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Claims  |
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What is claimed is:
1. A projection exposure apparatus comprising:
an illumination optical system comprising an illumination source for
illuminating an original having an exposure pattern, said illumination
optical system including a changing mechanism for changing a shape of the
illumination source, said changing mechanism including a selecting
mechanism for selecting one of predetermined illumination source shapes,
said selecting mechanism including a turret having a plurality of
apertures for determining the illumination source shapes;
a projection optical system for projecting an image of the exposure pattern
onto a surface to be exposed; and
adjusting means responsive to said changing mechanism to adjust said
projection optical system.
2. An apparatus according to claim 1, wherein said adjusting means adjusts
aberration of said projection optical system.
3. An apparatus according to claim 1, wherein said adjusting means adjusts
field of curvature of said projection optical system.
4. An apparatus according to claim 1, wherein said adjusting means adjusts
one side blurness of said projection optical system.
5. An apparatus according to claim 1, wherein said adjusting means adjusts
pivotal inclination of said projection optical system.
6. An apparatus according to claim 1, wherein said adjusting means adjusts
projection magnification of said projection optical system.
7. An apparatus according to claim 1, wherein said adjusting means adjusts
a distance between the original and said projection optical system.
8. An apparatus according to claim 1, wherein said adjusting means adjusts
power of said projection optical system.
9. An apparatus according to claim 1, further comprising input means for
inputting information indicative of a kind of the original, wherein said
changing mechanism changes the shape in accordance with information
inputted to said input means.
10. An apparatus according to claim 9, wherein said input means includes a
bar code reader for reaching a bar code on the original.
11. An apparatus according to claim 1, wherein said illumination optical
system includes a radiation source and an optical integrator, and wherein
said illumination source is formed behind the optical integrator as a
second illumination source.
12. An apparatus according to claim 1, wherein said plural illumination
source shapes includes one corresponding to a zone including the optical
axis.
13. An apparatus according to claim 1, wherein said plural illumination
source shapes include one corresponding to a zone outside the optical
axis.
14. An apparatus according to claim 13, wherein said one has a
substantially circular ring shape around the optical axis.
15. An apparatus according to claim 13, wherein the one has a substantially
rectangular ring shape around the optical axis.
16. An apparatus according to claim 13, wherein the one has four
illumination source portions in respective quadrants in an orthogonal
coordinate with its origin at the optical axis.
17. An apparatus according to claim 16, wherein the exposure pattern is
substantially codirectional with the ordinate and the abscissa of the
coordinate.
18. A projection exposure apparatus comprising:
an illumination optical system comprising an illumination source for
illuminating an original having an exposure pattern, said illumination
optical system including a changing mechanism for changing a shape of the
illumination source, said changing mechanism including a selecting
mechanism for selecting one of predetermined illumination source shapes,
wherein the selecting mechanism includes a turret having a plurality of
apertures for determining the illumination source shapes,
a projection optical system for projecting an image of the exposure pattern
onto a surface to be exposed; and
processing means responsive to said changing means to change a parameter
and for calculating an optical property of said projection optical system.
19. An apparatus according to claim 18, wherein the optical property
includes at least one of focus point and projection magnification of said
projection optical system.
20. An apparatus according to claim 18, further comprising adjusting means
responsive to said processing means to adjust said projection optical
system.
21. An apparatus according to claim 18, further comprising input means for
inputting information indicative of a kind of the original, wherein said
changing mechanism changes the shape in accordance with information
inputted to said input means.
22. An apparatus according to claim 21, wherein said input means includes a
bar code reader for reaching a bar code on the original.
23. A projection exposure apparatus, comprising:
an illumination optical system constituting an illumination source for
illuminating an original having an exposure pattern, said illumination
optical system including a changing mechanism for changing the shape of
the illumination source;
a projection optical system for projecting an image of the exposure pattern
onto the surface to be exposed; and
processing means, responsive to said changing mechanism to change a
parameter, for calculating an optical property of said projection optical
system, other than the focus point and the projection magnification
thereof.
