U.S. patent application number 17/112278 was filed with the patent office on 2021-03-25 for fluid handling structure, a lithographic apparatus and a device manufacturing method.
This patent application is currently assigned to ASML Netherlands B.V.. The applicant listed for this patent is ASML NETHERLANDS B.V.. Invention is credited to David BESSEMS, Victor Manuel BLANCO CARBALLO, Erik Henricus Egidius Catharina EUMMELEN, Giovanni Luca GATTOBIGIO, Cornelius Maria ROPS, Walter Theodorus Matheus STALS, Ronald VAN DER HAM, Frederik Antonius VAN DER ZANDEN, Wilhelmus Antonius WERNAART.
Application Number | 20210088912 17/112278 |
Document ID | / |
Family ID | 1000005253589 |
Filed Date | 2021-03-25 |
United States Patent
Application |
20210088912 |
Kind Code |
A1 |
ROPS; Cornelius Maria ; et
al. |
March 25, 2021 |
FLUID HANDLING STRUCTURE, A LITHOGRAPHIC APPARATUS AND A DEVICE
MANUFACTURING METHOD
Abstract
A fluid handling structure for a lithographic apparatus
configured to contain immersion fluid to a region, the fluid
handling structure having, at a boundary of a space: at least one
gas knife opening in a radially outward direction of the space; and
at least one gas supply opening in the radially outward direction
of the at least gas knife opening relative to the space. The gas
knife opening and the gas supply opening both provide substantially
pure CO.sub.2 gas so as to provide a substantially pure CO.sub.2
gas environment adjacent to, and radially outward of, the
space.
Inventors: |
ROPS; Cornelius Maria;
(Waalre, NL) ; STALS; Walter Theodorus Matheus;
(Veldhoven, NL) ; BESSEMS; David; (Eindhoven,
NL) ; GATTOBIGIO; Giovanni Luca; (Eindhoven, NL)
; BLANCO CARBALLO; Victor Manuel; (Eindhoven, NL)
; EUMMELEN; Erik Henricus Egidius Catharina; (Eindhoven,
NL) ; VAN DER HAM; Ronald; (Maarheeze, NL) ;
VAN DER ZANDEN; Frederik Antonius; (Veldhoven, NL) ;
WERNAART; Wilhelmus Antonius; (Veldhoven, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASML NETHERLANDS B.V. |
Veldhoven |
|
NL |
|
|
Assignee: |
ASML Netherlands B.V.
Veldhoven
NL
|
Family ID: |
1000005253589 |
Appl. No.: |
17/112278 |
Filed: |
December 4, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16778635 |
Jan 31, 2020 |
10859919 |
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17112278 |
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15537214 |
Jun 16, 2017 |
10551748 |
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PCT/EP2015/078842 |
Dec 7, 2015 |
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16778635 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/70775 20130101;
G03B 27/52 20130101; G03F 7/70716 20130101; B01D 19/0005 20130101;
G03F 7/70341 20130101; B01D 19/0021 20130101 |
International
Class: |
G03F 7/20 20060101
G03F007/20; B01D 19/00 20060101 B01D019/00; G03B 27/52 20060101
G03B027/52 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2014 |
EP |
14199085.3 |
Claims
1. An immersion system comprising a fluid handling structure
configured to contain immersion fluid to a region, the fluid
handling structure having, at a boundary of a space: at least one
gas knife opening in a radially outward direction from the space;
and at least one gas supply opening in the radially outward
direction from the at least one gas knife opening relative to the
space; and the immersion system further comprising a gas supply
system configured to supply substantially pure CO.sub.2 gas through
the at least one gas knife opening and the at least one gas supply
opening so as to provide an atmosphere of substantially pure
CO.sub.2 gas adjacent to, and radially outward of, the space.
2. The immersion system of claim 1, wherein the gas exits the at
least one gas knife opening at a first gas velocity and the gas
exits the at least one gas supply opening at a second gas velocity,
the first gas velocity being greater than the second gas
velocity.
3. The immersion system of claim 1, wherein the substantially pure
CO.sub.2 gas is humidified CO.sub.2 gas.
4. An immersion system comprising a fluid handling structure
configured to contain immersion fluid to a region, the fluid
handling structure having, at a boundary of a space: at least one
gas knife opening in a radially outward direction from the space;
at least one gas supply opening in the radially outward direction
from the at least one gas knife opening relative to the space; and
a gas supply system configured to supply gas through the at least
one gas knife opening and the at least one gas supply opening,
wherein gas exits the at least one gas knife opening at a higher
gas velocity than gas exiting the at least one gas supply
opening.
5. The immersion system of claim 1, wherein the fluid handling
structure comprises a meniscus controlling feature to resist
passage of the immersion fluid in a radially outward direction from
the space, the meniscus controlling feature being radially inward
of the at least one gas knife opening.
6. The immersion system of claim 1, wherein the gas exits the at
least one gas knife opening at a first flow speed and the gas exits
the at least one gas supply opening at a second flow speed, the
first flow speed being greater than the second flow speed.
7. The immersion system of claim 1, wherein the fluid handling
structure comprises the gas supply system.
8. The immersion system of claim 1, wherein the gas supply system
comprises at least one gas source to provide gas to the at least
one gas knife opening and the at least one gas supply opening.
9. The immersion system of claim 8, wherein the gas supply system
comprises a first path between a first gas source and the at least
one gas knife opening and a second path between a second gas source
and the at least one gas supply opening, wherein the second path
comprises a flow restrictor section, and optionally, wherein the
flow restrictor section is a bend and/or reduction in a
flow-through area in the second path.
10. The immersion system of claim 9, wherein the first gas source
and the second gas source are the same gas source.
11. The immersion system of claim 1, wherein the at least one gas
knife opening and the at least one gas supply opening are on a
surface of the fluid handling structure facing a substrate and/or a
substrate table, wherein the at least one gas knife opening is
closer to the substrate and/or substrate table than the at least
one gas supply opening, and/or the at least one gas knife opening
has a smaller surface area on the surface of the fluid handling
structure than the at least one gas supply opening.
12. The immersion system of claim 1, wherein the fluid handling
structure is configured to dynamically control the amount of gas
supplied to the gas knife opening by redirecting gas to the gas
knife opening from the gas supply opening, or from the gas knife
opening to the gas supply opening.
13. A device manufacturing method comprising using the fluid
handling structure of claim 1 in a lithographic apparatus.
14. A lithographic apparatus comprising an immersion system
comprising the fluid handling structure of claim 1.
15. A device manufacturing method comprising using the fluid
handling structure of claim 4 in a lithographic apparatus.
16. A lithographic apparatus comprising an immersion system
comprising the fluid handling structure of claim 4.
17. A fluid handling structure configured to contain immersion
fluid to a region, the fluid handling structure having, at a
boundary of a space: at least one gas knife opening in a radially
outward direction from the space; and at least one gas supply
opening in the radially outward direction from the at least one gas
knife opening relative to the space, wherein the at least one gas
supply opening comprises a mesh, a sieve, porous material and/or
array of holes.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/778,635, filed on Jan. 31, 2020, now
allowed, which is a continuation of U.S. patent application Ser.
No. 15/537,214, filed on Jun. 16, 2017, now U.S. Pat. No.
10,551,748, which is the U.S. national phase entry of PCT patent
application no. PCT/EP2015/078842, filed on Dec. 7, 2015, which
claims the benefit of priority of European patent application no.
14199085.3, filed on Dec. 19, 2014, each of the foregoing
applications is incorporated herein in its entirety by
reference.
FIELD
[0002] The present description relates to a fluid handling
structure, a lithographic apparatus and a method for manufacturing
a device using a lithographic apparatus.
BACKGROUND
[0003] 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.
[0004] It has been proposed to immerse the substrate in the
lithographic projection apparatus in a liquid having a relatively
high refractive index, e.g. water, so as to fill a space between
the final element of the projection system PS and the substrate. In
an embodiment, the liquid is distilled water, although another
liquid can be used. An embodiment of the invention will be
described with reference to liquid. However, another fluid may be
suitable, particularly a wetting fluid, an incompressible fluid
and/or a fluid with higher refractive index than air, desirably a
higher refractive index than water. Fluids excluding gases are
particularly desirable. The point of this is to enable imaging of
smaller features since the exposure radiation will have a shorter
wavelength in the liquid. (The effect of the liquid may also be
regarded as increasing the effective numerical aperture (NA) of the
system and also increasing the depth of focus.) Other immersion
liquids have been proposed, including water with solid particles
(e.g. quartz) suspended therein, or a liquid with a nano-particle
suspension (e.g. particles with a maximum dimension of up to 10
nm). The suspended particles may or may not have a similar or the
same refractive index as the liquid in which they are suspended.
Other liquids which may be suitable include a hydrocarbon, such as
an aromatic, a fluorohydrocarbon, and/or an aqueous solution.
[0005] Submersing the substrate, or the substrate and the substrate
table, in a bath of liquid (see, for example, U.S. Pat. No.
4,509,852) means that there is a large body of liquid that must be
accelerated during a scanning exposure. This requires additional or
more powerful motors and turbulence in the liquid may lead to
undesirable and unpredictable effects.
[0006] In an immersion apparatus, immersion fluid is handled by an
immersion system, device, structure or apparatus. In an embodiment
the immersion system may supply immersion fluid and may be referred
to as a fluid supply system. In an embodiment the immersion system
may at least partly confine immersion fluid and may be referred to
as a fluid confinement system. In an embodiment the immersion
system may provide a barrier to immersion fluid and thereby be
referred to as a barrier member, such as a fluid confinement
structure. In an embodiment the immersion system creates or uses a
flow of gas, for example to help in controlling the flow and/or the
position of the immersion fluid. The flow of gas may form a seal to
confine the immersion fluid so the immersion system may comprise a
fluid handling structure, which may be referred to as a seal
member, to provide the flow of gas. In an embodiment, immersion
liquid is used as the immersion fluid. In that case the immersion
system may be a liquid handling system.
SUMMARY
[0007] If the immersion liquid is confined by an immersion system
to a localized area on a surface which is under the projection
system, a meniscus extends between the immersion system and the
surface. If the meniscus collides with a droplet on the surface,
this may result in inclusion of a bubble in the immersion liquid.
The droplet may be present on the surface for various reasons, for
example, due to a leakage from the immersion system. A bubble in
the immersion liquid can lead to imaging errors, for example by
interfering with a projection beam during imaging of the
substrate.
