U.S. patent application number 09/781956 was filed with the patent office on 2001-09-06 for exposure apparatus.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Hagiwara, Shigeru.
Application Number | 20010019399 09/781956 |
Document ID | / |
Family ID | 27526629 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019399 |
Kind Code |
A1 |
Hagiwara, Shigeru |
September 6, 2001 |
Exposure apparatus
Abstract
An exposure apparatus for illuminating a mask pattern and
transferring the image of the pattern onto a photosensitive
substrate comprises a chamber which houses an exposure unit, an
air-conditioner for adjusting the atmosphere in the chamber to a
constant condition, a drain for draining condensate produced in the
air-conditioner, trapping system for temporarily trapping the
condensate before draining it, and a liquid supply system for
supplying clean liquid to the trapping system. A U-tube or a
solenoid valve is provided at a midway position of a drain pipe for
the trapping system to prevent the entry of impurities from the
outside into the apparatus. Otherwise, impurities may be prevented
from entering by interposing a waterproof filter between the
air-conditioner and drain to remove impurities in the condensate
produced in the air-conditioner.
Inventors: |
Hagiwara, Shigeru;
(Kawasaki-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
277 S. WASHINGTON STREET, SUITE 500
ALEXANDRIA
VA
22314
US
|
Assignee: |
NIKON CORPORATION
|
Family ID: |
27526629 |
Appl. No.: |
09/781956 |
Filed: |
February 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09781956 |
Feb 14, 2001 |
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09365022 |
Aug 2, 1999 |
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09365022 |
Aug 2, 1999 |
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08838650 |
Apr 9, 1997 |
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08838650 |
Apr 9, 1997 |
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08712354 |
Sep 11, 1996 |
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Current U.S.
Class: |
355/30 ; 355/53;
355/77 |
Current CPC
Class: |
G03F 7/70858
20130101 |
Class at
Publication: |
355/30 ; 355/53;
355/77 |
International
Class: |
G03B 027/52; G03B
027/42 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 1995 |
JP |
7-259259 |
Sep 12, 1995 |
JP |
7-259260 |
Apr 11, 1996 |
JP |
8-114218 |
Claims
What is claimed is:
1. An exposure apparatus comprising: an exposure unit for
illuminating a mask pattern to transfer an image of the mask
pattern onto a photosensitive substrate; a chamber which houses the
exposure unit, and in which an atmosphere is kept in a
predetermined condition; an air-conditioner for adjusting the
atmosphere in the chamber to the predetermined condition; a drain
for draining condensate produced in the air-conditioner; trapping
system for temporarily trapping the condensate before draining it;
and a liquid supply system for supplying clean liquid continuously
or intermittently to the trapping system.
2. An exposure apparatus according to claim 1, wherein the drain
includes a drain pipe, the trapping system being a U-tube which is
a midway portion of the drain pipe.
3. An exposure apparatus according to claim 2, wherein the U-tube
always holds an amount of liquid which is based on the pressure
difference between the inside of the air-conditioner and the
outside of the apparatus.
4. An exposure apparatus according to claim 1, and further
comprising a detector for directly or indirectly detecting the
amount of the liquid in the trapping system, and a flow controller
for controlling on the basis of the results of the detection by the
detector the quantity of the liquid supplied by the liquid supply
system so that a substantially constant amount of liquid always
stays in the trapping system.
5. An exposure apparatus according to claim 1, wherein the trapping
system is a drain pan interposed between the air-conditioner and
the drain.
6. An exposure apparatus according to claim 1, wherein the
air-conditioner includes a cooler, in which moisture condenses.
7. An exposure apparatus according to claim 1, wherein the clean
liquid is pure water.
8. An exposure apparatus according to claim 1, wherein the
photosensitive substrate is a semiconductor substrate coated with
chemically amplified resist.
9. An exposure apparatus according to claim 1, wherein the trapping
system prevents impurities from entering the exposure apparatus
through the drain from the outside of the apparatus.
10. An exposure apparatus comprising: an exposure unit for
illuminating a mask pattern to transfer an image of the mask
pattern onto a photosensitive substrate; a chamber which houses the
exposure unit, and in which an atmosphere is kept in a
predetermined condition; an air-conditioner for adjusting the
atmosphere in the chamber to the predetermined condition; a drain
for draining condensate produced in the air-conditioner; and a
filter interposed between the air-conditioner and the drain for
removing impurities in the condensate produced in the
air-conditioner.
11. An exposure apparatus according to claim 10, wherein the filter
is a waterproof chemical filter, which can remove impurities in the
condensate produced in the air-conditioner and adsorb impurities
flowing reversely from the drain.
12. An exposure apparatus according to claim 11, wherein the
waterproof chemical filter is made of ion exchange resin.
13. An exposure apparatus according to claim 11, and further
comprising an ion sensor fitted to the waterproof chemical filter
for detecting the concentration of the impurities adsorbed by the
filter.
14. An exposure apparatus according to claim 10, further comprising
trapping system for temporarily trapping the condensate before
draining it, and a liquid supply system for supplying clean liquid
continuously or intermittently to the trapping system.
15. An exposure apparatus according to claim 10, wherein the
air-conditioner includes a cooler, in which moisture condenses.
16. An exposure apparatus according to claim 10, wherein the
photosensitive substrate is a semiconductor substrate coated with
chemically amplified resist.
17. An exposure apparatus according to claim 10, wherein the
trapping system prevents impurities from entering the exposure
apparatus through the drain from the outside of the apparatus.
18. An exposure apparatus according to claim 14, which is a batch
exposure type projection exposure apparatus or a scanning
projection exposure apparatus.
19. An exposure apparatus comprising: an exposure unit for
illuminating a mask pattern to transfer an image of the mask
pattern onto a photosensitive substrate; a chamber which houses the
exposure unit, and in which an atmosphere is kept in a constant
condition; an air-conditioner for adjusting the atmosphere in the
chamber to the constant condition; a trapping system for
temporarily trapping condensate produced in the air-conditioner; a
detector for detecting the amount of the liquid in the trapping
system; a drain path for draining the condensate in the trapping
system to the outside of the exposure apparatus; an opening/closing
mechanism provided in the drain path for opening and closing the
drain path; and a controller for controlling the opening/closing
mechanism according to the amount of the liquid in the trapping
system detected by the detector.
20. An exposure apparatus according to claim 20, which further
includes a cleaning device having a liquid supply system for
supplying a clean liquid continuously or intermittently to the
trapping system, and in which the controller controls the
opening/closing mechanism and the cleaning device.
21. An exposure apparatus according to claim 20, wherein when a
predetermined upper-limit amount of the liquid is trapped in the
trapping system, the controller opens the opening/closing
mechanism; when the liquid in the trapping system has been drained
to less than a predetermined amount, the controller starts liquid
supply from the liquid supply system to the trapping system; and
when the liquid used to clean the trapping system has been drained
to below a predetermined lower-limit amount after cleaning by the
cleaning device is completed, the controller closes the
opening/closing mechanism.
22. An exposure apparatus according to claim 19, which further
includes a pump for forcing the liquid in the trapping system into
the drain path.
23. An exposure apparatus according to claim 19, wherein the clean
liquid is water containing a trace amount of a germicidal
ingredient and substantially free from chemical impurities or
microorganisms.
24. An exposure apparatus according to claim 19, wherein the
opening/closing mechanism is a solenoid valve.
25. An exposure apparatus according to claim 19, wherein the
air-conditioner includes a cooler, and the liquid is condensed in
the cooler.
26. An exposure apparatus according to claim 19, wherein the
photosensitive substrate is a semiconductor substrate coated with a
chemically amplified resist.
27. An exposure apparatus according to claim 19, which is a
one-time exposure type projection exposure apparatus, or a scan
type projection exposure apparatus.
28. An exposure apparatus comprising: an exposure unit for
illuminating a mask pattern to transfer an image of the mask
pattern onto a photosensitive substrate; a chamber which houses the
exposure unit, and in which an atmosphere is kept in a constant
condition; an air-conditioner for adjusting the atmosphere in the
chamber to the constant condition; a trapping system for
temporarily trapping condensate produced in the air-conditioner; a
drain path for draining the condensate in the trapping system to
the outside of the exposure apparatus; and a mechanism provided in
the drain path for preventing a pollutant from entering the
air-conditioner from the outside of the exposure apparatus through
the drain path.
