U.S. patent application number 11/507458 was filed with the patent office on 2006-12-14 for lithographic apparatus, device manufacturing method, and device manufactured thereby.
This patent application is currently assigned to ASML NETHERLANDS B.V.. Invention is credited to Robrecht Emiel Maria Leonia De Weerdt, Johannes Adrianus Antonius Theodorus Dams.
Application Number | 20060279141 11/507458 |
Document ID | / |
Family ID | 33522343 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060279141 |
Kind Code |
A1 |
De Weerdt; Robrecht Emiel Maria
Leonia ; et al. |
December 14, 2006 |
Lithographic apparatus, device manufacturing method, and device
manufactured thereby
Abstract
A bearing includes a passive magnetic bearing configured to
provide support between a first and second part of an apparatus and
allow both parts to be displaced relative to each other in a
direction perpendicular to the support direction. The passive
magnetic bearing includes first and second magnetic assemblies.
Each magnetic assembly includes at least one permanent magnet.
Inventors: |
De Weerdt; Robrecht Emiel Maria
Leonia; (Hoogstraten, BE) ; Theodorus Dams; Johannes
Adrianus Antonius; (Veldhoven, NL) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
ASML NETHERLANDS B.V.
Veldhoven
NL
|
Family ID: |
33522343 |
Appl. No.: |
11/507458 |
Filed: |
August 22, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10839712 |
May 6, 2004 |
7126666 |
|
|
11507458 |
Aug 22, 2006 |
|
|
|
Current U.S.
Class: |
310/12.06 ;
310/12.26; 310/12.31; 310/90.5; 355/72 |
Current CPC
Class: |
F16C 39/063 20130101;
G03F 7/70758 20130101; H02N 15/00 20130101 |
Class at
Publication: |
310/012 ;
355/072; 310/090.5 |
International
Class: |
H02K 41/00 20060101
H02K041/00; G03B 27/58 20060101 G03B027/58 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2003 |
EP |
03076395.7 |
Claims
1. A bearing configured to support a first part of an apparatus
with respect to a second part of the apparatus in a first direction
such that the first part is movable relative to the second part,
wherein the bearing comprises a passive magnetic bearing, wherein,
in use, the first part is supported by the second part in the first
direction such that the first part is movable with respect to the
second part in a second direction substantially perpendicular to
the first direction and the second part includes a second magnetic
assembly that is longer in the second direction than a first
magnetic assembly of the first part.
2. A bearing according to claim 1, wherein the bearing comprises a
first magnetic assembly and a second magnetic assembly, wherein
each of the first and second magnetic assembly assemblies is
provided with a permanent magnet and the magnetic assemblies are
arranged for mutual cooperation in such a way that, in use, a
repelling force is generated between the first and second
assemblies and a substantial part of the magnetic field lines of
the permanent magnets of the first and second magnetic assemblies
connect the permanent magnet of the first magnetic assembly with
the permanent magnet of the second magnetic assembly.
3. A bearing according to claim 2, wherein the first magnetic
assembly comprises a second permanent magnet, the permanent magnets
of the first assembly each have their magnetic polarization
parallel or anti-parallel to the first direction and define a space
between them in a third direction perpendicular to the first and
second direction, the permanent magnet of the second magnetic
assembly has its polarization substantially anti-parallel to the
polarization of the permanent magnets of the first magnetic
assembly, and the permanent magnet of the second magnetic assembly
is at least partly located in the space.
4. A bearing according to claim 2, wherein the first magnetic
assembly comprises a second permanent magnet, the permanent magnets
of the first magnetic assembly have their magnetic polarization
parallel or anti-parallel to the first direction and define a space
between them in a third direction perpendicular to the first and
second direction, the permanent magnet of the second magnetic
assembly has its polarization substantially perpendicular to the
polarization of the permanent magnets of the first assembly, and
the permanent magnet of the second magnetic assembly is at least
partly located in the space.
5. A lithographic projection apparatus according to claim 2,
wherein the first magnetic assembly comprises a second permanent
magnet, the permanent magnets of the first magnetic assembly have
their magnetic polarization parallel to each other and define a
space between them in a third direction perpendicular to the first
and second direction, the second magnetic assembly comprises a
second permanent magnet, one permanent magnet of the second
magnetic assembly having its polarization substantially parallel to
the polarization of the permanent magnets of the first assembly,
and the other permanent magnet of the second magnetic assembly
having its polarization substantially anti-parallel to the
polarization of the permanent magnets of the first magnetic
assembly, and the permanent magnets of the second magnetic assembly
are at least partly located in the space.
6. A lithographic projection apparatus according to claim 2,
wherein the first magnetic assembly comprises a plurality of
elongated permanent magnets arranged parallel to each other in the
second direction, each pair of adjacent permanent magnets defining
a space between them in a third direction substantially
perpendicular to the first and second direction, the second
magnetic assembly comprises a second permanent magnet, the
permanent magnets of the second magnetic assembly are placed
adjacent to each other in the third direction, each magnet is at
least partly located in one of the spaces defined by two adjacent
permanent magnets of the first magnetic assembly, the permanent
magnets of the first magnetic assembly have their magnetic
polarization substantially parallel or anti-parallel to each other,
and the permanent magnets of the second magnetic assembly have
their magnetic polarization substantially perpendicular to the
magnetic polarization of the permanent magnets of the first
magnetic assembly.
