror M12 and the reflecting mirror
M14.
[0262] Next, the seventh example of the embodiment will be
described with reference to the drawing. FIG. 16 is an illustration
showing a lens configuration of the catadioptric projection optical
system according to the seventh example of the embodiment. The
catadioptric projection optical system PL3 of the seventh example
is comprised of the following optical systems in order from the
object side (i.e., the reticle R3 side): a first imaging optical
system G5 for forming a first intermediate image and a second
intermediate image of the reticle R3 located on the first surface;
and a second imaging optical system G6 for relaying the second
intermediate image of the reticle R3 onto a wafer (not shown)
located on the second surface.
[0263] The first imaging optical system G5 is composed of a lens
unit with a positive refracting power (field lens unit) G51, and
after-described six reflecting mirrors M21-M26. The lens unit G51
functions to correct for distortion and others and to make the
optical system telecentric on the reticle R2 side. The lens unit
G51 functions to keep the size of the image of the reticle R3
unchanged even if the reticle R3 is placed with deviation from the
desired position in the direction of the optical-axis AX3;
therefore, the performance of the catadioptric projection optical
system PL3 can be maintained high.
[0264] The second imaging optical system G6 is entirely composed of
transmitting optical elements, and is composed of a lens unit with
a positive refracting power (first lens unit) G61; a lens unit with
a negative refracting power (second lens unit) G62; a lens unit
with a positive refracting power (third lens unit) G63; an aperture
stop AS3; and a lens unit with a positive refracting power (fourth
lens unit) G64. Since the second imaging optical system G6 is
entirely constructed of the transmitting optical elements, it is
free of the optical path separation load; therefore, the image-side
numerical aperture of the catadioptric projection optical system
PL3 can be set large and a reduced image can be formed at a high
reduction rate on the wafer located on the second surface. The lens
units G61-G64 advantageously function for satisfying the Petzval's
condition. The configuration of the lens units G61-G64 effectively
avoids an increase in the total length of the catadioptric
projection optical system PL3. The lens units G61-G63 can correct
for various aberrations such as coma.
[0265] Here the lens unit G51 is composed of the following
components in order of passage of rays from the object side
(reticle R3 side): a plane-parallel plate L51; a positive meniscus
lens L52 whose concave surface of aspherical shape is kept toward
the object; a biconvex lens L53; and a biconvex lens L54. The beam
transmitted by the biconvex lens L54 is reflected by the concave
reflecting mirror M21 with the concave surface of aspherical shape
kept toward the object, the convex reflecting mirror M22 with the
convex surface of aspherical shape kept toward the wafer, and the
concave reflecting mirror M23 with the concave surface kept toward
the object, to form the first intermediate image. The beam
reflected by the reflecting mirror M23 is reflected by the convex
reflecting mirror M24 with the convex surface kept toward the
wafer, the convex reflecting mirror M25 with the convex surface of
aspherical shape kept toward the object, and the concave reflecting
mirror M26 with the concave surface kept toward the wafer.
[0266] Since the beam is continuously reflected by the reflecting
mirrors M21-M26 without intervention of any lens, it is feasible to
readily satisfy the Petzval's condition through adjustment of each
reflecting mirror M21-M26. In addition, a region for holding each
reflecting mirror M21-M26 can be secured, and the curvature of
field can be readily corrected for by changing the radius of
curvature of each reflecting mirror M21-M26. The beam reflected by
the reflecting mirror M26 aims the second intermediate image.
[0267] In this case, the concave reflecting mirror M23 is located
at the position most distant from the optical axis AX3, and the
beam can be focused by this concave reflecting mirror M23;
therefore, the beam can be set largely apart from the optical axis
AX3 of the catadioptric projection optical system PL3, without
intervention of any lens between the reflecting mirrors M21-M26,
and it is feasible to avoid interference between beams. Since the
beam is continuously reflected by the four reflecting mirrors
M23-M26, it is feasible to avoid an increase in the total length of
the catadioptric projection optical system PL3.
[0268] The lens unit G61 is composed of the following components in
order of passage of rays: a biconvex lens L55; a positive meniscus
lens L56 whose concave surface of aspherical shape is kept toward
the wafer; a positive meniscus lens L57 whose convex surface is
kept toward the object; a negative meniscus lens L58 whose convex
surface is kept toward the object; and a negative meniscus lens L59
whose convex surface of aspherical shape is kept toward the object.
The lens unit G62 is composed of a biconcave lens L60 whose concave
surface of aspherical shape is kept toward the wafer. The lens unit
G63 is composed of the following components in order of passage of
rays: a biconvex lens L61 whose convex surface of aspherical shape
is kept toward the object; a negative meniscus lens L62 whose
convex surface is kept toward the object; a biconvex lens L63; a
biconvex lens L64; and a positive meniscus lens L65 whose concave
surface is kept toward the object.
[0269] The lens unit G64 is composed of the following components in
order of passage of rays: a biconvex lens L66; a positive meniscus
lens L67 whose convex surface is kept toward the object; a positive
meniscus lens L68 whose concave surface of aspherical shape is kept
toward the wafer; a positive meniscus lens L69 whose concave
surface of aspherical shape is kept toward the wafer; and a
planoconvex lens L70 whose convex surface is kept toward the
object.
