U.S. patent application number 09/870518 was filed with the patent office on 2001-09-27 for reaction force isolation system for a planar motor.
Invention is credited to Hazelton, Andrew J..
Application Number | 20010023927 09/870518 |
Document ID | / |
Family ID | 22462614 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010023927 |
Kind Code |
A1 |
Hazelton, Andrew J. |
September 27, 2001 |
Reaction force isolation system for a planar motor
Abstract
The present invention provides a structure for isolating the
reaction forces generated by a planar motor. Specifically, the
fixed portion of the reaction motor, which is subject to reaction
forces, is structurally isolated from the rest of the system in
which the planar motor is deployed. In accordance with one
embodiment of the present invention, the fixed portion of the
planar motor is separated from the rest of the system and coupled
to ground. The rest of the system is isolated from ground by
deploying vibration isolation means. Alternatively or in addition,
the fixed portion of the planar motor may be structured to move
(e.g., on bearings) in the presence of reaction forces, so as to
absorb the reaction forces with its inertia. In a further
embodiment of the present invention, the fixed portion of the
planar motor and the article to be moved are supported by the same
frame, with the fixed portion of the planar motor movable on
bearings.
Inventors: |
Hazelton, Andrew J.; (San
Carlos, CA) |
Correspondence
Address: |
Barry E. Breschneider, Esq.
Morrison & Foerster LLP
2000 Pennsylvania Avenue, N.W.
Washington
DC
20006-1888
US
|
Family ID: |
22462614 |
Appl. No.: |
09/870518 |
Filed: |
June 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09870518 |
Jun 1, 2001 |
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09134278 |
Aug 14, 1998 |
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6252234 |
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Current U.S.
Class: |
250/442.11 ;
318/560 |
Current CPC
Class: |
F16F 15/02 20130101;
G03F 7/70833 20130101; G03F 7/70758 20130101; G03F 7/709 20130101;
G03F 7/70358 20130101; G03F 7/70716 20130101 |
Class at
Publication: |
250/442.11 ;
318/560 |
International
Class: |
G05B 011/01; G21K
005/10 |
Claims
1. A stage device, comprising: a planar motor which has a fixed
portion and a moving portion, wherein said moving portion supports
an article for movement in a plane of the planar motor; and a
vibration isolation structure structured and configured to isolate
vibration induced by a reaction force between said moving portion
and said fixed portion.
2. A stage device according to claim 1, wherein said moving portion
is supported on a stationary support, and said vibration isolation
structure includes a structure in which said fixed portion is
structurally independent of said stationary support.
3. A stage device according to claim 2, wherein said fixed portion
is supported on a bearing.
4. A stage device according to claim 3, wherein said bearing
comprises an air bearing and/or a ball bearing.
5. A stage device according to claim 2, wherein said vibration
isolation structure further comprises a vibration isolation device
that supports said stationary support.
6. A stage device according to claim 5, wherein said vibration
isolation device includes an air damper and/or an actuator.
7. A stage device according to claim 2, wherein said stationary
support comprises a top plate on which the moving portion is
supported for movement and a base, and said fixed portion is
located between said top plate and said base.
8. A stage device according to claim 7, wherein said fixed portion
includes a coil array.
9. A stage device according to claim 7, wherein said top surface is
made of a non-magnetic material.
10. A stage device according to claim 7, wherein the stationary
support further comprises a support structure between said top
plate and said base for keeping said top plate from bending.
11. A stage device according to claim 2, wherein said moving
portion moves on a bearing surface.
12. A stage device according to claim 11, wherein said bearing
surface includes an air bearing.
13. A stage device according to claim 2, further comprising a
control device for controlling the positions of said moving portion
at least in two directions.
14. A stage device according to claim 13, wherein said fixed
portion includes a coil array, and said control device includes a
driver unit for supplying a current to said coil array to move the
moving portion.
15. A stage device according to claim 13, further comprising at
least two interferometers, wherein said control devise controls the
positions of said moving portion based in part on the outputs of
said interferometers.
16. A stage device according to claim 13, further comprising at
least three interferometers, wherein said control device controls
the X, Y and .theta. positions of said movable stage based in part
on the outputs of said interferometers.
17. A stage device according to claim 1, wherein said moving
portion includes a permanent magnet.
18. A stage device according to claim 2, wherein said stationary
support includes a platform on which the moving portion is
supported for movement and a frame that supports said platform, and
wherein said fixed portion is located beneath said platform.
19. A stage device according to claim 18, wherein said frame is
supported on a damping device.
20. A stage device according to claim 19, wherein said damping
device comprises an actuation means for maintaining the frame level
against any changes induced by a change in center of gravity.
21. A stage device according to claim 1, wherein said fixed portion
and said moving portion are supported by a same frame, and wherein
the fixed portion is supported on a bearing.
22. A stage device according to claim 21, wherein said frame is
supported on a damping device.
23. A stage device according to claim 21, wherein the moving
portion comprises a leveling stage for leveling said article.
