Illumination optical system, an exposure apparatus having the illumination system, and a method for manufacturing a semiconductor device

A change in the optical characteristics which is caused by an unevenness of the intensity of illumination, following a change of the form or the size of a multiple light source, is corrected by an adjustment mechanism with a simple structure. This mechanism further comprises a first correction device (21, 14B) which corrects unevenness of the intensity of illumination generated on a plane to be irradiated due to a change of the form and the size of the multiple light source made by a change device(13), and a second correction device (22, 14A1) which corrects at least one of a change of the back focus of a condenser optical system and a change in the telecentricity of the illumination light on the irradiated plane caused due to a correcting operation of the first correction device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an illumination optical system and an 
exposure apparatus having the optical system, and particularly, to 
correction of a distribution of an intensity of illumination in an 
illumination optical system in a semiconductor projection exposure 
apparatus. Also, the present invention relates to a method for 
manufacturing a semiconductor device using the illumination optical 
system. 
2. Related Background Art 
In a semiconductor exposure apparatus, a light ray emitted from a light 
source is incident on an optical integrator, and a multiple light source 
which is constituted by a plurality of light source images is formed on 
the rear focal plane of the optical integrator. The light ray from the 
multiple light source is passed through an aperture stop which is formed 
in the vicinity of the rear focal plane of the optical integrator and then 
is caused to enter a condenser optical system. The aperture stop causes 
the form or the size of the multiple light source to change into a desired 
one in accordance with a desired illumination condition. 
The light ray condensed by the condenser optical system illuminates a 
reticle (or a mask) in an overlapping manner through a reticle blind which 
is disposed in the condenser optical system. A pattern is formed on the 
reticle, and an illumination area of the pattern is determined by the 
reticle blind. The light passed through the pattern of the reticle is 
imaged on a wafer through a projection optical system. Thus, the reticle 
pattern is projection-exposed (transferred) onto the wafer. 
The pattern formed on the reticle is highly integrated, so that it is 
inevitably required to obtain a uniform distribution of the intensity of 
illumination on the wafer in order to correctly transfer the pattern onto 
the wafer. To this end, it is required to design and arrange the optical 
integrator and the condenser optical system in such a manner that the 
distribution of the intensity of illumination on the wafer should be 
uniform. However, even if the optical integrator and the condenser optical 
system are designed and arranged such that the distribution of the 
intensity of illumination becomes uniform, an unevenness in the intensity 
of illumination may be generated due to an error, or the like, in 
manufacturing the apparatus so that a uniform distribution of the 
intensity of illumination can not be obtained. Therefore, a conventional 
exposure apparatus is arranged such that a correction is properly 
performed by moving a movable lens group which constitutes a part of the 
condenser optical system in the direction of the optical axis so as to 
reduce a degree of unevenness in the distribution of illumination, thereby 
obtaining a uniform distribution of the intensity of illumination. 
Recently, attention is given to the fact that the sizes of the plurality of 
light source images formed by the optical integrator are changed by 
changing the aperture form of an aperture stop or the like arranged on the 
exit side of the optical integrator so as to change a coherency .sigma. 
(.sigma.=the aperture stop size/ the pupil size of the projection optical 
system) of the illumination, or that the forms of the plurality of light 
source images formed by the optical integrator are changed into those of 
annular band or the like so as to improve the original depth of focus or 
degree of resolution of the projection optical system. 
However, it has been clearly seen from various kinds of repeated 
experiments, etc., that, together with such change of the aperture form of 
the aperture stop or the like arranged on the exit side of the optical 
integrator, an unevenness of the intensity of illumination occurs on a 
reticle which serves as a plane to be irradiated, or a wafer which serves 
as a photosensitive substrate. 
Accordingly, the present invention has been conceived taking the 
above-mentioned problem into consideration, and an object of the invention 
is to provide an illumination optical system which can correct a 
fluctuation in an intensity distribution of illumination on an irradiated 
plane which follows a change of the form or the size of a secondary light 
source, and an exposure apparatus having such illumination optical system. 
Also, as a result of further repeated experiments, or the like, it has been 
found that when at least a certain optical system (a movable lens, or the 
like) which constitutes the condenser optical system is moved in the 
direction of the optical axis in order to correct an unevenness in the 
intensity of illumination which is generated on an irradiated plane due to 
a change of the aperture form of an aperture stop or the like arranged on 
the exit side of the optical integrator, the optical characteristics such 
as the back focus or the telecentricity of the condenser optical system 
are changed to deteriorate the illumination condition, owing to the 
movement of the optical system. 
Accordingly, another object of the present invention is, taking the 
above-mentioned problem into consideration, to provide an illumination 
optical system which can correct a change in optical characteristics 
generated due to the correction of the unevenness in the intensity of 
illumination following the change of the form or the size of the multiple 
light source by use of an adjusting mechanism of a simple structure, and 
an exposure apparatus provided with the illumination optical system. 
SUMMARY OF THE INVENTION 
In order to solve the above-mentioned problem, according to an aspect of 
the present invention, there is provided an illumination optical system 
which comprises a multiple light source forming device which forms 
multiplicity of secondary light sources on the basis of light rays from a 
light source, a change device which changes the form or the size of the 
multiple light source formed by the multiple light source forming device, 
and a condenser optical system which illuminates a plane to be irradiated 
in an overlapping manner by condensing light rays from the multiple light 
source having a form or size predetermined by the change device, wherein 
at least certain optical elements of the condenser optical system are 
moved in accordance with the changed form or size of the multiple light 
source by the change device so that the distribution of the intensity of 
illumination on the irradiated plane becomes substantially uniform. 
In this case, it is preferable that the multiple light source forming 
device has an optical integrator which is constituted by multiplicity of 
lens elements and the change device has a variable aperture stop having a 
variable aperture which sets the secondary light source formed by the 
optical integrator to have a predetermined form or a predetermined size. 
Also, according to another aspect of the present invention, there is 
provided an exposure apparatus for forming a pattern image of the mask on 
a photosensitive substrate which comprises: 
an illumination optical system which illuminates a mask having a 
predetermined pattern formed thereon, 
the illumination optical system comprises having a multiple light source 
forming device which forms a multiplicity of secondary light sources on 
the basis of light rays from a light source, a change device which changes 
the form or the size of the multiple light source formed by the multiple 
light source forming device, and a condenser optical system which 
illuminates a plane to be irradiated in an overlapping manner by 
condensing the light rays from the multiple light source having a form or 
a size predetermined by the change device, 
wherein at least certain optical elements of the condenser optical system 
are moved in accordance with the changed form or size of the multiple 
light source by the change device in such a manner the distribution of the 
intensity of illumination on the irradiated plane becomes substantially 
uniform. 
In this case, it is preferable that the multiple light source forming 
device has an optical integrator which is constituted by a multiplicity of 
lens elements, and the change device has a variable aperture stop which 
has a variable aperture for setting the secondary light source formed by 
the optical integrator to have a predetermined form or a predetermined 
size. 
Further, in order to solve the above-mentioned problem, according to yet 
another aspect the present invention, there is provided an illumination 
optical system provided with a light source device which supplies light 
rays, an optical integrator which forms a multiple light source consisting 
of a plurality of light source images on the basis of the light rays from 
the light source device, a change device which changes the form or the 
size of the multiple light source formed by the optical integrator, and a 
condenser optical system which illuminates a plane to be irradiated in an 
overlapping manner by condensing the light rays from the multiple light 
source having the form or the size changed by the change device, the 
illumination optical system further comprising: 
a first correction device for correcting an unevenness in the intensity of 
illumination which is generated on the irradiated plane due to the change 
of the form or the size of the multiple light source made by the change 
device; and 
a second correction device for correcting at least one of a change in the 
back focus of the condenser optical system and a change in the 
telecentricity of the illumination light on the irradiated plan, due to 
the correcting operation by the first correction device. 
