U.S. patent application number 10/693520 was filed with the patent office on 2004-05-06 for illumination system and exposure apparatus and method.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Komatsuda, Hideki.
Application Number | 20040085645 10/693520 |
Document ID | / |
Family ID | 26387556 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040085645 |
Kind Code |
A1 |
Komatsuda, Hideki |
May 6, 2004 |
Illumination system and exposure apparatus and method
Abstract
An illumination system and exposure apparatus and method
involving illuminating a surface over an illumination field (IF)
having an arcuate shape. The illumination system comprises a light
source (54) for providing a light beam (100), and an optical
integrator (56). The optical integrator comprises a first
reflective element group (60) having an array of first optical
elements (E) each having an arcuate profile corresponding to the
arcuate shape of the illumination field. Each of the first optical
elements has an eccentric reflecting surface (RS.sub.E) comprising
an off-axis section of either a spherical surface (S) or an
aspherical surface (AS.sub.E). The array of first optical elements
is designed so as to form a plurality of arcuate light beams (108)
capable of forming a plurality of light source images (I). The
illumination system further includes a condenser optical system
(64) designed so as to condense said plurality of arcuate light
beams to illuminate the surface over the arcuate illumination field
in an overlapping manner.
Inventors: |
Komatsuda, Hideki;
(Kawasaki, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
26387556 |
Appl. No.: |
10/693520 |
Filed: |
October 27, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10693520 |
Oct 27, 2003 |
|
|
|
10060340 |
Feb 1, 2002 |
|
|
|
10060340 |
Feb 1, 2002 |
|
|
|
09259137 |
Feb 26, 1999 |
|
|
|
6452661 |
|
|
|
|
Current U.S.
Class: |
359/626 |
Current CPC
Class: |
G03F 7/70233 20130101;
G03F 7/70108 20130101; G03F 7/70083 20130101; G03F 7/70358
20130101; G03F 7/70075 20130101 |
Class at
Publication: |
359/626 |
International
Class: |
G02B 027/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 1998 |
JP |
10-047400 |
Sep 17, 1998 |
JP |
10-263673 |
Claims
What is claimed is:
1. An illumination system for illuminating a surface over an
arcuate illumination field, comprising: a) a light source for
providing a light beam; b) optical integrator system capable of
forming from said light beam a plurality of arcuate light beams
capable of forming a plurality of light source images.
2. An illumination system according to claim 1, further comprising
a condenser optical system designed so as to condense said
plurality of arcuate light beams to illuminate the surface over the
arcuate illumination field in an overlapping manner.
3. An illumination system according to claim 2, wherein said
condenser optical system comprises a condenser mirror with a focal
point, said condenser mirror arranged such that said focal point
substantially coincides with the surface.
4. An illumination system according to claim 2, wherein said
condenser optical system comprises a condenser mirror having an
aspherical surface.
5. An illumination system according to claim 2, wherein said
optical integrator system comprises a plurality of reflecting
elements each having a focal length f.sub.F, said condenser optical
system has a focal length f.sub.C, and wherein the condition
0.01<.vertline.f.sub.F/f.sub- .C.vertline.<0.5 is
satisfied.
6. An optical integrator for an illumination system for
illuminating an illumination field having an arcuate shape, the
optical integrator comprising a first reflective element group
having an array of first optical elements each having an arcuate
profile corresponding to the arcuate shape of the illumination
field, and each having a reflecting surface.
7. An optical integrator according to claim 6, wherein said array
of first optical elements has a roughly circular outline.
8. An optical integrator according to claim 6, wherein said
reflecting surface comprises an off-axis section of a spherical
reflecting surface.
9. An optical integrator according to claim 6, wherein said
reflecting surface comprises an off-axis section of an aspherical
reflecting surface.
10. An optical integrator according to claim 6, further comprising
a second reflective element group having a plurality of second
optical elements, each second optical element having a rectangular
shape and a predetermined second reflecting curved surface, said
first and second reflecting element groups being opposingly
arranged such that said first reflecting group is capable of
forming, from a light beam incident thereon, a plurality of light
source images at said plurality of second optical elements.
11. An optical integrator according to claim 10, wherein each
second reflecting curved surface comprises an on-axis section of a
spherical reflecting surface.
12. An optical integrator according to claim 10, wherein said first
optical elements are arranged in a plurality of columns each with a
corresponding axis passing therethrough, and wherein at least one
of said plurality of first optical elements is rotatable about said
corresponding axis so as to be capable of forming, from a light
beam incident thereon, a plurality of light source images at one of
said second optical elements.
13. An illumination system for illuminating a surface over an
arcuate illumination field having an arcuate shape, comprising: a)
a light source for providing a light beam; b) a first optical
integrator comprising a first reflective element group having an
array of first optical elements each having an arcuate profile
corresponding to the arcuate shape of the illumination field and a
reflecting surface, said array of first optical elements designed
so as to form a plurality of arcuate light beams capable of forming
a plurality of light source images.
14. An illumination system according to claim 13, further
comprising a condenser optical system designed so as to condense
said plurality of arcuate light beams to illuminate the surface
over the arcuate illumination field in an overlapping manner.
15. An illumination optical system according to claim 13, wherein
said array of first optical elements has a roughly circular
outline.
16. An illumination optical system according to claim 13, wherein
said reflecting surface comprises an off-axis section of a
spherical reflecting surface.
17. An illumination optical system according to claim 13, wherein
said reflecting surface comprises an off-axis section of an
aspherical reflecting surface.
18. An illumination system according to claim 13, further including
a light beam converting unit removably arranged in said light beam
between said light source and said first optical integrator.
19. An illumination system according to claim 14, wherein said
condenser optical system comprises a condenser mirror with a focal
point, said condenser mirror arranged such that said focal point
substantially coincides with the surface.
20. An illumination system according to claim 14, wherein said
first optical elements each have a focal length f.sub.F, said
condenser optical system has a focal length f.sub.C, and wherein
the condition 0.01<.vertline.f.sub.F/f.sub.C.vertline.<0.5 is
satisfied.
21. An illumination optical system according to claim 13, further
comprising a second reflective element group having a plurality of
second optical elements, each second optical element having a
rectangular shape and a predetermined second reflecting curved
surface, said first and second reflecting element groups being
opposingly arranged such that said plurality of light source images
are formed at said plurality of second optical elements.
22. An optical integrator according to claim 21, wherein each
second reflecting curved surface comprises an on-axis section of a
spherical reflecting surface.
23. An illumination optical system according to claim 13 further
including an auxiliary optical integrator arranged between said
light source and said first optical integrator, said auxiliary
optical integrator having a first auxiliary reflective element
group comprising a first plurality of auxiliary optical elements,
and an opposing second auxiliary reflective element group
comprising a second plurality of auxiliary optical elements
24. An illumination optical system according to claim 23, wherein
said first plurality of first auxiliary optical elements and said
second plurality of second auxiliary optical elements are
identical.
25. An illumination optical system according to claim 24, wherein
each of said first and second auxiliary reflecting optical elements
in said first and second plurality of first and second auxiliary
reflecting optical elements are square.
26. An illumination optical system according to claim 23, further
including a relay reflecting system arranged between said auxiliary
optical integrator and said first optical integrator.
27. An illumination system according to claim 14, further including
an illumination numerical aperture value capable of being varied by
a variable aperture stop having a variable diameter, said variable
aperture stop arranged between said light source and said condenser
optical system.
28. An illumination system according to claim 27, further
comprising a first drive system operatively connected with said
variable aperture stop and capable of changing said variable
diameter.
29. An illumination system according to claim 13, further including
a rotatable turret plate having a plurality of apertures capable of
being inserted into said light beam.
30. An illumination system according to claim 29, further including
a first drive system operatively connected to said turret plate and
a control apparatus electrically connected to said drive system,
said control apparatus being capable of controlling the rotation of
said turret plate so as to insert one aperture of said plurality of
apertures into said light beam.
31. An exposure apparatus for exposing the image of a mask having a
predetermined pattern onto a photosensitive substrate comprising:
a) the illumination system according to claim 13; b) a mask stage
capable of supporting the mask; c) a substrate stage capable of
supporting the photosensitive substrate; and d) a projection
optical system, arranged between said mask stage and said substrate
stage, designed so as to project the predetermined pattern of the
mask onto the photosensitive substrate over an arcuate image field
corresponding to said arcuate illumination field.
32. An exposure apparatus according to claim 31, further including
a first drive system operatively connected to said mask stage, a
second drive system operatively connected to said wafer stage, and
a control system electrically connected to said first and second
drive systems for controlling the synchronous driving of said mask
stage and wafer stage relative to said projection optical
system.
33. An exposure apparatus according to claim 31, wherein said
illumination system includes a first variable aperture stop having
a first variable diameter.
34. An exposure apparatus according to claim 33, wherein said
projection optical system further includes a second variable
aperture stop having a second variable diameter.
35. An exposure apparatus according to claim 34, further including
first and second drive systems operatively connected to said first
and second variable aperture stops, and a control apparatus
electrically connected to said first and second drive units so as
to control the coherence factor by varying said first and second
variable aperture diameters.
36. An exposure apparatus according to claim 35, further comprising
an adjustable light beam converting unit removably arranged in said
light beam between said light source and said optical
integrator.
37. An exposure apparatus according to claim 35, further including
a third drive system operatively connected to said light beam
converting unit and electrically connected to said control
apparatus so as to cooperatively adjust in concert with said first
and second drive systems, said light beam converting unit, said
first variable aperture and said second variable aperture.
38. A method exposing a pattern of a mask onto a photosensitive
substrate with an arcuately shaped illumination field, the method
comprising the steps of: a) providing an illumination light beam;
b) reflectively dividing said illumination light beam into a
plurality of arcuate light beams corresponding to the arcuately
shaped exposure field; and c) condensing said arcuate light beams
onto the object over the arcuately shaped exposure field.
39. A method according to claim 38, further including the steps, in
said step b), of: i) reflecting said light beam from a first array
of reflecting elements each having an arcuate shape and a
reflecting surface having an eccentric curvature, and forming a
plurality of light source images.
40. A method according to claim 39, further including the step,
after said step i), of: ii) reflecting light from said plurality of
light source images with a second array of reflecting elements
opposingly arranged relative to said first array of reflecting
elements.
41. A method of patterning the surface of a photosensitive
substrate with a pattern on a mask in the manufacturing of a
semiconductor device, the method comprising the steps of: a)
providing an illumination light beam; b) reflectively dividing said
illumination light beam into a plurality of arcuate light beams
corresponding to an arcuately shaped illumination field; c)
condensing said arcuate light beams onto the mask over the
arcuately illumination field; and d) projecting light from the mask
onto the photosensitive substrate.
42. A method according to claim 41, wherein said step b) includes
the steps of: i) reflecting said light beam from a first array of
reflecting elements each having an arcuate shape and a reflecting
surface having an eccentric curvature, and forming a plurality of
light source images; and ii) reflecting light from said plurality
of light source images with a second array of reflecting elements
opposingly arranged relative to said first array of reflecting
elements.
43. An exposure apparatus for exposing a photosensitive substrate
with a mask having a pattern comprising: a) an illumination system
for illuminating the mask with an arcuate illumination field, said
illumination system comprising: i) a light source capable of
supplying a light beam with a wavelength .lambda.<200 nm; ii) an
optical integrator for splitting said light beam into a plurality
of light beams and comprising a plurality of reflecting elements;
and iii) a condenser optical system capable of condensing said
plurality of light beams so as to form said arcuate illumination
field, said condenser optical system having a reflecting element
with a second optical axis intersecting a first optical axis; and
b) a projection optical system disposed in an optical path between
the mask and the photosensitive substrate so as to form an image of
the mask pattern on the photosensitive substrate, said projection
optical system comprising said first optical axis and a plurality
of reflecting elements arranged relative thereto.
44. An exposure apparatus according to claim 43, wherein said
projection optical system includes a pupil with a light intensity
distribution thereat, the exposure apparatus further comprising an
illumination changing system capable of changing said light
intensity distribution at said pupil.
45. A method of exposing a photosensitive substrate, comprising the
steps of: a) providing the exposure apparatus according to claim
43; b) illuminating the mask with said arcuate illumination field
using said illumination system; and c) projecting an image of the
mask pattern onto the photosensitive substrate using said
projection optical system.
46. A method of exposing a photosensitive substrate with a mask
having a pattern, comprising the steps of: a) providing the
exposure apparatus according to claim 44; b) changing said light
intensity distribution at said pupil using said illumination
changing system; c) illuminating the mask with said arcuate
illumination field using said illumination system; and d)
projecting an image of the mask pattern onto the photosensitive
substrate using said projection optical system.
47. An exposure apparatus for exposing a photosensitive substrate
with a mask having a pattern comprising: a) an illumination system
for illuminating the mask with an arcuate illumination field, said
illumination system comprising i) a light source capable of
supplying a light beam of wavelength .lambda.<200 nm, and ii) a
plurality of reflecting members designed so as to direct said light
beam to form said arcuate illumination field on the mask; b) a
projection optical system disposed in an optical path between the
mask and the photosensitive substrate so as to form an image of
said predetermined pattern on the photosensitive substrate, said
projection system comprising a plurality of reflecting members and
having a pupil with a light intensity distribution thereat; and c)
an illumination changing system for changing said light intensity
distribution at said pupil.
48. An exposure apparatus according to claim 47, wherein said
illumination system further includes an optical integrator having a
plurality of reflecting elements.
