U.S. patent application number 11/662330 was filed with the patent office on 2008-03-20 for projection optical device and exposure apparatus.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Akimitsu Ebihara, Martin E. Lee, Bausan Yuan.
Application Number | 20080068568 11/662330 |
Document ID | / |
Family ID | 36142945 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080068568 |
Kind Code |
A1 |
Ebihara; Akimitsu ; et
al. |
March 20, 2008 |
Projection Optical Device And Exposure Apparatus
Abstract
A projection optical device includes a projection optical system
which projects an image of a pattern, a support device having a
flexible structure to support the projection optical system, and a
positioning device having an actuator to position the projection
optical system. The projection optical device can include a frame
to which one end of the flexible structure is attached. The
projection optical system may hang from the frame via the support
device, or it may be supported from below by the support device. A
projection optical device also can include a liquid supply which
supplies a temperature-controlled liquid to a side surface of a
projection optical system utilizing gravity to cause the
temperature-controlled liquid to flow along the side surface of the
projection optical system.
Inventors: |
Ebihara; Akimitsu;
(Fukaya-shi, JP) ; Lee; Martin E.; (San Jose,
CA) ; Yuan; Bausan; (San Jose, CA) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
NIKON CORPORATION
Fuji Bldg, 2-3 Marunouchi 3-chome
Chiyoda-ku, Tokyo
JP
100-8331
|
Family ID: |
36142945 |
Appl. No.: |
11/662330 |
Filed: |
July 18, 2005 |
PCT Filed: |
July 18, 2005 |
PCT NO: |
PCT/US05/25454 |
371 Date: |
March 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60614426 |
Sep 30, 2004 |
|
|
|
Current U.S.
Class: |
355/30 ; 355/53;
355/67 |
Current CPC
Class: |
G03F 7/70833 20130101;
G03F 7/70808 20130101; G03F 7/709 20130101; G03F 7/70891
20130101 |
Class at
Publication: |
355/030 ;
355/053; 355/067 |
International
Class: |
G03B 27/42 20060101
G03B027/42; G03B 27/54 20060101 G03B027/54 |
Claims
1. A projection optical device comprising: a projection optical
system which projects an image of a pattern; a support device
having a flexible structure to support the projection optical
system; and a positioning device having an actuator to position the
projection optical system.
2. The projection optical device of claim 1, wherein the flexible
structure has a lower characteristic frequency in a direction
perpendicular to an optical axis of the projection optical system
than in a direction parallel to the optical axis of the projection
optical system.
3. The projection optical device of claim 1, wherein the flexible
structure includes a wire.
4. The projection optical device of claim 3, wherein the flexible
structure includes a flexure coupled to the wire.
5. The projection optical device of claim 4, wherein the flexure is
a spring.
6. The projection optical device of claim 1, wherein a length of
the flexible structure is at least 1 meter.
7. The projection optical device of claim 1, wherein the flexible
structure includes a rod member and a flexure provided on at least
one end of the rod member.
8. The projection optical device of claim 7, wherein the rod member
has a flexure provided on both ends of the rod member.
9. The projection optical device of claim 1, wherein the support
device supports the projection optical system from an upper side of
the projection optical system.
10. The projection optical device of claim 1, wherein the support
device supports the projection optical system from below the
projection optical system.
11. The projection optical device of claim 1, further comprising a
vibration isolation portion which reduces a vibration in an optical
axis direction of the projection optical system, the vibration
isolation portion is provided at one end of the flexible
structure.
12. The projection optical device of claim 1, wherein the support
device comprises a frame to which one end of the flexible structure
is attached, such that the projection optical system hangs from the
frame via the flexible structure.
13. The projection optical device of claim 12, wherein the actuator
positions the projection optical system with respect to the frame
in a non-contact manner.
14. The projection optical device of claim 13, wherein the
positioning device comprises: a displacement sensor which measures
six degrees-of-freedom of displacement information of the
projection optical system with respect to the frame.
15. The projection optical device of claim 1, wherein the support
device supports the projection optical system via a flange portion
fixed to a side surface of the projection optical system; and
further comprising a measuring unit which is kinematically
supported with respect to the flange portion and which is provided
with a sensor for measuring a positional relationship between the
projection optical system and a predetermined member.
16. The projection optical device of claim 1, wherein a member in
which the pattern is formed is integrally fixed to the projection
optical system.
17. The projection optical device of claim 16, further comprising a
micro-moving mechanism which micro-moves the member in which the
pattern is formed with respect to the projection optical
system.
18. The projection optical device of claim 1, wherein the support
device comprises a frame to which one end of the flexible structure
is attached, such that the projection optical system hangs from the
frame via the flexible structure; and further comprising: a base
which is supported by the frame via a vibration isolation member;
and a stage which drives a member in which the pattern is formed,
on the base.
19. The projection optical device of claim 18, wherein the
vibration isolation member includes one of a pivot and a
flexure.
20. The projection optical device of claim 18, further comprising:
a countermass which moves on the base so as to cancel a reaction
force that is generated by movement of the stage; and a flexure
which supports the countermass on the base.
21. The projection optical device of claim 1, wherein the
projection optical system is arranged in a downflow
environment.
22. The projection optical device of claim 15, wherein the
measuring unit includes a laser interferometer, and further
comprising a local gas flow system which performs a local downflow
of a gas with respect to an optical path of a laser beam used by
the laser interferometer.
23. The projection optical device of claim 1, further comprising: a
tube which is arranged along a side surface of the projection
optical system; and a liquid supply which supplies a cooling liquid
to the tube.
24. An exposure apparatus provided with the projection optical
device of claim 1, wherein an image of the pattern is transferred
and exposed onto a substrate by the projection optical system.
25. A projection optical device comprising: a projection optical
system which projects an image of a pattern; and a liquid supply
which supplies a temperature-controlled liquid to a side surface of
the projection optical system utilizing gravity to cause the
temperature-controlled liquid to flow along the side surface of the
projection optical system.
26. The projection optical device of claim 25, wherein the liquid
supply comprises: a tube which is wrapped around the side surface
of the projection optical system; and a liquid circulation system
which circulates the temperature-controlled liquid through the tube
by a siphon principle.
27. An exposure apparatus provided with the projection optical
device of claim 25, wherein an image of the pattern is transferred
and exposed onto a substrate by the projection optical system.
28. The projection optical device of claim 25, wherein the liquid
supply comprises: a liquid reservoir located adjacent to a
vertically upper portion of the projection optical system; the tube
which is wrapped around the side surface of the projection optical
system, the tube in communication with the liquid reservoir; and a
liquid return path through which the fluid that has passed through
the tube is returned to the liquid reservoir.
29. The projection optical device of claim 28, wherein the liquid
return path includes a temperature control system that controls the
temperature of the liquid, the temperature control system includes
a pump that pumps the liquid to the liquid reservoir.
30. A method of controlling a temperature of a projection optical
system which projects an image of a pattern in a projection optical
device, the method comprising: supplying a temperature-controlled
liquid to a side surface of the projection optical system utilizing
gravity to cause the temperature-controlled liquid to flow along
the side surface of the projection optical system.
31. The method of claim 30, wherein: the temperature-controlled
liquid is supplied through a tube which is wrapped around the side
surface of the projection optical system in order to control the
temperature of the projection optical system; and further
comprising: circulating the cooling liquid through the tube by a
siphon principle.
32. The method of claim 30, further comprising: providing a liquid
reservoir located adjacent to a vertically upper portion of the
projection optical system; supplying the temperature-controlled
liquid to the tube which is wrapped around the side surface of the
projection optical system from the liquid reservoir; and returning
the fluid that has passed through the tube to the liquid reservoir
by a liquid return path.
33. The method of claim 32, further comprising: controlling the
temperature of the liquid in the liquid return path by using a
temperature control system; and pumping the liquid through the
liquid return path and into the liquid reservoir by using a
pump.
34. A method of supporting a projection optical system which
projects an image of a pattern in a projection optical device, the
method comprising: supporting the projection optical system by a
flexible structure of a support device; and positioning the
projection optical system by an actuator of a positioning
device.
35. The method of claim 34, wherein the flexible structure has a
lower characteristic frequency in a direction perpendicular to an
optical axis of the projection optical system than in a direction
parallel to the optical axis of the projection optical system.
36. The method of claim 34, wherein the flexible structure includes
a wire.
37. The method of claim 36, wherein the flexible structure includes
a flexure coupled to the wire.
38. The method of claim 37, wherein the flexure is a spring.
39. The method of claim 34, wherein a length of the flexible
structure is at least 1 meter.
40. The method of claim 34, wherein the flexible structure includes
a rod member and a flexure provided on at least one end of the rod
member.
41. The method of claim 40, wherein the rod member has a flexure
provided on both ends of the rod member.
42. The method of claim 34, wherein the support device supports the
projection optical system from an upper side of the projection
optical system.
43. The method of claim 34, wherein the support device supports the
projection optical system from below the projection optical
system.
44. The method of claim 34, further comprising: providing a
vibration isolation portion at one end of the flexible structure,
the vibration isolation portion reduces a vibration in an optical
axis direction of the projection optical system.
45. The method of claim 34, wherein the support device comprises a
frame to which one end of the flexible structure is attached, such
that the projection optical system hangs from the frame via the
flexible structure.
46. The method of claim 45, wherein the actuator positions the
projection optical system with respect to the frame in a
non-contact manner.
47. The method of claim 46, wherein the actuator measures six
degrees-of-freedom of displacement information of the projection
optical system with respect to the frame.
48. The method of claim 34, wherein the support device supports the
projection optical system via a flange portion fixed to a side
surface of the projection optical system, and further comprising:
providing a measuring unit which is kinematically supported with
respect to the flange portion and which includes a sensor for
measuring a positional relationship between the projection optical
system and a predetermined member.
49. The method of claim 34, further comprising: providing a
micro-moving mechanism which micro-moves a member in which the
pattern is formed with respect to the projection optical
system.
50. The method of claim 34, wherein the support device comprises a
frame to which one end of the flexible structure is attached, such
that the projection optical system hangs from the frame via the
flexible structure; and further comprising: providing a base which
is supported by the frame via a vibration isolation member; and
providing a stage which drives a member in which the pattern is
formed, on the base.
51. The method of claim 50, wherein the vibration isolation member
includes one of a pivot and a flexure.
52. The method of claim 50, further comprising: providing a
countermass which moves on the base so as to cancel a reaction
force that is generated by movement of the stage; and providing a
flexure which supports the countermass on the base.
53. The method of claim 34, further comprising: arranging the
projection optical system in a downflow environment.
