U.S. patent application number 16/971751 was filed with the patent office on 2020-12-24 for radiation shielding device and apparatus comprising such shielding device.
The applicant listed for this patent is ASML Netherlands B.V.. Invention is credited to Philippe Jacqueline Johannes Hubertus Anthonius Habets, Franciscus Johannes Joseph Janssen, Gunes Nakiboglu, Roger Wilhelmus Antonius Henricus Schmitz, Remco Van de Meerendonk, Joris Dominicus Bastiaan Johannes Van den Boom, Nicholas Peter Waterson.
Application Number | 20200401058 16/971751 |
Document ID | / |
Family ID | 1000005078628 |
Filed Date | 2020-12-24 |
![](/patent/app/20200401058/US20200401058A1-20201224-D00000.png)
![](/patent/app/20200401058/US20200401058A1-20201224-D00001.png)
![](/patent/app/20200401058/US20200401058A1-20201224-D00002.png)
![](/patent/app/20200401058/US20200401058A1-20201224-D00003.png)
![](/patent/app/20200401058/US20200401058A1-20201224-D00004.png)
United States Patent
Application |
20200401058 |
Kind Code |
A1 |
Janssen; Franciscus Johannes Joseph
; et al. |
December 24, 2020 |
RADIATION SHIELDING DEVICE AND APPARATUS COMPRISING SUCH SHIELDING
DEVICE
Abstract
An apparatus comprising a heat-sensitive device (F); a radiative
element (RE), the radiative element in operation generating first
electromagnetic radiation (ER), the first radiation propagating
towards the heat-sensitive device; and a radiation-shielding device
(20) arranged between the radiative element and the heat-sensitive
device such that, in operation, the first radiation impinges on the
radiation-shielding device. The radiation-shielding device
comprises a first shield element (21) having a first fluid channel
(215) arranged therein, the first shield element having a first
surface (213) and a second surface (214), the first surface being
arranged closer to the radiative element than the second surface;
and a second shield element (22) having a second fluid channel
(225) arranged therein, the second shield element having a third
surface (223) and a fourth surface (224), the third surface being
arranged closer to the radiative element than the fourth surface.
The first shield element is arranged closer to the radiative
element than the second shield element and the second shield
element is arranged closer to the heat-sensitive device than the
first shield element, the first shield element and the second
shield element spaced apart from each other and the second surface
and the third surface opposing each other.
Inventors: |
Janssen; Franciscus Johannes
Joseph; (Geldrop, NL) ; Habets; Philippe Jacqueline
Johannes Hubertus Anthonius; (Maastricht, NL) ;
Nakiboglu; Gunes; (Eindhoven, NL) ; Schmitz; Roger
Wilhelmus Antonius Henricus; (Helmond, NL) ; Van de
Meerendonk; Remco; ('s-Hertogenbosch, NL) ; Van den
Boom; Joris Dominicus Bastiaan Johannes; (Veldhoven, NL)
; Waterson; Nicholas Peter; (Veldhoven, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASML Netherlands B.V. |
Veldhoven |
|
NL |
|
|
Family ID: |
1000005078628 |
Appl. No.: |
16/971751 |
Filed: |
February 21, 2019 |
PCT Filed: |
February 21, 2019 |
PCT NO: |
PCT/EP2019/054258 |
371 Date: |
August 21, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/70891 20130101;
G03F 7/70033 20130101 |
International
Class: |
G03F 7/20 20060101
G03F007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2018 |
EP |
18160096.6 |
Claims
1. A lithographic apparatus configured to project a pattern from a
patterning device onto a substrate, the lithographic apparatus
comprising: a. a heat-sensitive device; b. a radiative element, the
radiative element in operation generating electromagnetic
radiation, the electromagnetic radiation propagating towards the
heat-sensitive device; c. a radiation-shielding device arranged
between the radiative element and the heat-sensitive device such
that, in operation, the electromagnetic radiation impinges on the
radiation-shielding device; and d. an optical system coupled to the
heat-sensitive device and configured to project a patterned beam of
electromagnetic radiation on the substrate; wherein the
radiation-shielding device comprises: e. a first shield element
having a first fluid channel arranged therein, the first shield
element having a first surface and a second surface, the first
surface being arranged closer to the radiative element than the
second surface; and f. a second shield element having a second
fluid channel arranged therein, the second shield element having a
third surface and a fourth surface, the third surface being
arranged closer to the radiative element than the fourth surface;
and wherein the first shield element is arranged closer to the
radiative element than the second shield element, and the second
shield element is arranged closer to the heat-sensitive device than
the first shield element, the first shield element and the second
shield element spaced apart from each other, and the second surface
and the third surface opposing each other.
2. The lithographic apparatus according to claim 1, wherein the
first shield element is provided with a first fluid port and a
second fluid port for flowing a fluid through the first fluid
channel and the second shield element is provided with a third
fluid port and a fourth fluid port for flowing a fluid through the
second fluid channel.
3. The lithographic apparatus according to claim 2, wherein a fluid
conditioning system is coupled to the fluid ports of at least one
of the first and the second shield element for conditioning the
fluid and flowing the fluid through the fluid channel of said at
least one of the first and the second shield element.
4. The lithographic apparatus according to claim 2, wherein the
second fluid port and the third fluid port are coupled and wherein
a fluid conditioning system is coupled to the first fluid port and
the fourth fluid port for conditioning the fluid and flowing the
fluid through the first and the second fluid channel.
5. The lithographic apparatus according to claim 1, wherein the
radiation-shielding device extends in a shielding plane, the
shielding plane being transverse to a radiation direction, the
radiation direction extending from the radiative element to the
heat-sensitive device.
6. The lithographic apparatus according to claim 5, wherein the
first shield element is provided with a first through hole, the
through hole extending in parallel to the shielding plane, and the
second shield element is provided with a second through hole, the
second through hole extending in parallel to the shielding plane,
and wherein the first through hole and the second through hole are
arranged such that the electromagnetic radiation propagating in the
radiation direction and passing through the first through hole
impinges on the second shield element.