[0008] It is desirable, for example, to provide a lithographic
apparatus in which the likelihood of bubble inclusion is at least
reduced.
[0009] In an embodiment, there is provided an immersion system
comprising a fluid handling structure configured to contain
immersion fluid to a region external to the fluid handling
structure, the fluid handling structure having, at a boundary of a
space: at least one gas knife opening in a radially outward
direction from the space; and at least one gas supply opening in
the radially outward direction from the at least one gas knife
opening relative to the space; and the immersion system further
comprising a gas supply system configured to supply substantially
pure CO.sub.2 gas through the at least one gas knife opening and
the at least one gas supply opening so as to provide an atmosphere
of substantially pure CO.sub.2 gas adjacent to, and radially
outward of, the space.
[0010] In an embodiment, there is provided a device manufacturing
method comprising projecting a projection beam of radiation via an
immersion fluid onto a substrate in a lithographic apparatus
comprising an immersion system, wherein the immersion system
comprises a fluid handling structure configured to contain the
immersion fluid to a region external to the fluid handling
structure, the fluid handling structure having, at a boundary of a
space: at least one gas knife opening in a radially outward
direction from the space; and at least one gas supply opening in
the radially outward direction from the at least one gas knife
opening relative to the space; and the method comprising supplying
substantially pure CO.sub.2 gas through the at least one gas knife
opening and the at least one gas supply opening so as to provide an
atmosphere of substantially pure CO.sub.2 gas adjacent to, and
radially outward of, the space.
[0011] In an embodiment, there is provided a lithographic apparatus
comprising an immersion system comprising a fluid handling
structure configured to contain immersion fluid to a region
external to the fluid handling structure, the fluid handling
structure having, at a boundary of a space: at least one gas knife
opening in a radially outward direction from the space; and at
least one gas supply opening in the radially outward direction from
the at least one gas knife opening relative to the space; and the
immersion system further comprising a gas supply system configured
to supply substantially pure CO.sub.2 gas the at least one gas
knife opening and the at least one gas supply opening so as to
provide an atmosphere of substantially pure CO.sub.2 gas adjacent
to, and radially outward of, the space.
[0012] In an embodiment, there is provided an immersion system
comprising a fluid handling structure configured to contain
immersion fluid to a region, the fluid handling structure having,
at a boundary of a space: at least one gas knife opening in a
radially outward direction from the space; at least one gas supply
opening in the radially outward direction from the at least one gas
knife opening relative to the space; and a gas supply system
configured to supply gas through the at least one gas knife opening
and the at least one gas supply opening, wherein gas exits the at
least one gas knife opening at a higher gas velocity than gas
exiting the at least one gas supply opening.
[0013] In an embodiment, there is provided a device manufacturing
method comprising projecting a projection beam of radiation via an
immersion fluid onto a substrate in a lithographic apparatus
comprising an immersion system, wherein the immersion system
comprises a fluid handling structure configured to contain the
immersion fluid to a region external to the fluid handling
structure, the fluid handling structure having, at a boundary of a
space: at least one gas knife opening in a radially outward
direction from the space; and at least one gas supply opening in
the radially outward direction from the at least one gas knife
opening relative to the space; and the method comprising supplying
gas through the at least one gas knife opening and the at least one
gas supply opening, wherein gas exits the at least one gas knife
opening at a higher gas velocity than gas exiting the at least one
gas supply opening.
[0014] In an embodiment, there is provided a lithographic apparatus
comprising an immersion system comprising a fluid handling
structure configured to contain immersion fluid to a region
external to the fluid handling structure, the fluid handling
structure having, at a boundary of a space: at least one gas knife
opening in a radially outward direction from the space; and at
least one gas supply opening in the radially outward direction from
the at least one gas knife opening relative to the space; and the
immersion system further comprising a gas supply system configured
to supply gas through the at least one gas knife opening and the at
least one gas supply opening, wherein gas exits the at least one
gas knife opening at a higher gas velocity than gas exiting the at
least one gas supply opening.
[0015] In an embodiment, there is provided a fluid handling
structure configured to contain immersion fluid to a region, the
fluid handling structure having, at a boundary of a space: at least
one gas knife opening in a radially outward direction from the
space; and at least one gas supply opening in the radially outward
direction from the at least one gas knife opening relative to the
space, wherein the at least one gas supply opening comprises a
mesh.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] 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:
[0017] FIG. 1 depicts a lithographic apparatus according to an
embodiment of the invention;
[0018] FIGS. 2 and 3 depict an immersion system for use in a
lithographic projection apparatus;
[0019] FIG. 4 depicts, in cross-section, a further immersion system
for use in a lithographic projection apparatus;
[0020] FIG. 5 depicts, in plan, an immersion system for use in a
lithographic projection apparatus;
[0021] FIG. 6 depicts, in plan, an immersion system for use in a
lithographic projection apparatus;
[0022] FIG. 7 illustrates, in cross-section, the forces acting on a
droplet on a surface which result in a particular contact
angle;
[0023] FIG. 8 is a graph of critical scan speed versus pH of
immersion liquid;
[0024] FIG. 9 depicts, in cross-section, a further immersion system
for use in a lithographic projection apparatus;
[0025] FIG. 10 depicts, in cross-section an immersion system for
use in a lithographic apparatus;
[0026] FIG. 11 depicts, in cross-section an immersion system for
use in a lithographic apparatus;
[0027] FIG. 12 depicts, in cross-section an immersion system for
use in a lithographic apparatus; and
[0028] FIG. 13 depicts, in cross-section an immersion system for
use in a lithographic apparatus.
DETAILED DESCRIPTION
[0029] FIG. 1 schematically depicts a lithographic apparatus
according to an embodiment of the invention. The lithographic
apparatus comprises: [0030] an illuminator (otherwise referred to
as an illumination system) IL configured to condition a projection
beam B, the projection beam B being a radiation beam (e.g. UV
radiation, DUV radiation or any other suitable radiation); [0031] a
support structure (e.g. a mask support structure/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 MA in accordance with certain
parameters; [0032] a support table, e.g. a sensor table to support
one or more sensors, and/or a substrate table (e.g. a wafer table)
WT or "substrate support" constructed to hold a substrate (e.g. a
resist-coated substrate) W connected to a second positioning device
PW configured to accurately position the substrate W in accordance
with certain parameters; and [0033] a projection system (e.g. a
refractive projection lens system) PS configured to project a
pattern imparted to the projection beam B by patterning device MA
onto a target portion C (e.g. comprising one or more dies) of the
substrate W.
[0034] The illuminator 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.
[0035] The support structure MT supports, i.e. bears the weight of,
the patterning device MA. The support structure MT holds the
patterning device MA in a manner that depends on the orientation of
the patterning device MA, the design of the lithographic apparatus,
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 MT 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."
[0036] The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
projection beam B with a pattern in its cross-section such as to
create a pattern in a target portion C of the substrate W. It
should be noted that the pattern imparted to the projection beam B
may not exactly correspond to the desired pattern in the target
portion C of the substrate W, for example if the pattern includes
phase-shifting features or so called assist features. Generally,
the pattern imparted to the projection beam B will correspond to a
particular functional layer in a device being created in the target
portion C, such as an integrated circuit.
[0037] The patterning device MA 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
(e.g. a projection beam B) in different directions. The tilted
mirrors impart a pattern in a projection beam B which is reflected
by the mirror matrix.
[0038] The term "projection system" used herein should be broadly
interpreted as encompassing any type of projection system PS,
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".
[0039] As here depicted, the lithographic apparatus is of a
transmissive type (e.g. employing a transmissive mask).
Alternatively, the lithographic 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).
[0040] The lithographic apparatus may comprise a measurement table
(not depicted in FIG. 1) that is arranged to hold measurement
equipment, such as sensors to measure properties of the projection
system PS. In an embodiment, the measurement table is not
configured to hold a substrate W. The lithographic apparatus may be
of a type having two (dual stage) or more tables (or stage or
support), e.g., two or more substrate tables WT, or a combination
of one or more substrate tables WT and one or more sensor or
measurement tables. In such "multiple stage" machines the multiple
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. The lithographic apparatus may have two or more
patterning device tables (or stages or support), e.g. two or more
support structures MT, which may be used in parallel in a similar
manner to substrate tables WT, sensor tables and measurement
tables.
[0041] Referring to FIG. 1, the illuminator IL receives a
projection beam B from a source SO of radiation. The source SO and
the lithographic apparatus 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 and
the projection 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, for example when the source SO 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.
[0042] The illuminator IL may comprise an adjuster AD configured to
adjust the angular intensity distribution of the projection beam B.
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 projection beam
B, to have a desired uniformity and intensity distribution in its
cross-section. Similar to the source SO, the illuminator IL may or
may not be considered to form part of the lithographic apparatus.
For example, the illuminator IL may be an integral part of the
lithographic apparatus or may be a separate entity from the
lithographic apparatus. In the latter case, the lithographic
apparatus may be configured to allow the illuminator IL to be
mounted thereon. Optionally, the illuminator IL is detachable and
may be separately provided (for example, by the lithographic
apparatus manufacturer or another supplier).
[0043] The projection 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 MA. Having
traversed the patterning device MA, the projection beam B passes
through the projection system PS, which focuses the projection beam
B onto a target portion C of the substrate W. With the aid of the
second positioning device PW and a 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 projection beam B.
Similarly, the first positioning device PM and another position
sensor (which is not explicitly depicted in FIG. 1) can be used to
accurately position the patterning device MA with respect to the
path of the projection beam B, e.g. after mechanical retrieval from
a mask library, or during a scan.
[0044] 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 both form part
of the first positioning device PM. Similarly, movement of the
substrate table WT may be realized using a long-stroke module and a
short-stroke module, which both form part of the second positioning
device PW. The long-stroke module is arranged to move the
short-stroke module over a long range with limited precision. The
short-stroke module is arranged to move the support structure MT
and/or substrate table WT over a short range relative to the
long-stroke module with high precision. 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.
[0045] Patterning device MA and substrate W may be aligned using
mask alignment marks M1, M2 and substrate alignment marks P1, P2.
Although the substrate alignment marks P1, P2 as illustrated occupy
dedicated target portions, they may be located in spaces between
target portions C. Marks located in spaces between the target
portions C are known as scribe-lane alignment marks). Similarly, in
situations in which more than one die is provided on the patterning
device MA, the mask alignment marks M1, M2 may be located between
the dies.
