U.S. patent application number 12/292964 was filed with the patent office on 2010-09-16 for lithographic apparatus and device manufacturing method.
This patent application is currently assigned to ASML Netherlands B.V.. Invention is credited to Nicolaas TEN KATE, Ronald VAN DER HAM, Willem VENEMA.
Application Number | 20100231875 12/292964 |
Document ID | / |
Family ID | 40797833 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100231875 |
Kind Code |
A2 |
TEN KATE; Nicolaas ; et
al. |
September 16, 2010 |
Lithographic Apparatus and Device Manufacturing Method
Abstract
An immersion lithographic apparatus is provided with an
electrode set to remove unwanted droplets of an immersion fluid
from a particular surface. Unwanted droplets of immersion fluid may
form on any number of different surfaces of the immersion
apparatus, such as on a liquid barrier member. If allowed to
evaporate and/or dry, these droplets may cause a problem such as
uncontrolled heat loading of the apparatus and/or staining of the
surface. An electrode set is provided on a surface where the
droplets are likely to be formed. A controlled voltage is applied
to the electrodes within the electrode set in order to
electrostatically remove the droplets from the surface.
Inventors: |
TEN KATE; Nicolaas;
(Almkerk, NL) ; VENEMA; Willem; (Eindhoven,
NL) ; VAN DER HAM; Ronald; (Maarheeze, NL) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
UNITED STATES
703-770-7900
703-770-7901
|
Assignee: |
ASML Netherlands B.V.
De Run 6501
Veldhoven
NL
NL-5504 DR
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20090168032 A1 |
July 2, 2009 |
|
|
Family ID: |
40797833 |
Appl. No.: |
12/292964 |
Filed: |
December 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60/996736 |
Dec 3, 2007 |
|
|
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61/006023 |
Dec 14, 2007 |
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Current U.S.
Class: |
355/30 |
Current CPC
Class: |
G03F 7/70341
20130101 |
Class at
Publication: |
355/030 |
International
Class: |
G03B 27/52 20060101
G03B027/52 |
Claims
1. An immersion lithographic apparatus comprising: a surface from
at least a portion of which a fluid droplet is to be removed; and
an active droplet removal system formed on or in the surface,
wherein the portion of the surface is sufficiently removed from
adjacent portions of the apparatus for there to be insufficient net
capillary force acting on a fluid droplet on the portion of the
surface to cause the fluid droplet to move by capillary action, and
the active droplet removal system is arranged to manipulate the
fluid droplet on the portion of the surface without the assistance
of capillary action.
2. The apparatus of claim 1, wherein the active droplet removal
system comprises an electrode set formed on or in the surface, the
electrode set comprising a plurality of electrodes.
3. The apparatus of claim 2, wherein the electrodes are arranged
within the electrode set such that a voltage can be applied to them
so as to electrostatically manipulate fluid on the surface.
4. The apparatus of claim 3, wherein the electrodes are arranged so
as to remove fluid from the surface or from a part of the
surface.
5. The apparatus of claim 3, wherein the electrodes are arranged in
the electrode set in rows.
6. The apparatus of claim 3, wherein the electrodes are arranged
along a direction in which fluid on the surface can be
manipulated.
7. The apparatus of claim 3, wherein a distance between the center
of each electrode is selected from the range of 0.1 mm to 1 mm.
8. The apparatus of claim 3, wherein the electrodes are arranged in
the electrode set in a grid pattern comprising two substantially
perpendicular rows of electrodes.
9. The apparatus of claim 3, comprising a controller arranged to
control the voltage applied to the electrodes.
10. The apparatus of claim 9, wherein the controller is arranged to
apply a continuously repeating cycle of different voltages to one
or more of the electrodes.
11. The apparatus of claim 9, wherein the controller is arranged to
control the voltage applied to the electrodes so that no voltage is
applied at a time when application of a voltage could result in
operation of one or more of the elements of the lithographic
apparatus being adversely affected.
12. The apparatus of claim 1, wherein the portion of the surface is
an open surface.
13. The apparatus of claim 12, wherein the open surface is an
unenclosed surface.
14. The apparatus of claim 12, wherein the open surface is a
surface whose center of curvature is on the opposite side of the
surface to the side on which the droplet is situated.
15. The apparatus of claim 1, wherein the surface is not one of a
plurality of surfaces that surround a space.
16. The apparatus of claim 1, wherein the surface is not a surface
that forms part of a channel.
17. The apparatus of claim 1, wherein the portion of the surface is
sufficiently removed from other surfaces for it not to be possible
for a fluid used as an immersion fluid in the immersion lithography
apparatus to form a meniscus between the portion of the surface and
another surface.
18. The apparatus of claim 1, wherein the surface can be any
surface of the immersion lithography apparatus other than a surface
through which a projection beam is transmitted.
19. The apparatus of claim 1, wherein the lithographic apparatus
comprises: a substrate table configured to hold a substrate, the
surface being part of the substrate table; and/or a projection
system configured to project a patterned radiation beam onto a
target portion of the substrate, the projection system comprising a
final element, the surface being part of the projection system;
and/or a fluid handling system comprising a barrier member and
configured to supply, contain, and/or remove fluid to a space
between the final element and the substrate, the surface being part
of the barrier member; and/or a sensor, the surface being part of a
sensor.
20. The apparatus of claim 3, wherein the electrodes are arranged
such that fluid can be manipulated on the surface using only
electrostatic forces generated by the electrodes.
21. The apparatus of claim 3, wherein the electrodes are arranged
to electrostatically manipulate immersion fluid.
22. The apparatus of claim 3, wherein the electrodes are arranged
to electrostatically manipulate a dilute ionic solution.
23. The apparatus of claim 22, wherein the dilute ionic solution is
acidic.
24. The apparatus of claim 23, wherein the dilute ionic solution
comprises water with dissolved carbon dioxide.
25. The apparatus of claim 3, wherein the surface and/or the
electrodes are at least partially covered in a liquid-phobic
material.
26. The apparatus of claim 25, wherein the liquid-phobic material
comprises a polytetrafluoroethylene type material.
27. An immersion lithographic apparatus comprising: a surface from
at least a portion of which a fluid droplet is to be removed; and
an active droplet removal system formed on or in the surface and
configured to manipulate a fluid droplet around the surface,
wherein the active droplet removal system is arranged to manipulate
a fluid droplet that is in contact with no surfaces other than the
surface comprising the portion from which it is to be removed.
28. An immersion lithographic apparatus comprising: a surface from
at least a portion of which a fluid droplet is to be removed; and
an active droplet removal system formed on or in the surface and
configured to manipulate a fluid droplet around the surface,
wherein the portion of the surface is sufficiently removed from all
other surfaces that surface tension of the fluid is not sufficient
for fluid to bridge a gap between the portion of the surface and
any other surface, and the active droplet removal system is
arranged to manipulate a fluid droplet on the portion of the
surface.
29. An immersion lithographic apparatus comprising: a surface from
at least a portion of which a fluid droplet is to be removed; and
an active droplet removal system formed on or in the surface and
configured to manipulate a fluid droplet around the surface,
wherein the active droplet removal system is arranged to manipulate
a fluid droplet on the portion of the surface, and a center of
curvature of the portion of the surface is on the opposite side of
the surface to the side on which the fluid droplet is to be
manipulated.
30. A device manufacturing method comprising: projecting a
patterned beam of radiation onto a substrate using a projection
system; supplying immersion fluid, using an immersion system, to a
space between the projection system and the substrate; and
removing, without the assistance of capillary action, an unwanted
droplet of the immersion fluid on which insufficient net capillary
force to cause the droplet to move by capillary action is acting
from a portion of a surface of the projection system or the
immersion system by applying a controlled voltage to electrodes
provided in or on the surface.
31. The method of claim 30, wherein the droplet is removed from an
open surface.
32. The method of claim 30, wherein the droplet is removed from a
portion of a surface that does not form part of a channel.
33. The method of claim 30, wherein the droplet is removed from a
portion of a surface that does not form part of a duct.
34. The method of claim 30, wherein the droplet is removed from a
portion of a surface that is not one of a plurality of surfaces
that surround a space.
35. The method of claim 30, wherein the droplet is not in contact
with any surface other than the surface that comprises the portion
from which it is to be removed.
36. The method of claim 30, wherein the surface tension of the
fluid of the droplet is not sufficient for the fluid to bridge a
gap between the portion of the surface and any other surface.
37. The method of claim 30, wherein the unwanted droplet is a
liquid droplet.
Description
[0001] This application claims priority and benefit under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Patent Application Ser. No.
60/996,736, entitled "Lithographic Apparatus and Device
Manufacturing Method", filed on Dec. 3, 2007, and to U.S.
Provisional Patent Application Ser. No. 61/006,023, entitled
"Lithographic Apparatus and Device Manufacturing Method", filed on
Dec. 14, 2007. The contents of those applications are incorporated
herein in their entirety by reference.
FIELD
[0002] The present invention relates to a lithographic apparatus
and a method for manufacturing a device.
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 (ICs). In that instance, a
patterning device, which is alternatively referred to as a mask or
a reticle, may be used to generate a circuit pattern to be formed
on an individual layer of the IC. This pattern can be transferred
onto a target portion (e.g. comprising part of, one, or several
dies) on a substrate (e.g. a silicon wafer). Transfer of the
pattern is typically via imaging onto a layer of
radiation-sensitive material (resist) provided on the substrate. In
general, a single substrate will contain a network of adjacent
target portions that are successively patterned. Known lithographic
apparatus include so-called steppers, in which each target portion
is irradiated by exposing an entire pattern onto the target portion
at one time, and so-called scanners, in which each target portion
is irradiated by scanning the pattern through a radiation beam in a
given direction (the "scanning"-direction) while synchronously
scanning the substrate parallel or anti-parallel to this direction.
