U.S. patent application number 12/921556 was filed with the patent office on 2011-01-20 for shear-layer chuck for lithographic apparatus.
This patent application is currently assigned to ASML Holding N.V.. Invention is credited to Samir A. Nayfeh, Justin Matthew Verdirame, Mark Edd Williams.
Application Number | 20110013164 12/921556 |
Document ID | / |
Family ID | 40752516 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110013164 |
Kind Code |
A1 |
Nayfeh; Samir A. ; et
al. |
January 20, 2011 |
Shear-Layer Chuck for Lithographic Apparatus
Abstract
A lithographic apparatus is described that comprises a support
structure (300) to hold an object (210). The object may be a
patterning device or a substrate to be exposed. The support
structure comprises a chuck (321), on which the object is
supported, and an array of shear-compliant elongated elements (325)
normal to the chuck and the stage (230), such that first ends of
the elongated elements contact a surface of the chuck and second
ends of the elongated elements contact a stage. Through using the
array of elongated elements, a transfer of stress between the stage
and the chuck is substantially uniform, resulting in minimization
of slippage of the object relative to the surface of the chuck
during a deformation of the chuck due to the stress.
Inventors: |
Nayfeh; Samir A.;
(Shrewsbury, MA) ; Williams; Mark Edd; (Amherst,
NH) ; Verdirame; Justin Matthew; (Cambridge,
MA) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
ASML Holding N.V.
Veldhoven
NL
|
Family ID: |
40752516 |
Appl. No.: |
12/921556 |
Filed: |
April 7, 2009 |
PCT Filed: |
April 7, 2009 |
PCT NO: |
PCT/EP2009/002577 |
371 Date: |
September 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61071059 |
Apr 10, 2008 |
|
|
|
Current U.S.
Class: |
355/53 ; 355/77;
361/234 |
Current CPC
Class: |
Y10S 414/141 20130101;
H01L 21/6875 20130101; G03F 7/70716 20130101; Y10T 279/34 20150115;
H01L 21/683 20130101; H01L 21/68714 20130101; G03F 7/70783
20130101; G03F 7/707 20130101 |
Class at
Publication: |
355/53 ; 361/234;
355/77 |
International
Class: |
G03B 27/42 20060101
G03B027/42; H01L 21/683 20060101 H01L021/683 |
Claims
1-35. (canceled)
36. A system, comprising: a chuck having a first surface and a
second surface, the second surface being located opposite the first
surface; and an array of elongated elements having first and second
respective ends and having longitudinal axes normal to the second
surface of the chuck, such that the first ends contact the second
surface of the chuck and the second ends contact a stage, whereby,
through using the array of elongated elements, a transfer of stress
between the stage and the chuck is rendered substantially uniform,
resulting in minimization of slippage of an object relative to the
first surface of the chuck during a deformation of the chuck due to
the stress.
37. The system of claim 36, wherein the stage is configured to be
accelerated causing the stress.
38. The system of claim 36, wherein a relative temperature
difference between the object, the chuck, and the stage is
configured to produce the stress.
39. The system of claim 36, wherein at least one of an acceleration
of the stage and a relative temperature difference between the
object, the chuck, and the stage is configured to produce the
stress.
40. The system of claim 36, wherein another object is supported on
the first surface of the chuck.
41. The system of claim 36, wherein the elongated elements of the
array are arranged evenly to distribute the stress uniformly.
42. The system of claim 36, wherein the array of elongated elements
is integral with the stage and coupled to the chuck.
43. The system of claim 36, wherein the array of elongated elements
is integral with the chuck and coupled to the stage.
44. The system of claim 36, further comprising: an interface
membrane layer disposed between the chuck and the stage, such that
the array of elongated elements passes through the interface
layer.
45. The system of claim 36, wherein the chuck, the array of
elongated elements, and the stage are coupled to one another by
compliant epoxy.
46. The system of claim 36, wherein at least one of the chuck and
the stage comprises cooling channels.
47. The system of claim 36, further comprising: an illumination
system configured to produce a beam of radiation; a patterning
device configured to pattern the beam of radiation; and a
projection system configured to project the patterned beam of
radiation onto a substrate, wherein the pattering device or the
substrate is configured to be the object.
48. A method, comprising: coupling an array of elongated elements,
having respective longitudinal axes and first and second ends,
between a chuck and a stage, such that the longitudinal axes are
normal to the chuck and the stage, the first ends contact a second
surface of the chuck, and the second ends contact the stage,
whereby under a condition of stress a transfer of the stress
between the stage and the chuck is substantially uniform;
supporting an object on a first surface of the chuck, the first
surface being opposite the second surface; subjecting the chuck and
the stage to the condition of stress; and measuring deformations of
the chuck under the condition of stress to correlate the measured
deformations with slippage of the object relative to the first
surface of the chuck.
