U.S. patent application number 09/005003 was filed with the patent office on 2002-02-14 for exposure apparatus and device producing method using the same.
Invention is credited to SUZUKI, TAKEHIKO.
Application Number | 20020018193 09/005003 |
Document ID | / |
Family ID | 27328348 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018193 |
Kind Code |
A1 |
SUZUKI, TAKEHIKO |
February 14, 2002 |
EXPOSURE APPARATUS AND DEVICE PRODUCING METHOD USING THE SAME
Abstract
An apparatus for exposing a wafer to ultraviolet light with a
constant intensity emitted from a super-high pressure mercury lamp
along an exposure beam path. A shutter opens and closes the
exposure beam path. When the mercury lamp cannot be turned off
during non-exposure, the mercury lamp is driven to maintain the
intensity of the ultraviolet light constant when the shutter is
open, and the mercury lamp is driven to maintain current, voltage
or power for driving the mercury lamp constant when the shutter is
closed, thereby decreasing deterioration in the mercury lamp.
Inventors: |
SUZUKI, TAKEHIKO;
(YOKOHAMA-SHI, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
27328348 |
Appl. No.: |
09/005003 |
Filed: |
January 9, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09005003 |
Jan 9, 1998 |
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08324702 |
Oct 18, 1994 |
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08324702 |
Oct 18, 1994 |
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08087264 |
Jul 8, 1993 |
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Current U.S.
Class: |
355/68 |
Current CPC
Class: |
G03F 7/70058 20130101;
G03F 7/70016 20130101; H05B 41/3922 20130101; G03F 7/7055 20130101;
H01J 61/822 20130101 |
Class at
Publication: |
355/68 |
International
Class: |
G03B 027/74 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 1992 |
JP |
4-204285 |
Claims
What is claimed is:
1. An exposure apparatus comprising: a light source for supplying
an exposure beam along an exposure beam path; a shutter for opening
and closing the exposure beam path; and driving means for driving
said light source to maintain intensity of the exposure beam
substantially constant when the exposure beam path is open, and to
maintain current for driving said light source substantially
constant when the path is closed.
2. An exposure apparatus according to claim 1, wherein said driving
means drives said light source so that the current supplied when
the path is closed substantially coincides with the current for
driving said light source immediately before the path is
closed.
3. An exposure apparatus according to claim 2, wherein said light
source comprises a super-high pressure mercury lamp.
4. An exposure apparatus according to claim 3, further comprising
scanning means for simultaneously moving a mask, which is
illuminated by the exposure beam and a substrate, which is exposed
to the exposure beam through said mask, relative to the exposure
beam.
5. An exposure apparatus according to claim 4, further comprising a
photodetector for detecting the intensity of the exposure beam,
wherein said driving means drives said light source to maintain the
intensity of the exposure beam substantially constant, on the basis
of an output of said photodetector, when the path is open.
6. An exposure apparatus according to claim 4, wherein said shutter
is provided between said photodetector and said light source on an
upstream side of said photodetector.
7. An exposure apparatus according to claim 6, wherein said shutter
is provided on a downstream side of said photodetector.
8. An exposure apparatus comprising: a light source for supplying
an exposure beam along an exposure beam path; a shutter for opening
and closing the exposure beam path; and driving means for driving
said light source maintain the intensity of tee exposure beam
substantially constant when the path is open, and to maintain a
voltage for driving said light source substantially constant when
the path is closed.
9. An exposure apparatus according to claim 8, wherein said driving
means drives said light source so that the intensity of voltage
supplied when the path is closed substantially coincides with the
voltage for driving said light source immediately before the path
is closed.
10. An exposure apparatus according to claim 9, wherein said light
source comprises a super-high pressure mercury lamp.
11. An exposure apparatus according to claim 10, further comprising
scanning means for simultaneously moving a mask, which is
illuminated by said exposure beam and a substrate, which is exposed
to the exposure beam through said mask, relative to the exposure
beam.
12. An exposure apparatus according to claim 11, further comprising
a photodetector for detecting the intensity of said exposure beam,
wherein said driving means drives said light source to maintain the
intensity of the exposure beam substantially constant, on the basis
of an output of said photodetector, when the path is open.
13. An exposure apparatus according to claim 12, wherein said
shutter is provided between said photodetector and said light
source on an upstream side of the photodetector.
14. An exposure apparatus according to claim 12, wherein said
shutter is provided on a downstream side of said photodetector.
15. An exposure apparatus comprising: a light source for supplying
an exposure beam along an exposure beam path; a shutter for opening
and closing the exposure beam path; and driving means for driving
said light source to maintain the intensity of the exposure beam
substantially constant when the path is open, and to maintain power
for driving said light source substantially constant when the path
is closed.
16. An exposure apparatus according to claim 15, wherein said
driving means drives said light source so that the power supplied
when the path is closed substantially coincides with the intensity
of the power for driving said light source immediately before the
path is closed.
17. An exposure apparatus according to claim 16, wherein said light
source comprises a super-high pressure mercury lamp.
18. An exposure apparatus according to claim 17, further comprising
scanning means for simultaneously moving a mask, which is
illuminated by said exposure beam and a substrate, which is exposed
to the exposure beam through said mask, relative to the exposure
beam.
19. An exposure apparatus according to claim 18, further comprising
a photodetector for detecting the intensity of the exposure beam,
wherein said driving means drives said light source to maintain the
intensity of the exposure beam substantially constant, on the basis
of an output of said photodetector, when the path is open.
20. An exposure apparatus according to claim 19, wherein said
shutter is provided between said photodetector and said light
source on an upstream side of said photodetector.
21. An exposure apparatus according to claim 19, wherein said
shutter is provided on a downstream side of said photodetector.
22. An exposure apparatus comprising: a light source for supplying
an exposure beam along an exposure beam path; an optical system for
receiving the exposure beam; a first shutter for opening and
closing the exposure beam path, provided downstream of said optical
system in the exposure beam path; and a second shutter for opening
and closing the exposure beam path, provided upstream of said
optical system in the exposure beam path, said second shutter being
opened before said first shutter is opened and being closed after
said first shutter is closed.
23. An exposure apparatus according to claim 22, further comprising
a beam splitter provided between said optical system and said first
shutter to extract a portion of the exposure beam, a photodetector
for receiving a portion of the exposure beam and for detecting the
intensity of the received portion, and driving means for driving
said light source to maintain an output of said photodetector
substantially constant when said second shutter is open.
24. An exposure apparatus according to claim 23, further comprising
scanning means for simultaneously moving a mask, which is
illuminated by the exposure beam and a substrate, which is exposed
to the exposure beam through said mask, relative to the exposure
beam.
25. An exposure apparatus according to claim 24, wherein said
driving means drives said light source to maintain a voltage for
driving said light source substantially constant when the second
shutter is closed.
26. An exposure apparatus according to claim 24, wherein said
driving means drives said light source to maintain a current for
driving said light source substantially constant when the second
shutter is closed.
27. An exposure apparatus according to claim 24, wherein said
driving means drives said light source to maintain a power for
driving said light source substantially constant when the second
shutter is closed.
28. An exposure apparatus according to claim 24, wherein said
driving means drives said light source to maintain substantially
the same power immediately before said second shutter is closed as
is supplied when said second shutter is closed.
29. An exposure apparatus according to claim 24, wherein said
driving means drives said light source to maintain substantially
the same voltage immediately before said second shutter is closed
as is supplied when the second shutter is closed.
30. An exposure apparatus according to claim 24, wherein said
driving means drives said light source to maintain substantially
the same current immediately before said second shutter is closed
as is supplied when the second shutter is closed.
