U.S. patent application number 10/935995 was filed with the patent office on 2006-03-09 for split coil linear motor for z force.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Michael B. Binnard.
Application Number | 20060049697 10/935995 |
Document ID | / |
Family ID | 35995497 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060049697 |
Kind Code |
A1 |
Binnard; Michael B. |
March 9, 2006 |
Split coil linear motor for z force
Abstract
Methods and apparatus for enabling a coil to be used to provide
a net force along more than one axis are disclosed. According to
one aspect of the present invention, an actuator includes a magnet
assembly and a coil assembly. The coil assembly moves at least
partially within the magnet arrangement, and includes a top coil
half and a bottom coil half. The top coil half and the bottom coil
half are independently controllable such that a first current
applied to the top coil half may be independently applied from a
second current applied to the bottom coil half.
Inventors: |
Binnard; Michael B.;
(Belmont, CA) |
Correspondence
Address: |
AKA CHAN LLP
900 LAFAYETE STREET
SUITE 710
SANTA CLARA
CA
95050
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
|
Family ID: |
35995497 |
Appl. No.: |
10/935995 |
Filed: |
September 8, 2004 |
Current U.S.
Class: |
310/12.22 |
Current CPC
Class: |
H02N 15/00 20130101;
H02K 2201/18 20130101; G03F 7/70758 20130101; H02K 41/03
20130101 |
Class at
Publication: |
310/012 |
International
Class: |
H02K 41/00 20060101
H02K041/00 |
Claims
1. An actuator comprising: a magnet arrangement; and a coil
assembly, the coil assembly being arranged to move at least
partially within the magnet arrangement, the coil assembly
including a top coil half and a bottom coil half, the top coil half
and the bottom coil half being arranged to he substantially
independently controlled such that a first current applied to the
top coil half may be applied substantially independently from a
second current applied to the bottom coil half.
2. The actuator of claim 1 wherein the coil assembly is arranged to
move at least partially within the magnet arrangement along a first
axis, and wherein the top coil half and the bottom coil half are
arranged to cooperate to produce a substantially non-zero net force
along a second axis when the first current and the second current
are applied in substantially opposite directions along a third
axis.
3. The actuator of claim 2 wherein the top coil half and the bottom
coil half are arranged to cooperate to produce a substantially
negligible net force along the first axis.
4. The actuator of claim 2 wherein when the top coil half and the
bottom coil half arranged to cooperate to produce a substantially
non-zero net force along the first axis when the first current and
the second current are applied in substantially a same direction
along the third axis.
5. The actuator of claim 4 wherein the top coil half and the bottom
coil half are arranged to cooperate to produce a substantially
negligible net force along the second axis.
6. The actuator of claim 1 wherein the actuator is one of a linear
motor and a voice coil motor.
7. A stage apparatus comprising the actuator of claim 1.
8. An exposure apparatus comprising the stage apparatus of claim
7.
9. A device manufactured with the exposure apparatus of claim
8.
10. A wafer on which an image has been formed by the exposure
apparatus of claim 8.
11. An actuator comprising: a magnet arrangement; and a coil
assembly, the coil assembly being arranged to move at least
partially within the magnet arrangement, the coil assembly
including a first coil and a second split coil, wherein the first
coil is arranged to provide a substantially non-zero net force
along a first axis and the second split coil is arranged to provide
a substantially non-zero net force along a second axis, the second
axis being substantially perpendicular to the first axis.
12. The actuator of claim 11 wherein the coil assembly is arranged
to move at least partially within the magnet arrangement along a
first axis, and wherein the second split coil includes a first coil
half and a second coil half, the first coil half and the second
coil half being arranged to be substantially independently
controlled such that a first current applied to the first coil half
is applied in a substantially opposite direction along a third axis
from a second current applied to the second coil half, the third
axis being substantially perpendicular to the first axis and to the
second axis.
13. The actuator of claim 12 wherein the second split coil is
arranged to provide a substantially negligible net force along the
first axis.
14. The actuator of claim 11 wherein the first coil is a first
split coil, the first split coil including a first coil half and a
second coil half, the first coil half and the second coil half
being arranged such that a first current applied to the first coil
half is applied in substantially a same direction along a third
axis as a second current applied to the second coil half, the third
axis being substantially perpendicular to a first axis and to the
second axis.
15. The actuator of claim 11 wherein a first current provided to
the first coil, and a second current and a third current provided
to the second split coil are substantially independently
controlled.
16. A stage apparatus comprising the actuator of claim 11.
17. An exposure apparatus comprising the stage apparatus of claim
16.
18. A device manufactured with the exposure apparatus of claim
17.
19. A wafer on which an image has been formed by the exposure
apparatus of claim 17.
20-26. (canceled)
27. The actuator of claim 1 wherein the first current is supplied
by a first current supply and the second current is supplied by a
second current supply.