According to a preferable embodiment of the present invention, the first 
correction device corrects the unevenness in the intensity of illumination 
by moving the first optical system for constituting the first portion of 
the condenser optical system along the optical axis of the condenser 
optical system, the second correction device corrects a change in the back 
focus of the condenser optical system by changing the focal length of the 
second optical system for constituting the second portion of the condenser 
optical system which is different from the first optical system. In this 
case, the second correction device preferably has a plurality of back 
focus correction optical systems each having a different focal length from 
that of the second optical system and an exchange device for setting one 
of the plurality of back focus correction optical systems in an 
illumination light path, instead of the second optical system. 
Also, according to the present invention, there is provided an exposure 
apparatus which is provided with a light source device for supplying light 
rays, an optical integrator for forming a multiple light source consisting 
of a plurality of light source images on the basis of the light rays from 
the light source device, a change device for changing the form or the size 
of the multiple light source which is formed by the optical integrator, a 
condenser optical system for illuminating a mask in an overlapping manner 
by condensing the light rays from the multiple light source having the 
form or the size changed by the change device, and a projection optical 
system for performing a projection-exposure of a pattern on the mask onto 
a photosensitive substrate, the exposure apparatus further comprising: 
a first correction device for correcting unevenness in the intensity of 
illumination which is generated on the mask or the photosensitive 
substrate due to the change of the form or the size of the multiple light 
source made by the change device; and 
a second correction device for correcting at least one of a change in the 
back focus of the condenser optical system and a change in the 
telecentricity of the illumination light on the mask or the photosensitive 
substrate which are generated due to the correcting operation by the first 
correction device. 
According to such preferable embodiment of the present invention, a second 
optical integrator for forming a multiple light source which is 
constituted by a plurality of light source images is provided between the 
light source device and the optical integrator on the basis of the light 
rays from the light source device; and 
the light rays from the multiple light source formed by the second optical 
integrator are guided to the optical integrator which is arranged at a 
position closer to the irradiated plane than the optical integrator. 
Also, according to the present invention, there is provided a method for 
manufacturing a semiconductor device, which comprises a step of exposing a 
pattern of a mask arranged on the irradiated plane onto the photosensitive 
substrate by use of an illumination optical system of the present 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First, description will be made on a fluctuation in a distribution of the 
intensity of illumination on a plane to be irradiated, which is caused by 
a change of an aperture form, that is, a change of the form or the size of 
a secondary light source. 
On the surface of each lens which constitutes an exposure apparatus, a 
reflection-preventing film is deposited by vaporization in order to 
improve the transmittance of the lens. However, the film thickness of the 
reflection-preventing film over the entire lens surface is not necessarily 
uniform owing to the curved surface from of each lens. For this reason, 
the transmittance of the lens surface is characterized by being different 
in accordance with the surface position thereof. 
Generally, when the reflection-providing film is deposited by evaporation 
onto the lens surface, the reflection-preventing film is formed to be a 
little thinner on the peripheral part of the lens surface than the central 
part thereof. As stated, since the reflection-preventing film on the lens 
surface is thinner as it is separated farther from the central axis 
(optical axis), the transmittance of the light ray also tends to be lower 
as it is separated farther from the optical axis. 
Also, the reflection-preventing film is arranged to prevent most 
satisfactorily the reflection of the light ray which is incident on the 
surface of the reflection-preventing film. Therefore, the transmittance of 
the light ray declines more as the incident angle of the light ray on the 
surface of the reflection-preventing film becomes larger. In general, the 
incident angle of the light ray onto the lens surface becomes larger as it 
is separated farther from the optical axis, so that the transmittance of 
the light ray declines more as it is separated farther from the optical 
axis. 
As stated before, the light ray which is passed through the lens surface 
separated from the optical axis tends to damage the uniformity of the 
distribution of the intensity of illumination on a wafer surface under the 
influence of the change of the film thickness of the reflection-preventing 
film and the change of the incident angle onto the reflection-preventing 
film. 
More specifically, an area of each lens surface through which the light ray 
is passed via an aperture stop is changed, by changing the aperture form 
of the aperture stop with respect to the secondary light source. As a 
result, upon reception of the influence of the change of the film 
thickness of the reflection-preventing film on each lens surface and the 
change of the incident angle on the reflection-preventing film, a 
fluctuation is generated in the distribution of the intensity of 
illumination on the irradiated plane. 
Next, with reference to FIGS. 6A to 8B, the fluctuation in the distribution 
if the intensity of illumination caused by the change of the aperture form 
of the aperture stop will be specifically described. 
Note that FIGS. 6A to 6E are views which respectively show various aperture 
forms of the aperture stop. Also, FIGS. 7A to 7C and FIGS. 8A and 8B are 
views for showing distributions of the intensity of illumination which 
respectively correspond to the aperture forms shown in FIGS. 6A to 6E. 
In a projection exposure apparatus, the aperture form of the aperture stop 
is changed in order to improve the illumination efficiency of the 
illumination optical system, with the intention of improving a degree of 
resolution and the depth of focus of the projection optical system. 
First, FIGS. 6A to 6C show aperture stops which have circular aperture 
portions 16a to 16c with different aperture sizes. 
Here, it is assumed that the distribution of the intensity of illumination 
with respect to the aperture form of the aperture portion 16b is adjusted 
to be substantially uniform from the central part to the peripheral part 
of the irradiated plane, as shown in FIG. 7B. In this case, if the 
aperture size is made large, like the aperture portion 16a, the 
distribution of the intensity of illumination shown in FIG. 7A can be 
obtained. That is, with the increase of the aperture size, the 
distribution of the intensity of illumination fluctuates in such a manner 
that the light intensity gradually decreases from the central part to the 
peripheral part of the irradiated plane. 
On the other hand, when the aperture size is decreased to be like the 
aperture portion 16c from the state in which the distribution of the 
intensity of illumination is adjusted to be substantially uniform with 
respect to the aperture portion 16b, the distribution of the intensity of 
illumination shown in FIG. 7C can be obtained. That is, with the decrease 
of the aperture size, the distribution of the intensity of illumination 
fluctuates in such a manner that the light intensity gradually increases 
from the central part to the peripheral part of the irradiated plane. 
Next, FIGS. 6D and 6E show an aperture stop having an aperture portion 16d 
in the form of an annular band, and an aperture stop having a fan-shaped 
aperture portion 16e. 
Here, when the aperture form is changed from a state in which the 
distribution of the intensity of illumination is adjusted to be 
substantially uniform with respect to the aperture portion 16b to the 
aperture form of the aperture portion 16d in the form of an annular band, 
the distribution of the intensity of illumination shown in FIG. 8A can be 
obtained. That is, with the change of the aperture form, the distribution 
of the intensity of illumination fluctuates in such a manner that the 
light intensity gradually decreases from the central part to the 
peripheral part of the irradiated plane. 
When the aperture form is changed from a state in which the distribution of 
the intensity of illumination is adjusted to be substantially uniform with 
respect to the aperture portion 16b to the aperture form of the fan-shaped 
aperture portion 16e, the distribution of the intensity of illumination 
shown in FIG. 8B can be obtained. That is, with the change of the aperture 
form, the distribution of the intensity of illumination fluctuates in such 
a manner that the light intensity gradually decreases from the central 
part to the peripheral part of the irradiated plane. 
Thus, in the same illumination optical system, if only the aperture form of 
the aperture stop is changed, the illumination distribution on the 
irradiated plane may fluctuate so that the uniformity of the distribution 
of the intensity of illumination may be damaged. 
Then, according to the present invention, at least one lens out of a lens 
group for constituting, for example, a condenser optical system, is 
properly moved along the optical axis in accordance with the change of the 
aperture form, i.e., the form or the size of the secondary light source, 
in such a manner that the distribution of the intensity of illumination on 
the irradiated plane is substantially uniform. Thus, the fluctuation in 
the distribution of the intensity of illumination caused by the change of 
the aperture form can be immediately corrected so as to always maintain 
the uniformity thereof satisfactorily. 