31. An exposure apparatus according to claim 24, wherein said
driving means comprises means for opening and closing said second
shutter during a time when said first shutter is closed.
32. A device producing method comprising the steps of: emitting an
exposure beam from a light source along an exposure beam path;
controlling incidence of the exposure beam on a substrate by
opening and closing the exposure beam path; and printing a device
pattern on the substrate by exposing the substrate to the exposure
beam when the path is open; and driving the light source to
maintain intensity of the exposure beam substantially constant when
the path is open, and to maintain current for driving the light
source substantially constant when the path is closed.
33. A device producing method comprising the steps of: emitting an
exposure beam from a light source along an exposure beam path;
controlling incidence of the exposure means on a substrate by
opening and closing the exposure beam path; printing a device
pattern on the substrate by exposing the substrate to the exposure
beam when the path is open; and driving the light source to
maintain intensity of the exposure beam substantially constant when
the path is open, and to maintain voltage for driving said light
source substantially constant when the path is closed.
34. A device producing method comprising the steps of: emitting an
exposure beam from a light source along an exposure beam path;
controlling incidence of the exposure means on a substrate by
opening and closing the exposure beam path; printing a device
pattern on the substrate by exposing the substrate to the exposure
beam when the path is open; and driving the light source to
maintain the intensity of the exposure beam substantially constant
when the path is open, and to maintain power for driving said light
source substantially constant when the path is closed.
35. A device producing method comprising the steps of: emitting an
exposure beam from a light source along an exposure beam path
through an optical system; controlling incidence of the exposure
means on a substrate by opening and closing the exposure beam path;
providing a first shutter for opening and closing the exposure beam
path downstream of the optical system and a second shutter for
opening and closing the exposure beam path upstream of the optical
system; opening the upstream shutter before opening the downstream
shutter, and closing the upstream shutter after closing the
downstream shutter; and printing a device pattern on the substrate
by exposing the substrate to the exposure beam when the path is
open.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an exposure apparatus and a
device producing method using the exposure apparatus. Particularly,
the present invention relates to a scanning exposure apparatus in
which each portion of a mask pattern is projected on a
corresponding portion of a substrate to be exposed by
simultaneously moving the mask and the substrate relative to an
exposure beam, and a method of producing a device such as a
semiconductor memory, a magnetic head, a liquid crystal panel, a
CCD or the like using the scanning exposure apparatus.
[0003] 2. Description of the Related Art
[0004] FIG. 17 shows an illuminating optical system and a
projection optical system in a reflection type projection exposure
apparatus in which a mask pattern image is transferred to a
substrate coated with a photosensitive material by using
ultraviolet light emitted from a super-high-pressure mercury lamp.
In FIG. 17, the ultraviolet light emitted from a
super-high-pressure mercury lamp 1 is passed through an optical
path formed by an elliptical mirror 2, bending mirrors 4 to 6, lens
7 and a bending mirror 8 and illuminates a slit 9. The ultraviolet
light is converted to a circular arc light by an opening in the
slit 9, is then reflected by a mirror 10 and is divided into two
portions by a half mirror 11. One of the light portions enters a
light quantity monitor sensor 12 for keeping illuminance constant,
and the other portion enters a shutter 13.
[0005] When the shutter 13 is open, the circular arc light is
reflected by mirrors 14 and 15 and is applied to a mask 16. The
light passing through the pattern of the mask 16 is reflected by a
reflection type projection optical system comprising mirrors 17 to
19 and is then directed to a wafer 22.
[0006] Since the above apparatus employs an exposure system in
which the mask and the wafer, which are maintained parallel, are
scanned by the circular arc light at a constant speed, exposure
must be kept constant by keeping the illuminance on an image plane
constant during exposure. In addition, the illuminance on the image
plane must be kept constant at each exposure in order to permit
control of the exposure conditions at a scanning speed in the
exposure process. The super-high-pressure mercury lamp must thus be
maintained lighted in a stable state.
[0007] In order to obtain stable illuminance (luminance) after the
super-high-pressure mercury lamp is lighted (started), the vapor
pressure of mercury in the lamp must be stabilized from the
viewpoint of the structural properties thereof. In the exposure
apparatus, several tens of minutes after starting are required for
stabilizing the lamp. In addition, although a high voltage must be
applied to the lamp at the start, if the power source of the
exposure apparatus is turned on, the super-high-pressure lamp can
be lighted only in a state wherein the power supplied to the
exposure apparatus is off because an error is produced in the
exposure apparatus due to the discharge noise caused by the high
voltage applied to the super-high-pressure mercury lamp. Namely,
the super-high-pressure mercury lamp must be constantly lighted in
a state wherein the exposure apparatus is operated, and it is
necessary and indispensable that the illuminance is kept constant
during a repeated exposure operation.
[0008] As described above, in the exposure apparatus, since the
super-high-pressure mercury lamp is continuously constantly
lighted, the optical parts nearer the super-high-pressure mercury
lamp than the shutter are continuously exposed to the strong
ultraviolet light. The surface of each of the mirrors and lenses
serving as the optical parts is coated with a multilayer film for
controlling the reflectance or transmittance. There are thus
problems that the film is deteriorated due to irradiation with the
ultraviolet light, and that the reflectance or transmittance is
decreased due to the deposition of a gas floating in air above the
film surface, which is caused by strong ultraviolet light.
[0009] In the exposure apparatus, a feedback loop for controlling
the electric power supplied to the super-high-pressure mercury lamp
1 so as to keep the quantity of light entering the light quantity
monitor sensor 12 constant during the repeated exposure operation,
comprises a light quantity monitor sensor 12, a super-high-pressure
mercury lamp 1 and a lighting device (driving device) (not shown)
for the mercury lamp 1, whereby the illuminance on an image plane
(mask surface) can be kept constant. Further, since the emission
efficiency of the super-high-pressure mercury lamp 1 gradually
deteriorates with lighting time, the deterioration is compensated
for by increasing power supply. In this feedback loop, the power
supply is thus continuously increased in view of a long-term
operation. This lighting method is referred to as a "constant
illuminance lighting method".
[0010] If constant illuminance lighting is performed during both
exposure and non-exposure, an electrode deteriorates, and the
transmittance deteriorates due to the adhesion of foreign materials
to the tube surface of the mercury lamp, which is caused by an
increase in the internal temperature, thereby causing a problem
that the performance of the super-high-pressure mercury lamp 1
deteriorates.
SUMMARY OF THE INVENTION
[0011] Accordingly, an object of the present invention is to
provide an exposure apparatus that reduces deterioration in a light
source and an optical system, and a method of producing a device
such as a semiconductor memory, a liquid crystal panel, a magnetic
head, a CCD or the like using the exposure apparatus.
[0012] In order to achieve the object, an exposure apparatus in a
first preferred embodiment comprises a light source for supplying
an exposure beam along an exposure path, a shutter for opening and
closing the exposure beam path, and driving means for driving the
light source to maintain the intensity of the exposure beam
substantially constant when the exposure beam path is open, and to
maintain current for driving the light source substantially
constant when the path is closed.
[0013] In order to achieve the object, an exposure apparatus in a
second preferred embodiment comprises a light source for supplying
an exposure beam along an exposure beam path, a shutter for opening
and closing the exposure beam path, and driving means for driving
the light source to maintain the intensity of the exposure beam
substantially constant when the path is open, and to maintain
voltage for driving the light source substantially constant when
the path is closed.
