U.S. patent number RE34,634 [Application Number 07/924,789] was granted by the patent office on 1994-06-07 for light illumination device.
This patent grant is currently assigned to Nippon Kogaku Kabushiki Kaisha. Invention is credited to Kunio Konno, Masashi Okada.
United States Patent |
RE34,634 |
Konno , et al. |
June 7, 1994 |
Light illumination device
Abstract
A device for providing an illumination of an object includes
first and second optical integrators disposed on an optical axis in
spaced-apart relationship. Light rays emitted from a point light
source formed by an elliptical reflector mirror having a
light-emitting source are incident on the first optical integrator,
which forms a plurality of secondary images of the point light
source. The second optical integrator receives luminous fluxes
emitted from the secondary light source images to form a
multiplicity of secondary images of the secondary light source
images formed by the first optical integrator. Luminous fluxes from
the secondary images formed by the second optical integrator are
superimposed by a condenser lens on the object for illuminating the
latter with light beams of uniform intensity.
Inventors: |
Konno; Kunio (Yokohama,
JP), Okada; Masashi (Yotsukaido, JP) |
Assignee: |
Nippon Kogaku Kabushiki Kaisha
(Tokyo, JP)
|
Family
ID: |
27286904 |
Appl.
No.: |
07/924,789 |
Filed: |
August 6, 1992 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
823873 |
Jan 28, 1986 |
|
|
|
Reissue of: |
468551 |
Feb 22, 1983 |
04497015 |
Jan 29, 1985 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Feb 26, 1982 [JP] |
|
|
57-30268 |
|
Current U.S.
Class: |
362/268; 353/38;
353/88; 355/67 |
Current CPC
Class: |
G03F
7/70075 (20130101); F21W 2131/402 (20130101) |
Current International
Class: |
F21S
8/00 (20060101); G03F 7/20 (20060101); F21V
007/04 () |
Field of
Search: |
;362/268,32,293,308,331,346 ;353/38,97,98 ;355/67,71
;359/619,621,622 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Cole; Richard R.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Parent Case Text
.Iadd.This is a continuation of application No. 07/823,873 filed
Jan. 28, 1986, abandoned. .Iaddend.
Claims
What is claimed is:
1. A device for uniformly illuminating an object comprising:
(a) means for providing a light source;
(b) first optical means disposed to intersect across light energy
emitted from said light source, said first optical means including
a first multiplicity of lens elements for forming a multiplicity of
images of said light source on a first focal plane and a second
multiplicity of lens elements disposed in the vicinity of said
first focal plane and corresponding respectively to said first
multiplicity of lens elements for forming an image of said first
multiplicity of lens elements on a second focal plane;
(c) second optical means disposed to intersect across light energy
emitted from said first optical means, said second optical means
including a third multiplicity of lens elements disposed in the
vicinity of said second focal plane for forming a multiplicity of
images of said second multiplicity of lens elements on a third
focal plane and a fourth multiplicity of lens elements disposed in
the vicinity of said third focal plane and corresponding
respectively to said third multiplicity of lens elements; and
(d) third optical means for superimposing light energy emitted from
said second optical means on said object.
2. A device according to claim 1, wherein said first optical means
includes collimator means disposed between said light source and
said first multiplicity of lens elements for converting the light
energy from said light source into collimated light energy.
3. A device according to claim 1, wherein said third optical means
includes condenser lens means, said fourth multiplicity of lens
elements cooperating with said condenser lens means to form an
image of said third multiplicity of lens elements on said
object.