49. A lithographic apparatus, comprising: an illumination system
configured to produce a beam of radiation; a patterning device
configured to pattern the beam of radiation; a projection system
configured to project the patterned beam of radiation onto a
substrate; and a support structure comprising, a chuck having a
first surface and a second surface, the second surface being
located opposite the first surface, and an array of elongated
elements having first and second respective ends and having
longitudinal axes, the longitudinal axes being normal to the second
surface of the chuck, such that the first ends contact the second
surface of the chuck and the second ends contact a stage, whereby,
through using the array of elongated elements, a transfer of stress
between the stage and the chuck is rendered substantially uniform,
resulting in minimization of slippage of an object relative to the
first surface of the chuck during a deformation of the chuck due to
the stress, wherein the pattering device or the substrate is
configured to be the object.
50. A system for supporting an object, comprising: a chuck having a
first surface that supports the object; a stage that supports the
chuck in one or more directions of translation or rotation; and an
interface layer between the chuck and the stage with a relatively
low stiffness in at least one direction of translation or rotation
with respect to the other directions of translation or rotation,
resulting in minimization of slippage of the object relative to the
first surface of the chuck during deformation of the chuck due to a
stress between the stage and the chuck.
51. The system of claim 50, wherein the stress arises from
acceleration of the stage.
52. The system of claim 50, wherein the stress arises due to a
relative temperature difference between the object, the chuck, and
the stage.
53. The system of claim 50, wherein at least one of an acceleration
of the stage and a relative temperature difference between the
object, the chuck, and the stage is configured to produce the
stress.
54. The system of claim 50, wherein the interface layer comprises
an array of elongated elements arranged to distribute the stress
uniformly.
55. A system comprising: a chuck having a first surface and a
second surface, the second surface being located opposite the first
surface, wherein the chuck is configured to hold an object; and an
array of elongated elements having first and second respective ends
and having longitudinal axes normal to the second surface of the
chuck, wherein the first ends contact the second surface of the
chuck and the second ends contact a stage to isolate the chuck from
the stage by rigidly coupling the chuck to the stage such that the
array of elongated elements uniformly distribute stress there
between whereby, through using the array of elongated elements,
slippage of the object relative to the first surface of the chuck
is minimized during a deformation of the chuck due to stress when
the stage is accelerated.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to a lithographic apparatus
and method of securely holding an object in the lithographic
apparatus.
[0003] 2. Related Art
[0004] A lithographic apparatus is a machine that applies a desired
pattern onto a substrate, usually onto a target portion of the
substrate. A lithographic apparatus can be used, for example, in
the manufacture of integrated circuits (ICs). In that instance, a
patterning device, which is alternatively referred to as a mask or
a reticle, may be used to generate a circuit pattern to be formed
on an individual layer of the IC. This pattern can be transferred
onto a target portion (e.g., comprising part of, one, or several
dies) on a substrate (e.g., a silicon wafer). Transfer of the
pattern is typically via imaging the pattern using a UV radiation
beam onto a layer of radiation-sensitive material (resist) provided
on the substrate. In general, a single substrate will contain a
network of adjacent target portions that are successively
patterned. Known lithographic apparatus include so-called steppers,
in which each target portion is irradiated by exposing an entire
pattern onto the target portion at one time, and so-called
scanners, in which each target portion is irradiated by scanning
the pattern through a radiation beam in a given direction (the
"scanning" direction) while synchronously scanning the substrate
parallel or anti-parallel to this direction. It is also possible to
transfer the pattern from the patterning device to the substrate by
imprinting the pattern onto the substrate.
[0005] Conventionally, a clamping device is used to securely hold
an object, such as a reticle or a substrate, to a supporting base
structure, referred to as a "stage." The "stage" is alternatively
referred to as a "table," a "frame," or a "force frame." The clamp
can be referred to as a "chuck." A stage may be coupled to a chuck
by a variety of means, including kinematic supports at three
points. A chuck may also be constructed integral to the stage.
During movement of the stage, or during an exposure operation, the
object is typically securingly coupled to the chuck using a normal
force (i.e., a force acting perpendicular to the chuck) generated
by electrostatic attraction or a partial vacuum between the object
and the chuck. The normal force and a normal stiffness of the chuck
serve to secure the object in a normal direction during the
movement or exposure. In a tangential direction, i.e., in a plane
of the chuck, the object is prevented from moving relative to the
chuck during movement or exposure through friction between the
chuck and the object.
[0006] When acceleration is imparted to the stage during exposure
or pre-exposure alignment, a stress is transferred from the stage
to the chuck, and this stress may cause the chuck as well as the
object to deform. Typically the transfer of acceleration-induced
stress from the stage to the chuck (as well as from the chuck to
the object) is not uniform. This gives rise to a potential for slip
between the chuck and the object, especially in cases where the
chuck deformation is large. Chuck deformation may also be caused by
temperature differences between the stage, the chuck, and/or the
object, resulting in slippage of the object relative to the
chuck.
[0007] A conventional approach to limit the transfer of stress
between the chuck and the stage is to use precision-machined
kinematic or semi-kinematic mounts to isolate the chuck from the
stage. However, kinematic mounts at a number of discrete locations
may not uniformly distribute the transfer of stress. An alternative
approach to distribute the transfer of stress more uniformly is to
use a chuck comprising a plurality of burls that make local
contacts with the supported object.
