U.S. patent application number 12/285733 was filed with the patent office on 2009-02-19 for contamination barrier and lithographic apparatus comprising same.
This patent application is currently assigned to ASML NETHERLANDS B.V.. Invention is credited to Arnoud Cornelis Wassink.
Application Number | 20090045357 12/285733 |
Document ID | / |
Family ID | 38190761 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090045357 |
Kind Code |
A1 |
Wassink; Arnoud Cornelis |
February 19, 2009 |
Contamination barrier and lithographic apparatus comprising
same
Abstract
A rotatable contamination barrier is disclosed that has a
plurality of closely packed blades configured to trap contaminant
material coming from a radiation source. The blades are radially
oriented relative to a central rotation axis of the contamination
barrier. The blades comprise a metal compound having crystals
oriented generally radially relative to the central rotation
axis.
Inventors: |
Wassink; Arnoud Cornelis;
(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: |
38190761 |
Appl. No.: |
12/285733 |
Filed: |
October 14, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11391691 |
Mar 29, 2006 |
7453071 |
|
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12285733 |
|
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Current U.S.
Class: |
250/504R ;
250/492.2; 29/894.32; 72/340; 72/352 |
Current CPC
Class: |
F24F 1/0071 20190201;
G03F 7/70916 20130101; F24F 13/28 20130101; F24F 8/10 20210101;
Y10T 29/49496 20150115; F24F 8/108 20210101; F24F 8/158 20210101;
G03F 7/70983 20130101 |
Class at
Publication: |
250/504.R ;
250/492.2; 72/352; 72/340; 29/894.32 |
International
Class: |
G03F 7/20 20060101
G03F007/20; B21K 1/36 20060101 B21K001/36; B21J 5/06 20060101
B21J005/06 |
Claims
1-15. (canceled)
16. A method of providing a rotatable contamination barrier, the
method comprising: axially compressing a rod of metal compound
material having orientable crystals by forging so that the rod
starts to expand in an expansion zone and the crystals radially
align in the expansion zone; and cutting a blade structure in the
expansion zone around a central zone, so as to provide the
contamination barrier.
17. The method of claim 16, wherein the forging is carried out at a
temperature above 800.degree. C.
18. The method of claim 16, wherein the cutting is performed by
arcing, electrochemical machining, or both.
19. A method of providing a rotatable contamination barrier, the
method comprising: providing a folded blade shape from a rolled
sheet of metal compound material having a uniform crystal
orientation oriented along a rolling direction, the fold oriented
transverse to the rolling direction; engaging the folds by mounting
elements to hold the folds parallel to a central rotation axis of
the contamination barrier; and orienting the blades radially
relative to the rotation axis, so as to provide the contamination
barrier.
20. A rotatable contamination barrier obtainable by the method of
claim 16.
21. (canceled)
22. A rotatable contamination barrier obtainable by the method of
claim 19.
23. The method of claim 16, wherein the metal compound has a creep
strength of more than 100 MPa for a production of 1 percent creep
in 1000 hours, at a temperature of 800.degree. C.
24. The method of claim 16, wherein the metal compound is a
molybdenum metal compound or an alloy thereof.
25. The method of claim 24, wherein the molybdenum alloy comprises
hafnium, zirconium, titanium, lantanum, cobalt, an oxide of any of
the foregoing, a carbide of any of the foregoing, or any
combination of the foregoing.
26. The method of claim 24, wherein the molybdenum alloy comprises
molybdenum, carbon, and at least one selected out of the group of
titanium, zirconium or hafnium.
27. The method of claim 24, wherein the molybdenum alloy comprises
an oxygen dispersed strengthened (ODS) reinforcement material.
28. The method of claim 16, wherein the metal compound comprises a
nickel, chromium, cobalt, molybdenum, aluminum, and titanium
alloy.
29. The method of claim 16, wherein the metal compound comprises at
least one selected out of the group of tantalum, hafnium, titanium,
zirconium, molybdenum, lantanum, cobalt, iron, nickel, chromium,
aluminum, tungsten, an oxide of any of the foregoing, or a carbide
of any of the foregoing.
30. The method of claim 16, wherein a blade of the blade structure
has an increased thickness at a position closer to the central zone
than at a position further away from the central zone.