7. A lithographic projection apparatus according to claim 2,
wherein the second magnetic assembly comprises a plurality of
magnets arranged adjacent to each other in the second
direction.
8. A lithographic projection apparatus according to claim 2,
wherein relative positions of at least two permanent magnets of at
least one of the first and second magnetic assemblies are
adjustable.
9. A bearing according to claim 1, wherein the bearing comprises a
first magnetic assembly and a second magnetic assembly, the first
magnetic assembly comprises at least one permanent magnet and the
second magnet assembly comprises at least one permanent magnet, and
each magnetic assembly substantially has a circular shape.
10. A bearing apparatus according to claim 9, wherein at least one
of the magnetic assemblies comprises two or more permanent magnets,
the relative position of the magnets being adjustable.
11. A bearing according to claim 1, further comprising a linear
motor configured to displace the first part relative to the second
part in direction perpendicular to the first direction.
12. A bearing according to claim 11, wherein the linear motor
comprises a magnet array attached to the second part and a coil
assembly attached to the first part.
13. A bearing according to claim 11, further comprising a linear
actuator configured to generate a force between the first part and
the second part in the first direction.
14. A bearing according to claim 9, further comprising a plurality
of linear actuators configured to position the first part relative
to the second part in at least one degree of freedom.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/839,712, filed May 6, 2004, which relied for priority on
European Application 03076395.7, filed May 6, 2003, the entire
contents of both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a lithographic projection
apparatus, a device manufacturing method and a device manufactured
thereby.
[0004] 2. Description of the Related Art
[0005] The term "patterning device" as here employed should be
broadly interpreted as referring to a device that can be used to
endow an incoming radiation beam with a patterned cross-section,
corresponding to a pattern that is to be created in a target
portion of the substrate. The term "light valve" can also be used
in this context. Generally, the pattern will correspond to a
particular functional layer in a device being created in the target
portion, such as an integrated circuit or other device (see below).
Examples of such patterning devices include a mask. The concept of
a mask is well known in lithography, and it includes mask types
such as binary, alternating phase-shift, and attenuated
phase-shift, as well as various hybrid mask types. Placement of
such a mask in the radiation beam causes selective transmission (in
the case of a transmissive mask) or reflection (in the case of a
reflective mask) of the radiation impinging on the mask, according
to the pattern on the mask. In the case of a mask, the support will
generally be a mask table, which ensures that the mask can be held
at a desired position in the incoming radiation beam, and that it
can be moved relative to the beam if so desired.
[0006] Another example of a patterning device is a programmable
mirror array. One example of such a device is a matrix-addressable
surface having a viscoelastic control layer and a reflective
surface. The basic principle behind such an apparatus is that, for
example, addressed areas of the reflective surface reflect incident
light as diffracted light, whereas unaddressed areas reflect
incident light as undiffracted light. Using an appropriate filter,
the undiffracted light can be filtered out of the reflected beam,
leaving only the diffracted light behind. In this manner, the beam
becomes patterned according to the addressing pattern of the
matrix-addressable surface. An alternative embodiment of a
programmable mirror array employs a matrix arrangement of tiny
mirrors, each of which can be individually tilted about an axis by
applying a suitable localized electric field, or by employing
piezoelectric actuators. Once again, the mirrors are
matrix-addressable, such that addressed mirrors will reflect an
incoming radiation beam in a different direction to unaddressed
mirrors. In this manner, the reflected beam is patterned according
to the addressing pattern of the matrix-addressable mirrors. The
required matrix addressing can be performed using suitable
electronics. In both of the situations described hereabove, the
patterning device can include one or more programmable mirror
arrays. More information on mirror arrays as here referred to can
be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and
5,523,193, and PCT Patent Application Publications WO 98/38597 and
WO 98/33096, which are incorporated herein by reference. In the
case of a programmable mirror array, the support may be embodied as
a frame or table, for example, which may be fixed or movable as
required.
[0007] Another example of a patterning device is a programmable LCD
array. An example of such a construction is given in U.S. Pat. No.
5,229,872, which is incorporated herein by reference. As above, the
support in this case may be embodied as a frame or table, for
example, which may be fixed or movable as required.
[0008] For purposes of simplicity, the rest of this text may, at
certain locations, specifically direct itself to examples involving
a mask and mask table. However, the general principles discussed in
such instances should be seen in the broader context of the
patterning devices as hereabove set forth.
[0009] Lithographic projection apparatus can be used, for example,
in the manufacture of integrated circuits (ICs). In such a case,
the patterning device may generate a circuit pattern corresponding
to an individual layer of the IC, and this pattern can be imaged
onto a target portion (e.g. including one or more dies) on a
substrate (silicon wafer) that has been coated with a layer of
radiation-sensitive material (resist). In general, a single wafer
will contain a whole network of adjacent target portions that are
successively irradiated via the projection system, one at a time.
