Illumination optical apparatus and projection exposure apparatus using it

The illumination optical apparatus of this invention is so arranged that light from a discharge lamp is collected by a rotationally symmetric collector mirror, the thus collected light is collimated into nearly parallel light by a collimator optical system, an optical integrator splits the parallel light into a plurality of light beams to form a plurality of secondary light sources, and thereafter the light from the secondary light sources is projected through a condenser optical system. A secondary light source distribution shaping portion is provided for shaping a light intensity distribution of the plural secondary light sources into a predetermined light intensity distribution, the two electrodes of the anode and cathode in the same discharge lamp are located in a predetermined relation, and an entrance surface of the optical integrator is located at a predetermined position with respect to a position where an image of a reflecting surface of the rotationally symmetric collector mirror is formed by the same collimator optical system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an illumination optical apparatus suitably 
applicable to projection exposure apparatus for fabricating semiconductor 
devices etc. by projection printing of a pattern of a photomask on a 
photosensitive substrate. 
2. Related Background Art 
The configuration shown in FIG. 1 is known as a conventional illumination 
optical apparatus of this type. Light emitted from a super-high pressure 
mercury lamp 1 disposed at a first focus position F1 of an ellipsoidal 
mirror 2 is reflected and collected by the ellipsoidal mirror 2 to be 
focused at a position A1 of a second focus F2 of the ellipsoidal mirror 2 
and thereafter to be collimated into nearly parallel light beams by a 
collimator lens 3, then entering a fly's eye lens 4 as an optical 
integrator. Here, the light incident into the fly's eye lens 4 is split 
into a plurality of light beams by the fly's eye lens 4, which form 
respective secondary light sources at a position A2 on the side of exit 
surfaces 4b of respective lens elements (41-43) composing the fly's eye 
lens 4. Light from these plural secondary light sources is limited by an 
aperture stop 5 having a circular aperture, and thereafter is condensed by 
a condenser lens 6 to illuminate a reticle R as an illuminated surface in 
a superimposed manner. The circuit pattern on the reticle R uniformly 
illuminated by the above illumination optical apparatus is projected 
through a projection optical system onto a substrate W, such as a wafer, 
coated with a photoresist. On this occasion, the position A2 of the plural 
secondary light sources formed by the fly's eye lens 4 or the aperture 
stop 5 is conjugate with a position of an aperture stop 7a disposed at a 
pupil position A3 inside the projection optical system 7, and plural 
images of the secondary light sources are formed on the aperture stop 7a, 
thus achieving so-called Kohler illumination. 
SUMMARY OF THE INVENTION 
The present invention relates to an illumination optical apparatus which 
has a discharge lamp for emitting light, a rotationally symmetric 
collector mirror for reflecting and collecting the light from the 
discharge lamp to form a light source image, a collimator optical system 
for collimating light from the light source image formed by the 
rotationally symmetric collector mirror into nearly parallel light, an 
optical integrator for splitting the light from the collimator optical 
system into a plurality of beams and forming a plurality of secondary 
light sources, and a condenser optical system for condensing light from 
the plurality of secondary light sources formed by the optical integrator 
to illuminate an illuminated surface in a superimposed manner, which 
further has a secondary light source distribution shaping means for 
shaping a light intensity distribution of the same plurality of secondary 
light sources into a predetermined light intensity distribution, in which 
the above discharge lamp has two electrodes of an anode and a cathode 
disposed as opposed to each other along and on a rotation axis of the 
rationally symmetric collector mirror, in which the anode is disposed on 
the side of the vertex of the rotationally symmetric collector mirror with 
respect to the cathode, and in which an entrance surface of the optical 
integrator is located at a defocused position shifted to the discharge 
lamp side from a position where an image of a reflecting surface of the 
rotationally symmetric collector mirror is formed by the above collimator 
optical system. 
This can largely increase light intensities of peripheral portions in the 
light beam entering the optical integrator and in those the secondary 
light sources formed by the optical integrator, whereby the illuminated 
surface can be illuminated at a high illumination efficiency in the normal 
illumination method or in any illumination method, such as oblique 
illumination. Accordingly, if it is applied as an illumination optical 
apparatus for exposure apparatus for transferring the pattern of reticle 
onto the wafer through the projection optical system, exposure can be 
realized with a high throughput in any illumination method including the 
normal illumination and oblique illumination. 
Based on the above configuration, a preferred embodiment may be so arranged 
that the secondary light source distribution shaping means has first and 
second aperture stops arranged as switchable on or near the exit surface 
of the optical integrator, the one first aperture stop has a circular 
aperture rotationally symmetric with respect to the optical axis of the 
condenser optical system, and the other second aperture stop has aperture 
portions in peripheral areas offset from the optical axis of the condenser 
optical system and has a light-shielding portion or light-reducing portion 
in the central area passing the optical axis of the condenser optical 
system. By this, the normal illumination and oblique illumination can be 
selectively realized for the illuminated surface at a high illumination 
efficiency and in a simple structure. Therefore, when the apparatus of the 
present invention is applied to illumination apparatus in exposure 
apparatus, exposure can be achieved with a high throughput in any 
arbitrarily selected illumination method including the normal illumination 
and oblique illumination. 
