U.S. patent application number 11/820375 was filed with the patent office on 2007-10-18 for illumination system.
This patent application is currently assigned to Carl Zeiss SMT AG. Invention is credited to Bernd Kleemann, Wolfgang Singer, Markus Weiss.
Application Number | 20070242799 11/820375 |
Document ID | / |
Family ID | 27214459 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070242799 |
Kind Code |
A1 |
Weiss; Markus ; et
al. |
October 18, 2007 |
Illumination system
Abstract
There is provided an illumination system. The illumination
system includes (a) a mirror, (b) a diaphragm in a light path
downstream of the mirror, and (c) a field plane in the light path,
downstream of the diaphragm.
Inventors: |
Weiss; Markus; (Aalen,
DE) ; Singer; Wolfgang; (Aalen, DE) ;
Kleemann; Bernd; (Aalen, DE) |
Correspondence
Address: |
OHLANDT, GREELEY, RUGGIERO & PERLE, LLP
ONE LANDMARK SQUARE, 10TH FLOOR
STAMFORD
CT
06901
US
|
Assignee: |
Carl Zeiss SMT AG
Oberkochen
DE
|
Family ID: |
27214459 |
Appl. No.: |
11/820375 |
Filed: |
June 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09961819 |
Sep 24, 2001 |
7248667 |
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11820375 |
Jun 19, 2007 |
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09679718 |
Sep 29, 2000 |
6438199 |
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09961819 |
Sep 24, 2001 |
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09305017 |
May 4, 1999 |
6198793 |
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09679718 |
Sep 29, 2000 |
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Current U.S.
Class: |
378/34 ;
359/850 |
Current CPC
Class: |
G03F 7/70083 20130101;
B82Y 10/00 20130101; G03F 7/70158 20130101; G21K 1/06 20130101;
G02B 19/0095 20130101; G03F 7/70233 20130101; G02B 19/0047
20130101; G03F 7/702 20130101; G02B 19/0023 20130101; G03F 7/70575
20130101; G02B 5/09 20130101 |
Class at
Publication: |
378/034 ;
359/850 |
International
Class: |
G02B 5/08 20060101
G02B005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2001 |
DE |
101 27 298 |
Claims
1-17. (canceled)
18. An illumination system comprising: a mirror; a diaphragm in a
light path downstream of said mirror; and a field plane in said
light path, downstream of said diaphragm.
19. The illumination system of claim 18, wherein said mirror is a
facetted mirror having a plurality of facets.
20. The illumination system of claim 19, further comprising a
normal incidence mirror in said light path, downstream of said
facetted mirror and upstream of said field plane.
21. The illumination system of claim 20, wherein said normal
incidence mirror is situated downstream of said diaphragm.
22. The illumination system of claim 20, further comprising a
grazing incidence mirror situated in said light path, downstream of
said normal incidence mirror and upstream of said field plane.
23. The illumination system of claim 22, wherein said diaphragm is
situated in said light path, downstream of said normal incidence
mirror and upstream of said grazing incidence mirror.
24. The illumination system of claim 19, further comprising a first
normal incidence mirror and a second normal incidence mirror, both
of which are in said light path, downstream of said facetted mirror
and upstream of said field plane.
25. The illumination system of claim 24, wherein said diaphragm is
situated downstream of said first normal incidence mirror and
upstream of said second normal incidence mirror.
26. The illumination system of claim 19, further comprising a
grazing incidence mirror situated in said light path, downstream of
said facetted mirror and upstream of said field plane.
27. The illumination system of claim 19, wherein said plurality of
facets includes a first facet and a second facet that are imaged
into said field plane as a first image and a second image that at
least partially overlap one another.
28. The illumination system of claim 19, wherein said facetted
mirror is a first facetted mirror, and said plurality of facets is
a first plurality of facets, and wherein said illumination system
further comprises a second facetted mirror having a second
plurality of facets, situated in said light path downstream of said
first facetted mirror and upstream of said diaphragm.
29. The illumination system of claim 28, wherein said second
plurality of facets includes a first facet and a second facet that
are imaged into an exit pupil of said illumination system.
30. The illumination system of claim 19, wherein said facetted
mirror is a first mirror, wherein said plurality of facets includes
a first facet and a second facet, and wherein said illumination
system further comprises a second mirror in said light path,
downstream of said first mirror and upstream of said field plane,
that images said first and second facets into said field plane.