[0046] The depicted lithographic apparatus may be used to expose a
substrate W in at least one of the following modes of use:
[0047] 1. In step mode, the support structure MT and the substrate
table WT are kept essentially stationary, while an entire pattern
imparted to the projection beam B 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 direction and/or Y
direction (i.e. a stepping 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 support structure MT and the substrate
table WT are scanned synchronously while a pattern imparted to the
projection beam B 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 a
non-scanning direction) of the target portion C in a single dynamic
exposure, whereas the length of the scanning motion determines the
height (in a scanning direction) of the target portion C.
[0049] 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 projection beam B is projected onto a target
portion C. In this mode, generally a pulsed radiation source is
employed as the source SO 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 a 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 a lithographic apparatus in the manufacture of integrated
circuits, it should be understood that the lithographic apparatus
described herein may have other applications in manufacturing
components with microscale, or even nanoscale, features, 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.
[0052] Arrangements for providing liquid between a final element of
the projection system PS and the substrate W can be classed into
three general categories of immersion system. These include a bath
type arrangement, a localized immersion system and an all-wet
immersion system.
[0053] In the bath type arrangement, substantially the whole of the
substrate W and optionally part of the substrate table WT is
submersed in a bath of liquid.
[0054] The localized immersion system uses a liquid supply system
in which liquid is only provided to a localized area of the
substrate W. The area filled by liquid is smaller in plan than the
top surface of the substrate W and the area filled with liquid
remains substantially stationary relative to the projection system
PS while the substrate W moves underneath that area. FIGS. 2-6 and
9-13 show different immersion systems which can be used as such a
liquid supply system. A meniscus controlling feature can be present
to seal liquid to the localized area. One way which has been
proposed to arrange for this is disclosed in PCT patent application
publication no. WO 99/49504. The meniscus controlling feature may
be a meniscus pinning feature.
[0055] In the all wet arrangement, the liquid is unconfined. The
whole top surface of the substrate W and all or part of the
substrate table WT is covered in immersion liquid. The depth of the
liquid covering at least the substrate W is small. The liquid may
be a film, such as a thin film, of liquid on the substrate W.
Immersion liquid may be supplied to or in the region of the
projection system PS and a facing surface facing the projection
system PS (such a facing surface may be the surface of the
substrate W and/or the substrate table WT). Any of the liquid
supply devices of FIG. 2 or FIG. 3 can also be used in such a
liquid supply system. However, a meniscus controlling feature is
not present, not activated, not as efficient as normal or otherwise
ineffective to seal liquid to only a localized area.
[0056] FIG. 2 schematically depicts an immersion system (which can
otherwise be referred to as a localized liquid supply system or
fluid handling system) with a fluid handling structure 12 (which
could also be referred to as a liquid confinement structure), which
extends along at least a part of a boundary of a space 11 between a
final element of the projection system PS and the substrate table
WT or substrate W. (Please note that reference in the following
text to surface of the substrate W also refers in addition or in
the alternative to a surface of the substrate table WT, unless
expressly stated otherwise.) In an embodiment, a seal is formed
between the fluid handling structure 12 and the surface of the
substrate W and which may be a contactless seal such as a gas seal
16 (such a system with a gas seal is disclosed in European patent
application publication no. EP-A-1,420,298). The seal can be
provided by a meniscus controlling feature.
[0057] The fluid handling structure 12 at least partly contains
liquid in the space 11 between the final element of the projection
system PS and the substrate W. The space 11 is at least partly
formed by the fluid handling structure 12 positioned below and
surrounding the final element of the projection system PS. Liquid
is brought into the space 11 below the projection system PS and
within the fluid handling structure 12 by opening 13. The liquid
may be removed by opening 13. Whether liquid is brought into the
space 11 or removed from the space 11 by the opening 13 may depend
on the direction of movement of the substrate W and substrate table
WT.
[0058] The liquid may be contained in the space 11 by the gas seal
16 which, during use, is formed between the bottom of the fluid
handling structure 12 and the surface of the substrate W. The gas
in the gas seal 16 is provided under pressure via inlet 15 to the
gap between the fluid handling structure 12 and substrate W. The
gas is extracted via a channel associated with outlet 14. The
overpressure on the gas inlet 15, vacuum level on the outlet 14 and
geometry of the gap are arranged so that there is a high-velocity
gas flow inwardly that confines the liquid. The force of the gas on
the liquid between the fluid handling structure 12 and the
substrate W contains the liquid in the space 11. Such a system is
disclosed in United States patent application publication no. US
2004-0207824, which is hereby incorporated by reference in its
entirety.
[0059] FIG. 3 is a side cross sectional view that depicts a further
immersion system according to an embodiment. The arrangement
illustrated in FIG. 3 and described below may be applied to the
lithographic apparatus described above and illustrated in FIG. 1.
The liquid supply system is provided with a fluid handling
structure 12, which extends along at least a part of a boundary of
a space 11 between the final element of the projection system PS
and the substrate table WT or substrate W. (Please note that
reference in the following text to surface of the substrate W also
refers in addition or in the alternative to a surface of the
substrate table WT, unless expressly stated otherwise.)
[0060] The fluid handling structure 12 at least partly contains
liquid in the space 11 between a final element of the projection
system PS and the substrate W. The space 11 is at least partly
formed by the fluid handling structure 12 positioned below and
surrounding the final element of the projection system PS. In an
embodiment, the fluid handling structure 12 comprises a main body
member 53 and a porous member 83. The porous member 83 is plate
shaped and has a plurality of holes (i.e., openings or pores). In
an embodiment, the porous member 83 is a mesh plate wherein
numerous small holes 84 are formed in a mesh. Such a system is
disclosed in United States patent application publication no. US
2010/0045949 A1, which is hereby incorporated by reference in its
entirety.
[0061] The main body member 53 comprises supply ports 72, which are
capable of supplying the liquid to the space 11, and a recovery
port 73, which is capable of recovering the liquid from the space
11. The supply ports 72 are connected to a liquid supply apparatus
75 via passageways 74. The liquid supply apparatus 75 is capable of
supplying the liquid to the supply ports 72. The liquid that is fed
from the liquid supply apparatus 75 is supplied to each of the
supply ports 72 through the corresponding passageway 74. The supply
ports 72 are disposed in the vicinity of the optical path at
prescribed positions of the main body member 53 that face the
optical path. The recovery port 73 is capable of recovering the
liquid from the space 11. The recovery port 73 is connected to a
liquid recovery apparatus 80 via a passageway 79. The liquid
recovery apparatus 80 comprises a vacuum system and is capable of
recovering the liquid by suctioning it via the recovery port 73.
The liquid recovery apparatus 80 recovers the liquid LQ recovered
via the recovery port 23 through the passageway 29. The porous
member 83 is disposed in the recovery port 73.
[0062] In an embodiment, to form the space 11 with the liquid
between the projection system PS and the fluid handling structure
12 on one side and the substrate W on the other side, liquid is
supplied from the supply ports 72 to the space 11 and the pressure
in a recovery chamber 81 in the fluid handling structure 12 is
adjusted to a negative pressure so as to recover the liquid via the
holes 84 (i.e., the recovery port 73) of the porous member 83.
Performing the liquid supply operation using the supply ports 72
and the liquid recovery operation using the porous member 83 forms
the space 11 between the projection system PS and the fluid
handling structure 12 on one side and the substrate W on the other
side.
[0063] FIG. 4 illustrates a fluid handling structure 12 which is
part of an immersion system (such as a liquid supply system). The
fluid handling structure 12 extends around the periphery (e.g.
circumference) of the final element of the projection system PS.
The fluid handling structure 12 is configured to contain immersion
fluid to a region. The region may be external to the fluid handling
structure 12. The region may be between the final element of the
projection system PS and the substrate W and/or substrate table WT.
The fluid handling structure 12 may comprise at least one meniscus
controlling feature to contain the immersion fluid.
[0064] A plurality of openings 20 in the surface which in part
defines the space 11 provide liquid to the space 11. The liquid
passes through openings 29 and 20 in side walls 28 and 22
respectively, through respective chambers 24 and 26 respectively,
prior to entering the space 11.
[0065] A seal is provided between the bottom of the fluid handling
structure 12 and a facing surface, e.g. a top surface of the
substrate W, or a top surface of the substrate table WT, or both.
The facing surface is the surface facing the bottom of the fluid
handling structure 12. In FIG. 4 a fluid handling structure 12 is
configured to provide a contactless seal and is made up of several
components. Radially outwardly from the optical axis of the
projection system PS, there is provided a (optional) flow control
plate 51 which extends into the space 11. The control plate 51 may
have an opening 55 to permit liquid to flow therethrough; the
opening 55 may be beneficial if the control plate 51 is displaced
in the Z direction (e.g., parallel to the optical axis of the
projection system PS). Radially outwardly of the flow control plate
51 on the bottom surface of the fluid handling structure 12, facing
(e.g., opposite) the facing surface may be an opening 180. The
opening 180 can provide liquid in a direction towards the facing
surface. During imaging this may be useful in preventing bubble
formation in the immersion liquid by filling a gap between the
substrate W and substrate table WT with liquid.
[0066] Radially outwardly of the opening 180 may be an extractor
assembly 70 to extract liquid from between the fluid handling
structure 12 and the facing surface. The extractor assembly 70 may
operate as a single phase or as a dual phase extractor. The
extractor assembly 70 acts as a meniscus controlling feature.
[0067] Radially outwardly of the extractor assembly 70 is a gas
knife. As depicted in FIG. 4, at least one gas knife opening 210
may be provided in a radially outward direction from the extractor
assembly 70 to provide a gas knife. The gas knife openings 210 may
be substantially parallel to the edge of the extractor assembly 70.
In an embodiment, the gas knife opening 210 may be a series of
discrete apertures provided along the edge of the extractor
assembly 70. In use, the gas knife opening 210 is connected to an
overpressure and forms a gas knife surrounding the meniscus
controlling feature formed by the extractor assembly 70. The gas
knife opening 210 may be adjacent to the meniscus controlling
feature and is in a radially outward direction relative to the
space 11 in plan view. An arrangement of the extractor assembly 70
and gas knife is disclosed in detail in United States patent
application publication no. US 2006-0158627 incorporated herein in
its entirety by reference.