4. A device for projecting a pattern on a photomask onto a base
plate through a projecting optical system, comprising:
(a) means for providing a light source;
(b) first optical means disposed to intersect across light energy
emitted from said light source, said first optical means including
a first multiplicity of lens elements for forming a multiplicity of
images of said light source on a first focal plane and a second
multiplicity of lens elements disposed in the vicinity of said
first focal plane and corresponding respectively to said first
multiplicity of lens elements for forming an image of said first
multiplicity of lens elements on a second focal plane;
(c) second optical means disposed to intersect across light energy
emitted from said first optical means, said second optical means
including a third multiplicity of lens elements disposed in the
vicinity of said second focal plane for forming a multiplicity of
images of said second multiplicity of lens elements on a third
focal plane and a fourth multiplicity of lens elements disposed in
the vicinity of said third focal plane and corresponding
respectively to said third multiplicity of lens elements; and
(d) third optical means disposed to intersect across light energy
emitted from said second optical means, said third optical means
forming an image of said fourth multiplicity of lens elements on a
pupil of said projecting optical system.
5. A device for uniformly illuminating an object, comprising:
(a) means for providing a light source;
(b) collimator means for converting the light energy from said
light source into collimated light energy;
(c) first multiplicity of imaging lens elements and second
multiplicity of imaging lens elements disposed in matrix form,
respectively, adjacent to a first plane and a second plane which
intersects perpendicular to said collimated light energy in order,
said second multiplicity of imaging lens elements each
corresponding to said first multiplicity of imaging lens
elements;
(d) third multiplicity of imaging lens elements and fourth
multiplicity of imaging lens elements disposed in matrix form,
respectively, adjacent to a third plane and a fourth plane which
intersect perpendicular to the light energy passing through said
first and second planes in order, said fourth multiplicity of
imaging lens elements each corresponding to said third multiplicity
of imaging lens elements; and
(e) wherein said light source, said second plane, and said fourth
plane .[.and said object.]. are in optically conjugate relation to
one another and said first plane and said third plane are in
optically conjugate relation to each other.
6. A device according to claim 5, wherein each of said lens
elements of said second multiplicity of imaging lens elements has
an image magnification .beta..sub.1 satisfying the relationship
.beta..sub.1 =R.sub.2 /d.sub.1, and each of said lens elements of
said third multiplicity of imaging lens elements has an image
magnification .beta..sub.2 satisfying the relationship .beta..sub.2
=d.sub.2 /R.sub.1, where R.sub.1 is the aperture of the first and
second multiplicities of imaging lens elements, d.sub.1 the
aperture of each of said lens elements of said first and second
multiplicities of imaging lens elements, R.sub.2 the aperture of
the third and fourth multiplicities of imaging lens elements, and
d.sub.2 the aperture of each of said lens elements of said third
and fourth multiplicity of imaging lens elements. .Iadd.
7. An illuminating apparatus for irradiating a surface, said
apparatus comprising:
illuminating means for forming a plurality of secondary light
sources;
multi-beam forming optical means for forming multiple light beams
from the radiant energy from said secondary light sources;
collimating optical means for substantially collimating the radiant
energy from said secondary light sources and directing the radiant
energy to said multi-beam forming optical means to be formed as
multiple light beams thereby; and
converging optical means for converging the radiant energy as the
multiple light beams from said multi-beam forming optical means on
the surface to be irradiated. .Iaddend. .Iadd.8. An illuminating
apparatus according to claim 7, wherein said illuminating means
comprises a light source, a multi-beam forming optical element for
forming multiple light beams as said plurality of light sources,
and converging optical element for converging the radiant energy
from said light source on said multi-beam forming optical element.
.Iaddend. .Iadd.9. An illuminating apparatus according to claim 8,
wherein said multi-beam forming optical element is a set of lens
arrays disposed at the focus positions thereof. .Iaddend. .Iadd.10.