29. An exposure apparatus according to claim 28, wherein the
mechanism for preventing a pollutant from entering the
air-conditioner from the outside of the exposure apparatus through
the drain path is a U-tube, and a liquid supply system for
supplying a clean liquid to the trapping system.
30. An exposure apparatus according to claim 28, wherein the
mechanism for preventing a pollutant from entering the
air-conditioner from the outside of the exposure apparatus through
the drain path is a solenoid valve for opening and closing the
drain path.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an exposure apparatus for
making semiconductor circuits or the like by photolithography, and
in particular to an exposure apparatus suitable for exposure of
photosensitive substrates coated with chemically amplified
resist.
[0003] 2. Description of the Related Art
[0004] A projection exposure apparatus, which is called a stepper,
is used in a photo-lithographic process for making semiconductor
circuits, liquid crystal substrates, or the like. Because the
apparatus needs to control its temperature with a high precision,
it has an air-conditioner for this purpose. Because the
air-conditioner needs to control the temperature within a very
strict range, which may be .+-.0.1 centigrade, with respect to a
set temperature, the air-conditioning system is constructed as a
circulatory system. The air-conditioner needs a fan for air
circulation. To avoid vibration and other problems, the
air-conditioner including a fan needs to be independent of the main
body including a chamber, which houses an exposure unit. FIG. 12 is
a schematic top plan of a conventional exposure apparatus with an
air-conditioner 1 independent of a main body 2. The
air-conditioning system in this type of apparatus is described
below with reference to FIG. 12.
[0005] The main body 2 has a chamber 3 housing an exposure unit,
which includes a reticle R and a projection lens PL. Because an
apparatus for making semiconductors needs to keep clean, there is a
need for the pressure in the chamber 3 to be always positive
relatively to that outside the chamber. The pressure difference
between the inside and outside of the chamber 3 makes air in the
chamber leak out. The leakage needs compensating by supplying air
from the outside. Formed for this purpose is an outside air (OA)
inlet 6 for natural intake through it to normally take in outside
air.
[0006] The air-conditioner 1 includes a cooler 7 having radiation
fins (not shown), a heater 8 and a fan 9. The air returning from
the chamber 3 enters the air-conditioner 1 together with the air
supplied from the outside. The air having entered the
air-conditioner 1 is first cooled by the cooler 7. On the radiation
fins condenses the superfluous moisture brought from the outside by
taking in outside air. The condensate is removed as stated later.
The cooled air is heated to a desired temperature by the heater 8.
The heated air is sent to the main body 2 by the fan 9. A
temperature sensor 11 is fitted downstream from the fan 9. The
values detected by the sensor 11 are sent to a controller (not
shown). Monitoring the output from the sensor 11, the controller
controls the cooler 7 and heater 8 so that the difference between
the output value and a target temperature is zero. Thus, the
temperature is adjusted by feedback control.
[0007] The main body 2 also includes a HEPA (high efficiency
particle air) box 13 having a HEPA filter 10. To maintain the
cleanliness of the air in the chamber 3, the air having passed
through the air-conditioner 1 is cleaned by the filter 10 before
supplied to the chamber 3.
[0008] Positioned below the cooler 7 is a drain pan 4, to which a
drain pipe 5 is connected. The moisture condensed by the cooler 7
is collected by the pan 4. The collected water is drained through
the pipe 5 from the apparatus.
[0009] Recently, it has been found that a very small amount of gas
in a clean room atmosphere affects the reduction projection
exposure apparatus or other apparatus for making semiconductors in
the atmosphere. This is explained below more specifically.
[0010] Sometimes insufficient is the luminance of the light sources
of excimer laser exposure apparatus with an excimer laser used as
the light source, X-ray exposure apparatus, electron beam exposure
apparatus, etc. To cope with the insufficiency by virtue of the
high sensitivity of resist, chemically amplified sensitive resist
is used. This resist contains an acid-generating agent as the
photosensitive agent in it. The acid generated by exposing the
resist induces catalytic reaction in the succeeding heat treatment
(PEB). This accelerates the insolubilization (negative type) or the
solubilization (positive type) in developer of the resist. For
example, if a chemically amplified resist is positive, a very small
amount of basic gas of a ppb level in the atmosphere neutralizes
the acid catalyst generated on the resist surface, and forms a
layer which makes the surface slightly soluble. After development
by exposure, the resist cross section, which should otherwise be
rectangular, has T-shaped eaves. Because a chemically amplified
resist, which is a sensitive resist, cannot be used as it is, it
may need overcoating, so that the throughput lowers.
[0011] As the wave length of exposure light has been shorter and
the illuminance has been higher, such a problem has been occurring
that a very small amount of gas in the atmosphere deposits or
precipitates as a clouding substance on the surfaces of
illumination system members. This is due to the photochemical
interaction between the exposure light and the small amount of gas
in the atmosphere. The reactant may be ammonia gas or sulfur oxide
in the air, an organosilicic compound, or the like. The clouding of
illumination system members results in remarkably low illuminance,
so that the throughput is reduced.
[0012] U.S. Pat. No. 5,430,303 discloses a chemical filter for
removing chemical substances, as means for removing a very small
amount of gaseous impurities in a clean room atmosphere.
[0013] Because a very small amount of such gas exists originally in
a clean room, it is desired to remove the gas by some means before
the gas enters an exposure apparatus. The removal is difficult,
however, due to the structure of the air-conditioner of the
apparatus. Specifically, the air-conditioner is open to the outside
through the drain piping, which is essential for temperature
control. In addition, the heater and cooler of a typical exposure
apparatus are positioned immediately upstream from the fan because
of the apparatus structure. Because of the fan characteristics, the
pressure in the drain pan of the apparatus is negative (about -30
mmAq.) relatively to the atmospheric pressure. As a result, the
following disadvantages arise.
[0014] 1. The drain piping is connected finally to other devices in
the semiconductor manufacturing factory where the apparatus is
installed. The pressure in the drain pan is negative relatively to
the atmospheric pressure. When no water stays in the pan, gaseous
impurities from a manufacturing device in the factory may flow
through the piping into the apparatus.
[0015] 2. Chemical substances are produced in the atmospheres of
other manufacturing devices by chemical processes of alkaline, acid
or other treatment in the devices. very small amounts of the
substances may dissolve in the air-conditioner drainage of the
devices. Such substances of a ppb level may probably flow through
the drain piping into the exposure apparatus. As far as piping
systems are not drains for drainage containing highly concentrated
chemical substances, chemical contamination of apparatus has been
given no particular consideration in many of them. The
air-conditioner drain piping system of an exposure apparatus may be
connected to a clean room atmosphere outside the apparatus.
[0016] 3. Depending on apparatus installation conditions,
condensate from the cooler of an exposure apparatus may always stay
in the drain pan. In such a case, although no outside air directly
enters the apparatus through factory piping, impurities in the
outside air may indirectly enter through the staying condensate. A
problem arises any way.
[0017] 4. The condensate staying in the drain pan does not flow out
for a long time due to the negative pressure. Therefore, a very
small amount of gas in the circulating air dissolves in the staying
condensate. After the solution is concentrated, microorganisms etc.
may propagate in it. Thus, the condensate may be a secondary source
of gas affecting the exposure apparatus, even if the influence of
factory piping is small.
SUMMARY OF THE INVENTION
[0018] It is the object of the present invention to provide an
exposure apparatus which can solve the problems in the conventional
art, prevent outside impurities from flowing reversely through the
drain and air-conditioner of the apparatus into the apparatus and
therefore effectively restrain the production of a layer making the
surface of a chemically amplified resist slightly soluble, the
decrease in illuminance due to a clouded optical material, and so
on.
[0019] According to the first aspect of the invention, there is
provided an exposure apparatus comprising:
[0020] an exposure unit for illuminating a mask pattern to transfer
an image of the mask pattern onto a photosensitive substrate;
[0021] a chamber which houses the exposure unit, and in which an
atmosphere is kept in a constant condition;
[0022] an air-conditioner for adjusting the atmosphere in the
chamber to the constant condition;
[0023] a drain for draining condensate produced in the
air-conditioner;
[0024] trapping system for temporarily trapping the condensate
before draining it; and
[0025] a liquid supply system for supplying clean liquid
continuously or intermittently to the trapping system.
