U.S. patent application number 12/718112 was filed with the patent office on 2010-06-24 for lithographic apparatus and device manufacturing method.
This patent application is currently assigned to ASML Netherlands B.V.. Invention is credited to Sjoerd Nicolaas Lambertus Donders, Christiaan Alexander Hoogendam, Nicolaas Rudolf KEMPER, Nicolaas Ten Kate, Frits Van Der Meulen.
Application Number | 20100157277 12/718112 |
Document ID | / |
Family ID | 36263975 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100157277 |
Kind Code |
A1 |
KEMPER; Nicolaas Rudolf ; et
al. |
June 24, 2010 |
LITHOGRAPHIC APPARATUS AND DEVICE MANUFACTURING METHOD
Abstract
A liquid confinement structure configured to contain a liquid in
a space between a projection system and a substrate has a recess in
its lower surface which is open to both a relatively low pressure
source and a relatively high pressure source and through which
liquid and/or gas from between the liquid confinement structure and
the substrate is extracted.
Inventors: |
KEMPER; Nicolaas Rudolf;
(Eindhoven, NL) ; Donders; Sjoerd Nicolaas Lambertus;
(Vught, NL) ; Hoogendam; Christiaan Alexander;
(Veldhoven, NL) ; Ten Kate; Nicolaas; (Almkerk,
NL) ; Van Der Meulen; Frits; (Eindhoven, NL) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
ASML Netherlands B.V.
Veldhoven
NL
|
Family ID: |
36263975 |
Appl. No.: |
12/718112 |
Filed: |
March 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11330394 |
Jan 12, 2006 |
7705962 |
|
|
12718112 |
|
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|
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60643626 |
Jan 14, 2005 |
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Current U.S.
Class: |
355/73 ;
355/77 |
Current CPC
Class: |
G03F 7/70341 20130101;
G03F 7/70866 20130101 |
Class at
Publication: |
355/73 ;
355/77 |
International
Class: |
G03B 27/60 20060101
G03B027/60; G03B 27/32 20060101 G03B027/32 |
Claims
1.-24. (canceled)
25. A lithographic projection apparatus arranged to project a
pattern from a patterning device onto a substrate using a
projection system, the lithographic apparatus comprising: a liquid
supply system arranged to supply immersion liquid to a space
between the projection system and a substrate table configured to
hold the substrate, the liquid supply system comprising a liquid
confinement structure to substantially contain the liquid in the
space, the liquid confinement structure comprising, in a surface
facing toward the substrate table, a recess having therein a first
port open to a first pressure source and a second port open to a
second pressure source, the first pressure source being at a lower
pressure than the second pressure source such that there is a flow
of fluid toward the first pressure source from the second pressure
source; and a liquid removal device positioned radially inwardly,
relative to the exposure area of the projection system, of the
recess.
26. The apparatus of claim 25, wherein the liquid removal device is
arranged to remove substantially only liquid.
27. The apparatus of claim 26, wherein the liquid removal device
comprises a porous plate.
28. The apparatus of claim 25, wherein the first port and the
second port are positioned in the recess opposite the opening of
the recess in the surface.
29. The apparatus of claim 25, wherein the first port is positioned
radially outwardly, relative to the exposure area of the projection
system, of the second port.
30. The apparatus of claim 25, wherein the liquid confinement
structure surrounds the space.
31. A device manufacturing method, comprising: containing a liquid
in a space between a projection system and a substrate by removing
liquid and/or gas from between a liquid confinement structure and a
surface of the substrate through a recess in a surface of the
liquid confinement structure facing the substrate, the recess
having a respective port to first and second pressure sources, the
first pressure source being at a lower pressure than the second
pressure source such that there is a flow of fluid toward the first
pressure source from the second pressure source; removing liquid at
a position radially inwardly, relative to the exposure area of the
projection system, of the recess; and projecting a patterned beam
of radiation through the liquid onto the substrate using the
projection system.
32. The method of claim 31, comprising removing substantially only
liquid at the position radially inwardly of the recess.