An illuminating apparatus according to claim 8, wherein said
multi-beam forming optical means is a set of lens arrays disposed
at the focus positions thereof, and wherein in the direction of the
optical axis of said apparatus, the forward one of said lens arrays
is disposed substantially on the rearward focal plane of said
collimating optical means, and the rearward one of said lens arrays
is disposed substantially on the forward focal plane of said
converging optical means. .Iaddend. .Iadd.11. An illuminating
apparatus according to claim 8, wherein said converging optical
element comprises an elliptical mirror. .Iaddend. .Iadd.12. An
illuminating apparatus according to claim 7, wherein said
multi-beam forming optical means is a set of lens arrays disposed
at the focus positions thereof. .Iaddend. .Iadd.13. An illuminating
apparatus for irradiating a surface, said apparatus comprising:
a light source for producing light;
first multi-beam forming optical means for forming multiple light
beams;
first converging optical means for converging the light produced by
said light source on said first multi-beam forming optical means to
be formed into multiple light beams thereby;
second multi-beam forming optical means for forming multiple light
beams;
lens means for converging the multiple light beams from said first
multi-beam forming optical means on said second multi-beam forming
optical means to be formed into multiple light beams thereby;
and
second converging optical means for converging the multiple light
beams from said second multi-beam forming optical means on the
surface to be
irradiated. .Iaddend. .Iadd.14. An illuminating apparatus according
to claim 13, wherein said surface to be irradiated is provided with
a mask. .Iaddend. .Iadd.15. An illuminating apparatus according to
claim 13, wherein said first multi-beam forming optical means is a
set of lens arrays disposed at the focus positions thereof.
.Iaddend. .Iadd.16. An illuminating apparatus according to claim
13, wherein said multi-beam forming optical means is a set of lens
arrays disposed at the focus positions thereof. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light illumination device for
illuminating an object with light rays uniform in intensity, and
more particularly to a light illumination system suitable for use
in an exposure device for fabricating semiconductor devices such as
ICs.
2. Description of the Prior Art
Exposure devices for transferring integrated-circuit patterns on
reticles or photomasks onto substrates need a light illumination
device for providing an illumination by light rays having a flat or
uniform intensity distribution in order to project an image of the
fine circuit patterns onto a substrate with a higher
resolution.
One such light illumination device is known from U.S. Pat. No.
3,296,923 issued on Jan. 10, 1967 to J. R. Miles.
The light illumination device as described in the above-mentioned
U.S. Patent has a collimating lens for collimating a luminous flux
or light beam from an elliptical reflector mirror, first and second
lenticular lenses for forming a plurality of secondary light
sources from the luminous flux from the collimating lens, and a
large aperture condenser lens disposed between the lenticular
lenses and a substrate. This prior art light illumination device is
capable of correcting luminous flux having an annular intensity
distribution pattern weaker in the vicinity of the optical axis and
stronger at the peripheral edge in the opening of the elliptical
mirror, into luminous flux having a substantially flat intensity
distribution on an object surface disposed behind the condenser
lens. With the conventional device, however, the luminous flux of
flat intensity distribution is available only on a plane
corresponding to the object surface, and the annular intensity
distribution pattern is left unremoved anywhere behind the
condenser lens except for the object surface. This is because the
luminous flux per se emitted from the first and second lenticular
lenses have such an intensity distribution pattern.
For providing an illumination of the object with luminous flux rom
the known device, it is necessary to position the object extremely
critically along the optical axis so as to attain a desired flat
intensity distribution pattern on the object. Where the
conventional system is employed, for example, as a light projection
system for projecting an image of the object onto a projection
surface with a projection lens, there is provided a flat intensity
distribution pattern on focal points of the projection lens, that
is, the object surface and the projection surface. However, an
annular intensity pattern is produced at other planes, in
particular, the pupil plane of the projection lens. As a result,
the light projection system suffers from various difficulties such
as a reduction in the resolving power of the projection lens, a
reduction in the depth of focus thereof, and the like.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a light
illumination device for illuminating an object with luminous flux
having a uniform intensity distribution, the light illumination
device being particularly capable of providing an illumination of
substantially uniform intensity in the vicinity of an object
surface.
Another object of the present invention is to provide a light
illumination device for emitting luminous flux having a
substantially uniform intensity distribution anywhere in the path
of illumination.