In a preferred embodiment, the collimator optical system has a collimator 
lens for forming an image of the reflecting surface of the rotationally 
symmetric collector mirror and collimating the light from the light source 
image formed by the rotationally symmetric collector mirror, and a relay 
lens for reimaging the image of the reflecting surface of the rotationally 
symmetric collector mirror formed by the collimator lens. 
The present invention will be more fully understood from the detailed 
description given hereinbelow and the accompanying drawings, which are 
given by way of illustration only and are not to be considered as limiting 
the present invention. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will be apparent to those skilled in the 
art from this detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Recently, attention is directed toward the technology to further improve 
the resolving power and the depth of focus originally owned by the 
projection optical system 7 by modifying the shape of the secondary light 
sources formed by the fly's eye lens and obliquely illuminating the 
reticle R, based on the structure as shown in FIG. 1. 
For example, Japanese Laid-open Patent Application No. 5-175101 etc. 
describe the technique to improve the resolving power and depth of focus 
of the projection optical system 7 by providing the aperture stop 5 
disposed on the exit side of the fly's eye lens 4 with an aperture portion 
of an annular shape (doughnut shape) as shown in FIG. 2 and thereby 
forming an annular shape of secondary light sources to obliquely 
illuminate the reticle R. In the following description, an annular 
illumination method is used for the illumination method for obliquely 
illuminating an illuminated object while forming the annular shape of 
secondary light sources. 
Further, Japanese Laid-open Patent Application No. 4-101148 etc. describe 
the technique to further improve the resolving power and depth of focus of 
the projection optical system 7, more than those in the annular 
illumination method, by providing the aperture stop 5 disposed on the exit 
side of the fly's eye lens 4 with four aperture portions offset as shown 
in FIG. 3 and thereby forming four offset regions of secondary light 
sources to obliquely illuminate the reticle R (which will be referred to 
as special oblique illumination). In the following description, a special 
illumination method is used for the illumination method to obliquely 
illuminate an illuminated object while forming a plurality of secondary 
light sources offset from the optical axis. 
The above techniques, however, show the profile of light intensity 
distribution as shown in FIG. 4 on the entrance surface 4a of the fly's 
eye lens, wherein the intensity is high in the central portion but 
gradually decreases to the periphery. Further, the above techniques have a 
trend of light intensity distribution as shown in FIG. 5 as to the 
plurality of secondary light sources formed on the exit surface 4b of the 
fly's eye lens. 
This will be explained in more detail. First, let us suppose the fly's eye 
lens 4 has, for example, three lens elements 41-43 as shown in FIG. 1. 
Then, d1, d2, d3 as represented by the solid lines in FIG. 5, represent 
light intensity distributions of light source images formed on the exit 
side by the lens elements 41, 42, 43, respectively. As shown, the light 
intensity distributions d1, d3 of the light source images formed by the 
lens elements 41 and 43 located in the periphery of the fly's eye lens 4 
are weaker than the light intensity distribution d2 of the light source 
image formed by the lens element 42 located in the central portion of the 
fly's eye lens 4; an envelope connecting the peaks of the light 
intensities formed by the respective lens elements 41-43 becomes a light 
intensity distribution as shown by the dashed line in FIG. 5, which is 
similar to the light intensity distribution on the entrance surface 4a of 
the fly's eye lens 4 as shown in FIG. 4. 
Accordingly, if the aperture stop with the annular aperture in the 
periphery as shown in FIG. 2 or the aperture stop with the four offset 
apertures in the periphery as shown in FIG. 3 is placed at the position 
where the plurality of secondary light sources are formed, the utility 
factor of light beams becomes extremely lowered, which would result in 
greatly decreasing the illuminance on the illuminated surface such as a 
reticle R, thereby making the exposure time longer and causing a great 
drop of the throughput. 
Next explained is a principle of the present invention. Discussed with 
FIGS. 4 and 5 was the point that the light intensity distribution was high 
in the central portion but became lower toward the periphery before and 
after the fly's eye lens as an optical integrator. This point was studied 
in various aspects and it was found that the phenomenon caused by a 
characteristic of luminous intensity distribution due to the shape of the 
electrodes in the super-high pressure mercury lamp 1 as a discharge lamp 
disposed at the first focus position of the ellipsoidal mirror 2 as a 
rotationally symmetric collector mirror. 
This will be explained in further detail. Tip portions of the electrodes of 
the super-high pressure mercury lamp are formed as shown in FIG. 6: the 
cathode 1a has the tip of a needlelike shape while the anode 1b has the 
tip of a shape of a truncated circular cone obtained by cutting the top 
part including the vertex from a circular cone; the anode of the 
super-high pressure mercury lamp is normally arranged to be larger than 
the cathode. Because of this arrangement, when a high voltage is applied 
between the two electrodes of the super-high pressure mercury lamp, the 
characteristic of luminous intensity distribution of the light generated 
by discharge at the two electrodes will show such a luminous intensity 
distribution as shown in FIG. 6, in which the luminous intensity is almost 
constant from the horizontal direction (0 degree) up to near 45 degrees on 
the side of cathode 1a, but the light quickly attenuates because of 
eclipse by the anode itself over near 30 degrees on the side of anode 1b. 
In the conventional apparatus, the two electrodes of the cathode 1a and 
anode 1b in the super-high pressure mercury lamp are arranged as opposed 
to each other near the first focus F1 and along and on the rotation axis 
(or optical axis Ax) of the ellipsoidal mirror 2 as a rotationally 
symmetric collector mirror, and the cathode 1a is located on the side of 
the vertex O of the ellipsoidal mirror with respect to the anode 1b, as 
shown in FIG. 7. 
