U.S. patent application number 12/702040 was filed with the patent office on 2010-06-03 for microlithography projection optical system and method for manufacturing a device.
This patent application is currently assigned to CARL ZEISS SMT AG. Invention is credited to Hans-Juergen Mann, Wilhelm Ulrich.
Application Number | 20100134907 12/702040 |
Document ID | / |
Family ID | 40381811 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100134907 |
Kind Code |
A1 |
Mann; Hans-Juergen ; et
al. |
June 3, 2010 |
MICROLITHOGRAPHY PROJECTION OPTICAL SYSTEM AND METHOD FOR
MANUFACTURING A DEVICE
Abstract
In some embodiments, a catoptric microlithgraphy projection
optical system includes a plurality of reflective optical elements
arranged to image radiation from an object field in an object plane
to an image field in an image plane. The image field can have a
size of at least 1 mm.times.1 mm. This optical system can have an
object-image shift (OIS) of about 75 mm or less. Metrology and
testing can be easily implemented despite rotations of the optical
system about a rotation axis. Such a catoptric microlithgraphy
projection optical system can be implemented in a microlithography
tool. Such a microlithography tool can be used to produce
microstructured components.
Inventors: |
Mann; Hans-Juergen;
(Oberkochen, DE) ; Ulrich; Wilhelm; (Aalen,
DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
CARL ZEISS SMT AG
Oberkochen
DE
|
Family ID: |
40381811 |
Appl. No.: |
12/702040 |
Filed: |
February 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12233384 |
Sep 18, 2008 |
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12702040 |
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PCT/EP2007/000067 |
Jan 5, 2007 |
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12233384 |
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PCT/EP2006/008869 |
Sep 12, 2006 |
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PCT/EP2007/000067 |
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60793387 |
Apr 7, 2006 |
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Current U.S.
Class: |
359/858 ;
359/857 |
Current CPC
Class: |
G03F 7/70233 20130101;
G03F 7/70058 20130101; G03F 1/62 20130101; G02B 17/08 20130101;
G03F 7/702 20130101 |
Class at
Publication: |
359/858 ;
359/857 |
International
Class: |
G02B 17/06 20060101
G02B017/06 |
Claims
1. A system, comprising: a plurality of reflective elements
configured to image radiation from an object field in an object
plane of the system to an image field in an image plane of the
system, wherein: the system has an optical axis that is a common
axis of rotational symmetry for each reflective element in the
projection objective system; d=h(1-M); h is a distance of a central
point of the object field from the optical axis in a direction
perpendicular to the optical axis; M is a magnification ratio of
the optical system; d is about 75 mm or less; the image field has a
size of at least 1 mm.times.1 mm; the system is a catoptric
microlithography projection optical system; and the system has an
image-side numerical aperture of about 0.2 or more.
2. The system of claim 1, wherein the image-side numerical aperture
of the system is more than 0.3.
3. The system of claim 1, wherein: a path of the radiation through
the system is characterized by chief rays; for a meridional section
of the optical system, a chief ray of a central field point has a
maximum angle of incidence on a reflective surface of each of the
plurality of reflective elements of .theta. degrees; the image side
numerical aperture of the optical system is more than 0.3; and a
ratio .theta./NA is less than 68.
4. The system of claim 1, wherein at least one of the plurality of
reflective elements has a rotationally asymmetric surface
positioned in a path of the radiation, and the rotationally
asymmetric surface deviates from a best-fit rotationally symmetric
surface by at least at one or more locations, where .lamda. is the
wavelength of the radiation.
5. The system of claim 4, wherein the best-fit rotationally
asymmetric surface deviates by about 0.1.lamda. or less from a
surface corresponding to the equation: z = cr 2 1 + 1 - ( 1 + k ) c
2 r 2 + j = 2 .alpha. C j x m y n ##EQU00005## where ##EQU00005.2##
j = ( m + n ) 2 + m + 3 n 2 + 1 , ##EQU00005.3## z is the sag of
the surface parallel to a Z-axis of a Cartesian co-ordinate system,
x and y are co-ordinates along an X-axis and a Y-axis,
respectively, of the Cartesian co-ordinate system,
r.sup.2=x.sup.2+y.sup.2, m and n are natural numbers, c is the
vertex curvature and k is the conical constant, C.sub.j is the
coefficient of the monomial x.sup.my.sup.n, and .alpha. is an
integer.
6. The system of claim 4, wherein the rotationally asymmetric
surface deviates from the best-fit rotationally symmetric surface
by about 10.lamda. or more at the one or more locations.
7. (canceled)
8. The system of claim 1, wherein the plurality of reflective
elements define a meridional plane and the plurality of reflective
elements are mirror symmetric with respect to the meridional
plane.
9. The system of claim 1, wherein the plurality of reflective
elements comprises two elements that are reflective elements and
that have rotationally asymmetric surfaces positioned in a path of
the radiation.
10. The system of claim 1, wherein the plurality of elements
includes at most two reflective elements that have a positive chief
ray angle magnification.
11. The system of claim 1, wherein the plurality of elements
includes at most one reflective element that has a positive chief
ray angle magnification.
12. The system of claim 1, wherein the system has a rectangular
field at the image plane, and the rectangular field in each
orthogonal direction has a minimum dimension of about 1 mm or
more.
13. The system of claim 1, wherein static distortion at the image
field is about 10 nm or less.
14. The system of claim 1, wherein wavefront error at the image
field is about .lamda./14 or less, where .lamda. is the wavelength
of the radiation.
15. (canceled)
16. The system of claim 1, wherein chief rays are parallel to each
other to within 0.05.degree. at the object plane.
17. The system of claim 1, wherein chief rays diverge from each
other at the object plane.
18. The system of claim 1 wherein, for a meridional section of the
system, chief rays have a maximum angle of incidence on a surface
of each of the elements of less than 20.degree..
19. (canceled)
20. The system of claim 1, wherein the system is telecentric at the
image plane.
21. The system of claim 1, further comprising a radiation source
configured to provide the radiation to an object plane, wherein a
wavelength of the radiation is about 30 nm or less.
22. (canceled)
23. (canceled)
24. A tool, comprising: an illumination system comprising one or
more optical elements; and a catoptric microlithography projection
optical system, comprising: a plurality of reflective elements
configured to image radiation from an object field in an object
plane of the catoptric microlithography projection optical system
to an image field in an image plane of the catoptric
microlithography projection optical system, wherein: the catoptric
microlithography projection optical system has an optical axis that
is a common axis of rotational symmetry for each reflective element
in the projection objective system; d=h(1-M); h is a distance of a
central point of the object field from the optical axis in a
direction perpendicular to the optical axis; M is a magnification
ratio of the optical system; d is about 75 mm or less; the image
field has a size of at least 1 mm.times.1 mm; the catoptric
microlithography projection optical system has an image-side
numerical aperture of about 0.2 or more; and the tool is a
microlithography tool.
25. (canceled)
26. (canceled)
27. A method, comprising using the microlithography tool of claim
24 to produce micro structured components.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 12/233,384, filed Sep. 18, 2008, which is a
continuation of international application PCT/EP 2007/000067, filed
Jan. 5, 2007, which is a continuation of international application
PCT/EP 2006/008869, filed Sep. 12, 2006. International application
PCT/EP 2007/000067 also claims the benefit of U.S. Ser. No.
60/793,387, filed Apr. 7, 2006. International application
PCT/EP2007/000067 is incorporated by reference herein in its
entirety.
FIELD
[0002] This disclosure relates to a microlithography projection
optical system, such as a projection objective, a microlithographic
tool including such an optical system, a method for
microlithographic production of microstructured components using
such a microlithographic tool and a microstructured component
produced by such a method.
BACKGROUND
[0003] Projection objectives are widely used in microlithography to
transfer a pattern from a reticle to a substrate by forming an
image of the reticle on a layer of a photosensitive material
disposed on the substrate. In general, projection objectives fall
into three different classes: dioptric objectives; catoptric
objectives; and catadioptric objectives. Dioptric objectives use
refractive elements (e.g., lens elements) to image light from an
object plane to an image plane. Catoptric objectives use reflective
elements (e.g., mirror elements) to image light from an object
plane to an image plane. Catadioptric objectives use both
refractive and reflective elements to image light from an object
plane to an image plane.
SUMMARY
[0004] In some embodiments, the disclosure provides an optical
system that can be used as projection objective in a
microlithography projection exposure apparatus and that can provide
enhanced performance with respect to its us in projection objective
metrology and testing.
[0005] In one aspect, the disclosure features a catoptric
microlithography projection optical system that includes a
plurality of reflective elements configured to image radiation from
an object field in an object plane of the system to an image field
in an image plane of the system. The system has an object-image
shift of about 75 mm or less, and the image field has a size of at
least 1 mm.times.1 mm.
[0006] In another aspect, the disclosure features a
microlithography tool including an illumination system and a
catoptric microlithography projection optical system as described
in the preceding paragraph.
[0007] In a further aspect, the disclosure features a method of
producing microstructared components that includes using the
microlithography tool described in the preceding paragraph.
[0008] In certain embodiments, the disclosure provides an optical
system with which metrology and testing can be easily implemented
despite rotations of the optical system about a rotation axis. For
example, embodiments of optical systems (e.g., high NA optical
systems) may have relatively small or zero object-image shift which
result in little or no translation of a central object field point
when the optical system rotates about the rotation axis. Thus, when
the optical system is subject to rotation, metrology and testing
can be repeatable performed in the same field position without
having to relocate that field position. The object-image shift in
particular may be 50 mm or less (e.g., 25 mm or less). In some
embodiments, the optical system can have zero object-image shift.
This means that a rotation of the optical system around the
object-image rotation axis causes no translation of an on-axis
field point at all. The image field size of at least 1 mm.times.1
mm allows a high throughput with respect to substrates which are
illuminated via the projection optical system.
[0009] The plurality of elements of the optical system may include
four or more reflective elements. For example, the optical system
may include six or more reflective elements. The projection
objective can be a catoptric projection objective. The image plane
of the optical system may be parallel to the object plane. The
optical system may have a field at the image plane having a minimum
radius of curvature of 300 mm The optical system may have an
entrance pupil which is located more than 2.8 m (e.g., more than 10
m) from the object plane. In general, in an optical system with
freeform surfaces, an exactly defined pupil plane does not exist.
When referring to an optical system having freeform surfaces, the
term pupil plane is used to characterize a region perpendicular to
the light being guided in the optical system where an intensity
distribution corresponds to an illumination angle distribution in
the object plane. The object plane of the optical system may be
positioned between the plurality of elements and an entrance pupil
of the optical system. Alternatively, the optical system may have
an entrance pupil located at infinity. The imaged radiation may be
reflected from an object positioned at the object plane. The object
positioned at the object plane may be a reticle that is imaged by
the plurality of elements to the image plane. The optical system
may have a demagnification of 4.times.. A plurality of elements may
be arranged to image the radiation to an intermediate image plane
between the object plane and the image plane. In this case, a field
stop may be positioned at or near the intermediate image plane. For
example, the plurality of elements may include five elements and
the intermediate image plane may be located between a fourth
element and a fifth element along the path of the radiation from
the object plane to the image plane. The object and image planes
may be separated by a distance L of about 1 m or more. The optical
path length of the radiation from the object plane to the image
plane may be about 2 L or more (e.g., about 3 L or more, about 4 L
or more). The plurality of elements may include at least one pair
of adjacent elements in the path of the radiation, where the pair
of adjacent elements is separated by about 0.5 L or more. In
certain embodiments, none of the plurality of elements causes an
obscuration of the exit pupil at the image plane. The plurality of
elements may include four or more elements having free boards of
about 25 mm or less and/or free boards of about 5 mm or more. The
plurality of elements may include a first mirror and a second
mirror, the first and second mirrors having a minimum distance from
the object plane of d.sub.1 and d.sub.2 respectively, where
d.sub.1/d.sub.2 is about two or more. The plurality of elements may
include a first element in the path of the radiation from the
object plane to the image plane, where the first element has
positive optical power. The optical system may include an aperture
stop positioned between the object plane and the image plane. The
plurality of elements may include three elements and the aperture
stop may be positioned between the second and third elements in the
path of the radiation from the object plane to the image plane.
Alternatively, the aperture stop may be positioned at the second
element or at the third element or at some other position in the
projection lens, e.g. between the first and the second element. The
radiation may pass through the aperture stop once or twice. A
radiation source which is used with the optical system may be a
laser radiation source having a wavelength of about 300 nm or less
(e.g., about 200 nm or less, about 100 nm or less).
[0010] In some embodiments, at least one of the elements is a
reflective element having a rotationally asymmetric surface
positioned in a path of the radiation, wherein the rotationally
asymmetric surface deviates from a best-fit rotationally symmetric
surface by at least .lamda. at one or more locations. In the
following specification, such a rotationally asymmetric surface is
referred to as a freeform surface. Unlike spherical or aspherical
mirrors, freeform surfaces do not have an axis of rotational
symmetry. Freeform surfaces according to the present disclosure
differ from known aspheric rotational symmetric mirror surfaces for
EUV projection objectives in that such known aspheric mirror
surfaces are described via a mathematical Taylor expansion, i.e.
having a sag being given by a rotational symmetric polynomial of
grade n. The center point of this Taylor expansion for all these
polynomial terms is defined by a common optical axis. Known mirror
surfaces are described by such an expansion, because the Taylor
expansion is easy to calculate, easy to optimize and there exists a
lot of experience in manufacturing such mirror surfaces. However,
it was realized by the inventors that the known Taylor expansion
with common center leads to an unwanted distortion which cannot be
lowered below a certain level. This distortion limitation is
inherent to rotational symmetric optical surfaces is avoided, when
according to the disclosure one of the optical surfaces is embodied
as freeform or rotationally asymmetric surface. In some
embodiments, a freeform surface may be a surface that is mirror
symmetric to a meridional plane of the optical system.
[0011] In certain embodiments, the best-fit rotationally asymmetric
surface deviates by about 0.1.lamda. or less from a surface
corresponding to the equation:
z = cr 2 1 + 1 - ( 1 + k ) c 2 r 2 + j = 2 .alpha. C j x m y n
##EQU00001## where ##EQU00001.2## j = ( m + n ) 2 + m + 3 n 2 + 1 ,
##EQU00001.3##
[0012] z is the sag of the surface parallel to an axis, c is the
vertex curvature and k is the conical constant, C.sub.j is the
coefficient of the monomial x.sup.my.sup.n, and .alpha. is an
integer. This mathematical expansion of the freeform surface can
give a good and reproducible manufacturing of the reflective
surfaces. In this expansion, .alpha. may be 66, for example.
Further, m may consist of even integers, for example. Further, m+n
may be equal to or bigger than 10, for example.
[0013] In some embodiments, the rotationally asymmetric surface
deviates from the best-fit rotationally symmetric surface by about
10.lamda. or more at the one or more locations. In certain
embodiments, the rotationally asymmetric surface deviates from the
best-fit rotationally symmetric surface by about 20 nm or more at
the one or more locations.
[0014] A deviation of the type described in the preceding paragraph
can provide for a proper reduction of the objective's distortion
below the limit which is reachable using rotationally symmetric
optical surfaces. The rotationally asymmetric surface may deviate
from the best-fit rotationally symmetric surface by about
100.lamda. or more at the one or more locations. The rotationally
asymmetric surface may deviate from the best-fit rotationally
symmetric surface by about 50 nm or more (e.g., about 100 nm or
more, about 500 nm or more, about 1000 nm or more) at the one or
more locations.
[0015] In some embodiments, the plurality of reflective elements
define a meridional plane, and the elements are mirror symmetric
with respect to the meridional plane. In such embodiments, for
example, restrictions on producing a freeform optical surface may
be reduced.
[0016] In some embodiments, having two reflective elements with
freeform optical surfaces can lead to the possibility of a better
aberration minimization while also allowing the possibility of
meeting certain desired aberration minimization properties with
less complicated to manufactured freeforms. The optical system also
may have, for example, three, four, five or six freeform reflective
elements.
[0017] An optical system having no more than two reflective
elements with a positive chief ray angle magnification can exhibit
relatively low incident ray angles on the mirrors, thus causing
lower aberrations at the outset. This can hold in particular where
the plurality of elements includes no more than one reflective
element that has a positive chief ray angle magnification. This can
be in particular advantageous for an optical system having
divergent chief rays at the object plane and at least one
intermediate image. Optical systems can be designed where it is
sufficient to have only one reflective element having a positive
chief ray angle magnification which serves to a redirection of the
chief rays towards a central image field axis.
[0018] In some embodiments, the optical system can help provide
high resolution.
[0019] The image-side numerical aperture may be, for example, 0.25
or more (e.g., 0.28 or more, 0.3 or more, 0.35 or more, 0.4 or
more).
[0020] In certain embodiments, the optical system can be
efficiently used in a microlithography projection apparatus.
[0021] In some embodiments, the optical system can have a
rectangular field at the image plane with, for example, a minimum
dimension of about 2 mm. In certain embodiments, the rectangular
field may have a first dimension of about 1 mm or more and a second
dimension of about 1 mm or more where the first and second
dimensions are orthogonal. The second dimension may be about 10 mm
(e.g., about 20 mm or more).
[0022] In certain embodiments, the projection quality may be
limited by only diffraction, i.e. by the wavelength of the
projection light. An optical system with such low distortion in
particular can be optimized for use, for example, with EUV light
sources in the range between 10 and 30 nm.
[0023] In some embodiments, the disclosure provides a higher degree
of flexibility with respect to the design of the optical system and
neighbouring components.
[0024] In certain embodiments, the chief rays may be at an angle of
about 3.degree. or more (e.g., 5.degree. or more, 7.degree. or
more) with respect to the object plane normal at the object
plane.
[0025] In some embodiments, chief ray relations can be such that
they lead to specific design and/or aberration minimization
advantages.
[0026] In certain embodiments, diverging chief rays can be such
that they give the possibility to control the distribution of
illumination angles in the object plane by controlling an intensity
distribution in the illumination optics in front of the projection
objective with a low number of optical components. In an optical
system with diverging chief rays, the object plane is positioned
between the plurality of elements and an entrance pupil of the
optical system. This may not be possible using an optical system
with convergent (negative) chief ray angles as this would involve
additional components to give access to a manipulation plane to
control the distribution of illumination angles via an intensity
distribution in this manipulation plane. Convergent chief rays can
have the advantage that a good aberration control is possible and
that smaller mirror sizes can be utilized to achieve a desired low
aberration amount.
[0027] Maximum angles of incidence of the chief ray can be such
that they help to avoid high aberrations at the outset. The maximum
angle of incidence on a surface of each of the elements may be, for
example, less than 18.degree. (e.g., less than 15.degree.).
[0028] In certain embodiments, a telecentric optical system can
allow an object, such as a phase shift mask, to be imaged in the
object plane having height variations.
[0029] In some embodiments, a telecentric optical system can
tolerate height variations of a substrate arranged in the image
plane.
[0030] In certain embodiments, the optical system can lead to a
very high resolution. For example, in some embodiments, the ratio
.theta./NA may be about 60 or less (e.g., 50 or less).
[0031] In some embodiments, the optical system can have a radiation
source and an illumination system that exploit advantageously the
aberration minimization by use of metrology and testing, as
aberrations and distortions in the range of the wavelength of such
a radiation source are possible. Optionally, the wavelength is in a
range from about 10 nm to about 15 nm.
[0032] In certain embodiments, the optical system can allow for
illumination in the image field without illumination angle
gaps.
[0033] The optical systems described herein can be used in a
microlithographic tool and can offer the features disclosed herein.
Such a tool can be used to make components.
[0034] Furthermore, embodiments can include one or more of the
following advantages.
[0035] In some embodiments, a catoptric projection objective is
telecentric at the image plane. This can provide for constant or
nearly constant image magnification over a range of image-side
working distances.
[0036] In certain embodiments, catoptric projection objectives have
extremely high resolution. For example, projection objectives can
have the capability of resolving structures smaller than about 50
nm. High resolution can be achieved in projection objectives that
have a high image-side numerical aperture that are designed for
operation at short wavelengths (e.g., about 10 nm to about 30
nm).
[0037] In some embodiments, projection objectives can provide
images with low aberrations. In certain embodiments, projection
objectives are corrected for wavefront error of about 30 m.lamda.
or less. In certain embodiments, projection objectives are
corrected for distortion below values of about 2 nm or less.
[0038] In some embodiments, catoptric objectives have a high
numerical aperture and provide imaging with low image distortion,
low wavefront error, and telecentricity at the image plane over a
relatively large image field. These features can be achieved by use
of one or more freeform mirrors.