49. A method of exposing a photosensitive substrate with a mask
having a pattern comprising the steps of: a) providing an exposure
apparatus comprising: i) an illumination system for illuminating
the mask with an arcuate illumination field, said illumination
system comprising a light source capable of supplying a light beam
of wavelength .lambda.<200 nm, and a plurality of reflecting
members designed so as to direct said light beam to said arcuate
illumination field on the mask; ii) a projection optical system
disposed in an optical path between the mask and the photosensitive
substrate so as to form an image of the pattern on the
photosensitive substrate, said projection system comprising a
plurality of reflecting members and having a pupil with a light
intensity distribution thereat; and iii) an illumination changing
system capable of changing said light intensity distribution at
said pupil; b) changing said light intensity distribution at a
pupil of said projection system using said illumination changing
system; c) illuminating the mask with said arcuate illumination
field using said illumination system; and d) projecting an image of
the mask pattern onto the photosensitive substrate using said
projection optical system.
50. A method according to claim 49, wherein one of said plurality
of reflecting members is an optical integrator having a plurality
of reflecting elements.
51. An exposure apparatus for exposing with a light intensity
distribution a photosensitive substrate with a mask having a
pattern, comprising: a) an illumination system for illuminating the
mask with an arcuate illumination field, said illumination system
comprising i) a light source capable of supplying a light beam of
wavelength .lambda.<200 nm, and ii) a plurality of reflecting
members designed so as to direct said light beam to said arcuate
illumination field on the mask; and b) a projection optical system
disposed in an optical path between the mask and the photosensitive
substrate so as to form an image of the pattern on the
photosensitive substrate, said projection system comprising a
plurality of reflecting members; and c) wherein at least one
reflecting member in said plurality of reflecting members is
adjustable so as to adjust the light intensity distribution at the
photosensitive substrate.
52. An exposure apparatus according to claim 5 1, wherein one of
said plurality of reflecting members is an optical integrator
having a plurality of reflecting elements.
53. A method of exposing with a light intensity distribution a
photosensitive substrate with a mask having a pattern, the method
comprising the steps of: a) providing an exposure apparatus
comprising: i) an illumination system for illuminating the mask
with an arcuate illumination field, said illumination system
comprising a light source capable of supplying a light beam of
wavelength .lambda.<200 nm, and a plurality of reflecting
members designed so as to direct said light beam to said arcuate
illumination field on the mask, at least one of said plurality of
reflecting members being adjustable so as to adjust said light
intensity distribution at the photosensitive substrate; ii) a
projection optical system disposed in an optical path between the
mask and the photosensitive substrate so as to form an image of the
predetermined pattern on the photosensitive substrate, said
projection system comprising a plurality of reflecting members; b)
adjusting the light intensity distribution at the photosensitive
substrate using said at least one of said plurality of reflecting
members; c) illuminating the mask with said arcuate illumination
field using said illumination system; and d) projecting an image of
the pattern onto the photosensitive substrate using said projection
system.
54. A method according to claim 51, wherein one of said plurality
of reflecting members is an optical integrator having a plurality
of reflecting elements.
55. A method of exposing with a light intensity distribution a
photosensitive substrate with a mask having a pattern, the method
comprising the steps of: a) providing an exposure apparatus
comprising: i) an illumination system for illuminating the mask
with an arcuate illumination field, said illumination system
comprising a light source system capable of supplying a light beam
of wavelength .lambda.<200 nm, and a plurality of reflecting
members designed so as to direct said light beam to said arcuate
illumination field on the mask; ii) a projection system having a
pupil and disposed in an optical path between the mask and the
photosensitive substrate so as to form an image of the pattern on
the photosensitive substrate, said projection system comprising a
plurality of reflecting members; b) changing the light intensity
distribution at said pupil; c) adjusting the light intensity
distribution at the photosensitive substrate; d) illuminating the
mask with said arcuate illumination field using said illumination
system; and e) projecting an image of the mask pattern onto the
photosensitive substrate using said projection system.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an illumination system
capable of providing uniform illumination, and more particularly
relates to an exposure apparatus incorporating the illumination
system, and a semiconductor device manufacturing method using
same.
BACKGROUND OF THE INVENTION
[0002] Conventional exposure apparatus for manufacturing
semiconductor devices include an illumination system for
illuminating a circuit pattern formed on a mask and projecting this
pattern through a projection optical system onto a photosensitive
substrate (e.g., a wafer) coated with photosensitive material
(e.g., photoresist). One type of projection optical system employs
an off-axis field (e.g., an arcuate field) and projects and
transfers only a portion of the mask circuit pattern onto the wafer
if the exposure were static. An exemplary projection optical system
having such a field comprises two reflecting mirrors, a concave
mirror and a convex mirror. In such projection optical systems,
transfer of the entire mask circuit pattern onto the wafer is
performed dynamically by simultaneously scanning the mask and wafer
in a fixed direction.
[0003] Scanning exposure has the advantage in that a high resolving
power is obtained with a comparatively high throughput. In
scanning-type exposure apparatus, an illumination system capable of
uniformly illuminating with a fixed numerical aperture (NA) the
entire arcuate field on the mask is highly desirable. Such an
illumination system is disclosed in Japanese Patent Application
Kokai No. Sho 60-232552. With reference to FIG. 1, an illumination
system 10, disclosed therein, comprises, along an optical axis A,
an ultrahigh-pressure mercury lamp 12, an elliptical mirror 14, and
an optical integrator 16. With reference now also to FIG. 2,
optical integrator 16 has an incident surface 16i, an exit surface
16e, and comprises a combination of four segmented cylindrical
lenses 1 6a-16d. Lenses 1 6a and 1 6d are located at the respective
ends of optical integrator 16, are oriented in the same direction,
and have a focal length f1.
[0004] Lenses 16b and 16c are located between lenses 16a and 16d
and are each oriented in the same direction, which is substantially
perpendicular to the orientation of lenses 16a and 16d.
[0005] Adjacent optical integrator 16 is a first condenser optical
system 18 and a slit plate 20. With reference now also to FIG. 3,
the latter includes an arcuate aperture 20A having a width 20W and
a cord 20C. Adjacent slit plate 20 is a condenser optical system 22
and a mask 24.
[0006] Mercury lamp 12 generates a light beam 26 which is condensed
by elliptical mirror 14 onto incident surface 16i of optical
integrator 16. By virtue of having two different focal lengths,
optical integrator 16 causes light beam 26, passing therethrough,
to have different numerical apertures in orthogonal directions to
the beam (e.g., in the plane and out of the plane of the paper, as
viewed in FIG. 1). Light beam 26 is then condensed by condenser
optical system 18 and illuminates slit plate 20 and arcuate
aperture 20A. Light beam 26 then passes therethrough and is
incident condenser optical system 22, which condenses the light
beam to uniformly illuminate a portion of mask 24.
[0007] With continuing reference to FIG. 3, a rectangular-shaped
region 28 on slit plate 20 is illuminated so that at least arcuate
aperture 20A is irradiated. Thus, light beam 26 is transformed from
a rectangular cross-section beam to an arcuate illumination beam,
corresponding to aperture 20A. Note that aperture 20A passes only a
small part of the beam incident slit plate 20.
[0008] Generally, arcuate cord 20C is made long to increase the
size of the exposure field on the wafer. In addition, arcuate slit
width 20W is set comparatively narrow to correspond to the
corrected region of the projection optical system used in
combination with illumination system 10. The illumination
efficiency is determined by the ratio of surface area of arcuate
aperture 20A to rectangular-shaped region 28. This ratio is small
for illumination system 10, an indication that the system is very
inefficient, which is disadvantageous. As a result, the amount of
light reaching mask 24 is fixed at a relatively low level. Since
the time of exposure of mask 24 is inversely proportional to the
amount of light (i.e., intensity) at the mask (i.e., the more
intense the light, the shorter the exposure time), the scanning
speed of the mask is limited. This limits the exposure apparatus'
ability to process an increasingly large number of wafers (e.g., to
increase throughput).
SUMMARY OF THE INVENTION
[0009] The present invention relates to an illumination system
capable of providing uniform illumination, and more particularly
relates to an exposure apparatus incorporating the illumination
system, and a semiconductor device manufacturing method using
same.
[0010] Accordingly, the present invention has the goals of
providing an illumination system capable of supporting higher
throughput with an illumination efficiency markedly higher than
heretofore obtained. Another goal is to maintain uniform
illumination (e.g., uniform Kohler illumination).
[0011] There has been a strong desire in recent years for a
next-generation exposure apparatus capable of projecting and
exposing a pattern having a much finer line width onto a
photosensitive substrate by using a light source, such as a
synchrotron, that supplies soft X-rays. However, prior art
illumination systems are not capable of efficiently and uniformly
illuminating a mask with X-ray wavelength light ("X-rays").
[0012] Consequently, the present invention has the further goal of
supplying an illumination system and exposure apparatus capable of
efficiently and uniformly illuminating a mask with X-rays, and
further to provide a method for manufacturing semiconductor devices
using X-rays.
[0013] Accordingly, a first aspect of the invention is an
illumination system for illuminating a surface over an illumination
field having an arcuate shape. The system comprises a light source
for providing a light beam and an optical integrator. The optical
integrator includes a first reflective element group having an
array of first optical elements each having an arcuate profile
corresponding to the arcuate shape of the illumination field. Each
first optical element also includes an eccentric reflecting surface
comprising an off-axis section of a spherical reflecting surface or
an off-axis section of an aspherical reflecting surface. The array
of first optical elements is designed so as to form a plurality of
arcuate light beams capable of forming multiple light source
images. The illumination system further includes a condenser
optical system designed so as to condense the plurality of arcuate
light beams to illuminate the surface over the arcuate illumination
field in an overlapping manner.
[0014] A second aspect of the invention is the illumination system
as described above, wherein the condenser optical system comprises
a condenser mirror with a focal point, with the condenser mirror
arranged such that the focal point substantially coincides with the
surface to be illuminated.
[0015] A third aspect of the invention is an illumination optical
system as described above, further comprising a second reflective
element group having a plurality of second optical elements. Each
of the second optical elements has a rectangular shape and a
predetermined second reflecting curved surface which is preferably
an on-axis section of a spherical or aspherical reflective surface.
The first and second reflecting element groups are opposingly
arranged such that the multiple light source images are formed at
the plurality of second optical elements when the light beam is
incident the first reflecting element group.
[0016] A fourth aspect of the invention is an exposure apparatus
for exposing the image of a mask onto a photosensitive substrate.
The apparatus comprises the illumination system as described above,
a mask stage capable of supporting the mask, and a substrate stage
capable of supporting the photosensitive substrate. A projection
optical system is arranged between the mask stage and the substrate
stage, and is designed so as to project a predetermined pattern
formed on the mask onto the photosensitive substrate over an
arcuate image field corresponding to the arcuate illumination
field.
[0017] A fifth aspect of the invention is an exposure apparatus as
described above, and further including drive apparatus designed so
as to synchronously move the mask stage and the wafer stage
relative to the projection optical system.
[0018] A sixth aspect of the invention is the exposure apparatus as
described above, wherein the illumination system includes a first
variable aperture stop having a first variable diameter. The
projection optical system further includes a second variable
aperture stop having a second variable diameter. First and second
drive systems are operatively connected to the first and second
variable aperture stops, respectively, so as to change the first
and second variable diameters, respectively. A control apparatus is
also preferably included. The control apparatus is electrically
connected to the first and second drive units so as to control the
coherence factor by varying the first and second variable aperture
diameters.
