U.S. patent application number 10/937431 was filed with the patent office on 2005-02-10 for projection exposure apparatus and device manufacturing method.
Invention is credited to Tsuji, Toshihiko.
Application Number | 20050030510 10/937431 |
Document ID | / |
Family ID | 28672571 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050030510 |
Kind Code |
A1 |
Tsuji, Toshihiko |
February 10, 2005 |
Projection exposure apparatus and device manufacturing method
Abstract
Disclosed is an exposure apparatus for illuminating a reflection
type mask with light from a light source and for exposing a
substrate with a pattern of the illuminated reflection type mask,
wherein the apparatus includes a projection optical system for
projecting the pattern of the reflection type mask onto the
substrate, the projection optical system having a stop, wherein the
stop has a first opening for defining a numerical aperture of the
projection optical system, and a second opening through which light
from the reflection type mask passes. This structure effective
avoids unwanted physical interference among optical components of
an illumination system or the projection optical system even when
the size of the whole exposure apparatus is made compact to some
degree.
Inventors: |
Tsuji, Toshihiko;
(Utsunomiya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 World Financial Center
New York
NY
10281-2101
US
|
Family ID: |
28672571 |
Appl. No.: |
10/937431 |
Filed: |
September 10, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10937431 |
Sep 10, 2004 |
|
|
|
10411834 |
Apr 11, 2003 |
|
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Current U.S.
Class: |
355/71 ; 355/53;
355/67 |
Current CPC
Class: |
G03F 7/70233 20130101;
G03F 7/70258 20130101; G03F 7/70283 20130101; G03F 7/7025
20130101 |
Class at
Publication: |
355/071 ;
355/067; 355/053 |
International
Class: |
G03B 027/72 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2002 |
JP |
112055/2002(PAT.) |
Claims
1-8. (Canceled)
9. An exposure apparatus for illuminating a reflection type mask
with light from a light source and for exposing a substrate with a
pattern of the illuminated reflection type mask, said apparatus
comprising: a projection optical system for forming an intermediate
image of the pattern of the reflection type mask and for re-imaging
the intermediate image upon the substrate; wherein said projection
optical system has a field stop at or adjacent the position where
the intermediate image is formed.
10. An apparatus according to claim 9, wherein said field stop has
an opening of variable shape.
11. An apparatus according to claim 10, wherein the opening of said
field stop has a width with respect to a scan direction, which
width is locally adjustable.
12. An apparatus according to claim 11, wherein the shape of the
opening of said field stop is adjusted in response to a change of a
coherence factor.
13. An apparatus according to claim 11, wherein the shape of the
opening of said field stop is adjusted in response to a change of
an illumination mode.
14-16. (Canceled)
17. A device manufacturing method, comprising the steps of:
exposing a substrate with a pattern by use of an exposure apparatus
as recited in claim 9; and developing the exposed substrate.
18. (Canceled)
Description
FIELD OF THE INVENTION AND RELATED ART
[0001] This invention relates generally to an exposure apparatus
and, more particularly, to an exposure apparatus for transferring a
fine pattern of an electronic circuit device, for example, formed
on a reflection type mask, by use of light in a wavelength region
of 200-10 nm as exposure light. Also, the invention concerns a
device manufacturing method that uses such an exposure
apparatus.
[0002] As a method of manufacturing a semiconductor circuit device
having a fine pattern, for example, there is a reduction projection
exposure method that uses EUV light of a wavelength 13-14 nm, for
example. In this method, a mask (reticle) having a circuit pattern
formed thereon is illuminated with EUV light, and an image of the
pattern of the mask is projected onto the surface of a wafer in a
reduced scale to expose a resist on the wafer surface, whereby the
pattern is transferred thereto.
[0003] Conventional EUV reduction projection exposure apparatuses
have a structure such as shown in FIG. 14, for example. More
specifically, FIG. 14 is a schematic view of a main portion of a
conventional EUV reduction projection exposure apparatus. FIG. 15
is a schematic and perspective view of a conventional reflection
type integrator. FIG. 16 is a view illustrating an illumination
region on the surface of a conventional a mask.
[0004] In these drawings, denoted at 1001 is a light emission point
for EUV light, and denoted at 1002 is an EUV light beam therefrom.
Denoted at 1003 is a filter, and denoted at 1004 is a first
rotation paraboloid mirror. Denoted at 1005 is a reflection type
integrator, and denoted at 1006 is a second rotation paraboloid
mirror. Denoted at 1007 is a reflection type mask. Denoted at 1008
are mirror systems, constituting a projection optical system.
Denoted at 1009 is a wafer. Denoted at 1010 is a mask stage, and
denoted at 1011 is a wafer stage. Denoted at 1012 is an aperture
having an arcuate opening. Denoted at 1013 is a laser light source,
and denoted at 1014 is a laser condensing optical system. Denoted
at 1015 is an illumination region defined on the mask surface, and
denoted at 1016 is an arcuate region in which pattern exposure is
to be carried out. Denoted at 1017 is a vacuum casing.
