U.S. patent application number 10/377700 was filed with the patent office on 2003-08-28 for method and apparatus for illuminating a surface using a projection imaging apparatus.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Goto, Akihiko, Kanayamaya, Nobumichi, Komatsuda, Hideki, Shibuya, Masato, Takahashi, Tetsuo, Tanitsu, Osamu.
Application Number | 20030160949 10/377700 |
Document ID | / |
Family ID | 27525497 |
Filed Date | 2003-08-28 |
United States Patent
Application |
20030160949 |
Kind Code |
A1 |
Komatsuda, Hideki ; et
al. |
August 28, 2003 |
Method and apparatus for illuminating a surface using a projection
imaging apparatus
Abstract
A method and illumination optical system forms a modified
illumination configuration on an optical integrator so that a
secondary light source having a desired modified illumination
configuration is formed and light loss is minimized. A light beam
shape changing element that diffuses illumination in a plurality of
directions, and an angular light beam forming element that forms a
plurality of light source images operate together to create a
modified illumination configuration on the optical integrator.
Since the secondary light source has a desired modified
illumination configuration, an aperture stop used to restrict the
size and/or shape of the secondary light source blocks only a small
amount of illumination, or can be eliminated altogether. It is
possible to alter the annular ratio and outer diameter of an
annular or quadrupole modified illumination configuration by
changing the magnification of a zoom optical system positioned
between the light beam shape changing element and the angular light
beam forming element. Furthermore, by changing the focal length of
a zoom optical system (which is positioned upstream of the optical
integrator), it is possible to change the outer diameter of the
annular or quadrupole secondary light source without changing the
annular ratio thereof.
Inventors: |
Komatsuda, Hideki;
(Kawasaki, JP) ; Tanitsu, Osamu; (Funabashi,
JP) ; Goto, Akihiko; (Setagaya, JP) ;
Kanayamaya, Nobumichi; (Kawasaki, JP) ; Shibuya,
Masato; (Ohmiya, JP) ; Takahashi, Tetsuo;
(Yokohama, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
100-8331
|
Family ID: |
27525497 |
Appl. No.: |
10/377700 |
Filed: |
March 4, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10377700 |
Mar 4, 2003 |
|
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|
09540874 |
Mar 31, 2000 |
|
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|
6563567 |
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09540874 |
Mar 31, 2000 |
|
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09465697 |
Dec 17, 1999 |
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Current U.S.
Class: |
355/71 |
Current CPC
Class: |
G03F 7/70183 20130101;
G03F 7/7025 20130101; G03F 7/70075 20130101; G03F 7/70158 20130101;
G03F 7/70108 20130101; G03F 7/701 20130101 |
Class at
Publication: |
355/71 |
International
Class: |
G03B 027/72 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 1999 |
JP |
11-90735 |
Oct 5, 1999 |
JP |
11-284213 |
Oct 29, 1999 |
JP |
11-308186 |
Dec 17, 1998 |
JP |
10-358749 |
Sep 9, 1999 |
JP |
11-255636 |
Claims
What is claimed is:
1. An illumination system for illuminating a surface by use of
light from a light source, the illumination system comprising: an
emission angle conserving optical unit effective to emit the light
from the light source at a constant divergent angle; and a
diffractive optical element for producing a desired light intensity
distribution on a predetermined plane, wherein the diffractive
optical element is disposed at or adjacent to a position where
light from the emission angle conserving optical unit is
collected.
2. The illumination system according to claim 1, further comprising
a multiple-beam producing element, and a light projecting element
for superposing light beams from the multiple-beam producing
element one upon another on the surface to be illuminated, wherein
the predetermined plane corresponds to a light entrance surface of
the multiple-beam producing element.
3. The illumination system according to claim 2, further comprising
a zoom optical system for projecting the light intensity
distribution, produced by the diffractive optical element, upon the
light entrance surface of the multiple-beam producing element at a
predetermined magnification.
4. The illumination system according to claim 3, wherein a
plurality of emission angle conserving optical units of different
divergent angles are provided, and wherein the emission angle
conserving optical units are interchangeably set at a light path in
accordance with a change in magnification of the zoom optical
system.
5. The illumination system according to claim 1, wherein a
plurality of diffractive optical elements for producing different
light intensity distributions on the predetermined plane are
provided, wherein the diffractive optical elements are
interchangeably set at a light path to produce a desired light
intensity distribution on the predetermined plane.
6. The illumination system according to claim 1, wherein the
diffractive optical element is a phase type.
7. The illumination system according to claim 1, wherein the
emission angle conserving optical unit comprises a flys eye lens
having small lenses arrayed two-dimensionally.
8. An exposure apparatus, comprising: an illumination optical
system for illuminating a mask surface, as a surface to be
illuminated, with use of light from a light source, the
illumination optical system including (i) an emission angle
conserving optical unit effective to emit the light from the light
source at a constant divergent angle, and (ii) a diffractive
optical element for producing a desired light intensity
distribution on a predetermined plane, wherein the diffractive
optical element is disposed at or adjacent to a position where
light from the emission angle conserving optical unit is collected;
and a projection optical system for projecting a pattern formed on
the mask surface, as illuminated with the light from the
illumination optical system, onto a wafer.
9. A device manufacturing method, comprising the steps of: applying
a photosensitive material to a wafer; illuminating a mask surface,
as a surface to be illuminated, with use of light from an
illumination optical system, wherein the illumination optical
system includes (i) an emission angle conserving optical unit
effective to emit the light from the light source at a constant
divergent angle, and (ii) a diffractive optical element for
producing a desired light intensity distribution on a predetermined
plane, wherein the diffractive optical element is disposed at or
adjacent to a position where light from the emission angle
conserving optical unit is collected; projecting, through a
projection optical system, a pattern formed on the mask surface
onto a wafer; and developing the transferred pattern.
10. An illumination system for illuminating a surface by use of
light from a light source, the illumination system comprising: an
optical integrator which is arranged in a light path of the
illumination system; an illumination pupil having a light intensity
distribution such that a lower light intensity is formed at a
position near an optical axis relative to positions away from the
optical axis; an annular ratio changer which is arranged in an
optical path between the light source and the optical integrator
and which changes the annular ratio of the light intensity
distribution; and an outer diameter changer which is arranged in an
optical path between the light source and the optical integrator
and which changes the outer diameter of the light intensity
distribution.
11. The system according to claim 10, wherein the light intensity
distribution comprises a multipole shape.
12. The system according to claim 11, further comprising an optical
element which is arranged in an optical path between the light
source and the changers and which converts the light from the light
source to a divergence light beam.
13. The system according to claim 12, wherein the optical element
has at least one of a diffractive and a refractive optical
element.
14. The system according to claim 12, further comprising another
optical element which is interchangeable with the optical element
and which converts the light from the light source to a divergence
light beam different from the divergence light beam created by the
optical element.
15. An exposure apparatus comprising: the illumination system
according to claim 1; and a projection system for imaging a pattern
onto a target portion of a substrate.
16. An exposure method comprising: illuminating a pattern with the
illumination system according to claim 1; and projecting the
illuminated pattern onto a target portion of a substrate.
17. A method of transferring a pattern on an original onto a work,
comprising the steps of: preparing said original; preparing said
work; illuminating said original with the illumination optical
system of claim 1; and transferring said pattern onto said
work.
18. An illumination optical system for a projection imaging
apparatus, comprising: a light source that emits illumination
light; a light beam shape changing element that diffuses incident
light emitted by the light source in a plurality of directions; a
zoom optical system that receives the diffused light; and an
optical integrator that receives light from the zoom optical system
in a modified illumination configuration having a light intensity
distribution such that a lower light intensity is formed at a
position near an optical axis relative to positions away from the
optical axis, and the optical integrator forms a secondary light
source having a modified illumination configuration from the
received light.
19. The system of claim 18, wherein: the light beam shape changing
element comprises a plurality of interchangeable optical
elements.
20. The system of claim 19, wherein: the light beam shape changing
element comprises a plurality of interchangeable diffractive
optical elements that each form a different modified illumination
configuration in cooperation with the zoom optical system at the
optical integrator.
21. The system of claim 20, wherein: at least one diffractive
optical element uses a phase difference of transmitted light to
form a modified illumination configuration.
22. The system of claim 18, wherein: the light beam shape changing
element forms a modified illumination configuration on the optical
integrator such that edges of illumination regions are inclined
with respect to a scanning direction of elemental lenses in the
optical integrator.
23. The system of claim 18, wherein: the light beam shape changing
element comprises at least one element housed within a protective
housing.
24. The system of claim 18, further comprising: a vibrator that
vibrates at least one of the light beam shape changing element and
an optical device positioned optically between the light beam shape
changing element and the optical integrator.
25. The system of claim 18, further comprising: an annular ratio
variable optical system that receives light from the light beam
shape changing element and transmits light to the zoom optical
system, wherein the light beam shape changing element is a
diffractive optical element that forms a ring shaped pattern in a
far field, and optical elements within the annular ratio variable
optical system are adjustable to vary the annular ratio of an
annular illumination pattern formed at the optical integrator.
26. The system of claim 25, wherein: the zoom optical system is
adjustable to vary a diameter of the annular illumination pattern
formed at the optical integrator.
27. The system of claim 25, wherein: the optical integrator is a
wave front splitting type optical integrator.
28. An illumination optical system for a projection imaging
apparatus, comprising: means for generating illumination light;
means for diffusing the emitted light in a plurality of different
directions; means for forming a plurality of light source images
from the emitted light; and means for forming a secondary light
source having a modified illumination configuration from light that
is diffused and used to form the plurality of light source images,
the modified illumination configuration having a light intensity
distribution such that a lower light intensity is formed at a
position near an optical axis relative to positions away from the
optical axis.
Description
INCORPORATION BY REFERENCE
[0001] The disclosures of the following priority applications are
herein incorporated by reference: Japanese Patent Application No.
11-90735, filed Mar. 31, 1999; Japanese Patent Application No.
11-284213, filed Oct. 5, 1999; Japanese Patent Application No.
11-308186, filed Oct. 29, 1999; Japanese Patent Application No.
10-358749, filed Dec. 17, 1998; and Japanese Patent Application No.
11-255636, filed Sep. 9, 1999.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The invention relates to a method and apparatus for
illuminating a surface, such as a mask or reticle surface, using a
projection imaging apparatus. The invention relates to a method and
apparatus for transferring a pattern, particularly a microdevice
(e.g., semiconductor device (IC, LSI, VLSI), liquid crystal
display, thin film magnetic head, image pick-up devices (CCD),
etc.) pattern, onto a work (e.g., a wafer, substrate, etc.) and
relates to a method for manufacturing the microdevice.
[0004] 2. Description of Related Art
[0005] In a typical exposure apparatus, light beams emitted from a
light source are incident on a fly-eye lens and form a secondary
light source that includes a plurality of light source images at
the focal surface on the back side of the fly-eye lens. Light beams
from the secondary light source are restricted by an aperture stop
positioned adjacent the back side focal surface of the fly-eye
lens, and are then incident on a condenser lens. The aperture stop
restricts the shape or size of the secondary light source to a
desired shape or size in accordance with the desired illumination
conditions (exposure conditions).
[0006] The light beams condensed by the condenser lens
overlappingly illuminate a mask that has a prescribed pattern.
Light that passes through the pattern in the mask forms an image on
a wafer via a projection optical system. In this manner, the mask
pattern is projected and exposed on the wafer. The pattern formed
in the mask is highly integrated, and in order to accurately copy
this detailed pattern onto the wafer, it is vital that a uniform
illumination intensity be obtained on the wafer.
[0007] In recent years, improvements in illumination performance
have been obtained by enabling variation of the size of the
secondary light source formed by the fly-eye lens and changing the
coherency .tau. (.tau.=aperture stop diameter/illumination optical
system pupil diameter, or .tau.=illumination optical system exit
side numerical aperture/illumination optical system incident side
numerical aperture) of the illumination by changing the size of the
aperture (light transmissive region) of the aperture stop
positioned on the exit side of the fly-eye lens. In addition, the
shape of the secondary light source formed by the fly-eye lens has
been restricted into an annular shape or quadrupole shape, which
results in improvements in the focal depth and resolving power of
the projection optical system.
[0008] In order to accomplish modified illumination (annular
modified illumination or quadrupole modified illumination) by
restricting the shape of the secondary light source to an annular
shape or a quadrupole shape, the light beams from the relatively
large secondary light source formed by the fly-eye lens are
restricted by an aperture-stop having an annular shape or
quadrupole shape aperture. In other words, with annular modified
illumination or quadrupole modified illumination in conventional
technology, the appropriate portions of the light beams from the
secondary light source are blocked by the aperture stop, and do not
contribute to illumination (exposure). As a result, the
illumination brightness on the mask and the wafer declines due to
the loss of light in the aperture stop, and the throughput as an
exposure apparatus also declines.
[0009] In consideration of the foregoing, it is an objective of the
present invention to provide an illumination optical apparatus
which can accomplish modified illumination such as annular
illumination or quadrupole illumination while satisfactorily
suppressing light loss in the aperture stop.
SUMMARY OF THE INVENTION
[0010] The invention provides an illumination method and apparatus
to change the type and parameters of modified illumination and to
obtain a focus depth and resolution for the projection optical
system suitable for the detailed patterns to be exposed and
projected. As a result, it is possible to accomplish satisfactory
projection exposure with high throughput under high exposure
brightness and satisfactory exposure conditions. In addition, with
an exposure method that exposes the pattern on a mask positioned at
the target illumination surface onto a photosensitive substrate
using the illumination optical apparatus of the present invention,
it is possible to accomplish projection exposure under satisfactory
exposure conditions, thereby making it possible to produce
satisfactory devices.
[0011] In one aspect of the invention, an illumination optical
system includes a light beam shape changing element that diffuses
illumination in a plurality of directions, and an angular light
beam forming element that forms a plurality of light source images.
Together, the light beam shape changing element and the angular
light beam forming element create a modified illumination
configuration, such as an annular or quadrupole illumination
configuration, on an optical integrator. Thus, the optical
integrator forms a secondary light source having a desired modified
illumination configuration. Since the secondary light source has a
desired configuration, an aperture stop used to restrict the size
and/or shape of the secondary light source blocks only a small
amount of illumination, or can be eliminated altogether.
[0012] The light beam shape changing element can be arranged
upstream of the angular light beam forming element, or the angular
light beam forming element can be arranged upstream of the light
beam shape changing element. The light beam shape changing element
can be any type of optical device that diffuses received light in a
plurality of directions. For example, the light beam shape changing
element can be a diffractive optical element or prism that forms a
ring-shaped or multi-pole-shaped illumination pattern in the far
field using incident parallel light. The angular light beam forming
element can be any optical device that forms a plurality of light
sources from incident light, and can be, for example, a fly eye
lens or micro fly's eye lens.
[0013] In addition, with the present invention it is possible to
alter the annular ratio and outer diameter of an annular or
quadrupole secondary light source by changing the magnification of
a zoom optical system positioned between the light beam shape
changing element and the angular light beam forming element.
Furthermore, by changing the focal length of a zoom optical system
(which is positioned upstream of the optical integrator), it is
possible to change the outer diameter of the annular or quadrupole
secondary light source without changing the annular ratio thereof.
As a result, it is possible to alter only the annular ratio of the
annular or quadrupole secondary light source without changing the
outer diameter thereof by appropriately changing the focal length
of the zoom lens and the magnification of the zoom optical
system.
[0014] The light beam shape changing element and the angular light
beam forming element can be made interchangeable with other light
beam shape changing elements and/or the angular light beam forming
elements or other optical elements to allow the illumination
optical system to create a variety of different types of modified
illumination configurations or conventional illumination. For
example, in one embodiment, the angular light beam forming element
can be replaced with an annular ratio variable optical system that
receives light from a light beam shape changing element and varies
an annular ratio of an annular illumination configuration formed by
the light beam shape changing element.
[0015] These and other aspects of the invention will be apparent
and/or obvious from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention is described in conjunction with the following
drawings in which like reference numerals refer to like elements,
and wherein:
[0017] FIG. 1 is a schematic diagram of an illumination optical
apparatus according to a first embodiment of the invention;
[0018] FIG. 2 is a schematic diagram of lens elements in an example
micro fly's eye lens;
[0019] FIGS. 3(a)-3(c) show how a first diffractive optical element
operates to diffuse received light;
[0020] FIGS. 4(a) and (b) show how an annular illumination
configuration is formed by superimposing a plurality of ring-shaped
images;
[0021] FIG. 5 shows an annular illumination configuration formed
from a plurality of ring-shaped images;
[0022] FIG. 6 is a schematic diagram of an aperture stop turret
plate having a plurality of aperture stop configurations;
[0023] FIGS. 7(a) and (b) shows how an annular ratio and diameter
of an annular illumination configuration can be changed;
[0024] FIG. 8 shows an example arrangement of lens elements in a
micro fly's eye lens;
[0025] FIGS. 9(a)-9(c) show how a second diffractive optical
element operates to diffuse received light;
[0026] FIG. 10 shows a quadrupolar illumination configuration
formed by superimposing a plurality of spot images;
[0027] FIG. 11 shows how a quadrupolar illumination configuration
can be adjusted in size and shape;
[0028] FIG. 12 is a schematic diagram of an illumination optical
apparatus according to a second embodiment of the invention;
[0029] FIGS. 13(a)-(b) schematically shows the illumination optical
apparatus from a conical prism to the incident surface of the first
fly-eye lens;
[0030] FIGS. 14(a)-(c) schematically show the illumination optical
apparatus from the first fly-eye lens to the aperture stop, and
show a state in which light beams obliquely incident on the
incident surface of the first fly-eye lens form an annular
illumination field at the incident surface of the second fly-eye
lens;
[0031] FIG. 15 schematically shows the illumination optical
apparatus from a conical prism to a second fly-eye lens, and the
relationship between the magnification of a first zoom lens and the
focal length of a second zoom lens, and the size and shape of the
annular illumination field formed at the incident surface of the
second fly-eye lens;
[0032] FIGS. 16(a)-(c) show a quadrupole secondary light source
formed at the back side focal plane of the second fly-eye lens and
a quadrupole aperture stop positioned adjacent thereto;
[0033] FIG. 17 is a schematic diagram of an illumination optical
apparatus according to a third embodiment of the invention;
[0034] FIGS. 18(a) and (b) show how a first exemplary diffractive
optical element diffuses received light;
[0035] FIGS. 19(a) and (b) show how a second exemplary diffractive
optical element diffuses received light;
[0036] FIGS. 20(a) and (b) schematically show the illumination
optical apparatus according to the third embodiment, with FIG.
10(b) showing a state in which the magnification of the first zoom
lens 5 expanded more than in the state shown in FIG. 10(a);
[0037] FIG. 21 is a schematic diagram of an illumination optical
apparatus according to a variation of the third embodiment of the
invention;
[0038] FIG. 22 is a schematic diagram of an illumination optical
apparatus according to a fourth embodiment of the invention;
[0039] FIG. 23 is a schematic diagram of an illumination optical
apparatus according to a fifth embodiment of the invention;
[0040] FIGS. 24A and 24B respectively show input and output sides
of an exemplary micro fly's eye lens used in the fifth
embodiment;
[0041] FIGS. 25A and 25B respectively show exemplary arrangements
for the micro fly's eye lens used in the fifth embodiment;
[0042] FIGS. 26A and 26B show first and second quad prism sets
included in the mircolens array;
[0043] FIGS. 27A-C and 28A-B show exemplary illumination
configurations formed on the optical integrator of the fifth
embodiment;
[0044] FIG. 29 is a schematic diagram of an illumination optical
apparatus according to a sixth embodiment of the invention;
[0045] FIG. 30A shows a revolver with an exemplary set of
interchangeable optical elements used with the sixth
embodiment;
[0046] FIG. 30B shows a revolver with an exemplary set of
interchangeable aperture stops used with the sixth embodiment;
[0047] FIGS. 31A-C schematically show an exemplary arrangement for
a diffractive optical element used with the sixth embodiment and an
illumination configuration intensity profile formed by the
diffractive optical element;
[0048] FIGS. 32A-C schematically show how a diffractive optical
element used with the sixth embodiment diffuses received light;
[0049] FIGS. 33 and 34A-C show exemplary modified illumination
configurations formed on the optical integrator in the sixth
embodiment;
[0050] FIGS. 35A and 35B show the relationship between the
effective region of the diffractive optical device and the element
lenses of the optical integrator in the sixth embodiment;
[0051] FIGS. 36A and 36B show exemplary modified illumination
configurations with four regions on the incident surface in the
optical integrator;
[0052] FIGS. 37A-37E show exemplary modified illumination
configurations having multiple regions with edges of the regions
continuously inclined relative to the scanning direction of the
element lenses of the optical integrator;
[0053] FIG. 38 shows another exemplary illumination configuration
on the incident surface of the optical integrator;
[0054] FIG. 39 schematically shows a protection container for the
diffractive optical element in the sixth embodiment;
[0055] FIG. 40 is a schematic diagram of an illumination optical
apparatus according to the seventh embodiment of the invention;
[0056] FIG. 41 is a schematic diagram of a portion of the
illumination optical apparatus according to an eighth embodiment of
the invention;
[0057] FIG. 42 is a schematic diagram of an illumination optical
apparatus according to a ninth embodiment of the invention;
[0058] FIG. 43 is a schematic diagram of an illumination optical
apparatus according to a tenth embodiment of the invention;
[0059] FIG. 44 is a flowchart of steps of a method for forming a
pattern of an original on a substrate using an imaging device in
accordance with the invention; and
[0060] FIGS. 45A-45D show cross sections of a numerical value
example.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0061] First Embodiment
[0062] FIG. 1 is a schematic diagram of an exposure apparatus
provided with the illumination optical apparatus according to a
first embodiment of the present invention.
