U.S. patent application number 09/916505 was filed with the patent office on 2001-11-29 for illumination apparatus, exposure apparatus and exposure method.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Kudo, Yuji.
Application Number | 20010046039 09/916505 |
Document ID | / |
Family ID | 24096413 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046039 |
Kind Code |
A1 |
Kudo, Yuji |
November 29, 2001 |
Illumination apparatus, exposure apparatus and exposure method
Abstract
An object of the invention is to provide an illumination
apparatus and exposure apparatus and method employing this, whereby
the illumination distribution on a mask or wafer can be compensated
to a desired distribution, and whereby it is possible to
independently alter the pupil shape (coherence factor) of
illuminating light in respect of various image heights above the
wafer. In order to achieve the above object, an illumination
apparatus as claimed in the invention is provided with: a rod-type
optical integrator forming a large number of light source images
from the light from a light source; a relay optical system that
illuminates a surface to be illuminated by respectively condensing
light from the large number of light source images formed by the
rod-type optical integrator; and means for controlling illumination
that respectively independently control the intensity distribution
of the light in the large number of light source images, being
arranged on the light source side of the rod-type optical
integrator.
Inventors: |
Kudo, Yuji; (Tokyo,
JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT &
DUNNER LLP
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
|
Family ID: |
24096413 |
Appl. No.: |
09/916505 |
Filed: |
July 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09916505 |
Jul 30, 2001 |
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09526216 |
Mar 15, 2000 |
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6281967 |
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Current U.S.
Class: |
355/67 ; 250/548;
355/53; 355/55; 355/68; 355/71; 356/399 |
Current CPC
Class: |
G03F 7/70075 20130101;
G03F 7/701 20130101; G03F 7/70091 20130101; G03F 7/70191 20130101;
G03F 7/70108 20130101; G03F 7/70133 20130101 |
Class at
Publication: |
355/67 ; 355/53;
355/55; 355/68; 355/71; 356/399; 250/548 |
International
Class: |
G03B 027/54 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 2000 |
JP |
11-069954 |
Claims
What is claimed is:
1. An illumination apparatus, comprising: a rod-type optical
integrator forming a large number of light source images from the
light from a light source; a relay optical system that illuminates
a surface to be illuminated, by respectively condensing light from
said large number of light source images formed by said rod-type
optical integrator; and illumination control means that
respectively independently control the intensity distribution of
the light in said large number of light source images, being
arranged on the light source side of said rod-type optical
integrator.
2. The illumination apparatus as claimed in claim 1, wherein a
condensing optical system that directs light through said
illumination control means to said rod-type optical integrator is
arranged between said illumination control means and said rod-type
optical integrator; said illumination control means include an
optical filter that controls the transmittance distribution of the
light from said large number of light source images respectively
independently; and said optical filter is provided in a position
that is substantially optically conjugate with said surface to be
illuminated, in relation to said condensing optical system, said
rod-type optical integrator and relay optical system.
3. The illumination apparatus as claimed in claim 1, wherein a
flare stop plate is provided at the emission plane of said rod-type
optical integrator or in a position conjugate to this emission
plane.
4. The illumination apparatus as claimed in claim 1, comprising
drive means, part of said relay optical system being moved by this
drive means.
5. The illumination apparatus as claimed in claim 2, wherein a
flare stop plate is provided at the emission plane of said rod-type
optical integrator or in a position conjugate to this emission
plane.
6. The illumination apparatus as claimed in claim 5, comprising
drive means, part of said relay optical system being moved by this
drive means.
7. An exposure apparatus, comprising: a rod-type optical integrator
forming a large number of light source images from the light from a
light source; a relay optical system that illuminates a mask, by
respectively condensing light from said large number of light
source images formed by said rod-type optical integrator; a
projection system that projects the pattern of said mask onto a
photosensitive substrate; and illumination control means that
respectively independently control the intensity distribution of
the light in said large number of light source images, being
arranged on the light source side of said rod-type optical
integrator.
8. The exposure apparatus as claimed in claim 7, wherein a
condensing optical system that directs light through said
illumination control means to said rod-type optical integrator is
arranged between said illumination control means and said rod-type
optical integrator; said illumination control means include an
optical filter that controls the transmittance distribution of the
light from said large number of light source images respectively
independently; and said optical filter is provided in a position
that is substantially optically conjugate with said surface to be
illuminated, in relation to said condensing optical system, said
rod-type optical integrator and relay optical system.
9. A method of exposure, comprising: an optical control step,
wherein the intensity distribution of the light in a large number
of light source images on the light source side of a rod-type
optical integrator is independently controlled using this rod-type
optical integrator, which forms a large number of light source
images from the light from a light source; a step of illuminating a
mask by respectively condensing light from said large number of
light sources whose optical intensity distribution is respectively
independently controlled by this optical control step; and an
exposure step of exposing the pattern of said mask onto a
photosensitive substrate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an illumination apparatus
and exposure apparatus and method employing this to form a desired
illumination distribution by condensing light from a light source,
and in particular relates to an illumination apparatus etc. that is
ideal for illumination of a mask for exposing minute semiconductor
circuitry on a photosensitive substrate.