[0005] A conventional EUV reduction projection exposure apparatus
comprises an EUV light source, an illumination optical system, a
mask 1007, a projection optical system 1008, a wafer 1009, mask and
wafer stages 1010 and 1011 for carrying a mask and a wafer thereon,
an alignment mechanism (not shown) for precision alignment of the
mask and wafer, a vacuum casing for maintaining a vacuum ambience
for the optical system as a whole to prevent attenuation of the EUV
light, an exhausting system (not shown), and so on.
[0006] As examples of EUV light source, laser plasma and undulator
are used. In the illumination optical system, the EUV light 1002
from the light emission point 1001 is collected by the first
paraboloid mirror 1004, and the light is then projected to the
reflection type integrator 1005 by which a plurality of secondary
light sources are produced. EUV light beams from these secondary
light sources are collected by the second paraboloid mirror 1006 so
that these light beams are superposed one upon another on the mask
1007 surface, by which the mask 1007 is uniformly illuminated.
[0007] The reflection type mask 1007 comprises, for example, a
multilayered-film reflection mirror having formed thereon a
transfer pattern with a non-reflective portion made of an EUV
absorptive material. The EUV light reflected by the reflection type
mask 1008 and thus having information about the circuit pattern on
the mask is imaged upon the wafer 1009 surface by the projection
optical system 1008. The projection optical system 1008 is designed
to provide superior imaging performance with respect to a narrow
arcuate region off the optical axis center. In order that the
exposure is carried out by using this narrow arcuate region only,
an aperture 1012 having a arcuate opening is provided just before
the wafer 1009. Then, for transfer of the pattern on the whole mask
having a rectangular shape, the exposure is carried out while the
mask 1007 and the wafer 1009 are synchronously scanningly moved.
The projection optical system 1008 comprises a plurality of
multilayered-film mirrors, and it is arranged to project the
pattern of the mask 1007 onto the wafer 1009 surface in a reduced
scale. Usually, a telecentric system being telecentric on the image
side is used. As regards the object side (reflection mask side),
usually it has a non-telecentric structure so as to avoid physical
interference with the illumination light impinging on the
reflection type mask 1007.
[0008] In FIG. 14, the illumination optical system comprises first
paraboloid mirror 1004, reflection type integrator 1005, and second
paraboloid mirror 1006. The reflection type integrator 1005
comprises a fly's eye lens, as shown in FIG. 15, having a number of
small convex or concave surfaces arrayed two-dimensionally.
[0009] The laser light from the laser light source 1013 is
collected by the laser condensing optical system 1014, at a target
(not shown) placed at the light emission point 1001 position,
thereby to produce a high temperature plasma light source 1001
there. The EUV light 1002 being emitted from this plasma light
source by thermal radiation is reflected by the first paraboloid
mirror 1004, whereby a parallel EUV light beam is produced. This
light beam is then reflected by the reflection type integrator
1005, whereby a large number of secondary light sources are
produced.
[0010] EUV light from these secondary light sources are reflected
by the second paraboloid mirror 1006, to illuminate the reflection
type mask 1007. Here, the distance from the secondary light sources
to the second paraboloid mirror 1006, and the distance from the
second paraboloid mirror 1006 to the reflection type mask 1007 are
set approximately equal to the focal length of the second
paraboloid mirror 1006. Namely, the focal point of the second
paraboloid mirror 1006 is disposed at the position of the secondary
light sources. As a result, the EUV light emitted from one
secondary light source illuminates the mask 1007, as a parallel
light beam. The projection optical system 1008 is designed so that
the image of the secondary light source is projected on an entrance
pupil plane of the projection optical system 1008. Thus, the
condition for Koehler illumination is satisfied. Namely, the EUV
light impinging on a certain point on the reflection type mask 1007
is provided by superposition of EUV light beams emitted from all of
the secondary light sources.
[0011] The shape of the illumination region 1015 defined on the
mask surface is, as shown in FIG. 16, analogous to the shape of the
convex or concave surface mirrors which are constituent components
of the reflection type integrator 1005. Since it is an
approximately rectangular shape region including an arcuate region
1016 where the exposure is to be actually carried out, many EUV
light beams impinge on a portion other than the exposure region
1016. These EUV light beams not contributable to the exposure are
intercepted by the aperture 1012 that defines the exposure
region.
[0012] Conventional EUV reduction projection exposure apparatuses
use a reflection type mask as described above, and the illumination
optical system as well as a projection optical system are disposed
on the same side with respect to the reflection type mask.
Therefore, in order to make the size of the whole exposure
apparatus compact to some degree, it may cause unwanted physical
interference among various optical components constituting the
illumination system or the projection optical system, for
example.
[0013] Furthermore, if an arcuate aperture is disposed just before
a wafer, it may cause physical interference with the wafer. The
aperture therefore has to be placed away from the wafer, but this
raises a problem that the exposure region cannot be defined very
precisely.
SUMMARY OF THE INVENTION
[0014] In consideration of the problems peculiar to EUV reduction
projection exposure apparatuses such as described above, it is an
exemplary object of the present invention to provide an exposure
apparatus by which, where a reflection type mask is used and even
when the size of the whole exposure apparatus is made compact,
there does not occur physical interference among optical components
constituting the exposure apparatus. Also, it is an object of the
present invention to provide a device manufacturing method which
uses such an exposure apparatus.
