U.S. patent application number 12/050675 was filed with the patent office on 2008-07-10 for high efficiency voice coil motor.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Michael B. Binnard, Jean-Marc Gery, Andrew J. Hazelton.
Application Number | 20080165451 12/050675 |
Document ID | / |
Family ID | 36260993 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080165451 |
Kind Code |
A1 |
Binnard; Michael B. ; et
al. |
July 10, 2008 |
High Efficiency Voice Coil Motor
Abstract
Methods and apparatus for increasing the efficiency of a voice
coil motor (VCM) are disclosed. According to one aspect of the
present invention, a cylindrical and radially symmetric VCM
includes a plurality of sets of magnets, and a single coil. The
plurality of sets of the magnets are each arranged in an array
configuration, and cooperate to form a magnetic field. The coil
receives current and has a plurality of windings. A first space is
defined within the coil, and the plurality of sets of the magnets
are arranged such that a first set of the magnets is positioned
within the first space and a second set of the magnets is
positioned external to the coil.
Inventors: |
Binnard; Michael B.;
(Belmont, CA) ; Gery; Jean-Marc; (Los Angeles,
CA) ; Hazelton; Andrew J.; (Yokohama, JP) |
Correspondence
Address: |
AKA CHAN LLP
900 LAFAYETTE STREET, SUITE 710
SANTA CLARA
CA
95050
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
|
Family ID: |
36260993 |
Appl. No.: |
12/050675 |
Filed: |
March 18, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10908178 |
Apr 29, 2005 |
7368838 |
|
|
12050675 |
|
|
|
|
60624243 |
Nov 2, 2004 |
|
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|
Current U.S.
Class: |
360/264.7 |
Current CPC
Class: |
H02K 41/0356 20130101;
H02K 2201/18 20130101 |
Class at
Publication: |
360/264.7 |
International
Class: |
G11B 5/55 20060101
G11B005/55 |
Claims
1. A voice coil motor (VCM) comprising a coil arrangement, the coil
arrangement including at least one coil having a first space and
being wound around a first direction that is getting through the
first space; a first set of magnets arranged in the first space,
the first set of magnets including at least one of magnets having a
component of a first magnetic field direction that is a radial
direction with respect to the first direction; and a second set of
magnets arranged external to the coil, the second set of magnets
including at least one of magnets having the component of the first
magnetic field direction.
2. The VCM of claim 1 wherein the first magnetic field direction is
substantially perpendicular to the first direction.
3. The VCM of claim 1 wherein the first set of magnets and the
second set of magnets have an overall donut shape, and the first
set of magnets and the second set of magnets are arranged coaxially
with respect to the first direction.
4. The VCM of claim 1 wherein at least one selected from the group
including the first set of magnets and the second set of magnets
includes at least one of magnets having a second magnetic field
direction that is parallel to the first direction.
5. The VCM of claim 4 wherein the magnets having the second
magnetic field direction have a cross-section that is
wedge-shaped.
6. The VCM of claim 1 wherein at least one selected from the group
including the first set of magnets and the second set of magnets
includes at least one of magnets having a third magnetic field
direction that crosses the first magnetic field directions and the
second magnetic field direction.
7. The VCM of claim 6 wherein the magnet having the third magnetic
field direction has a cross-section that is wedge-shaped.
8. The VCM of claim 6 wherein the magnet having the third magnetic
field direction has a cross-section that is trapezoidal in
shape.
9. The VCM of claim 1 wherein the coil arrangement includes a first
coil and a second coil, and directions of current provided to the
first coil and the second coil are opposite directions with respect
to each other.
10. The VCM of claim 1 wherein the first set of magnets includes a
first magnet, a second magnet, and a third magnet, the first magnet
being positioned between the second magnet and the third magnet
along a first direction and having the first magnetic field
direction, the second magnet having a second magnetic field
direction that is parallel to the first direction and towards the
first magnet, the third magnet having a third magnetic field
direction that is opposite to the second magnetic field direction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a divisional of U.S. patent
application Ser. No. 10/908,178, filed Apr. 29, 2005, which claims
the benefit of U.S. provisional patent application 60/624,243,
filed Nov. 2, 2004, which are incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates generally to actuators. More
particularly, the present invention relates to a radially symmetric
voice coil motor which utilizes a magnet array which includes
wedge-shaped cylindrical magnets.