24. An apparatus according to claim 23, further comprising adjusting means
responsive to said processing means to adjust said projection optical
system.
25. An apparatus according to claim 23, further comprising input means for
inputting information indicative of the type of the original, wherein said
changing mechanism changes the shape of the illumination source in
accordance with the information inputted to said input means.
26. An apparatus according to claim 25, wherein said input means includes a
bar code reader for reading a bar code provided on the original.
27. A projection exposure apparatus, comprising:
an illumination optical system having an illumination source, for
illuminating an original having an exposure pattern, said illumination
optical system including means for changing the shape of said illumination
source;
a projection optical system for projecting an image of the exposure pattern
onto a surface to be exposed; and
processing means responsive to said changing means to change a parameter
for calculating a change in the optical property of said projection
optical system, other than the imaging position and the projection
magnification thereof.
28. A exposure apparatus, comprising:
means for changing the shape of an illumination source illuminating a
pattern;
a projection optical system for projecting an image of the pattern
illuminated by said illumination source, onto a substrate; and
means for adjusting an aberration of said projection optical system, in
accordance with the change in said illumination source.
29. An apparatus according to claim 28, wherein said adjusting means
adjusts the distortion of the image of the pattern illuminated.
30. An apparatus according to claim 28, wherein said adjusting means
adjusts the field of curvature of said projection optical system, in
accordance with the change in said illumination source.
31. An apparatus according to claim 30, wherein said adjusting means
adjusts the distortion of the image of the pattern illuminated.
32. An apparatus according to claim 28, wherein said changing means serves
to define one of an on-axis illumination source and an off-axis
illumination source.
33. An exposure apparatus, comprising:
means for changing the shape of an illumination source illuminating a
pattern;
a projection optical system for projecting an image of the pattern
illuminated by said illumination source, onto a substrate; and
means for adjusting one side blurness of said projection optical system, in
accordance with the change in said illumination source.
34. An apparatus according to claim 33, wherein said changing means serves
to define one of an on-axis illumination source and an off-axis
illumination source.
35. An exposure apparatus, comprising:
means for changing the shape of an illumination source illuminating a
pattern;
a projection optical system for projecting an image of the pattern
illuminated by said illumination source, onto a substrate; and
means for adjusting the pivotal inclination of said projection optical
system, in accordance with the change in said illumination source.
36. An apparatus according to claim 26, wherein said changing means serves
to define one of an on-axis illumination system and an off-axis
illumination system. |
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Claims |
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Description |
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FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a projection exposure apparatus and a
semiconductor device manufacturing method, more particularly to the
apparatus and method in which even if a reticle pattern illumination
method is changed, a high optical performance can be maintained.
The recent development in the semiconductor manufacturing device
manufacturing techniques, and the development in the fine processing
techniques, are remarkable. 1M DRAM semiconductor device requires the
photoprocessing technique for sub-micron resolution. Heretofore, the
resolution has been improved by means of increasing NA (numerical
aperture) with a constant exposure light wavelengths. However, the recent
developments include the change of the exposure light from g-line to
i-line, using ultra high pressure mercury lamp. With the use of the g-line
and i-line, the photoresist process has also been developed. Thus, the
developments in the optical system and the photoresist system has been
contributable to the developments in the photolithographic process.
It is generally known that the depth of focus of an exposure apparatus in
the form of a stepper is reversely proportional to NA squared. Therefore,
when the sub-micron resolution is provided, the depth of focus decreases
correspondingly.
Japanese Patent Application No. 28631/1991 under the name of the assignee
of this application has proposed a projection exposure apparatus having a
higher resolution provided by the structure of illumination system
depending on the pattern to be projected and the line width.
In order to maintain the satisfactory resolution, it is important that the
optimum focus point of the projection optical system does not change.