28. The actuator of claim 1 wherein the first current is amplified
by a first current amplifier and the second current is amplified by
a second current amplifier.
29. The actuator of claim 11 wherein the second split coil includes
a top coil half and a bottom coil half, the top coil half having a
current supplied by a first current source and the bottom coil half
having a current supplied by a second current source.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates generally to actuators. More
particularly, the present invention relates to a coil design which
enables an actuator such as a linear motor to provide a net force
in along both an x-axis and a z-axis.
[0003] 2. Description of the Related Art
[0004] For many machines or instruments such as photolithography
machines which are used in semiconductor processing, space is often
at a premium. The lack of available space often forces components
to be sized as compactly as possible. As a result, restricting the
size of a component that is arranged to provide a particular force
or motion allows the space in an overall machine to be efficiently
utilized.
[0005] Many machines include linear motors which may be used to
provide a force that is used to drive an object or a structure,
e.g., a stage of a photolithography machine. FIG. 1 is a
diagrammatic representation of a typical linear motor. A linear
motor 100 includes a magnet structure 102 and a coil structure 104.
Often, linear motor 100 is sized such that a dimension along an
x-axis 106a and a dimension along a y-axis 106b are significantly
larger than a dimension along a z-axis 106c. When a current is
applied to coil 104, a force, i.e., a non-zero net force, is
generated along x-axis 106a.
[0006] FIG. 2a is a diagrammatic cross-sectional representation of
a symmetric linear motor. A linear motor 200 includes magnets 202
and coils 206, 207. Coil 206 includes sections 204a, 204b, while
coil 207 includes sections 204c, 204d. Sections 204a, 204b are
arranged to produce force in an x-direction 206a, while sections
204c, 204d are arranged to produce force in a z-direction 206c. As
shown in FIG. 2b, when current is applied to coils 206, 207 in a
y-direction 206b, magnetic flux 208c is generated in x-direction
206a, and magnetic flux 208a, 208b is generated in z-direction
206c. Since force that is generated by linear motor 200 is
generally perpendicular to both applied current and magnetic flux
208, coil 206 produces a force in x-direction 206a. Coil 207 is
capable of generating force in z-direction 206c. However, since
magnetic flux 208a is directed in a substantially opposite
direction from magnetic flux 208b, the net force in z-direction
206c is effectively zero.
[0007] Since linear motor 200 effectively only produces a non-zero
net force in x-direction 206a, linear motor 200 may generally only
be used to apply force on an object, as for example a stage
assembly (not shown), in x-direction 206a. In order for the object
to be moved in z-direction 206c, an additional linear motor which
is arranged to apply a force substantially only in z-direction 206c
generally must also be coupled to object. While the use of linear
motor 200 and an additional linear motor may be effective in
allowing an object to move in both x-direction 206a and z-direction
206c, the use of the additional linear motor may not always be
possible due to space constraints within an overall system.
Further, the use of an additional linear motor may cause issues
associated with the addition of mass to the overall system, and the
generation of heat within the overall system. As will be
appreciated by those skilled in the art, additional mass may cause
vibrations within the overall system, while additional heat may
adversely affect the performance of various components, e.g.,
sensors, within the overall system.
[0008] A planar motor, i.e., a motor with a substantially flat
plate of magnets and coils, is arranged to provide force in an
x-direction and a z-direction. Hence, a single planar motor may be
used in lieu of two linear motors to provide a non-zero net force
in an x-direction and a z-direction. However, a planar motor is
generally more complicated to control than a linear motor. Further,
since many systems are arranged to use linear motors, the use of a
planar motor instead of one or more linear motors may be
impractical.
[0009] Therefore, what is desired is a method and an apparatus
which enables a non-zero net force to be efficiently applied in an
x-direction and a z-direction. That is, what is needed is a method
and an apparatus which allows a single linear motor to be used to
apply non-zero net forces along an x-axis and a z-axis.
SUMMARY OF THE INVENTION
[0010] The present invention relates to a split coil design which
enables the overall direction in which a net force is applied by an
actuator to be altered. According to one aspect of the present
invention, an actuator includes a magnet assembly and a coil
assembly. The coil assembly moves at least partially within the
magnet arrangement, and includes a top coil half and a bottom coil
half. The top coil half and the bottom coil half are independently
controllable such that a first current applied to the top coil half
may be independently applied from a second current applied to the
bottom coil half.
[0011] In one embodiment, the top coil half and the bottom coil
half cooperate to produce a substantially non-zero net force along
a second axis when the first current and the second current are
applied in substantially opposite directions along a third axis. In
such an embodiment, the top coil half and the bottom coil half also
cooperate to produce a substantially negligible net force along a
first axis along which the coil assembly moves at least partially
within the magnet arrangement.