[0019] A seventh aspect of the invention is a method of patterning
the surface of a photosensitive substrate with a pattern on a mask
in the manufacturing of a semiconductor device. The method
comprising the steps of first, providing an illumination light
beam. The next (i.e., second) step is reflectively dividing the
illumination light beam into a plurality of arcuate light beams
corresponding to an arcuately shaped illumination field. The next
step is condensing the arcuate light beams onto the mask over the
arcuately shaped illumination field. The final step is projecting
light from the mask onto the photosensitive substrate. The present
method preferably further includes the steps in the above-mentioned
second step, of first reflecting the light beam from a first array
of reflecting elements each having an arcuate shape and a
reflecting surface having an eccentric curvature, and forming a
plurality of light source images, and then second, reflecting light
from the plurality of light source images with a second array of
reflecting elements opposingly arranged relative to the first array
of reflecting elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic optical diagram of a prior art
illumination system;
[0021] FIG. 2 is a close-up perspective view of the optical
integrator of the prior art illumination system of FIG. 1;
[0022] FIG. 3 is a top view of the slit aperture of the prior art
illumination system of FIG. 1, with the rectangular illumination
region superimposed;
[0023] FIG. 4 is a schematic diagram of the exposure apparatus
according to a first embodiment of the present invention;
[0024] FIG. 5 is a front view of the reflecting element group shown
in FIG. 4;
[0025] FIG. 6 depicts the X-Z plane geometry associated with the
reflecting elements in the reflecting element group of FIG. 5;
[0026] FIG. 7 depicts the Y-Z plane geometry associated with the
reflecting elements in the reflecting element group of FIG. 5;
[0027] FIG. 8 depicts the X-Y plane geometry associated with the
arcuate illumination field formed on the mask in the exposure
apparatus of FIG. 14;
[0028] FIG. 9 is a close-up of the exposure apparatus of FIG. 4
showing the reflecting action of the reflecting element group;
[0029] FIG. 10 depicts the X-Y plane geometry associated with a
reflecting element in the reflecting element group of FIG. 5 when
the reflecting element is aspherical;
[0030] FIG. 11 depicts the Y-Z plane geometry associated with the
arcuate illumination field when the reflecting elements are
aspherical;
[0031] FIG. 12 is a close-up view of the condenser optical system
of the exposure apparatus of FIG. 4 with an aspherical condenser
mirror showing the reflecting action associated with the creation
of secondary light sources;
[0032] FIG. 13 is a schematic diagram of the exposure apparatus
according to a second embodiment of the present invention, which
includes an optical integrator having two reflecting element
groups;
[0033] FIG. 14 is a front view of the first reflecting element
group of the exposure apparatus of FIG. 13;
[0034] FIG. 15 is a front view of the second reflecting element
group of the exposure apparatus of FIG. 13;
[0035] FIG. 16 depicts the geometry in the Y-Z plane associated
with the reflecting elements in the first reflecting element group
of FIG. 14;
[0036] FIG. 17 depicts the geometry in the X-Z plane associated
with the reflecting elements in the first reflecting element group
of FIG. 14;
[0037] FIG. 18 depicts the geometry associated with the reflecting
elements in the second reflecting element group of FIG. 14;
[0038] FIG. 19 depicts the geometry associated with the reflecting
elements in the second reflecting element group of FIG. 14;
[0039] FIG. 20 is a close-up of the exposure apparatus of FIG. 13
showing the reflecting action of the first and second reflecting
element groups and the condensing action of the condenser optical
system;
[0040] FIG. 21 is an alternate embodiment of the exposure apparatus
of FIG. 13, wherein the optical axes of the projection optical
system and the condenser optical system are colinear;
[0041] FIG. 22 is a front view of an alternate embodiment of the
first reflecting element group of the present invention;
[0042] FIG. 23 is a front view of an alternate embodiment of the
second reflecting element group of the present invention;
[0043] FIG. 24 is a perspective schematic illustration of the
reflecting action associated with a single column of the first and
second reflecting element groups shown in FIGS. 22 and 23,
respectively;
[0044] FIG. 25 is a first alternate embodiment of the exposure
apparatus of FIG. 4, further including a vacuum chamber, a light
source unit and variable aperture stop;
[0045] FIG. 26 is a second alternate embodiment of the exposure
apparatus of FIG. 4, further including a turret plate in place of
the first variable aperture stop, and an adjustable light beam
converting unit;
[0046] FIG. 27 is a perspective view of the aperture turret plate
of the exposure apparatus of FIG. 26;
[0047] FIG. 28 is a third alternate embodiment of the exposure
apparatus of FIG. 4, further including an auxiliary optical
integrator;
[0048] FIG. 29 is a front view of the first auxiliary reflecting
element group in the auxiliary optical integrator of the exposure
apparatus of FIG. 28;
[0049] FIG. 30 is a front view of the second auxiliary reflecting
element group in the auxiliary optical integrator of the exposure
apparatus of FIG. 28;
[0050] FIG. 31 is a fourth alternate embodiment of the exposure
apparatus of FIG. 4, wherein the function of the condenser mirror
is combined into the second reflecting element group of the optical
integrator; and
[0051] FIG. 32 is a fifth alternate embodiment of the exposure
apparatus of FIG. 4, further including a subchamber with a filter
for passing X-rays and not dust particles.
DETAILED DESCRIPTION OF THE INVENTION
[0052] The present invention relates to an illumination system
capable of providing uniform. Illumination, and more particularly
relates to an exposure apparatus incorporating the illumination
system, and a semiconductor device manufacturing method using
same.
[0053] With reference to FIGS. 4 and 5, exposure apparatus 50
comprises, along an optical axis A.sub.c, a light source 54 which
supplies light of wavelength .lambda.<200 nm. A preferred light
source is a laser, such as an ArF excimer laser supplying light of
wavelength .lambda.=193 nm, or an F.sub.2 laser supplying light of
wavelength .lambda.=157. Alternatively, light source 54 may be an
X-ray radiating apparatus such as a laser plasma X-ray source
radiating X-rays of wavelength .lambda.=10-15 nm or .lambda.=5-20
nm, a synchrotron generating apparatus radiating light of
wavelength .lambda.=10-15 nm, .lambda.=5-20 nm and the like.
[0054] Exposure apparatus 50 further comprises an optical
integrator (i.e., a multiple light source forming system) 56. Light
beam 100 from light source 54 is directed to optical integrator 56.
Optical integrator 56 is disposed in a predetermined position to
receive light beam 100. Optical integrator 56 comprises a
reflecting element group 60 having a plurality of reflecting
elements E (FIG. 5) arranged two-dimensionally in dense formation
(i.e., in an array) along a predetermined first reference plane
P.sub.1 parallel to the Y-Z plane. Specifically, as shown in FIG.
5, reflecting elements E have reflecting curved surfaces with an
arcuate shape (profile). In a preferred embodiment, reflecting
elements E are arranged in a number of columns 62 (e.g., five
columns, as shown) arranged along the Y-direction. Each column 62
comprises a plurality of reflecting elements E arranged along the
Z-direction. Furthermore, columns 62 are designed such that
together they roughly form a circular shape. The arcuate shape of
reflecting elements E is similar to the shape of the arcuate
illumination field formed on the mask, as discussed further
below.
[0055] With reference now to FIGS. 6 and 7, each reflecting element
E comprises an arcuate section, removed from an optical axis
A.sub.E, of a reflecting curved surface S of radius of curvature
R.sub.E. Surface S is centered on optical axis A.sub.E and has an
apex O.sub.E. Further, arcuate reflecting element E has a center
C.sub.E removed from optical axis A.sub.E by a heigh h.sub.E.
Accordingly, each reflecting element E comprises an eccentric
reflecting surface RS.sub.E which is a section of reflecting curved
surface S. Reflecting surface RS.sub.E is the effective reflecting
region of reflecting element E that reflects light (e.g., light
beam 100) from light source 54.
[0056] With reference again to FIG. 4, exposure apparatus 50
further comprises a condenser optical system 64 having a condenser
mirror 66 removed from optical axis A.sub.C. Condenser mirror 66
comprises a section of a spherical mirror 66' (dashed line)
centered on optical axis A.sub.C and having a radius of curvature
R.sub.C (not shown). Optical axis A.sub.C passes through the center
of a plane P.sub.2 located on optical axis A.sub.C. However, the
focal point (not shown) of condenser mirror 66 is located on
optical axis A.sub.C. The latter is also parallel to each optical
axis A.sub.E of plurality of optical elements E in optical element
group 60.
[0057] Exposure apparatus 50 further comprises a fold mirror 68 for
folding the optical path between condenser optical system 64 and a
reflective mask M, and a mask stage MS for movably supporting the
reflective mask M having a backside M.sub.B, and a reflective front
side M.sub.F with a pattern (not shown), such as a circuit pattern.
Mask stage MS is operatively connected to a mask stage drive system
72 for driving the mask stage in two-dimensional movement in the
X-Y plane. A control system 74 is electrically connected to drive
system 72 to control its operation.
[0058] A projection optical system 76 is disposed in the optical
path between reflective mask M and a photosensitive substrate such
as wafer W. Projection optical system 76 includes an optical axis
A.sub.P and is preferably an off-axis-type reduction system
comprising, for example, four aspherical mirrors 78a-78d. The
latter have effective reflecting surfaces at positions removed from
optical axis A.sub.P. Mirrors 78a, 78c and 78d comprise concave
aspherical mirrors, and mirror 78b comprises a convex aspherical
mirror. A pupil position P is located at a reflecting surface
S.sub.C of mirror 78c. An aperture stop (not shown) is provided at
pupil position P.
[0059] Exposure apparatus 50 further comprises a wafer stage WS for
movably supporting a wafer W having a surface W.sub.S coated with a
photosensitive material, such as photoresist. Wafer stage WS is
connected to a wafer stage drive system 92 for driving the wafer
stage in two-dimensional movement in the X-Y plane. Drive system 92
is also electrically connected to control system 74 which controls
drive system 92 and also coordinates the relative driving of drive
systems 72 and 92.
[0060] The operation of exposure apparatus 50 is now described with
reference to FIGS. 4 and 6. A light beam 100 having a wavefronts
105 and a beam diameter D.sub.B emanates from light source 54 and
travels parallel to optical axis A.sub.C and also parallel to
optical axis A.sub.E of reflecting element E (FIG. 6). Light beam
100 then reflects from each reflecting surface RS.sub.E of element
E and is condensed at a focal point position F.sub.E (FIG. 6) on
optical axis A.sub.E. A plurality of light source images I are
formed corresponding to each reflecting element E (FIG. 6). If
focal length f.sub.E of reflecting element E is equal to the
distance between apex O.sub.E and focal point position F.sub.E, and
R.sub.E is the radius of curvature of the reflecting curved surface
S, then the relationship in condition (1) below holds:
f.sub.E=-R.sub.E/2. (1)
[0061] With continuing reference to FIGS. 4 and 6, wavefronts 105
of light beam 100 are incident reflecting element group 60
substantially perpendicular, thereby forming, upon reflection from
reflecting elements E, a plurality of converging beams 108 each
having an arcuate cross-section (hereinafter, "arcuate light
beam"). This results in the formation of plurality of light source
images I at plane P.sub.2. Light source images I are displaced from
incident light beam 100 in direction perpendicular to optical axis
A.sub.E. The number of light source images I corresponds to the
number of reflecting elements E in reflecting element group 60. In
other words, assuming light beam 100 is incident reflecting
elements E from a direction parallel to each optical axis A.sub.E,
light source images I are respectively formed in plane P.sub.2
through which focal point position F.sub.E passes. In this manner,
reflecting element group 60 functions as an optical integrator,
i.e., a multiple-light-source forming optical system capable of
forming a plurality of secondary light sources.
[0062] With continuing reference to FIG. 4, light beams 110
emanating from plurality of light source images I are respectively
reflected and condensed by condenser mirror 66, which forms
condensed light beams 116. The latter are deflected by deflection
(fold) mirror 68 and arcuately illuminate front side M.sub.F of
mask M in a superimposed manner.
[0063] With reference now to FIG. 8, an arcuate illumination field
IF, as formed on mask M when viewed from backside M.sub.B, has a
center of curvature O.sub.IF on optical axis A.sub.P of projection
optical system 76. If fold mirror 68 were to be removed, arcuate
illumination field IF would be formed at position (plane) IP, and
center of curvature O.sub.IF of arcuate illumination field IF would
be located on optical axis A.sub.C.
[0064] In exposure apparatus 50 of FIG. 4, optical axis A.sub.C is
not deflected 90.degree. by a fold mirror. However, if optical axis
A.sub.C were so deflected by a hypothetical reflecting surface 68A,
optical axis A.sub.C and optical axis A.sub.P would become coaxial
and intersect mask M. Consequently, it can be said that optical
axes A.sub.C and A.sub.P are optically coaxial. Accordingly,
condenser mirror 66 and projection optical system 76 are arranged
such that optical axes A.sub.C and A.sub.P optically pass through
center of curvature O.sub.IF of arcuate illumination field IF.
[0065] Light from condensed light beams 116 reflects from front
side M.sub.F of mask M, thereby forming a light beam 118 which is
incident projection optical system 76. The latter forms an image of
the pattern present on mask front side M.sub.F over an arcuate
image field IF' on surface W.sub.S of wafer W. Mask stage MS moves
two-dimensionally in the X-Y plane via drive system 72, and
substrate stage WS moves two-dimensionally in the X-Y plane via
drive system 92. Control system 74 controls the drive amount of
drive systems 72 and 92. In particular, control system 74 moves
mask stage MS and substrate stage WS synchronously in opposite
directions (as indicated by arrows) via the two drive systems 72
and 92. This allows for the entire mask pattern to be scanned and
exposed onto surface W.sub.S of wafer W through projection optical
system 76. In this manner, semiconductor devices can be
manufactured, since satisfactory circuit patterns are transferred
("patterned") onto surface W.sub.S of wafer W.
[0066] The operation of reflecting element group 60 is now
explained in greater detail. With reference now to FIG. 9,
reflecting element group 60 comprises, for the sake of explanation,
three reflecting elements E.sub.a-E.sub.c arranged along plane
P.sub.1 parallel to the Y-Z plane such that the position of the
center of curvatures (the focal points) of each reflecting element
E.sub.a-E.sub.c reside on plane P.sub.2.
[0067] Light beam 100 comprises collimated light beams 100a and
100c comprising wavefronts 105a and 105c, respectively, that are
incident reflecting elements E.sub.a and E.sub.c. The latter form,
from light beams 100a and 100c, converging arcuate light beams 108a
and 108c, respectively, which correspond to the profile shape of
reflecting surface RS.sub.EA of reflecting element E.sub.a and
reflecting surface RS.sub.EC of reflecting element E.sub.c. Arcuate
light beams 108a and 108c converge to form light source images
I.sub.a and I.sub.c, respectively, at plane P.sub.2. Subsequently,
diverging light beams 110a and 110c emanate from light source
images I.sub.a and I.sub.c and propagate toward condenser mirror
66. The latter condenses light beams 110a and 110c, thereby forming
condensed light beams 116a (solid lines) and 116c (dashed lines).
Light beams 116a and 116c are condensed by condenser mirror 66 such
that they overlap (i.e., are super-imposed) and obliquely
illuminate front side M.sub.F of mask M over arcuate illumination
field IF. The Z-direction (i.e., the direction in the plane of the
paper) along mask front side M.sub.F is the width direction of
arcuate illumination field IF.