[0063] The exposure apparatus of FIG. 1 includes an excimer laser
light source 1 that outputs light having a wavelength of 248 nm or
193 nm, although other light sources and wavelength outputs are
possible. Substantially parallel light beams emitted along the Z
direction by the light source 1 have a rectangular cross-section
that extends lengthwise along the X direction, and are incident on
a beam expander 2 that includes a pair of cylindrical lenses 2a and
2b. The cylindrical lenses 2a and 2b have a negative refractive
power and a positive refractive power, respectively, in the plane
of the paper in FIG. 1 (the Y-Z plane), and function as plane
parallel plates in the plane orthogonal to the plane of the paper
and including the optical axis AX (the X-Z plane). Accordingly,
light beams incident on the beam expander 2 are expanded in the
plane of the paper in FIG. 1, and are shaped into light beams
having a predetermined rectangular cross-section.
[0064] The substantially parallel light beams transmitted through
the beam expander 2 are deflected in the Y direction by a folding
mirror 3, and are then incident on a micro fly's eye lens 4. The
micro fly's eye lens 4 is an optical element comprising a plurality
of microlenses 4a having positive refractive powers and regular
hexagonal shapes arranged densely in the vertical and horizontal
directions, as shown in FIGS. 1 and 2. In general, the microlens
groups of the micro fly's eye lens 4 are preferably formed by an
etching process on a plane parallel glass plate, for example.
[0065] Each of the microlenses of the micro fly's eye lens 4 is
smaller than the lens elements of a conventional fly-eye lens. In
addition, the micro fly's eye lens 4, unlike a conventional fly-eye
lens that has mutually isolated lens elements, are formed so that
the microlenses are not mutually isolated. However, the micro fly's
eye lens 4 is the same as a conventional fly-eye lens in that lens
elements having a positive refractive power are arranged in the
vertical and horizontal directions. In order to promote clarity in
FIGS. 1 and 2, only a very few of the microlenses 4a in the micro
fly's eye lens 4 are shown compared to the actual number of
microlenses 4a in the array 4.
[0066] Light beams incident on the micro fly's eye lens 4 are
two-dimensionally partitioned by the plurality of microlenses 4a,
and a light source image is formed at a back side focal plane of
each microlens 4a, i.e., at a plane downstream of the light source
1. The light beams from the plurality of light source images formed
at the back side focal plane of each microlens 4a are diffused
light beams each having, in this example, a regular hexagonal
cross-section, and are incident on an afocal zoom lens 5. Although
the zoom lens 5 is preferably an afocal zoom lens, a focal zoom
lens can be used, if desired. The afocal zoom lens 5 is composed so
that the magnification thereof is continuously changeable within a
predetermined range while maintaining an afocal optical system.
Thus, the micro fly's eye lens 4 is an angular light beam forming
element that converts substantially parallel light beams from the
light source 1 into a plurality of light source images that each
emit light beams at various angles with respect to the optical axis
AX.
[0067] The micro fly's eye lens 4 is removable from the
illumination optical path, and can be interchanged with another
micro fly's eye lens 40, as is discussed in more detail below. The
micro fly's eye lens 4 and the micro fly's eye lens 40 are
interchanged by a first driving system 22 which operates on the
basis of commands from a control system 21. The magnification of
the afocal zoom lens 5 is accomplished by a second driving system
23 which also operates on the basis of commands from the control
system 21.
[0068] Light beams that pass through the afocal zoom lens 5 are
incident on a diffractive optical element (DOE) 6. That is,
diffused light beams from each light source image formed at the
back side focal plane of the micro fly's eye lens 4 are condensed
onto the diffraction surface of the diffractive optical element 6
while maintaining the regular hexagonal cross-section. Thus, the
afocal zoom lens 5 links the back side focal plane of the micro
fly's eye lens 4 and the diffraction surface of the diffractive
optical element 6 as optical conjugates. Furthermore, the numerical
aperture of the light beams collected to one point on the
diffraction surface of the diffractive optical element 6 is
dependent on the magnification of the afocal zoom lens 5.
[0069] In this example, the diffractive optical element 6 includes
a succession of levels or steps in a glass substrate having a pitch
on the order of the wavelength of the exposure light (illumination
light), and diffracts an incident beam to a desired angle.
Specifically, the diffractive optical element 6 radially diffuses
orthogonally incident light beams parallel to the optical axis AX
in accordance with a predetermined diffusion angle, as shown in
FIG. 3(a). In other words, a narrow light beam orthogonally
incident on the diffractive optical element 6 along the optical
axis AX is diffracted in all directions at equal angles centered
about the optical axis AX. As a result, the narrow light beam
orthogonally incident on the diffractive optical element 6 is
converted into a diffused light beam having a ring-shaped
cross-section. Thus, the diffractive optical element 6 is a light
beam changing element that converts narrow incident light beams
into ring-shaped light beams diffused radially.
[0070] As shown in FIG. 3(b), when a wide parallel light beam is
orthogonally incident on the diffractive optical element 6, a
ring-shaped image (ring-shaped light source image) 32 is formed at
the focal position of a lens 31 positioned behind the diffractive
optical element 6. That is to say, the diffractive optical element
6 forms a ring-shaped light intensity distribution at the far field
(or the Fraunhofer diffraction zone).
[0071] As shown in FIG. 3(c), when a wide parallel light beam
incident on the diffractive optical element 6 is inclined with
respect to the optical axis AX, the ring-shaped image formed at the
focal position of the lens 31 is shifted. That is to say, when a
wide parallel light beam incident on the diffractive optical
element 6 is inclined along a predetermined plane (the plane of the
paper in FIG. 3), the center of the ring-shaped image 33 that is
formed at the focal position of the lens 31 is shifted in a
direction opposite the direction of inclination of the light beam
along a predetermined plane without the size of the ring-shaped
image 33 being changed.
[0072] As described above, the diffused light beams from each light
source image formed at the back side focal plane of the micro fly's
eye lens 4 converge on the diffraction surface of the diffractive
optical element 6 with the regular hexagonal cross-section
maintained. In other words, when light beams having a plurality of
angular components are incident on the diffractive optical element
6, the incident angle thereof is determined by the regular
hexagonal conical light beam range. Accordingly, as shown in FIG.
4(a), light beams incident at a maximum angle corresponding to each
ridge line of the regular hexagonal conical light beam range form
ring-shaped images 41-46 (indicated by the solid lines in the
diagram), centered about the ring-shaped image 47 (indicated by the
dotted lines in the diagram) formed by light beams orthogonally
incident on the diffractive optical element 6. In FIG. 4(b), the
condition with the ring-shaped images 41-47 thus formed at the
focal position of the lens 31 are shown superimposed.
[0073] In actuality, an infinite number of light beams having a
plurality of angular components determined by the regular hexagonal
conical light beam range are incident on the diffractive optical
element 6, and consequently, an infinite number of ring-shaped
images are superimposed at the focal position of the lens 31. Thus,
an overall annular image like that shown in FIG. 5 is formed when
the micro fly's eye lens 4 and the diffractive optical element 6
are positioned along the optical axis AX as shown in FIG. 1.
[0074] The diffractive optical element 6 can also be interchanged
with a diffractive optical element 60 and a diffractive optical
element 61, which are described in more detail below. The
diffractive optical element 6, the diffractive optical element 60
and the diffractive optical element 61 are interchanged by a third
driving system 24, which operates on the basis of commands from the
control system 21.
[0075] With reference again to FIG. 1, light beams that pass
through the diffractive optical element 6 are incident on a zoom
lens 7. In this example, the zoom lens 7 has the same function as
the lens 31 shown in FIG. 3. In addition, the incident surface of a
fly-eye lens 8 is positioned adjacent the back side focal plane of
the zoom lens 7. Accordingly, light beams passing through the
diffractive optical element 6 form an annular illumination field at
the back side focal plane of the zoom lens 7 and hence at the
incident surface of the fly-eye lens 8. The outer diameter of this
annular illumination field depends on the focal length of the zoom
lens 7. Thus, the zoom lens 7 makes the diffractive optical element
6 and the incident surface of the fly-eye lens 8 effectively have
the relationship of a Fourier transform. Changing the focal length
of the zoom lens 7 is accomplished by a fourth driving system 25
which acts on the basis of commands from the control system 21.
[0076] The fly-eye lens 8 includes a plurality of lens elements
having positive refractive powers that are arranged densely in the
vertical and horizontal directions. Each lens element of the
fly-eye lens 8 has a rectangular cross-section similar to the shape
of the illumination field to be formed on the mask (and hence,
similar to the shape of the exposure region to be formed on the
wafer). Additionally, the surface on the incident side of each lens
element of the fly-eye lens 8 has a spherical shape with the
convexity facing the incident side, and the surface on the exit
side of each lens element has a spherical shape with the convexity
facing the exit side.
[0077] Accordingly, light beams incident on the fly-eye lens 8 are
two-dimensionally partitioned by the plurality of lens elements,
and are formed into light source images at the back side focal
plane of each lens element on which the light beams are incident.
In this way, a plurality of annular light sources (hereafter
referred to as "secondary light sources") are formed at the back
side focal plane of the fly-eye lens 8.
[0078] Light beams from the annular secondary light sources formed
at the back side focal plane of the fly-eye lens 8 are incident on
an aperture stop 9. This aperture stop 9 is supported on a turret
(not shown in FIG. 1) capable of rotating about a predetermined
axis parallel to the optical axis AX.
[0079] FIG. 6 is a diagram schematically showing the composition of
the turret on which a plurality of aperture stops are positioned
circumferentially. As shown in FIG. 6, eight aperture stops 401-408
having optically transmissive regions indicated by the slanted
lines in the diagram are provided along the circumferential
direction on a turret substrate 400. The turret substrate 400 can
rotate about an axis parallel to the optical axis AX around a
center point O. Accordingly, by rotating the turret substrate 400,
it is possible to position one of the aperture stops 401-408 in the
illumination optical path. Rotation of the turret substrate 400 is
accomplished by a fifth driving system 26 which operates on the
basis of commands from the control system 21.
[0080] In this example, three annular aperture stops 401, 403 and
405 of differing annular ratios are formed in the turret substrate
400. The annular aperture stop 401 has an annular transmissive
region with an annular ratio of r11/r21. The annular aperture stop
403 has an annular transmissive region with an annular ratio of
r12/r22. The annular aperture stop 405 has an annular transmissive
region with an annular ratio of r13/r21.
[0081] Three quadrupole aperture stops 402, 404 and 406 of
differing annular ratios are also formed in the turret substrate
400. The quadrupole aperture stop 402 has four eccentric circular
transmissive regions within an annular region having an annular
ratio of r11/r21. The quadrupole aperture stop 404 has four
eccentric circular transmissive regions within an annular region
having an annular ratio of r12/r22. The quadrupole aperture stop
406 has four eccentric circular transmissive regions within an
annular region having an annular ratio of r13/r21.
[0082] Two circular aperture stops 407 and 408 of differing size
(aperture) are also formed in the turret substrate 400. The
circular aperture stop 407 has a circular transmissive region with
a size of 2*r22, while the circular aperture stop 408 has a
circular transmissive region with a size of 2*r21.
[0083] By selecting and positioning one annular aperture stop out
of the three annular aperture stops 401, 403 and 405 in the
illumination optical path, it is possible to form annular light
beams having three differing annular ratios and to accomplish three
types of annular modified illumination of differing annular ratios.
In addition, by selecting and positioning one quadrupole aperture
stop out of the three quadrupole aperture stops 402, 404 and 406 in
the illumination optical path, it is possible to accurately form
four eccentric light beams having three differing annular ratios
and to accomplish three types of quadrupole modified illumination
of differing annular ratios. Furthermore, by selecting and
positioning one circular aperture stop out of the two circular
aperture stops 407 and 408 in the illumination optical path, it is
possible to accomplish two types of regular circular illumination
of differing a values. A multiple pole aperture stop (e.g.,
binalpole or octalpole aperture stop) which has multi-eccentric
circular, elliptic, or fan-shaped transmissive regions can also be
used as an aperture stop on the turret substrate 400. The
transmissive regions of the quadrupole aperture stops 402, 404 and
406 are not only circular-shaped, but can also be elliptic-shaped,
or fan-shaped (e.g., the shape of quarter circles). It is possible
for the variable aperture stop (e.g., iris diaphragm) to be
attached to the turret substrate 400 instead of the circular
aperture stops 407 and 408.
[0084] In FIG. 1, annular secondary light sources are formed at the
back side focal plane of the fly-eye lens 8 when the micro fly's
eye lens 4 and the diffractive optical element 6 are positioned
along the optical axis AX, and consequently one of the annular
aperture stops can be selected from the three annular aperture
stops 401, 403 and 405 as the aperture stop 9. However, the
composition of the turret shown in FIG. 6 is intended to
illustrative and not limiting with regard to the type or number of
aperture stops positioned thereon. In addition, the invention is
not limited to a turret-type aperture stop 9, for it is also
possible to use an aperture stop that has an optically transmissive
region that is changeable in size and shape. Furthermore, in place
of the two circular aperture stops 407 and 408, it is possible to
provide an iris aperture stop that has a continuously variable
circular aperture diameter.
[0085] Light from the secondary light sources that has passed
through the aperture stop 9 having an annular aperture (light
transmission area) is condensed by a condenser optical system 10
that functions as a light-guiding optical system, and uniformly
illuminates a mask 11 in an overlapping manner. Light beams that
have passed through a pattern on the mask 11 form an image of the
mask pattern on a wafer 13 having a photosensitive substrate via a
projection optical system 12. In this manner, the pattern on the
mask 11 is successively exposed onto each exposure region of the
wafer 13 by accomplishing bulk exposure or scan exposure while
two-dimensionally drive controlling the wafer 13 in the plane
orthogonal to the optical axis AX of the projection optical system
12 (the X-Y plane).
[0086] In bulk exposure, the mask 11 pattern is exposed in bulk
onto each exposure region of the wafer 13 in accordance with the
so-called step and repeat method. In this case, the shape of the
illumination region on the wafer 13 is a nearly square rectangle,
and the cross-sectional shape of each lens element in the fly-eye
lens 8 is also a nearly square rectangle.
[0087] On the other hand, in scan exposure, the mask 11 pattern is
scan exposed onto each exposure region of the wafer 13 while moving
the mask 11 and wafer 13 relative to the projection optical system
12 in accordance with the so-called step and scan method. In this
case, the shape of the illumination region on the mask 11 is a
rectangle with the ratio of the length of the short sides to the
length of the long sides being for example 1:3, so the
cross-sectional shape of each lens element of the fly-eye lens 8
has a rectangular shape similar to this.
[0088] FIG. 7 is a drawing that schematically shows the
illumination optical apparatus from the micro fly's eye lens 4 to
the incident surface of the fly-eye lens 8, and explains the
relationship between the magnification of the afocal zoom lens 5
and the focal length of the zoom lens 7, and the size and shape of
the annular illumination field formed on the incident surface of
the fly-eye lens 8.
[0089] In FIG. 7, a light beam 70 incident along the optical axis
AX on the center of the microlens 4a positioned on the optical axis
AX of the micro fly's eye lens 4 exits along the optical axis AX.
The micro fly's eye lens 4 in this example has microlenses of size
"a" (a measurement corresponding to the diameter of a circle
circumscribed around a regular hexagon) and focal length f1. The
light beam 70 passes through the afocal zoom lens 5 and is then
incident on the diffractive optical element 6 along the optical
axis AX.
[0090] The diffractive optical element 6 forms a light beam 70a
exiting at an angle .THETA. with respect to the optical axis AX
from the light beam 70 orthogonally incident along the optical axis
AX. The light beam 70a exiting at angle .THETA. from the
diffractive optical element 6 reaches the incident surface of the
fly-eye lens 8 via the zoom lens 7 having focal length f2. The
position of the light beam 70a on the incident surface of the
fly-eye lens 8 has a height y from the optical axis AX.
[0091] On the other hand, a light beam 71 incident parallel to the
optical axis AX on the uppermost edge of the microlens 4a
positioned on the optical axis AX in the micro fly's eye lens 4
exits at an angle t with respect to the optical axis AX. This light
beam 71 passes through the afocal zoom lens 5 having magnification
m, and is then incident on the diffractive optical element 6 at an
angle t' with respect to the optical axis AX.
[0092] The light beam 71 which is incident on the diffractive
optical element 6 at an angle t' with respect to the optical axis
AX is converted into various light beams including a light beam 71a
exiting at an angle (.THETA.+t') with respect to the optical axis
AX. The light beam 71a exiting from the diffractive optical element
6 at an angle (.THETA.+t') with respect to the optical axis AX
reaches a height (y+b) from the optical axis AX at the incident
surface of the fly-eye lens 8.
[0093] Furthermore, a light beam 72 incident parallel to the
optical axis AX on the lowermost edge of the microlens 4a
positioned on the optical axis AX in the micro fly's eye lens 4
exits at angle t with respect to the optical axis AX. This light
beam 72 passes through the afocal zoom lens 5, and is then incident
on the diffractive optical element 6 at an angle t' with respect to
the optical axis AX.
[0094] The light beam 72 which is incident on the diffractive
optical element 6 at angle t' with respect to the optical axis AX
is converted into various light beams including a light beam 72a
exiting at an angle (.THETA.-t') with respect to the optical axis
AX. The light beam 72a exiting the diffractive optical element 6 at
an angle (.THETA.-t') with respect to the optical axis AX reaches a
height (y-b) from the optical axis AX at the incident surface of
the fly-eye lens 8.
[0095] Thus, the range reached at the incident surface of the
fly-eye lens 8 by the diffused light beams from the various light
source images formed near the back side focal plane of the micro
fly's eye lens 4 is a range having a width of 2b centered about the
height y from the optical axis AX. That is to say, as shown in FIG.
7(b), the annular illumination field formed at the incident surface
of the fly-eye lens 8, and hence the annular secondary light
sources formed at the back-side focal plane of the fly-eye lens 8,
have a central height of y from the optical axis AX and a width of
2b.
[0096] The exit angle t from the micro fly's eye lens 4 and the
incident angle t' on the diffractive optical element 6 are
expressed by equations (1) and (2) below.
t=a/(2.times.f1) (1)
t'=t/m=a/(2.times.f1.times.m) (2)
[0097] In addition, the central height y of the annular secondary
light sources, the maximum height (y+b) and the minimum height
(y-b) are expressed by equations (3) through (5) below.
y=f2.times.sin .THETA. (3)
y+b=f2(sin .THETA.+sin t') (4)
y-b=2(sin .THETA.-sin t') (5)
[0098] Accordingly, the annular ratio A stipulated by the ratio of
the inner diameter .o slashed.i to the outer diameter .o slashed.o
of the annular secondary light sources is expressed by equation (6)
below. 1 A = .0. i / .0. o = 2 ( y - b ) / ( 2 ( y + b ) ) = ( sin
- sin t ' ) / ( sin + sin t ' ) = ( sin - sin ( a / ( 2 .times. f1
.times. m ) ) ) / ( sin + sin ( a / ( 2 .times. f1 .times. m ) ) )
( 6 )
[0099] In addition, the outer diameter .o slashed.o of the annular
secondary light sources is expressed by equation (7) below. 2 .0. o
= 2 ( y + b ) = 2 .times. f2 ( sin + sin t ' ) = 2 .times. f2 ( sin
+ sin ( a / ( 2 .times. f1 .times. m ) ) ) ( 7 )
[0100] Thus, it can be seen by referring to equations (2) through
(6) that when the magnification m of the afocal zoom lens 5
changes, only the width 2b of the annular secondary light sources
changes, without the central height y thereof changing. That is to
say, by changing the magnification m of the afocal zoom lens 5, it
is possible to change both the size (outer diameter .o slashed.o)
and the shape (annular ratio A) of the annular secondary light
sources.
[0101] In addition, it can be seen by referring to equations (3)
through (7) that when the focal length f2 of the zoom lens 7 is
changed, the central height y and width 2b of the annular secondary
light source changes without the annular ratio A thereof changing.
That is to say, by changing the focal length 12 of the zoom lens 7,
it is possible to change the outer diameter .o slashed.o of the
annular secondary light source without changing the annular ratio A
thereof.
[0102] From the above, it is possible to change only the annular
ratio A of the annular secondary light source without changing the
outer diameter .o slashed.o thereof by appropriately changing the
magnification m of the afocal zoom lens 5 and the focal length 12
of the zoom lens 7.
