U.S. patent application number 12/382986 was filed with the patent office on 2009-07-30 for projection exposure apparatus, projection exposure method, and method for producing device.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Yoshitomo Nagahashi.
Application Number | 20090190113 12/382986 |
Document ID | / |
Family ID | 34386108 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090190113 |
Kind Code |
A1 |
Nagahashi; Yoshitomo |
July 30, 2009 |
Projection exposure apparatus, projection exposure method, and
method for producing device
Abstract
A projection exposure apparatus transfers a pattern formed on a
mask onto a substrate via a projection optical system. The
projection exposure apparatus includes electricity removal units
which removes electricity from a liquid supplied to a space between
the projection optical system and the surface of a substrate. This
makes it possible to prevent destruction of the circuit pattern or
malfunction of the device which would otherwise caused by charging
of the liquid.
Inventors: |
Nagahashi; Yoshitomo;
(Takasaki-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
34386108 |
Appl. No.: |
12/382986 |
Filed: |
March 27, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11390370 |
Mar 28, 2006 |
|
|
|
12382986 |
|
|
|
|
PCT/JP2004/014430 |
Sep 24, 2004 |
|
|
|
11390370 |
|
|
|
|
Current U.S.
Class: |
355/53 |
Current CPC
Class: |
G03F 7/70341
20130101 |
Class at
Publication: |
355/53 |
International
Class: |
G03B 27/32 20060101
G03B027/32 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2003 |
JP |
2003-336888 |
Claims
1. A projection exposure apparatus which transfers a pattern formed
on a mask onto a substrate through a liquid, the projection
exposure apparatus comprising: a projection optical system which
projects an image of the pattern onto the substrate; and an
electricity removal unit which removes electricity from the liquid
to be supplied to a space between the projection optical system and
a surface of the substrate.
Description
CROSS-REFERENCE
[0001] This is a Divisional of U.S. patent application Ser. No.
11/390,370 filed Mar. 28, 2006, which in turn is a Continuation of
International Application No. PCT/JP2004/014430 filed Sep. 24, 2004
claiming the conventional priority of Japanese patent Application
No. 2003-336888 filed Sep. 29, 2003. The disclosure of each of
these prior applications is incorporated herein by reference in its
entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a projection exposure
method and an apparatus to be used for transferring a mask pattern
onto a photosensitive substrate in the lithography step in order to
produce a device including, for example, semiconductor devices,
image pickup devices (for example, CCD), liquid crystal display
devices, and thin film magnetic heads. In particular, the present
invention relates to a projection exposure apparatus and a method
using the liquid immersion method.
[0004] 2. Description of the Related Art
[0005] A projection exposure apparatus is used, for example, when a
semiconductor device is produced, in which an image of a pattern on
a reticle as a mask is transferred to respective shot areas on a
wafer (or a glass plate or the like) coated with a resist as a
photosensitive substrate via a projection optical system. A
reduction projection type projection exposure apparatus (stepper),
which is based on the step-and-repeat system, has been hitherto
frequently used as the projection exposure apparatus. However, a
projection exposure apparatus, which is based on the step-and-scan
system, is also widely used recently to perform the exposure by
synchronously scanning the reticle and the wafer.
[0006] As for the resolution of the projection optical system
provided for the projection exposure apparatus, As the exposure
wavelength to be used is shorter, the resolution becomes higher,
while as the numerical aperture of the projection optical system is
larger, the higher the resolution becomes higher. Therefore, the
exposure wavelength, which is used for the projection exposure
apparatus, is shortened year by year as the integrated circuit
becomes fine and minute, and the numerical aperture of the
projection optical system is increased as well. The exposure
wavelength, which is dominantly used at present, is 248 nm of the
KrF excimer laser. However, the exposure wavelength of 193 nm of
the ArF excimer laser, which is shorter than the above, has been
already practically used as well.
[0007] When the exposure is performed, the depth of focus (DOF) is
also important in the same manner as the resolution. The resolution
R and the depth of focus .delta. are represented by the following
expressions respectively.
R=k1*.lamda./NA (1)
.delta.=k2.lamda./NA.sup.2 (2)
[0008] In the expressions, .lamda. represents the exposure
wavelength, NA represents the numerical aperture of the projection
optical system, and k1 and k2 represent the process coefficients.
According to the expressions (1) and (2), the following fact is
appreciated. That is, when the exposure wavelength .lamda. is
shortened and the numerical aperture NA is increased in order to
enhance the resolution R, then the depth of focus .delta. is
narrowed. Conventionally, in the case of the projection exposure
apparatus, the surface of the wafer is adjusted to match the image
plane of the projection optical system in the auto-focus manner to
perform the exposure. However, it is impossible to adjust and match
the wafer surface and the image plane with no error at all.
Therefore, it is desirable that the depth of focus .delta. is large
so that no influence is exerted on the image formation performance
even when any error remains to some extent. In view of the above,
for example, the phase shift reticle method, the modified
illumination method, and the multilayer resist method have been
hitherto suggested in order to substantially increase the depth of
focus as well.
[0009] As described above, in the case of the conventional
projection exposure apparatus, the depth of focus is gradually
decreased, as the exposure light beam has the shorter wavelength,
and the numerical aperture of the projection optical system is
increased. In order to respond to the further higher integration of
the semiconductor integrated circuit, the investigation is also
made to further shorten the exposure wavelength. If such a
situation is continued as it is, then the depth of focus is
excessively decreased, and it is feared that the margin may be
insufficient during the exposure operation.
[0010] Accordingly, the liquid immersion method has been suggested
as a method for substantially shorten the exposure wavelength and
increase the depth of focus. In this method, the space between the
lower surface of the projection optical system and the wafer
surface is filled with a liquid such as pure water or any organic
solvent so that the resolution is improved and the depth of focus
is magnified about n times by utilizing the fact that the
wavelength of the exposure light beam in the liquid is 1/n as
compared with that in the air (n represents the refractive index of
the liquid, which is about 1.2 to 1.6 in ordinary cases). A
technique, which is described, for example, in International
Publication No. 99/49504, is exemplified as a conventional
technique concerning the projection exposure apparatus and the
exposure method to which the liquid immersion method is
applied.
[0011] In the liquid immersion method as described above, for
example, the pure water or the organic solvent is used as the
liquid with which the space between the lower surface of the
projection optical system and the wafer surface is filled. Any one
of the liquids, which is used in this method, has the high electric
insulation. For example, the ultrapure water, which is used in the
semiconductor production factory, has a specific resistance of
about 15 M.OMEGA.cm which is high. The liquid, which has the high
insulation as described above, tends to be charged with the static
electricity due to the friction with the piping and/or the
cavitation generated in the orifice provided in the piping passage
when the liquid is made to flow through the piping passage. If the
liquid, which is charged with the static electricity, is used for
the liquid immersion method, it has been feared that the electric
discharge may be caused between the liquid and the circuit pattern
having been already formed on the wafer, and the circuit pattern
may be destroyed. Further, if the electric discharge is caused
between the liquid and any object other than the circuit pattern,
it has been feared that the electric equipment, which is arranged
around the projection optical system or around the wafer, may
malfunction due to the electric noise generated during the electric
discharge, and the projection exposure apparatus may cause any
error and/or the projection exposure apparatus may be stopped.
Further, the charged liquid attracts surrounding impurities by the
static electricity. Therefore, the impurities may inhibit the
exposure in some cases.
SUMMARY OF THE INVENTION
[0012] The present invention has been made taking the foregoing
viewpoints into consideration, an object of which is to provide a
projection exposure apparatus which makes it possible to avoid the
malfunction of the apparatus and the destruction of the circuit
pattern caused by the charging of the liquid to be used for the
liquid immersion method. Another object of the present invention is
to provide a projection exposure method and a method for producing
a device, in which it is possible to avoid the destruction of the
circuit pattern and the malfunction of the apparatus.