A light illumination device according to the present invention has
a plurality of optical means for separating incident light beams
into a multiplicity of luminous fluxes. Each of the optical means
is a functional equivalent of a pair of the first and second
lenticular lenses described above. The plurality of optical means
are arranged in series on the optical axis between an elliptical
mirror and an object. The first optical means receives light beams
emitted from a point light source formed by the elliptical mirror
and forms secondary light source images. The second optical means
receives luminous fluxes from the secondary light source images
formed by the first optical means and forms secondary images of the
secondary light source images.
The above and other objects, features and advantages of the present
invention will become more apparent from the following description
when taken in conjunction with the accompanying drawings in which
preferred embodiments of the present invention are shown by way of
illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a schematic plan view of a projection exposure system
having a light illumination device according to an embodiment of
the present invention;
FIG. 1B is a graph showing light intensity distributions in various
positions on an optical axis of the system shown in FIG. 1A;
FIG. 2 is a perspective view of an element lens of an optical
integrator;
FIG. 3 is a perspective view of a modified element lens of the
optical integrator;
FIG. 4 is a perspective view of fly-eye lenses; and
FIG. 5 is a schematic plan view of a contact or proximity type
exposure system incorporating a light ilumination device according
to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1A illustrates the arrangement of optical members of a
reduced-projection exposure system for printing on a wafer an
reduced image of a circuit pattern drawn on a photomask or reticle.
A light-emitting tube 1 has a light source 1a of high brightness
energy disposed in the vicinity of a first focal point of an
elliptical reflector mirror 2. An image P of the light source 1a is
focused by the elliptical reflector mirror 2 at a position near a
second focal point of the mirror 2, the image P serving
substantially as a point light source. A collimator lens 3 is
positioned with its front focal point at the light source image P
for collimating luminous flux from the image P. A first optical
integrator 4 is disposed in the collimated luminous flux for
separating the latter into a multiplicity of luminous fluxes, so
that a plurality of secondary light source images are formed on the
exit side of the optical integrator 4. The luminous fluxes leaving
the optical integrator 4 pass through an output lens 5 and enter a
second optical integrator 7 located between an input lens 6 and an
output lens 8.
Each of the optical integrators 4, 7 is composed of a number of
lens elements each comprising an optical glass block 101 in the
form of a hexagonal prism as shown in FIG. 2. The glass block 101
has front and rear end faces 101a, 101b formed as convex lenses.
The lens elements in each optical integrator are assembled into a
honeycomb configuration.
The transverse cross-sectional shape of each lens element may be
selected to meet a particular application of the light illumination
device. For example, where the region to be illuminated is of a
rectangular shape, it is preferable to employ a lens element 102 in
the form of a quadrangular prism as shown in FIG. 3. The lens
element 102 includes front and rear convex lenses 102a, 102b.
Each of the optical integrators 4, 7 may be composed of an lens
element 103 having a pair of front and rear fly-eye lenses 103a
103b spaced a preset interval from each other as illustrated in
FIG. 4. Each of the fly-eye lenses comprises a flat sheet of glass
having on one surface a multiplicity of small lenses formed by
pressing.
The front lenses 101a, 102a, 103a and the rear lenses 101b, 102b,
103b of the lens elements 101, 102, 103, respectively, have
substantially equal refractive powers. The front and rear lenses
are spaced apart from each other by an interval equal to the rear
focal length of the front lenses and also to the front focal length
of the rear lenses. Therefore, the front lenses 4a of the optical
integrator 4 serve to form the light source image P on the exit
surfaces of the corresponding rear lenses 4b of the optical
integrator 4. The lens 3 can form the light source image P on the
optical axes of the rear lenses 4b. The rear lenses 4b serve to
form the images of the front lenses 4a on the entrance surface of
the second optical integrator 7. The entrance surfaces of the
optical integrators 4, 7 are in conjugate relationship. The lens 5
has a power to position its rear focal point on the entrance
surface of the second optical integrator 7.