31. The method of claim 19, wherein the metal compound has a creep
strength of more than 100 MPa for a production of 1 percent creep
in 1000 hours, at a temperature of 800.degree. C.
32. The method of claim 19, wherein the metal compound is a
molybdenum metal compound or an alloy thereof.
33. The method of claim 32, wherein the molybdenum alloy comprises
hafnium, zirconium, titanium, lantanum, cobalt, an oxide of any of
the foregoing, a carbide of any of the foregoing, or any
combination of the foregoing.
34. The method of claim 32, wherein the molybdenum alloy comprises
molybdenum, carbon, and at least one selected out of the group of
titanium, zirconium or hafnium.
35. The method of claim 32, wherein the molybdenum alloy comprises
an oxygen dispersed strengthened (ODS) reinforcement material.
36. The method of claim 19, wherein the metal compound comprises a
nickel, chromium, cobalt, molybdenum, aluminum, and titanium
alloy.
37. The method of claim 19, wherein the metal compound comprises at
least one selected out of the group of tantalum, hafnium, titanium,
zirconium, molybdenum, lantanum, cobalt, iron, nickel, chromium,
aluminum, tungsten, an oxide of any of the foregoing, or a carbide
of any of the foregoing.
Description
FIELD
[0001] The present invention relates to a contamination barrier and
a lithographic apparatus comprising the same.
BACKGROUND
[0002] 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 onto a layer of
radiation-sensitive metal compound (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.
[0003] Radiation sources used in EUV lithography typically generate
contaminant material that is harmful to the optics and the working
environment wherein the lithographic process is carried out. Such
is especially the case for EUV sources operating via a laser
induced plasma or discharge plasma. Hence, in EUV lithography, a
desire exists to limit the contamination of the optical system
arranged to condition the beam of radiation coming from an EUV
source. To this end, a foil trap, for instance, as disclosed in
European patent application publication EP1491963, has been
proposed. A foil trap uses a high number of closely packed foils or
blades. Contaminant debris, such as micro-particles, nano-particles
and ions can be trapped in the walls provided by the blades. Thus,
the foil trap functions as a contamination barrier trapping
contaminant material from the source.
SUMMARY
[0004] In an embodiment, a rotatable foil trap may be oriented with
a rotation axis along an optical axis of the system, in particular
in front of an extreme ultraviolet radiation source configured to
provide extreme ultraviolet radiation. The blades configured to
trap contaminant material thus may be radially oriented relative to
a central rotation axis of the contamination barrier and may be
aligned substantially parallel to the direction of radiation. By
rotating the foil trap at a sufficiently high speed, traveling
contaminant debris may be captured by the blades of the contaminant
barrier. Due to design limitations, the rotation speed of the
contaminant barrier may be quite high, since otherwise the length
of the blades along the direction of travel of the debris would be
unacceptably large. Typical revolution speeds are 15000-30000 RPM,
speeds which may cause considerable stress in the metal compound of
the contaminant barrier, in particular, in the operative
temperature of the radiation source, where the contaminant barrier
may heat up to temperatures well above 600.degree. C. Furthermore,
potential breakdown of the contaminant barrier may be harmful for
the machine, and may cause considerable costly down time. In an
embodiment, a radiation system configured to provide a projection
beam of radiation comprises a rotatable contamination barrier
comprising a plurality of closely packed blades configured to trap
contaminant material coming from a radiation source.
[0005] It is desirable, for example, to provide a contamination
barrier that is more robust and which has an increased strength, in
particular, the blades thereof.
[0006] According to an aspect of the invention, there is provided a
rotatable contamination barrier for use in an EUV system, the
barrier comprising a plurality of closely packed blades configured
to trap contaminant material coming from an EUV radiation source,
the blades radially oriented relative to a central rotation axis of
the contamination barrier, wherein the blades comprise a metal
compound having a uniform crystal orientation oriented generally
radially relative to the central rotation axis.
[0007] According to an aspect of the invention, there is provided a
method of providing a rotatable contamination barrier, the method
comprising:
[0008] axially compressing a rod of metal compound material having
orientable crystals by forging so that the rod starts to expand in
an expansion zone and the crystals radially align in the expansion
zone; and
[0009] cutting a blade structure in the expansion zone around a
central zone, so as to provide the contamination barrier.