It is also possible to transfer the pattern from the patterning
device to the substrate by imprinting the pattern onto the
substrate.
[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 and the substrate. The
liquid may be distilled water, although other liquids can be used.
An embodiment of the present invention will be described with
reference to liquid. However, other fluids 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. 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 liquid such as
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
are a hydrocarbon, a fluorohydrocarbon, or an aqueous solution.
These are also included in an embodiment of the present
invention.
[0005] However, submersing the substrate or substrate and substrate
table in a bath of liquid (see, for example, U.S. Pat. No.
4,509,852, hereby incorporated in its entirety by reference) 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] One of the solutions proposed is for a liquid supply system
to provide liquid on only a localized area of the substrate and in
between the final element of the projection system and the
substrate using a liquid confinement system (the substrate
generally has a larger surface area than the final element of the
projection system). One way which has been proposed to arrange for
this is disclosed in PCT patent application publication no. WO
99/49504, hereby incorporated in its entirety by reference. As
illustrated in FIGS. 2 and 3, liquid is supplied by at least one
inlet IN onto the substrate, preferably along the direction of
movement of the substrate relative to the final element, and is
removed by at least one outlet OUT after having passed under the
projection system. That is, as the substrate is scanned beneath the
element in a -X direction, liquid is supplied at the +X side of the
element and taken up at the -X side. FIG. 2 shows the arrangement
schematically in which liquid is supplied via inlet IN and is taken
up on the other side of the element by outlet OUT which is
connected to a low pressure source. In the illustration of FIG. 2
the liquid is supplied along the direction of movement of the
substrate relative to the final element, though this does not need
to be the case. Various orientations and numbers of in- and
out-lets positioned around the final element are possible, one
example is illustrated in FIG. 3 in which four sets of an inlet
with an outlet on either side are provided in a regular pattern
around the final element.
[0007] An immersion lithography solution with a localized liquid
supply system is shown in FIG. 4. Liquid is supplied by two groove
inlets IN on either side of the projection system PL and is removed
by a plurality of discrete outlets OUT arranged radially outwardly
of the inlets IN. The inlets IN and outlets OUT can be arranged in
a plate with a hole in its center and through which the projection
is project. Liquid is supplied by one groove inlet IN on one side
of the projection system PS and removed by a plurality of discrete
outlets OUT on the other side of the projection system PL. This
causes a flow of a thin film of liquid between the projection
system PS and the substrate W. The choice of which combination of
inlet IN and outlets OUT to use can depend on the direction of
movement of the substrate W (the other combination of inlet IN and
outlets OUT being inactive).
[0008] In European Patent Application Publication No. 1420300 and
United States Patent Application Publication No. 2004-0136494, each
of which is hereby incorporated in its entirety by reference, the
idea of a twin or dual stage immersion lithography apparatus is
disclosed. Such an apparatus is provided with two tables for
supporting the substrate. Leveling measurements are carried out
with a table at a first position, without immersion liquid.
Exposure is carried out with a table at a second position, where
immersion liquid is present. Alternatively, the apparatus may have
only one table movable between exposure and measurement
positions.
[0009] In an immersion lithographic apparatus, droplets of
immersion liquid may be unintentionally transferred to, or left
behind on, a surface or part of a surface where no immersion liquid
is intended to be situated at a particular time. This may cause a
problem which may result in a defective substrate being
produced.
SUMMARY
[0010] It is desirable, for example, to remove unwanted droplets of
immersion liquid from a surface of an immersion lithographic
apparatus.
[0011] According to an aspect of the present invention, there is
provided an immersion lithographic apparatus comprising:
[0012] a surface from at least a portion of which a fluid droplet
is to be removed; and
[0013] an active droplet removal system formed on or in the
surface, wherein
[0014] the portion of the surface is sufficiently removed from
adjacent portions of the apparatus for there to be insufficient net
capillary force acting on a fluid droplet on the portion of the
surface to cause the fluid droplet to move by capillary action,
and
[0015] the active droplet removal system is arranged to manipulate
the fluid droplet on the portion of the surface without the
assistance of capillary action.
[0016] According to an aspect of the present invention, there is
provided an immersion lithographic apparatus comprising:
[0017] a surface from at least a portion of which a fluid droplet
is to be removed; and
[0018] an active droplet removal system formed on or in the surface
and for manipulating a fluid droplet around the surface, wherein
the active droplet removal system is arranged to manipulate a fluid
droplet that is in contact with no surfaces other than the surface
comprising the portion from which it is to be removed.
[0019] According to an aspect of the present invention, there is
provided an immersion lithographic apparatus comprising:
[0020] a surface from at least a portion of which a fluid droplet
is to be removed; and
[0021] an active droplet removal system formed on or in the surface
and for manipulating a fluid droplet around the surface,
wherein
[0022] the portion of the surface is sufficiently removed from all
other surfaces that surface tension of the fluid is not sufficient
for fluid to bridge a gap between the portion of the surface and
any other surface, and
[0023] the active droplet removal system is arranged to manipulate
a fluid droplet on the portion of the surface.
[0024] According to an aspect of the present invention, there is
provided an immersion lithographic apparatus comprising:
[0025] a surface from at least a portion of which a fluid droplet
is to be removed; and
[0026] an active droplet removal system formed on or in the surface
and for manipulating a fluid droplet around the surface,
wherein
[0027] the active droplet removal system is arranged to manipulate
a fluid droplet on the portion of the surface, and
[0028] the center of curvature of the portion of the surface is on
the opposite side of the surface to the side on which the fluid
droplet is to be manipulated.
[0029] According to an aspect of the present invention, there is
provided a device manufacturing method comprising:
[0030] projecting a projection beam of radiation onto a substrate
using a projection system;
[0031] supplying immersion fluid, using an immersion system, to a
space between the projection system and the substrate; and
[0032] removing, without the assistance of capillary action, an
unwanted droplet of the immersion fluid on which insufficient net
capillary force to cause the droplet to move by capillary action is
acting from a portion of a surface of the projection system or the
immersion system by applying a controlled voltage to electrodes
provided in or on the surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] 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:
[0034] FIG. 1 depicts a lithographic apparatus according to an
embodiment of the invention;
[0035] FIGS. 2 and 3 depict a liquid supply system for use in a
lithographic projection apparatus;
[0036] FIG. 4 depicts a further liquid supply system for use in a
lithographic projection apparatus;
[0037] FIG. 5 depicts a further liquid supply system for use in a
lithographic projection apparatus;
[0038] FIG. 6 depicts a close-up cross sectional view of an example
barrier member and surrounding area showing typical areas where
unwanted droplets may form;
[0039] FIG. 7 depicts a plan view of a substrate, substrate table,
and sensors;
[0040] FIG. 8 depicts the close-up view of the example barrier
member and surrounding area of FIG. 6, and also shows suitable
positions for an electrode according to an embodiment of the
present invention;
[0041] FIG. 9 depicts a plan view an arrangement of electrodes for
use in an embodiment of the present invention;
[0042] FIG. 10 depicts a cross sectional view of part of a barrier
member with electrodes thereon for use in an embodiment of the
present invention;
[0043] FIG. 11 depicts a plan view of a grid-pattern arrangement of
electrodes for use in an embodiment of the present invention;
[0044] FIG. 12 depicts a cross sectional view of a different type
of barrier member and surrounding area showing where droplets might
form in an immersion lithography apparatus;
[0045] FIG. 13 depicts a cross sectional view of part of a
substrate table, substrate and immersion fluid in an immersion
lithography apparatus to which an embodiment of the present
invention could be applied; and
[0046] FIG. 14 depicts a cross sectional view of the FIG. 13
apparatus showing possible locations of unwanted droplets and
suitable positions for electrodes according to an embodiment of the
invention.
DETAILED DESCRIPTION
[0047] FIG. 1 schematically depicts a lithographic apparatus
according to one embodiment of the invention. The apparatus
comprises:
[0048] an illumination system (illuminator) IL configured to
condition a radiation beam B (e.g. UV radiation or DUV
radiation);
[0049] a support structure (e.g. a mask table) MT constructed to
support a patterning device (e.g. a mask) MA and connected to a
first positioner PM configured to accurately position the
patterning device in accordance with certain parameters;
[0050] a substrate table (e.g. a wafer table) WT constructed to
hold a substrate (e.g. a resist-coated wafer) W and connected to a
seconds positioner PW configured to accurately position the
substrate in accordance with certain parameters; and
[0051] a projection system (e.g. a refractive projection lens
system) PS configured to project a pattern imparted to the
radiation beam B by patterning device MA onto a target portion C
(e.g. comprising one or more dies) of the substrate W.
[0052] The illumination system may include various types of optical
components, such as refractive, reflective, magnetic,
electromagnetic, electrostatic or other types of optical
components, or any combination thereof, for directing, shaping, or
controlling radiation.
[0053] The support structure holds the patterning device in a
manner that depends on the orientation of the patterning device,
the design of the lithographic apparatus, and other conditions,
such as for example whether or not the patterning device is held in
a vacuum environment. The support structure can use mechanical,
vacuum, electrostatic or other clamping techniques to hold the
patterning device. The support structure may be a frame or a table,
for example, which may be fixed or movable as required. The support
structure may ensure that the patterning device is at a desired
position, for example with respect to the projection system. Any
use of the terms "reticle" or "mask" herein may be considered
synonymous with the more general term "patterning device."