A s stated above, in order to correctly transfer a highly integrated mask 
pattern onto a wafer, it is inevitably necessary that the distribution of 
the intensity of illumination on the wafer should be uniform. Therefore, 
it is required to design and arrange a multiple light source forming 
device such as an optical integrator and a condenser optical system in 
such a manner that the distribution of the intensity of illumination 
should be uniform. However, when the uniformity of the distribution of the 
intensity of illumination can not be obtained due to a manufacturing error 
or the like, adjustment is required for making the distribution of the 
intensity of illumination to be uniform. The condenser optical system is 
frequently used in such an adjustment. 
The condenser optical system is generally constituted by a plurality of 
lenses, and when at least one of these lenses is moved along the direction 
of the optical axis, the distribution of the intensity of illumination on 
the irradiated plane changes in accordance with a direction and an amount 
of such movement. In other words, the uniformity of the distribution of 
the intensity of illumination can be easily improved by properly 
controlling the direction of movement and an amount of movement of at 
least one lens out of the plurality of lenses which constitute the 
condenser optical system. 
An embodiment of the present invention will be described with reference to 
the attached drawings. 
FIG. 1 is a view for schematically showing the structure of an exposure 
apparatus which is provided with an illumination optical system according 
to the first embodiment of the present invention. 
The apparatus shown in FIG. 1 is provided with a light source 1 which 
supplies collimated light rays. The collimated light rays from the light 
source 1 are incident on an optical integrator 2 such as a fly-eye lens. 
The light rays incident on the optical integrator 2 are two-dimensionally 
divided by a plurality of lens elements which constitute the optical 
integrator 2, and thereafter form a multiplicity of light source images, 
i.e., secondary light sources, at the rear focal positions of the optical 
integrator 2. Thus, the optical integrator 2 constitutes a multiple light 
source forming device for forming a multiplicity of secondary light 
sources based on the light rays from the light source 1. 
The light rays from the multiplicity of light source images are, after 
controlled by an aperture stop 3 having a variable aperture, incident on a 
condenser optical system 4 which is constituted by a plurality of lenses. 
The light through the condenser optical system 4 illuminates a mask 5 with 
a predetermined pattern formed thereon in an overlapping manner. 
The light rays passed through the mask 5 reach through a projection optical 
system 6 to a wafer 7 which is positioned at an image plane thereof. Thus, 
the pattern of the mask 5 is transferred onto the wafer 7 which serves as 
a photosensitive substrate. 
As stated, the light source 1, the optical integrator 2, the aperture stop 
3, and the condenser optical system 4 constitute the illumination optical 
system for illuminating the mask. 
FIGS. 2 to 5 are views which explain an operation for correcting a 
fluctuation in a distribution of the intensity of illumination caused by a 
change of the aperture form of the aperture stop 3. 
In FIGS. 2 to 5, the aperture form of the aperture stop 3 can be changed by 
a changing system 8 in order to obtain a desired illumination condition, 
and the light rays from the secondary light source formed through the 
optical integrator 2 are limited into a desired form. Also, the aperture 
stop 3 is made to be optically conjugate the pupil plane of the projection 
optical system 6 by use of the condenser optical system 4. Therefore, it 
is possible to arbitrarily change a range for the illumination light rays 
on the pupil plane of the projection optical system 6, by changing the 
aperture form of the aperture stop 9 (the form or the size of the variable 
aperture). 
Also in FIGS. 2 to 5, in accordance with a change of the aperture form of 
the aperture stop 3, a lens 4a out of the plurality of lenses for 
constituting the condenser optical system 4 is moved along the optical 
axis by a movement system 9 to a predetermined position. Upon this 
movement of the lens 4a, it is possible to change the distribution of the 
intensity of illumination on the wafer and to minimize an unevenness in 
the intensity of illumination. 
However, upon movement of the lens 4a, a change of the focal length of the 
condenser optical system or a fluctuation in the telecentricity is 
generated. For this reason, in order to obtain a desired uniformity with 
respect to the distribution of the intensity of illumination while 
maintaining substantially the same optical condition as that prior to the 
change of the aperture form of the aperture stop 3, it is required to 
constitute the lens system in such a manner that the lens system is not 
susceptible to a change which is caused by the movement of the lens 4a, 
and the change caused by the movement of the lens 4a can be easily 
corrected. 
In FIG. 2, the aperture stop 3 is arranged to have a circular aperture 
portion 16b, as shown in FIG. 6B. Then, the distribution of the intensity 
of illumination on the wafer 7 is adjusted substantially uniformly over a 
projection area of the projection optical system 6 from the central part 
to the peripheral part thereof, as shown in FIG. 7B. 
In the following, with the condition in FIG. 2 as the reference condition, 
a correction operation on a distribution of the intensity of illumination 
when the aperture form of the aperture stop 3 is changed into the form 
shown in FIG. 6C, to FIG. 6A and to FIG. 6D, will be described referring 
to FIGS. 3 to 5. 
In FIG. 3, the aperture form is changed into the form shown in FIG. 6C, in 
such a manner that the aperture size of the aperture stop 3 is decreased. 
Therefore, as shown in FIG. 7C, the distribution of the intensity of 
illumination on the wafer 7 fluctuates due to a change of the aperture 
form, so that such distribution in which the intensity of illumination 
gradually increases from the central part to the peripheral part can be 
obtained. 
Note that, the lens 4a of the condenser optical system 4 has a function of 
decreasing the intensity of illumination from the central part toward the 
peripheral part with its movement to the optical integrator side, and a 
function of increasing the intensity of illumination from the central part 
toward the peripheral part with its movement to the mask side. 
Accordingly, in FIG. 3, a fluctuation in the distribution of the intensity 
of illumination which is caused by a change of the aperture form is 
corrected, by moving the lens 4a of the condenser optical system 4 using 
the movement system 9 along the optical axis to the side of the optical 
integrator 2 by a predetermined amount. As a result, on the wafer 7, a 
substantially uniform distribution of the intensity of illumination can be 
maintained without depending on a change of the aperture form. 
In FIG. 4, the aperture form is changed into the form shown in FIG. 6A in 
such a manner that the aperture size of the aperture stop 3 is increased. 
Therefore, as shown in FIG. 7A, the distribution of the intensity of 
illumination on the wafer 7 fluctuates due to the change of the aperture 
form, so that such distribution in which the intensity of illumination 
gradually decreases from the central part to the peripheral part can be 
obtained. 
Accordingly, in FIG. 4, a fluctuation in the distribution of the intensity 
of illumination caused by a change of the aperture form is corrected, by 
moving the lens 4a of the condenser optical system 4 through the movement 
system 9 along the optical axis to the mask side by a predetermined 
amount. As a result, on the wafer 7, a substantially uniform distribution 
of the intensity of illumination can be maintained without depending on 
the change of the aperture form. 
In FIG. 5, the aperture form of the aperture stop 3 is changed into a form 
of an annular band, as shown in FIG. 6D. Therefore, as shown in FIG. 8A, 
the distribution of the intensity of illumination on the wafer 7 
fluctuates owing to the change of the aperture form, so that such 
distribution in which the intensity of illumination gradually decreases 
from the central part to the peripheral part can be obtained. 
Accordingly, in FIG. 5, in the same manner as in FIG. 4, a fluctuation in 
the distribution of the intensity of illumination caused by the change of 
the aperture form is corrected, by moving the lens 4a of the condenser 
optical system 4 through the movement system 9 along the optical axis to 
the mask side by a predetermined amount. As a result, on the wafer 7, a 
substantially uniform distribution of the intensity of illumination can be 
maintained without depending on the change of the aperture form. 
In the above-mentioned embodiment, the form or the size of the secondary 
light source is changed by changing the form or the size of the variable 
aperture of the aperture stop. However, as disclosed in Japanese Patent 
Laid-Open Application No. 4-225514, it is also possible to change the form 
or the size of the secondary light source, by changing the sizes of four 
eccentric light sources or properly changing the form of a fly-eye lens or 
a combination of fly-eye lenses. The present invention is effective for 
the correction of a fluctuation in a distribution of the intensity of 
illumination caused by the change of the form or the size of the secondary 
light source, without depending on a method of changing thereof. 