[0026] In the exposure apparatus of the invention, during
air-conditioning in the air-conditioner, the condensate from a
cooler of the air-conditioner is collected temporarily in the
trapping system. At the same time, the trapping system is supplied
with clean liquid such as clean water continuously or
intermittently by the supply system. Therefore, a sufficient amount
of water stays always in the trap, and the water in the trap keeps
flowing out. Consequently, the impurities dissolved in the drainage
including the condensate will be diluted, so that it is possible to
prevent them from being concentrated. It is also possible to
prevent the impurities from being concentrated in the trap. In
addition, because clean water flows always into the trap from
upstream, substances contained in the water in the trap keep
discharged. Therefore, it is possible to prevent impurities from
entering indirectly through the piping system downstream from the
trap. In other words, it is possible to prevent these impurities
from being released again. In this specification, the terms "clean
liquid" and "clean water" respectively mean the liquid and water in
which the impurities such as ammonia and/or microorganisms have
been removed to at least a ppb level.
[0027] In the exposure apparatus of the invention, it is preferable
that the drain include a drain pipe, and that the trapping system
be a U-tube which is a midway portion of the pipe. The U-tube
always holds the amount of liquid which is based on the pressure
difference between the inside of the air-conditioner and the
outside of the apparatus. The trapping system being the U-tube, it
is possible to securely collect in the trapping system a constant
amount of water, which is based on the difference between the
inside and outside pressures, without using a special controller or
the like, if clean water flows together with the condensate into
the trapping system from upstream. The portion of the water in
excess of the constant amount keeps flowing out.
[0028] The trapping system may be a drain pan interposed between
the air-conditioner and drain. The drain pan may be structured to
receive the condensate from the air-conditioner. The drain pan may
be connected to the inlet end of the drain pipe. The drain pan is
advantageous if the exposure apparatus is installed on a solid
floor, where there is no sufficient difference of elevation for
forming a U-shaped piping portion as stated above. In such a case,
it is preferable that there be such an amount of water in the pan
that the water surface in the drain pan is always higher than the
top of the inlet end of the drain piping. This can prevent air
which contains impurities from reversely flowing directly into the
apparatus from the piping downstream from the drain pan. In such a
case, by supplying the drain pan with clean water continuously or
intermittently, polar molecules such as ammonia which are highly
soluble in water dissolve in the water in the drain pan, and are
discharged from the exposure apparatus. Therefore, the drain pan
functions as a quasi-chemical filter.
[0029] It is preferable that the exposure apparatus comprise a
detector for directly or indirectly detecting the amount of the
liquid in the trapping system, and a flow controller for
controlling on the basis of the results of the detection by the
detector the quantity of the liquid supplied by the liquid supply
system so that a substantially constant amount of liquid always
stays in the trapping system. The detector for directly detecting
the amount of liquid may be a level sensor for detecting the height
of the water surface in the trapping system. The detector for
indirect detection may be a flow sensor for detecting the flow rate
of the water flowing out of the trapping system, or a flow sensor
for detecting the total flow of the water, which includes the
condensate, flowing into the trapping system. By thus providing the
detector and the flow controller, the quantity of water supplied
from the supply system is controlled so that there is a nearly
constant amount of water always in the trapping system. Therefore,
if the trapping system is a drain pan, it is possible to set the
amount of water so that the water surface in the pan is always
higher than the top of the inlet end of the drain piping. It is
also possible to keep the flow rate at a certain value or higher so
that no water in the drain pan stagnates.
[0030] According to the second aspect of the invention, an exposure
apparatus comprising:
[0031] an exposure unit in which a mask pattern is illuminated and
its image is transferred onto a photosensitive substrate;
[0032] a chamber which houses the exposure unit, and in which an
atmosphere is kept in a constant condition;
[0033] an air-conditioner for adjusting the atmosphere in the
chamber unit to the constant condition;
[0034] a drain for draining condensate produced in the
air-conditioner; and
[0035] a filter interposed between the air-conditioner and the
drain for removing impurities in the condensate produced in the
air-conditioner.
[0036] In the exposure apparatus of the invention, the filter can
remove impurities in the condensate, and adsorb gaseous impurities
which have entered from outside through the drain channel of the
drain, and therefore prevents them from entering the exposure unit.
Consequently, it is possible to effectively prevent impurities from
being accumulated at the drain channel inlet, where a drain pan is
fitted in general.
[0037] The filter may be a waterproof chemical filter, which may be
fitted at the end of the drain channel, which is adjacent to the
air-conditioner, in such a manner that the filter constitutes a
partition between the inside of the air-conditioner and the inside
of the drain channel. The drain channel interconnects the
air-conditioner and the outside of the apparatus. It is preferable
that the structure of the chemical filter be so devised or adapted
that the pressure loss of the filter is set at a large value to
some extent. In such a case, the filter itself is a trap, which
prevents polluted air from flowing reversely from the drain
pipe.
[0038] An ion sensor may be fitted to the filter. The sensor can
detect the concentration of the impurities adsorbed by the filter.
Consequently, it is possible to judge the filter life, and
therefore judge exactly when to replace the filter.
[0039] According to the third aspect of the invention, there is
provided an exposure apparatus comprising:
[0040] an exposure unit for illuminating a mask pattern to transfer
an image of the mask pattern onto a photosensitive substrate;
[0041] a chamber which houses the exposure unit, and in which an
atmosphere is kept in a constant condition;
[0042] an air-conditioner for adjusting the atmosphere in the
chamber to the constant condition;
[0043] a trapping system for temporarily trapping condensate
produced in the air-conditioner;
[0044] a detector for detecting the amount of the liquid in the
trapping system;
[0045] a drain path for draining the condensate in the trapping
system to the outside of the exposure apparatus;
[0046] an opening/closing mechanism provided in the drain path for
opening and closing the drain path; and
[0047] a controller for controlling the opening/closing mechanism
according to the amount of the liquid in the trapping system
detected by the detector.
[0048] When the air-conditioner performs an air-conditioning
operation while the opening/closing mechanism is closed, the
condensate from the air-conditioner, especially, a cooler of the
air-conditioner, is collected temporarily in the trapping system.
The amount of the liquid collected in the trapping system is
monitored by the detector. The controller controls the
opening/closing mechanism according to the amount of the liquid in
the trapping system that was detected by the detector. Normally,
therefore, a reverse flow of dirty air containing pollutants from
the downstream side of the drain path can be blocked by closing the
opening/closing mechanism. When a certain amount of the liquid
(condensate) accumulates in the trapping system, on the other hand,
the opening/closing mechanism is opened to drain the liquid
collected in the trapping system to the outside through the drain
path. By so doing, it becomes possible to prevent an undesired
degree of buildup of the pollutants in the liquid collected in the
trapping system.
[0049] Depending on the environment where the exposure apparatus is
installed, the humidity of the atmosphere makes a difference. This
produces a difference in the amount of the liquid collected in the
trapping system. According to the present invention, by contrast,
the amount of the liquid in the trapping system is monitored by the
detector. The controller can control the opening/closing mechanism
according to this amount. Therefore, the amount of the liquid in
the trapping system is not affected by the environment of
installation.
[0050] The exposure apparatus, the third aspect of the invention,
further includes a cleaning device having a liquid supply system
for supplying a clean liquid continuously or intermittently to the
trapping system. The controller can control the opening/closing
mechanism and the cleaning device, for example, in the following
manner: As mentioned above, the opening/closing mechanism is opened
to drain the liquid in the trapping system through the drain path.
When this liquid has been drained off (or the liquid remaining in
the trapping system reaches a certain amount), the controller
controls the cleaning device so that a clean liquid is supplied by
the liquid supply system continuously (or intermittently) to the
trapping system for cleaning purposes. The cleaning liquid washes
the trapping system. Even if the concentration of the impurities in
the trapping system occurs somewhat, the concentrated impurities
will be washed away, and can thus be prevented from being released
again from there.
[0051] In the exposure apparatus as the third aspect, when a
predetermined upper-limit amount of the liquid is trapped in the
trapping system, the controller opens the opening/closing
mechanism. When the liquid in the trapping system has been drained
to reach less than a predetermined amount, the controller starts
liquid supply from the liquid supply system to the trapping system.
After cleaning by the cleaning device is completed, the liquid used
to clean the trapping system is drained. When this liquid has been
drained to reach below a predetermined lower-limit amount, the
controller can close the opening/closing mechanism.