[0068] Thus, light reflects from each reflecting element E in
reflecting element group 60 and arcuately illuminates mask M over
arcuate illumination field IF in an overlapping (i.e.,
superimposed) manner, allowing uniform illumination to be achieved.
Uniform Kohler illumination is achieved when each light source
image I formed by each reflecting element E is re-imaged at pupil
position P of projection optical system 76
[0069] Even if the entire illumination system (i.e., elements 54
through 68) and projection optical system 76 includes only
catoptric members and catoptric elements, an arcuate illumination
field IF with uniform illumination intensity can be efficiently
formed on mask M while substantially maintaining Kohler
illumination.
[0070] By making the projective relationship of condenser optical
system 64 a positive projection, mask M can be illuminated with a
uniform numerical aperture (NA), regardless of illumination
direction.
[0071] With reference again to FIG. 5, by densely arranging
reflecting elements E such that reflecting element group 60 has a
roughly circular outline, the outline (profile) of the secondary
light sources formed by plurality of light source images I formed
at position P.sub.2 is also roughly circular. Accordingly, by
making the projective relationship of condenser mirror 66 a
positive projection and by simultaneously setting the outline
(profile) of plurality of light sources I, the spatial coherence
inside arcuate illumination field IF formed on mask M can be
rendered uniform regardless of the location and direction of
incident beams 116 (see FIG. 9).
[0072] Furthermore, by configuring the shape of reflecting surface
RS.sub.E of each reflecting element E so that the projective
relationship is identical to that of condenser mirror 66, the
illumination intensity in arcuate illumination field IF can be
rendered even more uniform, without generating distortion due to
reflecting element group 60 and condenser mirror 66.
[0073] With reference again to FIG. 8, an exemplary arcuate
illumination field IF has a central arc 130 of radius R.sub.IF and
an angle .alpha..sub.IF=60.degree., ends IF.sub.a and IF.sub.b
separated by a linear distance L.sub.IF=96 mm, a width W.sub.IF=6
mm, and an illumination numerical aperture NA=0.015 at mask M.
Further, the inclination of the principle ray (not shown) of the
illumination light with respect to the mask normal (not shown) is
approximately 30 mrad (i.e., the entrance pupil position of
projection optical system 76 is approximately 3119 mm from mask M),
and diameter D.sub.B of light beam 100 from light source 54 is on
the order of 42 mm (FIG. 4).
[0074] The above description considered reflecting elements E and
condenser mirror 66 both with eccentric spherical reflecting
surfaces. However, these surfaces can also be aspherical surfaces.
Below, specific numerical values for these surfaces as aspherical
surfaces are provided.
[0075] With reference now to FIG. 10, reflecting element E includes
an arcuate section, removed from optical axis A.sub.E, of a
reflecting curved aspherical surface AS.sub.E and a reference
spherical surface S.sub.E having a common apex O.sub.E. Spherical
surface S.sub.E has a center of curvature O.sub.RE. The X-axis
passes through apex O.sub.E in the direction perpendicular to a
plane P.sub.T tangential at apex O.sub.E (optical axis A.sub.E of
reflecting element E is co-linear with the X-axis). The Y-axis
passes through apex O.sub.E in the plane of the paper and is
perpendicular to the X-axis. The origin of the X-Y coordinate
system is apex O.sub.E. Accordingly, each reflecting element E
comprises an eccentric aspherical reflecting surface ARS.sub.E
which is a section of reflecting curved aspherical surface
AS.sub.E.
[0076] Aspherical reflecting surface AS.sub.E is described by the
expression for an aspherical surface, below, wherein x(y) is the
distance along the direction of the X-axis (optical axis A.sub.E)
from the tangential plane at apex O.sub.E to the surface AS.sub.E,
y is the distance along the direction of the Y-axis from the X-axis
(optical axis A.sub.E) to reflecting surface AS.sub.E, R.sub.E is
the radius of curvature of reference spherical surface S.sub.E, and
C.sub.2, C.sub.4, C.sub.6, C.sub.8 and C.sub.10 are aspherical
surface coefficients.
x(y)=(y.sup.2/R.sub.E)/[1+(1-y.sup.2/R.sub.E.sup.2).sup.0.5]+C.sub.2y.sup.-
2+C.sub.4y.sup.4+C.sub.6y.sup.6+C.sub.8y.sup.8+C.sub.10y.sup.10
[0077] An exemplary aspherical reflecting surface AS.sub.E has the
following parameter values:
R.sub.E=-183.3211
C.sub.2=-5.37852.times.10.sup.-4
C.sub.4=-4.67282.times.10.sup.-8
C.sub.6=-2.11339.times.10.sup.-10
C.sub.8=5.71431.times.10.sup.-12
C.sub.10=-5.18051.times.10.sup.-14
[0078] Each reflecting element E in reflecting element group 60 has
a reflecting cross-sectional shape that interposes heights y.sub.1
and y.sub.2 from optical axis A.sub.E and comprises an arcuate
aspherical eccentric mirror. In an exemplary illumination system 50
illustrated in FIG. 11, length L.sub.IF between ends IF.sub.a and
IF.sub.b of arcuate illumination field IF at an arc open angle
.alpha..sub.E of 60.degree. is approximately 5.25 mm (see FIG. 11),
height y.sub.1 is approximately 5.085 mm, height y is approximately
5.25 mm, and height y.sub.2 is approximately 5.415 mm.
[0079] In this case, plurality of light source images I (FIG. 10)
formed by reflecting element E are formed at a position axially
removed from apex O.sub.E by X.sub.I=76.56 mm, with height y=5.25
mm from the center diameter arc 130 (FIG. 11). The position of
light source images I in a direction perpendicular to optical axis
A.sub.E is removed by Y.sub.1=5.085 mm from the inner diameter
IF.sub.i of arcuate illumination field IF, and is removed by
y.sub.2=5.415 mm from the outer diameter IF.sub.o.
[0080] Thus, a satisfactory reflecting element group 60 (FIG. 5)
can be constituted by arranging, in columns, a plurality of
eccentric aspherical reflecting elements E having the above
dimensions.
[0081] Next, an exemplary condenser mirror 66 in condenser optical
system 64, for the case where reflecting element group 60 comprises
a plurality of eccentric aspherical reflecting elements E having
the above dimensions, is discussed.
[0082] With reference now to FIG. 12, condenser mirror 66
comprises, in a preferred embodiment, a section ARS.sub.C of
reflective an aspherical surface AS.sub.C, with associated
reference spherical surface S.sub.C having a common apex O.sub.C.
Reference spherical surface S.sub.C has a center of curvature
O.sub.RC. The X-axis is the direction perpendicular to a tangential
plane P'.sub.T at apex O.sub.C (optical axis A.sub.C is the
X-axis). The Y-axis is the direction parallel to tangential plane
P'.sub.T at apex O.sub.C. The origin of the X-Y coordinate system
is apex O.sub.C.
[0083] Reflecting aspherical surface AS.sub.C associated with
condenser mirror 66 is described by the expression for an
aspherical surface below, wherein x(y) is the distance along the
direction of the X-axis (optical axis A.sub.C) from tangential
plane P'.sub.T at apex O.sub.C to reflecting aspherical surface
AS.sub.C, y is the distance along the Y-axis from the X-axis
(optical axis A.sub.C) to reflecting aspherical surface AS.sub.C,
R.sub.C is the radius of curvature of reference spherical surface
S.sub.C, and C.sub.2, C.sub.4, C.sub.6, C.sub.8 and C.sub.10 are
aspherical surface coefficients.
x(y)=(y.sup.2/R.sub.C)/[1+(1-y.sup.2/R.sub.C.sup.2).sup.0.5]+C.sub.2y.sup.-
2+C.sub.4y.sup.4+C.sub.6y.sup.6+C.sub.8y.sup.8+C.sub.10y.sup.10
[0084] Specific numerical values for the present example are as
follows:
R.sub.C=-3518.74523
C.sub.2=-3.64753.times.10.sup.-5
C.sub.4=-1.71519.times.10.sup.-11
C.sub.6=1.03873.times.10.sup.-15
C.sub.8=-3.84891.times.10.sup.-20
C.sub.10=5.12369.times.10.sup.-25
[0085] With continuing reference to FIG. 12, light source images I
formed by reflecting element group 60 are formed in plane P.sub.2
orthogonal to optical axis A.sub.C (see FIG. 4). In the present
example, plane P.sub.2 is at a position removed by approximately
x.sub.IC=2009.8 mm along optical axis A.sub.C from apex
O.sub.C.
[0086] Arcuate illumination field IF having a uniform illumination
intensity distribution and spatial coherence is formed by condenser
mirror 66 receiving diverging light beams 110 and forming
converging light beams 116. Arcuate illumination field IF is formed
by condenser mirror 66 at a position C.sub.IF removed by
X.sub.M=1400 mm from apex O.sub.C (or plane P'.sub.T) and
approximately y.sub.MC=96 mm from optical axis A.sub.C.
[0087] By the abovementioned configuration, an arcuate illumination
field IF having a uniform illumination intensity and spatial
coherence can be formed on mask M.
[0088] In a preferred embodiment of the present invention,
condition (2) below, is satisfied:
0.01<.vertline.f.sub.F/f.sub.C.vertline.<0.5 (2)
[0089] wherein f.sub.F is the focal length of each reflecting
element E in reflective element group 60 and f.sub.C is the focal
length of condenser optical system 64 (e.g., the focal length of
condenser mirror 66).
[0090] If .vertline.f.sub.F/f.sub.c.vertline. exceeds the upper
limit in condition (2), the focal length f.sub.C of condenser
optical system 64 shortens in the extreme when an appropriate power
is given to each reflecting element E. Consequently, it is
difficult to form a uniform arcuate illumination field IF on mask
M, since strong aberrations are generated by condenser optical
system 64. On the other hand, if
.vertline.f.sub.F/f.sub.C.vertline. falls below the lower limit in
condition (2), the focal length f.sub.C of condenser optical system
64 increases excessively, with the result that the elements in the
condenser optical system (e.g., condenser mirror 66) increase in
size excessively. This makes it difficult to maintain a compact
illumination system when the appropriate power is given to each
reflecting element E.
[0091] By way of example, for the case where each reflecting
element E in reflecting element group 60 has radius of curvature
R.sub.E=-183.3211 mm, the reference focal length f.sub.F=91.66055
mm (f.sub.F=-R.sub.E/2). In addition, for a corresponding condenser
mirror 66 with a radius of curvature R.sub.C=-3518.74523 mm,
reference focal length f.sub.C=1759.3726 mm (f.sub.C=-R.sub.C/2).
Accordingly,
.vertline.f.sub.F/f.sub.C.vertline.=0.052.
[0092] Thus, condition (2) is satisfied and an illumination system
can be compactly constituted while maintaining a satisfactory
illumination region.
[0093] The above first mode for carrying out the present invention
shows an example wherein optical integrator 56 comprises one
reflecting element group 60 (FIG. 4). In a second mode for carrying
out the present invention, the optical integrator comprises two
reflecting element groups, as described below.
[0094] With reference now to FIG. 13, illumination system 200
comprises essentially the same components as illumination optical
system 50 of FIG. 4, except that optical integrator 220, analogous
to optical integrator 56 in system 50 of FIG. 4, comprises first
and second opposingly arranged reflecting element groups 220a and
220b. First reflecting element group 220a is constituted so that a
first plurality of reflecting elements E.sub.1 (not shown in FIG.
13) are densely arranged in two dimensions along a predetermined
reference plane (first reference plane) P.sub.a parallel to the Y-Z
plane. Specifically, with reference to FIG. 14, first reflecting
element group 220a includes a plurality of reflecting elements
E.sub.1, each having an arcuate curved reflecting surface, arranged
as described above in connection with elements E of reflecting
element group 60.
[0095] With reference now also to FIGS. 16 and 17, each reflecting
element E.sub.1 in first reflecting element group 220a has an
arcuate shape (profile) of one part of a reflecting curved surface
S.sub.1 of radius of curvature R.sub.E1 in a region eccentric from
optical axis A.sub.E1. Center C.sub.E1 of arcuate reflecting
element E.sub.1 is positioned at height h.sub.E from optical axis
A.sub.E1. Accordingly, the eccentric reflecting surface RS.sub.E1
of each reflecting element E.sub.1, as shown in FIGS. 16 and 17,
comprises an eccentric spherical mirror having a radius of
curvature R.sub.E1.
[0096] Consequently, with reference to FIG. 17, a portion of light
beam 100 impinging from an oblique direction with respect to
optical axis A.sub.E1 is condensed to form a light source image I
in plane P.sub.FO at a position removed from optical axis A.sub.E1
in a direction perpendicular to focal point position F.sub.E1 of
reflecting element E.sub.1. Reflecting element E.sub.1 has a focal
length f.sub.E1, which is the distance between apex O.sub.E1 and
focal point position F.sub.E1.
[0097] In a preferred embodiment of the present invention,
condition (3), below, is satisfied:
f.sub.E1=-R.sub.E1/2 (3)
[0098] With reference again to FIG. 15, second reflecting element
group 220b comprises a plurality of second reflecting elements
E.sub.2 densely arranged in two dimensions along a predetermined
reference plane (second reference plane) P.sub.b parallel to the
Y-Z plane. Specifically, second reflecting element group 220b
includes a plurality of reflecting elements E.sub.2 having
reflecting curved surfaces which have a rectangular profile
(outline). Second reflecting element group 220b has along the
Y-direction a plurality of columns 262 (e.g., five, as shown), each
comprising a plurality of second reflecting elements E.sub.2
arranged in a row along the Z-direction. Furthermore, columns 262
of second reflecting elements are arranged to collectively form a
near circular shape (i.e., outline).