[0039] In some embodiments, projection objective metrology can be
easily implemented despite rotations of the projection objective
about a rotation axis. For example, embodiments of projection
objectives (e.g., high NA projection objectives) may have
relatively small or zero object-image shift which result in little
or no translation of a central object field point when the
projection objective rotates about the axis. Thus, when the
projection objective is subject to rotation, metrology can be
repeatable performed in the same field position without having to
relocate that field position.
[0040] In certain embodiments, a catoptric projection objection has
no field dependent pupil obscuration or no central pupil
obscuration.
[0041] In some embodiments, projection objectives can be adapted
for operation at a variety of different wavelengths, including
visible and ultraviolet (UV) wavelengths. In certain embodiments,
projection objectives can be adapted for operation at Extreme UV
(EUV) wavelengths. Furthermore, in some embodiments, projection
objectives can be adapted for use at more than one wavelength, or
over a range of wavelengths.
[0042] In some embodiments, catoptric projection objectives can be
used in lithography tools (e.g., lithography scanners) and can
provide relatively low overscan. Low overscan is accomplished, for
example, by using projection objectives with rectangular image
fields. In such embodiments, the image can be aligned so that an
edge of the rectangular field is parallel to the leading edge of
the die sites, allowing one to avoid scanning the leading edge of
the die sites beyond the edge of the image field in order to scan
the site corners, as is typically the case when rectangular or
square die sites are scanned relative to arcuate fields.
[0043] In some embodiments, the disclosure provides lithography
tools with relatively high throughput. For example, in certain
embodiments, lithography tools can have relatively low overscan are
more efficient than comparable systems that have larger overscan.
Accordingly, these low overscan systems can provide higher wafer
throughput than the comparable systems.
[0044] In some embodiments, catoptric projection objectives are
provided that have low or no field dependence of shading effects.
For example, catoptric projection objectives can have their
entrance pupil located far from the object plane (e.g., at
infinity) providing uniform illumination angles of the chief rays
on the object field. This can reduce or avoid field dependent
shading effects that occurs where chief ray angles vary across the
object field. Alternatively, or additionally, projection objectives
can have relatively small values of chief ray incident angles
and/or small variations of incident angles for rays in the
meridional section for each mirror in the projection objective,
resulting in an increased average reflectivity of each mirror.
[0045] In certain embodiments, projection objective can include
features that allow a reduction in the complexity of the
illumination system. For example, the location of the entrance
pupil of projection objectives may be in front of the object plane.
In other words, chief rays starting at different field points are
divergent with respect to each other. This can make the entrance
pupil of the projection objective/exit pupil of the illumination
system accessible without using a telescope in the illumination
system to relay the illumination system's exit pupil to the
location of the projection objective's entrance pupil.
[0046] Other features and advantages will be apparent from the
description, the drawings, and the claims. All or selected features
from the subclaims may be combined to form embodiments which are in
particular advantageous.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a schematic view of a microlithography tool.
[0048] FIG. 2A is a schematic view showing a portion of the
microlithography tool shown in FIG. 1.
[0049] FIG. 2B is a cross-sectional view of a rotationally
asymmetric surface and a corresponding rotationally symmetric
reference surface.
[0050] FIG. 3 is a cross-sectional view of an embodiment of a
projection objective shown in meridional section.
[0051] FIG. 4 is a cross-sectional view of a portion of a mirror
from a projection objective shown in meridional section.
[0052] FIG. 5A is a schematic view of a ray path at a mirror having
a positive chief ray angle magnification.
[0053] FIG. 5B is a schematic view of a ray path at a mirror having
a negative chief ray angle magnification.
[0054] FIG. 6A is a view of a mirror's footprint.
[0055] FIG. 6B is a cross-section view of the mirror shown in FIG.
6A.
[0056] FIG. 7A is a plan view of an embodiment of a ring segment
field.
[0057] FIG. 7B is a plan view of a ring segment field relative to a
pair of wafer die sites.
[0058] FIG. 7C is a plan view of a rectangular field relative to a
pair of wafer die sites.
[0059] FIGS. 8A-8D are schematic views of the projection objective
of the embodiment of microlithography tool shown in FIG. 1.
[0060] FIG. 9 is a cross-sectional view of a portion of a
projection objective shown in meridional section.
[0061] FIG. 10 is a cross-sectional view of a projection objective
shown in meridional section.
[0062] FIG. 11 is a cross-sectional view of a projection objective
shown in meridional section.
[0063] FIG. 12 is a cross-sectional view of a projection objective
shown in meridional section.
[0064] FIG. 13 is a cross-sectional view of a projection objective
shown in meridional section.
[0065] FIG. 14 is a cross-sectional view of an optical system that
includes the projection objective shown in FIG. 13.
[0066] FIG. 15 is a cross-sectional view of a projection objective
shown in meridional section.
[0067] FIG. 16A is an x-y vector plot showing calculated distortion
as a function of position in the image field for the projection
objective shown in FIG. 15.
[0068] FIG. 16B is an x-y vector plot showing calculated chief ray
angle as a function of position in the image field for the
projection objective shown in FIG. 15.
[0069] FIG. 17 is a cross-sectional view of a projection objective
shown in meridional section.
[0070] FIG. 18 is a cross-sectional view of projection objective
shown in meridional section.
DETAILED DESCRIPTION
[0071] In one aspect, the disclosure relates to catoptric
projection objectives that have one or more mirrors having a
freeform mirror surface (referred to as freeform mirrors).
Catoptric projection objectives with freeform mirrors can be used
in microlithography tools. Referring to FIG. 1, a microlithography
tool 100 generally includes a light source 110, an illumination
system 120, a projection objective 101, and a stage 130. A
Cartesian co-ordinate system is shown for reference. Light source
110 produces radiation at a wavelength .lamda. and directs a beam
112 of the radiation to illumination system 120. Illumination
system 120 interacts with (e.g., expands and homogenizes) the
radiation and directs a beam 122 of the radiation to a reticle 140
positioned at an object plane 103. Projection objective 101 images
radiation 142 reflected from reticle 140 onto a surface of a
substrate 150 positioned at an image plane 102. The radiation on
the image-side of projection objective 101 is depicted as rays 152.
As shown in FIG. 1, the rays are illustrative only and not intended
to be accurately depict the path of the radiation with respect to
reticle 140, for example. Substrate 150 is supported by stage 130,
which moves substrate 150 relative to projection objective 101 so
that projection objective 101 images reticle 140 to different
portions of substrate 150.
[0072] Projection objective 101 includes a reference axis 105. In
embodiments where projection objective is symmetric with respect to
a meridional section, reference axis 105 is perpendicular to object
plane 103 and lies inside the meridional section.
[0073] Light source 110 is selected to provide radiation at a
desired operational wavelength, .lamda., of tool 100. In some
embodiments, light source 110 is a laser light source, such as a
KrF laser (e.g., having a wavelength of about 248 nm) or an ArF
laser (e.g., having a wavelength of about 193 nm). Non-laser light
sources that can be used include light-emitting diodes (LEDs), such
as LEDs that emit radiation in the blue or UV portions of the
electromagnetic spectrum, e.g., about 365 nm, about 280 nm or about
227 nm.
[0074] Typically, for projection objectives designed for operation
in lithography tools, wavelength .lamda. is in the ultraviolet
portion, the deep ultraviolet portion or the extreme ultraviolet
portion of the electromagnetic spectrum. For example, .lamda. can
be about 400 nm or less (e.g., about 300 nm or less, about 200 nm
or less, about 100 nm or less, about 50 nm or less, about 30 nm or
less). .lamda. can be more than about 2 nm (e.g., about 5 nm or
more, about 10 nm or more). In embodiments, .lamda. can be about
193 nm, about 157 nm, about 13 nm, or about 11 nm. Using a
relatively short wavelength may be desirable because, in general,
the resolution of a projection objective is approximately
proportional to the wavelength. Therefore shorter wavelengths can
allow a projection objective to resolve smaller features in an
image than equivalent projection objectives that use longer
wavelengths. In certain embodiments, however, .lamda. can be in
non-UV portions of the electromagnetic spectrum (e.g., the visible
portion).
[0075] Illumination system 120 includes optical components arranged
to form a collimated radiation beam with a homogeneous intensity
profile. Illumination system 120 typically also includes beam
steering optics to direct beam 122 to reticle 140. In some
embodiments, illumination system 120 also include components to
provide a desired polarization profile for the radiation beam.
[0076] Object plane 103 is separated from image plane 102 by a
distance L, which is also referred to as the lengthwise dimension,
or tracklength, of projection objective 101. In general, this
distance depends on the specific design of projection objective 101
and the wavelength of operation of tool 100. In some embodiments,
such as in tools designed for EUV lithography, L is in a range from
about 1 m to about 3 m (e.g., in a range from about 1.5 m to about
2.5 m). In certain embodiments, L is less than 2 m, such as about
1.9 m or less (e.g., about 1.8 m or less, about 1.7 m or less,
about 1.6 m or less, about 1.5 m or less). L can be more than about
0.2 m or more (e.g., about 0.3 m or more, about 0.4 m or more,
about 0.5 m or more, about 0.6 m or more, about 0.7 m or more,
about 0.8 m or more, about 0.9 m or more, about 1 m or more).
[0077] The ratio of the optical path length of imaged radiation to
the tracklength varies depending on the specific design of
projection objective 101. In some embodiments, the ratio of this
optical path length to tracklength can be relatively high. For
example, the ratio of this optical path length to tracklength can
be about two or more (e.g., about 2.5 or more, about three or more,
about 3.5 or more, about four or more, about 4.5 or more, about
five or more).
[0078] Projection objective 101 has a magnification ratio, which
refers to the ratio of the dimensions of the field at object plane
103 to the corresponding dimensions of the field at image plane
102. Typically, projection objectives used in lithography tools are
reduction projection objectives, meaning they reduce the dimensions
of, or demagnify, the image. In some embodiments, therefore,
projection objective 101 can produce a field at image plane 102
whose dimensions are reduced by about 2.times. or more (e.g., about
3.times. or more, about 4.times. or more, about 5.times. or more,
about 6.times. or more, about 7.times. or more, about 8.times. or
more, about 9.times. or more, about 10.times. or more) compared to
the dimensions at object plane 103. In other words, projection
objective 101 can have a demagnification of about 2.times. or more,
(e.g., about 3.times. or more, about 4.times. or more, about
5.times. or more, about 6.times. or more, about 7.times. or more,
about 8.times. or more, about 9.times. or more, about 10.times. or
more). More generally, however, projection objectives can be
designed to provide a magnified image or an image the same size as
the object.
[0079] Referring also to FIG. 2A, rays 152 define a cone of light
paths that form the reticle image at image plane 102. The angle of
the cone of rays is related to the image-side numerical aperture
(NA) of projection objective 101. Image-side NA can be expressed
as
NA=n.sub.o sin .theta..sub.max,
[0080] where n.sub.o refers to the refractive index of the
immersing medium adjacent the surface of substrate 150 (e.g., air,
nitrogen, water, or evacuated environment), and .theta..sub.max is
the half-angle of the maximum cone of image forming rays from
projection objective 101.
[0081] In general, projection objective 101 can have an image side
NA of about 0.1 or more (e.g., about 0.15 or more, about 0.2 or
more, about 0.25 or more, about 0.28 or more, about 0.3 or more,
about 0.35 or more). In some embodiments, projection objective 101
has a relatively high image-side NA. For example, in some
embodiments, projection objective 101 has an image-side NA of more
than 0.4 (e.g., about 0.45 or more, about 0.5 or more, about 0.55
or more, about 0.6 or more). In general, the resolution of
projection objective 101 varies depending on wavelength X and the
image-side NA. Without wishing to be bound by theory, the
resolution of a projection objective can be determined based on the
wavelength and image-side NA based on the formula,
R = k .lamda. NA , ##EQU00002##
[0082] where R is the minimum dimension that can be printed and k
is a dimensionless constant called the process factor. k varies
depending on various factors associated with the radiation (e.g.,
the polarization properties), the illumination properties (e.g.,
partial coherence, annular illumination , dipole settings,
quadrupole settings, etc.) and the resist material. Typically, k is
in a range from about 0.4 to about 0.8, but can also be below 0.4
and higher than 0.8 for certain applications.
[0083] Projection objective 101 is also nominally telecentric at
the image plane. For example, the chief rays can deviate by about
0.5.degree. or less (e.g., about 0.4.degree. or less, about
0.3.degree. or less, about 0.2.degree. or less, about 0.1.degree.
or less, about 0.05.degree. or less, 0.01.degree. or less,
0.001.degree. or less) from being parallel to each other at the
image plane over the exposed field. Thus, projection objective 101
can provide substantially constant magnification over a range of
image-size working distances. In some embodiments, the chief rays
are nominally orthogonal to image plane 102. Thus, a non flat
topography of the wafer surface or defocusing of the image plane
does not lead necessarily to distortion or shading effects in the
image plane.
[0084] In certain embodiments, projection objective 101 has a
relatively high resolution (i.e., the value of R can be relatively
small). For example, R can be about 150 nm or less (e.g., about 130
nm or less, about 100 nm or less, about 75 nm or less, about 50 nm
or less, about 40 nm or less, about 35 nm or less, about 32 nm or
less, about 30 nm or less, about 28 nm or less, about 25 nm or
less, about 22 nm or less, about 20 nm or less, about 18 nm or
less, about 17 nm or less, about 16 nm or less, about 15 nm or
less, about 14 nm or less, about 13 nm or less, about 12 nm or
less, about 11 nm or less, such as about 10 nm).
[0085] The quality of images formed by projection objective 101 can
be quantified in a variety of different ways. For example, images
can be characterized based on the measured or calculated departures
of the image from idealized conditions associated with Gaussian
optics. These departures are generally known as aberrations. One
metric used to quantify the deviation of a wavefront from the ideal
or desired shape is the root-mean-square wavefront error
(W.sub.rms). W.sub.rms is defined in the "Handbook of Optics," Vol.
I, 2.sup.nd Ed., edited by Michael Bass (McGraw-Hill, Inc., 1995),
at page 35.3, which is incorporated herein by reference. In
general, the lower the W.sub.rms value for an objective, less the
wavefront deviates from its desired or ideal shape, and the better
the quality of the image. In certain embodiments, projection
objective 101 can have a relatively small W.sub.rms for images at
image plane 102. For example, projection objective 101 can have a
W.sub.rms of about 0.1.lamda. or less (e.g., about 0.07.lamda. or
less, about 0.06.lamda. or less, about 0.05.lamda. or less, about
0.045.lamda. or less, about 0.04.lamda. or less, about 0.035.lamda.
or less, about 0.03.lamda. or less, about 0.025.lamda. or less,
about 0.02.lamda. or less, about 0.015.lamda. or less, about
0.01.lamda. or less, such as about 0.005.lamda.).
[0086] Another metric that can be used to evaluate the quality of
the image is referred to as field curvature. Field curvature refers
to the peak-to-valley distance for the field point dependent
position of the focal plane. In some embodiments, projection
objective 101 can have a relatively small field curvature for
images at image plane 102. For example, projection objective 101
can have an image-side field curvature of about 50 nm or less
(e.g., about 30 nm or less, about 20 nm or less, about 15 nm or
less, about 12 nm or less, 10 nm or less).
[0087] A further metric that can be used to evaluate the optical
performance is referred to as distortion. Distortion refers to the
maximum absolute value of the field point dependent deviation from
the ideal image point position in the image plane. In some
embodiments, projection objective 101 can have a relatively small
maximum distortion. For example, projection objective 101 can have
a maximum distortion of about 50 nm or less, (e.g. about 40 nm or
less, about 30 nm or less, about 20 nm or less, about 15 nm or
less, about 12 nm or less, 10 nm or less, 9 nm or less, 8 nm or
less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm
or less, 2 nm or less, such as 1 nm).
[0088] Further, in certain embodiments, distortion can vary by a
relatively small amount across the image field. For example,
distortion can vary by about 5 nm or less (e.g., about 4 nm or
less, about 3 nm or less, about 2 nm or less, about 1 nm or less)
across the image field.
[0089] Being a catoptric system, projection objective 101 includes
a number of mirrors arranged to direct radiation reflected from
reticle 140 to substrate 150 in a way that forms an image of
reticle 140 on the surface of substrate 150. Specific designs of
projection objectives are described below. More generally, however,
the number, size, and structure of the mirrors generally depends on
the desired optical properties of projection objective 101 and the
physical constraints of tool 100.
[0090] In general, the number of mirrors in projection objective
101 may vary. Typically, the number of mirrors is related to
various performance trade-offs associated with the optical
performance characteristics of the objective, such as the desired
throughput (e.g., the intensity of radiation from the object that
forms the image at image plane 102), the desired image-side NA and
related image resolution, and the desired maximum pupil
obscuration.
[0091] In general, projection objective 101 has at least four
mirrors (e.g., five or more mirrors, six or more mirrors, seven or
more mirrors, eight or more mirrors, nine or more mirrors, ten or
more mirrors, eleven or more mirrors, twelve or more mirrors). In
embodiments where it is desirable that all the mirrors of the
objective are positioned between the object plane and the image
plane, objective 101 will typically have an even number of mirrors
(e.g., four mirrors, six mirrors, eight mirrors, ten mirrors). In
certain embodiments, an odd number of mirrors can be used where all
the mirrors of the projection objective are positioned between the
object plane and image plane. For example, where one or more
mirrors are tilted at relatively large angles, a projection
objective can include an odd number of mirrors where all the
mirrors are positioned between the object plane and image
plane.
[0092] In general, at least one of the mirrors in projection
objective 101 has a freeform surface. Unlike spherical or
aspherical mirrors, freeform mirror surfaces do not have an axis of
rotational symmetry. Generally, a freeform surface deviates from a
best fit rotationally symmetric surface (e.g., a spherical or
aspherical surface). Rotationally-symmetric reference surfaces can
be determined for a freeform mirror surface as follows. First, one
obtains information that characterizes the freeform mirror surface
under consideration. In embodiments where optical data of the
mirror is known, this information includes determining the basic
radius of the mirror (e.g. 1/c, where c is the vertex curvature), a
conic constant of the mirror, k, and polynomial coefficients
characterizing the mirror. Alternatively, or additionally, the
information characterizing the mirror can be obtained from a
surface figure measurement of the mirror surface (e.g. obtained
using an interferometer). A surface figure measurement can provide
a function z'(x', y') describing the mirror's surface, where z' is
the sag of the mirror surface along the z'-axis for different (x',
y') coordinates, as illustrated in FIG. 2B. The initial step also
includes determining the footprint for the mirror, which refers to
an area of the mirror surface that is actually used to reflect
image-forming radiation in the objective. The footprint can be
determined by tracing rays through the objective using a ray
tracing program and extracting the mirror area contacted by the
rays.
[0093] After obtaining the information characterizing the
rotationally asymmetric surface, a local coordinate system for the
surface is established for which decentration and tilt of the
surface is zero. Setting the tilt and decentration of the surface
gives a well defined starting point for an optimization algorithm
to determine the reference surface and also define an axis, z',
along which the sag differences between the mirror surface and the
reference surface can be determined. Where optical data for the
mirror surface is known, the z'-axis is determined based on the
conic constant, k, and basic radius, 1/c. For the rotationally
symmetric portion of the optical data, the z'-axis is the symmetry
axis for the rotationally symmetric part of the rotationally
asymmetric surface. In embodiments where the mirror surface is
characterized from a surface figure measurement, the z'-axis
corresponds to the metrology axis (e.g. the interferometers optical
axis). FIG. 2B illustrates this for a two-dimensional section of a
rotationally asymmetric mirror 201, where the local coordinate
system is denoted by the x', y' and z' axes. The boundaries for the
footprint of the rotationally asymmetric mirror 201 are shown as
x.sub.min and x.sub.max for the cross-section shown in FIG. 2B.
[0094] An initial reference surface is then established with
respect to the coordinate system. The initial reference surface has
zero tilt and zero decentration. The initial reference surface is
either a spherical surface or a rotationally symmetric aspherical
surface. The initial reference surface is established by one
designating a rotationally symmetric surface that approximates the
rotationally asymmetric mirror surface. The initial reference
surface represents a starting point for an optimization algorithm.