Because of this arrangement, as shown in FIG. 7, the light emitted from the 
electrodes of the super-high pressure mercury lamp, having the 
characteristic of constant luminous intensity distribution from the 
vertical direction (0 degree) to near 45 degrees on the side of cathode 
1a, is reflected by an inside portion 2a of the ellipsoidal mirror 2 and 
thereafter is condensed by the collimator lens 3 to illuminate the central 
portion of the fly's eye lens 4. On the other hand, the light emitted from 
the electrodes of the super-high pressure mercury lamp, having the 
characteristic of nearly constant luminous intensity distribution from the 
vertical direction (0 degree) to near 30 degrees on the side of anode 1b, 
is reflected by an outside portion 2b of the ellipsoidal mirror 2 and 
thereafter is condensed by the collimator lens 3 to illuminate the 
periphery of the fly's eye lens 4. 
Consequently, it is understood that the light intensity distribution on the 
entrance side of the fly's eye lens 4 is high in the central portion but 
becomes weaker toward the periphery, as shown in FIG. 4. 
The present invention positively utilizes the characteristic of luminous 
intensity distribution of the super-high pressure mercury lamp as shown in 
FIG. 6. Namely, it was found that in order to relatively increase the 
intensity distribution in the peripheral portion relative to that in the 
central portion in the incident light entering the fly's eye lens 4, it 
was effective to locate the anode 1b of the super-high pressure mercury 
lamp on the side of the vertex O of the collector mirror with respect to 
the cathode 1a, opposite to the conventionally common practice, which the 
present invention utilizes. 
In that case, it is desired to increase the effective diameter of the 
collector mirror in order to expand an intake angle on the cathode side. 
However, in order to relatively increase the intensity distribution in the 
periphery to that in the central portion, it is not sufficient only to 
locate the anode 1b of the super-high pressure mercury lamp on the side of 
vertex O of the collector mirror with respect to the cathode 1a, opposite 
to the conventionally common practice, and another important factor is a 
condition of location of the fly's eye lens 4. 
This will be explained in further detail. First, only from the viewpoint of 
the utility factor of light, it is effective to arrange the reflecting 
surface of the ellipsoidal mirror 2 as conjugate with the entrance surface 
4a of the fly's eye lens 4 with respect to the collimator lens 3, as shown 
in FIG. 8, thereby making flat (plane) the image of the reflecting surface 
of the ellipsoidal mirror 2 formed on the entrance surface 4a of the fly's 
eye lens 4. 
However, if they are perfectly conjugate with each other, sharp images of a 
circular edge 2c of a hollow portion of the ellipsoidal mirror and a 
circular outer edge 2d are formed on the entrance surface 4a of the fly's 
eye lens 4, which will cause significant, negative influence on the 
illuminance uniformity on the illuminated surface R. 
It is thus necessary to defocus the position of the image (flat image) of 
the reflecting surface of the ellipsoidal mirror 2 formed by the 
collimator lens 3 relative to the entrance surface 4a of the fly's eye 
lens 4 to such an extent as not to degrade the utility factor of light so 
much. 
On this occasion the intensity distribution on the entrance surface 4a of 
the fly's eye lens 4 greatly differs depending upon whether the defocus is 
taken in a plus direction (which is a direction directed toward the 
illuminated surface) or in a minus direction (which is a direction 
directed toward the light source). 
This will be explained referring to FIG. 9 to FIG. 11. 
FIG. 9 is a drawing to show a state of rays where a point light source S, 
which isotropically emits light, is placed at the first focus F1 of the 
ellipsoidal mirror. As shown in FIG. 9, the light from the point light 
source, reflected by the ellipsoidal mirror 2, is focused at the position 
A1 of the second focus F2 and thereafter is collimated into nearly 
parallel light beams by the collimator lens 3. Here, plane a indicates a 
position of the image plane of the reflecting surface of the ellipsoidal 
mirror 2 formed by the collimator lens 3, and planes b and c represent 
planes defocused by a predetermined distance along the directions of the 
optical axis Ax of the ellipsoidal mirror 2 (or the optical axis Ax of the 
collimator lens 3) from the image plane a. 
In this case, since the light beams from the collimator lens 3 are nearly 
parallel light beams, the light intensity distribution is in a hollow 
state in which light intensities are distributed only in the periphery, as 
shown in FIG. 12, even if the entrance surface 4a of the fly's eye lens 4 
disposed on the illuminated surface side of the collimator lens 3 (on the 
right side of the collimator lens 3 in FIG. 9) is placed at any position 
out of the planes a to c. 
Next, let us discuss a case where the point light source S, which 
isotropically emits light, is placed at a position shifted along the 
optical axis from the position of the first focus F1. 
Since the ellipsoidal mirror 2 as a reflecting mirror is generally very far 
from the Herschel's condition, it suddenly gives rise to spherical 
aberration once an object is located at a position shifted from the first 
focus position F1 in the direction of the optical axis Ax. For example, if 
the point light source S is located at a position shifted in the minus 
direction (the direction toward the vertex O of the ellipsoidal mirror 2) 
from the first focus F1 of the ellipsoidal mirror 2 along the optical axis 
Ax, as shown in FIG. 10, the position of the light source image (or the 
focused position) formed by the ellipsoidal mirror 2 moves from the second 
focus position F2 in the plus direction (the direction directed toward the 
illuminated surface) and negative spherical aberration appears. Thus, the 
light beams passing through the collimator lens 3 are not parallel light, 
and the light intensity distribution formed on the entrance surface 4a of 
the fly's eye lens 4 greatly changes depending upon the position of the 
entrance surface 4a of the fly's eye lens 4 located on the side of the 
illuminated surface of the collimator lens 3. 