[0014] In order to achieve the object, an exposure apparatus in a
third preferred embodiment comprises a light source for supplying
an exposure beam along an exposure beam path, a shutter for opening
and closing he exposure beam path, and driving means for driving
the light source to maintain the intensity of the exposure beam
substantially constant when the path is open, and to maintain
electric power for driving the light source substantially constant
when the path is closed.
[0015] In order to achieve the object, an exposure apparatus in a
fourth preferred embodiment comprises a light source for supplying
an exposure beam along an exposure beam path, an optical system for
receiving the exposure beam, a first shutter provided on a
downstream side of the optical system in the exposure beam path,
for opening and closing the exposure beam path, and a second
shutter provided on an upstream side of the optical system in the
exposure beam path, for opening and closing the exposure beam path.
The second shutter is opened before the first shutter is opened and
closed after the first shutter is closed.
[0016] In order to achieve the object, a device producing method in
one preferred embodiment comprises the steps of emitting an
exposure beam from a light source along an exposure beam path,
controlling incidence of the exposure beam on a substrate by
opening and closing the exposure beam path, printing a device
pattern on the substrate by exposing the substrate to the exposure
beam when the path is open, and driving the light source to
maintain intensity of the exposure beam substantially constant when
the path is open, and to maintain the light source current for
driving the light source substantially constant when the path is
closed.
[0017] In order to achieve the object, a device producing method in
another preferred embodiment comprises the steps of emitting an
exposure beam from a light source along an exposure beam path,
controlling incidence of the exposure beam on a substrate by
opening and closing the exposure beam path, printing a device
pattern on the substrate by exposing the substrate to the exposure
beam when the path is open, driving the light source is driven to
maintain intensity of the exposure beam substantially constant when
the path is open, and to maintain voltage for driving the light
source substantially constant when the path is closed.
[0018] In order to achieve the object, a device producing method in
yet another preferred embodiment comprises the steps of emitting an
exposure beam from a light source along an exposure beam path,
controlling incidence of the exposure on a substrate by opening and
closing the exposure beam path, printing a device pattern on the
substrate by exposing the substrate to the exposure beam when the
path is open, driving the light source to maintain intensity of the
exposure beam substantially constant when the path is open, and to
maintain electric power for driving the light source substantially
constant when the path is closed.
[0019] In order to achieve the object, a device producing method in
still another preferred embodiment comprises the steps of emitting
an exposure beam from a light source along an exposure beam path,
controlling incidence of the exposure beam on a substrate by
opening and closing the exposure beam path, providing a first
shutter for opening and closing the exposure beam path on the
downstream side of the optical system and a second shutter for
opening and closing the exposure beam path upstream of the optical
system, the shutter on the upstream side being opened before the
shutter on the downstream side is opened, and closed after the
shutter on the downstream side is closed, and printing a device
pattern on the substrate by exposing the substrate to the exposure
beam when the exposure beam path is open.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a diagram showing the construction of a reflection
type projection exposure apparatus in accordance with first, second
and third embodiments of the present invention;
[0021] FIG. 2 is a timing chart showing the operation timing of
each section of an exposure apparatus in accordance with the first
embodiment of the present invention;
[0022] FIG. 3 is a diagram showing the circuit of a principal
portion of a lighting device in accordance with the second
embodiment for explaining the operation of maintaining electric
power;
[0023] FIGS. 4(a) to 4(h) are diagrams explaining the operation of
maintaining electric power when a mode is switched between constant
illuminance and power holding operation modes by opening and
closing a second shutter in accordance with the second
embodiment;
[0024] FIG. 5 is a timing chart showing an exposure sequence and
the switching timing of control modes of a mercury lamp in
accordance with the second embodiment;
[0025] FIG. 6 is a diagram illustrating changes with time of
electric power and illuminance in the constant illuminance lighting
and constant power holding lighting modes;
[0026] FIG. 7 is a diagram illustrating transient response when
constant power holding lighting is switched to constant illuminance
lighting;
[0027] FIGS. 8 to 10 are each flowcharts illustrating the operation
of the third embodiment of the present invention;
[0028] FIGS. 11 and 12 are schematic diagrams respectively
illustrating the elements of exposure apparatuses in accordance
with modified embodiments of the first to third embodiments of the
present invention;
[0029] FIG. 13 is a diagram illustrating the construction of a
reflection type projection exposure apparatus in accordance with a
fourth embodiment of the present invention;
[0030] FIG. 14 is a diagram illustrating the circuit of a principal
portion of a lighting device of the exposure apparatus shown in
FIG. 13 for explaining the operation of maintaining electric
power;
[0031] FIGS. 15(a) to 15(g) are diagrams explaining the operation
of maintaining electric power when a mode is switched between
constant illuminance and power holding operation modes by opening
and closing a second shutter in the exposure apparatus shown in
FIG. 13;
[0032] FIG. 16 is a timing chart showing an exposure sequence and
the switching timing of control modes of a mercury lamp in the
exposure apparatus shown in FIG. 13; and
[0033] FIG. 17 is a diagram illustrating a conventional reflection
type projection exposure apparatus.
[0034] Like reference numerals have been used throughout the
figures for like or corresponding elements.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] In one embodiment of the present invention, a second shutter
is disposed at a portion as near a super-high pressure mercury lamp
of an illuminating optical system as possible apart from a main
shutter that is disposed far away from the light source. The second
shutter is closed until the exposure operation of an exposure
apparatus is started so that strong ultraviolet light is not
continuously applied to the optical parts disposed in the
illuminating optical system, thereby preventing deterioration in
the film of each optical part and the adhesion of foreign materials
caused by deposition of gases. On the other hand, the
super-high-pressure mercury lamp is lighted with constant
illuminance (constant luminance) on the basis of the output from a
light quantity monitor sensor for detecting the quantity of
illuminating light. In this embodiment, if the light quantity
monitor sensor is positioned behind the second shutter, since no
light enters the light quantity monitor sensor when the second
shutter is closed, not only could the constant illuminance control
of the super-high-pressure mercury lamp not be made, but also the
power supply is increased to an upper limit, thereby causing
deterioration in the super-high-pressure mercury lamp. In this
embodiment, therefore, although the constant illuminance lighting
mode is performed when the second shutter is open, the lighting
mode is switched to a constant current mode, constant power mode,
or constant voltage mode when the second shutter is closed. This
prevents a supply of excessive power to the illumination light
source.
[0036] If there is a great difference between the illuminance in
the constant current, constant power or constant voltage lighting
mode and the illuminance in the constant illuminance lighting mode,
when the constant current, constant power or constant voltage
lighting state is switched to the constant illuminance lighting
state, much time is required for stabilizing the illuminance. When
exposure is immediately performed, unevenness of exposure thus
occurs. Conversely, when exposure is performed after the
illuminance becomes stable, throughput is decreased. In this
embodiment, when the second shutter is closed, constant current or
constant voltage lighting is controlled so that the electric power
supplied immediately before the second shutter is closed is
maintained.
[0037] Furthermore, when the state of the second shutter is changed
from the closed state to the open state, the lighting mode of the
super-high-pressure mercury lamp is switched from the constant
power mode, constant current mode or constant voltage mode to the
constant illuminance mode. At this time, since the emission
efficiency of the super-high-pressure mercury lamp in the constant
power, constant current or constant voltage state deteriorates with
time, the electric power, current or voltage in the constant power
state, constant current state or constant voltage holding state is
increased. When there is a large power difference, current
difference or voltage difference, much time is required for
stabilizing illuminance. During the sequential operation of the
apparatus, the constant power state, constant current state or
constant voltage state must be switched to the constant illuminance
state before an exposure operation is started. At this time, since
unevenness of exposure occurs in an unstable illuminance state,
time is required for stabilizing illuminance, thereby decreasing
throughput. This embodiment is thus provided with an automatic
maintenance function to automatically switch the constant power
mode, constant current mode or constant voltage mode to the
constant illuminance lighting mode and renew the maintained value
of power, current or voltage when the apparatus is idle, whereby
the above problem can be solved. Namely, a function to monitor the
closing time of the second shutter is provided so as to
automatically open the second shutter during idling in the
apparatus sequence when the closing time reaches a set time, and
renew the maintained power, current or voltage, thereby decreasing
the power difference, current difference or voltage difference
produced when the constant power, constant current or constant
voltage lighting is switched to the constant illuminance lighting.