[0008] FIG. 2A depicts a conventional chuck 200 comprising a
plurality of burls 225. A stage 230 holds an object 210, e.g., by
electrostatic force applied through a planar electrode 220 in a
normal direction. Object 210 has a top surface 212 and a bottom
surface 214, which is opposite top surface 212. Burls 225 support
object 210. Each of the burls 225 acts like a spring, shown
symbolically as spring 205, providing a predetermined amount of
shear compliance.
[0009] FIG. 2B is a bottom view showing bottom surface 214 of
object 210. Top ends of burls 225 form local contacts 227 at bottom
surface 214 of object 210.
[0010] Dimension and arrangement of burls 225 may be tailored to
some extent to provide shear compliance. However, materials used in
burls 225 have many additional requirements, including but not
limited to, hardness, machineability, coefficient of thermal
expansion, etc. Thus, it may be difficult to tailor burls 225 for a
desired shear compliance in all directions of interest. For
example, while it is desirable to have a high shear compliance at
an interface of object 210 and burls 225, it is also desirable to
have a low normal compliance at the interface. Burls 225 that
directly contact object 210 typically have high compliance in
normal direction as well, making it harder to optimize the overall
shear compliance of the system. Moreover, burls 225 with the
desired shear compliance are typically long and slender, and their
shape makes electrostatic clamping of the object quite challenging.
Additionally, planarity of object 210 may be compromised due to
non-uniform stress distribution in burls 225.
SUMMARY
[0011] It is desirable to design a chuck that provides a desired
shear compliance to minimize slippage of a supported object under a
condition of stress, but does not suffer from the limitations
described above.
[0012] According to a first embodiment of the present invention, a
system comprises a chuck and an array of elongated elements having
first and second respective ends, such that the first ends contact
the chuck and the second ends contact a stage. Through using the
array of elongated elements, a transfer of stress between the stage
and the chuck is rendered substantially uniform, resulting in
minimization of slippage of an object relative to the first surface
of the chuck during a movement of the chuck relative to the
stage.
[0013] According to another embodiment, a method comprises coupling
an array of elongated elements between a chuck and a stage, such
that longitudinal axes of the elongated elements are normal to the
chuck and the stage, and first ends of the elongated elements
contact a second surface of the chuck, and second ends of the
elongated elements contact the stage. Under a condition of stress,
a transfer of the stress between the stage and the chuck is
rendered substantially uniform through using the array of elongated
elements. The method further comprises supporting an object on a
first surface of the chuck, the first surface being opposite the
second surface. The method also comprises subjecting the chuck and
the stage to the condition of stress, and measuring deformations of
the chuck and the stage under the condition of stress to correlate
the measured deformations with slippage of the object relative to
the first surface of the chuck.
[0014] According to a further embodiment, a lithographic apparatus
comprises an illumination system configured to produce a beam of
radiation, a patterning device configured to pattern the beam of
radiation, a projection system configured to project the patterned
beam of radiation onto a substrate, and a support system. The
support system comprises a chuck having a first surface and a
second surface, and an array of elongated elements having first and
second respective ends and having longitudinal axes, the
longitudinal axes being normal to the second surface of the chuck,
such that the first ends contact the second surface of the chuck
and the second ends contact a stage. Through using the array of
elongated elements, a transfer of stress between the stage and the
chuck is substantially uniform, resulting in minimization of
slippage of an object relative to the first surface of the chuck
during a deformation of the chuck due to the stress. The pattering
device or the substrate is configured to be the object mounted on
the chuck.
[0015] According to yet another embodiment, a system supporting an
object comprises a chuck having a first surface that supports the
object; a stage that supports the chuck in one or more directions
of translation or rotation; and an interface layer between the
chuck and the stage with a relatively low stiffness in at least one
direction of translation or rotation with respect to the other
directions of translation or rotation, resulting in minimization of
slippage of the object relative to the first surface of the chuck
during deformation of the chuck due to a stress between the stage
and the chuck.
[0016] According to yet another embodiment, a system comprises a
chuck having a first surface and a second surface, which is located
opposite the first surface, wherein the chuck is configured to hold
an object; and an array of elongated elements having first and
second respective ends and having longitudinal axes normal to the
second surface of the chuck, wherein the first ends contact the
second surface of the chuck and the second ends contact a stage to
isolate the chuck from the stage by rigidly coupling the chuck to
the stage such that the array of elongated elements uniformly
distribute stress therebetween.
[0017] Further embodiments, features, and advantages of the present
inventions, as well as the structure and operation of the various
embodiments of the present invention, are described in detail below
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate one or more
embodiments of the present invention and, together with the
description, further serve to explain the principles of the
invention and to enable a person skilled in the pertinent art to
make and use the invention.
[0019] FIG. 1 schematically depicts a reticle-based lithographic
apparatus, according to an embodiment of the present invention.
[0020] FIGS. 2A and 2B schematically depict a chuck in a
lithographic apparatus comprising a plurality of burls supporting
an object.
[0021] FIG. 3 schematically depicts a support structure with a
chuck coupled to a stage through a shear layer comprising elongated
elements, according to an embodiment of the present invention.
[0022] FIGS. 4A and 4B schematically show details of the support
structure shown in FIG. 3, according to an embodiment of the
present invention.