[0054] The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
radiation beam with a pattern in its cross-section such as to
create a pattern in a target portion of the substrate. It should be
noted that the pattern imparted to the radiation beam may not
exactly correspond to the desired pattern in the target portion of
the substrate, for example if the pattern includes phase-shifting
features or so called assist features. Generally, the pattern
imparted to the radiation beam will correspond to a particular
functional layer in a device being created in the tar get portion,
such as an integrated circuit.
[0055] The patterning device may be transmissive or reflective.
Examples of patterning devices include masks, programmable mirror
arrays, and programmable LCD panels. Masks are well known in
lithography, and include-mask types such as binary, alternating
phase-shift, and attenuated phase-shift, as well as various hybrid
mask types. An example of a programmable mirror array employs a
matrix arrangement of small mirrors, each of which can be
individually tilted so as to reflect an incoming radiation beam in
different directions. The tilted mirrors impart a pattern in a
radiation beam which is reflected by the mirror matrix.
[0056] The term "projection system" used herein should be broadly
interpreted as encompassing any type of projection system,
including refractive, reflective, catadioptric, magnetic,
electromagnetic and electrostatic optical systems, or any
combination thereof, as appropriate for the exposure radiation
being used, or for other factors such as the use of an immersion
liquid or the use of a vacuum. Any use of the term "projection
lens" herein may be considered as synonymous with the more general
term "projection system".
[0057] As here depicted, the apparatus is of a transmissive type
(e.g. employing a transmissive mask). Alternatively, the apparatus
may be of a reflective type (e.g. employing a programmable mirror
array of a type as referred to above, or employing a reflective
mask).
[0058] The lithographic apparatus may be of a type having two (dual
stage) or more substrate tables (and/or two or more patterning
device tables). In such "multiple stage" machines the additional
tables may be used in parallel, or preparatory steps may be carried
out on one or more tables while one or more other tables are being
used for exposure.
[0059] Referring to FIG. 1, the illuminator IL receives a radiation
beam from a radiation source SO. The source and the lithographic
apparatus may be separate entities, for example when the source is
an excimer laser. In such cases, the source is not considered to
form part of the lithographic apparatus and the radiation beam is
passed from the source SO to the illuminator IL with the aid of a
beam delivery system BD comprising, for example, suitable directing
mirrors and/or a beam expander. In other cases the source may be an
integral part of the lithographic apparatus, for example when the
source is a mercury lamp. The source SO and the illuminator L,
together with the beam delivery system BD if required, may be
referred to as a radiation system.
[0060] The illuminator IL may comprise an adjuster AD for adjusting
the angular intensity distribution of the radiation beam.
Generally, at least the outer and/or inner radial extent (commonly
referred to as .sigma.-outer and .sigma.-inner, respectively) of
the intensity distribution in a pupil plane of the illuminator can
be adjusted. In addition, the illuminator IL may comprise various
other components, such as an integrator IN and a condenser CO. The
illuminator may be used to condition the radiation beam, to have a
desired uniformity and intensity distribution in its
cross-section.
[0061] The radiation beam B is incident on the patterning device
(e.g., mask) MA, which is held on the support structure (e.g., mask
table) MT, and is patterned by the patterning device. Having
traversed the patterning device MA, the radiation beam B passes
through the projection system PS, which focuses the beam onto a
target portion C of the substrate W. With the aid of the second
positioner PW and position sensor IF (e.g. an interferometric
device, linear encoder or capacitive sensor), the substrate table
WT can be moved accurately, e.g. so as to position different target
portions C in the path of the radiation beam B. Similarly, the
first positioner PM and another position sensor (which is not
explicitly depicted in FIG. 1) can be used to accurately position
the patterning device MA with respect to the path of the radiation
beam B, e.g. after mechanical retrieval from a mask library, or
during a scan. In general, movement of the support structure MT may
be realized with the aid of a long-stroke module (coarse
positioning) and a short-stroke module (fine positioning), which
form part of the first positioner PM. Similarly, movement of the
substrate table WT may be realized using a long-stroke module and a
short-stroke module, which form part of the second positioner PW.
In the case of a stepper (as opposed to a scanner) the support
structure MT may be connected to a short-stroke actuator only, or
may be fixed. Patterning device MA and substrate W may be aligned
using patterning device alignment marks M1, M2 and substrate
alignment marks P1, P2. Although the substrate alignment marks as
illustrated occupy dedicated target portions, they may be located
in spaces between target portions (these are known as scribe-lane
alignment marks). Similarly, in situations in which more than one
die is provided on the patterning device MA, the patterning device
alignment marks may be located between the dies.
[0062] The depicted apparatus could be used in at least one of the
following modes:
[0063] 1. In step mode, the support structure MT and the substrate
table WT are kept essentially stationary, while an entire pattern
imparted to the radiation beam is projected onto a target portion C
at one time (i.e. a single static exposure). The substrate table WT
is then shifted in the X and/or Y direction so that a different
target portion C can be exposed. In step mode, the maximum size of
the exposure field limits the size of the target portion C imaged
in a single static exposure.
[0064] 2. In scan mode, the support structure MT and the substrate
table WT are scanned synchronously while a pattern imparted to the
radiation beam is projected onto a target portion C (i.e. a single
dynamic exposure). The velocity and direction of the substrate
table WT relative to the support structure MT may be determined by
the (de-)magnification and image reversal characteristics of the
projection system PS. In scan mode, the maximum size of the
exposure field limits the width (in the non-scanning direction) of
the target portion in a single dynamic exposure, whereas the length
of the scanning motion determines the height (in the scanning
direction) of the target portion.
[0065] 3. In another mode, the support structure MT is kept
essentially stationary holding a programmable patterning device,
and the substrate table WT is moved or scanned while a pattern
imparted to the radiation beam is projected onto a target portion
C. In this mode, generally a pulsed radiation source is employed
and the programmable patterning device is updated as required after
each movement of the substrate table WT or in between successive
radiation pulses during a scan. This mode of operation can be
readily applied to maskless lithography that utilizes programmable
patterning device, such as a programmable mirror array of a type as
referred to above.
[0066] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0067] In an immersion lithographic apparatus, droplets of
immersion liquid may be unintentionally transferred to, or left
behind on, a surface or part of a surface where no immersion liquid
is intended to be situated at a particular time. This may cause a
problem which may result in a defective substrate being
produced.
[0068] A problem may be that the presence of unwanted immersion
liquid droplets may cause a defect itself. For example, if unwanted
droplets are formed or left behind on a lens or sensor element,
then this may alter the optical properties of that element and lead
to inaccuracy in, for example, measurement and/or focusing.
[0069] Further, if the unwanted immersion liquid droplets are left
on the surface, then they may evaporate. In turn, this evaporation
may cause a thermal load to be applied to the element of the
lithographic apparatus comprising the surface on which the unwanted
droplets are situated. This thermal loading may result in further
inaccuracy, for example by changing an optical property of the
element and/or physically deforming the element in an uncontrolled
manner.
[0070] A further problem caused by allowing the unwanted droplets
to remain on the surface and evaporate is that contaminants may
build-up on the surface once the liquid has evaporated. The
contaminants may be a result of impurities that have built up in
the immersion liquid or of additives in the immersion liquid.
[0071] A possible technique for removing the unwanted immersion
liquid droplets is to passively remove them from the surface on
which they are situated. This can be achieved by applying a
liquid-phobic coating to that surface. Alternatively, it can be
achieved by using a combination of liquid-phobic and liquid-philic
coatings. However these techniques for passively removing the
unwanted droplets may remove the droplets relatively slowly. Thus,
one or more of the problems associated with their presence outlined
above may occur.
[0072] A quicker way of removing the unwanted immersion liquid
droplets is to use a gas stream to blow them away from the surface.
However, using such a gas stream may result in partial evaporation
of the droplets, which in turn may result in one or more of the
associated problems discussed herein such as, for example, thermal
loading and/or build up of impurities.
[0073] It is desirable to remove unwanted droplets of immersion
liquid from a surface of an immersion lithographic apparatus,
desirably its immersion system, quickly and without incurring
significant evaporation of the immersion liquid droplets. As used
herein, the "immersion system" can comprise at least a liquid
handling system, the substrate table WT and a final element of the
projection system PS. Although an embodiment of the invention is
discussed below with reference to liquid, the same principles can
be used for another fluid. For example, it will be understood that
an embodiment of the present invention is applicable to at least
fluid droplets, liquid droplets, fluid droplets with solid
particles suspended therein, and liquid droplets with solid
particles suspended therein.
[0074] The term droplet can be taken to mean, for example, a
discrete droplet that does not form part of a body of liquid larger
than itself. Furthermore, a droplet could not be connected, via
liquid, to another body of liquid. It will also be understood that
references in this application to control or removal of a plurality
of droplets apply equally to the control or removal of a single
droplet and vice versa.
[0075] It will also be understood that an embodiment of the
invention may be applied to any component in a lithographic
apparatus. In particular, it may be applied to any component in an
immersion lithographic apparatus including the immersion system. An
embodiment of the invention is most likely to be applied to a
surface susceptible of having unwanted immersion liquid droplets
formed thereon. This may include, for example, a surface of and/or
around: the final element of the projection system PS; the
substrate W; the substrate table WT; a liquid handling system, such
as a barrier member 120 of a liquid handling system; and/or an
immersion system, namely a system for providing, confining or
controlling immersion liquid in an immersion lithography
apparatus.
[0076] An embodiment of the invention is particularly applicable to
any form of immersion lithography apparatus which may comprise an
immersion system having a localized liquid supply system (i.e.