[0103] Thus, when a diffractive optical element 6 and micro fly's
eye lens 4 for annular modified illumination are employed, it is
possible to form an annular secondary light source without
substantial light loss on the basis of light beams from the light
source 1, and as a result it is possible to accomplish annular
modified illumination while satisfactorily suppressing light loss
at the aperture stop 9.
[0104] As discussed above, the micro fly's eye lens 4 is
interchangeable with the micro fly's eye lens 40, and the
diffractive optical element 6 is interchangeable with the
diffractive optical element 60. Together, the micro fly's eye lens
40 and the diffractive optical element 60 operate to form a
quadrupole modified illumination.
[0105] The micro fly's eye lens 40 includes a plurality of
microlenses 40a that are square in shape, have a positive
refractive power and are arranged densely in the vertical and
horizontal directions, as shown in FIGS. 1 and 8. Accordingly, a
plurality of light source images are formed on the back side focal
plane of the micro fly's eye lens 40, and light beams from each
light source image are diffused light beams each having a square
cross-section that are incident on the afocal zoom lens 5. Light
beams that pass through the afocal zoom lens 5 are incident on the
diffractive optical element 60. The diffused light beams from each
light source image formed at the back-side focal plane of the micro
fly's eye lens 40 converge on the diffraction surface of the
diffractive optical element 60 while maintaining the square
cross-section.
[0106] The diffractive optical element 60 converts narrow light
beams orthogonally incident parallel to the optical axis AX into
four light beams diffused radially in accordance with a single
predetermined exit angle, as shown in FIG. 9(a). In other words,
narrow light beams orthogonally incident along the optical axis AX
are diffracted along four specific directions at equal angles
centered about the optical axis AX, and become four narrow light
beams. To be more detailed, narrow light beams orthogonally
incident on the diffractive optical element 60 are converted into
four light beams, the quadrilateral joining the points of the four
light beams passing through a plane on the back side parallel to
the diffractive optical element 60 forms a square, and the center
of that square is positioned at the incident axis of the narrow
light beam to the diffractive optical element 60.
[0107] Accordingly, as shown in FIG. 9(b), when a wide parallel
light beam is orthogonally incident on the diffractive optical
element 60, four point images (point-shaped light source images) 92
are formed at the focal position of a lens 91 positioned on the
back side of the diffractive optical element 60. When the wide
parallel light beam incident on the diffractive optical element 60
is inclined with respect to the optical axis AX, the four images
formed at the focal position of the lens 91 move, as shown in FIG.
9(c). That is to say, when the wide parallel light beam incident on
the diffractive optical element 60 is inclined along a specific
plane, the four point images 93 formed at the focal position of the
lens 91 move in a direction opposite the direction of inclination
of the light beams along the specific plane.
[0108] As discussed above, the diffused light beams from the light
source images formed at the back side focal plane of the micro
fly's eye lens 40 converge on the diffraction plane of the
diffractive optical element 60 while maintaining a square
cross-section. In other words, light beams having a plurality of
angular components are incident on the diffractive optical element
60, but the angle of incidence thereof is restricted by the square
conical light beam range. That is to say, because an infinite
number of light beams having a plurality of angular components
determined by the square conical light beam range are incident on
the diffractive optical element 60, an infinite number of point
images are superimposed at the focal position of the lens 91, so
that a quadrupole image such as the one shown in FIG. 10, is formed
overall. Accordingly, the light beams that have passed through the
diffractive optical element 60 form a quadrupole illumination field
at the back side focal plane of the zoom lens 7, and hence at the
incident surface of the fly-eye lens 8. As a result, a quadrupole
secondary light source the same as the illumination field formed at
the incident surface is also formed at the back side focal plane of
the fly-eye lens 8.
[0109] In response to switching from the micro fly's eye lens 4 to
the micro fly's eye lens 40 and from the diffractive optical
element 6 to the diffractive optical element 60, a switch is also
preferably made from the annular aperture stop 9 to an aperture
stop 9a. For example, the aperture stop 9a is one of the quadrupole
aperture stops selected from among of the three quadrupole aperture
stops 402, 404 and 406.
[0110] Thus, when the micro fly's eye lens 40 and diffractive
optical element 60 for quadrupole modified illumination are
employed, it is possible to form a quadrupole secondary light
source without substantial loss of light from the light source 1,
and as a result is it possible to accomplish quadrupole modified
illumination while satisfactorily suppressing light loss in the
aperture stop 9a.
[0111] As shown in FIG. 11, it is possible to define the shape and
size of the quadrupole secondary light source similar to the
annular secondary light source. In this case, the size of each
microlens 40a in the micro fly's eye lens 40 corresponds to the
diameter of a circle circumscribed around the square that is the
cross-sectional shape of the microlens 40a. Thus, similar to the
case of annular modified illumination, by changing the
magnification m of the afocal zoom lens 5, it is possible to alter
both the annular ratio A and the outer diameter .o slashed.o of the
quadrupole secondary light source. In addition, by changing the
focal length f2 of the zoom lens 7, it is possible to alter the
outer diameter .o slashed.o of the quadrupole secondary light
source without altering the annular ratio thereof. As a result, by
appropriately changing the magnification m of the afocal zoom lens
5 and the focal length f2 of the zoom lens 7, it is possible to
alter only the annular ratio A of the quadrupole secondary light
source without changing the outer diameter .o slashed.o
thereof.
[0112] Next, an explanation will be provided for the case of normal
circular illumination which is obtained by withdrawing both the
micro fly's eye lenses 4 and 40 from the illumination optical path,
and setting the diffractive optical element 61 for circular
illumination in the illumination optical path in place of the
diffractive optical elements 6 and 60.
[0113] In this case, light beams having a rectangular cross-section
are incident on the afocal zoom lens 5 along the optical axis AX.
Light beams incident on the afocal zoom lens 5 are enlarged or
reduced in accordance with the magnification of the lens, exit from
the afocal zoom lens 5 along the optical axis AX as light beams
still having a square cross-section, and are incident on the
diffractive optical element 61.
[0114] The diffractive optical element 61 for circular illumination
has the function of converting the incident square light beams into
circular light beams. Accordingly, the circular light beams formed
by the diffractive optical element 61 form a circular illumination
field centered about the optical axis AX at the incident surface of
the fly-eye lens 8. As a result, a circular secondary light source
centered about the optical axis AX is also formed at the back side
focal plane of the fly-eye lens 8. In this case, it is possible to
appropriately alter the outer diameter of the circular secondary
light source by changing the focal length f2 of the zoom lens
7.
[0115] Corresponding to the withdrawal of the micro fly's eye
lenses 4 and 40 from the illumination optical path and the setting
of the diffractive optical element 61 for circular illumination in
the illumination optical path, a change from the annular aperture
stop 9 or the quadrupole aperture stop 9a to the circular aperture
stop 9b is also preferably made. The circular aperture stop 9b can
be one circular aperture stop selected from among the two circular
aperture stops 407 and 408, and has an aperture the size of which
corresponds to the circular secondary light source.
[0116] Hereafter, the operation of interchanging illumination in
the present embodiment will be described in more detail.
[0117] First, information relating to the various types of masks to
be successively exposed in accordance with the step and repeat
method or the step and scan method is input into the control system
21 via an input means 20 such as a keyboard. The control system 21
stores in an internal memory unit information such as the optimum
line width (resolution) and focus depth relating to each type of
mask, and supplies appropriate control signals to the first driving
system 22 through the fifth driving system 26 in response to input
from the input means 20.
[0118] That is to say, when annular modified illumination is
required to form an optimum resolution and focus depth, the first
driving system 22 positions the micro fly's eye lens 4 for annular
modified illumination in the illumination optical path on the basis
of commands from the control system 21. In addition, the third
driving system 24 positions the diffractive optical element 6 for
annular modified illumination in the illumination optical path on
the basis of commands from the control system 21. Furthermore, in
order to obtain an annular secondary light source having the
desired size (outer diameter) and annular ratio at the back side
focal plane of the fly-eye lens 8, the second driving system 23
sets the magnification of the afocal zoom lens 5 on the basis of
commands from the control system 21, and the fourth driving system
25 sets the focal length of the zoom lens 7 on the basis of
commands from the control system 21. Additionally, in order to
restrict the annular secondary light source while satisfactorily
suppressing light loss, the fifth driving system 26 rotates the
turret on the basis of commands from the control system 21 and
positions the desired annular aperture stop in the illumination
optical path.
[0119] In this manner, it is possible to form an annular secondary
light source without substantial loss of light beams from the light
source 1, and as a result it is possible to accomplish annular
modified illumination without substantial light loss in the
aperture stop 9.
[0120] Furthermore, it is possible to appropriately adjust, as
necessary, the size and annular ratio of the annular secondary
light source formed at the back side focal plane of the fly-eye
lens 8 by changing the magnification of the afocal zoom lens 5
using the second driving system 23 and changing the focal length of
the zoom lens 7 using the fourth driving system 25. In this case,
the turret is rotated in accordance with changes in the size and
annular ratio of the annular secondary light source, and the
annular aperture stop 401, 403, 405 having the desired size and
annular ratio is selected and positioned in the illumination
optical path.
[0121] In this manner, it is possible to accomplish various types
of annular modified illumination by appropriately changing the size
and annular ratio of the annular secondary light source without
substantial light loss in the formation or restriction of the
annular secondary light source.
[0122] In addition, when quadrupole modified illumination is
required for an optimum resolution and focus depth, the first
driving system 22 positions the micro-fly's eye lens 40 for
quadrupole modified illumination in the illumination optical path
and the third driving system 24 positions the diffractive optical
element 60 for quadrupole modified illumination in the illumination
optical path. Furthermore, in order to obtain a quadrupole
secondary light source having the desired size (outer diameter) and
shape (annular ratio) at the back side focal plane of the fly-eye
lens 8, the second driving system 23 sets the magnification of the
afocal zoom lens 5 on the basis of commands from the control system
21, and the fourth driving system 25 sets the focal length of the
zoom lens 7 on the basis of commands from the control system 21.
Additionally, in order to restrict the quadrupole secondary light
source while satisfactorily suppressing light loss, the fifth
driving system 26 rotates the turret on the basis of commands from
the control system 21 and positions the desired quadrupole aperture
stop 402, 404, 406 in the illumination optical path.
[0123] In this manner, it is possible to form a quadrupole
secondary light source without substantial light loss on the basis
of light beams from the light source 1, and as a result it is
possible to accomplish quadrupole modified illumination without
substantial light loss in the aperture stop which restricts the
light beams from the secondary light source.
[0124] Furthermore, it is possible to appropriately adjust, as
necessary, the size and shape of the quadrupole secondary light
source formed at the back side focal plane of the fly-eye lens 8 by
changing the magnification of the afocal zoom lens 5 using the
second driving system 23 and changing the focal length of the zoom
lens 7 using the fourth driving system 25. In this case, the turret
is rotated in accordance with changes in the size and shape of the
quadrupole secondary light source, and the quadrupole aperture stop
402, 404, 406 having the desired size and shape is selected and
positioned in the illumination optical path.
[0125] In this manner, it is possible to accomplish various types
of quadrupole modified illumination by appropriately changing the
size and shape of the quadrupole secondary light source without
substantial light loss in the formation or restriction of the
quadrupole secondary light source.
[0126] Furthermore, when regular circular illumination is required
for an optimum resolution and focus depth, similar adjustments to
the illumination optical system can be made under the control of
the control system 21. In this manner, it is possible to form a
circular secondary light source without substantial loss of light
from the light source 1, and as a result it is possible to
accomplish regular circular illumination without substantial light
loss in the aperture stop which restricts the light beams from the
secondary light source.
[0127] With the above-described embodiment, it is possible to
accomplish regular circular illumination and modified illumination
such as annular modified illumination or quadrupole modified
illumination while satisfactorily suppressing light loss in the
aperture stop used for restricting the secondary light source.
Additionally, it is possible to change the parameters of modified
illumination or regular circular illumination while satisfactorily
suppressing light loss in the aperture stop, through the simple
operation of changing the magnification of the afocal zoom lens and
changing the focal length of the zoom lens. Accordingly, it is
possible to appropriately change the type of modified illumination
and the parameters thereof, and to obtain the resolution and focal
depth of the projection optical system suitable for the detailed
pattern to be exposed and projected. As a result, it is possible to
accomplish satisfactory projection exposure with high throughput
under satisfactory exposure conditions and high exposure
brightness.
[0128] Thus, in an exemplary embodiment of the present invention,
an angular light beam forming element and a light beam shape
changing element are positioned on the optical path between the
light source and the optical integrator. Specifically, the angular
light beam forming element includes a diffused light beam forming
element such as a micro fly's eye lens that converts the
substantially parallel light beams from the light source means into
a plurality of light source images from which light beams diffused
at various angles with respect to the standard optical axis emerge.
An optical system such as an afocal zoom lens condenses the
diffused light beams formed by the micro fly's eye lens and guides
the beams to the diffraction surface of a diffractive optical
element functioning as the light beam shape changing element.
Accordingly, substantially parallel light beams from the light
source that pass through the micro fly's eye lens and the afocal
zoom lens become light beams having a plurality of angular
components with respect to the standard optical axis and then are
incident on the diffractive optical element.
[0129] The light beam shape changing element includes a light beam
changing element such as a diffractive optical element that
converts narrow incident light beams into a radially diffused
ring-shaped light beam or plurality of light beams. An optical
system such as a zoom lens forms an annular illumination field or
plurality of illumination fields eccentric with respect to the
standard optical axis on the incident surface of the optical
integrator such as a fly-eye lens from the ring-shaped light beam
or plurality of light beams formed by the diffractive optical
element. In general, the plurality of illumination fields or
secondary light sources eccentric with respect to the standard
optical axis means are, for example, bipolar or multipole (tripole,
quadrupole octopole or the like) illumination fields or secondary
light sources, but quadrupole illumination fields or secondary
light sources will be formed for illustrative purposes.
[0130] By thus employing an angular light beam forming element
composed of a micro fly's eye lens, and a light beam shape changing
element including a diffractive optical element, an annular
illumination field or quadrupole illumination field can be formed
on the incident surface of the fly-eye lens. As a result, an
annular or quadrupole secondary light source is similarly formed on
the back side focal plane of the fly-eye lens. The light beams from
the annular or quadrupole secondary light source formed by the
fly-eye lens in this manner are restricted by the aperture stop
having an aperture corresponding to the size and shape of the
secondary light source and then overlappingly illuminate the mask
that is the target illumination surface.
[0131] The above explanation describes an example wherein
semiconductor devices are manufactured using a photolithography
process and a wafer process employing a projection exposure
apparatus, but liquid crystal display devices, thin-film magnetic
heads and image detectors (e.g., CCDs and the like) can also be
manufactured as semiconductor devices by a photolithography process
that uses this exposure apparatus.
[0132] In the above-described embodiment, it is possible to compose
the diffractive optical elements that function as light beam
changing elements and the micro fly's eye lenses that function as
angular light beam forming elements so as to be positioned in the
illumination optical path using a turret method, for example. In
addition, it is also possible to use a commonly-known slider
mechanism to accomplish mounting and removal or interchanging of
the above-described micro fly's eye lenses and diffractive optical
elements.
[0133] In addition, with the above-described embodiment, the shape
of the microlenses 4a comprising the micro fly's eye lens 4 for
annular modified illumination is set to a regular hexagon. A
regular hexagon was selected as a polygon close to a circle because
dense arrangement is impossible with circular microlenses, so light
loss is generated. This notwithstanding, the shape of each
microlens 4a in the micro fly's eye lens 4 for annular modified
illumination is not limited to this, and other appropriate shapes
can be used. Similarly, the shape of the microlenses 40a in the
micro fly's eye lens 40 for quadrupole modified illumination is set
to a square, but it is possible to use other appropriate shapes
including a rectangle.
[0134] In addition, with the above-described embodiment, the
refractive power of each microlens comprising the micro fly's eye
lens was assumed to be a positive refractive power, but the
refractive power of these microlenses may also be negative.
[0135] Furthermore, an afocal zoom lens was employed, but it is
also possible to employ a focal zoom lens in place of the afocal
zoom lens 5 or 7 and to position a diffractive optical element for
converting square light beams into circular light beams in front of
the micro fly's eye lens.
[0136] In addition, with the above-described embodiment, a single
fly-eye lens 8 was employed, but it is also possible to apply the
present invention to a double fly-eye method employing two fly-eye
lenses.
[0137] Furthermore, the diffractive optical element 61 was
positioned in the illumination optical path when accomplishing
regular circular illumination, but it is also possible to omit use
of this diffractive optical element 61.
[0138] In addition, it is also possible to use, as necessary, a
fly-eye lens or diffractive optical element in place of the micro
fly's eye lens as a diffused light beam forming element.
[0139] Furthermore, with the above-described embodiment, a
diffractive optical element is employed as a light beam changing
element, but this is intended to be illustrative and not limiting.
It is also possible to employ a refractive optical element such as
a micro fly's eye lens or a microlens prism, as shown in the fifth
embodiment described below.
[0140] Furthermore, with the above-described embodiment, an
aperture stop for restricting the light beams of the secondary
light source is positioned adjacent the back side focal plane of
the fly-eye lens 8. However, it is also possible to have an
arrangement where the aperture stop is omitted and the light beams
from the secondary light source are completely unrestricted, e.g.,
by making the cross-sectional area of each lens element comprising
the fly-eye lens sufficiently small.
[0141] In addition, with the above-described embodiment, the
present invention was described using as an example a projection
optical apparatus provided with an illumination optical apparatus,
but it is clear that it is possible to apply the present invention
to a general illumination optical apparatus for uniformly
illuminating a target illumination surface other than a mask.
[0142] In the above-described embodiment, light from the secondary
light source formed at the position of the aperture stop 9 is
condensed by the condenser lens 10 functioning as a light-guiding
optical system and overlappingly illuminates the mask 11, but an
illumination field aperture stop (mask blind) and a relay optical
system for forming an image of this illumination field aperture
stop on the mask 11 can be positioned between the condenser lens 10
and the mask 11. In this case, the light-guiding optical system
would include the condenser lens 10 and the relay optical system,
the condenser lens 10 would condense light from the secondary light
source formed at the position of the aperture stop 9 and
overlappingly illuminate the illumination field aperture stop, and
the relay optical system would form an image of the aperture of the
illumination field aperture stop on the mask 11.
[0143] In addition, in the above-described embodiment, a fly-eye
lens 8 which is a wave front dividing (splitting) integrator is
employed as an optical integrator, but if an internal reflection
type (Rod-type) integrator (e.g., light pipe, light tunnel, glass
rod, etc.) is used as the optical integrator, the system should be
arranged as described below. That is, a condenser optical system
should be added on the downstream side of the zoom lens 7 to form a
conjugate surface to the diffractive optical element 6.
Furthermore, the rod-type integrator should be positioned such that
the incident edge is positioned adjacent this conjugate plane.
Additionally, a relay optical system is preferably positioned for
forming an image of the illumination field aperture stop positioned
at the exit side surface or adjacent the exit side surface of this
rod-type integrator on the mask 11. In the case of this
arrangement, the second prescribed plane is the pupil plane of the
composite system of the zoom lens 7 and the above-described
condenser optical system, and the secondary light source is formed
on the pupil plane of the relay optical system (a virtual image of
the secondary light source is formed adjacent the incident side of
the rod-type integrator). In this case, the relay optical system
used for guiding light beams from the rod-type integrator to the
mask 11 becomes the light-guiding optical system.
[0144] Second Embodiment
[0145] FIG. 12 is a schematic diagram of an illumination optical
system in which a light beam shape changing element is positioned
upstream of an angular light beam forming element. That is, the
embodiment shown in FIG. 12 has the relative positions of the light
beam shape changing element and the angular light beam forming
element reversed compared to the embodiment shown in FIG. 1.
[0146] The system shown in FIG. 12 is similar in many respects to
that in FIG. 1, so description of common elements, functions or
other features is not provided.
[0147] Light beams transmitted by the beam expander 2 are deflected
in the Y direction by a folding mirror 3 and are incident on a
conical prism 6. The surface of the conical prism 6 on the mask 11
side (the surface to the right in the drawing) is formed in a
planar shape orthogonal to the optical axis AX. The surface of the
conical prism 6 on the light source 1 side (the surface to the left
in the drawing) has a conical concave surface. More specifically,
the refractive surface of the conical prism 6 on the light source 1
side corresponds to a surface of a cone symmetric with respect to
the optical axis AX. Accordingly, light beams incident on the
conical prism 6 are deflected along all directions at the same
angle centered about the optical axis AX and are then incident on
the afocal zoom lens 5. In this way, the conical prism 6 comprises
a light beam shape changing member for diffusing light beams from
the light source 1 into substantially annular light beams.
[0148] In FIG. 12, the conical concave surface of the conical prism
6 faces the light source 1 side, but the conical prism 6 can be
positioned such that the conical concave side faces the mask 11
side. In addition, the conical prism 6 is interchangeable with a
pyramidal prism 6a as another light beam shape changing member. The
composition and action of this pyramidal prism 6a will be described
below.
[0149] Similar to the embodiment shown in FIG. 1, the afocal zoom
lens 5 can be adjusted to continuously change the magnification
within a predetermined range while maintaining an afocal
system.