This decreases the stabilization time in response to the switching,
and thus prevents a decrease in throughput.
[0038] In another embodiment of the present invention, the light
quantity monitor sensor is provided between the second shutter and
the super-high-pressure mercury lamp, or a second light quantity
monitor sensor is provided therebetween so that the output from the
light quantity monitor sensor can be supplied to the lighting
device during the closing of the second shutter.
[0039] In still another embodiment of the present invention, the
lighting device for lighting the illumination light source is
designed so that the constant illuminance lighting mode and the
constant power mode, constant current mode or constant voltage
(lighting) mode can be switched, and the electric power or current
at the time of switching from the constant illuminance lighting
mode to the constant power lighting mode or constant current
lighting mode is maintained during the constant power lighting
mode, constant current lighting mode or constant voltage lighting
mode. For example, in a scanning exposure apparatus, although the
constant illuminance lighting must be performed for maintaining
constant illuminance during exposure, no problem occurs during an
operation other than the exposure operation and the operation of
measuring illuminance even if illuminance changes to some extent.
During this operation, therefore, constant power, constant current
or constant voltage maintained at a value at the end of exposure or
of the operation of measuring illuminance is supplied to the
super-high-pressure mercury lamp to light the mercury lamp. The
time interval of an increase in supply power, supply voltage or
supply current is thus increased, and deterioration in the
super-high-pressure mercury lamp is decreased, thereby increasing
the life of the lamp, as compared with the case when the constant
illuminance lighting is continuously made.
[0040] FIG. 1 is a schematic diagram of a reflection type
projection exposure apparatus for producing a device in accordance
with an embodiment of the present invention. In FIG. 1, reference
numeral 50 denotes an illumination system having a light source for
the exposure apparatus and an illumination optical system; and
reference numeral 20, a body having a mechanism for transferring a
mask device pattern to a wafer, an alignment mechanism (not shown)
and a projection optical system comprising parts 17 to 19.
Reference numeral 30 denotes a control box containing a CPU for
controlling the sequential operation of the exposure apparatus; and
reference numeral 40, a lighting device for lighting a
super-high-pressure mercury lamp 1 serving as a light source for
the exposure apparatus and controlling electric power during
lighting. Signal transmission and power supply to each of the units
are performed through cables.
[0041] In the illumination system 50, reference numeral 1 denotes
the super-high pressure mercury lamp as a light source; and
reference numeral 2, a spherical mirror for converging the light
(including ultraviolet rays) emitted from the mercury lamp 1 in the
direction of the set optical path shown by a one-dot chain line.
Reference numeral 3 denotes a second shutter provided apart from a
first shutter 13 to protect the optical parts.
[0042] In the projection exposure apparatus, the second shutter 3
is open during the exposure operation, and the light emitted from
by the mercury lamp 1 and reflected by the spherical mirror 2
travels along the optical path shown by the one-dot chain lines,
passes through mirrors 4, 5 and 6, a condenser lens 7 and a mirror
8 and enters a slit 9. Effective light used for projection exposure
is cut off by the slit 9 to produce slit (for example, circular
arc) light. The slit light is reflected by a concave mirror 10 and
divided by a half mirror 11 into a little portion of the light
which enters a light quantity monitor sensor 12 used for keeping
illuminance constant, and a greater portion of the light which
enters the first shutter 13 serving as an exposure control shutter
of this apparatus. The shutter 13 opens the optical path during
exposure in the operation sequence of the apparatus so that the
slit light is reflected by a mirror 14 and a concave mirror 15, and
is directed to a mask 16. The mask 16 and a wafer 22 are integrally
supported by a carriage 21. When the mask 16 and the wafer 22 are
simultaneously moved, the position of the slit light applied to the
mask 16 relative to the mask 16 and the wafer 22 is also moved, and
the whole device pattern image of the mask 16 is consequently
transferred to the whole surface of the wafer 22. The wafer 22 is
then treated to produce a device. Examples of devices include a
semiconductor memory, a CCD, a magnetic head, a liquid crystal
panel and the like.
[0043] The control box 30 comprises an ROM 31 for storing an
operation sequence program for the whole apparatus, a central
processing unit (CPU) 36 for computing the operation sequence
program and processing the sequence, an RAM 32 for storing
processed data, an interface circuit 33 for inputting and
outputting a signal to an actuator (not shown) for each of the
sections of the apparatus, a carriage driving circuit 34 for
driving an actuator (not shown) so as to move the carriage 21, and
a shutter driving circuit 35 for driving an actuator (not shown) so
as to open and close the exposure control shutter 13 and the second
shutter 3.
[0044] When the lighting device 40 is activated, the mercury lamp 1
is lighted (started) through a starter 43 for applying a high
voltage thereto. The lighting device 40 has two lighting modes
including a mode for lighting the mercury lamp 1 with a constant
current and another mode for lighting with a constant illuminance
(constant luminance). The mercury lamp 1 is in the constant current
mode immediately after lighting (starting).
[0045] In an exposure apparatus in which each of the mask 16 and
the wafer 22 is scanned at a constant speed, the mercury lamp 1
must be used in the constant illuminance mode during the exposure
operation. The lighting mode must be switched to the constant
illumination mode, for example, by a manual operation, for setting
a reference value of illuminance in the constant illuminance mode.
During switching, since no light enters the light quantity monitor
sensor 12 if the second shutter 3 is closed, the second shutter
must be opened. Before the lighting mode is switched to the
constant illuminance mode, the actuator (not shown) is operated by
operating a switch (not shown) provided on the body 20 through the
shutter driving circuit 35 using a special sequence in the sequence
list stored in the ROM 31 through the interface circuit 33 so as to
open the second shutter. In the open state, the mode of the mercury
lamp 1 is switched to the constant illumination mode by operating a
console panel of the lighting device 40. In this state, an
illumination meter is set on the apparatus, and an illumination
reference value is set by operating a dial mounted on the console
panel of the lighting device 40.
[0046] In this embodiment, although the mercury lamp 1 lighted in
the constant illuminance mode during the exposure sequential
operation, the second shutter 3 is closed for protecting the
optical parts in the illumination optical system in a sequential
operation other than the exposure sequential operation and the
operation of measuring illuminance. At this time, if the second
shutter 3 is closed in the constant illumination mode of the
lighting device 40, the internal circuit of the lighting device 40
increases electric power supplied to the mercury lamp 1 to a limit
value due to a decrease in the quantity of light detected by the
light quantity monitor sensor 12, though the output of the light
quantity monitor sensor 12 is constant during constant illumination
control in the exposure sequential operation or the like. In the
exposure apparatus, therefore, this problem is solved by switching
the lighting control modes of the lighting device 40.
[0047] FIG. 2 is a diagram showing the timing of switching between
opening and closing of the exposure shutter 13 and the second
shutter 3 before and after the exposure sequence in the operation
sequence of the apparatus, and the timing of switching between the
constant illumination mode and the constant current mode in
conjunction with the opening and closing operation of the shutters.