"local area") or having an unconfined liquid supply system such as
a "bath", and "all-wet" arrangement. In a "bath" arrangement, the
substrate is fully immersed (i.e. submerged) in a bath of the
immersion liquid. In an "all-wet" arrangement, the major surface of
the substrate facing the projection system is fully covered with
immersion liquid. The immersion liquid may cover the substrate in a
film, which is desirably thin. The immersion liquid may be supplied
so that it is free to flow over the substrate and may be over the
substrate table surrounding the major surface of the substrate.
Embodiments discussed below relate to "local area" and "all-wet"
immersion lithography apparatus, but embodiments could also relate
to any other type of lithography apparatus.
[0077] Another proposed immersion lithography apparatus has a
localized liquid supply system having a barrier member (or
so-called immersion hood) which extends along at least a part of a
boundary of the space between the final element of the projection
system and the substrate table. Such an apparatus is illustrated in
FIG. 5. The barrier member is substantially stationary relative to
the projection system in the XY plane. However, there may be some
relative movement in the Z direction (in the direction of the
optical axis). A seal is formed between the barrier member and the
surface of the substrate.
[0078] Referring to FIG. 5, a seal member 16 forms a contactless
seal to the substrate around the image field of the projection
system so that liquid is confined to fill a reservoir or an
immersion space 11 between the substrate surface and the final
element of the projection system. The reservoir 11 is formed by a
barrier member 12 positioned below and surrounding the final
element of the projection system PL. Liquid is brought into the
space below the projection system and within the barrier member 12.
For example, the liquid may be provided and/or removed through port
13. The barrier member 12 extends a little above the final element
of the projection system. The liquid rises above the final element
so that a buffer of liquid is provided. The barrier member 12 has
an inner periphery that at the upper end, in one arrangement,
closely conforms to the shape of the projection system or the final
element thereof and may, e.g., be round. At the bottom, the inner
periphery closely conforms to the shape of the image field, e.g.,
rectangular though this need not be the case.
[0079] The liquid is confined in the reservoir by a gas seal 16
between the bottom of the barrier member 12 and the surface of the
substrate W. The gas seal is formed by gas, e.g. air or synthetic
air. In one example, N.sub.2 or another inert gas, is provided
under pressure via inlet 15 to the gap between barrier member 12
and substrate W. The gas is extracted via first outlet 14. The
overpressure on the gas inlet 15, vacuum level on the first outlet
14 and geometry of the gap are arranged so that there is a
high-velocity gas flow radially inwards that confines the liquid.
Such a system is disclosed in United States patent application
publication no. US 2004-0207824.
[0080] A further example of an immersion lithography apparatus is
shown in FIG. 6. The apparatus of FIG. 6 has a liquid handling
system for, for example, supplying, containing, and removing
immersion liquid. The liquid handling system may comprise a barrier
member 120. The liquid handling system can have one or more of: a
liquid supply system (not shown in FIG. 6, but analogous to inlet
13 in FIG. 5); a liquid removal system 18, 181; and/or a seal
member 160 to hinder movement of immersion liquid past it. The seal
member 160 may serve to confine the immersion liquid to a volume. A
typical localized area immersion lithographic apparatus, such as
that shown in FIG. 6, may serve to contain a main body 200 of the
immersion liquid.
[0081] One or more unwanted droplets of immersion liquid can be
left or formed on any surface of an immersion lithography
apparatus, such as its immersion system. FIG. 6 shows a close up
view of a cross section through an immersion system and surrounding
features of an immersion lithographic apparatus. FIG. 6 shows the
position of various unwanted liquid droplets that may form on or be
left on one or more surfaces of the illustrated portion of an
immersion lithographic apparatus. For simplicity, only half of the
cross section through the immersion system and surrounding features
is shown. The location of the unwanted droplet(s) shown in FIG. 6
is typical of those that would be found in a conventional immersion
lithographic apparatus, as described below. However, it will be
understood that one or more unwanted immersion liquid droplets
could be formed on any other surface of an immersion lithography
apparatus, especially its immersion system.
[0082] The shaded areas indicate where the immersion liquid is
situated. The only part of the apparatus shown in FIG. 6 where the
presence of the immersion liquid is desirable is region 200. The
region 200 is bounded by the final element of the projection system
PS, the substrate W (or substrate table WT), and a surface of the
barrier member 120. A primary meniscus 201 extends between a bottom
surface 121 of the barrier member 120 and the substrate W. A liquid
edge 202 extends between the barrier member 120 and the final
element of the projection system PS. The liquid edge 202 may be
formed by, for example, surface tension.
[0083] A typical area on which unwanted immersion liquid droplets
may be formed is a surface 121 of the barrier member 120 facing the
substrate W. As shown in FIG. 6, the barrier member 120 is provided
with an immersion liquid extraction duct 18 formed in the surface
121 of the barrier member 120 facing the substrate W. The
extraction duct 18 is part of the liquid handling system that
controls the flow of immersion liquid through the immersion
lithographic apparatus. The duct 18 is one of several needle-type
extraction ducts located at different peripheral positions, which
may be circumferential positions. The ducts 18 are positioned to
surround the area 200. The ducts are arranged to remove the
immersion liquid, ultimately through outlet 181 which is open to an
underpressure. This system is effective in ensuring that most of
the immersion liquid does not pass radially beyond the inlet of
extraction duct 18. However some of the immersion liquid may not be
extracted through extraction duct 18, and this liquid may then form
unwanted droplets outside of the area 200 where the immersion
liquid is desired. Such droplets on the barrier member 120 may
subsequently fall onto the substrate resulting in defects on the
substrate W. Such defects may be shown as arcs and lines in a
pattern defect test.
[0084] Typically, an unwanted secondary body of immersion liquid
101 can form just beyond the entrance to the extraction duct 18.
This secondary body of immersion liquid 101 forms between the
surface 121 of the barrier member 120 facing the substrate W and/or
the substrate table WT, and the substrate W and/or substrate table
WT. When reference is made herein to the substrate W, or to the
substrate table WT, this can mean substrate W and substrate table
WT. As the substrate W and substrate table WT move relative to the
barrier member 120 and projection system PS, the secondary body of
immersion liquid 101 moves relative to the substrate W to form a
droplet 102 on the surface of the substrate W and/or substrate
table WT. This means that a trail of unwanted immersion liquid
droplets 102 may be left on the substrate W and/or the substrate
table WT. One or more unwanted droplets may also form on the
surface 121 of the barrier member. These droplets 102, resulting
from the secondary body of immersion liquid 101, may then cause
defects on the substrate W and/or substrate table WT. Such defects
may be shown as arcs and lines in a pattern defect test.
[0085] Liquid that has not been collected by extraction duct 18
could be transported further away from the main body of immersion
liquid 200. In order to prevent or at least reduce this, an
immersion lithographic device may have a gas seal 160. In the
illustrated embodiment, the gas seal 160 is a gas-knife having an
inlet 150 through which gas passes. A gas flow from the gas knife
160 is directed towards the substrate W. The gas knife 160 is
arranged so as to hinder any immersion liquid passing beyond it.
Ideally the gas knife 160 stops any immersion liquid passing beyond
it. Arrows 161 and 162 in FIG. 6 show the direction of gas flow
paths. Ultimately, the gas flow that follows path 161 (i.e. in the
direction towards the main body of immersion liquid 200) also exits
through outlet 181. There is provided a recess 170 in the barrier
member 120 radially inward (relative to the optical axis of the
projection system) of the gas knife 160. This recess 170 is to
provide a suitable gas flow exit path for the gas from the gas
knife that flows along a flow path 161 radially inward from the gas
knife 160.
[0086] Unwanted droplets of immersion liquid may form on either
side of the gas knife 160. For example, they could be formed on a
surface radially inward (relative to the optical axis of the
projection system). They could be formed radially outward of the
gas knife 160. Unwanted droplets of immersion liquid may form on a
surface radially outward of the gas knife 160 because of, for
example, gas from the gas knife causing droplets on the substrate
or substrate edge to splash upwards onto a surface of the immersion
system, such as the lower surface 121 of barrier member 120 that
faces the substrate W. In the example shown in FIG. 6, no unwanted
immersion liquid droplets are shown on a surface radially outward
of the gas knife 160.
[0087] In the illustrated example, unwanted immersion liquid
droplets have been formed on a surface radially inward of the gas
knife 160 (i.e. in the direction towards the main body of immersion
liquid 200). Two droplets are shown in the example of FIG. 6. One
droplet 103 is on a radially inward surface of the recess 170
forming gas outlet path 161. One droplet 104 is on a radially
outward surface of the recess 170 forming gas outlet path 161.
Droplets 103 and 104 could be susceptible to falling or draining
onto the substrate surface W, for example due to the force
resulting from gravity, potentially causing a problem such as
discussed above. Any surfaces which experience recirculating gas
flow from the operation of the gas knife 160 will be particularly
susceptible to having immersion liquid droplets formed thereon.
[0088] In addition to those droplets 102, 103 shown in FIG. 6 as
having been formed on the surface of the barrier member 120 which
faces the substrate W, unwanted immersion liquid droplets may form
at any other location. The precise location of the unwanted
immersion liquid droplets may depend on, for example, the
particular design of the liquid handling system. The precise
location of the unwanted immersion liquid droplets may depend on,
for example, the particular relative movement of the barrier member
120, projection system PS, substrate W, and substrate table WT.
[0089] Unwanted droplets may form on a surface that has a welded
joint. It may be particularly difficult to remove all of the
immersion liquid from the surface of such a joint.
