U.S. patent application number 15/381500 was filed with the patent office on 2017-05-25 for optical system illuminating surface to be illuminated, exposure apparatus, imprint apparatus, method for manufacturing article, optical element, and method for manufacturing optical system.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Nobuyuki Saito.
Application Number | 20170146914 15/381500 |
Document ID | / |
Family ID | 53265217 |
Filed Date | 2017-05-25 |
United States Patent
Application |
20170146914 |
Kind Code |
A1 |
Saito; Nobuyuki |
May 25, 2017 |
OPTICAL SYSTEM ILLUMINATING SURFACE TO BE ILLUMINATED, EXPOSURE
APPARATUS, IMPRINT APPARATUS, METHOD FOR MANUFACTURING ARTICLE,
OPTICAL ELEMENT, AND METHOD FOR MANUFACTURING OPTICAL SYSTEM
Abstract
An optical system illuminating a surface to be illuminated
includes a wavefront splitting type integrator configured to split
the wavefront of incident light to form a plurality of light
sources on the exit surface side, and an optical element whose
surface is polished in a scanning direction using a polishing tool.
The optical element is disposed between the wavefront splitting
type integrator and the surface to be illuminated, and has a
direction indicating portion indicating the scanning direction. The
arrangement direction of the plurality of light sources in a plane
perpendicular to the optical axis of the optical system is
non-parallel to the scanning direction indicated by the direction
indicating portion.
Inventors: |
Saito; Nobuyuki;
(Kawasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
53265217 |
Appl. No.: |
15/381500 |
Filed: |
December 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14558555 |
Dec 2, 2014 |
9563134 |
|
|
15381500 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 3/04 20130101; G03F
7/70375 20130101; G03F 7/0002 20130101 |
International
Class: |
G03F 7/20 20060101
G03F007/20; G02B 3/04 20060101 G02B003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2013 |
JP |
2013-250399 |
Claims
1. A method for manufacturing an optical system for illuminating a
surface to be illuminated, comprising: a disposing step of
disposing an optical element on which a linear polishing mark is
formed between an integrator that forms a plurality of secondary
light sources from light from a light source and the surface to be
illuminated, wherein, in the disposing step, the optical element is
disposed such that an arrangement direction of the plurality of
secondary light sources in a plane perpendicular to an optical axis
of the optical system is non-parallel to a direction in which the
linear polishing mark extends.
2. The method according to claim 1, wherein the optical element
comprises a direction indicating portion indicating a direction in
which the polishing mark extends.
3. The method according to claim 1, wherein the optical element
comprises a direction indicating portion indicating a scanning
direction with a polishing tool for polishing a surface of the
optical element.
4. The method according to claim 1, wherein the optical element
comprises a direction indicating portion is a surface formed in an
outer periphery of the optical element and parallel to the
direction in which the linear polishing mark extends.
5. The method according to claim 1, wherein the optical element is
an aspherical lens.
6. The method according to claim 1, wherein the optical element is
closest to the surface to be illuminated among a plurality of
optical elements constituting the optical system.
7. The method according to claim 1, wherein an angle formed between
the arrangement direction of the plurality of secondary light
sources and the direction in which the linear polishing mark
extends is greater than or equal to tan-1 (C/P), where C is a size
in the arrangement direction in a whole distribution of the
plurality of secondary light sources formed by the integrator, and
P is an external diameter of a light source among the plurality of
secondary light sources.
8. The method according to claim 1, wherein the plurality of
secondary light sources are arranged in two directions
perpendicular to each other and a direction oblique to the two
directions, and the direction in which the linear polishing mark
extends is non-parallel to the two directions and the oblique
direction.
9. The method according to claim 1, wherein the optical element is
rotatable about the optical axis.
10. The method according to claim 1, wherein the integrator is a
wavefront splitting type integrator configured to split a wavefront
of incident light to form the plurality of secondary light sources
on an exit surface side.
11. The method according to claim 1, the method further comprising:
polishing a surface of the optical element by scanning in a
scanning direction with a polishing tool, wherein the linear
polishing mark is formed on the polished surface of the optical
element.