[0012] An actuator, e.g., a linear motor, that provides a non-zero
net force along both an x-axis and a z-axis allows forces to be
applied along both axes substantially without requiring the use of
an additional actuator. Therefore, no extra space is generally
needed within a system to provide the capability of generating
non-zero net forces along two axes. An actuator that provides
non-zero net forces along two axes may be achieved by utilizing a
split coil which coil sections which may be independent controlled,
e.g., controlled using independent currents.
[0013] According to another aspect of the present invention, an
actuator includes a magnet arrangement and a coil assembly that
moves at least partially within the magnet arrangement along a
first axis and includes a first coil and a second split coil. The
first coil is arranged to provide a substantially non-zero net
force along the first axis and the second split coil is arranged to
provide a substantially non-zero net force along a second axis that
is substantially perpendicular to the first axis. In one
embodiment, the second split coil includes a first coil half and a
second coil half that are substantially independently controlled
such that a first current is applied to the first coil half in a
substantially opposite direction along a third axis from a second
current applied to the second coil half.
[0014] In accordance with another aspect of the present invention,
a method for controlling an actuator that has a magnet assembly and
a coil assembly, which has a first coil and a second coil, and
moves at least partially within the magnet assembly along a first
axis includes applying a first current to the first coil and
applying a second current to the second coil. The second current is
applied substantially independently from the first current, wherein
applying the first current and the second current causes a
substantially non-zero net force to be generated.
[0015] These and other advantages of the present invention will
become apparent upon reading the following detailed descriptions
and studying the various figures of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention may best be understood by reference to the
following description taken in conjunction with the accompanying
drawings in which:
[0017] FIG. 1 is a diagrammatic representation of a magnet and a
coil.
[0018] FIG. 2a is a diagrammatic cross-sectional representation of
an opposed set of magnets and a coil.
[0019] FIG. 2b is a diagrammatic cross-sectional representation of
an opposed set of magnets and a coil, i.e., magnets 202 and coil
204 of FIG. 2a, with magnetic flux lines.
[0020] FIG. 3 is a diagrammatic cross-sectional representation of
an opposed set of magnets and a split coil in accordance with an
embodiment of the present invention.
[0021] FIG. 4a is a block diagram representation of a split coil
assembly with substantially separate current supplies in accordance
with an embodiment of the present invention.
[0022] FIG. 4b is a diagrammatic block diagram representation of a
split coil assembly associated with a three-phase motor in
accordance with an embodiment of the present invention.
[0023] FIG. 4c is a diagrammatic block diagram representation of a
split coil assembly with controlling amplifiers in accordance with
an embodiment of the present invention.
[0024] FIG. 5 is a diagrammatic cross-sectional representation of
an opposed set of magnets and a coil assembly which includes a
non-split coil and a split coil in accordance with an embodiment of
the present invention.
[0025] FIG. 6 is a diagrammatic representation of a
photolithography apparatus in accordance with an embodiment of the
present invention.
[0026] FIG. 7 is a process flow diagram which illustrates the steps
associated with fabricating a semiconductor device in accordance
with an embodiment of the present invention.
[0027] FIG. 8 is a process flow diagram which illustrates the steps
associated with processing a wafer, i.e., step 1304 of FIG. 7, in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0028] Many systems such as photolithography systems used in
semiconductor wafer processing have spatial constraints. It is
often not possible to add additional components such as actuators
to the systems due to a lack of space. By way of example, when it
is desired for an object that is coupled to a linear motor, i.e., a
linear motor which is arranged to enable force to be generated
along an x-axis, to be moved along a z-axis, it may not be possible
to couple another linear motor, i.e., a linear motor which is
arranged to enable force to be generated along a z-axis, to the
object. When the addition of another linear motor is not possible,
then the overall performance of the system which includes the
object may be compromised, as the object may not be moved along the
z-axis as desired.
[0029] Configuring an actuator such as a linear motor to provide a
non-zero net force along both an x-axis and a z-axis allows forces
to be applied along both axes substantially without requiring the
use of an additional linear motor or voice coil motor. As a result,
no space is needed within an overall system to accommodate an
additional linear motor. In one embodiment, by utilizing a split
coil, e.g., a plurality of coils, within the linear motor, the
current applied to top and bottom halves of the split coil may be
controlled such that forces along a z-axis may be controlled.
[0030] With reference to FIG. 3, a split coil will be described in
accordance with an embodiment of the present invention. A motor 300
includes magnets 302, a split coil 304 that is made up of a top
half 308 and a bottom half 312, and a split coil 307 that is made
up of a top half 318 and a bottom half 322. In one embodiment,
motor 300 may be a linear motor, although it should be appreciated
that motor 300 may instead be a voice coil motor. The current
provided to top half 308 and the current provided to top half 318
may be controlled substantially independently from the current
provided to bottom half 308 and bottom half 322, respectively.