7. The lithographic apparatus according to claim 6, wherein an
interferometer system is arranged on a first side of the
radiation-shielding device and a wavelength tracking system is
arranged on the heat-sensitive device at a second side of the
radiation-shielding device, wherein the second side is opposite to
the first side.
8. (canceled)
9. The lithographic apparatus according to claim 1, wherein the
patterned beam of electromagnetic radiation comprises EUV radiation
having a wavelength in a range of 4-20 nm.
10. The lithographic apparatus according to claim 1, wherein the
heat-sensitive device is a frame supporting a part of the optical
system.
11. The lithographic apparatus according to claim 1, wherein the
radiative element is one of the elements comprised in a group of
radiative elements, the group comprising a cable, a tube and an
actuator.
12. The lithographic apparatus according to claim 1, wherein the
apparatus comprises: an illumination system configured to condition
a radiation beam; a support structure constructed to support the
patterning device, the patterning device being capable of imparting
the radiation beam with a pattern in its cross-section to form the
patterned beam of electromagnetic radiation; a substrate table
constructed to hold the substrate; and a projection system
configured to project the patterned radiation beam onto the
substrate.
13. A radiation-shielding device configured for protecting a
heat-sensitive device against electromagnetic radiation from a
radiative element, the radiation shielding device comprising: a. a
first shield element having a first fluid channel arranged therein,
the first shield element having a first surface and a second
surface; b. a second shield element having a second fluid channel
arranged therein, the second shield element having a third surface
and a fourth surface; and wherein the first shield element and the
second shield element are spaced apart from each other and wherein
the second surface and the third surface are arranged opposing each
other, and wherein the heat-sensitive device is within a
lithographic apparatus arranged to project a pattern from a
patterning device onto a substrate, the lithographic apparatus
being provided with an optical system for projecting a patterned
beam of electromagnetic radiation on the substrate, wherein the
optical system is coupled to the heat-sensitive device.
14. A method of protecting a heat-sensitive device against
electromagnetic radiation from a radiative element, wherein the
heat-sensitive device is within a lithographic apparatus arranged
to project a pattern from a patterning device onto a substrate, the
lithographic apparatus being provided with an optical system for
projecting a patterned beam of electromagnetic radiation on the
substrate, wherein the optical system is coupled to the
heat-sensitive device, the method comprising: a. arranging a first
shield element having a first fluid channel arranged therein
between the radiative element and the heat-sensitive device, the
first shield element having a first surface and a second surface;
b. arranging a second shield element having a second fluid channel
arranged therein between the first shield element and the
heat-sensitive device, the second shield element having a third
surface and a fourth surface, such that the first shield element
and the second shield element are arranged spaced apart from each
other and the second surface and the third surface oppose each
other; and c. flowing a fluid through the first fluid channel and
the second fluid channel.
15. The method according to claim 14, wherein step c further
comprises conditioning the fluid flowing through at least one of
the first fluid channel and the second fluid channel.
16. The radiation-shielding device according to claim 13, wherein
the first shield element is provided with a first fluid port and a
second fluid port for flowing a fluid through the first fluid
channel, and the second shield element is provided with a third
fluid port and a fourth fluid port for flowing a fluid through the
second fluid channel.
17. The radiation-shielding device according to claim 13, wherein
the radiation-shielding device extends in a shielding plane, the
shielding plane being transverse to a radiation direction, the
radiation direction extending from the radiative element to the
heat-sensitive device.
18. The radiation-shielding device according to claim 13, further
comprising a coupling channel through which the first fluid channel
and the second fluid channel are operatively coupled.
19. The radiation-shielding device according to claim 13, further
comprising a fluid configured to flow through the first fluid
channel, the fluid configured to absorb at least a part of the heat
generated at the first shield element.
20. The radiation-shielding device according to claim 19, wherein
the fluid is configured to flow through the second fluid channel,
the fluid configured to absorb at least another part of the heat
generated at the second shield element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of EP application
18160096.6, which was filed on 6 Mar. 2018 and which is
incorporated herein in its entirety by reference.
FIELD
[0002] The present invention relates to a radiation shielding
device and apparatus comprising such shielding device. In
particular, the radiation shielding device relates to a radiation
shielding device through which a fluid may flow to remove heat
generated by impinging radiation.
BACKGROUND
[0003] A lithographic apparatus is a machine constructed to apply a
desired pattern onto a substrate. A lithographic apparatus can be
used, for example, in the manufacture of integrated circuits (ICs).
A lithographic apparatus may for example project a pattern from a
patterning device (e.g. a mask) onto a layer of radiation-sensitive
material (resist) provided on a substrate.
[0004] The wavelength of radiation used by a lithographic apparatus
to project a pattern onto a substrate determines the minimum size
of features which can be formed on that substrate. A lithographic
apparatus which uses EUV radiation, being electromagnetic radiation
having a wavelength within the range 4-20 nm, for example 6.7 nm or
13.5 nm, may be used to form smaller features on a substrate than a
conventional lithographic apparatus (which may for example use
electromagnetic radiation with a wavelength of 193 nm).
[0005] With such smaller features being applied the lithographic
apparatus has also to be designed to apply the features accurately
for sufficient overlay performance, i.e. accurate positioning of
layers, that are separately applied on top of each other, relative
to each other. Any unexpected or uncontrolled mechanical
deformations and vibrations may cause defects in the circuit being
patterned and manufactured, which may be detrimental to the
functionality of a manufactured integrated circuit.
[0006] In the lithographic apparatus there are however parts and
devices that generate heat and consequently radiate electromagnetic
radiation. Since the above-mentioned lithographic apparatus using
EUV radiation may be interiorly kept substantially vacuum, i.e. at
a very low pressure and thus convective heat transportation may be
low, the radiated electromagnetic radiation may impinge on
heat-sensitive parts and devices. The electromagnetic radiation may
be absorbed and as a result the heat-sensitive parts may still be
heated. Inevitably, the heating results in mechanical expansion and
potentially mechanical deformations.