Once the initial reference surface is established, a local
distance, b.sub.i(i=1 . . . N) between a number of points of the
initial reference surface and points on the surface of the
rotationally asymmetric surface footprint measured along the
z'-axis of the local coordinate system are determined. Next, the
rotationally symmetric reference surface (surface 211 in FIG. 2B)
is established by determining a minimal value for the local
distances (d.sub.i) using a number fitting parameters and a fitting
algorithm. In the event that the rotationally symmetric reference
surface is a spherical surface, the parameters include the location
of the center of the sphere within the local coordinate system, the
radius, of the reference surface. In FIG. 2B, decentering of the
sphere center from the coordinate system origin is shown by
coordinates x.sub.c and z.sub.c (decentration along the y'-axis by
an amount y.sub.c is not shown in FIG. 2B). The radius of the
spherical surface is designated as R. The parameters R, x.sub.c,
y.sub.c and z.sub.c are optimized to provide a minimal value for
the local distances, d.sub.i, based on the equation:
z'=(R.sup.2-(x'-x.sub.c).sup.2-(y'-y.sub.c).sup.2).sup.1/2-z.sub.c,
[0095] which is the equation for a spherical surface of radius R,
centered at coordinate (x.sub.c, y.sub.c, z.sub.c).
[0096] Where the rotationally symmetric reference surface is an
aspherical surface, the parameters can include decentration and
tilt of the reference surface, base radius, conical constant and
aspherical coefficients. These parameters can be determined based
on the equation
z ' = c ' h 2 1 + 1 - ( 1 + k ' ) c '2 h 2 + j A j ' h 2 j ,
##EQU00003##
[0097] which is an equation describing conic and aspheric surfaces.
Here, h.sup.2=x'.sup.2+y'.sup.2, and A'.sub.j are coefficients
characterizing the deviation of the rotationally-symmetric
reference surface from a conic surface. Generally, the number of
aspherical coefficients, A'.sub.j, used to fit the reference
surface to the mirror surface can vary depending on the
computational power of the system being used to calculate the
surface, the time available, and the desired level of accuracy. In
some embodiments, the reference surface can be calculated using
aspherical coefficients up to third order. In certain embodiments,
coefficients higher than third order (e.g., fourth order, sixth
order) are used. For additional discussion on parameterization of
conic and aspheric surfaces see, for example, the product manual
for Code V, available from Optical Research Associates (Pasadena,
Calif.).
[0098] In general, fitting can be performed using a variety of
optimization algorithms. For example, in some embodiments, a least
squares fitting algorithm, such as a damped least squares fitting
algorithm, can be used. Damped least squares fitting algorithms may
be performed using commercially-available optical design software,
such as Code V or ZEMAX (available from Optima Research, Ltd.,
Stansted, United Kingdom) for example.
[0099] After the rotationally-symmetric reference surface is
determined, the local distance between additional points on the
mirror surface can be determined and visualized. Additional
characteristics of the rotationally-symmetric reference surface can
be determined. For example, a maximum deviation of the
rotationally-symmetric reference surface from the
rotationally-asymmetric mirror surface can be determined.
[0100] A freeform surface can, for example, have a maximum
deviation from a best fit sphere of about .lamda. or more (e.g.,
about 10.lamda. or more, about 20.lamda. or more, about 50.lamda.
or more, about 100.lamda. or more, about 150.lamda. or more, about
200.lamda. or more, about 500.lamda. or more, about 1,000.lamda. or
more, about 10,000.lamda. or more, about 50,000.lamda. or more). A
freeform surface can have, for example, a maximum deviation from a
best fit rotationally symmetric asphere of about .lamda. or more
(e.g., about 5.lamda. or more, about 10.lamda. or more, about
20.lamda. or more, about 50.lamda. or more, about 100.lamda. or
more, about 200.lamda. or more, about 500.lamda. or more, about
1,000.lamda. or more, about 10,000.lamda. or more). In some
embodiments, a freeform surface can have a maximum deviation from a
best fit rotationally symmetric asphere of about 1,000.lamda. or
less (e.g., about 900.lamda. or less, about 800.lamda. or less,
about 700.lamda. or less, about 600.lamda. or less, about
500.lamda. or less).
[0101] In certain embodiments, freeform surfaces have a maximum
deviation from a best fit sphere by 10 nm or more (e.g., about 100
nm or more, about 500 nm or more, about 1 .mu.m or more, about 5
.mu.m or more, about 10 .mu.m or more, about 50 .mu.m or more,
about 100 .mu.m or more, about 200 .mu.m or more, about 500 .mu.m
or more, about 1,000 .mu.m, about 2,000 .mu.m or more, about 3,000
.mu.m or more). Freeform surfaces can have a maximum deviation from
a best fit sphere by about 10 mm or less (e.g., about 5 mm or less,
about 3 mm or less, about 2 mm or less, about 1 mm or less, about
500 .mu.m or less).
[0102] Freeform surfaces can have a maximum deviation from a best
fit rotationally symmetric asphere by 10 nm or more (e.g., about
100 nm or more, about 500 nm or more, about 1 .mu.m or more, about
5 .mu.m or more, about 10 .mu.m or more, about 50 .mu.m or more,
about 100 .mu.m or more, about 200 .mu.m or more, about 500 .mu.m
or more, about 1,000 .mu.m). Freeform surfaces can have a maximum
deviation from a best fit rotationally symmetric asphere by about
10 mm or less (e.g., about 5 mm or less, about 3 mm or less, about
2 mm or less, about 1 mm or less, about 500 .mu.m or less).
[0103] The curvature of the mirror surfaces is characterized by a
first and second mean principal curvature, which are determined at
the point on each mirror surface that reflects the chief ray of the
central field point. First and second principal curvatures are
calculated as described in Handbook of Mathematics by I. N.
Bronstein, et al., 4.sup.th Ed. (Springer, 2004), p. 567. In
general, the first principal curvature for a mirror can be
different from the second principal curvature for that mirror. In
some embodiments, the absolute value of the difference between the
first and second principal curvatures can be about 10.sup.-8 or
more (e.g., 10.sup.-7 or more, 5.times.10.sup.-7 or more, about
10.sup.-6 or more, about 5.times.10.sup.-6 or more, about 10.sup.-5
or more, about 5.times.10.sup.-5 or more, about 10.sup.-4 or more,
about 5.times.10.sup.-4 or more, about 10.sup.-3 or more).
[0104] In general, the first and/or second principal curvatures can
be positive or negative. The first and/or second principal
curvatures for a mirror surface can be relatively small. For
example, in some embodiments, the absolute value of the first
principal curvature for one or more mirrors in projection objective
101 is about 10.sup.-2 or less (e.g., about 5.times.10.sup.-3 or
less, about 3.times.10.sup.-3 or less, about 2.times.10.sup.-3 or
less, about 10.sup.-3 or less). The absolute value of the sum of
the first principal curvatures for the mirrors in projective
objective 101 can be about 10.sup.-3 or less (e.g., about
5.times.10.sup.-4 or less, about 3.times.10.sup.-4, about
2.times.10.sup.-4 or less, about 10.sup.-4 or less,
5.times.10.sup.-5 or less, 10.sup.-5 or less).
[0105] In certain embodiments, the absolute value of the second
principal curvature for one or more mirrors in projection objective
101 is about 10.sup.-2 or less (e.g., about 5.times.10.sup.-3 or
less, about 3.times.10.sup.-3 or less, about 2.times.10.sup.-3 or
less, about 10.sup.-3 or less). The absolute value of the sum of
the second principal curvatures for the mirrors in projective
objective 101 can be about 10.sup.-3 or less (e.g., about
5.times.10.sup.-4 or less, about 3.times.10.sup.-4, about
2.times.10.sup.-4 or less, about 10.sup.-4 or less,
5.times.10.sup.-5 or less, 10.sup.-5 or less).
[0106] The sum of the first and second principal curvatures of the
mirrors in projection objective 101 can be relatively small. For
example, the absolute value of the sum of the first and second
principal curvatures of the mirrors can be about 10.sup.-3 or less
(e.g., about 5.times.10.sup.-4 or less, about 3.times.10.sup.-4,
about 2.times.10.sup.-4 or less, about 10.sup.-4 or less,
5.times.10.sup.-5 or less, 10.sup.-5 or less).
[0107] In certain embodiments, freeform mirror surfaces can be
described mathematically by the equation:
Z = cr 2 1 + 1 - ( 1 + k ) c 2 r 2 + j = 2 66 C j X m Y n
##EQU00004## where ##EQU00004.2## j = ( m + n ) 2 + m + 3 n 2 + 1
##EQU00004.3##
[0108] and Z is the sag of the surface parallel to a Z-axis (which
may or may not be parallel to the reference axis 105 in projection
objective 101, i.e. in general is decentered and tilted to the
reference axis 105 in projection objective 101), c is a constant
corresponding to the vertex curvature, k is a conic constant, and
C.sub.j is the coefficient of the monomial X.sup.mY.sup.n.
Typically, the values of c, k, and C.sub.j are determined based on
the desired optical properties of the mirror with respect to
projection objective 101. Further, the order of the monomial, m+n,
can vary as desired. Generally, a higher order monomial can provide
a projection objective design with a higher level of aberration
correction, however, higher order monomials are typically more
computationally expensive to determine. In some embodiments, m+n is
10 or more (e.g., 15 or more, 20 or more). As discussed below, the
parameters for the freeform mirror equation can be determined using
commercially-available optical design software. In some
embodiments, m+n is less than 10 (e.g., 9 or less, 8 or less, 7 or
less, 6 or less, 5 or less, 4 or less, 3 or less).
[0109] In general, freeform surfaces can be described
mathematically using equations other than those presented above.
For example, in some embodiments, freeform surfaces can be
described mathematically using Zernike polynomials (such as
presented in the manual for CODE V.RTM., commercially available
from Optical Research Associates, Pasadena, Calif.) or using
two-dimensional spline surfaces. Examples of two-dimensional spline
surfaces are Bezier splines or non-uniform rational Bezier splines
(NURBS). Two-dimensional spline surfaces can be described, for
example, by a grid of points in an x-y plane and corresponding
z-values or slopes and these points. Depending on the specific type
of spline surface, the complete surface is obtained by a specific
interpolation between the grid points using, e.g., polynomials or
functions that have certain properties with respect to continuity
or differentiability (e.g., analytical functions).
[0110] In general, the number and position of freeform mirrors in
projection objective 101 can vary. Embodiments include projection
objectives with two or more freeform mirrors (e.g., three or more
freeform mirrors, four or more freeform mirrors, five or more
freeform mirrors, six or more freeform mirrors).
[0111] Projection objective 101 generally includes one or more
mirrors with positive optical power. In other words, the reflective
portion of the mirror has a concave surface and is referred to as a
concave mirror. Projection objective 101 can include two or more
(e.g., three or more, four or more, five or more, six or more)
concave mirrors. Projection objective 101 can also include one or
more mirrors that have negative optical power. This means that one
or more of the mirrors has a reflective portion with a convex
surface (referred to as a convex mirror). In some embodiments,
projection objective 101 includes two or more (e.g., three or more,
four or more, five or more, six or more) convex mirrors.
[0112] An embodiment of a projection objective that includes six
mirrors is shown in FIG. 3. Specifically, projection objective 300
includes six freeform mirrors 310, 320, 330, 340, 350, and 360.
Data for projection objective 300 is presented in Table 1A and
Table 1B below. Table 1A presents optical data, while Table 1B
presents freeform constants for each of the mirror surfaces.
[0113] For the purposes of Table 1A and Table 1B, the mirror
designations correlate as follows: mirror 1 (M1) corresponds to
mirror 310; mirror 2 (M2) corresponds to mirror 320; mirror 3 (M3)
corresponds to mirror 330; mirror 4 (M4) corresponds to mirror 340;
mirror 5 (M5) corresponds to mirror 350; and mirror 6 (M6)
corresponds to mirror 360. "Thickness" in Table 1A and subsequent
tables refers to the distance between adjacent elements in the
radiation path. The monomial coefficients, C.sub.j, for the
freeform mirrors, along with the amount the mirror is decentered
and rotated (or tilted) from an initial projection objective
design, are provided in Table 1B. R, the radius, is the inverse of
the vertex curvature, c. Decenter is given in mm and rotation is
given in degrees. Units for the monomial coefficients are
mm.sup.-j.sup.+1. Nradius is a unitless scaling factor (see, for
example, the manual for CODE V.RTM.).
[0114] In FIG. 3, projection objective 300 is shown in meridional
section. The meridional plane is a symmetry plane for projection
objective 300. Symmetry about the meridional plane is as the
mirrors are decentered only with respect to the y-axis and tilted
about the x-axis. Further, the coefficients for the freeform
mirrors having an odd degree in the x-coordinate (e.g., x,
x.sup.3,x.sup.5, etc.) are zero.
[0115] Projection objective 300 is configured for operation with
13.5 nm radiation and has an image-side NA of 0.35 and a
tracklength of 1,500 mm. The optical path length of imaged
radiation is 3.833 mm. Accordingly, the ratio of optical path
length to tracklength is approximately 2.56. Projection objective
has a demagnification of 4.times., a maximum distortion of less
than 100 nm, W.sub.rms of 0.035.lamda., and a field curvature of 28
nm. Additional characteristics of projection objective 300 are
presented in the discussion of projection objective 101 that
follows.
[0116] For example, the first mirror in the radiation path from
object plane 103, mirror 310, has positive optical power. Mirrors
320, 340, and 360 are also P mirrors. Mirrors 330 and 35l have (N)
negative optical power. The sequence of mirrors in the radiation
path in projection objective 300 is thus PPNPNP.
TABLE-US-00001 TABLE 1A Surface Radius (mm) Thickness (mm) Mode
Object INFINITY 714.025 Mirror 1 -1678.761 -414.025 REFL Mirror 2
2754.233 564.025 REFL Mirror 3 350.451 -316.293 REFL Mirror 4
590.379 906.948 REFL Mirror 5 433.060 -435.447 REFL Mirror 6
521.283 480.767 REFL Image INFINITY 0.000
TABLE-US-00002 TABLE 1B Coefficient M1 M2 M3 M4 M5 M6 K
-5.917992E-01 1.401977E+00 -1.852312E+00 3.134672E+00 1.276852E+00
2.162747E-01 Y 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X.sup.2 2.486175E-04 6.462590E-04
8.097144E-05 3.683589E-05 -5.694587E-04 1.127522E-05 Y.sup.2
1.796052E-04 -1.218131E-05 -3.272168E-05 -7.479058E-05
-3.798909E-04 5.142215E-05 X.sup.2Y -3.704365E-08 -3.061838E-06
1.166808E-07 1.073313E-07 3.054784E-06 -1.901527E-08 Y.sup.3
-8.473076E-09 -4.336504E-06 -6.831514E-08 -2.680850E-08
1.944165E-06 2.077407E-09 X.sup.4 1.525482E-11 2.440415E-10
-2.839993E-11 -8.352784E-11 1.477727E-09 -1.231925E-10
X.sup.2Y.sup.2 4.909383E-11 1.819997E-09 -2.639958E-11
-7.953809E-11 1.884598E-08 -4.030921E-11 Y.sup.4 7.241758E-11
-1.924132E-08 -1.611187E-10 -1.805904E-10 2.829058E-09
-6.788132E-11 X.sup.4Y -3.944773E-14 -3.384346E-12 4.634420E-14
1.089774E-13 4.746215E-11 7.092901E-15 X.sup.2Y.sup.3 -2.485019E-13
-1.985647E-10 -1.749321E-13 2.706968E-13 1.878106E-10 7.623271E-14
Y.sup.5 -6.222758E-14 1.546404E-10 -7.306272E-14 1.121470E-13
2.713089E-11 1.059625E-13 X.sup.6 -2.853060E-17 1.499373E-14
-3.327224E-16 -3.396117E-16 1.122966E-13 -7.141998E-16
X.sup.4Y.sup.2 5.428060E-17 -4.560639E-13 -2.729510E-17
1.958645E-17 4.975385E-13 -1.157245E-15 X.sup.2Y.sup.4 9.034205E-16
4.633694E-13 -4.803414E-16 4.337124E-16 9.650331E-13 -6.079561E-16
Y.sup.6 9.726812E-16 -1.567936E-12 -9.119915E-19 3.224937E-16
-4.013641E-13 -1.910957E-16 X.sup.6Y 7.541120E-20 -5.491590E-16
-3.248735E-18 -4.999870E-18 1.809992E-15 1.533677E-19
X.sup.4Y.sup.3 -7.407407E-19 1.626025E-15 -4.175176E-19
-1.121906E-18 4.277794E-15 7.709209E-19 X.sup.2Y.sup.5
-3.053897E-18 -1.459850E-15 -5.190383E-19 9.702383E-19 5.157566E-15
9.414679E-19 Y.sup.7 -1.167661E-17 1.377526E-14 -3.283791E-21
9.398678E-20 -3.053184E-15 3.954522E-19 X.sup.8 -1.128385E-22
-2.091289E-19 -1.560172E-21 -2.941200E-21 2.054965E-18
-3.788563E-21 X.sup.6Y.sup.2 -2.424101E-21 -5.485841E-18
-1.205060E-20 -3.188366E-20 8.911569E-18 -9.560288E-21
X.sup.4Y.sup.4 4.347588E-22 -3.722786E-17 -1.249304E-21
-8.368608E-21 1.007777E-17 -8.789392E-21 X.sup.2Y.sup.6
2.577199E-21 -2.687589E-17 -2.354061E-22 8.597809E-22 1.143993E-17
-3.545101E-21 Y.sup.8 5.215288E-20 -7.369037E-17 -4.229309E-23
-6.689468E-22 -7.499429E-18 -1.703637E-21 X.sup.8Y 7.792174E-25
0.000000E+00 -7.813621E-24 -2.516130E-23 0.000000E+00 8.396981E-25
X.sup.6Y.sup.3 8.992421E-24 0.000000E+00 -1.921637E-23
-8.262460E-23 0.000000E+00 4.664369E-24 X.sup.4Y5 -4.714974E-25
0.000000E+00 -1.610571E-24 -1.778199E-23 0.000000E+00 9.398752E-24
X.sup.2Y.sup.7 6.059892E-24 0.000000E+00 3.848059E-26 1.222213E-24
0.000000E+00 1.042278E-23 Y.sup.9 -8.700880E-23 0.000000E+00
6.368781E-27 -2.288415E-25 0.000000E+00 7.789109E-24 X.sup.10
0.000000E+00 0.000000E+00 -5.411923E-27 -1.603639E-26 0.000000E+00
-3.929816E-26 X.sup.8Y.sup.2 0.000000E+00 0.000000E+00
-8.609679E-27 -4.538477E-26 0.000000E+00 -1.453997E-25
X.sup.6Y.sup.4 0.000000E+00 0.000000E+00 -1.127835E-26
-7.710579E-26 0.000000E+00 -1.839705E-25 X.sup.4Y.sup.6
0.000000E+00 0.000000E+00 -8.495275E-28 -1.413945E-26 0.000000E+00
-8.230974E-26 X.sup.2Y.sup.8 0.000000E+00 0.000000E+00 4.740792E-29
1.022008E-27 0.000000E+00 -8.755646E-27 Y.sup.10 0.000000E+00
0.000000E+00 1.728076E-29 1.964912E-28 0.000000E+00 -7.204080E-27
Nradius 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 Y-
-144.660 -98.223 42.173 -14.449 2.986 -10.929 decenter X-rotation
-8.868 -16.235 1.500 -3.658 -7.600 -1.635
[0117] For the mirrors in projection objective 300, the maximum
deviation of the freeform surfaces from a best fit sphere for each
mirror is as follows: 154 .mu.m for mirror 310; 43 .mu.m for mirror
320, 240 .mu.m for mirror 330; 1.110 .mu.m for mirror 340; 440
.mu.m for mirror 350; and 712 .mu.m for mirror 360. The maximum
deviation of the freeform surfaces from a best fit rotationally
symmetric asphere is 47 .mu.m for mirror 310; 33 .mu.m for mirror
320, 96 .mu.m for mirror 330; 35 .mu.m for mirror 340; 152 .mu.m
for mirror 350; and 180 .mu.m for mirror 360.
[0118] The first and second principal curvature for mirror 310 are
9.51.times.10.sup.-4 and 9.30.times.10.sup.-4 respectively.