In current apparatus, employing patterning by a mask on a mask
table, a distinction can be made between two different types of
machine. In one type of lithographic projection apparatus, each
target portion is irradiated by exposing the entire mask pattern
onto the target portion at once. Such an apparatus is commonly
referred to as a wafer stepper or step-and-repeat apparatus. In an
alternative apparatus, commonly referred to as a step-and-scan
apparatus, each target portion is irradiated by progressively
scanning the mask pattern under the beam in a given reference
direction (the "scanning" direction) while synchronously scanning
the substrate table parallel or anti-parallel to this direction.
Since, in general, the projection system will have a magnification
factor M (generally <1), the speed V at which the substrate
table is scanned will be a factor M times that at which the mask
table is scanned. More information with regard to lithographic
devices as here described can be gleaned, for example, from U.S.
Pat. No. 6,046,792, incorporated herein by reference.
[0010] In a manufacturing process using a lithographic projection
apparatus, a pattern (e.g. in a mask) is imaged onto a substrate
that is at least partially covered by a layer of
radiation-sensitive material (resist). Prior to this imaging, the
substrate may undergo various procedures, such as priming, resist
coating and a soft bake. After exposure, the substrate may be
subjected to other procedures, such as a post-exposure bake (PEB),
development, a hard bake and measurement/inspection of the imaged
features. This array of procedures is used as a basis to pattern an
individual layer of a device, e.g. an IC. Such a patterned layer
may then undergo various processes such as etching,
ion-implantation (doping), metallization, oxidation,
chemo-mechanical polishing, etc., all intended to finish off an
individual layer. If several layers are required, then the whole
procedure, or a variant thereof, will have to be repeated for each
new layer. Eventually, an array of devices will be present on the
substrate (wafer). These devices are then separated from one
another by a technique such as dicing or sawing, whence the
individual devices can be mounted on a carrier, connected to pins,
etc. Further information regarding such processes can be obtained,
for example, from the book "Microchip Fabrication: A Practical
Guide to Semiconductor Processing", Third Edition, by Peter van
Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4,
incorporated herein by reference.
[0011] For the sake of simplicity, the projection system may
hereinafter be referred to as the "lens." However, this term should
be broadly interpreted as encompassing various types of projection
system, including refractive optics, reflective optics, and
catadioptric systems, for example. The radiation system may also
include components operating according to any of these design types
for directing, shaping or controlling the beam of radiation, and
such components may also be referred to below, collectively or
singularly, as a "lens". Further, the lithographic apparatus may be
of a type having two or more substrate tables (and/or two or more
mask tables). In such "multiple stage" devices the additional
tables may be used in parallel, or preparatory steps may be carried
out on one or more tables while one or more other tables are being
used for exposures. Dual stage lithographic apparatus are
described, for example, in U.S. Pat. Nos. 5,969,441 and 6,262,796,
both incorporated herein by reference.
[0012] Within a lithographic apparatus, bearings are often required
between parts of the apparatus that provide support while allowing
the parts to move relative to each other. A well known solution for
realizing this movable support is an air bearing. The air bearing
maintains the parts at a predefined distance by generating the
appropriate bearing force. If a linear motor with a ferromagnetic
core is used for driving both parts relative to each other, the
normal force between the translator and the stator of the motor may
be used as a pre-load force for the air bearing. An alternative to
the use of an air bearing is to generate the required support by a
linear motor or by a Lorentz type actuator. A drawback of an air
bearing support is that it is difficult to provide such a system
under vacuum conditions. A drawback of the linear motor or actuator
support is that generation of the required bearing force results in
a constant additional heat dissipation in the current carrying
components of the linear motor or actuator.
SUMMARY OF THE INVENTION
[0013] It is an aspect of the present invention to provide a
bearing that may be suitable for use in vacuum and dissipates
substantially less heat than a bearing that uses a linear motor or
an actuator for providing the bearing force.
[0014] This and other aspects are achieved according to the present
invention in a lithographic apparatus including a radiation system
configured to supply a beam of radiation; a support configured to
support a patterning device, the patterning device configured to
pattern the beam according to a desired pattern; a substrate table
configured to hold a substrate; a projection system configured to
project the patterned beam onto a target portion of the substrate;
and a bearing configured to support a first part of the apparatus
with respect to a second part of the apparatus in a first direction
such that the first part is movable relative to the second part,
wherein the bearing includes a passive magnetic bearing.
[0015] A bearing force that is substantially provided by a passive
magnetic bearing and not by current carrying coils provides a more
efficient support compared to linear motor or actuator type
bearings, yielding a reduced power supply for the apparatus and
less heat dissipation inside the apparatus. The latter is
beneficial as thermal stability of a lithographic apparatus is
desirable.