[0004] 2. Description of the Related Art
[0005] For precision instruments such as photolithography machines
which are used in semiconductor processing, factors which affect
the performance, e.g., accuracy, of the precision instrument
generally must be dealt with and, insofar as possible, eliminated.
When the performance of a precision instrument such a wafer
scanning stage or a reticle scanning stage is adversely affected,
products formed using the precision instrument may be improperly
formed and, hence, function improperly.
[0006] Voice coil motors (VCMs) are often used in lithography
machines to enable accurate movement of a wafer scanning stage
along one axis. A VCM utilizes a magnetic coil that is placed in a
magnetic field. When current is applied to the coil, a force is
generated between the coil and the magnetic field predominantly in
a single degree of freedom. Small VCMs are capable of generating
force in one direction with a relatively high efficiency.
[0007] When a VCM is to be used in a system that is sensitive to
heat such as a lithography system, excessive heat may cause the
accuracy with which a lithography process may be performed to be
compromised. In addition, excessive heat may cause any insulating
material in coils of a VCM, as well as the copper from which coils
are often formed, to melt. The amount of force that may be
generated by a VCM is also limited by the amount of current which
may be supplied by an amplifier, or by electronics which are used
to control the VCM.
[0008] Therefore, what is needed is a method and an apparatus for
enabling the force generated by a VCM to be increased without
significantly increasing the current usage of the VCM or the heat
output of the VCM.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention relates to a voice coil motor (VCM)
which uses a magnetic circuit which includes magnets with
wedge-shaped cross-sections. According to one aspect of the present
invention, a cylindrical and radially symmetric VCM includes a
plurality of sets of magnets, and a coil. The plurality of sets of
the magnets are each arranged in an array configuration, and
cooperate to form a magnetic field. The coil receives current and
has a plurality of windings. A first space is defined within the
coil, and the plurality of sets of the magnets are arranged such
that a first set of the magnets is positioned within the first
space and a second set of the magnets is positioned external to the
coil. The coil is the only coil associated with the VCM which moves
within the magnetic field between the two sets of magnets.
[0010] In one embodiment, the first set of the magnets includes at
least a first magnet that is wedge-shaped. In another embodiment,
the VCM also includes a magnetic material that physically couples
the first set and the second set to enable a flux path created
within the VCM to pass between the first set and the second
set.
[0011] The use of Halbach arrays of magnets in a VCM generally
enables the strength of a magnetic field within the VCM to be
increased. By configuring the magnets in Halbach arrays such that
at least some of the magnets have a non-rectangular cross-section,
e.g., a substantially trapezoidal or triangular cross-section, the
strength of the magnetic field in a VCM which includes the Halbach
arrays may be further increased, thereby enabling the force
generated by the VCM to be increased without significantly
increasing the heat produced by the VCM. In some instances, the
configuration of the magnets with a non-rectangular cross-section,
i.e., the wedge-shaped magnets, is such that a single coil rather
than a pair of coils may be used within the VCM.
[0012] According to another aspect of the present invention, a VCM
includes a first magnet arrangement, a second magnet arrangement,
and a coil arrangement. The first magnet arrangement includes at
least a first magnet having a cross-section that is approximately
rectangular and a second magnet having a cross-section that is
non-rectangular relative to a plane. The first magnet is arranged
substantially at a center of the first magnet arrangement and the
first magnet and the second magnet are arranged to be in contact.
The second magnet arrangement includes at least a third magnet
having a cross-section that is approximately rectangular and a
fourth magnet having a cross-section that is non-rectangular
relative to the plane, where the third magnet is arranged
substantially at a center of the second magnet arrangement and the
third magnet and the fourth magnet are arranged to be in contact.
The coil arrangement is at least partially positioned between the
first magnet arrangement and the second magnetic arrangement, and
moves relative to the first magnet arrangement and the second
magnet arrangement within a magnetic field associated with the
first magnet arrangement and the second magnet arrangement.
[0013] In one embodiment, the VCM also includes at least one plate
from a magnetic material that is in physical contact with both the
first magnet arrangement and the second magnet arrangement. In
another embodiment, the coil arrangement includes a single-phase
coil.