31. The illumination system of claim 18, wherein said mirror is a
first mirror, and wherein said illumination system further
comprises a second mirror in said light path, downstream of said
first mirror and upstream of said field plane.
32. The illumination system of claim 31, wherein said second mirror
is a facetted mirror having a plurality of facets.
33. The illumination system of claim 31, wherein said diaphragm is
situated downstream of said second mirror.
34. The illumination system of claim 18, further comprising a light
source that emits light into said light path, upstream of said
mirror, having a wavelength of less than or equal to about 100
nm.
35. The illumination system of claim 34, wherein said diaphragm is
a first diaphragm, and wherein said illumination system further
comprises a second diaphragm situated in said light path downstream
of said light source and upstream of said mirror.
36. The illumination system of claim 18, wherein said diaphragm
suppresses stray light.
37. The illumination system of claim 18, wherein said diaphragm
partially surrounds said light path, and partially suppresses stray
light.
38. A projection exposure system comprising: (a) an illumination
system for illuminating a pattern-bearing mask, wherein said
illumination system includes: a mirror; a diaphragm in a light path
downstream of said mirror; and a field plane in said light path,
downstream of said diaphragm, for accommodating the pattern-bearing
mask; (b) a holder for holding a light-sensitive object; and (c) a
projection objective for imaging the pattern-bearing mask onto the
light-sensitive object.
39. A method, comprising: producing a microelectronic component,
wherein said producing includes employing a projection exposure
system having: (a) an illumination system for illuminating a
pattern-bearing mask, wherein said illumination system includes: a
mirror; a diaphragm in a light path downstream of said mirror; and
a field plane in said light path, downstream of said diaphragm, for
accommodating the pattern-bearing mask; (b) a holder for holding a
light-sensitive object; and (c) a projection objective for imaging
the pattern-bearing mask onto the light- sensitive object.
40. A method comprising: situating a diaphragm in a light path in
an illumination system, downstream of a facetted optical element
and upstream of a field plane, wherein said diaphragm suppresses
stray light in said illumination system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention concerns an illumination system for
wavelengths .ltoreq.100 nm, wherein the illumination system has an
object plane and a field plane. In illumination systems .ltoreq.100
nm, the problem exists that light sources of such illumination
systems emit radiation that can lead to an undesired exposure of
the light-sensitive object in the wafer plane. Furthermore optical
components of the exposure system, such as, for example, the
multilayer mirror, can be heated up in this way.
[0003] In order to filter out the undesired radiation, transmission
filters are used in illumination systems for wavelengths .ltoreq.1
00 nm. Such filters have the disadvantage of high light losses. In
addition, they can be disrupted very easily by heat stress.
[0004] The object of the invention is to provide an illumination
system for wavelengths .ltoreq.100 nm, particularly in the EUV
range, in which the above-named disadvantages can be avoided.
[0005] According to the invention, this object is solved by an
illumination system that has at least one grating element and at
least one physical diaphragm in a diaphragm plane. The physical
diaphragm is situated in the beam path from the object plane to the
field plane after the grating element.
[0006] 2. Description of the Prior Art
[0007] Grating elements, for example, reflection gratings,
particularly echelette gratings, which are also known as blazed
gratings, have been known for a long time from monochromator
construction for synchrotron radiation sources. For these elements
good experiences, particularly with very high fluxes, were
made.
[0008] With respect to the use of diffraction gratings in
monochromators, reference is made to the following publications,
whose disclosure content is incorporated to the full extent in the
present Application: [0009] H. Petersen, C. Jung, C. Hellwig, W. B.
Peatman, W. Gudat: "Review of plane grating focusing for soft x-ray
monochromators", Rev. Sci. Instrum. 66(1), January 1996. [0010] M.
V. R. K. Murty: "Use of convergent and divergent illumination with
plane gratings", Journal of the Optical Society of America, Vol.
52, No. 7, July 1962, pp. 768-773. [0011] T. Oshio, E. Ishiguro, R.
Iwanaga: "A theory of new astigmatism and coma-free spectrometer",
Nuclear Instruments and Methods 208 (1993) 297-301.
SUMMARY OF THE INVENTION
[0012] The inventors have now recognized that a grating element can
be used in the beam path from the object plane to the image plane
for spectral filtering in an illumination system for wavelengths
.ltoreq.100 nm, if the individual diffraction orders and the
wavelengths are clearly separated from one another.