[0270] The catadioptric projection optical system PL3 is
constructed to satisfy the condition of 0.2<M3/L3<0.7, where
M3 is a distance on the optical axis AX3 between the reflecting
mirror M23 and the aperture stop AS3, and L3 the distance between
the reticle R3 and the wafer. When M3/L3 is smaller than the lower
limit, it becomes difficult to place and keep each of the lenses
L55-L65 constituting the lens units G61-G63 indispensable for
correction for various aberrations, particularly, coma, at an
accurate position. Namely, when M3/L3 satisfies the lower limit, it
is feasible to avoid mechanical interference of the concave
reflecting mirror M23 with the lens units G61-G63. When M3/L3
satisfies the upper limit, it is feasible to avoid an increase in
the total length and an increase in the size of the catadioptric
projection optical system PL3. For placing and keeping each lens
L55-L70 at a more accurate position and securely avoiding the
increase in the total length of the catadioptric projection optical
system PL3, the optical system is more preferably constructed to
satisfy the condition of 0.25<M3/L3<0.6.
[0271] In this seventh example, the first intermediate image is
formed between the reflecting mirror M23 and the reflecting mirror
M24, but the first intermediate image may be formed in any optical
path between the reflecting mirror M22 and the reflecting mirror
M24.
[0272] In application of the catadioptric projection optical
systems PL1-PL3 of the fifth to seventh examples to the exposure
apparatus, pure water (deionized water) with the refractive index
of about 1.4 is interposed in the optical path between the
planoconvex lens L20, L41, or L70 and the wafer, where the
refractive index of the atmosphere in the catadioptric projection
optical system PL1-PL3 is 1. Therefore, the wavelength of the
exposure light in pure water is about 0.71 (1/1.4) times that in
the atmosphere, whereby the resolution can be enhanced.
[0273] The optical axis AX1-AX3 of every optical element included
in the catadioptric projection optical system PL1-PL3 and having
the predetermined refracting power is arranged substantially on the
single straight line, and the region of the image formed on the
wafer by the catadioptric projection optical system PL1-PL3 is the
off-axis region not including the optical axis AX1-AX3. Therefore,
it is feasible to reduce the degree of difficulty of production in
production of the catadioptric projection optical system PL1-PL3
and to readily achieve relative adjustment of each optical
element.
[0274] Since the catadioptric projection optical system PL1-PL3
according to the fifth to the seventh examples includes the six
reflecting mirrors M1-M6, M11-M16, M21-M26, it is feasible to
readily and securely achieve the optical path separation between
the beam toward the reticle R1-R3 and the beam toward the wafer,
without an increase in the total length of the catadioptric
projection optical system PL1-PL3, even in the case where the
reticle R1-R3-side and wafer-side numerical apertures of the
catadioptric projection optical system PL1-PL3 are increased in
order to enhance the resolution.
[0275] The catadioptric projection optical system PL1-PL3 according
to the fifth to seventh examples is a thrice-imaging optical system
for forming the first intermediate image and the second
intermediate image, in which the first intermediate image is an
inverted image of the reticle R1-R3, the second intermediate image
is an erect image of the reticle R1-R3, and the image formed on the
wafer is an inverted image. Therefore, in the case where the
catadioptric projection optical system PL1-PL3 is mounted on the
exposure apparatus and where the exposure is carried out with
scanning of the reticle R1-R3 and the wafer, the scanning direction
of the reticle R1-R3 can be opposite to that of the wafer, and it
is feasible to readily achieve such adjustment as to decrease a
change in the center of gravity of the entire exposure apparatus.
It is also feasible to reduce vibration of the catadioptric
projection optical system PL1-PL3 due to the change in the center
of gravity of the entire exposure apparatus and to achieve good
imaging performance throughout the entire region in the exposure
area.
[0276] In the catadioptric projection optical system PL1, PL3 of
each of the above examples, pure water (deionized water) is
interposed between the lens located nearest to the wafer, and the
wafer, but another medium having the refractive index larger than
1.1 may be interposed, where the refractive index of the atmosphere
in the catadioptric projection optical system PL1-PL3 is 1.
[0277] Next, values of specifications of the catadioptric
projection optical system PL1 according to the fifth example shown
in FIG. 14 will be presented. In the specifications, as shown in
FIG. 11 described above, A represents a radius of a portion where
the exposure light is blocked by the optical elements constituting
the catadioptric projection optical system PL1, with the center on
the optical axis AX1 of the catadioptric projection optical system
PL1, B a radius of the maximum image height with the center on the
optical axis AX1 of the catadioptric projection optical system PL1,
H a length along the Y-direction of the effective exposure region,
and C a length along the X-direction of the effective exposure
region. In the specifications, NA indicates the numerical aperture,
d the surface separation, n the refractive index, and .lamda. the
center wavelength. Furthermore, in the specifications, M indicates
the distance on the optical axis AX1 between the concave reflecting
mirror M3 and the unrepresented wafer, and L the distance between
the reticle R1 and the wafer.
[0278] Table 7 presents the specifications of the optical members
of the catadioptric projection optical system PL1 according to the
fifth example. In the specifications of the optical members of
Table 7, each surface number in the first column is an order of a
surface along the traveling direction of rays from the object side,
the second column a radius of curvature of each surface (mm), the
third column an on-axis spacing or surface separation (mm) of each
surface, and the fourth column a glass material of each optical
member.