[0023] FIGS. 4C and 4D schematically show top and side views of
detailed pin layouts of an example chuck with a shear layer,
according to an embodiment of the present invention.
[0024] FIG. 5 schematically depicts a deformation of the chuck, the
elongated elements, and the stage of FIG. 3, when an acceleration
force is imparted on the stage, according to an embodiment of the
present invention.
[0025] FIG. 6 schematically depicts an isometric view of a section
of a support structure, according to an embodiment of the present
invention, showing effects of thermal stress.
[0026] FIG. 7 schematically depicts deformations of the chuck, the
supported object, and the elongated elements of the shear layer
shown in FIG. 6, when there is no temperature gradient in the
stage, according to an embodiment of the present invention.
[0027] FIG. 8 schematically depicts deformations of the chuck, the
supported object, the stage, and the elongated elements of the
shear layer shown in FIG. 6, when there is an example temperature
gradient in the stage, according to an embodiment of the present
invention.
[0028] FIGS. 9A and 9B schematically show two different
configurations of the elongated elements of the shear layer of FIG.
3, according to two embodiments of the present invention.
[0029] FIGS. 10A-10C schematically show different views of an
embodiment of the present invention where an interface membrane
layer is used in between the chuck and the stage.
[0030] FIGS. 11 and 12 schematically show flowcharts describing
example processes, according to various embodiments of the present
invention.
[0031] One or more embodiments of the present invention will now be
described with reference to the accompanying drawings. In the
drawings, like reference numbers can indicate identical or
functionally similar elements. Additionally, the left-most digit(s)
of a reference number can identify the drawing in which the
reference number first appears.
DETAILED DESCRIPTION
[0032] This specification discloses one or more embodiments that
incorporate the features of this invention. The disclosed
embodiment(s) merely exemplify the invention. The scope of the
invention is not limited to the disclosed embodiment(s). The
invention is defined by the claims appended hereto.
[0033] The embodiment(s) described, and references in the
specification to "one embodiment", "an embodiment", "an example
embodiment", etc., indicate that the embodiment(s) described can
include a particular feature, structure, or characteristic, but
every embodiment cannot necessarily include the particular feature,
structure, or characteristic. Moreover, such phrases are not
necessarily referring to the same embodiment. Further, when a
particular feature, structure, or characteristic is described in
connection with an embodiment, it is understood that it is within
the knowledge of one skilled in the art to effect such feature,
structure, or characteristic in connection with other embodiments
whether or not explicitly described. Additionally, terms indicating
physical orientation, such as "top", "bottom", "side" etc. are used
for illustrative purposes only, and do not limit the invention to
any particular orientation.
[0034] Embodiments of the invention can be implemented in hardware,
firmware, software, or any combination thereof. Embodiments of the
invention can also be implemented as instructions stored on a
machine-readable medium, which can be read and executed by one or
more processors. A machine-readable medium can include any
mechanism for storing or transmitting information in a form
readable by a machine (e.g., a computing device). For example, a
machine-readable medium can include read only memory (ROM); random
access memory (RAM); magnetic disk storage media; optical storage
media; flash memory devices; electrical, optical, acoustical or
other forms of propagated signals (e.g., carrier waves, infrared
signals, digital signals, etc.), and others. Further, firmware,
software, routines, instructions can be described herein as
performing certain actions. However, it should be appreciated that
such descriptions are merely for convenience and that such actions
in fact result from computing devices, processors, controllers, or
other devices executing the firmware, software, routines,
instructions, etc.
Lithographic Apparatus
[0035] FIG. 1 schematically depicts an embodiment of lithographic
apparatus 100 suitable for use with one or more embodiments of the
present invention. The apparatus comprises an illumination system
(illuminator) IL configured to condition a radiation beam B (e.g.,
UV radiation or DUV radiation); a support structure (e.g., a mask
table) MT constructed to support a patterning device (e.g., a mask)
MA and connected to a first positioner PM configured to accurately
position the patterning device in accordance with certain
parameters; a substrate table (e.g., a wafer table) WT constructed
to hold a substrate (e.g., a resist-coated wafer) W and connected
to a second positioner PW configured to accurately position the
substrate in accordance with certain parameters; and a projection
system (e.g., a refractive projection lens system) PS configured to
project a pattern imparted to the radiation beam B by patterning
device MA onto a target portion C (e.g., comprising one or more
dies) of the substrate W.
[0036] The illumination system IL may include various types of
optical components, such as refractive, reflective, magnetic,
electromagnetic, electrostatic or other types of optical
components, or any combination thereof, for directing, shaping, or
controlling radiation.
[0037] The support structure MT supports, i.e., bears the weight
of, the patterning device MA. It holds the patterning device MA in
a manner that depends on the orientation of the patterning device
MA, the design of the lithographic apparatus 100, and other
conditions, such as for example whether or not the patterning
device MA is held in a vacuum environment. The support structure MT
can use mechanical, vacuum, electrostatic or other clamping
techniques to hold the patterning device MA. The support structure
MT may be a frame or a table, for example, which may be fixed or
movable as required. The support structure may ensure that the
patterning device MA is at a desired position, for example with
respect to the projection system PS. Any use of the terms "reticle"
or "mask" herein may be considered synonymous with the more general
term "patterning device."