[0013] This is most simple for a grating element within a
convergent beam bundle. The convergent beam bundle has a focus with
a limited diameter.
[0014] In order to obtain a stigmatic imaging of an object into the
plane of the physical diaphragm with the aid of a grating element
situated in a convergent beam path, in a first embodiment of the
invention the optical element is curved concave in a meridional
plane. The meridional plane of the optic element is defined as the
plane which is perpendicular to the carrier surface of the grating
element and to the grating lines.
[0015] Alternatively or additionally to this, the optical element
can be curved convex in the sagittal plane, which is perpendicular
to the carrier surface and the meridional plane, and contains the
centre of the grating element.
[0016] If an internal diffraction order (k=1, 2, 3) is used, the
refractive power in the meridional direction is greater than in the
sagittal direction, i.e., the element is concave, e.g., in the
meridional direction and planar in the sagittal direction, or it is
planar in the meridional direction and convex in the sagittal
direction, or it is formed concave in the meridional direction and
convex in the sagittal direction.
[0017] If an external diffraction order (k=-1, -2, -3) is used, the
refractive power in the sagittal direction is greater than in the
meridional direction, i.e., the element is concave in the sagittal
direction and planar in the meridional direction, or it is planar
in the sagittal direction and convex in the meridional direction,
or it is formed concave in the sagittal direction and convex in the
meridional direction.
[0018] In the present application, the order which is diffracted to
the surface normal line is denoted the internal order and assigned
positive numbers, while the order which is diffracted away from the
surface normal line is designated the external order and is
assigned negative numbers.
[0019] In another embodiment of the invention, the stigmatic
imaging is achieved by a variation of the distance between the
grating lines.
[0020] The at-least one physical diaphragm according to the
invention essentially serves for the purpose that light with
wavelengths far above 100 nm does not enter into the illumination
system. This can be achieved particularly by blocking the zeroth
diffraction order. Due to the one physical diaphragm, all
diffraction orders are preferably blocked except for a so called
used order. The used order, for example, can be the 1.sup.st
order.
[0021] It is particularly preferred if the rays have wavelengths in
the range of 7 to 26 nm after the physical diaphragm, due to the
combination of grating and physical diaphragm.
[0022] The grating element is preferably designed as a blazed
grating, which is optimized to a maximal efficiency in a pregiven
diffraction order. Blazed gratings are known, for example, from the
Lexikon der Optik [Optics Lexicon], edited by Heinz Haferkorn, VEB
Bibliographic Institute, Leipzig, 1990, pp. 48 to 49. They are
characterized by an approximately triangular groove profile.
[0023] In order to avoid too high of a heat load on the physical
diaphragm in the diaphragm plane, a part of the undesired radiation
can be filtered out by additional diaphragms in the illumination
system.
[0024] In addition to the illumination system, the invention also
provides a projection exposure system with such an illumination
system as well as a method for the production of microelectronic
components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] An example of the invention will be described below on the
basis of the figures.
[0026] Here:
[0027] FIG. 1 shows the arrangement of a grating element in the
beam path of the collector unit of an illumination system,
[0028] FIG. 2 shows the grating element and the physical diaphragm
of an illumination system,
[0029] FIG. 3 shows a blazed grating,
[0030] FIG. 4 shows the maximal possible diffraction efficiency for
grating elements designed as blazed gratings, and
[0031] FIG. 5 shows an EUV projection exposure system with an
illumination system according to the invention.
DESCRIPTION OF THE INVENTION
[0032] FIG. 1 shows an illumination system with a grating element 1
as well as a physical diaphragm in the diaphragm plane. The light
of light source 3 is collected by a collecting component, collector
5, in the illumination system shown. The collector 5 in this
example is an ellipsoid-shaped mirror, which produces an image of
light source 3. The convergent light bundle with an aperture of
approximately NA=0.1 behind collector 5 is deflected via grating
element 1 in grazing incidence in such a way that the intermediate
image of the light source comes to lie in or in the vicinity of the
diaphragm plane of the physical diaphragm 7.3.
[0033] Due to the several partial diaphragms 7.1, 7.2, arranged in
front of physical diaphragm 7.3, undesired radiation can be
filtered out beforehand, in order to reduce the heat load on
physical diaphragm 7.3. The physical diaphragm has a circular
opening, which is situated in the focal plane of the desired
diffraction order, here the -1. order 16. The diaphragms 7.1, 7.2
may also be cooled, but this is not shown. In addition, grating
element 1 can be cooled, for example, by a cooling on the back
side. The device 8 for back-side cooling of grating element 1 is
preferably a liquid cooling device with inlet 10.1 and outlet 10.2.
