U.S. patent application number 12/537536 was filed with the patent office on 2009-12-03 for lithographic apparatus, alignment apparatus, device manufacturing method, and a method of converting an apparatus.
This patent application is currently assigned to ASML NETHERLANDS B.V.. Invention is credited to Erik Roelof Loopstra, Johannes Catharinus Hubertus Mulkens, Marinus Aart Van Den Brink.
Application Number | 20090296061 12/537536 |
Document ID | / |
Family ID | 34678625 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090296061 |
Kind Code |
A1 |
Mulkens; Johannes Catharinus
Hubertus ; et al. |
December 3, 2009 |
LITHOGRAPHIC APPARATUS, ALIGNMENT APPARATUS, DEVICE MANUFACTURING
METHOD, AND A METHOD OF CONVERTING AN APPARATUS
Abstract
A detector detects liquid in the path of a projection beam or
alignment beam. A controller then determines which one or more of a
plurality of compensating optical elements may be provided in the
optical path of the projection beam or alignment beam in order to
focus the projection beam or alignment beam on the surface of the
substrate. The appropriate optical element may be placed in the
path of the projection beam or alignment beam directly as a final
element of the projection system or alignment system
respectively.
Inventors: |
Mulkens; Johannes Catharinus
Hubertus; (Maastricht, NL) ; Van Den Brink; Marinus
Aart; (Moergestel, NL) ; Loopstra; Erik Roelof;
(Heeze, 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: |
34678625 |
Appl. No.: |
12/537536 |
Filed: |
August 7, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10743266 |
Dec 23, 2003 |
7589818 |
|
|
12537536 |
|
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Current U.S.
Class: |
355/63 |
Current CPC
Class: |
B41C 1/1083 20130101;
G03F 7/70341 20130101; G03F 9/7026 20130101; G03F 7/70258 20130101;
B41C 1/1075 20130101 |
Class at
Publication: |
355/63 |
International
Class: |
G03B 27/52 20060101
G03B027/52 |
Claims
1.-88. (canceled)
89. A lithographic apparatus comprising: a support structure
configured to hold a patterning device, the patterning device
configured to provide a beam of radiation having a pattern in its
cross-section; a substrate table configured to hold a substrate; a
projection lens system configured to project the patterned beam
onto a target portion of the substrate; a plurality of optical
elements removably positionable in the path of the beam to adjust
the focal plane of the beam; and a plurality of docking stations at
different positions along the path of the beam configured to hold
the plurality of optical elements depending on the presence or
absence of liquid between the projection lens system and the
substrate.
90. An apparatus according to claim 89, wherein each docking
station is a predetermined distance from a final non-parallel plate
element of the projection lens system.
91. An apparatus according to claim 90, wherein at least one
docking station is arranged such that the focal point of the beam
is on the substrate, or the substrate table, or both the substrate
and the substrate table, when no liquid is present in the path of
the beam.
92. An apparatus according to claim 90, wherein at least one
docking station is arranged such that the focal point of the beam
is on the substrate, or the substrate table, or both the substrate
and the substrate table, when a liquid is present in the optical
path of the beam.
93. An apparatus according to claim 89, further comprising a
controller configured to control which one or more of the plurality
of optical elements is placed in the path of the beam dependent on
a quantity of liquid between the projection lens system and the
substrate table.
94. An apparatus according to claim 89, further comprising a liquid
supply system configured to at least partly fill a space between
the projection lens system and the substrate table, with a
liquid.
95. An alignment apparatus comprising: a substrate table configured
to hold a substrate, the substrate having a substrate mark; an
alignment lens system configured to detect alignment between a
reference mark and the substrate mark using an alignment beam of
radiation; a plurality of optical elements removably positionable
in the path of the alignment beam configured to adjust the focal
plane of the alignment lens system when detecting alignment; and a
plurality of docking stations at different positions along the path
of the alignment beam configured to hold the plurality of optical
elements depending on the presence or absence of liquid between the
alignment lens system and the substrate.
96. An apparatus according to claim 95, wherein each docking
station is a predetermined distance from a final non-parallel plate
element of the alignment lens system.
97. An apparatus according to claim 96, wherein at least one
docking station is arranged such that the focal point of the
alignment beam is on the substrate, or the substrate table, or both
the substrate and the substrate table, when no liquid is present in
the path of the alignment beam.
98. An apparatus according to claim 96, wherein at least one
docking station is arranged such that the focal point of the
alignment beam is on the substrate, or the substrate table, or both
the substrate and the substrate table, when a liquid is present in
the optical path of the alignment beam.