[0015] In accordance with an aspect of the present invention, there
is provided an exposure apparatus for illuminating a reflection
type mask with light from a light source and for exposing a
substrate with a pattern of the illuminated reflection type mask,
said apparatus comprising: a projection optical system for
projecting the pattern of the reflection type mask onto the
substrate, said projection optical system having a stop; wherein
said stop has a first opening for defining a numerical aperture of
said projection optical system, and a second opening through which
light from the reflection type mask passes.
[0016] In accordance with another aspect of the present invention,
there is provided an exposure apparatus for illuminating a
reflection type mask with light from a light source and for
exposing a substrate with a pattern of the illuminated reflection
type mask, said apparatus comprising: a projection optical system
for forming an intermediate image of the pattern of the reflection
type mask and for re-imaging the intermediate image upon the
substrate; wherein said projection optical system has a field stop
at or adjacent the position where the intermediated image is
formed.
[0017] In accordance with a further aspect of the present
invention, there is provided an exposure apparatus for illuminating
a reflection type mask with light from a light source and for
exposing a substrate with a pattern of the illuminated reflection
type mask, said apparatus comprising: a projection optical system
for projecting the pattern of the reflection type mask onto the
substrate, said projection optical system having a plurality of
optical elements; wherein the light illuminating the reflection
type mask passes between first and second optical elements of said
plurality of optical elements.
[0018] In accordance with a yet further aspect of the present
invention, there is provided a device manufacturing method,
comprising the steps of: exposing a substrate with a pattern by use
of an exposure apparatus as recited above; and developing the
exposed substrate.
[0019] These and other objects, features and advantages of the
present invention will become more apparent upon a consideration of
the following description of the preferred embodiments of the
present invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic view of an exposure apparatus
according to an embodiment of the present invention.
[0021] FIG. 2A is a schematic view of a first integrator as viewed
from a reflection surface.
[0022] FIG. 2B is a side view, illustrating a state in which light
beams are incident on a portion of the first integrator.
[0023] FIG. 3A is a schematic and perspective view, illustrating a
state in which parallel light is incident on a second integrator
having a plurality of convex cylindrical surfaces.
[0024] FIG. 3B is a schematic and perspective view, illustrating a
state in which parallel light is incident on a second integrator
having a plurality of concave cylindrical surfaces.
[0025] FIG. 4 is a schematic view for explaining reflection of
light at a cylindrical surface.
[0026] FIG. 5 is a schematic view for explaining an angular
distribution of light reflected by a cylindrical surface.
[0027] FIG. 6 is schematic view for explaining an arcuate region to
be defined by light reflected by a cylindrical surface.
[0028] FIG. 7 is a schematic view of an NA aperture.
[0029] FIG. 8 is a schematic view of a variable arcuate slit.
[0030] FIGS. 9A and 9B illustrate adjustment of a (sigma) by
switching the first integrator.
[0031] FIGS. 10A, 10B and 10C are schematic views, respectively,
for explaining shapes of aperture stops for transformed
illumination, respectively.
[0032] FIGS. 11A and 11B are schematic views, respectively, for
explaining ring-like illumination.
[0033] FIG. 12 is a flow chart for explaining device manufacturing
processes in an embodiment of the present invention.
[0034] FIG. 13 is a flow chart for explaining details of Step 4 in
FIG. 12.
[0035] FIG. 14 is a schematic view of a main portion of a
conventional example.
[0036] FIG. 15 is a schematic and perspective view of a
conventional reflection type integrator.
[0037] FIG. 16 is a view, illustrating an illumination region and a
arcuate region to be used for exposure, in a conventional
structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Preferred embodiments of the present invention will now be
described with reference to the attached drawings.
[0039] FIG. 1 is a schematic view of a main portion of an exposure
apparatus according to an embodiment of the present invention.
Denoted in the drawing at 1 is laser light, and denoted at 2 is a
plasma light emission point for emitting EUV light. Denoted at 3a
is a nozzle for discharging liquid drops as target in the plasma
production. Denoted at 3b is a liquid drop collecting portion for
collecting liquid drops, not irradiated with excited laser light,
for reuse of the same. Denoted at 4 is a condensing mirror, and
denoted at 5 is EUV light collected by the mirror 4. Denoted at 6
is a filter, and denoted at 7 is a window for passing EUV light
while maintaining a vacuum. Denoted at 8, 10a, 10b, and 10c are
mirrors having a rotation paraboloid surface, for example. Denoted
at 201a and 201b are first integrators which comprise a plurality
of concave mirrors and used interchangeably. Denoted at 11 is a
second integrator having a plurality of cylindrical surface
mirrors, and denoted at 12 is a condensing mirror for converging
light from the second integrator. Denoted at 13 is a plane mirror
for deflecting the light, and denoted at 14 is a masking blade.
Denoted at 16 is a reflection type mask, and denoted at 17 is a
mask stage. Denoted at 18a-18f are components constituting a
projection optical system, and denoted at 19 is a variable slit
having an arcuate and variable opening. Denoted at 20 is a wafer
having a photosensitive material applied thereto, and denoted at 21
is a wafer stage. Denoted at 22 and 23 are vacuum casings for
maintaining the whole optical system in a vacuum to prevent
attenuation of the EUV light.