FIG. 10 shows a state of rays where the point light source S, which 
isotropically emits light, is placed at a position shifted from the 
position of the first focus F1 of the ellipsoidal mirror to the side of 
the vertex O of the ellipsoidal mirror 2. In FIG. 10 positions of planes 
a-c correspond to the positions of the planes a-c, respectively, in FIG. 
9. 
When the entrance surface 4a of the fly's eye lens 4 is placed at the 
position of the plane c defocused in the plus direction (the direction 
directed toward the illuminated surface) from the image position a of the 
reflecting surface of the ellipsoidal mirror formed by the collimator lens 
3, as shown in FIG. 10, stronger light is irradiated to the peripheral 
portion than in the central portion of the fly's eye lens 4, thus 
presenting the light intensity distribution deflected to the periphery, as 
shown in FIG. 13. On the other hand, if the entrance surface 4a of the 
fly's eye lens 4 is placed at the position of the plane b defocused in the 
minus direction (the direction toward the vertex O of the ellipsoidal 
mirror 2) from the image position a of the reflecting surface of the 
ellipsoidal mirror formed by the collimator lens 3 in FIG. 10, stronger 
light is irradiated to the central portion of the fly's eye lens 4 than in 
the peripheral portion thereof, thus presenting the light intensity 
distribution deflected to the central portion, as shown in FIG. 14. The 
light intensity distribution at the image plane position a of the 
reflecting surface of the ellipsoidal mirror 2 formed by the collimator 
lens 3 in FIG. 10 is a distribution in a hollow state in which light 
intensities are distributed only in the periphery, as shown in FIG. 12. 
In contrast with it, if the point light source S, which isotropically emits 
light, is placed at a position shifted in the plus direction (the 
direction directed toward the illuminated surface) from the first focus F1 
along the optical axis Ax, as shown in FIG. 11, the trend becomes opposite 
to that shown in FIG. 10: the position of the light source image formed by 
the ellipsoidal mirror 2 (or the focused position) is moved in the minus 
direction (the direction toward the vertex O of the ellipsoidal mirror 2) 
from the second focus position F2 and positive spherical aberration 
appears. 
FIG. 11 shows a state of rays where the point light source S, which 
isotropically emits light, is placed at a position shifted from the 
position of the first focus F1 of the ellipsoidal mirror in the direction 
directed to the illuminated surface. Here, positions of planes a-c in FIG. 
11 correspond to the positions of the planes a-c, respectively, in FIG. 9 
and FIG. 10. 
If the entrance surface 4a of the fly's eye lens 4 is placed at the 
position of the plane c defocused from the image position a of the 
reflecting surface of the ellipsoidal mirror formed by the collimator lens 
3 in the plus direction (the direction directed toward the illuminated 
surface), as shown in FIG. 11, stronger light is irradiated to the central 
portion of the fly's eye lens 4 than in the peripheral portion thereof, 
thus presenting the light intensity distribution deflected to the central 
portion, as shown in FIG. 14. On the other hand, if the entrance surface 
4a of the fly's eye lens 4 is placed at the position of the plane b 
defocused from the image position a of the reflecting surface of the 
ellipsoidal mirror formed by the collimator lens 3 in the minus direction 
(the direction toward the vertex O of the ellipsoidal mirror 2), stronger 
light is irradiated to the peripheral portion of the fly's eye lens 4 than 
in the central portion thereof, thus presenting the light intensity 
distribution deflected to the peripheral portion, as shown in FIG. 13. The 
light intensity distribution at the image plane position a of the 
reflecting surface of the ellipsoidal mirror 2 formed by the collimator 
lens 3 in FIG. 11 is a distribution in a hollow state in which light 
intensities are distributed only in the periphery, as shown in FIG. 12. 
FIG. 9 to FIG. 11 as discussed above show the states of light intensity 
distributions at the position a of the image plane of the reflecting 
surface of the ellipsoidal mirror 2, and at the positions (b and c) of the 
planes defocused by the predetermined amount from the position a, where 
the point light source S for isotropically emitting light is located at or 
near the position of the first focus F1 of the ellipsoidal mirror. 
However, the rays shown in FIG. 9 to FIG. 11 are mixed in practice, 
because the two electrodes of the anode and cathode are arranged along the 
direction of the optical axis Ax on either side of the first focus F1 of 
the ellipsoidal mirror 2 and it can thus be assumed that there is a light 
source having a substantial size between the two electrodes. 
Thus, the optimal position of arrangement of the fly's eye lens 4 is 
preferably determined taking account of the fact that the rays as shown in 
FIG. 9 to FIG. 11 are mixed in the light emitted from the super-high 
pressure mercury lamp 1. 