[0013] According to a first aspect of the present invention, there
is provided a projection exposure apparatus which transfers a
pattern formed on a mask onto a substrate through a liquid; the
projection exposure apparatus comprising a projection optical
system which projects an image of the pattern onto the substrate;
and an electricity removal unit which removes electricity from the
liquid to be supplied to a space between the projection optical
system and a surface of the substrate.
[0014] According to the projection exposure apparatus of the
present invention, the liquid, from which the electricity has been
removed, can be supplied to the space between the projection
optical system and the substrate. Therefore, it is possible to
prevent the circuit pattern formed on the substrate from being
destroyed by the electric discharge of the static electricity.
Further, it is possible to prevent the electric equipment arranged
around the projection optical system and the substrate from
malfunctioning due to the electric discharge of the static
electricity. In this arrangement, the electricity removal unit may
have an electricity-removing filter which is provided in a flow
passage of a liquid supply piping for supplying the liquid to the
space between the projection optical system and the surface of the
substrate, and which is grounded. The electricity-removing filter
may be formed of a conductive metal foam or a conductive mesh
member. Accordingly, the static electricity, with which the liquid
is charged, can be removed from the liquid made to pass through the
electricity-removing filter. The exposure apparatus may further
comprise a liquid supply unit which supplies the liquid to the
space between the projection optical system and the surface of the
substrate. In this arrangement, the liquid supply unit may be
provided with the electricity removal unit. When the projection
exposure apparatus is a step-and-repeat type projection exposure
apparatus, the liquid supply unit may supply the liquid in a
direction in which the substrate is subjected to stepping. On the
other hand, when the projection exposure apparatus is a
step-and-scan type projection exposure apparatus, the liquid supply
unit may supply the liquid in a scanning direction.
[0015] According to a second aspect of the present invention, there
is provided a projection exposure apparatus which transfers a
pattern formed on a mask onto a substrate through a liquid; the
projection exposure apparatus comprising:
[0016] a projection optical system which projects an image of the
pattern onto the substrate; and
[0017] an electricity removal unit which removes electricity from
the liquid intervened between the projection optical system and a
surface of the substrate.
[0018] In this arrangement, the electricity removal unit may have
an electrode member which is provided in an optical element of the
projection optical system opposed to the substrate. The projection
exposure apparatus may have an electricity-removing filter which is
provided in at least one of a supply port of a liquid supply piping
for supplying the liquid and a recovery port of a liquid recovery
piping for recovering the liquid. Accordingly, the electricity can
be removed even in a state in which the space between the optical
element and the substrate is filled with the liquid. Therefore, the
liquid can be prevented from being charged during the exposure
and/or during the movement of the substrate.
[0019] According to a third aspect of the present invention, there
is provided a projection exposure method for irradiating a mask
with an exposure light beam and projecting a pattern formed on the
mask onto a substrate through a liquid with a projection optical
system, the projection exposure method comprising:
[0020] a step of removing electricity from the liquid; and
[0021] a step of supplying the liquid to a space between the
projection optical system and a surface of the substrate.
[0022] Accordingly, the static electricity is removed from the
liquid with which the space between the projection optical system
and the surface of the substrate is filled. It is possible to avoid
the malfunction of the projection exposure apparatus and the
destruction of the circuit pattern which is feared to be caused by
the electric discharge of the static electricity. The step of
removing the electricity may be performed prior to the step of
supplying the liquid. In this procedure, the liquid may be made to
pass through an electricity-removing filter in the step of
supplying the liquid to the space between the projection optical
system and the surface of the substrate. The electricity-removing
filter may be provided at an end portion of a liquid supply tube
for supplying the liquid to the space between the projection
optical system and the surface of the substrate. The liquid
supplied to the space between the projection optical system and the
surface of the substrate may be caused to make contact with a
conductive member in the step of removing the electricity from the
liquid.
[0023] According to a fourth aspect of the present invention, there
is provided a method for producing a device, comprising a
lithography step, wherein the projection exposure apparatus
according to any one of the aspects described above is used to
perform exposure in the lithography step.
[0024] Accordingly, it is possible to avoid the destruction of the
circuit pattern which is feared to be caused by the electric
discharge of the static electricity. Therefore, the yield of the
device to be produced is improved, and it is possible to avoid the
malfunction of the projection exposure apparatus which would be
otherwise caused by the electric discharge of the static
electricity.
[0025] Therefore, it is possible to maintain the high processing
ability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 shows a schematic arrangement illustrating a
projection exposure apparatus to be used in a first embodiment of
the present invention.
[0027] FIG. 2 shows an arrangement of supply ports, recovery ports,
and electricity removal units in the X direction in the first
embodiment of the present invention.
[0028] FIG. 3 shows an arrangement of supply ports, recovery ports,
and electricity removal units in the X direction and the Y
direction in the first embodiment of the present invention.
[0029] FIG. 4 shows an arrangement of supply ports, recovery ports,
and electricity removal units in a second embodiment of the present
invention.
[0030] FIG. 5 shows an arrangement of supply ports, recovery ports,
and electricity removal units in a third embodiment of the present
invention.
[0031] FIG. 6 shows the operation to be performed during the
scanning exposure in the third embodiment of the present
invention.
[0032] FIG. 7 shows a flow chart illustrating exemplary steps of
producing a semiconductor device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0033] An exemplary preferred embodiment of the present invention
will be explained below with reference to FIGS. 1 to 3 by way of
example. In this embodiment, the present invention is applied to a
projection exposure apparatus based on the step-and-repeat
system.
First Embodiment
[0034] FIG. 1 shows a schematic arrangement of the projection
exposure apparatus of this embodiment. With reference to FIG. 1, a
pattern formed on a reticle R is illuminated with an exposure light
beam IL composed of an ultraviolet pulse light beam having a
wavelength of 193 nm radiated from an illumination optical system 1
which includes, for example, an ArF excimer laser light source as
an exposure light source, an optical integrator (homogenizer), a
field diaphragm, and a condenser lens. The pattern on the reticle R
is reduced and projected onto an exposure area on a wafer W coated
with a photoresist at a predetermined projection magnification
.beta. (.beta. is, for example, 1/4 or 1/5) via a projection
optical system PL which is telecentric on the both sides (or on one
side on the side of the wafer W). Those appropriately usable as the
exposure light beam IL include, for example, the KrF excimer laser
beam (wavelength: 248 nm), the F.sub.2 laser beam (wavelength: 157
nm), and the i-ray (wavelength: 365 nm) of the mercury lamp. The
description will be made below assuming that the Z axis extends in
parallel to the optical axis AX of the projection optical system
PL, the Y axis extends perpendicularly to the sheet surface of FIG.
1 in the plane perpendicular to the Z axis, and the X axis extends
in parallel to the sheet surface of FIG. 1.
[0035] The reticle R is held on a reticle stage RST. A mechanism,
which finely moves the reticle R in the X direction, the Y
direction, and the direction of rotation, is incorporated into the
reticle stage RST. The two-dimensional position and the angle of
rotation of the reticle stage RST are measured in real-time by a
laser interferometer (not shown). A main control system 14
positions the reticle R on the basis of an obtained measured
value.
[0036] On the other hand, the wafer W is fixed on a Z stage 9 which
controls the angle of inclination and the focus position (position
in the Z direction) of the wafer W by the aid of a wafer holder
(not shown). A conductive coating is applied to the wafer holder in
order to prevent the wafer from being charged. The wafer holder is
grounded by the aid of an unillustrated ground wire. The Z stage 9
is fixed on an XY stage 10 which is movable along the XY plane that
is substantially parallel to the image plane of the projection
optical system PL. The XY stage 10 is placed on a base 11. The Z
stage 9 controls the angle of inclination and the focus position
(position in the Z direction) of the wafer W so that the surface of
the wafer W is adjusted to match the image plane of the projection
optical system PL in the auto-focus manner and the auto-leveling
manner. The XY stage 10 positions the wafer W in the X direction
and the Y direction. The two-dimensional position and the angle of
rotation of the Z stage 9 (wafer W) are measured in real-time as
the position of a movement mirror 12 by a laser interferometer 13.