[0016] In an exemplary embodiment of the present invention, the
first part of the lithographic apparatus is supported by the second
part in a first direction such that the first part is movable with
respect to the second part in a second direction substantially
perpendicular to the first direction.
[0017] According to another exemplary embodiment of the present
invention, a support having a low stiffness in the support
direction is provided by the arrangement of the magnetic
assemblies. A low stiffness bearing is more desirable than a higher
stiffness bearing because the transmission of vibrations from one
part of the bearing to the other is reduced. It should be
appreciated that `a permanent magnet` may be considered equivalent
to an array of individual permanent magnets having the same
magnetic polarization placed adjacent to each other.
[0018] According to yet another exemplary embodiment of the present
invention, an arrangement of magnetic assemblies provides a
comparatively large stroke in the second direction along which the
first and second parts can be displaced relative to each other
without any substantial variation of the bearing force.
[0019] According to a further exemplary embodiment of the present
invention, an arrangement of magnetic assemblies provides a lower
stiffness in the first direction.
[0020] According to a still further exemplary embodiment of the
present invention, an arrangement of magnetic assemblies provides a
bearing having a low stiffness along the first direction, the
second direction, and a third direction perpendicular to both first
and second directions. Low stiffness in three directions enables
control of the magnet bearing (i.e. maintaining a relative position
between the first and second parts in the first and third
direction) to be executed with minimal effort by, for example,
Lorentz type actuators or linear motors.
[0021] According to an even further exemplary embodiment of the
present invention, an arrangement of magnetic assemblies provides a
low stiffness in all three directions.
[0022] According to another exemplary embodiment of the present
invention, an arrangement of magnetic assemblies provides an
increased bearing force that can be obtained due to an increased
number of magnets. The required bearing force can also be more
evenly distributed. Extending the magnetic assemblies in the third
direction results in a more stable bearing with respect to tilt
around the second direction.
[0023] According to yet another exemplary embodiment of the present
invention, an arrangement of magnetic assemblies results in a more
stable bearing with respect to tilt around the third direction
because the bearing force is generated as the sum of contributions
of the different magnets to this bearing force.
[0024] According to an even further exemplary embodiment of the
present invention, an arrangement of magnetic assemblies in which
the relative position of at least two or more permanent magnets of
at least one of the magnetic assemblies is adjustable allows
flexible use of the bearing (e.g. for different loads) and also
allows for compensation of mechanical or magnetic tolerances of the
magnetic assemblies. The magnets whose relative position is
adjustable can be of equal size or of different size.
[0025] According to another exemplary embodiment of the present
invention, an arrangement of the magnetic assemblies is such that
first and second magnetic assemblies can rotate relative to each
other instead of allowing a linear displacement.
[0026] Although specific reference may be made in this text to the
use of the apparatus according to the invention in the manufacture
of ICs, it should be explicitly understood that such an apparatus
has many other possible applications. For example, it may be
employed in the manufacture of integrated optical systems, guidance
and detection patterns for magnetic domain memories, liquid-crystal
display panels, thin-film magnetic heads, etc. It should be
appreciated that, in the context of such alternative applications,
any use of the terms "reticle", "wafer" or "die" in this text
should be considered as being replaced by the more general terms
"mask", "substrate" and "target portion", respectively.
[0027] In the present document, the terms "radiation" and "beam"
are used to encompass all types of electromagnetic radiation,
including ultraviolet (UV) radiation (e.g. with a wavelength of
365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV)
radiation (e.g. having a wavelength in the range 5-20 nm), as well
as particle beams, such as ion beams or electron beams.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Exemplary embodiments of the present invention will now be
described, by way of example only, with reference to the
accompanying schematic drawings in which corresponding reference
symbols indicate corresponding parts, and in which:
[0029] FIG. 1 schematically depicts a lithographic projection
apparatus according to the present invention;
[0030] FIG. 2a schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0031] FIG. 2b schematically depicts a side view of the first
embodiment of FIG. 2a;
[0032] FIG. 2c schematically depicts the magnetic field lines
calculated for the passive magnetic bearing as shown in FIG.
2a;
[0033] FIG. 3a schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0034] FIG. 3b schematically depicts a bottom view of the bearing
of FIG. 3a;
[0035] FIG. 3c schematically depicts the magnetic field lines
calculated for the passive magnetic bearing of FIG. 3a;
[0036] FIG. 4a schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0037] FIG. 4b schematically depicts a bottom view of the bearing
of FIG. 4a;
[0038] FIG. 4c schematically depicts the magnetic field lines
calculated for the passive magnetic bearing of FIG. 4a;
[0039] FIG. 5a schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0040] FIG. 5b schematically depicts a bottom view of the bearing
of FIG. 5a;
[0041] FIG. 5c schematically depicts the magnetic field lines
calculated for a part of the passive magnetic bearing of FIG.