54. The method of claim 48, wherein the measuring unit includes a
laser interferometer, and further comprising: providing a local gas
flow system which performs a local downflow of a gas with respect
to an optical path of a laser beam used by the laser
interferometer.
55. The method of claim 34, further comprising: providing a tube
which is arranged along a side surface of the projection optical
system; and providing a liquid supply which supplies a cooling
liquid to the tube.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/614,426, filed Sep. 30, 2004. The disclosure of
U.S. Provisional Application No. 60/614,426 is incorporated herein
by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] This invention relates to a projection optical device
provided with a projection optical system which projects an image
of a predetermined pattern, and to an exposure apparatus which is
used in order to transfer a pattern of a mask onto a substrate in
order to manufacture various devices such as, for example, a
semiconductor device, a liquid crystal display, etc.
[0004] 2. Description of Related Art
[0005] In a lithography process, which is one process used to
manufacture a semiconductor device, an exposure apparatus is used
in order to transfer and expose a pattern formed on a reticle (or a
photomask, etc.) onto a wafer (or a glass plate, etc.) coated by
photoresist as a substrate. Various types of exposure apparatus,
such as, for example, a step and repeat exposure type (stationary
exposure type) projection exposure apparatus such as a stepper, and
a step and scan exposure type projection exposure apparatus
(scanning exposure apparatus) such as a scanning stepper, can be
used.
[0006] In exposure apparatus, rigidity of: (i) the stages which
move and position a reticle and a wafer, (ii) a support mechanism
of the stages, and (iii) a mechanism portion of the support
mechanism and the like of a projection optical system,
significantly affects the performance capability of the apparatus,
such as a vibration control performance capability, an exposure
accuracy (overlay accuracy or the like), weight of the mechanism
portion, and manufacturing cost of the exposure apparatus. In
general, an exposure apparatus having a mechanism portion with high
rigidity, while providing a high apparatus performance capability,
tends to have a heavy mechanism portion, and a higher manufacturing
cost. Furthermore, rigidity of the mechanism portion also is
related to the temperature characteristics of the apparatus
performance capability, and the stability of the apparatus
performance capability corresponding to changes of the apparatus
performance capability over time. That is, exposure apparatus
having a mechanism portion with high rigidity tend to have good
stability with respect to the apparatus performance capability, and
excellent temperature characteristics, but depending on the
structure of the mechanism portion, there are cases in which the
opposite trend occurs. For example, in a mechanism portion, when
members with high rigidity are coupled to each other through
members having high rigidity, vibration can be easily transmitted,
a bi-metal effect is generated at the time of temperature change
(if different materials are used for the members), and the
temperature characteristics may be deteriorated.
[0007] However, as a result of increasing rigidity of the mechanism
portion, when the weight of the mechanism portion increases, there
also is a possibility of increased construction cost of the device
manufacturing factory in which exposure apparatus is installed (in
order to deal with the weight of the exposure apparatus).
Therefore, conventionally, in order to maintain high rigidity and
perform positioning and scanning at a high speed while reducing the
apparatus weight, a lightweight material with specific stiffness
(value in which rigidity is divided by the weight per unit volume),
such as a ceramic, can be used as a material of a part of the
members which constitute a stage.
[0008] Furthermore, an exposure apparatus also has been proposed in
which the stages and the projection optical system are
independently supported by parallel link mechanisms, each having a
plurality of rods which can expand and contract. This system
maintains high rigidity in a necessary portion and lightens the
weight of the entire mechanism portion. See, e.g., International
Publication No. WO 01/022480.
[0009] Thus, in a conventional exposure apparatus, in order to
maintain a high device capability with respect to vibration control
performance or the like, it is desirable to improve rigidity of a
mechanism portion of a support mechanism or the like, while
reducing the weight of the mechanism portion. However, among
conventional technology, with respect to a method of using a
material with specific stiffness and light weight, the material can
be used only for a portion of the mechanism portion due to its high
manufacturing cost, the material shape, or the like, so the
lightening of the entire mechanism portion is not yet significantly
improved. In order to further lighten the entire mechanism portion,
it is desirable to change the structure itself of the mechanism
portion including the support mechanism of the projection optical
system.
[0010] Meanwhile, in the method that uses parallel link mechanisms,
each having a plurality of elongatable rods, it is desirable to
further improve the lightening of the mechanism portion, and the
control accuracy of a movable portion of a stage. However, there is
a possibility that control at the time of scanning and stage
positioning also becomes complex because the structure of the
mechanism portion becomes complex. Additionally, although the
projection optical system can be supported by using the parallel
link mechanism, this tends to cause the structure of the mechanism
portion to become even more complex. In this regard, in recent
exposure apparatus, a thermal distortion amount of the mechanism
portion and a fluctuation amount of imaging characteristics of the
projection optical system due to the exposure amount of the
exposure beam and the surrounding temperature are predicted in
advance. According to this prediction result, correction of the
imaging characteristics, positioning correction of the reticle and
the wafer, or the like is performed during use of the apparatus.
However, once the mechanism portion becomes complex, the estimated
accuracy of the thermal distortion amount of the mechanism portion
and the fluctuation amount of the imaging characteristic
deteriorates, and therefore it is possible that the exposure
accuracy may deteriorate.
[0011] Furthermore, conventionally, in order to control the
fluctuation amount of the imaging characteristic of the projection
optical system due to the temperature fluctuation, a cooling liquid
is supplied to the surrounding of the projection optical system. In
this case, in order to increase the vibration control performance
capability of the exposure apparatus, it is desirable that the
vibration of the motive force which supplies the cooling liquid
should be controlled.
SUMMARY OF THE INVENTION
[0012] This invention reflects on the above problems, and has as a
first object, the provision of a support for a projection optical
system using a relatively simplified, light mechanism in a state in
which a high vibration isolation performance capability is
obtained.
[0013] A second object of this invention is to provide an exposure
apparatus which can maintain a high device performance capability,
such as a positioning performance capability, and obtain high
rigidity where necessary, and lighten the entire mechanism
portion.
[0014] A third object of this invention is to reduce vibration when
a cooling liquid is supplied to the surrounding of the projection
optical system.
[0015] In a projection optical device according to a first aspect
of this invention, a projection optical system that projects an
image of a pattern is supported by a support device having a
flexible structure to support the projection optical system, and a
positioning device having an actuator to position the projection
optical system.
[0016] According to this aspect of the invention, the projection
optical system is supported by a predetermined member (e.g., frame
or the like) via the flexible structure. Therefore, in a relatively
simplified and light mechanism, the vibration of the predetermined
member is not easily transmitted to the projection optical system,
and the characteristic frequency of the flexible structure is low.
Thus, a high vibration control performance capability can be
obtained.
[0017] In this case, the predetermined member and the projection
optical system can be considered as a rigid structure with high
rigidity, whereas the flexible structure has low rigidity.
According to this aspect of the invention, a ratio occupied by
members having a rigid structure decreases within the device, and a
flexible structure is used. In general, a flexible structure has a
characteristic opposite to that of a rigid structure, is light, has
a low cost, and can obtain a preferable characteristic of shielding
vibration and receiving/transmitting thermal displacement depending
on the structure of the flexible structure. According to this
aspect of the invention, a rigid structure can be used for the
portion(s) which directly affect(s) device performance capability,
and a flexible structure can be used for the portion(s) that couple
rigid structures to each other. By this structure, the effects of
thermal displacement and the transmittance of the vibration are
minimized or prevented entirely. Therefore, the mechanism portion
can be lightened while the device performance capability is kept
high.
[0018] According to this aspect of the invention, in one example,
the flexible structure includes three coupling members, each of
which has a lower characteristic frequency in a direction
perpendicular to the optical axis than in the direction parallel to
the optical axis of the projection optical system. By having three
coupling members, the projection optical system is supported in a
stable manner. Furthermore, because the coupling members are
comprised of, for example, thin long members extending in a
direction along the optical axis, the characteristic frequency of
the coupling members becomes low in a direction perpendicular to
the optical axis. Thus, with respect to the vibration having a high
frequency component, blurring (deterioration of the contrast) of
the image position is reduced when the image pattern is transferred
via the projection optical system.
[0019] In one example, the coupling members include wires or rod
members provided with flexures on their top end portion and/or
their lower end portion. The length of the coupling members
preferably is 1 m or greater. Thus, when the length of the coupling
member is 1 m or greater, the characteristic frequency in the
direction perpendicular to the optical axis of the coupling member
is substantially 0.5 Hz or less, so the projection optical system
is extremely stably supported with respect to external
vibration.
[0020] Furthermore, in part of the coupling member, vibration
isolation portions can be arranged which reduce the vibration in
the optical axis direction of the projection optical system. By so
doing, the vibration in the direction parallel to the optical axis
of the projection optical system can be further reduced.
[0021] Furthermore, a frame which supports the coupling members,
and the positioning device which positions the projection optical
system without contacting the frame can be provided.
[0022] According to this aspect of the invention, the coupling
members have a flexible structure, so the frame with a rigid
structure and the projection optical system can be relatively
displaced at a low frequency. In such a case, by using the
positioning device, the relative position of the frame and the
projection optical system (i.e., the support member of the
projection optical system) is held at a target position, so a
preferable characteristic (the lightening of the mechanism portion
and shielding of vibration and effects of temperature changes) due
to having a flexible structure can be maintained, and the device
performance capability, such as stability of the position of the
projection image or the like can be improved. In other words, with
respect to vibration within the frequency range which can be
controlled by the positioning device, the projection optical system
is supported by an active suspension control method, and with
respect to the vibration at frequencies which exceed this frequency
range, the projection optical system is suspended and supported by
a passive vibration isolation structure.
[0023] The positioning device also can be provided with
displacement sensors which measure six degrees-of-freedom of
displacement information of the projection optical system with
respect to the frame, and six degrees-of-freedom actuators which
position the projection optical system in a non-contact manner with
respect to the frame. By using the measurement result of the
displacement sensors, the relative position of the projection
optical system with respect to the frame can be controlled.
[0024] Furthermore, in one example, the support device includes a
flange portion fixed to the side surface of the projection optical
system, and the flange portion kinematically supports a measurement
unit having a sensor which measures the positional relationship
between the projection optical system and a predetermined member
(e.g., the wafer stage). Therefore, the measurement unit is
supported in a state in which there is a predetermined positional
relationship with respect to the projection optical system, and
very little stress is applied, so the positional relationship
between the projection optical system and the predetermined member
can be measured with high accuracy.