[0038] The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
radiation beam with a pattern in its cross-section such as to
create a pattern in a target portion of the substrate. It should be
noted that the pattern imparted to the radiation beam may not
exactly correspond to the desired pattern in the target portion of
the substrate, for example if the pattern includes phase-shifting
features or so called assist features. Generally, the pattern
imparted to the radiation beam will correspond to a particular
functional layer in a device being created in the target portion,
such as an integrated circuit.
[0039] The patterning device may be transmissive or reflective.
Examples of patterning devices include masks, programmable mirror
arrays, and programmable LCD panels. Masks are well known in
lithography, and include mask types such as binary, alternating
phase-shift, and attenuated phase-shift, as well as various hybrid
mask types. An example of a programmable mirror array employs a
matrix arrangement of small mirrors, each of which can be
individually tilted so as to reflect an incoming radiation beam in
different directions. The tilted mirrors impart a pattern in a
radiation beam which is reflected by the mirror matrix.
[0040] The term "projection system" used herein should be broadly
interpreted as encompassing any type of projection system,
including refractive, reflective, catadioptric, magnetic,
electromagnetic and electrostatic optical systems, or any
combination thereof, as appropriate for the exposure radiation
being used, or for other factors such as the use of an immersion
liquid or the use of a vacuum. Any use of the term "projection
lens" herein may be considered as synonymous with the more general
term "projection system."
[0041] As here depicted, the apparatus is of a transmissive type
(e.g., employing a transmissive mask). Alternatively, the apparatus
may be of a reflective type (e.g., employing a programmable mirror
array of a type as referred to above, or employing a reflective
mask).
[0042] The lithographic apparatus 100 may be of a type having two
(dual stage) or more substrate tables (and/or two or more mask
tables). In such "multiple stage" machines 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 exposure.
[0043] Referring to FIG. 1, the illuminator IL receives a radiation
beam from a radiation source SO. The source SO and the lithographic
apparatus 100 may be separate entities, for example when the source
SO is an excimer laser. In such cases, the source SO is not
considered to form part of the lithographic apparatus 100 and the
radiation beam B is passed from the source SO to the illuminator IL
with the aid of a beam delivery system BD comprising, for example,
suitable directing mirrors and/or a beam expander. In other cases,
the source SO may be an integral part of the lithographic apparatus
100, for example when the source is a mercury lamp. The source SO
and the illuminator IL, together with the beam delivery system BD
if required, may be referred to as a radiation system.
[0044] The illuminator IL may comprise an adjuster AD for adjusting
the angular intensity distribution of the radiation beam.
Generally, at least the outer and/or inner radial extent (commonly
referred to as .sigma.-outer and .sigma.-inner, respectively) of
the intensity distribution in a pupil plane of the illuminator IL
can be adjusted. In addition, the illuminator IL may comprise
various other components, such as an integrator IN and a condenser
CO. The illuminator IL may be used to condition the radiation beam
B, to have a desired uniformity and intensity distribution in its
cross-section.
[0045] The radiation beam B is incident on the patterning device
(e.g., mask MA), which is held on the support structure (e.g., mask
table MT), and is patterned by the patterning device. Having
traversed the mask MA, the radiation beam B passes through the
projection system PS, which focuses the beam onto a target portion
C of the substrate W. With the aid of the second positioner PW and
position sensor IF (e.g., an interferometric device, linear encoder
or capacitive sensor), the substrate table WT can be moved
accurately, e.g. so as to position different target portions C in
the path of the radiation beam B. Similarly, the first positioner
PM and another position sensor (which is not explicitly depicted in
FIG. 1) can be used to accurately position the mask MA with respect
to the path of the radiation beam B, e.g., after mechanical
retrieval from a mask library, or during a scan. In general,
movement of the mask table MT may be realized with the aid of a
long-stroke module (coarse positioning) and a short-stroke module
(fine positioning), which form part of the first positioner PM.
Similarly, movement of the substrate table WT may be realized using
a long-stroke module and a short-stroke module, which form part of
the second positioner PW. In the case of a stepper (as opposed to a
scanner) the mask table MT may be connected to a short-stroke
actuator only, or may be fixed. Mask MA and substrate W may be
aligned using mask alignment marks M1, M2 and substrate alignment
marks P1, P2. Although the substrate alignment marks as illustrated
occupy dedicated target portions, they may be located in spaces
between target portions (these are known as scribe-lane alignment
marks). Similarly, in situations in which more than one die is
provided on the mask MA, the mask alignment marks may be located
between the dies.
[0046] The depicted apparatus could be used in at least one of the
following modes:
[0047] 1. In step mode, the mask table MT and the substrate table
WT are kept essentially stationary, while an entire pattern
imparted to the radiation beam is projected onto a target portion C
at one time (i.e., a single static exposure). The substrate table
WT is then shifted in the X and/or Y direction so that a different
target portion C can be exposed. In step mode, the maximum size of
the exposure field limits the size of the target portion C imaged
in a single static exposure.