[0099] In other words, each of second reflecting elements E.sub.2
in second reflecting element group 220b is arranged in a row
facing, in one-to-one correspondence, each of first reflecting
elements E.sub.1 comprising first reflecting element group
220a.
[0100] With reference now to FIGS. 18 and 19, each reflecting
element E.sub.2 has a reflecting surface RS.sub.E2 having a
rectangular profile (outline) that is one part of a reflecting
curved surface S.sub.2 with a radius of curvature R.sub.E2 in a
region including optical axis A.sub.E2. Accordingly, reflecting
element E.sub.2 has a rectangular perimeter 270 and a center
C.sub.E2 which coincides with optical axis A.sub.E2. Accordingly,
reflecting surface RS.sub.E2 of each reflecting element E.sub.2
comprises a concentric spherical mirror with radius of curvature
R.sub.E2.
[0101] With reference again to FIG. 13, wavefronts 105 in beam 100
are incident first reflecting element group 220a obliquely from a
predetermined direction and are split by the first reflecting
element group into arcuately shaped segments by the reflecting
action of plurality of reflecting elements E.sub.1. The latter form
a plurality of light source images I (not shown) at plane (second
reference plane) P.sub.b, parallel to the Y-Z plane and displaced
from incident light beam 100. The number of light source images I
corresponds to the number of reflecting elements E.sub.1. Second
reflecting element group 220b is arranged in plane P.sub.b.
[0102] Light beam 100 from light source 54, in addition to having a
parallel component, also includes a dispersion angle of a certain
range. Consequently, each light source image I having a certain
size is formed in plane P.sub.b by first reflecting element group
220a. Accordingly, second reflecting element group 220b functions
as a field mirror group to effectively utilize light supplied from
light source 54. In other words, each of the plurality of second
reflecting elements E.sub.2 in second reflecting element group 220b
functions as a field mirror.
[0103] With continuing reference to FIG. 13, plurality of light
source images I reflected by second reflecting element group 220b
forms a plurality of light beams 310 which are incident condenser
mirror 66 with a radius curvature R.sub.c. The focal point position
(not shown) of condenser mirror 66 coincides with secondary light
source plane P.sub.b. Center of curvature O.sub.C of condenser
mirror 66 exists at the center position of plurality of light
source images I formed on second reflecting element group 220b
(i.e., the position wherein optical axis A.sub.C and plane P.sub.b
intersect, or the center of reflective element group 220b).
[0104] Optical axis A.sub.C is parallel to each optical axis
A.sub.E1 associated with each reflecting element E.sub.1 in first
reflective element group 220a, but is not parallel to each optical
axis A.sub.E2 associated with each reflecting optical element
E.sub.2 in second reflective element group 220b. More particularly,
each optical axis A.sub.E2 associated with reflecting optical
elements E.sub.2 is preferably inclined at half the angle of
incidence of the obliquely impinging light beam.
[0105] With continuing reference to FIG. 13, light beams 310 from
plurality of light source images I are each reflected and condensed
by condenser mirror 66 thereby forming light beams 316. Light beams
316 are thus made to arcuately illuminate, in a superimposed
manner, front side M.sub.F of mask M. Plane mirror 68, as discussed
above in connection with apparatus 50 of FIG. 4, may be used as a
deflecting mirror to fold the optical path. With reference again
also to FIG. 8, arcuate illumination field IF is formed on mask M
when viewed from the back side M.sub.B of mask M. Center of
curvature O.sub.IF of arcuate illumination field IF exists on
optical axis A.sub.P (FIG. 13). If plane mirror 68 in system 200 of
FIG. 13 is temporarily eliminated, arcuate illumination field IF is
formed at plane IP, and center of curvature O.sub.IF of arcuate
illumination field IF exists on optical axis A.sub.C.
[0106] With continuing reference to FIG. 13, optical axis A.sub.C
of condenser optical system 64 is not deflected 90.degree..
However, if optical axis A.sub.C were deflected 90.degree. by
hypothetical reflecting surface 68a, optical axis A.sub.C and
optical axis A.sub.P would be coaxial on mask M. Consequently, it
can be said that optical axes A.sub.C and A.sub.P are optically
coaxial. Accordingly, as with exposure apparatus 50 of FIG. 4,
condenser optical system 64 and projection optical system 76 of
exposure apparatus 200 are arranged such that optical axes A.sub.C
and A.sub.P optically pass through center of curvature O.sub.IF of
arcuate illumination field IF.
[0107] Light beam 118 reflected by front side M.sub.F of mask M
passes through projection optical system 76, as described above,
thereby forming an image of the mask pattern on surface W.sub.S of
wafer W over an arcuate image field IF' (not shown: see FIG. 4).
Wafer surface W.sub.S is coated with photoresist and thus serves as
a photosensitive substrate onto which the mask pattern, via the
arcuately shaped image of mask M, is projected and transferred.
[0108] As discussed above in connection with exposure apparatus 50
of FIG. 4, mask stage MS and substrate stage WS move synchronously
in opposite directions (as indicated by arrows) via mask stage
drive system 72 and wafer stage drive system 92. Drive systems 72
and 92 are controlled by control system 74 in a manner that allows
the entire mask pattern on mask M to be scanned and exposed onto
wafer surface W.sub.S through projection optical system 76.
Consequently, satisfactory semiconductor devices can be
manufactured, since satisfactory circuit patterns are transferred
onto wafer W by a photolithography process that manufactures
semiconductor devices.
[0109] With reference now to FIG. 20, the operation of first and
second reflecting element groups 220a and 220b are described in
more detail. For ease of explanation, FIG. 20 omits plane mirror
68. Further, first reflecting element group 220a comprises only two
reflecting elements E.sub.a1, and E.sub.b1, and second reflecting
element group 220b comprises only two reflecting elements E.sub.a2
and E.sub.b2.
[0110] Reflecting elements E.sub.a1, and E.sub.b1 are arranged
along first reference plane P.sub.a at a position substantially
optically conjugate to mask M (an object plane of projection
optical system 76) or photosensitive substrate W (an imaging plane
of projection optical system 76). Reflecting elements E.sub.a2 and
E.sub.b2 are arranged along a second reference plane P.sub.b at a
position substantially optically conjugate to the pupil of
projection optical system 76. Light beam 100, which may be, for
example, an X-ray beam, comprises light beams 100a and 100b
(represented by the solid lines and dotted lines, respectively)
each including wavefronts 105a and 105b, respectively, which
impinge from respective directions onto reflecting element
E.sub.a1. Light beams 100a and 100b are then split into arcuate
light beams 108a and 108b, respectively, corresponding to the
profile shape of reflecting surface RS.sub.E1 of reflecting element
E.sub.a1, Arcuate light beams 108a and 108b form light source
images I.sub.1 and I.sub.2, respectively, at respective ends of
reflecting element E.sub.a2 in second reflecting element group 220b
by the condensing action of reflecting surface RS.sub.EA1 of
reflecting element E.sub.a1.
[0111] If the radiant light in light beam 100 spans the angular
range between light beams 100a and 100b and is incident reflecting
element E.sub.a1, a light source image is formed whose size spans
light source image I.sub.1 and light source image I.sub.2 on
reflecting element E.sub.a2 in second reflecting element group
220b. Subsequently, light beams 108a and 108b are condensed by the
reflecting and condensing action of reflecting element E.sub.a2 in
second reflecting element group 220b, thereby forming light beams
310a and 310b which are directed toward condenser mirror 66. Light
beams 310a and 310b are then further condensed by the reflecting
and condensing action of condenser mirror 66, thereby forming light
beams 316a (solid lines) and 316b (dotted lines). These beams
arcuately illuminate mask M from two directions such that they
superimpose at front side M.sub.F of mask M. The optical action due
to reflecting element E.sub.b1 and E.sub.b2 in reflecting element
groups 220a and 220b is the same as described above for reflecting
elements E.sub.a1 and E.sub.a2.
[0112] Thus, the light from plurality of light source images I
(i.e., I.sub.1, I.sub.2, etc.) arcuately illuminate mask M in a
superimposed manner, as described above. This allows for efficient
and uniform illumination. Moreover, since light beams 108a and 108b
are efficiently condensed due to the action of each reflecting
element E.sub.a2, E.sub.b2, etc., in second reflecting element
group 220b (i.e., by the action of these elements as field
mirrors), condenser optical system 64 can be made compact.
[0113] Since light source images I.sub.1, I.sub.2, etc., formed on
the surface of each reflecting element E.sub.a2, E.sub.b2, etc., in
second reflecting element group 220b are re-imaged at pupil
position P (i.e., the entrance pupil) of projection optical system
76, Kohler illumination is achieved.
[0114] As described above in connection with the second mode for
carrying out the present invention, light having a certain
dispersion angle and a particular wavelength, such as X-rays with a
wavelength .lambda.<100 nm, is preferably employed. The mask
pattern is then exposed onto wafer surface W.sub.S as a
photosensitive substrate with an arcuate image field IF', as
discussed above. The latter is efficiently formed with uniform
illumination intensity while substantially maintaining the
conditions of Kohler illumination, even if the illumination
apparatus (elements 54-68 of exposure apparatus 200 of FIG. 13) and
projection optical system 76 include only catoptric members.
[0115] In the second mode for carrying out the present invention,
as described above, reflecting elements E.sub.1 and E.sub.2 and
condenser mirror 66 are eccentric spherical surfaces. However,
these surfaces can be made aspherical surfaces, in a manner similar
to that described above in connection with the first mode for
carrying out the present invention.
[0116] In the second mode for carrying out the present invention,
as described above, condenser 10 optical system 64 and projection
optical system 76 are arranged so that optical axes A.sub.C and
A.sub.P are orthogonal. However, with reference to FIG. 21 and
exposure apparatus 350, condenser optical system 64, deflecting
(plane) mirror 68 and projection optical system 76 may be arranged
such that optical axes A.sub.C and A.sub.P are coaxial.
[0117] Next, a preferred embodiment of the second mode for carrying
out the present invention is explained with reference to FIGS. 22
and 23. In the present preferred embodiment, the illumination
efficiency of first and second reflecting element groups 360a and
360b, as described below, is even greater than first and second
reflecting element groups 220a and 220b (FIGS. 14 and 15).
[0118] With reference to FIG. 22, first reflecting element group
360a has, along the Y-direction, three columns G.sub.E11-GE.sub.13
of first reflecting elements E.sub.1 having a arcuate profile
(outline) and arranged in a row (i.e., stacked) along the
Z-direction.
[0119] Reflecting element columns G.sub.E11-G.sub.E13 each comprise
a plurality of reflecting elements E.sub.11a-E.sub.11v,
E.sub.12a-E.sub.12y, and E.sub.13a-E.sub.13v, respectively. Each
reflecting element columns G.sub.E11-G.sub.E13 are arranged such
that certain reflecting elements therein are each rotated by just a
prescribed amount about respective axes A.sub.1-A.sub.3 oriented
parallel to the Z-axis and traversing the center of their
respective columns.
[0120] With reference now to FIG. 23, second reflecting element
group 360b includes, along the Y-direction, nine columns C1-C9 each
comprising a plurality of second reflecting elements E.sub.2 having
a nearly rectangular profile (outline) and arranged in a row (i.e.,
stacked) along the Z-direction. Second reflecting element group
360b includes a first subgroup G.sub.E21 comprising columns C1-C3,
a second subgroup G.sub.E22 comprising columns C4-C6, and a third
subgroup G.sub.E23 comprising columns C7-C9.
[0121] First and second reflecting element groups 360a and 360b are
opposingly arranged, as described above in connection with
apparatus 200 and first and second reflecting element groups 220a
and 220b (see, e.g., FIG. 20). Reflecting elements
E.sub.11a-E.sub.11v of first reflecting element column G.sub.E11 in
first reflecting element group 360a condense light and form light
source images I in the manner described above in connection with
first reflecting element group 220a (see FIG. 20). In other words,
light source images I formed by reflecting elements
E.sub.11a-E.sub.11v are formed on the surfaces of reflecting
elements E.sub.2 in first subgroup G.sub.E21. Likewise, additional
light source images I are condensed by each reflecting element
E.sub.12a-E.sub.12y of second reflecting element column G.sub.E12
in first reflecting element group 360b on the surfaces of
reflecting elements E.sub.2 in second subgroup G.sub.E22. Further,
additional light source images I are condensed by each reflecting
element E.sub.13a-E.sub.13v of third reflecting element column
G.sub.E13 in first reflecting element group on the surfaces of
reflecting elements E.sub.2 in third subgroup G.sub.E23.
[0122] With reference now also to FIG. 24, reflecting elements
E.sub.11a-E.sub.11k in first reflecting element column G.sub.E11
are arranged such that arbitrary reflecting elements therein are
rotated by just a prescribed amount about axis A.sub.1 oriented
parallel to the Z-direction and traversing the center of the first
reflecting element column (centers C.sub.1a-C.sub.1k of reflecting
elements E.sub.11a-E.sub.11k).
[0123] For example, reflecting element E.sub.11a is provided and
fixed in a state wherein it is rotated by a prescribed amount
counterclockwise about axis A.sub.1. This amount of rotation is
preferably very small. Reflecting element E.sub.11a forms a
circular-shaped light source image I.sub.a having a certain size,
on the uppermost reflecting element E.sub.2 of column C3 of first
subgroup G.sub.E21.