99. An apparatus according to claim 95, further comprising a
controller configured to control which one or more of the plurality
of optical elements is placed in the path of the alignment beam
dependent on a quantity of liquid between the alignment lens system
and the substrate table.
100. An apparatus according to claim 95, further comprising a
liquid supply system configured to at least partly fill a space
between the alignment lens system and the substrate table, with a
liquid.
101. A lithographic projection apparatus comprising a support
structure configured to hold a patterning device that serves to
provide a beam of radiation according to a desired pattern, a
projection system configured to project the patterned beam onto a
target portion of the substrate, and an alignment apparatus
according to claim 95.
102. An apparatus according to claim 101, wherein the alignment
beam traverses at least part of the projection system.
103. An alignment apparatus comprising: a substrate table
configured to hold a substrate, the substrate having a substrate
mark; an alignment lens system configured to detect alignment
between a reference mark and the substrate mark using an alignment
beam of radiation; a plurality of optical elements removably
positionable in the path of the alignment beam configured to adjust
the focal plane of the alignment lens system when detecting
alignment; a detector configured to detect the presence or absence
of liquid between the alignment lens system and the substrate
table; and a controller configured to control which one or more of
the plurality of optical elements is placed in the path of the
alignment beam on the basis of results from the detector.
104. An apparatus according to claim 103, further comprising a
liquid supply system configured to at least partly fill a space
between the alignment lens system and the substrate table, with a
liquid.
105. A lithographic projection apparatus comprising a support
structure configured to hold a patterning device that serves to
provide a beam of radiation according to a desired pattern, a
projection system configured to project the patterned beam onto a
target portion of the substrate, and an alignment apparatus
according to claim 103.
106. An apparatus according to claim 105, wherein the alignment
beam traverses at least part of the projection system.
107. A lithographic projection apparatus comprising: a support
structure configured to hold a patterning device, the patterning
device configured to provide a beam of radiation having a pattern
in its cross-section; a substrate table configured to hold a
substrate; a projection lens system configured to project the
patterned beam onto a target portion of the substrate; a liquid
supply system configured to at least partly fill a space between
the projection lens system and the substrate table, with a liquid;
and a detector configured to detect the presence or absence of
liquid between the projection lens system and the substrate
table.
108. An apparatus according to claim 107, further comprising a
controller configured to control an optical element in the path of
the beam or control insertion of an optical element into the path
of the beam, dependent on the results from the detector.
Description
FIELD
[0001] The present invention relates to a lithographic apparatus,
an alignment apparatus, a device manufacturing method, and a method
of converting an apparatus.
BACKGROUND
[0002] A lithographic apparatus is a machine that applies a desired
pattern onto a target portion of a substrate. Lithographic
apparatus can be used, for example, in the manufacture of
integrated circuits (ICs). In that circumstance, a patterning
device, such as a mask, may be used to generate a circuit pattern
corresponding to an individual layer of the IC, and this pattern
can be imaged onto a target portion (e.g. comprising part of, one
or several dies) on a substrate (e.g. a silicon wafer) that has a
layer of radiation-sensitive material (resist). In general, a
single substrate will contain a network of adjacent target portions
that are successively exposed. Known lithographic apparatus include
so-called steppers, in which each target portion is irradiated by
exposing an entire pattern onto the target portion in one go, and
so-called scanners, in which each target portion is irradiated by
scanning the pattern through the projection beam in a given
direction (the "scanning"-direction) while synchronously scanning
the substrate parallel or anti-parallel to this direction.
[0003] 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.)
[0004] 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.
[0005] 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 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
[0006] In addition to the solution described above, a liquid supply
system in a second solution may be provided that comprises a seal
member 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. The seal member 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 seal member and the
surface of the substrate. In an embodiment, the seal is a
contactless seal such as a gas seal. Such a system is disclosed in
U.S. patent applications U.S. Ser. No. 10/705,805 and U.S. Ser. No.
10/705,783, both hereby incorporated in their entirety by
reference.
[0007] Due to the differing refractive indices of an immersion
liquid and a gas (such as air), the optical path lengths of the
projection beam in lithographic projection apparatus with immersion
liquid and without immersion liquid are different. Different
projection systems may therefore need to be designed for both "dry"
lithography and immersion lithography. Lens design is expensive and
therefore this adds considerably to the cost of production of, for
example, integrated circuits.
[0008] A similar problem occurs in the alignment of substrates. To
align a substrate, an alignment beam is projected towards a
reference mark on the substrate or substrate table from where it is
partially reflected back towards an alignment mark. If immersion
liquid is present between the substrate table and the alignment
system projecting the alignment beam, the optical path length of
the alignment beam will be changed and the alignment beam will no
longer focus accurately on the surface of the reference mark. There
could be residual liquid on the alignment mark or sensor on the
substrate table if immersion liquid has previously been on the
substrate table and a subsequent substrate and is being aligned
prior to exposure.