[0014] According to yet another aspect of the present invention, a
VCM includes a first magnet arrangement which includes a first
plurality of magnets which each have a cross-section that is
non-rectangular. The VCM also includes a second magnet arrangement
that includes a second plurality of magnets each having a
cross-section that is non-rectangular. The first magnet arrangement
and the second magnet arrangement are arranged to cooperate to
generate a magnetic field. A coil arrangement of the VCM is at
least partially positioned between the first magnet arrangement and
the second magnetic arrangement and is arranged to receive current
to generate a force between the coil arrangement and the first
magnet arrangement and the second magnet arrangement within the
magnetic field.
[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 cylindrical
Halbach magnet arrays in accordance with an embodiment of the
present invention.
[0018] FIG. 2 is a diagrammatic cross-sectional representation of a
radially symmetric cylindrical VCM which utilizes a substantially
cylindrical wedge Halbach array in accordance with an embodiment of
the present invention.
[0019] FIG. 3 is a diagrammatic cross-sectional representation of a
radially symmetric cylindrical VCM which utilizes a substantially
cylindrical wedge Halbach array in accordance with another
embodiment of the present invention.
[0020] FIG. 4 is a diagrammatic cross-sectional block diagram
representation of a portion of a single coil and a portion of two
wedge Halbach magnet arrays in accordance with an embodiment of the
present invention.
[0021] FIG. 5a is a block diagram representation of a magnet array,
e.g., magnet array 416 of FIG. 4, in accordance with an embodiment
of the present invention.
[0022] FIG. 5b is a diagrammatic representation of a portion of a
wedge-shaped magnet, e.g., wedge magnet 414b of FIG. 4, in
accordance with an embodiment of the present invention.
[0023] FIG. 6 is a representation of magnetic field equipotential
lines associated with a coil and wedge Halbach magnet arrays, i.e.,
coil 418 and wedge Halbach magnet arrays 406, 416 of FIG. 4, in
accordance with an embodiment of the present invention.
[0024] FIG. 7 is a cross-sectional block diagram representation of
approximately half of a VCM which uses wedge Halbach arrays and a
single coil in accordance with an embodiment of the present
invention.
[0025] FIG. 8 is a cross-sectional block diagram representation of
a VCM which uses wedge Halbach arrays and a single coil in
accordance with an embodiment of the present invention.
[0026] FIG. 9a is a diagrammatic representation of an overall
wedge-shaped cylindrical magnet, e.g., magnet 702b of FIG. 7, in
accordance with an embodiment of the present invention.
[0027] FIG. 9b is a diagrammatic representation of an overall
wedge-shaped cylindrical magnet, e.g., magnet 702e of FIG. 7, in
accordance with an embodiment of the present invention.
[0028] FIG. 10 is a diagrammatic representation of a
photolithography apparatus in accordance with an embodiment of the
present invention.
[0029] FIG. 11 is a process flow diagram which illustrates the
steps associated with fabricating a semiconductor device in
accordance with an embodiment of the present invention.
[0030] FIG. 12 is a process flow diagram which illustrates the
steps associated with processing a wafer, i.e., step 1304 of FIG.
11, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Typically, when a higher force is to be provided by a voice
coil motor (VCM), the current input into the VCM is increased, and,
consequently, the heat generated by the VCM is increased.
Increasing current requirements is often impractical, and increased
heat associated with the operation of a VCM may adversely affect
heat-sensitive systems, e.g., lithography equipment.
[0032] By increasing the magnetic field within a VCM, i.e., by
increasing the strength or the magnitude of the magnetic field
within a VCM, a higher force may be generated using the VCM,
substantially without increasing the amount of heat generated by
the VCM and increasing the amount of current used by the VCM. The
magnetic field within a VCM may be increased by utilizing a magnet
array in the VCM and, further, by varying the shape of magnets in
the magnet array. In one embodiment, the magnet array is a
substantially cylindrical wedge Halbach array.
[0033] A substantially cylindrical wedge Halbach array is an array
of magnets which includes at least one wedge-shaped magnet. A
wedge-shaped magnet is generally a magnet which has either a
substantially triangular cross-section with respect to at least one
plane or a substantially trapezoidal cross-section with respect to
at least one plane. When a wedge-shaped magnet has a substantially
trapezoidal cross-section with respect to a plane, while two
opposite sides of the cross-section are substantially parallel to
each other within the plane, the other two sides are not
substantially parallel to each other within the plane.