[0052] In other words, the controller opens the opening/closing
mechanism when the predetermined upper-level amount of the liquid
has been accumulated in the trapping system. As a result, the
liquid accumulated in the trapping system is drained to the outside
through the drain path. When the liquid in the trapping system has
been drained to less than a predetermined amount, liquid supply by
the liquid supply system to the trapping system is started by the
controller. As a result, the trapping system is washed with a
cleaning liquid. This washing is carried out using, say, a certain
amount of clean water. During this procedure, the opening/closing
mechanism remains open. After cleaning (washing) by the cleaning
device is completed, the liquid used for the cleaning of the
trapping system is drained. At a time when this liquid has been
drained to less than the predetermined lower-level amount, the
controller closes the opening/closing mechanism. After that, the
opening/closing mechanism is never opened until a certain amount of
the liquid is accumulated in the trapping system.
[0053] According to the above-described constitution, the cleaning
liquid flows through the drain path during cleaning (washing). A
certain time after completion of cleaning, a flow of this cleaning
liquid nearly vanishes. At a time when this has occurred, and after
then, the opening/closing mechanism keeps closed. Thus, reverse
flow of the impurities from the piping system downstream from the
trapping system can be prevented nearly without fail.
[0054] The exposure apparatus as the third aspect may further
include a pump for forcing the liquid in the trapping system into
the drain path. The air-conditioner is in a vacuum in order to
circulate clean air into the exposure apparatus. Thus, simply by
opening the opening/closing mechanism to leave the drain path open,
not all of the liquid accumulated in the trapping system may be
drained promptly. Even under these circumstances, the liquid in the
trapping system can be forced by the drain pump into the drain
path. Because of this constitution, the dwell time of the liquid in
the trapping system can be shortened, even when the vacuum of the
air-conditioner is high. Consequently, the dissolution and
concentration of the impurities can be minimized.
[0055] In the exposure apparatus as the third aspect, the clean
liquid may be water containing a trace amount of a germicidal
ingredient and substantially free from chemical impurities or
microorganisms. The chemical impurities refer, for example, to
nitrogen compounds which chemically change into substances, such as
ammonia gas, that will cause T-shaped deformation of a chemically
amplified resist upon photochemical interaction. The microorganisms
include, for example, bacteria. The freedom from the chemical
impurities or microorganisms refers, for instance, to the removal
of them to a ppb level or less. A typical example of the germicidal
ingredient is hydrogen peroxide. The use of such water can restrain
the multiplication of microorganisms in the trapping system, and
also prevent the chemical change of chemical impurities, such as
the conversion of nitrogen compounds into ammonia, etc.
[0056] According to the fourth aspect of the invention, there is
provided an exposure apparatus comprising:
[0057] an exposure unit for illuminating a mask pattern to transfer
an image of the mask pattern onto a photosensitive substrate;
[0058] a chamber which houses the exposure unit, and in which an
atmosphere is kept in a constant condition;
[0059] an air-conditioner for adjusting the atmosphere in the
chamber to the constant condition;
[0060] a trapping system for temporarily trapping condensate
produced in the air-conditioner;
[0061] a drain path for draining the condensate in the trapping
system to the outside of the exposure apparatus; and
[0062] a mechanism provided in the drain path for preventing a
pollutant from entering the air-conditioner from the outside of the
exposure apparatus through the drain path.
[0063] In the exposure apparatus as the fourth aspect, the
mechanism for preventing a pollutant from entering the
air-conditioner from the outside of the exposure apparatus through
the drain path may be a U-tube, and a liquid supply system for
supplying a clean liquid to the trapping system; or may be a
solenoid valve for opening and closing the drain path.
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] Preferred embodiments of the present invention are shown in
the accompanying drawings, in which:
[0065] FIG. 1 is a schematic top plan view of an exposure apparatus
according to the first embodiment;
[0066] FIG. 2 is a fragmentary view in vertical cross section of
the apparatus of FIG. 1, showing the structure near the drain
pan;
[0067] FIG. 3 is a vertical cross section showing the principle of
the trap of FIG. 2;
[0068] FIG. 4 is a vertical cross section of the trap of FIG.
2;
[0069] FIG. 5 is a fragmentary view in vertical cross section of an
exposure apparatus according to the second embodiment;
[0070] FIG. 6 is a conceptual view in vertical cross section of the
air-conditioner of an exposure apparatus according to the third
embodiment;
[0071] FIG. 7 is a vertical cross section of the chemical filters
and other parts in the air-conditioner of an exposure apparatus
according to the fourth embodiment; and
[0072] FIG. 8 is a schematic view of the structure of the exposure
unit of an exposure apparatus according to the fifth
embodiment;
[0073] FIG. 9 is a fragmentary view in vertical cross section of
the exposure apparatus according to the fifth embodiment, showing
the structure near the drain pan;
[0074] FIG. 10 is a fragmentary view in vertical cross section of
the exposure apparatus according to the fifth embodiment using a
floating water-level sensor, showing the structure near the drain
pan;
[0075] FIG. 11 is a fragmentary view in vertical cross section of
the exposure apparatus according to the fifth embodiment, showing
the washing of the drain pan by the cleaning device; and
[0076] FIG. 12 is a schematic plan view showing the structure of
the air-conditioner and the main body of the conventional exposure
apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0077] First Embodiment
[0078] The first embodiment of the present invention is described
below with reference to FIGS. 1-4. In FIGS. 1-4 and FIG. 12, which
shows the conventional art, the same numerals and symbols represent
identical or equivalent components or parts.
[0079] The exposure apparatus shown in FIG. 1 is a projection
exposure apparatus, which is generally called a stepper and used to
make semiconductor circuits by photo-lithography. In general, this
type of apparatus is installed in a factory for making
semiconductor devices or elements. The apparatus consists of an
air-conditioner 1 and a main body 2. The body 2 has a chamber 3
housing an exposure unit, which includes a reticle R and a
projecting optical system PL. The exposing unit also includes a
light source, a lighting system, a stage and a wafer, which are not
shown. The light source, which may be an excimer laser or a mercury
(vapor) lamp, can radiate exposure light. The light is arranged by
the lighting system, which includes lenses and a mirror, so as to
have required wave length, magnitude and illuminance uniformity.
The arranged light illuminates the reticle R having a specified
pattern formed in it. The pattern is then transferred through the
optical system PL to the wafer as an exposed substrate laid on the
stage. The wafer is coated with chemically amplified resist. The
environmental conditions (cleanliness, temperature, pressure,
humidity, etc.) in the chamber 3 are kept nearly constant. The
details of the body 2 may be the same as described in U.S. Pat. No.
5,430,303 or U.S. Pat. No. 5,194,893, which discloses a scanning
exposure apparatus. The disclosures of these patents are
incorporated as part of the description herein by reference.
[0080] An HEPA (high efficiency particle air) box 13 is fitted to
the inlet of the body 2, that is, upstream (right side in FIG. 1)
of the chamber 3. Fitted in the box 13 is an HEPA filter 10 for
cleaning the air flowing into the chamber 3. Fitted upstream of the
filter 10 is a chemical filter 16 for preventing the chemically
amplified resist from being "T-shaped", as disclosed in U.S. Pat.
No. 5,430,303. The chemical filter 16 is an air filter for removing
chemical substances, and may have any mechanism and material for
removing impurities.
[0081] Fitted near the chemical filter 16 in the HEPA box 13 is a
temperature sensor 11 for temperature control as stated later.
Formed on the downstream side (left side in FIG. 1) of the chamber
13 is a return passage 12 for returning the air in the chamber 13
into a return duct 14.
[0082] The air-conditioner 1 for air-conditioning in the chamber 3
includes a cooler 7, a heater 8 and a fan 9. As best shown in FIG.
2, a drain pan 4 is positioned below the cooler 7 to drain the
moisture condensed on radiation fins (not shown). The pan 4 is
connected to one end of a drain pipe 5.
[0083] The interior of the chamber 3 is kept under positive
pressure to maintain its cleanliness. Consequently, air leaks out
of the chamber 3 through the clearances at the front side of the
chamber, an in-line interface (not shown), etc. To compensate the
leakage, outside air is taken in through an outside air inlet port
6, which is formed in a side wall of the apparatus and communicates
with the return duct 14. In order to prevent the chemically
amplified resist from being "T-shaped" and for other purposes, a
chemical filter 17 is fitted in the port 6. The filter 17 is
similar to the chemical filter 16, and can take in only clean air
into the apparatus by removing chemical substances (impurities) in
the air taken in through the port 6. Because dust from the filter
17 may enter the apparatus, an HEPA filter 19 is fitted inward or
downstream from the filter 17 in the port 6. If the pressure loss
of the HEPA filter 19 itself is large, it is preferable to
interpose fans 18 between the filters 17 and 19 in order to secure
a required supply of air.