[0007] It is known to apply a plate-like shielding device having an
interior through which a coolant liquid, such as but not limited to
water, is flown. The shielding device may be arranged between the
radiative elements, i.e. the parts and devices that may radiate
during operation of the lithographic apparatus, and a
heat-sensitive device. The radiation impinges on the shielding
device. Heat generated in the shielding device as a consequence of
the impinging and absorbed radiation is removed by the coolant
liquid, preventing that the shielding device may heat up to the
extent that the shielding device becomes a radiating device.
[0008] The shielding device is however limited in practical use,
since the coolant liquid flow generates vibrations that may affect
the accuracy, which becomes even more of a disadvantage with an
increasing flow needed for further reduction of temperature
variations in the heat-sensitive device, which is needed for the
above-mentioned smaller features. Similarly, the closed plate-like
structure of the known shielding device divides the interior in
separate environments, which may be disadvantage in certain
applications. In general, the known shielding device has a limited
scope of applicability.
SUMMARY
[0009] It may be desirable to provide a lithographic apparatus
which addresses the problem identified above or some other problem
associated with the prior art. In particular, a shielding device
with a larger scope of applicability may be desirable.
[0010] In accordance with one embodiment of the invention,
provision is made of an apparatus comprising a heat-sensitive
device, a radiative element, and a radiation-shielding device. The
radiative element generates first electromagnetic radiation, when
the radiative element is in operation. The first electromagnetic
radiation propagates at least towards the heat-sensitive device.
The radiation-shielding device is arranged between the radiative
element and the heat-sensitive device such that, in operation, the
first radiation impinges on the radiation-shielding device. The
radiation-shielding device comprises a first shield element, which
first shield element has a first fluid channel arranged therein and
has a first surface and a second surface. The first surface is
arranged closer to the radiative element than the second surface.
The radiation-shielding device further comprises a second shield
element, which second shield element has a second fluid channel
arranged therein and has a third surface and a fourth surface. The
third surface is arranged closer to the radiative element than the
fourth surface. The first shield element is arranged closer to the
radiative element than the second shield element and the second
shield element is arranged closer to the heat-sensitive device than
the first shield element. The first shield element and the second
shield element are spaced apart from each other and the second
surface and the third surface are opposing each other.
[0011] In this way, having at least two layers of shielding, much
more applications for shielding against electromagnetic radiation
are enabled, a few of which are described in detail hereinbelow.
Still, other applications are contemplated too.
[0012] In an embodiment, the first shield element is provided with
a first fluid port and a second fluid port for flowing a fluid
through the first fluid channel and the second shield element is
provided with a third fluid port and a fourth fluid port for
flowing a fluid through the second fluid channel. Thus, the shield
elements may be coupled to a fluid supply and fluid drain for
flowing a fluid, i.e. either a liquid medium or a gaseous medium,
through at least one of the shield elements for temperature
control. In particular, any heat received or generated, for example
due to the electromagnetic radiation impinging on the shield
element, may be removed through the fluid flowing through the fluid
channel of the shield element. In an embodiment, the fluid is
employed to maintain at least one of the shield elements at a
predetermined temperature or at least at a temperature within a
predetermined temperature range.
[0013] In an embodiment, a fluid conditioning system is coupled to
the fluid ports of at least one of the first and the second shield
element for conditioning the fluid and flowing the fluid through
the fluid channel of said at least one of the first and the second
shield element. In another embodiment, the second fluid port and
the third fluid port are coupled and a fluid conditioning system is
coupled to the first fluid port and the fourth fluid port for
conditioning the fluid and flowing the fluid through the first and
the second fluid channel. Either of these embodiments is enabled
for accurate temperature control of the radiation-shielding device
in order to prevent that the radiation-shielding device provides
for an undesired heat load on the heat-sensitive device.
[0014] In an embodiment, the radiation-shielding device extends in
a shielding plane, wherein the shielding plane is transverse to a
radiation direction. The radiation direction extends from the
radiative element to the heat-sensitive device. In this embodiment,
the radiation-shielding device is configured and arranged to block
any electromagnetic radiation from propagating directly from the
radiative element to the heat-sensitive device. The electromagnetic
radiation will impinge on the radiation-shielding device instead of
impinging on the heat-sensitive device. The electromagnetic
radiation may completely or partly be absorbed by the
radiation-shielding device, thereby heating the radiation-shielding
device. The generated heat may be removed by a fluid flowing
through the fluid channel. It is noted that, in an embodiment, the
shielding plane may be under an angle different than (exactly) 90
degrees. Depending on the requirements, any other suitable angle
may be selected to shield the heat-sensitive device from the
electromagnetic radiation. Further, if more than one radiative
element is present, an orientation of the shielding plane may be
suitably selected relative to both radiative elements such that the
resulting heat transfer towards the heat-sensitive device remains
within predetermined limits.
[0015] It is noted that with the use of a single shield element
through which a fluid flows it is possible to remove the generated
heat. In particular, by increasing the flow of fluid, it is
possible to remove more heat. However, with increasing flow,
vibrations caused by the flow increase as well. In vibrational
sensitive systems, such increase in vibrations is undesirable. A
flow of fluid through the radiation-shielding device according to
the present invention is significantly reduced, while increasing a
heat removal capacity of the radiation-shielding device. Thus,
surprisingly, the radiation-shielding device according to the
present invention has an improved heat removal capacity with a
reduction in vibration generation.
[0016] In a particular embodiment, the first shield element is
provided with a first through hole, the through hole extending in
parallel to the shielding plane, and the second shield element is
provided with a second through hole, the second through hole
extending in parallel to the shielding plane. Further, the first
through hole and the second through hole are arranged such that
electromagnetic radiation propagating in the radiation direction
and passing through the first through hole impinges on the second
shield element. In other words, the electromagnetic radiation is
prevented from passing through both the first through hole and the
second through hole. The electromagnetic radiation propagating from
the radiative element towards the heat-sensitive device in the
radiation direction does not reach the heat-sensitive device, but
either impinges on the first shield element or passes through the
first through hole to impinge on the second shield element.