Due to grating element 1 and physical diaphragm 7.3, the 0.sup.th
order that encompasses all wavelengths of the light source can be
completely blocked out in the illumination system according to the
invention. In addition, all of the other orders except for the
-1.sup.st order are blocked.
[0034] If the grating in an illumination system with collector
according to FIG. 1 is designed as a planar grating with the same
grating period, then an astigmatic imaging of the light source
results. In order to be able to well separate the diffraction
orders from one another, a stigmatic imaging of light source 3 into
the plane of the physical diaphragm 7.3 is necessary for a
diffraction order, which is not the zeroth diffraction order. It
can be attempted by various methods to correct the astigmatism, for
example, by introducing additional refractive power in the
meridional plane or sagittal plane or by variation of the distance
between the grating lines.
[0035] How this is derived will be given in the following.
[0036] The starting point for subsequent considerations is the
grating equation for a parallel beam bundle: Nk.lamda.=sin
.alpha.+sin .beta. (1) wherein N is the number of lines, k is the
diffraction order, .lamda. is the wavelength, .alpha. is the angle
of incidence and .beta. is the diffraction angle (relative to the
surface normal of the carrier surface and referred to the chief ray
CR.sub.before or CR.sub.after). The nomenclature which is used in
the following derivation is oriented to the "Lexikon der Optik
[Optics Lexicon] in two volumes, edited by H. Paul, Heidelberg,
Berlin, Spektrum Academic Publishers, 1999, Vol. 1, A-L, pp.
77-80.
[0037] Reference is made to FIG. 2 for the explanation of the
following derivation.
[0038] In the case shown in FIG. 2, the convergent radiation of a
light source (not shown) through grating element 1 is spectrally
split and selected at intermediate focus 19 by physical diaphragm
7.3. An NA of 0.12 is achieved at intermediate focus 19. A
convergent incident light bundle 100 is shown in FIG. 2. This is
diffracted at grating 1. The beam bundle 12 which is diffracted in
the 0.sup.th diffraction order is shown along with the beam bundle
14 which is diffracted in the first diffraction order. The beam
bundle diffracted in the 0.sup.th diffraction order has a focal
point 112 and the beam bundle diffracted in the first order has a
focal point 114. The image widths s.sub.before and s.sub.after are
defined by the respective focal points 112, 114 and the striking
point 102 of the chief ray CR.sub.before of the incident beam
bundle 100 on grating 1. Here, s.sub.before designates the distance
of the striking point 102 from the focal point 112 of the beam
bundle diffracted in the zeroth diffraction order and s.sub.after
denotes the distance of striking point 102 from focal point 114 of
the beam bundle diffracted in the first order. Angle .alpha.
designates the angle of incidence of the chief ray CR.sub.before of
the incident beam bundle with respect to the surface normal line of
the carrier surface of grating 1 and .beta. denotes the diffraction
angle of the chief ray CR.sub.after of the beam bundle 14
diffracted in the 1.sup.st order, relative to the surface normal
line of the carrier surface. In addition, the planes 106, 108 are
designated, which stand at striking point 102 on grating 1
perpendicular to the chief ray CR.sub.before of the striking beam
bundle 100 and perpendicular to the chief ray CR.sub.after of the
beam bundle 14 diffracted in the 1.sup.st diffraction order.