[0150] Interchanging of the conical prism 6 and pyramidal prism 6a
is performed by a driving system 22 which operates on the basis of
commands from a control system 21. In addition, changing the
magnification of the afocal zoom lens 5 is accomplished by a zoom
driving system 23 on the basis of commands from the control system
21.
[0151] Light beams from the prism 6 that are incident on the afocal
zoom lens 5 form a ring-shaped light source image at the pupil
plane of the lens 5. Light from the ring-shaped light source image
forms substantially parallel light beams and exits from the afocal
zoom lens 5, to be incident on a first fly-eye lens 4 (an angular
light beam forming element) that functions as a first optical
integrator. Light beams from oblique directions substantially
symmetrical with respect to the optical axis AX are incident on the
incident surface of the first fly-eye lens 4. In other words, light
beams are obliquely incident along all directions at the same angle
centered about the optical axis AX.
[0152] The first fly-eye lens 4 includes, for example, of a
plurality of lens elements each having a square cross-section and a
positive refractive power, said lens elements arranged in the
vertical and horizontal directions along the optical axis AX. The
surface on the incident side of each lens element is formed into a
spherical shape with the convex surface facing the incident side,
and the exit side surfaces are formed into a planar shape.
[0153] Accordingly, light beams incident on the first fly-eye lens
4 are partitioned two-dimensionally by the plurality of lens
elements, and one ring-shaped light source image is formed at the
back side focal plane of each lens element. Light beams from the
plurality of ring-shaped light source images formed at the back
side focal plane of the first fly-eye lens 4 pass through a zoom
lens 7 and then overlappingly illuminate a second fly-eye lens 8
which functions as a second optical integrator. The zoom lens 7 is
a relay optical system that can continuously change its focal
length within a predetermined range, and links the back side focal
plane of the first fly-eye lens 4 and the back-side focal plane of
the second fly-eye lens 8 as substantially optical conjugates. In
addition, the zoom lens 7 comprises a telecentric optical system on
the back side. In order to satisfy the above-described conjugate
relationship and telecentricity, the zoom lens 7 is preferably a
multi-group zoom lens with at least three zoom lens groups capable
of independent movement. Changing the focal length of the zoom lens
7 is accomplished through a zoom driving system 24 which operates
on the basis of commands from the control system 21.
[0154] Accordingly, at the incident surface of the second fly-eye
lens 8, an illumination field with a shape in which infinitely many
illumination fields each having a square shape similar to the
cross-sectional shape of each lens element of the first fly-eye
lens 4 are arranged at positions equidistant from the optical axis
AX, that is to say an annular illumination field centered about the
optical axis AX, is formed.
[0155] The second fly-eye lens 8 includes a plurality of lens
elements, each having a positive refractive power, arranged in the
vertical and horizontal directions along the optical axis AX, the
same as the first fly-eye lens 4. However, each lens element
comprising the second fly-eye lens 8 has a rectangular
cross-section similar to the shape of the illumination field to be
formed on the mask (and hence, the shape of the exposure region to
be formed on the wafer). In addition, the surface on the incident
side of each lens element in the second fly-eye lens 8 is formed in
a spherical shape or an aspherical shape with the convex surface
facing the incident side, and the surface on the exit side is
formed in a spherical shape or an aspherical shape with the convex
surface facing the exit side.
[0156] Accordingly, light beams incident on the second fly-eye lens
8 are partitioned two-dimensionally by the plurality of lens
elements, and a plurality of light source images are respectively
formed at the back side focal plane of each lens element on which
the light beams are incident. In this way, a plural light source
(hereafter referred to as the "secondary light source") of the same
annular shape as the illumination field formed by the light beams
incident on the second fly-eye lens 8 is formed at the back side
focal plane of the second fly-eye lens 8.
[0157] Light beams from the annular secondary light source formed
at the back side focal plane of the second fly-eye lens 8 are
incident on an aperture stop 9. This aperture stop 9 is supported
on a turret capable of rotating about a predetermined axis parallel
to the optical axis AX. The turret can be constructed the same as
or similar to the turret described above and shown in FIG. 6.
[0158] In FIG. 12, annular secondary light sources are formed at
the back side focal plane of the second fly-eye lens 8, and
consequently one of the annular aperture stops is preferably
selected from the three annular aperture stops 401, 403 and 405 as
the aperture stop 9. However, the composition of the turret shown
in FIG. 6 is intended to illustrative and not limiting with regard
to the type or number of aperture stops positioned thereon or even
the use of a rotating turret for the aperture stop 9.
[0159] Light from the secondary light sources that passes through
the aperture stop 9 having an annular aperture (light transmission
area) is condensed by a condenser optical system 10, and then
uniformly illuminates a mask 11 in an overlapping manner. Light
beams that pass through the pattern on the mask 11 form an image of
the mask 11 pattern on a wafer 13 via the projection optical system
12.
[0160] FIG. 13 schematically shows the illumination optical system
from the conical prism 6 to the incident surface of the first
fly-eye lens 4.
[0161] As shown in FIG. 13(a), light beams deflected by the conical
prism 6 along all directions at the same angle .alpha. centered
about the optical axis AX pass through the afocal zoom lens 5
having a magnification ml and are then obliquely incident on the
incident surface of the first fly-eye lens 4 along all directions
at the same angle .THETA.1 centered about the optical axis AX. The
size of the illumination field formed at the incident surface of
the first fly-eye lens 4 is dl.
[0162] As shown in FIG. 13(b), when the magnification of the afocal
zoom lens 5 is changed from m1 to m2, light beams deflected by the
conical prism 6 along all directions at the same angle .alpha.
centered about the optical axis AX pass through the afocal zoom
lens 5 having a magnification m2 and are then obliquely incident on
the incident surface of the first fly-eye lens 4 along all
directions at the same angle .THETA.2 centered about the optical
axis AX. At this time, the size of the illumination field formed at
the incident surface of the first fly-eye lens 4 is d2.
[0163] The relationships shown by equations (8) and (9) below hold
for the angles of incidence .THETA.1 and .THETA.2 of the light
beams on the incident surface of the first fly-eye lens 4, the
sizes d1 and d2 of the illumination fields formed at the incident
surface of the first fly-eye lens 4, and the magnifications m1 and
m2 of the afocal zoom lens 5.
.THETA.2=(m1/m2).times..THETA.1 (8)
d2=(m2/m1).times.d1 (9)
[0164] With reference to equation (8), it can be seen that it is
possible to continuously change the incident angle .THETA. of the
light beams on the incident surface of the first fly-eye lens 4 by
continuously changing the magnification m of the afocal zoom lens
5.
[0165] FIG. 14 schematically shows the illumination optical system
from the first fly-eye lens 4 to the aperture stop 9.
[0166] In FIG. 14(a), light beams incident at a predetermined angle
from a predetermined direction onto the incident surface of the
first fly-eye lens 4 pass through each lens element and are then
obliquely incident on the zoom lens 7 while-maintaining the same
angle. Thus, an illumination field having a predetermined width at
a position eccentric to the optical axis AX by a predetermined
distance is formed on the incident surface of the second fly-eye
lens 8, as indicated by the solid lines in the drawing.
[0167] In actuality, light beams are incident on the incident
surface of the first fly-eye lens 4 from oblique directions
substantially symmetrical about the optical axis AX, as shown by
the dashed lines in the drawing. In other words, light beams are
incident along all directions at the same angle centered about the
optical axis AX. Accordingly, at the incident surface of the second
fly-eye lens 8, an annular illumination field centered about the
optical axis AX is formed, as shown in FIG. 14(b). In addition, an
annular secondary light source the same as the illumination field
formed at the incident surface is also formed at the back side
focal plane of the second fly-eye lens 8. On the other hand, as
discussed above, an annular aperture (the portion in white in FIG.
14(c)) corresponding to the annular secondary light source is
formed in the annular aperture stop 9 positioned adjacent the back
side focal plane of the second fly-eye lens 8.
[0168] In this manner, when the conical prism 6 is employed as the
light beam shape changing element, it is possible to form an
annular secondary light source with substantially no light loss,
and as a result it is possible to accomplish annular modified
illumination without substantial light loss at the aperture stop
9.
[0169] FIG. 15 schematically shows the illumination optical system
from the conical prism 6 to the incident surface of the second
fly-eye lens 8, and is used to explain the relationship between the
magnification of the afocal zoom lens 5 and the focal length of the
zoom lens 7, and the size and shape of the annular illumination
field formed at the incident surface of the second fly-eye lens
8.
[0170] In FIG. 15, the central light ray of the light beam exiting
from the conical prism 6 at an angle .alpha. centered about the
optical axis AX passes through the afocal zoom lens 5 having a
magnification of m, and is then incident on the first fly-eye lens
4 at an angle .THETA. from the optical axis. The first fly-eye lens
4 includes lens elements each of size "a" and focal length f1. The
central light ray exiting at an angle .THETA. from a lens element
of the first fly-eye lens 4 arrives at the second fly-eye lens 8
via the zoom lens 7 which has a focal length fr. At this time, the
incident range of the light beam at the incident surface of the
second fly-eye lens 8 is a range having a width b centered about a
height y from the optical axis AX. That is to say, the illumination
field formed at the incident surface of the second fly-eye lens 8,
and hence the secondary light source formed at the back side focal
plane of the second fly-eye lens 8, has a width b and a height y
from the optical axis, as shown in FIG. 14(b).
[0171] The exit angle .alpha. from the conical prism 6 and the
incident angle .THETA. on the first fly-eye lens 4 have the
relationship shown in the following equation (10).
.THETA.=(1/m).times..alpha. (10)
[0172] In addition, the height y and width b of the annular
secondary light source are respectively expressed by equations (11)
and (12) below.
y=fr.times.sin .THETA. (11)
b=(fr/f1).times..alpha. (12)
[0173] Accordingly, the annular ratio A stipulated by the ratio of
the inner diameter .o slashed.i to the outer diameter .o slashed.o
of the annular secondary light source is expressed by equation (13)
below.
A=.o slashed.i/.o
slashed.o=(2y-b)/(2y+b)={2f1.times.sin(.alpha./m)-a}/{2f-
1.times.sin(.alpha./m)+a} (13)
[0174] In addition, the outer diameter .o slashed.o of the annular
secondary light source is expressed by equation (14) below.
.o slashed.o=2y+b=fr{2 sin(.alpha./m)+a/f1} (14)
[0175] Changing the form of equation (14), the relationship shown
in equation (15) can be obtained.
fr=.o slashed.o/{2 sin(.alpha./m)+a/f1} (15)
[0176] Thus, with reference to equations (10) and (11), it can be
seen that when only the magnification m of the afocal zoom lens 5
changes with no change in the focal length fr of the zoom lens 7,
the height y of the annular secondary light source changes with no
change in the width b thereof. That is to say, by changing only the
magnification m of the afocal zoom lens 5, it is possible to change
both the size (outer diameter .o slashed.o) and the shape (annular
ratio A) of the annular secondary light source without changing the
width b thereof.
[0177] In addition, with reference to equations (11) and (12), it
can be seen that when only the focal length fr of the zoom lens 7
is changed with no change in the magnification m of the afocal zoom
lens 5, both the width b and height y of the annular secondary
light source change in proportion to the focal length fr. That is
to say, by changing only the focal length fr of the zoom lens 7, it
is possible to change the size (outer diameter .o slashed.o) of the
annular secondary light source without changing the shape (annular
ratio A) thereof.
[0178] Furthermore, with reference to equations (13) and (15), it
can be seen that by changing the magnification m of the afocal zoom
lens 5 and the focal length fr of the zoom lens 7 so as to satisfy
the relationship in equation (15) for an outer diameter .o
slashed.o of a certain size, it is possible change only the shape
(annular ratio A) of the annular secondary light source without
changing the size (outer diameter .o slashed.o) thereof.
[0179] An explanation is now provided below for changes in the
magnification m of the afocal zoom lens 5 and the focal length fr
of the zoom lens 7 for a case wherein the shape (annular ratio A)
of the annular secondary light source is changed without changing
the size (outer diameter .o slashed.o) thereof in accordance with a
specific numerical example.
[0180] In this first numerical example, the deflection angle
.alpha. by the conical prism 6 is taken to be 7 degrees, the size
"a" of each lens element of the first fly-eye lens 4 is taken to be
2.5 mm and the focal length f1 of each lens element is taken to be
50 mm. Furthermore, with the outer diameter .o slashed.o of the
annular secondary light source set to 96 mm and kept constant, the
magnification m of the afocal zoom lens 5 and the focal length fr
of the zoom lens 7 needed in order to change the annular ratio A of
the annular secondary light source from around 0.24 to around 0.95
are respectively found. Table (1) below shows the corresponding
relationships between the magnification m of the afocal zoom lens
5, the annular ratio A of the annular secondary light source, and
the focal length fr of the zoom lens 7 in the first numerical
example.
1TABLE 1 m A fr 0.1 0.94817 49.75678 0.2 0.916468 80.19026 0.3
0.881258 113.9927 0.4 0.846487 147.3723 0.5 0.812679 179.8279 0.6
0.779947 211.2513 0.7 0.748299 241.6332 0.8 0.717711 270.9975 0.9
0.688146 299.3801 1.0 0.659561 326.8211 1.1 0.631915 353.3616 1.2
0.605165 379.0419 1.3 0.57927 403.901 1.4 0.554191 427.9763 1.5
0.529893 451.3031 1.6 0.506338 473.9151 1.7 0.483496 495.8439 1.8
0.461334 517.1198 1.9 0.439822 537.7711 2.0 0.418933 557.8247 2.1
0.39864 577.3059 2.2 0.378918 596.2387 2.3 0.359744 614.6459 2.4
0.341095 632.549 2.5 0.32295 649.9682 2.6 0.305289 666.9228 2.7
0.288092 683.4313 2.8 0.271343 699.5108 2.9 0.255023 715.1778 3.0
0.239117 730.448
[0181] With reference to Table 1, it can be seen that in order to
change the annular ratio A from around 0.5 to around 0.69, it is
only necessary to change the magnification m of the afocal zoom
lens 5 from around 1.6 to around 0.9 and change the focal length fr
of the zoom lens 7 from around 474 mm to around 300 mm.
[0182] As discussed above, the conical prism 6 is interchangeable
with the pyramidal prism 6a. An explanation is now provided for the
case where the pyramidal prism 6a is set in the illumination
optical path instead of the conical prism 6.
[0183] With the pyramidal prism 6a, the mask-side surface has a
planar shape orthogonal to the optical axis AX. In addition, the
light-source-side surface has four refractive surfaces and is
formed with an overall pyramidal concavity facing the light source
1. The four refractive surfaces correspond to the pyramidal
surfaces (the side surfaces without the bottom surface) of a square
pyramid having four ridge lines along the X axis and the Z axis
with one point on the optical axis AX as the vertex. That is to
say, the four refractive surfaces correspond to the pyramidal
surfaces of a square pyramid symmetric about the optical axis AX.
Similar to the case of the conical prism 6, the pyramidal prism 6a
may also be positioned so that the pyramidal concavity faces the
mask 11.
[0184] When the pyramidal prism 6a is positioned in the
illumination optical path, light beams incident on the pyramidal
prism 6a are deflected along four predetermined directions at equal
angles centered about the optical axis AX and are incident on the
afocal zoom lens 5. In this way, the pyramidal prism 6a comprises a
light beam shape changing element that changes the light beams from
the light source 1 into four light beams eccentric to the optical
axis AX. The light beams incident on the afocal zoom lens 5 form
four point-shaped light source images on the pupil plane of the
lens 5. In this case, the quadrilateral joining the four
point-shaped light source images forms a square with sides parallel
to the X axis and the Z axis and centered about the optical axis
AX. Light from these four point-shaped light source images exits
the afocal zoom lens 5 as substantially parallel light beams and is
the incident on the first fly-eye lens 4. Here, light beams from
oblique directions substantially symmetrical with respect to the
optical axis AX are incident on the incident surface of the first
fly-eye lens 4. To be more specific, the light beams are oblique
along four specific directions at equal angles, centered about the
optical axis AX.
[0185] Accordingly, four point-shaped light source images are
respectively formed at the back-side focal plane of each lens
element of the first fly-eye lens 4. Light beams from the plurality
of point-shaped light source images formed at the back side focal
plane of the first fly-eye lens 4 pass through a zoom lens 7 and
then overlappingly illuminate the second fly-eye lens 8.
Accordingly, at the incident surface of the second fly-eye lens 8,
four square illumination fields similar to the cross-sectional
shape of each lens element of the first fly-eye lens 4 made
eccentric (parallel shifted) equidistantly outwardly along four
symmetric radial directions about the optical axis AX are formed.
As a result, as shown in FIG. 16(a) a quadrupole secondary light
source (the portion indicated by the shaded area in FIG. 16(a)) is
also formed at the back side focal plane of the second fly-eye lens
8.
[0186] In conjunction with the switch from the conical prism 6 to
the pyramidal prism 6a, a switch is also preferably made from the
annular aperture stop 9 to aperture stop 9a. The aperture stop 9a
is one quadrupole aperture stop selected from three quadrupole
aperture stops 402, 404 and 406. As shown in FIG. 16(b), four
circular apertures (the parts indicated by the white regions in
FIG. 16(b)) having the size of a circle that can be drawn
substantially inside the four square light sources are formed in
the quadrupole aperture stop 9a. Additionally, as shown in FIG.
16(c) it is also possible to use a quadrupole aperture stop 9a
having four apertures in the shape of quarter circles (the parts
indicated by the white regions in FIG. 16(c)).
[0187] In this manner, even when the pyramidal prism 6a is used as
the light beam shape changing element, it is possible to form a
quadrupole secondary light source without substantial light loss,
and as a result it is possible to accomplish quadrupole modified
illumination while satisfactorily suppressing light loss in the
aperture stop 9a.
[0188] Furthermore, by changing only the magnification m of the
afocal zoom lens 5, it is possible to change the position of the
light center of the four square light sources in the quadrupole
secondary light source. In other words, it is possible to change
the size and shape of the quadrupole secondary light source without
changing the width thereof. As shown by the dashed lines in FIG.
16(a), it is possible to define the size and shape of the
quadrupole secondary light source similarly to that of an annular
secondary light source. The annular ratio of the quadrupole
secondary light source can be defined on the basis of the ratio .o
slashed.i/.o slashed.o. In this case, the width b of the quadrupole
secondary light source is defined as {fraction (1/2)} the
difference between the diameter .o slashed.i of the small circle
and the diameter .o slashed.o of the large circle.
[0189] In addition, by changing only the focal length fr of the
zoom lens 7, it is possible to change only the size of the
quadrupole secondary light source without changing the shape
(annular ratio) thereof. Furthermore, by changing the magnification
m of the afocal zoom lens 5 and the focal length fr of the zoom
lens 7 so as to satisfy a prescribed relationship, it is possible
to change only the shape of the quadrupole secondary light source
without changing the size thereof.
[0190] On the other hand, when the conical prism 6 is withdrawn
from the illumination optical path, light beams having a square
cross-section are incident along the optical axis AX on the afocal
zoom lens 5. The light beams incident on the afocal zoom lens 5 are
reduced or enlarged in accordance with the magnification of the
lens, exit from the afocal zoom lens 5 along the optical axis AX
while maintaining a square cross-section, and are then incident on
the first fly-eye lens 4. Accordingly, one point-shaped light
source image is formed at the back side focal plane of each lens
element of the first fly-eye lens 4. In addition, at the incident
surface of the second fly-eye lens 8, a square illumination field
similar to the cross-sectional shape of each lens element of the
first fly-eye lens 4 is formed, centered about the optical axis AX.
As a result, a square secondary light source centered about the
optical axis AX can also be formed at the back side focal plane of
the second fly-eye lens 8.
[0191] In conjunction with withdrawing the conical prism 6 from the
illumination optical path, the annular aperture stop 9 is
preferably interchanged with the circular aperture stop 9b. The
circular aperture stop 9b is selected from the two circular
aperture stops 407 and 408, and has an aperture size that can be
substantially inscribed in the square secondary light source.
[0192] In this way, it is possible to form a square secondary light
source without substantial light loss, and to accomplish regular
circular illumination while satisfactorily suppressing light loss
in the aperture stop.
[0193] In this case, by changing the magnification m of the afocal
zoom lens 5 or the focal length fr of the zoom lens 7, it is
possible to appropriately change the size of the square secondary
light source.
[0194] With the above embodiment, light beam shape changing element
is positioned in the optical path between the light source and an
angular light beam forming element. The light beam shape changing
element converts light beams from the light source into light beams
incident on the angular light beam forming element from oblique
directions substantially symmetrical with respect to the standard
optical axis. Specifically, the light beam shape changing element
can include a conical prism or a pyramidal prism, although it is
also possible to employ a diffractive optical element, as discussed
above.
[0195] Light beams the shape of which has been altered by the light
beam shape changing element are condensed by a condenser optical
system and are overlappingly incident on the angular light beam
forming element from oblique directions substantially symmetrical
with respect to the standard optical axis. In this manner, a first
plural light source is formed by the angular light beam forming
element. Light beams from the first plural light source are
condensed by a relay optical system and are guided to an optical
integrator. As a result, it is possible to form an annular light
source or a plurality of light sources eccentric to the standard
optical axis as a second plural light source, that is to say a
secondary light source, using the optical integrator.