[0025] In one example, a member (reticle) in which the pattern is
formed can be integrally provided with the projection optical
system. This is effective, for example, when the pattern is
transferred by a step and repeat exposure method. In this case, a
micro-moving mechanism can be provided which micro-moves the
reticle with respect to the projection optical system. Positioning
of the reticle pattern can be performed by the micro-moving
mechanism.
[0026] In another example, a frame which supports the flexible
structure, a base which is supported to the frame via vibration
isolation members, and a stage which drives the member in which the
pattern is formed on the base can be provided. For example, when
the pattern is transferred by a scanning exposure method, the
member in which the pattern is formed can be scanned with the
stage. Furthermore, the vibration isolation member is operated as a
flexible structure which couples the base and the frame as a rigid
structure, and application of an extra stress to the base can be
suppressed by the vibration isolation member.
[0027] In this case, as an example, the vibration isolation member
can include pivots or flexures. Pivots or flexures allow a
rotational motion, so they can be vibration isolation members as a
simplified mechanism.
[0028] Furthermore, in order to cancel a reaction force caused by
the movement of the stage, a countermass member which is moved on
the base, and a flexure mechanism which supports the countermass
member on the base can be further provided. By so doing,
transmission of vibrations between the countermass member and the
base can be even more completely shielded.
[0029] According to another aspect of this invention, the
projection optical system can be arranged in a downflow
environment. The projection optical system is supported, so a gas
such as temperature-controlled air smoothly flows in the vicinity
of the projection optical system by a downflow method. Therefore,
temperature stability of the projection optical system is
improved.
[0030] Additionally, according to this aspect of the invention, the
measurement unit is provided with laser interferometers, and also
can be provided with a local gas flow system which performs a local
downflow with respect to the optical path of the laser beam of the
laser interferometers. By so doing, the measurement accuracy of the
laser interferometers is improved.
[0031] In addition, a pipe which is arranged along the side surface
of the projection optical system, from the flexible structure, and
a liquid supply system which supplies a cooling liquid to the pipe,
can be provided. In this structure, the flexible structure also can
be used to support the pipe, and the temperature stability of the
projection optical system is improved.
[0032] In a projection optical device according to a second aspect
of this invention, a projection optical system which projects an
image of a pattern is provided with a liquid supply device which
supplies a cooling liquid to the side surface of the projection
optical system by a gravity drive. According to this aspect of the
invention, the cooling liquid flows due to gravity, so hardly any
vibration is generated.
[0033] According to this aspect of the invention, in one example,
the liquid supply device is provided with a pipe which is wrapped
around the side surface of the projection optical system, and a
liquid circulation system which circulates the cooling liquid to
the pipe according to a siphon principle. With this structure, the
cooling liquid can be circulated by a simplified structure.
[0034] An exposure apparatus can be provided with a projection
optical device according to various aspects of this invention. Such
an exposure apparatus transfers and exposes an image of the pattern
onto a substrate by the projection optical system. In this exposure
apparatus, when the projection optical device according to the
first aspect of this invention is provided, in a portion in which
the projection optical system or the like is needed, high rigidity
can be obtained, and the device performance capability of the
vibration isolation performance capability or the like can be kept
high, and the entire mechanism portion can be lightened by
suspending and supporting the projection optical system.
[0035] Furthermore, by supporting the projection optical system as
a rigid structure, via a flexible structure, with respect to a
predetermined member having a rigid structure, the respective
advantages of the rigid and flexible structures can be utilized and
combined. Therefore, compared to a conventional example, the ratio
occupied by the rigid structure in the device can be reduced, so
without decreasing the device performance capability, such as
stability of the position of a projection image or the like, the
mechanism portion can be lightened and manufactured at a lower
cost.
[0036] In an exposure apparatus utilizing a projection optical
device according to the second aspect of this invention, when a
cooling liquid is supplied to the surrounding of the projection
optical system, the vibration can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The invention will be described in conjunction with the
following drawings in which like reference numerals designate like
elements and wherein:
[0038] FIG. 1 is a diagram showing a schematic structure of a
projection exposure apparatus of an embodiment of this
invention;
[0039] FIG. 2 is a perspective view showing a schematic structure
of a mechanism portion of a projection exposure device of a first
exemplary embodiment of this invention;
[0040] FIG. 3 is a plan view which cuts through a portion showing a
flange 18 and a projection optical system PL of FIG. 2;
[0041] FIG. 4 is a plan view which cuts through a portion showing a
modified example of FIG. 3;
[0042] FIG. 5A is a perspective view showing a coupling state of
the flange 18 and a measurement mount 15 of FIG. 2;
[0043] FIG. 5B is a perspective view showing a lower end portion of
a rod 38A of FIG. 5A;
[0044] FIG. 5C is a perspective view showing a convex portion and a
notch portion within the measurement mount 15 of FIG. 5A;
[0045] FIG. 6 is a perspective view showing a rod 43 which can be
used instead of rods 38A-38C of FIG. 5A;
[0046] FIG. 7 is a perspective view showing a schematic structure
of a mechanism portion of a projection exposure apparatus of a
second exemplary embodiment of this invention;
[0047] FIG. 8 is a diagram showing a liquid supply system of FIG.
7;
[0048] FIG. 9 is a schematic structural view showing a mechanism
portion of a projection exposure apparatus of a third exemplary
embodiment of this invention;
[0049] FIG. 10 is a schematic structural view which cuts through a
portion showing a mechanism portion of a projection exposure
apparatus of a fourth exemplary embodiment of this invention;
[0050] FIG. 11 is an enlarged cross-sectional view showing members
from a countermass 59 to an intermediate member 55 of FIG. 10;
[0051] FIG. 12 is a schematic structural view that cuts through a
portion of a projection exposure apparatus of a fifth embodiment;
and
[0052] FIG. 13 is a perspective view of the FIG. 12 exposure
apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First Embodiment
[0053] The following explains a first exemplary embodiment of this
invention with reference to FIGS. 1-6. In this embodiment, the
invention is applied to a step and repeat exposure type projection
exposure apparatus such as a stepper or the like, and to a step and
scan exposure type projection exposure apparatus such as a scanning
stepper or the like.
[0054] FIG. 1 is a block diagram of different functional units
which constitute a projection exposure apparatus of this
embodiment. In FIG. 1, a chamber in which the projection exposure
apparatus is located, is omitted. In FIG. 1, a laser light source 1
is provided. The laser light source 1 can be a KrF excimer laser
(wavelength 248 .mu.m) or an ArF excimer laser (wavelength 193
.mu.m), for example. The light source also could be a device which
radiates an oscillating laser beam in an ultraviolet range such as
an F.sub.2 laser (wavelength 157 nm), a device which radiates a
harmonic laser beam in a vacuum ultraviolet range which can be
obtained by wavelength-converting a laser beam in a near infrared
range supplied from a solid-state laser light source (YAG or a
semiconductor laser, or the like). A mercury discharge lamp, or the
like, which is often used in this type of exposure apparatus also
can be used.
[0055] Illumination light for exposure (exposure light) EL as an
exposure beam from the laser light source 1 irradiates a reticle
blind mechanism 7 with a uniform irradiation distribution via a
homogenizing optical system 2, which is constituted by a lens
system and a fly's eye lens system, a beam splitter 3, a variable
attenuator 4 for adjusting a light amount, a mirror 5, and a relay
lens system 6. The illumination light EL which is restricted to a
predetermined shape (e.g., a square shape in a step and repeat
exposure type, and a slit shape in a step and scan exposure type)
by the reticle blind mechanism 7 is irradiated onto a reticle R (a
mask) via an imaging lens system 8, and an image of an opening of
the reticle blind 7 is imaged on the reticle R. An illumination
optical system 9 is constituted by the above-described homogenizing
optical system 2, the beam splitter 3, the variable attenuator 4,
the mirror 5, the relay lens system 6, the reticle blind mechanism
7, and the imaging lens system 8.
[0056] In a circuit pattern region formed on the reticle R, the
image of the portion irradiated by the illumination light is imaged
and projected onto a wafer W coated by photoresist (a substrate) (a
photosensitive substrate or a photosensitive body) via a projection
optical system PL having a reduction projection magnification
.beta. and being both-side telecentric. For example, the projection
magnification .beta. of the projection optical system PL can be
1/4, 1/5, or the like, the imaging side numeral aperture NA can be
0.7, and a diameter of a field of view can be approximately 27-30
mm. The projection optical system PL is a refractive system, but a
cata-dioptric system or the like also can be used. The reticle R
and the wafer W also can be considered as first and second objects,
respectively. In the following explanation, a Z axis is defined to
be parallel to an optical axis AX of the projection optical system
PL, an X axis extends in a direction parallel to a paper plane of
FIG. 1, and is perpendicular to the Z axis, and a Y axis extends in
a direction perpendicular to a paper plane of FIG. 1. When a
projection exposure apparatus of this example is a step and scan
exposure type, a direction (Y direction) along the Y axis is a
scanning direction of the reticle R and the wafer W during scanning
exposure, and the illumination region on the reticle R becomes an
elongated shape extending in a direction (X direction) along the X
axis, which is a non-scanning direction.
[0057] Furthermore, the reticle R which is arranged on an object
surface side of the projection optical system PL is held by vacuum
pressure to a reticle stage RST (mask stage). In the case of a step
and repeat exposure type, the reticle stage RST (micro-moving
mechanism) is micro-moved on a reticle base (undepicted) in a
rotation direction about the X and Y directions and in the Z axis
direction, in addition to in the X and Y directions, so as to
position the reticle R. Meanwhile, in the case of the scanning
exposure apparatus, the reticle stage RST (stage) is moved at a
constant speed at least in the Y direction (scanning direction) via
an air bearing on a reticle base (undepicted). The moving
coordinate position (the positions in the X and Y directions, and
the rotation angle about the Z axis) of the reticle stage RST is
successively measured by a moving mirror Mr fixed to the reticle
stage RST, a reference mirror Me fixed to the upper portion side
surface of the projection optical system PL, and a laser
interferometer system 10 arranged opposite to these mirrors. The
laser interferometer system 10 includes a laser interferometer main
body portion 10a, a beam splitter 10b which divides the laser beam
into a beam for the moving mirror Mr and a beam for the reference
mirror Me, and a mirror 10c which supplies the laser beam to the
reference mirror Me. Furthermore, the moving mirror Mr, the
reference mirror Me, and the laser interferometer system 10
actually constitute at least a uniaxial laser interferometer system
in the X direction, and a biaxial or a triaxial laser
interferometer system in the Y direction.