Control information is fed from the main control system 14 to a
wafer stage-driving system 15 on the basis of an obtained result of
the measurement, on the basis of which the wafer stage-driving
system 15 controls the operation of the Z stage 9 and the XY stage
10. During the exposure, the operation, in which each of shot areas
on the wafer W is successively step-moved to the exposure position
and exposed with the image of the pattern of the reticle R, is
repeated in the step-and-repeat manner.
[0037] In this embodiment, the liquid immersion method is applied
in order that the exposure wavelength is substantially shortened to
improve the resolution, and the depth of focus is substantially
increased. Therefore, the space between the surface of the wafer W
and the end surface (lower surface) of a lens 4 of the projection
optical system PL opposed to the wafer W is filled with a
predetermined liquid 7 at least during the period in which image of
the pattern of the reticle R is being transferred onto the wafer W.
The projection optical system PL includes a barrel 3 for
accommodating the other optical system and the lens 4 thereof. The
projection optical system PL is constructed such that the liquid 7
makes contact with only the lens 4. Accordingly, the barrel 3
formed of metal is prevented from any corrosion or the like.
[0038] The projection optical system PL includes a plurality of
optical elements including the lens 4, and the lens 4 is attached
detachably (exchangeably) to the lowermost portion of the barrel 3.
In this embodiment, the optical element which is disposed most
closely to the wafer W and which is opposed to the wafer W, i.e.,
the optical element which makes contact with the liquid 7 is the
lens. However, the optical element is not limited to the lens. The
optical element may be an optical plate (for example, parallel flat
plate or plane parallel plate) which is usable to adjust the
optical characteristics of the projection optical system PL
including, for example, the aberration (for example, spherical
aberration and comatic aberration). On the other hand, the surface
of the optical element to make contact with the liquid 7 is
dirtied, for example, due to the adhesion of scattered particles
generated from the resist by being irradiated with the exposure
light beam or any impurity in the liquid 7. Therefore, it is
necessary to periodically exchange the optical element. However,
when the optical element to make contact with the liquid 7 is the
lens, then the cost is expensive for the exchange part, and a long
period of time is required for the exchange. As a result, the
maintenance cost (running cost) is increased, and the throughput is
lowered. Accordingly, the optical element, which makes contact with
the liquid 7, may be, for example, a plane parallel plate which is
cheaper than the lens 4. In this arrangement, it is enough that the
plane parallel plate is merely exchanged immediately before
supplying the liquid 7 even when any substance (for example, any
silicon-based organic matter), which deteriorates, for example, the
transmittance of the projection optical system PL, the illuminance
of the exposure light beam on the wafer W, and the uniformity of
the illuminance distribution, is adhered to the plane parallel
plate, for example, during the transport, the assembling, and/or
the adjustment of the projection exposure apparatus. An advantage
is also obtained such that the exchange cost is lowered as compared
with the case in which the optical element to make contact with the
liquid 7 is the lens.
[0039] When the optical element, which is disposed most closely to
the wafer W and which is opposed to the wafer W, is the optical
plate, it is necessary that the space between the optical plate and
an optical element (lens 4) disposed second most closely to the
wafer W with respect to the optical element is also filled with the
liquid 7. Accordingly, the effect of the liquid immersion method
can be sufficiently obtained such that the resolution is improved
and the depth of focus is substantially increased. In this
arrangement, a liquid supply piping and a liquid recovery piping,
which effect liquid communication with respect to the space between
the optical plate and the lens 4, may be connected to the side wall
of the projection optical system.
[0040] In this embodiment, for example, pure water is used as the
liquid 7. Pure water is advantageous in that pure water is
available in a large amount with ease, for example, in the
semiconductor production factory, and pure water exerts no harmful
influence, for example, on the optical lens and the photoresist on
the wafer W. Further, pure water exerts no harmful influence on the
environment, and the content of impurity is extremely low.
Therefore, it is also expected to obtain the function to wash the
surface of the wafer W and the surface of the lens 4. On the other
hand, in the case of pure water, the specific resistance is high,
and the electric insulation is high. Therefore, pure water has such
a property that pure water tends to be charged with the static
electricity, for example, due the friction generated when pure
water flows through a resin piping as an insulator and the
cavitation generated at an orifice portion.
[0041] It is approved that the refractive index n of pure water
(water) with respect to the exposure light beam having a wavelength
of about 193 nm is approximately 1.44, when pure water is used as
the liquid 7. Therefore, the wavelength of 193 nm of the ArF
exciter laser beam is shortened on the wafer W by 1/n, i.e., to
about 134 nm, and a high resolution is obtained. Further, the depth
of focus is magnified about n times, i.e., about 1.44 times as
compared with the value obtained in the air. Therefore, when it is
enough to secure an approximately equivalent depth of focus as
compared with the case of the use in the air, it is possible to
further increase the numerical aperture of the projection optical
system PL. Also in this viewpoint, the resolution is improved.
[0042] The liquid 7 is supplied onto the wafer W via a
predetermined liquid supply piping 21 in a temperature-controlled
state by a liquid supply unit 5 including, for example, a tank for
the liquid, a pressurizing pump, and a temperature control unit.
The liquid 7 is recovered from the surface of the wafer W via a
predetermined liquid recovery piping 23 by a liquid recovery unit 6
including, for example, a tank for the liquid and a suction pump.
The temperature of the liquid 7 is set, for example, approximately
identically with the temperature in the chamber in which the
projection exposure apparatus of this embodiment is accommodated.
The liquid supply piping 21 is principally constructed of a supply
tube 21a and a supply port 21b. One end of the supply tube 21a is
connected to the liquid supply unit 5, and the other end is
connected to the supply port 21b. The supply port 21b has an end
portion which is formed to be thin. The supply ports 21b, 22b are
arranged to interpose the end portion of the lens 4 of the
projection optical system PL in the X direction (see FIG. 2). An
electricity removal unit 40, which removes the electricity from the
liquid 7, is provided for the liquid supply piping 21. The
electricity removal unit 40 is principally constructed of an
electricity-removing filter 40a and a ground wire 40b. The
electricity-removing filter 40a, which is provided in the flow
passage of the supply tube 21a, is grounded via the ground wire.
The electricity removal unit 40 will be described in detail later
on. On the other hand, the liquid recovery piping 23 is principally
constructed of a recovery tube 23a and recovery ports 23b, 23c. One
end of the recovery tube 23a is connected to the liquid recovery
unit 6, and the other end is branched into two portions which are
connected to the recovery ports 23b, 23c (see FIG. 2). Further, one
set of supply port 22b and recovery ports 24b, 24c, which are
arranged at positions obtained by rotating those of one set of
supply port 21a and recovery ports 23b, 23c by approximately
180.degree., are also disposed. Furthermore, two sets of supply
ports and recovery ports, which are disposed to interpose the end
portion of the lens 4 in the Y axis direction, are arranged as well
(see FIG. 3).