[0048] 2. In scan mode, the mask table MT and the substrate table
WT are scanned synchronously while a pattern imparted to the
radiation beam is projected onto a target portion C (i.e., a single
dynamic exposure). The velocity and direction of the substrate
table WT relative to the mask table MT may be determined by the
(de-)magnification and image reversal characteristics of the
projection system PS. In scan mode, the maximum size of the
exposure field limits the width (in the non-scanning direction) of
the target portion in a single dynamic exposure, whereas the length
of the scanning motion determines the height (in the scanning
direction) of the target portion.
[0049] 3. In another mode, the mask table MT is kept essentially
stationary holding a programmable patterning device, and the
substrate table WT is moved or scanned while a pattern imparted to
the radiation beam is projected onto a target portion C. In this
mode, generally a pulsed radiation source is employed and the
programmable patterning device is updated as required after each
movement of the substrate table WT or in between successive
radiation pulses during a scan. This mode of operation can be
readily applied to maskless lithography that utilizes programmable
patterning device, such as a programmable mirror array of a type as
referred to above.
[0050] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0051] Although specific reference may be made in this text to the
use of lithographic apparatus in the manufacture of ICs, it should
be understood that the lithographic apparatus described herein may
have other applications, such as the manufacture of integrated
optical systems, guidance and detection patterns for magnetic
domain memories, flat-panel displays, liquid-crystal displays
(LCDs), thin-film magnetic heads, etc. The skilled artisan will
appreciate that, in the context of such alternative applications,
any use of the terms "wafer" or "die" herein may be considered as
synonymous with the more general terms "substrate" or "target
portion," respectively. The substrate referred to herein may be
processed, before or after exposure, in for example a track (a tool
that typically applies a layer of resist to a substrate and
develops the exposed resist), a metrology tool and/or an inspection
tool. Where applicable, the disclosure herein may be applied to
such and other substrate processing tools. Further, the substrate
may be processed more than once, for example in order to create a
multi-layer IC, so that the term substrate used herein may also
refer to a substrate that already contains multiple processed
layers.
[0052] The terms "radiation" and "beam" used herein encompass all
types of electromagnetic radiation, including ultraviolet (UV)
radiation (e.g., having a wavelength of or about 365, 248, 193, 157
or 126 nm) or extreme ultraviolet radiation (5 nm or above).
[0053] The term "lens," where the context allows, may refer to any
one or combination of various types of optical components,
including refractive and reflective optical components.
Example Embodiment of Object Support Structure
[0054] FIG. 3 shows an example support structure 300 for an object
210, according to an embodiment of the present invention. Support
structure 300 comprises an interface layer referred to as a
shear-compliant stress layer 320 (also referred to as the
"shear-layer") coupling a chuck 321 and a stage 230. Object 210 is
mounted on a first surface 322 of chuck 321. As mentioned above,
object 210 may be a patterning device or a substrate.
[0055] In various examples, stage 230 may be made of a variety of
materials, including, but not limited to, silicon-silicon carbide
(SiSiC), Invar, stainless steel, aluminum oxide, Zerodur.RTM. (a
glass-ceramic composite by Schott Glass Technologies), etc. In one
example, stage 230 may be kinematically supported by a plurality of
kinemetic mounts (not shown). A similar configuration may also be
used when various bearing arrangements, e.g., an air bearing, are
used for supporting of stage 230. In the example embodiment shown
in FIG. 3, stage 230 is driven magnetically in the XY plane. In
this example, a yoke 365 is housed within stage 230. Yoke 365 may
be comprise or any other suitable material. In this example,
z-direction magnetic actuators 370 are used to magnetically
levitate stage 230, so that stage 230 can be driven in the XY
plane.
[0056] In one example, chuck 321 is designed with high flatness, so
that object 210 is mounted with requisite flatness on first surface
322 of chuck 321. For example, chuck 321 may be made from a
material with a relatively low coefficient of thermal expansion,
such as Zerodur.RTM.. However, the present invention is not limited
to a Zerodur.RTM. chuck, and other materials may be used. Desirable
properties of the chuck material include chemical stability,
structural homogeneity, good machineability, etc.
[0057] In one example, shear-layer 320 may comprise an array of
elongated elements 325 (also referred to as "pins"), whose first
ends are coupled to a second surface 323 of chuck 321, second
surface 323 being opposite first surface 322 on which object 210 is
mounted. Elongated elements 325 may be evenly spaced. Elongated
elements 325 may not make direct contact with object 210, i.e., an
interface between elongated elements 325 and chuck 321 is some
distance away from the interface between chuck 321 and object 210.
In this configuration, it is easier to tailor the shear-compliance
of the elongated elements 325, because the normal compliance of
elongated elements 325 becomes less of a design issue.
Incorporation of shear-layer 320 enables achieving a relatively low
stiffness in at least one direction of translation or rotation with
respect to the other directions of translation or rotation of chuck
321. Elongated elements 325 may comprise materials including, but
not limited to, Invar, SiSiC, stainless steel, etc, depending on
the desired functionalities of shear-layer 320. In one example, a
primary functionality of shear-layer 320 may be to distribute
stress uniformly. Dimension and spatial arrangement of elongated
elements 325 may be chosen so that under a condition of stress, a
transfer of stress between stage 230 and chuck 321 is uniform. This
may be done, for example, because a uniform transfer of stress
minimizes the possibility of slippage of object 210 during
deformation of chuck 321.