[0058] Furthermore, the movement of the reticle stage RST is
performed by a driving system 11 comprised of a linear motor, a
micro-moving actuator, or the like. The measurement information of
the laser interferometer system 10 is supplied to a stage control
unit 14, and the stage control unit 14 controls the driving system
11 based on the control information (input information) received
from a main control system 20 comprised of a computer which
controls the operation of the entire device, and the measurement
information.
[0059] Meanwhile, the wafer W arranged on the image plane side of
the projection optical system PL is adsorbed and held on the wafer
stage WST (substrate stage) via an undepicted wafer holder. In the
case of the step and repeat exposure type, the wafer stage WST is
step-moved in the X and Y directions via an air bearing on a wafer
base (undepicted). In the case of the scanning exposure type, the
wafer stage WST can be moved at a constant speed at least in the Y
direction at the time of scanning exposure, and is mounted on a
wafer base (undepicted) via an air bearing so as to be step-moved
in the X and Y directions. The moving coordinate position (the
positions in the X and Y directions, the rotation angle about the Z
axis) of the wafer stage WST is successively measured by a
reference mirror Mf fixed to the lower portion of the projection
optical system PL, a moving mirror Mw fixed to the wafer stage WST,
and a laser interferometer system 12 arranged opposite to these
mirrors. The laser interferometer system 12 includes a laser
interferometer main body portion 12a, a beam splitter 12b which
divides a laser beam into a beam for the moving mirror Mw and a
beam for the reference mirror Mf, and a mirror 12c which supplies a
laser beam to the moving mirror Mw. The moving mirror Mw, the
reference mirror Mf, and the laser interferometer system 12
actually constitute at least a uniaxial laser interferometer system
in the X direction, and a biaxial or a triaxial laser
interferometer system in the Y direction. Furthermore, the laser
interferometer system 12 is further provided with a biaxial laser
interferometer for rotation angle measurement about the X and Y
axes.
[0060] The laser interferometer system 12 (laser interferometer)
can be considered as one sensor for measuring a positional
relationship between the projection optical system PL and the wafer
stage WST as a predetermined member. The laser interferometer
system 12 is fixed to the bottom surface of a measurement mount 15
(measuring unit) which is an annular flat plate-shaped member
arranged on the lower portion side surface of the projection
optical system PL. Furthermore, in order to reduce fluctuation
(fluctuation in an index of refraction) of air on the optical path
of the laser beam to be supplied to the moving mirror Mw and the
reference mirror Mf from the laser interferometer system 12, an air
duct 16 having flexibility is fixed to the measurement mount 15. As
shown in FIG. 2, the air duct 16 extends substantially parallel to
a column 33A, one side of an upper portion column 34, and a wire
35B. Gas such as highly clean air at a controlled temperature and
humidity is supplied from a small air conditioning device 17 (see
FIG. 2), and the gas is supplied to the optical path of the laser
beam of the laser interferometer system 12 by a local downflow
method. Furthermore, in order to couple a portion of the air duct
16 with the wire 35B, a fixed mount 16M (support member) is
arranged in the vicinity of a movable portion of the wire 35B. A
local gas flow system is constituted of the small air conditioning
device 17 and the air duct 16. By so doing, the measurement
accuracy of the laser interferometer system 12 is improved.
Additionally, a plurality of air ducts 16 also can be provided.
[0061] In FIG. 1, the movement of the wafer stage WST is performed
by a driving system 13 comprising an actuator such as a linear
motor, a voice coil motor (VCM), or the like. The measurement
information of the laser interferometer system 12 is supplied to
the stage control unit 14, and the stage control unit 14 controls
the operation of the driving system 13 based on the measurement
information and the control information (input information)
received from the main control system 20.
[0062] Additionally, the wafer stage WST is moved to control its
position (focus position) in the Z direction of the wafer W, by a
Z-leveling mechanism which also controls an inclination angle about
the X and Y axes. Furthermore, an oblique incident type multi-point
autofocus sensor (23A, 23B) is fixed to the measurement mount 15 of
the lower side surface of the projection optical system PL. The
oblique incident type multi-point autofocus sensor (23A, 23B) is
composed of a projection optical system 23A which projects a slit
image onto a plurality of measurement points on the surface of the
wafer W, and a light receiving optical system 23B which detects the
information relating to the horizontal shift amount of the image in
which these slit images were re-imaged by receiving the reflected
light from the surface, and supplies this information to the stage
control unit 14. The stage control unit 14 calculates a defocus
amount from the image plane of the projection optical system PL in
the plurality of measurement points by using the information of the
horizontal shift amount of the slit image, and drives the Z
leveling mechanism within the wafer stage WST by the autofocus
method so that the focus amount is maintained within predetermined
control accuracy at the time of exposure. A detailed structure of
one type of an oblique incident type multi-point autofocus sensor
is disclosed in, e.g., Japanese Laid-Open Patent Application
1-253603.
[0063] Furthermore, the stage control unit 14 includes a control
system on the reticle side which optimally controls the driving
system 11 based on the measurement information received from the
laser interferometer system 10, and a control system on the wafer
side which optimally controls the driving system 13 based on the
measurement information received from the laser interferometer
system 12. If the projection exposure apparatus of this example is
a scanning exposure type, when the reticle R and the wafer W are
synchronously scanned at the time of scanning exposure, both
control systems coordinate and control the respective driving
systems 11 and 13. Furthermore, the main control system 20 mutually
communicates with the respective control systems in the stage
control unit 14 with respect to parameters and commands, and the
respective control systems in the stage control unit 14, and
optimally performs exposure processing in accordance with a program
designated by an operator. Because of this, an undepicted operation
panel unit (including an input device and a display device) is
provided, and forms an interface between the operator and the main
control system 20.
[0064] Furthermore, at the time of exposure, it is desirable to
align the reticle R and the wafer W in advance. Therefore, in the
projection exposure apparatus of FIG. 1, a reticle alignment system
(RA system) 21 which sets the reticle R at a predetermined
position, and an off-axis type alignment system 22 which detects a
mark on the wafer W are provided. The alignment system 22 (mark
detection system) is fixed to the measurement mount 15. The
multi-point autofocus sensors (23A, 23B) and the alignment system
22 can be considered as one sensor which measures the positional
relationship between the projection optical system PL and the wafer
stage WST or the wafer W (predetermined member).
[0065] Furthermore, when the laser light source 1 is an excimer
laser light source, a laser control unit 25 which is controlled by
the main control system 20 is provided. Laser control unit 25
controls modes (one pulse mode, burst mode, waiting mode, or the
like) of pulse oscillation of the laser light source 1, and
controls a discharging high voltage of the laser light source 1 in
order to adjust an average light amount of the pulse laser light to
be radiated. Furthermore, a light amount control unit 27 controls a
variable attenuator 4 in order to obtain an appropriate exposure
dose based on the signal received from a photoelectric detector 26
(integrator sensor) which receives part of the illumination light
divided by the beam splitter 3, and sends intensity (light amount)
information of the pulse illumination light to the laser control
unit 25 and the main control system 20.
[0066] Additionally, in FIG. 1, in the case of a step and repeat
exposure type apparatus, an operation which, in the presence of the
illumination light IL, projects a pattern of the reticle R onto one
shot area on the wafer W via the projection optical system PL, and
an operation which step-moves the wafer W via the wafer stage WST
in the X and Y directions are repeated by a step-and-repeat method.
Meanwhile, in the case of a scanning exposure type apparatus,
according to the scanning exposure operation, a pattern image of
the reticle R is transferred to the shot area, in a state in which
irradiation of the illumination light IL to the reticle R is
provided, the image which passed through part of the pattern of the
reticle R of the projection optical system PL is projected onto one
shot area on the wafer W, and, using projection magnification
.beta. of the projection optical system PL as a speed ratio, the
reticle stage RST and the wafer stage WST are synchronously moved
(synchronized scanning) in the Y direction. Then, by repeating the
operation in which irradiation of the illumination light IL is
stopped and the wafer W is step-moved in the X and Y directions via
the wafer stage WST and the above-mentioned scanning exposure
operation, the pattern image of the reticle R is transferred onto
all of the shot areas on the wafer W by a step-and-scan method.
[0067] The following explains the details of a structure of the
mechanism portion of the projection exposure apparatus of this
example of the invention. This mechanism portion also can be
considered as a projection optical device provided with a
projection optical system PL. The following explains when the
projection exposure apparatus of this example is a step and repeat
exposure type.
[0068] FIG. 2 shows a schematic structure of the mechanism portion
of the projection exposure apparatus of this example. In FIG. 2,
short cylindrical seats 32A, 32B (the third seat, 32C, is
undepicted) are arranged at three locations located at the vertices
of a triangle on the floor surface. Long columns 33A, 33B, 33C are
located on the respective three seats 32A, 32B, 32C. The columns
are arranged in a state so that position shifting is not generated,
thus the thin, long cylindrical columns 33A, 33B, 33C slant
inwardly to some degree as shown in FIG. 2 (rather than being
perfectly vertical). The three columns 33A-33C are arranged so that
the spacing between their upper portions is more narrow than the
spacing between their lower ends, and a substantially triangle
frame-shaped upper column 34 is fixed on the top surfaces of the
columns 33A-33C. A column structural body comprised of the columns
33A-33C and the upper column 34 corresponds to a frame which
suspends the projection optical system PL.
[0069] That is, the projection optical system PL is arranged within
a space surrounded by the columns 33A-33C, and the flange 18
(support member) is integrally fixed to the projection optical
system PL so as to substantially surround the side surface of the
center in the Z direction of the projection optical system PL. The
flange 18 can be integrated with a lens barrel of the projection
optical system PL. Additionally, one end of coil springs 36A, 36B,
36C (vibration isolation portions), which are identical to each
other, is fixed to the respective center portion of each of the
three pieces of the upper column 34. The flange 18 is coupled to
the other end of the coil springs 36A, 366B, 36C via wires 35A,
35B, 35C, which are identical to each other and made of metal. The
wire 35A and the coil spring 36A correspond to one coupling member.
In the same manner, other wires 35B, 35C and coil springs 36B and
36C correspond to two other coupling members. These coupling
members are substantially parallel to each other and parallel to
the Z axis. In this example, the direction (-Z direction) toward
the floor surface is a vertical direction, and a plane (XY plane)
perpendicular to the Z axis is a substantially horizontal plane.
Therefore, from the upper column 34, the projection optical system
PL and the flange 18 are suspended and supported via the three
coupling members.
[0070] In this case, the optical axis of the projection optical
system PL is parallel to the Z axis, and the characteristic
frequency of the coupling members of this example is lower in the
direction perpendicular to the optical axis than in the direction
parallel to the optical axis of the projection optical system PL.