[0043] FIG. 2 shows the positional relationship among the end
portion 4A of the lens 4 of the projection optical system PL shown
in FIG. 1, the wafer W, and the two sets of the supply ports and
the recovery ports to interpose the end portion 4A in the X
direction. With reference to FIG. 2, the supply port 21b is
arranged on the side in the +X direction of the end portion 4A, and
the recovery ports 23b, 23c are arranged on the side in the -X
direction respectively. Each of the recovery ports 23b, 23c is
arranged in an open sector form with respect to the axis which
passes through the center of the end portion 4A and which is
parallel to the X axis. Another set of the supply port 22b and the
recovery ports 24b, 24c are arranged at positions obtained by
rotating those of the set of the supply port 21b and the recovery
ports 23b, 23c by approximately 180.degree.. The supply port 22b is
connected to the liquid supply unit 5 via the supply tube 22a. The
recovery ports 24b, 24c are connected to the liquid recovery unit 6
via the recovery tube 24a. The liquid supply piping 22 is
principally constructed of the supply tube 22a and the supply port
22b. The liquid recovery piping 24 is principally constructed of
the recovery tube 24a and the recovery ports 24b, 24c.
[0044] The electricity removal units 40, 41 are provided for the
liquid supply pipings 21, 22 respectively. Each of the electricity
removal units 40, 41 is principally constructed of the
electricity-removing filter 40a, 41a formed of a conductive metal
foam, and the ground wire 40b, 41b. The electricity-removing filter
40a, 41a is provided in the flow passage of the supply tube 21a,
22a, and the electricity-removing filter 40a, 41a is grounded via
the ground wire 40b, 41b. Each of the electricity-removing filters
40a, 41a is formed of the conductive metal foam including, for
example, porous copper and aluminum and so on. When the liquid 7 is
made to pass through the metal foam, then the static electricity,
with which the liquid 7 has been charged, is recovered by the
electricity-removing filter 40a, 41a, and the static electricity is
discharged to the ground by the aid of the ground wire 40b, 41b.
That is, the electricity can be removed from the liquid 7 by the
electricity-removing filter 40a, 41a. In this arrangement, it is
desirable that the electricity-removing filter 40a, 41a is provided
as closely as possible to the supply port 21b, 22b, for the
following reason. That is, it is intended to prevent the liquid 7
from being charged again after the liquid 7 passes through the
electricity-removing filter 40a, 41a and is supplied onto the wafer
W.
[0045] FIG. 3 shows the positional relationship among the end
portion 4A of the lens 4 of the projection optical system PL shown
in FIG. 1 and the two sets of the supply ports and the recovery
ports to interpose the end portion 4A in the Y direction. With
reference to FIG. 3, the supply port 27b is arranged on the side in
the +Y direction of the end portion 4A. The supply port 27b is
connected to the liquid supply unit 5 via the supply tube 27a. In
this arrangement, the liquid supply piping 27 is principally
constructed of the supply tube 27a and the supply port 27b. On the
other hand, the recovery ports 29b, 29c are arranged on the side in
the -Y direction of the end portion 4A respectively. The recovery
ports 29b, 29c are connected to the liquid recovery unit 6 via the
recovery tube 29a. In this arrangement, the liquid recovery piping
29 is principally constructed of the recovery tube 29a and the
recovery ports 29b, 29c. Another set of the supply port 28b and the
recovery ports 30b, 30c are arranged at positions obtained by
rotating those of the set of the supply port 27b and the recovery
ports 29b, 29c by approximately 180.degree.. The supply port 28b is
connected to the liquid supply unit 5 via the supply tube 28a. The
recovery ports 30b, 30c are connected to the liquid recovery unit 6
via the recovery tube 30a. These components construct main portions
of the liquid supply piping 28 and the liquid recovery piping 29
respectively. The liquid supply unit 5 supplies the
temperature-controlled liquid to the space between the wafer W and
the end portion 4A of the lens 4 via at least one of the liquid
supply pipings 21, 22, 27, 28. The liquid recovery unit 6 recovers
the liquid via at least one of the liquid recovery pipings 23, 24,
29, 30. Electricity removal units 42, 43 are also provided for the
liquid supply pipings 27, 28 which supply the liquid 7 in the Y
direction. Specifically, the electricity-removing filters 42a, 43a
are provided for the supply tubes 27a, 28a, and the
electricity-removing filters 42a, 43a are grounded via the ground
wires 42b, 43b, respectively. Accordingly, the electricity can be
removed even when the liquid 7 is supplied in the Y direction.
[0046] Next, an explanation will be made about the operation of the
projection exposure apparatus of this embodiment. The main control
system 14 (see FIG. 1) stores an exposure recipe corresponding to a
semiconductor device to be produced. Necessary operations are
instructed to the respective sections, for example, on the basis of
the best focus position and the exposure energy recorded in the
exposure recipe. An unillustrated wafer transport system transports
the wafer W onto the unillustrated wafer holder fixed on the Z
stage 9, on the basis of the instruction supplied from the main
control system 14. The reticle stage RST positions the reticle R,
and the wafer stage-driving system 15 positions the wafer W by
using the Z stage 9 and the XY stage 10. Concurrently with the
positioning operation, the liquid supply unit 5 supplies the liquid
7 to the liquid supply pipings 21, 22, 27, 28 on the basis of the
instruction from the main control system 14. The electricity is
removed from the liquid 7 by the electricity-removing filters 40a,
41a, 42a, 43a provided for the liquid supply pipings 21, 22, 27,
28. The liquid 7, from which the electricity has been removed, is
supplied to the space between the wafer W and the lens 4 of the
projection optical system PL to fill the space between the lens 4
and the wafer W therewith. After the reticle R and the wafer W are
positioned at the predetermined positions, and the space between
the lens 4 and the wafer W is filled with the liquid 7, the
illumination optical system 1 radiates the illumination light beam
IL to expose the first shot area on the wafer W with image of the
pattern of the reticle R. When the exposure is completed for the
first shot area, the wafer W is step-moved by the XY stage 10 to
the position at which the next shot area is to be exposed. The
liquid supply unit 5 and the liquid recovery unit 6 supply and
recover the liquid 7 simultaneously during the movement of the
wafer W by appropriately selecting the liquid supply piping and the
suitable liquid recovery piping depending on the direction of the
step movement. The liquid 7 is retained in the space between the
lens 4 and the wafer W. The step movement is thereafter repeated
(step-and-repeat) to perform the exposure for all of the shot areas
on the wafer W. As described above, in the case of the projection
exposure apparatus of this embodiment, the liquid 7 is subjected to
the removal of electricity before the liquid 7 is supplied to the
space between the lens 4 and the wafer W. Therefore, it is possible
to avoid the occurrence of the inconvenience which would be
otherwise caused, for example, such that the electric discharge is
caused on the wafer W by the charged liquid 7, the pattern formed
on the wafer W is destroyed, and/or the peripheral equipment
malfunctions.
[0047] An explanation will be made in further detail below about
the method for supplying and recovering the liquid 7 during the
step movement of the wafer W. With reference to FIG. 2, when the
wafer W is step-moved in the direction of the arrow 25A indicated
by the solid line (-X direction), the liquid supply unit 5 supplies
the liquid 7 to the space between the wafer W and the end portion
4A of the lens 4 via the liquid supply piping 21. In this
situation, the liquid 7 is gradually charged with the static
electricity by the friction with the interior of the liquid supply
unit 5 and/or the piping as the liquid 7 flows through the supply
tube 21a and/or by the cavitation generated at the orifice provided
in the piping passage. As a result, liquid 7 is in the charged
state. The liquid 7, which is in the charged state, passes through
the electricity-removing filter 40a provided in the supply tube 21a
of the liquid supply piping 21. The electricity-removing filter 40a
is formed of the conductive metal foam, which is grounded (earthed)
by the ground wire 40b. Accordingly, the static electricity is
recovered and discharged to the ground when the liquid 7 passes
through the electricity-removing filter 40a. Thus, the electricity
is removed from the liquid 7. Therefore, the liquid 7, which is not
charged, is supplied to the space between the wafer W and the lens
4.
[0048] The liquid recovery unit 6 recovers the liquid 7 from the
surface of the wafer W by the aid of the liquid recovery piping 23.