In FIG. 2, reference numeral 60 denotes an exposure sequence;
reference numeral 61, carriage movement for scanning exposure;
reference numeral 62, the timing of opening and closing of the
exposure shutter 13; and reference numeral 63, the timing of
opening and closing the second shutter 3. Reference numeral 64
denotes a timing signal of switching between the constant
illumination mode and the constant current mode, and corresponding
to a control mode switching signal 42 input to the lighting device
40 from the interface circuit 33 shown in FIG. 1. Reference numeral
65 denotes the operation timing of the constant illuminance mode,
and reference numeral 66, the operation timing of the constant
current mode.
[0048] In the state shown on the left of the timing chart 63 in
FIG. 2 wherein the second shutter 3 is closed, the constant current
mode of the mercury lamp 1 is turned on, as shown on the left of
the timing chart 66 in the drawing, and the lighting of the mercury
lamp 1 is controlled independently of the signal of the light
quantity monitor sensor 12. The second shutter 3 is opened before
the exposure sequence is started, as shown in the timing chart 63.
The control mode switching signal 42 shown in the timing chart 66
is changed after the second shutter 3 is completely opened (after
t1 seconds), and a signal indicating the change in the state of the
second shutter 3 is transmitted to the lighting device 40 shown in
FIG. 1. When the lighting device 40 receives this signal, the
control mode is automatically changed from the constant current
mode to the constant illuminance mode.
[0049] In the constant illuminance mode, since illuminance is
sometimes different from that in the constant current mode, the
exposure operation is started after elapse of time t2 sufficient to
stabilize the illuminance in a constant state. In the exposure
operation, the carriage 21 shown in FIG. 1 is first moved to a
position on the right of the drawing where no light is applied to
the mask and wafer. The exposure shutter 13 is then opened before
the carriage 21 is moved to the left of the drawing, as shown by
the timing chart 62, and the mask 16 and the wafer 22 are scanned
and exposed at a constant speed by movement of the carriage 21 to
the left of the drawing from the right thereof at a constant speed.
After the whole surfaces of the mask 16 and the wafer 22 are
exposed, the exposure shutter 13 is closed. The control mode
switching signal 42 is then changed after the completion of the
exposure sequence (after t3 seconds) so that the lighting control
mode is switched again to the constant current mode, and the second
shutter 3 is then closed t4 seconds after. Since the illumination
light is cut off by the second shutter 3 until the exposure
sequence is started, the optical parts in the illumination system
and projection optical system are protected. The above operation
sequence is then repeated.
[0050] When the second shutter 3 is closed, the super-high pressure
mercury lamp 1 may be lighted with a constant power or constant
voltage.
[0051] The lighting efficiency of the super-high pressure mercury
lamp 1 decreases with lighting time. Namely, if the supply current,
supply voltage or supply power is constant, the illuminance
(luminance) decreases with lighting time. When the super-high
pressure mercury lamp 1 is lighted with a constant current,
constant voltage or constant power while the set value of current,
voltage or power is fixed, a situation thus sometimes occurs in
which illuminance on constant current lighting, constant voltage
lighting or constant power lighting is greatly different from that
on constant illuminance lighting. If the illuminance on constant
current lighting, constant voltage lighting or constant power
lighting is greatly different from that on constant illuminance
lighting, the constant current lighting state, constant voltage
lighting state or constant power lighting state is switched to the
constant illuminance lighting state, much time is required for
stabilizing illuminance. If exposure is immediately started,
unevenness of exposure occurs. Conversely, if exposure is started
after the illuminance is stabilized, throughput is decreased.
[0052] The second embodiment is designed for preventing the
occurrence of unevenness of exposure and a decrease in throughput.
In an apparatus in accordance with the second embodiment, the
lighting device 40 of the first embodiment shown in FIG. 1 is
improved. The lighting device 40 of the second embodiment has three
lighting modes including a mode of lighting the mercury lamp 1 with
a constant current, a constant illuminance mode of keeping
illuminance constant, and a mode of holding the power supplied
immediately after the second shutter 3 is closed.
[0053] When the lighting device 40 is lighted, the mercury lamp 1
is lighted (started) through the starter 43 for applying a high
voltage thereto. The mercury lamp 1 is in the constant current mode
immediately after being lighted (started). In this apparatus, the
mercury lamp 1 must be used in the constant illuminance mode during
the exposure operation. It is therefore necessary that the lighting
mode is once switched to the constant illuminance mode by a manual
operation for setting a reference value of illuminance. At this
time, if the second shutter 3 is closed, no light enters the light
quantity monitor sensor 12. Thus, the second shutter 3 must be
opened. A switch (not shown) provided on the apparatus body is
operated before the lighting mode is switched to the constant
illuminance mode so that an actuator (not shown) is operated by the
shutter driving circuit using a special sequence in the sequence
list stored in the ROM 31 through the interface circuit 33 to open
the second shutter 3. In this state, an illuminance meter is set on
the apparatus, and the set value of illuminance is set by operating
a dial mounted on a console panel of the lighting device 40.
[0054] In this embodiment, the mercury lamp 1 is lighted in the
constant illuminance mode during the exposure sequential operation,
and the second shutter 3 is closed for protecting the optical parts
in the illumination system in an operational sequence other than in
the exposure sequential operation and the operation of measuring
illuminance. At this time, if the second shutter 3 is closed in the
state where the lighting device 40 is in the constant illuminance
mode, the internal circuit of the lighting device increases the
power supplied to the mercury lamp 1 to a limit value due to a
decrease in quantity of the light detected by the light quantity
monitor sensor 12, though the output of the light quantity is
constant during constant illuminance control. In the apparatus of
this embodiment, the lighting control mode of the lighting device
40 is switched.
[0055] FIG. 3 is a diagram illustrating the circuit used in this
embodiment. The circuit comprises a controlled section 41
comprising a power source 46 and a light source 1, a detector 12
comprising a photodiode for detecting the optical output from a
super-high pressure mercury lamp, which is the output of the
controlled section 41, a first error amplifier 47 for comparing the
detected output signal of the detector 12 with a reference voltage
of a reference power source to output an error signal, a holding
circuit 44, and a second error amplifier 45. Reference numeral 49
denotes an operational amplifier; and reference numeral 50, the
reference power source. Reference numerals 51 and 52 each denote a
buffer amplifier, and reference numeral 53 denotes an operational
amplifier. Reference numerals R1 to R5 each denote a resistor;
reference numerals C1 and C2, a capacitor; and reference numerals
SW1 and SW3, a change-over switch. Reference numeral SW2 denotes a
sampling switch.
[0056] The first error amplifier 47 comprises the operational
amplifier 49, the reference power source 50, the resistors R1 and
R2 and the capacitor C1. The second error amplifier 45 comprises
the operational amplifier 53 and the resistors R3 to R5. The
holding circuit 44 comprises the buffer amplifiers 51 and 52, the
capacitor C2 and the sampling switch SW2. The sampling switch SW2
is operated by a hold signal. Each of the change-over switches SW1
and SW3 is controlled in conjunction with the opening and closing
of the second shutter 3. When the light emitted from the super-high
pressure mercury lamp 1 is cut off by closing the second shutter 3,
the hold signal is supplied to the holding circuit 44, and each of
the change-over switches SW1 and SW3 is controlled so that the
light emitted from the super-high pressure mercury lamp 1 is
intercepted by the second shutter 3 after the switches SW1, SW3 are
switched from a position shown by a solid line with an arrow to a
position shown by a dotted line with an arrow. Conversely, when the
light emitted from the super-high pressure mercury lamp 1 is sent
by opening the second shutter 3, each of the change-over switches
SW1 and SW3 is controlled so as to be switched from the position
shown by a dotted line with an arrow to the position shown by a
solid line with an arrow after the second shutter 3 is opened. This
control function can easily be realized by various logic circuits,
microprocessors or the like.