33. A lithographic projection apparatus arranged to project a
pattern from a patterning device onto a substrate using a
projection system, the lithographic apparatus comprising: a liquid
supply system arranged to supply immersion liquid to a space
between the projection system and a substrate table configured to
hold the substrate, the liquid supply system comprising a liquid
confinement structure to substantially contain the liquid in the
space, the liquid confinement structure comprising, in a surface
facing toward the substrate table, a recess having therein a first
port open to a first pressure source and a second port open to a
second pressure source, the first pressure source being at a lower
pressure than the second pressure source such that there is a flow
of fluid toward the first pressure source from the second pressure
source and the first port, or the second port, or both the first
and second ports, comprising a plurality of discrete holes.
34. The apparatus of claim 33, wherein the first port is positioned
radially outwardly, relative to the exposure area of the projection
system, of the second port.
35. The apparatus of claim 33, wherein a gas jet is positioned
radially outwardly, relative to the exposure area of the projection
system, of the recess.
36. The apparatus of claim 35, wherein the gas jet creates a flow
of gas between the liquid confinement structure and the substrate
radially inwardly, relative to the exposure area of the projection
system, into the recess.
37. The apparatus of claim 35, wherein the gas jet supplies
humidified gas.
38. The apparatus of claim 33, wherein the first port and the
second port are positioned in the recess opposite the opening of
the recess in the surface.
39. The apparatus of claim 33, further comprising a liquid removal
device positioned radially inwardly, relative to the exposure area
of the projection system, of the recess.
40. The apparatus of claim 39, wherein the liquid removal device is
arranged to remove substantially only liquid.
41. The apparatus of claim 33, wherein the second pressure source
is ambient atmosphere.
42. The apparatus of claim 33, wherein the first port and the
second port are arranged at different radial distances in the lower
surface and arranged at a distance further away from the substrate
table than the recess opening.
43. A device manufacturing method, comprising: containing a liquid
in a space between a projection system and a substrate by removing
liquid and/or gas from between a liquid confinement structure and a
surface of the substrate through a recess in a surface of the
liquid confinement structure facing the substrate, the recess
having a respective port to first and second pressure sources, the
first pressure source being at a lower pressure than the second
pressure source such that there is a flow of fluid toward the first
pressure source from the second pressure source and the first port,
or the second port, or both the first and second ports, comprising
a plurality of discrete holes; and projecting a patterned beam of
radiation through the liquid onto the substrate using the
projection system.
44. The method of claim 43, further comprising removing liquid at a
position radially inwardly, relative to the exposure area of the
projection system, of the recess.
Description
RELATED APPLICATIONS
[0001] This application claims priority to and benefit of U.S.
Provisional Application No. 60/643,626, filed Jan. 14, 2005, the
entire contents of which is hereby incorporated 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
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 NA of the system and also increasing the depth of focus.)
Other immersion liquids have been proposed, including water with
solid particles (e.g. quartz) suspended therein.
[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 (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
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.
SUMMARY
[0007] Accordingly, it would be advantageous, for example, to
provide an arrangement to remove liquid from the vicinity of the
substrate effectively.
[0008] According to an aspect of the invention, there is provided a
lithographic projection apparatus, comprising: [0009] projection
system arranged to project a patterned beam of radiation onto a
substrate; and [0010] liquid supply system arranged to supply
liquid to a space between the projection system and the substrate,
the liquid supply system comprising a liquid confinement structure
configured to form a seal between its lower surface and the
substrate to substantially contain the liquid in the space, wherein
a recess in the lower surface is open to a first pressure source
for extraction of liquid and/or gas and the recess is also open to
a second pressure source, the first pressure source being at a
lower pressure than the second pressure source such that there is a
flow of gas toward the first pressure source from the second
pressure source.
[0011] According to an aspect of the invention, there is provided a
device manufacturing method, comprising: [0012] containing a liquid
in a space between a projection system and a substrate by removing
liquid and/or gas from between a liquid confinement structure and a
surface of the substrate through a recess in a lower surface of the
liquid confinement structure, the recess being open to first and
second pressure sources, the first pressure source being at a lower
pressure than the second pressure source; and [0013] projecting a
patterned beam of radiation through the liquid onto the
substrate.