BACKGROUND OF THE INVENTION
[0002] Conventionally, in illumination apparatus of this type, a
plurality of secondary light sources are formed by for example a
rod-type optical integrator, and uniform illumination of a mask on
which is described a circuit pattern is performed by utilizing the
illumination from these secondary light sources. The illuminated
circuit pattern is projected onto and exposes a wafer coated with
photosensitive material, through a projection lens.
[0003] Recently also, attention has been attracted by a technique
for improving the resolving power and depth of focus of the optical
projection system of the exposure apparatus by altering the pupil
shape of the illumination light by changing the shape of aperture
stops which are arranged in conjugate positions of the
two-dimensional light source, in accordance with the shape of the
pattern that is projected onto the wafer.
[0004] In an illumination device as above, it is generally
considered that the illumination distribution on the mask i.e. the
illumination distribution on the wafer when no pattern is formed on
the mask should be in a uniform condition; however, due to various
causes such as contamination or eccentricity of the optical system
or unevenness of the anti-reflective coating, if non-uniformity of
the illumination distribution on the wafer is found, more precise
exposure can be achieved by adjusting the illumination distribution
so as to compensate for this. Furthermore, in some cases, better
results are obtained by deliberately providing a distribution of
the illumination on the wafer, depending on the shape of the
pattern on the mask, and/or aberration of the projection lens, or
the pupil shape of the illuminating light etc.
[0005] Likewise, although it is generally considered that the pupil
shape of the illuminating light should be the same shape for all
image heights on the wafer, sometimes better results are obtained
by deliberately arranging for different pupil shapes for different
image heights.
SUMMARY OF THE INVENTION
[0006] Accordingly, an object of the present invention is to
provide an illumination apparatus and exposure apparatus and method
using this whereby the illumination distribution on the mask or
wafer can be compensated to a desired distribution, and wherein the
pupil shape (coherence factor) of the illuminating light can be
independently altered for various image heights on the wafer.
[0007] In order to solve the above problem, an illumination
apparatus as claimed in the invention comprises: a rod-type optical
integrator forming a large number of light source images from the
light from a light source; a relay optical system that illuminates
a surface to be illuminated, by respectively condensing light from
said large number of light source images formed by the rod-type
optical integrator; and illumination control means that
respectively independently control the intensity distribution of
the light in the large number of light source images, being
arranged on the light source side of the rod-type optical
integrator.
[0008] Since, with the illumination apparatus described above, the
optical intensity distributions at a large number of light source
images are respectively independently controlled by illumination
control means arranged on the light source side of a rod-type
optical integrator, the condition of the light that is supplied to
the illuminated surface from the light source images can be easily
and precisely controlled. Consequently, illumination conditions
such as the illumination distribution and/or the pupil shape over
the illuminated surface can be regulated to the desired condition.
In this context, the meaning of the term "optical intensity
distribution" includes both changing the absolute quantity of the
intensity and changing the distribution condition.
[0009] Also, in a preferred mode, a condensing optical system that
directs light through the illumination control means to the
rod-type optical integrator is arranged between the illumination
control means and the rod-type optical integrator; the illumination
control means include an optical filter that controls the
transmittance distribution of the light from the large number of
light source images respectively independently; and the optical
filter is provided in a position that is substantially optically
conjugate with the surface to be illuminated, in relation to the
condensing optical system, the rod-type optical integrator and
relay optical system.
[0010] With the illumination apparatus described above, light
corresponding to a large number of light source images has its
transmittance distribution respectively individually adjusted by
passing through the optical filter of the illumination control
means, and is easily individually input to the rod-type optical
integrator by the condensing optical system, so adjustment of the
illumination condition at the surface to be illuminated is
easy.
[0011] An exposure apparatus as claimed in the invention comprises:
a rod-type optical integrator forming a large number of light
source images from the light from a light source; a relay optical
system that illuminates a mask, by respectively condensing light
from the large number of light source images formed by the rod-type
optical integrator; a projection system that projects the pattern
of the mask onto a photosensitive substrate; and illumination
control means that respectively independently control the intensity
distribution of the light in the large number of light source
images, being arranged on the light source side of the rod-type
optical integrator.
[0012] With an exposure apparatus as described above, since the
illumination control means respectively independently controls the
intensity distribution of the light in a large number of light
source images, being arranged on the light source side of the
rod-type optical integrator, illumination conditions over the
surface to be illuminated, such as the illumination distribution
and/or the pupil shape, can be adjusted to the desired conditions,
making it possible to achieve exposure which is more precise and
matches the circumstances.
[0013] A method of exposure as claimed in the invention comprises:
an optical control step wherein the intensity distribution of the
light in a large number of light source images on the light source
side of a rod-type optical integrator is independently controlled
using this rod-type optical integrator, which forms a large number
of light source images from the light from a light source; a step
of illuminating a mask by respectively condensing light from the
large number of light sources whose optical intensity distribution
is respectively independently controlled by this optical control
step; and an exposure step of exposing the pattern of the mask onto
a photosensitive substrate.