[0196] Here, when a conical prism is employed as the light beam
shape changing element, an annular light source is formed, and when
a pyramidal prism is employed, a plurality of light sources
eccentric to the optical axis are formed. In particular, when a
four-sided pyramidal prism (hereafter referred to simply as
"pyramidal prism") is employed as the pyramidal prism, a secondary
light source composed of four light sources symmetrically eccentric
to the standard optical axis, that is to say a quadrupole secondary
light source, is formed. In this way, light beams from the annular
or quadrupole secondary light source formed by the optical
integrator illuminate the target illumination surface after being
restricted by an aperture stop preferably having an aperture
corresponding to the size and shape of the secondary light source.
Moreover, it is possible to use a multi-sided (e.g., an
eight-sided) pyramidal prism as the pyramidal prism.
[0197] In addition, with the present embodiment the condenser
optical system can include a zoom optical system of variable
magnification, and by changing the magnification of the zoom
optical system, it is possible to alter the annular ratio of the
annular light source formed as the second plural light source or to
alter the position of each light center of the plurality of light
sources formed as the second plural light source. Furthermore, if
the relay optical system positioned in the optical path between the
angular light beam forming element and the optical integrator
includes a zoom optical system of variable magnification, it is
possible to alter the size of the second plural light source by
changing the zoom ratio of this zoom optical system.
[0198] Third Embodiment
[0199] FIG. 17 schematically shows an illumination optical system
according to a third embodiment of the present invention. In
addition, FIGS. 18 and 19 are used to explain the action of the
diffractive optical element in this embodiment. In the drawings
relating to the embodiment and variations below (FIG. 17, FIG. 21
and FIG. 22), the input means 20, the control system 21, the light
beam shape changing member driving system 22, the zoom driving
systems 23 and 24 and the turret driving member 25 (which does not
exist in FIG. 12) are omitted.
[0200] The third embodiment has a composition similar to that of
the second embodiment. However, the only fundamental difference is
that in this embodiment diffractive optical elements are employed
as light beam shape changing elements. Accordingly, in FIG. 17,
elements having the same function as elements in the first and
second embodiments are assigned the same reference numbers as in
FIG. 1.
[0201] Light beams that pass through a beam expander 2 are
deflected by the folding mirror 3 and are then incident on a
diffractive optical element 6b. The diffractive optical element 6b
in this example includes binary or multiple levels (or steps)
having a pitch on the order of the wavelength of the exposure light
(illumination light) formed on a glass substrate, and diffracts the
incident beam to a desired angle. Specifically, as shown in FIG.
18(a), a narrow light beam orthogonally incident on the diffractive
optical element 6b along the optical axis AX is diffracted in all
directions at equal angles centered about the optical axis AX, and
forms a ring-shaped beam. Accordingly, when a parallel beam of
square cross-section is incident on this diffractive optical
element 6b along the optical axis AX, an annular beam results, as
shown in FIG. 18(b). Thus, the diffractive optical element 6b
constitutes a light beam shape changing element that diffuses light
beams from the light source 1 into annular light beams.
[0202] That is to say, the diffractive optical element 6b has the
same action as the conical prism 6 in deflecting beams orthogonally
incident thereon along the optical axis AX into beams in all
directions at equal angles centered about the optical axis AX.
However, whereas the conical prism 6 deflects the entirety of the
incident light beams in all directions at equal angles centered
about the optical axis AX, the diffractive optical element 6b
deflects each beam comprising the incident light beam in all
directions at equal angles centered about the incident axis thereof
(parallel to the optical axis AX). Accordingly, the afocal zoom
lens 5 is configured so as to link the diffractive optical element
6b and the incident surface of the first fly-eye lens 4 as
substantially optically conjugate.
[0203] In this way, as in the second embodiment, a ring-shaped
light source image is formed at the pupil plane of the afocal zoom
lens 5. Furthermore, substantially parallel light beams exiting
from the afocal zoom lens 5 are obliquely incident on the incident
surface of the first fly-eye lens 4 in all directions at equal
angles centered about the optical axis AX. As a result, an annular
secondary light source is formed at the back side focal plane of
the second fly-eye lens 8 without substantial light loss. In
addition, light loss for the most part does not occur at the
aperture stop 9 positioned adjacent the back side focal plane of
the second fly-eye lens 8. Furthermore, by appropriately changing
the magnification m of the afocal zoom lens 5 and the focal length
fr of the zoom lens 7, it is possible to change the size and shape
(annular ratio) of the annular secondary light source, the same as
in the first embodiment.
[0204] In the third embodiment, the diffractive optical element 6b
is interchangeable with another diffractive optical element 6c.
When the diffractive optical element 6b is withdrawn from the
illumination optical path, it is possible to accomplish regular
circular illumination the same as when the conical prism 6 and
pyramidal prism 6a are withdrawn in the second embodiment. The case
wherein the diffractive optical element 6c instead of the
diffractive optical element 6b is set in the illumination optical
path is explained below.
[0205] When the diffractive optical element 6c is used as the light
beam shape changing element, narrow beams orthogonally incident
along the optical axis AX are diffracted along four specific
directions at equal angles centered about the optical axis AX, and
form four narrow beams, as shown in FIG. 19(a). Accordingly, when
parallel beams with a square cross-section are incident on this
diffractive optical element 6c along the optical axis AX,
quadrupole beams result, as shown in FIG. 19(b). Thus, the
diffractive optical element 6c constitutes a light beam shape
changing element that changes light beams from the light source 1
into four light beams eccentric to the optical axis AX.
Accordingly, four point-shaped light source images are formed at
the pupil plane of the afocal zoom lens 5, the same as when the
pyramidal prism 6a is employed in the second embodiment.
[0206] Furthermore, substantially parallel light beams exiting from
the afocal zoom lens 5 are then obliquely incident on the incident
surface of the first fly-eye lens 4 along four specific directions
at equal angles centered about the optical axis AX. As a result, a
quadrupole secondary light source is formed at the back side focal
plane of the second fly-eye lens 8 without substantial light loss.
In addition, this quadrupole secondary light source is restricted
while satisfactorily suppressing light loss by an aperture stop 9a
positioned adjacent the back side focal plane of the second fly-eye
lens 8. Furthermore, by appropriately changing the magnification m
of the afocal zoom lens 5 and the focal length fr of the zoom lens
7, it is possible to change the size and shape of the quadrupole
secondary light source.
[0207] FIG. 20 schematically shows a configuration of an
illumination optical device according to a first variation of the
third embodiment. FIG. 20(b) shows a state in which the
magnification of the afocal zoom lens 5 is expanded more than the
state shown in FIG. 20(a).
[0208] This first variation differs from the third embodiment only
in that a micro fly's eye lens 4a is employed as the first optical
integrator (angular light beam forming element).
[0209] In the first variation shown in FIG. 20, a micro fly's eye
lens 4 is employed instead of the first fly-eye lens 4. The micro
fly's eye lens 4 is an optical element that includes a plurality of
microlenses arranged in the horizontal and vertical directions, and
for example is formed by etching a plane parallel glass plate.
Accordingly, each microlens is smaller than each lens element in a
typical fly-eye lens, but the element is the same as the fly-eye
lens in that lens elements having a positive refractive power are
arranged in the horizontal and vertical directions. Accordingly,
the micro fly's eye lens 4 accomplishes the same action as the
first fly-eye lens 4.
[0210] Changes in the magnification m of the afocal zoom lens 5 and
the focal length fr of the zoom lens 7 when changing only the shape
(annular ratio A) of the annular secondary light source without
changing the size (outer diameter .o slashed.o) thereof in the
first variation employing the diffractive optical element 6b and
the micro fly's eye lens 6a are now explained below with reference
to a specific numerical example.
[0211] In this second numerical example, the diffraction angle
(deflection angle) a by the diffractive optical element 6b is taken
to be 7 degrees, the size "a" of each microlens in the micro fly's
eye lens 6a is taken to be 0.5 mm and the focal length f1 of each
microlens is taken to be 10 mm. Furthermore, with the outer
diameter .o slashed.o of the annular secondary light source set to
96 mm and kept constant, the magnification m of the afocal zoom
lens 5 and the focal length fr of the zoom lens 7 needed in order
to change the annular ratio A of the annular secondary light source
from around 0.24 to around 0.95 are respectively found. Table 2
below shows the corresponding relationships among the magnification
m of the afocal zoom lens 5, the annular ratio A of the annular
secondary light source, and the focal length fr of the zoom lens 7
in the second numerical example.
2TABLE 2 m A fr 0.1 0.94817 49.75678 0.2 0.916468 80.19026 0.3
0.881258 113.9927 0.4 0.846487 147.3723 0.5 0.812679 179.8279 0.6
0.779947 211.2513 0.7 0.748299 241.6332 0.8 0.717711 270.9975 0.9
0.688146 299.3801 1.0 0.659561 326.8211 1.1 0.631915 353.3616 1.2
0.605165 379.0419 1.3 0.57927 403.901 1.4 0.554191 427.9763 1.5
0.529893 451.3031 1.6 0.506338 473.9151 1.7 0.483496 495.8439 1.8
0.461334 517.1198 1.9 0.439822 537.7711 2.0 0.418933 557.8247 2.1
0.39864 577.3059 2.2 0.378918 596.2387 2.3 0.359744 614.6459 2.4
0.341095 632.549 2.5 0.32295 649.9682 2.6 0.305289 666.9228 2.7
0.288092 683.4313 2.8 0.271343 699.5108 2.9 0.255023 715.1778 3.0
0.239117 730.448
[0212] Comparing Table 1 and Table 2, it can be seen that the
corresponding relationships among the magnification m of the afocal
zoom lens 5, the annular ratio A and the focal length fr of the
zoom lens 7 match in the first numerical example and the second
numerical example. This illustrates that when the micro fly's eye
lens 6a is employed instead of the first fly-eye lens 4, it is
possible to achieve the same action numerically as with the first
fly-eye lens 4 by appropriately setting the size a and focal length
f1 of each microlens.
[0213] FIG. 21 schematically shows the composition of an
illumination optical apparatus according to a second variation of
the third embodiment.
[0214] This second variation differs from the third embodiment only
in that the afocal zoom lens 5 is removed and the diffractive
optical element 6b and the first fly-eye lens 4 are positioned
adjacent each other, and the rest of the composition is the same as
that of the third embodiment. Accordingly, in FIG. 21, elements
having the same function as elements in the second embodiment are
assigned the same reference numbers as in FIG. 17.
[0215] As discussed above, the afocal zoom lens 5 links the
diffractive optical element 6b and first fly-eye lens 4 as optical
conjugates, and has the function of changing the angle of the
incident light beams on the incident surface of the first fly-eye
lens 4. Accordingly, even if the afocal zoom lens 5 is removed from
the illumination optical path and the diffractive optical element
6b and the incident surface of the first fly-eye lens 4 are
positioned adjacent each other, the angle of the incident light
beams on the incident surface of the first fly-eye lens 4 is
determined by the diffraction angle of the diffractive optical
element 6b. Accordingly, in the second variation, it is possible to
change the size of the annular secondary light source formed at the
back side focal plane of the second fly-eye lens 8 by changing the
focal length of the zoom lens 7, but it is not possible to change
the annular ratio thereof.
[0216] Fourth Embodiment
[0217] FIG. 22 schematically shows the composition of an
illumination optical apparatus according to a fourth embodiment of
the present invention.
[0218] The fourth embodiment has a composition similar to that of
the second embodiment. However, the only fundamental difference is
that in the second embodiment a fly-eye lens is employed as an
optical integrator, but in this fourth embodiment an internal
reflection type (Rod-type) integrator (e.g., light pipe, light
tunnel, glass rod, etc., hereafter referred to simply as a
"rod-type integrator") is employed as the optical integrator.
Accordingly, in FIG. 22, elements having the same function as
elements in the second embodiment are assigned the same reference
numbers as in FIG. 12.
[0219] In this embodiment, a rod-type integrator 8a and a condenser
lens 7a are mounted in the optical path between the zoom lens 7 and
an imaging optical system 10a, and the aperture stop for
restricting the secondary light source is removed. Here, the
composite optical system composed of the zoom lens 7 and the
condenser lens 7a links the back side focal plane of the first
fly-eye lens 4 and the incident surface of the rod-type integrator
8a as substantially optically conjugate. In addition, the imaging
optical system 10a links the exit surface of the rod-type
integrator 8a and the mask 11 as substantially optically
conjugate.
[0220] The rod-type optical integrator 8a is an internal
reflection-type glass rod formed of a glass material such as silica
glass or fluorite, and uses total reflection at the boundary
surface between the inside and the outside, that is to say at the
inner surface, to form light source images, the number of which
corresponds to the number of internal reflections, along a surface
that is parallel to the rod incident surface and that passes
through the convergence point. Nearly all of the light source
images formed are virtual images, with only the center (i.e., the
convergence point) light source image being a real image. That is
to say, light beams incident on the rod-type integrator 8a are
partitioned in the angular direction by internal reflection, and a
secondary light source which is composed of a plurality of light
source images is formed along a surface that is parallel to the
incident surface of the rod and that passes through the convergence
point. In the case of this fourth embodiment, an annular secondary
light source is formed when the conical prism 6 is employed as the
light beam shape changing element, and a quadrupole secondary light
source is formed when the pyramidal prism 6a is used.
[0221] Light beams from the secondary light source formed by the
rod-type integrator 8a at the incident side thereof are
superimposed at the exit surface thereof, and then pass through the
imaging optical system 10a and uniformly illuminate the mask 11. As
discussed above, the imaging optical system 10a links the exit
surface of the rod-type integrator 8a and the mask 11 (and hence,
the wafer 13) as substantially optically conjugate. Accordingly, a
rectangular illumination field similar to the cross-sectional shape
of the rod-type integrator 8a is formed on the mask 11.
[0222] In this manner, it is possible, while satisfactorily
suppressing light loss as in the above embodiments, to accomplish
annular modified illumination by using the conical prism 6 as the
light beam shape changing element, to accomplish quadrupole
modified illumination by using the pyramidal prism 6a as the light
beam shape changing element, and to accomplish regular circular
illumination by withdrawing the light beam shape changing element
from the illumination optical path. In addition, by appropriately
changing the magnification m of the afocal zoom lens 5 and the
focal length fr of the zoom lens 7, it is possible to change the
size and shape of the secondary light source.
[0223] In accomplishing circular aperture illumination in the
above-described embodiments and variations, the light beam shape
changing element is preferably withdrawn from the illumination
optical path. By withdrawing the light beam shape changing
element(6, 6a, 6b), it is possible to have the composition of a
so-called double fly-eye system, as is disclosed in U.S. Pat. No.
4,497,015 (which corresponds to Japanese Unexamined Patent
Publication No. Sho 58-147708).
[0224] When doing this, in the apparatus having the composition
illustrated in FIGS. 12, 17 and 22, the afocal zoom lens 5 may be
withdrawn at the same time. In addition, in the apparatus having
the composition illustrated in FIG. 21, the first fly-eye lens 4
may be withdrawn at the same time and in its place a different
fly-eye lens suitable for the illumination conditions may be
disposed in the illumination optical path as the first fly-eye
lens. In addition in the third embodiment, it is possible to used a
diffractive optical element which forms a circular illumination
field at a far field to accomplish circular illumination.
[0225] In addition in the fourth embodiment, the conical or
pyramidal prism was employed as the light beam shape changing
element, but it is also possible to employ a diffractive optical
element such as in the third embodiment.
[0226] In addition, in the above-described embodiments and
variations, a prism having a conical concave surface was employed
as the conical prism, but it is also possible to employ a prism
having a convex conical surface. Similarly, for the pyramidal
prism, it is possible to employ a prism having convex pyramidal
surfaces.
[0227] In addition, in the above-described embodiments and
variations, the present invention was explained using as an example
a projection exposure apparatus provided with an illumination
optical apparatus, but it is clear that it is also possible to
apply the present invention to a general illumination optical
apparatus for uniformly illuminating a target illumination surface
other than a mask.
[0228] Furthermore, in the above-described embodiments and
variations, the light source is a KrF excimer laser that supplies
light with a wavelength of 248 nm, or an ArF excimer laser that
supplies light with a wavelength of 193 nm, but naturally the
present invention can be applied to an apparatus provided with a
light source other than this. For example, it is possible to use as
the light source of the present invention a laser light source such
as an F.sub.2 laser that supplies light with a wavelength of 157
nm, or a light source unit or the like composed of the combination
of a laser light source that supplies light at a prescribed
wavelength and a non-linear optical element that changes the light
from the laser light source into light with a wavelength of 200 nm
or less.
[0229] In the second through fourth embodiments, the operation of
interchanging illumination is similar to the first embodiment. In
addition, in the third and fourth embodiments, driving systems and
control systems are not shown in FIGS. 17 and 21. The illumination
optical system of the third embodiment has a driving system which
controls interchanging the diffractive optical elements 6b and 6c,
a zoom driving system which controls the magnification of the
afocal zoom lens 5, a zoom driving system which controls the focal
length of the zoom lens 7, and a driving system which controls the
aperture stops (the turret substrate 400).
[0230] Fifth Embodiment
[0231] FIG. 23 is a schematic diagram of an illumination optical
apparatus according to a fifth embodiment of the present
invention.
[0232] The exposure apparatus of FIG. 23 preferably has either a
KrF or ArF excimer laser as a light source 601. Nearly parallel
light beams emitted from the light source 601 in the direction of
the Y-axis enter the diffractive optical device 604 through the
unit magnification relay optical system 602. In the unit
magnification relay optical system 602, the output side mirror of a
pair of (not shown) resonator mirrors in the light source 601 and
the diffractive optical device 604 are made to be substantially
optically conjugate.
[0233] The diffractive optical device 604 transforms and emits the
entering light with a rectangular cross-section as a nearly
circular cross-section in the far field (Fraunhofer diffraction
region). The light emitted from the diffractive optical device 604
enters is transmitted by an afocal zoom lens 605 to a special
fly-eye lens 606, which is removable relative to the illumination
path.
[0234] FIG. 24A is an oblique view of the special fly-eye lens 606
from the incident direction of the light, and FIG. 24B is an
oblique view of the special fly-eye lens 606 from the exit
direction of the light. In FIG. 24A and FIG. 24B, the same
coordinate system as FIG. 23 is provided.
[0235] The special fly-eye lens 606 has multiple lens surfaces 606a
densely arranged in a matrix shape as shown in FIG. 24A. The
special fly-eye lens 606 also has multiple prism surfaces 606b
densely arranged in a matrix shape as shown in FIG. 24B. The
multiple prism surfaces 606b each correspond to the multiple lens
surfaces 606a. Here, the multiple lens surfaces 606a and the
multiple prism surfaces 606b are formed by performing an etching
process, for example, on parallel flat glass plates.
[0236] FIG. 25 is a cross section of the special fly-eye lens
described in FIG. 24A and FIG. 24B. Preferably, the fly-eye lens
606 has the multiple lens surface 606a and the multiple prism
surface 606b on the front and the back surfaces of one substrate,
as described in FIG. 25A, but it may be structured, as described in
FIG. 25B, in such a manner that the multiple lens surface 631a is
provided on the front surface of a substrate 631 while the multiple
prism surface 632b is provided on the back surface of another
substrate 632. In this case, the surface 631b and the surface 632a,
which face each other, are preferably flat surfaces.
[0237] Moreover, in FIGS. 25A and 25B, an example is shown in which
the multiple lens surfaces 606a (631a) of the fly-eye lens 606 each
has positive refraction power, but these lens surfaces may have
negative refraction power as well.
[0238] The prism array formed on the side of prism surface 606b of
the special fly-eye lens 606 includes, for example, a cluster body
of a first quad small prism set and a cluster body of a second quad
small prism set. The first quad small prism set is shown in FIG.
26A and the second quad small prism set is shown in FIG. 26B.
[0239] In FIG. 26A, the first small prism set comprises a prism
surface 606b1 with a normal line inclined towards the positive Z
direction relative to the XZ plane, a prism surface 606b2 with a
normal line inclined towards the positive X direction relative to
the XZ plane, a prism surface 606b3 with a normal line inclined in
the negative Z direction relative to the XZ plane, and a prism
surface 606b4 with a normal line inclined in the negative X
direction relative to the XZ plane.
[0240] In FIG. 26B, the second small prism set comprises a prism
surface 606b5 obtained by rotating the prism surface 606b1 by -45
around the Y-axis, a prism surface 606b6 obtained by rotating the
prism surface 606b1 -135 around the Y-axis, a prism surface 606b7
obtained by rotating the prism surface 606b1 -225 around the
Y-axis, a prism surface 606b8 obtained by rotating the prism
surface 606b1 -315 around the Y-axis. In this example, clockwise
rotation is defined to be the positive direction.