The coupling members vibrate like a pendulum in a direction
perpendicular to the optical axis, so if the length in the Z
direction of the coupling members is L, and the acceleration
constant is G (=9.8 m/s.sup.2), as shown below, the longer the
length L becomes, the lower the characteristic frequency fg in the
direction perpendicular to the optical axis becomes. fg = 1 2
.times. .pi. .times. G / L ( 1 ) ##EQU1##
[0071] The lower the characteristic frequency fg becomes, the
better the vibration isolation performance capability (capability
which prevents vibration of the floor from being transmitted to the
projection optical system PL) in the direction perpendicular to the
optical axis of the projection optical system PL becomes. Thus, in
order to improve the vibration isolation performance capability,
the longer the length L of the coupling members becomes, the
better. However, on the other hand, in order to stably support the
projection optical system PL, it is preferable that the flange 18
which is suspended by coupling members should be fixed in the
vicinity of a center of gravity in the Z direction of the
projection optical system PL. Furthermore, in order to optimally
reduce the size of the projection exposure apparatus, it is
preferable that the height of the upper column 34 should not be
higher than the upper end portion of the projection optical system
PL. From this perspective, the length L of the coupling members
becomes approximately 1/2 or less of the Z direction length of the
projection optical system PL.
[0072] As an example, the length L of the coupling members is set
to be substantially 0.5 m. If this value is applied to equation
(1), the characteristic frequency fg becomes a small value, i.e.,
0.7 Hz. Furthermore, if the length L of the coupling members is set
to be lm or greater, according to equation (1), the characteristic
frequency fg becomes approximately 0.5 Hz which is sufficiently low
for the vibration isolation performance in the projection exposure
apparatus. fg<0.5 (Hz) (2)
[0073] Therefore, for example, if it is possible in view of the
length of the projection optical system PL, it is preferable that
the length of the coupling members be set approximately between lm
and several m.
[0074] Furthermore, the characteristic frequency in the optical
axis direction of the projection optical system PL of the wires
35A-35C in the coupling members becomes much higher than the
characteristic frequency fg. However, for example, among the
vibrations transmitted to the upper column 34 via the columns
33A-33C from the floor, most of the vibration components in the
optical axis direction are absorbed by the coil springs 36A-36C
(vibration isolation portions), so a high vibration isolation
performance capability can be obtained in a direction parallel to
the optical axis.
[0075] Furthermore, for example, between the columns 33A-33C and
the upper column 34, it is possible to arrange a vibration
isolation member such as a coil spring or an air damper. In such a
case, the coil springs 36A-36C in the coupling members can be
omitted.
[0076] In addition, in this example, the reticle stage RST (here,
micro-moving mechanism) is integrally fixed to the upper portion of
the projection optical system PL. The reticle R (member in which a
pattern is formed) is held by the reticle stage RST. The reticle
stage RST is provided with a base portion 311B fixed to the
projection optical system PL, an X stage 31X which can be
micro-moved in the X direction with respect to the base portion 31,
and a Y stage 31Y which can be micro-moved in the Y direction with
respect to the X stage 31X and that holds the reticle R. On the
pattern formation surface of the reticle R of this example, a pair
of alignment marks RMA and RMB are formed at a predetermined
interval in the X direction. Reticle alignment systems (RA system)
21A, 21B are arranged above the alignment marks RMA, RMB via the
respective mirrors 28A, 28B. The pair of RA systems 21A, 21B
corresponds to the RA system 21 of FIG. 1.
[0077] The projection exposure apparatus of this example is a step
and repeat exposure type, and before exposure, after positioning of
the alignment marks RMA and RMB of the reticle R by using the RA
systems 21A, 21B, it is not necessary to move the reticle R.
Because of this, the laser interferometer system 10 on the reticle
side of FIG. 1 is not provided in the projection exposure apparatus
of FIG. 2.
[0078] Furthermore, the mirrors 28A, 28B, and the RA systems 21A,
21B are fixed to an undepicted column coupled with the upper column
34, and an illumination system sub-chamber 19 which stores the
illumination optical system 9 of FIG. 1 is fixed with respect to
the column. In this case, the laser light source 1 of FIG. 1 is
arranged on the floor outside the columns 33A-33C of FIG. 2 as an
example, and the illumination light IL to be emitted from the laser
light source 1 is guided to the illumination optical system 9 via
an undepicted beam transmitting system.
[0079] In addition, a wafer base WB is arranged via a vibration
isolation pad (undepicted) on the floor surface below the
projection optical system PL, and the wafer stage WST which holds
the wafer W on the wafer base WB is movably arranged thereon via an
air bearing. On top of the wafer stage WST, a reference mark member
29 is fixed in which a reference mark is formed to perform
alignment of the reticle R and the wafer W.
[0080] Thus, the projection optical system PL having a rigid
structure of this example is suspended and supported via the coil
springs 36A-36C and the wires 35A-35C, which function as coupling
members having a flexible structure, with respect to the upper
column 34, which has a rigid structure. In this structure, a high
vibration isolation performance capability can be obtained, and the
mechanism portion can be significantly lightened. However, there is
a possibility that the relative position of the projection optical
system PL and the upper column 34 can change at a relatively low
frequency of vibration. Therefore, in order to maintain the
relative position of the projection optical system PL and the upper
column 34 (and the columns 33A-33C) in a predetermined state, as
shown in FIG. 3, a positioning device of a non-contact type is
provided.
[0081] FIG. 3 is a plan view of the projection optical system PL
and the flange 18 of FIG. 2. In FIG. 3, arm portions 37A, 37B, 37C,
which extend toward the flange 18 are fixed to the columns 33A,
33B, 33C. The arm portions 37A-37C are arranged at a substantially
120.degree. interval about the optical axis AX of the projection
optical system PL. Furthermore, between the first arm portion 37A
and the flange 18, a first actuator 40A which displaces the flange
18 in the Z direction and a second actuator 41A which displaces the
flange 18 in a circumferential direction are provided. Voice coil
motors can be used for the actuators 40A, 41A. In addition, a
non-contact electromagnetic actuator, e.g., an EI core type or the
like, also can be used as actuators 40A and 41A.
[0082] Additionally, on the flange 18 in the vicinity of the arm
portion 37A, a first biaxial acceleration sensor 39A is provided,
which detects acceleration in the Z direction and in the
circumferential direction of the flange 18. The biaxial
acceleration information detected by the acceleration sensor 39A is
supplied to a controller 42, and the controller 42 drives the
actuators 40A, 41A so that the flange 18 can be maintained
stationary with respect to the arm portion 37A (and thus the upper
column 34 of FIG. 2) or with respect to the earth based on the
acceleration information. In this embodiment, the acceleration
information is used to servo-control the actuators 40A, 41A to
maintain the flange 18 (and thus the projection optical system PL)
stationary. Prior to performing the servo-control, the flange 18
(and thus the projection optical system PL) is located at a
reference position at which the flange 18 and the arm portions
37A-37C have a predetermined relationship to each other (e.g., such
that the actuators will be effective at driving the flange). The
flange 18 can be moved to the reference position based on the
output of one or more (e.g., three) displacement sensors (not
shown), which can be, e.g., an interferometer, a capacitance type
displacement sensor, an eddy current displacement sensor, etc.
[0083] In FIG. 3, between the second arm portion 37B and the flange
18, and between the third arm portion 37C and the flange 18 as
well, third and fifth actuators 40B and 40C are provided which
displace the flange 18 in the Z direction, and fourth and sixth
actuators 41B and 41C are provided which displace the flange 18 in
the circumferential direction. The structures of the actuators 40B,
41B and 40C, 41C are the same as the actuators 40A, 41A.
Furthermore, on the flange 18 in the vicinity of the arm portions
37B and 37C, the second and third biaxial acceleration sensors 39B
and 39C are provided, which detect the acceleration in the Z
direction and in the circumferential direction of the flange 18.
The acceleration information of the acceleration sensors 39B and
39C also is supplied to the controller 42, and the controller 42
drives the actuators 40B, 41B and 40C, 41C so that the flange 18
can be maintained relatively stationary with respect to the
respective arm portions 37B and 37C (and thus the upper column 34
of FIG. 2) or with respect to the earth based on the acceleration
information.
[0084] As acceleration sensors 39A-39C, displacement sensors, a
piezoelectric type acceleration sensor which detects a voltage
generated by a piezoelectric element or the like, a semiconductor
type acceleration sensor which monitors changes of a logical
threshold value voltage of a CMOS converter, e.g., according to the
displacement and distortion of the mass, or the like can be used.
An advantage of using accelerometers is that once the servo-control
is started, the flange 18 (and thus the projection optical system
PL) can be maintained stationary in space, as opposed to being
maintained stationary only relative to the arm portions 37A-37C,
which can move slightly due to, e.g., vibrations that might be
transmitted from the ground through the seats 32A-32C. It also is
possible to forego using the acceleration sensors 39A-39C, and to
instead use one or more position sensors which directly measure the
relative position between the flange 18 and the arm portions
37A-37C (and thus the upper column 34). A position sensor, for
example, an eddy current displacement sensor, a capacitance type
displacement sensor, an optical type sensor, or the like can be
used.
[0085] Thus, the positioning device of the projection optical
system PL and the flange 18 is constituted by the six-axis
acceleration sensors 39A-39C (displacement sensors), the six-axis
actuators 40A-40C, 41A-41C, the six position sensors and the
controller 42. By this positioning device, the relative position,
in the X, Y and Z directions, of the projection optical system PL
with respect to the upper column 34 (assuming that the upper column
34 does not vibrate or otherwise move), and the relative rotation
angles about the X, Y, and Z axes are maintained in a constant
state (predetermined state). The response frequency of the
actuators 40A-40C, 41A-41C is approximately 10 Hz, and thus with
respect to vibrations up to the response frequency, the projection
optical system PL of this example is supported by an active
suspension method. Furthermore, with respect to vibrations of a
frequency which exceeds this, the projection optical system PL is
suspended and supported by a passive vibration isolation
structure.
[0086] In FIG. 3, the three columns 33A-33C are used. However, as
shown in FIG. 4, four columns 33A-33D also can be used.
[0087] FIG. 4 is a plan view showing the projection optical system
PL and the flange 18 when the four columns 33A-33D are used. In
this figure, the columns 33A-33D are stably arranged so that their
spacing at their upper portion is narrower at a position of
vertices of a substantially square shape, compared to at the lower
ends of the columns 33A-33D. Furthermore, a square frame-shaped
upper column 34A is fixed to the upper portion of the columns
33A-33D, and the wires 35A-35C which suspend the flange 18 are
coupled to three locations of the upper column 34A via the coil
springs 36A-36C of FIG. 2.