[0014] With this exposure method, in the optical exposure step, the
optical intensity distribution of the large number of light source
images is respectively independently controlled at the light source
side of the rod-type optical integrator, so illumination conditions
over the surface to be illuminated such as the illumination
distribution and/or pupil shape can be adjusted to the desired
condition, enabling exposure to be achieved which is more precise
and in accordance with the circumstances.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram given in explanation of the arrangement
of an exposure apparatus as claimed in the first embodiment;
[0016] FIG. 2 is a view given in explanation of a turret plate for
changing the aperture stop of the illuminating optical system;
[0017] FIG. 3 is a cross-sectional constructional view given in
explanation of a device for detecting illumination
distribution;
[0018] FIG. 4 is a view given in explanation of the construction of
a filter constituting illumination control means;
[0019] FIG. 5 is a diagrammatic view given in explanation of the
relationship between the filter pattern and secondary light
source;
[0020] FIGS. 6(a) and (b) are views given in explanation of two
types of filter pattern with which the filter is provided;
[0021] FIG. 7 is a graph illustrating the illumination distribution
on the wafer in the case of a second embodiment;
[0022] FIG. 8 is a graph given in explanation of the pupil shape of
the illuminating light of FIG. 7;
[0023] FIG. 9 is a view given in explanation of a method of pattern
arrangement of the filter of a third embodiment;
[0024] FIG. 10 is a view given in explanation of a flare stop plate
as claimed in a fourth embodiment;
[0025] FIG. 11 is a view given in explanation of another flare stop
plate as claimed in the fourth embodiment;
[0026] FIG. 12 is a diagram given in explanation of the
construction of an exposure apparatus as claimed in a fifth
embodiment;
[0027] FIG. 13 is a view illustrating changes of illumination
distribution produced by displacement of the front group 18b1 of
the relay optical system; and
[0028] FIG. 14 is a view illustrating changes of illumination
distribution produced by tilting of the rear group 18b2 of the
relay optical system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0029] FIG. 1 is a diagram given in explanation of the general
arrangement of an exposure apparatus as claimed in a first
embodiment of the invention.
[0030] First of all, a simple explanation will be given of the
essentials of the optical system of the illuminating light for
illuminating mask M. The illumination light from a light source 11
is passed through beam shaping optical system 12 to provide a
practically parallel beam, which is reflected by reflecting mirror
13, and, passing through an illumination control device 20
constituting illumination control means comprising a filter 14 and
condensing lens 15, is directed onto a rod-type optical integrator
(hereinbelow referred to as an integrator) 16.
[0031] The optical flux from a large number of secondary light
sources formed by this integrator 16 is restricted by a variable
field of view stop 17 and is then projected by a relay optical
system 18 with a desired magnification factor and numerical
aperture (NA) onto the mask M of a mask stage MS. In this way, the
illumination region on mask M is illuminated practically uniformly
in overlapping fashion by the secondary light sources. A reflecting
mirror 18c for bending the optical path is arranged between front
group 18a and rear group 18b of relay optical system 18, and a
turret plate 19 having a plurality of apertures of different shape
and/or size is arranged between reflecting mirror 18c and rear
group 18b. Turret plate 19 constitutes variable aperture means
which appropriately adjust the aperture shape at the pupil position
of the illumination optical system.
[0032] The image of the circuit pattern on mask M that is
illuminated by illuminating light IL from the illuminating optical
system described above constitutes exposure light EL consisting of
illuminating light IL that has passed through mask M and is
projected with reduced size onto a wafer W placed on a wafer stage
WS, by means of the projection optical system 31, and, as a result
of the photosensitive action of the resist which covers wafer W,
the circuit pattern image on mask M is transferred onto wafer
W.
[0033] Details of the various parts of the exposure apparatus
illustrated in FIG. 1 will now be described. The light source 11
comprised by the illumination optical system directs illumination
light IL of the photosensitive wavelength of the resist covering
wafer W thereonto as a practically parallel optical flux. The
illumination light from source 11 is shaped to an illumination beam
of prescribed cross-sectional shape by beam shaping optical system
12, and is input to illumination control device 20 through
reflecting mirror 13. This illuminating light can be for example a
laser pulse; in this case, the emission timing is regulated by a
trigger pulse that is output from a controller 50.
[0034] The front-stage filter 14 comprised by illumination control
device 20 is equipped with a plurality of filter elements provided
in a number corresponding to the number of secondary source images,
as will be described in detail later, and is arranged perpendicular
to the optic axis in the vicinity of a conjugate plane S1 that is
conjugate with mask M i.e. wafer W. Rear-stage condensing lens 15
is arranged in a position separated from the position of virtual
image plane S2 of the secondary light source formed by integrator
16 by the amount of the focal point distance, so that the
illuminating light IL that is output from filter 14 practically
parallel with the optical axis is first made to converge on this
virtual image plane S2.
[0035] Driven by an actuator 41 under the control of a controller
50, filter 14 is capable of being displaced in the direction
perpendicular to the direction of the illuminating light, so that
it can be retracted from the optical path of the illumination
optical system in accordance with conditions such as the pattern of
mask M that is to be transferred to wafer W.
[0036] Input face 16a of integrator 16 is arranged in the vicinity
of virtual image plane S2. The illumination light IL that is made
to converge by condensing lens 15 is input into integrator 16 from
input face 16a, and is output from output face 16b after being
reflected a prescribed number of times on the inside surface of
integrator 16. The illumination light IL that is output from
integrator 16 is output from an output plane as if from a virtual
image of discrete secondary light sources corresponding to the
number of times of reflection. Consequently, the angle of the
illumination light that is output from output plane 16b corresponds
to the output angle of the illumination light IL from the virtual
image of the secondary light sources arranged on virtual image
plane S2.