First, as described previously, it is necessary to locate the anode 1b of 
the super-high pressure mercury lamp on the side of the vertex O of the 
collector mirror with respect to the cathode 1a in order to relatively 
increase the light intensities in the periphery of the fly's eye lens 4 
relative to those in the center. However, the light intensity distribution 
of a light-emitting point of the super-high pressure mercury lamp 1 shows 
the highest intensity at a position 21 near the tip of the cathode 1a and 
becomes decreased as approaching the anode 1b, as shown by isointensity 
curves between the two electrodes of the mercury lamp in FIG. 15. 
Therefore, the portion 21 with the highest light intensity is located at a 
position shifted from the barycenter 22 of the light intensity 
distribution of the light source to the side of cathode 1a. In order to 
maximize a quantity of light reaching the fly's eye lens 4, the barycenter 
22 of light intensities between the cathode 1a and the anode 1b in the 
super-high pressure mercury lamp needs to be located near the first focus 
F1 of the ellipsoidal mirror. Thus, the portion 21 with the highest light 
intensity near the tip of cathode 1a is located at a position somewhat 
shifted in the plus direction (the direction toward the illuminated 
surface) from the first focus position F1 of the ellipsoidal mirror 2. 
As a result, the trend for the rays to pass the optical paths shown in FIG. 
11, as described above, becomes enhanced, so that the light intensity 
distribution at the focus position a is one in the hollow state in which 
light intensities are distributed only in the periphery, as shown in FIG. 
12, and the light intensity distribution at the defocus position b is one 
in which light intensities in the periphery are somewhat stronger than 
those in the central portion, as shown in FIG. 13. Further, the light 
intensity distribution at the defocus position c is one in which light 
intensities in the central portion are highest and gradually decrease as 
approaching the periphery. 
Accordingly, it is understood that in order to illuminate the illuminated 
surface at a high illumination efficiency in any illumination method 
including the normal illumination and oblique illumination, it is optimal 
to place the entrance surface 4a of the fly's eye lens 4 at the defocus 
position b (which is the position defocused from the position a of the 
image of the reflecting surface of the collector mirror 2 formed by the 
collimator lens 3 to the discharge lamp side) to achieve the light 
intensity distribution in which light intensities in the periphery are 
somewhat stronger than those in the central portion, as shown in FIG. 13. 
According to the above principle, the light intensities in the periphery of 
the fly's eye lens are increased relative to those in the central portion. 
Accordingly, a quantity of shielded light can be considerably decreased as 
compared with the conventional illumination optical systems, of course 
when the normal illumination is employed using the aperture stop with a 
circular aperture, which is one of the secondary light source distribution 
shaping means for setting or shaping the light intensity distribution of 
plural secondary light sources formed by the fly's eye lens 4 to a 
predetermined light intensity distribution, when oblique illumination is 
effected by forming an annular zone of secondary light sources with an 
aperture stop as shown in FIG. 2 or the like, which is one of the 
secondary light source distribution shaping means, or when oblique 
illumination is effected by forming four offset regions of secondary light 
sources with the aperture stop as shown in FIG. 3 or the like. Then it 
becomes possible to prevent a drop of the throughput. 
FIG. 16 shows an example in which the illumination optical apparatus of the 
present invention is applied to an exposure apparatus for fabricating 
semiconductor devices. In FIG. 16, members having same functions are 
denoted by same reference numerals as those in FIG. 1. This embodiment is 
next described in detail referring to FIG. 16. 
The light source 1, for example a mercury arc lamp as a discharge lamp for 
emitting the light such as the g-line (436 nm) or the i-line (365 nm), is 
set approximately at the first focus position F1 of the ellipsoidal mirror 
2 as a rotationally symmetric reflecting mirror, and light beams from this 
light source 1 are reflected and collected by the collector mirror 2 
having a circular aperture portion 2c and an ellipsoidal reflecting 
surface 2R to form a light source image of the light source 1 at the 
position A1 of the second focus position F2 of the ellipsoidal mirror 2. 
FIG. 17 shows the layout and structure of the electrodes of the mercury arc 
lamp 1 with respect to the ellipsoidal mirror 2. As shown in FIG. 17, the 
anode 1b is located on the side of the vertex O of the ellipsoidal mirror 
2 with respect to the cathode 1a along the optical axis Ax of the 
ellipsoidal mirror 2 as a rotation axis of the rotationally symmetric 
reflecting mirror. In other words, the two electrodes of cathode 1a and 
anode 1b are arranged as opposed to each other so that the cathode 1a is 
located on the illuminated surface side relative to the anode 1b. On this 
occasion, the two electrodes of cathode 1a and anode 1b are arranged on 
either side of the first focus F1 of the ellipsoidal mirror 2. More 
specifically, the electrodes are arranged so that the position of the 
barycenter of the light intensity distribution generated by discharge 
between the cathode 1a and the anode 1b is substantially coincident with 
the first focus F1 of the ellipsoidal mirror 2. 
The light beams once forming the light source image at the position A1 of 
the second focus position F2 of the ellipsoidal mirror 2 by the reflecting 
and collecting functions thereof are converted into nearly parallel light 
beams by the collimator lens 3 as a collimator optical system arranged so 
that the front focus thereof is located at the light source image position 
F2. After that, the parallel light beams are incident into the fly's eye 
lens 4 functioning as an optical integrator. 
The fly's eye lens 4 is an aggregate of plural lens elements 41-43 each 
having a circular or polygonal (rectangular, hexagonal, etc.) cross 
section in bundle, and a plurality of light source images are formed at 
the exit surface of the fly's eye lens 4 or at the position A2 near the 
exit surface, thus substantially forming the secondary light sources here. 