12. The method according to claim 1, further comprising: measuring
illuminance distribution on the surface to be illuminated, and
adjusting a rotation angle of the optical element about the optical
axis using a result of measured illuminance distribution.
13. A method for manufacturing an optical system for illuminating a
surface to be illuminated, comprising: a polishing step of
polishing a surface of the optical element by scanning in a
scanning direction with a polishing tool, a disposing step of
disposing an optical element on which a linear polishing mark is
formed between an integrator that forms a plurality of secondary
light sources from light from a light source and the surface to be
illuminated, wherein, in the disposing step, the optical element is
disposed such that an arrangement direction of the plurality of
secondary light sources in a plane perpendicular to an optical axis
of the optical system is non-parallel to a direction on the
polished surface of the optical element corresponding to the
scanning direction.
Description
[0001] This application is a Divisional of U.S. patent application
Ser. No. 14/558,555 filed Dec. 2, 2014 which claims the benefit of
Japanese Patent Application No. 2013-250399 filed Dec. 3, 2013.
U.S. patent application Ser. No. 14/558,555 and Japanese Patent
Application No. 2013-250399 are hereby incorporated by reference
herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] Field of the Invention
[0003] The present invention relates to an optical system
illuminating a surface to be illuminated, an exposure apparatus, an
imprint apparatus, a method for manufacturing an article, an
optical element, and a method for manufacturing an optical
system.
[0004] Description of the Related Art
[0005] In the lithography process of the manufacturing of a
semiconductor device, a liquid crystal display apparatus, or the
like, an exposure apparatus is used that illuminates a mask
(reticle) using an illumination optical system, and projects an
image of a pattern of the mask through a projection optical system
onto a substrate on which a photosensitive resist layer is
formed.
[0006] In optical systems of an exposure apparatus, aspherical
lenses for correcting various aberrations are used. Although an
aspherical surface has a complicated shape, it requires high shape
accuracy. So, in aspherical surface processing, a technique is used
in which a minute polishing pad is scanned in a predetermined
scanning direction while being in contact with the lens surface to
polish the surface (Japanese Patent Laid-Open No. 2000-263408).
[0007] However, if a polishing pad is scanned in a predetermined
scanning direction to polish the surface of an optical element as
in Japanese Patent Laid-Open No. 2000-263408, linear polishing
marks are left on the surface of the optical element along the
scanning direction. Light is not easily transmitted through the
polishing mark parts. Therefore, if a surface to be illuminated
(substrate) is illuminated using an optical element having
polishing marks, shadows such that light from the light source is
blocked by the polishing marks are projected onto the surface to be
illuminated. If, in an optical system of an exposure apparatus,
significantly uneven illuminance is caused by shadows cast on the
surface to be illuminated, a line width abnormality of the exposure
pattern projected onto the substrate can occur. If, for example,
linear polishing marks are about 1 mm in width, and uneven
illuminance of 0.05% or more is caused by them, a line width
abnormality of the exposure pattern can occur.
SUMMARY OF THE INVENTION
[0008] In an aspect of the present invention, an optical system
illuminating a surface to be illuminated includes a wavefront
splitting type integrator configured to split the wavefront of
incident light to form a plurality of light sources on the exit
surface side, and an optical element whose surface is polished in a
scanning direction using a polishing tool. The optical element is
disposed between the wavefront splitting type integrator and the
surface to be illuminated, and has a direction indicating portion
indicating the scanning direction. The arrangement direction of the
plurality of light sources in a plane perpendicular to the optical
axis of the optical system is non-parallel to the scanning
direction indicated by the direction indicating portion.
[0009] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic view of an exposure apparatus.
[0011] FIGS. 2A and 2B show the constitution of an integrator.
[0012] FIG. 3 is a plan view of an aspherical lens.
[0013] FIGS. 4A to 4E illustrate uneven illuminance caused by a
conventional aspherical lens.
[0014] FIGS. 5A to 5E illustrate uneven illuminance caused by an
aspherical lens of an embodiment.
[0015] FIG. 6 shows the relationship between the arrangement
direction of secondary light sources and the direction of a
polishing mark.