[0040] A high-power excited laser pulse light 1 emitted from an
excited laser light source (not shown) and a condensing optical
system (also not shown) is converged at the position of the light
emission point 2, and thus it provides a laser plasma light source.
Liquid drops (Xe, for example) as the target of the laser plasma
light source are successively discharged from the nozzle 3a at
regular time intervals, and they pass the convergence point 2. As a
liquid drop being discharged so just comes the position 2, the
excited pulse laser light 1 irradiates that liquid drop, whereby a
high-temperature plasma light emission point 2 is produced. EUV
light is produced from this plasma, by thermal radiation.
[0041] While Xe liquid drops are used as the target in this
embodiment, as a matter of course, Xe gas as a target may be blown
from a nozzle into a vacuum so that clusters produced by adiabatic
expansion may be used, or Xe gas may be cooled by a metal surface
and solidified Xe may be used. Also, a target produced by using a
metal such as Cu or Sn may be used. Alternatively, an undulator may
be used as an EUV light source, within the scope of the present
invention.
[0042] The EUV light emitted from the plasma light emission point 2
is collected by the rotation elliptical mirror 4, whereby an EUV
light beam 5 is provided. It passes through the filter 6 for
intercepting scattered particles from the plasma or from a
peripheral portion thereof and for blocking unwanted wavelengths
being unnecessary for exposure. The EUV light then passes through
the window 7 which is provided at the boundary between the vacuum
casings 21 and 22. Then, the light is reflected by the paraboloid
mirror 8, whereby an approximately parallel light beam 8' is
produced. The elliptical mirror 4 described above has a
multilayered reflective film formed thereon, for efficient
reflection of EUV light. Since it absorbs a portion of radiation
energies from the high-temperature plasma 2, the temperature
thereof rises during the exposure process. In consideration of it,
a material having high heat conductivity is used therefor. Also,
cooling means (not shown) is used to cool the same
continuously.
[0043] Although not mentioned to specifically in the following, the
reflection surfaces of various mirrors used in the optical system
similarly have a multilayered reflective film for efficient
reflection of EUV light. These mirrors may be made of a material
having good heat conductivity may be used, and also cooling means
may be used similarly.
[0044] The EUV light 8', now parallel light beam, enters the first
integrator 201a having a surface in which a plurality of small
concave surface mirrors are arrayed two-dimensionally. With these
concave surface mirrors, a large number light spots are produced,
by which a point light source array 202 is defined in the space.
EUV light beams emitted from this point light source array 202 are
collected by the paraboloid mirror 10a such that they are
superposed one upon another at the rear focal point position
thereof. As a result, a two-dimensional light source image 24
having a substantially uniform intensity distribution is
produced.
[0045] Here, the first integrator 201a will be explained in greater
detail, with reference to FIGS. 2A and 2B. FIG. 2A is a schematic
view of the first integrator, as viewed from the reflection
surface. Denoted at 210 is one of small concave surface mirrors.
The surface shape of the concave mirror is approximately spherical.
Thus, a large number of mirrors having the same shape are arrayed
two dimensionally, like a fly's eye. In FIG. 2A, the concave
surface mirrors 210 each having a hexagonal outside shape are
arrayed into a honeycomb structure. However, mirrors of quadrangle
outside shape may be arrayed in a grid-like structure. A large
number of mirror surfaces so combined into an integral structure
are provided with a reflective multilayered film, to assure
reflection of EUV light at a high efficiency.
[0046] FIG. 2B is a side view, illustrating the state in which
light is incident on arbitrary three consecutive mirror surfaces,
chosen from the large number of mirror surfaces 210 of the first
integrator. Namely, the concave surface mirror 210' is illustrated
as a sectional view. As shown in the drawing, when the EUV light is
incident on the concave surface mirror 210', the light is converged
at a focal point 202 thereof. This is also the case with the
neighboring mirror. Since the first integrator comprises such
mirrors being arrayed such as shown in FIG. 2A, the EUV light 8'
impinging on these reflection surfaces produces a large number of
light spots, at the focal point position 202, corresponding to the
array of the mirror surfaces. Thus, a point light source array 202
is provided.
[0047] The EUV light from the secondary light sources 24 produced
as described above is transformed by the paraboloid mirrors 10b and
10c into EUV light 11' having a desired size and having an
approximately uniform intensity within the beam diameter. This
light then enters a second reflection type convex cylindrical
surface integrator 11.
[0048] The function of the first integrator described above may be
provided by use of plural integrators.
[0049] Next, the principle of uniform illumination of an arcuate
region on a surface to be illuminated, by use of the second
integrator 11, will be explained in greater detail, with reference
to FIGS. 3-6.
[0050] FIG. 3A is a schematic and perspective view, illustrating a
case wherein parallel light is incident on a reflection type convex
cylindrical surface integrator, having a plurality of convex
cylindrical surfaces. EUV light 11' is projected in the direction
illustrated. FIG. 3B is a schematic and perspective view of a
reflection type concave cylindrical surface integrator, with a
plurality of concave cylindrical surfaces having a similar function
as of that of FIG. 3A. The integrator 11 shown in FIG. 1 is a
reflection type convex cylindrical surface integrator such as shown
in FIG. 3A. However, a reflection type concave cylindrical surface
integrator such as shown in FIG. 3B or, alternatively, a
combination of concave and convex cylindrical surfaces may be used
in place of it.