24. A stage device according to claim 21, wherein the frame
comprises a platform on which the fixed portion is supported, and
means for cooling said platform.
25. A stage device according to claim 1, wherein said fixed portion
comprises a first magnetic portion and a second magnetic portion
spaced apart to define a space in which said moving portion moves
laterally.
26. A stage device according to claim 25, wherein said vibration
isolation structure comprises a bearing system that supports said
second magnetic portion for lateral movement in reaction to
movement of said moving portion.
27. A stage device according to claim 26, wherein said first
magnetic portion and second magnetic portion form a rigid structure
resting on the bearing system.
28. A stage device according to claim 27, wherein at least one of
said first magnetic portion and second magnetic portion comprises a
magnetic coil array for effecting movement of the moving portion in
said space.
29. A stage device according to claim 25, wherein said fixed
portion is fixedly supported, and said vibration isolation
structure comprises a structure in which said fixed portion is
structurally independent of an external support structure.
30. A stage device according to claim 29, wherein said vibration
isolation structure comprises a damper to damp the vibration to
said external support structure induced by said reaction force
interaction between said moving portion and said fixed portion.
31. An exposure apparatus, comprising: an optical system for
imaging a mask pattern onto an article; a stage device for precise
positioning of the article for imaging, said stage device
comprising: a planar motor which has a fixed portion and a moving
portion, wherein said moving portion supports said article for
movement in a plane of the planar motor; and a vibration isolation
structure structured and configured to isolate vibration that is
induced by a reaction force between said moving portion and said
fixed portion.
32. An exposure apparatus according to claim 31, further comprising
means for scanning said mask pattern in synchronization with
movement of said article.
33. An exposure apparatus according to claim 32, wherein said mask
pattern is a circuit pattern for a semiconductor device and wherein
said article to be exposed is a wafer.
34. An exposure apparatus according to claim 31, wherein said fixed
portion comprises a first magnetic portion and a second magnetic
portion spaced apart to define a space in which said moving portion
moves laterally.
35. An exposure apparatus according to claim 34, wherein said
vibration isolation structure comprises a bearing system that
supports said fixed portion for lateral movement in reaction to
movement of said moving portion.
36. An exposure apparatus according to claim 35, wherein said
bearing system is supported by a frame structure that supports said
optical system in relation to said article.
37. An exposure apparatus according to claim 34, wherein said
optical system is supported on a frame structure, said fixed
portion is fixedly supported, and said vibration isolation
structure comprises a structure in which said frame structure is
structurally independent of said fixed portion.
38. A method of controlling reaction force induced vibration in a
stage device, comprising the steps of: providing a planar motor
which has a fixed portion and a moving portion; supporting an
article on said moving portion for movement in a plane of the
planar motor; and providing a vibration isolation structure that is
structured and configured to isolate vibration induced by a
reaction force between said moving portion and said fixed portion.
Description
BACKGROUND OF THE INVENTION
[0001] This is a continuation-in-part of U.S. patent application
Ser. No. 09/134,278, filed Aug. 14, 1998.
[0002] 1. Field of the Invention
[0003] The present invention relates, in general, to planar motor
driven positioning systems, and more particularly to such method
and apparatus for positioning and aligning a wafer in a
photolithographic system using a planar motor and isolating the
system from the reaction forces of the planar motor.
[0004] 2. Related Background Art
[0005] Various support and positioning structures are available for
positioning an article for precision processing. For example in
semiconductor manufacturing operations, a wafer is precisely
positioned with respect to a photolithographic apparatus. In the
past, planar motors have been advantageously utilized to position
and align a wafer stage for exposure in the photolithographic
apparatus. For example, U.S. Pat. Nos. 4,535,278 and 4,555,650 to
Asakawa describe the use of planar motors in a semiconductor
manufacturing apparatus.
[0006] A semiconductor device is typically produced by overlaying
or superimposing a plurality of layers of circuit patterns on the
wafer. The layers of circuit patterns must be precisely aligned.
Several factors may cause alignment errors. Vibrations of the
structures within the photolithographic system could cause
misalignment of the wafer. The reaction forces between the moving
portion and fixed portion of the planar motor are known to induce
vibrations in the system.
[0007] As the semiconductor manufacturing industry continues to try
to obtain increasingly tighter overlays due to smaller overlay
budgets and finer conductor widths, the importance of alignment has
been magnified. Precise alignment of the overlays is imperative for
high resolution semiconductor manufacturing. It is therefore
desirable to develop a means to reduce the effect of vibrations
caused by the planar motor.
SUMMARY OF THE INVENTION
[0008] The present invention provides a structure for isolating the
vibrations induced by reaction forces generated by a planar motor.
Specifically, the fixed portion of the reaction motor, which is
subject to reaction forces, is structurally isolated from the rest
of the system in which the planar motor is deployed. This can be
done in a number of ways.
[0009] In accordance with one embodiment of the present invention,
the fixed portion of the planar motor is separated from the rest of
the system and coupled to ground. The rest of the system is
isolated from ground by deploying a vibration isolation system.