[0088] In this case, the two columns 33A and 33B are arranged so as
to sandwich the projection optical system PL in the X direction,
and the column 33C is arranged in the +Y direction of the
projection optical system PL. In addition, between the flange 18
and the arm portion 37A fixed to the column 33A, the first and
second actuators 40A, 41A are provided which drive the flange 18 in
the Z and Y directions, respectively, and the third and fourth
actuators 40B, 41B which drive the flange 18 in the Z and Y
directions, respectively are provided on arm portion 37B.
Furthermore, between the flange 18 and the arm portion 37C fixed to
the column 33C, the fifth and sixth actuators 40C and 41C are
provided which drive the flange 18 in the Z and X directions,
respectively. Furthermore, the biaxial acceleration sensors 39A-39C
are arranged on the upper portion of the flange 18 in the vicinity
of the arm portions 37A-37C.
[0089] In the structure of FIG. 4, the projection optical system PL
(and the flange 18) can be driven in the X direction by the
actuator 41C, and the projection optical system PL (and the flange
18) can be driven by the actuators 41A, 41B in the Y direction and
in the rotation direction about the Z axis, so the actuators
41A-41C can be easily controlled.
[0090] In FIG. 2, on the bottom surface of the flange 18 (support
member) of the projection optical system PL, an annular flat-shaped
measurement mount 15 (measurement unit) is coupled via the three
cylindrical rods 38A, 38B, 38C (link members), which extend
substantially parallel to the Z axis. That is, the measurement
mount 15 is stably coupled to the flange 18 by a kinematic support
method comprised of a semi-three-point support. The alignment
system 22, the air duct 16, and the laser interferometer system 12
are fixed to the measurement mount 15.
[0091] FIG. 5A shows a state in which the flange 18 and the
measurement mount 15 of FIG. 2 are coupled via the rods 38A-38C. In
FIG. 5A, flexures 38Ab and 38Aa whose diameters are made small are
formed in both end portions of the rod 38A. Flexures also are
formed on both end portions of the two other rods 38B, 38C.
[0092] As shown in FIG. 5B, in one flexure 38Aa of the rod 38A,
displacement in the five degrees-of-freedom other than expansion in
the Z direction is possible. In the same manner, displacement in
five degrees-of-freedom also is possible in the other flexure 38Ab
of the rod 38A of FIG. 5A, and in the flexures of both end portions
of the other two rods 38B, 38C. Thus, virtually no stress is
applied between the flange 18 and the measurement mount 15.
Therefore, high measuring accuracy can be obtained in the laser
interferometer system 12 or the like fixed to the measurement mount
15.
[0093] Furthermore, a slot and a pad are formed at three locations
in the vicinity of the aperture at the center of the measurement
mount 15 (the aperture into which the projection optical system PL
is inserted), and the three pads contact the side surface of the
projection optical system PL.
[0094] FIG. 5C shows a slot 15a2 and a pad 15a1 of the measurement
mount 15 as a flexure. Because of this structure, the pad 15a1
allows displacement in five degrees-of-freedom including the
displacement in the Z direction and in the radius direction about
the optical axis with respect to the side surface of the projection
optical system PL, and displacement in the rotation direction about
the Z, X and Y axes. Therefore, virtually no stress is applied
between the measurement mount 15 and the projection optical system
PL, so the imaging characteristic of the projection optical system
PL can be stably maintained.
[0095] Furthermore, instead of the rods 38A-38C in which the
flexures are formed on both end portions as shown in FIG. 5A, a rod
43 (link member) shown in FIG. 6 can be used. In FIG. 6, in the
upper end portion of the rod 43, slots 43a, 43b are formed in two
perpendicular directions, and the lower end portion of the rod 43
is fixed to a member (in the example of FIG. 5A, the measurement
mount 15), and includes slots 43b, 43a, which are symmetrical to
the upper end portion. Even if the rods 38A-38C of FIG. 5A are
replaced with three rods that are the same as the rod 43 of FIG. 6,
at least displacement in five degrees-of-freedoms is possible in
both end portions of the rod 43, so the flange 18 and the
measurement mount 15 are coupled in a state in which virtually no
stress is applied (i.e., they are attached using a kinematic
support method).
[0096] In FIG. 2, the projection exposure apparatus of this example
is arranged in a downflow environment, and a predetermined gas
(e.g., air) having a controlled temperature and humidity, and being
subjected to particle prevention processing, is supplied to the
wafer base WB via the side surface of the projection optical system
PL, from the illumination system sub-chamber 19 side. The
projection optical system PL of this example is suspended and
supported by the upper column 34, and there are no members in the
way that would prevent predetermined gas flow. Therefore, the
predetermined gas can be supplied smoothly in the downward
direction, the temperature stability of the projection optical
system PL is improved, and the stability of the imaging
characteristics is improved.
[0097] Thus, in the projection exposure apparatus of FIG. 2 of this
example, the projection optical system PL and the flange 18 of a
rigid structure are suspended and supported by an active suspension
method via the coil springs 36A-36C and the wires 35A-35C, as
coupling members having a flexible structure, with respect to the
upper column 34, which has a rigid structure. Because of this, the
following advantages are possible.
[0098] (1) The projection exposure apparatus of this example is
constituted by an extremely simplified structural body, the
mechanism portion can be lightened, and the manufacturing cost can
be reduced.
[0099] (2) The projection optical system PL is suspended and
supported, and particularly the characteristic frequency of
vibration in the direction perpendicular to the optical axis of the
coupling member (projection optical system PL) is extremely low, so
the effects of vibrations from the floor surface are significantly
reduced. Therefore, an apparatus performance capability, such as a
vibration isolation performance capability, exposure accuracy
(overlay accuracy), or the like can be improved. Furthermore, even
if vibration becomes an issue, the vibration transmission path can
be easily identified, and for example, a countermeasure can be
easily performed, e.g., in which a vibration isolation member is
added to the portion in which vibration is transmitted, or the
like.
[0100] (3) When the environment temperature of the projection
exposure apparatus changes, thermal deformation of the structural
body also can be easily predicted, so by using a temperature
sensor, and measuring the temperature of each part of the
structural body, based on the measurement result, a positioning
error or the like can be corrected.
[0101] (4) There is a large space in the vicinity of the projection
exposure apparatus. Thus, when the next generation exposure
apparatus is designed and customized, there is no need to change a
platform (a support mechanism or the like of a base, a column, and
a projection optical system). Therefore, the degree of freedom for
design becomes large, and a preferable structure is possible for a
so-called modular design.
Second Embodiment
[0102] The following explains a second exemplary embodiment of this
invention with reference to FIGS. 7 and 8. With respect to the
projection exposure apparatus of this example, a mechanism which
stabilizes the temperature of the projection optical system PL is
added to the projection exposure apparatus of FIG. 2. In FIGS. 7
and 8, the same symbols are used for the portions corresponding to
the portions of FIG. 2, and their detailed description is omitted.
Furthermore, in FIG. 7, in order to clarify understanding of the
additional structure, the air duct 16 and the small air
conditioning device 17 of FIG. 2 are omitted.
[0103] FIG. 7 shows a schematic structure of a mechanism portion of
the projection exposure apparatus of this example. In FIG. 7, a
recovery tank 45 which collects a cooling liquid is provided on the
floor, a supply tank 48 which stores the liquid is provided in the
vicinity of one vertex of the triangle frame-shaped upper column
34, and a support member 49B which connects later-mentioned tubes,
is provided in the vicinity of another vertex of the upper column
34. As a cooling liquid, water or a fluorine group inert liquid
(e.g., FLUORNERT (manufactured by U.S. 3M Corporation)) can be
used. A so-called coolant also can be used as the liquid. In terms
of environment, water is preferable as the liquid.
[0104] The recovery tank 45 is coupled to a pipe 46A (see FIG. 8),
which is coupled to a temperature control device which adjusts the
temperature of the liquid passing through its inside to a target
temperature and which houses a pump 47, which in turn is coupled to
the upper portion of the supply tank 48 via the pipe 46B. The
bottom portion of the supply tank 48 is coupled to the pipe 46D via
the pipe 46C which is downwardly extended along the wire 35B. The
pipe 46D includes a pipe which cools the projection optical system
PL from a downward direction to an upward direction of the
projection optical system PL, and is coupled to the pipe 46E via a
pipe which extends along the flange portion 18 toward the upper
portion of the projection optical system PL. The pipe 46E includes
a pipe which is upwardly extended along the wire 35A and is coupled
to the recovery tank 45. Part of the pipe 46C is held by the fixed
mount 49A (support member) which is fixed to the movable portion of
the wire 35B, and the pipe 46E is fixed by a fixed mount
(undepicted) attached to the movable portion of the coil spring
36A. After the pipe 46E is fixed by the support member 49B, it
extends along the column 33A.
[0105] The pipes 46A-46E are formed of composite resin or the like
having flexibility, and the height of the supply tank 48 is greater
than that of the recovery tank 45, so even if the pipe moves up and
down, as described later, the cooling liquid can be circulated by a
siphon principal (an operation which pushes the liquid out by using
height difference) between the supply tank 48 and the recovery tank
45. Thus, the liquid supply device includes the recovery tank 45,
the pipes 46A-46E, the temperature control device housing a pump
47, and the supply tank 48.
[0106] FIG. 8 shows the liquid flow provided by the liquid supply
device of FIG. 7. In FIG. 8, the liquid within the recovery tank 45
is suctioned by the pipe 46A as shown by an arrow A1 due to the
pump 47 housed in the temperature control device. After being
cooled in the temperature control device, the liquid is supplied to
the supply tank 48 via the pipe 46B as shown by an arrow A2. Then,
the liquid within the supply tank 48 flows into the pipes 46C-46E
as shown by arrows A3-A4 and is collected by the recovery tank 45.
At this time, depending on the case, there is a possibility that
the pipe 46E goes through a position higher than the tank 48, but
once the liquid begins circulating, the circulation is maintained
by the siphon principle. Therefore, when the cooling liquid is
supplied to the side surface of the projection optical system PL, a
vibration source does not exist because the liquid is pushed out by
using the gravitational force caused by the height difference only,
so a vibration control performance capability does not
deteriorate.
Third Embodiment
[0107] The following explains a third embodiment of this invention
with reference to FIG. 9. In this example, in the same manner as in
the embodiment of FIG. 2, this invention is applied to a step and
repeat exposure type projection exposure apparatus. In FIG. 9, the
same symbols are used for the portions corresponding to the
portions of FIG. 2, and their detailed description is omitted.