DESCRIPTION OF THE EMBODIMENTS
[0016] Embodiments of the present invention will now be described
in detail with reference to the drawings.
First Embodiment
[0017] FIG. 1 is a schematic view showing the constitution of an
exposure apparatus 100 in a first embodiment.
[0018] The exposure apparatus 100 causes light from a light source
101 to be incident on an integrator 103 through a light beam
shaping portion 102. The light beam shaping portion 102 can change
the shape and size in cross-section of a light beam incident on the
integrator 103. The light beam shaping portion 102 bends the
optical path in the middle of the optical path using a mirror 102a.
The integrator 103 has a function of uniformizing the illuminance
distribution of a surface to be illuminated. Light emitted from the
integrator 103 illuminates a visual field (illumination field) stop
105 through a condenser lens 104. The visual field stop 105 is for
limiting the range of illumination of a mask 107. The visual field
stop 105 and the mask 107 are in an image forming relationship
owing to an image forming optical system 106. The image forming
optical system 106 bends the optical path in the middle of the
optical path using a mirror 106a. The light beam shaping portion
102, the integrator 103, the condenser lens 104, the visual field
stop 105, and the image forming optical system 106 form an
illumination optical system that illuminates the mask 107. A
pattern used for forming a circuit is formed on the mask 107. Light
from the pattern of the mask 107 illuminated by the illumination
optical system is imaged by a projection optical system 108 onto a
wafer (substrate) 109 held on a wafer stage 110.
[0019] The image forming optical system 106 has an aspherical lens
111a for correcting the telecentricity of light with which the
surface to be illuminated (mask surface) is irradiated. The
projection optical system 108 has an aspherical lens 111b for
correcting the aberration of the projection optical system. The
illumination optical system illuminates the mask 107, which is a
surface to be illuminated, and the projection optical system 108
illuminates the wafer 109, which is a surface to be
illuminated.
[0020] FIGS. 2A and 2B show the constitution of the integrator 103.
As shown in FIG. 2A, the integrator 103 is a wavefront splitting
type integrator that splits the wavefront of incident light to form
a plurality of secondary light sources 201 on the exit surface
side. The integrator 103 shown in FIGS. 2A and 2B is a fly-eye
lens. The integrator 103 has a plurality of lens elements such as
lens elements 103a, 103b, and 103c constituting the fly-eye lens.
Light from the secondary light sources 201 formed by the lens
elements illuminates a surface to be illuminated 203 in a
superimposed manner through the condenser lens 104, and performs
Kohler illumination. The surface to be illuminated 203 corresponds
to the wafer 109 surface, the mask 107 surface, or a surface
conjugate with them.
[0021] FIG. 2B shows a sectional view of the integrator 103 in an
xy sectional plane perpendicular to the optical axis AX (z
direction). The plurality of secondary light sources 201 formed by
the plurality of lens elements of the integrator 103 are arranged
in two directions perpendicular to each other (vertical and
horizontal directions) and an oblique direction. For example, the
secondary light sources 201a, 201b, and 201c formed by the lens
elements 103a, 103b, and 103c are arranged in the vertical
direction (y direction) 202a. The secondary light sources 201d,
201e, and 201f are arranged in the horizontal direction (x
direction) 202b, and the secondary light sources 201c, 201g, and
201f are arranged in the oblique direction 202c. Since, in a
fly-eye lens, lens elements correspond one-to-one with secondary
light sources formed by the lens elements, the arrangement
directions of the secondary light sources are the same as the
arrangement directions of the lens elements.
[0022] In order to improve the light use efficiency, the outer
shape of the lens elements of the integrator 103 is generally
similar to an illumination region that illuminates the surface to
be illuminated 203. Therefore, the arrangement directions of the
plurality of lens elements (secondary light sources) of the
integrator 103 are set according to the illumination region of the
surface to be illuminated 203. The integrator 103 is not limited to
a fly-eye lens. As described in Japanese Patent Laid-Open No.
2004-226661, a microlens array in which a plurality of microlenses
are formed two-dimensionally, or a combination of two cylindrical
lens arrays whose generatrix directions are perpendicular to each
other can be used. Alternatively, a diffraction type optical
element, a CGH, an internal reflection type optical pipe
(integrator), or the like can be used.