[0010] According to an aspect of the invention, there is provided a
method of providing a rotatable contamination barrier, the method
comprising:
[0011] providing a folded blade shape from a rolled sheet of metal
compound material having a uniform crystal orientation oriented
along a rolling direction, the fold oriented transverse to the
rolling direction;
[0012] engaging the folds by mounting elements to hold the folds
parallel to a central rotation axis of the contamination barrier;
and
[0013] orienting the blades radially relative to the rotation axis,
so as to provide the contamination barrier.
[0014] According to an aspect of the invention, there is provided a
lithographic apparatus, comprising:
[0015] a rotatable contamination barrier comprising a plurality of
closely packed blades configured to trap contaminant material
coming from a radiation source, the blades radially oriented
relative to a central rotation axis of the contamination barrier,
wherein the blades comprise a metal compound material having a
uniform crystal orientation oriented generally radially relative to
the central rotation axis;
[0016] an illumination system configured to condition a beam of
radiation;
[0017] a support constructed to support a patterning device, the
patterning device being capable of imparting the radiation beam
with a pattern in its cross-section to form a patterned radiation
beam;
[0018] a substrate table constructed to hold a substrate; and
[0019] a projection system configured to project the patterned
radiation beam onto a target portion of the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Embodiments of the 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:
[0021] FIG. 1 depicts a lithographic apparatus according to an
embodiment of the invention;
[0022] FIG. 2 shows a general setup of a rotatable foil trap
according to an embodiment of the invention;
[0023] FIG. 3 shows schematically the steps for manufacturing a
monolithic foil trap according to an embodiment of the
invention;
[0024] FIG. 4 shows schematically an embodiment of the invention
having folded blades;
[0025] FIG. 5 shows a graph showing creep strengths of various
metal compounds; and
[0026] FIG. 6 shows a micrograph of a cross sectional view of a
material for use in the foil trap according to an embodiment of the
invention.
DETAILED DESCRIPTION
[0027] FIG. 1 schematically depicts a lithographic apparatus
according to one embodiment of the invention. The apparatus
comprises:
[0028] an illumination system (illuminator) IL configured to
condition a radiation beam B (e.g. UV radiation or EUV
radiation);
[0029] 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;
[0030] 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
[0031] 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.
[0032] The illumination system 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.
[0033] The support structure holds the patterning device in a
manner that depends on the orientation of the patterning device,
the design of the lithographic apparatus, and other conditions,
such as for example whether or not the patterning device is held in
a vacuum environment. The support structure can use mechanical,
vacuum, electrostatic or other clamping techniques to hold the
patterning device. The support structure 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 is at a desired
position, for example with respect to the projection system. Any
use of the terms "reticle" or "mask" herein may be considered
synonymous with the more general term "patterning device."
[0034] 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.
[0035] 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.
[0036] 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".
[0037] As here depicted, the apparatus is of a reflective type
(e.g. employing a reflective mask). Alternatively, the apparatus
may be of a transmissive type (e.g. employing a transmissive
mask).
[0038] The lithographic apparatus may be of a type having two (dual
stage) or more substrate tables (and/or two or more support
structures). 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.
[0039] The lithographic apparatus may also be of a type wherein at
least a portion of the substrate may be covered by a liquid having
a relatively high refractive index, e.g. water, so as to fill a
space between the projection system and the substrate. An immersion
liquid may also be applied to other spaces in the lithographic
apparatus, for example, between the mask and the projection system.
Immersion techniques are well known in the art for increasing the
numerical aperture of projection systems. The term "immersion" as
used herein does not mean that a structure, such as a substrate,
must be submerged in liquid, but rather only means that liquid is
located between the projection system and the substrate during
exposure.
[0040] Referring to FIG. 1, the illuminator IL receives a radiation
beam from a radiation source SO. The source and the lithographic
apparatus may be separate entities, for example when the source is
an excimer laser. In such cases, the source is not considered to
form part of the lithographic apparatus and the radiation beam 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 may be an
integral part of the lithographic apparatus, 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.
[0041] The illuminator IL may comprise an adjuster for adjusting
the angular intensity distribution of the radiation beam.
Generally, at least the outer and/or inner radial extent (commonly
referred to as i-outer and .sigma.-inner, respectively) of the
intensity distribution in a pupil plane of the illuminator can be
adjusted. In addition, the illuminator IL may comprise various
other components, such as an integrator and a condenser. The
illuminator may be used to condition the radiation beam, to have a
desired uniformity and intensity distribution in its
cross-section.