5a;
[0042] FIG. 5d schematically depicts connecting an object table to
bearing of FIG. 5a;
[0043] FIG. 6a schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0044] FIG. 6b schematically depicts the magnetic field lines
calculated for the passive magnetic bearing of FIG. 6a;
[0045] FIG. 7 schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0046] FIG. 8 schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0047] FIG. 9a schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0048] FIG. 9b schematically depicts a top view of the passive
magnetic bearing of FIG. 9a;
[0049] FIG. 9c schematically depicts an actuator arrangement
provided between both parts of the passive magnetic bearing of FIG.
9a;
[0050] FIG. 9d schematically depicts a short stroke actuator system
provided between an object table and the passive magnetic
bearing;
[0051] FIG. 10 schematically depicts a front view of a passive
magnetic bearing according to the present invention;
[0052] FIG. 11a schematically depicts a front view of a passive
magnetic bearing according to the present invention; and
[0053] FIG. 11b schematically depicts a top view of the bearing of
FIG. 11a.
DETAILED DESCRIPTION
[0054] FIG. 1 schematically depicts a lithographic projection
apparatus 1 according to an exemplary embodiment of the present
invention. The apparatus includes a radiation system Ex, IL
configured to supply a beam PB of radiation (e.g. UV or EUV
radiation). The radiation system also includes a radiation source
LA. A first object table (mask table) MT is provided with a mask
holder configured to hold a mask MA (e.g. a reticle) and is
connected to a first positioning device PM that accurately
positions the mask with respect to a projection system ("lens") PL.
A second object table (substrate table) WT is provided with a
substrate holder configured to hold a substrate W (e.g. a
resist-coated silicon wafer) and is connected to a second
positioning device PW that accurately positions the substrate with
respect to the projection system PL. The projection system PL (e.g.
a refractive or catadioptric system, a mirror group or an array of
field deflectors) is configured to image an irradiated portion of
the mask MA onto a target portion C (e.g. including one or more
dies) of the substrate W.
[0055] As here depicted, the apparatus is of a reflective type
(i.e. has a reflective mask). However, in general, it may also be
of a transmissive type (i.e. has a reflective mask). Alternatively,
the apparatus may employ another kind of patterning device, such as
a programmable mirror array of a type as referred to above.
[0056] The source LA (e.g. an excimer laser, an undulator or
wiggler provided around the path of an electron beam in a storage
ring or synchrotron, a laser-produced plasma source, a discharge
source or an electron or ion beam source) produces radiation. The
radiation is fed into an illumination system (illuminator) IL,
either directly or after having traversed a conditioning device(s),
for example a beam expander Ex. The illuminator IL may include an
adjusting device(s) AM configured to set the outer and/or inner
radial extent (commonly referred to as .sigma.-outer and
.sigma.-inner, respectively) of the intensity distribution in the
beam. In addition, it will generally include various other
components, for example an integrator IN and a condenser CO. In
this way, the beam PB impinging on the mask MA has a desired
uniformity and intensity distribution in its cross-section.
[0057] It should be noted with regard to FIG. 1 that the source LA
may be within the housing of the lithographic projection apparatus
(as is often the case when the source LA is a mercury lamp, for
example), but that it may also be remote from the lithographic
projection apparatus. The radiation which it produces may be led
into the apparatus (e.g. with the aid of suitable directing
mirrors). This latter scenario is often the case when the source LA
is an excimer laser. The present invention encompasses both of
these scenarios.
[0058] The beam PB subsequently intercepts the mask MA, which is
held on a mask table MT. Having traversed the mask MA, the beam PB
passes through the projection system PL, which focuses the beam PB
onto a target portion C of the substrate W. With the aid of the
second positioning device PW (and interferometric measuring device
IF), the substrate table WT can be moved accurately, e.g. so as to
position different target portions C in the path of the beam PB.
Similarly, the first positioning device PM (and interferometric
measuring device IF) can be used to accurately position the mask MA
with respect to the path of the beam PB, e.g. after mechanical
retrieval of the mask MA from a mask library, or during a scan. In
general, movement of the object tables MT, WT will be realized with
the aid of a long-stroke module (coarse positioning) and a
short-stroke module (fine positioning), which are not explicitly
depicted in FIG. 1. However, in the case of a wafer stepper (as
opposed to a step-and-scan apparatus) the mask table MT may just be
connected to a short stroke actuator, or may be fixed. Mask MA and
substrate W may be aligned using mask alignment marks M1, M2 and
substrate alignment marks P1, P2.
[0059] The depicted apparatus can be used in two different modes:
[0060] 1. In step mode, the mask table MT is kept essentially
stationary, and an entire mask image is projected at once (i.e. a
single "flash") onto a target portion C. The substrate table WT is
then shifted in the X and/or Y directions so that a different
target portion C can be irradiated by the beam PB; and [0061] 2. In
scan mode, essentially the same scenario applies, except that a
given target portion C is not exposed in a single "flash". Instead,
the mask table MT is movable in a given direction (the "scanning
direction", e.g. the Y direction) with a speed v, so that the beam
PB is caused to scan over a mask image. Concurrently, the substrate
table WT is simultaneously moved in the same or opposite direction
at a speed V=Mv, in which M is the magnification of the projection
system PL (e.g., M=1/4 or 1/5). In this manner, a relatively large
target portion C can be exposed, without having to compromise on
resolution.