[0057] The state wherein each of the change-over switches SW1 and
SW3 is switched to the position shown by the solid line with the
arrow while the second shutter 3 is opened is the state wherein
constant illuminance control of the super-high pressure mercury
lamp 1 is carried out by a feedback loop. This state corresponds to
the state wherein the feedback loop is cut when the light emitted
from the super-high pressure mercury lamp 1 is cut off by closing
the second shutter 3. In this state, since each of the change-over
switches SW1 and SW3 is switched to the position shown by the
dotted line with the arrow, the signal output from the first error
amplifier 47 is input to the second error amplifier 45, and is
compared with the hold output signal from the holding circuit 44 as
a reference value to output an error output signal to the first
error amplifier 47. The output signal from the first error
amplifier 47 is thus maintained at a value specified by the hold
output signal of the holding circuit 44.
[0058] FIGS. 4(a) to 4(h) are diagrams explaining the operation of
this embodiment. FIG. 4(a) denotes the opening and closing of the
second shutter 3; FIG. 4(b), the hold signal; FIG. 4(c), the
switching operation of the change-over switch SW1; FIG. 4(d), the
switching operation of the change-over switch SW3; FIG. 4(e), the
detected output signal of the detector 12; FIG. 4(f), the output
signal of the first error amplifier 47; FIG. 4(g), the input signal
of the power source 46; and FIG. 4(h), the electric power supplied
to the light source 1.
[0059] The sampling switch SW2 is operated by the holding signal at
time t1 so that the output signal from the first error amplifier 47
is held in the capacitor C1. The change-over switch SW1 is switched
from the side of the first error amplifier 47 to the side of the
holding circuit 44, as shown by FIG. 4(c). The change-over switch
SW3 is switched from the side of the detector 12 to the side of the
second error amplifier 45, as shown by FIG. 4(d).
[0060] The light emitted from the super-high pressure mercury lamp
1 is intercepted by closing the second shutter 3 at time t2. This
makes the detected output signal of the detector 12 zero, as shown
by FIG. 4(e). At this time, the output signal from the second error
amplifier 45 is input to the first error amplifier 47. Since, in
the second error amplifier 45, the hold output signal of the
holding circuit 44 is input to the (-) terminal of the operational
amplifier 53 through the resistor R4, and the output signal from
the first error amplifier 47 is input to the (+) terminal of the
operational amplifier 53 through the resistor R3, the output signal
from the second error amplifier 45 which is input to the first
error amplifier 47 is a value corresponding to the hold output
signal from the holding circuit 44, and the output signal from the
first error amplifier 47 is maintained at the value of the signal
output immediately before the second shutter 3 is closed. Namely,
for example, the output signal of (1/3)V is maintained, as shown by
FIG. 4(f).
[0061] When the second shutter 3 is opened at time t3, the detected
output signal from the detector 12 is a value corresponding to the
intensity of the light emitted from the super-high pressure mercury
lamp 1, as shown by FIG. 4(e). At this time, since each of the
change-over switches SW1 and SW3 is switched to the position shown
by the dotted line with the arrow, the output signal from the first
error amplifier 47 is maintained in the previous state. When each
of the change-over switches SW1 and SW3 is switched from the
position shown by the dotted line with the arrow to the position
shown by the solid line with the arrow at time t4, the output
signal of the first error amplifier 47 is maintained at the value
of the signal output immediately before the second shutter 3 is
closed. In this case, if the luminance of the light emitted from
the super-high pressure lamp 1 is constant, the output signal of
the first error amplifier 47 is also constant, as shown by FIG.
4(f). Thus, the signal input to the power source is also constant,
and the power supplied to the super-high pressure mercury lamp 1 is
maintained at, for example, a constant value of (2/3) W.
[0062] FIG. 5 is a diagram showing the opening and closing
operation of the exposure shutter 12 and the second shutter 3
before and after the exposure sequence in the operational sequence
of this apparatus, and the timing of switching between the constant
illuminance mode and the constant power holding mode in conjunction
with the opening and closing operation. In FIG. 5, reference
numeral 60 denotes the exposure sequence; reference numeral 61, the
movement of the carriage 21 for scanning exposure; reference
numeral 62, the timing of opening and closing of the exposure
shutter 13; and reference numeral 63, the timing of opening and
closing the second shutter 3. Reference numeral 67 denotes a signal
which indicates the timing of switching between the constant
illuminance mode and the constant power holding mode and which
corresponds to the hold signal 42 shown in FIG. 1 input to the
lighting device 40 from the interface circuit 33. Reference numeral
68 denotes the operation timing of the constant illuminance mode,
and reference numeral 69 denotes the operation timing of the
constant power holding mode.
[0063] In the state shown on the left of the timing chart 63
wherein the second shutter 3 is closed, the constant power holding
mode as a control mode of the mercury lamp 1 is turned on, as shown
on the left of the timing chart 69 in FIG. 5 so that lighting of
the mercury lamp 1 is controlled independently of the output of the
light quantity monitor sensor 12. The second shutter 3 is opened
before the exposure sequence is started, as shown by the timing
chart 63. The hold signal is changed after the second shutter 3 is
completely opened (after t2 seconds) by the operation of an
actuator, and the change in state of the second shutter 3 is
transmitted to the lighting device 40 through the signal 42. When
the lighting device 40 receives the signal 42, the control mode is
automatically switched from the constant power holding mode to the
constant illuminance mode. At the same time, the electric power
supplied to the mercury lamp 1 is also changed.
[0064] FIG. 6 shows changes in illuminance on constant illuminance
lighting and constant power holding lighting for a long time. In
FIG. 6, electric power on constant power lighting is shown by
broken line a, and the corresponding change in illuminance is shown
by broken line c. With a constant power, the illuminance is
decreased due to the gradient deterioration in the lamp efficiency
during long-term lighting. On the other hand, electric power on the
constant illuminance lighting is shown by solid line b, and
illuminance on constant illuminance lighting is shown by solid line
d. This reveals that the deterioration in the lamp efficiency is
compensated for by increasing the electric power.
[0065] FIG. 7 shows changes in illuminance at a time of return to
the constant illuminance state from the constant power holding
state. In FIG. 7, character e denotes illuminance in the constant
power holding state; character f, illuminance after the return to
constant illuminance; and character W, the range of stable
illuminance. Referring to FIG. 7, a time tr is required for
changing the constant power holding state to the constant
illuminance stable state. The operational sequence is thus formed
so that the exposure operation is started after elapse of a time t2
over the response stabilization time tr at switching.
[0066] In the exposure operation, the carriage 21 shown in FIG. 1
is first moved to the right of the drawing to a position where no
light is applied to the surfaces of the mask and the wafer. The
exposure control shutter 13 is then opened (OPEN) before the
carriage 21 is moved to the left of the drawing, as shown in the
timing chart 62. When the carriage 21 is then moved from the right
to the left of the drawing at a constant speed, the mask 16 and the
wafer 22 are scanned and exposed at a constant speed. After the
whole surface of the wafer 22 is exposed, the shutter 13 is closed
(CLOSE). The hold signal 42 is changed after the exposure sequence
is completed (after time t3) so that the lighting control mode is
switched again to the constant power holding mode, and the second
shutter 3 is closed a time t4 after. The optical parts in the
illumination system and the projection optical system are protected
until the exposure sequence is started. The operation sequence is
then repeated.