[0037] Turret plate 19 is capable of regulating at least either
shape or size of the two-dimensional light sources, and is arranged
in the vicinity of real image plane S3 that is formed by the large
number of secondary light source images by the front group 18a. As
shown in FIG. 2, this turret plate 19 consists of a transparent
quartz substrate that is formed with a plurality of aperture stops
19a to 19f mutually differing in respect of at least either shape
or size. Of these, the two aperture stops 19a, 19b having circular
apertures serve for varying the .sigma. value etc.; the aperture
stops 19c, 19d are stops having apertures of mutually different
annular ratio (ratio of the internal diameter and external diameter
of the annular aperture); while the remaining aperture stops 19e,
19f are stops having four eccentric apertures for forming four
eccentric secondary light sources.
[0038] This turret plate 19 is arranged on the optical path of the
illuminating light IL with a single aperture stop selected in
accordance with the pattern of mask M to be transferred onto wafer
W by suitable rotation driven by motor 42 controlled by controller
50.
[0039] Mask M is arranged in practically a conjugate position with
respect to the output plane 16b of integrator 16 on the other side
of relay optical system 18 as described above, and is thus arranged
in a practically conjugate position with respect to filter 14.
Also, wafer W is arranged in a conjugate position with respect to
mask M, on the other side of projecting optical system 31.
[0040] Wafer stage WS is provided with a position detection device
61 comprising for example a laser interferometer that monitors
displacement of a disposable mirror 60 provided on wafer stage WS,
and an alignment optical system 62 to make it possible to align
wafer W and mask M. A drive device 65 that performs
three-dimensional drive of wafer stage WS is controlled by a
controller 50, so as to drive wafer stage WS into the desired
position in accordance with the output of position detection device
61 and alignment optical system 62.
[0041] Also, wafer stage WS is provided with an illumination sensor
67 for measuring the degree of illumination and/or pupil shape of
the illuminating light. As shown in FIG. 3, this illumination
sensor 67 comprises: an upper plate 67b having a pinhole 67e
arranged at the height of the upper surface of wafer W i.e. the
image-forming plane of projection optical system 31; a lens 67c
arranged in a position separated from pinhole 67e by the distance
of the focal point; and a CCD 67d that detects the light from
pinhole 67a through lens 67c. A diffraction pattern corresponding
to the cyclic pattern on mask M is projected onto CCD 67d by
displacing illumination sensor 67 directly below projection optical
system 31, by suitably displacing wafer stage WS. By analyzing the
output of CCD 67d and comparing it with previously stored data, the
pattern on mask M can be to a certain extent identified, and the
type of mask on mask stage MS ascertained. Also, if illumination
sensor 67 is displaced within the range of the exposure region of
projecting optical system 31 by removing mask M from mask stage MS
and suitably displacing wafer stage WS, an amount of light
corresponding to the degree of illumination at each point on wafer
W can be projected onto CCD 67d. That is, the illumination
distribution on wafer W can be obtained by detecting how the total
etc. of the outputs of CCD 67d vary in accordance with the image
height of wafer W. Furthermore, a brightness distribution
corresponding to the pupil shape at each point on wafer W is formed
on CCD 67d. That is, the pupil shape at each image height on wafer
W can be detected by detecting how the distribution of the output
of CCD 67d changes with image height of wafer W.
[0042] The operation of the exposure apparatus of FIG. 1 i.e. the
data or instructions necessary for operation of controller 50 can
be input from outside through an input device 55.
[0043] FIG. 4 is a view to a larger scale given in explanation of
the construction of filter 14 which is arranged in the vicinity of
conjugate plane S1. Rectangular filter patterns 14A, 14B are
arranged at the surface of this filter 14. These filter patterns
14A, 14B have characteristic transmissivity distributions, the
transmissivity distribution characteristics being different for the
middle filter patterns 14A and the peripheral filter patterns 14B.
In the Figure, for ease of understanding, the symbol A is placed at
the positions of the former filter patterns 14A, while the symbol B
is placed at the position of the latter filter patterns 14B, so as
to clarify the arrangement of these two types of filter patterns
14A and 14B. Filter patterns 14A, 14B respectively correspond to
the plurality of two-dimensional light sources formed by integrator
16.
[0044] FIG. 5 is a view to explain diagrammatically the
relationship between the shape and arrangement of the filter
patterns 14A and 14B of FIG. 4 with the plurality of
two-dimensional light sources formed by integrator 16. FIG. 5(a)
shows the optical path of the illuminating light that exits
parallel with the optical axis from filter 14, while FIG. 5(b)
shows the optical path of the illuminating light that exits from a
point on filter 14.
[0045] Filter pattern 140 arranged on filter 14 on the optic axis
controls the intensity of distribution of optical flux from
two-dimensional light source 100 that is not reflected at the
internal surface of integrator 16. Also, the pair of filter
patterns 141a, 141b that are adjacent on both outer sides of filter
pattern 140 control the intensity distribution of optical flux from
secondary light source images 101a, 101b that have suffered a
single reflection at the internal surface of integrator 16.