[0023] Next, the aspherical lens 111a will be described. The
aspherical lens 111a is polished using a polishing apparatus such
as that described in Japanese Patent Laid-Open No. H06-134666 or
2000-263408. That is, the polishing apparatus pours polishing
liquid on a workpiece (lens), or places the workpiece in the
polishing liquid. Then, a polishing tool (polishing pad) having a
diameter smaller than the workpiece is pressed against the surface
of the workpiece with a given load, and the polishing tool is
scanned relative to the surface of the workpiece to polish and
remove unnecessary parts from the workpiece. The polishing
apparatus includes the polishing tool, a holder for the polishing
tool, and a moving shaft to which a load generator is fixed and
that uses an actuator as a driving source. The polishing apparatus
further includes a position detecting unit that detects the current
position of the moving shaft, a position setting unit that sets a
target position, and a control unit that drives the moving shaft,
and compares a position signal from the position detecting unit
with a value of the position setting unit. The polishing apparatus
includes a calculator that calculates a target position of the
moving shaft on the basis of this comparison result and sends a
control signal to the control unit on the basis of this calculation
result. The polishing apparatus freely sets the scanning width in a
direction perpendicular to the scanning direction while scanning
the polishing tool in one scanning direction, thereby polishing the
lens surface.
[0024] FIG. 3 shows a plan view of the aspherical lens 111a. The
surface of the aspherical lens 111a is polished using the polishing
tool of the polishing apparatus in the scanning direction, and
linear polishing marks 302 are left on the surface of the
aspherical lens 111a along the scanning direction. The polishing
marks 302 are actually less visible but are schematically shown in
the figure. The polishing marks cause an optical phenomenon such as
light blocking, scattering, or refraction, and light is not easily
transmitted therethrough. Therefore, if a surface to be illuminated
is illuminated using an optical element having polishing marks,
shadows such that light from the light source is blocked by the
polishing mark regions are projected onto the surface to be
illuminated.
[0025] FIGS. 4A to 4E show uneven illuminance on the surface to be
illuminated 203 in the case where assembly is performed such that
the arrangement direction 202a of the secondary light sources 201
formed by the integrator 103 is parallel to the direction in which
a polishing mark 402 of a conventional aspherical lens 400 extends.
Suppose the aspherical lens 400 is also polished using the
above-described polishing apparatus, and a polishing mark is formed
in the scanning direction. FIG. 4A shows a sectional view of the
integrator 103 in an xy sectional plane perpendicular to the
optical axis. FIG. 4B shows a sectional view of the aspherical lens
400 in an xy sectional plane perpendicular to the optical axis.
FIG. 4C shows uneven illuminance on the surface to be illuminated
203 in an xy plane perpendicular to the optical axis. FIG. 4D is a
configuration diagram of the integrator 103 and the aspherical lens
400 in an xz plane. FIG. 4E shows the illuminance distribution on
the surface to be illuminated 203 in the x direction.
[0026] A plurality of light beams from the plurality of secondary
light sources 201 are incident on points on the polishing mark 402,
and the illuminance of light projected onto the surface to be
illuminated 203 from a plurality of directions decreases owing to
the scattering when the plurality of light beams pass through the
points on the polishing mark 402. FIGS. 4D and 4E show the decrease
in illuminance at points a, b, and c on the surface to be
illuminated 203. As shown in FIGS. 4A and 4B, the arrangement
direction 202a of the secondary light sources 201 formed by the
integrator 103 and the polishing mark 402 of the aspherical lens
400 are disposed in the y direction so as to be parallel to each
other. Therefore, shadows 204 in which the illuminance is decreased
by a point on the polishing mark 402 and that have the shape of the
nine secondary light sources 201 are formed on the surface to be
illuminated 203. Since the polishing mark 402 extends in the y
direction, shadows are formed by each point on the polishing mark
402 in the same manner, and illuminance distribution such that
shadows of light beams from the secondary light sources are
arranged in lines so as to overlap each other in the y direction is
formed on the surface to be illuminated 203. Therefore,
significantly uneven illuminance such that the illuminance
periodically decreases in the x direction occurs on the surface to
be illuminated 203. If such uneven illuminance occurs, the surface
to be illuminated 203 is illuminated unevenly, and therefore a
resolution error such that the image of the mask pattern projected
onto the wafer 109 becomes abnormal occurs. A line width
abnormality of the pattern formed on the wafer 109 can occur.