[0279] Table 8 presents the aspherical coefficients of the lenses
with the lens surface of aspherical shape and the reflecting
mirrors used in the catadioptric projection optical system PL1
according to the fifth example. In the aspherical coefficients of
Table 8, aspherical surface numbers in the first column correspond
to the surface numbers in the specifications of the optical members
of Table 7. The second column represents the curvature of each
aspherical surface (1/mm), the third column the conical coefficient
k and the 12th-order aspherical coefficient, the fourth column the
4th-order and 14th-order aspherical coefficients, the fifth column
the 6th-order and 16th-order aspherical coefficients, the sixth
column the 8th-order and 18th-order aspherical coefficients, and
the seventh column the 10th-order and 20th-order aspherical
coefficients.
[0280] In the fifth to seventh examples, each aspherical surface is
expressed by Eq (a) described above.
Fifth Example
Specifications
[0281] Image-side NA: 1.20
[0282] Exposure area: A=14 mm B=18 mm [0283] H=26.0 mm C=4 mm
[0284] Imaging magnification: 1/4
[0285] Center wavelength: 193.306 nm
[0286] Refractive index of silica: 1.5603261
[0287] Refractive index of fluorite: 1.5014548
[0288] Refractive index of liquid 1: 1.43664
[0289] Dispersion of silica (dn/d.lamda.):
-1.591.times.10.sup.-6/pm
[0290] Dispersion of fluorite (dn/d.lamda.):
-0.980.times.10.sup.-6/pm
[0291] Dispersion of pure water (deionized water) (dn/d.lamda.):
-2.6.times.10.sup.-6/pm
[0292] Values corresponding to Condition Mb=524.49 mm L=1400 mm
TABLE-US-00007 TABLE 7 (Specifications of Optical Members) #2 #3
#15 #1 .infin. 45.0000 1: .infin. 8.0000 #5 2: .infin. 9.4878 3:
ASP1 25.3802 #5 4: -244.04741 1.9583 5: 2654.01531 49.2092 #5 6:
-159.85154 1.1545 7: 294.54453 34.3095 #5 8: -572.08259 156.2051 9:
ASP2 -136.2051 #6 10: ASP3 412.6346 #6 11: -418.20026 -205.0204 #6
12: -604.04130 160.2153 #6 13: ASP4 -211.6245 #6 14: 320.60531
226.6245 15: 224.13260 25.2194 #5 16: 346.75878 1.0000 17:
215.47954 34.3600 #5 18: ASP5 1.0000 19: 266.87857 19.9995 #5 20:
329.19442 1.0000 21: 196.43240 20.0000 #5 22: 115.87410 6.4756 23:
ASP6 39.3045 #5 24: 99.87482 55.9109 25: -412.64757 24.7282 #5 26:
ASP7 94.8545 27: ASP8 57.3966 #5 28: -227.16104 1.0000 29:
504.83819 20.0000 #6 30: 407.86902 12.3535 31: 595.98854 43.0398 #5
32: -2001.40538 1.0000 #8 33: 711.19871 32.6046 #5 34: 8598.79354
32.0466 35: 36209.93141 30.0000 #5 36: -1731.78793 1.0000 37:
.infin. 12.6069 #7 38: 503.84491 53.3626 #5 39: -1088.61181 1.0000
40: 192.53858 61.7603 #5 41: 521.19424 1.0000 42: 122.79200 59.8433
#5 43: ASP9 1.0000 44: 79.97315 39.6326 #14 45: ASP10 1.0000 46:
84.68828 36.1715 #14 47: .infin. 1.0000 #8 #9 .infin. 0.0000 #1:
1st surface #2: Radius of curvature (mm) #3: Surface spacing (mm)
#5: silica glass #6: reflecting mirror #7: aperture stop #8: pure
water #9: 2nd surface #14: Fluorite #15: Name of glass material
TABLE-US-00008 TABLE 8 (Aspherical Coefficients) k c4 c6 c8 c10 #
12 # 13 c12 c14 c16 c18 c20 ASP1 -0.00059023 0.00000E+00
-2.87641E-08 -1.70437E-11 2.46285E-15 -2.74317E-19 2.07022E-23
-7.79530E-28 0.00000E+00 0.00000E+00 0.00000E+00 ASP2 -0.00205780
0.00000E+00 2.50612E-09 2.95240E-14 4.37607E-18 -5.55238E-22
3.88749E-26 -1.13016E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP3
-0.00058562 0.00000E+00 -0.92554E-09 1.39659E-13 -1.09871E-18
3.37519E-23 -1.45573E-27 2.27951E-32 0.00000E+00 0.00000E+00
0.00000E+00 ASP4 -0.00123249 0.00000E+00 1.93713E-09 1.07185E-12
-3.34552E-16 3.54315E-20 -5.95219E-24 3.41899E-28 0.00000E+00
0.00000E+00 0.00000E+00 ASP5 0.00020189 0.00000E+00 1.37544E-07
-1.06394E-11 7.70843E-17 4.90298E-20 -3.23126E-24 6.76814E-29
0.00000E+00 0.00000E+00 0.00000E+00 ASP6 0.00588235 0.00000E+00
2.41559E-07 -1.03766E-11 -6.75114E-17 1.11214E-19 -9.45408E-24
3.57981E-28 0.00000E+00 0.00000E+00 0.00000E+00 ASP7 0.00664255
0.00000E+00 2.62150E-08 -9.25480E-12 -1.77845E-16 5.60675E-20
-2.81549E-24 6.89450E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP8
0.00000000 0.00000E+00 -1.26430E-08 1.64939E-13 -6.24373E-18
2.07576E-22 -5.07100E-27 1.49848E-31 0.00000E+00 0.00000E+00
0.00000E+00 ASP9 0.00345726 0.00000E+00 5.92282E-08 -1.56640E-12
1.38582E-18 -4.07966E-21 1.49819E-25 1.10869E-30 0.00000E+00
0.00000E+00 0.00000E+00 ASP10 0.01038095 0.00000E+00 2.42802E-07
4.29652E-11 1.62230E-15 6.50272E-19 3.23667E-22 -9.21777E-26
0.00000E+00 0.00000E+00 0.00000E+00 #12: Aspherical surface number
#13: Curvature
[0293] FIG. 17 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system
PL1 according to the present example. In FIG. 17, Y indicates the
image height, each dashed line the transverse aberration at the
wavelength of 193.3063 nm, each solid line the transverse
aberration at the wavelength of 193.3060 nm, and each chain line
the transverse aberration at the wavelength of 193.3057 nm. As
shown in the transverse aberration diagram of FIG. 17, the
catadioptric projection optical system PL1 of the present example
has the large numerical aperture and is corrected in a good balance
for aberration throughout the entire exposure area though it has no
large optical element.