[0051] FIG. 4 is a schematic and sectional view of a reflection
type convex cylindrical surface integrator, and FIG. 5 is a view
for explaining EUV light reflection at the cylindrical surface of a
reflection type convex cylindrical surface integrator. FIG. 6
illustrates an angular distribution of EUV light as reflected by
the cylindrical surface of a reflection type convex cylindrical
surface integrator.
[0052] Reference numeral 11 in these drawings denotes a reflection
type convex cylindrical surface integrator. When an approximately
parallel EUV light beam is projected upon an integrator 11 having a
plurality of cylindrical surfaces, such as shown in FIG. 3A,
secondary light sources are produced by the integrator and,
additionally, the angular distribution of the EUV light emitted
from these secondary light sources is made into a conical surface
shape. Then, by reflecting this EUV light by use of a reflection
mirror having a focal point placed at the secondary light source
position, and by illuminating the mask or a surface being
substantially conjugate with the mask with the EUV light, the mask
or the surface can be illuminated with arcuate shape.
[0053] In order to explain the operation of a reflection type
integrator having a plurality of cylindrical surfaces, first, the
action of reflection light as parallel light is incident on one
cylindrical surface reflection mirror will be described with
reference to FIG. 5. Now, a case where parallel light is incident
upon one cylindrical surface, with an angle .theta. with respect to
a plane perpendicular to the central axis of the cylindrical
surface, will be considered.
[0054] Where a light ray vector of the parallel light is denoted by
P1=(0, -cos .theta., sin .theta.) while a normal line vector to the
reflection surface of cylindrical surface shape is denoted by
n=(-sin .alpha., cos .alpha., 0), then the light ray vector of the
reflection light is expressed by: 1 P2 = P1 - 2 ( P1 n ) n = ( -
cos x sin 2 , cos x cos 2 , sin ) .
[0055] By plotting the light ray vector of reflection light in a
phase space, as shown in FIG. 6, a circle of radius cos .theta. is
obtained on the x-y plane. Namely, the reflection light becomes
divergent light along a conical surface shape, and a secondary
light source (linear light source) is present at the position of
apex of the conical surface. Where the cylindrical surface of the
integrator 11 is concave, the secondary light source is present as
a real image, outside the reflection surface. Where it is convex,
the secondary light source is present, as a virtual image, inside
the cylindrical surface. Further, where the reflection surface is
defined by a limited portion of a cylindrical surface such as shown
in FIG. 4 and the central angle thereof is 2.phi., the range of
existence of the light ray vector P2 of the reflection light is in
an arcuate 601 (FIG. 6) having a central angle 4.phi. upon the x-y
plane.
[0056] Next, description will be made on a case of a rotation
paraboloid surface mirror having a focal length f and having a
focal point disposed at the secondary light source position defined
by parallel light, projected on a cylindrical surface reflection
mirror such as described above, wherein a surface to be illuminated
is placed at a position spaced by f from this reflection mirror.
Light emitted from the secondary light source is divergent light of
a conical surface shape and, after being reflected by the
reflection mirror with a focal length f, it is transformed into
parallel light. The reflection light here is a sheet-like beam of
arcuate sectional shape, having a radius fxcos .theta. and a center
angle 4.phi.. Thus, as shown in FIG. 6, only an arcuate region 601
upon the surface to be illuminated, having a radius fxcos .theta.
and a center angle 4.phi., is illuminated.
[0057] While the foregoing description has been made with reference
to a single cylindrical surface reflection mirror, now a case
where, as shown in FIG. 3A, parallel light of a thickness D is
incident on a wide-area integrator 11 having a large number of
cylindrical surfaces arrayed in parallel to each other, is
considered. If the mask is disposed at a position spaced from the
reflection mirror by a focal length f, like the foregoing example,
the angular distribution of the light reflected by the reflection
mirror, having many cylindrical surfaces arrayed in parallel to
each other, is unchanged from the foregoing example. Thus, upon the
mask, an arcuate region of a radius fxcos .theta. and a center
angle 4.phi. is illuminated. Also, since the light impinging on a
single point upon the mask comes from the entire illumination
region of the reflection mirror, having a number of cylindrical
surfaces arrayed in parallel, the angular expansion thereof is D/f.
Namely, the numerical aperture (NA) of the illumination system is
D/(2f). Where the mask side numerical aperture of the projection
optical system is Nap1, the coherence factor is:
.sigma.=D/(2fNAp1)
[0058] Thus, by changing the diameter of the parallel light
impinging on the integrator 11, an optimum coherent factor .sigma.
can be set.