[0009] Accordingly, it would be advantageous, for example, to
provide a lithographic projection apparatus and an alignment
apparatus for use both with and without immersion liquid.
[0010] According to an aspect, there is provided a method of
converting a projection lens system of a lithographic projection
apparatus, the method comprising at least one of exchanging a
compensating optical element in the optical path of the projection
lens system for another compensating optical element, adding a
further compensating optical element in the optical path of the
projection lens system, and removing a further compensating optical
element in the optical path of the projection lens system, such
that with a liquid between the projection lens system and the point
of focus of the projection lens system, the distance of the point
of focus of the projection lens system from a non parallel optical
element will remain the same as without the liquid between the
projection lens system and the point of focus of the projection
lens system.
[0011] According to a further aspect, there is provided a method of
converting a projection lens system of a lithographic projection
apparatus, the method comprising at least one of exchanging a
compensating optical element in the optical path of the projection
lens system for another compensating optical element, adding a
further compensating optical element in the optical path of the
projection lens system, and removing a further compensating optical
element in the optical path of the projection lens system, such
that without a liquid between the projection lens system and the
point of focus of the projection lens system, the distance of the
point of focus of the projection lens system from a non parallel
optical element will remain the same as with the liquid between the
projection lens system and the point of focus of the projection
lens system.
[0012] According to a further aspect, there is provided a method of
converting an alignment lens system of an alignment apparatus, said
method comprising at least one of exchanging a compensating optical
element in the optical path of the alignment lens system for
another compensating optical element, adding a further compensating
optical element in the optical path of the alignment lens system,
and removing a further compensating optical element in the optical
path of the alignment lens system, such that with a liquid between
the alignment lens system and the point of focus of the alignment
lens system, the distance of the point of focus of the alignment
lens system from a non parallel optical element will remain the
same as without the liquid between the alignment lens system and
the point of focus of the alignment lens system.
[0013] According to a further aspect, there is provided a method of
converting an alignment lens system of an alignment apparatus, the
method comprising at least one of exchanging a compensating optical
element in the optical path of the alignment lens system for
another compensating optical element, adding a further compensating
optical element in the optical path of the alignment lens system,
and removing a further compensating optical element in the optical
path of the alignment lens system, such that without a liquid
between the alignment lens system and the point of focus of the
alignment lens system, the distance of the point of focus of the
alignment lens system from a non parallel optical element will
remain the same as with the liquid between the alignment lens
system and the point of focus of the alignment lens system.
[0014] According to a further aspect, there is provided a method of
converting a projection lens system of a lithographic projection
apparatus, the method comprising at least one of exchanging a
compensating optical element in the optical path of the projection
lens system for another compensating optical element, adding a
further compensating optical element in the optical path of the
projection lens system, and removing a further compensating optical
element in the optical path of the projection lens system such that
the at least one of the presence and position of the compensating
optical element in the optical path of the projection lens system
is adjusted to ensure that the total optical path length between a
patterning device and the point of focus of a patterned beam
remains unchanged with a liquid between the projection lens system
and a substrate from without the liquid between the projection lens
system and the substrate.
[0015] According to a further aspect, there is provided a method of
converting a projection lens system of a lithographic projection
apparatus, the method comprising at least one of exchanging a
compensating optical element in the optical path of the projection
lens system for another compensating optical element, adding a
further compensating optical element in the optical path of the
projection lens system, and removing a further compensating optical
element in the optical path of the projection lens system such that
the at least one of the presence and position of the compensating
optical element in the optical path of the projection lens system
is adjusted to ensure that the total optical path length between a
patterning device and the point of focus of a patterned beam
remains unchanged without liquid between the projection lens system
and a substrate from with the liquid between the projection lens
system and the substrate.
[0016] According to a further aspect, there is provided a method of
converting an alignment lens system of an alignment apparatus, the
method comprising at least one of exchanging a compensating optical
element in the optical path of the alignment lens system for
another compensating optical element, adding a further compensating
optical element in the optical path of the alignment lens system,
and removing a further compensating optical element in the optical
path of the alignment lens system such that the at least one of the
presence and position of the compensating optical element in the
optical path of the alignment lens system is adjusted to ensure
that the total optical path length between a reference mark and the
point of focus of an alignment beam remains unchanged with a liquid
between the alignment lens system and a substrate from without the
liquid between the alignment lens system and the substrate.