[0039] If one now considers in the convergent beam path of an
illumination system a reflection grating, which is placed as shown
in FIG. 2 in front of the intermediate focus 19, which coincides in
the present example of embodiment with focal point 114 of the beam
bundle diffracted in the 1.sup.st order, then the optical effect of
the grating must be observed. This can be derived from the
conservation of the phase-space volume or the light value or the
Etendue. Since the diffraction angle .beta. for orders that are not
equal to the zeroth order is not equal to the angle of incidence
.alpha., the cross section of the beam bundle is modified in planes
106, 108, which stand perpendicular to the chief ray CR.sub.before
of the incident beam bundle or the chief ray CR.sub.after of the
diffracted beam pencil. Due to the above-named conservation of
balance, the divergence must be changed recriprocally. This means
that if a grating is operated in the internal arrangement
(|.alpha.|>|.beta.|), then the beam becomes larger by cos
(.beta.)/cos (.alpha.) and the divergence becomes smaller by the
same factor. By this, the distance up to the focus or focal point
is lengthened by the square quadratic factor. This factor is
denoted below as the fixed focus constant c.sub.ff: c.sub.ff=cos
(.beta.)/cos (.alpha.) (2)
[0040] The following results for the bundle cross-section at the
grating: d.sub.after=d.sub.beforec.sub.ff (3) or for the numerical
aperture NA NA.sub.after=NA.sub.before/c.sub.ff (4) wherein dafter
denotes the bundle cross-section of the diffracted beam bundle 14
in the plane 108 and d.sub.before denotes the bundle cross-section
of the incident beam bundle 100 in plane 106, NA.sub.after denotes
the numerical aperture of the diffracted beam bundle 14 and
NA.sub.before denotes the numerical aperture of the incident beam
bundle.
[0041] The following results for the image width s as previously
defined, calculated starting at the grating:
s.sub.after=s.sub.beforec.sub.ff.sup.2 (5)
[0042] Care has to be taken that the grating acts only in the
meridional or dispersive direction. In order to obtain a stigmatic
imaging it is advantageous to introduce an additional optical
effect, e.g., in the sagittal direction.
[0043] This can be achieved, for example, for the case when an
internal diffraction order (k=1, 2, 3) is used, by a convex
curvature in the sagittal direction.
[0044] For the case when an external diffraction order (k=-1, -2,
-3) is used, it is advantageous that the grating is selected as
sagittal concave.
[0045] Alternatively to a curved grating, the grating line distance
may also be varied.
[0046] For the case of a sagittal convex curvature, the radius must
be selected such that an image width of s.sub.beforec.sub.ff.sup.2
is obtained from the image width S.sub.before in the 0.sup.th
order. The sagittal focal distance f.sub.s can be calculated by
means of the imaging equation:
f.sub.s=s.sub.before/(1/c.sub.ff.sup.2-1) (6)
[0047] Finally, the sagittal radius results together with the angle
of diffraction: R.sub.s=f.sub.s(cos .alpha.+cos .beta.) (7)
[0048] It will be estimated in the following on an example of
embodiment how a grating element 1 must be constructed that the
following conditions are fulfilled: [0049] the beam bundles of the
0.sup.th and 1.sup.st order or -1.sup.st order are separated, i.e.,
at the focal point of one beam pencil of one diffraction order,
there is no overlap of this beam bundle by a beam bundle of another
diffraction order; [0050] the utilization wavelength used must be
separate from the unwanted wavelengths; [0051] the distance to the
intermediate focus must be small, so the grating does not become
too large; [0052] the diffraction geometry must be optimized for
best diffraction efficiency; [0053] the astigmatism, which produces
a defocusing effect for the internal order and a focusing effect
for the external order, should remain small.
[0054] In particular, the first condition is decisive for the
effectiveness of the grating element. A formula for estimating the
separation of the beam pencil of the different diffraction orders
from one another can be derived as follows with reference to FIG.
2. The distance .DELTA.x.sub.0 between the chief rays of the beam
bundles of different diffraction orders at the focal point of the 0
order from the diffraction angles is: .DELTA.x.sub.0=s.sub.before
sin (.alpha.+.beta.) (8) and the distance .DELTA.x.sub.1 between
the chief rays of the beam bundles of different diffraction orders
at the focal point of the diffraction order e.g. the 1.sup.st or
-1.sup.st diffraction order is:
.DELTA.x.sub.1=s.sub.beforec.sub.ff.sup.2 sin (.alpha.+.beta.)
(9)
[0055] Since the respective other beam bundle is not focused, which
means that it has an extension, it is necessary for estimating
whether the beam pencils do not overlap in the focal point, to
estimate the extension of the other beam bundle. This can be
estimated by the divergence or the numerical aperture. For the
extension of the beam bundle of the 0.sup.th order at the focal
point of the diffraction order, the following results:
.DELTA.d.sub.1=2NA
c.sub.ff|s.sub.beforec.sub.ff.sup.2-s.sub.before| (10) and for the
extension of the beam bundle of the 1.sup.st order or of the
-1.sup.st order at the focal point of the 1.sup.st order or the
-1.sup.st order:
.DELTA.d.sub.0=2NA|s.sub.beforec.sub.ff.sup.2-s.sub.before|
(11)
[0056] The difference between, e.g., .DELTA.x.sub.0 and
.DELTA.d.sub.0/2 yields, e.g., the distance of the edge rays of the
diffracted beam bundle from the focal point of the beam bundle of
the 0.sup.th order. In order to prevent an overlap of different
beam bundles, this distance should correspond to at least half the
diameter of the beam bundle in the focal point, which is denoted
.DELTA.x.sub.f; a sufficient separation of the beam bundle of the
0.sup.th diffraction order from the beam bundles of other
diffraction orders is then achieved.