[0042] 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 patterning device 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 IF2 (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 IF1 can be used to
accurately position the patterning device 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
support structure 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 support structure MT may be connected to a
short-stroke actuator only, or may be fixed. Patterning device MA
and substrate W may be aligned using patterning device 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 patterning
device MA, the patterning device alignment marks may be located
between the dies.
[0043] The depicted apparatus could be used in at least one of the
following modes:
[0044] 1. In step mode, the support structure 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.
[0045] 2. In scan mode, the support structure 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 support structure 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.
[0046] 3. In another mode, the support structure 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.
[0047] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0048] FIG. 2 schematically shows a radiation system 1 configured
to provide a projection beam of radiation. The radiation system 1
comprises an extreme ultraviolet radiation source 2 configured to
provide extreme ultraviolet radiation. In the Figure, the dashed
lines represent EUV radiation 3 coming from an EUV source 2,
typically a laser induced plasma source or a plasma discharge
source such as a tin, lithium or xenon source, however, other
sources are possible, in particular, any other source that produces
EUV radiation in combination with fast particles that escape from
the source 2 and that should be trapped in order to prevent damage
to the downstream optics of the lithographic apparatus (not shown).
Further, a rotatable contamination barrier 4 is provided comprising
a plurality of closely packed blades 5 configured to trap
contaminant material coming from the radiation source 2. The blades
5 are radially oriented relative to a central rotation axis 6 of
the contamination barrier 4. Another name for the barrier is a
(rotatable) foil trap. By rotation of the blades 5, fast moving
particles, in particular, tin particles and gaseous and ion like
particles traveling away from the source 2 can be trapped while EUV
radiation, due to the speed of light, can travel generally
unhindered by the blades 5.
[0049] The foil trap 4 thus functions as a contamination barrier to
trap contaminant material coming from the radiation source 2.
Typically, the blades 5 are arranged at a distance of 0.3-5 mm
apart and have a generally rectangular form. Advantageously, the
source 2 is positioned at an intersection of extended planes
through the plurality of blades 5 which define an optical center of
the contamination barrier 1, which in FIG. 2 coincides with the
central axis 6 of the foil trap 4: For an ideal point like EUV
source 2 at this center, radiation would pass in a direction
generally parallel to an orientation of the blades 5. Thus,
shielding of EUV radiation is low and only takes place over a
thickness of the blade (which, in an embodiment, is accordingly
kept small without compromising mechanical integrity). A typical
value of the thickness of the blade can be about 100 microns, which
may result in a shielding of about 10 percent of the radiation.
[0050] To improve structural integrity, according to an embodiment
of the invention, the blades 5 comprise a metal compound having
crystals oriented generally radially relative to the central
rotation axis 6. In this aspect, the term "compound" is deem to
encompass all type of combinations of metals, in pure form or in
alloy form, in combination with any other substance, in particular,
oxides and/or carbides thereof. Furthermore, the term "crystal" is
used to indicate the crystalline zones in metal, which have typical
dimensions of several tens to hundreds of micrometers and which
provide an orientation to the metal compound, in particular, a
configurable orientation, for instance, by forging the metal
compound to orient the crystal zones in a single general direction.
An example of such crystalline zones will be discussed below with
reference to FIG. 6. Due to the high rotation speed, in particular,
with a high process temperature of the contamination barrier of
well above 600.degree. C., considerable stress may arise in the
blades 5. For example, for a plasma source 2, an estimated particle
speed may be about 600-1000 m/s. Typical dimensions of the blades 5
are 40-50 mm long in the radial direction, and 15-25 mm long in the
axial direction. A typical thickness of a blade is 80-120
micrometers. For such dimensions, the blades 5, when rotated at
speeds of 15000-30000 RPM, may experience a tensile force of about
100-200 N/mm.sup.2.