[0031] Split coil 304 may be arranged such that portions of top
half 308a, 308b may have current flowing in an opposite direction
along a y-axis 306b than portions of bottom half 312a, 312b,
respectively, to provide a substantially non-zero net force along a
z-axis 306c. Specifically, current may flow in portion 308a in an
opposite direction along y-axis 306b than in portion 312a, and
current may flow in portion 308b in an opposite direction along
y-axis 306b than in portion 312b. When current in half 308 flows in
an opposite direction along y-axis 306b from current in half 312,
forces along x-axis 306a are effectively cancelled out. In other
words, when current flows in half 308 in an opposite direction
along y-axis 306b as current in half 312, the net force generated
along x-axis 306a by split coil 304 is effectively zero when the
currents have substantially the same magnitude, while the net force
generated along z-axis 306c is non-zero. Hence, as shown, split
coil 304 is arranged to provide a non-zero net force in a direction
along z-axis 306c when currents of equal magnitude and opposite
directions are applied to halves 308, 312. Reversing the direction
in which current is applied to both top half 308 and bottom half
312 provides net force in the opposite direction along z-axis
306c.
[0032] While split coil 304 is arranged to provide non-zero net
forces along z-axis 306c, in the embodiment as shown, split coil
307 is arranged to provide non-zero net forces along an x-axis
306a. Split coil 307 is arranged such that portions of top half
318a, 318b may have current flowing in the same direction along
y-axis 306b as portions of bottom half 322a, 322b, respectively, to
provide force along x-axis 306a. When approximately equal current
flows in the same direction in top half 318 and bottom half 322,
the net force along z-axis 306c is substantially zero, while there
is a non-zero net force along x-axis 306a.
[0033] By allowing the current that flows through top half 308 and
bottom half 312 of split coil 304 to flow in opposite directions
along y-axis 306b and by allowing the current that flows through
top half 318 and bottom half 322 of split coil 307 to flow in the
same direction along y-axis 306b, split coil 304 effectively
enables motor 300 to generate a non-zero net force with respect to
z-axis 306c while split coil 307 effectively enables motor 300 to
generate a non-zero net force with respect to x-axis 306a. As a
result, motor 300 is capable of being used to provide non-zero net
forces in both a direction along x-axis 306a and a direction along
z-axis 306c.
[0034] Separate current sources are generally needed for the top
half and the bottom half of a split coil, e.g., top half 308 and
bottom half 312 of split coil 304. As a motor moves, the directions
in which current is applied to the split coil may vary due to
commutation. FIG. 4a is a block diagram representation of a split
coil assembly with substantially separate current supplies in
accordance with an embodiment of the present invention. A split
coil assembly 402 includes a top half 408 and a bottom half 412.
Top half 408 is coupled to a current supply 414a which is arranged
to provide a current to top half 408, while bottom half 412 is
coupled to a current supply 414b which is arranged to provide a
current to bottom half 412. Current supplies 414 may each be
coupled to a current amplifier (not shown), and controlled by a
current command (not shown). In one embodiment, current supply 414a
provides a current of a given magnitude to top half 408 in one
direction, while current supply 414b provides a current of the same
magnitude to bottom half 412 in an opposite direction, although it
should be appreciated that current supplies 414a, 414b may also
provide currents in the same direction or of different magnitudes
to top half 408 and bottom half 412, respectively.
[0035] A motor which uses split coils may, in one embodiment, be a
3-phase motor which uses multiple split coils. FIG. 4b is a
representation of a split coil assembly that is suitable for use in
a 3-phase motor in accordance with an embodiment of the present
invention. A split coil assembly 420 includes a top `A` coil 422, a
bottom `A'' coil 424, a top `B` coil 426, a bottom `B'' coil 428, a
top `C` coil 430, and a bottom `C''' coil 432. Top coil 422 and
bottom coil 424 generally make up one overall split coil, while
coils 426, 428 and coils 430, 432 each also make up overall split
coils.
[0036] The three phases of a motor which includes split coil
assembly 420 are generally each 120 degrees out of phase. Each coil
included in split coil assembly 420 generally has a separate
current amplifier which enables the current provided to each coil
to be controlled substantially independently. By way of example,
top coil 422 may have a separate current amplifier from bottom coil
424 such that the current provided to top coil 422 and bottom coil
424 may be of a substantially equal magnitude, but provided in
opposite directions.
[0037] In general, split coil assembly 420 may include any number
of coils. That is, split coil assembly 420 may include a plurality
of `A` coil and `A'' coil pairs, `B` coil and `B'' coil pairs, and
`C` coil and `C'' coil pairs. With reference to FIG. 4c, an overall
coil assembly which is suitable for use in a 3-phase motor and
includes multiple coil pairs will be described in accordance with
an embodiment of the present invention. A split coil assembly 460
includes any number of `A` coils 462, and any number of `A'' coils
464. Each `A` coil 462 and each `A'' coil 464 effectively forms an
`A` coil and `A'' coil pair. As shown, split coil assembly 460
includes two `A` coil and `A'' coil pairs, although the number of
`A` coil and `A'' coil pairs may vary widely. Similarly, the number
of `B` coils 466 and `B'' coils 468 may vary, and the number of `C`
coils 470 and `C'' coils 472 may also vary.