[0068] In an embodiment, the extractor assembly 70 is a single
phase extractor which may comprise a liquid removal device,
extractor or inlet such as the one disclosed in United States
patent application publication no. US 2006-0038968, incorporated
herein in its entirety by reference. In an embodiment, the meniscus
controlling feature comprises a micro-sieve. In an embodiment, the
extractor assembly 70 comprises an inlet which is covered in a
porous material 111 which is used to separate liquid from gas to
enable single-liquid phase liquid extraction. The porous material
111 may also be a micro-sieve. An under pressure in chamber 121 is
chosen is such that the meniscuses formed in the holes of the
porous material 111 prevent ambient gas from being drawn into the
chamber 121 of the extractor assembly 70. However, when the surface
of the porous material 111 comes into contact with liquid there is
no meniscus to restrict flow and the liquid can flow freely into
the chamber 121 of the extractor assembly 70.
[0069] Although not specifically illustrated in FIG. 4, the fluid
handling structure 12 may have an arrangement to deal with
variations in the level of the liquid. This is so that liquid which
builds up between the projection system PS and the fluid handling
structure 12 can be dealt with and does not escape. One way of
dealing with this liquid is to provide a lyophobic (e.g.,
hydrophobic) coating on at least part of the fluid handling
structure 12.
[0070] Another localized immersion system with a fluid handling
structure 12 makes use of a gas drag principle. The so-called gas
drag principle has been described, for example, in United States
patent application publication nos. US 2008-0212046, US
2009-0279060 and US 2009-0279062. In that localized immersion
system the extraction holes are arranged in a shape which may
desirably have a corner. The extractions holes may be used to
provide a dual phase extractor. The corner may be aligned with a
preferred direction of movement, such as the stepping direction or
the scanning direction. This reduces the force on the meniscus
between two openings in the surface of the fluid handing structure
12 for a given speed in the preferred direction compared to if the
two openings were aligned perpendicular to the preferred direction.
However, an embodiment of the invention may be applied to a fluid
handling structure 12 which has any shape in plan, or has a
component such as the outlets are arranged in any shape. Such a
shape in a non-limiting list may include an ellipse such as a
circle, a rectilinear shape such as a rectangle, e.g. a square, or
a parallelogram such as a rhombus or a cornered shape with more
than four corners such as a four or more pointed star, for example,
as depicted in FIG. 5.
[0071] FIG. 5 illustrates schematically and in plan meniscus
controlling features of an immersion system including a fluid
handling structure 12 which may have outlets using the gas drag
principle and to which an embodiment of the present invention may
relate. The features of a meniscus controlling feature are
illustrated which may, for example, replace the meniscus
controlling features depicted by the gas seal 16, provided by the
inlet 15 and the outlet 14 in FIG. 2, or at least the extractor
assembly 70 shown in FIG. 4. The meniscus controlling feature of
FIG. 5 is a form of extractor, for example a dual phase extractor.
The meniscus controlling feature comprises a plurality of discrete
openings 50. Each opening 50 is illustrated as being circular,
though this is not necessarily the case. Indeed, the shape is not
essential and one or more of the openings 50 may be one or more
selected from: circular, elliptical, rectilinear (e.g. square, or
rectangular), triangular, etc. and one or more openings may be
elongate.
[0072] There may be no meniscus controlling features radially
inwardly of the openings 50. The meniscus is pinned between the
openings 50 with drag forces induced by gas flow into the openings
50. A gas drag velocity of greater than about 15 m/s, desirably
about 20 m/s is sufficient. The amount of evaporation of liquid
from the substrate W may be reduced, thereby reducing both
splashing of liquid as well as thermal expansion/contraction
effects.
[0073] Various geometries of the bottom of the fluid handling
structure are possible. For example, any of the structures
disclosed in U.S. patent application publication no. US
2004-0207824 or U.S. patent application Ser. No. 61/181,158, filed
on 26 May 2009, could be used in an embodiment of the present
invention.
[0074] As can be seen in FIG. 5, relative to the space 11, at least
one gas knife opening 210 may be provided outside the openings 50
to provide a gas knife. The gas knife opening 210 may be
substantially parallel to the lines joining the openings 50 of the
meniscus controlling feature. In an embodiment the gas knife
opening 210 may be a series of discrete apertures provided along a
side 54 of the shape. In use, the gas knife opening 210 is
connected to an over pressure and forms a gas knife (equivalent to
the gas knife provided by gas knife openings 210 in FIG. 4)
surrounding the meniscus controlling feature formed by openings 50.
The gas knife opening 210 may be adjacent to the meniscus
controlling feature and is in a radially outward direction relative
to the space 11 in plan view.
[0075] The gas knife in an embodiment of the invention functions to
reduce the thickness of any liquid film left on a facing surface,
such as the substrate W or substrate table WT. The gas knife helps
ensure that the liquid film does not break into droplets but rather
the liquid is driven towards the openings 50 and extracted. In an
embodiment the gas knife operates to prevent the formation of a
film. To achieve this, it is desirable that the distance between
the center lines of the gas knife and of the meniscus controlling
openings 50 is in the range of from 1.5 mm to 4 mm, desirably from
2 mm to 3 mm. The line along which the gas knife is arranged
generally follows the line of the openings 50 so that the distance
between adjacent ones of the openings 50 and the gas knife opening
210 is within the aforementioned ranges. Desirably the line along
which the gas knife opening 210 is arranged is parallel to the line
of the openings 50. It is desirable to maintain a constant
separation between adjacent ones of the openings 50 and the gas
knife opening 210. In an embodiment this is desirable along the
length of each center line of the gas knife. In an embodiment the
constant separation may be in the region of one of more corners of
the cornered shape.
[0076] Localized immersion systems such as those described above,
with reference to FIGS. 2-5, can suffer from bubble inclusion into
the space 11. As can be seen, a meniscus 320 extends between the
fluid handling structure 12 and the facing surface (e.g. the top
surface of the substrate W) under the fluid handling structure 12.
This meniscus 320 illustrated in FIG. 2 and FIG. 4 defines the edge
of the space 11. When the meniscus 320 and a droplet collide on the
surface, for example a droplet of liquid which has escaped the
space 11, a bubble of gas may be included into the space 11.
Inclusion of a bubble into the space 11 is detrimental because a
bubble of gas can lead to an imaging error.
[0077] There are certain circumstances in which it is more likely
that a droplet will be left behind on the surface. For example, a
droplet may be left behind on the surface when the immersion system
(and particularly the fluid handling structure 12) is located over
the edge of a substrate W when there is relative movement between
the immersion system/fluid handling structure 12 and the substrate
W. In another example, a droplet may be left behind when the
immersion system (and particularly the fluid handling structure 12)
is located over a step change in height of the facing surface
facing the fluid handling structure 12 and when there is relative
movement between the fluid handling structure 12 and the facing
surface. In another example, a droplet may be left behind due to a
relative speed between the fluid handling structure 12 and the
facing surface being too high, for example when the meniscus
becomes unstable, e.g. by exceeding the critical scan speed of the
facing surface. A bubble may be included into the space 11 at the
meniscus 400 illustrated in FIGS. 2 and 4 extending between the
fluid handling structure 12 and the projection system PS. Here a
bubble of gas could be created by liquid supplied from a liquid
inlet (e.g. inlet 13 in FIG. 2 and inlet 20 in FIG. 4) on a
radially inward facing surface of the fluid handling structure 12
entraining gas from between the projection system PS and the fluid
handling structure 12.
[0078] Ways of dealing with the difficulty of bubble inclusion have
concentrated on improving the confinement properties of the fluid
handling structure 12. For example, the relative speed between the
fluid handling structure 12 and the facing surface has been
decreased in order to avoid spilling of liquid.
[0079] Very small bubbles of gas may dissolve in the immersion
liquid before they reach the exposure area of the space 11. An
embodiment of the present invention uses the fact that dissolution
speed is dependent upon the type of the trapped gas and the
immersion liquid properties.
[0080] A bubble of carbon dioxide gas typically dissolves faster
than a bubble of air. A bubble of CO.sub.2, which has a solubility
fifty-five (55) times larger than that of nitrogen and a
diffusivity of 0.86 times that of nitrogen, will typically dissolve
in a time thirty-seven (37) times shorter than the time for a
bubble of the same size of nitrogen to dissolve. Supplying CO.sub.2
adjacent to the meniscus 320 or 400 means that a bubble of CO.sub.2
gas will dissolve into the immersion liquid much faster than if
other gases with lower diffusivity were used. Therefore, using
CO.sub.2 in an embodiment of the present invention will reduce the
number of imaging defects thereby allowing higher throughput (e.g.,
higher speed of the substrate W relative to the fluid handling
structure 12) and lower defectivity.
[0081] Therefore, an embodiment of the present invention may
provide a gas knife which supplies substantially pure CO.sub.2 gas
to a region (e.g. to a volume, or a towards an area) adjacent to
the space 11. In particular, CO.sub.2 gas is provided such that it
is present in the region adjacent to the meniscus 320 extending
between the facing surface (e.g. on substrate W or substrate table
WT) and the fluid handling structure 12.
[0082] Carbon dioxide is desirable because it is readily available
and may be used in immersion systems for other purposes. Carbon
dioxide has solubility in water at 20.degree. C. and 1 atm total
pressure of 1.69.times.10.sup.-3 kg/kg or 37.times.10.sup.-3
mol/kg. Other gases may have one or more disadvantages, for
example, other gases may react with components in the immersion
lithographic apparatus and/or may be poisonous and may therefore be
harder to handle and less desirable than carbon dioxide.
[0083] By using gaseous CO.sub.2 the problem associated with the
meniscus 320 colliding with a droplet of liquid may be reduced.
Typically a droplet of 300 micrometers would produce a bubble of 30
micrometers in diameter (i.e. a tenth the size). Such a bubble of
carbon dioxide would usually dissolve in the immersion liquid
before reaching the exposure area which may make problems caused by
a droplet less significant. Therefore, an immersion system may be
more tolerant of interacting with immersion liquid which had
escaped from the space 11.
[0084] Carbon dioxide gas is also provided through at least one gas
supply opening 220. The gas supply opening 220 is radially outward,
i.e. in a radially outward direction in plan view relative to the
space 11, of the gas knife opening 210 (and also the meniscus
controlling feature, such as the extractor 70 in FIG. 4 or the
outlets 50 in FIG. 5). The at least one gas supply opening 220 may
be adjacent to the at least one gas knife opening 210, as depicted
in FIGS. 4, 5, 6, 10, 11, 12 and 13.
[0085] Providing a gas knife opening 210 for providing
substantially pure CO.sub.2 gas and a gas supply opening 220 for
providing substantially pure CO.sub.2 gas means that an atmosphere
of substantially pure CO.sub.2 can be provided adjacent to and
radially outward of the space 11. The atmosphere adjacent to, and
radial outward of, the space 11 does not contain significant
amounts of gases which do not dissolve as readily as CO.sub.2
gas.