However, when the exposure light is applied to the projection optical
system to project the pattern of the reticle onto the wafer, the
projection optical system absorbs a part of the exposure light, with the
result of heat generated in the projection optical system. If this occurs,
the temperature of the lens material itself and the temperature between or
around the lens materials, change, and therefore, the optical performance
of the projection optical system changes. In other words, the optimum
focus point of the projection optical system changes.
In the above-mentioned Japanese Patent Application, the illumination method
is changed depending on the directions of the pattern of the reticle and
the required line width, and the optical path in the projection optical
system changes, accordingly. Then, the absorptions of the exposure beam in
the projection optical system change, and the change in the optical system
is different. For example, the ways of changes in the optimum focus point
and the projection magnification, may be different.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the present invention to provide a
projection exposure apparatus and method in which the high optical
performance is maintained even if the illumination method is changed.
It is a further object of the present invention to provide a semiconductor
device manufacturing method in which the illumination method is selected
in accordance with the nature of the circuit pattern, so that the
semiconductor devices can be produced with high precision.
These and other objects, features and advantages of the present invention
will become more apparent upon a consideration of the following
description of the preferred embodiments of the present invention taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a systematic diagram of the projection exposure apparatus
according to an embodiment of the present invention.
FIG. 2 illustrates a relationship between a pupil of a projection optical
system and an optical integrator.
FIGS. 3A and 3B illustrate the pupil of the projection optical system.
FIGS. 4A and 4B illustrate the aperture of the optical system.
FIG. 5 shows a cable extending from an ultra high pressure mercury lamp.
FIG. 6 illustrates a variation of a focus point of a projection optical
system when it absorbs a part of the exposure light energy.
FIG. 7 illustrates a pupil of another projection optical system.
FIG. 8 illustrates reading of bar code on a reticle surface.
FIG. 9 is a system diagram of an apparatus according to a second embodiment
of the present invention.
FIG. 10 illustrates a pupil of a projection optical system of another
illumination method.
FIG. 11 shows a lens arrangement of a projection optical system according
to an embodiment of the present invention.
FIG. 12 illustrates a manufacturing system for manufacturing a
semiconductor device.
FIG. 13 is a flow chart showing semiconductor device manufacturing process
steps.
FIG. 14 is a flow chart of a wafer process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
FIG. 1 is a schematic view of a projection exposure apparatus according to
an embodiment of the present invention. Denoted at 11 is a light source
(radiation source) comprising an ultra-high pressure Hg lamp, for example.
The point of light emission of it is disposed adjacent to the first focal
point of an elliptical mirror 12. The light produced by the lamp 11 is
collected by the elliptical mirror 12. Denoted at 13 is a deflecting
mirror, and denoted at 14 is a shutter for restricting the quantity of
light to be passed. Denoted at 15 is a relay lens system for efficiently
directing the light from the lamp 11 to an optical integrator 17 through a
wavelength selecting filter 16. The optical integrator 17 comprises a
plurality of small lenses arrayed two-dimensionally, to be described
later.
In this embodiment, the manner of imaging to the optical integrator 17 may
be either under critical illumination or under Koehler illumination. Also,
the exit port of the elliptical mirror 12 may be imaged on the optical
integrator 17. The filter 16 serves to select and pass only a desired
wavelength component or components out of the light from the Hg lamp 11.
Denoted at 18 is a stop shape adjusting member (selecting means) comprising
a turret having plural stops of different aperture shapes and sizes,
disposed after the optical integrator. The stop shape adjusting member 18
operates to select predetermined ones of the small lenses of the optical
integrator 17 in accordance with the shape of the optical integrator 17.
That is, in this embodiment, the manner of illumination suitable to the
configuration of a pattern of a semiconductor integrated circuit,
concerned, is selected and the exposure process is executed in the
selected manner of illumination. Details of selection of small lenses will
be explained later.