Respective first and second principal curvatures for the other
mirrors in projection objective 300 are as follows:
2.76.times.10.sup.-5 and 1.56.times.10.sup.-5 for mirror 320;
-2.38.times.10.sup.-3 and -2.17.times.10.sup.-3 for mirror 330;
1.79.times.10.sup.-3 and 1.75.times.10.sup.-3 for mirror 340;
-2.64.times.10.sup.-3 and -2.10.times.10.sup.-3 for mirror 350; and
1.93.times.10.sup.-3 and 1.91.times.10.sup.-3 for mirror 360. The
sum of the first principal curvature for projection objective 300
is -3.19.times.10.sup.-4. The sum of the second principal curvature
is 3.29.times.10.sup.-4. The sum of the first and second principal
curvatures is 9.97.times.10.sup.-6 and the inverse sum of the first
and second principal curvatures is 1.00.times.10.sup.5.
[0119] In certain embodiments, the arrangement of mirrors in
projection objective 101 images radiation from object plane 103 to
one or more intermediate-image planes. For example, projection
objective 300 images radiation from object plane 103 to an
intermediate image at a location 305 near mirror 360. Embodiments
that have one or more intermediate images, also include two or more
pupil planes. In some embodiments, at least one of these pupil
planes is physically accessible for the purposes of placing an
aperture stop substantially at that pupil plane. An aperture stop
is used to define the size of the projection objective's
aperture.
[0120] Coma at an intermediate image in projection objective 101
can be relatively large. Coma can be quantified by the distance
between the chief ray and the upper and lower rays at the point
where the upper and lower rays cross. In some embodiments, this
distance can be about 1 mm or more (e.g., about 2 mm or more, about
3 mm or more, about 4 mm or more, about 5 mm or more, about 6 mm or
more, such as about 7 mm) Coma at an intermediate image in
projection objective can be relatively small. In some embodiments,
the distance can be about 1 mm or less (e.g., about 0.1 mm or less,
0.01 mm or less).
[0121] In general, mirrors in projection objective 101 are formed
so that they reflect a substantial amount of radiation of
wavelength .lamda. normally-incident thereon or incident thereon
over a certain range of incident angles. Mirrors can be formed, for
example, so that they reflect about 50% or more (e.g., about 60% or
more, about 70% or more, about 80% or more, about 90% or more,
about 95% or more, 98% or more) of normally incident radiation at
.lamda..
[0122] In some embodiments, the mirrors include a multilayer stack
of films of different materials arranged to substantially reflect
normally incident radiation at .lamda.. Each film in the stack can
have an optical thickness of about .lamda./4. Multilayer stacks can
include about 20 or more (e.g., about 30 or more, about 40 or more,
about 50 or more) films. In general, the materials used to form the
multilayer stacks are selected based on operational wavelength
.lamda.. For example, multiple alternating films of molybdenum and
silicon or molybdenum and beryllium can be used to form mirrors for
reflecting radiation in the 10 nm to 30 nm range (e.g., for .lamda.
of about 13 nm or about 11 nm, respectively). Generally, multiple
alternating films of molybdenum and silicon can be used for
.lamda.=11 nm and multiple alternating films of molybdenum and
beryllium can be used for .lamda.=13 nm.
[0123] In certain embodiments, the mirrors are made of quartz glass
coated with a single layer of aluminum and overcoated with one or
more layers of dielectric materials, such as layers formed from
MgF.sub.2, LaF.sub.2, or, Al.sub.2O.sub.3. Mirrors formed from
aluminum with dielectric coatings can be used, for example, for
radiation having a wavelength of about 193 nm.
[0124] In general, the percentage of radiation at .lamda. reflected
by a mirror varies as a function of the angle of incidence of the
radiation on the mirror surface. Because imaged radiation
propagates through a catoptric projection objective along a number
of different paths, the angle of incidence of the radiation on each
mirror can vary. This effect is illustrated with reference to FIG.
4, which shows a portion of a mirror 400, in meridional section,
that includes a concave reflective surface 401. Imaged radiation is
incident on surface 401 along a number of different paths,
including the paths shown by rays 410, 420, and 430. Rays 410, 420,
and 430 are incident on portions of surface 401 where the surface
normal is different. The direction of surface normal at these
portions is shown by lines 411, 421, and 431, corresponding to rays
410, 420, and 430, respectively. Rays 410, 420, and 430 are
incident on surface 401 at angles .theta..sub.410, .theta..sub.420,
and .theta..sub.430, respectively. In general, angles
.theta..sub.410, .theta..sub.420, and .theta..sub.430 may vary.
[0125] For each mirror in projection objective 101, the incident
angles of imaged radiation can be characterized in a variety of
ways. One characterization is the maximum angle of incidence of
meridional rays on each mirror in a meridional section of
projection objective 101. Meridional rays refer to rays lying in
the meridional section. In general, .theta..sub.max can vary for
different mirrors in projection objective 101.
[0126] In some embodiments, the maximum value of .theta..sub.max
for all the mirrors in projection objective 101 is about 75.degree.
or less (e.g., about 70.degree. or less, about 65.degree. or less,
about 60.degree. or less, about 55.degree. or less, about
50.degree. or less, about 45.degree. or less). .theta..sub.max can
be more than about 5.degree. (e.g., about 10.degree. or more, about
20.degree. or more). In some embodiments, the maximum value of
.theta..sub.max can be relatively low. For example, the maximum
value of .theta..sub.max can be about 40.degree. or less (e.g.,
about 35.degree. or less, about 30.degree. or less, about
25.degree. or less, about 20.degree. or less, about 15.degree. or
less, about 13.degree. or less, about 10.degree. or less).
[0127] As an example, in projection objective 300, .theta..sub.max
for mirror 310 is 8.22.degree., .theta..sub.max for mirror 320 is
10.38.degree., .theta..sub.max for mirror 330 is 22.35.degree.,
.theta..sub.max for mirror 340 is 7.49.degree., .theta..sub.max for
mirror 350 is 24.58.degree., and .theta..sub.max for mirror 360 is
6.15.degree..
[0128] In some embodiments, the ratio of the maximum value of
.theta..sub.max (in degrees) to image-side NA can be about 100 or
less (e.g., about 80 or less, about 70 or less, 68 or less, about
60 or less, about 50 or less, about 40 or less, about 30 or
less).
[0129] Another characterization is the angle of incidence of the
chief ray corresponding to the central field point on each mirror
in a meridional section of projection objective 101. This angle is
referred to as .theta..sub.CR. In general, .theta..sub.CR can vary.
For projection objective 300, for example, mirror 310 has
.theta..sub.CR of 6.59.degree., mirror 320 has .theta..sub.CR of
7.93.degree., mirror 330 has .theta..sub.CR of 20.00.degree.,
mirror 340 has .theta..sub.CR of 7.13.degree., mirror 350 has
.theta..sub.CR of 13.06.degree., and mirror 360 has .theta..sub.CR
of 5.02.degree.. In some embodiments the maximum value of
.theta..sub.CR, .theta..sub.CR(max), in projection objective 101
can be relatively low. For example, .theta..sub.CR(max) can be
about 35.degree. or less (e.g., about 30.degree. or less, about
25.degree. or less, about 20.degree. or less, about 15.degree. or
less, about 13.degree. or less, about 10.degree. or less, about
8.degree. or less, about 5.degree. or less). For projection
objective 300, .theta..sub.CR(max), which is .theta..sub.CR for
mirror 330, is 20.00.degree..
[0130] In some embodiments, the ratio of the maximum value of
.theta..sub.CR(max) (in degrees) to image-side NA can be about 100
or less (e.g., about 80 or less, about 70 or less, 68 or less,
about 60 or less, about 50 or less, about 40 or less, about 30 or
less).
[0131] Each mirror in projection objective 101 can also be
characterized by the range of angles of incidence, .DELTA..theta.,
of rays for a meridional section of projection objective 101. For
each mirror, .DELTA..theta. corresponds to the difference between
.theta..sub.max and .theta..sub.min, where .theta..sub.min is the
minimum angle of incidence of rays on each mirror in a meridional
section of projection objective 101. In general, .DELTA..theta. may
vary for each mirror in projection objective 101. For some mirrors,
.DELTA..theta. can be relatively small. For example, .DELTA..theta.
can be about 20.degree. or less (e.g., about 15.degree. or less,
about 12.degree. or less, about 10.degree. or less, about 8.degree.
or less, about 5.degree. or less, about 3.degree. or less,
2.degree. or less). Alternatively, for some mirrors in projection
objective 101, .DELTA..theta. can be relatively large. For example,
.DELTA..theta. for some mirrors can be about 20.degree. or more
(e.g., about 25.degree. or more, about 30.degree. or more, about
35.degree. or more, about 40.degree. or more). For projection
objective 300, .DELTA..theta..sub.max for mirror 310 is
3.34.degree., .DELTA..theta..sub.max for mirror 320 is
4.92.degree., .DELTA..theta..sub.max for mirror 330 is
5.18.degree., .DELTA..theta..sub.max for mirror 340 is
0.98.degree., .DELTA..theta..sub.max for mirror 350 is
24.07.degree., and .DELTA..theta..sub.max for mirror 360 is
2.77.degree..
[0132] In some embodiments, the maximum value for .DELTA..theta.,
.DELTA..theta..sub.max, for all the mirrors in projection objective
101 can be relatively small. For example, .DELTA..theta..sub.max
can be about 25.degree. or less (e.g., about 20.degree. or less,
about 15.degree. or less, about 12.degree. or less, about
10.degree. or less, about 9.degree. or less, about 8.degree. or
less, about 7.degree. or less, about 6.degree. or less, about
5.degree. or less, such as 3.degree.). For projection objective
300, .DELTA..theta..sub.max is 24.07.degree..
[0133] Another way to characterize the radiation path in projection
objective 101 is by the chief ray magnification at each mirror,
which refers to the quotient of the tangent of the angle between
the chief ray (e.g. in the meridional section) and reference axis
105 before and after reflection from each mirror. For example,
referring to FIG. 5A where a chief ray 501 diverges from reference
axis 105 prior to reflection from a mirror 510, and reflects from
mirror 510 back towards reference axis 105, mirror 510 has a
positive chief ray angle magnification. Referring to FIG. 5B,
alternatively, where a chief ray 502 diverges from reference axis
105 both before and after reflection from a mirror 520, mirror 520
has a negative chief ray angle magnification. In both cases, the
chief ray magnification is given by tan(.alpha.)/tan(.beta.). In
certain embodiments, having multiple mirrors with positive chief
ray angle magnification can correspond to relatively large incident
angles on one or more mirrors in the projection objective.
Accordingly, projection objectives having only one mirror with
positive chief ray angle magnification can also exhibit relatively
low incident ray angles on the mirrors. For projection objective
300, mirrors 310, 320, 330 and 350 have negative chief ray angle
magnifications, while mirror 340 has positive chief ray angle
magnification.
[0134] The relative spacing of mirrors in projection objective 101
can vary depending on the specific design of the projection
objective. Relatively large distances between adjacent mirrors
(with respect to the path of the radiation) can correspond to
relatively low incident ray angles on the mirrors. In certain
embodiments, projection objective 101 can include at least one pair
of adjacent mirrors that separated by more than 50% of the
projection objective tracklength. For example, in projection
objective 300, mirrors 340 and 350 are separated by more than 50%
of the projection objective's track length.
[0135] In certain embodiments, having a large relative distance,
d.sub.op-1, between the object plane and the first mirror in the
radiation path compared to the distance, d.sub.op-2, between the
object plane and the second mirror in the radiation path can also
correspond to relatively low incident ray angles on the mirrors.
For example, embodiments where d.sub.op-1/d.sub.op-2 is about 2 or
more (e.g., about 2.5 or more, about 3 or more, about 3.5 or more,
about 4 or more, about 4.5 or more, about 5 or more) can also have
relatively low incident ray angles. In projection objective 300,
d.sub.op-1/d.sub.op-2 is 2.38.
[0136] In general, the footprint size and shape of the mirrors in
projection objective 101 can vary. The footprint shape refers to
the shape of the mirror projected onto the x-y plane of the local
coordinate system of the surface. The footprint of the mirrors can
be circular, oval, polygonal (e.g., rectangular, square,
hexagonal), or irregular in shape. In embodiments, the footprint is
symmetric with respect to the meridional plane of projection
objective 101.
[0137] In certain embodiments, mirrors can have a footprint with a
maximum dimension that is about 1,500 mm or less (e.g., about 1,400
nm or less, about 1,300 mm or less, about 1,200 mm or less, about
1,100 mm or less, about 1,000 mm or less, about 900 mm or less,
about 800 mm or less, about 700 mm or less, about 600 mm or less,
about 500 mm or less, about 400 mm or less, about 300 mm or less,
about 200 mm or less, about 100 mm or less.) Mirrors may have
footprint that has a maximum dimension that is more than about 10
mm (e.g., about 20 mm or more, about 50 mm or more).
[0138] An example of a mirror 600 with an oval footprint is shown
in FIG. 6A. Mirror 600 has a maximum dimension in the x-direction
given by M.sub.x. In embodiments, M.sub.x can be about 1,500 mm or
less (e.g., about 1,400 nm or less, about 1,300 mm or less, about
1,200 mm or less, about 1,100 mm or less, about 1,000 mm or less,
about 900 mm or less, about 800 mm or less, about 700 mm or less,
about 600 mm or less, about 500 mm or less, about 400 mm or less,
about 300 mm or less, about 200 mm or less, about 100 mm or less).
M.sub.x can be more than about 10 mm (e.g., about 20 mm or more,
about 50 mm or more).
[0139] Mirror 600 is symmetric with respect to meridian 601. Mirror
600 has a dimension M.sub.y along meridian 601. For mirror 600
M.sub.y is smaller than M.sub.x, however, more generally, M.sub.y
can be smaller, the same size, or larger than M.sub.x. In some
embodiments, M.sub.y is in a range from about 0.1 M.sub.x to about
M.sub.x (e.g., about 0.2 M.sub.x or more, about 0.3 M.sub.x or
more, about 0.4 M.sub.x or more, about 0.5 M.sub.x or more, about
0.6 M.sub.x or more, about 0.7 M.sub.x or more about 0.8 M.sub.x or
more, about 0.9 M.sub.x or more). Alternatively, in certain
embodiments, M.sub.y can be about 1.1 M.sub.x or more (e.g., about
1.5 M.sub.x or more), such as in a range from about 2 M.sub.x to
about 10 M. M.sub.y can be about 1,000 mm or less (e.g., about 900
mm or less, about 800 mm or less, about 700 mm or less, about 600
mm or less, about 500 mm or less, about 400 mm or less, about 300
mm or less, about 200 mm or less, about 100 mm or less). M.sub.y
can be more than about 10 mm (e.g., about 20 mm or more, about 50
mm or more).
[0140] In projection objective 300, M.sub.x and M.sub.y for mirror
310 are 303 mm and 139 mm, respectively; M.sub.x and M.sub.y for
mirror 320 are 187 mm and 105 mm, respectively; M.sub.x and M.sub.y
for mirror 330 are 114 mm and 62 mm, respectively; M.sub.x and
M.sub.y for mirror 340 are 299 mm and 118 mm, respectively; M.sub.x
and M.sub.y for mirror 350 are 99 mm and 71 mm, respectively; and
M.sub.x and M.sub.y for mirror 360 are 358 mm and 332 mm,
respectively.
[0141] In some embodiments, the base of the mirrors may extend
beyond the mirror surface (i.e., the portion of the mirror that
reflects imaged radiation) in one or more directions. For example,
a mirror's base can extend about 10 mm or more (e.g., about 20 mm
or more, about 30 mm or more, about 40 mm or more, about 50 mm or
more) beyond the optically active surface in the x- and/or
y-directions. Mirror base extension can facilitate mounting the
mirror in projection objective 101 by providing surfaces that are
not optically active that can be attached to mounting
apparatus.
[0142] Optionally, mirror base extensions should not be in a
direction that occludes the radiation path in projection objective
101. The distance between the edge of a mirror and the radiation
path as it passes the mirror is related to a parameter referred to
as the "freeboard," which is the minimum distance between the rays
closest to a mirror's edge and the rays nearest the mirror's edge
that are reflected by the mirror. In some embodiments, projection
objective 101 can include one or more mirrors with freeboards of
about 20 mm or more (e.g., about 25 mm or more, about 30 mm or
more, about 35 mm or more, about 40 mm or more, about 45 mm or
more, about 50 mm or more). Large freeboards provide flexibility in
mirror fabrication as the projection objective can accommodate an
extended mirror base without occlusion of the imaged radiation.
However, relatively small freeboards can correspond to low incident
ray angles on the mirrors in the projection objective. In some
embodiments, projection objective 101 can include one or more
mirrors with freeboards of about 15 mm or less (e.g., about 12 mm
or less, about 10 mm or less, about 8 mm or less, about 5 mm or
less). In certain embodiments, projection objective 101 includes
one or more mirrors having a freeboard between 5 mm and 25 mm. For
example, in projection objective 300, mirrors 310, 320, 330, 350,
and 360 have freeboards between 5 mm and 25 mm.
[0143] In general, the thickness of the mirrors in projection
objective 101 may vary. Mirror thickness refers to the dimension of
the mirror along the z-axis. Mirrors should generally have
sufficient thickness to facilitate mounting within the projection
objective. Referring to FIG. 6B, the thickness of mirror 600 can be
characterized by a maximum thickness, T.sub.max, and a minimum
thickness, T.sub.min. Typically, the difference between T.sub.max
and T.sub.min will depend on the curvature of the mirror surface
and the structure of the mirror's base. In some embodiments,
T.sub.max is about 200 mm or less (e.g., about 150 mm or less,
about 100 mm or less, about 80 mm or less, about 60 mm or less,
about 50 mm or less, about 40 mm or less, about 30 mm or less,
about 20 mm or less). In certain embodiments, T.sub.min is about 1
mm or more (e.g., about 2 mm or more, about 5 mm or more, about 10
mm or more, about 20 mm or more, about 50 mm or more, about 100 mm
or more).
[0144] In some embodiments, the maximum dimension of any mirror in
projection objective is about 1,500 mm or less (e.g., about 1,400
nm or less, about 1,300 mm or less, about 1,200 mm or less, about
1,100 mm or less, about 1,000 mm or less, about 900 mm or less,
about 800 mm or less, about 700 mm or less, about 600 mm or less,
about 500 mm or less, such as about 300 mm) In certain embodiments,
the maximum dimension of any mirror in projection objective is
about 10 mm or more (e.g., about 20 mm or more, about 30 mm or
more, about 40 mm or more, about 50 mm or more, about 75 mm or
more, about 100 mm or more).
[0145] In general, the shape of the field of projection objective
101 can vary. In some embodiments, the field has an arcuate shape,
such as the shape of a segment of a ring. Referring to FIG. 7A, a
ring-segment field 700 can be characterized by an x-dimension,
d.sub.x, a y-dimension, d.sub.y, and a radial dimension, d.sub.r.
d.sub.x and d.sub.y correspond to the dimension of the field along
the x-direction and y-direction, respectively. d.sub.r corresponds
to the ring radius, as measured from an axis 705 to the inner
boundary of field 700. Ring-segment field 700 is symmetric with
respect the y-z plane and indicated by line 710. In general, the
sizes of d.sub.x, d.sub.y, and d.sub.r vary depending on the design
of projection objective 101. Typically d.sub.y is smaller than
d.sub.x. The relative sizes of field dimensions d.sub.x, d.sub.y,
and d.sub.r at object plane 103 and image plane 102 vary depending
on the magnification or demagnification of projection objective
101.
[0146] In some embodiments, d.sub.x is relatively large at image
plane 102. For example, d.sub.x at image plane 102 can be more than
1 mm (e.g., about 3 mm or more, about 4 mm or more, about 5 mm or
more, about 6 mm or more, about 7 mm or more, about 8 mm or more,
about 9 mm or more, about 10 mm or more, about 11 mm or more, about
12 mm or more, about 13 mm or more, about 14 mm or more, about 15
mm or more, about 18 mm or more, about 20 mm or more, about 25 mm
or more). d.sub.x can be about 100 mm or less (e.g., about 50 mm or
less, about 30 mm or less). d.sub.y at image plane 102 can be in a
range from about 0.5 mm to about 5 mm (e.g., about 1 mm, about 2
mm, about 3 mm, about 4 mm)
[0147] Typically, d.sub.r at image plane 102 is about 10 mm or
more. d.sub.r can be, for example, about 15 mm or more (e.g., about
20 mm or more, about 25 mm or more, about 30 mm or more) at image
plane 102. In some embodiments, d.sub.r can be extremely large
(e.g., about 1 m or more, about 5 m or more, about 10 m or more).
In certain embodiments, the field is rectangular in shape and
d.sub.r is infinite. Projection objective 300, for example, has a
rectangular field. Specifically, projection objective 300 has a
rectangular field with a y-dimension of 2 mm and an x-dimension of
26 mm.