Although the lens elements 41-43 in the present embodiment have a biconvex 
shape, one surface may be plane or concave, or further, they may be 
biconcave. 
Here, the fly's eye lens 4 in the present embodiment is positioned in a 
specific relation relative to the collimator lens 3. This is described in 
detail. First, the collimator lens 3 has a function to form an image of 
the reflecting surface 2R of the ellipsoidal mirror 2 at a predetermined 
position a on the illuminated surface side of the collimator lens 3, as 
shown in FIG. 18, in addition to a function to collimate light beams from 
the light source image formed by the ellipsoidal mirror 2. At this time, 
the collimator lens 3 forms a flat or plane image of reflecting surface 2R 
from the curved reflecting surface 2R (object) of the ellipsoidal mirror 
2. 
In the present embodiment, as shown in FIG. 18, the entrance surface 4a of 
the fly's eye lens 4 is placed at the position b defocused from the image 
position a of the reflecting surface 2R of the ellipsoidal mirror 2 formed 
by the collimator lens 3 to the light source side, taking account of the 
light intensity distribution characteristic on the exit side of the 
collimator lens 3 resulting from the light intensity distribution between 
the two electrodes 1a, 1b opposed to each other on either side of the 
first focus F1 of the ellipsoidal mirror 2 on the optical axis Ax of the 
ellipsoidal mirror 2 (or collimator lens 3). 
Accordingly, the present embodiment synergistically achieves the effect 
that stronger light is guided to the periphery rather than to the center 
of the fly's eye lens 4 by placing the anode 1b on the side of the vertex 
O of the ellipsoidal mirror 2 relative to the cathode 1a, and the effect 
that the collimator lens 3 forms the light intensity distribution in which 
light intensities are stronger in the periphery than in the center on the 
entrance surface 4a of the fly's eye lens 4 by placing the entrance 
surface of the fly's eye lens 4 at the position b defocused from the image 
position a of the reflecting surface 2R of the ellipsoidal mirror 2 formed 
by the collimator lens 3 to the light source side. 
As a result, as shown in FIG. 19, intensities in the periphery increase 
relative to those in the central portion on the entrance surface of the 
fly's eye lens 4 in the present embodiment, thereby forming an 
approximately flat light intensity distribution from the central portion 
to the periphery as compared with the light intensity distribution on the 
entrance surface of the fly's eye lens 4 in the conventional apparatus as 
shown in FIG. 4. The fly's eye lens 4 in the present embodiment has the 
three lens elements 41-43 as shown in FIG. 16, and light intensity 
distributions of light source images formed on the exit side by the lens 
elements 41, 42, 43 are d1, d2, d3, respectively, as shown by the solid 
lines in FIG. 20. 
As shown by the solid lines in FIG. 20, the light intensity distributions 
d1, d3 of the light source images formed by the lens elements 41 and 43 
located in the periphery of the fly's eye lens 4 are greater than the 
light intensity distribution d2 of the light source image formed by the 
lens element 42 located in the central portion. As a result, an envelope 
connecting the peaks of the light intensity distributions formed by the 
respective lens elements 41-43 becomes a light intensity distribution as 
shown by the dashed line in FIG. 20, which is similar to the light 
intensity distribution on the entrance surface 4a of the fly's eye lens 4 
as shown in FIG. 19. 
Now, returning to FIG. 16, there are a plurality of aperture stops 50a-50f 
provided as a secondary light source distribution shaping means for 
shaping the light intensity distribution of secondary light sources into a 
predetermined light intensity distribution, at the position A2 of the 
plural light source images formed by the fly's eye lens 4 (the secondary 
light sources). The plurality of aperture stops are formed in a turret 
plate 51 arranged to rotate about a rotation shaft 52, as shown in FIG. 
21. Rotating the turret plate 51 to change over the aperture stop 50a-50f, 
an aperture stop of a desired shape is set on the secondary light sources. 
The predetermined light intensity distribution is formed on the aperture 
stop thus set. 
Here is explained shapes of the aperture stops formed in the turret plate 
51. As shown in FIG. 21, the aperture stop 50a is one for first annular 
illumination having an annular (or doughnut) aperture, and the aperture 
stop 50b and aperture stop 50e are those for first and second normal 
illumination having respective circular apertures of mutually different 
opening diameters. The aperture stop 50c is one for first special oblique 
illumination having four sector apertures, and the aperture stop 50d is 
one for second special oblique illumination having four circular 
apertures. Further, the aperture stop 50f is one for second annular 
illumination having an annular zone ratio (a ratio between the outer 
diameter and the inner diameter of the annular aperture) different from 
that of the aperture stop 50a. 
Now, light beams from the secondary light sources in a predetermined shape 
having the light intensity distribution of the predetermined shape formed 
by the aperture stop 50a-50f of the predetermined shape are condensed by 
the condenser lens 6 as a condenser optical system to illuminate the 
reticle R as an illuminated object in a superimposed manner. With any 
aperture stop 50a-50f being set on the secondary light sources formed by 
the fly's eye lens 4, the light intensity distribution on the reticle R is 
uniform as shown in FIG. 22, and the reticle R is always illuminated 
uniformly. 