Alternatively or in addition, the fixed portion of the planar motor
may be structured to move (e.g., on bearings) in the presence of
reaction forces, so as to absorb the reaction forces with its
inertia.
[0010] In a further embodiment of the present invention, the fixed
portion of the planar motor and the article to be moved are
supported by the same frame, with the fixed portion of the planar
motor movable on bearings.
[0011] In another aspect of the present invention, a reaction force
isolation system is structured more specifically for a two-sided
planar motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic representation of a planar motor
driven scanning type exposure system that implements a reaction
force isolation system in accordance with one embodiment of the
present invention.
[0013] FIG. 2 is a schematic exploded view of one embodiment of the
planar motor adopted in the system in FIG. 1.
[0014] FIG. 3 is a schematic representation of the projection
exposure system that implements another embodiment of planar motor
reaction force isolation system in which the coil array is
supported on bearings.
[0015] FIG. 4 is a schematic representation of the projection
exposure system that implements yet another embodiment of the
reaction force isolation system of the present invention in which
the top plate of the planar motor is supported by a frame.
[0016] FIG. 5 is a schematic representation of the projection
exposure system in which the reaction force isolation system is a
variation of the embodiment in FIG. 4.
[0017] FIG. 6 is a schematic representation of the projection
exposure system that implements a reaction force isolation system
in which the top plate of the planar motor and the coil array that
rides on a bearing are supported on a common support frame.
[0018] FIG. 7 is a schematic representation of a further embodiment
of the reaction force isolation system of the present invention
which also shows a wafer leveling stage and the planar motor is
cooled by coolant.
[0019] FIG. 8 is a schematic representation of a two-sided planar
motor driven scanning type exposure system that implements a
reaction force isolation system in accordance with another
embodiment of the present invention, in which the plate and coil
assembly is supported on bearings.
[0020] FIG. 9 is a schematic perspective view of the two-sided
planar motor adopted in the system in FIG. 8.
[0021] FIG. 10 is a schematic exploded view of the two-sided planar
motor in FIG. 9.
[0022] FIG. 11 is a schematic side view of the two-sided planar
motor in FIG. 9.
[0023] FIG. 12 is a schematic representation of the exposure system
that implements another embodiment of the reaction force isolation
system for a two-sided planar motor, in which the coil and plate
assembly is attached to ground.
DETAIL DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
[0024] The following description is of the best-contemplated mode
of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. The scope of the invention
is best determined by reference to the appended claims.
[0025] To illustrate the principles of the present invention, the
isolation of vibrations induced by reaction forces generated by a
planar motor is described in reference to a scanning-type
photolithography system for substrate processing. However, it is
understood that the present invention may be easily adapted for use
in other types of exposure systems for substrate processing (e.g.,
projection-type photolithography system or electron-beam (EB)
photolithography system disclosed in U.S. Pat. No. 5,773,837) or
other types of systems (e.g. pattern position measurement system
disclosed in U.S. Pat. No. 5,539,521, wafer inspection equipment,
machine tools, electron beam, microscope) for processing other
articles in which the reduction of vibrations induced by reaction
forces generated in a planar motor is desirable without departing
from the scope and spirit of the present invention.
[0026] FIG. 1 is a schematic representation of a scanning-type
exposure system 10 for processing a substrate, such as a wafer 12,
which implements the present invention. In an illumination system
14, light beams emitted from an extra-high pressure mercury lamp
are converged, collimated and filtered into substantially parallel
light beams having a wavelength needed for a desired exposure
(e.g., exposure of the photoresist on the wafer 12). Of course, in
place of the mercury lamp, g-line (436 nm), i-line (365 nm), Krf
(248 nm), Arf (193 nm) or F2 (157 nm) excimer laser can be used.
(Glass material that transmit far ultra-violet rays of the excimer
laser, such as quartz and fluorite, should be used. For F2 laser,
the optical system should be either catadioptric or refractive, and
the reticle should be a reflective type.)
[0027] The light beams from the illumination system 14 illuminates
a pattern on a reticle 16 that is mounted on a reticle stage 18.
The reticle stage 18 is movable in several (e.g., three to six)
degrees of freedom by servomotors or linear motor (not shown) under
precision control by a driver 20 and a system controller 22. The
structure of the reticle stage 18 is disclosed in U.S. application
Ser. No. 08/698,827. The light beams penetrating the reticle 16 are
projected on the wafer 12 via projection optics 24.
[0028] The wafer 12 is held by vacuum suction on a wafer holder
(not shown) that is supported on a wafer stage 26 under the
projection optics 24. The wafer stage 26 is structured so that it
can be moved in several (e.g., three to six) degrees of freedom by
a planar motor 30 (see also FIG. 2) under precision control by the
driver 32 and system controller 22, to position the wafer 12 at a
desired position and orientation, and to move the wafer 12 relative
to the projection optics 24. The driver 32 may provide the user
with information relating to X, Y and Z positions as well as the
angular positions of the wafer 12 and the driver 20 may provide
user with information relating to the position of the reticle
16.