Also, in the above-mentioned embodiment, the present invention was 
explained by using the projection exposure apparatus with an illumination 
optical system as example. However, it is apparent that the present 
invention can be applied to an exposure apparatus of a proximity scheme, 
or an illumination optical system of an ordinary type for uniformly 
illuminating an irradiated plane other than the mask. 
Further, in the above-mentioned embodiment, one lens which constitutes the 
condenser optical system was moved along the optical axis. However, it is 
possible to move a plurality of lenses for constituting the condenser 
optical system. 
Also, when an asymmetric unevenness in the intensity of illumination is 
generated on the irradiated plane, it is also possible to correct the 
asymmetric unevenness component in the intensity of illumination by 
shifting the lens or the lens group in the direction of the optical axis 
or tilting the same with respect to the optical axis. 
Further, according to the present invention, a first optical system which 
constitutes, for example, a first portion of the condenser optical system 
is moved along the optical axis, so as to correct an unevenness in the 
intensity of illumination which is caused by a change of the form or the 
size of the multiple light source. Then, at least a change in the back 
focus of the condenser optical system which is caused by this correction 
of unevenness in the intensity of illumination or a change in the 
telecentricity of the illumination light on the irradiated plane is 
corrected. More specifically, the change in the back focus of the 
condenser optical system is corrected by changing the focal length of a 
second optical system for constituting a second portion of the condenser 
optical system which is different from the first optical system, for 
example, by setting a back focus correction optical system which has a 
different focal length into the illumination light path, instead of, the 
second optical system. Also, the change in the telecentricity of the 
illumination light on the irradiated plane is corrected by changing the 
optical light path length of the optical member for constituting a third 
portion of the condenser optical system which is different from the first 
optical system or the second optical system, for example, by setting a 
light path length correction optical member having a different thickness 
into the illumination optical light path instead of the optical member. 
As stated above, according to the present invention, the change in the back 
focus of the condenser optical system or in the illumination light on the 
irradiated plane can be properly corrected, only by exchanging optical 
systems or optical members which constitute a part of the condenser 
optical system, without moving a lens group which is different from the 
movable lens group in the direction of the optical axis as in the 
conventional example. As a result, even when the form or the size of the 
multiple light source is changed in accordance with a desired illumination 
condition, the change in the back focus of the condenser optical system or 
in the telecentricity of the illumination light on the irradiated plane 
can be properly changed so that a uniform distribution of the intensity of 
illumination can be always obtained on the irradiated plane. Therefore, 
when the illumination optical system of the present invention is 
incorporated in an exposure apparatus, a projection-exposure with a high 
accuracy can be performed by maintaining a uniform distribution of the 
intensity of illumination on the photosensitive substrate and an excellent 
telecentricity of the exposure light. Also, according to a method for 
manufacturing a semiconductor device which comprises a step of exposing 
the pattern of a mask arranged on an irradiated plane onto a 
photosensitive substrate by use of the illumination optical system of the 
present invention, projection exposure can be conducted with a high 
accuracy by maintaining a uniform distribution of the intensity of 
illumination on the photosensitive substrate and an excellent 
telecentricity of the exposure light, so that an excellent semiconductor 
device can be manufactured. 
Note that, according to the present invention, only a change in the 
telecentricity on the irradiated plane can be corrected by changing the 
optical light path length of the optical member which constitutes a part 
of the condenser optical system and has substantially no refracting power. 
More specifically, the optical member has, for example, a plurality of 
plane parallel plates with thicknesses different from each other, and sets 
each of the plurality of plane parallel plates into the illumination light 
path or retracts it from the illumination light path, so as to change the 
optical light path length of the optical member. Or, the optical member 
has, for example, a pair of declination prisms, and one of these 
declination prisms is moved along a direction perpendicular to the optical 
axis, so as to change the optical light path length of the optical member. 
In this case, the optical member having no refracting power is disposed 
near to the optical member in the condenser optical system, whereby only a 
change in the telecentricity of the illumination light on the irradiated 
plane can be properly corrected without giving little influence onto the 
back focus or aberrations of the condenser optical system. 
Another embodiment of the present invention will be described with 
reference to the attached drawings. 
FIG. 9 is a view for schematically showing the structure of an exposure 
apparatus having the illumination optical system according to the second 
to fifth embodiments of the present invention. And FIG. 10 is a 
perspective view for schematically showing the structure of a main portion 
of the illumination optical system according to the second embodiment of 
the present invention. 
Referring to FIG. 9, a light ray emitted from a light source 11 enters an 
optical integrator 12, so as to form a multiple light source (secondary 
light source) consisting of a plurality of light source images on the rear 
focal plane of the integrator 12. The light ray from the multiple light 
source is passed through an aperture stop 13 which is formed near to rear 
focal plane of the optical integrator 12, and then enters a condenser 
optical system which is constituted by a lens group 14 and a lens group 
15. The aperture stop 13 has a function of changing the form or the size 
of the multiple light source into a desired form or size in accordance 
with a desired illumination condition, as described later. 
The light ray condensed by a condenser optical system (14, 15) is passed 
through a reticle blind RB which is arranged in the condenser optical 
system, and illuminates the reticle R serving as a mask in an overlapping 
manner. On the reticle R, an electronic circuit pattern, for example, is 
formed as a pattern to be transferred. The reticle blind RB has a function 
of specifying an illumination area on a pattern surface of the reticle R 
serving as a plane to be irradiated, i.e., a pattern area to be exposed. 
The light passed through the pattern of the reticle R is imaged on a wafer 
W serving as a photosensitive substrate through a projection optical 
system 16. Thus, patterns of the reticle R are projection-exposed 
(transferred) collectively on each exposure area on the wafer W. 
Referring to FIG. 10, in the illumination optical system according to the 
third embodiment, the aperture stop 13 has a plurality of aperture 
portions which have different forms or sizes from each other and are 
circumferentially formed on a turret (rotating plate). Then, a rotation of 
the turret of the aperture stop 13 is arranged to be controlled by a 
change control system 20. Accordingly, when the aperture stop 13 is 
rotated by the change control system 20 so as to set an aperture portion 
having a desired form or size in the illumination light path, the form or 
the size of the multiple light source which is formed through the optical 
integrator 12 can be changed into a desired one. 
In this manner, the aperture stop 13 and the change control system 20 
constitute a change device which is used to change the form or the size of 
the multiple light source formed by the optical integrator 12. 
As described above with reference to FIGS. 6A to 8B, in the same 
illumination optical system, a distribution of the intensity of 
illumination on the irradiated plane fluctuates only if the form or the 
size of the aperture portion of the aperture stop is changed, whereby the 
uniformity of the distribution of the intensity of illumination may be 
damaged. 
Then, in the second embodiment, there is provided a device for correcting 
an unevenness in the intensity of illumination which is caused by a change 
of the form or the size of the aperture portion of the aperture stop 13. 
That is, in the illumination optical system of the second embodiment shown 
in FIG. 10, a lens group 14 of the condenser optical system is arranged to 
have a lens 14A1, a lens group 14B and a lens group 14C in that order from 
the aperture stop. Then, the lens group 14B is a movable lens group which 
is movable in the direction of the optical axis, and a movement of the 
lens group 14B is arranged to be controlled by a movement control system 
21. Accordingly, when the lens group 14B is moved by the movement control 
system 21 which is interlocked with the change control system 20 in 
accordance with the change of the form or the size of the multiple light 
source, an unevenness in the intensity of illumination on the reticle R 
serving as an irradiated plane, and in its turn, on the wafer W can be 
corrected. In this manner, the movement control system 21 constitutes the 
first correction device for correcting an unevenness in the intensity of 
illumination which is generated on the irradiated plane due to the change 
of the form or the size of the multiple light source. Here, owing to the 
movement of the lens group 14B for correcting the unevenness in the 
intensity of illumination, optical characteristics of the illumination 
optical system are changed. In this case, the optical characteristics 
include a back focus of the condenser optical system, and the 
telecentricity, the numerical aperture, an illumination area, the light 
source distribution, aberrations, etc., of the illumination light on the 
irradiated plane (on the reticle R or on the wafer W). 