[0090] A further region where unwanted immersion liquid droplets
may be formed is on the opposing surfaces of the final element of
the projection system PS and the barrier member 120, for example on
a surface 122 of the barrier member 120 that faces away from the
substrate W. The surface 122 may be located between the substrate W
and the final element of the projection system PS, and may be
referred to as the upper surface 122 of the barrier member 120.
This surface is particularly susceptible to having unwanted
immersion liquid droplets formed. The lower surface of the final
element of the projection system PS is also particularly
susceptible to having unwanted immersion liquid droplets formed
thereon.
[0091] A reason for this is that, during stepping and/or scanning
operations, the substrate, table WT and substrate W move relative
to the projection system PS, the barrier member 120 and other parts
of the liquid handling system. The momentum of the immersion liquid
body 200 causes the liquid to move, so that its upper meniscus,
i.e. liquid edge 202, moves between the surface of the final
element of the projection system and the upper surface of the
barrier member 120. The part of the liquid edge at the front of the
barrier member in the direction of the scan direction moves towards
the optical axis of the projection system; the part of the liquid
edge at the rear of the barrier member in the scan direction moves
away from the optical axis. When the scan direction reverses in a
next scan step, the direction of movement of each portion of the
liquid edge changes. So through successive scanning motions, the
position of the liquid edge oscillates. As the scan motion is fast,
oscillation may be fast and uncontrolled. Thus droplets may be
formed by the movement of the liquid edge. This phenomenon is
referred to as "sloshing". This relative motion can result in
droplets of the immersion liquid being deposited on, for example,
the final element of the projection system PS and/or the upper
surface 122 of the barrier member 120. The final element of the
projection system PS, as referred to herein, could be, for example,
a projection lens, such as a so-called WELLE lens. It will be
appreciated that in normal use, the level of the immersion liquid
between the barrier member 120 and the final element of the
projection system PS may vary and that, whenever the immersion
liquid recedes from a surface, unwanted droplets may remain.
[0092] An immersion system, such as that shown in FIG. 6, may
comprise a two-phase extraction system. A function of this
two-phase extraction system is to control the position and/or level
of the main immersion liquid region 200. For example, the two-phase
extraction system may control the level and/or position of the
immersion liquid around the final element of the projection system
PS. In the embodiment shown in FIG. 6, the two-phase extraction
system comprises an extraction duct or outlet 18. An edge 202 of
the liquid region 200 that is between an upper surface 122 of
barrier member, 120 and a lower surface of the final element of the
projection system PS can move inwards (towards the axis of the
projection system PS), or outwards (away from the axis of the
projection system PS). This can be due to, for example, relative
movement of the substrate table WT (and/or substrate W) and the
barrier member 120 (and/or the projection system PS) which is too
rapid for the two-phase extraction system to compensate for.
[0093] The edge 202 of the liquid region 200 could, for example
move outward as a result of relative motion of the substrate table
WT and the barrier member 120. When the liquid edge 202
subsequently moves inward again, unwanted immersion liquid droplets
105, 106 may be left on the upper surface of the barrier member 120
and/or the lower surface of the final element of the projection
system PS.
[0094] A further way in which an unwanted droplet can form on the
surface 122 of the barrier member 120 (that faces away from the
substrate W and/or the substrate table WT) and the lower surface of
the final element of the projection system PS (that faces the
substrate W and/or the substrate table WT) is by the substrate
table WT and/or substrate W relatively moving towards the barrier
member 120. This could happen if, for example, an error in control
of the substrate W or substrate table WT were to occur. If this
happened, the main body of immersion liquid 200 could overflow into
the region between the surface 122 of the barrier member 120 facing
away from the substrate W, and the lower surface of the final
element of the projection system PS. When this overflow of
immersion liquid retreats (i.e. when the substrate W and substrate
table WT move back away from the barrier member 120), unwanted
droplets of immersion liquid could be left on the surface 122 of
the barrier member 120 and the lower surface of the final element
of projection system PS.
[0095] In the example shown in FIG. 6, one unwanted droplet 105 is
shown on the upper surface 122 of the barrier member 120. A further
unwanted droplet 106 is shown on the lower surface of the
projection system PS.
[0096] As explained previously, if any unwanted droplet is left on
one of the surfaces, then it may evaporate, thereby possibly
applying an unwanted heat load to the particular surface. In the
case of the droplet 106 on the lower surface of the final element
of projection system PS, this could be particularly problematic
because an unwanted heat load would be applied to the final element
of projection system PS by evaporation of the droplet. This could
affect an optical property, and performance, of the projection
system PS. This could be particularly problematic if, for example,
the final element of the projection system PS were a lens element.
During evaporation, the heat load could vary with time leading to
an unpredictable variation in an optical property of the projection
system PS. Compensating for such an unpredictable variation in
optical property may be extremely difficult to achieve.
[0097] The droplet 105 on the upper surface 122 of the barrier
member 120 may, if left, evaporate causing an unwanted heat load to
the barrier member 120. This unwanted heat load may cause
deformation of the barrier member 120. This may lead to difficulty
in, for example, positioning the barrier member 120. It may lead to
an optical property of the main body of immersion liquid 200 being
altered.
[0098] Further, evaporation of any droplet in the immersion system
may cause the various surfaces which bound the main body 200 of
immersion liquid to cool down. For example, the lower surface of
the final element of the projection system PS, a surface of the
barrier member 120, and/or the substrate surface itself could cool
down. In turn, this may lead the main body of immersion liquid 200
to cool down itself, thereby affecting an optical property of the
main body 200 of immersion liquid such as altering the refractive
index of the liquid.
[0099] Furthermore, droplet 105 formed on the upper surface 122 of
the barrier member 120 and droplet 106 formed on the lower surface
of the final element of projection system PS could dynamically
interact. For example if they are close enough to each other and/or
if they are large enough they could physically join. This could
lead to a further heat load related problem. For example it may
provide a direct heat conduction path between the final element of
projection system PS and the barrier member 120.
[0100] Another area where unwanted droplets may form is on the
surface of a sensor. For example, as shown in FIG. 7, unwanted
droplets could form on the surface of one or more sensors on the
substrate table WT. In the example of FIG. 7, four sensors 50, 51,
52, 53 are shown. The sensors 50, 51, 52, 53 may be located on
and/or formed in the substrate table WT. An unwanted droplet 107 is
located on one of the sensors 51. Unwanted droplets could
additionally or alternatively be found on any of the other sensors
50, 52, 53, or on a sensor of a different type. Types of sensor on
which unwanted droplets could form include: a positioning sensor, a
transmission image sensor (TIS), an integrated lens interferometer
at scanner (ILIAS) sensor, and/or a spot sensor.
[0101] According to an embodiment of the present invention, an
active droplet removal system may be used to move any unwanted
immersion liquid droplet formed on any surface of the immersion
lithographic apparatus. Desirably, the active droplet removal
system moves the droplet immediately after it forms. If this is not
possible, the active droplet removal system is arranged to move the
droplet as quickly as possible. The active droplet removal system
may also be arranged to move the droplet before any evaporation of
the droplet occurs. If this is not possible, the active droplet
removal system may be arranged to move the droplet before
significant evaporation of the droplets occur. According to the
embodiment shown in FIG. 8, the active droplet removal system
comprises a plurality of electrodes.
[0102] According to an embodiment of the present invention, the
surface or surfaces from which the unwanted droplets can be removed
can be open surfaces. For example, the surfaces do not have to be
one of a plurality of surfaces that define a volume within which
immersion liquid or immersion liquid droplets are enclosed or
partially enclosed. The unwanted droplets may be manipulated over a
surface using the active droplet removal system of an embodiment of
the present invention even if they are not part of a surface that
is one of a plurality of surfaces that define a channel, a flow
passage, or a conduit. In other words, the only surface which the
unwanted droplets are in contact with can be the surface from which
they are to be removed or manipulated about. As such, an active
droplet removal system according to an embodiment of the present
invention is able to move an unwanted immersion liquid droplet even
if any capillary force, or net capillary force, acting on the
droplet is not large enough to cause capillary action. Thus, even
though a capillary force may (or may not) act on the droplet to be
moved, it is not required for the droplet to be moved. Thus, the
movement of the immersion liquid droplet according to an embodiment
of the present invention can be caused by the force provided by the
active droplet removal system alone. For example, this could be an
electrostatic force provided by, for example, electrodes.
[0103] The surface or surfaces from which the unwanted droplets can
be removed or manipulated about can be far removed from an adjacent
surface. This means that there can be little or no capillarity,
i.e. little or no net capillary force due to capillary pressure
acting on the unwanted droplets.
[0104] The active droplet removal system of an embodiment of the
present invention can be applied to any surface of the immersion
system as required. This is regardless of the geometrical
properties of the surface or surfaces to which it is applied. For
example, the surface to which the active droplet removal system may
be applied could be flat, or locally flat. Alternatively, the
surface to which the active droplet removal system may be applied
could be such that the center of curvature and/or the local center
of curvature is on the same side of the surface as the side on
which the droplet is located. Alternatively, the surface to which
the active droplet removal system is applied could be such that the
center of curvature and/or the local center of curvature is on the
opposite side of the surface to the side on which the droplet is
located.
[0105] Additionally or alternatively, the shortest distance between
the center of curvature of the surface or the local center of
curvature of the surface and the surface itself can be greater than
the shortest distance between the geometric center of the droplet
and the surface.
[0106] An embodiment of the present invention can remove unwanted
immersion liquid droplets from a portion of a surface without
relying on capillary action.
[0107] United States patent application publication no. US
2004-0160582 discloses using a combination of capillary action and
electrostatic force to urge immersion liquid to flow in a given
direction. However, that arrangement relies on capillary action and
so would not be suitable to remove liquid droplets from a so called
"open surface".