Denoted at 19 is a mirror for deflecting the light path, and denoted at 20
is a lens system for collecting the light passing through the adjusting
member 18. The lens system 20 plays an important role in providing
uniformness of illumination. Denoted at 21 is a half mirror for dividing
the light from the lens system 20 into reflected light and transmitted
light. Of the divided lights, the light reflected by the half mirror 21
goes through a lens 38 and a pinhole 39 to a photodetector 40. The pinhole
39 is provided at a position which is optically equivalent to the reticle
30 having a pattern to be printed. The light passing through the pinhole
39 is detected by the photodetector 40, for controlling the amount of
exposure.
Denoted at 22 is a mechanical blade called a masking blade, whose position
can be adjusted by a driving system (not shown) in accordance with the
size of the pattern region of the reticle 30 to be illuminated. Denoted at
34 is a mirror; at 24 is a lens system; at 25 is another mirror; and at 26
is another lens system. These elements serve to illuminate the reticle 30
planed on the reticle stage 37 wit the light from the Hg lamp 11.
A projection optical system 31 projects a focused pattern of the reticle 31
onto the wafer 32. The wafer 32 is attracted and supported on a wafer
chuck 33, and the wafer chuck 33 is carried on a stage 34 controlled in
response to a detection of a laser interferometer 36. A mirror 35 is
placed on the wafer stage 34 and is effective to reflect the light from
the laser interferometer 36.
Light projecting system 52 and a light receiving system 53 detect a surface
level (in the direction of the optical axis 31b) of the wafer 32. The beam
from the light projecting system 52 is formed as a spot on the wafer 32.
The beam reflected by the wafer 32 is incident on a position sensor of the
light receiving system 53, and an image of a-light source is formed. In
the surface level detecting position for the wafer 32, as shown in the
figure, the light reflection point on the wafer 32 surface and a light
incident point on the position sensor of the light receiving optical
system, are disposed in an imaging relation, so that the vertical
positional deviation of the wafer 32 is detected on the basis of the light
incident point on the position sensor.
In this embodiment, the light exit surface 17a of the optical integrator 17
is substantially in an optically conjugate relationship with a pupil plane
31a of the projection optical system 31 with the intervention of the
elements denoted at 19, 20, 23, 24, 25 and 26. Namely, an effective light
source image corresponding to the light exit surface 17b, is formed on the
pupil plane 31a of the projection optical system 31.
Referring now to FIG. 2, the relationship between the pupil plane 31a of
the projection optical system 31 and the light exit surface 17a of the
optical integrator 17 will be explained. The configuration of the optical
integrator 17 corresponds to the configuration of the effective light
source as formed on the pupil plane 31a of the projection optical system
31. This is shown in FIG. 2 wherein the shape of the effective light
source image 17c on the light exit surface 17b as formed on the pupil
plane 31a of the projection optical system 31 is illustrated superposedly.
For standardization, the radius of the pupil 31a of the optical integrator
31 is taken as 1, and, within this pupil 31a, the small lenses of the
optical integrator 17 are imaged to form the effective light source image
17c. In this embodiment, each small lens of the optical integrator has a
square shape.
Here, orthogonal coordinates which define the major directions to be used
in design of a semiconductor integrated circuit are taken on x and y axes.
These directions correspond to the major directions of the pattern formed
on the reticle 30, and they substantially correspond to the directions of
the outside configuration (square shape) of the reticle 30.
Generally, if the wavelength is denoted by .lambda., the parameter is
denoted by k.sub.1 and the numerical aperture is denoted by NA, then the
resolution RP can be given by:
RP=k.sub.1..lambda./NA
The case wherein a high resolution illumination system provides its power
is a case where the k.sub.1 factor takes a level about 0.5.
In the present embodiment, in consideration thereof, under the influence of
a particular stop of the adjusting member 18, only the light that passes
through selected ones of the small lenses of the optical integrator 17,
selected in accordance with the shape of the pattern on the reticle 30
surface, is used to illuminate the reticle 30.