In the following, with reference to FIGS. 13 to 16, it will be described 
that a correction of a change of the back focus of the condenser optical 
system is specially important out of changes of the optical 
characteristics caused by the movement of the movable lens group 14B which 
corrects the unevenness in the intensity of illumination. 
Referring to FIG. 13, when the back focus of the lens group 14 is adjusted 
in such a manner that the rear focal point of the lens group 14 is 
positioned on the reticle blind RB, the intensity distribution on the 
reticle blind RB takes a rectangular form, which is uniform over the 
entire area, as shown in FIG. 14. 
However, when the back focus of the lens group 14 is changed due to the 
movement of the movable lens group 14B for correcting the unevenness in 
the intensity of illumination, the rear focal point of the lens group 14 
is displaced from the reticle blind RB, as shown in FIG. 15. As a result, 
as shown in FIG. 16, the corners of the rectangular form indicating the 
intensity distribution on the reticle blind RB are rounded to indicate 
that the distribution becomes uneven. This non-uniformity of the intensity 
distribution on the reticle blind RB reflects on the distribution of the 
intensity of illumination on the reticle R, and in its turn, the 
distribution of the intensity of illumination on the wafer W. Thus, it can 
be seen that the correction on the change of the back focus is specially 
important among the changes in the optical characteristics caused by the 
movement of the movable lens group 14B which corrects the unevenness in 
the intensity of illumination. 
Accordingly, the illumination optical system of the second embodiment is 
provided with an exchange system 22 which comprises a plurality of 
correction lenses each having a different focal length and which exchanges 
the lens 14A1 for constituting a part of the condenser optical system with 
a predetermined correction lens out of the plurality of correction lenses. 
Note that the exchange system 22 is arranged to be interlocked with the 
change control system 20 and the movement control system 21. Therefore, 
when the lens 14A1 is exchanged with an appropriate correction lens having 
a different focal length by the exchange system 22, a change in the back 
focus caused by the movement of the movable lens group 14B can be 
corrected, and the intensity distribution on the reticle blind RB and, in 
its turn, the distribution in the intensity of illumination on the reticle 
R or on the wafer W can be returned into substantially the same states as 
those prior to the change of the form or the size of the multiple light 
source. In this manner, the exchange system 22 constitutes an exchange 
device which has a plurality of correction lenses each having a focal 
length different from that of the lens 14A1 and sets one of the correction 
lenses, instead of the lens 14A1, in the illumination light path. 
As stated above, when the movable lens group 14B is moved to correct the 
unevenness in the intensity of illumination which is caused by the change 
of the form or the size of the multiple light source, the optical 
characteristics, especially the back focus of the condenser optical 
system, is changed due to the movement of the movable lens group 14B. In 
the second embodiment, the change of the back focus can be properly 
corrected only by exchanging the lens 14A1 which constitutes a part of the 
condenser optical system with another correction lens having a different 
focal length. As a result, even when the form or the size of the multiple 
light source is changed according to a desired condition, it is possible 
to properly correct the change in the back focus of the condenser optical 
system in a simple adjustment mechanism, and also, to obtain all the time 
a uniform distribution in the intensity of illumination on the reticle R 
or on the wafer W. Also, in the exposure apparatus in which the 
illumination optical system is incorporated, a projection exposure with a 
high accuracy can be performed by maintaining a uniform distribution in 
the intensity of illumination on the wafer W. 
FIG. 11 is a perspective view which schematically shows the structure of a 
main portion of an illumination optical system according to the third 
embodiment of the present invention. 
The third embodiment has a similar structure to that of the second 
embodiment, except that the structure of an exchange device which corrects 
a change in the optical characteristics caused by a movement of a movable 
lens group 4B is different from that in the second embodiment. 
Accordingly, components in FIG. 11 having the same functions as those of 
the second embodiment in FIG. 10 are given the same reference numerals and 
symbols as in FIG. 10. The third embodiment will be described below by 
paying attention to the difference from the second embodiment. 
As shown in FIG. 11, in the illumination optical system of the third 
embodiment, there is provided a turret 14A2 on which a plurality of 
correction lenses each having a different focal length are 
circumferentially arranged. Then, it is arranged, when the turret 14A2 is 
rotated by an exchange control system 23 which is interlocked with the 
change control system 20 and the movement control system 21, a desired 
correction lens can be set in an illumination light path. Accordingly, 
also in the third embodiment, when the turret 14A2 is rotated by the 
exchange optical system 23 so that a lens for constituting a part of the 
condenser optical system is exchanged with another appropriate correction 
lens having a different focal length, a change of the back focus caused by 
a movement of the movable lens group 14B can be corrected, and the 
intensity distribution on the reticle blind RB and, in its turn, the 
distribution in the intensity of illumination on the reticle R or on the 
wafer W can be returned to substantially the same states as those prior to 
the change of the form or the size of the multiple light source. 
FIG. 12 is a perspective view which schematically shows the structure of a 
main portion of an illumination optical system according to the fourth 
embodiment of the present invention. 
The fourth embodiment has a similar structure to that of the third 
embodiment, except that there are provided two sets of turrets for 
exchanging lenses. Accordingly, components in FIG. 12 having the same 
functions as those of the third embodiment in FIG. 11 are given the same 
reference numerals and symbols as in FIG. 11. The fourth embodiment will 
be described below by paying attention to the difference from the third 
embodiment. 
As shown in FIG. 12, there are provided a first turret 14A3 on which a 
plurality of first correction lenses having different focal lengths are 
circumferentially arranged and a second first turret 14A4 on which a 
plurality of second correction lenses having different focal lengths are 
circumferentially arranged in the illumination optical system of the 
fourth embodiment. Then, it is arranged, when the first turret 14A3 is 
rotated by a first exchange control system 24 and the second turret 14A4 
by a second exchange control system 25, respectively, desired first 
correction and second correction lenses can be respectively set in the 
illumination light path. Also, it is arranged that the first exchange 
control system 24 and the second exchange control system 25 are 
interlocked with the change control system 20 and the movement control 
system 21. 
Accordingly, also in the fourth embodiment, when a lens which constitutes a 
part of the condenser optical system on at least one of the first turret 
14A3 and the second turret 14A4 is exchanged with another appropriate 
first correction lens or second correction lens having a different focal 
length, a change of the back focus caused by a movement of the movable 
lens group 14B can be corrected, and the intensity distribution on the 
reticle blind RB and, in its turn, the distribution in the intensity of 
illumination on the reticle R or on the wafer W can be returned to 
substantially the same states as those prior to the change of the form or 
the size of the multiple light source. 
Note that, in case of the fourth embodiment, if three positive lenses are 
arranged on, for example, the first turret 14A3 and three negative lenses 
on the second turret 14A3, a combination of the total six lenses is 
equivalent in function to an arrangement of nine lenses having different 
focal lengths on one turret. Accordingly, it is possible to correct a 
change in the optical characteristics with a higher accuracy than that in 
the third embodiment by use of correction lenses in a smaller number than 
that in the third embodiment. 
Also, in the illumination optical system in the fourth embodiment shown in 
FIG. 12, a plurality of plane parallel plates having thicknesses different 
from each other may be circumferentially arranged on the first turret 
14A3, and a plurality of correction lenses having focal lengths different 
from each other may be circumferentially arranged on the second turret 
14A4. In this case, a change of the back focus can be corrected by 
exchanging the lenses on the second turret 14A4, and a change in the 
telecentricity can be corrected by exchanging the plane parallel plates on 
the first turret 14A3. In the same manner, a plurality of correction 
lenses having focal lengths different from each other may be 
circumferentially arranged on the first turret 14A3, and a plurality of 
plane parallel plates having thicknesses different from each other may be 
circumferentially arranged on the second turret 14A4, so that a change of 
the back focus and a change in the telecentricity can be corrected. Or, a 
plurality of correction lenses having focal lengths and thicknesses 
different from each other are circumferentially arranged on the first 
turret 14A3 and on the second turret 14A4, so that a change of the back 
focus and a change in the telecentricity can be corrected. 