[0057] The following is thus applied: s.sub.before sin
(.alpha.+.beta.)-NA|s.sub.beforec.sub.ff.sup.2-s.sub.before|>.DELTA.x.-
sub.f (12) or s.sub.beforec.sub.ff.sup.2 sin (.alpha.+.beta.)-NA
c.sub.ff|s.sub.beforec.sub.ff.sup.2-s.sub.before|c.sub.ff>.DELTA.x.sub-
.f (13)
[0058] With the above-given considerations and formulas, the
grating element with sagittal convex curvature, which is
characterized by a grating efficiency of 56% can be constructed,
which is characterized by the values given below in Table 1.
TABLE-US-00001 TABLE 1 Characteristic values of a grating element
with convex transverse curvature Wavelength 13.4 nm Photon energy
92.5 eV Number of lines 1600 l/mm Diffraction order 1 fixed focus
constant, c.sub.ff 1.2 angle of incidence .alpha. of the 72.360
degrees chief ray CR.sub.before Diffraction angle .beta. of the
chief -68.676 degrees ray CR.sub.after diffracted in the 1.sup.st
order Blazed depth 20.1 nm Grating-focus distance 432 mm Sagittal
radius 654.555 mm NA (after grating) 0.12 Grating length 237 mm
Material used Ru Microroughness 0.5 nm (rms) Grating efficiency 56
%
[0059] With the grating element 1 according to the embodiment in
Table 1 in combination with a diaphragm, wavelengths above
approximately 18 nm and below 8 nm can be almost completely
filtered out. The heat load on the mirror of a projection system
can be clearly reduced in this way.
[0060] In order to obtain a grating element 1 with optimal
diffraction efficiency, the grating element is preferably
configured as a blazed grating.
[0061] A blazed grating with approximately triangular groove
profile is shown in FIG. 3. Reference number 11 designates the ray
e.g., the chief ray of a beam bundle, striking the grating element
1 designed as a blazed grating; 12 denotes the ray, e.g. the chief
ray of a beam bundle, reflected at the grating in the 0.sup.th
order and 16 denotes the ray, e.g., the chief ray of a beam bundle,
diffracted in the -1.sup.st order. The blazed depth B is a function
of angles of incidence and reflection. Thus, it is advantageous if
the blazed depth is changed as a function of the position on the
grating in order to obtain a maximal diffraction efficiency with a
convergent beam pencil.
[0062] If one uses such a grating element, whose local blazed depth
B changes with position on the grating, then a maximal efficiency
is obtained according to FIG. 4. As FIG. 4 shows, the diffraction
efficiency (1) depends on the material used.
[0063] In FIG. 4, reference number 200 denotes the diffraction
efficiency .eta.(1) for a wavelength of .lamda.=13.5 nm for
ruthenium, reference number 202 for palladium, reference number 204
for rhodium and reference number 206 for gold.
[0064] As can be seen from FIG. 4, the greatest efficiency of 0.7
can be achieved with ruthenium. A coating of palladium or rhodium
has better long-time properties, but has an efficiency .eta.(1) of
only 0.67, which is 3% poorer. Gold is usually used for the
synchrotron grating, but has a clearly poorer efficiency than the
above-named materials at .lamda.=13.5 nm, as can be seen from curve
206.
[0065] An EUV projection exposure system with a grating element 1
according to the invention is shown in FIG. 5. The EUV projection
exposure system comprises a light source 3, a collecting optical
component, a so-called collector 5, which is formed as a nested
collector. Collector 5 images the light source 3 lying in the
object plane of the illumination system in a secondary light source
4 in or in the vicinity of a diaphragm plane 7.3.
[0066] Light source 3, which can be, for example, a laser plasma
source or a plasma discharge source, is arranged in the object
plane of the illumination system. The image of the primary light
source, which is also designated as the secondary light source,
comes to lie in the image plane 7.3 of the illumination system.