[0059] Here, the parallel light 11' entering the integrator 11 has
its sectional intensity already uniformed by the first integrator
201a as described hereinbefore, in the arcuate illumination region,
as regards a direction (.theta. direction) along the arcuate shape,
the uniformess is accomplished by superposition of plural light
beams from the integrator 11. As regards a direction (r direction)
perpendicular to the arcuate shape, the uniformess is assured by
superposition of plural light beams from the integrator 201a. With
this arrangement, arcuate illumination with less illuminance
irregularities and with good uniform intensity, as compared with
conventional structures, can be accomplished upon the surface to be
illuminated. Furthermore, since the arcuate illumination region is
never provided by cutting it out of a rectangular region as in the
conventional structures, the loss of exposure amount is very small
and the efficiency is remarkably better.
[0060] Referring now to FIGS. 9A and 9B, description will be made
on a method of adjusting the coherence factor .sigma. of the
illumination system by changing the above-described light beam
diameter D, in response to interchanging the integrators 201a and
201b.
[0061] FIGS. 9A and 9B are schematic views, respectively, of
fragmentary sections of a large number of concave mirrors at the
reflection surfaces of the integrators 201a and 201b (FIG. 1). As
shown in these drawings, the focal point position 201b of the
concave mirror 201a and the focal point position of the concave
mirror 201b are designed to be approximately coincident with each
other. Namely, these mirror are arranged to have substantially the
same focal length but the emission angle of light to be emitted
therefrom is different. More specifically, the concave surface
mirrors 201a and 201b have the same curvature radius, but only the
effective diameters of the concave mirrors are different. Namely,
the effective diameter 901a of the concave mirror 201a is made
larger than the effective diameter 901b of the concave mirror 201b.
With this setting, in regard to the EUV light 8' impinging on the
first integrator, the divergent or expansion angle 902a of the
light beam reflected by the mirror 201a becomes larger, in
accordance with the aperture ratio, than the expansion angle 902b
of the light beam reflected by the mirror 201b.
[0062] Referring back to FIG. 1, the light beam from the point
light source array at the focal point position 202 is Fourier
transformed by the paraboloid mirror 10a, and at the focal point
position 24, what is called Koehler illumination condition is
satisfied. Thus, the light beam there has an approximately uniform
sectional intensity. However, the light beam diameter at the
position 24 is approximately proportional to the expansion angle at
the focal point position 202. Namely, as shown in FIGS. 9A and 9B,
where the integrator 201a is used, since the expansion angle 202a
is larger, the light beam diameter at the position 24 is larger. If
on the other hand the integrator 201b is used, since the expansion
angle 902b is smaller, the beam diameter at the position 24 is
smaller.
[0063] Since the light beam at the position 24 is transformed by
the paraboloid mirrors 10b and 10c into a light beam 11' of desired
size, the light beam diameter 11' impinging on the second
integrator 11 can be changed as a result of interchanging the
integrators 201a and 201b.
[0064] By setting the light beam diameter 11' to a desired size as
described above, the coherence factor .sigma. (sigma) of the
illumination light impinging on the reflection type mask 16 can be
set to a desired magnitude, as has been described in the foregoing.
Furthermore, the light beam diameter can be adjusted by using the
aperture stop 204. Also, the light beam diameter can be adjusted by
changing the magnification of the paraboloid mirrors 10b and
10c.
[0065] The exposure method according to this embodiment will be
explained more. In FIG. 1, the EUV light 11' incident on the second
integrator is collected by the paraboloid mirror 12 in accordance
with the principle described above, and it is deflected by the
plane mirror 13. Then, after passing through an opening of an NA
stop 206 (to be described later) and the masking blade 14, the
light produces an arcuate illumination region upon the reflection
type mask 16, held by the mask stage 17, whereby arcuate
illumination is carried out. Here, the curvature center of the
arcuate illumination region is coincident with the optical axis
18AX of the projection optical system. The masking blade 14 serves
to block, to some degree and with respect to the reflection type
mask, those regions other than the desired region to be
exposed.
[0066] Here, it is important that the EUV light beam 12' collected
by the paraboloid mirror 12 passes between the mirrors 18a and 18b,
constituting the projection optical system. In the conventional
structure having been described with reference to FIG. 14, the
light beam of the illumination optical system and the light beam of
the projection optical system do not intersect with each other in
the space. In a case where, like this embodiment, the interval
between the mirror 18b of the projection optical system 18 and the
reflection type mask 16 is narrow, if the EUV light 12' directed
between the mirrors of the projection optical system as in the
present embodiment, undesirable interference of the paraboloid
mirror 12 or plane mirror 13 with the mask 16 can advantageously be
avoided. Although this embodiment is arranged so that the light
beam for illuminating the mask passes between first and second
mirrors 18a and 189b, in an order from the reflection type mask
side, the structure may be modified in accordance with the design
of the projection optical system so that a light beam passes
between mirrors having a relatively large interval. Substantially
the same advantageous effects are attainable also in that occasion.
Furthermore, as a matter of course, the structure may be modified
so that the light beam passes between a mirror and any optical
element other than the mirror of the projection optical system (for
example, NA stop 206 of this embodiment or variable slit 19), or
between optical elements other than mirrors.