[0034] A VCM which includes a substantially cylindrical wedge
Halbach array may have a variety of different configurations. In
general, the wedge-shaped magnets are arranged to form an overall
cylindrical Halbach array. As shown in FIG. 1, an outer Halbach
magnet array 360 typically has an overall, hollow cylindrical shape
or an overall donut shape. However, the individual magnets of
magnet array 360 may be wedge-shaped donuts. Similarly, an inner
Halbach magnet array 364 also has an overall hollow, cylindrical
shape, though the individual magnets of magnet array 364 may be
wedge-shaped donuts.
[0035] The orientation of wedge-shaped magnets and other magnets
within the substantially cylindrical wedge Halbach array may be
widely varied. FIG. 2 is a diagrammatic cross-sectional
representation of a radially symmetric cylindrical VCM which
utilizes a substantially cylindrical wedge Halbach array in
accordance with an embodiment of the present invention. A VCM 370,
as shown in cross-section, includes non-magnetic hollow cylinders
374a, 374b which are substantially centered about a central axis
378. Alternatively, either or both hollow cylinders 374a, 374b may
be formed from a magnetic material.
[0036] Magnet arrays 382, 392 are also effectively hollow cylinders
that are positioned within VCM 370 about central axis 378 such that
coils 398a, 398b, having center lines that are substantially
coincident with central axis 378, are positioned between magnet
arrays 382, 392. Coils 398a, 398b are such that the turns or
windings of coils 398a, 398b effectively define a ring or a donut
shape for coils 398a, 398b. Hollow cylinder 374b and magnet array
392 are positioned within the inner area of the ring or the donut
shape defined by coils 398a, 398b. As will be understood by those
skilled in the art, coils 398a, 398b are generally substantially
encased in cooling cans which are filled with coolant. However, for
ease of illustration, cooling cans have not been shown.
[0037] As shown, coils 398a, 398b are positioned between magnet
arrays 382, 392. Coils 398a, 398b move relative to magnet arrays
382, 392 and, hence, within a magnetic field associated with magnet
arrays 382, 392 when current is applied. Each magnet array 382, 392
includes a plurality of magnets, i.e., permanent magnets. By way of
example, magnet array 382 includes magnets 382a-382c which each
have an overall donut shape but each have a substantially
non-rectangular, e.g., triangular, cross-section in at least one
plane. That is, magnets 382a-c are each substantially wedge-shaped
donuts. By shaping magnets 382a-c as wedges, or with wedge-shaped
cross sections, the magnetic field associated with VCM 370 may be
enhanced. Magnets 392a-c are also each substantially wedge-shaped
donuts.
[0038] With reference to FIG. 3, a second radially symmetric
cylindrical VCM which utilizes a substantially cylindrical wedge
Halbach array will be described in accordance with another
embodiment of the present invention. A VCM 300, which is shown in
cross-section, includes non-magnetic cylinders 304a, 304b which are
substantially centered about a central axis 308. It should be
appreciated that cylinders 304a, 304b are each effectively a hollow
cylinder with a center that is coincident with central axis
308.
[0039] Magnet arrays 312, 322 are also arranged as hollow
cylinders, and are positioned within VCM 300 such that coils 318a,
318b, which each effectively form a hollow, cylindrical shape with
center lines that are substantially coincident with central axis
308, are positioned between magnet arrays 312, 322. Magnet arrays
312, 322 are also centered about central axis 308. Coils 318a, 318b
are such that the turns or windings of coils 318a, 318b effectively
define a ring or a donut shape for coils 318a, 318b.
[0040] Coils 318a, 318b are positioned between magnet arrays 312,
322 and, hence, within a magnetic field associated with magnet
arrays 312, 322 when current is applied. Each magnet array 312, 322
includes a plurality of magnets. By way of example, magnet array
312 includes magnets 312a-312e which each have an overall donut
shape. Magnets 312a and 312e, which make up the ends of magnet
array 312, are substantially block-shaped donuts. That is, magnets
312a, 312e have substantially rectangular, as for example square,
cross-sections in at least one plane. Magnets 312b-d are each
substantially wedge-shaped donuts, i.e., magnets 312b-d each have a
substantially triangular or trapezoidal cross-section in one plane.