[0029] For precise positional information, interferometers 34 and
36 and mirrors 35 and 37 are provided for detecting the actual
positions of the reticle and wafer, respectively, as schematically
shown in FIG. 1. For either or each of the wafer stage and reticle
stage, a set of three interferometers may be provided for detecting
the and X, Y and .theta. positions of the wafer stage and/or
reticle stage, so as to provide positional information that can be
used to drive the wafer stage and/or reticle stage in the X, Y and
.theta. directions. Furthermore, it is also acceptable to install
interferometers at three locations for detecting the position of
either the wafer stage or the reticle stage and drive the wafer
stage or the reticle stage in three directions (e.g., X, Y, and 0)
in accordance with the output from each of the interferometers.
[0030] In the scanning-type exposure apparatus, the reticle 16 and
the wafer 12 are scanned and exposed synchronously (in accordance
with the image reduction in place) with respect to an illumination
area defined by a slit having a predetermined geometry (e.g., a
rectangular, hexagonal, trapezoidal or arc shaped slit). This
allows a pattern larger than the slit-like illumination area to be
transferred to a shot area on the wafer 12. After the first shot
area has been completed, the wafer 12 is stepped by the planar
motor 30 to position the following shot area to a scanning start
position. This system of repeating the stepping and scanning
exposure is called a step-and-scan system. The scan-type exposure
method is especially useful for imaging large reticle patterns
and/or large image fields on the substrate, as the exposure area of
the reticle and the image field on the wafer are effectively
enlarged by the scanning process.
[0031] It is again noted that the configuration of the exposure
system 10 described above generally corresponds to a step-and-scan
exposure system that is known in the art. Further detail of the
components within a scanning-type exposure apparatus may be
referenced from U.S. Pat. No. 5,477,304 to Nishi and U.S. Pat. No.
5,715,037 to Saiki et al. (assigned to the assignee of the present
invention, which are fully incorporated by reference herein. It is
to be understood that the present invention disclosed herein is not
to be limited to wafer processing systems, and specifically to
step-and-scan exposure systems for wafer processing. The general
reference to a step-and-scan exposure system is purely for
illustrating an embodiment of an environment in which the concept
of isolation of planar motor reaction forces to reduce system
vibration may be advantageously adopted.
[0032] As illustrated in the FIG. 1, the illumination system 14,
the reticle stage 18 and the projection optics 24 are separately
supported by frames 38, 40 and 42, respectively. The frames are
coupled to the "ground" (or the surface on which the overall
exposure system is supported). As will be noted below, the frames
38, 40 and 42 may be coupled to the ground by means of vibration
isolation systems and the like.
[0033] Referring also to FIG. 2, the components of the planar motor
30 are schematically illustrated. The planar motor 30 comprises an
array 50 of magnetic coils that are electrically energized under
control of the driver 32. A top plate 52 is positioned above the
coil array 50. The top plate 52 may be made of non-magnetic
materials, for example, carbon fiber plastics, ceramics such as
Zerodur ceramics, Al2O3 ceramics, and the like materials that do
not impair the magnetic flux of permanent magnets 56. The wafer
stage 26 rests on the top plate 52 (preferably in the presence of
an air bearing). The underside of the wafer stage 26 has an array
of permanent magnets 56 configured to interact with the coil array
50 to produce forces in the X, Y and .theta. directions to move the
wafer stage 26 across the top plate 52. Consequently, a reaction
force acts on the coil array 50. According to the present
invention, this reaction force is isolated from the rest of the
exposure system 10.
[0034] For simplicity, many details of the planar motor are omitted
from the FIG. 2, as they alone do not constitute a part of the
present invention. Structural details and operational principles of
planar motors may be referenced to the prior art, such as the U.S.
Pat. Nos. 4,535,278 and 4,555,650 to Asakawa, which are fully
incorporated by reference herein.
[0035] In the embodiment shown in FIG. 1 and further illustrated in
FIG. 2, the top plate 52 is supported on support posts 54 that
project through clearance holes in the coil array 50. The support
posts 54 rest on a base 58 to prevent it from bending. Alternately,
the top plate 52 and the support posts 54 may be a unitary
structure. The base 58 is coupled to the ground by damping means
60, such as air or oil dampers, voice coil motors, actuators or
other known vibration isolation systems. Similarly, the frames 38,
40 and 42 may be coupled to the ground by similar damping means.
The coil array 50 is separately and rigidly coupled to the ground
by fixed stands 62. In this embodiment, when reaction forces are
created between the coil array 50 and the wafer stage 26, the
reaction forces push against the ground. Because of the large mass
of the ground, there is very little movement of the coil array 50
from the reaction forces. By providing damping means 60 to couple
the base 58 and the frames 38, 40 and 42 to the ground, any
vibration that may be induced by the reaction forces through the
ground is isolated from the rest of the system 10.