Furthermore, the pair of filter patterns 142a, 142b that are
adjacent on both outer sides of filter patterns 141a, 141b control
the intensity distribution of the optical flux from secondary light
source images 102a, 102b that have suffered double reflection at
the inside surface of integrator 16. With such an arrangement, the
transmissivity with regard to the respective optical fluxes of the
plurality of light sources formed by integrator 16 can be
independently controlled.
[0046] These filter patterns 140, 141a, 141b, 142a, 142b are
arranged in the vicinity of plane S1 that is conjugate with the
emission plane 16b of rod-type integrator 16; furthermore, the
magnification factor of condensing lens 15 corresponds to the ratio
of the size of emission plane 16b of integrator 16 and the size of
filter patterns 140 to 142b. Consequently, the shape of a single
filter pattern corresponds to an illumination region on mask M or
wafer W of FIG. 1, and the transmissivity distribution of filter
patterns 140 to 142b is reflected in the illumination distribution
of the illumination regions on wafer W.
[0047] FIG. 5 explains diagrammatically the shape and arrangement
of filter patterns; the density of arrangement of the filter
patterns is lower than in the case of the embodiment of FIG. 4. In
this case, insofar as filter pattern 140 is arranged in the middle,
it corresponds to filter patterns 14A of FIG. 4 and insofar as
filter patterns 142a, 142b are arranged at the periphery, they may
be considered as corresponding to filter patterns 14B of FIG.
4.
[0048] Returning to the description of FIG. 4, the periodicity with
which filter patterns 14A and 14B are arranged is determined by the
following condition. Specifically, if the magnification factor from
emission plane 16b of integrator 16 to the plane S1 that is
conjugate therewith is .sym. and assuming that there is no
distortion between emission plane 16b and conjugate plane S1, and
that the dimensions of the rod cross section of integrator 16 are
(Lx, Ly), the periodicity of the filter patterns 14A, 14B is
(.beta.Lx, .beta.Ly). However, if there is distortion between
emission plane 16b and conjugate plane S1, the arrangement of the
filter patterns may not necessarily have fixed periodicity. In this
case, since it is necessary to arrange the filter patterns in
positions corresponding to the two-dimensional light sources to
which each filter pattern corresponds, the pattern arrangement must
be compensated in accordance with the amount of distortion. Also,
in this case, since the shape of the filter patterns itself also
undergoes the effect of distortion, the shape must be altered in
accordance with the position in which the patterns are arranged.
Consequently, an arrangement of the optical system such that there
is no distortion between emission plane 16b and conjugate plane S1
is preferable from the point of view of ease of design of the
filter patterns, since it enables the shape and arrangement of the
filter patterns to be determined by the paraxial magnification
factor .beta. between the emission plane 16b and conjugate plane
S1.
[0049] Filter 14 is realized by a fine dot pattern of thin metallic
film such as for example Cr, Ni, or Al; the transmissivity
distribution of filter patterns 14A, 14B is controlled by varying
the density of this dot pattern. The transmissivity of the metallic
thin film itself need not necessarily be 0% and if it is desired to
raise the transmissivity of filter patterns 14A, 14B, the
transmissivity of the metallic thin film itself may be raised. If,
as in the former case, the transmissivity distribution is
controlled by the density of the dot pattern, if there is a precise
arrangement of filter patterns 14A, 14B on plane S1 that is
conjugate with the emission plane 16b of integrator 16, since
emission plane 16b and wafer W are conjugate, there is a risk that
the shape of the dots of the dot pattern itself will be transferred
onto the wafer W. Accordingly, in this embodiment, transfer of the
dots themselves is prevented by arranging filter patterns 14A, 14B
in a position slightly defocused from the plane S1 conjugate to
emission plane 16b. However, in some cases a construction may be
adopted such that emission face 16b is deliberately offset from the
conjugate plane of wafer W, with the object of preventing transfer
onto wafer W of the image of dirt, if there should be adhesion of
dirt to the emission face 16b; in such cases, filter patterns 14A,
14B can be arranged so as to be precisely conjugate with emission
plane 16b of integrator 16. In other words, filter patterns 14A,
14B may be arranged in not in a plane that is perfectly conjugate
with wafer W, but in its vicinity. In contrast, if the
transmissivity of filter patterns 14A, 14B is controlled by means
for example of the film thickness of thin metallic film or a
dielectric film rather than a dot pattern, there is no problem even
if filter patterns 14A, 14B are arranged in a position conjugate to
wafer W. If the size of the dot pattern formed in filter patterns
14A, 14B is too large, there is a risk of the dot pattern being
transferred onto wafer W; on the other hand, if it is too small,
there is the problem that efficiency is lowered since the
diffraction angle produced by the dot pattern becomes large. In
view of the above circumstances, the size of the dot pattern is
suitably in the range 1 .mu.m to 100 .mu.m.
[0050] FIG. 6 illustrates an example of the transmissivity
distribution of the filter patterns 14A, 14B shown in FIG. 4. FIG.
6(a) shows the transmissivity distribution of filter patterns 14A,
while FIG. 6(b) shows the transmissivity distribution of filter
patterns 14B. In filter patterns 14A that are arranged in the
middle of filter 14, for example a dot pattern is formed (see FIG.