[0294] Next, the specifications of the catadioptric projection
optical system PL2 according to the sixth example shown in FIG. 15
will be presented. Table 9 presents the specifications of the
optical members of the catadioptric projection optical system PL2
according to the sixth example. Table 10 presents the aspherical
coefficients of the lenses with the lens surface of aspherical
shape and the reflecting mirrors used in the catadioptric
projection optical system PL2 according to the sixth example. In
the specifications, the specifications of the optical members, and
the aspherical coefficients, the description will be given using
the same symbols as those in the description of the catadioptric
projection optical system PL1 according to the fifth example.
Sixth Example
Specifications
[0295] Image-side NA: 1.20
[0296] Exposure area: A=13 mm B=17 mm [0297] H=26.0 mm C=4 mm
[0298] Imaging magnification: 1/4
[0299] Center wavelength: 193.306 nm
[0300] Refractive index of silica: 1.5603261
[0301] Refractive index of fluorite: 1.5014548
[0302] Refractive index of liquid 1: 1.43664
[0303] Dispersion of silica (dn/d.lamda.):
-1.591.times.10.sup.-6/pm
[0304] Dispersion of fluorite (dn/d.lamda.):
-0.980.times.10.sup.-6/pm
[0305] Dispersion of pure water (deionized water) (dn/d.lamda.):
-2.6.times.10.sup.-6/pm
[0306] Values corresponding to Condition Mb=482.14 mm L=1400 mm
TABLE-US-00009 TABLE 9 (Specifications of Optical Members) #2 #3
#15 #1 .infin. 50.9535 1: .infin. 8.0000 #5 2: .infin. 12.7478 3:
ASP1 32.5506 #5 4: -184.43053 1.0000 5: 532.87681 45.9762 #5 6:
-271.53626 1.3173 7: 374.46315 38.0103 #5 8: -361.42951 147.1771 9:
-389.08052 20.0000 #5 10: -594.49774 5.5356 11: ASP2 -5.5356 #6 12:
-594.49774 -20.0000 #5 13: -389.08052 -127.0301 14: ASP3 430.8932
#5 15: -450.43913 -215.6393 #6 16: -704.67689 153.6952 #6 17: ASP4
-206.3833 #6 18: 317.07489 228.3275 #6 19: 248.60032 30.8186 #5 20:
964.03405 1.0000 21: 170.07823 20.0000 #5 22: ASP5 1.0778 23:
174.13726 29.8902 #5 24: 294.93424 1.0798 25: 160.77849 33.1276 #5
26: ASP6 9.4275 27: 1185.57325 20.0000 #5 28: 103.90360 46.9708 29:
-676.67026 24.5184 #5 30: ASP7 83.5410 31: ASP8 47.4275 #5 32:
-317.19307 1.0000 33: 688.27957 20.0000 #5 34: 513.64357 11.2866
35: 883.25368 40.1774 #5 36: -959.41738 1.0000 #8 37: 1222.93397
34.5841 #5 38: -1403.11949 16.9031 39: 2169.40706 37.3055 #5 40:
-889.78387 1.0000 41: .infin. 9.8461 #7 42: 458.32781 52.3568 #5
43: -1741.66958 1.0000 44: 215.86566 59.3939 #5 45: 659.70674
1.0000 46: 134.64784 58.8510 #5 47: ASP9 1.0004 48: 96.99608
49.9011 #5 49: ASP10 1.0194 50: 80.22245 40.8996 #5 51: .infin.