[0051] FIG. 3 schematically shows an embodiment of the invention,
wherein the crystalline zones of the metal compound are provided
oriented radially relative to the rotation axis 6 of the
contamination barrier 4. In this embodiment, a monolithic
contamination barrier, in particular, a blade structure 10 is
shown, which obviates the need for providing welds or bonds between
the blades 5 and the rotation axis 6. The monolithic rotatable
contamination barrier is formed from a rod-shaped metal compound 7
having crystals with a configurable orientation. In particular, a
compound 7 may be used which is a molybdenum alloy containing
molybdenum, 1-1.4 weight percentage hafnium, and 0.05-0.15 weight
percentage carbon, commercially obtainable as MHC.RTM. from, for
instance, Plansee SE. The term rod-shaped does not imply a specific
form, in particular, the cross-section may be any form such as
square, circular, etc. It merely implies that the metal compound 7
has a sufficient axial dimension so that it can be compressed while
leaving a substantial thickness equal to a desired axial length of
the contamination barrier. Through axial compressing of the rod,
schematically illustrated in FIG. 3A, the rod will start to expand
in an expansion zone, which typically would be the end side 8 of
the rod 7. This compressing step can be carried out by forging, in
particular, hammering (schematically illustrated by arrows H) the
compound at a sufficiently high temperature (typically
800-1000.degree. C.) so that the compound is axially shortened.
Consequently, the crystals in the expansion zone 8 will become
radially aligned. The object 9 thus obtained is a flattened piece,
illustrated in FIG. 3B, with a thickness generally corresponding to
the axial length of the contamination barrier 1 and with a diameter
generally corresponding to a diameter of the blade configuration of
the barrier 1.
[0052] Next, a blade structure 10 can be cut out in the expansion
zone 8 around a central zone as is illustrated in FIG. 3C. The
central zone thus forms the rotation axis 6 of the contamination
barrier 1. Typical cutting processes feasible for cutting the blade
structure 10 are arcing and/or electro-chemical machining. In the
arcing process, typically, a wire is held axially aligned to the
object 9 and the blade structure 10 is cut out following a radial
pattern of projected blades with an arcing wire. FIG. 3D
schematically shows a detail of blade structure 10 shown in FIG.
3C, in particular, the passage zone 11 forming a connection between
(part of) the central axis 6 and a single blade 5. In the passage
area 11, the orientation of the crystals is, due to the radial
expansion process, oriented radially, providing strength in the
passage zone 11. The blade connection may be made further stronger
by providing an increased thickness 12 to the passage zone 11
relative to a thickness 13 of the blade higher up along a radial
direction. This enforces the connection and at the same time
reduces the tensile force exerted on the connection by diminishing
the mass of the blade 5.
[0053] FIG. 4 shows a further embodiment of the invention showing
crystals oriented along a radial direction, in particular, aligned
along a force direction of centripetal forces exerted on the blades
5. In the shown embodiment, a blade structure 10 is provided having
blades 5 that are mounted as folded leafs. In addition, mounting
elements 14 are provided to engage the folds 15 of the folded
leafs. The mounting elements 14 hold the folds 15 substantially
parallel to the central axis 6 of the contamination barrier 1. The
mounting elements may be wire elements or the like which are
provided on a cylindrical wall of the central axis 6 as shown.
Alternatively, the wire elements 14 may be provided buried in a
groove axially provided in a cylindrical wall of the central axis
6. The structure shown in FIG. 4 may be provided by a rolled sheet
of metal compound having a uniform crystal orientation oriented
along a rolling direction. The metal compound may be a molybdenum
compound as previously discussed, or, other type of compound(s) to
be discussed. From the rolled sheet, a blade shape can be provided
having a fold oriented transverse to the rolling direction. Next,
the folds 15 can be engaged to the central axis 6 by mounting
elements 14 to hold the folds 15 substantially parallel to the
central axis 6 of the contamination barrier 1. Depending on the
stiffness of the blades, a further structure, for example, an outer
ring, or a coating or the like may be provided to orient the blades
5 radially relative to the central axis 6.
[0054] FIG. 5 further shows an analysis of creep strengths of a
selection of various metal compounds. To provide sufficient creep
strength, which means a tensile force of well over 200 N/mm.sup.2
(about 250-350 N/mm.sup.2), a limiting factor may be the
recrystallization temperature, which is a temperature near the
melting temperature where the structural integrity of the metal
compound starts to disintegrate due to disintegration of the
crystal zones referenced as crystals previously. In the graph, the
specific temperature shown is the temperature, wherein
recrystallization becomes complete (100%), within one hour. It is
therefore appropriate to select a material that has a
recrystallization temperature well above the process temperature,
which can typically range from 700-900.degree. C.