[0108] According to an embodiment of the present invention, a
plurality of electrodes is formed on any surface from which it is
desired, or may be desired, to remove unwanted immersion liquid
droplets. This may be a surface on which droplets are likely to
form, such as those described above. The electrodes are arranged to
manipulate and/or remove unwanted immersion liquid droplets across
or from a surface. The electrodes could be provided at any or all
of the location or locations where unwanted-immersion liquid
droplets may be formed.
[0109] A voltage can be applied to the electrodes so as to
electrostatically manipulate the unwanted immersion liquid droplets
on the surface. As such, the electrodes can form an electrostatic
pump system to transport unwanted immersion liquid droplets back
into the liquid handling system. For example, the immersion liquid
droplets may be transferred into the main body of immersion liquid
200 or into the immersion liquid supply system or extraction
system.
[0110] In order to manipulate an unwanted immersion liquid droplet,
a plurality of electrodes is used in each area where a droplet is
to be manipulated. The plurality of electrodes form an electrode
set. An example of such an electrode set is shown in FIG. 9. A
controller, such as a voltage controller VC, is used to control the
voltages applied to each of the electrodes 301, 302, 303, and 304
in the electrode set 30. The controller can be arranged so as to
control the voltage applied to the electrodes so that no voltage is
applied at a time when application of a voltage could result in
operation of one or more of the elements of the lithographic
apparatus being adversely affected. Typically, the distance between
the center of each electrode and the centers of adjacent electrodes
is in the range 0.1 mm to 1 mm. Desirably, the distance between the
center of each electrode and the centers of adjacent electrodes is
in the range of 0.25 mm to 0.75 mm. In an embodiment, the distance
between the center of each electrode and the centers of adjacent
electrodes is in the range of 0.4 mm to 0.6 mm. In an embodiment,
the distance between the center of each electrode and the centers
of adjacent electrodes is approximately 0.5 mm. The distance
between the center of the electrode and the center of adjacent
electrodes could be determined by, for example, the breakdown
voltage and the droplet size (or expected droplet size).
[0111] FIG. 8 shows the location of electrode sets 30, 31, 32, 33,
and 34 included in an immersion lithographic apparatus according to
an embodiment of the present invention. These electrode sets shown
in FIG. 8 are located so as to be able to manipulate the unwanted
immersion liquid droplets shown in the example of FIG. 6 and
described above. To improve the clarity of FIG. 8, some of the
numerals from FIG. 6 have not been included. However, the unwanted
droplets shown in FIG. 6 are in the same position in FIG. 8. Thus,
electrode set 30 is associated with droplet 105, electrode set 31
is associated with droplet 106, electrode set 32 is associated with
droplet 103, and electrode set 33 is associated with droplet 104.
As will be appreciated, any combination of the electrode sets could
be provided; not all of the electrode sets 30, 31, 32, 33 need be
provided.
[0112] The arrows on the droplets show the direction in which the
electrostatic force provided by the electrode set may act on each
droplet. In each case, the electrostatic force may act to guide the
unwanted immersion liquid droplets towards the immersion liquid in
the liquid handing system e.g. the main body of immersion liquid
200, the immersion liquid supply or the immersion liquid extraction
system. In other words, the electrostatic force may act to guide
the unwanted immersion liquid droplets towards areas within which
the immersion liquid is intended to be contained, and/or from which
the immersion liquid may be removed from the immersion system.
[0113] An example of an electrode set 30 is shown in detail in FIG.
9. Electrode set 30 comprises a row of separate electrodes 301,
302, 303, 304. The electrodes 301, 302, 303, 304 in electrode set
30 could be serially arranged. Electrode set 30 could be used, for
example, as the electrode set to remove unwanted immersion liquid
droplet 105 on the upper surface 122 of barrier member 120 shown in
FIG. 6. FIG. 9 shows the charge provided to the electrodes from a
voltage source at given times. At different times, different
voltages may be provided to a given electrode. FIG. 9 shows an
example of the voltage (or relative voltage) applied to the four
electrodes 301, 302, 303, 304 at four successive times: t.sub.1,
t.sub.2, t.sub.3, t.sub.4. In the example shown, at time t.sub.1,
electrode 301 is provided with a positive voltage, electrode 303 is
provided with a negative voltage, and electrodes 302 and 304 are
provided with no voltage. The voltages (or relative voltages)
applied to the electrodes at t.sub.2, t.sub.3 and t.sub.4 can be
seen in FIG. 9.
[0114] In some embodiments, a repeating pattern of voltages could
be applied to each, some, or all of the electrodes 301, 302, 303,
304 over time. Thus, for example, the voltages applied to the
electrodes at times t.sub.1-t.sub.4 shown in FIG. 9 could be cyclic
i.e. the pattern could continuously repeat. This continuously
repeating cycle of voltages could be configured to result in a
continuous movement of one or more of the unwanted droplets. In
other words, the voltages applied to the electrodes could be
controlled so as to move the droplets with a "pumping action".
Different voltage patterns may be used. For example, different
voltage patterns may be used at different times and/or different
locations.
[0115] It is not necessary to have some electrodes provided with a
positive voltage, and others with a negative voltage. Instead,
different relative voltages may be applied to the electrodes. As
such, all of the electrodes 301, 302, 303, 304 could be provided
with a positive voltage, but of differing magnitudes. Similarly,
all of the electrodes 301, 302, 303, 304 could be provided with a
negative voltage, but of differing magnitudes.
[0116] In an embodiment, the applied voltage is an alternating
current (A.C.). Alternatively, the applied voltage could be a
direct current (D.C.).
[0117] In the arrangement shown in FIG. 9, the electrodes are shown
to be in a parallel row. In the illustrated embodiment, several of
these electrode sets 30 are provided peripherally (e.g.,
circumferentially and/or at the same radial position) around the
top surface 122 of the barrier member 120. Thus, the voltage
applied to each individual electrode of each electrode set 30 can
be controlled individually.
[0118] In an embodiment, electrodes 301, 302, 303, 304 within the
electrode set 30 could each be provided as one continuous electrode
extending around at least part of the upper surface 122 of the
barrier member 120. There may be no peripheral (e.g.,
circumferential) gaps in each of the electrodes 301, 302, 303, 304.
Alternatively, there may be one or more peripheral gaps in one,
some, or all of the electrodes 301, 302, 303, 304, which may or may
not be at the same peripheral position for each electrode 301, 302,
303, 304. Each electrode within the electrode set 30 could be
formed at least partly as a band. For example, each electrode
within electrode set 30 could be at least partly annular. In this
embodiment, just one electrode set 30 could be provided on the top
surface 122 of the barrier member 120. In an embodiment, the
electrodes 301, 302, 303, 304 may not be parallel to each
other.
[0119] As explained above, the voltage applied to each of the
electrodes within the electrode set 30 can be varied over time. The
time variation of the voltage applied to the electrodes can be
predetermined. Alternatively, the time variation can be in response
to, for example, an unwanted immersion liquid droplet being
detected on the upper surface 122 of the barrier member 120 in the
region of the electrode set 30.
[0120] Applying voltages to electrodes on some surfaces could have
an affect on the function, operation and/or intended purpose of the
element comprising that surface, or on a neighboring element. For
example, a sensor which may be suitable for having an active
droplet removal system according to an embodiment of the present
invention applied to it may be affected by having voltages applied
to electrodes on, in, or near its surface. In order to reduce, or
eliminate this issue (should it arise), the time at which the
voltages are applied to the electrodes within the electrode set 30
can be carefully controlled. For example, the voltages could be
controlled so that no voltage is applied to any electrodes in, on,
or near (as appropriate) an element that may be affected by an
applied voltage during periods when those elements are active. For
example, a voltage could only be applied to an electrode in, near,
or on the surface of a sensor when that sensor is not active.
[0121] FIG. 10 shows a partial cross section through electrode set
30 and barrier member 120. Unwanted immersion liquid droplet 105 is
also shown in FIG. 10. The direction of arrow F.sub.1 shows the
electrostatic force acting on unwanted immersion liquid droplet 105
due to the voltage applied to electrodes 301, 302, 303 and 304. It
is this electrostatic force that urges the unwanted immersion
liquid droplet 105 towards the main body of immersion liquid 200,
according to the illustrated embodiment.
[0122] FIG. 10 shows the upper surface 122 of the barrier member
120 and the electrodes 301, 302, 303 and 304 as being covered by an
optional insulating layer 41. This insulating layer may cover each
of the electrodes (for example, to create a flat surface), while
ensuring each electrode is electrically isolated from the other
electrodes.
[0123] FIG. 10 also shows a coating 40 covering the insulating
layer 41. In an embodiment, the coating 40 could cover the upper
surface 122 of barrier member 120 and the electrode set 30
directly. This coating 40 is desirably a liquid-phobic coating. The
liquid-phobic coating may comprise a polytetraflouroethylene type
material. As such, the coating 40 may be such that the contact
angle between the immersion liquid and the surface is greater than
90 degrees, or greater than 120 degrees. The coating 40 may be
hydrophobic. The coating 40 further encourages the unwanted
immersion liquid droplet 105 away from the upper surface 122 of the
barrier member 120. A single coating may be provided on the upper
surface 122 of the barrier member 120 and the electrode set 30 that
is both electrically insulating and liquid-phobic.