[0014] According to an aspect of the invention, there is provided a
lithographic projection apparatus, comprising: [0015] a projection
system arranged to project a patterned beam of radiation onto a
substrate; and [0016] a liquid supply system arranged to supply
liquid to a space between the projection system and the substrate,
the liquid supply system comprising a liquid confinement structure
configured to at least partly confine the liquid in the space and
having a first port on a lower surface of the liquid confinement
structure open to a first pressure source and a second port on the
lower surface open to a second pressure source, the first pressure
source being at a lower pressure than the second pressure source
such that there is a flow of gas toward the first pressure source
from the second pressure source; and [0017] a liquid removal device
positioned radially inwardly of the first and second ports.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] 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:
[0019] FIG. 1 depicts a lithographic apparatus according to an
embodiment of the invention;
[0020] FIGS. 2 and 3 depict a liquid supply system for use in a
lithographic projection apparatus;
[0021] FIG. 4 depicts another liquid supply system for use in a
lithographic projection apparatus;
[0022] FIG. 5 depicts a further liquid supply system for use in a
lithographic projection apparatus; and
[0023] FIG. 6 depicts a liquid supply and removal system according
to an embodiment of the invention.
DETAILED DESCRIPTION
[0024] FIG. 1 schematically depicts a lithographic apparatus
according to one embodiment of the invention. The apparatus
comprises: [0025] an illumination system (illuminator) IL
configured to condition a radiation beam 13 (e.g. UV radiation or
DUV radiation); [0026] 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; [0027] a substrate table (e.g. a wafer table) WT
constructed to hold a substrate (e.g. a resist-coated wafer) W and
connected to a second positioner PW configured to accurately
position the substrate in accordance with certain parameters; and
[0028] 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.
[0029] 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.
[0030] The support structure holds the patterning device. It 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."
[0031] The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
radiation beam with a pattern in its cross-section such as to
create a pattern in a target portion of the substrate. It should be
noted that the pattern imparted to the radiation beam may not
exactly correspond to the desired pattern in the target portion of
the substrate, for example if the pattern includes phase-shifting
features or so called assist features. Generally, the pattern
imparted to the radiation beam will correspond to a particular
functional layer in a device being created in the target portion,
such as an integrated circuit.
[0032] 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.
[0033] 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".
[0034] 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 minor
array of a type as referred to above, or employing a reflective
mask).
[0035] The lithographic apparatus may be of a type having two (dual
stage) or more substrate tables (and/or two or more support
structures). In such "multiple stage" machines the additional
tables may be used in parallel, or preparatory steps may be carried
out on one or more tables while one or more other tables are being
used for exposure.
[0036] Referring to FIG. 1, the illuminator IL receives a radiation
beam from a radiation source SO. The source and the lithographic
apparatus may be separate entities, for example when the source is
an excimer laser. In such cases, the source is not considered to
form part of the lithographic apparatus and the radiation beam is
passed from the source SO to the illuminator IL with the aid of a
beam delivery system BD comprising, for example, suitable directing
mirrors and/or a beam expander. In other cases the source may be an
integral part of the lithographic apparatus, for example when the
source is a mercury lamp. The source SO and the illuminator IL,
together with the beam delivery system BD if required, may be
referred to as a radiation system.
[0037] 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.
[0038] 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. A liquid supply system IH,
which is described further below, supplies immersion liquid to a
space between the final element of the projection system PL and the
substrate W.
[0039] 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.
[0040] The depicted apparatus could be used in at least one of the
following modes:
[0041] 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.
[0042] 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.
[0043] 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.
[0044] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0045] A further 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 OUT can be arranged
in a plate with a hole in its center and through which the
projection beam is projected. Liquid is supplied by one groove
inlet IN on one side of the projection system PL and removed by a
plurality of discrete outlets OUT on the other side of the
projection system PL, causing a flow of a thin film of liquid
between the projection system PL 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).