By shaping magnets 312b-d as wedges, or with wedge-shaped cross
sections, the magnetic field associated with VCM 300 may be
enhanced. As shown, magnets 322b-d are also each substantially
wedge-shaped donuts, while magnets 322a, 322e are substantially
block-shaped donuts.
[0041] While the use of wedge-shaped magnets in a Halbach array
within a VCM improves the efficiency of the VCM, i.e., by
increasing the strength of the magnetic field within the VCM, the
efficiency of a VCM may further be increased by essentially
concentrating a magnetic field near a coil of a VCM. In one
embodiment, by altering the orientation of magnets associated with
a wedge Halbach array of a VCM such that the use of only a single
coil in the VCM is possible, the efficiency of the VCM is further
enhanced.
[0042] By orienting the magnets in a Halbach array of a VCM such
that a magnet with radial magnetization is effectively in the
center of the Halbach array, while magnets with longitudinal
magnetization are at the ends of the Halbach array, a single coil
may be used within the VCM. It should be appreciated that for a
Halbach array with a given total magnet height, the height of a
single coil is generally greater than or equal to the combined
height of two coils used in VCMs, e.g., VCM 300 of FIG. 3, with
magnet arrays of the given total magnet height. The use of a single
coil enables the magnetic field within a VCM to be substantially
concentrated through the coil, thereby further increasing the
efficiency of the VCM.
[0043] FIG. 4 is a diagrammatic cross-sectional block diagram
representation of a portion of a single coil and a portion of two
wedge Halbach magnet arrays in accordance with an embodiment of the
present invention. Within a VCM, a portion of a coil 418 is
positioned such that a first wedge Halbach magnet array 406 is
located in a space defined by an inner edge 424 of coil 418 and a
second wedge Halbach magnet array 416 is positioned outside an
outer edge 426 of coil 418.
[0044] Both magnet arrays 406, 416 include wedge magnets, or
magnets which have a cross-section that is either approximately
triangular or trapezoidal. Magnet array 406 includes wedge magnets
402a, 402b, 402d, 402e, whereas magnet array 416 includes wedge
magnets 414a, 414b, 414d, 414e. Magnets 402c, 414c, which are
arranged at the center of magnet arrays 406, 416, respectively, are
substantially block-shaped, or have approximately rectangular or
square cross-sections. Specifically, magnets 402c, 414c are
donut-shaped blocks. The orientation of magnets 402a-e within
magnet array 406, and the orientation of magnets 414a-e within
magnet array 416 are such that a magnetic field is centered
approximately along a horizontal centerline 438 of magnet arrays
406, 416. Magnetic field equipotential lines associated with an
arrangement of magnet arrays 406, 416 and coil 418 as shown will be
described below with respect to FIG. 6.
[0045] With reference to FIGS. 5a and 5b, the positioning and
shapes of magnets associated with magnet array 406 will be
described. FIG. 5a is a block diagram representation of magnet
array 416 of FIG. 4 in accordance with an embodiment of the present
invention. As previously described, magnet array 416 includes
magnets 414a-e which may each, in one embodiment, be permanent
magnets. Magnet 414c, which has a substantially rectangular
cross-section, generally has a magnetic field direction that is
substantially parallel to a y-axis 502, while magnets 414a, 414e,
which are each shaped as a wedge, have magnetic field directions
that are parallel to a z-axis 504. Magnets 414b, 414d, which are
each also shaped as a wedge and have a non-rectangular, e.g.,
substantially trapezoidal, cross-section generally have associated
magnetic field directions that are neither horizontal, e.g.,
parallel to y-axis 502, nor vertical, e.g., parallel to z-axis
504.
[0046] As shown, magnets 414a, 414b, 414d, 414e each have a
non-rectangular cross-section, e.g., a substantially trapezoidal
cross-section, at least in a plane that is defined by y-axis 502
and z-axis 504. Magnet 414c has a rectangular cross-section in the
plane that is defined by y-axis 502 and z-axis 504.