[0038] Each `A` coil 462 is coupled to an A-phase amplifier 480a
which may accept a current command 476, e.g., from a controller, to
provide a particular amount of current to each `A` coil 462. In
general, each type of coil has a dedicated amplifiers 480a-f which
is effectively controlled by current command 476. That is, `A''
coil 464 is coupled to an A'-phase amplifier 480b, `B` coil 466 is
coupled to B-phase amplifier 480c, `B'' coil 468 is coupled to
B'-phase amplifier 480d, `C` coil 470 is coupled to C-phase
amplifier 480e, and `C'' coil 472 is coupled to C'-phase amplifier
480e.
[0039] The current applied by each amplifier 480, which is
commanded by current command 476, is typically a function of a
desired amplitude of current (A.sub.x) associated with an x-axis
496a and a desired amplitude of current (A.sub.z) associated with a
z-axis 496b, as well as the position (.phi.) of a magnet (not
shown) relative to split coil assembly 460. In one embodiment, the
currents applied by each amplifier 480 may be expressed as follows:
I.sub.A=A.sub.x sin.phi.+A.sub.z cos.phi. I.sub.A'=A.sub.x
sin.phi.-A.sub.z cos.phi. I.sub.B=A.sub.x
sin(.phi.+120.degree.)+A.sub.z cos(.phi.+120.degree.)
I.sub.B'=A.sub.x sin(.phi.+120.degree.)-A.sub.z
cos(.phi.+120.degree.) I.sub.C=A.sub.x
sin(.phi.+240.degree.)+A.sub.z cos(.phi.+240.degree.)
I.sub.C'=A.sub.x sin(.phi.+240.degree.)-A.sub.z
cos(.phi.+240.degree.) where I.sub.A is the current applied by
amplifier 480a, I.sub.A' is the current applied by amplifier 480b,
I.sub.B is the current applied by amplifier 480c, I.sub.B' is the
current applied by amplifier 480d, I.sub.C is the current applied
by amplifier 480e, and I.sub.C' is the current applied by amplifier
480f.
[0040] As discussed above with respect to FIG. 3, a portion of a
split coil assembly that is arranged to provide a non-zero net
force along an x-axis generally has substantially the same current
applied in the same direction in both halves of a split coil. When
the split coil moves relative to a magnet along the x-axis, the
portion of the split coil that was arranged to provide a force
along the x-axis may be positioned such that by changing the
current applied to both halves of the portion of the split coil,
i.e., by applying current to the bottom half in an opposite
direction from the current applied to the top half, the portion
then provides a substantially non-zero net force along a z-axis. In
other words, when the relative motion between a split coil and a
magnet is relatively large, portions of the split coil may
effectively flip between being used to apply a non-zero net force
along an x-axis and being used to apply a substantially non-zero
net force along a z-axis. By varying the direction in which current
is applied to a top coil and a bottom coil of a portion of a split
coil, the direction of the net force applied by the portion may be
varied.
[0041] In one embodiment, when the relative motion between a coil
assembly and a magnet is relatively small along an x-axis, the use
of a split coil in the portion of the coil assembly which is
arranged to provide force along the x-axis may not be necessary, as
that portion of the coil assembly is unlikely to be positioned to
provide force along a z-axis. Hence, since the top half and the
bottom half of that portion of the coil assembly will generally
have current of substantially the same magnitude applied in the
same direction, that portion of the coil assembly may be replaced
by a conventional, or non-split, coil. FIG. 5 is a diagrammatic
representation of a motor which includes a coil assembly that has
both a split coil component and a non-split coil component in
accordance with an embodiment of the present invention. A motor 500
includes magnets 502, as well as a split coil 504 and a non-split
coil 507. Split coil 504 includes a top half 508 and a bottom half
512 which are positioned to provide a substantially non-zero net
force along a z-axis 306c when current applied to top half 508 is
of approximately the same magnitude as current applied to bottom
half 512, but applied in an opposite direction along a y-axis 506b.
Non-split coil 507 is positioned to apply a non-zero net force
along an x-axis 506a.
[0042] When the relative motion of coils 504, 507 between magnet
502a and magnet 502b is relatively small with respect to x-axis
506a, non-split coil 507 will effectively rarely be positioned to
provide a substantially non-zero net force along z-axis 506c. That
is, in most instances, non-split coil 507 will be positioned only
to provide a non-zero net force along x-axis 506a. Hence, the use
of non-split coil 507 is typically appropriate, as non-split coil
507, which has a single applied current, is suitable for use in
providing a non-zero net force along x-axis 506a.