[0241] Next, a case in which parallel light beams enter the special
fly-eye lens 606 is examined. In this case, multiple point light
sources are formed on the exit side of the special fly-eye lens 606
due to the function of the multiple lens surface 606a of the
special fly-eye lens 606. Moreover, because the front side
(incidence side) of the focal position of the zoom lens 607 is near
the position of the multiple point light sources (rear side (exit
side) focal position of the lens surface 606a), the multiple images
of the lens surfaces 606a are formed overlapping each other on the
rear side (exit side) focal plane of the zoom lens 607 which is
positioned near the incident surface of the fly-eye lens 608. At
this time, due to the function of the prism surfaces 606b1-606b8
which are positioned corresponding to the lens surface 606a, the
positions where the multiple images of the lens surface 606a are
formed vary within the XZ plane.
[0242] FIG. 27A shows an illumination region that is formed on the
incident surface of the fly-eye lens 608 by the light emitted from
the special fly-eye lens 606 and transmitted through the zoom lens
607 when parallel light beams enter the special fly-eye lens 606.
In FIG. 27A, the illumination region 661 is formed by the light
passing through the prism surface 606b1, the illumination region
662 is formed by the light passing through the prism surface 606b2,
the illumination region 663 is formed by the light passing through
the prism surface 606b3, the illumination region 664 is formed by
the light passing through the prism surface 606b4, the illumination
region 665 is formed by the light passing through the prism surface
606b5, the illumination region 666 is formed by the light passing
through the prism surface 606b6, the illumination region 667 is
formed by the light passing through the prism surface 606b7, and
the illumination region 668 is formed by the light passing through
the prism surface 606b8.
[0243] Returning to FIG. 23, the diffractive optical device 604
diffuses the parallel light beams from the light source 601 into
light beams with a predetermined numerical aperture (divergence
angle), and because the afocal zoom lens 605 makes the diffractive
optical device 604 and the special fly-eye lens 606 to be nearly
optically conjugate, the special fly-eye lens 606 is illuminated by
light beams with a numerical aperture (divergence angle)
corresponding to the angle of magnification of the afocal zoom lens
605.
[0244] The diffractive optical device 606 generates light beams
with circular cross-section in the far field, and a cone-shaped
body of light beams enter the special fly-eye lens 606. Here,
cone-shaped light beams entering the special fly-eye 606 may be
considered to be a set of an infinite number of light beams with
multiple angular components. Hence, multiple illumination regions
with slightly different positions in the XZ plane are formed on the
incident surface of the fly-eye lens 608. FIGS. 27B and 27C show
the circular illumination regions 671-678 and 681-688 that are
formed on the incidental surface of the fly-eye lens 608.
[0245] One difference between FIG. 27B and FIG. 27C is that the
vertical angles (divergence angle) of the cone-shaped light beams
entering the special fly-eye lens 606 are different. FIG. 27B shows
the state in which the light beams have a larger divergence angle
than the light beams in FIG. 28C. By changing the divergence angle
of light beams entering the special fly-eye lens 606, the width of
pseudo ring-shaped illumination regions (which includes clusters of
circular illumination regions 671-678 or 681-688) may be changed.
In this case, the distance Rm between the center of the width of
pseudo ring-shaped illumination regions and the optical axis is
constant. The divergence angle of the light beams entering the
special fly-eye lens 606 can be changed by changing the angular
magnification of the afocal zoom lens 605. In fact, the afocal zoom
lens 605 is capable of changing the width of the rings.
[0246] Next, the function of the zoom lens 607 is described in
reference to FIG. 28A and FIG. 28B. FIGS. 28A and 28B respectively
show illumination regions on the incident surface of the fly-eye
lens 608. By changing focal length of the zoom lens 607, the
illumination range enlarges or shrinks proportionally on the
incident surface of the fly-eye lens 608. Here, FIG. 28A shows a
condition in which the focal length of the zoom lens 607 is larger
than the focal length in FIG. 28B. The angular magnification of the
afocal zoom lens 605 is constant in both states shown in FIGS. 28A
and 28B.
[0247] By changing focal length of the zoom lens 607 in the above
manner, the value of the outer radius Ro of the pseudo
annular-shape illumination region may be changed freely while
keeping the ratio (annular ratio) of the inner radius Ri and the
outer radius Ro of the pseudo annular-shape illumination regions
formed in the illumination regions 671-678 or 681-688 constant.
[0248] Moreover, by combining the changing of the angular
magnification of the afocal zoom lens 605 and the changing of the
focal length of the zoom lens 607, the outer radius and the annular
ratio of the pseudo annular-shape illumination region formed on the
fly-eye lens 608 may be set to any desired values.
[0249] Because the fly-eye lens 608 forms a secondary light source
with a shape corresponding to the shape of the illumination region
on its incident surface, the outer radius and the annular ratio of
the annular-shaped secondary light source may be set to any desired
values by changing the angular magnification of the afocal zoom
lens 605 and the focal length of the zoom lens 607.
[0250] Returning to FIG. 23, a variable aperture stop 609, a
condenser lens 610, an illumination field stop 618, and an
illumination field stop imaging optical system 619 are arranged.
Light beams from the fly-eye lens 608 form an annular-shaped
secondary light source whose shape is restricted by a variable
aperture stop 609. Light beams from the annular-shaped light source
are overlapped in the condenser lens 610 and illuminate the
illumination field stop 618. Moreover, the aperture section of the
illumination field stop 618 and a reticle 611 are in a nearly
conjugate relationship through the illumination field stop imaging
optical system 619. Hence, an illumination region, which is an
image of the aperture section of the illumination field stop 618,
is formed on the reticle 611.
[0251] Here, the system from the reticle 611 to the wafer 613
similar to the above embodiments, thus the description of the
system is omitted.
[0252] The apparatus of FIG. 23 also includes a first driving
system 622 for mounting and removing the special fly-eye lens 606
relative to the illumination path, a second driving system 623 for
moving at least one of the plurality of lens groups composing
afocal zoom lens 605 in the direction of optical axis in order to
change the magnification of the afocal zoom lens 605, a fourth
driving system 625 for moving at least one of a plurality of lens
groups in the zoom lens 607 in the direction of optical axis in
order to change the focal length of the zoom lens 607, a fifth
driving system for driving the variable aperture stop 609 in order
to specify the size and the shape of the surface light source
(secondary light source), and a sixth driving system for driving
the variable aperture stop 617 in the projection optical system 612
in order to specify a numerical aperture of the projection optical
system 612. The apparatus in FIG. 23 also includes an input unit
620 for entering information related to the type of reticle (mask),
and a control system 621 for controlling the aforementioned
first-sixth driving systems 622-627 based on the information from
the input unit 620.
[0253] Sixth Embodiment
[0254] FIG. 29 is a schematic diagram of an illumination optical
system according to a sixth embodiment of the present invention.
Light beams from a light source 701, such as an excimer laser, are
shaped into a predetermined shape by a beam expander 702 and are
reflected by a mirror 703 to a first diffractive optical device 751
attached to a revolver 706A. Diffracted light beams from the first
diffractive optical device 751 are gathered by a relay lens 707 and
uniformly and overlappingly illuminate the incident surface of a
fly-eye lens 708, which is a wavefront dividing (splitting) type
integrator. As a result, a substantially surface light source is
formed at the exit surface of the fly-eye lens 708. The relay lens
707 is an imaging optical system, and is designed in such a manner
that the entire effective region near the exit side surface of the
diffractive optical device 751 forms an image over substantially
the entire exit side surface of the fly-eye lens 708.
[0255] Light beams emitted from the surface light source at the
exit side of the fly-eye lens 708 are gathered once overlappingly
by the condenser optical system 710 after the shape of the
transmitted light beams have been restricted by the aperture stop
766 attached to a revolver 706B. Once the light beams are thus
overlapped and pass through the relay optical system 712, they
uniformly and overlappingly illuminate the patterned reticle (or
mask, original projection plate) 714. An illumination field stop
(reticle blind) 711 for determining the illumination region is
arranged in the optical path between the condenser optical system
710 and the relay optical system 712. Moreover, the projection
optical system 715 projection exposes, using uniform illumination
light, the pattern which is formed on the reticle 714 onto the
wafer 716.
[0256] The revolver 706A carries a plurality of diffractive optical
devices 751, 752, 753 and a plurality of auxiliary fly-eye lenses
754, 755, 756, as shown in FIG. 30A. Moreover, the revolver 706A is
structured in such a manner that the rotation of the revolver 706A
around the optical axis AX by the driving motor MT1 enables the
selection of the diffractive optical devices 751, 752, 753 and the
auxiliary fly-eye lenses 754, 755, 756. Similarly, the aperture
stops 761-766 are structured in such a manner that stops with
various aperture shapes are selected by the revolver 706B, as shown
in FIG. 30B.
[0257] When the auxiliary fly-eye lenses 754-756 are selected by
rotating the revolver 706A, the illumination optical system becomes
a double fly-eye lens system (double integrator system). The double
fly-eye lens system is capable of forming multiple
three-dimensional light source images matching the number m*n, a
product of the number m of the lens elements in the auxiliary
fly-eye lens and the number n of the lens elements in the fly-eye
lens 708 on the exit surface of the fly-eye lens 708. Here, the
auxiliary fly-eye lens 754 corresponds to the aperture stop 765,
the fly-eye lens 755 corresponds to the stop 763, and the fly-eye
lens 756 corresponds to the stop 764. A technology for reducing the
amount of light loss for circular aperture stops with different
diameters by switching the first fly-eye lens is disclosed, for
example, in U.S. Pat. No. 5,392,094.
[0258] On the other hand, one of the merits of the present
embodiment is that the first through the third diffractive optical
devices 751-753 are also capable of being selected.
[0259] The first through third diffractive optical devices 751-753
preferably are phase-type diffractive optical devices and are
structured by arranging a plurality of minute phase patterns and
transmission rate pattern. FIG. 31A shows a cross-sectional shape
of the diffractive optical device 751 viewed from the X direction.
Light beams transmitted through the diffractive optical device 751
through the section denoted by A have a zero phase while the light
beams transmitted through the section denoted by B have a delay
phase n. Hence, wave optically, these two sets of light beams
offset each other, resulting in the disappearance of 0.sup.th order
light beams (direct transmission light beams), as shown in FIG.
31B. Hence, light beams transmitted through the diffractive optical
device 751 are diffracted and transmitted through the relay lens 7
as .+-.first order diffracted light beams (or .+-.second and higher
order diffracted light beams). Moreover, light beams passing
through the relay lens 707 become illumination having a delta
function type intensity distribution I on the predetermined
irradiation surface P, as shown in FIG. 31C. By using diffractive
optical devices to which various phase patterns and transmission
rate patterns are added, the desired light intensity distribution
may be obtained on the irradiation surface P, namely the incident
surface of the fly-eye lens 708. The diffractive optical device
need not be arranged as shown in FIG. 31, but can be any device
that diffracts light beams through differences in phases,
transmission rates and refraction rates.
[0260] FIG. 32A is an oblique view showing the incidence state of
light beams into the first diffractive optical device 751 as one
example. FIG. 32B shows a state in which the diffraction light
beams are viewed from the X direction, and FIG. 32C shows a state
in which diffraction light beams are viewed from the Y direction.
Here, assuming the optical axis to be the Z axis, and the vertical
direction perpendicular to the Z axis to be the Y axis and the
horizontal direction perpendicular to the Z axis to be the X axis,
the angle in the ZY plane is denoted by .THETA.y and the angle in
the ZX plane is denoted by .THETA.x. Because the incidental light
beams are diffracted within the diffraction angle ranges of
.THETA.x0-.THETA.x1 and .THETA.y0-.THETA.y1 due to the first order
diffraction characteristics, the cross-sectional shape of the
diffraction light beams become nearly ring-shaped. Moreover, an
annular-shaped light intensity distribution is formed on the
incident surface of the fly-eye lens 708 through the relay lens
707.
[0261] FIG. 33 is a diagram illustrating an illumination region
that is formed on the incident surface of the fly-eye lens 708 by
the first diffractive optical device 751. When the first
diffractive optical device 751 is used, the shape of the
cross-section of the diffracted light beams becomes nearly
ring-shaped due to the first diffraction characteristics. Moreover,
light beams transmitted through the relay lens 707 form a nearly
uniform light intensity distribution only in the ring-shaped
illumination region IA denoted by the shaded area on the incident
surface of the fly-eye lens 708. Here, the ring denoted by the
dotted line is an aperture region AA formed by the aperture stop
766 which is arranged along the optical axis AX corresponding to
the first diffractive optical device 751. As the figure shows
clearly, only the element lenses 708a of the fly-eye lens 708
corresponding to the aperture shape of the aperture stop 766 may be
illuminated by the ring-shaped light beams formed by the first
diffractive optical device 751 and the relay lens 707, and the
light from the light source 701 may be used with a high rate of
efficiency.
[0262] The first diffractive optical device 751 may be made to only
illuminate along the perimeter of element lenses 708a that
contribute to the light beams transmitting through the
annular-shaped aperture stop 766 in order to further increase the
illumination efficiency. In this case, by altering the ranges of
the diffraction angles .THETA.x and .THETA.y of the diffractive
optical device 751 as needed, the multi-angle annular-shaped
illumination region IA with different light intensity distributions
at the central section and at the perimeter region may be formed on
the incident surface of the fly-eye lens 708. Hence, since only the
necessary element lenses 708a are illuminated, the annular-shaped
aperture stop 766 may be illuminated with extremely high
efficiency.
[0263] Moreover, a diffractive optical device having diffraction
characteristics that transform the diffraction light beams into a
polygonal ring-shaped band with the outer shape of a barrel and the
inner shape of a hexagon may be used as the first diffractive
optical device 751, as shown in FIG. 34B. In this case, an
illumination region IA is formed corresponding to the size of only
those element lenses 708a used for illumination among all of the
lenses in the fly-eye lens 708, enabling an increase in
illumination efficiency while maintaining uniform illumination.
[0264] A diffractive optical device having diffraction
characteristics to transform into the illumination region IA with
both an outer and inner shape of an elliptic ring band may be used
as the first diffractive optical device 751, as shown in FIG. 34C.
In this case, only the element lenses 708a of all of the lenses in
the fly-eye lens 708 used for illumination are illuminated,
resulting in an increase in illumination efficiency while
maintaining uniform illumination.
[0265] FIG. 35 shows the relationship between the effective region
of the diffractive optical device 751 and the element lenses 708a
of the fly-eye lens 708, with FIG. 35A showing the diffractive
optical device 751 and FIG. 35B showing part of the fly-eye lens
708. As the figures clearly show, the effective region 751a of the
diffractive optical device 751 and the XY cross-section of each of
the element lenses 708A of the fly-eye lens 708 are set to be both
rectangular and similar. By setting them in this manner, the
macroscopic structure of the light point array LM that is formed at
the exit surface of the fly-eye lens 708 is most dense. In fact,
the uniformity of the macroscopic light intensity distribution at
the position of the aperture stop 766 at the exit side of the
fly-eye lens 708 may be improved, and further, the uniform
illumination of reticle 714 and wafer 716 may be achieved.
[0266] The effective region 751a of the diffractive optical device
751 nearly coincides with the narrower one of the XY cross-section
shape in the vicinity of the exit surface of the region out of the
diffraction device 751 or the XY cross-section shape of the
incident beam entering the diffractive optical device 751. In the
present embodiment, both the region on which the optical element of
the diffractive optical device 751 is formed and the shape of
incident beam entering the diffractive optical element 751 are made
to coincide with the cross-sectional shape of the element lenses
708a in the fly-eye lens 708.
[0267] In changing the illumination conditions, the revolver 706B
may be rotated by the motor MT2, for example, so that the ring
(annular)-shaped stop 763 with a larger diameter (the same shape
but a different diameter than the stop 766) shown in FIG. 30B may
be placed in the optical path. When the aperture stop is switched
to a ring-band stop with a larger diameter in the above manner, the
fly-eye lens 708 may be illuminated without loss in a slight amount
while keeping the first diffractive optical element 751, as long as
the relay lens 7 is a variable focal distance optical system (zoom
optical system).
[0268] Moreover, when the revolver 706B is rotated by the motor MT2
and the aperture stop 761 is selected, the revolver 706A is also
rotated by the motor MT1 to position the second diffractive optical
device 752 in the optical path. The second diffraction device 752
has second diffraction characteristics. The cross-sectional shape
of light beams diffracted by the second diffraction light device
752 have a shape that is scattered in four directions. Light beams
form, after passing through the relay lens 707, an illumination
region IA that has a light intensity distribution with four regions
on the incident surface in the fly-eye lens 708, as shown in FIG.
36A. Hence, useless illumination of the cross-shape region at the
center is eliminated, resulting in highly efficient
illumination.
[0269] More preferably, when one of the four regions having a
polygonal cross-section, particularly one with a pentagonal region
such as that shown in FIG. 36B, is used, optimum illumination
corresponding to the size of the element lenses 708a in the fly-eye
lens 708 is achieved, resulting in a further improvement in
illumination efficiency while maintaining the uniformity of the
illumination.
[0270] If each of the element lenses 708a in the fly-eye lens is
arranged randomly, namely not arranged in a lattice shape, optimum
illumination corresponding to the size of the necessary element
lenses 708a of all of the element lenses in the fly-eye lens 708
may be achieved by using a diffractive optical device having
diffraction characteristics that make the outer shape of the
four-region shape diffracted light into a polygonal shape.
[0271] When the present embodiment is applied to a scanning type
projection exposure apparatus which performs exposure while moving
the reticle as the original projection plate and the substrate as
work relative to the projection optical system, each shape of the
plurality of element lenses 708a of the fly-eye lens 708 is
preferably made rectangular. In this case, if the direction of the
edge of the illumination region being formed on the fly-eye lens
708 is parallel to the direction corresponding to the scanning
direction (typically, the direction along the minor side), the
intensity distribution on the wafer 716 may not be desirably
distributed in the direction perpendicular to the scanning
direction.
[0272] For this reason, particularly with quadrupolar illumination,
the directions of the edges of four illumination regions formed on
the incident surface of the fly-eye lens 708 by the diffractive
optical device 752 and by the relay lens 707 are preferably
inclined in the directions corresponding to the scanning direction
of the plurality of element lenses 708a of the fly-eye lens
708.
[0273] In FIG. 37A, the shapes of four illumination regions IA are
made to be elliptic in order to maintain the edges of the regions
in the direction that is continuously inclined relative to the
scanning direction in the element lenses 708a. Moreover, FIG. 37B
describes the relationship between the illumination region IA and
the incident surfaces of the plurality of element lenses 708a of
the fly-eye lens 708.
[0274] As FIG. 37B clearly shows, the edge of the elliptic
illumination region IA does not intersect the plurality of the
element lenses 708a at the same location. Hence, unevenness
(deviation from the desired distribution) of the intensity
distribution on the surface being irradiated may be reduced.
[0275] In this case, using the aperture stop 766 on the exit side
of the fly-eye lens 708, unevenness in illumination may be reduced
even if the edges of the illumination regions in the plurality of
the element lenses 708a that intersect are not shielded.
[0276] Furthermore, even if the aperture stop 766 is not used (or
in the case of the maximum aperture), uneven illumination may be
reduced. Hence, even if the positions of a plurality of
illumination regions are continuously changed using the relay lens
707 as a zoom optical system, it is unnecessary to continuously
change the positions of aperture unit of the illumination aperture
stop 766 corresponding to the illumination regions.
[0277] Moreover, as shown in FIG. 37C, the shape of four
illumination regions IA may be made to be circular. From a point of
view of improving imaging performance, it is more preferable to
make the shape of a plurality of illumination regions IA elliptic
as shown in FIG. 37A than to make them circular as shown in FIG.
37C, because it makes it possible to separate the light amount
distribution of the third order light source from the optical
axis.
[0278] In a scanning type exposure apparatus, it is not necessary
to consider the direction of the edges of a plurality of the
illumination regions IA even if the direction is the same as the
direction perpendicular to the scanning direction because the
unevenness of illumination along this direction is integrated by
the scanning exposure. Hence, the shapes of a plurality of the
illumination regions IA which are formed by the diffractive optical
device 752 and the relay lens 707 may be hexagonal, as shown in
FIG. 37D. In this case, uneven illumination on the surface being
irradiated may be reduced by setting the system in such a manner
that the edges of the illumination regions IA intersect at an angle
relative to the direction corresponding to the direction of
scanning of the element lenses 708a.
[0279] The shape of the illumination regions are not limited to
hexagonal, but other polygonal shapes may be used as long as the
system is set in such a manner that the edges of the illumination
regions intersect at angle relative to the direction corresponding
to the direction of scanning of the element lenses 708a. In fact,
the shape of the illumination regions IA may be rectangular as
shown in FIG. 37E.
[0280] Moreover, even if the shape of the illumination regions is
hexagonal, uneven illumination is not reduced, which is
undesirable, as long as the edges are parallel to the direction
corresponding to the scanning direction of the element lenses 708a
(for example the illumination region IA shown in FIG. 37D is
rotated 30 around its center of gravity.)
[0281] In the above examples, four illumination regions are formed
on the incident surface of the fly-eye lens 708 assuming
quadrupolar illumination, but the examples may be applied to
multiple polar illumination such as octopolar illumination.