[0027] So, in this embodiment, the arrangement direction of the
secondary light sources 201 formed by the integrator 103 and the
direction in which the polishing mark 302 of the aspherical lens
111a extends are disposed so as to be non-parallel to each other
(so as not to be parallel to each other).
[0028] FIGS. 5A to 5E show uneven illuminance on the surface to be
illuminated 203 in the case where assembly is performed such that
the arrangement direction of the plurality of secondary light
sources 201 formed by the integrator 103 is non-parallel to the
direction in which the polishing mark 302 of the aspherical lens
111a extends. FIG. 5A shows a sectional view of the integrator 103
in an xy sectional plane perpendicular to the optical axis. FIG. 5B
shows a sectional view of the aspherical lens 111a in an xy
sectional plane perpendicular to the optical axis. FIG. 5C shows
uneven illuminance on the surface to be illuminated 203 in an xy
plane perpendicular to the optical axis. FIG. 5D is a configuration
diagram of the integrator 103 and the aspherical lens 111a in an xz
sectional plane. FIG. 5E shows the illuminance distribution on the
surface to be illuminated 203 in the x direction.
[0029] As shown in FIG. 5B, the direction in which the polishing
mark 302 extends is non-parallel to any of the arrangement
directions 202a (y direction), 202b (x direction), and 202c
(45-degree direction to the x and y axes) of the secondary light
sources 201. The arrangement direction 202a of the secondary light
sources (y direction) and the direction in which the polishing mark
302 extends form a predetermined angle .theta. that is greater than
0 degrees (y direction) and less than 90 degrees and is not 45
degrees. As shown in FIGS. 5B and 5D, the illuminance of light
projected onto the surface to be illuminated 203 through points on
the polishing mark 302, for example, points d, e, and f decreases.
Since the polishing mark 302 is inclined at the angle .theta. to
the y direction, as shown in FIG. 5C, illuminance distribution such
that shadows 205 of light beams from the light sources are arranged
in lines so as to overlap each other in a direction inclined at the
angle .theta. to the y direction is formed on the surface to be
illuminated 203. The illuminance distribution on the surface to be
illuminated 203 in the x direction is as shown in FIG. 5E. That is,
shadows 205 of light beams from the light sources are not locally
concentrated but evenly distributed throughout the surface to be
illuminated 203, and illuminance distribution such that shadows are
evenly spread is formed. Therefore, illuminance distribution that
is more even than the periodic and significantly uneven illuminance
distribution of the illuminated state of FIG. 4C can be formed.
[0030] In this embodiment, the aspherical lens 111a is provided
with a direction indicating portion 301 that indicates the
direction in which the polishing marks 302 extend. As shown in FIG.
3, the direction indicating portion 301 is a plane portion formed
by cutting off an outer peripheral part of the aspherical lens 111a
in a direction parallel to the direction in which the polishing
marks 302 extend. When the aspherical lens 111a is disposed in the
optical path of the illumination optical system, the aspherical
lens 111a is disposed such that the arrangement directions of the
secondary light sources 201 are non-parallel to the direction in
which the polishing marks 302 extend, using the direction
indicating portion 301 as a guide. As described above, the
arrangement directions of the plurality of secondary light sources
formed by the integrator 103 are set in advance for each apparatus
according to the region of the mask (wafer) to be illuminated by
the exposure apparatus. Therefore, the aspherical lens 111a can be
disposed such that the direction in which the polishing marks 302
extend is non-parallel to the arrangement directions of the
secondary light sources, easily by using the direction indicating
portion 301. By disposing the integrator 103 and the aspherical
lens 111a in the optical path in this manner, an optical system can
be manufactured.