In this situation, the liquid 7 flows on the wafer W in the
direction of the arrow 25B (-X direction). The space between the
wafer W and the lens 4 is stably filled with the liquid 7.
[0049] On the other hand, when the wafer W is step-moved in the
direction of the arrow 26A indicated by the two-dot chain line (+X
direction), then the liquid supply unit 5 supplies the liquid 7 to
the space between the wafer W and the end portion 4A of the lens 4
by using the liquid supply piping 22, and the liquid recovery unit
6 recovers the liquid 7 by using the liquid recovery piping 24.
Prior to the supply of the liquid 7, the electricity is removed
from the liquid 7 by the electricity-removing filter 41a provided
in the supply tube 22a of the liquid supply piping 22. The supplied
liquid 7 flows on the wafer W in the direction of the arrow 26B (+X
direction). The space between the wafer W and the lens 4 is filled
with the liquid 7.
[0050] As described above, in the case of the projection exposure
apparatus of this embodiment, the liquid 7, from which the
electricity has been removed by the electricity-removing filters
40a, 41a, is supplied to the space between the wafer W and the lens
4. Therefore, it is possible to avoid the destruction of the
circuit pattern formed on the wafer W caused by the electric
discharge of the static electricity and the malfunction of the
apparatus arranged around the Z stage 9 and the XY stage 10 and the
projection optical system PL.
[0051] The two sets of the supply ports and the recovery ports,
which are mutually inverted in the X direction, are provided, and
the electricity-removing filters are provided in the flow passages
of the respective liquid supply pipings. Therefore, even when the
wafer W is moved in any one of the +X direction and the -X
direction, the space between the wafer W and the lens 4 can be
stably and continuously filled with the liquid 7 from which the
electricity has been removed. Even when any foreign matter
(including scattered particles from the resist) is adhered onto the
wafer W, the foreign matter can flowed out with the liquid 7,
because the liquid 7 flows on the wafer W. No surrounding impurity
is attracted by the static electricity, because the electricity has
been removed from the liquid 7 by the electricity removal units 40,
41. Further, the liquid 7 is adjusted to have the predetermined
temperature by the liquid supply unit 5. Therefore, the temperature
is adjusted for the surface of the wafer W, and it is possible to
avoid the decrease in the overlay accuracy or the like which would
be otherwise caused by the thermal expansion of the wafer due to
the heat generated during the exposure. Therefore, even when any
time difference arises between the alignment and the exposure as in
the alignment based on the EGA (Enhanced Global Alignment) system,
it is possible to avoid the decrease in the overlay accuracy which
would be otherwise caused by the thermal expansion of the wafer. In
the case of the projection exposure apparatus of this embodiment,
the liquid 7 flows in the same direction as the direction of the
movement of the wafer W. Therefore, it is possible to recover the
liquid which has absorbed the foreign matter and the heat, without
allowing the liquid to stay on the exposure area disposed just
below the end portion 4A of the lens 4.
[0052] When the wafer W is step-moved in the Y direction, the
liquid 7 is supplied and recovered in the Y direction. That is,
when the wafer is step-moved in the direction of the arrow 31A
indicated by the solid line in FIG. 3 (-Y direction), then the
liquid supply unit 5 supplies the liquid via the supply tube 27a
and the supply port 27b, and the liquid recovery unit 6 recovers
the liquid by using the recovery tube 29a and the recovery ports
29b, 29c. The liquid flows in the direction of the arrow 31B (-Y
direction) on the exposure area disposed just below the end portion
4A of the lens 4. When the wafer is step-moved in the +Y direction,
the liquid is supplied and recovered by using the supply tube 28a,
the supply port 28b, the recovery tube 30a, and the recovery ports
30b, 30c. The liquid flows in the +Y direction on the exposure area
disposed just below the end portion 4A. Accordingly, even when the
wafer W is moved in any one of the +Y direction and the -Y
direction, the space between the wafer W and the end portion 4A of
the lens 4 can be filled with the liquid 7, in the same manner as
in the case in which the wafer W is moved in the X direction. Also
in this case, the electricity is removed from the liquid 7 by the
electricity removal units 42, 43 provided for the liquid supply
pipings 27, 28.
[0053] The supply and recovery ports are not limited only to the
supply port and the recovery port for supplying and recovering the
liquid 7 in the X direction and the Y direction. For example, a
supply port and a recovery port for supplying and recovering the
liquid 7 in any oblique direction may be provided, and the
electricity-removing filter may be provided for the liquid supply
piping thereof.
[0054] The electricity removal unit 40, 41, 42, 43 of the
projection exposure apparatus of this embodiment is constructed
such that the electricity-removing filter 40a, 41a, 42a, 43a is
provided for the supply tube 21a, 22a, 27a, 28a, respectively.
However, it is allowable that the electricity-removing filter 40a,
41a, 42a, 43a is provided at any position provided that the
position is included in the flow passage of the liquid supply
piping 21, 22, 27, 28. However, if the route to be followed after
the liquid passes through the electricity-removing filter is long,
it is feared that the liquid 7 may be charged again. Therefore, it
is desirable that the electricity-removing filter is provided on
the downstream side of the liquid supply piping as much as
possible. For example, the electricity-removing filter can be
provided at the supply port 21b, 22b, 27b, 28b. In this
arrangement, the supply port and the electricity-removing filter
may be constructed as an integrated body. It is also allowable that
a plurality of electricity-removing filters are provided in the
flow passage of the liquid supply piping.
[0055] In this embodiment, the electricity-removing filter is
formed of the metal foam. However, there is no limitation to the
metal foam provided that the electricity-removing filter is
constructed so that the conductive material and the liquid 7 make
contact with each other. For example, the electricity-removing
filter may be composed of a conductive metal mesh. Alternatively,
at least a part of the supply tube 21a, 22a, 27a, 28a may be formed
of a conductive material. When the supply tube made of the
conductive material or the metal mesh is used for the
electricity-removing filter, then the electricity-removing filter
can be constructed simply as compared with the case in which the
metal foam is used, and it is possible to decrease the tube passage
resistance when the liquid 7 flows. Alternatively, the inner wall
of the liquid supply piping (as well as the liquid recovery piping)
may be subjected to the coating with an antistatic agent.
Second Embodiment
[0056] Next, a second embodiment of the present invention will be
explained with reference to FIG. 4. In the description of the
second embodiment of the present invention, the constitutive
components, which are the same as or equivalent to those of the
first embodiment, are designated by the same reference numerals,
any explanation of which will be omitted.
[0057] FIG. 4 shows the positional relationship among the end
portion 4A of the lens 4 of the projection optical system PL shown
in FIG. 1, and each two sets, i.e., four sets in total of the
supply ports and the recovery ports which interpose the end portion
4A in the X direction and the Y direction. As shown in FIG. 4, an
electrode member 44 is formed on the lower surface of the lens 4 in
this embodiment. The electrode member 44 is a conductor which is
formed by means of the vapor deposition on a part of the surface of
the lens 4. The electrode member 44 is formed in a circular zonal
form at the position at which the exposure light beam is not
inhibited and the electrode member 44 makes contact with the liquid
7 when the space between the lens 4 and the wafer W is filled with
the liquid 7, outside the exposure range of the end portion 4A of
the lens 4 in this embodiment. That is, the conductor is formed as
an annular member which is coaxial with the optical axis of the
lens 4. The electrode member 44 is grounded (earthed) via an
unillustrated ground wire. The electricity-removing filters 40a,
41a, 42a, 43a are provided for the supply tubes 21a, 22a, 27a, 28a
of the liquid supply pipings 21, 22, 27, 28 respectively. The
electricity-removing filters 40a, 41a, 42a, 43a are grounded
(earthed) via the unillustrated ground wires. Accordingly, the
liquid 7, from which the electricity has been removed, can be
supplied to the space between the lens 4 and the wafer W by using
the electricity-removing filters 40a, 41a, 42a, 43a. Further, the
electricity can be removed from the liquid 7 which is in a state of
being retained between the lens 4 and the wafer W, by using the
electrode member 44. In other words, the electricity is removed by
the electricity-removing filters 40a, 41a, 42a, 43a before the
supply of the liquid 7, and the electricity is removed by the
electrode member 44 after the supply of the liquid 7. Further,
according to this arrangement, the electricity can be removed from
the liquid 7 during the exposure as well. Therefore, the
electricity can be removed quickly even when the liquid 7 is
charged during the exposure. Further, the electricity can be
removed quickly even when the liquid 7 is charged during the
alignment and/or during the step movement. In this embodiment, the
electricity-removing filters 40a, 41a, 42a, 43a are provided for
the liquid supply pipings 21, 22, 27, 28, and the electrode member
44 is provided at the end portion 4A of the lens 4. However, it is
also possible to provide only the electrode member 44 without
providing any electricity-removing filter. Also in this
arrangement, the electricity can be removed from the liquid 7 in
the state of being retained between the lens 4 and the wafer W.