[0046] Another immersion lithography solution with a localized
liquid supply system solution which has been proposed is to provide
the liquid supply system with a liquid confinement structure 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.
An example of such a solution is illustrated in FIG. 5. The liquid
confinement structure is substantially stationary relative to the
projection system in the XY plane though there may be some relative
movement in the Z direction (in the direction of the optical axis).
A seal is formed between the liquid confinement structure and the
surface of the substrate. In an embodiment, the seal is a
contactless seal such as a gas seal. Such a system with a gas seal
is disclosed in U.S. patent application Ser. No. 10/705,783, hereby
incorporated in its entirety by reference.
[0047] FIG. 5 depicts an arrangement of a reservoir 10, which forms
a contactless seal to the substrate around the image field of the
projection system so that liquid is confined to fill a space
between the substrate's primary surface, which faces the projection
system PL, and the final element of the projection system PL. A
liquid confinement structure 12 positioned below and surrounding
the final element of the projection system PL forms the reservoir.
Thus, the liquid supply system provides liquid on only a localized
area of the substrate. The liquid confinement structure 12 forms
part of the liquid supply system configured to fill a space between
the final element of the projection system and the substrate W (or
substrate table WT) with a liquid. Liquid is brought into the space
below the projection system via, e.g., inlet 13 and within the
liquid confinement structure 12. The liquid confinement structure
12 extends a little above the final element of the projection
system and the liquid level rises above the final element so that a
buffer of liquid is provided. The liquid confinement structure 12
has an inner periphery that at the upper end preferably 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. The patterned beam passes through
this aperture.
[0048] The liquid is confined in the reservoir by a gas seal 16
between the bottom of the liquid confinement structure 12 and the
surface of the substrate W. The gas seal is formed by gas, e.g.
air, synthetic air, N.sub.2 or an inert gas, provided under
pressure via inlet 15 to the gap between liquid confinement
structure 12 and the substrate W and extracted via outlet 14. The
overpressure on the gas inlet 15, vacuum level on the outlet 14 and
geometry of the gap are arranged so that there is a high-velocity
gas flow inwards that confines the liquid. It will be understood by
the person skilled in the art that other types of seal could be
used to contain the liquid such as simply an outlet to remove
liquid and/or gas.
[0049] FIG. 6 shows a liquid removal device 30, 31, such as
disclosed in U.S. patent application Ser. No. 10/921,348, hereby
incorporated in its entirety by reference, in a liquid confinement
structure 12 of a liquid supply system according to an embodiment
of the invention. The liquid removal device comprises a chamber 31
which is maintained at a slight underpressure p.sub.c and is filled
with the immersion liquid. The lower surface of the chamber is
formed of a thin plate 30 having a large number of small holes,
e.g. of diameter d .sub.hole in the range of 5 to 50 .mu.m, and is
maintained at a height h.sub.gap 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. In an embodiment, perforated plate 30 is
slightly liquidphilic, i.e. having a contact angle of less than
90.degree. to the immersion liquid, e.g. water. The liquid removal
device 31 is designed substantially for single phase (liquid)
extraction. FIG. 6 is a cross-sectional view of one side of the
liquid confinement structure 12, which forms a periphery around the
exposure field of the projection system PL (not shown in FIG. 6).
In an embodiment, the liquid removal device comprises a chamber 31
near the innermost edge of the underside of the liquid confinement
structure 12 that forms a ring around the exposure field, the lower
surface of the chamber 31 having a porous plate 30 as described in
U.S. patent application Ser. No. 10/921,348. Chamber 31 is
connected to one or more suitable pumps or other low pressure
sources to remove liquid from the chamber and maintain the desired
underpressure. In use, the chamber 31 is full of liquid but is
shown empty for clarity.