[0062] FIGS. 2a and 2b show an arrangement of permanent magnets
according to an exemplary embodiment of a bearing according to the
present invention. FIG. 2a shows a front view and FIG. 2b shows a
side view. In this arrangement, the first magnetic assembly 2
includes a magnet 2.1 arranged on a first part 2.30 of the
lithographic apparatus and a second magnetic assembly 4 including a
magnet 4.1 arranged on a second part 4.30 of the lithographic
apparatus. The first and second parts 2.30 and 4.30 can move
relative to each other as indicated by the arrow 6. This can be
done, for example, by an electromagnetic motor positioned between
the first and second parts 2.30 and 4.30.
[0063] The arrows inside the magnets 2.1 and 4.1 indicate the
magnetic polarization of the magnets. This particular arrangement
of magnets produces a repelling magnetic force between the first
and second parts 2.30 and 4.30 in the Z-direction. As can be seen
in FIG. 2b, both magnetic assemblies 2 and 4 can be displaced
relative to each other in the Y-direction. Because the first
magnetic assembly 2 is substantially longer in the Y-direction than
the second magnetic assembly 4, the magnetic force exerted between
both magnetic assemblies 2 and 4 is substantially independent of
the Y-position of the second magnetic assembly 4, i.e. a low
stiffness in the Y-direction is encountered. The stiffness in the
X-direction and the Z-direction however, is rather high in this
arrangement of magnets. Therefore, a significant force variation is
encountered when the first and second parts 2.30 and 4.30 are
displaced relative to each other in the X-direction or in the
Z-direction. It should be noted that in order to maintain the first
part 2.30 in the appropriate position relative to the second part
4.30 (e.g. in the Z-direction, the X-direction or both), one or
more actuators (such as Lorentz actuators) may be positioned
between the first and second parts 2.30 and 4.30. Such actuators
may also be provided to prevent the moving part (e.g. part 2.30)
from tilting around the X, Y or Z-axis.
[0064] FIG. 2c shows the magnetic field lines calculated for this
particular arrangement of permanent magnets. As can be seen from
FIG. 2c, each of the magnetic field lines remains within one of the
magnetic assemblies. None of the field lines connects one of the
magnets of the first magnetic assembly with one of the magnets of
the second magnetic assembly.
[0065] FIGS. 3a and 3b show another arrangement of permanent
magnets according to an exemplary embodiment of the present
invention. FIG. 3a shows a front view and FIG. 3b shows a bottom
view. In this arrangement, the first magnetic assembly 2 includes
two magnets 2.2, 2.3 arranged on a first part of the lithographic
apparatus and a second magnetic assembly 4 including a magnet 4.2
arranged on a second part of the lithographic apparatus. The first
and second parts can move relative to each other as indicated by
the arrow 6. In this arrangement, a lower stiffness is obtained in
the Z-direction compared to the arrangement shown in FIGS. 2a-c.
This lower stiffness is obtained by arranging both magnetic
assemblies in such a way that a repelling force is generated
between both assemblies wherein, different from the situation
depicted in FIG. 2c, a substantial part of the magnetic field lines
of both assemblies connect both magnets 2.2 and 2.3 of the first
assembly 2 with the magnet 4.2 of the second assembly 4. This
situation is depicted in FIG. 3c showing the magnetic field lines
calculated for the configuration shown in FIG. 3a. This is
supported by extensive simulations showing that a low stiffness in
the support direction can be obtained by the following measures:
[0066] 1. The magnet assemblies are arranged to repel from each
other in the support direction. [0067] 2. A substantial portion of
the magnetic field lines connects a magnet from the first assembly
with a magnet from the second assembly.
[0068] It is desirable that at least 20% of the magnetic field
lines connect a magnet from the first assembly with a magnet from
the second assembly to obtain a comparatively small operating area
wherein a low stiffness is encountered. For practical embodiments,
it is desirable that at least 50% of the magnetic field lines
should connect a magnet from the first assembly with a magnet from
the second assembly to obtain an increased operating area wherein a
low stiffness is encountered. An increased percentage of magnetic
field lines connecting a magnet from the first assembly with a
magnet of the second assembly results in an increased reduction of
the stiffness of the bearing. Also in this exemplary embodiment,
the first part can be maintained in the appropriate position
relative to the second part by applying one or more actuators, for
example Lorentz actuators, between the first and second parts. As
an alternative, the electromagnetic motor to displace the first
part relative to the second part in the Y-direction may also be
equipped to generate a force between the first and second parts in
one or more additional degrees of freedom, i.e. apart from the
force generated in the Y-direction. As an example, the
electromagnetic motor may be a planar motor capable of displacing
both parts relative to each other in all six degrees of freedom. In
such an arrangement, the planar motor may drive both parts relative
to each other in the Y-direction while maintaining both parts in a
predefined position relative to each other in the other five
degrees of freedom. Combining the passive magnetic bearing with a
planar motor will result in an improved efficiency of the planar
motor since the weight of the moving part is compensated by the
permanent magnet bearing.