[0058] It is also allowable that an auxiliary plane plate, which
has the same height as that of the surface of the wafer W, is
arranged around the wafer W on the Z stage 9, and the electrode
member is provided on the auxiliary plane plate. Accordingly, the
liquid 7 can be retained between the Z stage 9 and the lens 4 even
on the auxiliary plane plate disposed outside the wafer W.
Therefore, the electricity can be removed from the liquid 7 by
moving the electrode member provided on the Z stage 9 to the
position below the lens 4. When the liquid 7 is present on the
wafer W, the electricity cannot be removed from the liquid 7
disposed on the wafer W even when the wafer W is grounded via the
wafer holder, because the resist, with which the wafer W is coated,
is usually an insulator. However, when a wafer W, which is coated
with a conductive resist, is used, the electricity can be removed,
because the liquid 7 is grounded via the conductive resist, the
wafer W, and the wafer holder.
Third Embodiment
[0059] Next, a third embodiment of the present invention will be
explained with reference to FIG. 5. In this embodiment, the present
invention is applied to a case of the exposure with a projection
exposure apparatus based on the step-and-scan system, i.e., the
so-called scanning type projection exposure apparatus. Also in this
embodiment, the space between the lens 4 and the surface of the
wafer W is filled with the liquid 7 during the scanning exposure by
applying the liquid immersion method. The supply and the recovery
of the liquid 7 are performed by a liquid supply unit 5 and a
liquid recovery unit 6 respectively. The electricity is removed
from the liquid 7 by electricity removal units 40, 41 provided for
liquid supply pipings 21, 22. In the description of this
embodiment, the constitutive components, which are the same as or
equivalent to those of the first and second embodiments, are
designated by the same reference numerals, any explanation of which
will be omitted.
[0060] FIG. 5 shows the positional relationship among an end
portion 4B of a lens 4 of a projection optical system PL and supply
ports and recovery ports for supplying and recovering the liquid 7
in the X direction. In the case of the scanning type projection
exposure apparatus of this embodiment, the lens 4, which is
disposed at the lowermost end of the projection optical system PL,
has the end portion 4B which is subjected to the cutting to have a
rectangular shape that is long in the Y direction (non-scanning
direction) and has a necessary portion for the scanning exposure.
The three supply ports 21b to 21d are arranged on the side in the
+X direction, and the two recovery ports 23b, 23c are arranged on
the side in the -X direction so that the end portion 4B of the lens
4 of the projection optical system PL is interposed between the
supply ports 21b to 21d and the recovery ports 23b, 23c.
[0061] The supply ports 21b to 21d are connected to the liquid
supply unit 5 via a supply tube 21a. The recovery ports 23b, 23c
are connected to the liquid recovery unit 6 via a recovery tube
23a. The supply ports 22b to 22d and the recovery ports 24b, 24c
are arranged at positions obtained by rotating those of the supply
ports 21b to 21d and the recovery ports 23b, 23c by approximately
180.degree.. The supply ports 21b to 21d and the recovery ports
24b, 24c are arranged alternately in the Y direction. The supply
ports 22b to 22c and the recovery ports 23b, 23c are arranged
alternately in the Y direction. The supply ports 22b to 22d are
connected to the liquid supply unit 5 via a supply tube 22a. The
recovery ports 24b, 24c are connected to the liquid recovery unit 6
via a recovery tube 24a.
[0062] The electricity removal unit 40 is provided for the liquid
supply piping 21. The electricity removal unit 40 is principally
constructed of electricity-removing filters 40a, 40c, 40d which are
provided at the supply ports 21b to 21d as the flow passages of the
liquid supply piping 21, and a ground wire 40b which is connected
to the electricity-removing filters. Similarly, the electricity
removal unit 41, which is provided for the liquid supply piping 22,
is principally constructed of electricity-removing filters 41a,
41c, 41d which are provided at the supply ports 22b to 22d as the
flow passages of the liquid supply piping 22, and a ground wire 41b
which is connected to the electricity-removing filters. Each of the
electricity-removing filters 40a, 40c, 40d, 41a, 41c, 41d is formed
of a conductive metal foam, which is grounded via the ground wire
40b, 41b.
[0063] In the projection exposure apparatus of this embodiment,
electricity removal units 45, 46 are also provided for the liquid
recovery pipings 23, 24. Specifically, electricity-removing filters
45a, 45b, 46a, 46b are provided at the recovery ports 23b, 23c,
24b, 24c, respectively as the flow passages of the liquid recovery
pipings 23, 24, which are grounded via lead wires 45c, 46c,
respectively.
[0064] Next, an explanation will be made about the exposure
operation of the scanning type exposure apparatus of this
embodiment. During the scanning exposure, a part of image of the
pattern of the reticle is projected onto the rectangular exposure
area disposed just below the end portion 4B. The reticle (not
shown) is moved at a velocity V in the -X direction (or in the +X
direction) with respect to the projection optical system PL, in
synchronization with which the wafer W is moved at a velocity
.beta.V (.beta. represents the projection magnification) in the +X
direction (or in the -X direction) by the aid of the XY stage 10.
After the completion of the exposure for one shot area, the next
shot area is moved to the scanning start position in accordance
with the stepping of the wafer W. The exposure is successively
performed for the respective shot areas thereafter in the
step-and-scan manner.
[0065] When the scanning exposure is performed while moving the
wafer W in the scanning direction (-X direction) indicated by the
solid line arrow, then the liquid 7 is supplied by using the supply
tube 21a, the supply ports 21b to 21d while removing the
electricity from the liquid by using the electricity-removing
filters 40a, 40b, 40d, and the liquid 7 is recovered by using the
recovery tube 23a, the recovery ports 23b, 23c, while removing the
electricity from the liquid by using the electricity-removing
filters 45a, 45b. The liquid 7 is made to flow in the -X direction
so that the space between the lens 4 and the wafer W is filled
therewith. On the other hand, when the scanning exposure is
performed while moving the wafer W in the direction (+X direction)
indicated by the two-dot chain line arrow, then the liquid 7 is
supplied by using the supply tube 22a, the supply ports 22b to 22d,
while removing the electricity from the liquid by using the
electricity-removing filters 41a, 41b, 41d, and the liquid 7 is
recovered by using the recovery tube 24a, the recovery ports 24b,
24c, while removing the electricity from the liquid by using the
electricity-removing filters 46a, 46b. The liquid 7 is made to flow
in the +X direction so that the space between the lens 4 and the
wafer W is filled therewith.