[0017] According to a further aspect, there is provided a method of
converting an alignment lens system of an alignment apparatus, the
method comprising at least one of exchanging a compensating optical
element in the optical path of the alignment lens system for
another compensating optical element, adding a further compensating
optical element in the optical path of the alignment lens system,
and removing a further compensating optical element in the optical
path of the alignment lens system such that the at least one of the
presence and position of the compensating optical element in the
optical path of the alignment lens system is adjusted to ensure
that the total optical path length between a reference mark and the
point of focus of an alignment beam remains unchanged without
liquid between the alignment lens system and a substrate from with
the liquid between the alignment lens system and the substrate.
[0018] A compensating optical element is used to compensate for the
change of path length due to the presence or absence of immersion
liquid so that the apparatus always focuses at substantially the
same position in space regardless of the presence or not of
immersion liquid. For example, the optical element(s) placed in the
projection beam may be chosen and arranged such that the optical
path length between a patterning device and the substrate or
substrate table remains constant regardless of the quantity of
liquid in the path of the projection beam, i.e. the position of
focus does not change. Similarly, for example, the optical
element(s) placed in the alignment may be chosen and arranged such
that the optical path length between a reference mark and a
substrate mark remains constant regardless of the quantity of
liquid in the path of the projection beam, i.e. the position of
focus does not change. The same projection or alignment system can
thus be used in apparatus' with and without immersion liquid
thereby reducing the cost of lens design and development. The
apparatus can be converted between an apparatus used in conjunction
with immersion liquid and an apparatus used without immersion
liquid.
[0019] Changing the arrangement of the compensating optical element
in the projection beam or alignment beam may comprise placing a
different compensating optical element in the path of the
projection beam or alignment beam. The appropriate compensating
optical element can be chosen depending on the quantity of liquid
in the projection or alignment beam. Alternatively or in addition,
an additional optical element could be placed in the path of the
projection beam or alignment beam. The compensating optical element
can be conveniently arranged to be the final element of the
projection system or the alignment system.
[0020] In an embodiment, the different compensating optical
elements may be placed in the projection beam or alignment beam at
different positions in the direction of the propagation of the
beam. For example, each optical element could have a mutually
exclusive station in the projection beam or alignment beam such
that the optical elements do not collide with each other when
placed simultaneously in the path of the projection beam or
alignment beam. In the case of a single optical element replacing
another optical element, the one for use with immersion liquid will
typically need to be placed closer to the substrate than the other
optical element. Some optical elements would for example be closer
to the substrate table and others would be closer to the radiation
source. The thickness of a compensating optical element may be, in
an embodiment, between 50 .mu.m and 500 .mu.m. In an embodiment,
the compensating optical element may be placed at a distance of
less than 3 mm from the substrate table. The compensating optical
element is therefore close to the image plane so spherical
aberrations may be constant over the field.
[0021] In an embodiment, the compensating optical element may be a
plane plate. To adjust the optical path length of the projection
beam or alignment beam, different compensating optical elements can
have different thicknesses and/or different optical properties, in
particular different refractive indices. For example, a
compensating optical element may be hollow and filled with a fluid
having a different refractive index. This can be done, for example,
by changing the salt concentration of the fluid or by changing the
ratio of a mixture of the fluids within the compensating optical
element.
[0022] The method described above may be carried out by a user. The
user may be an operator, the owner of the apparatus, an external
contractor employed specifically to convert apparatus or any other
person needing to convert such apparatus. The method may be
non-automatic.
[0023] According to a further aspect, there is provided a
lithographic apparatus comprising:
[0024] an illumination system configured to provide a beam of
radiation;
[0025] a support structure configured to hold a patterning device,
the patterning device configured to impart the beam with a pattern
in its cross-section;
[0026] a substrate table configured to hold a substrate;
[0027] a projection lens system configured to project the beam as
patterned onto a target portion of the substrate; and
[0028] a plurality of optical elements removably positionable in
the path of the beam to adjust the focal plane of the beam,
[0029] wherein the at least one of the presence and position of one
or more of the plurality of optical elements in the path of the
beam can be adjusted to ensure that the total optical path length
of the beam remains unchanged irrespective of the presence or
absence of liquid between the projection lens system and the
substrate table.