Also, in the illumination optical system of the third embodiment shown in 
FIG. 11, a plurality of plane parallel plates having thicknesses different 
from each other are circumferentially arranged on the turret 14A2, and the 
turret 14A2 is rotated to exchange the plane parallel plates, whereby a 
change in the telecentricity can be corrected. 
Note that in the third and fourth embodiments, the focal length of a lens 
is changed by a rotation of the turret. However, a plurality of lenses 
having the focal lengths different from each other or a plurality of plane 
parallel plates having thicknesses different from each other, for example, 
may be horizontally arranged and exchanged by the so-called sliding 
method. 
Further, in the fourth embodiment, by tilting the plane parallel plates 
arranged on the turret with respect to the optical axis, the tilt 
telecentricity can be corrected. In this case, a mechanism for tilting the 
plane parallel plates with respect to the turret may be provided inside 
the turret, or a mechanism for integrally tilting the plane parallel 
plates and the turret may be provided outside the turret. 
Also, in the third and fourth embodiments, it is desirable that an 
arrangement of the focal length or the number of lenses on one turret, and 
the number of turrets, etc., should be properly determined in accordance 
with a change of the aperture form of the aperture stop 13, an amount of 
movement of the lens group 14B, etc. 
Further, in the lens exchange in the second to fourth embodiments, a change 
in the telecentricity which is caused by a movement of the movable lens 
group 14B can be corrected by exchanging one lens with another proper lens 
having a different thickness. 
FIG. 22 is a perspective view which schematically shows the structure of a 
main portion of an illumination optical system according to the fifth 
embodiment of the present invention. 
The fifth embodiment has a similar structure to that of the third 
embodiment shown in FIG. 11, except that a change in the telecentricity of 
an illumination light on an irradiated plane is corrected by changing the 
light path length of an optical member 14A6 which is additionally provided 
between the turret 14A2 and the movable lens group 14B. Accordingly, 
components in FIG. 22 having the same functions as those of the third 
embodiment in FIG. 11 are given the same reference numerals and symbols as 
in FIG. 11. The fifth embodiment will be described below by paying 
attention to the difference from the third embodiment. 
As shown in FIG. 22, in the illumination optical system of the fifth 
embodiment, there is provided an optical member 14A6 which has no 
refracting power as a whole and is constituted by a pair of plane parallel 
plates 14a and 14d between a turret 14A2 for correcting a change of the 
back focus of the condenser optical system and a movable lens group 14B. 
There is also provided a measuring device DET which measures the 
telecentricity of the illumination light on the irradiated plane. It is 
arranged that an output from the measuring device DET is supplied to a 
third movement control system 27 for driving the optical member 14A6. 
Then, the third movement control system 27 sets or retracts each of the 
pair of plane parallel plates 14c, 14d into or from an illumination light 
path, depending on a result of measurement conducted by the measuring 
device DET, thereby changing the optical light path of the optical member 
14A6. The third movement control system 27 is arranged to be interlocked 
with the change control system 20 and the movement control system 23. 
As stated, the third movement control system 27 constitutes a light path 
change device for changing the optical light path of the optical member 
14A6 which substantially has no refracting power. 
Note that the measuring device DET is a sensor having a known structure 
which employs, for example, a knife edge detecting method. More 
specifically, as disclosed in the specification and the drawings of 
Japanese Patent Application No. 8-67220, while a space image of a mask 
pattern projected on a knife edge through a projection optical system is 
relatively moved with the knife edge, a light from the space image is 
received by a light-receiving sensor, so as to detect an intensity 
distribution of the space image. Then, on the basis of the detected 
intensity distribution of the space image, the optical characteristics of 
the projection optical system, such as the telecentricity of an 
illumination light on an irradiated plane (the wafer surface) can be 
measured. 
Also, as disclosed in Japanese Patent Laid-Open Application No. 8-264432, 
the Z-coordinate of an ISS (Imaging Slit Sensor) reference mark is 
successively changed with respect to an alignment sensor of the ISS 
scheme, whereby an amount of collapse of the telecentricity can be 
measured. 
The principle of correcting a change in the telecentricity of the 
illumination light by changing the optical light length of the optical 
member 14A6 having no refracting power will be described with reference to 
FIGS. 23 to 25. 
In FIG. 23, the position of the aperture stop 13 is displaced from the rear 
focal position F of lens group 14 toward the optical integrator (to the 
left in the drawing), owing to a movement of the movable lens group 14B, 
for example, for correcting an unevenness in the intensity of 
illumination. As a result, a chief ray a emitted from the lens group 14 is 
made not to parallel to the optical axis, and the telecentricity of the 
lens group 14 on the exit side, and in its turn, the telecentricity of the 
illumination light on the irradiated plane, change. 
FIG. 24 shows a state in which a plane parallel plate 14c is inserted into 
a light path between the aperture stop 13 and the lens group 14. As shown 
in FIG. 24, if the plane parallel plate 14c is inserted between the 
aperture stop 13 and the lens group 14, the position A of the entrance 
pupil of the lens group 14 (i.e., the position of the aperture stop 13) is 
moved into the apparent position B. In this case, if the thickness of the 
plane parallel plate 14c is d1 and the refractive index of the plane 
parallel plate 14c is n1, the distance X1 along the optical axis between 
the pupil position A and the apparent pupil position B is expressed by the 
following formula (1): 
EQU X1=d1-d1/n1 (1). 
As stated above, if the plane parallel plate 14c is set in the illumination 
light path between the aperture stop 13 and the lens group 14, or it is 
retracted from the illumination light path, the apparent pupil position B 
of the lens group 14 is moved along the optical axis in accordance with 
the refractive index and the thickness of the plane parallel plate 14. 
Accordingly, if the plane parallel plate 14c having appropriate refractive 
index and thickness is set in the illumination light path or is retracted 
from the illumination light path, the apparent pupil position B of the 
lens group 14 can be substantially made to meet the front focal position F 
of the lens group 14. As a result, the chief ray a emitted from the lens 
group 14 is made substantially parallel to the optical axis, so that a 
change in the telecentricity of the illumination light on the irradiated 
plane can be corrected. 
FIG. 25 shows a state in which another plane parallel plate 14d, in 
addition to the plane parallel plate 14c, is inserted into the light path 
between the aperture stop 13 and the lens group 14. In FIG. 25, the pupil 
position A of the lens group 14 is moved toward the apparent position C. 
In this case, if the thickness of the plane parallel plate 14d is d2, and 
the refractive index of the plane parallel plate 14d is n2, the distance 
X2 along the optical axis between the pupil position A and the apparent 
pupil position C is expressed by the following formula (2): 
EQU X2=d1-d1/n1+d2-d2/n2 (2). 
the first state in which both of the plane parallel plates 14c and 14d are 
set in the illumination light path, the second state in which the plane 
parallel plate 14c is set in the illumination light path and the plane 
parallel plate 14d is retracted from the illumination light path, the 
third state in which the plane parallel plate 14d is set in the 
illumination light path and the plane parallel plate 14c is retracted from 
the illumination light path, or the fourth state in which both of the 
plane parallel plates 14c and 14d are retracted from the illumination 
light path can be realized depending on a combination of the two plane 
parallel plates which are detachably provided in the illumination light 
path. The apparent pupil position of the lens group 14 can be changed in 
four ways in accordance with the above-mentioned states. As a result, a 
change in the telecentricity of the illumination light on the irradiated 
plane can be satisfactorily corrected more easily than by the other method 
in which only one plane parallel plate is inserted/detached with respect 
to the light path. 