However, any fluid such as a gaseous medium may flow through the
first through hole and the second through hole such that
environmental properties, such as a gas pressure and gas mixture,
on both sides of the radiation-shielding device are substantially
equal.
[0017] In an exemplary embodiment, an interferometer system is
arranged on a first side of the radiation-shielding device and a
wavelength tracking system is arranged on the heat-sensitive device
at a second side of the radiation-shielding device, wherein the
second side is opposite to the first side. The wavelength tracking
system may be employed for calibrating the interferometer. However,
in order to achieve an accurate calibration, it is needed that
similar environmental conditions apply, i.e. a similar gas
pressure, gas temperature, gas mixture, etc. Having through holes
extending from the first side of the radiation-shielding device to
the opposing second side allows such conditions to be similar on
both sides, while electromagnetic radiation that may negatively
affect temperature stability of the heat-sensitive device is
blocked and any generated heat is removed.
[0018] The apparatus according to the present invention may be very
suitable for use in optical systems and in particular in
lithographic system, in which temperature control and vibration
control are important to improve positional accuracy of the
projected beam. In such an embodiment, the apparatus is provided
with an optical system for projecting a beam of electromagnetic
radiation on a substrate and the optical system may be coupled to
the heat-sensitive device. The optical system may comprise
different parts and elements such as one or more optical elements
like a lens and a mirror, positioning devices for positioning an
optical element and a measurement device for measuring a position
of an optical element. In particular, the heat-sensitive device may
be a frame supporting at least a part of such an optical system.
Any heat load on the frame would incur an expansion of the frame.
Preventing such a heat load on the frame directly improves the
positional accuracy of the beam projected by (the part of) the
optical system supported by the frame. Similarly, any vibrations
are preferably prevented in the frame. Therefore, it is preferred
that any source of vibrations are eliminated from the apparatus or
at least the amount of vibrations is reduced or the vibrations are
sufficiently controlled with respect to frequency and/or amplitude.
In a particular embodiment, the projected beam of electromagnetic
radiation comprises EUV radiation having a wavelength in a range of
4-20 nm.
[0019] In an embodiment, the radiative element is one of the
elements comprised in a group of radiative elements, the group
comprising a cable, a tube and an actuator. Common sources of heat
load is cabling, tubing and actuators. As apparent to those skilled
in the art, such cabling, tubing and actuators cannot be prevented
in the apparatus and cannot be prevented from generating heat and
corresponding electromagnetic radiation. Using the
radiation-shielding device according to the present invention
prevents negative effects of such heat load and radiation, while at
the same time reducing vibrations generated by prior art
radiation-shielding devices.
[0020] In an aspect, the present invention provides a
radiation-shielding device for use in the apparatus according to
the invention. The radiation shielding device is configured for
protecting a heat-sensitive device against electromagnetic
radiation from a radiative element and comprises a first shield
element and a second shield element. The first shield element has a
first fluid channel arranged therein and has a first surface and a
second surface. The second shield element has a second fluid
channel arranged therein and has a third surface and a fourth
surface. The first shield element and the second shield element are
spaced apart from each other and the second surface and the third
surface are arranged opposing each other.
[0021] In a further aspect, the present invention provides method
of protecting a heat-sensitive device against electromagnetic
radiation from a radiative element. The method comprises arranging
a first shield element having a first fluid channel arranged
therein between the radiative element and the heat-sensitive
device, the first shield element having a first surface and a
second surface; arranging a second shield element having a second
fluid channel arranged therein between the first shield element and
the heat-sensitive device, the second shield element having a third
surface and a fourth surface, such that the first shield element
and the second shield element are arranged spaced apart from each
other and the second surface and the third surface oppose each
other; and flowing a fluid through the first fluid channel and the
second fluid channel.
[0022] In an embodiment, the step of flowing a fluid through the
first fluid channel and the second fluid channel further comprises
conditioning the fluid flowing through at least one of the first
fluid channel and the second fluid channel. Such conditioning may,
for example, include controlling a temperature of the fluid flowing
to such shield element.
[0023] Further, in an embodiment, the amount of flow may be
controlled in dependence of a temperature difference between a
temperature of the fluid flowing into a shield element and a
temperature of the fluid flowing out of the shield element. Such
control method may be applied in order to achieve a constant heat
load to the heat-sensitive device independent of an amount of
electromagnetic radiation originating from the radiative element.
In another example, such control method may be applied in order to
further reduce flow-induced vibrations by reducing the fluid flow
when less electromagnetic radiation is incident on the
radiation-shielding device.
[0024] Features described in the context of one aspect or
embodiment described above may be used with others of the aspects
or embodiments described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying schematic
drawings, in which:
[0026] FIG. 1 depicts a lithographic system comprising a
lithographic apparatus and a radiation source,
[0027] FIGS. 2A and 2B schematically depict a first embodiment of
an apparatus according to the present invention,
[0028] FIG. 3 depicts a graph illustrating an amount of
flow-induced vibrations as a function of flow rate,
[0029] FIG. 4 depicts a graph illustrating a heat load suppression
as a function of flow rate,
[0030] FIG. 5A depicts a first embodiment of a shield element
suitable for use in the first embodiment of the radiation shielding
device of FIGS. 2A and 2B,
[0031] FIG. 5B depicts a second embodiment of a shield element
suitable for use in the first embodiment of the radiation shielding
device of FIGS. 2A and 2B,
[0032] FIGS. 5C-5D depict a third embodiment of a shield element
suitable for use in the first embodiment of the radiation shielding
device of FIGS. 2A and 2B,
[0033] FIGS. 6A and 6B depict a second embodiment of a radiation
shielding device according to the present invention,
[0034] FIGS. 7A and 7B depict a first embodiment of a shield
element suitable for use in the second embodiment of the radiation
shielding device of FIGS. 6A and 6B, and
[0035] FIG. 7C depicts a second embodiment of a shield element
suitable for use in the second embodiment of the radiation
shielding device of FIGS. 6A and 6B.