More specifically, selection of small lenses is such that the light is
allowed to pass through plural zones on the pupil plane 31a of the
projection optical system 31, other than the central zone thereof.
FIGS. 3A and 3B are schematic views each illustrating on the pupil plane
31a the manner of selection of light, passing through particular ones of
the small lenses of the optical integrator 17 selected by a particular
stop of the adjusting member 18. In these drawings, the painted areas
depict light-blocked regions. The blank areas depict those regions to
which the light come.
More specifically, FIG. 3A illustrates an effective light source image upon
the pupil plane 31a to be defined in an occasion where resolution is
required with respect to x and y directions. Assuming the circle
representing the pupil 31a as x.sup.2 +y.sup.2 =1, the following four
circles should now be considered:
(x-1).sup.2 +y.sup.2 =1
x.sup.2 +(y-1).sup.2 =1
(x+1).sup.2 +y.sup.2 =1
x.sup.2 +(y+1).sup.2 =1
With these four circles, the circle representing the pupil 31a is divided
into eight zones 101-108.
The illumination system of high resolution and deep depth of focus with
respect to the x and y directions, is accomplished in this embodiment by
selected projection, with priority, of the light to small lens groups in
such zones denoted by reference numerals of even number, that is, the
zones 102, 104, 106 and 108. Since the small lenses adjacent to the origin
(x=0, y=0) are mainly contributable to enlarging the depth with respect to
a rough pattern, whether those at the central portion are to be selected
or not is a matter of selection to be determined by the pattern to be
printed.
In the example of FIG. 3A, those small lenses around the center are
excluded. The portion outside the optical integrator 17 is light-blocked
by an integrator holding member (not shown) within the illumination
system. In FIGS. 3A and 3B, for easy understanding of the relationship
between the small lenses to be light-blocked and the pupil 31a of the
projection lens, the pupil 31a and the effective light source image 17c of
the optical integrator are drawn in superposition.
On the other hand, FIG. 3B illustrates the configuration of a stop to be
used in an occasion where high resolution is required with respect to
patterns of .+-.45 deg. Similarly to the FIG. 4A case, there is
illustrated the relationship between the pupil 31a and the effective light
source image 17c of the optical integrator 17. For such .+-.45 deg.
patterns, under the same conditions as in the preceding case, the
following four circles are to be considered:
##EQU1##
By drawing these four circles in superposition on the pupil 31a, like the
FIG. 3A case, the pupil 31a is divided into eight zones 111-118. In this
case, the zones which are contributable to enhancement of resolution to
the .+-.45 deg. patterns are those zones denoted by reference numerals of
odd number, that is, the zones 111, 113, 115 and 117. Thus, by selecting
with priority those of the small lenses of the optical integrator 17 which
present in these zones, to such .+-.45 deg. patterns the depth of focus is
considerably enlarged at a k.sub.1 factor of about 1.5.
FIG. 4A illustrates an example of the stop shape adjusting member 18. As
illustrated, a turret type stop interchanging system is adopted in this
embodiment. A first stop 18a it to be used in a case where a pattern which
is not so fine (k.sub.1 is not less than 1) is to be printed. The first
stop 18a is of the same type as has been used in conventional illumination
optical system, and it is a fixed stop and may be so set as to block the
portion outside the small lenses of the optical integrator 17 as desired.
Stops 18b-18d are selected in accordance with the type of a reticle
pattern to be used.
In this embodiment, a secondary light source formed out of the optical
system has independent light source portions in the four quadrants,
respectively, of an orthogonal coordinates defined with the point of
origin coincident with the optical axis, depending on the selection of the
illumination system.
In this embodiment, a first original having a circuit pattern of relatively
large minimum line width and a second original having a circuit pattern of
relatively small minimum line width. When the first original is used, the
secondary light source is formed adjacent to the optical axis as shown by
an opening 18a in FIG. 4. When the second original is used, the secondary
light sources are formed outside the optical axis as indicated by openings
18b, 18c and 18d in the same figure.