[0058] In one example, support structure 300 allows for combining
disparate materials in a single construction that is easy to
manufacture, but provides for a flexible design. The structure may
allow for simultaneous reduction of mass and improvement of
stiffness in the normal direction. One example embodiment using
disparate materials comprises using Zerodur.RTM. for chuck 321,
Invar for pins 325, and SiSiC for stage 230. Another example
embodiment eliminates using Invar for pins 325, and comprises using
form-compliant pins or elongated burls integrated with stage 230
made of SiSiC or other materials, as appropriate. Yet another
embodiment comprises chuck 321, stage 230, and shear-layer 320
being made of a same material, e.g. Invar, Zerodur.RTM., etc.
[0059] Additionally, or alternatively, one or more additional
objects 350 and/or 360 may be supported by chuck 321. For example,
object 350 and/or 360 may be positional sensors, that are used for
determining a desired position and/or alignment of object 210.
Positional sensors 350 and/or 360 may measure displacement or
slippage of object 210 in the xy plane under a condition of stress
with respect to a reference position. The reference position may be
denoted by fixed coordinates or the initial position of object 210
prior to the condition of stress. Additional objects 350 and/or 360
may also be fiducial marks that facilitate initial positioning
and/or alignment of object 210. They may also assist in measuring a
relative displacement of object 210, and adjusting the position and
alignment of object 210.
[0060] FIG. 4A shows an upside-down view of support structure 300,
showing z-direction magnetic actuators 370 coupled to a bottom
surface 372 of stage 230.
[0061] FIG. 4B shows a cut-out view of the inner structure of stage
230, according to one embodiment of the present invention. In this
embodiment, stage 230 may not be constructed as a solid block in
order to reduce mass and accommodate other structures. A central
region 423 of stage 230 may comprise intersecting baffles 434 and
432 that cross each other in x and y directions, respectively. This
type of structure provides adequate structural strength and
stiffness for stage 230, while keeping the overall mass low.
[0062] FIG. 4C illustrates an example arrangement of elongated
elements 325 (i.e., an example pin layout) on a bottom surface 323
of the chuck 321. Contact areas of the elongated elements 325 on
the bottom surface 323 of the chuck 321 are denoted as 425. The
chuck 321 has a central region 424 that is aligned and coupled to
the central region 423 (shown in FIG. 4B) of the stage 230 through
the elongated elements 325. Although not specifically shown in FIG.
4C, object 210 may be mounted above central region 424. Extension
regions 422 and 427 outside central region 424 may also comprise
contact areas 425.
[0063] FIG. 4D illustrates a side view of chuck 321 coupled to
stage 230, and corresponds to the top view shown in FIG. 4C. In an
example embodiment, a height `h` of the elongated elements 325 may
be about 6 mm, and a pitch `p` of elongated elements 325 may be
about 20 mm. Each elongated element may have about a 2 mm diameter.
Other dimensional values may be used in alternative designs, as the
invention is not limited to any particular dimensional values, or
any particular arrangement of elongated elements 325.
Acceleration-Induced and Thermally-Induced Stress Simulation
[0064] FIGS. 5-8 illustrate results of computer simulations that
have been performed to predict expected deformation of chuck 321,
stage 230, and elongated elements 325 (shown in FIG. 3) under
expected conditions of stress. In one example, Computer Aided
Design (CAD) software, e.g., Solidworks.TM. (by Solidworks Corp. of
Concord, Mass.) can be used to construct the schematic geometric
figures to perform simulations. To perform the actual simulations
under conditions of stress, a design analysis software, e.g.,
ANSYS.RTM. (by ANSYS, Inc. of Canonsburg, Pa.) may be used.
[0065] In particular, FIG. 5 depicts deformations of components of
support structure 300 when an acceleration force 505 is imparted to
stage 230. In FIG. 5, a scale of the deformation is magnified to
more easily illustrate the nature of deformation of different
components of support structure 300. According to an example
simulation, deformation of chuck 321 beneath object 210 is as low
as about 1.5 nm when an acceleration force of about 10 g is
imparted to stage 230, deforming stage 230 by about 10-20 nm. An
exemplary shear stiffness value of about 30 N/um is exhibited by
elongated elements 325, which are assumed to be about 6 mm tall and
about 2 mm in diameter. In this example, chuck 321 is deformed in a
range of about 1-2 nm for acceleration as high as about 100
m/sec.sup.2. Compared to that, a conventional baseline support
structure construction may experience chuck deformation values as
high as 27 nm under similar acceleration.
[0066] FIG. 6 depicts an isometric view of a section 600 of a
support structure 300 (e.g., a quarter of the entire structure),
according to an embodiment of the present invention. In the
following FIGS. 7 and 8, deformations (greatly exaggerated)
produced due to temperature differences between object 210, chuck
321, and/or stage 230 are shown. The structure shown in FIG. 6 is
similar to the structure 300 shown in FIG. 3. The additional
objects 350 and 360 are not shown in FIG. 6. However, a cross
section view of optional cooling channels 615 are shown through
both chuck 321 and stage 230. Cooling channels 615 help in
maintaining a target temperature in portions of the support
structure. Baffles 434 and 432 running along x and y directions,
respectively, are also shown in FIG. 6.