DETAILED DESCRIPTION
[0036] The features and advantages of the present invention will
become more apparent from the detailed description set forth below
when taken in conjunction with the drawings. In the drawings, like
reference numbers generally indicate identical, functionally
similar, and/or structurally similar elements.
[0037] This specification discloses one or more embodiments that
incorporate the features of this invention. The disclosed
embodiment(s) merely exemplify the invention. The scope of the
invention is not limited to the disclosed embodiment(s). The
invention is defined by the claims appended hereto.
[0038] FIG. 1 shows a lithographic system comprising a radiation
source SO and a lithographic apparatus LA. The radiation source SO
is configured to generate an EUV radiation beam B and to supply the
EUV radiation beam B to the lithographic apparatus LA. The
lithographic apparatus LA comprises an illumination system IL, a
support structure MT configured to support a patterning device MA
(e.g., a mask), a projection system PS and a substrate table WT
configured to support a substrate W.
[0039] The illumination system IL is configured to condition the
EUV radiation beam B before the EUV radiation beam B is incident
upon the patterning device MA. Thereto, the illumination system IL
may include a facetted field mirror device 10 and a facetted pupil
mirror device 11. The faceted field mirror device 10 and faceted
pupil mirror device 11 together provide the EUV radiation beam B
with a desired cross-sectional shape and a desired intensity
distribution. The illumination system IL may include other mirrors
or devices in addition to, or instead of, the faceted field mirror
device 10 and faceted pupil mirror device 11.
[0040] After being thus conditioned, the EUV radiation beam B
interacts with the patterning device MA. As a result of this
interaction, a patterned EUV radiation beam B' is generated. The
projection system PS is configured to project the patterned EUV
radiation beam B' onto the substrate W. For that purpose, the
projection system PS may comprise a plurality of mirrors 13,14
which are configured to project the patterned EUV radiation beam B'
onto the substrate W held by the substrate table WT. The projection
system PS may apply a reduction factor to the patterned EUV
radiation beam B', thus forming an image with features that are
smaller than corresponding features on the patterning device MA.
For example, a reduction factor of 4 or 8 may be applied. Although
the projection system PS is illustrated as having only two mirrors
13,14 in FIG. 1, the projection system PS may include a different
number of mirrors (e.g. six or eight mirrors).
[0041] The substrate W may include previously formed patterns.
Where this is the case, the lithographic apparatus LA aligns the
image, formed by the patterned EUV radiation beam B', with a
pattern previously formed on the substrate W.
[0042] A relative vacuum, i.e. a small amount of gas (e.g.
hydrogen) at a pressure well below atmospheric pressure, may be
provided in the radiation source SO, in the illumination system IL,
and/or in the projection system PS.
[0043] The radiation source SO may be a laser produced plasma (LPP)
source, a discharge produced plasma (DPP) source, a free electron
laser (FEL) or any other radiation source that is capable of
generating EUV radiation.
[0044] FIG. 2A shows a radiation-shielding device 20 according to
the present invention. As an example, the radiation-shielding
device 20 is arranged in the lithographic apparatus as shown in
FIG. 1, while it is contemplated that the radiation-shielding
device 20 may be used in any other kind of apparatus.
[0045] In the embodiment of FIG. 2A, a support structure SS
supports the radiation-shielding device 20 and a frame F. The frame
F supports a mirror 1 of the projection system PS of the
lithographic apparatus LA as shown in FIG. 1. As an example, the
frame F is illustrated and described as a heat-sensitive device
shielded from radiation by the radiation-shielding device 20. It is
noted that the radiation-shielding device 20 may however be used
for shielding any other part of the lithographic apparatus LA as
well.
[0046] The radiation-shielding device 20 is arranged between the
frame F and a radiative element RE. The radiative element RE may be
any kind of element that may generate electromagnetic radiation ER,
which electromagnetic radiation ER may provide for an input heat
load Q.sub.1 when absorbed by an element or device. While the
electromagnetic radiation ER may be radiated by the radiative
element RE in any or all directions, in the present description
only the electromagnetic radiation ER radiated in a radiation
direction RD towards the heat-sensitive frame F is considered and
described.
[0047] FIG. 2B shows the embodiment of the radiation-shielding
device 20 shown in FIG. 2A in more detail. The radiation-shielding
device 20 comprises a first shield element 21 and a second shield
element 22. The first shield element 21 is provided with a first
fluid channel 215 operatively coupled to a first fluid port 211 and
a second fluid port 212. Further, the first shield element 21 has a
first surface 213 and a second surface 214. The second shield
element 22 is provided with a second fluid channel 225 operatively
coupled to a third fluid port 221 and a fourth fluid port 222.
Further, the second shield element 22 has a third surface 223 and a
fourth surface 224. The first fluid channel 215 and the second
fluid channel 225 are operatively coupled through a coupling
channel 23. Thus, a fluid may be supplied through the third fluid
port 221, flow through the first fluid channel 215 and the second
fluid channel 225 and be drained through the first fluid port 211.
In another embodiment, the coupling channel 23 may be omitted and
separate flows may be generated through the first fluid channel 215
and the second fluid channel 225. Such an embodiment may be
preferred if different fluids or different flow amounts are desired
in view of the application, for example.