1.0000 #9 .infin. #1: 1st surface #2: Radius of curvature (mm) #3:
Surface spacing (mm) #5: silica glass #6: reflecting mirror #7:
aperture stop #8: pure water #9: 2nd surface #14: Fluorite #15:
Name of glass material
TABLE-US-00010 TABLE 10 (Aspherical Coefficients) k c4 c6 c8 c10 #
12 # 13 c12 c14 c16 c18 c20 ASP1 -0.00057910 0.00000E+00
-9.03366E-08 3.28394E-12 -4.08402E-18 2.52900E-20 -9.19294E-25
2.02082E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP2 -0.00243076
0.00000E+00 3.35076E-09 2.88286E-14 8.73468E-18 -7.00011E-22
4.21327E-26 -9.88714E-31 0.00000E+00 0.00000E+00 0.00000E+00 ASP3
-0.00032257 0.00000E+00 -6.53400E-09 1.15038E-13 -0.61655E-19
8.51651E-23 -3.17817E-27 4.60017E-32 0.00000E+00 0.00000E+00
0.00000E+00 ASP4 -0.00058501 0.00000E+00 2.54270E-09 0.81523E-13
-1.08474E-16 0.27 15E-21 -7.45415E-25 6.45741E-29 0.00000E+00
0.00000E+00 0.00000E+00 ASP5 0.00574270 0.00000E+00 2.69000E-08
-1.93073E-12 -2.23058E-16 2.03519E-20 -2.27002E-24 8.48621E-29
0.00000E+00 0.00000E+00 0.00000E+00 ASP6 0.00281530 0.00000E+00
-7.99356E-08 1.14147E-11 -4.87397E-16 6.76022E-20 -3.55808E-24
1.84260E-28 0.00000E+00 0.00000E+00 0.00000E+00 ASP7 0.00667798
0.00000E+00 -1.01256E-08 -5.60515E-12 -6.85243E-17 2.18957E-20
-1.24639E-24 -1.61382E-29 0.00000E+00 0.00000E+00 0.00000E+00 ASP8
0.00000970 0.00000E+00 -1.68383E-08 1.90215E-13 -8.11478E-18
3.37339E-22 -1.15048E-26 5.21646E-31 0.00000E+00 0.00000E+00
0.00000E+00 ASP9 0.00313892 0.00000E+00 4.21089E-08 -8.07510E-13
5.31944E-17 -4.15004E-22 -5.28946E-27 1.60853E-30 0.00000E+00
0.00000E+00 0.00000E+00 ASP10 0.00959788 0.00000E+00 2.16924E-07
3.52791E-11 1.11831E-15 1.12987E-18 -4.81835E-23 1.62262E-26
0.00000E+00 0.00000E+00 0.00000E+00 #12: Aspherical surface number
#13: Curvature indicates data missing or illegible when filed
[0307] FIG. 18 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system
PL2 according to the present example. In FIG. 18, Y indicates the
image height, each dashed line the wavelength of 193.3063 nm, each
solid line the wavelength of 193.3060 nm, and each chain line the
wavelength of 193.3057 nm. As shown in the transverse aberration
diagram of FIG. 18, the catadioptric projection optical system PL2
of the present example has the large numerical aperture and is
corrected in a good balance for aberration throughout the entire
exposure area though it has no large optical element.
[0308] Next, the specifications of the catadioptric projection
optical system PL3 according to the seventh example shown in FIG.
16 will be presented. Table 11 presents the specifications of the
optical members of the catadioptric projection optical system PL3
according to the seventh example. Table 12 presents the aspherical
coefficients of the lenses with the lens surface of aspherical
shape and the reflecting mirrors used in the catadioptric
projection optical system PL3 according to the seventh example. In
the specifications, the specifications of the optical members, and
the aspherical coefficients, the description will be given using
the same symbols as those in the description of the catadioptric
projection optical system PL1 according to the fifth example.
Seventh Example
Specifications
[0309] Image-side NA: 1.20
[0310] Exposure area: A=13 mm B=17 mm [0311] H=26.0 mm C=4 mm
[0312] Imaging magnification: 1/5
[0313] Center wavelength: 193.306 nm
[0314] Refractive index of silica: 1.5603261
[0315] Refractive index of fluorite: 1.5014548
[0316] Refractive index of liquid 1: 1.43664
[0317] Dispersion of silica (dn/d.lamda.):
-1.591.times.10.sup.-6/pm
[0318] Dispersion of fluorite (dn/d.lamda.):
-0.980.times.10.sup.-6/pm
[0319] Dispersion of pure water (deionized water) (dn/d.lamda.):
-2.6.times.10.sup.-6/pm
[0320] Condition Mb=508.86 mm L=1400 mm
TABLE-US-00011 TABLE 11 (Specifications of Optical Members) #2 #3
#15 #1 .infin. 63.0159 1: .infin. 8.0000 #5 2: .infin. 11.6805 3:
ASP1 30.7011 #5 4: -244.82575 1.0000 5: 520.72375 50.6283 #5 6:
-283.00136 1.0000 7: 455.76731 37.0794 #5 8: -509.23840 143.7025 9:
ASP2 -123.7025 #5 10: ASP3 394.2980 #5 11: -398.57468 -201.7192 #6
12: -485.11237 157.8027 #6 13: ASP4 -206.6789 #6 14: 329.37813
221.6789 #6 15: 411.95851 28.1592 #5 16: -3890.38387 1.1778 17:
141.65647 33.4870 #5 18: ASP5 1.0000 19: 216.09570 28.6534 #5 20:
461.77835 1.0000 21: 202.12479 20.2182 #5 22: 117.79321 2.6054 23:
ASP6 20.0000 #5 24: 98.31887 51.9992 25: -251.39135 35.2622 #5 26:
ASP7 89.1855 27: ASP8 42.0591 #5 28: -303.33648 2.1164 29:
606.18864 28.5148 #5 30: 488.85229 11.9006 31: 811.09260 45.2273 #5
32: -813.38538 1.0000 33: 1012.41934 42.1336 #5 34: -973.64830
21.5611 35: -32382.97410 29.5159 #5 36: -1075.05682 1.0000 37:
.infin. 6.3302 #7 38: 371.59007 56.0505 #5 39: -4689.87645 9.3746
40: 204.82419 53.7618 #5 41: 494.59116 1.0000 42: 125.95227 57.4813
#5 43: ASP9 1.0101 44: 92.58526 43.4772 #5 45: ASP10 1.0360 46:
85.28679 42.2466 #5 47: .infin. 1.0000 #8 #9 .infin. #1: 1st
surface #2: Radius of curvature (mm) #3: Surface spacing (mm) #5:
silica glass #6: reflecting mirror #7: aperture stop #8: pure water
#9: 2nd surface #14: Fluorite #15: Name of glass material
TABLE-US-00012 TABLE 12 (Aspherical Coefficients) k c4 c6 c8 c10 #
12 # 13 c12 c14 c16 c18 c20 ASP1 -0.0004476 0.00000E+00
-6.28600E-08 2.01003E-12 -1.86171E-16 4.72866E-21 4.25382E-26
-8.36739E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP2 -0.0019308
0.00000E+00 5.30847E-09 2.32487E-13 -9.96057E-18 1.35214E-21
-9.28498E-26 2.73795E-30 0.00000E+00 0.00000E+00 0.00000E+00 ASP3
0.0000635 0.00000E+00 -1.46917E-08 2.39879E-13 1.88016E-18
-1.08670E-22 1.55922E-27 -1.05341E-32 0.00000E+00 0.00000E+00
0.00000E+00 ASP4 -0.0009742 0.00000E+00 2.25661E-09 8.15504E-13
-1.75777E-16 1.04720E-20 -2.44697E-24 2.57932E-28 0.00000E+00
0.00000E+00 0.00000E+00 ASP5 0.0045455 0.00000E+00 7.76937E-08
-8.42991E-12 3.25677E-16 8.77802E-23 -2.71916E-25 -2.25230E-30
0.00000E+00 0.00000E+00 0.00000E+00 ASP6 0.0078125 0.00000E+00
1.83201E-07 -2.17156E-11 1.87637E-15 -2.53394E-19 1.70711E-23
-1.55669E-27 0.00000E+00 0.00000E+00 0.00000E+00 ASP7 0.0063619
0.00000E+00 3.50299E-09 -5.60629E-12 -2.85922E-18 2.57458E-20
-2.26008E-24 3.14291E-29 0.00000E+00 0.00000E+00 0.00000E+00 Asp8
0.0001516 0.00000E+00 -1.73728E-08 2.07225E-13 -7.88040E-18
2.99860E-22 -0.28797E-27 3.18623E-31 0.00000E+00 0.00000E+00
0.00000E+00 ASP9 0.0037449 0.00000E+00 4.54024E-08 -8.98172E-13
6.42893E-17 5.94025E-22 -6.11068E-26 4.37709E-30 0.00000E+00
0.00000E+00 0.00000E+00 ASP10 0.0093466 0.00000E+00 2.17665E-07
2.75156E-11 1.89892E-15 3.45960E-19 7.23960E-23 -1.19099E-26
0.00000E+00 0.00000E+00 0.00000E+00 #12: Aspherical surface number
#13: Curvature
[0321] FIG. 19 is a transverse aberration diagram showing the
transverse aberration in the meridional direction and in the
sagittal direction of the catadioptric projection optical system
PL3 according to the present example. In FIG. 19, Y indicates the
image height, each dashed line the wavelength of 193.3063 nm, each
solid line the wavelength of 193.3060 nm, and each chain line the
wavelength of 193.3057 nm. As shown in the transverse aberration
diagram of FIG. 19, the catadioptric projection optical system PL3
of the present example has the large numerical aperture and is
corrected in a good balance for aberration throughout the entire
exposure area though it has no large optical element.
[0322] The projection optical systems of the respective examples
described above can be applied each to the projection exposure
apparatus shown in FIG. 1. The projection exposure apparatus shown
in FIG. 1 is able to increase the effective numerical aperture on
the wafer W side to 1.0 or more and to enhance the resolution,
because pure water with the refractive index of about 1.4 for the
exposure light is interposed between the projection optical system
PL and the wafer W. Since the projection exposure apparatus shown
in FIG. 1 has the projection optical system PL consisting of the
catadioptric projection optical system according to each of the
aforementioned examples, it is able to readily and securely achieve
the optical path separation between the beam toward the reticle and
the beam toward the wafer in the projection optical system PL, even
in the case where the reticle-side and wafer-side numerical
apertures are increased. Therefore, good imaging performance can be
achieved throughout the entire region in the exposure area and a
fine pattern can be suitably exposed.