[0084] The air-conditioning of the apparatus is explained below.
The air which has flowed through the chamber 13 is returned through
the return passage 12 into the return duct 14. The returned air
enters the air-conditioner 1 together with the outside air taken in
through the OA port 6. The mixed air which has entered the
air-conditioner 1 is first cooled by the cooler 7. The radiation
fins condense the superfluous moisture brought from the outside
with the air taken in. The condensed moisture is removed. The
cooled air is heated to a desired temperature by the heater 8. The
heated air is supplied by the fan 9 to the main body 2.
[0085] The chemical filter 16 and HEPA filter 10 clean the air
which has entered the main body 2. As a result, the chamber 3 is
supplied with only the air of high cleanliness, which contains no
fine particles. Similarly to the conventional art, the temperature
of the air supplied from the air-conditioner 1 to the body 2 is
adjusted by the feedback control with a controller (not shown),
which controls the cooler 7 and heater 8 on the basis of the output
from the temperature sensor 11.
[0086] As shown in FIG. 2, the drain pipe 5 has a trap 15 in the
form of a U-shaped portion of the pipe, which constitutes a water
collector. The trap 15 prevents outside air from entering from the
piping downstream or outward of the drain against the temperature
control drainage discharged from the apparatus through the pipe 5.
The principle of the trap 15 is explained below with reference to
FIG. 3. As shown in FIG. 3, there is a pressure difference between
the end points A and B of a U-tube. It is assumed that the pressure
at the point A is higher by .DELTA.P [mmAq.] than that at the point
B. If there is no water in the tube, the air flows in accordance
with the pressure gradient. If there were no pressure difference
with water in the tube, the water surfaces would balance with each
other at a height h of the water columns. The pressure difference
.DELTA.P [mmAq.] between the points A and B moves the surfaces by
1/2.DELTA.P from the height h, resulting in a difference of
elevation .DELTA.P [mm] between the surfaces. Therefore, a trap of
the tube which can resist the pressure difference .DELTA.P [mmAq.]
needs to contain such an amount of water that the height h of the
balanced water surfaces is greater than .DELTA.P/2, as shown in
FIG. 3. In fact, because the drainage through the trap 15 needs to
flow into piping of a factory, the shape of the trap 15 is like an
inverted S, as shown in FIG. 2.
[0087] The fan 9 keeps the pressure in the air-conditioner 1
negative in comparison with the pressure outside the
air-conditioner. If the pressure difference between the inside and
outside of the air-conditioner 1 is .DELTA.P [mmAq.], the water
surface on the inner side of the trap 15, which is provided
outside, is higher by .DELTA.P [mm] than the height ho of the water
surface on the outer side, as shown in FIGS. 2 and 4. For this
reason, the height h (FIG. 2) between the height ho and the bottom
of the inner end of the drain pipe 5 is sufficiently greater than
.DELTA.P [mm].
[0088] As shown in FIG. 2, a collecting funnel 23 is positioned
over the drain pan 4. The bottom of the funnel 23 is fitted with a
flow sensor 20. One end of pure water supply piping 21 extends
through a side wall of the funnel 23. The piping 21 is made of
chemically stable clean material. The funnel 23 is always supplied
with a small quantity of pure (clean) water cleaned chemically
through a filter (not shown) in the piping 21. The drain pan 4 is
supplied with the pure water mixed in the funnel 23 with the drops
of dew from the cooler 7.
[0089] Normally, the superfluous moisture in the atmosphere is
condensed into drops of water by the cooler 7 in the
air-conditioner 1. The drops are collected in the drain pan 4. The
water in the pan 4 flows through the drain pipe 5 to the trap 15.
In some environments where pieces of exposure apparatus are
installed, little moisture condenses. In such a case, air polluted
with impurities such as a very small amount of other gas may flow
reversely through the drain pipe. According to this embodiment,
however, the pan 4 is always supplied with pure water cleaned
chemically through a filter (not shown). Consequently, it is
possible to supply the trap 15 with a sufficient quantity of water
through the pipe 5. As a result, polluted air can be prevented from
flowing into the apparatus.
[0090] Contrariwise, if an exposure apparatus is installed in an
environment where a large quantity of moisture condenses, deposit
or sludge from the cooling fins of the cooler or a very small
quantity of gas in the atmosphere may dissolve in the water in the
drain pan, so that the impurities in the water may be more
concentrated. According to this embodiment, however, the drain pan
4 is always supplied with pure water, with which to dilute the
impurities dissolved in the drainage. It is therefore possible to
prevent the impurities from being concentrated in the pan 4.
[0091] The outlet of the pure water supply piping 21 has a flow
sensor 24 for detecting the flow rate of the pure water supplied
through the piping 21 to the collecting funnel 23. The piping 21
has a solenoid valve 22 for adjusting the supply flow rate of the
pure water through the piping 21.
[0092] The trap 15 cannot function if at least a certain amount of
water is not kept in it. In addition, if only a small quantity of
water flows into the trap 15, the water stagnates in it for a long
time. Such disadvantages can be avoided or overcome by a controller
25 monitoring the outputs from the flow sensors 24 and 20, and
controlling the solenoid valve 22 so that at least a certain
quantity of water flows into the drain pan 4, and eventually into
the trap 15. The controller 25 and valve 22 constitute a flow
control system.
[0093] As described above, clean water is made to flow always to
the trap 15 from the drain pan 4 etc. upstream of the trap 15 so as
to keep a certain amount of water in the trap 15. In addition, the
substances contained in the water in the trap 15 keep discharged,
so that the impurities brought from the piping system downstream of
the trap 15 can be prevented from entering indirectly, that is,
being released again.
[0094] By fitting the chemical substance removal filter in the
internal circulatory system of the apparatus, the life of the
system can be fairly long. If there were no space for the
collecting funnel 23, the funnel 23 might be omitted with the flow
sensor 20 fitted in the inlet of the drain pipe 5.
[0095] In this embodiment, while the flow sensors 20 and 24 are
detecting the supply flow rate of pure water and the flow rate of
the water supplied to the drain pan 4, pure water keeps supplied.
The invention, however, is not limited to the embodiment. The
control system could be simplified by omitting the collecting
funnel 23 and the sensors 20 and 24, and instead using a timer etc.
to intermittently supply pure water from the supply piping 21. For
example, pure water may be supplied in the order of one liter at a
time per hour. Otherwise, the apparatus might be so adapted that
the operator can arbitrarily supply water.
[0096] Instead of supplying pure water inside the apparatus, pure
water might be supplied outside it, for example, at the piping 5.
It is important to form a trap downstream from the drain piping in
order to prevent outside air from entering from the piping
downstream of the drain. Therefore, if there were a plurality of
air-conditioning systems and drain pipes, the pipes would need to
each have a trap, and to meet together downstream from the
traps.
[0097] Second Embodiment
[0098] The second embodiment of the invention is described below
with reference to FIG. 5. In FIG. 5, the components identical or
equivalent to those of the conventional art and first embodiment
are assigned the same numerals as used in FIG. 1, and are briefly
explained or not explained. FIG. 5 shows main part of this
embodiment. With reference to FIG. 5, the collecting funnel 23 and
flow sensors 20 and 24 of the first embodiment are omitted. Pure
water is supplied from the pure water supply piping 21 directly to
the drain pan 4. The flow rate of the water flowing from the pan 4
to the drain pipe 5 is detected by a flow sensor 25, which is
fitted in the inlet of the pipe 5. The structure of the other parts
is identical with that of the first embodiment.
[0099] As shown in FIG. 5, clean water is supplied so that water
always stays in the drain pan 4 to such a degree that the water
surface in the pan 4 is higher than the top of the inlet of the
drain pipe 5. In order for the water in the pan 4 not to stagnate,
the flow sensor 25 detects the drainage flow rate so that at least
a certain amount of water always exists in the pan 4. Thus, the pan
4 itself functions as a water collector equivalent to the trap 15
of the first embodiment.
[0100] By supplying water to the drain pan 4 of this embodiment
continuously or intermittently, polar molecules such as ammonia,
which has high solubility, dissolve in the water at any time and
are discharged with it from the apparatus. Therefore, the pan 4
functions as a quasi-chemical filter.