[0043] With reference to FIG. 6, a photolithography apparatus which
may include an actuator such as a linear motor with a split coil
design will be described in accordance with an embodiment of the
present invention. A photolithography apparatus (exposure
apparatus) 40 includes a wafer positioning stage 52 that may be
driven by linear motors or by a planar motor (not shown), as well
as a wafer table 51 that is magnetically coupled to wafer
positioning stage 52 by utilizing substantially any suitable
actuator such as an EI-core actuator. The motor or motors which
drive wafer positioning stage 52 generally use electromagnetic
force generated by magnets and corresponding armature coils
arranged in two dimensions. A wafer 64 is held in place on a wafer
holder or chuck 74 which is coupled either substantially directly
to or indirectly, e.g., through a quasi-kinematic mount, to wafer
table 51. Wafer positioning stage 52 and wafer table 51 are
arranged to move in multiple degrees of freedom, e.g., between tone
and six degrees of freedom, under the control of a control unit 60
and a system controller 62. The movement of wafer positioning stage
52 allows wafer 64 to be positioned at a desired position and
orientation relative to a projection optical system 46.
[0044] Wafer table 51 may be levitated in a z-direction 10b by any
number of voice coil motors (not shown), e.g., three voice coil
motors. In the described embodiment, at least three electromagnetic
actuators, e.g., EI-core actuators, (not shown) couple and move
wafer table 51 along a y-axis 10a, an x-axis 10c, and about a
z-axis 10b. The motor array of wafer positioning stage 52 is
typically supported by a base 70. Base 70 is supported to a ground
via isolators 54. Reaction forces generated by motion of wafer
positioning stage 52 may be mechanically released to a ground
surface through a frame 66. Reaction forces may be released to the
floor or ground through a VCM or voice coil motor (not shown) that
is substantially in contact with reaction frame 66. One suitable
frame 66 is described in JP Hei 8-166475 and U.S. Pat. No.
5,528,118, which are each herein incorporated by reference in their
entireties.
[0045] An illumination system 42 is supported by a frame 72. Frame
72 is supported to the ground directly or via isolators 54.
Illumination system 42 includes an illumination source, and is
arranged to project a radiant energy, e.g., light, through a mask
pattern on a reticle 68 that is supported by and scanned using a
reticle stage 44 which includes a coarse stage and a fine stage.
The radiant energy is focused through projection optical system 46,
which is supported on a projection optics frame 50 and may be
supported on the ground through isolators 54. Suitable isolators 54
include those described in JP Hei 8-330224 and U.S. Pat. No.
5,874,820, which are each incorporated herein by reference in their
entireties.
[0046] A first interferometer 56 is supported on projection optics
frame 50, and functions to detect the position of table 51 onto
which a mirrored surface has been polished. Interferometer 56
outputs information on the position of wafer table 51 to system
controller 62. In one embodiment, wafer table 51 has a force damper
which reduces vibrations associated with wafer table 51 such that
interferometer 56 may more accurately detect the position of wafer
chuck 74. A second interferometer 58 is supported on optics frame
46, and detects the position of reticle stage 44 which supports
reticle 68. Interferometer 58 also outputs position information to
system controller 62.
[0047] It should be appreciated that there are a number of
different types of photolithographic apparatuses or devices. For
example, photolithography apparatus 40, or an exposure apparatus,
may be used as a scanning type photolithography system which
exposes the pattern from reticle 68 onto wafer 64 with reticle 68
and wafer 64 moving substantially synchronously. In a scanning type
lithographic device, reticle 68 is moved perpendicularly with
respect to an optical axis of a lens assembly (projection optical
system 46) or illumination system 42 by reticle stage 44. Wafer 64
is moved perpendicularly to the optical axis of projection optical
system 46 by a wafer positioning stage 52. Scanning of reticle 68
and wafer 64 generally occurs while reticle 68 and wafer 64 are
moving substantially synchronously.
[0048] Alternatively, photolithography apparatus or exposure
apparatus 40 may be a step-and-repeat type photolithography system
that exposes wafer 64 while reticle 68 and wafer 64 are stationary,
i.e., at a substantially constant velocity of approximately zero
meters per second. In one step and repeat process, wafer 64 is in a
substantially constant position relative to reticle 68 and
projection optical system 46 during the exposure of an individual
field. Subsequently, between consecutive exposure steps, wafer 64
is consecutively moved by wafer positioning stage 52
perpendicularly to the optical axis of projection optical system 46
and reticle 68 so that the next field of semiconductor wafer 64 is
brought into position relative to illumination system 42, reticle
68, and projection optical system 46 for exposure. Following this
process, the images on reticle 68 may be sequentially exposed onto
the next field of wafer 64.