[0148] More generally, for other field shapes, projection objective
101 can have a maximum field dimension of more than 1 mm (e.g.,
about 3 mm or more, about 4 mm or more, about 5 mm or more, about 6
mm or more, about 7 mm or more, about 8 mm or more, about 9 mm or
more, about 10 mm or more, about 11 mm or more, about 12 mm or
more, about 13 mm or more, about 14 mm or more, about 15 mm or
more, about 18 mm or more, about 20 mm or more, about 25 mm or
more) at image plane 102. In certain embodiments, projection
objective has a maximum field dimension of no more than about 100
mm (e.g., about 50 mm or less, about 30 mm or less).
[0149] In some embodiments, the image field shape can correspond
(e.g., in one or more dimensions) to the shape of die sites on a
wafer that is exposed using projection objective 101. For example,
the image field can be shaped to reduce overscan when exposing the
wafer. Overscan refers to the need to scan the image field beyond
the edge of a die site to expose the entire site. Generally, this
occurs where the shape of the image field does not conform to the
shape of die site.
[0150] Overscan can be characterized by the ratio (e.g., expressed
as a percentage) of the maximum distance between the leading edge
of the image field and the trailing edge of the die site at the
position where the corners at the trailing edge of the die site are
exposed. Referring to FIG. 7B, overscan corresponds to the ratio of
d.sub.os to d.sub.r where d.sub.os is the distance between the
leading edge of image field 700 and the trailing edge of die sites
720 at the position where corners 721 and 722 are exposed. In
certain embodiments, projection objective can have relatively low
overscan. For example, projection objective can have an overscan of
about 5% or less (e.g., about 4% or less, about 3% or less, about
2% or less, about 1% or less, about 0.5% or less, 0.1% or
less).
[0151] In certain embodiments, projection objective 101 can be used
with zero overscan. For example, referring to FIG. 7C, in
embodiments where an image field 730 is used to expose square die
sites 740, scanning can be achieved with zero overscan.
[0152] Referring to FIG. 8, in general, projection objective 101
introduces an object-image shift, d.sub.ois, that varies depending
on the specific design of the projection objective. The
object-image shift refers to the distance of a point in the image
field from the corresponding point in the object field, as measured
in the x-y plane. For projection objectives that have an optical
axis (a common axis of rotational symmetry for each mirror in the
projection objective) the object-image shift can be calculated
using the formula:
d.sub.ois=h.sub.o(1-M)
[0153] where h.sub.o refers to the distance in the x-y plane of the
central field point in the object field from the optical axis and M
is the projection objective magnification ratio. For example, for a
projection objective have a demagnification of 4.times. (i.e.,
M=0.25) and where the central field point is 120 mm from the
optical axis, d.sub.ois is 90 mm.
[0154] Projection objective 101 has a relatively small object-image
shift. For example, projection objective has zero object-image
shift. Projection objectives having relatively small object image
shifts can be have a relatively slim optical design. Furthermore,
in embodiments that have zero object-image shift, projection
objective 101 can be rotated about the axis intersecting the
central field points in the object and image fields without the
central field point translating with respect to, e.g., stage 130.
This can be advantageous where, for example, metrology tools (e.g.,
detection optical systems, such as those disclosed in U.S. Pat. No.
6,240,158 B1) for inspecting and aligning wafers with respect to
projection objective 101 are placed at a nominal position of the
central field point because the central field point is not
translated with respect to this position when the projection
objective rotates. Accordingly, zero object-image shift can
facilitate easier metrology and testing of projective objective 101
where the projection objective is subject to rotations during the
course of operation.
[0155] This is illustrated with respect to FIGS. 8A, 8B, 8C and 8D.
FIG. 8A shows a view of the object field and the image field of a
projection of objective having a large object-image shift
d.sub.ois. After rotation of the projection objective 101 about a
rotation axis coinciding with reference axis 105, an object field
103A in the object plane 103 pivots into an object field position
103B. Accordingly, the respective image field 102A in the image
plane 102 pivots to an image field position 102B. A central object
field point C.sub.O of the object field 103A moves due to this
pivoting about rotation axis 105 from a position C.sub.OA to a
position C.sub.OB. Accordingly, a central image field point C.sub.I
moves from a position C.sub.IA to a position C.sub.IB. Thus, in the
system of FIG. 8A with large object-image shift d.sub.ois, the
central field points C.sub.O, C.sub.I escape a detection region and
therefore escape a measurement due to rotation about the rotation
axis 105. This is not desirable.
[0156] FIG. 8B shows the case, where the object-image shift
d.sub.ois of the projection objective 101 is zero. In that case,
rotation axis 105 intersects the object plane 103 and the image
plane 102 at the central field points C.sub.O, C.sub.I. During
rotation of the projection objective 101 about the rotation axis
105, the central field points C.sub.O, C.sub.I stay within a
measurement region. In that case, testing and metrology is
facilitated.
[0157] FIGS. 8C and 8D depict a dependency of the object-image
shift on the numerical aperture of the system which often is
observed when comparing different types of projection objectives.
FIG. 8C shows schematically a projection objective 101 having a
relatively small numerical aperture. In that case, most designs of
projection objectives exhibit a relatively small distance h.sub.0
between an axis through the central field point C.sub.O and the
optical axis OA.
[0158] Therefore, also d.sub.ois being directly proportional to
h.sub.0 can be kept small. FIG. 8D shows the case in a projection
objective 101 with high numerical aperture. In this case, the
projection objective often exhibits a large distance h.sub.0
between the axis through the central object field point C.sub.O and
the optical axis OA. Thus, also d.sub.ois is larger than in the
projection objective of FIG. 8C.
[0159] In the projection objectives disclosed herein, high
numerical aperture systems are presented having only a small
distance h.sub.0 or even h.sub.0=0. In that case, small
object-image shifts or zero object-image shifts can be realized
with high numerical aperture projection objectives.
[0160] In some embodiments, projection objective 101 has a
d.sub.ois of about 80 mm or less (e.g., about 60 mm or less, about
50 mm or less, about 40 mm or less, about 30 mm or less, about 20
mm or less, about 15 mm or less, about 12 mm or less, about 10 mm
or less, about 8 mm or less, about 5 mm or less, about 4 mm or
less, about 3 mm or less, about 2 mm or less, about 1 mm or less).
Projection objective 300, for example, has a d.sub.ois of 57 mm
[0161] Embodiments of projection objective 101 can have a
relatively large image-side free working distance. The image-side
free working distance refers to the shortest distance between image
plane 102 and the mirror surface of the mirror closest to image
plane 102 that reflects imaged radiation. This is illustrated in
FIG. 9, which shows a mirror 810 as the closest mirror to image
plane 102. Radiation reflects from surface 811 of mirror 810. The
image-side free working distance is denoted d.sub.w. In some
embodiments, d.sub.w is about 25 mm or more (e.g., about 30 mm or
more, about 35 mm or more, about 40 mm or more, about 45 mm or
more, about 50 mm or more about 55 mm or more, about 60 mm or more,
about 65 mm or more). In certain embodiments, d.sub.w is about 200
mm or less (e.g., about 150 mm or less, about 100 mm or less, about
50 mm or less). Projection objective 300, for example, has an
image-side free working distance of approximately 45 mm. A
relatively large working distance may be desirable because it can
allow the surface of substrate 150 to be positioned at image plane
102 without contacting the side of mirror 810 facing image plane
102.
[0162] Analogously, the object-side free working distance refers to
the shortest distance between object plane 103 and the mirror
surface of the reflective side of the mirror in projection
objective 101 closest to object plane 103 that reflects imaged
radiation. In some embodiments, projection objective 101 has a
relatively large object-side free working distance. For example,
projection objective 101 can have an object-side free working
distance of about 50 mm or more (e.g., about 100 mm or more, about
150 mm or more, about 200 mm or more, about 250 mm or more, about
300 mm or more, about 350 mm or more, about 400 mm or more, about
450 mm or more, about 500 mm or more, about 550 mm or more, about
600 mm or more, about 650 mm or more, about 700 mm or more, about
750 mm or more, about 800 mm or more, about 850 mm or more, about
900 mm or more, about 950 mm or more, about 1,000 mm or more). In
certain embodiments, the object-side free working distance is no
more than about 2,000 mm (e.g., about 1,500 mm or less, about 1,200
mm or less, about 1,000 mm or less). Projection objective 300, for
example, has an object-side free working distance of approximately
300 mm. A relatively large object-side free working distance may be
advantageous in embodiments where access to the space between
projection objective 101 and object plane 103 is desired. For
example, in embodiments where reticle 140 is a reflective reticle,
it is desirable to illuminate the reticle from the side that faces
objective 101. Therefore, there should be sufficient space between
projection objective 101 and object plane 103 to allow the reticle
to be illuminated by illumination system 120 at a desired
illumination angle. Furthermore, in general, a larger object-side
free working distance allows flexibility in design of the rest of
tool, for example, by providing sufficient space to mount other
components (e.g. an uniformity filter) between projection objective
101 and the support structure for reticle 140.
[0163] In general, projection objective 101 can be designed so that
chief rays either converge, diverge, or are substantially parallel
to each other at reticle 140. Correspondingly, the location of the
entrance pupil of projection objective 101 with respect to object
plane 103 can vary. For example, where chief rays converge at
reticle 140, the entrance pupil is located on the image plane side
of object plane 103. Conversely, where the chief rays diverge at
reticle 140, object plane 103 is located between the entrance pupil
and image plane 102. Furthermore, the distance between object plane
103 and the entrance pupil can vary. In some embodiments, the
entrance pupil is located about 1 m or more (e.g., about 2 m or
more, about 3 m or more, about 4 m or more, about 5 m or more,
about 8 m or more, about 10 m or more) from object plane 103
(measured along an axis perpendicular to object plane 103). In some
embodiments, the entrance pupil is located at infinity with respect
to object plane 103. This corresponds to where the chief rays are
parallel to each other at reticle 140. For projection objective
300, the incident angle of the chief ray at the central field point
at object plane 103 is 7.degree. and the maximum variation of the
chief ray angle form the central field point chief ray is
0.82.degree.. The entrance pupil is located 1,000 mm from object
plane 103 on the opposite side of object plane 103 from image plane
102.
[0164] Illumination system 120 may be arranged so that the exit
pupil of the illumination system is positioned substantially at the
entrance pupil of projection objective 101. In certain embodiments,
illumination system 120 includes a telescope subsystem which
projects the illumination system's exit pupil to the location of
the entrance pupil of projection objective 101. However, in some
embodiments, the exit pupil of illumination system 120 is
positioned at the entrance pupil of projection objective 101
without using a telescope in the illumination system. For example,
when the object plane 103 is between projection objective 101 and
the entrance pupil of the projection objective, the exit pupil of
illumination system 120 may coincide with the projection
objective's entrance pupil without using a telescope in the
illumination system.
[0165] In general, projection objective 101 can be designed using
commercially available optical design software like ZEMAX, OSLO, or
Code V. Typically, a design is started by specifying an initial
projection objective design (e.g., arrangement of mirrors) along
with parameters such as the radiation wavelength, field size and
numerical aperture, for example. The code then optimizes the design
for specified optical performance criteria, such as, for example,
wavefront error, distortion, telecentricity, and field
curvature.
[0166] In certain embodiments, the initial projection objective is
designated by rotationally symmetric mirrors (e.g., spherical or
aspherical mirrors) that are centered on an optical axis. Each
mirror is then decentered from the optical axis to a position where
the mirror satisfies some pre-established criterion. For example,
each mirror can be decentered from the optical axis by and amount
which minimizes the chief ray angle of incidence across the mirror
for particular field. In embodiments, mirrors can be decentered by
about 5 mm or more (e.g., about 10 mm or more, about 20 mm or more,
about 30 mm or more, about 50 mm or more). In certain embodiments,
mirrors are decentered by about 200 mm or less (e.g., about 180 mm
or less, about 150 mm or less, about 120 mm or less, about 100 mm
or less).
[0167] Alternatively, or additionally, each mirror can be tilted to
a position where the mirror satisfies some pre-established
criterion. The tilt refers to the orientation of each mirrors
symmetry axis with respect to the optical axis of the initial
configuration of the projection objective. Mirrors can be titled by
about 1.degree. or more (e.g., about 2.degree. or more, about
3.degree. or more, about 4.degree. or more, about 5.degree. or
more). In some embodiments, mirrors are tilted by about 20.degree.
or less (e.g., about 15.degree. or less, about 12.degree. or less,
about 10.degree. or less).
[0168] After decentering and/or tilting, a freeform shape for each
mirror can be determined to optimize the projection objective
design for specified optical performance criteria.
[0169] In addition to mirrors, projection objective 101 can include
one or more other components, such as one or more aperture stops.
In general, the shape of the aperture stop can vary. Examples of
aperture stops include circular aperture stops, elliptical aperture
stops, and/or polygonal aperture stops. Apertures stops can also be
positioned so that the image radiation makes a double pass or a
single pass through the aperture stop. Aperture stops can be
interchanged in projection objective 101 and/or may have an
adjustable aperture.
[0170] In some embodiments, projection objective 101 includes a
field stop. For example, in embodiments where projective objective
includes an intermediate image, the field stop can be positioned at
or near the intermediate image.
[0171] Embodiments can include baffles (e.g., to shield the wafer
from stray radiation). In some embodiments, projection objective
101 can include components (e.g., interferometers) for monitoring
changes in the position of mirrors within the projection objective.
This information can be used to adjust the mirrors to correct for
any relative movement between the mirrors. Mirror adjustment can be
automated. Examples of systems for monitoring/adjusting mirror
position are disclosed in U.S. Pat. No. 6,549,270 B1.
[0172] Referring to FIG. 10, an embodiment of a projection
objective 1000 includes six mirrors 1010, 1020, 1030, 1040, 1050,
and 1060, and has an image-side numerical aperture of 0.35 and an
operating wavelength of 13.5 nm. Mirrors 1010, 1020, 1030, 1040,
1050, and 1060 are all freeform mirrors. Projection objective 1000
images radiation from object plane 103 to image plane 102 with a
demagnification ratio of 4.times.. The tracklength of projection
objective 1000 is 1497 mm and the optical path length of imaged
radiation is 4760 mm. Accordingly, the ratio of the optical path
length to tracklength is approximately 3.18. Projection objective
1000 has an aperture stop positioned close to mirror 1020.
[0173] The entrance pupil of projection objective 1000 is located
1,000 mm from object plane 103 with object plane positioned between
the entrance pupil and the mirrors. Due to the reflective reticle
positioned at object plane 103, illumination optics can be
positioned at location 1070, corresponding to the entrance pupil.
The chief ray angle of the central field point at object plane 103
is 7.degree.. The maximum variation of chief ray angles at object
plane 103 is 0.82.degree..
[0174] Projection objective 1000 has a rectangular field. The
image-side field width, d.sub.x, is 26 mm. The image-side field
length, d.sub.y, is 2 mm. Projection objective 1000 has an
object-image shift of 13 mm.
[0175] The performance of projection objective 1000 includes an
image-side W.sub.rms of 0.021.lamda.. Distortion is less than 10
nm, and image-side field curvature is 19 nm. Projection objective
1000 provides an intermediate image between mirrors 1040 and 1050.
Coma at the intermediate image is relatively large. In particular,
the distance between the chief ray and the upper and lower rays at
the location where the upper and lower rays cross is 7 mm.
[0176] The optical power of the mirrors in the order of the
radiation path from object plane 103 to image plane 102 is as
follows: mirror 1010 has positive optical power; mirror 1020 has
negative optical power; mirror 1030 has positive optical power;
mirror 1040 has positive optical power; mirror 1050 has negative
optical power; and mirror 1060 has positive optical power.
[0177] The dimension of the footprint of each mirror, given as
M.sub.x.times.M.sub.y, is as follows: 323 mm.times.152 mm for
mirror 1010; 107 mm.times.59 mm for mirror 1020; 297 mm.times.261
mm for mirror 1030; 277 mm.times.194 mm for mirror 1040; 99
mm.times.72 mm for mirror 1050; and 268 mm.times.243 mm for mirror
1060.
[0178] The maximum deviation of mirror 1010 from a best fit sphere
is 475 .mu.m. Maximum deviation from best fit spheres of mirrors
1020, 1030, 1040, 1050, and 1060 are 1.234 .mu.m, 995 .mu.m, 1.414
.mu.m, 170 .mu.m, and 416 .mu.m, respectively. The maximum
deviation of each mirror from a best fit asphere is 236 .mu.m, 102
.mu.m, 102 .mu.m, 148 .mu.m, 54 .mu.m, and 372 .mu.m for mirrors
1010, 1020, 1030, 1040, 1050, and 1060, respectively.
[0179] The first and second principal curvature for mirror 1010 are
1.16.times.10.sup.-3 and 1.05.times.10.sup.-3 respectively.
Respective first and second principal curvatures for the other
mirrors in projection objective 1000 are as follows:
-3.02.times.10.sup.-3 and -1.13.times.10.sup.-3 for mirror 1020;
5.97.times.10.sup.-4 and 4.96.times.10.sup.-4 for mirror 1030;
5.50.times.10.sup.-4 and 3.63.times.10.sup.-4 for mirror 1040;
-2.24.times.10.sup.-3 and -2.04.times.10.sup.-3 for mirror 1050;
and 2.57.times.10.sup.-3 and 2.48.times.10.sup.-3 for mirror 1060.
The sum of the first principal curvature for projection objective
1000 is -3.78.times.10.sup.-4. The sum of the second principal
curvature is 1.22.times.10.sup.-3. The sum of the first and second
principal curvatures is 8.45.times.10.sup.-4 and the inverse sum of
the first and second principal curvatures is
1.18.times.10.sup.3.
[0180] The chief ray angle of incidence for the central field point
is 3.40.degree., 9.86.degree., 6.48.degree., 10.13.degree.,
13.66.degree., and 7.00.degree. for mirrors 1010, 1020, 1030, 1040,
1050, and 1060, respectively. The maximum angle of incidence,
.theta..sub.max, on each mirror for the meridional section is
3.94.degree., 10.42.degree., 7.45.degree., 14.34.degree.,
24.28.degree., and 8.61.degree. for mirrors 1010, 1020, 1030, 1040,
1050, and 1060, respectively. .DELTA..theta. for mirrors 1010,
1020, 1030, 1040, 1050, and 1060 are 1.13.degree., 2.74.degree.,
3.42.degree., 9.96.degree., 23.69.degree., and 3.95.degree.,
respectively.
[0181] Mirrors 1010, 1020, 1030, 1050, and 1060 have freeboards
that are more than 5 mm and less than 25 mm Mirror 1030 has
positive chief ray angle magnification while mirrors 1040 and 1050
have negative chief ray angle magnification.
[0182] The image-side free working distance of projection objective
1000 is 45 mm. The object-side free working distance is 252 mm.
[0183] In projection objective 1000, d.sub.op-1/d.sub.op-2 is 3.14.
Furthermore, adjacent mirror pairs 1020 and 1030, 1030 and 1040,
and 1040 and 1050 are separated by more than 50% of the projection
objective's tracklength. Further, the distance between mirror 1010
and object plane 103 is more than 50% of the projection objective's
tracklength.
[0184] Data for projection objective 1000 is presented in Table 2A
and Table 2B below. The parameters and units for the parameters for
Table 2A and 2B and subsequent tables are the same as the
corresponding parameters and units presented in Table 1A and 1B
above. Table 2A presents optical data, while Table 2B presents
freeform constants for each of the mirror surfaces. For the
purposes of Table 2A and Table 2B, the mirror designations
correlate as follows: mirror 1 (M1) corresponds to mirror 1010;
mirror 2 (M2) corresponds to mirror 1020; mirror 3 (M3) corresponds
to mirror 1030; mirror 4 (M4) corresponds to mirror 1040; mirror 5
(M5) corresponds to mirror 1050; and mirror 6 (M6) corresponds to
mirror 1060.