[0030] According to a further aspect, there is provided a
lithographic apparatus comprising:
[0031] an illumination system configured to provide a beam of
radiation;
[0032] a support structure configured to hold a patterning device,
the patterning device configured to impart the beam with a pattern
in its cross-section;
[0033] a substrate table configured to hold a substrate;
[0034] a projection lens system configured to project the beam as
patterned onto a target portion of the substrate; and
[0035] a plurality of optical elements removably positionable in
the path of the beam to adjust the focal plane of the beam,
[0036] wherein the at least one of the presence and position of one
or more of the plurality of optical elements in the path of the
beam is adjusted such that with a liquid between the projection
lens system and the point of focus of the projection lens system,
the point of focus of the projection lens system remains unchanged
from without a liquid between the projection lens system and the
point of focus of the projection lens system.
[0037] According to a further aspect, there is provided an
alignment apparatus comprising:
[0038] a substrate table configured to hold a substrate, the
substrate having a substrate mark;
[0039] an alignment lens system configured to detect alignment
between a reference mark and the substrate mark using an alignment
beam of radiation; and
[0040] a plurality of optical elements removably positionable in
the path of the alignment beam configured to adjust the focal plane
of the alignment lens system when detecting alignment,
[0041] wherein the at least one of the presence and position of one
or more of the plurality of optical elements in the path of the
alignment beam can be adjusted to ensure that the total optical
path length of the alignment beam remains unchanged irrespective of
the quantity of liquid between the alignment lens system and the
substrate table.
[0042] According to a further aspect, there is provided an
alignment apparatus comprising:
[0043] a substrate table configured to hold a substrate, the
substrate having a substrate mark;
[0044] an alignment lens system configured to detect alignment
between a reference mark and the substrate mark using an alignment
beam of radiation; and
[0045] a plurality of optical elements removably positionable in
the path of the alignment beam configured to adjust the focal plane
of the alignment lens system when detecting alignment,
[0046] wherein the at least one of the presence and position of one
or more of the plurality of optical elements in the path of the
alignment beam is adjusted such that with a liquid between the
alignment lens system and the point of focus of the alignment lens
system, the point of focus of the alignment lens system remains
unchanged from without a liquid between the alignment lens system
and the point of focus of the alignment lens system.
[0047] In an embodiment, there is provided a controller configured
to control which one or more of the plurality of optical elements
is placed in the projection beam or the alignment beam dependent on
the quantity of liquid between the projection system or the
alignment system and the substrate table. The controller could take
the form of a computer system or a program loaded on a computer
system. There may also be provided a liquid supply system
configured to at least partly fill a space between the projection
system or the alignment lens system and the substrate table, with a
liquid.
[0048] According to a further aspect, there is provided a
lithographic apparatus comprising:
[0049] an illumination system configured to provide a beam of
radiation;
[0050] a support structure configured to hold a patterning device,
the patterning device configured to impart the beam with a pattern
in its cross-section;
[0051] a substrate table configured to hold a substrate;
[0052] a projection lens system configured to project the beam as
patterned onto a target portion of the substrate;
[0053] a plurality of optical elements removably positionable in
the path of the beam to adjust the focal plane of the beam; and
[0054] a plurality of docking stations in the path of the beam
configured to hold the plurality of optical elements.
[0055] According to a further aspect, there is provided an
alignment apparatus comprising:
[0056] a substrate table configured to hold a substrate, the
substrate having a substrate mark;
[0057] an alignment lens system configured to detect alignment
between a reference mark and the substrate mark using an alignment
beam of radiation;
[0058] a plurality of optical elements removably positionable in
the path of the alignment beam configured to adjust the focal plane
of the alignment lens system when detecting alignment; and
[0059] a plurality of docking stations in the path of the alignment
beam configured to hold the plurality of optical elements.
[0060] Each docking station may be a predetermined distance from a
final non-parallel plate element of the projection system or the
alignment system. At least one docking station may be arranged such
that the focal point of the projection beam or alignment beam is on
the substrate or substrate table when no liquid is present in the
path of the projection beam or alignment beam. At least one docking
station may be arranged such that the focal point of the projection
beam or alignment beam is on the substrate or substrate table when
a liquid is present in the path of the projection beam or alignment
beam.
[0061] According to a further aspect, there is provided an
alignment apparatus comprising:
[0062] a substrate table configured to hold a substrate, the
substrate having a substrate mark;
[0063] an alignment lens system configured to detect alignment
between a reference mark and the substrate mark using an alignment
beam of radiation;
[0064] a plurality of optical elements removably positionable in
the path of the alignment beam configured to adjust the focal plane
of the alignment lens system when detecting alignment;
[0065] a detector configured to detect the presence of liquid
between the alignment lens system and the substrate table; and
[0066] a controller configured to control which one or more of the
plurality of optical elements is placed in the path of the
alignment beam on the basis of results from the detector.