[0048] The radiation-shielding device 20 is coupled to a fluid
conditioning system FCS. The fluid conditioning system FCS may be
configured to circulate a fluid, e.g. water, through the
radiation-shielding device 20 by supplying the fluid through the
third fluid port 221 and receiving the fluid through the first
fluid port 211. The fluid conditioning system FCS may be further
configured to monitor and/or control a temperature of the
circulating fluid. The fluid supplied to the radiation-shielding
device 20 may be maintained at a predetermined temperature, for
example, such to control a temperature of the radiation-shielding
device 20. Alternatively or additionally, a temperature of the
fluid returning from the radiation-shielding device 20 may be
measured and based on a temperature difference with the supplied
fluid an amount of incident electromagnetic radiation ER may be
derived in order to determine an amount of flow of the fluid needed
to protect the heat-sensitive element, in casu the frame F.
[0049] Referring to FIGS. 2A and 2B, the electromagnetic radiation
ER propagating from the radiative element RE towards the
heat-sensitive frame F impinges on the first surface 213 of the
first shield element 21. At least a part of the electromagnetic
radiation ER may be absorbed by the first shield element 21. Due to
the absorbed radiation, the first surface 213 of the first shield
element 21 is heated. The fluid flowing through the first fluid
channel 215 may absorb at least a part of the generated heat and
may transport the heat away through the first fluid port 211 to the
fluid conditioning system FCS. Another part of the generated heat
may however be transported to the second surface 214 where it may
generate electromagnetic radiation that propagates from the second
surface 214 towards the third surface 223. Due to the radiation
impinging on the third surface 223, the second shield element 22 is
heated. The fluid flowing through the second fluid channel 225 may
remove at least a part of such heat. A remaining part of the heat
may heat the fourth surface 224 due to which the fourth surface 224
will radiate electromagnetic radiation. This electromagnetic
radiation may be considered to form an output heat load Q.sub.out,
which output heat load is provided to the frame F. A heat load
suppression S of the radiation-shielding device 20 may thus be
defined as S=Q.sub.out/Q.sub.in.
[0050] As apparent to those skilled in the art, the
radiation-shielding device 20 may be further provided with a third
shield element and even further shield elements which may further
increase the heat load suppression.
[0051] As described hereinabove, a heat transfer may be generated
by radiation. However, depending on the circumstances and
properties, the heat may be transferred by convection and
conduction as well. Still, a person skilled in the art will
understand that conductive heat transport may be prevented
significantly by suitable thermal isolation. Convective heat
transport may be present, for example by a gaseous medium present
in the environment of the radiative element RE, the
radiation-shielding device 20 and/or the heat-sensitive frame F. It
is noted that the radiation-shielding device 20 may be employed to
reduce or prevent heat transfer by conduction and/or convection as
well as by radiation. Moreover, in a particular embodiment, the
heat transfer by conduction and/or convection may even be dominant
over the radiative heat transfer. In another embodiment, when used
in a vacuum environment, i.e. a low gas pressure environment, the
radiation-shielding device 20 may be primarily employed to prevent
radiative heat load reaching a heat-sensitive element. More in
general, the radiation shielding device according to the present
invention may be designed and used to provide for suitable
reduction of any kind of heat transfer.
[0052] As apparent to those skilled in the art, in order to provide
for thermal stability of the frame F, at least the fourth surface
224 of the second shield element 22 may be controlled to have a
same temperature as the frame F, e.g. a predetermined set
temperature. Therefore, a temperature of the fluid flowing through
the second fluid channel 225 may be set at such predetermined set
temperature. In an embodiment, the temperature of the fluid may be
set slightly below the predetermined set temperature such that,
with the heat generated due to the impinging radiation, the
temperature of the fourth surface 224 corresponds to the
predetermined set temperature.
[0053] In the prior art it is known to apply a heat shield having a
single shield element having a fluid channel. A heat load
suppression may be increased in such prior art heat shield by
increasing a fluid flow through such heat shield. However, with
increased flow, an amount of flow-induced-vibrations is increased
as well, as shown in FIG. 3. FIG. 3 shows a diagram with an amount
of fluid flow through a shield element in litre per minute on the
horizontal axis and pressure fluctuation in a frequency range of
50-1000 Hz in Pa on the vertical axis. The pressure fluctuation is
represented by a 3.sigma. value for the pressure, where .sigma. is
the standard deviation of the pressure over a predetermined
frequency range. This pressure fluctuation is representative of the
flow-induced vibrations. From FIG. 3, it is easily derivable that
the flow-induced vibrations increase rapidly and significantly with
an increasing fluid flow. For applications sensitive to mechanical
instabilities like vibrations, such as a lithographic projection
system, the flow-induced vibrations are preferably to be kept below
a predetermined threshold, if not completely circumventable or
preventable. At the same time, such mechanically sensitive systems
may also be needed to be prevented from thermal expansion and
contraction. Thus, such mechanically sensitive systems are
preferably protected with a heat shield against heat load by
radiation, convection and/or conduction. Moreover, in lithographic
apparatus, with a desire to project even finer patterns, the
mechanical accuracy requirements become tighter, which may require
higher heat load suppression and a lower amount of vibrations. For
a prior art heat shield the requirements with respect to heat load
reduction and vibration reduction are however contradictory.
[0054] FIG. 4 shows a diagram showing a heat load suppression S (on
the vertical axis with a logarithmic scale) in dependence of an
amount of fluid flow (on the horizontal axis with a logarithmic
scale, in litre per minute) through one, two or three layers of
shield elements in accordance with the present invention. With a
prior art single layer heat shield, the heat load suppression S
with a fluid flow of about 10 l/min is about 400. A same heat load
suppression S is obtainable with a two-layered shielding device
with a fluid flow of about 0.5 l/min and with a three-layered
shielding device with a fluid flow of less than 0.2 l/min. With
reference to FIG. 3, a pressure fluctuation--representative of
flow-induced vibrations--for a flow of about 10 l/min is slightly
less than 300 Pa, while for a flow well below 1 l/min, the pressure
variations are very small and may be considered insignificant,
depending on the application. In any case, for a same heat load
suppression S, the fluid flow may be considerably reduced resulting
in a significant reduction in flow-induced-vibrations. Moreover,
with a smaller flow, the fluid conditioning system may be simpler,
the tubing may be smaller and other elements may be simpler and/or
smaller and/or more cost-effective as well.