[0067] FIG. 7-8 show the deformations (exaggerated for illustrative
purposes) of object 210, chuck 321, and elongated elements 325,
when support structure 300 of FIG. 6 is under a thermal stress due
to relative temperature differences. In this example, stage 230 may
comprise SiSiC. FIG. 7 shows a condition where there is no thermal
gradient in stage 230. This simulation shows a thermal overlay of
about 1.7 nm.
[0068] FIG. 8 shows the deformations (exaggerated for illustrative
purposes) of object 210, chuck 321, and elongated elements 325 when
a thermal gradient of about 0.05 K is assumed in the SiSiC stage
230. Stage 230 itself is deformed in this situation. Thermal
overlay is slightly improved in this situation.
Shear-Layer Pin Configurations
[0069] FIGS. 9A and 9B show two different configurations of
elongated elements 325, e.g., 325A and 325B, respectively, of a
shear layer, according to various embodiments of the present
invention. In both the embodiments, an epoxy layer 980 is used to
couple chuck 321 with stage 230 through elongated elements 325. In
FIG. 9A, a pin configuration 325A is shown, which has a flat first
end 990 coupled to chuck 321, and a second end 985 coupled to stage
230, for example in a close-fit hole 986 of stage 230 that may be
filled with epoxy. In FIG. 9B, a pin configuration 325B is shown,
which has a first end 992 coupled to chuck 321 in a loose-fit hole
993 of chuck 321, which may be filled with epoxy, and a second end
985 coupled to stage 230 in a close-fit hole 986 of stage 230,
which also may filled with epoxy.
[0070] As will be appreciated by persons skilled in the art,
various other configurations of the pins or elongated elements 325
may be used too without departing from the scope of the invention.
For example, brazing the pins to the chuck and/or the stage, using
fasteners (e.g., threaded joints), machining the pins or other
shaped structures directly into the chuck and/or the stage, etc.
are all viable alternative embodiments of the present
invention.
Alternative Embodiment of Object Support Structure with Interface
Membrane
[0071] FIGS. 10A-10C show an alternative embodiment 1000 of the
support structure 300, employing a shear-layer 1020, wherein an
interface membrane layer 1035 (see FIG. 10B) is disposed between a
chuck 321 and a stage 230. FIG. 10A shows an isometric view of
support structure 1000, a portion of which (enclosed within the
bounding square A) is shown with greater magnification in FIG. 10B.
In FIG. 10B, interface membrane layer 1035 is clearly seen.
Interface membrane layer 1035 may have pin patterns machined into
it, through which elongated elements 325 pass. Interface membrane
layer 1035 and elongated elements 325 may be made integral to each
other out of the same material, e.g., Invar, SiSiC etc. Thickness
of interface membrane layer 1035 is designed so that shear-layer
1020 can provide a desired shear compliance. FIG. 10C shows a
further magnified side view of a portion of support structure 1000
in square A in FIG. 10A, showing details of shear-layer 1020.
Methods for Measuring Object Slippage under Stress
[0072] FIGS. 11 and 12 schematically illustrate flowcharts of
methods 1100 and 1200, respectively, according to embodiments of
the present invention. Method 1100 relates to acceleration-induced
stress in the support structure, and method 1200 relates to thermal
stress in the support structure. In one example, methods 1100 and
1200 can be practiced by one or more of the systems discussed
above.
[0073] In block 1110, a chuck and a stage are coupled through a
shear layer including elongated elements.
[0074] In block 1115, a patterning device or a substrate is
supported on the chuck.
[0075] In block 1120, an acceleration is imparted to the stage. As
a result, the stage, the elongated elements and the chuck are
deformed.
[0076] In block 1125, deformations of the chuck are measured.
[0077] In block 1130, measured deformations of the chuck is
correlated with a slippage of the patterning device or the
substrate on the chuck.
[0078] In FIG. 12, blocks 1210, 1215, 1225, and 1230 of method 1200
are substantially identical to blocks 1110, 1115, 1125, and 1130,
respectively, of method 1100. However, in block 1220, thermal
stress is induced in the support structure due to temperature
difference between the stage, the chuck, and the patterning device
or substrate.
[0079] Additionally, or alternatively, in other embodiments a
method may be used when a stress is produced by a combination of
acceleration and temperature difference.
CONCLUSION
[0080] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. It will be
apparent to persons skilled in the relevant art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention. Thus, the breadth and
scope of the present invention should not be limited by any of the
above-described exemplary embodiments, but should be defined only
in accordance with the following claims and their equivalents.
[0081] It is to be appreciated that the Detailed Description
section, and not the Summary and Abstract sections, is intended to
be used to interpret the claims. The Summary and Abstract sections
can set forth one or more, but not all exemplary embodiments of the
present invention as contemplated by the inventor(s), and thus, are
not intended to limit the present invention and the appended claims
in any way.
* * * * *