[0036] Referring to FIG. 3, instead of rigidly coupling the coil
array to the ground, a bearing coupling may be used. For example, a
planar (X, Y and Theta Z) journal bearing 64 may be provided at the
end of the supports 66. Ball bearings and air bearings may also be
used. When reaction forces are created by the coils between the
wafer stage 26 and the coil array 50, both the wafer stage 26 and
the coil array 50 move in opposite directions. The mass of the coil
array 50 is typically substantially larger than that of the wafer
stage 26. Consequently, in accordance with conservation of
momentum, the movement of the coil array 50 caused by the reaction
force is typically substantially smaller than the movement of the
wafer stage 26 under the same reaction force. The inertia of the
coil array 50 would absorb the reaction forces. It is to be
understood that in the embodiment of FIG. 3, the damping means 60
may be omitted if the bearing support can effectively isolate all
reaction forces that may induce vibrations in the rest of the
system 10.
[0037] In another embodiment of the present invention as
illustrated in FIG. 4, the coil array 50 is rigidly supported on
the ground on supports 62. In this embodiment, instead of
supporting the top plate 52 of the planar motor 30 on support posts
54 on the base 58 as was done in the earlier embodiments, the top
plate 52 is supported by frame 42. The invention as illustrated in
FIG. 4 does not have the support posts 54. Therefore the top plate
52 may be formed with a thick honeycomb structure or other types of
reinforced structure to prevent it from bending. The frame 42 is
isolated from vibration transmitted through the ground by damping
means 60.
[0038] FIG. 5 illustrates another configuration in which the top
plate 52 is supported by frame 42. Unlike FIG. 4 in which the top
plate 52 is supported at its ends by the side members 43 of frame
42, the top plate 52 is supported to the top member 45' of the
frame 42'. The coil array 50 remains rigidly supported to the
ground as in FIG. 4. The frame 42' is mounted on the supports 47
using damping means 60'. The center of gravity of the system 10 is
lower in reference to the damping means 60'. So the system 10 in
FIG. 5 is less susceptible to vibration than that in FIG. 4.
Additionally, in FIG. 5, frames 38' and 40' may be mounted on the
frame 42' to avoid the need for additional damping means, as the
damping means 60' isolates the combined structures 38', 40' and
42'. The damping means 60' prevents the vibration of the ground
from transmitting to the projection optics 24, the illumination
system 14 and the reticle 16. The system 10 in FIG. 5 is more
compact, but the center of gravity of the system 10 shifts
depending on the position of the wafer stage 26. Therefore, it is
preferred that the damping means 60' includes an actuator
(schematically shown at 61) that maintains the frame 42' level so
as to prevent misalignment of the optical axes of the projection
optics 24 and the illumination system 14. The actuator and
positional feedback scheme needed to achieve the leveling objective
may be implemented using known art.
[0039] As a further variation of the embodiments of FIGS. 4 and 5,
bearing supports may be utilized to support the coil array 50, for
the same reasons as for the embodiment of FIG. 3.
[0040] In yet another embodiment of the present invention as
illustrated in FIG. 6, both the top plate 52 and the coil array 50
are supported by the frame 42'. Specifically, the top plate 52 is
attached to the mid sections of the vertical members 70 that depend
from the top member 45' of the frame 42'. A horizontal support
platform 72 is attached to the ends of the vertical members 70. The
coil array 50 rides on bearings 74 (e.g. an air or ball bearings)
on the horizontal support platform 72. With this embodiment, the
reaction forces would cause the coil array 50 to move sideways on
its bearings 74, thus absorbing the reaction forces with its
inertia. In FIG. 6, frames 38' and 40' may be mounted on the frame
42' without additional damping means as in FIG. 5. In addition, the
reaction forces can be absorbed during the exposure process,
because reaction forces are very small compared to the weight of
the system 10 that comprises the projection optics 24, wafer stage
26, the reticle stage 18 and the illumination system 14.
[0041] The invention of FIG. 6 uses the principle of momentum
conservation, so the center of gravity of the system 10 does not
shift according to the position of the wafer stage 26. Therefore
damping means 60' of this invention does not need an actuator
(compared to the embodiment in FIG. 5.)
[0042] FIG. 7 shows a variation of the embodiment of FIG. 6. The
planar motor 30 includes a cooling platform 76 that is supported by
the horizontal support platform 72. The cooling platform 76
includes conduits 78 through which coolant 77 can pass through.
Alternatively, Peltier cooling or ventilating air cooling may be
deployed. The top plate 52 is supported on stands 80 that are
supported on the cooling platform 76. The cooling platform 76
provides a support surface on which the coil array 50 rests on
bearings 74. Further wafer stage 26 includes a leveling stage 83
that positions the wafer 12 in three additional degrees of freedom.
The leveling stage 83 has at least three actuators 84, e.g. voice
coil motors, which actuate in the direction of the axis of
projection optics 24 in accordance with focus sensors 82a and 82b.