[0086] In an embodiment of the present invention herein described,
a substantially pure CO.sub.2 gas atmosphere is formed around the
meniscus 320 of immersion liquid so that any inclusion of CO.sub.2
gas into the immersion liquid creates a gas inclusion which
dissolves in the immersion liquid. In an embodiment, the atmosphere
of substantially pure CO.sub.2 gas is at least 90% CO.sub.2 gas. In
an embodiment, the atmosphere of substantially pure CO.sub.2 gas is
at least 95% CO.sub.2 gas. In an embodiment, the atmosphere of
substantially pure CO.sub.2 gas is at least 99% CO.sub.2 gas. In an
embodiment, the atmosphere of substantially pure CO.sub.2 gas is at
least 99.5% CO.sub.2 gas. In an embodiment, the atmosphere of
substantially pure CO.sub.2 gas is at least 99.9% CO.sub.2 gas. It
is preferable that the substantially pure CO.sub.2 gas atmosphere
has as high a CO.sub.2 gas content as is achievable.
[0087] A difficulty with providing carbon dioxide gas in a
lithographic apparatus is that some components, for example
components of a position measurement system of the substrate table
WT, have impaired performance in a carbon dioxide atmosphere. In an
embodiment of the present invention, it is ensured that a pure
carbon dioxide environment is present near the meniscus 320 during
scanning. To achieve this, it may be necessary, for example in the
embodiment of FIG. 5, to have a flow rate of carbon dioxide out of
the gas knife opening 210 and the gas supply opening 220 greater
than the amount of CO.sub.2 extracted through the openings 50. This
may result in an excess of carbon dioxide leaking out from under
the fluid handling structure 12 into the environment of the machine
and particularly towards components of a position measurement
system of the substrate table WT.
[0088] In an embodiment of the invention, in order to ensure that
excess carbon dioxide does not leak from under the fluid handling
structure 12, at least one gas recovery opening 61 is provided
radially outward of the one or more meniscus controlling features,
the gas knife opening 210 and the gas supply opening 220 as
depicted in FIG. 6. The gas recovery opening 61 may be provided
with any of the embodiments. The gas recovery opening 61 may
comprise a dual phase extractor. As an example, the dual phase
extractor may have an extraction flow rate of approximately 40 to
80 NI/min, however, this may vary depending on the apparatus. In
this way an environment of carbon dioxide can still be provided
radially outwardly of the meniscus controlling features thereby
reducing bubble inclusion to the space 11. Also, possible
contamination or interruption of functioning of components of the
lithographic apparatus can be reduced or prevented.
[0089] An advantage of providing an atmosphere of substantially
pure carbon dioxide adjacent to the meniscus 320 is that the carbon
dioxide may then dissolve in immersion liquid at the meniscus 320
under the openings 50 of the meniscus controlling feature. This
results in the immersion liquid at the meniscus 320 becoming
slightly acidic (a decrease in pH). If the immersion liquid becomes
more acidic this increases the presence of H.sub.3O.sup.+ ions. An
increase in the number of H.sub.3O.sup.+ ions results in the
solid-liquid surface energy (.gamma..sub.SL) decreasing. The
solid-gas surface energy (.gamma..sub.SG) does not change and
neither does the liquid-gas surface energy (.gamma..sub.LG). The
change in the solid-liquid surface energy therefore affects the
equilibrium between the three surface energies. The surface tension
in the liquid meniscus, especially towards its interface with the
solid surface, is affected. The change in direction of the surface
tension as a consequence of the change in the surface energies is
illustrated in FIG. 7. FIG. 7 shows the contact angle .theta..sub.C
of the droplet 300 on the surface 310. The relationship between the
three surface energies and the contact angle is given in the
following equation:
.gamma..sub.LGcos .theta..sub.C=.gamma..sub.SG-.gamma..sub.SL
[0090] According to this equation a decrease in the solid-liquid
electrical surface energy (.gamma..sub.SL) results in an increase
in the contact angle .theta..sub.C. An increase in the contact
angle .theta..sub.C between liquid and the facing surface,
particularly at the meniscus 320, results in an improvement in
performance of the meniscus controlling feature (e.g. the openings
50). As such, a higher velocity between the fluid handling
structure 12 and the facing surface may be achieved before liquid
is lost from the immersion space 11, beyond the meniscus
controlling feature.
[0091] FIG. 8 is a graph showing the pH of immersion liquid along
the x axis and the critical scanning speed before liquid loss along
the y axis. The graph is for a particular type of fluid handling
structure and a substrate W having a top coat of TCX041 available
from JSR Micro, Inc. in CA, US.
[0092] FIG. 8 shows that a reduction in pH of immersion liquid
leads to an increase in critical scan speed. An increase in
critical scan speed would lead to an increase in throughput as a
high scan speed can be used without risk of liquid loss (which can
lead to imaging errors as described above). This is particularly so
for larger substrates W such as substrates with a diameter of 450
mm. This is because on such a larger substrate, relative to a
smaller substrate, more scans are performed a distance away from
the edge of the substrate W, for example in a region towards the
center of the substrate W. It is the scans in a region towards the
center of the substrate W which can be performed close to critical
scan speed; whereas scans performed closer to the edge of a
substrate W may need to be performed at a slower speed than the
critical scan speed. The reason for this difference in scan speed
can be, for example, the effect of the edge of the substrate W on
the stability of the meniscus 320.
[0093] Providing a gas supply opening 220 radially outwards of the
gas knife opening 210 may ensure that an atmosphere of
substantially pure CO.sub.2 gas is provided adjacent to the space
11, i.e. adjacent to the meniscus 320. If such a gas supply opening
220 was not provided, then to provide the substantially pure
CO.sub.2 gas atmosphere adjacent to the meniscus 320, the flow rate
of the substantially pure CO.sub.2 gas supplied by the gas knife
opening would have to be much higher, and more water marks would
occur due to the higher flow rate. For example, a gas knife opening
without an additional gas supply opening 220 may have to provide
gas at a flow rate approximately 10-20 NI/min more than the
extracted gas flow rate by the dual phase extractor. If there is no
gas supply opening 220 and the gas knife flow rate is kept low to
avoid water marks, then bubbles that enter the immersion liquid in
the space 11 would take longer to dissolve. Hence more imaging
errors would occur.
[0094] However, in an embodiment of the present invention, a gas
supply opening 220 provides CO.sub.2 gas radially outward of the
gas knife opening 210. Therefore, if gas external to the gas knife
is drawn into the atmosphere adjacent to the meniscus 320, the gas
is likely to be substantially pure CO.sub.2 gas emitted by the gas
supply opening 220, such that the atmosphere adjacent to the
meniscus 320 can be maintained as substantially pure CO.sub.2.
Therefore, the flow rate and/or the gas velocity, of the gas knife
can be reduced because it is not necessary to prevent gas radially
outward of the gas knife from entering the atmosphere adjacent to
the space 11, because the gas radially outward of the gas knife
opening is also CO.sub.2. As such, the substantially pure CO.sub.2
gas atmosphere can be maintained when the gas emitted from the gas
knife opening 210 is at a lower flow rate.
[0095] The gas knife has a first gas velocity at which the CO.sub.2
gas exits the gas knife opening 210. The gas supply opening 220 has
a second gas velocity at which substantially pure CO.sub.2 gas
exits the at least one gas supply opening 220. In an embodiment,
the first gas velocity is greater than the second gas velocity. In
an embodiment, the second gas velocity may be equal to or less than
approximately the dual extraction gas velocity.
[0096] The gas knife has a first flow rate at which the CO.sub.2
gas exits the gas knife opening 210. In an embodiment, first flow
rate is less than approximately 30 NI/min more than the extracted
gas rate by the dual phase extractor. In an embodiment, the first
flow rate is preferably less than approximately 15 NI/min more than
the extracted gas rate by the dual phase extractor. In an
embodiment, the first flow rate is preferably no more than the
extracted gas flow rate by the dual phase extractor. The gas supply
opening 220 has a second flow rate at which substantially pure
CO.sub.2 gas exits the at least one gas supply opening 220. In an
embodiment, the first flow rate is greater than the second flow
rate. In an embodiment, the second flow rate may be equal to or
less than approximately the dual extraction flow rate. In an
embodiment, the second flow rate is generally between 10-60
NI/min.
[0097] Generally, CO.sub.2 gas which is provided at the atmosphere
adjacent to the meniscus 320 may be humidified at high pressure. A
gas knife, such as the gas knife opening 210, provides a flow of
gas which results in a pressure peak on the facing surface (e.g.
substrate W). The gas knife has high stagnant pressure. Due to the
high pressure change across the gas knife, i.e. a high pressure
gradient, the pressure drop leads to a reduction in the relative
humidity of the carbon dioxide in the atmosphere adjacent to the
meniscus 320. By using a gas supply opening 220 in addition to the
gas knife opening 210 as described above, the flow rate and/or the
gas velocity, at which CO.sub.2 gas is provided from the gas knife
opening 210 is reduced (compared to when a gas substrate opening
210 is provided) and therefore, the pressure drop across the gas
knife is reduced also. The flow of gas from the gas supply opening
is generally a low impulse gas supply. Therefore, the reduction of
relative humidity of the gas across the gas knife is reduced, such
that there is a lower heat load on the substrate W.
[0098] In an embodiment, the gas knife opening 210, the gas supply
opening 220 and, if provided, the gas recovery opening 61 are
provided on the lower surface of the fluid handling structure 12
and are at the same distance with respect to the facing
surface.
[0099] In an embodiment, the distances between each of the openings
and the facing surfaces are variable. For example, a step may be
provided between the gas knife opening 210 and the gas supply
opening 220 such that the gas knife opening 210 is closer to the
facing surface than the gas supply opening 220 (and the gas
recovery opening 61 if included). Alternatively, the gas knife
opening 210 may be further away from the facing surface than the
gas supply opening 220 (and the gas recovery opening 61, if
provided). Additionally, or alternatively, a step may be provided
between the gas supply opening 220 and the gas recovery opening 61
such that the gas supply opening 220 is closer to the facing
surface than the gas recovery opening 61. Alternatively, the gas
supply opening 220 may be further from the facing surface than the
gas recovery opening 61.