[0067] In the above embodiment, when the second shutter 3 is
closed, the super-high pressure mercury lamp 1 may be lighted with
a constant current or constant power.
[0068] The above-described time t2 must be as small as possible in
order to prevent a decrease in the throughput of the apparatus.
Thus, the time tr must also be as small as possible. Particularly,
a problem actually occurs when a constant power is held for a long
time. Namely, a problem occurs when a difference in power between
the lighting modes is increased. In the embodiment below,
therefore, the power difference is maintained, and is automatically
compensated for when increasing to a level which causes a problem.
Namely, a function to monitor the closing time of the second
shutter 3 is provided so that the second shutter 3 is automatically
opened and closed during idling in the operation sequence to renew
the held power when the time reaches a set time.
[0069] FIGS. 8 to 10 shows operation sequence in the third
embodiment. In this embodiment, the operation sequence shown in
FIGS. 8 to 10 is added to the exposure sequential processing of the
second embodiment.
[0070] FIG. 8 shows the set timing of a timer. After the second
shutter 3 is closed, the timer is set. Although various setting
methods can be used, a variable set time may be input by a switch
(not shown), or a set time may be input by a console (not
shown).
[0071] FIG. 9 shows the processing of the timer. In the processing,
a timer value is subtracted at constant time intervals in the
interrupt sequence, and a flag is set when the timer value becomes
zero.
[0072] FIG. 10 shows a routine provided at a position where the
apparatus waits for the operation of next processing. The timer
flag is checked, and if the timer value is over the set time, the
second shutter 3 is opened so that the constant power mode is
switched to the constant illuminance mode by the hold signal 42.
After a time delay corresponding to the time the switching
operation of the second shutter 3 and the lighting device 40 is
completed, the constant illuminance mode is switched again to the
constant power holding mode by the hold signal 42. After a time
delay necessary for holding constant power, the second shutter 3 is
closed. This permits an automatic decrease in the power difference
and prevents an increase in the response stabilization time.
[0073] Although, in the above embodiment, constant illuminance
control is switched to constant current or constant power holding
by closing the second shutter 3, a light quantity monitor sensor 70
may be disposed before the second shutter 3 together with or in
place of the light quantity monitor sensor 12, as shown in FIG. 11.
In this case, the lighting mode need not be switched.
Alternatively, a half mirror 72 may be provided in place of the
mirror 4 shown in FIG. 1, and a light quantity monitor sensor 74
may be disposed so as to monitor light through optical fibers 73,
as shown in FIG. 12. In this case, a second shutter 71 is
provided.
[0074] Further, although the maintenance function using a soft
timer is employed in the case when the constant power is held for a
long time, the indicated power value is actually read by an A/D
converter, and a difference in the indicated power value is
corrected by periodically switching the control mode to the
constant illuminance mode so that the same processing as that
performed by using the timer can be made.
[0075] FIG. 13 is a schematic diagram illustrating a reflection
type projection exposure apparatus for producing a device in
accordance with a fourth embodiment of the present invention. In
FIG. 13, reference numeral 60 denotes an illumination optical
system having a light source for the exposure apparatus and an
illumination system; and reference numeral 20, a body having a
mechanism for transferring a device pattern image of a mask to a
wafer, an alignment mechanism (not shown) and a projection optical
system. Reference numeral 30 denotes a control box comprising a CPU
for controlling the sequential operation of the whole exposure
apparatus; and reference numeral 40, a lighting device for lighting
a super-high pressure mercury lamp 1 serving as the light source
for the exposure apparatus and controlling power during lighting.
Signal transmission and power supply to each of the units are made
through cables.
[0076] In the illumination system 60, reference numeral 1 denotes
the super-high pressure mercury lamp, and reference numeral 2
denotes a spherical mirror for converging the light emitted from
the mercury lamp 1 in the direction of the optical path (shown by
one-dot chain lines). The light directly emitted from the mercury
lamp 1 and the light reflected once by the spherical mirror 2
travels through the optical path shown by the one-dot chain lines,
passed through mirrors 4, 5 and 6, a condenser lens 7 and a mirror
8, and enters a slit 9. The slit 9 extracts effective light used
for projection exposure by using the opening thereof to form slit
(circular arc) light. The slit light is reflected by a spherical
mirror 10, and is divided by a half mirror 11 into a little portion
of the light which enters the light quantity monitor sensor 12 used
for keeping illuminance constant during constant illuminance
control, and a greater portion of the light which enters the
exposure control shutter 13. The exposure operation in the
apparatus operation sequence is started, the shutter 13 is opened,
the slit light is reflected by mirrors 14 and 15, and is directed
to the mask 16 disposed on the carriage 21 of the body 20.
[0077] Since the mask 16 and the wafer 22 are integrally supported
by the carriage 21, the position of the mask 16 and the wafer 22
relative to the slit light applied to the mask 16 is moved when the
mask 16 and the wafer 22 are integrally moved by the carriage 21 so
that the whole device pattern image of the mask 16 is transferred
to the whole surface of the wafer 22. The wafer 22 is then treated
to produce a device such as a semiconductor memory, a CCD, a liquid
crystal panel, a magnetic head or the like.
[0078] The control box 30 comprises a ROM 31 for storing an
operational sequence program for the whole apparatus, a central
processing unit CPU 36 for calculating the operational sequence
program and processing the sequence, a RAM 32 for storing processed
data, an interface circuit 33 for inputting and outputting a signal
to an actuator (not shown) of each of the units of the apparatus, a
carriage driving circuit 34 for driving an actuator (not shown) of
the carriage 21 to move the carriage 21, an exposure control
shutter 13 and a shutter driving circuit 35.
[0079] When the lighting device 40 is actuated, the mercury lamp 1
is lighted through a starter 43 for applying a high voltage
thereto. The lighting device 40 has three lighting modes including
a mode of lighting the mercury lamp 1 with a constant current, a
constant illuminance mode for keeping illuminance constant, and a
mode for holding the power supplied immediately before the shutter
13 is closed.
[0080] The mercury lamp 1 is in the constant current mode
immediately after lighting. In this apparatus, the lighting device
40 must be used in the constant illuminance mode during the
exposure operation, as described above with reference to a
conventional example. The control mode must be switched to the
constant illuminance mode once by a manual operation in order to
set a reference value of illuminance. The mode of the mercury lamp
1 is thus switched to the constant illuminance mode by manually
operating the console panel of the lighting device 40. In this
state, an illuminance meter is set on the apparatus, and a
reference value of illuminance is set by operating a dial mounted
on the console panel of the lighting device 40.
[0081] In this embodiment, the mercury lamp 1 is lighted in a
constant illuminance mode during the exposure operation and the
operation of measuring illuminance, and is lighted in the constant
power mode of holding the power supplied in the exposure operation
and the operation of measuring illuminance in other sequential
operations. This increases the time interval of power increase and
thus retards deterioration in the super-high pressure mercury lamp
1, as compared with the case when the constant illuminance mode is
continuously performed.
[0082] FIG. 14 is a diagram showing the circuit used in this
embodiment. The circuit comprises a controlled section 41
comprising a power source 46 and a light source 1, a detector 12
comprising a photodiode for detecting the optical output of the
super-high pressure mercury lamp 1 which is the output of the
controlled section 41, a first error amplifier 47 for comparing the
detected output signal of the detector 12 with the reference
voltage of the reference power source 50 to output an error signal,
a holding circuit 44, and a second error amplifier 45. Reference
numeral 49 denotes an operational amplifier, and reference numeral
50 denotes the reference power source. Reference numerals 51 and 52
each denote a buffer amplifier, reference numeral 53 denotes an
operational amplifier, and reference numeral 54 denotes a delay
circuit for delaying the hold signal 42. Reference numerals R1 to
R5 each denote a resistor; reference numerals C1 and C2, a
capacitor; and reference numerals SW1 and SW3, a change-over
switch. Reference numeral SW2 denotes a sampling switch.