[0124] Likewise, reflecting element E.sub.11f is provided and fixed
in a state wherein it is rotated by just a prescribed amount
clockwise about axis A.sub.1. Reflecting element E.sub.11f forms a
circular-shaped light source image I.sub.f having a certain size,
on the second reflecting element E.sub.2 from the top of first
column C.sub.1 of first subgroup G.sub.E21.
[0125] In addition, reflecting element E.sub.11k is provided and
fixed without being rotated about axis A.sub.1. Reflecting element
E.sub.11k forms a circular-shaped light source image I.sub.k having
a certain size, on the fourth reflecting element E.sub.2 from the
top of second column C.sub.2 of first subgroup G.sub.E21. The
optical axis (not shown) of reflecting element E.sub.11k and the
optical axis (not shown) of each reflecting element in first
subgroup G.sub.E21 are parallel to one another.
[0126] The arrangement as described above with reference to first
reflecting element column G.sub.E11 and first subgroup G.sub.E21
applies to that between second reflecting element column G.sub.E12
and second subgroup G.sub.E22, and that between third reflecting
element column G.sub.E13 and third subgroup G.sub.E23, in first
reflecting element group 360a.
[0127] As described above, illumination efficiency can be improved
if the configuration of the first and second reflecting element
groups 360a and 360b (FIGS. 23 and 24) is adopted. This
configuration has the advantage that light source images I.sub.a,
I.sub.f, I.sub.k, etc., are not easily obscured by the profile
(outline) of the second reflecting elements, as compared to the
configuration of the first and second reflecting elements in
reflecting element groups 220a and 220b.
[0128] In the above first and second modes for carrying out the
present invention, reflecting elements E of reflecting element
group 60, and reflecting elements E.sub.1 of reflecting element
group 220a have an arcuate profile (outline) and having reflective
surfaces RS.sub.E and RS.sub.E1 respectively, eccentric with
respect to the optical axes A.sub.E, and A.sub.E1, respectively.
Consequently, constraints from the standpoint of optical design are
significantly relaxed as compared to non-eccentric reflecting
elements. This is because aberrations need only be corrected in the
arcuate region at a certain image height (i.e., a certain distance
from the optical axis). Accordingly, aberrations generated by the
reflecting elements in the first reflecting element group can be
sufficiently controlled, resulting in very uniform arcuate
illumination.
[0129] Aberrations generated by condenser optical system 64 (FIGS.
4 and 13) can also be sufficiently controlled by configuring the
condenser optical system as an eccentric mirror system. This allows
the above advantages to be obtained synergistically. Furthermore,
condenser optical system 64 can comprise one eccentric mirror
(e.g., condenser mirror 66), or a plurality of such mirrors.
[0130] First and second reflecting element groups in the present
invention may be moved by a small amount independently or as a unit
in a prescribed direction (e.g., axially or orthogonal thereto).
Alternatively, first and second reflecting groups may be
constituted such that at least one of the first reflecting element
group and second reflecting element group is capable of being
inclined by a small amount. This allows for the illumination
intensity distribution in the arcuate illumination field IF formed
on front side M.sub.F or wafer W (photosensitive substrate) to be
adjusted. In addition, it is preferable that at least one eccentric
mirror in condenser optical system 64 be capable of being moved or
inclined by a minute amount in a prescribed direction (i.e., along
optical axis A.sub.C or orthogonal thereto).
[0131] In the present invention, it is advantageous to compactly
configure the exposure apparatus while simultaneously maintaining a
satisfactory arcuate illumination field IF. To this end, it is
preferable in the present invention that the first reflecting
element group (220a of FIG. 14 or 360a of FIG. 22) and condenser
optical system 64 satisfy condition (2), discussed above.
[0132] In addition, the above modes for carrying out the present
invention included optical integrators 56, 220, and 360 comprising
optical elements having reflective surfaces. However, the optical
integrators of the present invention may also comprise refractive
lens elements. In this case, the cross-sectional shape of such
refractive lens elements constituting a first "refractive" element
group are preferably arcuate.
[0133] Furthermore, in the present invention, first and second
reflecting element groups 220a and 220b and first and second
reflective element groups 360a and 360b are depicted as having
plurality of reflecting elements E.sub.1 and E.sub.2 which are
densely in an array arranged with essentially no gaps between the
individual elements. However, in the second reflective element
groups 220b and 360b (FIGS. 15 and FIG. 23), plurality of
reflecting elements E.sub.2 need not be so densely arranged. This
is because numerous light source images corresponding respectively
to the reflecting elements E.sub.2 are formed on second reflective
element group 220b and 360b, or in the vicinity thereof. Light loss
does not occur to the extent that the light source images fit
within the effective reflecting region of each reflecting element
E.sub.2. Accordingly, if the numerous light source images are
formed discretely, the numerous reflecting elements E.sub.2 in the
second reflective element group can be arranged discretely with
gaps. The same holds true for second reflective element group
360b.
[0134] With reference now to FIG. 25, exposure apparatus 400
performs the exposure operation by a step-and-scan method according
to the first mode for carrying out the present invention in a
manner similar to that described in connection with exposure
apparatus 50 of FIG. 4. The elements in exposure apparatus 400
having the same function as those in exposure apparatus 50 of FIG.
4 are assigned the same reference symbol. Exposure apparatus 400
uses, in a preferred embodiment, light in the soft X-ray region on
the order of .lambda.=5-20 nm EUV (Extreme Ultra Violet) light. In
FIG. 25, the Z-direction is the direction of optical axis A.sub.P
of projection optical system 76 that forms a reduced image of
reflective mask M onto wafer W. The Y-direction is the direction
within the paper surface and orthogonal to the Z-direction. The
X-direction is the direction perpendicular to the paper surface and
orthogonal to the Y-Z plane.
[0135] Exposure apparatus 400 projects onto wafer W the image of
one part of the circuit pattern (not shown) drawn on front side
M.sub.F of mask M through projection optical system 76. The entire
circuit pattern of mask M is transferred onto each of a plurality
of exposure regions on wafer W by scanning mask M and wafer W in a
one-dimensional direction (Y direction) relative to projection
optical system 76.
[0136] Since soft X-rays (EUV light) have a low transmittance
through the atmosphere, the optical path through which this light
passes is enclosed in vacuum chamber 410 and isolated from the
outside air.
[0137] With continuing reference to FIG. 25, light source 54
supplies light beam 100 having a high illumination intensity and a
wavelength from the infrared region to the visible region. Light
source 54 may be, for example, a YAG laser, an excimer laser or a
semiconductor laser. Light beam 100 from light source 54 is
condensed by condenser optical member 412 to a position 414. Nozzle
416 provides a jet of gaseous matter toward position 414, where it
receives laser light beam 100 of a high illumination intensity. At
this time, the jetted matter reaches a high temperature due to the
energy of laser light beam 100, is excited into a plasma state, and
discharges EUV light 419 when the gaseous matter transitions to a
low-energy state.
[0138] An elliptical mirror 418 is arranged at the periphery of
position 414 such that its first focal point (not shown) nearly
coincides with convergent position 414. A multilayer film is
provided on the inner surface 418S of elliptical mirror 418 to
reflect EUV light 419. The reflected EUV light 419 is condensed at
a second focal point 420 of elliptical mirror 418 and then proceeds
to a collimating mirror 422, which is preferably concave and may be
paraboloidal. Collimating mirror 422 is positioned such that the
focal point (not shown) thereof nearly coincides with second focal
point 420 of elliptical mirror 418. A multilayer film is provided
on the inner surface 422S of collimating mirror 422 to reflect EUV
light 419. Condenser optical member 412, elliptical mirror 418 and
collimating mirror 422 constitute a condenser optical system. Light
source 54, and the condenser optical system constitute a light
source unit LSU with optical axes A.sub.L1 and A.sub.L2. EUV light
419 reflected by collimating mirror 422 proceeds to optical
integrator (e.g. reflecting type fly's eye system) 220 in a nearly
collimated state. A multilayer film is provided onto the plurality
of reflecting surfaces constituting first and second reflecting
element groups 220a and 220b to enhance reflection of EUV light
419.
[0139] Exposure apparatus 400 further includes a first variable
aperture stop AS1 provided at the position of the reflecting
surface of second reflecting element group 220b or in the vicinity
thereof. Variable aperture stop AS1 is capable of varying the
numerical aperture NA of the light illuminating mask M (i.e., the
illumination numerical aperture). First variable aperture stop AS1
has a nearly circular variable aperture, the size of which is
varied by a first drive system DR1 operatively connected
thereto.
[0140] A collimated EUV light beam 428 from collimating mirror 422
includes a wavefront 430 that is split by first reflecting element
group 220a and is condensed to form a plurality of light source
images (not shown), as discussed above. The plurality of reflecting
elements E.sub.2 of second reflecting element group 220b are
positioned in the vicinity of the location of the plurality of
light source images. The plurality of reflecting elements E.sub.2
of second reflecting element group 220b substantially acts as field
mirrors. In this manner, optical integrator 220 forms a plurality
of light source images as secondary light sources from
approximately parallel light beam 428. The EUV lightbeam 432
(comprising a plurality of light beams) from the secondary light
sources formed by optical integrator 220 proceeds to condenser
mirror 66 positioned such that the secondary light source images
are formed at or near the focal point of the condenser mirror.
Light beam 432 is reflected and condensed by condenser mirror 66,
and is deflected to mask M by fold mirror 68. A multilayer film
that reflects EUV light is provided on surface 66S of condenser
mirror 66 and surface 68S of fold mirror 68. Condenser mirror 66
condenses EUV light in light beam 432 in a superimposed manner,
forming an arcuate illumination field on front side M.sub.F of mask
M.
[0141] A multilayer film that reflects EUV light is provided on
front side M.sub.F of mask M. Thus, EUV light incident thereon is
reflected from mask M as light beam 434. The latter passes to
projection system 76, which images mask M onto wafer W as the
photosensitive substrate.
[0142] In the present mode for carrying out the present invention,
it is preferable to spatially separate the optical paths of light
beam 432 that proceeds to mask M and light beam 434 reflected by
the mask that proceeds to projection optical system 76. In this
case, the illumination system is nontelecentric, and projection
optical system 76 is also nontelecentric on the mask M side.
Projection optical system 76 also includes multilayer films that
reflects EUV light provided on the reflecting surfaces of the four
mirrors 78a-78d for enhancing EUV light reflectivity.
[0143] Mirror 78c in projection optical system 76 is arranged at
the pupil position or in the vicinity thereof. A second variable
aperture stop AS2 capable of varying the numerical aperture of
projection optical system 76 is provided at the reflecting surface
of mirror 78C or in the vicinity thereof. Second variable aperture
stop AS2 has a nearly circular variable aperture, the diameter of
which is capable of being varied by second drive system DR2
operatively connected thereto.
[0144] The ratio of the numerical aperture of the illumination
system NA.sub.1 to the numerical aperture NA.sub.P of projection
optical system 76 is called the coherence factor, or .sigma. value
(i.e., .sigma.=NA.sub.I/NA.sub.p).
[0145] Due to the degree of fineness of the pattern on mask M to be
transferred to wafer W and the process of transferring this pattern
to wafer W, it is often necessary to adjust the resolving power and
depth of focus and the like of projection optical system 76 by
varying the .sigma. value. Consequently, exposure information
related to the exposure conditions of each wafer W sequentially
mounted on wafer stage WS by a transport apparatus (not shown)
(wafer transport map and the like that includes exposure
information), and the mounting information of each type of mask M
sequentially mounted on mask stage MS is input to a control
apparatus MCU through input apparatus IU, such as a console
electrically connected thereto. Control apparatus MCU is
electrically connected to first and second drive systems DR1 and
DR2. Based on the input information from input apparatus IU, each
time a wafer W is mounted on substrate stage WS, control apparatus
MCU determines whether to change the .sigma. value. If control
apparatus MCU determines that it is necessary to change the .sigma.
value, a signal is sent therefrom to at least one of two drive
systems DR1 and DR2, to vary at least one aperture diameter among
first variable aperture stop AS1 and second variable aperture stop
AS2. Consequently, the appropriate exposure can be achieved under
various exposure conditions. The light intensity distribution at a
pupil position of projection optical system 76 is changed by using
the illumination condition changing system including first variable
aperture stop AS1, second variable aperture stop AS2 and drive
systems DR1 and DR2.
[0146] With continuing reference to FIG. 25, it is preferable in
the present embodiment to replace collimating mirror 422 with a
collimating mirror having a different focal length, in response to
varying the aperture diameter of first variable aperture stop AS1.
As a result, the diameter of EUV light beam 428 incident optical
integrator 220 can be changed in accordance with the size of the
opening of first variable aperture stop AS1. In this manner,
illumination at an appropriate .sigma. value is enabled while
maintaining a high illumination efficiency.
[0147] The light illumination intensity distribution on mask M or
wafer W of exposure apparatus 400 may be nonuniform, in the sense
that it is biased. In this case, this bias can be corrected by
making light beam 428 eccentric prior to traversing reflecting
element group 220a. For example, by making collimating mirror 422
slightly eccentric, the bias of the light illumination intensity
distribution can be corrected. In other words, if the bias of the
intensity distribution occurs in the lateral X-direction of the
arcuate illumination field IF (or in arcuate image field IF' on
surface W.sub.S of wafer W), the bias can be corrected by moving
collimating mirror 422 in the X-direction. If the illumination
intensity in arcuate illumination field IF at the center part and
peripheral part differs in the width direction, respectively, the
bias of the light illumination intensity distribution can be
corrected by moving collimating mirror 422 in the same
direction.