[0031] The term "non-parallel" shows a relationship between the
arrangement directions of the secondary light sources and the
direction in which the polishing marks extend in a state where the
optical axis of the integrator 103 is parallel to the optical axis
of the aspherical lens 111a. In the optical path of FIG. 1, since
the optical path of light from the integrator 103 is bent at a
right angle in the middle and is incident on the aspherical lens
111a, the optical axis of the integrator 103 is perpendicular to
the optical axis of the aspherical lens 111a. So, suppose a state
where a plane perpendicular to the optical axis of the integrator
103 is overlaid on a plane perpendicular to the optical axis of the
aspherical lens 111a with a direction perpendicular to the paper
plane common, and the optical axis of the integrator 103 is
parallel to the optical axis of the aspherical lens 111a. In this
state, the arrangement directions of the secondary light sources
201 are non-parallel to the direction in which the polishing marks
302 extend.
[0032] The direction indicating portion 301 is not limited to the
above-described plane portion, and may be a straight line engraved
on the outer peripheral part of the lens so as to extend in the
direction in which the polishing marks 302 extend, or a straight
line or plane portion formed in a direction perpendicular to the
direction in which the polishing marks 302 extend. That is, the
direction indicating portion 301 may have any form as long as it
can indicate the direction in which the polishing marks 302 extend
and the direction in which the polishing marks 302 extend can be
detected on the basis of the appearance of the direction indicating
portion by human sight or a detector of the apparatus. For example,
a step extending in the direction in which the polishing marks 302
extend may be formed in an outer peripheral part of the lens, and
the outer peripheral part of the lens may not be completely cut
off. Since, in this case, the whole circumference of the shape of
one side surface of the lens remains, the whole circumference of
the one side surface of the lens can be held with a lens holding
frame.
[0033] The aspherical lens 111a may be provided with a mechanism
rotatable about the optical axis. The angle of the direction
indicated by the direction indicating portion 301 can be adjusted
at any timing, for example, when the arrangement of the aspherical
lens 111a is adjusted, or when the illuminance distribution is
changed with time. The aspherical lens 111a may be provided with a
drive mechanism 114 such as an actuator for rotating the aspherical
lens 111a about the optical axis to adjust the illuminance
distribution. First, the illuminance distribution on the image
plane (surface to be illuminated 203) is measured using a
measurement device (measurement portion) 112 on the wafer stage
110. Then, a control portion 113 (adjusting portion) acquires the
data of the result of measurement performed by the measurement
device 112, drives a drive mechanism 114 on the basis of the
acquired measurement result to adjust the rotation angle of the
aspherical lens 111a about the optical axis. By doing this, the
illuminance distribution can be improved so as to be more even.
When rotating the aspherical lens 111a about the optical axis, the
control portion 113 can perform control using the angle of the
direction indicated by the direction indicating portion 301 as a
control amount.
[0034] FIG. 6 is a diagram for illustrating a preferable angle
formed between the arrangement direction of the secondary light
sources 201 and the direction in which the polishing marks 302
extend. The black dots in the region 501 including shadows show
shadows of light beams from the secondary light sources projected
from a point 401 on the polishing mark 302. The black dots in the
region 501' including shadows show shadows of light beams from the
secondary light sources projected from a point 401' on the
polishing mark that is farthest from the point 401 of all points
from which shadows of light beams from the secondary light sources
are projected onto a position overlapping the region 501. The
shadow 501a shows a shadow of a light beam from one of the most
off-axis lens element of the integrator 103 in the region 501, and
the shadow 501b shows a shadow of a light beam from one of the most
off-axis lens element located on the side opposite to the shadow
501a. Similarly, the shadows 501a' and 501b' are shadows of light
beams from lens elements corresponding to shadows 501a and 501b in
the region 501'.