As for the configuration of the secondary light source outside the optical
axis, it may be in the form of a circular ring-like or rectangular
ring-like shape.
Generally, in an illumination system for providing a high resolution, for a
higher spatial frequency it is advantageous to use an outside region, upon
the pupil plane, beyond the size of the optical integrator 17 as required
in conventional illumination systems. For example, while it may be
preferable in a conventional illumination system to use small lenses
within a radius of 0.5, in an illumination system for high resolution it
may be preferable to use those small lenses in a circle of a maximum
radius of 0.75 although the small lenses in the central portion are not
used.
In consideration of this, it is desirable to set the size of the optical
integrator 17 as well as the effective diameter of the illumination system
and the like while taking into account both the conventional type and the
high resolution type. Further, it is desirable that the light intensity
distribution at the light entrance end 17a of the optical integrator 17
has a sufficient size so that it can function well even if a stop member
is inserted. The possibility of blocking outside small lenses by the stop
18a is for the reason described above. It may be possible that, while an
optical integrator 17 prepared is provided with a radius up to 0.75, the
stop 18a serves to select a portion within a radius 0.5.
In this manner, the stop shape may be determined while taking into account
the specificness of a pattern of a semiconductor integrated circuit to be
manufactured and, by doing so, it is possible to provide an exposure
apparatus best suited to the pattern. The selection of stops may be
executed automatically under the influence of a control computer which may
be provided to control the operation as a whole of the exposure apparatus.
What is illustrated in FIG. 4A is an example of stop shape adjusting
member formed with such stops and, in this example, a desired one of four
types of stops 18a-18d can be selected. As a matter of course, the number
of stops may be easily increased as desired. An example is illustrated in
FIG. 4B. In this example, stops 18a-18d are of the same structure as the
those of FIG. 4A example. Stop 18e has an opening of a size smaller than
the stop 18a. Stop 18f has an opening of further reduced size. Stop 18g
has a ring-like opening having a central light blocking portion. Stop 18h
has a rectangular ring-like opening.
There is a possibility that, when a stop is selected, the non-uniformness
of illuminance changes with the selection of stop. In this embodiment, in
consideration thereof, the non-uniformness of illuminance in that occasion
may be adjusted by using the lens system 20. The non-uniformness of
illuminance can be adjusted finely by adjusting the spacing or spacings of
lens elements of the lens system 20 in the direction of its optical axis.
Denoted at 51 is a driving mechanism for moving a or some lens elements of
the lens system 20. The adjustment of the lens system 20 may be made in
response to the selection of a stop. If desired, it may be possible to
replace the lens system 20 itself by a different one in accordance with
the stop shape adjustment. In that occasion, plural lens systems 20 may be
prepared and may be interchangeably used in a turret fashion in response
to the selection of a stop shape.
In this embodiment, as described, by changing the shape of stop, an
illumination system suitable to the characteristic of a pattern of a
semiconductor integrated circuit is selected. Another feature of this
embodiment resides in that, when an illumination system for high
resolution is selected, the formed effective light source comprise four
separate zones. What is important in this case is the balance of intensity
of these four zones. In the arrangement of FIG. 1, however, there is a
possibility that the shadow of a cable to the Hg lamp 11 adversely affects
the balance. In order to avoid this, it is preferable in the illumination
system for high resolution which uses the stop means shown in FIG. 4 to
connect the cable so that the linear shadow of the cable comes to the
position of the small lenses of the optical integrator as light-blocked by
the stop.
Namely, in the example of FIG. 3A, it is preferable that the cable 11a is
stretched in the x or y direction as illustrated in FIG. 5A. When the stop
of FIG. 3B is used, it is preferable to that the cable 11a is stretched in
a direction of .+-.45 deg. relative to the x or y direction as illustrated
in FIG. 5B. In this embodiment, the direction of stretching the cable may
be changed in accordance with the change of the shape of stop.