[0050] Outward of the ring chamber 31 are a gas extraction recess
32 and a gas supply 33. The gas extraction recess 32 and/or the gas
supply 33 may be formed as a ring around the exposure field. The
gas supply 33 comprises a chamber with a narrow slit in its lower
part and is supplied with gas, e.g. air, artificial air or N.sub.2,
at a pressure such that the gas escaping out of the slit forms a
gas knife 34. The gas forming the gas knife is extracted by one or
more suitable low pressure pumps or other sources connected to the
gas extraction recess 32, described below, so that the resulting
gas flow drives residual liquid inwardly where it can be removed by
the liquid removal device 31 and/or the gas extraction recess 32,
the low pressure pump(s) or other source(s) therefore should be
able to tolerate vapor of the immersion liquid and/or small liquid
droplets.
[0051] In the apparatus shown in FIG. 6, most of the gas that forms
the gas knife is extracted via the gas extraction recess 32, but
some gas may flow into the environment around the liquid
confinement structure 12 and potentially disturb the
interferometric position measuring system IF. This may be prevented
or reduced by the provision of an additional gas extraction recess
(not shown for clarity) radially outward from the gas knife 34.
This also helps to remove liquid drops on the substrate W or
substrate table WT outside (i.e., not under) of the liquid
confinement structure 12. The gas knife also functions as an
emergency buffer in case the liquid confinement structure 12
approaches the substrate W too closely.
[0052] Because in this embodiment, the liquid removal system can
remove most of the immersion liquid while at a height of 10 .mu.m
to 1 mm, or 50 to 300 .mu.m above the surface of the substrate W or
the substrate table WT, less onerous requirements are put on the
liquid confinement structure's vertical position than when a gas
bearing is used to confine the immersion liquid. This means that
the liquid confinement structure may be positioned vertically with
a simpler actuation and control system. It also means that the
requirements on the flatness of the substrate table and substrate
may be reduced, making it easier to provide devices such as sensors
in the upper surface of the substrate table WT.
[0053] The liquid confinement structure 12 can either be
constructed to be fixed relative to the projection system PL or can
be arranged to be moveable in the direction of the optical axis
and/or rotatable about one or more directions perpendicular to the
optical axis. One way of arranging for this is for the liquid
confinement structure 12 to bear on the substrate W such that its
weight is carried by the substrate W. This can be arranged, for
example, by arranging for the gas flow 34 of the gas knife to
create a force equal and opposite in direction to the force of
gravity on the liquid confinement structure 12. However, because
the area of the recess 32 in the lower surface of the barrier
member 12 is larger than the area of the slit through which gas
from the gas knife 34 exits the liquid confinement structure 12,
any variations in pressure of gas in the recess 32 may have a large
effect on the force created by that gas on the liquid confinement
structure 12 towards the substrate W. It is therefore desirable to
try to reduce or minimize pressure fluctuations of gas in the
recess 32. This is arranged as described below to prevent the
liquid confinement structure 12 from having a negative stiffness,
which could otherwise clamp the liquid confinement structure 12 to
the substrate W.
[0054] As the liquid confinement structure 12 approaches the
substrate W, the force exerted by the negative pressure in the
extraction recess 32 could increase faster than the force exerted
by the positive pressure in the gas knife 32 (because the area is
bigger) so that the liquid confinement structure 12 would be driven
down towards the substrate W. This can be mitigated by providing,
as well as an extraction port 50 which is connected to a relatively
low pressure source, an ambient port 40 which is open to a
relatively high pressure source such as the ambient atmosphere. In
this way, gas enters through the port 40 to take the place of gas
and/or liquid which exits through extraction port 50. Thus, it is
arranged that there is always a flow of gas through the ambient
port 40 so that pressure fluctuations, which change with the
distance between the liquid confinement structure 12 and substrate
W, are reduced.
[0055] The liquid removal device 31 and the relative pressures of
gas in chamber 33 and recess 32 (which is controlled by the
relative pressures of gases at the ambient and extraction ports)
are adjusted to prevent the liquid 11 meniscus being dragged
radially inwardly towards the exposure field (on the left hand side
of FIG. 6) by movement of the substrate W. Indeed, in an
embodiment, the liquid removal device 31 removes only liquid and no
gas such that the meniscus of the liquid 11 is positioned under the
recess 32. To arrange for this flow, one or more restrictions (or
other means) may be used to adjust the relative pressures of the
relatively low pressure gas source to which the extraction port 50
is connected and the pressure of the relatively high pressure
source to which the ambient port 40 is connected. In an embodiment,
a level of -20 to -10 mbar gauge in the recess 32 may be
maintained, though a range of from -50 to +100 mbar gauge is a
possible working range. If the relatively low pressure source is at
a pressure in the range from -50 to -500 mbar gauge or -50 to -200
mbar gauge, the ambient port 40 may be open to the atmosphere to
achieve the desired pressure in the recess 32.