The focus sensor 82a emits a focusing beam to the wafer 12 and the
focus sensor 82b receives the reflected beam from the wafer 12. The
leveling stage 83 can adjust the focal plane of the projection
optics 24 to align with the surface of the wafer 12. It is
preferable that the leveling stage 83 is structurally isolated
(without mechanical contact) on the wafer stage 26 so that the
vibration of the wafer stage 26 (e.g., caused by the air bearing)
may be isolated.
[0043] The above-described embodiments are all directed to exposure
systems that deploy a planar motor that is driven by magnetic
interactions on one side (the bottom side as illustrated in the
drawings) of the moving portion. In certain exposure systems, it is
desirable to deploy a two-sided planar motor in which the moving
portion is driven by magnetic interactions on both sides (top and
bottom sides) of the moving portion.
[0044] FIG. 8 shows an exposure system 100 in which a two-sided
planar motor 102 is deployed. As illustrated, except for the
configuration of the planar motor 102 and reaction force isolation
structure, the exposure system 100 is fumdamentally similar to the
earlier embodiments, such as FIG. 6.
[0045] Referring to FIGS. 9 to 11, the components of the two-sided
planar motor 102 are schematically illustrated. The two-sided
planar motor 102 comprises two planar coil arrays 104 and 106
(hidden from view in FIGS. 8 and 9). The array 104 is supported on
a bottom plate 108, and the array 106 is supported on a top plate
110. The top plate 110 and the bottom plate 108 are separated by
posts 112 to define a space 115 in which the moving portion of the
planar motor 102, i.e., a wafer stage 114, is free to move in a
plane. The bottom and top plates 108 and 110 and the posts 112 form
a rigid assembly (hereinafter referred to as the plate assembly
113). The wafer stage 114 has complimentary permanent magnet arrays
116 and 118 on the top and bottom sides of the wafer stage 114. The
wafer stage 114 supports a wafer 12. The top plate 110 is provided
with an opening 111 to allow illumination to be directed at the
wafer 12.
[0046] For simplicity, many details of the two-sided planar motor
102 are omitted from the drawings, as they alone do not constitute
a part of the present invention. Structural details and operational
principles of two-sided planar motors may be referenced to the
copending patent application Ser. No. ______, filed ______ (docket
PA0225-US); patent application Ser. No. 09/192,813, filed Nov. 16,
1998 (docket PA0162-US); and U.S. patent application Ser. No.
______ , filed ______ (docket PA0221-US), which are fully
incorporated by reference herein.
[0047] In the embodiment shown in FIGS. 8 to 10, the plate assembly
113 of the planar motor 102 is supported on a bearing system
supported on a base 122. (While the bearing system are
schematically represented as ball bearings 120, it is understood
that the bearing system may be air bearings or some other bearing
technology without departing from the scope and spirit of the
present invention.) Referring to FIG. 8, the base 122 is supported
from a fixed body 124 of the exposure system 100 by support posts
126. The body 124 supports the projection optics 24 such as
projection lenses. An appropriate opening 128 is provided on the
body 124 and aligned with opening 111 on the top plate 110 to allow
illumination to be directed to the wafer 12 that is supported on
the wafer stage 114.
[0048] When the magnetic coil arrays 104 and 106 are energized
under control of the driver 32, a magnetic force moves the wafer
stage 114 about in the space 115 of the plate assembly 113 to
position the wafer 12 with respect to the projection optics 24. The
force on the wafer 114 causes a reaction force on the plate
assembly 113. It is noted that the system illustrated in FIG. 8
consists of a fixed body 124 of the exposure system 100, and moving
plate assembly 113 and wafer stage 114. Because the plate assembly
113 is free to move due to the bearing system 120, it moves in the
opposite direction of the wafer stage 114 as governed by the
principle of conservation of momentum. If the mass of the plate
assembly 113 is significantly higher than the mass of the wafer
stage 114 (which is typically the case), the travel of the plate
assembly 113 due to the reaction force will be significantly less
than that of the wafer stage 114. As in the earlier embodiments,
because all of the momentum is conserved between the wafer stage
114 and the plate assembly 113, the body of the exposure system 100
will not move. This means that no vibrations or other forces will
enter the body due to the wafer stage motion. In effect, the
reaction force of the wafer stage 114 is absorbed in the inertia of
the plate assembly 113.
[0049] FIG. 12 illustrates another embodiment of reaction force
isolation for a two-sided planar motor in an exposure system 100
(for simplicity, many parts of the exposure system 100 have been
omitted from the drawing). In this embodiment, the plate assembly
113 is attached or supported directly to ground 130 as the base.
The body 124' of the exposure system which supports the projection
optics 24 is also supported to ground 130.
[0050] In this configuration, the momentum of the wafer stage 114
is conserved between it and the ground 130. Because the mass of the
ground 130 is significantly higher than the mass of the wafer stage
114, the motion of the ground 130 from the reaction force of the
wafer stage 114 is negligible. Higher frequency components of the
wafer stage motion (e.g., vibrations), however, can be transmitted
in the ground 130. To prevent these from being transmitted to the
body 124' of the exposure system, the body 124' is isolated from
the ground 130 using a vibration isolation system 132, such as the
damping means 60' in the earlier embodiments. Vibration isolation
systems are commercially available, for example, from Barry
Controls, Brighton, Mass.