[0047] The relative sizes of each magnet 414a-e within magnet array
416 may vary widely. It should be appreciated that the size and
shape of each magnet 414a-e may also vary. By way of example, as
shown in FIG. 5b, a portion 414b' of wedge 414b is shaped such that
in a plane defined by y-axis 502 and z-axis 504, a cross-section of
a wedge portion 414b' is approximately trapezoidal, whereas a
cross-section of wedge portion 414b' in a plane defined by z-axis
504 and an x-axis 506 is substantially rectangular. Wedge portion
414b' has at least some edges, as for example edges 540, 542, 544,
which have some curvature as wedge portion 414b' is a part of a
wedge 414b which is effectively a wedge-shaped donut.
[0048] FIG. 6 is a representation of magnetic field equipotential
lines associated with a coil and wedge Halbach magnet arrays, i.e.,
coil 418 and wedge Halbach magnet arrays 406, 416 of FIG. 4, in
accordance with an embodiment of the present invention. As shown,
equipotential or flux lines 602 are generally concentrated in the
vicinity of coil 418. Equipotential lines may be arranged to pass
substantially through a center of coil 418, and through magnet
block 402c of magnet array 406 and through magnet block 414c of
magnet array 416. It should be appreciated that only representative
equipotential lines 602 have been shown for ease of
illustration.
[0049] In general, equipotential lines 602 pass through a medium
which allows flux to pass from magnet array 406 to magnet array
416, and vice versa. The medium that allows flux to pass between
magnet array 406 and magnet array 416 is preferably a relatively
high permeability magnetic medium, as for example magnetic steel.
FIG. 7 is a cross-sectional block diagram representation of
approximately half of a VCM which uses wedge Halbach arrays and a
single coil in accordance with an embodiment of the present
invention. A portion 700 of a VCM includes a coil 718, which is
effectively shielded by a cooling can 720. In general, cooling can
720 may be formed from substantially any suitable material.
Suitable materials include, but are not limited to, plastic, sheet
metal, and carbon fiber. A coolant is typically provided within
cooling can 720 such that coil 718, which has an overall hollow
cylindrical shape, is surrounded by the coolant.
[0050] Flux is carried between "inner" magnets 702a-e and "outer"
magnets 714a-e, e.g., from magnets 714a-e to magnets 702a-e,
through magnetic material 770. Magnetic material 770 may be a
material such as magnetic steel or iron. Typically, magnetic
material 770 is arranged as plates which are substantially located
on top and on the bottom of portion 700 to enable flux to "return"
flux from magnets 714a-e to magnets 702a-e.
[0051] Coil 718 is powered by electronics 750 which often include
components such as an amplifier and a current supply. In one
embodiment, coil 718 is a single-phase coil. When current flows
through coil 718, coil 718 moves relative to magnets 702a-e, 714a-e
within a magnetic field associated with magnets 702a-e, 714a-e.
[0052] Since flux is conducted through magnets 702a-e, 714a-e and
magnetic material 770 which form a magnetic circuit, sides 760 of
portion 700 may be formed from a non-magnetic material. The
non-magnetic material may generally be a material such as stainless
steel, aluminum, ceramic, or plastic. Alternatively, sides 760 may
be formed from a magnetic material.
[0053] As mentioned above, portion 700 is a part of a VCM. With
reference to FIG. 8, a more complete cross-sectional representation
of a VCM will be described in accordance with an embodiment of the
present invention. A radially symmetric cylindrical VCM 800, which
has a centerline 808 that is parallel to a z-axis 890, includes
portion 700 of FIG. 7 as well as a portion 810, which is
effectively a mirror image of portion 700. Coil 718 moves within
space 820 and provides a force in a direction along z-axis 890, and
is substantially positioned at a center of VCM 800. It should be
appreciated that in addition to allowing movement along z-axis 890
and providing force in a direction along z-axis 890, VCM 800 may
also permit a slight rotation about z-axis 890, a y-axis 894, or an
x-axis 892, as well as slight movement in directions along x-axis
892 and y-axis 894.
[0054] Magnets within VCM 800 are generally configured as
block-shaped or wedge-shaped donuts. By way of example,
wedge-shaped magnet 702b may generally have a donut shape as shown
in FIG. 9a, whereas wedge-shaped magnet 702e may generally have a
donut shape as shown in FIG. 9b. The donut shapes are of magnets
702b, 702e are such that the footprints of magnets 702b, 702e,
taken with respect to a plane defined by x-axis 892 and y-axis 894,
are substantially ring-like in shape.