The description will be described as to the compensating method for optical
characteristics changes occurs in the projection optical system, for
example, a temperature change due to absorption of a part of exposure
light energy.
When .DELTA.F.sub.1 and .DELTA.F.sub.2 are differences of focus change
amount between non-exposure period and exposure period, at a time t, the
following results:
.DELTA.F.sub.1 =I.sub.o.exp {-k.sub.2.t}
.DELTA.F.sub.2 =I.sub.o.{1-exp (-k.sub.1.t)}
Where I.sub.o is proportional to the absorbed energy, and k.sub.1 and
k.sub.2 are thermal conductivity coefficient. The difference relating to
the magnification change .DELTA..beta..sub.1 and .DELTA..beta..sub.2, the
equations include substantially the same parameters.
Here, coefficient I.sub.o, k.sub.1 and k.sub.2 are called focus change
coefficient. It is assumed that the initial optimum focusing surface
(focusing position) of the projection optical system is F.sub.0 and the
exposure beam is applied to the projection optical system from the point
of time t.sub.0. Then, as shown in FIG. 6, the optimum focus surface
changes with time until it is stabilized at a position F.sub.C at time
t.sub.1. The position F.sub.C is a saturation point corresponding to the
incident energy.
When the exposure light application is stopped at time t.sub.2, the optimum
focusing surface returns in an exponential function fashion with time from
the position F.sub.C to the initial position F.sub.0 (time t.sub.3). Thus,
the change amount .DELTA.F from the initial level F.sub.0 to the saturated
level F.sub.C changes proportionally to the illumination energy (the
transmittance of the reticle and the illumination strength). The time
constant T.sub.1 in the rising profile from time t.sub.o to time t.sub.1,
and the time constant T.sub.2 of the falling profile from the time t.sub.2
to the time t.sub.3, are peculiar to the projection optical system.
Among the change amount .DELTA.F, the time constants T.sub.1 and T.sub.2,
the focus change coefficients I.sub.o, K.sub.1 and K.sub.2, satisfy the
following:
.DELTA.F=.DELTA.I=I.sub.o =I.sub.o..tau.xE
T.sub.1 =1/K.sub.1
T.sub.2 =1/K.sub.2
Where .tau. is a transmittance of the reticle, E is illumination light
quantity per unit time. The parameters I.sub.o, K.sub.1 and K.sub.2 are
different if the conditions of the light rays passing through the
projection optical system, that is, the illumination method. The
parameters .tau. and E can be predetermined based on measurements. The
following calculations can be carried out on the basis of measurements of
the opening and closing periods of the shutter 14 of the apparatus.
In view of the above, the optimum focus surface position is calculated
using optimum parameters I.sub.o, K.sub.1 and K.sub.2 which are different
depending on illumination method even when the same projection optical
system is used.
Table 1 shows the parameters I.sub.o, K.sub.1 and K.sub.2 used by the
calculating means upon the correction of the optical performance in the
projection optical system 31 when the illumination methods 1 and 2 having
the strength distribution on the pupil shown in FIGS. 7A and 7B, are
shown.
TABLE 1
______________________________________
Illumination Method
Parameter 1 2
______________________________________
I.sub.o (.mu.m) 1.2 1.1
K.sub.1 (/min) 0.2 0.15
K.sub.2 (/min) 0.2 0.15
______________________________________
In this embodiment, the parameters are properly selected on the basis of
the difference of the illumination method, so that the optical performance
change at the time of the temperature change of the projection optical
system attributable to the ejection light energy absorption, is corrected
in precision, thus permitting high accuracy projection exposure.
The description will be made as to the correction method on the basis of
the results of calculations from the calculating means 54 of FIG. 1. In
this embodiment, the calculating means 54 detects the illumination method
or mode for the reticle 30 on the basis of the signal from the driving
means 50 for driving the aperture shape adjusting member 18. The
calculating means 54 selects the focus coefficients I.sub.o, K.sub.1,
K.s | | |