[0148] When varying at least one aperture diameter among first
variable aperture stop AS1 and second variable aperture stop AS2,
there are cases wherein the illumination deteriorates. For example,
illumination non-uniformity occurs over the arcuate illumination
field IF. In this case, it is preferable to correct illumination
non-uniformity and the like over the arcuate illumination field IF
by slightly moving at least one of collimating mirror 422, optical
integrator 220 and condenser mirror 66.
[0149] With reference now to FIG. 26, exposure apparatus 450, which
is an alternate embodiment of exposure apparatus 400, is now
described by highlighting the difference between these two
apparatus.
[0150] The first difference between exposure apparatus 400 and
exposure apparatus 450 is that exposure apparatus includes a turret
plate 452 instead of first variable aperture stop AS1. Turret plate
452 is connected to a drive shaft 454, connected to first drive
system DR1. Turret plate 452 is thus rotatable about a rotational
axis A.sub.R by first drive system DR1. With reference to FIG. 27,
turret plate 452 comprises a plurality of aperture stops 456a-456f
having different shapes and sizes. Turret plate 452 is discussed in
more detail, below.
[0151] With reference again to FIG. 26, exposure apparatus 450
further includes an adjustable annular light beam converting unit
460. The latter converts EUV light beam 428 having a circular
cross-section to a light beam 428' having an annular (ring-shaped)
light beam cross section. Unit 460 is movably provided in the
optical path (e.g., light beam 428) between collimating mirror 422
and first reflecting element group 220a of optical integrator
220.
[0152] Annular light beam converting unit 460 has a first
reflecting member 460a with a ring-shaped reflecting surface and
second reflecting member 460b having a conical reflecting surface.
To vary the ratio of the inner diameter of the ring to the outer
diameter of (the so-called "annular ratio") of light beam 428',
first reflecting member 460a and second reflecting member 460b are
moved relative to one another.
[0153] The insertion and removal of annular light beam converting
unit 460 in and out of light beam 428 and the relative movement of
first reflecting member 460a and second reflecting member 460b is
performed by a third drive system DR3 in operable communication
with annular light beam converting unit 460 and electrically
connected to control apparatus MCU.
[0154] With reference now again to FIG. 27, further details
concerning turret plate 452 and annular light beam converting unit
460 are explained. Turret plate 452, as discussed briefly above,
includes a plurality of different aperture stops 456a-456f and is
rotatable about axis A.sub.R. Aperture stop 456a has an annular
(donut-shaped) aperture, and aperture stops 456b and 456e have
circular openings with different aperture diameters. Aperture stop
456c has four fan-shaped openings, and aperture stop 456d has four
circular openings. Aperture stop 456f has an annular ratio (ratio
of outer diameter r.sub.fo to inner diameter r.sub.fi of opening
456.sub.fo of the annular shape) different from that of aperture
stop 456a (with outer diameter r.sub.ao and inner diameter
r.sub.ai).
[0155] In exposure apparatus 450, input apparatus IU is for
inputting information necessary for selecting the method of
illuminating mask M and exposing wafer W. For example, input
apparatus IU inputs exposure information related to the exposure
conditions of each wafer W sequentially mounted by an unillustrated
transport apparatus (wafer transfer map and the like that includes
the exposure information), and mounting information of each type of
mask M sequentially mounted on mask stage MS. This information is
based on the degree of fineness of the mask pattern to be
transferred to wafer W and the process associated with transferring
the pattern to wafer W.
[0156] For example, control apparatus MCU can select illumination
states such as "first annular illumination," "second annular
illumination," "first normal illumination," "second normal
illumination," "first special oblique illumination," and "second
special oblique illumination," based on the information input into
apparatus IU.
[0157] "Annular illumination" aims to improve the resolving power
and depth of focus of projection optical system 76. It does so by
illuminating EUV light onto mask M and wafer W from an oblique
direction by setting the shape of the secondary light sources
formed by optical integrator 220 to an annular shape. "Special
oblique illumination" aims to further improve the resolving power
and depth of focus of projection optical system 76. It does so by
illuminating EUV light onto catoptric mask M and wafer W by making
the secondary light sources formed by optical integrator 220 a
discrete plurality of eccentric light sources. These light sources
are made eccentric by just a predetermined distance from the center
thereof. "Normal illumination" is one that aims to illuminate mask
M and wafer W based on an optimal .sigma. value by making the shape
of the secondary light sources formed by optical integrator 220
nearly circular.
[0158] Based on the input information from input apparatus IU,
control apparatus MCU controls first drive system DR1 to rotate
turret plate 452, second drive system DR2 to change the aperture
diameter of aperture stop AS2 of projection optical system 76, and
third drive system DR3 to insert and remove annular light beam
converting unit 460 in and out light beam 428. Control apparatus
MCU changes the relative spacing between the two reflecting members
460a and 460b in annular light beam converting unit 460.
[0159] If the illumination state on mask M is set to normal
illumination, control apparatus MCU selects "first normal
illumination" or "second normal illumination," based on the input
information from input apparatus IU. "First normal illumination"
and "second normal illumination" have different .sigma. values.
[0160] For example, if control apparatus MCU selects "first normal
illumination," control apparatus MCU rotates turret plate 452 by
driving first drive system DR1 so that aperture stop 456e is
positioned at the secondary light sources formed on exit side 220be
of second reflective element group 220b. Simultaneously, control
apparatus MCU changes, as needed, the aperture diameter of second
aperture stop AS2 via second drive system DR2. At this point, if
annular light beam converting unit 460 is set in light beam 428,
control apparatus MCU withdraws this unit from the illumination
optical path via third drive system DR3.
[0161] If EUV light illuminates the mask pattern of mask M based on
the set condition of the illumination system mentioned above, the
pattern can be exposed onto wafer W through projection optical
system 76 based on the appropriate "first normal illumination"
condition (i.e., an appropriate .sigma. value).
[0162] If control apparatus MCU selects "second normal
illumination," control apparatus MCU rotates turret plate 452 by
driving first drive system DR1 so that aperture stop 456b is
positioned at the secondary light sources formed on exit side 220be
of second reflective element group 220b. Simultaneously, control
apparatus MCU changes, as needed, the aperture diameter of the
second aperture stop AS2 via second drive system DR2. At this
point, if annular light beam converting unit 460 is set in light
beam 428, control apparatus MCU withdraws this unit from the
illumination optical path via third drive system DR3.
[0163] If EUV light illuminates the mask pattern of mask M based on
the set condition of the illumination system mentioned above, the
pattern can be exposed onto wafer W through projection optical
system 76 based on the appropriate "second normal illumination"
condition (i.e., .sigma. value larger than that of first normal
illumination).
[0164] As mentioned in connection with exposure apparatus 400 (FIG.
25), it is preferable in exposure apparatus 450 (FIG. 26) to
replace reflecting mirror 422 with a reflecting mirror having a
focal length different therefrom in response to the varying of the
aperture diameter of first variable aperture stop AS1. As a result,
the beam diameter of light beam 428 can be changed in response to
the size of the opening of first variable aperture stop AS1. Thus,
illumination is enabled with an appropriate .sigma. value while
maintaining a high illumination efficiency.
[0165] If the illumination with respect to mask M is set to oblique
illumination, control apparatus MCU selects, based on the input
information from input apparatus IU, one among "first annular
illumination," "second annular illumination," "first special
oblique illumination" and "second special oblique illumination."
"First annular illumination" and "second annular illumination"
differ in that the annular ratios of the secondary light sources
formed annularly are different. "First special oblique
illumination" and "second special oblique illumination" differ in
their secondary light source distributions. In other words, the
secondary light source in "first special oblique illumination" is
distributed in four fan-shaped regions (aperture stop 456c), and
the secondary light sources in "second special oblique
illumination" are distributed in four circular regions (aperture
stop 456d).
[0166] If "first annular illumination" is selected, control
apparatus MCU rotates turret plate 452 by driving drive system DR1
so that aperture stop 456a is positioned at the position of the
secondary light sources formed on exit side 220be of second
reflective element group 220b. If "second annular illumination" is
selected, control apparatus MCU rotates turret plate 452 by driving
drive system DR1 so that aperture stop 456f is positioned at the
position of the secondary light sources formed on exit side 220be
of second reflective element group 220b. If "first special oblique
illumination" is selected, control apparatus MCU rotates turret
plate 452 by driving drive system DR1 so that aperture stop 456c is
positioned at the position of the secondary light sources formed on
exit side 220be of second reflective element group 220b. If "second
special oblique illumination" is selected, control apparatus MCU
rotates turret plate 452 by driving drive system DR1 so that
aperture stop 456d is positioned at the position of the secondary
light sources formed on exit side 220be of second reflective
element group 220b.
[0167] If one among the above four aperture stops 456a, 456c, 456d,
and 456f is set in light beam 428, control apparatus MCU
simultaneously changes, as needed, the aperture diameter of second
aperture stop AS2 in projection optical system 76 via second drive
system DR2.
[0168] Next, control apparatus MCU sets annular light beam
converting unit 460 in light beam 428 via third drive system DR3
and adjusts the unit. The operation of setting and adjusting
annular light beam converting unit 460 is performed as described
below.
[0169] First, if annular light beam converting unit 460 is not set
in light beam 428, control apparatus MCU sets the unit in the light
beam via third drive system DR3.
[0170] Next, control apparatus MCU changes the relative spacing of
the two reflecting members 460a and 460b in annular light beam
converting unit 460 via third drive system DR3 so that the annular
light beam (now light beam 428') is efficiently guided to the
opening of one aperture stop among the four aperture stops 456a,
456c, 456d, and 456f set on exit side 220be of second reflective
element group 220b. As a result, annular light beam converting unit
460 can convert light beam 428 incident thereon to annular light
beam 428' having an appropriate annular ratio.
[0171] Secondary light sources (not shown) formed by optical
integrator 220 can, by the setting and adjustment of the above
annular light beam converting unit 460, be rendered annular
secondary light sources having an appropriate annular ratio
corresponding to the opening of each of the four aperture stops
456a, 456c, 456d, and 456f. Thus, oblique illumination of mask M
and wafer W can be performed with a high illumination efficiency.
The light intensity distribution at a pupil position of projection
system 76 is changed by using the illumination condition changing
system including turret plate 452 having plurality of aperture
stops 456a-456f, second variable aperture stop AS2, annular light
beam converting unit 460 and three drive systems DR1, DR2 and
DR3.
[0172] Thus, one of a plurality of aperture stops 456a-456f having
mutually differing shapes and sizes can be set in the illumination
optical path by rotating turret plate 452. Thus, the illumination
state, such as illumination unevenness, of the arcuate illumination
field IF or the arcuate image field IF' may change. It is
preferable to correct this illumination unevenness by slightly
moving at least one of collimating mirror 422, optical integrator
220 and condenser mirror 66.
[0173] With continuing reference to FIG. 26 and exposure apparatus
450, information like the illumination condition is input to
control apparatus MCU via input apparatus IU. However, a detector
(not shown) that reads the information on mask M may also be
provided. Information related to the illumination method is
recorded by, for example, a barcode and the like at a position
outside the region of the mask pattern of mask M. The detector
reads the information related to this illumination condition and
transmits it to control apparatus MCU. The latter, based on the
information related to the illumination condition, controls the
three drive apparatus DR1-DR3, as described above, to set the
illumination.
[0174] In exposure apparatus 450, one of aperture stops 456a-456f
is provided at exit side 220be of optical element group 220b (i.e.,
the position of the secondary light sources). However, illumination
by aperture stops 456c and 456d having four eccentric openings need
not be provided. Also, aperture stops 456a-456f formed on turret
plate 452 are not essential to the present invention in the case of
performing "annular illumination" or "normal illumination," as will
be understood by one skilled in the art from the theory of the
present invention.
[0175] Four eccentric light beams can be formed by constituting
first reflecting member 460a, in annular light beam converting unit
460, by two pairs of plane mirror elements (not shown) arranged
opposite one another and mutually inclined, and by constituting the
reflecting surface of reflecting member 460a in a square column
shape. As a result, the secondary light sources formed by optical
integrator 220 can be rendered quadrupole secondary light sources
eccentric to the center thereof. Accordingly, EUV light
corresponding to the openings of aperture stops 456c and 456d
having four eccentric openings can be formed.
[0176] With reference now to FIG. 28, exposure apparatus 500, which
is another modified version of exposure apparatus 400, is now
described. In exposure apparatus 500, as well as in exposure
apparatus 550 and 600 discussed below (FIGS. 29 and 30), elements
AS1, 452, AS2, DR1, DR2, IU and MCU are included, as discussed
above. However, these elements are not shown in FIGS. 28-36 for the
sake of illustration.
[0177] The difference between exposure apparatus 400 shown and
exposure apparatus 500 of FIG. 28 is that the latter includes an
auxiliary optical integrator 510. With reference also to FIGS. 29
and 30, auxiliary optical integrator 510 includes a first auxiliary
reflecting element group 510a and a second auxiliary reflecting
element group 510b. Exposure apparatus 500 further includes a relay
mirror 514 as a relay optical system. Optical integrator 510 and
mirror 5.14 are respectively arranged in the optical path between
reflecting mirror 422 and optical integrator 220. Auxiliary optical
integrator 510 is preferably a catoptric fly's eye system. If
viewed in order from light source 54, auxiliary optical integrator
510 can be seen as a first optical integrator (i.e., first multiple
light source forming optical system), and in combination with a
second or main optical integrator 220.