[0055] A VCM which utilizes a substantially cylindrical wedge
Halbach array is suitable for a variety of different uses. By way
of example, since the heat generated by such a VCM is not
significant, and such a VCM provides a significant amount of force,
such a VCM is particularly suitable for use as a component within a
photolithography apparatus. Referring next to FIG. 10, a
photolithography apparatus which may use a VCM with a substantially
cylindrical wedge Halbach array 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 a planar motor or linear motors (not
shown), as well as a wafer table 51 that is coupled to wafer
positioning stage 52 by utilizing an actuator spring or other
means. The planar motor which drives wafer positioning stage 52
generally uses an electromagnetic force generated by magnets and
corresponding armature coils. A wafer 64 is held in place on a
wafer holder or chuck 74 which is coupled to wafer table 51. Wafer
positioning stage 52 is arranged to move in multiple degrees of
freedom, e.g., between one to 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.
[0056] Wafer table 51 may be levitated in a z-direction 10b by any
number of VCMs (not shown), e.g., three voice coil motors. The VCMs
may include substantially cylindrical wedge Halbach arrays.
Optionally, at least one electromagnetic actuator (not shown) may
couple and move wafer table 51 along an x-axis 10c or a y-axis 10a.
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 stage 52
may be mechanically released to a ground surface through a 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.
[0057] An illumination system 42 is supported by a frame 72. Frame
72 is supported to the ground 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 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.
[0058] A first interferometer 56 is supported on projection optics
frame 50, and functions to detect the position of wafer table 51.
Interferometer 56 outputs information on the position of wafer
table 51 to system controller 62. A second interferometer 58 is
supported on projection optics frame 50, and detects the position
of reticle stage 44 which supports a reticle 68. Interferometer 58
also outputs position information to system controller 62.
[0059] 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 stage 52. Scanning of reticle 68 and wafer 64
generally occurs while reticle 68 and wafer 64 are moving
substantially synchronously.
[0060] Alternatively, photolithography apparatus or exposure
apparatus 40 may be a step-and-repeat type photolithography system
that exposes reticle 68 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 for exposure. Following this process, the images
on reticle 68 may be sequentially exposed onto the fields of wafer
64 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.
[0061] 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. Photolithography apparatus
40 may also be used as a part of an immersion lithography
system.
[0062] The present invention may be utilized in an immersion type
exposure apparatus when suitable measures for a liquid are
incorporated. By way of example, PCT patent application WO
99/49504, which is incorporated herein by reference in its
entirety, discloses an exposure apparatus in which a liquid is
supplied to a space between a substrate such as a wafer and a
projection lens system in an exposure process.
[0063] Further, the present invention may be utilized in an
exposure apparatus which includes two or more substrates and/or
reticle stages. In such an apparatus, the additional stage may be
used in parallel or preparatory steps while the other stage may be
used for exposing. Exemplary multiple stage exposure apparatuses
are described, for example, in Japan patent Application Disclosure
No. 10-163099, as well as in Japan patent Application Disclosure
No. 10-214783 and its counterparts U.S. Pat. No. 6,341,007, U.S.
Pat. No. 6,400,441, U.S. Pat. No. 6,549,269, and U.S. Pat. No.
6,590,634. Each of these references is herein incorporated by
reference in its entirety. Other exemplary multiple stage exposure
apparatuses are described in Japan patent Application Disclosure
No. 2000-505958, as well as in U.S. Pat. No. 5,969,441 and U.S.
Pat. No. 6,208,407. Each of these references is herein incorporated
by reference in its entirety
[0064] The present invention may also be utilized in an exposure
apparatus that has a movable stage which retains a substrate, e.g.,
a wafer, for exposure, and a stage having various sensor or
measurement tools for measuring, as described in Japan patent
Disclosure No. 11-135400. As far as is permitted, the disclosure of
Japan patent Disclosure No. 11-135400 is incorporated herein by
reference in its entirety.
[0065] In addition, the present invention may be utilized in an
exposure apparatus that is operated in a vacuum environment. It
should be appreciated that suitable measures may need to be
incorporated to the present invention to accommodate a vacuum
environment for the air, or fluid, bearing arrangements. Such an
exposure apparatus may be, but is not limited to being, an EB type
exposure apparatus, or an EUVL type exposure apparatus.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] Further, in photolithography systems, when linear motors
(see U.S. Pat. No. 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.