[0323] Since the projection exposure apparatus shown in FIG. 1 uses
the ArF excimer laser light as the exposure light, pure water is
supplied as the liquid for liquid immersion exposure. Pure water is
easily available in large quantity in semiconductor manufacturing
facilities and others and has the advantage of no adverse effect on
the photoresist on the substrate (wafer) W, the optical elements
(lenses), and others. Since pure water has no adverse effect on
environments and contains an extremely low amount of impurities, we
can also expect the action of cleaning the surface of the wafer W
and the surface of the optical element located on the end surface
of the projection optical system PL.
[0324] Pure water (water) is said to have the refractive index n of
about 1.44 for the exposure light of the wavelength of
approximately 193 nm. In the case where the ArF excimer laser light
(wavelength 193 nm) is used as a light source of exposure light,
the wavelength is reduced to 1/n, i.e., about 134 nm on the
substrate to achieve a high resolution. Furthermore, the depth of
focus is increased to about n times or about 1.44 times that in
air.
[0325] The liquid can also be another medium having the refractive
index larger than 1.1 for the exposure light. In this case, the
liquid can be any liquid that is transparent to the exposure light,
has the refractive index as high as possible, and is stable against
the projection optical system PL and the photoresist on the surface
of the wafer W.
[0326] Where the F.sub.2 laser light is used as the exposure light,
the liquid can be a fluorinated liquid, for example, such as
fluorinated oils and perfluorinated polyethers (PFPE), which can
transmit the F.sub.2 laser light.
[0327] The present invention is also applicable to the exposure
apparatus of the twin stage type provided with two stages
independently movable in the XY directions while separately
carrying their respective substrates to be processed, such as
wafers, as disclosed in Japanese Patent Applications Laid-Open No.
10-163099, Laid-Open No. 10-214783, Jp-A-2000-505958, and so
on.
[0328] When the liquid immersion method is applied as described
above, the numerical aperture (NA) of the projection optical system
PL can be 0.9 to 1.3. In cases where the numerical aperture (NA) of
the projection optical system PL is so large as described, use of
randomly polarized light conventionally applied as the exposure
light can degrade the imaging performance by virtue of its
polarization effect, and it is thus desirable to use polarized
illumination. A preferred configuration in those cases is such that
linearly polarized illumination is effected in alignment with the
longitudinal direction of line patterns of line-and-space patterns
on the reticle (mask) R so that diffracted light of the s-polarized
component (component in the polarization direction along the
longitudinal direction of the line patterns) is more emitted from
the patterns of the reticle (mask) R. When the liquid fills the
space between the projection optical system PL and the resist
applied on the surface of the wafer W, the transmittance becomes
higher on the resist surface for the diffracted light of the
s-polarized component contributing to improvement in contrast than
in the case where air (gas) fills the space between the projection
optical system PL and the resist applied on the surface of the
wafer W. For this reason, the high imaging performance can also be
achieved even in the case where the numerical aperture (NA) of the
projection optical system PL exceeds 1.0. It is more effective to
use the phase shift mask, the oblique incidence illumination method
(particularly, the dipole illumination) in alignment with the
longitudinal direction of line patterns as disclosed in Japanese
Patent Application Laid-Open No. 6-188169, etc. properly in
combination.
[0329] The exposure apparatus of the aforementioned embodiment can
produce microdevices (semiconductor devices, image pickup devices,
liquid-crystal display devices, thin-film magnetic heads, etc.) by
illuminating the reticle (mask) by the illumination device
(illumination step) and performing an exposure of a transcription
pattern formed on the mask, onto the photosensitive substrate by
the projection optical system (exposure step). An example of a
method for producing semiconductor devices as microdevices by
forming a predetermined circuit pattern on a wafer or the like as a
photosensitive substrate by use of the exposure apparatus of the
present embodiment will be described below with reference to the
flowchart of FIG. 20.
[0330] First, step 301 in FIG. 20 is to form an evaporated metal
film on each of wafers in one lot. Next step 302 is to apply a
photoresist onto the metal film on each of the wafers in the lot.
Thereafter, step 303 is to sequentially perform an exposure to
transcribe an image of a pattern on a mask into each shot area on
each of the wafers in the lot through the projection optical
system, using the exposure apparatus of the present embodiment.
Step 304 thereafter is to perform development of the photoresist on
each of the wafers in the lot, and next step 305 is to perform
etching with the resist pattern as a mask on each of the wafers in
the lot to form a circuit pattern corresponding to the pattern on
the mask, in each shot area on each wafer.
[0331] Thereafter, through formation of circuit patterns of upper
layers and others, the devices such as semiconductor devices are
produced. The semiconductor device production method described
above permits us to obtain the semiconductor devices with an
extremely fine circuit pattern at high throughput. Step 301 to step
305 are to perform the respective steps of evaporation of metal on
the wafers, application of the resist onto the metal film,
exposure, development, and etching, but it is needless to mention
that the method may be so arranged that, prior to these steps, a
silicon oxide film is formed on the wafer and thereafter the resist
is applied onto the silicon oxide film, followed by the respective
steps of exposure, development, etching, and so on.
[0332] The exposure apparatus of the present embodiment can also
produce a liquid-crystal display device as a microdevice by forming
predetermined patterns (circuit pattern, electrode pattern, etc.)
on a plate (glass substrate). An example of a method of this
production will be described below with reference to the flowchart
of FIG. 21. In FIG. 21, pattern forming step 401 is to execute a
so-called photolithography step of performing an exposure to
transcribe a pattern of a mask onto a photosensitive substrate (a
glass substrate coated with a resist or the like) by the exposure
apparatus of the present embodiment. This photolithography step
results in forming the predetermined pattern including a number of
electrodes and others on the photosensitive substrate. Thereafter,
the exposed substrate is processed through respective steps of
development, etching, resist removal, and so on to form a
predetermined pattern on the substrate, and is then transferred to
next color filter forming step 402.