[0067] The EUV reflection light from the reflection type mask 16
being illuminated in an arcuate shape, bears information regarding
the circuit pattern of the mask. By means of a projection optical
system which comprises mirrors 18a-18f, an NA stop 206 and an
arcuate variable slit 19, the light is projected and imaged on a
wafer (substrate) 20 with a photosensitive material coating, at an
optimum magnification best suited for the exposure. The exposure of
the circuit pattern is thus completed. The wafer 20 is fixedly
mounted on the wafer stage 21, and it is movable along a plane
orthogonal to the optical axis of the projection optical system 18
as well as along the optical axis direction. The movement thereof
is controlled by use of a measuring device such as a laser
interferometer, not shown. If the magnification of the projection
optical system is M, the reflection type mask 16 is scanned at a
velocity v along a plane orthogonal to the optical axis of the
projection optical system 18 and, concurrently therewith, the wafer
20 is synchronously scanned at a velocity v.multidot.M along a
plane perpendicular to the optical axis of the projection optical
system 18. The whole surface exposure is performed in this
manner.
[0068] Next, details of the NA stop 206 will be described with
reference to FIG. 7. Denoted in the drawing at 701 is an opening of
approximately circular shape, for restricting the NA of the
projection optical system. An opening of arcuate shape, being
denoted at 702, is defined so as to transmit the illumination light
from the illumination system as well as reflection light from the
reflection type mask 16. (In accordance with the design of the
projection optical system, this opening may be arranged so as to
transmit only the reflection light from the mask.) The projection
optical system 18 of this embodiment is designed so that a pupil
plane is defined in the neighborhood of the reflection surface of
the mirror 18b. Thus, by restricting the pupil diameter by use of a
stop, a desired numerical aperture NA can be set. In the FIG. 7
example, a plurality of openings having different diameters are
formed and disposed concentrically, into a turret structure. The
turret is disposed at the position 206 in FIG. 1. By means of a
rotation controller, not shown, a desired one of the openings can
be placed at the pupil plane position. Alternatively, openings may
be disposed along a one-dimensional array and used interchangeably,
or a variable aperture stop structure having an opening whose
diameter can be changed as desired may be used. Further, although
this embodiment uses a stop which has an opening for light from the
reflection type mask and an opening for light from the mirror of
the projection optical system, wherein the opening for the light
from the projection optical system defines the NA, the present
invention is not limited to this. For example, the opening may
function to define an exposure region.
[0069] Referring now to FIG. 8, an arcuate variable slit 19 will be
described. Denoted in the drawing at 801 is a movable edge portion
for locally changing the width of an arcuate slit. Denoted at 802
is a fixed edge portion which is set along the outside
configuration of the mirror 18f of the projection optical system.
This arcuate variable slit 19 is disposed at or adjacent an
intermediate imaging position of the projection optical system 18
(i.e. the position where an intermediate image of the pattern of
the mask 16 is formed), such as shown in FIG. 1. Here, the term
"intermediate image" includes not only an image in which the
pattern of the mask 16 is exactly imaged but also one in which it
is roughly imaged. By placing the slit at this position, rather
than at a position adjacent the reflection type mask 16,
interference between the arcuate variable slit 19 and the
reflection type mask 16 can be avoided. When a circuit pattern of
the mask 16 is reduced and transferred to a wafer 20 and if there
is non-uniformess of illuminance inside the arcuate slit, it
results in non-uniform exposure during the scan exposure. In order
to meet this problem, the slit width in such portion of the arcuate
slit as having a larger illuminance, may be narrowed in accordance
with a signal from a control system, not shown, so that the scan
exposure is carried out with a light quantity reduced by desired
amount. This procedure enables exposure of the whole exposure
region, with uniform intensity. In the example shown in the
drawing, the slit width at the central portion is narrowed a little
bit, if the illuminance at the central portion of the arcuate slit
is slightly higher than the peripheral portion.
[0070] Although this embodiment has been described with reference
to an example using a movable edge portion 801 and a fixed edge
portion 802, the edge 802 may of course be a movable edge.
[0071] Next, referring to FIGS. 10A-10C, description will be made
on how to perform modified or transformed illumination such as
ring-like illumination, on the basis of switching an aperture stop
204 disposed adjacent the reflection surface of the second
integrator. FIGS. 10A-10C illustrate shapes of openings formed in
an aperture stop 204. The blank areas correspond to openings
through which light can pass. The pattern 204a shows an opening for
standard illumination mode. The pattern 204b shows an opening for
ring-like illumination mode. The pattern 204c shows an opening for
quadruple illumination mode. Some opening patterns such as above
are prepared as a turret, for example, shown at 204 in FIG. 1. By
rotating the turret in response to a signal from a control system
(not shown) and by means of an aperture stop driving system 205, a
desired opening shape can be set interchangeably. In place of using
a turret, a mechanical method such as sequentially choosing plural
aperture stops disposed in an array may be used.
[0072] As described above, the aperture stop 204 is disposed
adjacent the reflection surface of the second integrator 11. Thus,
if the incidence angle of the light impinging on the integrator 11
is .alpha., on the reflection surface of the integrator 11 the
light beam diameter extends in a direction parallel to the sheet of
the drawing (incidence plane) with a magnification 1/cos .alpha..
In consideration of it, it is necessary that the aperture shape of
the aperture stop is similarly extended in the same direction with
a magnification 1/cos .alpha.. In FIG. 10A, the pattern 204a, for
example, is used to restrict the incident light beam diameter into
a circular shape, the aspect ratio of this ellipse is 1/cos
.alpha.. The same applies to the cases of 204b and 204c.