[0070] 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.
[0071] 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.
[0072] Isolaters such as isolators 54 may generally be associated
with an active vibration isolation system (AVIS). An AVIS generally
controls vibrations associated with forces 112, 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.
[0073] A photolithography system according to the above-described
embodiments, e.g., a photolithography apparatus which may include
one or more dual force actuators, 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.
[0074] Further, semiconductor devices may be fabricated using
systems described above, as will be discussed with reference to
FIG. 11. 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. 12. 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.
[0075] FIG. 12 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 1313, 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.
[0076] 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.
[0077] 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.
[0078] 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 the use of a single coil has been described
as being suitable for use with a cylindrical wedge Halbach array
with wedge-shaped magnets at the ends of the array, it should be
appreciated that more than a single coil may also be used with such
an array. In one embodiment, two coils may be used in lieu of a
single coil.
[0079] While the use of a wedge Halbach array of magnets has been
described in terms of being used in a cylindrical VCM, it should be
appreciated that an array of magnets which includes at least one
wedge-shaped magnet may be used within a variety of different VCMs.
In one embodiment, a VCM which utilizes a coil which is
substantially shaped as a square tube may utilize arrays of magnets
which have an overall rectangular block shape with at least one
component magnet being wedge-shaped.
[0080] A VCM may include substantially only a single magnet array
with at least one wedge-shaped component magnet. By way of example,
an inner magnet ring of a radially symmetric cylindrical VCM may
include at least one wedge-shaped component magnet, while an outer
magnet ring of the VCM may be formed as a substantially uniform
donut-shaped magnet, or may include only component magnets which
are not wedge-shaped. Alternatively, an outer magnet ring of a
radially symmetric cylindrical VCM may include at least one
wedge-shaped component magnet, and an inner magnet ring of the VCM
may include a substantially uniform donut-shaped magnet, or may
include only component magnets which are not wedge-shaped.
[0081] The parameters associated with a coil that is used in a
radially symmetric cylindrical VCM with a cylindrical wedge Halbach
array that includes wedge-shaped magnets at the ends of the array
may vary widely. By way of example, both the number of turns in a
coil as well as the gauge of the wire in the coil may vary. That
is, the coil geometry may vary. Typically, as the wire gauge
increases, the number of turns in a coil increases, and the
resistance associated with the coil increases. Since the force
generated by a VCM is proportional to the amount of current and the
number of turns in a coil, to maintain the same force with lower
current, the number of turns in the coil is increased. However, the
voltage provided to the coil is generally increased in order to
provide the same electric power, since power is proportional to
both current and voltage. As the efficiency of a VCM is dependent
upon the orientation of magnets within the VCM and not the number
of turns in a coil or the wire gauge associated with the coil, the
wire gauge may be selected such that the voltage and the current
requirements of the VCM are consistent with any requirements of an
amplifier or other electronics associated with the VCM.
[0082] In addition to coil-related parameters, other parameters
associated with a VCM in accordance with the present invention may
also be widely varied. For instance, the inner and outer radii of
the magnets in a cylindrical wedge Halbach array may vary. The
positioning of the coil within a VCM may also be varied depending
upon the requirements of a particular system. For example, the
radial clearance or gap between a magnet array and the coil may
vary depending upon the length of a trajectory stroke, such as a
stroke in an XY plane, and a maximum stage position error, among
other factors.
[0083] Since many magnets, e.g., NdFeB magnets, are anisotropic, it
is often preferable to fabricate each radially magnetized ring
magnet out of several sections. By way of example, approximately
six magnet sections may be used to form a single ring magnet.
Generally, the number of magnets included in a wedge Halbach array
may vary. In other words, although each wedge Halbach array
described above has been described as including five or six
magnets, a wedge Halbach array may include fewer or more magnets
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.
[0084] This description of the invention has been presented for the
purposes of illustration and description. It is not intended to be
exhaustive or to limit the invention to the precise form described,
and many modifications and variations are possible in light of the
teaching above. The embodiments were chosen and described in order
to best explain the principles of the invention and its practical
applications. This description will enable others skilled in the
art to best utilize and practice the invention in various
embodiments and with various modifications as are suited to a
particular use. The scope of the invention is defined by the
following claims.
* * * * *