[0124] In an embodiment, the liquid-phobic coating 40 may not be
present, but the unwanted immersion liquid droplet 105 could still
be urged towards the main body of immersion liquid 200. This is due
to the electrostatic force F.sub.1 provided by the electrode set
30. Thus, the liquid-phobic coating 40 is optional.
[0125] In an embodiment, a combination of liquid-phobic and
liquid-philic surfaces (liquid-philic surfaces being those which
have a contact angle to an immersion liquid droplet of less than 90
degrees) could be used to cover the upper surface 122 of barrier
member 120 and/or the electrode set 30. This combination of
liquid-phobic and liquid-philic surfaces could be arranged to
further encourage removal of unwanted immersion liquid droplets
from certain areas.
[0126] The use of a coating or surface with a specific contact
angle relationship with the immersion liquid, for example a
hydrophobic surface, may be undesirable when the coating or surface
is exposed to UV radiation for example in combination with
immersion liquid. The contact angle relationship may change.
Therefore for such a coating or surface which is exposed to
immersion liquid and UV radiation, for which stable contact angle
behavior with the immersion liquid is desirable, it may be
desirable to use an active droplet removal device in combination
with a coating, if not alone.
[0127] The surface or coating may undergo accelerated aging under
the influence of UV radiation and immersion liquid. The aging may
affect the optical properties of the surface or coating. So, for
example, having a coating over a critical feature in an immersion
system, for example a sensor or a specific feature of a sensor such
as the marks of a TIS, may be undesirable. The deterioration of the
coating or surface can affect overlay and focusing performance. So
using a coating on some features of an immersion system may be
undesirable. Application of an active droplet removal device in
combination with a coating (for example on an adjacent non-critical
feature), if not alone may be desirable.
[0128] According to the electrode set 30 shown in FIGS. 9 and 10 of
the embodiment shown in FIG. 8, the electrodes of an embodiment of
the present invention are arranged in a row. However, in an
embodiment, a grid pattern of electrodes could be used. Such a grid
pattern is shown in FIG. 11. Thus, there may be two substantially
perpendicular rows of electrodes intersecting each other. FIG. 11
shows a vertical set of electrodes 305 (as drawn), and a horizontal
set of electrodes 306 (as drawn). In this arrangement, the
perpendicular electrodes are desirably electrically isolated from
each other. Thus, while they form a grid pattern, they are
desirably not electrically interconnected. This embodiment
facilitates manipulation of the unwanted immersion liquid droplets
in two dimensions across the surface on which they are located.
This is because an electrostatic force could be provided in one
direction by one of the rows of electrodes in the grid pattern, and
in another direction by the perpendicular row of electrodes in the
grid pattern of the electrode set.
[0129] The choice of liquid used in the immersion lithographic
apparatus could have an affect on the magnitude of the force
provided to the unwanted immersion liquid droplets. For example,
droplets from an ionic solution would be more easily polarized, and
thus would experience a greater electrostatic force. The greater
the electrostatic force, the greater the magnitude of acceleration
of the unwanted immersion liquid droplet, and thus the quicker it
is removed from the surface on which it is located. Thus, in an
embodiment, an ionic solution would be used for the immersion
liquid. For example, a dilute ionic solution formed by dissolving
carbon dioxide in water may be used. It is not essential for an
ionic solution to be used with the apparatus of an embodiment of
the present invention, but use of such a solution would aid
manipulation of the unwanted immersion liquid droplets.
[0130] It will also be understood that, if an ionic solution is
used, then, if it is not removed for some period of time such that
some unwanted evaporation does occur, then the concentration of the
solutes in the droplets would increase. As it does so, the force to
mass ratio acting on the droplet would increase. Therefore, the
acceleration of the droplets away from the surface on which they
are located, and on which they need to be removed, would be
increased. Thus, even if some evaporation of the unwanted immersion
liquid droplets occurs, the possibility of significant evaporation
occurring is reduced further.
[0131] An embodiment of the invention has been described in
relation to unwanted immersion liquid droplets at specified
locations. However, it will be understood that an electrode set 30
according to an embodiment of the present invention may be provided
at any location where unwanted immersion liquid droplets may be
formed, located, or left. For example, an electrode set may be
located on the top surface of the substrate table WT. This may be
desirable because, for example, immersion liquid droplets may be
left on the top surface of the substrate table from when it is
immersed in immersion liquid during exposure of dies located
towards the edge of the substrate W.
[0132] An embodiment of the invention has been thus far described
in relation to an embodiment for use with an immersion lithographic
apparatus having a needle-type extraction duct or outlet 18.
However an embodiment of the invention could be used with any type
of immersion lithographic apparatus. According to an embodiment of
the invention, the active droplet removal system comprising
electrodes may be provided for an immersion lithographic apparatus
having a single-phase extraction system. This could be, for
example, a porous member immersion liquid extraction system as
shown in FIG. 12.
[0133] In this embodiment, the liquid extraction system comprises a
chamber 171 which is maintained at a slight underpressure and is
filled with the immersion liquid. The lower surface of the chamber
is formed of a porous member 17 (also known as a micro-sieve)
having a plurality of small holes, e.g. of diameter in the range of
5 to 50 .mu.m. The lower surface of the chamber is maintained at a
height in the range of 50 .mu.m to 1 mm, or in the range of 50
.mu.m to 300 .mu.m, above a surface from which liquid is to be
removed, e.g. the surface of a substrate W. The porous member 17
may be a perforated plate or any other suitable structure that is
configured to allow the liquid to pass therethrough. In an
embodiment, porous member 17 is at least slightly liquidphilic,
i.e. having a contact angle of less than 90.degree. to the
immersion liquid.
[0134] The underpressure is such that menisci formed in the holes
in the porous member 17 prevent gas being drawn into the chamber
171 of the immersion liquid extraction system. However, when the
porous member 17 comes into contact with liquid on the surface W
there is no meniscus to restrict flow. Thus, the liquid can flow
freely into the chamber 171 of the immersion liquid extraction
system. Such a device can remove most of the liquid from the
surface of a substrate W, and so contain the liquid in the main
liquid body 200.
[0135] In the example of FIG. 12, the immersion fluid extraction
system is formed by a ring-shaped chamber 171 near the innermost
edge of the underside of the barrier member 120. The lower surface
of the chamber 171 is formed by a porous member 17 (for example, a
perforated plate) as described above. Ring-shaped chamber 171 is
connected to a suitable pump or pumps to remove liquid from the
chamber and maintain the desired underpressure. In use, the chamber
171 is full of liquid but is shown empty in FIG. 12 for
clarity.
[0136] As shown in FIG. 12, unwanted droplets 108 may form on the
surface of the porous member 17. According to an embodiment of the
invention, an active immersion liquid removal system is provided to
remove these unwanted droplets 108 from the porous member 17. This
can assist in keeping the porous member 17 functioning properly.
This can be achieved by providing a set of electrodes to
electrostatically move the unwanted droplets, as explained above.
For example, these electrodes may be provided on the porous member
17 itself, or on a nearby surface.
[0137] For example, electrodes could be provided on a surface 121
of the barrier member 120 that faces the substrate W in order to
urge an unwanted droplet 109 towards the porous member 17, as shown
in FIG. 12.
[0138] According to an embodiment of the invention, one or more
electrode sets may be provided to remove unwanted immersion liquid
droplets formed on surfaces of an "all-wet" immersion lithographic
apparatus. In particular, one or more electrode sets may be
provided to remove unwanted immersion liquid droplets formed on
surfaces of an immersion system of an "all-wet" immersion
lithographic apparatus.
[0139] An "all-wet" immersion lithographic apparatus comprises an
immersion lithography system in which the immersion liquid is
unconfined by the liquid supply system of its immersion system.
Thus, at least the whole of the major surface of the substrate W
undergoing exposure is immersed by liquid during exposure. Thus,
even areas of the substrate that are not being exposed at a given
time are still covered by immersion liquid. This is in contrast to
the embodiments described above in which only an area surrounding
the target portion of a substrate W (i.e., that portion of the
substrate W currently being exposed) is covered by an immersion
liquid during exposure. An example of part of the substrate W,
substrate table WT and immersion liquid 300 for an "all-wet"
immersion lithographic apparatus is shown in FIG. 13.
[0140] The examples of where unwanted immersion liquid droplets may
be formed described above in relation to other embodiment are still
applicable to an "all-wet" immersion lithographic apparatus. In
addition or alternatively, an "all-wet" immersion lithographic
apparatus, such as that shown in part in FIG. 13, may use one or
more electrode sets to remove unwanted immersion liquid droplets
from other areas. For example, unwanted droplets may be removed
from the grid-plates, skits and encoder heads (all of which may
affect the positioning system), and from the substrate table
WT.
[0141] FIG. 13 shows that, in use, in an "all-wet"-immersion
system, the gap between the substrate edge 301 and the substrate
table WT is filled with immersion liquid during operation.
Furthermore, the gap between the lower surface 302 of the substrate
W (i.e. the surface that faces the substrate table WT in
operation), and the substrate table WT may also be filled with
immersion liquid during operation. In FIG. 13, the boundary 320 of
the liquid body 300 that is between the surface of the substrate W
facing the substrate table WT and the substrate table WT itself
could be a physical boundary present during operation.
Alternatively, the liquid boundary 320 could be formed by surface
tension.
[0142] It is undesirable for droplets of immersion liquid to remain
in these gaps, and/or on the substrate surfaces, even after drying.
Any droplets remaining on the substrate table WT may prevent a
subsequent substrate W being located properly on the substrate
table WT. This increases the chance of incorrect positioning of the
substrate W. Further, when the subsequent substrate W is located on
the substrate table WT, any unwanted immersion liquid droplets
remaining on the substrate table WT could splash onto other areas,
including onto the substrate W itself. As these unwanted immersion
liquid droplets may evaporate, they could lead to one or more
problems outlined above. These problems include leaving drying
stains and/or contaminating particles on, and/or causing unwanted
heat load in, the elements comprising the surface on which they are
located.