[0282] As described above, when a plurality of illumination regions
are formed by the diffractive optical device and the relay lens on
the incident surface of the wavefront dividing (splitting) type
integrator, imaging performance may be improved and light loss may
be reduced while reducing uneven illumination on the surface being
irradiated, by setting the system in such a manner that the edges
of a plurality of illumination regions are inclined relative to the
direction corresponding to the scanning direction of the wavefront
dividing (splitting) type integrator element lenses. Here, the
imaging performance may be further improved by setting the major
axis of the illumination regions in the tangential direction
(sagittal direction).
[0283] Application of this particular example may not be limited to
the fifth embodiment, can be used with any of the embodiments
described above and below.
[0284] Now, returning to FIG. 29, when the aperture stop 762 is
selected by rotating the revolver 706B, the third diffractive
optical device 753 is positioned in the optical path by rotating
the revolver 706A. The third diffractive optical device 753 has
third diffraction characteristics and across-section of the
diffraction light beams are near circular (barrel shaped) as shown
in FIG. 38. Moreover, the illumination region IA, which is a near
circular light intensity distribution, is formed on the incident
surface of the fly-eye lens 708 through the relay lens 707. For
this reason, the illumination efficiency may be improved
substantially compared to the case in which an auxiliary fly-eye
lens of the prior art is used.
[0285] Although three diffractive optical devices 751-753 with
different diffraction characteristics and three auxiliary fly-eye
lenses with different focal lengths are used, only three
diffractive optical devices 751-753 with different diffraction
characteristics may be used, if desired.
[0286] If each of the element lenses 708a in the fly-eye lens 708
are arranged randomly, namely the element lenses are not arranged
in a lattice, optimum illumination for the size of the element
lenses 708a needed in the fly-eye lens 708 may be achieved by
arranging the diffractive optical device with diffraction
characteristics to make the outer shape of the diffraction light
beams polygonal. As a result, the amount of light loss may be
reduced substantially while maintaining uniformity of the
illumination.
[0287] The effective region of the first diffractive optical device
751 is described above as being similar to the cross-section of the
element lenses 708a of the fly-eye lens 708, but the effective
regions of the second and the third diffractive optical devices
752, 753 can also be respectively similar to the cross-section of
the element lenses 708a of the fly-eye lens 708. Hence, even when
the second and the third diffractive optical devices are selected
with changes in illumination conditions, the uniformity of the
macroscopic light intensity distribution at the positions of
aperture stops 761, 762 on the exit side of the fly-eye lens 708
may be improved, and further, the uniform illumination of the
reticle 714 and the wafer 716 may be achieved.
[0288] Next, a case in which both the first diffractive optical
device 751 with ring-shape divergent characteristics and a circular
aperture stop 765 are used will be described.
[0289] In such combined illumination, the entire illumination
region may be utilized as far as the interior section of the ring
band illumination region formed by the diffractive optical device
751 due to the absence of an inner stop in the annular aperture.
Hence, annular illumination may be achieved while holding light
loss to a minimum. Combined use of the second diffractive optical
device 752 having four-region dispersion characteristics and a
circular stop 765 also results in a similar effect as a case in
which the diffractive optical device 751 and the aperture stop 765
are used together.
[0290] Next, a method of arranging diffractive optical devices
751-753 within the revolver 706A will be described. Each
diffractive optical device is stored in a protection container 770
as shown in FIG. 39. The protection container 770 includes a metal
holder 770a for supporting the diffractive optical devices 751-753,
and a cover glass 770b which is a pair of protective optical
members anchored by and held parallel to each other by the metal
holder 770a. In other words, the diffractive optical devices
751-753 are protected, in the direction of the optical axis, by the
pair of cover glasses 770b from foreign objects, such as gas
generated by oxygen outside of the protection container 770 being
excited by ultra-violet rays. In this case, the attachment of
foreign objects occurs only on the cover glass 770b, hence, even if
the transmission rate deteriorates due to the attachment of the
foreign objects, the recovery of the transmission rate may be
achieved by simply replacing the cover glass 770b without replacing
the relatively more expensive diffractive optical device
751-753.
[0291] Returning to FIG. 29, the diffraction surfaces of the
diffractive optical devices 751-753 are preferably set at a
position offset from a front focus of a relay optical system that
guides the diffraction light beams from any of the diffractive
optical devices 751-753 into the fly-eye lens 708 (optical
integrator), along the optical axis direction. In such a structure,
it becomes possible to reduce the interference noise (interference
fringe) being generated on the reticle 714 or the wafer 716.
[0292] It is preferable that the fly-eye lens 708 has an upstream
cover glass with an obscuration region on the optical axis. The
obscuration region shields the fly-eye lens 708 from 0.sup.th order
diffraction rays caused by the diffractive optical device 751-753,
and prevents the fly-eye lens 708 from damage.
[0293] Seventh Embodiment
[0294] FIG. 40 shows an illumination optical system in accordance
with a seventh embodiment of the invention. The basic structure is
similar to the apparatus in the sixth embodiment, thus, the
description of common portions or features is omitted.
[0295] When the first through the third diffractive optical devices
751-753 are positioned in the optical path, light beams passing
through the diffractive optical device and irradiated onto the
incident surface of the fly-eye lens 708 may result in a
non-uniform illumination intensity distribution due to the noise
caused by a speckled pattern. Hence, a speckled pattern on the
incident surface of the fly-eye lens 708 is made to vibrate by
vibrating the diffractive optical devices 751-753 together with the
revolver 706A by the vibration mechanical unit VB. As a result, the
speckled pattern becomes averaged over the exposure time period,
and uniform light intensity distribution is obtained.
[0296] Furthermore, by arranging a v-shaped (a wedge shaped)
deflection prism DP between the relay lens 707 and the fly-eye lens
708, and by rotating the prism under exposure by the motor MT3 with
the center of said prism DP nearly coinciding with the optical axis
AX, the light intensity distribution formed on the incident surface
of the fly-eye lens 708 may be rotated. As a result, the speckled
pattern also is rotated and the speckled pattern becomes averaged
over the exposure time period, and light beams with uniform
intensity may be obtained, as in the case of vibrating the
diffractive optical devices 751-753. Either the vibration of the
diffractive optical devices or the use of a deflection prism DP, or
both may be adopted.
[0297] Moreover, in the case of the light source 701 emitting pulse
light, the speckled pattern may become averaged by shifting or
tilting the diffractive optical devices 751-753 over a
predetermined number of pulses.
[0298] Eighth Embodiment
[0299] FIG. 41A is a schematic drawing of a portion of the
illumination optical system according to a eighth embodiment of the
invention. In this example, at least the position or the posture of
a portion of relay lens between two optical integrators is changed.
As a result, at least position matching or changing the size of the
illumination region on the downstream optical integrator is
executed, and adjustment of uneven illumination and adjustment of
telecentricity are performed on the wafer. In FIG. 41A, only the
structure between the upstream optical integrator (first optical
integrator) and the downstream optical integrator (second optical
integrator) is described.
[0300] In FIG. 41A, the relay optical system 807 which guides the
light beams from the first optical integrator 805 to the second
optical integrator comprises a front group 807a and a rear group
807b. A vibration mirror 807c is also arranged between the front
group 807a and the rear group 807b. In FIG. 41A, a folded optical
path by vibration mirror 807c is shown in an unfolded state. The
front group 807a and/or the rear group 807b are arranged in such a
manner that minute three dimensional motion and small rotation
around a pair of axes perpendicular to the optical axis is enabled.
A vibration mechanism 872 is connected to the front group 807a
and/or the rear group 807b and changes the position and the posture
of at least the front group 807a or the rear group 807b.
[0301] A driving mechanism 872 either moves the front group 807a
and/or the rear group 807b perpendicular to the optical axis, or
tilts the front group 807a and/or the rear group 807b relative to
the optical axis to perform position matching between the
illumination region formed by the first optical integrator and the
incident surface of the fly-eye lens 808.
[0302] A driving mechanism 873 is also provided for the vibration
mirror 807c to enable three dimensional minute movement or small
rotation around the pair of axes perpendicular to the optical axis
of the vibration mirror 807c. A driving mechanism that changes an
angle of the vibration mirror 807c during exposure time to reduce
interference noise is not shown here and is provided separately
from the driving mechanism 873. Position matching of the
illumination regions on the second optical integrator may be
performed by tilting the vibration mirror 807c relative to the
direction perpendicular to the optical axis.
[0303] The size of the illumination region on the incident surface
of the fly-eye lens 808 may be adjusted by moving at least the
front group 807a or the rear group 807b toward the optical axis
using the driving mechanism 872. In this case, due to the movement
of at least the front group 807a or the rear group 807b toward the
optical axis, the deformation of the relay optical system 807
itself changes and the position of the image formed by the relay
optical system 807 moves toward the optical axis. Hence, the
surface light source formed by the fly-eye lens 808 changes,
enabling adjustment of at least uneven illumination or
telecentricity on the wafer.
[0304] By appropriately operating driving mechanisms 872, 873
described above, uneven illumination and telecentricity may be
adjusted accurately on the pattern surface of the reticle or on the
exposure surface of the wafer. Here, telecentricity refers to the
small amount of tilt of the illumination light beams entering the
wafer 716 and the like, and to the imaging isotropy on the exposure
surface and the like of wafer 716. Uneven illumination and
telecentricity are adjusted by shifting or tilting the optical
elements contained in the condenser optical system provided at the
rear stage of the fly-eye lens 808, but even more precise
adjustment is enabled by combining the minute movement of the
optical elements which constitute the relay lens 807 provided in
the front stage of the fly-eye lens.
[0305] FIG. 41B is a schematic drawing describing a portion of the
illumination optical system of a variation of the eighth embodiment
in an unfolded state. In this example, the relay optical system is
made to be a zoom optical system with a continuously variable focal
length as opposed to the relay optical system being a fixed focal
length optical system.
[0306] In FIG. 41B, the relay optical system 907 which guides light
from the first optical integrator 905 to the second optical
integrator 908 comprises, in the following order from the first
optical integrator 905 side, a positive lens group 907a, a negative
lens group 907b, a positive lens group 907c, and a positive lens
group 907d. Out of a plurality of lens groups 907a-907d, the lens
groups 907b-907d are able to move in the direction of the optical
axis along a predetermined track denoted by an arrow in the figure.
The focal length of the relay optical system 907 is changed by the
movement of the lens groups 907b-907d.
[0307] At least one of the lens groups 907a-907d is structured to
move in the direction of the optical axis independent of the
aforementioned movement for changing the focal length. By this
movement, the deformation of the relay optical system 907 itself is
changed, and the position, in the direction of optical axis, of the
image formed by the relay optical system 907 also changes. As a
result, the image being formed on the second optical integrator 908
becomes out of focus and the surface light source formed by the
second optical integrator 908 changes.
[0308] The driving mechanism 972 is connected to at least one of
lens groups 907b-907d which move in the direction of optical axis
during the focal length change or the lens groups 907a-907d (at
least one out of 907a-907d) which move along optical axis during
defocusing. The driving mechanism 972 is controlled by a control
system connected to the input unit which receives information
corresponding to the type of reticle to be imaged. To be more
specific, the control system controls the driving mechanism 972 so
that the positions of a plurality of lens groups 907b-907d are
changed to the desired positions based on information corresponding
to the type of reticle. Moreover, the driving mechanism 972 changes
the positions, in the direction of the optical axis, of each lens
group 907a-907d.
[0309] At this time, the type of reticle or illumination condition,
and the position of each lens group may be stored beforehand in the
memory connected to the control system, and control of said driving
mechanism 972 may be performed by referring to the data stored in
said memory. Here, intensity distribution on the wafer surface may
be measured and the data stored in the memory may be updated using
the results of the measurement.
[0310] Moreover, instead of storing data in the aforementioned
memory relating to the type of reticle or to the relationship
between the position of each lens group, data concerning the
relationship between the amount of movement of each lens group and
the amount of change of uneven illumination may be pre-stored, and
each lens group may be controlled to operate based on a
relationship equation.
[0311] An illumination meter for measuring the intensity
distribution on the wafer surface is connected beforehand to a
control system so that the position of each lens group may be
changed depending on the intensity distribution on the wafer
surface measured by the illumination meter.
[0312] At least one of the lens groups 907a-907d of the relay
optical system 907 may be made movable on the surface perpendicular
to the optical axis and/or made to be tiltable relative to the
direction perpendicular to the optical axis.
[0313] Now, a case will be examined in which aforementioned
diffractive optical device 751 is adopted as the first optical
integrator 905. In this case, by changing the focal length of the
relay optical system 907, the outer diameter of the annulus may be
changed while maintaining the annular ratio of the illumination
region formed on the second optical integrator 908 constant.
Moreover, by defocusing the imaging position of the relay optical
system 907, the annular ratio may be changed.
[0314] In this example, a four-group zoom lens was adopted for the
relay optical system 907, but a two-group zoom lens, three-group
zoom lens or five-group zoom lens may be adopted instead of the
four-group zoom lens. In order to change the focal length while
maintaining the position of the image from the relay optical system
907 itself constant, it is sufficient to configure the relay
optical system 907 with at least two movable lens groups. In order
to maintain the telecentricity at the second optical integrator 908
constant while maintaining the image position constant during the
time of changing the focal length, the movable lens group in the
relay optical system 907 is preferably a three- or larger group
zoom lens.
[0315] In an illumination apparatus employing a wave surface
splitting type integrator and an inner surface reflection type
integrator, the optical system, for arranging the exit surface of
the wave surface splitting type optical integrator and the incident
surface of the inner surface reflection type integrator to be
conjugate of each other, may be arranged between the two
integrators. In applying such an illumination apparatus to the
above examples, it is sufficient to make the posture and/or the
position of the portion of the optical system arranged between the
two integrators changeable.
[0316] Moreover, variations described above may be applied to any
of aforementioned embodiments. For example, in applying to the
second through fourth embodiments, the relay optical system 7 (or
7a) between the first fly-eye lens 6 and the second fly-eye lens 8
can be replaced with the relay optical system 907.
[0317] As applied to the first embodiment, the relay optical system
7 between the diffractive optical device 6 and the first fly-eye
lens 8 can be replaced with the relay optical system 907.
[0318] As applied to the fifth embodiment shown in FIG. 23, the
relay optical system 607 between the specialty fly-eye lens 606 and
the fly-eye lens 608 can be replaced with the relay optical system
907.
[0319] As applied to the sixth embodiment, the relay optical system
707 between the diffractive optical device 751 (-753) and the
fly-eye lens 708 can be replaced with the relay optical system
907.
[0320] It is also possible to combine the first through eighth
embodiments mentioned above.
[0321] Ninth Embodiment
[0322] FIG. 42 is a schematic diagram of an illumination optical
system of an ninth embodiment of the invention. In this example,
the micro fly's eye lens 4 of the first embodiment, diffractive
optical device 6b of the third embodiment, and the diffractive
optical device 753 of the sixth embodiment are attached to a turret
T1. One of these devices is selected and inserted within
illumination optical path. Moreover, the diffractive optical device
6 of the first embodiment and the fly-eye lens (micro fly's eye
lens) 4 of the third embodiment are attached to a turret T2.
Moreover, the turret T2 also contains an aperture (hole) H. One of
these devices and the hole H is selected and arranged within the
illumination optical path.
[0323] Plural sets of magnification relay optical systems Re1, Re2
and an optical path delaying optical system RT are arranged between
the laser light source 1 and the turret T1. The optical path
delaying optical system is described in Japanese Unexamined Patent
Publication No. Hei. 11-174365, and U.S. patent application Ser.
No. 09/300,660, filed Apr. 27, 1999, which are hereby incorporated
by reference in their entirety. The afocal zoom optical system 5
described in the first through fourth embodiments is arranged
between the turret T1 and the turret T2, and a zoom optical system
7 is arranged between the turret T2 and the fly-eye lens 8.
[0324] By setting the micro array lens 4 on the turret T1 and the
diffractive optical device 6 on the turret T2 on the illumination
optical path, annular illumination is obtained. Moreover, by
setting the diffractive optical device 6b on the turret T1 and the
fly-eye lens 4 on the turret T2 in the illumination optical path,
quadrupolar illumination is obtained. By setting the diffractive
optical device 753 on the turret T1 and the hole H on the turret T2
in the illumination optical path, a regular circular illumination
is obtained.
[0325] Tenth Embodiment
[0326] FIG. 43 is a schematic diagram of an illumination optical
system in accordance with a tenth embodiment of the invention.
[0327] The light source 101 is preferably either KrF (oscillation
wavelength 248 nm) or ArF excimer laser light source (oscillation
wavelength 193 rim), but other light sources can be used. Nearly
parallel light beams emitted from the light source 1001 in the
direction of the Y-axis enter the diffractive optical device 1004
through a magnification relay optical system 1002.
[0328] The diffractive optical device 1004 transforms and emits the
entering excimer laser beam with a rectangular cross-section to
have a nearly ring shaped cross-section in the far field
(Fraunhofer diffraction region) of the diffractive optical device
1004. The diffractive optical device 1004 is equivalent to the
diffractive optical device 751 of the sixth embodiment. Here, the
diffractive optical device 1004 is provided in such a manner that
it is interchangeable with the diffractive optical device 1004b
which is equivalent to the diffractive optical device 752 in the
sixth embodiment and with the diffractive optical device 1004c,
which is equivalent with the diffractive optical device 753.
[0329] In the lower side of the diffractive optical device 1004,
lens group 1005A, a concave prism member 1005B with a concave cone
shape refraction surface, a convex prism member 1005C with a convex
cone refraction surface facing the concave surface of the concave
prism member 1005B, and an annular ratio variable optical system
1005 with a lens group 1005D are arranged.
[0330] The convex prism member 1005C is movable in the direction
along the optical axis of the illumination apparatus. Instead of
moving the convex prism member 1005C, the concave prism member
1005B may be moved, or both the concave prism member 1005B and the
convex prism member 1005C may be moved. Here, the order of the
concave prism member 1005B and the order of the convex prism member
1005C may be reversed.
[0331] Downstream of the annular ratio variable optical system
1005, a zoom optical system 1007 with a plurality of lens groups is
arranged. A zoom optical system equivalent of the zoom optical
system 907 in the eighth embodiment is used, for example, as the
zoom optical system 1007.
[0332] Downstream of the zoom optical system 1007, a fly-eye lens
1008 is arranged as a wave surface splitting type optical
integrator, and downstream of the fly-eye lens 1008, a variable
aperture stop 1009 is arranged.
[0333] At the exit side of the fly-eye lens 1008, a variable
aperture stop 1009, a condenser lens 1010, an illumination field
stop 1018 and an illumination field stop imaging optical system
1019 are arranged. Light beams from the fly-eye lens 1008 form an
annular shaped surface light source due to the function of the
variable aperture stop 609 which restricts a portion of the light
beams. Light beams from the annular shaped surface light source,
after being overlapped by the condenser lens 1010, illuminate the
illumination field stop 1018. The aperture unit of the illumination
field stop 1018 and the reticle 1011 are substantially in a
conjugate relationship due to the illumination field stop imaging
optical system 1019, and the illumination region, which is an image
of the aperture unit of the illumination field stop 1018, is formed
on the reticle 1011.
[0334] In this instance, the systems from the reticle 1011 to the
wafer 1013 are similar to each of aforementioned embodiments, hence
any further explanation is omitted.
[0335] Now, the conjugate relationship of each member will be
described. First, the variable aperture stop 1009 is arranged at
the pupil surface of the illumination apparatus, and the positions
nearly conjugate to the pupil surface of the illumination apparatus
are the front side (incident side) focal plane of the zoom optical
system 1007, the diffraction surface of the diffractive optical
device 1004, and the pupil of the illumination field stop imaging
optical system 1019. Here, the diffraction surface of the
diffractive optical device 1004 may be set at the defocus position
relative to the pupil conjugate surface.
[0336] The incident surface of the fly-eye lens 1008 is positioned
at a position conjugate to the wafer 1013, and the positions nearly
conjugate to the wafer 1013 are the pupil surface of the annular
ratio variable optical system 1005 (the surface on which the rear
focus of the lens (group) 1005A and the front focus of the lens
(group) 1005D coincide), the incident surface of said fly-eye lens
1008 and the illumination field stop 1018, and the pattern surface
of the reticle 1011.
[0337] In the annular ratio variable optical system 1005, the
concave cone prism 1005B receives light beams in a nearly annular
shaped cross-section which are diffracted by the diffractive
optical device 1004. By changing the distance between the concave
cone prism 1005B and the convex cone prism 1005C, the angle of
light beams emitted from the annular ratio variable optical system
1005 to the zoom optical system 1007 is changed.
[0338] Once the angle of light beams received by the zoom optical
system 1007 is changed, the outer diameter (inner diameter) is
changed while the width of the annulus of the annular shape
illumination region formed in the vicinity of the incident surface
of the fly-eye lens 1008 is maintained constant. Moreover, when the
focal length of the zoom optical system 1007 is changed, the outer
diameter (inner diameter) is changed, while the annular ratio (the
ratio of the inner diameter and the outer diameter of the ring) of
the annular shape illumination region formed in the vicinity of the
incident surface of the fly-eye lens 1008 is maintained
constant.