The front lenses 7a of the second optical integrator 7 are capable
of forming the image of the exit surface of the first optical
integrator 4 on the exit surfaces of the rear lenses 7b.
Accordingly, the exit surfaces of the optical integrators 4, 7 are
in conjugate relationship. The input lens 6 serves to form the
image of the exit surface of the optical integrator 4 formed on the
exit surfaces of the rear lenses 7b, on the optical axes of the
rear lenses 7b. The rear lenses 7b have powers and radii of
curvature selected to form the images of the entrance surfaces of
the corresponding front lenses 7a on a reticle R through a large
aperture condenser lens 9. By arranging the output lens 8 and the
large aperture condenser lens 9 so that a rear focal point of the
combined system of the lenses 8, 9 is placed on the pattern surface
of the reticle R, a multiplicity of luminous fluxed leaving the
second optical integrator 7 are all superimposed on the reticle
R.
Provision of the output lens 8 is effective in reducing the
aperture of the condenser lens 9 and shortening the distance from
the collimator lens 3 to the reticle R. The condenser lens 9 is
positioned to form the image of the exit surface of the second
optical integrator 7 on a pupil 10a of a projection lens 10. The
projection lens 10 forms the image of the circuit pattern of the
reticle R on a wafer W.
For irradiating the object or reticle R efficiently with luminous
fluxes from the light source image P, the two optical integrators
should be shaped and arranged in tandem or series on to meet the
following conditions:
Let the overall aperture of the first optical integrator 4 be
indicated by R.sub.1, the overall aperture of the second optical
integrator 7 by R.sub.2, the aperture of each lens element of the
first optical integrator 4 by d.sub.1, and the aperture of each
lens element of the second optical integrator 7 by d.sub.2. The
entrance surfaces of the optical integrators should be in mutually
conjugate relationship, and the image magnification .beta..sub.1 of
the rear lenses 4b should meet the relationship .beta..sub.1
=R.sub.2 /d.sub.1. The exit surfaces of the optical integrators
should be in mutually conjugate relationship, and the image
magnification .beta..sub.2 of the front lenses 7a should meet the
relationship .beta..sub.2 =d.sub.2 /R.sub.1. Where each optical
integrator is composed of lens elements of equal shape, the two
optical integrators should be arranged to satisfy the relationship
.beta..sub.1 .multidot..beta..sub.2 =1.
Light intensity distributions in the light path of the optical
system shown in FIG. 1A will be explained.
FIG. 1B is illustrative of such light intensity distributions at
the aperture plane A of the elliptical mirror 2, at the second
focal point plane B, at the entrance and exit surfaces C, D of the
first integrator 4, at the entrance and exit surfaces E, F of the
second optical integrator 7, at the pattern surface G of the
reticle R, at the pupil plane H of the projection lens 10, and at
the surface I of the wafer W. Since the elliptical mirror 2 has a
central opening for the installation of the light-emitting tube 1,
the intensity distribution a at the plane A is of an annular
pattern such that the intensity is weaker in the vicinity of the
optical axis l and stronger at the peripheral edge. The plane B has
an intensity distribution b having a sharp peak on the optical axis
because of the light source image P formed by the elliptical mirror
2. The intensity distribution c at the surface C is of an annular
pattern with a lower intensity in the vicinity of the optical axis
l, the intensity being greater than that of the intensity
distribution pattern at the surface A.
Reduced images of the plane B are formed at the rear ends of the
lens elements of the optical integrator 4. The surface D has a
light intensity distribution d of an annular pattern which is the
product of the intensity distribution at the surface C and the
light intensities at the element lenses.
The surface E has a flat intensity distribution pattern e as the
multiple secondary light source images formed on the surface D are
all superimposed at the surface E. Reduced images of the surface D
are formed on the surface F, that is, secondary light source images
of the secondary light sources are formed on the surface F.