[0108] FIG. 9 shows a schematic structure of a mechanism portion of
the projection exposure apparatus of this example. In FIG. 9, three
columns 33A, 33B (the third column, 33C, is undepicted) are fixed
to the floor F (which also could be a supporting frame located on a
floor), and extend parallel to the Z axis. The upper column 34B is
supported on the columns 33A, 33B, 33C via passive-type vibration
isolation members 51A, 511B (and undepicted 51C), which include,
for example, an air damper and/or a coil spring. Furthermore, the
flange 18 (support member) is integral with the projection optical
system PL, and is fixed thereto so as to surround the side surface
at substantially the center of the projection optical system PL in
the Z direction. Vibration isolation members 53A, 53B, 53C, e.g., a
leaf spring, are fixed to three locations of the upper column 34B.
Furthermore, from the vibration isolation members 53A, 53B, 53C,
the flange 18 (and thus the projection optical system PL) is
suspended via rods 52A, 52B, 52C, which are substantially parallel
to the Z axis, and in which flexures which are identical to each
other are formed on both ends.
[0109] In this case, the vibration isolation member 53A and the rod
52A correspond to one coupling member. In the same manner, the
other vibration isolation members 53B, 53C and rods 52B, 52C
correspond to two other coupling members. These coupling members
are substantially parallel to each other and parallel to the Z
axis. In this example, the rods 52A-52C can be easily displaced in
a direction perpendicular to the optical axis AX of the projection
optical system PL, so the characteristic frequency of the coupling
members is lower in the direction perpendicular to the optical axis
than in the direction parallel to the optical axis AX of the
projection optical system PL, in the same manner as in the first
embodiment. The length L of the coupling members is set at
substantially 0.5 m for example. If this value is applied to
equation (1), the characteristic frequency of the coupling members
in the direction perpendicular to the optical axis AX becomes a
small value, e.g., approximately 0.7 Hz. Furthermore, if the length
L of the coupling members is set at lm or greater, according to
equation (1), the value becomes approximately 0.5 Hz or less, which
is suitable for the characteristic frequency of the projection
exposure apparatus.
[0110] Furthermore, the characteristic frequency in the optical
axis AX direction of the rods 52A-52C within the coupling members
is considerably greater than the characteristic frequency in the
direction perpendicular to the optical axis AX. However, for
example, most of the vibration transmitted to the columns 33A, 33B,
33C from the floor is attenuated by the vibration isolation members
51A, 51B, 51C, and thus the vibration in the optical axis AX
direction is hardly transmitted to the upper column 34B. Thus, the
projection optical system PL is stably supported.
[0111] Furthermore, in order to control the relative position of
the flange 18 and the projection optical system PL with respect to
the columns 33A, 33B, 33C, between the columns 33A, 33B, and 33C
and the flange 18, the biaxial actuators 54A and 54B (and
undepicted 54C) are arranged which control the relative position in
the Z direction and in the circumferential direction. Furthermore,
position sensors (undepicted) for measuring the position in six
degrees-of-freedom are arranged on the flange 18. Based on the
measurement information of the position sensor, by driving the
six-axes actuators, the relative position of the flange 18 and the
projection optical system PL is controlled.
[0112] Other parts of the structure are the same as in the first
embodiment of FIG. 2. In this example as well, the reticle stage
RST which micro-moves the reticle R is integrally fixed to the
projection optical system PL, and the measurement mount 15 is
supported by a kinematic support method via the three rods 38A-38C
from the bottom surface of the flange 18. The laser interferometer
system 12, or the like, is fixed to the measurement mount 15.
Furthermore, the image of the whole reticle R pattern is
transferred to the respective shot areas on the wafer W via the
projection optical system PL.
[0113] According to this example, the projection optical system PL
is suspended and supported by the upper column 34B. Therefore, in
the same manner as in the first embodiment, a vibration isolation
performance capability can be improved, and the mechanism portion
can be lightened. Furthermore, the rods 52A-52C are used as
coupling members, so even when the projection optical system PL is
heavy, the projection optical system PL can be stably
supported.
Fourth Embodiment
[0114] The following explains a fourth exemplary embodiment of this
invention with reference to FIGS. 10 and 11. In this example, this
invention is applied to a scanning exposure type projection
exposure apparatus. In FIGS. 10 and 11, the same symbols are used
for the portions corresponding to the portions of FIGS. 2 and 9,
and their detailed description is omitted.
[0115] FIG. 10 shows a schematic structure of a mechanism portion
of a projection exposure apparatus of this example. In this figure,
the three columns 33A, 33B (the third column, 33C, is undepicted)
are fixed to the floor F (or a frame located on the floor), and
extend parallel to the Z axis. An intermediate member 55, which has
a flat shape and can be elastically deformed to some degree, and in
which an aperture into which an end portion of the projection
optical system PL is inserted, is supported on the columns 33A-33C
via the passive type vibration isolation members 51A, 51B (and
undepicted 51C). Furthermore, the flange 18 (support member) is
integrally provided with the projection optical system PLA, and is
fixed thereto so as to surround the side surface at substantially
the center, in the Z direction, of the projection optical system
PLA of this example. The flange 18 and the projection optical
system PLA are suspended via the three rods 52A, 52B, 52C (the rod
52B is positioned in front of the projection optical system PLA in
the same manner as in the example of FIG. 9, and is not depicted in
FIG. 10), which are identical to each other and extend
substantially parallel to the Z axis, at three locations from the
intermediate member 55. Flexures are formed on both end portions of
the rods 52A-52C. In this case, the rods 52A-52C correspond to
three coupling members, and a column mechanism body including the
columns 33A, 33B, 33C the vibration isolation members 51A, 51B, 51C
and the intermediate member 55 corresponds to a frame which
suspends these coupling members.
[0116] Furthermore, for example, via rotatable pivots 58A, 58B (a
third pivot (58C) is undepicted) (vibration isolation members) at
three locations of the upper surface of the intermediate member 55,
a reticle base 57 is provided which is a thick, flat plate, and in
which an aperture is formed for passing illumination light beam EL.
On the reticle base 57, via an air bearing, a reticle stage 60 is
provided which adsorbs and holds the reticle R so as to be movable
within the XY plane. The scanning direction of the reticle R during
scanning exposure of this example is the Y direction (direction
perpendicular to the paper plane of FIG. 10), and in order to
cancel a reaction force generated when the reticle stage 60 is
driven in the Y direction, a rectangular frame-shaped countermass
59 is provided on the reticle base 57, so as to surround the
reticle stage 60. Furthermore, a first Y-axis linear motor 61 is
constituted by a movable part 61a located at the end portion in the
+X direction of the reticle stage 60, and a stator 61b located on
(or in) the countermass 59. In symmetry to this linear motor 61, a
second Y-axis linear motor 62 is constituted by a movable part 62a
located at the end portion in the -X direction of the reticle stage
60, and a stator 62b located on (or in) the countermass 59. The
first and second Y-axis linear motors 61 and 62 each drive the
reticle stage 60 in the Y direction with respect to countermass 59.
At this time, the countermass 59 moves in the opposite direction,
so the driving reaction force is canceled, and the generation of
vibration is controlled. This is not depicted, but the reticle
stage 60 also can be provided with a micro-moving mechanism for the
rotation directions about the X, Y, and Z axes.
[0117] Furthermore, a measurement mount 56 is fixed to the
intermediate member 55, and in this measurement mount 56, based on
a reference mirror Me (see FIG. 11) on the side surface of the
projection optical system PLA, a laser interferometer system 10
(similar to FIG. 1) is incorporated which measures the position in
the rotation direction about the X, Y, and Z axes of the reticle
stage 60. Additionally, a reticle stage system RSTA which drives
the reticle R includes the intermediate member 55, the reticle base
57, the reticle stage 60, the countermass 59, and the measurement
mount 56.
[0118] FIG. 11 shows an enlarged cross-sectional view of the
members from the countermass 59 to the intermediate member 55 of
FIG. 10. In FIG. 11, the countermass 59 is arranged on the reticle
base 57 via a plurality of air pads 62A, 62B (others are omitted).
In this structure, the air pads 62A, 62B are smoothly moved on the
reticle base 57 by an air bearing method. Furthermore, the bottom
surface of the countermass 59 and the air pads 62A, 62B are each
coupled via a flexure 63 (flexure mechanism), which is a member
having a cross-sectional area that is small, in a state in which
relative rotation is possible to a degree.
[0119] In FIG. 10, in this example as well, in order to control the
relative position in the six degrees-of-freedom of the flange 18
and the projection optical system PLA with respect to the columns
33A, 33B, 33C, six-axis non-contact actuators 54A, 54B (the
remaining biaxial actuators are not depicted) are arranged. Other
mechanisms are the same as in the embodiment of FIG. 9, and the
measurement mount 15 is coupled to the bottom surface of the flange
18 by a kinematic support method, and the laser interferometer
system 12 or the like is fixed to the measurement mount 15.
[0120] In this example, the pattern of the reticle R is transferred
and exposed onto the respective shot areas on the wafer W via the
projection optical system PLA by a step-and-scan method. At this
time, the projection optical system PLA is suspended and supported
from the intermediate member 55, so in the same manner as in the
first embodiment, the vibration isolation performance capability
can be improved, and the mechanism portion can be lightened.
[0121] In addition, in this example, the countermass 59 is arranged
so as to cancel a reaction force generated when the reticle stage
60 is driven at a high speed (or acceleration) in the Y direction.
At this time, if the countermass 59 is simply arranged on the
reticle base 57, there is a possibility that the countermass 59
which receives a reaction force generates a vibration at a high
frequency, which vibrates the reticle base 57, and the measurement
accuracy of the position of the reticle stage 60 may be
deteriorated. In order to prevent this, in this example, as shown
in FIG. 11, the countermass 59 (rigid structure) and the air pads
62A, 62B (rigid structure) are coupled via the flexure 63 (flexible
structure), so the vibration generated by the countermass 59 is
hardly transmitted to the reticle base 57, and the position and the
speed of the reticle stage 60 can be controlled with high
accuracy.
[0122] In the same manner, as shown in FIG. 10, the intermediate
member 55 and the reticle base 57 (rigid structure) are coupled via
the pivots 58A, 58B (flexible structure), so the vibration of the
reticle base 57 is not transmitted to the measurement mount 56,
which is provided with a laser interferometer system. Thus, from
this perspective as well, the position and the speed of the reticle
stage 60 can be controlled with high accuracy.