TABLE-US-00003 TABLE 2A Surface Radius (mm) Thickness (mm) Mode
Object INFINITY 788.884 Mirror 1 -651.356 -537.372 REFL Mirror 2
-463.216 952.014 REFL Mirror 3 -1710.243 -783.854 REFL Mirror 4
1821.345 1032.444 REFL Mirror 5 309.420 -306.504 REFL Mirror 6
405.847 351.549 REFL Image INFINITY 0.000
TABLE-US-00004 TABLE 2B Coefficient M1 M2 M3 M4 M5 M6 K
-5.925412E-01 1.525505E+00 -1.851822E+00 3.314097E+00 1.983829E+00
2.009323E-01 Y 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X.sup.2 2.471303E-04 6.505963E-04
7.593410E-05 2.922157E-05 -4.716078E-04 1.426720E-05 Y.sup.2
1.863347E-04 6.677442E-05 -2.868206E-05 -7.428048E-05 -3.446472E-04
5.312976E-05 X.sup.2Y -3.545294E-08 -2.891983E-06 1.048420E-07
9.891278E-08 2.877558E-06 -2.714955E-08 Y.sup.3 -1.873281E-08
-3.078489E-06 -7.296056E-08 -3.920160E-08 1.288669E-06
-9.898583E-09 X.sup.4 1.180642E-11 3.342373E-10 -3.287877E-11
-8.971583E-11 3.862440E-10 -8.982825E-11 X.sup.2Y.sup.2
3.437144E-11 5.937123E-09 -2.687658E-11 -7.769409E-11 1.693138E-08
2.462964E-11 Y.sup.4 9.863178E-11 -2.340521E-08 -1.605207E-10
-1.806038E-10 -2.208217E-09 -3.099379E-11 X.sup.4Y -4.051355E-14
1.381955E-13 -2.895532E-14 5.170900E-14 4.797213E-11 -4.214964E-14
X.sup.2Y.sup.3 -2.144219E-13 -2.531232E-10 -1.637831E-13
2.916068E-13 1.961281E-10 -3.785260E-14 Y.sup.5 -2.415401E-14
1.279499E-10 -7.226386E-14 1.273503E-13 2.976407E-11 4.394992E-14
X.sup.6 -2.920211E-17 1.949737E-14 -1.774795E-17 -2.785422E-16
8.466233E-14 -5.281246E-16 X.sup.4Y.sup.2 7.135583E-17
-6.187267E-13 -2.447653E-16 -1.867205E-16 3.921385E-13
-5.767253E-16 X.sup.2Y.sup.4 5.606882E-16 4.378172E-13
-4.812153E-16 4.588123E-16 7.309790E-13 -7.534000E-17 Y.sup.6
-7.879310E-16 -6.710705E-13 6.992795E-19 3.331795E-16 -3.185164E-13
-9.186437E-17 X.sup.6Y 2.435160E-20 -3.445743E-16 -3.254844E-19
-4.053237E-18 1.681642E-15 -7.144774E-20 X.sup.4Y.sup.3
-1.325499E-18 2.205904E-15 -4.637731E-19 -1.132243E-18 6.530207E-15
-1.155827E-19 X.sup.2Y.sup.5 2.538976E-18 7.780251E-15
-5.473994E-19 9.042940E-19 5.583512E-15 1.826925E-19 Y.sup.7
6.001333E-18 7.757557E-15 -8.424804E-21 7.805993E-20 -2.390583E-15
3.562442E-19 X.sup.8 -2.140710E-22 -1.536511E-18 -5.293518E-23
-7.757919E-22 1.098261E-18 -2.871286E-21 X.sup.6Y.sup.2
-2.383343E-21 -3.017606E-17 -2.564847E-21 -2.918509E-20
-1.382527E-17 -5.946767E-21 X.sup.4Y.sup.4 4.328735E-21
-3.407893E-17 -3.923348E-22 -6.995732E-21 2.738740E-17
-2.968388E-21 X.sup.2Y.sup.6 -4.831336E-20 -1.206126E-16
-1.673186E-22 5.920827E-22 4.911090E-17 8.147751E-22 Y.sup.8
-3.800647E-20 -6.246834E-17 -5.575611E-23 -7.691743E-22
-4.049646E-18 -1.438562E-21 X.sup.8Y 2.973276E-24 6.697817E-20
-9.383994E-25 -1.349984E-23 8.777395E-22 -9.763800E-25
X.sup.6Y.sup.3 1.179538E-23 5.201215E-19 -6.639018E-24
-8.645373E-23 -3.199889E-19 -4.878981E-24 X.sup.4Y5 -1.203834E-23
-4.705218E-20 -1.462557E-25 -1.508808E-23 8.645921E-20
-3.908340E-24 X.sup.2Y.sup.7 2.304206E-22 1.208243E-19 2.562699E-25
1.368282E-24 4.649092E-19 2.276452E-24 Y.sup.9 1.418250E-22
-1.077428E-19 7.645118E-27 -3.895996E-25 1.402632E-20 5.582547E-24
X.sup.10 4.021654E-28 2.141815E-23 -3.668876E-27 -1.991462E-26
1.059359E-22 -2.694594E-26 X.sup.8Y.sup.2 -1.314266E-26
-8.696134E-22 -1.671744E-27 -3.158518E-26 -2.330392E-22
-7.617267E-26 X.sup.6Y.sup.4 -7.356431E-27 -3.656759E-21
-5.748164E-27 -9.269087E-26 -2.103517E-21 -6.065950E-26
X.sup.4Y.sup.6 1.059736E-26 3.564328E-22 -1.527905E-28
-1.292503E-26 -3.644105E-22 1.700246E-26 X.sup.2Y.sup.8
-3.817918E-25 2.574506E-21 1.902672E-28 1.728267E-27 1.530993E-21
1.267011E-26 Y.sup.10 -2.256936E-25 1.804566E-21 1.126083E-29
-2.712119E-28 -1.135939E-22 -1.049025E-26 Nradius 1.00E+00 1.00E+00
1.00E+00 1.00E+00 1.00E+00 1.00E+00 Y- -141.222 -91.036 45.162
-4.535 -0.554 -8.496 decenter X-rotation -9.184 -15.081 1.443
-3.391 -6.975 -1.780
[0185] Referring to FIG. 11, an embodiment of a projection
objective 1000 includes six mirrors 1110, 1120, 1130, 1140, 1150,
and 1160, and has an image-side numerical aperture of 0.35 and an
operating wavelength of 13.5 nm. Mirrors 1110, 1120, 1130, 1140,
1150, and 1160 are all freeform mirrors. Projection objective 1100
images radiation from object plane 103 to image plane 102 with a
demagnification ratio of 4.times.. The tracklength of projection
objective 1100 is 2000 mm and the optical path length of imaged
radiation is 5337 mm. Accordingly, the ratio of the optical path
length to tracklength is approximately 2.67. Projection objective
1100 has an aperture stop 1106 positioned at mirror 1120.
[0186] The entrance pupil of projection objective 1100 is located
at infinity with object plane positioned between the entrance pupil
and the mirrors. The chief ray angle of the central field point at
object plane 103 is 7.degree.. The maximum variation of chief ray
angles at object plane 103 is less than 0.06.degree..
[0187] Projection objective 1100 has a rectangular field. The
image-side field width, d.sub.x, is 26 mm. The image-side field
length, d.sub.y, is 2 mm. Projection objective 1100 has an
object-image shift of 31 mm.
[0188] The performance of projection objective 1100 includes an
image-side W.sub.rms of 0.025.lamda.. Image-side field curvature is
10 nm. Projection objective 1100 provides an intermediate image
between mirrors 1140 and 1150.
[0189] The optical power of the mirrors in the order of the
radiation path from object plane 103 to image plane 102 is as
follows: mirror 1110 has positive optical power; mirror 1120 has
positive optical power; mirror 1130 has negative optical power;
mirror 1140 has positive optical power; mirror 1150 has negative
optical power; and mirror 1160 has positive optical power.
[0190] The dimension of the footprint of each mirror, given as
M.sub.x.times.M.sub.y, is as follows: 291 mm.times.195 mm for
mirror 1110; 159 mm.times.152 mm for mirror 1120; 157 mm.times.53
mm for mirror 1130; 295 mm.times.66 mm for mirror 1140; 105
mm.times.86 mm for mirror 1150; and 345 mm.times.318 mm for mirror
1160.
[0191] The chief ray angle of incidence for the central field point
is 4.38.degree., 4.03.degree., 18.37.degree., 7.74.degree.,
12.64.degree., and 5.17.degree. for mirrors 1110, 1120, 1130, 1140,
1150, and 1160, respectively. The maximum angle of incidence,
.theta..sub.max, on each mirror for the meridional section is
6.48.degree., 6.44.degree., 20.05.degree., 9.12.degree.,
21.76.degree., and 7.22.degree.for mirrors 1110, 1120, 1130, 1140,
1150, and 1160, respectively. .DELTA..theta. for mirrors 1110,
1120, 1130, 1140, 1150, and 1160 are 4.27.degree., 4.92.degree.,
4.09.degree., 3.12.degree., 19.37.degree., and 4.61.degree.,
respectively.
[0192] Mirrors 1110, 1150, and 1160 have freeboards that are more
than 5 mm and less than 25 mm. Mirror 1140 has positive chief ray
angle magnification while mirrors 1110, 1120, 1130, and 1150 have
negative chief ray angle magnification.
[0193] The image-side free working distance of projection objective
1100 is 25 mm. The object-side free working distance is 163 mm.
[0194] In projection objective 1100, d.sub.op-1/d.sub.op-2 is 6.57.
Furthermore, adjacent mirror pair 1040 and 1050 are separated by
more than 50% of the projection objective's tracklength. Further,
the distance between mirror 1110 and object plane 103 is more than
50% of the projection objective's tracklength.
[0195] Data for projection objective 1100 is presented in Table 3A
and Table 3B below. Table 3A presents optical data, while Table 3B
presents aspherical constants for each of the mirror surfaces. For
the purposes of Table 3A and Table 3B, the mirror designations
correlate as follows: mirror 1 (M1) corresponds to mirror 1110;
mirror 2 (M2) corresponds to mirror 1120; mirror 3 (M3) corresponds
to mirror 1130; mirror 4 (M4) corresponds to mirror 1140; mirror 5
(M5) corresponds to mirror 1150; and mirror 6 (M6) corresponds to
mirror 1160.
TABLE-US-00005 TABLE 3A Surface Radius (mm) Thickness (mm) Mode
Object INFINITY 1070.002 Mirror 1 -2069.710 -907.121 REFL Mirror 2
1710.596 0.000 REFL STOP INFINITY 907.500 Mirror 3 414.111 -319.107
REFL Mirror 4 618.022 1223.709 REFL Mirror 5 406.139 -436.552 REFL
Mirror 6 522.609 461.570 REFL Image INFINITY 0.000
TABLE-US-00006 TABLE 3B Coefficient M1 M2 M3 M4 M5 M6 K
-2.012543E+00 -7.790981E+00 -9.061196E-01 -4.714699E-01
5.253415E+00 1.051556E-01 Y -1.801229E-01 -2.676895E-01
6.249715E-03 2.914352E-02 3.699848E-02 6.762162E-04 X.sup.2
-3.718177E-05 -1.568640E-04 -4.213586E-04 -1.680785E-04
-6.132874E-05 2.479745E-06 Y.sup.2 -5.757281E-05 -1.359112E-04
-3.015850E-04 -9.908817E-05 -6.383717E-05 1.909227E-06 X.sup.2Y
-3.283304E-08 -1.421641E-07 -4.802304E-08 -4.234719E-08
5.460366E-07 -5.398408E-09 Y.sup.3 -7.289267E-08 -9.447144E-08
3.714670E-07 1.405667E-07 2.644773E-08 -4.741511E-09 X.sup.4
-3.792148E-11 2.173390E-10 -8.723035E-10 -2.377992E-11 1.030821E-09
-1.926536E-11 X.sup.2Y.sup.2 -1.087876E-10 5.689855E-10
-5.959943E-10 -4.401654E-10 2.045233E-09 -4.586698E-11 Y.sup.4
-1.237594E-10 2.990476E-10 8.549602E-10 -4.022663E-11 5.551510E-11
-2.632066E-11 X.sup.4Y -3.587007E-14 -1.028868E-12 -8.033093E-12
1.716353E-13 5.551826E-12 -2.577816E-14 X.sup.2Y.sup.3 8.925822E-14
4.492952E-13 -1.186636E-12 -7.545064E-13 -4.309344E-12
-1.775797E-14 Y.sup.5 -7.423435E-14 5.791519E-13 8.705928E-14
-2.700779E-13 -7.302230E-12 -9.309635E-15 X.sup.6 1.876383E-17
2.916278E-16 -2.307341E-14 -1.670466E-15 8.878140E-15 -3.351380E-17
X.sup.4Y.sup.2 -3.009967E-16 -3.620666E-16 -2.232847E-14
1.589023E-15 4.463758E-14 -1.408427E-16 X.sup.2Y.sup.4 1.992400E-16
3.916129E-16 1.756497E-15 3.477633E-16 1.478648E-13 -1.372823E-16
Y.sup.6 8.315953E-18 -6.580116E-16 8.232062E-16 1.253553E-16
3.691569E-14 -3.799352E-17 X.sup.6Y -2.621825E-20 -1.237101E-17
-3.125465E-16 -7.682746E-18 3.293829E-16 -1.214309E-19
X.sup.4Y.sup.3 -1.344388E-18 3.730815E-17 1.376670E-16 5.918289E-18
8.409538E-16 5.369262E-20 X.sup.2Y.sup.5 -6.157858E-19 3.202677E-17
4.387074E-19 2.707480E-18 4.875870E-16 -1.363873E-20 Y.sup.7
2.770009E-20 8.487049E-18 2.518948E-18 1.820744E-19 1.274511E-16
2.776746E-21 X.sup.8 2.265356E-23 -1.881878E-20 6.916970E-19
3.815768E-20 -1.030207E-19 -2.085793E-23 X.sup.6Y.sup.2
-1.848041E-22 -1.667898E-19 -1.070800E-18 1.947584E-20
-6.071205E-19 -1.191227E-22 X.sup.4Y.sup.4 -1.617091E-21
-4.471313E-20 -2.039154E-19 -1.469302E-21 8.581801E-18
-2.848570E-22 X.sup.2Y.sup.6 -1.152811E-21 -1.417078E-19
-4.885470E-20 8.329380E-22 2.867618E-18 8.073429E-24 Y.sup.8
5.021474E-23 -1.270497E-20 -2.834042E-20 -1.011971E-21 1.813992E-18
-6.757839E-23 X.sup.8Y 0.000000E+00 0.000000E+00 7.973679E-21
2.492982E-22 0.000000E+00 -2.465296E-25 X.sup.6Y.sup.3 0.000000E+00
0.000000E+00 7.629111E-22 1.401277E-22 0.000000E+00 2.930653E-25
X.sup.4Y5 0.000000E+00 0.000000E+00 -7.196032E-21 -4.219890E-23
0.000000E+00 1.194933E-25 X.sup.2Y.sup.7 0.000000E+00 0.000000E+00
-1.090375E-22 -3.791571E-24 0.000000E+00 5.412579E-25 Y.sup.9
0.000000E+00 0.000000E+00 -5.080252E-23 1.076602E-24 0.000000E+00
3.891280E-26 X.sup.10 0.000000E+00 0.000000E+00 -6.129418E-25
-1.289913E-27 0.000000E+00 0.000000E+00 X.sup.8Y.sup.2 0.000000E+00
0.000000E+00 2.295090E-23 4.078311E-25 0.000000E+00 0.000000E+00
X.sup.6Y.sup.4 0.000000E+00 0.000000E+00 5.951785E-24 1.728297E-25
0.000000E+00 0.000000E+00 X.sup.4Y.sup.6 0.000000E+00 0.000000E+00
-1.732732E-23 -5.280557E-26 0.000000E+00 0.000000E+00
X.sup.2Y.sup.8 0.000000E+00 0.000000E+00 0.000000E+00 -1.410994E-27
0.000000E+00 0.000000E+00 Y.sup.10 0.000000E+00 0.000000E+00
0.000000E+00 3.484416E-27 0.000000E+00 0.000000E+00 Nradius
1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00
1.000000E+00 Y-decenter 194.936 -49.734 36.609 9.442 30.019 40.956
X-rotation -5.944 -17.277 -5.569 -0.579 0.301 -0.924
[0196] Referring to FIG. 12, an embodiment of a projection
objective 1200 includes six mirrors 1210, 1220, 1230, 1240, 1250,
and 1260, and has an image-side numerical aperture of 0.35 and an
operating wavelength of 13.5 nm. Mirrors 1210, 1220, 1230, 1240,
1250, and 1260 are all freeform mirrors. Projection objective 1200
images radiation from object plane 103 to image plane 102 with a
demagnification ratio of 4.times.. A reference axis 1205,
orthogonal to object plane 103 and image plane 102 intersects
corresponding field points in the object and image fields. The
tracklength of projection objective 1200 is 1385 mm and the optical
path length of imaged radiation is 4162 mm. Accordingly, the ratio
of the optical path length to tracklength is approximately 3.01.
Projection objective 1200 has an aperture stop positioned at mirror
1220.
[0197] The entrance pupil of projection objective 1200 is at
infinity with object plane positioned between the entrance pupil
and the mirrors. The chief ray angle of the central field point at
object plane 103 is 7.degree.. The maximum variation of chief ray
angles at object plane 103 is less than 0.06.degree..
[0198] Projection objective 1200 has a rectangular field. The
image-side field width, d.sub.x, is 26 mm. The image-side field
length, d.sub.y, is 2 mm. Projection objective 1200 has zero
object-image shift.
[0199] Projection objective 1200 provides an intermediate image
between mirrors 1240 and 1250.
[0200] The optical power of the mirrors in the order of the
radiation path from object plane 103 to image plane 102 is as
follows: mirror 1210 has positive optical power; mirror 1220 has
negative optical power; mirror 1230 has positive optical power;
mirror 1240 has positive optical power; mirror 1250 has negative
optical power; and mirror 1260 has positive optical power.
[0201] The dimension of the footprint of each mirror, given as
M.sub.x.times.M.sub.y, is as follows: 250 mm.times.153 mm for
mirror 1210; 70 mm.times.69 mm for mirror 1020; 328 mm.times.153 mm
for mirror 1230; 325 mm.times.112 mm for mirror 1240; 87
mm.times.75 mm for mirror 1250; and 269 mm.times.238 mm for mirror
1260.
[0202] The chief ray angle of incidence for the central field point
is 6.13.degree., 10.61.degree., 8.65.degree., 8.26.degree.,
14.22.degree., and 5.23.degree. for mirrors 1210, 1220, 1230, 1240,
1250, and 1260, respectively. The maximum angle of incidence,
.theta..sub.max, on each mirror for the meridional section is
6.53.degree., 11.63.degree., 8.91.degree., 11.39.degree.,
24.26.degree., and 7.44.degree. for mirrors 1210, 1220, 1230, 1240,
1250, and 1260, respectively. .DELTA..theta. for mirrors 1210,
1220, 1230, 1240, 1250, and 1260 are 1.07.degree., 3.64.degree.,
1.74.degree., 7.44.degree., 21.70.degree., and 4.51.degree.,
respectively.
[0203] Mirrors 1210, 1220, 1250, and 1260 have freeboards that are
more than 5 mm and less than 25 mm. Mirror 1240 has positive chief
ray angle magnification while mirrors 1210, 1220, 1230, and 1250
have negative chief ray angle magnification.
[0204] The image-side free working distance of projection objective
1200 is 40 mm. The object-side free working distance is 439 mm.
[0205] In projection objective 1200, d.sub.op-1/d.sub.op-2 is 1.91.
Furthermore, adjacent mirror pair 1240 and 1250 are separated by
more than 50% of the projection objective's tracklength. Further,
the distance between mirror 1210 and object plane 103 is more than
50% of the projection objective's tracklength.
[0206] Data for projection objective 1200 is presented in Table 4A
and Table 4B below. Table 4A presents optical data, while Table 4B
presents aspherical constants for each of the mirror surfaces. For
the purposes of Table 4A and Table 4B, the mirror designations
correlate as follows: mirror 1 (M1) corresponds to mirror 1210;
mirror 2 (M2) corresponds to mirror 1220; mirror 3 (M3) corresponds
to mirror 1230; mirror 4 (M4) corresponds to mirror 1240; mirror 5
(M5) corresponds to mirror 1250; and mirror 6 (M6) corresponds to
mirror 1260.