[0066] FIG. 6 shows a state of the supply ports 21b to 21d, the
recovery ports 23b, 23c, and the liquid 7 during the scanning
exposure. In FIG. 6, the wafer W is moved in the -X direction
indicated by the solid line arrow. In the scanning exposure
apparatus of this embodiment, the liquid is supplied and recovered
also during the scanning exposure as described above. Therefore, at
least one of the supply ports 21b to 21d and the recovery ports
23b, 23c always makes contact with the liquid 7 with which the
space between the lens 4 and the wafer W is filled.
[0067] As described above, according to the scanning type exposure
apparatus of this embodiment, the liquid 7, which exists between
the lens 4 and the wafer W, makes contact with at least any one of
the supply ports 21b to 21d and the recovery ports 23b, 23c during
the scanning exposure. Therefore, the electricity can be removed in
the state in which the space between the lens 4 and the wafer W is
filled with the liquid 7, by the electricity-removing filter 40a,
40c, 40d provided for the supply port 21b to 21d or the
electricity-removing filter 45a, 45b provided for the recovery port
23b, 23c. According to this arrangement, the electricity can be
always removed from the liquid 7 during the scanning exposure.
Therefore, it is possible to prevent the liquid 7 from being
charged during the exposure. It is possible to avoid the
inconvenience including, for example, the destruction of the
circuit pattern formed on the wafer W caused by the electric
discharge of the static electricity, and the malfunction of the
equipment arranged around the projection optical system PL, the Z
stage 9, and the XY stage 10.
[0068] This embodiment is constructed such that the
electricity-removing filters are provided for the liquid supply
piping and the liquid recovery piping. However, it is also
allowable that an electrode member is formed at the end portion 4B
of the lens 4 to remove the electricity from the liquid 7 in the
state in which the space between the lens 4 and the wafer W is
filled with the liquid 7, in the same manner as in the second
embodiment.
[0069] The projection exposure apparatus of this embodiment is
constructed such that the electricity-removing filters are provided
for both of the supply ports 21b to 21d, 22b to 22d and the
recovery ports 23b, 23c, 24b, 24c. However, it is also allowable
that the electricity-removing filter may be provided for any one of
them. In this embodiment, the two recovery ports are provided for
one liquid recovery piping each, and the electricity-removing
filter is provided for each of them. However, it is also allowable
that the electricity-removing filter is provided for only any one
of the two recovery ports. Even in this arrangement, it is possible
to reliably remove the electricity from the liquid 7. Further, it
is also allowable that at least one of the supply ports and the
recovery ports may be made of a conductive material, and may not
have any electricity-removing filters. Even in this simple
arrangement, at least one of the supply ports and the recovery
ports work as a part of the electricity removable unit because of
its electric conductivity, and it is possible to remove the
electricity from the liquid 7.
[0070] The numbers and the shapes of the supply ports and the
recovery ports are not specifically limited. For example, it is
also allowable that the liquid 7 is supplied and recovered with two
sets of the supply ports and the recovery ports for the long side
of the end portion 4B. In this arrangement, the supply ports and
the recovery ports may be arranged while being aligned vertically
in order to successfully supply and recover the liquid 7 in any one
of the directions of the +X direction and the -X direction. When
the wafer W is step-moved in the Y direction, it is desirable that
the liquid supply piping and the liquid recovery piping for
supplying and recovering the liquid 7 in the Y direction are
provided, in the same manner as in the first embodiment. Also in
this case, the electricity-removing filter as described above may
be provided for the liquid supply piping and/or the liquid recovery
piping. Accordingly, it is possible to avoid the charging of the
liquid caused upon the liquid supply when the step movement is
performed, and it is possible to start the scanning exposure for
the next shot area by the aid of the liquid from which the
electricity has been removed.
[0071] In the respective embodiments described above, the liquid,
which is to be used as the liquid 7, is not specifically limited to
pure water. It is possible to use liquids (for example, cedar oil)
which have the transmittance with respect to the exposure light
beam, which have the refractive index as high as possible, and
which are stable against the photoresist coated on the surface of
the wafer and the projection optical system.
[0072] A fluorine-based inert liquid, which is chemically stable,
i.e., which has a high transmittance with respect to the exposure
light beam, and which is a safe liquid, may be used as the liquid
7. For example, it is possible to use Fluorinert (trade name of 3M
of the United States) as the fluorine-based inert liquid. In
particular, when the F.sub.2 laser beam is used as the exposure
light beam, a fluorine-based liquid such as fluorine-based oil and
perfluoropolyether (PFPE), through which the F.sub.2 laser beam is
transmissive, may be used as the liquid. The fluorine-based inert
liquid as described above is also excellent in the cooling
efficiency. In view of the object of the present invention, it is
also allowable that an arbitrary additive is added in order to
prevent the liquid from being charged. For example, when pure water
is used as the liquid 7, it is possible to suppress pure water from
being charged, by injecting carbon dioxide into pure water.
[0073] The liquid 7, which is recovered in each of the embodiments
described above, may be reused. In this case, it is desirable that
a filter, which removes any impurity from the recovered liquid 7,
is provided, for example, for the liquid recovery unit or the
recovery tube.
[0074] It is enough that the range, in which the liquid 7 is
allowed to flow, is set to cover the entire area of the projection
area (irradiation area of the exposure light beam) of image of the
pattern of the reticle, and it is enough that the size thereof is
arbitrary. However, it is desirable that the range is made to be as
small as possible while making the range to be slightly larger than
the exposure area as in each of the embodiments described above, in
view of the control of, for example, the flow velocity and the flow
rate. It is difficult to recover all of the supplied liquid by the
recovery port. Therefore, for example, it is desirable that a
partition wall is formed to surround the wafer, and a piping for
recovering the liquid contained inside the partition wall is
further provided in order that the liquid does not overflow from
the surface of the Z stage.
[0075] In each of the embodiments described above, the liquid 7 is
allowed to flow in the direction of the movement of the wafer W (XY
stage 10). However, it is not necessarily indispensable that the
direction, in which the liquid 7 is allowed to flow, is coincident
with the direction of the movement. That is, the direction, in
which the liquid 7 is allowed to flow, may intersect the direction
of the movement. For example, when the wafer W is moved in the +X
direction, it is appropriate that the liquid 7 is made to flow in
such a direction that the velocity component of the liquid 7 in the
-X direction is zero or not more than a predetermined allowable
value. Accordingly, when the wafer is exposed in the
step-and-repeat manner or the step-and-scan manner (both including
the step-and-stitch manner), if the direction of the movement is
frequently changed in a short period of time (for example, about
several hundreds ms), then the direction, in which the fluid is
made to flow, can be controlled while following the change, and it
is possible to fill the space between the projection optical system
and the wafer with the liquid. In order to improve the throughput
in the scanning type projection exposure apparatus based on the
step-and-scan system, the movement of the XY stage is controlled so
that both of the velocity components of the XY stage in the
scanning direction and the non-scanning direction are not zero
during the movement of the wafer between the shot areas, i.e., the
stepping of the XY stage (movement in the non-scanning direction)
is started during the deceleration of the XY stage (before the
velocity component in the scanning direction becomes zero) after
the completion of the scanning exposure for one shot area, and that
the acceleration of the XY stage is started before the completion
of the stepping (for example, during the deceleration of the XY
stage before the velocity component in the non-scanning direction
becomes zero) in order to perform the scanning exposure for the
next shot area. Even in such a situation, the direction, in which
the liquid is made to flow, can be controlled depending on the
direction of the movement of the wafer, and the space between the
projection optical system and the wafer can be filled with the
liquid.
[0076] When the optical element of the projection optical system
PL, which is disposed most closely to the wafer W, is the optical
plate, it is desirable that the electricity is also removed from
the liquid 7 to be supplied to the space between the optical plate
and the optical element (lens 4) disposed second most closely to
the wafer W with respect to the above.