Generally, when n pieces of plane parallel plates having different 
thicknesses from each other are used for the optical member 14A6, the 
optical light path length of the optical member 14A6 can be varied in 2n 
ways and the apparent pupil position of the lens group 14 can be varied in 
2n ways by setting each of the plane parallel plates in the illumination 
light path or retracting it from the illumination light path. Here, if n 
pieces of plane parallel plates having the same refractive index and 
thicknesses different from each other are used, and if the thickness of 
the thinnest plane parallel plate is d, the plane parallel plates are 
preferably arranged to have the thicknesses d, 2d, 2.sup.2 d, . . . , and 
2.sup.n-1 d, respectively. In this case, it is possible to successively 
vary the total thickness of the plane parallel plates set in the 
illumination light path in 2n ways including 0, d, 2d, . . . , (2.sup.n 
-1), by setting each of the plane parallel plates in the illumination 
light path or retracting it from the illumination light path. As a result, 
the optical light length of the optical member 14A6 can be successively 
varied in 2n ways, so that a change in the telecentricity of the 
illumination light on the irradiated plane can be corrected with a higher 
accuracy. 
As stated, in the fifth embodiment, when the optical light path of the 
optical member 14A6 is properly varied on the basis of a result of the 
measurement of the telecentricity which is sent from the measuring device 
DET, a change in the telecentricity caused by the movement of the movable 
lens group 14B can be satisfactorily corrected and a uniform distribution 
of the intensity of illumination can be obtained on the reticle R or on 
the wafer W. 
Note that when the optical member 14A6 is provided in the condenser optical 
system, since the optical member 14A6 is positioned comparatively near the 
optical integrator, a change in the telecentricity of the illumination 
light on the irradiated plane can be effectively corrected by varying the 
optical light path length of the optical member 14A6. Specially, when the 
optical member 14A6 is positioned closest to the optical integrator in the 
condenser optical system as shown in FIG. 23 to 25, if a change in the 
telecentricity is corrected by an operation of the optical member 14A6 
after a change of the back focus is corrected by an operation of the 
turret 14A2, only the change in the telecentricity of the illumination 
light on the irradiated plane can be corrected only with a change of the 
pupil position of the condenser optical system and with little influence 
onto the back focus or aberrations of the condenser optical system. 
Accordingly, as shown in FIG. 22, when the opticalmember 14A6 is set in 
the condenser optical system, it is desirable to set the optical member 
14A6 at a position near the optical integrator as much as possible. 
FIG. 26 is a perspective view which schematically shows the structure of a 
main portion of an illumination optical system according to a modification 
of the fifth embodiment of the present invention. 
This modification is different from the fifth embodiment basically only in 
that a change in the telecentricity of the illumination light on the 
irradiated plane is corrected by changing the light path length of an 
optical member which is constituted by a pair of declination prisms. 
Accordingly, components in FIG. 26 having the same functions as those of 
the fifth embodiment in FIG. 22 are given the same reference numerals and 
symbols as in FIG. 22. This modification will be described below by paying 
attention to the difference from the fifth embodiment. 
As shown in FIG. 26, in the illumination optical system of this 
modification, a pair of declination prisms (wedge-shaped prisms) 14A5 is 
disposed between the aperture stop 13 and the movable lens group 14B in 
such a manner that the paired prisms have no refracting power as a whole. 
That is, the apex (the wedge angle) of the declination prism 14a which is 
disposed on the side of the aperture stop (in the left part of the 
drawing) is identical to the apex of the declination prism 14b which is 
disposed on the side of the irradiated plane (in the right part of the 
drawing). In addition, the plane of the declination prism 14a on the side 
of the aperture stop and the plane of the declination prism 14b on the 
irradiated plane are both disposed to be perpendicular to the optical 
axis, and the plane of the declination prism 14a on the side of the 
irradiated plane and the plane of the declination prism 14b on the 
aperture stop are disposed to be parallel to each other. Then, when the 
declination prism 14b is moved to a direction perpendicular to the optical 
axis by the second movement control system 26, the optical light path 
length of the paired declination prisms 14A5 can be changed. Also, the 
second movement control system 26 is arranged to be interlocked with the 
change control system 20 and the movement control system 21. 
As stated above, the second movement system 26 constitutes a light path 
change device for changing the optical light path length of the paired 
declination prisms 14A5. 
Accordingly, in this modification, when the optical light path length of 
the paired declination prisms 14A5 is changed by moving the declination 
prism 14b to the direction perpendicular to the optical axis by use of the 
second movement control system 26 in accordance with a change of the form 
or the size of the multiple light source, a change in the telecentricity 
which is caused by the movement of the movable lens group 14B can be 
corrected, and at the same time, a uniform distribution of the intensity 
of illumination can be obtained on the reticle R and on the wafer W. Also, 
in the same manner as in the fifth embodiment, when the optical light path 
length of the paired declination prisms 14A5 is changed, only a change in 
the telecentricity of the illumination light on the irradiated plane can 
be corrected without giving much influence on the back focus or 
aberrations of the condenser optical system. 
Note that, in this modification, only the declination prism 14b is moved to 
a direction perpendicular to the optical axis. However, only the 
declination prism 14a may be moved to a direction perpendicular to the 
optical axis, or the declination prism 14a and the declination prism 14b 
may be moved to directions opposite to each other. 
Further, in the second to fifth embodiments and in the modification of the 
fifth embodiment, a turret may be disposed on the light source side of the 
optical integrator 12, and a plurality of filters for correcting a change 
of optical characteristics such as an unevenness in the intensity 
distribution may be disposed circumferentially on this turret. In this 
case, not only an unevenness in the intensity of illumination which is 
revolutionary symmetrical with respect to the optical axis, but also a 
change of the optical characteristics including a rotationally 
asymmetrical unevenness in the inclination can be dealt with by setting an 
appropriate filter on the turret in the illumination light path 
interlockingly with a change of the aperture form of the aperture stop 13 
(i.e., a change of the form or the size of the multiple light source). 
Next, description will be made on a case in which an illumination optical 
system of the present invention is applied to an exposure apparatus of a 
so-called scan exposure type wherein a mask pattern is scan-exposed in 
each exposure area on the wafer when the mask and the wafer are relatively 
moved. 
FIG. 17 is a perspective view for schematically showing the structure of 
the exposure apparatus of the scan-exposure type into which the 
illumination optical system according to the third embodiment of the 
present invention is incorporated. In the apparatus shown in FIG. 17, a 
second optical integrator is further disposed on the light source side of 
a first optical integrator. 
In the illustrated exposure apparatus, an illumination light from a light 
source 1 such as a laser light source is incident on the first optical 
integrator 18 through a lens group 17. The light ray incident on the 
second optical integrator 18 is two-dimensionally divided by a plurality 
of lens elements, so as to from on the rear focal plane side thereof a 
secondary light source which is constituted by a plurality of light source 
images. 
The light ray from the secondary light source which is formed by the second 
optical integrator 18 is converted into collimated light rays by a lens 
group 19, so as to illuminate the incident plane of an optical integrator 
12 in an overlapping manner. The collimated light rays incident on the 
optical integrator 12 are divided by a plurality of lens elements, and a 
multiple light source (the tertiary light source) which is constituted by 
light source images in the number equal to the product of the number of 
the lens elements of the second optical integrator 18 and the number of 
the lens elements of the optical integrator 12 on the rear focal plane of 
the optical integrator 12. 
The light from the multiple light source which is formed by the optical 
integrator 12 is controlled by the aperture stop 13 disposed in the 
vicinity of the rear focal plane of the optical integrator 12, and then 
enters the condenser optical system. 
The light incident on the condenser optical system is condensed through a 
lens of a turret 14A2, a movable lens group 14B, and a lens group 14C, and 
then controlled by a fixed slit S having a rectangular aperture portion. 