TABLE-US-00007 TABLE 4A Surface Radius (mm) Thickness (mm) Mode
Object INFINITY 836.375 Mirror 1 -614.878 -397.397 REFL Mirror 2
-383.358 0.000 REFL STOP INFINITY 655.992 Mirror 3 -1204.989
-659.631 REFL Mirror 4 1885.915 909.840 REFL Mirror 5 302.954
-308.805 REFL Mirror 6 403.492 348.850 REFL Image INFINITY
0.000
TABLE-US-00008 TABLE 4B Coefficient M1 M2 M3 M4 M5 M6 K
-6.673329E-01 -2.825442E-01 -1.843864E+00 2.076932E+00 3.340547E+00
1.990979E-01 Y -5.045837E-02 2.263660E-01 -1.277806E-01
-3.310548E-02 -1.935522E-01 1.783092E-02 X.sup.2 1.827144E-04
1.686990E-04 9.963384E-05 5.203052E-05 -3.849892E-04 3.792405E-05
Y.sup.2 1.737812E-04 2.093994E-04 -1.747764E-05 -7.184095E-05
-3.329705E-04 1.662759E-05 X.sup.2Y 4.765150E-08 -1.595967E-06
-5.515151E-08 -8.752119E-10 1.213426E-06 5.552151E-08 Y.sup.3
5.091508E-08 -1.231538E-06 -1.294839E-07 -1.939381E-07 1.502735E-06
9.165146E-08 X.sup.4 -4.718889E-11 -6.941238E-09 -7.002011E-11
-5.996832E-11 -2.342602E-09 9.552648E-12 X.sup.2Y.sup.2
-4.340357E-11 -7.827867E-09 -1.801185E-10 -7.139217E-11
-1.234047E-08 -1.611525E-10 Y.sup.4 1.234053E-10 -3.130174E-09
-7.281275E-11 -1.598859E-10 -1.206604E-08 -1.662004E-10 X.sup.4Y
1.205203E-13 -6.495768E-11 -3.614883E-14 -4.344276E-14 2.268270E-11
2.930397E-13 X.sup.2Y.sup.3 2.259661E-13 -4.304439E-11
-1.048629E-13 -7.811421E-16 2.977954E-11 8.493936E-13 Y.sup.5
-5.198478E-13 -1.485266E-11 5.022687E-15 -1.422459E-14
-1.556209E-11 4.051187E-13 X.sup.6 -1.306395E-16 -4.159695E-14
0.000000E+00 -3.767576E-17 1.374773E-14 -9.890588E-17
X.sup.4Y.sup.2 8.838986E-17 1.462867E-14 0.000000E+00 -1.369883E-16
-3.320990E-13 -1.312584E-15 X.sup.2Y.sup.4 -1.745854E-16
4.353978E-13 0.000000E+00 -7.920443E-17 -1.008910E-13 -2.069868E-15
Y.sup.6 1.020155E-15 -1.927189E-13 0.000000E+00 -3.431888E-17
-9.148646E-14 -6.650861E-16 X.sup.6Y 1.090627E-19 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 1.607288E-18 X.sup.4Y.sup.3
-4.158749E-19 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
4.652411E-18 X.sup.2Y.sup.5 -1.758731E-18 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 4.087290E-18 Y.sup.7 -3.081679E-18
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 9.802736E-19
X.sup.8 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X.sup.6Y.sup.2 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 X.sup.4Y.sup.4
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 X.sup.2Y.sup.6 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 Y.sup.8 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
X.sup.8Y 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X.sup.6Y.sup.3 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 X.sup.4Y5
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 X.sup.2Y.sup.7 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 Y.sup.9 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
X.sup.10 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X.sup.8Y.sup.2 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 X.sup.6Y.sup.4
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 X.sup.4Y.sup.6 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 X.sup.2Y.sup.8 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
Y.sup.10 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 Nradius 1.00E+00 1.00E+00 1.00E+00
1.00E+00 1.00E+00 1.00E+00 Y-decenter -118.847 -100.000 100.000
24.472 -11.760 -37.772 X-rotation -7.782 7.388 1.406 -2.140 -8.177
6.989
[0207] Referring to FIG. 13, an embodiment of a projection
objective 1400 includes six mirrors 1410, 1420, 1430, 1440, 1450,
and 1460, and has an image-side numerical aperture of 0.40 and an
operating wavelength of 13.5 nm. Mirrors 1410, 1420, 1430, 1440,
1450, and 1460 are all freeform mirrors. Projection objective 1400
images radiation from object plane 103 to image plane 102 with a
demagnification ratio of 4.times.. The tracklength of projection
objective 1400 is 1498 mm and the optical path length of imaged
radiation is 3931 mm. Accordingly, the ratio of the optical path
length to tracklength is approximately 2.62. Projection objective
1400 has an aperture stop positioned between mirrors 1420 and
1430.
[0208] The entrance pupil of projection objective 1400 is located
1,000 mm from object plane 103 with object plane positioned between
the entrance pupil and the mirrors. The chief ray angle of the
central field point at object plane 103 is 7.degree.. The maximum
variation of chief ray angles at object plane 103 is
0.82.degree..
[0209] Projection objective 1400 has a rectangular field. The
image-side field width, d.sub.x, is 26 mm. The image-side field
length, d.sub.y, is 2 mm. Projection objective 1000 has an
object-image shift of 38 mm.
[0210] The performance of projection objective 1000 includes an
image-side W.sub.rms of 0.083.lamda.. Distortion is approximately
100 nm, and image-side field curvature is 36 nm. Projection
objective 1400 provides an intermediate image between mirrors 1440
and 1450.
[0211] The optical power of the mirrors in the order of the
radiation path from object plane 103 to image plane 102 is as
follows: mirror 1410 has positive optical power; mirror 1420 has
positive optical power; mirror 1430 has negative optical power;
mirror 1440 has positive optical power; mirror 1050 has negative
optical power; and mirror 1460 has positive optical power.
[0212] The dimension of the footprint of each mirror, given as
M.sub.x.times.M.sub.y, is as follows: 326 mm.times.159 mm for
mirror 1410; 210 mm.times.123 mm for mirror 1420; 120 mm.times.66
mm for mirror 1430; 312 mm.times.119 mm for mirror 1440; 112
mm.times.83 mm for mirror 1450; and 405 mm.times.379 mm for mirror
1460.
[0213] The chief ray angle of incidence for the central field point
is 6.70.degree., 8.08.degree., 20.41.degree., 6.68.degree.,
14.52.degree., and 5.67.degree. for mirrors 1410, 1420, 1430, 1440,
1450, and 1460, respectively. The maximum angle of incidence,
.theta..sub.max, on each mirror for the meridional section is
8.61.degree., 10.91.degree., 21.98.degree., 7.41.degree.,
27.19.degree., and 6.86.degree. for mirrors 1410, 1420, 1430, 1440,
1450, and 1460, respectively. .DELTA..theta. for mirrors 1410,
1420, 1430, 1440, 1450, and 1460 are 3.92.degree., 5.69.degree.,
3.82.degree., 1.79.degree., 26.83.degree., and 3.20.degree.,
respectively.
[0214] Mirrors 1410, 1420, 1430, 1450, and 1460 have freeboards
that are more than 5 mm and less than 25 mm Mirror 1440 has
positive chief ray angle magnification while mirrors 1410, 1420,
1430, and 1450 have negative chief ray angle magnification.
[0215] The image-side free working distance of projection objective
1400 is 45 mm. The object-side free working distance is 291 mm.
[0216] In projection objective 1400, d.sub.op-1/d.sub.op-2 is 2.47.
Furthermore, adjacent mirror pair 1440 and 1450 is separated by
more than 50% of the projection objective's tracklength.
[0217] Data for projection objective 1400 is presented in Table 6A
and Table 6B below. Table 6A presents optical data, while Table 6B
presents aspherical constants for each of the mirror surfaces. For
the purposes of Table 6A and Table 6B, the mirror designations
correlate as follows: mirror 1 (M1) corresponds to mirror 1010;
mirror 2 (M2) corresponds to mirror 1020; mirror 3 (M3) corresponds
to mirror 1030; mirror 4 (M4) corresponds to mirror 1040; mirror 5
(M5) corresponds to mirror 1050; and mirror 6 (M6) corresponds to
mirror 1060.
TABLE-US-00009 TABLE 6A Surface Radius (mm) Thickness (mm) Mode
Object INFINITY 719.154 Mirror 1 -1768.086 -427.871 REFL Mirror 2
2334.525 575.634 REFL Mirror 3 352.553 -347.888 REFL Mirror 4
610.853 933.638 REFL Mirror 5 431.588 -434.965 REFL Mirror 6
521.464 479.940 REFL Image INFINITY 0.000
TABLE-US-00010 TABLE 6B Coefficient M1 M2 M3 M4 M5 M6 K
-7.735395E+00 -6.005799E+01 -3.751432E-01 -8.758413E-01
6.604547E+00 8.612526E-02 Y 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 X.sup.2 -1.485069E-04
-1.263679E-04 -2.624294E-04 1.347923E-05 -1.388138E-04
-6.931036E-06 Y.sup.2 -1.726040E-04 -1.711814E-04 -1.005287E-03
-3.665045E-05 1.295215E-04 8.615161E-06 X.sup.2Y -5.200823E-08
-4.156617E-07 7.669496E-07 -5.478449E-08 9.580682E-07 -4.043887E-09
Y.sup.3 -3.734392E-08 -4.637041E-08 -5.212076E-07 4.563436E-08
1.158899E-07 -6.370253E-09 X.sup.4 -1.602036E-10 1.080674E-09
-1.784900E-08 3.290440E-10 2.227159E-09 -4.223672E-11
X.sup.2Y.sup.2 -5.655636E-10 1.150736E-09 9.356049E-09
-1.772824E-10 7.086270E-09 -3.649540E-11 Y.sup.4 7.840007E-11
1.816509E-09 1.947612E-09 9.043201E-10 3.962050E-09 5.321857E-12
X.sup.4Y -9.204024E-14 2.366905E-12 -2.677935E-11 -8.314955E-13
-1.528996E-11 2.788263E-15 X.sup.2Y.sup.3 1.079182E-12 3.100338E-12
3.708016E-11 -5.930044E-12 -2.181691E-11 -3.366047E-14 Y.sup.5
-4.579479E-13 -6.879640E-12 -4.466462E-13 9.529833E-13
-2.295402E-11 -2.906642E-14 X.sup.6 6.241273E-17 -3.829664E-15
1.521283E-13 1.097127E-15 -3.501249E-14 -6.862154E-17
X.sup.4Y.sup.2 1.666766E-15 1.243647E-14 5.320614E-14 7.533431E-16
8.652054E-14 -1.407857E-16 X.sup.2Y.sup.4 -2.345440E-15
2.162639E-15 -5.453363E-14 -1.396841E-14 4.036247E-13 1.131588E-17
Y.sup.6 -3.012261E-15 -1.224080E-14 -1.034267E-14 9.519542E-16
1.105527E-13 3.923271E-17 X.sup.6Y 3.484859E-18 -9.656525E-18
-6.882044E-16 7.124323E-18 8.790794E-16 2.032080E-20 X.sup.4Y.sup.3
-2.997302E-18 -1.020453E-16 -4.147278E-16 1.059357E-17 9.581262E-16
-8.784820E-20 X.sup.2Y.sup.5 3.436846E-18 2.303857E-17
-1.104525E-16 -1.635704E-17 -1.619074E-15 -2.001426E-19 Y.sup.7
1.247042E-17 1.643841E-16 4.675424E-17 -7.809506E-19 -3.824576E-15
-5.405817E-20 X.sup.8 6.566049E-22 4.616940E-20 -8.583253E-18
1.135128E-21 -4.651481E-19 -3.090479E-22 X.sup.6Y.sup.2
-1.894284E-20 -2.084017E-19 -4.140672E-18 3.271179E-20
-2.096068E-17 -7.650033E-22 X.sup.4Y.sup.4 -4.216883E-21
-3.239553E-19 -3.670866E-18 4.460462E-20 -8.776559E-17
-1.201625E-22 X.sup.2Y.sup.6 -2.826171E-21 -3.920562E-19
3.151001E-20 7.969094E-21 -5.615799E-17 3.016401E-22 Y.sup.8
-1.315593E-20 -3.058425E-19 2.416437E-20 8.284460E-22 -1.006196E-17
1.721317E-22 X.sup.8Y -9.935149E-25 -5.168771E-24 -2.316832E-20
-2.523681E-24 1.540486E-20 -3.155606E-26 X.sup.6Y.sup.3
3.001708E-23 1.226818E-21 -2.812819E-21 3.078069E-23 -1.510545E-19
-4.150182E-25 X.sup.4Y5 7.941504E-24 1.371322E-21 -5.440197E-21
3.362723E-23 -6.912241E-19 -2.930215E-25 X.sup.2Y.sup.7
-9.194045E-25 7.101398E-22 4.152263E-22 1.093452E-23 -4.418575E-19
3.377883E-25 Y.sup.9 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 X.sup.10 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
X.sup.8Y.sup.2 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X.sup.6Y.sup.4 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 X.sup.4Y.sup.6
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 X.sup.2Y.sup.8 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 Y.sup.10 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
Nradius 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 Y-
-182.329 -165.907 121.386 20.437 21.141 28.282 decenter X-rotation
-10.857 -0.974 -13.061 -5.217 -2.314 -0.850
[0218] Referring to FIG. 14, projection objective 1400 can be used
in an optical system 1401 that includes a light source 1405 and
illumination optics including a collector unit 1415, a spectral
purity filter 1425, a field facet mirror 1435 and a pupil facet
mirror 1445. Light source 1405 is an EUV light source configured to
provide radiation at 13.5 nm to the projection objective. Collector
unit 1415 gathers radiation from source 1405 and directs the
radiation towards spectral purity filter 1415 which filters
incident radiation at wavelengths other than 13.5 nm and directs
the radiation at 13.5 nm towards field facet mirror 1435. Together
with pupil facet mirror 1445, field facet mirror illuminates a
reflective reticle positioned at object plane 103 with radiation at
13.5 nm. The radiation is provided so that the chief rays diverge
from the reticle. The radiation is provided to the reticle in this
way without the use of additional components, such as a grazing
incidence mirror.
[0219] Referring to FIG. 15, an embodiment of a projection
objective 1500 includes six mirrors 1510, 1520, 1530, 1540, 1550,
and 1560, and has an image-side numerical aperture of 0.40 and an
operating wavelength of 13.5 nm. Mirrors 1510, 1520, 1530, 1540,
1550, and 1460 are all freeform mirrors. Projection objective 1500
images radiation from object plane 103 to image plane 102 with a
demagnification ratio of 4.times.. The tracklength of projection
objective 1500 is 1499 mm and the optical path length of imaged
radiation is 4762 mm. Accordingly, the ratio of the optical path
length to tracklength is approximately 3.18. Projection objective
1500 has an aperture stop positioned close to mirror 1520.
[0220] The entrance pupil of projection objective 1500 is located
1,000 mm from object plane 103 with object plane positioned between
the entrance pupil and the mirrors. Due to the reflective reticle
positioned at object plane 103, illumination optics can be
positioned at location 1501, corresponding to the entrance pupil.
The chief ray angle of the central field point at object plane 103
is 7.degree.. The maximum variation of chief ray angles at object
plane 103 is 0.82.degree..
[0221] Projection objective 1500 has a rectangular field. The
image-side field width, d.sub.x, is 26 mm. The image-side field
length, d.sub.y, is 2 mm. Projection objective 1500 has an
object-image shift of 7 mm.
[0222] The performance of projection objective 1500 includes an
image-side W.sub.rms of 0.040.lamda.. Referring also to FIG. 16A,
distortion is less than about 3 nm across the image field.
Image-side field curvature is 35 nm. Projection objective 1500
provides an intermediate image between mirrors 1540 and 1550.
Referring to FIG. 16B, the chief rays are orthogonal to image plane
102 to within about 0.001 rad (0.06.degree.) at the image
field.
[0223] The optical power of the mirrors in the order of the
radiation path from object plane 103 to image plane 102 is as
follows: mirror 1510 has positive optical power; mirror 1520 has
negative optical power; mirror 1530 has positive optical power;
mirror 1540 has positive optical power; mirror 1550 has negative
optical power; and mirror 1560 has positive optical power.
[0224] The dimension of the footprint of each mirror, given as
M.sub.x.times.M.sub.y, is as follows: 253 mm.times.162 mm for
mirror 1510; 105 mm.times.66 mm for mirror 1520; 227 mm.times.301
mm for mirror 1530; 182 mm.times.220 mm for mirror 1540; 111
mm.times.85 mm for mirror 1550; and 289 mm.times.275 mm for mirror
1560.
[0225] The chief ray angle of incidence for the central field point
is 3.96.degree., 12.21.degree., 7.51.degree., 11.98.degree.,
15.82.degree., and 8.08.degree. for mirrors 1510, 1520, 1530, 1540,
1550, and 1560, respectively. The maximum angle of incidence,
.theta..sub.max, on each mirror for the meridional section is
4.47.degree., 12.81.degree., 8.55.degree., 16.91.degree.,
27.68.degree., and 9.96.degree. for mirrors 1510, 1520, 1530, 1540,
1550, and 1560, respectively. .DELTA..theta. for mirrors 1510,
1520, 1530, 1540, 1550, and 1560 are 1.10.degree., 3.61.degree.,
4.19.degree., 12.12.degree., 27.17.degree., and 4.79.degree.,
respectively.
[0226] Mirrors 1510, 1520, 1540, 1550, and 1560 have freeboards
that are more than 5 mm and less than 25 mm Mirror 1530 has
positive chief ray angle magnification while mirrors 1510, 1520,
1540, and 1550 have negative chief ray angle magnification.
[0227] The image-side free working distance of projection objective
1500 is 45 mm. The object-side free working distance is 260 mm.
[0228] In projection objective 1500, d.sub.op-1/d.sub.op-2 is 3.05.
Furthermore, adjacent mirror pairs 1520 and 1530, 1530 and 1540,
and 1540 and 1550 are separated by more than 50% of the projection
objective's tracklength. Further, the distance between mirror 1510
and object plane 103 is more than 50% of the projection objective's
tracklength.
[0229] Data for projection objective 1500 is presented in Table 7A
and Table 7B below. Table 7A presents optical data, while Table 7B
presents aspherical constants for each of the mirror surfaces. For
the purposes of Table 7A and Table 7B, the mirror designations
correlate as follows: mirror 1 (M1) corresponds to mirror 1510;
mirror 2 (M2) corresponds to mirror 1520; mirror 3 (M3) corresponds
to mirror 1530; mirror 4 (M4) corresponds to mirror 1540; mirror 5
(M5) corresponds to mirror 1550; and mirror 6 (M6) corresponds to
mirror 1560.