6(a)) whose transmissivity at the center is higher than that at the
periphery, while in filter patterns 14B that are arranged at the
periphery of filter 14, for example a dot pattern is formed (see
FIG. 6(b)) whose transmissivity at the center is lower than that at
the periphery.
[0051] If the pattern arrangement shown in FIG. 4 and FIG. 6 is
adopted, if the diameter of the aperture stop of the illuminating
light IL is small (for example when the aperture stop 19a in the
turret plate 19 of FIG. 1 is on the optical path), the illuminating
light passing through filter pattern 14A becomes dominant; the
illumination on wafer W has a distribution reflecting the
transmissivity of filter pattern A, showing a tendency to be higher
in the central part of wafer W than in the peripheral part of wafer
W. Also, in the case where the diameter of the aperture stop of the
illuminating light IL gradually becomes larger (in the case where
for example aperture stop 19b in the turret plate 19 of FIG. 1 is
on the optical path), the illuminating light passing through filter
patterns 14B is increased, with the result that the effect of the
transmissivity distribution of the filter patterns 14B gradually
becomes larger. That is, as the diameter of the aperture stop of
turret plate 19 arranged on the optical path gets larger, the
illumination of wafer W tends to be higher in the peripheral region
than in the central region; contrariwise, as this aperture stop
diameter gets smaller, the illumination on wafer W tends to become
higher in the central region than in the peripheral region. This
means that the illumination distribution on wafer W can be suitably
changed in accordance with the diameter of the aperture stop of the
illuminating light by adopting a pattern arrangement as described
above in filter 14.
[0052] Utilizing this in the opposite way, even if, for some
reason, such as unevenness of the transmissivity of the
illuminating optical system etc., the illumination distribution on
wafer W is different depending on the shape of the aperture stop it
is possible to achieve an illumination distribution that does not
depend on the shape of the aperture stop by canceling this
illumination distribution. That is, it is possible to cancel the
phenomenon of the illumination distribution on wafer W being
different for different shapes of the aperture stop, by arranging
on filter 14 suitable filter patterns that compensate for changes
in the illumination distribution on wafer W produced by alteration
of the aperture stop. Thus, by positively controlling the
illumination distribution when the shape of the aperture stop is
changed, an illuminating light optical system etc. can be
constituted wherein there is no change in the illumination
distribution even though the shape of the aperture stop is changed,
thereby making it possible to increase the accuracy of transfer of
fine patterns.
[0053] Positively controlling the illumination distribution in this
way can be achieved not merely by advancing or retracting a single
filter 14 into the optical path of the illuminating optical system
in accordance with the condition of pattern etc. of mask M but also
by preparing a plurality of filters of different filter patterns
and suitably changing these filters in accordance with the type
etc. of pattern of mask M and/or changes in the illumination
distribution on wafer W. If this is done, the type of mask M
detected using illumination sensor 67 and/or the illumination
distribution on wafer W and distribution of the pupil shape may be
employed as the criteria for the decision regarding filter
replacement.
[0054] In the above first embodiment, since changeover of aperture
stops 19a to 19f is effected by rotation of turret plate 19, even
if the number of aperture stops is increased, the diameter of the
aperture stops of the illuminating light IL changes in
discontinuous manner. By employing a stop in which the diameter of
the aperture is continuously changed, instead of a turret plate 19,
the diameter of the aperture stop of the illuminating light IL can
be changed in a continuous manner.
Second Embodiment
[0055] The exposure apparatus of the second embodiment is a
modified example of the first embodiment. The construction of the
exposure apparatus as a whole is the same as that shown in FIG.
1.
[0056] In the case of the second embodiment, the pupil shape of the
illuminating light at each image height on wafer W is independently
controlled for each image height. It should be noted that, in this
context, the term "image height" is not used in the narrow sense of
the distance from the optic axis, but rather means the two
dimensional coordinates on the surface of wafer W.
[0057] In the apparatus of this second embodiment also, filter 14
is employed in the same way as illustrated in FIG. 5. However, as
the central filter pattern 140, a pattern is adopted as shown in
FIG. 6(a) such that the transmissivity in the middle is higher than
that at the periphery, while, as the peripheral filter patterns
142a, 142b, as shown in FIG. 6(b) a pattern is adopted such that
the transmissivity in the middle is lower than that in the
peripheral region, and for the intermediate filter patterns 141a,
141b, a pattern is adopted having uniform transmissivity. In this
case, filter patterns 140, 141a, 141b, 142a, 142b control the
intensity distribution of optical flux from the respective
two-dimensional light sources 100, 101a, 101b, 102a, and 102b.
[0058] FIG. 7 shows the illumination distribution on wafer W. On
wafer W, there is overlaid an illumination distribution in
accordance with filter patterns 140, 141a, 141b, 142a, 142b. In
this case, whereas, at the central position C on wafer W, the light
from two-dimensional light source 100 is more strongly observed
than the light from two-dimensional light sources 102a, 102b, in
the case of positions P1 and P2 remote from the center of wafer W,
on the contrary, light from secondary light source 100 is observed
as being weaker than light from secondary light sources 102a,
102b.
[0059] That is, the illumination distribution when the illuminating
light that is supplied onto wafer W from the two-dimensional light
sources 100, 101a, 101b, 102a, 102b is added practically
uniform.