Here, the reticle R is held by a reticle stage RS, the wafer W as a 
projection target is mounted on a wafer stage 8 arranged to 
two-dimensionally move, and the position B2 of reticle R and the position 
B3 of wafer W are set to be conjugate with each other with respect to the 
projection optical system 7. When the reticle R is uniformly illuminated, 
the predetermined circuit pattern formed on the reticle R is minified and 
projected onto the wafer W by the projection optical system 7, thereby 
transferring an image of the circuit pattern on the wafer W. 
Here, the position A2 of the secondary light sources formed by the fly's 
eye lens is conjugate with the position A3 of the variable aperture stop 
7a having a circular variable aperture provided at the pupil position of 
the projection optical system 7, so that images of the plural secondary 
light sources formed by the fly's eye lens 4 are formed on the variable 
aperture stop 7a in the projection optical system 7, thus illuminating the 
reticle R and wafer W under the so-called Kohler illumination. Further, 
the entrance surface B1 of the fly's eye lens, the position B2 of the 
reticle R, and the position B3 of the wafer W are conjugate with each 
other. 
The above description concerned the configuration of the present 
embodiment, and switching operation of the illumination methods is next 
explained. 
In FIG. 16, an input section 13 is provided for inputting information 
concerning selection of illumination method on the reticle R, by which the 
present embodiment is arranged as capable of selecting either one of the 
illumination methods including the "first annular illumination" by setting 
of the aperture stop 50a, the "second annular illumination" by setting of 
the aperture stop 50f, the "first normal illumination" by setting of the 
aperture stop 50b, the "second normal illumination" by setting of the 
aperture stop 50e, the "first special oblique illumination" by setting of 
the aperture stop 50c, and the "second special oblique illumination" by 
setting of the aperture stop 50d. This selection information is 
transmitted to a control unit 10. Then the control unit 10 executes 
control of a drive unit 11 for rotating the turret plate 51, based on the 
selection information from the input section 13, and also executes control 
of a drive unit 12 for changing the size of the aperture of the variable 
aperture stop 7a in the projection optical system 7, based on information 
concerning the illumination condition from the input section 13. The 
operation of the control unit 10 is next explained in further detail. 
First, for setting the first normal illumination as an illumination state 
on the reticle R, input through a keyboard or the like as the input 
section 13 is the selection information concerning the "first normal 
illumination" or "second normal illumination" and information concerning 
an optimum illumination condition according to each fabrication process, 
for example a coherence factor defined by a ratio of a reticle-R-side 
numerical aperture NA.sub.1 of the illumination optical system and a 
reticle-R-side numerical aperture NA.sub.2 of the projection optical 
system 7, which is a so-called .sigma. value (.sigma.=NA.sub.1 /NA.sub.2). 
Here, a difference between the "first normal illumination" and the "second 
normal illumination" resides in that .sigma. values thereof are different 
from each other because of a difference in size between the circular 
apertures in the aperture stops. 
For example, suppose the selection information concerning the "first normal 
illumination" is input into the input section 13. Based on this selection 
information, the control unit 10 drives the first drive unit 11 to rotate 
the turret plate 51 so that the aperture stop 50b is located at the 
position A2 of the plural light source images formed by the fly's eye lens 
4. In addition, according to the illumination condition concerning a 
.sigma. value input through the input section 13, the control unit 10 
drives the second drive unit 12 to set the variable aperture stop in the 
projection optical system 7 to a specific diameter of circular aperture. 
By this, the first normal illumination is achieved under the predetermined 
.sigma. value. The same operation as the above operation is also carried 
out when the selection information concerning the "second normal 
illumination" is input through the input section 13. Specifically, the 
control unit 10 executes the operation to set the aperture stop 50e to the 
position A2 of the plural light source images and the operation to set the 
aperture diameter of the variable aperture stop in the projection optical 
system 7 in accordance with the illumination condition concerning a 
.sigma. value input, thereby achieving the second normal illumination 
under the predetermined .sigma. value. 
For switching the illumination from the normal illumination to desired 
oblique illumination on the reticle R, input through the input portion 13 
is the selection information concerning either one of the "first annular 
illumination," "second annular illumination," "first special oblique 
illumination," and "second special oblique illumination" and the 
information of the .sigma. value etc. as the optimum illumination 
condition according to each fabrication process. Here, the difference 
between the "first annular illumination" and the "second annular 
illumination" is a difference between annular zone ratios of the secondary 
light sources formed in an annular shape. Further, a difference between 
the "first special oblique illumination" and the "second special oblique 
illumination" resides in that light intensity distributions thereof of the 
secondary light sources are different from each other. Namely, the 
secondary light sources in the "first special oblique illumination" 
include a distribution of light intensities in four sector regions, while 
the secondary light sources in the "second special oblique illumination" 
include a distribution of light intensities in four circular regions. 
For example, when the "first annular illumination" is selected, the control 
unit 10 controls the drive unit 11 to rotate the turret plate 51 so as to 
locate the aperture stop 50a at the position A2 of plural light source 
images; when the "second annular illumination" is selected, the control 
unit 10 controls the drive unit 11 to rotate the turret plate 51 so as to 
locate the aperture stop 50f at the position A2 of plural light source 
images. When the "first special oblique illumination" is selected, the 
control unit 10 controls the drive unit 11 to rotate the turret plate 51 
so as to locate the aperture stop 50c at the position A2 of plural light 
source images; when the "second special oblique illumination" is selected, 
the control unit 10 controls the drive unit 11 to rotate the turret plate 
51 so as to locate the aperture stop 50d at the position A2 of plural 
light source images. 