[0100] In an embodiment, the distance between the openings and the
facing surface can be chosen to control the speed of the CO.sub.2
gas on the facing surface, i.e. an increase in distance between an
opening and the facing surface will decrease the speed of gas on
the facing surface. In general, the velocity of a jet starts
decreasing after a distance from the opening of approximately four
times the diameter of the opening. This distance may be for
example, approximately 150-200 micrometers. At 350 micrometers the
velocity of the jet, and the resulting pressure on the facing
surface, is significantly decreased. Having a high pressure at the
facing surface may mean that the overall number and/or size of
droplets radially outward of the meniscus 320 is reduced, however,
resulting water marks on the substrate W may be made. Therefore,
the supply of gas through the gas supply opening 220 and the gas
knife opening 210 can be optimized in accordance with the height of
the openings above the facing surface to reduce the water
marks.
[0101] The gas knife opening 210 and the gas supply opening 220
each have a surface area on the lower surface of the fluid handling
structure 12. The overall surface area of the gas knife opening 210
may be smaller than the overall surface area of the gas supply
opening 220. The gas emitted from the gas knife opening 210 is at a
first flow speed and the gas emitted from the gas supply opening
220 is at a second flow speed. In an embodiment, the first flow
speed is greater than the second flow speed. In an embodiment, at
least one gas recovery opening 61 may be provided radially outward
of the gas supply opening 220, as depicted in FIGS. 4 and 6.
However, this is not necessarily the case. For example, in the
embodiment of FIG. 9 described below, the at least one gas recovery
opening 61 is provided radially inwardly of the gas supply opening
220.
[0102] In an embodiment, the gas supply opening 220 and/or gas
recovery opening 61 may be provided as a single slit or as a
plurality of discrete openings.
[0103] In an embodiment, the gas recovery opening 61 at least
partly surrounds the gas supply opening 220. It may not be possible
for the gas recovery opening 61 to completely surround the gas
supply opening 220. In an embodiment the gas recovery opening 61
surrounds the majority of the perimeter of the gas supply opening
220. In an embodiment the gas recovery opening 61 may surround at
least half of the perimeter. That said, in an embodiment the gas
recovery opening 61 may substantially completely surround the
perimeter of the gas supply opening 220. A high extraction rate out
of the gas recovery opening 61 (for example connecting a large
underpressure source to the gas recovery opening 61) at least
partly mitigates for the fact that the at least one gas recovery
opening 61 does not completely surround the gas supply opening
220.
[0104] In an embodiment depicted in FIG. 4, the at least one gas
recovery opening 61 is formed in the fluid handling structure 12.
In one embodiment the at least one gas recovery opening 61 is
formed in an undersurface of the fluid handling structure 12. In
one embodiment the at least one gas recovery opening 61 is formed
in a bottom surface of the fluid handling structure 12. In one
embodiment, the gas recovery opening 61 is formed in the same
surface in which the gas knife opening 210 and the gas supply
opening 220 are formed. The flow of gas out of the gas supply
opening 220 and the gas knife opening 210 is both radially inward
towards the meniscus 320 and radially outward.
[0105] In an embodiment the radially outward flow is greater than
the inward flow. This ensures that there is minimal or no flow of
gas radially inward from outside the fluid handling structure 12
reaching the meniscus 320. If the radially outward flow from the
gas supply opening 220 and the gas knife opening 210 is too low,
this could have the effect of sucking in gas from the outside of
the fluid handling structure 12.
[0106] The embodiments of FIG. 5 and FIG. 6 are the same as that of
FIG. 4 concerning the gas supply opening 220 and the gas knife
opening 210. The gas recovery opening 61, for example, as depicted
in FIG. 4, FIG. 6 and FIG. 9, is not essential.
[0107] The embodiment of FIG. 9 is the same as the embodiment of
FIG. 4 except as described below. In the embodiment of FIG. 9 the
at least one gas recovery opening 61 is radially outward of the gas
knife opening 210 and radially inward of the gas supply opening
220. The gas supply opening 220 is radially outward of the at least
one gas recovery opening 61. The gas knife opening 210 is radially
inward of the recovery opening 61 and the gas supply opening 220.
Optionally, there may be an additional gas recovery opening (not
shown) radially outwards of the gas supply opening 220. Such an
additional gas recovery opening would help reduce or avoid CO.sub.2
gas from leaking into the atmosphere around the lithographic
apparatus.
[0108] Because the gas exiting the gas knife opening 210 is carbon
dioxide, that gas has a higher kinetic energy than gas comprising
air at the same velocity. This is because the density of carbon
dioxide is higher than that of air.
[0109] The escape of carbon dioxide into the environment of the
lithographic apparatus is reduced by collecting the carbon dioxide,
radially outwardly of the gas knife opening 210, through the gas
recovery opening 61.
[0110] In all of the embodiments of FIG. 4, FIG. 6 and FIG. 9, the
at least one gas recovery opening 61 is provided in the fluid
handling structure 12 itself. In an embodiment the at least one gas
recovery opening 61 is provided in a separate component.
[0111] An advantage of using CO.sub.2 in the embodiments is that
the potential danger of providing an explosive vapour or liquid is
reduced by the presence of carbon dioxide.
[0112] In an embodiment an immersion system for an immersion
lithographic apparatus is provided. The immersion system comprises
a fluid handling structure 12 of any of the above embodiments and a
gas supply system configured to supply gas to the gas supply
opening 220 and the gas knife opening 210. The gas supplied by the
gas supply system is carbon dioxide.
[0113] In an embodiment, the gas supply system comprises a gas
source 211 to provide gas to the at least one gas knife opening 210
and the at least one gas supply opening 220. In an embodiment, the
same gas source 211 is used to provide gas to the at least one gas
knife opening 210 and the at least one gas supply opening 220, as
depicted in FIG. 10. In an embodiment, the gas supplied to the gas
supply opening 220 may be controlled using a valve 217, as depicted
in FIG. 11, to redirect gas from the gas knife opening 210 to the
gas supply opening 220. Using a valve 217 to control the gas supply
to the gas supply opening 220 means that the flow rate and/or gas
velocity of the gas being emitted from the gas supply opening 220
and the gas knife opening 210 may be more easily controlled, e.g.
the flow rate and/or gas velocity of the gas emitted from the gas
knife opening 210 and the gas supply opening 220 may be set to
selected predetermined values or altered to selected values. The
valve 217 is depicted as part of the fluid handling structure 12,
however, the valve 217 may be outside the fluid handling structure
12. For example, the valve 217 may be connected to or integral
with, the gas source 211 or the humidifier 212.
[0114] In an embodiment, the gas supply system comprises multiple
gas sources. In an embodiment, a first gas source 211a is used to
provide gas to the at least one gas knife opening 210 and a second
gas source 211b is used to provide gas to the at least one gas
supply opening 220, as depicted in FIG. 12. Using different gas
sources to supply gas to the gas knife opening 210 and the gas
supply opening 220 means that the flow rate and/or gas velocity of
the gas being emitted from the gas supply opening 220 and the gas
knife opening 210 may be more easily controlled. In an embodiment,
the gas supply system comprises multiple gas sources and a third
path 218 between a first path 214 and a second path 215 to redirect
gas to or from the gas knife opening 210 from or to the gas supply
opening 220 respectively. The amount of gas being redirected may be
dynamically controlled using a valve 219, as depicted in FIG. 12.
The gas supply opening 220 and the gas knife opening 210 depicted
in FIGS. 10, 11, 12 and 13 may be used in any of the embodiments,
for example, in combination with, and radially outward of, a
meniscus controlling feature of any of the above embodiments.
[0115] In an embodiment, gas is supplied to the gas knife opening
210 from the gas source 211 via the first path 214. In an
embodiment, gas is supplied to the gas supply opening 220 from the
gas source 211 via the second path 215. In an embodiment, the first
path 214 and the second path 215 may be joined together on one path
between the gas source 211 and the gas knife opening 210 and the
gas supply opening 220, for example, as depicted in FIG. 10. In
this embodiment, the first flow speed and the second flow speed may
be more or less the same. The first flow speed and the second flow
speed may be altered relative to each other. This may be done in
several ways, for example, by providing different shaped flow paths
and/or having different surface areas for the gas knife opening 210
and the gas supply opening 220.
[0116] The gas knife opening 210 and the gas supply opening 220 are
separate. This means that even if they are supplied by the same gas
source 211, the flow rate and/or gas velocity of gas exiting each
of the gas knife opening 210 and the gas supply opening 220 can be
controlled. Therefore, the flow of gas from the gas knife opening
210 and the gas supply opening 220 can be optimized.
[0117] In an embodiment, the gas supply system comprises a
humidifier 212 to control the humidity of the gas provided by at
least one of the gas sources. In an embodiment, the gas is
substantially pure CO.sub.2 gas and is humidified CO.sub.2 gas. In
an embodiment, the humidifier 212 increases the humidity of the
CO.sub.2 gas provided by at least one of the gas sources. In an
embodiment, a humidifier 212 is connected to a gas source 211 as
depicted in FIG. 1 and FIG. 10. In an embodiment, the gas supply
system comprises multiple humidifiers. In an embodiment, a
humidifier may be connected to each gas source, for example, as
depicted in FIG. 11. FIG. 11 shows a first humidifier 212a
connected to a first gas source 211a and a second humidifier 212b
connected to a second gas source 211b. In an embodiment, the
humidifier 212 may be part of the fluid handling structure 12. In
an embodiment, the humidifier 212 may not be included in the
immersion system of the gas supply system, i.e. the humidifier 212
is not essential.
[0118] In an embodiment, the fluid handling structure 12 may
comprise a reservoir 213. The reservoir may be between the at least
one gas supply system and the gas knife opening 210 and the gas
supply opening 220. In an embodiment, the reservoir 213 may be a
section between the gas supply system and at least one of the gas
knife opening 210 and the gas supply opening 220 which has an
increased cross-sectional area. In an embodiment, the fluid
handling structure 12 may comprise the first path 214 from the
reservoir 213 to the gas knife opening 210 and the second path 215
from the reservoir 213 to the gas supply opening 220. In an
embodiment, the reservoir 213 may not be provided, i.e. the
reservoir 213 is not essential.
[0119] Providing a reservoir 213 allows greater control of the gas
being omitted from the gas knife opening 210 and/or the gas supply
opening 220. For example, the gas may build up in the reservoir 213
and may be more uniformly distributed from the gas knife opening
210 and the gas supply opening 220 in plan view, for example as
depicted in FIG. 4. Providing a humidifier 212 allows greater
control of the gas being omitted from the gas knife opening 210
and/or the gas supply opening 220. For example, the humidity of the
gas being supplied to the gas knife opening 210 and/or the gas
supply opening 220 can be controlled to affect the humidity of the
gas atmosphere adjacent to the meniscus 320.