[0060] In contrast, when seen from the center C on wafer W, as
shown in FIG. 8(a), the intensity of the two-dimensional light
source image at the central part at pupil coordinates parallel to
the optic axis is greater than the intensity of the two-dimensional
light source images in the peripheral part at pupil coordinates
making a large angle with respect to the optic axis. And, when seen
from the periphery P1, P2 on wafer W, as shown in FIG. 8(b), the
intensity of a two-dimensional light source image at the periphery
making a large angle with respect to the optic axis is greater than
the intensity of a two-dimensional light source image in the
central region parallel to the optic axis. By utilizing this
phenomenon, positive control of the pupil shape such as to form any
desired secondary light source distribution at any desired point on
wafer W can be achieved by arranging a suitable filter pattern on
filter 14. That is, it becomes possible to independently control,
in respect of each image height, the shapes (coherence factors) of
two-dimensional light sources at arbitrary image height above the
surface of wafer W. The transfer accuracy of fine patterns can
thereby be increased.
Third Embodiment
[0061] An exposure apparatus as claimed in the third embodiment is
a modified example of the first embodiment.
[0062] The construction of the exposure apparatus as a whole is the
same as that illustrated in FIG. 1.
[0063] Although, in the practical example of FIG. 6 of the first
embodiment, a filter pattern is illustrated which is rotationally
symmetric, the invention is not restricted to this, and a filter
pattern could be employed having a rotationally asymmetric
distribution. If such a filter pattern is employed, any desired
illumination distribution can be formed at any desired two
dimensional point on wafer W.
[0064] FIG. 8 is a view given in explanation of a method of
arranging filter patterns 314F and 314R of filter 314 in the case
of a third embodiment. In the case of the rod-type integrator 16,
since the optical flux from adjacent two-dimensional light sources
is inverted, if the filter patterns 314F, 314R of filter 314 are
rotationally asymmetric as in the third embodiment, adjacent filter
patterns may be arranged to constitute mirror images of each other,
as shown in the drawing. The letters F, R that are affixed at the
positions of filters 314F, 314R indicate that there are two types
of transmissivity distribution at the center and at the outside of
filter 314. The rotational position of letters F, R indicates the
direction of asymmetry.
Fourth Embodiment
[0065] An exposure apparatus as claimed in a fourth embodiment is a
modified example of the first to third embodiments. The basic
construction of the exposure apparatus as a whole is the same as
that illustrated in FIG. 1.
[0066] An object of this embodiment is to obtain even more uniform
illumination than that of the embodiments described above.
[0067] In order to implement this, on the emission plane 16b of
integrator 16 there is arranged a flare stop plate 200 as shown in
FIG. 10 or flare stop plate 201 and 202 as shown in FIG. 11. These
flare stop plates comprise a transparent part 20a that transmits
light and an opaque part 20b that stops light. These flare stop
plates can be displaced in the directions of the arrows in the
drawing. By displacing the flare stop plates in this way in the
directions of the arrows, adjustment to the desired illumination
distribution can be achieved. The two types of flare stop plate
shown in FIG. 10 and FIG. 11 are preferably applied to an exposure
apparatus of the step and scan type, in particular; in this case,
the scanning direction of the exposure apparatus is the same as the
direction of the arrows in both drawings.
[0068] The flare stop plate 200 illustrated in FIG. 10 is
constituted by a single plate. In contrast to this, the flare stop
plate shown in FIG. 11 is constituted by two plates, namely, plate
201 and 202. The degrees of freedom for the illumination
distribution adjustment can be increased compared with the flare
stop plate shown in FIG. 10 by asymmetric movement of the
respective plates.
[0069] In the case of this embodiment, these plates were arranged
on emission plane 16b of integrator 16, but the same effect is
obtained by arranging these at any location so long as it is
conjugate with emission plane 16b of integrator 16.
[0070] Also, opaque part 20b of the flare stop plate is not
restricted to being completely opaque (i.e. transmissivity 0%), so
long as it shows reduced transmissivity.
Fifth Embodiment
[0071] An exposure apparatus as claimed in a fifth embodiment is a
modified example of the first to third embodiments. The basic
construction of the exposure apparatus as a whole is practically
the same as that illustrated in FIG. 1. Consequently, in FIG. 12,
structural elements that are the same as in the first embodiment
are given the same reference symbols as in the case of FIG. 1.
[0072] An object of this embodiment is to obtain even more uniform
illumination than in the case of the first to third
embodiments.
[0073] FIG. 12 illustrates diagrammatically the construction of an
exposure apparatus as claimed in the fifth embodiment of the
invention.
[0074] The difference between this embodiment and the first
embodiment is that the rear group 18b of the relay optical system
is constituted by a first component 18b1 and a second component
18b2, a first drive means 43a and a second drive means 43b being
respectively connected to first component 18b and second component
18b2. First drive means 43a and second drive means 43b are
connected to a controller 50. The first drive means 43a and second
drive means 43b are motors.
[0075] First component 18b1 is displaceable in the direction of the
optic axis, being arranged to be driven by first drive means 43a.