[0083] The first error amplifier 47 comprises the operational
amplifier 49, the reference power source 50, the resistors R1 and
R2, and the capacitor C1. The second error amplifier 45 comprises
the operational amplifier 53, and the resistors R3 to R5. The
holding circuit 44 comprises the buffer amplifiers 51 and 52, the
capacitor C2 and the sampling switch SW2. The sampling switch SW2
is operated by the hold signal. Each of the change-over switches
SW1 and SW3 is controlled in conjunction with a command value
switching signal obtained by delaying the hold signal 42 and output
from the delay circuit 54.
[0084] When the hold signal 42 input to the holding circuit 44 is
turned off, each of the change-over switches SW1 and SW3 is
switched to a position shown by a solid line with an arrow by a
command value switching signal which indicates hold-off. In the
state wherein each of the change-over switches SW1 and SW3 is
switched to the position shown by the solid line with the arrow,
the super-high pressure mercury lamp 1 is controlled with constant
power by a feed back loop. When the hold signal is turned on, since
each of the change-over switches SW1 and SW3 is switched from the
position shown by the solid line with the arrow to the position
shown by the dotted line with the arrow, the output of the holding
circuit 44 is input to the first error amplifier 47. The output
signal from the first error amplifier 47 is thus maintained at a
value specified by the hold output signal from the holding circuit
44.
[0085] FIGS. 15(a) to 15(g) are diagrams explaining the power or
current holding operation in this embodiment. FIG. 15(a) denotes
turning on and off of the hold signal 42; FIG. 15(b), the hold
state; FIG. 15(c), the switching operation of the change-over
switch SW1; FIG. 15(d), the switching operation of the change-over
switch SW3; FIG. 15(e), the output signal of the first error
amplifier; FIG. 15(f), the input signal of the power source 46; and
FIG. 15(g), the power supplied to the super-high pressure mercury
lamp 1.
[0086] The sampling switch SW2 is operated by the hold signal at
time t1 so that the output signal of the first error amplifier 47
is held by the capacitor C1. The change-over switch SW1 is switched
from the side of the first error amplifier 47 to the side of the
hold circuit 44, as shown by FIG. 15(c). The change-over switch SW3
is switched from the side of the detector 12 to the side of the
second error amplifier 45, as shown by FIG. 15(d).
[0087] When the hold signal is then turned on at time t2, the
output signal of the second error amplifier 45 is input to the
first error amplifier 47. Since, in the second error amplifier 45,
the hold output signal of the holding circuit 44 is input to the
(-) terminal of the operational amplifier 53 through the resistor
R4, and the output signal from the first error amplifier 47 is
input to the (+) terminal of the operational amplifier 53 through
the resistor R3, the output signal from the second error amplifier
45 is input as a value corresponding to the hold output signal of
the holding circuit 44, and the output signal from the first error
amplifier 47 is maintained at the value of the signal output
immediately before the hold signal is turned on. Namely, for
example, an output signal of (1/3) V is maintained, as shown by
FIG. 15(e).
[0088] When the hold signal is turned off at time t3, since each of
the change-over switches SW1 and SW3 remains switched to the
position shown by the dotted line with the arrow for time td from
the time t3, the output signal from the first error amplifier 47
maintains the previous state. When each of the change-over switches
SW1 and SW3 is switched from the position shown by the dotted line
with the arrow to the position shown by the solid line with the
arrow at time t4, the output signal from the first error amplifier
47 maintains the value of the signal output before the hold signal
is turned on. When the illuminance of the super-high pressure
mercury lamp 1 is constant, the output signal from the first error
amplifier 47 is also constant, as shown by a solid line in FIG.
15(e). Therefore, the signal input to the power source is also
constant, as shown by a solid line in FIG. 15(f), and the power
supplied to the super-high pressure mercury lamp 1 is maintained at
a constant value of, for example, (2/3) W, as shown by FIG.
15(g).
[0089] FIG. 16 is a diagram showing the opening and closing
operation of the exposure shutter 13 before and after the exposure
sequence in the operational sequence of the apparatus, and the
timing of switching between the constant illuminance mode and the
constant power holding mode in conjunction with the opening and
closing operation. In FIG. 16, reference numeral 60 denotes the
exposure sequence; reference numeral 61, the movement of the
carriage for scanning exposure; and reference numeral 62, the
timing of opening and closing of the exposure shutter. Reference
numeral 67 denotes a signal which indicates the timing of switching
between the constant illuminance mode and the constant power
holding mode and which corresponds to the hold signal 42 input to
the lighting device 40 from the interface circuit 33. Reference
numeral 68 denotes the operation timing of the constant illuminance
mode, and reference numeral 69 denotes the operation timing of the
constant power holding mode.
[0090] When the constant power holding mode of the three control
modes of the mercury lamp 1 is turned on, as shown on the left of
the timing chart 69 in FIG. 16, lighting of the mercury lamp 1 is
controlled independently of the signal from the light quantity
monitor sensor 12. The hold signal shown by the timing chart 67 is
switched t1 seconds before the exposure sequence is started so that
the change in the light mode is transmitted to the lighting device
40 through the signal 42. When the lighting device 40 receives the
signal 42, the control mode is automatically switched from the
constant power holding mode to the constant illuminance mode. Since
the illuminance in the constant illuminance mode is different from
that in the constant power holding mode, the carriage movement
sequence is started after the elapse of time t2 over the response
time on switching.
[0091] In the exposure operation, the carriage 21 shown in FIG. 13
is moved to a position on the right of the drawing where no light
is applied to the mask 16 and the wafer 22. The exposure shutter 13
is then opened with the timing 62 before the carriage 21 is moved
to the left of the drawing, and the mask 16 and the wafer 22 are
then scanned and exposed at a constant speed. After the mask 16 and
the wafer 22 are exposed, the exposure control shutter 13 is
closed. The hold signal shown by the timing chart 67 is changed
after the exposure sequence is completed (after t3 seconds) so that
the lighting control mode is switched again to the constant power
holding mode. The operational sequence is then repeated.
[0092] This embodiment can prevent a continuous increase in the
power of the lamp 1 and thus prevent deterioration in the electrode
of the mercury lamp 1, thereby increasing the life of the mercury
lamp 1. The constant voltage holding mode or the constant current
holding mode may be used in place of the constant power holding
mode.
[0093] Although, in this embodiment, the constant illuminance mode
is used in the exposure sequence of the apparatus and in
measurement of illuminance (or exposure), and the constant power,
constant current or constant voltage mode is used in other
operations, the idle state of the apparatus may be detected so that
the constant illuminance mode is used when the wafer is present in
the apparatus or cassette, i.e., when the apparatus is actually
operated, and the constant power, constant current or constant
voltage mode is used when the wafer 22 is absent, i.e., when the
apparatus is idle.
[0094] Except as other wise disclosed herein, the various
components shown in outline or in block form in the figures are
individually well-known in their internal construction and
operation and are not critical either to the making or using of
this invention or to a description of the best mode of the
invention.
[0095] While the present invention has been described with respect
to what is presently considered to be the preferred embodiments, it
is to be understood that the invention is not limited to the
disclosed embodiments. To the contrary, the invention is intended
to cover various modifications and equivalent arrangements included
within the spirit and scope of the appended claims. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
* * * * *