[0339] As a result, the annular shaped illumination region formed
on the incident surface of the fly-eye lens 1008 may be changed to
have an arbitrary outer diameter (inner diameter) and an arbitrary
annular ratio by combining the movement of the prism member in the
annular ratio variable optical system 1005 and the motion to change
the focal length of the zoom optical system 1007. Furthermore, the
outer diameter (inner diameter) and the annular ratio of the
annular shaped secondary light source formed on the exit side of
the fly-eye lens 1008 may be set to arbitrary values.
[0340] A first driving system 1022 for interchanging the
diffractive optical devices 1004, 1004b, 1004c, a second driving
system 1023 for changing the distance between prism members 1005B
and 1005C in the annular ratio variable optical system 1005 in
order to change the angle of light beams from the annular ratio
variable optical system 1005, a fourth driving system 1025 for
moving at least one of the plurality of lens groups in the zoom
lens 1007 in the direction of the optical axis in order to change
the focal length of the zoom lens 1007, a fifth driving system 1026
for driving the variable aperture stop 1009 to specify the size and
the shape of the surface light source (secondary light source), and
a sixth driving system 1027 for driving the variable aperture stop
1017 in the projection optical system 1012 to specify the aperture
number of the projection optical system 1012. An input unit 1020
for entering information concerning the type of reticle (mask), and
a control system 1021 for controlling said first-sixth driving
systems 1022-1027 based on the information from the input unit 1020
are also provided.
[0341] When performing quadrupolar (multi-polar) illumination, the
diffractive optical device 1004b is inserted in the illumination
path. In this case, the positions of four illumination regions
formed on the incident surface of the fly-eye lens 1008 may be
changed by controlling the distance between the prism members 1005B
and 1005C in the annular ratio variable optical system 1005, and
the sizes of the four illumination regions may be changed by
changing the focal length of the zoom optical system 1007.
[0342] By controlling these two optical systems (the annular ratio
variable optical system 1005 and the zoom optical system 1007), the
size and the distance from the optical axis of four surface light
sources formed at the pupil position of the illumination apparatus
may be adjusted freely.
[0343] In performing quadrupolar illumination, a pyramid shaped
prism member is preferably used instead of a cone shape prism
member. In this case, interchanging the cone-shaped prism member
with a pyramid shaped prism member may be automatically executed
with the interchanging of the diffractive optical devices.
[0344] When performing normal illumination, the diffractive optical
device 1004c is inserted in the illumination optical path by the
first driving system 1022. In this case, the size of the circular
surface light source formed at the pupil position of the
illumination apparatus may be adjusted freely by changing the focal
length of the zoom optical system 1007.
[0345] In each of the embodiments above, the downstream-most
optical integrator preferably has a wave splitting number (integral
number) of 300 or larger. Thus, unevenness of illumination on the
surface being irradiated may be reduced by the aperture unit of the
illumination aperture stop arranged on the exit side of the optical
integrator, even if the edge section of the surface light source
including many light sources formed by the wave surface splitting
type optical integrator is not specified.
[0346] The reasons for above are described hereafter. First, the
case in which the shape of each of a plurality of element optical
systems (a plurality of lens surfaces or a plurality of reflection
surfaces) is square and in which a circular irradiation region is
formed on the incident surface of the wave surface splitting type
optical integrator will be examined. In this case, the integral
number N (the number of wave surface splits) of the wave surface
splitting type optical integrator is given by the formula:
N=.pi.(R.sup.2/d.sup.2) (16)
[0347] where d is the length of the side of the element optical
system and R is the radius of the irradiation region.
[0348] In the wave surface splitting region (corresponding to the
irradiation region above) of the wave surface splitting optical
integrator, the number Ns of the splitting regions which exist
around the perimeter is given by the formula:
Ns=2.pi.(R/d) (17)
[0349] Here, the interior of the splitting regions that exist
around the perimeter may suffer uneven illumination with a maximum
uneven illumination in one splitting region around the perimeter
being 100%. However, the intensity of light beams reaching the
splitting regions around the perimeter is weaker than the regions
around the center. Hence, the effect of uneven illumination becomes
small and the degree of the absolute effect on the surface being
irradiated also becomes small.
[0350] Based on a comprehensive analysis of the above factors,
uneven illumination which occurs in one split region around the
perimeter may be estimated as {fraction (1/3)} the unevenness of
that in the region around the center. Moreover, due to the
statistical randomness in the regions around the perimeter, the
square root of the number Ns of the splitting regions around the
perimeter may have an effect on uneven illumination on the surface
being irradiated.
[0351] Hence, in order to reduce the uneven illumination on the
surface being irradiated to 1% or less, the condition;
(({fraction (1/3)})Ns.sup.(1/2))/N<0.01 (18)
[0352] is preferably satisfied. Substituting (16) and (17) above in
(18),
N>249 (19)
[0353] is obtained.
[0354] Hence, the wave surface splitting number by the optical
integrator must exceed about 300 in order to control uneven
illumination on the surface being irradiated, which leads to even
control of uneven illumination on the surface being irradiated, and
particularly when, the illumination conditions are changed.
[0355] In an optical integrator of the illumination apparatus which
is applied to a scanning type exposure apparatus, the shape of the
element optical system is rectangular, but an argument similar to
above argument may be applied. Moreover, the argument used above is
based on the integrator in which the element optical system such as
fly-eye lenses is arranged in a two-dimensional matrix, but the
above argument may be applied to an inner reflection type
integrator such as a rod-type integrator (light pipe, light tunnel,
glass rod).
[0356] In conclusion, in an illumination apparatus employing an
optical integrator which splits incidental light beams from the
light source and which uses the split light beams to illuminate the
surface being irradiated overlappingly, the integral number for the
optical integrator is preferably set to be 300 or larger. As a
result, changes in uneven illumination on the surface being
irradiated may be minimized even if the illumination regions on the
incident surface (the opening angle (aperture angle) of incident
light beams in the case of a wave surface splitting type optical
integrator and in the case of an inner reflection type integrator)
of the optical integrator change.
[0357] The following explains one example of operation when forming
a predetermined circuit pattern on a wafer using an exposure
apparatus of the above embodiments with reference to the flowchart
99 shown in FIG. 44.
[0358] First, after the "start" step 100, in step 101, metal films
are deposited onto each wafer in a lot of wafers. In step 102,
photoresist is coated onto the metal films of each wafer in the lot
of wafers. Subsequently, in step 103, using the exposure apparatus
of any one of above embodiments, the image of the pattern on the
reticle is sequentially exposed and transferred onto the
photoresist (photosensitive material) on each exposure region on
each wafer. Subsequently, in step 104, the photoresist on each
wafer in the lot of wafers is developed. By performing etching
using the resist patterns as a mask in step 105, the circuit
pattern corresponding to the pattern on the reticle is formed in
each exposure region on each wafer. Subsequently, the manufacture
of devices like a semiconductor device is completed by further
forming circuit patterns on upper layers, as indicated by step 106,
"next process."
[0359] In addition, detailed description of the diffractive optical
element that can be used in above embodiments is disclosed in U.S.
Pat. No. 5,850,300, which is hereby incorporated by reference in
its entirety.
[0360] In the above embodiments, it is possible to form the
diffractive optical element for example of silica glass because
exposure light having a wavelength of not less than 180 nm is
utilized by using as the light source a KrF excimer laser
(wavelength: 248 nm) or an ArF excimer laser (wavelength: 193 nm)
or the like.
[0361] When a wavelength of 200 nm or less is used for the exposure
light, it is preferable for the diffractive optical element to be
formed of material selected from among fluorite, silica glass doped
with fluorine, silica glass doped with fluorine and hydrogen,
silica glass with a structure determining temperature of 1200K or
less and an OH-radical concentration of 1000 ppm or greater, silica
glass with a structure determining temperature of 1200K or less and
a chlorine concentration of 50 ppm or less, and silica glass with a
structure determining temperature of 1200K or less and a hydrogen
molecule concentration of 1.times.10.sup.17 molecules/cm.sup.3 or
greater and a chlorine concentration of 50 ppm or less.
[0362] Silica glass with a structure determining temperature of
1200K or less and an OH-radical concentration of 1000 ppm or
greater is disclosed in Japanese patent 2,770,224 (which
corresponds to European patent 720970 B) by the present applicant,
while silica glass with a structure determining temperature of
1200K or less and a hydrogen molecule concentration of
1.times.10.sup.17 molecules/cm.sup.3 or greater, silica glass with
a structure determining temperature of 1200K or less and a chlorine
concentration of 50 ppm or less, and silica glass with a structure
determining temperature of 1200K or less and a hydrogen molecule
concentration of 1.times.10.sup.17 molecules/cm.sup.3 or greater
and a chlorine concentration of 50 ppm or less are disclosed in
Japanese patent 2,936,138 (which corresponds to U.S. Pat. No.
5,908,482) by the present applicant.
[0363] In addition, in the above described embodiments, the fly-eye
lens 8, 608, 708, 808, 908 and 1008 are formed by integrating a
plurality of element lenses, but it is also possible to make this a
micro fly-eye lens. A micro fly-eye lens is created by providing a
plurality of microlens surfaces in a matrix shape through a method
such as etching or the like on an optically transmissive substrate.
With regard to forming a plurality of light source images, there is
no material difference in function between a fly-eye lens and a
micro fly-eye lens, but a micro fly-eye lens has the benefits of
enabling the size of the aperture of a single element lens
(microlens) to be made extremely small, allowing a large reduction
in production costs and greatly reducing the thickness in the
optical axis direction. Moreover, the microlens surface on the
incident and/or exit sides can be formed in an aspherical
shape.
[0364] In the above-mentioned embodiments, a zoom optical system
having the numerical value example shown in FIG. 45 can be used as
the zoom optical systems 7, 607, 707 and 710. FIGS. 45A-D are
diagrams showing the movement path of the respective lens groups
along with the change of the focal length from a maximum focal
length state to a minimum focal length state of the zoom optical
system according to the first numerical value embodiment. FIG. 45A
shows a maximum focal length state (focal length F=570 mm). FIG.
45B shows a first intermediate focal length state (focal length
F=380 mm). FIG. 45C shows a second intermediate focal length state
(focal length F=285 mm). FIG. 45D shows a minimum focal length
state (focal length F=190 mm).
[0365] The zoom optical system relating to this numerical value
embodiment has a first lens group G1 having a positive refractive
power, a second lens group G2 having a negative refractive power, a
third lens group G3 having a positive refractive power, and a
fourth lens group G4 having a negative refractive power.
[0366] Furthermore, in the zoom optical system of this numerical
value embodiment, with respect to a change of the focal length from
the maximum focal length state to the minimum focal length state,
the first lens group G1 through the third lens group G3 move along
the paths shown in FIGS. 45A-D, and the fourth lens group G4 is
fixed. That is, with respect to a change of a focal length from the
maximum focal length state to the minimum focal length state, the
first lens group G1 moves toward the image side (downstream fly eye
lens 8 side), and the second lens group G2 moves toward the object
side (the upstream side). Furthermore, in the minimum focal length
state, the first lens group G1 and the second lens group G2
approach each other.
[0367] Furthermore, with respect to a change of the focal length
from the maximum focal length state to the minimum focal length
state, the third lens group G3 moves toward the object side from a
position (in FIG. 45A) where it approached the fixed fourth lens
group G4.
[0368] Thus, in the zoom optical system of this numerical value
embodiment, the interval between the first lens group G1 and the
second lens group G2 in the maximum focal length state is larger
than the interval between G1 and G2 in the minimum focal length
state, and the interval between the third lens group G3 and the
fourth lens group G4 in the maximum focal length state is smaller
than the interval between G3 and G4 in the minimum focal length
state.
[0369] Thus, in the zoom optical systems of this numerical value
embodiment, when it is considered that an aperture diaphragm is
arranged at a position in which the light source image (secondary
light source) is formed and the incident surface of the fly eye
lens 8 is an image plane, the structure is such that the positions
of the exit pupil and of the entrance pupil and the positions of
the image plane and the object plane do not substantially change
when the focal length changes.
[0370] The following Table 3 shows lens data of a zoom optical
system of this numerical value embodiment. In Table 3, F is the
focal length of the zoom optical system, f1 is the focal length of
the first lens group G1, f2 is the focal length of the second lens
group G2, f3 is the focal length of the third lens group G3, and f4
is the focal length of a fourth lens group G4. Furthermore, d1 is
an axial variable interval between an aperture diaphragm (light
source image formation position, which is pupil conjugate position)
and the first lens group G1, d3 is an axial variable interval
between the first lens group G1 and the second lens group G2, d5 is
an axial variable interval between the second lens group G2 and the
third lens group G3, and d13 is an axial variable interval between
the third lens group G3 and the fourth lens group G4. Furthermore,
the surface numbers are the respective lens surfaces along the
direction in which the light beam proceeds, r is the radius of
curvature (mm) of the respective surfaces, d is the axial interval,
that is, a surface interval (mm) of the respective surfaces, and n
is the refractive index with respect to wavelength of exposure
light.
3TABLE 3 (General system data) Focal length F: 570 mm.about.380
mm.about.285 mm.about.190 mm Zoom ratio: 3 Aperture diaphragm
diameter .phi. (Diameter): 60 mm Light beam incident angle to the
aperture diaphragm A: 0.degree., 2.5.degree., 3.6.degree.,
5.1.degree. (Lens data) Surface number r d n 1 (Aperture (d1 =
Variable) diaphragm) 2 171.43815 18.000000 1.50839 (First lens
group 3 -1132.08474 (d3 = Variable) G1) 4 171.92962 10.000000
1.50839 (Second lens group G2) 5 64.53113 (d5 = Variable) 6
-60.25508 13.000000 1.50839 (Third lens group G3) 7 723.78037
8.551388 8 -675.45783 30.000000 1.50839 9 -110.00000 1.000000 10
1541.19265 40.000000 1.50839 11 -130.00000 1.000000 12 288.43523
30.000000 1.50839 13 -274.48506 (d13 = Variable) 14 -1242.27153
13.000000 1.50839 (Fourth lens group G4) 15 173.46912 60.000000 16
(Image plan) (Variable interval for zooming) First intermediate
Maximum Minimum focal Second intermediate focal length focal length
state focal length state state length state F 190.0 285.0 380.0
570.0 d1 77.96687 24.25432 10.00000 10.00000 d3 15.00000 105.08205
145.98277 172.83221 d5 40.00000 42.40557 51.65276 81.87262 d13
142.49166 103.70659 67.81301 10.74371
[0371] Furthermore, the following Table 4 shows ray tracing data
for a light beam that has an incident angle A on the aperture
diaphragm of 0.degree., a light beam (R1) with an incident angle A
of 2.5.degree., a light beam (R2) with an incident angle A of a
3.6.degree., and a light beam (R3) with an incident angle A of
5.1.degree..
[0372] In Table 4, .theta. is the angle of the chief ray (the light
beam crossing the optical axis in the aperture diaphragm), with
respect to the optical axis, and Y is the distance, that is, the
image height, from the optical axis of the chief ray that reaches
the image plane. Furthermore, the inclination angle of the chief
ray at the image plane is the inclination angle of the chief ray
with respect to the optical axis at the image plane.
4TABLE 4 (Maximum focal length state) Focal length F 570 mm Axial
interval between the aperture diaphragm and 500 mm the image plane
Inclination angle of the chief ray at the image plane 5.4' (R1:
.theta. = 2.5.degree.) Inclination angle of the chief ray at the
image plane 4.5' (R2: .theta. = 3.6.degree.) Inclination angle of
the chief ray at the image plane 4.7' (R3: .theta. = 5.1.degree.)
Image height Y 24.9 mm (R1: .theta. = 2.5.degree.) Image height Y
35.8 mm (R2: .theta. = 3.6.degree.) Image height Y 50.7 mm (R3:
.theta. = 5.1.degree.) (First intermediate focal length state)
Focal length F 380 mm Axial interval between the aperture diaphragm
and 500 mm the image plane Inclination angle of the chief ray at
the image plane 3.0' (R1: .theta. = 2.5.degree.) Inclination angle
of the chief ray at the image plane 3.0' (R2: .theta. =
3.6.degree.) Inclination angle of the chief ray at the image plane
0.4' (R3: .theta. = 5.1.degree.) Image height Y 16.6 mm (R1:
.theta. = 2.5.degree.) Image height Y 23.9 mm (R2: .theta. =
3.6.degree.) Image height Y 33.8 mm (R3: .theta. = 5.1.degree.)
(Second intermediate focal length state) Focal length F 285 mm
Axial interval between the aperture diaphragm and 500 mm the image
plane Inclination angle of the chief ray at the image plane 5.2'
(R1: .theta. = 2.5.degree.) Inclination angle of the chief ray at
the image plane 6.9' (R2: .theta. = 3.6.degree.) Inclination angle
of the chief ray at the image plane 7.9' (R3: .theta. =
5.1.degree.) Image height Y 12.4 mm (R1: .theta. = 2.5.degree.)
Image height Y 17.9 mm (R2: .theta. = 3.6.degree.) Image height Y
25.3 mm (R3: .theta. = 5.1.degree.) (Minimum focal length state)
Focal length F 190 mm Axial interval between the aperture diaphragm
and 500 mm the image plane Inclination angle of the chief ray at
the image plane 3.0' (R1: .theta. = 2.5.degree.) Inclination angle
of the chief ray at the image plane 4.8' (R2: .theta. =
3.6.degree.) Inclination angle of the chief ray at the image plane
8.1' (R3: .theta. = 5.1.degree.) Image height Y 8.3 mm (R1: .theta.
= 2.5.degree.) Image height Y 11.9 mm (R2: .theta. = 3.6.degree.)
Image height Y 16.8 mm (R3: .theta. = 5.1.degree.)
[0373] Furthermore, if the light beam incident upon the fly eye
lens 8 that follows the zoom optical system is inclined with
respect to the optical axis of the respective lens elements of the
fly eye lens 8, eclipse of the light beam is generated at the exit
surface of the fly eye lens 8 and the effectiveness of illumination
deteriorates. According to a general design example, in order to
substantially avoid eclipse of the light beam at the emitting
surface of the fly eye lens 8, the inclination angle needs to be
within approximately .+-.5.degree. with respect to the optical axis
of the chief ray at the image plane of the zoom optical system, and
preferably within approximately .+-.1.degree. in order to properly
suppress the change of the illumination distribution on the
mask.
[0374] With reference to Table 4, in the zoom optical system of the
numerical value embodiment, the inclination angle is extremely
small with respect to the optical axis of the chief ray at the
image plane, and the position of the exit pupil hardly changes from
an infinite distance when the focal length changes. Additionally,
there is absolutely no change in the position of the image plane
when the focal length changes. In addition, needless to say, there
is absolutely no change in the position of the entrance pupil as
well.
[0375] Thus, in the zoom optical system of this numerical value
embodiment, all the lens components are arranged toward the image
plane from the pupil plane, and a desired zoom ratio can be secured
without substantially changing the positions of the emitting pupil
and the incident pupil and the positions of the image plane and the
object plane with respect to the change of the focal length.
[0376] Furthermore, in the above-mentioned numerical value example,
a positive.cndot.negative.cndot.positive.cndot.negative refractive
power arrangement was used, but a
negative.cndot.positive.cndot.negative.cndot.- positive refractive
power arrangement can also be used as shown in the following Table
5.
5TABLE 5 (General system data) Focal length F: 600 mm.about.400
mm.about.300 mm.about.200 mm Zoom ratio: 3 Aperture diaphragm
diameter .phi. (Diameter): 60 mm Light beam incident angle A to the
aperture diaphragm A: 0.degree., 2.4.degree., 3.3.degree.,
4.8.degree. (Lens data) Surface number r d n 1 (Aperture (d1 =
Variable) diaphragm) 2 -185.06450 13.000000 1.50839 (First lens
group G1) 3 3586.41632 (d3 = Variable) 4 384.28464 27.438625
1.50839 (Second lens group G2) 5 -271.20132 1.000000 6 97.04956
39.694311 1.50839 7 -2482.11415 1.000000 8 93.60504 21.938153
1.50839 9 144.92710 17.078265 10 -219.42806 8.000000 1.50839 11
52.67801 (d11 = Variable) 12 -100.31175 13.000000 1.50839 (Third
lens group G3) 13 -199.93788 (d13 = Variable) 14 713.30899
21.983709 1.50839 (Fourth lens group G4) 15 -168.61553 60.000000 16
(Image plane) (Variable interval for zooming) First intermediate
Maximum Minimum focal Second intermediate focal length focal length
state focal length state state length state F 200.0 300.0 400.0
600.0 d1 29.834241 8.531256 15.409789 8.531256 d3 176.157154
121.422675 70.994410 10.000000 d11 60.419144 30.985358 60.209359
162.073170 d13 9.456398 114.927649 129.253380 95.262510
[0377] While the present invention has been described with
reference to preferred embodiments thereof, it is to be understood
that the invention is not limited to the disclosed embodiments or
constructions. To the contrary, the invention is intended to cover
various modifications and equivalent arrangements. In addition,
while the various elements of the disclosed invention are shown in
various combinations and configurations, that are exemplary, other
combinations and configurations, including more, less or only a
single element, are also within the spirit and scope of the
invention.
* * * * *