Next, the control unit 10 drives the second drive unit 12 in accordance 
with the illumination condition concerning the .sigma. value input through 
the input section 13 to set the variable aperture stop 7a in the 
projection optical system 7 to a predetermined aperture diameter. 
As described, setting of the modified aperture stop 50a, 50c, 50d, 50f 
permits the secondary light sources to be formed according to the aperture 
configuration of the modified aperture stop, thereby permitting oblique 
illumination of reticle R and wafer W, and setting of the aperture 
diameter of the variable aperture stop 7a permits the wafer W to be 
illuminated at an optimum .sigma. value. Thus, fine patterns can be 
transferred onto the wafer W under a deep depth of focus as compared with 
the first or second normal illumination by the aperture stop 50b or 
aperture stop 50e. 
The present embodiment is arranged to input various conditions etc. for 
selecting the illumination method through the input section 13, but a 
modification may include a detecting unit 14 for reading information on 
the reticle R, as shown by the dashed line in FIG. 16. In this case, the 
information concerning the illumination method, the illumination 
condition, etc. is recorded for example by a bar code or the like at a 
position outside the region of the circuit pattern on the reticle R. The 
detecting unit 14 reads the information concerning the illumination method 
to transmit it to the control unit 10. The control unit 10 controls the 
drive units 11 and 12, as described above, based on the information 
concerning the illumination method and the illumination condition, etc. In 
this case, the control unit 10 may be arranged to control the drive units 
11 and 12 after execution of predetermined arithmetic, judgment, etc., 
based on the information concerning the illumination method and 
illumination condition, etc. 
As described above, the present embodiment forms the light intensity 
distribution in which intensities in the periphery are relatively 
increased to those in the central portion, as shown in FIG. 19, on the 
entrance surface of the fly's eye lens 4. Thus, the present embodiment can 
achieve any illumination method from the normal illumination, the oblique 
illumination (annular illumination and special oblique illumination), etc. 
at considerably high illumination efficiencies, as compared with the 
conventional apparatus, and can always realize projection exposure at high 
throughput. 
The present embodiment is so arranged that in order to realize the oblique 
illumination, the turret plate 51 includes the aperture stop 50a for the 
"first annular illumination," the aperture stop 50f for the "second 
annular illumination," the aperture stop 50c for the "first special 
oblique illumination," and the aperture stop 50d for the "second special 
oblique illumination" and that in order to form light sources in an 
annular shape or in an offset state from the optical axis Ax, portions 
other than the annular aperture portion or the four offset aperture 
portions, respectively, are constructed of light-shielding portions formed 
to have the transmittance of zero. It is needless to mention that the 
light-shielding portions may be replaced by an optically transparent 
light-reducing member having the transmittance of about 30%. In this case, 
a preferred example may be constructed in such a manner that the member 
constituting the turret plate 51 is comprised of a glass substrate, 
chromium is vapor-deposited to form a thin film over the light-shielding 
portions, or that the light-reducing member is formed by lowering the 
vapor deposition density of the thin film of chromium. 
The embodiment of FIG. 16 showed an example in which the collimator lens 3 
directly forms the image of the reflecting surface 2R of the ellipsoidal 
mirror 2, but without having to be limited to it, the configuration as 
shown in FIG. 23 may be employed for example. This modification is 
different from the embodiment of FIG. 16 in that a relay optical system 
31, 32 is placed between the collimator lens 3 and the fly's eye lens 4. 
The collimator lens 3 has a function to form an image of the reflecting 
surface 2R of the ellipsoidal mirror 2 at the position B0 and a function 
to collimate the light from the light source image formed by the 
ellipsoidal mirror 2. The relay lenses 31, 32 reimage the image of the 
reflecting surface 2R of the ellipsoidal mirror 2 formed at the position 
B0 by the collimator lens 3, at the position a. The collimator lens 3 and 
the relay lenses 31, 32 compose the collimator optical system. 
In this case, the entrance surface 4a of the fly's eye lens 4 is located at 
the position b defocused from the position a of the image of the 
reflecting surface 2R of the ellipsoidal mirror 2 formed by the collimator 
optical system 3, 31, 32 to the light source side. 
According to this arrangement, the distance can be taken long enough 
between the lens 32 closest to the illuminated surface, constituting the 
collimator optical system, and the image position a of the reflecting 
surface 2R of the ellipsoidal mirror 2, whereby the entrance surface 4a of 
the fly's eye lens 4 can be set sufficiently distant from the imaging 
position a. If with the embodiment of FIG. 16 there is a possibility of 
mechanical interference between the collimator lens 3 and the fly's eye 
lens 4 because of a short distance between the collimator lens 3 and the 
image position a of the reflecting surface 2R of the ellipsoidal mirror 2, 
it is preferred to employ the configuration as shown in FIG. 23. 
From the invention thus described, it will be obvious that the invention 
may be varied in many ways. Such variations are not to be regarded as a 
departure from the spirit and scope of the invention, and all such 
modifications as would be obvious to one skilled in the art are intended 
for inclusion within the scope of the following claims. 
The basic Japanese Application No. 286217/1994 (6-286217) filed on Nov. 21, 
1994, is hereby incorporated by reference.