[0101] As stated above, the drain pan 4 itself of this embodiment
functions equivalently to the trap 15 of the first embodiment.
Therefore, similarly to the first embodiment, it is possible to
prevent impurities from factory piping from entering the exposure
apparatus, and the impurities in the pan 4 from being concentrated.
As a result, the chemical atmosphere in the apparatus can always be
kept clean. The apparatus of this embodiment is effective
particularly if it is installed on a solid floor where the
difference of elevation required for forming a trap cannot be
secured.
[0102] The flow sensor 25 for detecting the drainage flow rate
constitutes a detector. Instead, a detector might be constituted by
a level sensor for detecting the water surface in the drain pan 4.
In short, it is sufficient to be able to check that a certain
amount of water exists in the pan 4 as a water collector, and that
the pan 4 functions equivalently to the trap 15 of the first
embodiment.
[0103] Third Embodiment
[0104] In the conventional exposure apparatus, the superfluous
moisture in the atmosphere is normally condensed by the cooler 7 in
the air-conditioner 1, and collected into the drain pan 4. If the
apparatus is installed in an environment where little moisture
condenses, air polluted with impurities such as a very small amount
of other gas may flow reversely through the drain pipe 5. In an
environment where a large quantity of moisture condenses, deposit
or sludge from the cooling fins of the cooler 7 or a very small
quantity of gas in the atmosphere may dissolve in the water in the
pan 4, so that the impurities in the water may be more
concentrated. These disadvantages can be avoided or overcome by
this embodiment adopting different structure for the
air-conditioner from those of the first and second embodiments.
[0105] FIG. 6 conceptually shows the structure of the
air-conditioner 1 in vertical cross section along the line A-A of
FIG. 1. The basic structure of the main body and air-conditioner of
the exposure apparatus according to this embodiment is as shown in
FIG. 1. Explained below are the points of the air-conditioner which
differ from those in the first and second embodiments. As shown in
FIG. 6, the air-conditioner 1 of this embodiment includes a drain
pan 4 for receiving the drops of dew produced on the radiation fins
(not shown) of a cooler 7. A waterproof chemical filter 15 is
placed on top of the pan 4. The filter 15 divides the interior of
the air-conditioner 1 from the drainage channel consisting of the
pan 4 and a drain pipe 5, which is connected to the pan 4. The
junction between the filter 15 and pan 4 is sealed so sufficiently
that outside air, even if it flows reversely from the pipe 5 toward
the apparatus, passes all through the filter 15 before it enters
the apparatus.
[0106] The chemical filter 15 adsorbs gaseous impurities flowing
reversely from downstream of the drain pan 4, in order to prevent
them from entering the main body. The filter 15 also removes
impurities contained in the drops of dew falling from the radiation
fins of the cooler 7, in order to prevent impurities from being
accumulated and concentrated in the pan 4. For these purposes, the
filter 15 is a chemical substance adsorption filter, which is a
filter for both gas and liquid, and which does not lose its
function when wet with water. For example, the filter 15 may be a
waterproof chemical filter made of ion exchange resin or the like,
which adsorbs and removes ammonia and other polar substances (a
type of impurity). The waterproof chemical filter might be made of
activated carbon or other adsorbent.
[0107] The fan 9 keeps the pressure in the air-conditioner 1
negative. In order to prevent air downstream of the drain pipe 5
from flowing reversely due to the pressure difference between
inside and outside, the pressure loss .DELTA.PF of the chemical
filter 15 itself is set to be large to some extent so that the
filter 15 serves the same as a piping trap. If the filter 15 is
made of fiber of ion exchange resin in the form of layers of
pleated cloth, the adsorption capacity, pressure loss .DELTA.PF and
trap(ping) effect of the filter 15 increase with the number of
layers and the number of pleats. If the pressure loss is large, it
is difficult for vapor phase substances to move. There is no
problem, however, because the condensate from the cooler 7 is moved
toward the drain pan 4 by penetration or permeation. As the moister
which a chemical filter of ion exchange resin holds becomes large,
the reactivity of polar substances such as ammonia and amines are
accelerated. Therefore, this embodiment is advantageous also in
terms of removal of polar substances and other impurities.
[0108] As stated above, the waterproof chemical filter 15 placed
over the drain pan 4 can prevent impurities from factory piping
from entering the apparatus, and the impurities in the pan 4 from
being concentrated. As a result, the chemical atmosphere in the
apparatus can keep clean. Therefore, the life of the internal
circulatory system of the apparatus can be fairly long by fitting
the system with the chemical substance removal filter.
[0109] Fourth Embodiment
[0110] FIG. 7 shows modifications in structure of the chemical
filter 15 and drain pan 4 of the third embodiment. As shown in FIG.
7, a semiconductor ion sensor 20 is fitted between two chemical
filters 15 in order for the operator to know when the filters
should be replaced.
[0111] The semiconductor ion sensor 20 may have an ion selective
electrode (film) for detecting the concentration of NH.sub.4.sup.+
instead of a metal electrode for the gate of a MOSFET. Impurities
penetrate through the upper chemical filter 15 from the top and
through the lower filter 15 from the bottom. The sensor 20 between
the filters 15 detects the ion concentration of the ppm order at
it, so that a warning device (not shown) such as a lamp and a
buzzer makes the operator know when to replace the filters. The
order of the concentration at which the filters should be replaced
is high in consideration of actual circumstances etc. One of the
circumstances is that, as a chemical filter is more contaminated
and adsorbs more impurities, the concentration of the impurities in
it becomes higher. The other circumstance is that it is not
possible for a semiconductor ion sensor, because of its performance
or sensitivity, to accurately detect ion concentration lower than
the ppm order. According to this embodiment, it is possible to
judge accurately when to replace the waterproof chemical filters
15.
[0112] Fifth Embodiment
[0113] The exposure apparatus of this embodiment has constituent
elements in common with the exposure apparatus of the first
embodiment, and thus its description uses FIG. 1. The same
constituent elements as in the first embodiment are assigned the
same numerals and symbols as used therein. As shown in FIG. 1, the
exposure apparatus consists of two parts, an air-conditioner 1 and
a main body 2.
[0114] The main body 2 has a chamber 3, which houses an exposure
unit (to be described later on) for transferring a pattern of a
reticle R as a mask via a projecting optical system PL onto a
substrate to be exposed. The environmental conditions (cleanliness,
temperature, pressure, humidity, etc.) in the chamber 3 are kept
nearly constant.
[0115] FIG. 8 schematically shows the structure of an exposure unit
20. The exposure unit 20 comprises a substrate stage 22 bearing a
substrate to be exposed, W, such as a wafer, and moving in a
horizontal plane two-dimensionally; a drive system 24 for driving
the substrate stage 22; a projecting optical system PL disposed
above the substrate W with its optical axis AX being normal to the
moving plane of the stage 22; a reticle stage RS disposed above the
projecting optical system PL for holding a reticle R parallel to
the moving plane of the stage 22; and an illumination system 30
disposed above the reticle R.
[0116] A moving mirror 28 is fixed onto the substrate stage 22. The
two-dimensional coordinate position of the substrate stage 22,
i.e., the position of the substrate W, is measured by a laser
interferometer 26 which casts a laser beam on the moving mirror 28.
The positional information obtained by means of the laser
interferometer 26 is fed to a stage controller 38 which controls
the position of the substrate stage 22 via the drive system 24.
Above the substrate W, an off-axis alignment sensor 32 is disposed
for detecting an alignment mark formed on the substrate W. The
output of this alignment sensor 32 is also supplied to the stage
controller 38.
[0117] The illumination system 30 includes a light source 34, and
an illuminating optical system 36 having various lenses, mirrors,
blinds, and aperture stops (none shown). The light source 34 is an
excimer laser such as a laser from KrF (wavelength 248 nm) or ArF
(wavelength 193 nm). In harmony with this, the instant embodiment
uses as the substrate W to be exposed a substrate, such as a wafer,
coated on its surface with a chemically amplified resist for
excimer light. The reason for this use is as follows: When excimer
light is projected onto a novolak resin, absorption by the resist
rein is so great that adequate energy does not reach the bottom
layer of the resist, thereby minimizing resolution. Thus, a highly
transparent resin should be used, but such a resin has low
sensitivity. A contrivance for increasing the sensitivity is
required. A means of imparting increased sensitivity is the use of
a chemically amplified resist for excimer light, the resist showing
a chemical amplification effect.