[0067] According to a further aspect, there is provided a
lithographic projection apparatus comprising an illumination system
configured to provide a beam of radiation, a support structure
configured to hold a patterning device that serves to pattern the
beam according to a desired pattern, a projection system configured
to project the patterned beam onto a target portion of the
substrate, and an alignment apparatus according to the above.
[0068] The alignment beam may traverse at least part of the
projection system.
[0069] According to a further aspect, there is provided a device
manufacturing method comprising:
[0070] projecting a beam as patterned by a patterning device onto a
target portion of a substrate; and
[0071] adjusting the focal plane of the beam by interposing one or
more of a plurality of optical elements in the path of the beam, to
ensure that the focal point of the beam focuses on the same point
regardless of the presence or absence of liquid in the beam.
[0072] 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, 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) or
a metrology or 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.
[0073] The terms "radiation" and "beam" used herein encompass all
types of electromagnetic radiation, including ultraviolet (UV)
radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126
nm), in particular optical radiation.
[0074] The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
projection 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 projection beam may not
exactly correspond to the desired pattern in the target portion of
the substrate. Generally, the pattern imparted to the projection
beam will correspond to a particular functional layer in a device
being created in the target portion, such as an integrated
circuit.
[0075] A patterning device may be transmissive or reflective.
Examples of a patterning device 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; in this manner, the reflected beam is
patterned. In each example of a patterning device, the support
structure may be a frame or table, for example, which may be fixed
or movable as required and which 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".
[0076] The term "projection system" used herein should be broadly
interpreted as encompassing various types of projection system,
including refractive optical systems, reflective optical systems,
and catadioptric optical systems, as appropriate for example 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 "lens" herein may be considered as synonymous with the more
general term "projection system".
[0077] The illumination system may also encompass various types of
optical components, including refractive, reflective, and
catadioptric optical components for directing, shaping, or
controlling the projection beam of radiation, and such components
may also be referred to below, collectively or singularly, as a
"lens".
[0078] The lithographic apparatus may be of a type having two (dual
stage) or more substrate tables (and/or two or more mask tables).
In such "multiple stage" machines the additional tables may be used
in parallel, or preparatory steps may be carried out on one or more
tables while one or more other tables are being used for
exposure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0079] 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:
[0080] FIG. 1 depicts a lithographic apparatus according to an
embodiment of the invention;
[0081] FIG. 2 depicts a liquid supply system;
[0082] FIG. 3 is an alternative view of the liquid supply system
shown in FIG. 2;
[0083] FIG. 4 shows a lithographic projection apparatus according
to an embodiment of the invention with an optical element arranged
in the projection beam;
[0084] FIG. 5 is the lithographic projection apparatus shown in
FIG. 4 with a different optical element arranged in the projection
beam;
[0085] FIG. 6 depicts a lithographic projection apparatus according
to an embodiment of the invention with a combination of optical
elements in the projection beam;
[0086] FIG. 7 depicts an arrangement of a liquid filled optical
element in a lithographic projection apparatus according to an
embodiment of the invention;
[0087] FIG. 8 shows an alignment apparatus according to an
embodiment of the invention;
[0088] FIG. 9 is an alternative alignment apparatus according to an
embodiment of the invention;
[0089] FIG. 10 depicts a projection system in an alignment mode
according to an embodiment of the invention; and
[0090] FIG. 11 shows an alternative arrangement of the optical
element in an alignment apparatus according to an embodiment of the
invention.
DETAILED DESCRIPTION
[0091] FIG. 1 schematically depicts a lithographic apparatus
according to a particular embodiment of the invention. The
apparatus comprises:
[0092] an illumination system (illuminator) IL for providing a
projection beam PB of radiation (e.g. UV radiation).
[0093] a first support structure (e.g. a mask table) MT for
supporting a patterning device (e.g. a mask) MA and connected to a
first positioning device PM for accurately positioning the
patterning device with respect to item PL;
[0094] a substrate table (e.g. a wafer table) WT for holding a
substrate (e.g. a resist-coated wafer) W and connected to a second
positioning device PW for accurately positioning the substrate with
respect to item PL; and
[0095] a projection system (e.g. a refractive projection lens) PL
for imaging a pattern imparted to the projection beam PB by
patterning device MA onto a target portion C (e.g. comprising one
or more dies) of the substrate W.
[0096] 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).
[0097] The illuminator IL receives a beam of radiation 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 integral part of
the 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.
[0098] The illuminator IL may comprise an adjusting device AM for
adjusting the angular intensity distribution of the 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 generally comprises
various other components, such as an integrator IN and a condenser
CO. The illuminator provides a conditioned beam of radiation,
referred to as the projection beam PB, having a desired uniformity
and intensity distribution in its cross-section.