[0333] Next, the color filter forming step 402 is to form a color
filter in a configuration wherein a number of sets of three dots
corresponding to R (Red), G (Green), and B (Blue) are arrayed in a
matrix, or in a configuration wherein a plurality of sets of
filters of three stripes of R, G, and B are arranged in the
direction of horizontal scan lines. After the color filter forming
step 402, cell assembly step 403 is then executed. The cell
assembly step 403 is to assemble a liquid crystal panel (liquid
crystal cell), using the substrate with the predetermined pattern
obtained in the pattern forming step 401, the color filter obtained
in the color filter forming step 402, and so on. In the cell
assembly step 403, for example, a liquid crystal is poured into the
space between the substrate with the predetermined pattern obtained
in the pattern forming step 401 and the color filter obtained in
the color filter forming step 402, thereby producing a liquid
crystal panel (liquid crystal cell).
[0334] Module assembly step 404 thereafter is to attach each of
components such as an electric circuit, a backlight, etc. for
display operation of the assembled liquid crystal panel (liquid
crystal cell), thereby completing a liquid-crystal display device.
The production method of the liquid-crystal display device
described above permits liquid-crystal display devices with the
extremely fine circuit pattern to be produced at high
throughput.
[0335] As described above, the projection optical system according
to the first aspect of the embodiment comprises at least two
reflecting mirrors and the boundary lens with the surface on the
first surface side having the positive refracting power, has all
the transmitting members and reflecting members arranged along the
single optical axis, and has the effective imaging area not
including the optical axis, wherein the optical path between the
boundary lens and the second surface is filled with the medium
having the refractive index larger than 1.1. As a result, the
embodiment successfully realizes the relatively compact projection
optical system having the excellent imaging performance as well
corrected for various aberrations such as chromatic aberration and
curvature of field and being capable of securing the large
effective image-side numerical aperture while well suppressing the
reflection loss on the optical surfaces.
[0336] In the projection optical system according to the second
aspect of the embodiment, the intermediate image of the first
surface is formed in the first imaging optical system, and it is
thus feasible to readily and securely achieve the optical path
separation between the beam toward the first surface and the beam
toward the second surface, even in the case where the numerical
apertures of the projection optical system are increased. Since the
second imaging optical system is provided with the first lens unit
having the negative refracting power, it is feasible to shorten the
total length of the catadioptric projection optical system and to
readily achieve the adjustment for satisfying the Petzval's
condition. Furthermore, the first lens unit relieves the variation
due to the difference of field angles of the beam expanded by the
first field mirror, so as to suppress occurrence of aberration.
Therefore, good imaging performance can be achieved throughout the
entire region in the exposure area, even in the case where the
object-side and image-side numerical apertures of the catadioptric
projection optical system are increased in order to enhance the
resolution.
[0337] The projection optical system according to the third aspect
of the embodiment comprises at least six mirrors, and thus the
first intermediate image and the second intermediate image can be
formed without increase in the total length of the catadioptric
projection optical system, even in the case where the object-side
and image-side numerical apertures of the catadioptric projection
optical system are increased in order to enhance the resolution.
Therefore, it is feasible to readily and securely achieve the
optical path separation between the beam toward the first surface
and the beam toward the second surface. Since the projection
optical system is provided with at least six mirrors and the second
lens unit having the negative refracting power, the Petzval's
condition can be readily met and correction for aberration can be
readily made, through the adjustment of each mirror or each lens
forming the second lens unit, or the like.
[0338] The projection optical system according to the third aspect
of the embodiment is the thrice-imaging optical system, whereby the
first intermediate image is an inverted image of the first surface,
the second intermediate image an erect image of the first surface,
and the image formed on the second surface an inverted image.
Therefore, in the case where the catadioptric projection optical
system of the embodiment is mounted on the exposure apparatus and
where the exposure is carried out with scanning of the first
surface and the second surface, the scanning direction of the first
surface can be made opposite to that of the second surface and it
is feasible to readily achieve such adjustment as to decrease the
change in the center of gravity of the entire exposure apparatus.
By reducing the change in the center of gravity of the entire
exposure apparatus, it is feasible to reduce the vibration of the
catadioptric projection optical system and to achieve good imaging
performance throughout the entire region in the exposure area.
[0339] Accordingly, the exposure apparatus and exposure method
using the projection optical system of the embodiment are able to
perform the exposure to transcribe a fine pattern with high
precision, through the projection optical system having the
excellent imaging performance and the large effective image-side
numerical aperture, consequently, high resolution. With use of the
exposure apparatus equipped with the projection optical system of
the embodiment, it is feasible to produce good microdevices by the
high-precision projection exposure through the high-resolution
projection optical system.
[0340] From the invention thus described, it will be obvious that
the invention may be varied in many ways. Such variations are not
to be regarded as a departure from the spirit and scope of the
invention, and all such modifications as would be obvious to one
skilled in the art are intended for inclusion within the scope of
the following claims.
* * * * *