[0055] Referring to the graph, pure (that is, having a weight
percentage of more than 99.95% Mo) molybdenum having a
recrystallization temperature of about 1000.degree. C. appears less
appropriate for use as a foil trap material. On the other hand, a
TZM alloy, which is a molybdenum alloy containing molybdenum,
0.3-0.7 weight percentage titanium, 0.06-0.1 weight percentage
zirconium and 0.005-0.06 weight percentage carbon has a
recrystallization temperature of 1200.degree. C. which is
considerably higher. Other materials having higher
recrystallization temperatures are tungsten (about 1100.degree. C.)
and tungsten rhenium (about 1400.degree. C.).
[0056] FIG. 6 shows a micrograph of a cross-sectional view of
oriented crystals 16 of a material for use in the foil trap
according to an embodiment of the invention. The particular
material is MLR, which is a molybdenum alloy comprising one or more
lantanum oxides that are provided by 0.1-1 weight percentage
La.sub.2O.sub.3. MLR (Molybdenum Lantanum Recrystallized) is
commercially obtainable from Plansee SE. Other materials of
interest are so called oxygen dispersed strengthened (ODS) alloys
or superalloys, which preserve a high structural integrity, even
when approaching a melting temperature. The ODS materials, such as
the above mentioned MLR, comprise one or more oxides provided on
the boundaries of the crystals amounting to increased structural
strength. Other types of such materials which can be used to
provide a metal compound material having crystals with configurable
orientation are ML (Molybdenum Lantanum) and MLS (Molybdenum
Lantanum Stress Free annealed) also obtainable from Plansee SE.
[0057] Another type of material having high structural (creep)
strength of above 200 N/mm.sup.2 is the superalloy Haynes 282.TM.,
which is a wrought gamma-prime strengthened alloy and contains
56-60 weight percentage nickel, 17-21 weight percentage chromium,
8-12 weight percentage cobalt, 8-9 weight percentage molybdenum,
1-2 weight percentage aluminum and 1.5-2.5 weight percentage
titanium. In particular, this material shows creep strength values
for 1 percentage creep in 1000 hours, of 33 N/mm.sup.2 for a
temperature of 927.degree. C.; 68 N/mm.sup.2 for a temperature of
871.degree. C.; 145 N/mm.sup.2 for a temperature of 816.degree. C.
and 241 N/mm.sup.2 for a temperature of 760.degree. C. It may
therefore provide reliable structural integrity having a creep
strength of more than 100 MPa for a production of 1 percent creep
in 1000 hours, at a working temperature of 800.degree. C.
[0058] Generally, metal compounds of interest to carry out one or
more embodiments of the invention are alloys comprising at least
one selected out the group of tantalum, hafnium, titanium,
zirconium, molybdenum, lantanum, cobalt, iron, nickel, chromium,
aluminum, oxides thereof, and/or carbides thereof.
[0059] 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.
[0060] Although specific reference may have been made above to the
use of embodiments of the invention in the context of optical
lithography, it will be appreciated that the invention may be used
in other applications, for example imprint lithography, and where
the context allows, is not limited to optical lithography. In
imprint lithography a topography in a patterning device defines the
pattern created on a substrate. The topography of the patterning
device may be pressed into a layer of resist supplied to the
substrate whereupon the resist is cured by applying electromagnetic
radiation, heat, pressure or a combination thereof. The patterning
device is moved out of the resist leaving a pattern in it after the
resist is cured.
[0061] 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, 355, 248, 193,
157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g.
having a wavelength in the range of 5-20 nm), as well as particle
beams, such as ion beams or electron beams.
[0062] The term "lens", where the context allows, may refer to any
one or combination of various types of optical components,
including refractive, reflective, magnetic, electromagnetic and
electrostatic optical components.
[0063] While specific embodiments of the invention have been
described above, it will be appreciated that the invention may be
practiced otherwise than as described. For example, the invention
may take the form of a computer program containing one or more
sequences of machine-readable instructions describing a method as
disclosed above, or a data storage medium (e.g. semiconductor
memory, magnetic or optical disk) having such a computer program
stored therein.
[0064] The descriptions above are intended to be illustrative, not
limiting. Thus, it will be apparent to one skilled in the art that
modifications may be made to the invention as described without
departing from the scope of the claims set out below.
* * * * *