Therefore, as many reduced images are formed on the surface F as
there are element lenses, and the intensity pattern f at the
surface F is generally flat, not annular as is the intensity
pattern d at the surface D, though the pattern f includes small
intensity variations. The surface G of the reticle R has an
intensity distribution g of a flat pattern since all of luminous
fluxes from the lens elements of the second optical integrator 7
are superimposed on the reticle R. The plane H, which is in
conjugate relationship with the surface F, has an intensity
distribution h similar to the intensity distribution f. The
intensity distribution i at the surface I is of a flat pattern as
it is similar to the intensity distribution g at the surface G.
As described above, the optical integrators serve to break up
uneven light rays incident thereon into as many luminous fluxes as
there are lens elements thereof to generate a multiplicity of
secondary light sources immediately behind the optical integrators.
Luminous fluxes emitted from these secondary light sources are
superimposed on the surface illuminated. The secondary light
sources have orientation characteristics that are small divisions
of the orientation characteristics of the original light source.
The divided orientation characteristics are each comparatively
uniform, and will be superimposed so that their irregularities can
be cancelled out. Therefore, the intensity distribution at the
irradiated surface is rendered uniform. If the orientation
characteristics of the original light source remain the same, the
intensity uniformity at the illuminated surface becomes better as
the number of the secondary light sources increase. Assuming that
the number of the lens elements of the first optical integrator 4
is n.sub.1, and the number of the lens elements of the second
optical integrator 4 is n.sub.2, the light source image P at the
second focal point of the elliptical mirror 2 is duplicated into
n.sub.1 light source images at the exit surface of the first
optical integrator 4. Since the image of the surface D is projected
in n.sub.2 duplicates onto the exit surface F of the second optical
integrator 7, a total of n.sub.1 .times.n.sub.2 secondary light
source images of the light source image P are formed on the surface
F. The increased number of the secondary light source images on the
surface F makes the light intensity uniform thereon as a whole.
This uniform intensity is equivalent to that which would be given
by an optical integrator having n.sub.1 .times.n.sub.2 lens
elements. The secondary light source images on the exit surface of
each optical integrator may not necessarily be formed on the
surfaces of the lens elements, but may be generated on positions
spaced from the lens element surfaces in view of flaws and dust on
such surfaces.
With the embodiment of the present invention, not only the reticle
R and the wafer W are uniformly illuminated, but also the exit
plane 10a of the projection lens 10 has a uniform intensity
distribution pattern. As a result, the resolving power of a
projected image is increased, and the projection lens 10 has an
increased depth of focus.
FIG. 5 shows a contact or proximity type exposure system
incorporating a light illumination device of the present invention.
The exposure system has optical elements 1 through 8 which are the
same as those having the same reference numbers in FIG. 1A. The
exposure system of the type described is required to irradiate a
photomask M and a wafer W with parallel luminous fluxes. To this
end, the exposure system includes a condenser lens 11 for
collimating light rays from the exit surface of the second optical
integrator 7, that is, light rays emitted from the multiple
secondary light source images formed on the surface F. The images
of the entrance surfaces E of the front lenses 7a of the lens
elements of the second optical integrator 7 are all superimposed on
the photomask M and the wafer W. Accordingly, the photomask M is
irradiated with highly uniform, parallel luminous fluxes.
With this embodiment, the exit surface of the second integrator 7
has a uniform intensity distribution for a uniform illumination of
the photomask M and the wafer W and a uniform angular spread of
illuminating light rays. As a consequence, ringing due to the
Fresnel diffraction can be removed, and blurred images can be
smoothed.
Three or more optical integrators may be employed. For an efficient
illumination of an object, adjacent ones of such optical
integrators should be arranged so that the entrance surfaces will
be mutual conjugates and also the exit surfaces will be mutual
conjugates with the magnifications selected as described above.
Although certain preferred embodiments have been shown and
described, it should be understood that many changes and
modifications may be made therein without departing from the scope
of the appended claims.
* * * * *