[0067] Additional diaphragms 7.1, 7.2 are arranged between grating
element 1 and the physical diaphragm 7.3 in order to block the
light of undesired wavelengths, particularly wavelengths longer
than 30 mm. According to the invention, the focus of the 1.sup.st
order comes to lie in the plane of diaphragm 7.3, i.e., light
source 3 is imaged nearly stigmatic in the plane of diaphragm 7.3
by the collector and the grating spectral filter in the 1.sup.st
diffraction order. The imaging in all other diffraction orders is
not stigmatic.
[0068] In addition, the illumination system of the projection
system comprises an optical system 20 for forming and illuminating
field plane 22 with a ring-shaped field. The optical system
comprises two faceted mirrors 29.1, 29.2 as well as two imaging
mirrors 30.1, 30.2 and a field-forming grazing-incidence mirror 32
as the mixing unit for homogeneous illumination of the field.
Additional diaphragms 7.4, 7.5, 7.6, 7.7 are arranged in optical
system 20 for suppressing stray light.
[0069] The first faceted mirror 29.1, the so-called field-faceted
mirror, produces a plurality of secondary light sources in or in
the vicinity of the plane of the second faceted mirror 29.2, the
so-called pupil-faceted mirror. The subsequent imaging optics image
the pupil-faceted mirror 29.2 in the exit pupil of the illumination
system, which comes to lie in the entrance pupil of the projection
objective 26. The angle of inclination of the individual facets of
the first and second faceted mirrors 29.1, 29.2 are designed in
such a way that the images of the individual field facets of the
first faceted mirror 29.1 overlap in the field plane 22 of the
illumination system and thus an extensively homogenized
illumination of a pattern-bearing mask, which comes to lie in the
field plane 22, is possible. The segment of the ring field is
formed by means of the field-forming grazing-incidence mirror 32
operated under grazing incidence.
[0070] A double-faceted illumination system is disclosed, for
example, in U.S. Patent US-B-6,198,739, imaging and field-forming
components in PCT/EP/00/07258. The disclosure contents of these
documents is incorporated to the full extent in the present
Application.
[0071] The pattern-bearing mask, which is also designated as the
reticle, is arranged in field plane 22. The mask is imaged by means
of a projection objective 26 in the image plane 28 of field plane
22. The projection objective 26 is a 6-mirror projection objective,
such as disclosed, for example, in U.S. application No. 60/255214,
filed on Dec. 13, 2000, in the U.S. Patent Office for the Applicant
or DE-A-10037870, the disclosure content of which is fully
incorporated into the present application. The object to be
exposed, for example, a wafer, is arranged in image plane 28.
[0072] The replica technique is considered, for example, as a
possible manufacturing method for a grating element according to
the invention.
[0073] The invention gives for the first time an illumination
system, with which undesired wavelengths can be selected directly
after the light-source unit and which represents an alternative to
filter foils, which are problematic, particularly with respect to
the heat load.
REFERENCE LIST
[0074] 1 grating element [0075] 3 light source [0076] 5 collector
[0077] 7 .1, 7.2, 7.3 [0078] 7.4, 7.5, 7.6
[0079] 7.7 diaphragms [0080] 8 cooling device [0081] 10.1,10.2
inlet and outlet of the cooling device [0082] 11 incident radiation
[0083] 12 0.sup.th order of the wavelength used [0084] 14 1.sup.st
order of the wavelength used [0085] 16 -1.sup.st order of the
wavelength used [0086] 20 optical system [0087] 22 field plane
[0088] 26 projection objective [0089] 28 image plane of the field
plane [0090] 29.1, 29.2 faceted mirrors [0091] 30.1, 30.2 imaging
mirrors [0092] 32 field-forming mirror [0093] 34 exit pupil of the
illumination system [0094] 100 convergent incident beam bundle
[0095] 102 striking point of the chief ray CR.sub.before on grating
1 [0096] 106 plane, which is perpendicular to the chief ray
CR.sub.before [0097] 106 plane, which is perpendicular to the chief
ray CR.sub.after [0098] 112 focal point of the beam pencil
diffracted in the 0.sup.th order [0099] 114 focal point of the beam
pencil diffracted in the 1.sup.st order [0100] 200, 202 [0101] 204,
206 diffraction efficiency .eta.(1) for different materials
* * * * *