[0099] The projection beam PB is incident on the mask MA, which is
held on the mask table MT. Having traversed the mask MA, the
projection beam PB passes through the lens PL, which focuses the
beam onto a target portion C of the substrate W. With the aid of
the second positioning device PW and position sensor IF (e.g. an
interferometric device), the substrate table WT can be moved
accurately, e.g. so as to position different target portions C in
the path of the beam PB. Similarly, the first positioning device PM
and another position sensor (which is not explicitly depicted in
FIG. 1) can be used to accurately position the mask MA with respect
to the path of the beam PB, e.g. after mechanical retrieval from a
mask library, or during a scan. In general, movement of the object
tables MT and WT will be realized with the aid of a long-stroke
module (coarse positioning) and a short-stroke module (fine
positioning), which form part of the positioning devices PM and PW.
However, in the case of a stepper (as opposed to a scanner) the
mask table MT may be connected to a short stroke actuator only, or
may be fixed. Mask MA and substrate W may be aligned using mask
alignment marks M.sub.1, M.sub.2 and substrate alignment marks
P.sub.1, P.sub.2.
[0100] The depicted apparatus can be used in the following
preferred modes:
1. In step mode, the mask table MT and the substrate table WT are
kept essentially stationary, while an entire pattern imparted to
the projection beam is projected onto a target portion C in one go
(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. 2. In scan mode the mask table MT and the
substrate table WT are scanned synchronously wile a pattern
imparted to the projection beam is projected onto a target portion
C (i.e. a single dynamic exposure). The velocity and direction of
the substrate table WT relative to the mask table MT is determined
by the (de-)magnification and image reversal characteristics of the
projection system PL. 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. 3. In another mode, the mask
table MT is kept essentially stationary holding a programmable
patterning device and the substrate table WT is moved or scanned
while a pattern imparted to the projection 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 a programmable patterning device, such as a programmable
mirror array of a type as referred to above.
[0101] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0102] As shown in FIG. 4, a detector 22 detects the presence or
absence of immersion liquid present on the substrate W. In this
example, the detector 22 detects the presence of liquid on the
substrate W by the reflection of low intensity electromagnetic
waves. However, the presence of liquid could also be detected
using, for example, sonar pulses, electric currents or the physical
detection of the liquid. In an embodiment, the detector 22 detects
the presence of liquid on the target portion C of the substrate, as
shown in FIG. 4. Additionally or alternatively, the detector 22 can
determine the quantity of immersion liquid present. Based on the
measurement by detector 22, the controller 21 determines which one
or more of optical elements 9, 10, 11, 12 is/are necessary. The
controller 21 can determine which one or more of optical elements
9, 10, 11 and 12 can ensure that the projection beam PB is
accurately focused on the upper substrate surface. The selected
optical element (e.g., optical element 10) is then moved into the
path of the projection beam directly after the final lens element
50 of the projection system PL. The projection beam PB is
therefore, to a first order, brought into focus on the upper
surface of the substrate and distance d.sub.l between the final
non-parallel element of the projection system and the point of
focus of the projection beam remains constant. As shown in FIG. 4,
the optical element 10 is a plane parallel plate arranged
perpendicularly to the direction of propagation of the projection
beam PB.
[0103] In FIG. 5, the same lithographic apparatus is used in
conjunction with liquid supply system 30. Liquid supply system 30
supplies liquid with a higher refractive index than the surrounding
gaseous environment to the path of the projection beam. Due to the
difference in refractive indices the optical path length changes.
The detector 22 detects liquid between the projection system and
the substrate and the controller determines that a different
optical element 9 is necessary in the path of the projection beam
PB to focus projection beam PB on substrate W. The optical path
length between the radiation source and the surface of the
substrate and d.sub.l therefore remains constant despite the
presence of a liquid with a higher refractive index in the path of
the projection beam PB. Optical element 9 is placed in the
projection beam PB at a different (lower) position from the
original position of optical element 10.
[0104] The length of the optical path of the projection beam PB can
be varied by adjusting the thickness d.sub.p of the optical
element. To adjust the optical path by an amount d.sub.o (to
compensate for the presence or absence of liquid) using a material
of refractive index n.sub.o the plane plate should have a thickness
d.sub.p, given by d.sub.p=cd.sub.o where
c = n 1 n 1 - n 0 ##EQU00001##
where n.sub.l, is the refractive index of the plane plate optical
element.