[0049] It should be understood that the use of photolithography
apparatus or exposure apparatus 40, as described above, is not
limited to being used in a photolithography system for
semiconductor manufacturing. For example, photolithography
apparatus 40 may be used as a part of a liquid crystal display
(LCD) photolithography system that exposes an LCD device pattern
onto a rectangular glass plate or a photolithography system for
manufacturing a thin film magnetic head.
[0050] The illumination source of illumination system 42 may be
g-line (436 nanometers (nm)), i-line (365 nm), a KrF excimer laser
(248 nm), an ArF excimer laser (193 nm), and an F.sub.2-type laser
(157 nm). Alternatively, illumination system 42 may also use
charged particle beams such as x-ray and electron beams. For
instance, in the case where an electron beam is used, thermionic
emission type lanthanum hexaboride (LaB.sub.6) or tantalum (Ta) may
be used as an electron gun. Furthermore, in the case where an
electron beam is used, the structure may be such that either a mask
is used or a pattern may be directly formed on a substrate without
the use of a mask.
[0051] With respect to projection optical system 46, when far
ultra-violet rays such as an excimer laser is used, glass materials
such as quartz and fluorite that transmit far ultra-violet rays is
preferably used. When either an F.sub.2-type laser or an x-ray is
used, projection optical system 46 may be either catadioptric or
refractive (a reticle may be of a corresponding reflective type),
and when an electron beam is used, electron optics may comprise
electron lenses and deflectors. As will be appreciated by those
skilled in the art, the optical path for the electron beams is
generally in a vacuum.
[0052] In addition, with an exposure device that employs vacuum
ultra-violet (VUV) radiation of a wavelength that is approximately
200 nm or lower, use of a catadioptric type optical system may be
considered. Examples of a catadioptric type of optical system
include, but are not limited to, those described in Japan Patent
Application Disclosure No. 8-171054 published in the Official
gazette for Laid-Open Patent Applications and its counterpart U.S.
Pat. No. 5,668,672, as well as in Japan Patent Application
Disclosure No. 10-20195 and its counterpart U.S. Pat. No.
5,835,275, which are all incorporated herein by reference in their
entireties. In these examples, the reflecting optical device may be
a catadioptric optical system incorporating a beam splitter and a
concave mirror. Japan Patent Application Disclosure (Hei) No.
8-334695 published in the Official gazette for Laid-Open Patent
Applications and its counterpart U.S. Pat. No. 5,689,377, as well
as Japan Patent Application Disclosure No. 10-3039 and its
counterpart U.S. Pat. No. 5,892,117, which are all incorporated
herein by reference in their entireties. These examples describe a
reflecting-refracting type of optical system that incorporates a
concave mirror, but without a beam splitter, and may also be
suitable for use with the present invention.
[0053] Further, in photolithography systems, when linear motors
(see U.S. Pat. Nos. 5,623,853 or 5,528,118, which are each
incorporated herein by reference in their entireties) are used in a
wafer stage or a reticle stage, the linear motors may be either an
air levitation type that employs air bearings or a magnetic
levitation type that uses Lorentz forces or reactance forces.
Additionally, the stage may also move along a guide, or may be a
guideless type stage which uses no guide.
[0054] Alternatively, a wafer stage or a reticle stage may be
driven by a planar motor which drives a stage through the use of
electromagnetic forces generated by a magnet unit that has magnets
arranged in two dimensions and an armature coil unit that has coil
in facing positions in two dimensions. With this type of drive
system, one of the magnet unit or the armature coil unit is
connected to the stage, while the other is mounted on the moving
plane side of the stage.
[0055] Movement of the stages as described above generates reaction
forces which may affect performance of an overall photolithography
system. Reaction forces generated by the wafer (substrate) stage
motion may be mechanically released to the floor or ground by use
of a frame member as described above, as well as in U.S. Pat. No.
5,528,118 and published Japanese Patent Application Disclosure No.
8-166475. Additionally, reaction forces generated by the reticle
(mask) stage motion may be mechanically released to the floor
(ground) by use of a frame member as described in U.S. Pat. No.
5,874,820 and published Japanese Patent Application Disclosure No.
8-330224, which are each incorporated herein by reference in their
entireties.
[0056] Isolaters such as isolators 54 may generally be associated
with an active vibration isolation system (AVIS). An AVIS generally
controls vibrations associated with forces, i.e., vibrational
forces, which are experienced by a stage assembly or, more
generally, by a photolithography machine such as photolithography
apparatus 40 which includes a stage assembly.