[0073] Next, description will be made on the principle of
transformed deformation based on the aperture stop 204, disposed
adjacent the reflection surface of the integrator 11, with
reference to an example of aperture stop 204b being adapted to
ring-like illumination.
[0074] FIGS. 11A and 11B illustrate a fragmentary portion of the
integrator 11 and paraboloid mirror 12 in FIG. 1, wherein FIG. 11A
is a side view and FIG. 11B is a top view. The aperture stop 204b
for defining the ring-like illumination mode is disposed such as
shown in FIG. 11A. Here, the aperture stop 204b is not illustrated,
for explanation purpose.
[0075] The light beam incident on the integrator 11 is reflected.,
while an optical axis central portion and an outside diameter
portion thereof are intercepted by the aperture stop 204b. The
intensity distribution of this reflection light upon the integrator
11 surface duly corresponds, as a matter of course, to the shape of
the opening of the aperture stop 204b. Further, by means of plural
cylindrical surfaces, the light beam is reflected with an angular
distribution of arcuate shape, as has already been described. The
paraboloid surface 12 collects this light beam, to thereby produce
a uniform illumination region of arcuate shape at the focal point
position 1101 thereof. Here, the position 1101 is approximately
equivalent to the position of the reflection type mask 16 in FIG.
1. Since the central portion of the light beam is blocked, the
collected light defines a light beam such as shown at 1102 (hatched
area). This is also with the case of FIG. 11B. This means that, at
the position of intersection between the principal light ray and
the optic axis, that is, at the position 1103 being conjugate with
the pupil plane, the intensity has a distribution such as shown at
1104. Namely, it means that ring-like illumination is
accomplished.
[0076] There may be a case where non-uniform illuminance is
produced inside the illumination region on the reflection type mask
in response to the change of coherence factor or illumination mode
described above. In that occasion, illuminance non-uniformess is
similarly produced at corresponding sites in the arcuate slit. As
described hereinbefore, such non-uniform illuminance can be reduced
by controlling the arcuate variable slit 19 and, as a result of it,
the exposure non-uniformess on the wafer can be reduced. In this
embodiment, the arcuate variable slit 19 is disposed within the
projection optical system. If however there is a space inside the
illumination system, the arcuate variable slit may be disposed
inside the illumination system, to correct illuminance
non-uniformess in the illumination region, to be produced in
response to the change of coherence factor or illumination mode,
similarly.
[0077] Next, referring to FIGS. 12 and 13, an embodiment of a
device manufacturing method which uses an exposure apparatus
described above, will be explained.
[0078] FIG. 12 is a flow chart for explaining the procedure of
manufacturing various microdevices such as semiconductor chips
(e.g., ICs or LSIs), liquid crystal panels, or CCDs, for example.
Here, production of semiconductor ships will be described, as an
example.
[0079] Step 1 is a design process for designing a circuit of a
semiconductor device. Step 2 is a process for making a mask on the
basis of the circuit pattern design. Step 3 is a process for
preparing a wafer by using a material such as silicon. Step 4 is a
wafer process which is called a pre-process wherein, by using the
thus prepared mask and wafer, a circuit is formed on the wafer in
practice, in accordance with lithography. Step 5 subsequent to this
is an assembling step which is called a post-process wherein the
wafer having been processed at step 4 is formed into semiconductor
chips. This step includes an assembling (dicing and bonding)
process and a packaging (chip sealing) process. Step 6 is an
inspection step wherein an operation check, a durability check an
so on, for the semiconductor devices produced by step 5, are
carried out. With these processes, semiconductor devices are
produced, and they are shipped (step 7).
[0080] FIG. 13 is a flow chart for explaining details of the wafer
process. Step 11 is an oxidation process for oxidizing the surface
of a wafer. Step 12 is a CVD process for forming an insulating film
on the wafer surface. Step 13 is an electrode forming process for
forming electrodes upon the wafer by vapor deposition. Step 14 is
an ion implanting process for implanting ions to the wafer. Step 15
is a resist process for applying a resist (photosensitive material)
to the wafer. Step 16 is an exposure process for printing, by
exposure, the circuit pattern of the mask on the wafer through the
exposure apparatus described above. Step 17 is a developing process
for developing the exposed wafer. Step 18 is an etching process for
removing portions other than the developed resist image. Step 19 is
a resist separation process for separating the resist material
remaining on the wafer after being subjected to the etching
process. By repeating these processes, circuit patterns are
superposedly formed on the wafer.
[0081] Where an illumination system according to an embodiment of
the present invention is used, an arcuate illumination region on
the surface to be illuminated can be illuminated with uniform
intensity, as compared with conventional structures, yet the light
from an EUV light source can be shaped at a high efficiency, with a
significantly decreased loss of light quantity.
[0082] Further, where the illumination system such as described
above is incorporated into an exposure apparatus, it ensures
reduction of exposure time and increase of throughput.
[0083] While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set
forth and this application is intended to cover such modifications
or changes as may come within the purposes of the improvements or
the scope of the following claims.
* * * * *