[0051] It is appreciated that the exposure systems described in the
foregoing embodiments can be built by assembling various
subsystems, including the planar motor, projection optics,
illumination system, positioning control system, and vibration
isolation system. The subsystems are assembled in a manner that
optimizes the mechanical accuracy, electrical accuracy and optical
accuracy. In order to maintain various accuracy of the various
subsystems, every optical system is adjusted to achieve it optical
accuracy, every mechanical system is adjusted to achieve its
mechanical accuracy, and every electrical system is adjusted to
achieve its electrical accuracy before and after its assembly. The
process of assembling each subsystem into an exposure system
includes mechanical connections, electrical circuit wiring
connections and air pressure plumbing connections. Each subsystem
may be assembled prior to integrating the subsystems to construct
the exposure system. Once the exposure system is assembled with
various subsystems, overall adjustment is performed so as to
optimize the individual subsystem accuracy as well as overall
system accuracy. The exposure shall preferably be manufactured and
assembled in a clean room environment.
[0052] While the general process for manufacturing semiconductor
devices using the exposure system of the present invention have not
been described in detail, it is understood that one skilled in the
art can readily apply the exposure system to the fabrication of
semiconductor devices by conventional procedures, which may include
the steps of designing the device functions and performance,
designing the reticle, fabricating the wafer, exposing the reticle
pattern on the wafer using the exposure system of the present
invention, assembling the device (including dicing, bonding, and
packaging processes), and inspection and quality control.
[0053] While the invention has been described with respect to the
described embodiments in accordance therewith, it will be apparent
to those skilled in the art that various modifications and
improvements may be made without departing from the scope and
spirit of the invention. For example, in the above embodiments of
FIGS. 1, 3 and 4, frames 38, 40 and 42 are separately coupled to
the ground. Alternatively, frames 38 and 40 can be mounted on the
frame 42 without damping means as in FIGS. 5 and 6. Conversely, the
frames 38', 40' and 42' in the embodiments of FIGS. 5, 6, 7 and 8
may be separately supported on damping means as in FIGS. 1, 3 and
4. The above embodiments of FIGS. 1, 3, 4 and 5 also may be
implemented with focus sensors 82 and the leveling stage 83.
Additionally, various combinations of damping means and bearing
support may be deployed to provide the reaction force isolation
function, and/or to provide redundancy in such function.
[0054] While the foregoing embodiments have been described with
reference to planar motors that have a coil array on the moving
portion of the planar motor and magnets on the fixed portion of the
planar motor, it is to be understood that the coil array may be
provided on the moving portion and the magnets may be provided on
the fixed portion instead, without departing from the scope and
spirit of the present invention.
[0055] The structure of the planar motor was explained as having a
coil array on the fixed part side and magnets on the moving part
side, but the arrangement could be other way around. In other
words, magnets can be placed on the fixed part side, and the coil
array can be placed on the moving part side.
[0056] Furthermore, although the wafer stage employing a planar
motor was explained as an example, the present invention is also
applicable to the case where a planar motor is employed in a
reticle stage. In that case, an opening as shown in FIG. 8-12
should be made in a reticle stage where a planar motor is mounted
so that the illumination from the illumination system 14 can be
transmitted through the reticle 16 and intercepted by the wafer
12.
[0057] In each of the embodiments, a scanning-type exposure system,
where a mask and a wafer are moving synchronously to expose a mask
pattern, was used as an example. However, it does not have to be
limited to this. For instance, the present application is also
applicable to a step-and-repeat-type exposure system, where a mask
pattern is exposed while the mask and the wafer are stationary, and
the wafer is stepped and moved in order of succession.
[0058] Furthermore, it is also applicable to a proximity exposure
system, where a mask pattern is exposed by closely placing the mask
and the wafer, without using projection optics.
[0059] The use of the exposure system does not need to be limited
to semiconductor manufacturing: for instance, it can be widely
applied to an LCD exposure system, where LCD pattern is exposed
onto a rectangular glass plate, or an exposure system for
manufacturing a thin film magnetic head.
[0060] In terms of the light source for the exposure system
according to the present embodiment(s), not only the g-line (436
nm), i-line (365 nm), KrF excimer laser (248 nm), ArF excimer laser
(193 nm), and he F2 laser (157 nm) but also charged particle beams
such as the x-ray and electron beams can be used. If an electron
beam is used, thermionic emission type lanthanum hexaboride (LaB6)
or tantalum (Ta) can be used as an electron gun. Furthermore, when
an electron beam is used, the structure could use a mask, or it
could be structured such that a pattern can be formed directly onto
a wafer without using a mask.
[0061] In terms of the magnification of the projection optical
system, it does not have to be limited to a reduction system: it
could be 1.times. or a magnification system as well.