[0069] FIGS. 4a and 4b show another arrangement of permanent
magnets according to an exemplary embodiment of the present
invention. FIG. 4a shows a front view and FIG. 4b shows a bottom
view. In this configuration, the first magnetic assembly 2 includes
two magnets 2.4, 2.5 arranged on a first part of the lithographic
apparatus and a second magnetic assembly 4 including a magnet 4.3
arranged on a second part of the lithographic apparatus. The first
and second parts can move relative to each other as indicated by
the arrow 6. In this arrangement, the stiffness obtained in the
Z-direction is even further reduced compared to the configuration
shown in FIGS. 2a-c. The bearing force generated between both
magnetic assemblies 2 and 4 is a repelling force in the
Z-direction. This repelling force is generated by the attraction
between poles of different polarity (between poles 2.4b and 4.3a
and between 2.5a and 4.3b) and the repulsion between poles of the
same polarity (between poles 2.4a and 4.3a and between poles 2.5b
and 4.3b). In this situation, when first and second part of the
lithographic apparatus are displaced relative to each other in the
Z-direction one of the attraction or repulsion will increase while
the other will decrease resulting in a comparatively small
variation of the resulting force. FIG. 4c shows the calculated
magnetic field lines for the magnet arrangement shown in FIG. 4a.
As is shows in FIG. 4c, a substantial portion of the magnetic field
lines of this arrangement of magnets connects a magnet from the
first assembly with a magnet from the second assembly.
[0070] FIGS. 5a and 5b show another arrangement of permanent
magnets according to an exemplary embodiment of the present
invention. FIG. 5a shows a front view and FIG. 5b shows a top view
of the arrangement. In this arrangement, a first magnetic assembly
2 includes two magnets 2.6, 2.7 arranged on a first part of the
lithographic apparatus and a second magnetic assembly 4 includes
two magnets 4.4, 4.5 arranged on a second part of the lithographic
apparatus. FIG. 5c shows the calculated magnetic field lines for
part of the magnetic assemblies of FIG. 5a (the magnetic field of
magnets 2.6 and 4.4 is calculated). Since the magnetic field lines
shown in FIG. 5c connect the magnet 2.6 of the first assembly with
the magnet 4.4 of the second assembly, also in this arrangement, a
low stiffness between both assemblies is obtained. FIG. 5d
schematically depicts an object table 5 (e.g. a mask table)
connected to the second magnetic assembly 4 of the bearing
arrangement. Such a connection can, for example, be accomplished by
leaf springs 6. The object table 5 may also be connected directly
to the second magnetic assembly 4. In order to increase the
positioning accuracy of the object table, an actuator system may be
provided between the object table 5 and the bearing assembly. Such
an actuator system may, for example, include electromagnetic
actuators such as Lorentz actuators or reluctance actuators or
piezo-electric actuators. Similar arrangements to connect the
object table to the bearing assembly or to position the object
table can also be made with the bearing arrangements shown in FIGS.
2a-4c and 6a-10.
[0071] FIGS. 6a and 6b show a front view of another arrangement of
permanent magnets according to an exemplary embodiment of the
present invention. In this configuration, the first magnetic
assembly includes two magnets 2.8, 2.9 arranged on a first part of
the lithographic apparatus and a second magnetic assembly 4
includes two magnets 4.6, 4.7 arranged on a second part of the
lithographic device. In this arrangement, all magnets have their
magnetization parallel or anti-parallel to each other. Also in this
arrangement, low stiffness is obtained. As can be seen from FIG. 6b
showing the calculated magnetic field lines, a substantial part of
the magnetic field lines connects the surface of a magnet from the
first assembly with a magnet from the second assembly.
[0072] FIG. 7 shows another exemplary embodiment of the present
invention where two magnet arrangements according to FIGS. 3a-c are
combined.
[0073] FIG. 8 shows another exemplary embodiment of the present
invention that can be constructed by combining magnet
configurations shown in previous figures. It should be appreciated
that the magnetic assemblies as shown can be extended even further
in X-direction if required. The magnetic assemblies as shown in
FIGS. 7 and 8 provide a more stable configuration with respect to
tilting around the Y-axis. Combining a plurality of configurations
can also be done in Y-direction to obtain an increased bearing
force or provide a more evenly distributed bearing force as shown
in FIGS. 9a and 9b. FIGS. 9a and 9b combine two configurations
according to FIGS. 4a-c into one assembly. In this case, the
required bearing force is provided as the sum of the force in the
Z-direction acting on the four magnets 4.13, 4.14, 4.15 and 4.16.
This assembly provides a more stable arrangement with respect to
tilting of the second magnet assembly around the X-axis. In FIG.