TABLE-US-00011 TABLE 7A Surface Radius (mm) Thickness (mm) Mode
Object INFINITY 793.452 Mirror 1 -652.351 -533.717 REFL Mirror 2
-459.234 946.263 REFL Mirror 3 -1711.458 -789.999 REFL Mirror 4
1814.404 1037.812 REFL Mirror 5 310.131 -304.837 REFL Mirror 6
407.712 349.882 REFL Image INFINITY 0.000
TABLE-US-00012 TABLE 7B Coefficient M1 M2 M3 M4 M5 M6 K
-5.917992E-01 1.401977E+00 -1.852312E+00 3.134672E+00 1.276852E+00
2.162747E-01 Y 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X.sup.2 2.486175E-04 6.462590E-04
8.097144E-05 3.683589E-05 -5.694587E-04 1.127522E-05 Y.sup.2
1.796052E-04 -1.218131E-05 -3.272168E-05 -7.479058E-05
-3.798909E-04 5.142215E-05 X.sup.2Y -3.704365E-08 -3.061838E-06
1.166808E-07 1.073313E-07 3.054784E-06 -1.901527E-08 Y.sup.3
-8.473076E-09 -4.336504E-06 -6.831514E-08 -2.680850E-08
1.944165E-06 2.077407E-09 X.sup.4 1.525482E-11 2.440415E-10
-2.839993E-11 -8.352784E-11 1.477727E-09 -1.231925E-10
X.sup.2Y.sup.2 4.909383E-11 1.819997E-09 -2.639958E-11
-7.953809E-11 1.884598E-08 -4.030921E-11 Y.sup.4 7.241758E-11
-1.924132E-08 -1.611187E-10 -1.805904E-10 2.829058E-09
-6.788132E-11 X.sup.4Y -3.944773E-14 -3.384346E-12 4.634420E-14
1.089774E-13 4.746215E-11 7.092901E-15 X.sup.2Y.sup.3 -2.485019E-13
-1.985647E-10 -1.749321E-13 2.706968E-13 1.878106E-10 7.623271E-14
Y.sup.5 -6.222758E-14 1.546404E-10 -7.306272E-14 1.121470E-13
2.713089E-11 1.059625E-13 X.sup.6 -2.853060E-17 1.499373E-14
-3.327224E-16 -3.396117E-16 1.122966E-13 -7.141998E-16
X.sup.4Y.sup.2 5.428060E-17 -4.560639E-13 -2.729510E-17
1.958645E-17 4.975385E-13 -1.157245E-15 X.sup.2Y.sup.4 9.034205E-16
4.633694E-13 -4.803414E-16 4.337124E-16 9.650331E-13 -6.079561E-16
Y.sup.6 9.726812E-16 -1.567936E-12 -9.119915E-19 3.224937E-16
-4.013641E-13 -1.910957E-16 X.sup.6Y 7.541120E-20 -5.491590E-16
-3.248735E-18 -4.999870E-18 1.809992E-15 1.533677E-19
X.sup.4Y.sup.3 -7.407407E-19 1.626025E-15 -4.175176E-19
-1.121906E-18 4.277794E-15 7.709209E-19 X.sup.2Y.sup.5
-3.053897E-18 -1.459850E-15 -5.190383E-19 9.702383E-19 5.157566E-15
9.414679E-19 Y.sup.7 -1.167661E-17 1.377526E-14 -3.283791E-21
9.398678E-20 -3.053184E-15 3.954522E-19 X.sup.8 -1.128385E-22
-2.091289E-19 -1.560172E-21 -2.941200E-21 2.054965E-18
-3.788563E-21 X.sup.6Y.sup.2 -2.424101E-21 -5.485841E-18
-1.205060E-20 -3.188366E-20 8.911569E-18 -9.560288E-21
X.sup.4Y.sup.4 4.347588E-22 -3.722786E-17 -1.249304E-21
-8.368608E-21 1.007777E-17 -8.789392E-21 X.sup.2Y.sup.6
2.577199E-21 -2.687589E-17 -2.354061E-22 8.597809E-22 1.143993E-17
-3.545101E-21 Y.sup.8 5.215288E-20 -7.369037E-17 -4.229309E-23
-6.689468E-22 -7.499429E-18 -1.703637E-21 X.sup.8Y 7.792174E-25
0.000000E+00 -7.813621E-24 -2.516130E-23 0.000000E+00 8.396981E-25
X.sup.6Y.sup.3 8.992421E-24 0.000000E+00 -1.921637E-23
-8.262460E-23 0.000000E+00 4.664369E-24 X.sup.4Y5 -4.714974E-25
0.000000E+00 -1.610571E-24 -1.778199E-23 0.000000E+00 9.398752E-24
X.sup.2Y.sup.7 6.059892E-24 0.000000E+00 3.848059E-26 1.222213E-24
0.000000E+00 1.042278E-23 Y.sup.9 -8.700880E-23 0.000000E+00
6.368781E-27 -2.288415E-25 0.000000E+00 7.789109E-24 X.sup.10
0.000000E+00 0.000000E+00 -5.411923E-27 -1.603639E-26 0.000000E+00
-3.929816E-26 X.sup.8Y.sup.2 0.000000E+00 0.000000E+00
-8.609679E-27 -4.538477E-26 0.000000E+00 -1.453997E-25
X.sup.6Y.sup.4 0.000000E+00 0.000000E+00 -1.127835E-26
-7.710579E-26 0.000000E+00 -1.839705E-25 X.sup.4Y.sup.6
0.000000E+00 0.000000E+00 -8.495275E-28 -1.413945E-26 0.000000E+00
-8.230974E-26 X.sup.2Y.sup.8 0.000000E+00 0.000000E+00 4.740792E-29
1.022008E-27 0.000000E+00 -8.755646E-27 Y.sup.10 0.000000E+00
0.000000E+00 1.728076E-29 1.964912E-28 0.000000E+00 -7.204080E-27
Nradius 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 Y-
-144.660 -98.223 42.173 -14.449 2.986 -10.929 decenter X-rotation
-8.868 -16.235 1.500 -3.658 -7.600 -1.635
[0230] FIG. 17 shows another embodiment of the disclosure having
six mirrors being all designed as freeform surfaces. Depicted is
the object plane 3000, the image plane 3002, a first mirror Ml, a
second mirror M2, a third mirror M3, a fourth mirror M4, a fifth
mirror M5 and a sixth mirror M6. This projection objective has an
image side numerical aperture of 0.40. The field shape is
rectangular with a width of 26 mm and a height of 2 mm. The
operating wavelength is 13.5 nm. The sequence of optical power of
mirrors is PNPNNP. This optical system has one intermediate image
between mirrors M4 and M5. The entrance pupil of this projection
objective is located 1000 mm from object plane 3000, with the
object plane 3000 positioned between the entrance pupil and the
mirrors. A pupil plane is positioned between mirrors M2 and M3. The
tracklength is 1736 mm. The object image shift is 65 mm. The
optical path length is 4827 mm.
[0231] The performance of this projection objective includes an
image-side W.sub.rms of 0.037.lamda.. Distortion is smaller than 12
nm. Image-side field curvature is 25 nm.
[0232] The chief ray angle of the central field point at the object
is 7.degree.. The maximum variation of chief ray angles at object
plane 3000 is 0.82.
[0233] The dimension of the footprint of each mirror, given as
M.sub.x.times.M.sub.y is as follows: 323 mm.times.215 mm for mirror
M1; 131 mm.times.102 mm for mirror M2; 267 mm.times.183 mm for
mirror M3; 70 mm.times.52 mm for mirror M4; 124 mm.times.109 mm for
mirror M5; 447 mm.times.433 mm for mirror M6.
[0234] The chief ray angle of incidence for the central field point
for the mirrors M1 to M6 is 4.06.degree.; 11.34.degree.;
12.20.degree.; 31.60.degree.; 12.27.degree. and 7.64.degree.. The
maximum angles of incidence in meridional section for the mirrors
M1 to M6 is 4.96.degree.; 12.38.degree., 16.54.degree.,
41.24.degree.; 29.42.degree. and 9.25.degree.. The bandwidth of
angle of incidence in meridional section for mirrors M1 to M6 is
1.08.degree.; 2.71.degree.; 9.83.degree.; 22.72.degree.;
29.13.degree. and 4.28.degree.. Mirrors M2 and M4 have freeboards
that are more than 5 mm and less than 25 mm. Mirror M3 has positive
chief ray angle magnification while mirrors M1, M2, M4 and M5 have
negative chief ray angle magnification.
[0235] The image-side free working distance of this projection
objective is 45 mm. The object-side free working distance is 400
mm.
[0236] In this projection objective, d.sub.OP-1/d.sub.OP-2 is 2.67.
Further, reticle and mirror M1 as well as mirrors M2 and M3 are
separated by more than 50% of the projection objective
tracklength.
[0237] Data for the projection objective of FIG. 17 is presented in
Tables 8A, 8B below. Table 8A presents optical data, while Table 8B
presents aspherical constants for each of the mirror surfaces.
TABLE-US-00013 TABLE 8A Surface Radius Thickness Mode Object
INFINITY 1067.761 Mirror 1 -1219.687 -668.241 REFL Mirror 2
-747.811 1291.054 REFL Mirror 3 -969.893 -374.588 REFL Mirror 4
-549.105 374.588 REFL Mirror 5 470.063 -502.811 REFL Mirror 6
618.025 547.811 REFL Image INFINITY 0.000
TABLE-US-00014 TABLE 8B Coefficient M1 M2 M3 M4 M5 M6 K
5.078166E-01 2.515234E+00 4.458912E-01 -5.135256E+00 3.709497E+00
1.305537E-01 Y 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X2 -4.229616E-06 4.423002E-05
-1.137338E-04 6.243736E-04 -4.439433E-04 1.714681E-05 Y2
-2.042693E-05 -3.200090E-04 -1.490188E-04 4.230830E-05
-3.941063E-04 1.369711E-05 X2Y -2.456512E-08 -1.681122E-06
1.278895E-08 1.439095E-06 1.109021E-07 -7.066857E-09 Y3
-1.017618E-08 -1.085440E-06 -9.040764E-08 -8.248306E-07
6.038369E-07 -8.198184E-09 X4 2.532498E-11 -4.655202E-10
-6.082020E-11 -7.879275E-09 -9.475896E-10 -9.236663E-12 X2Y2
2.917327E-11 -4.875362E-09 -7.951092E-11 -6.364830E-09
-2.626820E-09 -1.778520E-11 Y4 1.116055E-11 9.584332E-10
-1.259982E-10 2.921676E-09 -8.367567E-10 -1.348267E-11 X4Y
-7.018800E-15 -9.924549E-12 -5.700215E-14 -7.337153E-11
-3.015573E-13 -5.057127E-15 X2Y3 -2.588267E-14 -2.065300E-11
-1.623609E-13 -4.830483E-11 -3.421535E-12 -8.177430E-15 Y5
-5.631482E-14 1.175099E-13 -3.257076E-14 2.900148E-11 -5.156003E-12
-7.754740E-16 X6 2.507037E-17 7.181890E-15 -6.970398E-17
1.896541E-13 -2.402650E-14 -1.687447E-17 X4Y2 1.805398E-16
2.845435E-14 -1.726885E-16 -3.660328E-13 -3.460882E-14
-5.258270E-17 X2Y4 3.234883E-16 4.275982E-14 -3.443645E-16
-1.119940E-13 -2.515640E-14 -4.418332E-17 Y6 5.139221E-17
1.240058E-14 -4.807113E-19 2.665448E-14 -3.989968E-14 -9.729792E-18
X6Y -1.655261E-20 2.112846E-16 -6.490967E-20 2.217817E-15
3.565159E-17 -2.533468E-21 X4Y3 6.406762E-19 7.287537E-16
-1.578781E-19 -1.022968E-15 -2.246920E-17 -9.556211E-21 X2Y5
1.095531E-18 4.084428E-16 -1.899934E-19 8.581644E-18 -4.609677E-16
-8.095822E-21 Y7 3.534107E-19 -1.119501E-16 -6.323108E-20
-1.566387E-16 -4.089822E-16 7.022063E-21 X8 -2.127854E-23
5.631762E-20 -1.645304E-22 -2.809082E-18 -2.426092E-19
-2.519698E-23 X6Y2 -2.911239E-22 1.595162E-18 1.240419E-22
8.883017E-18 -3.131391E-18 -1.169336E-22 X4Y4 2.052045E-21
3.313410E-18 -2.644748E-22 -1.246599E-18 -8.074234E-18
-1.413514E-22 X2Y6 2.303292E-21 8.331439E-19 -5.379641E-23
2.833584E-19 -6.891166E-18 -6.982184E-23 Y8 7.915735E-22
-4.495038E-19 -9.241853E-23 -3.000322E-19 -2.367176E-18
-1.361196E-23 X8Y -3.633622E-25 -1.145501E-22 -8.423039E-26
-1.268652E-20 2.592347E-21 4.570116E-27 X6Y3 -1.500591E-24
1.545859E-21 6.330084E-25 1.171733E-20 1.459272E-21 1.168279E-26
X4Y5 2.954923E-24 3.997308E-21 1.050127E-26 -4.257185E-23
-1.756358E-22 1.479131E-26 X2Y7 1.472672E-24 3.951572E-22
8.889089E-29 -7.100170E-25 5.863402E-23 6.095900E-27 Y9
4.265712E-25 -3.958881E-23 -1.136961E-30 -9.034885E-27 7.298215E-25
4.531322E-28 X10 1.301003E-29 1.955419E-24 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 X8Y2 -6.199954E-28
-8.094414E-25 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00
X6Y4 -1.564267E-27 -8.554437E-24 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 X4Y6 2.214569E-27 1.149257E-24
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 X2Y8
-6.083137E-29 6.386629E-26 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 Y10 1.486303E-30 1.060932E-26 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 Nradius 1.00E+00 1.00E+00
1.00E+00 1.00E+00 1.00E+00 1.00E+00 Y-decenter 248.450 92.818
-2.826 26.446 -4.799 29.811 X-rotation 8.882 -0.938 1.151 -1.082
-3.174 -3.333
[0238] The projection objective of FIG. 17 differs from the
embodiments of FIGS. 3, 10, 11, 12, 13 and 14 mainly in the shape
of mirror M4. In contrast to these earlier described embodiments,
mirror M4 of the embodiment of FIG. 17 is convex.
[0239] FIG. 18 shows another embodiment of the disclosure having
six mirrors being all designed as freeform surfaces. Depicted is
the object plane 3000, the image plane 3002, a first mirror M1, a
second mirror M2, a third mirror M3, a fourth mirror M4, a fifth
mirror M5 and a sixth mirror M6. This projection objective has an
image side numerical aperture of 0.35. The field shape is
rectangular with a width of 26 mm and a height of 2 mm. The
operating wavelength is 13.5 nm. The sequence of optical power of
mirrors is PPNPNP. This optical system has one intermediate image
between mirrors M4 and M5. The entrance pupil of this projection
objective is located on the image plane side of the object plane
3000 in a distance of 1749 mm. An aperture stop is positioned on
mirror M2. The tracklength is 1700 mm. The object image shift is 41
mm. The optical path length is 4156 mm.
[0240] The performance of this projection objective includes an
image-side W.sub.rms of 0.020.lamda.. Distortion is smaller than
1.1 nm. Image-side field curvature is 17 nm.
[0241] The chief ray angle of the central field point at the object
is 6.degree.. The maximum variation of chief ray angles at object
plane 3000 is 0.58.
[0242] The dimension of the footprint of each mirror, given as
M.sub.x.times.M.sub.y is as follows: 169 mm.times.148 mm for mirror
M1; 159 mm.times.136 mm for mirror M2; 120 mm.times.61 mm for
mirror M3; 265 mm.times.118 mm for mirror M4; 101 mm.times.77 mm
for mirror M5; 345 mm.times.329 mm for mirror M6.
[0243] The chief ray angle of incidence for the central field point
for the mirrors M1 to M6 is 8.11.degree.; 9.49.degree.;
21.03.degree.; 8.01.degree.; 13.67.degree.; 5.03.degree. . The
maximum angle of incidence in meridional section for the mirrors M1
to M6 is 10.31.degree.; 12.06.degree.; 21.56.degree.; 8.45.degree.;
24.59.degree.; 6.36.degree.. The bandwidth of angle of incidence in
meridional section for mirrors M1 to M6 is 4.56.degree.;
5.34.degree.; 1.85.degree.; 1.23.degree.; 22.98.degree.,
3.16.degree.. Mirror M4 has positive chief ray angle magnification
while mirrors M1, M2, M3 and M5 have negative chief ray angle
magnification.
[0244] The image-side free working distance of this projection
objective is 45 mm. The object-side free working distance is 441
mm.
[0245] In this projection objective, d.sub.OP-1/d.sub.OP-2 is 1.89.
Further, mirrors M4 and M5 are separated by more than 50% of the
projection objective tracklength.
[0246] Data for the projection objective of FIG. 18 is presented in
Tables 9A, 9B below. Table 9A presents optical data, while table 9B
presents aspherical constants for each of the mirror surfaces.
TABLE-US-00015 TABLE 9A Surface Radius Thickness Mode Object
INFINITY 831.483 Mirror 1 -2519.290 -390.700 REFL Mirror 2 1736.318
0.000 REFL STOP INFINITY 510.700 Mirror 3 353.216 -404.591 REFL
Mirror 4 691.089 1108.132 REFL Mirror 5 454.789 -432.650 REFL
Mirror 6 522.649 477.625 REFL
TABLE-US-00016 TABLE 9B Coefficient M1 M2 M3 M4 M5 M6 K
-5.620176E+01 -8.079329E+00 -8.913161E-01 -1.320517E+00
4.540035E+00 8.058603E-02 Y 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 X2 -8.081674E-05
-2.443257E-05 -2.909041E-04 -5.514277E-05 -2.176416E-04
-1.481415E-05 Y2 -1.409006E-04 -8.853894E-05 -5.146801E-04
-2.593301E-05 1.796509E-04 7.215641E-06 X2Y 1.932586E-07
4.504714E-08 9.969292E-07 -1.801177E-07 1.153365E-06 5.683301E-09
Y3 -1.223280E-07 -1.884294E-08 -4.877028E-07 1.179942E-07
-2.117705E-07 -5.600182E-09 X4 -7.040228E-11 7.425419E-11
2.136430E-09 4.622733E-10 -1.333652E-09 -5.926598E-11 X2Y2
-1.318594E-10 1.067519E-10 9.622356E-09 -4.928633E-10 1.322772E-08
-2.894278E-11 Y4 6.586919E-11 1.598749E-10 9.675806E-10
8.019884E-10 3.924061E-09 1.500259E-11 X4Y -1.333049E-12
9.551370E-14 4.142100E-11 7.245165E-13 -2.333334E-11 8.269178E-15
X2Y3 -7.486772E-12 -5.744418E-13 2.571945E-11 -5.121409E-12
-4.081436E-11 -1.142259E-14 Y5 -7.859762E-14 -1.146786E-12
1.015135E-12 7.149294E-13 -3.294173E-11 -6.514010E-14 X6
-1.349693E-17 -2.093126E-15 5.786287E-14 7.466543E-16 3.666869E-14
-1.312132E-16 X4Y2 -4.117907E-15 3.600153E-15 1.917870E-13
4.761724E-15 1.666994E-13 -1.600140E-16 X2Y4 2.686652E-14
2.433374E-14 1.452311E-14 -1.001928E-14 1.713311E-13 4.528614E-17
Y6 -6.985464E-16 -1.574024E-15 -4.040479E-15 1.285725E-15
3.233877E-13 1.795344E-16 X6Y -6.324670E-18 1.672711E-17
6.549813E-16 7.589572E-18 1.109670E-15 7.389564E-20 X4Y3
1.633680E-16 -5.475446E-17 2.838607E-16 1.219368E-17 1.040774E-15
-3.901601E-20 X2Y5 2.578083E-17 -2.114042E-17 -8.191058E-17
-1.112382E-17 -4.281539E-15 -8.922758E-19 Y7 -5.352170E-18
-4.852332E-17 -8.778735E-18 1.658599E-18 -1.041652E-15
-5.361021E-19 X8 3.930907E-20 -3.041873E-20 1.620935E-18
3.142617E-21 -2.044671E-18 -3.471237E-22 X6Y2 2.642712E-19
1.926793E-19 2.461846E-18 4.103145E-20 9.496169E-18 -5.396836E-22
X4Y4 -1.209256E-18 7.815308E-19 2.461216E-20 2.400689E-20
2.006336E-17 4.153767E-23 X2Y6 -5.242330E-19 -2.345008E-19
-1.129636E-20 -4.573196E-22 -8.505126E-18 2.958769E-21 Y8
5.723961E-20 -4.523191E-19 2.359743E-20 2.441529E-21 2.039563E-17
1.076978E-21 X8Y -5.843186E-22 4.059084E-22 1.256052E-20
1.926704E-23 -6.283441E-20 8.511910E-25 X6Y3 -1.725684E-21
-3.122858E-21 2.334258E-21 9.329420E-23 -1.729457E-19 2.027558E-25
X4Y5 4.331458E-21 -1.961697E-21 8.015847E-22 2.907419E-23
2.503951E-19 -5.006594E-24 X2Y7 1.628473E-21 -1.158132E-20
2.742066E-22 8.412546E-24 -3.164177E-19 -7.133872E-24 Y9
-2.174037E-22 -5.641899E-21 -6.405172E-23 1.117517E-24 1.693513E-19
-7.896547E-25 X10 3.942480E-26 -1.611794E-24 -3.181193E-25
1.249724E-27 -2.648224E-23 -6.952534E-28 X8Y2 2.026760E-24
2.715637E-24 2.416966E-23 3.491430E-26 -5.242301E-22 -5.078551E-27
X6Y4 3.177651E-24 1.517348E-23 -1.929381E-24 8.815740E-26
-7.406490E-22 -1.604907E-26 X4Y6 -6.089337E-24 -2.527074E-23
2.506522E-24 2.875808E-26 3.978023E-21 4.391294E-28 X2Y8
-1.609759E-24 -7.803424E-23 1.589355E-25 1.072608E-26 -2.716665E-21
4.653881E-27 Y10 2.665008E-25 -1.428174E-23 -2.253314E-25
5.234796E-28 1.510394E-21 -1.026184E-27 Nradius 1.00E+00 1.00E+00
1.00E+00 1.00E+00 1.00E+00 1.00E+00 Y-decenter -107.723 -48.244
142.711 9.140 15.331 1.453 X-rotation -3.086 0.713 -20.000 -1.900
0.245 2.474
[0247] The projection objective of FIG. 18 has chief rays
converging to each other while starting from the object plane
3000.
[0248] Other embodiments are in the claims.
* * * * *