[0062] With respect to the projection optical system, when far
ultra-violet rays such as the excimer laser is used, glass
materials that transmit far ultra-violet rays such as quartz and
fluorite should be used: when the F2 laser or the x-ray is used,
the optical system should be either catadioptric or refractive (the
reticle should be a reflective type), and when an electron beam is
used, electron optics should consist of electron lenses and
deflectors. It is needless to say that the optical path for
electron beams should be in vacuum.
[0063] When linear motors (see U.S. Pat. No. 5,623,853 or U.S. Pat.
No. 5,528,118) are used in a reticle stage, they could be either
the air levitation type using air bearings or the magnetic
levitation type using the Lorentz force or reactance force. In
addition, the reticle stage could move along a guide, or it could
be a guideless type where no guide is installed.
[0064] Reaction force generated by the reticle stage motion can be
mechanically released to the ground by using a frame member, as
described in JP Hei 8-330224 published patent (U.S. Ser. No.
08/416,558).
[0065] As described above, the exposure system according to the
embodiments of the present application can be built by assembling
various subsystems, including the elements listed in the claims of
the present application, in the manner that prescribed mechanical
accuracy electrical accuracy and optical accuracy are maintained.
In order to maintain various accuracy of various subsystems, every
optical system is adjusted to achieve its optical accuracy, every
mechanical system is adjusted to achieve its mechanical accuracy
and every electrical system is adjusted to achieve its electrical
accuracy before and after its assembly. The process of assembling
each subsystem into an exposure system includes mechanical
interface, electrical circuits' wiring connections and air pressure
plumbing connections. It is needless to say that there is a process
where each subsystem is assembled prior to assembling the exposure
system from various subsystems. Once the exposure system is
assembled with various subsystems, total adjustment is performed so
as to make sure that every accuracy is maintained in the total
system. Incidentally, it is desirable to manufacture an exposure
system in a clean room where the temperature and the cleanliness
are controlled.
[0066] Semiconductor devices are fabricated by going through the
following steps: the step where the device's function and
performance are designed; the step where a reticle is designed
according to the previous designing step; the step where a wafer is
made from a silicon material; the step where the reticle pattern is
exposed on a wafer by the exposure system in the aforementioned
embodiments; the step where device is assembled (including the
dicing process, bonding process and packaging process); and the
inspection step, etc.
[0067] The planar motors described above may also be implemented
for actuation of the reticle stage. For example, for the
embodiments of FIGS. 8-12, a suitable opening is provided in the
two-sided planar motor installed in the reticle stage so that
illumination from the illumination system 14 can transmit through
the reticle 16 to be projected onto the wafer 12. When linear
motors (see U.S. Pat. No. 5,623,853 and U.S. Pat. No. 5,528,118)
are used in a reticle stage, they could be based on air levitation
by air bearings or magnetic levitation by Lorentz force or
reactance force. In addition, the reticle stage could move along a
guide or without a guide. Reaction force generated by the reticle
stage motion can be mechanically released to the ground by using a
frame member, as described in published JP patent applicatioin JP
Hei 8-330224.
[0068] Further, the present invention is not limited to scanning
type exposure system. For example, the present invention may be
adopted in other types of exposure apparatus, such as a
step-and-repeat type exposure system in which a pattern is exposed
in successive sections of the mask and the wafer remain stationary.
Instead of applying to a reduction projection optical system, the
present invention may also be applied to a magnification projection
optical system, including a 1.times. magnification system. The
present invention may also be adopted in a proximity exposure
system, in which a mask closely positioned with the wafer is
exposed without using projection optics.
[0069] The present invention is not limited to semiconductor
manufacturing. The present invention may be applicable to other
types of processing systems in which precision positioning
utilizing a planar motor is desired. For example, it may be applied
to exposure systems for the manufacture of LCD panels, in which a
pattern is exposed onto a rectangular glass plate. It may also be
applied to exposure systems for the manufacture of thin film
magnetic heads.
[0070] Exposure systems not using illumination may also take
advantage of the present invention. For example, the present
invention may be applied to systems that use charged particle beams
such as X-ray beams and electron beams. If an electron beam is
used, thermionic emission type lanthanum hexaboride (LaB.sub.6) or
tantalum (Ta) can be used as the source of an electron beam.
Furthermore, when an electron beam is used, the exposure system
could use a mask, or it could be structured such that a pattern can
be formed directly onto a wafer without using a mask. Electron
optics for the exposure system should consist of electron lenses
and deflectors. The optical path for the electron beams should be
contained a vacuum environment. If a X-ray beam is used, the
optical system should be either catadioptric or refractive (the
reticle should be a reflective type).
[0071] While the described embodiment illustrates planar motors
used in an X-Y plane, planar motors used in other orientations and
having more or less dimensions may be implemented with the present
invention.
[0072] Accordingly, it is to be understood that the invention is
not to be limited by the specific illustrated embodiments, but only
by the scope of the appended claims.
* * * * *