[0057] A photolithography system according to the above-described
embodiments, e.g., a photolithography apparatus which may include a
split coil actuator, may be built by assembling various subsystems
in such a manner that prescribed mechanical accuracy, electrical
accuracy, and optical accuracy are maintained. In order to maintain
the various accuracies, prior to and following assembly,
substantially every optical system may be adjusted to achieve its
optical accuracy. Similarly, substantially every mechanical system
and substantially every electrical system may be adjusted to
achieve their respective desired mechanical and electrical
accuracies. The process of assembling each subsystem into a
photolithography system includes,-but is not limited to, developing
mechanical interfaces, electrical circuit wiring connections, and
air pressure plumbing connections between each subsystem. There is
also a process where each subsystem is assembled prior to
assembling a photolithography system from the various subsystems.
Once a photolithography system is assembled using the various
subsystems, an overall adjustment is generally performed to ensure
that substantially every desired accuracy is maintained within the
overall photolithography system. Additionally, it may be desirable
to manufacture an exposure system in a clean room where the
temperature and humidity are controlled.
[0058] Further, semiconductor devices may be fabricated using
systems described above, as will be discussed with reference to
FIG. 7. The process begins at step 1301 in which the function and
performance characteristics of a semiconductor device are designed
or otherwise determined. Next, in step 1302, a reticle (mask) in
which has a pattern is designed based upon the design of the
semiconductor device. It should be appreciated that in a parallel
step 1303, a wafer is made from a silicon material. The mask
pattern designed in step 1302 is exposed onto the wafer fabricated
in step 1303 in step 1304 by a photolithography system. One process
of exposing a mask pattern onto a wafer will be described below
with respect to FIG. 8. In step 1305, the semiconductor device is
assembled. The assembly of the semiconductor device generally
includes, but is not limited to, wafer dicing processes, bonding
processes, and packaging processes. Finally, the completed device
is inspected in step 1306.
[0059] FIG. 8 is a process flow diagram which illustrates the steps
associated with wafer processing in the case of fabricating
semiconductor devices in accordance with an embodiment of the
present invention. In step 1311, the surface of a wafer is
oxidized. Then, in step 1312 which is a chemical vapor deposition
(CVD) step, an insulation film may be formed on the wafer surface.
Once the insulation film is formed, in step 313, electrodes are
formed on the wafer by vapor deposition. Then, ions may be
implanted in the wafer using substantially any suitable method in
step 1314. As will be appreciated by those skilled in the art,
steps 1311-1314 are generally considered to be preprocessing steps
for wafers during wafer processing. Further, it should be
understood that selections made in each step, e.g., the
concentration of various chemicals to use in forming an insulation
film in step 1312, may be made based upon processing
requirements.
[0060] At each stage of wafer processing, when preprocessing steps
have been completed, post-processing steps may be implemented.
During post-processing, initially, in step 1315, photoresist is
applied to a wafer. Then, in step 1316, an exposure device may be
used to transfer the circuit pattern of a reticle to a wafer.
Transferring the circuit pattern of the reticle of the wafer
generally includes scanning a reticle scanning stage which may, in
one embodiment, include a force damper to dampen vibrations.
[0061] After the circuit pattern on a reticle is transferred to a
wafer, the exposed wafer is developed in step 1317. Once the
exposed wafer is developed, parts other than residual photoresist,
e.g., the exposed material surface, may be removed by etching.
Finally, in step 1319, any unnecessary photoresist that remains
after etching may be removed. As will be appreciated by those
skilled in the art, multiple circuit patterns may be formed through
the repetition of the preprocessing and post-processing steps.
[0062] Although only a few embodiments of the present invention
have been described, it should be understood that the present
invention may be embodied in many other specific forms without
departing from the spirit or the scope of the present invention. By
way of example, while an actuator with a split coil which has
halves that may be substantially independently controlled has
generally been described as being a linear motor, a split coil may
be implemented for use in substantially any suitable actuator.
Substantially any actuator which typically produces force in an
x-direction and is to be configured to produce a non-zero net force
in a z-direction may use a split coil which has halves that may be
independently controlled. An actuator, e.g., a voice coil motor,
which requires a relatively large force in a z-direction, but has a
shape that is small in a z-direction, may also benefit from the use
of a split coil.
[0063] An actuator which includes a split coil has been described
as being suitable for use in a photolithography apparatus. Within a
photolithography apparatus, an actuator with a split coil may be
used to position a wafer stage, a reticle stage, or a wafer table,
for example. An actuator which includes a split coil may also be
suitable for use in substantially any other apparatus in which
non-zero net forces in an x-direction and a z-direction are
desired, but space constraints are such that the use of more than a
single actuator to generate forces in two directions is
impractical. In addition, an actuator which includes a split coil
may be used with substantially any apparatus which needs a force in
a z-direction, but requires that the dimension of the actuator in
the z-direction is small.
[0064] The number of split coils in a coil assembly may vary
depending upon the overall size of an actuator which uses the coil
assembly without departing from the spirit or the scope of the
present invention. Therefore, the present examples are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein, but may be
modified within the scope of the appended claims.
* * * * *