[0178] First auxiliary reflecting element group 510a comprises a
plurality of reflecting elements E.sub.510a (FIG. 29) arranged on
the entrance side 510ae of auxiliary optical integrator 120.
Elements E.sub.510a are preferably formed in a shape similar to the
overall shape (outline) of first reflecting element group 220a
arranged on the entrance side of optical integrator 220 (see FIGS.
14 and 22). However, if reflecting elements E.sub.510a are
constituted in a shape as shown in FIGS. 14 and 22, it is difficult
to densely arrange the reflecting elements without gaps in between.
Consequently, with reference to FIGS. 29 and 30, each of the
reflecting elements E.sub.510a in first auxiliary reflecting
element group 510a is nearly square in shape. Now, the cross
section of light beam 428 incident first auxiliary reflecting
element group 510a is nearly circular, and reflecting elements
E.sub.510a are arranged in a row so that the overall shape
(outline) of this group is nearly circular. As a result, first
auxiliary reflecting element group 510a can form numerous light
source images (secondary light sources) with high illumination
efficiency at the position of second auxiliary reflecting element
group 510b, or in the vicinity thereof.
[0179] The overall shape (outline) of second auxiliary reflecting
element group 510b arranged on the exit side of auxiliary optical
integrator 510 is preferably formed in a similar shape to that of
reflecting elements E.sub.2 comprising second reflecting element
group 220b arranged on the exit side of optical integrator 220, as
shown in FIGS. 15 and 23. Each reflecting element E.sub.510b in
second auxiliary reflecting element group 510b is preferably shaped
similar to the shape of the light source images formed by
reflecting elements E.sub.510a in first auxiliary reflecting
element group 510a so that it receives all the light source
images.
[0180] In exposure apparatus 500, main optical integrator 220
preferably comprises first and second reflecting element groups
360a and 360b (FIGS. 22 and 23) in place of reflecting element
groups 220a and 220b (both reference numbers being used hereinafter
to indicate either can be used for the first and second reflecting
element groups of main optical integrator 220). Consequently,
plurality of reflecting elements E.sub.2 in second reflecting
element group 360b (220b) arranged on the exit side of optical
integrator 220 have a shape that is nearly square, as shown in FIG.
23.
[0181] With continuing reference to FIG. 28, the light source
images (not shown) formed by each of the plurality of reflecting
elements E.sub.510a comprising first auxiliary reflecting element
group 510a in auxiliary optical integrator 510 are nearly circular.
Thus, the shape of each reflecting element E.sub.510b of second
auxiliary reflecting element group 510b is nearly square, as shown
in FIG. 30. In addition, since the shape of each reflecting element
E.sub.2 that comprises second reflecting element group 360b (220b)
arranged on the exit side of main optical integrator 220 is nearly
square, the reflecting elements therein are arranged in rows so
that the overall shape (outline) of second auxiliary reflecting
element group 510b is nearly square, as shown in FIG. 30.
[0182] In this manner, in exposure apparatus 500 of FIG. 28, first
and second auxiliary reflecting element groups 510a and 510b are
preferably constituted by the same type of reflecting element
group. This allows manufacturing costs to be controlled.
[0183] It is also preferable that second reflecting element group
220b and condenser mirror 66 satisfy the relation in condition (2),
discussed above.
[0184] With continuing reference to FIG. 28, the action of optical
integrators 220 and 510 are now explained in more detail. By the
arrangement of optical integrators 220 and 510, a plurality of
light source images (not shown) are formed. The number of light
source images corresponds to the product of the number (N) of
reflecting elements in one of the reflecting element groups in
optical integrator 510 and the number (M) of reflecting elements in
one of the reflecting element groups in main optical integrator
220. The plurality of light source images are formed on the surface
of one of the second reflecting element groups 360b (220b) in main
optical integrator 220, or in the vicinity thereof. Accordingly,
many more light source images (tertiary light sources, not shown)
than the light source images (secondary light sources) formed by
auxiliary optical integrator 510 are formed on the surface of main
reflecting element group 360b (220b), or in the vicinity thereof.
Light from the tertiary light sources from main optical integrator
220 arcuately illuminate mask M in a superimposed manner. Thus, the
illumination distribution in arcuate illumination field IF formed
on mask M and arcuate image field IF' formed on wafer W can be
rendered more uniform, allowing for a much more stable
exposure.
[0185] Relay mirror 514 arranged between optical integrators 510
and 220 condenses light beam 520 from the numerous light source
images (secondary light sources) from optical integrator 510,
thereby forming a light beam 522 directed to optical integrator
220. Relay mirror 514 serves the function of making the near
surface (i.e., entrance side 510ae) of reflecting element group
510a and the near surface (i.e., entrance side 220ae) of the
reflecting element group 220a (360a) optically conjugate. Relay
mirror 514 also serves the function of making the near surface
(i.e., exit side 510be) of reflecting element group 510b and the
near surface (i.e., exit side 220be) of the reflecting element
group 360b (220b) optically conjugate. Surface 510ae and surface
220ae are optically conjugate mask M and wafer W. Also, surface
220be and surface 510be are optically conjugate the pupil of
projection optical system 76 and the position of aperture stop
AS2.
[0186] With continuing reference to FIG. 28 and exposure apparatus
500, if the illumination intensity distribution in arcuate
illumination field IF is biased, it is preferable to move auxiliary
optical integrator 510 (i.e., move reflecting element groups 510a
and 510b as a unit). If reflecting element groups 360a (220a) and
360b (220b) in main optical integrator 220 are made eccentric in
the X-direction or Z-direction, the biased component of the
illumination intensity distribution can be corrected and a uniform
illumination intensity distribution can be obtained by the action
of coma generated by main optical integrator 220.
[0187] For example, if bias occurs in the illumination intensity
distribution in the lateral direction (X-direction) of arcuate
illumination field IF or in arcuate image field IF', respectively,
the bias can be corrected by moving optical integrator 510 in the
X-direction. In addition, if the illumination intensity differs
between the center part and peripheral part in the width direction
of the arcuate illumination field IF or arcuate image field IF',
the bias in the illumination intensity distribution can be
corrected by moving auxiliary optical integrator 510 in the same
direction.
[0188] For exposure apparatus 500 to properly form an image of mask
M on wafer W, it is preferable to form a well-corrected image of
the exit pupil of the illumination system at the center of the
entrance pupil of projection optical system 76 (i.e., an image of
tertiary light sources formed by optical integrator 220). If this
condition is not satisfied, it is preferable to move the position
of the exit pupil of the illumination system, to adjust the
telecentricity of the illumination system, and to coordinate with
the position of the entrance pupil of projection optical system 76.
For example, by moving main optical integrator 220 (i.e., two
reflecting element groups 360a (220a) and 360b (220b)) and first
aperture stop AS1 as a unit, the telecentricity of the illumination
system is adjusted, and the center of the exit pupil image of the
illumination system is made to coincide with the center of the
entrance pupil of projection optical system 76. However, if it is
not necessary to provide aperture stop AS1 at the position of the
tertiary light sources, then reflecting element groups 360a (220a)
and 360b (220b) in main optical integrator 220 are preferably moved
as a unit.
[0189] In exposure apparatus 400 (FIG. 25) and exposure apparatus
450 (FIG. 26), discussed above, to match the image of the exit
pupil of the illumination system to the center of the entrance
pupil of projection optical system 76, the center of the exit pupil
image of the illumination system can be made to coincide with the
center of the entrance pupil of projection optical system 76 by
moving optical integrator 220 and first aperture stop AS1 as a
unit. If it is not necessary to provide aperture stop AS1 at the
position of the secondary light sources, then reflecting element
groups 360a (220a) and 360b (220b) are preferably moved as a
unit.
[0190] In exposure apparatus 400 (FIG. 25), 450 (FIG. 26) and 500
(FIG. 28), discussed above, light source unit LSU in practice
generally occupies a considerable volume. It is a possibility that
this volume can become equal to or larger than the exposure
apparatus body unit (optical system and control system from optical
integrator 220 to wafer stage WS). Consequently, it may be
preferred to separate light source unit LSU and the exposure
apparatus body unit, with light source unit LSU and the exposure
apparatus body unit installed independently on a base. In this
case, strain in the floor may occur due to, for example, vibration
of the floor caused by people near the apparatus, or due to the
weight of the light source unit and the exposure apparatus body
unit themselves. Thus, there is a risk that the light source unit
optical axes (A.sub.L1 and A.sub.L2) and the optical system axis
(e.g., axis A.sub.P or A.sub.C) in the exposure apparatus body unit
will become displaced, upsetting the adjustment state of the
exposure apparatus.
[0191] Accordingly, with reference to FIG. 28, it is preferable to
arrange a photoelectric detector 528 in the optical path of the
exposure apparatus body unit (i.e., in the optical path from
optical integrator 220 to wafer stage WS). Photodetector 528
photoelectrically detects a relative displacement of light source
unit optical axis A.sub.L1 and/or A.sub.L2, and provides a control
signal to a detector control unit 530 that is operably connected to
and controls the inclination of collimating mirror 422.
Consequently, even if vibration of the floor due to walking and the
like of operators or strain in the floor occurs, at least one of
light source unit optical axes A.sub.L1 and A.sub.L2 and an optical
axis (e.g., optical axis A.sub.p or A.sub.c) of the optical system
inside the exposure apparatus body unit can be aligned
automatically.
[0192] Because it is difficult to obtain high reflectance for soft
X-ray mirrors, it is desirable to reduce the number of mirrors in
the optical system of a soft X-ray exposure apparatus. One
technique to reduce the number of mirrors in the present invention
involves eliminating condenser mirror 66. This is achieved by
bending the entirety of one of second reflecting element group 360b
(220b) in optical integrator 220 (FIG. 15 and FIG. 23). In other
words, by constituting second reflecting element group 360b (220b)
by arranging in a row numerous reflecting elements E.sub.2 within a
reference spherical surface (reference curved surface) having a
predetermined curvature, the function of condenser mirror 66 can be
incorporated into second reflecting element group 360b (220b).
Thus, with reference now to FIG. 31, and exposure apparatus 550 and
also to FIG. 21, a second reflective element group 220c combines
the function of condenser mirror 66 in one of second reflecting
element group 360b (220b) in optical integrator 220. By modifying
the configuration of second reflecting element group 360b (220b) of
main optical integrator 220 of exposure apparatus 500 (FIG. 28),
the function of condenser mirror 66 can be combined therein as
well. Projection optical system 76 in FIG. 31 comprises six mirrors
78a-78f to still further improve imaging performance.
[0193] Exposure apparatus 400 to 550 of the present invention
preferably use a laser plasma light source. However, such a light
source has the disadvantage of generating a spray of microscopic
matter. If optical parts are contaminated by this fine spray, the
performance of the optical system, which is based in part on mirror
reflectance and reflection uniformity, deteriorates. Thus, with
reference to FIG. 32 and exposure apparatus 600, it is preferable
to arrange, with vacuum chamber 410, a sub-chamber 602 which houses
a portion of nozzle 416, and elliptical mirror 418. Chamber 602
includes a filter window 604 capable of transmitting only soft
X-rays while blocking transmission of the dispersed microscopic
particles. A thin film of a light element (i.e., a membrane) may be
used as filter 604. In the present arrangement, vacuum chamber 410
also includes a second window 606 capable of passing light from
light source 54 into chamber 602. This arrangement may be used with
any of exposure apparatus 400-550 of the present invention as
well.
[0194] If filter 604 is provided between elliptical mirror 418 and
collimator collimating mirror 422, operating costs can be kept low
by replacing elliptical mirror 418 and filter 604 when
contamination occurs.
[0195] Exposure apparatus 400-600 are enclosed in vacuum chamber
410, since the transmittance of soft X-rays through the atmosphere
is relatively low. Nevertheless, it is difficult for the heat
remaining in the optical parts to escape. As a result, the mirror
surfaces tend to warp. Accordingly, it is preferable to provide a
cooling mechanism (not shown) for each of the optical parts inside
vacuum chamber 410. More preferably, if a plurality of cooling
mechanisms is attached to each mirror and the temperature
distribution inside the mirror controlled, then warping of the
mirrors during the exposure operation can be further
controlled.
[0196] In addition, a multilayer film is provided on the reflecting
surfaces in exposure apparatus 400-600. It is preferable that this
multilayer film be formed by layering a plurality of materials from
among molybdenum, lithium, rhodium, silicon and silicon oxide.
[0197] As is apparent from the above description, the present
invention has many advantages. A first advantage of the present
invention is that a surface of an object, such as a mask surface,
can be illuminated uniformly and efficiently over an arcuately
shaped illumination field while maintaining a nearly fixed
numerical aperture of the illumination light. A second advantage is
that the illumination coherence can be varied to suit the
particular pattern on the mask to be imaged onto the wafer by
varying the size of the aperture stops in the illuminator and in
the projection optical system. A third advantage is that the
illumination beam can be altered through the use of an adjustable
annular light beam converting unit. A fourth advantage is that one
of a plurality of aperture stops can be inserted into the
illumination system to alter the illumination coherence. A fifth
advantage is that a bias in the illumination uniformity can be
compensated by measuring the light beam uniformity and adjusting
the collimating mirror in the illuminator based on the uniformity
measurement.
[0198] While the present invention has been described in connection
with preferred embodiments, it will be understood that it is not so
limited. On the contrary, it is intended to cover all alternatives,
modifications and equivalents as may be included within the spirit
and scope of the invention as defined in the appended claims.
* * * * *