[0118] According to the exposure unit 20, the stage controller 38
aligns the substrate W with the reticle R by use of the alignment
sensor 32 to perform exposure in the following manner: Exposing
light emitted by the light source 34 is configured to the required
wavelength, size and illuminance uniformity while passing through
the illuminating optical system 36. Then, this light illuminates
the reticle R. A circuit pattern formed on a pattern surface PA of
this reticle R is transferred through the projecting optical system
PL to the substrate w to be exposed that is laid on the substrate
stage 22.
[0119] Returning to FIG. 1, an HEPA box 13 is fitted to the inlet
of the body 2, that is, upstream (right side in FIG. 1) of the
chamber 3. Inside the HEPA box 13, an HEPA filter 10 is provided
for cleaning air flowing into the chamber 3. In the instant
embodiment, moreover, a chemical filter 16 as used in the first
embodiment is provided upstream from the HEPA filter 10.
[0120] Near the chemical filter 16 in the HEPA box 13, a
temperature sensor 11 is disposed for temperature control to be
described later on.
[0121] On the most downstream side (left side in FIG. 1) of the
chamber 13, a return passage 12 is formed for returning the air in
the chamber 13 into a return duct 14.
[0122] The air-conditioner 1, a constituent part for
air-conditioning in the chamber 3, includes a cooler 7, a heater 8
and a fan 9. Below the cooler 7 and deep in the sheet face of FIG.
1, a drain pan 4 is positioned as a water reservoir for receiving
and draining the moisture condensed on radiation fins (not shown).
The drain pan is connected to one end of a drain pipe 5
constituting a drain path.
[0123] In the apparatus of this embodiment, a solenoid valve 40 as
an opening/closing mechanism is provided at a midway position of
the drain pipe 5, as illustrated in FIG. 9. The opening and closing
of this solenoid valve 40 are controlled by a controller 25. The
reason for the provision of the solenoid valve 40 midway in the
drain pipe 5 is as follows:
[0124] Normally, superfluous moisture in the atmosphere is
condensed into drops of water by the cooler 7 in the
air-conditioner 1. The drops are collected in the drain pan 4. The
water in the drain pan 4 flows through the drain pipe 5 in a
downstream direction. Depending on the environment where the
exposure apparatus is installed, little moisture is condensed. If
the drain pipe 5 is kept open in this situation, air polluted with
impurities such as traces of gases may flow reversely into the
drain pan 4 through the drain pipe 5. Thus, the solenoid value 40
is provided in the drain pipe 5, and is normally kept closed. The
closure of the drain path in the drain pipe 5 can prevent the
polluted air from entering the apparatus.
[0125] Assume that the solenoid valve 40 is closed in a normal
condition in which superfluous moisture in the atmosphere is
condensed into drops of water by the cooler 7 in the
air-conditioner 1 as stated above. Over time, the condensate builds
up in the drain pan 4. If left as such, the accumulated water
overflows the drain pan 4. A prolonged dwell time of the
accumulated water in the drain pan 4 would accelerate the
concentration of the impurities in the condensate in the drain pan
4. These situations should be avoided. Thus, when more than a
certain level of water accumulates in the drain pan 4, it is
necessary to open the solenoid valve 40, discharging the collected
water to the outside through the drain pipe 5.
[0126] Under these circumstances, the apparatus of this embodiment
is equipped with a water level sensor 42 at a predetermined
latitudinal position inside the drain pan 4. This water level
sensor 42 serves as a detector for detecting whether or not the
level of water accumulated in the drain pan 4 has reached a certain
value. An example of the water level sensor 42 is a semiconductor
sensor, such as an ISFET (ion-selective field-effect transistor),
which detects the presence or absence of the direct contact of
water with the sensor electrode. The output of this water level
sensor 42 is monitored by the controller 25. The controller 25
performs control in such a manner as to open the solenoid valve 40
when the water level sensor 42 turns on.
[0127] Besides the above sensor that detects whether the liquid
level of water accumulated in the drain pan 4 has reached a certain
value, the water level sensor may be a floating water level sensor
43 as shown in FIG. 10. When this water level sensor 43 is used, it
produces an output signal corresponding to the position of the
float in the sensor (liquid level). Thus, the controller 25 becomes
able to monitor fluctuations in the liquid level over time. This is
convenient. In the same sense, the water level sensor may be a
noncontact level sensor, such as an ultrasonic level sensor.
[0128] In the instant embodiment, furthermore, a piping 44 for
cleaning is laid horizontally as a liquid supply system at an upper
place of the drain pan 4, as shown in FIGS. 9 and 11. This cleaning
piping 44 comprises a pipe with wash ports (exhaust nozzles) 46 for
cleaning water that are formed at predetermined intervals in the
longitudinal direction. Supply and cutoff of water from the water
source to the cleaning piping 44 are carried out by a solenoid
valve (not shown). This solenoid valve is controlled by the
controller 25. As illustrated in FIG. 11, the cleaning piping 44
and the solenoid valve (not shown) constitute a cleaning device
which sprays cleaning water (washing water) in a shower over the
bottom surface, etc. of the drain pan 4 through the wash ports 46,
to clean the inside of the drain pan 4.
[0129] Returning to FIG. 1, the interior of the chamber 3 is kept
under positive pressure to maintain its cleanliness. Consequently,
air leaks to the outside from the front surface of the chamber 3,
an in-line interface (not shown), etc. To compensate for this
leakage, the outside air is taken in through an outside air inlet
port (OA port) 6, which is formed in a side wall of the apparatus
and communicates with the return duct 14. With the apparatus of
this embodiment, in order to prevent the chemically amplified
resist from being "T-shaped" and for other purposes, a chemical
filter 17 is fitted in the OA port 6. This filter 17 is similar to
the chemical filter 16, and can take only clean air into the
apparatus by removing chemical substances (impurities) in the air
to be taken in through the OA port 6. Since dust from the chemical
filter 17 may enter the apparatus, an HEPA filter 19 is disposed
inward or downstream of the filter 17. If the pressure loss of the
HEPA filter 19 itself is large, fans 18 as shown in FIG. 1 are
preferably interposed between the chemical filter 17 and the HEPA
filter 19 in order to secure a required supply of air.
[0130] The air-conditioning of the exposure apparatus constructed
as above is described. The air that has passed through the chamber
13 is returned through the return passage 12 into the return duct
14. The returned air enters the air-conditioner 1 together with the
outside air taken in through the OA port 6, the outside air supply
port. The mixed air that has entered the air-conditioner 1 is first
cooled by the cooler 7. The superfluous moisture carried with the
outside air that has been taken in is condensed by radiation fins
(not shown). The condensed moisture is removed. Then, the cooled
air is heated to a desired temperature by the heater 8. The heated
air is supplied by the fan 9 to the main body 2.
[0131] The air that has entered the main body 2 is cleaned by the
chemical filter 16 and the HEPA filter 10. Only the highly clean
air free from fine particles is supplied to the chamber 3.
[0132] Similar to the aforementioned earlier technologies, the
temperature of the air supplied from the air-conditioner 1 to the
main body 2 is adjusted by feedback control exercised by a
controller (not shown). In the feedback control, the controller
controls the cooler 7 and heater 8 on the basis of output from the
temperature sensor 11.
[0133] The condensate produced by the radiation fins is collected
in the drain pan 4. The level (liquid level) of water accumulated
in the drain pan 4 is always monitored by the water level sensor 42
(or 43). The output of this water level sensor 42 (or 43) is
monitored by the controller 25. When the liquid level reached a
predetermined upper level (concretely, the level at point A in
FIGS. 9 and 10), the water level sensor 42 (or 43) detects this
fact. Based on the output of the water level sensor 42 (or 43), the
controller 25 opens the solenoid valve 40 to render the drain pipe
5 open. As a result, the water accumulated in the drain pan 4 is
discharged to the outside of the apparatus through the drain pipe
5.
[0134] A predetermined period of time after the opening of the
solenoid valve 40, the controller 25 opens the solenoid valve (not
shown) constituting the cleaning device, thereby initiating the
spraying of cleaning water through the wash ports 46 of the piping
44 for cleaning (see FIG. 11). The spraying of cleaning water need
not be continuous, but may be intermediate. The cleaning water is
clean water in which impurities, such as ammonia, or microorganisms
have been removed, at least, to a ppb level or less.