When first component 18b1 is displaced, as shown in FIG. 13, it is
capable of generating a "concave/convex" component of the
illumination irregularity
[0076] In contrast, the second component 18b2 is constructed so
that it can be driven by second drive means 43b so that it can be
tilted with respect of the optic axis. When the second drive means
43b is tilted, as shown in FIG. 14, it can generate a graded
component of the illumination irregularity. This tilting mechanism
holds the rotary shaft biaxially, having a construction that is
capable of tilting this in any direction with respect to the optic
axis. Instead of tilting, the same effect can be obtained by
shifting, as another form of eccentricity, i.e. by displacing in
the direction perpendicular to the optic axis of relay optical
system 18. In this case, the power layout of relay optical system
18 and the position of the rotary axis of tilting are arranged to
be such that the variation of telecentricity of the wafer surface
produced by the displacement of the first component 18b1 and second
component 18b2 does not present a practical problem.
[0077] In this embodiment, since the illumination irregularity is
regulated by displacement of the first component 18b1, which is
part of the relay optical system constituting an optical member
having refraction power, or the eccentricity of second component
18b2, unlike the case where regulation is achieved by the
transmittance of the filter etc., there is no loss of the quantity
of light.
[0078] If for example it is assumed that good illumination
uniformity is obtained when the aperture stop of 19b of FIG. 2 is
arranged as the aperture stop, when the aperture stop is altered to
the aperture stop of 19c of FIG. 2, there is a possibility that
illumination irregularity with a concave/convex component and
graded component may be generated by the characteristics of the
optical system.
[0079] In order to compensate for such illumination irregularity,
this embodiment is so constructed that excellent uniformity of
illumination can be maintained by respectively compensating the
concave/convex component or the graded component of the
illumination irregularity by displacement of the first component
18b1 of relay optical system 18 described above in the optic axis
direction or tilting of the second component 18b2.
[0080] The amount of illumination irregularity generated is
measured by illumination sensor 67. At this point, the amount of
displacement of the first component 18b1 and the amount of tilt of
the second component 18b2 are set by controller 50, and the
illumination irregularity is compensated by driving respectively
the first component 18b1 and second component 18b2 by first drive
means 43a and second drive means 43b.
[0081] When performing this compensation, an excellent compensated
condition of the illumination uniformity can be achieved by
repeated measurement, control and drive until the illumination
uniformity is brought within a predetermined restricted range.
[0082] Also, the method may be adopted of ascertaining and storing
beforehand for each aperture stop the optimum positions of first
component 18b1 and second component 18b2 for the change of
illumination irregularity produced by alteration of the aperture
stop, and effecting drive to the stored position in a manner linked
with the alteration of the aperture stop. This is excellent in view
of speed in that there is no need for repeated drive in response to
the measured value obtained by the illumination sensor 67, but
resetting is necessary if for some reason the change of
illumination irregularity produced by alteration of the aperture
stop alters.
[0083] In this embodiment, the second component 18b2 is arranged to
be tiltable, but, depending on the construction of the optical
system, the same effect could be obtained even by shifting. In this
case, in order to reduce the variation of telecentricity on the
wafer produced by shifting, a construction is even more preferred
in which shifting is performed by two or more lenses in at least
two or more different directions.
[0084] In this embodiment, compensation is performed of the
illumination irregularity produced by alteration of the shape of
the secondary light sources. However, it is possible to compensate
for illumination irregularity produced by factors other than this,
such as for example change of illumination irregularity produced by
factors such as changes due to light source replacement or
maintenance or secular changes such as change of the transmittance
of the optical system.
[0085] In this embodiment, it was assumed that the condition in
which there is little illumination irregularity of the wafer W
surface is the condition in which there is good uniformity of
illumination. However, there is no restriction to this, and in some
cases, depending on the mask pattern and/or conditions of the
optical system, it may be preferable for example for the
illumination in the peripheral region to be higher than that in the
center, or lower. In such cases also, with the present embodiment,
control to the desired illumination distribution can be
achieved.
[0086] Also, although a construction was described in which the
first component 18b1 was displaced in the optic axis direction
while the second component 18b2 was moved off-center, it would be
possible for the opposite arrangement to be employed, in which the
first component 18b1 is moved off-center while the second component
18b2 is displaced in the optic axis direction.
[0087] Furthermore, although, in this embodiment, the rear group
18b of the relay optical system was displaced, the same effect
could be obtained by similarly tilting condensing lens 15 or
displacing it in the optic axis direction.
[0088] The invention was described above with reference to
embodiments, but the invention is not restricted to the above
embodiments. For example, although, in the above embodiments, as
the rod-type optical integrator, an integrator 16 is employed
consisting of a rod of rectangular cross section, the
cross-sectional shape is not restricted to this, and an integrator
having another cross-sectional shape such as hexagonal could be
employed. In this case, it is desirable, from the point of view of
efficient utilization of the illuminating light, that the
respective filter patterns formed on the filter 14 etc. should be
closely similar to the cross-sectional shape of the rod-type
optical integrator.
[0089] Since, with the illumination apparatus described above, the
optical intensity distributions at a large number of light source
images are respectively independently controlled by illumination
control means arranged on the light source side of a rod-type
optical integrator, the condition of the light that is supplied to
the illuminated surface from the light source images can be easily
and precisely controlled. Consequently, illumination conditions
such as the illumination distribution and/or the pupil shape over
the illuminated surface can be regulated to the desired
condition.
* * * * *