[0143] FIG. 14 shows examples of where unwanted immersion liquid
droplets 110 may be located after removal of the substrate W from
the substrate table WT in an "all-wet" immersion system and
subsequent drying. In the example shown in FIG. 14, all of the
droplets 110 are shown to be on the surface of the substrate table
WT that faces the lower surface 302 of the substrate W during
operation. However, droplets may be formed on any other surface of
the substrate table WT or of the substrate W. For example, droplets
could be left on the surface of the substrate table WT located next
to the peripheral edge surface 301 of the substrate W during
operation.
[0144] Additional or alternative electrode sets can be provided in
appropriate areas of the "all-wet" immersion system in order to
remove such unwanted immersion liquid droplets. For example,
electrode sets may be provided on the base of the substrate table
WT, i.e. on the surface of the substrate table WT that faces the
substrate W.
[0145] In the example shown in FIG. 14, an electrode set 35 is
provided. Electrode set 35 can urge the unwanted droplets 110
towards the liquid outlet 310. As such, the force provided to the
droplets 110 could be in the direction of arrow F.sub.2 in FIG.
14.
[0146] Electrode sets may be provided in a gap between the
substrate table WT and the peripheral edge surface of substrate W
itself. Indeed, electrode sets could be provided anywhere where
removal or manipulation of unwanted droplets is desirable.
[0147] Although specific reference may be made in this text to the
use of lithographic apparatus in the manufacture of ICs, it should
be understood that the lithographic apparatus described herein may
have other applications, such as the manufacture of integrated
optical systems, guidance and detection patterns for magnetic
domain memories, flat-panel displays, liquid-crystal displays
(LCDs), thin-film magnetic heads, etc. The skilled artisan will
appreciate that, in the context of such alternative applications,
any use of the terms "wafer" or "die" herein may be considered as
synonymous with the more general terms "substrate" or "target
portion", respectively. The substrate referred to herein may be
processed, before or after exposure, in for example a track (a tool
that typically applies a layer of resist to a substrate and
develops the exposed resist), a metrology tool and/or an inspection
tool. Where applicable, the disclosure herein may be applied to
such and other substrate processing tools. Further, the substrate
may be processed more than once, for example in order to create a
multi-layer IC, so that the term substrate used herein may also
refer to a substrate that already contains multiple processed
layers.
[0148] 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).
[0149] 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. For example, the invention
may take the form of one or more computer programs containing one
or more sequences of machine-readable instructions describing a
method as disclosed above, or one or more data storage medium (e.g.
semiconductor memory, magnetic or optical disk) having such one or
more computer program stored therein. The one or more different
controllers referred to herein may 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. One or more processors are configured to communicate
with the at least one of the controllers; thereby the controller(s)
operate according the machine readable instructions of one or more
computer programs.
[0151] 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, or is unconfined. In an unconfined
arrangement, the immersion liquid may flow over the surface of the
substrate and/or substrate table so that substantially the entire
uncovered surface of the substrate table and/or substrate 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.
[0152] 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 between
the projection system and the substrate and/or substrate table. It
may comprise a combination of one or more structures, one or more
liquid inlets, one or more gas inlets, one or more gas outlets,
and/or one or more liquid outlets that provide liquid to the space.
In an embodiment, a surface of the space may be a portion of the
substrate and/or substrate table, or a surface of the space may
completely cover a surface of the substrate and/or substrate table,
or the space may envelop the substrate and/or substrate table. 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.
[0153] In an embodiment, there is provided an immersion
lithographic apparatus comprising: a surface from at least a
portion of which a fluid droplet is to be removed; and an active
droplet removal system formed on or in the surface, wherein the
portion of the surface is sufficiently removed from adjacent
portions of the apparatus for there to be insufficient net
capillary force acting on a fluid droplet on the portion of the
surface to cause the fluid droplet to move by capillary action, and
the active droplet removal system is arranged to manipulate the
fluid droplet on the portion of the surface without the assistance
of capillary action.
[0154] The active droplet removal system may comprise an electrode
set formed on or in the surface, the electrode set comprising a
plurality of electrodes. In an embodiment, the electrodes are
arranged within the electrode set such that a voltage can be
applied to them so as to electrostatically manipulate fluid on the
surface. In an embodiment, the electrodes are arranged so as to
remove fluid from the surface or from a part of the surface. In an
embodiment, the electrodes are arranged in the electrode set in
rows. In an embodiment, the electrodes are arranged along a
direction in which fluid on the surface can be manipulated. In an
embodiment, a distance between the center of each electrode is
selected from the range of 0.1 mm to 1 mm. In an embodiment, the
electrodes are arranged in the electrode set in a grid pattern
comprising two substantially perpendicular rows of electrodes.
[0155] The apparatus may comprise a controller arranged to control
the voltage applied to the electrodes. In an embodiment, the
controller is arranged to apply a continuously repeating cycle of
different voltages to one or more of the electrodes. In an
embodiment, the controller is arranged to control the voltage
applied to the electrodes so that no voltage is applied at a time
when application of a voltage could result in operation of one or
more of the elements of the lithographic apparatus being adversely
affected.
[0156] The portion of the surface may be an open surface. In an
embodiment, the open surface is an unenclosed surface. In an
embodiment, the open surface is a surface whose center of curvature
is on the opposite side of the surface to the side on which the
droplet is situated. In an embodiment, the surface is not one of a
plurality of surfaces that surround a space. In an embodiment, the
surface is not a surface that forms part of a channel. In an
embodiment, the portion of the surface is sufficiently removed from
other surfaces for it not to be possible for a fluid used as an
immersion fluid in the immersion lithography apparatus to form a
meniscus between the portion of the surface and another surface.
The surface can be any surface of the immersion lithography
apparatus other than a surface through which a projection beam is
transmitted.
[0157] In an embodiment, the lithographic apparatus comprises: a
substrate table configured to hold a substrate, the surface being
part of the substrate table; and/or a projection system configured
to project a patterned radiation beam onto a target portion of the
substrate, the projection system comprising a final element, the
surface being part of the projection system; and/or a fluid
handling system comprising a barrier member and configured to
supply, contain, and/or remove fluid to a space between the final
element and the substrate, the surface being part of the barrier
member, and/or a sensor, the surface being part of a sensor.
[0158] In an embodiment, the electrodes are arranged such that
fluid can be manipulated on the surface using only electrostatic
forces generated by the electrodes. In an embodiment, the
electrodes are arranged to electrostatically manipulate immersion
fluid. In an embodiment, the electrodes are arranged to
electrostatically manipulate a dilute ionic solution. In an
embodiment, the dilute ionic solution is acidic. In an embodiment,
the dilute ionic solution comprises water with dissolved carbon
dioxide.
[0159] In an embodiment, the surface and/or the electrodes are at
least partially covered in a liquid-phobic material. In an
embodiment, the liquid-phobic material comprises a
polytetrafluoroethylene type material.
[0160] In an embodiment, there is provided an immersion
lithographic apparatus comprising: a surface from at least a
portion of which a fluid droplet is to be removed; and an active
droplet removal system formed on or in the surface and configured
to manipulate a fluid droplet around the surface, wherein the
active droplet removal system is arranged to manipulate a fluid
droplet that is in contact with no surfaces other than the surface
comprising the portion from which it is to be removed.
[0161] In an embodiment, there is provided an immersion
lithographic apparatus comprising: a surface from at least a
portion of which a fluid droplet is to be removed; and an active
droplet removal system formed on or in the surface and configured
to manipulate a fluid droplet around the surface, wherein the
portion of the surface is sufficiently removed from all other
surfaces that surface tension of the fluid is not sufficient for
fluid to bridge a gap between the portion of the surface and any
other surface, and the active droplet removal system is arranged to
manipulate, a fluid droplet on the portion of the surface.
[0162] In an embodiment, there is provided an immersion
lithographic apparatus comprising: a surface from at least a
portion of which a fluid droplet is to be removed; and an active
droplet removal system formed on or in the surface and configured
to manipulate a fluid droplet around the surface, wherein the
active droplet removal system is arranged to manipulate a fluid
droplet on the portion of the surface, and a center of curvature of
the portion of the surface is on the opposite side of the surface
to the side on which the fluid droplet is to be manipulated.
[0163] In an embodiment, there is provided a device manufacturing
method comprising: projecting a patterned beam of radiation onto a
substrate using a projection system; supplying immersion fluid,
using an immersion system, to a space between the projection system
and the substrate; and removing, without the assistance of
capillary action, an unwanted droplet of the immersion fluid on
which insufficient net capillary force to cause the droplet to move
by capillary action is acting from a portion of a surface of the
projection system or the immersion system by applying a controlled
voltage to electrodes provided in or on the surface.
[0164] In an embodiment, the droplet is removed from an open
surface. In an embodiment, the droplet is removed from a portion of
a surface that does not form part of a channel. In an embodiment,
the droplet is removed from a portion of a surface that does not
form part of a duct. In an embodiment, the droplet is removed from
a portion of a surface that is not one of a plurality of surfaces
that surround a space. In an embodiment, the droplet is not in
contact with any surface other than the surface that comprises the
portion from which it is to be removed. In an embodiment, the
surface tension of the fluid of the droplet is not sufficient for
the fluid to bridge a gap between the portion of the surface and
any other surface. In an embodiment, the unwanted-droplet is a
liquid droplet.
[0165] 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.
* * * * *