[0077] When the liquid immersion method is used as described above,
the numerical aperture NA of the projection optical system PL is
0.9 to 1.3 in some cases. When the numerical aperture NA of the
projection optical system PL is large as described above, it is
desirable to use the polarized illumination, because with the
random polarized light which has been hitherto used as the exposure
light beam, the image formation performance is deteriorated due to
the polarization effect in some cases. In this case, it is
appropriate that the linear polarized illumination, which is
adjusted to the longitudinal direction of the line pattern of the
line-and-space pattern of the reticle R, is effected so that the
diffracted light of the S-polarized light component (component in
the polarization direction along with the longitudinal direction of
the line pattern) is dominantly allowed to outgo from the pattern
of the reticle R. When the space between the projection optical
system PL and the resist coated on the surface of the wafer W is
filled with the liquid, the diffracted light of the S-polarized
light component, which contributes to the improvement in the
contrast, has the high transmittance on the resist surface, as
compared with the case in which the space between the projection
optical system PL and the resist coated on the surface of the wafer
W is filled with the air (gas). Therefore, it is possible to obtain
the high image formation performance even when the numerical
aperture NA of the projection optical system PL exceeds 1.0.
Further, it is more effective to appropriately combine, for
example, the phase shift mask and the oblique incidence
illumination method (dipole illumination method) as disclosed in
Japanese Patent Application Laid-open No. 6-188169.
[0078] Further, it is also effective to use the combination of the
oblique incidence illumination method and the polarized
illumination method in which the linear polarization is effected in
the tangential (circumferential) direction of the circle having the
center of the optical axis as disclosed in Japanese Patent
Application Laid-open No. 6-53120, without being limited to only
the linear polarized illumination (S-polarized illumination)
adjusted to the longitudinal direction of the line pattern of the
reticle R. In particular, when the pattern of the reticle R
includes not only the line pattern extending in one predetermined
direction, but the pattern also includes the line patterns
extending in a plurality of different directions in a mixed manner,
then it is possible to obtain the high image formation performance
even when the numerical aperture NA of the projection optical
system is large, by using, in combination, the zonal illumination
method and the polarized illumination method in which the light is
linearly polarized in the tangential direction of the circle having
the center of the optical axis, as disclosed in Japanese Patent
Application Laid-open No. 6-53120 as well.
[0079] The present invention is also applicable to a twin-stage
type exposure apparatus which is provided with two stages capable
of moving independently in the XY direction while separately
placing processing objective substrates such as wafers. In this
case, the exposure apparatus is constructed so that the liquid
immersion exposure can be performed on each of the substrate
stages, wherein the electricity removal unit as explained in the
foregoing embodiment may be provided for each of the stages. The
structure and the exposure operation of the twin-stage type
exposure apparatus are disclosed, for example, in Japanese Patent
Application Laid-open Nos. 10-163099 and 10-214783 (corresponding
to U.S. Pat. Nos. 6,341,007, 6,400,441, 6,549,269, and 6,590,634),
Published Japanese Translation of PCT International Publication for
Patent Application No. 2000-505958 (corresponding to U.S. Pat. No.
5,969,441), and U.S. Pat. No. 6,208,407, contents of which are
incorporated herein by reference within a range of permission of
the domestic laws and ordinances of the state designated or
selected in this international application.
[0080] As disclosed in Japanese Patent Application Laid-open No.
11-135400, the present invention is also applicable to the
projection exposure apparatus which is provided with a wafer stage
that is movable while holding a processing objective substrate such
as a wafer, and a measuring stage that is provided with measuring
sensors for measuring various types of data in relation to the
exposure, the measuring stage being movable independently from the
wafer stage. In this case, the electrode member for removing the
electricity may be provided on the measuring stage to remove the
electricity from the liquid 7 which is retained between the
measuring stage and the projection optical system PL.
[0081] The way of use of the projection exposure apparatus of this
embodiment is not limited to the projection exposure apparatus for
the semiconductor production. The present invention is also widely
applicable, for example, to the projection exposure apparatus for
the liquid crystal for exposing a rectangular glass plate with a
liquid crystal display device pattern and the projection exposure
apparatus for producing a thin film magnetic head.
[0082] The reticle or the mask, which is to be used for the
device-producing projection exposure apparatus for producing the
semiconductor element or the like, is produced, for example, by the
projection exposure apparatus using the far ultraviolet light beam
or the vacuum ultraviolet light beam in some cases. The projection
exposure apparatuses according to the respective embodiments
described above are also appropriately usable in the
photolithography step of producing the reticle or the mask.
[0083] Further, it is also allowable to use the high harmonic wave
obtained such that the single wavelength laser in the infrared
region or the visible region, which is oscillated from a fiber
laser or a DFB semiconductor laser as an illumination light beam
for the exposure, is amplified with a fiber amplifier doped with,
for example, erbium (Er) (or both of erbium and ytterbium (Yb)),
followed by being subjected to the wavelength conversion into the
ultraviolet light beam by using a nonlinear optical crystal.
[0084] The projection optical system PL may be any one of the
dioptric system, the catoptric system, and the cata-dioptric
system. As for the cata-dioptric system, it is possible to use an
optical system in which a plurality of dioptric optical elements
and two cata-dioptric optical elements (at least one of them is a
concave mirror) are arranged on an optical axis extending in a
straight line without being bent, as disclosed, for example, in
U.S. Pat. No. 5,788,229. In the case of the projection exposure
apparatus having the cata-dioptric system disclosed in this United
States patent document, the optical element, which is disposed most
closely to the wafer, i.e., which makes contact with the liquid, is
the catoptric optical element. The contents of this U.S. Pat. No.
5,788,229 are incorporated herein by reference within a range of
permission of the domestic laws and ordinances of the state
designated in this international application or the state selected
in this international application.
[0085] The projection exposure apparatus according to the
embodiment of the present invention can be produced such that the
illumination optical system and the projection optical system,
which are constructed of a plurality of lenses, are incorporated
into the main body of the exposure apparatus to perform the optical
adjustment; the reticle stage and the wafer stage, which are
constructed of a large number of mechanical parts, are attached to
the main body of the exposure apparatus to connect wirings and
pipings thereto, the pipings (for example, the supply tubes and the
supply ports) for supplying and recovering the liquid are
installed; and the overall adjustment (for example, the electric
adjustment and the confirmation of the operation) is performed. It
is desirable that the exposure apparatus is produced in a clean
room in which, for example, the temperature and the cleanness are
managed.
[0086] As shown in FIG. 7, the microdevice such as the
semiconductor device is produced by performing, for example, a step
201 of designing the function and the performance of the
microdevice, a step 202 of manufacturing a reticle (mask) based on
the designing step, a step 203 of producing a substrate as a base
material for the device, a substrate-processing step 204 of
exposing the substrate with a pattern of the reticle by using the
exposure apparatus of the embodiment described above, a step 205 of
assembling the device (including a dicing step, a bonding step, and
a packaging step), and an inspection step 206.
[0087] The present invention is not limited to the embodiments
described above, which may be embodied in other various forms
without deviating from the gist or scope of the present
invention.
[0088] According to the projection exposure apparatus of the
present invention, it is possible to remove the electricity from
the liquid to be used for the liquid immersion method. Therefore,
it is possible to avoid the malfunction of the apparatus and the
destruction of the circuit pattern which would be otherwise caused
by the electric discharge of the charged liquid. Further, according
to the projection exposure method of the present invention, the
exposure can be performed without causing the destruction of the
circuit pattern and the malfunction of the apparatus, because the
electricity is removed from the liquid to be used for the liquid
immersion method. Further, according to the method for producing
the device of the present invention, neither destruction of the
circuit pattern nor malfunction of the apparatus is caused.
Therefore, the yield is improved when the device is produced, and
it is possible to maintain the high processing ability.
* * * * *