[0056] With this arrangement, a flow of gas out of the gas knife 34
is created both radially inwardly towards the recess 32 and
radially outwardly towards the radially outer edge of the liquid
confinement structure 12. The gas flow traveling radially inwardly
from the gas knife 34 toward the recess 32 helps maintain the
position of the liquid meniscus substantially under the recess 32
and gas and/or liquid is extracted through extraction port 50. Gas
is also drawn into the recess 32 through ambient port 40 thereby to
avoid pressure fluctuations in the recess 32 when there is a change
in height of the liquid confinement structure 12 above the
substrate W or a change in flow conditions of either the gas coming
from the gas knife 34 or of liquid coming from the space between
the final element of the projection system and the substrate W.
[0057] In an embodiment, the ambient port 40 is positioned radially
inwardly of the extraction port 50 and these ports are, in an
embodiment, positioned in a top surface of the recess 32 opposite
the side of the recess 32 which is open to the bottom surface of
the liquid confinement structure 12 which faces the substrate W.
The ambient port 40 and extraction port 50 may be circular grooves
(in the same way that recess 32 may be a circular or other loop
shape) or those ports may be a plurality of discrete holes in the
top surface of the recess 32.
[0058] Some operating conditions for the various components of the
liquid confinement structure 12 are given. The pressures mentioned
are gauge. Therefore the pressure of the relatively high pressure
source to which the ambient port 40 is connected is 0 mbar. The
relatively low pressure source to which the extraction port 50 is
connected is about -100 mbar. In an embodiment, this extraction
arrangement is for gas only because removing a mixture of gas and
liquid may lead to undesirable vibrations.
[0059] In an embodiment, the gas in chamber 33 is at a pressure of
about 800 mbar and is humidified gas to reduce or minimize
evaporation and thereby cooling of the substrate W though the gas
is not necessarily humidified. A typical gas flow rate of 100
liter/min may be used and the gas knife 34 may be provided through
an annular continuous cavity or through a plurality of discrete
holes. A gas flow rate of about 50 liter/min through the extraction
port 50 may be envisaged and a gap between the bottom of the liquid
confinement structure 12 and the substrate W of approximately 100
.mu.m (in an embodiment, in the range of 80 to 130 .mu.m).
[0060] As used herein, the term ring may be any appropriate shape
including circular or rectangular.
[0061] In European patent application publication no. EP 1420300
and United States patent application publication no. US
2004-0136494, each hereby incorporated in their 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 a substrate. Leveling measurements are
carried out with a table at a first position, without immersion
liquid, and exposure is carried out with a table at a second
position, where immersion liquid is present. Alternatively, the
apparatus has only one table.
[0062] 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.
[0063] 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).
[0064] 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.
[0065] While specific embodiments of the invention have been
described above, it will be appreciated that the invention may be
practiced otherwise than as described. For example, the invention
may take the form of a computer program containing one or more
sequences of machine-readable instructions describing a method as
disclosed above, or a data storage medium (e.g. semiconductor
memory, magnetic or optical disk) having such a computer program
stored therein.
[0066] One or more embodiments of the invention may be applied to
any immersion lithography apparatus, such as those types mentioned
above, and whether the immersion liquid is provided in the form of
a bath or only on a localized surface area of the substrate. A
liquid supply system is any mechanism that provides a liquid to a
space between the projection system and the substrate and/or
substrate table. It may comprise any 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, the
combination providing and confining the liquid to the space. In an
embodiment, a surface of the space may be limited to a portion of
the substrate and/or substrate table, 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.
[0067] 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.
* * * * *