[0120] In an embodiment, the second path 215 between the gas source
211 and the at least one gas supply opening 220 may comprise a flow
restrictor section to reduce the flow rate and/or gas velocity of
gas being omitted from the gas supply opening 220. The flow
restrictor section may be a bend and/or reduction in the
flow-through area in the second path 215. An example of a bend in
the second path 215 is depicted in FIG. 10. A schematic example of
a reduction in flow-through area 216 is depicted in FIG. 11. The
flow velocities can be altered and tuned to optimize the gas flow
through each of the gas knife opening 210 and the gas supply
opening 220. The flow velocities can be controlled by selecting the
cross-sectional areas of the first path 214 and the second path 215
and providing reductions in the cross-sectional area of the second
path 215. As such, the ratio of gas passing through the first path
214 and the second path 215 can be controlled.
[0121] The surface area of the openings can be selected to help
control the speed at which the gas (e.g. CO.sub.2) exits from the
openings. If the gas knife opening 210 and the gas supply opening
220 are supplied with gas (e.g. CO.sub.2) from the same gas source,
then having a smaller surface area for the gas knife opening 210
than the gas supply opening 220 can be used to increase the speed
of the gas exiting the gas knife opening 210 compared to the speed
of the gas exiting the gas supply opening 220. The surface areas of
the openings can be selected in addition, or as an alternative, to
restricting the second path 215, as a way of controlling the speed
of the gas exiting the first path 214 and the second path 215. It
is not essential that the overall area of the gas knife opening 210
is smaller than the overall area of the gas supply opening 220, and
the areas may be similar or the same, or the area of the gas knife
opening 210 may be larger than the gas supply opening 220.
[0122] Although providing a gas knife opening 210 and a gas supply
opening 220 in any of the above embodiments can have advantages
such as reducing the number of bubbles entering into space 11, the
gas knife flow rate may still result in water marks on the wafer W
when above a certain threshold. Therefore, it may be beneficial to
reduce the gas knife flow rate and/or gas knife velocity to try to
avoid water marks. This can be done by modulating the gas knife
flow rate when the fluid handling structure 12 is in use.
[0123] In an embodiment, the amount of gas supplied to the gas
supply opening 220 and/or the gas knife opening 210 is variable. In
an embodiment, the gas supplied to the gas supply opening 220
and/or the gas knife opening 210 is dynamically controlled, i.e.
the gas supplied can be controlled and varied during use. For
example, the gas emitted from either the gas supply opening 220
and/or the gas knife opening 210 may be dynamically controlled
depending on certain characteristics of the fluid handling
structure 12, including but not limited to, the direction of
movement, the speed, the velocity, and/or the location of the fluid
handling structure 12.
[0124] In an embodiment, the gas knife opening 210 comprises a
series of discrete apertures. For example, the gas knife opening
210 may be provided with two discrete apertures, for example each
aperture being two sides of the shape formed by the gas knife
opening 210 shown in FIGS. 5 and 6. Alternatively, the gas knife
opening 210 may have a single discrete aperture along each side of
the shape formed by the gas knife opening 210 shown in FIGS. 5 and
6. Thus, the gas knife opening 210 may be provided by four discrete
apertures. The shape of each aperture is not particularly limited
and the gas knife opening 210 may be provided by any number of
discrete apertures.
[0125] Each aperture may be individually controlled to vary the gas
flow rate and/or gas velocity of the gas exiting the different
apertures of the gas knife opening 210. At least one of the
apertures may be dynamically controlled depending on certain
characteristics of the fluid handling structure 12, including but
not limited to, the direction of movement, the speed, the velocity,
and/or the location of the fluid handling structure 12. For
example, when in use, apertures of the gas knife opening 210 on the
advancing side of the fluid handling structure 12 may be controlled
to have gas exiting at a lower gas flow rate and/or gas velocity
than the flow rate and/or gas velocity respectively of gas exiting
apertures of the gas knife opening 210 on the receding side of the
fluid handling structure.
[0126] Similarly, the gas supply opening 220 may additionally or
alternatively comprise a series of discrete apertures as herein
described, which may be individually controlled as herein
described.
[0127] In an embodiment, the gas supplied to the gas knife opening
210 may be dynamically controlled such as to reduce the amount of
gas being supplied to the gas knife opening 210. In an embodiment,
the gas supplied to the gas knife opening 210 may be reduced by
redirecting some of the gas from the gas knife opening 210 to the
gas supply opening 220. In other words, some of the gas is
redirected so that instead of passing through the first path 214,
some of the gas passes through the second path 215. The amount of
gas passing through the second path 215 may be dynamically
controlled to alter the gas flow rate and/or gas velocity of the
gas exiting the gas knife opening 210.
[0128] In an embodiment, a valve may be provided which allows more
gas to be directed to the gas supply opening 220, thus reducing the
amount of gas exiting the gas knife opening 210. Alternatively, the
valve may be varied to reduce the amount of gas directed to the gas
supply opening 220, thus increasing the amount of gas exiting the
gas knife opening 210. The valve may be variable to allow the
amount of gas passing through it to be dynamically controlled. The
gas passing through the second path 215 may be dynamically
controlled by using a valve 217 in the second path 215, as depicted
in FIG. 11. The valve 217 may be variable to allow different
amounts of gas to pass through the second path 215. In this way,
gas can be by-passed from the gas knife opening 210 to reduce the
gas flow rate and/or gas velocity of the gas exiting the gas knife
opening 210.
[0129] In an embodiment, the gas supply reservoir 213 may a device
configured to dynamically control the gas flow rate and/or gas
velocity exiting the gas supply opening 220 and/or the gas knife
opening 210. For example, the gas supply reservoir 213 may comprise
a valve, similar to valve 217, except located in the gas supply
reservoir 213.
[0130] Although FIG. 11 depicts the gas supply reservoir 213 and a
reduction in flow-through area 216, these are both optional
features which may or may not be included as part of the means for
controlling gas flow out of the gas knife opening 210 and/or the
gas supply opening 220.
[0131] In an embodiment, the first gas supply 211a and/or the
second gas supply 211b, as depicted in FIG. 12 may be controlled to
vary the gas flow rate and/or gas velocity exiting the gas knife
opening 210 and the gas supply opening 220 respectively. In an
embodiment, at least one of the first gas supply reservoir 213a or
the second gas supply reservoir 213b may comprise means for
dynamically controlling the gas flow rate and/or gas velocity
exiting the gas supply opening 220 and/or the gas knife opening
210. In an embodiment, a device configured to control the flow rate
and/or gas velocity exiting the gas knife opening 210 and the gas
supply opening 220 may be provided along, or as part of, the first
path 214 or the second path 215 respectively. For example, a valve
(such as depicted in FIG. 11) may be provided to vary the gas flow
through the first path 214 and/or second path 215 respectively.
[0132] In an embodiment, whether or not any one of the first gas
supply 211a, second gas supply 211b, first gas supply reservoir
213a or second gas supply reservoir 213b is dynamically controlled,
gas exiting the gas knife opening 210 may be dynamically controlled
by re-directing gas flow towards the gas supply opening. 220 For
example, the fluid handling structure 12 may comprise a third path
218 between the first path 214 and the second path 215, as depicted
in FIG. 13. The third path 218 may comprise a device configured,
for example valve 219, to dynamically control the gas flow from the
first path 214 to the second path 215, or vice versa. When the
valve 219 is closed, no flow may travel to or from the first path
214 from or to the second path 215 respectively. However, the valve
219 may be opened by varying amounts to control gas flow from the
first path 214 to the second path 215, to re-direct gas from the
gas knife opening 210 to the gas supply opening 220. Alternatively,
the valve 219 may be opened by varying amounts to control gas flow
from the second path 215 to the first path 214, to re-direct gas
from the gas supply opening 220 to the gas knife opening 210.
[0133] FIG. 13 depicts the third path 218 being located before the
first gas supply reservoir 213a and the second gas supply reservoir
213b. However, the third path 218 could be located between any
point on the first path 214 and the second path 215. In an
embodiment, the third path 218 could be located after the first gas
supply reservoir 213a and the second gas supply reservoir 213b,
i.e. on the side of the reservoirs nearer the gas knife opening 210
and the gas supply opening 220 respectively. In an embodiment, the
third path 218 may be located between a point before a reservoir on
one path and a point after a reservoir on the other path. In an
embodiment, a fluid handling structure 12 could be provided as in
FIG. 13 except that only one of the reservoirs is provided, or
neither.
[0134] The valve in any of the above embodiments, e.g. valve 217
and valve 219, may be any type of valve which allows variable
control of gas through the respective path and/or reservoir as
appropriate. Any of the above mentioned valves may be
electronically controlled. Any of the above mentioned valves may
comprise an actuator.
[0135] In an embodiment the lithographic apparatus comprises an
underpressure source 222 (illustrated in FIG. 1) connectable to the
at least one gas recovery opening
[0136] In an embodiment the immersion liquid provided may be acidic
or alkali, irrespective of the type of fluid handling structure 12.
The idea of providing an acidic immersion liquid has previously
been described in European patent application publication no. EP
1,482,372, herein incorporated in its entirety by reference, in
connection with reducing interaction of immersion liquid with top
coat. However, this document does not appreciate the possibility of
increasing scan speed as a result of the acidic immersion liquid.
In an embodiment, normal (e.g. neutral) immersion liquid may be
used and acidic or alkaline immersion liquid may be provided
through a liquid supply opening in the undersurface of the fluid
handling structure 12 radially inwardly of the meniscus controlling
feature. An example of such a liquid supply opening is the opening
180 illustrated in FIG. 4. A similar opening may be present in any
of the other embodiments described herein.
[0137] In any of the above embodiments, the gas supply opening 220
may be in a radially inward direction of the at least one gas knife
opening 210. Thus the gas knife opening 210 may be radially outward
of the gas supply opening 220 and the space 11.
[0138] In any of the above embodiments, the fluid handling
structure 12 may be controlled to switch off the gas knife, i.e. to
prevent gas exiting from the at least one gas knife opening 210. In
such an embodiment, other aspects of the lithographic apparatus may
be altered to avoid or reduce the likelihood of a bubble being
included in the immersion liquid, for example, the scan speed may
be reduced when the gas knife is turned off.