[0105] In FIG. 6, the detector detects no liquid between the
projection system and the substrate and the optical element 11 is
added to the projection system. Optical elements 9 and 11 have a
combined thickness and refraction indices sufficient to focus the
projection beam on the surface of the substrate. The optical
element 11 can be placed in the projection beam either above or
below optical element 9. In this example, each optical element 9,
10, 11, 12 has a (mutually exclusive) position assigned in the
projection beam so that any combination of optical elements 9, 10,
11, 12 can be placed in the projection beam without colliding with
another optical element.
[0106] Alternatively, the thickness d.sub.p of the optical element
10, 11 is fixed but the refractive index is varied. This could be
achieved by replacing a plane plate made of for example glass, by a
plane plate made of, for example, perspex. Alternatively, the
optical element could be a hollow plane plate filled with a fluid
of known refractive index. The refractive index of the optical
element 10 is then varied by changing the composition of the fluid.
As shown in FIG. 7, the fluid 15 inside the optical element 14 can
be replaced and the composition adjusted by the fluid replacement
device 16. The composition can be adjusted by, for example,
changing the salt concentration in the fluid or changing the ratio
of two or more fluids in mixture. The replacement and refreshment
of the fluid 15 in the optical element 14 also keeps the optical
element 14 cool, thus reducing errors and damage caused by thermal
expansion and contraction of components.
[0107] FIG. 8 illustrates an alignment apparatus in which an
alignment beam AB is projected towards a substrate mark P.sub.1
where it is partially reflected through the alignment system AS.
The alignment beam is then imaged onto alignment mark M.sub.1. The
alignment of substrate mark P.sub.1 and alignment mark M.sub.1 are
detected in a known manner to determine the alignment of substrate
W. As shown in FIG. 8, a detector 22 detects the presence and/or
quantity of liquid on the substrate and the controller 21 then
selects an optical element 10 accordingly.
[0108] Alignment can also take place in a so-called through the
lens systems shown in FIG. 9. In such systems the alignment beam AB
is projected through the projection lens PL towards the substrate
mark P.sub.1 and reflected back towards the mark M.sub.1 on the
mask MA. Again, a detector (not shown in FIG. 9 but shown, for
example, as detector 22 in FIG. 8) detects the presence and/or
quantity of liquid between the final element of the projection
system and the substrate and a controller (not shown in FIG. 9 but
shown, for example, as controller 21 in FIG. 8) selects an
appropriate optical element to place in the alignment beams to
ensure the alignment beam is accurately focused on the substrate
mark P.sub.1.
[0109] In FIG. 10, the projection system is being used to project
an alignment beam AB towards a reference mark F.sub.1 on the
substrate table WT. The reference mark F.sub.1 is a partially
reflective phase grating. Although the clarity of the partially
reflected alignment beam AB is reduced by the non-uniformity of the
liquid thickness it is still sufficiently clear to enable alignment
to take place. If the detector 22 has detected a small amount of
liquid present on the substrate W, a thin optical element 11 is
selected by the controller 21 and placed in the path of the
alignment beam AB. If the detector detects even less liquid, a
thicker optical element 10 could be chosen; if more liquid is
detected, an even thinner optical element 9 can be chosen.
[0110] Although in the examples above the optical elements are
placed in the alignment beam or projection beam directly after the
projection system PL or alignment system AS to ensure spherical
aberrations are constant over the field, they could also be placed
at a different position in the system as shown, for example, in
FIG. 11. The optical element 10 is placed in the alignment beam AB
prior to projection through the projection system PL. The optical
element 10 still ensures that the alignment beam AB is accurately
focused on the substrate mark P.sub.1. To focus the projection beam
PB or alignment beam AB onto the surface of the substrate or
substrate mark to second or higher orders, the positions of optical
elements in the projection system PL or alignment system AS can be
adjusted when a different optical element is inserted in the path
of the projection beam or alignment beam.
[0111] Instead of detector 22 and controller 21 determining if, and
which, optical element should be placed in the path of the
projection beam PB or alignment beam AB, an operator could decide
to change the apparatus from an immersion style apparatus to a
"dry" apparatus. The optical element 9, 10, 11, 12 could be screwed
to or otherwise permanently attached to the bottom of the
projection system PL or alignment system AS at an appropriate
distance. When the operator decides to change the apparatus from a
"dry" apparatus to an immersion apparatus, the optical element 9,
10, 11, 12 is removed and liquid supply system 30 supplies liquid
to the space between the projection system PB or alignment system
AS and substrate W. The operator may also adjust the positioning
and perhaps shape of some of the other optical elements of the
projection system to take account of higher order optical
effects.
[0112] While specific embodiments of the invention have been
described above, it will be appreciated that the invention may be
practiced otherwise than as described. The description is not
intended to limit the invention.
* * * * *