After that, the condensed light enters the reticle blind RB. The light 
coming through the reticle blind RB is deflected by a mirror M, and then, 
illuminates the reticle R on which a circuit pattern to be transferred is 
formed in an overlapping manner through a lens group 15 for constituting a 
part of the condenser optical system. The light passed through the pattern 
of the reticle R is imaged on the wafer W which serves as a photosensitive 
substrate via a projection optical system 16. 
Note that the reticle R is supported on a reticle stage RS along a 
direction indicated by an arrow R1 on a plane perpendicular to the optical 
axis of the projection optical system 16. On the other hand, the wafer W 
is supported by a wafer stage WS which is two-dimensionally movable on a 
plane perpendicular to the optical axis of the projection optical system 
16. Thus, the wafer stage WS is moved to a direction indicated by an arrow 
W1 while the reticle stage RS is moved to the direction indicated by the 
arrow R1, that is, a scan exposure is performed while the reticle R and 
the wafer W are relatively moved in opposite directions to each other, 
whereby a pattern of the reticle R is transferred onto each exposure area 
of the wafer W. 
As shown in FIG. 17, in an exposure apparatus of the scan-exposure type, 
the fixed slit S is disposed at a position separated away from the reticle 
blind RB to the light source by a slight distance, in order to reduce a 
dynamic unevenness in an exposure amount. An influence of a change of the 
back focus on the intensity distribution on the reticle blind RB when the 
fixed slit S is not provided, as in the above-mentioned embodiments, is 
different from that when the fixed slit S is not provided in the scan 
exposure. Description will be made below on the influence on the intensity 
distribution on the reticle blind RB, which is given by a change of the 
back focus caused the movement of the movable lens group 14B, with 
reference to FIGS. 18 to 21. 
Referring to FIG. 18, when the back focus of the lens group 14 is adjusted 
such that the rear focal point of the lens group 14 is positioned on the 
reticle blind RB, the intensity distribution on the reticle blind RB is 
limited by the fixed slit S to take the form of a trapezoid which is 
suitable for the scan exposure. 
However, when the back focus of the lens group 14 is changed due to the 
movement of the movable lens group 14B which corrects an unevenness in the 
intensity of illumination, the rear focal point of the lens group 14 is 
displaced from the reticle blind RB, as shown in FIG. 20. As a result, as 
shown in FIG. 21, with respect to the intensity distribution on the 
reticle blind RB, the corners of the trapezoid are rounded to indicate an 
unevenness in the distribution. The unevenness in the intensity 
distribution on the reticle blind RB reflects on the distribution of the 
intensity of illumination on the reticle R and on the wafer W. 
In the exposure apparatus of the scan exposure type shown in FIG. 17, when 
the turret 14A2 is rotated to exchange the lens which constitutes a part 
of the condenser optical system with another proper correction lens which 
has a different focal length, a change of the back focus generated due to 
the movement of the movable lens group 14B is corrected so that the 
intensity distribution on the reticle blind RB and, in its turn, the 
distribution of the intensity of illumination on the reticle R and on the 
wafer W can be returned to the states prior to the change of the form or 
the size of the multiple light source. As a result, it is possible to 
maintain a uniform distribution of the intensity of illumination on the 
wafer W, thereby performing a high-precision projection exposure. 
Since the reticle R can be illuminated by the exposure apparatus shown in 
each of the foregoing embodiments much more uniformly than in the 
conventional apparatus, an excellent reticle pattern can be 
projection-exposed on the wafer W which serves as a photosensitive 
substrate through the projection optical system. Then, the wafer which has 
undergone an exposure step by the exposure apparatus of the second 
embodiment (the photolithographic step) further undergoes a developing 
step, an etching step for removing a part other than the developed resist, 
and then, a resist removal step for removing unnecessary resist after the 
etching step, whereupon the wafer process is completed. Then, upon 
completion of the wafer process, an actual assembling process including a 
dicing step for cutting the wafer into chips for each printed circuit, a 
bonding step for providing a wire, etc. , to each chip, and packaging step 
for packaging each chip are performed to manufacture a semiconductor 
device (an LSI, or the like) as a finished device. Note that the above 
description was made on a case in which a semiconductor device is 
manufactured by the photolithographic step in the wafer process using the 
projection exposure apparatus. However, semiconductor devices such as a 
liquid crystal display device, a thin film magnetic head, and an image 
pick-up device (a CDD, or the like) can be manufactured by the 
photolithographic step using an exposure apparatus. 
When a semiconductor device is thus manufactured by using the illumination 
optical system according to the present invention, it is possible to 
perform a projection exposure with a high accuracy by maintaining a 
uniform distribution of the intensity of illumination on a photosensitive 
substrate and an excellent telecentricity of the exposure light, so that 
an excellent semiconductor device can be manufactured. 
In each of the foregoing embodiments, the form or the size of the multiple 
light source is changed by changing the aperture form of the aperture 
stop. However, as disclosed in Japanese Patent laid-Open Application No. 
4-225514, it is possible to change the form or the size of the multiple 
light source by changing the sizes of the four eccentric light sources, or 
by properly changing the forms of the optical integrators or a combination 
thereof. The present invention is effective for correction of a 
fluctuation in the distribution of the intensity of illumination caused by 
a change of the form or the size of the multiple light source, regardless 
of method for changing thereof. 
Further, in each of the foregoing embodiments, the present invention was 
described by using a projection exposure apparatus with an illumination 
optical system as an example. However, it is clearly seen that the present 
invention can be applied to an exposure apparatus of the proximity scheme, 
or an ordinary illumination optical system for uniformly illuminating a 
plane to be irradiated other than a mask. 
Also, in each of the foregoing embodiments, a fly-eye lens which is 
constituted by a plurality of lens elements tied up in a bundle is used as 
the optical integrator. However, a rod-shaped optical member of a 
inner-plane reflection type may be used, instead. 
Also, each of the foregoing embodiments shows a case in which at least a 
certain optical system which is a part of the condenser optical system is 
moved to the direction of the optical axis in accordance with a change of 
the size or the form of each of a plurality of light source images which 
are formed by the optical integrator, by way of example. However, the 
present invention is not limited to such case, and it is possible to 
replace at least a certain optical system which is a part of the condenser 
optical system with an optical system with a different focal length, by 
use of a turret, or the like. Also, in each of the foregoing embodiments, 
in order to simplify the structure of the condenser optical system, at 
least a certain optical system which is a part of the condenser optical 
system is replaced with an optical system having a different focal length 
by use of a turret or the like so as to suppress a fluctuation in the back 
focus or the like of the condenser optical system. However, if there is no 
need to simplify the structure of the condenser optical system, such 
structure may be employed in which the focal length of the condenser 
optical system can be successively changed, that is, a fluctuation in the 
back focus or the like of the condenser optical system is suppressed with 
intention of using the condenser optical system as a zoom lens. 
As described above, in the illumination optical system of the present 
invention and the exposure apparatus provided with the optical system, at 
least one lens out of a plurality of lenses for constituting the condenser 
optical system is moved along the optical axis, so that a fluctuation in 
the distribution of the intensity of illumination caused by a change of 
the form or the size of the secondary light sources can be corrected. 
Further, in the illumination optical apparatus of the present invention, it 
is possible to properly correct the back focus of the condenser optical 
system or a change in the telecentricity of the illumination light on the 
irradiated plane only by exchanging optical systems or optical members for 
constituting a part of the condenser optical system. Thus, it is possible 
to constantly maintain a uniform distribution of the intensity of 
illumination or an excellent telecentricity on the irradiated plane. 
Accordingly, in the exposure apparatus in which the illumination optical 
system of the present invention is incorporated, a uniform distribution of 
the intensity of illumination and an excellent telecentricity of the 
exposure light can be maintained on the photosensitive substrate, so as to 
perform a projection exposure with a high precision. Also, when 
manufacturing a semiconductor device by using the illumination optical 
system of the present invention, the projection exposure with a high 
precision can be performed by maintaining a uniform distribution of the 
intensity of illumination and an excellent telecentricity of the exposure 
light on the photosensitive substrate, so that an excellent semiconductor 
device can be manufactured.