[0139] As will be appreciated, any of the above described features
can be used with any other feature and it is not only those
combinations explicitly described which are covered in this
application. The immersion system of any one of the above
embodiments may be used in a device manufacturing method or in a
lithographic apparatus.
[0140] A fluid handling structure 12 may be provided as any one of
the fluid handling structures 12 described above or for use in any
of the immersion systems described above. The fluid handling
structure 12 may be configured to maintain immersion fluid to a
region, the fluid handling structure 12 having, at a boundary of a
space 11. The fluid handling structure 12 may have at least one gas
knife opening 210 in a radially outward direction from the space 11
and at least one gas supply opening 220 in the radially outward
direction from the at least one gas knife opening 210 relative to
the space 11. The at least one gas supply opening 220 may comprise
a mesh. The mesh may be replaced with a sieve, porous material
and/or an array of holes. For example, the array of holes may be an
array of two or three rows of holes. The array of holes may
comprise holes of approximately 10 .mu.m to 60 .mu.m. The gas
supply opening 220 may have a mesh, sieve, porous material and/or
array of holes to make the flow of gas exiting the gas supply
opening 220 more laminar (than if no mesh, sieve, porous material
or array of holes is provided) to avoid, or reduce the likelihood
of, gas exiting the gas supply opening 220 from mixing with
air.
[0141] In an embodiment, there is provided an immersion system
comprising a fluid handling structure configured to contain
immersion fluid to a region, the fluid handling structure having,
at a boundary of a space: at least one gas knife opening in a
radially outward direction from the space; and at least one gas
supply opening in the radially outward direction from the at least
one gas knife opening relative to the space; and the immersion
system further comprising a gas supply system configured to supply
substantially pure CO.sub.2 gas through the at least one gas knife
opening and the at least one gas supply opening so as to provide an
atmosphere of substantially pure CO.sub.2 gas adjacent to, and
radially outward of, the space.
[0142] In an embodiment, the gas exits the at least one gas knife
opening at a first gas velocity and the gas exits the at least one
gas supply opening at a second gas velocity, the first gas velocity
being greater than the second gas velocity. In an embodiment, the
substantially pure CO.sub.2 gas is humidified CO.sub.2 gas. In an
embodiment, the fluid handling structure comprises a meniscus
controlling feature to resist passage of the immersion fluid in a
radially outward direction from the space, the meniscus controlling
feature being radially inward of the at least one gas knife
opening. In an embodiment, the gas exits the at least one gas knife
opening at a first flow speed and the gas exits the at least one
gas supply opening at a second flow speed, the first flow speed
being greater than the second flow speed. In an embodiment, the
fluid handling structure comprises the gas supply system. In an
embodiment, the gas supply system comprises at least one gas source
to provide gas to the at least one gas knife opening and the at
least one gas supply opening. In an embodiment, the gas supply
system comprises a first path between a first gas source and the at
least one gas knife opening and a second path between a second gas
source and the at least one gas supply opening, wherein the second
path comprises a flow restrictor section, and optionally, wherein
the flow restrictor section is a bend and/or reduction in a
flow-through area in the second path. In an embodiment, the first
gas source and the second gas source are the same gas source. In an
embodiment, the at least one gas knife opening and the at least one
gas supply opening are on a surface of the fluid handling structure
facing a substrate and/or a substrate table, wherein the at least
one gas knife opening is closer to the substrate and/or substrate
table than the at least one gas supply opening, and/or the at least
one gas knife opening has a smaller surface area on the surface of
the fluid handling structure than the at least one gas supply
opening. In an embodiment, the fluid handling structure is
configured to dynamically control the amount of gas supplied to the
gas knife opening by redirecting gas to the gas knife opening from
the gas supply opening, or from the gas knife opening to the gas
supply opening.
[0143] In an embodiment, there is provided an immersion system
comprising a fluid handling structure configured to contain
immersion fluid to a region, the fluid handling structure having,
at a boundary of a space: at least one gas knife opening in a
radially outward direction from the space; at least one gas supply
opening in the radially outward direction from the at least one gas
knife opening relative to the space; and a gas supply system
configured to supply gas through the at least one gas knife opening
and the at least one gas supply opening, wherein gas exits the at
least one gas knife opening at a higher gas velocity than gas
exiting the at least one gas supply opening.
[0144] In an embodiment, the fluid handling structure comprises a
meniscus controlling feature to resist passage of the immersion
fluid in a radially outward direction from the space, the meniscus
controlling feature being radially inward of the at least one gas
knife opening. In an embodiment, the gas exits the at least one gas
knife opening at a first flow speed and the gas exits the at least
one gas supply opening at a second flow speed, the first flow speed
being greater than the second flow speed. In an embodiment, the
fluid handling structure comprises the gas supply system. In an
embodiment, the gas supply system comprises at least one gas source
to provide gas to the at least one gas knife opening and the at
least one gas supply opening. In an embodiment, the gas supply
system comprises a first path between a first gas source and the at
least one gas knife opening and a second path between a second gas
source and the at least one gas supply opening, wherein the second
path comprises a flow restrictor section, and optionally, wherein
the flow restrictor section is a bend and/or reduction in a
flow-through area in the second path. In an embodiment, the first
gas source and the second gas source are the same gas source. In an
embodiment, the at least one gas knife opening and the at least one
gas supply opening are on a surface of the fluid handling structure
facing a substrate and/or a substrate table, wherein the at least
one gas knife opening is closer to the substrate and/or substrate
table than the at least one gas supply opening, and/or the at least
one gas knife opening has a smaller surface area on the surface of
the fluid handling structure than the at least one gas supply
opening. In an embodiment, the fluid handling structure is
configured to dynamically control the amount of gas supplied to the
gas knife opening by redirecting gas to the gas knife opening from
the gas supply opening, or from the gas knife opening to the gas
supply opening.
[0145] In an embodiment, there is provided a device manufacturing
method comprising projecting a projection beam of radiation via an
immersion fluid onto a substrate in a lithographic apparatus
comprising an immersion system, wherein the immersion system
comprises a fluid handling structure configured to contain the
immersion fluid to a region, the fluid handling structure having,
at a boundary of a space: at least one gas knife opening in a
radially outward direction from the space; and at least one gas
supply opening in the radially outward direction from the at least
one gas knife opening relative to the space; and the method
comprising supplying substantially pure CO.sub.2 gas through the at
least one gas knife opening and the at least one gas supply opening
so as to provide an atmosphere of substantially pure CO.sub.2 gas
adjacent to, and radially outward of, the space, or supplying gas
through the at least one gas knife opening and the at least one gas
supply opening, wherein gas exits the at least one gas knife
opening at a higher gas velocity than gas exiting the at least one
gas supply opening.
[0146] In an embodiment, there is provided a lithographic apparatus
comprising an immersion system comprising a fluid handling
structure configured to contain immersion fluid to a region, the
fluid handling structure having, at a boundary of a space: at least
one gas knife opening in a radially outward direction from the
space; and at least one gas supply opening in the radially outward
direction from the at least one gas knife opening relative to the
space; and the immersion system further comprising a gas supply
system configured to supply substantially pure CO.sub.2 gas the at
least one gas knife opening and the at least one gas supply opening
so as to provide an atmosphere of substantially pure CO.sub.2 gas
adjacent to, and radially outward of, the space, or a gas supply
system configured to supply gas through the at least one gas knife
opening and the at least one gas supply opening, wherein gas exits
the at least one gas knife opening at a higher gas velocity than
gas exiting the at least one gas supply opening.
[0147] In an embodiment, there is provided a fluid handling
structure configured to contain immersion fluid to a region, the
fluid handling structure having, at a boundary of a space: at least
one gas knife opening in a radially outward direction from the
space; and at least one gas supply opening in the radially outward
direction from the at least one gas knife opening relative to the
space, wherein the at least one gas supply opening comprises a
mesh, a sieve, porous material and/or array of holes.
[0148] Although specific reference may be made in this text to the
use of lithographic apparatus in the manufacture of integrated
circuits, 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 W
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 W 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 W may be processed more
than once, for example in order to create a multi-layer integrated
circuit, so that the term substrate W used herein may also refer to
a substrate W that already contains multiple processed layers.
[0149] 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). 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.
[0150] While specific embodiments of the invention have been
described above, it will be appreciated that the invention may be
practiced otherwise than as described.
[0151] Any controllers described herein may each or in combination
be operable when the one or more computer programs are read by one
or more computer processors located within at least one component
of the lithographic apparatus. The controllers may each or in
combination have any suitable configuration for receiving,
processing, and sending signals. One or more processors are
configured to communicate with the at least one of the controllers.
For example, each controller may include one or more processors for
executing the computer programs that include machine-readable
instructions for the methods described above. The controllers may
include data storage medium for storing such computer programs,
and/or hardware to receive such medium. So the controller(s) may
operate according the machine readable instructions of one or more
computer programs.
[0152] One or more embodiments of the invention may be applied to
any immersion lithography apparatus. In particular, but not
exclusively, those types mentioned above and whether the immersion
liquid is provided in the form of a bath, only on a localized
surface area of the substrate W, or is unconfined. In an unconfined
arrangement, the immersion liquid may flow over the surface of the
substrate W and/or substrate table WT so that substantially the
entire uncovered surface of the substrate table WT and/or substrate
W is wetted. In such an unconfined immersion system, the liquid
supply system may not confine the immersion liquid or it may
provide a proportion of immersion liquid confinement, but not
substantially complete confinement of the immersion liquid.
[0153] One or more embodiments of the invention may be used in a
device manufacturing method.
[0154] A liquid supply system as contemplated herein should be
broadly construed. In certain embodiments, it may be a mechanism or
combination of structures that provides a liquid to a space 11
between the projection system PS and the substrate W and/or
substrate table WT. It may comprise a combination of one or more
structures, one or more fluid openings including one or more liquid
openings, one or more gas openings or one or more openings for two
phase flow. The openings may each be an inlet into the immersion
space 11 (or an outlet from a fluid handling structure) or an
outlet out of the immersion space 11 (or an inlet into the fluid
handling structure). In an embodiment, a surface of the space 11
may be a portion of the substrate W and/or substrate table WT, or a
surface of the space 11 may completely cover a surface of the
substrate W and/or substrate table WT, or the space 11 may envelop
the substrate W and/or substrate table WT. The liquid supply system
may optionally further include one or more elements to control the
position, quantity, quality, shape, flow rate or any other features
of the liquid.
[0155] 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.
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