[0135] The above predetermined period of time is the time required
for the water in the drain pan 4 to be drained out. In this case,
the start of water spraying is performed, for example, by timer
control. Alternatively, when a water level sensor, such as the
water level sensor 43 in FIG. 10 is used, the predetermined period
of time refers to the time taken for the level detected by the
water level sensor 43 to reach a certain value. In other words, the
start of water spraying may be controlled by a timer; otherwise,
the controller 25 may monitor fluctuations in the output of the
water level sensor 43, and shift to a water spraying operation when
the change in the output reaches nearly a certain value.
[0136] Spraying of clean water (cleaning water) is intended to wash
the drain pan 4. The flow rate of water and the duration of water
spraying for the purpose of washing can be set at arbitrary values
depending on the environment where the apparatus is installed.
[0137] During water spraying, the internal wall of the drain pan 4
may be cleaned physically using a scrub means such as a rotary
brush (not shown). It is permissible to raise the pressure of
cleaning water in the cleaning piping 44, thereby ejecting a jet
stream through the wash ports 46. It is also acceptable to combine
an ultrasonic wave with cleaning water, thereby increasing the
efficiency of washing. A scrub means may be further combined with
these means to raise the washing efficiency further.
[0138] As the cleaning water, there may be used clean water in
which impurities, such as ammonia, or microorganisms have been
removed, at least, to a ppb level or less, and which contains a
trace amount of a germicidal substance such as hydrogen peroxide.
In this case, the multiplication of microorganisms in the drain pan
4 can be inhibited, and the chemical change of nitrogen compounds
into ammonia, etc. can be prevented.
[0139] The pressure in the air-conditioner 1 is kept negative. The
degree of negative pressure is governed by the degree of sealing of
the air-conditioner 1 and the main body 2. At a high degree of
sealing, water may fail to be completely discharged from the drain
pan 4, simply by opening the solenoid valve 40 to open the drain
pipe 5. In this view, it is advisable to provide a drain pump 50
(see FIG. 10), such as a water pump mechanism, in the drain pan 4,
thereby forcing the water in the drain pan 4 to the outside.
[0140] In either case, the solenoid valve 40 continues to be opened
until the amount of water in the drain pan 4 decreases to less than
a predetermined lower-level amount after stoppage of water
spraying. The predetermined lower-level amount may be a value
representing the liquid level corresponding to the lower limit that
can be measured by the water level sensor 43 of FIG. 10, if it is
used. This is because some water may remain undischarged owing to
the negative pressure inside the air-conditioner 1. In this case,
the water in the drain pan 4 may be forced out by the water pump
mechanism 50 after stopping water spraying.
[0141] After the drain pan 4 is washed and the water inside is
discharged, the controller 25 closes the solenoid valve 40.
[0142] The amount of water (water level) in the drain pan 4 that
determines the timing of opening the solenoid valve 40 needs to be
set separately depending on the environment where the exposure
apparatus is installed. This is because the impurities in the
atmosphere in the exposure apparatus dissolve and become
concentrated in the water in the drain pan 4. Concretely, the rate
of accumulation of water in the drain pan 4 differs according to
the environment of installation of the exposure apparatus. If the
amount of water (water level), the basis for discharge, is fixed,
the dwell time of water in the drain pan 4 will differ. In a low
humidity environment of installation, the dwell time will be
prolonged to accelerate the concentration of the impurities. Hence,
it is desired to determine the amount of water with which to start
drainage from the drain pan 4, so that the dwell time of water in
the drain pan 4 will become constant. That is, in the case of FIG.
9, the position of mounting (height) of the water level sensor 42
is determined by the environment of installation of the exposure
apparatus. In the case of FIG. 10, the position of point A is
determined by the environment of installation of the exposure
apparatus.
[0143] In such an extremely low humidity environment of
installation that no water is condensed in the cooler 7, the
solenoid valve 40 may always be closed.
[0144] The foregoing methods can prevent not only the entry of
pollutants from the outside of the apparatus, but also the
concentration of impurities in the drain pan 4. They can also
prevent the secondary pollution that the concentrated impurities
are released again.
[0145] In the above-described constitution, the solenoid valve may
be replaced by an ordinary manual valve. In this case, the operator
opens or closes the valve, and begins an operation for spraying
cleaning water. Thus, the task of the controller 25 is merely to
display the amount of water in the drain pan 4 and a message to the
operator about instruction on work; or to display only the amount
of water. The frequency of washing may also be set arbitrarily.
[0146] If there are a plurality of air-conditioning systems, and
the drain piping is divided into a plurality of pipings, then there
is need to dispose the solenoid valve in each piping.
[0147] According to the exposure apparatus of the instant
embodiment, as described above, the solenoid valve 40 provided in
the drain pipe 5 is normally closed. This inhibits the entry into
the apparatus of pollutant-containing outside air from downstream
of the drain pipe 5. The amount of water in the drain pan 4 is
monitored by the water level sensor 42 (or 43), and the solenoid
valve 40 is opened by the controller 25 with such a timing that the
dwell time of water is not prolonged. Each time the solenoid valve
40 is opened, the condensate is discharged, and the drain pan 4
washed. Thus, the concentration and recurrent release of impurities
in the environmental atmosphere can be diminished. While the
solenoid valve 40 is open, reverse flow of pollutants from
downstream can be prevented. Hence, it becomes possible to
effectively restrain hazards, such as the formation of a layer
making the surface of a chemically amplified resist slightly
soluble, and the decrease in illuminance due to a clouded optical
material. Furthermore, the above-described mechanisms act to flush
out the impurities in the atmosphere in the exposure apparatus.
Thus, when a filter for removing chemical substances is fitted in
the internal circulation system of an exposure apparatus, its life
can be extended.
[0148] According to the first, second and fifth embodiments,
impurities are removed by means of the water collector and water
supplier. According to the third and fourth embodiments, impurities
are removed by means of the chemical filters. Otherwise, a water
collector, a water supplier and a chemical filter might be used in
combination to more effectively prevent impurities from entering
the apparatus from outside.
[0149] The present invention has been described in detail by
showing the embodiments, to which it is not limited. The invention
includes modifications and improvements obvious to those skilled in
the art, within the scope of the appended claims. According to each
of the embodiments, pure water is supplied to the drain pan.
Otherwise, a liquid composed of ingredients which mix with water
and are not impurities against the manufacture of semiconductors
might be used. The waterproof chemical filters may be made of
various materials in accordance with the environment where the
exposure apparatus is used and the type of the photo resist used
with the apparatus (in accordance with the impurities to be
removed).
[0150] The exposure body of the exposure apparatus can be applied
to, not only projection exposure apparatus called a stepper, but
also scanning exposure apparatus of the batch scanning type,
step-and-scan type, etc. for making liquid crystal substrates,
aligner type exposure apparatus, mirror projection exposure
apparatus, and any other exposure apparatus.
[0151] In the foregoing first to fifth embodiments, an excimer
laser was used as the source of exposure light, and a chemically
amplified resist for excimer light was used as a photosensitive
material adapted to this use. However, the scope of application of
the present invention is in no way restricted thereto. Imagine, for
example, an exposure apparatus using a mercury lamp or the like as
an exposure light source, e.g., a projection exposure apparatus,
such as a stepper, using i-rays as exposure light. In this type of
exposure apparatus, modified illumination may be performed in
exposing a contact hole. That is, the aperture stop of an
illumination system is not an ordinary circular diaphragm, but an
aperture stop with a much smaller aperture (so-called small a
diaphragm). At this time, the sensitivity of the resist should be
increased to compensate for the insufficient quantity of light. For
this purpose, a chemically amplified resist may be coated onto a
substrate. As noted above, the present invention is effective in
any cases in which a chemically amplified resist needs to be used
depending on the light source, lighting conditions, etc.
[0152] As stated above, the water collector and the water supply
system for supplying water to the collector can prevent impurities
from indirectly entering the exposure apparatus from outside, and
the impurities in the collector from being concentrated. In
addition, the chemical filters remove impurities in the condensed
moisture, and adsorb gaseous impurities which have entered through
the drainage channel from outside, so that the gaseous impurities
are prevented from entering the exposure body. This effectively
prevents impurities from accumulating at the inlet of the drainage
channel. It is therefore possible to keep the chemical atmosphere
in the apparatus clean, and effectively restrain the occurrence of
evils such as the occurrence of a layer which makes the surface of
a chemically amplified resist slightly soluble and a decrease in
illuminance due to a blur in an optical material.
* * * * *