[0055] Moreover, with the mechanical requirements corresponding to
the desire to provide for finer patterns with a correspondingly
accurate positioning, the radiation-shielding device of the present
invention may provide for an improved heat load suppression S,
while reducing the flow-induced-vibrations, as compared to the
single layered heat shield of the present invention. For example,
if compared to the prior art heat shield with a flow of 10 l/min a
ten times better heat load suppression S is required, a two layered
radiation-shielding device according to the present invention would
require a fluid flow of about 1.6 l/min would be needed. As
derivable from FIG. 3, corresponding pressure fluctuation is about
10 Pa, while for 10 l/min the pressure fluctuation is about 400 Pa.
Thus, with a heat load suppression increase of about 10 times, the
flow-induced vibrations are reduced with a factor of about 40
times.
[0056] More in general, it is noted that the heat load suppression
S for an ideal shield element is about S=40*flow, with the flow
expressed in litres per minute. So, with a cascade of N shield
elements, the heat load suppression becomes S=(40*flow).sup.N.
Flow-induced vibrations (FiV) may be represented by
FiV=c.sub.0*flow.sup.2, with c.sub.0 a constant. The flow-induced
vibrations do not multiply for multiple shield elements, but only
add up due to the longer fluid channels. So, for a cascade of N
shield elements, the flow-induced vibrations may be determined to
be FiV=N*c.sub.0*flow.sup.2.
[0057] FIGS. 5A-5E show three embodiments of a shield element 21
for use in the shielding device 20 according to the present
invention as either of the shield elements (e.g. 21 and 22 in FIGS.
2a and 2B) used therein. The shield element 21 is provided with a
first fluid port 211 and a second fluid port 212 which are
operatively coupled through a fluid channel 215.
[0058] FIG. 5A shows a first embodiment of the shield element 21.
In the first embodiment, the fluid channel 215 is a hollow space in
the shield element 21. A fluid may enter through either the first
fluid port 211 or the second fluid port 212, which may be suitably
selected by the skilled person based on application, requirements
and any other considerations. In the first embodiment, the fluid
flows through the hollow space 215 and preferably fills the hollow
space 215 such that the outer surfaces of the shield element 21 are
each maintained at a same temperature over their respective
surfaces. As apparent to those skilled in the art, in order to
obtain an equal temperature over the whole surface, it may be
desirable to use a thermally conductive material to form the outer
surface of the shield element 21. Still, it is believed to be
within the ambit of the skilled person to select a suitable
material for forming the shield element 21.
[0059] FIG. 5B shows a second embodiment of the shield element 21.
In this second embodiment, a meandering fluid channel 215 is
arranged in the shield element 21. While in the first embodiment,
the fluid may fill the hollow space and in some parts of the hollow
space a fluid flow may be different from a fluid flow in other
parts of the hollow space, in this embodiment, the fluid flow in
each part of the fluid channel 215 may be expected to be
substantially the same. Further, in this second embodiment, the
fluid ports 211, 212 are arranged on a same side of the shield
element 21. Positioning the fluid ports for any of the embodiments
may be suitably performed by the skilled person in dependence of
application, requirements and any other suitable considerations.
Similarly, the skilled person may suitably select any other form or
shape of the meandering fluid channel 215.
[0060] FIGS. 5C-5E show a third embodiment of a shield element 21
for use in the shielding device according to the present invention.
The third embodiment may be preferred if a relatively thin shield
element 21 is desired. The shield element 21 of the this third
embodiment is formed by at least two plates that are bonded at
local bonding points 216 and that are spaced apart at other
positions. As shown in FIG. 5D, which is a cross-sectional view
through a number of such bonding points 216 along the line D-D
shown in FIG. 5C, at the bonding points 216, a first plate 217 and
a second plate 218 are bonded. Away from the bonding points 216,
the plates 217, 218 are spaced apart forming the fluid channel 215.
Similarly, in a cross-section along line E-E, as shown in FIG. 5E,
the plates 217, 218 may be spaced apart over the whole
cross-section to form the fluid channel 215.
[0061] This third embodiment is easily and cost-effectively
manufacturable, while being relatively thin. For example, the third
embodiment of the shield element 21 may be manufactured by
positioning two metal plates on top of each other and providing the
bonding points 216 by spot welding. After spot welding and bonding
the edges of the plates the plates may be spaced apart by applying
a gas at a sufficiently high pressure between the plates due to
which the plates are pushed apart. A suitable thickness for such a
shield element may be about 1 mm. Using a cascade of such shield
elements 21 in accordance with the present invention provides for a
relatively thin, shielding device with a high heat load suppression
and little flow-induced vibrations.
[0062] FIG. 6A illustrates a part of a lithographic apparatus and
in particular the substrate W held by the substrate table WT. In
the illustrated embodiment, the substrate table WT is moveably
arranged to enable a scanning operation as well known in the art.
For accurate position control an interferometer system IFM is
provided. Merely exemplary, a first and a second interferometer
measurement beam B.sub.1, B.sub.2 are shown. In practice, any other
number of interferometer beams may be applied depending on the
application and corresponding requirements. The interferometer
system IFM is supported on a frame F.
[0063] To prevent misalignments due to thermal expansion and/or
contraction, the frame F is preferably protected against heat load.
Thereto, a heat shield HS is provided. The heat shield HS protects
the frame F against heat generated during operation of the
lithographic apparatus. For example, the patterning beam may
generate heat in the substrate W, actuators moving the substrate
table WT may generate heat, cabling and tubing connected to the
substrate table WT and any other elements may generate heat. For
clarity, not all sources of radiation and corresponding heat load
on the frame F are illustrated. As an example, a cabling heat load
Q.sub.C radiated towards the heat-sensitive frame F is
illustrated.