[0123] In other words, in this example, flexible coupling is
performed by the flexure 63 so that the moment by the vibration of
the countermass 59 is not transmitted to the reticle base 57, which
is another structural body. Furthermore, flexible coupling is
achieved by the pivots 58A, 58B so that the moment by the vibration
of the reticle base 57 is not transmitted to the intermediate
member 55 which is another structural body. Because of this,
instead of the pivots 58A, 58B, a flexure mechanism also can be
used. Support through this type of flexible structure also can be
called "kinematic support" (including semi-kinematic support and
pseudo-kinematic support for avoidance of stress concentration and
for vibration attenuation).
[0124] In this case, as shown in FIG. 10, for example, when the
reticle base 57 is vibrated, the position of the node of the first
vibration mode is not displaced. Only the rotation moment is
generated, and flexible coupling is achieved which allows rotation
due to the pivots 58A, 58B. Therefore, virtually no vibration
energy is transmitted to the intermediate member 55 or to the
measurement mount 56.
[0125] This type of structure is used, and the measurement mount 56
having a laser interferometer system which monitors the position of
the reticle stage 60 is provided in the intermediate member 55
instead of in the reticle base 57. Therefore, for example, Abbe
errors (errors determined by the sine of a curved angle) due to the
bow of the reticle base 57 can be reduced. Furthermore, the
projection optical system PLA is suspended from the intermediate
member 55, so flexible coupling is achieved in the horizontal
direction, which further shields vibration transmission.
[0126] Meanwhile, the vibration shielding effect is relatively
small in the vertical direction (Z direction). Thus, ideally, a
structure is desirable in which the reticle base 57 is loaded on
the vibration isolation member, and its position is actively
controlled. For this purpose, for example, in FIG. 10, the reticle
base 57 can be supported via three active type vibration isolation
members on an undepicted column. These active vibration isolation
members include an air damper and an electromagnetic damper (such
as a voice coil motor) which generates a variable thrust in the Z
direction. In this structure, with respect to the three active
vibration isolation members for the reticle base 57, only three
degrees-of-freedom (the position in the Z direction, pitching
angle, and rolling angle) in the vertical direction can be
controlled with respect to the projection optical system PLA. The
control band range is, for example, approximately 10 Hz.
[0127] If flexible coupling by this type of active vibration
isolation member is used, there is no relative interference of
vibration energy, fluctuation load, and thermal displacement
between the reticle base 57 (reticle stage 60) and the projection
optical system PLA. Furthermore, active relative positioning of the
rigid structures is performed, so there is no problem due to
flexible coupling. In particular, in the case of the scanning
exposure apparatus of this example, if a function is provided in
which the reticle base 57 and the projection optical system PLA are
coupled by the above-mentioned flexible mechanism, and positioning
is actively performed with respect to each other, the support
mechanism which supports the reticle base 57 and the projection
optical system PLA does not need to have high rigidity, and this
contributes to lightening of the device, temperature stability, and
obtaining of a large space.
[0128] Furthermore, according to the embodiment of FIG. 10, the
projection optical system PLA is suspended from the intermediate
member 55 of the upper portion, so there is nothing that interferes
with air flow from the center to the lower portion. Because of
this, air conditioning of the device can be effectively performed
by, for example, a downflow method. In addition, a large space is
obtained, so the degree of freedom for designing various sensors or
the like arranged in the measurement mounts 15 and 56 can be
increased. Furthermore, in the case of replacing the projection
optical system PLA, the projection optical system PLA can be easily
taken in and out by a method in which the projection optical system
PLA with the measurement mount 15 is removed from the rods 52A-52C
(coupling members) and passes through an undepicted gate-type
column. If this type of structure is used, the positioning
relationships between the measurement system and the projection
optical system PLA is adjusted in advance, and incorporation into
the device is possible as-is. Thus, assembly process reduction and
cost reduction can be improved.
Fifth Embodiment
[0129] The following explains a fifth embodiment of this invention
with reference to FIGS. 12 and 13. In this example, that the
projection optical system PL is supported from below by using a
support mechanism that has rods. In FIGS. 12 and 13, the same
symbols are used for the portions corresponding to FIGS. 1-11, so a
detailed explanation of those portions is omitted here. A flange 18
of the projection optical system PL is mounted to a base molding 64
in which an opening is disposed. This base molding 64 is supported
by the support mechanism from a base plate BP. The support
mechanism flexibly supports the projection optical system PL in the
Z direction via the base molding 64 and flexibly supports the
projection optical system PL in the horizontal direction (XY
direction) as well. In this embodiment, the support mechanism is
provided with three rods 65 that are rigid in the Z direction and
flexible in the horizontal direction (XY direction), flexures 66A,
66B formed at both end portions of the rods 65, and a coupling
portion that connects the base molding 64 with the upper side of
flexure 66A. Furthermore, in this embodiment, the rods 65 and the
flexure 66A are integrally formed, but it is also acceptable to
separate them using a leaf spring, etc. In addition, in this
embodiment, the length of the rods 65 is 1 m or longer.
[0130] With respect to the flexures 66A, 66B, in the same manner as
the flexures 38Aa, 38Ab shown in FIG. 5, displacement in five
degrees-of-freedom other than expansion in the Z direction is
possible. Because of this, hardly any applied force acts between
the base molding 64 and the base plate BP. Thus, the base molding
64 is not easily deformed by vibration, etc. from the base plate
BP.
[0131] Furthermore, the support mechanism of this embodiment is
provided with a vibration isolation pad 67 arranged on the base
plate BP, and that suppresses vibration in the Z direction
transmitted from the base plate BP. For example, an air mount can
be used as this vibration isolation pad 67.
[0132] Furthermore, in this embodiment, as shown in FIG. 13, the
base molding 64 is supported by three support mechanisms.
[0133] In addition, in this embodiment, as shown in FIG. 13, the
reticle base 57 is supported by four columns 33A-33D. Undepicted
coils including a vertical coil and a horizontal coil that
constitute a stator of the actuator 54A is arranged between the
columns 33A and 33C, opposite to the base molding 64. In the same
manner, undepicted coils including a vertical coil and a horizontal
coil that constitute a stator of the actuator 54B is arranged
between the columns 33B and 33D, opposite to the base molding 64.
Permanent magnets that constitute movable elements of the actuators
54A, 54B are arranged in the base molding 64.
[0134] The actuators 54A, 54B are constituted by three actuators
that displace the base molding 64 in the Z direction and three
actuators that displace the base molding in the circumferential
direction. The actuators 54A, 54B control the base molding 64 with
six degrees-of-freedom.
[0135] If the projection optical system PL is supported by a
parallel link mechanism, the projection optical system PL is
rigidly supported in the Z direction and the horizontal direction
(XY direction). In contrast, as described above, the support
mechanism of this embodiment flexibly supports the projection
optical system PL in the Z direction and the horizontal direction
(XY direction), so the weight of the support mechanism can be made
light, and the vibration of the projection optical system PL can be
effectively cut off.
[0136] Furthermore, in this embodiment, the projection optical
system PL is supported via the base molding 64, but the projection
optical system PL can be directly supported. In this case, the
support mechanism can, for example, directly support the projection
optical system PL using the flange 18 of the projection optical
system PL.
[0137] Furthermore, the projection optical system PL can be
suspended from above using the support mechanism of this
embodiment. In addition, in the above-described embodiment, the
projection optical system PL was supported by using wires or rods,
but the projection optical system can be supported by using a
chain. The exposure apparatus of this embodiment can be applied to
the above-mentioned stationary exposure type exposure apparatus, or
to a scanning type exposure apparatus.
[0138] The projection exposure apparatus of the above-mentioned
embodiments can be manufactured by incorporating and optically
adjusting an illumination optical system composed of a plurality of
lenses and a projection optical system into the main body of the
exposure apparatus, and installing the reticle stage and the wafer
stage composed of a plurality of mechanical parts to the main body
of the exposure apparatus, connecting wires and pipes, and
performing overall adjustment (electrical adjustment, operation
check, etc.). Furthermore, it is preferable that manufacturing of
the projection exposure apparatus is performed in a clean room with
controlled temperature and cleanliness.
[0139] Furthermore, when a semiconductor device is manufactured by
using the projection exposure apparatus of the above-described
embodiments, the semiconductor device is manufactured by a step of
designing a performance capability and function of the device, a
step of manufacturing a reticle based on the designing step, a step
of forming a wafer from a silicon material, a step of performing
alignment by the exposure apparatus of the above-mentioned
embodiment and exposing a pattern of the reticle onto a wafer, a
step of forming a circuit pattern such as etching or the like, a
step of assembling a device (including a dicing process, a bonding
process, a packaging process), a step of testing, and the like.
[0140] This invention can be applied to a liquid crystal panel
manufacturing exposure apparatus disclosed in, for example,
International Publication No. WO 99/49504. Furthermore, this
invention can be applied to a projection exposure apparatus using
extreme ultraviolet light (EUV light) having a wavelength of
several nm-100 nm as an exposure beam.
[0141] Furthermore, this invention is not limited to the
application for the exposure apparatus for manufacturing a
semiconductor device. For example, this invention can be applied to
an exposure apparatus for manufacturing various devices such as a
liquid crystal display element formed on a square-shaped glass
plate, or a display device such as a plasma display or the like, or
an imaging element (CCD), a micro-machine, a thin-film magnetic
head, a DNA chip, or the like. Furthermore, this invention can be
applied to an exposure process (exposure apparatus) in which a mask
(photomask, reticle, or the like) having a mask pattern of various
devices is formed by using a photolithographic process.
[0142] According to some aspects of this invention, when a
projection optical system as a rigid structure is suspended and
supported with respect to a predetermined member as a rigid
structure via a coupling member as a flexible structure, there is a
possibility of using the advantages of both rigid and flexible
structures. Therefore, compared to a conventional example, a ratio
occupied by a rigid structure can be reduced, so without reducing a
device performance capability, a mechanism portion can be
lightened, and the cost can be reduced.
[0143] The coupling members can extend through holes in the support
member (flange 18) and attach to the lower surface of the flange
18, or can be attached inside of the flange 18, as opposed to being
attached to the top surface of the flange 18, as illustrated in the
drawings.
[0144] While the invention has been described with reference to
preferred embodiments thereof, which are exemplary, it is to be
understood that the invention is not limited to the preferred
embodiments or constructions. The invention is intended to cover
various modifications and arrangements. In addition, while the
various elements of the preferred embodiments are shown in various
combinations and configurations, that are exemplary, other
combinations and configurations, including more, less or only a
single element, are also within the spirit and scope of the
invention.
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