9c, the bearing arrangement is combined with an actuator
arrangement. The actuator arrangement is schematically illustrated
by elements 4.17 and 4.18. Element 4.17 may, for example, include a
magnet array that cooperates with a coil assembly 4.18. The magnet
assembly 4 may be displaced relative to the magnet assembly 2 in
one or more degrees of freedom by the actuator arrangement. In
general, the actuator assembly may includes a linear motor or a
planar motor to displace both assemblies 2 and 4 relative to each
other over comparatively large distances and may further include
electromagnetic actuators such as Lorentz actuators or reluctance
actuators to position both assemblies relative to each other over
comparatively small distances in the other degrees of freedom.
Similar actuator arrangements may be combined with the bearing
arrangements of FIGS. 2a-10. The mask table, or the object table,
that requires accurate positioning may be directly coupled to the
second magnetic assembly 4, for example by leaf springs. In case
the positioning accuracy of the bearing assembly and actuator
assembly is not sufficient, an additional actuator arrangement (a
so-called short stroke actuator system) may be applied between the
object table and the bearing arrangement. Such an arrangement is
schematically depicted in FIG. 9d.
[0074] FIG. 9d schematically depicts a short stroke actuator system
arranged between the object table 5 and the magnetic assembly 4 of
the magnetic bearing. In such an arrangement, the coarse
positioning of the magnetic assembly 4 may be provided by the
actuator system 4.17, 4.18 while the short stroke actuator system
4.19, 4.20 can be applied for accurate positioning of the object
table 5. The short stroke actuator system may, for example, include
a plurality of Lorentz actuators, each including a magnet array
4.19 and a coil assembly 4.20.
[0075] FIG. 10 shows another exemplary embodiment of the present
invention wherein the first magnetic assembly 2 includes four
magnets 2.20, 2.21, 2.22, and 2.23. The distance in the Z-direction
between the magnets 2.20 and 2.21 and between the magnets 2.22 and
2.23 is adjustable in order to adjust the bearing force. The
arrangement shown in FIG. 10 has the same performance with respect
to stiffness as the arrangement shown in FIGS. 4a-c. Subdividing
each of the magnets 2.4 and 2.5 of the arrangement shown in FIGS.
4a-c into two magnets with the same polarization and displacing
them relative to each other in Z-direction results in the
arrangement shown in FIG. 10. Subdividing the magnets of one or
both of the magnet assemblies in order to make the bearing force
adjustable can be applied to all of the arrangements of the present
invention. In general, if at least one of the magnet assemblies is
provided with at least two magnets and the distance between those
magnets is adjustable, the bearing force can be adjusted. For
example, the bearing force generated by the arrangement shown in
FIGS. 3a-c can be adjusted by displacing magnets 2.2 and 2.3
relative to each other in the X-direction. As an other example, the
magnets 4.6 and 4.7 in the arrangement shown in FIGS. 6a-b can be
used for adjusting the bearing force if the distance between both
arrays is adjustable.
[0076] For all the arrangements shown in FIGS. 2a-10, a similar
performance can be obtained when the second magnetic assembly is
substantially longer than the first magnetic assembly in the
Y-direction instead of the first magnetic assembly being longer
than the second magnetic assembly.
[0077] FIGS. 11a and 11b show another arrangement of permanent
magnet assemblies according to an exemplary embodiment of the
present invention wherein the magnet assemblies have a
substantially circular shape. FIG. 11a shows a front view and FIG.
11b shows a top view. In the arrangement shown, the first magnetic
assembly includes a magnet 2.24 and the second magnet assembly
includes a magnet 4.22. Both circular assemblies are arranged to
have the same axis of symmetry. This allows both parts of the
bearing to rotate relative to each other around the axis of
symmetry. In order to maintain the appropriate relative position
between both permanent magnet assemblies, the arrangement shown may
further be equipped with one or more actuators. Such actuators may
include rotary electromagnetic motors, piezo-electric motors,
linear actuators, etc. It should further be noted that each of the
arrangements shown in FIGS. 2a-10 may be modified in order to
provide a passive magnetic bearing for a substantially circular
arrangement.
[0078] The passive magnetic bearing can be applied to all
components of the lithographic apparatus that require a movable
support. Some examples are the use of the passive magnetic bearing
between a base frame and a dynamic component such as a support for
the patterning device or a substrate table or between a balance
mass and a base frame. For example, the passive magnetic bearing
may be applied in a positioning device that positions a mask table
over comparatively large distances relative to a frame in the
scanning direction. In such an arrangement, the positioning device
may include a linear motor, the linear motor operating between the
mask table and the frame. In such an arrangement, the passive
magnetic bearing may also be applied between the mask table and the
frame. In general, the positioning device may further be equipped
with actuators (e.g. Lorentz actuators) to maintain the mask table
in the appropriate position relative to the frame. In order to
increase the accuracy of the positioning of the mask table, the
positioning device may further be equipped with a short stroke
actuator system that accurately positions the mask table relative
to, for example, a projection system of the apparatus. The passive
magnetic bearing can also be applied to movably support optical
elements, such as lenses or mirrors.
[0079] While specific embodiments of the present invention have
been described above, it will be appreciated that the present
invention may be practiced otherwise than as described. The
description is not intended to limit the invention.
* * * * *