[0064] On the other hand, in order to be able to control patterning
alignment on the substrate W, heat load to the substrate W is
preferably accurately controlled as well. For example, the heat
shield HS may be considered to radiate a heat shield heat load
Q.sub.HS towards the substrate W. While a constant and known heat
shield heat load Q.sub.HS is acceptable, an unknown and varying
heat shield heat load Q.sub.HS results in an uncontrollable, and
consequently non-compensatable, thermal expansion or contraction of
the substrate W, which may be unacceptable.
[0065] Further, in the surroundings of the substrate table WT, a
gaseous medium may be present providing for a gas pressure.
Moreover, a flow of such a gaseous medium may be purposefully
generated, for example for thermal control of certain elements or
for prevention of contamination of certain elements. As a result
and also due to movement of the substrate table WT, local and
temporal variations in gas pressure may result. Such gas pressure
variations however affect the accuracy of the interferometer system
IFM as known in the art. In order to compensate for such inaccuracy
due to pressure variations, it is known to apply a wavelength
tracking system WLT using a third interferometer beam B.sub.3. The
wavelength tracking system WLT is preferably mounted to the same
frame F and experiencing at least the same gas pressure conditions
as the actual interferometer measurement beams B.sub.1,
B.sub.2.
[0066] In order for the wave length tracking system WLT to
experience same gas pressure conditions, at least a part of the
heat shield HS needs to allow a gas flow G of the gaseous medium
towards the wave length tracking system WLT. Removal of a part of
the heat shield HS results in an opening through which also
electromagnetic radiation may pass resulting in a heat load on the
frame F. For example, the cabling heat load Q.sub.C may reach the
frame F providing an undesired heat load on the frame F, which is a
heat-sensitive element.
[0067] As illustrated in FIG. 6B, an embodiment of a radiation
shielding device 20 in accordance with the present invention may be
employed as a part of the heat shield HS to prevent the heat load
(e.g. cabling heat load Q.sub.C) on the frame F, while allowing a
gas flow G towards the wave length tracking system WLT such to have
a similar gas pressure on both sides of the heat shield HS. In this
embodiment of the radiation shielding device 20, each shield
element is provided with at least one through hole through which
gas may flow. The through holes in different shield elements are
however positioned relative to each other such that electromagnetic
radiation cannot pass through, thereby preventing a heat load such
as the cabling heat load Q.sub.C to be able to reach the frame F.
Such an embodiment of the radiation shielding device 20 is
illustrated in more detail in FIGS. 7A-7C.
[0068] FIGS. 7A and 7B illustrate an embodiment of a radiation
shielding device 20 having through holes to allow a gas to pass
through the radiation shielding device 20. In particular, the first
shield element 21 is provided with through holes 216 and the second
shield element 22 has through holes 226. The through holes 216 in
the first shield element 21 and the through holes 226 in the second
shield element 22 are shifted relative to each other such that the
through holes 216 do not overlap with the through holes 226. As a
consequence, a gas flow G is enabled, while electromagnetic
radiation ER, travelling in a substantially straight direction,
impinges on either the first shield element 21 or the second shield
element 22.
[0069] The first fluid channel 215 and the second fluid channel 225
are illustrated with different cross-sections such as rectangular,
circular and elliptical. It is noted any suitable cross-sectional
shape of the fluid channels may be used. Similarly, while in the
embodiment of FIGS. 7A and 7B tubular elements with a rectangular
cross-section are shown, a cross-sectional shape of the tubular
elements may be suitably selected by the skilled person as well.
For example, as illustrated in FIG. 7C, the shield elements 21, 22
may be formed by tubular elements having a circular cross-section
arranged adjacent to each other to form a shield element according
to the invention.
[0070] Referring to FIG. 7C, the shielding device 20 having through
holes may extend in accordance with the embodiment of FIGS. 2A and
2B having two planar shield elements 21, 22 or may extend as a
single-layered heat shield 30, for example.
[0071] As apparent to those skilled in the art, while embodiments
having two layers of shield elements are shown and described
herein, the radiation shielding device according to the present
invention may have any suitable number of two or more layers. In
particular, in an application requiring low vibration and high heat
load suppression, more than two shield elements, e.g. three of four
shield elements, may be suitably selected.
[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. Possible other applications include 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.
[0073] Although specific reference may be made in this text to
embodiments of the invention in the context of a lithographic
apparatus, embodiments of the invention may be used in other
apparatus. Embodiments of the invention may form part of a mask
inspection apparatus, a metrology apparatus, or any apparatus that
measures or processes an object such as a wafer (or other
substrate) or mask (or other patterning device). These apparatus
may be generally referred to as lithographic tools. Such a
lithographic tool may use vacuum conditions or ambient (non-vacuum)
conditions.
[0074] Although specific reference may have been made above to the
use of embodiments of the invention in the context of optical
lithography, it will be appreciated that the invention, where the
context allows, is not limited to optical lithography and may be
used in other applications, for example imprint lithography or any
other apparatus for any other application in which heat sensitive
devices may need to be protected against a heat load from other
elements.
[0075] Where the context allows, embodiments of the invention may
be implemented in hardware, firmware, software, or any combination
thereof. Embodiments of the invention may also be implemented as
instructions stored on a machine-readable medium, which may be read
and executed by one or more processors. A machine-readable medium
may include any mechanism for storing or transmitting information
in a form readable by a machine (e.g., a computing device). For
example, a machine-readable medium may include read only memory
(ROM); random access memory (RAM); magnetic storage media; optical
storage media; flash memory devices; electrical, optical,
acoustical or other forms of propagated signals (e.g. carrier
waves, infrared signals, digital signals, etc.), and others.
Further, firmware, software, routines, instructions may be
described herein as performing certain actions. However, it should
be appreciated that such descriptions are merely for convenience
and that such actions in fact result from computing devices,
processors, controllers, or other devices executing the firmware,
software, routines, instructions, etc. and in doing that may cause
actuators or other devices to interact with the physical world.
[0076] 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 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.
* * * * *