[0035] The angle .theta. of the direction of the polishing mark 302
with respect to the arrangement direction of the secondary light
sources 201 (x direction) can be greater than or equal to
tan.sup.-1 (C/P), where C is the size in the x direction of the
whole distribution of the plurality of secondary light sources 201
formed by the integrator 103, and P is the external diameter of one
or more, or all of the secondary light sources 201. FIG. 6 shows a
state where shadows of light beams from the secondary light sources
201 are projected onto the surface to be illuminated 203 when the
angle .theta. with respect to the arrangement direction 202b of the
secondary light sources 201 is greater than or equal to tan.sup.-1
(C/P). Since the angle .theta. is greater than or equal to
tan.sup.-1 (C/P), the shadow 501b does not overlap the line region
601a connecting the shadow 501a and the shadow 501a'. Therefore,
the amount of decrease of the illuminance in the line region 601a
is reduced, and as a result, the occurrence of a significant local
decrease in illuminance can be suppressed.
[0036] The aspherical lens 111b in FIG. 1 also has polishing marks
as with the aspherical lens 111a and has a direction indicating
portion. So, when the aspherical lens 111b is disposed in the
optical path of the projection optical system, the aspherical lens
111b is disposed such that the arrangement directions of the
secondary light sources 201 are non-parallel to the direction in
which the polishing marks of the aspherical lens 111b extend, using
the direction indicating portion of the aspherical lens 111b as a
guide.
[0037] An aspherical lens has been described as an example of a
lens having polishing marks. However, this embodiment can be
applied not only to this but also to optical elements such as a
spherical lens and a parallel plate whose surfaces are polished in
the scanning direction using the above-described polishing
apparatus.
[0038] The location and number of optical elements to which this
embodiment can be applied are not limited. However, the closer to
the surface to be illuminated 203 or a surface conjugate with the
surface to be illuminated an optical element is disposed, the more
clearly shadows of light beams from the secondary light sources due
to the polishing marks are projected onto the surface to be
illuminated 203, and therefore the more significantly the uneven
illuminance on the surface to be illuminated 203 is worsened.
Therefore, it is recommended that the optical element closest to
the surface to be illuminated or a surface conjugate therewith of
all the optical elements constituting the optical system, or an
optical element disposed in the vicinity of those surfaces be
incorporated such that the arrangement directions of the secondary
light sources are non-parallel to the direction of the polishing
marks. By doing this, worsening of uneven illuminance can be
suppressed more effectively.
[0039] The scanning direction in which the surface of an optical
element is polished by the polishing tool is not limited to one
direction. There is a case where, first, the polishing tool is
scanned in a first direction A to polish the surface, and then the
polishing tool is scanned in a second direction B perpendicular to
the first direction A to polish the surface. In the case where
there are a plurality of scanning directions of the polishing tool,
linear polishing marks are left on the surface of the optical
element along the last-scanned second direction B. So, an optical
element polished by scanning in a plurality of directions is
provided with a direction indicating portion by which the
last-scanned second direction B can be detected.
[0040] The direction indicating portion indicating the direction in
which polishing marks extend may be formed on a holding frame
holding a lens.
[0041] The constitution of the above-described illumination optical
system can also be applied to apparatuses other than an exposure
apparatus, for example, a nano-imprint apparatus and a liquid
crystal projector.
[0042] As described above, according to this embodiment, uneven
illuminance can be reduced in an optical system including an
optical element having polishing marks.
Second Embodiment
[0043] Next, a method for manufacturing an article (a semiconductor
IC element, a liquid crystal display element, a filter, or the
like) using the above-described exposure apparatus will be
described. A device is manufactured through a step of exposing a
substrate (a wafer, a glass substrate, or the like) coated with
photoresist, using the above-described exposure apparatus, a step
of developing the substrate (photoresist), and other known steps.
Other known steps include etching, resist removing, dicing,
bonding, and packaging. An article can also be manufactured using a
nano-imprint apparatus equipped with the above-described
illumination optical system. That is, with a pattern of a mold
pressed against a light curing resin on a substrate, the light
curing resin is illuminated through the mold to harden the light
curing resin. Then, the mold is separated from the light curing
resin. Thus, the pattern of the mold is formed in the light curing
resin. Then, a desired pattern is formed on the substrate using the
pattern formed in the light curing resin, and processing such as
etching is performed on the substrate on which the pattern is
formed. Thus, an article is formed. According to this manufacturing
method, an article having higher quality than ever before can be
manufactured.
[0044] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
* * * * *